# Simulation Structure-Structure Interaction Five Boxes on Stair

In this article, we present a structure-structure interaction (SSI) simulation between falling boxes on stairs. All boxes behave like rigid bodies and this is referred to as a so-called rigid body simulation (RBS).
The boxes are modeled as rigid bodies and are free to move unconstrained when forces act on them. The individual rigid bodies can collide with each other and can change their direction of movement. The collisions between the rigid bodies and the walls are assumed to be completely inelastic. An inelastic collision, unlike an elastic collision, is a collision in which kinetic energy is not conserved due to the effect of internal friction. The NOGRID software can compute both collision regimes controlled by a plasticity coefficient.

Figure 1: CAD groups created in NOGRID's COMPASS

Figure 2: Setup the SSI Five Steps case

Figure 3: Result view of the SSI Five Steps case within NOGRID points' GUI

Figure 4: Animation SSI Five Boxes on Steps

Rigid body simulation (RBS) is the simulation of the transient movement of rigid bodies. Rigid body mechanics is about physical bodies that are not deformable. During the simulation, the rigid bodies move, but the shape or structure remains unchanged. Various types of forces can act on the rigid body: gravity, magnetic forces, frictional forces, etc. These forces accelerate the rigid body and the translational and rotational speeds change. In addition, there can be collisions between the rigid bodies. Collisions suddenly change the translational and rotational speeds of the bodies involved.

In this 3D example, several boxes fall and interact with each other (see figures 1 - 4). The simulation is solved fully coupled with the Lagrange method. Fully coupled means that the stresses within the bodies are simultaneously resolved in a large solution matrix. The Euler method can also be used to solve this case.

As with any rigid body in the FS coupling, the boxes in this simulation are assigned a weight and a mass moment of inertia. The rigid body thus behaves in accordance with the forces acting on it. If several rigid bodies are involved, the movement of one body can of course also be influenced by collisions with other bodies.

NOGRID points can perfectly be used for designing and problem solving for all kinds of FSI processes. NOGRID points helps to understand the flow by being able to compute and visualize the mass, momentum and motion of single and multiple rigid bodies. You receive transient values ​​with which you can analyze and evaluate the efficiency of the components or processes.

NOGRID unites abilities to handle free surface flow and moving parts in the domain and allows the simulation of any conceivable geometry and operation modes such as

• computation is in full 3D solving complete Navier-Stokes-Equations
• easy and intuitive setup also for SSI (Structure-Structure Interaction) cases
• free 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

## Nogrid's strengths

Particular strengths of NOGRID's fluid flow CFD software are the rapid preprocessing (no fluid grid needs to be generated, only the boundary mesh, inner finite points are generated automatically depending on User setting initially and during computation), and the outstandingly short computation time even for complicated cavities.
As you can see in the image below, the boundary of the geometry still requires a mesh to allow the interior finite points to detect the boundary. The boundary must therefore be meshed and the finite points inside are automatically generated during the simulation controlled by User specifications.

## What is CFD from NOGRID?

CFD solves the fundamental equations that define the fluid flow process. With CFD software from NOGRID every engineer makes better decisions by predicting, analyzing and controlling fluid flow, heat and mass transfer or chemical reaction. By using NOGRID software for flow modeling you receive information on essential flow characteristics as for example flow distribution. Using it additional to testing and experimentation NOGRID software helps to improve the evaluation of your design – resulting in better construction and operation parameters, increasing planning security and money savings due to faster time to the marketplace for your product or process.

## Choose NOGRID

With NOGRID, you choose professional CFD software and services – our aim is helping you to be successful. When you decide to work with NOGRID you choose close cooperation with a dynamic, flat hierarchies-organization. Short information channels result in quick and accurate professional support and service. Our team consists of highly qualified employees, who are experts in fields such as numerical simulation or computational fluid dynamics. Based on our know-how, we are pleased to offer the following services, responding to your individual requirements:

## TRAINING

In our two-days training courses you will learn, how to use NOGRID CFD software efficiently. Our technical support team will teach you how to handle and solve different cases.

For more details please refer to Training Courses →

## Technical Support

We offer full professional support from the minute you start using our software, by telephone or by email. Contact us, when ever needed.

For more details please refer to Software Support

## Service

Lack of time or resources and other constraints often make outsourcing an attractive solution. We help you with your flow modeling needs. Based on our engineering expertise in this field we offer individual numerical simulation services matching the unique needs of your organization.

For more details please refer to Simulation Services →

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