Knowledge Base

Article Number: 8 | Post Date: July 15, 2016 | Last Updated: July 15, 2016

Can I include guard rails in my simulations?

Yes. As with most things, in Virtual CRASH 3 there are a couple of ways to do this.  In this example, we're going to use a Google Earth aerial of our highway:

Let's locate the barrier objects that are included in the Virtual CRASH 3 objects library. These can be found in the gallery as well as by going to vehicles > barrier > 0:

You can see the various types of barriers included in Virtual CRASH 3 in the Vehicles & Objects list

For this case, we'll use crash-barrier "9 x 0.8 x 0.16 m." Here we'll place three in our scene:

Each of these barriers by default will act as effectively an immovable barrier object, though you can set the weight to your needed value. We want to combine them into a single geometry so that its collision volume is unified. That is, we want the bounding box used by the Kudlich-Slibar collision model to enclose the full volume of the guard rail. So, first select all three barriers, then go to Create > Physics > Remove Physics From Selection. 

Align the barriers so that they all have yaw = 0 and are aligned in y. Don't worry if they don't line up with your aerial yet. 

With the three aligned guard rail objects selected, export them as a vcm file by going to Project > Export. 

Let's place another guard rail object in from the vehicle database. Now, drag and drop your vcm file icon from your Windows browser on top of your new guard rail object.

 You'll be asked if you want to replace the mesh. Answer yes. You'll notice the combined mesh of your three-guard rail object is fit into the volume of the fourth guard rail. 

Now simply increase the length of this guard rail to match the length of the original three:

Finally, you can delete the original three guard rails or hide them. Since physics has been removed, they won't interact with your vehicles. 

Adjust the CG location ("pivot point") such that it is in the geometrical center of your guard rail object:

Finally, adjust the orientation of your guard rail. Place your vehicles in your simulation, and adjust the depth of penetration, coefficient of restitution, and maximum coefficient of friction parameters in the contact menu as is appropriate for your case. Here we show depth of penetration = 0, coefficient of restitution = 0, and maximum coefficient of friction = 1. Remember, the Kudlich-Slibar model assumes a common velocity condition will be satisfied in both the collision normal direction and the tangent direction, up to the maximum allowed coefficient of friction threshold. For side swipe type impacts, if the coefficient of friction needed to achieve common velocity along the tangent direction is larger than the maximum coefficient of friction threshold, then the objects will continue to move with a non-zero relative tangent velocity post-impact.

Note, you can ensure your simulation is using the Kudlich-Slibar model for vehicle versus guard rail impacts by confirming that "preferred:kudlich-slibar" is selected in the contact menu for both your vehicle and your guard rail objects. If "default-auto" is selected for either object (or both), then the collision will be simulated using the default-auto model. Kudlich-Slibar is preferred for these impacts since its interpretation is straight-forward, easy to correlate with hand calculation techniques, and the resulting data is accessible through the auto-ees data container object as well as in the Report.

One more thing to keep in mind: the "friction-ground" parameter under the guard rail object's contact menu specifies the coefficient of friction at the ground contact points for the guard rail. Since the guard rail is set to an extremely high mass, the ground contact friction effectively prevents the guard rail from moving at impact. This could also be accomplished by using joints attached to a ground plane. 

Tags: Guardrail, guard rail, coefficient of friction, coefficient of restitution, barrier impact, Kudlich-Slibar, Kudich, Slibar, vcm file, rigid barrier. 

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