Performing surface wrapping over an engine assembly in ANSA

Objective:

      The goal is to clean the surface geometry to avoid errors and create a surface wrap that accurately captures the input domain geometry(a powertrain control) with high-quality cells so as to make subsequent calculations intractable. The element size for various parts is as shown below:

• Engine -  8 mm
• Transmission -  5 mm
• Gearbox - 5 mm

      The above-said goal is achieved by using the most widely used Pre-processing software named ANSA.

What is ANSA?

      ANSA is an advanced multidisciplinary CAE pre-processing tool that provides all the necessary functionality for full-model build up, from CAD data to ready-to-run solver input file, in a single integrated environment.

      ANSA is the user's preference due to its wide range of features and tools that meet their needs. The list of productive and versatile features is long and the alternative tasks and processes to be completed using them are countless.

Mesh generation:

        Mesh generation is the practice of creating a mesh, a subdivision of a continuous geometric space into discrete geometric and topological cells. Often these cells form a simplicial complex. Usually, the cells partition the geometric input domain. Mesh cells are used as discrete local approximations of the larger domain.

Purpose of meshing:

        Meshes are used for rendering to a computer screen and for physical simulation such as finite element analysis or computational fluid dynamics.

        Finite element calculations cannot be done directly on solid parts. We know to perform those calculations only on points created by the mesh generation process. Thus generating mesh is a must and most important step for any CFD or FEA calculations to be performed.

Surface wrap:

The surface wrapper can be used to provide a closed, manifold, non-intersecting surface when starting from poor quality CAD data. It is typically used when the imported surface includes problems such as:

The surface wrapper can achieve many different aims simultaneously when applied to such data. These include:

The resulting surface quality from the surface wrapper is not optimal so it is usually used in conjunction with the surface remesher to provide a high-quality starting surface for the volume meshers.

Steps involved in geometry clean-up by ANSA:

1. The solid part made using any cad modeling software is imported into ANSA. The Procedure is File>Open and select the required solid part.

2. The solid part is initially imported as a wireframe model in ANSA and it is changed into a solid model by clicking on the surface icon as shown below.

3. We have 6 unchecked faces and we used untrim option to clear the unchecked faces.

4. before performing the surface wrap we delete the unwanted reference models which were used such as the rings, sphere, balls  as these are not essential.

5. You can highlight any of the problematic areas by left-clicking on it, or isolate it on the screen by right-clicking on it and selecting “Show only”. Depending on the type of problem ANSA also offers the option to automatically fix it.

6. Before performing surface wrap we close all the open surfaces in the model because when we apply the wrap on the model before closing the open surfaces it will create skewness on the model so we do first close all the open surfaces.

7.De-activate “Shadow” mode and the visibility flag button for “Double” CONS. You will now isolate a region of your part to work on. Activate the “Or” function located in the Focus Toolbar. Make a box selection of the area shown on the left using the left mouse button. The “Or” function leaves visible only the selected Faces. (If you accidentally select wrong Faces, press the All function of the same Group to bring all the entities back to visible).

8. Activate the “Lock” flag button in the Focus Toolbar to lock the currently visible entities. Now when you press the “All” button, only the selected and locked entities will become visible.

9. To view the complete Faces that you have left visible, activate again the “Double” CONS visibility flag. Activate also the “Cross Hatches” visibility flag. This allows the visualization of two green dashed lines along the center isoparametric of the Faces. Apart from visualization purposes, the crosshatches are also used for selecting Faces.

10. In order to close the open holes we initially release all the cons and we use the fill hole option to completely close all the open holes. The model after closing all the open holes is shown below.

11. Similarly the other two parts namely gearbox and transmission box is cleaned up and the holes are closed as shown below.

Steps involved in creating the surface wrap in ANSA:

1. The first step is to go to the mesh mode and selecting the wrap option under the elements tab.

2. A new dialog box appears as shown below

3. The target length determines the mesh element size of the surface wrap and the smoothness factor determines how well the surface wrapper covers the geometric details of the solid surface.

4. different element size is applied for different parts as shown below.

• Engine -  8 mm
• Transmission - 5 mm
• Gearbox - 5 mm

5. On clicking on next button Ansa shows a preview of the wrap as shown below

6. On clicking on the next button the wrap is done as shown below.

7.Similarly, the other two parts namely gearbox and transmission box is cleaned up and the holes are closed as shown below.

Steps involved in merging different parts and defining models in the model browser in ANSA:

1. Next step is to merge the three different parts into a single assembly.

2. go to file>merge>and select the different parts. The merged assembly is shown below

3. Click on the model browser icon and the following window appears

4. The empty part is the leftovers of the deleted components. It occupies an unwanted system space and creates confusion. Compress option is used to delete the temporary files.

5. The merged assembly consists of three different models. So these three models have to be separately defined in the model browser window. It is done by right-clicking inside the model browser window and selecting the create new part option. The model browser ater adding the new parts is shown below.

Steps involved in creating a single continuous volume in ANSA:

1. The merged model is made up of three different volumes but the idea is to create a part comprising of a single continuous volume.

2.first the intersecting regions are isolated using not and i-not operators as shown below

3. Now the intersecting area is deleted and manipulated by using various tools namely delete, mvsurf, and release nodes options.

4. after removing the intersecting area, The connections are made using paste, fill, and new elements options. After performing these operations the below connection is made.

5. Similarly, the intersecting area between the transmission box and the engine is isolated as shown below.

6. Here a new technique i used to create a volume. New elements are created using the above-said tools and the intersecting PID region is deleted as shown below.

7. Finally, the seamless connection is obtained in the assembly as shown below

Conclusion:

1. Three individual parts are successfully surface wrapped with different element sizes.

2. The individual models are merged together and a single continuous volume is created.