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This study focused on the equation of motion, hydrodynamic derivatives, and course stability with respect to ship maneuvering in a canal. Based on the potential theory, a consistent linearized equation of motion was derived when a ship maneuvers near the center line of a canal with a symmetrical cross-section and uniform length. In the new equation of motion, hydrodynamic derivatives for the lateral force and yaw moment with respect to ship heading angle ψ ( Y ψ , N ψ ) appear, which have not been considered in existing studies. Y ψ and N ψ are measured by captive tests using a container ship model in a canal model, and they are significant. Furthermore, the course stability criterion for ships in the canal was derived by considering the Y ψ and N ψ , and the course stability was investigated. As a result, we found that the effect of Y ψ and N ψ on course stability cannot be neglected when the water depth becomes shallower. In case of the studied container ship, the consideration of Y ψ and N ψ causes the ship to shift to the course stable direction. [ABSTRACT FROM AUTHOR]

The paper describes the developed curvilinear motion simulation model for a vehicle with two traction electric motors moving on a solid surface used to study the dynamic properties of a wheeled vehicle and to subject the developed methods to virtual testing. The simulation model of the electric all-wheel drive vehicle is carried out in the Simcenter Amesim environment to account for the dynamic characteristics and features of the vehicle. The simulation model was developed based on the drawn requirements while the assumptions were justified. Inertia characteristics, tire characteristics, suspension elements, grip characteristics, and surface and air resistance were considered, as these factors affect the vehicle longitudinal and transverse dynamics. The article presents the model implemented in the "Labcar" system and confirms its adequacy by comparing it with the data obtained during the full-scale prototype tests. The bench and range tests of a test vehicle with electric transmission equipped with a measuring complex confirmed the adequacy of the developed model. The results of comparative tests allow for the conclusion that the developed model complex is suitable for modeling purposes, including studying, debugging and initial calibrations of the algorithm of torque distribution on the driving axles of all-wheel drive electric vehicle. [ABSTRACT FROM AUTHOR]

Compared to open water, the presence of ice floes in ice-covered water may pose additional challenges to the towing operations of offshore platforms. This paper proposes a numerical model for analyzing course stability of a gravity-based structure during towing operation in managed ice fields, considering coupled motions of tugs, towed platform, and ice floes. A discrete element method is applied to simulate interaction between drifting ice floes and structures, and verified by existing model tests. The motions of tug and towed platform are coupled through a catenary towline model. A proportional-differential controller is employed to adjust heading and lateral position of tug. The effects of main factors, such as tugs' number, towline length, ice concentration, rudder area and controller gains on course stability are discussed through numerical case studies. The presented numerical approach is expected to provide practical guidance for towing design, and ensure safety of towing operation. [ABSTRACT FROM AUTHOR]

To reach a port, a ship must pass through a shallow water zone where seabed effects alter the hydrodynamics acting on the ship. This study examined the maneuvering characteristics of an autonomous surface ship at 3-DOF (Degree of freedom) motion in deep water and shallow water based on the in-port speed of 1.54 m/s. The CFD (Computational fluid dynamics) method was used as a specialized tool in naval hydrodynamics based on the RANS (Reynolds-averaged Navier-Stoke) solver for maneuvering prediction. A virtual captive model test in CFD with various constrained motions, such as static drift, circular motion, and combined circular motion with drift, was performed to determine the hydrodynamic forces and moments of the ship. In addition, a model test was performed in a square tank for a static drift test in deep water to verify the accuracy of the CFD method by comparing the hydrodynamic forces and moments. The results showed changes in hydrodynamic forces and moments in deep and shallow water, with the latter increasing dramatically in very shallow water. The velocity fields demonstrated an increasing change in velocity as water became shallower. The least-squares method was applied to obtain the hydrodynamic coefficients by distinguishing a linear and non-linear model of the hydrodynamic force models. The course stability, maneuverability, and collision avoidance ability were evaluated from the estimated hydrodynamic coefficients. The hydrodynamic characteristics showed that the course stability improved in extremely shallow water. The maneuverability was satisfied with IMO (2002) except for extremely shallow water, and collision avoidance ability was a good performance in deep and shallow water.

The paper presents an experimental investigation of course stability on the barge due to the damage conditions of one or more adjacent void tanks. The effects of various towline lengths and load conditions on the course stability of the barge were taken into account and incorporated with trim and heel conditions. The sway motion, defined as the towline's motion, was captured using the camera, and the yaw motion was measured using the Euler compass. The investigation results revealed that increased towline lengths, flooding locations, and load conditions affect the barge's course stability. The smallest value is the increased sway and yaw amplitudes affected by the flooded condition of one or adjacent two void tanks on the amidship part. The overall sway amplitude on the port side or starboard side increases significantly high, affected by towline length from 1L to 1.5L. Also, the overall yaw amplitude on the port side or starboard side increases significantly high, affected by towline length from 1.5L to 2L. The difference in the increased sway amplitude based on the flooding locations between stern, amidship, and bow parts is less than 10% on the port side and 2% on the starboard side. The difference in the increased yaw amplitude is less than 5% on the port side and 5% on the starboard side. The number of longitudinal bulkheads on the port side and starboard side must be considered for the reduction of the oscillation of the water mass inside the tank to reduce the degradation of the course stability.

The paper describes the developed curvilinear motion simulation model for a vehicle with two traction electric motors moving on a solid surface used to study the dynamic properties of a wheeled vehicle and to subject the developed methods to virtual testing. The simulation model of the electric all-wheel drive vehicle is carried out in the Simcenter Amesim environment to account for the dynamic characteristics and features of the vehicle. The simulation model was developed based on the drawn requirements while the assumptions were justified. Inertia characteristics, tire characteristics, suspension elements, grip characteristics, and surface and air resistance were considered, as these factors affect the vehicle longitudinal and transverse dynamics. The article presents the model implemented in the “Labcar” system and confirms its adequacy by comparing it with the data obtained during the full-scale prototype tests. The bench and range tests of a test vehicle with electric transmission equipped with a measuring complex confirmed the adequacy of the developed model. The results of comparative tests allow for the conclusion that the developed model complex is suitable for modeling purposes, including studying, debugging and initial calibrations of the algorithm of torque distribution on the driving axles of all-wheel drive electric vehicle.

The article analyzes the effectiveness of methods for monitoring motor vehicles during operation. The relevance of the study lies in the fact that the braking system is an important element responsible for the safe operation of the car. Purpose. To increase the efficiency of the technical operation of motor vehicles on the basis of the road method for diagnosing brake systems. Methodology or methodology for conducting work. The article considers the road method using accelerometers. Results. The main disadvantages of the road method and stands of various designs are considered, which give low reliability of the determined parameters of efficiency and stability during vehicle braking. The effectiveness of the implementation of on-line road diagnostics of automotive braking systems of multi-channel accelerometers is shown, which, when assessing course stability during braking, provide visually convincing information with a fairly high level of reliability. Practical implications: the results of the study can be used by car service organizations.

In the conventional experiment to assess the towing operations, the towing stability of the towed vessel has been evaluated under the condition without lateral motion of the tug-boat. However, the tug-boats may have a lateral force to change the direction of the towed vessel. In this study, experiments have been conducted considering unsteady conditions in the towing system. First, a towing test system in a Circular Water Channel (CWC) using the conventional experimental method is built. Second, the towing characteristics of the towed vessel are investigated using the conventional method, and they are compared with other research results and stability discriminant criteria. Third, the lateral motion of the tug-boat was modeled as a sinusoidal motion using a forced oscillation device changing frequency and amplitude. Finally, the discussion is given in terms of both towing- and course-stability of the towed vessel according to the lateral motion of the tug-boat.

This article presents the results of complex theoretical and experimental studies on creating universal continuous earthmoving machinery operating under non-standard loading conditions, namely, cyclic lateral loading on the actuator during digging. The lateral loading is due to the complex nature of the actuator motion when digging the soil, namely, the longitudinal motion of the machinery, the actuator digging the soil, and the lateral reciprocating motion of the actuator. This allows for variable width excavations in the soil, whose width exceeds the width of the actuator. The key issue of this machinery operation is to provide its course stability. The article considers the choice of soil-developing actuator and shows the developed calculation schemes of external loading on the operating equipment and a base tractor when digging long excavations in the soil. The dependencies to define external forces acting on the actuator when digging the soil and determining the machinery course stability, considering their spatial nature, have been developed and suggested for practical use. The conditions to ensure the stability of the course of universal earthmoving machinery have been formulated and substantiated. The developed method for determining course stability can be used when creating industrial samples of trenching earthmoving machinery. [ABSTRACT FROM AUTHOR]

In this study, the motion control problem of the vessel towed by a towing ship (tugboat) is considered. The non-powered towed ship is dragged by the towing ship. Even though the towed ship is equipped with propulsion systems, they cannot be used at low or constant speeds due to safety issues. In narrow canals, rivers, and busy harbor areas especially, where extreme tension is required during towing operation, the course stability of the towed vessel depends on the towing ship. Therefore, the authors propose a new control strategy in which the rudder system of the towed vessel is activated to provide its maneuverability. Based on the leader-follower system configuration, a nonlinear mathematical model is derived and a back-stepping control is designed. By simulation and experiment results with a comparison study, the usefulness and effectiveness of the proposed strategy are validated.

The shape of the carapace protecting the body of boxfishes has been attributed an important hydrodynamic role in drag reduction and in providing automatic, flow-direction realignment and is therefore used in bioinspired design of cars. However, tight swimming-course stabilization is paradoxical given the frequent, high-performance manoeuvring that boxfishes display in their spatially complex, coral reef territories. Here, by performing flow-tank measurements of hydrodynamic drag and yaw moments together with computational fluid dynamics simulations, we reverse several assumptions about the hydrodynamic role of the boxfish carapace. Firstly, despite serving as a model system in aerodynamic design, drag-reduction performance was relatively low compared with more generalized fish morphologies. Secondly, the current theory of course stabilization owing to flow over the boxfish carapace was rejected, as destabilizing moments were found consistently. This solves the boxfish swimming paradox: destabilizing moments enhance manoeuvrability, which is in accordance with the ecological demands for efficient turning and tilting.

This article presents the results of complex theoretical and experimental studies on creating universal continuous earthmoving machinery operating under non-standard loading conditions, namely, cyclic lateral loading on the actuator during digging. The lateral loading is due to the complex nature of the actuator motion when digging the soil, namely, the longitudinal motion of the machinery, the actuator digging the soil, and the lateral reciprocating motion of the actuator. This allows for variable width excavations in the soil, whose width exceeds the width of the actuator. The key issue of this machinery operation is to provide its course stability. The article considers the choice of soil-developing actuator and shows the developed calculation schemes of external loading on the operating equipment and a base tractor when digging long excavations in the soil. The dependencies to define external forces acting on the actuator when digging the soil and determining the machinery course stability, considering their spatial nature, have been developed and suggested for practical use. The conditions to ensure the stability of the course of universal earthmoving machinery have been formulated and substantiated. The developed method for determining course stability can be used when creating industrial samples of trenching earthmoving machinery.

This paper presents a method to efficiently calculate steady sailing conditions such as check helm, speed drop, hull drift angle, etc. of a ship moving in parallel to a bank wall under steady wind, together with the course stability at the equilibrium condition. Using this method, this study investigates the bank effect on the steady sailing condition and the course stability of a pure car carrier in steady wind and it evaluates the limiting wind condition for safe navigation (maneuvering limit). In case of head wind, a significant speed drop appears. In case of oblique head wind from the port side, the hull drift angle increases significantly and there is a distinct possibility that the ship touches the bank wall. In case of oblique following wind from the port side, the check helm increases significantly, because the wind force is added to the bank suction force. This becomes critical when the ship moves closer to the bank and in more shallow water areas, and the maneuvering limit level becomes more severe. The present method is a useful tool for measuring the maneuvering limit of a ship moving in close proximity to the bank under steady wind. [ABSTRACT FROM AUTHOR]

For the navigation safety of ships, it is essential to monitor the maneuvering characteristics under external disturbances due to wind and waves. For this purpose, evaluating the average steady sailing conditions such as check helm, speed drop, hull drift angle, etc. of a ship moving straight in steady wind and waves is beneficial. In addition, the dynamic stability (course stability) of the ship should be evaluated under its steady sailing condition. This study proposes a method for predicting the steady sailing conditions and course stability under external disturbances, based on the MMG standard method presented by Yasukawa and Yoshimura (J Mar Sci Technol 20(1):37–52, 2015). The calculation accuracy of the MMG method has been validated through experiments. The steady sailing conditions and the course stability of a pure car carrier are calculated using the proposed method under external disturbances in deep and shallow waters. In addition, the environmental conditions that limit safe navigation (maneuvering limit) are also discussed, while investigating the effect of the main engine output in particular. In both deep and shallow waters, a significant effect on the maneuvering limit is observed due to a reduction in engine output. Thus, the presented method is useful in capturing the maneuvering limit of the ship under external disturbances. [ABSTRACT FROM AUTHOR]

Due to the highly complex phenomenon of a ship towing system associated with the presence of a dynamic nonlinear towline tension, a reliable investigation allowing for an accurate prediction of the towed ship’s course stability is obviously required. To achieve the objective, a Computational Fluid Dynamic simulation approach is proposed by investigating attainable and precise course stability outcomes, whilst a hydrodynamic description underlying the rationale behind the results is explained. Several towing parameters such as various towline lengths and tow point locations with respect to the centre of gravity of the barge have been taken into account. Here, tug and barge is employed in the simulation as the tow and towed ship, respectively. In addition, a towing velocity is constantly applied on the tug. The results revealed that the course stability of the towed ship increases in the form of more vigorous fishtailing motions as the towline length subsequently increases from 1.0 to 3.0. Meanwhile, the increase of tow point location from 0.5 to 1.0 leads to a significant improvement in the course stability of the towed ship, as indicated by the reduction of the sway and yaw motions by 227% and 328%, respectively. It is concluded that the increase of tow point location is a recommended decision to achieve a better towing course stability for the barge.

The course stability and the steerability of the two-section wheeled vehicle at high velocities during the lane change manoeuvre are studied in this paper. Mechanic-mathematical model is developed, on which base simulation programmes are elaborated. Simulation studies of the course stability at different velocities depend on some constructive and exploitation factors are made by these models. Based on the simulation results an idea for an algorithm and a semi-active control system of the resistance in the pulling-supporting device is proposed.

A pusher-barge system (P/B) has been one of the main transportation systems particularly for rivers and inland waterway services. Since a P/B normally sails in restricted waters such as a sharp bend in a river, the maneuverability is important for safe navigation. Although the barge draft changes drastically with an increase of the amount of cargo, the draft of the pusher which normally equips a small ballast tank does not change so much. It indicates that the step appears or disappears around the pusher-barge connection due to the load condition of the barge. This phenomenon is a unique and interesting characteristic of a P/B. Therefore, this study aims to discuss the effect of the barge load condition on the maneuverability. For this purpose, the towing tank experiments were conducted under the empty and full load conditions of the barge, and the mathematical model to simulate maneuvering motions of the P/B was established. At that time, the hydrodynamic force data in the range of high yaw rate was made up by the CFD method. We found that the course stability of the P/B deteriorated with an increase of the barge draft. It is related to the change of the pressure filed spread over the pusher bow which is influenced by the wake shed from the barge. Besides, the simulation study revealed that the turning ability due to small steering was worse under the empty load condition than the full load condition of the barge. However, it appears to be improved with an increase of the steering angle. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of bilge keels on maneuverability of a fine ship experimentally and theoretically. To capture the effect, first, free-running model tests were conducted using a KCS container ship model with detachable bilge keels. We found that bilge keels improve the turning performance and enlarge overshoot angles in zig-zag maneuvers, and that this tendency becomes more pronounced with increasing ship speed. Next, captive model tests were conducted to capture the hydrodynamic forces’ effects on maneuvering to clarify the reason for the difference in maneuvering in the presence of bilge keels. By attaching bilge keels, the absolute values of Yv′, Nv′, and Kv′ (the linear derivatives of lateral force, yaw moment, and roll moment acting on the ship with respect to lateral velocity v, respectively) are increased and Yϕ′ (the derivative of the lateral force with respect to roll ϕ) is also increased. It can be explained theoretically that the change of the hydrodynamic derivatives leads to course instability according to the course stability criterion presented by Yasukawa and Yoshimura [3]. The special feature of the criterion is to include the roll-coupling effect. Thus, the roll-coupling significantly affects ship maneuverability through hydrodynamic derivative changes by attaching bilge keels to fine ships with small metacentric height GM¯. [ABSTRACT FROM AUTHOR]

The synthetic fiber ropes are commonly employed as the main material for the towing line to connect the towed ship and tug boat. The diversity of material e.g. polyester, aramid, and HMPE could impact the behavior of towing system and lead the instability of towed ship. Following the practical method previously proposed for the towing system analysis, authors aim to present a numerical model to properly take into account the characteristics of fiber ropes into the towing system. Specially, the dynamic stiffness of fiber ropes which is determined according to the mean load of the towing line is considered when solving the governing equations in the time domain. A detailed iteration procedure for the calculation of dynamic stiffness is described. The performance of dynamic yaw and lateral offset of towed ship under various wind speeds are discussed. The effect of various types of fiber ropes for the towing line and the initial length is also investigated thoroughly. Results of case study show that diverse material characteristics could influence the ship's directional stability significantly. The shorter towing line and stronger wind can reduce the fishtailing effect of the towed ship while the longer towing line would make the motion period larger. • Three types of synthetic fiber ropes are studied in the towing operation. • The dynamic stiffness considering mean load is employed in the numerical model. • Dynamic towing analyses are performed to study the ship behavior under wind loads. • The impacts of material diversity, towing line length, dynamic stiffness and wind speed are discussed. [ABSTRACT FROM AUTHOR]

When the large vessels, such as very large container ships and conventional VLCCs, are navigated in shallow water, it is necessary to accurately estimate the course stability as well as the squat of the ship to ensure safety. The purpose of this study is to analyze the course stability characteristics by vessel type, which can evaluate the navigation safety of very large vessels navigating at low speed in shallow water. Numerical simulations were carried out using CFD for KVLCC2 and DTC with respect to depth of water, drift angle, and angular velocity. The maneuvering performance in shallow water were analyzed by estimating the hydrodynamic derivative from the results of the numerical calculations. As the drift angle and angular velocity increased, the magnitudes of sway force and yaw moment became larger. The hydrodynamic derivatives at H/T = 1.2 were very large compared with that at other depths. The course stability at H/T = 1.2 was significant regardless of the type of vessel, and found to be more significant in KVLCC2 compared to DTC. The nonlinear effects such as vortex flow and pressure distribution on the hull were also analyzed through a flow field analysis around the hull. [ABSTRACT FROM AUTHOR]

Conditions concerning conservation of automobiles course stability at braking during operation are considered.

In this paper, the effects of changes in hull attitude and the presence of stern appendages such as rudders, shaft brackets, bossing, and propeller shafts on the maneuverability of a high-speed ship are investigated. The study is conducted for a ship operating within a Froude number range of 0.6-1.0. To determine the effect of attitude changes on the hydrodynamic derivatives during maneuvering, the hydrodynamic forces acting on the ship model with/without stern appendages are measured in three conditions: an even keel with the designed draft, and the same setup including hull rise or trim. For each condition, measurements are conducted for oblique motion, steady turning, and straight motion with heel, for various ship speeds. The hydrodynamic derivatives excluding the attitude change are obtained from the measured results, along with the changes in these derivatives due to hull rise and trim. Using the hydrodynamic derivatives, the maneuverability indexes are calculated. Hence, the following results are obtained: By inclusion of the ship attitude change, the linear derivative of lateral force with respect to the sway velocity Y 'υ becomes less negative, the linear derivative of yaw moment with respect to the yaw rate N 'r becomes more negative slightly, and the difference between Y 'r and added mass in the x direction Y 'r - m 'x, along with N0υ , becomes significantly large in the positive direction. Primarily by the contribution of Y 'r - m 'x , and N 'υ , inclusion of the attitude change improves the course stability. A bare-hull ship becomes unstable as regards course keeping, although a ship with stern appendages is stable. Thus, the addition of stern appendages has a significant effect on the course stability, which is primarily due to the increase in the negative direction of Y 'υ , and N 'r , caused by their presence. [ABSTRACT FROM AUTHOR]

The course stability and the steerability of the two-section wheeled vehicle at high velocities during the lane change manoeuvre are studied in this paper. Mechanicmathematical model is developed, on which base simulation programmes are elaborated. Simulation studies of the course stability at different velocities depend on some constructive and exploitation factors are made by these models. Based on the simulation results an idea for an algorithm and a semi-active control system of the resistance in the pulling-supporting device is proposed. [ABSTRACT FROM AUTHOR]

The work presents advanced methods of evaluating line stability of all-wheel drive and rear-wheel drive vehicles using computer.

In a water tank experiment, it was found that slewing motions differ according to the bow shape of a barge. Due attention should be paid to the differing effects of skegs in accordance with the bow shape, and it is necessary to estimate the course stability of each barge by identifying the hydrodynamic forces acting on it. This study analyzed the skeg-induced characteristics of course stability of different types of barges. To this end, we used CFD to analyze the effects of nonlinearity, such as the generation of three-dimensional vortices; computed the sway force and yaw moment during drift and steady yaw motions of barges with different bow shapes; and analyzed the flow fields around the barges. As a result, it was verified that skeg contributed to the improvement of the course stability and the shape of a vortex generated in the stern section was found to be significantly influenced by skeg position and number. [ABSTRACT FROM AUTHOR]

Based on real events that occurred in the East Atlantic few years ago, the paper is analyzing and interprets a range of parameters for ship and for external forces that act on the ship captured by heavy weather and the effect they have on the maneuvering capabilities. The paper, wants to explain the strong influence of forces beyond the ship, forces caused by wind, waves or currents. Course stability and ship's maneuverability are strongly affected when the vessel proceed in a cyclonic area with extreme weather conditions due to external forces that act negatively on the ship's hull and its ability to maintain the desired course. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a numerical model for analyzing the course stability of a towed ship in uniform and constant wind. The effects of an unstable towed ship and a stable towed ship were recorded using numerical analysis at various angles and velocities of wind. The stability investigation of the ship towing system was discussed using the linear analysis, where a tug''s motion was assumed to be given. When the tug and the towed ship''s motions were coupled through a towline as a proper model of the ship towing system, their dynamic interactions during towing was then captured using towing trajectories and analyzed using nonlinear time-domain simulation. With increasing wind velocity, the simulation results revealed that the towing instability of the unstable towed ship was recovered in the range of beam to quartering winds; however, the towing stability of the stable towed ship in head and following winds gradually degraded. It should be noted that this towing instability might have resulted in the impulsive towline tension and could led to serious towing accident e.g. towline breakage or collisions. [Copyright &y& Elsevier]

In order to achieve safe navigation, it is important to be able to understand and calculate the effects of an external force on the maneuvering behavior of a ship. This paper analyzes the course stability and yaw motion of a ship traveling under steady wind conditions. A course stability criterion and approximate formulae for the yaw motion in steady wind, including the aero/hydrodynamic force derivatives for the ship, are derived. To confirm the reliability of the criterion and formulae, they were used to investigate a pure car carrier in steady wind. The results of this investigation revealed that course instability appears in the head and following wind directions, mainly under the influence of aerodynamic derivatives with respect to the yaw restoring forces. However, this course instability can be reduced by applying steering control. For winds ranging from head winds to beam winds, yaw oscillation appears when the period is relatively long and the damping is small. The analytical formulae derived here can be used to gain a better understanding of ship maneuvering behavior in steady wind. [ABSTRACT FROM AUTHOR]

The paper treats the important problem of prediction of ship's inherent course stability, based on a large amount of model experimental data for a well-known bare hull shape - the Delft catamaran 372, covering a comparatively wide range of Froude numbers and depth to draught ratios. The analysis is based on a linearized maneuvering model.As a result, dependency of the stability criterion on Froude number and the water depth to draught ratio is established and clearly demonstrated for this particular ship case. [ABSTRACT FROM AUTHOR]

A four-degree-of-freedom mathematical model was established to investigate the course stability of an air cushion vehicle (ACV). The forces of aerodynamic, propeller and rudder were obtained by wind tunnel experiments. A series of constrained model experiments with horizontal-planar-motion-mechanism (HPMM) were conducted to determine the hydrodynamics. The ACV’s course stability was analyzed by using Hurwitz determination method with differential equation of perturbation, and the four-degree-of-freedom course stability was then checked by simulated calculation. The analysis and simulation results show that the course stability of four-degree-of-freedom is applicable to ACV and is stricter than that of two-degree-of-freedom. [ABSTRACT FROM AUTHOR]

A container ship transferring numerous containers must stow them in the proper slots. There are many factors to consider, such as the handling efficiency, stability, and hull strength due to weight distribution. Because the number of cargo containers depends on the shipping market, this can affect the displacement or draft of the hull. Optimizing the trim for improved fuel efficiency is another important consideration these days. Thus, a container ship navigates under various loading conditions in the daily voyage. Although the trim and draft effects on the resistance and propulsive performances are of concern, more research is required on their effect on maneuverability, which is important for the ease of ship control and safe navigation. Therefore, this study aims to determine the trim and draft effects on the container ship's maneuverability by conducting free-running tests to measure the maneuvering motions and captive model tests to clarify the hydrodynamic forces. Each test was under five loading conditions and comparative analysis was performed. Especially, since we found the course stability became better as the shallower draft or larger trim by the stern, the analysis based on computational fluid dynamics was conducted to explain its mechanism. Visualizing the flow velocity and pressure fields around the container ship under different loading conditions, the mechanism is clarified in association with them. • Five loading conditions (i.e., draft and trim combinations) were target. • Difference in maneuverability was clarified by free-running model tests. • Difference in hydrodynamic forces was clarified by captive model tests. • Mechanism for changes in course stability was clarified by CFD analysis. [ABSTRACT FROM AUTHOR]

Three-legged triangular tension leg platforms (TLPs), which are a kind of compliant-type floating structure, are drawing attention from industrial society. To reduce the transportation cost, a multiple linked ship towing system that the platform and anchor are linked and wet towed is studied. A unified seakeeping and maneuvering method which can take account of the hydrodynamic interaction between the bodies and utilize the experimental results for tuning the damping coefficients is proposed to model the towing system. In the method, a low-pass filter is applied to separate the slowly and fast motion components for the maneuvering and seakeeping calculations. The maneuvering and seakeeping problems can thus be solved simultaneously with a same time scale. SimMechanics™, which provides multi-body simulation environment for mechanical systems, is applied to implement the numerical model for studying the fully coupled six degrees-of-freedom (DOFs) motion of the towing system. Besides, experiments are carried out to demonstrate the feasibility of the system and the effectiveness of the numerical model. A circular motion in irregular waves is studied at the end and the issues of the system are discussed accordingly. • A numerical method for fast simulating a multiple linked ship towing system in a seaway is proposed. • The maneuvering and seakeeping problems are solved simultaneously based on the slowly and fast motion components. • The damping coefficients are tuned based on experimental results so that the model could be of high accuracy. • A circular motion of the towing system in irregular wave is studied and the issues of the system are discussed. [ABSTRACT FROM AUTHOR]

Some new-built ship-shaped offshore structures like FPSO or FPU are found to show insufficient course stability due to rough design, which makes the towing operation hazardous. This paper aims at investigating the stern fin as a proposed solution for improving the poor course stability of a FPSO in towing operation by creating a practical approach. The fin's hydrodynamic lift coefficient is predicted by the vortex lattice method. The numerical towing system is of three degrees of freedoms and accounts for hydrodynamic forces, the interactions acting on the hull and other appendages, as well as the towing line. Various hydrodynamic derivatives are considered linear and estimated by the empirical method. The configurations of single fin, double fins, and twin fins, as well as the influence on towing stability, are studied. In particular, the hydrodynamic interaction of twin fins, lift coefficient reduction and the impact of spacing are analysed. Different stable and unstable behaviours in the time domain are observed and discussed in depth. The eigenvalue analysis is conducted based on the linearized towing system. • The fin is used to improve the FPSO course stability during towing. • Vortex lattice method is used for hydrodynamic derivatives of fin. • Hydrodynamics of multiple fins and the effect of spacing are discussed. • Time-domain dynamics and eigenvalue were studied for diverse towing behaviours. [ABSTRACT FROM AUTHOR]

Captive model tests are conducted for a pure car carrier in the proximity of a sloped bank with variations in water depth, distance between ship hull and bank, hull drift angle and heel angle. Using the hydrodynamic derivatives obtained, the check helm and hull drift angle required at equilibrium conditions are estimated. Course stability of the ship sailing in the proximity of the bank is also studied based on a simplified analysis method. In h ∕ d = 1. 2 where h ∕ d means ratio of water depth h to ship draft d , the check helm of the ship reaches 35° near η 0 ∕ L = 0. 27 where η 0 is the distance between the ship center line and the bank. Although this ship is course unstable in case of no rudder control, the ship becomes course stable in any water depths by employing the autopilot with appropriate control gains. The present analysis method is useful for conventionally assessing the course stability of a ship in the proximity of a bank. • To provide the hydrodynamic derivatives data related to a bank by captive model tests. • To present a simplified analysis method for the course stability of a ship close to a bank. [ABSTRACT FROM AUTHOR]