Variational modelling of wave–structure interactions with an offshore wind-turbine mast

We consider the development of a mathematical model of water waves interacting with the mast of an offshore wind turbine. A variational approach is used for which the starting point is an action functional describing a dual system comprising a potential-flow fluid, a solid structure modelled with nonlinear elasticity, and the coupling between them. We develop a linearized model of the fluid–structure or wave–mast coupling, which is a linearization of the variational principle for the fully coupled nonlinear model. Our numerical results for the linear case indicate that our variational approach yields a stable numerical discretization of a fully coupled model of water waves and an elastic beam. The energy exchange between the subsystems is seen to be in balance, yielding a total energy that shows only small and bounded oscillations amplitude of which tends to zero with the second-order convergence as the timestep approaches zero. Similar second-order convergence is observed for spatial mesh refinement. The linearized model so far developed can be extended to a nonlinear regime.     

Fixture modelling for an automotive assembly line

This paper proposes an efficient fixture modelling procedure for automotive body assembly lines. A fixture model consists of two sub-models; a geometric model and a kinetic model that should be remodelled frequently whenever design changes occur. We develop an algorithm extracting the kinetic model from the geometric model of a fixture to reduce the fixture modelling time and effort. Although the geometric models of fixtures used in automotive assembly lines vary, most follow the same kinetic mechanism, the so-called slider-crank mechanism; this is a four-axis system of three revolute and one prismatic joint. The prismatic axis of a fixture represents a pneumatic actuator involving a piston and a cylinder. It is very important to identify the prismatic axis from a given geometric model to extract the kinetic model of a fixture. We use the concept of the ‘moment of inertia’, which is a measure of an object's resistance to changes in its rotation rate, to identify the prismatic axis. Since the exact computation of the moment of inertia for an arbitrary solid model requires complicated computations, we introduce an approximating method for the moment of inertia. The proposed procedure has been implemented and tested with various examples.     

Generation of Antibunched Light by an Inhibited Poisson Stream

A model of a conditioned Poisson stream of events is proposed in which the intensity is a Markov chain assuming the values f, g, 0 with 0 < f < g. The conditioned Poisson process is specified by assuming that an emission results in the intensity making a transition to the next lower value. In the absence of emissions, the intensity which is a process by itself has a propensity to move up in its state space, the residence time in any state being exponentially distributed with parameter n. It is shown that such a model of emissions possesses antibunching and sub-Poisson properties.     

Magnetic Field Analysis of an Ironless Brushless DC Machine

This paper presents an analytical solution for the magnetic field inside an unconventional ironless brushless (ILBL) dc motor design. We discuss the unique characteristics of the design, which adopts an “inside-out” construction with an internal ironless stator. With the intention of obtaining an analytical solution for the magnetic field, we propose a model based on a magnetic pole concept for representing the magnetic circuit. The magnetic field inside the motor, which has no iron for guiding magnetic flux paths, is obtained by solving Laplace's equation for magnetic scalar potential. We present both analytical and numerical solutions for the magnetic field and compare them with measured results of a 20-pole prototype IL design to show the validity of the model. The IL design is simple, easy to manufacture and, as indicated by the results, has an optimum number of magnets, for which its performance becomes maximum.     

Flooding and sinking of an originally skimming body

The effects of flooding on an originally skimming body in shallow water are analysed. A two-dimensional flow model is presented which is based on mass flux, momentum, a stream-wise pressure jump across the leading edge of the body and an equi-pressure condition at the trailing edge. Linearised and numerical analyses are performed over a wide range of model parameters; the conditions under which a body is able to either emerge from or sink deeper into water are examined, with particular respect to the body’s incident angle, rotation, scaled gravity and buoyancy. The findings here enlarge the existing skimming theory and give a first mathematical account of the complete life cycle of a skimming or sinking body.     

Modelling of adhesively bonded joints by an asymptotic method

To utilize the potential of adhesive bonding, there is an increasing need for effective and accurate computational methods. The geometry and behaviour of an adhesive joint is, however, not so simple to model effectively by regular finite elements. The main reason is that the very thin adhesive layer with a low Young’s modulus must be modelled by a large number of finite elements in the thickness direction to achieve sufficiently accurate calculations. To overcome this difficulty, a material surface treatment of the adhesive and the joined parts can be attempted. This paper concerns the derivation of such a model by introducing scalings on the geometry and on the material properties in terms of a perturbation parameter. Within the framework of three-dimensional elasticity, together with an asymptotic expansion method, a family of limit models are obtained through a systematic procedure. In such a derivation no a priori assumptions on the displacements or stress fields are needed. The final result is a variational equation posed over a single reference surface. In regions near the boundary of the joint a boundary layer phenomena occurs. This indicates that the asymptotic series needs to be complemented by additional terms, in order to satisfy all boundary conditions. A structural model including shear- and peel deformation is finally proposed which improves the solution close to the boundary.     

Numerical simulation of a two-dimensional turbulent wall jet in an external stream

Turbulent wall jets possess a region with negative production of turbulent kinetic energy between the points of maximum velocity and vanishing shear stress. This characteristic feature cannot be shown with many turbulence models. The use of an extended expression for the primary turbulent shear stress together with a k–? or an algebraic Reynolds stress model results in a model which can show this physical property. Computed results obtained with this concept are compared with measurements and results obtained with the standard k–? model and a full Reynolds stress closure. It is shown that the computed results with the present and the Reynolds stress model are of similar quality. However, the Reynolds stress solution is more costly in computing time.     

Modeling and numerical study of electrical characteristics of polymer light-emitting diodes containing an insulating buffer layer

In order to improve the electrical characteristic of polymer light-emitting diodes, a simple model for the device characteristic with an insulating buffer layer at cathode is proposed. This model is based on Fowleer-Nordhein tunneling mechanism and Poission's equation. An additional tunneling factor which characterises the tunneling effect of buffer layer is introduced. The simulated current-voltage characteristic indicates how an insulating buffer layer with suitable thickness decreases the barrier height at the cathode and therefore increases the electron injection. The model is validated by experimental results of devices with BaO as the buffer material and poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] as the emission material. An optimum thickness of the buffer layer is also obtained from the model, which provides a guide to device design.     

Synthesis of a simulation model for an electromagnetic flowmeter

The principles of constructing a simulation model for an electromagnetic flowmeter are considered by means of which it is possible to carry out research into the metrological characteristics of instruments. __________ Translated from Izmeritel’naya Tekhnika, No. 5, pp. 38–43, May, 2006.     

Stability against dynamic remodeling of an arterial tissue

Geometry and structure of the arterial wall are maintained through continuous growth and remodeling (G&R). To understand these processes, mathematical models have been proposed in which the outcome of G&R depends on a mechanical stimulus through evolution equations. Rate parameters in these equations cannot be determined easily from experimental data. Assuming that the healthy artery is stable against remodeling, a physiologically acceptable range for the two rate parameters in the framework of an existing model of arterial G&R is determined here. The model is explicitly evaluated for the example of a cylindrical blood vessel, both thick-walled and thin-walled. For the thin-walled vessel a criterion for stability against remodeling is derived by means of a linear stability approach, and is expressed in terms of the ratio of the rates of remodeling parameters. It is shown that this criterion is equivalent to the condition that the physiological healthy state of the artery can be reached, implying that if the healthy state exists then it is stable. Explicit numerical results are presented for a typical cerebral artery and an abdominal aorta.     

On the numerical integration of an advanced Gurson model

This article is focused on a new extended version of Gurson's model (J. Eng. Mater. Technol. 1977; 99 :2–15), its numerical integration scheme and its consistent tangent matrix being within an FE code. First, this new advanced Gurson model is proposed, which is an extension of the original to take into account plastic anisotropy and mixed (isotropic+kinematic) hardening. In this paper, only the growth phase of cavities is considered (the nucleation of new voids is ignored). Second, a new numerical algorithm for the integration of this new Gurson model is presented. The algorithm is implicit in all variables and is unconditionally stable. This algorithm is generic and could be used for other anisotropic yield functions and other hardening laws. Third, the consistent tangent matrix is computed in an explicit way by exact linearization of the constitutive equations. To check its efficiency and robustness, the proposed integration algorithm is compared, under some simplified assumptions and choices, with the algorithms of Aravas (Int. J. Numer. Meth. Engng 1987; 24 :1395–1416) and Kojic (Int. J. Numer. Meth. Engng 2002; 53 (12):2701–2720). The performance of the developed consistent modulus, compared to other techniques for the computation of the tangent matrix is assessed. The paper ends with numerical simulations of tensile tests on homogeneous and notched specimens. Copyright © 2010 John Wiley & Sons, Ltd.     

Factors influencing the probability of an incident at a junction: results from an interactive driving simulator

Using data generated from a fixed-base interactive driving simulator, which was used to evaluate a driver decision aid, a model is built to predict the probability of an incident (i.e. an accident or a ‘near miss’) occurring as a result of a right-turn across left-hand traffic at an unsignalised junction. This can be considered to be the product of two separate probabilities, the first being the probability that the gap between a pair of vehicles in the traffic stream is accepted, and the second the probability that the time needed to cross the on-coming stream of traffic causes the time-to-collision with the nearest vehicle in this traffic stream to be less than a second. The model is developed from the results of experimental trials involving a sample of drivers, the majority of whom were aged 60 years or older, in order to demonstrate the effect of various parameters on these probabilities. The parameters considered include the size of the gap between successive vehicles, vehicle characteristics such as size, colour and velocity, driver characteristics such as age and sex, and both daytime and night-time conditions.     

Estimation of the nonstationary variance of an acoustic signal

A model of the residual fluctuations of a primary-processing subsystem is proposed, on the basis of which the noise immunity of an algorithm for estimating nonstationary variance is investigated. __________ Translated from Izmeritel’naya Tekhnika, No. 4, pp. 57–60, April, 2007.     

A mathematical model for an upper convected Maxwell fluid with an elastic core: Study of a limiting case

In this paper we formulate a mathematical model for a continuum which behaves like an upper convected visco-elastic Maxwell fluid if the stress is above a certain threshold and like a neo-Hookean elastic solid if the stress is below that threshold. The constitutive equations for each phase are derived within the context of the theory of natural configurations and by means of the criterion of the maximization of the rate of dissipation [11]. We then focus on a limiting case in which the continuum becomes an elastic-rigid body. In this limiting case the constitutive relation of the material becomes implicit and, although there is no energy dissipation, it cannot be included in the class of hyperelastic (or Green) bodies. The stress indeed cannot be expressed as a function of the strain. This class of materials was first introduced by Rajagopal in [15] and is the subject of the forthcoming papers [3] and [4].     

Nonlinear model for an optical read-only-memory disk readout channel based on an edge-spread function

A point-spread function (PSF) is commonly used as a model of an optical disk readout channel. However, the model given by the PSF does not contain the quadratic distortion generated by the photo-detection process. We introduce a model for calculating an approximation of the quadratic component of a signal. We show that this model can be further simplified when a read-only-memory (ROM) disk is assumed. We introduce an edge-spread function by which a simple nonlinear model of an optical ROM disk readout channel is created.     

A plasticity based model and an adaptive algorithm for finite element analysis of reinforced concrete panels

This paper deals with an adaptive finite element procedure for the analysis of plain and reinforced concrete panels in a state of plane stress. Therefore, we will present a plasticity based model for plain concrete which captures the two failure modes of concrete within one formulation. In spite of a simple formulation the model is capable to describe the different mechanisms for tensile failure as well as for compression fracture. To restrict the time discretization error and the spatial discretization error to certain tolerances, the constitutive model is embedded in an adaptive algorithm which controls the size of the incremental load steps and leads to a hierarchical mesh refinement if necessary. The application of the model will be shown by various numerical examples. Copyright © 2002 John Wiley & Sons, Ltd.     

Cumulative manufacturing capabilities: an extended model and new empirical evidence

There has been intense debate in the manufacturing strategy literature on the way in which firms work on different manufacturing capabilities, with two opposing approaches considered – the trade-off model and the sand cone model. Analysis of these models has essentially been based on study of the links amongst four classic manufacturing capabilities (quality, delivery, flexibility, and cost efficiency) and has obviated the need to consider environmental protection as an important manufacturing capability. This study analyses the theoretical arguments and the prior empirical evidence on the two models, and proposes and tests an extended sand cone model which includes the environmental protection objective alongside the four traditional ones. The research uses structural equation modelling and data from a sample of 274 manufacturers to contribute additional empirical evidence on the existence of cumulative effects amongst manufacturing capabilities. It is observed that the predominant strategic model in these firms is one of multiple, non-incompatible capabilities with cumulative effects according to the following sequence: quality, delivery, flexibility, environmental protection, and cost efficiency.     

A study of the spatial distribution of transportation‐an alternative approach and evaluation

Abstract

This study intends to investigate a calibration procedure for a proposed combined trip generation and distribution model which is based on the concept of accessibility. Apart from the proofs of the existence and uniqueness of the solution, the computation efficiency is evaluated by using Cesario's data (1). The calibration procedure is further tested with empirical data which is obtained from an actual transportation survey carried out in Kaohsiung City of Taiwan, the Republic of China.     

Refined mathematical model of an ultrasonic flowmeter

A refined mathematical model of an ultrasonic flowmeter is presented. The model makes it possible to measure the discharge of liquids and gases over a broad range of Reynolds numbers with an error no larger than 0.3%. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 25–27, June, 1998.     

Feasibility of an In Vitro Microbiological Model as an Alternative to the Rabbit Eye Model

Ocular inserts of gentamicin sulfate with polyvinyl alcohol (PVA) 1.5%, 2.0%, and 2.5% and a combination of methyl cellulose 2% and Eudragit NE 30D 30%, 35%, and 40% w/w of methyl cellulose were fabricated by a casting technique. The inserts were sterilized by gamma radiation at 25 kGy and tested for sterility. The microbiological efficacy of the ocular inserts against Staphylococcus aureus ATCC 6538P and Pseudomonas aeruginosa NCIM 2200 was evaluated by developing an in vitro microbiological model and an in vivo noninvasive rabbit eye model. Parameters of the in vitro microbiological model were varied, and the results correlated with a noninvasive rabbit eye model. The in vitro model proved to be a viable alternative to the rabbit eye model in evaluating the microbiological efficacy of gentamicin sulfate ocular inserts.