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Midsurface Introduction

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In Finite Element Analysis, structures can be represented with a variety of elements including 0D, 1D, 2D and 3D elements. Thin structures in particular are commonly represented with 2D or surface elements.

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Different dimension elements can be used represent the same geometry. An I-Beam (W Shape) can be idealized as 1D, 2D, or 3D elements.

Surface elements, also called two-dimensional (2D) elements, are used to represent a structure whose thickness is small compared to its other dimensions. Surface elements can model plates, which are flat, or shells, which have single curvature (e.g., cylinder) or double curvature (e.g., sphere). Surface elements can also be used to model sections that are uniform or non-uniform in thickness.

Below are various examples of thin structures and their respective midsurface representations. Click on the thumbnails for a closer look.

Midsurface Creation Process

A common way to produce a surface element mesh is to first create midsurface geometry that represent the midplanes of the thin walls and then mesh the midsurface geometry. For more details on the process, refer to 3 Steps to Create Midsurface Geometry.

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Midsurface Creation Process

 

Midsurface Creation for Beginners

The video below shows fundamental concepts that can get you started in your midsurface extraction, creation, and meshing process.

3 Steps to Create Midsurface Geometry

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The goal of this post is to bring you up to speed on how to create midsurface geometry for finite element analysis. While the process requires numerous actions, each action can be generalized into one of 3 categories. Video explanations complement each section.

1) Extract Midsurfaces

Thin structures will be composed of numerous thin walls. Individual midsurfaces may be extracted manually, but automatic and semi-automatic methods can extract midsurfaces for numerous thin sections. The advantages of each method are given below.

Automatic Midsurface Extraction

This method traditionally works well for designs that have uniform thicknesses or have been through a stamping manufacturing process.

 

Semi-automatic Midsurface Extraction

This method works well for designs that have multiple thickness changes, non-uniform thicknesses and the walls have a large variation of position to one another.

 

Individual Midsurface Extraction

There may be the situation when certain midsurfaces were excluded from the automatic or semi-automatic and must be created manually. In other cases, when the extracted midsurfaces are poor and severely distorted, it is best to delete the midsurfaces and recreate it individually.

2) Free Edges

A free edge is an edge that is not connected to another edge or face. If a continuous mesh is intended at an edge and it happens to be a free edge, it can produce a discontinuous mesh. The goal is to resolve the necessary free edges.

Individually Resolving Free Edges

If it is one edge, closing a gap is as simple as taking a free edge and dragging it to a nearby edge or face. The benefit of this dynamic behavior is that you do not have to created and delete construction geometry each time an edge operation is performed.

Stitching

Suppose the scenario when an edge is already resting on an edge or face. A stitching function can be used to connect the free edge to the edge or face.

Extending Free Edges

After you have extracted numerous midsurfaces, there will be numerous free edges to resolve. Individually moving and closing each free edge is too time consuming. An automatic method can be leveraged to extend the free edges up to nearby edges or faces, and in addition, a simultaneous option to stitch the edges can be used.

 

3) Final Clean Up with Mesh Quality

To confirm the midsurface geometry is suitable, the resulting mesh must have elements that are within satisfactory levels of quality. In other words, nothing in the midsurface geometry should cause poorly distorted elements. With the mesh superimposed on the midsurface geometry, the mesh quality may be viewed and edits can be continuously made without having to delete and recreate the mesh.

MSC Apex Free Trial

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Why try MSC Apex?

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Figure 1

Meshing is long and hard. You probably spend hours using a pre/post processor to fix and mesh geometry. Save your self the time and move through your meshing process faster with MSC Apex.

To illustrate an example, Figure 1 shows a bracket where the CAD to mesh process involved extracting midsurfaces, connecting the midsurfaces, meshing, and attributing it with thickness and offset properties. With a traditional Pre/Post processor, the CAD to Mesh process of this bracket required 5.5 hours. With MSC Apex, the CAD to mesh process required only 24 minutes.

How long is the trial?

The free trial is good for 30 days. The trial period begins once you receive a trial license from MSC Software.

Where can I sign up for the MSC Apex Free Trial?

What are the hardware and OS requirements for MSC Apex?

See this post.

What geometry and other file formats does MSC Apex support?

See this post.

Who can I contact if I have any questions?

You may contact me, Christian Aparicio. See my contact info below.

Faster Methods of Constructing Finite Element Meshes with MSC Apex

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The process of constructing finite element meshes can often require hours or days to complete. Part of the challenge is that original geometry is in a state not suitable for meshing. The original geometry  must be significantly edited before a mesh can be created. On average, this CAD to FE mesh process can constitute over 60% of the entire FEA workflow.

Existing pre/post processors contain sophisticated meshing functionality, but lack modern geometry editing tools necessary to expedite the meshing process.

MSC Apex is the first in the CAE platform in the industry to feature both direct modeling and meshing technology that has been demonstrated to show performance gains of up to 50x (Click here for benchmark). Below are a collection of presentations for your viewing that cover MSC Apex functionality.

Read More

CAD to Mesh Challenge

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Everyone likes a challenge! At MSC we believe that challenges bring out your best. Your best people – Your best process – Your best tools. MSC Apex Modeler is a CAE-specific direct modeling & meshing solution that streamlines CAD clean-up, simplification & meshing workflow. We are so confident in its ability to accelerate your CAD to Mesh (C2M) performance were willing to put our money where our mouth is.

MSC is offering to conduct a C2M challenge on your parts at 50% off. That’s right – we’ll take your CAD geometry and deliver back to you mid-surfaced meshed parts of comparable quality at a cost savings of 50% of your current expense. This offer is only available in Canada and the United States.

The Challenge

Simple – give us your dirtiest, ugliest looking CAD parts or your most difficult geometry and challenge us to outperform your current process. We will deliver a mid-surfaced meshed part in a fraction of the time and cost. You have nothing to lose – except 50% of what you’re spending today!

MSC Apex

As another awarding winning product from MSC, Apex is the world’s first computational parts based CAE system. It is transforming the way engineers perform simulation by reducing critical CAE modeling and process time from days to hours.

The table below showcases the actual productivity gains achieved from CAD to Mesh for an aviation bulkhead. The steps performed included CAD import, geometry clean up, extraction of mid-surfaces, connection of separate surfaces, meshing, and assignment of thicknesses and offsets.

For more information, please visit: www.mscapex.com.

Table 1

Step Today’s Workflow MSC Apex Workflow
Expertise Required
High
Low
Anaysis Geometry Creation
3 h
.3 h
Mesh Creation
1 h
.05 h
Property Assignments
1.5 h
.05 h
Complete Entire Scenario
5.5 h
.4 h
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1) Original solid geometry 2) Extraction of mid-surfaces 3) Repair of mid-surfaces 4) Automatic attribution of thickness and offset properties

 

How to sign up?

Simply fill out the form below and we will get back to you. This offer is only available in Canada and the United States.

How long does it take you to create mid-surface models or clean up geometry for FEA?

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Feel free to share your thoughts by participating in our survey.

Click Here to Start Survey

 

URL: http://questionpro.com/t/AB6PyZSYFi

The process of creating dozens of mid-surfaces from solid geometry, connecting the surfaces, meshing, and attributing thickness and offset properties is a very time consuming process. This process is also very common when taking advantage of Finite Element Analysis for structural analysis. We have developed new technology to expedite this workflow. Below is a quick demonstration. For more information, please visit www.mscapex.com.

MSC Apex Free Trial Challenge

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If you have the MSC Apex Free Trial today, you are welcome to take this meshing challenge.

This model, download it here, has an embedded text message.

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Note this is an example of what the message may look like.

The first 5 individuals to find and email me the embedded text message wins. My email is at the bottom of the post. Please put the embedded text message in the Subject line when emailing me.

 

Note that decoy messages are also present in the model, directions to find the correct embedded message is given below.

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Step 1: Solid mesh the magenta colored solid, use the default meshing settings.

Here is how you find the message.

  1. Solid mesh the magenta/purple solid. Use the default mesh settings, e.g. mesh size of 10mm, Element Type = Quadratic, etc.
  2. Change the Geometry Render Styles to Wireframe. See image below.
  3. Review the mesh quality by clicking the Element Quality icon. See image below.
    1. Ensure 3D is selected under Element Types.
    2. Search the model for a region with a concentration of red elements. You may also see purple elements.
  4. Zoom into this region of red elements. Hide the solid elements by clicking on the 3D icon.
    1. The message should be visible at this point.
  5. Email me the message. My contact info is at the end of the post.
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Steps 2, 3, and 4

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Step 3.1: When viewing the element quality, ensure 3D is selected under Element Types.

What do you win?

The first to win will receive:

  • A certificate of recognition from MSC Software
  • A special mention on this page along with their name and company name
    • e.g. Christian Aparicio, MSC Software

My contact info

See below.

Winner

I am glad to announce that the winner of this challenge is Gokulan Udayakumar, CAE Exhaust Engineer at Ford Motor Company Ltd. Congrats to Gokulan and everyone at Ford.

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Geometry obstalces that can prevent meshing

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Geometry and CAD can be very complex, and sometimes the complexity of the model can hinder meshing for FEA. I present three common obstacles and solutions to overcome them.

1) Features and Details

Often features and details can be disregarded in a subsequent structural analysis with FEA.

Threads such as these is an example of how detailed a model can be, but can be disregarded in FEA. In MSC Apex Modeler, we can use the Direct Modeling technology to remove the threads.

Dips or extrusions like these can also be ignored in FEA. MSC Apex Modeler can be used to raise the surface so it is flush with the rest of the surface.

Fillets are not always necessary, and can be easily removed with defeaturing tools such as the one built into MSC Apex Modeler.

2) Extra Edges on solids

Meshers will naturally follow the edges of a solid. If a model has numerous edges, meshers will force elements to follow the edges leading to severely distorted elements. MSC Apex Modeler has a tool that allows you to suppress edges such that they do not conflict with the mesher. This results in meshes that have fewer distorted elements.

In this example, you see the elements are severely distorted, but supress operation hides the edges from the mesher.

3) Spikes through the model

In some scenarios, you may find that a sharp spike is piercing the solid geometry. These spikes are usually unintended, but may be remedied in MSC Apex Modeler as the demo below shows.

The content in this post was orignally inspired by a webinar titled Easy Editing and Repairing Solid Geometry for FEA Meshing by Mica Parks.