• Journal of the Korean Solar Energy Society
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• v.29 no.5
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• pp.73-80
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• 2009

A tidal current turbine is designed and analyzed numerically by using blade element momentum theory. The rated power has a limitation because the diameter of the tidal current turbine cannot exceed the depth of sea water. This study investigates a horizontal axis tidal-current turbine with a rated power of 500 kW. NACA-6 series laminar foil shape is used for basic airfoil along the blade span. The distributions of chord length and twist angle along the blade span are obtained from the hydrodynamic optimization procedure. Prandtl's tip loss correction and angle of attack correction considering the three-dimensional effect are applied for this study. The power coefficient curve shows maximum peak at the rated tip speed ratio of 6.0, and the maximum torque coefficient is developed at the tip speed ratio of 4. The drag coefficient reaches about 0.85 at the design tip speed ratio.

• Geophysics and Geophysical Exploration
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• v.7 no.4
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• pp.245-250
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• 2004

Horizontal-axes on the seismic section have been represented in a distance unit by applying horizontal-distance correction transformation on a 2-D seismic section of single channel marine seismic data. By drawing horizontal-axes in a distance unit, distortion of horizontal distances shown on the seismic section when the ship speed varies during a survey can be diminished considerably. Position information obtained by GPS and stored in each trace of seismic data as well as data collection windows were used for horizontal distance correction. The minimum window length was decided by considering ship speed and shot interval, and the maximum window length wat determined by reflecting radius of the 1st Fresnel zone. In choosing an optimum window length, horizontal resolution and stacking effect were considered simultaneously. By applying horizontal distance correction we could get a 2-D seismic section which is considered at reflecting the real subsurface structure analogously.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.7
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• pp.529-537
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• 2021

Wind tunnel tests were carried out with a scramjet high speed vehicle. Since the scramjet engine does not have a compressor, it has a simple structure, but it is important to design the intake for the supersonic combustion in the combustion chamber. In this study, internal flow characteristics and the starting condition were analyzed by measuring the pressure at the isolator exit just before the combustion chamber, and the intake performance parameters were calculated and compared the result on every Mach number. The aerodynamic characteristics of the flow-through high speed vehicle were analyzed and internal drag correction is required to precisely analyze the aerodynamic characteristics. In this paper, an experimental technique using three probes for internal drag correction was proposed. By applying internal drag correction, it was able to figure out the effect of the internal flow on the aerodynamic force of the vehicle.

• Journal of Korea Port Economic Association
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• v.39 no.2
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• pp.129-141
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• 2023

This study analyzes the dynamic characteristics of daily freight rates of dry bulk and tanker shipping markets and their forecasting accuracy by using the error correction models. In order to calculate the error terms from the co-integrated time series, this study uses the common stochastic trend model (CSTM model) and vector error correction model (VECM model). First, the error correction model using the error term from the CSTM model yields more appropriate results of adjustment speed coefficient than one using the error term from the VECM model. Furthermore, according to the adjusted determination coefficients (adjR²), the error correction model of CSTM-model error term shows more model fitness than that of VECM-model error term. Second, according to the criteria of mean absolute error (MAE) and mean absolute scaled error (MASE) which measure the forecasting accuracy, the results show that the error correction model with CSTM-model error term produces more accurate forecasts than that of VECM-model error term in the 12 cases among the total 15 cases. This study proposes the analysis and forecast tasks 1) using both of the CSTM-model and VECM-model error terms at the same time and 2) incorporating additional data of commodity and energy markets, and 3) differentiating the adjustment speed coefficients based the sign of the error term as the future research topics.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.314-321
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• 2019

The Self-Adaptive Vision Correction Algorithm (SAVCA) developed in this study was suggested for improving usability by modifying four parameters (Modulation Transfer Function Rate, Astigmatic Rate, Astigmatic Factor and Compression Factor) except for Division Rate 1 and Division Rate 2 among six parameters in Vision Correction Algorithm (VCA). For verification, SAVCA was applied to two-dimensional mathematical benchmark functions (Six hump camel back / Easton and fenton) and 30-dimensional mathematical benchmark functions (Schwefel / Hyper sphere). It showed superior performance to other algorithms (Harmony Search, Water Cycle Algorithm, VCA, Genetic Algorithms with Floating-point representation, Shuffled Complex Evolution algorithm and Modified Shuffled Complex Evolution). Finally, SAVCA showed the best results in the engineering problem (speed reducer design). SAVCA, which has not been subjected to complicated parameter adjustment procedures, will be applicable in various fields.

• Proceedings of the KIEE Conference
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• 1990.11a
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• pp.287-290
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• 1990

The paper describes the correction of the switching dead times avoiding a bridge leg short circuit in pulse width modulated voltage sorce inverters. The co consequences on AC variable speed drives with synchronous and asynchronous motors are described by harmonic analysis and by computer simulation.

• Journal of Welding and Joining
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• v.33 no.2
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• pp.91-96
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• 2015

The laser-arc hybrid welding of SS400 steel was carried out with the use of disk laser equipment of 6.6kW maximum power and MAG equipment of pulse mode. Parameter regarding heat input is one of the most important factors that directly affect penetration characteristics and welding defect. Therefore in this study, the effects of laser power, welding speed and current, voltage and pulse correction were investigated. As experiment result, it was found that the lower heat input, the more likely humping bead is formed at the back, and such humping bead could be suppressed by increasing laser power and arc current or decreasing welding speed, thus increasing heat input. Also deep penetration could be achieved by reducing arc voltage or pulse correction parameter in the same welding condition.

• Proceedings of the KSRS Conference
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• 1998.09a
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• pp.252-256
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• 1998

Accurate mapping of satellite images is one of the most important Parts in many remote sensing applications. Since the position and the attitude of a satellite during image acquisition cannot be determined accurately enough, it is normal to have several hundred meters' ground-mapping errors in the systematically corrected images. The users which require a pixel-level or a sub-pixel level mapping accuracy for high-resolution satellite images must use a number of Ground Control Points (GCPs). In this paper, the performance of two geometric correction algorithms is tested and compared. One is the polynomial warping algorithm which is simple and popular enough to be implemented in most of the commercial satellite image processing software. The other is full camera modelling algorithm using Physical orbit-sensor-Earth geometry which is used in satellite image data receiving, pre-processing and distribution stations. Several criteria were considered for the performance analysis : ultimate correction accuracy, GCP representatibility, number of GCPs required, convergence speed, sensitiveness to inaccurate GCPs, usefulness of the correction results. This paper focuses on the usefulness of the precision correction algorithm for regular image pre-processing operations. This means that not only final correction accuracy but also the number of GCPs and their spatial distribution required for an image correction are important factors. Both correction algorithms were implemented and will be used for the precision correction of KITSAT-3 images.

• Journal of the Korean Solar Energy Society
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• v.34 no.3
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• pp.98-106
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• 2014

The effect of blockage ratio on wind tunnel testing of small vertical-axis wind turbine has been investigated in this study. Height and rotor diameter of the three blades Darrieus vertical axis wind turbine used in present test were 0.4m and 0.35m respectively. We measured the wind speeds and power coefficient at three different wind tunnels where blockage ratio were 3.5%, 13.4% and 24.7% respectively. The test results show that the measured powers have been strongly influenced by blockage ratio, generally increased as the blockage ratio increases. The maximum power at higher blockage ratio has been obtained at relatively high tip speed ratio compared with that at low blockage ratio. The measured power coefficients under high blockage ratio can be improved from proper correction using the simple correction equation based on blockage factor. In present study, the correction error for power coefficient can be less than 5%, however correction effectiveness reveals relatively poor at high blockage ratio and low wind speed.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.82-92
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• 2011

This paper presents a PFC(Power Factor Correction) system to control the power factor of input current of the converter system which is working in the propulsion system of KTX high speed train. In the KTX train system, initially introduced from ALSTOM, the thyristor converter with phase controlling technique is adopted in the current fed type powering system. The input current induces harmonic losses highly because the waveform becomes rectangular shapes according to the filter inductor current increased as the train speed increasing gradually. Especially the interference with the signalling systems is severe concerned due to high current harmonics on the catenary line. To protect this problem, a frequency trap filter(notch filter) is operating with the input converter system. In this paper, an analysis work and PC simulation have been done on the PFC system to upgrade its performance and maintenance efficiency.