Modeling And Simulation Of Car Ride Comfort Based On Finite Element Model

Ride comfort is one of the basic properties of modern vehicles.Studying ride comfort is helpful for vehicles to maintain their advantages in the competition of the same type vehicle market.Through modeling and simulation,vehicle ride comfort has the advantages of repeatability,low cost,safety and reliability,good controllability and access to diverse information.Modeling and Simulation of vehicle ride comfort need to establish a reasonable vehicle model.There are four types of vehicle models based on different principles at home and abroad: the vehicle model based on assembly characteristic parameters,the multi-rigid-body dynamic model,the rigid-flexible coupling model and the finite element model.Compared with other models,the advantages of ride comfort modeling and simulation based on vehicle finite element model are as follows: all parts can be considered as elastomers,the model has more degrees of freedom and is closer to the real vehicle;the existing finite element model for vehicle static,fatigue,collision simulation analysis,which were established by vehicle enterprises,can be used to save modeling time.However,when the vehicle finite element model is large in scale,there are shortcomings of long simulation time and low efficiency.Therefore,there are few studies on vehicle ride comfort modeling and simulation based on finite element model in the past.The finite element model of small-scale vehicle and the frequency domain model of road surface have been established,and the ride comfort of vehicle has been analyzed by frequency simulation.With the development of finite element theory such as forced motion and transient response,and the improvement of computer software and hardware,we can already model and simulate vehicle ride comfort based on large-scale finite element model(grids exceed millions)under random excitation of time-domain road surface on PC.In this paper,the process of vehicle ride comfort modeling and simulation based on finite element model is studied.The application of road excitation finite element method,the process of establishing finite element model,the selection of finite element solution method and the way of solution document creation are described.The pavement incentive model and the content format and settings of NX Nastran solution file are studied.The related software is developed by using the Guide module of matlab,which can simplify the operation.The comparison between classical and finite element plane models of car ride comfort is made,and the validity of the simulation process and the developed software is verified.Based on the space finite element model of a car with about 1.67 million elements,the ride comfort of a car is modeled and simulated,and its ride comfort is evaluated.The details are as follows:(1)The general modeling and simulation process of car ride comfort is studied,and the finite element modeling and simulation process of car ride comfort is established.The basic principles of the large mass method,the large stiffness method,the inertial loading method,the Largrange multiplier method and the direct method are analyzed.The direct method of forced motion is chosen to apply the road surface excitation.The basic principles of direct method and modal method of transient response analysis are studied.It is suggested that the direct method of transient response analysis is used in small-scale finite element model simulation and the modal method of transient response analysis is used in large-scale finite element model simulation.From three aspects of simulation solution,simulation result extraction and ride comfort evaluation,the contents of finite element simulation solution and post-processing are explained.(2)The time-domain models of white noise filtering for single-wheel,double-wheel and four-wheel pavement are established.The method of generating single-sided power spectral density Gauss white noise in MATLAB is studied.The time-domain model of pavement excitation is simulated and tested.The solution file structure and data format of NX Nastran are studied,as well as the setting methods of restart for direct method,modal method and direct method of forced displacement analysis,Lansos method of modal analysis and modal method of transient response analysis.Using the Guide module of matlab,the pavement excitation generation software and NX Nastran finite element solution file automatic generation software are developed respectively.(3)The classical six-degree-of-freedom model of car ride comfort and Simulink simulation model are established,in which road excitation is generated by road excitation automatic generation software.Using the same parameters as the classical car plane model,the rigid and elastic car body finite element plane models are established respectively,and the same road excitation as the classical plane model is applied to simulate ride comfort.The simulation results of classical plane model and rigid body and elastic body finite element plane model are compared respectively.The results show that the rigid body finite element plane model is consistent with the classical plane model.The simulation results of elastic body finite element plane model and classical plane model are different,which shows that the body elasticity will affect ride comfort.(4)The method of dealing with the three-dimensional geometric model of car Catia based on Hyper Mesh and the method of building the finite element space model of car are put forward.The structure of the finite element space model of car used is described in detail,and the finite element space model of car is established.Based on GB 4970-2009,a series of ride comfort simulation experiments were designed.The comprehensive weighted acceleration root mean square values at driver’s seat and rear seat were selected as ride comfort evaluation indexes.The software for solving weighted acceleration root mean square values is developed by using the Guide module of matlab.The scale of the finite element space model of the car is large and it needs to carry out a number of simulation tests at different speeds.Therefore,on 8G memory and i7 processor PC,NX Nastran is used to solve the first10 modes,which takes about 7.8 hours.Then,based on the modal analysis results,the restart method is used to complete the transient response analysis modal method,each group of tests takes less than 3 hours.The results show that the simulation efficiency is high and the cost is low.With the increase of the computer memory,the time consumed decreases sharply.The hyper Graph is used to read and save the simulation results into the xls table file,and the weighted acceleration root mean square value is used to solve the software to read the table data and calculate the evaluation index.The results show that in the range of 40-120 km/h,the root mean square value of the total weighted acceleration at the front and rear seats of the driver is less than 0.69m/s2,the passengers are not uncomfortable and the ride comfort of the vehicle is good.