Acoustic properties of composite materials in defence

With the focus of future warfare planning, Australia, through the Royal Australian Navy (RAN) is procuring new submarines and anti-submarine warfare frigates. Both programmes require vessels to be able to operate with high levels of stealth, part of which relies on a low acoustic signature.

Written by Kerryn Caulfield, Executive Director, Composites Australia Inc.

Noise and vibration are inevitable by-products of vessels’ engines, propulsion and flow noise, and the sound waves from which propagate as an acoustic signature that travels for long distances in the ocean. These signatures are used by vessels, particularly submarines to see deep into the seas they protect to detect enemy targets and enable safe navigation.

Managing acoustic signatures of naval vessels is a critical function of the survivability and operational effectiveness of Australia’s maritime force and also an area in which composites are a material solution.

Noise inevitably compromises a vessel’s anonymity and so suppressing and masking an acoustic signature is an equally central protective measure.

The function of SONAR domes – on vessels above and below water – is to house, protect and optimise electronic equipment critical for detection, navigation and ranging. They are built to last more than 30 years in corrosive and challenging marine environments and to withstand enemy attack. A well-engineered composite laminate permits acoustic energy to pass through with minimal sound transmission interference optimising the acoustic performance of a vessel’s SONAR system.

For submarines, an acoustic window enables acoustic energy signals or ‘ping’ – to pass unhindered with little reflection or attenuation. It is an acoustically transparent housing that surrounds the SONAR transducer array, the function of which is for detecting enemy targets and to enable safe navigation.

They are typically flooded compartments which means that when the submarine submerges it fills with water equalising on both sides of the window. Sonar domes are emptied for sonar dome maintenance or replacement and are always emptied when a vessel is in drydock.

RPC has been providing engineering services, sovereign manufacturing capability and providing

Through Life Support for composite components for defence applications for over 30 years working continually with both Collins Class submarines, the second largest non-nuclear powered submarines in the world, and the ANZAC frigate fleet.

The Collins Class submarine fleet was expected to be retired in about 2026, however the 2016 Defence White Paper extended this into the 2030s. The recent pivot from the Naval Group’s Attack-class submarine under the AUKUS agreement will see the Collins Class life extended, possibly until 2050 with significant capability upgrades.

RPC continues to be contracted to upgrade, re-engineer and replace various composite components which often requires significant R&D on the materials and construction, and validation of new materials.

HMAS Anzac conducts a passage exercise in company with JSS ISE and USS Stockdale during a South East Asia deployment. *** Local Caption *** HMAS Anzac and her crew of 191 personnel are deployed to South-East Asia to participate in a number of exercises and activities including Exercise Komodo 2016, Exercise Bersama Shield 2016 and the Indonesian Fleet Review. HMAS Anzac is the first in class of the Anzac Class frigate and is capable of operating in a multi-threat environment. Anzac is fitted with an advance package of air surveillance radars, hull mounted sonar and electronic support systems that interface with state-of-the-art Evolved Sea Sparrow Missiles and Ship Launched Torpedoes. The ship can embark a multi-role Seahawk helicopter to enhance anti-submarine, anti-surface warfare and Search and Rescue capabilities. Embarkation of a helicopter also provides the ship with the capability to deliver air-launches torpedoes. In 2014, Anzac was the third Anzac Class Frigate to complete the Anti-Ship Missile Defence upgrade program, which also provides an enhanced sensor and weapons systems capability. The upgrade showcases Australian design and integration capability, with new Phased Array Radar technology designed by CEA Technologies in Canberra, upgrades to combat systems performed by Saab Systems in South Australia, and platform integration design by BAE Systems in Victoria.