C++ DiffContext::get_elem_solution_accel方法代码示例

bool NewmarkSolver::_general_residual (bool request_jacobian,
                                       DiffContext & context,
                                       ResFuncType mass,
                                       ResFuncType damping,
                                       ResFuncType time_deriv,
                                       ResFuncType constraint)
{
  unsigned int n_dofs = context.get_elem_solution().size();

  // We might need to save the old jacobian in case one of our physics
  // terms later is unable to update it analytically.
  DenseMatrix<Number> old_elem_jacobian(n_dofs, n_dofs);

  // Local velocity at old time step
  DenseVector<Number> old_elem_solution_rate(n_dofs);
  for (unsigned int i=0; i != n_dofs; ++i)
    old_elem_solution_rate(i) =
      old_solution_rate(context.get_dof_indices()[i]);

  // The user is computing the initial acceleration
  // So upstream we've swapped _system.solution and _old_local_solution_accel
  // So we need to give the context the correct entries since we're solving for
  // acceleration here.
  if( _is_accel_solve )
    {
      // System._solution is actually the acceleration right now so we need
      // to reset the elem_solution to the right thing, which in this case
      // is the initial guess for displacement, which got swapped into
      // _old_solution_accel vector
      DenseVector<Number> old_elem_solution(n_dofs);
      for (unsigned int i=0; i != n_dofs; ++i)
        old_elem_solution(i) =
          old_solution_accel(context.get_dof_indices()[i]);

      context.elem_solution_derivative = 0.0;
      context.elem_solution_rate_derivative = 0.0;
      context.elem_solution_accel_derivative = 1.0;

      // Acceleration is currently the unknown so it's already sitting
      // in elem_solution() thanks to FEMContext::pre_fe_reinit
      context.get_elem_solution_accel() = context.get_elem_solution();

      // Now reset elem_solution() to what the user is expecting
      context.get_elem_solution() = old_elem_solution;

      context.get_elem_solution_rate() = old_elem_solution_rate;

      // The user's Jacobians will be targeting derivatives w.r.t. u_{n+1}.
      // Although the vast majority of cases will have the correct analytic
      // Jacobians in this iteration, since we reset elem_solution_derivative*,
      // if there are coupled/overlapping problems, there could be
      // mismatches in the Jacobian. So we force finite differencing for
      // the first iteration.
      request_jacobian = false;
    }
  // Otherwise, the unknowns are the displacements and everything is straight
  // foward and is what you think it is
  else
    {
      if (request_jacobian)
        old_elem_jacobian.swap(context.get_elem_jacobian());

      // Local displacement at old timestep
      DenseVector<Number> old_elem_solution(n_dofs);
      for (unsigned int i=0; i != n_dofs; ++i)
        old_elem_solution(i) =
          old_nonlinear_solution(context.get_dof_indices()[i]);

      // Local acceleration at old time step
      DenseVector<Number> old_elem_solution_accel(n_dofs);
      for (unsigned int i=0; i != n_dofs; ++i)
        old_elem_solution_accel(i) =
          old_solution_accel(context.get_dof_indices()[i]);

      // Convenience
      libMesh::Real dt = _system.deltat;

      context.elem_solution_derivative = 1.0;

      // Local velocity at current time step
      // v_{n+1} = gamma/(beta*Delta t)*(x_{n+1}-x_n)
      //         + (1-(gamma/beta))*v_n
      //         + (1-gamma/(2*beta))*(Delta t)*a_n
      context.elem_solution_rate_derivative = (_gamma/(_beta*dt));

      context.get_elem_solution_rate()  = context.get_elem_solution();
      context.get_elem_solution_rate() -= old_elem_solution;
      context.get_elem_solution_rate() *= context.elem_solution_rate_derivative;
      context.get_elem_solution_rate().add( (1.0-_gamma/_beta), old_elem_solution_rate);
      context.get_elem_solution_rate().add( (1.0-_gamma/(2.0*_beta))*dt, old_elem_solution_accel);



      // Local acceleration at current time step
      // a_{n+1} = (1/(beta*(Delta t)^2))*(x_{n+1}-x_n)
      //         - 1/(beta*Delta t)*v_n
      //         - (1/(2*beta)-1)*a_n
      context.elem_solution_accel_derivative = 1.0/(_beta*dt*dt);

      context.get_elem_solution_accel()  = context.get_elem_solution();
//.........这里部分代码省略.........