scholarly journals Calculations of near-field emissions in frequency-domain into time-dependent data with arbitrary wave form transient perturbations

2012 ◽  
Vol 1 (2) ◽  
pp. 26
Author(s):  
Y. Liu ◽  
B. Ravelo ◽  
J. Ben Hadj Slama
Keyword(s):  
Time Domain ◽  
Near Field ◽  
Wave Spectrum ◽  
Computational Method ◽  
Time Dependent ◽  
Dependent Data ◽  
Wave Form ◽  
Frequency Dependent ◽  
Transient Electromagnetic ◽  
The Time Domain

This paper is devoted on the application of the computational method for calculating the transient electromagnetic (EM) near-field (NF) radiated by electronic structures from the frequency-dependent data for the arbitrary wave form perturbations i(t). The method proposed is based on the fast Fourier transform (FFT). The different steps illustrating the principle of the method is described. It is composed of three successive steps: the synchronization of the input excitation spectrum I(f) and the given frequency data H0(f), the convolution of the two inputs data and then, the determination of the time-domain emissions H(t). The feasibility of the method is verified with standard EM 3D simulations. In addition to this method, an extraction technique of the time-dependent z-transversal EM NF component Xz(t) from the frequency-dependent x- and y- longitudinal components Hx(f) and Hy(f) is also presented. This technique is based on the conjugation of the plane wave spectrum (PWS) transform and FFT. The feasibility of the method is verified with a set of dipole radiations. The method introduced in this paper is particularly useful for the investigation of time-domain emissions for EMC applications by considering transient EM interferences (EMIs).

Time-Domain Nonlinear SSI Analysis of Foundation Sliding Using Frequency-Dependent Foundation Impedance Derived From SASSI

2008 ◽  
Author(s):  
Mansour Tabatabaie ◽  
Thomas Ballard
Keyword(s):  
Frequency Domain ◽  
Linear Systems ◽  
Time Domain ◽  
Soil Structure ◽  
Wave Radiation ◽  
Far Field ◽  
Frequency Dependent ◽  
Nonlinear Springs ◽  
Mat Foundation ◽  
The Time Domain

Dynamic soil-structure interaction (SSI) analysis of nuclear power plants is often performed in frequency domain using programs such as SASSI [1]. This enables the analyst to properly a) address the effects of wave radiation in an unbounded soil media, b) incorporate strain-compatible soil shear modulus and damping properties and c) specify input motion in the free field using the de-convolution method and/or spatially variable ground motions. For structures that exhibit nonlinearities such as potential base sliding and/or uplift, the frequency-domain procedure is not applicable as it is limited to linear systems. For such problems, it is necessary to solve the problem in the time domain using the direct integration method in programs such as ADINA [2]. The authors recently introduced a sub-structuring technique called distributed parameter foundation impedance (DPFI) model that allows the structure to be partitioned from the total SSI system and analyzed in the time domain while the foundation soil is modeled using the frequency-domain procedure [3]. This procedure has been validated for linear systems. In this paper we have expanded the DPFI model to incorporate nonlinearities at the soil/structure interface by introducing nonlinear shear and normal springs arranged in series between the DPFI and structure model. This combination of the linear far-field impedance (DPFI) plus nonlinear near-field soil springs allows the foundation sliding and/or uplift behavior be analyzed in time domain while maintaining the frequency-dependent stiffness and radiation damping nature of the far-field foundation impedance. To check the accuracy of this procedure, a typical NPP foundation mat supported at the surface of a layered soil system and subjected to harmonic forced vibration was first analyzed in the frequency domain using SASSI to calculate the target linear response and derive a linear, far-field DPFI model. The target linear solution was then used to validate two linear time-domain ADINA models: Model 1 consisting of the mat foundation+DPFI derived from the linear SASSI model and Model 2 consisting of the total SSI system (mat foundation plus a soil block). After linear alignment, the nonlinear springs were added to both ADINA models and re-analyzed in time domain. Model 2 provided the target nonlinear solution while Model 1 provided the results using the DPFI+nonlinear springs. By increasing the amplitude of the vibration load, different levels of foundation sliding were simulated. Good agreement between the results of two models in terms of the displacement response of the mat and cyclic force-displacement behavior of the springs validates the accuracy of the procedure presented herein.

Electromagnetic modeling of 3-D sources over 2-D inhomogeneities in the time domain

Geophysics ◽  
1992 ◽  
Vol 57 (8) ◽  
pp. 994-1003 ◽  
Author(s):  
Michael Leppin
Keyword(s):  
Differential Equations ◽  
Diffusion Equation ◽  
Time Domain ◽  
Magnetic Induction ◽  
Host Rock ◽  
Vertical Component ◽  
Wavenumber Domain ◽  
Transient Electromagnetic ◽  
Wide Range ◽  
The Time Domain

A numerical method is presented by which the transient electromagnetic response of a two‐dimensional (2-D) conductor, embedded in a conductive host rock and excited by a rectangular current loop, can be modeled. This 2.5-D modeling problem has been formulated in the time domain in terms of a vector diffusion equation for the scattered magnetic induction, which is Fourier transformed into the spatial wavenumber domain in the strike direction of the conductor. To confine the region of solution of the diffusion equation to the conductive earth, boundary values for the components of the magnetic induction on the ground surface have been calculated by means of an integral transform of the vertical component of the magnetic induction at the air‐earth interface. The system of parabolic differential equations for the three magnetic components has been integrated for 9 to 15 discrete spatial wavenumbers ranging from [Formula: see text] to [Formula: see text] using an implicit homogeneous finite‐difference scheme. The discretization of the differential equations on a grid representing a cross‐section of the conductive earth results in a large, sparse system of linear equations, which is solved by the successive overrelaxation method. The three‐dimensional (3-D) response has been computed by an inverse Fourier transformation of the cubic spline interpolated scattered magnetic induction in the wavenumber domain using a digital filtering technique. To test the algorithm, responses have been computed for a two‐layered half‐space and a vertical prism embedded in a conductive host rock. These examples were then compared with results obtained analytically or numerically using frequency‐domain finite‐element and time‐domain integral equation methods. The new numerical procedure gives satisfactory results for a wide range of 2-D conductivity distributions with conductivity ratios exceeding 1:100, provided the grid is sufficiently refined at the corners of the conductivity anomalies.

On: “Time‐Dependent Electromagnetic Fields of an Infinite, Conducting Cylinder Excited by a Long Current‐Carrying Cable” by S. K. Verma (GEOPHYSICS, April 1973, p. 369–379)

Geophysics ◽  
1974 ◽  
Vol 39 (3) ◽  
pp. 355-355
Author(s):  
Shri Krishna Singh
Keyword(s):  
Magnetic Field ◽  
Frequency Domain ◽  
Electric Current ◽  
Electromagnetic Fields ◽  
Time Domain ◽  
Static Solution ◽  
Transverse Magnetic ◽  
Time Dependent ◽  
Axially Symmetric ◽  
The Time Domain

In this paper Verma obtains a time‐domain solution by inverting the frequency‐domain solution given by Wait (1952). However, it has been recently pointed out by Singh (1973a) (see also Wait, 1973) that there is an error in the quasi‐static solution of Wait. Wait neglected the axially symmetric inducted electric current in the cylinder giving rise to a secondary transverse magnetic field outside (the n=0 term in the scattered wavefield). Singh (1973a) has shown that this term dominates. [It should be noted that Wait in his other works on the cylinder retains this term (e.g., Wait, 1959).] It is clear that this term would be dominant in the time‐domain also. This has been shown by Singh (1972, 1973b). Since the theoretical solution given by Verma in the paper under discussion is incomplete, his interpretation schemes are meaningless.

scholarly journals Scattering of an Impact Wave by a Crack in a Composite Plate

1992 ◽  
Vol 59 (3) ◽  
pp. 596-603 ◽  
Author(s):  
S. K. Datta ◽  
T. H. Ju ◽  
A. H. Shah
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Impact Load ◽  
Near Field ◽  
Boundary Integral ◽  
Transition Elements ◽  
Element Discretization ◽  
Crack Tips ◽  
Time Domain Response ◽  
The Time Domain

The surface responses due to impact load on an infinite uniaxial graphite/epoxy plate containing a horizontal crack is investigated both in time and frequency domain by using a hybrid method combining the finite element discretization of the near-field with boundary integral representation of the field outside a contour completely enclosing the crack. This combined method leads to a set of linear unsymmetric complex matrix equations, which are solved to obtain the response in the frequency domain by biconjugate gradient method. The time-domain response is then obtained by using an FFT. In order to capture the time-domain characteristics accurately, high-order finite elements have been used. Also, both the six-node singular elements and eight-node transition elements are used around the crack tips to model the crack-tip singularity. From the numerical results for surface responses it seems possible to clearly identify both the depth and length of this crack.

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