Optimization Design Of Viscoelastic Composite Structures By Genetic Algorithms

It is widely used in advanced aircraft structure because of the high specific strength, high specific modulus, easy designed of composites. Vibration and noise of composite structures will be produced under complex work environment, and some of mechanical properties of the structure will be affected severely. However, the use of composite materials in the aerospace has been unstoppable. In order to improve the vibration and noise of the structure, it has became the main measures to reduce vibration and noise by damping energy in composite sandwich structure. The strength and stiffness properties will vary for the addition of damping material. It is the key to take advantage of the directional properties of composite materials and design freedom of structural properties in the design of composite structure. In this paper, Viscoelastic composite structure has been optimized in order to weigh mechanical properties and damping characteristics of the structure.The Genetic algorithm is an adaptive probabilistic search algorithm for global optimization which emulate genetic and evolutionary processes in the natural.Compared to the other optimization algorithms, the genetic algorithm has its unique advantages, and could be used in the optimal design of composite structure very well.However, chapter 2 of this article for some defects of basic genetic algorithm, such as precocious, poor local search ability, optimization for a long time, an improved adaptive genetic algorithm has been proposed based on elitist strategy and immigration strategy. The simulation results show that the proposed adaptive genetic algorithm has obvious advantages of better convergence stability, convergence accuracy and convergence rate.Based on the classical plate theory, shear deformation theory, for dynamic nonlinear analysis with composite laminates in chapter 3. Deducing the corresponding vibration control equation based on the principle of virtual displacement and change points. Set up the natural frequency calculation model, and discuss the impact of fiber angle, length to thickness ratio, elastic modulus ratio on the natural frequency of composite laminates. The improved genetic algorithm can be used to optimal design of laminates natural frequency which design variables for fiber laying angle and to maximize the natural frequency. The increases of fundamental frequency of compositelaminates can effectively reduce the probability for its resonance.Based on the assumption that it has no mutual dislocation between layers for small deformation, the composite layer displacement can be used to represent viscoelastic damping layer displacement. The calculation model of viscoelastic composite laminates natural frequency and loss factor of structure can be established by the principle of Hamilton and change points in chapter 4. The damping performance of viscoelastic composite structure can be optimized based on the improved genetic algorithm. The results show that improving the structural loss factor significantly to achieve the purpose of noise damping by the design of fiber laying angle, the relative thickness of viscoelastic layer and shear modulus ratio of damping layer and composite layer.In chapter 5, it introduces the multi-objective optimization problem, and viscoelastic composite structural strength can be established based on the Tsai-Hill strength theory. Clearly, it is consistent with the needs of practical applications by trade-off the properties of composite structures legitimately. Weight Coefficient Transformation Method can be used to establish the double target model for damping properties and structural strength of viscoelastic composite structure. Then to optimize the damping and strength of the structure by improved algorithm, and optimization results are satisfactory.