Pressure and noise induced by a cavitating marine screw propeller

In this study, the hydrodynamics and noise prediction of a five blade marine propeller were analyzed through numerical and experimental methods under variety operational conditions. The hydrodynamics of the propeller was studied and the characteristic curves were presented in both numerical and experimental methods. Inception and development of sheet cavitation conditions are obtained in both numerical and experimental methods. The cavitation was started and developed by either increasing the propeller rotational speed in constant pressure or decreasing pressure, while the velocity was kept constant. Good agreements are observed between numerical and experimental results, qualitatively and quantitatively. The noise of the propeller was analyzed through Computational fluid dynamics (CFD) method, based on the formulation of Ffowcs Williams and Hawkings (FW-H). Similarly, the experimental results collected from hydrophones were compared with numerical simulations. Finally, the effects of reflection in cavitation tunnel were obtained by considering overall sound pressure levels in numerical and experimental results.

Mathematical and Computational Applications

The study numerically investigated the noise dissipation, cavitation, output power, and energy produced by marine propellers. A Ffowcs Williams–Hawkings (FW–H) model was used to determine the effects of three different marine propellers with three to five blades and a fixed advancing ratio. The large-eddy Simulations model best predicted the turbulent structures’ spatial and temporal variation, which would better illustrate the flow physics. It was found that a high angle of incidence between the blade’s leading edge and the water flow direction typically causes the hub vortex to cavitate. The roll-up of the cavitating tip vortex was closely related to propeller noise. The five-blade propeller was quieter under the same dynamic conditions, such as the advancing ratio, compared to three- or four-blade propellers.

An experimental investigation on a cavitating propeller in a uniform inflow is presented. Flow field investigations by advanced imaging techniques are used to extract quantitative information on both the cavity extension and thickness. A refined map of the propeller cavitating behavior is established. Measurements are compared to numerical results obtained using an inviscid flow boundary element method for the analysis of blade sheet partial and super-cavitation. The effect of the trailing wake vorticity on the prediction of the cavitation pattern is analyzed via a wake alignment technique. ✆ 0 65 σ n ✆ 0 528 and J ✆ 0 88 σ n ✆ 0 387: bubble cavitation occurs in

Journal of Marine Science and Engineering

Low-frequency broadband shipping noise causes a growing concern for marine fauna together with the demand for noise reduction. Detailed analyses of the cavitation behaviour in the time domain serve as a prerequisite for steps toward quieter propellers. Underwater noise measurement data from the propeller of a full-scale container vessel are used for the analysis of the cavitation volume behaviour. Sequencing methods, polynomial models, and stochastic evaluation methods feeding Monte Carlo simulations of unsteady sheet cavitation are applied to identify the cause of an often observed, yet unexplained similarity in shipping noise spectra. Characteristic features of the volume evolution are identified to enhance the understanding of noise generation by sheet cavitation.

Journal of Naval Architecture and Marine Engineering

In this study, numerical simulations on the noise of the underwater marine propeller for different pressures, skew angles, and performance conditions are investigated. The study has been carried out for the prediction of cavity and noise cavitation characteristics of the propeller. The blade sheet cavitation created by an underwater propeller is then evaluated using numerical analysis. The cavitation and cavity around marine propellers were predicted using MRF (Multiple Reference Frame) techniques. The simulation uses the Reynolds Averaged Navier-Stokes (RANS) formulation with the turbulence model k-ω Shear Stress Transport and the Fast Fourier Transform. The FW-H equation is used to measure far-field radiation under various operating conditions. The simulation is carried out to present that the pressure and skew propeller angles have an effect on the form and area of the cavity, as well as cavitation noise. The noise characteristics at various positions of hydrophones and speeds of...

Scientia Iranica, 2015

Marine propeller hydrodynamics and noise study is an important problem in the suitable performance of ships and submarines. In the first step of this paper, the hydrodynamics of two propellers was studied under different operating conditions.Thensheet cavitation inception and development conditions were obtained in order to understand the impact of varying rotational speed of the propeller and pressure drop on the propeller noise. In the second step overall sound pressure levels (SPLs) under non-cavitating and sheet cavitating conditions were extracted for each of these models. The overall SPLs were calculated from Ffowcs Williams and Hawkings(FW-H) equations and its integral solutions. In this work, the flow field was analysed with the FVM, and then flow data including; pressure fluctuations, sheet cavitation volume and velocity magnitude results of the flow solution were used as the input for the FW-H formulation to predict the overall SPLs. The results from flow analysis are sig...

Proceedings of the 10th International Symposium on Cavitation (CAV2018), 2018

In this paper, the authors have been investigating the possibility of the prediction of propeller cavitation noise. This method is hybrid method of CFD analysis and bubble dynamics model. Obtaining a cavitation volume by using a commercial CFD code, we estimate the size distribution of the cavitation bubbles and calculate the propeller cavitation noise by the bubble dynamics model.

European Journal of Economics and Economic Policies: Intervention, 2020

The paper opens with a consideration of the historical developments on the nature and features of money and endogenous money, and the post-Keynesian revival of ideas of endogenous money. Particular attention is drawn to the work of Basil Moore in relation to endogenous money, including the location of that analysis with commercial banks (some of whose liabilities are transferable and widely accepted as a means of payment) and the post-Keynesian-inspired revival of endogenous money. There is a brief outline of the aspects of financialization since the late 1970s which have relevance for the analysis of banks and money. Some thoughts are offered on the impact which those changes of the financial system have for the analysis of banks and of money.