Balanced Multi-objective Optimization Of Non-circular Hole Based On Continuous & Discrete Variables

Non-circular clearance holes are new connection structures adopted in the high-pressure turbine component of aero-engine.In the practice of advanced foreign aero-engines,well-designed non-circular holes can effectively lessen stress around bolt hole and increase fatigue life of disks.In home recently,studies of non-circular holes have improved.The existed optimization models are benefit to lessen stress around the hole,but they are not perfect enough.There are still some deficiencies both in optimization qualities and stabilities,which should be attribute to their oversimplified objective and inadequate constraints.In this thesis,several mathematical models,optimization models and optimization methods for non-circular holes have been thoroughly studied.The main contents are as follows:Multi-objective optimization models were proposed with continuous variables and discrete variables separately.Based on the idea of balanced design,these two models are optimized by NSGAII method and self-regulated weighting factors method respectively.The designs obtained can sufficiently decrease the stress and avoid the over-design as well.Stress situations of disks in the connection parts of high-pressure turbine for a given aero-engine were analyzed,and mechanics models of the disks were built to optimize non-circular holes on it.The profile parameters' influences on the stress situations of the disks were studied,and the stresses were found to decrease slowly in a wide range of design domains,which can be considered as so called “Quasi weak minimum”.To solve this problem and keep a balanced design,both a specific stress and profile variations objectives were introduced in the new models,and the stress around the hole can be reduced to a given level and the variation of the hole's profile were also well controlled.The structure characteristics of bolt joints were studied,and multi-objective optimization models with continuous variables of two different non-circular holes(eight-arc hole and hyper-elliptic hole)were introduced to solve the “Quasi weak minimum” problem.And NSGA-II was adopted to optimize these two clearance holes on the turbine disk and labyrinth disk.To standardize designs and facilitate processing,discrete variables optimization models for eightarc holes were built.Also,a surrogate genetic coding algorithm and self-regulated weighting factors method were designed.The former ensured designs meet industry specifications.The latter selfregulated weighting factors with variables' domains to guarantee design robustness and balance.Finally,differences at efficiency and effectiveness of various optimization models or methods were compared.