• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1994년도 추계학술대회논문집; 한국종합전시장, 18 Nov. 1994
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• pp.323-330
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• 1994

본 연구에서는 다공질 흡음재료 중 closed cell 구조를 갖는 발포수지재료(Foamed Material)에 음(sound)이 입사할 때 발생하는 흡음현상을 보다 정확히 예측하기 위해서 다공질 흡음재료에 대한 Biot 이론에 근거한 Allard의 모델링기법[4]을 이용하여 해석 프로그램을 개발하였고, 이를 이용하여 다공질 흡음재료가 단층(single layer)일 때 이 재료의 Surface Impedance와 흡음률(Absorption Coefficient)을 예측하고, 물성치(parameters)변화에 따른 다공질 흡음재료의 흡음특성을 분석하였으며, 이 재료가 자동차 제조시 사용되는 압연강판(rolled steel piate)에 부착되었을 때의 투과손실(Transmission Loss)을 예측하였고, 또한 다공질 흡음재료는 중고주파 대역의 음에 대한 흡음특성은 좋지만 저주파 대역의 음에 대한 흡음특성은 좋지 않으므로 흡음 재료의 저주파 대역의 흡음특성을 향상시키기 위해서 2층(two layers)으로 하였을 때의 흡음특성을 분석하였다. 본 논문의 연구결과는 자동차 제조시 사용되어지는 다공질 흡음재료는 물론 산업용기계나 건축용등 여러 분야에서 사용되어지는 다공질 흡음재료의 흡음특성 분석에 응용될 수 있으리라 기대된다.

• 전자공학회논문지
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• 제50권2호
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• pp.54-59
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• 2013

이중대역에서 동작하는 브랜치 라인 커플러를 나타낸다. 새로운 설계 구조에서는 단락 스터브가 병렬로 추가된 전송선로가 2개의 주파수에서 $90^{\circ}$의 위상 천이를 구현하기 위하여 사용된다. 제안하는 브랜치 라인의 특성 임피던스와 전기적 길이는 종래의 구조와 비교하여 조정된다. ABCD 행렬 파라미터를 이용하여 설계 방정식을 유도하였다. 설계 개념을 검증하기 위하여 0.8 GHz 및 1.85 GHz에서 동작하는 마이크로스트립 커플러를 제작하고 측정하였다.

• 한국통신학회논문지
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• 제18권1호
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• pp.143-149
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• 1993

An approach is presented for efficient numerical integration of the Sormnerfeld type integrals pertinent to the microstrip surface Green's function arising in the problem of an electric current point source on an infinite planar grounded dielectric substrate. This approach, valid for both lossless and lossy dielectric substrates, is based on the deformation of the integration contour via a coordinate transformation and Cauchy's residue theory, and identifies clearly the effects of surface waves. I ts useful application is in a rigorous moment method analysis of micros trip antenna arrays and microstrip guided wave structures. The efficiency and the usefulness of the present approach are emphasized through some numerical calculations of the impedance matrix elements with associated CPU times.

• 소음진동
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• 제6권6호
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• pp.717-726
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• 1996

In this report, the underwater sound radiation from finite cylindrical shell with stiffeners which is the basic configuration of submerged vehicle is studied analytically and experimentally. The shell vibrations are obtained by using the shell theory of Sanders-Koitter. The stiffeners and modeled for I-type and the stiffness matrices are obtained by using beam model. In the analytical stuides, the vibrations of cylindrical shell are expressed by using cosine series expansions to consider the arbitrary end boundary conditions. It is agree to the theoretical and experimental results well.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.770-773
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• 2004

The transmission loss coefficient is very important acoustic property in parallel with absorption and acoustic impedance categorizing the acoustical materials, which can control the acoustical problems. At the same time, the transmission loss coefficient is a key parameter to choose the optimum material for the analysis of acoustical characteristics of material using SEA(Statistical Energy Analysis). In this paper, the acoustic transmission loss measurement system using 4-microphone TL tube is applied to the exhaust system, which is one of the most important acoustic control parameters in a car, based on the idea calculating the full transfer matrix. The theoretical background and measurement system are introduced, and finally the measurement results are verified.

• 한국정밀공학회지
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• 제12권2호
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• pp.69-78
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• 1995

Nonlinear analysis methods are developed which will enable the reliable prediction of the dynamic behavior of the space shuttle main engine(SSME) turbopumps in the presence of bearing clearances and other local nonlinearities. A computationally efficient convolution method, based on discretized Duhamel and transition matrix integral formulations, is developed for the transient analysis. In the formulation, the coupling forces due to the onlinearities are treated as external forces acting on the coupled subsystems. Iteration is utilized to determine their magnitudes at each time increament. The method is applied to a nonlinear generic model of the high pressure oxygen turthods, the convolution approach proved to be more accurate and highly more efficient. For determining the nonlinear, steady-state periodic responses, an incremental harmonic balance(IHB) method was also developed. The method was successfully used to determine dominantly harmonic and subharmonic(subsynchronous) responses of the HPOTP generic model with bearing clearances. A reduction method similar to the impedance formulation utilized with linear systems is used to reduce the housing-totor models to their coordinates at the bearing clearances.

• 대한자원환경지질학회:학술대회논문집
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• 대한자원환경지질학회 2002년도 춘계 공동학술발표회
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• pp.163-166
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• 2002

Initial velocity model close to real velocity structure of the subsurface governs the quality of image of prestack depth migration. Geophysicists employ velocity estimation tools such as velocity analysis (curvature method, coherency inversion), tomography and waveform inversion. We present a reflection tomography that parameterizes the subsurface into the movable blocks. By interpreting the depth-migrated section or stacked section, we can design an initial constant velocity model having only impedance boundaries. We use shooting-raytracing method that allows us to calculate the Jacobian-matrix efficiently.

• 한국통신학회논문지
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• 제21권3호
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• pp.753-762
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• 1996

In this paper, aperture coupled stacked microstrip array antennas are proposed and their operating characteristics are analyzed based on analytical. In order to evaluate mutual coupling between slot-coupled microstrip patches in finite array, analysis uses the reciprocity theorem and the spectral domain Green's functions for dielectric slab in a moment method solution for the unknown patches and solts current distrbution. By introducing an N-port equivalent network, the impedance matrix of an affay of N-element slot-coupled patches is evaluated directly from its network current matix of order N$^{2}$, and it can be programmed to be run on a PC. Numerical results show mutual coupling, radiation pattern, active reflection coefficient versus scan angle, radiation efficiency and active element gain pattern.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.317-324
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• 1999

Dynamic interaction analysis of surface structure on layered half-space is performed in frequency domain under incident wave excitation. This present study adopts a coupling method that combines the finite element(FE) for the flexible structures and boundary element(BE) for the layered half-space. A semi-analytical approach is employed to reduce the integration range of wavenumbers in the BE formula. For the incident wave input, the response is decomposed and formulated after the impedance matrix for the structure system. Numerical examples are presented to demonstrate the accuracy of the method. The examples show the feasibility of an extended application to the complicated dynamic analysis of structures on layered media under incident wave excitation.

• 한국통신학회논문지
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• 제21권10호
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• pp.2703-2709
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• 1996

This paper proposes an exact numerical method for analyzing a dipole antenna attached on a dielectric slab. A Green's function for an infinitesimal current filament on a dielectric slab is derived and a field integral equation is formulated using a boundary condition. The moment Method is used to solve the field integral equation to otain current distribution on the antenna. Since an asymptotic function is used to compute the impedance matrix elements, the computataion time is significantly reduced. Using the computed current distributions, the input impedances, the resonance lengths and the resonant resistances of the antennas for various values of the thichnessandthe dielectric constant of the slab are obtained. It was found that the resonant length and the resonant resistance are decrease monotonically as the dielectric constant increases, however, those are changed up-and-down as the substrate thickness increases.