Değişim (28.08.2018)

Geçenlerde bir arkadaş,
Sen çok değiştin dedi.
Şaşırdım.
En çok korktuğum,
Köşe bucak kaçtığım,
İsteyip de yapamadığım şey değişmek.

Keşke iyiye doğru değişsek,
Ama sormadım öyle mi diye.
Korkarım ki diğerine.

New Research Paper (21.06.2018)

This is the third paper published from Ali's PhD work. It combines the techniques mentioned in the earlier two papers with an incompressible, unsteady multiphase Navier-Stokes solver. It is based on high-order nodal discontinuous Galerkin finite element discretization. Interface is tracked with level set formulation on adaptive unstructured meshes. Implicit systems arising from the semi-explicit time discretization are solved with a p-multigrid preconditioned conjugate gradient method to minimize the memory requirements and increase the run-time performance. With the proposed method it is possible to capture the interface topology accurately with good mass conservation even in relatively coarse grids. Efficiency and high-order accuracy of the method are confirmed using test problems of sloshing, Rayleigh–Taylor instability and dam break. Full paper can be accessed here.

New Research Paper (18.04.2018)

This paper, published recently in the Journal of Rail and Rapid Transit, is the outcome of Dr. Gencer Koc's PhD. work. Prof. Albayrak and I were the advisors of Gencer. This is the second paper we published from Gencer's work. The idea here is to use artificial neural networks to predict time dependent air speeds developing inside metro stations, which is important due to safety and comfort concerns. Three artificial neural networks are used, each trained for the most basic configuration of a single train moving in a single tunnel. The first two are trained to provide the maximum and time averaged values of the induced air speeds while the train is moving inside the approach tunnel of the station. The third one is used to simulate the time-dependent air speed variation during train stoppage and departure. Typical structures of a metro system such as staircases and ventilation shafts are introduced into the solution using simple analytical relations based on loss coefficients. The developed approach is tested using two different metro stations that are currently in operation in Turkey. The results show that the time variation of the air speed predicted by the developed model is, in general, in good agreement with the results of the Subway Environmental Simulation (SES) software, although further studies are necessary to model the acceleration and deceleration of trains more realistically. Full paper can be accessed here.

New Research Paper (15.02.2018)

This paper, published recently in the Journal of Spacecraft and Rockets, is the outcome of the masters thesis of my student Erdem Dikbaş. Dr. Özgür Uğraş Baran was his co-advisor. The paper is about grid fins, which are unconventional control devices used for aerodynamic control of missiles. We proposed a new idea called "Unit Grid Fin (UGF)" for easy parametrization and fast numerical simulation of missiles with grid fins. The long term goal is to develop a quick prediction tool that can generate aerodynamic force and moment databases necessary for preliminary designs. Such tools exist for missiles with conventional planar fins, but not for those with grid fins. We were able to show that, although requiring much less computational resources and time compared to a full CFD solution, the UGF approach provides acceptable results. The body interference correction to account for the effects of missile fuselage turns out to be critical in the performance of the proposed method, and we showed the deficiency of a simple potential flow based approach. The full article can be accessed here.

365 Güneş (01.01.2018)

Bir yıl daha bitti,
Koskoca yıldı, geçti gitti.
365 sabahı vardı, uyandırmadı,
365 güneş battı, hiç dokunmadı.

Ne yalan söyleyeyim, bir ara içim bir kıpırdadı,
Gel gör sadece Ankara ayazıymış, olmadı.
Halbuki ışıkları kapatıp 10'dan geriye de saydıydım,
Ama tutmadı.
Dün gece rüyamda öldüğümü gördüm,
Sabah kalktığımda hiç dokunmadı.

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