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Effects of load variation on a Kaplan turbine runner

  • Amiri, K.;Mulu, B.;Cervantes, M.J.;Raisee, M.
    • International Journal of Fluid Machinery and Systems
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    • v.9 no.2
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    • pp.182-193
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    • 2016
  • Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations since they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating directions called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

Strength Degradation and Failure of Circular RC Bridge Columns with Longitudinal Steel Connection under Cyclic Lateral Load (반복횡하중을 받는 철근콘크리트 원형 교각의 축방향철근 연결상세에 따른 강도저감 및 파괴거동)

  • Lee Jae-Hoon;Jung Chul-Ho;Ko Seong-Hyun;Son Hyeok-Soo
    • Journal of the Korea Concrete Institute
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    • v.16 no.1 s.79
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    • pp.111-124
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    • 2004
  • This research is a part of a research program to verify the seismic performance of circular reinforced concrete bridge columns with respect to longitudinal steel connection details under cyclic lateral load. A total of 21 column specimens were constructed and tested. Main variables in this test program were longitudinal steel connection details(continuous, lap-spliced, and mechanically connected), confinement steel ratio, and axial force ratio, etc. The test results of the columns with different longitudinal steel connection details showed different failure mode, strength degradation, and seismic performance. From the quasi-static test, it was found that the columns with all longitudinal reinforcement lap-spliced showed significantly reduced ductility. However, seismic performance of the columns with half of longitudinal reinforcement lap-spliced showed limited ductility but much more ductile behaviour than the columns with all longitudinal reinforcement lap-spliced. It was also found that the seismic performance, failure mode and strength degradation of columns with mechanical connected longitudinal reinforcement were similar to those of columns with continuous longitudinal reinforcement.

Implementation of a Mobile Sensor Device Capable of Recognizing User Activities (사용자 움직임 인식이 가능한 휴대형 센서 디바이스 구현)

  • Ahn, Jin-Ho;Park, Se-Jun;Hong, Eu-Gene;Kim, Ig-Jae;Kim, Hyoung-Gon
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.46 no.10
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    • pp.40-45
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    • 2009
  • In this paper, we introduce a mobile-type tiny sensor device that can classify the activities of daily living based on the state-dependent motion analysis using a 3-axial accelerometer in real-time. The device consists of an accelerometer, GPS module, 32bit micro-controller for sensor data processing and activity classification, and a bluetooth module for wireless data communication. The size of device is 50*47*14(mm) and lasts about 10 hours in operation-mode and 160 hours in stand-by mode. Up to now, the device can recognize three user activities ("Upright", "Running", "Walking") based on the decision tree. This tree is constructed by the pre-learning process to activities of subjects. The accuracy rate of recognizing activities is over 90% for various subjects.

A Study of the Vibration Safety Criterion on the Dynamic Behavior of Buried Pipeline with the Free Ends (양단자유 경계조건을 가진 매설관의 동적거동에서 진동안전 기준에 관한 연구)

  • 이병길;정진호;장봉현;안명석
    • Explosives and Blasting
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    • v.22 no.3
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    • pp.13-26
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    • 2004
  • This work reports results of our study on the dynamic response of buried pipelines depending on their boundary conditions. We have studied behavior of the buried pipelines both along the axial and the transverse direction with a boundary condition of free ends. The buried pipelines are modeled as beams on elastic foundation while the seismic wave as a ground displacement in the form of a sinusoidal wave. The natural frequency, its mode, and the effect of parameters have been interpreted in terms of the free vibration. In order to investigate the response on the earthquake, the resulting frequency and the mode shape obtained from the free vibration have been utilized to derive the mathematical formula for the farced vibration. We have also completed the computer program to simulate the time-displacement graphs of the pipe lines with free ends for both cases of vibrations.

Structural Performance of Beam-Middle Column Connection of 12m × 3m Steel Modular System (12m × 3m 스틸 모듈러 시스템의 보-중간기둥 접합부 구조성능)

  • Shim, Sung Chul;Lee, Sang Hyun;Jo, Bong Ho;Woo, Sung Sik;Choi, Mun Sik
    • Journal of Korean Society of Steel Construction
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    • v.20 no.6
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    • pp.793-805
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    • 2008
  • Recently, steel modular systems are developed and have been applied to the projects requiring fast construction such as military barracks and vertical expansion of school buildings. The existing modular system with standard module of 6m×3m has a problem that many columns are duplicated in the module connection and the wall thickness increases. In this study, 12m×3m module is proposed to solve this problem. Various types of beam-middle column connection which are essential for realizing the 12m×3m module are proposed and their maximum load capacity and failure mode are analytically and experimentally evaluated. The comparison between analytical and experimental results shows that the maximum axial load and failure mode can be accurately estimated by finite element analysis. Some connection types which have higher failure load than the design load of the column, can be used as the beam-middle column connection detail of the 12m×3m module.

Investigation of the BSR Noise characteristics in Seat Cushion-frame with respect to Vibration Durability Test Using Multi-simulator (다축 가진기를 이용한 시트 쿠션 프레임의 내구 전후 BSR 진동특성 연구)

  • Choi, Ho-Il;Nam, Jae-Hyun;Kang, Jae-Young;Park, Jung-Hee
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.8
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    • pp.4776-4783
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    • 2014
  • Many studies have examined the reduction of primary noise sources, but quality-related noise, such as BSR, is rarely studied. This study describes the quantitative BSR test method using a multi-axial simulator. The sine sweep test was conducted to detect the system resonance and its relation to BSR noise with high frequency. This method is applied to the seat frame with/without the vibration durability test. The results showed that the 1st lateral resonance leads to higher BSR frequency noise. In addition, the reduction of the lateral mode system stiffness after the durability test results in a decrease in the BSR noise in sine sweep test mode.

Measurement of Patient Dose from Computed Tomography Using Physical Anthropomorphic Phantom (물리적 팬텀을 이용한 CT 촬영 환자의 피폭 선량 측정 및 평가)

  • Jang, Ki-Won;Lee, Choon-Sik;Kwon, Jung-Wan;Lee, Jai-Ki
    • Journal of Radiation Protection and Research
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    • v.30 no.3
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    • pp.113-119
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    • 2005
  • The computed tomogrpahy(CT) provides a high quality in images of human body but contributes to the relatively high patient dose. The frequency of CT examination is increasing and, therefore, the concerns about the patient dose are also increasing. In this study the experimental determination of patient dose was performed by using a physical anthropomorphic phantom and thermoluminescent dosimeter(TLD). The measurements were done for the both axial and spiral scan mode. As a result the effective doses for each scan mode were 17.78mSv and 10.01 mSv respectively and the fact that the degree of the reduction in the patient dose depends on the pitch scan parameter was confirmed. The measurement methods suggested in this study can be applied for the reassessment of the patient dose when the technique in CT equipment is developed or the protocol for CT scanning is changed.

Linear Stability Analysis of a Baffled Rocket Combustor (배플이 장착된 로켓 연소기의 선형 안정성 해석)

  • Lee, Soo Yong
    • Journal of the Korean Society of Propulsion Engineers
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    • v.22 no.3
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    • pp.46-52
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    • 2018
  • A simple Crocco's nτ time delay model and linear analysis of fluid flow coupled with acoustics are combined to investigate the high frequency combustion instability in the combustion chamber of LOX/hydrocarbon engines. The partial differential equation of the velocity potential is separated into ordinary differential equations, and eigenvalues that correspond to tangential resonance modes in the cylindrical chamber are determined. A general solution is obtained by solving the differential equation in the axial direction, and boundary conditions at the injector face and nozzle entrance are applied in order to calculate the chamber admittance. Frequency analysis of the transfer function is used to evaluate the stability of system. Stability margin is determined from the system gain and phase angle for the desired frequency range of 1T mode. The chamber model with variable baffle length and configurations are also considered in order to enhance the 1T mode stability of the combustion chamber.

A Study on the Heat Storage System for Chemical Heat Pump Using Inorganic Hydrates(I) - Heat Storage Characteristics - (화학열펌프에 있어서의 무기수화물계 축열시스템에 관한 연구(I) - 탈수 축열 성능연구 -)

  • Park, Young-Hae;Kim, Jong-Shik
    • Solar Energy
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    • v.15 no.3
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    • pp.29-38
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    • 1995
  • The heat-storage characteristics accompanied by exothermic reaction at the regeneration of Ca(OH)2 in tile heat-storage mode of a chemical heat pump system using a Ca(OH)2/CaO reversible thermochemical reaction was examined in a lab-scale unit. In this heat-storage mode, the particle bed of CaO could be regenerated by heating the Ca(OH)2 packed bed to the higher temperature at which the equilibrium pressure in the reactor is greater than the water vapor pressure in the condenser. The results are i) the dehydration, thermal decomposition, rate of Ca(OH)2 was higher at the lower part of particle bed than at the upper part, ii) in the reactor, the dehydration was proceeded along radial and axial direction, from inner part to the outer part, which explains heat transfers from the center to wall and from the tenter to lower or upper part of reactor.

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A Study on the Mechanical Properties of Concrete Filled Steel Tube Column under Centric Axial Load (중심축력을 받는 콘크리트 충전강관 기둥의 역학적 거동 특성에 관한 연구)

  • 박정민;김화중
    • Magazine of the Korea Concrete Institute
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    • v.7 no.5
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    • pp.133-144
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    • 1995
  • This study investigated to the properties of structural behaviors through a series of experiment with the key parameter, such as diameter-to-thickness(D/t) ratio, selenderness ratio of steel t~ube and strength of concrete under loading condition simple confined concrete by steel tube as a fundmental study on adaptability with structural members in high-rise building. The obtained results are sumnarised as follow. (1) The fracture mode of confined concrete was presented digonal tension fracture in the direction of 45 with compression failure at the end of specimen in stub column, but the fracture mode of long column was assumed an aspect of bending fracture transversely. (2) The deformation capacity and ductility effect was increased by confine steel tube for concrete. (3) 'The emprical formula to predict the ultimate capacity of confined concrete by steel tube and concrete filled steel tube column using restraint of concrete considered D / t ratio, selenderness ratio of steel tube anti strength of' concrete were proposed.