The vibrational spectra of rectangular plates

The wire drive pulse-echo system has been extensively used to excite and measure modes of vibration of thin rectangular plates. The frequency spectra of different modes have been investigated as a function of the material elastic moduli and the plate geometry. Most of the work was carried out on isotropic materials. For square plates a wide selection of materials were used. These were made isotropic in their in-plane dimensions where the displacements are taking place. The range of rnaterials enabled the dependence on Poisson's ratio to be investigated. A method of determining the value of Poisson's ratio resulted from this investigation. Certain modes are controlled principally by the shear modulus. Of these the fundamental has two nodal lines across the plate surface. One of them, which has nodes at the corners, (the Lame mode) is uniquely a pure shear mode where the diagonal is a full wave length. One controlled by the Young's modulus has been found. The precise harmonic relationship of the Lame mode series in square and rectangular plates was established. Use of the Rayleigh-Lamb equation has extended the theoretical support. The low order modes were followed over a wide range of sides ratios. Two fundamental types of modes have been recognised; These are the longitudinal modes where the frequency is controlled by the length of the plate only and the 2~f product has an asymptotic value approaching the rod velocity. The other type is the in-plane flexural modes (in effect a flexurally vibrating bar where the -2/w is the geometrical parameter). Where possible the experimental work was related to theory. Other modes controlled by the width dimension of the plate were followed. Anisotropic materials having rolled sheet elastic symmetry were investigated in terms of the appropriate theory. The work has been extended to examine materials from welds in steel plates.

Flowback of solids through distribution plates of gas fluidized beds and associated phenomena

This work is concerned with a study of certain phenomena related to the performance and design of distributors in gas fluidized beds with particular regard to flowback of solid particles. The work to be described is divided into two parts. I. In Part one, a review of published material pertaining to distribution plates, including details from the patent specifications, has been prepared. After a chapter on the determination of the incipient fluidizing velocity, the following aspects of multi-orifice distributor plates in gas fluidized beds have been studied: (i) The effect of the distributor on bubble formation related to the way in which even distribution of bubbles on the top surface of the fluidized bed is obtained, e.g. the desirable pressure drop ratio ?PD/?PB for the even distribution of gas across the bed. Ratios of distributor pressure drop ?PD to bed pressure drop at which stable fluidization occurs show reasonable agreement with industrial practice. There is evidence that larger diameter beds tend to be less stable than smaller diameter beds when these are operated with shallow beds. Experiments show that in the presence of the bed the distributor pressure drop is reduced relative to the pressure drop without the bed, and this pressure drop in the former condition is regarded as the appropriate parameter for the design of the distributor. (ii) Experimental measurements of bubble distribution at the surface has been used to indicate maldistribution within the bed. Maldistribution is more likely at low gas flow rates and with distributors having large fractional free area characteristics (i.e. with distributors having low pressure drops). Bubble sizes obtained from this study, as well as those of others, have been successfully correlated. The correlation produced implies the existence of a bubble at the surface of an orifice and its growth by the addition of excess gas from the fluidized bed. (iii) For a given solid system, the amount of defluidized particles stagnating on the distributor plate is influenced by the orifice spacing, bed diameter and gas flow rate, but independent of the initial bed height and the way the orifices are arranged on the distributor plate. II. In Part two, solids flowback through single and multi-orifice distributors in two-dimensional and cylindrical beds of solids fluidized with air has been investigated. Distributors equipped with long cylindrical nozzles have also been included in the study. An equation for the prediction of free flowback of solids through multi-orifice distributors has been derived. Under fluidized conditions two regimes of flowback have been differentiated, namely Jumping and weeping. Data in the weeping regime have been successfully correlated. The limiting gas velocity through the distributor orifices at which flowback is completely excluded is found to be indepnndent of bed height, but a function of distributor design and physical properties of gas and solid used. A criterion for the prediction of this velocity has been established. The decisive advantage of increasing the distributor thickness or using nozzles to minimize solids flowback in fluidized beds has been observed and the opportunity taken to explore this poorly studied subject area. It has been noted, probably for the first time, that with long nozzles, there exists a critical nozzle length above which uncontrollable downflow of solids occurs. A theoretical model for predicting the critical length of a bundle of nozzles in terms of gas velocity through the nozzles has been set up. Theoretical calculations compared favourably with experiments.

The mechanics of continuous roller bending of plates

This research initiates a study of the mechanics of four roll plate bending and provides a methodology to investigate the process experimentally. To carry out the research a suitable model bender was designed and constructed. The model bender was comprehensively instrumented with ten load cells, three torquemeters and a tachometer. A rudimentary analysis of the four roll pre-bending mode considered the three critical bending operations. The analysis also gave an assessment of the model bender capacity for the design stage. The analysis indicated that an increase in the coefficient of friction in the contact region of the pinch rolls and the plate would reduce the pinch resultant force required to end a plate to a particular bend radius. The mechanisms involved in the four roll plate bending process were investigated and a mathematical model evolved to determine the mechanics of four roll thin plate bending. A theoretical and experimental investigation was conducted for the bending of HP30 aluminium plates in both single and multipass bending modes. The study indicated that the multipass plate bending mechanics of the process varied according to the number of bending passes executed and the step decrement of the anticipated finished bend radius in any two successive passes (i.e. the bending route). Experimental results for single pass bending indicated that the rollers normally exert a higher bending load for the steady-continous bending with the pre-inactive side roll oper?tive. For the pre-bending mode and the steady-continous bending mode with the pre-active side roll operative, the former exerted the higher loads. The single pass results also indicated that the force on the side roll, the torque and power steadily increased as the anticipated bend radius decreased. Theoretical predictions for the plate internal resistance to accomplish finished bend radii of between 2500mm and 500mm for multipass bending HP30 aluminium plates, suggested that there was a certain bending route which would effectively optimise the bender capacity.

Failure of steel gusset plates

This thesis examines the parameters associated with the failure of triangular steel gusset plates. Eighty two results are presented investigating the position of the applied load, the gusset plate height to length ratio, size, thickness, internal angle and the removal of the inside corner. The thickness of the loaded plate and its influence on the gusset plates failure is also investigated. Twenty two similar gusset plates were tested to investigate the welds connecting the gusset plate to the adjacent loaded and support edges. The experimental results are compared with existing methods, none of which cover all the variables tested. Some methods do not consider buckling and most of those that do are inadequate. Most of the methods do not accurately take account of the load position. An alternative method based on experimental observations is presented for design purposes. The method covers any combination of the variables tested. To test assumptions made in the theoretical work forty seven strut tests took place to investigate buckling characteristics and fifteen special gusset plates were also tested. The gusset plates were found to fail in an elastic-plastic buckling manner. A gusset plate has a specific moment of resistance capacity about it’s inside corner and the ultimate load that can be applied is dependent upon the position of the load relative to the supported edge. There is an optimum height to length ratio for strength and any increase in the internal angle from 90 degrees produces little change in moment capacity. The removal of small portions of the inside corner of a gusset plate has little effect upon its moment capacity. The loaded plate does not provide any significant moment of resistance to the applied load at failure. The main functions of the loaded and supported edge welds is to prevent the gusset plate from slipping from between the plates.

How accurate are photographic surrogate markers used to detect macular oedema in the english national Screening Programme?

Introduction: Macular oedema is not directly visible on digital photographs used in screening. Photographic surrogate markers are used to detect patients who may have macular oedema. Evidence suggests that only around 10% of patients with these surrogate markers referred to an ophthalmologist have macular oedema when examined by slit-lamp biomicroscopy. Purpose: The purpose of this audit was to determine how many patients with surrogate markers were truly identified by optical coherence tomography (OCT) as having macular oedema. Method: Data were collected from patients attending digital diabetic retinopathy screening. Patients who presented with surrogate markers for macular oedema also had an OCT scan. The fast macula scan on the Stratus OCT was used and an ophthalmologist reviewed the scans to determine whether macular oedema was present. Results: Out of 66 patients with maculopathy defined as haemorrhages or microaneurysms within one optic disc diameter (DD) of the fovea and visual acuity (VA) worse than 6/9 11 (17%) showed thickening on the OCT, only 4 (6%) had macular oedema. None required laser. Out of 155 patients with maculopathy defined as any exudate within one DD of the fovea or circinate within two DD 45 (29%) showed thickening on the OCT of these 27% required laser. Conclusion: OCT is a useful tool in screening to help identify those who need a true referral to ophthalmology for maculopathy. If exudate is present the chance of having macular oedema and requiring laser treatment is greater than the presence of microaneurysms within one DD and reduced VA.

How accurate are photographic surrogate markers used to detect macular edema in the English national screening programme?

DESIGN. Retrospective analysis PURPOSE. Macular oedema is not directly visible on two dimensional digital photographs such that surrogate markers need to be used. In the English National Screening Programme these are exudate within one optic disc diameter (DD) of the fovea, group of exudates within two DD of the fovea and haemorrhages or microaneurysms (HMA) within one DD of the fovea with best corrected visual acuity (VA) worse than 6/9. All patients who present with any of these surrogate markers at screening are referred to an ophthalmology clinic for slit lamp examination. The purpose of this audit was to determine how many patients with positive maculopathy diagnosis on photography were truly identified by optical coherence tomography (OCT) with macular oedema. METHODS. Data was collected from patients attending digital diabetic retinopathy screening. Patients who presented with surrogate markers for macular oedema also had an OCT scan. The fast macula scan on the Stratus OCT was used and an ophthalmologist reviewed the scans to determine whether macular oedema was present. RESULTS. Maculopathy by exudates: Of 155 patients 45 (29%) showed thickening on the OCT of these 12 required laser. Those who also had pre-proliferative retinopathy (n=20) were more likely to have macular oedema (75%) than those with background diabetic retinopathy. Maculopathy by HMA and VA worse than 6/9: Of 66 patients 11 (16.7%) showed thickening on the OCT. 5 (7.6%) of these had macular oedema, 5 (7.6%) epi-retinal membrane, and 1 (1.5%) age related macular degeneration. None of these patients required laser. CONCLUSIONS. The likelihood of the presence of macular oedema and requiring laser treatment is greater with macular exudation than HMA within one DD and reduced VA. Overall the surrogate markers used show low specificity for macular oedema, however combining OCT with photography does identify those with macular oedema who require a true referral for an ophthalmological slit lamp examination.

Sparse representation of astronomical images

Sparse representation of astronomical images is discussed. It is shown that a significant gain in sparsity is achieved when particular mixed dictionaries are used for approximating these types of images with greedy selection strategies. Experiments are conducted to confirm (i) the effectiveness at producing sparse representations and (ii) competitiveness, with respect to the time required to process large images. The latter is a consequence of the suitability of the proposed dictionaries for approximating images in partitions of small blocks. This feature makes it possible to apply the effective greedy selection technique called orthogonal matching pursuit, up to some block size. For blocks exceeding that size, a refinement of the original matching pursuit approach is considered. The resulting method is termed "self-projected matching pursuit," because it is shown to be effective for implementing, via matching pursuit itself, the optional backprojection intermediate steps in that approach. © 2013 Optical Society of America.

A study of stray load losses in core clamp plates of salient pole synchronous machines

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Improving the cost-effectiveness of photographic screening for diabetic macular oedema:a prospective, multi-centre, UK study

Background/aims: Retinal screening programmes in England and Scotland have similar photographic grading schemes for background (non-proliferative) and proliferative diabetic retinopathy, but diverge over maculopathy. We looked for the most cost-effective method of identifying diabetic macular oedema from retinal photographs including the role of automated grading and optical coherence tomography, a technology that directly visualises oedema. Methods: Patients from seven UK centres were recruited. The following features in at least one eye were required for enrolment: microaneurysms/dot haemorrhages or blot haemorrhages within one disc diameter, or exudates within one or two disc diameters of the centre of the macula. Subjects had optical coherence tomography and digital photography. Manual and automated grading schemes were evaluated. Costs and QALYs were modelled using microsimulation techniques. Results: 3540 patients were recruited, 3170 were analysed. For diabetic macular oedema, England's scheme had a sensitivity of 72.6% and specificity of 66.8%; Scotland 's had a sensitivity of 59.5% and specificity of 79.0%. When applying a ceiling ratio of £30 000 per quality adjusted life years (QALY) gained, Scotland's scheme was preferred. Assuming automated grading could be implemented without increasing grading costs, automation produced a greater number of QALYS for a lower cost than England's scheme, but was not cost effective, at the study's operating point, compared with Scotland's. The addition of optical coherence tomography, to each scheme, resulted in cost savings without reducing health benefits. Conclusions: Retinal screening programmes in the UK should reconsider the screening pathway to make best use of existing and new technologies.

Prediction of welding distortion in butt joint of thin plates

This paper investigates distortions and residual stresses induced in butt joint of thin plates using Metal Inert Gas welding. A moving distributed heat source model based on Goldak's double-ellipsoid heat flux distribution is implemented in Finite Element (FE) simulation of the welding process. Thermo-elastic-plastic FE methods are applied to modelling thermal and mechanical behaviour of the welded plate during the welding process. Prediction of temperature variations, fusion zone and heat affected zone as well as longitudinal and transverse shrinkage, angular distortion, and residual stress is obtained. FE analysis results of welding distortions are compared with existing experimental and empirical predictions. The welding speed and plate thickness are shown to have considerable effects on welding distortions and residual stresses. © 2009 Elsevier Ltd. All rights reserved.

Improving the economic value of photographic screening for optical coherence tomography-detectable macular oedema:a prospective, multicentre, UK study

Objectives: To determine the best photographic surrogate markers for detecting sight-threatening macular oedema (MO) in people with diabetes attending UK national screening programmes. Design: A multicentre, prospective, observational cohort study of 3170 patients with photographic signs of diabetic retinopathy visible within the macular region [exudates within two disc diameters, microaneurysms/dot haemorrhages (M/DHs) and blot haemorrhages (BHs)] who were recruited from seven study centres. Setting: All patients were recruited and imaged at one of seven study centres in Aberdeen, Birmingham, Dundee, Dunfermline, Edinburgh, Liverpool and Oxford. Participants: Subjects with features of diabetic retinopathy visible within the macular region attending one of seven diabetic retinal screening programmes. Interventions: Alternative referral criteria for suspected MO based on photographic surrogate markers; an optical coherence tomographic examination in addition to the standard digital retinal photograph. Main outcome measures: (1) To determine the best method to detect sight-threatening MO in people with diabetes using photographic surrogate markers. (2) Sensitivity and specificity estimates to assess the costs and consequences of using alternative strategies. (3) Modelled long-term costs and quality-adjusted life-years (QALYs). Results: Prevalence of MO was strongly related to the presence of lesions and was roughly five times higher in subjects with exudates or BHs or more than two M/DHs within one disc diameter. Having worse visual acuity was associated with about a fivefold higher prevalence of MO. Current manual screening grading schemes that ignore visual acuity or the presence of M/DHs could be improved by taking these into account. Health service costs increase substantially with more sensitive/less specific strategies. A fully automated strategy, using the automated detection of patterns of photographic surrogate markers, is superior to all current manual grading schemes for detecting MO in people with diabetes. The addition of optical coherence tomography (OCT) to each strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. Conclusions: Compared with all current manual grading schemes, for the same sensitivity, a fully automated strategy, using the automated detection of patterns of photographic surrogate markers, achieves a higher specificity for detecting MO in people with diabetes, especially if visual acuity is included in the automated strategy. Overall, costs to the health service are likely to increase if more sensitive referral strategies are adopted over more specific screening strategies for MO, for only very small gains in QALYs. The addition of OCT to each screening strategy, prior to referral, results in a reduction in costs to the health service with no decrement in the number of MO cases detected. © Queen's Printer and Controller of HMSO 2013.