Roll Amplitude Research Articles

Experimental and numerical investigation on the influence of bilge keel shape on roll damping

Excessive roll amplitudes due to roll motion are undesirable in marine ships. Consequently, it is imperative to conduct a detailed analysis of roll motion and the associated roll damping characteristics. This study experimentally and numerically investigates the roll damping characteristics of bilge keels with various geometric shapes on a ship model under different roll amplitudes. By comparing the non-dimensional roll damping coefficients obtained from experiments and numerical analyses, it is observed that bilge keels with geometries differing from the conventional plate shape exhibit distinct roll damping coefficients. Specifically, bilge keels with sharper tip ends demonstrate higher roll damping coefficients. Based on these findings, it is recommended that the corners and tip end of bilge keels be sharpened to enhance the roll damping coefficient.

Transmission and Dissipation of Vibration in a Dynamic Vibration Absorber-Roller System Based on Particle Damping Technology

The research of rolling mill vibration theory has always been a scientific problem in the field of rolling forming, which is very important to the quality of sheet metal and the stable operation of equipment. The essence of rolling mill vibration is the transfer of energy, which is generated from inside and outside. Based on particle damping technology, a dynamic vibration absorber (DVA) is proposed to control the vertical vibration of roll in the rolling process from the point of energy transfer and dissipation. A nonlinear vibration equation for the DVA-roller system is solved by the incremental harmonic balance method. Based on the obtained solutions, the effects of the basic parameters of the DVA on the properties of vibration transmission are investigated by using the power flow method, which provides theoretical guidance for the selection of the basic parameters of the DVA. Furthermore, the influence of the parameters of the particles on the overall dissipation of energy of the particle group is analyzed in a more systematic way, which provides a reference for the selection of the material and diameter and other parameters of the particles in the practical application of the DVA. The effect of particle parameters on roll amplitude inhibition is studied by experiments. The experimental results agree with the theoretical analysis, which proves the correctness of the theoretical analysis and the feasibility of the particle damping absorber. This research proposes a particle damping absorber to absorb and dissipate the energy transfer in rolling process, which provides a new idea for nonlinear dynamic analysis and stability control of rolling mills, and has important guiding significance for practical production.

Numerical study on hydrodynamic interaction between two parallel surge-released ships advancing in head regular waves based on the hybrid method

This study examines the hydrodynamic interaction between two parallel surge-released ships in head regular waves. A hybrid approach combining potential flow theory and functional-decomposition URANS is used for an efficient and accurate simulation. The methodology involves a surge-released module, 4DOF motion equations, multiple coordinate systems, and a dynamic structured grid. Two ship models are used for validation, comparing numerical and experimental results in ship motions and wave loads. The analysis shows good agreement, with differences of less than 5 % in heave and pitch motions, less than 8 % in roll motions, and less than 15 % in total resistance and sway interference forces. Present study also observes consistent trajectories of the wave system between the two ships. The influence of surge motion and wave height on wave-ship-ship interaction is investigated, emphasizing the importance of considering surge motion in seakeeping performance and longitudinal separation. The occurrence of parametric roll in Ship B is accurately resolved by the hybrid method and the parametric roll amplitude is smaller under ship-to-ship interaction conditions. Wave-induced moments play a limited role in this phenomenon, while the dominating roll restoring moment exhibits a hardening effect. Accordingly, roll motion and moments remain relatively unchanged with increasing wave height, indicating the strong nonlinear nature of parametric roll.

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.

Probability density function of roll amplitude for parametric rolling using moment equation

For the ship stability estimation and ship design, it is helpful to know the probability of the roll amplitude exceeding a certain threshold. Therefore, it is necessary to obtain the probability density function of the roll amplitude. In this study, first, we derive the moment values of roll amplitude by combining the moment equations and the linearity of expectation. With this, we propose a method to estimate the probability density function of the roll amplitude by using the obtained moment values. The results of our proposed method are compared to those obtained from Monte Carlo simulations. When the higher-order cumulant neglect closure method is used, the moment values resulting from the moment equations are close to the results of corresponding Monte Carlo simulations. In addition, our proposed method for deriving the probability density function of the roll amplitude is validated by comparison with Monte Carlo simulation results. In conclusion, we can state that the proposed methods for deriving the moments and the probability density function of the roll amplitude are available for practical use cases.

Input saturated [formula omitted] optimal control to mitigate DTMB 5415 combatant roll motion using anti roll gyro stabilizer

Despite technological advances, rolling motion is the most critical motion for the stability and survivability of ships. This study examines the possibility of using Anti Roll Gyrostabilizer System (ARGS) as a control actuation system to mitigate the roll motion of the DTMB 5415. In the scope of conceptual study, state space model of the DTMB 5415 Combatant Warship has been obtained. Then, ARGS dynamics have been integrated into the roll motion dynamics. Parameters of the DTMB 5415 and actuator are identified from the literature. Comparing experimental and numerical studies in the literature have also expanded the damping term parameters in the equation of roll motion. However, a Monte Carlo analysis is carried out to define the preliminary parameters of ARGS. An actuator-saturated Linear Matrix Inequality (LMI) Full State-Feedback H∞ Optimal Controller is tested for this design iteration. The results are also contrasted with the requirements that military ships must meet. Ship roll amplitudes have significantly decreased (over 95% for various sea conditions) and have complied with STANAG 4154 standards. The 1 radian Precession Angle limit has not been overshot. Continuous and discrete-time control rules are implemented, thus demonstrating the applicability of this actuation and control method are shown.

Parametric Roll Motion Reduction of a Ship with a Passive Anti-Roll Tank

In this study, the influence of a U-tube passive anti-roll tank on parametric roll motion has been investigated as a mechanical absorber of a dynamic system. Specifically, this paper concentrates on how the initial conditions of a coupled roll motion and fluid motion in the tank act on the performance of an anti-roll tank. Parametrically excited roll motion was modeled as a single degree of freedom system incorporating heave and pitch effects by means of a time-varying restoring moment. Fluid motion in the tank was modeled as a single degree of freedom system. Coupled equations of motion were solved numerically and the results were presented in the time domain. Furthermore, the results were comparatively depicted as maximum roll amplitudes vs. initial values for a ship with and without an anti-roll U-tube tank.

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>

Requirements for the vessels operation at heavy-lift cargoes carriage

The approaches used by different classification societies to standardize calculated acceleration under ship motion during heavy lift cargoes transportation are analyzed in the paper. The methods of estimating the efficiency of securing devices of “non-standardized cargoes” carried on ships are investigated. The analysis of the parameters taken into account in determining the design accelerations at ship motion is carried out. Five representative vessels, which had previously carried heavy lift cargoes under different conditions, are selected. Computer modelling of these vessels motion at different course angles is performed in “SafeSea” programme, and calculated (conditional) amplitudes of motion regulated by the Rules of the Russian Classification Society are determined by “Stabedit” programme. The forced and own periods of onboard rolling are calculated in the specialised software complex “Anchored Structures” at variation of wave modes, loading states and values of metacentric height. The calculation results for representative vessels have shown a satisfactory matching of own and forced rolling periods. It is noted that in the range of 1.5 m ≤ h3 % ≤ 4.5 m for the considered intervals of metacentric height, in most cases the forced rolling periods are slightly longer than the own ones. Based on the results of the research, the recommendations for determination of rolling amplitudes of inland and mixed navigation vessels of “P”, “O”, “M”, “O-PR”, “M-PR”, “M-SP” classes carrying heavy lift cargoes are given. The proposals on standardised design acceleration at motion of a ship carrying heavy lift cargo are also given for the mentioned classes of ships. The results of the research are included in the draft Guidelines for the assignment of design acceleration at rocking of mixed (river-sea) and inland navigation vessels and safety margins of heavy lift cargoes securing systems, developed for the Russian Classification Society

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.

Pressure fluctuations preceding critical heat flux during subcooled flow boiling in a one-side heated mini-channel under rolling motion

This study investigates effects of rolling motion on pressure fluctuations leading to Critical Heat Flux (CHF) during subcooled flow boiling in a mini-channel. Experiments were conducted at rolling amplitudes of 15° and 25° and periods of 10 and 30 s under two mass flow rates. Results obtained in static and rolling cases were compared. The rolling case showed higher pressure fluctuations, leading to higher CHF values, compared to the static case. The rolling intensity was the highest in the case with a higher amplitude and a shorter rolling period, whereas it was the lowest in the case with a lower amplitude and a longer rolling period. Correspondingly, the pressure fluctuations and CHF followed a similar trend, with the highest values observed in the case with the highest rolling intensity. The pressure fluctuations in the rolling experiments were also found to increase with increasing power, particularly at high heat flux values.

Numerical investigation of departure from nucleate boiling for subcooled flow boiling in a rolling tube

A crucial issue in floating nuclear plants is the critical heat flux (CHF) under oscillatory conditions by ocean waves. CHF must be predicted considering the dynamic motion of the floating platform. We present numerical simulations for predicting the DNB (departure-from-nucleate-boiling)-type CHF of subcooled R134a flow in a rolling tube and provide physical insight into the dynamic flow behavior regarding the DNB, considering rolling amplitudes of 15°, 30°, and 40° and a rolling period of 6 s. The local wall temperature and void fraction depended mainly on the dynamic changes in the gravitational direction. Gravity had the effect of lowering DNB. The Euler force created a secondary liquid flow that somewhat reduced the liquid temperature at the heating wall during the rolling period, thereby enhancing the convective and quenching heat fluxes. Furthermore, the secondary flow rapidly increased the liquid area fraction at the overheated wall and decreased the temporarily increased wall temperature before DNB occurred. The secondary flow had the effect of increasing DNB. In this study, the effect of increasing the DNB value is greater than the effect of reducing the DNB value. The occurrence of DNB depended on sufficient cooling of the downward-facing wall during the rolling period.

Numerical Analysis of the Impact Parameters on the Dynamic Response of a Submerged Floating Tunnel under Coupling Waves and Flows

The Submerged Floating Tunnel (SFT) is a highly promising cross-sea transportation structure. Due to its body being suspended in water, waves and flows are the primary environmental loads it encounters. Existing numerical simulations have been based on potential flow theory, which fails to fully consider shear forces and the nonlinear characteristics of the flow field. To overcome this limitation, the Computational Fluid Dynamics (CFD) approach, relying on solving the Navier-Stokes equations, can be employed. In this study, we establish a CFD model for the SFT and analyze the impact mechanisms of wave-flow coupling on its dynamic response, considering parameters such as wave height, flow velocity, wave direction, and flow direction. With increasing wave height, the acceleration, mooring tension, and heave amplitude of the SFT significantly increase, and the nonlinear characteristics of its dynamic response become more pronounced. For example, when wave height, Hi, increases from 0.046 m to 0.138 m, the maximum value of dimensionless heave, δz/Hi, increases from 0.075 to 0.284, nearly quadrupling in magnitude. When waves and flows propagate in the same direction, the heave amplitude of the SFT increases compared to the case with waves acting alone, while sway and roll amplitudes decrease. Under conditions of higher flow velocity, the SFT displaces significantly along the direction of flow and water depth, deviating significantly from its original equilibrium position. At this point, the tunnel primarily experiences periodic forces due to vortex shedding, and the anchor chain on the downstream side remains slack. In scenarios where waves and flows propagate in opposite directions, both the maximum acceleration and mooring tension of the SFT increase significantly. For instance, the onshore tension of the cable, Fon, increases by 36%, while the offshore tension, Foff, increases by 89%.

Experimental and numerical study of the hydrodynamics of a flapping fin at zero speed

The flapping fins can be used as effective actuators of roll stabilizers at zero speed. They provide anti-roll torques to reduce the roll motion of ships in waves. The effects of roll amplitude, flapping frequency and aspect ratio on the hydrodynamic forces and moments at zero speed have been studied through experiments and numerical simulations. It is found that the forces and moments can be described using the added mass forces and damping forces respectively. Empirical formulas to calculate the forces and moments have been derived. The flapping frequency has no significant effects on the force coefficients and moment coefficients. The drag coefficients can be described by an exponential function of KC number, the added mass coefficients are the function of roll amplitude and aspect ratio due to the 3D flow separation.

Analysis of Roll Decay for Surface-Ship Model Experiments With Uncertainty Estimates

Abstract Roll decay of David Taylor model basin (DTMB) Model 5720, a 23rd-scale free-running model of the research vessel (R/V) Melville, is evaluated with uncertainty estimates. Experimental roll-decay time series was accurately modeled as an exponentially decaying cosine function, which is the solution of a second-order ordinary differential equation for damping coefficient of less than one (N < 1). The curve-fit provides damping coefficient (N), period (T), and offset. Roll period in calm water was dependent on Froude number (Fr) and initial roll angle (a). Roll decay data are from 76 runs for three nominal Froude numbers, Fr = 0, 0.15, and 0.22. The initial roll angle variation was 3 deg–25 deg. The natural roll period was 2.139 ± 0.041 s (±1.9%). The decay coefficient data were approximated by a plane in three dimensions with Fr and initial roll amplitudes (a) as the independent variables. Curve-fit results are compared to decay coefficient by log decrement and period from time between zero crossings. Examples demonstrate average values for a single roll decay event from log decrement are the same as values by the curve-fitting method within uncertainty estimates. The uncertainty estimate for the decay coefficient is significantly less by curve-fit method in comparison to log-decrement method. By log decrement, the relative uncertainty increases with decreasing roll amplitude peak; consequently, focus should be on the damping coefficient at the largest peaks, where the uncertainty is the smallest.

Front Crawl and Backstroke Sprint Swimming have Distinct Differences along with Similar Patterns Regarding Trunk Rotations

Background: Front crawl and backstroke share similar trunk rotating characteristics and tempt coaches to transfer teaching parts from one stroke to the other intuitively. However, the degree of similarity has yet to be determined. The coordination of the pelvis and the 7th cervical vertebrae (C7), during yaw and roll rotation, when sprint swimming front crawl, and backstroke was studied. Methods: Thirty-four swimmers were assessed on their performance in25m-sprint of each stroke. Using inertial sensors, each segment’s time series of angular displacement was calculated. Their amplitudes, mean autocorrelation values, max cross-correlation coefficient, phase lag, and relative power at the main frequency were analyzed. For all comparisons, the p-value was set to 0.05. Results: Pelvis yaw and roll and C7 roll amplitudes were greater at backstroke, C7 yaw was greater at front crawl. Autocorrelations ranged from 0.79 to 0.82 except for the pelvis at front crawl in yaw which was 0.72±0.16. Relative power at the main frequency ranged from 47% to 52% except for the yaw pelvis’ at the front crawl which was lower (32.81±14.09%). Backstroke had larger mean values in all cases and roll had larger mean values than yaw. Cross-correlation between the two segments yielded higher values at roll. At roll direction, the leading segment in the front crawl was the pelvis while in backstroke, it was the C7 which was true in all cases. In all cases, the coupling was slightly deviating from in-phase mode except from backstroke yaw which yield phase lag values of -13.35±1.14% of stroke cycle time. Conclusions: Although both strokes share similar characteristics their intersegmental coupling differs. The findings of the study imply that proper focus should be given to enhance only a positive transfer of learning between the two strokes.

An experimental study of stabilizing ordinary fishing nets (SOFNets) on a stationary SWATH ship seakeeping behavior under irregular waves

The present research aims to experimentally demonstrate the effectiveness of an innovative method for reducing the ship motions using Stabilizing Ordinary Fishing Nets that we call it SOFNets from now on. To this end, the influence of a range of SOFNets on the seakeeping behavior of a Small-Waterplane-Area Twin Hull (SWATH) ship in irregular waves is investigated physically in a towing tank laboratory. Understanding, controlling, and improving the seakeeping behavior of ships has always been a major concern of ship designers. As a result, various techniques have been utilized to stabilize ships, including the use of anti-rolling tanks, gyrostabilizers, and stabilizer fins, all three of which are bulky, heavy, and costly. These disadvantages have prevented many ships from using conventional rolling reduction methods. In contrast, the present idea, SOFNets, does not suffer from these shortcomings and can be used in any type of ship with any tonnage. The prepared model is tested in the towing tank of the National Iranian Marine Laboratory (NIMALA) using three different net samples in order to compare the behavior of those nets. This research has introduced for the first time the concept of using a SOFNets to reduce motion amplitude in waves. The length of the SWATH model was 2.1 m, and the tests were carried out according to the International Towing Tank Conference (ITTC) guidelines. The research findings for the SWATH ship indicate that the heave and pitch amplitudes in the head sea state were reduced by up to 21%, and the roll amplitude in the beam sea state was reduced by up to 36%.

Researches on the motion and flooding process of a damaged passenger ship in regular and irregular beam waves

The motion and flooding process of a damaged passenger ship in regular and irregular beam waves are investigated experimentally and numerically at zero forward speed. Experiments are carried out on the intact and damaged ship models with varied wave periods and different wave steepness in regular and irregular waves. The water height inside the damaged compartments and ship's roll are measured and compared to the numerical results from the potential flow method with a flooding model based on the modified Bernoulli's equation. Experiments are conducted to verify numerical method's capability of predicting ship's motion under unsteady condition in the irregular wave. The results indicate that the potential flow method can accurately estimate ship roll and internal water height, but it fails to capture the multi-frequency characteristic of wave height variation in large-wave-steepness cases. The flooding into the side damaged opening increased the period of ship's roll and the roll amplitude increased with increasing wave steepness in both ship states. The roll amplitude of the damaged ship is smaller than that of an intact one under same condition in both regular and irregular wave, although the maximum rolling angle can exceed the latter under certain conditions. More nonlinear effects throughout the flooding process, as well as unsteady effects in irregular waves, should be added to improve the accuracy of the numerical method.

A novel multi-module coupled algorithm for the wreck off-bottom simulation

This paper proposes a novel multi-module coupled algorithm for the wreck off-bottom simulation (MCAWOS), involving several structures, multiple mediums, and three modules: the wreck-soil interaction module, the lifting-buffering module, and the barge-cable coupled module. In the present algorithm, the finite element method, the potential flow method and the lumped mass method are integrated and used to simulate the off-bottom process. The dynamic response characteristics of a typical salvage case with rated lifting tensions are investigated. It is found that the salvage system in waves exhibits a special breakout phenomenon, where the wreck displacements increase abruptly, and uneven distributions of the lifting tensions are observed. Case studies are conducted to further ascertain the mechanism of the breakout. As the rated lifting tension increases, the salvage efficiency rises, while the maximum roll and pitch amplitudes of the wreck decrease. Meanwhile, larger rated tension may result in more waste in equipment lifting capacity, thus 229 ton is finally selected as the appropriate preset lifting tension. In addition, when the wave direction angle increases from 90∘ to 180∘, the maximum roll value of the wreck shows a roughly decreasing trend and the planar deflection of the salvage barge relative to the wreck decreases. However, the maximum values of pitch, yaw, lifting tension and Mises seabed soil stress show irregular fluctuations. Taking all dynamic indicators into account, the wave heading interval of 150∘ to 180∘ is expected to be an ideal operating window. Conversely the 105∘ case is a dangerous state.

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.