Underwater 3-D Spatial Attenuation Characteristics of Electromagnetic Waves With Omnidirectional Antenna

Kyungmin Kwak,Daegil Park,Wan Kyun Chung,Jinhyun Kim IEEE 2016 IEEE/ASME transactions on mechatronics Vol.21 No.3

<P>In this paper, an underwater 3-D spatial attenuation model of electromagnetic waves is proposed to establish a position recognition system in underwater 3-D space using distance estimation. The distance estimation is based on signal attenuation characteristics of electromagnetic waves radiated through several omnidirectional antennas. Positions in underwater environments have been predominantly estimated by an ultrasonic position recognition system using travel time and phase difference. However, such a system provides inaccurate estimation on account of the multipath effect in a structured environment or complex environment with many obstacles. A position estimation method that uses signal attenuation of electromagnetic waves has been proposed to overcome this limitation. That method can precisely estimate position on a structured 2-D plane. In this paper, an existing underwater position estimation system based on electromagnetic waves is expanded into 3-D space using the Friis formula and plane wave equation, thereby classifying attenuation characteristics of electromagnetic waves into the effects of medium, radiation, and antenna. These effects are summarized to deduce the signal attenuation characteristics of electromagnetic waves in 3-D space. In addition, the relative position (R, Theta, Phi) and attitude (phi, theta, psi) of transceiver antennas are used to define a coordinate system for 3-D estimation; moreover, an attenuation model is defined for individual factors in the coordinate system. A generalized attenuation model of an omnidirectional antenna in 3-D space is presented, and the validity of the proposed model is demonstrated through experiments. Based on the results, the proposed model demonstrates the potential application to an omnidirectional antenna and expansion into an attenuation model based on the 3-D position between random antennas.</P>

Prediction of Nucleate Pool Boiling Heat Transfer Coefficients of Ternary Refrigerant R407C

Kyungmin Kwak,Cheolho Bai,Mo Chung 대한설비공학회 1998 International Journal of Air-Conditioning and Refr Vol.6 No.-

The nucleate boiling heat transfer experiments are performed using a ternary refrigerant R407C which is a candidate of alternatives of HCFC 22. The boiling phenomena of R-32, R-l25 and R-l34a which are the constituent refrigerants of R407C are also investigated. The nucleate boiling heat transfer coefficients of R407C are less than those of HCFC 22 which have the similar physical and transport properties. In our experimental pressure range, which is similar to the operational pressure of air conditioning system, the deterioration of boiling heat transfer coefficients of mixture refrigerant R407C does not appear for moderate wall superheat region. Since nucleate boiling heat transfer coefficients cannot be obtained from ideal mixing law of mixture, Thome's method was used to predict. To account for the heat flux effect and system pressure in Thome's method, the correcting factor, α(P, ΔT), was introduced and obtained from experiments for ternary refrigerant R407C.

전자기파의 감쇠패턴 및 깊이 정보 취득을 이용한 수중 위치추정 기법

곽경민(Kyungmin Kwak),박대길(Daegil Park),정완균(Wan Kyun Chung),김진현(Jinhyun Kim) 한국로봇학회(논문지) 2016 로봇학회 논문지 Vol.11 No.3

전자기파의 방사패턴을 이용한 수중 3 차원 위치추정 기법 연구

곽경민(Kyungmin Kwak),박대길(Deagil Park),김진현(Jinhyun Kim) 한국소음진동공학회 2017 한국소음진동공학회 학술대회논문집 Vol.2017 No.4

임상간호사의 직무착근도와 이직의도의 관계

곽경민(Kyungmin Kwak),문미경(Mikyung Moon) 한국문화융합학회 2023 문화와 융합 Vol.45 No.12

본 연구는 임상간호사의 직무착근도, 직장생활의 질과 이직의도의 정도를 파악하고, 직무착근도와 이직의도의 관계에서 간호사 직장생활의 질의 매개효과를 확인하기 위한 서술적 조사연구이다. 연구방법은D시 소재의 100병상 이상의 6개의 종합병원에 1년 이상 근무하고 있는 161명의 간호사를 대상으로 설문조사하였다. 수집된 자료는 SPSS 21.0을 이용하여 t-test, ANOVA, Pearson correlation coefficient, mulitple regression으로 분석하였다. Baron & Kenny(1986)의 절차에 의한 매개효과 증명과 더불어Sobel Test를 실시하였다. 연구결과 직무착근도는 직장생활의 질에 유의한 정적인 영향을, 이직의도에는 부적인 영향을 미치는 것으로 나타났고, 직장생활의 질은 이직의도에 부적인 영향을 미치는 것으로나타났다. 최종적으로 직장생활의 질은 직무착근도와 이직의도 간의 관계에서 부분매개 하는 것으로 나타났다. 이러한 연구 결과를 바탕으로 임상간호사의 이직의도를 낮추기 위한 전략으로 직무착근도 뿐아니라 직장생활의 질을 함께 향상시키는 프로그램을 개발하여 적용할 필요가 있겠다. The purpose of this study was to investigate the mediating effect of quality of nursing work life on the relationship between job embeddedness and turnover intention in hospital nurses. The subjects were 161 nurses who had one or more years of working experiences in hospitals in D city in Korea. The collected data were analyzed using descriptive statistics, Pearsons'correlation coefficient, and a hierarchical multiple regression analysis as suggested by Baron and Kenny(1986). The significance of medication effect was verified by Sobel test. Turnover intention had a significant negative correlation with job embeddedness and quality of nursing work life. The results of this study indicate that quality of nursing work life has a partial mediating effect on the relationship between job embeddedness and turnover intention in hospital nurses. To reduce nurses’ turnover, nursing organizations should focus on enhancing quality of nursing work life as well as job embeddedness.

자동차용 응축기의 휜 열전달 및 압력강하 특성

곽경민(Kyungmin Kwak),이홍열(Hongyeol Lee) 한국자동차공학회 2004 한국 자동차공학회논문집 Vol.12 No.3

반전력빔폭을 이용한 전방향성 안테나의 수중 환경 수직 평면 감쇠 모델

곽경민(Kyungmin Kwak),박대길(Daegil Park),김영현(Younghyeon Kim),정완균(Wan Kyun Chung),김진현(Jinhyun Kim) 제어로봇시스템학회 2015 제어·로봇·시스템학회 논문지 Vol.21 No.11

In this paper, we use the characteristics of electromagnetic waves underwater attenuation for estimating linear distance between a transmitting node and receiving node, and research underwater vertical plane attenuation model for constructing the underwater localization system. The underwater localization of 2 dimensional with the plane attenuation model in the horizontal plane (H-plane) was proposed previous research. But for the 3 dimensional underwater localization, the additional vertical plane (Eplane) model should be considered. Because the horizontal plane of omnidirectional antenna has the same attenuation tendency in x-y plane according to the distance, whereas in vertical plane shows an irregular pattern in x-z plane. For that reason, in the vertical plane environment, the attenuation should be changed by the position and inclination. Hence, in this paper the distance and angle between transmitting and receiving node are defined using spherical coordinate system and derive an antenna gain pattern using half power beam width (HPBW). The HPBW is called a term which defines antenna’s performance between isotropic and other antennas. This paper derives omnidirectional antenna’s maximum gain and attenuation pattern model and define vertical plane’s gain pattern model using HPBW. Finally, experimental verifications for the proposed underwater vertical plane’s attenuation model was executed.

UUV의 수중 도킹을 위한 전자기파 신호 기반의 위치인식 센서 개발

곽경민 ( Kyungmin Kwak ),박대길 ( Daegil Park ),정완균 ( Wan Kyun Chung ),김진현 ( Jinhyun Kim ) 한국센서학회 2017 센서학회지 Vol.26 No.3

In this paper, we developed an underwater localization system for underwater robot docking using the electromagnetic wave attenuation model. Electromagnetic waves are generally known to be impossible to use in water environment. However, according to the conclusions of the previous studies on the attenuation characteristics in underwater, the attenuation pattern is uniform and its model was accurately proposed and verified in 3-dimensional space via the omnidirectional antenna. In this paper, a docking structure and localization sensor system are developed for a widely used cone type docking mechanism. First, we fabricated electromagnetic wave range sensor transmit modules. And a mobile sensor node is equipped with unmanned underwater vehicle(UUV)s. The mobile node senses the four different signal strength (RSS: Received Signal Strength) from fixed nodes, and the obtained RSS data are transformed to each distance information using the 3-Dimensional EM wave attenuation model. Then, the relative localization between the docking area and underwater robot can be achieved according to optimization algorithm. Finally, experimental results show the feasibility of the proposed localization system for the docking induction by comparing the errors in the actual position of the mobile node and the theoretical position through the model.

Subcooling Bypass Technology를 적용한 압축기 토출 냉매 온도 감소에 관한 연구

곽경민(Kyungmin Kwak),배철호(Cheolho Bai) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.6

The purpose of the study is to decrease the refrigerant temperature at the outlet of the compressor under high thermal load conditions for air cooled vapor compression refrigeration system. The subcooling bypass line called subcooling bypass technology(SBT) is installed to the window type A/C system to investigate the performance test. The standard air calorimeter test method is applied to measure the refrigerant temperature at the outlet of the compressor, cooling capacity, power consumption, and system EER. The refrigerant temperature at the outlet of the compressor decreases as the bypass rate increases. When the bypass rate is 8.2%, the refrigerant temperature at the outlet of the compressor decreases 2.8 ℃ while the cooling capacity and EER are the same as the conventional A/C unit.

저 레이놀즈 수 영역에서 휜ㆍ관 열교환기의 성능특성 연구

곽경민(Kyungmin Kwak) 한국자동차공학회 2005 한국자동차공학회 지부 학술대회 논문집 Vol.- No.-

The present paper reports the method for evaluation of heat-transfer performance of fin-tube heat exchangers to be operated in a low Reynolds number regime (typically, Re=lOO-500) and also reports the data of heat transfer and pressure loss taken from a fin-tube heat exchanger with/without vortex generators(VGs) installed as a heat-transfer enhancement device. The evaluation is based on the modified single blow method conducted in a specially designed low Reynolds number duct. Three different test core geometries, i.e., fin only, fin-tube without VGs and that with VGs, are studied here. The data of heat transfer and pressure loss taken from the fin only geometry agree well with the empirical correlations, thus validating the present method as used for low Reynolds number regime. The data taken from the fin-tube geometries with and without VGs are presented and compared to examine the effect of VGs in the low Reynolds number regime.