Sloshing Effects Accounting for Dynamic Coupling Between Vessel and Tank Liquid Motion

This paper presents model test and analytical correlation results of a single point moored Floating Production, Storage and Offloading tanker based system (FPSO). Both Permanent and Disconnectable turret mooring system are considered. Analytical calculation of green water effects, vessel motions, turret and mooring line loads are compared with model test results. Frequency and time domain analysis techniques of calculating line tensions are demonstrated and results are compared to the model tests measured time histories. The analysis procedure discussed in this paper is aimed toward estimating I)motions at bow relative to the water surface, 2)mooring line tensions and 3)turret design loads for a turret moored FPSO with a reasonable degree of accuracy. it is demonstrated that mooring line tensions can be calculated accurately with a finite element time domain computer simulation of the line dynamics provided the input fairlead motions are correct. Thus the method of computing time histories of mooring line tensions based on free-floating vessel motions is applicable for other spread moored floating systems in the same range of water depth. CONCLUSIONS AND RECOMMENDATIONS The model test results confirm the feasibility of both types of turret moored systems and validate the analytical tools and procedures. Results derived from the time domain line dynamic analysis agree well with the model tests. The dynamics of slack line are over estimated by using the frequency domain approach. Two methods of API mooring line fatigue calculation are compared. This paper demonstrates that a frequency domain quasistatic approach provides an efficient tool for initial sizing of mooring components. The maximum global mooring line and turret loads may be estimated by combining the frequency domain line dynamic results with the quasistatic approach. A time domain line dynamic approach can confirm and/or predict the maximum line tension with a high level of confidence, provided the vessel motion at the line top can be prescribed accurately. INTRODUCTION A turret moored 140,000 DWT tanker system is being designed for 1,000 feet of water in the South China Sea. The turret moored tanker is an attractive concept for both production facilities and offshore storage. Design of the weather vaning turret mooring system and riser system connected to the seafloor are two key system components for FPSO development. In the design of a turret mooring system the prediction of the extreme motion responses of the moored vessel is of the utmost importance. A moored tanker exposed to severe environmental conditions experiences motion responses in two distinct frequency ranges:Wave frequency responses around the wave period range (12-15 seconds).Low frequency responses around the tanker natural period range (100 seconds); The wave frequency response is generally well predictable, whereas estimates on the low frequency responses are more difficult and may vary by an order of magnitude depending on analytical tools and design procedures. Often a well executed model test program in parallel with analytical approach is imperative to ensure a reliable design of the turret mooring system.

This paper presents a boundary-layer model to predict dynamic characteristics of liquid motion in partially filled tanks of a spinning spacecraft. The solution is obtained by solving three boundary-value problems: an inviscid fluid problem, a boundary-layer problem, and a viscous correction problem. The boundary-layer solution is obtained analytically, and the solutions to inviscid and viscous correction problems are obtained by using finite element methods. The model has been used to predict liquid natural frequencies, mode shapes, damping ratios, and nutation time constants for a spinning spacecraft. The results show that liquid motion in general will contain significant circulatory motion due to Coriolis forces except in the first azimuth and first elevation modes. Therefore, only these two modes can be represented accurately by equivalent pendulum models. The analytical results predict a sharp drop in nutation time constants for certain spacecraft inertia ratios and tank fill fractions. This phenomenon was also present during on-orbit liquid slosh tests and ground air-bearing tests. I. Introduction A RECENT trend in geosynchronou s spacecraft design is to use liquid apogee motors, which results in liquid constituting almost half of the spacecraft mass during transfer orbit. In these spacecraft, liquid motion significantly influences the spacecraft attitude stability and control. LEAS AT, a geosynchronous spacecraft with liquid apogee motor, launched in September 1984, experienced attitude control motion instability1 during the pre-apogee injection phase, immediately following the activation of despin control. The instability was found to be the result of interaction between liquid lateral sloshing modes and the attitude control. This experience demonstrated that the analysis of dynamic interaction between liquid slosh motion and attitude control is critical in the attitude control design of these spacecraft. To perform this analysis, accurate determination of liquid dynamic characteristics, such as natural frequencies, mode shapes, damping, and modal masses becomes important. Accurate prediction of liquid dynamic characteristics is, however, a difficult problem because of the complexity of the hydrodynamical equations of motion. Several investigators have analyzed the fluid motion in rotating containers. Greenspan2 analyzed the transient motion during spin up of an arbitrarily shaped container filled with viscous imcompressible fluid. Stewartson3 developed a stability criterion for a spinning top containing fluid. This stability criterion was corrected by Wedemeyer 4 by considering fluid viscosity. Nayfeh and Meirovitch5 analyzed a spinning rigid body with a spherical cavity partially filled with liquid. Viscous effects are considered only for a boundary layer near the wetted surface. Hendricks and Morton6 analyzed the stability of a rotor partially filled with a viscous incompressible fluid. Stergiopoulous and Aldridge7 studied inertial waves in a partially filled cylindrical cavity during spin up. Pfeiffer8 introduced the concept of homogeneous vorticity to the problem of partially filled containers. El-Raheb and Wagner9 developed a finite element model based on a homogeneous vorticity as

This paper presents a simple and fast method to include the effect of liquid tanks of a vessel in the prediction of the vessel motions. The effects are expressed in terms of modifications to the added mass and stiffness matrices of the vessels calculated with the liquids in the tanks assumed being rigid. The flows in the liquid tanks are solved using a panel method based on the desingularized boundary integral equations (DBIEs). The numerical results were validated by the experiments of a square tank partially filled. An application example for a vessel with two internal liquid tanks is demonstrated.

In this paper, a method used to analyze the sloshing of liquid in a tank subjected to forced pitching and (or) yawing oscillation is presented. First, a variational principle for a liquid in a container under pitching and (or) yawing oscillation is proposed. Based on the preceding variational principle and new Lagrangian, the nonlinear sloshing of liquid in a circle cylindrical tank under pitching excitation is studied analytically for the first time.

A mathematical model was developed to compute the motions of semisubmersible drilling vessels in waves for a wide variety of semisubmersible configurations. The model was derived from a linear representation of motions, ocean waves, and forces. The semisubmersible is represented as a rigid space frame composed of a number of cylindrical members with arbitrary diameters, lengths and orientations. Forces on the semisubmersible are derived from anchorline properties, and hydrostatic hydrodynamic principles. A solution is obtained for motions in six degrees of freedom for a sinusoidal wave train of arbitrary height, period, direction and water depth. Results from the analysis of three semisubmersibles are compared with results from available model test data to verily the mathematical model. Introduction An accurate and complete representation of the response of a drilling vessel to waves is a valuable engineering tool for predicting vessel performance and designing drilling equipment. The performance and designing drilling equipment. The wave response for a floating vessel may be obtained to various degrees of accuracy from model tests or analytical means, as described by Barkley and Korvin-Kroukovsky and as applied by Bain. A review of the works cited shows that the evaluation of the wave response for a particular vessel requires considerable time and effort, either in model construction and testing or in computer programming and calculations. In order to reduce programming and calculations. In order to reduce the amount of time and effort required to evaluate a particular vessel, means were investigated to generalize and automate, on a digital computer, methods for evaluating wave response for vessels of arbitrary configuration. The mathematical model described in this paper is the result of such an investigation for semisubmersible-type drilling vessels. The paper presents a general description of the mathematical model and the basic principles and assumptions from which it was derived. The validity of the model is evaluated by comparing results of the analysis of three semisubmersibles with available model test data. MATHEMATICAL MODEL The mathematical model for calculating the motions of a semisubmersible in waves is derived from basic principles and empirical relationships in classical mechanics. All equations are derived for "small amplitude" waves and motions. The nonlinear equations that appear in the problem are replaced by "equivalent" linear equations in order to conform to the linear analysis method used in obtaining a solution. The model is implemented in a computer program that computes vessel response in all six degrees of freedom for a broad range of semisubmersible configurations and wave parameters. The basic elements in the theoretical model are outlined, with a more detailed discussion of the principles and derivations used to obtain the model principles and derivations used to obtain the model presented in the Appendix. presented in the Appendix. SEMISUBMERSIBLE DESCRIPTION AND EQUATIONS OF MOTION The semisubmersible is characterized as a space-frame of cylindrical members and is described geometrically by specifying end-coordinates and diameters for all of the members. Specification of the mass, moments of inertia, center of gravity and floating position are required to complete the description. The six equations of motion for the semisubmersible derive from Newton's second law for a rigid body. These differential equations, when written in matrix form, equate the product of the six-component acceleration vector, {x}, and the inertia matrix, I, to a six-component, force-moment vector, {FT}. SPEJ P. 311

Experimental investigation on the dynamic responses of a free-hanging water intake riser under vessel motion

With the rapid development of society, the demand for liquid carrier ships and vehicles is increasing rapidly. Under the action of external load, the liquid in the tank would move relative to different degrees and produce hydrodynamic pressure on the local part of the liquid bulkhead, which will cause local damage or complete destruction of the structure, and then lead to leakage or other safety accidents. In this paper, computational fluid dynamics method is used to simulate the sloshing characteristics of the liquid in the cargo tank, and the instantaneous characteristic data of the free surface displacement fluctuation of the sloshing liquid are monitored. Through the pressure acquisition system, the hydrodynamic pressure distribution acting on the side wall of the cargo tank under external excitation is obtained. Through the free surface displacement fluctuation and the maximum hydrodynamic pressure acting on the side wall, the severity of liquid sloshing in cargo tank under external excitation is evaluated. The effects of different baffle combinations on liquid sloshing in cargo tanks are studied and discussed. The effects of baffles with holes on liquid sloshing are also discussed.

Nonlinear roll damping of a barge with and without liquid cargo in spherical tanks

Reduced gravity undergraduate student flight experiment - Liquid transfer in reduced gravity

Rules of Classification Societies all around the world have made changes on design wave loads’ value and fatigue influence factor modification due to the influence of springing and whipping on ultra-large containerships. The paper firstly introduced 3-D linear hydroelastic theory in frequency domain and 3-D nonlinear hydroelastic theory in time domain, considering large amplitude motion nonlinearity and slamming force due to the severe relative motion between ship hull and wave. Then the spectrum analysis method and time domain statistical analysis method were introduced, which can make fatigue analysis under a series of standard steps in frequency and time domain, respectively. Finally, discussions on the influence factor of springing and whipping on fatigue damages of 8500TEU and 10000TEU containerships with different loading states were made. The fatigue assessment of different position on the midship section was done on the basis of nominal stress. The fatigue damage due to whipping can be the same as the fatigue damage due to springing and even sometimes can be larger than the springing damage. Besides, some suggestions on calculating load case selection were made to minimize the quantity of work in frequency and time domain. Thus, tools for fatigue influence factor modification were provided to meet the demand of IACS-UR.

ABSTRACTIn the study of the motions of vessels floating side by side, it is necessary to employ accurate methods of analysis other than potential theory to overcome inaccurate solutions due to viscous effects. In this study, computational fluid dynamics (CFD) simulations for the analysis of single- and side-by-side vessels are performed. The CFD codes are formulated for solving the Navier–Stokes equations using the finite-volume method with OpenFOAM, an open-source CFD software program. Taking into consideration viscous damping and vortex shedding effects, advantage of viscous damping and vortex shedding, three-dimensional numerical simulations for six-degree-of-freedom motions of a single vessel and side-by-side vessels are conducted. The simulation results for a single vessel are validated by comparison with results obtained from ANSYS AQWA software and from model testing. Simulation results for side-by-side vessels are compared with the AQWA results in order to show that the CFD code can be used effectively in predicting the motions of side-by-side vessels in regular waves.

Offshore drilling risers, top-tensioned risers and many production risers are top tensioned, connecting the vessel and seabed via joints. External loads such as currents, waves and vessel motions introduce cyclic loads and motions on riser sections, which may shorten the service life due to accumulated fatigue damage. Dynamic responses under combined currents and waves are more complicated than vortex-induced vibrations (VIV) due to pure currents, and it is not fully understood. Several model test campaigns on top-tensioned riser (TTR) have been carried out at SINTEF Ocean (former MARINTEK) during the past decades. Currents, waves and vessel motions were modelled, and the riser model responses were measured. In this study, selected cases from such model tests are analysed, and used to validate a semi-empirical time domain VIV prediction tool — VIVANA-TD. A better understanding of the dynamic responses of TTR under combined currents and waves has been achieved. By comparing the results from numerical simulation using VIVANA-TD and model test measurements, validity and limitation of the time domain tool have been investigated. Important features that need to be considered are discussed. The experience gained from the present study establishes a good basis for VIV and wave load prediction of full-scale TTRs under combined currents and waves where the uncertainty of VIV prediction is further reduced.

This study uses a CFD approach to perform numerical simulations of the hydrodynamic interactions between LNG ship motions induced by waves and the sloshing behavior of cargo tanks. First, a CFD simulation is performed by solving the RANS equations to analyze the sloshing behavior of liquid in a three-dimensional rectangular tank subjected to forced simple harmonic motion. The accuracy of the RANS solver in addressing the sloshing problem is validated through comparisons with experimental data and other numerical methods. Next, the study considers the coupling effects of both the internal sloshing flow field and the external wave field on the motion of a simplified LNG vessel. The motion response of the LNG carrier in regular waves was simulated, and the sloshing impact pressure on the bulkheads under various conditions was analyzed. The simulation results of the LNG ship’s hydrodynamic behavior were compared with experimental and numerical data from previous studies. The effect of liquid tank sloshing on ship motion and tank wall pressure was examined under both head and beam wave conditions. Additionally, different forward speeds under head wave conditions were considered. It is crucial to account for the coupled effects of tank sloshing and ship dynamics when designing and evaluating liquid cargo ships.

Out-of-plane vortex-induced vibration of a steel catenary riser caused by vessel motions

Multi-body hydrodynamic resonance and shielding effect of vessels parallel and nonparallel side-by-side