scholarly journals Time-Dependent Motion of a Floating Circular Elastic Plate

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 29
Author(s):  
Michael H. Meylan
Keyword(s):  
Elastic Plate ◽  
Time Domain ◽  
Single Frequency ◽  
Complex Motion ◽  
Matching Method ◽  
Gaussian Profile ◽  
Focused Wave ◽  
The Time Domain ◽  
Incident Waves ◽  
Focused Wave Group

The motion of a circular elastic plate floating on the surface is investigated in the time-domain. The solution is found from the single frequency solutions, and the method to solve for the circular plate is given using the eigenfunction matching method. Simple plane incident waves with a Gaussian profile in wavenumber space are considered, and a more complex focused wave group is considered. Results are given for a range of plate and incident wave parameters. Code is provided to show how to simulate the complex motion.

scholarly journals Time-Dependent Motion of a Floating Circular Elastic Plate

2020 ◽  
Author(s):  
Michael Meylan
Keyword(s):  
Elastic Plate ◽  
Time Domain ◽  
Single Frequency ◽  
Complex Motion ◽  
Matching Method ◽  
Gaussian Profile ◽  
Focused Wave ◽  
The Time Domain ◽  
Incident Waves ◽  
Focused Wave Group

The motion of a circular elastic plate floating on the surface is investigated in the time–domain. The solution is found from the single frequency solutions and the method to solve for the circular plate is given using the eigenfunction matching method. Simple plane incident waves with a Gaussian profile in wavenumber space are considered and a more complex focused wave group is considered. Results are given for a range of plate and incident wave parameters are investigated. Code is provided to show how to simulate the complex motion.

scholarly journals A SFTD Algorithm for Optimizing the Performance of the Readout Strategy of Residence Time Difference Fluxgate

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3985 ◽  
Author(s):  
Siyu Chen ◽  
Yanzhang Wang ◽  
Jun Lin
Keyword(s):  
Residence Time ◽  
Time Domain ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Transformation Method ◽  
Time Difference ◽  
Single Frequency ◽  
Time Frequency ◽  
Frequency Magnetic Field ◽  
The Time Domain

Residence time difference (RTD) fluxgate sensor is a potential device to measure the DC or low-frequency magnetic field in the time domain. Nevertheless, jitter noise and magnetic noise severely affect the detection result. A novel post-processing algorithm for jitter noise reduction of RTD fluxgate output strategy based on the single-frequency time difference (SFTD) method is proposed in this study to boost the performance of the RTD system. This algorithm extracts the signal that has a fixed frequency and preserves its time-domain information via a time–frequency transformation method. Thereby, the single-frequency signal without jitter noise, which still contains the ambient field information in its time difference, is yielded. Consequently, compared with the traditional comparator RTD method (CRTD), the stability of the RTD estimation (in other words, the signal-to-noise ratio of residence time difference) has been significantly boosted with sensitivity of 4.3 μs/nT. Furthermore, the experimental results reveal that the RTD fluxgate is comparable to harmonic fluxgate sensors, in terms of noise floor.

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 The application of improved FDTD algorithm based on mode-matching in shielding cavity

2018 ◽  
Vol 232 ◽  
pp. 03030
Author(s):  
Xuelian Gao ◽  
Lingli Kong
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Fdtd Method ◽  
Mode Matching ◽  
Electromagnetic Environment ◽  
Matching Method ◽  
Boundary Problems ◽  
Mode Matching Method ◽  
Regular Waveguide ◽  
The Time Domain

Due to the increasing complexity of the electromagnetic environment, the cavity with apertures are used more and more widely in electromagnetic shielding. At present, the time domain finite difference (FDTD) method has a good application effect for the transmission line response problem of a double-layer shield cavity with apertures, but this method usually encounters the boundary problem of semi-open and open areas. Due to the limited computing resources, the truncation of the FDTD region has an impact on the accuracy and speed of the calculation because that is very important. Based on that, this paper puts forward a method of combining mode-matching method with FDTD algorithm, which overcomes the limitation that mode-matching method can only be used for regular waveguide analysis and uses mode-matching method to solve FDTD boundary problems. The improved FDTD algorithm based on mode-matching method enhances the accuracy of the algorithm and guarantees the calculation speed.

Effect of topography on surface motion

1973 ◽  
Vol 63 (2) ◽  
pp. 615-632 ◽  
Author(s):  
Michel Bouchon
Keyword(s):  
Time Domain ◽  
Surface Displacement ◽  
Single Frequency ◽  
Wavelength Interval ◽  
Frequency Method ◽  
Surface Motion ◽  
Surface Irregularities ◽  
San Fernando ◽  
The Time Domain ◽  
P And Sv Waves

abstract The effect of topography on surface motion is investigated in the cases of incident SH, P and SV waves. Several types of topography ranging from a ridge to a valley are used. Different incidence angles are considered for a wavelength interval extending from 2h to 20h, where h is the vertical dimension of the anomaly. The computation is made by using a single frequency method developed by Aki and Larner and by synthesizing the results in order to get a solution in the time domain. A method of correction taking into account the residual stress is added. The surface displacement appears to be very much influenced by surface irregularities. In the case of a ridge, a zone of amplification takes place near the top, whereas, for a depression, a zone of attenuation occurs near the bottom. An application to the Pacoima Dam accelerograph site suggests that the high accelerations recorded there during the San Fernando earthquake could have been amplified between 30 and 50 per cent by the uneven topography.

scholarly journals Coupled Motion and Sloshing Analysis of a Rigid Cylindrical Closed Fish Cage in Regular Waves

2019 ◽  
Author(s):  
Yuelin Tan ◽  
Yanlin Shao ◽  
Robert Read
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Equations Of Motion ◽  
Irregular Waves ◽  
Diffraction Radiation ◽  
Regular Waves ◽  
Ongoing Research ◽  
Coupled Numerical Model ◽  
The Time Domain ◽  
Incident Waves

Abstract In this paper, a coupled numerical model in the time domain has been developed to study the interaction between interior liquid sloshing and the motion of a cylindrical closed fish cage when the cage is exposed to regular waves. The single-dominant nonlinear multimodal theory for sloshing in a cylindrical cage presented in [1] was implemented to simulate the liquid responses in the cage. A time-domain simulator based on the Cummins formulation of the equations of motion [2] is used to solve for the cage motion, while WAMIT is used to provide all required frequency-domain hydrodynamic coefficients for the external diffraction/radiation problems. Details of the coupling between cage motion and sloshing will be presented. The coupled solver is verified against the linear frequency-domain solution from WAMIT for the very small wave steepness, where linear theory is valid. The results show that the sloshing effect is a vital factor in the coupling process, which means that the liquid in the closed cage cannot be treated as a solid mass. This is particularly true close to the resonant frequencies of the liquid in the tank. Furthermore, the importance of nonlinearity due to sloshing responses is investigated by applying incident waves with different steepness. When the cage is exposed to regular waves, if certain criteria are met, nonlinear swirling waves are observed in the closed cage. The nonlinear swirling waves are due to the interactions between different sloshing modes, which can only be explained by a proper nonlinear theory, such as the multimodal theory applied in this study. The influence of the swirling waves on the cage motions will also be discussed in the paper. How this effect will impact the design of a closed fish cage and its mooring system can only be answered by studying the cage responses in irregular waves, which is the subject of ongoing research.

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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