[Gad]

Thank you for your answer Vincent,

My idea is to keep the same unit system (ei SI system m, sec, kg, etc) but different size/volume. The analogy with the scene attached would be simulating a swiss ball, a basketball ball and a small rubber ball with the same solver without tweaking each object.

Regarding your answer, having a single set of parameters for the three objects isn’t feasible but they have to be set individually.

[Gad]

Hi,

I also have some questions regarding units, size of objects and parameters tweaking.

Here is a scene with two livers, one with its default size and another one 10 times smaller. Here is the full scene.

<Node name="root" gravity="0 -9.81 0" dt="0.005">
    <VisualStyle displayFlags="hideVisual hideBehaviorModels showForceFields hideInteractionForceFields showCollisionModels hideBoundingCollisionModels hideMapping hideOptions" />
    <DefaultPipeline name="DefaultCollisionPipeline" verbose="0" draw="0" depth="6" />
    <BruteForceDetection name="Detection" />
    <MinProximityIntersection name="Proximity" alarmDistance="3" contactDistance="0.2" />
    <DefaultContactManager name="Response" response="default" />
    
	
	<!-- REAL SIZE LIVER -->
	<Node name="Object" gravity="0 -9.81 0">
        <EulerImplicitSolver name="Implicit Euler Solver" />
        <CGLinearSolver template="GraphScattered" name="Conjugate Gradient" iterations="25" tolerance="1e-5" threshold="1e-5"/>
        <SparseGridTopology name="Embedded Sparse Grid" fileTopology="mesh/liver.obj" n="7 6 5" />
        <MechanicalObject template="Vec3d" name="Particles" restScale="1" position="0 0 0" />
        <UniformMass template="Vec3d" name="Mass" mass="1"/>
        <HexahedronFEMForceField template="Vec3d" name="FEM" poissonRatio="0.45" youngModulus="2000" />
        <Node name="CollisionNode" gravity="0 -9.81 0">
            <MeshTopology name="Mesh" fileTopology="mesh/liver.obj" />
            <MechanicalObject template="Vec3d" name="CollisionObject" scale3d="1 1 1" restScale="1" />
            <PointModel name="Points"  contactStiffness="5000" />
            <LineModel name="Lines"  contactStiffness="5000" />
            <TTriangleModel template="Vec3d" name="Triangles"  contactStiffness="5000" />
            <BarycentricMapping  name="MechanicalMapping"  />
        </Node>
    </Node>
    <Node name="Obstacle" gravity="0 -9.81 0">
        <MeshTopology name="Mesh" fileTopology="mesh/cube.obj" />
        <MechanicalObject template="Vec3d" name="Obstacle" translation="0 -10 0" rotation="0 0 0" scale3d="10 1 10" restScale="1" />
        <TTriangleModel template="Vec3d" name="Triangles" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
        <LineModel name="Lines" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
        <PointModel name="Points" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
    </Node>

	<!-- DOWNSIZED LIVER -->
	<Node name="Object" gravity="0 -9.81 0">
        <EulerImplicitSolver name="Implicit Euler Solver" />
        <CGLinearSolver template="GraphScattered" name="Conjugate Gradient" iterations="25" tolerance="1e-08" threshold="1e-16"/>
        <SparseGridTopology name="Embedded Sparse Grid" fileTopology="mesh/liver.obj" n="7 6 5" />
        <MechanicalObject template="Vec3d" name="Particles" restScale="1" translation="20 0 0" scale3d="0.1 0.1 0.1"/>
        <UniformMass template="Vec3d" name="Mass" mass="0.001"/>
        <HexahedronFEMForceField template="Vec3d" name="FEM" poissonRatio="0.45" youngModulus="2000" />
        <Node name="CollisionNode" gravity="0 -9.81 0">
            <MeshTopology name="Mesh" fileTopology="mesh/liver.obj" />
            <MechanicalObject template="Vec3d" name="CollisionObject" scale3d="1 1 1" restScale="1" />
            <PointModel name="Points"  contactStiffness="5000" />
            <LineModel name="Lines"  contactStiffness="5000" />
            <TTriangleModel template="Vec3d" name="Triangles"  contactStiffness="5000" />
            <BarycentricMapping  name="MechanicalMapping"  />
        </Node>
    </Node>
    <Node name="Obstacle" gravity="0 -9.81 0">
        <MeshTopology name="Mesh" fileTopology="mesh/cube.obj" />
        <MechanicalObject template="Vec3d" name="Obstacle" translation="20 -10 0" rotation="0 0 0" scale3d="1 1 1" restScale="1" />
        <TTriangleModel template="Vec3d" name="Triangles" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
        <LineModel name="Lines" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
        <PointModel name="Points" moving="0" simulated="0" contactStiffness="5000" contactFriction="0.9" />
    </Node>	
</Node>

Keeping the same Young’s modulus for both result in blowing up the smallest liver.
Increasing the Young’s modulus for the smallest results in a slower fall, unless decreasing dt to 0.001

My question here, from a simple user point of view, is how one can easily keep consistency between useful parameters to keep the same results with different scales.

[Author]

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