A CLOSED-FORM APPROXIMATE SOLUTION FOR COUPLED VIBRATIONS OF COMPOSITE THIN-WALLED BEAMS WITH MID-PLANE SYMMETRY
Original scientific paper The purpose of this paper is to develop and present an approximate analysis procedure to estimate the natural frequencies and mode shapes of thin-walled beams with arbitrary open cross-section, made of laminates with mid-plane symmetry. Theory of thin-walled composite beams is based on assumptions consistent with the Vlasov's beam theory and classical lamination theory. The equations of motion for coupled bending-torsional vibrations are derived from the principle of virtual displacements. In the case of simply supported thin-walled beam the frequency equation, given in determinant form, is expanded in an explicit analytical form, which gives the natural frequencies of free harmonic vibrations. For verification, the analytical study by other researchers and the FEM analysis using ANSYS are compared with the current results.
Response of Balanced Laminate Subjected to Abrupt Heat Flux: A New Perspective
A new perspective presents how the interaction between the material stiffness of both matrix and fibre took place to form the laminate response. Thin square simply supported balanced laminated composite plate of different ply arrangements subjected to abrupt heat flux is utilized in this investigation. The effect of ply arrangement on the elapse time for vibrations to vanish and the maximum response amplitude is also investigated. The finite element analysis results show that the response is an amplitude modulated signal that represents frequencies of both fibre and matrix. The analysis shows that the ratio of the carrier frequency to the modulating frequency matches the ratio of the fibre stiffness to ply lateral stiffness. Through the investigation, the maximum static deformation and the dynamic amplitude are illustrated for different ply arrangements. Furthermore, it is found that almost all laminates have a similar elapsed time for vibrations to vanish.
Ocean thermal energy conversion: The promise of a clean future
Due to the world's heavy dependence on fossil fuels for electricity, pollution and global warming is on the rise. However, numerous countries are still relying on diesel generators as their main source of energy. There is a lack of practical alternative energy source that can meet the global energy demand without posing any threat to the natural environment. Ocean Thermal Energy Conversion (OTEC) is a concept that has the potential to address this growing issue. It is basically a mechanism that exploits the temperature difference between warm surface seawater and cold deep ocean water, to produce electricity. Although OTEC has a low energy density, the thermal energy in the ocean is vastly abundant. OTEC development has been dormant for a long time since it was first proposed in 1881. However, it has now regained recognition worldwide as a realistic solution to our world energy issue. Instead of having a great potential for power generation, it also carries the ability to produce high value products from the large volume of Deep Sea Water (DSW) that can be released as byproducts of OTEC plant operation. These products can hold a very profitable place in industries such as pharmaceutical, food, cosmetics and mineral water production. Further research on ocean current and DSW properties can someday lead to the commercial used of OTEC. This paper is a review of the basic concept, present status and future prospects of OTEC around the world.