Numerical and experimental analysis of harmonic distortion in a moving-coil loudspeaker

The nonlinear effect of a moving-coil loudspeaker, originating from its magnetic coupling factor and the system’s stiffness, presents a significant impact on the sound quality. For improving the sound quality, this article proposes an approach to reduce the total harmonic distortion (THD) by adjusting the initial position of its voice-coil. First, a mathematical model involving the nonlinearities of force factor, mechanical stiffness, and inductance of voice coil is constructed and then solved using a novel algorithm called the parameter spline difference method (PSD). In the course of pursuing reduction of the corresponding THD of a typical moving-coil loudspeaker, the model was used to analyze the nonlinearity of the THD, revealing itself as a nonlinear function of force factor, the system’s stiffness and inductance of voice coil. For various initial positions of the voice-coil, the coupled nonlinear differential equations were solved using the PSD to yield corresponding sound pressure level and THD. To our satisfaction, the loudspeaker driver with its voice-coil optimally tuned for the initial position turns out to have a THD reduction of 10%, which is also consistent with our experimental observations.     

Robust design and numerical simulation on drag reduction by a mixture film for liquid turbulence in a channel

An important way of increasing the speed and lowering the fuel consumption of ships is by decreasing the frictional drag. One of the most promising techniques for reducing drag is the use of air bubbles. The goal of this investigation is to establish a set of optimum robust parametric levels for drag reduction by a mixture (air–water) film in turbulent channel flow. Based on the conditions laid out by the Taguchi orthogonal array method, turbulent flows, with air bubbles injected into a channel, are simulated using commercial computational fluid dynamics software. The local shear stress on the upper wall is computed to evaluate the efficiency of drag reduction. Many factors can affect drag reduction. The factors investigated in this study are the rate of air injection, bubble size, area of air injection, flow speed, and measured position of the shear stress. These factors have been investigated through the analysis of variance, which has revealed that the rate of air injection and water flow speed dominate the efficiency of drag reduction by a mixture film. According to the results, the drag can be reduced by an average of 83.4%; and when the configuration of the parametric levels is optimum the maximum drag reduction of 88.5% is achieved. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis of 8-aza-15-hydroxy-7-oxo-12S-13E-prostenoic acids

The synthesis of a prostaglandin E₁ analog, 8-aza-15-hydroxy-7-oxo-12S-13E-prostenoic acid, is reported.     

Boundary element elastic stress analysis of 3D generally anisotropic solids using fundamental solutions based on Fourier series

The authors have very recently proposed an efficient, accurate alternative scheme to numerically evaluate etc. Green’s function, U(x), and its derivatives for three-dimensional, general anisotropic elasticity. These quantities are necessary items in the formulation of the boundary element method (BEM). The scheme is based on the double Fourier series representation of the explicit, exact, algebraic solution derived by Ting and Lee (1997) [Ting, T.C.T., Lee, V.G., 1997. The three-dimensional elastostic Green’s function for general anisotropic linear elastic solid. Q. J. Mech. Appl. Math. 50, 407–426] expressed in terms of Stroh’s eigenvalues. By taking advantage of some its characteristics, the formulations in this double Fourier series approach are revised and several of the analytical expressions are re-arranged in the present study. This results in significantly fewer terms to be summed in the series thereby improving further the efficiency for evaluating the Green’s function and its derivatives. These revised Fourier series representations of U(x) and its derivatives are employed in a BEM formulation for three-dimensional linear elastostatics. Some numerical examples are presented to demonstrate the veracity of the implementation and its applicability to the elastic stress analysis of generally anisotropic solids. The results are compared with known solutions in the literature where possible, and with those obtained using the commercial finite element code ANSYS. Excellent agreement is obtained in all cases.     

An activity coefficient model for predicting salt effects on vapor–liquid equilibria of mixed solvent systems

In the present study, an activity coefficient model, based on the concept of local volume fractions and the Gibbs–Helmholtz relation, has been developed. Some modifications were made from Tan–Wilson model (1987) and TK–Wilson model (1975) to represent activity coefficients in mixed solvent–electrolyte systems. The proposed model contains two groups of binary interaction parameters. One group for solvent–solvent interaction parameters corresponds to that given by the TK–Wilson model (1975) in salt-free systems. The other group of salt–solvent interaction parameters can be calculated either from vapor pressure or bubble temperature data in binary salt–solvent systems. It is shown that the present model can also be used to describe liquid–liquid equilibria. No ternary parameter is required to predict the salt effects on the vapor–liquid equilibria (VLE) of mixed solvent systems. By examining 643 sets of VLE data, the calculated results show that the prediction by the present model is as good as that by the Tan–Wilson model (1987), with an overall mean deviation of vapor phase composition of 1.76% and that of the bubble temperature of 0.74 K.     

The two‐dimensional streamline upwind scheme for the convection–reaction equation

This paper is concerned with the development of the finite element method in simulating scalar transport, governed by the convection–reaction (CR) equation. A feature of the proposed finite element model is its ability to provide nodally exact solutions in the one‐dimensional case. Details of the derivation of the upwind scheme on quadratic elements are given. Extension of the one‐dimensional nodally exact scheme to the two‐dimensional model equation involves the use of a streamline upwind operator. As the modified equations show in the four types of element, physically relevant discretization error terms are added to the flow direction and help stabilize the discrete system. The proposed method is referred to as the streamline upwind Petrov–Galerkin finite element model. This model has been validated against test problems that are amenable to analytical solutions. In addition to a fundamental study of the scheme, numerical results that demonstrate the validity of the method are presented. Copyright © 2001 John Wiley & Sons, Ltd.