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## MPHYS API
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[MPHYS](https://github.com/openMDAO/MPHYS) (Multi-PHYSics) is a framework designed to perform multi-physics analysis and optimization, and is built on top of [openMDAO](https://openmdao.org/). The API allows to interface DART with other software through MPHYS, and is implemented under [api/mphys](https://gitlab.uliege.be/am-dept/dartflo/blob/master/dart/api/mphys.py).
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**0. Importing the modules**
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Since MPHYS couples multiple software, it is required to install them before using MPHYS. As such, DART cannot be used from a development environement (it must be installed), and must be imported by calling,
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```python
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from dartflo.dart.api.mphys import DartBuilder
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```
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Additionaly, the interface must be setup in an MPHYS class,
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```python
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from mphys import Multipoint
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class Top(Multipoint):
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...
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```
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**1. Defining the parameters**
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The list of parameters required to setup the interface is essentialy a simplified version of that used for the internal API. Parameters are listed hereunder:
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```python
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p = {
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# Options
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'Threads' : int, # number of threads
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'Verb' : int, # verbosity
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# Model (geometry or mesh)
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'File' : str, # Input file containing the model
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'Pars' : dict, # parameters for input file model
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'Dim' : int, # problem dimension (2 or 3)
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'Format' : str, # save format (vtk or gmsh)
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# Markers...
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'Fluid' : str, # name of physical group containing the fluid
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'Farfield' : list of str, # LIST of names of physical groups containing the farfield boundaries (downstream should be last element)
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# ... only 2D
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'Wing' : str, # name of physical group containing the airfoil boundary
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'Wake' : str, # name of physical group containing the wake
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'Te' : str, # name of physical group containing the trailing edge
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# ... only 3D
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'Wings' : list of str, # LIST of names of physical groups containing the lifting surface boundary
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'Wakes' : list of str, # LIST of names of physical group containing the wake
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'WakeTips' : list of str, # LIST of names of physical group containing the edge of the wake (not for 2.5D)
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'TeTips' : list of str, # LIST of names of physical group containing the edge of the wake and the trailing edge
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# ... optional for 3D
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'Symmetry' : str, # name of physical group containing the symmetry boundaries
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# Freestream
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'M_inf' : float, # freestream Mach number
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'AoA' : float, # freestream angle of attack [deg] (optional, default=0)
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'AoS' : float, # freestream angle of sideslip [deg] (optional, default=0)
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'Q_inf' : float, # freesteam dynamic pressure (only required for aerostructural computations)
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# Geometry
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'S_ref' : float, # reference surface length
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'c_ref' : float, # reference chord length
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'x_ref' : float, # x-coordinate of reference point for moment computation
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'y_ref' : float, # y-coordinate of reference point for moment computation
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'z_ref' : float, # z-coordinate of reference point for moment computation
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# Numerical
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'LSolver' : 'GMRES', # inner solver (PARDISO, MUMPS or GMRES)
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'G_fill' : int, # fill-in factor for GMRES preconditioner (optional, default=2)
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'G_tol' : float, # tolerance for GMRES (optional, default=1e-5)
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'G_restart' : int, # restart for GMRES (optional, default=50)
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'Rel_tol' : float, # relative tolerance on solver residual
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'Abs_tol' : float, # absolute tolerance on solver residual
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'Max_it' : int # maximum number of iterations for nonlinear solver
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}
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```
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*Note* DART can be coupled with [pyGeo](https://github.com/mdolab/pyGeo), which uses the free-form deformation technique, to perform aerodynamic shape optimization. Since pyGeo only handles 3D geometries, users wanting to perform 2D shape optimization must provide a so-called 2.5D geometry, which consists of an extruded 2D geometry enclosed between two symmetry walls. In such a case, the parameters `'WakeTips'` MUST NOT be given.
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**2. Using the interface**
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Once the parameters have been defined, the interface can simply be setup by calling,
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```python
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dart = DartBuilder(p, scenario=..., task=...)
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```
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where valid choices for `scenario` are `'aerodynamic'` or `'aerostructural'`, and valid choices for `task` are `'analysis'` or `'optimization'`.
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Users must then refer to the MPHYS documention to connect the interface through MPHYS. In version 0.4.0, this is done by calling,
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```python
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# for pure aerodynamic computations...
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from mphys.scenario_aerodynamic import ScenarioAerodynamic
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self.mphys_add_scenario('...', ScenarioAerodynamic(aero_builder=dart))
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# ... or for aerostructural computations
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from mphys.scenario_aerostructural import ScenarioAeroStructural
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self.mphys_add_scenario('...', ScenarioAeroStructural(aero_builder=dart, struct_builder=..., ldxfer_builder=...), coupling_nonlinear_solver=..., coupling_linear_solver=...)
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``` |
