Large Amplitude Roll Motion Research Articles

Seakeeping simulation of surfaced submarines and statistical validation based on model tests in open waters as part of the development of the new stability regulation DMS 1030-2 for the German navy

ABSTRACT This paper explains the need for the new surface stability regulation recently developed for the submarines of the German Navy and gives an overview of its general setup and main principles. Further, the test setup and main findings of open water model tests using two submarine hull forms on Eckernförde Bay are presented, which contributed towards the development of the new standard. Building on this introduction of the model tests, the results of an exemplary test run at specific combination of speed, stability, sea state and encounter angle are compared via statistical analysis with seakeeping simulation results using E4-ROLLS, a potential flow theory-based computation method. The comparison aims to check the suitability of E4-ROLLS for analyzing stability-dependent large-amplitude roll motions of surfaced submarines in natural seaways. The quality of results is discussed, whereby limitations of the simulation method are pointed out and the relevance of the presented research becomes apparent.

Free roll decay simulation of a polar research vessel with an anti-roll tank based on CFD

The Polar Research Vessel (PRV) must consider both icebreaking and ocean navigation performance, but its hull lines can result in large amplitude roll motion in storms. To address this issue, an anti-roll tank (ART) is fitted to restrain the roll. Using the viscous CFD method, a numerical model is established to couple ship motion with fluid motion in the ART. The simulation accurately captures the fluid motion characteristics in the ART and solves the nonlinearity of fluid motion coupled with roll motion. The study reveals the suppression rule of ART parameters on ship motion and completes the design of ART for polar icebreakers. Investigating the effects of water load, channel height, and installation height of ART on roll motion suppression using an equivalent damping evaluation method provides insight into ART parameter suppression rules on ship motion, facilitating ART design for polar icebreakers.

An Improved Method for Predicting Roll Damping and Excessive Acceleration for a Ship With Moonpool Based on Computational Fluid Dynamics Method

AbstractExcessive acceleration is one of the stability failure modes involving large roll motion of ships. The overset method is applied to solve the six degrees-of-freedom motion of the ship with moonpool in beam waves. Based on a computational fluid dynamics (CFD) method, the improved method of considering the roll damping of square moonpool is proposed. The improved method of considering moonpool damping is used in vulnerability assessment for excessive acceleration. The comparative analysis of the level 1 and level 2 vulnerability assessment of the excessive acceleration of a ship with moonpool is completed. The influence of moonpool on the vulnerability assessment of excessive acceleration is studied by comparing the model test results. The results show that the main factor affecting the estimation accuracy of lateral acceleration of the ship is the accuracy of roll amplitude calculation. The existence of moonpool will reduce the roll damping coefficient of the ship. The improved methods proposed in this paper can effectively improve the estimation of lateral acceleration of ships with moonpool in the level 1 vulnerability criteria and increase the safety margin in the level 2 vulnerability assessment. In the direct stability assessment, the CFD method can simulate the large-amplitude roll motion of the ship with moonpool and bilge keels, and can capture the strong nonlinear phenomena.

Approximate analytical investigation of large-amplitude rolling motion of ships with the improved Galerkin method

In this study, the large-amplitude rolling motion of a ship was studied. First, the harmonic balance method was used to construct a reasonable initial approximate solution. Subsequently, the Newton linearization and Galerkin method were combined to obtain the analytical approximate solution of the ship's large-amplitude roll motion. By comparing with the numerical solution, the accuracy of the analytical approximation solution was verified. The results showed that the third-order analytical approximation had a higher accuracy for small and large amplitudes. Based on the analytical approximate solution, the influence of nonlinear quadratic damping and nonlinear restoring moment on the global stability of the ship under different amplitudes was analyzed. The theoretical results can guide the design and stability analysis of large rolling motions of ships.

Study on Roll Restoring Arm Variation Using a Three-Dimensional Hybrid Panel Method

Providing a reliable numerical tool for the prediction of parametric roll and pure loss of stability is a difficult task. It is acknowledged that the occurrence of these two failure modes is mainly attributed to the variation of roll restoring arm, which should be calculated accurately. This work studies exclusively the roll restoring arm variation numerically and experimentally. First, partially restrained experimental tests at different constant heeling angles (up to 30°) are conducted to measure the variation of roll restoring arm in regular waves. Second, a numerical method for the calculation of roll restoring arm in waves taking radiation and diffraction moments into account is adopted. The calculation results are benchmarked against experimental model test data. Third, the characteristics of roll restoring arm variation and the effects of radiation and diffraction moments on roll restoring arm variation (GZRD) in head and following seas are investigated. Finally, the feasibility of GZ calculated by the integral of instantaneously average wetted surface is studied by comparing the results with that calculated by the integral of the fully instantaneously wetted surface. The research show that the GZRD can be ignored in following seas. The GZ in head seas consists of two important harmonic components, and GZRD is the main contribution of the second harmonic component. Therefore, GZRD should be calculated with consideration of the instantaneous heeling angles and Froude number in head seas, especially for the prediction of large amplitude roll motion at high speed. 1. Introduction Currently, the second-generation intact stability criteria are under development by the International Maritime Organization (IMO) (IMO SLF 53/WP.1-Add.1 2011; IMO SDC 3/WP.5 2016). Five different kinds of potentially dangerous dynamic stability failure modes in waves were proposed. Parametric roll and pure loss of stability are two of the stability failure modes that may lead to capsizing of a ship. According to the proposed drafts, a multilevel structure was adopted to make sure that numerical assessment procedures are only applied when the vulnerability to dynamical stability failures is beyond reasonable doubt. Assessment of the vulnerability criteria is normally based on simplified geometry characteristics or empirical formulas. However, direct stability assessment requires highly accurate prediction (Kobylinski 2012).

Volterra approach – a new method to accurately calculate the non-linear and time-varying roll restoring arm of ships in irregular longitudinal seas

ABSTRACTWith several incidents of large amplitude roll motion of ships observed at sea over the past two decades, the dynamic stability of modern ship types has assumed significant importance. The move by the International Maritime Organization to develop a second generation level-2 criteria has resulted in considerable attention to the development of simplified analytical models for roll motion. Especially for the problem of parametric roll, there is still no analytical model which accurately captures the non-linear roll restoring stiffness taking into account the combined effect of incident waves and dynamic heave and pitch motions of the vessel. This paper extends our previous work to accurately capture both the linear and higher-order time-varying roll stiffness coefficients through an analytical model while taking into account incident waves and dynamic motion of the vessel. This approach called the Volterra method is compared against the existing simplified models and a non-linear time-domain simulation program to demonstrate better agreement of the proposed approach.

Ince-Strutt stability charts for ship parametric roll resonance in irregular waves

Ince-Strutt stability chart of ship parametric roll resonance in irregular waves is conducted and utilized for the exploration of the parametric roll resonance in irregular waves. Ship parametric roll resonance will lead to large amplitude roll motion and even wreck. Firstly, the equation describing the parametric roll resonance in irregular waves is derived according to Grim’s effective theory and the corresponding Ince-Strutt stability charts are obtained. Secondly, the differences of stability charts for the parametric roll resonance in irregular and regular waves are compared. Thirdly, wave phases and peak periods are taken into consideration to obtain a more realistic sea condition. The influence of random wave phases should be taken into consideration when the analyzed points are located near the instability boundary. Stability charts for different wave peak periods are various. Stability charts are helpful for the parameter determination in design stage to better adapt to sailing condition. Last, ship variables are analyzed according to stability charts by a statistical approach. The increase of the metacentric height will help improve ship stability.

規則波中パラメトリック横揺れの定量的数値予測に関する研究

Since parametric roll is well known as one of the most dangerous phenomena which could lead to serious accidents due to large amplitude roll motion, a new Intact Stability code, which is under development at IMO, is required to cover this phenomena. To realize quantitative prediction of parametric roll, systematic forced roll motion tests were conducted to measure roll restoring variation and roll damping with relevant roll angle/amplitude up to 30 degrees. Then, a 3DOF numerical model based on nonlinear strip method is developed and compared with model experiment to validate its prediction accuracy and applicability as a direct assessment method towards the new Intact Stability code.

On unpredictable ship rolling in irregular seas

Indirectly excited large amplitude roll motions of container ships and roll-on/roll-off ferries represent a considerable threat to goods and life in modern navigation. Especially when ships are heading into rough seas, or sailing away from following seas, large roll responses have been reported to occur in an unpredictable, random way. We approach this topic from deterministic bifurcation theory and generalize the analysis by characterizing the seaway as narrow band stochastic processes. It is demonstrated how the intermittent behavior of zero and large amplitude motions in irregular seas is related to the deterministic bifurcation scenario. Further, we identify parameter regions of intermittent roll motions and show how the on-/off intermittency can be characterized by the probability density function of the response amplitude.

The effect of sea irregularities on ship rolling

Modern ships' large-amplitude roll motions represent a considerable threat to goods and life in today's ocean navigation. The authors investigate an indirectly excited nonlinear oscillator that describes the ship's roll motion and discuss suitable models for wave excitation processes.

Prediction of Extreme Ship Motions in Irregular Waves

AbstractThe occurrence of indirectly excited large amplitude roll motions of ships is investigated under the influence of a time‐varying righting lever curve in waves. In order to account for the irregular character of ocean waves appropriately, the ship motions are described within the framework of nonlinear dynamics and stochastic process theory. The analysis of roll motions in regular waves provides a qualitative understanding of the occurrence of unpredictable large amplitude roll motions as observed in ocean waves. However, quantitative information on the rolling behavior in irregular waves may be retrieved only from a probabilistic analysis. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An investigation of a semiactive suspension for a fork lift truck

This paper investigates the feasibility of a semiactive suspension of the cabin of a fork lift truck as a way of reducing the effect of harmful vibrations on the health of truck drivers. A suspension based on MR fluid dampers has been designed and implemented on an actual vehicle and heuristic control strategy has been developed, which preserves the filtering properties of the passive suspension when the vehicle moves in a straight line with a constant velocity and suppresses the large amplitude pitch and roll motion during turns and braking. Field tests have demonstrated a substantial comfort improvement with respect to the passive suspension, during the braking and turning phases, without any noticeable detrimental effects.

Robust Stabilization of Large Amplitude Ship Rolling in Beam Seas

The dynamics and control of a strongly nonlinear 3-DOF model for ship motion are investigated. The model describes the roll, sway, and heave motions occurring in a vertical plane when the vessel is subjected to beam seas. The ship is installed with active antiroll tanks as a means of preventing large amplitude roll motions. A robust state feedback controller for the pumps is designed that can handle model uncertainties, which arise primarily from unknown hydrodynamic loads. The approach for the controller design is a combination of sliding mode control and composite control for singularly perturbed systems, with the help of the backstepping technique. It is shown that this design can effectively control roll motions of large amplitude, including capsize prevention. Numerical simulation results for an existing fishing vessel, the twice-capsized Patti-B, are used to verify the analysis. [S0022-0434(00)02701-5]

Estimation of nonlinear damping coefficients from large-amplitude ship rolling motions

A new asymptotic method is applied to the analysis of roll decrement data which can determine nonlinear damping coefficients from large-amplitude roll motions. The roll restoring moment can be strongly nonlinear. The accuracy of the method is assessed by rolling with an initial amplitude, using given nonlinear equations of motion. The difference between the input and predicted damping coefficients will demonstrate the applicability of the analysis method. Using an iterative correction procedure, accurate coefficients can be obtained for large rolling angles up to the amplitude at the maximum value of the restoring moment.

Computer-aided simulations of large amplitude roll motions of ships in waves and of dynamic stability

This paper deals with accounting for nonlinearities in damping and restoring terms in the development of a simplified but fundamental equation of roll motion. For the restoring term, this includes coupling with heave motion, a constant bias, and regular wave excitation. Both analytical-numerical and computer-aided methods are used to study roll response and the stability of the formulated nonlinear differential equation.