So, I think I am finally understanding this problem. I worked out a very long winded solution, using FEA and Rayleigh-Ritz as well as an analytical solution that I put here if anyone wants to check it out and tell me if I am really getting this: http://www.siue.edu/~rkrauss/sfepy/axial_rod_2_out.pdf
Attached is a png showing my 1D analytical solution vs. the z axis displacement from SfePy. I think they look pretty close (SfePy is a little stiffer, but I think that is reasonable). The comparison is also between a 3D and a 1D model, so I think perfect agreement is unreasonable to expect.
If you have any input, please let me know. Otherwise I will now focus on understanding how the linear material model is implemented in SfePy in preparation to create a nonlinear material.
Ryan
On Sat, Jul 12, 2008 at 4:03 PM, Ryan Krauss <ryan...@gmail.com> wrote:
So, everything is correctly installed and thanks to Robert I can now work in the directory of my choice. Basically, things are working. Now I need to understand what the code is actually doing.
My intention is to ask some questions about the attached setup file, increase my understanding, add some comments to, and possibly have a good tutorial problem when it's done.
Referring to the attached file, which gets passed to simple.py as an input, I have the following questions:
The file starts with
field_1 = { 'name' : 'displacement', 'dim' : (3,1), 'domain' : 'Omega', 'bases' : {'Omega' : '3_4_P1'} }
variable_1 = { 'name' : 'u', 'kind' : 'unknown field', 'field' : 'displacement', 'order' : 0, } variable_2 = { 'name' : 'v', 'kind' : 'test field', 'field' : 'displacement', 'dual' : 'u', }
All 3 of these are displacements, I am trying to understand how they are related or different. I assume a field is a vector. Maybe the variables are scalars. If 'u' is one component of the vector field displacement, where is the degree of freedom specified (i.e. which component of 'displacement' does 'u' refer to)?
From the description, it sounds like 'v' is a test field of 'u'. Does that mean that when 'v' converges, 'u' is the result? Or something else?
I assume 'Omega' is a domain that includes the whole problem, but that I can also name domains and some how use different domains for different purposes. Is this correct?
What does the '3_4_P1' mean?
Does this section of the setup file determine what the output is that is dumped to the vtk output files? Is the variable 'u' what is ultimately being sought, reported, and visualized?
What are the units on 'u'?
======================
The next section I have questions about is this:
equations = { 'balance_of_forces' : """dw_lin_elastic_iso.i1.Omega( solid.lame, v, u ) = dw_surface_ltr.isurf.Top( traction.val, v )""", }
material_1 = { 'name' : 'solid', 'mode' : 'here', 'region' : 'Omega', 'lame' : {'lambda' : 1e1, 'mu' : 1e0}, # Lame coefficients. }
What are lambda and mu and what are their units? Youngs modulus and mass density per unit length? Something else? I assume it is something mass related and something stiffness related.
It seems like equations is setting up a force balance on the top of the material specimen where the load is being applied. Is this correct?
It seems like this function:
def tractionLoad( ts, coor, region, ig ): """ts = TimeStepper, coor = coordinates of field nodes in region.""" import numpy as nm from sfepy.base.base import pause, debug nt = ts.nt
val = nm.zeros( (coor.shape[0],), dtype = nm.float64 ) val.fill( 1e-1 * nt )
print val return {'val' : val}
defines a traction load at all nodes (or maybe on some infinitesimal volume or area) that is the same at all points and ramping up in time with a slope of 0.1 per time step. Can this force be an arbitrary function of time? What are the units of the traction load? Is it compressive or tensile? What direction is associated with it?
I think that is enough for now. Thanks for your ongoing help and patience.
Ryan
