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.

scholarly journals Determination of the response of a class of nonlinear time invariant systems

1981 ◽  
Vol 4 (3) ◽  
pp. 615-623
Author(s):  
Sudhangshu B. Karmakar
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Inverse Laplace Transform ◽  
New Approach ◽  
Functional Expansion ◽  
Expansion Time ◽  
Time Domain Response ◽  
The Time Domain ◽  
Time Invariant

This paper illustrates by means of a simple example a new approach for the determination of the time domain response of a class of nonlinear systems. The system under investigation is assumed to be described by a nonlinear differential equation with forcing term. The response of the system is first obtained in terms of the input in the form of a Volterra functional expansion. Each of the components in the expansion is first transformed into a multidimensional frequency domain and then to a single dimensional frequency domain by the technique of association of variables. By taking into consideration the conditions for the rapid convergence of the functional expansion the response of the system in the frequency domain can effectively be obtained by taking only the first few terms of the expansion. Time domain response is then found by inverse Laplace transform.

Approximate Structural Response Characterization Using Parametric and Envelope Models for Multimodal Systems

1986 ◽  
Vol 108 (1) ◽  
pp. 39-43
Author(s):  
P. Davies ◽  
J. K. Hammond
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Structural Response ◽  
Parametric Models ◽  
Response Signal ◽  
Response Characteristics ◽  
Multimodal Systems ◽  
Time Domain Response ◽  
The Time Domain

In the study of the response of systems to an excitation there are circumstances when it is desirable to obtain some overall or average characterization of the system and its response rather than a detailed description. In this paper two methods are used to describe the overall features of the system: one appropriate for the frequency domain and one for the time domain. For modally dense systems the main features of the frequency response function are described in terms of low-order parametric models. While these models may be adequate for the frequency domain representation, they may not produce a good approximation to the response of the system in the time domain. The second approach relates the envelope of the input signal to the envelope of the response signal, in order to describe the overall time domain response characteristics.

The Application of Adaptive Canceling in Chaos Identification

2003 ◽  
Author(s):  
Shuyong Liu ◽  
Shijian Zhu ◽  
Zhenming Liu ◽  
Weiian Qian
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Chaotic Signal ◽  
Lms Algorithm ◽  
Measuring System ◽  
Adaptive Technique ◽  
Time Domain Response ◽  
The Time Domain

The time domain response of a system is inevitably contaminated by noise arising from the environment as well as the measuring system itself. So an effective method is needed to reduce the noise components. The characteristic of the chaotic signal and noise in the frequency domain is analyzed. An adaptive canceling system based on the LMS algorithm is applied to process the contaminated signal. The simulation result shows that the adaptive technique can meet the goal.

A Musical Use for the Haar Function Wavelet

2005 ◽  
Author(s):  
Daryl Caswell
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Near Field ◽  
French Horn ◽  
Sound Analysis ◽  
Concert Hall ◽  
Analysis Techniques ◽  
Haar Function ◽  
Musical Tone ◽  
The Time Domain

The utility of the Haar function wavelet has long been dismissed due to its inability to transpose between the time domain and the frequency domain. However, the Haar function possesses attributes that make it an ideal wavelet for certain applications. In this paper, we explore the use of the Haar function as a means to expose aspects of musical tone that are not available through other sound analysis techniques. Specifically, the method presented here was used to identify the differences in the tone of the French Horn created by different acoustically reflective surfaces placed in the near field of the horn bell. The fundamentals of the Haar function wavelet are described and its use as a signal analyzer is explained. Results are shown that demonstrate the effect of two different kinds of sound reflectors constructed for a major North American concert hall.

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 Approach for Acoustic Scattering of Rotorcraft Noise

2012 ◽  
Vol 57 (4) ◽  
pp. 1-12 ◽  
Author(s):  
Seongkyu Lee ◽  
Kenneth S. Brentner ◽  
Philip J. Morris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Impulsive Noise ◽  
Near Field ◽  
Acoustic Scattering ◽  
Frequency Domain Analysis ◽  
Computational Time ◽  
Computationally Efficient ◽  
Time Saving ◽  
The Time Domain

This paper addresses acoustic scattering of rotorcraft noise in the time domain. A time-domain equivalent source method is used since it is considered to be a computationally efficient method to solve acoustic scattering. In addition, the time-domain method provides a solution for all frequencies of interest in a single computation and is able to predict the acoustic scattering of aperiodic signals. The prediction is validated against exact solutions for a monopole source. The numerical method is then used to predict acoustic scattering of noise from a BO105 tail rotor by a representative fuselage. Complex directivity patterns are seen in the near field, and a large scattering effect is observed in the far field to the side of the fuselage. The time-domain code results of sound pressure level are validated against the results obtained by a frequency-domain analysis. Finally, acoustic scattering for an impulsive noise source is investigated to simulate main rotor blade–vortex interaction noise. The scattered pressure has a comparable amplitude as that of the incident pressure so that the total pressure is dramatically changed compared to the incident pressure. For the impulsive noise, a large computational time saving is achieved compared to the frequency-domain approach, in which the computation must be repeated for each frequency.

Laplace Plane Analysis of Impedance on the H Meridian

1979 ◽  
Vol 07 (02) ◽  
pp. 188-193 ◽  
Author(s):  
Maria Reichmanis ◽  
Andrew A. Marino ◽  
Robert O. Becker
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Voltage Pulse ◽  
Input Voltage ◽  
Ac Impedance ◽  
Acupuncture Points ◽  
Plane Analysis ◽  
Time Domain Response ◽  
The Time Domain ◽  
Laplace Plane

The AC impedance of a length of the H meridian not containing any acupuncture points was studied by means of Laplace plane analysis of the time domain response to an input voltage pulse. The ensuing frequency domain data were compared to the results of an identical analysis for two anatomically similar controls on either side of the meridian. The resistance of the meridian was significantly lower than either control.

Time domain finite element method for metamaterial-based low frequency near field systems

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Zhi Gong ◽  
Shiyou Yang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Frequency Domain ◽  
Time Domain ◽  
Near Field ◽  
Low Frequency ◽  
Electromagnetic Properties ◽  
Content Type ◽  
The Time Domain ◽  
Element Method

Purpose The purpose of this work is to develop a computational paradigm for performance analysis of low-frequency electromagnetic devices containing both magnetic metamaterials (MTMs) and natural media. Design/methodology/approach A time domain finite element method (TDFEM) is proposed. The electromagnetic properties of the MTMs are modeled by a nonstandard Lorentz model. The time domain governing equation is derived by converting the one from the frequency domain into the time domain based on the Laplace transform and convolution. The backward difference is used for the temporal discretization. An auxiliary variable is introduced to derive the recursive formula. Findings The numerical results show good agreements between the time domain solutions and the frequency domain solutions. The error convergence trajectory of the proposed TDFEM conforms to the first-order accuracy. Originality/value To the best knowledge of the authors, the presented work is the first one focusing on TDFEMs for low-frequency near fields computations of MTMs. Consequently, the proposed TDFEM greatly benefits the future explorations and performance evaluations of MTM-based near field devices and systems in low-frequency electrical and electronic engineering.

JOINT INTERPRETATION OF AIRBORNE ELECTROMAGNETIC DATA IN THE TIME DOMAIN AND FREQUENCY DOMAIN

2018 ◽  
Vol 12 (7-8) ◽  
pp. 76-83
Author(s):  
E. V. KARSHAKOV ◽  
J. MOILANEN
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Time Domain ◽  
Frequency Interval ◽  
Single Spectrum ◽  
Simultaneous Inversion ◽  
Homogeneous Half Space ◽  
Time Domain Data ◽  
The Time Domain

Тhe advantage of combine processing of frequency domain and time domain data provided by the EQUATOR system is discussed. The heliborne complex has a towed transmitter, and, raised above it on the same cable a towed receiver. The excitation signal contains both pulsed and harmonic components. In fact, there are two independent transmitters operate in the system: one of them is a normal pulsed domain transmitter, with a half-sinusoidal pulse and a small "cut" on the falling edge, and the other one is a classical frequency domain transmitter at several specially selected frequencies. The received signal is first processed to a direct Fourier transform with high Q-factor detection at all significant frequencies. After that, in the spectral region, operations of converting the spectra of two sounding signals to a single spectrum of an ideal transmitter are performed. Than we do an inverse Fourier transform and return to the time domain. The detection of spectral components is done at a frequency band of several Hz, the receiver has the ability to perfectly suppress all sorts of extra-band noise. The detection bandwidth is several dozen times less the frequency interval between the harmonics, it turns out thatto achieve the same measurement quality of ground response without using out-of-band suppression you need several dozen times higher moment of airborne transmitting system. The data obtained from the model of a homogeneous half-space, a two-layered model, and a model of a horizontally layered medium is considered. A time-domain data makes it easier to detect a conductor in a relative insulator at greater depths. The data in the frequency domain gives more detailed information about subsurface. These conclusions are illustrated by the example of processing the survey data of the Republic of Rwanda in 2017. The simultaneous inversion of data in frequency domain and time domain can significantly improve the quality of interpretation.

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