SIMULATION OF TIME‐DOMAIN, AIRBORNE, ELECTROMAGNETIC SYSTEM RESPONSE

Geophysics ◽  
1969 ◽  
Vol 34 (5) ◽  
pp. 739-752 ◽  
Author(s):  
A. Becker
Keyword(s):  
Frequency Domain ◽  
Response Function ◽  
Time Domain ◽  
Digital Simulation ◽  
Thin Sheet ◽  
Scale Model ◽  
System Response ◽  
Electromagnetic System ◽  
Frequency Domain Response ◽  
Conducting Sheet

The response of a time‐domain electromagnetic system over a thin conducting sheet may be simulated by purely electronic means and without recourse to scale model experiments. The simulation is based on the similarity between the frequency domain response function for a thin sheet and the transfer function of certain RC active networks. Since this type of experiment employs actual field equipment, the proposed technique also constitutes a valid means of data quality control. It is difficult to carry out an analog simulation for conductors which do not resemble a thin sheet. If, however, the frequency domain response function for the situation in question is known, the simulation may be carried out on a digital computer. The digital simulation process involves a numerical Fourier decomposition of the primary field waveform (as seen by the receiver), the calculation of the effect of the ground on each harmonic component, and the recombination of the secondary field harmonics to form the observed transient. The technique is illustrated with some calculations of theoretical responses for an EM system over a homogeneous ground and over a thin horizontal conducting sheet. The digital simulation technique is more useful than the analog.

Transient axisymmetric motion of a floating cylinder

1985 ◽  
Vol 157 ◽  
pp. 17-33 ◽  
Author(s):  
J. N. Newman
Keyword(s):  
Free Surface ◽  
Frequency Domain ◽  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Surface Effects ◽  
Added Mass ◽  
The Body ◽  
The Time Domain

A linear theory is developed in the time domain for vertical motions of an axisymmetric cylinder floating in the free surface. The velocity potential is obtained numerically from a discretized boundary-integral-equation on the body surface, using a Galerkin method. The solution proceeds in time steps, but the coefficient matrix is identical at each step and can be inverted at the outset.Free-surface effects are absent in the limits of zero and infinite time. The added mass is determined in both cases for a broad range of cylinder depths. For a semi-infinite cylinder the added mass is obtained by extrapolation.An impulse-response function is used to describe the free-surface effects in the time domain. An oscillatory error observed for small cylinder depths is related to the irregular frequencies of the solution in the frequency domain. Fourier transforms of the impulse-response function are compared with direct computations of the damping and added-mass coefficients in the frequency domain. The impulse-response function is also used to compute the free motion of an unrestrained cylinder, following an initial displacement or acceleration.

Optimization of Frequency Domain Fatigue Analysis for Unbonded Flexible Risers

2021 ◽  
Author(s):  
Jiabei Yuan ◽  
Yucheng Hou ◽  
Zhimin Tan
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Transfer Functions ◽  
Hybrid Approach ◽  
Fatigue Analysis ◽  
System Response ◽  
Similar Response ◽  
Potential Cost ◽  
Spectrum Prediction ◽  
Flexible Risers

Abstract Fatigue analysis of flexible risers is a demanding task in terms of time and computational resources. The traditional time domain approach may take weeks of time in global simulation, local modelling and post-processing of riser responses to get fatigue results. Baker Hughes developed a fast hybrid approach, which is based on a frequency domain technique. The new approach was first implemented at the end fitting region and then to all other regions of the riser. Studies showed that the hybrid approach achieved convenient and conservative results in a significant shorter period of time. To improve the accuracy and reduce conservatism of the method, Baker Hughes has further optimized the analysis procedure to seek better results approaching true solutions. Several methods were proposed and studied. The duration of representative cases and noncritical cases have been extended. The steps to predict stress spectrum based on transfer functions have also been updated. From previous studies, only one transfer function was built for fatigue load cases with similar response spectra. This assumption linearizes the system response and produces certain level of discrepancy against true time domain solution. In this study, multiple ways of spectrum prediction are evaluated and compared. The paper summarizes several techniques to further optimize the hybrid frequency domain approach. The updated fatigue results are found to be more accurate. The optimized approach therefore gives more flexibility to engineers to approach the true solutions, which were originally acquired from full 3-hr time domain simulations. The approach requires less analysis time and reduces iterations in pipe structure and riser configuration design, which leads to faster project execution and potential cost reduction.

Depth sounding by means of a coincident coil frequency‐domain electromagnetic system

Geophysics ◽  
1997 ◽  
Vol 62 (1) ◽  
pp. 49-55 ◽  
Author(s):  
Kenneth Duckworth ◽  
Edward S. Krebes
Keyword(s):  
Frequency Domain ◽  
Half Space ◽  
Free Space ◽  
Thin Sheet ◽  
Electromagnetic System ◽  
Homogeneous Half Space ◽  
Scale Modeling ◽  
Physical Scale ◽  
Depth Sounding ◽  
Theoretical Developments

The concept of electromagnetic depth sounding by means of a coincident‐coil frequency‐domain electromagnetic system is developed in theory and demonstrated by means of physical scale modeling. The concept is based on the use of distance from the target as the sounding variable. The theoretical developments are confined to soundings conducted in free‐space with respect to either a homogeneous half‐space or a thin sheet conductor in conditions that approach the resistive limit. The use of distance from the target as the sounding variable becomes practical when the sounding system is a single compact unit of the type that a coincident coil concept inherently provides. In this method of sounding, the distance from the target is determined by taking the ratios of the fields measured at a variety of distances from the target conductor. This permits not only the distance to the target to be determined but also the direction to that target as may be of interest in soundings conducted in mines.

scholarly journals Stored electromagnetic energy and quality factor of radiating structures

2016 ◽  
Vol 472 (2188) ◽  
pp. 20150870 ◽  
Author(s):  
Miloslav Capek ◽  
Lukas Jelinek ◽  
Guy A. E. Vandenbosch
Keyword(s):  
Frequency Domain ◽  
Quality Factor ◽  
Time Domain ◽  
Unsolved Problem ◽  
Electromagnetic Energy ◽  
Frequency Domain Method ◽  
Stored Energy ◽  
Electromagnetic System ◽  
System A ◽  
The Time Domain

This paper deals with the old yet unsolved problem of defining and evaluating the stored electromagnetic energy—a quantity essential for calculating the quality factor, which reflects the intrinsic bandwidth of the considered electromagnetic system. A novel paradigm is proposed to determine the stored energy in the time domain leading to the method, which exhibits positive semi-definiteness and coordinate independence, i.e. two key properties actually not met by the contemporary approaches. The proposed technique is compared with an up-to-date frequency domain method that is extensively used in practice. Both concepts are discussed and compared on the basis of examples of varying complexity.

Investigation and Modification of Frequency Response Function Using Digital Fourier Analysis for High Speed Dynamic Testing Facility

2009 ◽  
Author(s):  
Chandrashekhar K. Thorbole ◽  
Keshavanarayana S. Raju
Keyword(s):  
Frequency Response ◽  
Frequency Domain ◽  
Response Function ◽  
Time Domain ◽  
Frequency Response Function ◽  
Detection System ◽  
Structural Response ◽  
Wave Form ◽  
Data Set ◽  
Load Detection

The increasing application of composites in the aviation and automobile industry demands a better understanding of composite material behavior under high loading rate. This shall provide a better insight of actual loads on occupants while preserving livable crashworthy structure. In this study, a high stroke rate MTS servo-hydraulic testing machine is used to characterize the behavior of composite materials at high strain rates. At higher stroke rates, the output of the load detection system acquired by the load cell deviates from the true load-time wave form of the specimen. This is due to the convolution of the structural response of the detection system with the true characteristic of the specimen. To identify the true nature of the specimen load-time behavior, the de-convolution of the detection system response is necessary to restore the specimen characteristic wave form closer to its true behavior. The convolution of data set in the time domain is a time consuming process which explains the benefit of using the frequency domain; as the convolution in time domain corresponds to multiplication in the frequency domain. This process requires the transformation of the time domain data to frequency domain data via Fast Fourier Transform (FFT). In the frequency domain the complex division of the Fourier transfer of the detection system output with frequency response function of the detection system shall provide the true complex input characteristic. This paper elaborates the methodology utilized for obtaining the Frequency Response Function (FRF) of the load detection system using digital Fourier analysis with a single input/output data set. This also emphasizes precautions and guidelines for improving results with FFT to obtain true FRF measurements of the load detection system. The FRF obtained is successfully used to identify the actual specimen wave form characteristic. This is achieved by extracting the structural response of the load detection system from the load cell output.

Design PID controllers for desired time-domain or frequency-domain response

2002 ◽  
Vol 41 (4) ◽  
pp. 511-520 ◽  
Author(s):  
Weidong Zhang ◽  
Yugeng Xi ◽  
Genke Yang ◽  
Xiaoming Xu
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Pid Controllers ◽  
Frequency Domain Response

scholarly journals Pipeline Leak Detection by Transient-Based Method Using MATLAB® Functions

2017 ◽  
Author(s):  
Albert Carbó-Bech ◽  
Salvador A. De Las Heras ◽  
Alfredo Guardo
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Transfer Functions ◽  
Leak Detection ◽  
Pipeline System ◽  
Model Transfer ◽  
Time Domain Response ◽  
Frequency Domain Response ◽  
The Time Domain ◽  
Dissipative Model

This paper shows a method for pipeline leak detection using a transient-based method with MATLAB® functions. The simulation of a pipeline systems in the time domain are very complex. In the case of the dissipative model, transfer functions are hyperbolic Bessel functions. Simulating a pipeline system in the frequency domain using a dissipative model we could find an approximate transfer function with equal frequency domain response to in order get the pipeline system's time domain response. The method described in this paper can be used to detect, by comparison, to detect a leak in a pipeline system model.

Time Domain VIV Analysis of a Free Standing Hybrid Riser

2009 ◽  
Author(s):  
Nicole Liu ◽  
Yongming Cheng ◽  
Jaap de Wilde ◽  
Roger Burke ◽  
Kostas F. Lambrakos
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Production Systems ◽  
System Response ◽  
Free Standing ◽  
Finite Element Software ◽  
Transient Nature ◽  
Frequency Domain Methods ◽  
Structural Nonlinearities ◽  
Flexible Jumper

A free standing hybrid riser (FSHR) is a proven solution for deepwater floating production systems. In this system, a submerged buoyancy can supports and tensions a vertical riser. The riser top is connected to a floating production system through a flexible jumper. The FSHR has been used in West Africa and Brazil and will be put into application in the Gulf of Mexico. Experimental and analytical efforts are continuing to better understand the vortex-induced vibration (VIV) response of this riser system. This paper presents a comparison of experimental and numerical results of the VIV response of a FSHR. The analysis is performed with a time domain VIV code ABAVIV, which uses the finite element software package ABAQUS to calculate the response from the VIV forcing. Unlike frequency domain VIV codes, ABAVIV captures structural nonlinearities and the transient nature of the VIV phenomenon. Comparisons between numerical and experimental results for buoyancy can VIV response and loading at the bottom of the riser are presented and show generally good agreement. The relative contributions of buoyancy can and riser VIV to the overall system response are investigated. The paper will also include calculated VIV response from frequency domain methods.

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