When the winners were announced for the 9th International Submarine Races (ISR) at the end of June, there was one seeming incongruity.
Among the well-known engineering universities from the United States, Canada, Mexico and the United Kingdom was a high school – Sussex County Technical School in Sparta, N.J. Sussex took home first prize for innovation among the 26 human-powered submarines in the competition, and third place in best overall performance.
Four major factors can be attributed to Sussex’s unusual success: a talented and motivated group of students; experience gained from the school’s previous two entries in the competition; an instructor and project manager who served as an engineering officer on a nuclear-powered submarine; and the use of advanced digital design and engineering tools, especially CFdesign upfront CFD software.
“I don’t think you are going to find too many high schools delving into computational fluid dynamics at this level,” says Chris Land, the instructor and project manager. “Our kids are gaining some real knowledge of how upfront CFD works within the design process.”
The need for CFD
Sussex realized that it had a need for CFD based on its ISR experiences in 2005 and 2003, coupled with Land’s work toward a masters degree in mechanical engineering at the Stevens Institute of Technology.
During the 2006 school year, Terry O’Connor, who peddled Sussex’s UmptySquatch II entry in the 8th annual ISR competition, began working on a senior project to redesign the sub’s propeller system and increase speed. At the same time, Land was studying fluid flow as part of his masters’ program.
“I told Terry that there must be software that can help us do CFD analysis,” says Land. “We saw an ad for CFdesign and it seemed like a good fit: It is integrated with Solid Edge, which we are using for CAD, and the software’s developer, Blue Ridge Numerics, was open to working with us.”
A close fit
Land probably didn’t know at the time just how closely the fit was between Sussex’s needs and CFdesign’s unique attributes. Sussex needed a tool that would rapidly assess fluid flow early in the design process, so changes could be made quickly and tested again. There was no luxury of doing multiple physical prototypes.
“This isn’t a theoretical educational exercise,” says Land. “We have 10 months to design and manufacture the entire submarine. You can’t jump into manufacturing until you are comfortable with design. And, you don’t want to spend student’s time and energy on something that doesn’t work.”
From its inception, CFdesign was created to enable multi-tasking engineers to perform computational fluid dynamics analysis early in the design cycle, when it is most cost-effective to explore and validate designs. Virtual prototyping of different design options replaces traditional testing methods. In larger organizations, this saves the more costly physical prototyping for final design verification. In Sussex’s case, it replaces physical prototyping altogether.
One other factor fit into Sussex’s goals and approach: ease-of-use.
The Sussex team didn’t have the luxury of learning the theory and practice of CFD over the course of six months to a year. The CFD software had to be easy enough to be used productively within a couple of weeks by students with limited CAD backgrounds and no CFD knowledge.
“You certainly have to understand the inputs into the software,” says Land, who took a three-day CFdesign course to better understand how the software worked, and to help his students apply it to design of UmptySquatch III. “But CFdesign allows you to step through the tutorials and learn as you go. I don’t think it could be any more user-friendly.”
Shaping the hull
The first CFD challenge Land and his team took on was the shape of the submarine’s hull. The team settled on an ellipsoidal hydrofoil wrapped around a common axis. They didn’t know it at the time, but the shape was similar to that of the ISR world record holder.
Adam Schatteman, a senior in charge of the technical design group, experimented with eight to 10 shape profiles for the hull, running CFdesign and reviewing the results. One of the things he learned early on was to define what he wanted from the software.
“You need to know the vocabulary and how to ask it what to do,” says Schatteman. “If you have that knowledge, you can go very far.”
Land and Schatteman worked on defining the scope of the problems they wanted to address, and to determine early on within a CFdesign run whether the results were going to be worthwhile.
The CFD results brought some surprises that challenged long-standing assumptions. After testing, the best hull design turned out to be 16 feet long, about six feet longer than any previous design.
“I asked the students to take about four feet off the end and test a shorter profile,” says Land. “But the longer hull proved to have the best thrust-to-drag ratio. Once I found that out, the hull didn’t look so big.”
Getting the right twist
Because of resource constraints – the school had only one computer on which it could run CFdesign – the UmptySquatch team needed to select the best areas in which to apply its upfront CFD technology. Besides the hull, the other critical area was the propeller.
With Terry O’Connor having graduated and moved on to West Point, Schatteman took over the task of refining the new propeller design. Unlike a motor-driven sub propelled at a high, constant speed, a human-powered sub is subject to greater flow fluctuations. The human pedal-power that drives the sub tends to create an irregular flow, making propeller efficiency especially important. Sussex’s previous designs contained flat portions that would cause drag as water flowed over the surface.
“We were able to use CFdesign to do iterations that helped us determine the amount of twist needed in the blade to reduce drag,” says Land. “Testing with CFdesign gave us a lot more confidence, especially since we didn’t have the luxury of testing with physical prototypes.”
Investment for the future
Land believes that the 10 months of experience with upfront CFD, coupled with another year of ISR experience, will enable Sussex to continually improve in the years ahead. As for the students, exposure to upfront CFD in high school will give them an advantage at the university level.
“Adam and the others who use CFdesign will know about FEA and CFD, not just from a theoretical standpoint, but at a very hands-on level,” says Land. “That’s a tremendous advantage. There’s a lot of negative talk about the future of American engineering, but this is a great example of what can be achieved when people stop complaining and start motivating kids and giving them the right tools to succeed.”
Bob Cramblitt is a technology writer who focuses on new developments and processes that make a definitive difference in how we work and live.