Using BeamAdapter with non-aligned beams (how to define frame orientations for beam segments)?

[mmonem1996]

Hello everyone,

I’m having some difficulty understanding how to use the BeamAdapter plugin to model the object shown below.

This object is a 3D-printed part with a Young’s modulus of approximately 2 GPa.
I attempted to model it in SOFA using the BeamAdapter plugin as follows:

        <MechanicalObject name="dofs" template="Rigid3d"
            position="0.0025 0 0 0 0 0 1
                    0.0025 0.0475 0 0 0 0 1
                    0.0375 0.0475 0 0 0 0 1
                    0.0375 0 0 0 0 0 1"/>
        <MeshTopology name="lines" lines="0 1  1 2  2 4"/>
        <BeamInterpolation name="BeamInterpolation" radius="0.005" dofsAndBeamsAligned="0"/>

        <!-- Material + mass for the beam -->
        <BeamFEMForceField name="BeamFF"
            youngModulus="2e9"
            poissonRatio="0.3"
            radius="@BeamInterpolation.radius"/>

        <UniformMass template="Rigid3d" totalMass="0.05"/>
         <!-- Boundary condition -->
        <FixedProjectiveConstraint indices="1 2"/>

        <!-- ========== Visual & collision surface mapped to the beam ========== -->
        <Node name="Surface">
            <MeshSTLLoader name="stl" filename="snap_fit_component_resized.stl"/>
            <MeshTopology src="@stl"/>
            <MechanicalObject name="x" template="Vec3d" />
            <TriangleCollisionModel/>
            <LineCollisionModel/>
            <PointCollisionModel/>
            <AdaptiveBeamMapping isMechanical="true" input="@../dofs"  output="@x" interpolation="@../BeamInterpolation" mapForces="0" mapMasses="0"/>	

            <Node name="Visual">
                <OglModel src="@../stl"/>
                <IdentityMapping input="@../x" output="@Visual"/>
            </Node>
        </Node>

However, I’m having trouble correctly mapping the collision mesh to the mechanical object.

[WARNING] [AdaptiveBeamMapping(AdaptiveBeamMapping1)] When using useCurvAbs==true, points must be sorted according to their curvAbs:   
- invalid ordering at index: 0 : -0.00166707 > 0.00357505  
- invalid ordering at index: 2 : -0.00180447 > 0.00386971  
- invalid ordering at index: 6 : -0.000134619 > 0.000288691  
- invalid ordering at index: 7 : -0.00042082 > 0.000902451  
- invalid ordering at index: 12 : -0.000361767 > 0.000775811  
- invalid ordering at index: 14 : -0.00181292 > 0.00388783  
- invalid ordering at index: 16 : -0.00165821 > 0.00355605  
- invalid ordering at index: 18 : -0.0017966 > 0.00385282  
- invalid ordering at index: 22 : -0.00151569 > 0.00325041  
- invalid ordering at index: 24 : -0.00124199 > 0.00266347  

In addition, the mesh topology does not capture the beam segment rotations that are necessary to correctly connect the DOFs.

Questions:

1. Are these types of geometries supported by the BeamAdapter plugin? Or in this case do I instead need to use a volume mesh and something like the TetrahedronFEMForceField?

2. How should I configure the .scn file so that beam segments at arbitrary orientations (i.e., not aligned with the primary axes) are correctly modeled?