How to set moving boundary conditions in the software?

[yang-yifeng]

Describe the bug
Here is a summary of what we want to achieve in ECOGEN. For the wall conditions in the ECOGEN Euler equations model, my understanding is the normal velocity of the flow should be zero. What we want to achieve is moving wall boundary conditions. The boundary is still fixed and does not need to move, but the normal velocity is non-zero. For example, for a wall at x = 0, we try to achieve the horizontal velocity at the wall varies with time as u = Asin(omegat), where A and omega are amplitude and oscillating frequency. May I please check whether this can be achieved in ECOGEN?

To Reproduce
Steps to reproduce the behavior:
Its mainly about the setting in the file "initialConditions.xml".

Expected behavior
I have tried to use the Symmetry Wall and inlet injection using stagnation state to establish my BC, but all failed. I just want to figure out how to set the above moving boundary conditions.

Screenshots
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Input files
If applicable, add your input simulation files.

OS
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Additional context
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Institution and research field
I am a research Fellow in UCL, and work on fluid mechanics.

[kevinschmidmayer]

Hello @UKLdsadf,

Thank you for the details. To respond to your question, yes having a moving wall as boundary condition can be achieved. We indeed already did a quick implementation and test of it for a new model we are working on. However, this won't be available soon since it is a work in progress.

Here are a few details of the approach we used:

• Create a new boundary condition for your problem (copy paste an existing one such as wall). Add to it a new attribute which is the wall velocity.
• Pass this attribute as argument to a new Riemann solver for the moving wall within the method solveRiemannBoundary.
• Add to your model class (ModEuler in your case) the new Riemann solver which will use the moving wall velocity.

Let us know if this helps and please, if you manage to make it work, share with us your development so it could eventually be included in the next ECOGEN version.

Best,
Kevin

[yang-yifeng]

Hi Kevin,

I hope you're doing well.

I’m currently trying to implement a moving wall boundary condition in ECOGEN, where the wall imposes a time-dependent normal velocity, such as a sinusoidal function. While I’ve explored several approaches, I’m having difficulty accessing the current simulation time within the solveRiemannWall function (e.g., in ModEuler.cpp).

Could you kindly advise if there is an existing function (e.g., getTime()), a global variable (like g_currentTime), or a class (e.g., TimeManager) that provides the current simulation time during runtime?

Any guidance or reference to the relevant part of the code would be greatly appreciated.

[Algiane]

Hi @UKLdsadf ,

The physical time is stored in the physicalTime public member of the Tools class.
See

ECOGEN/src/Tools.h

Line 145 in dab2c84

double physicalTime; //!< Current physical time

The TB variable is an extern pointer to the this class.
See

ECOGEN/src/Tools.h

Line 148 in dab2c84

extern Tools *TB;

The Tools.h header is included in almost all the files of the code so you should be able to access the physical time in Mod<X>.cpp files using: TB->physicalTime.

Best,

[kevinschmidmayer]

Hello @UKLdsadf ,

Any update on this issue?

Kevin

[yang-yifeng]

Hi @kevinschmidmayer

Many thanks. I am so sorry for late reply!

We have solved the issue, the physical time function you suggested has been used, and the a time-dependent oscillational wall BC is established. But we are still testing whether the established condition is correct by doing some simulations. Once we finished this, I will share our developed scripts with you!

Best regards

[kevinschmidmayer]

Very good, thanks!

Best,
Kevin