Sarnak’s Disjointness Conjecture states that the Mobius function is disjoint with any zeroentropy flow. This note establishes this conjecture, with a rate, for Furstenberg’s irregular flows on the infinite-dimension...Sarnak’s Disjointness Conjecture states that the Mobius function is disjoint with any zeroentropy flow. This note establishes this conjecture, with a rate, for Furstenberg’s irregular flows on the infinite-dimensional torus.展开更多
The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine a...The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine accelerate by itself up to a certain speed for the best turbine performance. In order to clarify the self-starting characteristic and running performance of the Wells turbine in an irregular oscillating flow, a numerical simulation process is established in this paper on the rational assumption of quasi-steady flow conditions, Both self-starting characteristics and running performance are obtained through the numerical simulation and subsequently compared with the experimental data achieved on a computer-controlled oscillating flow test rig which could realize some irregular oscillating flow according to the specified spectrum. Results show that the self-starting time decreases with the increase of the significant wave height and the mean frequency of the irregular oscillating flow, Therefore, it is possible to predict accurately the performance of the Wells turbine by computer simulation.展开更多
A new algorithm to automatically extract drainage networks and catchments based on triangulation irregular networks(TINs) digital elevation model(DEM) was developed. The flow direction in this approach is determined b...A new algorithm to automatically extract drainage networks and catchments based on triangulation irregular networks(TINs) digital elevation model(DEM) was developed. The flow direction in this approach is determined by computing the spatial gradient of triangle and triangle edges. Outflow edge was defined by comparing the contribution area that is separated by the steepest descent of the triangle. Local channels were then tracked to build drainage networks. Both triangle edges and facets were considered to construct flow path. The algorithm has been tested in the site for Hawaiian Island of Kaho'olawe, and the results were compared with those calculated by ARCGIS as well as terrain map. The reported algorithm has been proved to be a reliable approach with high efficiency to generate well-connected and coherent drainage networks.展开更多
In order to improve the finite analytic method’s adaptability for irregular unit, by using coordinates rotation technique this paper establishes a five-point element scheme of finite analytic method. It not only solv...In order to improve the finite analytic method’s adaptability for irregular unit, by using coordinates rotation technique this paper establishes a five-point element scheme of finite analytic method. It not only solves unsteady groundwater flow equation but also gives the boundary condition. This method can be used to calculate the three typical questions of groundwater. By compared with predecessor’s computed result, the result of this method is more satisfactory.展开更多
为解决超低温螺杆冷冻水机组中干式蒸发器管侧R507A制冷剂分配不均匀导致的蒸发器吸气过热度低、视镜带液及制冷量不足等问题,基于制冷循环系统工艺流程,构建并阐述了蒸发器管侧制冷剂的气-液两相时空演变流动机理。基于气-液流动机理图...为解决超低温螺杆冷冻水机组中干式蒸发器管侧R507A制冷剂分配不均匀导致的蒸发器吸气过热度低、视镜带液及制冷量不足等问题,基于制冷循环系统工艺流程,构建并阐述了蒸发器管侧制冷剂的气-液两相时空演变流动机理。基于气-液流动机理图,通过计算流体动力学(computational fluid dynamics,CFD)评估了优化前干式蒸发器内制冷剂的空间分布,明确揭示了蒸发器入口分流弯管的离心效应及支管内部的旋流效应是导致换热管内制冷剂分配不均的关键因素。基于上述诊断结果,提出了3种包含T形入口分流管的进口管路优化方案,并进行数值模拟分析与对比。结果表明,T形结构能有效改善换热管内制冷剂的不均匀度,且方案3被确定为最优方案。在此基础上进一步研究了不同流动方向、不同入口分流支管间距及边界工况(最大负荷、最小负荷、最大压差、最小压差)等因素对方案3制冷剂分配均匀性的影响。分析发现,流动方向对方案3的不均匀度影响较小,而入口分流支管间距对制冷剂不均匀度的影响表现为两端区域显著、中间区域较小。经优化,方案3的不均匀度较优化前降低了50.01%,且边界工况下的不均匀度均远低于优化前模型。该优化方案经机组整改及实验测试验证,在名义工况下,优化后的干式蒸发器相比优化前制冷量提升约6.95%,吸气过热度提升7.23℃,制冷系数(coefficient of performance,COP)提高8.11%,并针对优化后的边界工况进行了测试,均无异常现象,并且有效解决了蒸发器出口带液问题。该方案对优化蒸发器性能、解决吸气带液等问题具有重要的工程指导意义。展开更多
文摘Sarnak’s Disjointness Conjecture states that the Mobius function is disjoint with any zeroentropy flow. This note establishes this conjecture, with a rate, for Furstenberg’s irregular flows on the infinite-dimensional torus.
基金This subject was financially supported by the National Natural Science Foundation of China (Grant No. 59976047)
文摘The Wells turbine is an axial-flow air-turbine designed to extract energy from ocean waves. An important consideration is the self-starting capability of the Wells turbine, a phenomenon encountered where the turbine accelerate by itself up to a certain speed for the best turbine performance. In order to clarify the self-starting characteristic and running performance of the Wells turbine in an irregular oscillating flow, a numerical simulation process is established in this paper on the rational assumption of quasi-steady flow conditions, Both self-starting characteristics and running performance are obtained through the numerical simulation and subsequently compared with the experimental data achieved on a computer-controlled oscillating flow test rig which could realize some irregular oscillating flow according to the specified spectrum. Results show that the self-starting time decreases with the increase of the significant wave height and the mean frequency of the irregular oscillating flow, Therefore, it is possible to predict accurately the performance of the Wells turbine by computer simulation.
基金the National Basic Research Program(973)of China(No.2007CB714103)
文摘A new algorithm to automatically extract drainage networks and catchments based on triangulation irregular networks(TINs) digital elevation model(DEM) was developed. The flow direction in this approach is determined by computing the spatial gradient of triangle and triangle edges. Outflow edge was defined by comparing the contribution area that is separated by the steepest descent of the triangle. Local channels were then tracked to build drainage networks. Both triangle edges and facets were considered to construct flow path. The algorithm has been tested in the site for Hawaiian Island of Kaho'olawe, and the results were compared with those calculated by ARCGIS as well as terrain map. The reported algorithm has been proved to be a reliable approach with high efficiency to generate well-connected and coherent drainage networks.
基金Comprehensive analysis,evaluation theory and application on profiled risk of flood disaster(50579019)
文摘In order to improve the finite analytic method’s adaptability for irregular unit, by using coordinates rotation technique this paper establishes a five-point element scheme of finite analytic method. It not only solves unsteady groundwater flow equation but also gives the boundary condition. This method can be used to calculate the three typical questions of groundwater. By compared with predecessor’s computed result, the result of this method is more satisfactory.
文摘为解决超低温螺杆冷冻水机组中干式蒸发器管侧R507A制冷剂分配不均匀导致的蒸发器吸气过热度低、视镜带液及制冷量不足等问题,基于制冷循环系统工艺流程,构建并阐述了蒸发器管侧制冷剂的气-液两相时空演变流动机理。基于气-液流动机理图,通过计算流体动力学(computational fluid dynamics,CFD)评估了优化前干式蒸发器内制冷剂的空间分布,明确揭示了蒸发器入口分流弯管的离心效应及支管内部的旋流效应是导致换热管内制冷剂分配不均的关键因素。基于上述诊断结果,提出了3种包含T形入口分流管的进口管路优化方案,并进行数值模拟分析与对比。结果表明,T形结构能有效改善换热管内制冷剂的不均匀度,且方案3被确定为最优方案。在此基础上进一步研究了不同流动方向、不同入口分流支管间距及边界工况(最大负荷、最小负荷、最大压差、最小压差)等因素对方案3制冷剂分配均匀性的影响。分析发现,流动方向对方案3的不均匀度影响较小,而入口分流支管间距对制冷剂不均匀度的影响表现为两端区域显著、中间区域较小。经优化,方案3的不均匀度较优化前降低了50.01%,且边界工况下的不均匀度均远低于优化前模型。该优化方案经机组整改及实验测试验证,在名义工况下,优化后的干式蒸发器相比优化前制冷量提升约6.95%,吸气过热度提升7.23℃,制冷系数(coefficient of performance,COP)提高8.11%,并针对优化后的边界工况进行了测试,均无异常现象,并且有效解决了蒸发器出口带液问题。该方案对优化蒸发器性能、解决吸气带液等问题具有重要的工程指导意义。
