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AIM: To implement connections for a Rear Door FE model. OBJECTIVE: Understand car rear door assembly Understand different types of connections and 1D elements. Perform connections for a FE model. Methodology for giving connections: Import the FE model Understand the geometry and mechanism Give connection…
Akash M
updated on 17 Oct 2021
AIM:
To implement connections for a Rear Door FE model.
OBJECTIVE:
Methodology for giving connections:
Introduction:
Car Rear Door Assembly
Connection and 1D Elements:
There are mainly 5 types of connection
1D Element :
one of the dimension is very large compared to the other two
If a large number of bolts are to be modeled, then the use of solid element representation can be far too burdensome in terms of setup time, contact complexity, and computational cost. An alternative is to use a 1D beam element representation. This can also use a similar preload method.
There are many different implementations of this approach, but we will focus on a method which uses a rigid element to spider out the head and nut tend of the bolt to the top and bottom plate respectively, and can connect to 2D or 3D element representation
They are simply the connection between nodes. There are few working elements majorly used:
CROD:
CBAR:
CBEAM:
Rigid Elements:
A rigid element is a link from one node to one or more other nodes, where the motion of the node(s) is governed by the "degrees of freedom" you choose to connect. A rigid element is actually a constraint equation rather than an actual element.
RB2: Rigid link to transfer motion from the independent node to the dependent node(s).(figure below)
RB3: Rigid link to distribute loads and will not induce any stiffness.(figure below)
Note:
Connectors:
These are the geometrical representations of the connection between the entities. The advantage of connectors is the ability to create multiple connections at a single time.
Spot
Bolt
Seam
Area
Role of a seal in the NVH behavior of a car :
Automotive weather seals are typically dual extrusion bulbs of sponge and dense rubber that are attached to either the door or the car body in order to seal the passenger compartment. The seals can be held in place in several manners, e.g. intermittent pushpins, continuous carriers, etc., and have a vast variety of shapes with a height of approximately 10-30 mm. The seal wall thickness is typically a few millimeters to provide a maximum sealing area at a low compression force.
The seal strip induces some residual stiffness and viscoelastic contribution to the door support conditions and plays a role in the way exterior noise and vibration can be transmitted to the interior of the car. The initial use of seals in automotive applications was aimed at accommodating construction variations.
Lately, the isolation issue became important, and the design was oriented to better isolate the passenger compartment from dust, water, and air leakage. Nowadays the general trend in seal design is mainly oriented on the isolation of the passenger compartment from noise and vibration. For automotive applications the material requirements aspect, such as resilience, weather resistance (including ultraviolet radiation effects), bonding strength, tear, abrasion resistance, etc. also need to be considered when designing for optimal weather seals.
At a certain driving speed, the pressure difference between the interior and the exterior of the car pushes the seal outward. If the resultant pressure is higher than the frictional forces at the contact area, separation occurs. The occurrence of separation is influenced by the compression rate and the friction coefficient of the rubber to the metal contact area. When separation occurs, an open path for direct noise is created and turbulence at the door edge is generated. The turbulence is due to the interaction between the escaping air fluxes from the passenger compartment, encountering the air fluxes at the exterior of the car.
The damping, stiffness, and the mass distribution influence the car door vibration levels and the mechanism of energy transmission from the door to the car body. The support and isolation characteristic of the seal becomes important performance factors that should be taken into account in seal design and analysis.
PROCEDURE:
Import FE model
The FE model is in a .nas format so we need open by using 'input' shown below
Once you open the model understand the mechanism and necessary areas that need to rigidised or made connected.
Firstly, we will cover all bolt connections through the RB2 stem element. we will perform this connection by using the auto-mode for the selection of nodes.
Open the connection manager to select the type of element and surfaces to be made connected.
Assign the values and P1, P2 surface to be made connections with.
Assign search distance as: 20, zone: In/outX check the Body column to keep RB2 stem body(see below).
once you are done with assigning values then apply and realize the connection.
Do the same with all other bolt holes and this can be done for all the holes by selecting them in a one GO process.
Note: surface selection(P1, P2,etc.) by modify-> then use F1 key-> then after selecting press twice Enter key
Hinge connection
connect the surface of the overlapping surface with the help of RB2 cluster element
Once the cluster RB2 elements are assigned the rotating link is made using a two-node RB2 element where the CM parameter represents the DOF here we assign 12345. As it is to be noted that 6 is intentionally not provided to allow rotation DOF about Z-axis. Therefore DOF in all directions is arrested to expect rotational motion about Z_axis, so as to allow the opening movement of the door.
A similar process can be done for the lower hinge joint.
Open holes and slots connections
We will use RB2 many nodes option to rigidise those nodes. one by one we will select the open slots and holes any assign them many nodes RB2 rigid elements. (shown below)
Note:
Handle connection
We need to assign the mass to the COG of the element connecting two slots with cluster nodes connection. For doing so we will use COMM2 & assign value for mass ('M' as 0.0001 tons).
Weather seal with the window glass
Now we have to finally make connections for weather seal strip and window glass. To do so we need to follow certain steps.
1) Hide the FE model except for the glasses.
2) construct the curve all around the glass edge using Fea2curve tab. Select each edge of the glass one by one to do so.(as shown below)
3)Covert the curve to spot lines. (one curve at a time)
4)Go to the connection manager to assign a connection. we use the RB3-CBUSH-RB3 element to assign connection. Also, set the PBUSH ID (doorlinks) to assign the stiffness values.
note:
5) Select the P1 P2 carefully then apply and realize.
6) Change all the CBUSH element orient as 'cord' and CID as 0. To change the orientation of the element from local to global coordinate system.
CONCLUSION:
After the completion of the challenge, it can be concluded that for any type of model the understanding of the mechanism is very important. As the mechanism will decide in analysis ways to make decisions regarding assigning connections. The connection procedure is moreover the same for any type of model but the requirement to assign the connection may differ from model to model with the requirement of the analysis. So for the NVH analysis, the weather seal was important to capture and is captured in a pretty good way with help of CBUSH element. Most of the areas are covered and are been rigidised as well as connected as per the requirements.
LEARNING OUTCOME:
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