I have a complicated 3d shape which I have created in Autocad that needs to be analyzed in SAP2000.
SAP2000 is only capable of reading a 3D solid made out of Polygon Mesh.
The present Autocad Versions can only mesh as Polyface meshes.
Is there any software that converts 3D solid to Polygon Mesh.
I have tried GMSH, SALOME. The meshing is good but again they mesh them as a Polyface and not Polygon.
There are several ways to tackle it:
You can try importing the DXF/DWG directly to SAP2000. Sometimes, you have to Explode complicated surfaces in AutoCAD to be importable.
You can also save it in the IGES format (at least, via GMSH/Salome) and import it into SAP2000 then.
This would generally import the model into SAP2000, not the mesh. However, I don't see why that would be a problem since you are already starting from a solid CAD model in AutoCAD.
This page on SAP2000 website describes different ways to import into SAP2000.
Related
I want to create a structured mesh with boundary layers over an rather complex geometry in GMSH. For this reason I need to seperate my geometry to smaller portions, one of them is pictured:
Since structured meshes can only be created by extrusion, i would like to know wether it is possible to extrude a rectangle with a dilation, or if there is any other workaround known to generate a similar shape with a structured mesh.
In gmsh structured meshs can also be generated with the 'transfinite' commands.
See examples/simple_geo/hex.geo in the gmsh installation directory for an example.
I'm trying to use Polygonal Surface Reconstruction with building point cloud to create simplified building models.
I did first tests with this CGAL code example and got first promising results.
As an example, I used this point cloud with vertex normals correctly oriented and got the following result from PSR. Some faces are clearly inverted (dark faces with normals pointing inside the watertight mesh and therefore not visible).
I was wondering if there a way to fix this face orientation error. I've noticed orientation methods on Polygon mesh but I don't really know to apply them to the resulting PSR surface mesh. As far as logic is concerned making normal point outwards should not be too complicated I guess.
Thanks in advance for any help
You can use the function reverse_face_orientations in the Polygon mesh processing package.
Note that this package has several functions that can help you to correct/modify your mesh.
For my thesis I'm using a finite element flow solver to simulate the flow through a flume. The flow solver is capable of solving the flow in a 3D unstructured mesh constructed of tetrahedrons. However, the meshes I generate with Gmsh somehow seem to be too unstructured. Which leads too unsolvable and very slow runs.
At the moment I've tried to do simulations with both unstructured and structured meshes. Simulation with very coarse unstructured meshes go very well, however once I make the element size smaller, the flow solver only produces NaN values and doesn't run at all.
For the simulations with structured meshes I've used the transfinite technique to produce a very fine structured mesh. This mesh contains way more element than the unstructured one and the results are fine. However, in future runs I need to refine the mesh in certain areas which doesn't seem possible with the transfinite volume technique in 3D.
Does anyone have any what could possibly go wrong in this case? And is there a way to improve the quality of a 3D gmsh mesh? Can the structure of the mesh be improved somehow?
Thanks in advance!
Bart
I think the middle ground between a transfinite structured grid and a completely unstructured one would be one made of 8-node hexs. If your 3D case can be built from an extruded 2D case, you could try setting Mesh.Algorithm=8 to get right triangles (rather than equilaterals) and then use the Recombine Surface option to turn them into quads.
I need to generate a tetrahedral (volume) mesh of thin-walled object object. Think of objects like a bottle or a plastic bowl, etc, which are mostly hollow. The volumetric mesh is needed for an FEM simulation. A surface mesh of the outside surface of the object is available from measurement, using e.g. octomap or KinectFusion. Therefore the vertex spacing is relatively regular. The inner surface of the object can be calculated from the outside surface by moving all points inside, since the wall thickness is known.
So far, I have considered the following approaches:
Create a 3D Delaunay triangulation (which would destroy the existing surface meshes) and then remove all tetrahedra which are not between the two original surfaces. For this check, it might be required to create an implicit surface representation of the 2 surfaces.
Create a 3D Delaunay triangulation and remove tetrahedra which are "inside" (in the hollow space) or "outside" (of the outer surface) with Alphashapes.
Close the outside and inside meshes and load them into tetgen as the outside hull and as a hole respectively.
These approaches seem to be a bit inelegant to me, and they still have some pitfalls. I would probably need several libraries/tools for them. For 1 and 2, probably tetgen or another FEM meshing tool would still be required to create well-conditioned tetrahedra. Does anyone have a more straight-forward solution? I guess this should also be a common problem in 3D printing.
Concerning tools/libraries, I have looked into PCL, meshlab and tetgen so far. They all seem to do only part of the job. Ideally, I would like to use only open source libraries and avoid tools which require manual intervention.
One way is to:
create triangular mesh of surface points,
extrude (move) that surface to inner for a given thickness. That produces volume (triangular prism) mesh of a wall,
each prism can be split in three tetrahedrons.
The problem I see is aspect ratio.
A single layer of tetrahedra will not reproduce shell or bending behavior very well. A single element through the thickness will already require a large mesh. Putting more than one will likely break the bank in order to keep aspect ratios and angles acceptable.
I'd prefer brick or thick shell elements to tetrahedra in this case. I think the modeling will be easier and the behavior will be more faithful to the physics.
I am trying to create a 3D mesh using VTK. VTK appears to provide a number of ways to create a mesh representing the surface of a 3D object. Filling in the object appears to be more difficult. The reason I want to do this is to pass the output to a FEM tool as a solid, not a balloon.
At the moment, I am playing with spheres and there seems to be a number of ways to create a mesh for the surface of a 3D object. What I can't seem to do is create a sphere with points inside the volume. The vtkUnstructuredGrid class allows me to represent such an object, but I can't seem to mesh this in the same way I can a vtkPolyData.
Is this a fundamental limitation of VTK or am I just not seeing the right tool?
As you said:
I want to do this is to pass the output to an FEM tool as a solid not a balloon
I asume you have your FEM mesh in your own format and you want to visualize it. To do so, you can turn your FEM mesh into a vtkUnstructuredGrid modifiying the code described here:
How to convert a mesh to VTK format?