Model Hierarchy

MPhys uses a pattern to build multiphysics optimization problems. Each level of the pattern is a different type of group that MPhys provides.

The highest level of the model is the multipoint group. The multipoint group consist of scenarios which represent different conditions and/or types of multiphysics analyses to performed. Within the scenario is the coupling group which represents the primary multiphysics problem for the scenario.

Builders are used to help populate these levels of the model hierarchy with subsystems from the solvers. Tagged Promotion is used to promote specific variables to the level of scenario.

Coupling Groups

The CouplingGroup is the primary physics coupling being solved. That is it contains physics modules, such as an aerodynamic or structural solver, and potentially modules that transfer or interpolate between the physics modules, such as a load or displacement transfer schemes.

Each type of scenario typically has an associated coupling group that it will add automatically given the proper builders. Within the Scenario group, the coupling group will have the name ‘coupling’. The scenario-specific coupling group will have a default nonlinear and linear solvers, but these can be overwritten with the optional arguments to mphys_add_scenario().

Scenario Groups

The scenario level is an OpenMDAO group that represents a specific condition in a multipoint optimization. For example, a scenario could be a cruise flight condition that requires a coupling group to determine the lift and drag. The scenario group contains a coupling group and any scenario-specific computation that needs to occur before or after the associated coupled problem is solved. For example, a sonic boom propagator requires the flow solution as an input but this one-way coupling does not require it to be in the coupling group; therefore, it should be put in the scenario group to be solved after the coupling group converges.

MPhys provides a library of these Scenario groups designed for specific type problems. See MPhys Scenario Library for details about specific standardized scenarios. If a particular multiphysics problem is not covered by the MPhys library, new scenarios and coupling groups can be created by subclassing the MphysGroup.

Multipoint Groups

There are two versions of the multipoint group:

1. Multipoint is derived from the standard OpenMDAO Group

2. MultipointParallel is derived for the OpenMDAO ParallelGroup.

For both versions have a function, mphys_add_scenario(), is used to populate the lower levels of the model hierarchy.

Multipoint

The Multipoint group will sequentially evaluate the scenario groups. The Multipoint group can be the top group of the OpenMDAO model or a subsystem.

In the setup method of the Multipoint group, the following steps must be done:

1. Instantiate the builders

2. Call initialize() for each builder with the Multipoint’s comm (self.comm)

3. Add the mesh components and/or other mesh coordinate source like geometry.

4. Add the scenarios

5. Connect the mesh coordinates to the scenarios

Additionally, the Multipoint group can hold the design variables or other inputs and subsystems to be evaluated after the scenarios. These extra subsystem can then be connected to the scenarios by the user.

class mphys.multipoint.Multipoint(**kwargs)

An extension of the standard OpenMDAO group that adds the mphys_add_scenario() method. For sequential evaluations of the MPhys scenarios.

Set the solvers to nonlinear and linear block Gauss–Seidel by default.

mphys_add_scenario(name, scenario, coupling_nonlinear_solver=None, coupling_linear_solver=None)

Add an MPhys scenario

Parameters:

namestr

The name of the scenario

Scenario: :class:`~mphys.scenario.Scenario`

The scenario object

coupling_nonlinear_solver: openmdao.solvers.solver.NonlinearSolver

The nonlinear solver to assign to the coupling group primal problem

coupling_linear_solver: openmdao.solvers.solver.LinearSolver

The linear solver to to assign to the coupling group sensitivity problem

mphys_connect_scenario_coordinate_source(source, scenarios, disciplines)

A helper method to aid in connecting mesh coordinate sources to the scenarios in this multipoint group. The source and target variable names are assumed to be ‘x_{discipline}0’

Parameters:

source: openmdao.api.Group or openmdao.api.Component

The source subsystem for the mesh coordinate variables

scenariosstr or list[str]

The names of the scenarios to be the target of the connections

disciplinesstr or list[str]

The names of the disciplines for the mesh coordinates.

MultipointParallel

If given a number of MPI ranks greater than or equal to the number of scenarios, the MultipointParallel group will simultaneously evaluate the scenario groups. Unlike the sequential Multipoint group, the MPI communicators are different for each scenario in MultipointParallel, so the scenarios will call the builder’s initialize method.

In the setup method of the MultipointParallel group, the following steps must be done:

1. Instantiate the builders

2. Add the scenarios using the in_MultipointParallel=True option

Because this is a ParallelGroup, other subsystems that hold the inputs outside the scenario and subsystems to be evaluated after the scenarios cannot be added directly to the MultipointParallel group. These extra subsystem should be added to a higher level of the model and then connected to the scenarios by the user.

class mphys.multipoint.MultipointParallel(**kwargs)

An OpenMDAO parallel group that adds the mphys_add_scenario() method. For simultaneous evaluations of the MPhys scenarios.

Set the mpi_proc_allocator option to ‘parallel’.

mphys_add_scenario(name, scenario, coupling_nonlinear_solver=None, coupling_linear_solver=None)

Add an MPhys scenario

Parameters:

namestr

The name of the scenario

Scenario: :class:`~mphys.scenario.Scenario`

The scenario object

coupling_nonlinear_solver: openmdao.solvers.solver.NonlinearSolver

The nonlinear solver to assign to the coupling group primal problem

coupling_linear_solver: openmdao.solvers.solver.LinearSolver

The linear solver to to assign to the coupling group sensitivity problem