Some Extensions of the Classical Approach to Strip Theory of Ship Motions, Including the Calculation of Mean Added Forces and Moments

1978 ◽  
Vol 22 (01) ◽  
pp. 1-19 ◽  
Author(s):  
Theodore A. Loukakis ◽  
Paul D. Scfavounos
Keyword(s):  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Dynamical Theory ◽  
Forced Oscillations ◽  
Ship Motions ◽  
Regular Waves ◽  
Strip Theory ◽  
Calm Water ◽  
Exciting Forces ◽  
New Formulation

The application of the dynamical theory to the problem of a ship moving with constant forward speed on a free surface has been extended to include the exciting forces in oblique regular waves. As a result, it has become possible to derive a new formulation for the equations of motion, for a ship moving with five degrees of freedom. The application of the same theory has yielded formulas for the calculation of the mean added resistance and drift force in oblique regular waves and the calculation of all mean forces and moments for the forced oscillations of a ship in calm water.

A Nonlinear Mathematical Model for Ship Turning Circle Simulation in Waves

2005 ◽  
Vol 49 (02) ◽  
pp. 69-79 ◽  
Author(s):  
Ming-Chung Fang ◽  
Jhih-Hong Luo ◽  
Ming-Ling Lee
Keyword(s):  
Mathematical Model ◽  
Degrees Of Freedom ◽  
Regular Waves ◽  
Nonlinear Mathematical Model ◽  
Ship Maneuvering ◽  
Sea Trial ◽  
Six Degrees Of Freedom ◽  
Strip Theory ◽  
Calm Water ◽  
Maneuvering Motion

In the paper, a simplified six degrees of freedom mathematical model encompassing calm water maneuvering and traditional seakeeping theories is developed to simulate the ship turning circle test in regular waves. A coordinate system called the horizontal body axes system is used to present equations of maneuvering motion in waves. All corresponding hydrodynamic forces and coefficients for seakeeping are time varying and calculated by strip theory. For simplification, the added mass and damping coefficients are calculated using the constant draft but vary with encounter frequency. The nonlinear mathematical model developed here is successful in simulating the turning circle of a containership in sea trial conditions and can be extended to make the further simulation for the ship maneuvering under control in waves. Manuscript received at SNAME headquarters February 19, 2003; revised manuscript received January 27, 2004.

Parametric Rolling Simulations of Container Ships

2013 ◽  
Author(s):  
Anton Turk ◽  
Jasna Prpić-Oršić ◽  
Carlos Guedes Soares
Keyword(s):  
Time Domain ◽  
Degrees Of Freedom ◽  
Equations Of Motion ◽  
Full Range ◽  
Ship Motions ◽  
Computationally Efficient ◽  
Parametric Roll ◽  
Parametric Rolling ◽  
Strip Theory ◽  
The Time Domain

A hybrid nonlinear time domain seakeeping analysis is applied to the study of a container ship advancing at different headings and encounter frequencies. A time-domain nonlinear strip theory in six degrees-of-freedom has been extended to predict ship motions by solving the unsteady hydrodynamic problem in the frequency domain and the equations of motion in the time domain which allows introducing nonlinearities in the linear model. The code is used to make parametric roll predictions for various speeds and headings and the results are summarized in a very intuitive 2D and 3D polar plots showing the full range of the parametric rolling realizations. The method developed is fairly accurate, robust, very computationally efficient, and can predict nonlinear ship motions. It is well suited to be used as a tool in ship design or as part of a path optimization model.

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.

scholarly journals Enhancement of a 3-DOF submerged wave energy device using bistability

2020 ◽  
Vol 3 (2) ◽  
pp. 73-82
Author(s):  
Benjamin Schubert ◽  
William S. P. Robertson ◽  
Benjamin S. Cazzolato
Keyword(s):  
Wave Energy ◽  
Degrees Of Freedom ◽  
Phase Relationship ◽  
Bistable System ◽  
Viscous Drag ◽  
Regular Waves ◽  
Point Absorber ◽  
Exciting Forces ◽  
Bistable Mechanism ◽  
The Impact

The dynamic response of a submerged CETO shaped quasi-point absorbing wave energy converter coupled to a bistable power take off is presented in this study. Whilst the impact of bistability has been shown in a limited number of situations to improve the amount of power generated, many models have been restricted to a single degree of freedom and often ignore drag effects. To overcome these model limitations, a submerged single tether point absorber with a bistable power take off was modelled using both 1 and 3 degrees of freedom. The device was subjected to regular waves and included a simple model of viscous drag. The bistable mechanism was provided by a magnetic dipole model quantified by a dimensionless parameter applicable to any bistable system. The performance of the device was is assessed by the theoretical power generated. Over each model, the previously observed benefit of bistability was not consistently obtained. Simulations of regular waves demonstrated an increase in generated power for suboptimal conditions for some frequencies, while a reduction in generated power was observed in optimal conditions. The performance increase showed strong correlation to the phase relationship between the motion and exciting forces as a result of bistability.

scholarly journals The Exciting Forces on Fixed Bodies in Waves

1962 ◽  
Vol 6 (04) ◽  
pp. 10-17 ◽  
Author(s):  
J. N. Newman
Keyword(s):  
Wave Amplitude ◽  
Amplitude Ratio ◽  
Exciting Force ◽  
The Body ◽  
Forced Oscillations ◽  
Wave Number ◽  
Far Field ◽  
Two Dimensional ◽  
Calm Water ◽  
Exciting Forces

General expressions, originally given by Haskind, are derived for the exciting forces on an arbitrary fixed body in waves. These give the exciting forces and moments in terms of the far-field velocity potentials for forced oscillations in calm water and do not depend on the diffraction potential, or the disturbance of the incident wave by the body. These expressions are then used to compute the exciting forces on a submerged ellipsoid, and on floating two-dimensional ellipses. For the ellipsoid, the problem is solved using the far-field potentials, and detailed results and calculations are given for the roll moment. The other forces agree, for the special case of a spheroid, with earlier results obtained by Havelock. In the case of two-dimensional motion the exciting forces are related to the wave amplitude ratio A for forced oscillations in calm water, and this relation is used to compute the heave exciting force for several elliptic cylinders. Expressions are also given relating the damping coefficients and the exciting forces. A = wave amplitude A = wave-height ratio for forced oscillations(a1 a2 a3) = semi-axis of ellipsoidBij = damping coefficientsC4 = nondimensional roll exciting-force coefficientDj = virtual-mass coefficients, defined by equations (18) and (19)g = gravitational accelerationh = depth of submergencei = √ — 1j = index referring to direction of force or motionn(z) = spherical Bessel function, K = wave number, K = ω2/gPj = functions defined following equation (17)R = polar coordinateV, = velocity components (x, y, z) = Cartesian coordinatesαi = Green's integrals, defined by equation (20)β = angle of incidence of wave systemθ = polar coordinateρ= fluid densityφj = velocity potentialsω = circular frequency of encounter

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.

Numerical Simulation of Submarine Surfacing With Six Degrees of Freedom in Regular Waves

2016 ◽  
Author(s):  
Weijian Jiang ◽  
Zhilin Wang ◽  
Ran He ◽  
Xianzhou Wang ◽  
Dakui Feng
Keyword(s):  
Numerical Simulation ◽  
Wave Height ◽  
Velocity Fluctuation ◽  
Degrees Of Freedom ◽  
Wave Length ◽  
Roll Angle ◽  
Regular Waves ◽  
Rolling Moment ◽  
Six Degrees Of Freedom ◽  
Calm Water

Submarine surfacing in waves is three dimensional unsteady motion and includes complex coupling between force and motion. This paper uses computational fluid dynamics (CFD) to solve RANS equation with coupled six degrees of freedom solid body motion equations. RANS equations are solved by finite difference method and PISO arithmetic. Level-set method is used to simulate the free surface. Computations were performed for the standard DARPA SUBOFF model. The structured dynamic overset grid is applied to the numerical simulation of submarine surfacing (no forward speed) in regular waves and computation cases include surfacing in the calm water, transverse regular waves with different ratio of wave height and submarine length (h/L = 0.01, 0.02, 0.03, 0.04) and transverse regular waves with different ratio of wave length and submarine length (λ/L = 0.5, 1, 1.5). The asymmetric vortices in the process of submarine surfacing can be captured. It proves that roll instability is caused by the destabilizing hydrodynamic rolling moment overcoming the static righting moment both under the water and in regular waves. Relations among maximum roll angle, surfacing velocity fluctuation and wave parameters are concluded by comparison with variation trend of submarine motion attitude and velocity of surfacing in different wave conditions. Simulation results confirm that wave height h/L = 0.04 and wave length λ/L = 1.5 lead to surfacing velocity fluctuation significantly. Maximum roll angle increases with the increase of wave height and wave length. Especially the law presents approximate linear relationship. Maximum roll angle with wave height (h/L = 0.04) can reach to 7.29° while maximum roll angle with wave length (λ/L = 1.5) can reach to 5.79° by contrast with 0.85° in calm water. According to the above conclusions, maneuverability can be guided in the process of submarine surfacing in waves in order to avoid potential safety hazard.

Numerical and Experimental Study of the Parametric Rolling of a Fishing Vessel in Regular Head Waves

2013 ◽  
Vol 155 (A4) ◽  
Keyword(s):  
Degrees Of Freedom ◽  
Assessment Tool ◽  
Prediction Method ◽  
Theory Model ◽  
Design Stage ◽  
Ship Motions ◽  
Fishing Vessel ◽  
Parametric Rolling ◽  
Strip Theory ◽  
Head Waves

The dynamic behaviour of a fishing vessel in waves is studied in order to reveal its parametric rolling characteristics. This paper presents experimental and numerical results in longitudinal regular waves. The experimental results are compared against the results of a time-domain non-linear strip theory model of ship motions in six degrees-of-freedom. These results contribute to the validation of the parametric rolling prediction method, so that it can be used as an assessment tool to evaluate both the susceptibility and severity of occurrence of parametric rolling at the early design stage of these types of vessels.

NUMERICAL AND EXPERIMENTAL STUDY OF THE PARAMETRIC ROLLING OF A FISHING VESSEL IN REGULAR HEAD WAVES

2021 ◽  
Vol 155 (A4) ◽  
Author(s):  
E Uzunoglu ◽  
S. Ribeiro E Silva ◽  
C. Guedes Soares ◽  
R. Zamora ◽  
L. Perez Rojas
Keyword(s):  
Degrees Of Freedom ◽  
Assessment Tool ◽  
Prediction Method ◽  
Theory Model ◽  
Design Stage ◽  
Ship Motions ◽  
Fishing Vessel ◽  
Parametric Rolling ◽  
Strip Theory ◽  
Head Waves

The dynamic behaviour of a fishing vessel in waves is studied in order to reveal its parametric rolling characteristics. This paper presents experimental and numerical results in longitudinal regular waves. The experimental results are compared against the results of a time-domain non-linear strip theory model of ship motions in six degrees-of-freedom. These results contribute to the validation of the parametric rolling prediction method, so that it can be used as an assessment tool to evaluate both the susceptibility and severity of occurrence of parametric rolling at the early design stage of these types of vessels.

The Transient Capsize Diagram—A New Method of Quantifying Stability in Waves

1991 ◽  
Vol 35 (01) ◽  
pp. 58-62 ◽  
Author(s):  
R. C. T. Rainey ◽  
J. M. T. Thompson
Keyword(s):  
Computer Simulation ◽  
Dynamic Systems ◽  
Wave Steepness ◽  
Dynamic Systems Theory ◽  
Regular Waves ◽  
Desktop Computers ◽  
Strip Theory ◽  
Calm Water ◽  
Recent Developments ◽  
The Stability

It is argued that a plot of wave steepness against wave period, showing the combinations which cause capsize, is a well-defined measure of the stability of a ship or ocean vehicle in waves, provided the conditions are transient, that is, the vessel is initially in relatively calm water, and is suddenly hit by a train of regular waves. This conclusion is a consequence of recent developments in dynamic systems theory. Such Transient Capsize Diagrams can obviously be obtained by model testing; it is also argued that they could be obtained by computer simulation on contemporary desktop computers, taking advantage of recent developments in nonlinear strip theory.

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