Expansion of Indicial Function Approximations for 2-D Subsonic Compressible Aerodynamic Loads

2012 ◽  
Author(s):  
T. Farsadi ◽  
J. Javanshir
Keyword(s):  
Time Domain ◽  
Step Function ◽  
Aerodynamic Loads ◽  
Indicial Function ◽  
Starting Point ◽  
Function Approximations ◽  
The Time Domain ◽  
New Generation ◽  
Duhamel’S Integral ◽  
General Time

This article deals with the new generation of proper Mach dependent exponential approximations of the indicial aerodynamic functions toward the aeroelastic formulation of 2-D lifting surface in the subsonic compressible flow. The indicial lift response is a useful starting point in the development of a general time-domain unsteady aerodynamic theory. By definition, an indicial function is the response to a disturbance that is applied instantaneously at time zero and held constant thereafter; that is a disturbance given by a step function. If the indicial response is known, then the unsteady loads to arbitrary changes in angle of attack can be obtained through the superposition of indicial responses using Duhamel’s integral. The indicial functions have been used to modify the circulatory part of the lifting force and pitching moment in unsteady compressible aerodynamic models. The coefficients of the approximation are obtained with an indirect approach by relating numerical results obtained for oscillating airfoil in the frequency domain back into the time domain. compressible and supersonic flight speed regimes. Exponential approximations of the subsonic compressible indicial functions in the existing research works are available only in limited Mach numbers (M = 0.5, 0.6, 0.7, 0.8). In the present study, a novel exponential approximation is developed which represent the coefficients of approximations as functions of Mach number (0.5 < M < 0.8).

Circuit Implementation of Multiscroll Chaotic Attractors Generated Using Step Function

2015 ◽  
Vol 25 (12) ◽  
pp. 1550160
Author(s):  
Yingjie Ma ◽  
Hua Jiang ◽  
Lei Ju
Keyword(s):  
Time Domain ◽  
Nonlinear Function ◽  
Step Function ◽  
Experimental Results ◽  
Chaotic Attractors ◽  
Circuit Implementation ◽  
New Chaotic System ◽  
The Time Domain ◽  
Hardware Circuit ◽  
The Physical Realization

A new chaotic system is proposed to generate multiscroll chaotic attractors. The major method used is for the step function to act as a nonlinear function. To prove that the proposed system can generate multiscroll chaotic attractors, the equilibrium point, the time domain waveform and the phase diagram of the proposed system are calculated. Finally, the design of the hardware circuit produces experimental results at a maximum of 8-scroll hardware. Theoretical analysis, simulation and hardware experimental results are fully matched, which further proves the existence of the proposed system and the physical realization. This provides the possibility for future applications in engineering.

scholarly journals The CFD Method-Based Research on Damaged Ship’s Flooding Process in Time-Domain

2019 ◽  
Vol 26 (1) ◽  
pp. 72-81
Author(s):  
Hu Li-Fen ◽  
Qi Huibo ◽  
Li Yuemeng ◽  
Li Wubin ◽  
Chen Shude
Keyword(s):  
Time Domain ◽  
Vof Method ◽  
Dynamic Mesh ◽  
Navier Stokes ◽  
Ship Motions ◽  
Starting Point ◽  
Cfd Method ◽  
The Time Domain ◽  
Dead Ship Condition ◽  
Damaged Ship

Abstract The flooding process is one of the main concerns of damaged ship stability. This paper combines the volume of fluid (VOF) method incorporated in the Navier-Stokes (NS) solver with dynamic mesh techniques to simulate the flooding of a damaged ship. The VOF method is used to capture the fluid interface, while the dynamic mesh techniques are applied to update the mesh as a result of transient ship motions. The time-domain flooding processes of a damaged barge and a rectangular cabin model are carried out based on the abovementioned method, and the computational results appear compatible with the experimental data. During the flooding process, the motion of the flooding flow at different stages is observed and compared with that observed in real conditions. The time-domain research of the flooding process is the starting point for subsequent establishment of damaged ship’s roll movement and capsizing the mechanism of dead ship condition in wave.

scholarly journals Rigorous time domain responses of polarizable media

1997 ◽  
Vol 40 (2) ◽  
Author(s):  
M. Caputo
Keyword(s):  
Fractional Order ◽  
Time Domain ◽  
Order Differential Equation ◽  
Step Function ◽  
Induced Polarization ◽  
Fractional Order Differential Equation ◽  
Polarization Phenomena ◽  
Electric Flux ◽  
The Time Domain ◽  
Derivatives Of

The scope of this note is to study a model of induced polarization which fits the usually accepted frequency dependent formula of Cole and Cole, but is more general and allows the time domain observations to retrieve the parameters describing the induced polarization phenomena of the medium. By introducing the memory mechanisms, represented by derivatives of fractional order, in the relation between the electric flux density and the electric field and considering the fractional order differential equation which follows, I solve it with mathematically rigorous and closed formulae and compute the responses to a step function, a box, a set of positive boxes and a set of alternating positive and negative boxes. I also introduce a method which retrieves the parameters describing the medium when comparing the theoretical curves with the observed ones. The responses to these signals also allow to estimate the temporary alteration of the medium when repeated positive (negative) signals are input; the response increases (decreases) in amplitude when the signals are all positive (negative), it decreases when the signals are alternatively positive and negative in agreement with the known attitude of the medium to induced polarization.

scholarly journals Analytic resolution of time-domain half-space Green's functions for internal loads by a displacement potential-Laplace-Hankel-Cagniard transform method

2020 ◽  
Vol 476 (2235) ◽  
pp. 20190610
Author(s):  
Ronald Y. S. Pak ◽  
Xiaoyong Bai
Keyword(s):  
Half Space ◽  
Time Domain ◽  
Surface Force ◽  
Point Load ◽  
Wave Group ◽  
Branch Points ◽  
Transform Method ◽  
Displacement Potential ◽  
Starting Point ◽  
The Time Domain

A refined yet compact analytical formulation is presented for the time-domain elastodynamic response of a three-dimensional half-space subject to an arbitrary internal or surface force distribution. By integrating Laplace and Hankel transforms into a method of displacement potentials and Cagniard's inversion concept, it is shown that the solution can be derived in a straightforward manner for the generalized classical wave propagation problem. For the canonical case of a buried point load with a step time function, the response is proved to be naturally reducible with the aid of a parametrized Bessel function integral representation to six wave-group integrals on finite contours in the complex plane that stay away from all branch points and the Rayleigh pole except possibly at the starting point of the contours. On the latter occasions, the possible singularities of the integrals can be rigorously extracted by an extended method of asymptotic decomposition, rendering the residual numerical computation a simple exercise. With the new solution format, the arrival time of each wave group is derivable by simple criteria on the contour. Typical results for the time-domain response for an internal point force as well as the degenerate case of a surface point source are included for comparison and illustrations.

A recursive method for the separation of upgoing and downgoing waves of vertical seismic profiling data

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2206-2218 ◽  
Author(s):  
F. Aminzadeh
Keyword(s):  
Time Domain ◽  
Fourier Transforms ◽  
A Priori ◽  
Computational Time ◽  
Linear Filter ◽  
Seismic Profiling ◽  
Vertical Seismic Profiling ◽  
Starting Point ◽  
Vsp Data ◽  
The Time Domain

An important part of the processing of vertical seismic profiling (VSP) data is the separation of upgoing and downgoing waves. I introduce a new method for separation based on a time‐domain recursive linear filter. The separation method uses an approximation to an optimal, frequency‐domain, nonlinear filter solution as the starting point. The time‐domain recursive linear (approximate) filter converges to the optimal (exact) solution. Since the computation is in the time domain and since this filter is linear, some of the temporal aliasing and other problems resulting from the forward and inverse Fourier transforms are avoided. Specifically, instability for some frequencies (spectral singularities) is not experienced here. This method uses a priori information of the opposite stepouts of the upgoing and downgoing waves. Equal spacing between borehole measurement points is not required. Further, the computational time may be controlled according to the desired accuracy. An important feature of this method is that it locates the reflecting boundaries of the subsurface. Having located the homogeneous layers, it allows variable‐length windows of traces for separation, which eliminates the undesirable effects of smearing and extending wave fields beyond their origins. Also, knowledge of acoustic impedances for accurate implementation of the optimum filter is no longer required.

scholarly journals Heart Rate Variability in Children with Tricyclic Antidepressant Intoxication

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Ener Cagri Dinleyici ◽  
Zubeyir Kilic ◽  
Sabiha Sahin ◽  
Rabia Tutuncu-Toker ◽  
Makbule Eren ◽  
...  
Keyword(s):  
Intensive Care Unit ◽  
Spectral Analysis ◽  
Intensive Care ◽  
Time Domain ◽  
Tricyclic Antidepressant ◽  
Noninvasive Testing ◽  
Testing Method ◽  
Starting Point ◽  
Hrv Analysis ◽  
The Time Domain

The aim of this study was to evaluate HRV in children requiring intensive care unit stays due to TCA poisoning between March 2009 and July 2010. In the time-domain nonspectral evaluation, the SDNN (P<0.001), SDNNi (P<0.05), RMSDD (P<0.01), and pNN50 (P<0.01) were found to be significantly lower in the TCA intoxication group. The spectral analysis of the data recorded during the first 5 minutes after intensive care unit admission showed that the values of the nLF (P<0.05) and the LF/HF ratio (P=0.001) were significantly higher in the TCA intoxication group, while the nHF (P=0.001) values were significantly lower. The frequency-domain spectral analysis of the data recorded during the last 5 minutes showed a lower nHF (P=0.001) in the TCA intoxication group than in the controls, and the LF/HF ratio was significantly higher (P<0.05) in the intoxication group. The LF/HF ratio was higher in the seven children with seizures (P<0.001). These findings provided us with a starting point for the value of HRV analysis in determining the risk of arrhythmia and convulsion in TCA poisoning patients. HRV can be used as a noninvasive testing method in determining the treatment and prognosis of TCA poisoning patients.

Apodisation in the time domain

1992 ◽  
Vol 2 (4) ◽  
pp. 615-620
Author(s):  
G. W. Series
Keyword(s):  
Time Domain ◽  
The Time Domain

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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