Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currentl...Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currently a hot topic in hydraulics research.The present study addresses this question.The various formulae used for bulk velocity estimation in previous work were reviewed and compared.The main novelty of this paper is that a new expression of friction factor is proposed as a function of two dimensionless factors,and the number of tuning parameters is less than that in previous work.A comparison of measured and calculated data was conducted for flow through submerged rigid and flexible vegetation.The comparison showed that the proposed new model can make more accurate predictions than previous models.It is envisaged that the proposed formulation can be usefully employed in eco-hydraulics predictions.展开更多
In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wid...In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wide-band spectrum sensing because of hardware limitations. However,cooperation among cognitive users may provide a way to do so. In this paper,we consider such a cooperative wide-band spectrum sensing problem with each of the cognitive users able to imperfectly sense only a small portion of spectrum at a time. The goal is to maximize the average throughput of the cognitive network,given the primary network's collision probability thresholds in each spectrum sub-band. The solution answers the essential questions:to what extent should each cognitive user cooperate with others and which part of the spectrum should the user choose to sense? An exhaustive search is used to find the optimal solution and a heuristic cooperative sensing algorithm is proposed to simplify the computational com-plexity. Inspired by this optimization problem,two practical cooperative sensing strategies are then presented for the centralized and distributed cognitive network respectively. Simulation results are given to demonstrate the promising performance of our proposed algorithm and strategies.展开更多
基金Supported by the National Key Research and Development Program of China(Grant No.2019YFD1100205)the National Natural Science Foundation of China(Grant Nos.51809286,51809288).
文摘Vegetation is of great significance in river ecosystems in terms of hydrodynamics,water environment and ecology.The question of how to predict the bulk velocity in channel flow through submerged vegetation is currently a hot topic in hydraulics research.The present study addresses this question.The various formulae used for bulk velocity estimation in previous work were reviewed and compared.The main novelty of this paper is that a new expression of friction factor is proposed as a function of two dimensionless factors,and the number of tuning parameters is less than that in previous work.A comparison of measured and calculated data was conducted for flow through submerged rigid and flexible vegetation.The comparison showed that the proposed new model can make more accurate predictions than previous models.It is envisaged that the proposed formulation can be usefully employed in eco-hydraulics predictions.
基金supported in part by the National Basic Research Program (973) of China (No. 2009CB320405)the National Natural Science Foundation of China (No. 60972057)the National High-Tech Research and Development Program (863) of China (No. 2007AA 01Z257)
文摘In cognitive radio systems,the design of spectrum sensing has to face the challenges of radio sensitivity and wide-band frequency agility. It is difficult for a single cognitive user to achieve timely and accurate wide-band spectrum sensing because of hardware limitations. However,cooperation among cognitive users may provide a way to do so. In this paper,we consider such a cooperative wide-band spectrum sensing problem with each of the cognitive users able to imperfectly sense only a small portion of spectrum at a time. The goal is to maximize the average throughput of the cognitive network,given the primary network's collision probability thresholds in each spectrum sub-band. The solution answers the essential questions:to what extent should each cognitive user cooperate with others and which part of the spectrum should the user choose to sense? An exhaustive search is used to find the optimal solution and a heuristic cooperative sensing algorithm is proposed to simplify the computational com-plexity. Inspired by this optimization problem,two practical cooperative sensing strategies are then presented for the centralized and distributed cognitive network respectively. Simulation results are given to demonstrate the promising performance of our proposed algorithm and strategies.
