International Journal of Maritime Engineering (IJME) - Discussion

Comment is invited on the papers listed below which have been accepted for publication in forthcoming issues of the International Journal of Maritime Engineering(RINA Transactions Part A).

Comments, together with the author(s) response, will be published in the Discussion section of subsequent issues of the IJME. Comment may also be forwarded on papers published in the current issue of the IJME. Comments should not normally exceed 500 words and may contain two illustrations.

Comments may be forwarded online using the Online (Written Comment) form, or by email to , with the title of the paper as the Subject, and quoting the name and affiliation which will be printed with the comment. Illustrations may be forwarded as an attachment.

IJME discussion papers are published in PDF format and can be downloaded free. Just click on the paper title to download. These PDF files can be saved and viewed on screen but cannot be edited or printed out.

International Journal of Maritime Engineering Part A3 2009

IJME 134: A Simplified Pump Tower Approach for Realistic CFD Simulation of Sloshing in LNG Tanks

B Godderidge, S R Turnock, and M Tan, University of Southampton, UK.
C Earl, BMT SeaTech Ltd, UK.

SUMMARY

The complexity of the sloshing analysis for liquefied natural gas carriers can be reduced by neglecting the pump tower.The validity of this assumption is examined by studying the effect of the pump tower, located near the aft bulkhead of a typical LNG tank on the sloshing flow evolution. Results are compared for surge-induced sloshing in a rectangular tank with pump tower to that without such an obstruction. A commercial flow solver is used to solve the unsteady Reynolds Averaged Navier Stokes equations for an inhomogeneous multiphase flow. Initial validation of the sloshing flow uses the experimental data of Hinatsu. It was found that a simplified pump tower consisting of a single vertical tube was suitable to capture the effect of the pump tower without the necessity of discretising the fine geometric detail of the pump tower structure. A suitable size for the simplified tower diameter was found using the total fluid force on a real pump tower in a steady flow for a similar range of Reynolds Number. This reduces the required mesh size by an order of magnitude. Although it is found that the effect of the pump tower on the overall force levels is small reductions of local impact pressures of up to 50% are observed and the sloshing flow develops a phase lag compared to the unobstructed tank.

IJME 147: Influence of Lifting Effects in Seakeeping Calculation

M-H Nguyen, M Guilbaud, S Huberson and M Ba, LEA, University of Poitiers-ENSMA-CNRS, France

SUMMARY

Lifting effects are actually present in a lot of ship hydrodynamic problems and are predominant when considering the action of appendages like fins, rudders or stabilizing foils. Beside this, they are seldom accounted for in calculations because they require specific modelling. In this paper, a global model, including both hull and appendages is presented. It was built within the framework of the "Poseidon" seakeeping solver. It is based on a boundary integral formulation: a Green doublet distribution over the mean surface of the body and semi infinite strips simulating a plane wake, extending from the sharp part of the body trailing edge, were added to the source distribution on the hull. The numerical results enable us to answer the question of whether a Kutta-Joukovsky condition can be dispensed with. This is achieved through predictions compared with available numerical or experimental results for aerodynamic as well as hydrodynamic problems.

IJME 148: Waterjet Performance Characteristics Prediction Based on CFD Simulation and Basic Principles of Waterjet Propulsion

Jiangming Ding and Yongsheng Wang, Naval University of Engineering, Wuhan, China

SUMMARY

The method of predicting the performance characteristics of waterjets based on CFD simulation and the basic principles of waterjet propulsion is introduced in this paper. The characteristics of waterjet pump are derived from the numerical calculation by means of CFD. The head and power of pump as a function of flow rate at design rotational speed are calculated firstly and converted into dimensionless form, from which the pump characteristics for varying rotational speed are deduced easily according to the similarity law of standard pump technology. Then the performance characteristics of waterjets are represented both in the form of constant power lines and in the form of constant rotational speed lines and compared with each other, of which procedures to be determined are stated in brief by the aid of schematic diagrams. The results of this paper can be used for the propulsive performance prediction of waterjet systems in preliminary stages and to assist the deck officers in manoeuvring vessels in an easier way.

IJME 151: A Theoretical Approach to Facilitating Transition Phase Motion in a Positively Buoyant Autonomous Underwater Vehicle

A R Palmer and G E Hearn, University of Southampton, UK
P Stevenson, National Oceanography Centre, Southampton, UK

SUMMARY

Positively buoyant autonomous underwater vehicles (AUVs) operate at survey speeds with a pitch angle that is maintained through application of the control surfaces, sufficient to generate hydrodynamic forces to counteract the excess buoyancy. To facilitate lower forward speeds and the ability to hover requires some additional method of control. This paper reviews possible options and then indicates how control can be achieved using a single or pair of through-body tunnel thrusters. New equations appropriate to AUVs are proposed and experimental results are used to estimate the equation parameters. These equations are used within a simulation of the Autosub AUV to determine the response of the AUV during the transition between survey and low speed operation. The results obtained from the simulations are analysed in terms of the performance of the AUV and the demanded energy levels to assess the feasibility of using tunnel thrusters as a low speed control device.

IJME 158: William Froude - A Sacred Duty of Doubt

D K Brown, RCNC (retired), UK
(Foreword by R Eatock Taylor, University of Oxford, UK)

FORWARD

Eur Ing David K Brown, M Eng, C Eng, FRINA, RCNC sadly died on 15th April 2008, before arrangements could Be made for publication of this paper. He was educated at Leeds Grammar School and Liverpool University graduating in 1949 with a First Class B Eng. Four years post graduate work led to a First in Warship Design at the Royal Naval College, and a career with the Royal Corps of Naval Constructors. His activities included early work on propeller noise, responsibility for trials of the first British nuclear submarine Dreadnought, and a spell on the academic staff at the RN College leading to a new postgraduate course in naval architecture at University College London. While working at the Admiralty Experiment Works, Haslar (the direct successor to William Froude's original experimental facility in Torquay), he was in charge of the Froude Centenary in 1972. Subsequently as Deputy Chief Naval Architect he was responsible for RN standards for Safety, Stability, Strength, Materials, Hydrodynamics and Seakeeping. He was a Vice President of the Royal Institution of Naval Architects for many years. Following retirement in 1988 he wrote 11 historical books, including "The Way of the Ship in the Midst of the Sea - The Life and Work of William Froude" [1]. This paper is an edited version of a lecture given by David Brown at the Department of Engineering Science, University of Oxford, on Tuesday, 30th October 2007. The lecture was sponsored by Froude Hofmann Ltd. It was one of a series celebrating the Centenary of the Department and of the first Professor of Engineering Science at Oxford, Charles Frewin Jenkin. David's lecture was his last public presentation before his death. It is fittingly being published posthumously, as was Froude's last paper.

Internation Journal of Maritime Engineering Part A2 2009

IJME 126: Simulation of a Ship with Partially Filled Tanks Rolling in Waves by Applying Moving Particle Semi-Implicit Method

Jen-Shiang Kouh, Hung-Pin Chien and Chun-Chung Chang, National Taiwan University, Taiwan
Yen-Jen Chen, Lunghwa University of Science and Technology, Taiwan

SUMMARY

Free surface behaviour is a common phenomenon in nature. It combines spray creation, large deformation and break-up of water. Due to its unfixed computational boundary, the boundary position needs to be solved as a portion of the result. However, it is a challenge to give sufficient spatial resolutions along the time-dependently changing free surface. In this paper, a mesh free method, moving particle semi-implicit method (MPS), based on the "particle mechanics" will be used and applied to analyze the phenomena of a ship with partially filled tanks rolling in regular waves. Thereby, not only the external flow around the hull but also the free surface flow inside partially filled tanks can be simulated together by using a single algorithm based on this method. The influences of the sloshing effect resulted from the free surface flow to the rolling of a ship will be discussed in this paper. Some case studies will be chosen for demonstrating results thanks to the advantage of this method.

IJME 150: Motions of Catamarans in Oblique Seas at Speed

G Thomas, T Lilienthal and T Magnuson Australian Maritime College, University of Tasmania, Australia
M Davis and D Holloway, University of Tasmania, Australia
L J Doctors, The University of New South Wales, Australia
P Couser, Sunnypowers Limited, France

SUMMARY

Motions, particularly roll, may have significant implications for passenger comfort when operating a catamaran in oblique seas. Designers of high-speed catamarans therefore need tools for predicting a vessel's seakeeping performance. This work presents three numerical methods for predicting vessel motions in oblique seas: a boundary-element method combined with a strip-theory approach modified for multihulls, a two-dimensional Green function time-domain strip-theory and a modified strip-theory method. Experiments to measure the motion response of a catamaran in oblique seas were conducted using an NPL 5b model at three speeds (Fn = 0.203, 0.406 and 0.508). The experiments showed that all motions tended to increase with increasing speed. Generally the boundary-element method and modified strip-theory method correctly predicted responses in all of the experimental configurations. The two-dimensional Green function time-domain strip-theory was used to predict the motions at the two higher speeds only and was also found, in general, to predict the motions satisfactorily.

IJME 152: Vessel Trans-Critical Wave Wake, Divergent Wave Angle and Decay

A Robbins, G Thomas, M Renilson and G Macfarlane, Australian Maritime College, Tasmania
I Dand, BMT SeaTech, UK

SUMMARY

Vessel wave wake in the "deep water" condition, or the sub-critical depth Froude number range, is well understood, trans-critical wave wake less so, despite vessels frequently operating within this region. The significant effect of water depth on catamaran wave wake and the fundamental changes in the wave pattern are presented. Specific attention is paid to wave height, bow wave angle and the rate of decay coefficient. From model test results a simple and novel method for the prediction of catamaran wave wake, across the trans-critical depth Froude range is presented. The experiments showed that the decay coefficient of the vessel generated waves varies with depth Froude number. Also that the maximum bow wave angle closely corresponds to that predicted by theory, however the peak value is found to occur closer to Frh =0.9 than 1.0.

IJME 154: Ultimate Strength Performance of Suezmax Tanker Structures: Pre-CSR Versus CSR Designs

J K Paik and D K Kim, Pusan National University, Korea
M S Kim, Lloyd's Register Asia, Korea

SUMMARY

This paper presents a comparison of the ultimate strength performance of Suezmax-class double-hull oil tanker structures designed using pre-Common Structural Rules (CSR) versus those designed using CSR in terms of hull girder collapse and buckling collapse of stiffened plate structures on the deck and at the bottom. The ALPS/ULSAP code for the ultimate strength calculation of stiffened plate structures and the ALPS/HULL code for progressive hull collapse analysis are employed for this purpose. Three types of structural scantlings, namely, net, gross (as-built) and 50% corrosion margin scantlings, are considered in association with ultimate strength performance. The insights and conclusions developed from the present study are documented.