Ship In Shallow Water Research Articles

Investigation of Vessel Manoeuvring Abilities in Shallow Depths by Applying Neural Networks

A set of planar motion mechanism experiments of the Duisburg Test Case Post-Panamax container model executed in a towing tank with shallow depth is applied to train a neural network to analyse the ability of the proposed model to learn the effects of different depth conditions on ship’s manoeuvring capabilities. The motivation of the work presented in this paper is to contribute an alternative and effective approach to model non-linear systems through artificial neural networks that address the manoeuvring simulation of ships in shallow water. The system is developed using the Levenberg–Marquardt backpropagation training algorithm and the resilient backpropagation scheme to demonstrate the correlation between the vessel forces and the respective trajectories and velocities. Sensitivity analyses were performed to identify the number of layers necessary for the proposed model to predict the vessel manoeuvring characteristics in two different depths. The outcomes achieved with the proposed system have shown excellent accuracy and ability in predicting ship manoeuvring with varying depths of shallow water.

Numerical Simulations of a Ship’s Maneuverability in Shallow Water

It is necessary to maintain maneuverability for ship navigation in shallow water, such as channels, ports and other confined waters. In this study, a turning circle maneuver with 35° rudder deflection and a 20/5 zigzag maneuver for KVLCC2 in shallow waters are tested numerically to directly predict the maneuverability of the ship in shallow water. A viscous in-house CFD solver is applied with the dynamic overset grid approach. The impacts of the water depth on the ship’s maneuverability in terms of turning and zigzag competence are evaluated, and the underlying mechanism is analyzed. The numerical method is validated by comparing it with experimental data on the turning indices, which shows good agreement. It is demonstrated that the turning capability become worse with a smaller depth–draft ratio, thus resulting in a lower yaw rate and a greater steady turning diameter. However, the drift angle and lateral speed are reduced with a smaller depth–draft ratio for zigzag maneuvers, but the overshoot angle and turn lag vary with the water depth non-monotonically.

Four-DOF Maneuvering Motion of a Container Ship in Shallow Water Based on CFD Approach

With the continuous increase in ship size combined with the generally slower increase in the sizes of waterways, the need for the prediction of ship maneuvering in shallow waterways continues to attract attention from the international scientific community. Ship behavior in shallow water is relevant in seabed effects that result in changing the hydrodynamic forces acting on a ship. In this study, the maneuvering characteristics of a container ship with four degrees of freedom in shallow water are analyzed. The Reynolds-Averaged Navier Stokes approach in Ansys Fluent code is used to produce the maneuvering coefficients through the simulations of forward running, static drift, static heel, circular motion, the combined motions, and the pure roll motion of the KRISO container ship. The maneuvering characteristics of the ship are estimated for evaluating the ship behaviors in shallow-water conditions. The obtained results show that the roll has a significant decrease and the ship’s turning diameter has a significant increase when the ship operates in a shallow waterway. The predictions of the maneuvering characteristics of the ship are in good agreement with those of free-running model tests, indicating that the numerical simulation based on the Computational Fluid Dynamics method has compromising capability to predict the maneuvering derivatives and the four-DOF ship maneuvering motion in shallow water as well.

Enhancement of Green's functions based on striation pattern

Enhancement of Green's function is accomplished from the striation pattern obtained from data. The waveguide invariant theory allows a Green's function observed at one location to be extrapolated into adjacent ranges [Song and Byun, J. Acoust. Soc. Am. 147, 2150–2158 (2020)]. Conversely, Green's functions observed at adjacent ranges can converge towards a central location for coherent combination to improve the signal-to-noise ratio (SNR). This can be accomplished from the frequency shift in the striation pattern without prior range information of each Green's functions. We demonstrate a significant improvement of SNR in the broadband Green's function from a moving ship in shallow water.

The resistance of a trans-critically accelerating ship in shallow water

ABSTRACT The acceleration resistance of a vessel advancing in shallow water is investigated. Four acceleration intensities and two water depths are modelled using the CFD and potential flow methods. The results show a pronounced peak in resistance exists near the critical depth Froude number, but its location and magnitude are sensitive to the acceleration intensity and water depth. Excellent agreement between the results obtained from the CFD and potential flow methods is found in the low and high depth Froude number ranges regardless of water depth or acceleration, indicating that linear and unsteady methods can provide robust results at a low cost in those ranges. The magnitude of the resistance peak and its position are sensitive to nonlinear effects, evidenced by slight disagreements between the two adopted methodologies. The variation in the results produced by the two solvers is found to be sensitive to the parameters investigated.

The Influence of Shallow Waters on the Maneuvering of Large Ships

The increasing demand for goods that can be transported by sea and the reduction in transportation costs have led to a trend toward larger ships. The increase in ship capacity leads to an increase in ship length and, thus, a decrease in transportation costs. The maneuverability of large ships in shallow water when calling at ports is becoming increasingly difficult. This is due to the discrepancy between increasing ship dimensions and unchanged waterway structures such as approach channels, harbors, and ports. The maneuverability of a vessel in shallow waters is different from the maneuverability in deep waters. The reasons for this are due to the shallow water effect. Shallow water affects the maneuverability of ships due to hydrodynamic forces caused by the current, shallower depth under the keel and proximity to the shore. It is a major challenge both for shipbuilders to design such vessels and for shipowners to have trained and well-educated officers who can navigate large vessels in shallow waters. This article presents the effects of shallow waters on large ship maneuvering and mathematical models that have been used to predict ship behavior under the influence of these forces.

RANS investigation of the hydrodynamic interactions between two approaching ships in shallow water considering the effects of drift motion and rudder deflection

There exists a high risk of collision between two approaching ships in the lightering operation. The investigations of the hydrodynamic interactions between such two ships are of great interest to ensure navigation safety. To this end, the RANS (Reynolds-Averaged Navier-Stokes) technique based on OpenFOAM is employed to simulate the flow around two approaching Wigleys in this work. The two Wigleys are identical. Due to the slow ship speed, the water-air flow is simplified as the double-body flow in the present consideration. The computed hydrodynamic side forces and yaw moments are compared with the available experimental data, and acceptable agreements are found. The effects of lateral distance between the two ships, water depth, rudder deflection, ship scale and drift motion on the hydrodynamic forces and moments on both ships are analyzed. This study shows that the suction forces and bow-out moments generally become larger as the water depth or lateral distance decreases, while the suction forces trends to become repulsion forces when both the water depth and lateral distance are very small. It is also found that the rudder deflection of one ship has a very little hydrodynamic disturbance on the other ship, rather than the drift motion which affects much the hydrodynamic forces and moments on the other ship especially in very shallow water.

A modeling and comparative study of bottom pressure signals generated by waves and ship in shallow water

For the bottom pressure signal generated by an advancing ship in the ocean, the bottom pressure signal generated by waves is a strong background disturbance. Aiming at the differences between their characteristics, the modeling methods for predicting the bottom pressure signals generated by ship and waves in shallow water are presented and validated, meanwhile, their characteristics in time and frequency domains are simulated, compared, and analyzed. The findings clearly show that their characteristics differ in some key parameters, such as the pressure spectrum, the pressure peak, and the negative duration, etc. The modeling and comparative studies proposed in this paper are very beneficial for the design of underwater weapons, and helpful for identifying whether the target is indeed a ship or just an ocean environment interference.

Experimental study of adaptive course controllers with nonlinear modulators for surface ships in shallow water

The present paper proposes a new adaptive controller with nonlinear modulators to improve the controller adaptability and rudder efficiency so that a satisfactory course tracking performance of ships can be achieved. First, a new adaptive control law on basis of Internal Model Control (IMC) is designed to address the speed dependency of the controller. Three types of nonlinear modulators are then added to the developed adaptive controller to increase the rudder efficiency. Subsequently, the control system’s stability is analysed. Both course keeping and changing performance of the proposed controller are investigated via towing tank tests using a ship model of a Liquefied Natural Gas carrier. Finally, the applicability of controllers in shallow water is discussed. During experiments the developed algorithms show satisfactory course tracking ability in shallow and deep water. The advantages of better adaptability and higher rudder efficiency are verified by comparative results. Moreover, the impact of water depth on the controller cannot be ignored.

Viscous effects on squat

Potential theory was used to predict trim and sinkage of ships in shallow water for moderate water depths. However, for very shallow water depths leading to small under keel clearances, viscosity may have significant effects. Our paper presents a systematic numerical study on these effects. Numerical computations were carried out for the Duisburg Test Case containership in different water depths. The numerical predictions relied on inviscid, laminar, and turbulent flow assumptions. All calculations were performed on the same grid and with the same time step to ensure that discretization errors did not influence the results. Results showed that viscosity affected a ship’s trim and that these viscous effects became more prevalent with decreasing under keel clearance.

Maneuvering simulations of twin-propeller and twin-rudder ship in shallow water using equivalent single rudder model

Maneuvering simulations of twin-propeller and twin-rudder ship in shallow water using equivalent single rudder model

Hydrodynamic analysis of ship manoeuvrability in shallow water using high-fidelity URANS computations

The manoeuvring performance of a ship in shallow water is substantially different from its performance in deep water, attributed to shallow water effects caused by the presence of a finite water depth. Without a doubt a ship will navigate in areas of shallow water at various times during its operational life (such as when approaching harbours or ports), which underscores the importance of understanding the shallow water effects on ship manoeuvrability. In the present paper, the manoeuvrability of the KRISO Container Ship (KCS) model in different shallow water conditions was comprehensively analysed by means of the unsteady Reynolds-Averaged Navier-Stokes (URANS) computations coupled with the equations of rigid body motion with full six degrees of freedom (6DOF). A dynamic overset grid approach was implemented to allow the ship hull to move in 6DOF in a computational domain and to enable the rudder to be deflected according to a rudder controller for free-running manoeuvres. A series of manoeuvring simulations were performed in shallow waters with water depth to draft ratios varying between 1.2 and 4.0, and partially validated with the available experimental data from a free running test. The numerical results revealed that the ship advance, transfer, and tactical diameter mainly increased with the decrease in the ratio of water depth to draft, closely associated with the complicated interactions between the hull wake, boundary layer, propeller, vortex, and sea floor.

Range estimation of a distant ship using a vertical array and a guide ship

In this talk, we present a method for estimating the range of a distant ship in shallow water using a vertical array and a guide ship at a known range close to the array. The method involves a combination of four well-known approaches: (1) blind deconvolution; (2) waveguide invariant; (3) virtual receiver; and (4) array invariant. The main idea is to transform theoriginal task of estimating the range of a distant ship using a vertical array into estimating the range with a synthesized horizontal array aroundthe guide source exploiting the waveguide invariant theory. The proposed method is demonstrated for a surface ship radiating broadband noise (100–500 Hz) at 10 km range, using a 56.25-m long vertical array in approximately 100-m water and the same ship at 2 km range as the guide ship.

Reduction of UKC for Very Large Tanker and Container Ship in Shallow Water

The decrease in under keel clearance (UKC) due to the increase of draft that occurs during advancing and turning of very large vessels of different types was analyzed based on computational fluid dynamics (CFD). The trim change in the Duisburg test case (DTC) container ship was much smaller than that of the KRISO very large crude oil carrier 2 (KVLCC2). The sinkage of both ships increased gradually as the water depth became shallower. The amount of sinkage change in DTC was greater than that in KVLCC2. The maximum heel angle was much larger for DTC than for KVLCC2. Both ships showed outward heel angles up to medium-deep water. However, when the water depth became shallow, an inward heel was generated by the shallow water effect. The inward heel increased rapidly in very shallow water. For DTC, the reduction ratio was very large at very shallow water. DTC appeared to be larger than KVLCC2 in terms of the decreased UKC because of shallow water in advancing and turning. In this study, a new result was derived showing that a ship turning in a steady state due to the influence of shallow water can incline inward, which is the turning direction.

Localization of a distant ship using a guide ship and a vertical array.

A method is presented for estimating the range of a distant ship in shallow water using a vertical array and a guide ship at a known range close to the array. The method involves a combination of four different approaches: blind deconvolution, waveguide invariant, virtual receiver (VR), and array invariant. (1) Blind deconvolution extracts a time-domain Green's function from the broadband acoustic source (guide ship). (2) The Green's function is extrapolated into adjacent ranges using the waveguide invariant, generating a horizontal array of synthetic guide sources. (3) Each guide source then turns into a VR where the output approximates the signal that the distant (objective) ship will produce at the location of the guide source. (4) The horizontal virtual array around the guide ship applies the blind deconvolution again to estimate the Green's function for the objective source, followed by the array invariant to estimate the distance between the two ships. The proposed method is demonstrated using a ship of opportunity radiating broadband noise (100-500 Hz) and a 56.25-m long vertical array in approximately 100-m water.

Numerical Analysis of Hydrodynamic Loads on Passing and Moored Ships in Shallow Water

In this study, hydrodynamic interactions between passing and moored ships were studied by applying a time-domain numerical simulation method. The boundary value problem for a fluid domain was formulated based on a potential flow theory. A numerical method was developed based on a finite element method with an efficient re-mesh algorithm. Regarding the free-surface boundary conditions, both double-body and free-surface models were considered for examining the free-surface effect on the hydrodynamic forces due to the passing ship. First, numerical results were validated by comparison with the model test results of Kriebel et al. (2005), where generic Series 60 hulls were considered as the target model for the passing and moored ships. In addition, hydrodynamic pressure fields and force time-series were investigated to understand the passing ship problem. Second, a series of numerical simulations were performed to study the effects of the passing ship speed, separation distance, water depth, and relative vessel size, which were used to compare the peak values of hydrodynamic forces. The applicability and limitations of the double-body and free-surface models are discussed for predicting passing ship loads.

Manoeuvring prediction of a container ship in shallow water using numerical planar motion mechanism

ABSTRACT Manoeuvring behaviour of a vessel changes drastically when it enters from deep water region to a shallow water region. Flow characteristics, around the hull changes and the vessel, respond poorly to the use of control surfaces. Aim of this paper is to study the manoeuvring behavioural changes in a container ship for different water depth conditions. Computational fluid dynamic (CFD) methods are used for simulating static and dynamic captive model tests. Variation in hydrodynamic reaction forces and moments caused by the reduction in water depth and the subsequent effect in hydrodynamic derivatives appearing in the equation of motion are explained in detail. Standard turning circle and zigzag manoeuvring tests are simulated using the CFD generated hydrodynamic derivatives to assess the manoeuvring characteristics of the vessel.

Characteristics of Turning Circle and Zig-Zag Manoeuvres of An Indonesian Ferry Ship In Shallow Water

Ship manoeuvring performance is very important in navigation safety, especially when ships operate in shallow water. This paper describes the characteristics of turning circle and zig-zag manoeuvres of Indonesian ferry ships in shallow water. A time-domain simulation program was developed for this purpose. Several parameters such as ship speed and water depth levels have been considered in the simulation. The results shows a significant difference in the ship’s trajectory and speed when the ship manoeuvring in different water depths. The ship manoeuvre trajectory diameter for shallow water (h/T=1.3) is greater than in deep water (h/T=4.0). Meanwhile, the speed of the ship during turns increases with the decreasing depth of the water (h). Likewise, the 20/20° zig-zag manoeuvre of the ship shows that the heading angle in shallow waters has a smaller overshoot angle when compared to the ship manoeuvres in the deep waters.

Experimental investigation of practical autopilots for maritime autonomous surface ships in shallow water

To evaluate the performance of autopilots in real scenarios for maritime autonomous surface ships (MASS), this article investigates four autopilots via the experimental study instead of the theoretical analysis and discusses their application capabilities. Free running model tests with four autopilot algorithms were performed using a scale model of a Liquefied Natural Gas (LNG) carrier in the towing tank at Flanders Hydraulics Research (FHR), and they were tested at different forward speeds and Under Keel Clearances (UKCs) focusing on the autopilot performance in shallow water. Furthermore, an innovative method combining the model evaluation mechanism and the grey relational decision-making theory was proposed to comprehensively evaluate the performance of autopilots. Finally, we discussed the application potential of the autopilots for controlling a surface ship in shallow water and presented shallow water effects on autopilots’ performance. The four autopilots presented in this research could successfully follow the desired trajectories with satisfactory control effects in shallow water, but their performance varied in different scenarios. Our results indicate the tested controllers can be applied in the towing tank, but for optimum selection of autopilot algorithms, we should take into consideration multiple factors including controller parameters, trajectory, and test condition, etc.

Prediction of Hydrodynamic Derivatives of KCS Based on Computational Fluid Dynamics

Aiming at predicting the maneuverability of the ship in shallow water, KCS was selected as the research object. Static drift motion, pure sway motion, and pure yaw motion were performed to calculate the dimensionless hydrodynamic derivatives of KCS. A commercial software, STAR-CCM+ was used to simulate various kinds of movement conditions, by which the force and moment on the hull can be monitored. Then, through the curve fitting, hydrodynamic derivatives of KCS were predicted, and the maneuverability of KCS can be predicted.