Ktisis Cyprus University of Technologyhttps://ktisis.cut.ac.cyThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 06 Apr 2020 17:53:53 GMT2020-04-06T17:53:53Z5041Microfluidics flow and heat transfer in microstructured fibers of circular and elliptical geometryhttps://ktisis.cut.ac.cy/handle/10488/9439Title: Microfluidics flow and heat transfer in microstructured fibers of circular and elliptical geometry
Authors: Christodoulides, Paul; Florides, Georgios A.; Davies, Edward M.; Kalli, Kyriacos; Dias, Frédéric
Abstract: The field of microfluidics utilizes micron-scale devices to control the flow of fluids. The principal application is the manipulation of very small volumes of fluids on the order of nanoliters to femtoliters that are typically seeded with nanoparticles. Hence the control and sorting of nanoparticles is a primary goal using this technology. There is recent interest in the use of microstructure optical fibers for many applications that are principally related to optical sensing and new forms of optical spectroscopy as part of this, knowledge of the heat transfer of fluids, whereby the guided light interacts with a fluid in the region of the air-hole structure, demands special attention. In this work we study the fluid transport capabilities of microstructured fibers with cross-sections containing circular or elliptical holes, while considering the effects of flow rates, fluid viscosity, and the channel shape. The role of heat flux is considered in relation to the fluid characteristics. Results can be obtained through the solution of the time-dependent Navier-Stokes equations and the convection-diffusion equation. This work is of importance as one cannot assume that the flow dynamics in microstructured fibers will be the same as conventional microfluidic channels. Through the study of the heat transfer, for pressure-driven and other flows and for low Reynolds numbers, we confirm the anticipated behavior of the fluids in the microchannel structure.
Wed, 20 May 2015 00:00:00 GMThttps://ktisis.cut.ac.cy/handle/10488/94392015-05-20T00:00:00ZWill oscillating wave surge converters survive tsunamis?https://ktisis.cut.ac.cy/handle/10488/9416Title: Will oscillating wave surge converters survive tsunamis?
Authors: O'Brien, Laura; Christodoulides, Paul; Renzi, Emiliano; Stefanakis, Themistoklis S.; Dias, Frédéric
Abstract: With an increasing emphasis on renewable energy resources, wave power technology is becoming one of the realistic solutions. However, the 2011 tsunami in Japan was a harsh reminder of the ferocity of the ocean. It is known that tsunamis are nearly undetectable in the open ocean but as the wave approaches the shore its energy is compressed, creating large destructive waves. The question posed here is whether an oscillating wave surge converter (OWSC) could withstand the force of an incoming tsunami. Several tools are used to provide an answer: an analytical 3D model developed within the framework of linear theory, a numerical model based on the non-linear shallow water equations and empirical formulas. Numerical results show that run-up and draw-down can be amplified under some circumstances, leading to an OWSC lying on dry ground!
Wed, 01 Jul 2015 00:00:00 GMThttps://ktisis.cut.ac.cy/handle/10488/94162015-07-01T00:00:00ZInteraction of ocean waves of nearly equal frequencies and the effect on pressurehttps://ktisis.cut.ac.cy/handle/10488/13380Title: Interaction of ocean waves of nearly equal frequencies and the effect on pressure
Authors: Christodoulides, Paul; Pellet, Lauranne; Donne, Sarah; Bean, Chris; Dias, Frédéric
Abstract: We study the superposition of a train of freely traveling waves in a form that includes the possibility for each wave of complex amplitude An to have a ‘sister’ wave of complex amplitude Bn with equal frequency and opposite direction. For an ideal, incompressible and homogeneous fluid, we consider three-dimensional flows that are irrotational and spaceperiodic. Through a weakly nonlinear analysis we obtain full second-order expressions for the free-surface elevation, the velocity potential and the dynamic pressure. Then we generalize and unify all related expressions in the literature, without any assumption on the water depth. When the frequencies of the surface waves of nearly opposite directions are nearly equal, a second-order pressure can be felt all the way to the sea bottom. Hence, in particular, we apply a theoretical analysis on the dynamic pressure obtained, and we quantify the degree of nearness in amplitude, frequency and incidence angle that must be reached to observe the phenomenon. Such phenomena of the second-order pressure, independent of the depth, have been supposed to be at the origin of so-called secondary microseisms. A comparison with real data for pressure induced by waves in the ocean is also presented.
Wed, 01 Mar 2017 00:00:00 GMThttps://ktisis.cut.ac.cy/handle/10488/133802017-03-01T00:00:00ZPressure induced by the interaction of water waves with nearly equal frequencies and nearly opposite directionshttps://ktisis.cut.ac.cy/handle/10488/12648Title: Pressure induced by the interaction of water waves with nearly equal frequencies and nearly opposite directions
Authors: Pellet, Lauranne; Christodoulides, Paul; Donne, Sarah; Bean, Chris; Dias, Frédéric
Abstract: We present second-order expressions for the free-surface elevation, velocity potential and pressure resulting from the interaction of surface waves in water of arbitrary depth. When the surface waves have nearly equal frequencies and nearly opposite directions, a second-order pressure can be felt all the way to the sea bottom. There are at least two areas of applications: reflective structures and microseisms. Microseisms generated by water waves in the ocean are small vibrations of the ground resulting from pressure oscillations associated with the coupling of ocean surface gravity waves and the sea floor. They are recorded on land-based seismic stations throughout the world and they are divided into primary and secondary types, as a function of spectral content. Secondary microseisms are generated by the interaction of surface waves with nearly equal frequencies and nearly opposite directions. The efficiency of microseism generation thus depends in part on ocean wave frequency and direction. Based on the second-order expressions for the dynamic pressure, a simple theoretical analysis that quantifies the degree of nearness in amplitude, frequency, and incidence angle, which must be reached to observe the phenomenon, is presented.
Mon, 01 May 2017 00:00:00 GMThttps://ktisis.cut.ac.cy/handle/10488/126482017-05-01T00:00:00Z