Method Of Structure Optimization To Resist Crack In Bad Service Environgment And Its Application

Due to the bad influence, defects exist in structures under the real condition. When the defects occur on the defect-sensitive area, the structure will be scrapped in advance because of the vulnerable area. In order to enhance the availability of the sensitive area, a new method for optimizing structure to prevent defects is proposed. A crack model derived from the edge of real crack and the depth from the assumed V-shape is developed to model the geometrical changes of the crack. The max equivalent stress is picked as the index to quantificat the crack damage. The model which reflects the geometrical relationship between the structure and the crack is defined to change the analysis object from structure to crack. Under the sobol sensitivity technique, the damage degree of crack parameters can be acquired on the basis of structural analysis. The sensitive area and parameters which are vulnerable can be labeled by comparing the damage degree. Regarding the sensitive area as the object of detail structure optimization, the optimization variables can be selected tendentiously according to the damage degree of parameters. This method applies multi-objective particle swarm algorithm to find the optimal distribution of the variables in order to improve the safety of the sensitive structure area. The crack model is located in the impeller and the max equivalent stress decreases 18 percent, compared with other optimization methods of impeller without considering crack. The optimization results show that the proposed method decreases the weakening effect of crack. This method can improve the safety of the structure effectively.In the first chapter, the related research is summarized. The structure analysis and structure optimization of the vulnerable area are reviewed, which includes the application of the finite element method, the fully stress method, the intelligent algorithm and the topology optimization method. The existing problems of these technologies are discussed, and the structure of the article is introduced.In the second chapter, a crack parameterized model derived from the edge of the real crack is proposed to model the geometry features of the crack in the cracked structure. The surface shape is constructed by the crack edge and the gradient information. Contour linearization is employed to regularize crack surface shape. The depth of crack is constructed based on the assumption of V-shape. Parameterization is applied to express the length, the width, the depth, the bending orientation and the occurrence position of the crack.In the third chapter, the relationship between the structure and the crack is analyzed, which provides reference for cracked structure. The max equivalent stress is picked as damage index to quantize the weakening effect of crack. The geometrical relationship between the structure and the crack is defiend, which converts the structure analysis to the crack analysis. The parameters coupling is considered in structure analysis, which can reflect the mutual weakening effect of different crack parameters.In the fourth chapter, the optimization structure method with the consideration of crack is proposed. Under the sobol sensitivity technique, the damage degree of parameters of the crack model can be acquired on the basis of structural analysis. The vulnerable area which is sensitive to crack can be labeled by comparing the damage degree. Regarding the crack-sensitive area as the object of anti-crack structure optimization, the optimization variables can be selected tendentiously according to the damage degrees of crack parameters. The support vector machine (SVM) is applied to bulid the prediction model of the optimization variables and optimization goals. The multi-objective particle swarm algorithm is applied to find the optimal distribution of the variables in order to improve the safety of the sensitive area of structure.In the fifth chapter, this optimization method is verified in impeller structure. The proposed method is applied in the optimization of the impeller structure. The vulnerable area of impeller is labled to optimize, and the proposed method decreases the damage effect caused by crack and enhances the anti-crack performance of impeller.In the sixth chapter, the achievements of this article are summarized, and the future studies are discussed.