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Poojari D.B.,Indian Register of Shipping | Kar A.R.,Indian Register of Shipping
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2014

Maneuverability predictions of a surface ship are highly important from navigational-safety point of view. A ship should be assessed for its maneuverability well before it is built. The age-old model testing techniques have always been the most reliable source for maneuverability-related information. Model testing facilities such as rotating arm and planar motion mechanism being formidably expensive and rare, alternate methods are being resorted to. Reynolds Averaged Navier Stokes Equation (RANS) based Computational Fluid Dynamics (CFD) is an emerging and powerful tool and has been successfully applied in computing flow and associated forces in the field of offshore and marine hydrodynamics. Present work uses a steady RANS solver, SHIPFLOW for the determination of hydrodynamic derivatives or maneuvering-coefficients appearing in the maneuvering equations of motion. Though maneuvering is a dynamic phenomenon, a quasi-static approach has been used here to evaluate the hydrodynamic derivatives. A container ship (S 175 prototype) has been assessed for its maneuverability by numerically mimicking the conventional towing tank experiments such as straight line, rotating arm and the combination of both, using RANS based CFD simulations. Derivatives have been obtained by plotting and cross-plotting the Surge force, Sway force and Yaw moment against linear and angular velocities. Taylor's series method has been adopted wherever cross-plotting turned out to be tedious. The derivatives have been compared with those of experimental (published) ones and the important and most important ones are found to be in reasonably good agreement. The trajectories of the vessel in standard maneuvers have also been obtained using an in-house developed MATLAB code. The trajectories thus predicted have been analyzed for the course-keeping and course changing abilities of the vessel and the elements of trajectory have also met the requirements laid by the International Maritime Organization (IMO) for safe navigation to certain extent. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).

Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: SST-2007-4.1-01 | Award Amount: 4.17M | Year: 2009

The traditional fire safety regulations that apply to ship design have been widely described as inadequate in two ways. Firstly they do impose unnecessary and inapplicable constraints on novel designs. Secondly novel designs can have features that do not satisfy the premise of existing rules, thereby setting them free from fire safety rules by default, often leading to unsafe designs. In order to remedy this problem the proposed project FIREPROOF would develop a very universally applicable regulatory framework for maritime fire safety based on probabilistic models and numerical models of ignition, growth and impact of fires. The framework would be quite similar in principle to the well established probabilistic damage stability regulation. The methodology of the proposed fire safety regulation is summarized as follows: The methodology would consist of a mathematical model that would generate instances of fire scenarios according to the correct probability distribution of the elements of the scenario. It would also consist of numerical models to assess the consequence of the scenarios so generated. For any given ship - traditional or novel, a large number of scenarios would be generated and their consequences assessed, and the results would be aggregated to give rise to fire risk metrics. Constraints based on such risk metrics would serve as statutory regulations that would be completely applicable to novel and unprecedented designs. It would offer the designer greater freedom on the design while enforcing a greater level of safety.

Vhanmane S.,Indian Register of Shipping | Bhattacharya B.,Indian Institute of Technology Kharagpur
Journal of Offshore Mechanics and Arctic Engineering | Year: 2011

The ultimate strength of a ship's hull depends on its material and geometric properties, some or all of which may be random in nature. In addition, initial imperfections in the form of initial deflection and residual welding stresses in plating between stiffeners can significantly affect the hull ultimate strength. In this paper, the effect of randomness in yield strength and in the initial imperfections on ultimate hull girder strength is determined. Different levels of statistical dependence between yield strength and initial imperfection of stiffeners and plating between stiffeners have been considered. The methodology is applied on a bulk carrier and a VLCC tanker. © 2011 American Society of Mechanical Engineers.

Ganesan T S.,Indian Register of Shipping | Sen D.,Indian Institute of Technology Kharagpur
Applied Ocean Research | Year: 2015

In this paper, motion response of a moored floating structure interacting with a large amplitude and steep incident wave field is studied using a coupled time domain solution scheme. Solution of the hydrodynamic boundary value problem is achieved using a three-dimensional numerical wave tank (3D NWT) approach based upon a form of Mixed-Eulerian-Lagrangian (MEL) scheme. In the developed method, nonlinearity arising due to incident wave as well as nonlinear hydrostatics is completely captured while the hydrodynamic interactions of radiation and diffraction are determined at every time step based on certain simplifying approximations. Mooring lines are modelled as linear as well as nonlinear springs. The horizontal tension for each individual mooring line is obtained from the nonlinear load-excursion plot of the lines computed using catenary theory, from which the linear and nonlinear line stiffness are determined. Motions of three realistic floating structures with different mooring systems are analyzed considering various combinations of linear and approximate nonlinear hydrodynamic load computations and linear/nonlinear mooring line stiffness. Results are discussed to bring out the influence and need for consideration of nonlinearities in the hydrodynamics and hydrostatics as well as the nonlinear modelling of the line stiffness. © 2015 Elsevier Ltd.

Ganesan T. S.,Indian Register of Shipping | Sen D.,Indian Institute of Technology Kharagpur
Applied Ocean Research | Year: 2016

The coupled system of two side-by-side fixed and/or floating bodies interacting with a large amplitude nonlinear wave is studied using a direct time domain solution method. The numerical model is based on a three-dimensional mixed Eulerian-Lagrangian (MEL) method under certain simplifying approximations permitting Rankine panel scheme to be implemented over a time-invariant boundary surface to solve the boundary value problem for the unknown velocity potentials. A 4th order Adams-Bashforth-Moulton scheme is used for time marching of rigid-body motion histories of the individual bodies and evolution of the free-surface including the gap region in which large resonant fluid motions occur. A systematic study has been carried out to evaluate the performance of the developed time domain method in simulating the forces and motions as well as the fluid motion in the gap region for the two body system under various arrangements and in different wave-headings. At first, the computed numerical results have been validated and verified with computational and experimental results available in literature for standard geometries such as vertical truncated cylinders and rectangular boxes. Secondly, effectiveness of the damping lid model which is introduced to suppress wave resonance in the gap region is investigated including its influence on maximum sway forces on fixed and floating rectangular barges in side-by-side configurations. Thirdly, comparative studies on absolute and relative motion response for two cases (two rectangular barges, and a FLNG-FPSO + shuttle tanker) in side-by-side arrangement are detailed to bring out the importance of nonlinearities arising due to steep nonlinear incident waves. Finally, coupled motions of the two-body system of an FPSO and a shuttle tanker floating in side-by-side configuration in a steep nonlinear wave field are studied in which the two bodies are connected through hawsers, and also the FPSO is moored to the ground. Additionally there is a fender between the two bodies. © 2016 Elsevier Ltd.

Rajesh G.,Indian Institute of Technology Madras | Giri Rajasekhar G.,Indian Register of Shipping | Bhattacharyya S.K.,Indian Institute of Technology Madras
Journal of Ship Research | Year: 2010

This paper deals with the application of nonparametric system identification to the nonlinear maneuvering of ships using neural network method. The maneuvering equations contain linear as well as nonlinear terms, and one does not attempt to determine the parameters (or hydrodynamic derivatives) associated with nonlinear terms, rather all nonlinear terms are clubbed together to form one unknown time function per equation, which are sought to be represented by neural network coefficients. The time series used in training the network are obtained from simulated data of zigzag and spiral maneuvers. The neural network has one middle or hidden layer of neurons and the Levenberg-Marquardt algorithm is used to obtain the network coefficients. Using the best choices for number of hidden layer neurons, length of training data, convergence tolerance, and so forth, the performances of the proposed neural network models have been investigated and conclusions drawn.

Doshi K.,Indian Register of Shipping | Vhanmane S.,Indian Register of Shipping
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

This paper presents a non-linear finite element analysis (FEA) and subsequent formula development for ultimate strength of stiffened panels of ship structures. A review of studies on ultimate strength of ship plating subjected to lateral pressure was carried out. The present work takes into account, the influence due to the lateral pressure on the ultimate strength of stiffened plates with initial imperfections subject to longitudinal compressive loads. ANSYS non-linear FE software was used for non linear finite element analyses of stiffened panels (864 cases) considering VLCC hull. Based on regression analysis, a set of semi-analytical formulae were proposed and described. It is observed that depending upon the failure mode, scantlings of the stiffened panel and magnitude of lateral pressure, ultimate strength of the stiffened panels in compression is affected. Copyright © 2014 by ASME.

Doshi K.,Indian Register of Shipping | Vhanmane S.,Indian Register of Shipping
Ocean Engineering | Year: 2013

Present ship building rules follow SN curve approach to evaluate the fatigue damage at identified locations while use of fracture mechanics approach is yet to receive due attention. In the present work, a methodology of evaluation of fatigue life of the longitudinal stiffener and transverse web frame connection using fracture mechanics has been demonstrated. Since, various factors such as the crack dimensions, the crack growth law parameters and the applied loads are random in nature; they have been accounted for considering their randomness. Numerical results obtained with the present method for fatigue life of an oil tanker are compared with those based on IACS Common structural rules and a good agreement is observed between them. The present method may find useful application to risk based inspection of ship structures. © 2013 Elsevier Ltd.

Dhavalikar S.S.,Indian Register of Shipping
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2011

Over the years many methods are evolved for computing ship motions and loads, i.e. seakeeping analysis. All of these methods are known as potential flow methods where fluid is assumed to be irrotational. In these methods velocity vector is represented as a gradient of scalar potential phi (f) known as velocity potential. One of the oldest methods is strip theory method where ship is descretized into number of 2D strips. Other methods are panel methods where entire hull is descretized into number of panels. These are also known as Green's function methods. Various formulations of Green's function do exist. In a recent development Green's function methods are extended to Rankine Panel method (RPM) where free surface in the vicinity of vessel is panelized for computations. In RPM Green's function computations are made easy. Again these methods are divided into frequency domain and time domain. Time domain methods take into account various nonlinearities which generally cannot be handled by frequency domain methods. For zero and non-zero forward speed of the vessel different formulations exist. All these methods have their own advantages and disadvantages. Hence, it is very important in the initial design stage to decide on method of seakeeping analysis. Here an attempt is made to compare the results of seakeeping analysis using various tools based on various seakeeping methods. Copyright © 2011 by ASME.

Poojari D.B.,Indian Register of Shipping | Saj A.V.,Indian Register of Shipping | Kar A.R.,Indian Register of Shipping
RINA, Royal Institution of Naval Architects - International Conference on Ship and Offshore Technology, ICSOT India 2015: Coastal and Inland Shipping | Year: 2015

The topic of ship maneuverability prediction has been an area of wide research for some time now. It is a known fact that maneuvering in shallow waters has been more demanding and complicating than in open sea. Sea trials are conducted by class societies to determine turning ability, course keeping ability, stopping ability etc, for which IMO demands certain minimum standards. But these criteria are limited to deep waters and practically no such criteria exists for shallow water conditions making it difficult to assess maneuverability near ports and harbors. The ship operators thus are forced to rely on statistical data and/or their experience when plying in restricted waters.In a growing storm near a port/harbor, the usual tendency of a vessel is to move away from the coast to deep waters to avoid grounding, contact etc. However a vessel becomes too difficult to handle under such conditions thanks to pronounced wind and waves. To start with, the vessel become sluggish and is prone to squat because of its small under keel clearance. Moreover the vessel's turning ability deteriorates making it further difficult to handle. The fact remains that a vessel is not designed for shallow water condition. The work aims to present a prediction method to assess maneuverability in shallow waters, of any given vessel at an early design stage with a considerable level of acceptance. KVLCC2 tanker is the vessel picked for analyses. Hull dynamics/characteristics for maneuvering are determined for three different flow depths using a RANSE based CFD solver. A suitable mathematical model encompassing hull, rudder and propeller along with wind parameter is chosen. The equations of motion have then been numerically integrated to obtain the turning characteristics in standard turning circle test. Squat prediction is also carried out for various depth and speed with key emphasis on under keel clearance. © 2015: The Royal Institution of Naval Architects.

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