Dynamics of an elastic beam and a jumping oscillator moving in the longitudinal direction of the beam

Luis Baeza,Huajiang Ouyang 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.3

An oscillator of two lumped masses linked through a vertical spring moves forward in the horizontal direction, initially at a certain height, over a horizontal Euler beam and descends on it due to its own weight. Vibration of the beam and the oscillator is excited at the onset of the ensuing impact. The impact produced by the descending oscillator is assumed to be either perfectly elastic or perfectly plastic. If the impact is perfectly elastic, the oscillator bounces off and hits the beam a number of times as it moves forward in the longitudinal direction of the beam, exchanging its dynamics with that of the beam. If the impact is perfectly plastic, the oscillator (initially) sticks to the beam after its first impact and then may separate and reattach to the beam as it moves along the beam. Further events of separation and reattachment may follow. This interesting and seemingly simple dynamic problem actually displays rather complicated dynamic behaviour and has never been studied in the past. It is found through simulated numerical examples that multiple events of separation and impact can take place for both perfectly elastic impact and perfectly plastic impact (though more of these in the case of perfectly elastic impact) and the dynamic response of the oscillator and the beam looks noisy when there is an event of impact because impact excites higher-frequency components. For the perfectly plastic impact, the oscillator can experience multiple events of consecutive separation from the beam and subsequent reattachment to it.

Dynamics of an elastic beam and a jumping oscillator moving in the longitudinal direction of the beam

Baeza, Luis,Ouyang, Huajiang Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.3

An oscillator of two lumped masses linked through a vertical spring moves forward in the horizontal direction, initially at a certain height, over a horizontal Euler beam and descends on it due to its own weight. Vibration of the beam and the oscillator is excited at the onset of the ensuing impact. The impact produced by the descending oscillator is assumed to be either perfectly elastic or perfectly plastic. If the impact is perfectly elastic, the oscillator bounces off and hits the beam a number of times as it moves forward in the longitudinal direction of the beam, exchanging its dynamics with that of the beam. If the impact is perfectly plastic, the oscillator (initially) sticks to the beam after its first impact and then may separate and reattach to the beam as it moves along the beam. Further events of separation and reattachment may follow. This interesting and seemingly simple dynamic problem actually displays rather complicated dynamic behaviour and has never been studied in the past. It is found through simulated numerical examples that multiple events of separation and impact can take place for both perfectly elastic impact and perfectly plastic impact (though more of these in the case of perfectly elastic impact) and the dynamic response of the oscillator and the beam looks noisy when there is an event of impact because impact excites higher-frequency components. For the perfectly plastic impact, the oscillator can experience multiple events of consecutive separation from the beam and subsequent reattachment to it.

Design and homogenization of metal sandwich tubes with prismatic cores

Zhang, Kai,Deng, Zichen,Ouyang, Huajiang,Zhou, Jiaxi Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.4

Hollow cylindrical tubes with a prismatic sandwich lining designed to replace the solid cross-sections are studied in this paper. The sections are divided by a number of revolving periodic unit cells and three topologies of unit cells (Square, Triangle and Kagome) are proposed. Some types of multiple-topology designed materials are also studied. The feasibility and accuracy of a homogenization method for obtaining the equivalent parameters are investigated. As the curved elements of a unit cell are represented by straight elements in the method and the ratios of the lengths of the curved elements to the lengths of the straight elements vary with the changing number of unit cells, some errors may be introduced. The frequencies of the first five modes and responses of the complete and equivalent models under an internal static pressure and an internal step pressure are compared for investigating the scope of applications of the method. The lower bounds and upper bounds of the number of Square, Triangular and Kagome cells in the sections are obtained. It is shown that treating the multiple-topology designed materials as a separate-layer structure is more accurate than treating the structure as a whole.

Design and homogenization of metal sandwich tubes with prismatic cores

Kai Zhang,Zichen Deng,Huajiang Ouyang,Jiaxi Zhou 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.4

Hollow cylindrical tubes with a prismatic sandwich lining designed to replace the solid cross-sections are studied in this paper. The sections are divided by a number of revolving periodic unit cells and three topologies of unit cells (Square, Triangle and Kagome) are proposed. Some types of multiple-topology designed materials are also studied. The feasibility and accuracy of a homogenization method for obtaining the equivalent parameters are investigated. As the curved elements of a unit cell are represented by straight elements in the method and the ratios of the lengths of the curved elements to the lengths of the straight elements vary with the changing number of unit cells, some errors may be introduced. The frequencies of the first five modes and responses of the complete and equivalent models under an internal static pressure and an internal step pressure are compared for investigating the scope of applications of the method. The lower bounds and upper bounds of the number of Square, Triangular and Kagome cells in the sections are obtained. It is shown that treating the multiple-topology designed materials as a separate-layer structure is more accurate than treating the structure as a whole.

Dynamic performance of a rotor system with an initial bow and coupling faults of imbalance-rub during whirling motion

Yang Yang,Yiren Yang,Huajiang Ouyang,Xin Li,Dengqing Cao 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.10

The dynamic characteristics of a rotor system with an initial bow and coupling fault of imbalance-rub are investigated in this work. The geometrical nonlinearity of shafts becomes significant due to the large-amplitude whirling motion. Then, the influences of the initial bow and geometrical nonlinearity on the natural frequencies corresponding to the linear part of the rotor system are studied. Moreover, the coupling faults of imbalance-rub are introduced to the rotor system. Complicated nonlinear phenomena are revealed by bifurcation diagrams, time histories, Poincaré sections, and spectra. The influences of several key design parameters, such as initial bow, shaft radius, and casing stiffness, are analyzed. One of the main findings of this investigation is that when initial bow and geometrical nonlinearity coexist in a system, the resonance characteristics are obviously affected by the initial bow’s degree. This coexistence can result in the jump phenomenon, which rapidly increases the amplitude of whirling motion. These findings are useful in the fault diagnosis and feature recognition of rotating machines.

Aerodynamic noise numerical simulation and noise reduction study on automobile alternator

Chunrong Hua,Yadong Zhang,Dawei Dong,Bin Yan,Huajiang Ouyang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5

Aerodynamic noise is the predominant component of automobile alternator noise at high speed, which directly affects the noise characteristic and noise control of alternator. Based on Lighthill acoustic theory, the aerodynamic noise of an automobile alternator was simulated with three-dimensional, Large eddy simulation (LES) and Ffowcs Williams-Hawkings (FW-H) acoustic model, and the aerodynamic noise reduction research was conducted through optimizing the front fan blade spacing angle of alternator with vector composition method while considering high fan flow and optimal noise frequency components for reduced harmonic rotating noise of alternator. The results show that the sound pressure amplitude of the primary aerodynamic noise components simulated with LES are in good agreement with experimental ones, and the dominant harmonic frequency components of aerodynamic noise are in the 4th, 6th, 8th, 10th, 12th and 18th orders and the A-weighted sound pressure level of one-third octave mainly concentrates in 1120-7000 Hz. The average total noise level of alternator noise is decreased by 2.58 dB, and the mass flow of monitoring surface of fan blade is increased by 1.36 g/s with 5.80 dB decrease in the sound level of the 12th and 18th harmonic orders on average with optimized front fan blade spacing angles, which verifies the effectiveness of the noise reduction method proposed in this paper.