Journal ArticleDOI

# Numerical simulation of ship stability for dynamic environment

01 Jul 2003-Ocean Engineering (Elsevier BV)-Vol. 30, Iss: 10, pp 1305-1317
TL;DR: In this article, a nonlinear approach has been tried to predict the roll response of a vessel in a beam sea and various representations of damping and restoring terms found in the literature are investigated.
Abstract: The prediction of ship stability during the early stages of design is very important from the point of vessel’s safety. Out of the six motions of a ship, the critical motion leading to capsize of a vessel is the rolling motion. In the present study, particular attention is paid to the performance of a ship in beam sea. The linear ship response in waves is evaluated using strip theory. Critical condition in the rolling motion of a ship is when it is subjected to synchronous beam waves. In this paper, a nonlinear approach has been tried to predict the roll response of a vessel. Various representations of damping and restoring terms found in the literature are investigated. A parametric investigation is undertaken to identify the effect of a number of key parameters like wave amplitude, wave frequency, metacentric height, etc.
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TL;DR: In this article, the authors present the coupled nonlinear equations of motion in heave, roll, and pitch based on physical grounds, where the ingredients of the formulation are the inertia forces and moments, restoring forces and moment, and damping forces with an emphasis on the roll damping moment.
Abstract: In order to study the dynamic behavior of ships navigating in severe environmental conditions it is imperative to develop their governing equations of motion taking into account the inherent nonlinearity of large-amplitude ship motion The purpose of this paper is to present the coupled nonlinear equations of motion in heave, roll, and pitch based on physical grounds The ingredients of the formulation are comprised of three main components These are the inertia forces and moments, restoring forces and moments, and damping forces and moments with an emphasis to the roll damping moment In the formulation of the restoring forces and moments, the influence of large-amplitude ship motions will be considered together with ocean wave loads The special cases of coupled roll-pitch and purely roll equations of motion are obtained from the general formulation The paper includes an assessment of roll stochastic stability and probabilistic approaches used to estimate the probability of capsizing and parameter identification

72 citations

Journal ArticleDOI
, S.K. Lee2
TL;DR: In this article, the lift characteristics of the fins in hydrodynamic flow were studied using CFD package fluent. Good amount of reduction in roll amplitude is achieved from various simulations in random sea.
Abstract: The very purpose of attaching fins to the hull is to reduce the roll motions of a ship. Roll minimization is a requisite for various operations in the seas. The presence of fin system provides enhanced state of stabilization especially when the vessel is performing a fast maneuvering amidst rough environmental disturbance. The fins in turn are activated by electro-hydraulic mechanism based on the in-built intelligence as per control theory like proportional–integral–derivative (PID) or fuzzy logic. As per this paper, fin system is activated using PID control algorithm. A frigate-type warship is considered for the demonstration purpose. Nonlinear roll motions are controlled using active fins. Lift characteristics of the fins in hydrodynamic flow were studied using CFD package fluent . Good amount of reduction in roll amplitude is achieved from various simulations in random sea. The approach can be used for any irregular sea conditions.

50 citations

Journal ArticleDOI
TL;DR: In this article, the authors deal with the problem of modeling of rolling motion under a variety of excitation parameters, focusing on the analysis and prediction of the frequency of the resonant mode of rolling, since it is often an essential issue in terms of motion of a ship related to her safety against capsizing or excessive amplitudes of roll.
Abstract: The paper deals with the problem of modeling of rolling motion under a variety of excitation parameters. Special emphasis is put on the analysis and prediction of the frequency of the resonant mode of rolling, since it is often an essential issue in terms of motion of a ship related to her safety against capsizing or excessive amplitudes of roll. The research is performed for both free rolling and excited rolling and it is based on the one-degree-of-freedom equation. The conducted simulations were carried out paying special attention to the effects related to non-linear characteristics of stiffness represented by the GZ-curve and also the non-linearity of damping. A group of ships were considered in order to research and define the key factors governing rolling characteristics. The novel method for rolling period prediction was elaborated and tested revealing significant discrepancies between the results of the pending GM-based IMO-recommended method and the results of numerical simulations performed for a wide range of ships operational loading conditions. Since the research shows a drawback of the IMO formula for rolling period prediction a new formula is proposed instead.

31 citations

Journal ArticleDOI
TL;DR: In this article, an efficient modeling approach is presented to determine coupled roll and yaw motions of a symmetric and slender floating body when the influences of small amplitude regular waves are dominant.
Abstract: The prediction of resonance is very important with respect to the vessels stability in the early stages of design. In this paper, an efficient modeling approach is presented to determine coupled roll and yaw motions of a symmetric and slender floating body when the influences of small amplitude regular waves are dominant. The angular motions described in time domain by considering all internal and external forces are transformed into frequency domain to obtain motion characteristics. We adopt a semi-analytical treatment to obtain roll and yaw motions and derive system instability due to roll resonance. To compute hydrodynamic forces, we employ strip theory method where frequency dependent sectional added-mass, damping and restoring coefficients are derived from the Frank’s close-fit curve. Numerical experiments carried out for a vessel of mass 19,190 ton under the action of wave of frequencies 0.56 and 0.76 rad/s with zero and non-zero initial conditions are reported and the effect of various parameters on system stability is investigated. Model results indicate that damping factor ( ς ) plays a pivotal role when wave encountering frequency ( ω ) and undamped natural frequency ( β ) are nearly equal. The essence of this study lies in the efficient modeling technique to evaluate damping factor and critical encountering frequency regime for a given ship particulars when experimentally derived resonance zone is absent.

30 citations

Journal ArticleDOI
TL;DR: In this paper, the one degree-of-freedom rolling equation is applied with using the non-linear stiffness moment and linear damping moment formulas for predicting the ship rolling period.
Abstract: The paper deals with the problem of prediction of the rolling period. A special emphasis is put on the practical application of the new method for rolling period prediction with regard to non-linearity of the GZ curve. The one degree-of-freedom rolling equation is applied with using the non-linear stiffness moment and linear damping moment formulas. A number of ships are considered to research the discrepancies between the pending GM-based IMO-recommended method and the results of conducted numerical simulations performed for a wide range of operational loading conditions. Since the research shows some drawbacks of the IMO formula for the ship rolling period, a new formula is worked out and proposed instead.

25 citations

##### References
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Book
01 Jan 1988

628 citations

Book
01 Jun 1978
TL;DR: In this article, the Dynamics of Marine Vehicles (DVMV) is discussed in the context of marine vehicle dynamics, including the dynamics of marine vehicles and their dynamics of propulsion.
Abstract: Dynamics of marine vehicles , Dynamics of marine vehicles , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

413 citations

### "Numerical simulation of ship stabil..." refers background or result in this paper

• ...Bhattacharyya (1978) discussed rolling motion of a ship and the devices for roll...

[...]

• ...It is interesting to note that the present simulation agrees very well with the method suggested by Bhattacharyya (1978). The published literature gives a closed form solution to this linear dynamic problem....

[...]

Journal ArticleDOI
TL;DR: In this paper, a form of nonlinear equation governing the motion of a rolling ship subjected to synchronous beam waves is suggested and solved by the generalized Duffing's method in the frequency domain.
Abstract: Many researchers have studied a wide range of nonlinear equations of motion describing a ship rolling in waves. In this study, a form of nonlinear equation governing the motion of a rolling ship subjected to synchronous beam waves is suggested and solved by the generalized Duffing's method in the frequency domain. Various representations of damping and restoring terms found in the literature are investigated and their solutions are analyzed by the above-mentioned method. Comparative results of nonlinear roll responses are obtained for four distinct vessel types at resonance conditions which constitute the worst situation. The results indicate the importance of roll damping and restoring, when constructing a nonlinear roll model. An inappropriate selection of damping and restoring terms may lead to serious discrepancies with reality, especially in peak roll amplitudes.

114 citations

Journal ArticleDOI
TL;DR: In this article, the authors developed an approximation to the conventional mixed linear-plus-quadratic ship roll damping model so that analytical obstacles could be overcome in the application of the functional series expansion to non-linear ship rolling.
Abstract: : The objective of the present work was to develop an approximation to the conventional mixed linear-plus-quadratic ship roll damping model so that analytical obstacles could be overcome in the application of the functional series expansion to non-linear ship rolling. A mixed linear-plus-cubic approximation was found to be reasonable for this purpose. In the course of analyses there were indications that this model may be more generally valid than had initially been thought. (Author)

104 citations

Journal ArticleDOI
TL;DR: In this article, the roll damping of a large floating structure in waves is computed by the linear diffraction/radiation theory and the damping is used for an accurate prediction of the rigid body motions of the structure at the wave frequencies.
Abstract: For a large floating structure in waves, the damping is computed by the linear diffraction/radiation theory. For most degrees of freedom, this radiation damping is adequate for an accurate prediction of the rigid body motions of the structure at the wave frequencies. This is not particularly true for the roll motion of a long floating structure. For ships, barges and similar long offshore structures, the roll damping is highly nonlinear. In these cases the radiation damping is generally quite small compared to the total damping in the system. Moreover, the dynamic amplification in roll may be large for such structures since the roll natural period generally falls within the frequency range of a typical wave energy spectrum experienced by them. Therefore, it is of utmost importance that a good estimate of the roll damping is made for such structures. The actual prediction of roll damping is a difficult analytical task. The nonlinear components of roll damping are determined from model and full scale experiments. This paper examines the roll damping components and their empirical contributions. These empirical expressions should help the designer of such floating structures. The numerical values of roll damping components of typical ships and barges in waves and current (or forward speed) are presented.

104 citations