İlyas Kandemir

A hardware test setup for grid connected and island operation of micro hydro power generation systems

This paper presents a micro hydro power generation hardware setup, established via a research project at Gebze Institute of Technology (GIT), Turkey. This project is founded by the government and aims to increase utilization of potential for small, local hydro power generation. The hardware setup consists of a newly designed cross flow type hydro turbine, two different generators (asynchronous and synchronous up to 20 kW power range) and all equipment necessary for grid connected operation and islanding. The setup can be used for two purposes: primarily performance tests of newly designed micro hydro turbines, and research and development studies to provide new regulations and technical guidelines regarding to energy management and grid connected and island (stand-alone) operation which concern for distributed generation versatility. The hardware setup offers a similar environment to that of real site which can easily be adapted to the clients test and turbine evaluation requirements.

Molecular dynamics simulation of helium–argon gas mixture under various wall conditions

As computational capabilities increase, molecular dynamics (MD) simulations become important tools of simulating reality. These simulations are especially useful for compressible gas mixture problems. In this study, binary diffusion of helium and argon was examined using a hard-sphere MD simulation method. For the sake of computational speed, low spacing ratios were chosen. Binary mass diffusion of gases in two equally sized halves of a box was simulated for identical initial kinetic energies and number densities. It has been noted that a purely mass diffusion mechanism of different gases is not physically possible. The resultant gas mixtures of several diffusion simulations were used as initial conditions for combined heat transfer – Couette flow, and heating and cooling experiments. The results showed the interesting behaviour of the mixture, which was subjected to various wall conditions. Energy of heavier molecules is found to be more sensitive to the wall velocities and less sensitive to the wall temperatures than lighter molecules. Diffusion, heat transfer, viscosity and heat capacity coefficients are deduced as well.

Event-Driven Molecular Dynamics Simulation of Hard-Sphere Gas Flows in Microchannels

Classical solution of Navier-Stokes equations with nonslip boundary condition leads to inaccurate predictions of flow characteristics of rarefied gases confined in micro/nanochannels. Therefore, molecular interaction based simulations are often used to properly express velocity and temperature slips at high Knudsen numbers (Kn) seen at dilute gases or narrow channels. In this study, an event-driven molecular dynamics (EDMD) simulation is proposed to estimate properties of hard-sphere gas flows. Considering molecules as hard-spheres, trajectories of the molecules, collision partners, corresponding interaction times, and postcollision velocities are computed deterministically using discrete interaction potentials. On the other hand, boundary interactions are handled stochastically. Added to that, in order to create a pressure gradient along the channel, an implicit treatment for flow boundaries is adapted for EDMD simulations. Shear-Driven (Couette) and Pressure-Driven flows for various channel configurations are simulated to demonstrate the validity of suggested treatment. Results agree well with DSMC method and solution of linearized Boltzmann equation. At low Kn, EDMD produces similar velocity profiles with Navier-Stokes (N-S) equations and slip boundary conditions, but as Kn increases, N-S slip models overestimate slip velocities.

KONTROL SİSTEMLERİNDE BELİRSİZLİKLE BAŞ ETME YÖNTEMLERİ: LYAPUNOV TARZI YAKLAŞIMLAR

Endustriyel denetim sistemlerinde genel olarak sistem modeli ve icerebilecegi belirsizlikler gozardi edilerek, kapali cevrim yapisi sadece cikis hatasina dayali olan, Oranti tipi (P-tipi), Integral tipi (I-Tipi), Oranti arti Integral etkili (PI-Tip), Oranti arti Turev etkili (PD-Tip), ve son olarak Oranti arti Integral arti Turev etkili (PID-Tip) denetim algoritmalari kullanilir. Kontrol kazanclari, sistem performansi tatminkâr bulununcaya kadar ayarlanan bu basit denetim algoritmalari cogu zaman uretim kayiplarina yol acmakta ve cok degerli olan hammadde sarfiyatini arttirmaktadir. Bir diger yanilgi ise sistem belirsizlikleri ile basa cikabilen akilli denetleyicilerin yuksek islemci gucune gerek duydugu ve bu sebeple yuksek maliyet gerektirdigi kanisidir. Gunumuz mikro-islemcileri cok karmasik algoritmalari bile gercek zamanli denetim gerektiren sistemlerde basari ile uygulayabilmektedir. Geriye kalan sorun; geliskin kontrol algoritmalarinin hangisinin denetimini yapmak istedigimiz, cogunlukla da dogrusal olmayan parametreler iceren sistemler icin daha uygun oldugunu belirlemek, ki bu genellikle zaman ve ekonomi acisindan onemli bir bilgidir, ve kullanilacak algoritmadan ne tur sonuc beklenmesi gerektiginin bilinmesidir. Bu bilginin degerlendirilmesinde, algoritmanin sistemimizin kararliligini saglayip saglamayacaginin bilinmesi oncelik tasimaktadir. Bu calismamizda, sistem denklemi bilinmesine karsin parametrik belirsizlikler de icerebilen genel bir denetim sistemi icin tasarlanmis akilli denetim algoritmalarinin derlemesi olacak bir kilavuz sunulmustur. Calismamizda sistem kararlilik analizleri Lyapunov tarzi yaklasimlar isiginda ele alinmis, hangi kontrol yonteminin hangi problemde daha uygun olabilecegini iceren bir tartisma da sonuc bolumunde sunulmustur

Molecular dynamics simulation of unsteady diffusion

The behavior of diffusion of monatomic gases is examined by molecular dynamics simulation, using a multi-cell computational method. The gases are modeled as hard spheres, undergoing elastic intermolecular and boundary coollisions in a parallelopiped domain. Accordingly, the process is entirely causal. The computational procedure traces the time evolution of the mixing process, starting with initially unmixed gases. The time history of the diffusion process is described, and diffusion coefficients are determined from the long time behavior. The molecular parameters for binary diffusion correspond to a heliumargon mixture. The effects of Knudsen number are examined. In self diffusion, the early time behavior indicates faster mixing than one would obtain using Fick’s law with a constant diffusion coefficient. In binary diffusion, early time behavior of the molecular concentration is found to be non-monatonic.