A fluid-structure interaction method for flexible multi-body thin-walled structures

Abstract

The application discloses a kind of fluid-solid coupling methods for flexible multi-body thin-walled structure, it is related to marine research technical field.The large deformation fluid-solid coupling solver under inertial coordinate system one multi-step iteration direct force immersed boundary method is applied to the no-slip boundary condition of arbitrary rigid or flexible boundary, and based on absolute coordinate finite element method, the rigidity and dynamic response of structure are predicted, and the grid refinement and asynchronous propulsion method are coupled with structure solver and fluid solver, and the large deformation fluid-solid coupling calculation method of multi-body thin-walled structure is developed.The method is applied to the no-slip boundary condition of arbitrary dynamic boundary under orthogonal grid, and it has the ability to simulate the rigid-flexible coupling dynamic response characteristics of large deformation and large amplitude rigid body motion.The grid refinement and asynchronous propulsion method can improve the numerical stability of fluid-solid coupling model, and it has the ability to simulate light and high rigidity structure.Fluid-solid coupling solver has outstanding solving performance, compared with serial CPU solver, can obtain close to 100 times acceleration ratio.

Description

Technical Field

[0001] This invention relates to the field of marine research technology, and more specifically, to a fluid-structure interaction method for flexible multibody thin-walled structures. Background Technology

[0002] With the continuous development of deep-sea oil and gas resources, flexible thin-walled marine structures are emerging, such as biomimetic robotic fish and composite material propellers. Furthermore, with the widespread use of high-strength steel and composite materials, structures are developing towards larger sizes, more diverse structural forms, and lighter weights. As structural walls become thinner, their stiffness inevitably decreases, leading to increasingly prominent interactions between fluids and elastic structures. Examples include the localized hydroelastic slamming effect on overhanging bow decks and the flutter of offshore wind turbine blades. These new devices and trends pose challenges to current marine structure analysis theories and design methods, urgently requiring research on the large deformation fluid-structure interaction dynamic response of multibody thin-walled structures. This research aims to enhance our understanding of the fluid-structure interaction mechanisms of new marine engineering equipment and related fundamental sciences to meet the needs of deep-sea resource development and future marine engineering equipment development.

[0003] Numerical simulation technology provides a powerful tool for the study of fluid-structure interaction phenomena. However, the study of fluid-structure interaction problems of thin-walled structures involves knowledge from multiple interdisciplinary fields, including large displacement, large deformation and resonance response of structures, unsteady shear layers in the flow field, transition and turbulence of vortex leakage, and hydrodynamic interference between multiple bodies. At present, the academic community is still in the exploratory stage in the development of coupling mechanisms and numerical analysis tools for such complex problems, and numerically solving such fluid-structure interaction systems is extremely challenging. Existing numerical analysis methods for fluid-structure interaction mostly rely on commercial or open-source software and have achieved success on single or small deformation problems [2-3], but lack effective numerical tools for large deformation fluid-structure interaction problems of multi-body thin-walled structures.

[0004] Currently, scholars both domestically and internationally have conducted extensive research and achieved preliminary results in fluid-structure interaction theory and numerical analysis methods. However, some important issues still require further exploration, including:

[0005] (1) Existing numerical analysis tools for fluid-structure interaction are mostly based on boundary fitting methods and have achieved success in fluid-structure interaction problems with small deformations of structures. Numerical research on fluid-structure interaction with large deformations of multi-body thin-walled structures is still limited and immature, which is precisely the problem that urgently needs to be solved in the current design of marine structures.

[0006] (2) Non-boundary fitting methods have unique advantages for flow problems involving complex multibody or topologically varying interfaces, and are widely used in fluid-structure interaction problems with rigid boundaries or forced oscillation problems with flexible boundaries. However, for the interaction between flexible structures and flow fields, existing numerical models are either too simplified or have obvious limitations. It is necessary to conduct in-depth research on the handling of boundary conditions at deformable interfaces and data transfer between mismatched meshes.

[0007] (3) Computational efficiency is an important aspect of evaluating the quality of numerical analysis tools and a key factor limiting the application and promotion of fluid-structure interaction numerical tools in engineering practice. Currently popular fluid simulation software such as Fluent, STAR-CCM+, and OpenFOAM mainly support multi-core CPU acceleration, which is difficult to meet the computational efficiency requirements of the engineering community. A promising alternative is GPU / CPU heterogeneous parallel acceleration technology, which is a future trend in high-performance scientific computing.

[0008] Therefore, conducting research on fluid-structure interaction methods for flexible multibody thin-walled structures and developing corresponding high-precision and efficient numerical analysis tools is not only of great scientific significance but also an urgent need for engineering applications. Summary of the Invention

[0009] The purpose of this invention is to provide a fluid-structure interaction (FSI) method for flexible multi-body thin-walled structures. For numerical research on the coupled dynamic response of flexible multi-body thin-walled structures and flow fields, a large deformation FSI solver in an inertial coordinate system is proposed. A multi-step iterative direct force immersion boundary method is used to apply no-slip boundary conditions to arbitrary rigid or flexible boundaries. Based on the absolute coordinate finite element method, the rigid-flexible and flexible dynamic responses of the structure are predicted. Furthermore, a mesh refinement and asynchronous propagation method is combined to couple the structural solver and the fluid solver, thus developing a large deformation FSI calculation method for multi-body thin-walled structures.

[0010] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a fluid-structure interaction method for flexible multi-body thin-walled structures, comprising the following steps: S1: using interface mesh interpolation technology to identify errors in mesh phase attributes caused by large deformation irregular interfaces, thereby improving the accuracy of boundary condition application; and using an improved multi-step direct force immersion boundary method to apply no-slip boundary conditions for rigid or flexible boundaries.

[0011] S2: Construct a dynamic response model based on the absolute nodal coordinate method, develop different types of finite element elements, and use the Newton-Raphson iterative method and load increment method to solve the nonlinear finite element equations and predict the response of structural deformation.

[0012] S3: Construct a large deformation fluid-structure interaction (FSI) computing platform. Through flexible interface mass point reconstruction and asynchronous propagation methods, data between mismatched meshes can be transferred. This is achieved by maintaining asynchronous propagation of the time steps of the fluid solver and the structural solver, and reducing the rigid constraints of the FSI solver. Develop a GPU / CPU heterogeneous parallel large deformation FSI model to accelerate the large deformation FSI solver and optimize the program to improve the speedup ratio.

[0013] The present invention is further configured such that: in step S3, program optimization is performed from the aspects of parallelism, memory, data transmission and load balancing.

[0014] In summary, this invention has the following beneficial effects: 1. This method solves the large deformation response of flexible slender bodies in an inertial frame, and applies no-slip boundary conditions with arbitrary moving boundaries under a rectangular mesh, enabling it to simulate the dynamic response characteristics of rigid-flexible coupling with large deformation and large-amplitude rigid body motion. 2. The proposed mesh refinement and asynchronous propagation methods can improve the numerical stability of the fluid-structure interaction model, enabling it to simulate lightweight and highly rigid structures. 3. The fluid-structure interaction solver has outstanding solution performance, achieving a speedup of nearly 100 times compared to a serial CPU solver. Attached Figure Description

[0015] Figure 1 This is a large deformation fluid-structure coupling model of GPU / CPU heterogeneous parallelism in this embodiment of the invention. Detailed Implementation

[0016] The following is in conjunction with the appendix Figure 1 The present invention will be described in further detail below.

[0017] Example: A fluid-structure interaction method for flexible multibody thin-walled structures improves the accuracy of boundary condition application by using interface mesh interpolation technology to address mesh phase attribute identification errors caused by large deformation irregular interfaces; and employs an improved multi-step direct force immersion boundary method to apply no-slip boundary conditions for arbitrary rigid or flexible boundaries.

[0018] A dynamic response model based on the absolute nodal coordinate method was constructed, and different types of finite element elements were developed. The Newton-Raphson iterative method and the load increment method were used to solve the nonlinear finite element equations to predict the structural deformation response. Examples of such elements include two-dimensional two-node four-DOF Euler beam elements, two-dimensional two-node six-DOF Timoshenko beam elements, and three-dimensional two-node twelve-DOF cable elements.

[0019] A large deformation fluid-structure interaction (FSI) computational platform was constructed. Flexible interface mass point reconstruction and asynchronous propagation methods were used to transfer data between mismatched meshes. The asynchronous propagation of the time steps of the fluid solver and the structural solver was maintained, and the rigidity constraints of the FSI solver were reduced. A GPU / CPU heterogeneous parallel large deformation FSI model was developed to accelerate the large deformation FSI solver. The program was optimized in terms of parallelism, memory, data transmission, and load balancing, achieving a speedup of hundreds of times.

[0020] Large deformation fluid-structure interaction models with heterogeneous parallelism of GPU / CPU, such as Figure 1 Its storage is located within the CPU of the host computer. During use, a geometric model is generated and built through mesh generation, with memory allocation and initialization performed on both the CPU and GPU. After initialization, time progression is initiated. Following time progression, a multi-step iterative immersion boundary method is applied on the GPU to convert fluid forces into equivalent nodal loads. This is then performed using the ANCF finite element solver, followed by mesh refinement and asynchronous time progression. A check is performed to determine if the total time has been exceeded. If it has, global variables are transferred from the GPU to the CPU for output and visualization; otherwise, the process returns to the time progression phase.

[0021] When performing the multi-step iterative immersion boundary method on the GPU, the momentum equation and the pressure Poisson equation are solved after the boundary conditions of the computational region are applied within the GPU device. After updating the velocity, the multi-step direct force immersion boundary method is applied to apply no-slip boundary conditions. If it is in RK3 format, it returns to the boundary step of applying the computational region. Otherwise, it calculates the fluid load output on the object surface and converts the fluid force into equivalent nodal loads.

[0022] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A fluid-structure interaction method for a flexible multi-body thin-walled structure, characterized by: Comprising the following steps: S1: By interface grid interpolation technology, use processing large deformation irregular interface caused by grid phase attribute identification error, improve the accuracy of the application of boundary conditions; using improved multi-step direct force immersed boundary method to impose rigid or flexible boundary non-slip boundary conditions; S2: Constructing dynamic response model based on absolute node coordinate method, and developing different types of finite element units, using Newton-Raphson iteration method and load increment method to solve nonlinear finite element equation, and predicting the response of structural deformation; S3: Constructing large deformation fluid-structure coupling calculation platform, through flexible interface particle reconstruction and asynchronous advancing method, to transfer data between non-matching grids, and to keep the asynchronous advancing of fluid solver and structure solver time step and to reduce the rigid constraint of fluid-structure coupling solver; developing GPU / CPU heterogeneous parallel large deformation fluid-structure coupling model, whose storage is set in CPU of host; using, through grid generation and establishing geometric model, and performing memory allocation and initialization in CPU and GPU; After initialization, time advancing is performed, and after time advancing, multi-step iterative immersed boundary method on GPU is performed, fluid force is converted into equivalent node load, ANCF finite element solver is performed, grid refinement and asynchronous advancing method are performed; Judging whether the total time is exceeded, if the total time is exceeded, global variables are transferred from GPU to CPU, output and visualization are performed; if the total time is not exceeded, time advancing link is returned to; When multi-step iterative immersed boundary method on GPU is performed, after boundary conditions of calculation region are applied in GPU device, momentum equation is solved, pressure Poisson equation is solved, velocity is updated, multi-step direct force immersed boundary method is applied to impose non-slip boundary conditions, if it is RK3 format, boundary link of calculation region is returned to, if not, fluid load output on object surface is performed, fluid force is converted into equivalent node load.

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