Deploying connections on the Rear Door of a Passenger car

AIM:

To deploy connections on the given FE model of a passenger car rear door.

OBJECTIVE:

The objective of the project is to learn & practise the concepts of deploying connections on FE models.

PROCESS:

1. Importing method for .nas model
2. Deploying various connections
3. Defining CONMASS
4. Creating spot weld
5. Changing the orientation of CBUSH elements

 

SOFTWARE USED:

ANSA (Automatic Net generation for Structural Analysis) v19.0.1 64 bit

MODEL:

In this project, we are given a FE model of a rear door of a passenger car on which the connections need to be deployed before the model is loaded into the solver.

IMPORTING METHOD FOR .nas MODEL:

The importing method for .nas models is different from that of .IGES or .ANSA models. Once the ANSA application is opened, under the FILE tab we have an option INPUT. Under this the NASTRAN option is selected. The solver for NVH analysis will be NASTRAN .

Then in the dialog box, the file path is entered and the required file is selected and opened.

PROCEDURE:

DEPLOYING VARIOUS CONNECTIONS:

There are many types of connections available. They will be used and deployed depending on the model and the instance where it is used.

Rigid Body Element (RBE2):

As the name suggests, this is a type of connection which makes the selected nodes rigid and prevents movement with respect to the translational & rotational x, y, & z axis. This type of connection is generally called as RBE2. It is of two types, Many node RBE2 and Two node RBE2.

The RBE2 command is in the NASTRAN deck module under ELEMENTS module button. In the options select Many nodes.

This connection is given in the holes of the door hinges which connect the door with the car body or BIW. The nodes can be selected one by one, or by using the Loop selection method.

Upon clicking the Next button in the dialog box further, the Rigid Body Element (RBE2) connection is created.

In this connection, the selected nodes are called the Slave nodes and a Master node is created. These slave nodes’  movement is dependent on the movement of the Master node.

Cluster RBE2 (or RBE2 spider):

This type of connection is similar to the RBE2 connection, but differs in the manner the connection is deployed. This type of connection is given between the two or more holes and is deployed using the same RBE2 command. The nodes of the two holes are selected.

Upon clicking the Next button in the dialog box, the Cluster RBE2 (or RBE2 spider) connection is deployed.

This type of connection is deployed in places where there is very less movement involved unlike the RBE2 connection where no movement is involved.

Similarly, other holes of the hinges are also given connections using the Cluster RBE2 connection.

As in RBE2 connection, the nodes selected manually are called the Slave nodes and a Master node is created. The movement of the slave nodes is dependent on the movement of the Master node.

Two node RBE2 (Stem representation for bolts):

This type of connection is given between two Master nodes of a RBE2 or Cluster RBE2 connection. It is also called as the stem representation as the connection once deployed looks like the stem of a bolt with the two sides of the connection rigid resembling a nut & a bolt. This connection is available as an option under the RBE2 command. In the options select Two nodes.

Now, the two master nodes are selected.

After accepting, the dialog box appears where the name of the connection is given.

After the command is accepted, the connection is deployed.

The value EID denotes the Element ID and CM denotes the Degrees of Freedom. Here, 123456 denotes that the movement is restricted in translational and rotational x,y and z axis.

Similarly the two node RBE2 connection is given to the other hinge.

The window glass in the inside & outside is covered with black rubber like material. These are called the Weather strips. The weather strips are a very important part of the Air-conditioning system in any vehicle. These are the ones which help us to realize the effect of the air-conditioning system. Without the weather strips, there would not be any effect of the air-conditioning system as there would be a constant heat transfer between the interior and exterior of the vehicle. These are given connections using the CBUSH elements with Spot weld.

 To create a spot weld we need to create a spot line. Spot line is created by converting curves into spot lines. So the window glass is separated from the rest of the model using the !NOT command and the curves are created.

The curves are created using the FEATURE2CURVE command under PERIMETERS module button in the MESH mode. The edge of the window glass is selected one by one using the Feature line selection method with the angle 40^°.

After accepting, the curve is created.

Similarly, the curves are generated for other edges.

Then, a copy of the curves is generated using the TRANSFORM -> COPY command. The TRANSFORM command is under the UTILITIES tab.

The curves are selected and the distance and axis on which the curves need to be offset are given. Then the curves are created.

The created curves are then converted to Spot lines. This is done using the CONVERT command. It is under the ASSEMBLY  tab. Under the CONVERT command select CURVES.

Then a curve is selected and upon clicking the middle mouse button, a dialog box appears. It can be seen that many options are available. In the dialog box, the SPOT LINE option is chosen.

After clicking OK the Spot line is created.

Similarly all the other curves are converted to Spot lines using the same command.

Then the Spot lines are used to deploy CBUSH connections. This is done in the CONNECTION MANAGER command. It is under the ASSEMBLY tab.

In the CONNECTION SELECTION ASSISTANT dialog box, the Spot line to which the connection is to be deployed is selected.

Upon accepting, the CONNECTION MANAGER dialog box appears. In that the spacing between the CBUSH entities (S) in the left side bottom is given without which the CBUSH connections cannot be deployed.

Then the surfaces P1 and P2 are selected. These are surfaces between which the CBUSH connections need to be deployed. In this case, we select P2 as the window glass and P1 as the surface in the inner side of the door panel.

Under the FE Representation settings in the right side, FE Representation Type is chosen as RBE3-CBUSH-RBE3.

Then the SEARCH DISTANCE is given. It is the distance within which the ANSA software searches for deploying the connections. The KEEP ALL BRANCHES checkbox needs to be ticked. This is done to create 3 or more nodes for connection of RBE3 because if a RBE3 is created with <3 nodes, the connection would not be proper.

Then a CBUSH ID needs to be created. In the PBUSH ID value box, press the SHIFT button and ? to open a PBUSH help window. Here the PBUSH ID can be created with a mouse right click, NEW command.

In the PBUSH dialog box, the name for the PBUSH connection is entered and the stiffness values K1 to K6 are entered.

NOTE: The stiffness values K1 to K6 are pre-requisites for doing the analysis.

After the PBUSH ID is created, the same PBUSH ID is selected by double clicking.

Then click the APPLY & REALIZE button to apply the CBUSH connection in that region and realize the connection.

The same way, the CBUSH connections are made using the other spot lines.

DEFINING CONMASS

Next, we have to model the door handle of the vehicle. To model the door handle, we will be modelling it as a solid mass or conmass.

First, the holes on which the handle is mounted are made rigid using the RBE2 connection.

Then another RBE2 connection is given between the master nodes of the two connections.

Now, the conmass needs to be defined. It is defined using the CONMi command, which is under the ELEMENTS module button. In the options select CONM2 -> Nodes.

Now select the master node of the two RBE2 connections.

After accepting, the CONM2 dialog box appears. In the dialog box, the name of the conmass is entered and the solid mass value is entered. The mass value should be entered in tonnes.

Upon accepting, the mass is defined.

CREATING SPOT WELD

Next, we need to create a spot weld. This is done by creating a 3D point. The 3D point is created using the ON COG command under the POINTS module button in the TOPO module.

The point is created by selecting the perimeters of the FE elements and accepting.

After creating the 3D point, the point needs to be converted to Spot weld point. It is done using the CONVERT command in the ASSEMBLY tab. In the options select 3D points.

Now the 3D point is selected and in the connection type dialog box, Spot weld point is selected.

Spot weld is created using the CONNECTION MANAGER command which is under the ASSEMBLY tab. In the Connection selection assistant, select the Spot weld point and accept.

In the CONNECTION MANAGER dialog box in the left side bottom pane, select the P1 and P2 surfaces. These are surfaces between which the spot weld needs to be created.

Under the FE Representation settings in the right side pane, select RBE3-HEXA-RBE3 as the FE representation type.

 

 Then give the search distance. In the RBE3 pinflags, give the value as 123456. It denotes that the Degree of Freedom is locked in translational and rotational x, y & z directions. Select a PSOLID ID by clicking on the PSOLID ID value box and pressing SHIFT and ?.

 

 Now click on the APPLY and REALIZE to deploy the weld.

 

 CHANGING ORIENTATION OF CBUSH ELEMENTS:

The Orientation of each CBUSH element is different from the other. In this case, if the model is imported into the solver and the analysis is done, the result may vary. So the orientation of all the CBUSH elements should be same and should match with that of the vehicle during analysis.

To change the orientation of the CBUSH elements, we need to select all the elements together. Open the DATABASE which is under the LISTS tab. The keyboard shortcut to open the Database is F12.

 

 In the Database, the CBUSH elements are under the ELEMENT sub-category.

 

 

 On double-clicking the CBUSH, another window opens within the Database with the CBUSH elements and their IDs. Select all the CBUSH elements with their IDs and right-click and click on MODIFY to modify the CBUSH elements.

 

 

In the MODIFY dialog box under Modify rules, search for Orient – With Cord.

 

Also the Coordinate ID of the CBUSH elements needs to be changed. Using the + icon, search for CID and in the value box for CID enter 0.

On clicking OK, a warning message appears.

After accepting the message, the Orientation of all the CBUSH elements are changed according to the local co-ordinate system.

LEARNING OUTCOME:

In the above project, I have learnt the various types and methods of deploying connections, Rigid Body Element (RBE2) & its’ types, Spot weld, CBUSH connection and defining CONMASS. I have also learnt how and why the CBUSH elements' orientation needs to be changed before importing the model into the solver for analysis.

CONCLUSION:

Thus, the connections are deployed on the given FE model of a Passenger car rear door.