Ship source level Aleksander Klauson, Janek Laanearu, Mirko Mustonen Gothenburg, 01 June 2016
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?
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.
1. Why ship noise? 1 meter
2. How to measure ship noise. Testing methods. ISO 17208-1:2016 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 S12.64-2009/Part 1, Quantities and Procedures for Description and Measurement of Underwater Sound from Ships Part1: General Requirements.
2. How to measure ship noise. Testing methods. ANSI/ASA S12.64-2009/Part 1, Quantities and Procedures for Description and Measurement of Underwater Sound from Ships Part1: General Requirements.
2. How to measure ship noise. Testing methods.
2. How to measure ship noise. Testing methods. Precision method applicable in deep water!
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!
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.
3. Sources of ship noise Vibrations AIS GPS positionning ACOUSTIC CENTER Propeller cavitation Machinery noise Wave noise
3. Sources of ship noise 3. Sources of ship noise OVERSEAS HARRIETTE - IMO 7516993
3. Sources of ship noise B - blade rate F - firing rate G - generator
3. Sources of ship noise Directionality can be important!
4. Source Level (SL) measure of ship noise intensity. Deep water measurements
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
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
4. Source Level (SL) measure of ship noise intensity. RANDI model (Resrearch Ambient Noise Directionality)
5. How can BIAS measured data help to find SL?
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
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
5. How can BIAS measured data help to find SL? Statistics for GOF passenger ferries
5. How can BIAS measured data help to find SL? Case study: Identification of ship noise sources with AIS Ro-Ro Cargo
5. How can BIAS measured data help to find SL? Tracing of individuaal ship with AIS Ro-Ro Cargo, course 193deg
5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, 01.01.2014 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
5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, 01.01.2014 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
5. How can BIAS measured data help to find SL? BIAS 23, Saaremaa, 01.01.2014 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
5. How can BIAS measured data help to find SL? Source Level in 1/3 octave bands 14,0 knots 13,6 knots
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
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.
Thanks!