Elastic displacement of primary waves from explosive sources

1964 ◽  
Vol 54 (3) ◽  
pp. 947-959 ◽  
Author(s):  
Joseph W. Berg ◽  
George E. Papageorge
Keyword(s):  
Fourier Transform ◽  
Natural Frequency ◽  
Nuclear Explosion ◽  
Fractional Power ◽  
Elastic Displacement ◽  
Cavity Size ◽  
Velocity Range ◽  
Cavity Radius ◽  
Pressure Function ◽  
Long Period

Abstract Equations derived from Blake's (1952) model of diverging waves from a point source were programmed for computer analysis. Variations of the displacement resulting from changes in the pressure function, propagational velocity, range, and cavity size were investigated. Results of the research indicate that: (1) a step pressure function used with this model gives displacements that closely approximate the displacements measured at 0.4 km from the Gnome nuclear explosion; (2) near the source, long-period displacements are inherent with this model; (3) the periods of the maximum Fourier transform amplitude of the radiation field is proportional to the equivalent cavity radius; (4) the peak displacements scale to the two-thirds power of charge size for values of a between 80 (0.5 kt) and 600 m (275 kt); and (5) between 0.1 and 3.0 cps, the amplitudes of given frequencies scale to the first power of charge size for values of a between 145 (3 kt) and 305 m (28 kt). In general, Fourier amplitudes at frequencies below the natural frequency of the cavity scale to the first power of charge size, and Fourier amplitudes at frequencies above the natural frequency of the cavity scale to a fractional power of charge size. It is suggested that this may be a good model with which to compare near-source observations of seismic phenomena.

scholarly journals Sensing Fractional Power Spectrum of Nonstationary Signals with Coprime Filter Banks

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Xiaomin Li ◽  
Huali Wang ◽  
Wanghan Lv ◽  
Haichao Luo
Keyword(s):  
Fourier Transform ◽  
Power Spectrum ◽  
Filter Banks ◽  
Fractional Fourier Transform ◽  
Linear Time ◽  
Sampling Rate ◽  
Fractional Power ◽  
Fourier Domain ◽  
Wide Sense ◽  
Fractional Power Spectrum

The coprime discrete Fourier transform (DFT) filter banks provide an effective scheme of spectral sensing for wide-sense stationary (WSS) signals in case that the sampling rate is far lower than the Nyquist sampling rate. And the resolution of the coprime DFT filter banks in the Fourier domain (FD) is 2π/MN, where M and N are coprime. In this work, a digital fractional Fourier transform- (DFrFT-) based coprime filter banks spectrum sensing method is suggested. Our proposed method has the same sampling principle as the coprime DFT filter banks but has some advantages compared to the coprime DFT filter banks. Firstly, the fractional power spectrum of the chirp-stationary signals which are nonstationary in the FD can be sensed effectively by the coprime DFrFT filter banks because of the linear time-invariant (LTI) property of the proposed system in discrete-time Fourier domain (DTFD), while the coprime DFT filter banks can only sense the power spectrum of the WSS signals. Secondly, the coprime DFrFT filter banks improve the resolution from 2π/MN to 2π sin α/MN by combining the fractional filter banks theory with the coprime theory. Simulation results confirm the obtained analytical results.

Wave Spectrum Analysis of Kerry Deepwater Port Sea in Cameroon

2014 ◽  
Vol 638-640 ◽  
pp. 1280-1284
Author(s):  
Hui Xiao ◽  
Yi Feng Zhang ◽  
Hong Bo Zhao
Keyword(s):  
Fourier Transform ◽  
Spectrum Analysis ◽  
Wave Spectrum ◽  
Transform Method ◽  
Long Period ◽  
Fast Fourier Transform Method ◽  
Spectrum Characteristics ◽  
One Year ◽  
Sea Area ◽  
Period Wave

According to the measured wave data for one year in Kerry deepwater port sea area, Cameroon, the wave spectrum characteristics calculate using fast Fourier transform method; the result shows that the bimodal spectrum is given priority to this sea area, and the big wave appears in summer and autumn, the long period wave influence is opposite bigger that should be pay attention.

Assessing the Influence of Fourier Analysis Parameters on Short-Time Modal Parameter Extraction

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Matthew Lamb ◽  
Vincent Rouillard
Keyword(s):  
Fourier Transform ◽  
Fourier Analysis ◽  
Natural Frequency ◽  
Spectral Resolution ◽  
Parameter Extraction ◽  
Modal Parameter ◽  
Zero Padding ◽  
Spectral Enhancement ◽  
The Fourier Transform ◽  
Modal Parameter Extraction

It is sometimes necessary to determine the manner in which materials and structures deteriorate with respect to time when subjected to sustained random dynamic loads. In such cases a system’s fatigue characteristics can be obtained by continuously monitoring its modal parameters. This allows for any structural deterioration, often manifested as a loss in stiffness, to be detected. Many common structural integrity assessment techniques make use of Fourier analysis for modal parameter extraction. For continual modal parameter extraction, the Fourier transform requires that a compromise be made between the accuracy of the estimates and how frequently they can be obtained. The limitations brought forth by this compromise can be significantly reduced by selecting suitable values for the analysis parameters, mainly subrecord length and number of averages. Further improvements may also be possible by making use of spectral enhancement techniques, specifically overlapped averaging and zero padding. This paper uses the statistical analysis of results obtained from numerous physical and numerical experiments to evaluate the influence of the analysis parameters and spectral enhancement techniques on modal estimates obtained from limited data sets. This evaluation will assist analysts in selecting the most suitable inputs for parameter extraction purposes. The results presented in this paper show that when using the Fourier transform to extract modal characteristics, any variation in the parameters used for analysis can have a significant influence on the extraction of natural frequency estimates from systems subjected to random excitation. It was found that for records containing up to 10% noise, subrecord length; hence spectral resolution, has a more pronounced influence on the accuracy of modal estimates than the level of spectral averaging; therefore spectral uncertainty. It was also found that while zero padding may not increase the actual spectral resolution, it does allow for improved natural frequency estimates with the introduction of interpolated estimates at the nondescribed frequencies. Finally, it was found that for modal parameter extraction purposes (in this case natural frequency), increased amounts of overlapped averaging can significantly reduce the variance of the estimates obtained. This is particularly useful as it allows for increased precision without compromising temporal resolution.

scholarly journals Microplastics abundance in four different species of commercial fishes in Bali Strait

2020 ◽  
Vol 20 (1) ◽  
pp. 1 ◽  
Author(s):  
Dara Sarasita ◽  
Agung Yunanto ◽  
Defri Yona
Keyword(s):  
Fourier Transform ◽  
Polyvinyl Chloride ◽  
Marine Environment ◽  
Marine Species ◽  
Indian Mackerel ◽  
Long Period ◽  
Trichiurus Lepturus ◽  
Fish Samples ◽  
Plastic Wastes ◽  
Infra Red

Plastic wastes in marine environment will be degraded for long period of time to become microplastics. The small size of microplastics could be ingested by marine species which has lead to harmful impacts not only to the marine species but also to human. This research aimed to investigate microplastics ingestion in four commercial fishes in the Bali Strait, namely largehead hairtail (Trichiurus lepturus), Indian scad (Decapterus ruselli), Bali sardinella (Sardinella lemuru), and Indian mackerel (Rastrelliger kanagurta). Thirty fish samples from each species of fishes were obtained from the fishermen. Microplastics contents were identified visually using microscope from the gastrointestinal tracks of the fish and polymer of microplastics were identified using Fourier Transform Infra-Red (FTIR) test.  The results showed that three types of microplastics (fiber, film and fragment) were found in the four species of fishes with different total abundances. The highest abundance was found in Bali sardine (7.03±0.49 particle individual-1), followed by Indian mackerel (5.03±0.50 particle individual-1), Indian scad (4.23±0.38 particle individual-1) and largehead hairtail (3.83±0.50 particle individual-1). FTIR test showed that polymer types of microplastic found were polyvinyl chloride (PVC), polyamide (PA), polycarbonate (PC), dan polyethylene (PE).

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