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I've always been a terrible pool player. Until recently, I attributed this complete lack of talent to my abysmal hand-eye coordination skills. As it turns out, I may have been too hard on myself in that my inability is almost entirely due to the fact that I generally fail to properly take account of all the physical phenomena that influence the pool table when making a shot. More specifically, it's because I usually neglect to to take account the gravitational attraction of the big dude sitting at the opposite corner of the bar. In the past few blog posts we've talked about the importance of 'simulating the system', the process by which we try to account for all the factors that are likely to significantly influence the performance of a design in operation, and how failing to account for some of those physics can reduce the accuracy of your prediction. Exactly the same principles apply when lining up a pool shot!

Pool Break

On paper at least, calculating the elastic collision of two pool balls is a relatively trivial task. Let me explain…

Over the last couple of days, the “World of CFD” has been buzzing about our recent acquisition of Red Cedar Technology. The word “acquisition” can sound a little frightening as it’s often associated with mis-management, changes to the way customers interact with vendors and a myriad of other oh so fearful changes. Anyone old enough to remember that debacle in the 1980’s between Bendix and Martin Marietta (one of the most complicated takeovers in corporate US history) knows what I’m talking about.

Twelve months ago, Red Cedar Technology and CD-adapco announced a partnership to expand multidisciplinary process automation and design exploration.  We had a clear vision for how to enable engineers to quickly discover better designs rather than spend the majority of their time on tedious model building and validation.

This vision comprised solutions for the following typical obstacles to broad-based design exploration:

Last week we announced the release of STAR-CCM+ v8.04, the second of our three v8 series for 2013. I can see from the download logs of the Steve Portal that many of you downloaded the new version within the first few minutes. I hope you are enjoying all the new features and enhancements. While I could talk at length about these new bells and whistles, I'd prefer to explain the rationale behind STAR-CCM+ v8.04, and explore the philosophy of our development strategy.

One of the consequences in maintaining our aggressive release cycle is that it’s easy to become distracted by the list of individual features that arrive thick and fast every four months. One may miss the bigger picture of what we are trying to achieve.  You see, very few new features in each release are 'one-off enhancements.' Most of them could be better viewed as building blocks towards a larger development objective (although we do hope that many of these new features are instantly useful).

We've all been mesmerized for years by that thing of beauty rising out of the water majestically in that James Bond movie... If you're thinking Ursula Andress or Halle Berry or Daniel Craig, think again. I'm an Engineer and to me, the submarining Lotus Espirit from The Spy who Loved Me is my equivalence of a teenager's infatuation with water entry of matinee idols. In my fantasy world, my car would run on road, swim in water, fly in air and even brew me a nice, cold beer while I watch football. The Lotus Espirit ticked off two of those boxes quite handsomely.

When I was tasked with showing off new application areas with STAR-CCM+’s Overset Mesh feature, I scoured the internet for a model of the Lotus Espirit. In the end, I had to settle for a worthy substitute, the Assault Amphibious Vehicle (AAV7A1) used by the United States Marine Corps. The engineering design challenges for an amphibious vehicle are primarily the reason they are few and far between. In the case of vehicles like the AAV7A1, requirements of dual capability of speed in water and land in extreme conditions combined with a light armor to keep the weight down result in working within a tight design space. One of the major concerns when designing such a vehicle is the crossing from land to water or vice versa. Safety of the crew and the vehicle as a whole is of paramount importance when crossing into a different environment.

Water entry simulation

Numerous parameters play a role in the vehicle’s behavior when entering water or land: vehicle speed, direction relative to water and slope of the beach being the most important. Key factors in assessing the safety of the beach ingress are the maximum pitch and roll angles as the vehicle enters water, maximum accelerations on the vehicle and flooding of engine and passenger compartment. The body shape, weight distribution and size of the vehicle are already defined based on the mission requirements to achieve proper performance for land or sea. Safety tests are usually done on a prototype in a test basin using varying angles of ground slope and speed for entry into the water.

Simulation of water entry is currently being used in analysing the vehicle body shape; correcting for proper trim, body accelerations and flooding behavior before testing a prototype. Amphibious vehicles are well known for ballooning design times and project costs stemming from extensive testing for adequate safety. Simulation can reduce both time and cost, while giving insight on vehicle behavior.

One thing most engineers have in common is a fascination for elliptic gears. And with the impending release of STAR-CCM+ v8.04, it will be easier than ever to set the wheels in motion.

Indeed, one of the most exciting features of STAR-CCM+ v8.04 is an enhanced overset mesh technology which allows for multiple overlapping overset zones. Overset meshes, also known as “Chimera” or overlapping grids, may be used to simulate the relative motion of one or more bodies, including arbitrary or tangential motions of objects in close proximity. And whereas it has been possible to overlap overset grids with a background mesh since the release of STAR-CCM+ v7.02, it will now also be possible to overlap overset grids with each other.

The biggest challenge of gradient-based shape optimization using high-fidelity CFD has always been the formidable computational expense tied to constructing the sensitivity of the objective (or cost) functions with respect to the design variables.

When it comes to systems, one of the most complex (and perhaps least understood) of all is that of the human body. The average adult human body is, on average, 57% - 60% water. That's a lot of fluid! So it stands to reason that CFD is a great tool for simulating the systems of things like medical implants, surgical techniques, diagnostic systems and the like.

A recent artilce published in Desktop Engineering examines how CFD is making an impact in the medical field. Our own Krisitan Debus Ph.D. talks about our work with an ASME sub-committee, writing verification and validation guidelines for biomedical devices as well as STAR-CCM+'s very useful overset mesh feature. Read the entire article here.

One of the best illustrations of "Simulating Systems" is this video from the STAR Global Conference 2013, in which Scott D. Reynolds of M/E Engineering explores the use of CFD for studying the impact of wind on the built environment.

Asked to examine the influence of helicopter exhaust plumes  on surrounding bulidings, M/E Engineering decided to simulate the whole system, including fully unsteady wind profiles (with gusts that vary in speed and direction), and the full complexity of the local urban landscape. Best of all, the simulation includes an actual moving helicopter that entrains gas from nearby building plumes as it takes off and lands.

 

"Prediction is very difficult, especially if it's about the future"
 - Niels Bohr, Nobel laureate in Physics

Whether you like it or not, as a simulation engineer you are in the prediction game. Put simply, your job is to predict how an abstract design would perform in the real world, hopefully accounting for the most challenging operating conditions that it would likely experience during its working life.Compared with other professional forecasters such as economists, television meteorologists or political commentators, the audience for engineering predictions is more critical and less likely to forgive. While incorrect weather forecasts are quickly forgotten (at least those that don't involve hurricanes), and one rarely takes economists seriously, the cost of getting an engineering prediction wrong can be enormous.  The failure of a product in service can have serious consequences, particularly in the case of safety critical applications where unforeseen failure can result in injury or loss-of-life. Even in less serious circumstances, the unexpected failure of a product can act to de-motivate consumers, damaging brand reputation, potentially incurring large warranty expenses.

The problem is that uncertainty is a fundamental part of all prediction; no engineering prediction is perfect and no simulation model is a complete representation of the real world scenario. Every model is based upon a set of underlying assumptions that allows it to be solved numerically, but ultimately influences the accuracy of the prediction.  As engineers, we are responsible for acknowledging and understanding the uncertainty in our predictions and, wherever possible, to try and minimize that uncertainty through the application of judicious modeling assumptions.

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Brigid Blaschak
Communications Specialist
Dr Mesh
Meshing Guru
Stephen Ferguson
Communications Manager
Sabine Goodwin
Senior Engineer, Technical Marketing
Joel Davison
Product Manager, STAR-CCM+
Prashanth Shankara
Technical Marketing Engineer
Jean-Claude Ercolanelli
Senior Vice President, Product Management at CD-adapco
Bob Ryan
President Red Cedar Technology