Numerical investigation on a new local preconditioning method for solving the incompressible inviscid, non-cavitating and cavitating flows

A locally power-law preconditioning algorithm is developed. This is applied to compute incompressible inviscid, steady-state, non-cavitating and cavitating flows. The preconditioning parameters are adapted automatically from the pressure of computational domain. This method suggests better convergence rates rather than the standard artificial compressibility and the standard preconditioning method. Single-fluid Euler equations, cast in their conservative form, along with the barotropic cavitation model are employed. The cell-centred Jameson's finite volume discretization technique is used to solve the preconditioned governing equations. The stabilization is achieved via the second and fourth, order artificial dissipation scheme. Explicit four-stage Runge-Kutta time integration is applied to find the steady-state condition. In this paper, the method is assessed through simulations of incompressible inviscid, steady-state, non-cavitating and cavitating flows over a 2D NACA0012 and a 2D NACA66(MOD)+a=0.8 hydrofoil section. The results show satisfactory agreement with others numerical and experimental works in pressure distribution and hydrodynamic forces. Using the power-law preconditioner decreases the convergence rate significantly. In addition, information such as the effects of the new locally power-law preconditioner, the effects of the artificial dissipation terms, and the effects of the artificial compressibility parameter, on convergence speed and solution accuracy is highlighted.     

A guide to the literature on the history of engineering available in the cooper union library: Cooper Union Bulletin. Engineering and science series,Number 28, 46 pages, 18 × 2S CMS., paper. New York,The Cooper Union for the Advancement of Science and Art, 1946.

The linear logarithmic relations between deformation and temperature and pressure, previously empirical, have been directly derived from the defining equations for compressibility and thermal expansivity and shown to apply to all three stages of every deformation.Gibbs' thermodynamic potential function is shown to lead directly to simple and exact expressions for the energy of change of phase and of deformation within any one phase. The latter, a general equation of state, amounts to a simple relation between the four internal pressures.The derived deformation and energy functions are applied to some experimental data on steel tape which included thermal and relaxation observations.Thermodynamic relations governing both elastic and viscous behavior are developed. Plastic behavior involves both single phase and multiple phase applications of the second law. Precise thermal measurements should give the constants.     

Representation and realization of operational differential equations with time-varying coefficients

An algebraic treatment of operational differential equations with time-varying coefficients is presented in terms of skew rings of differential polynomials defined over a Noetherian ring. Included in this framework are delay differential equations with time- varying coefficients. The operator equations are characterized by transfer matrices which are utilized to construct realizations given by first-order vector differential equations with operator coefficients. It is shown that the realization of matrix equations can be reduced to the realization of scalar equations. Finally, a simple procedure is derived for realizing scalar equations.     

美国农业焚烧管理对中国秸秆禁烧管理的启示

为解决秸秆露天焚烧给中国环境保护与农村建设带来的难题,本文系统梳理了美国农业焚烧管理中最主要的内容即烟雾管理计划,重点研究了烟雾管理计划对中国秸秆焚烧治理的启示。通过归纳分析表明,美国烟雾管理计划通常由焚烧授权、烟雾管理组件、公众教育、监督与执法、实施效果评价等5个方面组成,具体做法是针对不同等级的焚烧规模进行不同的分级管理,制定规范的焚烧授权标准以明确是否可以焚烧,依据烟雾扩散能力、风向、安全距离等确定可焚烧时间和可焚烧区域、最大可焚烧量,并进行严格的执法监督和处罚。基于上述分析,建议中国出台专门针对秸秆焚烧治理的法律规定,制定秸秆焚烧授权管理办法,因地制宜制定秸秆焚烧气象指数分级办法,加强秸秆焚烧过程中的管控工作。     

A matrix generalization of heaviside's expansion theorem

Starting with the energy and dissipation functions of the general n mesh linear bilateral network and using the operational methods of the Laplacian transformation, a solution is obtained for the Lagrangian equations of the system subject to initial boundary conditions. The equations take a particularly simple and general form if matrix notation is used.It is noted that the general case bears a close resemblance to the simple, one mesh, series circuit when the scalar factors which appear in this circuit are generalized to matrix form.     

Radiant Flux Through Apertures— II

Equations for the radiant flux through apertures are well-known. But the exact equations are cumbersome and give little direct insight into the behavior of aperture systems. The present paper considers simple approximate equations for rectangular apertures in parallel planes and in perpendicular planes. It extends the previous work (square apertures) to the general case of rectangular apertures.     

Dynamic programming,Fermat's principle and stochastic Eikonal equations

An extension of Fermat's principle to the stochastic case is presented in order to treat ray propagation in random media. The concept of dynamic programming permits one to derive a sequence of stochastic eikonal equations from which a sequence of rays can be traced using Hamilton's equations. The extension is motivated by analogous stochastic control problems in which the concepts and methods are adapted to the present problem. To facilitate understanding of the main ideas the presentation is given in a simple and somewhat naive manner. Two simple examples are presented to demonstrate the ideas and techniques.     

Effect of electrical double layer on electric conductivity and pressure drop in a pressure-driven microchannel flow

The effect of an electrical double layer (EDL) on microchannel flow has been studied widely, and a constant bulk electric conductivity is often used in calculations of flow rate or pressure drop. In our experimental study of pressure-driven micropipette flows, the pipette diameter is on the same order of magnitude as the Debye length. The overlapping EDL resulted in a much higher electric conductivity, lower streaming potential, and lower electroviscous effect. To elucidate the effect of overlapping EDL, this paper developed a simple model for water flow without salts or dissolved gases (such as CO₂) inside a two-dimensional microchannel. The governing equations for the flow, the Poisson, and Nernst equations for the electric potential and ion concentrations and the charge continuity equation were solved. The effects of overlapping EDL on the electric conductivity, velocity distribution, and overall pressure drop in the microchannel were quantified. The results showed that the average electric conductivity of electrolyte inside the channel increased significantly as the EDL overlaps. With the modified mean electric conductivity, the pressure drop for the pressure-driven flow was smaller than that without the influence of the EDL on conductivity. The results of this study provide a physical explanation for the observed decrease in electroviscous effect for microchannels when the EDL layers from opposing walls overlap.     

Non-Linear Functional Relations and Superposition Principles in Viscoelasticity

Non-linear constitutive functional equations for isotropic viscoelastic materials with small and finite deformations are derived on the basis of tensorial expansions. These equations express the first-order as well as simple and joint second-order effects. Further, the corresponding non-linear superposition principles are formulated.     

饱和土体中半封闭压力隧洞的应力和位移场

基于Biot固结理论，研究分析了饱和土体中半封闭压力隧洞问题，建立了压力隧洞的半封闭边界条件．通过对控制方程的解耦，得到了孔隙水压力的消散方程．在Laplace变换域中得到隧洞边界上作用轴对称荷载和流体压力条件下的应力、位移和孔隙水压力解答，考虑了土体和孔隙流体的压缩性，运用Laplace数值逆变换得到时域中的解．文末给出了算例，分析了隧洞的半封闭特性对应力、位移和孔隙水压力的影响。     

总有机碳（TOC）自动分析仪进样研究

燃烧氧化-NDIR法是总有机碳（TOC）自动分析仪普遍采用的一种方法,但在实际应用中,影响其测量精度和误差的因素有很多,包括水汽干扰、载气流量、载气压力、燃烧温度、标液误差、进样精度、阀件死体积、密封性、检测器精度、基线漂移、积分精度等,其中进样精度是其中最关键、最重要的因素之一。提高进样精度会大大提高总有机碳（TOC）自动分析仪的测量精度和误差。     

The impulse strength of solid and gas-filled high voltage cables

A method is presented that allows the computation of the impulse strength of insulating oil and of solid and gas-filled cables. The principle of the calculation is that breakdown is initiated by currents due to an electronic emission from the cathode; in gas-filled cables these currents are increased by means of gaseous ionization in the butt spaces. Approximate equations are deduced and numerical impulse strength values for insulating oil and solid cable computed, resulting in fair agreement with experimental observations. Extending the equations to gas-filled cables, numerical impulse data for varying gas pressure and for varying radial butt-space alignment are evaluated.     

锦东电厂调速器比例伺服阀不能自动调整空载扰动问题分析

锦东电厂#1机组调试过程中,调速器控制部分监测油压远低于油压装置压力罐压力值,导致在机组空载扰动试验过程中,给予控制部分向下扰动量后,在A套比例伺服阀主用工况下,机组导叶快速关闭,不能实现扰动量自动调整。本文对该问题的分析及处理过程进行了简要介绍,供参考。     

Relationship of the hypercircle technique to the energy theorems

In this paper, a system of thermodynamic relations governing the deformation of strain-rate sensitive elastic-plastic materials is developed. These relations are obtained by assuming that the deformation and entropy of the material are dependent on stress state and temperature, and on certain internal variables which are identified in this paper with dislocation densities, and the mobile fractions of each kind of dislocation. It is postulated (on the basis of physical arguments) that the densities and fractions are governed by certain evolutionary equations. An example is given of a material that derives from these evolutionary equations under quite simple assumptions. It is shown by numerical calculations that this material exhibits the main features observed experimentally in uniaxial stress tests of metals.     

Application of numerical inverse Laplace transform algorithms in fractional calculus

Laplace transform technique has been considered as an efficient way in solving differential equations with integer-order. But for differential equations with non-integer order, the Laplace transform technique works effectively only for relatively simple equations, because of the difficulties of calculating inversion of Laplace transforms. Motivated by finding an easy way to numerically solve the complicated fractional-order differential equations, we investigate the validity of applying numerical inverse Laplace transform algorithms in fractional calculus. Three numerical inverse Laplace transform algorithms, named Invlap, Gavsteh and NILT, were tested using Laplace transforms of fractional-order equations. Based on the comparison between analytical results and numerical inverse Laplace transform algorithm results, the effectiveness and reliability of numerical inverse Laplace transform algorithms for fractional-order differential equations was confirmed.     

Discrete-time nonlinear observer design with general criteria

A class of discrete-time nonlinear system and measurement equations having incrementally conic nonlinearities and finite energy disturbances is considered. A linear matrix inequality-based design approach is presented, which guarantees the satisfaction of a variety of performance criteria ranging from simple estimation error boundedness to dissipativity. Some simulation examples are included to illustrate and provide support to the proposed design methodology.     

Numerical solving initial value problem for Fredholm type linear integro-differential equation system

In this paper, we introduce a numerical method for solving initial value problems for a system of linear integro-differential equations. The main idea is based on the interpolations of unknown functions at distinct interpolation points. We next use Clenshaw-Curtis quadrature formulae required in the approximation of the integral equations. The technique is very effective and simple. In the end, to show the efficiency of this method, we present some numerical examples.     

水电站调速系统用油压装置的容量选择计算

针对某大型、单机容量为350MW机组的接力器大小及机组运行要求,对整个调速系统的用油量进行准确计算,以设计出满足要求的油压装置。     

水电站调速系统用油压装置的容量选择计算

针对景洪电站接力器的大小及机组的运行要求,对整个调速系纯的用油量进行准确计算,以设计出满足要求的油压装置。     

移动荷载作用下桥梁动力响应的精细时程积分计算

桥梁与车辆的耦合振动方程为时变系数微分方程,用解析的方法求解这类问题有很大的局限性,解决这类问题的最为有效的工具之一是数值方法中的有限单元法.对移动衙载这种简化模型在时程积分时采用了精细积分法,为了保持精细时程积分法的高精度,对动力方程中的非齐次项进行离散计算时选用了积分精度较高的科茨积分格式,对于Euler-Bernouili梁单元采用二节点的Hermite插值函数,模拟了移动常量荷载、移动简谐荷载作用下的等截面和变截面简支梁桥模型的振动情况,并与解析的结果及一些其它的数值解法进行了对比,显示了采用精细时程积分时对动力响应过程的数值模拟的高精度.