A co‐rotational grid‐based model for fabric drapes

Fabric drapes are typical large displacement, large rotation and small strain problems. Compared to conventional geometric non‐linear shell analyses, computational fabric drape analysis is particularly challenging due to the extremely weak bending rigidities of fabrics. Compared to continuum shell finite element methods, grid‐ or particle‐based methods appear to be more successful in high drapeability problems. The latter methods often resort to simple particle mechanics and formulate the elastic energy in terms of the inter‐particle distances and trigonometrical functions of the angles between the straight lines joining adjacent particles. In this paper, the co‐rotational approach and commonly employed assumptions for small strain problems in finite element analysis will be adopted to formulate the elastic energy. It will be seen that the internal force vector and the stiffness matrix are considerably simpler than other grid‐based models, yet the sparsity of the tangential stiffness matrix remains unchanged. A number of examples are considered and the predicted results are promising. Copyright © 2003 John Wiley & Sons, Ltd.     

冰雪融水型多沙河流水库泥沙设计

以新疆喀拉喀什河乌鲁瓦提水库泥沙设计为实例，分析了冰雪融水型多沙河流的水、沙特性，并根据水库担负的任务，利用水动力学泥沙数学模型及经典的三角洲整体平衡模型，进行了多方案水库淤积率比较。在此基础上，确定了水库调水、调沙运行方式，并布设了与之相应的泄流排沙设施，得出乌鲁瓦提水库有效库容可长期保持。     

计算机化织物悬垂性测试器

用最低限度硬件和最合理软件研制的悬垂性测试器,测量精确、操作简便、效果显著。     

M11康明斯发动机燃油系工作原理与故障分析实训台设计

针对M11康明斯发动机PT泵燃油系维护保养中面临的困难,研制了其工作原理与故障分析实训台。在研制过程中应用了单片机技术、故障树理论和大规模薄膜开关矩阵制作工艺,使实训台逼真模拟了燃油系的工作原理。实训台也设置了燃油系常见故障现象、故障原因和故障排除方法的教学实训功能,模拟了燃油系故障的分析过程。该实训台在一些部队单位进行了实际应用,具有很好的应用前景。     

文丘里液体喷射技术在真空系统的工业应用

介绍了以文丘里液体喷射抽真空技术在炼油厂常减压系统的工业运行情况。用一级液体喷射取代原来的三级蒸汽喷射。工业装置的运行及标定结果表明,文丘里液体喷射抽真空技术在低于蒸汽喷射抽真空技术能耗的前提下,真空度高于蒸汽喷射抽真空技术。用于喷射的液体采用装置自产的减一线油,运行结果表明,用于炼厂常减压装置的文丘里液体喷射系统流程设计合理,塔顶压力低于蒸汽喷射真空系统,加热炉出口温度、减一线产品质量、减一及减二线的产量等未受到影响。     

蒸气喷射准双级压缩制冷系统的实验研究

实验探究了蒸气喷射准双级制冷系统中,气体喷射器进出口参数对喷射器喷射系数、COP和制冷量的影响,并与单级蒸气压缩制冷系统进行对比。实验数据显示:随着混合流体出口压力的增加,喷射系数和系统制冷量逐渐减小,而COP则先增加后减小;喷射系数、COP和制冷量随着工作流体压力的增加均呈现先增加后降低的趋势;随着引射流体压力的增加,喷射系数和制冷量均增加,COP先增加后减小;当蒸发温度到-31.4℃时(t_k=35.0℃),单级蒸气压缩式制冷系统将不再产生冷量,而蒸气喷射准双级制冷系统可达到的最低蒸发温度为-36.5℃。     

Herd-level variables associated with delayed milk ejection in Michigan dairy herds

The objective of this study was to determine which herd-level variables were associated with delayed milk ejection (bimodal milk let-down) in 64 Michigan dairy herds. Median herd size was 294 cows (range 59 to 2,771 cows). For each herd, milking protocols were observed and milk flow dynamics were estimated by use of digital vacuum recorders. Surveys were also administered to the producers to measure mastitis management practices and attitudes. Milk flow dynamics were recorded for a total of 3,824 cow milkings, with a mean of 60 milkings per herd (range of 11 to 154). Backward multivariable analysis was used to determine which of the 47 herd-level milking and management variables were associated with delayed milk ejection (cows with milk let-down periods between milking cluster attachment and the incline phase of milk flow of >30 s). Delayed milk ejection occurred in an average of 25% of the cows in each herd (range 0 to 75%). A multivariable model found that the proportion of cows in a herd with delayed milk ejection was negatively associated with mean total time of tactile stimulation during premilking routines and positively associated with herd size.     

Suitability of somatic cell count,electrical conductivity,and lactate dehydrogenase activity in foremilk before versus after alveolar milk ejection for mastitis detection

Mastitis is responsible for substantial economic loss and significant animal welfare concerns for the dairy industry. Sensors that measure electrical conductivity (EC) and enzyme concentrations of lactate dehydrogenase (LDH) are presently used for automatic detection of mastitis. However, EC is not sensitive enough to detect mastitis, and the ability of LDH activity to identify mastitis caused by different pathogens is a potential option that needs to be investigated. This study was conducted to test the following hypotheses: (a) strict foremilk before milk ejection is more informative in detecting mastitis, in general, than foremilk removed after cows were stimulated for milk ejection; and (b) the value of LDH activity as a mastitis indicator depends on the type of pathogen associated with the infection. Milk samples (before afternoon milking) from 48 Holstein-Friesian cows at the University of Sydney's dairy farm (Camden, New South Wales, Australia) with EC > 7.5 mS/cm in any of the 4 quarters were collected over a period of 2 mo. Quarter milk samples (n = 343) from 48 cows were collected manually in the automatic milking rotary in 3 steps: foremilk before (strict foremilk) and after milk ejection, followed by an aseptic sample for bacteriological culture. The EC (mS), LDH (U/L), SCC (cells/mL), and milk protein and fat content (%) of foremilk in both sampling times were compared and used as predictors for gram-positive and gram-negative mastitis. Quarter (n = 515) observations from 44 cows were analyzed using a logistic mixed or linear mixed model, with cow and quarter nested within cow as random effects. Milk from both sampling times was also assessed by producing a receiver operating characteristic (ROC) curve and calculating the area under the curve (AUC) to determine ability to detect mastitis. Overall, EC and LDH were greater and milk protein (%) was lower in strict foremilk than in milk fractions obtained after milk ejection. Data from strict foremilk samples had slightly higher AUC values (0.98 to 0.99 vs. 0.97 to 0.98, respectively) than did the after-ejection milk samples. Although gram-negative coliform mastitis had significantly higher LDH activity than did gram-positive mastitis (6.19 vs. 5.34 log₁₀ U/L), the robustness of this result is questionable due to limited sample size. We concluded that milk samples taken before ejection can influence major mastitis indicators, suggesting that automatic milking system sensors could be modified to monitor milk before ejection for more efficient mastitis detection.     

微滴喷射化学沉积工艺条件对成形银导线的影响

为制备具有良好导电特性的柔性线路,研究了织物表面微滴喷射打印化学沉积的工艺条件变化对成形导电线路性能的影响。利用开发的气动式双喷头微滴按需喷射系统,通过改变反应溶液中硝酸银和抗坏血酸的用量、分散剂聚乙烯吡络烷酮(PVP)的浓度及反应体系的pH值,在系统稳定喷射条件下打印导电线路,对不同条件下成形导线的微观形貌进行观察,并测试成形导线的方阻。结果表明:在稳定喷射条件下,当硝酸银和抗坏血酸用量分别为50%和30%(质量体积比)时,反应生成的银导线平均方阻为2.92 Ω/□,标准差为0.46 Ω/□;分散剂PVP在银导线反应过程中具有控制银微粒大小和改善粒子间团聚的作用,且当分散剂PVP添加量为6%时,银颗粒成“米粒”状,颗粒间连接成网状结构;不同pH值条件下反应体系的反应情况不同,当反应体系的pH值为2~3时,反应生成银粒子较多,且颗粒形状规则统一。     

扎染中的褶皱艺术

从扎染的定义入手,阐明了扎染所具有的色晕、褶皱、作品唯一性的独特魅力;以扎染的褶皱展开论述,探讨了在传统扎染基础上发展起来的现代扎染.利用高温定型技术可使扎染服装呈现永久的褶皱,更具空间感与艺术性.