Counterintuitive problems in dynamics and vibration

Mechanical Vibration and Dynamics are taught to undergraduates as if they simple sciences. The mass-on-a-spring, uni-axial vibration of a rod, viscous damping, modal analysis - all these are the bread and butter of vibration science. As for rigid-body dynamics undergraduate courses remain fixed in 2-D planar motion. But real dynamic and vibrating systems just don't behave simply. There are pitfalls in even the most ordinary cases and some of these will be demonstrated: a tuning fork; a bottle of coke; a bending beam; a turbocharger wheel, a bouncing ball, a rolling ball and boomerangs. All of these things behave counter-intuitively. The talk accompanying the paper will be filled with practical demonstrations - seeing is believing. Most are demonstrations that can be repeated at home

reSearch : enhancing information retrieval with images

Combining image and text search is an open research question. The main issues are what technologies to base this solution on, and what measures of relevance to employ. Our reSearch prototype mashes up papers indexed using information retrieval techniques (Terrier) with Google image search for faces and Google book search. The user can interactively employ query expansion with additional terms suggested by Terrier, and use those terms to expand both the text and image search. We test this solution with a selection of recent publications and queries concerning people engaged in research. We report on the effectiveness of this solution. It seems that the combination works to a large extent, as testified by our observations

Accuracy, and the prediction of ground vibration from underground railways

This paper demonstrates the capability of a new – and freely-available – PiP software for calculating vibration from railway tunnels. PiP is used to examine the sources of uncertainly in models used to predict vibration from underground railways. By varying slightly the parameters of the model, consistent with uncertainties in measured data, the vibration levels predicted by the model vary significantly, often by 10dB or more. This error is hard to predict so it cannot be good practice to rely on prediction models for accuracy better than 10dB. The presentation will demonstrate the PiP model in real time

An update on engineering issues concerning stratospheric aerosol injection for geoengineering

Abstract: Solar Radiation Management (SRM) geoengineering is a proposed response to anthropogenic global warming (AGW). Stratospheric aerosol injection (SAI) is one proposed method, reliant on lofting material into the stratosphere. Engineering reviews related to this technology approach have been sparse, with most major primary analyses now at least five years old. We attempt to bridge this gap—with a short, qualitative review of recent developments in various fields of engineering that have potential applicability to SAI. Our analysis shows that a new conventional aircraft design is still likely to be the most dependable and affordable technology solution (cost estimates start around $1000–1500 per ton lofted), with hybrid or vacuum airships a potential challenger. Rockets, gas guns and MAGLEV/coilguns show some potential—although they lack the inherent level-flight capability that would be needed for direct aerosol distribution (versus distribution of gaseous precursors), without substantial additional engineering. Should very high-altitude access be required, rockets, jet-hybrid rockets, and various guns (especially light-gas guns) potentially offer the required capability. Costs and performance for tethered balloons remain highly uncertain. Towers are not found to be promising. The extreme accessibility of free balloons suggests that this method may be used primarily for reasons of political leverage, as opposed to being an optimal engineering solution

A methodology for matching lightning detection network data with ground-truth records

In this dissertation a methodology of matching external ground-truth records of lightning events with data reported by a Lightning Detection Network (LDN) is investigated. The methodology allows for matching events where the time of the ground-truth record is unknown. It is shown that the location accuracy of an LDN is a ected by the number of sensors that are able to detect lightning strokes and this observation is then used to de ne criteria for matching lightning strokes with LDN data. An evaluation of the methodology is presented in which the results of applying the methodology are compared with the results of a known methodology (time correlation) to determine if the same data is extracted. Photographs of lightning attachment to the Brixton tower in Johannesburg, South Africa are used as ground- truth events and LDN data is obtained from the South African Lightning Detection Network (SALDN). A practical application, in the context of an insurance claim scenario, is also presented in which the methodology is used to determine whether lightning is the cause of damage to a tree and when this may have occurred. It is found that the methodology extracts many of the possible strokes but that it also returns false positive results and makes some false exclusions. It is concluded that the proposed methodology should be used as a \ lter" to reduce a dataset of LDN records but that corroborating evidence is required if the methodology is to be used as intended

Recognition of lightning-induced trauma to the skeleton: a forensic taphonomic study

Lightning related deaths can be hard to recognize in most circumstances, unless explicitly looked for, and impossible when the remains are fully skeletonized. There is a crucial need for this for forensic authorities in South Africa, where there is a high incidence of lightning deaths and a high rate of recovery of unidentified bodies in the skeletonized state. The effects of a 15 kA, 8/20 I-Ls impulse current applied to a series of pig femurs was investigated as well as a comparison with a skeletal element from a giraffe struck by lightning. A distinct pattern of traumatization was observed and is described in detail. Further analysis and comparison to human results should be carried out and a method for accurately identifying lightning related fatalities should be created

Dynamic model of a cylindrical roller on a rough surface with applications to wind turbine gearbox planetary bearings

Wind turbines of larger power ratings have become increasingly prevalent in recent years, improving the viability of wind energy as a sustainable energy source. However, these large wind turbines have been subjected to higher rates of failure of the wind turbine gearbox, resulting in larger downtime of operation and an increase in cost due to repairs. These failures most frequently initiate in the gearbox's bearings, especially in the planetary bearings of the planetary stage and high-speed bearings. Currently, most of the research on the detection of planetary bearing faults only address the case of localised faults in the outer bearing race, while little research considers the detection of distributed bearing faults. The research that does consider distributed bearing faults relies on techniques -- such as machine learning for the identification of faulty bearings -- that do not account much for the underlying physics of the bearing. In this paper, a model is developed to simulate and analyse the dynamic interaction of a planetary bearing in the presence of surface roughness -- which can be used to represent a distributed fault. The model presented uses random vibration theory for simulating the response of the planet bearing induced by distributed faults. The input of the model considers statistical expressions of the roughness geometry using multiple parallel tracks. Numerical simulation of the random vibration of the model is performed using 16 tracks, and the power spectral density of the radial deflection of the roller and the roller-race contact force is determined. The results of the simulation with the multi-track model show that a single-track model significantly overestimates the power spectral densities, and also suggests the stiffness of the bearing race is too high to have an effect on the roller dynamics for a planet bearing

Predictions of the dynamic response of piled foundations in a multi-layered half-space due to inertial and railway induced loadings

In this paper, the dynamic pile-soil-pile interaction (PSPI) in a multi-layered half-space is investigated for the prediction of the response of piled foundations due to railway vibrations. Two methods of modelling piled foundations in a multi-layered half-space are presented. The first is an efficient semi-analytical model that calculates the Green’s functions of the multi-layered half-space soil using the thin layer and the dynamic stiffness matrix methods. The second is a fully-coupled model that utilises the boundary element (BE) method to simulate the soil, where the Green’s functions are calculated using the ElastoDynamics Toolbox (EDT). The paper aims to investigate the accuracy and the efficiency of the semi-analytical model by comparing the predictions of the two methods. A set of comparisons is performed, including the driving point response of a single pile and the interaction between two piles. The comparisons reveal that, at most frequencies, the semi-analytical model can predict the driving point response and the dynamic interaction with acceptable accuracy and computational efficiency. The model is then used for predicting the response of a pile-group due to the vibration field generated by a railway in varying distance from the piles. The vibration field generated by the railway is modelled as the superposition of the response due to harmonic loadings generated at the wheel-rail interface and the vibration response is examined at different points on the free surface away from the piles. The comparisons highlight the efficiency and accuracy of the semi-analytical model and illustrate its practical application