A RANS modelling approach for predicting powering performance of ships in waves

In this paper, a modelling technique for simulating self-propelled ships in waves is presented. The flow is modelled using a RANS solver coupled with an actuator disk model for the propeller. The motion of the ship is taken into consideration in the definition of the actuator disk region as well as the advance ratio of the propeller. The RPM of the propeller is controlled using a PID-controller with constraints added on the maximum permissible RPM increase rate. Results are presented for a freely surging model in regular waves with different constraints put on the PID-controller. The described method shows promising results and allows for the studying of several factors relating to selfpropulsion. However, more validation data is needed to judge the accuracy of the mode

Investigation of surface water behavior during glaze ice accretion

A series of experimental investigations that focused on isolating the primary factors that control the behavior of unfrozen surface water during glaze ice accretion were conducted. Detailed microvideo observations were made of glaze ice accretions on 2.54 cm diam cylinders in a closed-loop refrigerated wind tunnel. Distinct zones of surface water behavior were observed; a smooth wet zone in the stagnation region with a uniform water film, a rough zone where surface tension effects caused coalescence of surface water into stationary beads, and a zone where surface water ran back as rivulets. The location of the transition from the smooth to the rough zone was found to migrate towards the stagnation point with time. Comparative tests were conducted to study the effect of the substrate thermal and roughness properties on ice accretion. The importance of surface water behavior was evaluated by the addition of a surface tension reducing agent to the icing tunnel water supply, which significantly altered the accreted glaze ice shape. Measurements were made to determine the contact angle behavior of water droplets on ice. A simple multizone modification to current glaze ice accretion models was proposed to include the observed surface roughness behavior

Use of acoustic analogy for marine propeller noise characterisation

Being able to predict shipborne noise is of significant importance to international maritime community. Porous Ffowcs-Williams Hawkings acoustic analogy is used with cavitation model by Sauer & Schnerr in order to predict the noise signature of the Potsdam Propeller operating in open water. The radiation pattern is shown to be predominantly affected by a dipole source, in addition to less prominent sources at the propeller plane and in the wake. It is shown that the predicted sound pressure levels depend on the choice of the control surface and grid density. The unsteady RANS method is shown to be capable of capturing the blade harmonic noise components but lacks the ability to deal with the broadband part of the noise spectrum, both cavitation and turbulence induced, if no additional modelling is used

Impact of hull propeller rudder interaction on ship powering assessment

It is the complex flow at the stern of a ship that controls the overall propulsive efficiency of the hull-propeller-rudder system. This work investigates the different analysis methodologies that can be applied for computing hull-propeller-rudder interaction. The sensitivity into which the interaction between the propeller and rudder downstream of a skeg is resolved as well as varying the length of the upstream skeg are also discussed including techniques to consider in such computations. Throughout the work, the importance of hull-propeller-rudder interaction for propulsive power enhancement is demonstrated. A final case study examines the performance of a twin skeg, twin screw arrangement

Numerical simulation of an ultrasonic vibratory cavitation device

Cavitation erosion prediction is one of the most important tasks in the ship propeller design. While predominantly qualitative methods are used such as paint tests or high speed video image analyses, there have been efforts to quantify such risks especially in the field of computational fluid dynamics (CFD).As an experimental quantitative method to assess erosion risk, the acoustic emission (AE) technique has been employed, for example, by Lloyds Register for more than a decade now to complement their borescopic cavitation observation at the ship scale. Boorsma and Fitzsimmons (2009) reported (see Fig. 1,) its correlation with borescope observed cavitation events appeared very positive and the location of cavitation impingement on the rudder (shown in the left image of Fig. 1) coincided with the estimated location by multiple synchronous measurements of AE at different locations. If it is possible to decipher how the AE connected with the pressure waves emitted from any given cavitation event, predicting the pressure waves we may be able to predict AE and eventually where and what intensity of cavitation events occur on any given propeller or ship structures. The transfer function can be useful for establishing quantitative correlations between CFD, full-scale trial data and with model test data.As the first step in being able to model this process and gain greater understanding in links between acoustic signal and type/location of cavitation, an open source Computational Fluid Dynamics programme openFOAM (version. 3.0.1) has been used to simulate ultrasonic cavitation on a sonotrode and hence to predict cavitation phenomena and pressure impact loads on a test specimen under the ultrasonic horn. The aim of the work is to evaluate the physical realism required and the limitations of current cavitation models

The influence of turbulence modelling techniques on the predicted cavitation behaviour on a NACA0009 foil

The work presented here forms part of a project focusing on the development of cost-effective measures of classifying the noise levels from ship propellers with the use of numerical techniques available in OpenFOAM software. It is also related to the on-going research within the Faculty of Engineering and the Environment at the University of Southampton, looking at underwater noise of tidal turbines. Ultimately, the aim of the complete study is to enable the assessment of the environmental impact of a ship on the marine ecosystems. In this work a set of results from numerical experiments applied to the NACA0009 foil is presented in the context of quantifying the noise levels produced by a cavitating body in a uniform flow. The simulations utilise both URANS and LES methods and provide a means of characterising the differences between the observed flow patterns from the cavitation modelling point of view. In particular, the interactions of the cavitation phenomena with the turbulence, both modelled and resolved, are studied. Furthermore, an overview of how the considered cavitation models may be used for the purpose of noise prediction is give

Assessment of underwater glider performance through viscous computational fluid dynamics

The process of designing an apt hydrodynamic shape for a new underwater glider is discussed. Intermediate stages include selecting a suitable axi-symmetric hull shape, adding hydrofoils and appendages, and evaluating the performance of the final design. All of the hydrodynamic characteristics are obtained using computational fluid dynamics using the kT - kL - ω transition model. It is shown that drag reduction of the main glider hull is of crucial importance to the ultimate performance. Suggested steps for achieving this are the encouragement of natural laminar flow, integration of sensors into the streamlined hull shape, and sound operational practic

An investigation of the heat transfer and transport mechanisms which control surface water during glaze ice accretion

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1988.Bibliography: leaves 135-137.by Stephen Richard Turnock.M.S