Leader Path Research Articles

A26 フォロアの初期移動を考慮したリーダ追従型隊列誘導(OS10 分散・協調・フォーメーション)

In this paper, we discuss the leader-following formation navigation (LFFN), which is one of the most important issues in formation control. In this formation, one leader is controlled by a human operator, while multiple followers pass along the leader's trajectory in the same motion to the leader. The collision avoidance problem in the LFFN has been discussed in a previous work. However, the problem of initial movements of followers still remains. The followers move along the leader's path behind the leader at some intervals. Thus, around the initial time, the followers cannot determine routes to track because there is no leader's path before the initial time. This paper discusses how the followers should move around the initial time in order to start up naturally and to achieve the LFFN afterwards. The effectiveness of the proposed method is demonstrated by a simulation with three mobile robots.

Lightning path simulation based on the stepped leader: Electrical conductivity effects

A numerical simulation for the stepped leader path in the earth atmosphere has been developed to study the influence of the tropospheric electric conductivity on the lightning behaviour. This model is based on the assumption that the leader path follows the gradient of the electric potential. In the model, the charge configuration (amount of charge and location), the variation of the atmospheric conductivity, the charge deposited along the leader channel and the charge at the leader tip are considered. A perfectly conducting ground surface and a curl-free electric field assumption are considered too. The result of the simulation is that the inclusion of an atmospheric conductivity of exponentially increasing value with height alters the percentage of positive cloud-to-ground flashes compared to that percentage obtained assuming a constant conductivity profile. A higher amount of positive flashes occur for high altitude (low latitude) clouds even in the case of little horizontal displacement between the positive and the negative dipole charges in the cloud, that is, with no significant wind shear in the horizontal wind. The simulation has shown that positive lightning, the most dangerous kind, can occur in clear air at great distances from the thundercloud, with safety risk implications.

Initiation and development of first lightning leader: The effects of coronae and position of lightning origin

This paper addresses, by means of numerical simulations, the issues of lightning initiation near tall, grounded objects and lightning development in the cloud-to-ground gap. Taken into account is the effect of coronae on the initiation of an upward leader from the top of a fixed grounded structure that is exposed to the electric field produced by the storm-cloud and approaching downward leader. It is shown that the potential carried by a downward leader to the ground and, consequently, the return stroke current depend greatly on the position of a bi-directional leader origin inside a cloud and on the shape of the leader path.

Double impulse tests of long airgaps. Part 2: Leader decay and reactivation

The behaviour of large air-insulated structures subjected to complex multiple-peak surge overvoltages is influenced by the presence of already established leader overvoltages in influenced by the presence of already established leader development in the space. The decay processes of a positive leader channel following current interruption appear not to have been studied in detail, and Part 2 provides electrical and optical measurements of leader decay and reactivation in a 6 m rod-plane gap. It is found that, for a positive leader created by a switching impulse (SI) of critical time to crest, the leader path could be rapidly reactivated over at least part of its length by a second voltage application at times of up to about 1 ms after its original formation. For longer times, new leader growth may still retrace the original basic leader path. The temporal and spatial characteristics of the reactivated leader are substantially different from those of the basic leader. The causes of the large statistical variation in behaviour are discussed. The results presented should provide the basis for improved physical knowledge of the leader and corona processes, and contribute to improved engineering models for insulation co-ordination.

The Mechanism of the High Velocity of Propagation of Lightning Discharges

Observations by Schonland and Collens with Boys' camera show that the luminous tip of the leader stroke of the lightning discharge advances with a high velocity sometimes exceeding 3×109 cm per second. From the fact that electrons traveling 109 cm per second produce about 6000 new electrons per cm of actual path and that 6000 new electrons per cm in the direction of the field (i.e., α=6000) requires 4×106 volts per cm shows that to give the electrons a velocity in the direction of the field of 109 cm per second would require a field exceeding 4×106 volts per cm even at the tip of the stroke. The fields, and therefore the electron velocities, are certainly far less than this value. Accordingly the velocity of the tip greatly exceeds the velocity of the electrons in the tip. It is possible to account for this velocity as follows: Calculations based on justified assumptions concerning the conditions known to exist in a lightning stroke show that if the field just ahead of the tip averages 105 volts per cm for about one centimeter, ionization by collision by the electrons present in the gas before the stroke would be great enough to advance the tip at the observed rate. Such a field is found not too high to be consistent with the low conductivity of the leader path. In this way a propagation of the leader stroke of a velocity many times higher than the velocity of the electrons can be attained.