变几何涡轮的损失研究

变几何涡轮与定几何涡轮相比,在静叶顶部多了一个端部间隙,端部间隙大小的选取十分重要,既要保证间隙损失不至于过大,又要保证其能够自由转动,不至于受热而被卡死。所以,在保证静叶能够转动的前提下,静叶的端部间隙应尽可能的小。以某一四级动力涡轮为例,分析了第一级静叶的端部间隙大小以及第一级静叶转角给涡轮损失带来的影响,建议变几何动力涡轮的静叶端部间隙选取为静叶叶高的1.8%。     

风力发电高塔系统阵风荷载因子法

给出了风力发电高塔系统阵风荷载因子法。与传统的阵风荷载因子法不同的是,因桨叶/塔体相互作用的存在,风力发电高塔系统阵风荷载因子包含两项共振分量。一般地,风力发电高塔系统包含桨叶和塔体两个子结构,每个子结构都可视为单自由度体系,二者耦合在一块构成两自由度体系。因桨叶和塔体自振频率可能相近,系统响应的共振分量包含了桨叶/塔体耦合系统前两阶振型的贡献。为获得风力发电高塔系统阵风荷载因子的准确值,给出了塔顶位移和基底弯矩阵风荷载因子数值解以及塔顶位移阵风荷载因子精确解。同时,针对桨叶不同转速给出了一系列考虑桨叶/塔体耦合的两自由度体系阵风荷载因子,并与不考虑桨叶/塔体耦合的单自由度体系阵风荷载因子比较,两者有一定的区别。     

Coefficients of the crack tip asymptotic field for wedge splitting specimens

The stress intensity factor (SIF) and the coefficients of higher order terms of the crack tip asymptotic field of typical wedge splitting specimens with two different loading arrangements are directly computed using a hybrid crack element. Accurate analytical expressions for the first five terms are obtained by fitting the computed data. Numerical results show that the coefficients of terms higher than three are negligibly small, this may explain that the wedge splitting specimen is more stable than other geometries. The first five terms are not sensitive to support conditions. However, for short cracks coefficients of terms, except the SIF, are quite sensitive to the loading arrangement even when the loads are statically equivalent.     

A new nonlocal cohesive stress law and its applicable range

In this paper, we attempt to provide a new analytical method to determine the cohesive law in the framework of nonlocal continuum mechanics. Firstly, the equivalence between the cohesive stress and the surface-induced traction (nonlocal surface residual) is established on the basis of the nonlocal stress boundary condition. Then a new cohesive stress law is derived logically from the perspective of rational mechanics, which characterizes the dependence of the cohesive stress on the crack opening displacement (COD) within the cohesive zone. Finally, we apply this new cohesive crack model to two fracture examples with different cohesive zone sizes, and investigate the stress field ahead of the crack tip in detail. The results show that the stress singularity at the crack tip is removed, and the maximum stress occurs within the cohesive zone away from the crack tip. Moreover, the stress in the large-scale cohesive zone drops rapidly to a constant approaching zero, exhibiting a stronger softening behavior.     

An enriched radial point interpolation method (e-RPIM) for analysis of crack tip fields

In this paper, an enriched radial point interpolation method (e-RPIM) is developed for the determination of crack tip fields. In e-RPIM, the conventional RBF interpolation is novelly augmented by the suitable trigonometric basis functions to reflect the properties of stresses for the crack tip fields. The performance of the enriched RBF meshfree shape functions is firstly investigated to fit different surfaces. The surface fitting results have proven that, comparing with the conventional RBF shape function, the enriched RBF shape function has: (1) a similar accuracy to fit a polynomial surface; (2) a much better accuracy to fit a trigonometric surface; and (3) a similar interpolation stability without increase of the condition number of the RBF interpolation matrix. Therefore, it has proven that the enriched RBF shape function will not only possess all advantages of the conventional RBF shape function, but also can accurately reflect the properties of stresses for the crack tip fields. The system of equations for the crack analysis is then derived based on the enriched RBF meshfree shape function and the meshfree weak-form. Several problems of linear fracture mechanics are simulated using this newly developed e-RPIM method. It has demonstrated that the present e-RPIM is very accurate and stable, and it has a good potential to develop a practical simulation tool for fracture mechanics problems.     

柴油/二甲氧基甲烷混合燃料喷雾特性的研究

开展了柴油/二甲氧基甲烷(DMM)混合燃料喷雾特性的研究。研究结果表明,在相同环境压力和喷嘴直径下,随着燃料中二甲氧基甲烷掺混比例的增加,喷雾锥角增大,贯穿距离减小;环境压力的增加使得燃油喷雾锥角增大,贯穿距离度减小。对于不同燃油,喷雾锥角与环境压力均呈现θ∝p0a.15的关系;随着喷孔直径增加,喷雾锥角增大,贯穿距离增长;在非破碎段区间内各种燃料的贯穿距离与时间均成正比关系;在破碎段区间内贯穿距离与时间呈现s∝tn关系,对于柴油n=0.6,而且随着DMM含量的增加n值逐渐减小,直至纯DMM时n=0.5。     

桩周土阻尼系数的研究

通过对武汉某码头2根钢管桩动静载试验研究,探讨了桩周土阻尼系数对波动理论Smith法预测单桩静极限承载力和打桩时桩身最大锤击应力的影响规律.通过对打桩实测最大锤击应力的拟合,推荐了符合本地区地质条件的最佳土阻尼系数和吸着系数,其适用性在相同地质条件下的钢管桩中得到了证实.     

蒙脱石卷烟过滤材料的研制

实验证实：蒙脱石对卷烟烟气物质吸附具有明显的选择性，对具香味的非极性物质吸附的很少，对强极性的有毒的物质吸附量很高。研制的蒙脱石──醋酸纤维丝束两段复合滤嘴，在香味、杂气、刺激、余味等方面，与醋酸纤维丝束滤嘴接近，在焦油降低和烟碱降低指标上，优于海泡石制的复合滤嘴。     

纤维增强混凝土断裂过程区试验研究

目的研究纤维增强混凝土的韧性.方法利用激光散斑法对混凝土及纤维增强混凝土切口梁的断裂过程区进行了研究.结果对失稳断裂前微裂纹发展的全过程进行了跟踪测量,并得到了载荷与裂纹尖端张开位移P-dCTO曲线.结论断裂过程区呈不规则狭长带状形,且混凝土中加入纤维后微裂纹区的扩展受到限制,使主裂纹的亚临界扩展长度、临界裂纹尖端张开位移增加,材料韧性增强.     

利用岩体经验强度准则确定嵌岩桩村端阻力的探讨

本文考虑了岩体结构面,岩块单轴抗压强度,应力状态的影响,引入了Ｈｏｅｋ－Ｂｒｏｗｎ岩体经验强度准则,利用极限平衡原理,推导了嵌岩桩桩端阻力的计算式,并分析了桩端阻力与桩长,嵌岩深度的关系,文中最后指出,尽管桩端阻力在所受荷载中所占比例不大,但正确估计桩端阻力对优化嵌岩桩的设计,节约造价仍有重要意义。