System matrices filled with nan values

[Emin Torabi]

Dear all,

I am trying to build a model and then use the system matrices in a postprocessing step. But The system matrices are filled with nan values, even when I use the simplest model possible (4 nodes, 1 element). The code is added here. Do you see the problem with this simple model?

Many thanks,

Emin

# import libraries

import pychrono as chrono

import pychrono.fea as fea

import pychrono.irrlicht as chronoirr

my_system = chrono.ChSystemSMC()

my_mesh = fea.ChMesh()

my_nodes = []

my_nodes.append(fea.ChNodeFEAxyz(chrono.ChVectorD(0,0,0)))

my_nodes.append(fea.ChNodeFEAxyz(chrono.ChVectorD(1,0,0)))

my_nodes.append(fea.ChNodeFEAxyz(chrono.ChVectorD(0,1,0)))

my_nodes.append(fea.ChNodeFEAxyz(chrono.ChVectorD(0,0,1)))

for node in my_nodes:

    my_mesh.AddNode(node)

    

# create material and elements. add elements to mesh

E_steel  = 210e9

nu_steel = 0.265

ro_steel = 7750

my_material = fea.ChContinuumElastic(E_steel, nu_steel)

my_material.Set_density(ro_steel)

my_element = fea.ChElementTetra_4()

my_element.SetMaterial(my_material)

my_element.SetNodes(my_nodes[0],

                    my_nodes[1],

                    my_nodes[2],

                    my_nodes[3])

my_mesh.AddElement(my_element)

my_mesh.SetAutomaticGravity(False)

my_system.Add(my_mesh)

# add a ground body and fix a node

Isys = chrono.ChBody()

Isys.SetBodyFixed(True)

my_system.Add(Isys)

Fix_const_container = []

Fix_const_container.append(fea.ChLinkPointFrame())

Fix_const_container[-1].Initialize(my_nodes[0], Isys)

my_system.Add(Fix_const_container[-1])

file_title = 'test'

my_system.DoFullAssembly() 

my_system.DumpSystemMatrices(True, True, True, True, file_title)

[Alessandro Tasora]

dear Emin,

probably the DoAssembly() could have destroyed the system - please do a 3d visualization and a time stepping simulation to understand if your system is effectively a structure that can stay in place.

Do you have the same issue if you just do  my_system.Update()  instead of my_system.DoAssembly() ?

A.

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[Emin Torabi]

dear Alessandro,

Thanks a lot for the reply. I simulated 1 timestep and then called the DumpSystemMatrices. Now it is fine, I get the system matrice that I expect. So the problem was DoFullAssembly(). Interestingly,  DoFullAssembly() worked well with systems that contained beams only.

Best regards,

Emin