Near-field Rayleigh waves from surface explosions

1981 ◽  
Vol 71 (1) ◽  
pp. 223-248
Author(s):  
John R. Murphy
Keyword(s):  
Rayleigh Waves ◽  
Scaling Laws ◽  
Near Field ◽  
Low Frequency ◽  
Surface Shear ◽  
Low Frequencies ◽  
Wave Source ◽  
Near Surface ◽  
Frequency Components ◽  
The One

abstract The low-frequency components of the near-field ground motions produced by surface explosions are investigated and evidence is presented which suggests that much of this motion can be accounted for by the Rayleigh waves induced by the airblast loading acting on the surface exterior to the region of strong nonlinear response (i.e., the crater). Scaling laws are derived for this component of the motion which indicate that the amplitude of the Rayleigh wave source function is expected to be directly proportional to yield and independent of site geology at low frequencies and to scale as yield to the one-third power and increase with the near-surface shear wave velocity at high frequencies. Finally, an unusual arrival recorded interior to a hexagonal array of surface explosions is analyzed and shown to be consistent with Rayleigh waves converging on the center from an exterior, axisymmetric, surface-ring load which may correlate physically with the multi-burst spall closure for this event.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2011 ◽  
Author(s):  
Gundula B. Runge ◽  
Al Ferri ◽  
Bonnie Ferri
Keyword(s):  
Time Scale ◽  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Selection Of

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.

scholarly journals Deep learning for low-frequency extrapolation from multioffset seismic data

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. R989-R1001 ◽  
Author(s):  
Oleg Ovcharenko ◽  
Vladimir Kazei ◽  
Mahesh Kalita ◽  
Daniel Peter ◽  
Tariq Alkhalifah
Keyword(s):  
Deep Learning ◽  
Seismic Data ◽  
Signal To Noise Ratio ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Low Frequencies ◽  
Seismic Surveys ◽  
Full Waveform ◽  
Frequency Components ◽  
Marine Seismic

Low-frequency seismic data are crucial for convergence of full-waveform inversion (FWI) to reliable subsurface properties. However, it is challenging to acquire field data with an appropriate signal-to-noise ratio in the low-frequency part of the spectrum. We have extrapolated low-frequency data from the respective higher frequency components of the seismic wavefield by using deep learning. Through wavenumber analysis, we find that extrapolation per shot gather has broader applicability than per-trace extrapolation. We numerically simulate marine seismic surveys for random subsurface models and train a deep convolutional neural network to derive a mapping between high and low frequencies. The trained network is then tested on sections from the BP and SEAM Phase I benchmark models. Our results indicate that we are able to recover 0.25 Hz data from the 2 to 4.5 Hz frequencies. We also determine that the extrapolated data are accurate enough for FWI application.

Dispersion and the dissipative characteristics of surface waves in the generalized S-transform domain

Geophysics ◽  
2012 ◽  
Vol 77 (1) ◽  
pp. V11-V20 ◽  
Author(s):  
Roohollah Askari ◽  
Robert J. Ferguson
Keyword(s):  
Cost Function ◽  
Surface Waves ◽  
Joint Inversion ◽  
Scaling Factor ◽  
Surface Shear ◽  
Low Frequencies ◽  
Near Surface ◽  
S Transform ◽  
Generalized S Transform ◽  
The Cost

Wavenumber, group velocity, phase velocity, and frequency-dependent attenuation characterize the propagation of surface waves in dispersive, attenuating media. We use a mathematical model based on the generalized [Formula: see text] transform to simultaneously estimate these characteristic parameters for later use in joint inversion for near-surface shear wave velocity. We use a scaling factor in the generalized S transform to enable the application of the method in a highly dispersive medium. We introduce a cost function in the [Formula: see text]-domain to estimate an optimum value for the scaling factor. We also use the cost function to generalize the application of the method for noisy data, especially data with a low signal-to-noise ratio at low frequencies. In that case, the estimated wavenumber is perturbed. As a solution, we estimate wavenumber perturbation by minimizing the cost function, using Simulated Annealing. We use synthetic and real data to show the efficiency of the method for the estimation of the propagation parameters of highly dispersive and noisy media.

The lung-eardrum pathway in three treefrog and four dendrobatid frog species: some properties of sound transmission.

1994 ◽  
Vol 195 (1) ◽  
pp. 329-343 ◽  
Author(s):  
G Ehret ◽  
E Keilwerth ◽  
T Kamada
Keyword(s):  
High Frequency ◽  
Body Wall ◽  
Low Frequency ◽  
Sound Intensity ◽  
The Body ◽  
Response Curves ◽  
Low Frequencies ◽  
Best Response ◽  
Lateral Body ◽  
Frequency Components

Frequency-response curves of the tympanum and lateral body wall (lung area) were measured by laser Doppler vibrometry in three treefrog (Smilisca baudini, Hyla cinerea, Osteopilus septentrionalis) and four dendrobatid frog (Dendrobates tinctorius, D. histrionicus, Epipedobates tricolor, E. azureiventris) species. The high-frequency cut-off of the body wall response was always lower than that of the tympanum. The best response frequencies of the lateral body wall were lower than those of the tympanum in some species (S. baudini, O. septentrionalis, D. tinctorius), while in the others they were rather similar. Best tympanic frequencies and best body wall response frequencies tended to differ more with increasing body size. Stimulation of the tympanum by sound transfer through 3.14 mm2 areas of the lateral body wall showed that the lung-eardrum pathway can be in two states, depending on breathing activity within the lungs: 44% (in Smilisca), 39% (in Hyla) and 31% (in Osteopilus) of the eardrum vibrations were 2.5-8 times (8-18 dB) larger when the frogs were breathing with the lungs compared with non-breathing conditions. The vibration amplitudes of the tympanum and lateral body wall of the treefrogs followed the same dependence on sound intensity, only absolute amplitudes differed between species. Our results suggest that the lung-eardrum pathway attenuates high-frequency components of species-specific calls and enhances low-frequency components. In addition, an amplitude modulation is imposed on the low frequencies during the rhythm of breathing.

Enhancing the low-frequency amplitude of ground force from a seismic vibrator through reduction of harmonic distortion

Geophysics ◽  
2013 ◽  
Vol 78 (4) ◽  
pp. P9-P17 ◽  
Author(s):  
Zhouhong Wei ◽  
Thomas F. Phillips
Keyword(s):  
Harmonic Distortion ◽  
Low Frequency ◽  
Seismic Exploration ◽  
Control Algorithms ◽  
Hydraulic Systems ◽  
Force Output ◽  
Low Frequencies ◽  
Near Surface ◽  
Fundamental Frequencies ◽  
Inversion Techniques

Extending the vibroseis bandwidth toward low frequencies (below 10 Hz) can bring many benefits for land seismic exploration such as deeper signal penetration and for near-surface inversion techniques. Due to physical limitations in vibrator mechanical and hydraulic systems, the ground force output from a vibrator at low frequencies is limited. This limited ground force output is severely distorted by harmonic distortion such that the ground force in fundamental frequencies is reduced. We focused on reducing harmonic distortion through vibrator control algorithms to improve vibrator performance at low frequencies. The purpose was to show that with only vibrator control algorithms, the fundamental ground force from a vibrator can be noticeably improved at low frequencies. In addition, we demonstrated a synthetic case using the weighted-sum ground force to simulate slip-sweep acquisition. Presumably, reducing source generated harmonic distortion can help decrease the slip time in slip-sweep operations thereby increasing productivity rates.

Sensitive Response to Low-Frequency Cochlear Distortion Products in the Auditory Midbrain

2009 ◽  
Vol 101 (3) ◽  
pp. 1560-1574 ◽  
Author(s):  
Cornelius Abel ◽  
Manfred Kössl
Keyword(s):  
Low Frequency ◽  
Otoacoustic Emission ◽  
Threshold Level ◽  
Auditory Midbrain ◽  
Low Frequencies ◽  
Distortion Product ◽  
Distortion Products ◽  
Third Phase ◽  
Complex Stimuli ◽  
Frequency Components

During auditory stimulation with several frequency components, distortion products (DPs) are generated as byproduct of nonlinear cochlear amplification. After generated, DP energy is reemitted into the ear channel where it can be measured as DP otoacoustic emission (DPOAE), and it also induces an excitatory response at cochlear places related to the DP frequencies. We measured responses of 91 inferior colliculus (IC) neurons in the gerbil during two-tone stimulation with frequencies well above the unit's receptive field but adequate to generate a distinct distortion product (f2-f1 or 2f1-f2) at the unit's characteristic frequency (CF). Neuronal responses to DPs could be accounted for by the simultaneously measured DPOAEs for DP frequencies >1.3 kHz. For DP frequencies <1.3 kHz ( n = 25), there was a discrepancy between intracochlear DP magnitude and DPOAE level, and most neurons responded as if the intracochlear DP level was significantly higher than the DPOAE level in the ear channel. In 12% of those low-frequency neurons, responses to the DPs could be elicited even if the stimulus tone levels were below the threshold level of the neuron at CF. High intracochlear f2-f1 and 2f1-f2 DP-levels were verified by cancellation of the neuronal DP response with a third phase-adjusted tone stimulus at the DP frequency. A frequency-specific reduction of middle ear gain at low frequencies is possibly involved in the reduction of DPOAE level. The results indicate that pitch-related properties of complex stimuli may be produced partially by high intracochlear f2-f1 distortion levels.

scholarly journals Spectra of Low-Frequency Ground Vibrations Generated by High-Speed Trains on Layered Ground

1997 ◽  
Vol 16 (4) ◽  
pp. 257-270 ◽  
Author(s):  
V.V. Krylov
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Ground Vibration ◽  
Ground Vibrations ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
High Speed Trains ◽  
Frequency Components ◽  
Noticeable Reduction ◽  
Layered Ground

Increase in speeds of modern railway trains is usually accompanied by higher levels of generated ground vibrations. In the author's earlier paper [V.V. Krylov, Applied Acoustics, 44, 149–164 (1995)], it has been shown that especially large increase in vibration level may occur if train speeds v exceed the velocity of Rayleigh surface waves in the ground cR., i.e., v > cR. Such a situation might arise, for example, with French TGV trains for which speeds over 515 km/h have been achieved. The present paper investigates the effect of geological layered structure of the ground on ground vibrations generated by high-speed trains. It is shown that, since Rayleigh wave velocities in layered ground are dispersive and normally increase at lower frequencies associated with deeper penetration of surface wave energy into the ground, the trans-Rayleigh condition v > cR may not hold at very low frequencies. This will cause a noticeable reduction in low-frequency components of generated ground vibration spectra. Theoretical results are illustrated by numerically calculated frequency spectra of ground vibrations generated by single axle loads travelling at different speeds and by TGV or Eurostar high-speed trains.

scholarly journals Control the Frequency Response of a Loudspeaker by Changing Its Enclosure

2021 ◽  
Vol 4 (2) ◽  
Author(s):  
Pavlo Olehovych Riabokon
Keyword(s):  
Resonant Frequency ◽  
Resonance Frequency ◽  
Frequency Response ◽  
Rock Music ◽  
Low Frequency ◽  
Total Quality ◽  
Frequency Range ◽  
Low Frequencies ◽  
Frequency Components ◽  
Internal Volume

This article analyzes how to control frequency response of a loudspeaker by changing the volume of its closed-box enclosure. The calculation is performed by the method of  Thiele-Small on the basic of a pre-calculated loudspeaker, the parameters of which are given in third section. This became possible because of the simplification of the circuit on figure 1 to the form of circuit on figure 2. This allowed us to consider it as a second order filter (presence of two reactive elements). Obtained results are compared with corresponding characteristics of open-box enclosure of the same loudspeaker, that was pre-calculated by the author too. Results are presented graphically in figure 3 and 4. As can be seen from them, the resonant frequency of the loudspeaker in the closed-box enclosure is higher than the resonant frequency of the loudspeaker in the open box. The result in the form of a ratio  is listed in table 2. Analyzing the obtained data, it can be noticed that with the change of the internal volume of the closed box (and hence its total quality factor), it is possible to affect both the resonance frequency and the peak amplitude values in these frequencies by changing the FR. The result shown in figure 3 and 4 is achieved by taking into account effect of radiation only on the one side of the driver (in the case of open-box enclosure). Closed box was calculating by taking into account both sides radiation of the driver. Shifting the resonance frequency of the system towards higher frequencies and increasing the sound pressure on the resonance generally worsens the FR of the loudspeaker (reduces the reproduction of low-frequency components of sound and increases the unevenness of the frequency). However, certain variants of this group of frequency characteristics may be useful depending on the reproducible frequency range and need of emphasize the low-frequency components (for example, in rock music). If you need a smoothed low-frequency sound, it is appropriate to use systems with low overall quality and increased internal volume or open-box enclosure. Therefore, the volume of the closed-box enclosure significantly affects the resonant frequency and the shape of the frequency response of the loudspeaker. Reducing the volume of the enclosure of the loudspeaker leads to a decrease in its frequency range due to low frequencies and at the same time increase in the unevenness of the frequency response. The change in the resonant frequency of the system as the volume of the closed-box enclosure decreases, the less the volume of the closed-box.

scholarly journals Effect on Doppler Resonance From a Near-Surface Shear Layer

2017 ◽  
Author(s):  
Benjamin K. Smeltzer ◽  
Yan Li ◽  
Simen Å. Ellingsen
Keyword(s):  
Shear Layer ◽  
Finite Depth ◽  
Gravitational Acceleration ◽  
Surface Shear ◽  
Constant Frequency ◽  
Wave Source ◽  
Near Surface ◽  
Strong Shear ◽  
Uniform Current ◽  
Source Velocity

For waves generated by a wave source which is simultaneously moving and oscillating at a constant frequency ω, a resonance is well known to occur at a particular value τres of the nondimensional frequency τ = ωV/g (V: source velocity relative to the surface, g: gravitational acceleration). For quiescent, deep water, it is well known that τres = 1/4. We study the effect on τres from the presence of a shear flow in a layer near the surface, such as may be generated by wind or tidal currents. Assuming the vorticity is constant within the shear layer, we find that the effects on the resonant frequency can be significant even for sources corresponding to moderate shear and relatively long waves, while for stronger shear and shorter waves the effect is stronger. Even for a situation where the resonant waves have wavelengths about 20 times the width of the shear layer, the resonance frequency can change by ∼ 25% for even a moderately strong shear VS/g = 0.3 (S: vorticity in surface shear layer). Intuition for the problem is built by first considering two simpler geometries: uniform current with finite depth, and Couette flow of finite depth.

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