doc:user:elements:volumes:fluid_iso_hypo_materials
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doc:user:elements:volumes:fluid_iso_hypo_materials [2016/04/01 15:49] – [FluidHypoMaterial] carretta | doc:user:elements:volumes:fluid_iso_hypo_materials [2017/12/01 12:07] – [FluidHypoMaterial] boemer | ||
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<note warning> | <note warning> | ||
- | Convergence when using this law may be difficult to achieve since there is no stiffness when shearing the material. If you encounter this kind of isssue, you may used **NortonHoffHypoMaterial** discussed below with a low viscosity parameter. | + | Convergence when using this law may be difficult to achieve since there is no stiffness when shearing the material. If you encounter this kind of issue, you may use **NortonHoffHypoMaterial** discussed below with a low viscosity parameter |
</ | </ | ||
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=== Description === | === Description === | ||
- | Norton-Hoff law descriding | + | Norton-Hoff law describing |
Stresses are computed with | Stresses are computed with | ||
Line 75: | Line 75: | ||
<note warning> | <note warning> | ||
- | To model low viscosity | + | To model Newtonian fluid with low viscosity (0.3 Pa.s for instance) it is important to used SRI elements instead of SRIPR. Indeed, SRIPR elements might induce oscillations in pressure and velocity fields. This seems to come from the different pressure value that can be stored at the deviatoric gauss points of SRIPR elements. For SRI elements, the hydrostatic pressure value is computed and stored at centre of each element. In that case, the pressure value on each element is unique. |
</ | </ | ||
<note important> | <note important> | ||
- | Boundary conditions might also have a huge impact on the convergence and the validity of the results. It is therefore crucial to check the way the elements deform along the boundaries and the corners. | + | Boundary conditions might also have a huge impact on the convergence and the validity of the results. It is therefore crucial to check the way the elements deform along the boundaries and the corners. From these observations, |
</ | </ | ||
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- | === Accounting for bulk modulus variation with pressure === | + | === Accounting for bulk modulus |
As mentionned above, the bulk modulus dependance with pressure must be linear. | As mentionned above, the bulk modulus dependance with pressure must be linear. | ||
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Therefore two parameters must be provided by the user: the bulk modulus at atmospheric pressure and the derivative $\frac{dK}{dp}$ | Therefore two parameters must be provided by the user: the bulk modulus at atmospheric pressure and the derivative $\frac{dK}{dp}$ | ||
+ | |||
+ | <note warning> | ||
+ | With Metafor, the pressure is negative in compression. Therefore, the value of $\frac{dK}{dp}$ has to be negative (otherwise the bulk modulus would decrease in compression which has no physical meaning). | ||
+ | </ | ||
The function $K(p)$ is provided by the user through a **PythonDirectorOneParameterFunction**: | The function $K(p)$ is provided by the user through a **PythonDirectorOneParameterFunction**: | ||
Line 155: | Line 159: | ||
</ | </ | ||
- | This class has to be defined above or below **getMetafor()**. | + | The user has more freedom for the viscosity evolution with pressure. The viscosity variation and its derivative have to be provided trough a class similar to the one below |
+ | |||
+ | < | ||
+ | class MyViscoPFunction(PythonDirectorOneParameterFunction): | ||
+ | def __init__(self, | ||
+ | print " | ||
+ | PythonDirectorOneParameterFunction.__init__(self) | ||
+ | self.debugRefs() | ||
+ | self.p | ||
+ | print " | ||
+ | def __del__(self): | ||
+ | print " | ||
+ | print " | ||
+ | exit(1) | ||
+ | def evaluate(self, | ||
+ | if pres> | ||
+ | return self.p[' | ||
+ | else : # pression négative en compression ! | ||
+ | return self.p[' | ||
+ | |||
+ | def computeDerivation(self,pres): | ||
+ | if pres> | ||
+ | return 0.0 | ||
+ | else : | ||
+ | return -self.p[' | ||
+ | </ | ||
- | The instance | + | The instances |
< | < | ||
- | bulkLaw | + | bulkLaw |
+ | viscoLaw = MyViscoPFunction(p) # <- " | ||
# for parameters dictionnary and not pressure | # for parameters dictionnary and not pressure | ||
| | ||
materset = domain.getMaterialSet() | materset = domain.getMaterialSet() | ||
materset.define(1, | materset.define(1, | ||
- | materset(1).put(BULK_MODULUS | + | materset(1).put |
- | materset(1).depend(BULK_MODULUS | + | materset(1).depend(BULK_MODULUS , bulkLaw |
- | materset(1).put(NORTON_MU | + | materset(1).put |
- | materset(1).put(NORTON_M | + | materset(1).depend(NORTON_MU |
- | materset(1).put(MASS_DENSITY | + | materset(1).put |
+ | materset(1).put | ||
</ | </ | ||
doc/user/elements/volumes/fluid_iso_hypo_materials.txt · Last modified: 2017/12/01 12:11 by boemer