Connections of Car door FE model for NVH Simulation

AIM : To prepare the given car door FE subsystem for NVH simulation by deploying all the necessary connections.

PROCEDURE :

• The FE model of the Car door sybsystem is imported in ANSA.
  
  
• Firstly, different PIDs are assigned to all the individual entities present in the model.
  
  
  
  
• The NASTRAN deck is opened. In order to rigidise the holes, RBE2 - Many Nodes command is used under the Elements module. The restricted degrees of freedom are provided correctly as per the type of rigid available.
• Washer elements are deployed around certain holes where bolt connections are to be made, in order to effectively rigidise the entities. This is done by using the Zone Cut command under Shell Mesh module.
  
  
• The parts where bolt connections are to be established within the door subsystem itself, are connected by using either of the two methods -
  a) Manual method - By connnecting the master nodes of the rigidised elements using the RBE2 command.
  Even, connection between similar PIDs can be established by the clustered RBE2 method.
  b) Bolt connection method - By providing a 3D point at the COG of any of the rigidised elements, converting it into bolt connection and then using the connection manager to realize the bolt connection.
• The door hinge connection is also an exapmle of one such bolt connection. One thing to keep in mind here is, removing the one particular rotational degree of freedom around which the door is not constrained (here, global Z direction). Accordingly, the numbers specified under CM are only upto 5.
  
  
  
  
  
  
• Spot connections are established where two adjacent parts of the subsystem are connected by spotweld. To do this, a 3D point is created and converted into spotweld point. And finally, the connection manager is used to realize the connection. The FE represeantation is RBE3-HEXA-RBE3.
  
  
  
  
• The door handle connection is done in a slight different way. This is due to the fact that we model the door handle as a solid instead of shell modelling.
• To do this, the handle is represented as a point mass using the CONMi command under the Elements module. The mass is provided in tonnes.
  
  
  
  
• In practical automobile applications, the window glass panes are connected using elastic strips to ensure they won't get damaged due to the rubbing friction. Such strips are present on on either side of the glass pane along the bottom edge of the pane, while only on the outer side along the remaining three edges.
• In FE representation, the connection is established using the FE representation of RBE3-CBUSH-RBE3 in the connection manager. This representation ensures, elastic property of the connection elements in the three mutually perpendicular directions.
• The values of the six stiffness constants are provided while defining the PID of the bush elements.
  
  
  
  
  
  
• As per the latest modelling guidelines, all the bush elements are oriented as per the global coordinate system to ensure better simulation results.
  
  
  
  
• Similarly, the connections for the supplementary window glass pane are deployed.
  
  
  
  

LEARNING OUTCOMES : Got to know couple of important things -

• How to prepare the FE model for NVH simulation in NASTRAN
• How to deploy the different types of connections - bolt, weld, bush, etc
• What is the importance of rigidising the parts. If not done properly, what would be the effects on simulation.
• The different types of mechanisms present in the car door subsystem.
  
  

Sharable Google Drive link -

https://drive.google.com/file/d/1rBg6GEAC4gyyLs49Z46T5qqEui2AoGPq/view?usp=sharing