Imagine yourself at the controls of a hydroplane skimming across the water at 400 miles per hour with only a few square inches of the boat touching the surface. As the pilot of the boat, your task is to maintain a very delicate balance. If your boat loses contact with the water, it’s likely to go airborne and come crashing back into the water with potentially fatal results. On the other hand, if you push the boat too hard into the water, the boat can quickly submerge, again with potentially fatal results. In fact, the 11,000-pound thrust of the engine is almost equal to the weight of the entire craft -- even a gentle turn at the craft’s projected top speed of 400 mph generates a lateral force of 4 G’s. Now you understand why there are few endeavors more dangerous than attempting to break the world water speed record.
Keeping a record-breaking attempt on track. Despite the risk, Nigel Macknight is out to break the current record – 317.6 mph, set in 1978. Macknight is building a turbofan-propelled hydroplane, called Quicksilver, and is planning an attempt at the world record in Coniston Water in the English Lake District of the UK.
Quicksilver relies heavily on modern analytical methods and computer-driven active control systems to maintain stability in an environment where human reaction times aren’t nearly fast enough. What’s more, traditional methods of designing complex structures like Quicksilver’s spaceframe, are not robust enough, which posed a significant challenge for Macknight. The spaceframe uses hundreds of members to harness the Rolls Royce Spey engines and withstand high-speed water impact.
Attempting to overcome this hurdle and achieve his goal, Macknight selected one of the UK’s leading structural engineers, Rod Giles, Technical Director of Elite Consulting Limited. Giles’ extensive experience includes structural analysis of the Lotus Superbike that Chris Boardman used to win Olympic Gold in 1992.
Conventional structural design methods don’t hold water. Giles says that the Quicksilver spaceframe represents one of the most complicated structural engineering projects that he has ever been involved in. “The members of the spaceframe used in Quicksilver form over 1,000 connections with each other, at every conceivable angle,” explains Giles. “Analyzing the frame would have been a horrendous task using conventional solid modeling and finite element software.”
Using conventional 3D modeling techniques, Giles would have had to manually define each of the beams entity by entity and then calculate the cuts needed to join them up with the other beams in the structure. To prepare the structure for analysis, he would have had to create midwall surfaces so that shell elements, which require less computational time, could be used. Finally, once he had opened the model in the finite element analysis software, he would have had to check each of the 1,000 or so connections because one mistake would have blown up the analysis. “I estimate that using conventional modeling, it would have taken three weeks to model the frame, 10 days to prepare it for structural analysis, and then four days to check the resulting finite element model,” Giles said. “We didn’t have that kind of time.”
Enter EFX. Instead, Giles used Pro/ENGINEER Expert Framework (EFX), which dramatically reduces the time needed to design a structural framework by automating repetitive and tedious tasks. For Giles, all he needed to do was conceptually model the spaceframe using points and curves, which represented the locations of the members. Then, using the comprehensive EFX library, he selected standard cross-sections to assemble to these points and lines -- in this case, a square section tubing. When the beams were inserted, EFX automated the creation of joints, negating the requirement to manually create cuts for the hundreds of joints. What’s more, all the joint cuts EFX created were made at the part level, eliminating assembly references and making the design robust and flexible.
From starting line to optimized design in three days. Next, Giles needed to analyze and identify weaknesses in the structure. He took advantage of the Mechanica library that’s embedded in the latest version of EFX (4.0). The Mechanica library has all the information in each profile that is required for an efficient analysis in Mechanica.
Giles’ Mechanica analysis showed that there were a few areas where the stress was too high, particularly on the engine mounts and one of the actuator mounting surfaces. But modifying the structure was easy. Giles made changes to the original wireframe structure and to the cross-sections. Then EFX instantly generated the new model and it was ready for another analysis run.
This was a pretty neat feature, accordingly to Giles. “Having Mechanica built into EFX was a lifesaver for me. I was able to spend all of my time on creative engineering, like applying the loads to represent forces generated by the engine and testing and simulating the impact of the water on the structure. And I didn’t have to go back and forth, designing and simulating, designing and simulating. It was done all together in one place. Instead of spending five weeks to design the spaceframe and prepare it for analysis, I was able to do the same job in three days with EFX,” Giles concluded.
This smooth process helped to keep Macknight and the Quicksilver team on schedule toward the ultimate goal of breaking the world water speed record in 2007. Stay tuned…
Elite Consulting provides mechanical engineering consultancy services to industry and manufacturing businesses. They specialize in stress analysis, failure modes, and effects analysis, as well as CFD analysis. They are a primary provider of Pro/ENGINEER and Mechanica consultancy, support, and training.
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