Anti-shock analysis, vibration and noise control, underwater application of composite materials, marine engineering equipment structure design
1.Based on the Euler equation, a three-dimensional dynamic model of underwater explosion is established by the discontinuous Galerkin method. In view of the situation that millions of grid cells may appear after the three-dimensional numerical model is discretized, AMR method is used to independently develop and write the fluid calculation program based on OpenMP parallel architecture, which has high calculation efficiency and stability, and the calculation results are in good agreement with the experiment. The effects of charge characteristics, compressibility and different gas and liquid state equations on the propagation characteristics of underwater explosion shock wave are studied.
2.Based on the Level Set method to locate the position of the bubble interface, the Ghost Fluid method handles the discontinuity of the physical quantity on both sides of the interface. Combined with the AMR method, a high-resolution bubble interface capture method is proposed. Because of the unevenness of the velocity field and the accumulation of calculation errors, the Level Set function in the flow field no longer represents the distance function from the bubble interface, so it needs to be re-initialized. The high-order discontinuous Galerkin method is used to solve the Level Set equation, and the AMR method is used to arrange multiple grids near the interface, so as to improve the accuracy of interface positioning and provide technical support for the study of dynamic characteristics of bubbles.
3.Based on the potential flow theory, a boundary element bubble dynamics model is used to numerically simulate the development process of underwater exhaust bubbles near the wall. First, the basic theory is used to establish the control equation of bubble motion, then the state equation of the bubble is derived according to the law of conservation of mass and the law of thermodynamics. Finally, the bubble dynamics theory is used to establish the dynamics numerical models of axisymmetric and three-dimensional bubble.
4.Noise Analysis and Control
The improved Fourier method is used to establish various unified analysis models for the acoustic characteristics of acoustic cavities, the vibration characteristics of composite plates and shells structures, and acoustic vibration characteristics of composite plates and shells coupled with acoustic cavities. The Rayleigh-Ritz energy method is used to solve the models. The results provide theoretical guidance for engineering applications.
5.Multiscale optimization of fibre reinforced composite frame structure
Fibre reinforced composite frame structure is an ideal lightweight and high-span structure in the field of aerospace. A two-scale integrated optimization design problem is proposed by considering the coupled nature in material and structure. In the optimization, the fibre winding angle in micro-material scale and the geometrical parameter of components of the frame in macro-structural scale are introduced as the independent variables on the two geometrical scales. To eliminate the spurious design caused by intermedia element density and material selection, the improved Heaviside penalization discrete material optimization (HPDMO) interpolation scheme has been developed. Moreover, six kinds of manufacturing constraints are explicitly included in the optimization model as series of linear inequalities or equalities to the meet the manufacturing requirement and decrease the risk of structural failure as well. A two-steps optimization scheme is then proposed to enhance the optimization solver find the global optimum design.
6.Multiscale equivalent Analysis
Multi-layer helically wound structuresare widely applied in ocean and civil engineering as load-bearing structures with high flexibility, such as wire ropes, umbilical cables and flexible risers. Their structures are usually composed of a number of twisted subcomponents with relatively large slender ratio and have the one-dimensional periodic characteristic in the axial direction.In engineering practice, the length is usually hundreds of metres while the cross-sectional size is only several decimetres.As the huge difference between the axial length and the cross-section size of this type of structures, the finite element modeling and theoretical analysis based on some assumption are usually unavailable leading to the reduction of computability; even the optimization design becomes infeasible.
Because of the axial periodicity of the helically wound structure, the structure with one periodic length is taken as a unit-cell to conduct the analysis. where a heterogeneous structure with the one-dimensional periodicity is equivalent to be a homogeneous beam.Based on the asymptotic homogenization theory, A novel implementation of the homogenization (NIAH)is derived for the analysis of the effective mechanical properties of the helically wound structurefrom both up and down scales.The tensile, bending, torsional and coupling stiffness properties of the effective beam model are obtainedfrom the analysis of a unit-cell. On this basis, a downscaling analysis formation for the micro-component stress in the one-dimensional periodic wound structure is constructed. The stress of micro-components in the specified geometry position of the helically wound structure is obtained basing on the asymptotic homogenization theory simultaneously.
MMC topology optimization is introduced to find the most flexible structure, which is used widely in various fields such as industries, metamaterial, electric device and biology organ.
Traditional design methodology of flexible riser is divided to global configuration analysis and local sectional analysis, which is an uncouple process. So, the bi-scale integrated design methodology combining global and sectional riser is introduced to given the optimal design for flexible pipes and umbilicals.