• Journal of KSNVE
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• v.8 no.5
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• pp.974-980
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• 1998

The analysis of dynamic responses are carried out on several orthotropic systems due to transient line source. These include infinite and semi-infinite spaces. The media possess orthotropic or higher symmetry. The lode is in the form of a normal stress acting with parallel to symmetry axis on the plane of symmetry within the materials. The results are first derived for responses of infinite media due to a harmonic line source. Subsequently the results for semi-infinite are derived by using superposition of the solution in the infinite medium together with a scattered solution from the boundaries. The sum of both solutions has to satisfy stress free boundary conditions thereby leading to the complete solutions. Explicit splutions for the displacements due to transient line loads are then obtaind by using Cargniard-DeHoop contour.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.3
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• pp.282-290
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• 2013

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 guided 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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.311-318
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• 2021

Underwater, signals are transmitted by sound waves. Sound waves are transmitted through a multipath, either directly or through reflection, due to the variety of underwater environmental characteristics. In such diverse and complex underwater environments, tests must be conducted to determine the extent of the hazard from the survivability and pitfalls of submarines by measuring the underwater radiated noise. Usually, the sound source level measurement of underwater radiated noise should be made within the closest point (CPA: Closest Point of Approach) ± a few meters between the measurement sensor and the submarine. In this study, FDOA and TDOA methods were proposed to estimate the underwater source range. A simulation based on the underwater channel model confirmed the performance of the proposed method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.7
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• pp.586-603
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• 2004

One of the subtle problems that make noise control difficult for engineers is “the invisibility of noise or sound.” The visual image of noise often helps to determine an appropriate means for noise control. There have been many attempts to fulfill this rather challenging objective. Theoretical or numerical means to visualize the sound field have been attempted and as a result, a great deal of progress has been accomplished, for example in the field of visualization of turbulent noise. However, most of the numerical methods are not quite ready to be applied practically to noise control issues. In the meantime, fast progress has made it possible instrumentally by using multiple microphones and fast signal processing systems, although these systems are not perfect but are useful. The state of the art system is recently available but still has many problematic issues : for example, how we can implement the visualized noise field. The constructed noise or sound picture always consists of bias and random errors, and consequently it is often difficult to determine the origin of the noise and the spatial shape of noise, as highlighted in the title. The first part of this paper introduces a brief history, which is associated with “sound visualization,” from Leonardo da Vinci's famous drawing on vortex street (Fig. 1) to modern acoustic holography and what has been accomplished by a line or surface array. The second part introduces the difficulties and the recent studies. These include de-Dopplerization and do-reverberation methods. The former is essential for visualizing a moving noise source, such as cars or trains. The latter relates to what produces noise in a room or closed space. Another mar issue associated this sound/noise visualization is whether or not Ivecan distinguish mutual dependence of noise in space : for example, we are asked to answer the question, “Can we see two birds singing or one bird with two beaks?"

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1993.10a
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• pp.38-43
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• 1993

현재의 오피스는 공간이 좁고, 바닥위의 배선이 장애물이며, 형광전구가 노출된 조명으로 실내 작업환경에 대한 고려가 매우 미약한 점에 의심할 여지가 없다고 생각된다. 특히 OA기기의 도입에 따른 집무 공간의 감소, 프린터 소음, 기기의 발생열, 배선, VDT(Visual Display Terminal:화면이 있는 OA기기) 작업과 관련된 환경 관리, 작업관리, 건강관리의 필요성등의 문제가 발생하고 있다. 그러므로 쾌적한 분위기를 구성요소로 조명은 실의 LAY OUT, 표면처리, 배색등 인테리어 디자인과 함께 그 효과를 최대한으로 연출하도록 되리라 생각된다. 따라서, 자연채광 이용을 통하여 절감될 수 있는 인공조명(형광등)의 제어방법으로서 본 논문에서는 점멸방식(ON,OFF)을 시도하였으며 점멸에 따른 급격한 조도저하를 보다 심리적인 차원을 고려한 실내조명 조광장치(천정형태와 외부에 댄 반사판)로 인한 실내조도 분포의 영향에 대하여 파악하고자 하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.1
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• pp.1-9
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• 2017

In this study, a test-bed system simulated a tunnel and concrete track is tested on cite and invested an allowed limit of multi-layered sound absorbing panel for reducing noise reflected on the concrete track in train tunnel considering the criteria and limitation on the theoretical back ground. The studied results are an effective evaluating system of the sound absorbing coefficient influenced fluid effects depending on the vehicle speed in the urban train tunnel and measuring not only structural behaviors of maximum displacement and acceleration of the panel but also dynamic characteristics of damping ratio and natural frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.104-110
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• 1995

지반과 구조물의 동적 상호작용은 건설분야에서의 중요한 현상으로, 특히 지반을 통해 인근구조물로 전달되는 진동은 구조물 자체의 구조적인 문제 뿐 아니라 그 속에 거주하는 사람이나 설비에 대한 안전성 또는 사용성에 나쁜 영향을 야기할 수 있다. 본 논문에서는 이러한 진동을 저감시키기 위해, 지반내에 정상적인 진동전파를 방해하는 구조물을 시공하여 진동 저감효과를 만들어 내는 방법을 연구하였다. 이러한 연구의 발상은 다음과 같다. 충진지반에서의 지반진동의 진폭을 해석하면서 진동의 크기가 기저암의 위치에 따라 큰 영향을 받는 것을 알았고 이로부터 지반내에 인위적인 층을 만들수 있다면 지반진동의 크기를 변화시킬 수 있지 않을까라는 생각에서 본 연구를 시작하였다. 또한 지반 내에서의 정상적인 진동의 전파를 방해하기 위한 차진 구조물을 만드는 방법은 연약지반의 강도중대 또는 차수의 목적으로 주로 사용하고 있는 그라우팅공법의 사용이 가능할 것이므로, 기존의 그라우팅현장에서 만들어진 지반의 물성치들을 사용하여 경계요소법에 의한 수치해석적 방법을 택하였다. 본 연구에서는 그라우팅공법의 시공성에 관한 것은 포함되지 않는다. 본 논문에서는 지반의 구조를 경사구조와 수평지반구조라는 두가지 특징적인 경우에 대해 검토하였다. 이중 경사진 기저암층을 가진 지반의 경우에는 기저암에서 진동의 비대칭적인 반사에 의해 수평기저암에서와는 달리 기저암의 한쪽에서 다른쪽에 비해 큰 진동이 발생한다. 그라우팅층의 효과를 검토하기 위한 연구의 순서는 일정주파수의 조화진동에 대해 먼저 여러 가지 크기의 그라우팅층과 함께 블록으로 볼 수 있는 크기의 그라우팅층에 대해 진동저감효과를 해석하였고, 이를 통해 보강층의 소요크기 및 최적위치를 구하였다. 사용된 물성치는 실제 지하철 건설현장에서 나타난 지반물성치 및 그라우팅후의 지반강도 및 전단파전파속도를 이용하였다. 또한 마지막에서 검토된 기차하중에 대한 효과를 알아보기 위해 사용된 기차운행에 의한 지반가속도도 역시 측정된 값을 사용하였다. 그러나 당시의 기차운행속도가 낮아 정상적인 운행에서는 더 큰 값이 나올 것으로 판단되었으나 측정된 값을 그대로 사용하였다.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.349-354
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• 2001

The present study addresses the open end correction associated with the reflection and discharge phenomena of a weak shock wave from an open end of a duct. The open end correction of the weak shock wave is investigated experimentally and by numerical computation. An experiment is made using a simple shock tube with an open end, and computation is performed to simulate the experimental flow field using the unsteady, axisymmetric, compressible, flow governing equations. The results obtained show that an open end correction should be involved for shock wave discharge and reflection problems generated from the exit of the duct with an open end baffle plate. With a baffle plate less than three times the duct diameter, it is found that the open end correction is a function of both the diameter of the baffle plate and normal shock wave magnitude. However, for a baffle plate larger than three times the duct diameter, it is independent of the baffle plate diameter. The present computations predict the results of shock tube experiment with good accuracy. A new empirical equation for prediction of the open end correction is found for the weak shock reflection and discharge phenomena occurring at the open end of the duct with and without a baffle plate.

• The Journal of the Acoustical Society of Korea
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• v.32 no.3
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• pp.237-246
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• 2013

This paper proposes a hydrophone array design optimization technique for cavitation tunnel noise measurements. The optimization technique comprises of design parameters, an objective function and an optimization algorithm. The design parameters are defined for circular, spiral and multi-spiral arrays. The objective function is defined so as to consider the mainlobe beamwidth and the maximum sidelobe level simultaneously. A global optimization scheme is applied to the array design using very fast simulated reannealing (VFSR). After applying the optimization technique to arrays respectively, the peak sidelobe level and the mainlobe beamwidth of optimum arrays are analyzed. Finally the array patterns considering multiple reflections in the cavitation tunnel are evaluated to validate the proposed method.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.3
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• pp.1-6
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• 2003

It is difficult to detect and to track the moving targets like tanks and diesel vehicles due to the variety of terrain and moving of targets. It is possible to be happened the aliasing conditions as the difficulty of antenna deployment in the complex environment like the battle fields. In this paper, we study the problem of detecting and tracking of moving targets which are emitting wideband signals under severe spatial aliasing conditions because of the sparse arrays. We developed a direction of arrival(DOA) estimation algorithm based on subband MUSIC(Multiple Signal Classification) method which produces high-resolution estimation. In this algorithm, the true bearings are invariant regardless of changes of frequency bands while the aliased false bearings vary. As a result, the proposed algorithm overcomes the aliasing effects and improves the localization performance in sparse passive arrays.