Project - 2 - Meshing on the suspension Assembly

Aim:

        According to the given quality criteria, mesh the given rear suspension model in both 2D and 3D (according to the given quality criteria) after checking for and clearing geometrical errors. Also, to deploy appropriate connections as required between various parts of the assembly after which the model is symmetrically replicated using the reflect tool.

Quality Critetria:

Tyre and Rim (Trias):

S.No	Quality Criteria	Value
1	Target/Average length	6.5
2	Minimum Length	5
3	Maximum Length	10
4	Skewness	45

Other Regions:

S.No	Quality Criteria	Value
1	Target/Average length	4
2	Minimum Length	2
3	Maximum Length	6
4	Skewness	45

Tetra elements Quality check:

S.No	Quality Criteria	Value
1	Tet-collapse	0.2

2D midsurface and meshing: 

S.No	Quality Criteria	Value
1	Target/Average length	4
2	Minimum Length	2
3	Maximum Length	6
4	Aspect	3
5	Warpage	15
6	Skewness	45
7	Jacobian	0.7
8	Minimum Quad Angle	45
9	Maximum Quad Angle	135
10	Minimum  Tria Angle	30
11	Maximum Tria Angle	120

Procedure:

              1.To start, the topo tool is used to take care of all the single cons and to ensure there are no free edges. It can be accessed via Faces > Topo in the topo module. In this case, due to the proximity of edges in this assembly, it's a good idea to carry this out separately on each part to avoid triple conformation.

2. Then, before we carry out any other actions, we need to carry out a geometry check and fix all abnormalities. That is done via Checks > Geometry where we can execute checks of certain defects that can be selected from the menu and the algorithm looks for said defects. After detection, we can select all the defects and right-click > fix to fix them.

 3. Along with taking thickness measurements, it would be easier to assign PIDs to various parts of the model as well. To set up some connections, it is important to differentiate components with the help of PIDs. This entails the first step. The entire model will be separated into different PIDs. This requires creating said PIDs, which can be done via Faces > Set PID in the topo deck. The part is then selected and the middle mouse is clicked to bring up the properties window Here, the new property can be created and assigned as seen above (Thickness - T in this case). This process is repeated until PIDs have been assigned for every component/part in the model.

  4. While assigning PIDs, we can midsurface the parts that will require 2D meshing and then assign PIDs to these mid surfaces as well. For midsurfacing, I used the offset tool (Faces > Offset). When activated, it will ask us to select the surfaces to offset. We can select the surfaces on one side of the part. After that, we can assign the offset value (half the thickness). The offset tool will show the direction of the offset in the form of an arrow. If it is in the opposite direction of the required offset, the offset value needs to be in the negatives. If we proceed, the surface will be offset and we will have the option of keeping the parent surfaces

 5. After this, the surfaces need to be prepared for meshing. This means regions that can result in minimum length failures need to be tended to. In such locations, cons can be suppressed at the expense of features as long as it's minimal. This is done by right-clicking the cons using the Faces > Cut tool.

6. Before meshing, we need to set the target length (through perimeter > length). With that taken care of, we can assign the other parameters. This is done by accessing mesh parameters and quality criteria from the top toolbar.

The following are parameters and quality criteria for parts:

the parameters and criteria for tria 2D meshes on the tyre and rim:

the parameters and criteria for the midsurface 2D meshes:

7.We can then start meshing each of the parts as per the mesh requirements (2D Mixed mesh using Mesh Generation > Best from the Mesh module and 2D tria mesh using Mesh Generation > Spot).

we can make use of the reconstruct tool (Shell Mesh > Reconstruct) to generate a better mesh if the initial mesh is not satisfactory. If required, the smooth tool (Shell Mesh > Smooth) can be used as well.

8. After meshing all regions, we can proceed to the next step of assigning volumes manually to each set of closed-shell elements (for the volumetric meshing). This is done by using Volumes > Define > Manual and then selecting the regions that comprise a particular volume. Auto automatically detects and defines closed volumes that are selected whereas the manual option lets us define properties for the volume that is to be defined. Either method works here 

After the volume is defined, the list of defined volumes can be accessed from Volumes > List. The volumes that are unmeshed can be 3D meshed by rt. clicking the particular volume and selecting 'remesh' as shown

9. Next, we need to check the solid elements to see if any fail for the tet collapse criteria of 0.2. Before doing that, we will need to access the solids tab as well on the quality criteria window to input the tet collapse criteria.

Now we need to switch to hidden mode to check for tet collapse errors. There are two ways to fix tet collapse failures. One is by using the Fix Quality tool from the volume mesh module (Improve > Fix Quality). This is an algorithm that works on failing elements

To avoid this, the MV free tool can be used (Grids > MV Free) which is available in the mesh module. This lets us manually drag particular nodes of the failing element such that the height of the tetra element can be increased. This helps pass the test collapse criteria. Understandably, to avoid the same problem as in the Fix Quality tool, care should be taken to not move nodes that are on the surface of the component but the ones that are below the surface.

Meshing Spring component: 

10. For this, we shall be using 1D CBAR elements to represent the part. Firstly, we can generate a middle curve that runs through the entire spring by using the middle tool from the curve options (Curves > Middle) of the topo deck. We will need to select the cons that run through the entire length of the spring that are on opposite sides of the part as shown:

We then have to convert the curves into a single one, if it has been broken up into multiple curves. This is done using the Curves > Connect > Multi-tool.

11. Having done that, we can move to the NASTRAN deck and go to Elements > CBAR and in the window that pops up, 'orientation with nodes' needs to be checked and the selection needs to be 'Curve (box)'. The curve is then selected and we can click the middle mouse button.

After that, we are asked to pick the orientation point and we can select the COG for that. On proceeding, we are to specify the element length as well. We can go for 4mm.

12. After that, on clicking the middle mouse button, we are to assign a property to this curve. We can go ahead and create a new PID. In the next window, we are to input the area (A). In that selection box, we can press Shift + ? to open another window where we simply need to specify the cross-sectional radius of the spring. In doing so, the algorithm automatically calculates and populates the other values on the PID card as per the given radius.

13. These can be represented as 3D solids as well. To do that, we simply need to check the 'Lines Element Cross Section' box and select 'as solids'. These options are available in the presentation parameters tab of the Quality Criteria window.

Connections:

14. Now that all the parts have meshed, we can move onto deploying the connections.

 To connect regions where a bolt and nut is required, we can use the Two node RBE2 option. The RBE2 tool can be accessed via Elements > RBE2 in the NASTRAN deck. It primarily has the 'many nodes' and 'two nodes' options. This procedure involves connecting two sets of RBE2 spiders using a double con.

Firstly, the RBE2 component is created separately for each hole using the Elements > RBE2 > Many Nodes option. We can select the nodes surrounding the hole and the middle mouse click to form the elements.

15. Another type of connection deployed in this model would be the seam weld connection. In the case of seam welds, the basis is creating the weld locations from curves derived from the particular feature. Therefore, we shall be using the Curves > Cons2Curve option from the topo deck.

16.After we have meshed the entire model and deployed all possible connections, we can go ahead and reflect it to produce the other half of this rear suspension system. This is done using the reflect option from the Transform tool.

Result:

The meshing of midsurface part:

With Shell as solids active in midsurface parts:

The meshing of Tyre and Rim:

The meshing of remaining regions:

Full suspension model with no tet collapse :

Full model with connections:

Learning Outcomes:

1.  Tetra-meshing and connection deployment processes.

2. Learnt to use 1D CBAR elements to represent spring components.

3.Learnt more about various parts involved in a standard suspension assembly.

Conclusion:

The given suspension assembly was checked for geometrical errors and fixed accordingly. In addition to that, it was meshed in both 2D and 3D as per the given quality criteria and parameters. Connections were deployed and finally, the symmetrical half was created and reflected to complete the other side of the assembly.