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how to change the status of a parameter
Posted Jun 25, 2010, 2:10 p.m. EDT 3 Replies
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how do i make a constant parameter begin to vary as a function of another parameter.
for example, for a newtonian fluid model, the viscosity is declared as a constant. how can i make this viscosity vary with shear rate for a case of non-newtonian fluid.
for example, for a newtonian fluid model, the viscosity is declared as a constant. how can i make this viscosity vary with shear rate for a case of non-newtonian fluid.
3 Replies Last Post Jun 26, 2010, 11:43 a.m. EDT
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Posted:
1 decade ago
Hi
for me a "Parameter" by definition is supposed to be fixed = Constant and evaluated once at the beginning of the solving sequence.
However if you add a "variable", and initialise it with a constant parameter you can have it changing during the modelling, but you must also decide if its a driver or a passive follower or an unknow to be solved for, and add more equations depending on your need.
Hope this helps
Good luck
Ivar
for me a "Parameter" by definition is supposed to be fixed = Constant and evaluated once at the beginning of the solving sequence.
However if you add a "variable", and initialise it with a constant parameter you can have it changing during the modelling, but you must also decide if its a driver or a passive follower or an unknow to be solved for, and add more equations depending on your need.
Hope this helps
Good luck
Ivar
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Posted:
1 decade ago
thanx for d reply. i ve an expression in comsol multiphysics fluid flow model which contains viscosity as constant (newtonian). However, i want my viscosity to change as a function of shear rate (non-newtonian behaviour). Is there a way i can declare the viscosity as a function of the shear rate within the subdomain using established formulae like power law and carreau model.
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Posted:
1 decade ago
Hi
normally in COMSOL you can enter a functions or an expression in about any field, and COMSOL detects mostly correctly when you turn your problem into a non-linear one, and adapts the solver settings nicely (but still might not manage to converge without some external help)
Its the same for looped values, but these comes out sometimes as error on matrix inversion.
Try it out, replace your viscuosity by an expression linked to the shear or the temperature or ....
You can also define global expressions and have COMSOL search for the "optimum" of a physical property, if on your side you have enough data to define fully the solution. If you have many variables to optimise it's worth to get the optimisation module of COMSOL. There are several examples in the docs for single optimisation values.
Have fun Comsoling
Ivar
normally in COMSOL you can enter a functions or an expression in about any field, and COMSOL detects mostly correctly when you turn your problem into a non-linear one, and adapts the solver settings nicely (but still might not manage to converge without some external help)
Its the same for looped values, but these comes out sometimes as error on matrix inversion.
Try it out, replace your viscuosity by an expression linked to the shear or the temperature or ....
You can also define global expressions and have COMSOL search for the "optimum" of a physical property, if on your side you have enough data to define fully the solution. If you have many variables to optimise it's worth to get the optimisation module of COMSOL. There are several examples in the docs for single optimisation values.
Have fun Comsoling
Ivar