Editorial

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2 pages, 154 KiB

Open AccessEditorial

Special Issue on Energy Saving Device in Ship

by Moon-Chan Kim

Appl. Sci. 2022, 12(9), 4445; https://0-doi-org.brum.beds.ac.uk/10.3390/app12094445 - 28 Apr 2022

Viewed by 1160

Abstract

In recent years, interest in fossil energy depletion and global warming has increased [...] Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

Research

Jump to: Editorial

19 pages, 31902 KiB

Open AccessArticle

Hull Form Optimization Study Based on Multiple Parametric Modification Curves and Free Surface Reynolds-Averaged Navier–Stokes (RANS) Solver

by Sung-Woo Park, Seung-Hyeon Kim, Yang-Ik Kim and Inwon Lee

Appl. Sci. 2022, 12(5), 2428; https://0-doi-org.brum.beds.ac.uk/10.3390/app12052428 - 25 Feb 2022

Cited by 5 | Viewed by 2125

Abstract

In this study, the hull form optimization process to minimize resistance of KCS (KRISO containership) at

F n = 0.26

is described. The bow hull form of KCS was modified by varying such design parameters as sectional area curve (SAC), section shape, bulb [...] Read more.

In this study, the hull form optimization process to minimize resistance of KCS (KRISO containership) at

F n = 0.26

is described. The bow hull form of KCS was modified by varying such design parameters as sectional area curve (SAC), section shape, bulb breadth, and bulb height using multiple parametric modification curves devised by the authors. The resistance performances of modified hull forms were analysed by the viscous flow Reynolds-Averaged Navier–Stokes (RANS) solver of WAVIS ver.2.2. With a view to saving computational time during iterative analyses in the optimization process, the sinkage and trim were set to the fixed values which had been obtained for the original hull form with free condition. The validity of such constant sinkage/trim was then verified by conducting analysis for the optimal hull form with free condition. Optimization to minimize the cost function of the total resistance coefficient of model

C_{T M}

was performed by sequential quadratic programming (SQP), which is one of the gradient-based local optimization methods. Utilization of parallel computing led to the simultaneous calculation of the gradient, thereby speeding up the whole optimization process. At the design speed of 24 knots, the optimal hull yielded

C_{T M}

reduction by 1.8%, which is extrapolated to 3.1% reduction of effective power

P_{E}

in full scale. Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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17 pages, 9464 KiB

Open AccessArticle

Performance Improvement in a Wavy Twisted Rudder by Alignment of the Wave Peak

by Yong-Jin Shin, Moon-Chan Kim, Jin-Gu Kang and Jin-Wook Kim

Appl. Sci. 2021, 11(20), 9634; https://0-doi-org.brum.beds.ac.uk/10.3390/app11209634 - 15 Oct 2021

Cited by 3 | Viewed by 1590

Abstract

An improved wavy twisted rudder (WTR) is proposed based on a previous study. The misalignment of the wavy and propeller centers and the computational work of the previous study are supplemented to determine the effectiveness of the developed wavy twisted rudder. The aligned [...] Read more.

An improved wavy twisted rudder (WTR) is proposed based on a previous study. The misalignment of the wavy and propeller centers and the computational work of the previous study are supplemented to determine the effectiveness of the developed wavy twisted rudder. The aligned wavy twisted rudder (AWTR) was also applied to a KRISO container ship (KCS). The resistance, self-propulsion performance, and rudder forces due to the angular variation in the WTR and AWTR were compared using computational fluid dynamics (CFD). The numerical results were compared with the experimental results. The self-propulsion performance of the AWTR was superior to that of the WTR, with an efficiency gain of approximately 0.3% in both the model test and numerical analyses. The effectiveness of the AWTR was demonstrated using CFD; the CFD improved for the WTR in comparison with a conventional twisted rudder, especially at large rudder angles. The stall point of the AWTR was approximately 5° greater than that of the WTR in both directions. The results confirm the superiority of the AWTR in terms of its delayed stall and high lift-to-drag ratio, which was investigated by visualizing the streamline around the rudder. The actual maneuverability, such as the turning circle, realized with AWTR shall be compared with that realized with a WTR and conventional TR in the near future. Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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12 pages, 3627 KiB

Open AccessArticle

Full-Scale Measurements of the Propeller Thrust during Speed Trials Using Electrical and Optical Sensors

by Se-Myun Oh, Dong-Hyun Lee, Hyun-Joe Kim and Byoung-Kwon Ahn

Appl. Sci. 2021, 11(17), 8197; https://0-doi-org.brum.beds.ac.uk/10.3390/app11178197 - 03 Sep 2021

Cited by 3 | Viewed by 2649

Abstract

Full-scale sea trials demonstrate a ship’s performance under real operating conditions to confirm whether a ship meets its specifications and requirements. The determination of the performance through a sea trial is the most important stage in the ship design cycle. If one is [...] Read more.

Full-scale sea trials demonstrate a ship’s performance under real operating conditions to confirm whether a ship meets its specifications and requirements. The determination of the performance through a sea trial is the most important stage in the ship design cycle. If one is relying on measurements of propeller shaft power or fuel consumption, the distinction between the propeller and hull efficiencies may not be made. In order to be able to identify the propeller efficiency separate from the hull, full-scale propeller thrust should be accurately measured. In this study, full-scale measurements of the propeller thrust, torque, and revolution for a series of crude oil tankers and twin-skeg LNG carrier were conducted during the speed trials. Two different measuring systems, strain gauge and optical type, were implemented to compare the performance of sensors. As a result, it was shown that the strain gauge type-measuring device matched the model test results relatively well compared to the optical device. Above all, in the case of the optical device, it has been demonstrated that the zero setting is important to increase the accuracy of the full-scale measurements. Full article

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23 pages, 10387 KiB

Open AccessArticle

Numerical Study on Tip Vortex Cavitation Inception on a Foil

by Ilryong Park, Jein Kim, Bugeun Paik and Hanshin Seol

Appl. Sci. 2021, 11(16), 7332; https://0-doi-org.brum.beds.ac.uk/10.3390/app11167332 - 09 Aug 2021

Cited by 6 | Viewed by 1769

Abstract

In this paper, the inception of tip vortex cavitation in weak water has been predicted using a numerical simulation, and a new scaling concept with variable exponent has also been suggested for cavitation inception index. The numerical simulations of the cavitating flows over [...] Read more.

In this paper, the inception of tip vortex cavitation in weak water has been predicted using a numerical simulation, and a new scaling concept with variable exponent has also been suggested for cavitation inception index. The numerical simulations of the cavitating flows over an elliptic planform hydrofoil were performed by using the RANS approach with a Eulerian cavitation model. To ensure the accuracy of the present simulations, the effects of the turbulence model and grid resolution on the tip vortex flows were investigated. The turbulence models behaved differently in the boundary layer of the tip region where the tip vortex is developed, which resulted in different pressure and velocity fields in the vortex region. Furthermore, the Reynolds stress model for the finest grid showed a better agreement with the experimental data. The tip vortex cavitation inception numbers for the foil, predicted by using both wetted and cavitating flow simulation approaches, were compared with the measured cavitation index values, showing a good correlation. The current cavitation scaling study also suggested new empirical relations as a function of the Reynolds number substitutable for the two classic constant scaling exponents. This scaling concept showed how the scaling law changes with the Reynolds number and provided a proper scaling value for any given Reynolds numbers under turbulent flow conditions. Full article

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24 pages, 21506 KiB

Open AccessArticle

The Prediction of the Performance of a Twisted Rudder

by Ilryong Park, Bugeun Paik, Jongwoo Ahn and Jein Kim

Appl. Sci. 2021, 11(15), 7098; https://0-doi-org.brum.beds.ac.uk/10.3390/app11157098 - 31 Jul 2021

Cited by 6 | Viewed by 2885

Abstract

A new design approach using the concept of a twisted rudder to improve rudder performances has been proposed in the current paper. A correction step was introduced to obtain the accurate inflow angles induced by the propeller. Three twisted rudders were designed with [...] Read more.

A new design approach using the concept of a twisted rudder to improve rudder performances has been proposed in the current paper. A correction step was introduced to obtain the accurate inflow angles induced by the propeller. Three twisted rudders were designed with different twist angle distributions and were tested both numerically and experimentally to estimate their hydrodynamic characteristics at a relatively high ship speed. The improvement in the twisted rudders compared to a reference flat rudder was assessed in terms of total cavitation amount, drag and lift forces, and moment for each twin rudder. The total amount of surface cavitation on the final optimized twin twisted rudder at a reference design rudder angle decreased by 43% and 34.4% in the experiment and numerical prediction, respectively. The total drag force slightly increased at zero rudder angle than that for the twin flat rudder but decreased at rudder angles higher than 4° and 6° in the experiment and numerical simulation, respectively. In the experimental measurements, the final designed twin twisted rudder gained a 5.5% increase in the total lift force and a 37% decrease in the maximum rudder moment. Regarding these two performances, the numerical results corresponded to an increase of 3% and a decrease of 66.5%, respectively. In final, the present numerical and experimental results of the estimation of the twisted rudder performances showed a good agreement with each other. Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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14 pages, 3842 KiB

Open AccessArticle

Cavitator Design for Straight-Running Supercavitating Torpedoes

by Min-Jae Kim, Seon-Hong Kim, Kurn-Chul Lee, Bu-Geun Paik and Moon-Chan Kim

Appl. Sci. 2021, 11(14), 6247; https://0-doi-org.brum.beds.ac.uk/10.3390/app11146247 - 06 Jul 2021

Cited by 2 | Viewed by 3467

Abstract

A practical cavitator design method for straight-running-type supercavitating torpedoes was developed in this paper. Design requirements were first drawn in terms of torpedo performance characteristics, such as maximum range and motion stability. This method determines the optimum cavitator satisfying the design requirements that [...] Read more.

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

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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11 pages, 29216 KiB

Open AccessArticle

An Optimization Study on the Hull Form and Stern Appendage for Improving Resistance Performance of a Coastal Fishing Vessel

by Jin-Won Yu, Min-Kyung Lee, Yang-Ik Kim, Sung-Bu Suh and Inwon Lee

Appl. Sci. 2021, 11(13), 6124; https://0-doi-org.brum.beds.ac.uk/10.3390/app11136124 - 30 Jun 2021

Cited by 5 | Viewed by 2518

Abstract

In response to the increasing number of free trade agreements (FTA) and the Trans-Pacific Partnership (TTP), it is necessary to develop next-generation fishing vessels for the littoral sea of the Republic of Korea. The main objectives of such fishing vessels are to enhance [...] Read more.

In response to the increasing number of free trade agreements (FTA) and the Trans-Pacific Partnership (TTP), it is necessary to develop next-generation fishing vessels for the littoral sea of the Republic of Korea. The main objectives of such fishing vessels are to enhance the comfort of the crew and to improve fuel efficiency under the newly established principal dimension. This paper employs the hull form variation method to obtain a series of forebody hull forms of the 19 gross tonnage class of a coastal composite fishing vessel. Chine breadth modification has been used for hull form variations. The objective function is the minimum value of wavemaking resistance. A parametric study was conducted to observe the effects of design parameters on the objective functions, and hull-form optimization was performed. In addition to the hull-form optimization, the effect of the stern flap was investigated in terms of both resistance and operational performances. Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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26 pages, 13252 KiB

Open AccessArticle

Experimental and Numerical Study on the Performance Change of a Simple Propeller Shape Using the Coanda Effect

by Ju-Han Lee, Kwang-Jun Paik, Soon-Hyun Lee, Gu-Hyeon Kim and Jun-Hui Cho

Appl. Sci. 2021, 11(9), 4112; https://0-doi-org.brum.beds.ac.uk/10.3390/app11094112 - 30 Apr 2021

Cited by 3 | Viewed by 1902

Abstract

In this study, a jet injection propeller was designed to increase its efficiency, and the results were compared by open water tests and numerical computations. Also, the change in shape of the slit and injection volume conditions, which are difficult to perform experiments [...] Read more.

In this study, a jet injection propeller was designed to increase its efficiency, and the results were compared by open water tests and numerical computations. Also, the change in shape of the slit and injection volume conditions, which are difficult to perform experiments with, were analyzed through computations. The jet injected from the blade surface generates additional thrust due to the Coanda effect, and the jet injection generates a moment in the direction of propeller rotation, resulting in a decrease in the total torque. Computations were performed for three slit heights. When the height of the slit is high, the efficiency of the propeller increases, even if the power of the pump required for jet injection is considered. The result was found to increase the efficiency by about 8.7%, even when the efficiency was compared under the condition of generating the same thrust by controlling the injection volume of the jet by designing a normal propeller that does not inject a jet. Full article

(This article belongs to the Special Issue Energy Saving Devices in Ship)

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