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The Volume 20, No 3, September 2015



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Improved Crack Closure Line Position: An Improved Model for Crack Breathing Phenomenon

R. Ramezanpour, M. Ghayour, S. Ziaei-Rad


https://doi.org/10.20855/ijav.2015.20.3376


The dynamic behaviour of a cracked Jeffcott rotor is investigated in this paper. The crack is located at the midpoint of the rotor. It is known that when the static deflection dominates the vibration of the rotating shaft, the crack opens and closes according to the shaft rotation. This phenomenon is known as crack breathing. There are several models for classifying crack breathing phenomena, such as the switching crack model, harmonic approach model, and response-dependent breathing crack model. In order to model the breathing of the crack in the response-dependent breathing crack model, the concept of a crack closure line position (CCLP) is proposed and used by some researchers. The main scope of this work is to present an improved crack closure line position (ICCLP). By using several contour plots over the crack's surface, it is shown that the imaginary line that separates the open and closed parts of a breathing crack should not be considered perpendicular to the crack tip. It is also shown that the improved model positively agrees with those proposed in the literature. The effects of ICCLP on the coefficients of the local flexibility matrix are investigated.


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Generation of Acoustic Disturbances in Supersonic Laminar Cavity Flows

Weipeng Li, Taku Nonomura, and Kozo Fujii


https://doi.org/10.20855/ijav.2015.20.3377


The generation of acoustic disturbances in supersonic laminar cavity flows is investigated by large-eddy simulations of supersonic laminar flow (M=1.2, 2.0, and 3.0) past a rectangular cavity with a length-to-depth ratio of 2. Results suggest that well-originated large-scale vortical structures with strong spanwise coherence are present in the shear layer. Compressibility effects have significant impacts on the shear-layer development and the fluctuation properties. The dominant mechanism for the acoustic radiation in supersonic laminar cavity flows is shown to be associated with the successive passage of large-scale vortices over the cavity trailing edge. It is found that Mach waves radiated from the cavity shear layer may have cbox{significant} contributions for the noiseradiation in terms of enhancing the strength of the feedback compression waves.


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Meshless Numerical Solution of Boundary Integral Equations based on Non Uniform Rational Basis-Splines

Vincenzo Marchese and Umberto Iemma


https://doi.org/10.20855/ijav.2015.20.3378


The paper deals with the use of Non Uniform Rational Basis-Splines (NURBS) for the global representation of domain geometry and unknown functions aimed at the numerical solution of Boundary Integral Equations (BIE). The use of a global NURBS function basis yields a meshless method which does not need the partition of the boundary into elements. The level of the accuracy in the representation of dependent and independent variables can be changed in each simulation, according to the problem requirements, thanks to the recursive definition of NURBS. The solving system of equations is assembled by means of the collocation of the integral equation onto the Greville abscissae in the NURBS parametric space. The unknowns are the locations of the control points in the vector space the unknown function belongs to. Preliminary numerical results have been obtained in potential aerodynamics and acoustic scattering. The numerical solution reveals a remarkable level of accuracy in all the test cases analyzed with a convergence rate always higher than the order of the NURBS adopted.


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Rotor Faults Diagnosis Using Artificial Neural Networks and Support Vector Machines

Sukhjeet Singh and Navin Kumar


https://doi.org/10.20855/ijav.2015.20.3379


Unbalance and misalignment are the commonly occurring faults in rotating mechanical systems. These faults are caused mainly due to improper installation or premature failure of the machine components. Detection and diagnosis of faults in rotating machinery is crucial for its optimal performance. In this study artificial neural networks (ANN) and support vector machine (SVM) techniques have been used to determine the effectiveness of statistical features for fault diagnosis in rotating mechanical system using healthy and faulty rotors. The vibration signature responses are obtained and analyzed for healthy shaft without disk (HSWD), healthy shaft with an unbalanced disk (HSWUD), centrally bent shaft without disk (CBSWD) and centrally bent shaft with an unbalanced disk (CBSWUD) with zero bow phase angle. Their predominant features were fed as input for training and testing ANN and SVM, whereas the relative efficiency of these techniques have been compared for classifying the faults in the test system. The study concludes that these machine learning algorithms can be used for fast and reliable diagnosis of rotor faults.


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Nonlinear Vibration Analysis of Flexible Hoisting Rope with Time-Varying Length

Ji-hu Bao, Peng Zhang, Chang-ming Zhu, Ming Zhu


https://doi.org/10.20855/ijav.2015.20.3380


The nonlinear vibration of a flexible hoisting rope with time-varying length and axial velocity is investigated. The flexible hoisting rope is modeled as a taut translating string with a rigid body attached at its low end. A systematic procedure for deriving the system model of a flexible hoisting rope with time-varying length and axial velocity is presented. The governing equations were developed by employing the extended Hamilton's principle considering coupling of axial movement and flexural deformation of the rope. The derived governing equations are nonlinear partial differential equations(PDEs) with time-varying coefficients. The Galerkin's method and the 4th Runge-Kutta method were employed to numerically analyze the resulting equations. Further, the dynamic stability of the flexible hoisting rope was investigated according to the Lyapunov stability theory. The motions of an elevator hoisting system were presented to illustrate the proposed mathematical models. The results of simulation show that the dynamic motions of the flexible hoisting string are stable during downward movement but are unstable during upward movement. The proposed systematic procedures in analyzing the dynamic stability can facilitate further development in dynamic control of the flexible hoisting system in practice.


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Active Sway Control of a Gantry Crane by an Electrical Ducted Fan

Mohammad Javad Maghsoudi and Z. Mohamed


https://doi.org/10.20855/ijav.2015.20.3381


Sway reduction is very vital in a nonlinear oscillatory system such as a gantry crane. In this paper, a new design is proposed for active sway control of a gantry crane using an electrical ducted fan. The thrust force developed by the motor is used to cancel out payload oscillation. A dynamic model of the crane with a ducted fan is derived and simulated using Matlab. Performance of the proposed technique is investigated for a crane subjected to initial sway and an external force input. In addition, cases with different payloads and cable lengths are also studied. Simulation results show satisfactory performance of the fan-controlled system in eliminating the payload sway. The proposed design can also handle changes in payload and cable length. A main advantage of this approach is that it does not require modeling of the crane in real time experiments.


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Determination of Modal Constant for Fundamental Frequency of Perforated Plate by Rayleigh's Method using Experimental Values of Natural Frequency

Kiran D. Mali and Pravin M. Singru


https://doi.org/10.20855/ijav.2015.20.3382


In the present work, an expression for the modal constant of the fundamental frequency of the perforated plate was determined experimentally. Rayleigh's formulation was used to calculate the modal constant. The displacement solution was considered to be a linear combination of cosines. In Rayleigh's formulation, fundamental frequency values were taken from experimental analysis. This problem was solved in reverse order by considering known experimental values of the fundamental frequency. Thus, the modal constant expression for fundamental frequency was discovered.


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