scholarly journals Time-domain observation and synthesis of split spheroidal and torsional free oscillations of the 1960 chilean earthquake: Preliminary results

1978 ◽  
Vol 68 (2) ◽  
pp. 325-332 ◽  
Author(s):  
Seth Stein ◽  
Robert J. Geller
Keyword(s):  
Time Domain ◽  
Normal Modes ◽  
Wave Form ◽  
Central Frequency ◽  
Complex Wave ◽  
Location Depth ◽  
The Time Domain ◽  
Theoretical Results ◽  
Good Agreement ◽  
Chilean Earthquake

Abstract The rotationally and elliptically split normal modes of the earth are observed for the 1960 Chilean earthquake by analysis in the time domain. One hundred and fifty hours of the Isabella, California, strain record are narrow band filtered about the central frequency of each split multiplet to isolate the complex wave form resulting from the interference of the different singlets. We compute synthetic seismograms using our previous theoretical results, which show the dependence of the amplitude and phase of the singlets on source location, depth, mechanism, and the position of the receiver. By comparing these synthetics to the filtered record, we conclusively demonstrate the splitting of modes whose splitting had not been definitely resolved: torsional modes (0T3, 0T4) and spheroidal modes (0S4, 0S5). The splitting of 0S2 and 0S3 is reconfirmed. We obtain good agreement between the synthetics and the filtered data for a source mechanism (previously determined from long-period surface waves) of thrust motion on a shallow dipping fault.

High Amplitude Sound Propagation at Low Frequencies in a Flow Duct Lined With Resonators: A Time Domain Solution

1988 ◽  
Vol 110 (4) ◽  
pp. 545-551 ◽  
Author(s):  
A. Cummings ◽  
I.-J. Chang
Keyword(s):  
Time Domain ◽  
Internal Combustion Engines ◽  
Sound Propagation ◽  
Sound Field ◽  
High Amplitude ◽  
Combustion Engines ◽  
Low Frequencies ◽  
The Time Domain ◽  
Flow Duct ◽  
Good Agreement

A quasi one-dimensional analysis of sound transmission in a flow duct lined with an array of nonlinear resonators is described. The solution to the equations describing the sound field and the hydrodynamic flow in the neighborhood of the resonator orifices is performed numerically in the time domain, with the object of properly accounting for the nonlinear interaction between the acoustic field and the resonators. Experimental data are compared to numerical computations in the time domain and generally very good agreement is noted. The method described here may readily be extended for use in the design of exhaust mufflers for internal combustion engines.

Research on the Static and Dynamics Characteristics of Soft Yoke Mooring System Based on Multi-Rigid Body Interaction

2020 ◽  
Author(s):  
Hongwei Wang ◽  
Zizhao Zhang ◽  
Gang Ma ◽  
Rongtai Ma ◽  
Jie Yang
Keyword(s):  
Time Domain ◽  
Rigid Bodies ◽  
Coupled Analysis ◽  
Mooring System ◽  
Accurate Analysis ◽  
Restoring Force ◽  
Stiffness Characteristics ◽  
The Time Domain ◽  
Multi Body ◽  
Good Agreement

Abstract Select the common mooring system-soft yoke mooring system as the research object. The soft yoke mooring system is regarded as a structure composed of multiple rigid bodies, and the theoretical analysis of multi-body dynamics is used to discuss the interaction of multi-rigid bodies. The classical HYSY113 FPSO is selected as an example, for the soft yoke mooring system, the stiffness characteristics and static restoring force curved compared with those of software OrcaFlex, and they are in good agreement, which verify the reliability of the formula derived, and it is a prerequisite for the accurate simulations in further steps. Coupled analysis to the whole system in time domain is also carried out both in OrcaFlex and AQWA, and the representative response of the FPSO under different environmental conditions is compared, the results are consistent well with each other. It is a good reference for the future study in this field. Good static characteristics are a prerequisite for accurate analysis of time-domain motion. By comparing the results in the time domain, it is found that under the same working conditions, the analysis results calculated by different commercial software (AQWA and OrcaFlex) may be different. We need to perform design analysis based on the characteristics of the software.

Thermoacoustic interplay between intrinsic thermoacoustic and acoustic modes: non-normality and high sensitivities

2019 ◽  
Vol 878 ◽  
pp. 190-220 ◽  
Author(s):  
Francesca M. Sogaro ◽  
Peter J. Schmid ◽  
Aimee S. Morgans
Keyword(s):  
Time Domain ◽  
Time Scale ◽  
Initial Conditions ◽  
Normal Modes ◽  
Time Domain Analysis ◽  
Normal Behaviour ◽  
Optimal Perturbation ◽  
Acoustic Modes ◽  
Energy Growth ◽  
The Time Domain

This study analyses the interplay between classical acoustic modes and intrinsic thermoacoustic (ITA) modes in a simple thermoacoustic system. The analysis is performed using a frequency-domain low-order network model as well as a time-domain spatially discretised model. Anti-correlated modal sensitivities are found to arise due to a pairwise interplay between acoustic and ITA modes. The magnitude of the sensitivities increases as the interplay between the modes grows stronger. The results show a global behaviour of the modes linked to the presence of exceptional points in the spectrum. The time-domain analysis results in a delay-differential equation and allows the investigation of non-normal behaviour and its consequences. Pseudospectral analysis reveals that energy amplification is crucially linked to an interplay between acoustic and ITA modes. While higher non-orthogonality between two modes is correlated with peaks in modal sensitivity, transient energy growth does not necessarily involve the most sensitive modes. In particular, growth estimates based on the Kreiss constant demonstrate that transient amplification relies critically on the proximity of the non-normal modes to the imaginary axis. The time scale for transient amplification is identified as the flame time delay, which is further corroborated by determining the optimal initial conditions responsible for the bulk of the non-modal energy growth. The flame is identified as an active and dominant contributor to energy gain. The frequency of the optimal perturbation matches the acoustic time scale, once more confirming an interplay between acoustic and ITA structures. Flame-based amplification factors of two to five are found, which are significant when feeding into the acoustic dynamics and eventually triggering nonlinear limit-cycle behaviour.

Second-Order Fourier Synthesis of Broadband Acoustic Signals Using Normal Modes

1997 ◽  
Vol 05 (04) ◽  
pp. 355-370 ◽  
Author(s):  
E. K. Skarsoulis
Keyword(s):  
Time Domain ◽  
Normal Modes ◽  
Acoustic Signals ◽  
Second Order ◽  
Single Frequency ◽  
Closed Form Expression ◽  
Fourier Synthesis ◽  
Eigenvalues And Eigenfunctions ◽  
Intermediate Order ◽  
The Time Domain

A scheme for approximate normal-mode calculation of broadband acoustic signals in the time domain is proposed based on a second-order Taylor expansion of eigenvalues and eigenfunctions with respect to frequency. For the case of a Gaussian impulse source a closed-form expression is derived for the pressure in the time domain. Using perturbation theory, analytical expressions are obtained for the involved first and second frequency-derivatives of eigenvalues and eigenfunctions. The proposed approximation significantly accelerates arrival-pattern calculations, since the eigenvalues, the eigenfunctions and their frequency-derivatives need to be calculated at a single frequency, the central frequency of the source. Furthermore, it offers a satisfactory degree of accuracy for the lower and intermediate order modes. This is due to the fact that essential wave-theoretic mechanisms such as dispersion and frequency dependence of mode amplitudes are contained in the representation up to a sufficient order. Numerical results demonstrate the efficiency of the method.

scholarly journals Calculations of near-field emissions in frequency-domain into time-dependent data with arbitrary wave form transient perturbations

2012 ◽  
Vol 1 (2) ◽  
pp. 26
Author(s):  
Y. Liu ◽  
B. Ravelo ◽  
J. Ben Hadj Slama
Keyword(s):  
Time Domain ◽  
Near Field ◽  
Wave Spectrum ◽  
Computational Method ◽  
Time Dependent ◽  
Dependent Data ◽  
Wave Form ◽  
Frequency Dependent ◽  
Transient Electromagnetic ◽  
The Time Domain

This paper is devoted on the application of the computational method for calculating the transient electromagnetic (EM) near-field (NF) radiated by electronic structures from the frequency-dependent data for the arbitrary wave form perturbations i(t). The method proposed is based on the fast Fourier transform (FFT). The different steps illustrating the principle of the method is described. It is composed of three successive steps: the synchronization of the input excitation spectrum I(f) and the given frequency data H0(f), the convolution of the two inputs data and then, the determination of the time-domain emissions H(t). The feasibility of the method is verified with standard EM 3D simulations. In addition to this method, an extraction technique of the time-dependent z-transversal EM NF component Xz(t) from the frequency-dependent x- and y- longitudinal components Hx(f) and Hy(f) is also presented. This technique is based on the conjugation of the plane wave spectrum (PWS) transform and FFT. The feasibility of the method is verified with a set of dipole radiations. The method introduced in this paper is particularly useful for the investigation of time-domain emissions for EMC applications by considering transient EM interferences (EMIs).

scholarly journals Solids Content of Black Liquor Measured by Online Time-Domain NMR

2019 ◽  
Vol 9 (10) ◽  
pp. 2169 ◽  
Author(s):  
Ekaterina Nikolskaya ◽  
Petri Janhunen ◽  
Mikko Haapalainen ◽  
Yrjö Hiltunen
Keyword(s):  
Time Domain ◽  
Black Liquor ◽  
Pulp Mill ◽  
Temperature Correction ◽  
Industrial Environment ◽  
Spin Relaxation Rate ◽  
Recovery Unit ◽  
Solids Content ◽  
The Time Domain ◽  
Good Agreement

Black liquor, a valuable by-product of the pulp production process, is used for the recovery of chemicals and serves as an energy source for the pulp mill. Before entering the recovery unit, black liquor runs through several stages of evaporation, wherein the solids content (SC) can be used to control the evaporation effectiveness. In the current study, the time-domain nuclear magnetic resonance (TD-NMR) technique was applied to determine the SC of black liquor. The TD-NMR system was modified for flowing samples, so that the black liquor could be pumped through the system, followed by the measurement of the spin-spin relaxation rate, R2. A temperature correction was also applied to reduce deviations in the R2 caused by the sample temperature. The SC was calculated based on a linear model between the R2 and the SC values determined gravimetrically, where good agreement was shown. The online TD-NMR system was tested at a pulp mill for the SC estimation of weak black liquor over seven days without any fouling, which demonstrated the feasibility of the method in a harsh industrial environment. Therefore, the potential of the TD-NMR technology as a technique for controlling the black liquor evaporation process was demonstrated.

Nonlinear modeling, time-domain analysis and simulation of non-Foster elements

2016 ◽  
Vol 9 (4) ◽  
pp. 747-755
Author(s):  
Hamed Khoshniyat ◽  
Abdolali Abdipour ◽  
Gholamreza Moradi
Keyword(s):  
Time Domain ◽  
Linear Time ◽  
Nonlinear Modeling ◽  
Current Source ◽  
Time Domain Analysis ◽  
Circuit Performance ◽  
Modeling Analysis ◽  
The Stability ◽  
The Time Domain ◽  
Good Agreement

In this paper, the structure of a common field-effect transistor (FET)-based negative impedance converter (NIC) that behaves as a negative capacitor is presented. The nonlinear modeling, analysis, and simulation of this non-Foster structure are presented in the time domain and the transient response of the circuit can be used to study the stability of the circuit. For the analysis of the circuit performance, the linear time-dependent modeling approach is used. This method is based on determination of the circuit parameters at each step according to parameters of the previous steps, bias voltages, and the input signal. Results of the proposed method for analysis of non-Foster circuit are compared with those of nonlinear analysis using commercial software, which shows a good agreement together and the proposed method is validated. Based on the analysis, the nonlinear capacitance of non-Foster circuit is extracted and based on the simple second order model of current source of FET, the analytic model of negative capacitor is extracted and improved by curve fitting. The proposed model results have a good agreement with simulation results of NIC's circuit.

scholarly journals Analysis of Longitudinal Guided Wave Propagation in a Liquid-Filled Pipe Embedded in Porous Medium

2021 ◽  
Vol 11 (5) ◽  
pp. 2281
Author(s):  
Nana Su ◽  
Qingbang Han ◽  
Yu Yang ◽  
Minglei Shan ◽  
Jian Jiang
Keyword(s):  
Porous Medium ◽  
Time Domain ◽  
Saturated Porous Medium ◽  
Guided Wave ◽  
Guided Wave Propagation ◽  
Partial Mode ◽  
The Media ◽  
The Time Domain ◽  
Good Agreement

To study the leakage situation of a liquid-filled pipe in long-term service, a model of a liquid-filled pipe embedded in an infinite porous medium as well as in a finite porous medium is designed. The principal motivation is to perform detailed quantitative analysis of the longitudinal guided wave propagating in a liquid-filled pipe embedded in a saturated porous medium. The problems of pipeline leakage and porosity as well as the media outside the pipe are solved to identify the characteristics of the guided wave in a more practical model. The characteristics of the guided wave are investigated theoretically and numerically, with special emphasis on the influence of porous medium parameters on the dispersion properties. Assuming the pipe is a cylindrical shell buried in an isotropic, homogeneous, and porous medium, the dispersion equations are established based on the elastic-dynamic equations and the modified Biot liquid-saturated porous theory. The characteristics of dispersion, time-domain waveform and attenuation curves varying with porous medium parameters, wrapping layer material, and thickness, are all analyzed. The increase in porosity decreases the partial mode phase velocity in the liquid-filled pipe embedded in the finite porous medium. The characteristics of attenuation are in good agreement with the dispersion curves and the time-domain waveform results.

scholarly journals A Time-Shifting Algorithm for Alleviating Convergence Difficulties at Interior Acoustic Resonance Frequencies

2021 ◽  
Vol 11 (6) ◽  
pp. 2701
Author(s):  
Jui Hsiang Kao
Keyword(s):  
Point Source ◽  
Time Domain ◽  
Internal Resonance ◽  
Acoustic Resonance ◽  
Time Step ◽  
Resonance Frequencies ◽  
True Frequency ◽  
The Time Domain ◽  
Acoustic Domain ◽  
Good Agreement

This paper proposes a time-shifting boundary element method in the time domain to calculate the radiating pressures of an arbitrary object pulsating at eigenfrequencies of the interior (i.e., interior resonance frequencies). In this paper, the frequency shifting is time-step-dependent and could be viewed as an iterative, or relaxation, technique for the solution of the problem. The proposed method avoids numerical problems due to the internal resonance frequency by initializing the iteration with each scaled frequency. The scaled frequency is approximately equal to the true frequency at the last iterating time step. A sphere pulsating at the eigenfrequency in an infinite acoustic domain was calculated first; the result was compared with the analytical solution, and they were in good agreement. Moreover, two arbitrary-shaped radiators were taken as study cases to predict the radiating pressures at the interior resonance frequencies, and robustly convergent results were obtained. Finally, the accuracy of the proposed method was tested using a problem with a known solution. A point source was placed inside the object to compute the surface velocities; the computed surface pressures were identical to the pressures computed using the point source.

SPICE Modeling Nonlinearity Effects on Ultrasonic Waves

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Noureddine Aouzale ◽  
Ahmed Chitnalah ◽  
Hicham Jakjoud
Keyword(s):  
Ultrasonic Wave ◽  
Time Domain ◽  
Burgers Equation ◽  
Ultrasonic Waves ◽  
Spice Model ◽  
Ultrasound Propagation ◽  
Wave Distortion ◽  
Simulation Results ◽  
The Time Domain ◽  
Good Agreement

Nonlinearity is one of the phenomena that affect the ultrasonic wave during its propagation in a given medium. In the time domain the nonlinearity is seen as a variation of the phase velocity which leads to a distortion of the waveform. This corresponds in the frequency domain to energy transfer from the fundamental frequency to the harmonic and among the harmonic themselves. Our purpose in this paper is to introduce a SPICE implementation of the computational model of the nonlinear ultrasound propagation. We first study the plane wave distortion based on the Burgers’ equation. Our SPICE model allowed studying the temporal profile of the ultrasonic wave during its propagation. The simulation results are compared to the analytical solution of the Burgers’ equation showing the validity of the model. An experimental device based on ultrasonic transmission mode is used to carry out measurements and the comparison with the simulation results shows a good agreement.

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