SHELL MESHING OF AN INTERIOR PANEL SUBSTRATE FOR FINITE ELEMENT ANALYSIS

SHELL MESHING OF A INTERIOR PANEL SUBSTRATE FOR FINITE ELEMENT ANALYSIS

OBJECTIVE: Structural mesh is oftained for the complex interior panel plastics of a car for finite element analysis, by extracting mid surfaces with thickness elements using manual and auto generated methods.

ABSTRACT & PRE-REQUISITES: Firstly, let's understand what is the modeling philosophy, for which we need to consider about Finite Element Method.

Analysis is key to product design. It helps with understanding issues like stresses, heat transfers, fluid flows, and more. Analysis can help estimate the performance of a product before it even exists! In engineering practice, analysis is largely performed with the use of finite element computer programs, typically interfaced with computer-aided design. Proper meshing is a core part of this analysis. Meshing can be 2.5D or 3D, depending on what is needed.

Now extending the concept of the elements to the modeling methodology in FEM as known popularly, it takes shape into - Beam modeling, plate modeling and solid modeling. There are criterias for every method and to which it has specific applications.

In FEA, it is popularly known as SHELL modeling. This methodology follows the KirchKoff’s Plate and membrane hypothesis. According to which one of the rule says that plane sections remain plane about the neutral axis, reffering that bending moment is zero at the mid plane. The structure behaves a plate with in plane stresses and strains.

A well-known fact by most CAE engineers, structures can take up a tremendous part of an engineer’s time in the meshing phase. A complex fabrication may use very little of available CAD geometry when meshing or be just a 2D drawing image. For most structures, a good understanding of meshing is important for productivity. Factors regarding this can include effective techniques in meshing tools, how analysis objectives affect the mesh, correct element types, and the level of accuracy needed.

The general concepts of meshing are simple, but that the practice of creating meshes that provide solid analysis results requires significant knowledge and experience. The first step in meshing is the idealization of the CAD geometry. Typically this encompasses simplifying the model, eliminating details that are not pertinent to your analysis, or that have a marginal influence on the results.  Once the model is ready, the next step is to create the mesh. The actual process to create the simulation model and the mesh will depend on which program is used. The end result of the process, will be a mesh made up of one or more forms of geometric elements.  Any kind of analysis is only as good as the tools and processes used. A good mesh applies physics, with the understanding that things can change, and need to be taken into consideration during analysis.

Proper meshing allows for accurate analysis, regardless of whether the process is automated or manual. For any product development project to be successful, analysis is critical, and proper meshing is an important part of that analysis. If your project requires analysis before moving to the next stage of project design, be sure to use a product development professional to help insure the analysis is done accurately and thoroughly for best results.

PROCEDURE:

There are two ways in which a mid plane extraction is done in shell meshing forte. Firstly, it is carried out manually for the rendering engineer to get in depth access of the CAD and the nuances it poses to extract the skinning result.

The complexity of the CAD and the process involved in mid skin extraction is better experienced when the cycle of extraction is doen manually, however, the computational time is yeilding and rather costly while performing the extraction process manually.

Socondly, the sophistiction of the workbench that comes with pre-processing platforms like ANSA is that it is built with complex algorithms to extract the mid plane of any given CAD with only 1/3rd of the time taken to carry out the extraaction manually. However, the CAd has to be error free, else ANSA has to work it's algorithms past the geometrical errors to render a mid plane, which indeed might be very unrealistic and analytically not similar to the manual extraaction.

Now, let's take a look at the snippets of manual mid plane extraction and later will be compared to the ANSA iterated mid plane.

1. RUNNING GEOMETRY CHECKS:

2. TOPOLOGICAL CORRECTIONS:

Extracted mid surfaces after projecting non uniform cons on either sides onto either sides to have uniform cons on both the sides of the CAD.

Then the CAD is stuck with weld points that is projected from the inner ide fo the panel to the outer side.

MID PLANE EXTRACTION OF THE RIBS AND THEIR TOPOLOGICAL ERROR CORRECTIONS:

POST HEALING:

ITEREATED MANUAL MID SKIN MESH:

SMOOTHENING OF MESH AROUND THE RIBS AREA:

FIXING THE RIB ALIGNMENT:

EXTRACTED MID PLANE MESH USING ANSA'S INBUILT ALGORITHM:

PIDs WITH DIFFERENT THICKNESS:

SUBSTRATE PART 2:

GEOMETRY CHECKS:

EXTRACTED SURFACE MESH WITH DIFFEREN THICKNESS:

SUBSTRATE PART 3:

GEOMETRY CHECKS:

EXTRACTED MID SURFACE MESH:

Alligning the mesh that are off from the actual CAD are corrected using the allign tool under SHELL MESH. The nodes that are to be sligned are first selected and middle clicked to select the reference plance to which the nodes to be alligned.

SUBSTRATE PART 4:

GEOMETRY CHECKS:

RENDERED MID PLANE MESH:

SUBSTRATE PART 5:

GEOMETRY CHECKS:

The single cons popped up as errors in the geometry checks are then closed using fill hole tool.

POST ERROR CORRECTION:

RENDERED MID PLANE MESH VIEW:

NOTE: The tools used for healing the geomerical errors and topological errors are pretty intutional depending in the ease and comfort of the meshing engineer. Certain approach might not be always the right approach, can be time consuming and computationally heavy.

QUALITY CRITERIA:

The quality criteria of the mesh parameters plays a vital role in FEA analysis. The OEM's requierement of stringent limitations for the criterion values are due to the quality analysis report that has to be as close as the real time simulation. These values play a vital role in crash analysis, NVH and aerodynamics simulation for CFD.