How to Improve Your Engineering Designs. Pump It Up Like Schwarzenegger!
Those who have seen the 1977 docudrama ‘Pumping Iron’ will know the dedication, strict diet and gruelling exercise regime that is needed to compete in the world of competitive bodybuilding.
“The greatest feeling you can get in a gym or the most satisfying feeling you can get in the gym is the pump. Let’s say you train your biceps, blood is rushing in to your muscles and that’s what we call the pump”.
Bodybuilders understand that to win competitions requires the right proportions, definition and not just sheer size. They constantly review their shape and work on selected muscles to achieve their idea of the perfect body, very much like a sculptor. In others words, they identify a deficiency, isolate and improve.
Preparing for a bodybuilding competition calls for analytical thinking. There is a fine balance between exercise, rest and diet. The muscles need to be worked in isolation, rested and nourished in just the right proportions at just the right time.
The engineering design process has similarities with bodybuilding training in the sense that the project resource must also be directed to the right task at the right time and in the right proportions.
Getting the right balance between design, analysis and testing is easier said than done.
When to Pump Up the Design
Every product and component is doing a job and different industry sectors have different priorities. For example, an overhead travelling crane carrying hazardous materials would be heavily biased towards safety. There’s usually not much restrictions placed on weight and the design may be a one off.
It is important to remember that efficient, lean designs cost more to develop than over designed products. A simple hand calculation may give you enough confidence in that design but it could contain overly conservative assumptions. Now that may be fine if your main priority is safety because you have to weigh up the cost of the steel versus the cost of analysis.
For safety critical machinery, it’s not just the cost of the calculations or finite element analysis (FEA), it’s the cost of convincing the design authority that your design is safe and this involves having someone check those calculations. In addition, the design must be shown to be compliant with the relevant codes and standards which also adds to the cost.
If your design has a reserve factor of 6, there is clearly room for improvement but what is the cost of achieving that improvement and how much money would you save on steel for a one off fabrication? Sometimes it is better to focus resource on other things instead of developing multiple design iterations to trim off all the fat.
If you want your design to be safe and strong, then pump it up like Schwarzenegger!
When to Pump Up the Analysis
Safety is crucial in the aerospace sector but so is weight. Aerospace components have to ‘sail close to the wind’ otherwise they become too heavy and the aeroplane won’t fly. Small reductions in component mass can yield big savings in fuel over the aeroplanes lifetime.
Squeezing the last drops of reserve factor out of the aerospace component is worth it and this is achieved through analysis and testing. The testing of aerospace components is complex and fatigue is a key consideration.
Testing is expensive and time consuming so anything you can do to speed up the design process is welcome. This is where FEA is useful in the sense that you can try out your designs in the virtual world of simulation rather than go straight from design to testing.
If you build and test a prototype you may find that it fails at 50% design life. You will then build another prototype, make the failed section thicker and re-test. You may then find that your prototype fails at 75% design life in a different place. The design and test cycle is repeated until you reach 100% design life without any failures or damage.
On the other hand, your prototype may pass first time without using FEA but you will not know what your reserve factors are unless of course you test to destruction or fatigue failure. In this case you will need to test many prototype components for each design iteration.
If you want to reduce the number of prototypes and testing, then pump up the analysis!
When to Pump Up the Testing
Have you ever seen a washing machine walk? During the spin cycle, the clothes may not be evenly spread around the drum leading to out of balance. The centrifugal force induced as the drum spins causes vibration and in severe cases the washing machine can chase you around the kitchen. You can probably out run it, being the finely tuned athlete that you are but you would ideally like to prevent this from happening in the first place.
FEA and other simulation tools can just about model anything but somethings are harder to predict than others such as the weather. The more complicated the simulation, the more you must rely on testing to validate your analysis.
For example, your washing machine may be too noisy during the spin cycle due to excessive vibration. Try stripping it down and rebuilding it using exactly the same parts and sometimes the problem goes away in the short term. This is because you dismantled it and didn’t rebuild it exactly as it was before. You may have tightened a nut and bolt that was coming loose. It is these very subtle variations that can make analysis of large assemblies tricky.
If you want to validate your analysis, then pump up the testing!
Finding the right balance between design, analysis and testing is the key factor for all design and development workouts. Good advice for any kind of workout is ‘don’t forget to stay hydrated!’.
“Milk is for babies. When you grow up you have to drink beer”.