Optimization Design And Experiment Of Stiffened Cylindrical Shells In Heavy-Lift Launch Vehicle

The lightweight and detailed design of the stiffened cylindrical shells is a vital technology in the development of the heavy-lift launch vehicle.To meet the requirement in the development of the heavy-lift launch vehicle,this dissertation focuses on the efficientoptimization theoretical methods and experimental verification methods for largecomplex structures(LCS),and emphatically carries out the optimization design andexperimental investigation on the stiffened cylindrical shells in the heavy-lift launchvehicle.The main research of this dissertation is as follows:The mixed-integer sequential space-filling sampling algorithm for the high dimensional irregular design domain is established.Considering the uniformity requirement of the Latin Hypercube Design(LHD)with integers,the sampling method for high-dimensional cubic domain is studied.To this end,a sequential enlarged mixedinteger sampling algorithm based on recursive evolution and probabilistic transition is proposed.To obtain the uniform samples in the high dimensional irregular domain,the constrained space-filling and non-collapsing sequential sampling algorithm(CSFSS)based on the improved local density function and the CSFSS considering mixed integers based on point by point sampling – permutation optimization are proposed respectively.The augmented radial basis function(ARBF)approximate modeling method,sequential approximate modeling method and multi-fidelity approximate modeling method are established.To enhance the efficiency and accuracy of the ARBF approximate modeling,the scale factor is introduced.Thus ARBF approximate modeling methods based on moment estimation and sliced splitting-based K-fold cross-validation(SSKCV)are presented respectively.To improve the global/local accuracy of the ARBF approximate model sequentially,the “demand degree” of the ARBF approximate model for the samples is quantified by the bias-variance decomposition,while the “information redundancy” among the infilled samples is reduced by the inexact Voronoi diagram algorithm.Then an ARBF sequential approximate modeling method is presented for global approximation.In addition,a multi-fidelity augmented radial basis function(MFARBF)approximate modeling method based on SSKCV is proposed to make comprehensive use of the high-and low-fidelity analysis model.The sequential approximate optimization method for the design of the LCS is established.As for the LCS design problem containing expensive constraints,the inexact differential evolution algorithm is utilized for exploitation sampling while the sequential enlarged mixed-integer sampling algorithm is employed for exploration sampling.Meanwhile,the exploitation/exploration competitive mechanism is introduced for the balance between exploitation and exploration.Thus,a sequential approximate optimization method based on exploitation/exploration competing for a parallel sampling strategy(SAOCPS)is presented.As for the LCS design containing analytical constraints,the searching space is shrunk based on the analytical constraints.A sequential approximate optimization method based on space reconstruction strategy is proposed by incorporating the inexact Vonoroi diagram algorithm for the intensive sampling in the reduced design space.As for the LCS design containing a high-and low-fidelity analysis model,the inexact Vonoroi diagram algorithm is used for the high-fidelity sampling,while the leave-one-out cross-validation(LOOCV)is applied for the low-fidelity sampling.Thus,a multi-fidelity sequential approximate optimization method based on search space reconstruction strategy(MFSAOSR)is proposed.Based on the abovementioned optimization methods,the lightweight design and experiment of the stiffened cylindrical shells in the heavy-lift launch vehicle are studied.The lightweight optimization of the large-diameter stiffened cylindrical shells is studied.The SAOCPS method is applied to the lightweight optimization of the stiffened cylindrical shells is carried out,and the optimum structures with an 11.7%weight reduction are obtained.To avoid the collapse of the whole structure induced by local buckling of stringers,the collapse mechanism of the large-diameter stiffened cylindrical shells is investigated,and the global sensitivity indices for the load-carrying capacity of the large-diameter stiffened cylindrical shells are further analysed and obtained.Then the SAOSR method is applied to the lightweight optimization of the stiffened cylindrical shells considering the buckling of the stringers,and the optimum structures with 10.6% weight reduction satisfy the requirements of the engineering application.The lightweight optimization of the concentrated-force diffusion compartment(CFDC)is studied.Load-carrying capacity and load-diffusion performance are two primary factors to design the CFDC in launch vehicles.To improve the two factors simultaneously,a novel structural configuration of the CFDC is designed.Meanwhile,a novel integrated design method combining variable profile,proportional layout and multi-region design is presented.And the optimization model based on the linear static method and Euler buckling strength estimation is established.Moreover,a novel cooperatively coevolving simulated annealing(CCSA)algorithm is proposed based on the structural decomposition strategies for the facilitation of the optimization.And the optimum CFDC with obvious weight reduction is obtained.To realize the complementary advantages of the linear static method and post-buckling analysis method,the MFSAOSR method is used in the lightweight optimization of the CFDC.Compared with the literature method and CCSA,the maximum weight reduction is up to 22%,which demonstrates the effectiveness of the MFSAOSR method.The experimental tests of the principle specimens are studied.The principle stiffened panel and concentrated-force diffusion structure are designed respectively according to the equivalence of the mechanical behaviour.The large cylindrical wrapped heating equipment is invented.The static axial compression collapse test of the stiffened panel,the axial compression test at normal temperature and the axial compression collapse test at high temperature of the principle concentrated-force diffusion are carried out respectively.The ultimate collapse loads of the two specimens are obtained and the load-diffusion performance of the concentrated-force diffusion structure is validated.To sum up,the optimization methods of the LCS are studied and applied to the lightweight optimization of stiffened cylindrical shells in the heavy-lift launch vehicle.The present work not only directly serves for the development of the heavy-lift launch vehicle but also can be extended to the optimization design of the similar LCS,which has a certain theoretical significance and engineering application value.