• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.367-373
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• 2011

Guided waves inspection techniques that are different with inspection technique by bulk waves are widely used in pipe line evaluation due to advantages of long distance inspection. However, most of pipe lines at industrial fields are buried and/or coated. In this case, due to the attenuation effect from soil and/or coating material, there are a lot of difficulty on inspection by conventional ultrasonic technique. In this paper, guided waves propagating patterns are calculated with respect to excitation mode by Normal Mode Expansion(NME). Guided waves patterns based on excited by single transducer and guided wave focusing technique have employed to analyze focusing pattern on a pipe. A longitudinal mode and high order flexural modes are used with various number of transducers to determine sensitivity. Guided waves energy excited by multi transducer with focusing algorithm was successfully focused at a desired point.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.3
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• pp.238-245
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• 2000

유도초음파를 이용하면 배관 및 박판과 같은 파유도체에 대한 광범위한 비파괴탐상을 할 수 있게되어 시간과 경비를 절약할 수 있는 장점이 있다. 그래서 유도초음파를 이해하고 활용하기 위한 연구가 활발히 진행되고 있다. 유도초음파가 기존의 체적 초음파와 크게 다른 점은 분산성있어 초음파의 전파속도가 진동수와 파유도체의 두께에 의존한다는 것과 전파 특성이 다른 무한개의 모드가 존재한다는 것이다. 본 논문에서는 박판과 배관에서의 유도초음파를 이해하고 비파괴탐상에 적용하기 위해 필요한 모드의 분산과 선택 그리고 확인에 대해 이론적인 결과와 및 실험적인 예를 제시하여 그 개념을 소개하였다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.10a
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• pp.590-593
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• 2012

There are a few formula for calculation of propagation constant of buried pipeline. These formula are basically based on the Wait's analytical expressions. Each transformed expression is from America and Japan. And also a propagation constant calculated by a developed bidirectional search algorithm for an application to an exact solution of underground fields represented. This solution is presented by Bridge's article. So several methods are used and values by them are compared whether they are appropriate to estimate an induction voltage. Japan's formula and exact solution are similar to apply for calculation of propagation constant.

• 전기의세계
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• v.20 no.4
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• pp.37-43
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• 1971

전파전송개념은 기본회로 소자인 인덕터와 커패시터의 이해에 입각하여 보다 쉽게 파악할 수 있다. 송전선은 전화신호와 전력을 한 곳에서 다른곳으로 전도하며, 이러한 전도성이 고주파 신호에 대해서는 존재하지 않지만 전파에의 초보로서 두 평행도체 사이의 전파전송을 이용하는 것이 설명에 쉽다. 전송선은 단위길이마다 커패시턴스 C와 인덕턴스 L을 가지므로, 전송선 방정식을 유도하려면 회로소자 인덕터와 커패시터의 기본성질을 알아야 한다 .

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.103-109
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• 2005

Fiber reinforced plastic material should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic techniques, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Laser-based ultrasonic technique was tried to evaluate CFRP plate. Laser-based ultrasonic waves propagated on CFRP were received with various transducers such as accelerometer and AE sensor in order to evaluate the properties of waves due to the variation of frequency. Velocities of laser-based ultrasonic waves were evaluated for various fiber orientation. In addition, laser interferometry was used to receive ultrasonic wave in CFRP and frequency was analysed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37C no.12
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• pp.1211-1221
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• 2012

This paper describes separation distance to protect radiocommunication services from the interference of inductive systems using frequencies below 30 MHz for the co-existence between radiocommunication services and inductive systems. For the analysis, the interference scenario model is proposed between inductive system and radiocommunication services. Then the calculation method of protection distance is suggested by comparing the radiation power of inductive system with the allowable interference level of victim services, radiocommunication services, according to the applied propagation model. Also, the protection distance for protecting radiocommunication services in the 30 MHz below is calculated through the interference analysis from RFID(Radio Frequency IDentification) and PDP(Plasma Display Panel) TV based on the suggested method. The proposed calculation method was adopted as ITU-R recommendation in related with resolution 63 at ITU-R SG(Study Group) 1 meeting in June, 2012. It will be available to use for the protection of radiocommunication services from the interference of wireless power transfer system and power line telecommunication system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1257-1264
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• 2011

Guided ultrasonic waves propagating over long distances within a short period provide a fast long-range inspection method. However, structures with arbitrary cross-sections, such as rails, have complicated dispersion characteristics that make analysis of the ultrasonic signal difficult. Therefore, an understanding of the characteristics of the propagating waves in rails is important for the creation of a reliable and practical inspection system using guided waves. In particular, it is necessary to investigate the dispersion characteristics of the guided waves. This paper introduces a method for the calculation of the dispersion curves of KS60 rails by adopting a SAFE method, and discusses the possibility of using guided waves as a technique for rail inspection.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.40-41
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• 2011

동해를 전파하는 지진해일은 세계적으로 다른 지역에서 발생하는 지진해일과 비교하였을 때 상대적으로 파장이 짧고, 이에 비해 먼 거리를 전파한다. 그러므로 동해에서 발생한 지진해일의 전파에 대한 해석을 수행할 때 물리적인 분산효과가 매우 중요하다. 따라서 지배방정식으로 분산 효과가 충분히 고려된 선형 Boussinesq 방정식을 사용한다. 기존의 연구에서는 leap-frog 기법을 사용하여 선형 천수방정식을 차분할 때 발생하는 수치분산항에 분산 보정계수를 이용하여 선형 Boussinesq 방정식의 물리적 분산항과 같은 형태로 나타나도록 유도하여 수치모의를 수행하였다. 그러나 기존에 사용한 지배방정식은 수심이 일정하다는 가정을 통하여 유도된 것으로, 수심에 변화가 있는 실제 지형을 통과하는 지진해일에 대한 수치모의를 수행한 결과의 정확도에 문제가 생길 수 있다. 본 연구에서는 기존의 연구에서 발생할 수 있는 수심 변화에 따른 오류를 개선하기 위하여 바닥 지형이 1차원으로 변한다는 가정을 이용하여 지배방정식을 유도하였으며, 이로 인해 발생하는 수심 변화가 고려된 항을 기존의 분산보정기법에 추가하였다. 그리고 적용성을 높이기 위하여 수치모의 기법의 제한을 최소화하는 연구를 진행하였다. 본 연구에서 제안한 수정 기법이 수심이 변화하는 지형을 전파하는 지진해일 수치모의 과정에서 경사에 대한 분산효과가 충분히 고려되는지 확인하기 위하여 Gaussian hump를 이용한 가상 지진해일을 원형 천퇴 지형에 통과시켰다. 본 연구에서 사용한 지형을 통과하는 Gaussian hump에 대한 해석해를 구하는 방법이 존재하지 않으므로, Boussinesq 방정식을 직접 차분하여 푸는 FUNWAVE를 사용하여 동일한 조건 하에서 수치모의를 수행하였다. 비교 결과를 통하여 본 연구에서 제안한 기법의 정확도 향상을 확인하게 되면, 실제 지형을 통과하는 지진해일의 수치모의에 대한 활용성을 높일 수 있을 것이다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.2
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• pp.95-103
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• 2007

An analytical closed-form solution for wave propagation velocity and damping in saturated porous media is presented in this paper The fully coupled field model with compressible solid Brains and pore water were used to derive this solution. An engineering approach for the analysis of fully saturated porous media was adopted and closed-form solutions for one dimensional wave propagation in a homogeneous domain were derived. The solution is highly versatile in that it considers compression of the solid grains, compression of the pore water, deformation of the porous skeleton, and spatial damping and can be used to compute wavespeeds of first and second kind and damping coefficients in various geologic materials. This solution provides a means of analyzing the influence of material property variations on wavespeed and attenuation. In Part 2 of this work the theoretical solution is incorporated into the numerical code and the code is used in a parametric study on wave propagation velocity and damping.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.1
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• pp.9-16
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• 2009

In this paper, a method is proposed for the analysis of radiowave receiving characteristics of an ammunition with electric detonator. In this method, an ammunition with electric detonator is modelled as a receiving antenna with its gain obtained by computer simulation or measurement. The induced radiowave power is obtained by inserting the gain of the electric detonator in the antenna coupling formula. Radiowave receiving characteristics at very close distances are obtained by Treasuring the transmission coefficient between a half-wave dipole and the electric detonator model. Radiowave receiving characteristics of the electric detonator in a 105mm tank ammunition are obtained using the proposed method and the safety of the 900 MHz RFID reader on the detonator is assessed.