/ALE/GRID/FLOWTRACKING
Block Format Keyword Mean velocity within ALE mesh is used to determine automatically mesh displacement, mesh deformation, and also mesh rotation. The general idea is to have an ALE mesh acting as a tracking window.
Format
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/ALE/GRID/FLOWTRACKING  
I_def  scale_def  
I_rot  scale_rot 
Definition
Field  Contents  SI Unit Example 

I_def  Enable deformation flag.


scale_def  Deformation scale factor. Default = 1.0 (Real) 

I_rot  Enable rotation flag.


scale_rot  Rotation scale factor. Default = 1.0 (Real) 
Comments
 The grid velocity is calculated based on the massweighted average velocity of the material within the ALE mesh. A common application is modeling ALE impactors, such as ALE birdstrikes.
 For all nodes i, the mesh velocity i, is set as:$${w}_{i}={u}_{avg}+{\left[D\right]}_{avg}\left({X}_{i}C\right)+{\Omega}_{avg}\times \left({X}_{i}C\right)$$Where,
 ${u}_{avg}$
 Mass averaged velocity
 ${X}_{i}$
 Node coordinates
 $C$
 Center of mass
 ${\left[D\right]}_{avg}=\frac{1}{2}\left({\left[L\right]}_{avg}+{}^{t}\left[L\right]{}_{avg}\right)$
 Average strain rate tensor
 ${\Omega}_{avg}=\frac{1}{2}\left({\left[L\right]}_{avg}{}^{t}\left[L\right]{}_{avg}\right)$
 Average spin tensor
 ${\left[L\right]}_{avg}=\frac{{\displaystyle \sum {m}_{i}}{\left[L\right]}_{i}}{{\displaystyle \sum {m}_{i}}}$
 Average gradient of velocity
 $\left[L\right]=\nabla u=\left[\begin{array}{ccc}{\partial}_{x}{u}_{x}& {\partial}_{x}{u}_{y}& {\partial}_{x}{u}_{z}\\ {\partial}_{y}{u}_{x}& {\partial}_{y}{u}_{x}& {\partial}_{y}{u}_{x}\\ {\partial}_{z}{u}_{x}& {\partial}_{z}{u}_{x}& {\partial}_{z}{u}_{x}\end{array}\right]$
 Gradient of velocity
 It is possible to disable mesh deformation and/or mesh rotation. It can also be amplified or reduced using scale factors scale_def and scale_rot.
 It is recommended to define NonReflecting Frontier on ALE mesh boundaries (/EBCS/NRF).
 A specific treatment is introduced to amplify mesh deformation to track material that tends to escape the ALE boundaries. Without this treatment, average quantities may not adequately track the main flow when there are large velocity gradient differences.