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/* -------------------------------------------------------------------------- *
* Simbody(tm) *
* -------------------------------------------------------------------------- *
* This is part of the SimTK biosimulation toolkit originating from *
* Simbios, the NIH National Center for Physics-Based Simulation of *
* Biological Structures at Stanford, funded under the NIH Roadmap for *
* Medical Research, grant U54 GM072970. See https://simtk.org/home/simbody. *
* *
* Portions copyright (c) 2008-12 Stanford University and the Authors. *
* Authors: Peter Eastman *
* Contributors: *
* *
* Licensed under the Apache License, Version 2.0 (the "License"); you may *
* not use this file except in compliance with the License. You may obtain a *
* copy of the License at http://www.apache.org/licenses/LICENSE-2.0. *
* *
* Unless required by applicable law or agreed to in writing, software *
* distributed under the License is distributed on an "AS IS" BASIS, *
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
* See the License for the specific language governing permissions and *
* limitations under the License. *
* -------------------------------------------------------------------------- */
#include "SimTKsimbody.h"
using namespace SimTK;
using namespace std;
const Real TOL = 1e-5;
#define ASSERT(cond) {SimTK_ASSERT_ALWAYS(cond, "Assertion failed");}
template <class T>
void assertEqual(T val1, T val2) {
ASSERT(abs(val1-val2) < TOL || abs(val1-val2)/max(abs(val1), abs(val2)) < TOL);
}
template <int N>
void assertEqual(Vec<N> val1, Vec<N> val2) {
for (int i = 0; i < N; ++i)
assertEqual(val1[i], val2[i]);
}
void testForces() {
MultibodySystem system;
SimbodyMatterSubsystem matter(system);
GeneralContactSubsystem contacts(system);
GeneralForceSubsystem forces(system);
// Create a triangle mesh in the shape of a pyramid, with the
// square base having area 1 (split into two triangles).
vector<Vec3> vertices;
vertices.push_back(Vec3(0, 0, 0));
vertices.push_back(Vec3(1, 0, 0));
vertices.push_back(Vec3(1, 0, 1));
vertices.push_back(Vec3(0, 0, 1));
vertices.push_back(Vec3(0.5, 1, 0.5));
vector<int> faceIndices;
int faces[6][3] = {{0, 1, 2}, {0, 2, 3}, {1, 0, 4},
{2, 1, 4}, {3, 2, 4}, {0, 3, 4}};
for (int i = 0; i < 6; i++)
for (int j = 0; j < 3; j++)
faceIndices.push_back(faces[i][j]);
// Create the mobilized bodies and configure the contact model.
Body::Rigid body(MassProperties(1.0, Vec3(0), Inertia(1)));
ContactSetIndex setIndex = contacts.createContactSet();
MobilizedBody::Translation mesh(matter.updGround(), Transform(), body, Transform());
contacts.addBody(setIndex, mesh, ContactGeometry::TriangleMesh(vertices, faceIndices), Transform());
contacts.addBody(setIndex, matter.updGround(), ContactGeometry::HalfSpace(), Transform(Rotation(-0.5*Pi, ZAxis), Vec3(0))); // y < 0
ElasticFoundationForce ef(forces, contacts, setIndex);
Real stiffness = 1e9, dissipation = 0.01, us = 0.1, ud = 0.05, uv = 0.01, vt = 0.01;
ef.setBodyParameters(ContactSurfaceIndex(0), stiffness, dissipation, us, ud, uv);
ef.setTransitionVelocity(vt);
ASSERT(ef.getTransitionVelocity() == vt);
State state = system.realizeTopology();
// Position the pyramid at a variety of positions and check the normal
// force.
for (Real depth = -0.1; depth < 0.1; depth += 0.01) {
mesh.setQToFitTranslation(state, Vec3(0, -depth, 0));
system.realize(state, Stage::Dynamics);
Real f = 0;
if (depth > 0)
f = stiffness*depth;
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)[mesh.getMobilizedBodyIndex()][1], Vec3(0, f, 0));
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)[matter.getGround().getMobilizedBodyIndex()][1], Vec3(0, -f, 0));
}
// Now do it with a vertical velocity and see if the dissipation force is correct.
for (Real depth = -0.105; depth < 0.1; depth += 0.01) {
mesh.setQToFitTranslation(state, Vec3(0, -depth, 0));
for (Real v = -1.0; v <= 1.0; v += 0.1) {
mesh.setUToFitLinearVelocity(state, Vec3(0, -v, 0));
system.realize(state, Stage::Dynamics);
Real f = (depth > 0 ? stiffness*depth*(1+dissipation*v) : 0);
if (f < 0)
f = 0;
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)[mesh.getMobilizedBodyIndex()][1], Vec3(0, f, 0));
}
}
// Do it with a horizontal velocity and see if the friction force is correct.
Vector_<SpatialVec> expectedForce(matter.getNumBodies());
for (Real depth = -0.105; depth < 0.1; depth += 0.01) {
mesh.setQToFitTranslation(state, Vec3(0, -depth, 0));
Real fh = 0;
if (depth > 0)
fh = stiffness*depth;
for (Real v = -1.0; v <= 1.0; v += 0.1) {
mesh.setUToFitLinearVelocity(state, Vec3(v, 0, 0));
system.realize(state, Stage::Dynamics);
const Real vrel = std::abs(v/vt);
Real ff = (v < 0 ? 1 : -1)*fh*(std::min(vrel, 1.0)*(ud+2*(us-ud)/(1+vrel*vrel))+uv*std::fabs(v));
const Vec3 totalForce = Vec3(ff, fh, 0);
expectedForce = SpatialVec(Vec3(0), Vec3(0));
Vec3 contactPoint1 = mesh.findStationAtGroundPoint(state, Vec3(2.0/3.0, 0, 1.0/3.0));
mesh.applyForceToBodyPoint(state, contactPoint1, 0.5*totalForce, expectedForce);
Vec3 contactPoint2 = mesh.findStationAtGroundPoint(state, Vec3(1.0/3.0, 0, 2.0/3.0));
mesh.applyForceToBodyPoint(state, contactPoint2, 0.5*totalForce, expectedForce);
SpatialVec actualForce = system.getRigidBodyForces(state, Stage::Dynamics)[mesh.getMobilizedBodyIndex()];
assertEqual(actualForce[0], expectedForce[mesh.getMobilizedBodyIndex()][0]);
assertEqual(actualForce[1], expectedForce[mesh.getMobilizedBodyIndex()][1]);
}
}
}
int main() {
try {
testForces();
}
catch(const std::exception& e) {
cout << "exception: " << e.what() << endl;
return 1;
}
cout << "Done" << endl;
return 0;
}
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