title: Area code 612

text: When the American Telephone and Telegraph Company (AT&T) created the first nationwide telephone numbering plan in 1947, Minnesota was divided into two numbering plan areas (NPAs), which were identified with area codes 612 and 218. According to historical maps, 612 comprised roughly the southeastern third of Minnesota. The rest of the state received area code 218, which formed an "r"-shaped region around the 612 NPA. The separating line extended westward from Duluth to the center of the state, then south through the center.


title: Area code 612

text: In 1954, the state's area code boundaries were redrawn and the state was divided into three numbering plan areas. 612 was rotated to cover most of the central portion of Minnesota, stretching border to border from Wisconsin through the Twin Cities to South Dakota. In the process, it absorbed some of 218's southern portion, including St. Cloud and Alexandria. Part of the southern portion of the original 612 territory, including Rochester and Mankato, was combined with the southwestern portion of 218 to form the new area code 507. The 218 region was reshaped to be more square, absorbing much of the old 612's northeastern portion, and now consisted of roughly the northern half of the state. This configuration remained in place for 42 years.


title: Area code 612

text: In 1996, the northern and western portion of 612, including almost all of its territory outside of the Twin Cities, became area code 320. This was intended as a long-term solution. However, the continued growth of the Twin Cities and the proliferation of cell phone and pager services pushed 612 back to the brink of exhaustion within a year. In 1998, the 612 region was roughly split in half, mostly following the Mississippi River. Minneapolis and the area west of the Mississippi retained the old code, while most of the area east of the Mississippi, including St. Paul, became the new area code 651.


title: Area code 612

text: Within another year, however, it became apparent that the creation of 651 would not free up enough numbers in the western Twin Cities to meet demand. The Twin Cities are home to most of the state's landlines, pagers, and cell phones, and their continued proliferation forced a three-way split of 612 that took effect in 2000. Minneapolis and a few suburbs to the north and south kept 612. The northwest suburbs (Brooklyn Park, Coon Rapids, Maple Grove) became area code 763 while the southwest suburbs (Bloomington, Eden Prairie, Minnetonka. St. Louis Park) got area code 952.


title: Area code 612

text: The eastern half of the University of Minnesota, Twin Cities campus, in the St. Paul suburb of Falcon Heights, is an exception to the regional numbering plan. Because of an integrated telephone system linking both campuses, the Falcon Heights campus remained in 612 after the 1998 split.


title: Area code 612

text: 612 is one of the few urbanized area codes without an area code overlay, making Minneapolis one of the few major cities where seven-digit dialing is still possible. Under current projections, it will stay that way until at least 2039.


title: Area code 612

text: The area code splits in the Twin Cities are unusual because they split along municipal, rather than exchange area boundaries. This led to a division of numerous exchange areas between the two area codes, and a few being divided among three.


title: Area code 612

text: Even with the split into four area codes, most of the Twin Cities region is still a single rate center. The four Twin Cities area codes comprise one of the largest local calling areas in the United States; with a few exceptions, no long-distance charges are applied from one part of the Twin Cities to another. Portions of area codes 320 and 507 are local calls from the Twin Cities as well.


title: Zoo Tycoon

text: Zoo Tycoon is a series of business simulation video games. The worlds focus around building and running successful zoo scenarios. The series was initially developed by Blue Fang Games and published by Microsoft Studios who later in 2001–2008 went on to create two stand-alone video games and seven expansion packs for PC and Macintosh platforms. In 2013, Microsoft Studios released a new "Zoo Tycoon" game, developed by Frontier Developments for Xbox One and Xbox 360. An enhanced version of the Xbox game, "Zoo Tycoon: Ultimate Animal Collection", was released for Windows 10 and the Xbox One on October 31, 2017.


title: Zoo Tycoon

text: Frontier Developments, the developer of the final "Zoo Tycoon" game, released the spiritual successor to the series, "Planet Zoo", in 2019.


title: Zoo Tycoon

text: "Zoo Tycoon" is a zoo simulation video game putting the player in control of their own fictional zoo business. The gameplay formula introduced in the original "Zoo Tycoon" in 2001 received updates throughout the series, but its theme and main motifs remain unchanged: Players must build, expand, and/or upgrade a zoo by purchasing animals, creating suitable animal habitats, and allocate staff and resources for animal maintenance and care. As the ultimate goal of the game is revenue, players must also provide for visitors by building food/drink stands, sanitary facilities, picnic areas, and an aesthetically pleasing environment. Higher revenue is generated by keeping both animals and visitors happy. If the animals are released from their enclosure, they can kill the visitors.


title: Zoo Tycoon

text: "Zoo Tycoon" features four modes: Training, Scenario, Challenge, and Freestyle. The Scenario mode puts players in control of a preset scenario in which they have to accomplish multiple objectives within a time period. New items are unlocked as the scenario progresses. The Challenge mode, first introduced in "Zoo Tycoon 2", resembles the Scenario mode in that the player is in a preset scenario with limited funds and must accomplish certain goals. It differs in that this mode is not progressive. The Freestyle mode differs in each game, but usually leaves the player free to build a zoo from scratch however they see fit.


title: Zoo Tycoon

text: "Zoo Tycoon", released in 2001, was followed in 2002 by two expansion packs: "" and "". Within a year, "Zoo Tycoon" had sold over 1 million units, reaching the top-selling status on the software charts. Also, a free "Endangered Species" download was available from Microsoft.com. In 2003, "Zoo Tycoon: Complete Collection" was released which included everything: the original game, the expansion packs, and the downloadable content.


title: Zoo Tycoon

text: "Zoo Tycoon 2" was released in 2004 and was followed by the first expansion pack, "", in 2005. The "" and were released the following year. Also available as a premium download was the "", available for purchase by credit card from the Zoo Tycoon website. Finally, "" was released in 2007.


title: Zoo Tycoon

text: "Zookeeper Collection" was a compilation of the original game, the "Endangered Species", and the "African Adventure" expansions. "Ultimate Collection" was a compilation of the original game and all of its expansions.


title: Zoo Tycoon

text: Microsoft released a "Zoo Tycoon" game for Xbox One and Xbox 360 in 2013 as an Xbox One Launch Title.


title: Zoo Tycoon

text: Microsoft announced a remaster of the 2013 game, "Zoo Tycoon: Ultimate Animal Collection", for Windows 10 and the Xbox One on August 20, 2017. It features 4K resolution, HDR and 60 FPS support on Xbox One X. In addition to improved graphics and gameplay, new animals such as kangaroos, koalas, and cougars were included. It was released on October 31, 2017. There are multiple campaigns and challenges with animals from across the globe.


title: Zoo Tycoon

text: In addition to the main series, there are several handheld and mobile games. "Zoo Tycoon DS" (2005) and "Zoo Tycoon 2 DS" (2008). "Zoo Tycoon 2" and its expansion are both available for the mobile phone. With the exception of "Zoo Tycoon 2 DS", none of these games were developed by Blue Fang Games. "Zoo Tycoon: Friends" was a free-to-play title developed by Behaviour Interactive, released in 2014. In April 2015, Microsoft permanently shut down "Zoo Tycoon: Friends" servers due to technical problems.


title: Nilgiri Mountain Railway

text: The Nilgiri Mountain Railway (NMR) is a railway in Nilgiris district, Tamil Nadu, India, built by the British in 1908. The railway is operated by the Southern Railway and is the only rack railway in India.


title: Nilgiri Mountain Railway

text: The railway relies on its fleet of steam locomotives. NMR switched to diesel locomotives on the section between Coonoor and Udhagamandalam. Local people and visitors led a campaign to return to steam locomotives in this section.


title: Nilgiri Mountain Railway

text: In July 2005, UNESCO added the Nilgiri Mountain Railway as an extension to the World Heritage Site of Darjeeling Himalayan Railway. The site then became known as Mountain Railways of India.


title: Nilgiri Mountain Railway

text: In 1854, plans were made to build a mountain railway from Mettupalayam to the Nilgiri Hills. However, it took the decision-makers 45 years to cut through the bureaucratic red tape and complete the construction. The line was completed and opened for traffic in June 1899. It was operated first by the Madras Railway under an agreement with the government.


title: Nilgiri Mountain Railway

text: The Madras Railway Company continued to manage the railway line on behalf of the government for a long time until the South Indian Railway company purchased it.


title: Nilgiri Mountain Railway

text: In 1907, the railway received four Double Fairlie locomotives to work the line. These were part of a batch built by the Avonside Engine Company in 1879 and 1880 for service in Afghanistan, but had been in store since 1887. The Fairlies continued in use until at least 1914.


title: Nilgiri Mountain Railway

text: Initially, Coonoor was the final station on the line. In September 1908, the line was extended to Fernhill. By 15 October 1908, it was extended to Udagmandalam. These extensions from Coonoor on the same gauge over a distance of were done at a cost of 2,440,000.


title: Nilgiri Mountain Railway

text: The NMR and all of its assets, including the stations, the line, and the track vehicles, belong to the Government of India and are managed by the Ministry of Railways. The Southern Railway performs the day-to-day maintenance and management, but several programs, divisions and departments of the Indian Railways are responsible for operating, maintaining and repairing the NMR.


title: Nilgiri Mountain Railway

text: Between Mettupalayam and Coonoor, the line uses the Abt rack and pinion system to climb the steep gradient. The NMR is the only rack railway in India.


title: Nilgiri Mountain Railway

text: NMR uses 'X' Class steam rack locomotives, most manufactured by the Swiss Locomotive and Machine Works of Winterthur in Switzerland, on the rack and pinion section of its tracks. The X Class locomotives are up to eight decades old, but the newest was completed August 2021 at the Golden Rock workshops in India. These locomotives give NMR a distinct charm, taking scores of passengers to Coonoor and Udhagamandalam, crossing , 108 curves, 16 tunnels and 250 bridges.


title: Nilgiri Mountain Railway

text: The steam locomotives can be used on any part of the line, while the diesel locomotives can operate only on the section between Coonoor and Udagamandalam.


title: Nilgiri Mountain Railway

text: Each diesel engine weighs a little over 50 tonnes and cost Rs. 10 crore. They have pilot and primary burners. Separate tanks hold about of diesel and of furnace oil. The hauling capacity of this new engine is . It can run at a speed of on plains and at an hour climbing a gradient. The arrival of the new engines eliminated the disruptions in service that occurred frequently.


title: Nilgiri Mountain Railway

text: The steam locomotives are marshalled at the downhill (Mettupalayam) end of the train. The average gradient in this rack section is 1 in 24.5 (4.08%), with a maximum of 1 in 12 (8.33%). Between Coonoor and Udagamandalam, the train is operated by a YDM4 diesel locomotive using conventional rail adhesion principles. On this section, the locomotive is always at the Coonoor end of the train as although the line is not steep enough to need a rack rail, the ruling gradient out of Coonoor is steep at 1 in 25 (4%).


title: Nilgiri Mountain Railway

text: Southern Railway carries out the majority of the locomotive repairs at the Coonoor shed but has rebuilt many of the steam locomotives at the Golden Rock Workshops. Many carriage repairs take place at Mettupalayam. Like the locomotives, major work on the carriages takes place at one of the larger railway workshops.


title: Nilgiri Mountain Railway

text: The uphill journey takes around 290 minutes (4.8 hours), and the downhill journey takes 215 minutes (3.6 hours). It has the steepest track in Asia with a maximum gradient of 8.33%. During Meter Gauge era in 1990s, The Nilgiri Express used to run between Chennai(then Madras) & Udhagamandalam(then Ooty) directly. Timings were:- Madras 21.00; Ooty 10.20 & in return:- Ooty 16.30; Madras 05.50.But it was stopped after NMR got UNESCO World Heritage Tag in 1994. As of 2007, a daily train crosses the rack section, which starts from Mettupalayam at 07:10 and reaches Udhagamandalam at noon. The return train starts from Udhagamandalam at 14:00, and reaches at 17:35. The train is scheduled to connect to the Nilgiri Express, which travels from Mettupalayam to Chennai via Coimbatore. A summer special service runs in April and May, starting from Mettupalayam at 09:30 am and from Udhagamandalam at 12:15 pm. Between Coonoor and Udagamandalam, four daily trains run each way.


title: Nilgiri Mountain Railway

text: Even though the NMR supplies networked computerized ticketing systems for onward journeys, it still issues Edmondson style manual tickets for the Udhagamandalam-Mettupalayam journey to preserve its 'World Heritage Site' status. Ticket booking is similar to conventional trains and can be done via the Indian Railway website. It is advisable to book tickets well in advance, especially during peak season.


title: Nilgiri Mountain Railway

text: Coonoor station was one of two used as locations in the David Lean film "A Passage to India". Coonoor station and its heritage locomotive appear in many Indian films. Wellington station finds a place in most of the films casting the Indian army or army training storyline, mainly due to the MRC Indian Army Regiment, Defence Services Staff College, the Cantonment and the Cordite Factory. Ketti station was used as the location in a Malayalam film "Summer in Bethlehem". Lovedale station is featured in films including the Tamil hit, "Moonram Pirai". The famous Hindi song "Chaiyya Chaiyya" from "Dil Se.." was shot on the rooftop of NMR. Udhagamandalam station has featured in Tamil and other South Indian films. It is prominently featured in some Bollywood films. One of the X Class locomotives on the Nilgiri Mountain Railway was the model for Ashima in the film "". Ashima also appeared in the 22nd, 23rd, and 24th seasons of Thomas & Friends.


title: Nilgiri Mountain Railway

text: In the UK, the BBC made three 2010 documentaries dealing with Indian Hill Railways, featuring NMR in the second programme. (The first film covers the Darjeeling-Himalayan Railway and the third film, the Kalka-Shimla Railway.) The films were directed by Tarun Bhartiya, Hugo Smith, and Nick Mattingly, and produced by Gerry Troyna. The series won the UK Royal Television Society Award in June 2010.


title: Insubordination

text: Insubordination is the act of willfully disobeying a lawful order of one's superior. It is generally a punishable offense in hierarchical organizations such as the armed forces, which depend on people lower in the chain of command obeying orders.


title: Insubordination

text: Insubordination is when a service member willfully disobeys the lawful orders of a superior officer. If a military officer disobeys the lawful orders of their civilian superiors, this also counts. For example, the head of state in many countries, is also the most superior officer of the military as the Commander in Chief. Generally, however, an officer or soldier may disobey an unlawful order to the point of mutiny (see Nuremberg defense).


title: Insubordination

text: In the U.S. military, insubordination is covered under Article 91 of the Uniform Code of Military Justice. It covers disobeying lawful orders as well as disrespectful language or even striking a superior. The article for insubordination should not be confused with the article for contempt. While Article 91 of the UCMJ deals predominantly with disobeying or disrespecting a superior and applies to enlisted members and warrant officers, Article 88 involves the use of contemptuous words against certain appointed or elected officials and only applies to commissioned officers.


title: Insubordination

text: According to a 2021 typology, military disobedience can take four forms: "defiance, refinement, grudging obedience, and exit." A 2019 study argued that military disobedience may arise when a tension is created in the social networks of a soldier, which gives the soldier motivations and justifications to disobey orders.


title: Insubordination

text: Other types of hierarchical structures, especially corporations, may use insubordination as a reason for dismissal or censure of an employee.


title: Insubordination

text: There have been court cases in the United States which have involved charges of insubordination from the employer with counter charges of infringement of First Amendment rights from the employee. A number of these cases have reached the U.S. Supreme Court usually involving a conflict between an institution of higher education and a faculty member.


title: Insubordination

text: In the modern workplace in the Western world, hierarchical power relationships are usually sufficiently internalized so that the issue of formal charges of insubordination are rare. In his book "Disciplined Minds", American physicist and writer Jeff Schmidt points out that professionals are trusted to run organizations in the interests of their employers. Because employers cannot be on hand to manage every decision, professionals are trained "to make sure that the subtext of each and every detail of their work advances the right interests—or skewers the disfavored ones" in the absence of overt control.


title: Insubordination

text: There have been a number of famous and notorious people who have committed insubordination or "publicly" objected to an organizational practice.


title: Let's Hear It for the Boy

text: "Let's Hear It for the Boy" is a song by Deniece Williams that appeared on the soundtrack to the feature film "Footloose". The song was released as a single from both the soundtrack and her album of the song's same name on February 14, 1984, by Columbia Records. It was written by Tom Snow and Dean Pitchford and produced by George Duke. The song became Williams' second number one on the US "Billboard" Hot 100 on May 26, 1984, also topping the dance and R&B charts, and peaked at number two on the UK Singles Chart, behind "Wake Me Up Before You Go-Go" by Wham!. It was nominated for an Academy Award for Best Original Song, and was certified platinum in the US, gold in Canada and silver in the UK by the RIAA, Music Canada and the British Phonographic Industry respectively. The music video was released in mid-April 1984. The song features background vocals from George Merrill and Shannon Rubicam, who would go on to form the duo Boy Meets Girl.


title: Let's Hear It for the Boy

text: In 2011, country singer Jana Kramer covered the song for the remake of "Footloose". In 2017 the song was covered by UK hi-NRG dance artist Allan Jay in aid of the Retired Greyhound Trust and their Let's Hear It for the Boy campaign.


title: Let's Hear It for the Boy

text: The music video for the song features Williams along with several young men, one of them being the singer Aaron Lohr as the young boy who is the first person to appear in the video.


"Break Up with Your Girlfriend, I'm Bored" (stylized in all lowercase) is a song by American singer Ariana Grande from her fifth studio album, "Thank U, Next" (2019). The song was written by Grande, Savan Kotecha, Kandi Burruss, Kevin Briggs, and the producers Max Martin and Ilya Salmanzadeh. It was released through Republic Records on February 8, 2019, as the third and final single from the album. The pop-R&B and trap-pop song consists of a bass guitar and interpolates the NSYNC song "It Makes Me Ill" in the bridge. The lyrics depict Grande convincing a man to break up with his girlfriend.


"Break Up with Your Girlfriend, I'm Bored" peaked at number one in eight countries and received platinum certifications in 11 countries. The song debuted and peaked at number two on the US "Billboard" Hot 100, allowing Grande to become the second artist after the Beatles to have songs on the top three positions of the Hot 100 and the first solo and female artist to accomplish this feat. An accompanying music video was directed by Hannah Lux Davis and depicts Grande in a love triangle with a couple including a doppelgänger of herself. A scene in the video was compared to "Single White Female" (1992), while some publications criticized it for queerbaiting. Grande included "Break Up with Your Girlfriend, I'm Bored" on the setlist of the Sweetener World Tour and performed the song with NSYNC on the first show at the 2019 Coachella Valley Music and Arts Festival.


Grande announced the inclusion of "Break Up with Your Girlfriend, I'm Bored" on the "Thank U, Next" track listing on January 22, 2019. It replaced the initial song "Remember", as she believed that it was too personal to release and wanted a "fun" song instead. Grande additionally uploaded a snippet of the song on her social media accounts prior to its release. It was released as the third and final single from "Thank U, Next" on February 8, 2019, and was distributed to contemporary hit radio and rhythmic contemporary radio in the United States on February 12, 2019.


Musically, "Break Up with Your Girlfriend, I'm Bored" is a pop-R&B and trap-pop song, which includes Grande's "semi-rapped, disenfranchised" vocals placed over a "booming" bass guitar, and is accompanied by a "subterranean click beat". "Break Up with Your Girlfriend, I'm Bored" contains an interpolation of the NSYNC song "It Makes Me Ill" from their third studio album "No Strings Attached" (2000), which is heard in the bridge. Grande inherits the cadence and lyrics from "It Makes Me Ill", and changes the lyric in the original song: "You can say I'm crazy, if you want to / That's true, I'm crazy 'bout you" to the lyric in "Break Up with Your Girlfriend, I'm Bored": "You can call me crazy cuz I want you / And I never even never fuckin met you". "Billboard" staff writers believed that Grande altered the song to become "a hyper-sexualized, alluring and suspenseful paen", while Elias Leight of "Rolling Stone" noted that the lyrics contrast from the "tale of envy [...] overflow[ing] with jealousy" in "It Makes Me Ill" to the possibility of "escap[ing] dullness" in "Break Up with Your Girlfriend, I'm Bored". "Break Up with Your Girlfriend, I'm Bored" was written by Grande, Max Martin, Ilya Salmanzadeh, Savan Kotecha, and the songwriters of "It Makes Me Ill", Kandi Burruss and Kevin Briggs. The lyrics depict Grande convincing a man to break up with his girlfriend.


"Rolling Stone" writer Rob Sheffield praised "Break Up with Your Girlfriend, I'm Bored" for being "the perfect way to end "Thank U, Next" and compared it to the Britney Spears song "Get Naked (I Got a Plan)". Ross Horton of "The Line of Best Fit" described the song as "positively filthy" and opined that Grande's vocals should contain an "advisory warning". Writing for "The Independent", Helen Brown stated that "Break Up with Your Girlfriend, I'm Bored" is "sexy" with Grande "embracing her inner mean girl". "The Irish Times" writer Ed Powers opined that it is "a sultry exorcism" where Grande searched for "merciful oblivion in the arms of a forbidden lover". At the 2020 Hito Music Awards, "Break Up with Your Girlfriend, I'm Bored" won the award for Best Western Song.


However, Wren Graves of "Consequence of Sound" believed that the placement of "Break Up with Your Girlfriend, I'm Bored" on "Thank U, Next" as the final track gave the album "a sour aftertaste". Writing for "HotNewHipHop", Devin Ch described the song as a "humorous quip at worst", while "Entertainment Weekly" writer Maura Johnston claimed that "Break Up with Your Girlfriend, I'm Bored" is "self-indulgent" and negatively compared it to Grande's song "7 Rings" through the character Veruca Salt.


In the United States, "Break Up with Your Girlfriend, I'm Bored" debuted at number two on the US "Billboard" Hot 100 behind Grande's "7 Rings", which was her 13th top 10 song on the chart. With "7 Rings", "Break Up with Your Girlfriend, I'm Bored", and "Thank U, Next" simultaneously occupying the top three positions on the Hot 100 chart dated February 23, 2019, Grande became the first artist to monopolize the entire top three positions on the chart since the Beatles did so in 1964, and the first solo and female artist to accomplish this feat. The song remained on the chart for a total of 20 weeks, and was certified triple platinum by the Recording Industry Association of America (RIAA) on June 15, 2020, for sales of over 3,000,000 equivalent units in the United States.


The song debuted on the "Billboard" Streaming Songs and Digital Songs charts at number two, lodging 59.2 million first week streams, and 36,000 digital downloads sold within its first week respectively. Additionally, on the Dance Club Songs chart dated May 4, 2019, "Break Up with Your Girlfriend, I'm Bored" became Grande's seventh overall number one song and her fourth number one song in 2019, which was assisted with remixes by Dirty Werk, Country Club Martini Crew and Eric Kupper. On the Mainstream Top 40 chart issued May 4, 2019, it peaked at number three and remained for 20 weeks. "Break Up with Your Girlfriend, I'm Bored" ranked at number 21 on The 25 Most-Consumed Songs of 2019 chart compiled by BuzzAngle Music, having sold more than 2,258,795 units. The song debuted at its number two peak behind "7 Rings" on the Canadian Hot 100 chart dated February 23, 2019, and was certified quadruple platinum by Music Canada (MC) on April 16, 2021, for 320,000 track-equivalent sales in the country.


In the United Kingdom, "Break Up with Your Girlfriend, I'm Bored" debuted atop the UK Singles Chart issued February 15, 2019, with 85,000 combined sales and replaced "7 Rings", which charted at the number two position that week. Grande became the first female artist to replace herself at number one on the chart and the second female artist to occupy the top two spots on the chart since Madonna in August 1985. She also became the first female artist to achieve three chart-topping singles in under 100 days and the fourth overall artist after Elvis Presley, John Lennon, and Justin Bieber, and was the first female artist with three songs in the top 10 as a lead artist after Ruby Murray in March 1955. The following week, "Break Up with Your Girlfriend, I'm Bored" declined to the number two position, as "7 Rings" regained its number one peak. Grande subsequently became the first artist in the chart's history to self-replace for two consecutive weeks. The song received a platinum certification by the British Phonographic Industry (BPI) on August 30, 2019, for sales of 600,000 track-equivalent units in the United Kingdom.


title: Break Up with Your Girlfriend, I'm Bored

text: In the Republic of Ireland, the song peaked at the summit of the Irish Singles Chart and became Grande's fifth song to top the chart. The latter achievement allowed Grande to become the second female artist with the most number one songs in the 2010s decade, after Rihanna's six songs. Grande was the first person to replace themselves on the chart since Ed Sheeran in 2017, and was the second female artist since Britney Spears to reach four number ones on the chart in less than a year during the 2000s millennium.


text: In Australia, "Break Up with Your Girlfriend, I'm Bored" debuted at the number two peak on the ARIA Singles Chart dated February 24, 2019, where it remained for 13 weeks. It was eventually certified platinum by the Australian Recording Industry Association (ARIA) for selling 70,000 equivalent units in the country. "Break Up with Your Girlfriend, I'm Bored" topped the New Zealand Singles Chart issued February 18, 2019, and charted for 14 weeks. The song was later certified platinum by Recorded Music NZ (RMNZ) for selling 30,000 units in the country.


text: An accompanying music video for the song was released at midnight on February 8, 2019, which coincided with the release of the album. It was directed by American music video director Hannah Lux Davis and filmed inside a mansion in the Hollywood Hills. The music video is Davis' third consecutively-directed video from "Thank U, Next", after the album's title song and "7 Rings". Davis stated that the video's concept was based around a love triangle between Grande and a couple including a doppelgänger of the former, which Davis described as an "element of narcissism". It features actor Charles Melton and model Ariel Yasmine.


text: The video begins with Grande arriving in a nightclub while sporting a platinum wig. She notices Melton and his girlfriend Yasmine, the latter resembles Grande with her "sky-high ponytail". Although Melton is holding Yasmine, he is fixated by Grande's appearance. Grande is next seen at a house party without the platinum wig, as she attempts to gain Melton's affection. Throughout several scenes, Grande and Yasmine intimately dance together and caress the other person's hair, while the former portrays a "third wheel" as she follows the couple while rolling her eyes. Towards the end of the video, Grande advances towards the couple as they are lounging poolside. She approaches Melton, but swiftly pushes him away before turning towards Yasmine as they both lean in to kiss.


text: "Billboard" staff considered the music video to be "sexy and stylish", while Tallie Spencer of "Spin" opined that it "complements the song's sassy tone". Writing for MTV News, Madeline Roth considered it to be "trippy" and compared the scene where Grande changes her appearance to the film "Single White Female" (1992), while "Elle" writer Alyssa Bailey noted that the music video is portrayed as "a good CW drama". However, some publications accused the video's climax for queerbaiting.


text: Grande debuted the live performance of "Break Up with Your Girlfriend, I'm Bored" on the Sweetener World Tour on March 19, 2019, where it was the fourth song included on the setlist in Albany, New York. She performed the song at both shows of the Coachella Valley Music and Arts Festival in 2019. During the first show on April 14, 2019, Grande paused midway through the song to introduce NSYNC members JC Chasez, Chris Kirkpatrick, Joey Fatone, and Lance Bass on stage to sing "It Makes Me Ill" with "intense choreography". They then followed up their performance with NSYNC's 1997 song "Tearin' Up My Heart", with Grande performing the dance moves while the video screens resembled a VHS tape with numbers and ripples. NSYNC's appearance during both performances elicited a loud crowd reaction.


text: American singer Lana Del Rey performed a cover version of "Break Up with Your Girlfriend, I'm Bored" during her BBC Radio 1 "Live Lounge" appearance on September 9, 2019, which was approved by Grande on Twitter. Nick Reilly of "NME" stated that Del Rey's cover "is largely faithful to the original". It was nominated for Best Cover Song on the 2020 iHeartRadio Music Awards.


title: Titanic 666

text: Titanic 666 (also known as Titanic 3) is a 2022 American supernatural horror film directed by Nick Lyon and produced by The Asylum. It is a sequel to "Titanic II" (2010) and stars Jamie Bamber and Keesha Sharp. It was released on Tubi on the United States on April 15, 2022, on the 110th anniversary of the sinking of the "Titanic". The film received generally unfavorable reviews, and users on social media noted the film's similarity to "Titanic" (1997) and "Studio 666" (2022).


title: Titanic 666

text: After embarking on the maiden voyage of "Titanic 3", a group of digital influencers are surrounded by macabre events.


title: Titanic 666

text: Waldemar Dalenogare Neto evaluated it with a score of 1/10 and said that "whoever sees it, does not believe it: The Asylum managed to overcome itself (...) I already knew it was a bad movie, the trailer is already a disgrace (...) the bad taste when dealing with a tragedy (on the anniversary of the sinking of the Titanic) (...) It's not a horror movie, as much as the title may lead you to this idea, here you actually have a big joke at the cost of extremely poor graphical effects and a completely lost cast."


title: Titanic 666

text: In his review in "Paste" magazine, Matt Donato rated it 4/10 saying that "while Netflix harbors Oscar aspirations for its originals, Tubi appears content being the streaming equivalent of SYFY after midnight. (...) I’ve seen worse films this year than Titanic 666, but also too many better examples (...) Against all odds, Titanic 666 is too dramatic and straight-faced for its own good."


title: Titanic 666

text: On Crooked Marquee, Josh Bell rated it a "C-" saying that "is a slow, dull haunted-ship story that takes far too long to get to its meager terrors. Lydia Hearst finds the right campy tone as a descendant of one of the original Titanic victims who summons their spirits to curse this shameless exploitation of their memories, and AnnaLynne McCord is fun to watch as a narcissistic influencer who exits the movie too early. But the ghosts themselves are tame, poorly rendered apparitions, and the valiant, self-sacrificing captain (Keesha Sharp) makes for a weak protagonist as the voyage predictably devolves into chaos."


title: Gutian people

text: The Guti () or Quti, also known by the derived exonyms Gutians or Guteans, were a nomadic people of West Asia, around the Zagros Mountains (Modern Iran) during ancient times. Their homeland was known as Gutium (Sumerian: ,"Gu-tu-um" or ,"Gu-ti-um").


title: Gutian people

text: Conflict between people from Gutium and the Akkadian Empire has been linked to the collapse of the empire, towards the end of the 3rd millennium BC. The Guti subsequently overran southern Mesopotamia and formed the Gutian dynasty of Sumer. The Sumerian king list suggests that the Guti ruled over Sumer for several generations following the fall of the Akkadian Empire.


title: Gutian people

text: By the 1st millennium BC, usage of the name Gutium, by the peoples of lowland Mesopotamia, had expanded to include all of western Media, between the Zagros and the Tigris. Various tribes and places to the east and northeast were often referred to as "Gutians" or "Gutium". For example, Assyrian royal annals use the term Gutians in relation to populations known to have been Medes or Mannaeans. As late as the reign of Cyrus the Great of Persia, the famous general Gubaru (Gobryas) was described as the "governor of Gutium".


title: Gutian people

text: Little is known of the origins, material culture or language of the Guti, as contemporary sources provide few details and no artifacts have been positively identified. As the Gutian language lacks a text corpus, apart from some proper names, its similarities to other languages are impossible to verify. The names of Gutian-Sumerian kings suggest that the language was not closely related to any languages of the region, including Sumerian, Akkadian, Hurrian, Hittite, and Elamite.


title: Gutian people

text: W. B. Henning suggested that the different endings of the king names resembled case endings in the Tocharian languages, a branch of Indo-European known from texts found in the Tarim Basin (in the northwest of modern China) dating from the 6th to 8th centuries BC, making Gutian the earliest documented Indo-European language. He further suggested that they had subsequently migrated to the Tarim. Gamkrelidze and Ivanov explored Henning's suggestion, as possibly supporting their proposal of an Indo-European "Urheimat" in the Near East. However, most scholars reject the attempt to connect the two groups of languages, Gutian and Tocharian, that were separated by more than two millennia.


title: Gutian people

text: Since Gutian appears to have been an unwritten language, for information about the Guti, scholars must rely on external sources – often highly biased texts composed by their enemies. For example, Sumerian sources generally portray the Guti as an "unhappy", barbarous and rapacious people from the mountains – apparently the central Zagros east of Babylon and north of Elam. The period of the Gutian dynasty in Sumer is portrayed as chaotic.


title: Gutian people

text: Initially, according to the Sumerian king list, "in Gutium ... no king was famous; they were their own kings and ruled thus for three [or five] years". This may indicate that the Gutian kingship was rotated between tribes/clans, or within an oligarchical elite.


title: Gutian people

text: The Guti appear in texts from Old Babylonian copies of inscriptions ascribed to Lugal-Anne-Mundu (fl. circa 25th century BC) of Adab as among the nations providing his empire tribute. These inscriptions locate them between Subartu in the north, and Marhashe and Elam in the south. They were a prominent nomadic tribe who lived in the Zagros mountains in the time of the Akkadian Empire.


title: Gutian people

text: Sargon the Great (r. circa 2340 – 2284 BC) also mentions them among his subject lands, listing them between Lullubi, Armanum and Akkad to the north; Nikku and Der to the south. According to one stele, Naram-Sin of Akkad's army of 360,000 soldiers defeated the Gutian king Gula'an, despite having 90,000 slain by the Gutians.


title: Gutian people

text: The epic "Cuthean Legend of Naram-Sin" claims "Gutium" among the lands raided by Annubanini of Lulubum during the reign of Naram-Sin (c. 2254–2218 BC). Contemporary year-names for Shar-kali-sharri of Akkad indicate that in one unknown year of his reign, Shar-kali-sharri captured Sharlag king of Gutium, while in another year, "the yoke was imposed on Gutium".


title: Gutian people

text: As the Akkadians went into decline, the Gutians began a decades-long campaign of hit-and-run raids against Mesopotamia. Their raids crippled the economy of Sumer. Travel became unsafe, as did work in the fields, resulting in famine. The Gutians eventually overran Akkad, and as the King List tells us, their army also subdued Uruk for hegemony of Sumer, in about 2147–2050 BC. However, it seems that autonomous rulers soon arose again in a number of city-states, notably Gudea of Lagash.


title: Gutian people

text: The Gutians seem also to have briefly overrun Elam at around the same time, towards the close of Kutik-Inshushinak's reign (c. 2100 BC). On a statue of the Gutian king Erridupizir at Nippur, an inscription imitates his Akkadian predecessors, styling him "King of Gutium, King of the Four Quarters".


title: Gutian people

text: The Sumerian ruler Utu-hengal, Prince of the Sumerian city of Uruk is similarly credited on the King List with defeating the Gutian ruler Tirigan, and removing the Guti from the country in circa 2050 BC (short chronology).


title: Gutian people

text: Following this, Ur-Nammu of Ur ordered the destruction of Gutium. The year 11 of king Ur-Nammu also mentions "Year Gutium was destroyed". However, according to a Sumerian epic, Ur-Nammu died in battle with the Gutians, after having been abandoned by his own army.


title: Gutian people

text: A Babylonian text from the early 2nd millennium refers to the Guti as having a "human face, dogs’ cunning, [and] monkey's build".


title: Gutian people

text: Biblical scholars believe that the Guti may be the "Koa" ("qôa"), named with the Shoa and Pekod as enemies of Jerusalem in Ezekiel 23:23, which was probably written in the 6th century BC. "Qôa" also means "male camel" in Hebrew, and in the context of "Ezekiel" 23, it may be a deliberate, insulting distortion of an endonym such as "Quti".


title: Gutian people

text: According to the historian Henry Hoyle Howorth (1901), Assyriologist Theophilus Pinches (1908), renowned archaeologist Leonard Woolley (1929) and Assyriologist Ignace Gelb (1944), the Gutians were pale in complexion and blond. But this was asserted on the basis of assumed broad links to peoples mentioned in the Old Testament. This identification of the Gutians as fair haired first came to light when Julius Oppert (1877) published a set of tablets he had discovered which described Gutian (and Subarian) slaves as "namrum" or "namrûtum", one of its many meanings being "light colored". This racial character of the Gutians as light skinned cannot be equated to being blond. But yet it was also claimed by Georges Vacher de Lapouge in 1899 and later by historian Sidney Smith in his "Early History of Assyria" (1928).


title: Gutian people

text: Ephraim Avigdor Speiser, however, criticised the translation of "namrum" as "light colored". A note was published by Speiser in the "Journal of the American Oriental Society" criticizing Gelb's translation and consequent interpretation. Gelb in response accused Speiser of circular reasoning. In response, Speiser claimed the scholarship regarding the translation of "namrum" or "namrûtum" is unresolved.


title: Gutian people

text: The historical Guti have been regarded by several scholars as having contributed to the ethnogenesis of the Kurds.


title: Gutian people

text: There is no linguistic evidence linking Gutians to modern ethnic identities. Most scholars reject the attempt to link Gutian king names to Indo-European languages.


title: Zinc–air battery

text: Zinc–air batteries (non-rechargeable), and zinc–air fuel cells (mechanically rechargeable) are metal–air batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. Sizes range from very small button cells for hearing aids, larger batteries used in film cameras that previously used mercury batteries, to very large batteries used for electric vehicle propulsion and grid-scale energy storage.


title: Zinc–air battery

text: During discharge, a mass of zinc particles forms a porous anode, which is saturated with an electrolyte. Oxygen from the air reacts at the cathode and forms hydroxyl ions which migrate into the zinc paste and form zincate (), releasing electrons to travel to the cathode. The zincate decays into zinc oxide and water returns to the electrolyte. The water and hydroxyl from the anode are recycled at the cathode, so the water is not consumed. The reactions produce a theoretical voltage of 1.65 Volts, but is reduced to 1.35–1.4 V in available cells.


title: Zinc–air battery

text: Zinc–air batteries have some properties of fuel cells as well as batteries: the zinc is the fuel, the reaction rate can be controlled by varying the air flow, and oxidized zinc/electrolyte paste can be replaced with fresh paste.


title: Zinc–air battery

text: Zinc–air batteries can be used to replace now discontinued 1.35 V mercury batteries (although with a significantly shorter operating life), which in the 1970s through 1980s were commonly used in photo cameras and hearing aids.


title: Zinc–air battery

text: Possible future applications of this battery include its deployment as an electric vehicle battery and as a utility-scale energy storage system.


title: Zinc–air battery

text: The effect of oxygen was known early in the 19th century when wet-cell Leclanche batteries absorbed atmospheric oxygen into the carbon cathode current collector. In 1878, a porous platinized carbon air electrode was found to work as well as the manganese dioxide () of the Leclanche cell. Commercial products began to be made on this principle in 1932 when George W. Heise and Erwin A. Schumacher of the National Carbon Company built cells, treating the carbon electrodes with wax to prevent flooding. This type is still used for large zinc–air cells for navigation aids and rail transportation. However, the current capacity is low and the cells are bulky.


title: Zinc–air battery

text: Large primary zinc–air cells such as the Thomas A. Edison Industries "Carbonaire" type were used for railway signaling, remote communication sites, and navigation buoys. These were long-duration, low-rate applications. Development in the 1970s of thin electrodes based on fuel-cell research allowed application to small button and prismatic primary cells for hearing aids, pagers, and medical devices, especially cardiac telemetry.


title: Zinc–air battery

text: Zinc–air batteries cannot be used in a sealed battery holder since some air must come in; the oxygen in 1 liter of air is required for every ampere-hour of capacity used.


title: Zinc–air battery

text: Zinc–air batteries have higher energy density than many other types of battery because atmospheric air is one of the battery reactants, in contrast to battery types that require a material such as manganese dioxide in combination with zinc. Energy density, when measured by weight (mass) is known as specific energy. The following table shows the calculation of specific energy for a specific zinc-air battery and several other commonly available batteries of different chemistries.


title: Zinc–air battery

text: Zinc–air cells have long shelf life if sealed to keep air out; even miniature button cells can be stored for up to 3 years at room temperature with little capacity loss if their seal is not removed. Industrial cells stored in a dry state have an indefinite storage life.


title: Zinc–air battery

text: The operating life of a zinc–air cell is a critical function of its interaction with its environment. The electrolyte loses water more rapidly in conditions of high temperature and low humidity. Because the potassium hydroxide electrolyte is deliquescent, in very humid conditions excess water accumulates in the cell, flooding the cathode and destroying its active properties. Potassium hydroxide also reacts with atmospheric carbon dioxide; carbonate formation eventually reduces electrolyte conductivity. Miniature cells have high self-discharge once opened to air; the cell's capacity is intended to be used within a few weeks.


title: Zinc–air battery

text: Because the cathode does not change properties during discharge, terminal voltage is quite stable until the cell approaches exhaustion.


title: Zinc–air battery

text: Power capacity is a function of several variables: cathode area, air availability, porosity, and the catalytic value of the cathode surface. Oxygen entry into the cell must be balanced against electrolyte water loss; cathode membranes are coated with (hydrophobic) Teflon material to limit water loss. Low humidity increases water loss; if enough water is lost the cell fails. Button cells have a limited current drain; for example an IEC PR44 cell has a capacity of 600 milliamp-hours (mAh) but a maximum current of only 22 milliamps (mA). Pulse load currents can be much higher since some oxygen remains in the cell between pulses.


title: Zinc–air battery

text: Low temperature reduces primary cell capacity but the effect is small for low drains. A cell may deliver 80% of its capacity if discharged over 300 hours at , but only 20% of capacity if discharged at a 50-hour rate at that temperature. Lower temperature also reduces cell voltage.


title: Zinc–air battery

text: Large zinc–air batteries, with capacities up to 2,000 ampere–hours per cell, are used to power navigation instruments and marker lights, oceanographic experiments and railway signals.


title: Zinc–air battery

text: Primary cells are made in button format to about 1 Ah. Prismatic shapes for portable devices are manufactured with capacities between 5 and 30 Ah. Hybrid cell cathodes include manganese dioxide to allow high peak currents.


title: Zinc–air battery

text: Button cells are highly effective, but it is difficult to extend the same construction to larger sizes due to air diffusion performance, heat dissipation, and leakage problems. Prismatic and cylindrical cell designs address these problems. Stacking prismatic cells requires air channels in the battery and may require a fan to force air through the stack.


title: Zinc–air battery

text: Rechargeable zinc–air cells require zinc precipitation from the water-based electrolyte to be closely controlled. Challenges include dendrite formation, non-uniform zinc dissolution, and limited solubility in electrolytes. Electrically reversing the reaction at a bi-functional air cathode, to liberate oxygen from discharge reaction products, is difficult; membranes tested to date have low overall efficiency. Charging voltage is much higher than discharge voltage, producing cycle energy efficiency as low as 50%. Providing charge and discharge functions by separate uni-functional cathodes increases cell size, weight and complexity. A satisfactory electrically recharged system potentially offers low material cost and high specific energy. As of 2014, only one company has commercial units for sale, as described in a Dept. of Energy produced video at the ARPA-e Energy Innovation Summit in 2013. Fluidic Energy has apparently covered hundreds of thousands of outages in Asia at distributed critical load sites. EOS Energy Storage has deployed a 1MWh system for a microgrid at a New Jersey wastewater treatment plant and has previously tested grid-scale backup applications. AZA Battery has announced development of pilot production of prismatic zinc air cells with characteristics suitable for both stationary storage and mobility applications.


title: Zinc–air battery

text: Rechargeable systems may mechanically replace the anode and electrolyte, essentially operating as a refurbishable primary cell, or may use zinc powder or other methods to replenish the reactants. Mechanically recharged systems were investigated for military electronics uses in the 1960s because of the high energy density and easy recharging. However, primary lithium batteries offered higher discharge rates and easier handling.


title: Zinc–air battery

text: Mechanical recharging systems have been researched for decades for use in electric vehicles. Some approaches use a large zinc–air battery to maintain charge on a high discharge–rate battery used for peak loads during acceleration. Zinc granules serve as the reactant. Vehicles recharge via exchanging used electrolyte and depleted zinc for fresh reactants at a service station.


title: Zinc–air battery

text: The term zinc–air fuel cell usually refers to a zinc–air battery in which zinc metal is added and zinc oxide is removed continuously. Zinc electrolyte paste or pellets are pushed into a chamber, and waste zinc oxide is pumped into a waste tank or bladder inside the fuel tank. Fresh zinc paste or pellets are taken from the fuel tank. The zinc oxide waste is pumped out at a refueling station for recycling. Alternatively, this term may refer to an electrochemical system in which zinc is a co-reactant assisting the reformation of hydrocarbons at the anode of a fuel cell.


title: Zinc–air battery

text: The benefits of mechanical recharging systems over rechargeable batteries include the decoupling of energy and power components, providing design flexibility for different charge rate, discharge rate, and energy capacity requirements.


title: Zinc–air battery

text: Cobalt oxide/carbon nanotube hybrid oxygen reduction catalyst and nickel-iron layered double hydroxide oxygen evolution cathode catalysts exhibited higher catalytic activity and durability in concentrated alkaline electrolytes than precious metal platinum and iridium catalysts. The resulting primary zinc–air battery showed peak power density of ~265 mW/cm, current density of ~200 mA/cm at 1 V and energy density >700 Wh/kg.


title: Zinc–air battery

text: Rechargeable Zn–air batteries in a tri-electrode configuration exhibited an unprecedented small charge–discharge voltage polarization of ~0.70 V at 20 mA/cm, high reversibility and stability over long charge and discharge cycles.


title: Zinc–air battery

text: In 2015, researchers announced a carbon-based, metal-free electrocatalyst that works efficiently in both reduction and oxygenation reactions. Organic compound aniline, polymerized into long chains in a phytic acid solution, was freeze-dried into a stable, mesoporous carbon aerogel with 2–50 nm pores, providing high surface area and room for the battery electrolyte to diffuse. The researchers pyrolized the aerogel to 1,000 degrees Celsius, turning the foam into a graphitic network, with many catalytic graphene edges. The aniline doped the foam with nitrogen, which enhances reduction. Phytic acid infuses the foam with phosphorus, helping oxygen evolution. The foam has a surface area of ∼1,663 m/gr. Primary batteries demonstrated an open-circuit potential of 1.48 V, a specific capacity of 735 mAh/gr (Zn) (energy density of 835 Wh/kg (Zn)), a peak power density of 55 mW/cm³ and stable operation for 240 h after mechanical recharging. Two-electrode rechargeable batteries cycled stably for 180 cycles at 2 mA/cm.


title: Zinc–air battery

text: Metallic zinc could be used as an alternative fuel for vehicles, either in a zinc–air battery or to generate hydrogen near the point of use. Zinc's characteristics have motivated considerable interest as an energy source for electric vehicles. Gulf General Atomic demonstrated a 20 kW vehicle battery. General Motors conducted tests in the 1970s. Neither project led to a commercial product.


title: Zinc–air battery

text: In addition to liquid, pellets could be formed that are small enough to pump. Fuel cells using pellets would be able to quickly replace zinc-oxide with fresh zinc metal. The spent material can be recycled. The zinc–air cell is a primary cell (non-rechargeable); recycling is required to reclaim the zinc; much more energy is required to reclaim the zinc than is usable in a vehicle.


title: Zinc–air battery

text: One advantage of utilizing zinc–air batteries for vehicle propulsion is the mineral's relative abundance when compared to lithium. As of 2020, the total global zinc reserves are estimated to be around 1.9 billion tons, whereas total lithium reserves are estimated as 86 million tons.


title: Zinc–air battery

text: The Eos Energy System battery is about half the size of a shipping container and provides 1 MWh of storage. Con Edison, National Grid, Enel and GDF SUEZ began testing the battery for grid storage. Con Edison and City University of New York are testing a zinc-based battery from Urban Electric Power as part of a New York State Energy Research and Development Authority program. Eos projects that the cost of storing electricity with such EOS batteries is US$160/kWh and that it will provide electricity cheaper than a new natural-gas peaking power station. Other battery technologies range from $400 to about $1,000 a kilowatt-hour.


title: Zinc–air battery

text: When a load is applied over zinc-air batteries without access to oxygen, they generate hydrogen gas at a fairly controllable rate, proportional to the load. This can build up pressure, which is used in certain applications to expel another liquid over a longer period, like automatic lubricators or air fresheners.


title: Zinc–air battery

text: Zinc corrosion can produce potentially explosive hydrogen. Vent holes prevent pressure build-up within the cell. Manufacturers caution against hydrogen build-up in enclosed areas. A short-circuited cell gives relatively low current. Deep discharge below 0.5 V/cell may result in electrolyte leakage; little useful capacity exists below 0.9 V/cell.


title: Zinc–air battery

text: Older designs used mercury amalgam amounting to about 1% of the weight of a button cell, to prevent zinc corrosion. Newer types have no added mercury. Zinc itself is relatively low in toxicity. Mercury-free designs require no special handling when discarded or recycled.


title: Zinc–air battery

text: In United States waters, environmental regulations now require proper disposal of primary batteries removed from navigation aids. Formerly, discarded zinc–air primary batteries were dropped into the water around buoys, which allowed mercury to escape into the environment.


title: Wind turbine design

text: Wind turbine design is the process of defining the form and configuration of a wind turbine to extract energy from the wind. An installation consists of the systems needed to capture the wind's energy, point the turbine into the wind, convert mechanical rotation into electrical power, and other systems to start, stop, and control the turbine.


title: Wind turbine design

text: In 1919, German physicist Albert Betz showed that for a hypothetical ideal wind-energy extraction machine, the fundamental laws of conservation of mass and energy allowed no more than 16/27 (59.3%) of the wind's kinetic energy to be captured. This Betz' law limit can be approached by modern turbine designs which reach 70 to 80% of this theoretical limit.


title: Wind turbine design

text: In addition to the blades, design of a complete wind power system must also address the hub, controls, generator, supporting structure and foundation. Turbines must also be integrated into power grids.


title: Wind turbine design

text: Blade shape and dimension are determined by the aerodynamic performance required to efficiently extract energy, and by the strength required to resist forces on the blade.


title: Wind turbine design

text: The aerodynamics of a horizontal-axis wind turbine are not straightforward. The air flow at the blades is not the same as that away from the turbine. The way that energy is extracted from the air also causes air to be deflected by the turbine. Wind turbine aerodynamics at the rotor surface exhibit phenomena that are rarely seen in other aerodynamic fields.


title: Wind turbine design

text: Rotation speed must be controlled for efficient power generation and to keep the turbine components within speed and torque limits. The centrifugal force on the blades increases as the square of the rotation speed, which makes this structure sensitive to overspeed. Because power increases as the cube of the wind speed, turbines have must survive much higher wind loads (such as gusts of wind) than those loads from which they generate power.


title: Wind turbine design

text: A wind turbine must produce power over a range of wind speeds. The cut-in speed is around 3–4 m/s for most turbines, and cut-out at 25 m/s. If the rated wind speed is exceeded the power has to be limited.


title: Wind turbine design

text: A control system involves three basic elements: sensors to measure process variables, actuators to manipulate energy capture and component loading, and control algorithms that apply information gathered by the sensors to coordinate the actuators.


title: Wind turbine design

text: Any wind blowing above the survival speed damages the turbine. The survival speed of commercial wind turbines ranges from 40 m/s (144 km/h, 89 MPH) to 72 m/s (259 km/h, 161 MPH), typically around 60 m/s (216 km/h, 134 MPH). Some turbines can survive .


title: Wind turbine design

text: A stall on an airfoil occurs when air passes over it in such a way that the generation of lift rapidly decreases. Usually this is due to a high angle of attack (AOA), but can also result from dynamic effects. The blades of a fixed pitch turbine can be designed to stall in high wind speeds, slowing rotation. This is a simple fail-safe mechanism to help prevent damage. However, other than systems with dynamically controlled pitch, it can not produce a constant power output over a large range of wind speeds, which makes it less suitable for large scale, power grid applications.


title: Wind turbine design

text: A fixed-speed HAWT inherently increases its angle of attack at higher wind speed as the blades speed up. A natural strategy, then, is to allow the blade to stall when the wind speed increases. This technique was successfully used on many early HAWTs. However, the degree of blade pitch tended to increase noise levels.


title: Wind turbine design

text: Vortex generators may be used to control blade lift characteristics. VGs are placed on the airfoil to enhance the lift if they are placed on the lower (flatter) surface or limit the maximum lift if placed on the upper (higher camber) surface.


title: Wind turbine design

text: Furling works by decreasing the angle of attack, which reduces drag and blade cross-section. One major problem is getting the blades to stall or furl quickly enough in a wind gust. A fully furled turbine blade, when stopped, faces the edge of the blade into the wind.


title: Wind turbine design

text: Loads can be reduced by making a structural system softer or more flexible. This can be accomplished with downwind rotors or with curved blades that twist naturally to reduce angle of attack at higher wind speeds. These systems are nonlinear and couple the structure to the flow field - requiring design tools to evolve to model these nonlinearities.


title: Wind turbine design

text: Standard turbines all furl in high winds. Since furling requires acting against the torque on the blade, it requires some form of pitch angle control, which is achieved with a slewing drive. This drive precisely angles the blade while withstanding high torque loads. In addition, many turbines use hydraulic systems. These systems are usually spring-loaded, so that if hydraulic power fails, the blades automatically furl. Other turbines use an electric servomotor for every blade. They have a battery-reserve in case of grid failure. Small wind turbines (under 50 kW) with variable-pitching generally use systems operated by centrifugal force, either by flyweights or geometric design, and avoid electric or hydraulic controls.


title: Wind turbine design

text: Fundamental gaps exist in pitch control, limiting the reduction of energy costs, according to a report funded by the Atkinson Center for a Sustainable Future. Load reduction is currently focused on full-span blade pitch control, since individual pitch motors are the actuators on commercial turbines. Significant load mitigation has been demonstrated in simulations for blades, tower, and drive train. However, further research is needed to increase energy capture and mitigate fatigue loads.


title: Wind turbine design

text: A control technique applied to the pitch angle is done by comparing the power output with the power value at the rated engine speed (power reference, Ps reference). Pitch control is done with PI controller. In order to adjust pitch rapidly enough, the actuator uses the time constant Tservo, an integrator and limiters. The pitch angle remains from 0° to 30° with a change rate of 10°/second.


title: Wind turbine design

text: As in the figure at the right, the reference pitch angle is compared with the actual pitch angle b and then the difference is corrected by the actuator. The reference pitch angle, which comes from the PI controller, goes through a limiter. Restrictions are important to maintain the pitch angle in real terms. Limiting the change rate is especially important during network faults. The importance is due to the fact that the controller decides how quickly it can reduce the aerodynamic energy to avoid acceleration during errors.


title: Wind turbine design

text: Modern large wind turbines operate at variable speeds. When wind speed falls below the turbine's rated speed, generator torque is used to control the rotor speed to capture as much power as possible. The most power is captured when the tip speed ratio is held constant at its optimum value (typically 6 or 7). This means that rotor speed increases proportional to wind speed. The difference between the aerodynamic torque captured by the blades and the applied generator torque controls the rotor speed. If the generator torque is lower, the rotor accelerates, and if the generator torque is higher, the rotor slows. Below rated wind speed, the generator torque control is active while the blade pitch is typically held at the constant angle that captures the most power, fairly flat to the wind. Above rated wind speed, the generator torque is typically held constant while the blade pitch is adjusted accordingly.


title: Wind turbine design

text: One technique to control a permanent magnet synchronous motor is field-oriented control. Field-oriented control is a closed loop strategy composed of two current controllers (an inner loop and cascading outer loop) necessary for controlling the torque, and one speed controller.


title: Wind turbine design

text: In this control strategy the d axis current is kept at zero, while the vector current aligns with the q axis in order to maintain the torque angle at 90. This is a common control strategy because only the Iqs current must be controlled. The torque equation of the generator is a linear equation dependent only on the Iqs current.


title: Wind turbine design

text: Thus, the complete system of the machine side converter and the cascaded PI controller loops is given by the figure. The control inputs are the duty rations m and m, of the PWM-regulated converter. It displays the control scheme for the wind turbine in the machine side and simultaneously how the I to zero (the torque equation is linear).


title: Wind turbine design

text: Large turbines are typically actively controlled to face the wind direction measured by a wind vane situated on the back of the nacelle. By minimizing the yaw angle (the misalignment between wind and turbine pointing direction), power output is maximized and non-symmetrical loads minimized. However, since wind direction varies, the turbine does not strictly follow the wind and experiences a small yaw angle on average. The power output losses can be approximated to fall with (cos(yaw angle)). Particularly at low-to-medium wind speeds, yawing can significantly reduce output, with wind common variations reaching 30°. At high wind speeds, wind direction is less variable.


title: Wind turbine design

text: Braking a small turbine can be done by dumping energy from the generator into a resistor bank, converting kinetic energy into heat. This method is useful if the kinetic load on the generator is suddenly reduced or is too small to keep the turbine speed within its allowed limit.


title: Wind turbine design

text: Cyclically braking slows the blades, which increases the stalling effect and reducing efficiency. Rotation can be kept at a safe speed in faster winds while maintaining (nominal) power output. This method is usually not applied on large, grid-connected wind turbines.


title: Wind turbine design

text: A mechanical drum brake or disc brake stops rotation in emergency situation such as extreme gust events. The brake is a secondary means to hold the turbine at rest for maintenance, with a rotor lock system as primary means. Such brakes are usually applied only after blade furling and electromagnetic braking have reduced the turbine speed because mechanical brakes can ignite a fire inside the nacelle if used at full speed. Turbine load increases if the brake is applied at rated RPM.


title: Wind turbine design

text: Turbines come in size classes. The smallest, with power less than 10 kW are used in homes, farms and remote applications whereas intermediate wind turbines (10-250 kW ) are useful for village power, hybrid systems and distributed power. The world's largest wind turbine as of 2021 was Vestas' V236-15.0 MW turbine. The new design's blades offer the largest swept area in the world with three blades giving a rotor diameter of . Ming Yang in China have announced a larger 16 MW design.


title: Wind turbine design

text: For a given wind speed, turbine mass is approximately proportional to the cube of its blade-length. Wind power intercepted is proportional to the square of blade-length. The maximum blade-length of a turbine is limited by strength, stiffness, and transport considerations.


title: Wind turbine design

text: Labor and maintenance costs increase slower than turbine size, so to minimize costs, wind farm turbines are basically limited by the strength of materials, and siting requirements.


title: Wind turbine design

text: Utility-scale wind turbine generators have minimum temperature operating limits that apply in areas with temperatures below . Turbines must be protected from ice accumulation that can make anemometer readings inaccurate and which, in certain turbine control designs, can cause high structure loads and damage. Some turbine manufacturers offer low-temperature packages at extra cost, which include internal heaters, different lubricants, and different alloys for structural elements. If low-temperatures are combined with a low-wind condition, the turbine requires an external supply of power, equivalent to a few percent of its rated output, for internal heating. For example, the St. Leon Wind Farm in Manitoba, Canada, has a total rating of 99 MW and is estimated to need up to 3 MW (around 3% of capacity) of station service power a few days a year for temperatures down to .


title: Wind turbine design

text: The nacelle houses the gearbox and generator connecting the tower and rotor. Sensors detect the wind speed and direction, and motors turn the nacelle into the wind to maximize output.


title: Wind turbine design

text: In conventional wind turbines, the blades spin a shaft that is connected through a gearbox to the generator. The gearbox converts the turning speed of the blades (15 to 20 RPM for a one-megawatt turbine) into the 1,800 (750-3600) RPM that the generator needs to generate electricity. Analysts from GlobalData estimate that the gearbox market grew from $3.2bn in 2006 to $6.9bn in 2011. The market leader was Winergy in 2011. The use of magnetic gearboxes has been explored as a way of reducing maintenance costs.


title: Wind turbine design

text: For large horizontal axis wind turbines (HAWT), the generator is mounted in a nacelle at the top of a tower, behind the rotor hub. Older wind turbines generate electricity through asynchronous machines directly connected to the grid. The gearbox reduces generator cost and weight. Commercial generators have a rotor carrying a winding so that a rotating magnetic field is produced inside a set of windings called the stator. While the rotating winding consumes a fraction of a percent of the generator output, adjustment of the field current allows good control over the output voltage.


title: Wind turbine design

text: The rotor's varying output frequency and voltage can be matched to the fixed values of the grid using multiple technologies such as doubly fed induction generators or full-effect converters which converts the variable frequency current to DC and then back to AC using inverters. Although such alternatives require costly equipment and cost power, the turbine can capture a significantly larger fraction of the wind energy. Most are Low Voltage 660 Volt, but some offshore turbines (several MW) are 3.3 kV Medium Voltage.


title: Wind turbine design

text: In some cases, especially when offshore, a large collector transformer converts the wind farm's medium-voltage AC grid to DC and transmits the energy through a power cable to an onshore HVDC converter station.


title: Wind turbine design

text: Gearless wind turbines (also called direct drive) eliminate the gearbox. Instead, the rotor shaft is attached directly to the generator, which spins at the same speed as the blades.


title: Wind turbine design

text: Advantages of permanent magnet direct drive generators (PMDD) over geared generators include increased efficiency, reduced noise, longer lifetime, high torque at low rpm, faster and precise positioning, and drive stiffness. PMDD generators "eliminate the gear-speed increaser, which is susceptible to significant accumulated fatigue torque loading, related reliability issues, and maintenance costs."


title: Wind turbine design

text: To make up for a direct drive generator's slower rotation rate, the diameter of the generator's rotor is increased so that it can contain more magnets to create the required frequency and power. Gearless wind turbines are often heavier than geared wind turbines. An EU study showed that gearbox reliability is not the main problem in wind turbines. The reliability of direct drive turbines offshore is still not known, given the small sample size.


title: Wind turbine design

text: Experts from Technical University of Denmark estimate that a geared generator with permanent magnets may require 25 kg/MW of the rare-earth element neodymium, while a gearless may use 250 kg/MW.


title: Wind turbine design

text: In December 2011, the US Department of Energy announced a critical shortage of rare-earth elements such as neodymium. China produces more than 95% of rare-earth elements, while Hitachi holds more than 600 patents covering neodymium magnets. Direct-drive turbines require 600 kg of permanent magnet material per megawatt, which translates to several hundred kilograms of rare-earth content per megawatt, as neodymium content is estimated to be 31% of magnet weight. Hybrid drivetrains (intermediate between direct drive and traditional geared) use significantly less rare-earth materials. While permanent magnet wind turbines only account for about 5% of the market outside of China, their market share inside of China is estimated at 25% or higher. In 2011, demand for neodymium in wind turbines was estimated to be 1/5 of that in electric vehicles.


title: Wind turbine design

text: The ratio between the blade speed and the wind speed is called tip-speed ratio. High efficiency 3-blade-turbines have tip speed/wind speed ratios of 6 to 7. Wind turbines spin at varying speeds (a consequence of their generator design). Use of aluminum and composite materials has contributed to low rotational inertia, which means that newer wind turbines can accelerate quickly if the winds pick up, keeping the tip speed ratio more nearly constant. Operating closer to their optimal tip speed ratio during energetic gusts of wind allows wind turbines to improve energy capture from sudden gusts.


title: Wind turbine design

text: Noise increases with tip speed. To increase tip speed without increasing noise would reduce torque into the gearbox and generator, reducing structural loads, thereby reducing cost. The noise reduction is linked to the detailed blade aerodynamics, especially factors that reduce abrupt stalling. The inability to predict stall restricts the use of aggressive aerodynamics. Some blades (mostly on Enercon) have a winglet to increase performance and reduce noise.


title: Wind turbine design

text: In simple designs, the blades are directly bolted to the hub and are unable to pitch, which leads to aerodynamic stall above certain windspeeds. In more sophisticated designs, they are bolted to the pitch bearing, which adjusts their angle of attack with the help of a pitch system according to the wind speed. Pitch control is performed by hydraulic or electric systems (battery or ultracapacitor). The pitch bearing is bolted to the hub. The hub is fixed to the rotor shaft which drives the generator directly or through a gearbox.


title: Wind turbine design

text: The number of blades is selected for aerodynamic efficiency, component costs, and system reliability. Noise emissions are affected by the location of the blades upwind or downwind of the tower and the rotor speed. Given that the noise emissions from the blades' trailing edges and tips vary by the 5th power of blade speed, a small increase in tip speed dramatically increases noise.


title: Wind turbine design

text: Wind turbines almost universally use either two or three blades. However, patents present designs with additional blades, such as Chan Shin's multi-unit rotor blade system. Aerodynamic efficiency increases with number of blades but with diminishing return. Increasing from one to two yields a six percent increase, while going from two to three yields an additional three percent. Further increasing the blade count yields minimal improvements and sacrifices too much in blade stiffness as the blades become thinner.


title: Wind turbine design

text: Theoretically, an infinite number of blades of zero width is the most efficient, operating at a high value of the tip speed ratio, but this is not practical.


title: Wind turbine design

text: Component costs affected by blade count are primarily for materials and manufacturing of the turbine rotor and drive train. Generally, the lower the number of blades, the lower the material and manufacturing costs. In addition, fewer blades allow higher rotational speed. Blade stiffness requirements to avoid tower interference limit blade thickness, but only when the blades are upwind of the tower; deflection in a downwind machine increases tower clearance. Fewer blades with higher rotational speeds reduce peak torque in the drive train, resulting in lower gearbox and generator costs.


title: Wind turbine design

text: System reliability is affected by blade count primarily through the dynamic loading of the rotor into the drive train and tower systems. While aligning the wind turbine to changes in wind direction (yawing), each blade experiences a cyclic load at its root end depending on blade position. However, these cyclic loads when combined at the drive train shaft are symmetrically balanced for three blades, yielding smoother operation during yaw. One or two blade turbines can use a pivoting teetered hub to nearly eliminate the cyclic loads into the drive shaft and system during yawing. In 2012, a Chinese 3.6 MW two-blade turbine was tested in Denmark.


title: Wind turbine design

text: Aesthetics are a factor in that the three-bladed rotor rates more pleasing to look at than a one- or two-bladed rotor.


title: Wind turbine design

text: Metals are undesirable because of their vulnerability to fatigue. Ceramics have low fracture toughness, resulting in early blade failure. Traditional polymers are not stiff enough to be useful, and wood has problems with repeatability, especially considering the blade length. That leaves fiber-reinforced composites, which have high strength and stiffness and low density.


title: Wind turbine design

text: Wood and canvas sails were used on early windmills due to their low price, availability, and ease of manufacture. Smaller blades can be made from light metals such as aluminium. These materials, however, require frequent maintenance. Wood and canvas construction limits the airfoil shape to a flat plate, which has a relatively high ratio of drag to force captured(low aerodynamic efficiency) compared to solid airfoils. Construction of solid airfoil designs requires inflexible materials such as metals or composites. Some blades incorporate lightning conductors.


title: Wind turbine design

text: Increasing blade length pushed power generation from the single megawatt range to upwards of 10 megawatts. A larger area effectively increases tip-speed ratio at a given wind speed, thus increasing its energy extraction. Software such as HyperSizer (originally developed for spacecraft design) can be used to improve blade design.


title: Wind turbine design

text: As of 2015 the rotor diameters of onshore wind turbine blades reached 130 meters, while the diameter of offshore turbines reached 170 meters. In 2001, an estimated 50 million kilograms of fiberglass laminate were used in wind turbine blades.


title: Wind turbine design

text: An important goal is to control blade weight. Since blade mass scales as the cube of the turbine radius, gravity loading constrains systems with larger blades. Gravitational loads include axial and tensile/ compressive loads (top/bottom of rotation) as well as bending (lateral positions). The magnitude of these loads fluctuates cyclically and the edgewise moments (see below) are reversed every 180° of rotation. Typical rotor speeds and design life are ~10 and 20 years, respectively, with the number of lifetime revolutions on the order of 10^8. Considering wind, it is expected that turbine blades go through ~10^9 loading cycles.


title: Wind turbine design

text: Wind is another source of rotor blade loading. Lift causes bending in the flatwise direction (out of rotor plane) while airflow around the blade cause edgewise bending (in the rotor plane). Flaps bending involves tension on the pressure (upwind) side and compression on the suction (downwind) side. Edgewise bending involves tension on the leading edge and compression on the trailing edge.


title: Wind turbine design

text: Wind loads are cyclical because of natural variability in wind speed and wind shear (higher speeds at top of rotation).


title: Wind turbine design

text: Failure in ultimate loading of wind-turbine rotor blades exposed to wind and gravity loading is a failure mode that needs to be considered when the rotor blades are designed. The wind speed that causes bending of the rotor blades exhibits a natural variability, and so does the stress response in the rotor blades. Also, the resistance of the rotor blades, in terms of their tensile strengths, exhibits a natural variability. Given the increasing size of production wind turbines, blade failures are increasingly relevant when assessing public safety risks from wind turbines. The most common failure is the loss of a blade or part thereof. This has to be considered in the design.


title: Wind turbine design

text: In light of these failure modes and increasingly larger blade systems, researchers seek cost-effective materials with higher strength-to-mass ratios.


title: Wind turbine design

text: The majority of commercialized wind turbine blades are made from fiber-reinforced polymers (FRPs), which are composites consisting of a polymer matrix and fibers. The long fibers provide longitudinal stiffness and strength, and the matrix provides fracture toughness, delamination strength, out-of-plane strength, and stiffness. Material indices based on maximizing power efficiency, high fracture toughness, fatigue resistance, and thermal stability are highest for glass and carbon fiber reinforced plastics (GFRPs and CFRPs).


title: Wind turbine design

text: In turbine blades, matrices such as thermosets or thermoplastics are used; as of 2017, thermosets are more common. These allow for the fibers to be bound together and add toughness. Thermosets make up 80% of the market, as they have lower viscosity, and also allow for low temperature cure, both features contributing to ease of processing during manufacture. Thermoplastics offer recyclability that the thermosets do not, however their processing temperature and viscosity are much higher, limiting the product size and consistency, which are both important for large blades. Fracture toughness is higher for thermoplastics, but the fatigue behavior is worse.


title: Wind turbine design

text: Manufacturing blades in the 40 to 50-metre range involves proven fiberglass composite fabrication techniques. Manufacturers such as Nordex SE and GE Wind use an infusion process. Other manufacturers vary this technique, some including carbon and wood with fiberglass in an epoxy matrix. Other options include pre-impregnated ("prepreg") fiberglass and vacuum-assisted resin transfer moulding. Each of these options uses a glass-fiber reinforced polymer composite constructed with differing complexity. Perhaps the largest issue with open-mould, wet systems is the emissions associated with the volatile organic compounds ("VOCs") released. Preimpregnated materials and resin infusion techniques contain all VOCs, however these contained processes have their challenges, because the production of thick laminates necessary for structural components becomes more difficult. In particular, the preform resin permeability dictates the maximum laminate thickness; also, bleeding is required to eliminate voids and ensure proper resin distribution. One solution to resin distribution is to use partially impregnated fiberglass. During evacuation, the dry fabric provides a path for airflow and, once heat and pressure are applied, the resin may flow into the dry region, resulting in an evenly impregnated laminate structure.


title: Wind turbine design

text: Epoxy-based composites have environmental, production, and cost advantages over other resin systems. Epoxies also allow shorter cure cycles, increased durability, and improved surface finish. Prepreg operations further reduce processing time over wet lay-up systems. As turbine blades passed 60 metres, infusion techniques became more prevalent, because traditional resin transfer moulding injection times are too long compared to resin set-up time, limiting laminate thickness. Injection forces resin through a thicker ply stack, thus depositing the resin in the laminate structure before gelation occurs. Specialized epoxy resins have been developed to customize lifetimes and viscosity.


title: Wind turbine design

text: Carbon fiber-reinforced load-bearing spars can reduce weight and increase stiffness. Using carbon fibers in 60-metre turbine blades is estimated to reduce total blade mass by 38% and decrease cost by 14% compared to 100% fiberglass. Carbon fibers have the added benefit of reducing the thickness of fiberglass laminate sections, further addressing the problems associated with resin wetting of thick lay-up sections. Wind turbines benefit from the trend of decreasing carbon fiber costs.


title: Wind turbine design

text: Although glass and carbon fibers have many optimal qualities, their downsides include the fact that high filler fraction (10-70 wt%) causes increased density as well as microscopic defects and voids that can lead to premature failure.


title: Wind turbine design

text: Carbon nanotubes (CNTs) can reinforce polymer-based nanocomposites. CNTs can be grown or deposited on the fibers or added into polymer resins as a matrix for FRP structures. Using nanoscale CNTs as filler instead of traditional microscale filler (such as glass or carbon fibers) results in CNT/polymer nanocomposites, for which the properties can be changed significantly at low filler contents (typically < 5 wt%). They have low density and improve the elastic modulus, strength, and fracture toughness of the polymer matrix. The addition of CNTs to the matrix also reduces the propagation of interlaminar cracks.


title: Wind turbine design

text: Research on a low-cost carbon fiber (LCCF) at Oak Ridge National Laboratory gained attention in 2020, because it can mitigate the structural damage from lightning strikes. On glass fiber wind turbines, lightning strike protection (LSP) is usually added on top, but this is effectively deadweight in terms of structural contribution. Using conductive carbon fiber can avoid adding this extra weight.


title: Wind turbine design

text: Some polymer composites feature self-healing properties. Since the blades of the turbine form cracks from fatigue due to repetitive cyclic stresses, self-healing polymers are attractive for this application, because they can improve reliability and buffer various defects such as delamination. Embedding paraffin wax-coated copper wires in a fiber reinforced polymer creates a network of tubes. Using a catalyst, these tubes and dicyclopentadiene (DCPD) then react to form a thermosetting polymer, which repairs the cracks as they form in the material. As of 2019, this approach is not yet commercial.


title: Wind turbine design

text: Further improvement is possible through the use of carbon nanofibers (CNFs) in the blade coatings. A major problem in desert environments is erosion of the leading edges of blades by sand-laden wind, which increases roughness and decreases aerodynamic performance. The particle erosion resistance of fiber-reinforced polymers is poor when compared to metallic materials and elastomers. Replacing glass fiber with CNF on the composite surface greatly improves erosion resistance. CNFs provide good electrical conductivity (important for lightning strikes), high damping ratio, and good impact-friction resistance.


title: Wind turbine design

text: For wind turbines, especially those offshore, or in wet environments, base surface erosion also occurs. For example, in cold climates, ice can build up on the blades and increase roughness. At high speeds, this same erosion impact can occur from rainwater. A useful coating must have good adhesion, temperature tolerance, weather tolerance (to resist erosion from salt, rain, sand, etc.), mechanical strength, ultraviolet light tolerance, and have anti-icing and flame retardant properties. Along with this, the coating should be cheap and environmentally friendly.


title: Wind turbine design

text: Super hydrophobic surfaces (SHS) cause water droplets to bead, and roll off the blades. SHS prevents ice formation, up to -25 C, as it changes the ice formation process.; specifically, small ice islands form on SHS, as opposed to a large ice front. Further, due to the lowered surface area from the hydrophobic surface, aerodynamic forces on the blade allow these islands to glide off the blade, maintaining proper aerodynamics. SHS can be combined with heating elements to further prevent ice formation.


title: Wind turbine design

text: Lightning damage over the course of a 25-year lifetime goes from surface level scorching and cracking of the laminate material, to ruptures in the blade or full separation in the adhesives that hold the blade together. It is most common to observe lightning strikes on the tips of the blades, especially in rainy weather due to embedded copper wiring. The most common method countermeasure, especially in non-conducting blade materials like GFRPs and CFRPs, is to add lightning "arresters", which are metallic wires that ground the blade, skipping the blades and gearbox entirely.


title: Wind turbine design

text: Wind turbine blades typically require repair after 2–5 years. Notable causes of blade damage comes from manufacturing defects, transportation, assembly, installation, lightning strikes, environmental wear, thermal cycling, leading edge erosion, or fatigue. Due to composite blade material and function, repair techniques found in aerospace applications often apply or provide a basis for basic repairs.


title: Wind turbine design

text: Depending on the nature of the damage, the approach of blade repairs can vary. Erosion repair and protection includes coatings, tapes, or shields. Structural repairs require bonding or fastening new material to the damaged area. Nonstructural matrix cracks and delaminations require fills and seals or resin injections. If ignored, minor cracks or delaminations can propagate and create structural damage.


title: Wind turbine design

text: After the past few decades of rapid wind expansion across the globe, wind turbines are aging. This aging brings operation and maintenance(O&M) costs along with it, increasing as turbines approach their end of life. If damages to blades are not caught in time, power production and blade lifespan are decreased. Estimates project that 20-25% of the total levelized cost per kWh produced stems from blade O&M alone.


title: Wind turbine design

text: The Global Wind Energy Council (GWEC) predicted that wind energy will supply 28.5% of global energy by 2030. This requires a newer and larger fleet of more efficient turbines and the corresponding decommissioning of older ones. Based on a European Wind Energy Association study, in 2010 between 110 and 140 kilotonnes of composites were consumed to manufacture blades. The majority of the blade material ends up as waste, and requires recycling. As of 2020, most end-of-use blades are stored or sent to landfills rather than recycled. Typically, glass-fiber-reinforced polymers (GFRPs) comprise around 70% of the laminate material in the blade. GFRPs are not combustible, and so hinder the incineration of combustible materials. Therefore, conventional recycling methods are inappropriate. Depending on whether individual fibers are to be recovered, GFRP recycling may involve:


title: Wind turbine design

text: Start-up company Global Fiberglass Solutions claimed in 2020 that it had a method to process blades into pellets and fiber boards for use in flooring and walls. The company started producing samples at a plant in Sweetwater, Texas.


title: Wind turbine design

text: Wind velocities increase at higher altitudes due to surface aerodynamic drag (by land or water surfaces) and air viscosity. The variation in velocity with altitude, called wind shear, is most dramatic near the surface. Typically, the variation follows the wind profile power law, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%. To avoid buckling, doubling the tower height generally requires doubling the tower diameter, increasing the amount of material by a factor of at least four.


title: Wind turbine design

text: During the night, or when the atmosphere becomes stable, wind speed close to the ground usually subsides whereas at turbine hub altitude it does not decrease that much or may even increase. As a result, the wind speed is higher and a turbine will produce more power than expected from the 1/7 power law: doubling the altitude may increase wind speed by 20% to 60%. A stable atmosphere is caused by radiative cooling of the surface and is common in a temperate climate: it usually occurs when there is a (partly) clear sky at night. When the (high altitude) wind is strong (a 10-meter wind speed higher than approximately 6 to 7 m/s) the stable atmosphere is disrupted because of friction turbulence and the atmosphere turns neutral. A daytime atmosphere is either neutral (no net radiation; usually with strong winds and heavy clouding) or unstable (rising air because of ground heating—by the sun). The 1/7 power law is a good approximation of the wind profile. Indiana was rated as having a wind capacity of 30,000 MW, but by raising the expected turbine height from 50 m to 70 m raised the wind capacity to 40,000 MW, and could be double that at 100 m.


title: Wind turbine design

text: For HAWTs, tower heights approximately two to three times the blade length balance material costs of the tower against better utilisation of the more expensive active components.


title: Wind turbine design

text: Road restrictions make tower transport with a diameter of more than 4.3 m difficult. Swedish analyses showed that the bottom wing tip must be at least 30 m above the tree tops. A 3 MW turbine may increase output from 5,000 MWh to 7,700 MWh per year by rising from 80 to 125 meters. A tower profile made of connected shells rather than cylinders can have a larger diameter and still be transportable. A 100 m prototype tower with TC bolted 18 mm 'plank' shells at the wind turbine test center Høvsøre in Denmark was certified by Det Norske Veritas, with a Siemens nacelle. Shell elements can be shipped in standard 12 m shipping containers.


title: Wind turbine design

text: As of 2003, typical modern wind turbine installations used towers. Height is typically limited by the availability of cranes. This led to proposals for "partially self-erecting wind turbines" that, for a given available crane, allow taller towers that locate a turbine in stronger and steadier winds, and "self-erecting wind turbines" that could be installed without cranes.


title: Wind turbine design

text: Currently, the majority of wind turbines are supported by conical tubular steel towers. These towers represent 30% – 65% of the turbine weight and therefore account for a large percentage of transport costs. The use of lighter tower materials could reduce the overall transport and construction cost, as long as stability is maintained. Higher grade S500 steel costs 20%-25% more than S335 steel (standard structural steel), but it requires 30% less material because of its improved strength. Therefore, replacing wind turbine towers with S500 steel offer savings in weight and cost.


title: Wind turbine design

text: Another disadvantage of conical steel towers is meeting the requirements of wind turbines taller than 90 meters. High performance concrete may increase tower height and increase lifetime. A hybrid of prestressed concrete and steel improves performance over standard tubular steel at tower heights of 120 meters. Concrete also allows small precast sections to be assembled on site. One downside of concrete towers is the higher emissions during concrete production. However, the overall environmental impact should be positive if concrete towers can double the wind turbine lifetime.


title: Wind turbine design

text: Wood is another alternative: a 100-metre tower supporting a 1.5 MW turbine operates in Germany. The wood tower shares the same transportation benefits of the segmented steel shell tower, but without the steel.


title: Wind turbine design

text: Grid-connected wind turbines, until the 1970s, were fixed-speed. As recently as 2003, nearly all grid-connected wind turbines operated at constant speed (synchronous generators) or within a few percent of constant speed (induction generators). As of 2011, many turbines used fixed speed induction generators (FSIG). By then, most newly connected turbines were variable speed.


title: Wind turbine design

text: Early control systems were designed for peak power extraction, also called maximum power point tracking—they attempted to pull the maximum power from a given wind turbine under the current wind conditions. More recent systems deliberately pull less than maximum power in most circumstances, in order to provide other benefits, which include:


title: Wind turbine design

text: The generator produces alternating current (AC). The most common method in large modern turbines is to use a doubly fed induction generator directly connected to the grid. Some turbines drive an AC/AC converter—which converts the AC to direct current (DC) with a rectifier and then back to AC with an inverter—in order to match grid frequency and phase.


title: Wind turbine design

text: A useful technique to connect a PMSG to the grid is via a back-to-back converter. Control schemes can achieve unity power factor in the connection to the grid. In that way the wind turbine does not consume reactive power, which is the most common problem with turbines that use induction machines. This leads to a more stable power system. Moreover, with different control schemes a PMSG turbine can provide or consume reactive power. So, it can work as a dynamic capacitor/inductor bank to help with grid stability.