# Questions tagged [fenics]

Questions about the finite element method software FEniCS and its subpackages (Dolfin, UFL, FFC).

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### Assembling FE tensors using different quadrature degrees

Assume we have few terms contributing to element tensor and each requires different quadrature degree to be integrated exactly. Does it generally worth using different quadrature degrees for each term ...
849 views

### Flux across a non-boundary line segment in FEniCS

I am solving an elliptic boundary value problem on a subset of the rectangle [-1,1]x[-1,1]. The domain contains the line segment x=0, however this does not need to be a part of the boundary, so it is ...
2k views

### FeniCS: Visualizing high order elements

I've just started messing around with FEniCS. I am solving Poisson with 3rd order elements and would like to visualize the results. However, when I use plot(u), the visualization is just a linear ...
362 views

### Mixed FEM vector indices of pressure and velocity in FEniCS

Looking at the stokes-iterative demo of FEniCS, after solving the linear system using U = Function(W) solver.solve(U.vector(), bb) the solution ...
606 views

### Stochastic Galerkin projection approach for using generalized polynomial chaos expansion (GPCE) in solving PDE

I want to know if there is any way to define the test and trial function in the way that I want instead of using the default functions. So if I want define the polynomial and basis and coefficient, ...
146 views

### Speed up DG FunctionSpace evalutation [closed]

today I tried some evaluation on a DG function space (Fenics 1.2.0). In my calculations I need to use meshes with a large number of cells (~10mio). At the moment it takes a very long time to create a ...
854 views

### How can I build a mesh with holes for use in FEniCS?

This is my first time using FEniCS. I am trying to solve an elliptic PDE, fairly similar to the Laplace equation, on a rectangle with two holes in it. The holes are level sets of an energy function, ...
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### Fenics: msh to xml conversion

I generated a mesh file in gambit and wanted to convert it to xml format. I tried the code below, but there is no output. ...
371 views

### 2d-mini element-can't use sub(0),but bubble element is ok

My program (in Python, using FEniCS): ...
427 views

### Fenics: time-independent Sine-Gordon equation

Is there a code for the equation $$\frac{\partial^2u}{\partial x^2}+\frac{\partial^2u}{\partial y^2} = \sin(u)$$ or for the sine gordon equation in two dimensions because I want to change some ...
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### Fenics: Meshfunction usage

I am confused most of the time with the application of boundary conditions in Fenics. Suppose I have an xml mesh for a rectangular beam and want to apply Dirichlet BC ($u =0$) on the left side of the ...
641 views

### How to apply periodic boundary conditions to a Raviart-Thomas finite element space in Fenics? [closed]

I'm trying to use periodic boundary conditions within a Raviart-Thomas finite element space in Fenics (dolfin 1.2.0) in a Ubuntu 12.04 (amd64) machine (with python 2.7). If other FE space is used, ...
596 views

### Fenics : boundary condition

`I am working on a problem found here " http://www.caesarsystems.co.uk/NAFEMS_benchmarks/le10.html" ..I am really confused about the boundary conditions and tried my level best to compute it but ...
815 views

### Fenics : Elementwise stress computation

In a elastodynamics problem, I define the stress as def sigma(v): return 2.0*mu*sym(grad(v)) + lmbda*tr(sym(grad(v)))*Identity(v.cell().d) I have computed ...
385 views

### Fenics : looking forward to compute displacements at nodes

I just went through the Fenics book to get the nodal displacements and tried this code .... ...
279 views

### Fenics: problem with the mesh generation

while executing my script i get this error Traceback (most recent call last): File "/media/oss/Fenics/demo/box_3delasticity.py", line 33, in mesh = Box (0, 0, 0, 1, 1, 1, 1, 1, 1) File "/usr/...
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### Tutorial for flow around a cylinder in FEniCS

I am continuing my dive into computational fluid dynamics. I would like to build a simple test case for modelling the flow around a cylinder in FEniCS and then continue to model turbulence in order to ...
881 views

For the numerical integration of reaction terms in my PDE on a 2D triangular mesh, I would like to use the scheme $$\int_T \Phi(x) \approx \frac{|T|}{3} (\Phi(x_0) + \Phi(x_1) + \Phi(x_2))$$ where ...
437 views

### Poiseuille flow

I have probably a very stupid problem. I can't solve a simple Poiseuille flow in a straight 2-D channel driven by a pressure drop. Results are complete nonsense. (Setting zero pressure on the outflow ...
409 views

### Simple turbulence model appropriate for buoyancy-driven cavity like problem

Which turbulence model is suitable for resolving incompressible buoyancy-driven flow of a fluid within an cylindrical ampoule? I prefer turbulence model which is sufficiently simple so that fully ...
3k views

### Poisson equation: Impose full gradient as boundary condition via Lagrange multipliers

I have a physical problem governed by the Poisson equation in two dimensions $$-\nabla^2 u = f(x,y), \; in \; \Omega$$ I have measurements of the two gradient components $\partial{u}/\partial{x}$ ...
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### Fenics, initialize vector of degrees of freedom for function

With the move away from launchpad I hope this is the right place for this question. Is there a way to initialize the DOFs for a function? generated by u = Function(V) When I run a code which I ...
787 views

### Compute lengths of the longest edge of each cell

Having mesh = UnitSquareMesh(2, 2) Q = FunctionSpace(mesh, 'DG', 0) this works as expected ...