Ship Speed Research Articles

Wave Drift Force and Moment in Deep and Shallow Water

To attain a low Energy Efficiency Design Index (EEDI), large ships possibly lack the necessary propulsion power to avoid stranding in case of strong adverse wind and wave conditions. To estimate this danger, here, the longitudinal and transverse drift force and the yaw drift moment caused by regular waves of arbitrary frequency and direction are computed using a 3-dimensional Rankine panel method. In many cases, drift forces are larger in shallow than in deep water. Therefore, the theory for computing drift force and moment is extended to shallow water. As published results for shallow water are lacking, the method is verified only for deep water by comparisons with results of model experiments and CFD computations for three ships. For one of them, the dependence of non-dimensional coefficients of longitudinal and transverse drift force and of the drift yaw moment on wave frequency, wave angle, water depth and ship speed is shown. The source files of the programs used for these computations may be obtained from the author if an adequate fee is donated to the Medecins Sans Frontieres or to the author.

Research on ship speed prediction based on time series imaging and deep convolutional network fusion method

Research on ship speed prediction based on time series imaging and deep convolutional network fusion method

소형 플레저보트 저항성능 향상을 위한 선형디자인 연구

This study was designed to propose a non-commercial “small pleasure boat” design of a catamaran with a vessel length of less than 12 meters, with relatively simplified construction procedures and safety inspection standards compared to general ships, in order to strengthen the design and design capabilities of small and medium-sized ships. Using the programs Rhino 4.0 & Maxsurf, stability and effective horsepower were calculated for the 1st, 2nd, and 3rd stages. A small pleasure boat design was proposed by applying a line with improved resistance. In order to propose a design to improve resistance performance, the resistance performance of symmetrical catamaran type A and asymmetric catamaran type B was calculated to calculate the required horsepower (EHP) for each ship speed and compare the resistance performance.

Optimal Design of BOG Reliquefaction Systems for LNG Carriers: A Focus on GMS Performance During Loaded Voyages

AbstractThis study proposes a strategy for evaluating efficient design of the Gas Management System (GMS) on LNG carriers by decomposing its performance to subsystems: the reliquefaction system (RS) and the fuel gas supply system (FS). With increasingly stringent maritime regulations on greenhouse gas emissions, the need for efficient LNG carrier operations has become critical. A major factor in reducing fuel consumptions and carbon emissions is optimizing the design of the RS, given its significant power demand for processing NBOG. However, effective GMS design must account for variations in RS operation performance, as well as the contributions of the FS in treating NBOG with changes in ship speed. This study compares GSM configurations with reliquefaction systems based on two representative refrigeration cycles: the nitrogen reverse Brayton cycle (NRBC) and the single mixed refrigerant cycle (SMRC), both analyzing effects of cold BOG utilization. Results indicate that the RS of GMS4A-aSMRC [the aSMRC is the refrigeration cycle which utilizes cold BOG within the Single Mixed Refrigerant Cycle (SMRC)] demonstrates superior RS design performance. However, the most efficient GMS configuration varies with the Boil-off Rate (BOR): GMS2-aNRBC [the aNRBC is the refrigeration cycle which utilizes cold BOG within the Nitrogen Reverse Brayton Cycle (NRBC)] is optimal aligning with its RS performance for a 0.11%/day BOR, while GMS3-SMRC without cold BOG in RS is the most efficient for a 0.075%/day BOR, owing to increased contributions from the FS. In this study, a performance index with a consistently comparable baseline is derived to accommodate compositional deviations from flash gas recirculation at NBOG disposal streams, enabling the GMS performance to be correlated with compatible values of its decomposed subsystem.

Research Progress on Using Modified Hydrogel Coatings as Marine Antifouling Materials.

The adhesion of marine organisms to marine facilities negatively impacts human productivity. This phenomenon, known as marine fouling, constitutes a serious issue in the marine equipment industry. It increases resistance for ships and their structures, which, in turn, raises fuel consumption and reduces ship speed. To date, numerous antifouling strategies have been researched to combat marine biofouling. However, a multitude of these resources face long-term usability issues due to various limitations, such as low adhesion quality, elevated costs, and inefficacy. Hydrogels, exhibiting properties akin to the slime layer on the skin of many aquatic creatures, possess a low frictional coefficient and a high rate of water absorbency and are extensively utilized in the marine antifouling field. This review discusses the recent progress regarding the application of hydrogels as an important marine antifouling material in recent years. It introduces the structure, properties, and classification of hydrogels; summarizes the current research status of improved hydrogels in detail; and analyzes the improvement in their antifouling properties and the prospects for their application in marine antifouling.

Numerical study on hydroelastic responses and bending-torsion coupled loads of a ship in oblique regular waves

In this paper, the CFD-FEM two-way coupled method is extended to simulate the asymmetric motions and wave load responses of a ship in oblique regular waves considering hydroelasticity effects. The numerical results of ship motions and loads including time series and response amplitude operators are validated by comparing with the tank experimental results. Then the ship motions, vertical bending moment, horizontal bending moment and torsion moment in oblique waves are analyzed in both time domain and frequency spectra; and the influence of wave height, wave length and ship speed on the results are systematically analyzed. Moreover, the correlation between horizontal bending moment and torsion moment as well as their component loads is analyzed by cross-spectral analysis method. The effect of springing responses corresponding to the bending-torsion coupled mode on the sectional loads is also discussed.

Effect of multiple appendages on maritime surveillance ship resistance at various ship speeds

Resistance is a critical factor affecting the operational performance and economic efficiency of marine surveillance ships. To enhance the enforcement efficiency of marine surveillance ships, this study investigates the impact of five types of appendages on ship resistance performance. In this study, resistance experiments and numerical simulation calculation on the ship model were carried out. Based on Computational Fluid Dynamics (CFD) and the Volume of Fluid (VOF) method, the study captures the variations in ship resistance and the free surface Cases around the hull. A comparative analysis was then conducted on the resistance effects of different appendages installed on the ship model. It was found that the installation of stern shaft brackets, bilge keels, and ductkeel increased the ship's resistance. In contrast, the installation of spray rails reduced resistance by approximately 2.5%. However, the effectiveness of the spray rails diminished at high speeds due to their inability to prevent wave overtopping. Since stern flaps are commonly used drag-reducing appendages, this study improved the original design. Comparative analysis revealed that the modified curved structural design of the stern flaps exhibited enhanced drag reduction capabilities.

Research on Effect of Ship Speed on Unsteady Hydrodynamic Performance of Bow Thrusters in Berthing and Departure Directions

With the continuous development of the shipping market, bow thrusters have become more important for ship maneuvering. Therefore, the performance of bow thrusters is studied in this paper. In order to obtain an unsteady performance of the bow thruster under different ship speed conditions, the SST k-ω turbulence model is adopted to predict the hydrodynamics of the bow thruster. With the ship’s speed increasing gradually, the variation characteristics of hydrodynamic coefficients and the flow field distribution at key positions are analyzed. The results show that with an increase in ship speed to three knots, the thrust coefficient and torque coefficient of the bow thruster decrease by 2.69~4.07% and 2.34~3.08%. In addition, the blade vibration amplitude intensifies. In the departure direction, the propeller load is more susceptible to being influenced and decreases by an additional 2.34~4.16% compared with that in the berthing direction. Meanwhile, it is found that the velocity distribution is asymmetrical. The inlet velocity at the bow side is faster, which results in the maximum peak pressure being about three times the minimum peak pressure. In addition, the pressure’s nonuniformity in the tunnel increases gradually with the increase in ship speed. Compared with the pressure distribution in the berthing direction, the pressure distribution before and after the propeller is more uniform, which is consistent with the results of hydrodynamic change and velocity distribution. The research in this paper has a certain reference significance for understanding the hydrodynamic performance of bow thrust operation.

Research on Course-Changing Performance of a Large Ship with Spoiler Fins

The poor maneuverability inherent to large ships is a non-negligible problem that restricts the development of the shipping industry, as large ships can only cruise at an excessively conservative speed when they encounter complicated traffic conditions; nevertheless, ship collision accidents still occasionally occur. In the present study, the novel concept of spoiler fins for modern large ships is proposed. In order to assess their effectiveness in enhancing ship maneuverability, a KRISO container ship (KCS) was selected to carry a pair of spoiler fins, after which a simplified simulation approach for saving the calculation resource was designed for ship collision avoidance conditions, and a full-scale numerical model, including the ship hull, fin, and fluid field domain, was established. Transient-state hydrodynamic forces were calculated during collision avoidance maneuvers using the CFD method; the pressure and velocity contours around the ship were demonstrated; and the ship motion trajectories under different initial ship speeds were simulated and predicted through the adoption of overset mesh and 6-DOF dynamic mesh techniques. Eventually, the improved course-changing performance, dependent on the spoiler fins, was validated.

Hydroelasticity of a 21000TEU containership under freak waves by fluid-flexible structure interaction simulations

In this paper the CFD-FEM two-way coupled method is used to simulate the motions and wave loads on a 21000TEU containership subjected to freak waves. A numerical wave tank is established for the generation of long-crested freak waves by wave focusing method based on superimposing sinusoidal component waves. The ship hull is modeled with a backbone beam which reproduces the vertical bending vibration modal behaviour of real ship. The simulated freak waves are checked and the evolution of freak waves during propagation is analyzed first. The ship responses in regular waves at different wave heights and ship speeds are compared. The extreme responses of ship motion and sectional loads in freak waves are analyzed and compared with those in regular waves. The influence of ship forward speed and wave height of freak waves on ship motion and load responses are analyzed and discussed.

Wingsail performance in unsteady atmospheric surface layer winds

The performance of wind propulsion systems is evaluated in unsteady inhomogeneous winds with tools that are routinely used to predict the performance of wind turbines and which give access to the unsteady aerodynamic forces acting on the wingsail. A rigid wingsail exposed to a realistic atmospheric surface layer wind is used as a testbed. For this case, we show that standard deviations of the aerodynamic driving force are larger than 15%–20% of the mean values when the true wind velocity is larger than the ship speed. We also show that the mean aerodynamic driving forces computed by averaging the unsteady driving forces are only slightly smaller than the ones computed on the mean wind despite the strongly nonlinear dependence of the unsteady forces on the wind velocity and direction.

An Enhanced Shuffle Attention with Context Decoupling Head with Wise IoU Loss for SAR Ship Detection

Synthetic Aperture Radar (SAR) imagery is widely utilized in military and civilian applications. Recent deep learning advancements have led to improved ship detection algorithms, enhancing accuracy and speed over traditional Constant False-Alarm Rate (CFAR) methods. However, challenges remain with complex backgrounds and multi-scale ship targets amidst significant interference. This paper introduces a novel method that features a context-based decoupled head, leveraging positioning and semantic information, and incorporates shuffle attention to enhance feature map interpretation. Additionally, we propose a new loss function with a dynamic non-monotonic focus mechanism to tackle these issues. Experimental results on the HRSID and SAR-Ship-Dataset demonstrate that our approach significantly improves detection performance over the original YOLOv5 algorithm and other existing methods.

Trajectory tracking for autonomous surface ships using Gaussian process regression and model predictive control with BVS strategy

Autonomous navigation is critical to the development of next-generation shipping systems. The proposal of intelligent ships enables innovation in the shipping and shipbuilding industry and increases the safety and efficiency of ship operations. Autonomous control of surface ships to follow a prescribed trajectory is critical in a variety of maritime applications. This paper proposes a trajectory tracking control strategy for autonomous surface ships that combines nonparametric modelling using Gaussian Process Regression (GPR) with the Model Predictive Control (MPC) framework. A Bézier curve-based Virtual Ship(BVS) guidance strategy is proposed to convert dynamic trajectory points into reference heading angles and speeds, such that the trajectory tracking problem can be decomposed into heading control and speed control problems. Gaussian process regression is utilised to identify the correlation between propeller revolution speed and ship speed, as well as the correlation between rudder angle and heading angle based on experimental data. Two GPR models are therefore constructed as the prediction models for designing MPC controllers for heading control and speed control, respectively. Nonlinear optimisation algorithms are utilised to search for optimal control commands in each sampling interval to solve the optimisation problem in MPC with GPR models and input constraints. Simulations are carried out to evaluate the effectiveness of the proposed method.

Ship Forebody Optimization Based on Rankine Source Method

Abstract The shape of the ship’s forebody has a greater impact on the ship’s resistance, and a reasonable optimization of the forebody can play a role in reducing the propulsion power and optimizing the resistance performance. Under the premise of Rankine source method of potential flow wave theory as the theoretical basis, SHIPFLOW software is used as the calculation tool, and CAESES software is used as the optimization tool to study the optimal design of the ship with minimum wave resistance. In the optimization process, a real ship is taken as the object, and the optimal solution of the rising wave resistance coefficient is calculated with the rising wave resistance coefficient as the objective function and the ship speed and displacement as the constraints. The real ship is selected as the mother ship, the parameters of the hull shape are taken as the design variables, and the shape of the forebody is optimized by the Lackenby shift method, so as to obtain a ship shape with less wave resistance at the same speed and within the displacement limit. The results show that the improved ship shape has obvious effect of reducing the wave resistance, which verifies the effectiveness and feasibility of this method for ship shape optimization

Simulation and optimization of paddle control for small electric ship

Abstract Aiming at the problems of weak anti-interference ability, slow response speed, and unstable motor speed of traditional PID control for electric small ships, a simulation model of the oar is designed by combining the key factors of ship displacement, ship speed, and ship situation resistance. The load of the ship’s propulsion motor during operation is simulated. Combined with the motor model, the motor speed curve and the ship speed prediction curve under PID control and fuzzy control are observed. A more stable and faster response speed electric ship control method is obtained.

The effect of failure on energy efficiency in maritime vessels autopilot systems

The increasing demands for energy efficiency and environmental sustainability in the maritime industry have underscored the critical importance of optimizing autopilot systems, which, despite their significance, are often overlooked in ship energy efficiency management. The objective of this study is to enhance the energy efficiency of ships by focusing on the efficiency of autopilot systems, which play a significant role in the management of energy efficiency. The research emphasizes the need for effective decision support systems for ship operators, not only for optimizing ship speeds but also for making informed operational decisions. By utilizing Fuzzy Fault Tree Analysis (FFTA), the study identifies and prioritizes the causes of efficiency losses in autopilot systems and examines their frequency. Based on expert opinions, the research delves into the complexity of autopilot systems and the interactions among various components. Notably, the study highlights the impact of multiple factors on the efficiency of complex autopilot systems, elucidating their relationships through Minimum Cut Sets (MCS) analysis. Furthermore, attention was drawn to the “Improper Alarm Input” event caused by insufficient knowledge and awareness among ship operators, which hinders the effective use of autopilot systems. The findings demonstrate that decision support systems can increase energy efficiency and contribute to the reduction of operational errors by reducing the human factor, which is 99% effective on the “Inefficient Heading Control System”. Additionally, proper utilization of autopilot systems can lead to a decrease in a ship's carbon footprint and operating costs. Overall, the results can affect strategic decisions in ship energy efficiency management and encourage significant steps toward achieving International Maritime Organization's (IMO) sustainability objectives.

Predicting practical ship powering and speed loss in waves using added resistance test results

ABSTRACT This paper introduces a practical technique for accurately estimating ship propulsion and speed loss in the presence of waves. Utilising the previously established self-propulsion estimation framework, our approach enhances the method, which previously solely considered bare hull resistance, propeller performance, thrust deduction factor, and wake fraction, by incorporating added resistance test results. The full-scale DTC container ship is the focus of our investigation, providing a thorough examination of its performance in different sea states. The model's predictive abilities are enhanced by incorporating test data on added ship resistance, and it addresses a crucial aspect that is generally disregarded while estimating self-propulsion. This research is considered to be a contribution to the advancement of ship hydrodynamics, as it offers a practical and reliable tool for ship designers, operators, and researchers to accurately assess powering requirements and speed loss in harsh ocean conditions.

Big Data Analysis of the Speed Performance of a 176k DWT Bulk Carrier in Real Operating Conditions

Assessment of ship performance under in-service conditions is challenging due to the complex effects of many environmental disturbances. ISO 15016 and ISO 19030 standards are commonly used to evaluate ship operating performance. However, ISO 15016 requires numerous variables, a complex calculation formula, and considerable time and cost, and ISO 19030 only evaluates the reduction of ship speed caused by wind and neglects the effect of waves. To improve both standards and achieve a more accurate ship performance assessment, this study proposes a new performance prediction model, the multi-input single-output (MISO) system, which assumes that each ship has specific frequency characteristics according to type and size. Based on this new model, in-service navigation data collected from a 176k DWT bulk carrier, which amount to 5.7 million data points, are analyzed to assess the speed performance of the vessel subject to environmental disturbances. The proposed model was validated by comparing its results with ISO 19030 and specifically assessing the speed–power curves and speed reduction measured in operational data with the influence of environmental disturbances removed.

Influence of energy-saving devices on the hydrodynamic characteristics of a waterjet-propelled ship: Experimental and numerical investigation

Installing stern energy-saving devices can help conserve energy and enhance ship speed, particularly for medium-to-high-speed ships. This study focuses on a waterjet-propelled ship and examines the performance of two energy-saving devices: the interceptor and stern flap. The investigation involves conducting a comparative analysis through towing-tank experiments and utilising Reynolds-averaged Navier–Stokes (RANS) numerical methods. The findings suggest that incorporating energy-saving devices alters the capture flow of the waterjet-propelled ship. Furthermore, these devices reduce ship resistance, resulting in a maximum decrease in the impeller speed of the self-propulsion point up to 5%. Following the installation of energy-saving devices, the propulsion efficiency of the waterjet-propelled ship demonstrates an enhancement ranging from 0.5% to 5.7%. This increase in propulsion efficiency emerges as a principal factor contributing to the energy savings facilitated by the stern energy-saving device. Upon comparison, it was found that within the Fr range of 0.3–0.5, the stern flap exhibited a superior energy-saving effect. Conversely, when Fr exceeded 0.5, the interceptor demonstrated a more pronounced energy-saving effect. Finally, the mechanisms of the stern energy-saving devices are elucidated based on the momentum velocity coefficient, thrust deduction fraction, and changes in the internal and external flow fields of the waterjet-propelled ship.

Ship visual trajectory exploitation via an ensemble instance segmentation framework

Maritime traffic safety is of utmost importance in the shipping industry. It is common to avoid potential traffic accident via the support of varied kinematic maritime data (e.g., ship position, ship speed). The study aims to fulfill maritime traffic safety enhancement by extracting multiple ship trajectories from maritime video data. The proposed framework is implemented with three steps. Firstly, the framework obtains initial ship imaging positions by proposing an ensemble YOLOX (You Only Look Once X) with CenterNet model. Secondly, ship contours from each maritime frame are explored with the deep snake module. Thirdly, consecutive ship imaging trajectory is identified with an enhanced Bytetrack multi-ship target tracking algorithm. Experimental results demonstrate that our model outperforms other ship trajectory extraction-like models considering that the identification F-Score (IDF1), IDP (identification Precision), IDR (identification recall), and MOTA (multi-object tracking accuracy) for our proposed framework were 0.965, 0.995, 0.933, and 0.925, respectively. The research findings can help ship crew better aware on-site traffic situations, and thus make optimal ship maneuvering operations for the purpose of enhancing maritime traffic system safety and sustainability.