Head-on Encounter Research Articles

Ship Hydrodynamics of Several Typical Scenes During Inland Waterway Transport

Environmental effects on ship hydrodynamics during inland waterway transport are investigated using both CFD (Computational Fluid Dynamics) and towing tank experiments. Three important scenes, the confinement effect of the waterway, head-on encounter and ship-bridge pier interactions are studied. The testing conditions cover a wide range, including various channel dimensions, water depths, ship draughts and speeds. The ship resistance, wave pattern, Kelvin angle and wave elevations are investigated as functions of these parameters.

ATC Separation Assurance for RPASs and Conventional Aircraft in En-Route Airspace

Remotely-piloted aircraft systems (RPASs) present interesting and complex challenges for air traffic management. One of the most critical aspects of the integration of RPASs in non-segregated airspace is safety assessments. This paper lays out a methodology for estimating the minimum protection distance (MPD) that is required to avoid potential conflicts between RPASs and conventional aircraft. The MPD determines the final moment that air traffic control may instruct a RPAS to start climbing with a fixed rate of climb (ROC) to avoid separation minima infringement. The methodology sets out a conflict-resolution algorithm to estimate the MPD. It also models the impact of communication, navigation, and surveillance requirements on the MPD. The main difference between RPASs and conventional aircraft is that the former needs additional communication between the RPAS and pilot in the form of a required Comand and Control link performance (RLP). Finally, the authors carried out Monte Carlo simulations to estimate the value of the MPD only for the head-on encounter, which is the worst scenario. The results showed that the main factors affecting the MPD were RLP and ROC. By increasing RLP and decreasing ROC it was possible to reduce the MPD from 28 to 17 nautical miles; however, the variation in the MPD was not linear.

Avoiding traffic jams: Hitchhiking behavior as a strategy to reduce ant workers’ traffic on the foraging trail

During foraging, thousands of leaf-cutting ant workers travel along high traffic foraging trails which, when narrow, reduce the leaf delivery rate due to the reduction in workers’ travel-speed. On the other hand, high worker traffic promotes head-on encounters which are supposed to mediate worker task allocation and so could constitute a cue which induces traffic reduction. Very small workers along trails, for example, could change their task between marking the trail chemically to hitchhiking. Since they assume the hitchhiker function even in the absence of phorid parasitoids, one can suppose that hitchhiker behavior could be a strategy mediated by head-on encounters to avoid the high density of workers. Thus, we studied how the variation of worker density on the trail influences the hitchhiker frequency, testing the hypothesis that very small workers climb on the transported leaves to reduce trail traffic. Therefore, five Acromyrmex subterraneus colonies were linked to a foraging area by trails of different width (1.5 or 3 cm). We counted the number of hitchhikers and the outbound worker flow. The frequency of hitchhikers increased along narrow trails, and also due to outbound workers in both trail widths. Regardless of outbound foraging flow being comparable in both trail widths, the narrower ones had high density of workers leading to a presumed increase in head-on encounters. Head-on encounter rates cause a reduction in travel speed and, furthermore, are regulatory factors of task-allocation. Thus, high density trails lead to an increase in the rate of head-on encounters which could constitute as a stimulus to task-allocation of very small workers to the function of hitchhiker to avoid traffic jams.

Bi-directional movement characteristics of Camponotus japonicus ants during nest relocation.

Foraging and nest relocation forming a bi-directional traffic of outbound and inbound individuals in one-lane organization are two main activities in an ant's life. In this paper, we conducted an experiment on nest relocation of loaded and unloaded ants, moving back and forth between the old nest and the new one. In the experiment, we observed both uni- and bi-directional traffic flow. The headway-speed relationships indicate that the ants showed the same sensitivity to the distance headway in the two types of flow. For bi-directional traffic flow, head-on encounters and giving-way behavior between ants moving in opposing directions were a common occurrence. It took one unloaded ant 2.61s to solve a head-on encounter with another unloaded ant. Compared with unloaded ants, loaded ants had a lower moving speed, but were less likely to be impacted by a head-on encounter. In the observation region, both sudden stop and head-on encounters contained two phases: deceleration and acceleration. Our analysis indicates that the relaxation time in the deceleration process is less than that in the acceleration process. The reduction of movement efficiency of encountering two discontinuous ants is larger than that when encountering two successive ants (0.18). This is owing to the absence of head-on encounters with following ants. The bi-directional traffic of ants under experimental conditions investigated in this study may inform future studies of high-efficiency movement in collective behavior and traffic systems.

On Vessel to Vessel Interaction during Head-on encounter

Interaction of two vessels during head-on encounter acts as short and strong force. Consequences can reflect on vessels’ handling causing unwanted effects. This phenomenon was elaborated in the paper, considering influence of interaction force and its dependence on main recognized factors: mutual vessels’ distance, speed and depth under the keel. Besides interaction force components, analyses comprised other relevant factors as vessel’ heading, course alterations and drift of vessel due to interaction. Planned and, according to main factors, defined scenarios were conducted in navigational simulator with usage of navigational areas creation tools. After simulations and data post-processing, obtained results were summarized. Correlation of results with mathematical relations describing interaction was conducted. In the conclusion chapter, final inferences are stated, with some of observations which in the opinion of authors are significant. Conducted analyses, obtained results and derived conclusions represent basis for further research, thus future activities regarding interaction phenomenon are proposed.

Behavior of luminous matter in the head-on encounter of two ultralight BEC dark matter halos

Within the context of ultralight BEC dark matter, we analyze the head-on encounters of two structures. These structures are made of a BEC component, which is a ground state equilibrium solution of the Gross-Pitaevskii-Poisson system, together with a component of luminous matter. The evolution of the Condensate dark matter is carried out by solving the time dependent GPP equations, whereas the luminous matter is modeled with particles interacting gravitationally on top of the BEC dark matter halos. We track the evolution of frontal encounters for various values of the collision velocity and analyze the regime of high velocity regime showing solitonic behavior of the BEC halos and that of slow velocities producing a single final structure. We measure the relative velocity of the dark matter with respect to the luminous matter after the encounters in the solitonic case and track the evolution of luminous matter in the case of merger.

Numerical simulation of hydrodynamic interaction produced during the overtaking and the head-on encounter process of two ships

Purpose Based on past studies on the bank effect, the purpose of this paper is to use hydrodynamic principles to simulate the overtaking and the head-on encounter phenomenon of two ships.

Information transfer in head-on encounters between leaf-cutting ant workers: food, trail condition or orientation cues?

Living in large societies involves costs associated with high density of individuals, but being near others includes the benefit of access to conspecifics' information. High densities of workers in ant colonies impose traffic congestion costs on foraging trails. It has been postulated that crowding also increases foraging efficiency by facilitating information transfer between workers in head-on encounters. However, this hypothesis remains untested. Here we assessed, in 24 field nests of the leaf-cutting ant Atta cephalotes, whether head-on encounters between workers facilitate information transfer about trail condition, orientation and food. Several experimental manipulations failed to fit predictions of certain types of communication. (1) Trail disturbance (and thus potential need for information transfer) did not affect the rate of head-on encounters, (2) head-on encounters did not decrease the time required for laden ants to properly orient when entering a trail, and (3) ants that had been experimentally disoriented did not increase the number of head-on encounters when they returned to the trail. Nevertheless, one experiment strongly suggested information acquisition: (4) outbound ants were more likely to find and collect food after a head-on encounter with an ant carrying the same kind of food. These results do not support the hypotheses that workers exchange information about trail condition and orientation in head-on encounters, but suggest that workers acquire food information. The information transferred in head-on encounters could thus increase foraging efficiency under crowded conditions. The cost of the reduced speed due to worker collisions might be outweighed by the benefits of information acquisition, and could explain why leaf-cutting ants do not form distinct lanes of outbound and returning workers. Our results reinforce the key role of information use in the adaptive behaviour of animals and in the maintenance of group living.

Modeling the excluded volume effect between the chains in linear polymers

A model of dodging (random) walk is proposed for the excluded volume effect between the chains in linear polymers, and computer simulations were performed for four model systems. The calculated results indicate that: (1) the relationship between the end-to-end distance of the coils 〈R2〉 and the walk steps N is still linear, same as that of the random coil; (2) but the coil size is suppressed compared with that of the random coils; and (3) the suppression of the coil size produced by dodging in the case of headon encounter is stronger than that in the case of walking abreast.

Head-on encounter rates and walking speed of foragers in leaf-cutting ant traffic

Trail traffic of the leaf-cutting ant Atta cephalotes involves intermingled flows of outbound and returning foragers. Head-on encounters between workers from the opposite flows are a common occurrence in this traffic. Each encounter momentarily delays the two ants involved, and these small delays might pose a significant cost to the colony's foraging performance when summed over thousands of workers along many metres of trail. We videotaped outbound and returning foragers over a 1 m course, and measured the encounter rates they experienced and their velocity. Our analysis indicates that locomotion speed is diminished by increasing encounter rate, but that the effect is small relative to the effects of ant body size and load mass. Head-on encounters allow exchange of information and leaf fragments between workers, and we consider how the benefits of such encounters may make this form of traffic organization superior to segregated outbound and returning lanes, despite the measurable c ost of encounters in mixed traffic.

To see and not be seen:the visibility of predator and prey with respect to feeding behaviour

The visibility of herring Clupea harengus and mysids Praunus flexuosus was studied in the shallow water of the Kiel Fjord (Baltic Sea). The apparent brightness contrast of the predator (hernng) and its prey (mysid) were measured from various visual angles with a n underwater video system. The camera looked at the prey from the predator's point of view and vice versa. During a head-on encounter, the contrast of the prey against the ocean background was very poor. With increasing visual angles (relative to a horizontal plane), the visibility of the prey unproved. The predator was most visible from below, but was excellently camouflaged when observed from above or from a horizontal line of vision. When the herring was located 30 to 90' below the mysid, the prey was fairly visible to the predator but the predator was nearly invisible to the prey. By incorporating these ocean optics and taking into account the limits of the maneuvering potential of cruis~ng herring, an optimal attack angle can be postulated: a t oblique predator-prey configurations between 30 and 60°, herring are still capable of modulating their normal cruising to an upward directed position while the preconditions of a successful attack to see and not to be seen are fulfilled. In Kiel Aquarium, adult herring attacked mysids from an average angle of 48 from below. In sltu measurements from inside a feeding school of juvenile herring showed a mean attack angle of 43

The goose chase

The case of a farmer chasing his stray goose is considered from the point of view of a physicist. It is shown that the best strategy for capturing the goose is to arrange for a head-on encounter. The physics involved fits well in an upper level mechanics course, and helps to elucidate several important concepts.

Stagnation-point pressure on a body in flight as the result of a head-on encounter with a shock wave

Stagnation-point pressure on a body in flight as the result of a head-on encounter with a shock wave

The diffraction of blast. II

The head-on encounter of a plane shock, of any strength, with a solid corner of angle π - δ is investigated mathematically, when δ is small, by a method similar to that of part I. The incident shock is found to be reflected from each face as a straight segment, the two segments being joined by a shorter curved portion. Behind each straight segment is a region of uniform flow, the two regions being joined by one of non-uniform flow, bounded by arcs of a circle with centre at the corner, which expands at the local speed of sound, and by the shock, which is curved only where intersected by the said circle. The pressure is approximately equal in the two regions of uniform flow, but is less in the region of non-uniform flow between them; and it is found that if the deficiency of pressure therein, divided by the angle δ and by the excess of pressure behind the reflected shock over that of the atmosphere, be plotted at points along the solid surface, after the incident shock has travelled a given perpendicular distance beyond the corner, then the curve is independent of δ and of the precise angle of incidence of the shock, and changes remarkably little in the whole range of incident shock strengths from 0 to ∞ (see figures 5 to 8). It is suggested that some of the above qualitative conclusions may be true even if δ is not small. The case δ<0, when the corner is concave to the atmosphere, is also considered. Shock patterns are found in cases when the incident shock has already been reflected from one, or both, walls before reaching the corner (figures 9 to 11).