• Title, Summary, Keyword: harmonic loading

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Dynamic analysis of non-symmetric FG cylindrical shell under shock loading by using MLPG method

  • Ferezghi, Yaser Sadeghi;Sohrabi, Mohamad R.;MosaviNezhad, Seyed M.
    • Structural Engineering and Mechanics
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    • v.67 no.6
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    • pp.659-669
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    • 2018
  • The Dynamic equations in the polar coordinates are drawn out using the MLPG method for the non-symmetric FG cylindrical shell. To simulate the mechanical properties of FGM, the nonlinear volume fractions for radial direction are used. The shape function applied in this paper is a form of the radial basis functions, by using this function all the requirements for an effective and suitable shape function are established. Hence in this study, the multiquadrics (MQ) radial basis functions are exploited as the shape function governing the problem. The MLPG method is combined with the the Newmark time approximation scheme to solve dynamic equations in the time domain. The obtained results by the MLPG method to be verified are compared with the analytical solution and the FEM. The obtained results through the MLPG method show a good agreement in comparison to other results and the MLPG method has high accuracy for dynamic analysis of the non-symmetric FG cylindrical shell. To demonstrate the capability of the present method to dynamic analysis of the non-symmetric FG cylindrical shell, it is analyzed dynamically with different volume fraction exponents under harmonic and rectangular shock loading. The present method shows high accuracy, efficiency and capability to dynamic analysis of the non-symmetric FG cylindrical shell with nonlinear grading patterns.

Vibration response of saturated sand - foundation system

  • Fattah, Mohammed Y.;Al-Mosawi, Mosa J.;Al-Ameri, Abbas F.I.
    • Earthquakes and Structures
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    • v.11 no.1
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    • pp.83-107
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    • 2016
  • In this study, the response and behavior of machine foundations resting on dry and saturated sand was investigated experimentally. A physical model was manufactured to simulate steady state harmonic load applied on a footing resting on sandy soil at different operating frequencies. Total of (84) physical models were performed. The parameters that were taken into consideration include loading frequency, size of footing and different soil conditions. The footing parameters are related to the size of the rectangular footing and depth of embedment. Two sizes of rectangular steel model footing were used. The footings were tested by changing all parameters at the surface and at 50 mm depth below model surface. Meanwhile, the investigated parameters of the soil condition include dry and saturated sand for two relative densities; 30 % and 80 %. The dynamic loading was applied at different operating frequencies. The response of the footing was elaborated by measuring the amplitude of displacement using the vibration meter. The response of the soil to dynamic loading includes measuring the stresses inside soil media by using piezoelectric sensors. It was concluded that the final settlement (St) of the foundation increases with increasing the amplitude of dynamic force, operating frequency and degree of saturation. Meanwhile, it decreases with increasing the relative density of sand, modulus of elasticity and embedding inside soils. The maximum displacement amplitude exhibits its maximum value at the resonance frequency, which is found to be about 33.34 to 41.67 Hz. In general, embedment of footing in sandy soils leads to a beneficial reduction in dynamic response (displacement and excess pore water pressure) for all soil types in different percentages accompanied by an increase in soil strength.

Dominant components of vibrational energy flow in stiffened panels analysed by the structural intensity technique

  • Cho, Dae-Seung;Choi, Tae-Muk;Kim, Jin-Hyeong;Vladimir, Nikola
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.10 no.5
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    • pp.583-595
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    • 2018
  • Stiffened panels are widely used in naval architecture and ocean engineering, and knowledge about their dynamic behaviour represents important issue in the design procedure. Ordinary vibration analysis consists of natural frequencies and mode shapes determination and can be extended to forced response assessment, while the Structural Intensity (SI) analysis, assessing magnitude and direction of vibrational energy flow provides information on dominant transmission paths and energy distribution including sink positions. In this paper, vibrational energy flow in stiffened panels under harmonic loading is analyzed by the SI technique employing the finite element method. Structural intensity formulation for plate and beam element is outlined, and developed system combining in-house code and general finite element tool is described. As confirmed within numerical examples, the developed tool enables separation of SI components, enabling generation of novel SI patterns and providing deeper insight in the vibrational energy flow in stiffened panels, comparing to existing works.

In-situ fatigue monitoring procedure using nonlinear ultrasonic surface waves considering the nonlinear effects in the measurement system

  • Dib, Gerges;Roy, Surajit;Ramuhalli, Pradeep;Chai, Jangbom
    • Nuclear Engineering and Technology
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    • v.51 no.3
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    • pp.867-876
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    • 2019
  • Second harmonic generation using nonlinear ultrasonic waves have been shown to be an early indicator of possible fatigue damage in nuclear power plant components. This technique relies on measuring amplitudes, making it highly susceptible to variations in transducer coupling and instrumentation. This paper proposes an experimental procedure for in-situ surface wave nonlinear ultrasound measurements on specimen with permanently mounted transducers under high cycle fatigue loading without interrupting the experiment. It allows continuous monitoring and minimizes variation due to transducer coupling. Moreover, relations describing the effects of the measurement system nonlinearity including the effects of the material transfer function on the measured nonlinearity parameter are derived. An in-situ high cycle fatigue test was conducted using two 304 stainless steel specimens with two different excitation frequencies. A comprehensive analysis of the nonlinear sources, which result in variations in the measured nonlinearity parameters, was performed and the effects of the system nonlinearities are explained and identified. In both specimens, monotonic trend was observed in nonlinear parameter when the value of fundamental amplitude was not changing.

Analysis of Vibration-Frequency Spectrum of Distribution Transformer for Noise Reduction (배전용변압기의 소응저감을 위한 진동주파수의 스펙트럼분석)

  • Lee, Do-Hoon;Kim, Jae-Chul;Song, Seung-Youp;Lee, Hyun-Gu;Kim, Kwang-Whoa
    • Proceedings of the KIEE Conference
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    • pp.346-348
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    • 2002
  • This paper analyze spectrum of vibration-frequencies to reduce noise level of distribution transformer. Using loading back method on same condition of a real load to grasp the effect of core and winding which are caused by the transformer vibration. we were measured the vibration-frequency by varing applied voltage and load current of a transformer. The major cause of a transformer vibration is occured by the harmonic effects, and was identified that the vibration is less influenced by the coil. As the result of this paper, comparing the transformer with some isolated material with the general transformer the transformer with some isolated material could reduce spectral amplitude of vibration-frequencies.

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A Study on Prediction of vibration and Sound Radiation by Plate With Four Edges Clamped (네 변이 고정된 평판의 진동 및 방사 소음 예측에 관한 연구)

  • 심현진;이정윤;오재응
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.743-747
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    • 2003
  • In recent years, several studies of the practical application of active sound and vibration control have been developed to plate to plate response with various boundary conditions. This study considers vibration and sound radiation for the clamped rectangular plate. The radiation of a sound from rectangular plate can be calculated that the velocity of a vibrating plate is analyzed. The vibration formulation is based on a variation method for the vibration of the plate, and assumes no damping, no fluid loading of the structure. And the plate is exited by harmonic point force. The radiation of sound from plate is analyzed in the far field, and is calculated from the Rayleigh integral. The prediction results of vibration and sound level have proved with FEM or BEM.

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Voltage Gain Characteristics of Piezoelectric Transformer Operation in Second Thickness Extensional Vibration Mode (2차 두께방향 지동모드로 동작되는 압전트랜스포머의 Voltage Gain 특성)

  • 김성진;이수호;류주현;임인호;홍재일
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.11 no.10
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    • pp.855-860
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    • 1998
  • This paper presents a new structure for a piezoelectric transformer, operating in thickness extensional vibration mode. Modified $PbTiO_3$ family ceramics were used for the piezoelectric transformer, because it was a material with large anisotropy between elecromechanical coupling factors $K_t$ and $K_p$ . The size of piezoelectric transformer was 20mn long, 20mm wide and 3.1mm thick. The second harmonic resonant frequency of thickness extensional vibration mode was 0.72MHz at loading resistance 100[$\omega$], And Voltage gin of piezoelectric ceramics showed 0.53 at resonant frequency of sencond thickness extensional vibration mode.

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Parallel operation of rectifier with unit-power factor (단위역률 정류기의 병렬운전)

  • Lee, Seung-Heui;Kim, Tae-Won;Park, Jae-Wook
    • Proceedings of the KIEE Conference
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    • pp.1212-1213
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    • 2011
  • PWM(pulse width modulation) rectifier has unit power factor and low harmonic distortion with high power conversion efficiency in entire loading range. These merits of PWM rectifier help the spread of DC distribution system. In addition, if multiple PWM rectifiers can be operated in parallel connection, maintenance process can be simple and reliability of power source can be advanced because of the hot swapping is available. The other way, the load unbalance among rectifiers can force a converter to stop by over current. The surge current by closed circuit composition between rectifiers can force switching devices damage. In this paper, some problems that can occur in case of parallel operation of PWM rectifiers and problem eliminating methods are considered.

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An Asymptotic Solution and the Green's Function for the Transverse Vibration of Beams with Variable Properties

  • Kim, Yong-Chul
    • Journal of Ocean Engineering and Technology
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    • v.24 no.1
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    • pp.34-38
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    • 2010
  • An analytical solution procedure for the dynamic response of beams with variable properties is developed by using an asymptotic solution and the Green's function. This asymptotic closed form solution is derived for the transverse vibration of beams under the assumption of slowly varying properties, such as mass, cross-section, tension etc., along the beam length. However, this solution is still found to be very accurate even in the case of large variation, such as step change in cross-section, mass, and tension. Therefore, this derived asymptotic closed form solution and the Green's function can be easily applied to find dynamic responses for various kind of beam vibration problems.

Characterization and Performance Evaluation of Advanced Aircraft Electric Power Systems

  • Eid, Ahmad;El-Kishky, Hassan;Abdel-Salam, Mazen;El-Mohandes, Mohamed T.
    • Journal of Power Electronics
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    • v.10 no.5
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    • pp.563-571
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    • 2010
  • A model of an advanced aircraft electric power system is developed and studied under variable-speed constant-frequency (VSCF) operation. The frequency of the generator's output voltage is varied from 400-Hz to 800-Hz for different loading scenarios. Power conversions are obtained using 12-pulse power converters. To reduce the harmonic contents of the generator output waveforms, two high-pass passive filters are designed and installed one at a time at the generator terminals. The performance of the two passive filters is compared according to their losses and effectiveness. The power quality characteristics of the studied VSCF aircraft electric power system are presented and the effectiveness of the proposed filter is demonstrated through compliance with the newly published aircraft electrical standards MIL-STD-704F.