Browsing by Author "Leverone, Fiona Kay."

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Development of a design methodology of a composite monocoque chassis.
(2018) Denny, Jason Andrew.; Adali, Sarp.; Veale, Kirsty Lynn.; Leverone, Fiona Kay.
The concept of the composite monocoque chassis has been implemented in many vehicle designs; however, there is little open-access literature defining the primary considerations when simulating one. The purpose of this research is to develop a methodology for determining the structural integrity of a composite monocoque chassis, through finite element analysis, with the intention of developing a lightweight solar powered vehicle. Factors that influence this methodology include; the definition of the vehicle loading conditions, failure criteria, and important design parameters, chief among which is the torsional stiffness. Chassis design specifications were developed from the 2017 Bridgestone World Solar Challenge rules and regulations as these are the most common and complete specifications for this particular type of vehicle. The primary design criteria considered is the torsional stiffness, which was determined from the application requirements and literature, and resulted in a suitable value of 4000 Nm/deg. Siemens NX Nastran was used to develop a torsional stiffness model, which uses the torsional loading condition, to determine the torsional stiffness value. The design methodology then follows an iterative process where various geometry and layup modifications were considered, under the same loading conditions, with the aim of increasing the torsional stiffness to achieve the required value. Aerodynamic properties were adapted from existing UKZN solar vehicle knowledge; however, this research does not consider the optimisation of the aerodynamic properties of a monocoque chassis. Only a structural simulation was conducted. The ultimate strength of the material was also considered throughout the simulation process, however in all cases the model failed to meet the required torsional stiffness parameter before material failure modes. The door recesses had the most significant effect on the torsional stiffness. By compacting the door recesses the torsional stiffness was increased by 29.04 %. A final torsional stiffness was of 4097 Nm/deg was attained with the implementation of an aluminium honeycomb core. Additionally; an analysis of the mounting points was conducted to ensure that the layup can withstand the concentrated loads at the suspension mounts. This analysis is concerned with the principal stresses, where the principal stresses give insight into the most suitable orientation of the layup. The torsional stiffness model resulted in a maximum principal stress of 81.68 MPa, below the 464.4 MPa tensile strength of the reinforcement material orientated in the direction of the fibres. To verify the significance of the torsional stiffness failure criterion, vertical and lateral bending analyses were conducted. A vertical bending model was developed where the chassis is modelled as a simply supported beam, simulating the squatting and diving of a chassis under acceleration and deceleration respectively. The maximum deflection was 5.28 mm, which is below the vi maximum allowable deflection of 12.29 mm, determined from a maximum deflection ratio of 1/360th of chassis length. A lateral bending model modelled the chassis as a simply supported beam with the maximum stress being analysed. The maximum stress experienced by the chassis under this loading condition was 18.73 MPa, which was 75.8 % less when compared to the maximum stress exhibited by the chassis under the torsional loading condition. Flexural bending tests were conducted on various laminate sandwich structures used in the finite element analysis to validate the simulation material properties. The peak load and mid-span deflection of each specimen was recorded to determine the maximum flexural stress and flexural modulus of elasticity. The flexural stress at specific midspan deflections was compared, under the same loading conditions, to that of the bending stress exhibited by a flexural bend test model finite element analysis conducted in Siemen’s NX Nastran. Graphs of the stress versus midspan deflection were plotted for each specimen layup type and the curves of the simulated and experimental results were compared. In each laminate sandwich structure case, the simulation curve exhibited a linear relationship between the midspan deflection and flexural bend stress and the experimental curve exhibited a linear relationship until the elastic limit of the specimens was reached. Thereafter the curve exhibited an exponential relationship as plastic deformation occurs until the specimen failure. An iterative finite element analysis design methodology was used to develop a composite monocoque chassis. The design process of a composite monocoque chassis is simplified by using finite element analysis to iterate through many different configurations, such as core thicknesses, layup orientations, and geometry features, to customise the properties of the structure. With these properties, it is possible to determine chassis performance. The finite element analysis results illustrated that geometry modifications, such as compacting door recesses, and applying strategic layup orientations, such as implementing a honeycomb core, significantly affected the torsional stiffness of a chassis. In addition, a chassis with sufficient torsional stiffness exhibits sufficient bending stiffness. The methodology presented in this research stands to be supportive in designing a fully composite monocoque chassis for lightweight race vehicle applications.
Performance modelling and simulation of a 100km hybrid sounding rocket.
(2013) Leverone, Fiona Kay.; Brooks, Michael John.; Pitot de la Beaujardiere, Jean-Francois Philippe.; Roberts, Lancian Willett.
The University of KwaZulu-Natal (UKZN) Phoenix Hybrid Sounding Rocket Programme was established in 2010. The programme’s main objective is to develop a sounding rocket launch capability for the African scientific community, which currently lacks the ability to fly research payloads to the upper atmosphere. In this dissertation, UKZN’s in-house Hybrid Rocket Performance Simulator (HYROPS) software is used to improve the design of the Phoenix-2A vehicle, which is intended to deliver a 5 kg instrumentation payload to an apogee altitude of 100 km. As a benchmarking exercise, HYROPS was first validated by modelling the performance of existing sub-orbital sounding rockets similar in apogee to Phoenix-2A. The software was found to approximate the performance of the published flight data within 10%. A generic methodology was then proposed for applying HYROPS to the design of hybrid propellant sounding rockets. An initial vehicle configuration was developed and formed the base design on which parametric trade studies were conducted. The performance sensitivity for varying propulsion and aerodynamic parameters was investigated. The selection of parameters was based on improving performance, minimising cost, safety and ease of manufacturability. The purpose of these simulations was to form a foundation for the development of the Phoenix-2A vehicle as well as other large-scale hybrid rockets. Design chamber pressure, oxidiser-to-fuel ratio, nozzle design altitude, and fin geometry were some of the parameters investigated. The change in the rocket’s propellant mass fraction was the parameter which was found to have the largest effect on performance. The fin and oxidiser tank geometries were designed to avoid fin flutter and buckling respectively. The oxidiser mass flux was kept below 650 kg/m2s and the pressure drop across the injector relative to the chamber pressure was maintained above 15% to mitigate the presence of combustion instability. The trade studies resulted in an improved design of the Phoenix-2A rocket. The propellant mass of the final vehicle was 30 kg less than the initial conceptual design and the overall mass was reduced by 25 kg. The Phoenix-2A vehicle was 12 m in length with a total mass of 1006 kg. The fuel grain length of Phoenix-2A was 1.27 m which is approximately 3 times that of Phoenix-1A. The benefit of aluminised paraffin wax as a fuel was also investigated. The results indicated that more inert mass can be delivered to the target apogee of 100 km when using a 40% aluminised paraffin wax.