Browsing by Author "Harrison, A."
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Item Open Access An aerospace requirements setting model to improve system design(Elsevier, 2014-10-31) Tomas Centrich, X.; Shehab, Essam; Sydor, Piotr; Mackley, Tim; John, Philip; Harrison, A.Decisions at an early conceptual stage of the product lifecycle, are made with relatively low confidence, but such decisions greatly influence the overall product and service development. It is, therefore, critical to define the risks involved in order to help designers to make informed decisions. This research project investigates the risk and uncertainties in delivering products to meet top-level business requirements. The aim is to improve the existing process of setting business requirements and the current design approaches to achieve an optimised system design. This project also examines different approaches in assessing the risk of product and service delivery. To achieve that, a dedicated software tool, based on Weibull distribution function reliability model, has been created. An example of Rolls-Royce Civil Large Engine (CLE) gas turbine design process is used in this research as the case study. An analysis of the gap between the current design achievements and the targeted business requirements of a new product is performed at whole engine, module and component level. Further comparison of the new product business requirements, the novelty in the design and the historical reliability data is used to define and assess the risk of new product delivery.Item Open Access Enhancing service requirements of technical product-service systems(Elsevier, 2015-10-09) Estebanez, L. Ruiz; Shehab, Essam; Sydor, Piotr; Mackley, Tim; John, Philip; Harrison, A.Due to the integration of product and services as a new business model, product reliability and strategies for cost reduction at the early design stage have become important factors for many manufacturing firms. It is, therefore, critical at this phase to analyse the risk involved with Service Requirements noncompliance in order to help designers make informed decisions; as these decisions have a large impact on the Product Life Cycle (PLC). An investigation has been performed into how Service Requirements are analysed in a service orientated business to achieve reduced Life Cycle Cost (LCC) and improvements of existing Service Requirements. Weibull distribution and Monte Carlo principle have been proposed to do so; as they are considered as the most widely used in product reliability studies in the industry sector. A generic methodology for risk evaluation of failure to deliver a new product against Service Requirements is presented in this paper. This is part of the ongoing research project which aims to, apart from comparing current and targeted Service Requirements, it also facilitates an optimisation of them at the minimum risk of nonconformity.Item Open Access Friction characteristics of skewed roller brakes(Cranfield University, 1998-10) Oliver-Hall, Richard.; Jones, R. I.; Strothers, P.; Harrison, A.The project sponsors design and manufacture skewed roller brake devices for use in aircraft flight control actuation systems. Design tools have previously been developed to predict the torque characteristics ofthese devices. A fundamental deficiency ofthese tools is the use ofempirical friction coefficient data gathered from a limited test sample. A need was identified to develop a friction coefficient model based on the operational parameters ofthe design, namely load, speed and lubricant viscosity. The development and validation ofthis model formed the basis ofthe technical research objective. A cost benefit analysis indicated that the sponsors could reasonably expect to gain a significant technical competitive advantage over their competitors ifthe technical research objective could be achieved. This advantage should provide opportunities for premium pricing ofthe product and enhanced opportunities to enter new markets. Additionally, the sponsors could expect lead time reductions and cost savings of £69000 from the removal ofthe need to conduct prototype tests to assess the effective friction coefficient. A friction coefficient model and skewed roller torque equation design tool have been successfully developed, satisfying the technical research objective. The friction coefficient model is defined in terms of lubrication number. The lubrication number parameter incorporates lubricant viscosity, roller speed, roller load and contact surface roughness terms, fully describing the operational parameters ofa design. Experimental evidence has validated the model using two lubricants, a hydraulic fluid, Brayco 795 and a mineral oil, Catenex 79. The tests cover a lubrication number range from 2 x 10-5 to 6 X 10-2 with a mean Hertzian stress from 0.27 to 0.61 Gpa. The success ofthis project has ensured that the sponsors will reap the cost and design lead time savings predicted in the cost benefit analysis and have the tools necessary to develop new markets and premium pricing business opportunities.Item Open Access An integrated aerospace requirement setting and risk analysis tool for life cycle cost reduction and system design improvement(Elsevier, 2015-10-27) Estébanez, L. Ruiz; Shehab, Essam; Sydor, Piotr; Mackley, Tim; John, Philip; Harrison, A.In the early conceptual stage of the service orientated model, decisions regarding the design of a new technical product are largely influenced by Service Requirements. Those decisions, therefore, have to merge both technical and business aspects to obtain desired product reliability and reduced Whole Life Cost (WLC). It is, therefore, critical at that phase to define the risk of potential noncompliance of Service Requirements in order to ensure the right design choices; as these decisions have a large impact on the overall product and service development. This paper presents outcome of research project to investigate different approaches used by companies to analyse Service Requirements to achieve reduced Life Cycle Cost (LCC). Analysis using Weibull distribution and Monte Carlo principle have been proposed here; based on the conducted literature review these are considered as the most widely used techniques in product reliability studies. Based on those techniques, a methodology and its software tool for risk evaluation of failure to deliver a new product against Service Requirements are presented in this paper. This is part of the on-going research project which, apart from analysing the gap between the current Service Requirements achievements and the design targets for a new aircraft engine, it also facilitates an optimisation of those requirements at the minimum risk of nonconformity.Item Open Access Performance modelling of windmilling gas turbines(Cranfield University, 2002-10-04) Jones, Geoffrey B.; Pilidis, Pericles; Harrison, A.; Brook, A.This thesis presents work carried out with the aim of improving the modelling of windmilling in gas turbine performance. The work also examines the phenomenon of relight. Methods of representing the performance of the turbomachinery components are investigated and recommendations are made for the use of a number of non- dimensional variables on which to map turbomachinery performance. A performance model was built using the turbomachinery characteristics proposed in order to test the robustness of the representations. The model was written in Fortran 90 and coupled directly to a spreadsheet package to allow easy analysis of the results. The effect of choice of representation, in terms of both the robustness and the results obtained, is presented. Techniques for the extrapolation of above-idle turbomachinery characteristics to the sub-idle region for starting and windmilling modelling are examined. A number of techniques are analysed and two new methods are proposed. These are the use of computational fluid dynamics to generate a zero speed torque and pressure loss relationship and the use of a semi-empiricalstage-by-stageextrapolation method. Some aspects of relight combustion, particularly in respect of ignition, are studied. Also investigated were the accessory systems acting on the gearbox of the engine. An assessment of the design process and the consequent benefits to the company of improved modelling were presented, in terms of the reduction in design risks and in project development costs. It was shown that research of this nature can have a substantial impact on an engine's development programme Throughout the doctoral programme, Masters and exchange students were used to broaden the scope and depth of the research. This thesis examines how best to ensure that the results of such collaboration are positive and presents the approach which this researcher used.