# Questions tagged [unstructured-mesh]

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### Which algorithms exist to create a tetrahedral volume mesh from an STL file?

Basically just that. I am trying to write a C++ program that reads in an STL and should compute an unstructured tetrahedral volume mesh based on the surface triangulation given by the STL file. I ...
1 vote
35 views

### Simultaneously partition all mesh elements (nodes, edges and cells) among processors

The numerical method that I'm implementing stores various fields in various elements of an unstructured triangular mesh. Data may be stored in cells, nodes and even edges of the mesh. For a parallel ...
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### Convert unstructured mesh to structured mesh

I need help to know, how can I convert an unstructured 2d mesh for structured mesh? (Software Gmsh version 4.9.3). This is my script in Gmsh. ...
124 views

### Unstructured mesh preprocessing

For solving PDE with self written code it is needed to preprocess the data from mesh generators. I recently started shifting from cartesian grid to unstructured. I finished reading up to FVM part of ...
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1 vote
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### Interpolation of a Concave Mesh

I would like to have an algorithm that interpolates the values attached to nodes in a concave mesh mesh. To be me precise, assume we have a point cloud P (e.g. in 3 dimensions) and a list of edges E ...
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### Partition mesh into predetermined submeshes

I have a mesh already partitioned into disjoint groups of cells. What I want to achieve is the following. Obtain the adjacency graph for the cell groups. Partition the mesh, i.e. generate submeshes ...
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### Developing a meshfree contouring algorithm

I would like to find the contours of a scalar function $u(x,y)$ available as a discrete set of function values $u_i = u(x_i,y_i)$ over a scattered set of points $(x_i,y_i), i=1,...,N$. In my case, the ...
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1 vote
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### How to evaluate the average value of a polynomial inside the triangle area in finite volume sense?

Consider we have a linear bivariate polynomial: $$p(x,y)=ax+by+c.$$ To construct the linear polynomial using least square method, we need to evaluate the value of the average polynomial $p$ in at ...
350 views

### Meshing surface of a sphere with a subdomain

I am trying to build a triangle mesh of the surface of a sphere which also includes a subdomain defined by a 'polygon'. Here is a successful example (subdomain defined by the red dots): Note that the ...
74 views

### How to calculate the interior value of triangular element in edge (vector) finite element?

I was using an edge (vector) finite element to solve electromagnetic diffusion (two-dimensional cases). The element that I used was a triangular element. I have got the result of the finite element in ...
1 vote
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### How to compute gradient of a cell having a boundary face?

In many situations in unstructured mesh solvers, one needs to compute gradient of arbitrary variable $\phi$ such as temperature or velocity at face centers (one of such situations is correction for ...
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### How to calculate skewness for a mesh?

I am writing a code to calculate mesh quality stats such as: cell volume, face areas and non-orthogonality between faces (basically something like OpenFOAM's ...
• 284
1 vote
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### Stress visualization for structured and unstrcutured mesh

I put together a FEM solver to do some structural analysis. At the moment I am trying to add stress visualization feature to my code. The post-processing is done with Paraview and the results with ...
• 418
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### How is central difference scheme second-order accurate?

In an arbitrarily unstructured mesh, shown in the figure below, in the context of finite volume method, I want to obtain an approximation of $\phi_f$, where $N$ and $P$ are cell centers of adjacent ...
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### Parallel mesh partitioning

When a mesh partitioning takes place and every process works on a part of the mesh is any way to rename the global numbering of nodes(on each process) into a local numbering?Is there any software that ...
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### Why FVM can handle unstructured meshes while FDM cannot?

How come Finite Volume Method(FVM) handle the unstructured meshes and Finite difference Method cannot, whereas in FVM to approximate the fluxes at the boundary we use the central differencing? My ...
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### 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 ...
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### 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 ...
548 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 ...
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1 vote
506 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 ...
518 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 ...
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1 vote
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### 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 ...
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1 vote
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### 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 ...
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1 vote
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### 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 ...
1 vote
64 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 ...
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### 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 ...
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### 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 ...
665 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 ...
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 ...
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1 vote
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### 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 ...
221 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 ...
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### 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 ...
69 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. ...
140 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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
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### 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 ...
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1 vote
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### 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. ...
254 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, ...
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27 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 ...
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### 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 ...
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### 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
209 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 ...
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1 vote
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### 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}...
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1 vote
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### 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 ...
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### 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{\...
1 vote
451 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?
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