Shock Intensity Research Articles

Shock wave characteristics and spalling behavior of non-coherent Cu/Nb multilayers

We investigate shock wave characteristics and spalling failure of Cu/Nb nanolaminates under shock loading via molecular dynamics simulations. The features of stress wave propagation in the Cu/Nb multilayers, including the reflection-loading and reflection-unloading of wave-front stress, and the strong interfacial discontinuities of transverse normal stress components, maximum shear stress and average kinetic energy are revealed by atomistic simulations. Continuum models are proposed to explain these shock wave evolution characteristics. In addition, the simulations well reproduce experimentally observed abnormal ductile damage distribution, i.e., voids nucleate in the Cu phase rather than in the Nb phase or interfaces. Such abnormality is intrinsic dynamic characteristics of nanolaminates, independent of layer thickness and shock intensity. Differences in theoretical spall strengths of Cu, Nb and the interfaces are calculated using the Cauchy-Born kinematic constraint. Moreover, we bring novel insight into the cause of the abnormality from a dynamic perspective that the maximum tensile stress in the stronger Nb phase is restricted by the spall strength of the weaker Cu phase, sound velocity, strain rate and layer thickness. The simulations also indicate that dynamic ductility can be enhanced by reducing the layer thickness, due to that more spall fracture surfaces are generated in nanolaminates with finer layer thickness.

Residual Stress Enhancement by Laser Shock Treatment in Chromium-Alloyed Steam Turbine Blades.

In-service turbine blade failures remain a source of concern and research interest for engineers and industry professionals with attendant safety and economic implications. Very high-pressure shock impacts from laser shots represent an evolving technique currently gaining traction for surface improvement and failure mitigation in engineering components. However, the physical characteristics and effects of parameter variations on a wide range of materials are still not fully understood and adequately researched, especially from a computational point of view. Using the commercial finite element code ABAQUS©, this paper explores the application of laser shock peening (LSP) in the enhancement of residual stresses in Chromium-based steel alloyed turbine blade material. Results of the numerically developed and experimentally validated LSP model show that peak compressive residual stresses (CRS) of up to 700 MPa can be induced on the surface and sub-surface layers, while the informed varying of input parameters can be used to achieve an increase in the magnitude of CRS imparted in the peened material. Analysis of the hierarchy of influence of the five input parameters under investigation on residual stress enhancement reveals the laser shock intensity as the most influential, followed in descending order of influence by the exposure time, shot size, degree of overlaps, and the angle of shot impact.

The saturated convex bending curvature of 7075 aluminum panel bent by orthogonal laser shock forming

Laser shock forming is an innovative and flexible forming technology that induces bending deformation in thin panel by the action of laser shock wave. In the convex deformation, laser shock forming lacks the ability to continuously enhance the bending curvature for one panel, especially for thick panel. This paper explores the saturated convex bending curvature by increasing overlapping ratio, the number of repeated shock and laser power intensity sequentially in orthogonal laser shock forming. The induced bending moment and bending curvature are calculated by the average induced stress obtained from representative cell model, and this method improves the efficiency of evaluating the saturated bending curvature. 50% overlapping ratio can improve the bending curvature, and ensure the processing efficiency and quality of laser shock forming. The induced stress gradually tends to be saturated in the repeated shocks. Based on 50% overlapping ratio and 5 repeated shocks, when the laser power intensity exceeds 6.37GW/cm2, the bending curvature cannot be significantly improved by increasing laser power intensity for the saturation effect and the bending moment reduction. The curvature prediction method can effectively predict the saturated bending behavior of one panel in laser shock forming, and the method can avoid the invalid forming process design, which is a guidance for laser shock forming and the selection in forming methods.

Saline short-term shock and rapid recovery on anammox performance

Anaerobic ammonia oxidation (anammox) is an environmental-friendly biological nitrogen removal process, which has been developed as a promising technology in industrial wastewater treatment. However, anammox nitrogen removal under high saline conditions still faces many challenges. This study investigated the performance of anammox sludge under saline short-term shock and the strategy of rapid recovery. Salinity concentration, saline exposure time, and NaCl/Na2SO4 ratio were selected as three critical factors for short-term shock. The activity inhibition of anammox sludge were tested by using response surface methodology (RSM). Our results showed that, compared with the NaCl/Na2SO4 ratio, the salinity concentration and saline exposure time were the significant factor causing the anammox inhibition. The addition of glycine betaine (GB) in moderate amounts (0.1–5 mM) was found to help anammox to resist in relative low saline shock intensities (e.g., IC25 and IC50), with the activity retention rate of 94.7%. However, glycine betaine was not worked effectively under relatively high saline shock intensities (e.g., complete inhibition condition). Microbial community analysis revealed that Brocadiaceae accounted for only about 7.6%–13.2% at inhibited conditions. Interestingly, 16S rRNA analysis showed that the abundance of activated Brocadiaceae remarkably decreased with time after high-level saline shock. This tendency was consistent with the results of qPCR targeted hzsA gene. Finally, based on quorum sensing, the anammox activity was recovered to 93.5% of original sludge by adding 30% original sludge. The study realized the rapid recovery of anammox activity under complete inhibition, promoting the development and operation of salt-tolerant anammox process.

An Interacting Negative Feedback Mechanism in a Coupled Extreme Weather–Humans–Infrastructure System: A Case Study of the 2021 Winter Storm in Texas

Extreme weather has long been a threat to human life and critical infrastructures. Previous studies have focused on the reliability and vulnerability of single or interdependent infrastructures under extreme weather threats. However, knowledge of the interactions between coupled real-world complex systems, especially the cascading failure process induced by external shocks, is essential, but the interactions receive less attention. Here, we took the historical winter storm of Texas that occurred in February 2021 as a case study and collected multisource data to explore the interaction between humans and the power system affected by extreme weather. A connectivity-based network was proposed to analyze the connectivity robustness and simulate the cascade of overload failures under random and malicious attacks. Results showed that this network presents higher robustness under random attacks in terms of network connectivity. However, a highly heterogeneous distribution of load was shown in this network, making it particularly vulnerable to attacks and easier to trigger cascading failures. An interacting negative feedback mechanism was discovered in this coupled extreme weather–humans–infrastructure system. Extreme weather events directly caused physical failure in infrastructures, while their impact on individuals stimulated the power demand for heat. An increase in demand further intensified the load on the power network, which induced functional failure in infrastructure systems and finally aggravated the adverse impact on people as end-users in return. This feedback loop inspired us to reconsider the relationship among natural disasters, critical infrastructure, and humans. Furthermore, even under the background of climate change, the impact of extremely cold weather on electric infrastructures is still worthy of attention since the fluctuation of yearly minimum temperature outstood in eastern Texas, where the majority of the population and electric transmission facilities are located. Thus, it is noteworthy to integrate the interaction between systems in the vulnerability assessment of infrastructure systems or the impact prediction of intense external shocks in future research.

The grain boundary effect on shock induced spallation of polycrystalline uranium

The shock-induced spallation mechanism of polycrystalline uranium is explored by molecular dynamics, and the role of grain boundaries in it is analysed. Present work reveals that the growth and fusion of voids are the main mechanism of uranium during spallation, and the grain boundaries have significant effects on nucleation and growth of voids. The spallation strength of polycrystalline uranium is lower than that of single crystal uranium, and the relative instability of the structure at the grain boundaries causes the conjunction point of multiple grains is the first nucleation position of voids. Besides, a mutual promotion relationship between the growth of voids and local thermal dissipation is verified, which greatly promotes the development of spallation. Furthermore, the grain boundary effect on the spallation is influenced by the shock intensity. Under lower shock intensity (0.3 km/s, 0.4 km/s, 0.5 km/s), the mechanical properties of the grain boundary are the major influence factor of the spalling strength of polycrystalline uranium. The lower the speed, the more obvious the grain boundary effect, and the larger the gap between the spallation strength of single crystal uranium and polycrystalline uranium. As the shock intensity gradually increases (0.6 km/s, 0.8 km/s), the grain boundary effect is gradually weakened. When the shock intensity approaches the melting intensity, the spallation behavior of single-crystalline and polycrystalline uranium tends to be consistent.

Shock loss measurements in non-ideal supersonic flows of organic vapors

This paper presents the first ever direct measurements of total pressure losses across shocks in supersonic flows of organic vapors in non-ideal conditions, so in the thermodynamic region close to the liquid–vapor saturation curve and the critical point where the ideal gas law is not applicable. Experiments were carried out with fluid siloxane MM (hexamethyldisiloxane, C_6H_{18}OSi_2), commonly employed in medium-/high-temperature organic Rankine cycles (ORCs), in the Test Rig for Organic VApors (TROVA), a blowdown wind tunnel at the Laboratory of Compressible fluid dynamics for Renewable Energy Applications (CREA lab) of Politecnico di Milano. A total pressure probe was inserted in superheated MM vapor flow at Mach number sim 1.5 with total conditions in the range 215-230~^circ hbox {C} and 2-12~hbox {bar} at varying levels of non-ideality, with a compressibility factor evaluated at total conditions between Z_text {T}=0.68-0.98. These operating conditions are representative of the first-stage stator of ORC turbines. Measured shock losses were compared with those calculated from pre-shock quantities by solving conservation equations across a normal shock, with differences always below 2 % attesting a satisfactory reliability of the implemented experimental procedure. An in-depth analysis was then carried out, highlighting the direct effects of non-ideality on shock intensity. Even at the mildly non-ideal conditions with Z_text {T}gtrsim 0.70 considered here, non-ideality was responsible for a significantly stronger shock compared to the ideal gas limit at same pre-shock Mach number, with differences as large as 6%.Graphical abstract

Effect of active ignition on the end-gas autoignition with detonation combustion in confined space

In spark-ignition engines, the presence of knock significantly prevents the engines from further improving thermal efficiency. In this work, the effect of active ignition in the end-gas region on the end-gas autoignition with detonation combustion was optically observed in the self-designed constant volume combustion bomb (CVCB-TJU). The different combustion modes together with pressure oscillation were presented. The results indicate that advancing the ignition timing of the end-gas spark can reduce the pressure oscillation intensity and even suppress the occurrence of autoignition. In addition, the present work observed a statistically positive relationship between unburned mass fraction (UMF) and detonation intensity for the knock induced by developing detonation. The underlying influencing mechanism of end-gas ignition on auto-ignition was presented. The end-gas ignition influences the occurrence and intensity of detonation and pressure oscillation by two means: 1) reducing the UMF burned by autoignition, 2) influencing the flame acceleration, thereby reducing the flame tip velocity, and the subsequent shock intensity. Furthermore, the burned mass fraction (BMF) consumed by end-gas flame when jet flames emerge is applied to substitute the ignition timing when measuring its influence at different oxygen concentrations of 29% and 33%. It is found there exists a critical BMF above which the autoignition would be suppressed. And this critical value increases with increased oxygen concentration.

Darting across space and time: parametric modulators of sex-biased conditioned fear responses.

Pavlovian fear conditioning is a widely used behavioral paradigm for studying associative learning in rodents. Despite early recognition that subjects may engage in a variety of both conditioned and unconditioned responses, the last several decades have seen the field narrow its focus to measure freezing as the sole indicator of conditioned fear. We previously reported that female rats were more likely than males to engage in darting, an escape-like conditioned response that is associated with heightened shock reactivity. To determine how experimental parameters contribute to the frequency of darting in both males and females, we manipulated factors such as chamber size, shock intensity, and number of trials. To better capture fear-related behavioral repertoires in our animals, we developed ScaredyRat, an open-source custom Python tool that analyzes Noldus Ethovision-generated raw data files to identify darters and quantify both conditioned and unconditioned responses. We found that, like freezing, conditioned darting occurrences scale with experimental alterations. While most darting occurs in females, we found that with an extended training protocol, darting can emerge in males as well. Collectively, our data suggest that darting reflects a behavioral switch in conditioned responding that is a product of an individual animal's sex, shock reactivity, and experimental parameters, underscoring the need for careful consideration of sex as a biological variable in classic learning paradigms.

A circulation prediction model for ramp and vortex generator in supersonic flow: A numerical study

The circulation growth of supersonic streamwise vortex (SSV) formed by a ramp is complicated and essential to estimate scramjet mixing behavior, while a predictive model for circulation growth is still lacking. Through well-validated RANS simulations, it is observed that the circulation growth of streamwise vortex for a ramp is similar to one for vortex generator, which determines three important geometric parameters for SSV growth, i.e., ramp angle, swept angle, and length of the leading edge. The results of different geometries with these three parameters further show that the SSV circulation growth is proportional to the downwash speed influenced by oblique shock intensity. By building the relation between downwash speed and geometric parameters, an SSV circulation prediction model is proposed and validated by the circulation curves of all cases under a wide range of free stream Mach numbers. The novel circulation model has the potential for the preliminary mixing enhancement design for a scramjet ramp injector.

Trade shock, refugee, and the rise of right-wing populism: Evidence from European Parliament elections

Recent years have witnessed the rising support for right-wing populism in European politics. We rely on the outcomes of the 2014 European Parliament elections to empirically examine the economic and cultural mechanisms that fuel this trend. Using import competition to measure economic shocks and regional-level refugee shocks, we find that regions exposed to more intense trade shocks are more likely to vote for right-wing parties. We further show the increasing support for economically far-right parties is mainly caused by trade shocks, and the electoral support for culturally far-right parties stems mainly from refugee shocks.

Effects of repeated exposure to escalating versus constant punishment intensity on response allocation.

The present experiment investigated the effects of 1) repeated exposures to escalating punishment intensities and 2) repeated exposure to punishment after periods of vacation on response allocation between punished and unpunished responding in three groups of rats. The first group (intensity + vacation) experienced repeated exposures to escalating punishment intensities after a period of vacation (i.e., return to baseline) from punishment. The second group (intensity-only) experienced repeated exposures to escalating punishment intensities without vacation from punishment. The third group (vacation-only) experienced repeated exposures to a constant punishment intensity after a period of vacation from punishment. Results showed that superimposition of punishment on one of two concurrently available responses decreased allocation toward the punished response and increased allocation toward the unpunished response. Furthermore, greater changes in allocation were observed with the introduction of a moderate constant intensity than with the introduction of a low intensity that increased across sessions. Reexposure to punishment had different effects between the groups. Although there was evidence that high shock intensities can enhance the efficacy of lower intensities to shift allocation away from the punished response and toward the unpunished response, there was little evidence of changes in response allocation with reintroduction of punishment after a period of vacation.

Shock compression of nanoporous silicon carbide at high strain rate

The dynamic material response and void collapse mechanisms of nanoporous silicon carbide (SiC) under shock compression are systematically investigated by large scale molecular dynamic simulations. The effects of shock intensity are revealed by varying shock particle velocities (Up) from 1.0 to 3.5 km/s. The influences of different void sizes in samples are evaluated as well. Results show that the void collapse mechanism is highly related to the impact velocity. Under low and medium impact velocities (1.0 km/s, 1.5 km/s, 2.0 km/s, respectively), the atoms in the earliest collapse region flow vertically and decompose the voids into two sub-voids. Besides, a theoretical model is applied to explain the earliest collapse region at low impact velocity. Meanwhile, the internal jetting dominates the void collapse under high impact velocities (2.5 km/s, 3.0 km/s, 3.5 km/s, respectively), making the voids horizontally filled. In addition, the formation mechanism of hotspot is revealed, which is determined by the void collapse modes. Larger voids are more likely to collapse when subjected to the same impact velocity. The nanoporous SiC samples with larger voids can better weaken the stress wave by converting the mechanical energy into thermal energy. The results provide deep insights into void collapse in SiC and promote the designs of advanced nanoporous ceramics in the application of shock-protect system under extreme conditions.

Theoretical and numerical studies on compressible flow around a subsonic evacuated tube train

Based on one-dimensional inviscid isentropic theory, the equations of flow parameters around a subsonic evacuated tube train are derived. In choked condition, the flow of tube throat reach the speed of sound and mass flow will not increase for a fixed upstream pressure and temperature. The flow around the subsonic evacuated tube train is a non-choked or a choked flow, under different operating speeds and blockage ratios. The flow parameters inside the tube can be solved. The theoretical results are compared and verified by numerical simulation using the overset mesh technique. The results show that the error between the theoretical and numerical results in the non-choked condition is within 2%. The maximum relative error in the choked state is 6.6%. When using the overset mesh technique for transient simulations, the initial speed of the train in the numerical simulation causes a higher intensity of shock and expansion waves inside the tube, but does not affect the results in other regions. In summary, the theoretical equation can predict the characteristics of compressible flow around a subsonic evacuated tube train.

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

AbstractThis paper describes the stall mechanism in an ultrahigh-pressure-ratio centrifugal compressor, composed of a double-splitter impeller, radial diffuser, and axial diffuser. 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's throat toward the diffuser leading edge. When the diffuser passage recovers from the 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.

Effect of Sample Transportation on the Proteome of Human Circulating Blood Extracellular Vesicles.

Circulating extracellular vesicles (cEV) are released by many kinds of cells and play an important role in cellular communication, signaling, inflammation modulation, coagulation, and tumor growth. cEV are of growing interest, not only as biomarkers, but also as potential treatment targets. However, very little is known about the effect of transporting biological samples from the clinical ward to the diagnostic laboratory, notably on the protein composition. Pneumatic tube systems (PTS) and human carriers (C) are both routinely used for transport, subjecting the samples to different ranges of mechanical forces. We therefore investigated qualitatively and quantitatively the effect of transport by C and PTS on the human cEV proteome and particle size distribution. We found that samples transported by PTS were subjected to intense, irregular, and multidirectional shocks, while those that were transported by C mostly underwent oscillations at a ground frequency of approximately 4 Hz. PTS resulted in the broadening of nanoparticle size distribution in platelet-free (PFP) but not in platelet-poor plasma (PPP). Cell-type specific cEV-associated protein abundances remained largely unaffected by the transport type. Since residual material of lymphocytes, monocytes, and platelets seemed to dominate cEV proteomes in PPP, it was concluded that PFP should be preferred for any further analyses. Differential expression showed that the impact of the transport method on cEV-associated protein composition was heterogeneous and likely donor-specific. Correlation analysis was nonetheless able to detect that vibration dose, shocks, and imparted energy were associated with different terms depending on the transport, namely in C with cytoskeleton-regulated cell organization activity, and in PTS with a release of extracellular vesicles, mainly from organelle origin, and specifically from mitochondrial structures. Feature selection algorithm identified proteins which, when considered together with the correlated protein-protein interaction network, could be viewed as surrogates of network clusters.

A comparative study of high‐resolution methods for nonlinear hyperbolic problems

AbstractThis paper reviews some of the established high‐resolution (HR) schemes for computing solutions to hyperbolic systems by means of a finite volume (FV) framework. The objective of this research is to assess the ability of various HR flux limiting techniques to capture intense shocks and discontinuities. A crucial design factor in developing these methods is selecting a suitable flux‐limiter, so a review of different flux‐limiters for standard explicit FV frameworks has also been included. A brief discussion of the HR total variation diminishing (TVD) numerical schemes, starting from some historical introduction, going on to exploring the design principles behind the HR, second‐order, oscillation free schemes, turning towards high order nonlinear techniques and ending with an overview of some of the most significant developments and applications in the last decades has been covered. Several one‐dimensional and two‐dimensional benchmark examples with severe and challenging wave configurations have been utilized to compare the various numerical approaches. These nonlinear test cases have been selected such that the computational setups are as basic as possible.

Triple apheresis platelet concentrate quality after pneumatic tube system, conveyor box, and courier transport: An observational study.

Background and AimsPlatelets are prone to activation from handling; they are therefore transported as gently as possible, most commonly by courier. Speedier methods like pneumatic tube system (PTS) transport could improve patient care but may subject platelets to mechanical stress. To test the impact of mechanical stress caused by transport, we compared a PTS with a conveyor box and courier transport on apheresis platelet function.MethodsFourteen apheresis platelet concentrate triple donations were analyzed by light transmission aggregometry (LTA), rotational thrombelastometry (ROTEM), and flow cytometry before and after indoor transport over 800 m by PTS, conveyor, and courier, respectively, while recording shocks and vibrations with a high‐frequency acceleration data logger. Shock index scores were calculated as shock intensity (g‐force) times frequency.ResultsThe shock index was 81 for courier, 6279 for conveyor, and 9075 for PTS. Flow cytometry revealed no significant difference in platelet surface expression of CD62p before (16%) and after transport via courier (15%), conveyor (14%), or PTS (16%). LTA with adenosine phosphate and thrombin receptor‐activating peptide‐6 resulted in comparable platelet aggregation for courier, conveyor, and PTS. ROTEM assays showed no relevant differences in coagulation time, clot formation time, and maximum clot firmness between transport modes.ConclusionThough the mechanical challenge was smallest with courier transport, there were no significant differences in platelet activation or aggregation between the three transport modes. These data contradict restrictions on the use of PTSs for platelet concentrate transport.

Similarity solution for one dimensional motion of a magnetized self-gravitating gas with variable density under the absorption of monochromatic radiation

Abstract The impendence of azimuthal or axial magnetism in one-dimensional shock wave prevalence via a gas with monochromatic radiation for cylindrical and spherical geometry is examined. The travelling piston supplies the varying input of energy continuously and conditions of equilibrium flow through the whole field are retained. A regime of ODEs is derived by means of the regime of governing motion’s equations using the similarity process. The distributions of gas-dynamical quantities, obtained by their numerical integration, are discussed through figures. It is observed that the adiabatic index and the impendence of magnetism, as well as gravitation, lessen the shock intensity, however, the initial density variation index has the opposite behaviour on it.

Effects of CO addition on shock wave propagation, self-ignition, and flame development of high-pressure hydrogen release into air

In this study, an experimental investigation is conducted to study the effects of CO addition (0%–7.5% vol.) on the self-ignition of pressurized hydrogen leakage. The result shows that more CO addition significantly decreases the likelihood of self-ignition inside the tube and the formation of self-sustained jet flame outside the tube. This can be mostly explained by the reduction of leading shock intensity inside the tube. Furthermore, CO addition effectively inhibits the flame propagation and development inside the tube. For pure hydrogen, the ignited flame quickly develops an intense flame spanning the tube width and eventually form a jet flame in ambient air. However, the H 2 –CO diffusion flame initiated approaching tube sidewall tends to propagate adjacent to the wall or be soon quenched with more CO addition. If the CO-weakened flame spouts to the tube exit, it may not survive the expansion at the tube exit and thus it is quenched. • The shock intensity is reduced in the presence of CO. • The critical pressure for self-ignition increases with CO addition concentration. • Shock intensity variation by CO addition is the main factor affecting self-ignition onset. • Small CO addition can effectively inhibit flame development inside the tube. • H 2 –CO flame spouting from the tube exit tends to be blown out.