GCRIS

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Numerical study of influence of air ceiling diffusers on room air flow characteristics
(2016) Chowaid, Mehdi
A theoretical study includes details flow turbulence in air-conditioned Turkey spaces with the determination of the boundary conditions depending on the Code of cooling is done in this thesis. Two kinds of two-dimensional and three-dimensional ventilation problems have been considered. Isothermal ventilation in simple rooms. And non-isothermal ventilation with coupled heat or mass transfer. The investigation has studied the flow and thermal boundary conditions for four different diffusers (displacement, grille, slot, and square diffusers). The dimensions of the physical model are (5.16×3.65 m) with (2.43 m high). The supply condition for four diffusers are (displacement (0.0768 kg/s), grille (0.0768 kg/s), slot (0.1410kg/s), square (0.750kg/s)) and temperature at supply for all types is (15° C), the return considered as the type of diffusers has been imposed zero flow pressure and temperature at (24° C). A modified version of a three-dimensional computer program (fluent 6.3.26) by using finite-volume method was used to simulate the complex flow with buoyant inside the model room. They have been investigated numerically by using several turbulence models and the method solution by using k-ε and k-ω models. The numerical results can be divided into: 1. Results which compared with the measured ones obtained from ASHRAE RP-1009 three-dimensional as non-Isothermal and two cases of two-dimensional as Isothermal. 2. There is a good agreement with (k-ω) model gives more accurate fitting and closer to reality, the reason for this is due to the overall average error for displacement ventilation (19.87 % at velocity carves) and (14.20 % at temperature carve). 3. The Effective Draft Temperature (EDT) for four types of diffusers for three orientations simulating the Iraqi condition (east, south, and west) for these models are as follow: The EDT performance of various commonly used turbulence models for complex airflows and temperature distributions with forced ventilation conditions for different buildings in Iraq, also obtain displacement outlet is better than other types. The accuracy of the results can be found at different levels in terms of average temperature.
The scattering process of cylindrical waves by a convex hyperbolic reflector
(2015) Çelik, Süleyman Burak
In this thesis, the scattered fields by a perfectly conducting convex hyperbolic reflector were investigated by using the methods of modified theory of physical optics and physical optics. Furthermore, the geometrical optics and edge diffracted fields were evaluated by the stationary phase method and the edge point technique, respectively. The uniform diffracted field expressions were obtained by the method of the uniform theory of diffraction. Moreover, the results of modified theory of physical optics and physical optics were plotted and compared numerically. The results of geometrical optics and uniform diffracted fields were also plotted and analyzed numerically.
Satellite based passive radar system
(2019) Ünal, Nihat Mert
Bu tezde uydu tabanlı pasif radarların elektromanyetik yayılımı incelenmiştir. Uydudan yayılan elektromanyetik alanlar tüm atmosferi geçecek ve hedeften saçılacaktır. Bu hedefler sivil uçak ve görünmez savaş uçağıdır. Birinci olarak, Modified Theory of Physical Optics (MTPO)'den bahsedilmiştir. Physical Optics (PO) metodunun kırınan alanlardaki eksikliği MTPO kullanılarak giderilmiştir. İkinci olarak, mükemmel iletken yüzeye sahip silindirik parabolik yansıtıcı uydu anteninden saçılan alanlardan bahsedilmiştir. Silindirik parabolik yansıtıcı antenin yansıyan saçılan alanları bu tezde uydudan yayılan alan olarak kullanılacaktır. Bu tezin bir başka ana noktası da uydu anteninden yayılan alanın Gauss ışınları olarak modellenmesidir. Gauss ışınlarından gelen Geometrik Optik (GO) alanı uydudan yayılan alan olarak kullanılmıştır. Bu tezde, bu alan tüm atmosferi geçecek olan alandır. Dördüncü olarak, atmosfer International Telecommunication Union Radiocommunication (ITU-R) tavsiyeleri kullanılarak modellenmiştir. Atmosferdeki bozulmalar ortaya konmuştur. Sivil uçağın modeli olan mükemmel iletken yüzeye sahip çizgi şeritten düzlemsel dalga saçılımı açıklanmıştır. Ayrıca, görünmez savaş uçağının modeli olan mükemmel soğurucu yüzeye sahip çizgi şeritten düzlemsel dalga saçılımından bahsedilmiştir. Son olarak, atmosferdeki bozulumlardan kaynaklı sönümlenmeler, gerçek uzunlukları hesaba katılmış sivil uçak ve gerçek uzunlukları hesaba katılmış görünmez savaş uçağı numerik olarak analiz edilmiştir. Sonuçlar tartışılmıştır.
Line integral representation of fringe waves for perfectly conducting and impedance surfaces
(2014) Başdemir, Hüsnü Deniz
In this thesis, surface diffraction was investigated for perfectly conducting and impedance cylinders. Moreover, the line integral representations of fringe fields were derived analytically and generalized with using the unit vectors of related edge contours. Hence, the method of physical theory of diffraction was improved with reducing the scattering surface integral to line integral. The derived expressions were applied to perfectly conducting parabolic reflector geometry for investigation of exact diffracted fields. In addition, uniform expressions of scalar fringe waves which are based on the physical theory of diffraction method are derived for an impedance half-plane. The asymptotic and uniform expressions were compared for the impedance half-plane geometry. All these mentioned fields were plotted and analyzed numerically.

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