Sway Motion Research Articles

Dynamic analysis and experimental testing of a multi-tagline anti-sway and positioning system for slender-beam payload lifting during offshore operations

To address the issues of anti-slip and anti-sway during the lifting of slender-beam payloads (SBP) in offshore environment, this paper presents a novel Multi-Tagline Anti-Sway and Positioning System (MTAPS). The entire lifting process is divided into two stages: the single-point lifting stage and the multi-tagline damping constraint stage. Dynamic modeling is performed at these two stages, and both Damping Control (DC) and Hierarchical Control (HC) strategies are designed for the MTAPS. Matlab/Simulink is used to analyze the dynamic characteristics of the SBP from the horizontal position to the lift-off stage. The sway reduction effect of the two MTAPS control strategies are then compared. Comprehensive experiments are conducted to validate the accuracy of the dynamic models and the effectiveness of the control methods. These experiments demonstrate that the MTAPS effectively mitigates the swinging of the SBP caused by single-point lifting, achieving an average reduction of sway motion by 86.25% during the suspension stage. The simulations and experiments shed lights on multi-tagline control strategies, as well as on the optimization of the offshore lifting process of SBP.

Experimental and numerical investigation of dynamic characteristics and safe mooring criteria of moored outfitting ships under swell conditions

Outfitting ships are characterized by a small draft and a large wind area. As a kind of unpowered ship, when subjected to strong lateral loads, excessive sway motion could cause cable breakage, resulting in potential ship damage or casualties. In this paper, physical and numerical model experiments have been carried out to investigate the effects of swells on moored outfitting ships. The data is analyzed in time and frequency domains to discover the relationship between swells, mooring patterns, ship motions and mooring forces. Subsequently, a numerical model is developed in AQWA, and in conjunction with the physical model experiments, safe mooring criteria for outfitting ships under swell are proposed. Results show that both reducing the sea severity and increasing the number of cables is effective in reducing the risk of cable breakage. The horizontal and heave motions of outfitting ships are controlled by swell period, while the roll and pitch motions are mainly controlled by own parameters. For the cables at different locations, the bow/stern line, breast line and spring line are mainly controlled by sway/yaw motions, sway motion and surge motion, respectively. Additionally, the safe mooring criteria could be widely applied to outfitting quays to ensure the safe operation.

A Numerical Method on Large Roll Motion in Beam Seas Under Intact and Damaged Conditions

The second-generation intact stability criteria, including five stability failure modes, were approved by the International Maritime Organization (IMO) in 2020, and it is an urgent task to develop the numerical method for the significant roll motion under dead conditions. Both intact and damaged stability focus on the large roll motion in beam seas. A unified numerical method is studied to predict the large roll motion in regular and irregular beam seas under intact and damaged conditions. Firstly, a sway–heave–pitch–roll–yaw coupled equation named 5-DOF and a sway-roll-yaw coupled motion with the roll-righting arm in still water named 3-DOF are used to predict the large roll motion in regular beam seas under the intact and damaged conditions. Secondly, the method is extended for the large roll motion in irregular beam seas, where the diffraction force in the roll direction and the sway and yaw motion under intact and damaged conditions are calculated by the subharmonic superposition method. Thirdly, the roll-righting arm in the calm water, roll-damping coefficients, and the roll natural roll period, under the intact and damaged conditions, are obtained by software and a free roll decay experiment, respectively. Finally, the numerical results of a patrol boat under intact and damaged conditions are compared to the experimental results. The results show that the sway-roll-yaw coupled motion with the roll-righting arm in still water named 3-DOF can predict the large roll motion in regular and irregular beam seas under intact and damaged conditions.

Experimental Analysis of the Condensation Flow and Heat Transfer characteristic in a spiral tube under Ocean Swell conditions

The floating liquefied natural gas platform is a key enabling technology for the development of marine natural gas resources. It’s core component, the spiral wound heat exchanger, is frequently subjected to offshore sloshing conditions, which present a significant challenge for the technology. To clarify the condensation flow and heat transfer characteristics in the spiral tube under offshore shaking conditions, an experimental system with a sloshing platform was constructed. The impact of sloshing mode (sway and roll), displacement (sway: 250∼1500mm or roll: 3∼15°), and period (10∼16s) on the heat transfer coefficient (h) and frictional pressure drop (ΔPfric) were analyzed under different operational parameters (mass flux, vapor quality and pressure). Additionally, the comprehensive sloshing factor (CSF) was used to evaluate the overall effect of shaking on condensation process. The results show that the sway and roll motions positively impact the h and ΔPfric. The impact decreases with the increases in mass flux and vapor quality and is negatively correlated with operating pressure. In sway motion, the CSF ranges from 1.39% to 11.82%, with an average of 5.15%. In roll motion, the CSF ranges from 1.15% to 5.13%, with an average of 2.57%.

Flow memory effects on the nonlinear hydrodynamic load of an ROV in translational maneuvering

This paper describes experimental and numerical investigations of the flow memory effect on the nonlinear hydrodynamic load response of a work-class remotely operated vehicle (ROV) under surge, sway, and heave impulse motions. The hysteresis loops of the dynamic drag coefficients during impulse motion tests are analyzed by comparing them with those obtained in steady drag tests. The areas of the loops and differences between the maximum and minimum dynamic and steady coefficients are used to quantify the flow memory effect. A novel unsteady hydrodynamic model for ROVs in translational maneuvering is established. This model considers the flow memory effect in terms of the unsteady hydrodynamic load response obtained from impulse motion response tests. The results given by the unsteady model are found to be in good agreement with those from CFD simulations. The unsteady hydrodynamic characteristics (including the asymmetric forces, force magnitude, and phase delay), motion amplitude, and frequency effect on the hydrodynamic forces of the ROV are analyzed by comparing the unsteady model results with those obtained from the steady model, revealing the rules governing the flow memory effect.

Design, motions, capabilities, and applications of quadruped robots: a comprehensive review

Robots are becoming integral to society and industries due to their enormous advantages. Among the various categories of mobile robots, including wheeled robot, tracked robot, and legged robots, the latter stands out as a better choice for most field applications due to their adaptability across various terrains. The purpose of this review is to study the locomotion capabilities of quadruped robots and judge their suitability for climbing applications as most unexplored applications of automation and robotics are required to climb. This review explores the locomotion capabilities of quadruped robots. It covers different aspects of quadruped robots like types of legs, leg design, gait patterns, and their mathematical formulations, and types of motions like omnidirectional motion and body sway motion. It also emphasizes its fault-tolerant gait, adaptability, and reliability. The paper also focuses on slope and stair climbing, outlining design requirements and applications. The study includes an examination of the applicability of various gaits under different conditions and the methods for increasing stability without compromising speed. Overall, the review serves as a valuable resource for future research in this field.

The hydrodynamic pressure analysis and simplified calculation method of added mass of oscillating horizontal cylinder in finite water depth

Based on the potential flow theory, the hydrodynamic pressure governing equation of an incompressible and ideal fluid acting on a single oscillating horizontal cylinder in finite water depth is derived, solved using the variable separation method. Analytical solutions for the hydrodynamic pressure of the oscillating horizontal cylinder in both sway and heave directions are established via the multipole expansion method and verified against numerical solutions. Using these analytical solutions, the hydrodynamic pressure distributions of the horizontal cylinder under sway and heave motions, varying with dimensionless parameters immersion ratio H (H=h0/h) and diameter-depth ratio L (L=2a/h), are studied. It is found that at the distance of the cylinder from the free surface and seabed is the key factor influencing hydrodynamic pressure distribution. Additionally, the added mass was calculated through integration of hydrodynamic pressure, and the variation of added mass coefficients with L‾ (L‾=2a/h0) and H‾(H‾=2a/(h−h0)) is analyzed. It is observed that, in both sway and heave motions, added mass coefficients increase with decreasing L‾ and increasing H‾. Simplified calculation formulas for added mass coefficients of the horizontal cylinder under sway and heave motions are developed using a two-step fitting method. Finally, errors in calculating the added mass coefficients are compared between the simplified calculation formulas and the analytical solution, showing errors of less than 5%, indicating high accuracy of the proposed simplified calculation formulas for added mass coefficients.

A rapid motion forecast strategy for ships in waves using seakeeping and maneuvering modules

This paper develops a new navigation assisted system for ships with time-varying wave disturbances. A new framework is presented using seakeeping and maneuvering modules to achieve the fast forecast of ship motions. S175 containership and KVLCC2 tanker are adopted to verify the seakeeping module. Based on the validated module, the heave, roll and pitch motions of a cruise ship in different conditions are calculated by using three-dimensional Rankine panel method. The horizontal surge, sway and yaw motions of ships can be rapidly evaluated by using MMG model considering the wave drift forces. Finally, the motion amplitudes of 6°-of-freedom can be forecasted rapidly by using seakeeping and maneuvering modules. The study provides the insight into the motions of ships in waves. It is of great engineering application value to evaluate the total ship motion amplitudes and to improve the safety of navigation of ships in waves.

Carbody hunting behaviour of high speed vehicles in low effective conicity of wheel-rail contact

In the past, bogie hunting instability garnered more attention due to its potential for causing serious safety issues. However, with the rise in high-speed vehicle speeds and operational mileage, the concerns arising from carbody hunting can no longer be overlooked. This article investigates the causes and solutions for low-frequency carbody swaying under low effective conicity in wheel-rail contact, employing a combination of experimental and numerical techniques. Initially, the study involves an in-depth analysis of time-domain signals from lateral and vertical accelerations of the carbody and bogie frame during a high-speed train field-test. The carbody vibration mode resulting from carbody hunting displays a swaying motion at a frequency of 1.5 Hz. Subsequently, a dynamic system model of the high-speed vehicle was established and the suspension mode of the model were verified. The frequency of the carbody upper sway motion is determined to be 1.39 Hz. Low effective conicity is induced when grinding wheel match with new rail or new wheel match with grinding rail. Under this low effective conicity, the hunting frequency of the vehicle is around 1.5 Hz, close to the frequency of the carbody upper sway motion. The coincidence of the hunting frequency and the upper sway motion frequency leads to the low-frequency swaying of the carbody. At last, the effects of wheel profiles, rail profiles and suspension parameters on the carbody hunting have been studied. The study demonstrates that addressing low-frequency carbody swaying can be achieved through targeted rail grinding. This process involves modifying the rail profile while ensuring careful grinding of the rail inner corner. Furthermore, it has been confirmed in the article that replacing suitable yaw dampers is also effective.

Определение нелинейных сил второго порядка, возникающих при поперечно-горизонтальных, вертикальных и бортовых колебаниях накрененных шпангоутных контуров

В статье рассматривается определение нелинейных сил и моментов второго порядка для различных изолированных видов качки на основании применения двухмерной потенциальной теории. Приводится сравнение результатов расчета нелинейных сил и моментов соответствующих видов качки при использовании классического и модифицированного методов интегральных уравнений для жидкости как неограниченной, так и ограниченной глубины. Результаты расчетов, полученные при использовании модифицированных методов, сопоставляются с результатами расчетов, полученных классическими методами. Показано удовлетворительное согласование результатов расчета между собой в большинстве случаев. Представлено исследование влияния угла накренения различных типов шпангоутных контуров на величину нелинейных сил и моментов второго порядка. Делается вывод о целесообразности дальнейшего использования модифицированного метода интегральных уравнений в условиях мелководья при определении нелинейных сил и моментов, действующих на накрененные контура. The article considers the calculation of second-order non-linear forces and moments for various isolated types of ship motions based on the application of two-dimensional potential theory. The calculation results of non-linear forces and moments are given for the corresponding types of ship motions using classical and modified methods of integral equations for fluid of both infinite depth and in shallow waters. The calculation results obtained using modified methods are compared with the calculation results obtained by classical methods. Most of the time, calculation yields a satisfying result. An investigation of the heel angle influence for the various types of frame sections on the values of second-order non-linear forces and moments is shown. The conclusion is made about the expediency of further use of the modified method of integral equations in shallow water conditions when determining nonlinear forces and moments acting on heeled contours.

Determination of Maneuvering Force Coefficients for a Destroyer Model with OpenFOAM

_ Ship maneuvering performance can be predicted using various methods, including physical model tests, rapid simulations using coefficient-based forces, and high-fidelity computational fluid dynamics. This article considers the application of computational fluid dynamics for the prediction of hull force coefficients to be used as inputs to rapid maneuvering simulations. The open-source software OpenFOAM was used to simulate forces on the destroyer model DTMB 5415 for steady drift, oscillatory pure sway motion, and oscillatory yaw motion. Recommendations are provided regarding best practices in a number of areas, including domain size, mesh refinement, time step size, and turbulent modeling. Predicted forces for steady drift angles up to 12 degrees are typically within 10%of experimental values. For oscillatory sway and yaw motions, predicted forces are typically within 25%of experimental values. Keywords maneuvering; OpenFOAM; best modeling practices

Feasibility investigation of tuned mass damper for vibration control of curved floating bridge in winds and waves

This paper investigates the feasibility and operability of a tuned mass damper (TMD) to control the lateral vibrations of a curved floating bridge. A curved floating bridge was designed with a bridge girder, 38 columns, and 19 pontoons, which was the same concept proposed for crossing Bjørnafjorden in Norway, except that the cable-stayed bridge was excluded in the present model. TMD was then attached to the mid-length of the bridge girder. Time-domain model was built to consider the girder-column-pontoon interaction based on the Cummins equation for pontoons and the lumped-mass line model for the bridge girder and columns, while TMD was modeled by the mass-spring-damper system. First, the genetic algorithm was employed to optimize the spring and damping coefficients of TMD at a fixed TMD mass under white noise wave excitations, and the fitness function was a summation of the standard deviation of the sway motion of 19 pontoons. Then, its feasibility was evaluated by comparing lateral vibrations and vertical bending moments with and without TMD under various combinations of wind/wave/current loads. Results demonstrate that TMD contributes to a reduction in the lateral vibration when resonance at the second wet natural frequency occurs, which can improve passenger comfort. Wind-induced lateral motions are significantly reduced at the second wet natural frequency while TMD has limited effects under other environmental loads. Moreover, bending moments are governed by higher modes mostly induced by storm waves, which cannot be controlled by TMD effectively.

Experimental study on the effects of hydrodynamic loads on the seismic response of end-anchored floating bridges

This study focuses on seismic hydrodynamic testing and presents a 1:100-scaled experiment conducted on an end-anchored floating bridge. A series of underwater experiments with varying wave heights and wave periods were conducted to evaluate the effects of hydrodynamic properties on the dynamic behavior of floating bridges under the combined action of earthquakes and waves. The experimental results showed that sway motion resonance occurred when the wave period increased under a multihazard effect. The lateral motion of the pontoon is generated by the earthquake-induced lateral seismic radiation waves on both sides of the pontoon. However, as the wave height increased, the laterally expanding radiation waves on both sides of the pontoon were diminished by the incident waves, resulting in the fragmentation of the seismic radiation waves. Furthermore, independent of the wave height or earthquake, the roll motion of the pontoons induced by the earthquake steadily stabilized as the wave period increased. The effect of wave loads on the translational and rotational responses of floating structures under multihazard effects depends on the hydrodynamic properties of the input sea state.

Operability analysis and line failure risk assessment for a tanker moored at berth

Oil terminals are critical infrastructures for the safe transfer of oil between ships and facilities on land. However, the presence of waves can pose a substantial risk to the mooring system, particularly when dealing with period waves that exceed 8 s. To better understand this relationship and minimize potential risks such as displacement and line failure, physical model tests were conducted. These tests sought to analyse how waves interact with the mooring system, which consists of ships, lines, and fenders. The findings of the research indicate that under experimental conditions, the ship's ability to operate safely is largely determined by its sway and roll motion. Among the various lines in the mooring system, the force exerted on the breast lines was found to be the highest, making them more susceptible to failure. This highlights the importance of paying close attention to these specific lines during operations, and considering necessary adjustments to ensure safety. Furthermore, the study also evaluated the maximum allowable operating wave height of the ship, taking into consideration the limitations imposed by movement and mooring force. These test results can serve as a valuable reference for determining the safe operating conditions for ships in oil terminals, contributing to improved mooring safety. Lastly, the study also took into account the potential occurrence of mooring failure. The event of one breast-fore line failure (Case1) and two breast-fore lines failure (Case2) were both tested. The results showed that the most significant impact was on the adjacent headlines, which increased approximately 40% and 70% respectively. Furthermore, it is important to recognize that the failure of one line may trigger a cascade effect, leading to the gradual failure of other lines and significantly jeopardizing mooring safety.

Effect of the heave plate's diameter on the transitional motions of a straked marine circular cylinder under different marine conditions

This numerical study investigated the influence of the heave plate's diameter on the amplitude of the transitional motions of a marine circular cylinder (MCC) with a low aspect ratio under the marine current and regular waves. Due to the experimental model of the straked MCC, different diameters of the circular heave plate were chosen to be installed at the keel of the 3-straked MCC. In this numerical study, the diameter of the heave plate varied from 1.2 to 1.6 DMCC, while other parameters, such as reduced velocity (VR), Reynolds (Re) number, and Froude number, were kept constant. In this study, the transitional motions, including surge, sway, and heave, were analyzed. The results showed that increasing the heave plate's diameter decreased the amplitude of the transitional motions in both marine current and regular waves. Also, the finding revealed that the heave plate not only reduced the amplitude of the heave motion but also decreased the amplitude of surge and sway motions. Moreover, the outcomes indicated that the heave plate's diameter increased by approximately 20%–40% more than the MCC's diameter. This caused the smaller amplitude of the transitional motions under both marine currents and regular waves.

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>

The examination of operator performance when controlling a shipboard crane anti-sway control system within a virtual-reality simulator

Anti-sway control systems are valuable tools for cranes to prevent unexpected payload sway and undesired motion. However, for shipboard cranes, where the operator moves with the ship, anti-sway control systems can result in significant relative motion between the payload and operator, particularly in rough seas while attempting to align the payload with an ocean-frame target. Therefore, an important question to ask is, do operators actually find anti-sway systems intuitive, or do they feel they have to “fight” the system to achieve their desired performance? To address the question, this paper presents a human factors study designed to evaluate the effectiveness of a shipboard crane anti-sway system with an operator-in-the-loop. Participants completed a series of tests in a virtual-reality simulator, in which they attempted to align the payload of a nine degree-of-freedom shipboard knuckle boom crane with targets in both the ocean/world coordinate frame and ship deck coordinate frame, using an anti-sway system that provided complete motion compensation in both coordinate frames. The study found that there was a statistically significant improvement in the participant’s ability to track a desired payload target with the use of the anti-sway system of up to 49.1%. In addition, as the participant had no knowledge of how the anti-sway system operated, or even if it was active, the results indicate anti-sway control systems can be intuitive for operators to use.

Resolvent-based motion-to-wake modelling of wind turbine wakes under dynamic rotor motion

We propose a linearized deterministic model for predicting coherent structures in the wake of a floating offshore wind turbine subject to platform motions. The model's motion-to-wake predictive capability is achieved through two building blocks: a motion-to-forcing (M2F) part and a forcing-to-wake (F2W) part. The M2F model provides a unified framework to parameterize the effects of arbitrary floating wind turbine motions as unsteady loads of a fixed actuator disk, requiring only the radial distribution of the aerodynamics force coefficient on the blade as input. The F2W model is derived based on a bi-global resolvent model obtained from the linearized Navier–Stokes equations, using the time-averaged wake of a fixed wind turbine as input. In addition to its capability of predicting sensitive frequency ranges, the model excels linear stability analysis by providing spatial modes of the wake response in a motion-specific and phase-resolved manner. The model successfully predicts the wake pulsing mode induced by surge, as well as the similarity and difference of the wake meandering modes caused by sway and yaw. Large-eddy simulations under different inflow turbulence intensities (TIs) and length scales are further conducted to analyse the wake meandering triggered by the simultaneous excitation of free-stream turbulence and sway motion. The results show distinct frequency signatures for the wake dynamics induced by ambient turbulence and sway motion. The inflow TI is found to have a stabilizing effect on the wake, reducing the motion-induced wake responses. Such a stabilizing effect is captured satisfactorily with the proposed model, provided that the effective viscosity is calibrated properly using the data from the fixed turbine wake under the corresponding turbulent inflow.

Comparative analysis on the performance of different types of input‐ and command‐shaping controllers in minimizing payload residual vibration of an overhead crane with an inclined supporting track

AbstractReducing the effects of external disturbance on overhead crane systems is crucial, as they can impair the controller performance and cause excessive vibrations or oscillations of the payloads. One such external disturbance is the inclination of the supporting track of the crane trolley, which causes the system dynamics model to change. An open‐loop control strategy is widely utilized to control the payload sway motion and generally does not require any alterations in the physical structure of a system or the installation of sensors and/or actuators. Input and command shaping are two common open‐loop control techniques applied to control overhead cranes. In this paper, the effect of moving an overhead crane system along an inclined supporting track is investigated. In addition, the ability of different types of input‐ and command‐shaping control schemes to suppress the residual vibrations due to trolley track inclination is demonstrated. Two types of input‐shaping controllers, which are double‐step, zero vibration, and one command waveform (WF) shaper based on a trigonometric function, are used and tested. A linear equation of motion of the overhead crane resting on an inclined surface is developed to simulate the overhead crane and payload motion. The effectiveness of the different types of open‐loop controllers to suppress residual vibrations is verified by both simulation and experimental results. In addition, a new WF command shaper is proposed and designed to overcome track inclination while eliminating payload residual vibration. A comprehensive comparative analysis, both numerically and experimentally, is performed on the new proposed shaper to measure its effectiveness in handling inclination when compared to other types of open‐loop controllers. The new shaper outperforms other controllers in eliminating payload residual vibration for a wider range of inclination angles.

Analysis of Wave-Induced Forces on a Floating Rectangular Box with Analytical and Numerical Approaches

A three-dimensional mathematical hydrodynamic model associated with surface wave radiation by a floating rectangular box-type structure due to heave, sway, and roll motions in finite water depth is investigated based on small amplitude water wave theory and linear structural response. The analytical expressions for the radiation potentials, wave forces, and hydrodynamic coefficients are presented based on matched eigenfunction expansion method (MEFEM). The correctness of the analytical results of wave forces is compared with the construction of a numerical model using the open-source boundary element method code NEMOH. In addition, the present result is compared with the existing published experimental results available in the literature. The effects of the different design parameters on the floating box-type rectangular structure are studied by analyzing the vertical wave force, horizontal wave force, torque, added mass, and damping coefficients due to the heave, sway, and roll motions, and the comparison analysis between the forces is also analyzed in detail. Further, the effect of reflection and transmission coefficients by varying the structural width and drafts are analyzed.