Low Speed Ship Manoeuvrability: Mathematical Model and its Simulation

Validation of 4DOF maneuvering coefficients optimization using hydrodynamic force and moment estimated from free-running model test results

To investigate the flow field characteristics of full-scale ships advancing through confined waters, the international standard container ship (KRISO Container Ship) was considered as a research object in this study. Using the RANS equation, the volume of fluid method and the body force method were selected to investigate the hydrodynamic characteristics of a model-scale ship (the model-scale ratio λ=31.6) and a full-scale ship advancing through confined waters at low speed. A virtual disk was used in the full-scale model to determine the influence of the propeller on the ship’s flow field. First, the feasibility of the numerical calculations was verified. This proves the feasibility of the numerical and grid division methods. The self-propulsion point of the full-scale ship at Fr=0.108 is determined. The calculation cases of model-scale and full-scale ships (with or without virtual disks) at different water depths and distances between the ship and the shore were calculated, and the changes in the hull surface pressure, the flow field around the ship, and the wake fraction near the ship propeller disk in different calculation cases were determined and compared. The variations in the surge force, sway force, and yaw moment between the model- scale and full-scale ships were generally consistent. In very shallow water (H/T=1.3), the non-dimensional force and moment coefficients for model-scale ships increase more rapidly with decreasing distance from shore, suggesting that using model-scale ships to investigate the wall effect in very shallow water will result in predictions that are biased towards safety. By comparing full-scale ships with and without propellers, it was discovered that the surge force, sway force, and yaw moment were marginally greater in the propeller-equipped ship due to the suction effect, and the accompanying flow before and after the propeller was slightly smaller, with less asymmetry.

URANS study of scale effects on hydrodynamic manoeuvring coefficients of KVLCC2

Predicting ship resistance in shallow water conditions is very important for the operational considerations of a ship. Shallow waters greatly affect viscous resistance, wave resistance and also propulsion efficiency. This study aims to determine the effect of water depth on the resistance of the ferry. The CFD method was used to simulate this phenomenon and its effects on the hull starting from the coefficient of ship resistance, surge force, sway force and yaw (hydrodynamic moment). Input speed at 9 – 13 knots with depth ratio H/T = 4 (deep water), H/T = 3 (deep water), H/T = 2 (medium water), H/T = 1.3 (shallow water), and H/T = 1 (very shallow water). The simulation results show a significant increase in total resistance, surge force, sway force, and hydrodynamic moment in shallow water conditions in every speed variation. This condition is caused by the increase in pressure received by the ship's hull when operating in shallow water.

Several off-line teaching robot-welding systems for shipbuilding were developed in these ten years. These systems have been used mainly at sub-assembling stages in shipyards and utilize several robots and the geometrical design data in three-dimensional CAD. However, the systems usually have less efficiency in robot utilization due to the interference of robots, less adaptability to various types of ships, and less compliance with contingencies in daily operation such as robot malfunction and schedule change. Understanding these disadvantages of conventional robot welding systems, the authors have overcome these in developing a new off line teaching robot-welding system with four robots. High efficiency in robot utilization has been achieved by carefully designed locations of robots avoiding the interference of robots. Moreover, the robot can detect interference with another robot in advance and skip the welding line. It also can detect the malfunction of other robots next to it and carry out the welding that the troubled robots should have done. The robot welding can be applied to multi-layer welding with Hyper Arc Sensor for tracing the weld line and detecting the end of line. These development items have made the newly developed system efficient in robot utilization, adaptable to various types of ships, and compliant with robot malfunction and schedule change.

CFD, system-based and EFD study of ship dynamic instability events: Surf-riding, periodic motion, and broaching

An experiment was conducted in the SIMONA Research Simulator to investigate the influence of sway, roll and yaw motion cues on pilot performance, control and motion perception during decrab maneuvers. In the experiment, six pilots were instructed to perform manual decrab maneuvers in heavy crosswind conditions with a Cessna Citation 500 model. The contributions of yaw, roll and sway motion stimuli were varied independently, such that their individual effects on objective measures and subjective ratings could be examined. The results of this experiment show that yaw motion had a positive influence on touchdown performance in terms of lateral position with respect to the runway centerline. Roll motion significantly decreased roll rate variations during decrab, which indicates its importance in aircraft handling. High workload and the relatively low intensity of lateral motion cues led to the fact that pilots were unable to give consistent fidelity ratings. This emphasizes the need for an objective and quantifiable method to determine motion fidelity for such maneuvers. Pilot models can possibly be used to investigate the influence of different motion cues in these transient control tasks and it is hoped the results and lessons learned in this experiment can contribute to this future work.

This paper investigates sway, roll and yaw motions of a floating body with the aim to determine coupled motion characteristics based on the order-wise analysis of hydrodynamic coefficients. To compute the hydrodynamic coefficients and wave force exerted on the floating body, we employ speed-dependent strip theory. The governing equations are solved analytically for linear restoring moment. For nonlinear restoring moment which is expressed as an odd-order polynomial of fifth degree in roll angle, we apply the Runge–Kutta–Gill method to solve the coupled equations. To investigate the effect of initial disturbances on sway, roll, yaw and speed of the body, numerical experiments have been carried out for a Panamax Container ship under the action of a sinusoidal wave of periodicity 11.2 s with varying wave height and speed. For the linear restoring moment, we first derive associated motion equations for various cases based on the relative magnitude of the hydrodynamic coefficients. The order-wise analysis leads to the classification of coupled characteristics exhibiting the nature of coupling. For the nonlinear restoring moment, we notice that the initial disturbance plays an important role in the ship’s stability. The effects of forward speed and variation in wave heights are illustrated through typical numerical experiments.

The International Maritime Organization (IMO) finalized the second-generation intact stability criteria in 2022. However, an accurate and practical numerical method for stability loss has yet to be established. Therefore, a 6 DOF numerical model is further improved based on the previous study. Firstly, the rolling motion is simulated using a seakeeping model instead of the previous maneuvering mathematical model. Secondly, the roll-restoring variation is calculated directly considering the instantaneous wet hull instead of the previous pre-calculated method. Thirdly, transferring frequency to time is used to obtain heave and pitch motions, further considering yaw angle and sway velocity. Fourthly, the dynamic forces for sway, roll, and yaw motions are calculated, further considering the effect of the speed variation. Fifthly, the 6 DOF motions are used to determine the instantaneous wet hull, and the FK force and the hydrostatic force are calculated by the body’s exact method. Finally, a new conclusion is obtained that the sway and yaw motions’ effect on the ship speed loss, the relative longitudinal wave profile by the speed loss, the rudder angles, and the accompanying rudder forces in the rolling direction are significant, and much more than their centrifugal force or coupled force in the rolling direction.

ellipsoids are taken as an example. By coupling the motion equations of the two bodies and the fluid flow equations, the interaction forces and moments are calculated, and the tracks are predicted. The numerical results for the model fixed motion (only free to surge) at constant speed are compared with those published in literature for the validation of the method proposed in this paper, and good agreement is found. On this basis, more complicated multi-degree of freedom motions in surge, sway and yaw directions induced by the interaction effects are simulated. By systematically comparing and analyzing the numerical results obtained at different speeds, lateral distances and body sizes, the influences of speed and lateral distance and body size The sway and yaw motion will be induced additionally due to the interaction effects when two encountering bodies sail in close proximity, which may lead to the collision accident. In the present study, two on the hydrodynamic forces are elucidated.

The national power currently standards are not uniform, it can be used for all kinds of transport such as cars, various types of ships, and the vehicle's voltage regulator power inverter using widely. In the field of solar and wind power, the regulator power inverter plays an irreplaceable role. With the voltage regulator power inverter, we can use the direct current (batteries, switching power supply, fuel cells, etc.) into alternating current to provide a stable and reliable power for the electrical. Voltage and variable frequency power supply's studying in the current national economic development is of great significance. The purpose of this design is the design voltage and variable frequency power supply, use the intelligent control chip AT89C51 as the control of the core components of the PWM control signal. Combined with CPT technology in the converter, in isolation for the drive circuit to achieve power on-off controlling. To realize the power supply voltage and frequency adjustable.

Radar is commonly used to detect and track ships in maritime surveillance. Unfortunately the systems are costly and do not provide any visual information about the object's type. To complement the ship identity information given by a radar system, we propose a supplementary system using active visual cameras that can robustly detect and track ships in harbours. By combining a high-quality, non real-time robust object detector with a feature point tracker with low computational complexity, it is possible to track ships in real time over long intervals and large distances. In addition to controlling pan and tilt, we dynamically control camera zoom to provide a high resolution image of the tracked object over a large range of distances. The tracking system is improved by a special motion estimation model for the feature points, which also incorporates zooming of the camera. The system is robust and sustains tracking even under challenging conditions, such as multiple viewpoints, a large variety of ships and various weather conditions. During experiments, various types of ships were successfully tracked for up to 18 minutes, and over a distance of almost 1.5km in the port of Rotterdam. The proposed system is generic and can be utilized in various tracking applications, by training the detector for a different object class.

_ The International Maritime Organization (IMO) has been discussing technical issues by dividing the second-generation intact stability criteria for ships into five types. In this paper, we paid attention to the dead ship condition and introduced the process for the assessment of Levels 1 and 2 in detail. Dead ship condition refers to a case where a large angle of rolling motion occurs due to waves incident on the side of the ship’s hull after the ship’s engine has failed. Basically, in the dead ship condition, if the Level 1 criterion for analysis related to the GZ curve is not satisfied, an evaluation is performed against the Level 2 criterion considering the hydrodynamics of waves. The method for the effective wave slope function required to obtain the spectrum of the effective relative roll angle, which is the most important factor in the calculation of Level 2, was implemented. In particular, unlike existing ship types in terms of various experiences, this study performed stability evaluation using special ship data of a 5000HP tug boat and obtained results that satisfied both Level 1 and 2 standards. Through this example of dead ship condition evaluation for a tug boat, we aim to ensure the expansion of IMO second-generation intact stability evaluation targets for various types of ships. Keywords IMO second generation intact stability criteria; dead ship condition; GZ curve; effective wave slope function; tug boat

Abstract. Reliable ship detection plays an important role in both military and civil fields. However, it makes the task difficult with high-resolution remote sensing images with complex background and various types of ships with different poses, shapes and scales. Related works mostly used gray and shape features to detect ships, which obtain results with poor robustness and efficiency. To detect ships more automatically and robustly, we propose a novel ship detection method based on the convolutional neural networks (CNNs), called SCNN, fed with specifically designed proposals extracted from the ship model combined with an improved saliency detection method. Firstly we creatively propose two ship models, the “V” ship head model and the “||” ship body one, to localize the ship proposals from the line segments extracted from a test image. Next, for offshore ships with relatively small sizes, which cannot be efficiently picked out by the ship models due to the lack of reliable line segments, we propose an improved saliency detection method to find these proposals. Therefore, these two kinds of ship proposals are fed to the trained CNN for robust and efficient detection. Experimental results on a large amount of representative remote sensing images with different kinds of ships with varied poses, shapes and scales demonstrate the efficiency and robustness of our proposed S-CNN-Based ship detector.

Improvement of the prediction of the added resistance in waves of ships with extreme main dimensional ratios through numerical experiments