• Title/Summary/Keyword: 횡파

Search Result 127, Processing Time 0.023 seconds

H/V Spectral-ratio Analysis of Microtremors in Jeju Island (제주도 상시미동의 H/V 스펙트럼비 분석)

  • Hong, Myung-Ho;Kim, Ki-Young
    • Geophysics and Geophysical Exploration
    • /
    • v.13 no.2
    • /
    • pp.144-152
    • /
    • 2010
  • To study the thickness variation of volcanic rocks of Jeju Island, microtremor data were recorded at eight and four sites using short-period and broadband seismometers, respectively, for 30 ~ 60 minutes with a 100 Hz sampling rate. During the daytime, these records show increased cultural noise at frequencies above 1.8 Hz. Natural noise occurs in the frequency range of 0.4 to 0.8 Hz in both daytime and nighttime data. Predominant frequencies determined by the H/V spectral-ratio method are in the range of 0.2 ~ 0.7 Hz. These frequencies decrease gradually as the central part of the Mt. Halla is approached. This may indicate that the basement is warped downward beneath the center of the island, which is consistent with previous gravimetric and magnetic models. Assuming an average shear-wave velocity of 1,800 m/s for the overburden basalts, the depths to basement are estimated to be between 640 and 2,140 m.

Numerical Assessment of LNGC Berthing Operation to FLBT (FLBT를 향해 접안하는 LNGC의 수치해석 및 안정성 평가)

  • Jung, Sung-Jun;Jung, Dong-Woo;Oh, Seung-Hoon;Kim, Yun-Ho;Jung, Dong-Ho
    • Journal of Navigation and Port Research
    • /
    • v.45 no.3
    • /
    • pp.87-94
    • /
    • 2021
  • The IMO has adopted emission standards that strictly restrict the use of bunker C oil for vessels. Accordingly, research and bunkering pilot projects for LNG fueled ships are being actively carried out, which is expected to substantially reduce environmental pollution. In this study, we have adopted the turret moored Floating LNG Bunkering Terminal (FLBT) designed to receive the LNG from LNGCs and to transfer LNG to LNG bunkering shuttles in ship to ship moored condition. Numerical simulations have been performed with a 1-year return period of wind, wave, and current. Damping values of numerical model were adjusted from the results of model tests to obtain accurate simulation results. The results confirm safe berthing operation during the 1-year return period of environmental condition. Safety depends on the direction of environment, with increasingly stable operation facilitated by the application of heading-control function of FLBT to avoid beam-sea conditions.

New Design and Application of PVDF Ultrasonic Transducer for Measurement of Material Properties (재료물성 측정을 위한 직선집속 PVDF 초음파 트랜스듀서의 새로운 설계 및 응용)

  • Hong Soung-Wook;Kim Jung-Soon;Kim Sang-Yoon;Kim Moo-Joon;Ha Kang-Lyeol
    • The Journal of the Acoustical Society of Korea
    • /
    • v.25 no.4
    • /
    • pp.164-171
    • /
    • 2006
  • If the velocities of longitudinal, transverse and leaky surface acoustic waves in an isotropic material are given, the elastic constants and density of the material can be deduced analytically. Those velocities have been measured using three ultrasonic transducers with different vibrational modes so far. In this paper a line-focusing PVDF transducer with divided electrodes was newly proposed and designed for measuring approximate velocities of the three waves. The measurement method established in this study for each waves using the transducer was applied to several isotropic materials including fused quartz. The elastic stiffness constants and densities of the materials were calculated using the measured velocities, and the accuracies were discussed. It was shown that the obtained results are in good accord with the reference values.

Experiments on the stability of the spatial autocorrelation method (SPAC) and linear array methods and on the imaginary part of the SPAC coefficients as an indicator of data quality (공간자기상관법 (SPAC)의 안정성과 선형 배열법과 자료 품질 지시자로 활용되는 SPAC 계수의 허수 성분에 대한 실험)

  • Margaryan, Sos;Yokoi, Toshiaki;Hayashi, Koichi
    • Geophysics and Geophysical Exploration
    • /
    • v.12 no.1
    • /
    • pp.121-131
    • /
    • 2009
  • In recent years, microtremor array observations have been used for estimation of shear-wave velocity structures. One of the methods is the conventional spatial autocorrelation (SPAC) method, which requires simultaneous recording at least with three or four sensors. Modified SPAC methods such as 2sSPAC, and linear array methods, allow estimating shear-wave structures by using only two sensors, but suffer from instability of the spatial autocorrelation coefficient for frequency ranges higher than 1.0 Hz. Based on microtremor measurements from four different size triangular arrays and four same-size triangular and linear arrays, we have demonstrated the stability of SPAC coefficient for the frequency range from 2 to 4 or 5 Hz. The phase velocities, obtained by fitting the SPAC coefficients to the Bessel function, are also consistent up to the frequency 5 Hz. All data were processed by the SPAC method, with the exception of the spatial averaging for the linear array cases. The arrays were deployed sequentially at different times, near a site having existing Parallel Seismic (PS) borehole logging data. We also used the imaginary part of the SPAC coefficients as a data-quality indicator. Based on perturbations of the autocorrelation spectrum (and in some cases on visual examination of the record waveforms) we divided data into so-called 'reliable' and 'unreliable' categories. We then calculated the imaginary part of the SPAC spectrum for 'reliable', 'unreliable', and complete (i.e. 'reliable' and 'unreliable' datasets combined) datasets for each array, and compared the results. In the case of insufficient azimuthal distribution of the stations (the linear array) the imaginary curve shows some instability and can therefore be regarded as an indicator of insufficient spatial averaging. However, in the case of low coherency of the wavefield the imaginary curve does not show any significant instability.

Usefulness of Color-overlay Pattern of Breast Elastic Ultrasonography (유방 탄성초음파의 Color overlay pattern에 대한 유용성)

  • An, Hyun;Im, In-Chul
    • Journal of the Korean Society of Radiology
    • /
    • v.11 no.5
    • /
    • pp.401-406
    • /
    • 2017
  • Breast cancer rates are increasing every year, biopsy for diagnosing breast cancer is increasing as well. Biopsy also invasive test, have bad side effects from patients anxiety, infection, bleeding. In this study, Conduct a survey of 69 patients who brest lesion patient, both B-mode ultrasound and elastography exam and B-mode ultrasound was classified according to the BI-RADS category, and the elastography exam was classified according to the Color overlay pattern that the value of the kPa expressed in relation to the propagation velocity of Transverse waves. The optimal cut off value of the highest sensitivity and specificity was 54.70 kPa. In the color overlay pattern, Dark Blue 42 people, Light blue ~ Red 27 people classified results and BI-RADS classification results, benign 40 people and malignant 29 people classified results showed similar results. Therefore, It is judged that the color overlay pattern is positive when classified into Dark Blue, and malignant when classified into Light blue ~ Red. In conclusion, breast elastography is expected to play a innovative role in reducing the number of breast cancer examinations and classify between benign and malignant tumor.

Study on the Nonlinear Electromagnetic Acoustic Resonance Method for the Evaluation of Hidden Damage in a Metallic Material (금속 재료의 잠닉손상 평가를 위한 비선형 전자기음향공진 기법에 관한 연구)

  • Cho, Seung-Wan;Cho, Seung-Hyun;Park, Choon-Su;Seo, Dae-Cheol;Jhang, Kyung-Young
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.34 no.4
    • /
    • pp.277-282
    • /
    • 2014
  • Recently, much attention has been paid to nonlinear ultrasonic technology as a potential tool to assess hidden damages that cannot be detected by conventional ultrasonic testing. One nonlinear ultrasonic technique is measurement of the resonance frequency shift, which is based on the hysteresis of the material elasticity. Sophisticated measurement of resonance frequency is required, because the change in resonance frequency is usually quite small. In this investigation, the nonlinear electromagnetic acoustic resonance (NEMAR) method was employed. The NEMAR method uses noncontact electromagnetic acoustic transducers (EMATs) in order to minimize the effect of the transducer on the frequency response of the object. Aluminum plate specimens that underwent three point bending fatigue were tested with a shear wave EMAT. The hysteretic nonlinear parameter ${\alpha}$, a key indicator of damage, was calculated from the resonance frequency shift at several levels of input voltage. The hysteretic nonlinear parameter of a damaged sample was compared to that of an intact one, showing a difference in the values.

A Study on Suppression of UT Grain Noise Using SSP MPO Algorithms (SSP MPO 알고리즘을 이용한 초음파 결정립 잡음 억제에 관한 연구)

  • Koo, Kil-Mo;Jun, Kye-Suk
    • The Journal of the Acoustical Society of Korea
    • /
    • v.15 no.6
    • /
    • pp.81-89
    • /
    • 1996
  • It is very important for ultrasonic test method to evaluate the integrity of the class I components in nuclear power plants. However, as the rltrasonic test is affected by internal structures and configurations of test materials, backscattering, that is, time invariant noise is generated in large grain size materials. Due to the above reason, the received signal results in low signal to noise(S/N) ratio. Split spectrum processing(SSP) technique is effective to suppress the grain noise. The conventional SSP technique. however, has been applied to unique algorithm. This paper shows that MPO(minimization and polarity threshold) algorithm which two algorithms are applied simulatancously, was utilized, the signal processing time was shorten by using the new constant-Q SSP with the FIR filter which frequency to bandwidth ratio is constant and the optimum parameters were analysed for the signal processing to longitudinal wave and shear wave with the same requirements of inspection on nuclear power plant site. Moreover, the new ultrasonic test instrument, the reference block of the same product form and material specification, stainless stell test specimens and copper test specimens block of the same fabricated for the application of new SSP technique. As the result of experimental test with new ultrasonic test instrument and test specimens, the signal to noise ratio was improved by appying the new SSP technique.

  • PDF

Finite Element Simulation of Laser-Generated Ultrasound and Interaction with Surface Breaking Cracks (유한요소법을 이용한 레이저 유도 초음파와 표면 균열과의 상호작용 모델링)

  • Jeong, Hyun-Jo;Park, Moon-Cheol
    • Journal of the Korean Society for Nondestructive Testing
    • /
    • v.24 no.3
    • /
    • pp.259-267
    • /
    • 2004
  • A finite element method is used to simulate interaction of laser-based ultrasounds with surface breaking tracks in elastic media. The laser line source focused on the surface of semi-infinite medium is modeled as a shear dipole in 2-D plane strain finite elements. The shear dipole-finite clement model is found to give correct directivity patterns for generated longitudinal and shear waves. The interaction of surface waves with surface breaking cracks (2-D machined slot) is considered in two ways. Both the source and receiver are fixed with respect to the cracks in the first case, while the source is moving in another case. It is shown that the crack depth tested in the range of 0.3-5.0mm $({\lambda}_R/d=0.21{\sim}3.45)$ can be measured using the corner reflected waves produced by the fixed laser source. The moving laser source is found to cause a large amplitude change of reflected waves near crack, and the crack whose depth is one order lower than the wavelength ran be detected from this change.

On the motion characteristics of small trawler in trawling job and sailing (소형 트롤 어선의 예망과 항해중의 동요특성)

  • Kang, Il-Kwon;Kim, Hyung-Seok;Kim, Jung-Chang;Kim, Min-Seok;Jo, Hyo-Jae;Lee, Chun-Ki
    • Journal of the Korean Society of Fisheries and Ocean Technology
    • /
    • v.40 no.4
    • /
    • pp.311-318
    • /
    • 2004
  • It is very important for the safe navigation and fishing operation to ensure the hull response of a fishing vessel in rough seas. This is an experimental study on the dynamical characteristics of ship's motion during operating job and sailing in the real sea. The experiments were carried out on the small stern trawler in operating job and sailing, and then the ship's roll and pitch motion were simultaneously recorded by P/C according to the wave directions. From these data, the statistical properties and power spectra were obtained and the analysis of ship's motions in the both case were made. The results obtained are summarized follows : (1) The amplitudes of pitch motion don't appear a big different between trawl job and sailing, but at bow seas, its in sailing have a tendency to increase more than in trawl job. The amplitudes of roll motion appear a bog different between trawl job and sailing, but at beam sea, that slightly decreasing tendency. (2) The peak period of pitch motion in trawl job and sailing change, but that of roll motion don't change according to the direction of waves. (3) The warp tention cause the motion of hull to be reduce, if the tention of each side have a ballance.

Rayleigh-wave Phase Velocities and Spectral Amplitudes Affected by Insertion of an Anomalous Velocity Layer in the Overburden (천부 속도이상층이 레일리파 위상속도 및 수직변위 스펙트럼 진폭에 미치는 영향)

  • Kim, Ki Young;Jung, Jinhoon
    • Geophysics and Geophysical Exploration
    • /
    • v.15 no.4
    • /
    • pp.155-162
    • /
    • 2012
  • The Thomsen-Haskell method was used to determine sensitivities of the Rayleigh-wave phase velocities and spectral amplitude of vertical ground motion to insertion of a single velocity-anomaly layer into overburden underlain by a basement. The reference model comprised a 9-m thick overburden with shear-wave velocity (${\nu}_s$ of 300 m/s above a half-space with ${\nu}_s$ = 1000 m/s. The inserted layer, with a velocity of 150, 225, 375, or 450 m/s and a thickness of 1, 2, or 3 m, was placed at depths increasing from the surface in increments of 1 m. Phase velocities were computed for frequencies of 4 to 30 Hz. For inserted layer models, we placed an anomalous layer with thickness of 1 ~ 3 m, shear-wave velocity of 150 ~ 450 m/s, and at depths of 0 ~ 8 m in the overburden. The frequency range of 8 ~ 20 Hz were the most sensitive to the difference of $C_R$ between the inserted and reference models (${\Delta}C_R$) for h = 1 m and the frequency range got wide as h increased. For all of the models, the spectral amplitudes of the fundamental mode exceeded those of the $1^{st}$-higher mode except at frequencies just above the low-frequency cutoff of the $1^{st}$-higher mode.