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Posted:
5 years ago
Jun 6, 2019, 12:47 p.m. EDT
Updated:
5 years ago
Jun 6, 2019, 12:47 p.m. EDT
From your expression you are computing
![](data:image/png;base64,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)
And apparently the numerator of this expression was identically 0 during your simulation.
So the solution depends on these questions:
- Is the above expression correct?
- Is it physically possible for
p
and P0
to be equal in your case (or equal and opposite) ?
- if you answered yes to both of the questions above, what do you expect will happen physically when
p= ± P0
?
From your expression you are computing
\frac{1}{\sqrt{p^2 - P0^2}}
And apparently the numerator of this expression was identically 0 during your simulation.
So the solution depends on these questions:
* Is the above expression correct?
* Is it physically possible for `p` and `P0` to be equal in your case (or equal and opposite) ?
* if you answered yes to both of the questions above, what do you expect will happen physically when `p= ± P0` ?
Henrik Sönnerlind
COMSOL Employee
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Posted:
5 years ago
Jun 7, 2019, 5:30 a.m. EDT
I do not know the exact source of the problem in this case, but it is not uncommon that there is nothing suspicious in original expression, and that the problematic expression occurs only after internal symbolic differentiation. As soon as an expression contains a variable raised to a power <1, there is a risk of getting singular derivatives at zero.
In such cases, it often helps to add a small number (like the built-in variable ‘eps’) to the expression, so that the problematic denominator is never exactly zero.
Here is an example where the definition of a built-in variable within the field of soil plasticity is safeguarded in this way, since the square root is ‘dangerous’:
sqrt(solid.II2s+eps)+solid.lemm1.soil1.alpha*solid.I1s-solid.lemm1.soil1.k
Regards,
Henrik
-------------------
Henrik Sönnerlind
COMSOL
I do not know the exact source of the problem in this case, but it is not uncommon that there is nothing suspicious in original expression, and that the problematic expression occurs only after internal symbolic differentiation. As soon as an expression contains a variable raised to a power
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Posted:
5 years ago
Jun 12, 2019, 5:40 p.m. EDT
Updated:
5 years ago
Jun 12, 2019, 5:41 p.m. EDT
Thank you Mr. Alexis and Mr. Henrik for taking time to provide your valuable suggestions for the problem.
When i used the abs operator for the modulus and added the in built variable 'eps' to the expression, I was thankfully able to get over the failed to evaluate negative power of zero error.
Then I faced the error message
Feature: Time-Dependent Solver 1 (sol2/t1)
Failed to find consistent initial values.
Last time step is not converged.
I have improved my meshing by using boundary layer meshes and made it lot more finer with more nodes. Does this error mean a problem with the boundary condition/initial condition or it could also have other factors solver configuration affecting it? Kindly suggest.
Thanks in advance for your help.
Thank you Mr. Alexis and Mr. Henrik for taking time to provide your valuable suggestions for the problem.
When i used the abs operator for the modulus and added the in built variable 'eps' to the expression, I was thankfully able to get over the failed to evaluate negative power of zero error.
Then I faced the error message
Feature: Time-Dependent Solver 1 (sol2/t1)
Failed to find consistent initial values.
Last time step is not converged.
I have improved my meshing by using boundary layer meshes and made it lot more finer with more nodes. Does this error mean a problem with the boundary condition/initial condition or it could also have other factors solver configuration affecting it? Kindly suggest.
Thanks in advance for your help.