135 research outputs found

    Quotient method for stabilising a ball-on-a-wheel system – Experimental results

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    This paper extends the quotient method proposed in [1] and applies it to stabilize a “ball-on-a-wheel” system. The quotient method requires a diffeomorphism to obtain the normal form of the input vector field and uses canonical pro- jection to obtain the quotient. However, the whole process can be done without computing the normal form, which requires defining a quotient generating function and a quotient bracket. This paper presents the steps necessary to apply the quotient method without obtaining the normal form. Furthermore, a Lyapunov function is introduced to prove stability. This paper also presents the experimental implementation of the quotient method to stabilize a ball-on-a-wheel system

    Controlling the interstitial element concentration in Ti-6Al-4V using calciothermic reduction

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    The production of Ti-6Al-4V components via powder metallurgy routes is looked upon as an efficient production method that reduces wastage, but leaves finished products with high interstitial oxygen concentrations that do not meet industrial standards. The ability to control the interstitial oxygen concentration in Ti-6Al-4V powder metallurgy would improve the viability of near net shape processing for the production of industrial components. One process that has demonstrated the ability to remove oxygen from titanium alloys is calciothermic reduction, which is a reduction process originally developed to reduce titanium dioxide to commercial purity titanium using a molten flux of calcium and calcium chloride. The aim of this thesis is to examine whether calciothermic reduction can be used to control the interstitial concentration of oxygen and nitrogen in powder metallurgy Ti-6Al-4V and understand the reaction mechanisms that enable this process to work. By understanding these mechanisms, the process can then be optimised to improve the properties of powder metallurgy Ti-6Al-4V components, and provide a basis to extend this to other alloy systems. Calciothermic reduction was demonstrated to be effective at reducing the interstitial oxygen concentration in powder metallurgy Ti-6Al-4V to acceptable industrial standards (< 2,000 wt .ppm). The optimisation of the process required the balance of thermodynamics and kinetics to be controlled; thermodynamics was important to ensuring the reaction would begin, with the kinetics becoming more important during the reduction process because the removal of interstitial oxygen concentration relied upon a diffusion based mechanism. Evaluation of the mechanism that underpins the removal of oxygen via calciothermic reduction, was assessed using a FIB-SIMS based technique. This method of analysis was developed during this research and demonstrated to be effective at quantifying interstitial oxygen concentrations in titanium alloy, which was used to confirm the formation of oxygen concentration gradients from titanium alloy bulk to the surface during calciothermic reduction. Further investigation of the reduction process indicated that calciothermic reduction could facilitate the nitriding of Ti-6Al-4V in a sealed air environment, forming a wear resistant surface layer in a novel process referred to as “Calciothermic Assisted Immersion Nitriding” (CAIN). The nitriding process produced a consistent TiCxNyOZ surface layer where the chemical composition of the layer developed in a three stage reaction involving the inward diffusion of interstitial carbon and nitrogen, whilst oxygen was removed from the surface. This surface layer improved the tribological properties of the Ti-6Al-4V samples by changing the wear mechanism from adhesive to abrasive, which resulted in an increased wear resistance, which was comparable to a commercial produced, physical vapour deposition TiCN coating.Open Acces

    Contributions of precision engineering to the revision of the SI

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    All measurements performed in science and industry are based on the International System of Units, the SI. It has been proposed to revise the SI following an approach which was implemented for the redefinition of the unit of length, the metre, namely to define the SI units by fixing the numerical values of so-called defining constants, including c, h, e, k and NA. We will discuss the reasoning behind the revision, which will likely be put into force in 2018. Precision engineering was crucial to achieve the required small measurement uncertainties and agreement of measurement results for the defining constants

    Advanced Testing and Characterization of Bituminous Materials, Two Volume Set

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    Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin

    Development of a vehicle dynamics controller for obstacle avoidance

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    As roads become busier and automotive technology improves, there is considerable potential for driver assistance systems to improve the safety of road users. Longitudinal collision warning and collision avoidance systems are starting to appear on production cars to assist drivers when required to stop in an emergency. Many luxury cars are also equipped with stability augmentation systems that prevent the car from spinning out of control during aggressive lateral manoeuvres. Combining these concepts, there is a natural progression to systems that could assist in aiding or performing lateral collision avoidance manoeuvres. A successful automatic lateral collision avoidance system would require convergent development of many fields of technology, from sensors and instrumentation to aid environmental awareness through to improvements in driver vehicle interfaces so that a degree of control can be smoothly and safely transferred between the driver and vehicle computer. A fundamental requirement of any collision avoidance system is determination of a feasible path that avoids obstacles and a means of causing the vehicle to follow that trajectory. This research focuses on feasible trajectory generation and development of an automatic obstacle avoidance controller that integrates steering and braking action. A controller is developed to cause a specially modified car (a Mercedes `S' class with steer-by-wire and brake-by-wire capability) to perform an ISO 3888-2 emergency obstacle avoidance manoeuvre. A nonlinear two-track vehicle model is developed and used to derive optimal controller parameters using a series of simulations. Feedforward and feedback control is used to track a feasible reference trajectory. The feedforward control loops use inverse models of the vehicle dynamics. The feedback control loops are implemented as linear proportional controllers with a force allocation matrix used to apportion braking effort between redundant actuators. Two trajectory generation routines are developed: a geometric method, for steering a vehicle at its physical limits; and an optimal method, which integrates steering and braking action to make full use of available traction. The optimal trajectory is obtained using a multi-stage convex optimisation procedure. The overall controller performance is validated by simulation using a complex proprietary model of the vehicle that is reported to have been validated and calibrated against experimental data over several years of use in an industrial environment

    Advanced Testing and Characterization of Bituminous Materials, Two Volume Set

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    Bituminous materials are used to build durable roads that sustain diverse environmental conditions. However, due to their complexity and a global shortage of these materials, their design and technical development present several challenges. Advanced Testing and Characterisation of Bituminous Materials focuses on fundamental and performance testin

    Eleventh International Conference on the Bearing Capacity of Roads, Railways and Airfields

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    Innovations in Road, Railway and Airfield Bearing Capacity – Volume 3 comprises the third part of contributions to the 11th International Conference on Bearing Capacity of Roads, Railways and Airfields (2022). In anticipation of the event, it unveils state-of-the-art information and research on the latest policies, traffic loading measurements, in-situ measurements and condition surveys, functional testing, deflection measurement evaluation, structural performance prediction for pavements and tracks, new construction and rehabilitation design systems, frost affected areas, drainage and environmental effects, reinforcement, traditional and recycled materials, full scale testing and on case histories of road, railways and airfields. This edited work is intended for a global audience of road, railway and airfield engineers, researchers and consultants, as well as building and maintenance companies looking to further upgrade their practices in the field

    Understanding and stimulating the development of perceptual-motor skills in child bicyclists

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