径向无叶扩压器的稳定性区域

径向无叶扩压器的稳定性区域窦华书（清华大学水利水电系北京１０００８４）关键词：无叶扩压器，旋转失速，喘振，稳定性区域一、导怕旋转失速和喘振是离心压气机中两种不同的气动不稳定现象。无叶扩压器是可能导致这些不稳定现象的主要通流部件之一。近三十年来，许多作...     

伪随机扩散体的吸声性能及其应用

本文介绍伪随机扩散体吸声性能的应用，提出减少扩散体结构厚度的实用设计，并应用于剧场观众厅以减少混响时间．     

响应面方法在叶片扩压器优化设计中的应用研究

本文应用响应面方法完成了某叶片扩压器的优化设计。通过改变叶片数和出口安装角构造扩压器,进行CFD分析,建立样本数据。基于不同的样本数,用响应面方法寻求的最佳设计点在大致相同的区域,而且与CFD分析结果相比误差很小。表明,响应面方法可以通过较少的样本准确拟合设计变量与响应变量的关系,在流体机械性能预测和多变量优化设计问题中有很好的应用前景。     

静载荷作用下正交各向异性旋转扁壳的非线性自由振动

本文用加权残值法和Lindstedt－Poincare摄动法研究了圆柱型正交各向异性扁薄球壳和锥壳在均布静载荷作用下的轴对称非线性自由振动问题，得到了其非线性固有频率和振幅间的特征关系，并讨论了静载荷及壳体的几何参数和材料参数对其振动特性的影响。     

Riemannian Geometry of Conical Singular Sets

In this paper, we study a class of singular Riemannian manifolds. The singular set itself is a smooth manifold with a cone-like neighborhood. By imposing a reasonable convergence condition on the metric, we can determine the local geometrical structure near the singular set. In general, the curvature near the singular set is unbounded. We prove that a bounded curvature assumption would have a strong implication on the geometrical and topological structures near the singular set. We also establish the Gauss–Bonnet–Chern formula, which can be applied to the study of singular Eistein 4-manifolds.     

Excited-state relaxation of protonated adenine.

The excited state dynamics of protonated adenine in the gas phase were investigated by femtosecond pump-probe transient mass spectroscopy. Adenine was protonated in an electrospray ionization source and transferred to a Paul trap. Two femtosecond laser pulses at 266 nm and 800 nm excited the lowest electronic pipi* state and probed the excited-state dynamics by monitoring ion fragment formation. The measured excited state decay is monoexponential with a lifetime shorter than 161 fs. This agrees with a theoretical prediction of very fast internal conversion via a conical intersection with the ground state.     

Displacement type unified equation for bending, buckling and vibration of conical shells and its applications

By using Donnell's simplication and starting from the displacement type equations of conical shells, and introducing a displacement functionU(s,,) (In the limit case, it will be reduced to cylindrical shell displacement function introduced by V. S. Vlasov) and a generalized loadq,(s,,),the equations of conical shells are changed into an eighth—order solvable partial differential equation about the displacement functionU(s,,). As a special case, the general bending problem of conical shells on Winkler foundation has been studied. Detailed numerical results and boundary coefficients for edge unit loads are obtained.The project supported by the National Natural Science Foundation of China.     

Maximal points with respect to cone dominance in Banach spaces and their existence

Given a convex cone in a Banach spaceV, an examination of the cone maximal points of a setX inV (with respect to the cone dominance induced by ) with respect to their characterization and existence is undertaken. The totality of cone maximal points ofX is called the conical frontier ofX. Comparisons of the conical frontiers of related sets and corresponding to related cones are made. By relaxing the compactness requirements of the underlying setX and by assuming some cone-related weaker forms of compactness, existence theorems for cone maximal points are developed. These theorems are believed to be generalizations of the existing results in one way or another.Maximizing points onX of certain linear functionals in the dual cone * of provide natural examples of cone maximal points. Properties characterizing a maximizing point of a linear functional in *, including the generalized version of Geoffrion's characterization of proper efficiency, are compiled and proved to be valid characterizations. Functionals in * with special properties are studied. Existence theorems are also obtained for the maximizing points of these functionals.The author is indebted to Professor James V. Whittaker for helpful discussions and comments and to Professors P. S. Bullen, C. W. Clark, B. N. Moyls, and F. Y. M. Wan for their encouragement and support.     

Experimental and computational study of the flow induced by a plasma actuator

A complementary experimental and computational study of the flow field evoked by a plasma actuator mounted on a flat plate was in focus of the present work. The main objective of the experimental investigation was the determination of the vector force imparted by the plasma actuator to the fluid flow. The force distribution was presently extracted from the Navier–Stokes equations directly by feeding them with the velocity field measured by a PIV technique. Assuming a steady-in-mean, two-dimensional flow with zero-pressure gradient, the imbalance between the convective term and the momentum equation’s right-hand-side terms reveals the desired resulting force. This force-distribution database was used afterwards as the source term in the momentum equation. Furthermore, an empirical model formulation for the volume-force determination parameterized by the underlying PIV-based model is derived. The model is tested within the RANS framework in order to predict a wall jet-like flow induced by a plasma actuator. The Reynolds equations are closed by a near-wall second-moment closure model based on the homogeneous dissipation rate of the kinetic energy of turbulence. The computationally obtained velocity field is analysed along with the experimental data focussing on the wall jet flow region in proximity of the plasma actuator. For comparison purposes, different existing phenomenological models were applied to evaluate the new model’s accuracy. The comparative analysis of all applied models demonstrates the strength of the new empirical model, particularly within the plasma domain. In addition, the presently formulated empirical model was applied to the flow in a three-dimensional diffuser whose inflow was modulated by a pair of streamwise vortices generated by the present plasma actuator. The direct comparison with existing experimental data of Grundmann et al. (2011) demonstrated that the specific decrease of the diffuser pressure corresponding to the continuous forcing was predicted correctly.     

Dynamic ice loads on conical structures

Two series of model tests were performed to observe the dynamic ice loads on conical structures. The variable testing parameters include the water line diameter of the model cone and ice parameters. During small water line diameter tests, two-time breaking is found to be the typical failure of ice on steep conical structure, and also be controlled by other factors, such as ice speed and the cone angle. During big water line diameter tests, the ice sheet failed nonsimultaneously around the cone. Several independent zones of bending were found in the nonsimultaneous failure process of ice. With the increase of the ratio of D/h and the number of independent zones, the total ice force was found being gradually reduced.