A new modeling method is developed in this paper for the active minimization of noise within a three-dimensional irregular enclosure using distributed lead zirconate titanate piezoelectric (PZT) actuators, and the control mechanisms for irregular enclosure are analyzed. The irregular enclosure is modeled with four rigid walls and two simply supported flexible panels, and PZT actuators are bound to one of the flexible panels. The process of the new modeling method is as follows. First, the modal coupling method is used to establish the motion equations, which contain important coefficients such as modal masses and modal coupling coefficients, etc., of acoustic-structural-piezoelectric coupling system. Then, the acoustic modes and the modal masses of irregular enclosure are calculated by numerical methods. Last, the modal coupling coefficients in motion equations are calculated according to the numerical results of the acoustic modes of irregular enclosure and the modes of two panels. The validity of this modeling method is verified by a regular hexahedron enclosure. Two cost functions are applied to this model. With the two cost functions, good results are obtained in minimizing the sound-pressure level (SPL) within irregular enclosure according to numerical investigations. By comparing the results obtained under controlled and uncontrolled states, the control mechanisms of the system are discussed. It is found that the control mechanisms vary with disturbance frequencies. At most disturbance frequencies, the SPL within enclosure is reduced by restructuring the modes of two panels simultaneously. When the disturbance frequency comes close to one of the natural frequencies of panel a, the dominant mode of panel a is suppressed, while the modes of panel b are reconstructed. While the disturbance frequency is near one of the natural frequencies of panel b, the modes of two panels are restructured at the same time.
The quasi-zero-stiffness vibration isolation system has witnessed significant development due to the pressing demands for low frequency and ultra-low frequency vibration isolation. In this study, the isolation theory and the characteristic of the quasi-zero-stiffness vibration isolation system are illustrated. Based on its implementation mechanics, a comprehensive assessment of recent advances of the quasi-zero-stiffness vibration isolation system is presented. The future research directions are finally prospected.
A 2-D finite element model of human cochlea is established in this paper. This model includes the structure of oval window, round window, basilar membrane and cochlear duct which is filled with fluid. The basilar membrane responses are calculated with sound input on the oval window membrane. In order to study the effects of helicotrema on basilar membrane response, three different helicotrema dimensions are set up in the FE model. A two-way fluid-structure interaction numerical method is used to compute the responses in the cochlea. The influence of the helicotrema is acquired and the frequency selectivity of the basilar membrane motion along the cochlear duct is predicted. These results agree with the experiments and indicate much better results are obtained with appropriate helicotrema size.
In this paper, influencing factors and evaluation standards of vibration on human comfort were summarized. The mainly influencing factors were analyzed including vibration acceleration, frequency, exposure time and other factors. The evaluation standards of human comfort were analyzed contrastively. The conclusion was that countries around the world have established unified body vibration comfort evaluation methods and evaluation standards on the basis of ISO series standards. The new methods and standards were also needed for special vibration and shock environment.
An accurate finite element (FE) model of the human ear can help in understanding the physiological mechanismof human ear and facilitate the design of implantable hearing devices. In this paper,a FE modelof the human ear consisting of the external ear canal, middle ear, and cochlea was developed. The geometry of the external ear canal and middle ear model was based on a fresh specimen of human temporal boneviamicro-computer tomography imaging. A harmonic sound pressure of 90 dB SPL was applied in the ear canal and the multi-field coupled FE analysis was conductedamong the ear canal air, cochlea fluid, and middle ear and cochlea structures. The results were compared with the established physiological data. The satisfactory agreements between the model and published experimental measurementsindicate the middle ear and cochlea functions can be well simulated and further application in terms of human ear can be achieved by the model.
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