Geometrical representations for efficient aircraft conceptual design and optimisation

Geometrical parameterisation has an important role in the aircraft design process due to its impact on the computational efficiency and accuracy in evaluating different configurations. In the early design stages, an aircraft geometrical model is normally described parametrically with a small number of design parameters which allows fast computation. However, this provides only a course approximation which is generally limited to conventional configurations, where the models have already been validated. An efficient parameterisation method is therefore required to allow rapid synthesis and analysis of novel configurations. Within this context, the main objectives of this research are: 1) Develop an economical geometrical parameterisation method which captures sufficient detail suitable for aerodynamic analysis and optimisation in early design stage, and2) Close the gap between conceptual and preliminary design stages by bringing more detailed information earlier in the design process. Research efforts were initially focused on the parameterisation of two-dimensional curves by evaluating five widely-cited methods for airfoil against five desirable properties. Several metrics have been proposed to measure these properties, based on airfoil fitting tests. The comparison suggested that the Class-Shape Functions Transformation (CST) method is most suitable and therefore was chosen as the two-dimensional curve generation method. A set of blending functions have been introduced and combined with the two-dimensional curves to generate a three-dimensional surface. These surfaces form wing or body sections which are assembled together through a proposed joining algorithm. An object-oriented structure for aircraft components has also been proposed. This allows modelling of the main aircraft surfaces which contain sufficient level of accuracy while utilising a parsimonious number of intuitive design parameters ... [cont.]

5-axis double-flank CNC machining of spiral bevel gears via custom-shaped milling tools -- Part I: modeling and simulation

A new category of 5-axis flank computer numerically controlled (CNC) machining, called \emph{double-flank}, is presented. Instead of using a predefined set of milling tools, we use the shape of the milling tool as a free parameter in our optimization-based approach and, for a given input free-form (NURBS) surface, compute a custom-shaped tool that admits highly-accurate machining. Aimed at curved narrow regions where the tool may have double tangential contact with the reference surface, like spiral bevel gears, the initial trajectory of the milling tool is estimated by fitting a ruled surface to the self-bisector of the reference surface. The shape of the tool and its motion then both undergo global optimization that seeks high approximation quality between the input free-form surface and its envelope approximation, fairness of the motion and the tool, and prevents overcutting. That is, our double-flank machining is meant for the semi-finishing stage and therefore the envelope of the motion is, by construction, penetration-free with the references surface. Our algorithm is validated by a commercial path-finding software and the prototype of the tool for a specific gear model is 3D printed.RYC-2017-22649 BERC 2014-201

Conceptual design methodology for blended wing body aircraft

The desire to create an environmentally friendly aircraft that is aerodynamically efficient and capable of conveying large number of passengers over long ranges at reduced direct operating cost led aircraft designers to develop the Blended Wing Body(BWB) aircraft concept. The BWB aircraft represents a paradigm shift in the design of aircraft. The design offers immense aerodynamics and environmental benefits and is suitable for the integration of advanced systems and concepts like laminar flow technology, jet flaps and distributed propulsion. However, despite these benefits, the BWB is yet to be developed for commercial air transport. This is due to several challenges resulting from the highly integrated nature of the configuration and the attendant disciplinary couplings. This study describes the development of a physics based, deterministic, multivariate design synthesis optimisation for the conceptual design and exploration of the design space of a BWB aircraft. The tool integrates a physics based Athena Vortex Lattice aerodynamic analysis tool with deterministic geometry sizing and mass breakdown models to permit a realistic conceptual design synthesis and enables the exploration of the design space of this novel class of aircraft. The developed tool was eventually applied to the conceptual design synthesis and sensitivity analysis of BWB aircraft to demonstrate its capability, flexibility and potential applications. The results obtained conforms to the pattern established from a Cranfield University study on the BlendedWing Body Aircraft and could thus be applied in conceptual design with a reasonable level of confidence in its accuracy

Fairing arc spline and designing by using cubic bézier spiral segments

This paper considers how to smooth three kinds of G 1 biarc models, the C-, S-, and J-shaped transitions, by replacing their parts with spiral segments using a single cubic Bézier curve. Arc spline is smoothed to G 2continuity. Use of a single curve rather than two has the benefit because designers and implementers have fewer entities to be concerned. Arc spline is planar, tangent continuous, piecewise curves made of circular arcs and straight line segments. It is important in manufacturing industries because of its use in the cutting paths for numerically controlled cutting machinery. Main contribution of this paper is to minimize the number of curvature extrema in cubic transition curves for further use in industrial applications such as non-holonomic robot path planning, highways or railways, and spur gear tooth designing

An extensive analysis of frequency and transient responses in S and C-shaped gears

Gears are crucial mechanical components and considerably used in consumer and industrial machinery. Gears can be grouped into five types namely spur, helical, rack and pinion, worm and bevel. Spur gear has been selected as a case model in this study mainly because it is one of the basic types of gear which can be easily constructed and fabricated. Spur gear tooth is designed using S and C-shaped transition curves. These curves are constructed using the G2 parametric Said-Ball cubic curve and clothoid templates. The result demonstrates that the C-shaped gear model which consists of the natural frequency of0.7408 Hz and low onaverage and standard deviation of 1.00E-3 mm and 8.072E-3 mm offers the most affordable displacement when compared with S-shaped and existing gear model

Multi-Fidelity Design Optimization of a Long-Range Blended Wing Body Aircraft with New Airframe Technologies

The German Cluster of Excellence SE²A (Sustainable and Energy Efficient Aviation) is established in order to investigate the influence of game-changing technologies on the energy efficiency of future transport aircraft. In this paper, the preliminary investigation of the four game-changing technologies active flow control, active load alleviation, boundary layer ingestion, and novel materials and structure concepts on the performance of a long-range Blended Wing Body (BWB) aircraft is presented. The BWB that was equipped with the mentioned technologies was designed and optimized using the multi-fidelity aircraft design code SUAVE with a connection to the Computational Fluid Dynamics (CFD) code SU2. The conceptual design of the BWB aircraft is performed within the SUAVE framework, where the influence of the new technologies is investigated. In the second step, the initially designed BWB aircraft is improved by an aerodynamic shape optimization while using the SU2 CFD code. In the third step, the performance of the optimized aircraft is evaluated again using the SUAVE code. The results showed more than 60% reduction in the aircraft fuel burn when compared to the Boeing 77

Computer-Aided Geometry Modeling

Techniques in computer-aided geometry modeling and their application are addressed. Mathematical modeling, solid geometry models, management of geometric data, development of geometry standards, and interactive and graphic procedures are discussed. The applications include aeronautical and aerospace structures design, fluid flow modeling, and gas turbine design

Aerodynamic and cost modelling for aircraft in a multi-disciplinary design context.

A challenge for the scientific community is to adapt to and exploit the trend towards greater multidisciplinary focus in research and technology. This work is concerned with multi-disciplinary design for whole aircraft configuration, including aero performance and financial considerations jointly for an aircraft program. A Multi-Disciplinary (MD) approach is required to increase the robustness of the preliminary design data and to realise the overall aircraft performance objectives within the required timescales. A pre-requisite for such an approach is the existence of efficient and fully integrated processes. For this purpose an automatic aero high-speed analysis framework has been developed and integrated using a commercial integration/building environment. Starting from the geometry input, it automatically generates aero data for loads in a timescale consistent with level requirement, which can afterwards be integrated into the overall multi-disciplinary process. A 3D Aero-solution chain has been implemented as a high-speed aerodynamic evaluation capability, and although there is not yet a complementary fully automated Aerodynamic design process, two integrated systems to perform multi-objective optimisation have been developed using different optimisation approaches. In addition to achieving good aircraft performance, reducing cost may be essential for manufacturer survival in today's competitive market. There is thus a strong need to understand the cost associated with different competing concepts and this could be addressed by incorporating cost estimation in the design process along with other analyses to achieve economic and efficient aircraft. For this reason a pre-existing cost model has been examined, tested, improved, and new features added. Afterwards, the cost suite has been integrated using an integration framework and automatically linked with external domains, providing a capability to take input from other domain tool sets. In this way the cost model could be implemented in a multi-disciplinary process allowing a trade-off between weight, aero performance and cost. Additionally, studies have been performed that link aerodynamic characteristics with cost figures and reinforce the importance of considering aerodynamic, structural and cost disciplines simultaneously. The proposed work therefore offers a strong basis for further development. The modularity of the aero optimisation framework already allows the application of such techniques to real engineering test cases, and, in future, could be combined with the 3D aero solution chain developed. In order to further reduce design wall-clock time the present multi- level parallelisation could also be deployed within a more rapid multi-fidelity approach. Finally the 3D aero-solution chain could be improved by directly incorporating a module to generate aero data for performance, and linking this to the cost suite informed by the same geometrical variables.Engineering and Physical Sciences (EPSRC)PhD in Aerospac