| The ride comfort of the stretcher-support on vehicle is one of the important evaluation indices of wounded transportation vehicle.In order to reduce the vibration energy and improve the ride comfort of the supine wounded,the vibration absorption property of stretcher-support is simulated and optimized in this dissertation.The present situation and developing trend of the key technology related to the study of the comfortable characteristic of the stretcher-support on vehicle is summarized,including the theory of multi-body system dynamics,the study methods of vehicle ride comfort,the related technology of stretcher-support vibration absorption about wire rope spring and vibration damping.According to the vibration characteristics of the emergency ambulance,the vibration differential equation of nine DOFs(Degrees of Freedom) is founded based on the theory of multi-body system dynamics,including simple suspension system,vehicle body,vehicle stretcher-support system and the body mass of recumbent position crew.In this model,the collision of rigid limiters is also considered,and the wire rope springs are simplified to three direction springs.The model is analyzed in ADAMS,the automatic analysis software of multi-body system dynamics.In accordance with the relevant provisions of GB4970-1996 " Method of random input running test--Automotive ride comfort",QC/T677-2001 "Method of random input running test-ride comfort of sleeper bus" and GB/T18368-2001 "Comfort evaluation of human exposure to whole-body vibration in recumbent position",the road test of common speed under the excitation of two representative roads(graveled road and bituminous road ) is carried out at the test ground of reequipped military vehicle of the Mechanical Industry Department(located in Yanqing,Beijing),the acceleration signal transferred to the occupants in the recumbent position and seated position is sampled.Through two terms' weighting of 1/3 OCT of sample acceleration signals on the occupants' corresponding parts,the ride comfort in the recumbent position and seated position is evaluated.The analysis results of test data shows that the vibration absorbing efficiency of stretcher-support under the two types of road can't meet the requirement of engineering design(vibration absorbing efficiency≮30%), and the vibration even causes the occupants' uncomfortableness under the exciting of the gravel,road,therefore,the numerical simulation and optimization for the vibration absorbing efficiency of stretcher-support is carried out under this case.The virtual prototype model of vehicle vibration system according with the prototype, including four wheels,vehicle body,equivalent suspension system,stretcher-support system and the body mass of recumbent position,is built in the simulation analysis software ADAMS based on mechanical system dynamics,in which,the suspension parameters are obtained through the parameters identification method based on genetic algorithm,the wire rope springs are simulated by bushing model,and the collision force of rigid limiter is calculated through the function of impact.The simulation model is excited in the time domain by the four channels acceleration signals on the end of axletree from the road test and the real vibration condition is fully simulated.From the results comparison between the test and simulation,the calculation error under the exciting of the two roads is only 8.267%and 7.611%,which shows that this model has a higher precision.Through the optimization study of this virtual model,considered such factors as the number,stiffness,position and direction of the wire rope springs,the reasonable absorbing vibration scheme is founded.From the analysis results,the vibration absorption system only made up of wire rope springs can't match the industry design targets,although the vibration response characteristics of stretchers has been largely improved.To deal with the problem that the damping ratio of wire rope spring is comparatively small,a new kind of vibration absorption scheme is set up using less stiff springs with vibration damping device.And the matching relation of stiffness and damping is simulated and optimized.As a result,the vertical stiffness of wire rope spring K_y is 2737N/m,damping coefficient C is 2605Ns/m and the vibration absorbing efficiency under the gravel road excitation is 32.53%and 34.26%under the excitation of bituminous road.The result of this analysis can meet the design requirements of the project in theory,but in the engineering application,it is comparatively difficult to achieve because the stiffness of wire rope spring is too little and the initial deformation to maintain the system static equilibrium is larger.Based on the study of vibration damping,four types of two-stage combined vibration absorbing schemes are designed in order to get over the shortcoming of wire rope spring's soften characteristic.The best scheme is selected after simulation and optimization study.Not only the vibration absorbing efficiency in this scheme can reach to 31.29%and 32.51% corresponding to the exciting of gravel road and bituminous road,but also the stiffness of the two-stage wire rope spring(11545.6 N/m and 30141.4 N/m respectively) has been largely improved compared to the optimization results of damping vibration(2737N/m),which is conducive to realize in the engineering application.The emergency ambulance mainly runs on the stationary random road but sometimes it will pass the convex surface or pits on the road,the vibration presents shock excitation in this case.In order to evaluate whether the design schemes can match the security requirements under shocking excitation,the shock vibration isolation efficiency is simply analyzed in the Simulink module for the optimized results on the vibration isolation scheme of pre/post adding;dampers as well as the best scheme of the two-stage combined.The analysis results show that in the optimized results of original scheme,the maximal response acceleration is comparatively little,but the attenuation is very slow,and the maximal response displacement is too large,the system stability is comparatively weak;In comparison,in the two schemes of adding vibration damping device,the decrease of the maximal response acceleration became little,but the attenuation is fast,and the maximal response displacement is also little,therefore the system stability and vibration absorption efficiency are balanced reasonably.In the selected scheme of the two-stage combined vibration absorbing,the vibration absorbing efficiency reaches to 68.69%using the maximal response acceleration as evaluation indicator and the maximal response displacement is only 3.4mm,the stability of stretcher-support system is improved largely.
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