• Journal of the Society of Naval Architects of Korea
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• v.57 no.5
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• pp.287-296
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• 2020

The present study aims to improve the accuracy of the maneuvering simulations based on captive model test results. To derive the hydrodynamic coefficients in a self-propelled condition, a mathematical maneuvering model using a whole vehicle model was established. Captive model tests were carried out using the Vertical Planar Motion Mechanism (VPMM) equipment. A motor controller was used to control the constant propeller revolution rate during pure motion tests. The resistance tests, self-propulsion tests, static drift tests, and VPMM tests were performed in the towing tank of Seoul National University. When the vertical drift angle changes, the gravity load on the sensors were changed. The hydrodynamic forces were deduced by subtracting the gravity load from the measured forces. The hydrodynamic coefficients were calculated using the least-square method. The simulation of the turning circle test was compared with the free-running model test result, and the error of the turning radius was 8.3 % compared to the free-running model test.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.892-901
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• 2020

We used a numerical method to estimate the hydrodynamic maneuvering derivatives for the heave-pitch coupling motion of an underwater glider. It is very important to assess the hydrodynamic maneuvering characteristics of a specific hull form of an underwater glider in the initial design stages. Although model tests are the best way to obtain the derivatives, numerical methods such as the Reynolds-averaged Navier-Stokes (RANS) method are used to save time and cost. The RANS method is widely used to estimate the maneuvering performance of surface-piercing marine vehicles, such as tankers and container ships. However, it is rarely applied to evaluate the maneuvering performance of underwater vehicles such as gliders. This paper presents numerical studies for typical experiments such as static drift and Planar Motion Mechanism (PMM) to estimate the hydrodynamic maneuvering derivatives for a Ray-type Underwater Glider (RUG). A validation study was first performed on a manta-type Unmanned Undersea Vehicle (UUV), and the Computational Fluid Dynamics (CFD) results were compared with a model test that was conducted at the Circular Water Channel (CWC) in Korea Maritime and Ocean University. Two different RANS solvers were used (Star-CCM+ and OpenFOAM), and the results were compared. The RUG's derivatives with both static drift and dynamic PMM (pure heave and pure pitch) are presented.

• Earthquakes and Structures
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• v.3 no.6
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• pp.869-887
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• 2012

Ground motion scaling techniques are actively debated in the earthquake engineering community. Considerations such as what amplitude, over what period range and to what target spectrum are amongst the questions of practical importance. In this paper, the effect of various ground motion scaling approaches are explored using three reinforced concrete prototypical building models of 8, 12 and 20 stories designed to respond nonlinearly under a design level earthquake event in the seismically active Southern California region. Twenty-one recorded earthquake motions are selected using a probabilistic seismic hazard analysis and subsequently scaled using four different strategies. These motions are subsequently compared to spectrally compatible motions. The nonlinear response of a planar frameidealized building is evaluated in terms of plasticity distribution, floor level acceleration and uncorrelated acceleration amplification ratio distributions; and interstory drift distributions. The most pronounced response variability observed in association with the scaling method is the extent of higher mode participation in the nonlinear demands.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.2
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• pp.10-18
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• 2001

The very large floating structure which can be used for as airport may be as large as several kilometer long and wide. The first order wave forces as well as wave drift forces are very important forces on such a very large floating structures. In the present study, the time simulation of motion responses for dolphin-moored VLFS in waves is presented. The hydrodynamic coefficients and wave forces involved in the equations are obtained from a three-dimensional panel method in the frequency domain. The horizontal drift forces and mooring forces for dolphin systems are taken into account. As for numerical example, time domain analyses are carried out for a VLFS(Phase I) in irregular wave condition.

• Journal of Ocean Engineering and Technology
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• v.31 no.5
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• pp.340-345
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• 2017

It is important to predict the hydrodynamic maneuvering derivatives, which consist of the forces and moment acting on a hull during a maneuvering motion, when estimating the maneuverability of a ship. The estimation of the maneuverability of a ship with a change in the stern hull form is often performed at the initial design stage. In this situation, a method that can reflect the change in the hull form is necessary in the prediction of the maneuverability of the ship. In particular, the linear hydrodynamics maneuvering derivatives affect the yaw checking motion as the key factors. In the present study, static drift calculations were performed using Computational Fluid Dynamics (CFD) based on Reynolds Average Navier-Stokes (RANS) for a 40-segment hull. A prediction method for the linear hydrodynamic maneuvering derivatives was proposed using the slender body theory from the distribution of the lateral force acting on each segment of the hull. Moreover, the results of a comparison study to the model experiment for KVLCC1 performed by KRISO are presented in order to verify the accuracy of the static drift calculation. Finally, the linear hydrodynamic maneuvering derivatives obtained from both the model test and calculation are compared and presented to verity the usefulness of the method proposed in this study.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.3C
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• pp.408-418
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• 2004

In this paper, we propose a novel scalable video coding algorithm based on adaptively weighted multiple reference frame method. To improve the coding efficiency in the enhancement layer, the enhancement frame is predicted by the sum of adaptively weighted double motion compensated frames in the enhancement layer and the current frame in the base layer, according to the input video characteristics. By employing adaptive reference selection scheme at the decoder, the proposed method reduce the drift problem significantly. From the experimental results, the proposed algorithm shows more than 1.0 ㏈ PSNR improvement, compared with the conventional scalable H.263+ for various packet loss rate channel conditions.

• Journal of the Society of Naval Architects of Korea
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• v.59 no.5
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• pp.296-305
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• 2022

In order to investigate maneuvering characteristics of KCS in waves, captive model test in regular waves was conducted. Purpose of the test is measuring maneuvering hull forces when ship is maneuvering in waves. Model test was carried out using CPMC (Computerized Planar Motion Carriage) of ocean engineering basin in KRISO (Korea Research Institute of Ships and Ocean engineering). Total 6 degrees-of-freedom motion were fixed by two points supporting captive model test device, which is specially designed for this test. This system estimates 6 degrees-of-freedom forces and moments through 12 strain gauge signals. Mapping matrix from strain gauge signals to 6 degrees-of-freedom forces and moments was derived by a well-organized calibration test. Static drift test was conducted in calm sea and in regular waves with various wave conditions. Hydrodynamic coefficients related to drift angle were extracted for each wave conditions, and the effect of waves on course stability was analyzed.

• Ocean Systems Engineering
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• v.7 no.4
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• pp.435-460
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• 2017

The main objective of this study is to investigate the turning and zig-zag maneuvering performance of the well-known naval surface combatant DTMB (David Taylor Model Basin) 5415 hull with URANS (Unsteady Reynolds-averaged Navier-Stokes) method. Numerical simulations of static drift tests have been performed by a commercial RANS solver based on a finite volume method (FVM) in an unsteady manner. The fluid flow is considered as 3-D, incompressible and fully turbulent. Hydrodynamic analyses have been carried out for a fixed Froude number 0.28. During the analyses, the free surface effects have been taken into account using VOF (Volume of Fluid) method and the hull is considered as fixed. First, the code has been validated with the available experimental data in literature. After validation, static drift, static rudder and drift and rudder tests have been simulated. The forces and moments acting on the hull have been computed with URANS approach. Numerical results have been applied to determine the hydrodynamic maneuvering coefficients, such as, velocity terms and rudder terms. The acceleration, angular velocity and cross-coupled terms have been taken from the available experimental data. A computer program has been developed to apply a fast maneuvering simulation technique. Abkowitz's non-linear mathematical model has been used to calculate the forces and moment acting on the hull during the maneuvering motion. Euler method on the other hand has been applied to solve the simultaneous differential equations. Turning and zig-zag maneuvering simulations have been carried out and the maneuvering characteristics have been determined and the numerical simulation results have been compared with the available data in literature. In addition, viscous effects have been investigated using Eulerian approach for several static drift cases.

• Biomedical Engineering Letters
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• v.8 no.4
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• pp.365-371
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• 2018

Uninterrupted monitoring of multiple subjects is required for mass causality events, in hospital environment or for sports by medical technicians or physicians. Movement of subjects under monitoring requires such system to be wireless, sometimes demands multiple transmitters and a receiver as a base station and monitored parameter must not be corrupted by any noise before further diagnosis. A Bluetooth Piconet network is visualized, where each subject carries a Bluetooth transmitter module that acquires vital sign continuously and relays to Bluetooth enabled device where, further signal processing is done. In this paper, a wireless network is realized to capture ECG of two subjects performing different activities like cycling, jogging, staircase climbing at 100 Hz frequency using prototyped Bluetooth module. The paper demonstrates removal of baseline drift using Fast Fourier Transform and Inverse Fast Fourier Transform and removal of high frequency noise using moving average and S-Golay algorithm. Experimental results highlight the efficacy of the proposed work to monitor any vital sign parameters of multiple subjects simultaneously. The importance of removing baseline drift before high frequency noise removal is shown using experimental results. It is possible to use Bluetooth Piconet frame work to capture ECG simultaneously for more than two subjects. For the applications where there will be larger body movement, baseline drift removal is a major concern and hence along with wireless transmission issues, baseline drift removal before high frequency noise removal is necessary for further feature extraction.

• The Korean Journal of Financial Management
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• v.24 no.4
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• pp.1-43
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• 2007

The traditional Black-Scholes model for option pricing is based on the assumption that the log-return of the underlying asset follows a Brownian motion. But this assumption has been criticized for being unrealistic. Thus, for the last 20 years, many attempts have been made to adopt different stochastic processes to derive new option pricing models. The option pricing models based on L$\acute{e}$vy processes are being actively studied originating from the Gerber-Shiu model driven by H. U. Gerber and E. S. W. Shiu in 1994. In 2004, G. H. L. Cheang derived an option pricing model under multiple L$\acute{e}$vy processes, enabling us to adopt drift and jumps to the Gerber-Shiu model, while Gerber and Shiu derived their model under one L$\acute{e}$vy process. We derive the Gerber-Shiu model which includes drift and jumps under L$\acute{e}$vy processes. By adopting a Gamma distribution, we expand the Heston model which was driven in 1993 to include jumps. Then, using KOSPI200 index option data, we analyze the price-fitting performance of our model compared to that of the Black-Scholes model. It shows that our model shows a better price-fitting performance.