Abstract. Nowadays there are some path planning algorithms for mobile robot which have been documented and explained individually in detail such as A*, LPA*, D* and D* Lite. However, there is still a lack of a comparative analysis of these algorithms. Therefore, in this paper a research of comparing A* and D* Lite algorithm for AGV's path planning is conducted by using simulation and experiment. The goal is to compare the characteristic of each algorithm when they are applied in a real differential drive AGV and give the reader a guide in choosing algorithms for their own planning domains. The emphasis of this comparison is on the computation time of generating trajectory and the distance of the generated trajectory. The simulation and experimental results show that generally D* Lite can plan the shorter path with faster computation time than A*. However, there are some cases when D* Lite is less effective than A*. It means which of the algorithms should be chosen depends on the requirement of the system.
An efficient and reliable pressurization system for an oxidizer and fuel of a liquid
propellant rocket is critical for a successful launch. A liquid helium pressurization system employing a heater can reduce its mass, and be made simpler and more reliable than conventional pressurization systems. The key issue to minimize the total mass of the system is the optimization of the size of the liquid helium tank. In this paper, we describe a method to determine the optimal size of a liquid helium tank, and present one set of results under a given set of requirements. In this pressurization system, the heater design is represented by the heater efficiency. To estimate the heater efficiency, the convection heat transfer coefficient should be known beforehand. The guideline how to estimate this convection heat transfer coefficient based on the preliminary experimental data is also presented in this paper.
Since glass microsphere has high crush strength, low density and small particle size, it becomes alternative thermal insulation material for cryogenic systems, such as storage and transportation tank for cryogenic fluids. Although many experiments have been performed to verify the effective thermal conductivity of microsphere, prediction by calculation is still inaccurate due to the complicated geometries, including wide range of powder diameter distribution and different pore sizes. The accurate effective thermal conductivity model for microsphere is discussed in this paper. There are four mechanisms which contribute to the heat transfer of the evacuated powder: gaseous conduction (k g ), solid conduction (k s ), radiation (k r ) and thermal contact (k c ). Among these components, k g and k s were calculated by Zehner and Schlunder model (1970). Other component values for k c and k r, which were obtained from experimental data under high vacuum conditions were added. In this research paper, the geometry of microsphere was simplified as a homogeneous solid sphere. The calculation results were compared with previous experimental data by R. Wawryk (1988), H. S. Kim (2010) and the experiment of this paper to show good agreement within error of 46%, 4.6% and 17 % for each result.
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