Research On Lightweight Of The Dump Truck Carriage With Frequency Constraint

With the rapid development of economy, the demand of energy is increasing, which is lead to the growing energy crisis. As one of the pillar industry of national economy, people are faced the problems of high pollution and energy consuming of the automobile industry. In order to solve the problems, automotive lightweight is an important instrument for researchers who are investigate the modern cars. In China, on the one hand, the pace of urbanization construction is accelerating, on the other hand, the sales of the load dump truck is increasing, too. Today, oil price is rising, while the load dump truck weight is too large. What’s more, the high fuel consumption is undoubtedly increased the cost. In order to reduce the cost of the dump truck and improve its working efficiency, reducing the weight of load dump truck is an effective means. However, the research of automotive lightweight is started later than west countries. The proportion of load dump truck produced by our country is higher than west countries. There are many problems in the research of load dump truck lightweight.The load dump truck is a kind of special automobile, which is often driven on the uneven road and working on the bad environment. The uneven ground and vehicle itself factors cause the vehicles vibrate when it is driven on such a road. So the vibration analysis of the dump truck carriage is highly required. In order to avoid the resonance phenomenon, under the constraints of natural frequency, we discuss the problem about the lightweight of the dump truck carriage.After finite element discrete, undamped free vibration differential equation is Mx+Kx=0(1) The solution for the equations is x=X sin(pt+φ)(2) where X is array of amplitude, p is circular frequency, φ is initial phase. Substituting Eq.(2) into Eq.(1) we have [K-p2M]X=0(3) The conditional of the above equation has a non-zero solution is|K-p2M|=0(4) This is the characteristic equation of multi degree of freedom vibration system. The solution of equation p2has n positive real root pi2. pi is natural frequency of the system. Substituting respectively n natural frequency pi into Eq.(3) results in [K-pi2M]Xi=0, i=1,…,n The equation is called main vibration modal equation. Xi is the main vibration mode of the system. Substituting Xi into Eq.(2) we obtain xi=Xisin(pit+φ),i=1,…,n where X. is the i order principle mode of vibration.Design variables, objective function and constraint conditions are three elements of the optimal design. In the process of optimization, according to changing the design variables and satisfy the constraint conditions, the best optimal design of objective function can be found. The math model of optimization design is expressed as Minimum:f(X)=f(x1,x2,...,xn) Constraint conditions:gi(X)<0j=1,...,m hk(X)=0k=1,...,mh xiL≤xi≤xiU i=1,…,n where X=x1,x2,...,xn is design variables,f(X) is objective function, g(X) is inequality constraint conditions, h(X) is equality constraint function, xL is upper limit of design variables, xU is lower limit of design variables, respectively.By using topography optimization, shape optimization and size optimization of OptiStruct, we complete the procedure of optimization of the carriage structure. The positions of the ribs are first located by using topography optimization; their widths, heights and thicknesses are then determined by shape optimization and size optimization. The process of structure optimization of OptiStruct is as follows:(1) Establish the finite element model and set the boundary conditions in HyperMesh.(2) Define the optimization problem in HyperMesh:1. Define optimization design variables and the range of optimization design. 2. Define the response of the structures, including the response of the objective functionand the response of the constraint conditions.3. Define objective function and constraint conditions.(3) Run the OptiStruct.In this thesis, we use Pro/E establish geometric model of the dump truck carriage based onthe original drawings and output the IGES file. We import the IGES file into HyperMesh fordividing grid, give material properties, create load and loadstep in HyperMeshh, conductmodal analysis to the carriage by Radioss, output the results by HyperView and conducttopography optimization, shape optimization and size optimization for structure of thecarriage using OptiStruct. Detail steps are given as follows:1. Remove the rib on the carriage. Conduct topography optimization to the carriage with7order natural frequency maximization as the objective function. Determine the new positionof the rib by topography optimization. And output the result of topography optimization byHyperView.2. Build finite element model of the new rib in HyperMesh based on the result oftopography optimization. The width of the new rib refers to the result of topographyoptimization. The height and thickness of the new rib refer to the height and thickness of therib of the original carriage.3. Conduct shape optimization and size optimization to the new carriage with the firstnonzero natural frequency is greater than that of the original carriage as constraint conditionsand the weight of the carriage minimum as objective function. Optimize the width, height andthickness of the rib. And output the result of optimization by HyperView.The results of optimization show that the carriage is able to reach the purpose of weightloss under the constraints of natural frequency.