Collision Sequences Research Articles

Effect of load limiting the shoulder-belt on right-front passenger kinematics in oblique-offset and NCAP frontal crash tests

Objective The effect of shoulder-belt load-limiting was evaluated on right-front passenger kinematics in 90 km/h oblique OMDB (offset moving deformable barrier) impacts and compared to kinematics in 56 km/h NCAP crash tests. The study focused on the influence of webbing pulling out of the retractor increasing forward excursion of the upper torso and head. Methods 18 OMDB crash tests were conducted by NHTSA at 90 km/h. The barrier was aligned at a 15 deg angle to the left (345 deg PDOF) with 35% overlap of the struck vehicle. The kinematics and biomechanical responses of the 50th THOR passenger dummy were analyzed. The tests included 3 onboard video cameras covering the front occupants. The lap and shoulder belt loads were measured and displacement of the shoulder belt was available for most tests. The responses were compared to those in 11 NCAP frontal impacts at 56 km/h with a 5th Hybrid III passenger. Results The delta V was 62.6 ± 2.8 km/h in the passenger car OMDB tests. The pretensioners and airbags deployed by 40 ms. The pretensioner pulled in −62 ± 29 mm of webbing at 13–15 m/s. With the retractor locked, belt loads increased as the passenger moved forward and inboard. The load-limiter paid out 280 ± 67 mm of shoulder belt webbing at 6–11 m/s and peak load of 4,170 ± 557 N. The shoulder belt slipped off the shoulder at 97 ± 10 ms. By 120 ms, the left shoulder impacted the center of the instrument panel and the head either impacted the panel or perched on the left edge of the airbag with the head rotated 80–135 deg about the z-axis (eyes right). There was 187.3 ± 37.4 mm of loose webbing after the test. Similar dummy responses were seen in the SUV and truck tests. In contrast, the passenger kinematics were centered on the airbag in NCAP tests without impact on the interior. Conclusions Excursion of the upper torso with the load-limiting shoulder belt enabled the belt to slip off the right shoulder in ODMB tests. The passenger flexed forward around the lap belt with impact on the center of the instrument panel. The upper torso lacked sufficient restraint with the level of load limiting in the tests. The belts were loose after pretensioning and load-limiting reducing the restraint effectiveness if there were a second or third impact or rollover in the collision sequence.

Intermediate-mass Black Hole Progenitors from Stellar Collisions in Dense Star Clusters

Very massive stars (VMSs) formed via a sequence of stellar collisions in dense star clusters have been proposed as the progenitors of massive black hole seeds. VMSs could indeed collapse to form intermediate-mass black holes, which would then grow by accretion to become the supermassive black holes observed at the centers of galaxies and powering high-redshift quasars. Previous studies have investigated how different cluster initial conditions affect the formation of a VMS, including mass segregation, stellar collisions, and binaries, among others. In this study, we investigate the growth of VMSs with a new grid of Cluster Monte Carlo star cluster simulations—the most expansive to date. The simulations span a wide range of initial conditions, varying the number of stars, cluster density, stellar initial mass function (IMF), and primordial binary fraction. We find a gradual shift in the mass of the most massive collision product across the parameter space; in particular, denser clusters born with top-heavy IMFs provide strong collisional regimes that form VMSs with masses easily exceeding 1000 M ⊙. Our results are used to derive a fitting formula that can predict the typical mass of a VMS formed as a function of the star cluster properties. Additionally, we study the stochasticity of this process and derive a statistical distribution for the mass of the VMS formed in one of our models, recomputing the model 50 times with different initial random seeds.

Simulation of threshold displacement energy in Fe-Cr-Al alloys using molecular dynamics

The threshold displacement energy of Fe and Fe-Cr-Al alloys and the influence factors were investigated using molecular dynamic simulations. The mechanism of defect recombination was discussed, as was the evaluation of the recombination radius for Fe and Fe-Cr-Al. The simulation results show that Fe and Fe-Cr-Al have big differences in threshold displacement energies and directional dependencies at low temperatures, but the differences become less pronounced at high temperatures. The cause might be that the replacement collision sequence can effectively separate an interstitial from a vacancy in Fe-Cr-Al and greatly reduce threshold displacement energy at low temperatures. In addition, the energy transfer efficiency of primary knock-on Al atoms is low due to the difference in atomic mass, and the recombination effect for Cr is hindered by the formation of Fe-Cr 〈110〉 dumbbell. However, the effect of solute atoms on threshold displacement energy is insignificant at high temperatures, due to the increase in the recombination radius and a reduction in the effect of the aforementioned factors.

Collisions of weakly-bound kinks in the Christ-Lee model

We investigate soliton collisions in a one-parameter family of scalar field theories in 1+1 dimensions which was first discussed by Christ and Lee [1]. The models have a sextic potential with three local minima, and for suitably small values of the parameter their kinks have an internal structure in the form of two weakly-bound subkinks. We show that for these values of the parameter kink collisions are best understood as an independent sequence of collisions of these subkinks, and that a static mode analysis is not enough to explain resonant structures emerging in this model. We also emphasise the role of radiation and oscillon formation in the collision process.

Hybrid causal logic model for estimating the probability of an icebreaker–ship collision in an ice channel during an escort operation along the Northeast Passage

Under severe Arctic ice conditions, escort operations are the most efficient methods for facilitating shipping. Nevertheless, escort operations are among the most dangerous operations, as they may result in icebreaker–ship collisions and/or ship besetting in ice. To mitigate the risk of collisions, it is essential to understand the event sequences of collisions and the risk control options that can be implemented to reduce the occurrence of undesired events. This paper proposes a hybrid causal logic model to estimate the likelihood of an icebreaker–ship collision while considering human factors during an escort operation along the Northeast Passage. The model relies on inputs from four icebreaker captains. Its applicability is demonstrated for a 2018 summer voyage of a cargo ship assisted by an icebreaker. Risk control options are then proposed based on qualitative and sensitivity analyses of the model. The results of this study can assist shipping companies to better understand the sequence of events prior to icebreaker–ship collisions during escort operations in ice-covered waters. This paper provides information on risk reduction measures. In addition, the proposed model can assist in route planning.

From a to z and back again: motion and mobility in the fiction of John Muckle

Abstract The narrative fictions of John Muckle reflect the increased motion and mobility of people and things in the late twentieth and twenty-first centuries. This increase is a significant, although often invisible, part of the narrative and can be read through both the form and content of the writing. The working lives of his characters, and their sense of identity, are changed through acts of movement, while the objects that make up the environment they live in are similarly always in the process of change. Motion is not, however, the article claims, initiated or determined by social forces, or the inevitable consequence of a capitalist system that demands ever more productivity and growth. Motion is always and already there, and therefore is changed, but not initiated, by economic and social pressures. It is this interplay between people and things that are always and already moving, and a capitalism that seeks to change or direct that movement, that provides the tensions within the narrative and the events in the lives of the characters, both tragic and joyful. Narratives, and the movements they often describe, become less about beginnings and endings, and more about sequences of collisions and moments of change in direction and velocity.

A Monte Carlo algorithm to measure probabilities of rare events in cluster-cluster aggregation

We develop a biased Monte Carlo algorithm to measure probabilities of rare events in cluster-cluster aggregation for arbitrary collision kernels. Given a trajectory with a fixed number of collisions, the algorithm modifies both the waiting times between collisions, as well as the sequence of collisions, using local moves. We show that the algorithm is ergodic by giving a protocol that transforms an arbitrary trajectory to a standard trajectory using valid Monte Carlo moves. The algorithm can sample rare events with probabilities of the order of 10−40 and lower. The algorithm's effectiveness in sampling low-probability events is established by showing that the numerical results for the large deviation function of constant-kernel aggregation reproduce the exact results. It is shown that the algorithm can obtain the large deviation functions for other kernels, including gelling ones, as well as the instanton trajectories for atypical times. The dependence of the autocorrelation times, both temporal and configurational, on the different parameters of the algorithm is also characterized.

Biquadratic nontwist map: a model for shearless bifurcations

Area-preserving nontwist maps are used to describe a broad range of physical systems. In those systems, the violation of the twist condition leads to nontwist characteristic phenomena, such as reconnection–collision sequences and shearless invariant curves that act as transport barriers in the phase space. Although reported in numerical investigations, the shearless bifurcation, i.e., the emergence scenario of multiple shearless curves, is not well understood. In this work, we derive an area-preserving map as a local approximation of a particle transport model for confined plasmas. Multiple shearless curves are found in this area-preserving map, with the same shearless bifurcation scenario numerically observed in the original model. Due to its symmetry properties and simple functional form, this map is proposed as a model to study shearless bifurcations.

Wave Function Realization of a Thermal Collision Model.

An efficient algorithm to simulate dynamics of open quantum system is presented. The method describes the dynamics by unraveling stochastic wave functions converging to a density operator description. The stochastic techniques are based on the quantum collision model. Modeling systems dynamics with wave functions and modeling the interaction with the environment with a collision sequence reduces the scale of the complexity significantly. The algorithm developed can be implemented on quantum computers. We introduce stochastic methods that exploit statistical characteristics of the model such as Markovianity, Brownian motion, and binary distribution. The central limit theorem is employed to study the convergence of distributions of stochastic dynamics of pure quantum states represented by wave vectors. By averaging a sample of functions in the distribution we prove and demonstrate the convergence of the dynamics to the mixed quantum state described by a density operator.

Modeling experimental low energy ion scattering multi-angle maps with molecular dynamics FAN

Multi-angle maps obtained with low energy ion scattering (LEIS) are not only a convenient way to visualize the atomic-level surface structure of single crystals, but also provide a comprehensive data set that is useful for quantitative fitting with models. However, modeling these maps is often difficult due to the complexity of the scattering process, as well as the number of simulations needed to accurately reproduce a single experimental map. For example, traditional molecular dynamics (MD) and binary collision approximation (BCA) simulations typically require on the order of one billion simulated ion trajectories to obtain sufficient statistics. This problem is exacerbated when modeling impact-collision ion scattering spectroscopy (ICISS) maps, as backscattering cross sections are much smaller than forward-scattering cross sections. A workaround to this problem was given by Neihus and Spitzl in the form of FAN (Niehus and Spitzl, 1991), a simulation that approximates the angular dependence of the backscattering signal by only simulating ion trajectories that reach and emanate from lattice atoms, using a BCA code. This greatly reduces the number of trajectories that must be calculated, though it can oversimplify some of the more complex collision sequences. In this work, we develop a fully three-dimensional FAN code that uses MD to simulate trajectories rather than the BCA. Our approach exploits the improved speed of FAN, while retaining the more accurate ion trajectory calculations of MD. We apply the MD-FAN simulation to model LEIS measurements on two surfaces. First, we benchmark our MD-FAN simulation in a comparison to a BCA simulation for 3 keV He+ incident on W(111) that has been previously reported in Wong et al. (2020). The MD-FAN map had stronger agreement with the experimental ICISS measurements than did the BCA map, despite containing nearly 100-fold fewer ion trajectories. Second, to obtain experimental data sets for a more complex surface, we perform experimental ICISS measurements using a 3 keV He+ beam on a magnetite single crystal, Fe3O4(001) to generate a multi-angle map. The simulated MD-FAN map for the Fe3O4(001) surface once again agreed well with the experimental map, allowing for quantitative comparisons. The MD-FAN simulation also provided insight into the scattering processes, revealing that some of the observed pattern arises from 3 keV He+ that have backscattered into the detector from Fe atoms more than 2 nm below the surface.

Planning of Obstacle-Aided Navigation for Multi-Legged Robots Using a Sampling-Based Method Over Directed Graphs

Existing work in legged robot navigation in cluttered environments often seeks collision-free paths that avoid obstacle interactions. Here we present a new approach for multi-legged robots to utilize leg-obstacle collisions to generate desired dynamics. To predict the change of robot state under repeated leg-obstacle collisions, we construct a discretized directed graph model: each node of the graph represents a different robot state, whereas the directed edges pointing from one node to another represent the transitions from one robot state to the next within one stride. These obstacle-modulated state transitions can depend on the robot gaits used. To capture this dependence, an empirical interaction model is used to compute the change of robot state based on initial contact positions between robot legs and obstacles. To validate the prediction of robot state transitions, we experimentally measure the state of a quadrupedal robot as it traverses a periodic obstacle field with three different gaits: bound, trot, and pace. We observed that the robot could passively converge to different steady state orientations, and these steady states corresponded well with the Strongly-Connected-Path-Components (SCPCs) within the directed graph. Searching over the graph for connected paths of SCPCs allows development of a gait planner that can generate gait switching strategies for a robot to achieve desired states by simply engaging with a sequence of leg-obstacle collisions. We demonstrate in experiments that using this method an open-loop quadrupedal robot was able to achieve desired orientations within a periodic obstacle field without any sensory input or active steering.

Hierarchical merger of primordial black holes in dwarf galaxies

We study the merger history of primordial black holes (PBHs) in a scenario where they represent the dominant dark matter component of a typical dwarf galaxies' core. We investigate the possibility of a sequence of collisions resulting in a hierarchical merger of black holes, and look at the final mass spectrum in such clusters, which initially present a monochromatic (single-mass) PBH population. Our study shows that the merging process results in the transfer of about 40% of the total mass of the core to the merger products regardless of the initial mass of PBHs, with about 5% of energy radiated out in the form of gravitational waves. We find that, in the lighter mass limit, black holes up to eight times more massive than the original population can be formed within a Hubble time.

Curvature flows, scaling laws and the geometry of attrition under impacts

Impact induced attrition processes are, beyond being essential models of industrial ore processing, broadly regarded as the key to decipher the provenance of sedimentary particles. Here we establish the first link between microscopic, particle-based models and the mean field theory for these processes. Based on realistic computer simulations of particle-wall collision sequences we first identify the well-known damage and fragmentation energy phases, then we show that the former is split into the abrasion phase with infinite sample lifetime (analogous to Sternberg’s Law) at finite asymptotic mass and the cleavage phase with finite sample lifetime, decreasing as a power law of the impact velocity (analogous to Basquin’s Law). This splitting establishes the link between mean field models (curvature-driven partial differential equations) and particle-based models: only in the abrasion phase does shape evolution emerging in the latter reproduce with startling accuracy the spatio-temporal patterns (two geometric phases) predicted by the former.

Between synchrony and turbulence: intricate hierarchies of coexistence patterns

Coupled oscillators, even identical ones, display a wide range of behaviours, among them synchrony and incoherence. The 2002 discovery of so-called chimera states, states of coexisting synchronized and unsynchronized oscillators, provided a possible link between the two and definitely showed that different parts of the same ensemble can sustain qualitatively different forms of motion. Here, we demonstrate that globally coupled identical oscillators can express a range of coexistence patterns more comprehensive than chimeras. A hierarchy of such states evolves from the fully synchronized solution in a series of cluster-splittings. At the far end of this hierarchy, the states further collide with their own mirror-images in phase space – rendering the motion chaotic, destroying some of the clusters and thereby producing even more intricate coexistence patterns. A sequence of such attractor collisions can ultimately lead to full incoherence of only single asynchronous oscillators. Chimera states, with one large synchronized cluster and else only single oscillators, are found to be just one step in this transition from low- to high-dimensional dynamics.

Molecular dynamics simulation of stress induced by energetic particle bombardment in Mo thin films

Molecular dynamics (MD) simulations are performed to analyze the evolution of defects and stress caused by low-energy (25-400 eV) Ar bombardment of polycrystalline Mo thin films. Simulations were performed under different conditions to explore the role of grain boundaries (GBs), Ar-atom's kinetic energies, and incident directions on defect generation. The results show that the GBs enhance the production of interstitial defects, producing compressive stress at much larger depths than the implantation range. This is attributed to sequences of atomic collisions that knock atoms into GBs instead of a diffusional process. Decreasing the grain size or increasing the kinetic energy of the incoming particles increases the number of interstitials in the film, which increases the compressive stress. The incident angle has little influence on the number of interstitials in the film, but the sputtering yield depends on the polar angle. The stress distribution can be modeled by a superposition of the different defect distributions with the appropriate relaxation volumes.

On the Approximations of Point Measures Associated with the Brownian Web by Means of the Fractional Step Method and Discretization of the Initial Interval

UDC 519.21 We establish the rate of weak convergence in the fractional step method for the Arratia flow in terms of the Wasserstein distance between the images of the Lebesque measure under the action of the flow. We introduce finite-dimensional densities that describe sequences of collisions in the Arratia flow and derive an explicit expression for them. With the initial interval discretized, we also discuss the convergence of the corresponding approximations of the point measure associated with the Arratia flow in terms of such densities.

Modelling the primary damage in Fe and W: Influence of the short range interactions on the cascade properties: Part 1 – Energy transfer

The primary damage in metallic alloys, i.e. the point defect distribution resulting from the interaction between an energetic particle and a metallic matrix has been investigated for more than 60 years using atomistic simulations. The defect distribution produced in cascades is sensitive to the equilibrium part of the potential as well as its hardened part. An analysis based on large statistics of molecular dynamics simulations and comparison with different embedded atom method potentials in Fe and W allows to rationalize the potential behavior. Correlations between static non-equilibrium properties (quasi static drag (QSD)), threshold displacement energies (TDE), replacement collision sequences (RCS) along the 〈110〉 direction have been revealed. Along this direction, the lower the TDE, the lower the QSD and the more energy is transmitted along the 〈110〉 direction during the RCS, i.e. the softest potentials are the ones for which the most energy is transmitted from the PKA to the first head-on atom in the direction of the RCS sequence.

Understanding Newton’s cradle. II: exploring a real cradle

Newton’s cradle is a well-known physics toy that is commonly used by teachers to demonstrate conservation laws in mechanics. It can also be used to investigate the physics of colliding objects, by recording motion of the balls on video film. Various experiments are described using 3-ball and 5-ball cradles, showing how different types of collision can be investigated depending on whether the balls are touching or separated. The sequence of collisions was examined as a function of time, with the surprising observation that very small gaps between the balls, invisible on video film, make a significant difference to the collision dynamics. Additional experiments illustrate the effects of changes in ball stiffness and the mass of the middle ball and provide an introduction for students and teachers into possible research projects. Each experiment is illustrated with a supplementary video.

Absence of a Crystal Direction Regime in which Sputtering Corresponds to Amorphous Material.

Erosion of material by energetic ions, i.e., sputtering, is widely used in industry and research. Using experiments and simulations that, independently of each other, obtain the sputter yield of thousands of individual grains, we demonstrate here that the sputter yield for heavy keV ions on metals changes as a continuous function of the crystal direction. Moreover, we show that polycrystalline metals with randomly oriented grains do not sputter with the same yield as the amorphous material. The key reason for this is attributed to linear collision sequences rather than channeling.

Graphical composite modeling and simulation for multi-aircraft collision avoidance

Modeling and simulation for multi-aircraft collision avoidance to understand the mechanistic behavior is an important activity. Building models using general programming language typically requires specialist knowledge, and this limits the spread of modeling and simulation approach among multi-aircraft collision avoidance scenario. Thus, a software environment is needed to support convenient development of models by assembling components, when analysis demands changes. In this work, the graphical composite modeling and simulation software (GMAS extended) for multi-aircraft collision avoidance is introduced, with the basic graphical components and a graphical assembly editor. We define the serial and parallel execution semantics of GMASE-based model and then introduce the high-level graphical modeling interface, the low-level runtime engine of GMAS, and the simulation-based decision tree, which transforms a complex decision-making process into a collection of simpler decisions of finding the no collision or optimal sequence from some initial state to the goal state. To validate its efficiency and practicability, a three-aircraft collision avoidance model with TCAS operations is built on GMAS, which shows that using GMAS increases reusability and hiding complexity in graphical programming by splitting complex behavior into data flow and function components. The experimental result proves that GMAS not only provides a better representation for multi-aircraft collision avoidance, but also a useful approach for analyzing the potential collision occurrences.