• Title/Summary/Keyword: natural frequency sensitivity

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Free vibration of deep curved FG nano-beam based on modified couple stress theory

  • Rahmani, O.;Hosseini, S.A.H.;Ghoytasi, I.;Golmohammadi, H.
    • Steel and Composite Structures
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    • v.26 no.5
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    • pp.607-620
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    • 2018
  • Vibration analysis of deep curved FG nano-beam has been carried out based on modified couple stress theory. Material properties of curved Timoshenko beam are assumed to be functionally graded in radial direction. Governing equations of motion and related boundary conditions have been obtained via Hamilton's principle. In a parametric study, influence of length scale parameter, aspect ratio, gradient index, opening angle, mode number and interactive influences of these parameters on natural frequency of the beam, have been investigated. It was found that, considering geometrical deepness term leads to an increase in sensitivity of natural frequency about variation of aforementioned parameters.

Mode-decoupling Controller for Feedback Model Updating (궤환 모델 개선법을 위한 모드 분리 제어기)

  • 정훈상;박영진
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.14 no.10
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    • pp.955-961
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    • 2004
  • A novel concept of feedback loop design for modal test and model updating is proposed. This method uses the closed-loop natural frequency information for parameter modification to overcome the problems associated with the conventional method employing the modal sensitivity matrix. To obtain new modal information from closed-loop system, controllers should be effective in changing modal data while guaranteeing the stability of closed-loop system. But it is very hard to guarantee the stability of the closed-loop system with non-collocated sensor and actuator set. In this research, we proposed a controller called mode-decoupling controller that can change a target mode as much as the designer wants guaranteeing the stability of closed-loop system. This controller can be computed Just using measured open-loop modeshape matrix. A simulation based on time domain input/output data is performed to check the feasibility of proposed control method.

Modal Parameter Extraction Using a Digital Camera (카메라를 이용한 구조물의 동특성 추출)

  • Kim, Byeong-Hwa
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.18 no.12
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    • pp.1229-1236
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    • 2008
  • A set of modal parameters of a stay-cable have been extracted fi:on a moving picture captured by a digital camera supported by shaking hands. It is hard to identify the center of targets attached on the cable surface from the blurred cable motion image, because of the high speed motion of cable, low sampling frequency of camera, and the shaking effect of camera. This study proposes a multi-template matching algorithm to resolve such difficulties. In addition, a sensitivity-based system identification algorithm is introduced to extract the natural frequencies and damping ratios from the ambient cable vibration data. Three sets of vibration tests are conducted to examine the validity of the proposed algorithms. The results show that the proposed technique is pretty feasible for extracting modal parameters from the severely shaking motion pictures.

Estimation of Dynamic Characteristics of an Offshore Meteorological Tower using Ambient Measurements (상시계측을 통한 해상기상탑의 동적특성 평가)

  • Gyehee Lee;Le Quoc Cuong;Daejin Kwag
    • Journal of Wind Energy
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    • v.14 no.3
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    • pp.91-99
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    • 2023
  • In research conducted on a southwestern Korean offshore meteorological tower, acceleration datasets were gathered over half a year with time-history sensors. To enhance data credibility, a parallel measurement system was used for verification. A model of the tower was configured using beam elements, and with modifications accounting for added stiffness from auxiliary structures. Ground interactions were considered as calibrated springs based on soil layer properties. The tower's dynamic attributes and mass sensitivity were discerned using eigenvalue analysis. The structural natural frequency was consistent, with variations primarily due to new equipment adding approximately 1400 kgs. With free vibration damping assumptions, a damping ratio of roughly 1 % was derived.

Integrated Microdisk Gold Electrode Modified with Metal-porphyrin and Metal-phthalocyanines for Nitric Oxide Determination in Biological Media

  • Kim, Il-Kwang;Bae, Hyun-Ok;Oh, Gi-Soo;Chung, Hun-Taeg;Kim, Young-Jin;Chun, Hyun-Ja
    • Bulletin of the Korean Chemical Society
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    • v.24 no.11
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    • pp.1579-1584
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    • 2003
  • An integrated gold microdisk electrode was constructed and modified with metal-porphyrin or metal-phthalocyanines for NO determination in biological media. Microanalysis of NO using square wave anodic stripping voltammetry in $1\;{\times}\;10^{-2}$ M $HClO_4$ was optimal when the accumulation potential was 0.1 V, frequency 100 Hz, and the scan rate was 200 mV/s. When the electrode was modified with metal-porphyrin or metal-phthalocyanines, the anodic peak currents of NO increased due to the catalytic oxidation of NO. In case of Fe(II)-phthalocyanine modified electrode, the peak currents remarkably increased and the sensitivity was high. The calibration curve had good linearity in the range from $3.6\;{\times}\;10^{-5}$ M to $7.2\;{\times}\;10^{-7}$ M, and the detection limit was $5.7\;{\times}\;10^{-7}$ M. For the structural stability and increased sensitivity, Fe(II)-phthalocyanine modified gold microdisk electrode coated with Nafion was applied to determination of NO released from cultured macrophase.

The Study on the Vibration Characteristics of Vehicle Compact Disk Player (차량탑재용 컴팩트 디스크 플레이어의 진동 특성에 관한 연구)

  • Lee Tae-Keun;Kim Byoung-Sam
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.14 no.6
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    • pp.117-124
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    • 2005
  • This study developes the vibration model to estimate the vibration energy of compact disc player's mainbase assembly which is supported by dampers and springs, and this model is verified by experiment. From frequency response function, we investigate the natural frequency and mode shape in the up/down direction for mainbase assembly. In order to determine the analysis frequency band, we investigate the excitation frequency of road from the vehicle test. As the characteristics of dampers and springs are changed, we carry out the sensitivity analysis of vibration energy for mainbase assembly which include optical pick-up and feeding system. And we found out that the properties of damper were dominant element in the vibration energy of mainbase assembly's CG(center of gravity).

A Study on the Structure for the Improvement of Vibration Characteristics of a Vehicle Seatbelt (자동차 시트벨트의 진동특성 개선을 위한 구조에 관한 연구)

  • Kim, Chang-Hee;Oh, Chea-Eun;Kim, Tea-Woo;Song, Chul-Woo;Lee, Seok-Soon
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.2
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    • pp.97-102
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    • 2020
  • To prevent vibration of a vehicle's interior parts due to external impacts, the vehicle should be designed to reduce vibration and increase rigidity. In this paper, we conducted a vehicle test in which the vibration characteristics of a seatbelt resulting from the impact of a person closing a car door were measured and analyzed. A correlation analysis was performed using the finite analysis method. Based on this, a sensitivity analysis was performed, and an improved model was designed. We compared the natural frequencies and mode shapes of the improved and the initial models, which confirmed that the natural frequency of the improved model was more than 10 Hz higher than that of the initial model. Moreover, the response frequency of the improved model was three times higher than the input frequency applied in the vehicle test.

Wafer Level Vacuum Packaged Out-of-Plane and In-Plane Differential Resonant Silicon Accelerometers for Navigational Applications

  • Kim, Illh-Wan;Seok, Seon-Ho;Kim, Hyeon-Cheol;Kang, Moon-Koo;Chun, Kuk-Jin
    • JSTS:Journal of Semiconductor Technology and Science
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    • v.5 no.1
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    • pp.58-66
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    • 2005
  • Inertial-grade vertical-type and lateral-type differential resonant accelerometers (DRXLs) are designed, fabricated using one process and tested for navigational applications. The accelerometers consist of an out-of-plane (for z-axis) accelerometer and in-plane (for x, y-axes) accelerometers. The sensing principle of the accelerometer is based on gap-sensitive electrostatic stiffness changing effect. It says that the natural frequency of the accelerometer can be changed according to an electrostatic force on the proof mass of the accelerometer. The out-of-plane resonant accelerometer shows bias stability of $2.5{\mu}g$, sensitivity of 70 Hz/g and bandwidth of 100 Hz at resonant frequency of 12 kHz. The in-plane resonant accelerometer shows bias stability of $5.2{\mu}g$, sensitivity of 128 Hz/g and bandwidth of 110 Hz at resonant frequency of 23.4 kHz. The measured performances of two accelerometers are suitable for an application of inertial navigation.

Damage Detection of Structures using Peak and Zero of Frequency Response Functions (주파수 응답함수의 피크와 제로를 이용한 구조물의 손상탐지)

  • Park, Soo-Yong
    • Journal of the Earthquake Engineering Society of Korea
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    • v.11 no.2 s.54
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    • pp.69-79
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    • 2007
  • In this paper, a technique to detect structural damage and estimate its severity using peaks and zeros of frequency response functions (FRFs) is developed. The peaks in FRFs represent the natural frequencies of the structure and the zeros provide additional information. The characteristics of peaks and zeros are defined and the calculation procedure to obtain the peaks and zeros from the relationship between frequency response function and stiffness and mass matrices are clearly explained. A structural system identification theory which is utilizing the sensitivity of stiffness of a structural member to eigenvalues, i.e., peaks and zeros, is established. The proposed method can identify damage location and its severity, with natural and zero frequencies, by estimating structural stiffness of the structure in the process of making a analytical model The accuracy and feasibility is demonstrated by numerical models of a spring-mass system and a beam structure.

Nonlinear vibration analysis of fluid-conveying cantilever graphene platelet reinforced pipe

  • Bashar Mahmood Ali;Mehmet AKKAS;Aybaba HANCERLIOGULLARI;Nasrin Bohlooli
    • Steel and Composite Structures
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    • v.50 no.2
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    • pp.201-216
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    • 2024
  • This paper is motivated by the lack of studies relating to vibration and nonlinear resonance of fluid-conveying cantilever porous GPLR pipes with fractional viscoelastic model resting on nonlinear foundations. A dynamical model of cantilever porous Graphene Platelet Reinforced (GPLR) pipes conveying fluid and resting on nonlinear foundation is proposed, and the vibration, natural frequencies and primary resonant of such system are explored. The pipe body is considered to be composed of GPLR viscoelastic polymeric pipe with porosity in which Halpin-Tsai scheme in conjunction with fractional viscoelastic model is used to govern the construction relation of the nanocomposite pipe. Three different porosity distributions through the pipe thickness are introduced. The harmonic concentrated force is also applied on pipe and excitation frequency is close to the first natural frequency. The governing equation for transverse motion of the pipe is derived by the Hamilton principle and then discretized by the Galerkin procedure. In order to obtain the frequency-response equation, the differential equation is solved with the assumption of small displacement, damping coefficient, and excitation amplitude by the multiple scale method. A parametric sensitivity analysis is carried out to reveal the influence of different parameters, such as nanocomposite pipe properties, fluid velocity and nonlinear viscoelastic foundation coefficients, on the primary resonance and linear natural frequency. Results indicate that the GPLs weight fraction porosity coefficient, fractional derivative order and the retardation time have substantial influences on the dynamic response of the system.