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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) 2008-19 Stanford University and the Authors. *
* Authors: Antoine Falisse, Gil Serrancoli *
* Contributors: Peter Eastman *
* *
* 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-10;
#define ASSERT(cond) {SimTK_ASSERT_ALWAYS(cond, "Assertion failed");}
template <class T>
void assertEqual(T val1, T val2) {
ASSERT(abs(val1-val2) < TOL);
}
template <int N>
void assertEqual(Vec<N> val1, Vec<N> val2) {
for (int i = 0; i < N; ++i)
ASSERT(abs(val1[i]-val2[i]) < TOL);
}
void testForces() {
MultibodySystem system;
SimbodyMatterSubsystem matter(system);
GeneralForceSubsystem forces(system);
const Vec3 gravity = Vec3(0, -9.8, 0);
Force::UniformGravity(forces, matter, gravity, 0);
const Real radius = 0.8;
const Real k = 1500.0;
const Real stiffness = 0.5*std::pow(k, 2.0/3.0);
const Real dissipation = 0.5;
const Real us = 1.0;
const Real ud = 0.5;
const Real uv = 0.1;
const Real vt = 0.001;
const Real cf = 1e-5;
const Real bd = 300;
const Real bv = 50;
Body::Rigid body1(MassProperties(1.0, Vec3(0), Inertia(1)));
MobilizedBody::Translation sphere(matter.updGround(),
Transform(), body1, Transform());
Body::Rigid body2(MassProperties(1.0, Vec3(0), Inertia(1)));
MobilizedBody::Free halfSpace(matter.updGround(),
Transform(), body2, Transform());
SmoothSphereHalfSpaceForce hc_smooth(forces);
hc_smooth.setParameters(k,dissipation,us,ud,uv,vt,cf,bd,bv);
hc_smooth.setContactSphereBody(sphere);
hc_smooth.setContactSphereLocationInBody(Vec3(0));
hc_smooth.setContactSphereRadius(radius);
Transform testFrame(Rotation(-0.5*Pi, ZAxis), Vec3(0));
hc_smooth.setContactHalfSpaceFrame(testFrame);
hc_smooth.setContactHalfSpaceBody(halfSpace);
State state = system.realizeTopology();
// Position the sphere at a variety of positions and see if the normal
// force and potential energy are correct.
for (Real height = radius+0.2; height > 0; height -= 0.1) {
sphere.setQToFitTranslation(state, Vec3(0, height, 0));
system.realize(state, Stage::Dynamics);
const Real depth = radius-height;
Real f = (4./3.)*stiffness*std::pow(std::sqrt(depth*depth+cf),3./2.)
*std::sqrt(radius*stiffness);
Real f_smooth = f*(1./2.+(1./2.)*std::tanh(bd*depth));
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)
[sphere.getMobilizedBodyIndex()][1], gravity+Vec3(0, f_smooth, 0));
assertEqual(hc_smooth.calcPotentialEnergyContribution(state),
(2./5.)*f_smooth*depth);
}
// Now do it with a vertical velocity and see if the dissipation force is
// correct.
for (Real height = radius+0.2; height > 0; height -= 0.1) {
sphere.setQToFitTranslation(state, Vec3(0, height, 0));
const Real depth = radius-height;
Real fh = (4./3.)*stiffness*std::pow(std::sqrt(depth*depth+cf),3./2.)
*std::sqrt(radius*stiffness);
Real fh_smooth = fh*(1./2.+(1./2.)*std::tanh(bd*depth));
for (Real v = -1.0; v <= 1.0; v += 0.1) {
sphere.setUToFitLinearVelocity(state, Vec3(0, -v, 0));
system.realize(state, Stage::Dynamics);
Real f = fh_smooth*(1.+(3./2.)*dissipation*v);
Real f_smooth = f*(1./2.+(1./2.)
*std::tanh(bv*(v+(2./(3.*dissipation)))));
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)
[sphere.getMobilizedBodyIndex()][1],
gravity+Vec3(0, f_smooth, 0));
}
}
// Now do it with a horizontal velocity and see if the friction force is
// correct.
Vector_<SpatialVec> expectedForce(matter.getNumBodies());
for (Real height = radius+0.2; height > 0; height -= 0.1) {
sphere.setQToFitTranslation(state, Vec3(0, height, 0));
const Real depth = radius-height;
Real fh = (4./3.)*stiffness*std::pow(std::sqrt(depth*depth+cf),3./2.)
*std::sqrt(radius*stiffness);
Real fh_smooth = fh*(1./2.+(1./2.)*std::tanh(bd*depth));
for (Real v = -1.0; v <= 1.0; v += 0.1) {
sphere.setUToFitLinearVelocity(state, Vec3(v, 0, 0));
system.realize(state, Stage::Dynamics);
Vec3 vec3v(v,0,0);
UnitVec3 normal = (halfSpace.getBodyRotation(state)*testFrame.x());
Real vnormal = dot(vec3v, normal);
Vec3 vtangent = vec3v - vnormal*normal;
Real aux = vtangent.normSqr() + cf;
Real vslip = pow(aux,1./2.);
Real vrel = vslip / vt;
Real ff_smooth_scalar = fh_smooth*(std::min(vrel,Real(1))*
(ud+2*(us-ud)/(1+vrel*vrel))+uv*vslip);
Vec3 ff_smooth = ff_smooth_scalar*(vtangent) / vslip;
const Vec3 totalForceOnSphere =
gravity - ff_smooth - fh_smooth*normal;
expectedForce = SpatialVec(Vec3(0), Vec3(0));
Vec3 contactPointInSphere = sphere.findStationAtGroundPoint(state,
Vec3(0, -stiffness*depth/(stiffness+stiffness), 0));
sphere.applyForceToBodyPoint(state, contactPointInSphere,
totalForceOnSphere, expectedForce);
SpatialVec actualForce = system.getRigidBodyForces(state,
Stage::Dynamics)[sphere.getMobilizedBodyIndex()];
assertEqual(actualForce[0],
expectedForce[sphere.getMobilizedBodyIndex()][0]);
assertEqual(actualForce[1],
expectedForce[sphere.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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