Questions tagged [fenics]
Questions about the finite element method software FEniCS and its subpackages (Dolfin, UFL, FFC).
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eigenvalues of inhomogeneous Helmholtz equation violate superposition using FEM
I am trying to solve the in-homogeneous Helmholtz equation with damping and forcing using finite element method (FEM) with FEniCSx. The equation is;
$c^2\nabla^2p - c^2\omega i d \nabla^2p + \omega^2 ...
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2
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1
answer
175
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Neumann BC in the current configuration in a finite-strain problem
For a hyperelastic problem, I understand the variational formulation can be written as the minimisation of $\Pi$ with
$\Pi = \int_{\Omega} \psi( \pmb{u} )dx - \int_{\partial\Omega} \pmb{T}\cdot \pmb{u}...
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63
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Accessing nodal and degree of freedom organisation in the solution vector in Fenics and Firedrake
Context
Let suppose a solution to a finite element problem (associated to a mesh) stored in a vector $X$ of size $(N \cdot d)$ corresponding to $N$ nodes in the mesh and $d$ degrees of freedom for ...
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81
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It is possible to solve integro-differential equations using in Fenics?
I am interested in solve the following integro-differential equation:
\begin{align}
\frac{\partial{\rho(\theta, t)}}{\partial{t}} = D \frac{\partial{\rho(\theta, t)}}{\partial{\theta^2}} - \beta \...
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1
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85
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How can I define an equipotential surface/volume in FEniCS?
I want to solve electrostatic problem for potential. Charge density and medium permittivity are known, so is the potential of a grounded surface. I know how I can implement that.
But I would like to ...
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1
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95
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Solving for two interconducting fluids in FEniCS
I'm trying to model in FEniCS a steady-state situation in which a coolant fluid flows through a nuclear fluid. There is finite rate of conduction between the two fluids. The simulation should output ...
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4
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1
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498
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Weak Formulation of Poisson's Equation for Electrostatics with Surface Charge
I am currently attempting to use FEnICS to solve an electrostatic problem with two materials of different permittivity $\varepsilon_1$ and $\varepsilon_2$ forming an interface:
Consider a domain $\...
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215
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Solving coupled PDEs with self-consistency condition
I am figuring out how to attack a problem (the Usadel equations of superconductivity) in which I need to solve a set of nonlinear PDEs for the fields $\{G_i (r)\}$
$$ U(G_i(r), \nabla G_i(r), \Delta(r)...
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0
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106
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Dolfin convert : How to interpolate data at vertices of (3D) cells?
I hope that one of you guys can help me because i have been stuck here for a week.
I am trying to read a gmsh file (.msh) using dolfin convert to XML and then download it with dolfin.
The thing is ...
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196
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How to use FEniCS to calculate the electric field of an isolated charged sphere
Initially I thought that this is the kind of question which ought to have already been answered in the form of an example online, but so far I haven't found one. I will admit that I am very new to ...
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FEM with elastic inhomogeneous properties leads to mesh-induced anisotropy
I'm solving an elastic homogenization problem and I'm having problems with mesh artifacts.
I would like to first give a brief summary of what I do: I have a system with inhomogeneous (but isotropic) ...
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52
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Add orthogonality constraint to PDE over entire domain finite element
I have a nonlinear differential equation for $u:\mathbb{R}^2\rightarrow\mathbb{R}^3$ that I can express in the form:
$ \nabla (g(u)_{ij} \nabla(u)^j) = 0 $
which is similar to the "Nonlinear Poisson" ...
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529
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Time-dependent Schrodinger equation implementation in FEniCS
For our Bachelors thesis we're trying to solve the Schrodinger equation $i\partial_tu = -\nabla^2u+Vu$ in FEniCS. Given the domain $[-5, 5]^2$ with an initial value of $u_0(x, y)=e^{(-2(x^2+y^2))}$ ...
- 119
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419
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Heat diffusion simulation in a 3D piston using FENICS
I'm trying to simulate the heat diffusion in a 3D piston. I marked the boundaries on GMSH.
I have used a Dirichlet BC of 300 on the top face of piston. But the results look abnormal. There is a ...
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496
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Immersed boundary method in FEniCS?
I have looked at the FEniCS tutorials and documentation but I cannot find any mention to the possibility of implementing an immersed boundary method (IBM) for fluid dynamics.
In particular, I want ...
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2
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How to use natural logarithm inside Expression on FENICS
I'm trying to evaluate the exact solution of heat diffusion in circular plate.
I'm not able to use the natural logarithm inside expression.
...
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147
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FEniCS, refinement not 'respecting' domain boundary
Short question: how to ensure that extra points are not included as 'boundary' points after calling the refine function.
More details.
I am working with a hexahedral mesh in $3$d. Let $X$ be the set ...
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0
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43
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Setting up diffusion with integral B.C. in Fenics
I'm trying to model diffusion through a cylindrical domain $D = \{ (x,y,z) : x^2 + y^2 \leq 1, \;\; 0 \leq z \leq 1\}$.
The is an initial concentration of the diffusant at the upper flat surface, ...
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1
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592
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Fenics: solving the same PDE multiple times
I am new to Fenics and just started reading the tutorial Solving PDEs in Python. For simplicity, we can refer to simplest example, page 17 (the linear poisson equation), despite not necessary.
My ...
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169
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FEniCS implementation of Maxwell equations for a dipole antenna
someone knows where I can find a FEniCS implementation of Maxwell equations for a dipole or other type of antenna? I mean a dipole antenna with an arbitrary geometry of every 'leg' in the dipole.
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83
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Coupling 1D-3D problem in FENICS
I was wondering whether any of you knew if FENICS has the capability to solve coupled 1D-3D problems that are linear non-iteratively? As an example, pipes embedded in a porous domain will provide ...
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Library for Discontinuous Galerkin method: FEniCS vs deal.ii
I am aware that both FEniCS and deal.ii are capable of solving problems with Discontinuous Galerkin (DG) method. I would like to specifically know if any of these two softwares can cater these ...
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3
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3k
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Spectral Element vs Finite Element
I am trying to understand the difference between SEM and FEM. If I go by this paper, spectral element methods are a subset of FEM methods and the only difference lies in the choice of basis functions. ...
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2
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2k
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Electromagnetism FEM (FEniCS) interpolation - leakage effect
As for the background of what is going on:
I'm using FEniCS that is dedicated FEM solver
The problem I'm solving is magnetostatic problem where the governing PDE is $$ \bf{\nabla} \times \frac{1}{\mu}...
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95
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Stokes Equation fails to converge for an ellipse
This might be because of the mesh, but the following code blows up for all values of b not 1. Does anybody have any experience working with the ellipse mesh in Fenics?
...
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2
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How to use MeshFunction in FEniCS (dolfin)?
I'm a beginner user of FEniCS and still struggling with some of the basics. Specifically,
I have some issues doing the tutorials in the Langtangen-Logg book Solving PDEs in Python - The FEniCS ...
- 123
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1
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667
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Load the mesh file with boundary marks
I'm want to load a mesh from a file, generated by triangle, and I want to use the boundary marks of its nodes (boundary marks of the file). It is possible?
Also, I can change the mesh generator (or ...
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329
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Solving Vectorial Poisson Equation in FENICS
I am trying to solve the following, "test problem" involving a vectorial Poisson equation:
$$-\nabla^2 \vec{A}=\vec{J} \quad \forall x\in\Omega=[-1,1]^3$$
$$ \vec{A}=\vec{0} \quad \forall x\in\...
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1
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1
answer
240
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Penalization parameter for DG with jump penalization
I adapted this FEniCS code for my problem and I'm wondering if there is any good resource about how to choose the penalty parameter $\alpha$? Best case would be, if I can define it through some ...
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2
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127
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Computable alternative to "almost everywhere"
I am working with finite elements for Maxwell's Equations (i.e. with Nedelec's edge elements) and for computation I'm using the FEniCS-project. While implementing the Augmented Lagragian Method, I ...
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137
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Hello word in FEniCS? [closed]
I am trying to start using FEniCS, but have a problem with the simple hello world examples given in the books. Could you please give me the simplest hello world ...
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Anyone knows where I can find a simple FEniCS code where I can understand basic implantation? [closed]
I found this one, but does not work: http://www.karlin.mff.cuni.cz/~hron/warsaw_2014/pl2014_lecture5.pdf
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2
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854
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Schrödinger equation with time dependent Hamiltonian
I need to solve the Schrödinger equation with a time dependent Hamiltonian
$$i\hbar \frac{\partial}{\partial t} \Psi = \left[-\frac{\hbar^2}{2m}\nabla^2 +\frac{1}{2} k(t)(x^2+y^2) + V(r)\right]\Psi $...
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computational tool for higher order Lagrangian interpolation for finite element
In finite element, I can calculate the Lagrangian interpolation shape functions for each degree of freedom in an element, from the the number of nodal degrees of freedom and the number of nodes ...
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3
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Are there any "light-weight" FEM packages around?
Basically, FEM seems to be a problem that is pretty much "solved". There are numerous powerful frameworks existing, like Trilinos, PETSc, FEniCS, Libmesh or MOOSE.
One thing they have in common: They ...
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2
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1k
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Developing a C++ solid mechanics program
I am a beginner in computational science and programming. I am doing research in non linear solid mechanics analysis and using C++ for coding. I have been exploring various finite element open source ...
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2
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185
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What would be a simple approach to validate a wave propagation code?
I have a linear elastic wave propagation code and an elastoplastic wave propagation code based on FEniCS.
For now, I keep the 2D mesh (100, 100) fineness unit square and give a source wave of $\sin(...
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1
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imposing "measured data" to Dirichlet boundary conditions in fenics
I'm relatively new to fenics and I just looked through all questions related to Dirichlet boundary conditions. I don't seem to find a well-described question or answer about what I'm about to ask.
I'...
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0
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397
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How to add a Ricker Wavelet (Mexican Hat) to a 2D/ 3D fem mesh?
I have a 2D square mesh and a 3D beam shaped mesh and I want to propagate a seismic wave in them. I am trying to simulate them using Open source FEM codes (fenics). I have left the top surface to be ...
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Weak form for elastoplastic wave propagation
I am trying to simulate elastoplastic seismic wave propagation using Fenics Solid Mechanics Application.
The app. provides some quasi-static demos to show elastoplastic behaviour in a cube/ beam/ ...
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105
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Need suggestions on how to implement this time stepping for wave equation [closed]
I have the following system of equations obtained by implementing Sympletic Euler time scheme to wave equation. I want to model this in Fenics. Here 'u' is the displacement and 'p' is corresponding ...
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FEniCS: both normal and shear stress boundary conditions for elasticity? [closed]
I would like to have both the normal (xx) component and shear (xy) component of a 2D (stress) tensor defined on a boundary (y=const, for instance) for an equation which is of the type
$$
\nabla \cdot ...
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1
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FENICS subdomains - restriction/ prolongation operators
I am trying to implement my own multigrid method in fenics. Is there any "smart/ fenics" way how to assemble subdomains and obtain restriction/ prolongation operators ?
Thanks!
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160
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Petrov-Galerkin enrichment method for Darcy equation
I was reading about Petrov-Galerkin Enrichment Method for Darcy equations. Here are a couple papers that discuss this in detail:
A Petrov–Galerkin enriched method: A mass conservative finite element ...
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1
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242
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Please explain the meaning of these Boundary conditions [closed]
I am trying to learn Gmsh and Fenics and was looking at an example which shows the application of Boundary conditions on a simple Poisson problem.
Here is the link:
http://fenicsproject.org/...
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Comparing various implementations/software packages for large-scale finite element simulations
I currently use FEniCS and Deal.II to solve various FEM problems. I am also writing my own implementation of these problems by directly implementing the data structures, routines, and solvers within ...
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0
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375
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Stationary 2D/3D Navier-Stokes source code
Trying to solve stationary Navier-Stokes problem for incompressible laminar Newtonian fluid.
I've found a couple solutions for instationary Navier-Stokes equations (like FeniCS examples or CFD Python)...
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2
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1
answer
424
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Filling out a mesh (for Fenics FEM)
I have been using Fenics to model some simple electrostatic problems, but now I need to simulate more complicated geometries. Assuming
I have created a mesh of several objects, and know their ...
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1k
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Poisson equation with pure Neumann boundary conditions (using FEM)
I am trying to derive the correct variational form for the Poisson equation with pure Neumann boundary conditions, and an additional contraint $\int_{\Omega} u \, {\rm d} x = 0$, as described in this ...
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218
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4th order tensor [closed]
I'm new with FEniCS and Python and I'm stuck with this issue:
is there a way to write a 4th order tensor in an easy way to implement?
I have to compute the following stiffnes tensor:
$A_{ijkl}= \...
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