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CONTENTS
Volume 4, Number 2, June 2014
 

Abstract
Wave propagation in a three-dimensional (3D) fully nonlinear numerical wave tank (NWT) is studied based on velocity potential theory. The governing Laplace equation with fully nonlinear boundary conditions on the moving free surface is solved using the indirect desingularized boundary integral equation method (DBIEM). The fourth-order predictor-corrector Adams-Bashforth-Moulton scheme (ABM4) and mixed Eulerian-Lagrangian (MEL) method are used for the time-stepping integration of the free surface boundary conditions. A smoothing algorithm, B-spline, is applied to eliminate the possible saw-tooth instabilities. The artificial wave speed employed in MTF (multi-transmitting formula) approach is investigated for fully nonlinear wave problem. The numerical results from incorporating the damping zone (DZ), MTF and MTF coupled DZ (MTF+DZ) methods as radiation condition are compared with analytical solution. An effective MTF+DZ method is finally adopted to simulate the 3D linear wave, second-order wave and irregular wave propagation. It is shown that the MTF+DZ method can be used for simulating fully nonlinear wave propagation very efficiently.

Key Words
NWT; DBIEM; multi-transmitting formula; damping zone; MTF+DZ

Address
G. Xu: Department of Mechanical and Industrial Engineering, Qatar University, Doha-2713, Qatar;
School of Naval Architecture and Ocean Engineering, Jiangsu University of Science and Technology,
Zhenjiang, China
A.M.S. Hamouda:Department of Mechanical and Industrial Engineering, Qatar University, Doha-2713, Qatar
B.C. Khoo: Department of Mechanical Engineering, National University of Singapore, 10 Kent Ridge Crescent, 119260, Singapore

Abstract
When caissons are mounted on a floating transportation barge and towed by a tug boat in waves, motion of the floating dock creates inertia and gravity induced slip forces on the caisson. If its magnitude exceeds the corresponding friction force between the two surfaces, a slip may occur, which can lead to an unwanted accident. In oblique waves, both pitch and roll motions occur simultaneously and their coupling effects for slip and friction forces become more complicated. With the presence of strong winds, the slip force can appreciably be increased to make the situation worse. In this regard, the safety of the transportation process of a caisson mounted on a floating dock for various wind-wave conditions is investigated. The analysis is done by both frequency-domain approach and time-domain approach, and their differences as well as pros and cons are discussed. It is seen that the time-domain approach is more direct and accurate and can include nonlinear contributions as well as viscous effects, which are typically neglected in the linear frequency-domain approach.

Key Words
caisson transport; floating barge; safety; slip force; friction force; inertia/gravity effects; nonlinear terms; roll-pitch coupling; frequency-domain and time-domain analysis; irregular waves/winds. initial inclination; deck flooding

Address
H.Y. Kang and M.H. Kim:Ocean Engineering Program, Department of Civil Engineering, Texas A&M University, 3136 TAMU, College Station, TX, USA, 77843-3136

Abstract
The increased interest in the design of energy efficient ships post IMO regulation on enforcing EEDI has encouraged researchers to reevaluate the numerical methods in predicting important hull design parameters. The prediction of added resistance and stability of ships in the rough sea environment dictates selection of ship hulls. A 3D panel method based on Green function is developed for vessel motion prediction. The effects of parametric instability are also investigated using the Volterra series approach to model the hydrostatic variation due to ship motions. The added resistance is calculated using the near field pressure integration method.

Key Words
added resistance; 3D panel method; EEDI; parametric roll

Address
Abhilash Somayajula, Amitava Guha and Jeffrey Falzarano: OceanEngineeringProgram, Texas A&M University, USA
Ho-Hwan Chun and Kwang Hyo Jung: Department of Naval Architecture and Ocean Engineering, Pusan National University, Korea

Abstract
In the marine industry although there has been significant growth towards safety, security and risk assessments or risk-based strategies such as marine insurance and regulations to avoid the risks of damage to properties and the environment or the prospect of premature death caused by accidents etc, the moves toward managing the risks which are linked directly to the business functions and decision making processes have been very slow. Furthermore in the marine industry most perceptions, methodologies and frameworks of dealing with hazards, risks, safety and security issues are for their assessment rather than their management. This trend reveals the fact that in different marine industry sectors such as logistics and shipping there is a lack of coherent risk management framework or methodology from which to understand the risk-based decisions especially for the purpose of design, construction, operation, management and even decommissioning of the marine related applications. On the other hand risk management is not yet viewed holistically in the marine industry in order to, for example, assign a right person, i.e. risk manager, who can act as a coordinator and advisor with responsibilities that are only specific to risk management. As a result this paper, by examining the present physical borders and risk-based activities in the marine industry, aims to propose an appropriate risk management methodology in addition to the emergent role of risk managers which will enable the industry users initially to become familiar with the concept of risk management at its holistic level. In the later stages this eventually can lead to development of risk management capabilities at an exclusive level and its integration into the marine industry functions in future.

Key Words
maritime logistics; supply chain management; port operations; risk management

Address
Kambiz Mokhtari and Jun Ren:Liverpool Logistics, Offshore and Marine (LOOM) Research Institute, School of Engineering, Technology and Maritime Operations, Liverpool John Moores University, UK

Abstract
It is common that analyses of offshore platforms being carried out with the assumption of rigid tubular joints. However, many researches have concluded that it is necessary that local joint flexibility (LJF) of tubular joints should be taken into account. Meanwhile, advanced analysis of old offshore platforms considering local joint flexibility leads to more accurate results. This paper presents an extensive finite-element (FE) based study on the flexibility of uni-planner multi-brace tubular Y-T and K-joints commonly found in offshore platforms. A wide range of geometric parameters of Y-T and K-joints in offshore practice is covered to generate reliable parametric equations for flexibility matrices. The formulas are obtained by non-linear regression analyses on the database. The proposed equations are verified against existing analytical and experimental formulations. The equations can be used reliably in global analyses of offshore structures to account for the LJF effects on overall behavior of the structure.

Key Words
fixed offshore platforms; tubular joints; local joint flexibility (LJF)

Address
Behrouz Asgariana, Vahid Mokarram and Pejman Alanjari: K.N.Toosi University of Technology, Faculty of Civil Engineering, Tehran, Iran


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