Friction coefficient of a disk in a sheet of viscous fluid: numerical calculation

We study the class C of (generalized) orthogonal polynomial sequences {Pn(x)}n=0∞ satisfying a recurrence relation of the type Pn(x) = (x − cn)Pn−1(x) − λnPn−2(x), n> 1, where λn ≠ 0 and the sequence {λn+1/(cncn+1)}n=1∞ constitutes a chain sequence. We obtain a new characterization of C in terms of the moment sequence associated with an orthogonal polynomial sequence, and contribute to the solution of the problem of determining a (signed) orthogonalizing measure for a member of C

Decay of travelling waves in dissipative Poisson systems

In many finite and infinite dimensional systemslow-dimensional behaviour is often observed. That is to say, the dynamics, observed experimentally or numerically, looks as if it can be described (approximately) with only a few essential parameters. Choosing the correct set of such ldquorobust observablesrdquo is an essential ingredient of a successful low dimensional description. This paper reports on a specific example of a more general approach that aims at describing certain (low dimensional) phenomena in (high dimensional) damped/driven equations with parameters that are essentially determined from the underlying conservative part of the equation. In particular, a Hamiltonian or a Poisson structure of the conservative part is exploited to find (characterize) families of exact solutions. These solutions are then used as the ldquobase functionsrdquo with the aid of which the solutions of the disturbed system are approximated. This approximation is accomplished using the parameters that characterize the family as variables that depend on time. In this paper, this procedure is applied to a class of systems which admit travelling waves when dissipation is ignored

Cross-sectional river shapes: A variational discharge-resistance formulation

Cross-sectional river shapes were obtained from a variational principle: minimizing the bed friction for a given discharge and a given maximum lateral bed slope (angle of repose). The optimal shape is found to be independent of both the exponent in the friction law adopted and the value of the discharge, but it does depend on the angle of repose. The optimal profile is a single stream; for braided rivers the solution is suboptimal

Eindwaarde: waar of niet waar?

Eindwaarde is het verwachte bedrag dat op de laatste dag van de beschouwde disconteringsperiode wordt overeengekomen voor een vastgoedobject tussen een willige verkoper en een willige koper, die op een gepaste afstand van elkaar staan, na een behoorlijke marketing en waarbij partijen met kennis, voorzichtigheid en zonder dwang handelen’

Effects of intraparticle heat and mass transfer during devolatilization of a single coal particle

The objective of the present work is to elucidate the influence of intraparticle mass and heat transfer phenomena on the overall rate and product yields during devolatilization of a single coal particle in an inert atmosphere. To this end a mathematical model has been formulated which covers transient devolatilization kinetics and intraparticle mass and heat transport. Secondary deposition reactions of tarry volatiles also are included. These specific features of the model allow a quantitative assessment to be made of the impact of major process conditions such as the coal particle size, the ambient pressure and the heating rate on the tar, gas and total volatile yield during devolatilization. Model predictions are compared to a limited number of experimental results, both from the present work and from various literature sources

Calculations on the current density and the voltage-current relation under a.c. conditions of filaments

Technical applications of multifilamentary wires indicate that filaments are used in complex magnetic fields (a combination of non-parallel a.c./d.c. transverse and rotating fields) carrying an a.c./d.c. transport current of various frequency. Furthermore, due to technical manufacturing processes the filaments are heavily distorted. Therefore, a numerical model is developed to compute the current density of a filament of arbitrary shape in any external transverse field carrying an a.c./d.c. transport current. The great flexibility of the model is shown in several examples

Mass transfer with complex reversible chemical reactions I. Single reversible chemical reaction

An improved numerical technique was used in order to develop an absorption model with which it is possible to calculate rapidly absorption rates for the phenomenon of mass transfer accompanied by a complex reversible chemical reaction. This model can be applied for the calculation of the mass transfer rates (and enhancement factors) for a wide range of processes and conditions, for both film model and penetration model, complex kinetic expressions and equilibrium reactions. With the aid of this method it is demonstrated that reversibility has a substantial effect on the absorption rate. Approximate analytical solutions for the calculation of the mass transfer rates presented in literature are checked for their validity. All approximations are of restricted use and can be applied only for a limited number of reactions and it is desirable to check the approximation with the aid of a numerical solution before it is used for mass transfer calculations. The linearization method of Hikita and Asai (Kagaku Kogaku 11, 823¿830, 1963) cannot be applied generally for reversible reactions and therefore can lead to erroneous results. Experimentally determined absorption rates of H2S and CO2in various aqueous alkanolamine solutions can be predicted satisfactorily for the several mass transfer regimes studied

Numerical calculation of simultaneous mass transfer of two gases accompanied by complex reversible reactions

A discretization technique is described, which makes it possible to calculate numerically mass transfer behaviour between two media in which complex chemical reactions occur. To show the stability of the technique it has been applied to the industrially well-known system of simultaneous absorption or desorption of H2S and CO2 to or from an amine solution, accompanied by simultaneously occurring strongly interfering overall chemical reaction(s) of complex, non elementary kinetics. For previously published limit cases of the transfer system considered, i.e. for the single transfer of H2S or CO2 accompanied by reversible chemical reaction, a comparison has been made with analytical and approximate solutions of previous authors. The agreement is very good. In studying simultaneous transfer of H2S and CO2, on which hardly any previous work was available, special attention has been paid to the effects of the reversibility of the reactions involved. It has been shown how, under certain conditions due to reversibility occurring in the transferzone, desorption takes place though absorption would be expected on basis of the driving forces. This revealed that not only enhancement factors larger than unity but also smaller, even negative values are possible