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Yayın Waves in an elastic tube filled with a heterogeneous fluid of variable viscosity(Pergamon-Elsevier Science Ltd, 2009-07) Demiray, HilmiBy treating the artery as a prestressed thin elastic tube and the blood as an incompressible heterogeneous fluid with variable viscosity. we studied the propagation of weakly non-linear waves in such a composite medium through the use of reductive perturbation method. By assuming a variable density and a variable viscosity for blood in the radial direction we obtained the perturbed Korteweg-deVries equation as the evolution equation when the viscosity is of order of epsilon(3/2). We observed that the perturbed character is the combined result of the viscosity and the heterogeneity of the blood. A progressive wave type of solution is presented for the evolution equation and the result is discussed. The numerical results indicate that for a certain value of the density parameter sigma, the wave equation loses its dispersive character and the evolution equation degenerates. It is further shown that, for the perturbed KdV equation both the amplitude and the wave speed decay in the time parameter tau.Yayın Nonlinear wave modulation in a prestressed thin elastic tube filled with an inviscid fluid(Wit Press, 2002) Bakırtaş, İlkay; Demiray, HilmiIn the present work, employing the nonlinear equations of an incompressible, isotropic and elastic thin tube and the approximate equations of an incompressible inviscid fluid and then utilizing the reductive perturbation technique, the amplitude modulation of weakly nonlinear waves is examined. It is shown that, the amplitude modulation of these waves is governed by a nonlinear Schrödinger (NLS) equation. The result is compared with some previous works on the same subject. The modulational instability of the monochromatic wave solution is discussed for some elastic materials and initial deformations. It is shown that the amplitude modulation of weakly nonlinear waves near the marginal state is governed by the Generalized Nonlinear Schrödinger equation (GNLS).Yayın Photogrammetric deformation monitoring of the second Bosphorus Bridge in Istanbul(International Society for Photogrammetry and Remote Sensing, 2014) Avşar, Özgür; Akça, Mehmet Devrim; Altan, Mehmet OrhanImproving the efficiency of bridge inspection and minimizing the impact of dynamic load on the long term deterioration of the bridge structure reduces maintenance and upkeep costs whilst also improving bridge longevity and safety. This paper presents the results of an on-going project whose ultimate goal is the real-time photogrammetric monitoring the structural deformations of the second Bosphorus Bridge of Istanbul.Yayın Precursors of instability in a natural slope due to rainfall: a full-scale experiment(Springer Heidelberg, 2018-09) Askarinejad, Amin; Akça, Mehmet Devrim; Springman, Sarah MarcellaA full-scale landslide-triggering experiment was conducted on a natural sandy slope subjected to an artificial rainfall event, which resulted in mobilisation of 130m(3) of soil mass. Novel slope deformation sensors (SDSs) were applied to monitor the subsurface pre-failure movements and the precursors of the artificially triggered landslide. These fully automated sensors are more flexible than the conventional inclinometers by several orders of magnitude and therefore are able to detect fine movements (<1mm) of the soil mass reliably. Data from high-frequency measurements of the external bending work, indicating the transmitted energy from the surrounding soil to these sensors, pore water pressure at various depths, horizontal soil pressure and advanced surface monitoring techniques, contributed to an integrated analysis of the processes that led to triggering of the landslide. Precursors of movements were detected before the failure using the horizontal earth pressure measurements, as well as surface and subsurface movement records. The measurements showed accelerating increases of the horizontal earth pressure in the compression zone of the unstable area and external bending work applied to the slope deformation sensors. These data are compared to the pore water pressure and volumetric water content changes leading to failure.Yayın Uni-axial behavior of energy dissipative steel cushions(Techno Press, 2018-06-25) Özkaynak, Hasan; Khajehdehi, Arastoo; Güllü, Ahmet; Azizisales, Faraz; Yüksel, Ercan; Karadoğan, Hüseyin FarukSeismic excitations may impart a significant amount of energy into structures. Modern structural design attitudes tend to absorb some part of this energy through special dissipaters instead of heavy plastic deformations on the structural members. Different types of dissipater have been generated and utilized in various types of structures in last few decades. The expected earthquake damage is mainly concentrated on these devices and they may be replaced after earthquakes. In this study, a low-cost device called energy dissipative steel cushion (EDSC) made of flat mild steel was developed and tested in the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University (ITU). The monotonic and cyclic tests of EDSC were performed in transversal and longitudinal directions discretely. Very large deformation capability and stable hysteretic behavior are some response properties observed from the tests. Load vs. displacement relations, hysteretic energy dissipation properties as well as the closed form equations to predict the behavior parameters are presented in this paper.Yayın On the existence of some evolution equations in fluid-filled elastic tubes and their progressive wave solutions(Pergamon-Elsevier Science Ltd., 2004-09) Demiray, HilmiIn the present work, by employing the nonlinear equations of motion of an incompressible, isotropic and prestressed thin elastic tube and the approximate equations of an incompressible inviscid fluid, we studied the existence of some possible evolution equations in the longwave approximation and their progressive wave solutions. It is shown that, depending on the set of values of the initial deformation, it might be possible to obtain the conventional Korteweg-deVries (KdV) and the modified KdV equations of various forms. Finally, a set of progressive wave solutions is presented for such evolution equations.Yayın El Greco ve Francis Bacon'ın '' varlık ve zaman'' bağlamında deformasyon ilkesine yönelik bir analoji(Işık Üniversitesi, 2011-09-30) Sürsal, Ekber; Akdeniz, Halil; Işık Üniversitesi, Sosyal Bilimler Enstitüsü, Sanat Kuramı ve Eleştiri Yüksek Lisans ProgramıBu çalışmada, deformasyon ilkesinin El Greco ve Francis Bacon'ın elinde nasıl sanatsal bir ifade aracı olarak kullanıldığı ve bunların kullanım yöntemleri incelendi. Çalışmada incelemeye alman iki sanatçının sanatsal bakış açılarının birbirleriyle hem benzer, hem de farklı dayanakları olduğu görüldü. Bu bağlamda, kendi zamanlarında, dâhil oldukları Maniyerizm ve Modem dönemlere ait üslup geleneklerine bağlı işler üreten El Greco ve Francis Bacon'ın, dönemleriyle bağlantılı temel üsluplar da ana hatlarıyla ele alındı. Yapıtlarının incelenmesi ile Bacon'ın, resimlerinde Varlık ve Zaman kavramı ile örtüşen, deformasyonun hangi formlarını kullandığı ve bunları kullanmasının altında yatan amaçlar incelendi. Yine Bacon'ın çalışmaları da Varlık ve Zaman kavramıyla ilintili olarak Deformasyon Analojileri'nin (Örnekleme) ifade araçlarını ne derece temsil ettiği, özellikle geleneksel unsurların kullanımının hangi amaca, ne kadar ulaşılmasını sağladığı incelemeye çalışılmıştır. Sonuç olarak, görüldüğü üzere, hem yaşadıkları hem de sonraki dönemleri üslup ve biçim açısından etkilemiş iki sanatçının deformasyonu başat bir anlatım aracı olarak kullandıklarını söyleyebiliriz.Yayın Weakly nonlinear waves in a viscous fluid contained in a viscoelastic tube with variable cross-section(Gauthier-Villars/Editions Elsevier, 2005-03) Demiray, HilmiIn the present work, treating the arteries as a thin walled prestressed viscoelastic tube with variable cross-section, and using the longwave approximation, we have studied the propagation of weakly nonlinear waves in such a fluid-filled viscoelastic tube by employing the reductive perturbation method. By considering the blood as an incompressible viscous fluid, depending on the order of various physical entities, various evolution equations with variable coefficients are obtained and progressive wave solutions to these evolution equations are given whenever possible. It is shown that this type of equations admit solitary wave type of solutions with variable wave speeds.Yayın Localized travelling waves in a prestressed thick elastic tube(Pergamon-Elsevier Science, 2001-10) Demiray, HilmiIn the present work, by using the exact non-linear equations of an incompressible inviscid fluid contained in a prestressed thick elastic tube, the propagation of localized travelling wave solution in such a medium is investigated. Employing the hyperbolic tangent method and considering the long-wave limit, we showed that the lowest-order term in the perturbation expansion gives a solitary wave equivalent to the localized travelling wave solution of the Korteweg-de Vries equation. The progressive wave type of solution is also sought for the second-order terms in the perturbation expansion. The correction terms in the speed of propagation are obtained as part of the solution of perturbation equations.Yayın Dynamic extension of a compressible nonlinearly elastic membrane tube(Oxford Univ Press, 2005-02) Erbay, Hüsnü Ata; Tüzel, Vasfiye HandeThe dynamic response of an isotropic compressible hyperelastic membrane tube is considered when one end is fixed and the other is subjected to a suddenly applied dynamic extension. The equations governing dynamic axially symmetric deformations of the membrane tube are presented for a general form of compressible isotropic elastic strain-energy function. Numerical results, obtained using a Godunov-type finite volume method and valid up to the time at which reflections occur at the fixed end of the tube, are given for two specific forms of the strain-energy function that characterizes a class of compressible elastomers (the Blatz-Ko model). The question of how the numerical results are related to the exact solution obtained for a limiting case is discussed.
