Rev 4.0 - Fixed Chassis, Accelerating Object

File Name: August22_KL_Rev4.0.wbpj

(Copied from: "July 1_TommyRev.wbpj")

Goal

• Previously, we fixed the back face of the collision object and accelerated the chassis into the object. Fixing this face fixes the entire body of the object as it is a single solid body.

• Rev 4.0 attempts to fix the chassis and accelerate the object into the chassis.

Simulation Set-up

• The following steps were used to set up the simulations

  • Suppress existing 5G acceleration

  • Suppress the existing fixed support on the collision object

  • Add new fixed support to the chassis

  • Add the equivalent force

  • Add displacement constraints to control the motion of the collision object if needed

Fixed Supports

• The general approach was to fix a minimal number of entities (vertices were used) and as far from the collision object contact region as possible.

• The proposed set-up introduces ambiguities due to the fact that the chassis is composed of multiple bodies/tubes, unlike the collision object. Thus, fixing different combinations of chassis entities will change the stress results.

  • For example, two cases are shown for the side 60 wall case.

Open

6 vertices fixed in the rear right corner.

Max Combined Stress: 1226.8 MPa

Open

Top tube of the C-plane is fixed.

Max Combined Stress: 586.29 MPa

Replacing Acceleration with an Equivalent Force

• Note that the 5G acceleration we specify is applied to all bodies in the model (i.e. collision object and chassis tubes). 

• In this set-up, we only want the collision object to accelerate however, any chassis tubes that are not fixed will also accelerate. So, we have the object and chassis tubes accelerating in the same direction and we may see lower stresses because of this.

  • Previously, we had fixed the object so only the chassis tubes accelerate.

• One option to work around this is to apply an equivalent force instead of acceleration. An equivalent force is calculated using the mass of the vehicle and the 5G acceleration. It is applied to the collision object face in contact with the chassis and acting in the direction normal to this face.

  • F=m*a=(720-160 kg)(5*9.81 m/s^2) = 27468 N (this force is for 2 passengers only)

Stress Results

Conclusions & Recommendations

• stress results can change drastically depending on the fixed supports selected (much higher or much lower)

• This setup can be used to our advantage to obtain lower stresses however, we will need to have strong justification for the fixed supports we choose.

• Overall, it might be best to stick with the fixed object setup to avoid ambiguities or any issues getting the VDR approved.