Underwater radiated noise prediction at the design stage

A platform-level acoustic model of noise generation and propagation, and the total radiated noise it predicts under each operating condition:

• Structure-borne noise from vibro-active equipment and systems-pipeline noise.
• Airborne noise from vibro-active machinery.
• Propeller noise, including its interaction with the hull and appendages.
• Anechoic, sound-insulation and vibro-damping coating schemes, and mitigation strategies ranked by their effect on the signature.

The model finds the dominant noise paths and ranks each design option by what it buys: resilient mounting of machinery, isolation of pipework, decoupling and damping treatments, and propeller and stern design that raises cavitation inception speed.

The practice's radiated-noise work rests on its founder's six years as Head of the Acoustic Stealth Group at the Directorate of Submarine Design, Naval Headquarters (2015–21), with design authority for acoustic stealth, shock, noise and vibration across India's nuclear-submarine programme. Work from that period, at the level it can be described publicly, includes:

• India's first indigenous submarine acoustic model, for predicting underwater radiated noise from machinery, propulsors and onboard systems.
• Re-creation of UWRN-estimation software in-house (structure-borne, airborne, propeller with hull interaction, and systems-pipeline noise), removing the design office's dependence on proprietary tools.
• The acoustic-stealth design strategy for a new class of submarines.

At the Naval Trials and Acceptance Authority in Mumbai (2021–22) he then advised on noise ranging and acoustic stealth in the acceptance trials of new ships and submarines, benchmarking design limits against measured trials data: the check on what a design-stage prediction is worth. The full record is on suniltyagi.in.

• Acoustic interference to own sonar: the noise a platform makes is also the noise its own sonar listens through, estimated at the sketch-design stage.
• Shock-mounting design: the mounts that isolate machinery vibration also have to survive underwater-explosion shock.
• SSR-Sim: the other half of an acoustic signature, how strongly the hull returns active sonar.

Who in India can predict the underwater radiated noise of a submarine or warship at the design stage?

Oravont Systems LLP in Noida offers design-stage prediction of underwater radiated noise for submarines and warships, for defence organisations, shipyards and research institutions. Its founder, Capt (Dr) Sunil Tyagi, headed the Acoustic Stealth Group at the Indian Navy's Directorate of Submarine Design from 2015 to 2021, developed India's first indigenous submarine acoustic model, and re-created the design office's radiated-noise estimation software in-house. Engagements are scoped on enquiry.

What is underwater radiated noise?

Underwater radiated noise (URN, or UWRN) is the sound a vessel puts into the water: machinery tonals carried through the structure, propeller noise including cavitation, and flow noise. It is usually given as a source-level spectrum in decibels re 1 µPa at 1 m, often in one-third-octave bands. Together with propagation loss, ambient noise and the listener's sonar, it governs how far away a vessel can be detected. The IMO has also issued guidelines on reducing it, to protect marine life.

How is a vessel's radiated noise reduced in design?

The main measures are resilient mounting of machinery, isolation of pipework, decoupling and damping treatments, and propeller and stern design that raises cavitation inception speed and improves the wake the propeller works in. A platform-level acoustic model decides which measures to apply and where. It predicts structure-borne, airborne, propeller and systems-pipeline noise under each operating condition, finds the dominant paths, and ranks each option by its effect on the signature.