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Enhancing the Reconstruction of Acoustic Source Field using Wavelet Transformation
고병식,이승엽 대한기계학회 2005 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.19 No.8
This paper shows the use of wavelet transformation combined with inverse acoustics to reconstruct the surface velocity of a noise source. This approach uses the boundary element analysis based on the measured sound pressure at a set of field points, the Helmholtz integral equations and wavelet transformation for reconstructing the normal surface velocity field. The reconstructed field can be diverged due to the small measurement errors in the case of nearfield acoustic holography (NAH) using an inverse boundary element method. In order to avoid this instability in the inverse problem, the reconstruction process should include some form of regularization for enhancing the resolution of source images. The usual method of regularization has been the truncation of wave vectors associated with small singular values, although the order of an optimal truncation is difficult to determine. In this paper, a wavelet transformation is applied to reduce the computation time for inverse acoustics and to enhance the reconstructed vibration field. The computational speed-up is achieved, with solution time being reduced to 14.5%.
고병식,Go, Byeong-Sik 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.5
This paper present as experimental demonstratio of DSP and a sensory actuator that is used to actively control sound transmission/radiation through a vibrating plate. A plane acoustic wave incident on a clamped, thin circular plate was used as a noise source, and a sensory actuator bounded to the plate was used to control and sense vibration of the plate. The sound transmission reduction problem was tranformed as a structural vibration control problem that actively control the structural vibration modes coupled to acoustic modes. The results show that the first structural vibration mode is controlled with a reduction of 78 percent in the displacement and velocity of the plate. This corresponds to a 13dB reduction in the acoustic response. These experimental results indicate that a sensory actuator bounded to the plate can be employed to attenuate the sound transmitted to radiated from the plate.
압전형 센서/액추에이터를 이용한 진동구조물의 능동-수동제어
고병식 한국소음진동공학회 1995 소음 진동 Vol.5 No.3
Two active/passive vibration dampers were designed to control a cantilever beam first mode of vibration. The active element was a piezoelectric polymer, polyvinlidene fluoride (PVDF). The passive damping was provided by the application of a viscoelastic layer on the surface of the steel beam. Two substantially different damper configurations were designed and tested. One damper consisted of a piezoelectric actuator bonded to one face of the beam, with a viscoelastic layer applied to the other surface of the beam. The second one was composed of a layer viscoeastic layer with one surface bonded to the beam, and with other being constrained by nine piezoelectric actuators connected in parallel. A control law based on the sign of the angular velocity of the cantilever beam was implemented to control the beam first mode of vibration. The piezoelectric sensor output was digitally differentiated to obtain the transverse linear velocity, and its sign was used in the control algorith. Two dampers provided the system a damping increase of a factor of four for the first damper and three for the second damper. Both dampers were found to work well at low levels of vibration, suggesting that they can be used effectively to prevent resonant vibrations in flexible structure from initiating and building up.
A Study on Iterative Learning Control for Vibration of Stewart Platform
고병식,김동원,박종욱 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.1
This paper presents the replication of a desired vibration response by iterative learning control systemfor a Stewart platform. The Stewart platform is a multi-input, multi-output system with parameter uncertainties includingsystem nonlinearity and joint nonlinearity. Most vehicle manufacturers are relying on road test simulationfacilities in order to reduce development time and to enhance product quality. Road simulation algorithm is essentialfor developing road test simulation system. With digital signal processing technology, more complex controlalgorithms including iterative learning control can be utilized. In this paper, a controller based on iterative learningcontrol (ILC) algorithm was developed to produce the desired target response in case of a single actuator as the firstexperiment after programmed with C language. As a next experiment, the control algorithm was implemented in aroad test simulation system using a Stewart platform. A real test was carried out to replicate total six channels ofacceleration signals measured at top and left side points of audio player system installed to a car running on Belgianroad. The convergence rate and test simulation accuracy higher than 90% showed that the algorithm was acceptableto replicate the target vibration response.