Slip boundary conditions

hvwahl
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5 years 10 months ago #1978 by hvwahl

Slip boundary conditions was created by hvwahl

Hi everyone,

is there "automatic" way to enable free-slip boundary conditions on one boundary and Dirichlet on another using the VectorH1 space?

Alternatives would of course to be a separate H1 space for each component each with different Dirichlet flags like here , using Nitsche to enforce the Dirichlet on only one component or to manually set the freedofs array like here .

Best wishes,
Henry

Guosheng Fu
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5 years 10 months ago #1979 by Guosheng Fu

Replied by Guosheng Fu on topic Slip boundary conditions

There is a "manual" way, which is pretty good.
See the post

ngsolve.org/forum/ngspy-forum/846-bounda...-vector-valued-funcs

Guosheng Fu
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5 years 10 months ago #1980 by Guosheng Fu

Replied by Guosheng Fu on topic Slip boundary conditions

Here is a snipplet that works for me:

Code:

V = VectorH1(mesh, order = 3)
Q = H1(mesh,order=2)
X = FESpace([V,Q])
freedofs = X.FreeDofs()
fesx,fesy = V.components
for el in fesx.Elements(BND):                                               
          if (el.mat=="dir"):                                                     
              for dof in el.dofs:                                                 
                  freedofs.Clear(dof)                                             
                  freedofs.Clear(fesx.ndof+dof) # y-component                     
          if (el.mat=="neu"):                                                     
              for dof in el.dofs:                                                 
                  freedofs.Clear(dof)                                             
          if (el.mat == "wall" or el.mat =="inlet" or el.mat =="outlet"):         
              for dof in el.dofs:                                                 
                  freedofs.Clear(fesx.ndof+dof) # y-component                     

hvwahl
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5 years 10 months ago #1981 by hvwahl

Replied by hvwahl on topic Slip boundary conditions

Hi Guosheng,

thank for your help! I was was hoping to avoid a loop over the elements, as I have to update the freedofs array in every time-step, but your way is probably still the best.

Best wishes, Henry

christopher
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5 years 10 months ago #1982 by christopher

Replied by christopher on topic Slip boundary conditions

What is your criteria for selecting fixed dofs in each time step?

hvwahl
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5 years 10 months ago #1987 by hvwahl

Replied by hvwahl on topic Slip boundary conditions

Hi Christopher,

within the bulk, the dofs are selected with element markers obtained via a level-set function (which changes in each time-step). The mesh boundary dofs will stay the same in each time-step.

Best wishes, Henry

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