balance equation in rate form and boundary conditions
Hi, everyone!
I'm trying to implement an example with hypoelastic material, i.e. a material whose stress-strain relationship is given in rate-form: $$ d_stress = E : d_strain $$ The linear elastic material is a subset of this, but one can obtain different types of behavior with non-constant E.
I tried two approaches (enclosed), both contain the balance equation in
rate-form. The equation consists of a single dw_lin_elastic_iso term in
both cases.
When displacements are prescribed, the problem is not solved as expected: the solution is zero everywhere except where the EBCs are prescribed. The approach with two fields (displacement and velocity) works with boundary conditions prescribed for velocities. Actually, the second field (displacements) is present only to directly output displacements, since I am not interested in velocities.
My questions:
- Is the above described behavior correct in Sfepy? Is it a bug/feature? There is also the possibility that the formulations are not equivalent, but I can't see it now.
- What is the difference between the [hypo]elastic term and e.g. diffusion?
(There is a time-derivative term in
time_poisson_interactive.pytogether with Dirichlet boundary conditions and everything seems to work.) Is it the fact that there is no term without time derivative in the balance equation? I guess not - I tried to add an elastic term (multiplied by either 0, 1e-4), but that doesn't change the results much.
Thanks, Jan
Hi Jan,
it is a bug. Can you try [1]? Also verify, please, that your example mentioned in [2] still works - this is related.
r.
[1] https://github.com/rc/sfepy/tree/fix-variable-state-data-sharing [2] https://groups.google.com/forum/?_escaped_fragment_=topic/sfepy-devel/DOaxK9...
On 27.3.2017 13:09, Jan Heczko wrote:
Hi, everyone!
I'm trying to implement an example with hypoelastic material, i.e. a material whose stress-strain relationship is given in rate-form: $$ d_stress = E : d_strain $$ The linear elastic material is a subset of this, but one can obtain different types of behavior with non-constant E.
I tried two approaches (enclosed), both contain the balance equation in rate-form. The equation consists of a single
dw_lin_elastic_isoterm in both cases.When displacements are prescribed, the problem is not solved as expected: the solution is zero everywhere except where the EBCs are prescribed. The approach with two fields (displacement and velocity) works with boundary conditions prescribed for velocities. Actually, the second field (displacements) is present only to directly output displacements, since I am not interested in velocities.
My questions:
- Is the above described behavior correct in Sfepy? Is it a bug/feature? There is also the possibility that the formulations are not equivalent, but I can't see it now.
- What is the difference between the [hypo]elastic term and e.g. diffusion? (There is a time-derivative term in
time_poisson_interactive.pytogether with Dirichlet boundary conditions and everything seems to work.) Is it the fact that there is no term without time derivative in the balance equation? I guess not - I tried to add an elastic term (multiplied by either 0, 1e-4), but that doesn't change the results much.Thanks, Jan
Hi Robert, your fix seems to solve the problem (the single-field formulation gives the expected displacements) and the other examples work as well. Thank you! J.
On 27 Mar 2017 15:22, "Robert Cimrman" <cimr...@ntc.zcu.cz> wrote:
Hi Jan,
it is a bug. Can you try [1]? Also verify, please, that your example mentioned in [2] still works - this is related.
r.
[1] https://github.com/rc/sfepy/tree/fix-variable-state-data-sharing [2] https://groups.google.com/forum/?_escaped_fragment_=topic/ sfepy-devel/DOaxK9CTK2c#!topic/sfepy-devel/DOaxK9CTK2c
On 27.3.2017 13:09, Jan Heczko wrote:
Hi, everyone!
I'm trying to implement an example with hypoelastic material, i.e. a material whose stress-strain relationship is given in rate-form: $$ d_stress = E : d_strain $$ The linear elastic material is a subset of this, but one can obtain different types of behavior with non-constant E.
I tried two approaches (enclosed), both contain the balance equation in rate-form. The equation consists of a single
dw_lin_elastic_isoterm in both cases.When displacements are prescribed, the problem is not solved as expected: the solution is zero everywhere except where the EBCs are prescribed. The approach with two fields (displacement and velocity) works with boundary conditions prescribed for velocities. Actually, the second field (displacements) is present only to directly output displacements, since I am not interested in velocities.
My questions:
- Is the above described behavior correct in Sfepy? Is it a bug/feature? There is also the possibility that the formulations are not equivalent, but I can't see it now.
- What is the difference between the [hypo]elastic term and e.g. diffusion? (There is a time-derivative term in
time_poisson_interactive.pytogether with Dirichlet boundary conditions and everything seems to work.) Is it the fact that there is no term without time derivative in the balance equation? I guess not - I tried to add an elastic term (multiplied by either 0, 1e-4), but that doesn't change the results much.Thanks, Jan
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OK, I have created a PR and merged it. Also, there is now [#378] - I need to resolve the problem properly.
r. [#378] https://github.com/sfepy/sfepy/issues/378
On 03/28/2017 08:04 AM, Jan Heczko wrote:
Hi Robert, your fix seems to solve the problem (the single-field formulation gives the expected displacements) and the other examples work as well. Thank you! J.
On 27 Mar 2017 15:22, "Robert Cimrman" <cimr...@ntc.zcu.cz> wrote:
Hi Jan,
it is a bug. Can you try [1]? Also verify, please, that your example mentioned in [2] still works - this is related.
r.
[1] https://github.com/rc/sfepy/tree/fix-variable-state-data-sharing [2] https://groups.google.com/forum/?_escaped_fragment_=topic/ sfepy-devel/DOaxK9CTK2c#!topic/sfepy-devel/DOaxK9CTK2c
On 27.3.2017 13:09, Jan Heczko wrote:
Hi, everyone!
I'm trying to implement an example with hypoelastic material, i.e. a material whose stress-strain relationship is given in rate-form: $$ d_stress = E : d_strain $$ The linear elastic material is a subset of this, but one can obtain different types of behavior with non-constant E.
I tried two approaches (enclosed), both contain the balance equation in rate-form. The equation consists of a single
dw_lin_elastic_isoterm in both cases.When displacements are prescribed, the problem is not solved as expected: the solution is zero everywhere except where the EBCs are prescribed. The approach with two fields (displacement and velocity) works with boundary conditions prescribed for velocities. Actually, the second field (displacements) is present only to directly output displacements, since I am not interested in velocities.
My questions:
- Is the above described behavior correct in Sfepy? Is it a bug/feature? There is also the possibility that the formulations are not equivalent, but I can't see it now.
- What is the difference between the [hypo]elastic term and e.g. diffusion? (There is a time-derivative term in
time_poisson_interactive.pytogether with Dirichlet boundary conditions and everything seems to work.) Is it the fact that there is no term without time derivative in the balance equation? I guess not - I tried to add an elastic term (multiplied by either 0, 1e-4), but that doesn't change the results much.Thanks, Jan
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participants (2)
-
Jan Heczko -
Robert Cimrman