Collision Duration Research Articles

Study on motion states of sphere based on empirical Fourier decomposition

This study uses Empirical Fourier Decomposition (EFD) to decompose the signal of motion of a sphere on a rough planar surface, which is a mixture of three main states: sliding, rolling, and collision. The simulation results show that the decomposed sub- signals are consistent with the original signals. Furthermore, we conducted a laboratory experiment to study the movement of a sphere on a rough inclined chute. The movement of the sphere is divided into two main stages: low-speed rolling and bouncing forward. In the first stage, the sphere motion consists mainly of rolling and collision. In the second stage, the sphere motion consists of sliding, rolling, and collision. We propose for the first time that the duration and peak acceleration of collisions from two stages follow a normal distribution.

Pore-scale modelling of particle transport in a porous bed

A computational study was performed of the transport of both non-adhesive and adhesive particles in a porous bed with a body-centred cubic (BCC) structure. Pore-scale simulation of the flow within the porous bed was achieved through combining the immersed boundary method and the lattice Boltzmann method. Particle transport is computed using an adhesive discrete-element method based on a multi-time-scale soft-sphere model. The fluid flow results are validated by comparison with experimental data for dimensionless permeability of flow in a porous bed of spheres. For computations with non-adhesive particles, the particles are observed to drift to the centre of ‘channels’ in the BCC array, within which most of the fluid flow occurs. The mechanism of this inward drift was found to be related to the phenomenon of oscillatory clustering, which is an inertial drift mechanism observed for particles in a corrugated channel. A measure for particle drift into these channels was developed, and the time rate of change of this measure was found to compare closely with an approximate theoretical prediction based on oscillatory clustering theory. The drift measure was observed to be limited at long time by hold-up of outlier particles caught in long-duration collisions with the fixed bed particles in regions of low fluid velocity magnitude. Simulations with adhesive particles exhibited marked increase in collision duration, as well as inhibition of the tendency to drift toward the flow channels due to adhesive hold-up.

Spatial Variation of the Coefficient of Restitution for Frictionless Impacts on Circular Beams

Abstract The spatial variation of the coefficient of restitution for frictionless impacts along the length of a circular beam is investigated using a continuous impact model. The equations of motion are obtained using the finite element method, and direct time integration is used to simulate the collision on a fast time scale. For collision of a pinned beam with a fixed cylinder, the spatial variation of the coefficient of restitution, impulse magnitude, duration of collision, energetics, and the role of damping are investigated. In the absence of significant external damping, the kinematic and kinetic definitions of the coefficient of restitution provide identical results. Experiments validate the results from simulation which indicate that the coefficient of restitution is sensitive to the location of impact.

Massive core/star formation triggered by cloud–cloud collision – II. High-speed collisions of magnetized clouds

ABSTRACT We present a study of the effects of magnetic fields on the formation of massive, self-gravitationally bound cores (MBCs) in high-speed cloud–cloud collisions (CCCs). Extending our previous work, we perform magnetohydrodynamic simulations of the high-speed (20–40 km s−1) collisions between two magnetized (initial 4 $\mu\!$ G), turbulent clouds of different sizes in the range of 7–20 pc. We show that a magnetic field hinders the growth of cores, particularly in the case of short-duration collisions where cores are not seen to reach a highly bound state. In such cases, a shocked region created by the collision rapidly expands into the ambient medium owing to the enhanced magnetic pressure, resulting in the destruction of the highly unbound cores and suppression of gas accretion. This negative effect on the formation of MBCs has not been reported in previous hydrodynamic simulations of CCCs. Together with our previous work, we conclude that magnetic fields provide two competing effects on the MBC formation in CCCs; while they promote the mass accumulation onto cores during a collision, they operate to destroy cores or hinder the core growth after the collision. The duration of such collisions determines which effect prevails, resulting in a maximum collision speed for the MBC formation within given colliding clouds. Our results agree with the observed trend among CCC samples in the column density range probed in the simulations presented here; CCCs with higher relative velocities require higher column densities for the formation of massive stars.

Gravity effects in mass-spring-damper models of inelastic collisions

A ball bouncing on a rigid surface is modeled as a mass-spring-damper system. We consider the effect of including or neglecting the force of gravity, extending previous work that shows that including gravity yields a velocity-dependent coefficient of restitution (COR). This velocity dependence is most pronounced at low-impact velocities and high damping. Previously-published models differ in defining the termination of the collision, with some referencing the ball’s position and others noting when the contact force becomes zero. We propose a new model that combines aspects of these approaches. The various models are compared in their predictions for the COR and collision duration, and are compared to experimental data from a cart on an inclined track bouncing repeatedly on a spring. While the new model shows some improvement over the prior collision termination conditions, the inclusion of gravity is the more important consideration in modeling repeated bouncing.

Motility induced phase separation of deformable cells.

Using a multi-phase field model, we examine how particle deformability, which is a proxy for cell stiffness, affects motility induced phase separation (MIPS). We show that purely repulsive deformable, i.e., squishy, cells phase separate more effectively than their rigid counterparts. This can be understood as due to the fact that deformability increases the effective duration of collisions. In addition, the dense regions become increasingly disordered as deformability increases. Our results contextualize the applicability of MIPS to biological systems and have implications for how cells in biological systems may self-organize.

Effects of interlayer on the interfacial microstructures and thermomechanical kinetics of explosive welded 2A14 aluminum alloy-niobium composite

The explosive welding of 2A14 aluminum alloy and niobium with and without a 1060 Al interlayer is investigated by experiments and a two-step numerical simulation. Microstructure observations revealed a continuous molten layer with plenty of micro-defects at the joint interface by direct welding, and for the welding situation with an interlayer, straight and curled joints devoid of imperfections were obtained at the upper and lower interfaces, respectively. The tensile-shear strength for the direct welded samples was 84.4 MPa, while a rise of 38.2% was achieved for the composite with an interlayer. The coupled Lagrange-Eulerian simulation showed a dramatic decline in impact velocity and an obvious increase in collision area and duration due to the insertion of the interlayer, the resulting less kinetic energy loss at the joint interfaces eliminates the formation of the intermetallic compounds. In addition, the smoothed particles hydrodynamics simulation demonstrated that the distribution of strain, temperature, and pressure is more pronounced at the lower interface, and different bonding processes were elucidated for these two interfaces. The introduction of the interlayer strengthened the weldment by adjusting the way the interface accommodates the impact-induced strain.

Deposition of micron-sized inertial particles on flat surfaces: effects of electrostatic forces and surface roughness

Micron-sized particles are prone to deposit on smooth surfaces. A micron-sized particle collision-deposition model including the effects of electrostatic forces, integrated with the factors of particle size, material properties, elastic–plastic deformation, particle charging, surface roughness, and van der Waals forces, is proposed. The effects of the electrostatic forces on the critical deposition velocity, collision duration, and coefficient of restitution (COR), which is the ratio of particle velocity after and before the collision, are investigated for 1–20 μm sand particles colliding with glass, steel, and aluminum alloy surfaces. The results show that the electrostatic forces of sand particles are approximately 106–108 times their gravity and increase the impact duration. Moreover, these forces increase the critical deposition velocity by 2.32–6.89% for the glass surface and decrease the COR by 0.6–3.5% for the three surfaces, while the particle size is below 20 μm and the roughness is 1 nm. The electrostatic forces ranked from the maximum to the minimum are those of the aluminum alloy, steel, and glass surfaces for the same particle size and surface roughness. The developed model can perfect the theory of particle flow and gas-particle two-phase flow.

Performance of Lunar Regolith Shield under Meteoroid Impact: Uncertainties of a Numerical Prediction

The protection of the future lunar base from radiation, thermal stresses and impacts of meteoroids can be achieved by several options, generally consisting in a shielding system, made of either regolith or combined materials. In the present paper, the incidence of two sources of uncertainty on the FEM calculation of stress propagation through the covering regolith layer has been assessed. First, the investigation has pointed out, for a given impact and a given constitutive model, the uncertainty in the stress prediction related to the strain interval adopted for the soil stiffness measurement. Thereafter, calculation has been performed, for a given stiffness value, changing the assumed collision duration of one order of magnitude for equal impact momentum, that is, changing the maximum impact force too, correspondingly. The simulation has been performed based on physical and mechanical parameters of DNA-1A lunar simulant. The results provide indication of the relative importance of the calculation assumptions, which could address the design of a regolith shield.

Enhanced single-nanoparticle collisions for the hydrogen evolution reaction in a confined microchannel

Single nanoparticle (NP) collisions technique has been widely employed in electrocatalysis. However, the short collision duration of single NPs hinders the further improvement in their electrocatalytic performance. Here, to increase the dynamic collision duration of single NPs in the electron tunneling region, enhanced near-wall hindered diffusion is introduced in the stochastic collision process by coupling a Au ultramicroelectrode (UME) with a confined microchannel. In the case of single palladium nanoparticle (Pd NP) collisions for the hydrogen evolution reaction (HER), the hydrodynamic trapping confined in the microchannel effectively permits the activation of the HER on the single Pd NPs. The microchannel-based Au UME is promising in the application of single-NP collisions to energy conversion.

What are the ideal systolic and diastolic blood pressure which do not injure the intima of iliac and coronary arteries?

Abstract For patients with coronary artery disease, hypertension (HTN) is a major risk factor. How could uncontrolled HTN start atherosclerosis? In our prior research, laminar flow in coronary arteries prevented the formation of plaques while turbulent flow injured the intima and triggered atherosclerosis. In this present study our question was: Which blood pressure (BP) level is optimal in not producing turbulence and so not injuring the intima? Methods At first, a systolic BP<120mmHg and diastolic BP<75mmHg) were arbitrarily set as controlled (group A) while a BP of >160/105mmHg as uncontrolled (group B). All patients underwent a dynamic coronary angiogram recorded at 15 images/second or 0.06 seconds per image. The first image was of the index artery completely filled with contrast. In subsequent images the blood in white color moved in over a background of black contrast (Figure 1A). In 1B, 0.06 seconds later, the blood arrived at the mid segment (white arrow). In 1C, the flood moved forward, however there was darker contrast hanging at the mid segment, marking the location of collision from the retrograde against the antegrade flow (white arrow). The reason was that in uncontrolled BP the contraction of the left ventricle was stronger so in systole, the coronary blood could reverse its course, run on a retrograde direction, collide against the antegrade flow and create turbulence (1C). At the end, before deploying a vascular closure device, an iliac angiogram was performed. In Figure 2, on a black background of contrast, the blood in white color moved forward with a pointed tip of laminar flow. 0.06 seconds later, the laminar tip was stopped abruptly with all the layers recoiling on each other like a falling stack of dominoes. In the next image. a large swirl of disorganized mixing of blood and contrast suggested the presence of turbulence caused by the collision. The data to be collected were (1) the duration of the antegrade and retrograde flow, (2) duration of the collision (turbulence at the collision site) Results In the group A (BP <120/75 mmHg), 90% of 20 patients had no retrograde flow nor collision in the iliac and short collision in coronary arteries (<0.12 secs). In 30 patients of group B (BP >160/105 mmHg), the duration of retrograde flow and collision in the iliac artery were prolonged at >0.24 msecs. In the coronary arteries, the duration was prolonged at 0.18 msecs (all p<0.05 compared with group A). These locations of turbulence correlated with the location of plaques in our prior studies. Conclusion In patients with uncontrolled HTN, the retrograde flow was prolonged, and the turbulence was intense. In contrary, for patients with controlled BP, there was no retrograde flow and weaker collision in coronary arteries. The results suggest that a BP of <120/75 mmHg may not trigger the atherosclerotic process. New clinical trials with larger number of patients should be performed in search for the lowest ideal blood pressure. Funding Acknowledgement Type of funding sources: None.

Full-Duplex Multiple Access Mechanism for Connected Vehicles Operating at Different Autonomous Levels in NR eV2X VANETs

Future connected and autonomous vehicles (CAVs) will operate at different autonomous levels for decades. Therefore, we propose a novel prioritisation scheme according to the autonomous levels of CAVs, and a corresponding multiple access mechanism, to be named full-duplex prioritised scheduling (FDPS) protocol, to enhance the delivery of high-priority packets in future New Radio (NR) enhanced vehicle-to-everything communication (eV2X) vehicular ad hoc networks (VANETs). Comparing to the standardised sensing-based semi-persistent scheduling (SB-SPS) protocol, this paper presents how collision detection is enabled during the broadcast, how collisions are resolved, how the priority of a packet from a colliding CAV is recognised, and how the broadcast of high-priority packets is enhanced. Both protocols are evaluated through mathematical formulations and simulations in terms of average successful packet delivery rate (PDR), collision duration, and latency. Simulation results have firstly validated the mathematical analysis, they have also shown the enhancement of packets delivery in future NR eV2X VANETs when the self-interference suppression (SIS) factor is better than 16%, which is achievable by deploying the existing SIS technologies.

The influence of gravity on granular impacts

Context. Slow interactions on small body surfaces occur both naturally and through human intervention. The resettling of grains and boulders following a cratering event, as well as observations made during small body missions, can provide clues regarding the material properties and the physical evolution of a surface. In order to analyze such events, it is necessary to understand how gravity influences granular behavior. Aims. In this work, we study slow impacts into granular materials for different collision velocities and gravity levels. Our objectives are to develop a model that describes the penetration depth in terms of the dimensionless Froude number and to use this model to understand the relationship between collision behavior, collision velocity, and gravity. Methods. We used the soft-sphere discrete element method to simulate impacts into glass beads under gravitational accelerations ranging from 9.81 m s−2 to 0.001 m s−2. We quantified collision behavior using the peak acceleration, the penetration depth, and the collision duration of the projectile, and we compared the collision behavior for impacts within a Froude number range of 0–10. Results. The measured penetration depth and collision duration for low-velocity collisions are comparable when the impact parameters are scaled by the Froude number, and the presented model predicts the collision behavior well within the tested Froude number range. If the impact Froude number is low (0 < Fr < 1.5), the collision occurs in a regime that is dominated by a depth-dependent quasi-static friction force. If the impact Froude number is high enough (1.5 < Fr < 10), the collision enters a second regime that is dominated by inertial drag. Conclusions. The presented collision model can be used to constrain the properties of a granular surface material using the penetration depth measurement from a single impact event. If the projectile size, the collision velocity, the gravity level, and the final penetration depth are known and if the material density is estimated, then the internal friction angle of the material can be deduced.

Dense shearing flows of soft, frictional cylinders.

We perform discrete numerical simulations at a constant volume of dense, steady, homogeneous flows of true cylinders interacting via Hertzian contacts, with and without friction, in the absence of preferential alignment. We determine the critical values of the solid volume fraction and the average number of contacts per particle above which rate-independent components of the stresses develop, along with a sharp increase in the fluctuations of angular velocity. We show that kinetic theory, extended to account for a velocity correlation at solid volume fractions larger than 0.49, can quantitatively predict the measured fluctuations of translational velocity, at least for sufficiently rigid cylinders, for any value of the cylinder aspect ratio and friction investigated here. The measured pressure above and below the critical solid volume fraction is in agreement with a recent theory originally intended for spheres that conjugates extended kinetic theory, the finite duration of collisions between soft particles and the development of an elastic network of long-lasting contacts responsible for the rate-independency of the flows in the supercritical regime. Finally, we find that, for sufficiently rigid cylinders, the ratio of shear stress to pressure in the subcritical regime is a linear function of the ratio of the shear rate to a suitable measure of the fluctuations of translational velocity, in qualitative accordance with kinetic theory, with an intercept that increases with friction. A decrease in the particle stiffness gives rise to nonlinear effects that greatly diminishes the stress ratio.

Dynamics of a bouncing table tennis ball from the acoustic signature using an optical fibre sensor

We describe an optical fibre-based method to estimate impact force and collision duration using time measurements recorded from acoustic signals of a table tennis ball bouncing on a table. The technique combines measurements obtained from a polarisation dependent optical fibre sensor with graphical analysis and kinetics through numerical calculations. The presented coefficient of restitution (COR), collision time, impact force, and elastic deformation during each bounce of the table tennis ball were obtained using corresponding time series measurements and numerical analysis. A peak impact force of 38.4 N was estimated for a ball of mass 2.83 g and 39.7 mm diameter dropped from a height of 31.5 cm. The impact duration for the associated bounce was 0.68 ms with a centre of gravity shift of 0.40 mm and COR of 0.88. While the observed results are unique to the ball and table surface, the approach is an attempt to fully quantify collision parameters from basic measurement and instrumentation applicable to undergraduate students. The sensor developed in this paper finds application in sports performance monitoring, infrastructural health early warning systems and pressure sensitive manufacturing processes.

The influence of gravity on granular impacts

Context. Impacts on small-body surfaces can occur naturally during cratering events or even strategically during carefully planned impact experiments, sampling maneuvers, and landing attempts. A proper interpretation of impact dynamics allows for a better understanding of the physical properties and the dynamical process of their regolith-covered surfaces and their general evolution. Aims. This work aims to first validate low-velocity, low-gravity impact simulations against experimental results, and then to discuss the observed collision behaviors in terms of a popular phenomenological collision model and a commonly referenced scaling relationship. Methods. We performed simulations using the soft-sphere discrete element method and two different codes, Chrono and pkdgrav. The simulations consist of a 10-cm-diameter spherical projectile impacting a bed of approximately 1-cm-diameter glass beads at collision velocities up to 1 m s−1. The impact simulations and experiments were conducted under terrestrial and low-gravity conditions, and the experimental results were used to calibrate the simulation parameters. Results. Both Chrono and pkdgrav succeed in replicating the terrestrial gravity impact experiments with high and comparable computational performance, allowing us to simulate impacts in other gravity conditions with confidence. Low-gravity impact simulations with Chrono show that the penetration depth and collision duration both increase when the gravity level decreases. However, the presented collision model and scaling relationship fail to describe the projectile’s behavior over the full range of impact cases. Conclusions. The impact simulations reveal that the penetration depth is a more reliable metric than the peak acceleration for assessing collision behavior in a coarse-grained material. This observation is important to consider when analyzing lander-regolith interactions using the accelerometer data from small-body missions. The objective of future work will be to determine the correct form and applicability of the cited collision models for different impact velocity and gravity regimes.

FDCR: A Full-Duplex Collision Resolution Scheme for Next-Generation Wireless LANs

Full-duplex capable wireless stations can detect incoming signals during transmission. Therefore, they can reduce channel time wasted in collisions by detecting a collision and stopping the ongoing transmission immediately. However, in collisions between full-duplex and legacy stations, even if the full-duplex station stops transmitting, the collision duration does not decrease since legacy stations cannot detect the collision. This letter proposes a novel medium access control scheme, called FDCR, which resolves a collision between full-duplex and legacy stations. FDCR provides collision resolution without modifying the 802.11 standard of legacy stations. When a collision occurs, the full-duplex station reports information on the colliding stations to the access point. Then transmission opportunity is granted to them. The analytical model and simulation results show that the throughput of FDCR outperforms existing studies.

Impact of an ice particle onto a dry rigid substrate: Dynamic sintering of a residual ice cone

Ice particle impact onto a cold dry rigid substrate leads to particle deformation and breakup. If the impact velocity is high enough, the deformation is governed mainly by inertial and plastic stresses. Particle deformation may lead to the development of multiple cracks and the formation of a fragmented particle zone in the vicinity of the target surface. Moreover, a small solid residual ice cone, formed from fine particle fragments, remains attached to the substrate.In the present study the normal impact of nearly spherical ice particles, their deformation and fragmentation are observed using a high-speed video system. The size and mass of the residual ice cone are measured for impact velocities ranging from 11.2ms-1 to 73.2ms-1 and initial particle diameters ranging from 1.89mm to 4.44mm.A theoretical model for the ice particle collision and deformation is used to estimate the residual ice cone size. The model is based on a hydrodynamic approach describing particle deformation and is able to predict well the maximum radius of impression and the collision duration. The radius of the impression is used as the main length scale for an empirical model for the geometry of the residual ice cone.

A new discontinuous impact model with finite collision duration

In the work it is proposed a new discontinuous impact model based on the restitution coefficient and the finite duration of the collision, which are functions of the velocity before the collision. The model was validated during modelling, experimental and simulation studies of the bifurcation dynamics of an oscillator of one-degree-of-freedom with a one-sided limiter. The simulation results using the new discontinuous impact model were compared with numerical solutions obtained with the use of the continuous five-parameter Hunt-Crossley model assuming the obstacle compliance. It was shown that the new discontinuous model produces results that are as realistic and consistent with the experimental data as the compliant impact model. Moreover, the significance of the dependence of the restitution coefficient on the speed before the collision and the contact time during the collision in obtaining a good agreement of the simulation results with the experimental data were shown.

Transoral Robotic Surgical Proficiency Via Real-Time Tactile Collision Awareness System.

In 2009, the Food and Drug Administration approved the use of the surgical robotic system for removal of benign and malignant conditions of the upper aerodigestive tract. This novel application of robotic-assisted surgery, termed transoral robotic surgery (TORS), places robotic instruments and camera system through the mouth to reach recessed areas of the pharynx and larynx. Over the successive decade, there was a rapid adoption of TORS with a surgical growth rate that continues to increase. Despite the rapid clinical acceptance, the field of TORS has not yet seen substantive changes or advances in the technical shortcomings, the lack of which has restricted objective TORS-specific surgical skills assessment as well as subsequent skills improvement efforts. One of the primary technical challenges of TORS is operating in a confined space, where the robotic system is maneuvered within the restrictive boundaries of the mouth and throat. Due to these confined boundaries of the pharynx, instruments can frequently collide with anatomic structures such as teeth and bone, producing anatomic collisions. Therefore, we hypothesized that anatomic collisions negatively impact TORS surgical performance. Secondarily, we hypothesized that avoidance of unwanted anatomic collisions could improve TORS surgical proficiency. Design and fidelity testing for a custom TORS training platform with an integrated anatomic collision-sensing system providing real-time tactile feedback is described. Following successful platform assembly and testing, validation study using the platform was carried through prospective surgical training with trial randomization. Twenty otolaryngology-head and neck surgery residents, each trainee performing three discrete mock surgical trials (n = 60), performed the initial system validation. Ten of the 20 residents were randomized to perform the surgical trials utilizing the real-time feedback system. The remaining 10 residents were randomized to perform the surgical trials without the feedback system, although the system still could record collision data. Surgical proficiency was measured by Global Evaluative Assessment of Robotic Skills (GEARS) score, time to completion, and tumor resection scores (categorical scale ranging 0-3, describing the adequacy of resection). Major anatomic collisions (greater than 5N of force) negatively affected GEARS robotic skills. A mixed model analysis demonstrated that for every additional occurrence of a major collision, GEARS robotic skills assessment score would decrease by 0.29 points (P = .04). Real-time collision awareness created significantly fewer major (> 5 N) anatomic collisions with the tactile feedback system active (n = 30, mean collisions = 2.9 ± 4.2) as compared with trials without tactile feedback (n = 30, mean collisions = 12.53 ± 23.23) (P < .001). The second assessment measure of time to completion was unaffected by the presence of collisions or by the use of tactile feedback system. The third proficiency assessment was measured with tumor resection grading. Tumor resection scores was significantly (P = .02) improved with collision awareness system activated than trials without collision awareness. In order to test our primary hypothesis, a novel TORS training platform was successfully developed that provides collision force measurements including frequency, severity, and duration of anatomic collisions. Additionally, the platform was modulated to provide real-time tactile feedback of the occurrence of out-of-field collisions. Utilizing this custom platform, our hypothesis that anatomic collisions during TORS diminishes surgical performance was supported. Additionally, our secondary hypothesis that subsequent reduction of anatomic collisions improves TORS proficiency was supported by the surgical trial. Dedicated investigation to characterize the effect size and clinical impact is required in order to translate this finding into training curriculums and into clinical utilization. II (Randomized trial) Laryngoscope, 130:S1-S17, 2020.