Ok, sorry, I was confused by the naming : for "d_surface_flux" I was expecting a vector field as the parameter, not a scalar over which the gradient is computed before taking the actual flux. But the documentation is correct.

David.

Le mercredi 29 août 2012 15:38:39 UTC+2, Robert Cimrman a écrit :

Le mercredi 29 août 2012 15:38:39 UTC+2, Robert Cimrman a écrit :

Hi David,

On 08/29/2012 02:05 PM, David Libault wrote:

> Hi Robert,

>

> From the poisson.py I would like to probe the flux of grad(T) over a

> surface (Gamma_Left or Gamma_right), but I am not sure which term to use...

IMHO it's the same term as in my answer to Alec (thread "Question on the

``examples/diffusion/poisson.py''") - look at the post_process() function - the

term is d_surface_flux.

> I would use it in electrostatics (temperature is replaced by voltage), to

> compute the resistance of the volume imposing a voltage of 1 across two

> surfaces with dirichlet conditions and computing the electrical current.

> For a ohmic conductor, j = \sigma E = - \sigma grad(V), \sigma being the

> conductivity. j being the current density, the current intensity thru a

> surface is the flux of j thru that surface. For the case of homogenous

> \sigma, the term asked for above would do...

OK, let us know if d_surface_flux works for you - it can take a general

permeability tensor.

r.

> Le dimanche 26 août 2012 22:55:49 UTC+2, Robert Cimrman a écrit :

>>

>> On 08/26/2012 12:32 PM, Alec Kalinin wrote:

>>> Hi Robert,

>>>

>>> Did you mean "linear_elastic_probes.html" instead of

>>> "linear_elastic_tractions.html" example? I found the

>>> "linear_elastic_probes.html" very useful example for my purposes to

>> probe a

>>> solution in the given (x, y, z) points. Also the documentation

>>> "src/sfepy/fem/probes.html" gives all necessary information to help me

>>> implement what I want to do. Thank you!

>>

>> Sorry, I cut&pasted a wrong url, the correct one is [1]. But you found

>> another one that solves the problem.

>>

>>> But, despite this, could you tell me more about low-level way to

>> evaluate a

>>> variable in the given (x, y, z) point?

>>

>> It's exactly how the probes do that: the key function is

>> variable.evaluate_at() [2], where variable is an unknown or parameter

>> variable. It takes just one compulsory parameter - the coordinates of

>> points in which you wish to evaluate the variable. You can get the

>> variables of a problem by problem.get_variables(), where problem is the

>> second argument of the post_process_hook function.

>>

>> Best regards,

>> r.

>>

>> [1] http://sfepy.org/doc-devel/primer.html#probing

>> [2] http://sfepy.org/doc-devel/src/sfepy/fem/variables.html ,

>> http://sfepy.org/doc-devel/src/sfepy/fem/fields.html

>>

>>>

>>> On Sunday, August 26, 2012 12:47:50 AM UTC+4, Robert Cimrman wrote:

>>>>

>>>> Hi Alec,

>>>>

>>>> On 08/25/2012 05:45 PM, Alec Kalinin wrote:

>>>>> Dear SfePy users,

>>>>>

>>>>> Is it possible to evaluate a solution not only in the FEM mesh node,

>> but

>>>> in

>>>>> any arbitrary point in the domain with the given (x, y, z)

>> coordinates?

>>>>

>>>> Yes, it is possible. Either, you could use a probe as described in the

>>>> Primer [1] - the available probes are described in [2]. Or, you could

>>>> directly evaluate a variable in given points - this is a bit low-level

>>>> operation, but I could provide you instructions, if the probes are not

>>>> enough for you.

>>>>

>>>> Cheers,

>>>> r.

>>>>

>>>>> For example, consider Dirichlet problem for Poisson equation. We apply

>>>>> essential boundary conditions on the surface nodes and after the

>> problem

>>>>> has been solved we have the solution vector, i.e. vector of values in

>>>> the

>>>>> FEM mesh nodes. But I want to know the solution in point v(x, y, z)

>> that

>>>> is

>>>>> not FEM mesh node. What is the best way to obtain solution in this

>> point

>>>> v?

>>>>>

>>>>> Sincerely,

>>>>> Alec Kalinin

>>>>

>>>> [1] doc-devel/examples/linear_elasticity/linear_elastic_ tractions.html

>>>> [2] http://sfepy.org/doc-devel/src/sfepy/fem/probes.html