• The Journal of the Acoustical Society of Korea
• /
• v.43 no.4
• /
• pp.391-399
• /
• 2024

In order to analyze the distribution of sound fields radiating from a circular plate vibrated by a Langevin transducer, a theoretical analysis model was derived. The boundary conditions of the driving area and fixed boundary area were appropriately applied to the equation of motion of the vibrating plate, which was derived by L. Rayleigh. By calculating the vibration displacement distributed on the surface of the vibrating plate using the derived analysis model and then calculating the sound field formed by the ultrasonic waves radiating from it, it was confirmed that the radiation characteristics vary significantly depending on the area of the vibrating plate. For comparison, a simulation of the same system was performed using the COMSOL program, a finite element method, and showed good agreement with the theoretical calculation results, confirming the effectiveness of the theoretical analysis model derived in thisstudy. It is expected that the theoretical analysis model derived from this study can be used in the design and development of related devices, such as in the ultrasonic chemistry field.

• Proceedings of the Optical Society of Korea Conference
• /
• 2000.02a
• /
• pp.274-275
• /
• 2000

광결정(photonic crystal)으로 광원의 자발 방출을 조절하면 문턱전류 없는 레이저, 고효율 다이오드, 파장 크기에서 손실 없이 급격히 꺾을 수 있는 광도파로 등 기존의 광소자에서 얻을 수 없는 좋은 성능을 얻을 수 있을 것으로 예상된다. 이러한 광결정은 유전체를 파장정도 크기에서 주기적으로 배치시킨 인공적인 결정인데 고체에서 원자의 주기적인 배치로 전자가 전파할 수 없는 진동수 영역, 즉 밴드갭이 생기는 것과 유사하게 빛에 대해서 빛이 전파할 수 없는 진동수 영역인 광밴드갭(photonic bandgap)을 가진다. 그런데 관심있는 광영역에서 3차원 모든 방향으로 광밴드갭이 있는 구조물은 마이크로미터보다 작은 내부 구조를 가지는 복잡한 3차원 구조물로 제작이 어렵다. 이러한 어려움을 극복하기 위해 제작이 비교적 용이한 3차원 광밴드갭 구조물이 찾아지고 있다. 다른 접근 방법으로 평면(x-y)에서는 2차원 광밴드갭을 이용하고 제 3의 방향(z축)으로는 전반사를 이용하는 구조는 제작이 용이할 뿐만 아니라 처음부터 광원의 편광을 TE 또는 TM 모드로만 방출 되도록 준비해 줄 수 있으면 거의 3차원 광결정에서 얻을 수 있는 효과를 낼 수 있는 것으로 발표되었다.$^{(1)}$ 이 방법을 이용하여 최근에 미국의 캘리포니아 공과대학(Caltech)을 중심으로 레이저 동작을 보여 주었다.$^{(2.3)}$ 공기로 둘러싸인 얇은 유전체 평판에서 생기는 전반사와 평판 위에 2차원 삼각형살창(triangular lattice)에 구멍을 뚫어 얻는 2차원 광밴드갭을 이용해 3차원 공진모드를 형성하였다. 이러한 구조에서 1개만 구멍을 매워서 만든 공진기는 저온(143 K)에서 레이저 발진을 보였고 여러 개의 구멍을 매운 경우는 상온에서 펌프 펄스의 유지시간이 0.5% 인 경우 레이저가 동작하는 것을 보여주었다. 이는 구조내에서 열전도가 문제가 된다는 것을 의미하는데 위아래가 공기로 둘러 싸여 있어 발생한 열이 가는 유전체 네트웍을 통해서만 전달 될 수 있기 때문이다. (중략)

• The Journal of the Acoustical Society of Korea
• /
• v.35 no.4
• /
• pp.253-260
• /
• 2016

In this paper, derivation of the STL (Sound Transmission Loss) of the double plates installed in an impedance tube is discussed using an analytic method, where an air cavity exists between the plates. Vibration of the plates and sound pressure field inside the tube are expressed in terms of infinite series of modal functions. Under the plane wave assumption, it is shown that consideration of the first few modes yields sufficiently accurate results, and locations of peaks and dips are investigated. It is determined that the peak frequencies of the double plates coincide with those of each single plate. When the two plates are identical, the STL of the double plates as well as that of the single plate become zero at the natural frequencies of the single plate. The location and amplitude of the dips are investigated using an approximation solution when the cavity depth is very small.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.5
• /
• pp.282-293
• /
• 2005

Sonoelastography is an ultrasound-based technique that visualizes the elastic properties of soft tissues by measuring the tissue motion generated by an externally applied vibration. In this paper. the characteristics of wave generation in soft tissues due to an acoustic vibrator are studied. The effects of modal patterns on the detectability of lesions such as tumors in senoelastography are also investigated These are accomplished by analyzing the vibration patterns calculated using theoretical equations and finite element methods in halt space, infinite plate. and finite-sized tissue. A finite-width source generates shear waves with large amplitude Propagating in specific directions. and the generation characteristics depend both on the width and frequency of the vibrator. as well as the distance from it. It is shown in a finite-sized tissue that the lesion detection in displacement images is quit dependent on the modal patterns inside tissue. In contrast it Is also found that the lesion detectability in strain images is less dependent on the modal Patterns and is much better than that in displacement images.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.18 no.10
• /
• pp.1082-1090
• /
• 2008

In this paper, a general solution for the vibrational energy and intensity distribution through a compliant and dissipative joint between plate structures is derived on the basis of energy flow analysis (EFA). The joints are modeled by four sets of springs and dashpots to show their compliancy and dissipation in all four degrees of freedom. First, for the EFA, the power transmission and reflection coefficients for the joint on coupled plate structures connected at arbitrary angles were derived by the wave transmission approach. In numerical applications, EFA is performed using the derived coefficients for coupled plate structures under various joint properties, excitation frequencies, coupling angles, and internal loss factors. Numerical results of the vibrational energy distribution showed that the developed compliant and dissipative joint model successfully predicted the joint characteristics of practical structures vibrating in the medium-to-high frequency ranges. Moreover, the intensity distribution of a compliant and dissipative joint is described.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1994.10a
• /
• pp.35-39
• /
• 1994

One of the important characteristics of the response of nonlinear systems is the existence of subharmonic resonances. When some conditions in parameter space are satisfied. It is possible even in the presence of damping for a periodically excited nonlinear system to possess a response which is the combination of a contribution at the excitation frequency and a component at the system natural frequency. The system natural frequency being a submultiple of the excitation frequency implies that the resulting response is a subharmonic oscillation. In general, there also co-exists, for the system, a response at the excitation frequency, and initial conditions determine which of the steady-state responses is achieved in an experiment or a numerical simulation. In single-degree-of-freedom systems with harmonic excitation, depending on the type of the nonlinearity, e.g., cubic or quadratic the frequency of subharmonic response is respectively, one-third or one-half of that of the excitation frequency. Although subharmonic resonance is one of the principal characteristics of a nonlinear system the subharmonic responses of structures in the presence of internal resonances have been studied very rarely. In this work, we consider subharmonic responses in the two-mode approximation of the plate equations. It is assumed that the two modes are in one-to-one internal resonance. Constant and periodic steady-state solutions of the averaged equations are studied. Finally, the results of direct time integration of the original equations of motion are presented and compared with those obtained from the averaged equations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.527-535
• /
• 2012

This paper reports the active vibration control of plates using positive position feedback controller (PPF). The equations of motion of the plate under force and moment pairs were derived and the equations of PPF controllers were formulated. The effect of the parameters - gain and damping ratio - of the PPF controllers on the open loop transfer function was investigated mainly in terms of the system stability. Increasing the gain of the PPF controller tuned at a mode, the magnitude of the open loop transfer function is increased at all frequencies without changing the phase behavior. The increase of the damping ratio of the PPF controller leads to decrease the magnitude of the open loop transfer function and to modify its phase characteristics to be more stable. Two PPF controllers connected in parallel, Each PPF controller is tuned at the $1^{st}$ and $2^{nd}$ modes, respectively. Their parameters were determined to remain the system to be stable based on the results of the parametric study. A significant reduction in vibration at the 2 modes can be obtained.

• Journal of KSNVE
• /
• v.10 no.5
• /
• pp.843-848
• /
• 2000

BEA(Boundary Element Analysis) based on Kirchhoff-Helmholtz integral equation is widely used in the prediction of sound radiation problems of vibrating structures. Accurate estimation of sound pressure distribution by BEA can be [possible if and only if dynamic behavior of the relating structure was described correctly. Another plausible method of sound radiation phenomena could be the NAH(Nearfield Acoustic Holography) method. NAH also based on the identical governing equation with BEA could be one of the best acoustic imaging schemes but it has disadvantages of the complexity of measurement and of the need of large amount of measuring points. In this paper, modal expansion method is presented for taking accurate dynamic data of the structures efficiently. This method makes use of vibration principle an arbitrary dynamic behavior of the structure is described by the summation of that structures mode shapes which can be calculated by FEA easily and accurately. Sound pressure field from a vibration flat plate is calculated using the combination of vibration signal on that flat plate from experiment, and of the natural mode shapes form FEA. When sound pressure field from vibration signal is calculated the importance of the phase information was emphasized.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 1995.10a
• /
• pp.289-295
• /
• 1995

구조물의 동적부하에 대한 동적변형 응답을 정확히 예측하고, Over Design이나 Under Design이 아닌 합리적인 설계방안의 개발은 중요한 과제이다. 동적강도해석이나 소음 승차감과 같은 진동 및 충격에 기인하는 제반 문제를 복잡한 구조물을 대상으로 합리적으로 처리하기 위한 Dynamic Design Analysis는 높은 신뢰성의 추구와 더불어 필요불가결한 기술이 되고 있다. 동적해석 방법으로는 현재 유한요소법이 널리 사용되고 있으며 여러 종류의 범용 프로그램들이 보급되어 있는 실정이다. 그러나 특히 동적문제에 있어서는 형상이나 거동이 복잡한 구조물의 경우, 또는 차량의 차체와 같이 많은 장착물이 부착된 경우에는 유한요소법의 적용이 곤란하여, 지금까지 대처할 수 있는 유용한 방법이 없었다. 따라서 비교적 용이하고 간단하게 적용가능한 진동실험을 기초로 한 구조물의 동적 응답해석 및 설계 방안의 개발이 필요하다. 본 연구에서는 진동시험으로 얻어진 부분구조물의 응답특성과 결합특성으로부터 결합 후의 응답특성을 예측할 수 있는 방법을 전달함수합성이론을 기초로하여 프로그래밍 package화 한다. 그리고 평판구조물에 대하여 진동시험과 컴퓨터 시뮬레이션을 통하여 개발된 방법의 타당성을 검증한다. 또한 실제 차량에서 차체만의 진동시험과 엔진의 자유진동시험에 의한 시험데이터로부터 차체와 엔진이 마운트 결합된 후의 진동특성을 예측한다. 진동시험시에 입력과 출력에 노이즈가 필연적으로 혼입되어 주파수응답함수의 크기(magnitude)와 위상(phase)을 왜곡시킨다. 특히 위상의 왜곡은 복소수연산을 하는 전달함수합성법의 결과에 중요한 영향을 미치게 된다. 본 연구에서는 데이타 획득시 입력과 출력의 시간지연으로 생기는 위상왜곡을 보정하는 방법을 제시하고, 그 개선 정도를 조사한다.는 소견의 확실도로서 가능성을 표현한 것이다. 예를 들면, 진동진폭 스펙트럼상에 2X 성분이 상당히 크게 나타나 정렬불량의 가능성이 0.7 정도라고 판정하는 것 등은 이러한 수치적진리치를 이용하는 방법이다. 그러나 상기의 수치적 표현만으로는 확실도를 한개의 수치로서 대표하게 하는 것은 진단의 정밀도에 문제가 있을 것으로 생각된다. 따라서 언어적진리치가 도입되어 [상당히 확실], [확실], [약간 확실] 등의 언어적인 표현을 이용하여 애매성을 표현하게 되었다. 본 논문에서는 간이진단 결과로부터 추출된 애매한 진단결과중에서 가장 가능성이 높은 이상원인을 복수로 선정하고, 여러 종류의 수치화할 수 없는 언어적(linguistic)인 정보ㄷㄹ을 if-then 형식의 퍼지추론으로 종합하는 회전기계의 이상진단을 위한 정밀진단 알고리즘을 제안하고 그 유용성을 검토한다. 존재하여도 모우드 변수들을 항상 정확하게 구할 수 있으며, 또한 알고리즘의 안정성이 보장된 것이다.. 여기서는 실험실 수준의 평 판모델을 제작하고 실제 현장에서 이루어질 수 있는 진동제어 구조물에 대 한 동적실험 및 FRS를 수행하는 과정과 동일하게 따름으로써 실제 발생할 수 있는 오차나 error를 실험실내의 차원에서 파악하여 진동원을 있는 구조 물에 대한 진동제어기술을 보유하고자 한다. 이용한 해마의 부피측정은 해마경화증 환자의 진단에 있어 육안적인 MR 진단이 어려운 제한된 경우에만 실제적 도움을 줄 수 있는 보조적인 방법으로 생각된다.ofile whereas relaxivity at high field is not affected by τS. On the other hand, the change in τV does not affect low field profile but strongly in fluences on bot

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.839-844
• /
• 2003

The effect of water level on the free vibration of a partially water-filled two rectangular plates structure was investigated by experimental modal analysis and finite element analysis using ANSYS computer program. Modal parameters of two rectangular plates coupled with water were obtained by means of experiment and the FEM solutions were compared with the experimental solutions to verify the finite element model. As a result, the comparison between the experiment and FEM results showed excellent agreement. The transverse vibration modes, in-phase and out-of-phase, were observed alternately in the fluid-coupled system. The effect of water level and water gap size on the fluid-coupled natural frequency were investigated. It was found that the natural frequency of the partially water-filled two rectangular plates are not proportional to the water level, but depend on mode number of plates.