Two‐dimensional topographic responses in magnetotellurics modeled using finite elements

Geophysics ◽  
1986 ◽  
Vol 51 (11) ◽  
pp. 2131-2144 ◽  
Author(s):  
Philip E. Wannamaker ◽  
John A. Stodt ◽  
Luis Rijo
Keyword(s):  
Finite Elements ◽  
Rayleigh Scattering ◽  
Linear Interpolation ◽  
Transverse Magnetic ◽  
Two Dimensional ◽  
Transverse Magnetic Mode ◽  
Finite Element Program ◽  
Earth Resistivity ◽  
Element Program ◽  
Transverse Magnetic Polarization

We simulate the magnetotelluric response to two‐dimensional earth topography using finite elements. Linear interpolation of the secondary field parallel to strike over triangular elements allows accurate modeling of inclined resistivity boundaries, including topographic surfaces. To avoid discontinuities in field derivatives or resistivity, care must be taken that the nodal values of the field parallal to strike used to obtain the auxiliary secondary fields are kept within uniform earth media. The nodal locations may be shifted, but the derivatives still are evaluated at the field points of interest. Correct values may be returned at gentle breaks in slope as well as along straight surfaces. The finite‐element program is verified by comparison with the analytic transverse magnetic response of a hemicylindrical depression and with Rayleigh scattering and transmission surface results for transverse electric and transverse magnetic polarization. Agreement with the other methods generally is excellent, with the exception of some results of the transmission surface technique (especially the transverse magnetic mode). A result presented shows that placing the H-field sensors horizontally reduces topographic anomalies compared to locating sensors parallel to the slope. Moreover, if earth resistivity increases with elevation, the apparent resistivity is relatively nonanomalous near the base of the topography.

Field measured two-way slab deflections

1987 ◽  
Vol 14 (6) ◽  
pp. 807-819 ◽  
Author(s):  
Eric P. Jokinen ◽  
Andrew Scanlon
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Key Words ◽  
High Variability ◽  
Time Dependent ◽  
Concrete Construction ◽  
Finite Element Program ◽  
Element Program

Results of a survey of two-way slab deflections both during and after construction of a 28-storey office tower are presented. A comparison is made between measured deflections and deflections computed using a finite element program that includes the effects of cracking. Effects of construction loading and time-dependent deformations are included in the calculations. The measured and calculated deflections illustrate the high variability that can be expected in two-way slab deflections. Key words: concrete construction, deflection, finite elements, loads, multistorey construction, two-way slabs, variability.

Two‐dimensional terrain correction in magnetotelluric surveys

Geophysics ◽  
1988 ◽  
Vol 53 (6) ◽  
pp. 854-862 ◽  
Author(s):  
Michel Chouteau ◽  
Karl Bouchard
Keyword(s):  
Terrain Correction ◽  
Topographic Effects ◽  
Two Dimensional ◽  
Subsurface Structure ◽  
Finite Element Program ◽  
Practical Procedure ◽  
Topographic Features ◽  
Correction Technique ◽  
Element Program

Field distortions caused by topography hamper the interpretation of magnetotelluric (MT) data. Topographic features that can be simulated by two‐dimensional models seriously affect the H-polarization results. A technique to reduce those effects in MT data uses a finite‐element program to compute correction coefficients. After correction, the resulting data can be interpreted as if they were obtained over a flat surface and depended only on the subsurface structure. The technique is applied to four examples representative of MT survey targets in high‐relief terrain. Results indicate that terrain correction removes the misleading topographic anomalies and improves the quality of subsurface interpretation in regions where the surface relief is two‐dimensional. The correction technique yields some geometrical distortion of the original subsurface structure, but the distortion is usually of small importance. In practice, telluric dipoles of realistic length do not smooth out topographic effects having wavelengths longer than the telluric dipole. A practical procedure derived from the proposed technique allows terrain correction when the relief is approximately two‐dimensional.

scholarly journals Simulation of Isotropic Acoustic Metamaterials

2016 ◽  
Vol 65 ◽  
pp. 43-52
Author(s):  
S.M. Premarathna ◽  
K.A.I.L. Wijewardena Gamalath
Keyword(s):  
Normal Incidence ◽  
Wave Pattern ◽  
Transverse Magnetic ◽  
Normal Space ◽  
Two Dimensional ◽  
Acoustic Metamaterials ◽  
Transverse Magnetic Mode ◽  
Multiple Cycle ◽  
Leapfrog Scheme ◽  
The Waves

The model use to study electromagnetic metamaterials in transverse electric mode was modified to study the pressure distribution in an acoustic metamaterial in a two dimensional geometry. An electromagnetic wave of 30 GHz in transverse magnetic mode at normal incidence propagating through a two dimensional isotropic semi infinite double negative metamaterial slab of 640×830 cells embedded in free space with low loss damping frequency 108s-1was studied by finite difference time dependent method with Yee’s algorithm with an explicit leapfrog scheme. The multiple cyclem-n-mpulses generating beams were used as sources. The simulations for refractive indices n=-1 and n=-16 at different time steps are presented. For n=-1, the sub-wavelength imaging is apparent, diverging the waves from source into two sources, one inside and the other outside the slab. The reverse propagation is much more significant for showing that the group velocity is much larger inside the metamaterial by the closely packed wave front, making the continuation of the wave pattern much more significant through the metamaterial into the normal space.

The Response of a New Lightweight Rail Track System (LR55) to Various Loading Environment

1997 ◽  
Author(s):  
H. Al Nageim ◽  
F. Mohammad ◽  
Lewis Lesley
Keyword(s):  
Finite Element ◽  
Elastic Behaviour ◽  
Two Dimensional ◽  
Element Analysis ◽  
Finite Element Program ◽  
Vertical Pressure ◽  
Rail Track ◽  
Track System ◽  
Dimensional Finite Element ◽  
Element Program

The finite element method is used to determine the response of a new lightweight rail track system (LR55) to various loading environments. To calculate the vertical displacement of the rail track system and the vertical pressure in the sub-base and sub-grade layers due to wheel loads and loads exerted by transversely passing vehicles across the track, the global stiffness matrix of the structure is determined. This is done by using one and two dimensional finite element programs. In the two dimensional finite element analysis, linear isoparametric elements with 4-node quadrilateral and 3-node triangular shapes in the discretised mesh of the whole structure are used, also non-homogeneous materials with isotropic of linear elastic behaviour are assumed for all the components forming the track system and surrounding media. The results of the one dimensional finite element program are compared with those predicted from analytical approach in order to validate the finite element program developed. From the various examples presented the LR55 proves to withstand the main-line railway loading and the vertical pressure distribution in the sub-base and sub-grade of the pavement are within the allowable limit.

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