基于计算流体力学和人工神经网络对断阶式滑行艇的水动力性能预测

In the present paper,the hydrodynamic performance of stepped planing craft is investigated by computational fluid dynamics(CFD)analysis.For this purpose,the hydrodynamic resistances of without step,one-step,and two-step hulls of Cougar planing craft are evaluated under different distances of the second step and LCG from aft,weight loadings,and Froude numbers(Fr).Our CFD results are appropriately validated against our conducted experimental test in National Iranians Marine Laboratory(NIMALA),Tehran,Iran.Then,the hydrodynamic resistance of intended planing crafts under various geometrical and physical conditions is predicted using artificial neural networks(ANNs).CFD analysis shows two different trends in the growth rate of resistance to weight ratio.So that,using steps for planing craft increases the resistance to weight ratio at lower Fr and decreases it at higher Fr.Additionally,by the increase of the distance between two steps,the resistance to weight ratio is decreased and the porpoising phenomenon is delayed.Furthermore,we obtained the maximum mean square error of ANNs output in the prediction of resistance to weight ratio equal to 0.0027.Finally,the predictive equation is suggested for the resistance to weight ratio of stepped planing craft according to weights and bias of designed ANNs.

近视人群中角膜生物力学特性的分布(英文)

目的:分析伊朗近视眼及散光人群中角膜生物力学参数的分布特征。方法:对接受激光矫正手术的近视眼及散光患者180眼进行前后节、显然验光等效球镜度、Orbscan II和Zywave全面的术前检查。用眼反应分析仪测量角膜滞后量,角膜阻力因子,模拟Goldmann眼压值及角膜补偿后眼压值。分析所有角膜生物力学的分布特性及其与显然验光等效球镜度、性别和年龄的相关性。数据采用SPSS 17软件进行统计学分析,以P<0.05为有显著性差异。结果:平均年龄为28.20±6.78岁。平均显然验光等效球镜为-4.21±1.19D。平均角膜滞后量,角膜阻力因子,模拟Goldmann眼压值和角膜补偿后眼压值分别为10.00±1.28mmHg,10.17±1.45mmHg,15.71±2.67mmHg和16.68±2.41mmHg。近视人群中,28.4%角膜滞后量约为10mmHg,71%从9mmHg增长到11mmHg。25.9%的近视人群的角膜阻力因子为10mmHg,48.7%为9mmHg增长到11mmHg。显然验光等效球镜与角膜滞后量(Rs=0.001,P=0.71)和显然验光等效球镜与角膜阻力因子(Rs=0.01,P=0.18)之间正相关性不明显。结论:研究显示了伊朗近视眼人群中角膜生物力学的分布特征(角膜滞后量,角膜阻力因子,模拟Goldmann眼压值及角膜补偿后眼压值),并证实了角膜生物力学特性参数和显然验光等效球镜,年龄及性别之间没有统计学相关性。

角膜胶原蛋白交联疗法对人工晶状体大泡性角膜病变的作用(英文)

目的:研究核黄素和紫外线(UVA)交联疗法对晚期大泡性角膜病的疗效。方法:15例人工晶状体大泡性角膜病变(PBK)患者参与研究。分别于角膜交联前和干预后1,6mo,对患者行裂隙灯检查、视敏度、异物调查表、角膜透明度分级、眼部疼痛度范围、分析仪角膜厚度分析及超声波角膜厚度测量。氯化钠溶液处理1wk后,去除8mm直径范围的中央角膜上皮,在角膜上频繁点滴核黄素30min,后行3min紫外线(UVA)照射交联疗法。结果:15例患者(5男,10女),平均年龄为66±13岁。平均随访时间6.2mo。治疗后1mo全眼角膜透明度统计结果明显优于术前(P<0.05)。6mo时8眼角膜透明度较术前更佳,5眼持平,2眼低于术前(P=0.218)。70%病患异物感减弱。处理后1mo平均中央角膜厚度(CCT)减少(P<0.05)。6mo时,除3眼外均出现渐进性肿胀,但统计显示CCT明显薄于术前(P=0.006)。统计显示术后1mo平均矫正远视力(CDVA)明显优于术前(P=0.010)。6mo后无显著差异(P=0.130)。1mo痛值统计结果明显优于术前(P=0.007)。但6mo平均痛值较1mo高,较术前无明显差异(P=0.070)。结论:术后1mo结果显示角膜胶原交联疗法可显著改善角膜透明度、角膜厚度和眼痛。但是,它对减少PBK患者疼痛和维持角膜透明度方面似乎并无长期持久的效果。这种方法延长了角膜移植的时间间隔,并提高了角膜内皮移植术(DSAEK)过程的可视化。

On hydrodynamic analysis of stepped planing crafts

Using transverse steps is one of the adopted strategies to improve the hydrodynamic characteristics of planing crafts.In the present paper,hydrodynamic characteristics of stepped planing crafts are numerically investigated.For this purpose,we analyzed the effects of five different types of transverse steps on lift to drag ratio,resistance,trim angle and sinkage of high speed planing crafts.Contours of pressure distribution on the bottom of crafts,water volume fraction and free-surface are also presented at different hull velocities.Computed numerical results are properly validated against our conducted towing tank experimental tests.