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How to add a new model

The numerical methods in integration and modeldisc need a definition of a physical model with at least some methods which are listed in modelphybase. Obviously, existing models are examples but all definitions are not necessary.

compulsory methods

  • __init__ should be adapted the new model ; at least define model name and number of equations
  • prim2cons and cons2prim methods must be defined even if they are the same (see Burgers)
  • numflux is the definition of the physics of the model ; there is currently no different definition of physical flux (of one only state) and numerical flux (from two states)
  • timestep must be defined as a kind of definition of spectral radius of the dynamical system, with dependency to mesh size and a user time condition

variables

  • primitive (user) variables must be defined by the prim2cons and cons2prim methods
  • a set of variables can be defined through a dictionary model._vardict with a name and associated fonction, computed from conservative data. For example :
def __init__(self, ...):
    ...
    self._vardict = { 'pressure': self.pressure, 'velocity': self.velocity }

def pressure(self, qdata): # returns (gam-1)*( rho.et) - .5 * (rho.u)**2 / rho )
        return (self.gamma-1.0)*(qdata[2]-0.5*qdata[1]**2/qdata[0])

def velocity(self, qdata): # returns (rho u)/rho
    return qdata[1]/qdata[0]

boundary conditions

Available boundary conditions are also listed in a dictionary which is updated python decorator of _bcdict attribute (registry class) of the class model. Then the method can be defined:

def bc_outsub(self, dir, data, param):
        return [ data[0], data[1], param['p'] ]

where * dir is a variable used to specify either the direction or side of the boundary condition * data is the local interior primitive data * param is a dictionary which has been defined by the user and is associated to this boundary condition

Note that per for periodic and dirichlet conditions are already defined in modelphy.base.