Kinetic Energy Threshold Research Articles

Evaluation of the drone-human collision consequences

The operational safety assessment of the unmanned vehicles is crucial for their subsequent practical use. The safety limit criteria used for the operation assessment, especially values closely related to the safety of persons and their vulnerability to collision with these vehicles, represent nowadays a significant limitation. This contribution presents the currently discussed and proposed human safety criteria for the UAS, evaluates the available data from the collision dynamic tests and computer modelling and provides the possibility to compare and evaluate these criteria on a validated set of data. A total of five small UAS, three multi-rotor quadcopters and two fixed-wing aircrafts were used to verify the current methods and serve as a basis for the assessment. The results of the measurements obtained through the crash tests demonstrate the excessive restrictiveness of the currently used kinetic energy threshold values and the limited value of some proposed criterions, e.g. the blunt criterion. On the contrary, they point to the appropriateness of the application of car vulnerability criterions. The UAS mass or kinetic energy tests represent an easily definable threshold value, however, the available data sets and the tests performed showed limitations of its applicability for the deformable and fragile UAS structures. The article aims to verify, based on its own impact tests, the adequacy of the evaluation of the safety criteria of the UAS operation in relation to the development of the current legislation that defines the conditions of use of these machines.

Assessing hazard and potential impact associated with volcanic ballistic projectiles: The example of La Soufrière de Guadeloupe volcano (Lesser Antilles)

The fallout of ballistic blocks and bombs ejected from eruptive vents has the potential to produce severe injuries to people and damage to infrastructure in areas proximal to volcanoes. The dimensions and dispersions of ballistic ejecta from explosive eruptions are pivotal parameters to forecast the potential impact associated with future eruptions based on the compilation of probabilistic hazard maps.In this study, we propose a new probabilistic hazard quantification strategy to provide the probability of Volcanic Ballistic Projectiles (VBPs) to exceed some critical kinetic energy thresholds, considering a variability on the site of the eruptive vents and the effect of wind. La Soufrière de Guadeloupe (Lesser Antilles) is chosen as a test case, focussing on the most likely explosive scenario associated with the eruption of an active lava dome (including phreatic, Vulcanian and Strombolian eruptions). Sensitivity analyses have guided the optimization of input parameters to balance the results stability and computational costs, showing that the topography is a pivotal factor when accounting for the spatial uncertainty on vent locations in the proximity of the dome area. Given an eruption within the adopted scenario, we provide maps showing the probability to exceed different energy reference thresholds for roof's perforation if at least one VBP falls in a target area. These maps are then combined with exposed elements to produce a qualitative exposure-based risk map. We compute the overall probability, conditional on the selected scenario, for roof perforation in a given area when a VBP is ejected. Results show probabilities varying from ca. 2% up to 40% within a few km from the volcano, quickly dropping away from the dome. However, when the probability to exceed the energy reference threshold is only conditional on falling of VBPs in a target area, most of Basse-Terre island would be affected by the 20–60% probability of roof perforation. This work confirms how the choice of a probabilistic approach is key to estimate the likelihood of occurrence of VBPs impacts as a first step towards the development and implementation of pro–active risk reduction strategies in volcanic areas.

Relationship between three-dimensional velocity of filament eruptions and CME association

It is widely recognised that filament disappearances or eruptions are frequently associated with Coronal Mass Ejections (CMEs). Since CMEs are a major source of disturbances of the space environment surrounding the Earth, it is important to investigate these associations in detail for the better prediction of CME occurrence. However, the proportion of filament disappearances associated with CMEs is under debate. The estimates range from sim 10 to sim 90% and could be affected by the manners to select the events. In this study, we aim to reveal what parameters control the association between filament eruptions and CMEs. We analysed the relationships between CME associations and the physical parameters of filaments including their length, maximum ascending velocity, and direction of eruptions using 28 events of filament eruptions observed in Halpha. We found that the product of the maximum radial velocity and the filament length is well correlated with the CME occurrence. If the product is larger than 8.0 times 10^{6}text {km}^{2}text {s}^{-1}, the filament will become a CME with a probability of 93%, and if the product is smaller than this value, it will not become a CME with a probability of 100%. We suggest a kinetic-energy threshold above which filament eruptions are associated with CMEs. Our findings also suggest the importance of measuring the velocity vector of filament eruption in three-dimensional space for the better prediction of CME occurrence.

Simulation Study on the Average Specific Kinetic Energy and Safety Radius of Stun Grenade Fragments for Different Initiation Point

In order to evaluate the lethality and injury radius of fragments and weaken the average specific kinetic energy, the calculation model of average specific kinetic energy of stun grenade fragments is established based on the Monte Carlo subdivision projection simulation. With the joint simulation method of LS-DYNA and programming, the calculation model of the specific kinetic energy of the semi-prefabricated fragments is solved and compared at different initiation points of the same charge. The mass distribution, vertical target distribution, average specific kinetic energy threshold and safety radius of the whole time-domain fragments at the initiation points 1.5cm, 3cm, 4.5cm, 6cm, 7.5cm and 9cm from the top of the shell are obtained. For the same charge parameters, the results show that the number of fragments near the initiation point of the charge center is less, the mass mean value and standard deviation are larger, and the threshold value of specific kinetic energy is lower than that of both ends of charge; the injury radius of the initiation points 1.5cm, 6cm and 9cm is 4.9m, 2.94m and 4.1m respectively. The initiation point near the charge center can significantly reduce the injury radius of the fragments and improve the safety of the stun grenade.

Development of Solenoid-Driven and Pneumatic Punches for Launching High-Z Cryogenic Pellets for Tokamak Disruption Mitigation Experiments

Mitigation of disruption events in future high energy density tokamaks is essential for machine longevity. The creation of runaway electrons, large electromagnetic forces, and high localized heat loads during a disruption can be devastating to machine components. Shattered pellet injection is currently the most effective method of disruption mitigation. Injection of cryogenically solidified deuterium, neon, or argon (or mixtures thereof) have been shown to efficiently radiate thermal energy of the plasma so that the heat load is distributed on the walls of the machine. Pellets are formed by desublimating gas in the barrel of a pipe gun and fired using a pulse of high-pressure light gas. Current gas gun designs cannot reach sufficient pressure to dislodge pure neon and argon pellets at low temperatures because the material strength is too high. Pellet temperatures must be kept low (to well below the triple-point temperature of the material) to ensure minimal gas flow into the machine due to vapor pressure of the pellet. A gas-driven punch device has been designed and tested to dislodge pure neon or argon pellets. The breakaway strength of a pellet is proportional to the surface area of the pellet in contact with the inner diameter of the barrel. As pellets get larger in diameter, the amount of force needed to dislodge them increases. To better understand the mechanics behind how a punch dislodges a pellet, a solenoid-operated punch was designed so that kinetic energy of the punch, when striking a pellet, can be varied by changing input current to the solenoid. This solenoid punch will be used to determine kinetic energy versus pellet surface area threshold for breakaway. These data will be used to design mechanical punches for use in a high-field tokamak environment. This paper outlines the modeling, design, experimental testing, and results of the punch development activities.

Atomic photoionization cross sections beyond the electric dipole approximation.

A methodology is developed to compute photoionization cross sections beyond the electric dipole approximation from response theory, using Gaussian type orbitals and plane waves for the initial and final states, respectively. The methodology is applied to compute photoionization cross sections of atoms and ions from the first four rows of the periodic table. Analyzing the error due to the plane wave description of the photoelectron, we find kinetic energy and concomitant photon energy thresholds above which the plane wave approximation becomes applicable. The correction introduced by going beyond the electric dipole approximation increases with photon energy and depends on the spatial extension of the initial state. In general, the corrections are below 10% for most elements, at a photon energy reaching up to 12 keV.

Dependence of inertial confinement fusion ignition energy threshold on electron thermal conduction

In inertial confinement fusion, ignition conditions of the thermonuclear deuterium–tritium fusion reactions depend on the electron thermal heat conduction that affects the hot-spot mass accretion and energy balance. One-dimensional hydrodynamic calculations have been performed to simulate the implosion of a capsule directly irradiated by laser beams. For these calculations, the laser-capsule configuration has been scaled using homothetic transformations to scan the transition to ignition while keeping the implosion velocity constant. The electronic heat conduction has been modified by two alternative ways: (i) the classical Spitzer heat flux has been harmonically limited to the free streaming limit using a flux limit factor φ, and (ii) the classical Spitzer coefficient is reduced by a multiplicative factor α < 1. A change of the thermal conductivity affects the performances of the implosion and it can be beneficial or harmful. Parametric studies have been performed for both alternatives, looking for the kinetic energy threshold that generates a unitary energy gain as a function of parameters φ or α, respectively. These studies show how the energy threshold is modified by acting on the heat flux and that there is a minimum ignition energy that can be tuned by appropriately reducing the heat conduction. A simple qualitative model is developed to understand the relation between energy threshold and heat conduction.

Correlated Production and Analog Transport of Fission Neutrons and Photons Using Fission Models FREYA, FIFRELIN, and the Monte Carlo Code TRIPOLI-4

Fission modeling in general-purpose Monte Carlo transport codes often relies on average nuclear data provided by the international evaluation libraries. As such, only average fission multiplicities are available and correlations between fission neutrons and photons are missing. Whereas uncorrelated fission physics is usually sufficient for standard reactor core and radiation shielding calculations, correlated fission secondaries are required for specialized nuclear instrumentation and detector modeling. For coincidence counting detector optimization for instance, the precise simulation of fission neutrons and photons that remain correlated in time from birth to detection is essential. New developments were recently integrated into the Monte Carlo transport code TRIPOLI-4 to model fission physics more precisely, the purpose being to access event-by-event fission events from two different fission models: Fission Reaction Event Yield Algorithm (FREYA) and Fission Fragment Evaporation Leading to an Investigation of Nuclear Data (FIFRELIN). TRIPOLI-4 simulations can now be performed, either by connecting via an application programming interface to the Lawrence Livermore National Laboratory fission library including FREYA, or by reading the external fission event data files produced by FIFRELIN beforehand. These new capabilities enable us to easily compare results from the Monte Carlo transport calculations using the two fission models in a nuclear instrumentation application. In the first part of this paper, the broad underlying principles of the two fission models are recalled. We then present the experimental measurements of neutron angular correlations for 252Cf(sf) and 240Pu(sf). The correlations were measured for several neutron kinetic energy thresholds. In the latter part of this paper, simulation results are compared with the experimental data. Spontaneous fissions in 252Cf and 240Pu are modeled by FREYA or FIFRELIN. Emitted neutrons and photons are subsequently transported to an array of scintillators by TRIPOLI-4 in the analog mode to preserve their correlations. Angular correlations between fission neutrons obtained independently from these TRIPOLI-4 simulations, using either FREYA or FIFRELIN, are compared with the experimental results. For 240Pu(sf), the measured correlations were used to tune one of the FREYA model parameters. Similarly, different sets of parameters have been tested in FIFRELIN to try to improve the agreement with the experimental data.

Study on Kinetic Threshold of Raindrop Splash Bubble Sound

Rainfall noise is mainly composed of the initial impact sound and bubble sound. Bubbles are divided into three categories according to the diameter of the raindrops. It is generally believed that only a small raindrop hitting the water surface will produce the first type of bubble, larger diameter rains will only produce the second and third types of bubbles. In this paper, in order to verify the relationship between the diameter of raindrops and the type of bubbles, experiments were carried out to hit free water surface with different particle sizes of raindrops, The critical conditions for the raindrops to hit the water surface and generate air bubbles are found, and the kinetic thresholds of the raindrops under the critical conditions are obtained. The results show that in addition to the generally considered small raindrops will produce the first type of bubbles, the large raindrops and great raindrops will also produce a certain level of bubbles. Kinetic energy threshold is not a constant, but with the diameter and height of the drop

Study on single raindrop noise and energy conversion

The measurement of rainfall in the ocean is more difficult than in land, but the noise signals produced by rainfall can be used for measuring the rainfall in the ocean. In this paper, a single raindrop measurement system was set up to measure the noise of the raindrop, the bubble sound are classified by the radius of the raindrop which was measured by the splash method. The mechanism of the initial impact and the bubble sound are analyzed, and the kinetic energy threshold and acoustic energy conversion efficiency of the single raindrops are also investigated. The results show that the bubble noise is the main noise compared with initial impact noise, the initial impact noise will become larger with the radius of raindrop, the acoustic energy of great and large raindrop is much larger than that of small one, but the tiny and medium raindrop have no acoustic energy. The kinetic energy threshold is not a constant, but it is proportional to the raindrop size.The acoustic energy conversion rate is about 1.04×10-3% for small raindrops, 10-5% for heavy rains and great raindrops, there are almost no acoustic energy for tiny raindrops and medium-sized raindrops.

Correlated Production and Analog Transport of Fission Neutrons and Photons using Fission Models FREYA, FIFRELIN and the Monte Carlo Code TRIPOLI-4® .

Fission modeling in general-purpose Monte Carlo transport codes often relies on average nuclear data provided by international evaluation libraries. As such, only average fission multiplicities are available and correlations between fission neutrons and photons are missing. Whereas uncorrelated fission physics is usually sufficient for standard reactor core and radiation shielding calculations, correlated fission secondaries are required for specialized nuclear instrumentation and detector modeling. For coincidence counting detector optimization for instance, precise simulation of fission neutrons and photons that remain correlated in time from birth to detection is essential. New developments were recently integrated into the Monte Carlo transport code TRIPOLI-4 to model fission physics more precisely, the purpose being to access event-by-event fission events from two different fission models: FREYA and FIFRELIN. TRIPOLI-4 simulations can now be performed, either by connecting via an API to the LLNL fission library including FREYA, or by reading external fission event data files produced by FIFRELIN beforehand. These new capabilities enable us to easily compare results from Monte Carlo transport calculations using the two fission models in a nuclear instrumentation application. In the first part of this paper, broad underlying principles of the two fission models are recalled. We then present experimental measurements of neutron angular correlations for 252Cf(sf) and 240Pu(sf). The correlations were measured for several neutron kinetic energy thresholds. In the latter part of the paper, simulation results are compared to experimental data. Spontaneous fissions in 252Cf and 240Pu are modeled by FREYA or FIFRELIN. Emitted neutrons and photons are subsequently transported to an array of scintillators by TRIPOLI-4 in analog mode to preserve their correlations. Angular correlations between fission neutrons obtained independently from these TRIPOLI-4 simulations, using either FREYA or FIFRELIN, are compared to experimental results. For 240Pu(sf), the measured correlations were used to tune the model parameters.

The acoustic energy conversion efficiency of a single raindrop

The measurement of rainfall in the ocean is more difficult than in land, but the noise signals produced by rainfall can be used for measuring the rainfall in the ocean. In this paper, a single raindrop measurement system was set up to measure the noise of the raindrop, the bubble sound is classified by the radius of the raindrop which was measured by the splash method. The mechanism of the initial impact and the bubble sound are analyzed, and the kinetic energy threshold and acoustic energy conversion efficiency of the single raindrops is also investigated. The results show that the bubble sound is the main compared with initial impact sound, the initial impact sound will become larger with the radius of raindrop, the bubble acoustic energy of large and great raindrop is much larger than that of small one, but the tiny and medium raindrop have no bubble acoustic energy. The kinetic energy threshold is not a constant, but proportional to the raindrop size. The acoustic energy conversion efficiency is about 1.04×10-3% for small raindrops, but 10-5% for heavy rain and great raindrops.

An improved experimental scheme for simultaneous measurement of high-resolution zero electron kinetic energy (ZEKE) photoelectron and threshold photoion (MATI) spectra

An improved detection scheme is presented for threshold ionization spectroscopy with simultaneous recording of the Zero Electron Kinetic Energy (ZEKE) and Mass Analysed Threshold Ionisation (MATI) signals. The objective is to obtain accurate dissociation energies for larger molecular clusters by simultaneously detecting the fragment and parent ion MATI signals with identical transmission. The scheme preserves an optimal ZEKE spectral resolution together with excellent separation of the spontaneous ion and MATI signals in the time-of-flight mass spectrum. The resulting improvement in sensitivity will allow for the determination of dissociation energies in clusters with substantial mass difference between parent and daughter ions.

Bed turbulent kinetic energy boundary conditions for trapping efficiency and spatial distribution of sediments in basins.

The purpose of this study is to develop and validate a numerical tool for evaluating the performance of a settling basin regarding the trapping of suspended matter. The Euler-Lagrange approach was chosen to model the flow and sediment transport. The numerical model developed relies on the open source library OpenFOAM®, enhanced with new particle/wall interaction conditions to limit sediment deposition in zones with favourable hydrodynamic conditions (shear stress, turbulent kinetic energy). In particular, a new relation is proposed for calculating the turbulent kinetic energy threshold as a function of the properties of each particle (diameter and density). The numerical model is compared to three experimental datasets taken from the literature and collected for scale models of basins. The comparison of the numerical and experimental results permits concluding on the model's capacity to predict the trapping of particles in a settling basin with an absolute error in the region of 5% when the sediment depositions occur over the entire bed. In the case of sediment depositions localised in preferential zones, their distribution is reproduced well by the model and trapping efficiency is evaluated with an absolute error in the region of 10% (excluding cases of particles with very low density).

Critical Criterion for the Shock Initiation/Ignition of Cylindrical Charges with Thin Aluminum Shell Impacted by Steel Fragment

AbstractThe shock initiation/ignition of Cylindrical Charges Covered with thin Aluminium Shell (CCCAS) by steel fragment impact was experimentally and theoretically investigated. The critical specific kinetic energy criterion and threshold for the shock reaction of CCCAS were obtained. During the experiments, the response characteristics of CCCAS by steel fragment impact were studied. Then the surface microstructures of explosives were examined by scanning electron microscope (SEM). According to the experimental phenomena and existing theories, a calculation model for critical criterion for the shock reaction of CCCAS was developed by dimensional analysis. Based on the calculation model and numerous tests of cylindrical charges covered with 3 mm aluminium shell under the impact of steel fragments with the mass from 1.0 g to 2.0 g, the critical specific kinetic energy threshold for the shock initiation of CCCAS was obtained.

Challenges and Safety Aspects of a Disaster Relief Exercise

Small Unmanned Aerial Systems (sUAS) spread rapidly in the last years, both for civil and military applications. The performance of Dangerous, Dull and Dirty missions implies a wide use of the sUAS, in particular to manage hazardous events, such as natural or manmade major incidents or mass casualty situations. The management and control of an emergency are crucial aspects for the rescue teams and training activities-through joined exercises-are basic for the development of coordination capabilities. The aim of this paper is to report an example of a joined exercise between Italian civil and military authorities performed in Moncalieri city (Turin) on May 2015. The main procedures and challenges of the civil and military protection services are analyzed. The exercise was performed in a critical scenario where the safety of the operators and population on the ground had to be taken into account. Therefore, international and national regulations are analyzed in the paper, in particular in terms of safety requirements and kinetic energy threshold at the impact. The paper deals with all aspects concerning the human health, from the safety during the small UAS operations to the medical applications.

Reactions of liquid and solid aluminum clusters with N2: the role of structure and phase in Al114 (+), Al115 (+), and Al117 (+).

Kinetic energy thresholds have been measured for the chemisorption of N2 onto Al114 (+), Al115 (+), and Al117 (+) as a function of the cluster's initial temperature, from around 200 K up to around 900 K. For all three clusters there is a sharp drop in the kinetic energy threshold of 0.5-0.6 eV at around 450 K, that is correlated with the structural transition identified in heat capacity measurements. The decrease in the thresholds corresponds to an increase in the reaction rate constant, k(T) at 450 K, of around 10(6)-fold. No significant change in the thresholds occurs when the clusters melt at around 600 K. This contrasts with behavior previously reported for smaller clusters where a substantial drop in the kinetic energy thresholds is correlated with the melting transition.

Impact resistance and energy absorption of regular and functionally graded hexagonal honeycombs with cell wall material strain hardening

This paper highlights the effects of cell wall material strain hardening and density functional gradation (FG) on in-plane constant-velocity dynamic crushing response and impact behavior of hexagonal honeycombs. Results show that cell wall material strain hardening influences the distinct deformation modes induced by crushing velocity generally observed in regular hexagonal honeycombs. This is seen by a delay in the onset of localized deformation up until intermediate crushing velocities after which localization becomes dominant smearing out differences brought about by cell wall material strain hardening (plasticity convergence). In addition, during the impact loading on regular honeycombs, it was found that increasing the cell wall material strain hardening decreases the rate of gain of maximum crushing strain with increments in initial kinetic energy of impact. On the other hand, introducing FG brings about new deformation patterns due to changes in material distribution and preferential cell wall collapse of the weaker members. Interestingly, although the dynamic localization effect at higher crushing velocities observed earlier was not found to be particularly affected by FG, gradient convergence (i.e. smearing out the effects of FG due to higher velocities analogous to plasticity convergence) was not observed. On the contrary, gradient convergence emerged at higher impacting velocities primarily brought about by a combination of initial deformation localization and its subsequent advancement into FG region ahead. The kinetic energy threshold for the emergence of this gradient convergence effect was found to be considerably delayed by cell wall material strain hardening.

On the lower energy limit of electronic stopping in simulated collision cascades in Ni, Pd and Pt

We have investigated the effect of the choice of kinetic energy threshold Tc for electronic stopping (Se) in molecular dynamics (MD) simulations of collision cascades. We find that while the choice of Tc has only a negligible effect in low energy cascades, it has a pronounced effect on the fraction of defects found in clusters in high energy cascades. In order to gain insight into the level of energy losses expected in cascades, we have simulated a large number of cascades in Ni, Pd and Pt, with primary knock-on atom (PKA) energies between 30eV and 200keV. Since the energy losses affect the total atomic displacements especially in high energy cascades, we use this measure to determine a reasonable value of Tc. By directly comparing the simulated mixing efficiency to ion beam mixing experiments, we conclude that a threshold of Tc=1eV is too low for simulations of high energy cascades in all materials considered. A value of Tc=10eV is more realistic, although for Pd and Pt, this results in a slight over-prediction of the mixing efficiency.

Objectively Determined Fair-Weather NBL Features in ARW-WRF and Their Comparison to CASES-97 Observations

AbstractHeights of nocturnal boundary layer (NBL) features are determined using vertical profiles from the Advanced Research Weather Research and Forecasting Model (ARW-WRF), and then compared to data for three moderately windy fair-weather nights during the April–May 1997 Kansas-based Cooperative Atmosphere–Surface Exchange Study (CASES-97) to evaluate the success of four PBL schemes in replicating observations. The schemes are Bougeault–LaCarrere (BouLac), Mellor–Yamada–Janjić (MYJ), quasi-normal scale elimination (QNSE), and Yonsei University (YSU) versions 3.2 and 3.4.1. This study’s chosen objectively determined model NBL height h estimate uses a turbulence kinetic energy (TKE) threshold equal to 5% , where TKE′ is relative to its background (free atmosphere) value. The YSU- and MYJ-determined h could not be improved upon. Observed heights of the virtual temperature maximum hTvmax and wind speed maximum hSmax, and the heights h1wsonde and h2wsonde, between which the radiosonde slows from ~5 to ~3 m s−1 as it rises from turbulent to nonturbulent air, and thus brackets h, were used for comparison to model results. The observations revealed a general pattern: hTvmax increased through the night, and hTvmax and hSmax converged with time, and the two mostly lay between h1wsonde and h2wsonde after several hours. Clear failure to adhere to this pattern and large excursions from observations or other PBL schemes revealed excess mixing for BouLac and YSU version 3.2 (but not version 3.4.1) and excess thermal mixing for QNSE under windy conditions. Observed friction velocity was much smaller than model values, with differences consistent with the observations reflecting local skin drag and the model reflecting regional form drag + skin drag.