Preprocessor of Automobile's Door for NASTRAN - NVH Simulation using ANSA

Objective:

• For the Automobile's Rear Door part, Connections parameters to be defined for NASTRAN-NVH simulation solving.
• In this case, connection setups like RBE2, RBE3-HEXA-RBE3, RBE3-CBUSH-RBE3, Overlap-Shells, Bolts, Seam Welds, Seam Line Joints, etc. were used for their respective applications.

Geometry Preparation:

These CAD models were now to be checked against any geometrical errors such us normal orientation, Needle faces, etc. This can be done with the ANSA's checks manager which helps us to find the surface errors on the CAD geometry. In the checks manager, some options can be checked ON / OFF depending on the parameters required to be checked.

In the checks manager by clicking the Execute button ANSA will check for the surface errors on the visible geometry. Using several surface repairing tools provided by the ANSA these errors should be rectified. some errors can be automatically rectified using the AutoFix option in the checks manager.

After fixing the surface geometry the status icon on the checks managers shows a Green Trick Marks which resembles that the Geometry is error-free. The above images show that the part geometry is passed according to the checks manager criteria. In the beginning, the surface orientation set automatically may be in an incorrect direction as shown in the above picture.

So surfaces to be oriented manually oriented as shown in the above picture.

After the Mid Surface Extraction is processed the total assembly with its sub-assembly parts is defined with the respective property which helps for easy selection of parts to define its connection between them. The property Dialog box with the sub-assembly parts for this case is shown below.

Defining Connections:

Bolt Connection:

In the red ballooned area represented on the above picture, we know that a bolt is to be mounted/riveted during door manufacturing constraining the Door's Hinge along six degrees of freedom. So on ANSA, a 3D point is created at the center of the bolt hole. The point generated is further converted to Bolt entity where the connection parameters can be defined under the connection manager.

The above picture represents the connection manager interface where connection parameters were defined. Under Rep Type section 'Bolt' is selected. Then Part 1 & Part 2 components are selected which helps the software to understand where the bolt specification to be applied.

RBE2 Connection:

In the red ballooned area represented on the above picture, we know that part will be mounted/riveted on the Car's Body pannel. So for this NVH simulation setup, those points are considered as Rigid Body Element (RBE). On the above picture, the values for CM are inputted as 123456. Here the numbers from one to six represent the six respective degrees of freedom. 1, 2, 3 represents the degree of freedom along X, Y, Z Axises respectively in Translatory motion. 4, 5, 6 represents the degree of freedom along X, Y, Z Axises respectively in Rotational motion. For this Many Nodes RBE2 feature is used.

In the red ballooned area represented on the above picture, we can see that the two hinges of the door assembly are connected by hinge pins. For this kind of connection, we must ensure that the degree of freedom along Z-Axis rotational motion is not constrained which makes the door's opening & closing actions. For this Two Nodes RBE2 feature is used as shown on the below picture.

On the above picture representing 2 Node RBE2 wizard, the CM values are inputted as 12345 while excluding 6 as this parameter represents not constraining the rotational motion along Z-Axis.

SpotWeld Connection:

In the Door assembly, For two brackets with small surface contact areas that were welded together by spot welding for structural properties. So on ANSA, 3D points are created on both brackets where the spot weld needs to be applied. The points generated are further converted to spot weld point entity where the connection parameters can be defined under the connection manager as shown above. In the connection manager, for Spot Welding Connection the FE Rep Type is set to RBE3-HEXA-RBE3 with RBE3 Pinflags as 123456 constraining all degrees of freedom.

OverLap Weld Connection:

In the Door assembly, For two brackets with large surface contact areas that were welded together by Seam welding for structural properties. So on ANSA, A Feature Curve is created between those brackets where the seam weld needs to be applied. The curve generated is further converted to a seam line weld entity where the connection parameters can be defined under the connection manager as shown above. In the connection manager, for Seam Welding Connection the FE Rep Type is set to OVERLAP-SHELL with base sheet selected with the bracket which has a higher thickness value.

Bush Connection:

In the Door assembly, the connection between Glass and the bushes can't be defined as a Rigid connection. So the RBE3-CBUSH-RBE3 is used as FE Rep type for these kinds of Bush connections. In the PBUSH ID, a new part property with below shown predefined stiffness values is provided.

After setting up the bush connection parameters, ANSA represents the bush connection as shown above.