13 results on '"Genel, Ömer Ekim"'
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2. Analysis of the Friction Impact on the Performance of the Linear Quadratic Regulator Controller Applied to the Multibody Model of the Furuta Pendulum
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Pappalardo, Carmine Maria, La Regina, Rosario, Genel, Ömer Ekim, Guida, Domenico, Ceccarelli, Marco, Series Editor, Corves, Burkhard, Advisory Editor, Glazunov, Victor, Advisory Editor, Hernández, Alfonso, Advisory Editor, Huang, Tian, Advisory Editor, Jauregui Correa, Juan Carlos, Advisory Editor, Takeda, Yukio, Advisory Editor, Agrawal, Sunil K., Advisory Editor, Ciulli, Enrico, editor, and Ruggiero, Alessandro, editor
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- 2024
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3. Axial–torsional coupled static behavior of inhomogeneous pretwisted cantilever beams
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Genel, Ömer Ekim and Tüfekci, Ekrem
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- 2023
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4. Performance Comparison of the Simscape Multibody Solvers for Articulated Mechanical Systems
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Genel, Ömer Ekim, La Regina, Rosario, Pappalardo, Carmine Maria, Kacprzyk, Janusz, Series Editor, Gomide, Fernando, Advisory Editor, Kaynak, Okyay, Advisory Editor, Liu, Derong, Advisory Editor, Pedrycz, Witold, Advisory Editor, Polycarpou, Marios M., Advisory Editor, Rudas, Imre J., Advisory Editor, Wang, Jun, Advisory Editor, Karabegovic, Isak, editor, Kovačević, Ahmed, editor, and Mandzuka, Sadko, editor
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- 2023
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5. Performance Comparison of the Simscape Multibody Solvers for Articulated Mechanical Systems
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Genel, Ömer Ekim, primary, La Regina, Rosario, additional, and Pappalardo, Carmine Maria, additional
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- 2023
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6. Bending-bending coupled static analysis of functionally graded and porous pretwisted cantilever beams using initial values method.
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Genel, Ömer Ekim and Tüfekci, Ekrem
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MATRIX exponential , *CURVILINEAR coordinates , *CANTILEVERS , *FINITE element method , *POWER law (Mathematics) - Abstract
In this study, the bending-bending coupled static behavior of functionally graded and porous pretwisted cantilever Timoshenko beams is reported. Symmetric power-law distribution is employed as the material profile and it is assumed that porosity can disperse over the cross-section in two forms namely, even and uneven distributions. Two different yet equivalent forms of governing equations are obtained by formulating the problem in the fixed and curvilinear coordinate systems, respectively. The initial values method is adopted as the solution methodology. While the fundamental matrix is computed numerically by using the multiplicative integral of Volterra to obtain the solution in the fixed coordinate formulation, the matrix exponential which allows for obtaining exact expressions is utilized in the curvilinear coordinate formulation. Exact analytical deflection expressions are presented for space-fixed vertical tip force and body-fixed uniform distributed force cases. It is shown that both formulation approaches yield consistent results with each other and those obtained from the finite element analyses. In addition, several parametric studies that investigate the effects of the volume fraction index, porosity coefficient, and porosity distribution on the tip deflections are presented. [ABSTRACT FROM AUTHOR]
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- 2024
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7. Free vibrations of spatial frame structures: Analytical modelling and solution.
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Genel, Ömer Ekim, Tüfekci, Mertol, and Tüfekci, Ekrem
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ANALYTICAL solutions , *STRUCTURAL frames , *FREE vibration , *SHEAR (Mechanics) , *FINITE element method - Abstract
This study analytically handles the three-dimensional free vibrations of spatial frames using the initial values method, considering the axial and shear deformations alongside rotary inertias, namely, torsional, in-plane bending and out-of-plane bending. To handle the spatial geometry, the direction cosine matrices are used. Validation is performed with three cases in total, one case available in the literature alongside two numerical examples that are solved analytically and compared to the finite element models. Excellent agreements are found between the analytical results and the results in the literature, as well as those obtained from the finite element models. [ABSTRACT FROM AUTHOR]
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- 2023
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8. Analysis of the dynamical behaviour of spinning annular disks with various boundary conditions.
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Koç, Hilal, Genel, Ömer Ekim, Tüfekci, Mertol, and Tüfekci, Ekrem
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BEHAVIORAL assessment , *GALERKIN methods , *FINITE element method , *STRESS concentration , *STRUCTURAL dynamics - Abstract
This study investigates the vibration characteristics of spinning annular disks with various boundary conditions aiming to investigate the effect of radius ratio parameter and the rotation speed on natural frequencies of a spinning disk analytically for nine different types of boundary conditions. The stress distributions on the disks are obtained for all boundary conditions. The Galerkin method is employed with polynomial functions as approximate displacement functions. Analytical results are presented and compared to the results of the finite element analyses as well as experimental ones. [ABSTRACT FROM AUTHOR]
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- 2023
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9. Bending-bending coupled static analysis of functionally graded and porous pretwisted cantilever beams using initial values method
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Genel, Ömer Ekim, primary and Tüfekci, Ekrem, additional
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- 2023
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10. Free vibrations of spatial frame structures: Analytical modelling and solution
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Genel, Ömer Ekim, primary, Tüfekci, Mertol, additional, and Tüfekci, Ekrem, additional
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- 2022
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11. Analysis of the dynamical behaviour of spinning annular disks with various boundary conditions
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Koç, Hilal, primary, Genel, Ömer Ekim, additional, Tüfekci, Mertol, additional, and Tüfekci, Ekrem, additional
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- 2021
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12. Dynamic Analysis of Composite Wind Turbine Blades as Beams: An Analytical and Numerical Study
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Tüfekci, Mertol, primary, Genel, Ömer Ekim, additional, Tatar, Ali, additional, and Tüfekci, Ekrem, additional
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- 2020
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13. Nanoteknolojide eğri eksenli çubukların düzlem içi davranışları için bir sonlu eleman formülasyonu
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Genel, Ömer Ekim, Tüfekci, Ekrem, and Makine Mühendisliği Ana Bilim Dalı
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Mechanical Engineering ,Makine Mühendisliği - Abstract
Nanoteknoloji, özellikle son yıllarda hayatımızın her alanında kendine yer bulmaktadır. Bu araştırma alanının gelişmesi sayesinde, geleneksel malzemelere kıyasla fiziksel, kimyasal ve elektriksel yönlerden daha üstün davranış gösteren malzemeler geliştirilmiştir. En iyi bilinen örnekleri karbon nanotüp ve grafen levha olan bu üstün nitelikli malzemelerin mekanik özelliklerinin tespitine ve bu malzemelerden yapılan mühendislik yapılarının tasarımına günümüzde sıklıkla ihtiyaç duyulmaktadır. Bu sebeple, malzemelerin ve yapıların nano ölçekte davranışlarını inceleyen nanomekanik adı verilen bir çalışma alanı ortaya çıkmıştır. Mühendislik yapılarının tasarımında ve modellenmesinde sıklıkla kullanılan yapısal elemanlardan olan çubuklar, nano ölçekteki yapılarda da kullanılmaktadır ve nanomekaniğin ana inceleme konularından birini oluşturmaktadırlar. Ana olarak makina mühendisliğinin uygulama sahasına giren bu yapıların mühendisler tarafından statik ve dinamik analizinin yapılması önem arz etmektedir. Genellikle klasik (yerel) elastisite teorisinin kullanıldığı çalışmalarda, atomlar arasındaki boşlukların etkilerinin ihmal edilebilecek kadar az olduğu kabul edilmektedir. Ancak, çalışma ölçeğinin nanometre mertebelerine inmesiyle, bu boşlukların etkisi artık göz ardı edilemeyecek seviyelere çıkmaktadır. Böyle durumlarda, boşlukların etkisini ihmal eden klasik (yerel) elastisite teorisinin yerine yerel olmayan elastisite teorisinin kullanılması daha doğru sonuçlar vermektedir. Bu çalışmada, eksenel uzama, kayma deformasyonu ve dönme eylemsizliği etkilerini dikkate alan eğri eksenli Timoshenko nanoçubuklarının, düzlem içi statik ve dinamik davranışlarının analizi için yerel olmayan elastisite teorisi kullanılarak elde edilmiş kesin analitik çözümlere dayalı bir sonlu eleman formülasyonu geliştirilmiştir. Yukarıda değinilen kapsamıyla bir ilk olma özelliği taşıyan bu formülasyonda, yerel olmayan elastisite teorisi ile elde edilmiş kesin analitik çözümlerinden hareketle katılık (rijitlik) ve kütle matrisleri elde edilmiştir. Geliştirilen sonlu eleman formülasyonundan elde edilen sonuçlar, literatürdeki çalışmalarla karşılaştırılmıştır. Bu bağlamda, birinci bölüm, nanoçubukların günümüz mühendislik bilimi içerisindeki yerine ve uygulama alanlarına dair bilgileri, gerçekleştirilen tezin amacını ve kapsamını içermektedir. İkinci bölümde, nispeten yakın bir geçmişe sahip olan nanoçubuklar hakkında bir literatür araştırması sunmaktadır. Literatür araştırması, nanoçubukların statik ve dinamik davranışlarını yerel olmayan elastisite teorisi ile inceleyen çalışmalar kapsamıyla sınırlı tutulmuştur. Gerçekteştirilen literatür araştırması, analitik ve sonlu eleman yaklaşımları olmak üzere iki alt grup olarak sunulmuştur. Üçüncü bölümde, bu çalışmaya temel teşkil eden, nanoçubukları yerel olmayan elastisite teorisi perspektifiyle inceleyen analitik yaklaşıma yer verilmiştir. Bu bölümde, yerel ve yerel olmayan elastisite teorileri arasındaki ilişkilere, varsayımlara ve kesin analitik çözümü elde etmek için başlangıç değerleri yönteminin kullanımına değinilmiştir. Bu bölümde açık ifadeleri verilen yer değiştirme alanları, bir sonraki bölümde şekil fonksiyonları olarak kullanılmıştır. Dördüncü bölüm, şekil fonksiyonu olarak kesin analitik çözümleri kullanan bir sonlu eleman formülasyonu sunmaktadır. Bu bölümde, rijitlik matrisi, ilk olarak literatürde `direkt metot (direct method)` olarak geçen yöntemle formüle edilmiştir. Ardından, kütle matrisi, dönme eylemsizliğinin göz önünde bulundurulduğu durum için formüle edilmiştir. Son olarak, elde edilmiş rijitlik ve kütle matrislerinin, Hamilton Prensibi olarak adlandırılan varyasyonel yaklaşımla da elde edilebileceği gösterilmiştir. Beşinci bölümde, geliştirilen sonlu eleman formülasyonu, sayısal örneklerle doğrulanmıştır. Literatürdeki statik ve dinamik örnekleri içeren bu bölümde, sonlu eleman yaklaşımıyla elde edilen sonuçlar, analitik ve sayısal çalışmalarla karşılaştırılmıştır. Altıncı bölümde genel bir değerlendirme yapılmış ve gelecek çalışmalar için çeşitli önerilerde bulunulmuştur. Yapılan bu çalışmanın, eğri eksenli nanoçubuklar ile ilgili yapılacak çalışmaların gelişmesine katkı sağlayacağına ve önerdiği formülasyon sayesinde bu çubukların statik ve dinamik davranışının incelenmesini içeren tasarım süresinin kısaltılmasına önemli ölçüde yardımcı olacağı düşünülmektedir. Nanotechnology takes wider place in our life especially in recent years. Thanks to development of that research field, better materials were developed in terms of physical, chemical and electrical aspects when compared to conventional ones. Most well-known examples of these advanced materials are carbon nanotubes and graphene sheets and determining mechanical properties of these new materials and designing engineering structures which are made of them is frequently needed. Therefore, nanomechanics, a new research area which studies behaviours of materials and structures in nano-scale, is emerged. Beams, which are frequently used in designing and modelling of engineering structures, are also used in nano-scale structures and they are considered as one of the fundamental research topics of nanomechanics. Mainly, these structures belong to mechanical engineering application field and static and dynamic analyses of them are essential. It is observed that most of studies in the literature are related with nanobeams which have curved axis. However, due to design purposes and having some difficulties in manufacturing processes to produce an exact straight beam, investigating static and dynamic properties of curved beams is significant. In the literature, there are three main approaches to investigate mechanical behaviours of nanobeams: molecular dynamics simulations, hybrid and continuum mechanics approaches. The first one uses potential energies between atoms and integrates them into equations of motion. However, due to dealing with large-scale matrices, this approach is considered computationally expensive. Hybrid approach is an approach that combines molecular dynamic simulations and continuum mechanics approaches. Nonetheless, this approach is directly linked to advances in computational chemistry research field. Unlike previous approaches, continuum mechanics approach requires less computational effort and is considered as more independent field. Also, it can present more analytical models. This approach separates into two subareas for nanobeams: local and nonlocal theories of elasticity. It is generally accepted that in the classical (local) theory of elasticity, effects of gaps between atoms are negligible. However, by narrowing our working scale into nanometer levels, effects of these gaps can not be ignored anymore. In that case, using the nonlocal theory of elasticity provides more accurate results rather than classical theory of elasticity which neglects effects of gaps between atoms.In this study, developing a new finite element formulation based on exact analytical solutions obtained from nonlocal theory of elasticity for in-plane static and dynamic analyses of curved nanobeams which take into consideration of axial extension, shear deformation and rotatory inertia effects is aimed. Within the scope of mentioned content, this formulation is considered as the first study in that area in the literature and stiffness and mass matrices are obtained from exact analytical solutions based on nonlocal theory of elasticity. Accomplished results from developed finite element formulation are compared with those given in the literature. In this sense, in the first chapter, informations about the place of nanobeams in current engineering sciences and their application fields, aim and content of this thesis are presented. The second chapter includes a literature survey about nanobeams in order to give relatively short history. The content of survey is limited to studies which investigate statics and dynamics of nanobeams by using nonlocal theory of elasticity. Presented survey consists of two subgroups; analytical and finite element approaches. In addition to studies which investigate only static and dynamic behaviours of nanobeams, other studies which are also contain buckling behaviour, nonlinear vibrations, cracked beams and mixed approach are also examined. It is observed that there are relatively small number of studies which deal with finite element formulation of nanobeams in the literature than analytical studies. Moreover, it can be also stated that there are very few studies which investigate mechanical behaviours of curved nanobeams. In the third chapter, theoretical basis of this study, the analytical approach which investigates in-plane behaviour of nanobeams by using nonlocal theory of elasticity is presented. This chapter includes relations between local and nonlocal theories of elasticity, assumptions and usage of initial values method which is used to obtain the exact analytical solutions. Explicit displacement fields, which are obtained in that chapter, are used as shape functions in following chapter. The fourth chapter presents a finite element formulation which uses exact analytical solutions as shape functions. In that chapter, stiffness matrix is formulated by using direct method, a well-known method in the literature. Then, the mass matrix is obtained also by considering rotatory inertia. Finally, it is shown that these stiffness and mass matrices can also be obtained by using Hamilton's Principle, a variational approach. In the formulation of mass matrix, Mindlin's kinetic energy formulation is utilized. This formulation expresses kinetic energy as a summation of macrostructure and microstructre effects. The first term, which corresponds to macrostructure effect, is the classical kinetic energy formulation which uses time derivatives of local nodal displacements. However, the second term, which corresponds to microstructure effect, uses time derivatives of gradients of local nodal displacements. After formulation of element stiffness and mass matrices, under harmonic vibrations assumption, eigenvalue problem can be built.In the fifth chapter, developed finite element formulation is validated with numerical examples. This chapter contains both static and vibration problems from the literature, and obtained results by using presented finite element approach are compared with those given in the literature. In static problems, there are three examples. The first and the second ones investigate static behaviours of circular clamped-free nanobeams under a tip force with 90° and 180° opening angles, respectively. Due to having only one region, both problems are solved by using one element. In these examples, curvature value is taken 5? and aspect ratio values are taken as 20 and 30, respectively. In the third static example, a nanoring under two normal forces is analyzed. It is solved by using two elements because of having two region and the model is built as a half model. In that example, curvature and aspect ratio values are taken 5? and 50. All static examples are compared with the literature and results are discussed. In dynamic problems, there are two examples. In the first dynamic example, under clamped-clamped boundary conditions, the curvature of a nanobeam which has 60° opening angle is changed for a constant nonlocal parameter value and dimensionless frequencies are calculated. A mesh convergence study is performed and minimum number of elements is determined as 10 in order to be able to perform a reliable analysis. Then, the analysis is performed and results which are obtained by using developed finite element formulation are compared with analytical results. It is observed that for increasing values of small scale parameter, ??⁄, dimensionless frequencies, which are obtained by using nonlocal theory of elasticity, converges to a constant value asymptotically. That constant value is the dimensionless frequency value which is obtained by using local theory of elasticity. In the second dynamic example, nonlocal parameter values are changed for a nanobeam which has clamped-clamped boundary conditions. For 30° and 120° opening angle values, variations of first and second dimensionless frequencies are investigated for different nonlocal parameter values. In that example, aspect ratio values are taken as 5 and 50. Obtained results are compared with the literature and effects of aspect ratio and nonlocal parameter values on dimensionless frequencies are also discussed. It is observed that for increasing values of nonlocal parameter, dimensionless frequencies are decreasing. Obtained results are in well agreement with SIN shear deformation theory based beam model in the literature for both first and second dimensionless frequencies. In the last chapter, a general evaluation is performed and some recommendations are discussed for the future studies. It is believed that the presented study will be instructive for the future studies about curved nanobeams and thanks to recommended formulation, design processes of nanobeams which include static and dynamic analyses can be shortened significantly. 85
- Published
- 2018
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