Signal Simulation of Ship-radiated Noise in Time Domain Based on the Inverse Fourier Transform

2010 ◽  
Author(s):  
Wei Lai ◽  
Zhou Sui-hua
Keyword(s):  
Fourier Transform ◽  
Time Domain ◽  
Inverse Fourier Transform ◽  
Radiated Noise ◽  
Signal Simulation

A New Derivation of TGR with Naked Antenna in Lossy Medium

2013 ◽  
Vol 380-384 ◽  
pp. 4098-4102
Author(s):  
Xin Bo Qu ◽  
Bi Hua Zhou ◽  
Zheng Wan ◽  
Wei Shi ◽  
Xiao Gang Xie
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Integral Equations ◽  
Time Domain ◽  
Inverse Fourier Transform ◽  
Input Resistance ◽  
Grounding System ◽  
Grounding Resistance ◽  
Lossy Medium

A new derivation of Transient Grounding Resistance (TGR) has been proposed in this paper. Take grounding system as naked antenna in lossy medium, and then get the input resistance of naked antenna in a given frequency based on Helen current integral equations. With inverse Fourier transform, the resistance calculation equations can be translated from frequency domain to time domain. The result can be applied to design a new grounding system and to calculate its TGR .

scholarly journals Fourier analysis of spectral characteristics of a matrix photodetector in the frequency and time domain

2021 ◽  
pp. 39-46
Author(s):  
Stanislav Zienko ◽  
Vera Zhbanova
Keyword(s):  
Fourier Transform ◽  
Time Domain ◽  
Inverse Fourier Transform ◽  
Spectral Characteristics ◽  
Analytical Form ◽  
Time Characteristic ◽  
Absorption Of Light ◽  
The Matrix ◽  
Trans Ducer ◽  
Good Agreement

The purpose of this paper is to research the frequency and time characteristics of the photo-detector using the direct and inverse Fourier transform. The spectral characteristics of the matrix photodetector were selected as the object of research. For the channels of the trans-ducer it was found that the frequency spectrum consists of two elementary bands in the form of Gaussian curves. It was revealed that the spectra have super-broadband properties. The impulse (time) characteristic of the spectra is described by the equation in an analytical form, which is in good agreement with the calculation. The rise time of the transient response is 1.8–2.9 fs. The process of absorption of light is significantly influenced by dielectric relaxa-tion of the charge. The results obtained provide important information on the properties of the photodetector in the frequency and time domain.

On the problem of simulation of influence flooded compartment on the dynamics of the ship's navigation.

2021 ◽  
pp. 67-72
Author(s):  
В.В. Макарова ◽  
В.М. Набока ◽  
Ю.П. Потехин
Keyword(s):  
Fourier Transform ◽  
Frequency Domain ◽  
Time Domain ◽  
Inverse Fourier Transform ◽  
Simulation Models ◽  
Hydrodynamic Problem ◽  
The Stability ◽  
The Time Domain ◽  
Stability Of The Solution

В статье рассматривается возможность применения имеющихся в настоящее время решений задачи о влиянии динамического переливания жидкости в аварийных отсеках 2-й категории или успокоительных цистернах на качку судна в системах имитационного моделирования динамики плавания аварийных судов. Существующие решения получены в интересах исследования качки в частотной области и формально могут быть перенесены во временну́ю область, отвечающую существованию имитационных моделей, посредством обратного преобразования Фурье, что связано с определенными затруднениями. В работе показано, что при определенной формулировке гидродинамической задачи о колебаниях жидкости в отсеке или цистерне во временно́й области могут быть использованы непосредственно исходные уравнения. Выполнены расчеты, подтверждающие корректность такого подхода с позиций обеспечения устойчивости решения задачи и физической адекватности результатов реально наблюдаемым процессам. The article discusses the possibility of using the currently available solutions to the problem of the effect of dynamic fluid overflow in emergency compartments of the 2nd category or damping tanks on the pitching of a ship in systems for simulation of the dynamics of navigation of damaged ships. The existing solutions were obtained in the interests of studying the pitching in the frequency domain and can formally be transferred to the time domain corresponding to the existence of simulation models by means of the inverse Fourier transform, which is associated with certain difficulties. It is shown in the work that with a certain formulation of the hydrodynamic problem of fluid oscillations in a compartment or tank in the time domain, the original equations can be used directly. Calculations have been performed that confirm the correctness of this approach from the standpoint of ensuring the stability of the solution to the problem and the physical adequacy of the results to the actually observed processes.

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.

scholarly journals Smooth Wavelet Approximations of Truncated Legendre Polynomials via the Jacobi Theta Function

2014 ◽  
Vol 2014 ◽  
pp. 1-24 ◽  
Author(s):  
David W. Pravica ◽  
Njinasoa Randriampiry ◽  
Michael J. Spurr
Keyword(s):  
Fourier Transform ◽  
Theta Function ◽  
Legendre Polynomial ◽  
Legendre Polynomials ◽  
Inverse Fourier Transform ◽  
Recursion Relations ◽  
Jacobi Theta Function ◽  
Convergence Results ◽  
The Family ◽  
Reciprocal Symmetry

The family ofnth orderq-Legendre polynomials are introduced. They are shown to be obtainable from the Jacobi theta function and to satisfy recursion relations and multiplicatively advanced differential equations (MADEs) that are analogues of the recursion relations and ODEs satisfied by thenth degree Legendre polynomials. Thenth orderq-Legendre polynomials are shown to have vanishingkth moments for0≤k<n, as does thenth degree truncated Legendre polynomial. Convergence results are obtained, approximations are given, a reciprocal symmetry is shown, and nearly orthonormal frames are constructed. Conditions are given under which a MADE remains a MADE under inverse Fourier transform. This is used to construct new wavelets as solutions of MADEs.

Effect of the Condition Number of the Inverse Fourier Transform Matrix on the Solution Behavior of the Time Spectral Equation System

2020 ◽  
Author(s):  
Sen Zhang ◽  
Dingxi Wang ◽  
Yi Li ◽  
Hangkong Wu ◽  
Xiuquan Huang
Keyword(s):  
Fourier Transform ◽  
Stability Analysis ◽  
Condition Number ◽  
Inverse Fourier Transform ◽  
Real Life ◽  
Equation System ◽  
Time Instant ◽  
Transform Matrix ◽  
Spectral Equation ◽  
The Impact

Abstract The time spectral method is a very popular reduced order frequency method for analyzing unsteady flow due to its advantage of being easily extended from an existing steady flow solver. Condition number of the inverse Fourier transform matrix used in the method can affect the solution convergence and stability of the time spectral equation system. This paper aims at evaluating the effect of the condition number of the inverse Fourier transform matrix on the solution stability and convergence of the time spectral method from two aspects. The first aspect is to assess the impact of condition number using a matrix stability analysis based upon the time spectral form of the scalar advection equation. The relationship between the maximum allowable Courant number and the condition number will be derived. Different time instant groups which lead to the same condition number are also considered. Three numerical discretization schemes are provided for the stability analysis. The second aspect is to assess the impact of condition number for real life applications. Two case studies will be provided: one is a flutter case, NASA rotor 67, and the other is a blade row interaction case, NASA stage 35. A series of numerical analyses will be performed for each case using different time instant groups corresponding to different condition numbers. The conclusion drawn from the two real life case studies will corroborate the relationship derived from the matrix stability analysis.

IDENTIFICATION OF INTERHARMONICS BASED ON WAVELET PACKET TRANSFORM

2021 ◽  
Vol 3 (1) ◽  
pp. 031-036
Author(s):  
S. A. GOROVOY ◽  
◽  
V. I. SKOROKHODOV ◽  
D. I. PLOTNIKOV ◽  
◽  
...  
Keyword(s):  
Fourier Transform ◽  
Simulation Model ◽  
Frequency Domain ◽  
Time Domain ◽  
Wavelet Packet ◽  
High Accuracy ◽  
Wavelet Packet Transform ◽  
Mathematical Apparatus ◽  
Nonlinear Load ◽  
The Time Domain

This paper deals with the analysis of interharmonics, which are due to the presence of a nonlinear load. The tool for the analysis was a mathematical apparatus - wavelet packet transform. Which has a number of advantages over the traditional Fourier transform. A simulation model was developed in Simulink to simulate a non-stationary non-sinusoidal mode. The use of the wavelet packet transform will allow to determine the mode parameters with high accuracy from the obtained wavelet coefficients. It also makes it possible to obtain information, both in the frequency domain of the signal and in the time domain.

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