• 한국컴퓨터정보학회논문지
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• 제20권3호
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• pp.89-96
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• 2015

IT 기술이 생체역학 분야와 폭넓게 접목되고 있으며 AHRS 센서가 스포츠 모션분석 분야에 소형화 및 가격 경쟁력 측면에서 조명을 받고 있다. 본 논문에서는 피겨스케이트화에 소형의 AHRS 센서를 부착하고, 스핀(spin), 점프, 전/후진, 인/아웃 에지, 토(toe) 등의 기본 동작을 AHRS를 통해 측정한다. AHRS 센서의 측정 오차를 줄이기 위해 Madgwick의 상보필터를 적용하였으며, 짐벌락 현상(Gimbal Lock)을 줄이기 위해 쿼터니언(Quaternion)을 이용하였다. 취득한 9축 궤적 정보에 대해 PCA, ICA, LDA, SVM의 패턴인식 알고리즘을 적용하여 인식정확도 및 실행시간을 구하고, 여러 패턴인식 알고리즘 중에서 어떤 알고리즘이 인식정확도 및 실행시간 측면에서 적용이 가능한지 제시한다. 실험결과, PCA, ICA는 인식정확도가 낮아 사용하기에 부적합하며 LDA, SVM은 인식정확도가 우수하여 피겨스케이팅 기본 동작 인식에 사용이 적합함을 보인다.

• 스마트미디어저널
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• 제7권4호
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• pp.90-98
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• 2018

심전도 신호는 기본적으로 심장의 전기적 활동에 포함되며 이를 통해 심박수 측정, 심장 박동의 리듬 검사, 심장 이상 진단, 정서 인식 및 생체 인식과 같은 다양한 목적으로 분석 및 활용된다. 본 논문의 목적은 다차원 데이터 배열인 텐서 특성을 가진 다선형 판별분석(MLDA: Multilinear Linear Discriminant Analysis) 기법을 이용하여 개인식별을 수행하고자 한다. MLDA는 상위 차원의 텐서를 포함하는 분류 문제에 대해서 차원 문제를 해결 할 수 있으며, 상호 연관된 부분 공간은 서로 다른 클래스를 구별하기 위해 사용될 수 있다. 제시된 방법의 성능을 검증하기 위해 Physionet의 MIT-BIH데이터베이스를 적용하였다. 이 데이터베이스에 대해 실험한 결과, MLDA는 기존 PCA와 LDA와 비교하여 개인식별 성능이 우수함을 확인하였다.

• 한국컴퓨터정보학회논문지
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• 제21권3호
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• pp.83-89
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• 2016

Internet of Things (IoT) is widely used for biomechanics in sports activities and AHRS(Attitude and Heading Reference System) is a more cost effective solution than conventional high-grade IMUs (Inertial Measurement Units) that only integrate gyroscopes. In this paper, we attach the AHRS to the snowboard to measure the motion data like Air To Fakie, Caballerial and Free Style. In order to reduce the measurement error, we have adopted the sensors equipped with Kalman filtering and also used Euler angle to quaternion conversion to reduce the Gimbal-lock effect. We have tested and evaluated the accuracy and execution time of the pattern recognition algorithms like PCA, ICA, LDA, SVM to show the recognition possibility of it on the basic motions of Snowboarding from the 9-axis trajectory information which is gathered from AHRS sensor. With the result, PCA, ICA have low accuracy, but SVM have good accuracy to use for recognition of basic motions of Snowboarding.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.72.3-72.3
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• 2008

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.146-149
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• 2006

단일액체추진제 하이드라진 추력기의 인젝터로부터 발생하는 분무 특성을 파악하기 위해 입자영상유속계 및 레이저 도플러 유속계 기법을 적용하였다. 입자영상유속계를 이용하여 순간 평면 이미지를 획득하고 이 영상 자료를 통해 압력에 따른 분무정도 및 인젝터 분무성능을 판단하였다. 영상 이미지에서 누락된 분무 입자의 속도 및 입경 계측을 위해 레이저 도플러 유속계 계측방법을 적용하였다. 계측된 두 실험결과를 비교함으로써 분무 특성에 대한 명확한 이해 뿐만 아니라 인젝터 설계 변수 도출이 본 연구의 목적이다.

• Communications for Statistical Applications and Methods
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• 제30권1호
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• pp.75-94
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• 2023

The growing trend of cyber risk has put forward the importance of cyber risk management. Cyber risk is defined as an accidental or intentional risk related to information and technology assets. Although cyber risk is a subset of operational risk, it is reported to be handled differently from operational risk due to its different features of the loss distribution. In this study, we aim to detect the characteristics of cyber loss and find a suitable model by measuring value at risk (VaR). We use the loss distribution approach (LDA) and the time series model to describe cyber losses of financial and non-financial business sectors, provided in SAS^® OpRisk Global Data. Peaks over threshold (POT) method is also incorporated to improve the risk measurement. For the financial sector, the LDA and GARCH model with POT perform better than those without POT, respectively. The same result is obtained for the non-financial sector, although the differences are not significant. We also build a two-dimensional model reflecting the dependence structure between financial and non-financial sectors through a bivariate copula and check the model adequacy through VaR.

• 대한기계학회논문집B
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• 제23권9호
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• pp.1192-1200
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• 1999

The present study investigates flow characteristics in a cavity with one rotating disk and co-rotating disks for application to HDD. The experiments are conducted for rotating Reynolds numbers of $5.5{\times}104$ to $1.10{\times}105$ and for gap ratios of 0.059 to 0.175 in a single rotating and 0.047 to 0.094 in co-rotating disk. Time-resolved velocity components and turbulence intensity on the rotating disks are obtained by using LDA measurements. Detailed Knowledge of the flow characteristics is essential to analyze flow vibration and heat transfer and to design head-arm assembly and hub height in HDD. The results indicate that the velocity field in HDD is changed largely by the rotating Reynolds numbers and hub height of the disk.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.382-389
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• 2001

In the present study, local heat transfer rates for co-rotating disks with two modified hubs having ventilation holes are investigated for Rossby number of 0.04, 0.1 and 0.35 to evaluate the influence of incoming flows through hub holes. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients on the rotating disks using the heat and mass transfer analogy. Flow field measurements are conducted using Laser Doppler Anemometry (LDA) and numerical calculations are performed simultaneously to analyze the flow patterns induced by the disk rotation. The basic flow structure in a cavity between co-rotating disks consists of three regions; the solid-body rotating inner region, the outer region with turbulence vortices and the shroud boundary layer region. The heat/mass transfer. rates on the co-rotating disks are very low near the hub due to the solid-body rotation and those increase rapidly in the outer region due to turbulence mixing. The modified hubs with ventilation holes enhances significantly the heat/mass transfer rates on the region near the hub. The results also show that the heat transfer of Hub-2 is superior to that of Hub-1, but Hub-1 is more profitable for destructing the solid-body rotating inner region.

• 대한기계학회논문집B
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• 제21권6호
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• pp.793-803
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• 1997

This experimental study was mainly investigated on the swirl flow characteristics in the cylinder generated by a helical intake port. LDA system was used for the measurement of in-cylinder velocity fields. Tangential and axial velocity profiles, with varying valve lifts, valve eccentricity ratios and axial distance, were measured. When the intake valve was set in the cylinder center, we could find that in-cylinder swirl flow fields were composed of a forced vortex motion and a free vortex motion in the vicinity of the cylinder center and the cylinder wall respectively. In case of valve eccentricity ratio, N$_{y}$ = 0.45, the vortex flow which rotates to the opposite direction of a main rotating flow in the cylinder was found. And the reverse flow toward the cylinder head surface was also found in axial velocity profile and it showed the tendency of the linear decrease in the region of 0.leq.Y/B.leq.1.2.2.

• 대한기계학회논문집B
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• 제24권8호
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• pp.1029-1037
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• 2000

The present study investigates the local heat/mass transfer characteristics on a rotating disk which is the top disk covered with a shroud in HDD. The naphthalene sublimation technique is employed to determine the local heat/mass transfer coefficients on the rotating disk. Flow field measurements using Laser Doppler Anemometry (LDA) and numerical calculations are performed to analyze the flow patterns induced by the disk rotation. HDD has been developed for compactness and speedy data access, thus the rotating velocity of the disk is increased and the height of a hub is decreased. The experiments are conducted for the various hub heights of 5, 10 and 15 mm, for the rotating Reynolds numbers of $5.5{\times}10^4$ to $1.1{\times}10^5$ and for the effects of the presence of a read/write head arm. The results show that the heat transfer on the rotating disk is enhanced considerably for the decrease of the hub height and for the increase of the rotating Reynolds number. The head arm inserted in the cavity decreases the heat transfer despite the enhancement of tangential RMS velocity because of the deficit of the momentum in the flow field.