Perform electrostatics analysis (demo_FEA_electrostatics.cpp)

Tutorial that teaches how to use the FEA module to compute the electrostatic solution for a volume (Poisson problem) given boundary conditions. The tetrahedral mesh is imported from an Abaqus file. There are two node sets (boundaries) where high voltage is applied. The rest of the volume is considered to be air.

// =============================================================================
// PROJECT CHRONO - http://projectchrono.org
//
// Copyright (c) 2014 projectchrono.org
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be found
// in the LICENSE file at the top level of the distribution and at
// http://projectchrono.org/license-chrono.txt.
//
// =============================================================================
// Authors: Alessandro Tasora
// =============================================================================
//
// FEA electrostatics
//
// =============================================================================
 
#include "chrono/physics/ChSystemSMC.h"
#include "chrono/solver/ChIterativeSolverLS.h"
 
#include "chrono/fea/ChContinuumElectrostatics.h"
#include "chrono/fea/ChElementBar.h"
#include "chrono/fea/ChElementHexaCorot_20.h"
#include "chrono/fea/ChElementHexaCorot_8.h"
#include "chrono/fea/ChElementTetraCorot_10.h"
#include "chrono/fea/ChElementTetraCorot_4.h"
#include "chrono/fea/ChLinkPointFrame.h"
#include "chrono/fea/ChMesh.h"
#include "chrono/fea/ChMeshFileLoader.h"
#include "chrono/fea/ChNodeFEAxyzP.h"
#include "chrono/assets/ChVisualShapeFEA.h"
 
#include "chrono_irrlicht/ChVisualSystemIrrlicht.h"
 
// Remember to use the namespace 'chrono' because all classes
// of Chrono::Engine belong to this namespace and its children...
 
using namespace chrono;
using namespace chrono::fea;
using namespace chrono::irrlicht;
 
using namespace irr;
 
int main(int argc, char* argv[]) {
    GetLog() << "Copyright (c) 2017 projectchrono.org\nChrono version: " << CHRONO_VERSION << "\n\n";
 
    // Create a Chrono::Engine physical system
    ChSystemSMC sys;
 
    // Create a mesh, that is a container for groups
    // of elements and their referenced nodes.
    auto my_mesh = chrono_types::make_shared<ChMesh>();
    my_mesh->SetAutomaticGravity(false);
 
    // Create a material, that must be assigned to each element,
    // and set its parameters
    auto mmaterial = chrono_types::make_shared<ChContinuumElectrostatics>();
    mmaterial->SetPermittivity(1);
    // mmaterial->SetRelativePermettivity(1000.01);
 
    //
    // Add some TETAHEDRONS:
    //
 
    // Load an Abaqus .INP tetrahedron mesh file from disk, defining a complicate tetrahedron mesh.
    // This is much easier than creating all nodes and elements via C++ programming.
    // Ex. you can generate these .INP files using Abaqus or exporting from SolidWorks simulation.
 
    std::map<std::string, std::vector<std::shared_ptr<ChNodeFEAbase> > > node_sets;
 
    try {
        ChMeshFileLoader::FromAbaqusFile(my_mesh, GetChronoDataFile("fea/electrostatics.INP").c_str(), mmaterial,
                                         node_sets);
    } catch (const ChException &myerr) {
        GetLog() << myerr.what();
        return 1;
    }
 
    //
    // Set some BOUNDARY CONDITIONS on nodes:
    //
 
    // Impose potential on all nodes of 1st nodeset (see *NSET section in .imp file)
    auto nboundary = "IMPV1";
    for (unsigned int inode = 0; inode < node_sets.at(nboundary).size(); ++inode) {
        if (auto mnode = std::dynamic_pointer_cast<ChNodeFEAxyzP>(node_sets[nboundary][inode])) {
            mnode->SetFixed(true);
            mnode->SetP(0);  // field: potential [V]
        }
    }
    // Impose potential on all nodes of 2nd nodeset (see *NSET section in .imp file)
    nboundary = "IMPV2";
    for (unsigned int inode = 0; inode < node_sets.at(nboundary).size(); ++inode) {
        if (auto mnode = std::dynamic_pointer_cast<ChNodeFEAxyzP>(node_sets[nboundary][inode])) {
            mnode->SetFixed(true);
            mnode->SetP(21);  // field: potential [V]
        }
    }
 
    // Remember to add the mesh to the system!
    sys.Add(my_mesh);
 
    // Visualization of the FEM mesh.
    // This will automatically update a triangle mesh (a ChTriangleMeshShape
    // asset that is internally managed) by setting  proper
    // coordinates and vertex colors as in the FEM elements.
    // Such triangle mesh can be rendered by Irrlicht or POVray or whatever
    // postprocessor that can handle a colored ChTriangleMeshShape).
 
    // This will paint the colored mesh with temperature scale (NODE_P is the scalar field of the Poisson problem)
 
    auto mvisualizemesh = chrono_types::make_shared<ChVisualShapeFEA>(my_mesh);
    mvisualizemesh->SetFEMdataType(ChVisualShapeFEA::DataType::NODE_P);  // plot V, potential field
    mvisualizemesh->SetColorscaleMinMax(-0.1, 24);
    my_mesh->AddVisualShapeFEA(mvisualizemesh);
 
    // This will paint the wireframe
    auto mvisualizemeshB = chrono_types::make_shared<ChVisualShapeFEA>(my_mesh);
    mvisualizemeshB->SetFEMdataType(ChVisualShapeFEA::DataType::SURFACE);
    mvisualizemeshB->SetColorscaleMinMax(-0.1, 24);
    mvisualizemeshB->SetWireframe(true);
    my_mesh->AddVisualShapeFEA(mvisualizemeshB);
 
    // This will paint the E vector field as line vectors
    auto mvisualizemeshC = chrono_types::make_shared<ChVisualShapeFEA>(my_mesh);
    mvisualizemeshC->SetFEMdataType(ChVisualShapeFEA::DataType::NONE);
    mvisualizemeshC->SetFEMglyphType(ChVisualShapeFEA::GlyphType::ELEM_VECT_DP);
    mvisualizemeshC->SetSymbolsScale(0.00002);
    mvisualizemeshC->SetDefaultSymbolsColor(ChColor(1.0f, 1.0f, 0.4f));
    mvisualizemeshC->SetZbufferHide(false);
    my_mesh->AddVisualShapeFEA(mvisualizemeshC);
 
    // Create the Irrlicht visualization system
    auto vis = chrono_types::make_shared<ChVisualSystemIrrlicht>();
    vis->AttachSystem(&sys);
    vis->SetWindowSize(800, 600);
    vis->SetWindowTitle("FEM electrostatics");
    vis->Initialize();
    vis->AddLogo();
    vis->AddSkyBox();
    vis->AddLight(ChVector<>(20, 20, 20), 90, ChColor(0.5f, 0.5f, 0.5f));
    vis->AddLight(ChVector<>(-20, 20, -20), 90, ChColor(0.7f, 0.8f, 0.8f));
    vis->AddCamera(ChVector<>(0., 0.2, -0.3));
 
    // SIMULATION LOOP
 
    auto solver = chrono_types::make_shared<ChSolverMINRES>();
    sys.SetSolver(solver);
    solver->SetMaxIterations(300);
    solver->SetTolerance(1e-20);
    solver->EnableDiagonalPreconditioner(true);
    solver->SetVerbose(true);
 
    sys.SetSolverForceTolerance(1e-20);
 
    // In electrostatics, you have only a single linear (non transient) solution
    sys.DoStaticLinear();
 
    while (vis->Run()) {
        vis->BeginScene();
        vis->Render();
        vis->EndScene();
    }
 
    // Print some node potentials V..
    for (unsigned int inode = 0; inode < my_mesh->GetNnodes(); ++inode) {
        if (auto mnode = std::dynamic_pointer_cast<ChNodeFEAxyzP>(my_mesh->GetNode(inode))) {
            if (mnode->GetP() < 6.2) {
                // GetLog() << "Node at y=" << mnode->GetPos().y << " has V=" << mnode->GetP() << "\n";
            }
        }
    }
 
    return 0;
}