• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.120-127
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• 2016

This study examined the dynamic characteristics of the gate to identify the optimal gate installation direction according to the installation direction. A 1:31 scale model was constructed for a 47.5m prototype gate using acrylic. The scaled weights were tuned by adding lead weights. The first step was to measure the natural frequencies of the model gates, and compare them with finite-element analysis of the prototypes as a calibration. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of the gate orientation on structural vibrations. Vertical vibrations were measured under a range of operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. For large bottom opening heights in the normal direction, relatively large vibrations were induced by vortices shed at the plate bottom that would strike the horizontal truss member. This phenomenon was avoided in the reverse direction. For small bottom opening heights in the normal direction, these vibrations were caused by a suction force that developed at the gate bottom. The gate model in the reverse direction was preferred because of its low overall vibrational response under general gate opening and flow level combinations.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.64.3-65
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• 2016

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared instrument optimized to the Next Generation of small satellite series (NEXTSat). The capability of both imaging and low spectral resolution spectroscopy in the near-infrared range is a unique function of the NISS. The major scientific mission is to study the cosmic star formation history in local and distant universe. For those purposes, the main observational targets are nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optical design is optimized to have a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $3.8{\mu}m$. Two linear variable filters are used to realize the imaging spectroscopy with the spectral resolution of ~20. The mechanical structure is considered to endure the launching condition as well as the space environment. The compact dewar is confirmed to operate the infrared detector as well as filters at 80K stage. The electronics is tested to obtain and process the signal from infrared sensor and to communicate with the satellite. After the test and calibration of the engineering qualification model (EQM), the flight model of the NSS is assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. Here, we report the test results of the flight model of the NISS.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.1
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• pp.40.1-40.1
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• 2010

The Main payload of the STSAT-3 (Korea Science & Technology Satellite-3), MIRIS (Multipurpose Infra-Red Imaging System) has been developed for last 3 years by KASI, and its Flight Model (FM) is now being developed as the final stage. All optical lenses and the opto-mechanical components of the FM have been completely fabricated with slight modifications that have been made to some components based on the Engineering Qualification Model (EQM) performances. The components of the telescope have been assembled and the test results show its optical performances are acceptable for required specifications in visual wavelength (@633 nm) at room temperature. The ensuing focal plane integration and focus test will be made soon using the vacuum chamber. The MIRIS mechanical structure of the EQM has been modified to develop FM according to the performance and environment test results. The filter-wheel module in the cryostat was newly designed with Finite Element Analysis (FEM) in order to compensate for the vibration stress in the launching conditions. Surface finishing of all components were also modified to implement the thermal model for the passive cooling technique. The FM electronics design has been completed for final fabrication process. Some minor modifications of the electronics boards were made based on EQM test performances. The ground calibration tests of MIRIS FM will be made with the science grade Teledyne PICNIC IR-array.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.40.1-40.1
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• 2017

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared spectro-photometric instrument optimized to the Next Generation of small satellite series (NEXTSat). To achieve the major scientific objectives for the study of the cosmic star formation in local and distant universe, the spectro-photometric survey covering more than 100 square degree will be performed. The main observational targets will be nearby galaxies, galaxy clusters, star-forming regions and low background regions. The off-axis optics was developed to cover a wide field of view ($2deg.{\times}2deg.$) as well as the wide wavelength range from 0.95 to $2.5{\mu}m$, which were revised based upon the recent test and evaluation of the NISS instrument. The mechanical structure were tested under the launching condition as well as the space environment. The signal processing from infrared sensor and the communication with the satellite were evaluated after the integration into the satellite. The flight model of the NSS was assembled and integrated into the satellite. To verify operations of the satellite in space, the space environment tests such as the vibration, shock and thermal-vacuum test were performed. The accurate calibration data were obtained in our test facilities. Here, we report the test results of the flight model of the NISS.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.42-47
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• 2007

To reduce the chattering errors of reed switch sensors in the automatic remote measurement of water meter a reed switch sensor was analyzed and improved. The operation of reed switch sensors can be described as a mechanical contact switch by approximation of permanent magnet piece to generate an electrical pulse. The reed switch sensors are used mostly in measurement application to detect the rotational or translational displacement. To apply for water flow measurement devices, the reed switch sensors should keep high reliability. They are applied for the electronic digital type of water flow meters. The reed switch sensor is just mounted simply on the conventional mechanical type flow meter. A small magnet is attached on a pointer of the water meter counter rotor. Inside the reed sensor two steel leaf springs make mechanical contact and apart repeatedly as rotation of flow meter counter. The counting electrical contact pulses can be converted as the water flow amount. The MCU sends the digital flow rate data to the server using the wireless communication network. But the digital data is occurred difference or won by chattering noise. The reed switch sensor contains chattering error by it self at the force equivalent position. The vibrations such as passing vehicle near to the switch sensor installed location causes chattering. In order to reduce chattering error, most system uses just software methods, for example using filter algorithm and also statistical calibration methods. The chattering errors were reduced by changing leaf spring structure using mechanical characteristics.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.6
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• pp.455-463
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• 1998

RCCA(rod cluster control assembly) End-Tip suffers from neutron irradiation and constant vibration due to high-speed internal flow of primary coolant during plant operation. Such operating conditions cause the RCCA end-tip crackings around tile circumferential weldment of the end-tip, and in some cases, the defective end-tips were completly broken loose. However, no reliable inspection techniques for end-tip crackings were developed in the past, although some techniques exist for inspecting RCCA control rod wears. Therefore, NDE group at KEPRI has developed an ECT technique for the detection and the sizing of the end-tip crackings. The technique uses a specially designed surface-riding probe that can detect size of circumferential crackings with an accuracy of ${\pm}5.31%$ RMS error. This paper describes the ECT instrumentation including the ECT probes, calibration bars, as well as technical approaches.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.1-10
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• 2023

In the seismic design of structures, seismic forces are calculated based on structural models and analysis. In order to accurately address the dynamic characteristics of the actual structure in the structural model, calibration based on actual measurements is required. In this study, a 4-story frame test specimen was manufactured to simulate frame building, accelerometers were attached at each floor, and 1-axis shaking table test was performed. The natural period of the specimen was similar to that of the actual 4 story frame building, and the columns were designed to behave with double-curvature having the infinite stiffness of the horizontal members. To investigate the effects seismic waves characteristics, historical and artificial excitations with various frequencies and acceleration magnitudes were applied. The natural frequencies, damping ratios, and mode shapes were obtained using frequency response functions obtained from dynamic response signals, and the mode vector deviations according to the input seismic waves were verified using the Mode assurance criterion (MAC). In addition, the damping ratios obtained from the vibration tests were applied to the structural model, and the method with refined dynamic characteristics was validated by comparing the analysis results with the experimental data.