Three related methodologies relating to the modelling and design of aero elastic aircraft structures are considered. In the first study, a procedure for devel9pirig efficient aeroelastic Nonlinear Reduced Order (NROM) Models for aerospace structures containing geometric nonlinearities is described. The structural modelling is based upon a combined modal/FE approach (CMFE) that describes the nonlinear stiffening effects from nonlinear static analyses for a range of prescribed inputs. The prescribed load cases and resultant displacements from the static nonlinear test cases are transformed into modal coordinates using the modal transformation of the underlying linear system. A regression analysis is then performed to curve-fit the sets of nonlinear stiffness force / displacement maps in order to find the unknown nonlinear modal stiffness coefficients. Once the structural NROM has been defined, it is coupled to the Rational Fraction Approximation of the doublet lattice aerodynamic model corresponding to the wing planform. The aeroelastic model can then be used to predict the dynamic aeroelastic behaviour of the defined structure. The methodology is demonstrated on an aeroelastic model of a flexible high aspect ratio wing with the static deflections, limit cycle oscillation (LCO) behaviour and gust response being predicted. To further understand the aeroelastic behaviour of high aspect ratio wings, and to validate the mathematical model, an experimental model is developed. Experimental modal testing was employed to analyze the dynamical behaviour of the structure and the Finite Element (FE) representation updated to bring the model close to the experimental counterpart. The wing was analyzed in both deformed and undeformed shapes. The static and dynamic response of the wing was demonstrated and a comparison made with the numerical model; a good agreement was achieved. In the second study, an Ant Colony Optimisation (ACO) approach is used to maximize the flutter-divergence speed of a simple rectangular composite wing through determination of the best combination of ply orientations. An improved aeroelastic tailoring implementation is proposed based upon a combination of rank based and min-max ant system algorithms, and compared with several different implementations. A statistical investigation is performed on the example aeroelastic tailoring problem in order to investigate the effectiveness and robustness of the approaches. Consideration is also made to the best weightings of the pheromone addition and evaporation parameters. In the third study, innovative metallic wing structural designs are introduced that can be used to influence the bending I torsion coupling behaviour of aircraft wings, leading to the possibility of metallic aeroelastic tailoring. It is intended that the aeroelastic behaviour, such as the flutter I divergence speed or gust loads response, can be influenced in a beneficial way without any increase in weight. Two different approaches are demonstrated: using ribs with varying orientations, and making use of crenellations in the wing skins. The concepts are demonstrated using two simple FE models: a rectangular wing box and a more realistic wing model. In both cases it is shown that bending-torsion coupling can be achieved in metallic structures using both approaches and that this has an encouraging influence on the wing aeroelastic behaviour.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:572610 |
| Date | January 2012 |
| Creators | Harmin, Mohammad Yazdi |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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