Roll Damping Research Articles

An insight about roll damping within the second generation intact stability criteria

AbstractDespite the recognized complexity to estimate the damping influence on ship roll motion, some efficient semi-empirical methodologies have been developed along the years to this purpose. CFD methods, in principle the most appropriate tools to predict roll damping, are not a favorite option in preliminary design at present due to their implications in terms of complexity and computational time. In this paper, an integration of the semi-empirical Ikeda’s simplified method has been formulated with modification of the bilge keels and lift components, following a contribution found in the literature and relevant for Ro–Ro ships. Moreover, with focus on damping evaluation, the second generation intact stability criteria (SGISc) have been investigated: the second-level vulnerability criteria for dead ship condition and parametric roll have been applied to a Ro–Ro passenger ship. Both the consolidated and the new proposed roll damping prediction methods have been implemented in order to appreciate their effects on the final outcome.

Research on parametric roll of the polar environmental transport ship based on time-domain Rankine panel method

In this study, the roll damping of a polar environmental transport ship (PETS) is estimated using viscous CFD method, and the parametric roll is simulated based on time-domain Rankine panel method. This method's reliability is validated by contrasting the simulation results with the experimental data of C11 container ship. The roll damping of C11 container ship is estimated using CFD method and improved Ikeda's method, respectively. Then, the time-domain Rankine panel method is adopted to simulate the roll motions of C11 container ship, and the simulation results are contrasted with experimental data. It confirms that the roll damping is calculated by CFD method and the roll motions of ships are simulated based on time-domain Rankine panel method has good applicability. Finally, the influence of wave steepness, wavelength, and the ratio of encounter frequency ωe to natural roll frequency ωroll on the parametric roll of PETS are studied. It is found that the maximum roll angle of PETS increases along with wave steepness. As the wavelength increases, the possibility of parametric roll for PETS is also increasing. When the parametric roll of PETS occurs, the ωe/ωroll tends to increase.

Numerical Study on the Effect of Weight Variables on the Roll Damping Coefficients for a Fishing Vessel

Abstract The roll damping coefficient is essential when considering the viscous effect in the potential-based hydrodynamic analysis of fishing vessels; it is an important factor in the roll motion response. The present study performs free roll decay simulations, altering weight variables using Computational Fluid Dynamics (CFD) to investigate the correlation between the roll damping coefficient and the weight variation of a fishing vessel. The time series of roll amplitude and roll damping coefficient are compared, for varying vertical and longitudinal centres of gravity and radii of gyration in roll motion. As the vertical centre of gravity increases, both the roll decay period and the roll damping coefficient also increase. The roll decay period tends to increase with the increase in the radius of gyration during roll motion, while the roll damping coefficient exhibits a decrease. A longitudinal centre of gravity has a limited effect on free roll decay characteristics. The roll damping coefficients between the maximum and minimum combinations of weight variables show significant differences. The findings of the present study could enhance the understanding of the safety of fishing vessels based on their loading conditions. Consequently, future research could further improve the results obtained in the present study by considering various hull shapes and speeds.

Flight dynamics of aircraft incorporating the semi-aeroelastic hinge

Aircraft like the Boeing 777-X use on-ground folding wingtips to meet the airport gate size restriction while increasing the aspect ratio during flight to reduce induced drag. A recent concept of aircraft design is to utilise in-flight floating wingtips as a means of load alleviation, which is known as semi-aeroelastic hinge (SAH). This device allows wingtips to be released during manoeuvre and severe gusts to alleviate wing loads, while locking the wingtips during cruise to maintain an optimum aerodynamic shape. This paper develops a flight mechanics model incorporating flexible wings to study the influence of the SAH device on multiple aspects of aircraft flight dynamics. The dynamic responses of the aircraft to gusts and control surface inputs are computed and compared for various hinge and wingtip configurations and release times. It was found that the gust load measured from the wing with free hinge configuration was approximately 40% lower compared to that of the fixed hinge case. It is also shown that when the SAH is released, it can significantly reduce an aircraft's roll damping and the frequency of the short-period mode, leading to higher roll and pitch rates. Furthermore, it shows that the transient responses following the wingtip release will exacerbate the responses induced by gusts, and greater load alleviation can be achieved by manipulating the hinge release time for each gust length. Finally, a step input of the elevator during the hinge release was found to be beneficial for enhancing the gust load alleviation.

Numerical Investigation of Motion Response of the Tanker at Varying Vertical Center of Gravities

<i>The vertical center of gravity (VCG) has a significant impact on the roll motion response of a surface ship, particularly oil tankers based on the oil level in the tanker after discharging oil at several stations or positional changes, such as changes in the superstructure and deck structure. This study examined the motion response of the Korea very large crude carrier 2 (KVLCC2) at various VCGs, especially roll motion when the VCG changed. The potential theory in the Ansys AQWA program was used as a numerical simulation method to calculate the motion response. On the other hand, the calculations obtained through potential theory overestimated the roll amplitudes during resonance and lacked precision. Therefore, roll damping is a necessary parameter that accounts for the viscosity effect by performing an experimental roll decay. The roll decay test estimated the roll damping coefficients for various VCGs using Froude’s method. The motion response of the ship in regular waves was evaluated for various VCGs using the estimated roll-damping coefficients. In addition, the reliability of the numerical simulation in motion response was verified with those of the experiment method reported elsewhere. The simulation results showed that the responses of the surge, sway, heave, pitch, and yaw motion were not affected by changing the VCG, but the natural frequency and magnitude of the peak value of the roll motion response varied with the VCG.</i>

Bir Konteyner Gemisi İçin Kapsamlı Yalpa Sönümü Değerlendirmesi ve Hareket Analizi

The primary purpose of this study is to investigate the damping characteristics of the ship’s roll motion. The second goal is to explore the damping effects on the solution of roll motion, considering the ship’s forward speed, wave frequency, and initial roll amplitude. Roll motion is a more critical yet less understood response compared to other degrees of freedom due to the complexity arising from viscosity. Roll damping comprises several components, which are divided into five categories with the assistance of empirical formulas created as a result of experiments. Wave damping is calculated by linear diffraction/radiation theory so it is a linear damping. Lift damping is also considered linear. However, eddy making, skin friction, and bilge keel damping are not linear due to dependency on the initial roll amplitude. The effects of roll amplitude, the ship’s forward speed, and wave frequency are investigated in this paper with the empirical formulas developed by Ikeda and Himeno. Frequency domain analyses of the roll motion are also conducted for the selected cases to demonstrate the credibility of the proposed paper. All algorithms have been developed in the MATLAB environment which is embedded with the YTU DEEP Ship Motion Program.

Experimental and CFD analysis of roll damping of a wind turbine installation vessel

The global transition to renewable energy has put pressure on wind turbine installation vessels (WTIV), thus creating an urgent demand for optimizing their operation. This includes more accurate predictions of the ship motions at sea, at which roll motion is of particular interest. For accurate prediction of the roll motion, roll damping is important to consider and is commonly found from empirical methods if experimental data are not available. Since the hull geometry and loading conditions of WTIVs are significantly different from conventional ships the validity of existing empirical methods has not been justified. This paper studies an alternative approach of determining the roll damping, by utilizing CFD to simulate free roll decay of a WTIV, from which the roll damping can be extracted. A WTIV is simulated under different loading conditions, varying the vertical center of gravity and adding a bilge keel to study the influence on the roll damping. Model tests are carried out to validate the CFD simulations. CFD simulations are performed in both model scale and full scale. The implied extreme roll motions in irregular waves are compared with empirical methods. It is found that CFD can predict roll damping accurately and that roll damping decreases for high centers of gravity. The viscous scaling effects for a 2m long model is significant, causing too large damping in model scale. The investigated bilge keel reduced roll motions significantly. The empirical methods consistently overestimated the roll damping, especially near the resonant frequency.

Integrated design of lateral-directional control law and vertical tail load for civil aircraft

According to new requirements of airworthiness regulation CS25.353, the advanced lateral-directional P-Beta control law design is studied in this paper. The LQR method based on the tracking command model is used to design the lateral-directional control law parameters. At the same time, the vertical tail load model of aircraft for yaw maneuver is introduced into the lateral-directional control law design model. The aim is to build the integrated design of control law and flight load. Finally, the simulation results show that the P-Beta control law can not only improve Dutch roll damping and coordination turn characteristics, but it can also reduce the yaw maneuver load by 18.5%. Thus, the structure weight of the aircraft’s vertical tail can be reduced.

On the application of overset meshing to numerical studies of roll damping of hulls in complex scenarios

The application of computational fluid dynamics (CFD) and overset meshing, to predict the roll response of ships is of significant interest to ocean engineering. Despite its growing popularity, it remains essential to validate the efficacy of computations using overset meshing for modelling strong vortex flows, particularly in complex geometric scenarios involving relative motion and narrow gaps, and for deriving roll damping coefficients. This study presents a new series of results in which the solvers and overset meshing methods in the open-source CFD code, OpenFOAM, were applied to compute the vortex flow from sharp edges and the roll damping of hulls, including the particularly complex scenario of a hull rolling next to a solid vertical wall. It has been demonstrated that the methods can effectively model the intricate flow physics associated with flow separation, including the shedding of primary and secondary vortices, and reliably estimate damping coefficients. Further, the study provides suitable numerical configurations for overset mesh applications and new insights to explain the discrepancies between experimental and numerical results. These new results not only contribute to the understanding of wave-induced roll response but also reinforce the value of the overset mesh technique for the prediction of related problems in fluid mechanics.

Numerical study on damaged ship rolling and capsizing in irregular beam waves during quasi-steady flooding

To study roll dynamics and capsizing occurrence of damaged ship in irregular beam waves, computational fluid dynamics is used to simulate damaged ship motions at rough sea to high sea states. The velocity-inlet boundary and momentum source are combined for wave generation. A modified formula is adopted to calculate turbulent viscosity to prevent unphysical decay of wave. The lateral drift restrained model is integrated with a combined dynamic mesh strategy to handle the ship's sway, heave and roll motions. Benchmarking study of irregular wave generation and roll response of damaged ship in regular waves is performed. Based on the simulations of motions of intact and damaged ships in irregular waves, the effects of cross flooding and damage orientation on the roll response of ship are discussed. For symmetrical flooding, the roll behaviour of ship is insensitive to the damage orientation. Due to the increase of roll damping, the roll response of damaged ship is smaller than that of intact ship. For asymmetric flooding, the ship is liable to roll toward the damaged side with a large angle. The probability of capsizing of ship caused by waveward damage is high at high sea state.

Seakeeping Behaviour of a Flettner Rotors-Propelled Catamaran in Beam Waves

This paper deals with the seakeeping of a catamaran propelled by Flettner rotors. The case study is an energy ship. The prediction of the roll motion of such a ship is of particular interest since she will mostly sail in beam seas. We used a numerical model based on the boundary element method to deal with the interactions of the ship with waves. It is supplemented by a model for the aerodynamic damping effect due to the rotors, the gyroscopic effects from the rotors and by the ITTC correction for roll damping. In the present study, it has been assumed that the Flettner rotors can be modelled as a distribution of elementary airfoils whose lift and drag depend on the local apparent wind speed. Interaction effects between the rotors and between the hull and rotors have been neglected. Regular waves have been investigated. For the considered case study, it is found that the Flettner rotors can have a small destabilizing effect or a small stabilizing effect on the ship motion depending on the ship speed and the rotors’ rotational speed.

Eksperimentalno istraživanje o učinku položaja ljuljne kobilice na desantnim pomoćnim brodovima

The issue of energy efficiency in using fossil fuels and reducing the effects of greenhouse gas emissions is an urgent problem. So fuel-saving measures, including in the marine transportation sector, are needed, even if only by a small percentage. Landing Craft Utility (LCU) is a type of sea transport for defense matters that requires the addition of a rolling motion stabilizer for the safety and comfort of the ship, cargo, and passengers. The use of roll-damping devices can affect the increase in the resistance value of the ship and cause an increase in fuel consumption. The bilge keel is a roll-damping device that is suitable for LCU vessels. The experimental study roll decay tests and resistance tests were carried out to determine the effect of the bilge keel placement on roll damping and additional ship resistance. The flow around the vessel’s surface was observed with a paint smear test to determine the placement position. The bilge keel installed in the transitional position between the bottom and side hull has the highest total roll damping coefficient, up to 28.57%, compared to the bare hull condition. However, this placement has increased the average resistance up to 8.84%. Alternately, placement close to the draft line has a fairly good roll-damping coefficient of up to 21.27%, increasing the resistance to only 3.66%.

Severity assessment of sudden plunging motion for jet transport aircraft in response to severe atmospheric turbulence

PurposeThe purpose of this paper is to present a comparative study of flight circumstances, dynamic stability characteristics and controllability for two transport aircraft in severe atmospheric turbulence at transonic cruise flight for the purpose to obtain the prevention concepts of injuries to passengers and crew members for pilot training in International Air Transport Association (IATA) – Loss of Control In-flight (LOC-I) program.Design/methodology/approachA twin-jet and a four-jet transport aircraft encountering severe atmospheric turbulence are the study cases for this paper. The nonlinear unsteady aerodynamic models are established through flight data mining and the fuzzy-logic modeling technique based on the flight data of flight data recorder. This method can be adopted to examine the influence of horizontal wind shear and crosswind on loss of control, dynamic stability characteristics and controllability for transport aircraft in different weights and different sizes in tracking aviation safety of existing different types of aircraft.FindingsThe horizontal wind shear or crosswind before the turbulence encounter will easily induce rolling motion and then initiate the sudden plunging motion during the turbulence encounter. The roll rate will increase the oscillatory rolling motion during plunging motion, if the rolling damping is insufficient. The drop-off altitude will be enlarged by the oscillatory rolling motion during the sudden plunging motion.Research limitations/implicationsA lack of the measurement data of vertical wind speed sensor on board to verify the estimated values of damping term is one of the research limitations for this study. The fact or condition of being severe in sudden plunging motion can be judged through the analysis of oscillatory derivatives with both dynamic stability and damping terms.Practical implicationsThe roll rate will increase the oscillatory rolling motion during plunging motion, if the rolling damping is insufficient. The drop-off altitude will be enlarged by the oscillatory rolling motion during the sudden plunging motion. The horizontal wind shear or crosswind before the turbulence encounter will easily induce rolling motion and then initiated the sudden plunging motion during the turbulence encounter. If the drift angle is large, to turn off the autopilot of yaw control first and stabilize the rudder by the pedal. When passing through the atmosphere turbulence area, the pilots do not need to amend the heading angle urgently.Social implicationsThe flight safety prevention in avoidance of injuries for passengers and cabin crews is essential for the airlines. The horizontal wind shear or crosswind before the turbulence encounter will easily induce rolling motion and then initiated the sudden plunging motion during the turbulence encounter.Originality/valueThe flight safety prevention in avoidance of injuries for passengers and cabin crews is essential. The present assessment method is an innovation to examine the loss of control problems of aviation safety and promote the understanding of aerodynamic responses of the jet transport aircraft. It is expected to provide a valuable lecture for the international training courses for IATA – LOC-I program after this paper is being published.

Coherent solutions to roll damping derivatives evaluation for a generic rocket model

This paper presents a coherent approach to evaluate the roll damping derivatives for the standard Basic Finner Model. The study compares and analyses the results obtained through a range of techniques, including experimental testing, numerical simulations and semi-empirical models. The study aims to evaluate the reliability and accuracy of these methods and to identify the factors that contribute to their sensitivity. The paper concludes by summarizing the findings of the study and discussing the implications of the results for the design and operation of rockets. The experimental and numerical analysis used in this study provides a robust and comprehensive evaluation of the roll damping coefficient.

Probabilistic analysis of the instantaneous center of rotation of a floating structure under regular and irregular beam waves

Accurate prediction of roll motion is crucial to the safety of ships and floating structures. The “roll center” mentioned in the literature is ambiguous and various definitions exist. Hence, the instantaneous center of rotation (ICR) is preferred, being an established kinematic concept. Understanding the ICR is important on account of its significant influence on roll damping. A previous study postulated that the ICR moves in a straight line for regular beam waves, based on experimental observations. In this paper, the probability distribution of the ICR coordinates (y1, y2) is derived analytically for regular and irregular beam waves. For regular waves, it is proven a fortiori that the ICR lies on a straight line, and that y1 and y2 follow the Cauchy distribution, for which the mean and variance are undefined. For irregular waves, it is shown that the joint probability density of y1 and y2 is a bivariate Cauchy distribution, thus the iso-density contour lines are concentric ellipses. Regular and irregular wave experiments are performed to investigate realistic conditions. The analytical solutions are found to be quite accurate, notwithstanding some discrepancies arising from nonlinearities and experimental imperfections. The theoretical results presented herein have potential practical applications, for example since the ICR governs damping, the ICR distribution allows damping to be modeled as a stochastic process.

Estimation of ship roll damping and natural frequency using an extended Kalman filter applied to URANS output

Estimation of ship roll damping and natural frequency using an extended Kalman filter applied to URANS output

Roll Damping Measurements on Basic Finner Model Using Both Forced and Free Methods

Determination of aerodynamic damping coefficients has always been difficult due to the dynamic nature of measurements for both forced and free methods. Although aerodynamic damping identification is available since the 1960s, this testing capability is not available in most of the high-speed wind tunnels due to its complexity, although the aerodynamic damping coefficients are needed for every aerospace vehicle. Herein are presented the development of the rig for roll damping determination, which uses both free and forced methods in the working cycle; the calibration process using the basic Finner model with reference data; and the experimental results obtained. Also, considering the challenges for computational fluid dynamics to match the experimental results, numerical results are presented for the calibration points required for interpolation of the roll damping coefficient along a Mach number range. The calibration points cover all regimes from subsonic to supersonic at Mach numbers ranging between 0.4 and 3.5. Conclusions are presented, focusing on the comparison between forced and free methods, as well as the rotation direction, considering the flow deflection that is increasing the level of uncertainty.

Advances on numerical and experimental investigation of ship roll damping

Advances on numerical and experimental investigation of ship roll damping

Ship rolling equation: Comparison of the different damping models

In the paper, a comparison of the ship rolling numerical simulations results for four roll damping models is presented. In the first two models, constant damping coefficients are used, in linear and nonlinear notation. These damping models are commonly used, however have a significant disadvantage - the damping coefficients are independent of the roll amplitude and frequency. In the next two models, the damping coefficients are dependent on rolling amplitude and frequency and are implemented in roll equation with linear and nonlinear notation. The overall goal of the study is to test the effect of value and notation of damping on the results of the ship rolling numerical simulations. However, the main goal is to test if the damping dependent on roll amplitude and frequency will have an effect on ship rolling numerical simulations results. Comparison of roll damping models comprises three tests. The first two tests refer to the frequency response curve while the third test concerns the rolling equation unstable solution area. Research shows that the rolling equation is sensitive to the applied damping model and that the damping dependent on roll amplitude and frequency can have a significant impact on the results of ship rolling numerical simulations.

Formulation of ship roll damping models from free-decay data

Estimation of roll damping of a ship is essential to the prediction of its response in waves. The formulation of ship roll damping models from experiment or CFD data involves two parts: the determination of the model form and the calculation of the model coefficients, and both have significant influences on damping accuracy. To improve the roll motion prediction of a particular ship, this paper made an investigation of the typical damping models and its influence factors based on benchmark experiment data. The results show that the typical damping models can not reflect the fluid physics of roll motion. A conclusion is given that all roll angle, angular roll velocity, and angular roll acceleration should be considered in damping model determination. For the convenience of solving the roll motion equation, damping models with angle and angular velocity as independent variables are proposed due to the coupling of the angle, angular velocity, and the angular acceleration in roll. A procedure of damping model formulation is developed based on the Prony-SS method which was introduced into roll damping identification recently. Examples that follow the procedure show good performance. Furthermore, forward speed and flow memory effects on ship roll damping are discussed.