Prestress and deformation control in flexible structures

Saeed, Najmadeen 2014. Prestress and deformation control in flexible structures. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

A direct method for controlling nodal displacements and/or internal bar forces has been developed for prestressable structural assemblies including complex elements (“macro-elements”, e.g. the pantographic element), involving Matrix Condensation. The method is aimed at static shape control of geometrically sensitive structures. The dissertation discusses identification of the most effective bars for actuation, without incurring violation in bar forces, and also with objective of minimal number of actuators or minimum actuation. The method can also be used for adjustment of bar forces to either reduce instances of high forces or increase low forces (e.g. in a cable nearing slack). The techniques of controlling nodal displacement, bar force and simultaneously nodal displacement and bar force for a structure made of non-complex elements have been verified by experiments on the physical model of a cable-stayed bridge. Likewise the technique of joint displacement controlling of structures constructed from complex structural elements, has been also been confirmed by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. This dissertation also concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this thesis, two suitable morphing aerofoil structures were made of curved pantographic units. Results show that the configuration with a large number of small pantograph elements exhibits a wider range of Lift Coefficient (CL) and Drag Coefficient (CD) than achievable by the first, and also by the standard NACA2415 aerofoil with flaps. In addition, it was found that the morphing aerofoil can decrease the drag by more than 18%, especially in the early stages of morphing. Finally, two useful and relatively simple methods have been presented in this dissertation which provide a direct method for calculating required morphing shape displacements and calculating set of length actuations for bar assembly to adjust shape imperfection. Keywords: Static shape control, Prestress control, Displacement control, Actuator placement, Force Method, Pantographic unit, Morphing structure, Morphing aerofoil, NACA aerofoil, Aerodynamic characteristics.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Engineering
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Uncontrolled Keywords:	Static Shape Control; Displacement and Prestress Control; Force Method; Pantographic Unit; Morphing Structure; Morphing Aerofoil.
Date of First Compliant Deposit:	30 March 2016
Last Modified:	10 Jan 2024 09:51
URI:	https://orca.cardiff.ac.uk/id/eprint/69777

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