Large Amplitude Roll Research Articles

Rolling table centrifuge modelling of partially saturated granular material to inform on instability during solid bulk cargo transport

The response of partially saturated granular cargoes during maritime transportation has resulted in the capsize and sinking of 27 bulk carriers at sea and the loss over 90 seafarers’ lives in the last decade. The partially saturated granular material response to energy imparted during cargo loading, ship engine vibrations and vessel rolling motions from sea states causes a change in state of the granular cargo, which can lead to vessel instability and ultimately capsize. However, the mechanisms driving the response of partially saturated granular cargos within a bulk carrier hold are not well understood. This paper presents results from an experimental study of rolling table centrifuge model tests on a partially saturated silica sand to contribute to improved understanding of the response of granular cargoes during maritime transport. Observed settlement, pore pressure, moisture content and density changes during and/or following a sequence of large amplitude rolling motions are presented. The results indicate that for the conditions considered, a progressive upwards migration of pore water during rolling led to creation of a free surface of water above the granular sample that was left in a denser, lower moisture content sample compared to its initial state. Sloshing of free water on top of even a competent cargo during rolling motions of the ship can contribute to loss of ship stability and ultimately capsize.

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

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

Research on the sloshing characteristics of the ship tank with baffles under rolling motion based on smoothed particle hydrodynamics method

The problem of liquid sloshing is widespread in the field of naval architecture and ocean engineering. During the sloshing process, the liquid will produce a large slamming force on the bulkhead. At the same time, the coupled sloshing of the liquid in tank and the hull will also affect the floating state and stability of the hull, and even induce safety accidents. The tank sloshing simultaneous with baffles and under rolling excitation is particularly focused in this paper, which is rarely concerned preciously. Based on the theory of fluid dynamics, the program of tank sloshing under large-amplitude rolling conditions by the smoothed particle hydrodynamics method is compiled, and the accuracy of the numerical model is validated through existing experimental results. Furthermore, the slamming pressure and the wetted height of the tank wall are studied for the cases of different excitation amplitudes and excitation frequencies. Then, the dynamic response characteristics of the sloshing tank with vertical and horizontal baffles are studied, and the effects of different baffle lengths are analyzed. The result shows that under rolling excitation the vertical baffle longer than the water depth can mitigate sloshing to some extent, but the vertical baffle whose length is less than the water depth and the horizontal baffles cannot play a role in mitigating the sloshing.

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

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

Numerical study on motion responses and added resistance for surge-free KCS in head and oblique waves based on the functional decomposition method

A hybrid approach of potential and viscous flows is developed, based on the functional decomposition model SWENSE (Spectral Wave Explicit Navier-Stokes Equations), to investigate the seakeeping performance of the surge-free ship models accurately and efficiently. In the SWENSE method, the total physical field, including velocity, pressure and the signed distance function of the free surface, are decomposed into the incident field and the complementary field. For the incident wave field, the linear wave model is used and the physical field is extended to the flows up to the air zone using the Wheeler stretching method. With respect to the complementary field, the variables are governed by SWENSE. The adapted single-phase level-set model is used to capture the free surface. Based on this hybrid approach, an in-house code HUST-SWENSE is developed. The spring-mass-damper module, 4DOF (Degrees of Freedom) motion equations of the rigid body, three coordinate systems and the dynamic structured grid with the overset technology are applied to deal with the 4DOF ship motions. Firstly, the size of the computational domain for the simulations of the oblique waves is discussed. The numerical results can be convergent for HUST-SWNESE when the radius R/L of the cylindrical computational domain is larger than 2.0. After determining the grid system and the time step based on the verification and validation study, simulations are conducted using the HUST-SWENSE to predict the surge, heave, roll, and pitch motions of the KCS in regular oblique waves. Wave conditions are based on the benchmark cases provided by the Tokyo2015 CFD workshop. The simulated results are then compared with experimental data and other numerical results. The comparison shows that the respective differences were less than 2% for incident regular waves, 10% for heave and pitch motion responses, 5% for roll motions and 20% for added resistances. Therefore, the HUST-SWENSE model can be considered reliable for the prediction of ship motions and added resistance in head and oblique waves. Finally, the influences of different DOFs, wavelengths and wave heights on the motions and added resistance for the surge-free ship model in oblique waves are investigated in detail. It is found that the importance of surge motion in the seakeeping performance prediction of the ship in astern seas, especially for the added resistance. Moreover, the nonlinearity of wave heights is analyzed, and the results indicate that the nonlinearity of the large-amplitude roll is mainly induced by the roll restoring moments, while the nonlinear features of the incident, radiation and diffraction wave systems were responsible for the nonlinearity of added resistance and surge motions.

Deep learning machine based ship parametric rolling simulation and recognition algorithms

In this work, we propose a “grey box” algorithm consisting of a deep learning network and parametric roll equation to provide the parametric roll simulations. A basic unsupervised method——principal component analysis is introduced into this algorithm to improve efficiency and accuracy. Besides, it has been proved that different wave time histories generated by the same wave spectrum will induce very different parametric rolling behaviors. Thus, we also proposed an algorithm that combines the deep learning method with spectral analysis to recognize the wave time histories that induce large amplitude rolling. A convolution layer and a pooling layer are added to the recognition network to reduce the input dimension. Besides, according to our study of training methods, we have found that extreme learning machine performs much better than back propagation network. Using the principal component analysis technique and the “grey box” based extreme learning machine, we can obtain very accurate simulations of the parametric roll of the C11 container ship in a short time. Besides, by using the spectral analysis and the extreme learning machine with convolution and pooling layer, we can accurately recognize the time histories induce large-amplitude parametric roll of the C11 container ship.

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

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

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

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

Modeling of two-phase refrigerant distribution in brazed plate heat exchangers

This paper presents a mechanistic model that predicts two-phase refrigerant distribution in brazed plate heat exchangers. The modeling of two-phase distribution is based on the flow visualization in the inlet header, in which the flow regime is identified to be periodic and one cycle includes two or three flow stages, given a fully developed stratified/stratified-wavy flow is present at the heat exchanger entrance. To predict the vapor refrigerant distribution, this model considers two different flow stages in the inlet header: for the top corner vapor flow, the vapor refrigerant distribution is predicted by the balance between the suction force (radial pressure gradient) and the axial momentum of each phase; for the vapor jet flow, the vapor refrigerant is assumed to be distributed evenly among the channels. The time ratio of the two flow stages is estimated by assuming the irregular large-amplitude rolling waves in the feeding tube, which lead to the vapor jet flow in the header, to have the most dangerous wavelength and their traveling time can be related to the liquid slug frequency. The apparent vapor refrigerant distribution is the time average of the vapor distributions at the two stages. For the liquid refrigerant distribution, it is predicted by imposing an equal total pressure drop for each flow path. The proposed model is validated against the experimental results: quantified two-phase refrigerant distribution, heat exchanger capacities, pressure profiles in the headers, and surface temperature of the sidewalls.

CONTROLLING THE PARAMETRIC ROLL OF A CONTAINER SHIP MODEL BY CHANGING THE HEADING ANGLE

Parametric roll on ships is an auto-parametric resonance phenomenon whose onset causes a sudden rise in roll oscillations leading to dangerous situations for the ship, the cargo and the crew. In the paper, we have numerically investigated the effect of modifying the heading angle on the roll amplitudes. We followed three strategies. In the first, we allowed the heading angle to decrease with a constant angular acceleration so that the encounter frequency has left the dangerous region of the resonance. However, this option involves changing the course of the ship in the long run, which is of course a shortcoming. In the second strategy, we changed the heading angle up and down around an average value that generates large roll amplitudes, by using different periodic sinusoidal or triangular profiles. The beneficial effect of this action is to keep the course, even if at the cost of a momentary delay. We noticed that both control techniques listed above generally managed to significantly reduce the roll amplitudes if certain thresholds have been exceeded. As a last idea for decreasing the parametric roll amplitudes, we used the combined effect of ship forward speed and heading angle change.

Nonlinear vibration analysis of the large-amplitude asymmetric response of ship roll motion

Ship roll motion is the single most important factor responsible for ship capsizes. Yet, there is still much to be understood about this subject; especially, how critical parameters influence the asymmetric response during large initial roll amplitudes. Consequently, this paper presents an investigation of the nonlinear vibration of the large-amplitude asymmetric response during ship roll motion. The dynamic model governing the roll motion accounted for quadratic damping and cubic nonlinear restoring moment with softening behaviour. The continuous piecewise linearization method was adopted to solve the governing model. Hence, the effect of four critical parameters (i.e. initial roll amplitude, added mass, quadratic damping and nonlinear restoring moment) on the asymmetric roll response and capsize tendency was investigated. It was observed that capsize tendency was strongly linked to the offset of the equilibrium point and the asymmetric response, which amplified the initial roll amplitude. An increase in the initial roll amplitude or quadratic damping produced a stronger asymmetric response and an increased capsize tendency, while an increase in the added mass or nonlinear restoring moment weakened the asymmetric response and decreased the capsize tendency. Also, an increase in any of the four critical parameters produced a decrease in the frequency of vibration.

Numerical and experimental investigation of sloshing under large amplitude roll excitation

Numerical and experimental investigation of sloshing under large amplitude roll excitation

Opening the air‐chamber of an oscillating water column spar buoy wave energy converter to avoid parametric resonance

The oscillating-water-column (OWC) spar-buoy is a type of wave energy converter that may exhibit undesirable large roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. The occurrence of this phenomenon not only reduces the power extraction but significantly increases the structural loads on the buoy, the turbine rotor and on the mooring system. The paper compares the parametric resonance behaviour of two configurations of an OWC spar-buoy using experimental data obtained in a wave flume at a scale of 1:100. The configurations investigated were: (1) closed and (2) fully open-air chamber. The experimental tests covered a wide range of regular and irregular waves, as well as in free decay experiments. Results showed that opening the air chamber reduces the coupling between the buoy and the OWC within, thus shifting the damped natural heave frequency of the system in comparison with the closed chamber configuration. This effect changes parametric resonance characteristics of the two configurations due to the coupling between roll/pitch and heave modes. Moreover, for specific wave frequencies, the occurrence of parametric resonance observed when the chamber is closed do not occur while the air chamber is fully open. These results suggest the possibility of controlling a pressure relief valve installed on top of the device to reduce parametric resonance whenever this dynamic instability is detected.

Effect of aerodynamic force change caused by car-body rolling on train overturning safety under strong wind conditions

Understanding the relationship between car-body vibration and train aerodynamic forces is very important for developing a reasonable operation plan when the train passes through the complex terrain under strong wind conditions. In this study, car-body vibration under strong wind conditions was initially investigated with a full-scale test. Then the train aerodynamic forces for different rotation configurations with a train speed of 250 km/h and a wind speed of 25 m/s were further studied using a Computational Fluid Dynamics simulation. The results revealed that the car-body vibration was primarily a low-frequency and large-amplitude rolling and transverse coupling motion in windy conditions, and the roll angle of the car-body with respect to the bogie frame was greater than that of the bogie frame with respect to the track. The train aerodynamic force coefficients are sensitive to the car-body rolling motion in windy conditions. When the car-body rolling from the windward side to the leeward side, the significant reduction in the negative pressure at the bottom of the car-body was the dominant reason for the train lift force increase, and the effect of the aerodynamic force change caused by car-body rolling on the train overturning risk was not significant.

Controlling the parametric roll of a container ship model by changing the forward velocity

Parametric roll on ships is a resonance phenomenon whose onset causes heavy roll oscillations leading to dangerous situations for the ship, the cargo and the crew. It affects both small vessels with marginal stability and large container ships if four conditions are met simultaneously: the wave length and ship length are approximately equal, the frequency of encounter wave is twice the roll natural frequency, the ship’s roll damping is low enough and the wave height exceeds a limit value characteristic to each vessel. A good start to capture the basic features of the parametric roll is to cancel the couplings between roll and the other motions of the ship and to analyse the influence of parameters on the ship stability and the appearance of large roll amplitudes by using one-degree-of-freedom model. By doing this, one realizes that, besides increasing the damping, the roll motion can be stabilized by changing the wave encounter frequency in such a way that the resonance condition is no longer fulfilled. Two parameters mainly affect the encounter frequency: the ship forward velocity and the heading angle. In the paper, we have numerically investigated the effect of increasing or decreasing the forward speed on the roll amplitudes. We followed two strategies. In the first, we allowed the speed to change with a constant acceleration (positive or negative) so that the encounter frequency has left the dangerous region of the resonance. In the second strategy, we changed the forward speed up and down around a value that generates large roll amplitudes, by using different periodic profiles such as sinusoidal, saw tooth or trapezoidal. We noticed that both control techniques generally managed to significantly reduce the roll amplitudes (with a few exceptions). At the same time, we found that very important in how the amplitudes diminish are parameters like the moment of time when the control is activated, the speed rate of change or the period and amplitude of the speed change around the average value (in the second strategy). The data used in the paper have been obtained from experiments with a container ship model in a towing tank followed by expansion to a full scale ship.

Detecting parametric resonance in a floating oscillating water column device for wave energy conversion: Numerical simulations and validation with physical model tests

The wave energy sector has faced enormous technological improvements over the last five decades, however, due to the complexity of the hydrodynamic processes, current numerical models still have limitations in predicting relevant phenomena. In particular, floating spar-type wave energy converters are prone to large undesirable roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. Detecting this phenomenon accurately is essential as it impacts drastically on power extraction, structural loads and mooring forces. This paper presents the validation of results from a numerical model, capable of detecting parametric resonance, using experimental data. Experiments were carried out for a scaled model of the Spar-buoy OWC (Oscillating Water Column) device at a large ocean basin. The buoy uses a slack-mooring system attached to the basin floor. The scaled turbine damping effect is simulated by a calibrated orifice plate. Two different buoy draft configurations are considered to analyse the effect of different mass distributions. The numerical model considers the nonlinear Froude-Krylov forces, which allows it to capture complex hydrodynamic phenomena associated with the six-degree-of-freedom motion of the buoy. The mooring system is simulated through a quasi-static inelastic line model. Real fluid effects are accounted for through drag forces based on the Morison’s equation and determined from experimental data. The comparison of results from regular-wave tests shows good agreement, including when parametric resonance is detected. Numerical results show that parametric resonance can produce a negative impact on power extraction efficiency up to 53%.

Review of self-induced roll oscillations and its attenuation for low-aspect-ratio wings

Micro aerial vehicles are currently receiving growing interest because of their broad applications in many fields. In their flight tests, the onset of unwanted large amplitude roll oscillations was reported, which resulted in difficulties with flight control, and this has become one of the major challenges of current micro aerial vehicles design. In this review type of article, the low Reynolds number flow characteristics of a low-aspect-ratio wing are reviewed, and the self-induced roll oscillations are discussed with special attention being payed to the interaction between the three-dimensional flow structure and wing in reciprocatively rolling motion. The roll attenuation methods are introduced via flow control approaches, which can suppress the roll oscillations effectively by manipulating the leading-edge flow separation and tip vortices of the low-aspect-ratio wings.

О численном моделировании поверхностных волн в бассейне с подвижными непроницаемыми границами

Представлены результаты, связанные с разработкой вычислительного алгоритма для изучения поверхностных волн в областях с подвижными непроницаемыми границами (подвижные боковые стенки бассейна, подвижные фрагменты дна). Алгоритм основан на конечноразностной аппроксимации на подвижных сетках двумерной модели потенциальных течений несжимаемой жидкости со свободной границей. Предложены новые начальные данные для задачи о движении уединенной волны, неотражающие условия, способ задания нулевого итерационного приближения для расчета потенциала скорости и результаты исследования устойчивости численного метода. Показано, что поверхностные волны, вызванные подводным оползнем, существенно влияют на процесс наката на берег одиночной волны и могут увеличить ее максимальный заплеск. In numerical simulation of fluid flows with a free surface, the most difficult problems are those in which not only the free boundary is mobile, but also some other parts of the boundary of the region occupied by the liquid. For example, these are the problems of surface waves caused by underwater and coastal landslides, the generation of waves by wavemakers in laboratory flumes and tanks, the problem of waves runup on the shore, the interaction of waves with moving wave protection walls and problems addressed moving semisubmerged or fully immersed objects. The purpose of this paper is to analyze the properties and evaluate the capabilities of the computational algorithm based on the finitedifference approximation of the equations of potential fluid flows with a free boundary and designed to study surface waves in a confined basin, part of the impermeable boundary of which can be mobile. The algorithm relies on the use of curvilinear grids that adapt to all parts of the boundary, both moving and stationary. New initial data are proposed for the problem of motion of a solitary or a single wave, consistent with the initial data for the shallow water equations of the second longwave approximation. New nonreflecting conditions have been developed that allow waves to be emitted across the boundary of a flow region with very little reflection. A new initial approximation is proposed for the iterative process of calculating the potential of the velocity vector. By using this approach we significantly reduce the number of iterations at each time step. The original stability condition of the linearized difference scheme is derived. The reasons for the appearance of two peaks in the chronograms of pressure when the long waves of large amplitude roll onto a vertical wall are discussed. The capabilities of the numerical algorithm are demonstrated on the problem of generating waves by a moving wall travelling in the initial part of the flume. The results of the calculations well reproduce the experimental data, in particular, the decrease in the length and increase in the amplitude of the wave when it moves towards the shallow part of the flume, as well as the formation of a dispersion tail as the waves reverse motion after reflection from the vertical wall installed at the end of the flume. The developed algorithm was used to study the process of generation for surface waves by an underwater landslide moving along an uneven bottom, and the interaction of these landslide waves with a single surface wave moving towards the shore. It is shown that the surface waves caused by an underwater landslide significantly affect the process of rolling of a single wave on the shore and it could increase its maximum splash.

Numerical study of a container ship model for the uncoupled parametric rolling

Parametric roll on ships is a resonance phenomenon whose onset causes heavy roll oscillations leading to dangerous situations for the ship, the cargo and the crew. It affects both small vessels with marginal stability and large container ships if four conditions are met simultaneously: the wave length and ship length are approximately equal, the frequency of encounter wave is twice the roll natural frequency, the ship’s roll damping is low enough and the wave height exceeds a limit value characteristic to each vessel. For a container ship, the first two conditions result in a time-varying geometry of the submerged hull and thus to a periodic variation of the transverse stability. In the last two decades, several mathematical models for parametric rolling have been proposed by scientists. In the paper, we cancelled the couplings terms between heave, pitch and roll in a 3 DOF model proposed by Neves and Rodriguez to obtain an uncoupled 1 DOF model for the parametric roll. Even if it seems too simplistic, such a model based on Mathieu type equation is a good start to capture the basic features of the analysed phenomenon. There are no less than seven parameters that can influence the ship stability and the appearance of large roll amplitudes. By modifying two of these parameters one by one and keeping the others constant, a series of colour plots have been drown that capture the role played by the ship’s parameters in obtaining dangerous roll amplitudes or too short times to take countermeasures. Analysing the instability regions suggested by these colour plots, one can imagine control measures to reduce the roll amplitudes, such as changing the forward velocity or the heading angle. The data used in the paper have been obtained from experiments with a container ship model in a towing tank followed by expansion to a full scale ship.

Estimation of Nonlinear Roll Damping by Analytical Approximation of Experimental Free-Decay Amplitudes

Damping is critical for the roll motion response of a ship in waves. A common method for the assessment of damping in a ship’s rolling motion is to perform a free-decay experiment in calm water. In this paper, we propose an approach for estimating nonlinear damping that involves a linear exponential analytical approximation of the experimental roll free-decay amplitudes, followed by parametric identification based on the asymptotic method. The restoring moment can be strongly nonlinear. To validate this method, we first analyzed numerically simulated roll free-decay data using rolling equations with two alternative parametric forms: linear-plus-quadratic and linear-plus-cubic damping. By doing so, we obtained accurate estimates of nonlinear damping coefficients, even for large initial roll amplitudes. Then, we applied the proposed method to real free-decay data obtained from a scale model of a bulk barrier, and found the simulated results to be in good agreement with the experimental data. Using only free-decay peak data, the proposed method can be used to estimate nonlinear roll-damping coefficients for conditions with a strongly nonlinear restoring moment and large initial roll amplitudes.