Line data    Source code

       1             : // The libMesh Finite Element Library.
       2             : // Copyright (C) 2002-2025 Benjamin S. Kirk, John W. Peterson, Roy H. Stogner
       3             : 
       4             : // This library is free software; you can redistribute it and/or
       5             : // modify it under the terms of the GNU Lesser General Public
       6             : // License as published by the Free Software Foundation; either
       7             : // version 2.1 of the License, or (at your option) any later version.
       8             : 
       9             : // This library is distributed in the hope that it will be useful,
      10             : // but WITHOUT ANY WARRANTY; without even the implied warranty of
      11             : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12             : // Lesser General Public License for more details.
      13             : 
      14             : // You should have received a copy of the GNU Lesser General Public
      15             : // License along with this library; if not, write to the Free Software
      16             : // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
      17             : 
      18             : #ifndef LIBMESH_FIRST_ORDER_UNSTEADY_SOLVER_H
      19             : #define LIBMESH_FIRST_ORDER_UNSTEADY_SOLVER_H
      20             : 
      21             : #include "libmesh/unsteady_solver.h"
      22             : 
      23             : namespace libMesh
      24             : {
      25             : /**
      26             :  * Generic class from which first order UnsteadySolvers should subclass.
      27             :  *
      28             :  * Subclasses of this class are meant to solve problems of the form
      29             :  * \f[ M(u)\dot{u} = F(u)\f]
      30             :  *
      31             :  * There is also infrastructure for subclasses to support solving second
      32             :  * order-in-time systems (or both first order and second order).
      33             :  * In particular, consider the second system
      34             :  * \f[ M(u)\ddot{u} + C(u)\dot{u} + F(u) = 0 \f]
      35             :  * If we introduce the equation \f$\dot{u} = v\f$, then, we have the
      36             :  * following first order system:
      37             :  * \f{eqnarray}{ \dot{u} &=& v \\ M(u)\dot{v} + C(u)v + F(u) &=& 0\f}
      38             :  * Such systems are supported by the user specifying that the time order
      39             :  * of the variable \f$u\f$ is 2 when adding the variable using
      40             :  * FEMSystem::time_evolving. This class will then add the \f$v\f$ variables
      41             :  * to the FEMSystem (named "dot_u" if the second order variable name is "u").
      42             :  * Subclasses will then need to make sure to use the function
      43             :  * FirstOrderUnsteadySolver::prepare_accel() to prepare data structures for the
      44             :  * users to use from FEMContext. Furthermore, subclasses will need to appropriately
      45             :  * call damping_residual functions. Finally, subclasses will call
      46             :  * FirstOrderUnsteadySolver::compute_second_order_eqns() to actually assemble
      47             :  * residual and Jacobians for the \f$ \dot{u} = v\f$ equations. These aspects
      48             :  * should be invisible ot users during their element assembly.
      49             :  *
      50             :  * Unfortunately, complete usage of the feature of treating second order
      51             :  * equations as a system of first order equations is not completely invisible
      52             :  * to the user. The user must assemble their residual in the correct equation.
      53             :  * In particular, the residual must go in the \f$v\f$ residual equation, i.e.
      54             :  * \f$ M(u)\dot{v} + C(u)v + F(u) = 0 \f$, and,
      55             :  * subsequently, they must also be careful to populate to the correct Jacobian
      56             :  * blocks. The function to help facilitate this is get_second_order_dot_var.
      57             :  * If you have a second order variable, you pass that variable index and
      58             :  * get_second_order_dot_var will return the index of the corresponding velocity
      59             :  * variable, \f$v\f$ in the notation above. Then, the user knows what blocks to
      60             :  * populate.
      61             :  *
      62             :  * \note The API is designed so that if the user codes to this
      63             :  * paradigm, the TimeSolver will be interchangeable for those element
      64             :  * kernels.  That is, they'll be able to use either a
      65             :  * FirstOrderUnsteadySolver or a SecondOrderUnsteadySolver.
      66             :  *
      67             :  * This class is part of the new DifferentiableSystem framework,
      68             :  * which is still experimental.  Users of this framework should
      69             :  * beware of bugs and future API changes.
      70             :  *
      71             :  * \author Paul T. Bauman
      72             :  * \date 2015
      73             :  */
      74             : class FirstOrderUnsteadySolver : public UnsteadySolver
      75             : {
      76             : public:
      77             :   /**
      78             :    * Constructor. Requires a reference to the system
      79             :    * to be solved.
      80             :    */
      81             :   explicit
      82          76 :   FirstOrderUnsteadySolver (sys_type & s)
      83        2673 :     : UnsteadySolver(s) {}
      84             : 
      85             :   /**
      86             :    * Destructor.
      87             :    */
      88        2673 :   virtual ~FirstOrderUnsteadySolver () = default;
      89             : 
      90    86467762 :   virtual unsigned int time_order() const override
      91    86467762 :   { return 1; }
      92             : 
      93             :   virtual void integrate_qoi_timestep() override = 0;
      94             : 
      95             : #ifdef LIBMESH_ENABLE_AMR
      96             :   virtual void integrate_adjoint_refinement_error_estimate(AdjointRefinementEstimator & adjoint_refinement_error_estimator, ErrorVector & QoI_elementwise_error) override = 0;
      97             : #endif // LIBMESH_ENABLE_AMR
      98             : 
      99             : protected:
     100             : 
     101             :   /**
     102             :    * If there are second order variables in the system,
     103             :    * then we also prepare the accel for those variables
     104             :    * so the user can treat them as such.
     105             :    */
     106             :   void prepare_accel(DiffContext & context);
     107             : 
     108             :   /**
     109             :    * If there are second order variables, then we need to compute their residual equations
     110             :    * and corresponding Jacobian. The residual equation will simply be
     111             :    * \f$ \dot{u} - v = 0 \f$, where \f$ u \f$ is the second order variable add
     112             :    * by the user and \f$ v \f$ is the variable added by the time-solver as the
     113             :    * "velocity" variable.
     114             :    */
     115             :   bool compute_second_order_eqns(bool compute_jacobian, DiffContext & c);
     116             : 
     117             : };
     118             : 
     119             : } // end namespace libMesh
     120             : 
     121             : #endif // LIBMESH_FIRST_ORDER_UNSTEADY_SOLVER_H