scholarly journals Anomalous effect in Schumann resonance phenomena observed in Japan, possibly associated with the Chi-chi earthquake in Taiwan

2005 ◽  
Vol 23 (4) ◽  
pp. 1335-1346 ◽  
Author(s):  
M. Hayakawa ◽  
K. Ohta ◽  
A. P. Nickolaenko ◽  
Y. Ando
Keyword(s):  
Frequency Shift ◽  
Main Shock ◽  
Peak Frequency ◽  
Resonance Mode ◽  
Resonance Phenomenon ◽  
Meridian Plane ◽  
Schumann Resonance ◽  
Anomalous Effect ◽  
Arrival Angle ◽  
Small Magnitude

Abstract. The Schumann resonance phenomenon has been monitored at Nakatsugawa (near Nagoya) in Japan since the beginning of 1999, and due to the occurance of a severe earthquake (so-called Chi-chi earthquake) on 21 September 1999 in Taiwan we have examined our Schumann resonance data at Nakatsugawa during the entire year of 1999. We have found a very anomalous effect in the Schumann resonance, possibly associated with two large land earthquakes (one is the Chi-chi earthquake and another one on 2 November 1999 (Chia-yi earthquake) with a magnitude again greater than 6.0). Conspicuous effects are observed for the larger Chi-chi earthquake, so that we summarize the characteristics for this event. The anomaly is characterized mainly by the unusual increase in amplitude of the fourth Schumann resonance mode and a significant frequency shift of its peak frequency (~1.0Hz) from the conventional value on the By magnetic field component which is sensitive to the waves propagating in the NS meridian plane. Anomalous Schumann resonance signals appeared from about one week to a few days before the main shock. Secondly, the goniometric estimation of the arrival angle of the anomalous signal is found to coincide with the Taiwan azimuth (the unresolved dual direction indicates toward South America). Also, the pulsed signals, such as the Q-bursts, were simultaneously observed with the "carrier" frequency around the peak frequency of the fourth Schumann resonance mode. The anomaly for the second event for the Chia-yi earthquake on 2 November had much in common. But, most likely due to a small magnitude, the anomaly appears one day before and lasts until one day after the main shock, with the enhancement at the fourth Schumann resonance mode being smaller in amplitude than the case of the Chi-chi earthquake. Yet, the other characteristics, including the goniometric direction finding result, frequency shift, etc., are nearly the same. Although the emphasis of the present study is made on experimental aspects, a possible generation mechanism for this anomaly is discussed in terms of the ELF radio wave scattered by a conducting disturbance, which is likely to take place in the middle atmosphere over Taiwan. Model computations show that the South American thunderstorms (Amazon basin) play the leading role in maintaining radio signals, leading to the anomaly in the Schumann resonance.

scholarly journals Prediction of Vertical Tail Buffet Using CFD/CSD Coupling Method

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Bing Han ◽  
Min Xu
Keyword(s):  
Vortex Breakdown ◽  
Peak Frequency ◽  
Basis Functions ◽  
Resonance Phenomenon ◽  
Structural Dynamic ◽  
Flexible Tail ◽  
Bending Mode ◽  
Tail Structure ◽  
Tail Buffet ◽  
Modal Coordinates

The vertical tail buffet induced by the vortex breakdown flow is numerically investigated. The unsteady flow is calculated by solving the RANS equations. The structural dynamic equations are decoupled in the modal coordinates. The radial basis functions (RBFs) are employed to generate the deformation mesh. The buffet response of the flexible tail is predicted by coupling the three sets of equations. The results show that the presence of asymmetry flow on the inner and outer surface of the tail forced the structural deflection offsetting the outboard. The frequency of the 2nd bending mode of the tail structure meets the peak frequency of the pressure fluctuation upon the tail surface, and the resonance phenomenon was observed. Therefore, the 2nd bending responses govern the flow field surrounding the vertical tail. Finally, the displacement of the vertical tail is small, while the acceleration with a large quantitation forces the vertical tail undergoing severe addition inertial loads.

scholarly journals The determination of Schumann resonance mode frequencies using iterative procedure of complex demodulation

2013 ◽  
Vol 43 (4) ◽  
pp. 305-326 ◽  
Author(s):  
Adriena Ondrášková ◽  
Sebastian Ševčík
Keyword(s):  
Low Frequency ◽  
Peak Frequency ◽  
Precise Determination ◽  
Primary Sources ◽  
Frequency Noise ◽  
Schumann Resonance ◽  
Complex Demodulation ◽  
Vertical Electric Field ◽  
Short Signal

Abstract The more precise determination of instantaneous peak frequency of Schumann resonance (SR) modes, especially based on relatively short signal sequences, seems to be important for detailed analysis of SR modal frequencies variations. Contrary to commonly used method of obtaining modal frequencies by Lorentzian fitting of DFT spectra, the attempt was made to employ the complex demodulation method in iterated form. The results for SR signals contaminated with low-frequency noise and hum in various degree as well as the comparison with standard method are presented. Real signals of vertical electric field component picked up at the Astronomical and Geophysical Observatory of Comenius University at Modra, Slovakia, were the primary sources.

Estimation of quality factor based on peak frequency-shift method and redatuming operator: Application in real data set

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. N1-N12 ◽  
Author(s):  
Francisco de S. Oliveira ◽  
Jose J. S. de Figueiredo ◽  
Andrei G. Oliveira ◽  
Jörg Schleicher ◽  
Iury C. S. Araújo
Keyword(s):  
Frequency Shift ◽  
Quality Factor ◽  
Real Data ◽  
Peak Frequency ◽  
Accurate Estimation ◽  
Layer By Layer ◽  
Data Set ◽  
Seismic Reflection Data ◽  
Energy Dissipated ◽  
Factor Estimation

Quality factor estimation and correction are necessary to compensate the seismic energy dissipated during acoustic-/elastic-wave propagation in the earth. In this process, known as [Formula: see text]-filtering in the realm of seismic processing, the main goal is to improve the resolution of the seismic signal, as well as to recover part of the energy dissipated by the anelastic attenuation. We have found a way to improve [Formula: see text]-factor estimation from seismic reflection data. Our methodology is based on the combination of the peak-frequency-shift (PFS) method and the redatuming operator. Our innovation is in the way we correct traveltimes when the medium consists of many layers. In other words, the correction of the traveltime table used in the PFS method is performed using the redatuming operator. This operation, performed iteratively, allows a more accurate estimation of the [Formula: see text] factor layer by layer. Applications to synthetic and real data (Viking Graben) reveal the feasibility of our analysis.

The Effect of Upstream Edge Geometry on the Acoustic Resonance Excitation in Shallow Rectangular Cavities

2014 ◽  
Author(s):  
Ahmed Omer ◽  
Nadim Arafa ◽  
Atef Mohany ◽  
Marwan Hassan
Keyword(s):  
Flow Instability ◽  
Acoustic Resonance ◽  
Resonance Mode ◽  
Resonance Phenomenon ◽  
Resonance Excitation ◽  
Base Case ◽  
Pressure Amplitude ◽  
Cavity Depth ◽  
Edge Geometry ◽  
Aspect Ratios

The flow-excited acoustic resonance phenomenon is created when the flow instability oscillations are coupled with one of the acoustic modes, which in turn generates acute noise problems and/or excessive vibrations. In this study, the effect of the upstream edge geometry on attenuating these undesirable effects is investigated experimentally for flows over shallow rectangular cavity with two different aspect ratios of L/D = 1 and 1.67, where L is the cavity length and D is the cavity depth, and for Mach number less than 0.5. The acoustic resonance modes of the cavity are self-excited. Twenty four different upstream cavity edges are investigated in this study; including round edges, chamfered edges, vortex generators and spoilers with different sizes and configurations. The acoustic pressure is measured with a flush-mounted microphone on the cavity floor and the velocity fluctuation of the separated shear layer before the onset of acoustic resonance is measured with a hot-wire probe. The results for each upstream cavity edge are compared with the base case when square cavity edge is used. It is observed that when chamfered edges are used, the amplitude of the first acoustic resonance mode is highly intensified with values reaching around 5000 Pa (compared to 2000 Pa for the base case) and a clear shift in its onset of resonance to higher flow velocities is observed. Similar trend is observed when round edges are used. The amplitude of the generated pressure of the first acoustic resonance mode is amplified with values exceeding 4000 Pa and a delay in its onset of acoustic resonance is observed as well. Most of the spoiler edges are found to be effective in suppressing the pressure amplitude of the excited acoustic resonance. However, the performance of each spoiler depends on its specific geometry (i.e. thickness, height, and angle) relative to the cavity aspect ratio. A summary of the results is presented in this paper.

scholarly journals Quality factor estimation based on the peak frequency shift method using a robust Fourier transform to VSP data

2019 ◽  
Vol 16 (6) ◽  
pp. 1061-1070 ◽  
Author(s):  
Rómulo Sandoval ◽  
José L Paredes ◽  
Flor A Vivas
Keyword(s):  
Fourier Transform ◽  
Frequency Shift ◽  
Quality Factor ◽  
Peak Frequency ◽  
Estimation Methods ◽  
Signal Spectrum ◽  
Q Factor ◽  
Shift Method ◽  
Vsp Data ◽  
Factor Estimation

Abstract Quality factor estimation (Q estimation) of vertical seismic profile (VSP) data are necessary for the process referred to as inverse Q-filtering, which is used, in turn, to improve the resolution of seismic signals. In general, the performances of Q estimation methods, based on the standard Fourier transform, are severely degraded in the presence of heavy-tailed distributed noise. In particular, these methods require a bandwidth detection which is difficult to estimate due to instabilities caused by outliers or gross errors, leading to an incorrect Q estimation. In this paper, an improvement of the Q-factor estimation based on the peak frequency shift method is proposed, where the signal spectrum is obtained using a robust transform algorithm. More precisely, the robust transform method assumes that the perturbations that contaminate the signal of interest can be characterized as random samples following a zero-mean Laplacian distribution, leading to the weighted median as the optimal operator for determining each transform coefficient. The proposed method is validated on synthetic datasets using different levels of noise and its performance is compared to those yielded by various methods based on the standard Fourier transform. Furthermore, a non-Gaussianity test is performed in order to characterize the noise distribution in real data. From the non-Gaussianity test, it can be observed that the underlying noise is better characterized using a Laplacian statistical model, and therefore, the proposed method is a suitable approach for computing the Q factor. Finally, the proposed methodology is applied to estimate the Q factors of real VSP data.

Damage Detection and Quantitative Assessment for the Cracked Beam Structures

2007 ◽  
Vol 353-358 ◽  
pp. 2431-2435 ◽  
Author(s):  
Yong Hong ◽  
Byung Jin Kim ◽  
Dong Pyo Hong ◽  
Young Moon Kim
Keyword(s):  
Frequency Shift ◽  
Quantitative Assessment ◽  
Evaluation Method ◽  
Mechanical Impedance ◽  
Peak Frequency ◽  
Beam Specimen ◽  
Cracked Beam ◽  
Beam Structures ◽  
Large Structures ◽  
Work Done

Beam structures are a common form in many large structures, and therefore the real-time condition monitoring and active control of beams will improve the reliability and safety of many structures. However, the incipient damage, i.e. cracks, is not easy to be detected with using the traditional methods, such as modal analysis, etc. Piezoceramic (PZT) sensors offer special opportunities for the health monitoring of structures constructed by beams. The change of mechanical impedance of structures along with the occurrence of damage is sensitively indicated by the change of electro-impedance of PZT sensors. This paper presents work done on developing and utilizing PZT sensors to detect and quantitatively assess the extent and locations of cracks occurred in simulated structures. The PZT sensors are conducted particularly to generate the longitudinal wave along the beam specimen, and systematic experiments conducted on statistical samples of incrementally damaged specimens were used to fully understand the method, the cracks with different length and location are simulated to indicate the feasibility of the detection and assessment. To estimate the damage conditions numerically, in this paper, we propose the evaluation method of impedance peak frequency shift F and CC (Correlation Coefficient), Cov (Covariance). The results of experiments verify that the impedance peak frequency shift Δ F uniformly assesses the location of cracks, and as well CC. and Cov assesses the size of cracks efficiently. The study presents the method that is satisfied for much higher frequencies, alternate power, and minute damages.

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