Digital and Computational Approaches to Migration Studies: 3 Essays

This dissertation aims to contribute to the literature on computational social sciences and presents three essays in migration studies and demography, using digital data and computational methods. The first essay focuses on visual comparison of migration patterns using Turkey as a case study. The internal migration patterns in Turkey are compared with the settlement patterns of Syrians under temporary protection in Turkey, while questioning whether there is a possibility for replacement migration policies. The second essay also uses the case of Syrians under temporary protection in Turkey and contributes to the literature on nowcasting & forecasting based on digital data by following the mobility patterns of Syrians inside Turkey using online search data from Google Trends. The third essay contributes to the literature on high-skilled migration and the use of bibliometric data. The essay uses the Brexit decision in 2016 and the academic environment in the United Kingdom as a case study and monitors the change that occurred in the in- and out-migration patterns of researchers with respect to the UK, before and after the Brexit referendum

Analytical Formulation of the Jacobian Matrix for Non-linear Calculation of the Forced Response of Turbine Blade Assemblies with Wedge Friction Dampers

A fundamental issue in turbomachinery design is the dynamical stress assessment of turbine blades. In order to reduce stress peaks in the turbine blades at engine orders corresponding to blade natural frequencies, friction dampers are employed. Blade response calculation requires the solution of a set of non-linear equations originated by the introduction of friction damping. Such a set of non-linear equations is solved using the iterative numerical Newton-Raphson method. However, calculation of the Jacobian matrix of the system using classical numerical finite difference schemes makes frequency domain solver prohibitively expensive for structures with many contact points. Large computation time results from the evaluation of partial derivatives of the non-linear equations with respect to the displacements. In this work a methodology to compute efficiently the Jacobian matrix of a dynamic system having wedge dampers is presented. It is exact and completely analytical. The proposed methods have been successfully applied to a real intermediate pressure turbine (IPT) blade under cyclic symmetry boundary conditions with underplatform wedge dampers. Its implementation showed to be very effective, and allowed to achieve relevant time savings without loss of precision

Qualitative Analysis of Forced Response of Blisks With Friction Ring Dampers

A damping strategy for blisks (integrally bladed disks) of turbomachinery involving a friction ring is investigated. These rings, located in grooves underside the wheel of the blisks, are held in contact by centrifugal loads and the energy is dissipated when relative motions between the ring and the disk occur. A representative lumped parameter model of the system is introduced and the steady-state nonlinear response is derived using a multi-harmonic balance method combined with an AFT procedure where the friction force is calculated in the time domain. Numerical simulations are presented for several damper characteristics and several excitation configurations. From these results, the performance of this damping strategy is discussed and some design guidelines are given

Plasma deposition of constrained layer damping coatings

Plasma techniques are used to generate constrained layer damping (CLD) coatings on metallic substrates. The process involves the deposition of relatively thick, hard ceramic layers on to soft polymeric damping materials while maintaining the integrity of both layers. Reactive plasma sputter-deposition from an aluminium alloy target is used to deposit alumina layers, with Young's modulus in the range 77-220GPa and thickness up to 335 μ, on top of a silicone film. This methodology is also used to deposit a 40 μ alumina layer on a conventional viscoelastic damping film to produce an integral damping coating. Plasma CLD systems are shown to give at least 50 per cent more damping than equivalent metal-foil-based treatments. Numerical methods for rapid prediction of the performance of such coatings are discussed and validated by comparison with experimental results

Acoustic and mechanical properties of luffa fiber-reinforced biocomposites

This chapter presents an overview of acoustic and mechanical behaviors of luffa fiber reinforced biocomposites. A growing number of studies are examining the composites of biodegradable fibers such as flax, hemp, kenaf and luffa due to the adverse effects of chemical materials on nature. The low cost and superior acoustic and acceptable mechanical properties of biocomposites make them very attractive for practical applications such as sound and vibration isolation. However, the acoustic and mechanical characteristics of biocomposites and their dynamic behaviors should be fully determined before considering them for practical applications. In this chapter, acoustic properties, such as sound absorption and transmission loss, and mechanical properties, such as damping and elasticity of luffa fiber reinforced composites, are presented. The variations in acoustic and mechanical properties due to different samples and manufacturing process are explored.WOS:000532438200017Scopus - Affiliation ID: 60105072Book Citation Index- ScienceArticle; Book ChapterOcak2019YÖK - 2018-1

Identification of modal parameters from noisy transient response signals

In the process of impact testing of large-scale mechanical equipment, the measured forced response signals are often polluted by strong background noise. The forced response signal has a low signal-to-noise ratio, and this makes it difficult to accurately estimate the modal parameters. To solve this problem, the mean averaging of repeatedly measured frequency response function estimates is often employed in practical applications. However, a large number of impact tests are not practical for the modal testing of large-scale mechanical equipment. The primary objective of this paper is to reduce the averaging operation and improve the accuracy of the modal identification by using a noise removal technique. A hybrid denoising method is proposed by combining the Wiener and improved minimum mean-square-error short-time spectral amplitude estimators. The proposed method can effectively remove both stationary and highly nonstationary noise while preserving the important features of the true forced response signals. The simulation results show that the proposed noise removal technique improves the accuracy of the estimated modal parameters using only one impulse response signal. The experimental results show that the proposed method can accurately identify a natural frequency that is very close to a strong interference frequency in the modal test of a 600-MW generator casing

A new damping modelling approach and its application in thin wall machining

In this paper, a new approach to modelling the damping parameters and its application in thin wall machining is presented. The approach to predicting the damping parameters proposed in this paper eliminates the need for experiments otherwise used to acquire these parameters. The damping model proposed was compared with available damping models and experimental results. A finite element analysis and Fourier transform approach has been used to obtain frequency response function (FRF) needed for stability lobes prediction. Several predicted stable regions using both experimental and numerical FRF’s for various examples gave a good comparison.Engineering and Physical Sciences Research Counci

Performance of Being State: Exceptional and Fictitious Performances in prescriptive village; Pyla

In the hybrid Turkish and Greek Cypriot village of Pyla, different languages, segregated public places such as schools and markets, as well as the United Nations (UN) inspection towers determine everyday life. This thesis deals with the implications of the UN’s vision for Pyla as a prototype of integrity and bi-communality. Performance of Being State analyses and problematises the UN mandate system in order to challenge its ‘peace-keeping’ and ‘peace-making’ strategies. Through applying Michel Foucault’s notion of power the aim is to explore the indirect ways in which power is exercised in social life, by paying attention to the mundane practices and ideas that structure inhabitants’ everyday life. The word performance in the thesis title refers to the prescriptive regulations and rules whose aim is to establish a unified Pyla, and to also show how this overlaps and is resisted by Turkish and Greek Cypriots’ divergent subjectivities; being state calls attention to how this codification is a performance that attempts to create a normalised or ideal state. Such power relations and normalisation strategies were questioned by means of performative design interventions in Pyla through the concept of Performance of Being State. These spatial performances can be understood as acts that challenge the UN mandate system. Furthermore, this thesis aims to critically reflect on such actions to examine dialectical power relations and their embodiment in space. My objective is to look beyond a radical ideology of conflict resolution, and to instead propose a spatial methodology for working with and across conflict by engaging performative narrative

Analysis and optimization of tuned mass dampers attached to structures via an efficient method

Tuned Mass Dampers (TMD) are often used to reduce the excessive vibrations levels of mutli-degree-of-freedom systems. However, in contrast to the situation for single-degre-of-freedom systems, the optimisation of TMD’s for multi-degree-of-freedom systems is not an easy task. In this work, an efficient method is utilised for analyses of structures with TMDs, and for optimising these TMDs for maximum damping. The method used for this purpose is based on structural modification approach which allows very efficient calculations of Frequency Response Functions (FRFs) of a modified structure if the natural frequencies and mode shapes of the original structure are already available. The application of the method is demonstrated by considering a high-rise structure and results corresponding to analysis and optimisation of the structure with a TMD are presented. Furthermore, how to optimise damping, using a TMD, for more than one mode of vibration is also demonstrated in this study