The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Y.q. Shi - One of the best experts on this subject based on the ideXlab platform.

  • Vibro-impact dynamics of a two-degree-of freedom periodically-forced system with a clearance: Diversity and parameter matching of periodic-impact motions
    International Journal of Non-Linear Mechanics, 2014
    Co-Authors: G.w. Luo, Y.q. Shi
    Abstract:

    A two-degree-of-freedom system with a clearance and subjected to harmonic excitation is considered. The correlative relationship and matching law between dynamic performance and system parameters are studied by multi-parameter and multi-performance co-simulation analysis. Two key parameters of the system, the Exciting Frequency ω and clearance δ, are emphasized to reveal the influence of the main factors on dynamic performance of the system. Diversity and evolution of periodic impact motions are analyzed. The fundamental group of impact motions is defined, which have the period of Exciting force and differ by the numbers p and q of impacts occurring at the left and right constraints of the clearance. The occurrence mechanism of chattering-impact vibration of the system is studied. As the clearance δ is small or small enough, the transition from 1–p–p to 1–(pþ1)–(pþ1) motion (the fundamental group of motions, pZ1) basically goes through the processes as follows: pitchfork bifurcation of symmetric 1–p–p motion, period-doubling bifurcation of asymmetric 1–p–p motion, non-periodic or chaotic motions caused by a succession of period-doubling bifurcations, symmetric 1–(pþ1)–(pþ1) motion generated by a degeneration of chaos. As for slightly large clearance, a series of grazing bifurcations of periodic symmetrical impact motions occur with decreasing the Exciting Frequency so that the number p of impacts of the fundamental group of motions increases two by two. As p becomes big enough, the incomplete chattering-impact motion will appear which exhibits a chattering sequence in an excitation period followed by a finite sequence of impacts with successively reduced velocity and reaches the non-sticking region. Finally, the complete chattering-impact motion with sticking will occur with decreasing the Exciting Frequency ω up to the sliding bifurcation boundary. A series of singular points on the boundaries between existence regions of any adjacent symmetrical impact motions with fundamental period are found, i.e., two different saddle-node bifurcation boundaries of one of them, real-grazing and bare-grazing bifurcation boundaries of the other alternately and mutually cross themselves at the points of intersection and create inevitably two types of transition regions: narrow hysteresis and small tongue-shaped regions. A series of zones of regular periodic and subharmonic impact motions are found to exist in the tongue-shaped regions. Based on the sampling ranges of parameters, the influence of dynamic parameters on impact velocities, existence regions and correlative distribution of different types of periodic-impact motions of the system is emphatically analyzed.

Zhang Pi-zhuang - One of the best experts on this subject based on the ideXlab platform.

  • Study on Simulation of Influence of Size and Exciting Frequency of Transducer on Radiation Field
    Computer Simulation, 2011
    Co-Authors: Zhang Pi-zhuang
    Abstract:

    The size and the Exciting Frequency of the transducer have an important influence on the sound field distribution,so it is great significant for people to understand the laws of this affection in the right choice for transducers in actual process of Ultrasonic Testing.This paper studies how the size and Exciting Frequency influence on the radiaton field of transducer by simulation.The difficulty lies in the establishment of mathematical model.The mathematical models given by the past articles have many defects,for example,they can not give the analytical expressions of the whole sound field radiated by the transduce,and the use of a numerical method of calculation is very cumbersome.The Gaussian beam model used in this paper overcomes the shortcomings of previous methods,and it can provide a simple analytical expression describing the sound field radiated by the transducer.This paper adopts this method with the Matlab software to simulate the different sizes and different Exciting frequencies of circular piston transducer sound field,and gives the laws that how the size and Exciting Frequency influence on the radiaton field of transducer intuitively.

G.w. Luo - One of the best experts on this subject based on the ideXlab platform.

  • Vibro-impact dynamics of a two-degree-of freedom periodically-forced system with a clearance: Diversity and parameter matching of periodic-impact motions
    International Journal of Non-Linear Mechanics, 2014
    Co-Authors: G.w. Luo, Y.q. Shi
    Abstract:

    A two-degree-of-freedom system with a clearance and subjected to harmonic excitation is considered. The correlative relationship and matching law between dynamic performance and system parameters are studied by multi-parameter and multi-performance co-simulation analysis. Two key parameters of the system, the Exciting Frequency ω and clearance δ, are emphasized to reveal the influence of the main factors on dynamic performance of the system. Diversity and evolution of periodic impact motions are analyzed. The fundamental group of impact motions is defined, which have the period of Exciting force and differ by the numbers p and q of impacts occurring at the left and right constraints of the clearance. The occurrence mechanism of chattering-impact vibration of the system is studied. As the clearance δ is small or small enough, the transition from 1–p–p to 1–(pþ1)–(pþ1) motion (the fundamental group of motions, pZ1) basically goes through the processes as follows: pitchfork bifurcation of symmetric 1–p–p motion, period-doubling bifurcation of asymmetric 1–p–p motion, non-periodic or chaotic motions caused by a succession of period-doubling bifurcations, symmetric 1–(pþ1)–(pþ1) motion generated by a degeneration of chaos. As for slightly large clearance, a series of grazing bifurcations of periodic symmetrical impact motions occur with decreasing the Exciting Frequency so that the number p of impacts of the fundamental group of motions increases two by two. As p becomes big enough, the incomplete chattering-impact motion will appear which exhibits a chattering sequence in an excitation period followed by a finite sequence of impacts with successively reduced velocity and reaches the non-sticking region. Finally, the complete chattering-impact motion with sticking will occur with decreasing the Exciting Frequency ω up to the sliding bifurcation boundary. A series of singular points on the boundaries between existence regions of any adjacent symmetrical impact motions with fundamental period are found, i.e., two different saddle-node bifurcation boundaries of one of them, real-grazing and bare-grazing bifurcation boundaries of the other alternately and mutually cross themselves at the points of intersection and create inevitably two types of transition regions: narrow hysteresis and small tongue-shaped regions. A series of zones of regular periodic and subharmonic impact motions are found to exist in the tongue-shaped regions. Based on the sampling ranges of parameters, the influence of dynamic parameters on impact velocities, existence regions and correlative distribution of different types of periodic-impact motions of the system is emphatically analyzed.

Jyoti K Sinha - One of the best experts on this subject based on the ideXlab platform.

  • Application of curvature of residual operational deflection shape (R-ODS) for multiple-crack detection in structures
    Structural Monitoring and Maintenance, 2014
    Co-Authors: Erfan Asnaashari, Jyoti K Sinha
    Abstract:

    Detection of fatigue cracks at an early stage of their development is important in structural health monitoring. The breathing of cracks in a structure generates higher harmonic components of the Exciting Frequency in the Frequency spectrum. Previously, the residual operational deflection shape (R-ODS) method was successfully applied to beams with a single crack. The method is based on the ODSs at the Exciting Frequency and its higher harmonic components which consider both amplitude and phase information of responses to map the deflection pattern of structures. Although the R-ODS method shows the location of a single crack clearly, its identification for the location of multiple cracks in a structure is not always obvious. Therefore, an improvement to the R-ODS method is presented here to make the identification process distinct for the beams with multiple cracks. Numerical and experimental examples are utilised to investigate the effectiveness of the improved method.

  • Development of residual operational deflection shape for crack detection in structures
    Mechanical Systems and Signal Processing, 2013
    Co-Authors: Erfan Asnaashari, Jyoti K Sinha
    Abstract:

    Abstract Excitation of a cracked structure at a Frequency always generates higher harmonic components of the Exciting Frequency due to the breathing of the crack. In this paper, the deflection of cracked structures at the Exciting Frequency and the second harmonic component is mapped by a new method based on the operational deflection shape (ODS) for the purpose of crack detection. While the ODS is helpful in understanding dynamic behaviour of structures and machines, it is not always possible to determine the location of cracks in structures or machines based on the ODS itself. Therefore, a new concept called residual ODS (R-ODS) has been defined for crack detection in beam-like structures. This paper presents the details of the proposed method and its results when applied to numerical and experimental examples.

  • Operational Deflection Shape for Crack Detection in Structures
    Key Engineering Materials, 2013
    Co-Authors: Erfan Asnaashari, Jyoti K Sinha
    Abstract:

    Crack detection in structures has been one of the active research areas for decades. Several crack detection methods have been suggested in the literature with their own advantages and limitations. In this paper, a very simplified method has been presented which assumes the vibration of entire structure can be scanned through a laser vibrometer. Therefore, measurement at a large number of locations in any structure is possible. Excitation of the cracked structure at a Frequency always generates higher harmonic components of the Exciting Frequency due to the breathing of the crack. The deflection of the structure at higher harmonics of the Exciting Frequency is mapped by (a) amplitude of deflection (AOD) at higher harmonics as suggested in the literature, and (b) a new method based on the operational deflection shape (ODS) (both amplitude and phase) at higher harmonics for the crack detection. This paper presents the proposed method and the results through numerical examples.

Jie Liu - One of the best experts on this subject based on the ideXlab platform.

  • A tunable electromagnetic vibration absorber: Characterization and application
    Journal of Sound and Vibration, 2006
    Co-Authors: Jie Liu, Kefu Liu
    Abstract:

    The paper presents a newly designed electromagnetic vibration absorber (EMVA), whose stiffness is on-line tunable. The EMVA is capable of suppressing vibration of the primary system excited by a harmonic force with a variable Frequency. The EMVA consists of a clamped–clamped aluminum beam and a permanent magnet that is embedded in the center of the beam and placed between two poles of a C-shaped electromagnet. By varying the current of the electromagnet, stiffness of the EMVA can be adjusted instantaneously such that the absorber Frequency can be tuned. A detailed characterization of the EMVA is presented. The effective stiffness of the absorber is determined numerically and validated experimentally. To test its effectiveness in vibration suppression, the EMVA is used to track two types of the Exciting Frequency variations: multi-step and linear. The response of the absorber mass is used to tune the EMVA to ensure that the absorber Frequency equals the Exciting Frequency.

  • COMPARISON OF TWO AUTO-TUNING METHODS FOR A VARIABLE STIFFNESS VIBRATION ABSORBER
    Transactions of the Canadian Society for Mechanical Engineering, 2005
    Co-Authors: Kefu Liu, Liang Liao, Jie Liu
    Abstract:

    A tunable vibration absorber is developed and its stiffness can be varied on-line. The absorber system is mounted on a clamped-clamped beam acting as a primary system. The objective is to suppress vibration of the primary beam subject to a harmonic excitation whose Frequency may vary. A system modeling is conducted. The Frequency response of the system is given to show the operating range of the absorber system. Using a simplified two-degree-of-freedom model, two auto-tuning methods are studied. The methods differ in the way of how to identify the Exciting Frequency. The first method follows a common practice that uses the Frequency of the maximum peak in the response spectrum as the Exciting Frequency. The second method makes use of information of both the response spectrum and the natural frequencies. An experimental study is conducted to compare the two methods. The study has shown that the second method performs better than the first method in terms of Frequency tracking ability and robustness to dist...