Finite Element Analysis in PVP Design: What You Should Know
In pressure vessel and piping (PVP) design, various analysis methods are used to assess the safety and performance of systems. While hand...
4 min read
Dr. Delin Wang, Ph.D - Aerospace Engineering Apr 17, 2023 2:52:20 PM
In finite element analysis, two types of meshes, structured and unstructured, are commonly used to represent a geometric domain by smaller discrete grid cells. The main difference between the two is the regularity and organization of the grid cells. As differences exist within each, so do their advantages. But mostly, the choice of either depends highly on the specific geometry and the time and resources available to analyze the model.
In the following blog, you'll read more about the benefits of using structured and unstructured mesh modelers to rapidly produce verification results for your pressure equipment.
As mentioned before, when performing finite element analysis, both structured and unstructured meshes are commonly used to represent a geometric domain by smaller discrete grid cells.
A structured mesh consists of a regular and structured arrangement of cells, which are typically quadrilaterals or hexahedra in two and three dimensions, respectively. The sides of the cells are usually parallel, and the grid spacing is uniform. With this type of mesh, both advantages and disadvantages can occur.
Unstructured meshes, on the other hand, have an irregular arrangement of grid cells, which can be any shape and size. The cells can be quadrilaterals and triangles in two dimensions, hexahedra and tetrahedra in three dimensions, and the grid spacing is not uniform. Both advantages and disadvantages occur here as well.
Overall, the choice of whether to use a structured mesh or unstructured mesh depends on the specific geometry of the problem being analyzed, as well as the available computational resources and time constraints.
In general, unstructured meshes are more suitable for complex geometries with irregular boundaries, where they can provide accurate solutions while reducing computational costs.
Paulin Research Group's latest release now includes a model-dependent unstructured mesher, which is accessible in PVPTPro, FEPipe and NozzlePRO.
In a nutshell, here's what it includes:
The updated weld contour model is used in the software automatically. Contoured shell elements from the penetration line to the toe of any connecting fillet are sized so that the rotational shell model inertias match those of the actual tapered volumetric geometry creating a more accurate local stiffness at any nozzle-shell intersection.
What's more is that these models can be exported to Ansys via the /PREP7 interface, thus preventing Ansys users from manually computing and reproducing these contours in Ansys shell models of branch connections.
The grid localization feature should be used for all PVPTPro models and for FEPipe and NozzlePRO models when the user requests unstructured meshing or when the unstructured mesh modeler is automatically selected by the software.
Localization incorporates a uniform regular mesh inside an unstructured mesh in most areas of the model with refinement only in particular cylindrical extents.
The structured regular mesher observes the (RT)0.5 sized interaction regions around nozzles in close proximity producing more uniform stress distributions regardless of the potential irregularity of surrounding models.
The user can still control mesh densities, and further, any irregular unstructured meshing in PVPTPro can usually be resolved by increasing the overall mesh density. Users should find, however, that solutions in the vicinity of nozzles and other discontinuities converge well before the surrounding mesh takes on a uniform appearance.
In this sense, PVPTPro can and should be thought of as a NozzlePRO for multiple nozzles. Large elements and zones are used in large areas of the model that are then removed from discontinuities and thus improves model efficiency.
Since NozzlePRO deals only with individual nozzles, structured meshes can typically be used to appropriately place elements around the penetration line and simulate weld leg contour thicknesses. And since PVPTPro deals with single or any number of nozzles, unstructured meshes can be used with the localization option to compute accurate stresses around all nozzles regardless of the unstructured mesh in areas far removed from the discontinuity.
With smart FEA software, there are benefits of using structured and unstructured mesh modelers to rapidly produce verification results for your pressure equipment.
Request a consult today to further see how this works in action.
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