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고낙차 수력 펌프/터빈 런너에 대한 진동 모드해석 및 실험
류석주,하현천 한국소음진동공학회 1998 소음 진동 Vol.8 No.6
This paper describes the vibration characteristics of a high head pump-turbine runner. with nine blades and an outer diameter of 4.410 mm. of the pumped storage power plant. Mode shapes and natural frequencies were obtained by means of both the finite element analysis and modal testing. both in air and in water. The natural frequencies in air were calculated using the finite element method by ANSYS software. In order to confirm calculation results. the natural frequencies and mode shapes of the runner were measured using a hydraulic exciter both in air and in water. Natural frequencies of the pump-turbine runner were found at 174. 310 Hz in air, and at 107. 184 Hz in water. The first mode shape is flat plate mode with two nodal diameter and the second one is also flat plate mode with three nodal diameter. It can be shown that the natural frequencies of the pump-turbine runner in water is reduced approximately 40 % due to additional mass effect. Natural frequencies in air predicted by ANSYS software are in good agreement with test results.
柳碩柱,李聖喆,朴泰永,柳文集,金明昊,鄭宣根 단국대학교 1995 論文集 Vol.29 No.-
We studied 25 cases of patients with anterior knee joint pain without any other knee problems with a isokinetic evaluation technique using Cybex. The results are 1. The peak torques for the knee extensor muscles were decreased statistically 2. The peak torques for the knee flexor muscles were decreased relatively also but not statistically 3. TAE(Torque Acceleration Energy) values for knee extensor & flexors were all decreased from disuse atrophy 4. The torque curve for extensors showed decreased power around 30 degrees of knee flexion
朴泰永,柳錫柱,李聖喆,金明昊 단국대학교 1995 論文集 Vol.29 No.-
Authors has analysed bone mineral density(BMD) of spine and proximal femur of 55 normal male patients who visited Dankook University hospital, college of medicine from may 1994 to February 1995. The aims of the study is the investigation of correlation between BMD and age distribution and the change of the BMD. 1. The ages of maximal BMD from the 2nd lumbar spine to the 4th lumbar spine exist between 26 years old and 30 years old. The average decrease rate of BMD is 5% per 10 years from the age the maximal BMD. 2. Te BMD of the 12th thoracic spine and 1st lumbar spine is lower than that of the average BMD from the 2nd. to 4th lumbar spine. 3. The correlation cofficient of the lateral projection with anteroposterior projection is 0.632 at the 2nd lumbar spine and 0.500 at the 3rd lumbar spine. 4. The ages of maximal BMD of proximal femur exist between 21 years old and 25 years old. The average decrease rate of BMD is 7% per 10 years from the age of maximal BMD.
김철홍,류석주,박종포 한국소음진동공학회 1999 소음 진동 Vol.9 No.3
This paper presents numerical and experimental results of modal parameter identification in a generator stator frame for 500 MW fossil power plants. A commercial finite element analysis S/W was employed for modal analysis. The generator is excited by alternating electromagnetic forces, mainly of 120 Hz in 60 Hz machines, due to magnetic field and electric current in windings. It is necessary to verify that the stator frame has adequate frequency margin from the excitation frequency to avoid possible resonance when operating. Thus, frequency margin required for the stator frame is established using the numerical and experimental results. The results show that the stator frame meets the frequency-margin requirements. Also, results of modal analysis for design modification in order to reduce weights of the stator frame without deteriorating vibration characteristics are presented.
하현천,이동진,류석주 한국소음진동공학회 2001 소음 진동 Vol.11 No.3
This paper describes an experimental analysis for improving the stability of blade failure due to the vibration resonance, which happens in the low-pressure steam turbine. Some cracks due to high cycle fatigue were found in the blades of a low-pressure turbine after long time operation. Impact test showed that such failure was mainly caused by the resonance. In other words, since one of the natural frequencies of the grouped blade is very close to the excitation frequency of the nozzle, the resonant vibration leads to a large amplitude of displacement and results in a large amount of stress that may cause fatigue failures in the blades. It is interesting that the blade failures occur only at blades neighboring with the nodal points of the natural vibration mode whose natural frequency is close to the nozzle passing frequency. The effective methods for increasing the reliability against the blade vibration are a heightening the fatigue limit of the blade using an advanced material and a removing the resonance away from the operating speed. It is well known that the removal of theresonance could be obtained by the installation of different types of shrouds, wires, and links between the blades as well as by the chance of the number of nozzles. In the present work, two kinds of modification for avoiding the resonance haute been considered; 1) slot-type finger, 2) long span cover. Full-scale mockup tests have been performed in order to confirm the verification for modification in the shop. Test results show that the use of long span cover is very useful to change the natural frequencies of the grouped blade and to avoid the resonance effectively.
하현천,이동진,류석주 한국소음진동공학회 2001 한국소음진동공학회 논문집 Vol.11 No.3
This paper describes an experimental analysis for improving the stability of blade failure due to the vibration resonance, which happens in the low-pressure steam turbine. Some cracks due to high cycle fatigue were found in the blades of a low-pressure turbine after long time operation. Impact test showed that such failure was mainly caused by the resonance. In other words, since one of the natural frequencies of the grouped blade is very close to the excitation frequency of the nozzle, the resonant vibration leads to a large amplitude of displacement and results in a large amount of stress that may cause fatigue failures in the blades. It is interesting that the blade failures occur only at blades neighboring with the nodal points of the natural vibration mode whose natural frequency is close to the nozzle passing frequency. The effective methods for increasing the reliability against the blade vibration are a heightening the fatigue limit of the blade using an advanced material and a removing the resonance away from the operating speed. It is well known that the removal of the resonance could be obtained by the installation of different types of shrouds, wires, and links between the blades as well as by the change of the number of nozzles. In the present work, two kinds of modification for avoiding the resonance have been considered; 1) slot-type finger, 2) long span cover. Full-scale mockup tests have been performed in order to confirm the verification for modification in the shop. Test results show that the use of long span cover is very useful to change the natural frequencies of the grouped blade and to avoid the resonance effectively.