Carl T.F. Ross

A robotic welding system using image processing techniques and a CAD model to provide information to a multi‐intelligent decision module

Purpose – The paper aims to propose a system that uses a combination of techniques to suggest weld requirements for ships parts. These suggestions are evaluated, decisions are made and then weld parameters are sent to a program generator.Design/methodology/approach – A pattern recognition system recognizes shipbuilding parts using shape contour information. Fourier‐descriptors provide information and neural networks make decisions about shapes.Findings – The system has distinguished between various parts and programs have been generated so that the methods have proved to be valid approaches.Practical implications – The new system used a rudimentary curvature metric that measured Euclidean distance between two points in a window but the improved accuracy and ease of implementation can benefit other applications concerning curve approximation, node tracing, and image processing, but especially in identifying images of manufactured parts with distinct corners.Originality/value – A new proposed system has bee...

Vibration and elastic instability of thin-walled domes under uniform external pressure

Abstract Two thin-walled varying meridional curvature axisymmetric shell elements are presented for the vibration and elastic instability of thin-walled hemi-ellipsoidal domes under uniform external pressure. The theoretical analysis is an extension of previous work carried out by the author, where for the two elements presented in the present report, a cubic and a quadratic variation was assumed for the meridional and the circumferential displacements along the meridian of these elements. In the previous study, only linear variations were assumed for the meridional and circumferential displacements along the meridian of these elements. Comparisons were made between experiment and theory for both buckling and vibration of hemi-ellipsoidal shell domes, which varied from very flat oblate vessels to very long prolate vessels. In general, agreement between experiment and theory was good for the hemi-spherical dome and the prolate vessels, but not very good for the fat oblate vessels. Additionally, the two new elements gave poorer results than the original simpler element for the cantilever mode of vibration, but better results for the lobar modes of vibration.

Collapse of composite tubes under uniform external hydrostatic pressure

This paper describes an experimental and a theoretical investigation into the collapse of 22 circular cylindrical composite tubes under external hydrostatic pressure. The investigations were on the collapse of fibre reinforced plastic tube specimens made from a mixture of three carbon and two E-glass fibre layers. The theoretical investigations were carried out using an in-house finite element computer program called BCLAM, together with the commercial computer package, namely ANSYS. It must be emphasised here that BS 5500 does not appear to exclusively cater for the buckling of composite shells under external hydrostatic pressure, so the work presented here is novel and should be useful to industry. The experimental investigations showed that the composite specimens behaved similarly to isotropic materials previously tested, in that the short vessels collapsed through axisymmetric deformation while the longer tubes collapsed through non-symmetric bifurcation buckling. Furthermore it was discovered that the models failed at changes of the composite lay-up due to the manufacturing process of these models. These changes seemed to be the weak points of the specimens.

The buckling of GRP hemi-ellipsoidal dome shells under external hydrostatic pressure

The paper reports on a theoretical and an experimental investigation into six GRP hemi-ellipsoidal dome shells, which were tested to destruction under external hydrostatic pressure. All six domes were of oblate shape and of three different aspect ratios. Each aspect ratio consisted of two dome shells, one made from two layers of glass fibre and one made from three layers of glass fibre. The theoretical analysis was via the finite element method where a non-linear theory was used which allowed for both geometrical and material non-linearity. Comparison between theory and experiment was good.

Inelastic buckling of thick-walled circular conical shells under external hydrostatic pressure

The paper reports on a theoretical and an experimental study into the collapse of three thick-walled circular conical shells, which were tested to failure under external hydrostatic pressure. All three vessels failed by plastic non-symmetric bifurcation buckling. Two theoretical analyses were carried out, both based on the finite element method. One of the theoretical analyses was based on inelastic non-symmetric bifurcation buckling and the other analysis was based on plastic axisymmetric buckling. Both of these theoretical analysis and the experimental observations appeared to indicate that there is a link between plastic non-symmetric bifurcation buckling and plastic axisymmetric buckling.

Plastic collapse of circular conical shells under uniform external pressure

Abstract The article reports on two theoretical investigations and an experimental investigation into the collapse of six circular conical shells under uniform external pressure. Four of the vessels collapsed through plastic non-symmetric bifurcation buckling and one vessel collapsed through plastic axisymmetric buckling. A sixth vessel failed in a mixed mode of plastic non-symmetric bifurcation buckling, combined with plastic axisymmetric buckling. The theoretical and experimental investigations appeared to indicate that there was a link between plastic non-symmetric bifurcation buckling and plastic axisymmetric buckling. The theoretical investigations were via the finite element method and were used to provide a design chart for these vessels.

Plastic axisymmetric collapse of thin-walled circular cylinders and cones under uniform external pressure

Abstract This paper reports on two theoretical investigations and an experimental investigation into the plastic axisymmetric buckling of two thin-walled conical shells and several thin-walled circular cylindrical shells, under uniform external pressure. One of the theoretical investigations was a non-linear finite element solution for plastic axisymmetric buckling, which gave good results. The other theoretical solution was for the plastic non-symmetric bifurcation buckling of thin-walled circular cylinders. This second solution was a very simple one and, although it was based on plastic lobar buckling, it gave very good predictions for plastic axisymmetric collapse. This latter observation prompted the conclusion that there may be a link between plastic lobar buckling and plastic axisymmetric buckling.

The buckling of a corrugated carbon fibre cylinder under external hydrostatic pressure

A theoretical and an experimental investigation was carried out, where a carbon fibre corrugated circular cylinder was tested to destuction under external hydrostatic pressure. The theoretical investigation was via the finite element method, where the structure was modelled with several orthotropic axisymmetric thin-walled shell elements. The experimental observations were aided with strategically placed strain gauges. Comparison between theory and experiment showed that the experimentally observed buckling pressure was a little lower than the theoretical prediction. This may have been due to the fact that the model had slight initial geometrical imperfections in the circumferenential direction.

The buckling of corrugated circular cylinders under uniform external pressure

Abstract Several partially corrugated circular cylinders were tested to destruction under uniform external pressure. Some of the vessels failed by inelastic general instability and some failed by a local buckling mode, which was neither the classical shell instability mode nor the classical general instability mode. The experimentally obtained buckling pressures were found to be related to the magnitude of the initial out-of-roundness for the vessels that failed through inelastic general instability. The theoretical buckling pressures showed virtually no relationship with the experimentally observed buckling pressures, for the vessels that failed via the local buckling mode.

Plastic General Instability of Ring-Stiffened Conical Shells under External Pressure

The paper describes experimental tests carried out on three ring-stiffened circular conical shells that suffered plastic general instability under uniform external pressure. The cones were carefully machined from EN1A mild steel to a very high degree of precision. The end diameters of the cones, together with their thicknesses were the same, but the size of their ring stiffeners was different for each of the three vessels. In the general instability mode of collapse, the entire ring-shell combination buckles bodily in its flank. The paper also provides three design charts using the results obtained from these three vessels, together with the results obtained for twelve other vessels from other tests. All 15 vessels failed by general instability. One of these design charts was based on conical shell theory and two of the design charts were based on the general instability of ring-stiffened circular cylindrical shells, using Kendrick’s theory, which were made equivalent to ring-stiffened circular conical shells suffering from general instability under uniform external pressure. The design charts allowed the possibility of obtaining plastic knockdown factors, so that the theoretical elastic buckling pressures, for perfect vessels, could be divided by the appropriate plastic knockdown factor, to give the predicted buckling pressure. The theoretical work is based on the solutions of Kendrick, together with the finite element program of Ross, namely RCONEBUR and the commercial finite element package ANSYS. This method can also be used for the design of full-scale vessels.