• Smart Structures and Systems
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• 제15권4호
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• pp.997-1018
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• 2015

Structural health monitoring along with damage detection and assessment of its severity level in non-accessible reinforced concrete members using piezoelectric materials becomes essential since engineers often face the problem of detecting hidden damage. In this study, the potential of the detection of flexural damage state in the lower part of the mid-span area of a simply supported reinforced concrete beam using piezoelectric sensors is analytically investigated. Two common severity levels of flexural damage are examined: (i) cracking of concrete that extends from the external lower fiber of concrete up to the steel reinforcement and (ii) yielding of reinforcing bars that occurs for higher levels of bending moment and after the flexural cracking. The purpose of this investigation is to apply finite element modeling using admittance based signature data to analyze its accuracy and to check the potential use of this technique to monitor structural damage in real-time. It has been indicated that damage detection capability greatly depends on the frequency selection rather than on the level of the harmonic excitation loading. This way, the excitation loading sequence can have a level low enough that the technique may be considered as applicable and effective for real structures. Further, it is concluded that the closest applied piezoelectric sensor to the flexural damage demonstrates higher overall sensitivity to structural damage in the entire frequency band for both damage states with respect to the other used sensors. However, the observed sensitivity of the other sensors becomes comparatively high in the peak values of the root mean square deviation index.

• Smart Structures and Systems
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• 제15권4호
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• pp.1159-1175
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• 2015

In this study, the effect of temperature variation on the wireless impedance monitoring is analyzed for the tendon-anchorage connection of the prestressed concrete girder. Firstly, three impedance features, which are peak frequency, root mean square deviation (RMSD) index, and correlation coefficient (CC) index, are selected to estimate the effects of temperature variation and prestress-loss on impedance signatures. Secondly, wireless impedance tests are performed on the tendon-anchorage connection for which a series of temperature variation and prestress-loss events are simulated. Thirdly, the effect of temperature variation on impedance signatures measured from the tendon-anchorage connection is estimated by the three impedance features. Finally, the effect of prestress-loss on impedance signatures is also estimated by the three impedance features. The relative effects of temperature variation and prestress-loss are comparatively examined.

• 한국가시화정보학회지
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• 제17권1호
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• pp.10-18
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• 2019

In this study, the temperature behavior of Pulsating Heat Pipe (PHP) according to the diameter change were studied by limiting the diameter change to only the evaporator. To investigate operation of PHP in various heat input, heat input power was increased from 10 to 120 W. The results show operation can be divided into 3 regimes by temperature behavior. Thermal resistance was increased before start-up and decreased with increasing heat input. At 110 W heat input, thermal conductivity of 2 mm PHP was 8 .times higher compare to thermal conductivity of copper. Further, to investigate details of temperature behavior in higher heat input, FFT analysis was conducted. Based on the results, when the deviation of peak frequency in each section is lowest, the thermal resistance has lowest value.

• 한국음향학회지
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• 제6권3호
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• pp.43-51
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• 1987

본 논문에서는 쌍극성 임펄스형 데이터열을 AWQPSK(Amplitude Weighted QPSK) 신호로 변환하는 변조기를 탄성표면파 소자로 구현하고 그 특성을 측정하였다. 탄성표면파 변조기는 입력 비정규형 IDT와 출력 정규형 IDT로 구성되어 있으며, 중심 주파수 fc는 20MHz, 비트폭은 250nsec 를 갖도록 설계하여 압전물질인 $YZ-LiNbO_3$, substrate 위에 Photolithography방법으로 제작하고 그 특성을 측정하였다. 측정된 중심 주파수와 영점-영점 대역폭은 각각 20MHz와 8.8MHz이고 제 1 side lobe는 -60dB로서 이는 이론치와 거의 일치하는 결과이다.

• 대한전기학회논문지:시스템및제어부문D
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• 제54권4호
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• pp.274-283
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• 2005

Coronary Perfusion Pressure(CPP) is known for the most important parameter related to the Return of Spontaneous Circulation (ROSC), however, clinically measuring CPP is difficult either invasive or non-invaisive method. En this paper, we analyze the correlation between the extracted parameter from VF ECG wave and the CPP with the statistical method, and predict CPP value using the extracted parameters within significance level. the extracted parameters are median frequency(MF), peak frequency(PF), average segment amplitude(ASA), MSA(maximum segment amplitude), Two parameters, MF, and ASA are selected in order to predict CPP value with general regression neural network, and then we evaluated the agreement statistics between the simulated CPP and the measured CPP. In conclusion, the mean and variance of the difference between the simulated CPP and the measured CPP are 8.9716±1.3526 mmHg, and standard deviation 6.4815 mmHg with one hundred-times training and test results. the simulated CPP and the measured CPP are agreed with the overall accuracy $90.68\%$ and kappa coefficient $81.14\%$ as a discriminant parameter of ROSC.

• 한국전문물리치료학회지
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• 제28권1호
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• pp.65-71
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• 2021

Background: The hamstring is a muscle that crosses two joints, that is the hip and knee, and its flexibility is an important indicator of physical health in its role in many activities of daily living such as sitting, walking, and running. Limited range of motion (ROM) due to hamstring tightness is strongly related to back pain and malfunction of the hip joint. High-frequency diathermy (HFD) therapy is known to be effective in relaxing the muscle and increasing ROM. Objects: To investigate the effects of HFD on active knee extension ROM and hamstring tone and stiffness in participants with hamstring tightness. Methods: Twenty-four participants with hamstring tightness were recruited, and the operational definition of hamstring tightness in this study was active knee extension ROM of below 160° at 90° hip flexion in the supine position. HFD was applied to the hamstring for 15 minutes using the WINBACK device. All participants were examined before and after the intervention, and the results were analyzed using a paired t-test. The outcome measures included knee extension ROM, the viscoelastic property of the hamstring, and peak torque for passive knee extension. Results: The active knee extension ROM significantly increased from 138.8° ± 9.9° (mean ± standard deviation) to 143.9° ± 10.4° after the intervention (p < 0.05), while viscoelastic property of the hamstring significantly decreased (p < 0.05). Also, the peak torque for knee extension significantly decreased (p < 0.05). Conclusion: Application of HFD for 15 minutes to tight hamstrings immediately improves the active ROM and reduces the tone, stiffness, and elasticity of the muscle. However, further experiments are required to examine the long-term effects of HFD on hamstring tightness including pain reduction, postural improvement around the pelvis and lower extremities, and enhanced functional movement.

• 한국운동역학회지
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• 제17권4호
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• pp.115-125
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• 2007

Grould Reaction force(GRF) is important in human movements and GRF measurements are one of the most frequently used tool in biomechanical studies. In the studies of the golf swing motion, people refer to GRF as weight transfer. A successful golf swing motion requires many segments activation sequences which are controled by the nerve system. Due to the inter- and intra-individual variability of the human movement and the movement strategies, reliability of the measurements are important in human movement studies. Previous golf researches were based on group studies and certain events' values were analyzed. The purposes of this study were to determine the number of trials for the reliable golf swing GRF data collection, to reveal the variability level of the meaningful components of the golf swing GRF, and to classify the types of the golf swing GRF patterns. Twenty three male professional golfers($26.4{\pm}6.6$ years, $174.3{\pm}5.2\;cm$, $71.3{\pm}6.5\;kg$) signed an informed consent form prior to participation in this study. GRFs of driver swings were collected with Kistler 9285 force platform and 9865A amplifier, and calculated by the KwonGRF program(Visol, Korea). Sampling frequency was 1080 Hz. GRF data were trimmed from 1.5 s prior to the impact to 0.5 s after the impact. The number of trials for the reliable GRF collection was determined when the change in floating mean overs the 25 % of the standard deviation of that variable. Variabilities of the variables were determined by the coefficient of variation(CV) of 10 %. The types of GRF patterns were determined by visual inspection of the peak GRF shapes. The minimum number of trials for the reliable golf swing GRF data collection was five. Ten-trial seems more conservative. The value of the peak GRF was more reliable than the value of the impact GRF. The CV of the peak GRF and impact GRF were 7.4 %, 15.2 %, respectively. Because of the +/- sigh of the peak GRF appearance time, it was impossible to calculate CV of the peak GRF appearance time. Golf swing GRF patterns were classified as sing peak type, double peak type, and plateau peak type. This classification suggests the presence of the different golf swing weight transfer strategies.

• 한국수산과학회지
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• 제27권5호
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• pp.594-604
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• 1994

The storm surges caused by the typhoon Brenda in 1985 were studied by analysing tidal observation data at 7 stations along the south coast of the Korean peninsula. The tidal deviation at these stations along the coast are discussed in association with meteorological data. The sea level anomalies were studied by means of the Empirical Orthogonal Function (EOF) analysis and the Fast Fourier Transform(FFT) method. From the result of EOF analysis, the temporal and spatial variations of storm surge were described by the first mode of EOF, which is $73\%$ of the total variances during the passage of typhoon Brenda. From the results of FFT spectral analysis, the peak energy of the autospectrum for surge, atmospheric pressure, and wind stress appeared in the low frequency fluctuations band. The result of FFT analysis showed that the typhoon surge was related chiefly to the atmospheric pressure change in an open bay such as Cheju and Keomundo harbor, while it was influenced mainly by the wind stress in the semi-enclosed waters of Yeosu, Chungmu and Kadukdo.

• 한국재료학회지
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• 제4권7호
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• pp.783-791
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• 1994

rf 마그네트론 스퍼터링법을 이용하여 7059 유리기판 위에 ZnO압전박막을 증착하고, 공정변수인 rf 인가전력, 반응기 압력, $O_{2}$/Ar의 조성비등이 증착되는 박막의 결정성 및 전기적 특성에 미치는 영향을 고찰하였다. 증착된 ZnO박막은 문헌에 보고된 증착속도보다 높은 값(200-1000$\AA$/min)을 가졌으며, XRD(002)피크의 rocking curve 표준편차가 SAW 필터로의 응용이 가능한 $6^{\circ}$미만의 값을 가졌다. $O_{2}$Ar 유입비가 25%이상의 경우에는 매우 높은 저항치를 가짐을 알 수 있었다. ZnO박막의 두께와 파장의 비, $\frac{h}{\lambda}$=0.25인 조건에서 필터를 제조하였다. 측정한 주파수 응답특성과 이론치에 의해 계산한 주파수응답특성은 비교적 잘 일치함을 알 수 있었다. 이때 중심주파수는 39.08MHz였으며, 상속도는 \ulcorner 2501m/sec, 삽입손실은 약 29dB였다.

• 터널과지하공간
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• 제19권6호
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• pp.490-497
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• 2009

최근 발생한 5개의 중규모 지진으로부터 관측된 지반진동 파형을 이용하여 응답스펙트럼을 분석하고 결과를 국내 원자력 관련 구조물의 내진설계 기준과 국내 일반 구조물 및 건축물 내진설계기준과 각각 비교하였다. 연구에 이용된 지반진동 개수는 수평성분 및 수직성분 각각 74개 및 89개이며 주파수별 지반응답을 구하고 최대 지반 가속도 값를 이용하여 정규화 분석을 수행하였다. 본 연구결과를 국내 원자력시설물의 내진기준으로 이용되고 있는 Reg. Guide 1.60과 비교한 결과 특히 약 1 Hz 이상의 전체 고주파수 영역에서 수평 성분 스펙트럼 이 Reg. Guide 1.60 보다 높은 값을 보여 주었다. 수직성분은 약 7~8 Hz 부근에서 약간 초과하였다. 또한 국내 일반 구조물 및 건축물 내진설계기준인 표준 설계응답스펙트럼을 3개 지반조건에 적용한 결과를 분석 자료와 동시에 비교한 결과 특히 약 2초(0.5 Hz) 이하의 단주기 영역의 전체 대역(SE 지반조건)에서 수평 성분 자료처리 결과가 기준을 크게 초과하는 현상을 보여 주었다. 수직성분은 전체 주기 영역에서 SD 지반조건의 기준과 유사한 특징을 보여 주었다. 물론 이러한 현상은 국내 지각의 주파수별 감쇠 및 부지 직하부의 감쇠 특성 등과 복합적으로 관련되어 발생한 현상으로 판단된다. 향후 국내 지진활동 실정에 적합한 내진설계 기준 마련을 위해 관측자료의 질적 향상 및 양적인 축적 등을 통하여 특히 수평 성분의 약 1 Hz 이상의 고주파수 대역에서 응답스펙트럼 기준의 보수성을 심각하게 고려할 필요가 있다.