Method addModalDampingForce

SRC/analysis/integrator/IncrementalIntegrator.cpp:501–559

int 
IncrementalIntegrator::addModalDampingForce(const Vector *modalDampingValues)
{
  int res = 0;
  
  if (modalDampingValues == 0)
    return 0;

  int numModes = modalDampingValues->Size();

  const Vector &eigenvalues = theAnalysisModel->getEigenvalues();
  int numEigen = eigenvalues.Size();

  if (numEigen < numModes) {
    numModes = numEigen;
    opserr << "WARNING: HAving to reset numModes to : " << numModes << "as not enough eigenvalues. NOTE if 0 you have done something to require new analysis or have not issued eigen command\n";
  }

  int numDOF = theSOE->getNumEqn();

  if (eigenValues == 0 || *eigenValues != eigenvalues) {
    this->setupModal(modalDampingValues);
  }

  const Vector &vel = this->getVel();

  dampingForces->Zero();

  for (int i=0; i<numModes; i++) {

    double eigenvalue = (*eigenValues)(i);
    double modalDampingValue = (*modalDampingValues)(i);
    if (eigenvalue > 0 && modalDampingValue != 0.0) {
      double wn = sqrt(eigenvalue);

      double *eigenVectorI = &eigenVectors[numDOF*i];
      double beta = 0.0;
      
      for (int j=0; j<numDOF; j++) {
	double eij = eigenVectorI[j];
	if (eij != 0) {
	  beta += eij * vel(j);
	}
      }

      beta = -2.0 * modalDampingValue * wn * beta;

      for (int j=0; j<numDOF; j++) {
	double eij = eigenVectorI[j];
	if (eij != 0)
	  (*dampingForces)(j) += beta * eij;
      }
    }
  }

  theSOE->setB(*dampingForces);
  
  return res;