Fluid–structure interaction

The fluid - structure interaction (english fluid -structure interaction) the consideration of the interaction between structure and flow is called engineering. In this case, numerical methods for fluid and structural calculation are coupled together.

Introduction

The mutual influence of structure and flow is an interesting, in nature and technology frequently occurring phenomenon. It occurs in elastic, easily deformable, vibratory, rotary or sliding bearings, flow around or through which flow structures. The detachment of vortices can enable the flow-around structure in noticeable vibrations. Flow -induced vibrations occur, for example, on aircraft wings, propeller blades of, but also in the flow around in front of buildings. If the oscillations are large enough to affect the flow in return. Other popular examples of a fluid-structure interaction, the flow in blood vessels or the flow around heart valves.

Numerical Methods

With a numerical simulation of the real behavior of a component or a flow can be represented as models. Commonly used numerical methods for fluid and structural calculation are the finite volume method and the finite element method. Both methods are based on the solution of partial differential equations. The computational domain is to using a computational grid is divided into individual cells (spatial discretization ), where the differential equations are solved taking into account appropriate boundary conditions. The resulting large systems of equations are solved directly or iteratively numerically. The considered processes can be stationary (time- independent) or transient ( time-dependent). Instationary processes in the solution is calculated at discrete points in time, wherein the solution to the current time of the solutions at earlier time points is dependent ( discretization ).

Transfer of boundary conditions

Principle for the solution of coupled problems are two solution methods are available:

Iterative coupling between fluid and solid

For the fluid-structure coupling constraints have to be exchanged between the programs for fluid and structural calculation. Resulting from the flow pressure forces and wall shear stresses acting on the adjacent walls and put a strain on the structure; they are interpolated at the interfaces to the computational grid of the structure. The computing grid on the flow side and on the structural side can be different. Perform the flow-induced forces to a shift or deformation of the structure is in the next calculation step, the altered position of the computational grid as a new constraint in the flow simulation on. This process is iteratively traversed until the required convergence criterion or the predetermined maximum number of iterations is reached. In non-stationary processes, then the solution is determined at the new time.

Direct solution of the complete system

In addition to the iterative coupling direct solution method used in strong transient interactions, with a single solution matrix for the entire system ( fluid and structure) is set up and solved.

One-sided and two-sided coupling

A real, two-way fluid-structure coupling occurs when the flow is noticeably affected by the structural change. Often, however, is the retroactive effect of structural change on the flow is so weak that it can be neglected. In this case we speak of a one-sided fluid-structure coupling.