• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.25-32
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• 2015

Dielectric barrier discharge (DBD) plasma actuator was designed to reduce aerodynamic drag in a cylindrical model and wind tunnel test was performed at various wind velocities. In addition, computational fluid dynamics (CFD) analysis and flow visualization were used to investigate the effect of the plasma on the flow stream in the cylinderical model. At low wind velocity, the plasma actuator had no effects because flow separation did not appear. The aerodynamic drag was reduced by 14% at 14 m/s and by 27% at 17 m/s, respectively. It was confirmed by CFD analysis and flow visualization that the DBD plasma actuator decreased in pressure difference around the cylindrical model, thus decreasing the magnitude of wake vortex.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.3
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• pp.222-232
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• 2011

This article examines the scale effect of the flow characteristics, resistance and propulsion performance on a 317k VLCC. The turbulent flows around a ship in both towing and self-propulsion conditions are analyzed by solving the Reynolds-averaged Navier-Stokes equation together with the application of Reynolds stress turbulence model. The computations are carried out in both model- and full-scale. A double-body model is applied for the treatment of free surface. An asymmetric body-force propeller is used. The speed performances including resistance and propulsion factors are obtained from two kinds of methods. One is to analyze the computational results in model scale through the revised ITTC' 78 method. The other is directly to analyze the computational results in full scale. Based on the computational predictions, scale effects of the resistance and the self-propulsion factors including form factor, thrust deduction fraction, effective wake fraction and various efficiencies are investigated. Scale effects of the streamline pattern, hull pressure and local flow characteristics including x-constant sections, propeller and center plane, and transom region are also investigated. This study presents a useful tool to hull-form and propeller designers, and towing-tank experimenters to take the scale effect into consideration.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.3
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• pp.205-211
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• 2014

Interests on energy saving devices (ESDs) have been increased with the concern of the energy efficiency design index (EEDI) developed by the international maritime organization (IMO). To study the influence of ESDs, KVLCC2 with energy saving pre-swirl stator (PSS) was selected. To validate the computations, computed nominal wake of the model scale ship was compared with the experimental data, and the numerical uncertainty assessment was done for the full scale ship computations. The PSS changed rotational flow, which was assistant to the propeller thrust for the model and full scale ships. Performances of the full scale ships were predicted by ITTC methods, and new prediction method was proposed.

• Journal of Ship and Ocean Technology
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• v.10 no.4
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.9-25
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• 1994

In the present study, the Reynolds-averaged Navier-Stokes equations, together with the equations of the $k-{\varepsilon}$ model of turbulence, were solved numerically in a general body-fitted coordinate system for three-dimensional turbulent flows around the six basic shapes of the magnetically levitated train(MAGLEV). The numerical computations were conducted on the MAGLEV model configurations to provide information on shapes of this type very near the elevated track at a constant Reynolds number of $1.48{\times}10^{6}$ based on the body length. The coordinate system was generated by numerically solving a set of Poisson equations. The convective transport equations were discretized using the finite-analytic scheme which employed analytic solutions of the locally-linearized equations. A time marching algorithm was employed to enable future extensions to be made to handle unsteady and fully-elliptic problems. The pressure-velocity coupling was treated with the SIMPLER-algorithm. Of particular interests were wall effect by the elevated track on the aerodynamic forces and flow characteristics of the six models calculated. The results indicated that the half-circle configuration with extended sides and with smooth curvature of sides was desirable because of the low aerodynamic forces and pitching moment. And it was found that the separation bubble was occured at wake region in near the elevated track.

• Journal of the Society of Naval Architects of Korea
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• v.50 no.3
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• pp.138-144
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• 2013

New experimental devices and methods to measure shaft forces of ships are proposed in this paper. The strain gauge type six-component load cell was newly designed and installed to the end of the propeller shaft. The signals generated from the sensor in the propeller rotating are transferred to the new data amplifying and processing board on the shaft and the data is transmitted to the self-made wireless receiver. To find out the characteristics of shaft forces during port and starboard turning motions in sea trial, oblique and combined yaw maneuvering tests at straight, transient, maximum yaw rate, steady conditions were performed with the model ship installed the shaft forces measuring device using circular motion tester of Samsung Ship Model Basin. Characteristics of the measured shaft forces in model tests show quantitatively good agreement with the computed values obtained by the CFD programs using the measured wake data in oblique towing conditions. In the near future, It is hoped that the estimated shaft forces for a ship from this experimental method could be validated through comparison with directly measured values of a ship.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.6
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• pp.516-525
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• 2015

In this paper, the acoustic pressure of a helicopter rotor in hovering and low speed descent flight is predicted and compared with experimental data. Ffowcs Williams-Hawkings equation is used to predict the acoustic pressure. Two different wind tunnel test data are used to validate the predicted results. Boeing 360 model rotor test results are used for the low-frequency noise in hover, and HART II test results are employed for the mid-frequency noise, especially BVI noise, in low speed descent flight. A simple free-wake model as well as the state-of-the-art CFD/CSD coupling method are adopted to perform the analysis. Numerical results show good agreement against the measured data for both low-frequency and mid-frequency harmonic noise signal. The noise carpet results predicted using the FFT(Fast Fourier Transform) shows also reasonable correlation with the measured data.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.1
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• pp.37-44
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• 2016

Recently researchers are conducting a lot of research related to EEDI in order to satisfy IMO resolution MEPC. Especially they are interested in design of energy saving device. This paper is to design the asymmetric pre-swirl stator for 160K LNG carrier in order to reduce energy. Two types of the asymmetric pre-swirl stator are taken into account; constant and variable pitch angle stators. “constant” and “variable” mean state that the pitch of stators change by radius. The dimensions of the stators are initially determined using potential-flow code. The propulsion performances of the stators are predicted using viscous-flow code. The model test is carried out in towing tank in PNU. Prediction of ship performance generally follow ITTC recommended. Ship wake prediction was done by two method, ITTC 1978 and ITTC 1999. Therefore propulsion performances were compared ITTC 1978 with ITTC 1999 methods. Comparison components are delivered power and thrust deduction coefficient of the model. Final pre-swirl stator is selected by comparing experiment and CFD.

• Journal of the Korea Society of Computer and Information
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• v.26 no.12
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• pp.255-264
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• 2021

In this paper, we propose operations and maintenance (O&M) planning approach for floating offshore wind farm using the mathematical optimization. To be specific, we present a MILP (Mixed Integer Linear Programming that suggests the composition of vessels, technicians, and maintenance works on a weekly basis. We reflect accessibility to wind turbines based on weather data and loss of power generation using the Jensen wake model to identify downtime cost that vary from time to time. This paper also includes a description of two-stage approach for maintenance planning & detailed scheduling and numeric analysis of the number of vessels and technicians on the O&M cost. Finally, the MILP model could be utilized in order to establish the suitable and effective maintenance planning reflecting domestic situation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.419-428
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• 2020

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v²-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v²-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v²-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.