Initial-value ordinary differential equation solution via variable order Adams method (SIVA/DIVA) package is collection of subroutines for solution of nonstiff ordinary differential equations. There are versions for single-precision and double-precision arithmetic. Requires fewer evaluations of derivatives than other variable-order Adams predictor/ corrector methods. Option for direct integration of second-order equations makes integration of trajectory problems significantly more efficient. Written in FORTRAN 77.

Solving Ordinary Differential Equations

Turbulence, Coherent Structures, Dynamical Systems and SymmetryP. Holmes, J. L. Lumley, G. Berkooz, and C. W. Rowley, 2nd ed., Cambridge University Press, Cambridge, England, U.K., 2012, 386 pp., $90

When a gas of bosonic particles is cooled below a critical temperature, it condenses into a Bose-Ei…

Bose-Einstein condensation

Computer Methods in Applied Mechanics and Engineering

Economic Theory and Operations Analysis.

A new derivative-free method is developed for solving unconstrained nonsmooth optimization problems. This method is based on the notion of a discrete gradient. It is demonstrated that the discrete gradients can be used to approximate subgradients of a broad class of nonsmooth functions. It is also shown that the discrete gradients can be applied to find descent directions of nonsmooth functions. The preliminary results of numerical experiments with unconstrained nonsmooth optimization problems as well as the comparison of the proposed method with the nonsmooth optimization solver DNLP from CONOPT-GAMS and the derivative-free optimization solver CONDOR are presented.

http://www.optimization-online.org/DB_FILE/2006/05/1382.pdf

Discrete Gradient Method: Derivative-Free Method for Nonsmooth Optimization

This review paper is devoted to the numerical analysis of abstract differential equations in Banach spaces. Most of the finite difference, finite element, and projection methods can be considered from the point of view of general approximation schemes (see, e.g., [207,210,211] for such a representation). Results obtained for general approximation schemes make the formulation of concrete numerical methods easier and give an overview of methods which are suitable for different classes of problems. The qualitative theory of differential equations in Banach spaces is presented in many brilliant papers and books. We can refer to the bibliography [218], which contains about 3000 references. Unfortunately, no books or reviews on general approximation theory appear for differential equations in abstract spaces during last 20 years. Any information on the subject can be found in the original papers only. It seems that such a review is the first step towards describing a complete picture of discretization methods for abstract differential equations in Banach spaces. In Sec. 2 we describe the general approximation scheme, different types of convergence of operators, and the relation between the convergence and the approximation of spectra. Also, such a convergence analysis can be used if one considers elliptic problems, i.e., the problems which do not depend on time. Section 3 contains a complete picture of the theory of discretization of semigroups on Banach spaces. It summarizes Trotter–Kato and Lax–Richtmyer theorems from the general and common point of view and related problems. The approximation of ill-posed problems is considered in Sec. 4, which is based on the theory of approximation of local C-semigroups. Since the backward Cauchy problem is very important in applications and admits a stochastic noise, we also consider approximation using a stochastic regularization. Such an approach was never considered in the literature before to the best of our knowledge. In Sec. 5, we present discrete coercive inequalities for abstract parabolic equations in Cτn([0, T ];En), C τn([0, T ];En), L p τn([0, T ];En), and Bτn([0, T ];C (Ωh)) spaces.

Approximation of abstract differential equations

The turbulent flow field in a mixing tank generated by the six-blade Rushton turbine impeller is predicted by using computational fluid dynamics The governing differential equations of the fluid flow are approximated by an algebraic set of equations through a finite volume method, while large eddy simulation is employed to handle the effects originating from the turbulence The relative motion between the rotating impeller and the stationary baffle is considered by clicking mesh method The effects of impeller clearance and disc thickness on the power number are determined and it is found that the power number decreases with decreasing clearance and increasing disc thickness The results are comparable with those of well-established measurement techniques in terms of time-averaged velocity field, turbulent kinetic energy, dissipation rate, and power number

Numerical investigation of the effect of the Rushton type turbine design factors on agitated tank flow characteristics

A finite volume technique is presented for the numerical solution of steady laminar flow of Oldroyd-B fluid in a lid-driven square cavity over a wide range of Reynolds and Weissenberg numbers. Second order central difference (CD) scheme is used for the convection part of the momentum equation while first order upwind approximation is employed to handle viscoelastic stresses. A non-uniform collocated grid system is used. Momentum interpolation method (MIM) is used to evaluate face velocity. Coupled mass and momentum conservation equations are solved through iterative SIMPLE (semi-implicit method for pressure-linked equation) algorithm. Detailed investigation of the flow field is carried out in terms of velocity and stress fields. Differences between the behavior of Newtonian and viscoelastic fluids, such as the normal stress effects and secondary eddy formations, are highlighted.

Bülent Karasözen

Papers

Discrete Gradient Method: Derivative-Free Method for Nonsmooth Optimization

Approximation of abstract differential equations

Numerical investigation of the effect of the Rushton type turbine design factors on agitated tank flow characteristics

Finite volume simulation of viscoelastic laminar flow in a lid-driven cavity

Symplectic and multi-symplectic methods for coupled nonlinear schrödinger equations with periodic solutions