在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-...在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE802.11DCF和IEEE802.11eEDCA机制.展开更多
研究如下一类p-Laplace方程多点边值问题的数值计算方法(Φ_p(u′))′+f(t,u)=0,t∈(0,1),u′(0)=sum from 1 to (m-2)(b_iu′(ξ_i)),u(1)=sum from 1 to (m-2)(a_iu(ξ_i)).构造一类差分格式,并对该差分格式进行误差分析和数值实验....研究如下一类p-Laplace方程多点边值问题的数值计算方法(Φ_p(u′))′+f(t,u)=0,t∈(0,1),u′(0)=sum from 1 to (m-2)(b_iu′(ξ_i)),u(1)=sum from 1 to (m-2)(a_iu(ξ_i)).构造一类差分格式,并对该差分格式进行误差分析和数值实验.结果表明,所给出的计算方法有效.展开更多
By discretizing the convection terms with AUSM+-up scheme in the rotating coordinate system,a finite volume analysis code based on multi-block structured grids was developed independently so as to realize the numerica...By discretizing the convection terms with AUSM+-up scheme in the rotating coordinate system,a finite volume analysis code based on multi-block structured grids was developed independently so as to realize the numerical solving of internal flow fields of turbomachineries.Taking an unshrouded radial impeller with the working fluid of water vapour as the research object,the flow response to the fluctuation of rotational speed was calculated.By comparing the surface pressure profiles and velocity contours calculated by the code and commercial software respectively,the accuracy of flow solver was verified.The analysis of flow response data indicates that,as the working condition shifts closer towards the surge boundary,the response of flow parameters such as mass flow and aerodynamic torque will be more nonsynchronous with the fluctuation of rotational speed,and also the influence of density variation on mass flow variation will be smaller.Moreover,the transient variation region of working condition performance will deviate farther away from the steady performance curve as the working condition approaches the surge boundary.Compared to the working conditions with small mass flows,the distribution characteristics of pressure difference load on the blade surface vary little under large mass flow conditions.The reduction of fluctuation amplitude of rotational speed exerts no influence on abating the hysteresis of flow response.展开更多
文摘在无线局域网中提供服务质量(QoS)保证的MAC算法应该满足业务区分服务的要求和系统性能的整体最优.以往的此类自适应MAC算法依赖于对不同级别的竞争业务数目进行估计,计算过于复杂.提出一种基于QoS区分的自适应p-persistentMAC算法,QDA-MAC(QoS differentiation based adaptive MAC scheme).该算法引入了新的参数-坚持因子(persistent factor),其优化值能够实时反映网络负载的变化情况,结合近似优化的自适应方法,每次发送尝试后,该算法不需要估计每类竞争业务的数目,利用坚持因子的优化值实时更新各类优先级业务的发送概率,调整相应的协议参数,系统的性能也能接近最优.仿真结果验证了该算法不仅能够根据竞争业务数目的变化对系统的性能进行整体优化,而且能够提供业务区分服务,在QoS区分的基础上可以为实时业务提供严格的QoS保证,尤其在信道利用率和时延等方面明显优于标准的IEEE802.11DCF和IEEE802.11eEDCA机制.
文摘研究如下一类p-Laplace方程多点边值问题的数值计算方法(Φ_p(u′))′+f(t,u)=0,t∈(0,1),u′(0)=sum from 1 to (m-2)(b_iu′(ξ_i)),u(1)=sum from 1 to (m-2)(a_iu(ξ_i)).构造一类差分格式,并对该差分格式进行误差分析和数值实验.结果表明,所给出的计算方法有效.
基金supported by the National Key Basic Research Program of China (No.2012CB026000 )the National Science Foundation for Young Scientists (No.2014011155)
文摘By discretizing the convection terms with AUSM+-up scheme in the rotating coordinate system,a finite volume analysis code based on multi-block structured grids was developed independently so as to realize the numerical solving of internal flow fields of turbomachineries.Taking an unshrouded radial impeller with the working fluid of water vapour as the research object,the flow response to the fluctuation of rotational speed was calculated.By comparing the surface pressure profiles and velocity contours calculated by the code and commercial software respectively,the accuracy of flow solver was verified.The analysis of flow response data indicates that,as the working condition shifts closer towards the surge boundary,the response of flow parameters such as mass flow and aerodynamic torque will be more nonsynchronous with the fluctuation of rotational speed,and also the influence of density variation on mass flow variation will be smaller.Moreover,the transient variation region of working condition performance will deviate farther away from the steady performance curve as the working condition approaches the surge boundary.Compared to the working conditions with small mass flows,the distribution characteristics of pressure difference load on the blade surface vary little under large mass flow conditions.The reduction of fluctuation amplitude of rotational speed exerts no influence on abating the hysteresis of flow response.
