Jerome P. Jarrett

Design for patient safety: A review of the effectiveness of design in the UK health service

In 2002 the UK Department of Health and the Design Council jointly commissioned a scoping study to deliver ideas and practical recommendations for a design approach to reduce the risk of medical error and improve patient safety across the National Health Service (NHS). The research was undertaken by the Engineering Design Centre at the University of Cambridge, the Robens Institute for Health Ergonomics at the University of Surrey and the Helen Hamlyn Research Centre at the Royal College of Art. The research team employed diverse methods to gather evidence from literature, key stakeholders, and experts from within healthcare and other safety-critical industries in order to ascertain how the design of systems—equipment and other physical artefacts, working practices and information—could contribute to patient safety. Despite the multiplicity of activities and methodologies employed, what emerged from the research was a very consistent picture. This convergence pointed to the need to better understand the healthcare system, including the users of that system, as the context into which specific design solutions must be delivered. Without that broader understanding there can be no certainty that any single design will contribute to reducing medical error and the consequential cost thereof.

Toward designing with three-dimensional bumps for lift/drag improvement and buffet alleviation

The desire to design more efficient transport aircraft has led to many different attempts to minimize drag. One approach is the use of three-dimensional shock control bumps, which have gained popularity in the research community as simple, efficient and robust devices capable of reducing the wave drag of transonic wings. This paper presents a computational study of the performance of three-dimensional bumps, relating key bump design variables to the overall wing aerodynamic performance. An efficient parameterization scheme allows three-dimensional bumps to be directly compared to two-dimensional designs, indicating that two-dimensional bumps are capable of greater design point aerodynamic performance in the transonic regime. An advantage of three-dimensional bumps lies in the production of streamwise vortices, such that, while two-dimensional bumps are capable of superior performance near the design point, three-dimensional bumps are capable of breakingup regions of separated flow at high Mach numbers, suggesting improvement in terms of buffet margin. A range of bump designs are developed that exhibit a tradeoff between design point aerodynamic efficiency and improvementinbuffet margin, indicating the potential for bespoke designs to be generated for different sections of a wing based on its flow characteristics. Copyright

Robust Design Optimization of Gas Turbine Compression Systems

Gas turbine compression systems are required to perform adequately over a range of operating conditions. Complexity has encouraged the conventional design process for compressors to focus initially on one operating point, usually the most commonor arduous, to draw up an outline design. Generally, only as this initial design is refined is its offdesign performance assessed in detail. Not only does this necessarily introduce a potentially costly and timeconsuming extra loop in the design process, but it also may result in a design whose offdesign behavior is suboptimal. Aversion of nonintrusive polynomial chaos was previously developed in which a set of orthonormal polynomials was generated to facilitate a rapid analysis of robustness in the presence of generic uncertainties with good accuracy. In this paper, this analysis method is incorporated in real time into the design process for the compression system of a three-shaft gas turbine aeroengine. This approach to robust optimization is shown to lead to designs that exhibit consistently improved system performance with reduced sensitivity to offdesign operation.

Adaptive polynomial chaos for gas turbine compression systems performance analysis

The design of a gas turbine, or one of its constituentmodules, is generally approachedwith some specific operating condition in mind (its design point). Unfortunately, engine components seldom exactly meet their specifications and do not operate at just one condition, but over a range of power settings. This simplification can then lead to a product that exhibits performance worse than nominal in real-world conditions. The integration of some consideration of robustness as an active part of the design process can allow products less sensitive to the presence of the noise factors commonly found in real-world environments to be obtained. To become routinely used as a design tool, minimization of the time required for robustness analysis is paramount. In this study, a nonintrusive polynomial chaos formulation is used to evaluate the variability in the performance of a genericmodular-core compression system for a three-spool modern gas turbine engine subject to uncertain operating conditions with a defined probability density function. The standard orthogonal polynomials from the Askey scheme are replaced by a set of orthonormal polynomials calculated relative to the specific probability density function, improving the convergence of the method.

An Integrated System for the Aerodynamic Design of Compression Systems—Part I: Development

The design of gas turbine engines is a complex problem. This complexity has led to the adoption of a modular design approach, in which a conceptual design phase fixes the values for some global parameters and dimensions in order to facilitate the subdivision of the overall task into a number of simpler subproblems. This approach, while making a complex problem more tractable, necessarily has to rely on designer experience and simple evaluations to specify these process-intrinsic constraints at a point in the design process where very little knowledge about the final design exists. Later phases of the design process, using higher-fidelity tools but acting on a limited region of the design space, can only refine an already established design. While substantial improvements in performance have been possible with the current approach, further gains are becoming increasingly hard to achieve. A gas turbine is a complex multidisciplinary system: a more integrated design approach can facilitate a better exploitation of the trade-offs between different modules and disciplines, postponing the setting of these critical interface parameters (such as flow areas, radii, etc.) to a point where more information exists, reducing their impact on the final design. In the resulting large, possibly multimodal, highly constrained design space, and with a large number of objectives to be considered simultaneously, finding an optimal solution by simple trial-and-error can prove extremely difficult. A more intelligent search approach, in which a numerical optimizer takes the place of the human designer in seeking optimal designs, can enable the design space to be explored significantly more effectively, while also yielding a substantial reduction in development times thanks to the automation of the design process. This paper describes the development of a system for the integrated design and optimization of gas turbine engines, linking a metaheuristic optimizer to a geometry modeler and to evaluation tools with different levels of fidelity. In recognition of the substantial increase in design space size required by the integrated approach, an improved parameterization based on the concept of principal components’ analysis was implemented, allowing a rotation of the design space along its most significant directions and a reduction in its dimensionality, proving essential for a faster and more effective exploration of the design space.

The benefits of adaptive parametrization in multi-objective Tabu Search optimization

In real-world optimization problems, large design spaces and conflicting objectives are often combined with a large number of constraints, resulting in a highly multi-modal, challenging, fragmented landscape. The local search at the heart of Tabu Search, while being one of its strengths in highly constrained optimization problems, requires a large number of evaluations per optimization step. In this work, a modification of the pattern search algorithm is proposed: this modification, based on a Principal Components’ Analysis of the approximation set, allows both a re-alignment of the search directions, thereby creating a more effective parametrization, and also an informed reduction of the size of the design space itself. These changes make the optimization process more computationally efficient and more effective – higher quality solutions are identified in fewer iterations. These advantages are demonstrated on a number of standard analytical test functions (from the ZDT and DTLZ families) and on a real-world problem (the optimization of an axial compressor preliminary design).

On the coupling of designer experience and modularity in the aerothermal design of turbomachinery

The turbomachinery aerodynamic design process is characterized both by its complexity and the reliance on designer experience for success. Complexity has led to the design being decomposed into modules; the specification of their interfaces is a key outcome of preliminary design and locks-in much of the final performance of the machine. Yet preliminary design is often heavily influenced by previous experience. While modularity makes the design tractable, it complicates the appropriate specification of the module interfaces to maximize whole-system performance: coupling of modularity and designer experience may reduce performance. This paper sets out to examine how such a deficit might occur and to quantify its cost in terms of efficiency. Two disincentives for challenging decomposition decisions are discussed. The first is where tried-and-tested engineering “rules of thumb” accord between modules: the rational engineer will find alluring a situation where each module can be specified in a way that maximizes its efficiency in isolation. The second is where there is discontinuity in modeling fidelity, and hence difficulty in accurately assessing performance exchange rates, between modules. In order to both quantify and reduce the potential cost of this coupling we have recast the design problem in such a way that what were previously module interface constraints become key system design variables. An example application of our method to the design of a generic turbofan core compression system is introduced. It is shown that nearly 1 percentage point equivalent compressor adiabatic efficiency can be saved.Copyright

Axial compressor intermediate duct design and optimisation

Modern turbofan engines are designed with pressure ratios as high as 40 and with bypass ratios in excess of 8. Multiple spools with substantial radial offset are essential to achieve the desired design and off-design performance and s-shaped ducts are necessary to deliver the flow from the exit of a turbomachine to the inlet of the following one in the minimum possible space to reduce the weight and the size of the gas turbine, without the risk of incurring in flow separation. In the absence of practical design rules or performance correlations for annular s-shaped ducts, a practical design approach could be the use of Computational Fluid Dynamics (CFD) for performance evaluation together with optimisation techniques for seeking the best design. Numerical optimisation methods (either deterministic or stochastic) can be linked to CFD solvers to provide a more thorough exploration of the design space, trying to produce a better design than the datum one, subject to a number of constraints. This paper reports the development and testing of an automatic framework for design optimisation of s-shaped ducts and its initial application to the optimisation of an axialsymmetric inter-compressor duct.

OPTIMIZATION ALGORITHMS AND ODE'S IN MDO

There is a need for a stronger theoretical understanding of Multidisciplinary Design Optimization (MDO) within the field. Having developed a differential geometry framework in response to this need, we consider how standard optimization algorithms can be modeled using systems of ordinary differential equations (ODEs) while also reviewing optimization algorithms which have been derived from ODE solution methods. We then use some of the frameworks tools to show how our resultant systems of ODEs can be analyzed and their behaviour quantitatively evaluated. In doing so, we demonstrate the power and scope of our differential geometry framework, we provide new tools for analyzing MDO systems and their behaviour, and we suggest hitherto neglected optimization methods which may prove particularly useful within the MDO context. Copyright

Integrated Design Optimisation of Gas Turbine Compression Systems

Designing a new gas turbine is a challenging task: complex physical mechanisms and multiple disciplines are coupled with a large design space and numerous often conicting objectives. These attributes have led to the decomposition and fragmentation of the design process: starting from a preliminary engine design that sets the requirements and the limits for each engine component, each module is designed autonomously in several phases, using an ever higher level of detail, with the support of progressively higher delity tools. While improving the tractability of the design process, this approach has two important limitations: the decomposition can conceal important trade-os between components, leading to sub-optimal overall designs, and the use of high delity tools is limited to the very last phases of the process, reducing the possibility of introducing decisive design changes. The structure of the design process often leads to conservative design decisions, dictated by previous experience rather than real physical constraints. This study concentrates on reducing the level of decomposition in the design of gas turbine compression systems, seeking to perform the simultaneous preliminary design optimisation of an IP and an HP compressor and of the inter-connecting s-shaped duct. CFD has been used to evaluate the duct performance, overcoming the lack of design and evaluation rules for annular curved ducts that has often led to conservative designs. Response surfaces have been used extensively to limit the increase in design time arising from the integration of codes with dierent levels of delity in a preliminary design environment. The results demonstrate how integrated optimisation can improve compression system design by reducing the development time and by improving overall performance when compared to that achieved through the isolated optimisation of individual components.