Full3D model fail to solve.

[AndreasBak]

The following test throws a zero determinant exception.

    [Test]
    public void PortalFrameNegativeCoordinates()
    {
        FiniteElementModel model = new FiniteElementModel(ModelType.Full3D);
        FiniteElementNode node1 = model.NodeFactory.Create(-10,0,0); 
        model.ConstrainNode(node1, DegreeOfFreedom.X);
        model.ConstrainNode(node1, DegreeOfFreedom.Y);
        model.ConstrainNode(node1, DegreeOfFreedom.Z);
        model.ConstrainNode(node1, DegreeOfFreedom.XX);
        model.ConstrainNode(node1, DegreeOfFreedom.YY);
        model.ConstrainNode(node1, DegreeOfFreedom.ZZ);

        FiniteElementNode node2 = model.NodeFactory.Create(-10,0,10);

        FiniteElementNode node3 = model.NodeFactory.Create(0,0,14);
        FiniteElementNode node4 = model.NodeFactory.Create(10,0,10);
        FiniteElementNode node5 = model.NodeFactory.Create(10,0,0);
        model.ConstrainNode(node5, DegreeOfFreedom.X);
        model.ConstrainNode(node5, DegreeOfFreedom.Y);
        model.ConstrainNode(node5, DegreeOfFreedom.Z);

        model.ConstrainNode(node5, DegreeOfFreedom.XX);
        model.ConstrainNode(node5, DegreeOfFreedom.YY);
        model.ConstrainNode(node5, DegreeOfFreedom.ZZ);

        IMaterial material = new GenericElasticMaterial(100, 2000, 0.2, 1000);
        ICrossSection section = new SolidRectangle(0.5, 0.1);

        model.ElementFactory.CreateLinear3DBeam(node1, node2, material, section);
        model.ElementFactory.CreateLinear3DBeam(node2,node3,material,section);
        model.ElementFactory.CreateLinear3DBeam(node3,node4,material,section);
        model.ElementFactory.CreateLinear3DBeam(node4,node5,material,section);

        ForceVector force = model.ForceFactory.Create(10, 0, 0,0,0,0);
        model.ApplyForceToNode(force, node3);

        IFiniteElementSolver solver = new LinearSolver(model);
        FiniteElementResults results = solver.Solve();

        DisplacementVector displacement = results.GetDisplacement(node2);
        Assert.AreNotEqual(0.0, displacement.X);
        Assert.AreEqual(0.0, displacement.Y, 0.001);
    }

[iainsproat]

I've amended the example and created a similar example for the 1D beam.

It seems that the negative coordinates are not the problem. The 1D beam examples works OK, so the problem seems to be either: (a) some problem with not enough boundary conditions i.e. constraining nodes (b) implementation of the 3D beam stiffness matrix class

[iainsproat]

It works if you constrain either node2, node3 or node4 in the X-axis, however this modifies the intent of the model so is not a valid fix.

[AndreasBak]

I should think that a moment frame fully fixed at both supports (node1 and node5) should be constrained sufficiently.

[AndreasBak]

I'm having the same issue trying to implement the ConstantStrainTriangle in the Full3d model. I'll write a test later to show this issue. This however this suggest that the issue might not be in the beam stiffness matrix class.

[AndreasBak]

Great job.