Murat Hakki Eres

Fingering phenomena for driven coating films

A theoretical and numerical model is formulated to describe the instability and the long-time evolution of both gravity-driven and surface-shear-stress-driven thin coating films. A single evolution equation, of higher-order diffusive type, models the flow for either problem. It is derived using the lubrication approximation. For partially wetting systems, the effect of finite contact angle is incorporated in the equation using a particular disjoining pressure model. The base state, in each case, is a two-dimensional steadily propagating capillary front. Slight perturbations of the base state, applied along the front, initiate the fingering instability. Early-time results accurately reproduce the wavelengths of fastest growth and the corresponding eigenmodes as reported in published linear stability analyses. As time proceeds, depending on parameter values, various fingering patterns arise. For conditions of perfect wetting with the substrate downstream of the moving front covered with a thin precursor layer, predicted nonlinear finger evolution agrees well with published experiments. The ultimate pattern, in this case, is a steadily translating pattern of wedge-shaped fingers. Alternatively, for partially wetting systems that exhibit sufficiently large static contact angles, long straight-sided fingers or rivulets are formed. Finally, for larger contact angles, or at relatively low speeds, we predict that the flowing rivulets will become unstable and break up into strings of isolated droplets.

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.

A grid-enabled problem solving environment (PSE) for design optimisation within Matlab

The process of design search and optimisation using computational fluid dynamics (CFD) is computationally and data intensive, a problem well-suited to Grid computing. The Geodise toolkit is a suite of Grid-enabled design optimisation and search tools within the Matlab environment. The use of these tools by the engineer is facilitated by intelligent design advisers targeted initially at CFD. The role of remote computation and data access in constructing a Grid-enabled problem solving environment is discussed. The use of the Geodise toolkit for design optimisation from within the Matlab environment is considered with an exemplar problem.

A Hierarchical Life Cycle Cost Model For A Set Of Aero-Engine Components

The aero-engine is probably the most complex and vital part of civil and military aircrafts, and it is usually an important cost element of the aircraft at acquisition and operation periods. The reduction of acquisition, operation and support costs for civil and defence sectors is going to be the main driving force for aero-engine manufacturers during the next decades. Additionally, it is a well known fact that the maintenance costs of aero-engines can surpass their acquisition costs by a factor of two. Therefore, ecient and accurate prediction of aero-engine maintenance life cycle cost is vitally important for aero-engine manufacturers. For this paper we restrict ourselves to a simplied problem that deals with the life cycle cost of a set of aero-engine components, such as high pressure turbine blades, in isolation of other components of the engine. These engine components are assumed be suering from a number of dierent deterioration mechanisms that may force that component to be repaired or replaced at predetermined shop visits. A hierarchical and object oriented costing model will be presented and its scope, extensibility and maintainability will be discussed.

Value modelling for multi-stakeholder and multi-objective optimisation in engineering design

ABSTRACT The work presented culminates in the development of a value model used in the conceptual phase of engineering design, with the preferences of more than one stakeholder addressed in the multi-stakeholder and multi-objective optimisation. The ‘value’ of proposed solutions is assessed in an objective way from both performance and economic perspectives, while the optimal solution is identified based on the needs of the user and manufacturer, as major stakeholders. This novel value model for consistent value assessment synthesises the multi-attribute value/utility analysis with Game Theory and Analytic Hierarchy Process (AHP) assessment methodologies. During the multi-criteria decision analysis, the deficiencies, introduced by the arbitrary numerical scales used in the AHP to convert the linguistic preferences of the user between the various attributes to numerical values, are resolved. The preferences of a group of experts/decision-makers are synthesised in the group value model through the extraction of weighting factors from the individuals’ AHP pairwise comparison matrices. Moreover, Game Theory is used in a hybrid cooperative/bargaining, non-cooperative non-zero sum game between the stakeholders as players, identifying the optimal design through the simultaneous employment of the Nash bargaining solution and the Nash equilibrium.

An integrated framework for Bayesian uncertainty quantification and probabilistic multi-criteria decision making in aero-engine preliminary design

The following paper presents a novel framework that enables making early design decisions based on probabilistic information obtained from fast, deterministic, low-fidelity tools, calibrated against high-fidelity data that is supported by experts’ knowledge. The proposed framework integrates a Probabilistic Multi-Criteria Decision Making technique with Bayesian Uncertainty Quantification concepts supported by the Kennedy and O’Hagan Framework. It allows continuous improvement of low-fidelity design tools as high-fidelity data is gathered and therefore facilitates investigation into the impacts the accumulation of high-fidelity data has on preliminary design process risk. The paper discusses theoretical concepts behind the framework and demonstrates its relevance by application in an illustrative combustor preliminary design case study.

Modelling the Life Cycle Cost of Aero-engine Maintenance

This paper presents an approach of modelling the maintenance Life Cycle Cost (LCC) of an aero-engine which links the capabilities of hierarchical modelling and discrete-event simulation (DES) tools. It follows up on work previously done on a component level hierarchical cost estimation model [1]. It is concluded that, as the calculation of LCC involves a highly diverse set of representations and processes, it is undesirable to use a single software tool to undertake this task. This work seeks to demonstrate how different modelling paradigms should be used in tandem to produce an elegant solution. The individual parts of the model and the results generated are presented and discussed. Essentially, the approach shows how a design parameter can be linked to the resultant LCC to help form cause and effect relationships.

Cost-driven build orientation and bin packing of parts in Selective Laser Melting (SLM)

Selective Laser Melting (SLM) is an additive manufacturing process capable of producing mixed batches of parts simultaneously within a single build. The build orientation of a part in SLM is a key process parameter, affecting the build cost, time and quality, as well as batch size. Choosing an optimal arrangement of multiple heterogeneous parts inside the SLM machine also presents a challenging irregular bin packing problem. Since the two problems are interdependent, this paper addresses the combined problem of finding an optimal build orientation and two-dimensional irregular bin packing solution of a mixed batch of parts across identical SLM machines. We address this problem specifically in the context of low-volume high-variety (LVHV) production in the aerospace sector, using total build cost as the objective function. To solve this problem, we present an Iterative Tabu Search Procedure (ITSP), which consists of six distinct stages. We test each stage in the ITSP on 27 manually generated instances, based on 68 unique geometries ranging in convexity and size, including six real-life components from the aerospace industry. Two of the six stages, which are driven by support structure volume, returned the highest improvement in cost. Overall, the results showed an average cost improvement of 16.2% over the initial solution. The initial solution of the procedure was benchmarked against a commercial software, showing comparable results.

An Improvement of the Concept Design Analysis Method by the Use of the Avoidance Function

Avoiding disasters due to resonance is a major concern in construction projects such as buildings, bridges and pipelines. This paper uses the Concept Design Analysis (CODA) method that is capable of supporting the described Value-Driven Design (VDD) methodology. While VDD promotes the use of a system wide ‘value’ function during conceptual design, the CODA method allows mapping customer needs into engineering characteristics in order to calculate a single normalized design metric. The CODA method employs three different merit functions: maximizing (more is better), minimizing (less is better), and optimizing (target is better). This paper proposes a new merit function called avoidance function that allows excluding a range of engineering characteristics, e.g. avoiding a range of resonant frequencies. An example of a simple CODA model for a bicycle wheel design selection with the proposed the avoidance function is presented.

A Systems Engineering Approach to Aero-Engine Life Cycle Costing

A life cycle cost (LCC) analysis considers all the costs that a product/system incurs throughout all phases of its life. As a consequence of the scope that LCC encompasses, LCC models have difficulty being standardized. Additionally, the complexity of the aero-engine necessitates an approach to LCC analysis that has the ability to consider multiple disciplines and sub-systems from different levels. This paper discusses how systems engineering methods can be used in the LCC process to achieve an approach which will be able to adapt to these demands. This approach was then applied to a case study to analyse how LCC changes with the TET and cooling flow fraction. The results from this case study illustrates how a LCC analysis can be used to make design trade-offs and allow the system of interest to be analysed from different aspects.