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Rigid Body Motion (RBM) Use in EnSight

Are you using Multiple Rotating Reference Frames (MRF) in your solver? There are a few instances when utilizing the Rigid Body Motion capability in EnSight can provide a distinct advantage in analyzing your results. If you are trying to evaluate streamlines in a MRF model within EnSight, you will need the Rigid Body Motion capability. EnSight has an ability called “Rigid Body Motion” based on Euler Transformations of both parts and vector variables as a function of time. How does this help? It is common practice in many CFD codes to utilize a single reference of the grid, and either solve this portion of the equations this in a rotating reference frame (MRF), or apply a fixed rotation and solve a transient solution. When operating in either of these types of situations, you can utilize EnSight’s Rigid Body Motion to perform either simply visual rotation of the rotating parts, or to correctly integrate pathlines through that region of the domain.

 

Initially, the Rigid Body Motion capability in EnSight was written to dynamically move geometry from FEA or Rigid Body Solvers according to the commonly used “Euler Transformations”. This capability was expanded to support its application in CFD models as well.  The general capability of Rigid Body Motion in EnSight allows for generic per part application of euler transformations of both the part’s coordinates as well as vector quantities, so that you may use it to describe any rigid body motion. However, this discussion here is focused on a common subset of this generic motion : Fixed rotation rate about an axis. As this is a common requirement found in all types of analyses from pumps to hvac units, fans, stir tanks, or turbomachinery, we have constructed a short User Defined Tool to ease the setup of the Rigid Body Motion. This document will focus on the use of this tool for fixed rotate rate about an axis.

 

Example Dataset

An example dataset to be used for this can be downloaded from:

https://www3.ensight.com.s3.amazonaws.com/EnSight%20Dataset%20Repository/STAR-CCM%2B%20HVAC%20Fan%20Rigid%20Body%20Motion%20Example.ens

 

Example Tutorial:

An example tutorial using this dataset and the UserDefinedTool for Rigid Body Motion setup :

http://video.ceisoftware.com/media/use-of-the-rigid-body-motion-userdefinedtool-for-m

http://www.ceisoftware.com/wp-content/uploads/screencasts/rigid_body_motion_MRF/rigid_body_motion_MRF.html

 

Caveats:

  1. Users should be using EnSight Case Gold format files.
  2. Users ‘can’ setup multiple rotating parts, but this tool does not cater to that use-case.
  3. No solvers exporting to EnSight Case Gold format currently take advantage of this, so users will have to be aware of this capability, how to setup, and when to use it correctly.

 

Uses:

  1. Solver generated a single solution for an MRF solved domain. Pathlines + Rigid Body Motion will be required to obtain correct integration of particle traces through moving domain.
  2. Solver generated transient solution with fixed rotation of the grid. Rather than multiple Geometry files for EnSight to load for each timestep, users should revert to a single geometry file + rigid body motion setup to create efficient operation of ensight.
  3. Fixed motion boundary values (tires rotating). Use of Rigid Body Motion can be utilized to visualize the rotation of the boundary. This is purely a visual alternative to frame mode rotation. 

 rbm_sample_image.png

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