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RISS 인기검색어
- 검색키워드
- 저자 : Mehdi Keshmiri (검색결과 3 건)
- 무료
- 기관 내 무료
- 유료
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Esmaeil Ghorbani,Mehdi Keshmiri 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7
Wind turbines, helicopters, and turbo-machineries’ rotary motion, along with a variety of nonlinear structures linearized with their periodic limit cycles, may all contain time-periodic terms in their equations of motion even if the equations remain linear. The purpose of this study is to model these systems into a beam-moving mass system. Natural frequencies of the beam are calculated using past work in which pseudo-natural frequencies of a beam-moving mass system were extracted, followed by the homotopy perturbation method. The findings of this study are valuable to the industry, and they decrease error margin in resonance range assessment. This approach indicates that for beam-moving mass systems, extraction of natural frequencies that ignore the moving mass effect can lead to inaccurate results, whereas only a limited amount of physical data are needed obtain accurate calculations. Furthermore, this study used homotopy perturbation for operational modal analysis purposes and not for solving nonlinear equations.
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Identification of pseudo-natural frequencies in a beam-moving mass system with periodic passages
Esmaeil Ghorbani,Mehdi Keshmiri 대한기계학회 2015 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.29 No.7
The response of a linear time-invariant (LTI) system to harmonic input generates a harmonic output with constant frequency but varyingmagnitude and phase. Many structural dynamic systems have been modeled as linear time-varying periodic (LTP) systems. Previousstudies have reported that the response of an LTP system to an exponential input establishes an infinite number of frequencies. Thesestudies have presented a new, exponentially modulated periodic signal space and a corresponding harmonic transfer function as usefultools in the operational modal analysis of LTP systems. In consideration of this new approach, this study mainly identifies the frequenciesof a typical LTP system, such as a beam that is subject to the intermittent passage of moving masses. Upon obtaining the harmonic transferfunction for the beam-moving mass system, conventional frequency domain methods for LTI systems are used to derive the frequencycharacteristics of the LTP system from the system response. These methods include the peak-picking method. As expected in anLTP system, an infinite number of pseudo-natural frequencies resonate in the beam-moving mass system.
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Active structural acoustic control of a smart cylindrical shell using a virtual microphone
Loghmani, Ali,Danesh, Mohammad,Kwak, Moon K,Keshmiri, Mehdi Institute of Physics Publishing 2016 Smart materials & structures Vol.25 No.4
<P>This paper investigates the active structural acoustic control of sound radiated from a smart cylindrical shell. The cylinder is equipped with piezoelectric sensors and actuators to estimate and control the sound pressure that radiates from the smart shell. This estimated pressure is referred to as a virtual microphone, and it can be used in control systems instead of actual microphones to attenuate noise due to structural vibrations. To this end, the dynamic model for the smart cylinder is derived using the extended Hamilton’s principle, the Sanders shell theory and the assumed mode method. The simplified Kirchhoff–Helmholtz integral estimates the far-field sound pressure radiating from the baffled cylindrical shell. A modified higher harmonic controller that can cope with a harmonic disturbance is designed and experimentally evaluated. The experimental tests were carried out on a baffled cylindrical aluminum shell in an anechoic chamber. The frequency response for the theoretical virtual microphone and the experimental actual microphone are in good agreement with each other, and the results show the effectiveness of the designed virtual microphone and controller in attenuating the radiated sound.</P>
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