Explicit characteristic‐based finite volume element method for level set equation

Accurate modeling of interfacial flows requires a realistic representation of interface topology. To reduce the computational effort from the complexity of the interface topological changes, the level set method is widely used for solving two‐phase flow problems. This paper presents an explicit characteristic‐based finite volume element method for solving the two‐dimensional level set equation. The method is applicable for the case of non‐divergence‐free velocity field. Accuracy and performance of the proposed method are evaluated via test cases with prescribed velocity fields on structured grids. By given a velocity field, the motion of interface in the normal direction and the mean curvature, examples are presented to demonstrate the performance of the proposed method for calculating interface evolutions in time. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical models for vehicle exhaust dispersion in complex urban areas

Two numerical models are presented for predicting vehicle exhaust dispersion in complex urban areas with or without the wind field. The models not only reflect the effect of building and street canyon configuration on the pollutant propagation, but also are able to predict the turbulent energy produced by moving vehicles on the road. In particular, in the discrete model, turbulent energy and pollutant concentration produced by each vehicle are dynamically described in the Lagrangian method. The pollutant propagation is calculated with the advection–diffusion equation. The Reynolds averaged Navier–Stokes equations are numerically solved for the wind flows. The movement and heat release rate of the vehicles are treated as sources of the turbulent energy equation for the computation of turbulent energy produced by the moving vehicles. This paper reports the detailed implementation of the models. Four typical numerical tests were carried out to represent the performance of the proposed numerical models. Copyright © 2010 John Wiley & Sons, Ltd.     

A stabilized formulation for the advection–diffusion equation using the Generalized Finite Element Method

This paper presents a stable formulation for the advection–diffusion equation based on the Generalized (or eXtended) Finite Element Method, GFEM (or X‐FEM). Using enrichment functions that represent the exponential character of the exact solution, smooth numerical solutions are obtained for problems with steep gradients and high Péclet numbers in one‐ and two‐dimensions. In contrast with traditional stabilized methods that require the construction of stability parameters and stabilization terms, the present work avoids numerical instabilities by improving the classical Galerkin solution with enrichment functions (that need not be polynomials) using GFEM, which is an instance of the partition of unity framework. This work also presents a strategy for constructing enrichment functions for problems involving complex geometries by employing a global–local‐type approach. Representative numerical results are presented to illustrate the performance of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Cost-effective modeling strategies for the analysis of spliced steel connections

The paper presents several cost-effective modeling strategies that can be used by structural engineers in practice to determine the stresses in the spliced members. The computational efficiency and the modeling effort required for the several modeling options are also discussed. The deformation mechanisms and load transfer for several types of connections are illustrated. Optimization techniques are also presented to economize the computer time for connections with large number of bolts. Results are presented to compare the accuracy of several modeling strategies commonly used in practice. It is shown that for eccentric connections, the flexural bending largely affect the maximum tensile and compressive stresses within the joint. The difference may reach up to 54%. Finally, Experimental comparisons are made with the numerical procedures for typical connection model.     

A boundary element method to price time-dependent double barrier options

In this paper we propose a new method for pricing double-barrier options with moving barriers under the Black-Scholes and the CEV models. First of all, by applying a variational technique typical of the boundary element method, we derive an integral representation of the double-barrier option price in which two of the integrand functions are not given explicitly but must be obtained solving a system of Volterra integral equations of the first kind. Second, we develop an ad hoc numerical method to regularize and solve the system of integral equations obtained. Several numerical experiments are carried out showing that the overall algorithm is extraordinarily fast and accurate, even if the barriers are not differentiable functions. Moreover the numerical method presented in this paper performs significantly better than the finite difference approach.     

A Stokes model with cavitation for the numerical simulation of hydrodynamic lubrication

We present a cavitation model based on the Stokes equation and formulate adaptive finite element methods for its numerical solution. A posteriori error estimates and adaptive algorithms are derived, and numerical examples illustrating the theory are supplied, in particular with comparison to the simplified Reynolds model of lubrication. Copyright © 2010 John Wiley & Sons, Ltd.     

Note on the Design Differentiability of the Static Response of Elastic Structures

This paper provides a new proof of design sensitivity of the static response of some typical structures. These structures (beams, plates, and plane elastic solids) have been described previously. A proof of design sensitivity of the inverse state operator was provided there, and design sensitivity of static response was derived. The proof presented here is simpler and self-contained.     

蔗渣纤维素黄原酸酯的制备及稳定性研究

以甘蔗渣为原材料,于20％(wt)的NaOH溶液中碱化24 h,在碱性条件下加入用量为0.5 mL/g的CS2,在30℃反应2.5 h,合成了蔗渣纤维素黄原酸酯(BCX)；并对其合成条件进行了优化,对其处理重金属离子的效果进行了评价.研究结果表明,BCX对重金属废水中的Ni2+、Cu2+、Zn2+、pb2+的去除率均在...     

Are upwind techniques in multi-phase flow models necessary?

Two alternatives of primary variables are compared for two-phase flow in heterogeneous media by solving fully established benchmarks. The first combination utilizes pressure of the wetting fluid and saturation of the non-wetting fluid as primary variables, while the second employs capillary pressure of the wetting fluid and pressure of the non-wetting fluid. While the standard Galerkin finite element method (SGFEM) is known to fail in the physical reproduction of two-phase flow in heterogeneous media (unless employing a fully upwind correction), the second scheme with capillary pressure as a primary variable without applying an upwind technique produces correct physical fluid behaviour in heterogeneous media, as observed from experiments.