Hello, everyone
I am very confused about Dirichlet Boundary Conditions.
Such as the example given by the manual:
[pylithapp.problem]
bc = [mybc]
[pylithapp.problem.bc.mybc]
label = group A
bc_dof = [2] ; fixed displacement in z direction
db_initial = spatialdata.spatialdb.SimpleDB
db_initial.iohandler.filename = disp_A.spatialdb
db_initial.query_type = nearest ; change query type to nearest point algorithm
db_rate = spatialdata.spatialdb.UniformDB
db_rate.values = [displacement-rate-z]
db_rate.data = [1.0e-06 * m/s] ; velocity is 1.0e-06 m/s
From the manual, bc_dof = [2] (fixed displacement in z direction) means the displacement in z direction is fixed, but it laterly says group A moves at a speed of 1.0e-06 m/s in the z direction. How could this happen? Group A is fixed and moves at a speed of 1.0e-06m/s in z direction at the same time? I mean if Group A is fixed, it cannot move, right?
Hope someone can give a detailed explanation.
Best regards,
Tu Xiang
I would like to ask for clarification regarding the boundary condition behavior in PyLith.
I have a set of nodes located on the +Y face. I applied a Dirichlet boundary condition only to the top layer (top nodes) of the +Y face using SimpleGridDB. However, after running the model and examining the results, I observed that all nodes on the +Y face appeared to move consistently, as if the Dirichlet boundary condition had been applied to the entire surface (all nodes).
Does PyLith interpolate the Dirichlet boundary condition across the entire +Y face? Or is there a specific parameter I may have overlooked in the configuration files if I intend the displacement to occur only on the top layer of the +Y face?
I am using PyLith version 2.2.1. Please find attached the screenshot and the spatial database files for your reference.
If you don’t apply a boundary condition to the exterior of the domain, it will be a free surface. When you apply a Dirichlet boundary condition to the top portion of an exterior boundary, then the bottom portion will usually deform to maintain a traction-free surface. In other words, if you pull or push on the top portion of the boundary and have a roller boundary preventing only vertical deformation on the bottom boundary, then the bottom portion will move along with it. If you were to fix the bottom boundary so that it could not move horizontally or vertically while pulling or pushing on the top portion of a lateral boundary, then you would get a much different deformation pattern; the lower portion of the boundary would have complex deformation to match the constraints while maintaining a free surface.
My apologies for not being able to respond during the shutdown of the US government.
Thank you for the clear explanation. The information is very helpful for understanding the behavior in my model and to further build the model that I wanted. I really appreciate your help. Thanks.
