An automatic mesh generation scheme for plane and curved surfaces by ‘isoparametric’ co-ordinates

A computer orientated method is presented which generates meshes of triangular elements in plane and curved surfaces. Depending on geometrical and material variations, the region to be discretized is divided into a number of four sided zones. By using curvi-linear co-ordinate systems, nodes within and on the boundary of each zone are automatically positioned and referenced to a global Cartesian co-ordinate system. Elements are automatically assembled from these nodes. Input data is required to specify the positions and material properties of each zone and how they are connected. Examples are given which illustrate the range of meshes that can be generated. Extension of the method to generate three-dimensional tetrahedral elements is indicated.     

Synthesis and characterization of chiral main chain polyesters with polar segments tailored for second harmonic generation

The synthesis, characterization and solvatochromic behavior of a new series of chiral polyesters are reported. These polymers with -conjugated donor-acceptor segments were synthesized with a view to be suitable for second harmonic generation. The polyesters were prepared by the reaction of diacid chlorides with biphenolic azo chromophores with -conformation and optically active dihydroxy compound (isosorbide). The polymers containing isosorbide units are optically active. They showed T _g between 100°C to 160°C and are stable up to 400°C. A red shift in the longer wavelength absorption band of these polymers in UV-Vis. absorption spectra (positive solvatochromism) shows that the dipole moment of excited state is higher than that of the ground state. Therefore these polyesters are expected to have good second harmonic generation capability.     

Restrictions in the application of automatic mesh generation schemes by ‘isoparametric’ co-ordinates

To obtain meshes of reasonable form there have to be made some restrictions in the application of automatic mesh generation schemes using ‘isoparametric’ co-ordinates. In this present paper it will be shown that such restrictions exist for plane meshes. The results figured here are also valid for three-dimensional meshes.     

Note on ‘Construction of Double Sampling s‐Control Charts for Agile Manufacturing’

He and Grigoryan (Quality and Reliability Engineering International 2002; 18 :343–355) formulated the design of a double‐sampling (DS) s control chart as an optimization problem and solved it with a genetic algorithm. They concluded that the DS s control charts can be a more economically preferable alternative in detecting small shifts than traditional s control charts. We explain that, since they only considered the average sample size when the process is in control, their conclusion is questionable. Copyright © 2006 John Wiley & Sons, Ltd.     

Least square-finite element for elasto-static problems. Use of ‘reduced’ integration

A least square based finite element algorithm is developed for some elasto-static problems. In the formulation both stresses and displacements appear as simultaneous variables. In two dimensional (plane) analysis, parabolie isoparametric elements are used. Considerable improvement of performance is obtained with a numerical integration based on 2 × 2 Gauss point distribution over more accurate integration schemes. Reasons for this are presented. The formulation is extended in the section ‘General least square formulation’ to beams and plates with a similar success of ‘reduced’ integration.     

Crack identification by ‘arrival time’ using XFEM and a genetic algorithm

A computational framework is developed in which cracks in two‐dimensional structures are identified, in conjunction with non‐destructive testing of specimens. As opposed to a previous study by the authors, which was based on time‐harmonic excitation with a single frequency, here the transient response of the structure to a short‐duration signal is measured along part of the external boundary. Crack detection is performed using the solution of an inverse time‐dependent problem. It is shown that the arrival time of the input signal to the points of measurement is a good criterion for crack identification in the time domain. The inverse problem of identification is solved using a genetic algorithm, while each forward problem is solved by the time‐dependent extended finite element method (XFEM). The XFEM scheme is efficient in that it allows the use of a single regular mesh for a large number of forward time response problems with different crack geometries. Numerical examples involving a crack in a flat membrane are presented. Identification based on ‘arrival time’ is shown to perform better than that based on time‐harmonic response. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of the molecular-dispersed structure of a polar dye solution on its photoluminescence spectra and second harmonic generation in a liquid crystal matrix

The influence of aggregation of polar dye molecules in a nematic liquid crystal (NLC) matrix of 4-p-pentyl-4′-cyanobiphenyl on the formation of a molecular-dispersed ordered system, its photoluminescence spectra, and second harmonic generation (SHG) has been studied. It is established that there is a certain dye concentration in the molecular-dispersed polar dye-NLC system, below which only SHG takes place upon IR (1064 nm) laser excitation. Above this dye concentration, the laser excitation leads to both SHG and an intense two-photon luminescence. A possible mechanism of this phenomenon is proposed.     

A simple approximate expression for finite life fatigue behaviour in the presence of ‘crack‐like’ or ‘blunt’ notches

In this note, we explore the possibility of simple extensions of the heuristic El Haddad formula for finite life, as an approximate expression valid for crack‐like notches, and of the ‘Luká? and Klesnil’ equation for blunt notches. The key starting point is to assume, in analogy to the Basquin power‐law SN curve for the fatigue life of the uncracked (plain) specimen, a power law for the ‘finite life’intrinsic El Haddad crack size. The approach has similarities with what recently proposed by Susmel and Taylor as a Critical Distance Method for Medium‐Cycle Fatigue regime. Reasonable agreement is found with the fatigue data of Susmel and Taylor for notches, and in particular the error seems smaller in finite life than for infinite life, where these equations are already used. In these respects, the present proposal can be considered as a simple empirical unified approach for rapid assessment of the notch effect under finite life.     

‘Expert information’ versus ‘expert opinions’. Another approach to the problem of eliciting/ combining/using expert knowledge in PRA

In the traditional approach to eliciting expert knowledge for use in risk assessment and decision analysis, the expert is asked for his opinion about, say, the numerical value of some unknown parameter λ. This opinion is then expressed as a point estimate, λ_i, or a probabilistic estimate, P_i(λ). Much attention and debate is then given, in the traditional approach, to methods of weighing and combining the opinions from the individual experts.The present paper advocates another approach in which we ask each expert, instead, for his body of evidence, E_i, relevant to the value of λ. In this way, the approach first arrives at a consensual body of evidence, E − {E_i}, and second, at a consensual curve p(λ|E) that expresses our knowledge about λ based on that body of evidence.The essential difference between this ‘expert information’ approach and the traditional ‘expert opinion’ approaches may be captured in the slogan: lsWeigh evidence, not experts!’     

Similitude of sandwich panels with a ‘soft’ core in buckling

The paper presents the similarity analysis of a sandwich unidirectional panel with a transversely flexible core under buckling loads. The governing equations are those used in the high-order analysis of sandwich panels with a ‘soft’ core. The study derives the similitude conditions in the case of external in-plane compressive loads that yield buckling of the panel with and without imperfections. In the first part, the buckling analysis is presented and it is based on the linearized version of the governing equations of the non-linear geometrical bending equations. The presentation includes an analytical proof of the applicability of similarity for the buckling of a sandwich panel with identical faces and a numerical demonstration of the response when full similarity and partial similarity exist. The effects of full and partial similarity are presented for a panel with imperfections.     

A review of the ‘taguchi methods’ for off-line quality control

The Taguchi methods have recently become popular in the U.S.A following a realization of their importance in Japanese quality design. This review is an initial attempt to extract the important ideas while drawing on the ‘Western’ experience with response surface methodology and experimental design.     

An assessment of flow oriented schemes for reducing ‘false diffusion’

An important limiting factor in the accurate modelling of fluid flow problems is the numerical representation of the convection terms in the Navier-Stokes equations. This paper reviews several approaches used to approximate the convection terms and reduce the so-called false-diffusion errors, within the context of finite-difference and finite-volume methods. Numerical errors are characterized as those due to discretization of the differential terms and those due to the influence of the multidimensional nature of the flow. Necessary criteria are identified which a numerical scheme must satisfy, if it is to be a candidate, at least in terms of accuracy and practicality, for the successful solution of the Navier-Stokes equations. One of the criteria is the need of the scheme to account explicitly for the multidimensionality of the flow in the transport of scalar variables. All schemes except Raithby's SKEW approximation are deficient in this respect. However, the SKEW scheme does not satisfy some of the other criteria and does not always perform well. A new scheme called CUPID (Corner UPwInDing), which is based on the ideas of the SKEW scheme, yet obeys more of the criteria identified above, is described. The scheme is tested on a series of discriminating test problems which, the authors contend, demonstrate its potential for practical use in solving accurately the Navier-Stokes equations.