| Stiffened structures are widely applied in aerospace,marine engineering,automobile and machine tools,etc.As these equipment structures bear complex dynamic loads during working conditions,it is important to improve the structural dynamic performance,so as to ensure the normal working requirements and service life.At the same time,the lightweight design can reduce the material consumption,assembly and transportation costs,and improve working efficiency.Therefore,it is significant to carry out the lightweight design under the premise of ensuring the dynamic performance of the structure.By adopting structural optimization methods,the structural dynamic performance is improved effectively,so as to achieve lightweight design and reduce economic costs.Based on the growth principle of branch structures in nature,the Adaptive Growth Method can optimize the stiffened structure of equipment effectively to obtain a clear,reasonable and geometrically-featured stiffener layout,which has been successfully applied in static problems.However,in the Adaptive Growth Method,the initial ground structure has a great impact on the structural dynamic performance,and the local solution may happen.In this paper,an improved Adaptive Growth Method with material property penalty is proposed to optimize the stiffener layout under dynamic excitation.In addition,structural design can be conducted from the aspects of stiffness and damping,and a reasonable layout of structural materials/stiffeners,damper layers,or optimal tuning of Tuned Mass dampers is obtained.However,the existing optimization methods usually focus on only one aspect of stiffness and damping,which limits the improvement of dynamic performance.To solve this problem,a new simultaneous design optimization method combining stiffness and damping is proposed,and the interaction between the layout of structural materials/stiffeners related to stiffness and the distribution of TMDs/damping layers related to damping are considered.Thus,the dynamic performance is further improved,and the lightweight design is achieved.The main research contents are as follows:1.Starting with the application of 2D structure,the simultaneous design optimization method for SIMP-based structural material layout together with TMDs is suggested.The main structure with the attached TMDs are modeled by the continuum FEA method to consider the change of TMDs’ locations.Then they are optimized simultaneously by introducing a multi-level optimization frame,where the locations and damping parameters of TMDs are optimized in every step of the topology optimization of the main structure,so as to fully consider the interactions between each other.Compared with the results from non-simultaneous optimization(conduct topology optimization first,then conduct TMD tuning),the dynamic performance of the main structure in the simultaneous optimization is improved by nearly 50% with the same mass,and the efficient utilization of structural materials is realized.This is because when the main structure and TMDs are optimized simultaneously,the modal strain energy is more concentrated,the dynamic compliance of the target mode can be dramatically reduced.2.An improved adaptive growth method is proposed for the stiffener layout optimization of 3D box structure under harmonic excitation.A stiffeners’ material attribute penalty is introduced to reduce the influence of the initial ground structure on the dynamic performance.At the same time,the MMA algorithm is adopted as the iterative formula to avoid the problem of local optimal solution.The panel thickness of box structures has great influence on the stiffener layout in dynamic optimization results,which should be chosen practically.3.Based on the improved Adaptive Growth Method,the simultaneous optimization method for stiffener layout of 3D box structure together with TMDs is proposed to reduce the dynamic compliance of the box structure in the target mode.In order to fully consider the interaction between box structure and TMDs,the locations and damping parameters of TMDs are optimized in every iterative step of the stiffener growth process of the box structure.Numerical example results show that when the stiffener layout and TMDs are optimized simultaneously,the modal strain energy of the box structure is more concentrated than that of sequential optimization results.4.A simultaneous design optimization method based on the improved adaptive growth method is proposed to optimize the layout of stiffeners and damping layers simultaneously for thin-walled structures.In order to fully consider the interaction between the stiffeners and damping layers,the SIMP method is adopted to optimize the layout of the damping layers in each step of the stiffener growth process of the thinwalled structure,and the optimal layout of the damping layers in the current step of stiffener layout is obtained.5.Based on the proposed simultaneous optimization method and the improved Adaptive Growth Method,the dynamic design optimization of a vertical machining center structures is studied.Firstly,a new structural dynamic design optimization method for the holistic machine tool is suggested.The dynamic sensitivities of the components are analyzed based on modal test data,which can help to determine which components need to be optimized.The improved Adaptive Growth Method is adopted to optimize the stiffener layout of the machine tool structures.The physical prototype test results show that the first eigenfrequency of the optimized holistic machine tool is increased by 22.5% while the total weight is reduced by 1.1%.Then,for the machine tool bed,the simultaneous optimization of the stiffener layout with TMDs is applied to design the bed structure from the aspects of stiffness and damping.The dynamic performance of the bed is verified by the scale model experiment.The innovation of this paper is mainly reflected in the following aspects:(1)The improved Adaptive Growth Method is proposed to optimize the stiffener layout of 3D box structures under dynamic excitations,and the local solution is avoided;(2)The simultaneous design optimization method combining stiffness with damping is proposed,and the interaction between stiffness and damping is fully considered.The dynamic performance of equipment structures is effectively improved,and the efficient utilization of structural materials and lightweight design are realized;(3)Based on the dynamic sensitivity analysis and the improved Adaptive Growth Method,the structural dynamic optimization method of the holistic machine tool is suggested.The dynamic performance is improved,and the total mass is reduced. |
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