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이형일(Hyeongill Lee) 한국소음진동공학회 2016 한국소음진동공학회 논문집 Vol.26 No.7
This study investigates the vibro-acoustic characteristics of an automotive brake drum given free boundaries using the hybrid approach combining numerically obtained structural properties with analytical solution for acoustic radiation. Structural vibrations of the drum are investigated with the finite element method, and modal displacements on the outer surfaces of the drum are idealized as simple mathematical expressions. Based on the expressions, modal sound radiations of the drum are calculated using the Rayleigh integral method. Structural and acoustic responses of the drum for a harmonic excitation are obtained from above results using the modal expansion technique. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the vibro-acoustic characteristics of a brake drum can be accurately investigated with the process used in this study. Also, many noise and vibration problems in drum brake can be addressed using the procedure proposed in this study.
후판 환형 디스크 래디얼 모드에 의한 음향방사에 관한 연구
이형일(Lee, Hyeongill) 한국소음진동공학회 2005 한국소음진동공학회 논문집 Vol.15 No.4
This article proposes analytical solutions for sound radiation from radial vibration modes of a thick annular disk. Structural eigensolutions are calculated using the transfer matrix method. The far-field sound pressure distribution is obtained using two alternate methods. In the first method, pressure is calculated using the Rayleigh integral technique. The second method treats sound radiating radial surfaces as cylindrical radiators of finite length. The Sinc function approach is employed for calculations. Acoustic powers and radiation efficiencies of radial modes are also determined from the far-field sound pressure calculations. Analytical predictions match well with measured data as well as computational results from a finite element code in terms of structural eigensolutions and from a boundary element code in terms of sound pressure, directivity etc.
이형일(Lee, Hyeongill) 한국소음진동공학회 2013 한국소음진동공학회 논문집 Vol.23 No.7
This study introduces a hybrid approach combining numerical results with pre-developed analytical calculations for the sound radiation from the modal vibration of a thick, finite length cylinder with various boundary conditions. Structural vibrations of the cylinder are numerically investigated with the finite element method, and distributions of vibratory displacements on the cylinder surface are idealized as simple mathematical expressions based on the numerical results. Sound radiations from the normal vibration of the cylinder are calculated based on idealized modal displacements using a previously introduced theoretical solution. The results are confirmed with numerical analyses using the boundary element method. Based on these results, it can be concluded that the solutions suggested in this study have good accuracies in calculating the vibro-acoustic properties of a thick, finite cylinder with various boundary conditions. Also, the sound radiation characteristics of many practical components such as brake drums and motor housings are expected to be investigated using the procedure proposed in this study.
적응형 재귀 분할 평균법을 이용한 메모리기반 추론 알고리즘
이형일(Hyeongil Lee),최학윤(Hakyoon Choi) 한국정보과학회 2004 정보과학회논문지 : 소프트웨어 및 응용 Vol.31 No.4
메모리 기반 추론에서 기억공간의 효율적인 사용과 분류성능의 향상을 위하여 제안되었던 RPA(Recursive Partition Averaging)알고리즘은 대상 패턴 공간을 분할 한 후 대표 패턴을 추출하여 분류 기준 패턴으로 사용한다. 이 기법은 메모리 사용 효율과 분류 성능 면에서 우수한 결과를 보였지만, 분할 종료 조건과 대표패턴의 추출 방법이 분류 성능 저하의 원인이 되는 단점을 가지고 있었다. 여기에서는 기존 RPA의 단점을 보안한 ARPA(Adaptive RPA) 알고리즘을 제안한다. 제안된 알고리즘은 패턴 공간의 분할 종료 조건으로 특징별 최빈 패턴 구간(FPD: Feature-based population densimeter) 추출 알고리즘을 사용하며, 학습 결과 패턴의 생성을 대표패턴 추출기법 대신 최빈 패턴 구간을 이용하여생성한 최적초월평면(OH: Optimized Hyperrectangle)을 사용한다. 제안된 알고리즘은 k-NN분류기에서 필요로 하는 메모리 공간의 40%정도를 사용하며, 분류에 있어서도 RPA보다 우수한 인식 성능을 보이고 있다. 또한 저장된 패턴의 감소로 인하여, 실제 분류에 소요되는 시간 비교에 있어서도 k-NN보다 월등히 우수한 성능을 보이고 있다. We had proposed the RPA(Recursive Partition Averaging) method in order to improve the storage requirement and classification rate of the Memory Based Reasoning. That algorithm worked not bad in many area, however, the major drawbacks of RPA are it's partitioning condition and the way of extracting major patterns. We propose an adaptive RPA algorithm which uses the FPD(feature-based population densimeter) to stop the ARPA partitioning process and produce, instead of RPA's averaged major pattern, optimizing resulting hyperrectangles. The proposed algorithm required only approximately 40% of memory space that is needed in k-NN classifier, and showed a superior classification performance to the RPA. Also, by reducing the number of stored patterns, it showed an excellent results in terms of classification when we compare it to the k-NN.
Study on the Acoustic Modes of a Short, Thick, Asymmetric Cylinder
Hyeongill Lee(이형일) 한국소음진동공학회 2017 한국소음진동공학회 논문집 Vol.27 No.2
This study investigates vibro-acoustic characteristics of a short, thick cylinder containing a slot given a pined-free boundaries. Using the finite element analysis results, structural modes of the asymmetric cylinder (with a slot) are expressed as the linear combinations of modes of the symmetric cylinder made of same material with identical geometry except the slot. Based on synthesized modal vibrations, acoustic modes of the asymmetric cylinder are obtained with two approaches, i.e., Rayleigh integral calculation and modal expansion of the acoustic modes of the symmetric cylinder. Also, acoustic powers, max. sound pressure and directivity pattern are obtained from acoustic modes and verified with the boundary element analyses. Based on these results, the accuracy of proposed approaches in calculating the vibro-acoustic properties of a short, thick, asymmetric cylinder has been confirmed. The procedure can be applied to the similar cylinders with other boundaries or asymmetric properties. Also, attenuation of vibration and/or sound radiation of the cylinder type practical components can be studied using these approaches.
전달행렬법을 이용한 레버형 반공진 진동 절연기 특성 연구
윤종환(Jong-Hwan Yun),이형일(Hyeongill Lee) 한국소음진동공학회 2018 한국소음진동공학회 논문집 Vol.28 No.5
Transfer matrix for the lever type dynamic anti-resonance vibration isolator (L-DAVI) is defined by the vector type four pole parameter method. Defined matrix is applied to a 2-DOF vibratory system with an L-DAVI to obtain the transfer matrix for the total system. The accuracy of the transfer matrix for the L-DAVI is validated by comparing system accelerance from transfer matrix method (TMM) with that from conventional method. Accelerance for a 4-DOF target system simulating a real mechanical system is calculated using TMM. Finally the optimal configuration and location of the L-DAVI(s) to improve system accelerance are investigated using the transfer matrix for the L-DAVI in the first step. The effects of L-DAVI are studied by comparing response characteristics of the modified system with that of original system along with the advantages of TMM over the conventional method.
Gyubin Kwak(곽규빈),Hyung-Ju Cho(조형주),Hyeongill Lee(이형일) 한국소음진동공학회 2023 한국소음진동공학회 논문집 Vol.33 No.4
The present study evaluates two procedures for measuring the rotational vibration of a shaft, using an incremental and an absolute encoder, respectively. First, the procedures for rotational vibration measurement using the two encoders are explained. The validity of these procedures is examined through computer simulations, which demonstrate that both procedures are accurate in measuring rotational vibration. Furthermore, the simulation results for both procedures exhibit good correlations in both the time and frequency domains. Finally, the procedures are experimentally verified using a simple test setup with a universal joint to generate rotational vibration. The test results match well with each other and with the theoretical data, confirming that the proposed method is capable of accurately measuring the rotational vibration of rotating machines.