Hydrodynamic Evaluation of Interceptor Configuration on a High-Speed Ship with Tunnel Propeller for Resistance Reduction

Speed of commercial displacer vessels on inland waterways is a major disadvantage in comparison to truck and railway. A solution to shift cargo from congested roads and railways to inland waterways may be with high speed vessels as those issued in coastal waters. Inland waterways are restricted in depth and often in width, which leads to hydraulic impact on bottom and banks. Screening of existing high speed ship concepts in unrestricted waters showed twin hulls (catamarans) with and without air-cushion and monohulls as technically feasible on inland waterways. Three types of high speed ships were modeled and tested in a restricted laboratory canal regarding hydraulic impacts from generation of waves, water-level variations, and flow velocities. Ship interaction with existing structures and interference with other ships, as well as channel bed and banks, were also modeled and tested. For the air-cushioned twin hull (SES-Catamaran), high speed model tests showed that water-level variation and flow velocitie...

Speed on water is a key indicator of amphibious vehicles. However, due to the inherent non-streamlined configuration, when reaching a certain velocity, the resistance acting on the vehicle hull is so large and the maximum speed on water is hard to be further enhanced. Moreover, the trim gets so larger that leads the stern submerged into water when speed up. In order to solve this problem of a semi-planing amphibious cargo truck, this paper proposed a method by installing interceptors, hydrofoils, and combination of them on the stern. Experimental tests and numerical studies were performed respectively, and the numerical results were in good agreement with experiment. In what continues, the effect of interceptors, hydrofoils, and combination of them on trim and resistance was investigated. The results showed that the interceptor had a better effect than hydrofoil when height is not so big, but the effect got more and more powerful with interceptor height increasing, finally lead to an excessive trim control. Combination of interceptor with hydrofoil in suitable size were beneficial to trim control and resistance reduction.

Numerical and experimental hydrodynamic assessment of a dihedral bulbous bow retrofit for a semi-planing fishing vessel

In this paper an attempt has been made to study the effectiveness of interceptor on lift and drag as this device is nowadays used by both partial and dynamic lift crafts. There is change in pressure distribution at the stern region where interceptor is fitted which helps in the lift of vessel. This study focuses on the effect of interceptor in high speed planing hull with 20deg deadrise angle based on experimental, numerical and empirical approaches. Experiments were conducted in the Towing Tank facility, Department of Ocean Engineering at IIT Madras and numerical simulations were carried out in still water condition for the cases of the hull with and without interceptor. Results showed good reduction in resistance and trim of the vessel when fitted with interceptor in planing regime. Savitsky empirical relations for bare hull and Steen empirical equations for hull with interceptor are used to estimate lift and drag on the vessel. The results of this study show that interceptor creates more lift on the vessel due to the pressure created at the stern region which helps in drag reduction and further in better control of trim on the vessel. Measurements were also made to confirm that interceptor has an effect on the dynamic lift of the hull and hence a change in resistance resulting in control of the trim angle.

The air entrainment in sumps (Pump Intake) is a commonly observed phenomenon at low water level and high Froude number corresponding to flow rates higher than the rated flow. The air entrainment initiates with the formation of small vortex like structure on the surface with its position varying in the vicinity of Pump intake portion. Normally it calls for two-phase flow analysis (and possibly transient also) to correctly predict the air entrainment phenomenon using computational fluid dynamics approach. We at CRED, Kirloskar Brothers Limited could predict the root cause for air entrainment by studying the vortex formation well within the flow. A single-phase steady state flow was analyzed. Two test cases were studied. IOWA University had published a sump case with results from computational fluid dynamics studies. The other case was the actual sump model study carried out using experimental setup wherein the air entrainment was observed. The paper presents the comparison of the predictions with results from these two test cases.

Biofouling on ship hulls increases drag, fuel consumption and environmental impact. This study uses Computational Fluid Dynamics (CFD) to simulate biofouling roughness effects on the FAO1 fishing vessel, analysing changes in hydrodynamic resistance. Simulations, validated against experimental data, considered varying roughness levels and vessel speeds. The results show that increased roughness raises both total and frictional resistance, especially at higher speeds, emphasising smooth hull maintenance for fuel efficiency. Moreover, CFD results closely matched empirical data, confirming accuracy. The study found frictional drag increased with roughness, while biofouling reduced hydrodynamic pressure, wake and wave elevation, suggesting lower wave-making resistance in some cases. These findings imply maintaining a smooth hull minimises frictional resistance, but balancing this with potential reductions in residual resistance may optimise overall efficiency.

Wake wash is one of the serious problems for high speed ships, because it may cause damage on the coastal aquaculture using rafts or nets. Since some important parts of high speed ships are catamaran, a CFD code for the catamaran ship is developed. It can properly evaluate wave resistance of both symmetric and asymmetric demi-hulls with consideration on wake wash. The code is applied to the development of a catamaran type commuter ship operated for domestic services. Wave resistance and wake wash characteristics are demonstrated to be improved by the numerical simulation. The towing tank experiment for the evaluation of wave resistance and wake wash is carried out for the verification. It is clarified that the improved hull form shows lower resistance with smaller wake wash at higher Froude number when the displacement is reduced by 30%.

This work shows the performance of LincoSim, a web-based virtual towing tank enabling automated and standardized calm water computational fluid dynamics (CFD) data sampling, extending previous published applications to the case of a high-speed hull. The calculations are performed for a 1:10 scale model of a 43 ft powerboat hull form in the Froude number range from 0.3 to 2.0. The counterpart physical model is the experimental fluid dynamics (EFD) campaign performed at the University of Naples Federico II, where the resistance, sinkage and trim data have been measured. The EFD/CFD data comparison is performed and shown with a discussion of the spotted differences. The average percentage differences between the EFD and CFD data for the whole speed range are 1.84, 6.87 and 6.94 for the resistance, dynamic trim, and sinkage, respectively. These results confirm the maturity of the standardized and automated CFD modeling for calm water hydrodynamic analysis included in LincoSim, even at very high Froude numbers. The wetted length of the keel and chine and the wetted surface are calculated from numerical data using the advanced post-processing. Finally, as a work in progress, we test a first comparison for the same hull of the EFD and CFD data, considering two seakeeping conditions for head waves at a given wavelength for two velocity conditions. Also, this kind of analysis confirms the tight correlation between the measured and computed outcomes. This synergic interplay of EFD and CFD can link the advantages of both methods to support hull design but also requires experiment planning and final data analysis to obtain physical parameters not easily measurable in laboratory, such as the wetted surface, wetted lengths, proper viscous contribution, and pressure distribution both in calm water and in waves.

Experimental and numerical study on the high-speed ship hydrodynamics influenced by an interceptor with varied angle of attack

The acting on the planing hull is the most complex hydrodynamics simulation. Therefore, an analysis was done to evaluate drag, lift force, and seakeeping in two degrees of freedom (2-DOF) which is heave and trim. It was fundamental aspects of the overall high-speed vessel. This article focused on the hydrodynamic performance of a complete interceptor configuration that could control the motion behavior of deep-V planing hull in calm water conditions. The benchmark study was undertaken by comparing numerical results with experimental study by Park at al. Models with and without interceptors had been analyzed by numerical simulation performed using Reynold Averaged Navier Stokes (RANS) to describe turbulence model with k epsilon based on computational fluid dynamic (CFD). In this study, the interceptor proper applies at a speed of less than Froude number 0.87. Interceptor reduce by 21% drag at Froude number 0.87 and also reduce by 16% trim and 6% heave at Froude number 0.58. Nevertheless, applied interceptor in high Froude number such as more than Froude number 1.16 caused interceptor lose effectiveness due to producing a decisive moment which made negative trim (bow-down) and increase total drag.

High-speed vessels exhibit various motions and accelerations in calm water and sea waves. For examining the behavior of high-speed vessels, it is possible to examine these movements in laboratory models. In this paper, a single-step model in calm water is experimentally tested and compared with a model of no step. The speed range of these vessels is 1 m/s to 9 m/s equivalent to Beam Froude numbers of 0.43 to 3.87. During these experiments, the resistance parameters, trim, bow, and stern rise-up as well as the center of the gravity are measured. The non-step model has longitudinal instability at a speed of 8 m/s. This instability is avoided when the vessel is equipped by a transversal step. The vessel's trim and resistance are also reduced in the planing mode in calm water. Subsequently, hydrodynamic performance and its seakeeping condition in the planing regime are investigated for both vessels in regular waves. The single-step and non-step vessels are tested in the wavelength range of [Formula: see text], and the wave height range of 6 to 18 centimeters. It is observed that stepped vessel experiences lower motions and bow accelerations and less added resistance in comparison to the non-stepped vessel.

The mode of transportation for offshore supply/tug vessels dictates that speed and reliability are the two most important prerequisites. As the weight of the propulsion system would have an important influence on the speed, range and payload of the vessel, it was decided to use a light weight gas turbine prime mover, a light weight reduction gearbox and a CRP propeller. This-lead to the development of the "TURBOPITCH" Propulsion System. The following paper presents, in detail, the design and operation of the system. Although the individual items of the system were of designs of known proven equipment, the "TURBOPITCH" packaged system presents many unique features. The paper is presented in three sections:PropellerReduction GearboxEngine INTRODUCTION The "TURBOPITCH" System is designed with two configurations:Straight drive where the prime mover is mounted forward of the gearbox."U" drive where the prime mover is mounted aft of the gearbox and over the propeller shaft. This configuration is necessary where the arrangement of the vessel does not permit the prime mover forward as in the case of vessels that require the area normally used for machinery to be used as accommodation space or cargo area. This configuration is compact and the machinery space is kept to a minimum. As the type, size and speed of vessels would vary considerably, it was decided to standardize as much as possible and keep to a minimum the different sizes of the major components. The system was developed primarily for horsepower from 1000 to 2500. This appeared to meet the requirements of owners who operated medium and high speed vessels from 75 feet to 120 felt in length and speeds from 25 knots to 40 knots with single or twin screw configurations. The speed of the propeller was another variable. This could vary between 900 RPM and 1400 RPM depending on vessel speed and parameters. The 1200 RPM was selected as being the propeller speed most suitable. A data sheet, Figure 1, shows for a range of horsepower from 1000 to 2500, two different sizes of propeller hubs and reduction gearboxes and four sizes of gas turbines, 1000; 1250, 2009 and 2500 horsepower respectively. These being normal marine production line models. The "TURBOPITCH" System has the following main advantages over the conventional system:savings in horsepower and engine WeightFull power/speed regardless of light or loaded displacementReverse gear not required as propeller blades can be reversedIncreased cruising range at reduced speed as it is possible to match the most economical operation of the gas turbine and the propellerImproved control when maneuvering at low speedsFaster response

Measurements of unsteady stress have been made on an INCAT wave-piercing catamaran during an extended period of passenger operations under varying sea conditions, vessel speed and heading relative to the sea. It has been found that the stress fluctuations are consistent with unsteady bending of the hull cross section. The measured results are compared with the predictions of a time domain, spatially fixed, strip theory method suitable for computation at high Froude number. It is found that there is a progressive nonlinear reduction of global bending moment and sectional shear fluctuations relative to wave height as the wave height increases. The intensity of the observed stress fluctuations is shown to be consistent with the loading predictions of the time domain method. © 2005: Royal Institution of Naval Architects.

Improved application of a solar chimney concept in a two-story building: An enhanced geometry through a numerical approach

Some improvements are attempted in an experimental technique to study radiation and diffraction waves of a ship at forward speed which was previously proposed by one of the present authors. Those improvements aim at using this technique for measuring and analyzing the radiation and diffraction waves at high Froude number on the purpose of studying seakeeping of a high speed ship.Measured diffraction wave patterns of a high speed ship obtained by this technique are presented. A new method of Fourier transforming those patterns is proposed to determine their Kochin functions more correctly at high speed than the previous one.Inaccuracy of the so-called high speed theory in predicting the diffraction waves of the high speed ship is revealed by direct comparison of measured and theoretically computed wave pattern. We find this is caused by ignoring the transverse waves which are not to be ignored even at high Froude number.