扇环形截面弯曲管道内的粘性流动

本文利用涡量－流函数法系统地研究了扇环形截面弯曲管道内的二次流动，计算结果表明了采用控制体积积分法对涡量－流函数方程进行离散来求解弯曲管道内粘性流动问题是成功的，这样可以避免对压力项的处理；对所得结果的分析揭示了该二次流动不仅受雷诺数和曲率影响，而且扇形中心角、内外径之比对该流动的影响也是显著的。     

Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide

The metabolic consequence of suboptimal (400 μmol mol⁻¹ or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO₂] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO₂]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO₂] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO₂] and physiological age. In general, plants grown under high [CO₂] exhibited a metabolite profile characteristic of older plants under ambient CO₂. Elevated [CO₂] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO₂] to a much greater extent at 10,000 ppm CO₂ than at 1500 ppm CO₂. The percentage increase of starch content resulting from CO₂ enrichment declined as plants develope. In contrast, elevated [CO₂] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO₂] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO₂] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO₂-grown plants, both elevated CO₂ levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO₂] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO₂ on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO₂ levels.     

Secondary instability of separated shear layers

The process through which a laminar flow undergoes transition to turbulence is of great fundamental and practical interest. Such a process is hugely complex as there are many diverse routes for a laminar flow to become turbulent flow. The transition process is usually initiated by flow instabilities—a primary instability stage followed by a secondary instability stage. This forms a rational framework for the early stage of a transition process and it is crucially important to understand the physics of instabilities leading to turbulence. This article reviews the results of studies on secondary instability of separated shear layers in separation bubbles and summaries the current status of our understanding in this area.     

静压延时矫直策略在头部翘曲板材矫直过程中的应用

随着厚规格、高强度品种钢的大量开发,头部翘曲成为中厚板生产过程中的一种常见缺陷,同时国产化的矫直机矫直能力不足,使得头部翘曲板材矫直过程困难。以某板卷厂开发厚规格、高强度品种钢过程中,频繁出现头部翘曲呈蛇形问题为依托,采用弹塑性差分的曲率积分方法,分析头部翘曲板材的传统矫直策略中残余曲率与矫直力的变化,讨论传统矫直策略和静压延时矫直策略的选择原则,研究静压延时矫直工艺。某板卷厂现场证明:静压延时矫直可以有效解决头部翘曲板材矫直问题,同时改善板材的板形。     

预先危险分析方法在航管二次雷达站运行管理中的应用

本文对预先危险分析方法作了简单介绍。重点研究了PHA在航管二次雷达站运行管理中的应用，找出了广汉机场航管二次雷达站运行管理中存在的危险源，采用定性和定量的方法从危险的后果严重程度和发生可能性两方面对风险进行了分析，提出了控制危险性的有效措施。     

两端弹性转动约束跨中受集中力作用梁的弯曲分析

研究了两端弹性转动约束跨中受集中力作用梁的弯曲特性,给出了弯矩和挠度计算公式,分析了转动约束刚度对弯曲特性的影响。梁的弯曲特性不仅与转动约束刚度有关,而且还与梁的长度及弯曲刚度有关。当转动约束刚度参数小于0.01时,可近似按刚性转动约束计算;当转动约束刚度参数大于12时,可近似按自由转动约束计算。     

支承座三工序复合冲压模具

介绍一种新型支承座三工步复合冲压模具的结构、工作原理、主要工作部件的设计技术和参数计算。使用此种模具，可以在一个工步中完成支承座毛坯的落料、冲孔和弯曲成形，生产效率高，工艺质量好。     

弯曲模故障模糊预测方法研究

建立了弯曲模故障模糊预测模型，使用Delphi语言开发了一个弯曲模故障模糊预测系统。介绍了系统的总体结构和各模块功能。     

喷射角对涡轮叶栅端壁气膜冷却的气动影响

在大尺寸低速平面叶栅风洞中,对前缘上游有单排气膜孔的涡轮导向叶栅端壁气膜冷却进行了气动实验。在喷射角25°,35°和45°以及吹风比1,2,3下详细测量了叶栅通道中的三维流场,得到了全速度和二次流速度分布,并由此计算了二次流动能的大小。着重研究了喷射角对端壁气膜冷却的气动特性和对叶栅通道中特别是端壁附近的流场结构的影响。数据表明减小喷射角度可以减小通道涡的强度和尺寸,使冷气射流核心更贴近壁面,但同时也明显地增大了壁面附近的气流速度。在高吹风比下,35°喷射时射流将冷气输运到压力边的能力比25°喷射和45°喷射都要强。     

广义协调条件的薄板弯曲三角形元和矩形元

其中兀_p和π_(mp)是最小势能原理和修正势能原理的泛函;w是单元内挠度;(?)、_(?)_n、(?)_s是单元间的位移;Q_n、M_n、M_(ns)是单元周线(?)A_e上的边界力。如果单元内部位移场在单元周线上的位移[w、((?)w)/((?)n)、((?)w)/((?)s)]和单元边界位移[(?)、(?)_n、(?)_s]~T满足广义协调条件