One of the great things about working for CD-adapco is that I get to see a lot of cool animations that illustrate the exciting capabilities that are coming soon in STAR-CCM+. The frustrating part is that usually I can’t share these with you until just before the new feature is released. Which is why today I’m excited to show you two of my favorites, which I find myself watching over and over again.
Both videos illustrate the new contact model for the DFBI (Dynamic Fluid Body Interaction) solver in STAR-CCM+ v9.04, which allows you to directly model contact and collisions between moving bodies and boundaries.
As you probably know by now, STAR-CCM+ is rather excellent at simulating moving bodies, particularly when using the DFBI model coupled with overset mesh. For those not familiar with this technology, the DFBI model is a six (or less) degree of freedom (6DOF) solver that calculates the motion of a moving body from the fluid forces and moments acting upon it, whilst overset mesh allows bodies to freely move in response to those forces and moments without tying the mesh in knots.
Before the release of STAR-CCM+ v9.04, and without the ability to handle contact, moving bodies had to remain in free space and not collide or overlap, and if contact did occur the simulation would have to be stopped. This capability, whilst sufficient for many usage scenarios where it was enough to merely detect that contact had occurred, ruled out the simulation of some important application areas.
The new DFBI Contact Coupling, as the new model is known, joins the existing Linear Spring and Catenary coupling models for modelling additional (non fluid) forces acting on DFBI bodies, and to get an idea of what this model makes possible, I come to the first animation that caught my eye...
Now assuming you can tear yourself away from pressing play, I shall continue…
Here we see a ball valve simulation carried out entirely within STAR-CCM+ where the inlet pressure varies sinusoidally from a negative to a positive driving pressure difference. Initially the ball is in position closing the valve, with the pressure and gravity forces in perfect balance with the new contact coupling force, previously the ball would have drifted through the wall like a ghostly apparition (to stay on our theme of things that go bump). As the driving pressure goes positive and becomes sufficient to overcome gravity, the ball lifts up and collides with the retaining ring above which it then bounces off a few times before settling in place. The driving pressure then drops and the ball returns to it’s initial position.
So, having seen it in action, how does the contact coupling model work?
The normal contact force is based on a spring and damper model which acts once the DFBI body comes within a specified distance from boundaries. The further the body travels over this line, the greater the repulsive force, a bit like an aircraft carrier trap, allowing objects to be stopped before impact. When using overset mesh, it should be noted that it is still necessary to retain up to 4 cells in the gap, so in this case the contact coupling model would be set up so objects effectively bounce off the 4th prism layer. The examples shown here are done in this way.
The contact coupling model can be used in tandem with any of the other DFBI coupling models, such as the catenary coupling model, which brings me to my second example of a moored boat…
Again, I think you will agree, worth watching more than once. In this case , the boat is reacting to the buoyancy forces due to the water, gravity, two catenaries , and most importantly the contact coupling model which prevents it from passing through the harbor wall, making another application that could not be done previously, possible.
Now it is over to you, and with the upcoming release of STAR-CCM+ v9.04, which is released at the end of June, I am sure we will be seeing a lot more great examples over the coming months.
Stay tuned to the CD-adapco Blog for all the latest information.