In this paper we propose a new clustering based data gathering mechanism for large scale wireless sensor networks. Our proposed mechanism first stores the locations of the sensors by GPS information and then sends a mobile data-collector (which can be an autonomous robot or a vehicle equipped with a transceiver and battery) which can move into the whole sensing field like a movable base station and collect data from the static sensors. Here at first our algorithm divides the region into a number of compact regions according to the range of the mobile collector and then determines a geometrical routing path along which the mobile collector can move and collect data from the sensors all in single hop data transmission technique and in minimal time. In wireless sensor networks, the data packets are directly gathered without relays and collisions. As a result, the lifetime of the sensors are prolonged. In our algorithm we have focused mainly on the facts like maximizing the network coverage, minimizing the overlapping of the regions , maximizing the number of nodes getting attended in one poll by the mobile collector and minimizing the path length so that the collector can cover the whole region in minimum time. The simulation results show a significant improved performance of proposed model.
In the present work, a detailed investigation in the wake region of the flow for the case of a two dimensional, laminar, incompressible flow past a rotating and translating circular cylinder has been carried out by applying a second order time accurate finite difference method using primitive variable formulation for different values of α ranging between 0 and 8 for Re = 200, where α is a nondimensional peripheral velocity of the cylinder. It has been observed that lift coefficient increases monotonically with α. But the effect of rotational speed on the steadiness of the flow is found significantly critical. Within the present range of α it is found that there have been back and forth regimes of unsteadiness in the flow. The flow remains unsteady for α ≤ 1.95, becomes steady for 1.95 ≤ α ≤ 4.33 and is unsteady again for 4.33 ≤ α ≤ 4.73. For α > 4.73 the flow is again steady. It is found that while the first steady regime of flow is characterised by two oppositely rotating static vortices, the second steady regime is characterised by only one rotating static vortex wrapping around the cylinder. It is also found that the nature of two unsteady regimes are not same. Detailed investigation reveals that in the first mode of vortex shedding, vortices are shed alternatively from both top and bottom surfaces, while in the second mode, the shedding occurs only from the bottom surface. Investigation also explains the cause behind increase of lift, decrease of drag with respect to α. From FFT analysis it can be concluded that lift curves corresponding to the first unsteady regime are simple sinusoidal waves, while those corresponding to the second unsteady regime are combinations of different harmonics. On the other hand, simple sinusoidal nature of the drag variation is found only when α is zero. By tracking the vortex shedding process closely, it is observed that during the process of formation, a small anticlockwise vortex is formed inside a large anticlockwise wrapping vortex around the cylinder to result into a higher pressure stagnation region just below the cylinder which in turn, effects maximum lift and detaches the small vortex from the lower surface of the cylinder resulting into vortex shedding from the bottom surface.
In the present work, two dimensional flow simulations have been performed to study the effect of tangential blowing on the drag force for the case of flow around a circular cylinder only at Reynolds number (Re) 200. Blowing ports have been placed symmetrically with respect to the horizontal flow axis. The effect of blowing on the boundary layer has been studied with respect to the intensity of blowing as well as port position of blowing. For a particular intensity of blowing, oscillations of the front stagnation point and the separation point was studied. It was found that oscillation frequencies were identical with that of lift coefficient. It was also observed that with the increase of the intensity of the blowing the position of the separation point shifts downstream (separation delay)thus the wake becomes narrower resulting the decrease of drag. Strouhal number was found to increase with the intensity of blowing. It was observed that the Strouhal number as well as the position of the separation point is influenced by the position of the blowing port. Although, for a significant range of the blowing port positions the Strouhal number is observed to be constant. Drag was found to be influenced by the position of the blowing ports. Pressure drag was found to be more significant. Thus total drag is influenced primarily by the pressure drag. It was observed that in the range of 40° to about 110° for the position of the blowing port drag decreased. But beyond 110° it increased again.
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