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Egress System Design Project for Mira. A cooperative project of The Oregon Zoo and Portland State University. Mission Statement: Design a device which will allow Mira, a blind elephant seal, to exit her pool habitat without raising the water level. How am I going to get out of here?.
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Egress System Design Project for Mira A cooperative project of The Oregon Zoo and Portland State University
Mission Statement:Design a device which will allow Mira, a blind elephant seal, to exit her pool habitat without raising the water level. How am I going to get out of here?
Product Design Specifications • Allow Mira to exit pool without raising the water level. • No Major Aesthetic or Physical Changes to habitat. • Preferably Removable (and easily storable) • Manageable by two trainers • Five year life
First Ramp Design Concept Clears Beach head Approx. 70 degree ramp pitch Provides mechanical advantage Extends existing beach slope surface area for Mira to exit water.
Mira’s Biomechanics • Propels herself with flippers • Moves body along much like an inch worm • With traction, she can negotiate much steeper slopes
Second Design Concept • Reduced distance of 70 degree pitch to 10 inches • Allowed Mira a foothold to advance up the 70 degree portion of the deck • Stress concentrations at bend made the design weak High Stress
Design Optimization • Gusset Tube was added to take up stress in bend. • Dual extension legs reduced to one for reduced weight. • Some bends were replaced with mitered and welded joints.
Design Optimization • Traction strips were added for Mira to push-off of • Polyethylene decking was reduced to ¼ in thickness to reduce weight by 40 pounds • Gusset tube was moved to bottom to be in compression and relieve bend angles.
Fabrication Begins • Fabrication was done by student team. • 2 x 2 x ¼, 6061-T6 tubing could not be bent without annealing. • Welding the aluminum will create heat-affected zones which will weaken it to less than half of the original T6 yield strength (safety factor drops to 0.85).
The Fix • Aging the aluminum after welding would only recover 7-10% of annealed properties, while the unaffected areas would over-age and lose strength. • Decided to cut and weld the apparatus, and heat treat it. • No oven in Portland was large enough to accommodate the entire assembled structure (24in x 44in x 86in).
Still Fixing • Gusset plates were added to raise the safety factor to 2.4 so the welding could be done and the s.f. would only fall to 1.25 (without heat-treatment). • ‘Stack Metellurgical’ could heat treat pieces up to 60 in long. • The structure was to be cut at low stress planes so it could be welded together after the critical welds were heat treated and artificially aged.
Proof of Concept • Ramp was tested for impact with human subjects. • Ramp was statically tested with impact forces on ANSYS.
FEA Analysis • Minimum Safety Factor under maximum loading > 1.5
Meeting PDS Requirements • Easily Stored • Removable
Meeting PDS Requirements • Easily handled by two trainers. • No major aesthetic or physical changes.