Week 6-Meshing of Hood Challenge

AIM :

To extract the Midsurface and Mesh the given Hood component by following the specified quality criteria and assigning thickness using HYPERMESH.

SOFTWARE TOOL USED :

Altair HyperWorks Version 2022

OBJECTIVE :

• Import the Hood Component, extract the Mid-surface, and Mesh the given geometry with the target element size of 5 units.
• Check all the quality criteria parameters with good mesh quality.

GIVEN DATA :

• Quality criteria

S.N	Quality Criteria	Value
1	Target Element Length	5
2	Aspect Ratio	5
3	Skewness	45
4	Warping	15
5	Taper	0.5
6	Min. Length	2 Units
7	Max. Length	8 Units
8	Min angle Quad	45
9	Max angle Quad	135
10	Min angle Tria	20
11	Max angle Tria	120
12	Tria %	10

• Cad Model

THEORY :

1. Computer-Aided Engineering (CAE) :

Computer-aided engineering (CAE) is the use of computer software to simulate performance in order to improve product designs or assist in the resolution of engineering problems for a wide range of industries. This includes simulation, validation, and optimization of products, processes, and manufacturing tools.

A typical CAE process comprises of Pre-processing, Solving, and Post-processing steps. In the pre-processing phase, engineers model the geometry (or a system representation) and the physical properties of the design, as well as the environment in the form of applied loads or constraints. Some of the Pre-processors are ANSA and Hypermesh. Next, the model is solved using an appropriate mathematical formulation of the underlying physics. Some of the solvers are ABAQUS (for durability analysis), NVH (for noise, vibration, and harshness analysis), and LS DYNA (for crash, safety, and impact analysis). In the post-processing phase, the results are presented to the engineer for review. Some of the Post-processing are METAPOST and HYPERVIEW.

2. HYPERMESH :

Altair HyperMesh is a high-performance finite element pre-processor that allows users to prepare even the largest models, and produce fine-tuned, high-quality surface meshes of their CAD geometry starting from the import of CAD geometry to exporting an analysis run for various disciplines.

With HyperMesh, you get advanced control over the type and style of meshing done on each CAD face or edge along with many automated tools to make complex meshing tasks a piece of cake. With the high-quality surface meshes from HyperMesh, you can create powerful and efficient 3D meshes for use in Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), Smoothed particle hydrodynamics (SPH), and more.

3. Engine Cover or Engine Hood :

The engine cover or Engine hood is the most eye-catching body component and an important opening piece to the body, which directly affects the overall performance and comfort. Front cover assembly not only plays an important role in air guiding but also protects the engine and surrounding pipeline accessories, meanwhile it can sufficiently avoid impact, corrosion, rainwater, and electric interference.

The following are the design consideration involved in the Design of the Engine Hood.

a. Pedestrian Safety :

Pedestrian safety is always a factor involved in the design of the hood. This is achieved by the proper selection of material that can readily deform avoiding risk during impact, Providing embosses to inner panels, etc. This is one of the major factors for a vehicle to have better safety ratings.

b. Vehicle Quality :

This involves how best the hood can be designed to have better quality in terms of Torsional stiffness, dent resistance (Hailstone and stone chippings), Corrosion resistance better weight distribution, and noise attenuation.

c. Occupant Safety :

The design consideration must include the impact caused due to Frontal Crash Collapse. Such a scenario is expected that the Hood maintains its Integrity with hinges and also retains any loosed components from Engine Compartments.

d. Styling :

Better Surface quality (A-class Surface Finishing), Tight radii on hemmed panel edges & low strain between curved regions of the inner and outer panel.

e. Manufacturability :

The design should be always considered for manufacturability e.g., Embossing on the inner Panel should have sufficient draft angles provided for the Punching tool to flow in and flow out. Any Design should be studied for Manufacturability in order to produce it.

4. Geometry Clean-up :

Designers have different priorities while creating CAD geometry than analysts who are seeking to use the data. Usually, a single smooth surface is divided into smaller patches, each of which is a distinct mathematical face. And often, there will be gaps, overlaps, or other alignment issues at the junction of two surfaces.

In geometry cleanup, analysts integrate several faces onto a single smooth surface to make the geometry more suitable for meshing. This enables the creation of the elements across the entire region at once and eliminates the need for false or unintentional edges in the finished mesh.

Some commands for the geometry cleanup are as follows :

1. Geometry -----> Edge edit -----> Replace
2. Geometry -----> Surfaces -----> Ruled
3. Geometry -----> Quick edit -----> Filler surface

5. Meshing/Mesh generation :

Mesh generation is the process of discretizing the entire model into smaller elements in other words Mesh is a network that is formed of cells and points. Meshing is often used in FEA and CFD domains.

There are two types of meshing, 2D Mesh & 3D Mesh. In 2D Mesh, the mid surface is extracted from the component and then meshing is done on the mid surface whereas in 3D Mesh, direct meshing is done on the component from inside out. The difference between the 2D & 3D mesh is that the mesh type in 2D Mesh is mixed whereas in 3D Mesh the mesh type is Ortho tria (for complex regions such as fillets and hemmings) or Tria (For regions that are flat and not as complicated).

PROCEDURE :

Step 01 : Importing CAD Model.

• The initial step is to import the geometry into HYPERMESH Software.

Import Model -----> Import Geometry -----> File type - IGES ----> Select Location -----> Click Import -----> Fress F to fit the model.

Step 02 : Geometry Cleanup.

Check if there's any extra surface, free edges, missing surfaces are present or not. For this enable wireframe geometry mode and then try to observe and find irragularities and discontinuities in the model. If found then fix it manually.

Step 03 : Mid-surface generation.

• The mid surface is generated to reduce the complexity as by simplifying the cad model we get more accurate simulation results in a shorter time.
• In Hypermesh there are many ways to extract the mid surface, an engineer must try to take the exact mid surface on every edge, curve, and complex area. Capturing the exact mid-surface is important because it can later lead to irregular mesh flow and quality issues during meshing.

The following approaches are some methods to extract mid-surface.

1. Offset Approach.
2. Offset + planes + sweep Approach.
3. Offset + planes Approach.
4. Skin Offset Approach.

Offset Approach :

Geometry -----> Midsurface -----> Automidsurface ----> Select the Extraction options and in that Offset -----> Now select auto extraction again -----> Select the component -----> Extract.

• After the mid-surface extraction, there might be some errors such as free edge, extra surface, etc. Fixation of these errors must be done manually.

Step 04 : Assigning of Material, Property & Thickness.

• Here new property and material must be created for assigning them to the Hood component.

For creating Material :

Mouse right-click on the Tab area -----> Create -----> Material.

For creating properties :

Mouse right-click on the Tab area -----> Create -----> Property.

• While creating the property give the thickness (T) as 1.

Step 05 : Identify and delete the symmetry surfaces.

• Delete one side of the symmetry surfaces of the Car hood Component.

Toolbar -----> Red Cross Symbol (Delete symbol) -----> Select one side of the symmetry surface -----> Delete entity.

Step 06 : Setting up the Quality Criteria and Mesh Parameter.

• Setting up the quality criteria as well as mesh parameter is very important in every pre processing process. This will make the mesh proper as per the requiremnt. Here the parameters is given, as per the given data fill the dialogue box and apply to the component.

For Mesh Parameter :

Title bar -----> Preferences -----> Parameter file setting -----> Basic -----> Fill the necessary data as per the requirement (Target element size : 5, Element type : Mixed) -----> OK.

For Quality Criteria :

Title bar -----> Preferences -----> Criteria file setting -----> Change the criteria values as per given data -----> Fill the necessary data as per the requirement (Target element size : 5, Element type : Mixed) -----> OK.

Step 07 : Creation of Washer Split.

• Creating the washer splits at the holes as these splits will give better mesh flow and rigidness at the holes.

Geometry -----> Quick edit -----> Washer split and enter the offset value as 5mm ----> Select the holes which need the washer split.

Step 08 : Mesh Generation

2D -----> Automesh -----> Enter element size as 5mm ----> Mouse Right-click on the Surfs and Select displayed -----> Mesh.

• After Meshing there will be some errors that will not follow the quality criteria and will be seen in different colors. To make the mesh proper some manual adjustments must be done, for that there are a few commands i.e. Create element, Split element, Combine element, smooth, drag tria element, delete element, etc.

  1. Create element : 2D -----> edit element -----> Create -----> Select nodes where the element must be created -----> Create.
  2. Split element : 2D -----> edit element -----> Split -----> draw a splitting line by points -----> Split.
  3. Combine element : 2D -----> edit element -----> Combine -----> draw a splitting line by points -----> Split.
  4. Smooth : 2D -----> qualityindex -----> Smooth -----> Select the elements which need to be smooth -----> Mouse middle click.
  5. Drag tria element : 2D -----> qualityindex -----> drag tria element -----> Select the elements which need to be smooth -----> Mouse middle click.
  6. Delete element : Toolbar -----> Red Cross Symbol (Delete symbol) -----> Select the element that must be deleted -----> Delete entity.
  7. Rebuild Mesh : 2D -----> Rebuild mesh -----> Select the element which needs to be remeshed -----> Rebuild.

• After using all the above commands the mesh can be created properly and with minimal errors.

Step 09 : Creating the other half of the Hood and joining it.

• As shown in the above fig the Mesh is done with the help of different commands (explained above). Since the meshing is done of the half Car Hood Midsurface now the other half surface must be mirrored.

This is done by following the steps,

Tools -----> Reflect -----> Select the elements which need to be reflected (as shown in fig below) -----> Select Duplicate and the reflect must be with respect to the y-axis & select the base -----> Reflect.

• Here the other half is created but it's not joined with the first half. Hence it must be joined and for doing that following steps must be followed.

Tools -----> Elements -----> Select the whole component -----> Preview equivalence -----> Tolerance : 0.1 -----> Equivalence.

Step 10 : Checking the Normals.

1. Checking Normals.

Tools -----> Normal -----> Display -----> Adjust.

• Hence the component (Car Hood) is ready for further operations.

LEARNING OUTCOMES :

By doing this challenge, the following aspects can be learned:

• Basic tools in Hypermesh
• Extracting mid-surface in Hypermesh
• Generating a 2D mesh on the extracted mid-surface.
• Using reflect command to reflect.
• Assigning the thickness to the mid-surface.
• performing basic checks at the end.

CONCLUSION :

• Extracted the mid-surface of the given Car hood model.
• Generated a 2D mesh on the component based on the given quality criteria & parameters, deleting the half component and reflecting it for making the process easy and time efficient, and assigned the thickness.