James Scanlan

Stress Analysis of Shaft-Tube Bonded Joints Using a Variational Method

Functionally modulus graded bondline (FMGB) adhesives can be employed in bonded joints to reduce stress concentration and, hence, achieve higher joint strength. This study presents an analytical framework for the stress analysis of a shaft-tube bonded joint based on a variational technique which minimises the complimentary energy of the bonded system. This cylindrical assembly consists of similar or dissimilar adherends and a FMGB adhesive. The effect of functional grading of adhesive elastic modulus on the peak stresses and their distributions in the adhesive layer are studied. The joint with various modulus grading profiles is assessed and the results are compared with a conventional mono-modulus bondline (MMB) adhesive joint. Stress analysis indicates that the peel and shear peak stresses in the FMGB are much smaller and their distributions along bondlength are more uniform than those of MMB adhesive joints under the same axial tensile load. Numerical examples are provided to illustrate the effects of geometrical and material properties on the distributions and intensities of stresses in the bondline. Furthermore, optimal peel and shear strengths of the joint can be achieved by spatially controlling the modulus of the adhesive.

DATUM project : Cost estimating environment for support of aerospace design decision making

The results of a Rolls-Royce sponsored programme of design to cost research are outlined. The role of cost modelling within the design process for the development of a civil gas turbine engine is outlined. The novel application of a generic financial modelling tool to an engineering cost estimating problem is demonstrated. This use of this tool to capture and disseminate costing knowledge is described and the use of modular library elements to develop cost models is shown. A prototype systems for the creation of an elegant cost model structure to enable direct integration with a CAD representation of a part and the integration of the costing capability within an automated design search and optimization environment is described

Cost modelling for aircraft design optimization

This paper summarizes work that has been carried out to date on the Implied Cost Evaluation System (ICES) research project. This is an EPSRC-funded project that is sponsored by BAe (Airbus) and Rolls Royce (Defence Europe). The paper identifies the need for detailed and reliable cost information in order to optimize a product design. This is illustrated with reference to recent cost modelling work carried out in support of preliminary designs for the proposed Airbus A380 600 seat aircraft. The merits of the various alternative approaches are identified and the genealogy of current systems and techniques is briefly outlined. It is argued that current tools lack a number of key features and capabilities. In particular, it is suggested that current cost modelling tools are not able to deal with the multiplicity of levels of abstraction associated with an emerging design. Furthermore, there is no generally accepted method for expressing the uncertainty associated with a cost estimate in a rigorous and systematic way. This paper outlines some of the initial development work on the ICES project. This concerns the development of an object-oriented product data structure that supports multiple levels of abstraction, statistical modelling and decision support constructs.

Planning in the dark: why major engineering projects fail to achieve key goals

Abstract The arguments, analysis and observations in this paper are based on 10 years of research with partners in the European and US aerospace and defence industries. During this period, the authors were part of a team of researchers who were seeking to develop a new methodology and tool set for project management, particularly aimed at large aerospace projects. The research was motivated by the seemingly ubiquitous reality of project failure, with large engineering projects apparently always late and over budget. Here the authors focus on aerospace and defence, but the problems are generic across all branches of engineering. In their view, aerospace and defence have more excuses than most, because not only are the projects huge, but also they are globally distributed and highly complex. As work progressed, a fundamental conundrum emerged. Through discussions with project managers and assessment of the teams that were undertaking the projects, it became obvious that they were well educated, intelligent, highly motivated and very capable people. So why were so many projects going wrong? And it was not just aerospace and defence, as projects were failing in many different sectors and in numerous geographic locations. Obviously the problems were not to do with incompetence, as they were clearly so generic. As a result, the authors focused their analysis on factors inherent in the way all major projects are undertaken. The ultimate finding has been that the very technology available for managing projects today is inadequate. As argued within the paper, modern, complex projects cannot be planned and executed using 50-year-old project management tools. The paper tells the story of what is wrong with the current technology and how and why it needs to change. The authors are well aware that there are also cultural problems in project management, but many of these are exacerbated by the use of inadequate tools.

Mapping customer needs to engineering characteristics: an aerospace perspective for conceptual design

Designing complex engineering systems, such as an aircraft or an aero-engine, is immensely challenging. Formal systems engineering practices are widely used in the aerospace industry throughout the overall design process to minimise the overall design effort, corrective re-work, and ultimately overall development and manufacturing costs. Incorporating the needs and requirements from customers and other stakeholders into the conceptual and early design process is vital for the success and viability of any development programme. This paper presents a formal methodology, the value-driven design (VDD) methodology that has been developed for collaborative and iterative use in the extended enterprise (EE) within the aerospace industry, and that has been applied using the concept design analysis (CODA) method to map captured customer needs into engineering characteristics and to model an overall ‘design merit’ metric to be used in design assessments, sensitivity analyses, and engineering design optimisation studies. Two different case studies with increasing complexity are presented to elucidate the application areas of the CODA method in the context of the VDD methodology for the EE within the aerospace sector.

Application of value-driven design to commercial aeroengine systems

Value-Driven Design provides a framework to enhance the systems engineering processes for the design of large systems. By employing economics in decision making, Value-Driven Design enables rational decision making in terms of the optimum business and technical solution at every level of engineering design. This paper explains the application of ValueDriven Design to the aero-engine system through two case studies, which were conducted through workshops under the Rolls-Royce plc Advanced Cost Modeling Methodologies project. The Surplus Value Theory was utilized to provide a metric that can trade-off component designs with changes in continuous and discrete design variables. Illustrative results are presented to demonstrate how the methodology and modeling approach can be used to evaluate designs and select the value-enhancing solution.

Design search and optimization in aerospace engineering

In this paper, we take a design-led perspective on the use of computational tools in the aerospace sector. We briefly review the current state-of-the-art in design search and optimization (DSO) as applied to problems from aerospace engineering, focusing on those problems that make heavy use of computational fluid dynamics (CFD). This ranges over issues of representation, optimization problem formulation and computational modelling. We then follow this with a multi-objective, multi-disciplinary example of DSO applied to civil aircraft wing design, an area where this kind of approach is becoming essential for companies to maintain their competitive edge. Our example considers the structure and weight of a transonic civil transport wing, its aerodynamic performance at cruise speed and its manufacturing costs. The goals are low drag and cost while holding weight and structural performance at acceptable levels. The constraints and performance metrics are modelled by a linked series of analysis codes, the most expensive of which is a CFD analysis of the aerodynamics using an Euler code with coupled boundary layer model. Structural strength and weight are assessed using semi-empirical schemes based on typical airframe company practice. Costing is carried out using a newly developed generative approach based on a hierarchical decomposition of the key structural elements of a typical machined and bolted wing-box assembly. To carry out the DSO process in the face of multiple competing goals, a recently developed multi-objective probability of improvement formulation is invoked along with stochastic process response surface models (Krigs). This approach both mitigates the significant run times involved in CFD computation and also provides an elegant way of balancing competing goals while still allowing the deployment of the whole range of single objective optimizers commonly available to design teams.

A knowledge-based system for cost modelling of aircraft gas turbines

This paper presents a novel technique for representing cost information of a candidate design. The underlying principle is to provide a knowledge-based system for cost modelling that makes the cost effects of design decisions more visible and quickly available to the designer. The development of a hybrid between hierarchical trees and object-oriented knowledge representation environment to represent cost information is shown. The development of an abstract product structure, reusable tree object libraries and an automated system to extract design information needed for estimation from computer-assisted design geometry is discussed. It is shown how the tool provides fast incremental cost fluctuations in response to changes in component geometry. This paper also considers the uncertain quantities present in cost models and analyses cost risk. A case study demonstrating the research applied to a Rolls-Royce aircraft gas turbine engine component is presented.

Conceptual design of UAV airframes using a generic geometry service

With the increased freedom in layout selection possible when designing an Unmanned Air Vehicle (UAV) concept (compared, for example, to the relatively constrained and mature world of commercial airliner design), comes the significant challenge of building a geometry engine that will provide the variety of airframe models demanded by the highly global nature of the design search. In order to enable multidisciplinary trade-off studies, both an external surface and an internal structure are required – we use a single, generic model to supply these, in the form of a parametric geometry residing in a commercial CAD tool. In addition to discussing the challenges of offering a truly flexible geometry service, we also delve into the UAV-specific issues of the initial sizing of the model. A wealth of statistical data provides one of the traditional handholds for this step in manned aircraft conceptual design – we discuss the applicability of such statistical approaches to their unmanned counterparts.

Applying Multiobjective Cost and Weight Optimization to the Initial Design of Turbine Disks

Aerospace design optimization typically explores the effects of structural performance and aerodynamics on the geometry of a component. This paper presents a methodology to incorporate manufacturing cost and fatigue life models within an integrated system to simultaneously trade off the conflicting objectives of minimum weight and manufacturing cost while satisfying constraints placed by structural performance and fatigue. A case study involving hte design of a high pressure turbine disk from an aircraft engine is presented. Manufacturing cost and fatigue life models are developed in DECISIONPRO, a generic modeling tool, wheras finite element anaylsis is carried out in the Rolls-Royce PLC proprietary solver SC03. A multiobjective optimization apprach based on the nondominated sorting genetic algorithm (NSGA) is used to evaluate the Pareto front for minimum cost and volume designs. A sequential workflow of the different models embedded within a scripting environment developed in MATLAB is used for automating the entire process.