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射水减弱混流式水轮机尾水管内压力脉动的数值模拟 总被引:1,自引:0,他引:1
选用RNGk-ε湍流模型,对一台混流式模型水轮机在部分负荷工况下的流动进行了全流道三维瞬态湍流数值模拟.数值计算结果与模型试验结果进行了比较,成功预测了水轮机尾水管内压力脉动的幅值与频率特性.从混流式水轮机泄水锥处向尾水管内射水可减弱尾水管内低频压力脉动,对射水后水轮机内的流动进行了数值模拟.计算结果表明,通过射水可以有效减弱尾水管内的压力脉动,减小压力脉动幅值.随着射水量的增加,压力脉动幅值减小更加明显,但是同时会导致水轮机效率的下降.为了尽可能大的减小压力脉动幅值,并兼顾水轮机效率,建议选择0.03~0.05倍该工况流量的射水量.此时,水轮机压力脉动幅值降低明显,而水轮机效率下降不大. 相似文献
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考察了温度变化对拖拉机用压敏胶平面标签180°剥离强度的影响,并模拟季节变化及现场粘贴情况,对压敏胶标签的剥离强度进行分析。结果表明,不同品种的压敏胶标签由于压敏胶粘剂自身特性的不同,达到最佳剥离性能的粘贴环境温度也不同。拖拉机压敏胶标签粘贴时,可根据环境温度的不同,选择合适的压敏胶标签,或适当控制被粘贴面温度,以达到理想的粘贴效果。 相似文献
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滴灌具有高效节水、省工节地、增加产量等优点。山地滴灌工程设计、灌溉参数的设计与压力控制是保证工程正常运行的关键,为了充分发挥滴灌工程效益,结合实际工程,对微灌工程的耗水强度、补水强度、土壤湿润比、灌水均匀度等参数做了计算,对管道布置、毛管长度、轮灌组做了设计并对支管入口压力与减压阀位置做了分析,得出了滴灌耗水强度和补水强度均为6mm·d-1,湿润带宽75cm,灌溉湿润比值48%,在计算水压为3~4kg范围内安放减压阀的结论,可为类似的工程设计提供参考。 相似文献
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AIM:To investigate the protective effect of zacopride (ZAC) on the pressure-overload left ventricular remodeling in the rats induced by coarctation of abdominal aorta. METHODS:Male Sprague-Dawley (SD) rats with pressure overload were induced by the coarctation of abdominal aorta. The model rats were intraperitoneally administered with ZAC, chloroquine (Chlor), and zacopride+chlorquine (ZAC+Chlor). The study duration was 8 weeks. The cardiac structure and function were assessed by echocardiography. The heart weight/body weight (HW/BW) ratio and the left ventricular weight/body weight (LVW/BW) ratio were calculated. The changes of structure and shape in myocardial tissue were observed with HE staining. The ultrastructure of the myocytes was observed under transmission electron microscope. The inward rectifier potassium channel (IK1) protein expression was determined by Western blot. The mRNA expression of Kir2.1 was detected by RT-PCR. RESULTS:Compared with vehicle group, ZAC improved cardiac function, as indicated by the decreased left ventricular end-diastolic dimension (LVEDD) and left ventricular end systolic dimension (LVESD) (P<0.05), and the increased left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) (P<0.01). The HW/BW and LVW/BW ratios were significantly decreased, and the cross-sectional area of the cardiomyocytes was significantly less in ZAC group than that in vehicle group (P<0.01). The ultrastructure of the myocytes was significantly improved. Chlor blocked the protective effect of zacopride on the pressure-overload left ventricular remodeling. The protein level of IK1 and mRNA expression of Kir2.1 in the cardiac tissues in ZAC group were significantly increased compared with vehicle group (P<0.01). CONCLUSION:IK1 agonist ZAC significantly attenuates pressure overload-induced ventricular remodeling in rats. 相似文献
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Summary The radial pressures generated by the earthworm Aporrectodea rosea were measured in a study of the conditions under which the worms were able to crack soil discs into which they were encouraged to tunnel. The tensile strength of replicate discs was determined by indirect tension tests and by expansion of rubber membranes in soil discs. Simple engineering theory was used to relate the stress required to fracture a disc with the applied internal stress. Mean values for the radial stress applied by the earthworms in tunnelling through the discs was 230 kPa. With some assumptions about the distribution of muscles across the worm diameter, it was estimated that the mean maximum force generated by all the longitudinal muscles in any segment was 3.2 N. 相似文献
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超高压处理对绵羊肉嫩化机理的研究 总被引:14,自引:2,他引:14
实验研究了超高压处理条件下绵羊肌肉感官特性、显微结构、钙激活酶(Calpains)粗酶活性和剪切力值的变化,并探讨了超高压处理对绵羊肌肉的嫩化机理。超高压处理后绵羊肌肉的感官特性发生变化,随处理压力升高,绵羊肌肉颜色变淡,出现轻微的类似蒸煮的成熟风味。在压力为400 MPa,保压时间为10 min的处理条件下,绵羊肌肉显微组织结构变化明显:肌节收缩,肌原纤维的Z线断裂,M线降解,I带变白。当压力水平在100~400 MPa范围变动时,随压力升高,Calpains粗酶活性显著下降(P<0.01);当压力达到400 MPa时,Calpains粗酶活性几乎失活。超高压处理后绵羊肉的剪切力值显著下降(P<0.05)。实验结果表明,超高压处理促进了绵羊肉的嫩化。 相似文献
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