The CAD model was taken from GrabCAD from the user Stelu Harsan. The complete original model is as shown below:
The model was used to perform a simulation of the trailer undergoing a bump on the road. For this purpose, it was decided to perform first a dynamic simulation, and then use the results from the same to perform a dynamic simulation on the model.
The simulation is first edited, to make it simpler to mesh and analyze. All the parts unnecessary for simulation were removed. This included most bolts, suspension systems, and fillets and holes. After cleaning for simulation, the model looked like this:
The model above was used for Frequency analysis, but to save computational time and costs, the body was cut in half and only a symmetrical part taken for the Dynamic analysis.
The CAD was then uploaded to the SimScale platform and then meshed using fully automatic tetrahedrals, and with a few extra refinements added (to the parts coming in contact) for the dynamic simulation.
The results of frequency analysis are as shown below:
The first real mode (7th mode in the table) from this analysis (13.38 Hz) was decided to be used as an input for the dynamic analysis.
In the dynamic analysis, sliding contacts were used between the leaf-springs and the frame on one side, and bonded contacts were used on the bottom.
For the other side of the leaf-spring-frame contact, a physical contact was provided:
A load was then applied to the frame (ramped for the first 0.2 seconds, and then kept at a constant value) of the simulation, and this replicates the load acting on the frame due to things kept on the trailer.
After the first 0.2 seconds, a vertical displacement of 1cm was given to the front axle- this replicates the body going through a bump on the road. This 1cm can be varied easily, and is based on the assumption that the tyres and the suspension system act as superior dampers to allow little displacement to the axle itself.
The back of the body is allowed to undergo rotation along the Y-Axis and displacement along the X-Axis (caused by the vertical motion of the front of the body).
The results of the Dynamic simulation are shown below:
As the results show, the frame is first loaded from the top and hence not much deformation occurs in the first 0.2 seconds, but the stress values change by a small amount. The load has been ramped up, and hence there is a progression in the way the stress increases. Once the loading is over, the front axle starts moving (due to a bump on the road). This causes a change in the stress values all over the body.
It is important to note that the motion of the body is happening at a resonance frequency, and the stresses are hence higher than what would be observed at frequencies other than that at resonance.
Other simulations have also been performed:
- The simulation run called “Simulation with initial velocity” shows the body moving with 30km/hr (8.33m/s) when it undergoes the assumed bump on the road. The bump gets over in 0.8seconds, mimicking the case in real situations.
- The simulation run called “Non-resonance Dynamic Analysis Symmetric Leaf Spring” shows the body undergoing the same bump at frequencies other than the resonance frequency. It can be observed that the highest stresses in these simulations are lower than that for the body at resonance, which was expected.