To achieve the best possible results for a two-way interaction like this, I would recommend using only a single solver for the entire setup.
You could use either FEM or Vellum, whatever your preference is.
For the bra, I would recommend creating a tube-shaped polygon mesh around the body.
This tube could have collisions turned off and interact with the body using attach and/or slide constraints, which are available in some form on both solvers.
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Houdini Indie and Apprentice » FEM and Vellum as mutual affectors?
- michiel
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Work in Progress » FEM Slide constraint state error
- michiel
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The error you're getting here is a bit deceiving.
The actual problem is that the ground plane is being run through the FEM solver, which doesn't know how to solve ground planes.
As a result, the solve fails, and as a side effect of the solve failing, the error that you're seeing shows up.
To quickly fix this network, delete the ground plane and add a new ground plane using the Ground Plane shelf tool in the Collisions tab.
The quickest way to learn more about FEM is to use the shelf tools and look into the DOP setups that they create.
It's also worth looking at the user guide for "finite elements" in our help docs.
Most aspects of an FEM simulation can be controlled by means of SOP attributes, which are discussed in the help of the FEM Solver node.
I hope this helps
The actual problem is that the ground plane is being run through the FEM solver, which doesn't know how to solve ground planes.
As a result, the solve fails, and as a side effect of the solve failing, the error that you're seeing shows up.
To quickly fix this network, delete the ground plane and add a new ground plane using the Ground Plane shelf tool in the Collisions tab.
The quickest way to learn more about FEM is to use the shelf tools and look into the DOP setups that they create.
It's also worth looking at the user guide for "finite elements" in our help docs.
Most aspects of an FEM simulation can be controlled by means of SOP attributes, which are discussed in the help of the FEM Solver node.
I hope this helps
Technical Discussion » In FEM, how could I get rid of edginess shapes...?
- michiel
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There are several ways to control and influence the look of your fractured surfaces with FEM.
Using an embedded tet mesh can help. You can manipulate the embedded tet mesh to get a look that you want for your fractured surfaces without impacting the sim very much.
The best option for directly controlling the shape of the fractured surfaces is to use the fracturepart primitive attribute. This allows you to create little chunks (fracture parts) that won't get separated no matter what happens. The fracturing remains dynamic, however it is restricted such that it does not fracture between tets that have the same fracturepart value. The Solid Fracture SOP creates such a fracturepart attribute for you, but you can create the attribute yourself if you like. If you use fracturepart to create fairly round parts then you'll avoid the edgy shapes that you're seeing.
You can take a look at what the Fractured Solid Object shelf tool does with regards to the embedded setup and the creation of a fracturepart attribute.
Using an embedded tet mesh can help. You can manipulate the embedded tet mesh to get a look that you want for your fractured surfaces without impacting the sim very much.
The best option for directly controlling the shape of the fractured surfaces is to use the fracturepart primitive attribute. This allows you to create little chunks (fracture parts) that won't get separated no matter what happens. The fracturing remains dynamic, however it is restricted such that it does not fracture between tets that have the same fracturepart value. The Solid Fracture SOP creates such a fracturepart attribute for you, but you can create the attribute yourself if you like. If you use fracturepart to create fairly round parts then you'll avoid the edgy shapes that you're seeing.
You can take a look at what the Fractured Solid Object shelf tool does with regards to the embedded setup and the creation of a fracturepart attribute.
Technical Discussion » Fracturecount attribute in FEM simulation not visible
- michiel
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The docs on this feature appear to be a bit out of date: The ‘fracturecount’ attribute is generated only when “Create Fracture Attributes” is enabled on the Solid Object.
I hope this helps.
I hope this helps.
Technical Discussion » A way to create static FEM?
- michiel
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I'm assuming that you want to have the face stay in mostly in the same place where it starts, but that you still want the face to react to external collisions.
The easiest way to do this is to enable “Target Deformation” under the Deformation Tab of the Solid Object.
By default, this will create a soft constraint that keeps the face in its original position.
You will have to find the right value for Target Strength for this to happen.
The higher you pick this value, the more the face will stay where it was.
Another option is to use the “Constrain Points To Target” shelf tool to make sure that parts of the face stay in place, while other parts can freely simulate and response to external collisions.
The easiest way to do this is to enable “Target Deformation” under the Deformation Tab of the Solid Object.
By default, this will create a soft constraint that keeps the face in its original position.
You will have to find the right value for Target Strength for this to happen.
The higher you pick this value, the more the face will stay where it was.
Another option is to use the “Constrain Points To Target” shelf tool to make sure that parts of the face stay in place, while other parts can freely simulate and response to external collisions.
Edited by michiel - Dec. 1, 2017 09:54:25
Technical Discussion » Overlapping Finite Elements
- michiel
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There are a number of different options to keep the embedding separate for sub-objects.
The finite element solver recognizes an integer primitive attribute called “fracturepart”.
If you provide this atttribute on both the embedded and the simulated geometry,
then the embedding will it to match what gets embedded in what.
Just make sure that you give all primitives in one sub-object the same integer,
but keep the integers different for different sub-objects.
Another option is to provide a “baseP” position attribute on both the simulated and embedded geometry.
If the objects are properly separated in this base position, then the embedding will be kept separate as well.
I hope this helps.
The finite element solver recognizes an integer primitive attribute called “fracturepart”.
If you provide this atttribute on both the embedded and the simulated geometry,
then the embedding will it to match what gets embedded in what.
Just make sure that you give all primitives in one sub-object the same integer,
but keep the integers different for different sub-objects.
Another option is to provide a “baseP” position attribute on both the simulated and embedded geometry.
If the objects are properly separated in this base position, then the embedding will be kept separate as well.
I hope this helps.
Technical Discussion » Cloth on a character not working well at all
- michiel
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The sim has no problem with the normal vectors appearing this long.
You can scale them down in the Display Options under “Guides”, by entering a lower value for “Scale Normal”.
I recommend doing this scale down, because when you display long normals, they may appear as if they're pointing outside when they're not. This is particularly tricky for convex shapes.
You can scale them down in the Display Options under “Guides”, by entering a lower value for “Scale Normal”.
I recommend doing this scale down, because when you display long normals, they may appear as if they're pointing outside when they're not. This is particularly tricky for convex shapes.
Technical Discussion » Cloth on a character not working well at all
- michiel
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I'm suspecting that the winding order of your collision geometry may be reversed.
If you display the default-generated normals in the viewport, they should be pointing outward.
You can use a reverse SOP on your collision geo to see whether that fixes the problem.
About explosions with collisions: there was a friction-related bug for cloth that caused instability.
This should be fixed in 16.0.776 and newer.
The number of collision passes that you want to use depends on the complexity of the cloth sim.
Depending on what you're doing, you may need to go as high as 8 or 10 for this.
If you display the default-generated normals in the viewport, they should be pointing outward.
You can use a reverse SOP on your collision geo to see whether that fixes the problem.
About explosions with collisions: there was a friction-related bug for cloth that caused instability.
This should be fixed in 16.0.776 and newer.
The number of collision passes that you want to use depends on the complexity of the cloth sim.
Depending on what you're doing, you may need to go as high as 8 or 10 for this.
Technical Discussion » OLD CLOTH SOLVER
- michiel
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NAHASSIA
P.S. what about the fan and wind forces ? still not reliable with cloth?
Among other issues, these forces don't provide the right kind of force information that the solver needs. This is Bug 81146.
Technical Discussion » OLD CLOTH SOLVER
- michiel
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In Houdini 16.0 there is again a dedicated Cloth Solver, which is put down whenever you use the Cloth Object shelf tool.
If you have a custom velocity field, you should be able to specify this in “External Velocity Field”,
for example by entering “vel”. (This functionality has not been removed.)
I'm attaching an updated example that uses this feature in H16.0.
If you have a custom velocity field, you should be able to specify this in “External Velocity Field”,
for example by entering “vel”. (This functionality has not been removed.)
I'm attaching an updated example that uses this feature in H16.0.
Technical Discussion » Fem guidelines to avoid blow-ups
- michiel
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You can search for “finite elements” in the help for an updated user guide.
Would it be possible to provide me with the hip file for this sim?
Would it be possible to provide me with the hip file for this sim?
Houdini Learning Materials » Cloth tearing in Houdini 16
- michiel
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The cloth solver recognizes a point attribute called “fracturethreshold”. This works as a multiplier for the Fracture Threshold parameter on the Cloth Object.
Technical Discussion » Debugging FEM self-collision
- michiel
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Thank you for trying this out.
Houdini 16.0.626 has a fix for the large number of collision passes needed.
The squab example should have self collisions working fine with just 2 collision passes on the solver.
Would it be possible to try your more complex example with Houdini 16.0.626?
It would be great to know if this issue is now resolved, or if there is still something else going on.
Houdini 16.0.626 has a fix for the large number of collision passes needed.
The squab example should have self collisions working fine with just 2 collision passes on the solver.
Would it be possible to try your more complex example with Houdini 16.0.626?
It would be great to know if this issue is now resolved, or if there is still something else going on.
Technical Discussion » Debugging FEM self-collision
- michiel
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To get collisions resolved properly, you may want to increase the Collision Passes from its default of 2 to something higher, say 8, in this case.
I do find it undesirable and a bit suspect that the collision passes needs to be increased to get this example to work. I will look into this. I've added bug 83037 for this. There will be a version log entry as soon as this get fixed or improved.
I do find it undesirable and a bit suspect that the collision passes needs to be increased to get this example to work. I will look into this. I've added bug 83037 for this. There will be a version log entry as soon as this get fixed or improved.
Technical Discussion » Max Iterations Linear Solve in H16 Fem
- michiel
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The parameter 'Max Iterations Linear Solve’ was never intended to control stretchiness.
Lowering this parameter may have created stretchy solutions for some shapes, but it could have created quite different kinds of effects on other shapes.
The quickest and recommended way to get stretchy solutions in 16.0 is to lower the stiffness multiplier on the Solid Object. This usually has the effect of reducing sim times as well.
Lowering this parameter may have created stretchy solutions for some shapes, but it could have created quite different kinds of effects on other shapes.
The quickest and recommended way to get stretchy solutions in 16.0 is to lower the stiffness multiplier on the Solid Object. This usually has the effect of reducing sim times as well.
Technical Discussion » Is it possible to attach a "Solid Object" to an animated object?
- michiel
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You can use the Cloth Attach Constraint for this. This constraint works for the Solid Object in addition to the Cloth Object. Perhaps this constraint type should be renamed to make this more clear.
You can set the type of this constraint to either “hard” or “soft”.
In the soft case, which is the default, you may want to tweak the strength (under soft controls tab) depending on your sim setup.
You can set the type of this constraint to either “hard” or “soft”.
In the soft case, which is the default, you may want to tweak the strength (under soft controls tab) depending on your sim setup.
Technical Discussion » Embedding Hi-Res Geometry - FEM
- michiel
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The Solid Object shelf tool will create the embedded setup for you, when you apply it on a SOP with a polygon mesh.
Technical Discussion » FEM object won't collide properly with bullet static objects
- michiel
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Thanks for reporting this. Deforming Geometry definitely should be turned on, but regardless there seems to be an issue here.
I've added Bug 82569 for this.
I've added Bug 82569 for this.
Houdini Indie and Apprentice » Strawberries falling problem (constrain)
- michiel
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Houdini Indie and Apprentice » How to make a waving flag... I still wonder (Wind not working in H16?)
- michiel
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Sorry for the confusion.
This tutorial is wrong and will be fixed.
For cloth wind effects, you should use the settings under the Drag tab of the Cloth Object.
Your wind velocity can be entered in the “External Velocity Offset” parameter under the Drag tab.
The Wind Force and the Fan Force should currently not be used with Cloth, because these DOP forces feed incorrect and inaccurate information into the cloth solver. Bug 81146 exists for this.
This tutorial is wrong and will be fixed.
For cloth wind effects, you should use the settings under the Drag tab of the Cloth Object.
Your wind velocity can be entered in the “External Velocity Offset” parameter under the Drag tab.
The Wind Force and the Fan Force should currently not be used with Cloth, because these DOP forces feed incorrect and inaccurate information into the cloth solver. Bug 81146 exists for this.
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