how to define a moving wall boundary condition in MRT

[ztdepztdep]

I want to compute the lid-driven cavity problem, but could you please tell me how to define a moving wall boundary condition.

[llaniewski]

Quick search for "MovingWall" provides a nice example in one of the multiphase models:

TCLB/models/multiphase/d2q9_pf_velocity/Dynamics.c.Rt

Lines 1365 to 1378 in 9e1ceb1

	CudaDeviceFunction void MovingWall_S_Dirichlet(){
	// The bounce-back formula for a Dirichlet boundary condition with a prescribed wall velocity
	// eq 5.26 p180 from The Lattice Boltzmann Method: Principles and Practice
	// T. Krüger, H. Kusumaatmaja, A. Kuzmin, O. Shardt, G. Silva, E.M. Viggen
	// TODO: IMPLEMENT ACTUAL BOUNDARY CONDITION
	g[2] = g[4];
	g[5] = g[7] + VelocityX/6.0;
	g[6] = g[8] - VelocityX/6.0;
	h[2] = h[4];
	h[5] = h[7];
	h[6] = h[8];
	}

In this case g[...] are standard LBM densities, and the S in the function name stands for "South", so bottom wall. From this you should be able to construct the moving wall condition you need.

[ztdepztdep]

hello sir:
I have tried, it always gives inf value of density and velocity. I can't figure it out where is the problem. I am wondering why this simple boundary condiction not be included in the standard d2q9 solver.

[ztdepztdep]

`CudaDeviceFunction void MovingWall_N_Dirichlet(){

f[4] = f[2];
f[7] = f[5] - WallX/6.0;
f[8] = f[6] + WallX/6.0;

}

I added this piece of code into the code. But it cann't work. hope you can help me out of this.
`

[llaniewski]

@ztdepztdep I recommend doing the tutorial on model development (https://docs.tclb.io/tutorials/model-development/1.-finite-difference-wave-equation/) to understand how the note-types work. You'll learn how to add your new node types to Run, etc.

[ztdepztdep]

`

   <?xml version="1.0"?>
   <CLBConfig version="2.0" output="output/" permissive="true">

<Geometry nx="120" ny="120">
	<MRT>
		<Box/>
	</MRT>
	<MovingWall_N mask="ALL">
		<Box dy="-1"/>
	</MovingWall>

	<Wall mask="ALL">
  		<Box nx="1"/>
		<Box dx="-1"/>
		<Box ny="1"/>
    </Wall>
    
</Geometry>

<Model>
	<Param name="VelocityX" value="1.0"/>
	<Param name="Viscosity" value="0.12"/>
</Model>
<VTK Iterations="5000" what="U,Rho"/>
<Log Iterations="5000" name="log.txt"/>
<Solve Iterations="100000"/>

` I added movingwall NodeType, and compiled it sucessfully. but when i run the xml file, it feed back the error about : error ! Error while parsing drivencavity-2D.xml: Start-end tags mismatch

[TravisMitchell]

This is likely because you have "Start-end tags mismatch" for the MovingWall_N element in your xml.

[ztdepztdep]

<MovingWall_N mask="ALL">	
<Box dy="-1"/>	
</MovingWall>

the north element is the last row of box ,as i have defined in the xml file.
i cann't figure it out what is the problem

[TravisMitchell]

You have <MovingWall_N> closed with </ MovingWall> ... These tags do not match.

[ztdepztdep]

Great! Thank you. It works now. I will upload the computational results once I have completed it.

[ztdepztdep]

no, I have tried many parameters combinations, it cann't give any meaningful results. full of "inf".