High-speed Displacement Research Articles

Design and Principles Analysis of Hydrofoil Appendages for Reducing Resistance of High-Speed Ships

To reduce the resistance of high-speed displacement ships with Froude numbers (Fr) between 0.4 and 0.5, this paper proposes the installation of hydrofoils at the bow and stern of the ship. Firstly, starting from the bow wave, this paper proposes the installation of a flat plate appendage at the free surface of the ship’s bow to suppress the height of the bow wave and thus reduce the hull resistance. Taking the DTMB 5415 ship model as the research object, CFD calculation results show that installing a flat plate appendage at the free surface of the ship’s bow can effectively suppress the height of the bow wave, and the total resistance reduction ratio can reach 6.49% when Fr = 0.45. Then, the flat plate appendage was improved to a hydrofoil appendage, further reducing the hull resistance. As a result, the total resistance reduction rate can reach 9.15% at Fr = 0.45. Following this, hydrofoil appendages were installed simultaneously at the bow and stern. The drag reduction effect and mechanism were studied, and the results show that the hydrofoils at the bow and stern have a good drag reduction effect. Suppressing the bow and stern waves and improving the flow field are the main reasons for the drag reduction. Finally, the drag reduction effect of the hydrofoil appendages was verified through experiments, demonstrating its excellent drag reduction effect when Fr = 0.4–0.5 and a maximum total resistance reduction ratio of 14.552%.

Numerical Investigation on a High-Speed Transom Stern Ship Advancing in Shallow Water

A high-speed advancing ship will cause significant squats in shallow water, which could increase the risk of grounding. To this end, a program based on the Rankine higher-order boundary element method (HOBEM) is developed to investigate a high-speed displacement ship with a transom stern moving in shallow water. The nonlinear free surface condition is satisfied by adopting an iterative algorithm on the real free surface. The transom condition is considered by implementing a modified transom condition. Computations of wave-making resistance, sinkage and trim in deep water are first performed, and satisfactory agreement is achieved by comparing with the experimental results; the simulations are then extended to the shallow water case. It indicates that the present method can provide a suitable balance of practicability and robustness, which can be considered as an efficient tool for the guidance in ship design stage.

External load of different format small-sided games in youth football players in relation to age

Background Monitoring of training tasks allows coaches to have a better knowledge of the loads applied to their players. Objectives The aim of this study was to analyze the variations in external load in small-sided games (SSGs) with young players U-12, U-15, and U-23 and compare the external load between age categories in each of the SSGs. Methods A group of 24 male soccer players performed five consecutive different formats of four vs. four SSGs composed of 3 minutes of play/rest. GPS devices were used during the tasks (WIMU PRO™). The data were analyzed using IBM SPSS Statistics 28.0, using descriptive statistics, graphical statistics, and ANOVA to compare the results between SSGs and between age groups. Results The increase in field areas promotes the increase of distance (DIST) covered and the high metabolic load distance (HMLd), with and without a goalkeeper (GK). The SSGs with GK recorded fewer PL values compared to SSGs without GK. In the U-12 and U-15 age groups, GK use promotes more acceleration (AC) and deceleration (DEC) of high intensity (>3 m/s2). The results also show that the larger areas are promoters of high-speed running (HSR). Age influences some external load variables (DIST, AC, DEC, HMLd) in the game formats studied. Conclusions The SSG formats analyzed using GK are promoters of high-intensity neuromuscular activity. Larger areas promote more high-speed displacement. Age is an influence on the external load in different SSGs.

Numerical and experimental study of stern flaps impact on resistance and propulsion of high–speed displacement ships

This study investigates hydrodynamic interactions between a high-speed displacement ship and various stern flap configurations. It combines towing tank model tests and advanced Computational Fluid Dynamics (CFD) simulations to explore hydrodynamics and energy-saving potential. Sixteen flap combinations were tested across Froude numbers (Fn) from 0.198 to 0.452 to understand post-installation hydrodynamics and energy-saving potential. The alignment between model tests and CFD simulations reinforces the potential of stern flaps to enhance efficiency and environmental friendliness in high-speed displacement vessels with transom sterns. CFD enhanced visualisation of flow, pressure, and other hydrodynamic parameters. The study reveals that the stern flaps reduce resistance and effective power, saving energy across all the combinations. However, the effectiveness of the flaps is limited at lower speeds (Fn < 0.198), where increasing flap angles incur higher resistance penalties. The greatest decrease in resistance is noted when the Froude number (Fn) is at 0.367, with a subsequent reduction after that. Stern flaps influence trim, sinkage, and hydrodynamic length, reducing wave-making resistance without increasing friction. Increased wake fraction and reduced thrust deduction enhance propulsion efficiency, while stern flaps suppress waves, lowering overall resistance. A reduction of effective power by 6% was observed in the present study. This research provides valuable insights into stern flap hydrodynamics and energy-saving potential, guiding ship design and operation.

Numerical investigation on the effect of hull vane for a high-speed displacement vessel

ABSTRACT Due to the International Maritime Organization's (IMO) mandatory standards for Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing Ship Index (EEXI) for new and existing ships, there is serious concern about lowering carbon emissions from ships in order to have a sustainable environment. A number of energy-saving technologies are used on ships to improve their efficiency and decrease fuel consumption. Hull vane is a fixed foil placed to the stern of a vessel to enhance local pressure by modifying the stern flow. This study examines the effects of retrofitting a hull vane to a high-speed displacement vessel at a 1:35 scale with various locations in X and Z directions from the transom of the vessel. The simulated resistance and trim values for the bare hull were validated with experimental results which are conducted in towing tank facility available in the Department of Ocean Engineering, Indian Institute of Technology Madras. The coefficient of residuary resistance value has been reduced by 21% at the HV5 location. Furthermore, the wave pattern behind the transom for the HV5 position was studied and reported at the operating Froude number.

Hydrodynamic performance of high-speed displacement vessel with hull vane

The hydrodynamic performance of high-speed displacement vessels can be enhanced by installing basic stern fittings such as stern wedges, stern flaps, interceptors, and hull vanes. The hydrodynamic performance of a high-speed displacement vessel with hull vane is analysed and compared to the bare hull condition in this study. The hull vane is a hydrofoil wing attached transversely to the bottom of the transom that focuses largely on minimising the wave-making resistance of the vessel by altering the flow at the stern. It increases flow on its upper surface, which interferes favourably with the stern wave system, hence lowering wave-making resistance. This research investigates the effects of installing the hull vane on a high-speed displacement vessel at various locations in the X and Z directions from the transom edge. The tests were carried out on model ship with and without a hull vane to verify the accuracy of the computational findings. The experiments were carried out in the towing tank facility available at Indian Institute of Technology Madras (IIT Madras), Department of Ocean Engineering (DOE). Computational fluid dynamics (CFD) simulations were carried out for model vessel with and without hull vane for a range of Froude numbers from 0.17 to 0.42 using RANSE-based commercial software. The research examines the resistance, trim, pressure distribution, and stern flow development of the vessel at various speeds and in calm water conditions. The results indicate that installing a stern hull vane reduces resistance and trim of the vessel. The effect of a hull vane is enhanced when it is positioned away from the stern of the vessel.

Об изучении зеркал скольжения в очагах палеоземлетрясений в Прибайкалье и Монголии

The paper presents some results of studying various samples of slip surfaces collected during expeditions, taken in the Baikal region and Mongolia from seismic dislocations of different ages, including from deep segments of seismically active fault zones exhumed to the earth's surface. Using methods of petrophysical study of the processes of hydrothermal-metasomatic transformation of abraded rock matter in slip surfaces, an analysis of petrochemical and thermodynamic processes in the foci of paleoearthquakes that occurred hundreds of millions of years ago in the deep segments of faults was carried out. Also presented are data from field and laboratory experiments conducted to study the mechanisms of formation of slip surfaces and tectonic pseudotachylytes that arose during frictional heating of rocks at moments of high-speed displacements in faults. An analysis of the totality of the new information obtained indicates that a comprehensive study of slip surfaces makes it possible to supplement existing ideas about the seismogeological conditions of the occurrence of paleoearthquake foci in the deep segments of active faults, and also contributes to the creation of new models of earthquake foci and the development of earthquake prediction methods. In the applied aspect, the obtained fundamental results become important for assessing seismic hazard and developing new methods for its reduction.

Control volume determination for submerged waterjet system in self-propulsion

The submerged waterjet is a novel propulsor designed for surface ships which is highly integrated with the aft-hull bottom. As the difficulty in measuring net thrust directly, the momentum flux method is suggested as the analysis procedure for ships propelled by submerged waterjets. This paper numerically investigates a high-speed displacement ship propelled by two submerged waterjets at 0.12 <Fr < 0.41 in model-scale. The control volume of the submerged waterjet system is firstly defined according to its working-principles. For the typical case here, the capture area of suction streamtube is appropriate to be located around 2.0–4.0 duct inlet diameter away from the duct inlet, while the capture area of jet streamtube is recommended to be 0.50 duct outlet diameter away from the duct outlet. The suction streamtube shows obvious contraction along inlet-direction, while the jet streamtube is much closer to an equal-diameter tube along jet-direction and its area keeps almost constant with Froude number. At 0.20 <Fr < 0.41, the jet system thrust deduction fraction hangs around a small negative-value for an appropriate control volume, showing small difference between gross thrust and net thrust of the submerged waterjet system in this paper.

A Proposal of Speed Zone Classification in Basketball: A New-Criteria Based on Maximum Registered Values

The quantification of training load has become mandatory for coaches and team staff. Within the analyzed variables, distance covered at different speed zones is one of the most studied. However, there is no consensus in the definition of speed zones in the published articles about each team sport, so it makes difficult a comparison between them. Therefore, the purposes of this article were to establish a criteria standard in the classification of speed zones in team sports and to analyze its practical application in basketball. Five speed categories were established for basketball following the methodology described above: 0-10km/h, &gt;10-13.8 km/h, &gt;13.8-17.6 km/h, &gt;17.6-21.5 km/h, and &gt;21.5 km/h. The results showed differences between periods in high-speed displacements and sprints, maximum speed, total decelerations, and accelerations. In conclusion, the categorization of workload based on standard deviation according to maximum speed could be a viable option to individualize the analysis of distance covered per speeds in team sports such as basketball. Its use may lead to a better understanding and contextualization of the locomotion data in specific sports and teams.

High speed time-of-flight displacement measurement based on dual-comb electronically controlled optical sampling.

We demonstrate a direct time-of-flight approach that utilizes dual-comb electronically controlled optical sampling (ECOPS) to measure small displacements. ECOPS is enabled by electrically controlling the repetition rate of one laser via an intracavity electric-optical modulator (EOM). The acquisition rate is set by the EOM modulation frequency, which is much higher than commonly used asynchronous optical sampling (ASOPS). In a proof-of-principle experiment, an 80-kHz acquisition rate is obtained with a pair of ∼105 MHz repetition rate Er-fiber lasers. At an average time of 30 ms, a measurement precision evaluated with Allan deviation reaches 26.1 nm for a 40-µm static displacement. In a dynamic measurement, a 500-Hz sinusoidal vibration with 15 µm amplitude has also been identified. The high-precision and high-speed displacement measurement technique can be potentially used in 3D surface profilometry of microelectronic step-structures and real-time monitoring of high frequency mechanical vibrations, etc.

Terahertz rainbow spectrum imager on reflective metasurfaces

The terahertz imagers that have already developed are usually with low frame rate and high cost, making them ineffective for moving target detection and fast imaging. Here, we experimentally report a high-frame-rate, high-resolution and low-cost real-aperture imager developed by combining the terahertz rainbow spectrum manipulation metasurface and quasi-optical method. As a wideband THz signal incidents on such metasurface (called as THz virtual prism), terahertz rainbow spectrum can be formed in one dimension just like a light beam passing through an optical prism, and complete real-aperture scanning imaging within 100 microseconds. By using high-speed displacement platform to realize another dimensional scanning, this imager will easily achieve high-frame-rate and high-resolution imaging with simple algorithm. The feasibility of this new THz imager was verified by imaging Siemens star and concealed targets, respectively. The results show that this imager has important potential applications in fields such as THz remote sensing, imaging radar, body scanner, etc.

Numerical research on mechanism of the effect of propeller shaft brackets on wake field and propulsion performance

Ship drag and self-propulsion simulations of a twin-screw high-speed displacement vessel were performed using the unsteady Reynolds-averaged Navier–Stokes (RANS) method. The sliding mesh and overset mesh methods were applied concurrently to simulate the coupling of the propeller rotation and the ship motion. The effects of the propeller shaft brackets on the drag, propulsion performance, wake field, and propeller excitation force were studied. The influence of the shaft brackets on the wake field was visualized. The high numerical accuracy of the proposed simulation method was proven through verification and validation analyses. The low-speed zones of nominal wake within the propeller disc were mainly caused by vortex shedding from the vicinity of the shaft brackets and the speed reduction of the frictional wake resulting from the velocity stagnation in front of the rudder. The tangential wake velocity, which was affected by the twist angle and vortex shedding, had a considerable effect on the propulsion performance. The wake non-uniformity coefficient was highly correlated with the vortex shedding. The spatial structure of the shaft bracket and the inward curved streamline around the stern aggravated the non-uniformity further, but the shaft bracket had a limited impact on the unsteady propeller bearing force in the absence of cavitation.

Experimental towing tank tests on high speed displacement ship

In the preliminary ship design stage certain methods are needed in order to predict the hydrodynamic resistance of the ship. An accurate estimation is important in order to ensure fulfilment of contractual requirements and minimize the costs of building and operating the ship and to design an eco-efficient ship. Eco-efficiency is getting increasingly important these days because of the increasing legislative requirements for a cleaner and greener shipping industry. The improvement of resistance and performance of high-speed mono-hull forms has been of interest for Naval Architect in the past decades. In consequence, a considerable amount of effort has been carried out in this area by using different devices to reduce the fuel consumption. The accurate evaluation of ship performance is mainly based on towing tank tests followed by extrapolation methods and correlation factors. The present work focuses on the reduction of ship resistance of a fast displacement ship using an interceptor. Towing tank tests has been performed for Froude numbers between 0.23 and 0.69 to evaluate the ship resistance, the pitch and the heave of the ship. In order to reduce the ship resistance, but also the amplitude of the ship motions, an interceptor has been mounted on the hull transom. Finally, comparative analysis revealed that the interceptor can reduce the ship resistance up to 14% mainly for the Froude numbers higher than 0.4. The model tests have been carried out at Galati University Towing Tank.

Effect of flap angle on transom stern flow of a High speed displacement Surface combatant

Hydrodynamic Drag of Surface combatants pose significant challenges with regard to fuel efficiency and exhaust emissions. Stern flaps have been used widely as an energy saving device, particularly by the US Navy (Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b). In the present investigation the effect of flap turning angle on drag reduction is numerically and experimentally studied for a high-speed displacement surface combatant fitted with a stern flap in the Froude number range of 0.17-0.48. Parametric investigations are undertaken for constant chord length & span and varying turning angles of 5 10 & 15. Experimental resistance values in towing tank tests were validated with CFD. Investigations revealed that pressure increased as the flow velocity decreased with an increase in flap turning angle which was due to the centrifugal action of the flow caused by the induced concave curvature under the flap. There was no significant change in stern wave height but there was a gradual increase in the stern wave steepness with flap angle. Effective length of the vessel increased by lengthening of transom hollow. In low Froude number regime, flow was not influenced by flap curvature effects and pressure recovery was marginal. In the intermediate and high Froude number regimes pressure recovery increased with the flap turning angle and flow velocity.

Development of an Energy Efficient Stern Flap for Improved EEDI of a Typical High speed Displacement Vessel

The surge in maritime trade is leading to large scale deployment of high-speed displacement ships by all nations. Cargo vessels are designed for a voyage in pre-determined routes at consistent speeds. On the other hand, high-speed displacement vessel engines designed with a capability to cater for top speeds are under-utilised during their normal course of operation. This sub-optimal utilisation impacts efficiency and increases emissions. In this study, a most favourable stern flap is designed for reducing the energy efficiency design index of a typical high-speed displacement vessel with a slender hull. CFD simulations and experimental model testing were conducted for 12 different stern flap configurations for determining most favourable flap design in the Froude no of 0.17-0.48. Performance of the most favourable stern flap was established by calculating, energy efficiency design index (EEDI) and fuel consumption based on typical operating profile. NOx, VOC and PM emissions were estimated in with and without flap condition. Studies demonstrated that the stern flap reduced effective power demand, average fuel consumption and emissions by about 8 per cent, which when considered for the ship’s operating life cycle, are significant. The most favourable stern flap reduced EEDI by 3.74 units and 1.98 units as compared to the bare hull condition and the required EEDI respectively, thereby demonstrating that EEDI could be used as an index to indicate stern flap efficiency.

Design and Validation of a Variable Reluctance Differential Solenoid Transducer

This paper presents a novel variable reluctance differential solenoid transducer (VRDST) that offers improved high-speed sensing performance over linear voltage differential transformers (LVDTs) and differential variable reluctance transformers (DVRTs). The VRDST has the unique ability to measure both position and velocity simultaneously using two independent measurements. This paper investigates a basic geometry for a VRDST. The position and velocity measurement methods are derived and implemented in a Simulink simulation. The simulated VRDST model is augmented with an FEA simulation to predict the magnetic characteristics of the investigated design. The results and predictions established by the simulation and analytical models are validated experimentally with a physical prototype. The similarity between the experimental and simulated results suggest the proposed FEA and Simulink simulations can be used to accurately predict the performance of a physical VRDST. The findings from the analytical modeling, simulation study and experimental validation all unanimously prove the position measurement performs well when measuring low-speed displacements, while the integrated-velocity measurement is useful for measuring high-speed displacements. The differing frequency ranges of these two independent measurements are found to complement each other and suggest the VRDST is superior compared to DVRTs or LVDTs for applications requiring wide bandwidth position measurements.

Evaluation of a Combustion-Based Mesoscale Thermal Actuator in Open and Closed Operating Cycles

A combustion-based mesoscale thermal actuator is proposed and its performance is studied in both open and closed cycle operations using a physics-based lumped-parameter model. The actuator design is unique as it implements a free-piston complaint architecture where the piston is free to move in a linear direction. Our objective is to study the actuator behavior in both the cycles to help identify the benefits and highlight the differences between the two cycles. The actuator is modeled as a spring-mass-damper system by taking an air standard cycle approach. Three observations are reported: (1) for nominal heat inputs (140 J/cycle), the actuator can produce large displacement strokes (16 cm) that is suitable for driving mesoscale robots; (2) the efficiency of the actuator depends on the heat input; and (3) for a specific heat input, both the open and closed cycles operate differently—with different stroke lengths, peak pressures, and thermal efficiencies. Our study reveals that the performance metrics of the actuator make it an ideal candidate for high speed, large force, and large displacement stroke related applications.

Energy Conservation Method Combining Anti spray Rail and Wedge Flap for High speed Displacement Hulls

The hydrodynamic mechanism and parametric influences of the wedge flap and the anti-spray rail in combination is investigates. A methodology with specific guidelines for incorporating these appendages with significant drag reduction is provided. Small crafts designs frequently require interventional changes to realise the desired guaranteed speed with their installed engine power. The appendages namely, the wedge, flap and anti-spray rails are used as retrofit measures or adapted in new hull forms, in isolation or in combination, to improve the drag and bring down the power requirement. A judicious combination of different appendages can result in significantly reduced drag and therefore power saving. The methodology combines the results of numerical and experimental investigations. The systematic study identifies the parameters for control namely, wedge flap size in terms of the chord length, its orientation vide the angle of the wedge flap, and the anti-spray rail location with respect to the water surface. The choice of the size of the wedge flap is a constrained problem since excessive wedge flap can cause problems related to length and hydrodynamic loading. This study establishes a solution by combination of a minimum integrated wedge flap with properly located anti-spray rail to reduce the drag. The study shows favourable influences due to local pressure and numerical results using a RANSE solver show good comparison with experimental test results. The methodology is a new approach towards drag reduction in new designs as well as drag control by retrofit.

Free-space micro-graphics with electrically driven levitated light scatterers.

The levitation of optical scatterers provides a new means to develop free-space volumetric displays. The principle is to illuminate a levitating particle displaced at high velocity in three dimensions (3D) to create images based on the persistence of vision (POV). Light scattered by the particle can be observed all around the volumetric display and, therefore, provides a true 3D image that does not rely on interference effects and remains insensitive to the angle of observation. The challenge is to control with high accuracy and at high speed the trajectory of the particle in 3D. Here we use electrically driven planar Paul traps (PPTs) to control the trajectory of electrically charged particles. A single gold particle colloid is manipulated in 3D through AC and DC electrical voltages applied to a PPT. The electric voltages can be modulated at high frequencies (150kHz) and allow for a high-speed displacement of particles without moving any other system component. The optical scattering of the particle in levitation yields free-space images that are imaged with conventional optics. The trajectory of the particle is entirely encoded in the electric voltage and driven through stationary planar electrodes. We show in this Letter the proof-of-concept for the generation of 3D free-space graphics with a single electrically scanned particle.

An investigation on HOBEM in evaluating ship wave of high speed displacement ship

A practical numerical tool is developed to evaluate ship waves of high speed displacement ships on the basis of potential flow theory, in which high order boundary element method (HOBEM) based on biquadratic shape functions is applied to solve the boundary value problem. Since the sinkage and trim of ship at high speeds are notable, influences of ship attitude on wave drag are investigated and three kinds of models are used to evaluate them. To make the numerical approach highly efficient, an incomplete LU factorization preconditioner is adopted and incorporated with the restarted generalized minimal residual method GMRES (m) to solve the boundary integral equation. A corresponding Fortran code is developed and applied to evaluate ship waves of the Wigley hull and 4a model, a transom stern ship. Computations are performed for both monohulls and catamarans over a wide range of Froude numbers (Fr = 0.10 - 1.00) . Numerical issues including mesh convergence and computational efficiency are investigated at first. Computed results of the wave drag, sinkage and trim show generally good agreement with experimental data. Reasonable wave patterns are obtained and physical phenomena that wake angle φmax, where the largest waves occur, would become narrow at high speeds is also captured by the present computations. Numerical results indicate the proposed method would be accurate and efficient to evaluate resistance for hull design of high speed displacement ship.