Research On Dynamic Modification And Size Optimization Of Plate And Shell Structures Based On Frequency Constraint

Engineering structures are more and more large and complex at present, and the working environment for them is more various than before. Therefore the structural static and dynamic strength and stiffness problem exist universally. The research of the structural dynamics which is the guide for engineering structure design and management is developing from analysis, modification, design into optimization. The technologies of dynamics work on each other. The structural modification and design approach perfection, but there is still some problems with the optimization of structure.Fast modal analysis and sensitivity analysis method is two of the most im-portant technologies of the structural dynamic modification and optimization. The natural frequency, damping ratio and natural mode of every modal can be ob-tained from modal analysis. Properties of a vibration system can be predicted by these modal parameters. The sensitivity analysis can be used to obtain the best design parameters. The two technologies are used repeatedly in the modification and optimization, so a fast method can bring benefit to the engineering design.Size optimization which is the parameter optimization in mathematics takes sizes of the sections for design parameters. In the finite element method, the geo-metric variables of normal element are taken as parameters for optimization, such as the section of beam and thickness of plate and so on, while the lightest weight and best properties are taken as optimization object. The mesh model doesn't change in the optimization program, so size optimization is effective. Response surface methodology (RSM) is one of the most commonly used algorithms for size optimizationThe light weight technology becomes more and more important in the car design. The car body stands in the breach for car light weight. Many properties are considering for the technology, such as static and dynamic stiffness, modal, strength, crashworthiness, stability and so on. A lower order modal analysis among them is the main content of car body design.Plate and shell structures are the main component of car body, which is the most important parameter for detail design. Nowadays, there are two methods for car body design, the one is structure sensitivity analysis, which is used for car body detail design; the other is topology optimization, which is used for concep-tual design of car body.There is four main parts in the content:1. With Fortran programming, use FEM method, set up the discrete model for a square steel plate, deduce the stiffness and mass matrices, use the SVI algo-rithm based on Guyan condensation for eigenproblem, compare the results with Altair HyperWorks software. In the lower order modal analysis, the two results are basically the same.2. With LMS Test. Lab software, take modal experiment for the square plate, validate the results by the computational modal analysis.3. With Fortran programming, take the thickness of the plate for design pa-rameter, SVI algorithm based on Guyan condensation and modal sensitivity analysis(SA) and RSM are used for dynamic modification of steel pale based on frequency constraint.4. With HyperWorks software, use SA and RSM, make size optimization for a car door, with constraints of total mass and static stiffness, the first order torsion and bend modal frequency have been improved.The SVI algorithm based on Guyan condensation, which is used for modal analysis and dynamic modification for lower order modal, reduces the calculation. With the SA and RSM, the result of structure dynamic modification and size op-timization is acceptable.