Experimental analysis of a separation control device based on plasma technology

In this thesis effects of plasma actuators based on Dielectric Barrier Discharge (DBD) technology over a NACA 0015 bidimensional airfoil have been analyzed in an experimental way, at low Reynolds number. Work developed on thesis has been carried on in partnership with the Department of Electrical Engineering of Università di Bologna, inside Wind Tunnel of the Applied Aerodynamic Laboratory of Aerospace Engineering faculty. In order to verify the effectiveness of these active control devices, the analysis has shown how actuators succeed in prevent boundary layer separation only in certain conditions af angle of attack and Reynolds numbers. Moreover, in this thesis actuators’ chordwise position effect has been also analyzed, together with the influence of steady and unsteady operations.

Separation control by means of oriented DBD plasma actuators: an experimental analysis in a wind tunnel

This thesis provides an experimental analysis of the effectiveness of oriented DBD plasma actuators over a NACA 0015 airfoil at low Reynolds numbers. Tests were performed in partnership with the Department of Electrical Engineering of Bologna University, in the wind tunnel of the Applied Aerodynamics Laboratory of Aerospace Engineering faculty. Lift coefficient measurements were carried out in order to verify how an oriented plasma jet succeeds in prevent boundary layer separation. Both actuators’ chord wise position and plasma jet orientation angle have been investigated to examine which configurations lead to the best results. A particular attention has been paid also to the analysis of results in steady and unsteady plasma actuation. Questa tesi offre un’analisi sperimentale sull’efficacia di attuatori al plasma orientabili, basati su una tecnologia DBD, installati su un profilo alare NACA 0015, a bassi numeri di Reynolds. Le prove sono state condotte in collaborazione con il Dipartimento di Ingegneria Elettrica dell’Università di Bologna, nella galleria del vento del Laboratorio di Aerodinamica Applicata della Facoltà di Ingegneria Aerospaziale di Forlì. Per verificare come un getto orientabile di plasma riesca a prevenire la separazione dello strato limite, sono state eseguite misure sul coefficiente di portanza. Sono state indagate sia la posizione degli attuatori lungo la corda che l’angolo con cui è orientato il getto di plasma, per vedere quali configurazioni conducono ai migliori risultati. Una particolare attenzione è stata riservata all’analisi dei risultati ottenuti con plasma continuo e pulsato.

A new method for continuous quality control of nsm cfrp systems

In the last decade the near-surface mounted (NSM) strengthening technique using carbon fibre reinforced polymers (CFRP) has been increasingly used to improve the load carrying capacity of concrete members. Compared to externally bonded reinforcement (EBR), the NSM system presents considerable advantages. This technique consists in the insertion of carbon fibre reinforced polymer laminate strips into pre-cut slits opened in the concrete cover of the elements to be strengthened. CFRP reinforcement is bonded to concrete with an appropriate groove filler, typically epoxy adhesive or cement grout. Up to now, research efforts have been mainly focused on several structural aspects, such as: bond behaviour, flexural and/or shear strengthening effectiveness, and energy dissipation capacity of beam-column joints. In such research works, as well as in field applications, the most widespread adhesives that are used to bond reinforcements to concrete are epoxy resins. It is largely accepted that the performance of the whole application of NSM systems strongly depends on the mechanical properties of the epoxy resins, for which proper curing conditions must be assured. Therefore, the existence of non-destructive methods that allow monitoring the curing process of epoxy resins in the NSM CFRP system is desirable, in view of obtaining continuous information that can provide indication in regard to the effectiveness of curing and the expectable bond behaviour of CFRP/adhesive/concrete systems. The experimental research was developed at the Laboratory of the Structural Division of the Civil Engineering Department of the University of Minho in Guimar\~aes, Portugal (LEST). The main objective was to develop and propose a new method for continuous quality control of the curing of epoxy resins applied in NSM CFRP strengthening systems. This objective is pursued through the adaptation of an existing technique, termed EMM-ARM (Elasticity Modulus Monitoring through Ambient Response Method) that has been developed for monitoring the early stiffness evolution of cement-based materials. The experimental program was composed of two parts: (i) direct pull-out tests on concrete specimens strengthened with NSM CFRP laminate strips were conducted to assess the evolution of bond behaviour between CFRP and concrete since early ages; and, (ii) EMM-ARM tests were carried out for monitoring the progressive stiffness development of the structural adhesive used in CFRP applications. In order to verify the capability of the proposed method for evaluating the elastic modulus of the epoxy, static E-Modulus was determined through tension tests. The results of the two series of tests were then combined and compared to evaluate the possibility of implementation of a new method for the continuous monitoring and quality control of NSM CFRP applications.

Laser shock peening treatment to control and moderate fatigue crack growth in aircraft structure based on residual stress engineering approach

Laser Shock Peening (LSP) is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses of up to several mm underneath the surface of metal components in order to improve the detrimental effects of the crack growth behavior rate in it. The aim of this thesis is to predict the crack growth behavior in metallic specimens with one or more stripes which define the compressive residual stress area induced by the Laser Shock Peening treatment. The process was applied as crack retardation stripes perpendicular to the crack propagation direction with the object of slowing down the crack when approaching the peened stripes. The finite element method has been applied to simulate the redistribution of stresses in a cracked model when it is subjected to a tension load and to a compressive residual stress field, and to evaluate the Stress Intensity Factor (SIF) in this condition. Finally, the Afgrow software is used to predict the crack growth behavior of the component following the Laser Shock Peening treatment and to detect the improvement in the fatigue life comparing it to the baseline specimen. An educational internship at the “Research & Technologies Germany – Hamburg” department of AIRBUS helped to achieve knowledge and experience to write this thesis. The main tasks of the thesis are the following: •To up to date Literature Survey related to “Laser Shock Peening in Metallic Structures” •To validate the FE model developed against experimental measurements at coupon level •To develop design of crack growth slowdown in Centered Cracked Tension specimens based on residual stress engineering approach using laser peened strip transversal to the crack path •To evaluate the Stress Intensity Factor values for Centered Cracked Tension specimens after the Laser Shock Peening treatment via Finite Element Analysis •To predict the crack growth behavior in Centered Cracked Tension specimens using as input the SIF values evaluated with the FE simulations •To validate the results by means of experimental tests

Magnetic actuators for nanosatellite attitude control

The research and the activities presented in the following thesis report have been led at the California Polytechnic State University (US) under the supervision of Prof. Jordi Puig Suari. The objective of the research has been the study of magnetic actuators for nanosatellite attitude control, called magnetorquer. Theese actuators are generally divided in three different kinds: air core torquer, embedded coil and torquerod. In a first phase of the activity, each technology has been analyzed, defining advantages and disadvantages, determining manufacturing procedures and creating mathematical model and designing equation. Dimensioning tools have been then implemented in numerical software to create an instrument that permits to determine the optimal configuration for defined requirements and constraints. In a second phase of the activities the models created have been validated exploiting prototypes and proper instruments for measurements. The instruments and the material exploited for experiments and prototyping have been provided by the PolySat and CubeSat laboratories. The results obtained led to the definition of a complete designing tool and procedure for nanosatellite magnetic actuators, introducing a cost analysis for each kind of solution. The models and the tools have been maintained fully parametric in order to offer a universal re-scalable instrument for satellite of different dimension class.