Another ConcreteCanoe.org exclusive!
ConcreteCanoe.org is very pleased to present the results from Team UAH's modal analysis of their 2004 entry... ConQuest. The team swept the technical events at the Southeast Regional Concrete Canoe Competition in Tampa and is currently gearing up for the national competition to be held in Washington, DC this June.
According to project engineer Robert Dudley, "Our boat is a Strategically Tuned Absolutely Resilient Structure (STARS) that acts as an energy storage device."
As the team pulls their paddles from the water, the elastic strain energy stored in the deformed shape is converted into forward momentum.
Sarah Yeldell, UAH Chapter president noted, "The hull shapes of the winning entries at nationals are designed to satisfy conflicting requirements and trade-offs must be made between speed, tracking, and maneuverability. Because all of the major competitors have similar goals, their boats have begun to look amazingly similar in shape" (see: "2003 NCCC Coverage" - includes photos of all boats at 2003 national competition). "But looks can be deceiving," she added.
John Gilbert, faculty advisor at UAH elaborated, "Boats of similar shape and weight are not equally efficient because their dynamic response and modal parameters depend on the density, stiffness, and position of the materials employed during fabrication, as well as the physical constraints imposed by structural members and boundary conditions encountered while racing."
Yeldell noted, "Last year, for example, we produced a concrete canoe that provided a 12% increase in speed over the speeds recorded by the same teams in a fiberglass prototype that had the same dimensions and weight. Since the prototype was made of different materials and included thwarts, it had a totally different modal response."
With regard to their ConQuest, Dudley continued, "The first mode is anti-symmetrical torsion and the second mode is flutter bending. When they combine as shown in the animation, the boat acts like a fish swimming along with its paddlers to increase their input efficiency."
Yeldell and Dudley plan to elaborate at the 2004 ASCE/MBT NCCC in Washington, DC this June when Team UAH delivers their oral presentation as the 2004 Southeast Regional Concrete Canoe Champion.
According to Gilbert, "We developed a finite element model that consisted of equally spaced quadrilateral membrane-bending plate elements with uniform thickness. Damping was neglected in the analysis and refinements in element sizes were made until the natural frequencies converged. Only the lower natural frequencies and their associated mode shapes in a free-free boundary condition were calculated because they adequately describe the dynamic behavior of the canoe. Impact hammer tests were used to verify our numerical predictions and results agreed to within a few percent error."
Gilbert added, "I'm very pleased and proud to see people that worked with me on thesis and dissertation research invest their time helping our Chapter." The computer animation was generated by Dr. Robert Vaughan, Lead Engineer in the Methods Branch at the U.S. Army's Aviation & Missile Research, Development & Engineering Center (AMRDEC). Impact hammer tests were supervised by Robert Engberg, Aerospace Engineer in the Structural and Dynamics Group at NASA's Marshall Space Flight Center. Finite element analyses were conducted using NASTRAN software under the supervision of Dr. Teng Ooi, Adjunct Faculty Member in the Department of Mechanical and Aerospace Engineering at UAH. Thanks guys!... jag
Additional information about the project can be found at TeamUAH.org.