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Move elasticity computation to mjCFlex.

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PiperOrigin-RevId: 675949380
Change-Id: Ia48f4fd6ae1ede206ccacd1205914e7e4b3c7aec
This commit is contained in:
Alessio Quaglino
2024-09-18 05:22:05 -07:00
committed by Copybara-Service
parent 0657e3e871
commit ddbc083810
7 changed files with 250 additions and 212 deletions
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plugin/elasticity/elasticity.h
+8 -54
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@@ -36,7 +36,10 @@ struct PairHash
struct Stencil2D {
static constexpr int kNumEdges = 3;
static constexpr int kNumVerts = 3;
static constexpr int kNumFaces = 2;
static constexpr int edge[kNumEdges][2] = {{1, 2}, {2, 0}, {0, 1}};
static constexpr int face[kNumVerts][2] = {{1, 2}, {2, 0}, {0, 1}};
static constexpr int edge2face[kNumEdges][2] = {{1, 2}, {2, 0}, {0, 1}};
int vertices[kNumVerts];
int edges[kNumEdges];
};
@@ -44,8 +47,13 @@ struct Stencil2D {
struct Stencil3D {
static constexpr int kNumEdges = 6;
static constexpr int kNumVerts = 4;
static constexpr int kNumFaces = 3;
static constexpr int edge[kNumEdges][2] = {{0, 1}, {1, 2}, {2, 0},
{2, 3}, {0, 3}, {1, 3}};
static constexpr int face[kNumVerts][3] = {{2, 1, 0}, {0, 1, 3},
{1, 2, 3}, {2, 0, 3}};
static constexpr int edge2face[kNumEdges][2] = {{2, 3}, {1, 3}, {2, 1},
{1, 0}, {0, 2}, {0, 3}};
int vertices[kNumVerts];
int edges[kNumEdges];
};
@@ -151,60 +159,6 @@ inline void AddFlexForce(mjtNum* qfrc,
}
}
// compute metric tensor of edge lengths inner product
template <typename T>
void inline MetricTensor(mjtNum* metric, int idx, mjtNum mu,
mjtNum la, const mjtNum basis[T::kNumEdges][9]) {
mjtNum trE[T::kNumEdges] = {0};
mjtNum trEE[T::kNumEdges*T::kNumEdges] = {0};
mjtNum k[T::kNumEdges*T::kNumEdges];
// compute first invariant i.e. trace(strain)
for (int e = 0; e < T::kNumEdges; e++) {
for (int i = 0; i < 3; i++) {
trE[e] += basis[e][4*i];
}
}
// compute second invariant i.e. trace(strain^2)
for (int ed1 = 0; ed1 < T::kNumEdges; ed1++) {
for (int ed2 = 0; ed2 < T::kNumEdges; ed2++) {
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
trEE[T::kNumEdges*ed1+ed2] += basis[ed1][3*i+j] * basis[ed2][3*j+i];
}
}
}
}
// assembly of strain metric tensor
for (int ed1 = 0; ed1 < T::kNumEdges; ed1++) {
for (int ed2 = 0; ed2 < T::kNumEdges; ed2++) {
k[T::kNumEdges*ed1 + ed2] = mu * trEE[T::kNumEdges * ed1 + ed2] +
la * trE[ed2] * trE[ed1];
}
}
// copy to triangular representation
int id = 0;
for (int ed1 = 0; ed1 < T::kNumEdges; ed1++) {
for (int ed2 = ed1; ed2 < T::kNumEdges; ed2++) {
metric[21*idx + id++] = k[T::kNumEdges*ed1 + ed2];
}
}
if (id != T::kNumEdges*(T::kNumEdges+1)/2) {
mju_error("incorrect stiffness matrix size");
}
}
// convert from Flex connectivity to stencils
template <typename T>
int CreateStencils(std::vector<T>& elements,
std::vector<std::pair<int, int>>& edges,
const std::vector<int>& simplex,
const std::vector<int>& edgeidx);
// copied from mjXUtil
void String2Vector(const std::string& txt, std::vector<int>& vec);