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The study investigates the tethered underwater robot's maneuverability and hydrodynamic performance in a uniform flow field. A tethered underwater robot that installs a symmetrically Ka 4–70/19A ducted propellers and vertical rudder is first constructed to simulate the motion. The numerical simulation is based on the multiples computational fluid dynamics (CFD) techniques, such as overlapping grid, sliding mesh, and finite volume method that solves the N–S equations. The six-degrees-of-freedom model and relative motion principle are also adopted to investigate the hydrodynamic performance of the tethered underwater robot at different towing speeds. The reliability of the numerical method is verified by the experimental result. The numerical results indicate that the control effect of control equipment is greatly influenced by the towing speeds, and the mutual effect between the tethered underwater robot and control equipment is not negligible.

This paper presented the results of an experimental investigation into the resistance performance of a wave-piercing trimaran with three alternative side hull forms, including asymmetric inboard, asymmetric outboard, and symmetric at various stagger/separation positions. Model tests were carried out at the National Iranian Marine Laboratory (NIMALA) towing tank using a scale model of a trimaran at the Froude numbers from 0.225 to 0.60. Results showed that by moving the side hulls to the forward of the main hull transom, the total resistance coefficient of trimaran decreased. Findings, furthermore, demonstrated that the symmetry shape of the side hull had the best performance on total resistance among three side hull forms. Results of this study are useful for selecting the side hull configuration from the resistance viewpoint.

Different innovative ideas on simple stern fixtures such as stern wedges, flaps, interceptors have evolved over the past few years to improve the hydrodynamic performance of high-speed vessels, including planing crafts. This paper examines the hydrodynamic performance of a planing craft fitted with an interceptor alone and also an interceptor-flap combination at its stern, and the results are compared with the case where the craft uses the interceptor alone. An interceptor-flap combination is the one where an interceptor extends vertically downward at the transom with a flap attached to its end. Different angular orientations of the flap attached to interceptor bottom end and project towards aft are considered in the present study. The effectiveness of the integrated interceptor-flap system on the hydrodynamic performance of the vessel is influenced by the angular orientation of flap to the interceptor. Experiments were carried out on a planing hull with and without interceptor in the towing tank, Department of Ocean Engineering, Indian Institute of Technology Madras. Computational fluid dynamics (CFD) simulations are performed for the planing hull fitted with an integrated interceptor and flap. The investigations look into the aspects of vessel resistance, trim and bottom pressure distribution while it operates in calm water condition and at different speeds. The results show that trim and resistance of the vessel reduce with the use of integrated interceptor-flap at the stern with the flap angle at about 4° to the horizontal and they are less compared with a case where the only interceptor is used.

В статье описана математическая модель проектирования барже-буксирного комплекса с учётом особенности эксплуатации в условиях Республики Союз Мьянма. В статье исследуются особенности ББК как объекта оптимизации, описана математическая модель ББК, отображается его как сложную техническую систему. В рамках модели приведены математические зависимости и алгоритмы для определения элементов теоретического чертежа, мощности главных двигателей, для решения некоторых вопросов общего расположения с учетом расстояния главных водонепроницаемых переборок корпуса, для расчета нагрузки и устойчивости. Метод комплексной оценки эффективности применения барже-буксирного комплекса на стадии технико-экономического обоснования проекта в условиях развивающихся стран, в частности в условиях Республики Союз Мьянмы. В результате работы были полностью определены параметры основных типов барже-буксировочных комплексов для перспективной системы внутреннего водного транспорта Республики Союза Мьянма. На базе методов случайного поиска создан алгоритм оптимизации элементов ББК, решающий задачу математического программирования с процедурным характером функции критерия и функциональных ограничений. Математическая модель и алгоритм оптимизации реализованы в виде программы для обеспечения компьютерного эксперимента. Программа, реализующая математическую модель проектирования ББК, состоит из отдельных программных модулей, что облегчает ее совершенствование в анализе результатов решения задачи. Создан программный комплекс с использованием языка программирования Паскаль в среде Delphi для обеспечения автоматизирования проектирования. Указанные программы могут быть использованы в исследовательском проектировании на начальных стадиях проектирования. The article describes a mathematical models for designing a barge-towing complex, taking into account the peculiarities of operation in the conditions of the Republic of the Union of Myanmar. The article examines the features of the BBK as an object of optimization, describes the mathematical model of the BBK, displays it as a complex technical system. Within the framework of the model, mathematical dependencies and algorithms are given for determining the elements of the theoretical drawing, the power of the main engines, for solving some issues of the general location, taking into account the distance of the main watertight bulkheads of the hull, for calculating the load and stability. The method of comprehensive assessment of the effectiveness of the use of the barge-tow complex at the stage of the feasibility study of the project in the conditions of developing countries, in particular in the conditions of the Republic of the Union of Myanmar. As a result of the work, the parameters of the main types of barge-towing complexes for the prospective inland water transport system of the Republic of the Union of Myanmar were fully determined. On the basis of random search methods, an algorithm for optimizing the BBK elements is created, which solves the problem of mathematical programming with the procedural nature of the criterion function and functional constraints. The mathematical model and the optimization algorithm are implemented as a program to provide a computer experiment. The program that implements the mathematical model of the design of the BBK consists of separate program modules, which facilitates its improvement in the analysis of the results of solving the problem. A software package was created using the Pascal programming language in the Delphi environment to provide design automation. These programs can be used in research design at the initial stages of design.

The work is devoted to the problem of towing space debris from a geostationary orbit to a graveyard orbit by a non-contact method using an ion beam created by the engine of an active spacecraft. For the planar case using the modified Hill task, the points of relative equilibrium (libration points) of the active spacecraft relative to the object of removal are determined and their stability is estimated. It is shown that, depending on the values of radial acceleration, there are up to 6 libration points, but only one point is suitable for towing a space debris object. The required amount of fuel was determined for different values of thrust and specific impulse of the active spacecraft compensating engine during simultaneous operation of electric propulsion thrusters. The results can be used to stabilize the relative motion of the active spacecraft and determine the required amount of fuel for the mission to remove space debris.

This paper discusses three phases of the space debris removal with harpoon assistance: capture, tether deployment, and towing. The harpoon impact momentum is used to detumble the target. Equations ...

Hull form selection, resistance and powering are important in designing underwater vehicle. An underwater vehicle bare hull form is based on the five parameters due to the interaction between the propeller and the hull. When they are running on the surface condition, there will be problems likely as surface vessel, but the main hull of the underwater vehicle is below the waterline with low freeboard. The underwater vehicles are operating with high speed at a high Froude Number. Therefore, the wave making component becomes important in surface resistance. The wave making resistance of the underwater vehicle model at surface condition is analyzed by using CFD tools. Friction component of resistance is calculated by using ITTC’57 correlation line. The flow around the ship’s hull is complicated, so that model experiments are still the most reliable data source on ship resistance determination. The bare hull form of underwater vehicle resistance is based on the model experiments and CFD results. The towing mechanism arrangement should be considered at model. Therefore, towing mechanism is designed for model testing. This paper discusses the towing method and result between model test and CFD. This paper also makes comparison of wave formation Towing tank test and CFD at various speeds. The model was tested with bare hull form of underwater vehicle in the Ship Model Towing Tank at Marine Hydrodynamics Centre, Myanmar Maritime University. CFD analysis is also carried out and the results are compared for surface condition. The three software packages XFLOW, XMESH and XPAN are used for CFD simulations. The comparison of results shows that the coefficient differences are less staggered based on the speed.

It is a well-known fact that the 1989 Exxon Valdez disaster caused the escort towing of laden tankers in many coastal areas of the world to become compulsory. In order to implement a new type of escort towing, specially designed to be employed in very adverse weather conditions, considerable changes in the hull form of escort tugs had to be made to improve their stability and performance. Since traditional winch and ropes technologies were only effective in calm waters, tugs had to be fitted with new devices. These improvements allowed the remodeled tugs to counterbalance the strong forces generated by the maneuvers in open waters. The aim of this paper is to perform a comprehensive literature review of the new high-performance automatic dynamic winches. Furthermore, a thorough analysis of the best available technologies regarding towline, essential to properly exploit the new winches, will be carried out. Through this review, the way in which the escort towing industry has faced this technological challenge is shown.

In the last five years, towing to increasing demand for liquefied natural gas (LNG), researchers have actively analyzed and conducted studies on the sloshing phenomenon. However, there are limitations in the 1:1 model experimental method for LNG tanks installed in actual vessels. This study verified the validity of the average pressure prediction according to the scale ratio of a prismatic LNG tank that was developed through a correlation analysis between the sloshing analysis and model test. We then presented an average pressure prediction for the tank of a full-scale vessel. In addition, to ensure the safety of the tank, this study investigated the degree of cumulative fatigue damage that could be caused by cyclic loading through a fatigue analysis.

HighlightsModeling provides the relationships between path, kinematics, geometry, and towed implements.Linear interpolation allows trajectories to be compared if data recording is random.Correction coefficients can be a solution to compensate for soil resistance.Abstract. Automatic guidance systems and autonomous vehicles require tested methods of path generation to ensure successful maneuvers (such as automatic trajectory correction and headland turn management). In this study, an evolution of Zakin’s kinematic modeling, as applied in the automobile industry, is proposed for an agricultural poly-articulated vehicle (representing a tractor or other type of towing vehicle with one or more towed implements attached with an articulated hitch). Geometry, vehicle ground speed, and angular steering velocity are considered in the generation of maneuvering paths. Based on the specifics of real field conditions (slope, plant residue, resistance due to soil compaction, etc.), the initial model was improved by introducing correction coefficients. An experimental setup is proposed using a tractor with two towed implements and a testing method involving point-to-point path comparison. The modeling method has potential for integrating more complex procedures (such as path generation, geolocation, and following) into the design of a maneuvering management system for agricultural machines, which can contribute to the efficiency of field operations. Keywords: Agricultural vehicle, Headland turn automation, Maneuverability, Modeling, Path generation, Path planning, Poly-articulated vehicle.

The present study concerns a series of model tests in a towing tank on waterjet propulsive performance. The test model was an armored vehicle consisting of a box-shaped hull, two waterjets, a bow flap, and a trim tab. As per the powering prediction procedure of high-speed vessels, resistance tests, waterjet system tests, and self-propulsion tests were performed. The Froude number based on the characteristic length and advance speed for the model tests ranged from .981 to 1.178. Bollard pull tests were also conducted to investigate the interaction between the hull and two installed waterjets and to validate the flow rate estimation. In the self-propulsion condition, the dry transom and nozzle end modification changed the interaction efficiency. The waterjet reduced the vehicle trim in the self-propulsion condition, owing to the nozzle exit flow onto the trim tab. Introduction Waterjet propulsion systems have been widely used in marine vessels, thanks to its advantages of low cavitation in high loading, safe operation in shallow water, and good maneuverability at low advance speed (Allison 1993). However, the propulsive performance of waterjets is a complicated problem and hard to analyze. The extrapolation method for the powering performance prediction of waterjet-propelled vessel is suggested by the International Towing Tank Conference (ITTC) (ITTC 2011), but it is less comprehensive than that of the conventional ship with screw propellers (ITTC 2017a), as test institutions for waterjet-propelled vessels are scarce and test methodology is not standardized (Altosole et al. 2012).

The increase of seakeeping performance is of particular importance for car and passenger ferries, service ships in the gas and oil extraction industry and offshore wind power farm industry, as well as for special purpose ships (including military applications). In the water areas of the Baltic Sea, North Sea, and Mediterranean Sea, which are characterised by a short and steep wave, the hull shape has a substantial impact on the operational capacity and propulsion efficiency of the ship, as well as on comfort and safety of navigation. The article analyses selected aspects of seakeeping for four variants of a selected case study vessel, indicating practical limitations of the strip method. The analysed aspects included hull heaving and pitching, added resistance, Motion Thickness Indicator (MSI), and Subjective Magnitude (SM). Experimental tests were also performed in the towing tank. Their comparison with the numerical results has indicated high inaccuracy of the strip method. What is more, the simplified representation of hull shape used in the strip method makes it impossible to analyse the effect of hull shape changes on the predicted seakeeping characteristics. Especially for the case of head wave, neglecting highly non-linear phenomena, such as slamming or head wave breaking, in strip method-based computer simulations will significantly decrease the reliability of the obtained results. When using the strip method, the seakeeping analysis should be complemented with model tests in a towing tank, or by another more complex numerical analysis, such as CFD for instance.

Williams, JJ, Heron, R, Spradley, B, and Saracino, P. Postactivation potentiation effect of heavy sled towing on subsequent sprints. J Strength Cond Res 35(5): 1229-1233, 2021-Recent research supports heavy sled towing as a tool used to improve subsequent sprints as part of postactivation potentiation (PAP) protocols. The purpose of this study was to examine the effect of heavy sled towing using a velocity decrement (Vdec) on subsequent unloaded sprinting in high school football (soccer) athletes sprinting on artificial turf. A sled load equating to a 40-50% Vdec range was used (66-70% body mass). Fifteen (n = 9 boys and n = 6 girls) high school football players volunteered for this study. The sled-towing intervention consisted of a dynamic warm-up, 3 submaximal sprint efforts (50, 75, and 95%), and 3 maximum speed 15-m sled sprints, separated by 2-minute rests, of which the fastest time was recorded for analysis. Peak preintervention 15-m baseline sprint times were compared with peak post sled-towing 15-m sprint times using a paired samples t-test. Thirteen of 15 athletes ran faster peak post sled-towing sprint times than peak preintervention baseline sprint times (9 boys and 4 girls). On average, peak post sled-towing sprint times (2.60 ± 0.10 seconds) were 0.10 seconds faster (p < 0.0001; Cohen's d = 0.92) than peak preintervention baseline sprint times (2.70 ± 0.09 seconds). This research established that sled-towing protocols using loads corresponding to Vdec of 40-50% significantly improved subsequent sprints in high school football (soccer) athletes running on artificial turf.

To develop seaplanes as a means of inter-island transportation, it is necessary to have a simulation, testing, and analysis of force measurements that work so that the aircraft can be designed optimally in terms of function and safety. To fulfill one type of test, the seaplane floater model is pulled in the Towing Tank to determine the hydrodynamic forces acting on the floater which include resistance (Fx), side force (Fy), lift force (Fz), and moments in all three axes. A method of measuring the force of 6 axis force and moment or 6 degrees of freedom (6 Degree of Freedom, 6 DOF) was built and designed by combining several single load cells so that these forces can be known optimally. From the results of the 6 DOF transducer design, it is proven that it can be used well in measuring 6 forces and moments with force measurement errors ranging from 1.38%. The distance between the 6 DOF transducer capture point and the floater force capture point will affect the measured moment transformation.

The semisubmersible platform is one of the most important equipment for the exploitation of deep-sea oil and gas. And its survival and operational capacities depend on the towing and motion performances. The present work investigates the properties of different platform component designs based on their towing and motion performances under wind and waves by using an integrated computational fluid dynamics (CFD) method. The joint application of RANS and a VOF/6-DOF solver compiled in a new Fluent UDF Library is adopted for the main calculation. Numerical simulations and results demonstrate that the VOF/6-DOF solver is accurate and stable, which could achieve the same functions as the previous OpenFOAM scheme. In order to acquire a better towing performance, different shapes are suggested for the pontoon end shape, the column cross section, and the brace longitudinal section, respectively. As to the motion response, among all the three design selections, the column cross section has the greatest influence on the whole platform. The simulation results reveal that circle section increases the roll and pitch response and reduces the heave response, to which the square section is adverse.

In the present research, the performance of a prototype tidal turbine is evaluated via towing tank tests. The examined model is a three-bladed horizontal axis with a 1.15 m diameter. Previously, we studied the hydrodynamic behavior of this turbine and calculated the hydrodynamic coefficients using a numerical approach. Thus, this work concentrates on overwhelming the challenges, from manufacturing and assembling to data acquisition and power storage. The turbine is tested under various conditions namely: pitch angle, electrical load, carriage speed, and immersion depth to improve efficiency. Our experiment indicated the turbine performance to be the best being close to the surface of the water at different flow speeds. The optimum electrical load was found to be 20 Ω adding 16–40% to efficiency. By fixing the optimum load and tip immersion depth, the maximum efficiency of the whole rotor achieved around 0.265 at less than 0.56 m/s as towing speed while at the speed of 1.1 m/s, the maximum output power was more than 120 W having the pitch of the blades fixed at 20.4°.

The full safety of operating industrial mechanical equipment, in particular the over-sized ones, with a complex structure, is ensured by compliance with all necessary requirements, starting with design, fabrication, transportation from the supplier to the recipient and operation within the working parameters. The present article that is continuing the analysis of transportation stages of over-sized and heavy equipment, as can be seen from the attached bibliography, takes into consideration the evaluation of the towing forces, in the case of two distant platforms. The masses of the transported components, the characteristics of the roadways, as well as the character of the movement and the influence of the wind loads are considered.

A process of a spent upper stage removal from low Earth orbit is considered, which consists of three phases: towing of the stage using a tether; descent of the stage into the low-density atmosphere; motion of its debris fragments after the breakup caused by the aerodynamic and thermal loads. It is shown that the attitude motion of the stage during its descent largely affects its breakup altitude and consequently the size of debris impact footprint and its position on the surface of the Earth. A certain number of ways to reduce the footprint extent are proposed. As an example of using the proposed method, a numerical simulation of the removal of a spent Ariane 4 upper stage H10 was performed. The results of the study can be used for planning missions to clean up space debris from low Earth orbit.

The purpose of this study is to analyze the RRF antenna tower under wind load action, the wind load is viewed from an angle of 0( to the towing cable to the largest angle on the two types of antenna towers, triangle and Square. Both types will produce different wind loads so that we can find out which load is the biggest from a combination of wind directions. The research method is by empirical analysis, calculating the wind load alone while other loads are not counted. As a result of wind loads, the tension cable and load direction correspond to each section and then the resultant values ​​of force and direction will arise. And finally, the force is changed to lift and the anchor will hold the force. The results use of triangle antenna towers is more beneficial, because the wind load that occurs is smaller, thus the construction costs are also smaller. Due to the wind load that works horizontally and will be provided by the tower that stands vertically, the tower requires several retaining cables in a diagonal position, the force that propagates on the diagonal cable will cause a force in the vertical direction or lift, so the lift must be placed using anchors that are embedded in the soil, the large load from the soil that will hold the anchor is determined based on the value of the analysis, the criteria are too light so the anchor will be lifted and friendly, it will cause waste.

In recent years, the global demand for oil has been increasing. In order to reduce production costs, horizontal drilling technology is basically used for deep oil storage, so a cable-driven downhole towing system (horizontal well tractor) has emerged. The traditional horizontal well tractor drive motor has large volume, low efficiency, high vibration and noise, and cannot meet the requirements. Therefore, a permanent magnet synchronous motor with small size, light weight and high efficiency is proposed as the horizontal well drive motor. The paper discusses the coordinate transformation and mathematical model of permanent magnet synchronous motor, analyzes the working principle of permanent magnet synchronous motor vector control technology, and establishes a permanent magnet synchronous motor vector control simulation model using MATLAB simulation software. The simulation results verify that the control system has fast response speed and strong anti-interference, and meets the working requirements of horizontal well tractors.

This paper describes the application of computational fluid dynamics rather than a towing tank test for the prediction of hydrodynamic derivatives using a RANS-based solver. Virtual captive model tests are conducted, including an oblique towing test and circular motion test for a bare model scale KVLCC2 hull, to obtain linear and nonlinear hydrodynamic derivatives in the 3rd-order MMG model. A static drift test is used in a convergence study to verify the numerical accuracy. The computed hydrodynamic forces and derivatives are compared with the available captive model test data, showing good agreement overall. Simulations of standard turning and zigzag manoeuvres are carried out with the computed hydrodynamic derivatives and are compared with available experimental data. The results show an acceptable level of prediction accuracy, indicating that the proposed method is capable of predicting manoeuvring motions.

Determination of hydrodynamic coefficients is a vital part of predicting the dynamic behavior of an Autonomous Underwater Vehicle (AUV). The aim of the present study was to determine the drag and lift related hydrodynamic coefficients of a research AUV, using Computational and Experimental Fluid Dynamics methods. Experimental tests were carried out at AUV speed of 1.5 m s-1 for two general cases: I. AUV without control surfaces (Hull) at various angles of attack in order to calculate Hull related hydrodynamic coefficients and II. AUV with control surfaces at zero angle of attack but in different stern angles to calculate hydrodynamic coefficients related to control surfaces. All the experiments carried out in a towing tank were also simulated by a commercial computational fluid dynamics (CFD) code. The hydrodynamic coefficients obtained from the numerical simulations were in close agreement with those obtained from the experiments.

Funding Information: This work was supported by the National Natural Science Foundation of China (Grant No.61973172, 61973175, 62003175, and 62003177), the National Key Research and Development Project (Grant No. 2019YFC1510900), the key Technologies Research and Development Program of Tianjin (Grant No.19JCZDJC32800), this project also funded by China Postdoctoral Science Foundation (Grant No.2020M670633), and Academy of Finland (Grant No.315660). Funding Information: Academy of Finland, 315660; China Postdoctoral Science Foundation, 2020M670633; Key Technologies Research and Development Program of Tianjin, 19JCZDJC32800; National Key Research and Development Project, 2019YFC1510900; National Natural Science Foundation of China, 61973172; 61973175; 62003175; 62003177 Funding information Publisher Copyright: © 2021 The Authors. International Journal of Robust and Nonlinear Control published by John Wiley & Sons Ltd. Towing is a widely used mode of transportation in offshore engineering, and towing of unpowered platforms is of particular significance. However, the addition of unpowered facilities has increased the difficulty of ship maneuvering. Moreover, the marine environment is complex and changeable, and sudden winds or waves can have unpredictable effects on the towing process. Therefore, it is of great significance to overcome the influence of the harsh marine environment while navigating the towing system following a planned course to a target sea area. To tackle the time-varying disturbances, a course control method for a towing system of unpowered cylindrical drilling platform is designed based on double deep Q-network (DQN) optimized linear active disturbance rejection control (LADRC). To be specific, to tackle the difficulty of LADRC tuning, double DQN is applied to select the best parameters of the LADRC at any time according to the states of the system, without relying on the specific information of the modeland the controller. The course control performance of the towing system is evaluated in a simulation environment under various disturbances. Moreover, the Monte Carlo experiment is used to test the robustness of the controller when the ship's mass changes and the robustness of the proposed method is verified by testing with various heading angles. The results show that the LADRC with adaptive parameters optimized by double DQN performs well under external interference and inherent uncertainty, and compared with the traditional LADRC, the proposed method has better course control effects.

With the advantages of large detection and abundant information, time-domain electromagnetic survey has become the most potential and significant method technology in the field of electromagnetic survey. However, this technology is still under development in China, there is no system with practical detection been formed at present. This paper has proposed a method of building the airborne time-domain electromagnetic system based on fixed-wing UAV, which aims to realize the information and intelligent detection in the complex area through "manned platform with manned system". The system is designed as follows. The transmitter wires which are designed into three circle are fixed on the UAV nose, wing tip and belly fin, which can transmit once electromagnetic field to detect and whose maximum emission moment can reach 62100A·㎡. The receiving system which is fixed under the UAV belly can receive the secondary electromagnetic field from ground. The collection monitoring system which is fixed in the UAV belly is used to data recording and states monitoring including the power of transmitter wires, the positon of receiving system and the tension of towing current conversion and data recording. The circle and length of the transmitter wires could be intelligently adjusted with the UAV and application tasks and the releasing program will be intelligently started in emergency. Above all, the research proposed in this paper can provide a good conference for the application and practical of time-domain electromagnetic survey.

In designing submarines, hull form selection, resistance, and powering are key aspects. The bare hull form of a submarine can be considered according to five parameters. Surface resistance is important should it be necessary to operate at relatively high Froude Numbers. Due to the complex nature of the flow around the hull, model experiments are still the most reliable approach to determining surface resistance. CFD simulations enable surface condition analysis using FINEMarine. The towing mechanism must be taken into account and so this was designed to fix the pitch motion and measure the hydrodynamic forces. This paper outlines the towing method, comparing the model test and the CFD results, as well as providing a comparison of wave formation from the towing test and the CFD results. The results show that resistance increased significantly above a model speed of 1.4 m/s. Furthermore, above this speed, as the resistance of the model rose, the downforce gradually decreased.

The wave-driven catamaran is a small surface vehicle driven by ocean waves. It consists of a hull and hydrofoils, and has a multi-body dynamic structure. The process of moving from static state to autonomous navigation driven by ocean waves is called “self-propulsion”, and reflects the ability of the wave-driven catamaran to absorb oceanic wave energy. Considering the importance of the design of the wave-driven catamaran, its self-propulsion performance should be comprehensively analysed. However, the wave-driven catamaran’s multi-body dynamic structure, unpredictable dynamic and kinematic responses driven by waves make it difficult to analyse its self-propulsion performance. In this paper, firstly, a multi-body dynamic model is established for wave-driven catamaran. Secondly, a two-phase numerical flow field containing water and air is established. Thirdly, a numerical simulation method for the self-propulsion process of the wave-driven catamaran is proposed by combining the multi-body dynamic model with a numerical flow field. Through numerical simulation, the hydrodynamic response, including the thrust of the hydrofoils, the resistance of the hull and the sailing velocity of the wave-driven catamaran are identified and comprehensively analysed. Lastly, the accuracy of the numerical simulation results is verified through a self-propulsion test in a towing tank. In contrast with previous research, this method combines multi-body dynamics with computational fluid dynamics (CFD) to avoid errors caused by artificially setting the motion mode of the catamaran, and calculates the real velocity of the catamaran.

In order to reduce the additional resistance of high-speed amphibious vehicles, Flanks are designed on the concave grooves. As a new drag reduction attachment, the principle of Flanks is analyzed and discussed in detail. In this paper, the HSAV model and Flanks coupling resistance tests are performed based on the Reynolds-averaged Navier–Stokes method and SST k−ω model. The accuracy of the numerical approach is verified by a series of towing tests. Results show that with a fixed installation angle and invariable characteristic parameters, Flanks can significantly reduce the total resistance at high speed, with a maximum drag reduction of 16%. In the meantime, Flanks also affect the attitude and flow field of the vehicle, consequently affecting the resistance composition and the sailing condition. A vehicle model self-propulsion test is designed and carried out, and it qualitatively verifies the drag reduction effect of the Flanks at high speed.

Ocean towing in general, and non-routine tows in particular, present unique technical challenges to towing vessel owners/operators, salvors, the offshore oil/gas and wind industries, and others. When such tows “go wrong”, the harm to human life, property and/or the environment can be significant. The authors have drawn from their work on the Towing Safety Advisory Committee’s investigation of the grounding of the MODU Kulluk to present methods and considerations in analyzing ocean towing evolutions, both “routine” and “non-routine”. (TASK 14-01) The methods and considerations presented should be employed in advance of a towing evolution, but can be used in accident reconstruction and forensic analysis when an evolution has failed. The methods presented are iterative, and consider 2 x 6 degree freedom of motion (of the towing vessel(s) and towed vessel respectively) and characteristics of the towline, and facilitate determination of: Worst Case Conditions. Extreme Towline Tension (ETT) as a function of sea state and speed. Limits of the Tow (Go-No Go Criteria). Recommended Catenary Length as a function of sea state and speed. Size and Selection of the Towing Vessel and Gear, including: Required Bollard Pull. Required Strength, Characteristics and Condition of the Towline. Limits and Set Points of the Towing Winch, Automatic or Manual. Required Strength and Characteristics of the Synthetic Emergency Towline and its methods of deployment and connection. Working Load Limit (WLL) of the Shackles, Delta Plate and Attachment Points. Required Strength and Characteristics of Bridles, Pendant and Surge Gear/Shock Lines. The authors further explore the implications of single point failure modes, redundancy in gear and towing vessel(s), high cycle fatigue, and strain monitoring.

Against the background of a drastically increased demand of marine proteins, off-bottom, bivalve aquaculture, provides significant potential for production growth when moved into more energetic marine waters. Hence, research, industry and politics are currently proposing the development of new offshore sites. The highly energetic conditions at these sites present a challenging environment for bivalve aquaculture. In this work, physical experiments of suspended bivalves provide new knowledge on the commonly used design parameters: the drag and inertia coefficients. Live bivalves and manufactured surrogate models at a 1:1 scale were tested in a towing tank as well as under waves. The drag coefficient of live blue mussels was determined to be Cd = 1.6 for Reynolds numbers between 2.3 × 104 and 1.4 × 105. The inertia coefficient obtained from the wave tests was Cm = 2.1 for Keulegan Carpenter numbers KC < 10. In a pursuit to better understand the differences between live mussels and surrogates in laboratory conditions, the analysis revealed that appropriate surrogates can be identified. A method to determine the characteristic diameter of mussel dropper lines is suggested. The results facilitate the future design of aquaculture systems in high-energy environments and allow for an integration into numerical models.

This paper presents a numerical study of the depth tracking control for an underwater towed system under wave–ship interference condition. To overcome the laminations of ignoring the hydrodynamic factors and wave–ship interference in the existing simulation model for the depth tracking operation of the underwater towed system, a numerical model combining the control system with the computational fluid dynamics (CFD) method based on the overset mesh technique is explored and constructed, the influence of towing ship and head waves is introduced into the numerical analysis of the underwater towed system, a depth control system based on the center of gravity adjustment is proposed and its control characteristics are discussed. The fluid motion around the towed vehicle and the towing ship is governed by the Navier–Stokes equations, and the overset mesh technique is applied for the numerical solution of the equations. The towing cable connecting the towed vehicle and towing ship is governed by the quasi-steady-state catenary equations. The depth tracking controller adjusting the longitudinal position of a shifting weight is constructed based on the proportional–integral–derivative (PID) algorithm. The simulation results show that the numerical simulation system is practicable, and the depth tracking control system is feasible, effective, and robust.

It is imperative to study towing deorbit technology because that invalid spacecraft occupy orbital resources and threaten other operational spacecraft. The invalid spacecraft generally rotates at high speed, so that the despun is the first step of being towed away from orbit. At present, electromagnetic despun technology has been widely concerned for its advantages such as non-contact control, no plume contamination and no fuel consumption. However, the precise measurement technology of eddy current magnetic field still needs to be excavated. Based on the background of spacecraft electromagnetic despun, The theoretical modeling and measurement techniques of eddy current magnetic field for invalid spacecraft are studied in this paper. Firstly, the equivalent model of eddy current magnetic field is derived for the spherical microsatellites. Then, aiming at the design of eddy current magnetic field measurement array, summarize the three principles of measuring point selection and propose a universally applicable determination method of magnetic measurement array. Build simple ground device and verify the magnetic measurement array method with the test data. Theoretical analysis and experimental results show that this method is effective, and can be applied to spacecraft electromagnetic eddy current magnetic field measurement, and can provide a reference for the design of other magnetic field measurement.

Maneuvering in waves is a complex and critical issue that confuses researchers for the last several decades. Among the existing methods for predicting the maneuverability in waves, the widely-used mathematical model approach (MMG model) is considered to be efficient and accurate in large wavelength and small wave steepness conditions. However, based on the assumption that the maneuvering forces in waves are the same as those in calm water, the wave effect on the hydrodynamic derivatives is neglected in most mathematical model approaches. According to the previous theoretical analysis and experimental data, this assumption is flawed. Therefore, several experiments and some numerical simulations have conducted to research the wave effect on hydrodynamic derivatives. In the present study, oblique towing tests and pure yaw tests will be simulated using the state-of-the-art CFD techniques to obtain the linear hydrodynamic derivatives in waves. The simulation cases in the present study are set according to previous PMM tests of S175 containership in surf-riding conditions. And the simulation results are in good agreement with experimental ones. Based on that, the wave effect on hydrodynamic derivatives is obtained and some discussions are made. Finally, the course stability of the containership on the different relative position of the wave are calculated to analyze the preliminary reason for the broaching-to phenomenon.

On the basis of the Italian B512 towing device, the torpedo launching device was redesigned, and the internal ballistic model of the torpedo launching was established, including the gas state model of the launching cylinder, the mathematical model of the launch valve, the mathematical model of the gas cylinder, and the towing device. Mathematical model and torpedo motion model. Finally, the launch process simulation was carried out, and the influence of the initial inflation pressure of the launching cylinder and the elasticity of the steel cable on the internal ballistics of the torpedo was analyzed. The simulation results show that the scheme meets the requirements of torpedo launching and is feasible in principle.

A practical cavitator design method for straight-running-type supercavitating torpedoes was developed in this paper. Design requirements were first drawn in terms of torpedo performance characteristics, such as maximum range and motion stability. This method determines the optimum cavitator satisfying the design requirements that not only minimize the total drag of the torpedo, extending the maximum range, but also provide hydrodynamic forces required for straight level flight. The design procedure includes determining a design cavitation number and cavitator type (disk or cone) for obtaining the optimal cavitator that minimizes the total drag of a torpedo in straight level flight. To determine such an optimal cavitator, the equations of force and moment equilibrium for straight level flight were iteratively solved by the existing mathematical models that determine the cavity shapes generated by disk- and cone-shaped cavitators and hydrodynamic forces acting on the vehicle. For validation, model experiments on a small-scale supercavitating vehicle were conducted in a towing tank, and the results agree well with those of the mathematical models used in this study. A preliminary design based on the newly proposed method was also implemented for a realistic supercavitating vehicle. More precise computations using CFD should be conducted to investigate the physics in more detail in the near future.

This paper presents an AUV with AI (artificial intelligence), which is able to perform real-time optical vision-based diver-following and forward looking altimeter-based obstacle avoidance. The AI AUV is equipped with thrusters and a standard navigation-related sensor suite. A diver detection convolutional neural network, a suite of motion controllers, and a diver detection payload device are developed to enable diver-following functionality of the AUV. An obstacle avoidance algorithm based on forward looking altimeters is developed to enhance the waypoint navigation security of the AUV with obstacle avoidance functionality. The diver-following and the obstacle avoidance capabilities of the Taiwan Moonshot AUV under different scenarios are evaluated through hardware-in-the-loop simulations. In addition, the designated single diver following capability of the Taiwan Moonshot AUV is also verified through closed water experiments conducted in a towing tank.

Fisheries management is generally based on the regulation of the fishing effort, by limiting fishing capacity and activity. The fishing capacity can be quantified objectively, however, the calculation of the fishing activity requires knowing the effective fishing time, for which it is essential to monitor the vessels activity. The European Vessel Monitoring System (VMS) only describes the geographical position, course and speed of the vessel at 2-h intervals, it is an expensive system used only in vessels over 12 m in length and there are no common criteria to infer the fishing activity from the VMS data. To evaluate more precisely the fishing activity, we propose to incorporate new sensors in the vessels that provide additional information. The sensors of mobile devices offer an economic solution that would allow their implementation throughout the fishing fleet. The objective of this work is to evaluate whether the most common sensors integrated in current mobile devices: GPS, accelerometer, gyroscope, and magnetic field, offer relevant information to identify the different phases of bottom trawling fishing activity. The results obtained indicate that these sensors detect, with very high precision, foreseeable changes in the movement of the vessel during the towing manoeuvre., Sí

When a ship model test is performed in a tank, particularly when the tank is small and the ship model is relatively large, the blockage effect will inevitably occur. With increased ship model scale and speed, the blockage effect becomes more obvious and must be corrected. In this study, the KRISO 3600 TEU Container Ship (KCS) is taken as a model and computational fluid dynamics techniques and ship resistance tests are applied to explore the mechanism and correction method of the blockage effect. By considering the degrees of freedom of the sinkage and trim, the resistance of the ship model is calculated in the infinite domain and for blockage ratios of 1.5%, 1.8%, 2.2%, and 3.0%. Through analysis of the free surface, pressure distribution, and flow field around the ship model, the action law of the blockage effect is studied. The Scott formula and mean flow correction formula based on the average cross sectional area are recommended as the main correction methods, and these formulas are improved using a factor for the return flow velocity correction based on comparison of the modified results given by different formulas. This modification method is verified by resistance test data obtained from three ship models with different scale ratios.

Ventilated cavitation has been successfully employed as ship drag reduction technology and potentially can mitigate flow-induced vibration. The obtained successes were based on solutions of design problems considered in the framework of ideal fluid theory with their following validation by towing tank tests. However, various aspects of the interaction of ventilated cavities with the viscous flows around the ship hulls remain unclear, whereas there is usually no possibility to simultaneously keep the full-scale Froude number and cavitation number in the test facilities. So, the further progress of the application of ventilated cavitation substantially depends on the ability of computational tools to predict this interaction. This paper briefly describes the state-of-the-art computation of ventilated cavitation and points out the most challenging unsolved problems that appeared in the model tests (prediction of air demand by cavities, ventilation effect on ship drag, on hydrofoil lift, and on the propagation of shock waves in cavities).

This paper employs computational tools to predict power increase (or speed loss) and propulsion performances in waves of KVLCC2. Two-phase unsteady Reynolds averaged Navier-Stokes equations have been solved using finite volume method; and a realizable k-ε model has been applied for the turbulent closure. The free-surface is obtained by solving a VOF equation. Sliding mesh method is applied to simulate the flow around an operating propeller. Towing and self-propulsion computations in calm water are carried out to obtain the towing force, propeller rotating speed, thrust and torque at the self-propulsion point. Towing computations in waves are performed to obtain the added resistance. The regular short head waves of λ/LPP = 0.6 with 4 wave steepness of H/λ = 0.007, 0.017, 0.023 and 0.033 are taken into account. Four methods to predict speed-power relationship in waves are discussed; Taylor expansion, direct powering, load variation, resistance and thrust identity methods. In the load variation method, the revised ITTC-78 method based on the ‘thrust identity’ is utilized to predict propulsive performances in full scale. The propulsion performances in waves including propeller rotating speed, thrust, torque, thrust deduction and wake fraction, propeller advance coefficient, hull, propeller open water, relative rotative and propulsive efficiencies, and delivered power are investigated. Keywords: Power increase, Speed loss, Propulsion performances, Regular short head waves, KVLCC2, CFD, Taylor expansion, Direct powering, Load variation, Resistance and thrust identity method

An investigation on vertical motion characteristics of a ship towing system incorporated with symmetrical bridle towline configuration set a real challenge for the naval architect engineer. This paper presents a Computational Fluid Dynamic (CFD) approach to analyse heave and pitch motion performances in waves. Several towing parameters such as various towline length and towing’s velocity have been taken into account. Here, 1B (barge) is employed in the simulation; and designated as a towed ship. The results revealed that the subsequent increase of the towline lengths has been basically proportional with the increase of her heave motion; while inversely decrease in pitch motions. In addition, the effect of the extending towline length = 1.0 to 3.0 resulted in insignificant effect to the towline tension. However, the increase of the towing’s velocity from 0.509 m/s to 0.728 m/s has led to significantly increase her heave motion and the towline tension by 40.46% and 24%, respectively; meanwhile, the pitch motion barge has sufficiently decreased by 35.94%. This simulation has been beneficial for the towing operator to ensure a higher level of the safety navigation of ship towing system.

Investigation of a ship towing system performance in waves incorporated with an asymmetrical towline configuration is necessarily to be studied to ensure a towing safety of navigation. To achieve the objective, this paper presents the ship towing motion performance in waves using Computational Fluid Dynamic (CFD) approach. Here, the heave and pitch motions of the towed ship so-called barge has been analysed, where several effects of the towing angle and towing speeds have been taken into account. In the calm water condition, the results revealed that the increase of tow angle was proportional with the sufficient reduction of the sway amplitude motion and inversely proportional to her yaw motion. The increase of the asymmetrical tow angle, however, has led to increase her sway motion amplitude in wave condition and conversely reduced the tow speed increased. In addition to the pitch motion characteristic, it subsequently increased by 12.1% as the tow angle raised from 25° to 35°; meanwhile the pitch motion of barge has by 10.2% as the tow speed increased from 0.655 m/s to 0.728 m/s. This CFD simulation is very useful as the preliminary prediction on the heave and pitch motion characteristics ensure a safety navigation of a towed ship in waves.

Animal-attached GPS loggers are used to monitor the movement of land animals, but obtaining the measurements of aquatic animals remains challenging. Current animal-attached speed sensors are placed close to the body and measure the speed of the disturbed fluid near the skin interface, potentially affecting the accuracy of the measurement. Furthermore, the absolute speed estimates derived from the sensor data are affected by the location on the animal, orientation with respect to flow, and device shape. Here, we evaluate the performance of a micro-turbine in both the steady and variable flows using particle image velocimetry to visualize and measure the flow field around the tag and sensor. A closed recirculating flume was used to generate a range of both steady and oscillating flows at the sensor. During steady flow, turbine rotation rate was linearly correlated with both the free stream and near-sensor flow speeds. Following the controlled measurements of fluid speed in the flume, a tag with the speed sensor was used to measure both the speed and the total distance traveled by the dolphins in a managed environment. The results compared well with the speed and distance made from the analysis of video collected by an overhead camera system. Finally, the measurement variability of four specially designed tags with speed sensors was tested in the towing tank in the Marine Hydrodynamics Laboratory at the University of Michigan. These results provide a foundation for interpreting in-situ speed measurements from swimming animals, and potentially autonomous underwater vehicles, and will guide the development of the improved algorithms for the localization and energetics estimation.

A novel and fast technique is proposed to predict the parameters of turning maneuvering performance of a surface combatant at mid and high Froude numbers. An empirical model with two parameters (ship advance speed and rudder angle) and three unknown coefficients is introduced. First, resistance of rudder appended hull has been computed by the time-dependent straight-ahead towing simulations. The code has been verified by implementing three different solution verification methods; Grid Convergence Index (GCI), Correction Factor (CF) and Factors of Safety (FS). After this, Direct Maneuvering Simulations (DMS) have been performed by implementing overset grid technique. Singular body forces located at the same position and direction with the propellers have been applied to the vessel for propulsion during DMS. The method has been validated by comparing the results of bare hull straight-ahead towing case and δ = 35° turning circle simulation ones with the available experimental data. The numerical results have then been used to calculate the unknown coefficients by linear regression analysis. It has been found that the proposed CFD-based empirical model is reliable and robust for both interpolated and extrapolated cases as well as the test matrix with reasonable accuracy and also applicable to similar surface ships.

Experimental and numerical studies on the hydrodynamic forces and moments of the ONR Tumblehome (ONRT) hull during oblique towing tests are performed. The experiments are carried out in the towing tank of Marine Design and Research Institute of China (MARIC) and the numerical simulations are based on the open-source CFD library OpenFOAM. Validations of the numerical methods are provided by comparison with experimental measurements from tests at two advancing speed. And then the investigations of advancing speed effects on hydrodynamic derivatives used in MMG model are performed numerically. Specifically, X v v , Y v , N v of the ONRT hull at four advancing speed are yielded via linear regression of the hydrodynamic forces and moments predicted by CFD calculations. Finally, the relationship between hydrodynamic derivatives and advancing speed are concluded and the expressions of hydrodynamic derivatives that can be used in MMG model are given.

A Reynolds-averaged Navier Stokes computational fluid dynamics (RANS-CFD) package will be one of the primary tools used during the development of a performance prediction program for wind-assisted commercial ships. This paper is Part 1 of a two-part series describing the RANS-CFD method adopted for this study. The modelling challenge presented by large separated flow structures in the wake of a sailing ship points to a conscientious validation study. A validation data set, consisting of hydrodynamic forces acting on the ships sailing with a leeway angle, was collected at the Delft University of Technology towing tank facility, for bare-hull and appended cases. Appended cases were designed to represent a broad range of appendage typologies: Rudder, Bilge-keels, Skeg, and Barkeel. A validation statement is made for simulations for the entire bare-hull series and for appended geometries, excepting the Bilge-keel case. The simulation method is described in Part 2, including the assessment of the numerical uncertainty.

Due to the EEDI regulation, recent merchant ships have strictly been required to achieve certain rate of energy saving, and thus equipment of energy saving devices (ESDs) has been quite popular. The purpose of this study is to investigate the working principle of pre and post swirl type ESDs via complementary use of experiment and viscous computational fluid dynamics (CFD). Three different hull forms (Japan Bulk Carrier: JBC, Duisburg Test Case container ship: DTC, and coastal tanker: COT) with three different ESDs are of the interest. Propeller open water, resistance and self propulsion tests are totally replaced by viscous CFD simulations, termed numerical towing tank procedure. For JBC, detailed investigations of self propulsion parameters, balance of kinetic energy flux, local flow and propeller loads clarify the working principle of its stern duct. For DTC, the present computations find out that vertical distribution of the twist angle of its rudder and the distance between propeller boss cap and the rudder bulb should be modified. For COT, the scale effect in axial and tangential components of its nominal and total wake are studied. In the meantime, the reason of deterioration/improvement in self propulsion coefficients by the pre swirl stator fins are identified.

This research was conducted as a way to uncover the socialization strategy of towing policies through social media by the West Jakarta Transportation Department, through a case study perspective. This is a way to socialize DKI Jakarta Regional Government Regulation No. 5 of 2014. This study uses a qualitative research method with a case study approach and a contrutivism paradigm. The theories used are Communication Management, Planning, and SWOT Analysis. The results that are known from this study are about four things as follows: 1). Planning for the socialization of the towing policy strategy by the West Jakarta Transportation Agency. 2). The source of the socialization strategy for towing policies by the West Jakarta Transportation Agency. 3). Obstacles to the socialization of the towing policy strategy by the West Jakarta Transportation Agency .; and 4) The description of the audience of the socialization of the towing policy by the West Jakarta Transportation Department.