Thermodynamic optimisation of the integrated design of a small‐scale solar thermal Brayton cycle

The Brayton cycle's heat source does not need to be from combustion but can be extracted from solar energy. When a black cavity receiver is mounted at the focus of a parabolic dish concentrator, the reflected light is absorbed and converted into a heat source. The second law of thermodynamics and entropy generation minimisation are applied to optimise the geometries of the recuperator and receiver. The irreversibilities in the recuperative solar thermal Brayton cycle are mainly due to heat transfer across a finite temperature difference and fluid friction. In a small‐scale open and direct solar thermal Brayton cycle with a micro‐turbine operating at its highest compressor efficiency, the geometries of a cavity receiver and counterflow‐plated recuperator can be optimised in such a way that the system produces maximum net power output. A modified cavity receiver is used in the analysis, and parabolic dish concentrator diameters of 6 to 18 m are considered. Two cavity construction methods are compared. Results show that the maximum thermal efficiency of the system is a function of the solar concentrator diameter and choice of micro‐turbine. The optimum receiver tube diameter is relatively large when compared with the receiver size. The optimum recuperator channel aspect ratio for the highest maximum net power output of a micro‐turbine is a linear function of the system mass flow rate for a constant recuperator height. For a system operating at a relatively small mass flow rate, with a specific concentrator size, the optimum recuperator length is small. For the systems with the highest maximum net power output, the irreversibilities are spread throughout the system in such a way that the internal irreversibility rate is almost three times the external irreversibility rate. Copyright © 2011 John Wiley & Sons, Ltd.     

大规模无等待流水调度问题的邻域迭代搜索算法

在分析大规模无等待流水调度问题特点的基础上,提出了利用相邻工件间完工时间距离求最小化完工时间的方法;通过研究工件插入和工件对的交换对最小化完工时间的影响,提出一种邻域迭代搜索算法,该算法降低了求解完工时间的时间复杂度,大大提高了算法效率;为避免算法在邻域搜索过程中陷入局部最优,将变邻域结构算法的思想应用于其中.仿真结果表明,所提出的算法能高效率解决大规模无等待流水调度问题,所得结果令人满意.     

混合流水车间的遗传算法调度策略(英文)

应用遗传算法对混合流水车间的总作业时间最小的调度问题进行了研究。混合流水车间是一类特殊的流水车间环境,但其每一级可以有多个机床。所提出的算法基于表调度原理,首先给出在第一级工件的排列顺序,并在其后的各级采用先入先出（FIFO）方式。试验表明,所提出的遗传算法调度策略优先于原有的启发式及随机搜索方法。     

机器不同时开工排序问题算法Akk的最坏情况性能比

对于经典排序中的同型机(identical machines)排序问题Pm||Cmax,1969年Graham根据Kleitman和Knuth的建议提出著名的近似算法——算法AKK。2005年李红英等对于算法AKK提出改进的最坏情况性能比。机器不同时开工排序问题Pm,ai||Cmax是经典的同型机排序问题的推广,是一种新型排序。把算法AKK用到机器不同时开工排序问题Pm,ai||Cmax上去,得到新的最坏情况性能比,并把此最坏情况性能比与Graham得到的和李红英等人得到的最坏情况性能比进行了比较。     

基于资源有效性分级的网格任务调度算法

为解决网格环境下有多QoS约束的任务调度问题,对异构环境下网格资源相对于任务的有效性进行分析,提出了资源有效性的概念,并根据有效资源的数量对所有任务分级,提出了一种分级约束下的网格任务调度算法GC-Min-Min.最后,通过一个网格任务调度仿真实验,考察了不同的有效资源比例对任务调度的影响,并将新算法与Min-Min算法进行了对比.实验结果表明,该算法有较小的任务完成时间,更适用于有多QoS约束下网格任务的调度.     

Efficient Recursive Digital Filters using Combined Look-Ahead Denominator Distribution and Numerator Decomposition

This paper presents a new efficient method for designing stable look-ahead pipelined recursive digital filters with reduced multipliers. The multiplier savings are obtained by generating pipelined transfer functions which combine numerator decomposition with look-ahead denominator distribution. This is achieved by not restricting the denominator to either the clustered or scattered forms while also preserving term count from the unpipelined filter transfer function. The coefficients of the pipelined transfer function are obtained by running product solved using matrices and an algorithm with two stages: pre and post distribution, each having a multiplier cost which are minimised independently. The proposed method can produce pipelined filter designs requiring fewer multipliers when compared with previously reported methods. For example, for a range of second order transfer functions and pipelining levels, an average 40% reduction in multipliers can be achieved while an 18% reduction in multipliers necessary for pipelining is obtained for a sixth order filter. Furthermore, the proposed two-stage algorithm can accommodate pipelined adders as well as pipelined multipliers in the recursive filter structure, avoiding delay penalties otherwise suffered by previously reported methods. A detailed analysis has been carried out confirming that filters designed using the proposed method do not suffer increased noise.     

考虑本地作业流时的网格资源调度算法

研究了网格资源上有和没有本地作业流两种情况下两种网格资源调度算法的性能优劣对比情况。建立了一个资源的本地随机作业流模型,提出了最快处理器可用资源优先(HRARF)和最适合作业并行度可用资源优先(MSNARF)两种网格资源调度算法,并对所提出的两种算法在资源有和没有本地作业流两种情况下调度网格作业的完工时间进行仿真。仿真结果显示,在资源负载较重时,在有和没有本地作业流两种情况下,HRARF和MSNARF两种算法的性能优劣对比正好相反。在网格中,两种算法在资源共享时和资源独占时的性能优劣对比可能不同。     

Accelerating DAG-Style Job Execution via Optimizing Resource Pipeline Scheduling

Journal of Computer Science and Technology - The volume of information that needs to be processed in big data clusters increases rapidly nowadays. It is critical to execute the data analysis in a...