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FSI frame settings

Posted 20 oct. 2011, 11:31 UTC−4 Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2 5 Replies

Sirisha Govindaraju
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What should I use for the frame setting in an FSI interface? Should it be in spatial or material? I never noticed this setting before v4.2.

I cannot locate any information in the manual as to how this setting influences the calculations.

Thanks,
Sirisha

5 Replies Last Post 22 oct. 2011, 03:41 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 20 oct. 2011, 14:46 UTC−4
Hi

check the FORUM for CFD the two frames are very important (Euler versus Langrange references), Ihavent foun a short and simple way to explain the differences, so I recommend to test it out on simple cases.

In V4 COMSOL uses the Spatial and the Material frame also in the structural physics, which approaches the CFD and Solid way of looking into the same, finally, physics, solid is just a special fluid, or the opposite, no ?

--
Good luck
Ivar
Hi check the FORUM for CFD the two frames are very important (Euler versus Langrange references), Ihavent foun a short and simple way to explain the differences, so I recommend to test it out on simple cases. In V4 COMSOL uses the Spatial and the Material frame also in the structural physics, which approaches the CFD and Solid way of looking into the same, finally, physics, solid is just a special fluid, or the opposite, no ? -- Good luck Ivar
Sirisha Govindaraju
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Posted: 1 decade ago 20 oct. 2011, 20:10 UTC−4
I read about the Eulerian vs Lagragian concepts multiple times before using the FSI interface.

But here is what is confusing:
The user's guide says "Physics can be formulated on the spatial frame or on the material frame, depending on whether it is more convenient to interpret the equations as Eulerian or Lagrangian, respectively"

The structural mechanics users guide says "The Fluid-Structure Interaction interface uses an arbitrary Lagrangian-Eulerian (ALE) method to combine the fluid flow formulated using an Eulerian description and a spatial frame with solid mechanics formulated using a Lagrangian description and a material (reference) frame.". It also says "Because the Navier-Stokes equations are solved in the spatial (deformed) frame while the solid mechanics interfaces are defined in the material (undeformed) frame, a transformation of the force is necessary"

So really ........the selection of the "frame" under the physics is upto the user?

Thanks,
Sirisha

PS:If you uncheck the displacements control spatial frame then the spatial and the material coordinates are the same (i think)
I read about the Eulerian vs Lagragian concepts multiple times before using the FSI interface. But here is what is confusing: The user's guide says "Physics can be formulated on the spatial frame or on the material frame, depending on whether it is more convenient to interpret the equations as Eulerian or Lagrangian, respectively" The structural mechanics users guide says "The Fluid-Structure Interaction interface uses an arbitrary Lagrangian-Eulerian (ALE) method to combine the fluid flow formulated using an Eulerian description and a spatial frame with solid mechanics formulated using a Lagrangian description and a material (reference) frame.". It also says "Because the Navier-Stokes equations are solved in the spatial (deformed) frame while the solid mechanics interfaces are defined in the material (undeformed) frame, a transformation of the force is necessary" So really ........the selection of the "frame" under the physics is upto the user? Thanks, Sirisha PS:If you uncheck the displacements control spatial frame then the spatial and the material coordinates are the same (i think)
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 21 oct. 2011, 02:34 UTC−4
Hi

No, leave the default, in solid the displced results are in the spatial frame with coordinates (Spatialframe) x = X (Material Frame) + u

--
Good luck
Ivar
Hi No, leave the default, in solid the displced results are in the spatial frame with coordinates (Spatialframe) x = X (Material Frame) + u -- Good luck Ivar
Sirisha Govindaraju
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Posted: 1 decade ago 21 oct. 2011, 18:21 UTC−4
Ivar,

Are you saying I should leave the default frame selection when I use the built-in physics of fluid-structure interaction or are you talking about leaving the defaults for displacements control spatial frame?

Thanks,
Sirisha
Ivar, Are you saying I should leave the default frame selection when I use the built-in physics of fluid-structure interaction or are you talking about leaving the defaults for displacements control spatial frame? Thanks, Sirisha
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 22 oct. 2011, 03:41 UTC−4
Hi

I'm saying leave COMSOL's defult frame settings. Then when you define coordinate frames, or BCs think twice, is it referrid to the original Material geometry, or for the deformed stationary deformed geometry

And read through te doc, not only in CFD to get a good grasp of what these frames do.

Note: if you define a material coordinate frame, and want to use it in a BC that refers to a spatial coordinate frame, comsol will not show you the coordinate frame in its drop down list. This gives you also indications which coordiante frame to use, then ask yourself why.

--
Good luck
Ivar
Hi I'm saying leave COMSOL's defult frame settings. Then when you define coordinate frames, or BCs think twice, is it referrid to the original Material geometry, or for the deformed stationary deformed geometry And read through te doc, not only in CFD to get a good grasp of what these frames do. Note: if you define a material coordinate frame, and want to use it in a BC that refers to a spatial coordinate frame, comsol will not show you the coordinate frame in its drop down list. This gives you also indications which coordiante frame to use, then ask yourself why. -- Good luck Ivar

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