Cihan Demir - Academia.edu (original) (raw)

Papers by Cihan Demir

Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca

PURPOSE OF THE STUDY In this study, our aim is to examine the effect of proximal fibular osteotom... more PURPOSE OF THE STUDY In this study, our aim is to examine the effect of proximal fibular osteotomy on knee and ankle kinematics with finite element analysis method. MATERIAL AND METHODS One 62-year-old, female volunteer's radiologic images were used for creating lower limb model. Osteotomized model (OM) which was created according to definition of PFO and non-osteotomized model (NOM) were created. To obtain a stress distribution comparison between the two models, 350 N of axial force was applied to the femoral heads of the models. RESULTS After PFO, the average contact pressure decreased 26.1% at the medial tibial cartilage and increased 42.4% at the lateral tibial cartilage. The Von Mises stresses decreased 57.1% at the femoral cartilage and decreased 79.1% at tibial cartilage. The stress on the tibial cartilage increased 44.6%, and stress on the talar cartilage increased 7.1% at the ankle joint. CONCLUSIONS FEA revealed that main loading at the knee joint shifted from medial tibial cartilage to the lateral tibial cartilage after PFO. Additionally, the stresses on each cartilage were redistributed across a wider and more peripheral area. FEA also demonstrated that the Von Mises stresses of the tibial and talar cartilages of the ankle joint increased after PFO.

The International Journal of Acoustics and Vibration

The frequency parameters of an Axially Functionally Graded (AFG) bar for viscoelastic and point m... more The frequency parameters of an Axially Functionally Graded (AFG) bar for viscoelastic and point mass boundary conditions are studied in this paper. The structures with functionally graded materials under axial loads can be modelled as AFG bars. Those may be considered as support elements with spring and dashpot in the vibration isolation. Keeping the ratio of force frequency and natural frequency at a certain level is ensured to control the natural frequency therefore dynamic amplification factor with different material combinations. Various boundary conditions are attained by changing the spring and damping coefficients of viscoelastic support elements and the ratio of rod mass to tip mass. Researchers assume that the beam material properties in directions of length and thickness change exponentially, individually, or both in their studies. There are a few studies on the AFG rods in the existing studies. Analysis is carried out via the finite element method for the non-dimensional ...

Machines

This study consists of constructing and analyzing gear mathematical models of torque split system... more This study consists of constructing and analyzing gear mathematical models of torque split systems for contact pressure distribution and dynamic transmission error at different gear positions concerning phase angles. According to the method specified in the AGMA 927 standard, load distribution is calculated by considering shaft torsion and bending deformations. Partial contact loss may occur as a result of shaft bending with asymmetric gear positioning on a long shaft. The contact separation can be decreased by reaction force balancing if the driven gears are in the opposite position with respect to the drive gear. In the calculation of the dynamic transmission error of the torque split model, a parametric phase difference for the gear positions is proposed using gear geometry parameters. The variation of the dynamic response according to the change in the parametric phase angle in the torque split system is analyzed for the same values of each gear. Small changes in the phase value...

International Journal of Physical Sciences, Apr 18, 2011

The fundamental frequencies of plate are important for engineering designs. Free vibration charac... more The fundamental frequencies of plate are important for engineering designs. Free vibration characteristics of isotropic rectangular plates with point, spring and viscoelastic supports have been studied by several researchers. However, the practical implementation of these boundary conditions in application is not at all trivial. In this study, the effects of the size of the support hole area on the fundamental frequencies of the plate have been analyzed numerically and experimentally. The process involves numerical modeling using finite elements and ANSYS software is used for the analysis of plates. It has advantages such as simplicity in use, applicability to various boundary conditions which solution is not available analytically. The convergence analysis and the analysis for comparison purposes are carried out for the elastic and point supported boundary conditions. For the rigid point supported plate with the specified size of the support area, the experimental study has been conducted and its results compared with the numerical results. The results show that the effects of support size might be considered in engineering vibration analysis of point supported plates.

Computer Methods in Biomechanics and Biomedical Engineering, 2021

The study aimed to evaluate the effects of fibers insertion and restorative material type on the ... more The study aimed to evaluate the effects of fibers insertion and restorative material type on the stress distribution in endocrowns with finite element analysis. Five 3D models of first mandibular molars were created and restored as follows: (1) IN: intact tooth, (2) IPS-E: tooth restored with lithium disilicat ceramic endocrowns, (3) C-E: tooth restored with composite endocrowns, (4) IPS-E + F: lithium disilicate ceramic endocrowns + fiber, (5) C-E + F: composite endocrowns + fiber. Vertical masticatory load was imitated with finite element analysis. The equivalent stress of von Mises failure criterion (mvM) was calculated. The maximum mvM stress, enamel/crown, dentin and cement were compared among models and strength of the materials. Endocrowns presented a lower mvM stress level than intact tooth. In IPS-E, the mvM stress values in the crown and dentin were higher than C-E, while the mvM stress values in cement were higher in C-E group. Fibers insertion did not affect the stress level of IPS-E and C-E groups. In IPS model, fiber showed more stress absorption than C-E. The restorative material type changed the stress distribution of endocrown restorations. The fiber application did not affect the stress distribution in either endocrown group. But, more stress absorption was observed in fiber under IPS-E than C-E.

Best to our knowledge, six-wheeled vehicles have better driving conditions and performance criter... more Best to our knowledge, six-wheeled vehicles have better driving conditions and performance criteria as compared to four-wheeled vehicles, especially for the use of military. Although, the six-wheeled vehicles have better features, in literature, there has been no dynamic analysis carried out on those vehicles. Generally, dynamic analysis of four-wheeled vehicle has been undertaken. In this work, the six-wheeled vehicle was modeled by using discrete mass, dashpot and spring, as 3 and 9 degree-of-freedom (DOF) systems that considered vehicle with / without suspension system. The vehicle model was constructed into a simulation tool so that input/output and vehicle parameters could be changed easily using the modulated approach. In the experimental studies, the excitation with an electrodynamic shaker driven by a sinusoidal signal were used to measure the frequency response of the system (sine-swept method). Vibration measurements were taken by B and K 2515 vibration analyzer. The resul...

Calculation of resonance frequencies of a six-wheeled vehicle has been proposed in this work by m... more Calculation of resonance frequencies of a six-wheeled vehicle has been proposed in this work by means of computational and experimental methods. In modelling vehicle, elastic body and rigid body tecniques were used in computational methods. Therefore a three ? dimensional finite element model was generated using beam elements and shell elements. The components of the experiment vehicle such as gas tank, main engine etc. have been modelled as lumped masses on original location at experiment vehicle. The other approache in modelling of vehicle is discrete mass model as rigid body. Tires were modelled as spring and dashpot elements. Impulse excitation using a hammer as well as the excitation with an electrodynamic shaker driven by a sinusoidal signal were used to measure the frequency response of the system. Vibration measurements were taken from several places (driver seat location etc.) by B and K 2515 vibration analyser. Finally, the results obtained from experiment were compared wi...

Sakarya University Journal of Science, 2017

Bu calismada farkli caplara sahip farkli tiplerdeki tek helis acisina sahip on gerilmeli monotron... more Bu calismada farkli caplara sahip farkli tiplerdeki tek helis acisina sahip on gerilmeli monotron halatlarin dogal frekans analizi teorik ve deneysel olarak yapilmistir. Teorik analizde daha once cikartilmis analitik formullerden yararlanilmistir. Bununla birlikte halat kati modeli olusturularak sonlu elemanlar yontemi ile dogal frekans analizi yapilmistir. Deneysel calismada, on gerilmeli kablonun basit mesnetli sinir sartlari olusturularak cesitli yukler altinda darbe cekici ile dogal frekans analizi gerceklestirilmistir. Deneysel ve teorik analizlerin sonuclari degerlendirilerek, halat dogal frekansinin uygulanan on gerilme kuvveti altinda, halat capina ve tel sayisina bagli olarak nasil degistigi incelenmistir.

SAÜ Fen Bilimleri Enstitüsü Dergisi, 2017

Bu çalışmada farklı çaplara sahip farklı tiplerdeki tek helis açısına sahip ön gerilmeli monotron... more Bu çalışmada farklı çaplara sahip farklı tiplerdeki tek helis açısına sahip ön gerilmeli monotron halatların doğal frekans analizi teorik ve deneysel olarak yapılmıştır. Teorik analizde daha önce çıkartılmış analitik formüllerden yararlanılmıştır. Bununla birlikte halat katı modeli oluşturularak sonlu elemanlar yöntemi ile doğal frekans analizi yapılmıştır. Deneysel çalışmada, ön gerilmeli kablonun basit mesnetli sınır şartları oluşturularak çeşitli yükler altında darbe çekici ile doğal frekans analizi gerçekleştirilmiştir. Deneysel ve teorik analizlerin sonuçları değerlendirilerek, halat doğal frekansının uygulanan ön gerilme kuvveti altında, halat çapına ve tel sayısına bağlı olarak nasıl değiştiği incelenmiştir.

INTERNATIONAL JOURNAL OF ADVANCES ON AUTOMOTIVE AND TECHNOLOGY, 2017

In scope of this study, main parameters of cam profile are determined. Also, their effects on cam... more In scope of this study, main parameters of cam profile are determined. Also, their effects on cam performance are examined starting with valve lift, velocity, acceleration curve. In order to be seen clearly cam behavior and obtain to needed smooth curve thanks to less jerk of cam follower, different valve lifts are calculated but more importantly one of the most critical design criteria on cam profile, acceleration jump as undesired influence, is investigated how to reduce & avoid. Primarily, relations related base circle & nose radius of cam profile, maximum lift of cam follower, lift angle of cam follower and acceleration jump are considered in terms of minimum acceleration jump, continuous contact, valve spring force & contact force-stress. Especially, determination of right valve spring stiffness is significant & affects other main parameters so it is plotted graphs of sudden acceleration change and described how it should be analyzed by analytical & using Matlab. .

Engineering Structures, 2017

The paper deals with the seismic behavior and retrofitting of a historical masonry building calle... more The paper deals with the seismic behavior and retrofitting of a historical masonry building called Treasury Building of Hagia Sophia (Skeuophylakion: a building where eucharistic elements were collected and prepared for services) which has experienced lots of earthquakes since it was constructed in 361 and suffered structural damage since then. A detailed finite element (FE) model of the treasure building was created based on the elaborate technical drawings of the structure. A macro modeling approach was adopted and equivalent material parameters were obtained from in-situ tests and the calibration of the FE model was used as the input of the model. Four different models were created considering both the physical and the geometrical nonlinearities in order to understand the seismic behavior of the existing structure and also to account for several retrofit effects on the seismic behavior of the structure. The treasure building was analyzed under very strong earthquake ground motions it might have been exposed during its life time to understand its response and the cause of the observed manner and paths of the observed cracks. It was found out that the plastic strain distribution obtained from the seismic analyses of the first two models and those of the significant cracks observed in situ on the dome and at the tips of arcs are completely compatible. Hence, it was concluded that these cracks are due to the earthquakes occurred until now. The results of seismic analysis of the third and fourth models show that the use of belts (rings) at the location close to the top elevation of arches of windows for retrofitting the structure improves the performance and seismic behavior of the structure considerably.

Advanced Materials Research, 2012

The dynamic behavior of plates with mixed boundary conditions has been the subject of intensive s... more The dynamic behavior of plates with mixed boundary conditions has been the subject of intensive study for many years due to its great importance in many engineering applications. On-trend approach in dynamic response analysis is to combine mathematical model, test results and computer simulation. Classical techniques of mathematical modeling of intricate structural systems for response analysis in frequency or time domain are tiresome and time consuming. In this study, a point supported rectangular plate considered and extraction of its system model from FE model, validated by the test results, by using commercially available computer programs such as Ansys and Matlab is demonstrated. State space mathematical model in principal coordinates obtained in Matlab from the modal analysis results of its FE model. Its modes sorted with respect to peak gain values, and the modes with the less contributions to the response truncated. To validate the accuracy of this method and truncation, tra...

Applied Ocean Research, 2021

Abstract It is a fact that specifying numerically the natural frequencies of a marine propeller r... more Abstract It is a fact that specifying numerically the natural frequencies of a marine propeller rotating in a water environment is quite difficult due to the problem that arises from the inability to consider the effect of rotation and pressure distribution in the modal acoustic module of the software. In the present study, an alternative approach to the experimental studies is proposed to come through this problem that enables researchers to predict numerically the change in natural frequency of a three-bladed marine propeller. The method based on the fluid-structure interaction (FSI) technique uses the modal stiffness and the modal mass that is calculated from the numerical analysis of a rotating marine propeller in air and then considers the effects of the added mass by utilizing the frequency reduction ratio (FRR) and finally defines the natural frequencies of the rotating propeller in the water. The simulations revealed that the natural frequencies of the propeller decrease substantially in water due to the added mass and the reduction in the natural frequencies with respect to frequencies in the air is 28% for the first, 34% for the second, and the third. Since natural frequencies of a rotating propeller in water cannot be simulated the equivalent stiffness and masses were defined for each frequency from the analyses of propeller rotating in the air. It was concluded that the natural frequency of the propeller decreases when the propeller is placed in water for the same boundary conditions.

Sakarya University Journal of Science, 2018

Bu çalışmada, mobilya sektöründe sıklıkla kullanılan menteşe çeşitlerinden düz frenli tas menteşe... more Bu çalışmada, mobilya sektöründe sıklıkla kullanılan menteşe çeşitlerinden düz frenli tas menteşelerin kinematik, statik ve yorulma analizleri yapılmıştır. Bu kapsamda menteşenin katı modellenmesi paket program kullanılarak yapılmıştır. Menteşe kinetik ve kinematik analizi, çok parçalı gövde analizi programı ile yapılmıştır. Bu analizden elde edilen yatak ve mafsal kuvvetleri kullanılarak, yapının sankistatik analizi için sonlu elemanlar programı kullanılmıştır. Analizler TS EN 15570 standardı göz önüne alınarak yapılmıştır. Yorulma analizi değerlendirmeleri ile yapıda değişiklikler önerilmiştir. Sistem için, çok parçalı gövde analiz programı ile yapılan kinematik ve kinetik analiz sonuçlarının, sonlu elemanlar yöntemi ile statik ve yorulma analizinde kullanılması, sonlu elemanlar programı geçici cevap analizine alternatif olarak gösterilmiştir.

The International Journal of Acoustics and Vibration

The harmonic response and resonance frequency behavior of the spring supported FGM beam against t... more The harmonic response and resonance frequency behavior of the spring supported FGM beam against the lateral motion for the various values of support stiffness at the ends are analyzed by using the force transmissibility parameter with the finite-element method and Lagrange's equations. The steady-state responses to a sinusoidal varying force are determined for the support reactions in a frequency domain. The problem is solved within the framework of the Timoshenko beam theory. For the convergence study, some of the results are compared with previous works' values, and a good agreement can be seen. The study concludes that the support stiffness, volume fraction coefficient and the ratio of young module level all strongly affect the natural frequencies and the force transmissibility. For some values of spring stiffness of support, the rigid body motion of the beam occurs and reduces the effect of volume fraction coefficient on the natural frequencies.

Sakarya University Journal of Science

Acta chirurgiae orthopaedicae et traumatologiae Cechoslovaca

PURPOSE OF THE STUDY In this study, our aim is to examine the effect of proximal fibular osteotom... more PURPOSE OF THE STUDY In this study, our aim is to examine the effect of proximal fibular osteotomy on knee and ankle kinematics with finite element analysis method. MATERIAL AND METHODS One 62-year-old, female volunteer's radiologic images were used for creating lower limb model. Osteotomized model (OM) which was created according to definition of PFO and non-osteotomized model (NOM) were created. To obtain a stress distribution comparison between the two models, 350 N of axial force was applied to the femoral heads of the models. RESULTS After PFO, the average contact pressure decreased 26.1% at the medial tibial cartilage and increased 42.4% at the lateral tibial cartilage. The Von Mises stresses decreased 57.1% at the femoral cartilage and decreased 79.1% at tibial cartilage. The stress on the tibial cartilage increased 44.6%, and stress on the talar cartilage increased 7.1% at the ankle joint. CONCLUSIONS FEA revealed that main loading at the knee joint shifted from medial tibial cartilage to the lateral tibial cartilage after PFO. Additionally, the stresses on each cartilage were redistributed across a wider and more peripheral area. FEA also demonstrated that the Von Mises stresses of the tibial and talar cartilages of the ankle joint increased after PFO.

The International Journal of Acoustics and Vibration

The frequency parameters of an Axially Functionally Graded (AFG) bar for viscoelastic and point m... more The frequency parameters of an Axially Functionally Graded (AFG) bar for viscoelastic and point mass boundary conditions are studied in this paper. The structures with functionally graded materials under axial loads can be modelled as AFG bars. Those may be considered as support elements with spring and dashpot in the vibration isolation. Keeping the ratio of force frequency and natural frequency at a certain level is ensured to control the natural frequency therefore dynamic amplification factor with different material combinations. Various boundary conditions are attained by changing the spring and damping coefficients of viscoelastic support elements and the ratio of rod mass to tip mass. Researchers assume that the beam material properties in directions of length and thickness change exponentially, individually, or both in their studies. There are a few studies on the AFG rods in the existing studies. Analysis is carried out via the finite element method for the non-dimensional ...

Machines

This study consists of constructing and analyzing gear mathematical models of torque split system... more This study consists of constructing and analyzing gear mathematical models of torque split systems for contact pressure distribution and dynamic transmission error at different gear positions concerning phase angles. According to the method specified in the AGMA 927 standard, load distribution is calculated by considering shaft torsion and bending deformations. Partial contact loss may occur as a result of shaft bending with asymmetric gear positioning on a long shaft. The contact separation can be decreased by reaction force balancing if the driven gears are in the opposite position with respect to the drive gear. In the calculation of the dynamic transmission error of the torque split model, a parametric phase difference for the gear positions is proposed using gear geometry parameters. The variation of the dynamic response according to the change in the parametric phase angle in the torque split system is analyzed for the same values of each gear. Small changes in the phase value...

International Journal of Physical Sciences, Apr 18, 2011

The fundamental frequencies of plate are important for engineering designs. Free vibration charac... more The fundamental frequencies of plate are important for engineering designs. Free vibration characteristics of isotropic rectangular plates with point, spring and viscoelastic supports have been studied by several researchers. However, the practical implementation of these boundary conditions in application is not at all trivial. In this study, the effects of the size of the support hole area on the fundamental frequencies of the plate have been analyzed numerically and experimentally. The process involves numerical modeling using finite elements and ANSYS software is used for the analysis of plates. It has advantages such as simplicity in use, applicability to various boundary conditions which solution is not available analytically. The convergence analysis and the analysis for comparison purposes are carried out for the elastic and point supported boundary conditions. For the rigid point supported plate with the specified size of the support area, the experimental study has been conducted and its results compared with the numerical results. The results show that the effects of support size might be considered in engineering vibration analysis of point supported plates.

Computer Methods in Biomechanics and Biomedical Engineering, 2021

The study aimed to evaluate the effects of fibers insertion and restorative material type on the ... more The study aimed to evaluate the effects of fibers insertion and restorative material type on the stress distribution in endocrowns with finite element analysis. Five 3D models of first mandibular molars were created and restored as follows: (1) IN: intact tooth, (2) IPS-E: tooth restored with lithium disilicat ceramic endocrowns, (3) C-E: tooth restored with composite endocrowns, (4) IPS-E + F: lithium disilicate ceramic endocrowns + fiber, (5) C-E + F: composite endocrowns + fiber. Vertical masticatory load was imitated with finite element analysis. The equivalent stress of von Mises failure criterion (mvM) was calculated. The maximum mvM stress, enamel/crown, dentin and cement were compared among models and strength of the materials. Endocrowns presented a lower mvM stress level than intact tooth. In IPS-E, the mvM stress values in the crown and dentin were higher than C-E, while the mvM stress values in cement were higher in C-E group. Fibers insertion did not affect the stress level of IPS-E and C-E groups. In IPS model, fiber showed more stress absorption than C-E. The restorative material type changed the stress distribution of endocrown restorations. The fiber application did not affect the stress distribution in either endocrown group. But, more stress absorption was observed in fiber under IPS-E than C-E.

Best to our knowledge, six-wheeled vehicles have better driving conditions and performance criter... more Best to our knowledge, six-wheeled vehicles have better driving conditions and performance criteria as compared to four-wheeled vehicles, especially for the use of military. Although, the six-wheeled vehicles have better features, in literature, there has been no dynamic analysis carried out on those vehicles. Generally, dynamic analysis of four-wheeled vehicle has been undertaken. In this work, the six-wheeled vehicle was modeled by using discrete mass, dashpot and spring, as 3 and 9 degree-of-freedom (DOF) systems that considered vehicle with / without suspension system. The vehicle model was constructed into a simulation tool so that input/output and vehicle parameters could be changed easily using the modulated approach. In the experimental studies, the excitation with an electrodynamic shaker driven by a sinusoidal signal were used to measure the frequency response of the system (sine-swept method). Vibration measurements were taken by B and K 2515 vibration analyzer. The resul...

Calculation of resonance frequencies of a six-wheeled vehicle has been proposed in this work by m... more Calculation of resonance frequencies of a six-wheeled vehicle has been proposed in this work by means of computational and experimental methods. In modelling vehicle, elastic body and rigid body tecniques were used in computational methods. Therefore a three ? dimensional finite element model was generated using beam elements and shell elements. The components of the experiment vehicle such as gas tank, main engine etc. have been modelled as lumped masses on original location at experiment vehicle. The other approache in modelling of vehicle is discrete mass model as rigid body. Tires were modelled as spring and dashpot elements. Impulse excitation using a hammer as well as the excitation with an electrodynamic shaker driven by a sinusoidal signal were used to measure the frequency response of the system. Vibration measurements were taken from several places (driver seat location etc.) by B and K 2515 vibration analyser. Finally, the results obtained from experiment were compared wi...

Sakarya University Journal of Science, 2017

Bu calismada farkli caplara sahip farkli tiplerdeki tek helis acisina sahip on gerilmeli monotron... more Bu calismada farkli caplara sahip farkli tiplerdeki tek helis acisina sahip on gerilmeli monotron halatlarin dogal frekans analizi teorik ve deneysel olarak yapilmistir. Teorik analizde daha once cikartilmis analitik formullerden yararlanilmistir. Bununla birlikte halat kati modeli olusturularak sonlu elemanlar yontemi ile dogal frekans analizi yapilmistir. Deneysel calismada, on gerilmeli kablonun basit mesnetli sinir sartlari olusturularak cesitli yukler altinda darbe cekici ile dogal frekans analizi gerceklestirilmistir. Deneysel ve teorik analizlerin sonuclari degerlendirilerek, halat dogal frekansinin uygulanan on gerilme kuvveti altinda, halat capina ve tel sayisina bagli olarak nasil degistigi incelenmistir.

SAÜ Fen Bilimleri Enstitüsü Dergisi, 2017

Bu çalışmada farklı çaplara sahip farklı tiplerdeki tek helis açısına sahip ön gerilmeli monotron... more Bu çalışmada farklı çaplara sahip farklı tiplerdeki tek helis açısına sahip ön gerilmeli monotron halatların doğal frekans analizi teorik ve deneysel olarak yapılmıştır. Teorik analizde daha önce çıkartılmış analitik formüllerden yararlanılmıştır. Bununla birlikte halat katı modeli oluşturularak sonlu elemanlar yöntemi ile doğal frekans analizi yapılmıştır. Deneysel çalışmada, ön gerilmeli kablonun basit mesnetli sınır şartları oluşturularak çeşitli yükler altında darbe çekici ile doğal frekans analizi gerçekleştirilmiştir. Deneysel ve teorik analizlerin sonuçları değerlendirilerek, halat doğal frekansının uygulanan ön gerilme kuvveti altında, halat çapına ve tel sayısına bağlı olarak nasıl değiştiği incelenmiştir.

INTERNATIONAL JOURNAL OF ADVANCES ON AUTOMOTIVE AND TECHNOLOGY, 2017

In scope of this study, main parameters of cam profile are determined. Also, their effects on cam... more In scope of this study, main parameters of cam profile are determined. Also, their effects on cam performance are examined starting with valve lift, velocity, acceleration curve. In order to be seen clearly cam behavior and obtain to needed smooth curve thanks to less jerk of cam follower, different valve lifts are calculated but more importantly one of the most critical design criteria on cam profile, acceleration jump as undesired influence, is investigated how to reduce & avoid. Primarily, relations related base circle & nose radius of cam profile, maximum lift of cam follower, lift angle of cam follower and acceleration jump are considered in terms of minimum acceleration jump, continuous contact, valve spring force & contact force-stress. Especially, determination of right valve spring stiffness is significant & affects other main parameters so it is plotted graphs of sudden acceleration change and described how it should be analyzed by analytical & using Matlab. .

Engineering Structures, 2017

The paper deals with the seismic behavior and retrofitting of a historical masonry building calle... more The paper deals with the seismic behavior and retrofitting of a historical masonry building called Treasury Building of Hagia Sophia (Skeuophylakion: a building where eucharistic elements were collected and prepared for services) which has experienced lots of earthquakes since it was constructed in 361 and suffered structural damage since then. A detailed finite element (FE) model of the treasure building was created based on the elaborate technical drawings of the structure. A macro modeling approach was adopted and equivalent material parameters were obtained from in-situ tests and the calibration of the FE model was used as the input of the model. Four different models were created considering both the physical and the geometrical nonlinearities in order to understand the seismic behavior of the existing structure and also to account for several retrofit effects on the seismic behavior of the structure. The treasure building was analyzed under very strong earthquake ground motions it might have been exposed during its life time to understand its response and the cause of the observed manner and paths of the observed cracks. It was found out that the plastic strain distribution obtained from the seismic analyses of the first two models and those of the significant cracks observed in situ on the dome and at the tips of arcs are completely compatible. Hence, it was concluded that these cracks are due to the earthquakes occurred until now. The results of seismic analysis of the third and fourth models show that the use of belts (rings) at the location close to the top elevation of arches of windows for retrofitting the structure improves the performance and seismic behavior of the structure considerably.

Advanced Materials Research, 2012

The dynamic behavior of plates with mixed boundary conditions has been the subject of intensive s... more The dynamic behavior of plates with mixed boundary conditions has been the subject of intensive study for many years due to its great importance in many engineering applications. On-trend approach in dynamic response analysis is to combine mathematical model, test results and computer simulation. Classical techniques of mathematical modeling of intricate structural systems for response analysis in frequency or time domain are tiresome and time consuming. In this study, a point supported rectangular plate considered and extraction of its system model from FE model, validated by the test results, by using commercially available computer programs such as Ansys and Matlab is demonstrated. State space mathematical model in principal coordinates obtained in Matlab from the modal analysis results of its FE model. Its modes sorted with respect to peak gain values, and the modes with the less contributions to the response truncated. To validate the accuracy of this method and truncation, tra...

Applied Ocean Research, 2021

Abstract It is a fact that specifying numerically the natural frequencies of a marine propeller r... more Abstract It is a fact that specifying numerically the natural frequencies of a marine propeller rotating in a water environment is quite difficult due to the problem that arises from the inability to consider the effect of rotation and pressure distribution in the modal acoustic module of the software. In the present study, an alternative approach to the experimental studies is proposed to come through this problem that enables researchers to predict numerically the change in natural frequency of a three-bladed marine propeller. The method based on the fluid-structure interaction (FSI) technique uses the modal stiffness and the modal mass that is calculated from the numerical analysis of a rotating marine propeller in air and then considers the effects of the added mass by utilizing the frequency reduction ratio (FRR) and finally defines the natural frequencies of the rotating propeller in the water. The simulations revealed that the natural frequencies of the propeller decrease substantially in water due to the added mass and the reduction in the natural frequencies with respect to frequencies in the air is 28% for the first, 34% for the second, and the third. Since natural frequencies of a rotating propeller in water cannot be simulated the equivalent stiffness and masses were defined for each frequency from the analyses of propeller rotating in the air. It was concluded that the natural frequency of the propeller decreases when the propeller is placed in water for the same boundary conditions.

Sakarya University Journal of Science, 2018

Bu çalışmada, mobilya sektöründe sıklıkla kullanılan menteşe çeşitlerinden düz frenli tas menteşe... more Bu çalışmada, mobilya sektöründe sıklıkla kullanılan menteşe çeşitlerinden düz frenli tas menteşelerin kinematik, statik ve yorulma analizleri yapılmıştır. Bu kapsamda menteşenin katı modellenmesi paket program kullanılarak yapılmıştır. Menteşe kinetik ve kinematik analizi, çok parçalı gövde analizi programı ile yapılmıştır. Bu analizden elde edilen yatak ve mafsal kuvvetleri kullanılarak, yapının sankistatik analizi için sonlu elemanlar programı kullanılmıştır. Analizler TS EN 15570 standardı göz önüne alınarak yapılmıştır. Yorulma analizi değerlendirmeleri ile yapıda değişiklikler önerilmiştir. Sistem için, çok parçalı gövde analiz programı ile yapılan kinematik ve kinetik analiz sonuçlarının, sonlu elemanlar yöntemi ile statik ve yorulma analizinde kullanılması, sonlu elemanlar programı geçici cevap analizine alternatif olarak gösterilmiştir.

The International Journal of Acoustics and Vibration

The harmonic response and resonance frequency behavior of the spring supported FGM beam against t... more The harmonic response and resonance frequency behavior of the spring supported FGM beam against the lateral motion for the various values of support stiffness at the ends are analyzed by using the force transmissibility parameter with the finite-element method and Lagrange's equations. The steady-state responses to a sinusoidal varying force are determined for the support reactions in a frequency domain. The problem is solved within the framework of the Timoshenko beam theory. For the convergence study, some of the results are compared with previous works' values, and a good agreement can be seen. The study concludes that the support stiffness, volume fraction coefficient and the ratio of young module level all strongly affect the natural frequencies and the force transmissibility. For some values of spring stiffness of support, the rigid body motion of the beam occurs and reduces the effect of volume fraction coefficient on the natural frequencies.

Sakarya University Journal of Science