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.

Can Mira Get Out?

Questions