Roll Amplitude Research Articles

Risk Accident Analysis Due to the Effect of Wrong Loading on Ship Stability

In this study, the effect of laying and shifting load is considered as one of the main factors of ship safety. Ferry Ro-Ro that carry vehicles and passengers were chosen as the object of study with the assumption that the vehicles are not lashed. Safety measurement is carried out through static stability analysis with criteria limits IMO Intact Stability Code 2008 and PM44 2021 and dynamic stability with roll motion limitations due to beam sea to result quantitative risk assessment data. The wave height is taken from the waters of the Bali strait with a Beaufort scale conversion of BF1 to BF6. Because of the vehicle is not lashed, the vehicle is simulated to shift horizontally as far as 10% to stack onto the starboard, while the assumption of passenger movement is vertical and horizontal. The biggest heel angle due to the shifting load is 9 degrees when all loads are stacked on the starboard (G1). Analysis of the calculation of static stability shows that several conditions do not meet the criteria with the greatest Roll Amplitude value of 39.56 deg at BF6 4 m. In dynamic stability conditions through maxsurf motion, the safe wave height for Ferry Ro-Ro operation is up to BF4 1.14 m. The highest risk of ship capsizing occurs when operating on BF5 with wave heights above 2 m.

Predicting Intoxication Using Motorcycle and Head Movements of Riders Wearing Alcohol Intoxication Goggles

The movement of a motorcycle is one of the critical factors that influences the stability of the ride. It has been established that the gait patterns of drunk and sober people are distinct. However, drunk motorcycle (MC) drivers’ balance has not been investigated as a predictor of intoxication. This paper characterized and used MC and head movements, such as pitch and roll, to predict intoxication while riding. Two separate experiments were conducted to monitor MC and head movement. Male participants were recruited between the ages of 23 and 50 to participate in the study. Participants used alcohol intoxication goggles (AIG) to simulate blood alcohol content (BAC) while driving on a straight path. Placebo goggles were used for control. Results showed that pitch and roll amplitudes of the MC could distinguish drivers wearing placebo and AIGs, as well as the pitch and roll frequency of the head. Deep learning can be used to predict the intoxication of MC riders. The predictive accuracy of the algorithm shows a viable opportunity for the use of movement to monitor drunk riders on the road.

Formula omitted] optimal control of DTMB 5415 combatant roll motion by using active fins with actuator saturations

This paper aims to obtain mathematical model of the full-scope roll motion for DTMB 5415 Combatant Warship and provide an optimal control by using Active Roll Fin Stabilizer (ARFS) structures. The mathematical model of the warship and the actuator model have been obtained in according to literature. Furthermore, the damping term parameters in the equation of the roll motion have been extended by comparing experimental and numerical studies in the literature. In order to ensure the required control moment and roll damping ratio, ARFS section (NACA 0015) has been selected and the fin structure is designed. As a controller method, actuator saturated Linear Matrix Inequality (LMI) Based State-Feedback H∞ Optimal Controller has been used to stabilize the roll motion of the DTMB 5415 Combatant Warship with ARFS Structure. Moreover, the results are compared with the criteria that military ships should comply. Significant decrement (above 90% for different sea states) of the ship roll amplitudes have been occurred and met the standard of STANAG 4154. Fin angle saturation limit of 24 degree has not been reached. Control rule are carried out for continuous and discrete time domains with similar performances. Hence applicability of this actuation and control method have been stated.

Motion Response on The Water Ambulance Ship

In designing a ship, it is necessary to know the response of the ship's motion before sailing. The purpose of this research is to determine the ship's motion response to waves as well as ship speed in ship loading operational conditions. The method used in this study is the B-spiline mathematical equation and the strip theory method, with the help of ship motion software, which varies the ship's load by 100% DWT, 50% DWT, and 25% DWT. While the highest significant amplitude heave value occurs on a ship with 100% DWT conditions with a speed of 18 knots and a wave direction of 900, which is 2.70 meters, the highest significant value of amplitude pitch occurs on a ship with a condition of 25% DWT with a speed of 6 knots and a wave arrival direction of 1800, namely 1.10 degrees, and the highest significant value of roll amplitude occurs in ships with 25% DWT conditions with speeds of 18 knots with a wave arrival direction of 900, which is 3.42 deg. The research results detected at a speed of 18 knots for the significant amplitude heave value, the significant amplitude pitch value, and the maximum RAO value still meet the Nordforsk criteria.

A viscosity equivalent reduced-order method and its application to ship roll prediction

The prediction of ship roll response in waves is still a major issue. The widely used potential flow theory can provide the results in a short time. However, its accuracy is highly dependent on the correction of fluid-viscosity. Viscous-flow theory can simulate the fluid viscosity directly, but it is accompanied by high computational costs. This study proposes a viscosity equivalent reduced-order method (VEROM) for predicting ship roll motion to achieve a balance between computational efficiency and prediction accuracy. To shorten the simulation time, the method neglects the fluid viscosity, solves the Euler equation, and uses large-size compatible meshes. To improve the prediction accuracy, the viscous effect is corrected in the time domain based on the principle of viscosity equivalence. A new type of forced roll motion with gradually increasing roll amplitude was introduced to obtain the nonlinear roll damping property for different KC numbers. The effectiveness of the VEROM model was examined by comparing the predicted roll responses with the experimental measurements. It was found that the maximum prediction error was less than 11%. Concerning the simulation time, the VEROM model is 20 times faster than the traditional viscous-flow model. The reduce-order method is effective for the seakeeping performance assessment.

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.

Experimental and numerical investigation on anti-rolling performance of a DP semi-submersible platform based on thruster group biasing

For semi-submersible platforms equipped with dynamic positioning (DP) system, which has a small water-plane area and low metacentric height, roll motion will be affected by the lateral control force of the thrusters, causing a larger roll amplitude. In view of this problem, present paper proposes a thrust allocation method based on thruster group biasing. The thruster axial forces in group counteract each other while the normal force directions are opposite to form an anti-rolling moment, so that the roll damping can be enhanced without affecting the positioning performance in the horizontal plane. The roll stabilization mechanism is studied experimentally and numerically. A numerical wave tank based on computational fluid dynamics (CFD) method is established, verified and validated against the experiments. Both experimental and numerical results show that the thruster group biasing strategy can increase roll damping and reduce the roll motion of the platform by approximately 16% under the given sea condition.

A TRUSTWORTHY COMPUTATION OF THE TRANSITORY AND STATIONARY RESPONSES FOR THE SHIP ROLLING BY A MODIFIED MULTIPLE TIME SCALE METHOD

An important step in any analysis concerning the ship behaviour in waves is a reasonable accurate assessment of high roll amplitudes. The most commonly used way to estimate the roll oscillations is to solve a nonlinear differential equation with the roll angle as unknown. The nonlinearities refer to different ways of approximating the damping and restoring moments. The lack of exact analytical solutions and the inability of a numerical solution to highlight the influence of various parameters on the ship motion, leads to the need to use approximate analytical methods. Operating the benefits of a modified multiple time scale method recently proposed in the literature, we obtained the governing equations for the transition towards the stationary solutions, the first – order approximations for these solutions and the frequency – amplitude relationship. The accuracy of the analytical results derived in the paper was demonstrated by comparing them with the numerical results (considered to be exact). The agreement between the two was excellent for relatively small forcing amplitude and satisfactory for high level of them on almost the entire range of used values for excitation frequency, including the primary resonance domain.

Investigation on time-domain simulation and experiment of harmonic rolling of ultra-large container ship in waves

When an accident due to harmonic rolling occurs, loss will be huge, especially for ultra-large container ships (ULCS). In the paper, the time-domain method is adopted to study and analyze the occurrence of non-linear harmonic rolling phenomenon of ULCS and subsequent motion behaviors. Under the weakly scattering hypothesis, six-degree-of freedom(6-DOF) time-domain ship motion equation is established by employing impulse response function. The incidental wave force and the restoring force are obtained by pressure integrating on instantaneous wet surface, while the roll damping coefficient is obtained by experiment. An ULCS navigating in regular waves of various frequencies is numerically simulated and investigated by model tests. The characteristics and mechanism of harmonic rolling of the ship with different metacenter-heights, which sails in head and following waves of different periods, are studied and analyzed. The result comparison shows that the time-domain method used in the paper can predict the occurrence and motion amplitude of the harmonic rolling very well. Although the seaworthiness of ULCS is generally better than smaller ships, there is still the possibility of triggering the problem of harmonic rolling in real sea navigation. Thus, it is necessary to study and analyze during ship design.

Full-scale URANS prediction of a vessel's transverse stability in wind and waves under lifting condition

Predicting a vessel’s motion response is important for the design as well as evaluating its operability and sustainability. This is often performed in towing tanks through captive model tests in towing tanks. However, discrepancies exist between model-scale and full-scale results. Besides, quite often, the wind is not included in the test, resulting in unrealistic assumptions of static pressure and constant heeling lever from the wind. This paper presents a study on transverse stability under wind, waves, and lifting conditions, incorporating several series of URANS-based simulations in model-scale and full-scale. According to the results, scaling effects accounts for about 3~15% in terms of roll amplitudes and it seems to be both frictional-force-related and wave-frequency-dependent. Wind force exerts limited influence on the vessel’s transverse stability, however, in waves especially for longer wavelength, a wind of 25 m/s increases the roll amplitude up to 53% and it appears to be wave frequency-dependant. The correlation between roll motion and wind/waves/lifting is complicated but their combination produces way more influence than any individual factor alone, indicating none of them should be neglected.

Experimental study on heat transfer characteristics of LBE flow in a vertical tube under static and rolling conditions

The heat transfer characteristics of liquid metals get much attention because of their low Prandtl number. In this paper, the heat transfer characteristics of a heavy liquid metal (LBE) in a vertical circular test section under static and rolling motions are experimentally investigated. The results show that the additional forces induced by rolling motion cause a periodic change in the flow rate of the forced circulation. The rolling motion reduces the mean circulation flow rate, especially in the low flow rate region. The cycle-averaged heat transfer characteristics are significantly enhanced in the low Peclet number region (<2500). In the high Peclet number region (>2500), the cycle-averaged heat transfer characteristics are not significantly different compared to those under static condition. At low flow rates, flow rate oscillations may lead to counterflow. The amplitude of the Reynolds number oscillation, the cycle-averaged Reynolds number, the roll period and the roll amplitude jointly determine the cycle-averaged Nusselt number. The correlations under static conditions cannot predict the Nussle number under rolling conditions well. Therefore, a correlation is developed to analyze the heat transfer characteristics of LBE under rolling conditions. This study may contribute to the design and safety analysis of liquid metal heat transfer when applied to moving conditions.

Hull Form Optimization of Fishing Vessels by Adoption of Stern Wedge and Bilge Keel

The most recent ships incorporate a number of significant design enhancements to improve the vessel’s seaworthiness. Bulbous bow, bilge keel, stern wedge, stern tunnel, spray rails, and others are examples. A stern wedge is a small modification of the buttock lines aft of station 19 1/2. The use of this hull design feature on small high-speed planning craft for the purpose of improved powering performance is an accepted naval architectural practice. However, its use on fishing vessels is uncommon. A bilge keel is a marine gear that reduces the tendency for a ship to roll. Hull shape modifications such as bilge keel can potentially increase safety by reducing roll motions. These enhancements have not been adopted or evaluated on fishing vessels, despite the fact that they have been employed on seagoing ships. The installation of bilge keels on fishing vessels was found to have a significant influence on the roll motion of the vessels, boosting their safety and efficiency. When compared to normal trawlers, the installation of bilge keels increased roll period by at least 40% and reduced roll amplitude by 16%.

Computation of parametric roll amplitude using energy method considering non-linear transverse stability

Parametric roll is a rare stability failure in waves leading possibly to large roll amplitude, which can be estimated in one degree of freedom from energy considerations. A previous paper presented by the authors introduced such a method to calculate the steady state roll amplitude on monochromatic longitudinal wave when the encounter period is twice the natural roll period, which is the resonance condition. This paper proposes an extend of this method to any ship's speed. It aims to propose an alternative to one-degree-of-freedom simulations in head seas. The extended energy method is applied to several vessels chosen for their different vulnerability to parametric roll. Results are compared with the ones obtained in a one-degree-of-freedom time domain simulator. The energy method provides an accurate estimation of the steady state roll amplitude at any speed within the range where parametric roll occurs.

Comparative Biomechanics of Canine Agility

Agility is a sport in which dogs compete on an obstacle course for both accuracy and time. Dogs that participate in competitions must negotiate a complex course of approximately 20 obstacles. We describe a literature review of the biomechanics of canine agility and our preliminary results. The number of articles that have reported biomechanics of canine agility has gradually increased since 2010. Most previous studies have focused on the bar jump, which is a basic obstacle to agility. In our preliminary study, we investigated the roll motion of the head and trunk using inertial sensors for Border Collies that completed weave poles (obstacles in which dogs weave through approximately 10 poles placed 0.6 m apart in a straight line). The roll angles of the head and trunk were measured based on the angular velocity and linear acceleration data using a sensor fusion algorithm. The head and trunk rotated about the roll axis nearly in unison. The roll amplitude of the head was lower than that of the trunk. We discuss the importance of biomechanical studies on canine agility to gain a deeper understanding of mammalian quadrupedal locomotion.

Experimental performance assessment of geometric hull designs for the E-Motions wave energy converter

E-Motions is a low-cost and versatile/adaptable wave energy converter conceived towards harnessing energy from wave/wind-induced roll oscillations of floating platforms. This paper focuses on a recently conducted parametric physical modelling stage with three hull designs (half-cylinder, half-sphere and trapezoidal prism), which features a disruptive Power Take-Off reproduction. Free decay, inclining and free-fall tests denoted a good agreement between the physical model's properties and the estimates. Parametric regular waves tests yielded data regarding reflection and transmission coefficients, while large peak-to-peak roll amplitudes (nearly 80°) were measured for the half-cylinder and, to a lesser extent, the half-sphere. Peak reduction was observed under resonant conditions, with the introduction of the Power Take-Off, to which adds a motion phase difference between it and the floating platform. On power output, the half-cylinder and half-sphere yielded the highest capture width ratios and power values per metre of device (nearly 0.8 kW/m, in prototype values) and per displaced volume (up to 0.08 kW/m3). Albeit sufficient for supporting some marine activities, these values can be bolstered, in the future, either through alternative mass/damping combinations or stacking various rows of generators. Maximum mean-to-max power ratios reached a value of 11, within the standard literature range, from literature.

Research on Influence of Tank Sloshing on Ship Motion Response under Different Wavelengths

The motion of the liquid-carrying ship under waves is simultaneously affected by the external wave moment and the sloshing moment of the internal tank, which makes the motion of the ship more complicated. In order to explore the influence of tank sloshing on the ship motion response, the motion of the ship model with tanks at different wavelengths were simulated based on the CFD software. This paper is based on the finite volume method (FVM) to solve the RANS (Reynolds averaged Navier-Stokes) equation for numerical simulation, and the VOF (volume of fluid) method was used to capture the free surface. Using the VOF method, it is necessary to ensure that the mesh at the free surface is sufficiently fine. Based on the above conditions, the pitching motion and rolling motion of the liquid carrier in the head sea condition and the transverse wave condition were simulated, respectively. The results showed that the sloshing of the tank has little influence on the pitching motion but has a greater influence on the rolling motion. When the liquid loading rates were 0, 0.8, 0.9, and 0.98, the pitch angle changes of the ship under different wavelengths were basically the same. However, when the liquid loading rates were 0, 0.4, and 0.8, the roll angle of the ship varied greatly under different wavelengths. By simulating the roll free decay motion of the liquid carrier (the loading rates were 0, 0.2, 0.4, 0.6, 0.8 and 0.98), it was found that the essence of the sloshing effect of the tank is to change the amplitude of the ship’s rolling motion by changing the natural frequency of the ship’s rolling motion. The closer the incident wave frequency is to the natural frequency of the roll of the liquid carrier, the greater the roll amplitude of the ship.

Numerical simulations of the spread of point‐source liquid spills in inclined and rolling rectangular packed beds

AbstractLiquid spreading in thin rectangular vertical/inclined and oscillating porous media was simulated using a two‐fluid dynamic model as a preliminary step in the design of fixed‐bed reactors dedicated to marine applications. The model assessed the influence of capillary pressure and mechanical dispersion forces arising from the spatial inhomogeneity of point‐source liquid injections in packed beds with different particle sizes, liquid and gas flow rates, liquid viscosity, static bed tilts, and rolling amplitudes and periods. In mildly static inclined beds, the lateral gravity force component and the capillary pressure force were the main factors affecting the liquid spreading. However, at considerable bed inclinations, the liquid phase accumulation in the lowermost regions of the packed bed tended to shrink the liquid spreading. Dynamic oscillatory evolutions of the liquid spills in the rolling bed enlarged the liquid spreading length as compared to the static vertical bed due to combined lateral liquid flow and increased liquid residence time.

CFD database method for roll response of damaged ship during quasi-steady flooding in beam waves

A database method is proposed to predict the roll response of a damaged ship upon quasi-steady flooding in regular beam waves. To construct the hydrodynamic database, the hydrodynamic loads acting on the damaged ship are decomposed into wave excitation moment and motion-induced moment, which are calculated based on computational fluid dynamics (CFD). The wave excitation moments for different wave frequencies are formulated using the high-order trigonometric function. The ship hydrodynamic coefficients (i.e., added moment of inertia and damping coefficient) for different roll frequencies and amplitudes are regressed from the motion-induced moment and then used as samples for database construction by cubic spline interpolation. The Runge-Kutta method is employed to solve the ship's roll motion equation, in which the hydrodynamic coefficients are updated according to the roll amplitude in real time. To test the performance of the present method, the roll motion responses of a damaged frigate DTMB-5415 are computed. The results obtained by the database method are in good agreement with the CFD results and experimental data. The characteristics of motion-induced moment, roll hydrodynamic coefficients and wave excitation moment are analyzed. In addition, the influence of various factors (e.g., sensitivity of mesh and time step, order of regression method, interval of sample points and type of load decomposition model) on the computation accuracy are also discussed. Compared to directly performing CFD simulation of damaged ship motion in waves, the proposed database method can predict the ship's roll response with high efficiency and acceptable accuracy.

Study on extreme roll event with capsizing induced by pure loss of stability for the free-running ONR Tumblehome

International Maritime Organization (IMO) has stated that the direct assessment for the pure loss of stability, one of the typical stability failure modes, is necessary for ship designers and under development currently. In this study, extreme roll motions with large amplitudes, induced by the pure loss of stability, are predicted for a benchmark combatant ONR Tumblehome running in stern quartering waves by the computational fluid dynamics (CFD) simulations. An unsteady Reynolds-averaged Navier–Stokes (RANS) solver coupled with a dynamic overset grid approach is used to predict six degree of freedom (DOF) motions. The discretized propeller model is applied to the free-running model, along with a course keeping controller. Different speed conditions are considered for the ship to investigate the instability zone where the pure loss of stability occurs and the CFD results for the roll amplitude are compared with the experimental data, with an average difference less than 3%. In addition, it is observed that ship capsizing occurs coupled with a rapid increase of yaw angle, which is consistent with the phenomenon in the existed model tests. Overall, it indicates that this viscous simulation model is capable for the prediction of the extreme roll as well as the capsizing.

HULL OPTIMISATION OF FISHING TRAWLERS USING ULSTEIN X-BOW AND BILGE KEEL

The most recent ships incorporate a number of significant design enhancements to improve the vessel's seaworthiness. Ulstein X-bow, bulbous bow, bilge keel, stern wedge, stern tunnel, spray rails, and others are some examples. Increasing the vessel's speed while lowering energy consumption necessitates lowering the vessel's resistance. Improved propeller efficiency and reduced vibrations can be achieved by optimizing the hull form. Hull shape modifications can potentially increase safety by reducing roll motions. These enhancements have not been adopted or evaluated on fishing vessels, despite the fact that they have been employed on seagoing ships The X-bow was discovered to be a feasible design upgrade, with a stem angle range of 6-8 degrees and the lowest resistance offered by a 10- degree stem angle. Also adding bilge keels to a fishing trawler resulted in a 40 percent increase in roll period and a 15% reduction in roll amplitude