A concept is established for adaptive vibration control of shaped alpine skis using smart materials – specifically magnetorheological (MR) fluid. This work presents the motivation behind the concept and the work to verify its viability, technically and commercially. Research is reviewed, relevant to understanding ski dynamics. Literature on smart materials is similarly researched and presented to establish understanding of the use of the technology for dynamic control. The influence of geometry, materials and construction on ski dynamics is presented. Conventional vibration control techniques and their influence on the dynamic control of modern alpine skis are explained. A review of the boundary conditions used in modelling ski dynamics is presented and the influence of skier position and environmental conditions are discussed. Application of smart technology in skis are presented with reference to a shape memory alloy concept and commercially available piezo-systems. Procedures for quantifying the physical characteristics of a ski are discussed and a custom-built laboratory rig is used to test skis under controlled, repeatable conditions. Results from static and dynamic laboratory tests on skis are used to perform system analysis, with reference to technical literature. Analysis of the signal generated by the moving ski during skiing (i.e. signal analysis) is carried out on results from field-tests of instrumental skis. The technical objectives and perceived benefits of adaptive vibration control of skies with MR fluid are examined and technical and commercial system constraints are identified. Results are presented from laboratory tests investigating fore-body vibration control on a concept demonstrator, comprising a MR fluid damper integrated on a simplified ski-like structure. Subsequent analysis is carried out to review the technical and commercial viability of the concept.

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The shock response of a complex laminate has been investigated using a single stage gas gun, with manganin pressure gauges employed to investigate the shock profile. The complex laminate investigated was known by the acronym TWCP and is a tape wrapped carbon fibre composite with phenolic resin matrix. Carbon fibre composites are used in the aerospace industry due to their high strength to weight ratio, so understanding of different loading conditions is needed. To investigate the shock response of the TWCP, four weave orientations were studied. The orientations investigated with respect to the shock front were 0◦ (parallel to the shock front or perpendicular to the direction of travel), 25◦, 45◦ and 90◦ (perpendicular to the shock front or parallel to the direction of travel). As well as the TWCP the shock response of the matrix material, a phenolic resin Durite SC-1008 was also investigated. For the phenolic resin matrix material a non-linear Hugoniot was found in the US-up plane with the equation of US = 2.14 + 3.79up - 1.68u2 p. Such non-linear Hugoniot behaviour has been seen in other polymeric materials, e.g. PMMA. In the pressure-volume plane deviation was seen in the higher pressure data most likely due to the materials non-linear response. For the TWCP composite, linear Hugoniots were found for all four orientations with the corresponding equations shown below. • 0◦ US = 3.69 + 0.59up • 25◦ US = 3.45 + 0.73up • 45◦ US = 3.44 + 1.12up • 90◦ US = 3.96 + 0.46up The four Hugoniots are comparable in nature and it is possible to assign a single Hugoniot with the equation US = 3.56 + 0.84up through the majority of data points. The largest deviation from this “average” response was obtained from the 90◦ orientation due to the high elastic sound speed of this weave angle. Convergence was also seen between the Hugoniots in the US-up plane towards the higher up values (approximately 1 mm μs−1). In the pressure-up plane there was very little difference between all of the experimental data, meaning that for the stress in this material, orientation makes no difference.

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Modern civil engineering structures exposed to human-induced dynamic loading due to walking, such as footbridges and long-span floors, are becoming increasingly slender and therefore more prone to vibrations generated by people. As a consequence, the vibration serviceability of these structures is becoming their governing design criterion. Currently, the design procedures for the vibration serviceability check used in practice are mainly of a deterministic nature. This means that the walking force is modelled via a unique set of parameters, such as walking frequency, step length and force amplitude assumed to be representative for all pedestrians. Therefore, the natural inter-subject variability that exists in these parameters generated by different people is neglected. Moreover, these parameters vary with each step even in the force time history of a single person (intra-subject variability). This implies that the walking force is a narrow-band random process rather than a deterministic force. As a result of these shortcomings, current design procedures based on deterministic forces do not predict reliably the vibration responses to single person walking across as-built slender structures. To improve design procedures, it is necessary to take into account the both inter- and intrasubject variabilities in the walking force. This implies that a probability-based approach, whereby the probability of occurrence of various walking parameters can be taken into account, might be more appropriate to model the walking excitation. In this thesis, a probability-based framework for a vibration serviceability check due to a single person walking is developed. For this, the probability density functions for walking frequencies, step lengths, magnitude of walking force and imperfections in human walking are proposed. They are used as building blocks to develop a design procedure that can estimate the probability of occurrence of a certain level of vibration response. Based on this result, a probability that the vibration response will not exceed certain predefined limiting values can be found. Moreover, a methodology for finding a reasonable limiting vibration level, based on the assumption that some human-structure dynamic interaction takes place when walking across perceptibly moving bridge, is suggested. A provisional value of 0.35 m/s2 is identified for two footbridges investigated. The probability-based design procedure developed in this thesis can be used for vibration serviceability check of footbridges responding in one or more vibration modes to excitation induced by a single walker. The method has potential to be used for vibration serviceability check of other slender structures.

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No description available.