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21.
Nikolaos Athanasios Malamataris 《国际流体数值方法杂志》2012,70(1):71-95
The influence of aspect ratio in three‐dimensional, numerical experiments of separated flows is studied in the case of the backward‐facing step at Reynolds numbers 600, 800, and 950. The computational domain is designed as an actual laboratory experiment. The governing equations are the steady state, isothermal, and incompressible Navier–Stokes equations. The expansion ratio of the computational domain is 1:2. The aspect ratio varies from 1:10 to 1:40. The results of the computations focus on the spanwise variations of the length and the strength of the two eddies along the lower and upper wall. It is concluded that both numerical and laboratory experiments should be designed with an aspect ratio of at least 1:20, if only the accuracy of the position of the detachment and the re‐attachment points matters. If the accuracy of the shear‐stress distributions is also taken into account, then an aspect ratio of at least 1:30 should be chosen. Finally, if the magnitudes of the vortex centers are also considered, then only the aspect ratio of 1:40 qualifies for a realization of two‐dimensional flow conditions in the plane of symmetry. This is contrary to the common practice in the field, at least from the side of laboratory experiments, where an aspect ratio of 1:10 is still considered adequate for this purpose. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Hyojin Lee Chi P. Huynh Stephen C. Hawkins Mustafa Musameh Dae Hyung Kim 《Liquid crystals》2013,40(3):322-327
We investigated the orientational and electro-optical properties of a nematic liquid crystal (LC) aligned with a directly spinnable carbon nanotube (CNT) web functioning both as an electrode and as an alignment layer. The LC molecules were uniformly oriented along the drawing direction of the CNT web and the spatially averaged birefringence was comparable to a rubbed polyimide sample. The CNT web sample also showed smaller residual DC and hysteresis compared to the polyimide sample. 相似文献
24.
Wan K. Jo Jong H. Lee 《International journal of environmental analytical chemistry》2013,93(15):1412-1424
A lesser degree of information is available with respect to microenvironments associated with potential exposure to naphthalene, in comparison with other volatile organic compounds. The current study investigated the levels of benzene as well as naphthalene, both in the indoor and outdoor air of apartments and in the cabins of passenger cars. Two groups of 20 apartment buildings (20 new and 20 old) were chosen on the basis of the selection criteria (apartment location and size). In addition, 10 actual commuters were recruited for this study. The equal number of drivers was recruited for the study for comparison of two types of fuels for vehicles (five drivers of gasoline-fuelled and five drivers of diesel-fuelled passenger cars). Indoor naphthalene concentrations were similar between old and new apartments, while the benzene concentrations in new apartments were significantly higher than those of old apartments. The naphthalene concentrations in bedrooms, where wardrobes with moth repellent (MRs) were placed, were significantly higher than those for living rooms where no MRs were present. In turn, these indoor concentrations were significantly higher than outdoor levels. It is noteworthy that the mean and median values of naphthalene measured in the bedrooms exceeded the USEPA RfC (inhalation reference concentration) of 3?µg?m?3, and the living room values were close to the RfC, while the residential benzene levels exceeded the European benzene limit of 5?µg?m?3. In contrast, the maximum outdoor levels were well below that of the RfC. The use of passenger cars appeared to be a significant daily activity for both naphthalene and benzene exposure. The naphthalene-to-benzene ratios varied with the type of microenvironments. Both the indoor naphthalene and benzene concentrations in the present study were much higher than those of other studies. 相似文献
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以固体废弃物磷石膏为原料,在传统常压醇水热法的基础上添加CaSO4·2H2O为晶种制备半水硫酸钙晶须。采用单因素试验法探究了晶种含量、丙三醇含量和磷石膏质量分数对晶须结构和形貌的影响,确定晶须的最佳制备工艺条件。采用SEM和XRD对样品进行表征分析,实验结果表明:添加CaSO4·2H2O晶种制备晶须的长径比(49.29)比只添加丙三醇的样品的长径比(30.99)提高了近60%;当丙三醇与水的体积比(V)为1、晶种含量为1%、磷石膏质量分数为5%时制备的晶须的平均直径为0.65 μm,长径比达到了62.15,晶须的尺寸均匀。这说明添加1%CaSO4·2H2O晶种、V为1的丙三醇和质量分数为5%的磷石膏在常压下能制备出高长径比和尺寸均匀的半水硫酸钙晶须。 相似文献
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提出利用同一波长的入射光在双面入射时两个能量之比的比值对光栅的参量进行测量,进一步提高准确度。首先从理论上比较正弦面形光栅在单一面入射及双面入射时各种衍射效率对光栅表面粗糙度的敏感程度;然后模拟测量出该正弦面型光栅在双面入射情况下的光栅参量;最后成功反演出体积相位全息光栅的三个参量,其测量结果为0.080μm,1.452μm,20.5μm准确度比单一入射面情况(0.080μm,1.451μm,20.1μm)时要高。同时该法继承了原来方法的无损伤、操作简便、可重复、易推广、成本低等优点。 相似文献
28.
在ESO中采用动态删除率能有效地提高优化效率和稳定性,但现有的动态删除率策略都含有经验参数,确定删除率的过程较为复杂。本文提出了一种用于BESO的无经验参数自适应单元删除率确定方法。通过分析单元删除率对优化稳定性的影响,得到了结构优化过程中单元删除率的理想变化规律和单元灵敏度均匀化信息对删除率的影响情况,并据此分析了经验参数引入的原因,从而构造了评价单迭代步的单元灵敏度均匀化程度指标。然后,基于单迭代步的单元灵敏度均匀化程度指标,构造了全部迭代步信息下的单元灵敏度均匀化程度相对指标,结合单元删除率的推荐范围值,给出了一种自适应于结构优化进程的单元删除率自适应函数。最后,给出了基于自适应单元删除率的BESO方法实现流程。经典算例的结果对比说明,本文方法在保证优化质量相近的情况下,具有更好的优化效率和稳定性。 相似文献
29.
宽板塑性弯曲成形过程中的板厚变化规律 总被引:7,自引:0,他引:7
根据宽板弯曲过程中的变形与应力分布特征,提出了一种计算弯曲过程中板料厚度随弯曲程度变化的新的近似解答方法.该方法基于塑性增量理论,应用塑性成形过程的体积不变假设和弯曲过程的平面假设.作为算例,得到了理想刚塑性材料的板料厚度、变薄系数以及应变中性层内移系数随板料弯曲内表面曲率半径变化的规律,并与实验数据进行了比较,两吻合良好. 相似文献
30.