Araştırma Çıktıları / Research Outputs

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A phenomenological study of instructors’ experiences on an open source learning management system
(Procedia - Social and Behavioral Sciences, 2011) Çiğdemoğlu, Ceyhan; Arslan, Harika Özge; Akay, Hasan; Automotive Engineering; Public Relations and Advertising
This paper focuses on instructors’ experiences on usage of an open-source Learning Management System (LMS), Moodle in their courses. The study was conducted in a private university in Ankara, Turkey where the widespread use of the Moodle has only recently started. The phenomenological design has been utilized as qualitative research method for this paper. The Participants comprised in structures from different faculties who are new users of the Moodle. Open-ended interviews were carried out, and the data was transcribed into codes and themes. The research findings indicate that instructors have different impressions from the system in terms of their effort and expectation.
Citation Count: 0
Effects Of Chamber Pressure Variation On Pollutant Formation In Cryogenic Combustion
(Ieee, 2021) Omair, Muhammad; Akay, Hasan U.; Automotive Engineering
Liquid rocket engines have played a major role in enabling the pursuit of space exploration. Cryogenic propellants have simplified the storage in liquid rocket engines with higher densities and lower pressures. One of the main driving forces in today's engine research is the reduction of pollutants while keeping the fuel consumption as low as possible. In this study cryogenic combustion has been simulated using the `Steady Laminar Flamelet' approach. Pollutant concentrations have been evaluated at different chamber pressures. It has been shown that combustion at higher chamber pressures results in less pollutant formation.
Citation Count: 6
Flows around moving bodies using a dynamic unstructured overset-grid method
(Taylor & Francis Ltd, 2010) Liu, Jingxin; Akay, Hasan U.; Ecer, Akin; Payli, Resat U.; Automotive Engineering
In this article, a computational fluid dynamics algorithm is presented for simulations of complex unsteady flows around rigid moving bodies using an unstructured overset-grid method. For this purpose, a highly automated, three-dimensional, tetrahedral, unstructured overset-grid method is developed with one-cell-width overlapping zone in order to model the arbitrary geometries for steady and unsteady flow simulations. A method has been described to obtain the inter-grid boundaries of the one-cell-wide overlapping zone shared by a background grid and a minor grid. In the overset-grid methodology, vector intersection algorithm and bounding box techniques have been utilised. The mesh refinement and overset-scheme conservation studies proved the accuracy and efficiency of the method developed here. The applications of the developed algorithms were also performed through simulations that included complex internal flows around a flow-control butterfly valve as well as flows in an internal combustion engine with a moving piston. Lastly, validations with experimental data were conducted for both steady and unsteady flows around rigid bodies with relative motions.
Citation Count: 0
Improved parallel preconditioners for multidisciplinary topology optimisations
(Taylor & Francis Ltd, 2016) Akay, H. U.; Oktay, E.; Manguoglu, M.; Sivas, A. A.; Automotive Engineering
Two commonly used preconditioners were evaluated for parallel solution of linear systems of equations with high condition numbers. The test cases were derived from topology optimisation applications in multiple disciplines, where the material distribution finite element methods were used. Because in this optimisation method, the equations rapidly become ill-conditioned due to disappearance of large number of elements from the design space as the optimisations progresses, it is shown that the choice for a suitable preconditioner becomes very crucial. In an earlier work the conjugate gradient (CG) method with a Block-Jacobi preconditioner was used, in which the number of CG iterations increased rapidly with the increasing number processors. Consequently, the parallel scalability of the method deteriorated fast due to the increasing loss of interprocessor information among the increased number of processors. By replacing the Block-Jacobi preconditioner with a sparse approximate inverse preconditioner, it is shown that the number of iterations to converge became independent of the number of processors. Therefore, the parallel scalability is improved.
Citation Count: 0
Improved simulation of cryogenic fluid mixing at supercritical pressures
(Public Library Science, 2023) Omair, Muhammad; Akay, Hasan U. U.; Automotive Engineering
The combustion chamber pressure of rockets, gas turbines and diesel engines is known to be above the critical pressure of fuel and oxidizers. In the case of rocket engines the fuel and/or oxidizer is often injected at cryogenic temperatures. This elevated combustion chamber pressure and low temperature demands special treatment for numerical analysis of mixing. Thus a novel implementation of an improved equation of state has been proposed which provides better estimation of densities. Experimental and numerical data from literature has been used for validation of the analysis methodology.
Citation Count: 0
INSTRUCTOR'S VIEWS ON DIGITALIZATION OF CAMPUS; ROLES AND RECOMMENDATIONS
(Iated-int Assoc Technology Education A& development, 2016) Cigdemoglu, Ceyhan; Akay, Hasan U.; Tekin, Yucel; Automotive Engineering; Public Relations and Advertising
This study delve into determine the faculty members' opinions on digitalization and their views on roles and recommendations to create a digital campus. An open-ended questionnaire was answered by eleven participants, and then semi-structured interviews are conducted with volunteers. In this qualitative research, the participants were purposively selected. All interview sessions were type recorded and the data was transcribed verbatim. Lack of a comprehensive project with its budgets and action plans, job descriptions are perceived as an obstacle to create a digital campus. Lack of motivation is perceived as another obstacle to design digital course contents. The respondents consider that lessons should be designed in more attractive ways through innovative teaching methods through online tools. Faculty members using more digital tools could suggest more accountable action plans for digitalization.
Mühimmat ayrılması problemlerinin openfoam ile çözümü
(2022) Abuhanıeh, Saleh; Akay, Hasan; Biçer, Barış; Automotive Engineering
Bu tezde, OpenFOAM'un bir hava aracından ayrılan mühimmatı (mühimmat ayrılması problemi) dinamik bir çözüm ağı (Overset/Chimera) tekniği kullanarak çözme yeteneği endüstriyel (transonik/süpersonik ve jenerik) bir kıyaslama test durumu için ele alınmıştır. Standart kütüphanelerin temel kısıtları saptanmıştır. Bu zorlu problemin üstesinden gelebilmek için, yalnızca açık kaynaklı kütüphaneler ve araçlar kullanılarak yeni bir strateji önerilmiştir ve ygulanmıştır. Bu strateji overset kütüphanesinin OpenFOAM platformunun bir çatalından (foam-extend) standart OpenFOAM platformuna (ESI) taşınması, değiştirilmesi ve uyarlanmasının birleşiminden oluşmaktadır. Bunun yansıra, standart OpenFOAM sıkıştırılabilir çözücülerinin iyi bilinen zayıflıklarının üstesinden gelebilmek için, yeni uyarlanmış overset kütüphanesi, OpenFOAM teknolojisini kullanan bir açık kaynaklı basınç tabanlı ve bağlaşık çözücü olan HiSA ile entegre edilmiştir. Gerekli doğrulama ve sağlama süreçlerinin ardından, durağan ve zamana bağlı simülasyonlar için HiSA çözücüsü kullanılmıştır. Doğrulama çalışmalarının bir kısmı bu tezde sunulmuştur. Ek olarak, mühimmat ejektörleri tarafından mühimmata dışarıdan uygulanan kuvvetleri dikkate almak için kuvvet kısıtlamalı bir model geliştirilmiştir. Geliştirilen bu stratejinin doğruluğu, rüzgâr tüneli testleri ve iyi bilinen iki ticari hesaplamalı akışkanlar dinamiği (HAD) kodunun çözümleri ile karşılaştırılmıştır ve bu sonuçlarla oldukça uyumlu olduğu gösterilmiştir. Bu çalışma viskoz olmayan Euler denklemi ile yapılan simülasyonlara odaklanırken (burada ele alınan test durumunun karakterıstiği), çözüm üzerindeki viskozite etkisi de ayrıca Navier-Stokes denklemi ile incelenmiş ve literatürdeki diğer sonuçlar ile karşılaştırılmıştır ve kayda değer bir farklılık gözlemlenmemiştir. Ek olarak, aynı test durumu için zamansal ve uzaysal bağımsızlık çalışması yapılmıştır. Bilindiği kadarıyla bu çalışma transonik ve süpersonik rejimlerde mühimmat ayrılması problemini OpenFOAM ile inceleyen ve doğrulayan ilk çalışmadır.
Citation Count: 2
A new strategy for solving store separation problems using OpenFOAM
(Sage Publications Ltd, 2022) Abuhanieh, Saleh; Akay, Hasan U.; Bicer, Baris; Automotive Engineering
The ability of OpenFOAM to solve the problem of a store separating from an air vehicle (store separation problem) has been evaluated using a dynamic mesh (Overset/Chimera) technique for an industry-class (transonic and generic) benchmark test case. The major limitations of the standard libraries have been determined. To tackle these challenges, a new strategy has been proposed and implemented using only open-source libraries and tools. The strategy combines porting, modifying, and adapting an overset library from the OpenFOAM fork platform (foam-extend) to the standard OpenFOAM platform (ESI). Furthermore, in order to overcome the well-known weakness of the standard OpenFOAM compressible solvers, the newly adapted overset library was integrated with an open-source, density-based, and coupled solver (HiSA), which uses the OpenFOAM technology. Additionally, a force restrained model was developed to consider the externally applied forces on the store by the store ejectors. The accuracy of the developed strategy has been compared with wind tunnel tests and the solutions of two well-known commercial codes, showing good agreements with them. While the study has focused on simulations with inviscid Euler equations (typical of the test case considered here), the viscosity effect on the solution has also been studied with Navier-Stokes equations and compared with other results in the literature, showing minor differences. To the best of the authors' knowledge, this is the first work which studies and validates the store separation problem in transonic regime with OpenFOAM.
Citation Count: 0
Numerical investigation of store separation from cavity problems at high speeds
(Sage Publications Ltd, 2023) Abuhanieh, Saleh; Akay, Hasan U.; Automotive Engineering
In this work, the ability of open-source CFD tools to conduct store separation simulations from cavities is evaluated and validated using a generic test case from the literature. Firstly, the ability and accuracy of these tools for solving cavity flows at high speeds are evaluated. Secondly, their competence in predicting the trajectory of a generic store from a generic deep cavity is checked. Finally, and in order to reduce the associated computational costs, a release-time dependability factor from the recent literature is studied and evaluated. The obtained results using the selected open-source CFD tools matched quite well with the wind tunnel results. Furthermore, the results show that predicting the release-time dependability using a quantified index/factor can be a potential remedy for reducing the computational cost for this type of CFD simulations.
Citation Count: 44
Parallelized structural topology optimization and CFD coupling for design of aircraft wing structures
(Pergamon-elsevier Science Ltd, 2011) Oktay, E.; Akay, H. U.; Merttopcuoglu, O.; Automotive Engineering
A set of structural optimization tools are presented for topology optimization of aircraft wing structures coupled with Computational Fluid Dynamics (CFD) analyses. The topology optimization tool used for design is the material distribution technique. Because reducing the weight requires numerous calculations, the CFD and structural optimization codes are parallelized and coupled via a code/mesh coupling scheme. In this study, the algorithms used and the results obtained are presented for topology design of a wing cross-section under a given critical aerodynamic loading and two different spar positions to determine the optimum rib topology. (C) 2011 Elsevier Ltd. All rights reserved.
Citation Count: 4
A phenomenological study of instructors' experiences on an open source learning management system
(Elsevier Science Bv, 2011) Cigdemoglu, Ceyhan; Arslan, Harika Ozge; Akay, Hasan; Automotive Engineering; Public Relations and Advertising
This paper focuses on instructors' experiences on usage of an open-source Learning Management System (LMS), Moodle in their courses. The study was conducted in a private university in Ankara, Turkey where the widespread use of the Moodle has only recently started. The phenomenological design has been utilized as qualitative research method for this paper. The Participants comprised in structures from different faculties who are new users of the Moodle. Open-ended interviews were carried out, and the data was transcribed into codes and themes. The research findings indicate that instructors have different impressions from the system in terms of their effort and expectation. (C) 2011 Published by Elsevier Ltd.
Citation Count: 18
Three-dimensional structural topology optimization of aerial vehicles under aerodynamic loads
(Pergamon-elsevier Science Ltd, 2014) Oktay, Erdal; Akay, Hasan U.; Sehitoglu, Onur T.; Automotive Engineering
A previously developed density distribution-based structural topology optimization algorithm coupled with a Computational Fluid Dynamics (CFD) solver for aerodynamic force predictions is extended to solve large-scale problems to reveal inner structural details of a wing wholly rather than some specific regions. Resorting to an iterative conjugate gradient algorithm for the solution of the structural equilibrium equations needed at each step of the topology optimizations allowed the solution of larger size problems, which could not be handled previously with a direct equation solver. Both the topology optimization and CFD codes are parallelized to obtain faster solutions. Because of the complexity of the computed aerodynamic loads, a case study involving optimization of the inner structure of the wing of an unmanned aerial vehicle (UAV) led to topologies, which could not be obtained by intuition alone. Post-processing features specifically tailored for visualizing computed topologies proved to be good design tools in the hands of designers for identifying complex structural components. (C) 2013 Elsevier Ltd. All rights reserved.
Citation Count: 0
USE OF ICT TOOLS AND THEIR EFFECT ON TEACHING AND LEARNING; STUDENTS' AND INSTRUCTOR'S VIEWS
(Iated-int Assoc Technology Education & development, 2016) Cigdemoglu, Ceyhan; Akay, Hasan U.; Automotive Engineering; Public Relations and Advertising
This study aims to reveal how instructors use ICT tools in their courses and determine what ICT tools they utilize as well as assessing the contribution of ICT to learning and teaching from both students' and instructors' perspectives. As a qualitative case study research, semi-structured interviews with instructors and focus group interviews with students were conducted. Both students' and instructors' responses indicated that there is a common belief that when these tools are employed, students' success will increase. Students verified that the use of educational technologies makes them to feel more successful. Instructors stated that such tools create more organized learning and alert instructor to search for best tools for students, and let course materials accessible whenever students need. Instructors stated that although there are number of factors impeding the whole utilization of ICT tools, they agree that traditional teaching is old fashioned and ineffective in these days. Based on the responses obtained, we can state that instructors lack in explaining and evaluating carefully the impact of ICT tools that may enhance or support students' in-depth learning. Their statements are generally anecdotal rather than data driven. Also, lack of motivation among faculty members due to time restrictions was perceived as obstacle to adopting ICT fully.

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