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Computing the volume and time drivation of the change of volume, ALE
Posted 7 ago 2009, 06:04 GMT-4 2 Replies
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Hello,
I using ALE in an axi-symmetrical model. For calculating the volume I use a integration coupling variable V and 2*pi*r for integration.
Now I need dV/dt (change of volume during time). I can not use d(V,t), because it gives 0 (?). What is the right formulation as integration coupling variable ?
Now I use 2*pi*r*(rt+zt), but I'm not shure. Testing the results manual gives some differences.
Are there any hints?
Best regards,
Michael
I using ALE in an axi-symmetrical model. For calculating the volume I use a integration coupling variable V and 2*pi*r for integration.
Now I need dV/dt (change of volume during time). I can not use d(V,t), because it gives 0 (?). What is the right formulation as integration coupling variable ?
Now I use 2*pi*r*(rt+zt), but I'm not shure. Testing the results manual gives some differences.
Are there any hints?
Best regards,
Michael
2 Replies Last Post 7 ago 2009, 09:33 GMT-4
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Posted:
2 decades ago
Hi Michael, you need to define a global equation:
Name: Vol
Equation: Vol-V
Init: whatever the initial volume is
Now you can use Volt for the time derivative of the volume (or d(Vol,t)). This is also more computationally efficient than trying to do it directly with an integration coupling variable (if you couple Volt back in the model somewhere) because the Jacobian matrix will not become unnecessarily populated.
With best regards,
Daniel Smith
COMSOL
Name: Vol
Equation: Vol-V
Init: whatever the initial volume is
Now you can use Volt for the time derivative of the volume (or d(Vol,t)). This is also more computationally efficient than trying to do it directly with an integration coupling variable (if you couple Volt back in the model somewhere) because the Jacobian matrix will not become unnecessarily populated.
With best regards,
Daniel Smith
COMSOL
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Posted:
2 decades ago
Hi Daniel,
this is right! Formulating this ODE gives the correct time derivation of Vol in place of V!
Thank you very much!
Best regards
Michael Rembe
this is right! Formulating this ODE gives the correct time derivation of Vol in place of V!
Thank you very much!
Best regards
Michael Rembe