Radiated Noise of Research Vessels

A multidisciplinary Acoustics and Vibration problem

CAV Workshop

15 May 2012

Christopher Barber

Applied Research Laboratory

Penn State University

Ship Radiated Noise

• What makes noise?

– Propulsion

– Machinery

– Hydrodynamic sources, transient sources and transducers

• How can you build and operate a quiet ship?

– Propulsor and hull design

– Noise control technologies

– Operational awareness

• Why care?

– Environmental Impact

– Shipboard Habitability

– ICES

– Impact on Shipboard Mission Systems (self-noise)

• How to measure it ?

– Acoustic ranges, portable systems

– Shallow water measurements

Radiated Noise Sources

• Sources – Propulsor Noise

– Motor and Aux Machinery Noise

– Sea connected systems (pumps)

– Transient sources

• incl. active acoustic transponders

– Hydrodynamic sources

• Paths – Direct acoustic propagation

– Shaft line propagation

– Sound/structure interaction

– Diffracted paths

– Tanks

Bearing Cap Vertical - 3600 RPM

Generator Rotational

2X - Rotor Mechanical

Figure courtesy of Noise Control Engineering 4

Machinery Sources

Stator Core Radial Bearing Cap Vertical - 3600 RPM

2E - Full load

2E - No load with excitation

Generator Rotational

2X - Rotor Mechanical

SHAFT ROTATING 1R

AND 2R

CORE MAGNETOSTRICTION 2E

5 to 15 Knots

Low Speed Limits

Frequency, Hz

25 MW Alstom Generator

Measurements

taken

30 Sept 1998

l

l l

2E

2X 1R

6

Paths for Machinery Noise

• Airborne

• First Structureborne

• Secondary Structureborne

• U/W Radiated Noise

Figure courtesy of Noise Control Engineering

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Sea Connected Systems – Fluid-coupled paths

Pump generated fluidborne

acoustic energy travels via

piping systems.

Figure courtesy of Noise Control Engineering

Frequency (Hz)

SP

L

101

102

103

104110

115

120

125

130

135

140

FRV-40 PropellerEstimated Broadband Noise Envelope

11 kts withTip Vortex Cavitationand Suction Side LeadingEdge Cavitation Inceptionat 10.5 knots

11 ktsNoncavitating(design)

FRV-40 Goal

Printed 10 Feb 1999 13:14:03

Propeller Noise

• Cavitation typical dominates

broadband ship signature

Mitigation:

– Design prop for maximum

cavitation inception speed

– Restrict noise-sensitive

operations to speeds less

than cavitation inception

Non-propulsion flow-related noise

Bow wave transients

– Acoustic source

– Bubble sweepdown

Hull and appendage cavitation

– Rudders, Struts

– Fairings, Bilge Keels

Mitigation: good

hydrodynamic

design

Sonar Self-Noise Sources

• Hull-mounted sonars

– Bow-area flow noise

– Bow wave transient

– Flow-induced structural excitation

• Installation details

– window material and attachment mechanism

– fairings

• Propagation of external ship sources into sonar

– machinery / prop noise via hull grazing path

– Bottom reflected path

SNR = [SL-2TL + 20logHTHR+TS]-{NR+(NL0-DIR)}

Source LevelTransmit/Receive

Directivity

Target StrengthTransmission

(Propagation) Loss

Receive Reverb Ambient + Self-Noise

Directivity Index

SNR = [SL-2TL + 20logHTHR+TS]-{NR+(NL0-DIR)}

Source LevelTransmit/Receive

Directivity

Target StrengthTransmission

(Propagation) Loss

Receive Reverb Ambient + Self-Noise

Directivity Index

Impact - Environmental Noise

• Studies ongoing to assess impact of anthropogenic

noise on marine mammals

– general shipping noise

– Local radiated noise

– Science mission sources

Table from Hildebrand, “Sources of Anthropogenic Sound in the Marine Environment”

ICES Criteria for Fisheries RV’s

From Mitson, “UNDERWATER NOISE OF RESEARCH VESSELS, 1995

• Impact of research vessel noise

on fish surveys

– Based on estimates of “fish

hearing” for various species

– Impact to both acoustic and

catch surveys

Radiated noise measurements in a harbor environment using a vertical

array of omnidirectional hydrophones

Brian Fowler

Graduate Program in Acoustics

Dr. D. Christopher Barber

The Applied Research Laboratory

The Pennsylvania State University

Research Sponsored by ONR 331

1 CAV Workshop, May 14-15, 2012

Overview

• Research Field Test

• Omni-directional measurements

• Beamforming

– Far-field

• Theory

• Measurements

– Near-field

2

Research Testing and Objectives

• Acoustic Research Detachment at Lake Pend Oreille in Bayview, Idaho

• Summer 2010 and 2011

• SEAJET

• In conjunction with near-field acoustic holography (NAH) testing

– Validate NAH estimates

3

Problems with a shallow water harbor environment

• Multipath Environment – Surface reflections

– Bottom reflections

– Reflections off other underwater interfaces

• Near-field Environment – Proximity from hydrophone to source may

prohibit far-field plane wave assumption

4

Hydrophone Array

16”

14 Element Hydrophone Array 5

Top-view Geometry

S

e

a

J

e

t

Barge Sources (varying depth)

A Few Array Locations (suspended by crane from barge)

6

Side-view Geometry

7

Range

SeaJet

14

Ele

me

nt

Arr

ay

ITC 1001

J9

Reference Hydrophone

Barge

Omni-directional measurements

9

Ambient Run

Reference Phone

Hydrophone 1

Far-field beamforming theory

p(r,𝜃, 𝑡) = 𝐴

𝑟𝑖′𝑒𝑗(𝜔𝑡−𝑘𝑟

′)

𝑁

𝑖=1

Far field assumptions:

𝑟 ≫ 𝑁 − 1 𝑑 so all 𝑟𝑖 are approximately parallel 1

𝑟𝑖≅1

𝑟 for all 𝑖 where 𝑟 is the distance from array center to source

𝑟 = 𝑟1 −1

2𝑁 − 1 ∆𝑟 where ∆𝑟 = 𝑑 sin 𝜃,

so 𝑟𝑖 = 𝑟1 − (𝑖 − 1)∆𝑟

Kinsler, Frey, Coppens, Sanders. (2000) Line Array [Figure]. In Fundamentals of Acoustics, 4th Ed. pg 195. Hamilton Press 10

Far-field beamforming theory

p(r,𝜃, 𝑡, 𝜃0) =𝐴

𝑟𝑒𝑗(𝜔𝑡−𝑘𝑟)𝑒

−𝑗𝑁−12 𝑘∆𝑟 𝑒𝑗[𝜙𝑖+ 𝑖−1 𝑘∆𝑟]

𝑁

𝑖=1

where 𝜙𝑖 = 𝑖2𝜋

λ𝑑 sin 𝜃

multiplying a 𝑒𝑗𝜙𝑖𝑁𝑖=1 to the unsteered FFT gives us the

beamsteered data in the frequency domain

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Calculated broadside beams

Changing the steered frequency affects the main lobe width as well as the number and size of the side lobes.

f = 1860 Hz f = 3720 Hz

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Calculated steered beams

Steering the beam affects the direction in which the main lobe points and also affects the size and direction of the side lobes

f = 1860 Hz, steered to 10 degrees

13

14

Calculated steered beams

14 Element Array steered in the direction of an oncoming plane wave

Far-field beamforming results

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Far-field beamforming results

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Near-field beamforming theory and application

• Measure from geometric center of array • Remove far-field assumptions and recalculate • This will negate the plane wave assumption and

account for spherical spreading from the source • Vary ranges to find accurate range

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References • Burdic, William S. Underwater Acoustic System Analysis.

Englewood Cliffs, NJ: Prentice Hall, 1991. Print.

• Kinsler, Lawrence E., Austin R. Frey, Alan B. Coppens, and James V. Sanders. Fundamentals of Acoustics. New York: J. Wiley, 2000. Print.

Acknowledgements

• Carlos Uribe, Wyatt Tyahla, and David Van Hoof (PSU)

• Earl Williams and Nicolas Valdivia (NRL)

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