• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.2
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• pp.151-158
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• 2016

Tidal farm is a multi-arrayed turbine system for utilizing tidal stream energy. For horizontal-axis turbine(HAT) system, it is recommended that each unit has to be deployed far apart in order to avoid hydrodynamic interference among turbines, as proposed by the European Marine Energy Centre(EMEC). But there is no rule for the arrangement of vertical-axis turbine(VAT) yet. Moreover it has been reported that a proper arrangement of adjacent turbines can enhance the overall efficiency even greater than an arrangement without mutual interference effect. This paper suggests the layout of VATs showing the better performances, which turned out to be quite different from HATs' arrangement. Numerical calculations were performed to investigate the performance variation in terms of the rotational direction as well as the distance between turbines. It has been shown that the best combination of rotational direction and distance between turbines can increase its performance higher about 9.2% than that of two independently operated turbines. It is likely that such improvement is due to the increased velocity between adjacent turbines. For diagonally arranged turbines, the maximum normalized mean power coefficient was obtained to be higher about 5.6% than that of two independent turbines. It is expected that the present results can be utilized for conceptual design of tidal farm to harness the tidal stream energy.

• 한국해양학회지
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• v.30 no.4
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• pp.355-364
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• 1995

A heavy fluid is injected to a rotating cylindrical container of flat or inclined bottom filled with homogeneous lighter fluid. Continuous flow-in and spreading patterns over the bottom of the container are observed and at the same time upper-layer motions induced by the movement of the heavy fluid are traced by thymol blue solution. Regardless of bottom geometry, the injected denser fluid is deflected toward "western wall" and continuous its path along the boundary with radial spreading which occurs in the bottom boundary layer to make a quite asymmetric flow. When the bottom contains a slope(${\beta}$-plane), increased pressure gradient causes the fluid move faster to produce a stronger Coriolis force. This makes the width of the flow narrower than that of f-plane. But, when the denser flow reaches the southern part of the container, a local-depth of denser fluid increases (much greater than the Ekman-layer depth) such that the spreading velocity along the wall is reduced and the interfacial slope increases to make the upper-layer adjust geographically to have oppositely directed upper-layer motion along the interfacial boundary. The role of the denser fluid in terms of vorticity generation in the upper-layer is such that it produces local topographic effect over the western half of the container and also induces vortex-tube stretching which is especially dominant in the f-plane.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.207-218
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• 2013

This study is based on a series of numerical modeling experiments to understand the circulation and its change in the Chunsu Bay (CSB), Yellow Sea of Korea. A skill analysis was performed for the tidal height and tidal current of the observation data using the amplitude and phase of the 4 major tidal constituents respectively for verification of modeling experimental results. As a result, most of the skill score was seen to be over 90%, so numerical model experiment results can be said to be in good agreement with the observed tidal height and tidal current. Tidal wave proceeded from the entrance of the CSB towards inside, and the tidal range gradually increased to the north. It took about 10 to 30 minutes for the tidal wave to reach to northern end. The tidal wave showed a characteristic to rotate counter-clockwise in the southern part. The tidal current flowed to the north-south direction along the bottom topography; the angle of the major axis appeared alongside the isobath. It showed the characteristics of reversing tidal current with the minor axis less than 10% of the major axis. The strength of the tidal residual current that is influenced by geographical factors including bathymetry and coastline showed the range of 1~30 cm/sec, greater in the south channel and smaller in northern Bay. Two pairs of cyclonic/anti-cyclonic eddies around Jukdo and 3~4 pairs of strong eddies at the southern part of CSB in hundreds of m to a few km size by relative vorticity derived from the tidal residual current.

• Journal of The Geomorphological Association of Korea
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• v.18 no.2
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• pp.39-51
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• 2011

In this study, the shape of the Baramarae beach, Anmyeondo Area in West Coast of Korea and the changes in the sedimentation and erosion environment were analyzed in time series. As a result of the time series analysis of the shape of the Baramarae beach using aerial photographs from 1967 to 2009, the sand spit that developed in the southern part of Halmi Island was found to have had an EEN direction, but it was changed to a NNS direction, as reflected in the 2009 aerial photographs, as it gradually shifted to the west. In the onsite measurement, the H-3, H-4, H-5, and H-6 spots showed a superior sedimentation environment and the H-7, H-8, and H-9 spots showed a superior erosion environment. It was thus found that sedimentation is superior in the southwest beach and that erosion is superior in the northeast beach. The results in the spots between H-3 and H-6 indicate that the sand in the beach could not move to the northeast beach of Halmi Island due to the bank that had been established in the southwest beach of the island. On the other hand, it seems that superior erosion takes place in spots H-7 to H-9 in the northeast beach, where sand is not provided from the southwest beach of Halmi Island. It was found from the seasonal analysis that the season when superior sedimentation takes place in all the spots is autumn, and that the season when superior erosion takes place is summer. Superior sedimentation takes place in winter and spring in the southeast side and in summer in the northwest side.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.9
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• pp.24-33
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• 2017

Multitemporal MODIS vegetation index (VI) data are widely used in vegetation monitoring research into environmental and climate change, since they provide a profile of vegetation activity. However, MODIS data inevitably contain disturbances caused by the presence of clouds, atmospheric variability, and instrument problems, which impede the analysis of the NDVI time series data and limit its application utility. For this reason, preprocessing to reduce the noise and reconstruct high-quality temporal data streams is required for VI analysis. In this study, a data reconstruction method for MODIS NDVI is proposed to restore bad or missing data based on the statistical properties of the oscillations in the NDVI temporal dynamics. The first derivatives enable us to examine the monotonic properties of a function in the data stream and to detect anomalous changes, such as sudden spikes and drops. In this approach, only noisy data are corrected, while the other data are left intact to preserve the detailed temporal dynamics for further VI analysis. The proposed method was successfully tested and evaluated with simulated data and NDVI time series data covering Baekdu Mountain, located in the northern part of North Korea, over the period of interest from 2006 to 2012. The results show that it can be effectively employed as a preprocessing method for data reconstruction in MODIS NDVI analysis.

• The KIPS Transactions:PartB
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• v.14B no.7
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• pp.531-540
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• 2007

In this research, we proposed a two-phase hybrid stock price forecasting model with cointegration tests and artificial neural networks. Using not only the related stocks to the target stock but also the past information as input features in neural networks, the new model showed an improved performance in forecasting than that of the usual neural networks. Firstly in order to extract stocks which have long run relationships with the target stock, we made use of Johansen's cointegration test. In stock market, some stocks are apt to vary similarly and these phenomenon can be very informative to forecast the target stock. Johansen's cointegration test provides whether variables are related and whether the relationship is statistically significant. Secondly, we learned the model which includes lagged variables of the target and related stocks in addition to other characteristics of them. Although former research usually did not incorporate those variables, it is well known that most economic time series data are depend on its past value. Also, it is common in econometric literatures to consider lagged values as dependent variables. We implemented a price direction forecasting system for KOSPI index to examine the performance of the proposed model. As the result, our model had 11.29% higher forecasting accuracy on average than the model learned without cointegration test and also showed 10.59% higher on average than the model which randomly selected stocks to make the size of the feature set same as that of the proposed model.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.5
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• pp.505-511
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• 2023

In the present study, a deep learning model was established to predict the motion response of small fishing vessels. Hydrodynamic performances were evaluated for two small fishing vessels for the dataset of deep learning model. The deep learning model of the Long Short-Term Memory (LSTM) which is one of the recurrent neural network was utilized. The input data of LSTM model consisted of time series of six(6) degrees of freedom motions and wave height and the output label was selected as the time series data of six(6) degrees of freedom motions. The hyperparameter and input window length studies were performed to optimize LSTM model. The time series motion response according to different wave direction was predicted by establised LSTM. The predicted time series motion response showed good overall agreement with the analysis results. As the length of the time series increased, differences between the predicted values and analysis results were increased, which is due to the reduced influence of long-term data in the training process. The overall error of the predicted data indicated that more than 85% of the data showed an error within 10%. The established LSTM model is expected to be utilized in monitoring and alarm systems for small fishing vessels.

• The korean journal of orthodontics
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• v.29 no.1 s.72
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• pp.113-127
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• 1999

The purpose of this study is to investigate the stability of counterclockwise rotation of mandible by sagittal split ramus osteotomy to correct the skeletal Class III malocclusion with anterior open bite. Twenty five skeletal Class III open bite patients(mean age 20.6 years) who were treated by the sagittal split ramus osteotonues with rigid fixation were examined in this study. Cephalometric radiographs were taken for each Patients Preoperative(T1), ewly Postoperative(T2), and late postoperative Period(T3). Mean postoperative period was 8.0 months. Cephalometric analysis was done and data from T1, T2, and T3 were analyzed statistically by Paired t-test and Pearson correlation analysis. The following results were obtained. 1. Mandibular plane angle decreased $2.9^{\circ}$ and mandibular occlusal plane angle related to SN Plane decreased $2.7^{\circ}$ after orthognathic surgery(T2). At 6 months after orthognathic surgery(T3), mandibular plane angle increased $1.0^{\circ}$, but mandibular occlusal plane angle did not changed. 2. The amount of horizontal relapse long time after orthognathic surgery(T3) was 1.6 mm at B point and it was $22\%$ of the total posterior movements. There was no vertical relapse in the anterior facial height. 3. The related factor with horizontal relapse at late postoperative period was mandibular plane angle(p<0.01). The related factors with decreasing posterior facial height were amount of mandibular setback(p<0.01), increasing of mandibular ramus height(p<0.01), and decrease of the mandibular plane angle during operation(p<0.01). 4. There was no relationship between the amount of changes in mandibular occlusal plan angle during operation and the amount of relapse after surgery.

• Proceedings of the KAIS Fall Conference
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• 2010.11b
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• pp.807-809
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• 2010

글로벌 금융위기를 거치면서 각국의 증시가 같은 방향으로 움직이는 동조화 현상이 뚜렷이 나타나고 있다. 주가 동조화 현상은 주로 시계열 분석 기법을 적용하여 연구가 이루어져 왔는데, 본 연구에서는 네트워크 분석 기법을 적용하고자 한다. 시가 총액이 큰 주요 국가들의 대표적 주가 지수들을 대상으로 상관계수를 구하고, 이러한 상관계수를 가중치로 설정하여 구성한 네트워크를 분석한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2000.10a
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• pp.75-78
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• 2000

정보의 양이 많아지면서 대용량의 자료에서 필요한 자료를 찾는 일의 중요성이 날로 증대되고 있다. 본 논문에서는 100만건 이상의 손익 자료에서 시계열성 매출액, 사원별 매출액 등과 같은 정보의 조회시 조회 속도를 향상시키기 위한 여러 방법들을 고려하여 손익 평가 시스템을 구축하고 앞으로의 발전방향을 알아본다.