Primary shock calibration with fast linear motor drive

This paper describes the implementation of a new, fast and precise linear motor drive for PTB’s primary shock calibration device. This device is used for monopole shock calibrations of accelerometers using the “hammer-anvil” principle according to ISO 16063-13:2001 and operates in a peak acceleration range from 50 m/s² to 5000 m/s². <br />The main challenge of implementing this kind of shock generator is accelerating a hammer to velocities up to 5 m/s within distances of less than 70 mm. <br />In this paper, a few helpful improvements are described which lead to an enhanced repeatability of pulse generation over the full shock intensity range as well as a substantial decrease of harmonic disturbing signals.

Volcanic earthquake foreshocks during the 2018 collapse of Kīlauea Caldera

SUMMARY The summit collapse of the Kīlauea Caldera—due to magma chamber drainage being directed to the Volcano's lower east rift zone—was accompanied by 50 large, nearly identical magnitude Mw 5 earthquakes between 29 May and 2 August 2 2018. I have examined the seismicity associated with these 50 primary earthquakes, and find that the typical pattern of earthquake aftershocks decaying in number and magnitude is not evident. Rather, immediately after the primary shock there is a hiatus of one-to-several hours before the associated earthquakes grow in number and magnitude up to the next primary shock. In essence, the associated seismicity consists of thousands of foreshocks. The magnitude of completeness is estimated at ML = 2.5. The trend of foreshocks does not fit an Omori power-law model. Rather, the pattern of foreshocks (number per hour) is fit well by a semi-Gaussian curve, which initially grows rapidly and slows hours prior to the primary earthquakes. The Gaussian fits (${r^2} > 0.98$) for three different magnitude thresholds are self-similar with a common half-width, $\sigma \sim 13$ hr. The pattern of foreshock seismic moments aligned with and stacked for the 50 primary events is fit by an exponential trend, growing at the mean (stacked intervals) rate of 17 per cent per hour. The power of foreshocks measured within each interval also grows with time—the total foreshock power per interval (J hr–1) increases by a factor of 18 through the first half of the sequence (May 29 through June 26), and then declines by half through to the end.

Implementations and pilot comparison of primary low intensity shock calibration

<p class="Abstract">This paper first presents two main technical concerns for a possible low intensity shock comparison: variety of primary shock calibration systems and feasibility of comparison artifact. For the primary calibration system, the mechanical excitation includes hammer-anvil collision, pneumatic driven projectile impact and Hopkinson bar. The shock pulses generated are smooth monopole shape by the first two types with air bearings, but dipole shape by the third type. For the comparison artifact, a standard accelerometer of single-ended type with a charge amplifier consists of an accelerometer measuring chain whose nonlinearity of amplitude and phase frequency responses is investigated. Based on the nonlinear fact of comparison artifact at frequency domain and the spectrum range difference of mechanical excitations of the calibration system, strict comparison conditions had to be laid down for measurement of shock sensitivity at specific acceleration levels and pulse durations.</p>The pilot comparison, coded as APMP.AUV.V-P1, is successfully organized by Asia Pacific Metrology Programme. Some comparison results of both monopole excitation and dipole excitation are shown with the expanded uncertainty. The completion of this pilot comparison can serve as part of the basis for a planned key comparison targeted at a low intensity shock range at Consultative Committee level.

Limit Theorems for Local Cumulative Shock Models with Cluster Shock Structure

This paper considers a more general shock model with insurance and financial risk background, in which the system is subject to two types of shocks called primary shocks and secondary shocks. Each primary shock causes a series of secondary shocks according to some cluster pattern. In reliability applications, a primary shock can represent an issue of insurance policies of an insurer company, and the secondary shocks then denote the relevant insurance claims generated by the policy. We focus on the local cumulative shock process where only a certain number of the most recent primary and secondary shocks are accumulated. This process is a very new topic in the available literature which is more flexible and realistic in modeling some more complex reliability situations such as bankrupt behavior of an insurance company. Based on the theory of infinite divisibility and stable distributions, we establish a central limit theorem for the local cumulative shock process and obtain the conditions for the process to converge to an infinitely divisible distribution or to anα-stable law. Also, by choosing the proper scale parameters, the process converges to a normal distribution.

A study of Savitzky-Golay filters for derivatives in primary shock calibration

This manuscript reports the result of an investigation into two types of digital filters for numerical differentiation of the displacement signal in the case of primary shock calibration of accelerometers. The first is a difference method with a 4^th-order Butterworth low-pass (4^th BW) filter; the other is a Savitzky-Golay (S-G) filter, which applies a moving polynomial approximation. The computational comparison was applied to low and high amplitude shocks using known excitation functions. Each sum of residuals was compared for the optimized conditions of the 4^th BW and S-G filters. The results of computer simulation indicated that the S-G filters exhibited better performance for the derivatives than the 4^th BW filters. In addition, an analytical comparison using experimental vibration data also indicated that the S-G filters exhibited better derivative characteristics than the 4^th BW filters.<br />

Study on the Effects of Shock Wave Propagation on Explosive Forming

Explosive forming is one of the unconventional techniques, in which, most commonly, the water is used as the pressure transmission medium. The explosive is set at the top of the pressure vessel filled with water, and is detonated by an electric detonator. The underwater shock wave propagates through the water medium and impinges on the metal plate, which in turn, deforms. There is another pressure pulse acting on the metal plate as the secondary by product of the expansion of the gas generated by detonation of explosive. The secondary pressure pulse duration is longer and the peak pressure is lower than the primary shock pressure. However, the intensity of these pressure pulse is based also on the conditions of a pressure vessel. In order to understand the effects of the configuration of the pressure vessel on the deformation of a metal plate, numerical simulation was performed. This paper reports those results.