Use of the Velocity Intensity Spectrum to Characterize Transient Data

This paper introduces and develops the Velocity Intensity Spectrum as an analytical tool for examining transient data in the frequency domain. The Velocity Intensity Spectrum is then compared with three common alternatives: the Shock Response Spectrum, the Pseudo Velocity Spectrum, and the lesser-known Shock Intensity Spectrum, upon which it is based. The various techniques are applied to an experimental data set and compared and discussed in a practical manner.

Microscopic and Macroscopic Fragmentation Characteristics under Hypervelocity Impact Based on MD and SPH Method

This work investigates the difference in the fragmentation characteristics between the microscopic and macroscopic scales under hypervelocity impact, with the simulations of Molecular Dynamics (MD) and Smoothed Particle Hydrodynamics (SPH) method. Under low shock intensity, the model at microscopic scale exhibits good penetration resistance due to the constraint of strength and surface tension. The bullet is finally embedded into the target, rather than forming a typical debris cloud at macroscopic scale. Under high shock intensity, the occurrence of unloading melting of the sample reduces the strength of the material. The material at the microscopic scale has also been completely penetrated. However, the width of the ejecta veil and external bubble of the debris cloud are narrower. In addition, the residual velocity of bullet, crater diameter and expansion angle of the debris cloud at microscopic scale are all smaller than those at macroscopic scale, especially for low-velocity conditions. The difference can be as much as two times. These characteristics indicate that the degree of conversion of kinetic energy to internal energy at the microscopic scale is much higher than that of the macroscopic results. Furthermore, the MD simulation method can further provide details of the physical characteristics at the micro-scale. As the shock intensity increases, the local melting phenomenon becomes more pronounced, accompanied by a decrease in dislocation atoms and a corresponding increase in disordered atoms. In addition, the fraction of disordered atoms is found to increase exponentially with the increasing incident kinetic energy.

Stall Behavior in an Ultra-High-Pressure-Ratio Centrifugal Compressor: Backward-Traveling Rotating Stall

This paper describes the stall mechanism in an ultra-high-pressure-ratio centrifugal compressor. A model comprising all impeller and diffuser blade passages is used to conduct unsteady simulations that trace the onset of instability in the compressor. Backward-traveling rotating stall waves appear at the inlet of the radial diffuser when the compressor is throttled. Six stall cells propagate circumferentially at approximately 0.7% of the impeller rotation speed. The detached shock of the radial diffuser leading edge and the number of stall cells determine the direction of stall propagation, which is opposite to the impeller rotation direction. Dynamic mode decomposition is applied to instantaneous flow fields to extract the flow structure related to the stall mode. This shows that intensive pressure fluctuations concentrate in the diffuser throat as a result of changes in the detached shock intensity. The diffuser passage stall and stall recovery are accompanied by changes in incidence angle and shock wave intensity. When the diffuser passage stalls, the shock-induced boundary-layer separation region near the diffuser vane suction surface gradually expands, increasing the incidence angle and decreasing the shock intensity. The shock is pushed from the diffuser throat toward the diffuser leading edge. When the diffuser passage recovers from stall, the shock wave gradually returns to the diffuser throat, with the incidence angle decreasing and the shock intensity increasing. Once the shock intensity reaches its maximum, the diffuser passage suffers severe shock-induced boundary-layer separation and stalls again.

Experiment on compaction of air-dried soil under drop shocks

For the requirement in container nursery culture that growing media should be achieved the appropriate degree compaction, this paper presents an experiment on the compaction dynamics of air-dried soil under repetitive drop shocks, as a preliminary step toward the mechanization of this compaction method. The drop height used to adjust the shock intensity included 2 mm, 4 mm, 5 mm and 6 mm. And the overall packing density of soil in a vertically stratified cylinder vessel and the local packing density in each layer were taken as indicators of soil compaction states. The stretched exponential function derived from KWW law than the empirical inverse-logarithmic function has been found to be more suitable for expressing the temporal evolution of soil compaction, according to the results of curve-fitting to test values of the overall and local density. It is inherent in this experimental configuration that the drop shock intensity even at a constant drop height varies with drop times, owing to the interaction between the soil packing itself and drop shocks caused by the combination of the packing and the container. But the function t/τf(t,H) is manifested as a straight line on the drop times t with the line slope related to the drop height H, so the soil compaction dynamics caused by its drop shocks and that under the condition with actively controlled intensity actually share the common relaxation law. In addition, the soil’s one-dimensional distribution of local packing density showed a slight positive gradient as similar as monodisperse particles did.

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.

Obeying orders reduces vicarious brain activation towards victims’ pain

ABSTRACTPast historical events and experimental research have shown complying with the orders from an authority has a strong impact on people’s behaviour. However, the mechanisms underlying how obeying orders influences moral behaviours remain largely unknown. Here, we test the hypothesis that when male and female humans inflict a painful stimulation to another individual, their empathic response is reduced when this action complied with the order of an experimenter (coerced condition) in comparison with being free to decide to inflict that pain (free condition). We observed that even if participants knew that the shock intensity delivered to the ‘victim’ was exactly the same during coerced and free conditions, they rated the shocks as less painful in the coerced condition. MRI results further indicated that obeying orders reduced activity associated with witnessing the shocks to the victim in the ACC, insula/IFG, TPJ, the MTG and dorsal striatum (including the caudate and the putamen) as well as neural signatures of vicarious pain in comparison with being free to decide. We also observed that participants felt less responsible and showed reduced activity in a multivariate neural guilt signature in the coerced than in the free condition, suggesting that this reduction of neural response associated with empathy could be linked to a reduction of felt responsibility and guilt. These results highlight that obeying orders has a measurable influence on how people perceive and process others’ pain. This may help explain how people’s willingness to perform moral transgressions is altered in coerced situations.

Aftershock Hazard Assessment Based on Utilization of Observed Main Shock Demand

This paper presents an aftershock hazard assessment method that is based on taking into account the macroseismic indicators of the main shock observed at the site. The proposed method is referred to as conditional aftershock hazard assessment (CAHA). The essence of the CAHA method is to estimate the aftershock hazard at the site conditioned on the main shock intensity exhibited at that location. This is achieved by exploiting the correlation between the ground motion intensities exhibited during the main shock and the aftershock events. Specifically, the correlation of the epsilons registered for the two events, is utilized. Investigation of the epsilon correlation indicates that highest correlation occurs at the range of periods between 0.8 and 1.0 s. Based on the estimated epsilon correlation, the mean and the dispersion of the aftershock ground motion intensity, are estimated. An application of the proposed method to a set of sites affected by the 2011 Van (Turkey) M w7.2 earthquake sequence is illustrated. The performance of the method is assessed in comparison with the conventional approaches. For the considered example application, the hazard estimated using the proposed method shows a better agreement with the actual aftershock recordings, compared to the existing approaches.

Mitigation of Turbine Vane Shock Waves Through Trailing Edge Cooling

The immense market demand on the high efficiency and lightweight aero-engines results in designs with compact high-pressure turbine stages experiencing supersonic flow field. In supersonic turbines, shocks appear at the vane trailing edges. The interaction of these shock with the neighbouring airfoils and blades on the adjacent rotor row and consequently create considerable amount of losses on the aerodynamic performance of the turbine. Moreover, periodic excitation created by the interaction of the shock waves and the motion of the turbine rotor causes fatigue problems and reduces the lifetime of the engine. Current study aims to alter the vane shock waves through blowing at the trailing edge. In order to characterize the effect of active blowing on the trailing edge flow field, a series of URANS simulations were conducted on OpenFOAM solver platform. Various blowing schemes were simulated over a simplified trailing edge geometry exposed in supersonic flow. The computations were compared in terms of shock intensity, oscillation frequency and exerted pressure forcing over the downstream components. The results showed that unsteady trailing edge blowing were able to modify the fluctuations observed on the shocks by altering the shock intensity, angle and frequency of oscillations. The classification of the wake unsteadiness, i.e. vortex shedding, in terms of trailing edge characteristics were also accomplished through frequency domain analysis of simulations.