Questions tagged [finite-element]

A means of solving ordinary and partial differential equations. The domain of the problem is broken up into elements, and the solution in each element is expanded in a basis of functions. The Finite Element Method lends itself well to adaptive refinement, irregular geometry, and good error estimates.

Filter by
Sorted by
Tagged with
1
vote
0answers
426 views

FEM Stiffness and Mass matrices for 2d cubic trial functions

I want to use FEM to solve a 2D eigenvalue problem for the biharmonic equation \begin{align} &K \psi= \lambda M \psi\\ &\psi=\nabla \psi\cdot \hat{n}=0\quad \text{on boundaries} \end{align} ...
0
votes
2answers
303 views

Boundary conditions for streamlines in enclosed flow

I am trying to solve Lid driven square cavity flow problem of Stokes equation using finite element method. I have boundary conditions for velocity as zeros on every boundary but u=1 on top boundary. ...
2
votes
2answers
187 views

How to precondition FEM problems using domain decomposition?

Let's say that I have a FEM code which yields the following problem: $$ \mathbf{A}\mathbf{x} = \mathbf{b}. $$ In order to solve this more efficiently with an iterative method, I would like to ...
1
vote
3answers
812 views

Pressure boundary condition in lid driven cavity using finite element method

Thank you all 1.) I am trying to solve lid driven cavity problem for an incompressible Stokes and Navier Stokes equations using general "Mixed" finite element method. dirchlet boundary conditions are ...
0
votes
2answers
340 views

Imposing total pressure over surface in FEM

I am trying to solve Stokes problem using Finite element method. My question is how to impose that total pressure over the surface is zero to remove the constant pressure mode?
1
vote
0answers
50 views

Computing dilogarithm

I'm measuring the integral of a quantity which, mathematically, requires the computation of a dilogarithm function. $$\operatorname{Li}_2(be^{ax})$$ where $b$ and $a$ (are real and) can be positive ...
1
vote
1answer
172 views

FiPy: Make diffusion coefficient dependent to orientation

I'm trying to solve the heat equation in FiPy and right now it works, but I have one problem: The material I have to simulate has different diffusion coefficients in the x and y direction (due to its ...
1
vote
1answer
1k views

Line integral along the edge of an isoparametrically mapped triangle

I need to integrate the following function on the line segment from $P_{1} = \begin{bmatrix} -2\\-1 \end{bmatrix}$ to $P_{2} = \begin{bmatrix} 1\\2 \end{bmatrix}$: $$\int_{P_{1}}^{P_{2}} 4x + y \ ds$$...
1
vote
0answers
97 views

Do DG methods for the Helmholtz equation always return positive quantities?

Helmholtz Diffusion equation with reaction term: $$ k\Delta u + u = f ~ \text{in} ~\Omega $$ $$ \nabla u \cdot \mathbf{n} = 0 ~ \text{in} ~\partial \Omega $$ For sufficiently small $k$ (relative to ...
1
vote
1answer
761 views

Computation of stiffness matrix with variable coefficient

I am implementing a finite element solver (in 2D) to solve the generic differential equation : $$-\nabla(a(x) \nabla u) = f$$ Brief explanation By integrating and multipling by a test function, the ...
0
votes
1answer
100 views

Need clarification on a piece of book excerpt about spectral element method!

I am reading "Using MPI (3rd edition)" from William Gropp, where in chapter 4 application section 4.13, it introduces an MPI application Nek5000/NekCEM which is based on spectral element method (SEM) ...
1
vote
1answer
76 views

How to deal with multi-region problems (in PETSc)

Consider a problem where space is filled with a liquid and a solid phase, with a large, complicated geometry. On each of the phases, there's an electrical potential/poisson equation. The equations are ...
1
vote
1answer
327 views

Algebraic multigrid in PETSc

Consider a potential/poisson equation on a very large, complicated geometry. Currently, an self-written FEM and linear solvers from NumPy are used. Performance is, of course, not good enough for ...
-1
votes
1answer
670 views

Eulerian vs Lagrangian vs Mesh-based vs Meshfree/Meshless methods

Hailing from the scicomp community recently getting into computer-graphics, I have noticed that the scicomp communities talk about mesh-based methods like FDM, FVM, FEM, etc, vs meshfree or meshless ...
3
votes
0answers
146 views

Alternating Schwarz does not converge without Dirichlet conditions on physical boundaries

Note: Thanks to comments, I realized that I have two problems, each which can be described more clearly on its own. This revised question covers the first. I would like to solve $$ -\Delta u - 1=0,\...
0
votes
1answer
168 views

Ritz, Galerkin, Weak Form, FEM: How to catch up the basics? [duplicate]

I have to deal with FEM and the numerical solution of PDEs a lot. While I'm doing ok when just applying or implementing it, I observe a lack of understanding when authors begin to argue with "Ritz", "...
2
votes
0answers
60 views

How can I numerically solve a saddle point problem with repeated constraints?

I am interested in numerically solving the following constrained minimization problem; Find the value of $x\in \mathbb{R}^n$ that minimizes $f$ where $f\colon \mathbb{R}^n\to \mathbb{R}$ is defined ...
-1
votes
1answer
73 views

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
2
votes
2answers
647 views

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 $...
3
votes
1answer
138 views

What is the global problem in the two-level additive Schwarz?

The two-level additive Schwarz method (additive Schwarz with a coarse space correction) is often written like this: $$ \mathbf{v} = \sum_{i=0}^N \mathbf{R}_i^T \mathbf{A}^{-1}_i\mathbf{R}_i\mathbf{w} $...
7
votes
0answers
234 views

What can be done with Finite Element Method and not with the Finite Volume Method, and vice versa?

What are some applications where you would absolutely go for either FEM, but not FVM, or vice versa? What are some applications where both methods are equally suited? I worked with the FEM so far and ...
2
votes
1answer
134 views

How to determine if Kelvin-Voigt elements are dissipating stress correctly?

I am using a program that creates viscous/absorbing boundaries by implementing Kelvin-Voigt elements. The theory behind 1-D Kelvin Voigt elements is given in this Wikipedia page. In my case I am ...
1
vote
0answers
114 views

Strange solutions using Finite Element Analysis

I've implemented the Finite Element Method to model the heat transfer between two different materials where one material is surrounded by the other. When I run the model I'm getting some strange ...
3
votes
1answer
181 views

Resources for solving fluid-structure interaction problems

I would like to get started solving Fluid-Structure interaction problems. I already have some experience with Finite Elements, including my own MATLAB and Julia software packages for developing ...
10
votes
1answer
369 views

DG local equation, how to interpret mean-averaged test function

In the paper http://www.sciencedirect.com/science/article/pii/S0045782509003521, an HDG element-local equation is described on page 584 equation (4), with one of the equations taking the following ...
1
vote
1answer
165 views

Fully discrete finite element method for 1D dynamic euler-bernoulli beam problem

I am trying to solve a 1D initial boundary value problem in MATLAB using Finite Elements with time stepping, for the purpose of learning scientific computing and to build up to more difficult problems....
0
votes
1answer
210 views

Euler-Bernoulli beam element versus continuum beam element

I am using OpenSees to model a simply supported beam with a point load in the middle. The model is in consistent units. The beam is made up of bilinear quad elements. I have used 30 elements along the ...
2
votes
1answer
123 views

Newton's method stagnates at small error

I have a system of the form $$A(u)f(u)=b$$ where $A$ is basically a matrix originating from the Finite Element Method. I try to solve it using the Newton method: $$R = A(u_{i}) f(u_{i}) - b $$ $$...
0
votes
1answer
92 views

Newbie help on FEM contact problem

I am modelling the time-evolution of a soft material with a tetrahedral mesh. I use an FEM method to compute the forces on each node, and then numerically integrate the positions and velocity of the ...
4
votes
3answers
704 views

Pre/Post-processor for an academic finite element solver

I'm currently developing a finite element solver for academic/research purposes. Therefore I'm searching for a pre- and postprocessor in my toolchain. For a previous project I have used gmsh as a ...
4
votes
1answer
298 views

Interpolating a mathematical function using a Hermite Cubic Finite Element Space

I have a Hermite Cubic Finite Element Space on a computer in the form of Matlab m-files. More specifically, I can evaluate four "shape functions" $N_1, N_2, N_3,$ and $N_4$, for which the following ...
0
votes
2answers
593 views

Mixed formulation of the Poisson equation (FEM)

I'm solving the Dirichlet problem for the Poisson equation in a 2d domain $D$: $$ \begin{cases} \Delta u = 0 \quad \text{in $D$}, \\ u|_{\partial D} = u_0. \end{cases} $$ I'm interested in ...
1
vote
0answers
64 views

How to get a theoretical background in nonlinear, coupled FEM systems

I'm currently developing simulations for coupled, nonlinear, multi-region systems. Basically, I use the Finite Element Method (FEM) to model each physical quantity in each region. The obtained ...
7
votes
0answers
523 views

Numerical implementation of the Dirichlet-to-Neumann map

I am solving the Dirichlet problem $$ \begin{cases} \Delta u = 0, \\ u|_{\partial D} = f, \end{cases} $$ in a $2d$ domain $D$ using the finite element method. What I want to get is the ...
1
vote
0answers
53 views

energy computation for BVP with Dirichlet boundary conditions

I am solving quadratic minimization problem \begin{align} \min_{x}\ \frac{1}{2} x^T A x -b^T x, \end{align} where matrix A results from discretization of Laplacian by FEM method, subjected to ...
1
vote
0answers
365 views

Implementing Neumann boundary condition for elasticity problem using the finite element method

I am solving the following mixed boundary elasticity problem with the finite element method on the unit circle, using a triangle mesh with 3 nodes on each element. In my problem I know $u_1$ and $t_2$...
1
vote
0answers
156 views

How to generate a tet10 mesh from a tet4 mesh

I am writing a FEN solver on tet10 elements. I right now have a CFD grid gen tool (Pointwise) which generates tet4 meshes. From this I have the element connectivity list and the node list. How do I go ...
4
votes
2answers
396 views

Solving Poisson equation with current BC using FEM

I have a 3-dimensional domain D, with 3 types of BC which I am trying to solve the Poisson equation on. $$-\nabla \cdot (\sigma(x,y,z)\nabla u)=0$$ Insulator (Neumann BC) Electrode set at some ...
1
vote
2answers
251 views

Assemble P2 finite elements - Matlab or references

I would like to implement P2 (or even P3...) finite elements in Matlab. I need to be able to control the construction of the rigidity and mass matrices ($ \int \nabla \varphi_i\cdot \nabla \varphi_j$ ...
1
vote
1answer
358 views

FEM on tet10 element: negetive determinant at the Gauss point

I am trying to implement a fem code on tet10 elements. I follow the lecture notes for tet10 implementation given in http://www.colorado.edu/engineering/CAS/courses.d/AFEM.d/AFEM.Ch10.d/AFEM.Ch10.pdf ...
0
votes
2answers
144 views

Halo Region Communication in Unstructured Mesh Problems

I'm currently using ParMETIS and it is required to determine the halo region of the local elements in a parallel unstructured mesh. Assume that the mesh is large and cannot be stored on a single ...
1
vote
0answers
59 views

FEM/FVM/FD for structural modeling and stability issues due to large structural constants?

I've read that in modeling structures problems, the finite element method (FEM) is typically used. I am unfamiliar with FEM, but I am wondering, in particular, if using FEM, as opposed to finite ...
2
votes
1answer
145 views

What's the definition of $L^{\infty}$-norm for nonconforming finite element?

We know that \begin{align*} \|u\|_{0,\infty,\Omega}={\text{ess} \sup}_{x\in \Omega}|u|. \end{align*} Moreover, the nonconforming Crouzeix-Raviart finite element space is \begin{align*} V_h=\{ v|_K\in ...
5
votes
2answers
1k views

Evaluating the surface integral in an FEM (Finite Elements Method) procedure

I want to evaluate the Surface force integral in an FEM procedure. The basic reference tet is shown in the figure. The faces are numbered corresponding to the node opposite to them. For example the ...
0
votes
2answers
474 views

Correctly setting boundary condition for periodic linear elasticity problem

From an old, wise engineering book Peterson's Stress Concentration Factors (http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0470048247.html page 324) I've got the following problem: There is 2D ...
1
vote
0answers
80 views

Discrete operator textbooks

This will be a vague question. When I was writing a finite element matrix assembly routine, a colleague noticed that I had a bug in my code because the sparsity pattern of the one of the blocks didn'...
0
votes
2answers
88 views

Parabolic differential equations with time delay

Let $d_1=1,d_2=2,a_{11}=\frac{5}{13},a_{12}=\frac{22}3,a_{21}=-2,a_{22}=\frac{6}7,\tau=\frac{5}7$, $\psi(t,x)=\cos^42x,\phi(t,x)=\frac{3}{13}x^4\sin^2 3x$, $\Omega=[0,200]$ How to solve: $$\left\{ \...
0
votes
1answer
314 views

FEM implementation on tet10 element stiffness matrix:(code snippet provided) [duplicate]

I am trying to implement a fem code on tet10 elements. I do not prefer to use open source at the moment as I would like to have the basic feel over the algorithm. I closely follow the lecture notes ...
2
votes
1answer
126 views

Higher order interpolation in DWR method

Based on page $35$ of the book: (W. Bangerth and R. Rannacher, "Adaptive Finite Element Methods for Solving Differential Equations", Birkhäuser, 2003,) for computing the error in dual weighted ...
5
votes
3answers
819 views

Computing accurate fluxes with FEM

I have solved Poisson equation on a 3d domain with neumann and dirichlet boundary condition. I get the potential, take the gradient for each element and integrate on a surface of an element, I do this ...

1
4 5
6
7 8
17