Kyung-Jo Park

Characterization of Pipe Defects in Torsional Guided Waves Using Chirplet Transform

ABSTRACT The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet trans-form, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and to estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. The reflection co-efficients are calculated using the modal energies of the separated mode. Results from experimental results on a carbon steel pipe are presented, which show that the accurate and quantitative defect characterization could become enabled using the proposed technique. * 1. 서 론 반사계수는 배관에 존재하는 결함을 정량적으로 특성화 할 수 있는 개념으로 현재 배관 유도파검사에 널리 사용되고 있는 방법이다. 관련된 주제에 대한 연구도 실험적 방법이나 유한요소 방법 모두 활발히 진행되고 있다. 일례로 Alleyne 등

Mode Separation in Torsional Guided Waves Using Chirplet Transform

ABSTRACT The sensor configuration of the magnetostrictive guided wave system can be described as a single continuous transducing element which makes it difficult to separate the individual modes from the reflected signal. In this work we develop the mode decomposition technique employing chirplet trans-form based on the maximum likelihood estimation, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor, and estimate the time-frequency centers and individual energies of the reflection, which would be used to locate and characterize defects. Simulation results on a carbon steel pipe are presented, which show the ac-curate mode separation and more discernible time-frequency representation could become enabled us-ing the proposed technique. * 1. 서 론 초음속 유도파(ultrasonic guided waves)는 현재 비파괴검사의 중요한 수단으로 자리 잡게 되었으며, 많은 기술적 진보에 힘입어 석유화학, 철강 산업에 쓰이는 배관 검사에 자주 이용되고 있다 (1) . 유도파 시험에는 종파(longitudinal wave)나 비틀림 모드(torsional mode)와 같은 축대칭 모드를 배관에 인가하는데, 종파 가진을 위해서는 다채널 시간지연 기능을 갖는 신호변환기 배열(transducer array)

Sludge Detection Inside Pipes Using Torsional Guided Waves

A new method is presented that uses guided wave techniques for sludge and blockages detection in long-range pipelines. Existing techniques have the limitations that the sludge position needs to be known a priori and the area to be inspected needs to be accessible. Two guided wave techniques have been developed which allow the sludge or blockages to be detected remotely without the need to access the specific location where the pipe is blocked, nor to open the pipe. The first technique measures the reflection of guided waves by sludge which can be used to accurately locate the blocked region; the second technique detects sludge by revealing the changes to the transmitted guid- ed waves propagating in the blocked region or after it. The two techniques complement each other and their combination leads to a reliable sludge or blockage detection. Various types of realistic sludge have been considered in the study and the practical capabilities of the two techniques have been demonstrated.

Identification of the Shear Velocities of Near Surface Soils Using Torsional Guided Waves

A technique is presented that uses a circular waveguide for the measurement of the bulk shear(S-wave) velocities of unconsolidated, saturated media, with particular application to near surface soils. The technique requires the measurement of the attenuation characteristics of the fumdamental T(0,1) mode that propagates along an embedded pipe, from which the acoustic properties of the surrounding medium are inferred. From the dispersion curve analysis, the feasibility of using T(0,1) mode which is non-dispersive and have constant attenuation over all frequency range is discussed. The principles behind the technique are discussed and the results of an experimental laboratory validation are presented. The experimental data are best fitted for the different depths of wetted sand and the shear velocities as a function of depths are formulated using power law curves.

Characterization of Axial Defects in Pipeline Using Torsional Guided Wave

ABSTRACT In this work we use the mode decomposition technique employing chirplet transform, which is able to separate the individual modes from dispersive and multimodal waveform measured with the magnetostrictive sensor. The mode decomposition technique is also used to estimate the time-fre-quency centers and individual energies of the reflection, which would be used to locate and charac-terize axial defects. The arrival times of the separated modes are calculated and the axial defect lengths can be evaluated by using the estimated arrival time. Results from an experiment on a car-bon steel pipe are presented and it is shown that the accurate and quantitative defect characterization could become enabled using the proposed technique. * 1. 서 론 유도파(guided waves)는 현재 비파괴검사의 중요한 수단으로 자리 잡게 되었으며, 많은 기술적 진보에 힘입어 석유화학, 철강, 발전설비에 쓰이는 배관의 검사에 자주 이용되고 있다 (1∼4) . 그러나 결함을 발견해도 그 크기를 정량적으로 평가하거나 이로 인한 배관의 위험성을 파악하는 것은 아직도 많은 연구가 필요한 분야라고 할 수 있는데, 그 이유는 결함에서 반사된 신호는 여러 신호들이 혼재되어 존재하는 매우 복잡한 양상을 갖기 때문이다

Free Vibrations of Cylindrical Shells on Inclined Partial Elastic Foundation

The free vibration characteristics of cylindrical shells on inclined partial elastic foundations are investigated by an analytical method. The cylindrical shell is partially surrounded by the elastic foundations, these are represented by the Winkler or Pasternak model. The area of elastic foundation is not uniform and varies along the axial direction of the shell. The motion of shell is represented by first-order shear deformation theory(FSDT) to account for rotary inertia and transverse shear strains. The governing equation is obtained using the Rayleigh-Ritz method and a variation approach. To validate the present method, the numerical example is presented and compared with the present FEA results. The numerical results reveal that the elastic foundation has significant effect on vibration characteristics.

Transient Response Analysis of Trapezoidal Corrugated Plates with Stiffeners

In this paper, the transient response analysis of the trapezoidal corrugated plate subjected to the pulse load is investigated by the theoretical method. Three types of pulse loads are considered: step- ped, isosceles triangular and right triangular pulse loads. The corrugated plates can be represented as an orthotropic plate. Both the effective extensional and flexural stiffness of this equivalent orthotropic plate are considered in the analysis. The plate is stiffened by concentric stiffeners perpendicular to the corrugation direction. The stiffening effect is represented by the discrete stiffener theory. This theoretical results are validated by those obtained from 3D finite element analysis based on shell elements. Some numerical results are presented to check the effect of the geometric properties.

Experimental Verification and Analysis for Ability of Defect Detection with Angle for Axis Direction of Guided Wave Using Magnetostrictive Sensor

In this paper we induced it by using disperse which is wave analysis program developed by Imperial College of United Kingdom. In this paper we sent and received longitudinal mode and torisional mode of guided wave using magnetostrictive sensor for test plate of mock-up with artificial defect of 90°, 75° 60° for axis direction of pipe. We review each characteristics of each mode compare with Vpp along with angle for axis direction of received defect signal.

Design of Self Magnetization MsS Sensor Using Crossed Coils

This paper propose a advanced technique for exciting and receiving the guided torsional wave to detect flaws in pipe systems. There are some difficulties in selecting and exciting of modes by using the nickel strip attached on pipe systems, such as qualification of residual magnetic field and multi-exciting of the unwanted modes etc. In order to there difficulties we propose the new sensor, so called Crossed-coils sensor. We will prove that it is possible to select the modes to be excited and to find a optimal excitation condition for torsional mode by using the proposed sensor.