Simulation 3D Fluid-Structure Interaction of Rigid Bodies in a Pipe Flow with a Water Filter

In this case study, we present a 3D simulation of a fluid-structure interaction involving rigid bodies in a pipe flow, which can pass through a water filter or grid if they are small enough.

Rigid Body Simulation (RBS) refers to the simulation of the transient motion of rigid bodies. Rigid body mechanics deals with physical bodies that are assumed to be non-deformable. During the simulation, a rigid body can move, but its shape and structure remain unchanged. Various types of forces can act on it: gravity, magnetic forces, frictional forces, etc. These forces accelerate the rigid body and thereby change its translational and rotational velocities. In addition, collisions between rigid bodies may occur, which cause sudden changes in the translational and rotational velocities of the bodies involved. 

The fluid-rigid body interaction simulated in this study is solved in a fully coupled manner using the Lagrangian method. Fully coupled means that the motion (translation and rotation) of the rigid bodies and the fluid variables for velocity and pressure are solved simultaneously in a large solution matrix (no need to iterate back and forth between the solution variables).
In engineering, Fluid-Structure-Interaction (FSI) refers to the consideration of the mutual influence of moving, not necessarily rigid bodies and a flow. Such interactions occur in many physical applications. When a fluid flows around a free rigid body, it can cause both displacement and rotation of the body due to the forces and torques exerted by the fluid. Conversely, the motion of the body alters the flow field.  If the flow is also affected by the structural response, this is referred to as a real, two-way fluid-rigid body coupling. When several rigid bodies are involved, the motion of one body may additionally be influenced by collisions with other bodies.

In this case study, a total of 12 spherical rigid bodies are considered, each with its own weight and moment of inertia. As a result, every body responds individually to the forces exerted on it by the fluid.  Conversely, the flow is also affected by the presence of the rigid bodies. You can see, for example, that some spheres are too large to pass through the filter and therefore block the corresponding filter passages.

This model can serve as a basis for more complex structures, providing a better understanding of fluid-structure coupling and helping to improve your design in terms of efficiency and cost. 

NOGRID points can be effectively used for the design and problem solving for all kinds of FSI processes. The movement of bodies and the resulting flow patterns can be predicted. NOGRID points helps to understand the flow by computing and visualizing mass, momentum, and rigid body motion. It provides transient quantities that can be used to analyze and avaluate the efficiency of FSI processes.

It provides transient quantities that can be used to analyze and evaluate the efficiency of FSI processes.

Capabilities of NOGRID points CFD software

NOGRID combines the capabilities to handle FSI problems and allows the simulation of virtually any geometry and operating mode, such as

• fully 3D computation solving the complete Navier-Stokes equations
• easy and intuitive setup also for FSI (Fluid-Structure-Interaction) cases
• freely definable material properties by equations or curves
• evaluation of chemical reactions and corresponding heat source terms
• open or closed domains including inflow and outflow areas (non-batch mode)
• moving of parts 

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