Collision Criterion Research Articles

Coalescence time of ellipsoidal-wobbling bubbles at surfactant-free interface: Experimental analysis and collision criteria

This work experimentally analyzed bubbles' coalescence with an air-water interface in the ellipsoidal-wobbling regime for different bubble approach velocities, encompassing the ranges of Eötvös, Weber, and Reynolds numbers of 2-3, 1-4, and 500-1100, respectively. We employed high-speed imaging to measure the bubbles' size, shape, velocity, coalescence time, and number of bounces at the interface. We investigated two criteria to determine the beginning of bubble-interface interaction (“collision”): the physical criterion, based on the distance between the bubble top surface and the interface, and the hydrodynamic criterion, based on the bubble velocity. Gamma distributions represented the coalescence times of bubbles at their terminal velocities well. We found a linear relationship between the coalescence time and the number of bounces. The hydrodynamic criterion was more consistent in representing our data on coalescence time.

Collision avoidance trajectory planning for a dual-robot system: using a modified APF method

AbstractDual-robot system has been widely applied to the field of handling and palletizing for its high efficiency and large workspace. It is one of the key problems of the trajectory planning to determine the collision avoidance method of the dual-robot system. In the present study, a collision avoidance trajectory planning method for the dual-robot system was proposed on the basis of a modified artificial potential field (APF) algorithm. The interference and collision criterion of the dual-robot system was given firstly, which was established based on the method of kinematic analysis in robotics. And then, in consideration of the problem of excessive virtual potential field force induced by using the traditional APF algorithm in the process of dual-robot trajectory planning, a modified APF algorithm was proposed. Finally, the modified APF algorithm was used for motion control of a dual-robot palletizing process, and the collision avoidance performance of the proposed collision avoidance algorithm was studied through a dual-robot palletizing simulation and experiment. The results have shown that with the proposed collision avoidance trajectory planning algorithm, the two robots in dual-robot system can maintain a safe distance at all times during palletizing process. Compared with the traditional APF and rapidly-exploring random tree (RRT) algorithm, the trajectory solution time of the modified APF algorithm is greatly reduced. And the modified APF algorithm’s convergence time is 14.2% shorter than that of the traditional APF algorithm.

Post-giant impact planetesimals sustaining extreme debris discs

ABSTRACT Extreme debris discs can show short-term behaviour through the evolution and clearing of small grains produced in giant impacts, and potentially a longer period of variability caused by a planetesimal population formed from giant impact ejecta. In this paper, we present results of numerical simulations to explain how a planetesimal populated disc can supply an observed extreme debris disc with small grains. We simulated a sample of giant impacts from which we form a planetesimal population. We then use the N-body code rebound to evolve the planetesimals spatially and collisionally. We adopt a simplistic collision criteria in which we define destructive collisions to be between planetesimals with a mutual impact velocity that exceeds two times the catastrophic disruption threshold, V*. We find that for some configurations, a planetesimal populated disc can produce a substantial amount of dust to sustain an observable disc. The semimajor axis at which the giant impact occurs changes the mass added to the observed disc substantially, while the orientation of the impact has less of an effect. We determine how the collision rate at the collision point changes over time and show that changes in semimajor axis and orientation only change the initial collision rate of the disc. Collision rates across all discs evolve at a similar rate.

Simulation of Heterogeneous Particle Deposition using Digital Visual Fortran

Granular particles have unique behaviour because it can behave like solids, liquids, and gaseous subtances. So, it is necessary to discuss the dynamics of these particles. Dynamical particles involve normal force, tangential force, and gravity force. Deposition is dropping particles at a medium, it produces a pile of particles. First step of simulation is assigned collision criteria. Next step is simulation using digital visual Fortran software and the final step is to analyze it. Based on simulation, dynamic behavior of particles is seen through on video created by assembling images of simulation result. The largest particles are fallen spread to underlying medium then followed by smaller particles. It fallen on center of pile until particles below bears a much heavier than the mass of particles. The smaller particles on center of pile pushes at the bottom and it makes cavity. As a result, the pile seems to have two peaks on static condition

Simultaneous Obstacle Avoidance and Target Tracking of Multiple Wheeled Mobile Robots With Certified Safety.

Collision avoidance plays a major part in the control of the wheeled mobile robot (WMR). Most existing collision-avoidance methods mainly focus on a single WMR and environmental obstacles. There are few products that cast light on the collision-avoidance between multiple WMRs (MWMRs). In this article, the problem of simultaneous collision-avoidance and target tracking is investigated for MWMRs working in the shared environment from the perspective of optimization. The collision-avoidance strategy is formulated as an inequality constraint, which has proven to be collision free between the MWMRs. The designed MWMRs control scheme integrates path following, collision-avoidance, and WMR velocity compliance, in which the path following task is chosen as the secondary task, and collision-avoidance is the primary task so that safety can be guaranteed in advance. A Lagrangian-based dynamic controller is constructed for the dominating behavior of the MWMRs. Combining theoretical analyses and experiments, the feasibility of the designed control scheme for the MWMRs is substantiated. Experimental results show that if obstacles do not threaten the safety of the WMR, the top priority in the control task is the target track task. All robots move along the desired trajectory. Once the collision criterion is satisfied, the collision-avoidance mechanism is activated and prominent in the controller. Under the proposed scheme, all robots achieve the target tracking on the premise of being collision free.

Multiple-AGV Path Planning Method for Two Industrial Links

Nowadays, increasing automatic guided vehicles (AGVs) are being introduced into the production line. The path planning and scheduling of multiple AGVs are complex tasks that are closely related to application scenarios. In this study, a robot’s working area was divided to minimize the collision probability. Improved ant colony optimization (ACO) and improved probabilistic road map (PRM) algorithms were used for path planning to enhance the transportation efficiency. The priorities of AGVs were specified. The collision criteria were determined, and the responses for different collision types were provided.

Role of proton-antiproton regeneration in the late stages of heavy-ion collisions

We investigate the long-standing question of the effect of proton-antiproton annihilation on the (anti-)proton yield, while respecting detailed balance for the five-body back-reaction for the first time in a full microscopic description of the late stages of heavy-ion collisions. This is achieved by employing a stochastic collision criterion in a hadronic transport approach (SMASH), which is used to account for the regeneration of (anti-)protons via $5\ensuremath{\pi}\ensuremath{\rightarrow}\mathrm{p}\overline{\mathrm{p}}$. We investigate $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collisions from $\sqrt{{s}_{NN}}=17.3\phantom{\rule{4pt}{0ex}}\mathrm{GeV}\ensuremath{-}5.02$ TeV in a viscous hybrid approach. Our results show that back-reactions happen for a fraction of 15%--20% of all annihilations, independent of the beam energy or centrality of the system. The inclusion of the back-reaction results in the regeneration of half of the (anti-)proton yield lost to annihilations at midrapidity. We also find that, concerning the multiplicities, treating the back-reaction as a chain of two-body reactions is equivalent to a single 5-to-2 reaction.

Mobile Robots’ Collision Prediction Based on Virtual Cocoons

The research work presents a collision prediction method of mobile robots. The authors of the work use so-called, virtual cocoons to evaluate the collision criteria of two robots. The idea, mathematical representation of the calculations and experimental simulations are presented in the paper work. A virtual model of the industrial process with moving mobile robots was created. Obstacle avoidance was not solved here. The authors of the article were working on collision avoidance problem solving between moving robots. Theoretical approach presents mathematical calculations and dependences of path angles of mobile robots. Experimental simulations, using the software Centaurus CPN, based on colored Petri nets, has shown, that the possible conflict can be predicted in advance using calculations of the angle of movement of two possibly colliding cocoons. Authors of the paper presents and explains experimental simulations, where robots are moving in different path angles, which intersects each other. Proposed collision avoidance algorithm solves collision avoidance task using several possibilities. Software Centaurus CPN gives possibility to stop simulation of manufacturing process in the place where it finds possible collision between two cocoons. In order to check correctness of proposed collision prediction and avoidance algorithm, further simulation is done step by step, while situation is solved. Simulated manufacturing process is continued till new possible collision is obtained.

Spatiotemporal instability of a shear-imposed viscous flow

We study the linear spatiotemporal instability of a two-dimensional gravity-driven viscous fluid flow where the fluid surface is subjected to an imposed shear stress. The fourth order Orr–Sommerfeld boundary value problem is derived and solved numerically up to moderate values of the Reynolds number. Numerical solution based on AUTO07p identifies four spatial branches, viz., I, II, III, and IV, where the spatial branches I, II, and IV lie in the upper half zone, while the spatial branch III lies in the lower half zone of the complex wavenumber plane. The spatial growth rate −ki corresponding to branch I becomes stronger as long as the imposed shear stress increases and ensures a destabilizing effect. Furthermore, the spatial branch I enters in the lower half zone of the complex wavenumber plane as soon as the temporal growth rate ωi decreases and may collide with other spatial branch lying in the lower half zone of the complex wavenumber plane. Moreover, a study of absolute and convective instabilities is carried out within the frameworks of saddle point technique and collision criterion. The saddle point technique provides only one unstable branch of the unstable wavepacket, while the collision criterion provides two unstable branches of the wavepacket. The unstable range of the wavepacket with ray velocity enhances in the presence of imposed shear stress. It is observed that the shear-imposed fluid flow is convectively unstable. In addition, the simplified second order two-equation model is developed for a shear-imposed flow in terms of the local fluid layer thickness and local flow rate, which in fact renders three spatial branches rather than four. However, the two-equation model recovers the physically relevant spatial branch I very well. Finally, nonlinear spatiotemporal simulation of the two-equation model displays a formation of the regular train of solitary waves downstream at low forcing frequency.

Small-Ncollisional dynamics – V. FromN≲ 10 toN≳ 103

ABSTRACTDirect collisions between finite-sized particles occur commonly in many areas of astrophysics. Such collisions are typically mediated by chaotic, bound gravitational interactions involving small numbers of particles. An important application is stellar collisions, which occur commonly in dense star clusters, and their relevance for the formation of various types of stellar exotica. In this paper, we return to our study of the collision rates and probabilities during small-number chaotic gravitational interactions ($N\, \lesssim$ 10), moving beyond the small-number particle limit and into the realm of larger particle numbers ($N\, \gtrsim$ 103) to test the extent of validity of our analytic model as a function of the particle properties and the number of interacting particles. This is done using direct N-body simulations of stellar collisions in dense star clusters, by varying the relative numbers of particles with different particle masses and radii. We compute the predicted rate of collisions using the mean free path approximation, adopting the point-particle limit and using the sticky-star approximation as our collision criterion. We evaluate its efficacy in the regime where gravitational focusing is important by comparing the theoretical rates to numerical simulations. Using the tools developed in previous papers in this series, in particular Collision Rate Diagrams, we illustrate that our predicted and simulated rates are in excellent agreement, typically consistent with each other to within 1 standard deviation.

Multiple-vehicle collision influenced by misjudgment of space headway in traffic flow under fog weather condition

The multiple-vehicle collision easily happens under fog weather condition. To illustrate the effect of misjudgment of space headway on the multiple-vehicle collision in traffic flow, this paper derives collision criterion of the car-following model including risk illusions in fog weather (RIFM). Numerical simulations are carried out by varying driver’s sensitivity, vehicular density and initial velocity. This paper obtains the region map for the multiple-vehicle collision when a vehicle stops suddenly in traffic flow. The results indicate that although under low density conditions, the collision will happen just because of the misjudgment of space headway. In general, when drivers are affected by the misjudgment of space headway, the number of crumpled vehicles has positive correlation with initial velocity and vehicular density, and negative correlation with driver’s sensitivity. Therefore, in order to ensure traffic safety, the initial velocity and vehicular density should be reduced, and driver’s sensitivity should be increased under fog weather condition.

Towards an assistance strategy that reduces unnecessary collision alarms: An examination of the driver's perceived need for assistance.

The activation of present-day collision avoidance systems mainly depends on the time to collision (TTC) criterion. Such a warning strategy that is based on kinematic criteria alone often yields warning signals that drivers perceive to be unnecessary. To increase system effectiveness and user acceptance, the reduction of alert rates by tailoring system activation to drivers' needs is of great interest. The present driving simulator study investigated if drivers' perceived need for assistance in potential collision situations is primarily predicted by the TTC or by drivers' subjective hazard perception that was assumed to be influenced by the current maneuver intention. Thirty participants encountered traffic scenarios with varying levels of TTC. Each scenario was experienced with 2 different maneuver intentions to manipulate the relevance of the potential hazard. A multilevel moderated mediation analysis revealed that drivers' subjective hazard perception mediated the relationship between the TTC-based crash likelihood and drivers' perceived need for assistance. Additionally, the mediated relationship was significantly stronger when the hazard interfered with the intended maneuver. These results suggest that to appropriately adapt driver assistance to drivers' perceived needs, a warning strategy is required that considers TTC as well as drivers' maneuver intentions. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Identifying linear absolute instabilities from differential eigenvalue problems using sensitivity analysis

Identifying the convective/absolute instability nature of a local base flow requires an analysis of its linear impulse response. One must find the appropriate singularity in the eigenvalue problem with complex frequencies and wavenumbers and prove causality. One way to do so is to show that the appropriate integration contour of this response, a steepest decent path through the relevant singularity, exists. Due to the inherent difficulties of such a proof, one often verifies instead whether this singularity satisfies the collision criterion. In other words, one must show that the branches involved in the formation of this singularity come from distinct halves of the complex wavenumber plane. However, this graphical search is computationally intensive in a single plane and essentially prohibitive in two planes. A significant computational cost reduction can be achieved when root finding procedures are applied instead of graphical ones to search for singularities. They focus on locating these points, with causality being verified graphically a posteriori for a small parametric sample size. The use of root-finding procedures require auxiliary equations, often derived by applying the zero group velocity conditions to the dispersion relation. This relation, in turn, is derived by applying matrix forming to the differential eigenvalue problem and taking the determinant of the resulting system of algebraic equations. Taking the derivative of the dispersion relation with respect to the wavenumbers generates the auxiliary equations. If the algebraic system is decoupled, this derivation is straightforward. However, its computational cost is often prohibitive when the algebraic system is coupled. Other methods exist, but often they can also be too costly and/or not reliable for two wavenumber plane searches. This paper describes an alternative methodology based on sensitivity analysis and adjoints that allow the zero group velocity conditions to be applied directly to the differential eigenvalue problem. In doing so, the direct and auxiliary differential eigenvalue problems can be solved simultaneously using standard shooting methods to directly locate singularities. Auxiliary dispersion relations no longer have to be derived, although it is shown that they are the algebraic equivalent of the auxiliary differential eigenvalue problems obtained by this alternative methodology. Using the latter dramatically reduces computational costs. The search for arbitrary singularities is then not only accelerated in single wavenumber planes but it also becomes viable in two wavenumber planes. Finally, the new method also allows group velocity calculations, greatly facilitating the verification of causality. Several test cases are presented to illustrate the capabilities of this new method.

An Automatic Approach to Reestablish Final Dental Occlusion for 1-Piece Maxillary Orthognathic Surgery.

Accurately establishing a desired final dental occlusion of the upper and lower teeth is a critical step in orthognathic surgical planning. Traditionally, the final occlusion is established by hand-articulating the stone dental models. However, this process is inappropriate to digitally plan the orthognathic surgery using computer-aided surgical simulation. To date, there is no effective method of digitally establishing final occlusion. We propose a 3-stage approach to digitally and automatically establish a desired final dental occlusion for 1-piece maxillary orthognathic surgery, including: 1) to automatically extract points of interest and four key teeth landmarks from the occlusal surfaces; 2) to align the upper and lower teeth to a clinically desired Midline-Canine-Molar relationship by minimization of sum of distances between them; and 3) to finely align the upper and lower teeth to a maximum contact with the constraints of collision and clinical criteria. The proposed method was evaluated qualitatively and quantitatively and proved to be effective and accurate.

Wave‐Induced Surge Motion and Collisions of Sea Ice Floes: Finite‐Floe‐Size Effects

AbstractAmong many mechanisms potentially contributing to wave energy attenuation in sea ice are wave‐induced ice floe collisions. At present, little is known about collision patterns and their phase‐averaged effects under different combinations of sea ice properties (ice thickness, floe size, etc.) and wave forcing (wavelength and steepness). The existing parameterizations of collision‐related effects are therefore based on several simplifying, unverified assumptions. In this work, wave‐induced motion and collisions of ice floes are analyzed numerically with a model based on momentum equations for an arbitrary number of floes, with source terms computed by integrating local forcing (wave‐induced dynamic pressure, surface drag, etc.) over the surface area/volume of each floe. It is shown that this simple model, with prescribed wave forcing (i.e., no wave‐ice interactions), is capable of reproducing observed surge amplitudes up to floe sizes comparable with wavelength. A full Hertzian contact model is used instead of a simple hard‐disk algorithm, which makes the model suitable for simulating both rapid collisions and prolonged contact between floes. The model equations are used to formulate heuristic collision criteria based on relative floe size, ice concentration, and wave steepness. The model is then run for different combinations of those three parameters, together with different restitution and drag coefficients, in order to analyze possible motion/collision patterns within the multidimensional parameter space, and phase‐averaged effects of collisions: kinetic and contact stress, granular temperature, and work done by forces acting on the ice.

Dynamics of singlet-doublet collisions of cohesive particles

As a first step toward a more physical understanding of the outcome of collisions between cohesive agglomerates, the dynamics of a cohesive particle (singlet) impacting an agglomerate of two particles (doublet) are studied via DEM simulations. Four collision outcomes are observed in simulations, namely “agglomeration”, “bounce”, “transfer” and “breakage”. The occurrence of each outcome shows complex dependency on the pre-collisional configurations, which has four degrees of freedom that characterize the position and velocity of the singlet. Sweeping the parameter space of the pre-collisional configurations reveals the existence of oscillatory transitions across the different collision outcomes with increasing speed of the singlet, in contrast to the unique transition criterion for binary collisions. Detailed kinematical analysis indicates the oscillatory transitions are consequences of multiple, consecutive impacts between the singlet and the two particles in the doublet. By summarizing the numerical results in non-dimensional form, a general method is proposed to estimate the critical speeds of the singlet at the transition of collision outcomes. The findings provide insights on establishing closures for the kinetic theory-based continuum models coupled with population balance to predict the behavior of cohesive particles in granular and multiphase flows, which is of particular interest to engineers handling fine/wet powders where interparticle cohesion is not negligible.

Selection of the elastic scattering events in interactions of the NICA colliding proton (deuteron) beams

The features of the kinematics of elastic pp (dd ) scattering in the collider system, as well as some issues concerning registration and selection of elastic scattering events in the NICA colliding beams are considered. Equality and the opposite direction of the scattered particle momenta provide a powerful selection criterion for elastic collisions. Variants of the organization of the trigger signal for recording tracks of secondary particles and DAQ system are given. The estimates of the characteristics of elastic NN processes are obtained from available dσ /d ΩCM data for the elastic pp and np scattering. The paper presents examples of simulations using the Monte-Carlo of elastic pp scattering in the colliding proton beams and quasi-elastic np scattering in the colliding deuteron beams and evaluates the outputs of these processes at the NICA collider.

Particle production and equilibrium properties within a new hadron transport approach for heavy-ion collisions

The microscopic description of heavy-ion reactions at low beam energies is achieved within hadronic transport approaches. In this article a new approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) is introduced and applied to study the production of non-strange particles in heavy-ion reactions at $E_{\rm kin}=0.4-2A$ GeV. First, the model is described including details about the collision criterion, the initial conditions and the resonance formation and decays. To validate the approach, equilibrium properties such as detailed balance are presented and the results are compared to experimental data for elementary cross sections. Finally results for pion and proton production in C+C and Au+Au collisions is confronted with HADES and FOPI data. Predictions for particle production in $\pi+A$ collisions are made.

Collision frequency and radial distribution function in particle-laden turbulent channel flow

We performed Eulerian–Lagrangian direct numerical simulation of particle-laden channel flow at a frictional Reynolds number of 950. A fully parallelized deterministic particle collision algorithm is applied for elastic collisions between two particles and particles and the walls. A total number of 51 million mono-disperse particles is considered, resulting in a particle volume fraction close to 1×10−4. We studied the results of the simulation after a statistically steady turbulent state and particle concentration were reached. In this state the particles close to the walls are preferentially located in the low-speed streaks, whereas the particle distribution in the center of the channel is rather non-uniform as well, showing large void regions. The presence of the particles results in a decrease of the turbulence dissipation rate of 20% close to the walls. We studied in particular the particle collision frequency as a function of the wall-normal coordinate and compared the simulation results with two theoretical expressions involving the radial distribution function at contact and the mean relative velocity of two colliding particles. It appeared that the radial distribution function diverges if the distance between the particles approaches the particle diameter. This is not only caused by the drift mechanisms but also by repeated collision events, which occur relatively more often in the center of the channel. We proposed a collision criterion that distinguishes repeated collisions from single collisions, and which is easy to apply during a simulation and in the computation of the radial distribution function and the mean relative velocity of two colliding particles. Simulation results and the two theoretical expressions for the collision frequency are in good agreement if this criterion is applied.

Spatiotemporal instability of an electrified falling film.

The linear spatiotemporal response to an infinitesimal disturbance is analyzed for an electrified falling film based on the Orr-Sommerfeld boundary value problem. Four spatial branches are identified, which lose their spatial symmetry in the presence of an electric field. In addition, the absolute and convective instabilities are studied within the frameworks of the saddle point approach and the collision criterion. The collision criterion offers two unstable branches that characterize the exact range of the unstable wave packet that is diminished in the presence of an electric field. In contrast, the saddle point approach offers only one unstable branch. The associated unstable range of the wave packet is similar to that predicted by the collision criterion only when the electric field is enhanced. It is shown that the electrified falling film is convectively unstable.