通气法控制超空泡流动的实验研究

在高速水洞中运用人工通气方法进行了航行体模型超空泡形态特性的系列实验研究.获得了不同通气流量、不同空化数和不同弗鲁德数下的空泡形态,建立了以弗鲁德数为参数的空泡几何特征参数与空化数的对应关系、空化数与通气流量系数之间的对应关系.验证了空化数是决定空泡尺度的主要无因次参数,通过改变通气流量可以有效地调控空化数,进而达到控制空泡形态的目的.文中同时给出了通气流量系数的实验曲线拟合公式,并与国外的相关实验和公式进行了比较,两者基本一致.所得结论对进一步的水下超高速航行体空泡形态控制技术研究具有参考价值.     

Nontangential Limit of the Weyl m-Functions for the Ergodic Schrödinger Equation

This paper deals with the spectral and qualitative problems associated with the one-dimensional ergodic Schrödinger equation. Let A ₂ be the set of those energies for which the real projective flow admits an invariant linear measure with square integrable density function. On this set we calculate the directional derivative of the Floquet coefficient and prove the existence of a nontangential limit of the Weyl m-functions in the L ¹-topology. In particular, we verify that the known Dieft–Simon inequality for the derivative of the rotation number obtained from Kotani's theory is in fact an equality. In the bounded orbit case we deduce the uniform boundedness of the Weyl m-functions and obtain necessary and sufficient conditions to assure their uniform convergence.     

Plasma in a high-frequency electric field with a reflective condition on the boundary

An analytical solution is obtained for the linearized problem of the behavior of a collisional gas plasma in a half-space in an external alternating electric field. It is assumed that the electrons are mirror-reflected from the plasma boundary. The solution is used for finding the screened field. The case of an external field frequency close to the plasma frequency is investigated separately.     

基于吸力量测确定膨胀土活动带和裂隙深度

采用M itchell公式和裂隙扩展深度方程两种吸力法确定安康地区膨胀土大气影响深度和裂隙开展深度。其一通过对安康地区两处天然边坡开挖观测井,利用张力计进行不同深度处吸力值的现场量测,根据M itchell提出公式计算大气影响深度;其二根据非饱和土抗拉强度公式,建立膨胀土裂隙扩展深度方程,利用基质吸力量测结果求其理论解。结果表明,安康地区膨胀土吸力变化曲线随深度增加变幅减小,呈“波浪式”推移。M itchell公式确定安康地区膨胀土的大气影响深度为3.35m以内,裂隙深度方程确定裂隙开展深度为3.06³.14m。利用M itchell公式计算大气影响深度与膨胀土断裂理论公式确定的裂隙开展深度结果接近。     

An improved scheme for determining heat transfer correlations from heat exchanger regression models with three unknowns

A nonlinear regression scheme for determining heat transfer correlations from overall heat exchanger measurements is presented. The proposed scheme is valid for any two-fluid heat exchanger data where only one fluid's thermal resistance varies. The resulting regression model has three unknowns; two are associated with the variable resistance, and the third is the sum of all other resistances. The model can be analyzed only by using nonlinear regression because it cannot be transformed into linear form. Unlike existing approximate methods of analysis (known as modified Wilson plots), the proposed scheme is guaranteed to converge if a solution exists. The scheme was successfully tested by analyzing data collected on a tube-fin heat exchanger with continuous plain fins.     

Solutions of the kinetic theory for bounded collisional granular flows

We consider collisional granular flows of nearly elastic spheres featuring a single constituent or binary mixtures in various bounded geometries. We review the equations of the kinetic theory for the conservation of mass, momentum, fluctuation energy and species concentration. We illustrate their solutions for shear flows in rectilinear or axisymmetric rectangular channels with or without a body force. We show that proper boundary conditions yield numerical solutions in good agreement with molecular dynamical simulations and with data from physical experiments carried out in microgravity.Received: 3 December 2002, Accepted: 3 February 2003, Published online: 27 June 2003PACS: 45.70.Mg, 45.70.-n, 05.20.Dd, 83.10.Rs     

Determination of Salt Diffusion Coefficient in Brick: Analytical Methods

This paper presents an investigation into salt diffusion in new, fully saturated brick under isothermal conditions. A commonly used experiment methodology, diffusion cell method, is adopted. The analytical and numerical solutions are obtained. The analytical solution is simple and straightforward, which determines temporally salt concentrations in the monitored chamber. It enables us to estimate salt diffusion coefficients in a fast and accurate way.     

重庆“朝天扬帆”钢结构工程风振研究

“朝天扬帆”是位于重庆朝天间广场的钢结构雕塑工程,该工程建筑型体复杂、结构布局不规则,通过该雕塑工程缩尺模型的几洞试验,确定其风载计算的体型系数;用时程法计算结构的风振响应,且在模拟作用于结构上的脉动风时程曲线时考虑结构的高度相关性,应用ALGOR93软件对结构进行风振时程分析,并自编程序加以前、后处理。通过对比该结构在脉动风和平均风作用下的杆件内力、节点位移响应,约定结构风振系数,为该雕塑工程抗风设计参数的确定提供理论依据。     

An experimental investigation of heat transfer to pulsating pipe air flow with different amplitudes

Heat transfer characteristics to both laminar and turbulent pulsating pipe flows under different conditions of Reynolds number, pulsation frequency, pulsator location and tube diameter were experimentally investigated. The tube wall of uniform heat flux condition was considered for both cases. Reynolds number varied from 750 to 12,320 while the frequency of pulsation ranged from 1 to 10 Hz. With locating the pulsator upstream of the inlet of the test section tube, results showed an increase in heat transfer rate due to pulsation by as much as 30% with flow Reynolds number of 1,643 and pulsation frequency of 1 Hz, depending on the upstream location of the pulsator valve. Closer the valve to the tested section inlet, the better improvement in the heat transfer coefficient is achieved. Upon comparing the heat transfer results of the upstream and the downstream pulsation, at Reynolds number of 1,366 and 1,643, low values of the relative mean Nusselt number were obtained with the upstream pulsation. Comparing the heat transfer results of the two studied test sections tubes for Reynolds number range from 8,000 to 12,000 and pulsation frequency range from 1.0 to 10 Hz showed that more improvement in heat transfer rate was observed with a larger tube diameter. For Reynolds number ranging from 8,000 to 12,000 and pulsation frequency of 10 Hz, an improvement in the relative mean Nusselt number of about 50% was obtained at Reynolds number of 8,000 for the large test section diameter of 50 mm. While, for the small test section diameter of 15 mm, at same conditions of Reynolds number and frequency, a reduction in the relative mean Nusselt number of up to 10% was obtained.     

Equivalence Classes and Symmetries of the Variable Coefficient Kadomtsev—Petviashvili Equation

We classify the variable coefficient Kadomtsev—Petviashvili (VCKP) equation into equivalence classes under the group of local point transformations, leaving the equation form invariant but changing the coefficient functions. We list the representatives of all equivalence classes with the corresponding transformations. Then, we obtain the symmetry group of the VCKP equation and in particular discuss how to use these transformations to classify low-dimensional symmetry algebras in the generic case. We conclude with a discussion of the implications of the present article.