Spherical Livestock

Doug Bell

If, like me, you are a fan of the sitcom The Big Bang Theory, you may have heard the Spherical Chicken joke in the episode “The Cooper-Hofstadter Polarization:”

There's this farmer, and he has these chickens, but they won't lay any eggs. So, he calls a physicist to help. The physicist then does some calculations, and he says, “I have a solution, but it only works with spherical chickens in a vacuum.”

When I saw the episode with my family, I laughed out loud at the joke (probably a little too much like the nerdy characters) and received strange, but not unfamiliar, looks from my wife and sons. The joke has existed for years starring a veritable barnyard of orb-like livestock such as a poorly performing race horse and low-yield dairy cattle. The punchline is always the same, though: the problem is solved with improbable assumptions.

Engineers (and physicists) understand the joke. We often apply simplifying assumptions to make a problem manageable. These assumptions take many forms: incompressible fluids, inviscid flow, lumped capacitance, to name a few. The very equations used by analysis software are based on simplifying assumptions.

While the trend has been for engineers to include details in the analysis software and let it mesh and run, there is much to be gained by using simplifying assumptions. I am not saying that detailed models don't have their place, but simplified models have their place and are often overlooked.

A simple model provides insight into the key physics of the problem. By stripping out all but the most basic physics and adding them back in one at a time, you understand what affects the solution. Also, your solution does not waste time on irrelevant physics that may require unnecessarily complicated calculations. For example, if you need to find out if albedo from the Moon and Earth are both significant during a transfer orbit, model a sphere (it can be a chicken or a horse) and have it traverse away from the Earth and toward the Moon without worrying about the geometry or trajectory. A quick review will determine if both reflected solar loads are worth including in the system model at all times.

A simple model makes validation easier. A simple model can make it easier to perform the necessary calculations by hand to ensure the model does not have errors before moving toward more complex calculations. I had a supervisor who would not allow anyone to present a thermal analysis without first presenting a sketch of the system's energy balance. A simple model allows evaluating each input and output.

A simple model solves quickly. A fast-solving model allows evaluating more design options while a detailed model will be more constrained. Investigating a wider possibility of designs can lead to an unexpected design. The ability to run many cases quickly also enables correlating the model to test data. This provides further validation of the model and strengthens the trust in the model when it is used to evaluate untestable conditions. Statistical treatment of uncertainties provides another reason for having a fast-running model.

A related note: you can always present the results of a simple model along with the assumptions, but you cannot present the results of a complex model if it is not complete.

So, while the spherical animals make for a good punchline, they have their place in analysis. Just be sure you don't stop at the simplest model so you don't become the joke.

Advanced Pipes in FloCAD
Thursday November 14, 9-10am MT (8-9am PT, 11am-noon ET)
This webinar introduces advanced features for FloCAD pipes in addition to working with complex geometry. Complex geometry includes interior fins and surfaces for heat transfer, flow around enclosed objects, annular flow, concentric pipes, and more. FK Locators and TEEs as modeling objects will also be introduced.
Custom Heat Transfer and Pressure Drops
Tuesday November 19, 2-3pm MT (1-2pm PT, 4-5pm ET)
Do you know what the default assumptions are in FloCAD, and whether or not they apply in your situation? Do you know how far you can go past that starting point? The answer: pretty far. There are numerous mechanisms in FloCAD for adjusting factors, scaling uncertainties, and applying different or supplemental correlations. This webinar summarizes the options available to you to customize your flow models to make sure that they apply to each new situation you encounter.
Heat Exchangers: Detailed and System-level
Thursday November 21, 2-3pm MT (1-2pm PT, 4-5pm ET)
This is two webinars in one. The first explains the use and assumptions behind the FloCAD HX system-level modeling object. The second webinar describes detailed-level modeling of complex heat exchanger passages, including application of Compact Heat Exchanger (CHX) methods.
Starting in 2020, we will begin offering Introduction to Thermal Desktop and Introduction to RadCAD as either in-person training or online training, alternating between online and in-person every three months. The training uses lectures and demonstrations to introduce you to basic Thermal Desktop and RadCAD usage. Hands-on tutorials provide practice building models and interpreting results (tutorials are completed by students outside of the online class time).
The next training class will be an online format in January 2020:
  • Introduction to Thermal Desktop (and SINDA) - A three-part series on January 14, 16, and 21 from 9am to 12pm, Mountain time
  • Introduction to RadCAD - January 23 from 9am to 12pm, Mountain time
For up-to-date schedules, fees, and policies, visit our Product Training page. To register for the class above, complete our registration form and select "Online" for the Training Format.
If you are interested in product training for your company based on your schedule, please contact us to obtain a quote for training between 8-12 attendees. We can come to your facility or the lectures can be presented online. Descriptions of the available classes can be found in our course catalog.
To keep up with our training opportunities, take a look at our new Events and Training Calendar.