About particle floating

[Zhangshi]

I’m a beginner of the OpenLB.Currently,I want to simulate the floating of a particle.At first,I read the code in the example of “settlingCube3D”.I changed some parameters,such as the density of fluid and particle,orientation of the cube particle.But something wrong happened when I saw the simulation result.
I found three problems.First,the Particle trajectory was always vertical upward.Second,the velocity of the pariticle kept increasing,which was not normal under the influnece of drag force in the daily situation.At last,although I changed the orientation of the cube particle obviously,it didn’t seem to rotate.
At the moment I don’t know how to modify the code. I really hope to get some ideas.Thanks a lot.

[robin.trunk]

Dear Zhangshi,

it depends on the way you changed the parameter and what you inspected. If the cubes density is below the fluid density it will rise to the top. It is relevant where you changed the densities as they enter “externalAcceleration” for the calculating of buoyant forces.
Depending on the density difference the particle might accelerate rapidly in this case it is possible for high velocities that the cube slips through the wall, in which case it no longer experiences drag forces. You might want to check if this is the case by checking wheater the cubes coordinates are still within the simulation domain.
To the orientation: The parameter sets the initial orientation. Wheather the cube rotates and to which extend is not always trivial as it depends on initial orientation, Reynolds number, density ratio, …
Did you have a look at the terminal output or the vtk output files? It is possible that e.g. the rotation is rather slow and therefore not visible when inspecting the graphical output.

Best
Robin

[Zhangshi]

Dear Robin.Trunk

Thank you very much for your prompt reply.I’m sorry that I can’t reply you in time because of time difference.First,allow me to express my best respect for you.Although my English is not very good,I’ll try my best to express clearly.
As you mentioned,this time I changed the ratio of the density,and the orientation became more obvious.But the change seemed to be unreasonable.It’s necessary for me to make further adjustment on parameters.May I ask another two questions?I’m sorry to take up your time again.First I tried to build a complex floating particle by combining geometric primitives,For example,combining two or there spheres into another further complex particle.I’m not aware that if the class ”SmoothIndicatorIdentity” can help me out.And last,for further simulation,I want to simulate the particle floating through the water-oil interface,as initially the oil layer is laid on the water surface quitely.I have some ideas about building the water-oil interface,just like the example “RayleighTaylor3D”.But it’s a problem for me to consider the dynamic setting of the particle,such as acceleration.
Thank you sincerely.

[robin.trunk]

Dear Zhangshi,

for all your plans the current version of OpenLB needs to be extended as it is not fully supported right now.

== Combining Primitives ==
While SmoothIndicatorIdentity is what you are looking for, it does not support the full range of functionality yet. It rather works like for the other indicators and combines it by shape to depict the object in the simulation. But calculations for the mass and moment of ineratia of the new object are still missing which will lead to unphysical behaviour. So this would need to be added to SmoothIndicatorIdentity.

== Floating in a oil layer ==
For such a simulation you also need a multiphase approach. In the current version there is no cobined dynamics supporting particulate flow combined with a multiphase approach. You somehow need to couple the FreeEnergyDynamcis with the PorousParticleDynamics of HLBM and also need to modify the external acceleration as the bouyant forces change dependent on the density of the surrounding fluid. However currently this is set globally.

Best regards
Robin

[Zhangshi]

Dear Robin.Trunk

Thanks for your detailed answers.Now,I’ve been more clear about my
further simulation.You really helped me a lot.But,I’m still thinking that if STLreader can perform better than the SmoothIndictorIdentity.
Whatever,it’s important for me to start the oil-water simulation.
Thank you!!

Best
Zhangshi

• This reply was modified 3 years, 11 months ago by Zhangshi.

[robin.trunk]

Dear Zhangshi,

if you have STL files at hand, this would be the better approach and should be working withoug modification.
For discussions and help on the modification of some approaches please also consider the upcoming SpringSchool in the UK: https://www.openlb.net/spring-school-2021/

Best regards
Robin

[Zhangshi]

Dear Robin

Thanks for your inviting.I have ever thought about the SpringSchool.
But it seems that UK is too far for me to get there.I feel sorry about that.But,I’m glad to share this information with my friends.

Best reagards
Zhangshi

[Zhangshi]

Dear Robin，

I’m so sorry to bother you again.I have no idea if I should choose the shan-chen model or the free energy model for simulating oil-water interface.Could you recommed some relevant code for me?
Have a nice day!

Best
Zhangshi

• This reply was modified 3 years, 11 months ago by Zhangshi.

[robin.trunk]

Dear Zhangshi,

the Free Energy model would be prefereable, you can find information and theory about it under the following DOI:
10.1103/physreve.93.033305
10.1007/978-3-319-44649-3

Best regards
Robin

[Zhangshi]

Dear Robin,

Thanks for your support and guidance!You are so kind.Now I’m reading relevant codes,such as “youngLaplace3D”.I hope I can get over it soon.

Best
Zhangshi

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