Nonlinear eddy viscosity modeling and experimental study of jet spreading rates

Indoor airflow pattern is strongly influenced by turbulent shear and turbulent normal stresses that are responsible for entrainment effects and turbulence‐driven secondary motion. Therefore, an accurate prediction of room airflows requires reliable modeling of these turbulent quantities. The most widely used turbulence models include RANS‐based models that provide quick solutions but are known to fail in turbulent free shear and wall‐affected flows. In order to cope with this deficiency, this study presents a nonlinear k‐ε turbulence model and evaluates it along with linear k‐ε models for an indoor isothermal linear diffuser jet flow measured in two model rooms using PIV. The results show that the flow contains a free jet near the inlet region and a wall‐affected region downstream where the jet is pushed toward the ceiling by entrainment through the well‐known Coanda effect. The CFD results show that an accurate prediction of the entrainment process is very important and that the nonlinear eddy viscosity model is able to predict the turbulence‐driven secondary motions. Furthermore, turbulence models that are calibrated for high Reynolds free shear layer flows were not able to reproduce the measured velocity distributions, and it is suggested that the model constants of turbulence models should be adjusted before they are used for room airflow simulations.     

Local and parallel finite element methods for the mixed Navier–Stokes/Darcy model

In this paper, the mixed Navier–Stokes/Darcy problem which describes a fluid flow filtrating through porous media is considered. Based on two-grid discretizations, two local and parallel finite element algorithms for solving this mixed model are proposed. Numerical analysis and experiments are presented to show the efficiency and effectiveness of the local and parallel finite element algorithms.     

“booster method” for singularly perturbed robin problems-II

Singularly perturbed Robin problems are considered in this paper. In order to get an improved numerical solution to these problems, a computational method (“Booster Method”) is suggested. In this method, an asymptotic approximation is incorporated into a finite difference scheme to improve the numerical solution. Error estimates are proposed when implemented in known difference schemes. Numerical examples are presented to illustrate the present method.     

A new analytical method for solving systems of Volterra integral equations

In this paper, a new modified homotopy perturbation method (NHPM) is introduced for solving systems of Volterra integral equations of the second kind. Theorems of existence and uniqueness of the solutions to these equations are presented. Comparison of the results of applying the NHPM with those of the homotopy perturbation method and Adomian's decomposition method leads to significant consequences. Several examples, including the system of linear and nonlinear Volterra integral equations, are given to demonstrate the efficiency of the new method.     

Solitons and periodic solutions of coupled nonlinear evolution equations by using the sine–cosine method

In this paper, we establish exact solutions for coupled nonlinear evolution equations. The sine–cosine method is used to construct exact periodic and soliton solutions of coupled nonlinear evolution equations. Many new families of exact travelling wave solutions of the (2+1)-dimensional Konopelchenko–Dubrovsky equations and the coupled nonlinear Klein–Gordon and Nizhnik–Novikov–Veselov equations are successfully obtained. The obtained solutions include compactons, solitons, solitary patterns and periodic solutions. These solutions may be important and of significance for the explanation of some practical physical problems.     

Application of meshless local integral equations for two-dimensional transient coupled hygrothermoelasticity analysis: Moisture and thermoelastic wave propagations under shock loading

This work develops the application of meshless local integral equations based on the meshless local Petrov–Galerkin (MLPG) method for two-dimensional (2D) coupled hygrothermoelasticity analysis. A unit Heaviside step function is used as the test function in the local weak forms. The analyzed domain is divided into some small subdomains with a circular shape. The radial basis functions are used for approximation of the spatial variation of field variables. For discretization of time variations, the Laplace transform technique is used. The moisture concentration diffuses through 2D domain with a finite speed similar to thermoelastic waves. The propagation of moisture diffusion, temperature, and elastic waves is obtained and discussed at various time instants. The MLPG method has a high capability to track the moisture diffusion, elastic and thermal wave fronts at every arbitrary time instant in 2D domain. The distribution profiles of moisture concentration, temperature, and displacements along two orthogonal directions are illustrated at various time instants.     

Variation of density of diesel and biodiesel mixtures in three different temperature ranges

The use of biodiesel fuel is becoming increasingly imperative nowadays and it is necessary to know the change of density. In this work the variation of density of diesel-biodiesel blends across the scale of 0–100% by adding each time 2% biodiesel and then measuring the density of three different temperatures (5, 15, 25°C) covering and the usual scale of temperatures the use of mixtures of diesel-biodiesel. Through the extraction of equations can be known in advance the relationship of density of diesel-biodiesel blend, and temperature that is used.     

线性方程组在工作流相关问题中的应用

为解决工作流中的模型正确性验证、资源分配、活动实例选择等相关问题,提出一种采用建立方程组的求解算法。该算法通过建立方程组描述工作流中的活动结构、资源分配、时间限制等约束条件,建立目标函数用于描述流程的最优目标,求解方程组得到资源分配的最优方案。通过建立等价关系对流程中的活动集合进行划分,再根据约束方程和目标函数求解得出流程的路径选择最佳方案。该算法确保了整个流程的正确性和完整性,实现了流程结构上和性能上的优化。     

A higher order method for multiple zeros of nonlinear functions

A method of order three for finding multiple zeros of nonlinear functions is developed. The method requires two evaluations of the function and one evaluation of the derivative per step.     

Book reviews

THE BRAIN AND BEHAVIORAL SCIENCES (ISSN 0140-525x).Published quarterly by Cambridge University Press (£35.00).

COMPUTATIONAL PROBABILITY AND SIMULATION by Sidney J.Yakowitz pub. Addison-Wesley Pub. Co. Inc., 1977, pp. 240, £10.00 paperbound £18.00 hardnbound.

THE WORLD FERTILITY SURVEY JAN-DEC 1977-ANNUAL REPORT.

COMPSTAT LECTURES I. LECTURES IN COMPUTATIONAL STATISTICS, Ed. by Horst Skarabis and Peter Sint 1978. 132 pages. Bound, pub. Physica-Verlag, Wurzburg, Germany (DM30).

COMPSTAT 1978. PROCEEDINGS OF 3RD SYMPOSIUM IN COMPUTATIONAL STATISTICS LEIDEN 1978, Ed. by L. C. A.

Corsten and J. Hermans, 1978, 538 pages, Bound, pub. Physica-Verlag, Germany (DM59).