The Numerical Modal Analysis And Structure Optimization Of A Heavy Duty Truck Cab

As the rapid development of computer technology, CAE analysis technology has also been rapidly developed. In west developed counties, CAE technology has been widely applied in the process of the new car's development and has acquired great success. In our country, CAE technology is comparatively dropped behind, especially on the dynamic characteristics of the new product analysis, which still at an early stage, and particularly in the development of heavy-duty trucks.European presents the world's highest level of heavy-duty trucks, the exploitation and design of our domestic heave-duty trucks has a relative short story and has a long way to go, especially in the exploitation of cab. This paper was from a project which is the design of the cab of a new duty truck, did the research of dynamic characteristics by modal analysis method and further achieved the purpose of structure light-weight.The main task of this paper included;1. Finite element modeling of heavy-duty trucks.2. Numerical modal analysis of the cab's finite element modeling.3. One step sensitivity analysis of the thickness of cab accessories.4. Dimension optimization design of the cab.In the part of finite element modeling, we briefly introduced the application of finite element analysis method, and introduced the process of building finite element model in detail, and had a further introduction of the predigesting and clearing of geometry model, choosing mesh unit type, choosing dimension, choosing materials, controlling mesh cell quality and simulating solder dot cell. In this part, the finite element model of heavy-duty truck, which is used to numerical model analysis, is built.In the part of cab numerical model analysis, first we introduced the basic theory of numerical model analysis as well as the purpose and significance of the method, and then made sure that the boundary condition of the cab numerical modal analysis was freedom/ freedom boundary condition. Afterwards, we gained the cab's frequencies and shapes after calculating its modal parameters and analyzed the results using matter element analysis. After calculation, the first torsion frequency of the cab was 18.3 Hz, which was a bit low and close to the natural frequency, so it needed adjustment to enhance the first torsion frequency. The first curve frequency of the cab was 46Hz, which had an evident difference compared to the first torsion frequency, so the modes coupling would not happen, meanwhile, the frequency was high, and the stiffness condition was good, so it didn't need adjustment.In the part of cab sensitivity analysis, first we introduced dynamic structure modification method and its sort,meanwhile we explained the dynamic structure modification method which based on the cab sensitivity analysis method of the structural part and fetched the formula which was used for sensitivity analysis of the thickness of shell elements. In the end, we analyzed sensitivity of thickness of every shell elements about the first torsion frequency and found the more sensitive parts (including positive sensitive and negative sensitive). From the result, we found that the parts which behaved positive sensitive to the first torsion frequency were: cab door frames, inside and outside the upper side circuit boards, in front of the door frame to strengthen the board, the former dash and so on, above all, strengthening to the outer surface was more effective compared to that of the inner surface. The parts which behaved negative sensitive to the first torsion frequency were: cap, left the floor, the floor, and the right floor, the upper plate back wall and so on. The sensitivity analysis of the thickness of shell elements provided reference for the dynamics modification.In the part of the dimension optimization of the cab, we optimized the structure dimension of the cab, from the aspect of modal frequency; we enhanced the first torsion frequency of the whole cab and reduced the whole mass of the cab. This paper used the structure dimension optimization theory, took the board thickness of the main parts as the optimization variable, and created 54 optimization variables in total, meantime, made the first torsion frequency as the optimization restrict and the whole mass of the cab as the optimization objective, then set up the optimized model. After calculation, the first torsion frequency of the cab enhanced from 18.3Hz to 21.5Hz, improving the torsion stiffness condition of the cab and reducing the whole mass of the cab about 8 Kg from this condition. The optimization result was satisfying.From this paper, we established the finite element model of the heavy-duty truck cab; analyzed the finite element model by modal analysis method, mastered its low order modal information, and primarily predicted its dynamic characteristic; then found the parts which were sensitive to the first torsion frequency using sensitivity analysis method; optimized the cab's dimension by changing the main parts'thickness, improved the cab's dynamic characteristic.