Thesis (PhD (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / Dissertation presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Stellenbosch University. / ENGLISH ABSTRACT: Airworthiness certification of unmanned aircraft systems (UAS) is normally considered to be a regulatory function. In the absence of comprehensive UAS airworthiness regulations, the development of new and unique UAS, and their introduction into non-segregated airspace, remain major challenges for the UAS industry and regulators. Thus, in response, the objective of this research was to establish a framework and guidelines, within the scope of the typical regulatory regime, that can be used by the UAS engineering domain to ensure the safe and reliable functioning of a UAS, whether regulated or not. UAS airworthiness is currently mainly based on manned aircraft regulations, and the focus is on the unmanned aircraft and the 'airworthiness' of the remote control station. The typical UAS as a system, however, consists of more than just these elements and a broader approach to the 'airworthiness' of a UAS is required. This study investigated and introduces the concept of UAS operability, where the term 'operability' addresses the safe and reliable functioning of the UAS as a system, the airworthiness of its airborne sub-systems, and the safe and reliable functioning of its non-airborne subsystems and functional payloads. To ensure that the results of this study are aligned with typical aviation regulatory systems, a regulatory basis was defined within which UAS operability guidelines could be developed. Based on the operability concept, and in the scope of the regulatory basis, a UAS operability framework was developed for the UAS engineering domain. This framework is an index and reference source from which appropriate operability elements can be selected for a particular UAS. The scope of the framework is generic, rather than UAS-type or -class specific, and includes operability elements for the UAS as a system, for its airborne and non-airborne sub-systems, and for its payloads. The framework was validated by developing lower hierarchical levels for the framework and by populating each operability element of the framework with appropriate engineering guidance criteria. The guidance criteria were derived and/or developed from industry 'best practices' found in the literature, or were newly developed where no existing practices were found. The significance of this study is found in its establishing of a generic UAS operability framework that not only focuses on the airworthiness of the unmanned aircraft, but addresses the operability of the UAS as a system, as well as the operability of its airborne sub-systems, its non-airborne sub-systems and its payloads. In practice, the UAS operability framework can be used in the UAS engineering domain as an index and reference source to select relevant operability elements for a particular UAS. The guidance criteria for the selected elements can subsequently be used to develop the appropriate processes, procedures, requirements and specifications to achieve initial operability of the UAS, and to maintain its continued operability. Although the objective of the research was achieved, the UAS operability framework must still be applied and tested in real-life UAS projects and, where necessary, revised to eliminate shortcomings and to provide for new and novel developments in UAS engineering technologies. / AFRIKAANSE OPSOMMING: Die lugwaardigheidsertifisering van onbemande vliegtuigstelsels (OVS) word normaalweg beskou as 'n reguleringsfunksie. In die afwesigheid van omvattende OVS lugwaardigheidsregulasies bly die ontwikkeling van nuwe en unieke OVS, en die inbedryfstelling daarvan in onafgesonderde lugruim, besonderse uitdagings vir beide die OVS nywerheid en reguleerders. Die doelwit van hierdie navorsing was dus om riglyne binne die bestek van die tipiese reguleringsregime te vestig wat deur die OVS ingenieursdomein benut kan word om die veilige en betroubare funksionering van 'n OVS te verseker, of dit gereguleer word aldan nie. OVS lugwaardigheid word tans hoofsaaklik gebaseer op lugwaardigheidsvereistes vir bemande vliegtuie. Die fokus is dan ook meerendeels op die onbemande vliegtuig en die 'lugwaardigheid' van die afstandbeheerstasie. Die tipiese OVS bestaan egter uit meer sub-stelsels en 'n weier beskouing van die 'lugwaardigheid' van 'n OVS is nodig. Die konsep van OVS bedryfbaarheid is in hierdie studie ondersoek en voorgestel. 'Bedryfbaarheid' beteken in hierdie konteks die veilige en betroubare funksionering van die OVS as 'n stelsel, die lugwaardigheid van die lug sub-stelsels, die veilige en betroubare funksionering van die nie-lug sub-stelsels, asook die veilige en betroubare funksionering van funksionele loonvragte. Om te verseker dat die resultate van hierdie studie versoenbaar is met tipiese lugvaart reguleringstelsels, is 'n reguleringsbasis omskryf vir die ontwikkeling van OVS bedryfbaarheidsriglyne. Gebaseer op die bedryfbaarheidskonsep, en binne die riglyne van die reguleringsbasis, is 'n OVS bedryfbaarheidsraamwerk ontwikkel vir die OVS ingenieursdomein. Die raamwerk is 'n indeks en verwysingsbron waaruit gepaste bedryfbaarheids-elemente gekies kan word vir 'n bepaalde OVS. Die bestek van die raamwerk is generies en nie beperk tot spesifieke OVS tipes of klasse nie. Die raamwerk sluit bedryfbaarheidselemente in vir die OVS as stelsel, asook vir die lug en nie-lug sub-stelsels van die OVS, en vir die loonvragte van die OVS. Die raamwerk se geldigheid was bevestig deur die struktuur van die raamwerk tot laer vlakke uit te brei en gepaste ingenieursriglyne vir elke bedryfbaarheids-element in die raamwerk te ontwikkel. Die riglyne was gebaseer op 'beste praktyke' soos beskryf in die literatuur, of was van nuuts af ontwikkel waar geen bestaande praktyke gevind kon word nie. Die bydrae van hierdie studie is gesetel in die vestiging van 'n generiese OVS bedryfbaarheidsraamwerk wat nie net gemik is op die lugwaardigheid van die onbemande vliegtuig nie, maar wat die bedryfbaarheid in geheel van die OVS as stelsel aanspreek, asook die bedryfbaarheid van die OVS se lug sub-stelsels, nie-lug sub-stelsels en loonvragte. In die praktyk kan die raamwerk in die OVS ingenieursdomein gebruik word om gepaste bedryfbaarheids-elemente vir 'n OVS te kies. Daarna kan die bedryfbaarheidsriglyne gebruik word om gepaste prosesse, prosedures, vereistes en spesifikasies te ontwikkel om die OVS se aanvanklike en voortgesette bedryfbaarheid te bewerkstellig. Alhoewel die doelwit vir die navorsing bereik is, moet die OVS bedryfbaarheidsraamwerk nog op werklike OVS projekte getoets word. Waar nodig, moet die raamwerk dan hersien word om tekortkominge, asook nuwe en unieke ontwikkelinge in OVS ingenieurstegnologie, aan te spreek.

<p>This report presents a study of the effect of reusing experience in the Hazards and Operability Analysis method (HazOp method) with regards to how the effectiveness of the method is affected. The study was conducted by first creating a software tool for experience reuse in HazOp, then testing that tool in a student experiment in which the participants used the tool when conducting a HazOp.</p><p>During the experiment it was found that students using the tool found 21% more hazards in the system under study than their counterparts. After conducting the experiment it was found that there was a 94% certainty that this improvement was not due to random effects.</p>

This report presents a study of the effect of reusing experience in the Hazards and Operability Analysis method (HazOp method) with regards to how the effectiveness of the method is affected. The study was conducted by first creating a software tool for experience reuse in HazOp, then testing that tool in a student experiment in which the participants used the tool when conducting a HazOp. During the experiment it was found that students using the tool found 21% more hazards in the system under study than their counterparts. After conducting the experiment it was found that there was a 94% certainty that this improvement was not due to random effects.

The North American forest products industry is primarily commodity-based and faces challenges. This has led to the proposal of a shift toward revenue diversification through the production of high-value specialty products along with the conventional commodity products. A key consideration for this new business strategy to remain competitive and sustainable is that the forest products supply chain designs must perform satisfactorily under the dynamic market conditions. The notion of supply chain operability attempts to characterize the ability of a supply chain to perform satisfactorily in the face of uncertainty. However, limited quantitative analysis is available in the current body of literature. In this work, the concepts originated within the context of process systems engineering are adapted to develop optimization-based frameworks in order to characterize supply chain operability measures, in particular, supply chain flexibility and dynamic responsiveness. Although motivated by the forest products industry, the practical mathematical formulations presented are widely applicable to general process supply chains in other industries. This thesis aims to extend the supply chain flexibility analysis formulation established by Mastragostino (2012) to include additional quantitative flexibility measures. The resulting framework provides a quantitative mapping to various types of flexibility frequently discussed in the operations research literature. Two case studies are included to illustrate the application of this framework for analyzing the flexibility of existing supply chain processes, as well as utilizing it in supply chain design. The work also builds on the analysis framework established by Mastragostino and Swartz (2014) to assess supply chain responsiveness, and to configure the framework in preparation for tackling design problems under uncertainty. Then a composite operability analysis framework is proposed to address both flexibility and responsiveness metrics simultaneously in forest products supply chain design and operation. A comprehensive case study based on a forest product company is performed and the trade-offs among flexibility, responsiveness and economics are examined. / Thesis / Master of Applied Science (MASc)

Membrane processes have found increasing industrial applications worldwide. For membrane processes to deliver their desired performances and mitigate the effect of disturbances, automatic controllers must be installed. Before the installation of controllers, operability analysis is a crucial step to evaluate how well the processes can be controlled, and to determine how process design can be improved for better control. However, existing applications of operability analysis in membrane processes are limited. This thesis extends the application of operability analysis to a multiple-stage membrane process, exemplified by a detailed case study of a 12-stage industrial whey ultrafiltration (UF) process. Process dynamic models are determined to describe the transient behaviour of process performance caused by disturbances and long-term fouling. Steady-state nonlinear operability analysis is conducted to identify inherent limitations of the process. Using the process dynamic models, dynamic operability analysis is performed to determine the effects of dynamic behaviour on process and controller design. Steady-state operability analysis shows that the whey UF process is not able to mitigate the effects of high concentrations of true protein in the fresh whey feed. The ability of the process to mitigate the effects of disturbances is also adversely affected by long-term membrane fouling. Mid-run washing is therefore necessary to restore control performance after long periods of operation. Besides demonstrating the adverse effects of long-term membrane fouling on operability, dynamic operability analysis identifies the manipulated variables that can deliver the best control performance. It also indicates that control performance can be improved by installing equipment (e.g. buffer tanks) upstream of the process. Dynamic operability analysis shows that recycling of the retentate stream has a profound effect on the plant-wide dynamics and reduces significantly the achievable speed of process response under automatic control. However, retentate recycling is essential during operation to minimize membrane fouling. Although reducing the number of stages in the whey UF process can improve the achievable speed of process response under automatic control, process performance will fluctuate significantly from its desired level. A trade-off therefore exists between process performance and control performance that should be addressed during process and controller design.

<p>Idag är det möjligt att modellera de hydrauliska och mekaniska systemen hos en hjullastare. Det går även i viss omfattning att simulera omgivningen samt de förarkommandon som krävs för utförandet av en önskad uppgift. Däremot är det enda sättet att få reda på hur en förare kommer att uppleva maskinen, dess körbarhet, att bygga en fungerande prototyp och be en förare att testa den.</p><p>Syftet med det här examensarbetet var att hitta en korrelation mellan förarens bedömningar och mätdata insamlade från en hjullastare under körning. Resultaten är sedan tänkta att användas i framtida simuleringar. Olika hjullastare testades av en grupp provförare och deras subjektiva bedömningar såväl som mätdata från hjullastarna samlades in.</p><p>Slutsatsen är att det går till en viss del att förutsäga körbarheten från insamlade data om förarens körstil är känd. Då förarnas körstil skiljer väldigt mycket är det är inte möjligt att dra allmänna slutsatser om körbarheten.</p> / <p>Today it is possible to model all hydraulic and mechanical systems of a wheel loader. To an extent the surrounding environment and the operator input required for a desired operation can also be simulated. However the only way to determine how an operator will perceive the handling qualities, the operability, of the wheel loader is to assemble a working prototype and ask an operator to try it out.</p><p>The purpose of this Master thesis was to find some correlation between the drivers’ opinions and data recorded from the machines during operation. The results are intended to be used in future simulations. Different machines were tested by a group of drivers and their subjective impressions, as well as measurements from the machines were collected.</p><p>The findings from the analysis are that the operability can be determined to a certain extent if the driver’s behaviour is known. Because of the differences in the way the drivers operate the machine it has not been possible to draw any general conclusions.</p>

Membrane processes have found increasing industrial applications worldwide. For membrane processes to deliver their desired performances and mitigate the effect of disturbances, automatic controllers must be installed. Before the installation of controllers, operability analysis is a crucial step to evaluate how well the processes can be controlled, and to determine how process design can be improved for better control. However, existing applications of operability analysis in membrane processes are limited. This thesis extends the application of operability analysis to a multiple-stage membrane process, exemplified by a detailed case study of a 12-stage industrial whey ultrafiltration (UF) process. Process dynamic models are determined to describe the transient behaviour of process performance caused by disturbances and long-term fouling. Steady-state nonlinear operability analysis is conducted to identify inherent limitations of the process. Using the process dynamic models, dynamic operability analysis is performed to determine the effects of dynamic behaviour on process and controller design. Steady-state operability analysis shows that the whey UF process is not able to mitigate the effects of high concentrations of true protein in the fresh whey feed. The ability of the process to mitigate the effects of disturbances is also adversely affected by long-term membrane fouling. Mid-run washing is therefore necessary to restore control performance after long periods of operation. Besides demonstrating the adverse effects of long-term membrane fouling on operability, dynamic operability analysis identifies the manipulated variables that can deliver the best control performance. It also indicates that control performance can be improved by installing equipment (e.g. buffer tanks) upstream of the process. Dynamic operability analysis shows that recycling of the retentate stream has a profound effect on the plant-wide dynamics and reduces significantly the achievable speed of process response under automatic control. However, retentate recycling is essential during operation to minimize membrane fouling. Although reducing the number of stages in the whey UF process can improve the achievable speed of process response under automatic control, process performance will fluctuate significantly from its desired level. A trade-off therefore exists between process performance and control performance that should be addressed during process and controller design.

The models used by model predictive controllers (MPCs) to predict future outcomes are usually unconstrained forms like impulse or step responses and discrete state space models. Certain MPC algorithms allow constraints to be imposed on the inputs or outputs of a system; but they may be infeasible as they are not checked for consistency via the process model. Consistent constraint handling methods - which account for their interdependence and disambiguate the language used to specify constraints – would therefore be an attractive aid when using any MPC package. A rigorous and systematic approach to constraint management has been developed, building on the work of Vinson (2000), Lima (2007) and Georgakis et al. (2003) in interpreting constraint interactions. The method supports linear steady-state system models, and provides routines to obtain the following information: <ul> <li> effects of constraint changes on the corresponding input and output constraints, </li><li> feasibility checks for constraints, </li><li> specification of constraint-set size and</li><li> optimal fitting of constraints within the desirable input and output space.</li></ul> Mathematical rigour and unambiguous language for identifying constraint types were key design criteria. The outputs of the program provide guidance when handling constraints, as opposed to rules of thumb and experience, and promote understanding of the system and its constraints. The metrics presented are not specific to any commercial MPC and can be implemented in the user interfaces of such MPCs. The method was applied to laboratory-scale test rigs to illustrate the information obtained. / Dissertation (MEng)--University of Pretoria, 2011. / Chemical Engineering / unrestricted

No description available.

Dynamic compressors are susceptible to aerodynamic instabilities while operating at low mass flow rates. These instabilities, rotating stall and surge, are detrimental to engine life and operational safety, and are thus undesirable. In order to prevent stability problems, a passive technique, involving fuel flow scheduling, is currently employed on gas turbines. The passive nature of this technique necessitates conservative stability margins, compromising performance and/or efficiency. In the past, model based active control has been proposed to enable reduction of margin requirements. However, available compressor stability models do not predict the different stall inception patterns, making model based control techniques practically infeasible. This research presents active stability management as a viable alternative. In particular, a limit detection and avoidance approach has been used to maintain the system free of instabilities. Simulations show significant improvements in the dynamic response of a gas turbine engine with this approach. A novel technique has been developed to enable real-time detection of stability limits in axial compressors. It employs a correlation measure to quantify the chaos in the rotor tip region. Analysis of data from four axial compressors shows that the value of the correlation measure decreases as compressor loading is increased. Moreover, sharp drops in this measure have been found to be relevant for stability limit detection. The significance of these drops can be captured by tracking events generated by the downward crossing of a selected threshold level. It has been observed that the average number of events increases as the stability limit is approached in all the compressors studied. These events appear to be randomly distributed in time. A stochastic model for the time between consecutive events has been developed and incorporated in an engine simulation. The simulation has been used to highlight the importance of the threshold level tosuccessful stability management. The compressor stability management concepts have also been experimentally demonstrated on a laboratory axial compressor rig. The fundamental nature of correlation measure has opened avenues for its application besides limit detection. The applications presented include stage load matching in a multi-stage compressor and monitoring the aerodynamic health of rotor blades.