Overview
ISO 20233-2:2019 - Ships and marine technology: Model test method for propeller cavitation noise evaluation in ship design - Part 2: Noise source localization defines a standardized model-test procedure to locate and visualize propeller cavitation noise sources. Intended for ship designers, acoustic engineers and test laboratories, the standard covers model test setup, hydrophone array instrumentation, data acquisition, array signal processing and result visualization to reproduce and localize cavitation patterns reliably in ship design verification.
Key Topics and Requirements
- Scope and objective: Localize the propeller cavitation noise source during model tests to support quieter ship designs. Works in conjunction with ISO 20233-1 (source level estimation).
- Model test setup: Reproduce cavitation patterns using similarity laws between model and ship; follow test conditions from ISO 20233-1.
- Hydrophone array:
- Use hydrophone arrays for high-directivity localization; 2‑dimensional arrays are recommended for cost‑performance balance.
- Recommended hydrophone specs: receiving sensitivity ≥ −220 dB re 1 V/µPa; frequency range ~1 Hz to 100 kHz; omni‑directional response; operating static pressure 40–100 atm.
- Arrays must be mounted to minimize flow/vibration effects and avoid mounting-induced resonances.
- Array calibration: individual hydrophones calibrated before tests and periodically (typically every 12 months) using a calibrator or per IEC 60565; verify array localization via a reference field (virtual source).
- Data acquisition:
- A/D sampling must satisfy Nyquist; at least 2× the highest test frequency (recommended >4×).
- Resolution: >12‑bit (16‑bit recommended).
- Synchronous multi-channel sampling for all hydrophones; apply anti-aliasing low-pass filtering before conversion.
- Acquisition time: typically corresponds to 1 000 propeller rotations (tens of seconds in cavitation tunnels, ~200 s in depressurized towing tanks).
- Post-processing and array signal processing:
- Processors covered include Bartlett and MV (minimum variance); other beamforming options may be used.
- Guidance on spatial resolution, graphical display and interpretation of localization output is provided.
- Informative annexes: array design methods and signal models.
Applications and Users
- Ship designers and naval architects assessing and reducing propeller cavitation noise during early design.
- Acoustic test laboratories and cavitation tunnel/towing tank facilities performing model-scale noise localization.
- Researchers developing array signal processing, beamforming and cavitation visualization techniques.
- Classification societies and regulatory bodies interested in standardized acoustic testing protocols.
Related Standards
- ISO 20233-1:2018 - Ships and marine technology - Part 1: Source level estimation (companion standard for source level prediction).
- IEC 60565 (referenced for hydrophone calibration procedures).
Keywords: ISO 20233-2:2019, propeller cavitation, noise source localization, hydrophone array, model test, ship design, array signal processing.