Topology Optimization Method For Thermal Protection Structure Considering Transient Effect

With the continuous improvement of miniaturization and lightweight design requirements,the demand for the fine design of thermal protection structures is becoming more and more urgent.How to reasonably arrange the heat conductive and insulation materials to optimize the thermal protection performance of the structure has become an urgent problem to be solved.Topology optimization can automatically obtain innovative structural configurations by reasonably designing the distribution of materials in a given area and the current topology optimization of thermal protection structures mainly focuses on steady-state heat conduction structures.However,the temperature field will change with time in practical engineering,which has transient characteristics.Whether the transient effect should be considered in the topology optimization of thermal protection structure and if the transient effect is considered,how to build the corresponding topology optimization method of thermal protection structure,these problems are the focus of this dissertation.In this dissertation,the transient effect is mainly reflected in two aspects,one is that the analysis is based on transient equations rather than steady-state equations,the other is reflected in the optimization level,that is,different working time conditions may correspond to different topology optimization designs.In order to solve the above problems,this dissertation studies and establishes the topology optimization method of thermal protection structure considering transient effect,aiming at the problems of minimizing the regional maximum temperature,maximizing the heat transfer efficiency,and designing the multi-functional structure with load-bearing and thermal insulation.The specific research contents include:(1)Design and performance analysis of typical heat conduction structures considering transient effect.To solve the problem of whether it is necessary to consider the transient effect in the optimization of thermal protection structure,this dissertation analyzes the influence of transient effect on the design through a practical engineering problem:the design of thermal protection structure of aircraft leading edge.Firstly,in order to meet the requirements of high heat dissipation performance of aircraft wing leading edge,this dissertation studies the design technique of thermal protection structure based on the dredging high-temperature heat pipe,establishes the modeling,numerical analysis,and optimization design method of thermal protection structure with the high-temperature heat pipe embedded in the wing leading edge considering transient effect,and simulates and analyzes the thermal dredging effect of thermal protection structure with high-temperature heat pipe embedded in the wing leading edge at different speeds.Secondly,the influence of structural parameters(heat pipe spacing,skin thickness,heat pipe radius,and heat pipe thickness)on the final structural temperature and weight of the thermal protection structure is studied.The design scheme of the dredging thermal protection structure is formed to meet the performance requirements,and the thermal performance simulation analysis of the design scheme is completed.Finally,the necessity of considering transient effect in the topology optimization of heat conduction structure is verified.It is found that the results of topology optimization under different short-term heat loads are quite different from those obtained by the topology optimization model based on steady-state heat conduction,so the transient effect needs to be considered.(2)Topology optimization method for minimizing the regional maximum temperature of transient heat conduction structure.In practical engineering,the maximum temperature of a specific area(short-term heat flow concentration area or key concern area)is too high,which is an important factor leading to the failure of the thermal protection structure.Aiming at the problem of minimizing the maximum temperature in a specific area,this dissertation proposes the characterization of the maximum temperature in a specific area during the whole working time:"the Regional Temperature Control Function",and establishes a topology optimization model of transient heat conduction structure with the regional temperature control function as the objective function,which is used to minimize the maximum temperature in a specific area during the whole working time.By using the adjoint variable method,the analytical sensitivity expression of the regional temperature control function with respect to the design variables is derived.Numerical examples show that compared with the transient heat compliance,the regional temperature control function can obtain the topology optimization design of the transient heat conduction structure with lower maximum temperature in the specified region.(3)Topology optimization method for maximizing the heat transfer efficiency of transient heat conduction structures.Maximizing the overall heat transfer efficiency(exchanging as much heat as possible per unit time)is an important design goal of thermal protection structures in engineering applications,such as heat exchangers,refrigeration,and energy storage systems.To maximize the heat transfer efficiency,a new performance index is proposed to describe the transient heat transfer efficiency,that is,"the Transient Thermal Dissipation Efficiency".The transient thermal dissipation efficiency takes into account not only the potential capacity dissipation caused by the heat flux(transient heat compliance),but also the potential capacity dissipation caused by the heat absorption due to material heating.A topology optimization model with the transient thermal dissipation efficiency as the objective function is established to maximize the transient heat transfer efficiency by minimizing the transient thermal dissipation efficiency.The sensitivity expression of the transient thermal dissipation efficiency with respect to design variables is derived.Numerical examples show that compared with the transient heat compliance,the transient thermal dissipation efficiency can obtain the topology optimization design of the transient heat conduction structure with higher transient heat transfer efficiency.(4)Topology optimization method for multi-functional structure with both loadbearing and thermal insulation capability considering transient effect.The multifunctional structure,which can meet the requirements of load-bearing and thermal insulation simultaneously,has attracted much attention in the design of hypersonic thermal protection structures.The load-bearing capacity of thermal insulation materials is weak,while the thermal insulation capacity of load-bearing materials is poor.How to balance the load-bearing and thermal insulation requirements in limited space has become a key problem.The aerodynamic heating time of hypersonic aircraft is limited,which has the characteristics of short-term heating time and large variation of heat load.Therefore,the influence of time and transient effect need to be considered in the structural design,but the existing multi-functional collaborative optimization design model of steady heat conduction and load-bearing cannot solve the above problems.In this dissertation,the design model and solution method of topology optimization for multi-functional structure with both load-bearing and thermal insulation capability considering transient effects are established,and the analytical sensitivity calculation format of the objective and constraint is given.Based on the density method and considering the volume constraint,this method takes the structural compliance as the design objective and the regional temperature control function as the design constraint to achieve the multi-functional design requirements of structural stiffness and thermal insulation.Numerical examples show that the proposed optimization model can accurately consider the transient effect of the structure,and realize the multi-functional coordination of load-bearing and thermal insulation design under the given allowable temperature and working time.In appendix A,the topological design of pentamode metamaterials is introduced.Pentamode metamaterials are a kind of unique three-dimensional mechanical metamaterials,which can be designed artificially to have unusual elastic properties with shear modulus close to 0.The pentamode here means that the effective elastic matrix of the material has only one non-zero eigenvalue but five zero eigenvalues.The pentamode materials are solid,but they can imitate the properties of the fluid.They are difficult to compress but easy to shear.Compared with the existing design methods based on the biconical rigid body deformation,a new threedimensional pentamode material microstructure is generated by the topology optimization method.A topology optimization model for pentamode materials is established,which makes the microstructure have a larger ratio of effective bulk modulus to shear modulus,and the effective Poisson’s ratio is close to 0.5.The larger the numerical ratio is,the better the simulation effect is.Finally,this dissertation verifies the design results from three aspects of stiffness,strength,and manufacturability,which demonstrates the effectiveness of the method.