• 한국전산구조공학회논문집
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• 제20권3호
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• pp.371-377
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• 2007

본 논문에서는 진동대를 이용하여 고층 건축물의 수평진동에 대한 지각임계가속도를 측정하였다. 바람에 의한 초고층 건축물의 과도한 진동은 거주자들에게 시각차와 현기증 같은 불쾌감을 줄 수 있다. 초고층 건축물 거주자들에게 쾌적한 환경을 제공하기 위해서는 가속도를 제한할 필요가 있다. 초고층 건축물은 1차 고유주기에 지배적이다 본 연구진은 1차 고유주기를 재연하기 위해 진동대를 사용하여 사인파진동에서 실험을 수행하였다. 실험은 진동하우스를 제작하고, 건장한 40명의 피험자를 대상으로 실시하였다 40명의 피험자를 8명씩 5개조로 나누고, 특정주파수범위$(0.2Hz{\sim}1.2Hz)$에서 가속도를 증가시키면서 수평진동에 대한 인지도를 측정하였다. 수평진동실험으로 피험자들의 진동에 대한 인지도를 누적분포표로 만들고, $0{\sim}20%,\;21{\sim}40%,\;41{\sim}60%,\;61{\sim}80%,\;81{\sim}100%$의 누적분포에 대해 추세선을 그려서 성능평가곡선을 작성하였다.

• 한국철도학회논문집
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• 제10권2호
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• pp.211-216
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• 2007

Rubber components are widely used in many application such as vibration isolators, damping, ride quality. Rubber spring is used in primary suspension system for railway vehicle. Characteristics and useful life prediction of rubber spring was very important in design procedure to assure the safety and reliability. Non-linear properties of rubber material which are described as strain energy function are important parameter to design and evaluate of rubber spring. These are determined by physical tests which are uniaxial tension, equi-biaxial tension and pure shear test. The computer simulation was executed to predict and evaluate the load capacity and stiffness for rubber spring. In order to investigate the useful life, the acceleration test were carried out. Acceleration test results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the acceleration test, several useful life prediction for rubber spring were proposed.

• International Journal of Railway
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• 제1권3호
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• pp.122-127
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• 2008

Rubber components are widely used in many application such as vibration isolators, damping, ride quality. Rubber spring is used in primary suspension system for railway vehicle. Characteristics and useful life prediction of rubber spring was very important in design procedure to assure the safety and reliability. Non-linear properties of rubber material which are described as strain energy function are important parameter to design and evaluate of rubber spring. These are determined by physical tests which are uniaxial tension, equi-biaxial tension and pure shear test. The computer simulation was executed to predict and evaluate the load capacity and stiffness for rubber spring. In order to investigate the useful life, the acceleration test were carried out. Acceleration test results changes as the threshold are used for assessment of the useful life and time to threshold value were plotted against reciprocal of absolute temperature to give the Arrhenius plot. By using the acceleration test, several useful life prediction for rubber spring were proposed.

• Journal of Positioning, Navigation, and Timing
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• 제4권4호
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• pp.195-203
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• 2015

In this study, the carrier acceleration-ramp-step test was applied to GPS carrier phase measurements, and the results were compared and analyzed. In the carrier acceleration-ramp-step test, the acceleration, ramp, and measurements are estimated using 10 consecutive carrier phase measurements for satellites observed at the same time based on the least square method. As for the characteristic of this test, if failure occurs in the measurement, the value jumps significantly compared to the previous result; but it judges that failure has occurred in all the satellites although failure has occurred in one satellite. Therefore, in this study, a method that eliminates a satellite with failure was suggested, and thresholds of the carrier acceleration, ramp, and step were suggested. The evaluation of the failure detection performance of carrier phase measurement using the suggested thresholds showed that failure could be detected when the carrier phase measurement changed abruptly by more than about 0.1 cycles.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.527-532
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• 2010

In this study, vertical and horizontal accelerometers were installed at the both side of car body and tachometer was installed on the bogie, for the purpose of stability analysis of Korail Airport Express Train during driving. By applying the developed algorithm, the peak-to-peaks of horizontal and vertical acceleration which were matched with location by tachometer were found and compared with the threshold values. The threshold values per velocities which were presented in the "Metro Train Performance Criteria" were applied here. The validity of the developed algorithm was shown by comparing the site investigation and the measured values at frost heave locations.

• 한국가시화정보학회지
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• 제10권3호
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• pp.25-29
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• 2012

This paper introduces a new parameter to design the $2{\times}2$ microfluidic centrifuge with single flow rotation positioned at the center of microchamber. The dimensional centrifugal acceleration momentum flux which is defined as the interfacial momentum flux divided by distance from the center of the chamber explains the flow rotation and its threshold provides a reference to expect single flow rotation. Through the numerical and experimental visualization of the flow rotation, the number and position of flow rotation in the $2{\times}2$ microfluidic centrifuge were examined. At a channel width of $50{\mu}m$ and chamber width of $250{\mu}m$, single flow rotation was obtained over at a Reynolds number of 300, while at a channel width of $100{\mu}m$ and chamber width of $500{\mu}m$, single flow rotation did not appear. The numerical analysis showed that the threshold centrifugal acceleration momentum flux to obtain single flow rotation was $3500kg/m{\cdot}s^2$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.15-25
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• 2004

This paper outlines a new convergence acceleration de-signed to solve scramjet flowfields with zones of re-circulation. Named the “marching-window”, the algorithm consists of performing pseudo-time iterations on a minimal width subdomain composed of a sequence of cross-stream planes of nodes. The upstream boundary of the subdomain is positioned such that all nodes upstream exhibit a residual smaller than the user-specified convergence threshold. The advancement of the downstream boundary follows the advancement of the upstream boundary, except in zones of significant streamwise ellipticity where a streamwise ellipticity sensor ensures its continuous progress. Compared to the standard pseudo-time marching approach, the march-ing-window is here seen to decrease the work required for convergence by up to 24 times for supersonic flows with little streamwise ellipticity and by up to 8 times for supersonic flows with large streamwise separated regions. The memory requirements are observed to be reduced sixfold by not allocating memory to the nodes not included in the computational subdomain. The marching-window satisfies the same convergence criterion as the standard pseudo-time stepping methods, hence resulting in the same converged solution within the tolerance of the user-specified convergence threshold. The extension of the marching-window to the weakly-ionized Navier-Stokes equations is also discussed.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.281-286
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• 2011

Station structures, one of important infrastructures, which have been being operated since the 1970s, are especially vulnerable to even the medium-level earthquake and they could be damaged by long-term internal or external vibrations such as ambient vibrations. Recently, much attention has been paid to real-time monitoring of the fatal defect or long-term deterioration of civil infrastructures to ensure their safety and adequate performance throughout their life span. In this study, a structural health monitoring methodology using acceleration responses is proposed to evaluate the health-state of the station structures and to detect initial damage-stage. A damage index is developed using the acceleration data and it is applied to outlier analysis, one of unsupervised learning based pattern recognition methods. A threshold value for the outlier analysis is determined based on confidence level of the probabilistic distribution of the acceleration data. The probabilistic distribution is selected according to the feature of the collected data.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.396-401
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• 2017

In this paper, a device to analyze gait pattern was developed by using a 2-axis acceleration sensor attached to the foot. The 1st low-pass filter was adapted to limit the frequency band up to 5 Hz. An algorithm to detect the peak value exceeding the threshold voltage of an X-axis acceleration sensor and a Z-axis acceleration sensor was developed and normal and abnormal walking patterns were thus differentiated. Also, MCU and Bluetooth were combined to transfer the data to other MCUs to display on an LCD; the size of the device could then be reduced. The new algorithm and the device allowed the individual walking patterns to be easily measured at a low cost and with less restriction on activities compared to conventional multiple pressure sensors or motion camera system.

• 센서학회지
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• 제23권4호
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• pp.251-258
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• 2014

While the feasibility of vertical velocity as a threshold parameter for pre-impact fall detection has been verified, effects of sensor attachment locations and methods calculating vertical acceleration and velocity on the detection performance have not been studied yet. Regarding the vertical velocity-based pre-impact fall detection, this paper investigates detection accuracies of eight different cases depending on sensor locations (waist vs. sternum), vertical accelerations (accurate acceleration based on both accelerometer and gyroscope vs. approximated acceleration based on only accelerometer), and vertical velocities (velocity with attenuation vs. velocity difference). Test results show that the selection of waist-attached sensor, accurate acceleration, and velocity with attenuation based on accelerometer and gyroscope signals is the best in overall in terms of sensitivity and specificity of the detection as well as lead time.