Ship source level. Aleksander Klauson, Janek Laanearu, Mirko Mustonen. Gothenburg, 01 June 2016

Transcription

1 Ship source level Aleksander Klauson, Janek Laanearu, Mirko Mustonen Gothenburg, 01 June 2016

2 Outline 1. Why ship noise? 2. How to measure ship noise. Testing methods. 3. Sources of ship noise. 4. Source Level (SL) measure of ship noise intensity. 5. How can BIAS measured data help to find SL?

3 1. Why ship noise? Among the diferent sources of ambient noise, merchant shipping is the principal contributor over the frequency band of 5 Hz to as high as 1 khz. Within this band, the shipping noise level can be as much as 40 db higher than the local wind-noise levels.

4 1. Why ship noise? 1 meter

5 2. How to measure ship noise. Testing methods. ISO :2016 Underwater acoustics Quantities and procedures for description and measurement of underwater sound from ships Part 1: Requirements for precision measurements in deep water used for comparison purposes ANSI/ASA S /Part 1, Quantities and Procedures for Description and Measurement of Underwater Sound from Ships Part1: General Requirements.

6 2. How to measure ship noise. Testing methods. ANSI/ASA S /Part 1, Quantities and Procedures for Description and Measurement of Underwater Sound from Ships Part1: General Requirements.

7 2. How to measure ship noise. Testing methods.

8 2. How to measure ship noise. Testing methods. Precision method applicable in deep water!

9 2. How to measure ship noise. Testing methods. Survey method: if distance at CPA =300m, d1=300*tan(20 o )=110m Distance at CPA = 100m d1=100*tan(20 o )=36m Can be done!

10 2. How to measure ship noise. Testing methods. For all Grades, the hydrophone(s) shall be arranged vertically in the water column. The hydrophone(s) shall be located to measure the beam aspect of the vessel under test. For all Grades, the hydrophone(s) shall not be located on the sea bed.

11 3. Sources of ship noise Vibrations AIS GPS positionning ACOUSTIC CENTER Propeller cavitation Machinery noise Wave noise

12 3. Sources of ship noise 3. Sources of ship noise OVERSEAS HARRIETTE - IMO

13 3. Sources of ship noise B - blade rate F - firing rate G - generator

14 3. Sources of ship noise Directionality can be important!

15 4. Source Level (SL) measure of ship noise intensity. Deep water measurements

16 4. Source Level (SL) measure of ship noise intensity. Deep water measurements SL Source Level RL = SL TL TL 20log( R) TL Transmission Loss RL Received Level Sphrerical spreading

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18 4. Source Level (SL) measure of ship noise intensity. 14,0 knots 13,6 knots Source Level in 1/3 octave bands Source Level in 1Hz octave bands

19 4. Source Level (SL) measure of ship noise intensity. RANDI model (Resrearch Ambient Noise Directionality)

20 5. How can BIAS measured data help to find SL?

21 5. How can BIAS measured data help to find SL? SL Source Level RL = SL TL TL? RL Received Level TL Transmission Loss In shallow water conditions TL can be modelled

22 5. How can BIAS measured data help to find SL? Sound speed profile Bathymetry Sea bottom properties Parabolic Equation method - RAM Fitting Transmission Loss Measured Data

23 5. How can BIAS measured data help to find SL? Statistics for GOF passenger ferries

24 5. How can BIAS measured data help to find SL? Case study: Identification of ship noise sources with AIS Ro-Ro Cargo

25 5. How can BIAS measured data help to find SL? Tracing of individuaal ship with AIS Ro-Ro Cargo, course 193deg

26 5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, bottom: sandy mud, Ro-Ro cargo, course 193 o, 1/3 octave 63Hz best fit SL=170 db re 1m depth of source 3m, Distance at CPA 600m modelling measurement

27 5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, bottom: sandy mud, Ro-Ro cargo, course 193 o, 1/3 octave 63Hz best fit SL=165 db re 1m depth of source 3m, Distance at CPA 600m

28 5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, bottom: sandy mud, Ro-Ro cargo, course 193 o, 1/3 octave 125Hz best fit SL=170 db re 1m Draught 6,5m, depth of source 3m, Distance at CPA 600m

29 5. How can BIAS measured data help to find SL? Source Level in 1/3 octave bands 14,0 knots 13,6 knots

30 5. How can BIAS measured data help to find SL? Passenger ship, conditions 0.1 <= distance => 0.5, course 10 <= course => 20 Determination of harmonics

31 6. CONCLUSIONS 1. Source Level is an important characteristic of ship noise emission. It depens on frequency, directionality, ship speed etc. 2. In deep water SL calculation is straightforward. RL can be calculated at the reference distance 1 m from ship. In shallow water reseived signal is contaminated by multiple reflections. 3. Transmission Loss can be found by modelling, if the propagation conditions are well known. 4. Harmonic lines, if present, provide information about the mashinery and propulsion system of the ship.

32 Thanks!