Simscape Multibody and Fluids: Hydropneumatic Suspension System

Hello,

I created a Simscape Multibody model of an agricultural Trailer. This vehicle has one axle and a tractor coupling. The axle is driven and the tires are connected via Spatial Contact Forces to the ground. I also integrated a mechnical damping system with two springs. In the described state the model is fully functional.

The next step was to "exchange" the mechanical springs with a hydropneumatic suspension. The following figure shows one cylinder of the suspension system (mechanical spring overwritten with hydraulic charecteristics by using a Translational Multibody Interface):

One end of the cylinder is connected to the axle the other one to the chassis. During the simulation the trailer drives on a test track with one hump (0.1 m height) at the end of th track. The simulation leads to the following piston discplacement (m) over time (s).

Now my problem: The total accumulator volume is currently set to 8 l in both Gas-Charged Accumulator (IL) and as soon as I try to reduce the volume the simulation starts but gets directly stuck at 10^-17 seconds. Does anyone know why I can't reduce the volume of the accumulators? The accumulators should have a size of ~1.5 l. I'm currently using the ode15s solver. If there are any public available Simscape Fluid models of hydropneumatic suspensions I would be glad if someone could post a link! I couldn't find any.

I'm also not sure why the the piston displacement is slowly increasing. The preasure is constant over time.

I hope the information are sufficient. I unfortunately cannot share the whole model, here.

Best Regards

Sven

Answer 1

[Yifeng Tang]

I suspect this has to do with the initial condition of the accumulator. For example, the I.C. starts at ~8L of liquid, so reducing total volume to less than that may cause problem. I won't be sure, of course, without seeing the actual model. If you could share that, I can take a look.