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마평식(Pyung Sik Ma),김재은(Jae Eun Kim),김윤영(Yoon Young Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
The topology optimization method is applied to the design of a vibration-powered, cantilevered Piezoelectric Energy Harvester (PEH) whose base is subject to a vibrating motion. The optimization problem is so formulated as to maximize the Electro-Mechanical Coupling Coefficient (EMCC) with volume constraints because the EMCC is the key factor affecting electrical power output for a given base input acceleration. Since the present PEH is supposed to operate at either short-circuit or open-circuit resonant frequencies for producing the maximum output power, the resonant frequency is also considered in the topology optimization formulation. In order to investigate the dimensional effects of a PEH on the power output, a number of different combinations of piezoelectric composite beam and tip mass dimensions are considered. The optimized results are presented and findings from this research that can be useful for practical design of PEH’s are summarized.
김현실,마평식,김봉기,이성현,서윤호 한국음향학회 2020 韓國音響學會誌 Vol.39 No.4
In this paper, sound transmission of Micro-Perforated Plates (MPPs) installed in an impedance tube with a circular cross-section is described using an analytic method. Vibration of the plates is expressed in terms of an infinite series of modal functions, where modal function in the radial direction is given by the Bessel function. Under the plane wave assumption, a low frequency approximation is derived, and a formula for the sound transmission coefficient of multi-layered MPPs is presented using the transfer matrix method. The Sound Transmission Losses (STLs) of single and double MPPs are computed using the proposed method and compared with those done by the Finite Element Method (FEM), which shows an excellent agreement. As the perforation increases, the STL is degraded, since the STL becomes dominated by the perforation ratio rather than by vibration of the plate. The STL shows dips at natural frequencies as well as at the mass-spring-mass resonance frequency. The proposed model for the STL prediction in this study can be applied to an arbitrary number of MPPs, where each MPP may or may not have a perforation. 본 논문은 원통형 임피던스 튜브내에 설치된 다중 미세천공판(Micro-Perforated Plate, MPP)의 음향투과를해석적으로 구하는 방법을 다루었다. 판의 진동을 무한 급수의 합으로 전개하였는데 반경방향으로는 Bessel 함수를포함한다. 평면파 가정하에서 저주파수 대역의 근사식을 유도하였으며 전달함수법을 이용하여 다중 MPP에 대한 음향투과율 공식을 제시하였다. 단일과 이중 MPP의 음향투과손실(Sound Transmission Loss, STL)을 본 논문에서 제안한 공식을 이용하여 계산하였으며 유한요소법(Finite Element Method, FEM)을 사용한 결과와 잘 일치 하였다. 천공율이 증가할수록 STL은 감소하는데 이는 판의 진동보다는 천공율이 더 큰 영향을 주기 때문이다. STL은 판의 공진주파수에서 골(dip)을 보이며 이중 MPP의 STL은 질량-스프링-질량 진동에 해당하는 공진주파수에서 골을 보인다. 본 연구에서 제안한 STL 예측 모델은 임의의 개수의 다중 MPP에 적용이 가능하며 각각의 판은 미세천공을 포함하거나 포함하지 않는 두 가지 경우가 모두 가능하다.