Roll Damping Research Articles

Roll Damping of Damaged Ship Based on OpenFOAM

Roll Damping of Damaged Ship Based on OpenFOAM

An Effect of Sweep Angle on Roll Damping Derivative for a Delta Wing with Curved Leading Edges in Unsteady Flow

This paper presents the results of an analytical study to account the effect of the sweep angle of a delta wing whose leading edges are curved on roll damping derivative at various angles of attack and the amplitude of the full sine waves. In the present theory, the effect of Leeward surface has been taken into consideration with the attached shock case at the leading edge. For a detached shock case, this theory will not be valid. Results have been obtained for the hypersonic flow of perfect gases over a wide range of angle of attack and the Mach number. The results indicate that the roll damping derivative decreases with a sweep angle, but increase with the increase in the flow deflection angle δ as well as with Mach M.

Grid‐Free Modelling Based on the Finite Particle Method for Incompressible Viscous Flow Problems

In this paper, we present a grid‐free modelling based on the finite particle method for the numerical simulation of incompressible viscous flows. Numerical methods of interest are meshless Lagrangian finite point scheme by the application of the projection method for the incompressibility of the Navier–Stokes flow equations. The moving least squares method is introduced for approximating spatial derivatives in a meshless context. The pressure Poisson equation with Neumann boundary condition is solved by the finite particle method in which the fluid domain is discretized by a finite number of particles. Also, a continuous particle management has to be done to prevent particles from moving into configurations problematic for a numerical approximation. With the proposed finite particle technique, problems associated with the viscous free surface flow which contains the study on the liquid sloshing in tanks with low volumetric fluid type, solitary waves movement, and interaction with a vertical wall in numerical flume as well as the vortex patterns of the ship rolling damping are circumvented. These numerical models are investigated to validate the presented grid‐free methodology. The results have revealed the efficiency and stability of the finite particle method which could be well handled with the incompressible viscous flow problems.

Ship roll damping via direct inverse neural network control system

Undesired roll motions of surface vessels under sea way have negative influence on passengers, crew members, equipment and cargo. Damping roll motions is a complex problem due to unpredictable and irregular nature of marine environmental disturbances that induce roll motions. There are several stabilizing systems regarding roll motions such as gyrostabilizers, anti-roll tanks, active fins and rudder roll stabilizers. Among all types of roll stabilizers or roll damping systems active fins practically represents the most effective roll damping technique and yet the most commonly used roll stabilizer. Assuming that the longitudinal location of fins corresponds to the vessel center of gravity a one degree of freedom nonlinear model can be used to identify ship dynamics. In this paper the performance and robustness of a proposed control system based on neural network approach applied to active fins that takes into account roll response spectral characteristics transitions due to not only varying sea state but also changing sailing conditions is assessed. The suggested control system achieves robust performance with adequate roll damping effect that ranges from 50 to 65% roll reduction according to severity of weather conditions and sailing status.

Optimal Control for Torpedo Motion based on Fuzzy-PSO Advantage Technical

The torpedo is a nonlinear object which is very difficult to control. Via to manage the rudder angle yaw, the diving plane angle, and the fin shake reduction, the torpedo yaw horizontal, the depth vertical and roll damping of the system are controlled accurately and steadily. In this paper, the particle swarm optimization is used to correct the imprecision of architecture fuzzy parameters. The coverage width of membership function and the overlap degree influence of neighboring membership functions are considered in the method to adjust dynamically from the system errors. Thereby optimizing the control signal and enhancing the torpedo motion quality. The proposed method results in a better performance compared to the other control method such as adaptive fuzzy-neural that proved effective of the proposed controller.

Experimental study on viscous effect in roll and heave motions of a rectangular structure

This study focuses on the interaction between roll and heave motions of a rectangular structure, and the heave influence on the viscous effect on the roll motion experimentally in a two-dimensional wave tank. The dynamic responses were investigated with a range of regular wave periods, including longer, equal to, shorter than the natural roll wave period of the structure with wave steepness in beam sea conditions. The velocity fields were obtained using particle image velocimetry in the vicinity of the structure to elucidate the viscous effect on the roll motion, and its different features between the heave fixed and free conditions. Velocity maps were compared systematically to understand the heave and roll influences on the viscous effect for four motion conditions of all fixed, roll fixed and heave free, roll free and heave fixed, and roll and heave free. It is found that the heave motion has a significant impact on the viscous effect and the roll motion. The roll motion has the nonlinearity and the vortex strength was intensifying with the increase of the wave steepness at the natural roll period. The heave motion should be considered to estimate accurate roll damping and motion of floating structures.

Numerical Assessment of Roll Motion Characteristics and Damping Coefficient of a Ship

Accurate calculation of the roll damping moment at resonance condition is essential for roll motion prediction. Because at the resonance condition, the moment of inertia counteracts restoring moment and only the damping moment resists increase in the roll angle. There are various methods to calculate the roll damping moment which are based on potential flow theory. These methods have limitations to taking into account the viscous effects in estimating the roll motion, while, CFD as a numerical method is capable of considering the viscous effects. In this study, a CFD method based on a harmonic excited roll motion (HERM) technique is used to compute the roll motion and the roll damping moment of a containership’s model in different conditions. The influence of excitation frequency, forward speed and degrees of freedom at beam-sea and oblique-sea realizations are considered in estimating the roll damping coefficients. The results are validated against model tests, where a good agreement is found.

Linear and non-linear roll damping of a FPSO via system identification of a third order equation with sway-roll coupled damping effects

This work focuses on roll decay experiments performed on hulls normally used as FPSOs. Considering the practical case of beam seas, Newton's second law and the Newton-Euler theorem lead to coupled sway, heave and roll equations for an arbitrary pole. Assuming symmetry, the heave equation is uncoupled, leaving the sway and roll equations coupled. The research shows that, even if inertia is decoupled, damping coupling is unavoidable and cannot be neglected. Nevertheless, a third order equation dealing only with roll can be constructed. The latter is used to develop a robust approach that uses system identification techniques to obtain damping properties from the decay tests. In this approach, non-linear damping is assessed using a cycle-by-cycle linear approach that uses system identification to match all the information obtained from the decay test. Both held-over and pre-oscillation tests are discussed, and new concept is presented: the coupled damping number (CDN), which relates the product of the main diagonal damping terms with coupling damping coefficients. The CDN is proven to be null for potential flows, and turns out to be very small even when viscous effects are present such as in decay tests, at least for typical FPSO hulls.

Estimation of damping through internally excited roll tests

Roll damping represents a key factor for a proper estimation of the ship behaviour in a seaway. However, due to the typical dominance of viscous effects, accurately estimating roll damping is a challenging task. The most common experimental approach for determining roll damping parameters is based on the analysis of roll decays, although forced and excited roll tests in calm water or in waves have been used as well. This paper proposes a technique for estimating roll damping from internally excited roll tests in calm water. Tests are performed by exciting roll motion through an internal shifting mass. Roll damping parameters can then be determined from the analysis of the obtained roll response curves. The paper describes the experimental technique and a nonlinear mathematical model for representing the system dynamics. A procedure is proposed for determining roll damping coefficients, using, as a basis for the analysis, the developed mathematical model. A case study is reported where damping coefficients are determined for a trawler fishing vessel using the proposed technique. Obtained results are compared with those from standard roll decays analysis. For model validation purposes, the experimental roll response curves are also compared with those simulated through the developed mathematical model.

A Body-Nonlinear Green’s Function Method with Viscous Dissipation Effects for Large-Amplitude Roll of Floating Bodies

A novel time-domain body-nonlinear Green’s function method is developed for evaluating large-amplitude roll damping of two-dimensional floating bodies with consideration of viscous dissipation effects. In the method, the instantaneous wetted surface of floating bodies is accurately considered, and the viscous dissipation effects are taken into account based on the “fairly perfect fluid” model. As compared to the method based on the existing inviscid body-nonlinear Green’s function, the newly proposed method can give a more accurate damping coefficient of floating bodies rolling on the free surface with large amplitudes according to the numerical tests and comparison with experimental data for a few cases related to ship hull sections with bilge keels.

Numerical simulations of free roll decay of DTMB 5415

Computational fluid dynamics (CFD) that implement finite volume method are offering accurate and precise solutions for ship roll problem. In this study, the free roll decay of the benchmark DTMB 5415 hull with bilge keels in calm water was numerically solved by applying this type of code. Contributions of viscosity, wave, eddy and forward ship speed were separately investigated for ship roll damping and these were integral part of experimental setups. Numerical results were first validated with experiments. Additionally, mathematical derivations of ship roll response were used where experiments were impractical or inapplicable. Related literature still lacks a validation procedure. Therefore, a detailed analysis was made for the numerical estimation of roll damping. The weaknesses of CFD and the mathematical model were identified and discussed by comparing the obtained results. The results indicated that although the numerical simulations successfully captured the decay coefficients, these simulations lacked accuracy in calculating the natural roll frequency.

A Thrust Allocation Algorithm considering Dynamic Positioning and Roll Damping Thrust Demands using multi-step Quadratic Programming

This contribution presents a thrust allocation module for combined Dynamic Positioning and active Roll Damping of ships using solely its main propulsion system. To achieve the given thrust demands a multi-step optimization approach which considers the different spectral properties of the two regimes is proposed. Limitations of the thrusters, such as maximum thrust or rate constraints, are considered. The algorithm is tested on a set of artificial demands, which demonstrate the operating principle. A second setup shows the interaction of the allocation and the ship within a closed-loop Dynamic Positioning simulation. The results are promising and show that combined positioning and roll stabilization is possible with a single marine actuator system.

Roll damping of a surface effect ship with split air cushion

This paper considers linear modeling of a surface effect ship (SES) where roll motions are damped by exclusively exploiting a longitudinally split air cushion design. On a SES, the pressurized air cushions can support up to approximately 80 % of the vessels weight. By implementing a separating wall midships in the longitudinally direction, motion control of roll is possible. When the vessel is subject to wave-induced roll motions, the starboard and port air cushion pressures are controlled in anti-phase, reducing these motions significantly. The effectiveness of the scheme is demonstrated through model scale experimental testing carried out in the Towing Tank, NTNU, Trondheim.1

Analysis on Rolling Damping of a Conventional Boat fitted with T-shaped Bilge Keels

This work presents a numerical study on the effect of T-shaped bilge keels on the roll damping of a conventional boat. A scaled boat model with the same dimensions as that of Irkal et al. [2] was fitted with two T-shaped bilge keels at the edges of the model. Computational Fluid Dynamics method was employed to simulate the roll decay motion of the boat. The motion of the boat is captured using a 6DOF model and the Overset grid approach. Comparison was performed on the damping characteristics of the conventional I-shaped and the T-shaped bilge keels. In addition, the impact of the aspect ratio of the keel bilges on the roll damping of the boat was evaluated. It was found that the bilge keel aspect ratio influences the damping coefficient non-linearly. Sufficiently large aspect ratio, i.e. an aspect ratio greater than 2, is necessary in order to obtain an effective damping on the peak angle.

Effect of the Roll Center Position on the Roll Damping of a Ship Section

Effect of the Roll Center Position on the Roll Damping of a Ship Section

Numerical and experimental studies on dynamic gangway response between monohull flotel and FPSO in non-parallel side-by-side configuration

As an important equipment, gangway and its safety are crucial during offshore operation, and its dynamic response raises concerns especially when gangway is deployed between two free-floating structures. In this paper, the response of a passive telescopic gangway between monohull flotel and FPSO in nonparallel side-by-side configuration is investigated numerically and experimentally. The numerical model is established within the frequency domain, where the hydrodynamics are solved by 3D potential flow theory. The nonlinear factor, roll damping, is treated by using stochastic linearization. The connection between gangway and vessel is assumed to be an ideal joint, subsequently, gangway responses are derived by properly taking into account various motions of flotel and FPSO. Gangway responses such as its extension and rotation are presented in simulation as well as measurement. To interpret physics, firstly vessel global motions in single-body and multi-body cases are compared; then, relative motions between gangway points at flotel and FPSO ends are illustrated. Notably, the impact of multi-body hydrodynamic interaction is analyzed. The interaction triggers two types of couplings i.e. coupling between two vessels as well as coupling within one vessel such as coupled sway and pitch which does not exist in the single-body case. Therefore, the contribution of respective degree of freedom (DOF) of flotel and FPSO to gangway response are detailedly discussed. The simulation has generally good agreement with the model test. Most extra peaks or troughs observed in results those reflect hydrodynamic and mechanical couplings are well captured.

Numerical study of forced roll oscillation of FPSO with bilge keel

This work shows a study about the bilge keel and its influence, width and form, on the roll damping of FPSO sections. A computational code was developed to simulate forced roll oscillation of a middle section of FPSO with different bilge keels types. The computational code calculates the solution of the Navier-Stokes equations in 2D, using the finite volume method and the upwind TVD scheme of Roe-Sweby. The effect of wave radiation is neglected. This work shows how the generated vortices influence the pressure distribution around the middle section of FPSO. The numerical results are compared with experimental results to validate the computational code. New bilge keel configurations were studied to improve the roll damping of FPSO.

Application of advanced system identification technique to extract roll damping from model tests in order to accurately predict roll motions

In this paper our previously developed advanced system identification technique [1] has been applied to extract the frequency dependent roll damping from a series of model tests run in irregular (random) waves. It is shown that this methodology accurately models the roll damping which can then be used to produce accurate predictions of the ships roll motion. These roll motion predictions are not only more accurate than the potential flow predictions but more accurate than potential flow models corrected using either empirical prediction methods [2] and even those corrected using roll damping obtained from free decay sallying experiments. This methodology has the potential to significantly improve roll motion prediction during full scale at sea trails of vessels in order to dramatically improve safety of critical operations such as helicopter landing or ship to ship cargo transfer.

Simulation and analysis of Magnus rotating roll stabilizer at low speed

Magnus rotating roll stabilizer generates lift to stabilize ship roll motion through the rotating rotor wing at the bilge of ship hull based on Magnus effect. The present work aims to investigate its hydrodynamic characteristics and anti-rolling effect at low ship speed. The roll damping mechanism of Magnus rotating roll stabilizer is analyzed and its lift/drag characteristics are achieved using Fluent. For practical purposes, the numerical simulation results of lift/drag force to the rotation speed at certain ship speeds are analyzed. The calculation model of the anti-rolling force is established with the vertical velocity components caused by ship roll motion into consideration. The LSR-based third order polynomial fitting is adopted to fit the lift and drag data from numerical simulations. The comparison of Magnus rotating roll stabilizer with the equivalent fin stabilizer for a given ship is accomplished. Finally, the roll reduction system of Magnus rotating roll stabilizer with an improved PID controller is developed to demonstrate its effectiveness. The simulation results show that Magnus rotating roll stabilizer is suitable and effective for roll reduction at low speed.

Rudder-roll stabilization using fgs-pid controller for sigma-e warship

The aim of rudder-roll stabilization (RSS) is controlling ship heading and reducing roll motion simultaneously using one actuator, rudder. In this paper, RSS using FGS-PID for SIGMA-e warship was performed, both in normal and disturbed sea conditions. The fuzzy system for determining PID controller are constructed from SIGMA-e linear mathematical model. The wave disturbances are generated based on the WMO. The results show that FGS-PID has superior performance compared to conventional PID controller in heading control and roll damping. It means that the proposed control method can encounter the environmental changes.