• Title/Summary/Keyword: continuous wave

Search Result 785, Processing Time 0.037 seconds

A Study on the Determination of Slip-up Time for Slip-Form System using Surface Wave Velocity (표면파 속도를 이용한 슬립폼 시스템 상승 시기 결정에 관한 연구)

  • Kim, Heeseok;Kim, Young Jin;Chin, Won Jong;Yoon, Hyejin
    • KSCE Journal of Civil and Environmental Engineering Research
    • /
    • v.32 no.5D
    • /
    • pp.483-492
    • /
    • 2012
  • The early setting time of concrete is an important factor determining the slip up velocity of the slip-form system. Accordingly, need is for a technique evaluating the early setting time in order to secure the safety of the slip-form system and the construction quality of concrete. This paper intends to estimate the early setting time by evaluating the setting degree of concrete using surface wave velocity so as to determine the slip up time of the slip-form system. Penetration resistance test and compressive strength test are performed first to clarify the relationship between the early setting time of concrete and the compressive strength. Then, compressive strength test and ultrasonic wave test are conducted to examine the relation between the compressive strength and the surface wave velocity. Continuous wavelet transform is adopted to measure the surface wave velocity. Numerical analysis is carried out to demonstrate the appropriateness of the application of continuous wavelet transform. Based on these results, the propagation velocity of the surface wave required for the slip up of slip-form system is suggested. Finally, a reduced model test of the slip-form system is conducted to verify the feasibility of the proposed surface wave velocity for the determination of th slip up velocity.

Improved Rayleigh Wave Velocity Measurement Technique for Early-age Concrete Monitoring (초기 재령 콘크리트의 모니터링을 위한 개선된 레일리파 속도 측정 기법)

  • Shin Sung-Woo;Yun Chung-Bang;Popovics John S.;Song Won-Joon
    • Proceedings of the Computational Structural Engineering Institute Conference
    • /
    • 2006.04a
    • /
    • pp.97-103
    • /
    • 2006
  • A modified one-sided measurement technique is proposed for Rayleigh wave (R-wave) velocity measurement in concrete. The scattering from heterogeneity may affect the waveforms of R-waves in concrete, which may make the R-waves dispersive. Conventional one-sided techniques do not consider the scattering dispersion of R-waves in concrete. In this study, the maximum energy arrival concept is adopted to determine the wave velocity by employing its continuous wavelet transform. Experimental study was performed to show the effectiveness of the proposed method. The present method is applied to monitor the strength development of early-age concrete. A series of experiments were performed on early-age concrete specimens with various curing conditions. Results reveal that the proposed method can be effectively used to measure the R-wave velocity in concrete structures and to monitor the strength development of early-age concrete.

  • PDF

Characteristics of wave propagation in a sloping-wall-type wave absorber

  • Zhu, Lixin;Lim, Hee Chang
    • Journal of Advanced Marine Engineering and Technology
    • /
    • v.39 no.8
    • /
    • pp.843-848
    • /
    • 2015
  • The objective of this study is to observe and optimize a typical ocean environment and reduce wave reflections in the wave flume. In order to generate ocean waves in the wave flume, a combination of a horizontal piston type wave generator and wave absorbers was installed in the channel. Two probes for measuring the wave heights, i.e., wave level gauges, were used to record the continuous variation of the wave surface, the phase difference, and the maximum (crest) and minimum (trough) points of the propagating waves. In order to optimize the shape and size of the propagating waves, several absorption methods were proposed. Apart from an active wave absorption method, we used methods that involved vertical porous plates, horizontal punching plates, and sloping-wall-type wave absorbers. To obtain the best propagating waves, a sloping-wall-type wave absorber was chosen and tested in terms of the constitutive filling materials and the location and shape of the plate. This study also focused on the theoretical prediction of the wave surface, separating them into the incident and reflective components. From the results, it is evident that the wave absorber comprising a hard filling material exhibits a better performance than the absorber comprising a soft material, i.e., the wave absorber can be a strong sink to control the energy of the incoming wave. In addition, larger wave absorbers correspond to lower reflectance because a larger volume can reduce the incoming wave energy. Therefore, at constant absorber conditions, the reflectance of the wave increases as the wave period increases. Finally, the reflectance of the wave was controlled to be less than 0.1 in this study so that the wave flume can be used to simulate an offshore environment.

Passive Control for the Augmentation of a Pulse Wave (펄스파 강도증가를 위한 피동제어)

  • 이동훈;김희동;강성황
    • Journal of KSNVE
    • /
    • v.11 no.2
    • /
    • pp.241-248
    • /
    • 2001
  • The present paper describes experimental and computational work to augment the magnitude of the impulsive wave. An experiment was performed using a simple shock tube with an open end and numerical calculations were carried out to solve the unsteady, axisymmetric, inviscid, compressible governing equations. The control strategy applied was to alter the exit geometry of a straight tube to a sudden enlargement tube and a flare tube. The effects of the configurations of the tube exit on the magnitude of the impulsive wave were investigated over the range of the weak shock Mach number from 1.01 to 1.10. The results obtained were compared to those of the straight tube tests. The numerical result predicted the magnitude of the experimented impulsive waves with a good accuracy. The present passive control technique enabled the magnitude of the impulsive wave to augment by about 23 percent, compared to that of the straight tube of no control.

  • PDF

TWO-DIMENSIONAL SHOCK WAVE DIFFREACTION IN DROPPET-LADEN GAS MEDIA (액적을 동반한 기체에서 이차원 충격파 회절)

  • Yeom, G.S.;Chang, K.S.
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2010.05a
    • /
    • pp.362-364
    • /
    • 2010
  • Shock wave interaction with droplet-gas medium is investigated in this paper. In the present computation, the shock wave is initially started in a pure gas and reflected from the wedge to interact with the droplet-ridden gas flows. We used the compressible two-fluid two-phase model that is solved by the two-fluid version of the HLL scheme. The interfacial drag force and heat transfer were included to model the interaction between continuous and dispersed phases. The parametric effect of void fraction on the shock wave reflection in the two-phase media was investigated.

  • PDF

Application of Directional Wavelet to Ocean Wave Image Analysis (방향 웨이브렛을 적용한 해양파 이미지 분석)

  • Kwon S. H.;Lee H. S.;Park J. S.;Ha M. K.
    • Proceedings of the KSME Conference
    • /
    • 2002.08a
    • /
    • pp.377-380
    • /
    • 2002
  • This paper presents the results of a study investigating methods of interpretation of wave directionality based on wavelet transforms. Two-dimensional discrete wavelet was used for the analysis. The proposed scheme utilizes a single frame of ocean waves to detect their directionality. This fact is striking considering the fact that traditional methods require long time histories of ocean wave elevation measured at various locations. The developed schemes were applied to the data generated from numerical simulations and video images to test the efficiency of the proposed scheme in detecting the directionality of ocean waves.

  • PDF

Directivity Analysis for Optimal Design of Ultrasonic Angle Beam Transducer (초음파 사각 트랜스듀서의 최적설계를 위한 지향성 해석)

  • Nam, Young-Hyun
    • Transactions of the Korean Society of Mechanical Engineers A
    • /
    • v.32 no.9
    • /
    • pp.796-803
    • /
    • 2008
  • Ultrasonic testing uses the directivity of the ultrasonic wave, which propagates in on direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of an ultrasonic wave is related to the choice of probe arrangement, testing sensitivity and scanning pitch and correct measurement of defect size and location. This paper describes on the directivity measurement of ultrasonic wave using the visualization method. The directivity of shear wave emitted from the angle beam transducer were constant during propagation. The difference of directivity was existed between 2 MHz and 4 MHz angle beam transducers. When these experimental results were compared with the theory which was based on the continuous wave, it showed good agreement with theoretical directivity on the principal lobe.

Wideband Lamb wave analysis based on continuous wavelet transform

  • Shi, Lihua;Wang, Xinwei;Li, Gang;Zhang, Lingyan
    • Smart Structures and Systems
    • /
    • v.1 no.3
    • /
    • pp.257-266
    • /
    • 2005
  • In Lamb wave detection of damages in smart structures, the excitation pulse is usually designed as a narrow band burst wave for the convenience of analysis and recognition. However, the wideband excitation can excite more modes in plate/shell structure and thus provides extra information for changes of the structure. This paper presents a method that can extract information in wideband Lamb wave signals. By transforming the detected signals into various sub-frequency band, the measured signal can be converted to its equivalences of narrow band excitations, therefore, the information in different frequency bands can be acquired from a single test and in the same time the complicity of wideband signal can be simplified. Some test results are provided to verify this method.

A study on the Development of Frequency Modulated Continuous Wave Radar for Distance Measurement (거리 측정용 주파수 변조 연속파 레이더 개발에 관한 연구)

  • Park, Dong-Kook;Han, Tae-Kyoung;Lee, Hyun-Soo
    • Proceedings of the Korean Society of Marine Engineers Conference
    • /
    • 2005.06a
    • /
    • pp.1005-1010
    • /
    • 2005
  • In this paper, it is presented a frequency modulated continuous wave radar (FMCW) for distance measurement. The frequency range is $10{\sim}11$ GHz and the sweep time of the signal is 100 ms. The test target is 0.8 m2 of metal plate. The experiment is performed in open ground and the pyramidal horn antenna of about 22 dBi gain is used. The beat frequency according to the target moving to 40 m is measured. There is a good agreement between measured and calculated results. But the resolution of the FMCW radar is not good such as about 10 cm. It is result from the nonlinear signal of voltage controlled oscillator (VCO). To improve the nonlinear characteristic of VCO, a high pass filter and phase locked loop (PLL) frequency synthesizer are included in the radar system.

  • PDF

A study on the development of CW(Continuous-Wave) Doppler System using FFT (FFT를 이용한 연속초음파 도플러 장치에 관한 연구)

  • Lee, Dae-Hyung;Kang, Chung-Shin;Park, Sei-Hyun;Kim, Young-Kil
    • Proceedings of the KIEE Conference
    • /
    • 1988.07a
    • /
    • pp.709-712
    • /
    • 1988
  • Ultrasonic Doppler Diagnostic System utilizes the Doppler effect for measurement of blood velocity. The sign of the Doppler frequency shift represents blood flow direction. CW(Continuous-Wave) Doppler System uses quadrature detection and phase rotation method to produce simultaneous independent audio and velocity signals for forward and reverse blood flow direction in the time-domain, had been fabricated. But time-domain analyzing such as audio evaluation and zero- crossing detection for instantaneous and mean frequnecy measurement do not provide both an accurate and quantitative result. Therefore, it is necessary to adopt frequency-domain technique to improve system performance. In this paper, we describe a unit which is composed of CW Doppler System and real-time spectrum analyzer (installed TMS 32010 DSP Chip). This unit shows time-dependent spectrum variation and mean velocity of Blood signal.

  • PDF