All Questions
112 questions
2
votes
2
answers
302
views
How to find out the difference between a structured and unstructured mesh using the file containing the mesh information?
I have two different mesh files (both are .inp files obtained from Abaqus) that represent the exact same geometries with the same boundary conditions, etc. The only difference is that one of them is ...
- 600
3
votes
0
answers
108
views
Correct approach for thermal finite element simulation of layered assembly
I would like to optimise the heat transfer on a PCB. Several dies are on the top and cooling air is going through the fins in heat sink on the bottom. The assembly consists of several layers like ...
- 570
2
votes
1
answer
434
views
Solution method of nonlinear heat transfer analysis
The governing equation of transient heat transfer analysis is described as follows:
$$C \frac{dT}{dt}+K T = Q$$
When using backward difference scheme for the discretization of the time we get the ...
- 840
0
votes
1
answer
51
views
Produce vertex displacements from volumetric shrinkage data on unstructured meshes
I was wondering what would be an efficient way to produce compatible displacements for mesh nodes/vertices if the computed data is volume shrinkage of each element/cell in the unstructured mesh?
...
- 1,413
2
votes
1
answer
311
views
Lumped matrices in thermal analysis using finite elements
The governing equation of the transient heat transfer problem is
$$C \frac{dT}{dt}+K T = Q$$
$C$ is the heat capacity matrix. $K$ is the thermal conductivity matrix. $T$ is the temperature vector. $...
- 840
4
votes
0
answers
488
views
Why wall shear stress calculated from LBM directly and the one calculated based on velocity profile are so different in some cases?
First of all, I hope you accept my apologizes if my question seems off topic here. But, I asked this question in ParaView forum and after a week still I did not receive any response yet, so I'm ...
- 2,332
6
votes
0
answers
743
views
Are there well-known methods for navigating on kd-trees?
When you have a mesh, there are many well-known methods to navigate it, as for example using a half-edge data structure, that allows easy circulation around faces and vertices.
Are there similar ...
- 617
1
vote
2
answers
191
views
Simulating the heat equation with insulating material
My plan is to solve the heat equation in the right half portion of the domain, while having the left half completely isolated with constant temperature. To do so, I model the left half with a very low ...
- 601
0
votes
2
answers
1k
views
(FEM) 1D time-dependent heat equation convergence problem
I'm simulating a simple 3-node bar with convection BCs at the edges to validate my FEM code. The following data was used:
Initial temperature = 25 ºC
Temperature surrounding the rod = 10 ºC
Thermal ...
user30551
0
votes
1
answer
614
views
Heat diffusion - Is this the correct approach to include Newmann boundary conditions?
Thank you for looking at this problem. Is this the correct approach to include neumann boundary conditions? With this solution temperature is not correct, and there´s no diffusion. The model seems ...
- 3
1
vote
1
answer
723
views
How I could calculate L2 norm of an unstructured grid?
I want to calculate L2 norm of a 3D unstructured grid to compare my simulation results in two different mesh sizes as coarse and fine. I read this answer and it seems in three-dimensional space, I ...
- 2,332
1
vote
1
answer
15k
views
Python Finite Difference Schemes for 1D Heat Equation: How to express for loop using numpy expression
Hello all,
I've recently been introduced to Python and Numpy, and am still a beginner in applying it for numerical methods. I've been performing simple 1D diffusion computations. I suppose my ...
4
votes
2
answers
742
views
Is there any open-source code for a hybrid 2D mesh (triangles and quadrilaterals)?
The question is pretty much the title. Note that I have lots of experience using open-source meshing tool, e.g. Gmsh and OpenFoam blockMesh & snappyHexMesh. Nevertheless, I have no idea on how to ...
- 253
1
vote
1
answer
302
views
Libraries to deal with unstructured grids
I am dealing with a *.cgns file. This mesh format, when saved as an unstructured grid, holds nodes coordinates, nodes connectivity per element and boundary ...
- 77
0
votes
1
answer
68
views
Modeling Diodes in Autodesk CFD
I'm extremely new to Autodesk CFD, and I'm working on a project that deals with diodes heating up and cooling down based on a fixed temperature regulated by a temperature switch. Basically, I have a ...
1
vote
0
answers
68
views
Combining fluid flow solver based on lattice Boltzmann method with a mechanical deformation solver based on finite element method
I'm thinking to couple my fluid flow solver based on lattice Boltzmann method with a mechanical deformation solver based on finite element method to take account for solid deformation in my models. In ...
- 173
1
vote
1
answer
1k
views
C++ library unstructured mesh writer to VTK format (or similar)
I am working on a 2D unstructured code in C++. I am using gmsh to generate a 2D unstructured mesh and reading it into my program with a library called ...
2
votes
1
answer
709
views
Solve 3-D Heat equation with Neumann boundaries
I want to solve the Poisson PDE for heat flow in a 3-D solid cube with given dimensions $x$, $y$, and $z$:
$$\rho C\frac{\partial T}{\partial t} = k \Delta T$$
The cube is irradiated with a constant ...
- 21
1
vote
1
answer
378
views
Analytical testcase for 2D/3D anisotropic Diffusion (Heat Kernel)
I want to verify and compare different Discretizations of the anisotropic diffusion equation in 2D / 3D.
In order to both test the timestepping and the spatial discretisations I had a look at using ...
- 11
8
votes
1
answer
550
views
Computing geodesic distances with diffusion
I am trying to solve an APSP (All-Pair Shortest Path) problem on a weighted graph.
This graph is actually a 1, 2 or 3 dimensional grid, and the weights on each edge represent the distance between its ...
- 131
1
vote
0
answers
69
views
Efficient initial identification of solid or liquid domains for a block structured Cartesian grid generation system
INTRO
Within the last 5 days I was able to generate a block structured Cartesian grid
generation system with a combination of Fortran,C++ and Python.
I am running intersection tests of the ...
- 11
6
votes
2
answers
969
views
Unstructured mesh vs hybrid structured/unstructured for numerical simulations
While answering one of the questions on meshing process, I encountered a lack of understanding on my end for the comparison of the mesh quality.
First, consider an unstructured mesh created in GMSH ...
- 8,742
0
votes
1
answer
99
views
Solving the diffusion/heat equation for a randomly distributed set of points in 3D
In this problem I am trying to solve, I have a messy set of points distributed in 3D space, each with a defined temperature. If I would want to calculate the heat transfer scenario in this system, how ...
- 121
1
vote
0
answers
953
views
Methods and tools to solve the two-temperature model (TTM)
I would like to model heat diffusion at the gold / water interface after excitation of the metal surface by an ultrafast laser pulse (ca. 80 fs).
An appropriate model to start with would be the "two ...
- 21
2
votes
1
answer
887
views
Convert Unstructured Mesh to Structured
I have solved a simple problem on Openfoam, which is a 3D rectangular parallelopiped, filled with rectangular hexahedrons as mesh elements. The structured, mapped mesh was made in ICEM and solved in ...
- 149
0
votes
0
answers
89
views
Reconstruction of cells information when given mesh in polyMesh format [duplicate]
The polyMesh format used in OpenFOAM is an intelligent format for which 'cells' file, i.e. the file giving list of nodes that make a cell, is not needed. The way to reconstruct geometry data such as ...
- 1,413
1
vote
0
answers
212
views
BTCS-like method for heat conduction in unstructured triangular grid
I want to write a simple simulation for heat conduction in a unstructured triangular mesh.
I already made it work for a structured rectangular grid with the ADI method, but now I need more complex ...
- 23
0
votes
2
answers
285
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 ...
- 587
7
votes
2
answers
784
views
Mesh ordering algorithms used by COMSOL Multiphysics
Ordering of elements in an unstructured mesh is undoubtedly very important for the performance of computations. For example, it determines the structure of sparse matrices arising from PDE ...
- 442
0
votes
1
answer
87
views
simple and fast graph-clustering for paralelization of finite element simulations
I'm learning to use OpenCL to optimize some of my simulations. I realized that I need some sort of Graph-clustering or graph-partitioning to exploit efficiently local memory for un-ordered meshes.
...
- 937
2
votes
0
answers
161
views
scalable parallel mesh/amr on unstructured grid
I am trying to code a scalable parallel AMR for unstructured grid. There seems to be three approaches for this
a) Store some global grid info on each processor and partition with parmetis (The ...
- 233
1
vote
2
answers
398
views
V-cycle Multigrid for 2D transient heat transfer on a square plate using finite difference
I'm currently developing a program to solve 2D transient state heat conduction on a square plate using the V-cycle multigrid. Althought my program is able to reach the steady state solution, it's ...
- 11
6
votes
1
answer
296
views
Working with large mesh files
I am working on some medium to large scale finite element codes. By using established and available tools I am able to have an algorithm that scales well up to about 10,000 cores. Investigating ...
- 3,293
0
votes
2
answers
976
views
2D mesh generator with geometric primitives
The question is exactly as the title:
Which 2D (triangular) mesh generator software can be used which has a set of geometric primitives, controlled mesh size and standard output (.vtk or something ...
- 254
5
votes
1
answer
574
views
Finite volume a posteriori error estimation
I'm wondering what alternatives there are to a grid convergence study to judge solution accuracy for a given grid resolution when doing steady-state RANS simulations on an automatically generated ...
- 729
0
votes
1
answer
232
views
Meshing software: connectivity between elements and boundary
I am implementing an algorithm which produces a 4d mesh for a cylinder with a given 3d base. This means, I have a 3d mesh and I want to generate a 4d mesh for the corresponding space-time cylinder.
...
- 254
1
vote
2
answers
2k
views
Finite Difference Grid Spacing and Scaling
I have been exploring finite differences and heat transfer using the 2D heat equation to further expand my knowledge. So far I think it is going well.
I am running into some confusion around grid ...
- 11
0
votes
1
answer
853
views
Heat equation with Neumann and Dirichlet conditions on same boundary
I am looking at numerical solutions to the heat equation with Dirichlet and Neumann conditions on the same boundary. That is $u(x,t)$ satisfying
$$
u_t = u_{xx}\,, \quad x \in[0,1]\,, \quad t>0\,,...
- 531
1
vote
1
answer
644
views
Physical interpretation of L2 norm of heat equation solution
For the heat equation
\begin{equation}
u_t(t,x) = \nu u_{xx}(t,x)
\end{equation}
for $x \in [0,1]$ with boundary conditions $u(t,0) = u(t,1) = 0$ and initial value $u(0,x) = u_0(x)$ it is easy to ...
- 1,273
2
votes
2
answers
1k
views
Getting adjacent cells map for an unstructured polyhedral mesh
I am doing a little project on solving the heat equation using finite-volume method on a solid cube, I converted the polyhedral mesh of the cube to an OpenFOAM mesh.
I have a Python code where I ...
- 304
1
vote
1
answer
104
views
Common nodes in two FEM grids
There are two independent tetrahedral FEM grids. Second grid is subset of the first. By subset, I mean: nodes from the second grid are exactly in the same positions as some nodes from the first grid. ...
16
votes
1
answer
276
views
Usefulness of elements with mesh-dependent stability
After doing some mathematics related to the stability of elements in 3D Stokes problem I was slightly shocked to realize that $P_2-P_1$ is not stable for an arbitrary tetrahedral mesh. More precisely, ...
- 2,104
2
votes
0
answers
36
views
Choosing suitable polynomial degree based on information in advection stencil
I'm working on a finite volume advection scheme for unstructured meshes which uses a multidimensional polynomial weighted least squares fit for interpolating from cell centres onto faces.
In 2D, the ...
- 222
5
votes
1
answer
674
views
unstructured grid AMR
Are there libraries for conducting parallel AMR on an unstructured grid ? For a finite volume code, polyhedral cells with arbitrarily shaped faces are as easy to handle as hexahedra, and infact ...
- 233
4
votes
0
answers
561
views
Large meshing with tetgen [closed]
So I have a point cloud that I am creating a 3D flat rectangular surface from. I'm then turning it into a hollow box and connecting the corners by just dropping this surface mesh down. I need it to ...
1
vote
1
answer
219
views
Conceptual question about fitting of scattered data
What are the problems that arise when fitting (2D or 3D) a set of scattered data? (non uniformly distributed)
I had some data I had to fit and I solved the problem using the ...
- 402
1
vote
1
answer
269
views
Jacobian matrices on unstructured grids: underlying map?
Suppose I have an unstructured polygonal mesh system like so:
Each node $x$ has Cartesian coordinates $(x_1,x_2)$, so for a given node can form matrices like this:
$$
J(x,y,z) = \left(\begin{array}...
- 423
1
vote
3
answers
704
views
Parallel solver for sparse matrices on unstructured grids
I am trying to solve Euler equations on unstructured grids. Consequently, the problem reduces to solving Ax=b where A is a ...
- 293
3
votes
4
answers
3k
views
Computing the derivative on a mesh
I have a 2-D mesh of triangles and I have a scalar function $f(x,y)$ defined at all the vertices of this mesh.
I want to accurately estimate the values of $\frac{\partial f}{\partial x}$ and $\frac{\...
- 131
1
vote
1
answer
542
views
Number of faces in a 3D multi-type unstructured grid
Given a 3D unstructured grid consisting of mixed types of shapes (hex, tet, ...), is there a method to know how many faces (including boundary faces) are contained in the grid?
- 293