DesignSpace Helps Visionary Graham Hawkes Prepare For Underwater 'Flight'

Approximately 70 percent of the earth's surface is covered by water. Mankind has flown over it for decades, sailed on it for millennia, but less than five percent of it has been explored. The main reason is that the available methods - scuba systems, submarines, and submersibles - have major shortcomings.

Scuba limits its users to the topmost slice of ocean since it does nothing about pressure. From an exploration standpoint, submarines are for all practical purposes blind. Submersibles solve the pressure and blindness challenges but they are kludgy, slow, noisy, and lit up like Christmas trees. Any organism that can flee does.

The above picture shows the two-person watercraft with the individual operators' PODs exposed. The stress result of the POD design is superimposed for clarity.

"Even the best of today's submersibles are equivalent to scouting the jungle for tigers with a marching band," says Graham Hawkes, who has dedicated his life, fortune, and considerable talents to this challenge.

Hawkes is just the kind of visionary engineer to do something about this. His solution is Hawkes Ocean Technologies (HOT) and its DeepFlight Aviator, which combines:

• The freedom of movement of scuba;
• The depth capability and underwater viewing of a submersible; and
• The mobility and low intrusiveness of a submarine.

Hawkes has garnered praise and awards worldwide. His work has appeared in Scientific American, National Geographic, Time, BusinessWeek, the New York Times, and dozens of scientific and engineering journals. HOT products have been on National Geographic TV and a Public Broadcasting System (PBS) special. Prestigious honors and nominations attest to his creativity and success, including the 2000 Science Award from the Computerworld-Smithsonian Awards program, "A Search for New Heroes." A Hawkes craft, the Mantis, even played a role in the James Bond film, "For Your Eyes Only."

DeepFlight Aviator is Hawkes' most sophisticated project to date - and the basis for another Hawkes first, a school for underwater aviation. The craft "flies" underwater using inverted airfoils and positive buoyancy. It is "flown" to its depth rather than sinking to it as conventional submersibles do. Conceptually, the craft combines a rigid diving suit with the simple, practical workings of a remotely operated vehicle (ROV). DeepFlight Aviator will be able to dive to 1,500 feet, enduring pressures of 670 pounds per square inch (PSI).

Withstanding pressure is, of course, the primary design criterion of DeepFlight Aviator. An aluminum pressure hull encases the pilot's body. (Just days before the Computerworld-Smithsonian ceremonies, a foundry successfully poured the first set of three pod castings.) The "helmet," a thick acrylic bubble, provides unparalleled 360-degree visibility and minimizes distortion due to water boundary refraction.

The key to DeepFlight Aviator is the way Hawkes' design optimizes the tradeoffs between power, weight, and mass. The problem to be addressed is that of achieving sufficient speed underwater - eight knots - to make the airfoils effective in overcoming DeepFlight Aviator's positive buoyancy.

Water may be frictionless but it is extremely dense. Increasing an underwater craft's speed to five knots from one requires a 100-fold increase in power. DeepFlight Aviator is self-propelled by eight 24-volt batteries. The low power-to-mass ratio of batteries dictates a very efficient hydrodynamic shape to minimize drag.

Submersibles move under their own power, but slowly; they rarely exceed speeds of two knots. They reach depth slowly, too. Ballast is loaded until the submersible is slightly heavier than the water it displaces. To return to the surface, the ballast is jettisoned. Hawkes estimates that a submersible spends 95 percent of its underwater time getting to and returning from the research site.

Submersibles are costly. Their size and crew require a mother ship, a specially equipped vessel 200 or more feet long. Charter rates are $20,000 or more per day and researchers may have to wait months for mother ship and submersible availability. These factors put submersibles out of reach of all but the heftiest R&D budgets.

Negative buoyancy, as in submarines, means bulky air tanks; redundant compressors, valves, and pumps; plus lots of piping, extra batteries, and a plethora of redundant, fail-safe controls.

Hawkes used factor of safety as a critical guide to the best design. Through numerous associative iterations, the optimum conditions of safety and minimal ballast requirements were met.

Another major design feature of DeepFlight Aviator is its life support system. To win certification from the American Bureau of Shipping (ABS), DeepFlight Aviator must be able to keep its pilot alive for 72 hours in case of trouble.

Crucial to the design's success is the engineering analysis software, DesignSpace® from ANSYS, Inc., Canonsburg, PA, USA. (NASDAQ: ANSS). "Like DeepFlight Aviator itself, the software is easy to use, tough but flexible, and very sophisticated," said Eric Hobson, mechanical engineer responsible for the craft's detailed design. Hobson uses DesignSpace in conjunction with new Autodesk Inventor design software.

The Computerworld-Smithsonian judges cited the Deep Flight projects for their use of engineering analysis and 3D design tools in "creating a small, inexpensive submersible craft that can take scientists deep into the ocean, making the exploration of this vast resource economical for the first time."

DesignSpace primarily is used to ensure that the drag of DeepFlight Aviator's components is minimized and that the craft can withstand nearly 700 PSI of pressure. Much of DeepFlight Aviator's simplicity is achieved by protecting only sensitive components from the pressure. This is done by "canning" them in oil-filled canisters whose sizes are carefully optimized with DesignSpace and Inventor.

Because of water density's effects on speed and power, DeepFlight Aviator has to be small and maneuverable. Explained Hobson, "As soon as you make any one component bigger, everything else seems to grow exponentially in size and weight. This growth has to be accommodated or compensated for. That triggers another round of design adjustments and size increases. It can go on forever. This is why submersibles are so clunky," he noted. "It is vital that DeepFlight Aviator move quickly without big motors and a lot of batteries and surfacing tanks. If we have to go that route, we cannot keep the mass and bulk down."

The pressure loads on the POD were calculated using the maximum potential depth of the vehicle during use.

Naturally, most of the pressure management effort goes into protecting the pilot. DeepFlight Aviator uses a rigid cast aluminum body. More than anything else, the pod resembles a bent cocoon. It is a cylinder tapering from 26 inches in diameter at the pilot's shoulder level to 18 inches at the feet.

The upper end of the pod cylinder is curved away from the cylinder's centerline, or "revolved," 30 degrees to accommodate the seated pilot. It was at the most inward curving section of the pod that DesignSpace indicated maximum stress. Hobson designed the pod to be three inches thick at that point. At the pilot's waist the metal in the pod's wall is one inch thick, at the pilot's feet, three-quarters of an inch.

"The design actually was optimized for the comfort of the user rather than for stress," said Hobson. Comfort was a significant design factor because one tends to become cramped, and possibly claustrophobic, after an hour or two beneath great masses of water.

"The stresses easily were within the capabilities of the 356 aluminum alloy for the pod castings and the 6061-T6 we used for the cast machined parts," such as the canisters, Hobson said.

Using DesignSpace, Hobson was able to run many design iterations in conjunction with Autodesk Inventor quickly. "Our design environment is straightforward," Hobson pointed out. "We know that the greatest stress on our pressure hulls is going to be from the ocean's pressure. Effectively, this is a static load that can be applied easily to our conceptual designs."

"But," he continued, "the results of our analyses are extremely important since there is no room for error when you dive deep. The key advantage of working with the latest DesignSpace and Inventor is that we are able to seamlessly attach our models to the DesignSpace database and retain all the associativity when we make changes to the Inventor models."

"Being able to bring changes made in Inventor directly into DesignSpace saves considerable time," Hobson explained. "Without this tight associativity, the constraints, loads, and supports would have to be reapplied to the geometry of the model in DesignSpace after almost every change. Reapplying takes perhaps ten minutes, but when repeated becomes very time consuming, very distracting and irritating. In the critical designs we might run 20 to 30 iterations. For us, this associativity works beautifully.

"DesignSpace," he said, "lets us bring in the entire assembly, throw the depth pressure on all surfaces, and know that the problem is solved correctly. It's a real time saver."

Essential to the design project's success is DesignSpace's ability to handle components in an assembly and not just individual parts. This was crucial in analyzing the stresses where a metal locking ring clamps the fittings for the acrylic bubble helmet to the pod. "With a system this complex, the results from analyses of individual components would be meaningless," Hobson pointed out.

"Sure, we could show that the locking ring would not deform under 670 pounds of pressure," he continued, "but what about seal for system integrity? That's what's important. There is no way to show that without analyzing the entire pod with all its parts. That's why the DesignSpace assemblies capability is so important," he added. "We really give it a workout."

The DesignSpace analyses were linear, stress, and noncontact. Solving variants of the pod model, even though it is 140 megabytes (MB), takes just five minutes at DesignSpace's standard tolerances. The method used was convergence to maximum stress. HHKW runs DesignSpace and Inventor on a customized Core Systems PC with dual 400 MHz. Intel Corp. Pentium III CPUs. The machine has 256 MB of RAM, a 9.2-GB disk drive, and a 200 MB SCSI interface.

Critical to the project's ultimate success is ABS certification. Hobson noted that ABS accepts analyses from designers and developers rather than requiring this work to be done on its own systems. As the classification society for all U. S.-registered ships, ABS represents the insurance industry's interests. It takes no chances. ABS will require radiographic tests to verify the integrity of the metal. Pressure tests to verify the DesignSpace results will be performed at a U. S. Navy facility in San Diego.

Hawkes has designed more than 70 percent of all manned underwater vehicles ever built for R&D or industrial uses, as well as more than 300 ROVs. He holds the record for the deepest solo ocean dive, 3,000 feet, reached during his testing of Deep Rover submersibles.

DesignSpace is particularly useful in designing the pressure hulls of our submersibles," Hawkes told the Computerworld-Smithsonian judges. "We are now confident [that we can] depart from simplified geometry. Whereas, in the past, we relied on conventional pressure hull geometries - spheres and cylinders - because we did not have the confidence in [the ability to analyze] complex geometries. DeepFlight Aviator's hull is optimized for a human pilot by form fitting his/her natural sitting position.

"This configuration creates a complex hull that is very difficult to analyze with simple hand calculations," Hawkes continued. "However, with FEA, we not only can analyze this new hull, we can freely test new configurations to find the true optimum design. Due to our limited budgets," he added, "we always try to use off-the-shelf components. However, we do use emerging technologies to produce superior products."