Picture1: The TFI technology includes an energy damper, extruded in DuPont? Hytrel? TPC-ET and shown in red in the photograph, within the mooring lines to reduce the forces along the whole tether. Image courtesy of TFI

Extruded thermoplastic elastomer helps keep marine devices afloat

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  • Device replaces chain and rope mooring
  • Extruded energy-dampening bellow using polyester thermoplastic elastomer
  • Design adapted from automotive Constant Velocity Joint (CVJ) boots

DuPont Performance Polymers and Ireland-based Technology from Ideas (TFI) collaborated to develop a novel way to allow moored devices to move with the sea, which significantly reduces peak loads up to 70 percent and improves durability of mooring lines that tether and protect high-value marine devices, such as wave energy devices and fish farms.

Device replaces chain and rope mooring

The new Dynamic Tethers wave protection system replaces chain and rope mooring, which pulls taut, rattles and wears quickly as it moves against the sea. It incorporates an energy-damping bellow that acts similar to a “shock absorber,” which delivers high load and fatigue resistance to protect devices from harsh sea wave conditions, designed to stay slightly taut and respond smoothly when stretched to its limit, while dramatically reducing wear and tear, improving stability, reliability and positioning and lowering cost.

The TFI technology solution is a tether with a combination of different polymer elements tailored to the wave environment

The TFI technology solution is a tether with a combination of different polymer elements tailored to the wave environment (source: TFI)

Extruded energy-dampening bellow using polyester thermoplastic elastomer

The energy-damping bellow is extruded by Radius Systems Ltd. in Banbridge, Ireland. The component is made with DuPont Hytrel TPC-ET polyester thermoplastic elastomer and a tensile elastomer element made of a soft material with low stiffness. Together they deliver the low force response of the system with elongations of up to 250 percent of the original length, while withstanding repeated low-force events (>3.5 million cycles per year). The energy-dampening bellow is 1.2 meters (nearly 4 ft.) long, 250 mm (nearly 10 inches) in diameter and weighs 20 kg (44 lb.) and is engaged as the tether reaches its maximum extension and is designed to deliver a specific targeted smooth response as it compresses.

Design adapted from automotive Constant Velocity Joint (CVJ) boots

The design takes advantage of the elasticity and flex fatigue of the Hytrel material. DuPont adapted its technology for constant velocity joint (CVJ) boots, which are a mainstay in the automotive industry, and developed a highly functional bellow to handle the extreme load conditions and meet the demanding overall performance requirements of the marine industry. In the development process, TFI provided the load deflection curve for a quarter-scale model and DuPont used their design knowledge from automotive shock-absorbing bellows to create a Hytrel bellow with corrugations of different pitch that compress at different rates to give increasing stiffness as the compression progresses. Advanced finite-element analysis (FEA) techniques were used to ensure the design met the performance specification.

The new tethers are being monitored at a number of installations in Europe and are expected to be commercially available in early 2015.

Main Picture: The TFI technology includes an energy damper, extruded in DuPont Hytrel TPC-ET and shown in red in the photograph, within the mooring lines to reduce the forces along the whole tether (source: TFI)

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