Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (AE. E.D.)--Polytechnic Institute of Brooklyn, 1945. / Cover title. Reproduced from typewritten copy.

Thesis (Ph. D.)--West Virginia University, 2005. / Title from document title page. Document formatted into pages; contains x, 144 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 117-120).

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xi, 121 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 90-95).

The aim of this research work was to develop an Acoustic Emission (AE) source location method suitable for Structural Health Monitoring (SHM) of composite aircraft structures. Therefore useful key signal features and sensor configurations were identified and the proposed method was validated using both artificially generated AE as well as actual AE resulting from damage. Acoustic Emission is a phenomenon where waves are generated in stressed materials. These waves travel through the material and can be detected with suitable sensors on the surface of the structure. These stress waves are attributed to propagating damage inside the material and can be monitored while the structure is in service. This makes AE very suitable for SHM, in particular for aircraft structures. In recent years composite materials such as carbon fibre reinforced epoxy (CFRP) are increasingly being used for primary and secondary structures in aircraft. The anisotropic layup of CFRP can lead to different failure mechanisms such as delamination, matrix cracking or fibre breakage which affects the remaining life time of the structure to different extents. Accurate damage location is important for SHM systems to avoid further inspections and allows for a maintenance scheme which considers the severity of the damage, due to damage type, extent and location. This thesis presents a novel source location method which uses a small triangular AE sensor array. The method determines the origin of an AE wave by a combination of time of arrival and modal analysis. The small footprint of the array allows for a fast and easy installation in hard-to-reach areas. The possibility to locate damage outside and at a relatively far distance from the array could potentially reduce the overall number of sensors needed to monitor a structure. Important wave characteristics and wave propagation in particular in CFRP were investigated using AE simulated by an artificial source and actual damage in composite specimens.

Corrugated panels have gained considerable popularity in a range of engineering applications, particularly in morphing skin applications due to their remarkable anisotropic characteristics. They are stiff to withstand the aerodynamic loads and flexible to enable the morphing deformations. In this thesis a detailed review of the literature on corrugated structures is presented. The specific characteristics of corrugated structures such as: high anisotropic behaviour, high stiffness and good durability, lightness and cost effectiveness are discussed comprehensively. However for the application in morphing aircraft, the optimal design of the corrugated panels requires simple models of these structures to be incorporated into multi-disciplinary system models. Therefore equivalent structural models are required that retain the dependence on the geometric parameters and material properties of the corrugated panels. In this regard, two analytical solutions based on homogenization and super element techniques are presented to calculate the equivalent mechanical properties of the corrugated skin. Different experimental and numerical models are investigated to verify the accuracy and efficiency of the presented equivalent models. The parametric studies of different corrugation shapes demonstrate the suitability of the proposed super element for application in further detailed design investigations. Then the design and multi-objective optimization of an elastomer coated composite corrugated skin for the camber morphing aerofoil is presented. The geometric parameters of the corrugated skin are optimized to minimize the in-plane stiffness and the weight of the skin and to maximize the flexural out-of-plane stiffness of the corrugated skin. A finite element code for thin beam elements is used with the aggregate Newton's method to optimize the geometric parameters of the coated corrugated panel. The advantages of the corrugated skin over the elastomer skin for the camber morphing structure are discussed. Moreover, a finite element simulation of the camber morphing internal structure with the corrugated skin is performed under typical aerodynamic and structural loadings to check the design approach.

Human information processing consists of multiple and limited resources; some of them are shared while some are separate and non-interchangeable. High pilot mental workload (PMWL) - and the subsequent decline in performance - results from the imbalance between the mental resources available to perform the task and the amount of resources needed to perform it. When the pilot’s proficiency is evaluated, s/he should deliver an acceptable performance while being able to reserve enough mental capacity for the unexpected, additional resource demands. The task demands and cognitive stressors of air combat have potential to degrade pilot performance to an unacceptable level. Therefore, it is important to understand the amount of mental workload the pilots are experiencing and how much spare capacity they have available to cope with the possible additional resource demands. This thesis was aimed at understanding the relationship between PMWL and performance. The approach presented in this thesis was expected to support the development of reliable metrics for predicting the pilot performance under the stress of combat. In terms of practical applications, this thesis contributed to the development of the methodological principles that could help assuring the pilots’ ability to cope with the task demands higher than those experienced during training or proficiency checks. Heart rate (HR) and heart rate variation (HRV) were used as indexes of PMWL. The selection was done for several reasons. HR and HRV measures were accepted by the pilots as they were non-intrusive and they appeared to be objective. In addition, the implementation requirements were by no means excessive. Considering the aims of this thesis, the low diagnosticity of HR/HRV was not an issue. Finally, HR and HRV proved to be sensitive measures of varying task demands – especially when measured together with the pilots’ awareness of the mission requirements. Simulated fighter missions were used to manipulate the pilots’ task demand and to measure their performance and HR/HR. The thesis is constructed around three studies. In the first study, the subjects were required to fly instrument approaches in a high fidelity simulator under various levels of task demand. The task demand was manipulated by increasing the load on the subjects by reducing the range at which they commenced the approach. HR and the time domain components of HRV were used as measures of PMWL. The findings indicated that HR and HRV were sensitive to varying task demands. HR and HRV were able to distinguish the level of PMWL after which the subjects were no longer able to cope with the increasing task demands and their performance fell to a sub-standard level. The major finding of the first study was the HR/HRV’s ability to differentiate the sub-standard performance approaches from the high performance approaches. In the second study, fighter pilots’ performance and PMWL were both measured during a real instrument flight rules proficiency check in an F/A-18 simulator. PMWL was measured using HR and HRV. Performance was rated using Finnish Air Force’s official rating scales. Results indicated that HR and HRV were able to differentiate varying task demands in situations where variations in performance were insignificant. It was concluded that during a proficiency check, PMWL should be measured together with the task performance measurement. In the third study, fighter pilots’ HRV and performance were examined during instrument approaches and air combat. The subjects’ performance was rated by a weapons instructor. In addition, the subjects’ HRV was measured and used as an indicator of PMWL. During the instrument approaches, low performance was associated with high PMWL as expected. However, during the combat phases of the mission, low performance was associated with low PMWL. When the subject’s awareness of the mission requirements was studied, it was found that the combination of low performance and low PMWL was associated with the subjects’ low awareness of the mission requirements. The major finding was that unless the subjects’ awareness of the mission requirements is examined, the relationship between the mental workload and performance during a complex combat mission may be difficult to explain. It is concluded that HR and HRV are sensitive measures of PMWL in a simulated fighter aviation environment. HR and HRV proved to be associated with the changes in task demands and pilots’ performance during simulated instrument approaches and air combat. However, the results of this thesis suggest that measuring just PMWL and performance is not sufficient – especially if the task of interest is complex and dynamic. To fully understand the pilot performance in such environment, the relationship between awareness of the mission requirements, workload and performance needs to be untangled. While this thesis provides encouraging results to understand this phenomena, further research is still needed before awareness of the situation requirements (or more broadly, situation awareness), performance and mental workload can be measured simultaneously, objectively and in real time.

During the last few years there has been an increasing interest in a high-lift wing configuration known as the flex-wing, or parawing. The parawing consists basically of a flexible membrane such as cloth, attached to two leading edges (or booms) and a keel as shown in Figure 1. At angles of attack (��) greater than the billowing angle (��). the air impinges on the under side of the membrane and forces it into a double-arch shape at each cross-section. When straight leading edges are used, each arch approximates the shape of a conical section. A cylindrical section is obtained by giving the leading edge a circular arch shape as seen from head on

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