Numerical simulation of turbomachinery flows considering two-spool effects: Application of the Almost-Periodic Fourier Transform

2022 ◽  
Author(s):  
Corentin Battistoni ◽  
Hagen Müller ◽  
Nina Wolfrum ◽  
Graham Ashcroft
Keyword(s):  
Numerical Simulation ◽  
Fourier Transform ◽  
Almost Periodic

Spectral phase measurement of complex pulses using delay controlled fringe free interferometry technique

2014 ◽  
Vol 23 (02) ◽  
pp. 1450017 ◽  
Author(s):  
Liang Lei ◽  
Xin Liu ◽  
Jin-Hui Wen ◽  
Xiao-Bo Xing ◽  
Bo Wang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Fourier Transform ◽  
Electric Field ◽  
Femtosecond Pulse ◽  
Phase Measurement ◽  
Spectral Phase ◽  
Pulse Measurement ◽  
Field Reconstruction ◽  
Small Delay ◽  
Free Spectra

The shortcomings in complex femtosecond pulse measurement of conventional spectral phase interferometry for direct electric-field reconstruction (SPIDER) are commented in this paper. To solve the problem, we propose an improved version of SPIDER, where single replica of the unknown pulse upconverts synchronously with two frequency-shifted narrow-banded long pulses. With the introduction of a suitable small delay between the upconverted pulses, the spectral phase of the unknown pulse can be directly calculated from the fringe-free spectra and Fourier-transform filtering is not required. The results of numerical simulation show that the accuracy of the new method in complex pulse measurement is higher than conventional SPIDER.

Note on the FFT Based Computational Code and Its Application

2008 ◽  
Author(s):  
Xiaoqing Jin ◽  
Leon M. Keer ◽  
Qian Wang
Keyword(s):  
Numerical Simulation ◽  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Toeplitz Matrix ◽  
Contact Problems ◽  
Point Of View ◽  
Fast Fourier Transform Algorithm ◽  
Discrete Convolution ◽  
Mathematical Point ◽  
Computational Code

The discrete convolution based Fast Fourier Transform algorithm (DC-FFT) has been successfully applied in numerical simulation of contact problems. The algorithm is revisited from a mathematical point of view, equivalent to a Toeplitz matrix multiplied by a vector. The nature of the convolution property permits one to implement the algorithm with fewer constraints in choosing the computational domains. This advantageous feature is explored in the present work, and is expected to be beneficial to many tribological studies.

scholarly journals Cloud Determination of All-Sky Images under Low-Visibility Conditions

2009 ◽  
Vol 26 (10) ◽  
pp. 2172-2181 ◽  
Author(s):  
Juan Huo ◽  
Daren Lu
Keyword(s):  
Numerical Simulation ◽  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Aerosol Optical Depth ◽  
Image Features ◽  
Threshold Method ◽  
Integrated Method ◽  
Low Visibility ◽  
Key Factor

Abstract The threshold method is commonly used to determine cloud in a sky image. This paper evaluates the method by numerical simulation and shows that the aerosol optical depth (AOD) is a key factor that influences the accuracy. Particularly when the visibility is low, a single threshold method is inappropriate. To improve the accuracy of cloud determination from low-visibility sky images, an integrated cloud-determination algorithm is presented that is based on the fast Fourier transform, symmetrical image features, and threshold methods. The preliminary comparison tests show that the new integrated method improves the ability to determine cloud under lower-visibility conditions.

scholarly journals Almost Periodic Solution of a Multispecies Discrete Mutualism System with Feedback Controls

2015 ◽  
Vol 2015 ◽  
pp. 1-14 ◽  
Author(s):  
Hui Zhang ◽  
Feng Feng ◽  
Bin Jing ◽  
Yingqi Li
Keyword(s):  
Numerical Simulation ◽  
Periodic Solution ◽  
Lyapunov Function ◽  
Sufficient Conditions ◽  
Almost Periodic Solution ◽  
Asymptotically Stable ◽  
Almost Periodic ◽  
Feedback Controls ◽  
Positive Almost Periodic Solution ◽  
Mutualism System

We consider an almost periodic multispecies discrete Lotka-Volterra mutualism system with feedback controls. We firstly obtain the permanence of the system by utilizing the theory of difference equation. By means of constructing a suitable Lyapunov function, sufficient conditions are obtained for the existence of a unique positive almost periodic solution which is uniformly asymptotically stable. An example together with numerical simulation indicates the feasibility of the main result.

scholarly journals Almost Periodic Solution of a Discrete Schoener’s Competition Model with Delays

2014 ◽  
Vol 2014 ◽  
pp. 1-9
Author(s):  
Hui Zhang ◽  
Yingqi Li ◽  
Bin Jing ◽  
Xiaofeng Fang ◽  
Jing Wang
Keyword(s):  
Numerical Simulation ◽  
Periodic Solution ◽  
Lyapunov Function ◽  
Sufficient Conditions ◽  
Almost Periodic Solution ◽  
Competition Model ◽  
Almost Periodic ◽  
Positive Almost Periodic Solution ◽  
Globally Attractive

We consider an almost periodic discrete Schoener’s competition model with delays. By means of an almost periodic functional hull theory and constructing a suitable Lyapunov function, sufficient conditions are obtained for the existence of a unique strictly positive almost periodic solution which is globally attractive. An example together with numerical simulation indicates the feasibility of the main result.

scholarly journals Almost Periodic Sequence in a Discrete Logistic Equation

2019 ◽  
pp. 1-15
Author(s):  
Tianwei Zhang
Keyword(s):  
Numerical Simulation ◽  
Coincidence Degree ◽  
Degree Theory ◽  
Periodic Sequence ◽  
Logistic Equation ◽  
Coincidence Degree Theory ◽  
Almost Periodic

This paper is concerned with an almost periodic discrete logistic equation. By using thecontinuation theorem of Mawhin’s coincidence degree theory, this paper investigates theexistence and stability of a unique positive almost periodic sequence solution of the equation.These results generalize and improve the previous works, and they are easy to check. An examplewith a numerical simulation is also given to demonstrate the effectiveness of the results in this paper.

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