Simulation Fluid-Structure Interaction 2D Sliding a filled Cup

The simulation of a fluid-structure interaction of the sliding of a filled cup in 2D can be performed with NOGRID points CFD software.

In this fluid-structure coupling, a wall is switched off at a certain time, a cup filled with water starts to move due to gravity and slides down an inclined plane. The cup is modeled as a rigid body and is free to move unconstrained when forces act on it. The single rigid body can collide with the bottom wall and can change the direction of movement. The collisions are assumed to be perfectly inelastic collisions in this study. An inelastic collision, unlike an elastic collision, is a collision in which the kinetic energy is not conserved due to the action of internal friction. The software can calculate both collision regimes controlled by a plasticity coefficient.

Figure 1: CAD groups created in NOGRID's COMPASS

Figure 2: Setup the FSI Sliding Cup Case

Figure 3: Result view of the FSI Sliding Cup case within NOGRID points' GUI

Figure 4: Animation FSI Sliding Cup case

The fluid-rigid body interaction simulated in this study is solved fully coupled with the Lagrangian method. Fully coupled means that the motion (translation and rotation) of the filled cup (= the rigid body) and the fluid variables for velocity and pressure are solved simultaneously in a large solution matrix (no iterative switching back and forth between the solution variables necessary). In engineering, this fluid-structure coupling (FSI Fluid-Structure-Interaction) refers to the consideration of the mutual influence of moving, not necessarily rigid bodies and a flow. The interaction between fluid flow and bodies occurs in many physical applications.
The fluid flow inside the cup causes both displacement and rotation of the rigid bodies due to the forces and torques exerted on the bodies by the fluid. Conversely, the movement of the cup causes changes in the flow. If the flow also changes due to the structure, there is a so-called real, two-sided fluid-rigid-body coupling. If several rigid bodies are involved, the movement of one body can of course also be influenced by collisions with other bodies.

The cup in this simulation is assigned a weight and a mass moment of inertia, as with any rigid body in the FS coupling. The rigid body thus behaves in accordance with the forces acting on it from the fluid. Conversely, of course, the flow is also influenced by the movable rigid bodies. The cup is positioned smoothly here, i.e. it can slide perfectly onto the ground. In this study the mutual rigid body-rigid body friction is force-free as well. The "dynamic friction" or Coloumb friction is implemented as the law of friction between the rigid bodies and walls and it can be switched off, as in this simulation.

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 FSI (Fluid-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.
Easy Modelling

Easy and fast modelling: Build geometry, mesh boundary, setup the case and start computation

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.




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:




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