• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.330-339
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• 2008

Ground-based interceptors(GBI) comprise a major element of the strategic defense against hostile targets like Intercontinental Ballistic Missiles(ICBM) and reentry vehicles(RV) dispersed from them. An optimum design of the subsystems is required to increase the performance and reliability of these GBI. Propulsion subsystem design and optimization is the motivation for this effort. This paper describes an effort in which an entire GBI missile system, including a multi-stage solid rocket booster, is considered simultaneously in a Genetic Algorithm(GA) performance optimization process. Single goal, constrained optimization is performed. For specified payload and miss distance, time of flight, the most important component in the optimization process is the booster, for its takeoff weight, time of flight, or a combination of the two. The GBI is assumed to be a multistage missile that uses target location data provided by two ground based RF radar sensors and two low earth orbit(LEO) IR sensors. 3Dimensional model is developed for a multistage target with a boost phase acceleration profile that depends on total mass, propellant mass and the specific impulse in the gravity field. The monostatic radar cross section (RCS) data of a three stage ICBM is used. For preliminary design, GBI is assumed to have a fixed initial position from the target launch point and zero launch delay. GBI carries the Kill Vehicle(KV) to an optimal position in space to allow it to complete the intercept. The objective is to design and optimize the propulsion system for the GBI that will fulfill mission requirements and objectives. The KV weight and volume requirements are specified in the problem definition before the optimization is computed. We have considered only continuous design variables, while considering discrete variables as input. Though the number of stages should also be one of the design variables, however, in this paper it is fixed as three. The elite solution from GA is passed on to(Sequential Quadratic Programming) SQP as near optimal guess. The SQP then performs local convergence to identify the minimum mass of the GBI. The performance of the three staged GBI is validated using a ballistic missile intercept scenario modeled in Matlab/SIMULINK.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.7
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• pp.508-516
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• 2019

In this paper, we propose a guidance law to control Impact Angle in consideration of look angle limit of the missile with strapdown seeker on the non-maneuvering target. The proposed law is based on sliding mode algorithm and generates acceleration commands using look angle and line of sight information provided by the strapdown seeker and navigation system. And, target velocity and target path angle are provided by like TADS (Target Acquisition and Designation System) at launch time. We can confirm that the target interception and impact angle control are possible through the convergence of the proposed sliding surface. In addition, it is possible to confirm that the sign of derivative result of the look angle at the maximum and minimum look angle is opposite to the sign of the look angle, so the look angle limit is not exceeded.

• International journal of advanced smart convergence
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• v.8 no.3
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• pp.184-192
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• 2019

The existing digital signage systems inside the elevators are a lack of tailored contents appropriate to the space and environment inside or outside the elevators. Also, they almost impossible to flexibly respond to various contents disclosure according to the demand of the consumers or the elevator markets. Therefore we design and implement an IoT(Internet of Things)-based smart digital signage system for the safety of elevator passengers.. In order to provide IoT-based information to the smart digital signage within the elevator, we propose an IoT system as a set-top box with gyroscope sensor, acceleration sensor, RFID(Radio-Frequency Identification), fine dust sensor, etc., which processes various data collected by the sensors and provides the elevator passengers with various tailored contents such as elevator driving information, environmental information inside and outside the elevator, and disaster information in addition to simple advertisement information. The proposed IoT system is a set-top box that operates the smart digital signage and has an independent information control processor based on the IoT sensors that do not depend on the elevator control system. For the proposed smart digital signage, it supports an operating system that is independent of the elevator driving service as well as the media service. So the smart signage system has a characteristic that it does not depend on the elevator control system since it is a stand-along IoT-based information control system. With the proposed system providing intuitive content for the surge, steep descent, and radical movements of an elevator due to an emergency situation, the elevator passengers should be able to recognize the situation quickly and respond accordingly. In the near future, the proposed system will expand the market of digital signage applied in conjunction with the development of contents in the disaster, safety and environment fields, and expect expected to revitalize related industries associated with signage.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.6
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• pp.261-266
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• 2021

Nuclear power plants in Korea were designed and evaluated based on the NRC's Regulatory Guide 1.60, a design response spectrum for nuclear power plants. However, it can be seen that the seismic motion characteristics are different when analyzing the Gyeongju earthquake and the Pohang earthquake that has recently occurred in Korea. Compared to the design response spectrum, seismic motion characteristics in Korea have a larger spectral acceleration in the high-frequency region. Therefore, in the case of equipment with a high natural frequency installed in a nuclear power plant, seismic performance may be reduced by reflecting the characteristics of domestic seismic motions. The failure modes of the equipment are typically structural failure and functional failure, with an anchorage failure being a representative type of structural failure. In this study, comparative analyses were performed to decide whether to consider the inelastic behavior of the anchorage or not. As a result, it was confirmed that the seismic performance of the anchorages could be increased by considering the inelastic behavior of an anchorage.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.2
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• pp.107-118
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• 2021

Due to the acceleration of road construction, the number and extension of tunnels are increasing every year. A lot of research has been done on the collapse of tunnels, but research on the invert heaving is insufficient. Therefore, in this study, a sensitivity analysis was performed using a geotechnical general-purpose program to analyze the effect of the invert curvature of a tunnel excavated on the soft ground. As a result, it was quantitatively confirmed that the stability of a tunnel was increased as the curvature of the tunnel invert was increased so that the safety factor was calculated to be large regardless of the ground conditions and the thickness of the support. In addition, it was confirmed that the stability of the tunnel was increased by reducing the convergence of the tunnel and the maximum bending stress supported by shotcrete. Therefore, when a tunnel is excavated on soft ground, it is believed that applying a curvature to the invert will increase the stability of the tunnel.

• The Journal of the Convergence on Culture Technology
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• v.8 no.1
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• pp.209-218
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• 2022

To study hotels related to early modern cultural heritage, this study has, first, attempted a historical approach through literature analysis and established an early modern hotel development history. Second, it has strived to suggest tourism industrial utilization measures by studying tourism industrial utilization cases through materials on the restoration of Daebul Hotel and interviews with related parties. Consequently, the researcher offers the following as tourism industrial revitalization measures for the restoration of early modern hotels. First, restoration plans for early modern hotels from early modern heritage in each region should be made on the basis of thorough examination of justifiability and of content development plans. Second, restoration of early modern hotels in each region requires the establishment and intent of an administrative management system by local governments. Third, restoration of early modern hotels is a thing of historical significance and value and should be promoted as a business that can contribute to revitalization of tourism and economic effects, acceleration of employment, etc., in each region. Fourth, preparation of a consistent, proactive advertisement methods regarding the restoration of early modern hotels is necessary.

• Nuclear Engineering and Technology
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• v.54 no.9
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• pp.3361-3379
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• 2022

A nuclear power plant (NPP) piping is designed against low-frequency earthquakes. However, earthquakes that can occur at NPP sites in the eastern part of the United States, northern Europe, and Korea are high-frequency earthquakes. Therefore, this study conducts bi-directional shaking table tests on actual-scale NPP piping and studies the response characteristics of low- and high-frequency earthquake motions. Such response characteristics are analyzed by comparing several responses that occur in the piping. Also, based on the test results, a piping numerical analysis model is developed and validated. The piping seismic performance under high-frequency earthquakes is derived. Consequently, the high-frequency excitation caused a large amplification in the measured peak acceleration responses compared to the low-frequency excitation. Conversely, concerning relative displacements, strains, and normal stresses, low-frequency excitation responses were larger than high-frequency excitation responses. Main peak relative displacements and peak normal stresses were 60%-69% and 24%-49% smaller in the high-frequency earthquake response than the low-frequency earthquake response. This phenomenon was noticeable when the earthquake motion intensity was large. The piping numerical model simulated the main natural frequencies and relative displacement responses well. Finally, for the stress limit state, the seismic performance for high-frequency earthquakes was about 2.7 times greater than for low-frequency earthquakes.

• International journal of advanced smart convergence
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• v.11 no.3
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• pp.222-228
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• 2022

As a means to cope with the climate change crisis caused by global warming, automobile manufacturers continue to make efforts to use the driving energy of vehicles as electricity. As a result, parts industry such as battery, motor, and controller are attracting attention. China is often seen in large cities, with electric vehicles such as electric bicycles, electric motorcycles, and small electric vehicles popularized and commercialized, mainly in large cities. However, small electric vehicles are not popular in Korea, which is why the country's topography is high in hills. In order to drive the hilly domestic roads, power performance including vehicle climbing ability should be improved. In order to improve the power performance and the climbing capacity of small electric vehicles, the capacity of the motor should be increased. However, when the performance of the motor is improved, the weight of the motor becomes heavy and the price competitiveness is likely to decrease. In addition, in order to operate a high-performance motor, the power consumption of the battery is rapidly increased, so various problems must be solved. In order to commercialize a small electric vehicle for one or two people who do not emit harmful exhaust gas to the human body in a hilly domestic terrain, it is effective to have a separate transmission system. In this study, we were conducted dynamometer test to produce a continuously variable transmission(CVT) system prototype using a spring that can be applied to a small electric vehicle and to install a CVT system prototype manufactured in a small electric vehicle. The dynamometer test results showed that the maximum speed performance, acceleration performance, and climbing performance were improved.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.11
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• pp.1649-1654
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• 2021

In this paper, we introduce a regularization of long short-term memory (LSTM) based fall detection system using TensorFlow that can detect falls that can occur in the elderly. Fall detection uses data from a 3-axis acceleration sensor attached to the body of an elderly person and learns about a total of 7 behavior patterns, each of which is a pattern that occurs in daily life, and the remaining 3 are patterns for falls. During training, a normalization process is performed to effectively reduce the loss function, and the normalization performs a maximum-minimum normalization for data and a L2 regularization for the loss function. The optimal regularization conditions of LSTM using several falling parameters obtained from the 3-axis accelerometer is explained. When normalization and regularization rate λ for sum vector magnitude (SVM) are 127 and 0.00015, respectively, the best sensitivity, specificity, and accuracy are 98.4, 94.8, and 96.9%, respectively.

• The Journal of the Convergence on Culture Technology
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• v.8 no.3
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• pp.589-594
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• 2022

In an acceleration of 'untact' society during the COVID-19 pandemic, video conferencing platforms have been provided to connect the isolated and to overcome the limit of having interpersonal relationships. While these services brought a great deal of benefits, they also increased the number of people who suffer from additional fatigue from video conferencing. This study, thus, aimed to identify the factors of using video conferencing services and further to examine the relationship between the factors and the users' overall fatigue. Through focus-group interviews and survey, four main factors of fatigue (restriction from untact communication, difficulty of use, background set-ups, discomfort from excessive attention) were identified. This study also found the positive relationships of restriction from untact communication and background set-ups on the users' overall fatigue. The results does not only provide implication on defining new fatigue factors from young generations but also help practitioners and service providers to improve the deficits of services that the real users currently experience.