Interaction, Neighborhood Selection and Housing Demand

social interactions, neighborhood selection, housing, neighborhood effects

A coupled finite-volume CFD solver for two-dimensional elasto-hydrodynamic lubrication problems with particular application to rolling element bearings

This paper describes a new computational fluid dynamics methodology for modelling elastohydrodynamic contacts. A finite-volume technique is implemented in the ‘OpenFOAM’ package to solve the Navier-Stokes equations and resolve all gradients in a lubricated rolling-sliding contact. The method fully accounts for fluid-solid interactions and is stable over a wide range of contact conditions, including pressures representative of practical rolling bearing and gear applications. The elastic deformation of the solid, fluid cavitation and compressibility, as well as thermal effects are accounted for. Results are presented for rolling-sliding line contacts of an elastic cylinder on a rigid flat to validate the model predictions, illustrate its capabilities, and identify some example conditions under which the traditional Reynolds-based predictions deviate from the full CFD solution

Modelling Retail Deposit Spreads in the UK

Models that are based on mean-variance analysis seek portfolio weights to minimise the variance of the portfolio for a given level of return. The portfolio variance is measured using a covariance matrix that represents the volatility and correlation of asset returns. However these matrices are notoriously difficult to estimate and ad hoc methods often need to be applied to limit or smooth the mean-variance efficient allocations that are recommended by the model. Moreover the mean-variance criterion has nothing to ensure that tracking errors are stationary. Although the portfolios will be efficient, the tracking errors will in all probability be random walks. Therefore the replicating portfolio can drift very far from the benchmark unless it is frequently re-balanced. Deposits, yield Cruves, Stochastic Interest Rates

A Bayesian test for the appropriateness of a model in the biomagnetic inverse problem

This paper extends the work of Clarke [1] on the Bayesian foundations of the biomagnetic inverse problem. It derives expressions for the expectation and variance of the a posteriori source current probability distribution given a prior source current probability distribution, a source space weight function and a data set. The calculation of the variance enables the construction of a Bayesian test for the appropriateness of any source model that is chosen as the a priori infomation. The test is illustrated using both simulated (multi-dipole) data and the results of a study of early latency processing of images of human faces. [1] C.J.S. Clarke. Error estimates in the biomagnetic inverse problem. Inverse Problems, 10:77--86, 1994.Comment: 13 pages, 16 figures. Submitted to Inverse Problem

Analysis of the Influence of Indentations on Contact Life

Applying the relation between stresses and contact fatigue as postulated by Ioannides & Harris, an investigation is carried out to determine the influence of dent geometry on contact life. This analysis is performed using line contact and point contact models. The stresses are calculated using a dry contact model and the elastic half-space assumption. Results from calculations using the line contact assumption are compared with the results of elliptical contact calculations, which model the dents more exactly. The difference in contact pressure between the line and point contact case is analysed in detail. The dent geometry has been obtained from an FEM analysis of an indentation process and the dent is scaled with respect to depth and width to obtain a family of dents. The FEM calculations were compared to experimentally obtained dent profiles. As was done previously for the line contact analysis, the influence of the residual stress field from the plastic indentation process was investigated for the calculated dent geometry (without scaling). The life reduction compared to the smooth contact case has been obtained for three different load cases for a large number of different dent sizes and dent slopes, employing the point contact analysis. The life reductions are compared to the results of an extended line contact analysis and the influence of the position of the dent on life reduction is investigated. This analysis is aimed at establishing the reduction of contact life caused by indentations stemming from handling damage and the overrolling of debris. © 1992

An investigation into the mechanisms of closed three-body abrasive wear

Contacting components frequently fail by abrasion caused by solid contaminants in the lubricant. This process can be classified as a closed three-body abrasive wear process. The mechanisms by which trapped particles cause material removal are not fully understood. This paper describes tests using model elastohydrodynamic contacts to study these mechanisms. An optical elastohydrodynamic lubrication rig has been used to study the deformation and fracture of ductile and brittle lubricant-borne debris. A ball-on-disk machine was used to study the behaviour of the particles in partially sliding contacts. Small diamond particles were used as abrasives since these were thought not to break down in the contact; wear could then be directly related to particles of a known size. The particles were found to embed in the softer surface and to scratch the harder. The mass of material worn from the ball surface was approximately proportional to the particle sliding distance and abrasive concentration. Small particles tumbled through the contact, whilst larger particles ploughed. Mass loss was found to increase with abrasive particle size. Individual abrasion scratches have been measured and related to the abrading particle. A simple model of the abrasive process has been developed and compared with experimental data. The discrepancies are thought to be the result of the uncertainty about the entrainment of particles into the contact. © 1994

Paper II (iv) Lubricant Screening for Debris Effects to Improve Fatigue and Wear Life

This paper discusses the mechanisms of surface damage induced by lubricant borne debris in rolling element contacts. Particular emphasis is placed on how debris particles cause damage and how the extent of this damage is related to debris size and material properties. The study is broadly divided into two parts: first, an investigation into the mechanisms of particle entry and behaviour in rolling contacts; and second, an analysis of the extent of rolling element surface damage caused by these particles. The results of optical ehd experiments show how various types of debris particle deform or fragment in the contact entry region. High speed video and short duration flash photography have been used to track the movement of debris particles as they approach and pass through an elastohydrodynamic contact, or are swept around the sides. Simple analyses are presented for predicting the maximum particle size and number which may be entrained into the contact. To investigate lubricant contaminant damage potential, a rig, designed to accumulate debris dent geometries, has been constructed. The results of experimentation, using this rig with lubricants contaminated with ductile and brittle particles, have been compared to theories for the prediction of surface damage. © 1992

Surface damage effects caused by debris in rolling bearing lubricants, with an emphasis on friable materials

The influence of debris in concentrated surface contacts is reviewed in terms of the fundamental mechanisms of 3-body contact, and how subsequent surface damage effects relate to rolling contact fatigue life. Particular emphasis is placed on how friable debris causes surface damage; experimental evidence is presented to show how various forms and sizes of friable debris fragment in the inlet to EHD contacts. Although this can lead to significant wear and surface roughening of the rolling elements, the effects on fatigue life are not always seen to be as severe as with ductile debris. The reasons for these differences are examined and discussed in detail. (A