Mitigation of shipping noise is a topical issue in marine engineering because of the dramatic increase in the levels of anthropogenic underwater noise and its impact on marine life. In recent years, hydro-acoustic research has been very much focused on the development of reliable methods for predicting underwater radiated noise (URN) due to cavitation, which is known to be the dominant contribution to the overall radiated noise spectrum of ships above the cavitation inception threshold. These methods are crucial both at the design phase of ships and to support the diagnostics of acoustic problems. On the other hand, model-scale experimental measurements are currently considered the most reliable approach to deal with URN problems. Model tests are indeed crucial for the verification and validation of numerical methods. They are, however, affected by several measurement uncertainties and scale effects for which suitable test procedures and post-processing techniques are needed. Even though there has been considerable advancement within the last 30 years in measuring techniques and facilities for cavitating propellers, the procedures and scaling formulas for cavitation noise were kept unrevised for a long time and only in the last decade have seen a rising interest with a number of international initiatives aiming at improving the reliability of noise measurements and the understanding of the underlying mechanisms of noise generation and radiation. Due to the complexity of the topic, international cooperation of the shipping industry, universities and research centres is needed and strongly encouraged by funding institutions as proved by the European Initiatives in the framework of FP 7 and H2020.
The Community of Practice on Noise was established as a continuation of the Project’s Joint Research Programme 10 “Noise Measurements” of the EU FP6 Network of Excellence Hydro Testing Alliance (HTA) with the objective to assess the current status of ship propeller cavitation noise prediction using model scale measurements and to develop procedures for further improvement. At the moment, the CoP Noise consists of 7 European institutes, i.e. CNR INM (Italy), DGA (France), MARIN, (Netherland), UNIVERSITY OF STRATHCLYDE (UK), UNIVERSITY OF NEWCASTLE (UK), UNIVERSITY OF GENOVA (Italy), SSPA (Sweden), and 1 extra-European Institute, i.e. KRISO (South Korea). The affiliation of new member institutions is strongly appreciated and very much welcome.
The work of the CoP is mostly focused on the following topics related to noise measurements:
1. Aspects of noise measurements at model scale.
2. Relating model scale to full scale noise measurements.
3. Hydrodynamic aspects influencing propeller noise.
4. Unconventional diagnostics techniques for URN source identification
In this framework, the Community of Practice “Noise” has developed, organized and performed a round robin test programme about the URN of a five-bladed, right-handed propeller operating in open water with horizontal and inclined shaft, under different vacuum and loading conditions. The RR test programme involves different propeller scale factors and facility types including small- and medium-scale cavitation tunnels, large-scale cavitation tunnels and large facilities such a free-surface cavitation channel and a depressurized towing tank. participants were reviewed. Specific aspects related to model scale noise measurements such as the influence of gas content, the free surface/ship hull/tank wall effects on noise transmission and reflection in model scale facilities are addressed.
In 2015 the scope was widened to all flow related topics and the CoP was renamed accordingly. Particle Image Velocimetry still plays a major role in the bi-annual CoP meetings and the bilateral exchange between. However, other techniques and topics like Laser Doppler Velocimetry and alternative methods of flow sensing in field and towing tank are discussed. These are for example acoustic based methods (runtime or Doppler), electro-magnetic methods (inductive current metres) as well as thermal and pressure based methods or flow visualization techniques.
The group consists of 13 institutes and is still open for new members. As round robin tests and alike were already done some years ago within the JRP 1, the work of the CoP is now based on an open exchange between all partners attending the meetings. Every institute is requested to prepare a small presentation on a recent project or trigger discussion on a topic of interest. This works very well as all CoP members experience common challenges every now and then and often have slightly different methods to cope with. Even though most partners are competitors to some extent outside the CoP we have a very open exchange and can discuss any detail protected by our CoP agreement. We discuss the exciting stories behind each other’s papers and conference presentations. This renders the contributions and traveling very worthwhile for all CoP members.