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Published Articles

The Volume 19, No 2, June 2014

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Elastodynamics for Non-linear Seismic Wave Motion in Real-Time Expert Seismology

Evangelos G. Ladopoulos


Based on the new theory of Real-Time Expert Seismology, a non-linear 3-D elastic wave real-time expert system is used for the exploration globa on-shore and off-shore petroleum and gas reserves. This highly innovative and ground-breaking technology uses elastic (seismic) waves moving in an unbounded subsurface medium to searching the on-shore and off-shore hydrocarbon reserves developed on the continental crust and in deeper water ranging from 300 to 3000+ m. This modern technology can be used in any depth of sea, in oceans all over the world, and for any depth in the subsurface of existing oil and gas reserves. Furthermore, the various mechanical properties of the rock regulating the wave propagation phenomenon appear as spatially-varying coefficients in a system of time-dependent hyperbolic partial differential equations. The propagation of the seismic waves through the earth subsurface is described by the wave equation, which is finally reduced to a Helmholz differential equation. Then the Helmholtz differential equation is numerically evaluated by using the Singular Integral Operators Method (SIOM). Also, several properties are analysed and investigated for the wave equation. Finally, an application is proposed for the determination of the seismic field radiated from a pulsating sphere into an infinite homogeneous medium. The acoustic pressure radiated from the above pulsating sphere is determined by the SIOM.

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3D Analysis of the Sound Reduction Provided by Protective Surfaces Around a Noise Source

Godinho, L., Costa, E.G.A., Santiago, J.A.F., Pereira, A. , Amado-Mendes, P.


In the present paper, the authors present a numerical analysis of the sound reduction provided by simple acoustic protective measures to attenuate the noise emitted by equipment placed near a facade. The noise source is assumed to be surrounded by an enclosed space, defined as a parallelepiped chamber with a rectangular opening. To perform the numerical analysis, a 3D Boundary Element formulation is implemented. This formulation makes use of the domain decomposition, together with Green's functions, specifically defined to reduce the size of the involved system matrices and to allow consideration for surface absorption. Indeed, these Green's functions, defined using the image-source technique, allow modelling of the building's facade and the ground as infinite surfaces with a given absorption coefficient. The numerical model is verified against an analytical solution known for the case of a point load acting within a parallelepiped space; additionally, it is validated by comparing its results with those obtained experimentally for a simple case. The implemented model is then used to perform a number of numerical simulations, illustrating the effect of different configurations of the protective surfaces in the sound reduction.

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Study on Linear Vibration Model of Shield TBM Cutterhead Driving System

Xianhong Li, Haibin Yu, Peng Zeng, Mingzhe Yuan, Jianda Han, Lanxiang Sun


In this paper, a general linear time-varying multiple-axis (LTVMA) vibration model of shield tunnel boring machine (TBM) cutterhead driving system is established. The corresponding multiple inputs and multiple outputs (MIMO) state-space model is also presented. The linear vibration model is analysed, and the vibration-torque transfer function matrix and the vibration-torque static gain matrix are obtained. The linear vibration model is simulated, and the physical parameters' effects on the vibration response are investigated. A preliminary approach is proposed to reduce vibration by increasing motor rotor inertia and viscous damped. The LTVMA vibration model provides a solid foundation for fault detection and diagnosis (FDD), as long as the health monitoring of cutterhead driving system.

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An Algorithm for Solving Torsional Vibration Problems Based on the Invariant Imbedding Method

Antonio Lopes Gama and Rafael Soares de Oliveira


In this work the invariant imbedding method has been used to develop an algorithm to study the torsional vibration of non-uniform systems. The algorithm is based on the propagation, reflection, and transmission of waves in a stepped waveguide and is part of a procedure to transform two-point boundary value problems in initial value problems. Based on this approach, a continuous model has been developed and a simple, versatile, and robust algorithm has been constructed to solve torsional vibration problems of non-uniform shafts with circular cross-sections. The proposed solution algorithm was extensively evaluated through comparisons with analytical solutions and the finite element method. The results show that the proposed method can provide the exact solution for uniform shafts with concentrated elements and accurate results for a wide variety of torsional vibration problems. Systems with continuously varying geometry may be approximated by stepped shafts. The proposed method can also be used to study the dynamic behaviour of others stepped systems.

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Free Flexural Vibration Response of Integrally-Stiffened and/or Stepped-Thickness Composite Plates or Panels

J.Javanshir, T.Farsadi, U.Yuceoglu


This study is mainly concerned with a general approach to the theoretical analysis and the solution of the free vibration response of integrally-stiffened and/or stepped-thickness plates or panels with one or more integral plate stiffeners. In general, the Stiffened System is considered to be composed of dissimilar Orthotropic Mindlin Plates with unequal thicknesses. The dynamic governing equations of the individual plate elements of the system and the stress resultant-displacement expressions are combined and algebraically manipulated. These operations lead to the new Governing System of the First Order Ordinary Differential Equations in state vector forms. The new governing system of equations facilitates the direct application of the present method of solution, namely, the Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials). As shown in the present study, the MTMM is sufficiently general to handle the free vibration response of the stiffened system (with, at least, one or up to three or four Integral Plate Stiffeners). The present analysis and the method of solution are applied to the typical stiffened plate or panel system with two integral plate stiffeners. The mode shapes with their natural frequencies are presented for orthotropic composite cases and for several sets of support conditions. As an additional example, the case of the stiffened plate or panel system with three integral plate stiffeners is also considered and is shown in terms of the mode shapes and their natural frequencies for several sets of the boundary conditions. Also, some parametric studies of the natural frequencies versus the aspect ratio, stiffener thickness ratio, stiffener length (or width) ratio and the bending stiffness ratio are investigated and are graphically presented.

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Vibrational Power Flow Analysis of a Cylindrical Shell Using a Four-Point Technique

H.Salimi-Mofrad, S. Ziaei-Rad, M. Moradi


The aim of studying and analysing vibrational characteristics of structures using power flow is to control the noise and vibration within the structure and prevent it from being transmitted into the environment. The power flow within a cylindrical shell is investigated because of its importance in designing spacecraft and marine structures. In this paper, a four-point power flow technique was used to examine the effects of flexural and shear forces on the total power flow in a cylindrical shell in free-free conditions. To obtain better results, the exponential window was used considering the use of a hammer for the excitation of the structure. The examining of the results and obtained diagrams determined that the effect of shear forces on the total power flow was more than the effect of flexural forces. Moreover, the precision of two-point and four-point techniques was compared.

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Non-Linear Thickness Variation on the Thermally-Induced Vibration of a Rectangular Plate: A Spline Technique

Arun Kumar Gupta, Mamta


The fourth order differential equation, governing the transverse motion of an elastic rectangular plate of a non-linear thickness variation with a thermal gradient, has been analysed on the basis of classical plate theory employing the Quintic spline interpolation technique. An algorithm for computing the solution of this differential equation is presented for the case of equal intervals. The effect of the thermal gradient, together with taper constants on the natural frequencies of vibration, is illustrated for the first three modes of vibration for C-S-C-S and S-S-S-S rectangular plates.

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