Material law describing a non viscous fluid.

Stresses are computed with

$$ \sigma_{ij} = s_{ij} + \delta_{ij} p $$ with $ s_{ij} = 0 $ in a non viscous fluid.

The equation which associates pressure and volume is $$ dP = -K \frac{dV}{V} $$ where $K$ is the bulk modulus.

Norton-Hoff law descriding a viscous fluid.

Stresses are computed with $$ \sigma_{ij} = s_{ij} + p \delta_{ij} $$

where $p$ is the hydrostatic pressure and $ s_{ij} $ the stress deviator tensor.

The stress deviator tensor ($ s_{ij} $) is determined upon the strain rate deviator tensor ($ D_{ij} $) through the following equation

$$ s_{ij} = 2 \mu D_{ij} \left( \sqrt{3} \ \sqrt{\frac{2}{3} D_{wz}.D_{wz}} \right)^{m-1}$$

Hydrostatic pressure is computed upon volume variation through the following eqation

$$ dp = K \frac{dV}{V} $$

where $K$ is the bulk modulus and $V$ the volume.

This law is identical to NortonHoffHypoMaterial but it can account for the variation of the bulk modulus and the viscosity parameter with the hydrostatic pressure $p$.

self.p['k0']+self.p['dkdp']*pres

class MyBulkFunction(PythonDirectorOneParameterFunction):
    def __init__(self,_p):
        PythonDirectorOneParameterFunction.__init__(self)
        self.debugRefs()
        self.p      = _p

    def __del__(self):
        print "MyBulkFunction : __del__ begin\n"
        print "callToDestructor of MyBulkFunction not allowed."
        print "Add MyBulkFunction.__disown__()"
        exit(1)

    def evaluate(self, pres):
        if pres>=0.0: # pression positive en traction !
            return self.p['k0']
        else :       # pression négative en compression !
            return self.p['k0']+self.p['dkdp']*pres

    def computeDerivation(self, pres):
        if pres>=0.0:
            return 0.0
        else :
            return self.p['dkdp']

    bulkLaw  = MyBulkFunction(p) 
    #print "help(bulkLaw) = ", help(bulkLaw)

    materset = domain.getMaterialSet()
    materset.define(1,NortonHoffPHypoMaterial)
    materset(1).put(BULK_MODULUS     ,  1.0)
    materset(1).depend(BULK_MODULUS  ,  bulkLaw,     Field(IF_P))

Norton-Hoff law including thermal aspects.