• Journal of the Korean Solar Energy Society
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• v.36 no.5
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• pp.73-89
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• 2016

To assure maximum economic benefits and the energy performance of solar water heating systems, the proper sizing of components and operating conditions need to be optimized. In recent years, a number of studies to design optimally solar water heating systems have been tried. This paper presents a design method for optimizing the various capacity-related and installation-related design variables based on life cycle cost using a genetic algorithm. The design variables considered in this study included the types and numbers of solar collector and auxiliary heaters; the types of storage tanks and heat exchangers; the solar collector slope; mass flow rates of the fluid on the hot and cold sides. The suggested method was applied for optimizing a solar water heating system for an elementary school in Seoul, South Korea. In addition, the effectiveness of the proposed optimization method was assessed by analyzing the obtained optimal solutions of six case studies, each of which was simulated with different solar fractions. It is observed that a trade-off between the equipment cost and the energy cost results in an optimal design that yields the lowest life cycle cost. Therefore, it could be helpful to apply the optimal solar water heating system by comparing the various design solutions obtained by using the optimization method instead of the engineer's experience and intuition.

• Journal of Drive and Control
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• v.13 no.3
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• pp.8-14
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• 2016

This study describes the effect of the critical pressure ratio of a control valve on the performance of an air spring system composed of an air spring, auxiliary chamber, control valve and mass in order to suggest a more efficient design for an air spring system. The critical pressure ratio of the control valve is assumed to have a fixed value, but the critical pressure ratio of the control valve is known to have various values between 0.05 and 0.6, and the effect of the variation of the critical pressure ratio on the performance of the air spring system has not yet been reported. The analysis derives nonlinear and linear governing equations of the air spring system, including the critical pressure ratio of the control valve. This simulation study is presented to show that the impedance and transmissibility characteristics of the air spring system change due to variations in the critical pressure ratio of the control valve as well as its sonic conductance. As a result, the critical pressure ratio of the control valve should be maintained as large as possible to improve the vibration isolation characteristics of the air spring system.

• Journal of Astronomy and Space Sciences
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• v.13 no.2
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• pp.105-116
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• 1996

This study is based upon the thermal modeling, analysis and operational results of KITSAT-1 and KITSAT-2 microsatellites launched on August 11, 1992 and Septermber 26, 1993, respectively. As KITSAT-1/2 was designed to be launched as an auxiliary payload of ARIANE launcher, the constraints on volume, power consumption, and mass were required to adopt passive thermal control method controlling absorptivity, emissivity, and conductivities among adjacent modules. The main of KITSAT was to take Earth images using CCD cameras positioned at the bottom of spacecraft, in which the cameras were always pointing to the center of Earth. This study is concerned with orbital analysis, thermal modeling, simulation results, and its verification by utilizing in-orbit telemetry data of KITSAT-2. The results of telemetry analysis show that the thermal modeling is matched to actual temperature data within 10 degrees of error range in average.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.6
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• pp.83-90
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• 2017

Performance analysis of the turboshaft engines for combined rotorcraft was executed. A tip jet and a ducted fan aircraft were selected for combined rotorcraft application. Gasturb 12 software was used for turboshaft engine performance analysis. In the results, maximum required power for the tip jet engine is about 1,600 hp class and maximum required power for the ducted fan engine is about 1,000 hp class at the required aircraft mission. This is due to the additional power of the auxiliary compressor to get a bleed air mass flow rate for the tip jet operation. At the same time, fuel consumption of the tip jet aircraft is 2.8 times larger than ducted fan case. Therefore ducted fan type aircraft is more efficient than tip jet aircraft in terms of fuel economy.

• Korean Journal of Remote Sensing
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• v.33 no.5_3
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• pp.855-866
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• 2017

Several research cases using remote sensing methods to analyze changes of storage and dynamics of groundwater aquifer were reviewed in this paper. The status of groundwater storage, in an area with regional scale, could be qualitatively inferred from geological feature, surface water altimetry and topography, distribution of vegetation, and difference between precipitation and evapotranspiration. These qualitative indicators could be measured by geological lineament analysis, airborne magnetic survey, DEM analysis, LAI and NDVI calculation, and surface energy balance modeling. It is certain that GRACE and InSAR have received remarkable attentions as direct utilization from satellite data for quantification of groundwater storage and dynamics. GRACE, composed of twin satellites having acceleration sensors, could detect global or regional microgravity changes and transform them into mass changes of water on surface and inside of the Earth. Numerous studies in terms of groundwater storage using GRACE sensor data were performed with several merits such that (1) there is no requirement of sensor data, (2) auxiliary data for quantification of groundwater can be entirely obtained from another satellite sensors, and (3) algorithms for processing measured data have continuously progressed from designated data management center. The limitations of GRACE for groundwater storage measurement could be defined as follows: (1) In an area with small scale, mass change quantification of groundwater might be inaccurate due to detection limit of the acceleration sensor, and (2) the results would be overestimated in case of combination between sensor and field survey data. InSAR can quantify the dynamic characteristics of aquifer by measuring vertical micro displacement, using linear proportional relation between groundwater head and vertical surface movement. However, InSAR data might now constrain their application to arid or semi-arid area whose land cover appear to be simple, and are hard to apply to the area with the anticipation of loss of coherence with surface. Development of GRACE and InSAR sensor data preprocessing algorithms optimized to topography, geology, and natural conditions of Korea should be prioritized to regionally quantify the mass change and dynamics of the groundwater resources of Korea.

• Herbal Formula Science
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• v.24 no.1
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• pp.17-30
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• 2016

Objectives Rehmanniae Radix Preparata was prepared in the traditional Rehmanniae Radix Preparata preparation method set forth in the 『Treasured Mirror of Eastern Medicine(Donguibogam)』 with a view to measuring the contents of 5-Hydroxymethyl-2-furaldehyde(5-HMF) at individual stages of steaming and sundrying and identifying new chemical components.Methods Based on the traditional Rehmanniae Radix Preparata preparation method set forth in the 『Treasured Mirror of Eastern Medicine』, Rehmanniae Radix Preparata steamed and sundried once through nine times was prepared. Thereafter, 5-HMF contents were analyzed and new chemical components were identified in the Rehmanniae Radix Preparata using Waters HPLC e2695, 2640 detectors, a Waters Acquity UPLC system, and a Micromass Q-TOF Premier mass spectrometer.Results The Rehmanniae Radix Preparata preparation method set forth in the 『Treasured Mirror of Eastern Medicine』 is a unique preparation method in Republic of Korea different from that in China. In the first stage of the method, fresh Rehmanniae Radix Crudus was divided into high quality, medium quality, and low quality ones named Rehmanniae Radix Crudus (Caelum)(天黃), Rehmanniae Radix Crudus (Homo)(人黃), and Rehmanniae Radix Crudus (Terra)(地黃) respectively to use Rehmanniae Radix Crudus (Caelum) and Rehmanniae Radix Crudus (Homo) for preparation of juice while using Rehmanniae Radix Crudus (Terra) to make Rehmanniae Radix Preparata. In the second stage, Rehmanniae Radix Crudus (Caelum) and Rehmanniae Radix Crudus (Terra) were made into juice and Rehmanniae Radix Crudus (Terra) was soaked in the juice. In the third stage, among auxiliary materials, rice wine named Purum Vinum Oryzae(淸酒) brewed from sticky rice was sprinkled on Rehmanniae Radix Crudus (Terra) to the extent that Rehmanniae Radix Crudus (Terra) became wet. In the fourth stage, Rehmanniae Radix Preparata steamed in earthenware steamer was dried under natural sunlight. The contents of 5-HMF in Rehmanniae Radix Preparata steamed and sundried once through nine times were shown to be below 0.1% in all cases. Pomolic acid was identified as a new chemical component.Conclusions In conclusion, the Rehmanniae Radix Preparata preparation method set forth in the 『Treasured Mirror of Eastern Medicine』 is thought to be a unique preparation method in South Korea in which Rehmanniae Radix Preparata is completed through the first stage in which fresh Rehmanniae Radix Crudus collected from fields is divided into high, medium, and low quality ones and fresh Rehmanniae Radix Crudus juice is made, the second stage in which the high quality fresh Rehmanniae Radix Crudus is soaked in the fresh Rehmanniae Radix Crudus juice, the third stage in which the fresh Rehmanniae Radix Crudus is steamed, and the fourth stage in which the steamed Rehmanniae Radix Crudus is dried.

• Journal of Korea Water Resources Association
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• v.50 no.3
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• pp.139-153
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• 2017

The variation in runoff due to global climate change and urbanization should be identified quantitatively because these two factors have been significantly accelerated during the last three decades in South Korea. However, only a few research to analyze the impacts due to two factors over different time scales can be found. Therefore, in this study, the hydrological model based approach and the hydrological sensitivity approach were used to separate relative impacts by two factors on monthly, seasonal, and annual time scales at the Soyang River upper basin and the Seom River basin in South Korea. The 3 techniques such as the double mass curve method, the Pettitt's test, and the BCP analysis were performed to detect change point occurred by abrupt change in the collected observed runoff. After detection of change ponts, SWAT models calibrated on the natural periods were used to calculate the changes due to human activities. Also, 6 Budyko based methods were auxiliary to verify the results from hydrological based approach.

• Journal of Korean Tunnelling and Underground Space Association
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• v.2 no.2
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• pp.11-21
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• 2000

Tunnelling has been created as a great extent in view of less land space available because the growth of population in metropolitan has been accelerated at a faster pace than the development of the cities. In tunnelling, it is often faced that measures are obliged to be taken without confirmation for such abnormality as diverged movement of surrounding rock mass, growing crack of shotcrete and yielding of rockbolts. In this case, it is usually said that the judgments of experienced engineers for the selection of measure are importance and allowed us to get over the situations in many construction sites. But decrease of such experienced engineers need us to develop the new system to assist the selection of measures for the abnormality without any experiences of similar tunnelling sites. In this study, After a lot of tunnelling reinforcement methods were surveyed and the detail application were studied, an expert system was developed to predict the safety of tunnel and choose proper tunnel reinforcement system using fuzzy quantification theory and fuzzy inference rule based on tunnel information database. The expert system developed in this study have two main parts named pre-module and post-module. Pre-module decides tunnel information imput items based on the tunnel face mapping information which can be easily obtained in-situ site. Then, using fuzzy quantification theory II, fuzzy membership function is composed and tunnel safety level is inferred through this membership function. The comparison result between the predicted reinforcement system level and measured ones was very similar. In-situ data were obtained in three tunnel sites including subway tunnel under Han river. This system will be very helpful to make the most of in-situ data and suggest proper applicability of tunnel reinforcement system developing more resonable tunnel support method from dependance of some experienced experts for the absent of guide.

• Journal of Internet Computing and Services
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• v.22 no.1
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• pp.109-135
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• 2021

his study classified the development process of artificial intelligence (AI) speakers through analysis of the news text of artificial intelligence (AI) speakers shown in traditional news reports, and identified the characteristics of each product by period. The theoretical background used in the analysis are news frames and topic frames. As analysis methods, topic modeling and semantic network analysis using the LDA method were used. The research method was a content analysis method. From 2014 to 2019, 2710 news related to AI speakers were first collected, and secondly, topic frames were analyzed using Nodexl algorithm. The result of this study is that, first, the trend of topic frames by AI speaker provider type was different according to the characteristics of the four operators (communication service provider, online platform, OS provider, and IT device manufacturer). Specifically, online platform operators (Google, Naver, Amazon, Kakao) appeared as a frame that uses AI speakers as'search or input devices'. On the other hand, telecommunications operators (SKT, KT) showed prominent frames for IPTV, which is the parent company's flagship business, and 'auxiliary device' of the telecommunication business. Furthermore, the frame of "personalization of products and voice service" was remarkable for OS operators (MS, Apple), and the frame for IT device manufacturers (Samsung) was "Internet of Things (IoT) Integrated Intelligence System". The econd, result id that the trend of the topic frame by AI speaker development period (by year) showed a tendency to develop around AI technology in the first phase (2014-2016), and in the second phase (2017-2018), the social relationship between AI technology and users It was related to interaction, and in the third phase (2019), there was a trend of shifting from AI technology-centered to user-centered. As a result of QAP analysis, it was found that news frames by business operator and development period in AI speaker development are socially constituted by determinants of media discourse. The implication of this study was that the evolution of AI speakers was found by the characteristics of the parent company and the process of co-evolution due to interactions between users by business operator and development period. The implications of this study are that the results of this study are important indicators for predicting the future prospects of AI speakers and presenting directions accordingly.