Browsing by Author "Chedid, Marwan Maurizio"
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Item Open Access Extension of Skopinski's approach to reduce (strain gauge) flight load measurement uncertainties.(2017-05) Chedid, Marwan Maurizio; Hughes, KevinStructural Health Monitoring (SHM) is an essential technique for assessment of the integrity of ageing structures or certification of new aircraft. The SHM approach developed by Skopinski, based on conventional strain gauges, is one of the most reliable experimental methods for assessment of the structural loads experienced by lifting surfaces. This thesis concerns the extension of Skopinski’s approach to low aspect ratio wings with multiple spars. This is challenging problem, as the redundant load paths increase the complexity and difficulty in defining load equations and fitness functions. Similarly, locating, calibrating and selecting relevant strain gauges becomes more difficult. One of the new developments is a methodology for load measurement based on physical metrics and load data that is independent from the ground calibration used to generate the load equations. The concepts of Influence Coefficient Plots of Strain Gauge and of Loads Equations, were used to identify the predominant loads. The developed fitness function equations are all driven exclusively by these physical quantity parameters. Another key development was reduction of the effort required during the experimental phase achieved using distributed load data, obtained by numerical superposition of individual load cases to develop loads equations. In addition, this approach reduces the risk of damage to the flying test article and increasing the accuracy of the final results as the magnitude of the loads introduced does not need to be limited. This new framework was coded in Python including a new automated load equation computation technique, Linearised Physical Properties (LPP) and environment Loads Equation Technique Evaluator (LETE). Different search engines, including Exhaustive Search, Strain Gauge Reduction, and Genetic Algorithm, were made available for load assessment. Code validation (and performance) was performed through root mean square error evaluation in shear, bending and torsion loads using CIRA Test Data for two identical unmanned Space Vehicles, Castore and Polluce. The validation process demonstrated that loads equations developed on Castore can be applied to Polluce, as long as the SHM system design and instrumentations are the same.Item Open Access Optimisation of composite materials using a multilevel decomposition approach(Cranfield University, 2009) Chedid, Marwan Maurizio; Hughes, Kevin; Vignjevic, RadeThe design optimisation of thick composite components requires dealing with large number of design variables, highly non-linear equations and huge computational demand. A multi-level decomposition process has been developed to optimise these elements, investigating the potentialities of pre-existing approaches of the bioengineering field of hip and femoral implants. The strength of exploiting a multi-level decomposition process is related to the flexibility of choosing at each level specific optimisation methods which modulate according to the design variables appointed and to the difficulty level of the application. Specifically the proposed framework is developed through two main applications, Basic and Intermediate Example, with increasing difficulty. The Basic Example uses Graphical Optimisation tools selecting the typical design variables such as thicknesses and orientation angles. Then, the Intermediate Example considers numerical optimisation conditions with Kuhn- Tucker and Lagrange Multipliers and again Graphical Methods, but using lamination parameters. The optimisation analyses and classical lamination theory calculations are performed through a Matlab code linked with an external solver, Nastran, to perform the numerical structural analysis. These two applications, designed as 2-level decomposition approach, do not consider any inter-laminar effect and out-of-plane loading that it will be taken into account in the proposed final frame work application, Advanced Example. A single level optimisation analysis is performed by commercial software optimiser, Nastran Sol 200, as alternative mean to validate the two numerical applications. Results show the potentiality of this technique, mainly related to the capability to control each design cycle, though the full understanding will come after a numerical application of the advanced example. In fact, adding within the current Matlab code genetic algorithms, sequential linear programming, and gradient based methods capable to deal with out-of-plane loadings, quadratic failure criteria taking into account the through-thickness stress effects is still a complex direction of enhancement recommended to be explored.