Underwater Radiated Noise Levels Research Articles

Prediction of cavity inception speed and underwater radiated noise of a full-scale marine propeller based on a cavitation tunnel model test

Propeller cavitation is a dominant source of underwater radiated noise (URN) from shipping, and the appropriate evaluation of propeller noise mitigation measures is important for ecological ship design. In this study, a model test procedure and scaling method to predict the full-scale URN level from hydrodynamic noise sources were introduced. The cavity size based on the empirical vortex model was considered in the proposed scaling method for a quiet cruise condition with isolated tip vortex cavitation. This relation provides information on the equivalent cavitation number for the model test to have the same relative radius as that of the full-scale tip vortex cavitation. The alternative test cavitation number can also be chosen as close as possible to the point that gives the equivalent tip vortex cavity size if sheet cavitation exists in the condition for the equivalent cavity size. In this case, additional noise scaling should be performed using the ratio of the tip vortex cavity radii. The new scaling exponent introduced in this study varies according to the distance from the cavitation inception condition and shows a decreasing trend from the value at the inception condition as the equivalent cavitation number for the model test decreases. The scaled URN levels based on the proposed method showed reasonable agreement with the measurement results of a full-scale ship. Finally, the noise reduction effect of the specially designed wake control fin and propeller was investigated through a comparative model test following the proposed scaling strategy, and significant noise reductions were observed with changes in the design configuration.

A study on the hydroacoustic characterisation of a cavitating propeller by dynamic adaptive mesh refinement technique

Underwater radiated noise (URN) of a marine propeller has received significant interest in recent decades due to its implications on marine fauna. Therefore, an accurate prediction of URN at an early stage of the propeller design is becoming imperative. This study presents a numerical investigation into the noise prediction of a marine propeller, including cavitation and a comparison with experimental test results obtained from the URN database from the King's College D (KCD) standard propeller series. Amongst the propellers tested in the series, the member KCD-193 was chosen to scrutinise in this study due to the significant variance of the cavitation types experienced by this propeller member and consequent characteristic variations observed in its URN spectral response. Numerical URN predictions of different flow conditions, represented by the advance coefficient and cavitation number, were conducted to investigate their effects on the noise spectrum. These predictions were compared with the experimental results to enable interpretation of the impact of various aspects of the simulation on URN prediction accuracy. In this investigation, one of the most prominent noise sources, tip-vortex cavitation (TVC), was identified as a critical aspect that needs to be captured by the numerical simulations for accurate URN predictions using CFD simulations. The influence of TVC on the spectrum was observed to be significant. The inception and stable presence of TVC dominated the frequency response of the broadband hump. In order to address this, a systematic adaptive mesh refinement strategy was implemented based on the vortex criterion to solve the flow characteristics in the propeller slipstream accurately. To further complement this task, a correlation between the cavitation bubble growth and collapse phenomenon by the sensitivity of the broadband hump on the spectrum was established based on the experimental results. The central frequency of the broadband hump was observed to vary with the advance coefficient and cavitation number. The reduction in the cavitation number resulted in a shift of this hump towards lower frequencies. The URN level of the hump decreased slightly in the high frequency by the reduction in the advance coefficient and the developing cavitation, demonstrating the cushioning effect on the spectrum. An accurate assessment of the noise spectrum, as far as numerical predictions are concerned, particularly on the broadband hump frequency bandwidth, was directly associated with the resolution of the TVC.

Experimental validation on structure-borne underwater radiated noise transfer function analysis for marine structure

In this paper, an experimental validation of a numerical procedure for estimating the structure-borne Underwater Radiated Noise (URN) Transfer Function (TF) of a marine structure based on the SEA theory has been performed. For the purpose, the structure-borne URN TF of a central point-excited one-side fluid-loaded four-edge stiffened plate in a reverberant water tank has been measured and compared with the SEA result. Additionally, the practical applicability of the procedure for a real ship structure has been demonstrated by comparing the URN analysis result based on the transfer function method and the measurement result for a Korean research vessel, ‘Cheong-Hae’. From the results, it is confirmed that the presented procedure can be used to estimate the structure-borne URN level emitted from the vibrating fluid-loaded side shells of a ship structure.

Verification of simplified underwater radiated noise estimation tool using Brown's formula

In recent years, the impact of underwater radiated noise from ships on marine life has attracted considerable global attention. Therefore, various research institutions are investigating this phenomenon through research and development efforts. In this study, authors have developed an underwater radiated noise estimation tool that can be used in the early stages of ship design. This tool calculates the underwater radiated noise level by applying Brown's formula, a simple estimation formula for predicting the noise generated by ships. The parameters required for Brown's formula are estimated using HOPE Light, a ship performance estimation software developed by the National Maritime Research Institute. The extent of cavitation is estimated using Burrill's diagram, a tool for assessing the occurrence of cavitation. The accuracy of the developed tool has been verified by comparing its results with full scale measurements of underwater radiated noise levels obtained off-board hydrophone array system.

Statistical analysis of measured underwater radiated noise from merchant ships using ship operational and design parameters.

Ships unintentionally radiate underwater noise mainly due to propeller cavitation under usual operations. In 2022, the International Maritime Organization started a review of the nonmandatory guidelines for the reduction of underwater radiated noise (URN) from ships. The characteristics of URN from ships have been studied for a long time, and quantitative variations in URN levels with ship size and speed have been reported. From the viewpoint of ship design, it is more reasonable that the effect of ship speed and draft is considered as the ratio to design speed and maximum draft, respectively. Therefore, in this study, underwater sound measurements were conducted in deep water (>300 m in depth) under a sea lane, and regression analysis was applied to the source levels of the URN from many merchant ships using ship length, ship speed ratio to design speed, and draft ratio to maximum draft. In this analysis, the source level is simplified based on the characteristics of URN due to propeller cavitation. This allows one coefficient to represent the approximate shape of the spectrum of URN level. Further, variations in the URN level for each ship type are discussed based on the results and comparisons with previous studies.

Small reductions in cargo vessel speed substantially reduce noise impacts to marine mammals.

Global reductions in the underwater radiated noise levels from cargo vessels are needed to reduce increasing cumulative impacts to marine wildlife. We use a vessel exposure simulation model to examine how reducing vessel source levels through slowdowns and technological modifications can lessen impacts on marine mammals. We show that the area exposed to ship noise reduces markedly with moderate source-level reductions that can be readily achieved with small reductions in speed. Moreover, slowdowns reduce all impacts to marine mammals despite the longer time that a slower vessel takes to pass an animal. We conclude that cumulative noise impacts from the global fleet can be reduced immediately by slowdowns. This solution requires no modification to ships and is scalable from local speed reductions in sensitive areas to ocean basins. Speed reductions can be supplemented by routing vessels away from critical habitats and by technological modifications to reduce vessel noise.

Optimal voyage scheduling of all-electric ships considering underwater radiated noise

Underwater radiated noise (URN) emanating from ships can adversely impact the life functions of certain marine mammals that rely on sound to navigate, communicate, and locate prey. This paper formulates an optimal voyage scheduling problem to mitigate the impact of URN on sensitive marine species by choosing amongst different possible paths and specifying the cruising speed along the selected path. We focus on all-electric ships (AESs) owing to their greater flexibility for speed regulation by coordinating an integrated power system. The proposed optimization model schedules generators and energy storage devices toward minimizing the operation cost while satisfying constraints pertinent to URN levels and atmospheric greenhouse gas (GHG) emissions, the electric power network and operational limits, and expected voyage timelines, culminating in a mixed-integer nonlinear programming problem. To promote computational tractability, we approximate the nonlinear relationships for URN, propulsion load, and fuel consumption with piecewise linear functions. This leads to a mixed-integer second-order cone programming problem, which enables convergence to the global optimum and computationally efficient solutions. We illustrate the effectiveness of the proposed model in curbing URN levels and GHG emissions with numerical case studies involving an 18-node ship test system.

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy part 3: Assessment of full-scale propeller hydroacoustic performance versus sea trial data

This paper assesses the full-scale The Princess Royal vessel Underwater Radiated Noise (URN) characteristics using a CFD method. Also, the cavitation extensions and propeller hydrodynamic characteristics are explored over a wide range of operating conditions. The numerical calculations were carried out using a hybrid method combining the DES and permeable formulation of the FWH equation. In the numerical calculations, two different permeable noise surfaces encapsulating the complete hull and only the propeller and its slipstream were utilised. In order to accurately solve the tip vortex flow and model the tip vortex cavitation (TVC) in the propeller slipstream, the developed V-AMR technique was applied in the numerical calculations together with the Schnerr-Sauer mass transfer model to model the cavitation. The results were validated with the full-scale measurements in terms of propeller hydrodynamic characteristics, cavitation extension and URN. The results showed that the sheet cavitation extensions predicted in the numerical calculations agreed with the sea trial observations despite the differences in the violent cavitation dynamics. Similarly, TVC was somewhat observed in the numerical calculations using the V-AMR technique with a lack of dynamics and extension in the propeller slipstream compared to the full-scale observations. The comparison of noise spectra at two different operating conditions, where similar cavitations were observed between the numerical calculations and full-scale observations, showed an agreement with the full-scale measurements. The lack of TVC and possible bursting phenomena predicted in the numerical calculations caused the underprediction of propeller URN levels up to 20 dB at certain frequencies over the noise spectrum at the lowest blade loading conditions. When the two different permeable noise surfaces were compared, it can be concluded that the permeable noise surface, encapsulating the complete hull, captures more noise information in the noise spectrum than the permeable surface, encapsulating only the propeller and its slipstream. Also, a more distinct spectral hump triggered by the tip vortex was observed using the permeable noise surface around the complete hull compared to one around the propeller. The results showed that the interaction between the cavitation and nonlinear noise sources occurring around the hull might influence the amplitude of the characteristic hump, apart from the possible hull interference on the ship hull and appendages induced by the propeller.

Numerical investigation into the effects of tip vortex cavitation on propeller underwater radiated noise (URN) using a hybrid CFD method

This study explores the influence of tip vortex cavitation (TVC) on propeller induced URN using a hybrid CFD method. The cavitating flow around the model and full-scale benchmark propeller belong to the Newcastle University's research vessel, The Princess Royal, operating under uniform, inclined and non-uniform flow conditions were solved using DES and mass transfer model. The recently developed advanced mesh refinement (V-AMR) technique was incorporated into the calculations for better modelling tip vortex flow and realising the TVC in the propeller slipstream. This technique enabled the inclusion of the nonlinear noise sources, mainly represented by turbulence and vorticity, including TVC, effectively for the accurate prediction of propeller URN. The numerical calculations were conducted in conditions where only the sheet cavitation was modelled without the V-AMR technique and where the sheet and tip vortex cavitation was modelled together using the V-AMR technique to understand the contribution of TVC to the overall propeller URN. The results were first validated with the available experimental data obtained in the model scale test campaign in the cavitation tunnel and sea-trial data for the propeller's hydrodynamic performance characteristics, cavitation extensions and URN. The results showed that the contribution of TVC to the overall propeller URN was minimal in conditions where the stable and structured TVC was present (i.e., under uniform flow conditions). However, when the propeller was operating under inclined and non-uniform flow conditions where the cavitation dynamics and vortex pulsation were dominant, the unstructured and unstable TVC was observed compared to the observations of TVC under uniform flow conditions. The unstructured TVC created several spikes, which can be associated with its strong cavitation dynamics and possible collapsing/bursting phenomena. These spikes created by the TVC and observed in the time domain acoustic pressure signal consequently contributed to the propeller URN at the different frequency ranges of the noise spectrum and increased the URN levels up to 15 dB under non-uniform flow conditions compared to the propeller URN predictions when only the sheet cavitation was present.

Hydroacoustic and hydrodynamic investigation of bio-inspired leading-edge tubercles on marine-ducted thrusters

Underwater radiated noise (URN) has a negative impact on the marine acoustic environment where it can disrupt marine creature's basic living functions such as navigation and communication. To control the ambient ocean noise levels due to human activities, international governing bodies such as the International Maritime Organization (IMO) have issued non-mandatory guidelines to address this issue. Under such framework, the hydroacoustic performance of marine vehicles has become a critical factor to be evaluated and controlled throughout the vehicles' service life in order to mitigate the URN level and the role humankind plays in the ocean. This study aims to apply leading-edge (LE) tubercles of the humpback whales’ pectoral fins to a benchmark ducted propeller to investigate its potential in noise mitigation. This was conducted using CFD, where the high-fidelity improved delayed detached eddy simulations (IDDES) in combination with the porous Ffowcs-Williams Hawkings (FW-H) acoustic analogy was used to solve the hydrodynamic flow field and propagate the generated noise to the far-field. It has been found that the LE tubercles have shown promising noise mitigation capabilities in the far-field, where the OASPL at J = 0.1 was reduced to a maximum of 3.4 dB with a maximum of 11 dB reduction in certain frequency ranges at other operating conditions. Based on detailed flow analysis researching the fundamental vortex dynamics, this noise reduction is shown to be due to the disruption of the coherent turbulent wake structure in the propeller slipstream causing the acceleration in the dissipation of turbulence and vorticity-induced noise.

Effect of biofouling roughness on a marine propeller's performance including cavitation and underwater radiated noise (URN)

This study aims to investigate the effects of biofouling-related roughness on a propeller's hydrodynamic and underwater radiated noise (URN) performance. Selected benchmark INSEAN E779A propeller operated in uniform & open water flow under non-cavitating and cavitating conditions. The hydrodynamic flow field around the propeller was first solved using RANS (Reynolds-averaged Navier Stokes) solver. The Schnerr-Sauer cavitation model, based on reduced Rayleigh-Plesset equation, was used to model the sheet cavitation on the propeller blades and tip vortex cavitation (TVC) in the propeller's slipstream. A vorticity-based Adaptive Mesh Refinement (AMR) technique was employed for the observation of TVC. The porous form of the Ffowcs-Williams Hawkings (P-FWH) equation, which is coupled with the RANS solver, was used to predict the URN (or hydroacoustic performance) of the propeller. The propeller performance characteristics, including cavitation, were validated with the available experimental data. Following that, the roughness functions representing the different roughness configurations obtained from the literature were employed using wall function model of Computational Fluid Dynamics (CFD) solver. The results showed that roughness has detrimental impacts on the propeller's performance characteristics. That is to say that the propeller's thrust decreases while the torque increases with increasing severity of the roughness. Hence, the efficiency loss of the propeller at the most severe roughness condition can be as high as 30% and 25% at J = 0.795 and J = 0.71 & σ=1.763, respectively. Unlike its detrimental effects on the hydrodynamic performance, the roughness had some positive effects by reducing the cavitation volume, especially for the TVC and hence on the propeller underwater radiated noise (URN). The results also indicated that the URN levels might be reduced up to 10 dB between 1 kHz and 2 kHz. Besides, 2nd and 3rd BPF values decrease between 1 and 7 dB under varying roughness configurations in comparison to the smooth case. The study reported the effect of a particular biofouling roughness on the URN levels of a propeller for the first time in model-scale and using the CFD simulations.

Cavitation observations, underwater radiated noise measurements and full-scale predictions of the Hydro-Spinna turbine

The development of marine current turbines has progressed rapidly with prototypes and full scale devices being deployed in sea. With research focusing on the hydrodynamic and design aspects of the technologies used, little is known of the impact of marine current turbine operation on marine life and environment. This paper looks at the underwater radiated noise (URN) produced from the operation of a novel tidal turbine, the Hydro-Spinna. URN measurements were taken from a 280 mm diameter model tested in Newcastle University. The model results were extrapolated to predict the full scale URN level for three turbine diameters of 5 m, 10 m and 15 m and compared to the fish reaction level acoustic level provided by the International Council for the Exploration of the Sea (ICES) as a reference. Analysis showed an increase in noise level with turbine diameters and that for all diameters, the highest noise levels were observed at Tip Speed Ratio = 1 where the thrust on the turbine is at its maximum. The noise levels predicted for the Hydro-Spinna at this off-design condition is above the ICES threshold, it was found that at optimal operating conditions the noise level would be below the threshold.

On-board measurement techniques to quantify underwater radiated noise level

Cavitating ship propellers are known to be the dominant noise source contributing significantly to the underwater radiated noise (URN) level. Innovative measurement methods using on-board devices need to be further investigated as they offer a serious alternative to traditional methods in terms of cost-efficiency and practicality. This exploratory study combined simultaneous on- and off-board noise and vibration measurements with cavitation views captured by digital photography and high speed cameras.Comprehensive full-scale trials were conducted on Newcastle University’s research vessel, The Princess Royal, in the framework of the FP7-EU project SONIC. On-board data were captured from multiple measurement systems (including. hull pressure sensors, accelerometers, optical devices, shaft strain gauges) provided by SONIC project partners CETENA, Wärtsilä , University of Southampton and Newcastle University. A new semi-empirical correlation method based on cavitating propeller pressure fluctuation and the URN level was established. Results offer clear evidence of successfully estimating URN with on-board measurements up to the middle frequency region where the blade passing fundamental and low harmonic frequencies occur. These illuminating insights reported in this paper provide valuable benchmark sea trial data in full scale.

Acoustic data quality assessment tools and findings for ocean observing systems

Ocean Networks Canada (ONC) operates long time series, ocean observatories in the Pacific and Arctic. These include the large VENUS and NEPTUNE observatories, many small community based observatories and the Underwater Listening Station (ULS) for the Vancouver Fraser Port Authority. Passive acoustic monitoring systems are a component of all ONC observatories and passive acoustic data quality is therefore a concern. All the observing systems have multiple underwater electronics and sensor types, many of which can negatively impact the passive acoustic sensor data. Hydrophone sensitivity degradation due to time, water absorption, and biofouling need to be assessed to ensure accurate ambient noise measurements and accurate vessel underwater radiated noise level measurements. The performance and suitability of the hydrophones for specific areas also needs to be assessed so the acoustic analysts can be aware of the hydrophone induced data limitations. ONC has been examining the use of in situ calibration verifications, spectral probability density (SPD) plots, spectrograms, and wave data as tools to assess the passive acoustic data quality. The preliminary findings on the impact of all of the above acoustic error sources are presented.

A Simple Model for the Underwater Noise Source Level of Ships

Underwater noise becomes a field of growing concern because of the possible interaction with sound vocalization of marine mammals. Modeling the effect of shipping noise being a predominant contribution worldwide requires more than statistics of measured ships in the field. This article is an attempt to characterize the underwater radiated noise level of a ship by relating spectral components of noise to naval architectural features of the ship.

Predicting underwater radiated noise levels due to the first offshore wind turbine installation in the United States

Noise generated by offshore impact pile driving radiates into the air, water, and sediment. Predicting noise levels around the support structures at sea is required to estimate the effects of the noise on marine life. Based on high demands developing renewable energy source, the United States will begin the first pile driving within one to two years. It is necessary to investigate acoustic impact using our previously verified coupled Finite Element (Commercial FE code Abaqus) and Monterey Miami Parabolic Equation (2D MMPE) models [J. Acoust. Soc. Am. 131(4), 3392 (2012)]. In the present study, we developed a new coupled FE-MMPE model for the identification of zone of injury due to offshore impact pile driving. FE analysis produced acoustic pressure outputs on the surface of the pile, which are used as a starting field for a long range 2D MMPE propagation model. It calculates transmission loss for N different azimuthal directions as function of distance from the location of piling with the inputs of corresponding bathymetry and sediment properties. We will present predicted zone of injury by connecting N different distances of equivalent level fishes may get permanent injury due to the first offshore wind farm installation in the United States.

Underwater radiated noise levels of a research icebreaker in the central Arctic Ocean

U.S. Coast Guard Cutter Healy's underwater radiated noise signature was characterized in the central Arctic Ocean during different types of ice-breaking operations. Propulsion modes included transit in variable ice cover, breaking heavy ice with backing-and-ramming maneuvers, and dynamic positioning with the bow thruster in operation. Compared to open-water transit, Healy's noise signature increased approximately 10 dB between 20 Hz and 2 kHz when breaking ice. The highest noise levels resulted while the ship was engaged in backing-and-ramming maneuvers, owing to cavitation when operating the propellers astern or in opposing directions. In frequency bands centered near 10, 50, and 100 Hz, source levels reached 190-200 dB re: 1 μPa at 1 m (full octave band) during ice-breaking operations.

A compound isolation system for T‐AGOS I class 600‐kW diesel generators

The T‐AGOS 1 class ocean surveillance ships are to tow a sonar array known as the Surveillance Towed Array Sensor (SURTASS). In order for the towed array to operate in a quiet environment, the underwater radiated noise level of the towing ship must be low. This paper presents a design for the installation of four 600‐kW diesel generator units. The radiated noise, due to two operating units, is estimated for a frequency range from 10 to 400 Hz by assuming that the hull acted as 16 simple pistons. Verification of the compound isolation system performance was made by conducting a land‐based test and measuring vibration throughout the system and the force transmitted to the foundation. The estimated radiated noise levels based on test data are compared with those based on mathematical analysis of the isolation system and found to be quite similar.