The Vibration Characteristics Analysis And Performance Optimization For Nonlinear Vibration Reduction System Of The Tracked Ambulance

The tracked ambulance can move over rough terrain, such as mountains, jungles, deserts, swamps. It can provide emergency care to the sick and wounded during the transit to the hospital, and is an important part of medical support in military conflicts and non-war military operations. Since the tracked ambulance is mainly used in rough terrain, its vibration environment is relatively poor. If the nonlinear vibration reduction system of tracked ambulance cannot reduce the vibration induced by the road roughness, the sick and wounded will become vulnerable to the secondary injury, especially for the patients with injured brain or injured spine. Therefore, it is of great practical significance to optimize the performance of nonlinear vibration reduction system of the tracked ambulance.The vibration characteristics analysis and performance optimization for nonlinear vibration reduction system of the tracked ambulance are carried out by using the intelligent optimization algorithm, the multiple scale method, the precise integration method and so on. The main works and conclusions are as follows:(1)Based on the specifications of vibration test, the road test of tracked ambulance was carried out. The vibration acceleration signals of the chassis, the carriage, the seat of medical staff and the stretcher base under cross country road(18km/h), rough road(15km/h), gravel road(20, 30, 40km/h) and cement concrete road(30, 40, 50km/h) were obtained by road test. The vibration signals obtained reflect the vibration condition of rear vehicle of the tracked ambulance roundly, and make an excellent first step for the following studies in this paper.(2)In order to identify the unknown parameters of nonlinear vibration reduction system of the tracked ambulance, a new multi-objective method for parameter identification was proposed in this paper. This method was composed of the improved partitioning and dimensional increment precise integration method and NSGA-II(Non-dominated Sorting Genetic Algorithm II), and used to identify the parameters of nonlinear vibration reduction system of the tracked ambulance by taking the power spectral density(PSD) and probability distribution of vertical vibration acceleration of the stretcher base as the evaluation index. After parameter identification, the equivalent physical parameters of nonlinear vibration reduction system under cross country road(18km/h), rough road(15km/h), gravel road(40km/h) and cement concrete road(40km/h) were obtained. Then the accuracy inspection of equivalent physical parameters obtained was carried out. According to the result of accuracy inspection, the probability distribution of identification result was in good agreement with that of test result. The peak value positions and the changing trends of PSD of identification result and test result were consistent, but there were some differences in the amplitude of PSD. However the differences were within the allowable range. This proves that the equivalent physical parameters are of high accuracy and meet the usage requirement, and demonstrates the validity of the multi-objective method for parameter identification proposed in this paper.(3)The analytical method and the numerical method for solving nonlinear vibration problem were compared. The multiple scale method was chose as the analytical method and the improved partitioning and dimensional increment precise integration method was chose as the numerical method. In addition, the Runge-Kutta method was used to check the computational accuracy of numerical method. The comparison result showed that we could get basically the same conclusions when using the analytical method and the numerical method to study the two-degrees-of-freedom model of nonlinear vibration reduction system of the tracked ambulance. The amplitude-frequency response curve obtained by the analytical method was well matched with that obtained by the numerical method in the position of main resonance. This indicates that two methods are substantially equivalent when they are used to analyze quantitatively low-degrees-of-freedom nonlinear vibration system. But the analytical method is subject to many constraints and difficult to analyze quantitatively the nonlinear vibration system under random excitation. However, the numerical method is not limited to these constraints. Therefore, the numerical method is chose as the research method for the following studies in this paper.(4)The characteristics analysis and performance optimization of nonlinear vibration reduction system of the tracked ambulance were carried out. First, the Sobol method was used to study the global parameter sensitivity of nonlinear vibration reduction system with respect to the weighted root mean square(RMS) value of vertical vibration acceleration of the stretcher base. The importance ranking of parameters was obtained as follows: C2, K2, C1, Ks, Kz, where Ks, Kz, C1 were the linear stiffness, cubic nonlinear stiffness and damper of zero stiffness shock absorber; K2, C2 were the stiffness and damper of rubber damping shock absorber. Then the improved partitioning and dimensional increment precise integration method was used to study the characteristics of nonlinear vibration reduction system of the tracked ambulance. The influence of parameter variations on the weighted RMS value of vertical vibration acceleration of the stretcher base was obtained. Finally, the genetic algorithm was used to optimize the performance of nonlinear vibration reduction system of the tracked ambulance. After optimization calculation, the weighted RMS value of vertical vibration acceleration of the stretcher base dropped by 27.6% and the probability of vertical vibration acceleration of the stretcher base within-0.12m/s2 to 0.12m/s2 increased by 9.8%. After above studies, the performance of nonlinear vibration reduction system of the tracked ambulance is improved greatly.(5)The structure optimization for nonlinear vibration reduction system of the tracked ambulance was carried out. First, two structure optimization schemes for stretcher base were proposed based on the mechanism of dynamic vibration absorber(DVA), namely, the linear and nonlinear structure optimization schemes. This was followed by the comparison of two schemes by taking the weighted RMS value of vertical vibration acceleration of the stretcher as the evaluation index. The comparison result showed that the weighted RMS values of the linear and nonlinear structure optimization schemes dropped by 23.3% and 19.1% respectively, compared with that before structure optimization. The linear structure optimization scheme worked better than the nonlinear structure optimization scheme. Furthermore, the vertical installation size of linear structure optimization scheme was smaller than that of nonlinear structure optimization scheme. Therefore, the linear structure optimization scheme was chose as the final scheme. After structure optimization, the shock weakening property of nonlinear vibration reduction system was also examined. It showed that the shock weakening property after structure optimization became better than that before structure optimization.Second, the Sobol method was used to study the global parameter sensitivity of nonlinear vibration reduction system after structure optimization with respect to the weighted RMS value of vertical vibration acceleration of the stretcher, and the importance ranking of parameters was obtained as follows: C2, C1, K2, Kd, Ks, Cd, Kz, where Kd and Cd were the stiffness and damper by which the storage box and steel frame are connected. Then, the improved partitioning and dimensional increment precise integration method was used to study the characteristics of nonlinear vibration reduction system after structure optimization. The influence of parameter variations on the weighted RMS value of vertical vibration acceleration of the stretcher was obtained. Finally, the NSGA-II was used to optimize the performance of nonlinear vibration reduction system after structure optimization. After optimization calculation, the weighted RMS value of vertical vibration acceleration of the stretcher dropped by 12.1% and the RMS value of relative displacement between stretcher and storage box dropped by 16.8%. The performance of nonlinear vibration reduction system of the tracked ambulance is further improved after above studies.The novelties of this paper lie in the multi-objective method for parameter identification and the structure optimization schemes for stretcher base. There is no need to set the initial value of the multi-objective method for parameter identification. The number of objective functions of the multi-objective method for parameter identification is unlimited. This method can identify the parameters of linear or nonlinear system under arbitrary excitation, and is widely used in engineering. In the structure optimization schemes for stretcher base, the storage box is separated from the stretcher base, and acts as a “DVA”. This structure design enables the storage box to absorb vibration energy and reduces the load of zero stiffness shock absorbers. It gives a solution to the structure optimization for all sorts of platforms with a larger attached mass, in particular, it has a high requirement for vibration environment.