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Wave Transmission Characteristics in Honeycomb Sandwich Structures using the Spectral Finite Element Method

Electronic Theses of Indian Institute of Science

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Title Wave Transmission Characteristics in Honeycomb Sandwich Structures using the Spectral Finite Element Method
 
Creator Murthy, MVVS
 
Subject Wave Propagation
Spectral Finite Element Methods
Spacecraft Structures
Honeycomb Sandwich Structures
Wave Transmission
Spacecraft Structural Joints
Waveguides
Sandwich Beams
Equivalent Single Layer (ESL) Theories
First Order Shear Deformation Theory (FSDT)
Laplace Transform Spectral Finite Element
Sandwich Plate Theory
Wave Propagation Analysis
Wavelet Transform based Spectral Finite Element (WSFE)
Fourier Transform based Spectral Finite Element (FSFE)
Aerospace Engineering
 
Description Wave propagation is a phenomenon resulting from high transient loadings where the duration of the load is in µ seconds range. In aerospace and space craft industries it is important to gain knowledge about the high frequency characteristics as it aids in structural health monitoring, wave transmission/attenuation for vibration and noise level reduction.
The wave propagation problem can be approached by the conventional Finite Element Method(FEM); but at higher frequencies, the wavelengths being small, the size of the finite element is reduced to capture the response behavior accurately and thus increasing the number of equations to be solved, leading to high computational costs. On the other hand such problems are handled in the frequency domain using Fourier transforms and one such method is the Spectral Finite Element Method(SFEM). This method is introduced first by Doyle ,for isotropic case and later popularized in developing specific purpose elements for structural diagnostics for inhomogeneous materials, by Gopalakrishnan. The general approach in this method is that the partial differential wave equations are reduced to a set of ordinary differential equations(ODEs) by transforming these equations to another space(transformed domain, say Fourier domain). The reduced ODEs are usually solved exactly, the solution of which gives the dynamic shape functions. The interpolating functions used here are exact solution of the governing differential equations and hence, the exact elemental dynamic stiffness matrix is derived. Thus, in the absence of any discontinuities, one element is sufficient to model 1-D waveguide of any length. This elemental stiffness matrix can be assembled to obtain the global matrix as in FEM, but in the transformed space. Thus after obtaining the solution, the original domain responses are obtained using the inverse transform. Both the above mentioned manuscripts present the Fourier transform based spectral finite element (FSFE), which has the inherent aliasing problem that is persistent in the application of the Fourier series/Fourier transforms. This is alleviated by using an additional throw-off element and/or introducing slight damping in to the system. More recently wave let transform based spectral finite element(WSFE) has been formulated which alleviated the aliasing problem; but has a limitation in obtaining the frequency characteristics, like the group speeds are accurate only up-to certain fraction of the Nyquist(central frequency). Currently in this thesis Laplace transform based spectral finite elements(LSFE) are developed for sandwich members. The advantages and limitations of the use of different transforms in the spectral finite element framework is presented in detail in Chapter-1.
Sandwich structures are used in the space craft industry due to higher stiffness to weight ratio. Many issues considered in the design and analysis of sandwich structures are discussed in the well known books(by Zenkert, Beitzer). Typically the main load bearing structures are modeled as beam sand plates. Plate structures with kh
 
Contributor Gopalakrishnan, S
 
Date 2017-12-11T19:38:01Z
2017-12-11T19:38:01Z
2017-12-12
2014
 
Type Thesis
 
Identifier http://hdl.handle.net/2005/2901
http://etd.ncsi.iisc.ernet.in/abstracts/3763/G26330-Abs.pdf
 
Language en_US
 
Relation G26330