scholarly journals Homogenization Models for a Simple Dielectric-Composite Slab upon Oblique Incidence

2014 ◽  
Vol 2014 ◽  
pp. 1-12 ◽  
Author(s):  
Jiaran Qi ◽  
Jinghui Qiu ◽  
Chongzhi Han
Keyword(s):  
Oblique Incidence ◽  
Model Parameters ◽  
Scattering Parameters ◽  
Composite Slab ◽  
Reflection Data ◽  
Dielectric Composite ◽  
Propagation Matrix ◽  
Independent Parameters ◽  
Transmission And Reflection ◽  
Stratified Model

Four different models are applied to effectively describe a geometrically simple dielectric-composite slab. The corresponding model parameters, when the oblique incidence is taken into account, are retrieved based on the transmission and reflection data and compensated with the nonmagnetic assumption. The scattering parameters of each model with derived parameters for various angles of incidence are then analytically calculated using the forward propagation matrix method and compared with the simulated scattering parameters from the real composite slab. According to these comparisons, it is shown that spatial dispersion makes it challenging to achieve angle-independent parameters for the applied four models. Moreover, when a stratified model is employed to describe the composite slab of our interest under oblique incidence, the boundary layers need to be anisotropic.

Precision analysis of first‐break times in grid models

Geophysics ◽  
1998 ◽  
Vol 63 (3) ◽  
pp. 1062-1065 ◽  
Author(s):  
Thomas Gruber ◽  
Stewart A. Greenhalgh
Keyword(s):  
Numerical Models ◽  
Grid Point ◽  
Tomographic Reconstruction ◽  
Velocity Model ◽  
Model Parameters ◽  
Seismic Reflection Data ◽  
Arrival Times ◽  
Velocity Models ◽  
Reflection Data ◽  
Inversion Techniques

Rectangular grid velocity models and their derivatives are widely used in geophysical inversion techniques. Specifically, seismic tomographic reconstruction techniques, whether they be based on raypath methods (Bregman et al., 1989; Moser, 1991; Schneider et al., 1992; Cao and Greenhalgh, 1993; Zhou, 1993) or full wave equation methods (Vidale, 1990; Qin and Schuster, 1993; Cao and Greenhalgh, 1994) for calculating synthetic arrival times, involve propagation through a grid model. Likewise, migration of seismic reflection data, using asymptotic ray theory or finite difference/pseudospectral methods (Stolt and Benson, 1986; Zhe and Greenhalgh, 1997) involve assigning traveltimes to upward and downward propagating waves at every grid point in the model. The traveltimes in both cases depend on the grid specification. However, the precision level of such numerical models and their dependence on the model parameters is often unknown. In this paper, we describe a two‐dimensional velocity model and derive an error bound for first‐break times calculated with such a model. The analysis provides clear guidelines for grid specifications.

Mathematical modeling of cement paste microstructure by mosaic pattern: Part I. Formulation

1996 ◽  
Vol 11 (8) ◽  
pp. 1943-1952 ◽  
Author(s):  
Yunping Xi ◽  
Paul D. Tennis ◽  
Hamlin M. Jennings
Keyword(s):  
Cement Paste ◽  
Present Model ◽  
Spatial Arrangement ◽  
Structural Features ◽  
Evaluation Procedure ◽  
Model Parameters ◽  
Multiphase Microstructure ◽  
Water To Cement Ratio ◽  
The Relationship ◽  
Independent Parameters

This paper develops a mathematical model using mosaic patterns to characterize structural features of complex, multiphase, and multidimensional microstructures, such as those for cement paste. A multiphase microstructure can be characterized by m independent parameters; the first m– 1 parameters are equivalent to the volume fractions of the phases, while the final parameter describes the grain size, and thus, the spatial arrangement of the microstructure. An evaluation procedure for the parameters is given; they can be evaluated based on a 2D image, and then the 3D microstructure can be simulated by the present model. The relationship among the model parameters and material parameters, such as water-to-cement ratio and particle size distribution, are also established.

scholarly journals Nonlinear finite element analysis of profiled steel deck composite slab system under monotonic loading.

2021 ◽  
Author(s):  
Shubhangi Attarde
Keyword(s):  
Finite Element ◽  
Mesh Size ◽  
Monotonic Loading ◽  
Nonlinear Finite Element ◽  
Experimental Results ◽  
Model Parameters ◽  
Element Analysis ◽  
Composite Slab ◽  
Composite Slabs ◽  
Steel Deck

This research concentrated on the nonlinear finite element (FE) modeling of one-way composite floor slab system comprising of profiled steel deck and two types of concrete namely, Engineered Cementitious Composites (ECC) and Self-Consolidating Concrete (SCC). Two FE models were developed based experimental results of composite slabs subjected to in-plane monotonic loading. The simulated load-deflection response, moment resistance, and shear bond capacity using two FE models were in reasonable good agreement with experimental results. The FE models were used in a comprehensive parametric study to investigate the effect of numerical model parameters such as mesh size, dilation angle, steel sheet-concrete interaction contact, material properties and composite slab span. In addition, FE models were used to determine shear bond parameters of ECC and SCC composite slabs that can be used for design purposes.

scholarly journals Phase Role in the Non-Uniformity of Main-Line Couplings in Asymmetric Extracted-Pole Inline Filters

Electronics ◽  
2021 ◽  
Vol 10 (24) ◽  
pp. 3058
Author(s):  
Ángel Triano ◽  
Patricia Silveira ◽  
Jordi Verdú ◽  
Eloi Guerrero ◽  
Pedro de Paco
Keyword(s):  
Phase Correction ◽  
Main Line ◽  
Hyperbolic Model ◽  
Characteristic Polynomials ◽  
Scattering Parameters ◽  
Transmission Zeros ◽  
And Topology ◽  
Ladder Network ◽  
Novel Method ◽  
Transmission And Reflection

The use of classical symmetrical polynomial definition to synthesize fully canonical inline filters with an asymmetrical distribution of the transmission zeros along the topology leads to the occurrence of uneven admittance inverter in the main-line. This form introduces some limitations to transform such topology into a ladder network. Despite circuital transformation can be used to accommodate both technology and topology, it is usual that extra reactive elements are necessary to implement phase shifts required to achieve the complete synthesis. This article introduces a novel method able to determine the required phase correction that has to be applied to the characteristic polynomials in order to equalize all the admittance inverters in the main path to the same value. It has been demonstrated that a suitable pair of phase values can be accurately estimated using a developed hyperbolic model which can be obtained from the transmission and reflection scattering parameters. To experimentally validate the proposed method, a Ladder-type filter with asymmetrical polynomial definition has been synthesized, fabricated, and measured, demonstrating the effectiveness of the developed solution.

Retrieving both the impedance contrast and background velocity: A global strategy for the seismic reflection problem

Geophysics ◽  
1989 ◽  
Vol 54 (8) ◽  
pp. 991-1000 ◽  
Author(s):  
R. Snieder ◽  
M. Y. Xie ◽  
A. Pica ◽  
A. Tarantola
Keyword(s):  
Seismic Reflection ◽  
Gradient Methods ◽  
Synthetic Seismograms ◽  
Small Scale ◽  
Model Parameters ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Reference Velocity ◽  
Impedance Contrast

Recorded seismic reflection waveforms contain information as to the small‐scale variations of impedance and the large‐scale variations of velocity. This information can be retrieved by minimizing the misfit between the recorded waveforms and synthetic seismograms as a function of the model parameters. Because of the different physical characters of the velocity and the impedance, we update these parameters in an alternating fashion, which amounts to a relaxation approach to the minimization of the waveform misfit. As far as the impedance is concerned, this minimization can be performed efficiently using gradient algorithms. For the inversion for seismic velocities, gradient methods do not work nearly as well; therefore, we use different minimization methods for determining impedances and velocities. However, the determination of the impedance and the determination of the velocity are strongly coupled; relaxation is most effective when this coupling is as weak as possible. Weak coupling can be achieved partially by parameterizing the impedances not as a function of depth but as a function of traveltime. A nonlinear, nonlocal method is presented for determining the smooth reference velocity from seismic reflection data. This technique is applied both to synthetic seismograms and to real marine data. In both cases, the velocity information implicitly contained in the curvature of the reflection hyperbolas was fully retrieved using nonlinear waveform optimization. In this way, it is possible to reconstruct both the impedance contrast and the smooth reference velocity from band‐limited seismic reflection data using a single waveform‐fit criterion.

Transmission‐reflection tomography: Application to reverse VSP data

Geophysics ◽  
1997 ◽  
Vol 62 (3) ◽  
pp. 884-894 ◽  
Author(s):  
Weijian Mao ◽  
Graham W. Stuart
Keyword(s):  
Seismic Profile ◽  
Transmission Tomography ◽  
Data Set ◽  
Lower Velocity ◽  
Surface Reflection ◽  
Reflection Data ◽  
Vsp Data ◽  
Reflection Tomography ◽  
Transmission And Reflection

A multiphase tomographic algorithm is presented that allows 2-D and 3-D slowness (inverse of velocity) and variable reflector depth to be reconstructed simultaneously from both transmission and reflection traveltimes. We analyze the ambiguity in the determination of velocity and depth in transmission and reflection data and realize that depth perturbation is more sensitive to reflection traveltime anomalies than slowness perturbation, whereas the reverse is true of transmission traveltime anomalies. Because of the constraints on velocity and depth provided by the different wave types, this algorithm reduces the ambiguity substantially between velocity and depth prevalent in reflection tomography and also avoids the undetermined problem in transmission tomography. The linearized inversion was undertaken iteratively by decoupling velocity parameters from reflector depths. A rapid 2-D and 3-D ray‐tracing algorithm is used to compute transmission and reflection traveltimes and partial derivatives with respect to slowness and reflector depth. Both depth and velocity are parameterized in terms of cubic B‐spline functions. Synthetic examples indicate the improvement in tomographic results when both transmission and reflection times are included. The method has been applied to a reverse vertical seismic profile (VSP) data set recorded on the British coal measures along a crossed‐linear array. Traveltimes were picked automatically by the simultaneous determination of time delays and stacking weights using a waveform matching technique. The tomographic inversion of the observed reverse VSP images two fault‐zones of lower velocity than the surrounding media. The location of the faults was confirmed by near‐by reflection lines. The technique can be applied to offset VSPs or reverse VSPs and coincident VSP and surface reflection data.

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