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VHF DSC 기반 Position Request Calling 분석
김병옥(Byungok Kim) 한국항해항만학회 2020 한국항해항만학회 학술대회논문집 Vol.2020 No.춘계
세계해상조난안전시스템(GMDSS)의 제도에 따라 호출응답 및 조난경보 전송 등에 활용하기 위한 VHF DSC(디지털선택호출) 장치가 도입되어 2톤 이상의 선박에 의무적으로 설치되어 있다. 우리나라에서는 VHF DSC를 연근해 어선들의 위치정보 수집을 위하여 위치정보요구호출(Position Request Calling) 기능에 주로 활용하고 있다. 그러나 VHF DSC를 설치한 선박이 증가함에 따라 해안국의 DSC를 사용한 호출도 급증하고 있으며, 이러한 결과로 인하여 조난경보 등 중요한 호출의 전송을 지연시키거나 호출신호 상호간의 혼신을 야기할 가능성이 높아지고 있다. 본 논문에서는 부산지역에서 수신된 VHF DSC 데이터를 기반으로 Position Request Calling의 현황과 문제점을 분석하고 개선방안을 제시하였다. The VHF DSC devices are introduced according to the GMDSS(Global Maritime Distress and Safety System) for use in the distress alert transmission as well as calling and acknowledgement, and are installed on all the vessels above 2 gross tons. In Korea, the VHF DSC is mainly used for the position request calling function in order to receive position information from fishing boats sailing near coastal sea area. According to the increasing number of fishing boats installed VHF DSC devices, the number of position request calling by coast radion stations are also increased rapidly. This result in a high possibility of transmission delay of important calling such as distress alerts or high possibility of interference among calling signals. Based on the received VHF DSC data in Busan area, this paper analyzed the status and problem of position request calling and proposed improvement measures.
초임계 CO<sub>2</sub> 발전용 파워터빈을 지지하는 틸팅패드 베어링의 열윤활 해석 및 패드 온도 측정
이동현,김병옥,임형수,Lee, Donghyun,Kim, Byungok,Lim, Hyungsoo 한국트라이볼로지학회 2018 한국윤활학회지(윤활학회지) Vol.34 No.2
This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical $CO_2$ cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around $55^{\circ}C$ which is approximately $15^{\circ}C$ higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.
초임계 CO<sub>2</sub> 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험
이동현,김병옥,선경호,임형수,Lee, Donghyun,Kim, Byungok,Sun, Kyungho,Lim, Hyungsoo 한국트라이볼로지학회 2017 한국윤활학회지(윤활학회지) Vol.33 No.1
This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical $CO_2$ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of $250^{\circ}C$ in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of $40^{\circ}C$ between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.
250 kW급 초임계 CO₂ 발전용 감속기의 유체 윤활 베어링 및 회전체 동역학 특성 해석
이동현(Donghyun Lee),김병옥(Byungok Kim) 한국트라이볼로지학회 2016 한국윤활학회지(윤활학회지) Vol.32 No.4
This paper presents a rotordynamic analysis of the reduction gear system applied to the 250 kW super critical CO₂ cycle. The reduction gear system consists of an input shaft, intermediate shaft, and output shaft. Because of the high rotating speed of the input shaft, we install tilting pad bearings, rolloer bearings support the intermediate and output shafts. To predict the tilting pad bearing performance, we calculate the applied loads to the tilting pad bearings by considering the reaction forces from the gear. In the rotordynamic analysis, gear mesh stiffness results in a coupling effect between the lateral and torsional vibrations. The predicted Campbell diagram shows that there is not a critical speed lower than the rated speed of 30,000 rpm of the input shaft. The predicted modes on the critical speeds are the combined bending modes of the intermediate and output shaft, and the lateral vibrations dominate when compared to the torsional vibrations. The damped natural frequency does not strongly depend on the rotating speeds, owing to the relatively low rotating speed of the intermediate and output shaft and constant stiffness of the roller bearing. In addition, the logarithmic decrements of all the modes are positive; therefore all modes are stable.
이동현(Donghyun Lee),김병옥(Byungok Kim),선경호(Kyungho Sun) 한국트라이볼로지학회 2018 한국윤활학회지(윤활학회지) Vol.34 No.5
A multi-stage compressor (MSC) is comprised of several impellers installed in the pinion gear shaft driven by a main bull gear. In the pinion shaft, a thrust collar (TC) is installed to support the thrust load. The TC makes the lubrication system simpler in the MSC; therefore, it is widely used in similar kinds of machinery. Typically, TCs are installed on both sides of the bull gear and pressure is developed in the lubricated area by creating a taper angle on the TC and bull gear surface. In the current study, we developed a numerical analysis model to evaluate the performance of the TC considering its design parameters. We sloved the Reynolds equation using the finite element method and applied the half Sommerfeld condition to consider cavitation. Based on the pressure calculated in the lubricated area, we calculated the power loss and minimum film thickness. In addition, we calculated stiffness and damping using perturbation method. We performed parametric studies using the developed model. The results of the analysis show that the maximum pressure presents in the center area of the TC and it increases with the taper angle. The area over which pressure is developed decreases with the taper angle. The results also show that there is an optimum taper angle providing minimum power loss and maximum film thickness. Additionally, the stiffness and damping decrease with the taper angle. As the applied load increases, the power loss increases and the minimum film thickness decreases. However, the stiffness and damping increase with the applied load.
초임계 CO₂ 발전용 파워 터빈의 회전체 동역학 해석 및 구동 시험
이동현(Donghyun Lee),김병옥(Byungok Kim),선경호(Kyungho Sun),임형수(Hyungsoo Lim) 한국트라이볼로지학회 2017 한국윤활학회지(윤활학회지) Vol.33 No.1
This paper presents a rotordynamic analysis and the operation of a power turbine applied to a 250 kW super-critical CO₂ cycle. The power turbine consists of a turbine wheel and a shaft supported by two fluid film bearings. We use a tilting pad bearing for the power turbine owing to the high speed operation, and employ copper backing pads to improve the thermal management of the bearing. We conduct a rotordynamic analysis based on the design parameters of the power turbine. The dynamic coefficients of the tilting pad bearings were calculated based on the iso-thermal lubrication theory and turbine wheel was modeled as equivalent inertia. The predicted Cambell diagram showed that there are two critical speeds, namely the conical and bending critical speeds under the rated speed. However, the unbalance response prediction showed that vibration levels are controlled within 10 mm for all speed ranges owing to the high damping ratio of the modes. Additionally, the predicted logarithmic decrement indicates that there is no unstable mode. The power turbine uses compressed air at a temperature of 250°C in its operation, and we monitor the shaft vibration and temperature of the lubricant during the test. In the steady state, we record a temperature rise of 40°C between the inlet and outlet lubricant and the measured shaft vibration shows good agreement with the prediction.
초임계 CO₂ 발전용 파워터빈을 지지하는 틸팅패드 베어링의 열윤활 해석 및 패드 온도 측정
이동현(Donghyun Lee),김병옥(Byungok Kim),임형수(Hyungsoo Lim) 한국트라이볼로지학회 2018 한국윤활학회지(윤활학회지) Vol.34 No.2
This paper presents the thermohydrodynamic analysis of tilting journal pad bearings supporting a power turbine rotor applied to a 250 kW super-critical CO₂ cycle. In the analysis, the generalized Reynolds equation and 3D energy equation are solved to predict oil film temperature and the 3D heat conduction equation is solved for pad temperature. The power turbine rotor is supported by two tilting pad bearings consisting of five pads with an oil supply block between the pads. Copper backing pads with higher thermal conductivity compared to steel backing pads are adopted to improve thermal management. The predicted maximum pad temperature is around 55 °C which is approximately 15 °C higher than oil supply temperature. In addition, the predicted minimum film thickness is 50 mm at a rotating speed of 5,000 rpm. These results indicate that there is no issue in the thermal behavior of the bearing. An operation test is performed with a power turbine module consisting of a power turbine, a reduction gear and a generator. Thermocouples are installed at the 75% position from the leading edge of the pad to monitor pad temperature. The power turbine uses compressed air at a temperature of 250 °C in its operation. The steady state pad temperatures measured in the test show good agreement with the predicted temperatures.