三维分区算法在复杂多连域湍流问题中的应用

提出并实现了一种适合于任意曲线坐标系下非交错网格系统的流体力学数值模拟的三维分区算法 ,通过三维立方块绕流问题对其进行了考证和优化工作 ,证明有良好、稳定的工作性能。在此基础上 ,将该算法有效地应用到了具有典型多连域特征的涉及内外流耦合作用的串列双空气冷却塔定常绕流流动问题 ,揭示了横向风对其运行性能产生不利影响的主要原因     

Two-Dimensional Electroelastic Problem for a Multiply Connected Piezoelectric Body

In this paper, we present the basic relationships for the complex potentials of a two-dimensional electroelastic problem, their general representations for a multiply connected domain, expressions for stress, displacement, electrostatic field intensity and induction, and potential. A closed solution is found for a body with one elliptic cavity or one elliptic crack under the action at infinity of a constant electroelastic field or concentrated forces and charges     

A new process for constructing coefficients of elliptic complex equations in multiply connected domains

This article concerns the inverse problem for linear elliptic systems of first-order equations with Riemann–Hilbert-type map in multiply connected domains. First the formulation and the complex form of the problem for the systems are given, and then the coefficients of the elliptic complex equations for the above problem are constructed by a complex analytic method, where the advantage of the methods in other papers is absorbed, and the used method in this article is more simple and the obtained result is more general. As an application of the above results, we can derive the corresponding results of the inverse problem for second-order elliptic equations from Dirichlet to Neumann map in multiply connected domains.     

Nuclear quadrupole resonance exchange spectroscopy with shaped radiofrequency pulses

Recent work on the nuclear quadrupole resonance (NQR) investigation of molecular dynamics in the solid state has relied on 2D methods. We report our studies of dynamic processes by 1D shaped pulse NQR spectroscopy. Significant advantages include considerably shorter experimental duration, clear definition of the exchange time window, and avoidance of off-resonance effects. The reorientation of the Cl₃C? group in polycrystalline chloral hydrate [Cl₃C–CH(OH)₂] is considered as a test case. This may be modelled as a three-site exchange process. An analysis of the generalised Bloch–McConnell equation is performed to formulate the kinetic matrix. The present approach involves simultaneous excitation of the sites that undergo chemical exchange by employing a suitably modulated shaped RF pulse, followed by a mixing time, and finally a suitable read pulse for signal detection. The experimental signal intensities are plotted against the mixing time to extract the kinetic parameters, i.e. the exchange rate and the spin-lattice relaxation rate. Variable temperature measurements are carried out to determine the activation parameters. Short experiment times are possible in our 1D mode, enabling a large number of runs to be readily performed as a function of mixing time and temperature. The kinetic and activation parameters obtained in the case of chloral hydrate are in good agreement with recent literature values.     

Ionic Liquids as Performance Ingredients in Space Lubricants

Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.     

Simulations of Unsaturated Flow in Multiply Zoned Media by Green Element Models

Flows in variably saturated media that exhibit second-type heterogeneity, in which abrupt changes of medium parameters occur, are simulated by the Green element method (GEM). Such media are usually encountered where soil formations have arisen by different geological or geomorphological processes spread over different time scales. Two challenges are posed when simulating flows in multiply zoned unsaturated media: one is the highly nonlinear nature of the flow within each zone, and the other is dealing with sharp contrast in medium parameters at the interfaces of different zones. Both challenges are accommodated in this paper using a flux-based Green element formulation to simulate the flow and incorporating the Picard and Newton–Raphson (N-R) algorithms to simplify the nonlinear discrete equations. Calculations are carried out on three numerical examples of infiltration into unsaturated soils in two spatial dimensions. The convergence rate of the N-R algorithm is superior to the Picard algorithm only for the first example, while none of the algorithms has a clear advantage for the other two examples. The N-R algorithm suffers from repeated calculation of derivatives of the medium parameters with respect to the pressure head, thereby compromising the accuracy of the solution and increasing computational cost.     

On the existence of multiply connected monolayered cyclofusenes with given parameters

For a given bipartite graph G its skewness is defined as the difference between the sizes of its classes of bipartition. We show that a multiply connected monolayered cyclofusene with m ≥ 2 internal holes and skewness k exists if and only if 0 ≤ k ≤ 2m − 2, thus settling in affirmative two conjectures raised in a recent paper by Karimi et al.     

INITIAL-OBLIQUE DERIVATIVE PROBLEMS FOR NONLINEAR PARABOLIC SYSTEMS WITH MEASURABLE COEFFICIENTS

This paper deals with some initial-oblique derivative boundary value problems for nonlinear nondivergent parabolic systems of several second order equations with measurable coefficients in multiply connected domains. Firstly, a priori estimates of solutions for the initial-boundary value problems are given, and then by using the above estimates of solutions and the Leray-Schauder theorem, the existence and uniqueness of solutions for the problems are proved.     

SHEAR STRESS ANALYSIS OF TIMOSHENKO''S BEAM WITH MULTIPLY CONNECTED CROSS SECTION

In this paper, a finite element method is developed to numerically evaluate the shear coefficient of Timoshenko's beam with multiply connectd cross section. With focus on analyzing shear stresses distributed at the neutral axis of the beam, an improved definition of the shear coefficient is presented. Based on this definition, a Galerkin-type finite element formulation is proposed to analyze the shear stresses and shear deflections. Numerical solutions of the examples for some typical cross-sections are compared with the theoretical results. The shear coefficient of tower sections of the Tsing Ma Bridge is calculated by use of the proposed approach, so that the finite element modeling of the bridge can be developed with the accurate values of the sectional properties.     

A Cartesian grid technique based on one‐dimensional integrated radial basis function networks for natural convection in concentric annuli

This paper reports a radial basis function (RBF)‐based Cartesian grid technique for the simulation of two‐dimensional buoyancy‐driven flow in concentric annuli. The continuity and momentum equations are represented in the equivalent stream function formulation that reduces the number of equations from three to one, but involves higher‐order derivatives. The present technique uses a Cartesian grid to discretize the problem domain. Along a grid line, one‐dimensional integrated RBF networks (1D‐IRBFNs) are employed to represent the field variables. The capability of 1D‐IRBFNs to handle unstructured points with accuracy is exploited to describe non‐rectangular boundaries in a Cartesian grid, while the method's ability to avoid the reduction of convergence rate caused by differentiation is instrumental in improving the quality of the approximation of higher‐order derivatives. The method is applied to simulate thermally driven flows in annuli between two circular cylinders and between an outer square cylinder and an inner circular cylinder. High Rayleigh number solutions are achieved and they are in good agreement with previously published numerical data. Copyright © 2007 John Wiley & Sons, Ltd.