• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.8
• /
• pp.957-964
• /
• 2011

This investigation presents a finite element method to obtain the transmission properties of bulk elastic waves in piezoelectric band gap structures(phonon crystals) for varying frequencies and modes. To this end, periodic boundary conditions are imposed on a three-dimensional model while both in-plane and out-of-plane modes are included. In particular, the mode decoupling characteristics between in-plane and out-of-plane modes are identified for each electric poling direction and the results are incorporated in the finite element modeling. Through numerical simulations, the proposed modeling method was found to be a useful, effective one for analyzing the wave characteristics of various types of piezoelectric phononic band gap structures.

• Economic and Environmental Geology
• /
• v.23 no.4
• /
• pp.393-409
• /
• 1990

Synthetic seismograms and deduced characteristic properties of the non-geometrical $S^*$ and $P^*$ waves are presented. These waves are excited on the free surface or an interface between two different media by an inhomogeneous P wave from a point source nearby, and propagate as homogeneous waves in the media. Synthetic seismograms are computed using an extended reflectivity method designed for buried source and receiver. An efficient computational procedure for propagator matrices of layers is devised to reduce the computational time and the RAM memory size in the implementation of the reflectivity method. Radiation patterns are obtained from the particle motions of the four types of the "*" waves, i.e., the $S^*$ wave generated near the free surface, and the reflected $S^*$, transmitted $S^*$ and transmitted $P^*$ waves generated near an interface. Some patterns show polarity changes of displacements and others reveal monotonic or non-monotonic variation of amplitude depending on the velocity structure. The decaying trend of amplitude with increasing epicentral distance are also shown for the head wave type of the "*" waves.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.23 no.2
• /
• pp.167-175
• /
• 2013

The wave propagation characteristics of an acoustic metamaterial composed of periodically repeated one-dimensional Helmholtz resonator array was investigated considering the effects of dimensional changes of the resonator geometry on the transmission coefficient and band gap. The effective impedance and transmission coefficient of the acoustic metamaterials are obtained based on the acoustic transmission line method. The designed acoustic metamaterials exhibit band gaps and negative bulk modulus that are non-existent properties in the nature. The band gap of the acoustic metamaterial is strongly dependent on the geometry parameters of Helmholtz resonators and lattice spacing. Also, a new type of metamaterial that is periodically constructed with two different resonators was designed to open the local resonance band gap without change of Bragg scattering.

• The Journal of the Acoustical Society of Korea
• /
• v.31 no.3
• /
• pp.142-150
• /
• 2012

The waveguide finite element (WFE) method is a useful numerical technique to investigate wave propagation along waveguide structures which have uniform cross-sections along the length direction ('x' direction). In the present paper, the vibration and radiated noise of the submerged pipe with fluid is investigated numerically by coupling waveguide finite elements and wavenumber boundary elements. The pipe and internal fluid are modelled with waveguide finite elements and the external fluid with wavenumber boundary elements which are fully coupled. In order to examine this model, the point mobility, dispersion curves and radiated power are calculated and compared for several different coupling conditions between the pipe and internal/external fluids.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.6
• /
• pp.763-773
• /
• 2004

This paper suggests the 2 D.O.F mathematical model of the High Frequency Vibro-Hammer (HFVH), introduces an experimental method for measuring of the attenuation of piling vibration and proves what experiments are coincident with the equation of wave propagation. As vibratory installation of piles and casings has many economic merits in the construction field, most of all contractors prefer to vibratory pile driving method than the other. Compared to impact pile driving, vibratory installation has the advantage of reducing vibration or noise pollution and can drive piles under high frequency. Experiments serve estimations of capabilities and limitations of the HFVH's excitation force and finding of sensitivity for important soil resistance parameters. Also, we discuss the HFVH that can drive with three kinds of input waves (triangular, sine and square wave) and propose the design of parameters to improve actuating performance in it.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.6
• /
• pp.605-611
• /
• 2010

The geostationary satellite COMS is going to be launched in 2010, and, in the series of test, there are some high-pressure tests concerning the vessel tank filled with helium gas of hundreds atmospheric pressure. In this paper, authors evaluates risk associated with accidental rupture of the test system. Two possible scenarios are considered: 1) the 310-bar helium tank ruptures at the center of the acoustic chamber, and 2) the 116-bar reduced-pressure helium tank ruptures in the test room shielded by bullet-proof glasses. Using the theory of blast wave propagation and computational simulation, the dynamics of wave reflected in a confined space is investigated for highly complex unsteady flow physics.

• Atmosphere
• /
• v.20 no.4
• /
• pp.505-518
• /
• 2010

We investigated the impacts of the diabatic heating location, vertical profile and basic state on the Rossby wave propagation. To examine the dynamical process of individual responses on the regional heat source, a dry version of the linear baroclinic model was used with climatological summertime (JJA) mean basic state and vertical structure of the diabatic heating for 1979-2008. Two sets of diabatic heating were constructed of those positioned in the mid-latitudes (Tibetan Plateau, eastern Mediterranean Sea, and the west-central Asia) and the tropics (the southern India, Bay of Bengal, and western Pacific). It was found that using the principal component analysis, atmospheric response to diabatic heating reaches to the steady state in 19th days in time. The prescribed mid-latitude forcing forms equivalent barotropic Rossby wave propagation along the westerly Asia jets, whereas the tropical forcing generates the Rossby wave train extending from the tropics to mid-latitudes. In relation to the maximum vertical profile, the mid-level forcing reveals a stronger response than the lower-level forcing, which may be caused by more effective Rossby wave response by the upper-level divergent flow. Under the different sub-seasonal mean state, both of the tropical and mid-latitude forcing induce the different sub-seasonal response intensity, due to the different basic-state wind.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.17 no.1
• /
• pp.1-8
• /
• 2005

For the simulation of tsunami propagation an active dispersion-correction two-dimensional finite element model has been developed based on a shallow-water wave equation. This model employs an arbitrary triangular mesh and an explicit time integration scheme. However, the physical dispersion effects as included in the Boussinesq equations can be taken into account in the computation. The validity of the dispersion-correction scheme developed in this study is verified through the comparison of numerical solutions calculated using the new scheme with analytical ones considering dispersion effect of waves. As a result, the present model is shown to be considerably accurate.

• Journal of the korean veterinary medical association
• /
• v.32 no.5
• /
• pp.285-316
• /
• 1996

소 해면형 뇌증(Bovine Spongiform Encephalpathy; BSE)이 처음 확인된 것은 1986년 11월이며, 영국에서의 최초발생을 시작으로 하여, 지난 10여년 동안 발생국가의 수는 다소 증가하고 있지만 전체적인 발생두수는 1993년을 정점으로하여 감소하는 추세를 보이고 있다. 아직까지도 확실한 병인체는 밝혀져 있지 않은 상태이며, 최초 확인당시 인체에의 감염 가능성은 없는 것으로 발표된 바 있으나, 지난 1996년 3월 20일, 영국정부 보건장관이 영구하원에서, 소 해면형 뇌증이 사람의 희귀한 뇌 질환인 크로이츠휄트-야곱병(CJD)의 새로운 스트레인(v-CJD)과 관련성이 있을 수 있다고 보고한 다음날, CNN 등 세계 각 매스컴을 통하여, '광우병 사람에게 전파될지도$\cdots$'(Mad cow illness may threaten humans)라는 제목으로 Top News로 보도되었으며, 수의학이나 의학적인 사실 확인의 여부를 떠나, 사회 경제적인 문제로 큰 놀라움과 많은 의문사항을 남겨둔 채, 국제적인 문제로 확대된 바있다. 본 편에서는, 소 해면형 뇌증 (BSE)과 관련, 영국의 광우병 파동이 일어난 지난 3월부터 지금까지 국내외 매스컴에 보도된 내용중 주요사항들을 스크랩하여 참고자료로 제공하고자 한다. 자료중에는 중복기사나 추측기사, 검증되지 아니한 오보, 지극히 개인적인 견해 등도 있을 수 있으며, 외신보도의 접수시간, 국내보도의 조간-석간, 지면구성, 수도권판과 지방판 등, 그리고 특히 병명이나 고유명사, 외래어 등의 전문용어 표기에 있어서 꼭 일치하지 아니하는 경우가 있을 수 있음을 참고로 하여야할 것이다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.10a
• /
• pp.221-226
• /
• 1995

터빈 익렬, 펌프 익차, 원형 냉각탑, 치차 등과 같이 동일한 형상이 원주 방향으로 반복되어 있는 순환 대칭 구조물의 진동특성을 유한 요소법을 사용하여 해석하는 경우에 전체구조를 모델링하는 대신에 구조물을 동일한 형상의 부분구조로 분할하여 부분구조 한개만을 모델링하고 분할된 경계에서 적절한 경계조건을 부과하여 진동해석을 수행함으로서 컴퓨터 기억용량을 절감시키고 계산시간을 단축할 수 있는 방법이 널리 사용되고 있다. Orris and Petyt[1]는 부분구조의 양쪽 분할 경계면, 즉 연결 경계상에 있는 절점변위의 상관관계를 복소파동전파식을 이용해서 구하여 부분구조의 감소된 복소강성행렬 및 질량행렬을 만들고 실수부와 허수부를 분리하여 유한요소해석을 수행하는 방법을 제안하였다. 유한요소 프로그램 ANSYS[2]에서는 이와 같은 방법을 사용하고 있다. Thomas[3]는 순회 정규모드를 이용하였고, 참고문헌[4]에서는 순회행렬을 이용하였다. 또한 유한요소 프로그램 MSC/NASTRAN[5]에서는 푸리에 급수를 이용하고 유한요소 절점의 위치 및 변위를 원통 좌표계를 표현하여 순환대칭구조물의 유한요소해석을 수행할 수 있도록 되어있다. 본 논문에서는 순환 대칭구조물의 형상의 주기성과 순환성을 고려하여 이산퓨리에 변환을 이용함으로써 순환대칭구조물의 유한요소진동해석을 체계적으로 저용량의 컴퓨터에서 신속하고 정확하게 수행할 수 있는 방법을 제안하고자 한다.