Cevdet Aygün

Simulation of Double Effect Absorption Refrigeration System

In this study the Double effect Absorption Refrigeration system (DAR) is developed and its thermodynamic analysis is performed using different working fluid pairs. The DAR consists of a high and low temperature generator, high and low temperature absorbers, condenser, evaporator, expansion valves, mixture and refrigerant heat exchangers and pumps and it is made up of two cycles.

Nonlinear buckling finite element analysis of stiffened B–Al plates

Abstract Nonlinear buckling behavior of stiffened composite B–Al plates was analyzed by means of finite element analysis (FEA) method. In the method, the composite material was taken as B matrix into which Al fibers were embedded in different configurations. The laminated B–Al material in the form of rectangular plates was subjected to lateral compressive loading. It is observed that stiffeners have significant effect on the buckling behavior of plates under compressive loading and for various geometrical configurations. The stiffeners used in the modeling are one-sided and have rectangular cross-sections. It is found that there are physically important loading intervals and the critical buckling modes make transitions back and forth between stable and unstable states. Bifurcation buckling regions resulting from various configurations of fiber orientations and different plate aspect ratios are determined. The whole analysis is performed by using ANSYS finite element computations. Only the buckling patterns of stiffened plate configurations under simply supported boundary conditions are studied. Distributions of compressive stresses ( σ x ) vs in-plane contractions ( u ) and compressive stresses ( σ x ) vs out-of plane deflections ( δ ) are obtained. Nonlinear analysis of the C2 fiber configuration yields the safest critical buckling stress amongst C1, C2, C3 and C4 configurations. It is concluded that FEA method for the nonlinear buckling analysis generates accurate results.

Empirical Formulation of Shear Modulus Functions for Tubular Pinewood Specimens Under Torsion

In this study, tubular pinewood (Pinus Sylvestris L.) specimens are tested and shear strain measurements are performed by applying torsion in z-direction. Strain gauge measurements are performed for the maximum shear stresses which develop on the tubular specimen, along the radial r (rin, rout), circumferential ϕ (ϕin, ϕout) and z directions, in a point-wise (pw) manner. The data is gathered and examined for the determination of the local variations of empirical shear modulus functions on transversely isotropic surfaces of the specimens. The coordinate dependent shear modulus functions of Gzϕ(r), Gzϕ(ϕ), Gzϕ(z) are derived for Gzϕ(r, ϕ, z) as the function of r, ϕ and z, respectively, by analyzing the gathered data. It is proposed to represent the shear modulus functions, Gzϕ(ϕ) and Gzϕ(z) with the parabolic polynomials, and, to represent the shear modulus function Gzϕ(r) with a linear equation.

Nonlinear Buckling Finite Element Analysis of Stiffened Steel Plates

In this paper, thin rectangular steel plates with stiffeners are examined under compressive loading. Consequently, nonlinear buckling finite element analysis (FEA) solutions are obtained by using ANSYS®. The local and global buckling patterns of stiffened steel plate geometries with simply supported boundary conditions are generated and critical buckling stresses are studied. Geometrically nonlinear buckling analyses are compared in order to evaluate the distributions of compressive stresses versus in-plane contractions and compressive stresses versus out-of plane deflections. Hence, it is concluded that there are critical load intervals. It is also observed that for critical loads, segments between stiffeners may switch from stable to unstable configurations under compressive stresses.

Experimental determination of the yield stress curve of the scotch pine wood materials

Yield stress curve is determined for the pine wood specimens by conducting a series of tests. In this work, pinewood is modeled as a composite material with transversely isotropic fibers. Annual rings (wood grain) of the wood specimens are taken as the major fiber directions with which the strain gauge directions are aligned. For this purpose, three types of tests are arranged. These are tensile, compression and torsion loading tests. All of the tests are categorized with respect to fiber orientations and their corresponding loading conditions. Each test within these categories is conducted separately. Tensile and compression tests are conducted in accordance with standards of Turkish Standards Institution (TSE) whereas torsion tests are conducted in accordance with Standards Australia. Specimens are machined from woods of Scotch pine which is widely used in boat building industries and in other structural engineering applications. It is determined that this species behaves more flexibly than the others. ...

Çok Katlı Bir Bina Etrafındaki Rüzgar Akışının Oluşturduğu Yüzey Basınçlarının Deneysel Olarak İncelenmesi

Bu arastirmada ornek bir cok katli bir bina modeli ile ruzgar tunelinde deneyler yapilarak binanin etrafinda degisik hiz ve acilardan esen ruzgar akisinin olusturdugu basinc dagilim profilleri cikartilmis ve ruzgarin pencere mahallerine uyguladigi kuvvetler hesaplanmistir. Bu deneyler, ornek binanin ozel imal edilen 1/300 olcekli modeli, Gazi Universitesi Muhendislik Mimarlik Fakultesi ruzgar tunelinin kesit alani 30.5x30.5 cm olan deney odasinda sabitlenerek yapilmistir. Bu deneylerde; bina modelinin muhtelif kesitleri etrafinda olusan noktasal basinc degerleri, ruzgarin bina uzerine esme hizina ve binaya olan esme acisina bagli olarak elde edilmis ve bu basinclarin model kesitleri etrafindaki dagilim profilleri ile pencere mahallerindeki yerel basinclarin hasil ettigi yuzey kuvvetleri incelenmistir. Son asamada deney hata cozumlemesi olarak, model kesitleri etrafindaki muhtelif deneysel basinc degerleri kumelerine, her bir kesit etrafindaki basinc degerlerini, bu noktalardan en az hata ile gecen bir egriye donusturen polinomsal regresyon yontemi uygulanmis ve kesitlerin ilgili basinc profili grafikleri bu yolla elde edilmistir.