Engineering News

Plastics create a winter sports wonderland

Newton, MA--Even as summer sports enthusiasts wind down their activities, sports-equipment makers are gearing up for the winter sports season. Drop into your local sports store and check out some of the latest designs. It will prove to be a big eye opener. Now, take a closer look. You will soon discover that many of the latest designs rely on plastics, and for good reason.

Take snowboards, for example. If the past two winters are any indication, sales of snowboards should soar. Two companies in particular hope to capitalize on the increased popularity of this sport.

Snowboarders, like skiers, prefer different styles of boards depending on where they will be used. Western snowboarders, for instance, might want more flexible boards for use in deep, powdered snow. Eastern terrain, by contrast, is icier, requiring stiffer boards.

Customized boards. U.S. Snowboard Technologies (USST), South Hampton, NH, designs its snowboards to customer specifications on a computer that develops nose radii, side cuts, and other dimensions, along with recommended laminate layers. Typically, the boards feature a wooden core surrounded with coextruded ABS/fiberglass sheet, rubber, and fillers. Wood cores consist of various combinations of maple, birch, and hickory.

Because of their laminated construction, the boards require an epoxy adhesive that will keep the layers in place through all types of terrain. USST found a solution in Ciba-Geigy's Araldite® AW 136R/HY 994H epoxy and Araldite LY 5085/HY 5046U resin hardener systems, especially when the customer wants a "see-through" surface.

Both adhesives, products of Ciba-Geigy's Formulated Systems Group, East Lansing, MI, offer excellent wet-out of the fiberglass and other reinforcing layers. They perform well under static and dynamic loading and withstand exposure to temperature extremes, water, and ice.

"We might use 160 grams of epoxy on one board and 310 grams on another to alter the flex pattern, without changing the weight of the fiberglass," says Horst Heuback, USST operation manager. "The more epoxy used, the stiffer and less flexible the board will be."

After the computer designs the board, USST pre-cuts the fabricating materials. Cores are milled to a precise size, shape, and length, also with a computer-programmed assist. ABS/fiberglass sheet is cut to the computer-specified dimensions, along with rubber and other board inserts used to secure the bindings in place.

After each board is laid up, it is put on a press and cured at 240F and 280 psi. Using a heating platen on the top and bottom enables USST to speed the curing cycle from 30 to 10 minutes.

Better bindings. Bindings make up another crucial part of snowboards. To improve the design of its bindings, Switzerland-based Fritschi Co. takes advantage of Verton® RF structural nylon composites from LNP Engineering Plastics, Exton, PA. The long-fiber skeletal structure of the material results in greater impact resistance even in sub-zero temperatures.

• Plastics give engineers the opportunity to provide more flexible, longer-lasting designs for sports gear

• Polymers can withstand cold-weather abuse, and weigh less than metal counterparts

• Use of plastic enables sports equipment makers to keep up with latest fashion trends

Also, using the injection-moldable compound instead of a metal die cast enabled Fritschi to develop colors that keep pace with fashion trends, saving considerable painting/finishing costs. And, with a density almost half that of aluminum, but with greater relative strength, Verton RF provides significant weight savings.

Fashion statement. Fashion concerns also play an important role in the buying decision. At the higher end of the market, skiers expect the product to provide topnotch performance--and look good while doing it.

French manufacturer Salomon achieved this balance through its Monocoque concept--essentially a shell that sheathes the ski, including its sides. To meet the demands of this design, Salomon selected Rilsan® polymide resin from Elf Atochem North America Inc., Philadelphia. A film of Rilsan about 0.8-mm thick envelops the contour of the ski and allows the use of a sublimation printing process that burns the company's graphics into the surface.

Canadian ice caper. In Canada, winter and hockey are synonymous. Therefore, the ability to give a skilled hockey player the slimmest advantage can result in big sales for a producer of skates. Sport Maska Inc., Montreal, thinks its new CCM 752 "Tack" skates offer much more than that--thanks to an assist from rugged, lightweight materials from DuPont Engineering Polymers, Wilmington, DE.

The company claims players gain added efficiency and quickness with the skate's advanced heel stabilizer wedge made of an engineering thermoplastic elastomer. "It improves the skater's efficiency by allowing more forward flexing than traditional skates, while providing increased lateral and tendon support," explains Craig Ryan, Sport Maska product manager.

Sport Maska designers reconciled requirements for flex and stiffness with a co-injection molded component made from two grades of Hytrel® polyester elastomer having different flexural characteristics. This allowed them to put stiff or flexible material where each is most needed in the part structure.

The skate's blade support, injection molded from Zytel® ST super-tough nylon, weighs far less than a metal support. It features a fatigue strength that can take repeated dynamic loading during the starts, stops, and thrusts of hockey, while providing low-temperature impact resistance to withstand hits from pucks or errant sticks.

The uppers employ a ballistic nylon fabric reinforced with Kevlar® aramid fiber. The fabric weighs about one-third less than a comparable all-nylon fabric, according to Sport Maska designers.

Upscale toddler sled. And, for the toddler set, comes a sled from J.R. Wright Engineering & Sales, Scottsdale, AZ, designed to be "the Mercedes of toddler sleds," says President John Wright. It had to be light and easy to push or pull, and fold down for storage or to transport in a compact car. It had to be low-maintenance, with no wood to give splinters or rails to rust. And, most important, it had to offer comfort and safety. After six or seven years of design and prototyping, the Fawn Tracker was born.

Made from a strong, tough blend of Texin® thermoplastic polyurethane and Makrolon® polycarbonate engineering resin from Bayer Inc., Pittsburgh, the sled resembles a racing stroller with runners. Sleek and colorful, the Fawn Tracker is popular at ski resorts, or with families who live in areas where heavy snowfall makes using a stroller difficult. Even cross-country skiers pull their kids behind the sleds.

Over 90% of the sled, including the frame and runners, consists of the Texin 4215 thermoplastic polyurethane/polycarbonate blend. Although the sled is shipped fully assembled, individual pieces are joined with twist grip locks, snaps, or brass pins. A seat belt and fabric seat complete the design.

"I considered polypropylene and nylon, but I was concerned about breakage due to their lack of shear strength," Wright explains. "I knew that the Texin blend was more expensive, but the superior performance was worth the added price."

Rapid prototyping comes to tool-making

Austin, TX--Injection-molding tools in two weeks?

DTM Corp. says that's the promise of its RapidTool™ process, which uses technology initially developed to make sample parts directly from CAD data. Now, the company is merging its Selective Laser Sintering technology with conventional furnace-firing to create insets--cores and cavity sets--for prototype injection molding.

"Customers can quickly create tooling allowing them to produce prototypes that replicate the actual manufacturing process," says DTM President John Murchison. "This can dramatically affect the manufacturing process by compressing the product-development cycle."

The company just announced a beta program for the process, which is expected to be commercially available by the end of this year. Xerox Corp. and the University of Louisville prototyping consortium will be beta-testing the technology.

DTM's SLS process creates 3-D parts from powdered materials by a computer-directed modulated laser beam. RapidTooling first uses SLS to generate an initial iron model of the tool. In a second step, the part must be heated in a furnace to 1100C so copper infiltrates the model to create an iron/copper composite.

While conventional tool-making can take eight to 10 weeks, RapidTool creates insets in four or five days. Another week or so would then be needed for polishing and insertion into a mold base. An inset for a 6-x 8-in tool, several inches deep, would cost less than $2,000--a fraction of traditional methods.

The process is designed for tooling prototypes, but could also be used for limited production runs.

R&D honors best inventions of '95

Des Plaines, IL--A super-bright lightbulb, high-precision machine tool, and wristwatch that communicates with a PC were among this year's winners of R&D 100 Awards. The competition, sponsored by R&D magazine, cites the year's 100 most technologically significant products.

The Solar 1000 microwave sulfur lamp is a golfball-sized device based on a process called molecular emision. Sulfur in the bulb, stimulated by microwave energy, emits broadband light to mimic ordinary sunlight. At its Washington, DC, headquarters, DOE replaced 240 200-watt mercury lamps with just two of the new bulbs. The Solar 1000 was developed by the U.S. Department of Energy; Fusion Lighting, Rockville, MD; and Lawrence Berkeley National Lab, CA.

The winning machine tool, VARIAX, uses a space frame structure based on a series of interconnected triangles. Three pairs of triangulated crossed-legs containing motor-driven ballscrews support the upper and lower platforms. The upper platform houses the spindle, which holds the cutting tool. By extending and retracting the six legs, the spindle can be lowered, raised, or tilted.

Because forces on the VARIAX structure are axial, the machine center is five times more rigid than conventional metal-cutting machines, according to its developers, Giddings & Lewis, Fond du Lac, WI. Accuracy: 0.0003 in, compared to 0.003 from most conventional machines.

Timex Corp., Middlebury, CT, garnered an award for its Timex Data Link, a watch that can carry up to 70 personal data entries. Using Data Link software codeveloped with Microsoft Corp., the wearer can point the watch at a PC and press some buttons--and the data entries are automatically sent from the computer and stored in the watch.

Among the other winners:

Contraband Detector, Quantum Magnetics, San Diego, a magnetic-sensing security system that employs quadrupole resonance (a variety of magnetic resonance) to scan for specific atoms found in drugs and explosives.

• Ignition system from ENOX Technologies, Natick, MA, which cuts NO_x emissions from stationary natural-gas engines by 90%. It adds more air to the air/fuel mixture while simultaneously enhancing combustion efficiency with a continuous ignition source.

• One-step automatic process for fabricating composite aircraft parts, Cincinnati Milacron, which downloads computer data to a fiber-placement machine. The device uses seven servo axes to accurately position and control up to 24 individual fiber strands.

For 1996 entry forms, fax R&D 100 at (708) 390-2618.

Controllers put excitement in exhibits

Newton, MA--If you think museums are just the past under glass, go to Chicago's Museum of Science and Industry. Under its MSI 2000 plan, designers there have created a veritable theme park for the intellect.

Best evidence: "Take Flight," a collection of more than 25 multimedia exhibits illustrating the science and engineering behind commercial aviation. As its centerpiece, Take Flight includes a retired Boeing 727 cantilevered off the East Court balcony. Visitors can board the gutted and reconfigured aircraft for interactive demonstrations of navigation instruments, aeronautical-engineering concepts, and air logistics planning.

Five times daily, 12 projectors, 75 spotlights, and eight speakers transform the Court into "Flight 727." With all systems now electrically or pneumatically operated, the plane's engines turn; and its lights, flight-control surfaces and landing gear deploy appropriately during a seven-minute simulation of a flight from San Francisco to Chicago.

According to MSI engineer Joe Schacter, the entire Take Flight exhibit took over two years work by more than two dozen contractors employing over 1,000 designers, engineers, and riggers. Underscoring the dynamic nature of the exhibits, not one of them is hard wired: Each employs programmable controllers to simplify set up, operation, and reconfiguration.

For example, ProMux® controller boards and MicroDAC controllers from Grayhill, Inc., LaGrange, IL operate all the 727's moving surfaces. Tom Wolcott, an engineer with Design Craftsman, the Midland, MI contractor that produced the display, explains the choice came down to experience and economics. "To coordinate all the surfaces, we'd need to wire up a dozen or more separate timers. It was simpler and less expensive to purchase the controllers, hook them to I/O boards, and move on from there."

ProMux boards control up to 24 modules, communicating at speeds to 38.4 baud. MicroDAC controllers handle as many as 32 analog or digital I/O modules and reach 115.2 baud. Both systems have RS-422/485 communications capability in multi-drop or repeat configurations. Either can be programmed via a host PC using Basic or C (ProMux) or Microsoft C, Borland C or Quick Basic (MicroDAC). Programming simplicity and clarity counts as an asset in the MSI application, since designers can't predict how visitors will interact with the exhibits. Bill Hogan, an Electronics Design Technician praises the reliability of the industrial-quality controllers. "The boards run 8-10 hours a day, flawlessly," he says.

According to MSI's Schacter, the public has responded favorably to the new exhibits: attendance figures have risen 25% compared to the same period last year.

Oven motor beats the heat

St. Louis, MO--You push a button, and 45 seconds later, a vending machine delivers fresh-cooked French fries. The new French Fry Vendor®, made by National Vendors for Ore Ida Foods, Inc., Boise, ID, may be great for potatoes, but it's tough on motors.

The machine's cooking basket and fan are controlled by a 0.5-horsepower, 56-frame motor from MagneTek, St. Louis, MO. During the cooking cycle, air temperature inside the machine reaches 460F. In order to bake off any residue, air temperature during the cleaning cycle hits 850F.

The application required a custom-designed motor that could operate on two speeds: 1,725 rpm for loading and unloading the fries in a cooking basket, and 3,450 rpm to cook the fries and for the self-cleaning cycle. "We created a motor that's almost two motors in one--a four-pole on low speed for loading and unloading fries, and a two-pole on high speed during cooking and cleaning," explains Greg Hall, MagneTek market specialist. "We used a switching device instead of tap winding to ensure that the motor could run slowly enough," he adds.

The high-temperature operating environment created a different challenge for MagneTek. Engineers realized that when the machine reached 850F, heat could be transferred through the motor shaft to the bearings. They solved this problem by using a stainless-steel shaft in place of conventional carbon steel.

MagneTek engineers also had to eliminate the danger of the open drip-proof motor overheating in an enclosed environment. Because an "air-over" cooling design wasn't possible, engineers designed the motor with reverse ventilation. This cools the motor as well as creating static pressure to keep hot air out of the motor, explains Hall. A specially balanced rotor keeps fan blades from wobbling and reduces vibration and noise.

Says Hall, "The key to the success of this project really is the communication between MagneTek and Ore Ida during the entire design process."

Add-on software for Excel enables data acquisition

Cleveland--Rather than acquiring data with one software package and then transferring it to spreadsheet software such as Microsoft's Excel™ to analyze it, wouldn't it be better to combine the two functions into one program? Now that's possible with IOtech's DaqViewXL, a data-acquisition and display application that seamlessly integrates into Excel.

DaqViewXL lets users set up data-acquisition applications from within Excel without programming. It also provides graphical access to all the functions of IOtech's parallel-port-based DaqBook, plug-in DaqBoard, and Daq PCMCIA data-acquisition hardware. The software allows hardware configuration via a graphical user interface by adding a new toolbar to Excel, and provides a strip-chart, recorder-like display that users can open within Excel to view acquired data in real time.

In turn, Excel lets users manipulate data and retrieve previously acquired data in a spreadsheet format. Excel also offers an array of graph and charting functions for presenting data in a graphical format, and mathematical and analysis functions, including frequency domain functions such as FFTs.

DaqViewXL is the first in IOtech's new series of "software components," which users can launch and operate from inside a "home" application such as Excel. Under this software-components concept, software developers divide their products into pieces that users can add on or embed into other applications. To access or attach these components, the developer must use an inter-application communication standard that all the components support. Dynamic Data Exchange (DDE) and Object Linking and Embedding (OLE) are examples of such standards.

By combining software components, users can customize general-purpose software such as Microsoft's Word™ or Excel into a specialized application without having to write a single line of code or glue together icons.

Compatible with Windows 3.1 and Windows95, Daq-ViewXL retails for $195. Demo disks are available free from IOtech.

Cyrix challenges Intel for desktop CPU performance

Richardson, TX--Computer designers and buyers looking for an alternative to Intel's advanced CPUs now have a real contender. Cyrix's new 6x86 microprocessor is faster than Intel's Pentium at the same clock speed, and the two chips are cost-competitive.

Preliminary performance figures show that a 100-MHz 6x86 scored 164 on the Winstone 95 benchmark, compared to the 159 scored by a 133-MHz Pentium running in the same system. Based on Intel's published benchmarks, Cyrix's chip is 30% faster than a 133-MHz P6 when both run under Windows for Workgroups 3.1.

"There's nothing on Intel's roadmap that's going to be dramatically faster than this chip," said Martin Reynolds, director of technology assessment at the San Jose-based market-research firm Data-quest. "It doesn't really matter whether it's the fastest processor--it's right up there with the fastest Intel has and that's not going to change."

The 6x86 sports two superpipelined integer units and a floating-point unit. All three use register renaming, out-of-order execution, data forwarding, branch prediction, and speculative execution to speed instruction throughput. In addition to Windows variants, the 6x86 runs DOS, UNIX, OS/2, and Solaris.

Reynolds believes the chip is more advanced than the Pentium--due to speculative execution, out-of-order instruction execution, and its ability to almost always be executing two instructions concurrently--but not as advanced as the P6. "But the Cyrix part performs a lot better in desktop applications than the P6," he notes, "which does not do very well with Windows code."

Production quantities are available now for $450 from Cyrix, IBM Microelectronics, and SGS Thomson Microelectronics. PCs based on the 6x86 are also available now from Epson, AST Research, and Peacock (Germany).

--Julie Anne Schofield, Associate Editor

Software helps design muscle exerciser

Midvale, UT--At least eight million older American women suffer from urinary incontinence. Recently, Utah Medical Inc. developed the Liberty™ "pelvic floor muscle exerciser" to address the problem. The battery-operated unit uses a low current to stimulate and strengthen pelvic floor muscles. To speed the unit's development, the company used solid modeling and rapid-prototyping techniques.

When designing the Liberty, Utah Medical created a compact battery enclosure to give mobility to users of the device. Fifty urethane prototypes of the enclosure and battery door latch were developed for testing against theoretical form, fit, and function criteria. They were also put through failure analysis, bicompatibility tests, and clinical validations of safety and efficiency.

The company used I-DEAS Master Series™ software from SDRC to prepare the device for clinic trials. "I-DEAS enabled us to cut the time for soft molding (silicon rubber molds of urethane parts) from 12 weeks to three," says Tod Cook, project leader for Liberty development.

Utah Medical's I-DEAS solid model files were converted to STL format to generate stereolithography models and patterns, silicon-rubber molds, and urethane parts. Utah Medical says the prototyping cost was money well spent since no changes were needed in the production tooling.

The firm was ready to begin production six months after Liberty's concept was finalized--half the usual time for a product this new, says Duane Sjoberg, manager of engineering services at Utah Medical. "Prototyping was done so quickly," Sjoberg says, "because iterations in the 3-D solid model can be done in hours and new SLA parts can be made overnight at a low cost."

Integrated countermeasures: alternative to heavier armor?

Newton, MA--The evolution of anti-armor weapons is changing the historical trend in tank design. Ever-more-powerful anti-tank projectiles over the years spurred the development of larger tanks with ever-thicker armor. But simply adding armor to deal with new smart rounds able to probe for a tank's weak spots jeopardizes its ability to fight and travel over tomorrow's battlefields.

Smarter weapons require a smarter response. Taking a cue from military aircraft that face similar threats without the freedom to add extra armored weight, tanks may soon sport active and passive counter-missile defenses in addition to armored defenses.

The Army recently awarded a $24.9 million contract for an advanced-technology demonstrator of an armored-vehicle integrated-defense system (IDS). Contract-team members include United Defense, TRW, and Lockheed Sanders, which represent a wealth of combat vehicle, electronics, software, and electronic-warfare experience.

IDS would scan the electromagnetic spectrum above and around the tank. "It detects when weapons have been launched against the vehicle," explains Tom Winant, IDS program manager. "An artificial-intelligence process then determines the best response and initiates countermeasures."

Sensors include electro-optical devices, laser and IR detectors, and MMIC radars. Countermeasures range from IR and radar jamming to automatic smoke-grenade and anti-missile launchers distributed around the tank's turret.

Reflecting the new realities in defense procurement, IDS includes mostly off-the-shelf equipment and software with a minimum of expensive new-technology development. Getting the components to work effectively together will consume the bulk of the contract costs. Each team member's system-integration laboratory will be electronically linked with that of the Army's Tank-Automotive Command in suburban Detroit to facilitate program development. Such virtual co-location should also keep program costs on track. An IDS technology demonstrator mated to an M1A1 Abrams main battle tank should begin full-up testing in 1997.

Urethane toughens auto glass

San Angelo, TX--With increasing stories of crime and violence on roadways around the world, some people are looking for ways to better protect themselves and their automobiles. One option: bullet-resistant and break-in proof glass from Safe Car Inc.

The company laminates layers of glass and polycarbonate together to achieve additional strength, depending on the safety level desired. Dan Medlin, glass plant manager at Safe Car, explains that the adhesive in these laminations is critical to ensure a strong, durable bond, with no delamination once it is in the field. Visibility is also an issue, since the windows have to be as clear as regular glass.

Safe Car chose an aliphatic Stevens Urethane from JPS Elastomerics Corp., Holyoke, MA, for use as an optical interlayer in its safety automobile glass. The company selected that material for its excellent adhesion properties with both glass and plastic, as well as high levels of optical clarity, light stability, and quality.

"If the adhesive is of poor quality, it will delaminate with daily exposure to UV light, weather variations, and temperature extremes," says Medlin. "The Stevens urethane is impervious to these conditions, and it provides the impact resistance and elasticity needed to stand up to rigorous conditions."

Safe Car's combination of glass, plastic, and urethane can absorb the thermal and mechanical shocks caused by bullets or other projectiles. Safe Car says the lamination does not splinter upon impact, but actually absorbs the incoming force and reflects it back in the opposite direction.

Drive combines servo, vector characteristics

Eden Prairie, MN--One of the most frustrating experiences for a machine designer is to learn, late in the design, that the machine's motion-control system is inadequate. Subsequently upgrading from an induction to a brushless motor can be complex and costly.

With the introduction of a new universal drive, however, those changes may now be far less painful. The BRU-Series Advantage Line, designed by engineers at Electro-Craft, automatically configures itself as an ac brushless servo drive or high-performance vector drive. It can also adapt to input from almost any type of controller, accepting traditional ñ 10V dc analog, step-and-direction, master encoder, or serial digital commands.

Using the new drive, engineers can easily optimize the motor and control system during the design process. "The advantage of this product is that you have the flexibility to control both types of motors or any type of controller," notes George A. Kaufman, director of engineering and business development for Reliance Motion Control.

Up to now, vendors haven't offered a drive that could be configured for both types of motors. The primary reason was that it wasn't cost effective to integrate the two technologies in hardware. Electro-Craft engineers solved that problem by integrating the logic and control elements in software. Even that, however, awaited the availability of cost-effective computer processing power to make the software work.

The universal drive's flexibility makes it well-suited to the packaging industry, where machinery typically employs brushless, vector, and stepper technology. Electro-Craft engineers say that the drive could also be used in web-converting, bag-making, and material-handling applications.

For the customer, the big advantage of the new system is flexibility, say Electro-Craft engineers. "By standardizing on a single drive, customers cut their inventory, their learning curve, and their maintenance costs," says Connell Smith, product marketing manager for Reliance's servo systems. "For example, if they have a conventional stepper drive and they want to upgrade to a servo, they have to tear it all out and put in a control that accepts an analog signal. But with this new drive, they simply reconfigure it in the software and they have the performance they need."

--Charles J. Murray, Senior Technical Editor

Honda of America finds a better way to bond

Anna, OH--When Honda of America sought to improve the gasketing process used to seal engine block ends (the oil pump and the main oil seal cover), the company looked for a gasketing material that would provide 100-percent adhesion on oily surfaces.

The challenge was to find a "drop-in" material that could be used in production without disrupting the assembly line. The outcome was Ultra-Grey™ 5699--an oil-resistant, primerless adhesive from Loctite Corp. that adheres to iron, light alloys, and plastics.

The Honda evaluation team tested Ultra-Grey™ 5699 in the laboratory, on the line, and over-the-road. They felt it offered the necessary sealing performance, fluid resistance, and high-torque retention. They also discovered that when the product is applied to oily surfaces, it offers oil resistance at higher temperatures. As a result, Honda specified it as the gasketing material to help seal and protect all of the Honda Civic 1.5 and 1.61, Accord 2.0 and 2.21, and Gold Wing motorcycle engines that are manufactured at the Ohio plant.

According to Honda, the implementation of Loctite Ultra-Grey™ 5699 was accomplished with minimal modifications. The sealant was dispensed using the existing equipment with only minor programming changes and air pressure adjustments, thus accomplishing the goal Honda had set forth--increased productivity and a better engine.

Aquaculture gains stability through software

Bainbridge Island, WA--While fish farms inshore have long been commonplace, offshore aquaculture has been more difficult. However, Ocean Spar Technologies (OST) recently was able to design an open-ocean pen system for raising fish.

The company studied the problem of keeping aquaculture pens stable in rough, open ocean waters for years before hitting on the "ocean spar" concept: vertical steel buoys anchored to the sea bottom that serve as floating fence posts for nets, keeping them relatively stable through constantly shifting currents.

Gary Loverich, chief engineer and part owner of OST, used computer simulations to test the stability of his net pen system before deploying an expensive, large-scale prototype in the deep sea.

Heavy currents and waves put a lot of fatigue on the net farming system. The most critical points are loads on the synthetic mooring lines that retain the nets' shape while securing them to the posts, or spars. Loverich used Working Model® software to measure these loads.

Once Loverich finds the proper load on the mooring lines, and the acceleration of the spar, he then exports the Working Model data to his COSMOS/M FEA program and tests the system to make sure that the hardware connecting the two components is strong enough.

In the Working Model simulation, a vertical spar or spars float in a coordinate axis system. The wave force is depicted by an arrow, which increases or decreases as the wave passes. Loverich measures the tension on the anchor lines, and the velocity of the spar buoys. Overall, he believes, motion analysis has helped decrease his risk and increase the dependability of his product.

Computer simulation key to mine-clearing system

Indian Head, MD--Thanks to computer-simulation technology, U.S. troops may avoid the dangers of minefields.

The Naval Surface Warfare Center is developing a defensive weapon system called the Distributed Explosive Technology (DET) system. It consists of a large net-like structure of rope woven with explosives. Towed downrange by a pair of rockets launched simultaneously, the net unfurls to cover thousands of square feet. Its array of explosives detonates upon impact, safely triggering detonation of all nearby mines without endangering personnel.

It's a simple concept, but the military's initial 2-D analysis code for simulating array deployment was useless. Engineers say it couldn't represent the three-dimensional nature of the system, especially the aerodynamic forces acting on the array.

ADAMS software from Mechanical Dynamics, Inc. (MDI) helped them predict the deployment characteristics more closely, and enabled them to do more design iterations. "We were able to choose the appropriate flight configuration before our test flights, which was critical because of our budget," says Robert Kaczmarek, program manager of the Mine Countermeasures Division.

Using a lumped-mass approach, they modeled the array by a large mesh of masses connected by elastic representations of the ropes. The result was a closer approximation of the actual trajectory of the DET system. Additionally, MDI devised a special module linked to ADAMS for computing airflows on the array. MDI obtained data for the model from extensive wind-tunnel tests it conducted at the University of Michigan.

To boost computational speed, MDI developed a point-mass element for the lumped-mass array model. Those elements reduce the number of equations to be solved.

--Gary Chamberlain, Senior Editor