// Set displacement differentiation matrix bmat.
// xi, et - local coordinates,
// returns determinant of Jacobian matrix
private double setBmatrix(double xi, double et)
{
// Derivatives of shape functions
double det = ShapeQuad2D.deriv(xi, et, ind, xy, dnxy);
if (det <= 0)
{
UTIL.errorMsg("Negative/zero 8Nr element area");
}
if (FeModel.stressState == FeModel.StrStates.axisym)
{
ShapeQuad2D.shape(xi, et, ind, an);
r = 0.0;
for (int i = 0; i < 8; i++)
{
r += an[i] * xy[i][0];
}
}
// Eight blocks of the displacement differentiation
// matrix
for (int ib = 0; ib < 8; ib++)
{
bmat[0][2 * ib] = dnxy[ib][0];
bmat[0][2 * ib + 1] = 0.0;
bmat[1][2 * ib] = 0.0;
bmat[1][2 * ib + 1] = dnxy[ib][1];
bmat[2][2 * ib] = dnxy[ib][1];
bmat[2][2 * ib + 1] = dnxy[ib][0];
if (FeModel.stressState == FeModel.StrStates.axisym)
{
bmat[3][2 * ib] = an[ib] / r;
bmat[3][2 * ib + 1] = 0.0;
}
}
return(det);
}
