Cavitation Noise Research Articles

Prediction of near field propeller cavitation noise by viscous CFD with semi-empirical approach and its validation in model and full scale

Propeller cavitation noise has been a large interest among maritime industries in terms of mariners' comfort and marine environmental protection. The objective of this study is to propose and validate practical computational methods to predict near field propeller cavitation noise by complementary use of viscous CFD and semi-empirical formula. Acoustic analogical method represented by Ffowcs Williams-Hawkings equation is not utilized at all in the present study.Four different propellers equipped on actual ships are of the interest. Cavitation phenomena around these propellers are reproduced by viscous CFD simulations behind full-scale ship wake. Time series of pressure fluctuations as well as the area of cavitation extent on the blades are logged. The former is directly utilized to quantify the level of tonal noise at near field while the latter is utilized to estimate upper bound of broadband noise together with the Brown's semi-empirical formula.The proposed methods accurately estimate the tonal noise up to 3rd blade frequency, in the meantime, upper limit of broadband noise is well predicted in comparison to the measurement results. The present method is very practical and thus it can be one of the criteria to estimate propeller cavitation noise in the near field.

Simulated cavitation noise from strong nonlinear coupling in a multi-bubble system

The mutual nonlinear coupling between cavitation bubbles in a bubble cloud has often been blamed for the complex nature of the cavitation noise. This noise is undesirable for two reasons. First, it affects the source air-gun signature which is crucial in later stages of seismic signal processing. Second, the generated noise may fall in the same frequency regime which is used by some types of whales for communication, and therefore interfere. The complete nonlinear theory of bubble interaction is used to solve the governing Keller-Miksis equation (KME) to simulate the experimentally observed cavitation noise. A qualitative comparison is made with the results from other scientific investigations and interesting inferences are drawn. It is believed that the findings reported here may have implications in the air-gun array design in seismic exploration industry since air-guns are the indirect source of cavitation noise. It may also have an impact on the study of communication systems in marine mammals.

An Improved Numerical Computation of Hull Pressure Fluctuations Due to Unsteady Sheet Cavitation of a Propeller

An operating propeller is the main source of vibration on the ship hull, especially on the stern. In this article, an improved numerical scheme is presented to predict the pressure fluctuations on the ship hull due to the unsteady sheet cavitation of a propeller. The calculated results are compared with the published results and experimental data carried out in the hydrodynamics and cavitation tunnel of Hamburgische Schiffbau-Versuchsanstalt to verify the improvement. The present method is based on a two-cycle iterating scheme which satisfies the boundary integral equation in time domain. The hull pressure fluctuations calculated by the first-cycle iterations are treated as the initial values for the second-cycle iterations. The solid angles of the elements will deviate from the standard value, .5, as the dramatic variation in geometry appears, and accumulate numerical errors in the calculating process. During the second-cycle iterations, a filter based on the solid angles on hull elements is proposed to minimize the iterating error. A container ship is treated as the computing sample in this study, and evidence is offered regarding the 16% improvement achieved by the present method. 1. Introduction A propeller operating in a nonuniform wake field in the ocean is one of the prime sources of vibration and noise affecting the ship. The prediction of hull pressure fluctuations caused by propellers is an important consideration for many vessels and worthy of being researched. Hull pressure fluctuation caused by the marine propeller has been widely investigated since the 1980s. Huse and Guoqiang (1982) developed a semi-empirical prediction method, in which the cavitation volume on the propeller blade surface can be estimated using experimental data. Breslin et al. (1982) proposed a model based on the potential flow theory, which simulates the ship hull by means of a simple panel method and the propeller by means of a lifting surface vortex lattice method. Kinns and Bloor (2004) used an acoustic boundary element (BE) model to simplify the problem of hull vibration excitation due to propeller sources and dipoles. The convergence of results for a cruise liner model was demonstrated with different element distributions. Kehr and Kao (2004) derived the incident blade rate pressure induced by unsteady sheet cavitation (monopole) and unsteady forces (dipole) of an operating propeller, for calculating the hull pressure fluctuations. Brouwer (2005) applied a stationary set of rings of monopole and dipole sources in the frequency domain to solve the propeller-induced noise and vibrations. Lee et al. (2006) integrated computational fluid dynamics (CFD) and the finite difference method for the computation of propeller-induced hull vibration. It was recommended that the phase difference of the propeller-induced pressure should be considered for preventing overprediction. Kao and Kehr (2006) developed a time domain iteration method to calculate the hull pressure fluctuations induced by the operating propeller. The phase difference is included in the iterating scheme, and the computation is robustly convergent. Seol and Moon (2009) derived the governing equation of pressure fluctuation induced by sheet cavitation according to the Ffowcs Williams approach. In the study by van Wijngaarden (2011), a potential flow boundary element method (BEM) with measured hull pressure data as input was applied to solve the hull pressure fluctuations, and the model experiments were also carried out. It was concluded that the computed hull pressure fluctuations due to non-cavitating propellers is reasonably accurate compared with the experimental data. Kehr and Kao (2011) calculated the pressure fluctuations on ship hull due to propeller sheet cavitation by using the method presented in Kao and Kehr (2006). The numerical result is higher than the experimental data provided by the hydrodynamics and cavitation tunnel (HYKAT) of HSVA (Wiemer 1999) by approximately 27%. The pressure fluctuations on ship stern induced by cavitating propellers were solved by Kanemaru and Ando (2011) with a surface panel method. The maximum amplitude appears in the first blade frequency and overestimates the experimental data by about 30%. Kim et al. (2012) predicted the hull pressure fluctuations induced by marine propeller sheet cavitation, and the Doppler effect was considered at the same time. Wei and Wang (2013) employed CFD to simulate the propulsion of a submarine. The finite element method and BEM were then combined to solve the submarine's structure and acoustic responses under the propeller excitations. The matched-field inversion technique applied in Lee et al. (2014) uses the fluctuating hull pressure field measured by receivers and the acoustic field calculated by BEM to define the sheet cavitation noise, source strengths, source positions, and number of sources. The equivalent source model for the propeller can result in more accurately extrapolated hull pressure distribution. In Wei et al. (2016), the unsteady forces of a submarine propeller were predicted by CFD, and the hull pressure fluctuations due to the non-cavitation propeller were calculated by the method proposed in Kao and Kehr (2006).

Adaptive pitch control for ships with diesel mechanical and hybrid propulsion

Shipping urgently needs to reduce its impact on the environment, both due to CO2, NOx and particulate matter (PM) emissions and due to underwater noise. On the other hand, multifunction ships such as offshore support vessels, anchor handling and towing vessels, naval vessels and wind farm construction and support vessels require fast and accurate manoeuvring and need highly reliable systems to support reduced or no crew. Diesel mechanical propulsion with controllable pitch propellers provides high efficiency and low CO2 emissions, but has traditionally been poor in manoeuvrability, can suffer from thermal overloading due to manoeuvring and requires significant measures to meet NOx and PM emission regulations. The control strategy of diesel mechanical propulsion with fixed combinator curves is one of the causes of the poor manoeuvrability, thermal overloading and cavitation noise during manoeuvring, such as slam start and intermediate acceleration manoeuvres. This paper proposes an adaptive pitch control strategy with slow integrating speed control that reduces fuel consumption, CO2, NOx and PM emissions and underwater noise, improves acceleration performance, limits engine loading and prevents engine under- and overspeed. A simulation study with a validated model of a case study Holland class Patrol Vessel demonstrates 5–15% reduction in fuel consumption and CO2 emissions, compared to the baseline transit control mode in the ship speed range from 6 to 15 kts, during constant speed sailing. Moreover, the adaptive pitch control strategy reduces acceleration time from 0 to 15 kts with the slam start procedure by 32% compared to the baseline manoeuvre control mode and by 84% for an intermediate acceleration from 10 to 15 kts, while preventing thermal overloading of the engine, during straight line manoeuvres. Combining this control strategy with hybrid propulsion, running an electric drive in parallel with the propulsion diesel engine, can potentially further reduce fuel consumption at low speeds while also improving acceleration performance even more. Therefore, hybrid propulsion plants with controllable pitch propellers and adaptive pitch control can provide a significant contribution to the urgent reduction of environmental impact of shipping and to the need for more autonomous and reliable ship systems.

Analysis of performance variation with cavitation test for a mixed-flow pump

Cavitation phenomenon affects the reduction in performance of the pump, as it exerts significant damage to the impeller of the pump. The user should be avoid driving this phenomenon and the criterion is set as NPSHa. Along with the cavitation phenomenon, noise and vibration can occur, which can predict cavitation. This study analyzed the characteristics of vibration emitted when cavitation occurred using the accelerometers.

An auto-test method based on acoustic theory of judging inception cavitation of runner blade of model Francis-turbine

The vibration and noise of large Francis-turbine units tends to increase, the efficiency decreases and the units operate unstably if the units operate under the cavitation condition. Hence it must be eradicated completely that the units run under the cavitation condition. Nowadays, the judgment of inception cavitation of model Francis-turbine runner blades remains stagnant at the stage of artificial observation so that the results lacks of objectivity and consistency. An auto-test method based on acoustics theory and the principle of cavitation is presented. When cavitation happens, the acoustic energy radiated by bubbles while collapsing is different at different stages of cavitation, for the size and number of bubbles are different. And therefore the distribution of cavitation noise energy in the frequency domain varies along with the severe degree of cavitation, according to which the inception cavitation can be determined exactly by acquiring the acoustics signals in the water with hydrophone mounted on the draft tube cone and then abstracting and analyzing the characteristics parameters of cavitation noise in the frequency domain when the model Francis-turbine operates. The rationality and accuracy have been proved by model tests, and it is significant to determine the inception cavition of model Francis-turbine runner blades by automatic way instead of artificial way.

Modeling and Simulation of Cavitation Noise of Supercavitating Vehicle

Supercavitating vehicle is a high speed object navigating in supercavitating state underwater, such as supercavitating torpedo, supercavitating projectile, etc. Cavitation noise is an important feature of underwater supercavitating vehicle, which is of great significance to its detection and stealth. Bubble cluster generate in the caudal closed area of supercavity around the vehicle. The cavitation noise source is the breakdown of the small bubble cluster. This paper firstly established cavitation noise model of single bubble, and further established cavitation noise model of bubble cluster with Rayleigh distribution radius. Based on this, the waveform and frequency spectrum of the cavitation noise of bubble cluster are simulated and analyzed in the conditions of different bubble radius, cavitation number, environment parameters, etc. The simulation results show that the cavitation noise of supercavitating vehicle is a kind of wide-band radiation noise of "bell shaped" spectrum with a strong middle frequency, and a gradual weakening low frequency and high frequency.

Registration of the cavitation regime in liquids under the action of ultrasonic vibrations

Ultrasonic vibrations are widely used in various industries and production: in metallurgy, in the chemical and food industries, in mechanical engineering, and in medicine. This is due to the physicochemical changes in the substance when superimposed sound fields. Cavitation in the ultrasonic field causes dispersion and emulsification of certain substances, promotes coagulation and degassing, affects the processes of crystallization and dissolution, it is known that ultrasonic vibrations cause a variety of chemical transformations of the substance, including oxidation, reduction, polymerization and depolymerization reactions. The researchers find the explanation of these phenomena in the diverse effect of cavitation on matter: shock waves, micro streams, acoustic wind. The experiments were carried out in a liquid medium (un-distilled water). The volume of the experimental test was 10 dm3. To obtain ultrasonic vibrations, the method of magnetostriction was used, the principle of which is to convert electric oscillations into mechanical ones. To assess the cavitation regime, the level of cavitation was recorded in two stages: the degree of erosion of the artificial obstacle, the measurement of the intensity of the cavitation noise in the volume

Numerical modelling of unsteady cavitation and induced noise around a marine propeller

The objective of this paper is to numerically investigate the cavitating flow around a marine propeller and to explore the intrinsic relationships between the sheet cavitation and its radiation noise. The k-ω SST turbulence model with the turbulence viscosity correction and the Zwart cavitation model are introduced to the simulation of cavitating flow around a propeller in a non-uniform wake. The loading noise and cavitation noise have been predicted based on the theory for acoustic fan source and the sound radiation theory for spherical bubble respectively. The periodic cavitation development has been captured, and the periodic large pressure fluctuation around the blade has been analyzed with the dominant frequencies in accordance to the first order of the blade passing frequency. For the non-cavitation case, the high sound pressure levels mainly concentrate in the low frequency stage and decrease from the low-order to the high-order blade passing frequency. While for the sheet cavitation case, the sound pressure level at the high-order of blade passing frequencies are enhanced. The sound pressure induced by the cavitation development is periodically varied accompanied with the periodic pulsating cavity evolution, and the acoustic energy mainly focus on the low order of blade passing frequencies.

Determination of the cavity mode in the water

Ultrasonic oscillations find their wide application in various sectors and industries: metallurgy, chemical and food industries, in engineering, in medicine. This is due to physical and chemical changes when exposed to the sound field. Cavitation in ultrasonic field causes the dispersion and emulsification of certain substances and promotes coagulation and degassing affects of crystallization and dissolution. It is known that ultrasonic vibrations also cause a variety of chemical transformations of substances such as oxidation, recovery, polymerization, and depolymerization. Researchers of cavitation action on the matter find the explanation of these phenomena: shock waves and, consequently, acoustic wind. The experiments were conducted in liquid environment (non-distilled water). The volume of the experimental sample amounted to 10 dm3. Method of the magnetostriction was applied to receive ultrasonic vibration, the principle of which consists in transforming electrical oscillations into mechanical. The level of cavitation was checked in two stages to evaluate the cavitation mode according to the degree of erosion of the artificial barriers and to measure the intensity of cavitation noise in the volume.

Reduction of acoustic cavitation noise emission with textile materials

Reduction of acoustic cavitation noise emission with textile materials

Cavitation heat effect and noise of hydraulic cone throttle valve

In order to study the thermal effect and noise of cavitation in hydraulic cone type throttle valve, a cone type throttle valve cavitation experiment platform is built. With the organic glass having a better transparency as the material, the model valve was made. The pressure characteristics of five kinds of spool case cone type throttle valves were analyzed through simulation and experimental study, and the main production parts of cone type throttle valve cavitation bubble were obtained. The results show that the frequency of cone type throttle valve noise is above 8kHz. On this basis, we can determine whether the cone type throttle valve noise is the main source of noise in hydraulic system by measurement of noise spectrum. Based on the above findings, it is concluded that it is helpful for fault diagnosis of hydraulic system. The cavitation has relatively great impact on the hydraulic oil temperature flowing through the throttle valve, and its impact cannot be ignored.

Novel scaling law for estimating propeller tip vortex cavitation noise from model experiment

The tip vortex cavitation (TVC) noise of marine propellers is of interest due to the environmental impacts from commercial ships as well as for the survivability of naval ships. Due to complicated flow and noise field around a marine propeller, a theoretical approach to the estimation of TVC noise is practically unrealizable. Thus, estimation of prototype TVC noise level is realized through extrapolation of the model TVC noise level measured in a cavitation tunnel. In this study, for the prediction of prototype TVC noise level from a model test, a novel scaling law reflecting the physical basis of TVC is derived from the Rayleigh-Plesset equation, the Rankine vortex model, the lifting surface theory, and other physical assumptions. Model and prototype noise data were provided by Samsung Heavy Industries (SHI) for verification. In applying the novel scaling law, similitude of the spectra of nuclei is applied to assume the same nuclei distribution in the tip vortex line of the model and the prototype. It was found that the prototype TVC noise level predicted by the novel scaling law has better agreement with the prototype TVC noise measurement than the prototype TVC noise level predicted by the modified ITTC noise estimation rule.

Stereoscopic PIV aided wake simulation of a catamaran research vessel using a dummy-hull model in a medium size cavitation tunnel

The rising marine environmental concern has recently targeted underwater radiated noise. Amongst various sources present on-board, propeller cavitation noise is known to be the dominant source that may be harmful to marine biodiversity. To be able to minimize anthropogenic noise footprint, full-scale and model-scale test campaigns are the most reliable tools to measure or predict the noise sound pressure level. Within this framework, hydro-acoustic cavitation tunnel experiments carry utmost importance for model-scale tests. Due to limited space of the cavitation tunnel, a shortened dummy-hull is often used, even though the flow passing through the propeller plane of the dummy model does not represent a fully developed wake. This paper presents a wake simulation methodology for a shortened dummy-hull model of Newcastle University research vessel “The Princess Royal” with the aid of stereoscopic particle image velocimetry in Emerson Cavitation Tunnel. With such method, after three iterations sufficient similarity between target wake and simulated wake has been achieved. Adopted approach has been found to be significantly effective in terms of reducing the time and the iterations during wake simulation process.

Pitch control for ships with diesel mechanical and hybrid propulsion: Modelling, validation and performance quantification

Ships, in particular service vessels, need to reduce fuel consumption, emissions and cavitation noise while maintaining manoeuvrability and preventing engine overloading. Diesel mechanical propulsion with controllable pitch propellers can provide high fuel efficiency with good manoeuvrability. However, the conventional control strategy with fixed combinator curves limits control freedom in trading-off performance characteristics. In order to evaluate performance of current state-of-the-art and future alternative propulsion systems and their control, a validated propulsion system model is required. To this end, this paper proposes a propulsion model with a Mean Value First Principle (MVFP) diesel engine model that can be parameterised with publicly available manufacturer data and further calibrated with obligatory FAT measurements. The model uses a novel approach to predict turbocharger performance based on Zinner blowdown, the Büchi power and flow balance and the elliptic law for turbines, and does not require detailed information such as compressor and turbine maps. This model predicts system performance within 5% of actual measurements during Factory Acceptance Tests (FAT) of the diesel engines and Sea Acceptance Tests (SAT) of a case study navy ship. Moreover, this paper proposes measures of performance that objectively quantify the fuel consumption, acceleration rate, engine thermal loading and propeller cavitation during trial, design and off-design conditions in specified benchmark manoeuvres, within an hour simulation time. In our experiments, we find that, depending on the control strategy, up to 30% of fuel can be saved, thermal engine loading can be reduced by 90K, and acceleration time by 50% for a case study Holland class patrol vessel.

Cavitation intensity monitoring in an axial flow pump based on vibration signals using multi-class support vector machine

The cavitation phenomenon, which is rampant in axial flow pumps, should be avoided due to its undesirable effects on the pump’s performance. Therefore, in this study the cavitation performance of an axial flow pump is monitored based on vibration signals. For this purpose, experimental vibration data is collected for five different levels of cavitation. Time-domain features are extracted based on statistical behavior of the measured signals. Considering the nonlinear and high-frequency nature of the cavitation noise in the signal, the second set of features including both time- and frequency-domain parameters are obtained based on statistical behavior of the first intrinsic mode function, via empirical mode decomposition combined with Hilbert Huang transform. Compensation distance evaluation technique is applied to pick the appropriate features. Multi-class support vector machine is trained for classification of the various levels of cavitation intensity. The results of testing the support vector machine algorithm show that the developed methodology can monitor the pump’s cavitation intensity in onsite operation with high accuracy.

Analysis of the incipient cavitation noise signal characteristics of hydroturbine

Hydroelectric power is widely used because of its environmental, renewable and green. The cavitation is inevitable phenomenon during the operation of hydroturbine which is related to the efficiency and service life of the unit. This paper is devoted to discriminate the phenomenon of the incipient cavitation, prevent the destruction early, and avoid the irreversible damage to hydroturbine.In order to find the characters of incipient cavitation. Use the method of wavelet time-frequency analysis and wavelet packet decomposition to process the cavitation noise signals. Use the value of peak factor and slope of power spectral density curve as a threshold when incipient cavitation to judge whether the cavitation occurs. The results shows that the characteristics of incipient cavitation can be detected in the auditory frequency band. The wavelet time-frequency analysis of noise signals can distinguish the different operating conditions, also can discriminate between the phenomenon of incipient cavitation and the other state of cavitation by visual observation. The wavelet packet decomposition can obtain the feature frequency of cavitation signal is 10–13kHz. The way of judge whether the incipient cavitation happens by threshold value can reach the accuracy rate up to 70% which meet the requirements of the detection for incipient cavitation.

The masking of beluga whale (Delphinapterus leucas) sounds by icebreaker noise in the Arctic

Beluga whales are an Arctic and subarctic cetacean, with an overall “near threatened” conservation status, yet some populations are considered endangered. Apart from threats such as whaling, predation, contamination, and pathogens, underwater noise is of increasing concern. In the early 1990s, Fisheries & Oceans Canada started to fund research on underwater noise emitted by icebreakers and its bioacoustic impacts. In collaboration with the Vancouver Aquarium, beluga whales were trained for masked hearing experiments. Apart from measuring pure-tone audiograms in quiet conditions, animals were trained to listen for beluga vocalizations in different types of noise, including artificially created white noise, naturally occurring thermal ice-cracking noise, and an icebreaker’s propeller cavitation and bubbler system noise. Based on this data, software models for masking in beluga whales were developed. More than 20 years later, this dataset remains the only one on masking in cetaceans using both complex signals (actual vocalizations) and complex noise (actual recordings of Arctic ambient and anthropogenic noise)—highlighting both Dave Farmer’s foresight as well as perhaps his lesser-known escapades into marine mammal bioacoustics.

Specifics of DEMON acoustic signatures for large and small boats

Marine vessel propellers produce noise by the formation and shedding of cavitation bubbles. This process creates both narrow-band tones and broad-band amplitude modulated noise. The Detection of Envelope Modulation on Noise (DEMON) is an algorithm to determine the frequencies that modulate this noise. Results of DEMON processing depend on the selection of a ship noise frequency band to analyze. It is well known that the best passband to use may vary dramatically between vessels. Despite this, there has been no systematic investigation how the DEMON spectra depend of the carrier noise frequencies, and the modulation indices of vessel noise have not been investigated. We use a modification of the Cyclic Modulation Spectrum (CMS) to determine the modulation index of cavitation noise across the entire spectrum of carrier frequencies. We investigated how speed and vessel size affect the modulation index and carrier frequency of vessel noise. Several phenomena in the distribution of modulation indices for large and small boats were observed. These can be used for vessel classification. For small boats, the DEMON spectra have a different set of frequency peaks at various carrier frequencies. This is explained by the engine exhaust which produces amplitude modulated noise much like a propeller.

Two medium size cavitation tunnel hydro-acoustic benchmark experiment comparisons as part of a round robin test campaign

The increase in marine transportation in the last decades has resulted in a rise of the different emissions linked to it. Amongst various detrimental emissions of shipping activities, underwater noise is known to affect ambient noise levels and hence threaten the life (or even survivability) of marine mammals. This concern brought the underwater radiated noise (URN) to the attention of regulators, considering the possible need to limits for commercial ships, thus resulting in a surge of interest.As being the main contributor to the URN of ships, the accurate prediction of propeller cavitation and hence associated noise in the design stage is crucial for achieving reductions in terms of emitted sound pressure levels. Whilst computational methods are developing at an exponential pace and so are prospective tools for the future, model scale experiments still represent the most reliable and largely adopted approach for the prediction of propeller radiated noise. Despite the importance of model tests, being the only reliable tool for cavitation noise prediction, a benchmark data is non-existent for facilities all over the world to compare and correlate their noise measurements.Within this framework, this paper presents the first comparison of a round robin test campaign amongst the Noise CoP (Community of Practice) of Hydro Testing Forum (HTF). Based on the extensive experiments conducted first at Emerson Cavitation Tunnel (ECT), a reduced test matrix is proposed to the forum members. University of Genoa (UNIGE) is the first member to complete the tests specified in the reduced matrix and this paper presents comparisons between the test results of ECT and UNIGE cavitation tunnel in terms of measured sound pressure levels, propeller open water performance, cavitation observations and cavitation inception characteristics. Moreover, in order to shed a light on the issue of propeller cavitation noise measurements, a series of investigations are carried out by UNIGE scrutinizing the effect of hydrophone position, oxygen content, propeller shaft revolution rate, sensitivity to thrust coefficient and cavitation number.