Current Issue : July - September Volume : 2014 Issue Number : 3 Articles : 5 Articles
This paper aims at realizing an automatic parking method through a bird�s eye view vision system.With this method, vehicles can\nmake robust and real-time detection and recognition of parking spaces. During parking process, the omnidirectional information\nof the environment can be obtained by using four on-board fisheye cameras around the vehicle, which are the main part of the\nbird�s eye view vision system. In order to achieve this purpose, a polynomial fisheye distortion model is firstly used for camera\ncalibration. An image mosaicking method based on the Levenberg-Marquardt algorithm is used to combine four individual images\nfrom fisheye cameras into one omnidirectional bird�s eye view image. Secondly, features of the parking spaces are extracted with a\nRadon transform based method. Finally, double circular trajectory planning and a preview control strategy are utilized to realize\nautonomous parking.Through experimental analysis, we can see that the proposed method can get effective and robust real-time\nresults in both parking space recognition and automatic parking....
Fully developed periodic laminar flow and heat transfer in an isothermal wall tube with 45�° upstream rectangular winglet vortex\ngenerators (RWVG) with closed end are investigated numerically. The fluid flow and heat transfer characteristics are proposed for\nReynolds numbers based on the diameter of the tube, Re = 100 to 2000.The RWVGs with an attack angle of 45�° are mounted with\nin-line arrangement on both sides of a plate and the closed tip pointing upstream is inserted in the middle of the tested tube to\nproduce longitudinal vortex flows through the tested section. Effects of different blockage ratios (b/D, BR) and pitch spacing ratios\n(P/D, PR) on heat transfer, pressure loss, and the thermal enhancement factor (TEF) in the round tube are studied.Theresults show\nthat the longitudinal vortex flows can induce impinging flows on a tube wall leading to an extreme increase in heat transfer rate\nover the round tube for all cases. Additionally, the rise in the BR and the reduction of PR result in the increase of both the Nusselt\nnumber and friction factor values. The optimum TEF in the range studied is around 2.9 at BR = 0.15, PR = 1, and Re = 2000....
In the process of hard rock breaking, the conical pick bears great cutting force and wear, and the cutting efficiency is lower.Thus\ndifferent combination ways of water jet and conical pick were proposed to solve this issue; for instance, water jet placed in the front\nof pick (JFP) and water jet through the center of pick (JCP) was researched by numerical simulation and experiments in this paper.\nFirst, the models of rock breaking were built based on SPH combined with finite element method. Then, the stress distribution of\nrock and the cut force of pick were analyzed when the rock broken by the conical pick assisted with the high pressure water jet. It\nindicates that the effect of the JCP on rock breaking is better than the JFP. At last, experiments about rock breaking with a conical\npick and the JCP were conducted to verify the reliability of the simulation. It indicates that the rock breaking with the assistance of\nhigh pressure water jet cannot only reduce the pick force, but also increase the rock crushing volume....
This paper presents friction-induced vibration (FIV) caused by combined mode-coupling and negative damping effects in a simple\nFIV model. In doing so, a new four-degree-of-freedom linear model which consists of a slider and a block is proposed and then\nsimulated using MATLAB/Simulink. Stability or instability of the FIV model is defined by the convergence or divergence of\ntime domain responses of the slider and the block. Having found critical slope of friction-velocity characteristics that generate\ninstabilities in the model, a conventional closed loop proportional-integral-derivative (PID) controller is first introduced into the\nmain model in order to attenuate the vibration level and subsequently to suppress it. Later, the model is integrated with the active\nforce control (AFC) element to effectively reject the disturbance and reduce the vibrations. It is found that the integrated PID-AFC\nscheme is effective in reducing vibration compared to the pure PID controller alone.Thus, the proposed control scheme can be one\nof the potential solutions to suppress vibration in a friction-induced vibration system....
Vibration-based damage detection, a nondestructive method, is based on the fact that vibration characteristics such as natural\nfrequencies andmode shapes of structures are changed when the damage happens. This paper presents cooperative coevolutionary\ngenetic algorithm(CCGA),which is capable for an optimization problem with a large number of decision variables, as the optimizer\nfor the vibration-based damage detection in beams. In the CCGA, a minimized objective function is a numerical indicator of\ndifferences between vibration characteristics of the actual damage and those of the anticipated damage. The damage detection\nin a uniform cross-section cantilever beam, a uniform strength cantilever beam, and a uniform cross-section simply supported\nbeam is used as the test problems. Random noise in the vibration characteristics is also considered in the damage detection. In the\nsimulation analysis, the CCGA provides the superior solutions to those that use standard genetic algorithms presented in previous\nworks, although it uses less numbers of the generated solutions in solution search. The simulation results reveal that the CCGA\ncan efficiently identify the occurred damage in beams for all test problems including the damage detection in a beam with a large\nnumber of divided elements such as 300 elements....
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