Week 12:Project 2-Meshing of Rear Wheel Holder challenge

Objective:

To mesh the 2D surface after extracting the middle surface for each component of the Rear wheel holder CAD Model using HyperMesh as per the Quality Criteria given and assigning thickness for the components.

PROCEDURE 

Importing CAD model and geometrical clean up

When the CAD model is clean then no need go through the geometry clean-up but we need to check the geometry properly before extract the mid surface. Depending on complexity of the model, we can make the model symmetrical so that it is easy to work on the model.

File (type) > Import > CAD model.

 

While Import the CAD model file (step or IGES etc.) the model may have geometrical errors like unconnected, missing and duplicate surfaces also overlap surfaces due to small geometry areas in the model. Cleanup operations include the equivalence of "red" free edges, fixing of small surfaces (relative to the eleme t size), and detection of features such as beads. It also performs specified surface editing or de-featuring operations like the removal of pinholes (less than specified size), removal of edge fillets, and the addition of a layer of washer elements around holes.

Disjoint offset and Continuous offset

Disjoint offset: Offset moves the selected surfaces without retaining their connections to surrounding geometry.

Continuous offset: Create new surfaces to connect the surface at its new position with lines that you specify, or morph any surrounding/attached surfaces to meet the offset surface if no separator lines are chosen.

There are two major types of offset disjointed and continuous.

Middle surface

It's easy to extract any model extracting the mid-surface using auto middle surface but we need to check up middle surface any fallen edges or any other geometrical errors present in the model after this step. Now we need to go through the auto cleanup.

We have two methods to extract middle surface 1). Auto middle surface. 2). Manual middle surface.

Manual middle surface is useful where auto middle surface is not going to work. Sometimes we get distorted surfaces after extracting the middle surface using auto middle surface in those case we can go for manual middle surface. It takes more time.

Using offset option is useful here so we used surface offset method to extract the middle surface.

Geometry > surface edit > offset

Use the Offset subpanel to offset a group of surfaces by a given distance along the normal of those surfaces. A negative offset value can be used to offset these surfaces in the opposite direction of the surface normal. The topology of the surface edges (free, shared edges, and so on) is maintained during the offset function. Some individual surfaces will be trimmed or extended to maintain the connectivity. This function moves the selected surfaces to the new location.

If you want to save the original surfaces, the selected surfaces can be duplicated before the offset. You can review the normal direction of the surfaces by clicking vector normal or color normal. If the offset direction is incorrect, the reverse normal function can be used to reverse the normal of a selected surface. If there are elements associated to the offset surfaces, the element will not move along with surfaces. The association between the elements and their surfaces is broken.

Using surface edit in the geometry we can extract the middle surface. But we have used auto middle surface because the complexity of the model and time

Auto-mid surface not worked here because of the complexity of the plastic model.

Auto Mid-surface: Automatically extracts mid-surfaces from surfaces that enclose a volume or a solid geometry can sometimes work if there are missing surfaces. The greater number of missing surfaces, the less reliable the result

Auto-middle surface extraction: Use the Auto Mid-surface subpanel to extract the mid-surface of a more complicated group of surfaces that represent a solid part in one step.

The Mid-surface panel can be used to extract the mid-surface of sheet metal stampings, molded plastic parts with ribs, and other parts that have thickness clearly smaller than width and length.

Geometry > mid-surface > Auto Mid-surface > change the extraction options like

Identify the places where a piece of plane or a piece of a sweep surface can be used as a middle surface. A middle surface is constructed at the remaining places in the model, this is offset . plane sweep method Using this method middle surface got distorted.

All other three methods like, offsetplane sweep, offset . plane, offset in the extraction option created are tried but did not give proper mid surface in some areas. In skin offset gave proper middle surface,

The fillet or shared edge fall less, the offset size of the fillet is small due that both surface got intersected in the below image after creating the mid-Surface.

 Due to the complexity of the model I have cut the model into two parts before going for the middle surface extraction  Using surface edit panel trim with surface/panels. Selecting surface and surface option we trim the model by click the box trim both option.

After extracting middle surface connecting the surfaces using extend option in the geometry > surface edit > extend extend over edge > line to over edge > surface to extend (cross extension).

Use the Offset subpanel to offset a group of surfaces by a given distance along the normal of those surfaces. A negative offset value can be used to offset these surfaces in the opposite direction of the surface normal. The topology of the surface edges (free, shared edges, and so on) is maintained during the offset function. Some individual surfaces will be trimmed or extended to maintain the connectivity. This function moves the

selected surfaces to the new location.

If you want to save the original surfaces, the selected surfaces can be duplicated before the offset. You can review the normal direction of the surfaces by clicking vector normal or color normal. If the offset direction is incorrect, the reverse normal function can be used to reverse the normal of a selected surface. If there are elements associated to the offset surfaces, the element will not move along with surfaces. The association

between the elements and their surfaces is broken.

Using surface edit in the geometry we can extract the middle surface. But we have used auto middle surface because the complexity of the model and time

Auto-mid surface not worked here because of the complexity of the plastic model.

Auto Mid-surface: Automatically extracts mid-surfaces from surfaces that enclose a volume or a solid geometry can sometimes work if there are missing surfaces. The greater number of missing surfaces, the less reliable the result

Auto-middle surface extraction: Use the Auto Mid-surface subpanel to extract the mid-surface of a more complicated group of surfaces that represent a solid part in one step.

The Mid-surface panel can be used to extract the mid-surface of sheet metal stampings, molded plastic parts with ribs, and other parts that have thickness clearly smaller than width and length.

Geometry > mid-surface > Auto Mid-surface > change the extraction options like Identify the places where a piece of plane or a piece of a sweep surface can be used as a middle surface. A middle surface is constructed at the remaining places in the model, this is offset . plane sweep method Using this method middle surface got distorted.

All other three methods like, offsetplane sweep, offset . plane, offset in the extraction option created are tried but did not give proper mid surface in some areas. In skin offset gave proper middle surface,

The fillet or shared edge fall less, the offset size of the fillet is small due that both surface got intersected in the below image after creating the mid- Surface

The final midsurface taken is shown below.

Avoid these type of surfaces it may result in element failurre while meshing .

Meshing

Creating the mesh on 2D surface using auto mesh option here. Before we create the meshing we need to edit he criteria by using F12 in the keyboard or preference > criteria, parameters.

Size and Blas.

Use the size and Bias subpanel to perform size and bias meshing, a flexible and powerful meshing method. A minimum of inputs are required for the element criteria settings.

Size and biasing meshing produces a mesh with consistent element size. If meshed interactively, the number of elements (elernent density node spacing (biasing), element type and mesh style can be modified for each surface face and edge.

Use the Auto mesh panel to generate a mesh of plate elements using surface geometry or existing shell elements to define the mesh area.

I have used mixed elements instead quad and other elements available.

Uses quads primarily, but inserts trias when making density transitions, resulting in improved mesh quality. I have used mixed elements here to improve the mesh quality and it's easy to work on surface mesh.

Set the options in the panel in any order that you feel comfortable using. Moving from subpanel to subpanel will not cause you to lose work. When you are finished making all your selections, click mesh to start the meshing process.

  

• Set the panel mode by selecting the appropriate subpanel.
• Select the meshing method by setting the entity selector to surfs or elements
• Make the required element criteria settings.
• Set any algorithm options.
• Select the area to be meshed using the entity selector and any extended selection methods

 

After rebuilding

Rebuilding the mesh or rearranging the mesh pattern where ever the mesh flow is not smooth by selecting the elements and click on the mesh option.we repeat the same steps to improve the mesh quality

The meshed surface is shown below .

Cleanup tools:

The Quality Index Cleanup Tools secondary panel's layout changes dynamically depending on the cleanup tool you select to meet the quality these cleanup tools make use to change or modify the elements and node in particular direction and place, it helps to reduce the errors.

 

Place node: To move nodes along the surface or normal to the surface.

Modify the hole or washer tool: To modify the elements or nodes around the hole without changing the hole radius and also moving the washer elements to modify the radius and angular movement of the element.

Swap edges: Use the Swap Edge tool to consider the elements to which the edge belongs, and find alternative orientations for it. To improve the mesh quality and rectify the fail elements. For a pair of trias, there are two possible positions for their shared edge. For a pair of quads, there are three possible positions. For a quad and a tria, there are six possible positions.

Smooth: To improve the mesh quality of surface based mesh.

Node optimize: Use the Node Optimize tool to authmatically move a selected node to optimize the overall quality of its surrounding elements. The options along surface, normal to surface and along and normal to surface work exactly as described for the place node tool. The only difference is that node optimize moves the node automatically, while place node requires you to choose the location manually.

Element optimize: Use the Element Optimize tool to automatically optimize the shape of the selected element and the elements surrounding it. It is similar to Node Optimize, except that its effects are wider-spread.

Drag tria: To move the trias from one location to another or out of location.

Split quad: sometime quad elements are out of size then we can split the quad by click on the quad element

Edit element also used here to do similar kind of function, like create, combine and split. 2D> edit element>create (quad, trias, hexa. Etc.) Or combine or split the element

Save the failed elements then we can retrieve the elements to rectify the error in that particular elements. Quality > clean up tools > save failed > mask> elements > retrieve > mask>reverse.

 

Component is symmetry so we can made into two symmetrical, Due to complexity of the component first we have made the component symmetry through the geometrical tools. Geometry > trim surface plane or distance using two point. After marking the middle point of the component, use surface symmetry option where we can trim the surface with line two symmetrical surfaces.

Tools > reflect > elements > axis(x.y and z or surface normal or nodes N1, N2 N3 and B etc.)

Geometrical errors after meshing: Use the Align Node subpanel to snap one or more nodes to an imaginary line connecting two other selected nodes. Any number of nodes may be aligned once a line is defined

Assigning the Thickness.

Organizing the each component according to the thickness we measured. Creating the property and assigning the thickness, before assigning the property card for the component we need to rename and give same in the property block which is displayed below the box.

 

Assign the property to the midsurface component.

FINAL IMAGE

Outcomes:

• Learned to extract the auto-middle surface for complex models using offset method.
• Learned to mesh for complicate model with intricate geometrical shapes.
• Achieved quality criteria with less tria percentage using cleanup and other tools.
• Learned how to use extend, translate and organize etc. tools
• Learned and understand the how to repair the mesh as well as geometry after reflection
• How to clear fallen elements as per the criteria given.
• Learned how to assign thickness to components.

CONCLUSION

2D surface meshing on Rear wheel holder and middle surface extraction for all components separately is done as per the given quality criteria and assigned thickness to the model.