Shock and Vibration - Volume 19, issue 4

Authors: Chaari, Fakher | Bartelmus, Walter | Zimroz, Radoslaw | Fakhfakh, Tahar | Haddar, Mohamed

Article Type: Research Article

Abstract: Gearboxes usually run under fluctuating load conditions during service, however most of papers available in the literature describe models of gearboxes under stationary load conditions. Main task of published papers is fault modeling for their detection. Considering real situation from industry, the assumption of stationarity of load conditions cannot be longer kept. Vibration signals issued from monitoring in maintenance operations differ from mentioned models (due to load non-stationarity) and may be difficult to analyze …which lead to erroneous diagnosis of the system. The objective of this paper is to study the influence of time varying load conditions on a gearbox dynamic behavior. To investigate this, a simple spur gear system without defects is modeled. It is subjected to a time varying load. The speed-torque characteristic of the driving motor is considered. The load variation induces speed variation, which causes a variation in the gearmesh stiffness period. Computer simulation shows deep amplitude modulations with sidebands that don't differ from those obtained when there is a defective tooth. In order to put in evidence the time varying load effects, Short Time Fourier Transform and then Smoothed Wigner-Ville distribution are used. Results show that the last one is well suited for the studied case. The experimental validation presented at the end of the paper confirms the obtained results. Such results offer useful information when diagnosing gear transmissions by avoiding confusing conclusions from vibration signals. Show more

Keywords: Gear transmission, varying load, gearmesh stiffness, amplitude modulation, frequency modulation, time frequency analysis

DOI: 10.3233/SAV-2011-0656

Citation: Shock and Vibration, vol. 19, no. 4, pp. 635-652, 2012

Authors: Zhang, Zhiyi | Hu, Fang | Li, Zeng | Hua, Hongxing

Article Type: Research Article

Abstract: Investigated are modeling and control approaches for vibration analysis of two identical beams which are coupled with fluid and active mechanical links. In the modeling of the coupled beam system, orthogonal functions are used to represent vibration of the beams and the fluid-structure interaction is considered. Frequency Response Functions (FRFs) are derived from the coupled governing equations and the superposition principle for linear vibration systems. In the control of vibration of the beams, impulse response …functions corresponding to the FRFs and an adaptive control algorithm are employed to attenuate vibration transmission between the two beams. Natural frequencies, mode shapes as well as the pressure distribution in the fluid are computed. The results obtained by the proposed modeling method are in good consistency with those obtained by the finite element analysis. Moreover, it is demonstrated that the active mechanical link is able to reduce vibration transmission and change the deformation of beams as well as the distribution of fluid pressure. Show more

Keywords: Fluid-structure interaction, modal analysis, frequency response function, active control

DOI: 10.3233/SAV-2011-0657

Citation: Shock and Vibration, vol. 19, no. 4, pp. 653-668, 2012

Authors: Stockham, Leo W. | Fry, Jr., Richard N. | Graham, Paul W. | Pierce, Todd H.

Article Type: Research Article

Abstract: In assessing the potential collateral effects of bomb attacks on tanks of stored liquids, it is useful to separate the liquid that is aerosolized as an escaping cloud from that which remains inside the tank or rapidly falls to the nearby ground. One relationship currently in use partitions the two categories using a linear model of aerosolized fraction versus fragment energy deposited per unit mass of liquid which is based on calculations and a few test …data points. Since this model is incorporated in popular programs used by an expanding number of first responders to assess potential hazards, there is a need for high-confidence test data across the parameter space of interest to improve and/or validate the model. Such a series of tests was conducted during November of 2008 in which 7.57-liter (ℓ) sized cans of water were impacted with fragments of known mass using scored cased explosive charges. Impact velocities were measured, and the remaining water in the can and on the nearby ground platform was collected and weighed. The missing water was assumed to be aerosolized. This new data establishes an S-curve as a more accurate relationship between aerosolized fraction (AF) and the fragment energy deposited per unit mass of liquid in the container. Show more

Keywords: Collateral effects, aerosolized liquids, aerosolized clouds, chemical clouds, chemical plumes, fragment effects on liquid filled tanks, fragment rammed tanks, rammed liquid tanks, aerosolized fraction

DOI: 10.3233/SAV-2011-0658

Citation: Shock and Vibration, vol. 19, no. 4, pp. 669-677, 2012

Authors: Dey, Sudip | Karmakar, Amit

Article Type: Research Article

Abstract: Location of delamination is a triggering parameter for structural instability of laminated composites. In this paper, a finite element method is employed to determine the effects of location of delamination on free vibration characteristics of graphite-epoxy cross-ply composite pre-twisted shallow conical shells. The generalized dynamic equilibrium equation is derived from Lagrange's equation of motion neglecting Coriolis effect for moderate rotational speeds. The formulation is exercised by using an eight noded isoparametric plate …bending element based on Mindlin's theory. Multi-point constraint algorithm is utilized to ensure the compatibility of deformation and equilibrium of resultant forces and moments at the delamination crack front. The standard eigen value problem is solved by applying the QR iteration algorithm. Finite element codes are developed to obtain the numerical results concerning the effects of location of delamination, twist angle and rotational speed on the natural frequencies of cross-ply composite shallow conical shells. The mode shapes are also depicted for a typical laminate configuration. Numerical results obtained from parametric studies of both symmetric and anti-symmetric cross-ply laminates are the first known non-dimensional natural frequencies for the type of analyses carried out here. Show more

Keywords: Delamination, finite element, cross-ply, conical shell, multi-point constraint, mode shape, vibration

DOI: 10.3233/SAV-2011-0659

Citation: Shock and Vibration, vol. 19, no. 4, pp. 679-692, 2012

Authors: Rocha, Joana | Suleman, Afzal | Lau, Fernando

Article Type: Research Article

Abstract: This paper discusses the development of analytical models for the prediction of aircraft cabin noise induced by the external turbulent boundary layer (TBL). While, in previous works, the contribution of an individual panel to the cabin interior noise was considered, here, the simultaneous contribution of multiple flow-excited panels is analyzed. Analytical predictions are presented for the interior sound pressure level (SPL) at different locations inside the cabin of a Blended Wing Body (BWB) aircraft, for the …frequency range 0–1000 Hz. The results show that the number of vibrating panels significantly affects the interior noise levels. It is shown that the average SPL, over the cabin volume, increases with the number of vibrating panels. Additionally, the model is able to predict local SPL values, at specific locations in the cabin, which are also affected with by number of vibrating panels, and are different from the average values. Show more

Keywords: Turbulent boundary layer, aircraft cabin noise prediction, fuselage panels

DOI: 10.3233/SAV-2011-0660

Citation: Shock and Vibration, vol. 19, no. 4, pp. 693-705, 2012

Authors: Mazzei, Jr., Arnaldo J.

Article Type: Research Article

Abstract: Radially rotating beams attached to a rigid stem occur in several important engineering applications. Some examples include helicopter blades, turbine blades and certain aerospace applications. In most studies the beams have been treated as homogeneous. Here, with a goal of system improvement, non-homogeneous beams made of functionally graded materials are explored. The effects on the natural frequencies of the system are investigated. Euler-Bernoulli theory, including an axial stiffening effect and variations of …both Young's modulus and density, is employed. An assumed mode approach is utilized, with the modes taken to be beam characteristic orthogonal polynomials. Results are obtained via Rayleigh-Ritz method and are compared for both the homogeneous and non-homogeneous cases. It was found, for example, that allowing Young's modulus and density to vary by approximately 2.15 and 1.15 times, respectively, leads to an increase of 23% in the lowest bending rotating natural frequency of the beam. Show more

Keywords: Axially rotating beams, FGM, spatially varying material properties

DOI: 10.3233/SAV-2011-0661

Citation: Shock and Vibration, vol. 19, no. 4, pp. 707-718, 2012

Authors: Nandi, A. | Neogy, S. | Bhaduri, S. | Irretier, H.

Article Type: Research Article

Abstract: The present work proposes a non-contact vibration attenuator made up of a permanent magnet mounted on a piezoelectric stack. Two such actuators are made to work simultaneously in a 'twin-actuator' configuration. It is conceived that a controlled change in the gap between the actuator and the structure is capable of attenuation of vibration of the structure. This appropriate change in gap is achieved by controlled motion of the piezoelectric stacks. It is shown that the actuator …works as an active damper when the extension and contraction of the actuators are made proportional to the velocity of the beam. The resolution of extension of a piezoelectric stack is in the order of nanometers. Thus in the proposed actuator the force of actuation can be applied with great precision. This actuator is also attractive for its simple constructional feature. Show more

Keywords: Piezoelectric stack, permanent magnet, active damper, non-contact actuator, non-linear simulation

DOI: 10.3233/SAV-2012-0664

Citation: Shock and Vibration, vol. 19, no. 4, pp. 719-734, 2012

Authors: Yesilce, Yusuf

Article Type: Research Article

Abstract: In the existing reports regarding free and forced vibrations of the beams, most of them studied a uniform beam carrying various concentrated elements using Bernoulli-Euler Beam Theory (BET) but without axial force. The purpose of this paper is to utilize the numerical assembly technique to determine the exact frequency-response amplitudes of the axially-loaded Timoshenko multi-span beam carrying a number of various concentrated elements (including point masses, rotary inertias, linear springs and rotational …springs) and subjected to a harmonic concentrated force and the exact natural frequencies and mode shapes of the beam for the free vibration analysis. The model allows analyzing the influence of the shear and axial force and harmonic concentrated force effects and intermediate concentrated elements on the dynamic behavior of the beams by using Timoshenko Beam Theory (TBT). At first, the coefficient matrices for the intermediate concentrated elements, an intermediate pinned support, applied harmonic force, left-end support and right-end support of Timoshenko beam are derived. After the derivation of the coefficient matrices, the numerical assembly technique is used to establish the overall coefficient matrix for the whole vibrating system. Finally, solving the equations associated with the last overall coefficient matrix one determines the exact dynamic response amplitudes of the forced vibrating system corresponding to each specified exciting frequency of the harmonic force. Equating the determinant of the overall coefficient matrix to zero one determines the natural frequencies of the free vibrating system (the case of zero harmonic force) and substituting the corresponding values of integration constants into the related eigenfunctions one determines the associated mode shapes. The calculated vibration amplitudes of the forced vibrating systems and the natural frequencies of the free vibrating systems are given in tables for different values of the axial force. The dynamic response amplitudes and the mode shapes are presented in graphs. The effects of axial force and harmonic concentrated force on the vibration analysis of Timoshenko multi-span beam are also investigated. Show more

Keywords: Axial force effect, dynamic response amplitudes, exact natural frequency, free and forced vibrations, numerical assembly technique.

DOI: 10.3233/SAV-2012-0665

Citation: Shock and Vibration, vol. 19, no. 4, pp. 735-752, 2012

Authors: Cao, Yanlong | He, Yuanfeng | Zheng, Huawen | Yang, Jiangxin

Article Type: Research Article

Abstract: In order to reduce the false alarm rate and missed detection rate of a Loose Parts Monitoring System (LPMS) for Nuclear Power Plants, a new hybrid method combining Linear Predictive Coding (LPC) and Support Vector Machine (SVM) together to discriminate the loose part signal is proposed. The alarm process is divided into two stages. The first stage is to detect the weak burst signal for reducing the missed detection rate. Signal is whitened to improve the …SNR, and then the weak burst signal can be detected by checking the short-term Root Mean Square (RMS) of the whitened signal. The second stage is to identify the detected burst signal for reducing the false alarm rate. Taking the signal's LPC coefficients as its characteristics, SVM is then utilized to determine whether the signal is generated by the impact of a loose part. The experiment shows that whitening the signal in the first stage can detect a loose part burst signal even at very low SNR and thusly can significantly reduce the rate of missed detection. In the second alarm stage, the loose parts' burst signal can be distinguished from pulse disturbance by using SVM. Even when the SNR is −15 dB, the system can still achieve a 100% recognition rate Show more

Keywords: Alarm signal, Loose Parts Monitoring System, Support Vector Machine, Linear Predictive Coding

DOI: 10.3233/SAV-2012-0672

Citation: Shock and Vibration, vol. 19, no. 4, pp. 753-761, 2012