When my kids were younger, one of the favorite entertainment options at children’s parties was the balloon artist. These artists were able to make anything from a monkey to a pirate hat simply by twisting balloons together. Usually, but not always, you could tell what the animal or object was meant to be, but it would take the most imaginative child to see the multi-colored lumpy lion in front of them as the real thing.

Whilst lions are not the most common shape for non-spherical DEM particles, should you have the need to model such a thing, previously your only option would have been the composite DEM particle and the result would have been much the same, a bunch of spheres of various sizes stuck together.

All of that is set to change with the polyhedral DEM particle in STAR-CCM+® software version 12.04. Now you will be able to accurately model real objects, putting the corners back into your particles, by building or importing a realistic representation as a geometry part which then forms the basis of your particle. For many objects, this new polyhedral particle is less computationally expensive then a composite particle which can require many spheres to get close to a realistic shape. Polyhedral particles also provide a more efficient solution, reducing simulation time.

If you pack too much matter into a small space, you are likely to get some undesirable consequences as anyone vacationing with small kids will be all too aware. If you have to sit on your suitcase to get it closed, you are likely to be greeted by the sight of your holiday clothes circling on the carousel at your destination. Similar consequences befall the engineer simulating two-way coupled fluid-particle systems when they overload cells in the CFD mesh with too much DEM matter.

I refer, of course, to the previous requirement that a DEM particle must be smaller than the flow cell it occupies for two-way coupled simulations. This limitation is due to the way the effects of the DEM particle are applied purely to the flow cell in which the particle centroid lies, and not to adjacent cells that are also overlapped by the particle. When DEM particles are larger than the cell, this results in large sources of momentum and energy being applied to individual cells causing instability and divergence. However, it is not just stability that can be compromised, but also accuracy, with the void fraction of the particle not being fully accounted for if the volume of the cell is smaller than the particle.

In practice, this rendered some applications impossible to simulate as geometrical features forced the mesh size to be smaller than particles.

The recent release of STAR-CCM+® v11.06 changes all that with DEM source smoothing…

As any connoisseur of champagne or beer knows, not all bubbles are the same. Creamy champagne and gassy stout have never caught on, although the former sounds vaguely appealing! The same goes for droplets for that matter – nobody likes a shower that produces a fine mist rather than an invigorating spray. These examples are an indication that the nature of a fluid is dramatically changed by the size of the droplets or bubbles contained within it.

The new automatic time stepping in STAR-CCM+® v11.04 automatically adjusts the timestep size of simulations dynamically. This helps to reduce time to achieve solutions for transient runs by avoiding the use of unduly small timesteps.

Deriving and supplying appropriate properties for complex structures has not been an easy task, but all that is about to change with the upcoming release of STAR-CCM+® v11.04, and the introduction of the multi-layer solid model for solids and shells. This feature allows for treating laminates made up from multiple layers of different materials as multicomponent solids.

Until the release of STAR-CCM+ v11.02, composite particles were needed when modelling anything cylindrical and, to get a realistic representation, this required a large number of spheres.With the introduction of cylindrical particles in v11.02, users will experience increased accuracy and reduced computational time, a rare win-win situation in simulation.

In the upcoming release of STAR-CCM+ v10.04, we have implemented a new equilibrium motion type for DFBI bodies is used for simulating the motion of moving bodies that tend towards a steady state equilibrium position. With this feature the body is incrementally ‘teleported’ to the current best estimate of the equilibrium position rather than allowing it to oscillate freely about it.

Multiphase modeling is coming of age in 2015 in STAR-CCM+ with the addition of a number of smart hybrid multiphase models that open up a range of new and exciting applications.
STAR-CCM+ now has no fewer than six multiphase models, each best suited for a particular range of applications and computational budgets, namely Eulerian Multiphase (EMP), Volume Of Fluid (VOF), Mixture Multiphase (MMP), Dispersed Multiphase (DMP), Lagrangian Multiphase (LMP), the Discrete Element Method (DEM), and the Fluid Film model.

In many applications, however, no one model is suitable for all the flow regimes that occur simultaneously at different points in the computational domain, and ideally we would like to combine the benefits of multiple models in a single simulation. Now with models such as the VOF-Fluid Film multiphase interaction model, this is possible.

STAR-CCM+ Part Coating Simulation

Rarely in life do we get the chance to get more for less, and the world of simulation is no different, or at least not until now.

Typically in our simulations we have to make compromises, and in choosing those compromises we need to know which models will give us the best information at the minimum cost. We must also understand the assumptions our choices carry and how these might influence the decisions we make. This after all is the art of being a good Simulation Engineer.

Before we begin and lose ourselves in the wonders of multiphase, imagine if you will a beach, the sun is beating down, the wind is blowing and the surf is up. The sea looks a little rough, but being a good Simulation Engineer the foamy seas pose no worries to you and your recent lunch…..

Island Eisberge am Schwarzen Strand 19

Overset Mesh is one of the coolest technologies in STAR-CCM+ as it allows objects to move around your computational domain freely without tying your mesh in knots, be that an overtaking car, an excavator arm, or the complex multiple motions involved in a production line. The motion does not even have to be prescribed, the Dynamic Fluid Body Interaction (DFBI) model allows you to solve for motion, in six degrees of freedom or less, based on the forces and moments acting on a body, such as a boat on a free surface, or a ball in a ball valve. To date, however, there has been one major constraint when using Overset Mesh, namely that all gaps had to be resolved with at least 2-4 cells, however small the gap, for Overset Mesh to work correctly. This limitation meant that for some cases with very small gaps, users had to choose between excessive cell counts or increasing the gap size in an unphysical manner.

No Need to Mind the Gap

The upcoming release of STAR-CCM+ v9.06 removes that constraint with the introduction of gap handling for Overset Mesh via the new “Zero Gap” Interface type.


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