1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
|
/* -------------------------------------------------------------------------- *
* 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-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);
GeneralContactSubsystem contacts(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 k1 = 1.0;
const Real k2 = 2.0;
const Real stiffness1 = std::pow(k1, 2.0/3.0);
const Real stiffness2 = std::pow(k2, 2.0/3.0);
const Real dissipation1 = 0.5;
const Real dissipation2 = 1.0;
const Real us1 = 1.0;
const Real us2 = 0.7;
const Real ud1 = 0.5;
const Real ud2 = 0.2;
const Real uv1 = 0.1;
const Real uv2 = 0.05;
Random::Uniform random(0.0, 1.0);
Body::Rigid body(MassProperties(1.0, Vec3(0), Inertia(1)));
ContactSetIndex setIndex = contacts.createContactSet();
MobilizedBody::Translation sphere(matter.updGround(), Transform(), body, Transform());
contacts.addBody(setIndex, sphere, ContactGeometry::Sphere(radius), Transform());
contacts.addBody(setIndex, matter.updGround(), ContactGeometry::HalfSpace(), Transform(Rotation(-0.5*Pi, ZAxis), Vec3(0))); // y < 0
HuntCrossleyForce hc(forces, contacts, setIndex);
hc.setBodyParameters(ContactSurfaceIndex(0), k1, dissipation1, us1, ud1, uv1);
hc.setBodyParameters(ContactSurfaceIndex(1), k2, dissipation2, us2, ud2, uv2);
const Real vt = 0.001;
hc.setTransitionVelocity(vt);
assertEqual(vt, hc.getTransitionVelocity());
State state = system.realizeTopology();
// Position the sphere at a variety of positions and check the normal force.
const Real stiffness = stiffness1*stiffness2/(stiffness1+stiffness2);
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 = 0;
if (depth > 0)
f = (4.0/3.0)*stiffness*depth*std::sqrt(radius*stiffness*depth);
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)[sphere.getMobilizedBodyIndex()][1], gravity+Vec3(0, f, 0));
}
// Now do it with a vertical velocity and see if the dissipation force is correct.
const Real dissipation = (dissipation1*stiffness2+dissipation2*stiffness1)/(stiffness1+stiffness2);
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 = 0;
if (depth > 0)
fh = (4.0/3.0)*stiffness*depth*std::sqrt(radius*stiffness*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*(1.0+1.5*dissipation*v);
if (f < 0)
f = 0;
assertEqual(system.getRigidBodyForces(state, Stage::Dynamics)[sphere.getMobilizedBodyIndex()][1], gravity+Vec3(0, f, 0));
}
}
// Do it with a horizontal velocity and see if the friction force is correct.
const Real us = 2.0*us1*us2/(us1+us2);
const Real ud = 2.0*ud1*ud2/(ud1+ud2);
const Real uv = 2.0*uv1*uv2/(uv1+uv2);
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 = 0;
if (depth > 0)
fh = (4.0/3.0)*stiffness*depth*std::sqrt(radius*stiffness*depth);
for (Real v = -1.0; v <= 1.0; v += 0.1) {
sphere.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 = gravity+Vec3(ff, fh, 0);
expectedForce = SpatialVec(Vec3(0), Vec3(0));
Vec3 contactPointInSphere = sphere.findStationAtGroundPoint(state, Vec3(0, -stiffness1*depth/(stiffness1+stiffness2), 0));
sphere.applyForceToBodyPoint(state, contactPointInSphere, totalForce, 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;
}
|
