An Experimental Investigation of Roll Motions of an FPSO

2008 ◽  
Author(s):  
Paulo T. T. Esperanc¸a ◽  
Joel S. Sales ◽  
Stergios Liapis ◽  
Joa˜o Paulo J. Matsuura ◽  
Wes Schott
Keyword(s):  
Degrees Of Freedom ◽  
Wind Waves ◽  
Scale Model ◽  
Ship Motions ◽  
Random Waves ◽  
Six Degrees Of Freedom ◽  
Campos Basin ◽  
Waves And Currents ◽  
Offshore Development ◽  
Bilge Keel

FPSO roll motions can be major contributor to riser fatigue. This is especially true in regions where wind, waves and currents are non-collinear. Roll motions as high as 23 degrees have been reported in the Campos Basin. The most common roll mitigation strategy consists of adding bilge keels to the FPSO. Motivation for this work came from a need to develop a better understanding of roll motions as a function of bilge keel width. In addition to roll motions, the hydrodynamic forces on the bilge keels were measured. A series of tests were conducted at the LabOceano offshore basin. This new facility has a length of 4 0 m, a width of 30 m, a depth of 15 m and is equipped with a multi-flap wave generator on one side. A ship-shaped FPSO design with sponsons for a deepwater offshore development in Brazil was tested. It has a length of 316 m, a breadth of 57.2 m and a draft of 28.3 m. A 1:70 scale model was constructed. A horizontal soft mooring system consisting of four lines with springs was used. Regular waves of different amplitudes as well as random waves were generated in the basin. Two different loading conditions, ballast (draft = 6.7 m) and loaded (draft = 21.7 m), as well as three wave headings, beam seas (90°), and quartering seas (22.5°, 45°) were considered. Tests were undertaken for four bilge keel configurations, corresponding to a case without bilge keels, as well as bilge keels of 3 different widths (1 m, 2 m and 3 m). In all cases, the bilge keels had a length of 200 m. An optical system was used to measure ship motions in all six degrees of freedom. The hydrodynamic loads on the bilge keels were measured using strain gages.

scholarly journals Design and Calibration of a Hall Effect System for Measurement of Six-Degree-of-Freedom Motion within a Stacked Column

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3740
Author(s):  
Olafur Oddbjornsson ◽  
Panos Kloukinas ◽  
Tansu Gokce ◽  
Kate Bourne ◽  
Tony Horseman ◽  
...  
Keyword(s):  
Hall Effect ◽  
Degrees Of Freedom ◽  
Reactor Core ◽  
Degree Of Freedom ◽  
Life Extension ◽  
Scale Model ◽  
Design Development ◽  
Seismic Safety ◽  
Six Degrees Of Freedom ◽  
Six Degree Of Freedom

This paper presents the design, development and evaluation of a unique non-contact instrumentation system that can accurately measure the interface displacement between two rigid components in six degrees of freedom. The system was developed to allow measurement of the relative displacements between interfaces within a stacked column of brick-like components, with an accuracy of 0.05 mm and 0.1 degrees. The columns comprised up to 14 components, with each component being a scale model of a graphite brick within an Advanced Gas-cooled Reactor core. A set of 585 of these columns makes up the Multi Layer Array, which was designed to investigate the response of the reactor core to seismic inputs, with excitation levels up to 1 g from 0 to 100 Hz. The nature of the application required a compact and robust design capable of accurately recording fully coupled motion in all six degrees of freedom during dynamic testing. The novel design implemented 12 Hall effect sensors with a calibration procedure based on system identification techniques. The measurement uncertainty was ±0.050 mm for displacement and ±0.052 degrees for rotation, and the system can tolerate loss of data from two sensors with the uncertainly increasing to only 0.061 mm in translation and 0.088 degrees in rotation. The system has been deployed in a research programme that has enabled EDF to present seismic safety cases to the Office for Nuclear Regulation, resulting in life extension approvals for several reactors. The measurement system developed could be readily applied to other situations where the imposed level of stress at the interface causes negligible material strain, and accurate non-contact six-degree-of-freedom interface measurement is required.

Ship Motions in Shallow Water

1970 ◽  
Vol 14 (04) ◽  
pp. 317-328 ◽  
Author(s):  
E. O. Tuck
Keyword(s):  
Shallow Water ◽  
Water Depth ◽  
Incident Wave ◽  
Degrees Of Freedom ◽  
Added Mass ◽  
Exciting Force ◽  
Ship Motions ◽  
Wave System ◽  
Six Degrees Of Freedom ◽  
Damping Coefficients

The problem discussed concerns small motions of a ship, in all six degrees of freedom, but at zero speed of advance, due to an incident wave system in shallow water of depth comparable with the ship's draft. The problem is completely formulated for an arbitrary ship, and is partially solved for the case when the ship is slender and the wavelength much greater than the water depth. Sample numerical computations of heave, pitch, and sway added mass and damping coefficients and the sway exciting force are presented.

Analyzing the Stabilizing Tank for the Control of Rolling Motion by Model Testing and the Dynamic Absorber Theory

2007 ◽  
Author(s):  
Arthur Curty Saad ◽  
Antonio Carlos Fernandes ◽  
Paulo de Tarso T. Esperanc¸a ◽  
Joel Sena Sales Junior
Keyword(s):  
Degrees Of Freedom ◽  
Ocean Basin ◽  
Offshore Platforms ◽  
Concentrated Mass ◽  
Classical Dynamic ◽  
Six Degrees Of Freedom ◽  
Resonant Wave ◽  
Parametric Studies ◽  
Dynamic Absorber ◽  
Bilge Keel

The FPSOs are a type of offshore platforms that are directional in nature. Since a large ship (presently the use of a VLCC - Very Large Crude Carrier - is very common) is used, there is a great importance the direction the waves hit the hull. Differently from a real ship, the FPSO cannot resort to maneuvering to avoid waves. It has been found that there is a possibility, in certain cases, that a rolling resonant wave may reach some stationary FPSOs and consequently, a very high response may be obtained. Sometimes, it is not possible to use large bilge keel and the alternative is to consider the use of other devices such as stabilizing tanks and U-tubes. Faced with this problem, the present work performed model tests in a deepwater ocean basin showing the effectiveness of the stabilizing tank. On the other hand, it is clear that due to the presence of mass, restoring motion and damping that the design problem may be tackled by the use of classical dynamic absorber theory. For this reason, a simplified problem was formulated by replacing the stabilizing tank by a passive concentrated mass on board. The fully nine dimensional and non-linear model are then recovered. Six degrees of freedom are to describe the ship motion and the renaming three are for the mass on board. Based on these preliminary studies, the work describes the use of tests with reduced models showing the usefulness of the theory in practice. The test results together with 2 and 4 degrees of freedom system addresses the importance of the roll-sway coupling. Subsequently, a careful linearization is made for the purpose of identifying the commanding variables such as the mass, the position above the keel, the damping, the dynamic absorber natural frequencies, etc. After that, several parametric studies have been performed, identifying the range of applicability of the variables. Finally, this theoretical-experimental exercise addresses back the use of the applicability of the stabilizing tank.

Numerical Simulation of Damaged Ship’s Motion in Beam Waves

2019 ◽  
Author(s):  
Qing Wang ◽  
Xuanshu Chen ◽  
Liwei Liu ◽  
Xianzhou Wang ◽  
MingJing Liu
Keyword(s):  
Degrees Of Freedom ◽  
Body Motion ◽  
Ship Motions ◽  
Rans Equations ◽  
Six Degrees Of Freedom ◽  
Calm Water ◽  
Unsteady Simulation ◽  
Ship Hydrodynamic ◽  
Physical Phenomena ◽  
Damaged Ship

Abstract The dangerous situation caused by the breakage of the ship will pose a serious threat to crew and ship safety. If the ship’s liquid cargo or fuel leaks, it will cause serious damage to the marine environment. If damage occurs accompanied by roll and other motions, it may cause more dangerous consequences. It is an important issue to study the damaged ship in time-domain. In this paper, the motions of the damaged DTMB 5512 in calm water and regular beam waves are studied numerically. The ship motions are analyzed through CFD methods, which are acknowledged as a reliable approach to simulate and analyze these complex physical phenomena. An in-house CFD (computational fluid dynamics) code HUST-Ship (Hydrodynamic Unsteady Simulation Technology for Ship) is used for solving RANS equations coupled with six degrees of freedom (6DOF) solid body motion equations. RANS equations discretized by finite difference method and solved by PISO algorithm. Level set was used for free surface simulation. The dynamic behavior of model was observed in both intact and damaged condition. The heave, roll and pitch amplitudes of the damaged ship were studied in calm water and beam wave of three wavelengths.

Recent Contributions Under the Bureau of Ships Fundamental Hydromechanics Research Program

1959 ◽  
Vol 3 (02) ◽  
pp. 47-64
Author(s):  
M. St. Denis ◽  
J.P. Craven
Keyword(s):  
Research Program ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Elastic Response ◽  
Inertial System ◽  
Ship Motions ◽  
Six Degrees Of Freedom ◽  
The Third ◽  
Ship Performance

The third main nautical objective, Seakeeping, refers to that aspect of ship performance in which the seaway enters in a dominant manner and affects fundamentally the character of the problem. In the section on Control [3],1 a pattern was introduced according to which seakeeping was related to the uncontrolled as well as the controlled oscillations which take place with reference to a ship's inertial system. But, more broadly speaking, seakeeping includes all of the following subjects:Description of the seaway.Determination of the forces imposed by the seaway on the vessel—the excitation (hydrodynamic loadings, wave bending moment, slamming forces, and so on).Determination of the response of the ship in her six degrees of freedom (ship motions).Prediction of the perils to which a ship may be exposed (capsizing, foundering, safety at sea).Prediction of the loss in speed she will sustain in heavy weather.Evaluation of the amount of stabilization necessary to prevent unacceptable or undesirable displacements and accelerations. The elastic response and strength of a vessel's structure, though not included under seakeeping, depend, nevertheless, in an essential manner thereon.

scholarly journals Prediction of Ship Unsteady Maneuvering in Calm Water by a Fully Nonlinear Ship Motion Model

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
Ray-Qing Lin ◽  
Tim Smith ◽  
Michael Hughes
Keyword(s):  
Experimental Data ◽  
Numerical Simulations ◽  
Degrees Of Freedom ◽  
Ship Motion ◽  
Ship Motions ◽  
Motion Model ◽  
Forward Speed ◽  
Fully Nonlinear ◽  
Six Degrees Of Freedom ◽  
Calm Water

This is the continuation of our research on development of a fully nonlinear, dynamically consistent, numerical ship motion model (DiSSEL). In this study we will report our results in predicting ship motions in unsteady maneuvering in calm water. During the unsteady maneuvering, both the rudder angle, and ship forward speed vary with time. Therefore, not only surge, sway, and yaw motions occur, but roll, pitch and heave motions will also occur even in calm water as heel, trim, and sinkage, respectively. When the rudder angles and ship forward speed vary rapidly with time, the six degrees-of-freedom ship motions and their interactions become strong. To accurately predict the six degrees-of-freedom ship motions in unsteady maneuvering, a universal method for arbitrary ship hull requires physics-based fully-nonlinear models for ship motion and for rudder forces and moments. The numerical simulations will be benchmarked by experimental data of the Pre-Contract DDG51 design and an Experimental Hull Form. The benchmarking shows a good agreement between numerical simulations by the enhancement DiSSEL and experimental data. No empirical parameterization is used, except for the influence of the propeller slipstream on the rudder, which is included using a flow acceleration factor.

scholarly journals Numerical and Experimental Studies on Ship Motions Induced by Passing Ship

2018 ◽  
Author(s):  
Francisco G. Pedro ◽  
João A. Santos ◽  
Liliana V. Pinheiro ◽  
Conceição J. Fortes ◽  
Miguel Hinostroza
Keyword(s):  
Degrees Of Freedom ◽  
Numerical Models ◽  
Experimental Studies ◽  
Hydrodynamic Forces ◽  
Model Tests ◽  
Scale Model ◽  
Ship Motions ◽  
Sea Waves ◽  
Ship Wake ◽  
The Time Domain

To investigate the ability of numerical models to simulate the behavior of moored ships subjected by ship-wake waves, use is made of scale model tests where a ship model sails with constant speed along a straight path at a constant distance from an otherwise motionless ship. The tests were carried out at one of the wave tanks of the Portuguese Civil Engineering Laboratory (LNEC). The moving ship is a self-propelled scale model of the “Aurora” chemical ship whereas the otherwise motionless ship is a scale model of the “Esso Osaka” tanker. The free-surface elevation was measured with a set of resistive wave gauges and ADVs. The tanker’s movements, induced by the wake waves, were measured along the six degrees of freedom with a gyroscope deployed inside the ship. The numerical model WAMIT provides, in the frequency domain, the quantities required to estimate the hydrodynamic forces associated to the interaction of a free-floating ship with waves. The BAS model uses those hydrodynamic forces to study in the time domain the ship interaction with any sea-waves acting on it. Wind and current actions can also be accounted for. The results of these numerical models are compared to the measurements made in the several repeats of one of those scale-model tests, in terms of the response amplitude to several wave components. These comparisons enabled the evaluation and validation of the numerical models parameters’ calibration process.

Non-Linear Time Domain Simulation of Dynamic Instabilities in Longitudinal Waves

2008 ◽  
Author(s):  
S. Ribeiro e Silva ◽  
C. Guedes Soares
Keyword(s):  
Time Domain ◽  
Degrees Of Freedom ◽  
Linear Time ◽  
Simulation Method ◽  
Ship Motions ◽  
Computational Technique ◽  
Parametric Rolling ◽  
Longitudinal Waves ◽  
Six Degrees Of Freedom ◽  
Strip Theory

A time domain numerical simulation method is developed to determine ship motions in six degrees-of-freedom and to detect dynamic instabilities in both regular and irregular longitudinal waves. The basic approach of the simulation program involves computation of hydrodynamic coefficients of added mass and damping, restoring coefficients and diffraction and Froude-Krylov excitation forces at each step in time according to the instantaneous waterline and vessel position, using a strip theory method and a pressure integration technique along the segments. This paper briefly describes the computational technique utilized and makes comparisons between numerical and experimental roll damping data to infer about its influence on roll amplitude under parametric rolling conditions. An investigation into the dynamic stability in waves of a container vessel example.

A New Technique for Testing a Sailing Yacht in Waves

1991 ◽  
Author(s):  
G. K. Kapsenberg
Keyword(s):  
Degrees Of Freedom ◽  
Water Resistance ◽  
Ship Motions ◽  
Added Resistance ◽  
Regular Waves ◽  
Six Degrees Of Freedom ◽  
Resistance Increase ◽  
Calm Water ◽  
Sailing Yacht ◽  
A New Technique

A new experimental technique is presented to test sailing yachts in waves. The method is suitable for the investigation of ship motions in all six degrees of freedom and added resistance for the close hauled condition. Measurements can be made both in regular waves and in irregular seas. The technique has been tried out on a model of a 12-Meter class yacht and showed a resistance increase for the yacht sailing to windward in a wind generated sea of 90% of the calm water resistance.

Scale Effect Studies on Hydrodynamic Performance for DTMB 5415 Using CFD

2018 ◽  
Author(s):  
Heng Zhang ◽  
Hang Zhang ◽  
Xuanshu Chen ◽  
Hao Liu ◽  
Xianzhou Wang
Keyword(s):  
Degrees Of Freedom ◽  
Wave Pattern ◽  
Resistance Coefficient ◽  
Body Motion ◽  
Hydrodynamic Performance ◽  
Scale Model ◽  
Ship Motions ◽  
Calm Water ◽  
Unsteady Rans ◽  
Scale Design

Making CFD with the capability of predicting ship scale design performance, rather than relying on scale model tests will help reduce design costs and provide a greater opportunity to develop more energy efficient ship designs. The key objective of this paper is to perform a fully nonlinear unsteady RANS simulation to predict the ship motions and resistance of a full scale DTMB 5415 ship model. The analyses are performed at design speeds, at a certain Fr number, using in-house computational fluid dynamics (CFD) to solve RANS equation coupled with six degrees of freedom (6DOF) solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Computations have been made using structured grid with overset technology. Simulation results shown that the total resistance coefficient in calm water at service speed is predicted by 2.36% error compared to the related towing tank results. The ship resistance for different scale demonstrated that the current in-house CFD model could predict the resistance in a reasonable range of the EFD data. The comparison of flow field for wave pattern for different scale model were analyzed and discussed.

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