仿鱼柔性长鳍波动运动分析与建模

研究了弓鳍目鱼“尼罗河魔鬼”的柔性波动长背鳍.针对波动长鳍大的柔性变形特征,提出了由N根刚性鳍条依靠柔性薄膜连接组成的柔性波动长鳍简化模型;在分析长背鳍运动和流固耦合的基础上,建立了柔性波动长鳍的运动学模型;进而,从弹性薄壳理论出发,考虑柔性长鳍结构的几何非线性,并引入无矩薄壳理论的假定,建立了柔性长鳍波动的平衡方程.依据所建立的运动学模型和柔性长鳍波动的平衡方程,可以进一步解析柔性长鳍波动运动的动力学性能.     

冷凝器铜翅片管泄漏原因分析

某冷水机组冷凝器在短时间使用后铜翅片管发生泄漏。通过现场的外观检查，并对管试样进行宏观、微观分析，以及对垢物的能谱和X射线衍射分析，结果表明：翅片管泄漏的原因是管内沉积物导致缝隙腐蚀引起的管材穿孔。     

船舶综合管理平台网络下减摇鳍预估控制

为满足船舶网络化、信息化和智能化的要求,研究了综合管理平台网络下减摇鳍的控制问题.在传统减摇鳍系统模式的基础上,提出了综合管理平台下减摇鳍网络控制系统的模型.分析了由于平台网络引入的诱导时延对系统性能的影响.以均值预测法为基础,引入预测控制算法中“误差预测”思想,设计了一类新的时延辨识器.在此基础上,对于海浪干扰和网络...     

Performance of symmetric polygonal fins with and without tip loss — A comparison of different methods of prediction

No analytical solution exists for estimating the efficiency of symmetric polygonal fins (SPFs) circumscribing circular tubes. Performance of such fins is conventionally determined from either of the two approximate techniques, namely, the equivalent annulus method and the sector method. The present work aims to judge the relative merits and applicability of these two methods critically. To this end, the results obtained from the approximate techniques have compared with those obtained from a semi‐analytical technique. It has been noted that, with the increase of the tip heat loss, the accuracy of prediction from any of the approximate methods decreases. For the sector method, a modification has been suggested. The prediction from the modified version of the sector method is always more accurate than that from the equivalent annulus method. It has been further illustrated that though the approximate techniques can be employed for the prediction of efficiency, they cannot be used to predict the tip temperatures accurately.     

CFD analysis of employing a novel ecofriendly nanofluid in a miniature pin fin heat sink for cooling of electronic components: Effect of different configurations

This research aims to study the thermal and hydraulic attributes as well as energy efficiency of a new ecofriendly nanofluid including functionalized graphene nanoplatelets in a mini heat sink with three different pin fins. The circular, triangular and drop-shaped pin fins are investigated and compared with each other. The effects of nanoparticle fraction and flow velocity on the thermal resistance, temperature uniformity, convective heat transfer coefficient, maximum surface temperature, average surface temperature, pressure loss and pumping power are assessed. Increasing the concentration or velocity reduces the temperature on the heated wall, and also improves the temperature distribution uniformity. At both constant velocity and invariant pumping power, the heat sink fitted with the circular pin fins leads to the best performance while that equipped with the triangular pin fins results in the worst efficiency. In addition, the Figure of Merit (FoM) is greater than 1 for all conditions, which proves that the nanoparticle suspension possesses a greater merit to be employed as the coolant in the heat sinks compared to the base fluid.     

胸鳍摆动推进仿生鱼的设计及水动力实验

为实现胸鳍摆动推进模式鱼类的游动,模仿牛鼻鲼构建了仿生鱼.首先,基于摆动胸鳍的生物学特征和运动规律,提出了具有主/被动复合柔性变形能力的仿生胸鳍原理模型.然后通过ADAMS运动学仿真验证了设计方案的可行性,并构建仿生样机.自由游动实验表明,仿生鱼游速可达0.46m/s,约1倍身长比,且具有原地转弯能力,最大转弯速度达60?/s.与国内外其他同类机器鱼相比,在游速和机动性方面均表现出明显的优势.基于准稳态叶素理论,提出了仿生胸鳍水动力简化计算模型.构建水动力实验平台,验证了计算模型的有效性,并通过一系列水动力实验研究了仿生胸鳍的水动力特性.实验结果表明,仿生胸鳍能够产生周期性变化的推、升力,且变化趋势与胸鳍运动控制参数密切相关.     

板翅式换热器中新型微凸翅片结构设计及性能分析

为提高翅片区域的换热效率、改善板翅式换热器的整体换热性能,提出了一种新型微凸翅片结构.基于结构参数多采样点处的热力学性能仿真结果构建近似模型,以翅片热功率最高为优化目标、压降为约束,使用序列二次规划法确定了微凸体结构参数(微凸高度、微凸夹角、微凸开口长度)的最优值;对微凸体排列间距、排列方式进行优化,确定了改进微凸翅片...     

空冷式换热器翅片管腐蚀失效分析

介绍了空冷式换热器翅片管失效的原因、特征、产物及机理,对工艺流程过程中脱硫、控制进入温度等提出了建议.     

花瓣形翅片管的强化传热研究概况

综述了花瓣形翅片管在低表面张力介质及其混合物中的冷凝强化传热、含不凝性气体水蒸气的冷凝强化传热以及空气和油的冷却强化传热等方面的研究概况、进展、成果及其工业应用前景。     

CFD analysis of natural convection heat transfer augmentation from square conductive horizontal and inclined pin fin arrays

Numerical investigations on natural convection heat transfer from a vertical isothermal plate with pin fins have been made by solving the Navier–Stokes equation along with the energy equation. Average Nusselt number for the plate with different configurations of pin fins have been obtained. It was observed that the maximum increase of the average Nusselt number occurs at S_v/L?=?0.2 for θ?=?45° with fin height of 24?mm (H/t?=?8). The average Nusselt number increases with fin aspect ratio and decreases with angle of inclination. There is not much difference between the average Nusselt number for in-line and staggered arrangement of fins for the range of parameters studied in the present work. A correlation is developed to predict the average Nusselt number of the plate as a function of fin spacing in stream- and span-wise direction, aspect ratio of fins and its angle of inclination.