Search

Weft tows in 3D woven composites are commonly approximated as perfectly straight, but their undulations are inevitable in reality, although the extent of undulations in the weft tows is not as pronounced as in the warp tows. Such minor undulations in weft tows have been simulated in this paper. A previously established parametrised modelling and analysis tool for 3D woven composites has been extended to reproduce the varying geometry of the weft tows. Two novel models have been proposed to introduce the undulations, allowing their effects to be simulated. The analysis reveals that, compared to the model with straight weft tows, the effective elastic properties can be affected by the weft tow undulations. In addition, the procedure for defining varying intra-tow fibre orientation was formulated and implemented, addressing lack of consistent and robust functionalities of this kind in modern finite element solvers. [ABSTRACT FROM AUTHOR]

When the landing position of a shipborne helicopter on the deck does not meet the requirements for towing it into the hangar, its position must first be corrected before towing can proceed. This paper studied the methods for using Shipborne Rapid Carrier Robots (SRCRs) to correct helicopter positions on the deck and proposed two correction methods, the stepwise correction method and the continuous correction method, aiming to improve the efficiency of the position adjustment process. Firstly, the actual helicopter landing position deviation was divided into two components—lateral offset and fuselage yaw angle—to quantitatively assess the deviations. Then, a mathematical model of the SRCR traction system was established, and its traction motion characteristics were analyzed. The kinematic characteristics and control processes of the two proposed position correction methods were subsequently studied, revealing the coordinated control relationships between key control elements. Finally, simulations were conducted to validate the feasibility of the proposed correction methods and compare their efficiencies. The results indicated that both the stepwise and continuous correction methods effectively achieved the position correction objectives. The stepwise method was more efficient when the initial yaw angle was small, while the continuous method proved more efficient when the initial yaw angle was large and the lateral offset was minimal. The results of this study may provide a valuable reference for correcting the positions of helicopters on deck. [ABSTRACT FROM AUTHOR]

Maneuver simulation of a standard ship model gives indication of numerical accuracy. In the numerical calculation of ship maneuvering, uncertainty analysis is a necessary step to ensure the accuracy of the calculation. In this study, uncertainty pair analysis is carried out in the simulation of the turning circle motion of the standard ship model ONRT in waves. According to the uncertainty analysis procedure recommended by the International Towing Tank Conference (ITTC), the change of ship resistance caused by the number of grids is studied to determine the influence of grid density on the numerical prediction. The simulation of turning motion in waves is carried out based on the uncertainty analysis. It is found that the minimum number of overset grids for this simulation is 1.4 million. The numerical results are fairly accurate compared to experimental results, and this technique provides a method with low calculated cost for this simulation. [ABSTRACT FROM AUTHOR]

Currently, cranes used at sea are insufficient in efficiency. Accordingly, a floating multi-robot coordinated towing system is proposed to meet offshore towing needs. However, the towing robot is prone to overturning because of the system's utilization of rope-driven robot flexibility and its floating attributes in fluid environments. First, the kinematics and dynamics of the towing system are analyzed through coordinate transformations and hydrodynamic theory. Subsequently, physical modeling of the towing system is conducted, with an emphasis on analyzing the system's fluid-structure coupling properties, supplemented by illustrative examples. Finally, the stability of the floating robot is assessed based on ship stability theory, encompassing analyses of the rope tension effects, size and shape of the floating base, and external environmental factors influencing system stability. Results show that the special shape of the floating base is beneficial in reducing water resistance and improving the stability of the floating robot in the flow field. The results provide a good basis for the system structural design and application. [ABSTRACT FROM AUTHOR]

Ship hydrodynamics in a constant waterway have been well studied. With a coordinate system fixed on the moving ship, the boundary value problem (BVP) is usually treated as a steady one. However, the hydrodynamics of a ship moving in confined waterways with abrupt changes in width or depth are complex due to their unsteady nature. The studies on such unsteady problems are insufficient. In the engineering practice, the hydrodynamic unsteadiness can be fully reflected by a scenario when a ship enters a lock. Prior studies have predominantly focused on predicting the ships' hydrodynamic forces without considering the unsteady terms on the free-surface boundary conditions. Obviously, such steady or quasi-steady methods overlooked the crucial unsteady phenomena on free water surface. To address this gap, the present study introduces a novel three-level difference scheme to discretize the free surface condition, preserving unsteady terms while maintaining temporal continuity of cells on the free surface. With the implementation of such fully unsteady BVP, we observed some interesting unsteady free surface motions, which were not well documented in the existing literature. To verify our new observations, as well as to validate the numerical method proposed in this study, two physical model tests were designed and conducted in a towing tank: a submerged ellipsoid enters a deep lock at relatively high speeds, and a box enters a shallow and narrow lock at very low speeds. The discussion is highlighted on the unsteady waves in front of the moving bodies, as well as the unsteady resistance induced by such waves. [ABSTRACT FROM AUTHOR]

AbstractAccurate characterization of mechanical perturbations on the seabed is essential for developing models assessing the environmental impacts from physical disturbances. Furthermore, understanding the relationship between (1) seabed resistance and (2) penetration depth, can also facilitate the development of more efficient and less impactful fishing gears. This study examines these two aspects of tickler chain rigged beam trawling via large-scale physical experiments. Three scaled down models (“light,” “medium,” and “heavy” designs) were developed to represent the impacts from typical beam trawl configurations used in the North Sea and were towed at various speeds on a saturated sand bed. Results reveal that increasing the towing speed reduces the mean penetration depth and the steady-state towing resistance of the gears. Smaller scale physical model tests incorporating tickler chains in sand, demonstrate that the towing resistance is significantly influenced by the soil compaction and particle sizes. Moreover, our study offers a simple and efficient method to estimate the penetration depth and towing resistance of prototype beam trawl gears in sand. This approach, along with the associated research, may be valuable for marine scientists assessing trawling impacts and demersal fishing gear designers seeking to optimize efficiency while minimizing seabed disturbance. [ABSTRACT FROM AUTHOR]

Large engineering structures like ships and other floating structures require reliable and complex computations to ensure their structural integrity over their lifetime. This work presents an analysis of the structural integrity of an aged single-bottom tanker during its towing from Croatia to a scrapheap in Turkey. The ship is subjected to wave loading (corresponding to the global response) and towing force (corresponding to the local response). Computations were performed by a general hydro-structure tool that combines a 3D finite element (FE) structural model and a 3D boundary element (BE) model based on the Rankine panel theory, according to the guidelines of the relevant classification society. Time domain simulations were performed to take account of Froude-Krylov nonlinearities for a wave determined within the Equivalent Design Wave (EDW) approach. After the calculation of wave loading and its transfer to the FE model of a ship structure, the stresses were calculated and compared with the allowable values. The local strength assessment of the ship forecastle deck structure was also performed, considering the prescribed towing force as an imposed load. Both the procedure and the used computational tools are general and can be applied to any kind of ship or other floating structure. [ABSTRACT FROM AUTHOR]

In the field of civil aviation, the nose landing gear is a critical component that is prone to damage during taxiing. With the advent of new technologies such as towing taxi-out and hub motors, the nose landing gear faces increasingly complex operational environments, thereby imposing higher performance demands. Ensuring the structural safety of the nose landing gear is fundamental for the successful application of these technologies. However, current research on aircraft nose landing gear under these new conditions is somewhat lacking, particularly in terms of reliable analysis models for real-world scenarios. This study focuses on a typical Class C aircraft, specifically the B-727 model, for which a finite element model of the nose landing gear is developed. Modal testing of the aircraft's nose landing gear is conducted using the impact hammer method, and the results are compared with those from the simulations. The experimental data indicate that the error range for the first seven natural frequencies is between 0.23% and 9.27%, confirming the high accuracy of the developed landing gear model. Furthermore, with towing taxi-out as the primary scenario, a dynamic model of the aircraft towing system is established, and an analysis on the structural strength and topological optimization of the nose landing gear under various conditions, including high speeds and heavy loads, is performed. The results show that the developed model can effectively support the analysis and prediction of the mechanical behavior of the nose landing gear. Under high-speed, heavy-load conditions, the nose landing gear experiences significantly increased loads, with the maximum deformation primarily occurring at the lower section of the shock strut's outer cylinder. However, no damage occurred. Additionally, under these conditions, an optimized structural design for the landing gear was identified, which, while ensuring structural strength, achieves a 22.32% reduction in the mass of the outer cylinder, also ensuring safety in towing taxi-out conditions. [ABSTRACT FROM AUTHOR]

Carbon fiber/epoxy tow prepreg is an intermediate material for filament winding, consisting of fibers pre-impregnated with a matrix resin in a specific ratio. This study predicted the long-term viscoelastic properties of tow prepreg using DMA and TTSP. Typically, DMA involves applying a wound or laminated flat specimen, but a strand specimen was attempted to predict the characteristics of tow prepreg. The long-term viscoelastic properties were storage modulus, creep compliance, and relaxation modulus. Three test modes were performed in DMA to obtain each result. Smoothly overlapped master curves were obtained in all results. From the master curves, the viscoelastic properties of the material were predicted for 1 year, 10 years, and more extended periods. For 10 years, it was estimated that the storage modulus, creep compliance, and relaxation modulus changed by 7%, 132%, and 48%, respectively. When tests are conducted, considering future design variables, such as temperature, humidity, and out time, the results can be utilized to predict the long-term performance of tow prepreg and optimize composite manufacturing processes. [ABSTRACT FROM AUTHOR]

Positioning technology is one of the key steps of automatic docking. At present, vehicle docking technology is widely used in airport baggage cars, towing trailers and other fields, and the docking process is mostly done manually. In order to realize the automatic docking of vehicles in mixed scenes, this paper proposes a fast positioning method for docking vehicles in mixed traffic scenes. First, using the regression relationship between the template size in the camera's field of view and the actual distance, FFT template matching and threshold judgment methods are employed to locate, track, and match the template, as well as verify the threshold results, in order to achieve template long-distance positioning and ROI extraction. Then, based on the regression relationship between AprilTag pixels in the camera's field of view and actual distance, the experiment of AprilTag minimum recognition pixel is designed. Finally, the real-time pixels of AprilTag are calculated from the real-time ranging results, and compared with the minimum recognition pixel of AprilTag, it is judged whether the recognition conditions are met, so as to carry out the subsequent AprilTag positioning. The experimental results demonstrate that the method proposed in this paper can achieve rapid and accurate positioning of a target docking vehicle at a long distance, while reducing the mismatch rate. On this basis, by designing the identification conditions of AprilTag, the rapid identification and positioning of AprilTag is realized, which reduces the traversal time of the algorithm. The feasibility of this positioning method is verified by the attitude angle error experiment, which provides supporting conditions for the subsequent docking path planning and vehicle control. [ABSTRACT FROM AUTHOR]

A simulation approach relying on a single grid topology has been employed to replicate the motion characteristics of different experimental facilities, including towing tank, rotating arm mechanism, and planar motion mechanism using a single mesh. The control volume and computational mesh setup was built in a way to enable to perform both steady and time dependent simulations to compute entire set of coefficients required by the standard submarine equations of motion. Mesh is consisted of a rectangular prism shaped background and a spherical overset domain which can be rotated, circulated and oscillated depending on the simulation type. To enable the implementation of this approach to the rotating arm simulations, modifications to source code of the open-source computational fluid dynamics software OpenFOAM have been made. Motivation is to change the perspective on the problem by using the knowledge of mathematics behind the solution algorithms and the software structure. In this study extensive set of time-independent coefficients obtained via straight and oblique towing as well as steady rotation simulations are presented for a fully appended generic submarine geometry. Results are then compared with the benchmark experimental data. It is found that the consistency between results are quite satisfactory. [ABSTRACT FROM AUTHOR]

The offshore wind sector is moving into deep waters and using floating platforms to harness the higher wind speeds in exposed locations. There are various floating platform types currently in development, but semi-submersibles are considered the most prominent early movers. Such floaters need to be towed to and from wind farm locations for installation, special cases of repair and decommissioning. As with any other offshore activity, metocean limits exist for towing operations which can impact the development of a wind farm. It is important to calculate the motion and loads of the platform before commencing the towing operations and to check whether they exceed the defined limits to enable safe execution. In this paper, two approaches using two different numerical tools to predict the motion of a fully assembled floating wind platform under tow are presented and compared. A potential flow-based method derived from a low forward speed approach and a hybrid approach combining potential flow and Morison equation methods are investigated, and the numerical predictions are compared and validated against experimental results. Both methods demonstrate accurate predictions, depending on the wave condition and towing speed, albeit differing in execution time and the simplicity of the simulation setup. The first method was found to provide good predictions of the motion in low-speed (0.514–1.543 m/s) towing conditions. The second method provides better results for all the towing speeds and wave heights. As the wave height and towing speed increase, deviations from experiments were observed, signifying non-linear phenomena that are difficult to analyse using the mentioned potential-flow-based methods. [ABSTRACT FROM AUTHOR]

The aviation industry has proposed multiple solutions to reduce fuel consumption, air pollution, and noise at airports, one of which involves deploying electric trucks for aircraft towing between the stand and the runway. However, the introduction of tow trucks results in increased surface traffic, posing challenges from the perspective of air traffic controllers (ATCOs). Various solutions involving automated planning and execution have been proposed, but many are constrained by their inability to manage multiple active runways simultaneously, and their failure to account for the tow truck battery state of charge during assignments. This paper presents a novel system for taxi operations that employs autonomous tow trucks to enhance ground operations and address deficiencies in existing approaches. The system focuses on identifying conflict-free solutions that minimise taxi-related delays and route length while maximising the efficient use of the tow trucks. The algorithm operates at a strategic level and uses a centralised approach. It has the capacity to cater for multiple active runways and considers factors such as the tow truck battery state of charge and availability of charging stations. Furthermore, the proposed algorithm is capable of scheduling and routing tow trucks for aircraft taxiing without generating traffic conflicts. [ABSTRACT FROM AUTHOR]

Marine towing cable serves an important bridge of power and signal transmission between the ship and towed body in the towed seismic cable system. The steady-state equilibrium configuration and natural frequency of towing cable which are valuable for preliminary design will change with different working requirements. In this paper, the steady-state characteristics of marine towing cable are investigated with different towing parameters. Cable length and towing speed have a greater effect on the configuration than other parameters, and the impact of cable weight and cable length is more obvious for the natural frequency. Based on plenty of numerical results, a proper neural network using back-propagation neural network (BPNN) to predict the configuration and natural frequency is introduced and validated. Finally, an approximate equation including the weights and biases of BPNN, which can reduce the calculation cost greatly compared with traditional method, is suggested to obtain the steady-state characteristics of marine towing cable rapidly and accurately. [ABSTRACT FROM AUTHOR]

A submerged hydrofoil interacting with incoming waves produces combined heaving and pitching motion, facilitating the conversion of wave energy into thrust. When the foil is attached to the ship hull, the generated "green" power from wave energy could assist the ship's propulsion system and significantly reduce fuel costs. This study experimentally assesses thrust generation from a fixed mid-hull foil by comparing towing force at different wave and traveling speeds. The optimal mid-hull foil demonstrates a fuel cost reduction ranging from 10.3% to 20.4% at diverse traveling speeds and wave parameters. Thrust generation increases at higher traveling speeds. Additionally, this study mathematically describes the hydrofoil motion with an outer pivot, which better suits the ship–foil model. This study then introduces a Strouhal number (S t A , S ) specifically for the ship–foil model, considering ship travel, ship response, and the hydrofoil's rotation around its outer pivot. [ABSTRACT FROM AUTHOR]

The present paper investigates the unexpected unstable failure observed commonly on fiber tows tensile-tested under strain-controlled loading, although the force on the fibers should theoretically be relaxed under controlled strain. A model of the reaction of the load train when the fibers break under strain-controlled conditions is proposed. The criterion for instability is based on the comparison of the filament strength gradient and the overstress induced by the reaction of the load train when the fibers fail. The contribution of multiplet filament failures attributed to the fiber inter-friction and stress waves was taken into account. The compliance of the load train for the test results considered in the present paper was measured. It is shown that, depending on the number of filaments sharing the overload, the values of the structural parameters, and the fiber characteristics, the condition of unstable failure may have been fulfilled by the SiC fiber tows that were tested in house, as discussed in the present paper. The critical parameters that were identified and quantified include the load train compliance, gauge length, fiber stiffness, and bonding of the tow ends. This should allow the proper conditions for stable failure. Important implications for the validity and an analysis of the strengths derived from the unstable fracture of the tows are discussed. [ABSTRACT FROM AUTHOR]

It is known that the toughest stage of operation of a tractor with massive towed objects is the takeoff regime. This is because it is necessary to overcome the force of friction of rest that substantially exceeds the force of friction of motion. As a variant of solution of this problem, the initial kinetic energy of the tractor can be considered, which can evolve when boundedly elastically deformed towing couplers are used. To optimize the mathematical model, the following assumptions are made: towing force at the hook of the tractor is an invariable quantity; the inert masses of the tractor and towed objects are identical and equal to . The initial conditions are as follows: for t = 0 because the towing coupler is undeformed, and no force is applied to the towed object. Period during which the towing coupler experiences the maximal strain is determined. For estimating the effectiveness of application of elastically deformed towing couplers, the obtained results must be compared with analogous results corresponding to absolutely rigid towing couplers. Comparison of displacements, velocities, and energies indicates the high efficiency of application of elastically deformed towing coupler. The use of elastically deformed towing couplers makes it possible to accumulate the initial kinetic energy of an airport tractor, which makes it possible to overcome the force of friction of rest and to ensure the takeoff of heavy objects being towed. Comparison of kinematic and dynamic parameters of the tractor and towed objects in variants with absolutely rigid and elastically deformed towing couplers shows that the efficiency for the latter variant increases with increasing number of towed objects. Elastically deformed towing couplers can cause vibrations of the tractor–towed object system. To prevent such vibrations, towing couplers should be blocked at the instant of their highest straining. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) is a composite material with high specific strength and is applied to transportation and aviation equipment. However, conventional processing methods require large-scale production apparatus or a high level of dexterity that only comes with extensive experience which makes it difficult to achieve high processing efficiency. The objective of this study is to develop a novel method for forming thermos-plastic CFRP (CFRTP) preforms implementing a 3D printer for press molding. Applying this method offers the advantage that continuous carbon fibers can be formed on a free-form surface. It also reduces the manufacturing time and operator skill required. The goal of this research is to establish a method for molding a free-form surface composed of continuous fibers by employing a 3D-printed preform designed to match the unfolded polygonised diagram of the free-form surface. Previous research introduced an unfolding approach for converting a three-dimensional shape to a plane surface based on a computer-aided design and manufacturing (CAD/CAM) system, enabling the generation of an unfolding diagram that maintains the continuity of fiber tow. Furthermore, the validity of unfolded diagram was confirmed by reproducing the objective three-dimensional shape from the unfolded diagram using thermos-setting CPRP (CFRTS) tow prepreg. In this study, the viability of the proposed molding process using CFRTP preform fabricated by a 3D printer was verified and an assessment of the formability of the molded parts was conducted. [ABSTRACT FROM AUTHOR]

Producing comparable/greater ground reaction forces (GRFs) at faster running speeds is beneficial for sprint performance, and assisted sprint training is used to induce faster running speed conditions. This study aimed to demonstrate the characteristics of assisted sprinting at the maximal speed phase and investigate acute differences to control sprinting. Fifteen sprinters completed control and assisted (5 kg) sprints over force platforms. Assisted sprinting increased running speed (9.3% mean difference), while propulsive mean force (−4.3%) and impulse (−12.4%) decreased, suggesting that running speed improvements were caused primarily by assisted pulling force rather than improvements in anteroposterior force production of athletes. In addition, vertical mean force increased (4.2%), probably due to braking mean force (34.2%) and impulse (32.5%) increases. Magnitude of control trial maximum speed was achieved earlier (during acceleration) in assisted trials, and net anteroposterior (includes both braking and propulsive components) mean force (67.2%) and impulse (67.9%) increased at this matched speed, suggesting that assisted sprints could be used to practice producing greater GRFs at comparable speeds. Running speed improvement by pulling force was associated with contact time decreases (r = -.565), suggesting that shortening contact time may be important for effective assisted sprinting. [ABSTRACT FROM AUTHOR]

An Automatic Identification System (AIS) was installed on a barge. The AIS is active using solar panels with charge controller and battery to supply electric power at day time and night time. Such a novel actively AIS can offer the Speed over Ground (SOG), Course over Ground (COG), and position to tugboat for informing the Master and Officer about the sailing conditions of barge to maintain the towline tension stably and safety of navigation. The AIS also broadcasts the sailing status of barge to other ships in vicinity to maintain situational awareness of collision avoidance. Using this reliable theoretical calculation about the limit tension value of towing line with yawing motion can avoid the limit value of towline tension less than total maximum displacement of tugboat and barge. Those results contribute practical significance for improving the safety of towing operation and navigation at real time. [ABSTRACT FROM AUTHOR]

In the face of developments in maritime transportation due to globalization, ports are tending toward new tugboat investments in order to respond to the increasing demand. Due to the high costs of tugboats, organizations may face high investment costs. It is important to determine the most suitable number of tugboats, considering the variables in a port area where towage services will be provided. In this study, a simulation model was developed to determine sufficient tugboat allocation according to some variables in ports. The simulation model was subjected to various experiments, and statistical analyses of the obtained results were performed. The relationships between the variables affecting the level of towage service were revealed. [ABSTRACT FROM AUTHOR]

The authors have developed a method to estimate the catch efficiency of sampling gear using acoustic information. Since different sampling conditions will cause different sampling results, it is necessary to know more details about catch efficiency to quantitatively catch juvenile fish. In this study, we estimated the catch efficiency of a framed midwater trawl (FMT) for juvenile walleye pollock, and investigated differences in the catch efficiency of the FMT due to various influencing factors. To clarify the effects of different sampling conditions on catch efficiency, we investigated changes in catch efficiency by survey time (daytime and nighttime), net color (black and cyan), and towing speed (2 kt, 3 kt, 4 kt). It was quantitatively shown that the catch efficiency was higher at nighttime than during the daytime, the catch efficiency of black net was higher than that of cyan net, and the catch efficiency was higher at the faster towing speed. Comparing the estimated catch efficiency under different conditions, we found that survey time was the most important influencing factor. [ABSTRACT FROM AUTHOR]

• Study describes power characteristics of an unmanned tracked vehicle. • Effect of the causative variables on tractive power efficiency was synergetic. • Slip power efficiency linearly dropped with augmentation of payload weight. • 3.35–43.62 % of vehicle motion power wasted inside track-surface interface. • Results are applicable for autonomous transportation of agricultural payloads. Elucidation of power characteristics of an unmanned tracked vehicle for autonomous transportation of agricultural payloads in greenhouse constructions leads to appearance of an applied research in this study. This novel aim has been chosen based on operational requirement of the vehicle. Hence, it can be highlighted that this paper is initiative study described results of power efficiencies (motion, slip, and tractive power efficiencies) of the vehicle. To this aim, various payloads mounted on a trailer (1–5 kN) were towed by the vehicle through diverse drive speeds (0.17–0.5 m/s). Results illuminate that vehicle drive speed and payload weight had consequential contribution to vehicle motion and tractive power efficiencies. While, vehicle slip power efficiency mainly depended on payload weight. Linear regression approximations demonstrate that dual cumulative contributory effect of the drive speed and payload weight on the motion power efficiency (84.98–97.69 %) and tractive power efficiency (78.62–92.92 %) was antagonist and synergetic, respectively. Meanwhile, the slip power efficiency (81.71–98.36 %) linearly dropped with augmentation of payload weight. Resultant slip and motion power inefficiency were associate with vehicle motion power loss in amplitude of 0.39–67.98 and 2.65–14.03 W, respectively. Consequently, tractive power inefficiency was associate with vehicle motion power loss in amplitude of 3.15–82.01 W. This amplitude spotlights that 3.35–43.62 % of vehicle motion power inevitably wasted inside track-surface interface in agricultural towing tasks. Overall, numerical and analytical descriptions of the results as well as practical suggestions provide appropriate guidelines for vehicle supervisor in order to optimize power characteristics. [ABSTRACT FROM AUTHOR]

The use of towed underwater unmanned vehicles equipped with photo, video, and sonar systems has proven its effectiveness in studying the seafloor surface in integrated research of the World Ocean. This class of devices solves a wide range of tasks, including biological studies of benthic fauna and surveys of underwater technogenic objects. The towed vehicle "Videomodule" was developed at the Shirshov Institute of Oceanology, Russian Academy of Sciences, and has been successfully employed for such surveys for several years. The paper discusses the technical features and application issues of working with the "Videomodule." [ABSTRACT FROM AUTHOR]

Purpose: Drownings are a societal phenomenon occurring worldwide, hence the importance of rescue skills, including directly towing a victim to a safe place. The purpose of this study was to evaluate the most effective towing techniques based on kinematic parameters, considering different types of drowning cases, for their recommendation for widespread use in water rescue. Methods: The research involved 18 water lifeguards aged 18-25 years. The evaluation included speed tests in towing a mannequin over a distance of 50 m using the Extended Arm Tow (EAT), Double Armpit Tow (DAT), "Sailor" Technique Tow (STT) and with a rescue tube (RT), accompanied by video recording to measure in the designated measurement area the number of cyclic paddling movements by the lower limbs, angles of the body attack, towing velocity, and its decrease during towing. Results: Number of cyclic paddling movements by the lower limbs, towing with a RT was considered the most beneficial, and least beneficial was the DAT. In the DAT, the lifeguard swam with the smallest body angle, in contrast to the STT, where this angle was the largest. The effect of the number of cyclic paddling movements and the body angle by the lifeguard was the velocity, with the highest value recorded in towing using a RT; in other techniques, velocity were similar. Conclusions: Institutions associated with water rescue should recommend towing using a RT for direct rescue actions in the water, as its use shortens the time, while simultaneously increasing safety for both the rescuer and the victim. [ABSTRACT FROM AUTHOR]

The effective assessment of risk and speed limitations in ice are critical for the route planning of polar cruise ships. While the Polar Operational Limit Assessment Risk Indexing System (POLARIS) is widely used to evaluate the operational risk in ice, its scope of assessment is limited to the ship's assigned ice class. For a specific ship with a given ice class, the propulsion performance under varying ice conditions is more essential for assessing the besetting risk and finding an optimal route. To establish a more detailed risk evaluation method for a PC6 class polar cruise ship, propulsion performance under various ice conditions is obtained via model tests in an ice tank. During the tests, the tow force, propeller torque, and thrust are measured under different ship velocities and propeller rotation rates, and the relations between required delivered power (P) and ship velocity (V) under the tested ice thicknesses and concentrations are obtained and extended to other ice conditions by curve fitting. A new risk index outcome, RIO*, is proposed after POLARIS according to the optimized load ranges of the ship's rated power. Four risk levels, including low, medium, high, and unnavigable, are classified with the required propulsion power in ice being 50%, 85%, 100%, and >100% of the rated power, respectively. The recommended speed limit for each risk level is proposed based on the economical service speed of 11 kn, the operational limit of 3 kn by POLARIS and the minimum speed of 0.5 kn to avoid besetting, respectively. Based on the RIO* and P–V relations, the speed map for varying ice thicknesses and concentrations can be calculated. On these bases, a route planning simulation for the present polar cruise ship is performed. Results of the case study show that 29% of the simulated area is identified as "unnavigable" by the present procedure, while only 8% is detected by POLARIS. [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The offshore wind sector is moving into deep waters and using floating platforms to harness the higher wind speeds in exposed locations. There are various floating platform types currently in development, but semi-submersibles are considered the most prominent early movers. Such floaters need to be towed to and from wind farm locations for installation, special cases of repair and decommissioning. As with any other offshore activity, metocean limits exist for towing operations which can impact the development of a wind farm. It is important to calculate the motion and loads of the platform before commencing the towing operations and to check whether they exceed the defined limits to enable safe execution. In this paper, two approaches using two different numerical tools to predict the motion of a fully assembled floating wind platform under tow are presented and compared. A potential flow-based method derived from a low forward speed approach and a hybrid approach combining potential flow and Morison equation methods are investigated, and the numerical predictions are compared and validated against experimental results. Both methods demonstrate accurate predictions, depending on the wave condition and towing speed, albeit differing in execution time and the simplicity of the simulation setup. The first method was found to provide good predictions of the motion in low-speed (0.514–1.543 m/s) towing conditions. The second method provides better results for all the towing speeds and wave heights. As the wave height and towing speed increase, deviations from experiments were observed, signifying non-linear phenomena that are difficult to analyse using the mentioned potential-flow-based methods.

For towed water sports, such as water skiing and wakeboarding, participant and boat kinematics vary by activity. The objective of this study was to characterize the participant kinematics and tow rope loads for different water sports activities. This article presents a sample of pilot testing data for ten participants to show that the methodology can be used to compare water sports activities. Four towed water sports were examined: towed inflatables, slalom skiing, wakeboarding, and barefoot skiing. Participant and boat position and velocity, and tow rope force were evaluated. Each sport was examined in normal operation; slalom skiing was examined as a "free ski", rather than a slalom course. The largest tow rope force occurred for the 6-person towable inflatable (5443 N). The largest peak tow rope force normalized to total participant body weight occurred during slalom skiing (4.1 BW). The largest participant velocity occurred during slalom skiing (22.8 m/s) and the largest peak participant velocity to boat velocity (m/s/m/s) ratio occurred during wakeboarding (3.1). These results show that slalom skiers and wakeboarders can generate velocities exceeding that of the boat and the magnitudes depend on the skill, whereas the towed inflatable velocity is determined by the manoeuvres of the boat driver. The manoeuvres of the participants can also influence tow rope force to loads greatly exceeding participant weight. Manufacturers can use the data in the design and testing of tow points, tow ropes, and other attachment points related to the tow force and boat drivers can use the data to boat safely on the water. [ABSTRACT FROM AUTHOR]

The debris-tether-tug (DTT) system, has been considered as one of the most promising techniques for the space debris removal. In order to decrease the control difficulty of the DTT system, the DTT system was usually designed with a single tether. However, when the target owns the complex attitude motion, the removal efficiency of the classic DTT system (towing the target by a single tether) is limited. A modified DTT model with the hierarchical-tethered architecture is proposed to improve the removal efficiency in this paper. Based on the Hamiltonian variational principle, the coupling non-smooth dynamic model for the hierarchical-tethered towing system is established, in which, four tethers are divided into two groups to describe the asymmetry of the DTT model well. The symplectic Runge-Kutta method is employed to simulate the evolution of the orbit radius of the target, the length of the tethers, the position of the tethers' mass center and the target attitude angle. The numerical results reported show that, the competition relationship between the attitude stability of the target and the stability of the variation of the sub-tethers is affected by the relative stiffness of the tethers. In addition, the capture ability of the modified DTT system for the space target with a certain spinning speed is illustrated, which provides a theoretical basis for the design of the DTT system in future. [ABSTRACT FROM AUTHOR]

The mono-column composite bucket foundation has gained practical application in offshore wind power due to its advantages of simple fabrication, fast construction, and low cost. To ensure the safe and stable transportation of this structure to its designated sinking position, this study focuses on producing a scaled model of the mono-column composite bucket foundation. Through model testing, the floating characteristics of the structure during towing in regular waves are examined. The conclusion of the study is as follows: a significant towing force is required to provide the initial velocity of the structure. As the wave period and height increase, the structure necessitates a larger towing force, experiences greater pitch and heave responses, and exhibits more noticeable fluctuations in internal air pressure. The paper aims at providing practical engineering insights. [ABSTRACT FROM AUTHOR]

In recent years, the International Maritime Organization (IMO) has gradually introduced more stringent new Ship Energy Efficiency Design Index (EEDI) bills, and transport ships are more inclined to reduce the speed and increase the length and square coefficient to meet the design requirements. However, the size of the ship model that can be accommodated in the towing tank is seriously limited. Under the action of the scale effect, the accuracy of the prediction results of the resistance performance of large ships is particularly prominent. To break through the limitations of the test site, a large-scale ship model resistance towing test system and data analysis method in the port were established. By comparing with the results of small-scale model tests in the towing tank, the applicability of the 1957 ITTC friction line and Grigson friction line in the resistance prediction of the full-formed ship was analyzed, and the scale effects of resistance components were also examined. The results show that the scale effect of the form factor of full-formed ships is weak. The three-dimension method based on the empirical formula of mixed-form friction resistance of ITTC-Grigson is more suitable for predicting the resistance performance of full-formed ships. [ABSTRACT FROM AUTHOR]

The process of design, build and eventual commissioning of the towing tank on the Boldrewood Innovation Campus is described. The design brief required a facility that would have a capability to test models at a commercial scale but that would be effective as teaching environment for the next generation of Naval Architects as well as providing a flexible space for future fundamental research. Each of these provided their own challenges but the eventual solution of a 138 m long, 3.5 m deep, 6 m wide facility has more than met the initial aspirations. Equipped with 12 independent 0.5 m wavemaking flaps at the West end, a passive beach at the East end, a deployable side beach along the South wall for post run wave absorption and a monocoque Aluminium alloy carriage, the Boldrewood towing tank has now been successfully operating for more than a year. The carriage position and speed are controlled by a twin winch arrangement using a laser positioning system and low embodied energy composite cables. The carriage can reach a maximum speed of 10 m/s with controllable acceleration rates and can have up to four constant speed phases per run. Initial commissioning results and comparisons with benchmark data for the KCS hull confirm the accuracy and repeatability of the facility. In particular, the position and speed of the carriage are known to a high level of precision. To date research and consultancy work has spanned the performance of high speed vessels, uncrewed underwater and surface vessels, wave energy and tidal current systems, floating platforms for wind turbines, performance sport work for sailing, kayaking, rowing and swimming, open water propeller tests as well as conventional displacement vessel testing for self-propulsion and resistance. All ship science and maritime engineering students use the facility as part of their taught modules in every year of their programme as well as for individual, MSc and group projects as appropriate. It has also made a strong impact on the many thousands of visitors a year to the campus for science and engineering open days. [ABSTRACT FROM AUTHOR]

In order to solve the problem of ignoring the cable and only planning the trajectory of the lifted object and the robot ends, a planning scheme of a multi-robot collaborative towing system aiming at the cable obstacle avoidance motion planning was proposed. The univariate polynomial equation group of the cable was obtained by constructing the cable sweep equation and defining the implicit equation of the obstacle. Then, the point-to-point decomposition trajectory was planned for the initial trajectory of the lifted object in the variable cable length workspace. And the differential manifold and manifold tangent space theories were used to plan the predicted trajectory of the lifted object. Based on the system dynamics characteristics, the tangent vector selection of the predicted trajectory was determined. Finally, the three-level planning strategy with the lifted object as the planning object, the end of robot as the planning intermediate, and the cable obstacle avoidance as the planning purpose was finally realized. [ABSTRACT FROM AUTHOR]

Because of EEDI regulations for ships and SDGs, it is of vital importance to develop ships with good propulsion performance, not only in still water, but also in waves. To predict the propulsion and seakeeping performance in waves, and in particular ship motions and added resistance, various theoretical calculation methods and CFD codes have been developed. To validate these estimation methods, experimental data on details of the flow induced by the ship disturbance are required. To meet this demand, the authors developed an innovative method for measuring and analyzing the spatial pressure distribution over the ship-hull surface using a large number of Fiber Bragg Grating (FBG) pressure sensors. However, pressure measurements with the conventional FBG pressure sensors are largely influenced by the difference in the temperature between water and air, referred to as the temperature interference. To resolve this issue, the authors developed a new FBG pressure sensor that incorporates three improvements and is significantly less influenced by temperature interference. Its performance was confirmed through comparisons with measured pressures obtained using existing strain-type and conventional FBG pressure sensors. Furthermore, the effects of different materials used for manufacturing ship models on the pressure measurement were investigated experimentally in towing tank tests. Finally, an experimental study was conducted to determine which of the three improvements in the latest FBG pressure sensor is essential for reducing the temperature interference. [ABSTRACT FROM AUTHOR]

One of the most crucial tasks for naval architects is computing the energy required to meet the ship's operational needs. When predicting a ship's energy requirements, a series of hull resistance tests on a scale model vessel is carried out in constant speed stages, while the acceleration stage measurements are ignored. Another important factor in seakeeping analysis is the ship's hydrodynamic added mass. The second law of dynamics states that all this valuable information, that is, the dependence of the hull resistance on the vessel's speed and the added mass, is accessible from just one acceleration stage towing test done up to the maximum speed. Therefore, the acceleration stage, often overlooked in traditional towing experiments, can be a valuable source of information. For this reason, this work aims to generalise Froude's scaling procedure to full-scale vessels for the accelerated stage towing tests. [ABSTRACT FROM AUTHOR]

A variety of mission equipment is mounted and utilized on UUVs (unmanned underwater vehicles) for the development of marine resources and underwater searching for military purposes. For exploration of a wide area, it is advantageous to use a towed underwater platform, and for precision exploration to a specific location, to use an active mobile ROV (remotely operated vehicles). Since the TUV (towed underwater vehicle) moves according to the speed of the towing vessel, it cannot be operated if the vessel is stationary or the speed is low. Therefore, TUVs do not have equipment that is useful at low speeds, such as optical cameras or forward looking sonars. If a TUV capable of active movement such as stationary or low-speed operation is developed, it can search a wide area and then accurately search for a specific location, with one platform mounting various mission equipment. In this paper, we propose a method for estimating the control model for a prototype of this novel TUV, and propose a depth and posture control algorithm to which the model is applied. The proposed TUV and control algorithm were verified by experiments under the flow rate environment in the circulating water channel. [ABSTRACT FROM AUTHOR]