An approach for improving the precision on short-range electronic distance measurement trigonometry
Consider the trigonometric leveling method is simple, flexible and less limited by terrain conditions, it commonly used to inconveniently implemented area. Through the total station rapid development, the horizontal distance measuring between station and target for the traditional triangulation has been substituted by a slope from the Electronic Distance Measurement(EDM) measured. When combined with the appropriate methods of observation and error correction, short-range EDM trigonometric levelingshould be able to improve the accuracy levels of precision leveling. It can be enhanced the efficiency of leveling jobs. The main error of short-range EDM trigonometric leveling is from atmospheric refraction, earth curvature and measurement error of height of instrument and prismatic. The first two errors can be reduced by reciprocal observation and intermediate point. Moreover, intermediate point just only measure the prismatic height between start and end point of the measuring leveling line, The results accuracy and observation efficiency is increased. In this study, about 2km selected sections of Highway 84 at Tainan Yujing District is chosen be an experimental zone. Three kinds of closed leveling line, 200m, 400m and 600m is consisted in this measured planning. Then, non-reciprocal observation, reciprocal observation and intermediate point are introduced to implement the measurement. Experimental results show that the EDM triangle elevation for 600m range or less, the fourth-level observation precision can be achieved in non-reciprocal observation. However, the loop closure error will be caused no any grade leveling accuracy. For the reciprocal observation or intermediate method, third-level precision of measurement accuracy and loop closure error can be accomplished. The results show that the short-range EDM triangle elevation has a higher level of feasibility to instead of the traditional measure.
Precise Height Determination Using Leap-Frog Trigonometric Leveling
Precise leveling has been used for the determination of accurate heights for many years. The application of this technique is difficult, time consuming, and expensive, especially in rough terrain. These difficulties have forced researchers to examine alternative methods of height determination. As a result of modern high-tech instrument developments, research has again been focused on precision trigonometric leveling. In this study, a leap-frog trigonometric leveling (LFTL) is applied with different sight distances on a sample test network at the Selcuk University Campus in Konya, Turkey, in order to determine the optimum sight distances. The results were compared with precise geometric leveling in terms of precision, cost, and feasibility. Leap-frog trigonometric leveling for the sight distance S=150 m resulted in a standard deviation of ±1.87 mm∕km and with a production speed of 5.6 km∕day .
Analysis of the stress wave effect during coal breakage by a high-pressure abrasive air jet
In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.