This article studies the strategic access of single-server retrial queue with two types of customers, where priority is given according to their category. On the basis of this concept, a cognitive-radio network was developed as retrial queue with energy harvesting. Cognitive radio allows for a secondary user to opportunistically access the idle spectrum of a primary user (PU). Upon arrival of a primary user, the service given to the secondary user by the cognitive radio is interrupted, and the PU band is available for the primary user. After completion of service for the primary user, the PU band is again available to secondary users. Performance metrics are derived to study the equilibrium strategies of secondary users. A Stackelberg game was formulated and Nash equilibrium was derived for the noncooperative strategy of the secondary user. Game-theory concepts are incorporated with queuing theory ideas to obtain the net benefit for the noncooperative strategy and social benefit for cooperative strategy. Lastly, analytical results are verified with numerical examples, and the effects of energy-harvesting rate are discussed.
Pipe-soil interaction behavior in the axial direction is an important design parameter for offshore pipe design. Governed primarily by the axial interaction behavior, the thermal expansion of the pipe wall could cause the pipe to either freely expand, or buckle on the founded seabed. Therefore, it emphasized that by controlling the axial interaction behavior, the overall pipe on-bottom stability can be effectively managed. This paper presents laboratory experiments performed at Monash University to understand the pipe-soil interaction behavior in the axial direction. A special 2-D actuator test setup was developed to study axial walking of pipe on clay seabed under both drained and undrained loading conditions. The effect of pipe loading rate, pipe embedment, and shutdown cycles on axial friction force were explored. Based on the experimental results, the pre-peak, peak and residual components of the axial force-displacement curve were identified and explained using a simplified theoretical framework.
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