Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resis...Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resistance strongly impact the overland flow process and watershed floods. In view of the universal existence of natural vegetation, such as Chlorophytum malayense(CM) or Ophiopogon bodinieri(OB), and the sand-gravel bed of the river channel, it is important to understand the role of different types of roughness elements in flow resistance. This study was performed to investigate and compare through flume experiments the behaviors of overland flow resistance by the reaction of multi-scale configuration of different roughness elements. The result showed that the resistance coefficient gradually reduced versus the increase of flow rate in unit width and tended to be a constant when q = 3.0 l/s.m, Fr = 1.0, and Re = 4000 for slopes of 6 to 10 degrees. The gap of the vegetated rough bed and the gravel rough bed is limited to the same as the gap of the two types of vegetation, CM and OB. It was noted that the vegetation contributed to the increase in form resistance negatively and may lead to the mean resistance on decrease. To classify the flow pattern, the laminar flows were described by DarcyWeisbach's equation. In the study the f-Re equation of vegetated bed was developed with f ?5000 Re.The friction coefficient for laminar flows can be regarded as the critical value for identifying the transformation point of the flow pattern.展开更多
Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering ...Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type.展开更多
针对部分机电产品在概念设计阶段未综合考虑客户和环境的需求,进而影响产品详细设计的问题,提出了一种基于功能—结构—客户和环境需求(function‒structure‒requirements of customer and environment,FSRce)模型的机电产品绿色概念设...针对部分机电产品在概念设计阶段未综合考虑客户和环境的需求,进而影响产品详细设计的问题,提出了一种基于功能—结构—客户和环境需求(function‒structure‒requirements of customer and environment,FSRce)模型的机电产品绿色概念设计方案生成方法。首先,从案例库中选择合适的功能和结构对现有产品设计树中的节点进行扩展和关联;同时通过数据挖掘、专家打分等方法获得产品的客户和环境需求重要度,以构建基于FSRce模型的产品概念设计空间。然后,先利用加权区间粗糙数法对客户和环境需求重要度进行分析,得到需求相对重要度,再运用模糊质量功能展开(fuzzy quality function deployment,FQFD)将需求相对重要度转化为产品的工程特性权重。最后,利用物元理论构建基于工程特性的产品物元域和各结构物元集,并结合工程特性权重得到各结构的满意度分值,通过比较满意度优选得到满足客户和环境需求的产品概念设计方案。以某小型工业吹风机为例,基于上述方法对其概念设计方案进行优化。相比于原始方案,优化后的吹风机在能源消耗上降低了15.38%,在碳排放上降低了15.32%,且客户满意度提高了44.66%,由此验证了所提出方法的可行性与有效性。所提出的方法为机电产品概念设计方案的生成提供了一种新思路,能更好地辅助设计人员实现对机电产品的绿色设计。展开更多
Covering-based rough sets process data organized by a covering of the universe. A soft set is a parameterized family of subsets of the universe. Both theories can deal with the uncertainties of data. Soft sets have no...Covering-based rough sets process data organized by a covering of the universe. A soft set is a parameterized family of subsets of the universe. Both theories can deal with the uncertainties of data. Soft sets have not any restrictions on the approximate description of the object,and they might form a covering of the universe. From this viewpoint,we establish a connection between these two theories. Specifically,we propose a complementary parameter for this purpose. With this parameter,the soft covering approximation space is established and the two theories are bridged. Furthermore,we study some relations between the covering and the soft covering approximation space and obtain some significant results. Finally,we define a notion of combine parameter which can help us to simplify the set of parameters and reduce the storage requirement of a soft covering approximation space.展开更多
A comparison between the efficacy of surface boundary structure and presence of nanoparticles on the condensation two-phase flow inside rough nanochannels has been accomplished by applying molecular dynamics procedure...A comparison between the efficacy of surface boundary structure and presence of nanoparticles on the condensation two-phase flow inside rough nanochannels has been accomplished by applying molecular dynamics procedure to evaluate the thermal conductivity and flow characteristics.Simulation is performed in a computational region with two copper walls containing rectangular rough elements under different saturated temperatures.The main properties of liquid–vapor interface including density and the number of liquid atoms,are obtained.It is observed that the density profile is more affected by nanoparticles than the roughness.Also,compared to the condensation of nanofluid in a smooth nanochannel,the rough wall causes a greater drop in the temperature at the early time steps and by development of liquid films,effects of the wall roughness reduce.At the first of the condensation process,adding nanoparticle causes that transferring argon particles to the liquid phase increases with a steeper slope.Furthermore,heat current autocorrelation function(HCACF)for nanofluid condensation flow over considered correlation time is analyzed and following that the thermal conductivity for different saturated conditions is calculated.It has been represented that at lower temperatures the roughness makes more significant influence on the heat transfer of two-phase flow,while at higher temperatures the importance of nanoparticles prevails.展开更多
基金support from the authorities of the National Natural Science Foundation of China (Grant No. 41171016)Sichuan Province Science and technology support program (Grant No. 2014SZ0163)the Open Foundation of State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (Grant No. SKHL1309 and SKHL1418)
文摘Roughness elements are various in a mountain area; they include gravel and ground surface vegetation that often result in surface friction drag to resist overland flows. The variation and characteristics of flow resistance strongly impact the overland flow process and watershed floods. In view of the universal existence of natural vegetation, such as Chlorophytum malayense(CM) or Ophiopogon bodinieri(OB), and the sand-gravel bed of the river channel, it is important to understand the role of different types of roughness elements in flow resistance. This study was performed to investigate and compare through flume experiments the behaviors of overland flow resistance by the reaction of multi-scale configuration of different roughness elements. The result showed that the resistance coefficient gradually reduced versus the increase of flow rate in unit width and tended to be a constant when q = 3.0 l/s.m, Fr = 1.0, and Re = 4000 for slopes of 6 to 10 degrees. The gap of the vegetated rough bed and the gravel rough bed is limited to the same as the gap of the two types of vegetation, CM and OB. It was noted that the vegetation contributed to the increase in form resistance negatively and may lead to the mean resistance on decrease. To classify the flow pattern, the laminar flows were described by DarcyWeisbach's equation. In the study the f-Re equation of vegetated bed was developed with f ?5000 Re.The friction coefficient for laminar flows can be regarded as the critical value for identifying the transformation point of the flow pattern.
基金Project supported by the National Natural Science Foundation of China(Grant No.61571366)the Natural Science Basic Research in Shaanxi Province of China(Grant No.2015JQ5199)the Fund of Science and Technology from the Underwater Test and Control Laboratory(Grant No.9140c260201130c26096)
文摘Acoustic scattering from a rough sea bottom is recognized as a main source of reverberation. In this study, scattering properties from a layered bottom were exploited based on the finite element model. The scattering strength and loss from the layered rough seabed were investigated by ensembling the realizations of rough interface. They were found to be dependent on the thickness of sediment, and interference was significant in the case of thin sediment. Through verification of the finite element model, the scattering loss could be evaluated using the Eckart model with a proper sound speed in the thick sediment. The multiple scattering effect on the sound field was also exploited. It revealed that the effect depended strongly on the bottom type.
文摘针对部分机电产品在概念设计阶段未综合考虑客户和环境的需求,进而影响产品详细设计的问题,提出了一种基于功能—结构—客户和环境需求(function‒structure‒requirements of customer and environment,FSRce)模型的机电产品绿色概念设计方案生成方法。首先,从案例库中选择合适的功能和结构对现有产品设计树中的节点进行扩展和关联;同时通过数据挖掘、专家打分等方法获得产品的客户和环境需求重要度,以构建基于FSRce模型的产品概念设计空间。然后,先利用加权区间粗糙数法对客户和环境需求重要度进行分析,得到需求相对重要度,再运用模糊质量功能展开(fuzzy quality function deployment,FQFD)将需求相对重要度转化为产品的工程特性权重。最后,利用物元理论构建基于工程特性的产品物元域和各结构物元集,并结合工程特性权重得到各结构的满意度分值,通过比较满意度优选得到满足客户和环境需求的产品概念设计方案。以某小型工业吹风机为例,基于上述方法对其概念设计方案进行优化。相比于原始方案,优化后的吹风机在能源消耗上降低了15.38%,在碳排放上降低了15.32%,且客户满意度提高了44.66%,由此验证了所提出方法的可行性与有效性。所提出的方法为机电产品概念设计方案的生成提供了一种新思路,能更好地辅助设计人员实现对机电产品的绿色设计。
基金supported by National Natural Science Foundation of China under Grant No. 60873077/F020107the Science Research Project of Zhangzhou Normal University under Grant No. SK09002
文摘Covering-based rough sets process data organized by a covering of the universe. A soft set is a parameterized family of subsets of the universe. Both theories can deal with the uncertainties of data. Soft sets have not any restrictions on the approximate description of the object,and they might form a covering of the universe. From this viewpoint,we establish a connection between these two theories. Specifically,we propose a complementary parameter for this purpose. With this parameter,the soft covering approximation space is established and the two theories are bridged. Furthermore,we study some relations between the covering and the soft covering approximation space and obtain some significant results. Finally,we define a notion of combine parameter which can help us to simplify the set of parameters and reduce the storage requirement of a soft covering approximation space.
文摘A comparison between the efficacy of surface boundary structure and presence of nanoparticles on the condensation two-phase flow inside rough nanochannels has been accomplished by applying molecular dynamics procedure to evaluate the thermal conductivity and flow characteristics.Simulation is performed in a computational region with two copper walls containing rectangular rough elements under different saturated temperatures.The main properties of liquid–vapor interface including density and the number of liquid atoms,are obtained.It is observed that the density profile is more affected by nanoparticles than the roughness.Also,compared to the condensation of nanofluid in a smooth nanochannel,the rough wall causes a greater drop in the temperature at the early time steps and by development of liquid films,effects of the wall roughness reduce.At the first of the condensation process,adding nanoparticle causes that transferring argon particles to the liquid phase increases with a steeper slope.Furthermore,heat current autocorrelation function(HCACF)for nanofluid condensation flow over considered correlation time is analyzed and following that the thermal conductivity for different saturated conditions is calculated.It has been represented that at lower temperatures the roughness makes more significant influence on the heat transfer of two-phase flow,while at higher temperatures the importance of nanoparticles prevails.
