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Showing papers in "International Journal of Offshore and Polar Engineering in 1999"


Journal Article
TL;DR: A review of recent studies on the prediction of hydroelastic responses of a very large floating structure (VLFS) is presented in this paper, where it is divided into the pontoon type and column-supported type structures.
Abstract: This paper presents a review of recent studies on the prediction of hydroelastic responses of a very large floating structure (VLFS). It is divided into the pontoon type and column-supported type structures. Studies on the pontoon type are divided further into the frequency-domain and time-domain analyses. A new calculation method for general time-dependent problems is also described, which is one of the future works required. The hierarchical interaction theory, developed recently by the author for analyzing hydrodynamic interactions among a large number of columns, is explained with some equations and numerical results. However, experimental work is not reviewed in detail, because main interest in this paper is placed on analytical calculation methods.

101 citations



Journal Article
Moo-Hyun Kim1, Z. Ran1, W. Zheng1, S. Bhat2, Pierre A. Beynet2 
TL;DR: In this paper, a nonlinear coupled dynamic analysis of a moored truss spar in waves with collinear winds and currents is numerically carried out in the time domain and the results are compared with 1:61 scale experiments and uncoupled analyses.
Abstract: Nonlinear coupled dynamic analysis of a moored truss spar in waves with collinear winds and currents is numerically carried out in the time domain and the results are compared with 1:61 scale experiments and uncoupled analyses. The first- and second-order wave forces, added mass and radiation damping, and wave drift damping are calculated from the hydrodynamics program WINTCOL. The total wave force time series are then generated based on a two-term Volterra series model. The mooring dynamics are solved using the software WINPOST which is based on a generalized-coordinate-based finite element method. The mooring lines are coupled to the platform through generalized springs and dampers. A case study was conducted for the Marlin truss spar with nine taut mooring lines in 3240-ft water depth. The numerical results show that dynamic effects are very important for the present mooring design. The motion and tension spectra of uncoupled analyses with linear spring or nonlinear spring are also compared with those obtained from fully coupled analysis to assess the importance of hull/mooring coupling.

65 citations


Journal Article
TL;DR: In this paper, the performance of the impulse turbine with fixed guide vanes was compared with that of the Wells turbine with a fixed guide vane, and it was shown that the running and starting characteristics of the latter were superior to those of the former under irregular wave conditions.
Abstract: The objective of this paper is to clarify the performance of impulse turbine with fixed guide vanes and to compare it with that of Wells turbine with guide vanes. As a result, a suitable choice of the design factors for the impulse turbine was shown for the inlet angle of rotor blade and the shape of guide vane. Furthermore, it was found that the running and starting characteristics of the impulse turbine were superior to those of the Wells turbine under irregular wave condition.

56 citations


Journal Article
TL;DR: In this paper, a new closed-form analytical solution to the equations governing the wave-induced seabed response, including inertia items, was presented, and the numerical results showed that the inertia forces cannot always be ignored in a softer seafloor and that the relative difference between the present solution and the previous solution may reach 5% of po under certain combinations of wave and soil conditions.
Abstract: The analysis of wave-induced seabed response is an important factor in the design of offshore installations. However, to simplify the complicated problem, most previous investigations have ignored the effects of inertia forces. This paper presents a newly closed-form analytical solution to the equations governing the wave-induced seabed response, including inertia items. The numerical results show that the inertia forces cannot always be ignored in a softer seabed. The relative difference between the present solution (with inertia items) and the previous solution (without inertia items) may reach 5% of po under certain combinations of wave and soil conditions. *ISOPE Member. Received February 9, 1999; revised manuscript received by the editors September 9, 1999. The original was submitted directly to the Journal.

51 citations


Journal Article
TL;DR: In this article, the effect of blade section on the performance of the Wells turbine was investigated and the results indicated that optimisation of the blade profiles could significantly delay the onset of separation.
Abstract: The paper presents an experimental investigation into the effect of blade section on the performance of the Wells turbine. The blades tested included one set of eight symmetrical constant chord NACA 0015 blades, one set of eight symmetrical optimised blades and two rotor solidities. The aim of the experiments was to validate predictive work which indicated that optimisation of the blade profiles could significantly delay the onset of separation.

40 citations


Journal Article
TL;DR: In this paper, the stiffness nonlinearity of polyester mooring cables has been analyzed using a set of model cables tests performed with actual full-scale cables with 5-in (0.127-m) or thicker diameters.
Abstract: The work presents expressions to deal with the stiffness nonlinearity of polyester mooring cables. The study is based on two efforts. One basic effort is a comprehensive set of model cables tests performed. The other effort has been completed by the analysis of the acceptance tests performed with actual full-scale cables with 5-in (0.127-m) or thicker diameters. For the parallel construction cables under analysis here, a weak dependence on the frequency has been detected, while the mild to significant dependence on the average load and load amplitude has become clear. A theoretical consideration is made through the Maxwell model. Finally, suggestions on how to deal with the expression in a mooring design are also addressed. *ISOPE Member. Received June 6, 1998; revised manuscript received by the editors April 21, 1999. The original version was submitted directly to the Journal on June 6, 1999.

31 citations


Journal Article
TL;DR: In this paper, a test program was carried out in the small geotechnical centrifuge of the University of Delft to investigate the horizontal bearing capacity of suction piles in sand and clay.
Abstract: A test programme was carried out in the small geotechnical centrifuge of the University of Delft to investigate the horizontal bearing capacity of suction piles in sand and clay. Thanks to the small size of the samples the soil density could be accurately reproduced, so that slight differences in design could be made visible. The influence of several parameters was tested, such as height/diameter ratio, the attachment point of the cable and loading angle. In some typical cases the failure mechanism was visualized in a three-dimensional test. The test results were compared with the API standard and with three-dimensional finite element calculations. It appeared that the optimum bearing capacity was achieved if the attachment point of the cable is at 2/5 of the pile height. The API calculations yield rather conservative values for the horizontal loads. The finite element calculations appeared to be in good agreement with the measured tendencies of the test results. It is believed that a combination of numerical calculations and tests in a small centrifuge yield a powerful design tool.

30 citations


Journal Article
TL;DR: In this article, a new method is presented to analyze the elastic response in waves of a large floating platform of thin plate configuration which is typical of a recent design for a floating airport.
Abstract: A new method is presented to analyze the elastic response in waves of a large floating platform of thin plate configuration which is typical of a recent design for a floating airport. An advantage of this new method is that the modal analysis of the body deflection is not needed; the solution of a hydrodynamic boundary value problem and the solution for the body vibration are simultaneously obtained. Results of numerical implementation of the method are presented. †Presently with Ship Research Institute, Tokyo. Received October 12, 1998: revised manuscript received by the editors November 9, 1998. The original was submitted directly to the Journal.

28 citations



Journal Article
TL;DR: In this paper, a numerical wave tank based on fully nonlinear potential flow theory is used to calculate changes in local properties of periodic waves shoaling over barred-beaches (wave height, celerity, front-to-back asymmetry).
Abstract: A numerical wave tank based on fully nonlinear potential flow theory is used to calculate changes in local properties of periodic waves shoaling over barred-beaches (wave height, celerity, front-to-back asymmetry). Results show that strongly nonlinear wave decomposition phenomena occur in a modulation region beyond the bars. These are analyzed in detail and discussed in the paper. Received December 7, 1998; revised manuscript received by the editors May 7, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 2429, 1998..

Journal Article
TL;DR: In this paper, the linear, wave-induced response of a 5-module, 1500m-long mobile offshore base (MOB) is investigated, where each module is a 2-pontoon, 8-column semisubmersible, and the MOB is represented by the lumped-parameter rigid module flexible flexible connector model.
Abstract: The linear, wave-induced response of a 5-module, 1500-m-long mobile offshore base (MOB) is investigated. Each module is a 2-pontoon, 8-column semisubmersible, and the MOB is represented by the lumped-parameter rigid module-flexible connector model. An extensive parametric study is carried out to determine the impact of the stiffness on the motions and connector loads. Results show that the hydrodynamic interaction between modules is relatively small. Although the response is a complicated function of the connector stiffness, the maximum extreme connector forces for hinged modules are often a result of horizontal bending induced by oblique waves. Also, it is shown that resonance can be a significant problem, especially for lower stiffnesses. *ISOPE Member. Received July 6, 1998: revised manuscript received by the editors January 25, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 24-29, 1998.

Journal Article
TL;DR: A Bayesian model is formulated to estimate the physical risk of grounding during transits into and out of port as a function of potential risk factors and changes in factors such as vessel type and size, wind speed, and visibility.
Abstract: We formulate a Bayesian model to estimate the physical risk of grounding during transits into and out of port as a function of potential risk factors We assemble and analyze information on factors surrounding groundings in three US ports between 1981 and 1995 Although the data are far from perfect, it is possible to establish associations between grounding risk and changes in factors such as vessel type and size, wind speed, and visibility

Journal Article
TL;DR: In this paper, the authors tried to make clear the roles of guide vanes for turbine systems with the simple momentum theory, and found that the upstream vanes are more effective for the efficiency than the downstream vanes.
Abstract: Guide vanes are installed in the Wells turbine in order to improve the performance such as efficiency, self-rotating characteristics and off-design one with stall. This paper tries to make clear the roles of guide vanes for turbine systems with the simple momentum theory. It is found that the upstream guide vanes are more effective for the efficiency than the downstream guide vanes. The guide vanes are designed by using experimental data from the rotor without guide vane and potential flow calculation around guide vane. Experimental investigations on the effect of the guide vanes for the performance of Wells turbine are carried out and rearranged to confirm the momentum theory proposed in this paper.

Journal Article
TL;DR: In this article, a morphological model for the local scour around pipelines is developed based on the Navier-Stokes equation and an erodible boundary adjustment technique, which predicts the equilibrium scour hole without using any sediment transport formula.
Abstract: A morphological model for the local scour around pipelines is developed. Based on the Navier-Stokes equation and an erodible boundary adjustment technique the model predicts the equilibrium scour hole without using any sediment transport formula. The calculation results clearly reveal that the lee-wakes behind the pipeline contribute significantly to the local scour hole development, especially to the gentle scour slope observed in experiments. The predicted maximum scour depth and the shape of the scour hole compare favorably with the experimental data published in the literature.

Journal Article
TL;DR: In this paper, single segmented mooring lines were tested in a geotechnical centrifuge for the purpose of calibrating the analytical solution developed for the analysis and design of various moorings associated with underwater drag/permanent anchors.
Abstract: Single segmented mooring lines were tested in a geotechnical centrifuge for the purpose of calibrating the analytical solution developed for the analysis and design of various mooring lines associated with underwater drag/permanent anchors. The model mooring lines included steel ball chains and wire cables placed at various depths within the soft clayey seafloor soil. The mooring lines were loaded to preset tensions at the water surface under an elevated acceleration inside the centrifuge to simulate the field stress conditions experienced by the prototype mooring lines. This paper describes the calibration of two factors that are used as part of the input parameters in the analytical solution of mooring lines and considers the effect of chasing wires that were used in the experiment to determine the locations of the mooring lines.

Journal Article
TL;DR: A Reynolds-Averaged Navier-Stokes (RANS) numerical method has been coupled with a six-degree-of-freedom motion program for time-domain simulation of ship and fender coupling during berthing operations, demonstrating the feasibility of the chimera RANS approach forTime- domain simulation of the hydrodynamic coupling between the ship and berthing structures.
Abstract: A Reynolds-Averaged Navier-Stokes (RANS) numerical method has been coupled with a six-degree-of-freedom motion program for time-domain simulation of ship and fender coupling during berthing operations. The method solves the mean flow and turbulence quantities on embedded, overlapped, or matched multiblock grids. The unsteady RANS equations were formulated in an earth-fixed reference frame and transformed into general curvilinear, moving coordinate systems. A chimera domain decomposition technique was employed to accommodate the relative motions between different computational blocks. Calculations were performed first for a full-scale motor vessel in berthing operations. Comparisons have been made between the computations and measurements to demonstrate the feasibility of the chimera RANS approach for time-domain simulation of the hydrodynamic coupling between the ship and berthing structures. The method was then employed for a parametric study of full-scale berthing ships under different approach speeds, water-depth-to-draft ratios, quay wall clearance distances, and fender stiffnesses.

Journal Article
TL;DR: In this paper, the possibility of obtaining an efficient description of the roll motion of a ship with liquids with free surface on board is discussed in detail and a mathematical model with concentrated parameters is implemented and compared with scale model experiments.
Abstract: In this paper, the possibility of obtaining an efficient description of the roll motion of a ship with liquids with free surface on board is discussed in detail. Available mathematical models with concentrated parameters are implemented and compared with scale model experiments. Critical points are evidenced by using a high efficiency Parameter Identification Technique. Finally a model with good simulation capability is presented. The proposed mathematical model fits well the experimental data requiting the estimation of a reduced set of parameters. The method appears of great interest in the frame of current research on the damaged ship behaviour.

Journal Article
Tetsuya Yao1
TL;DR: In this paper, the authors introduce the historical matters and state of the art regarding the research works on the ultimate longitudinal strength of a ship's hull girder and explain how the yielding and buckling affect the progressive collapse behaviour of a cross-section of the hull under longitudinal bending.
Abstract: This paper introduces the historical matters and state of the art regarding the research works on the ultimate longitudinal strength of a ship’s hull girder. At first, it describes how the longitudinal strength assessment started, and past experimental works on full-scale and small-scale hull girders applying longitudinal bending load are introduced. Then, the paper explains how the yielding and buckling affect the progressive collapse behaviour of a cross-section of a ship’s hull under longitudinal bending, showing the results of example calculations. The methods of analysis as well as research works on ultimate longitudinal strength and progressive collapse behaviour of a ship’s hull are reviewed, and some important results are introduced. At the end, benchmark calculation on progressive collapse behaviour under longitudinal bending is described. *ISOPE Member. Received March 17, 1998: revised manuscript received by the editors December 15, 1998. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 2429, 1998.

Journal Article
TL;DR: In this article, the authors proposed equations for ultimate and yield strength, initial stiffness and local deformation at ultimate strength for gusset-plate-to-chamber tube connections.
Abstract: Gusset-plate to CHS tube joints are connections where the end of a plate is directly welded to the outer surface of a tube. This study proposes equations for ultimate and yield strength, initial stiffness and local deformation at ultimate strength for these types of connections. These equations are based on a ring model with an effective width using multiple nonlinear regression analyses. To describe the load-deformation behavior of gusset-plate to CHS tube joints, each load-deformation curve is approximated by two straight lines using these equations.


Journal Article
TL;DR: In this article, the authors investigated the high-frequency resonant response of a flexibly mounted vertical cylinder due to waves in a wave-tank and found that the response was initiated by the impact of the deformed and breaking wave on the cylinder.
Abstract: Systematic experiments were carried out in a wave-tank in order to investigate the high-frequency resonant response of a flexibly mounted vertical cylinder due to waves. For this lightly damped structure, ringing responses with high structural accelerations were observed in breaking wave groups. Structural deflections (first bending mode) have also been measured. Ringing appears initiated by the impact of the deformed and breaking wave on the cylinder. The loads acting on the cylinder have been deduced from the measured response and appear to be closely correlated with the local wave slope at the cylinder. Complementary measurements of the response of the cylinder to loadings in Stokes waves were also made for a range of structural natural frequencies including the third harmonic of the wave frequency. These are shown to be distinct from ringing responses. The comparison between Stokes wave and deformed wave response is heightened through spectral analysis. *ISOPE Member. Received July 23, 1998; revised manuscript received by the editors June 22, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 24-29, 1998.

Journal Article
TL;DR: In this paper, the dynamics and control of a towed vehicle when it changes depth and course were studied theoretically and experimentally, and a mathematical model of motions of the vehicle was described in six degree freedom motion equations and that of the towing cable was done using the lumped mass model.
Abstract: The dynamics and control of a towed vehicle when it changes depth and course were studied theoretically and experimentally. A mathematical model of motions of the vehicle is described in six degree freedom motion equations and that of the towing cable is done using the lumped mass model. Control systems based on an optimal control theory (LQI synthesis) were developed to control the vehicle safely during the depth change. The performance of the controller and the accuracy of the mathematical model of motions have been evaluated by field experiments. The towing tension was also measured in field experiments to confirm the safety of the towing cable.

Journal Article
TL;DR: In this paper, an Oscillating Water Column wave energy device is simulated in a 2D numerical wave tank and a new wave generation by spinning dipole is proposed; when coupled to a robust wave absorption technique, it permits long time simulations without energy accumulation in the tank.
Abstract: An Oscillating Water Column wave-energy device is simulated in a 2D numerical wave tank. The fluid flow modelization is fully nonlinear. A new wave generation by spinning dipole is proposed; when coupled to a robust wave absorption technique, it permits long time simulations without energy accumulation in the tank. The turbine power take off mechanism is driven by a self-adaptive controller. The technique initially developed for active piston wave absorbers is applied successfully to OWC power plants. It is based on a Kalman filter frequency tracking algorithm. This control compares favourably with more conventional open loop systems.

Journal Article
TL;DR: Geotechnical and geo-acoustic characterization of sediments from Eckernförde Bay, Germany, are combined with a theoretical model to predict the influence of gas-bubble concentration on key engineering parameters as mentioned in this paper.
Abstract: Geotechnical and geo-acoustic characterization of sediments from Eckernförde Bay, Germany, are combined with a theoretical model to predict the influence of gas-bubble concentration on key engineering parameters. These sediments are organic in nature, very soft, and contain variable amounts of dissolved and undissolved methane gas. At the typically low gas volume fractions measured at the study site, on average less than 1%, gas pressure is predicted to be less than 36.4 kPa above hydrostatic water pressure, whereas undrained shear strength is estimated to fall within ±20% of the fully saturated strength. The instantaneous, undrained, elastic shear modulus is expected to decrease very little, whereas the bulk modulus and the compressional wave velocity show dramatic decreases. *ISOPE Member. Received March 10, 1998; revised manuscript received by the editors May 10, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 24-29, 1998.

Journal Article
TL;DR: In this paper, a propagation of periodic traveling waves of finite amplitude over the plane bottom in homogeneous fluid covered by floating broken ice is considered, and the dependence of the wave profile on the ice thickness and characteristics of an initial harmonic are analyzed.
Abstract: A propagation of periodic traveling waves of finite amplitude over the plane bottom in homogeneous fluid covered by floating broken ice is considered. The dependence of the wave profile on the ice thickness and characteristics of an initial harmonic are analyzed. The ice effect on the Stokes’ drift velocity and total mean mass transport is studied. Received February 24, 1998; revised manuscript received by the editors April 21, 1999. The original version was submitted directly to the Journal on February 24, 1998.

Journal Article
TL;DR: In this article, a numerical wave tank is applied to the study of chaotic roll motions of a two-dimensional floating body, which is constructed by a time-domain, fully nonlinear simulation method based on potential theory.
Abstract: A numerical wave tank is applied to the study of chaotic roll motions of a two-dimensional floating body. This numerical wave tank is constructed by a time-domain, fully nonlinear simulation method based on potential theory. In this simulation method, boundary value problems both on the velocity potential f and its time derivative ∂f/∂t are solved. The coupling condition between wave and floating body is imposed as the implicit boundary condition of ∂f/∂t on a wet body surface. The radiation condition at the tank ends is satisfied by artificial damping technique. Using this numerical wave tank, the chaotic motions of a 2-D unstable floating body with a small negative GM are simulated in time domain taking fully nonlinear fluidbody interaction into account. The simulated time history, phase plot and Poincare section of roll motions are presented and the dependency of the motion to wave height is discussed. *ISOPE Member. Received March 5, 1998: revised manuscript received by the editors October 2, 1998. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montreal, Canada, May 24-29, 1998.

Journal Article
TL;DR: In this paper, the authors derived analytical solutions for buckling propagation and fracture of a pipeline subjected to hydrostatic pressure by using rigid-plastic approximations to determine the plastic deformation of the pipeline.
Abstract: The objective of this paper is to derive analytical solutions for buckle propagation and fracture of a pipeline subjected to hydrostatic pressure. Rigid-plastic approximations are used to determine the plastic deformation of the pipeline. Because the transition zone of buckle propagation occurs over a finite region, the plastic collapse of a pipeline of finite length is first considered. The deformation model for the finite-length pipe is then extended to buckle propagation in pipelines of infinite length. Closed-form solutions for the steady-state buckle propagation pressure are derived by considering plastic work dissipation due to both circumferential bending and longitudinal stretching. Analytical predictions of the propagation pressure are within 5% of the experimental data on mild steel pipes. The present model is an improvement over previous analytical solutions, in which the longitudinal stretching resistance of the pipeline was ignored. It has been found that the plastic work due to longitudinal stretching accounts for 20% to 30% of the propagation pressure in the pipelines considered in this study. Finally, approximations of the maximum strains are made from the assumed deformation field. Fracture criteria based on the uniaxial rupture strain or the combinations of biaxial rupture strains are suggested to predict cracks in the pipe. Received May 7, 1998: revised manuscript received by the editors September 3, 1998. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 2429, 1998.

Journal Article
TL;DR: In this paper, a three-dimensional random walk model is used to predict the morphology and mass of the ice accretion on a cylindrical surface representing a transmission line cable.
Abstract: When water droplets encounter an object and the atmospheric conditions are sufficiently cold, ice will accrete on it. In this paper, we examine ice accretion due to freezing rain on a cylindrical surface representing a transmission line cable. A three-dimensional random walk model is used to predict the morphology and mass of the ice accretion. In this method, the motion of each drop or of drop ensembles is followed individually. The main advantage of the random walk approach is that it models realistically and with numerical efficiency the flow of water along the surface of the accretion. This model not only calculates the accretion on the side exposed to impinging droplets, but also the accretion below the object, including the formation of multiple icicles. The model prediction of the shape and mass of the ice accretion on a cylinder has been analyzed as a function of the convective heat flux and precipitation rate. While used here to simulate accretions on ground wires, the random walk model could also be used to simulate ice accretion on other elements of electrical power transmission lines.

Journal Article
TL;DR: In this article, the experimental data on the structural behavior of two side structures, namely standard VLCC with additional side stringers during ship-ship collision, and investigate the internal mechanics related with the structural deformation of struck ship.
Abstract: The aim of this study is to obtain the experimental data on the structural behaviour of two side structures, namely standard VLCC and VLCC with additional side stringers during ship-ship collision, and to investigate the internal mechanics related with the structural deformation of struck ship. Two quasi-static collision tests was carried out on side structure models of VLCC which were composed of a double hull. Assuming the how of striking ship as rigid, energy absorption capacity of two designs for VLCC was studied. Contribution of each structural component such as outer/inner shell plating, web frame, and side stringer etc. was discussed. Especially, the distribution of strain on the side shell plating during collision was collected in order to verify the usefulness of the numerical analysis by FEA codes.