This study presents an experimental methodology to predict the tool-tip dynamics including rotati... more This study presents an experimental methodology to predict the tool-tip dynamics including rotational effects in micromachining. In this approach, the ultra-high-speed spindle dynamics (i.e. the FRF matrix at the spindle tip) at different spindle speeds are obtained experimentally. Since the modal test are performed on a rotating tool, measured response includes unwanted error motions as well as the dynamic response to the excitation. Therefore, a frequency domain filtering algorithm is designed to isolate the dynamic response. Then, the experimentally obtained spindle dynamics are coupled with the tool dynamics calculated using the spectral-Tchebychev technique to predict the tool-tip dynamics. The developed approach/methodology is demonstrated on a micro machine tool incorporating miniature ultra-high-speed spindles (with air bearings), and a tungsten carbide tool blank. The predicted tool-tip dynamics are validated by direct measurements; it is concluded that the presented unifie...
Osteoporosis is a metabolic bone disease that needs to be properly diagnosed. The current diagnos... more Osteoporosis is a metabolic bone disease that needs to be properly diagnosed. The current diagnosing procedure of osteoporosis is based on the mineral density of bones measured by common methods such as dual energy X-ray absorptiometry (DXA). However, due to the deficiencies and limitations of these common methods, investigations on the utilization of other non-invasive diagnosing methods have been executed. For instance, using vibration measurements seems to be a promising technique in diagnosing metabolic bone diseases such as osteoporosis and also in monitoring fracture healing. Throughout this study, bone structural modal parameters obtained from vibrations experiments with decreasing mineral density are examined and therefore, it is aimed to find a new approach to detect osteoporosis or progressing osteoporosis by investigating a relation between structural dynamic properties and mineral density of bone. The main advantage of this study is that loss factor, which is an inherit ...
International Journal of Advances in Engineering and Pure Sciences
Titreşim testi yapıların dinamik davranışlarının bulunmasında veya oluşturulan modellerin doğrula... more Titreşim testi yapıların dinamik davranışlarının bulunmasında veya oluşturulan modellerin doğrulanmasında kullanılan bir yöntemdir. Literatürde kullanım kolaylığı ve hızlı uygulanabilirliğinden dolayı en yaygın olarak darbe testinden yararlanılmaktadır. Bu testte yapıya ucunda bir kuvvet algılayıcısı olan bir darbe çekici ile kuvvet iletimi yapılmaktadır. Sistem dinamiklerinin doğru olarak elde edilmesi için darbenin kalitesi ve yinelenebilirliği büyük bir önem taşımaktadır. Bu çalışmada, yapıların/parçaların titreşim testlerinde kullanılmak üzere yeni otomatik bir darbe tahrik sistemi geliştirilmiştir. Bu kapsamda, özel yapım bir esnek darbe mekanizmasına bir kuvvet algılayıcısı bağlanarak kuvvet ölçümlerinin yapılması sağlanmıştır. Sistem otomasyonunun sağlanması amacıyla esnek darbe mekanizmasını belirli bir başlangıç konumuna getirecek elektromıknatıs tabanlı bir sistem entegrasyonu gerçekleştirilmiştir. Uygun darbe için gerekli kontrol parametrelerinin elde edilebilmesi için ta...
Abstract This paper presents a novel spectral element method to predict the electromechanical dyn... more Abstract This paper presents a novel spectral element method to predict the electromechanical dynamics of panels having arbitrary geometries and multiple surface-bonded piezo-patches. The boundary value problem is derived following kinematic equations based on first order shear deformation and the generalized Hamilton’s principle. To solve the derived boundary value problem, a spectral element method based on Chebyshev polynomials is developed. The method combines the flexibility of the finite element method and the accuracy of the meshless methods. Thus, it includes three main parts. First, the whole domain is divided into elements, and then the system matrices for each element is derived using spectral Chebyshev approach. Finally, the individual system matrices are assembled to construct the overall/global system matrices of the investigated structure. The spectral Chebyshev approach enables capturing the structural and electromechanical dynamic behaviour of structures having arbitrary geometries (using a cross-section mapping) and boundary conditions. To demonstrate the performance and validate the accuracy of the presented spectral element method, four case studies are investigated. In each case study, the predicted natural frequencies, structural and voltage FRFs are compared to those obtained from a finite element approach.
Composite materials are widely used in various industries because of their distinct properties. H... more Composite materials are widely used in various industries because of their distinct properties. Hybridization is an efficient way of designing composite panels to decrease the cost and/or weight while maintaining stiffness properties. In this study, an accurate and efficient framework is developed to optimize laminated sandwich panels composed of high-stiffness face sheets and low-stiffness core. The stiffness properties of face sheets and core are represented using lamination parameters. The governing equations are derived following first-order shear deformation theory and solved using the spectral Chebyshev approach. In multi-objective optimization problems, genetic algorithm is used to determine Pareto-optimal solutions for fundamental frequency, frequency gap, buckling load, and cost metrics. In these analyses, optimal lamination parameters and thickness are found for face-sheets and core of sandwich panels, and the results are presented as 2D and 3D Pareto-optimal design points. When the individual performance metrics lead to different optimum points, a scattering behavior is observed in the 3D Pareto sets whose boundaries are defined by the 2-objective Pareto fronts. The results provide insights into the design requirements for improving the dynamic and load-carrying behavior of sandwich laminates while minimizing the cost that presents the usability of the presented approach in the multi-objective optimization.
The purpose of the current study was to develop an accurate model to investigate the nonlinear re... more The purpose of the current study was to develop an accurate model to investigate the nonlinear resonances in an axially functionally graded beam rotating with time-dependent speed. To this end, two important features including stiffening and Coriolis effects are modeled based on nonlinear strain relations. Equations governing the axial, chordwise, and flapwise deformations about the determined steady-state equilibrium position are obtained, and the rotating speed variation is considered as a periodic disturbance about this equilibrium condition. Multi-mode discretization of the equations is performed via the spectral Chebyshev approach and the method of multiple scales for gyroscopic systems is employed to study the nonlinear behavior. After determining the required polynomial number based on convergence analysis, results obtained are verified by comparing to those found in literature and numerical simulations. Moreover, the model is validated based on simulations carried out by commercial finite element software. Properties of the functionally graded material and the values of average rotating speed leading to 2:1 internal resonance in the system are found. Time and steady-state responses of the system under primary and parametric resonances caused by the time-dependent rotating speed are investigated when the system is tuned to 2:1 internal resonance. A comprehensive study on the time response, frequency response, and stability behavior shows that the rotating axially functionally graded beam exhibits a complicated nonlinear behavior under the effect of the rotating speed fluctuation frequency, damping coefficient, and properties of the functionally graded material.
This study presents an experimental methodology to predict the tool-tip dynamics including rotati... more This study presents an experimental methodology to predict the tool-tip dynamics including rotational effects in micromachining. In this approach, the ultra-high-speed spindle dynamics (i.e. the FRF matrix at the spindle tip) at different spindle speeds are obtained experimentally. Since the modal test are performed on a rotating tool, measured response includes unwanted error motions as well as the dynamic response to the excitation. Therefore, a frequency domain filtering algorithm is designed to isolate the dynamic response. Then, the experimentally obtained spindle dynamics are coupled with the tool dynamics calculated using the spectral-Tchebychev technique to predict the tool-tip dynamics. The developed approach/methodology is demonstrated on a micro machine tool incorporating miniature ultra-high-speed spindles (with air bearings), and a tungsten carbide tool blank. The predicted tool-tip dynamics are validated by direct measurements; it is concluded that the presented unifie...
Osteoporosis is a metabolic bone disease that needs to be properly diagnosed. The current diagnos... more Osteoporosis is a metabolic bone disease that needs to be properly diagnosed. The current diagnosing procedure of osteoporosis is based on the mineral density of bones measured by common methods such as dual energy X-ray absorptiometry (DXA). However, due to the deficiencies and limitations of these common methods, investigations on the utilization of other non-invasive diagnosing methods have been executed. For instance, using vibration measurements seems to be a promising technique in diagnosing metabolic bone diseases such as osteoporosis and also in monitoring fracture healing. Throughout this study, bone structural modal parameters obtained from vibrations experiments with decreasing mineral density are examined and therefore, it is aimed to find a new approach to detect osteoporosis or progressing osteoporosis by investigating a relation between structural dynamic properties and mineral density of bone. The main advantage of this study is that loss factor, which is an inherit ...
International Journal of Advances in Engineering and Pure Sciences
Titreşim testi yapıların dinamik davranışlarının bulunmasında veya oluşturulan modellerin doğrula... more Titreşim testi yapıların dinamik davranışlarının bulunmasında veya oluşturulan modellerin doğrulanmasında kullanılan bir yöntemdir. Literatürde kullanım kolaylığı ve hızlı uygulanabilirliğinden dolayı en yaygın olarak darbe testinden yararlanılmaktadır. Bu testte yapıya ucunda bir kuvvet algılayıcısı olan bir darbe çekici ile kuvvet iletimi yapılmaktadır. Sistem dinamiklerinin doğru olarak elde edilmesi için darbenin kalitesi ve yinelenebilirliği büyük bir önem taşımaktadır. Bu çalışmada, yapıların/parçaların titreşim testlerinde kullanılmak üzere yeni otomatik bir darbe tahrik sistemi geliştirilmiştir. Bu kapsamda, özel yapım bir esnek darbe mekanizmasına bir kuvvet algılayıcısı bağlanarak kuvvet ölçümlerinin yapılması sağlanmıştır. Sistem otomasyonunun sağlanması amacıyla esnek darbe mekanizmasını belirli bir başlangıç konumuna getirecek elektromıknatıs tabanlı bir sistem entegrasyonu gerçekleştirilmiştir. Uygun darbe için gerekli kontrol parametrelerinin elde edilebilmesi için ta...
Abstract This paper presents a novel spectral element method to predict the electromechanical dyn... more Abstract This paper presents a novel spectral element method to predict the electromechanical dynamics of panels having arbitrary geometries and multiple surface-bonded piezo-patches. The boundary value problem is derived following kinematic equations based on first order shear deformation and the generalized Hamilton’s principle. To solve the derived boundary value problem, a spectral element method based on Chebyshev polynomials is developed. The method combines the flexibility of the finite element method and the accuracy of the meshless methods. Thus, it includes three main parts. First, the whole domain is divided into elements, and then the system matrices for each element is derived using spectral Chebyshev approach. Finally, the individual system matrices are assembled to construct the overall/global system matrices of the investigated structure. The spectral Chebyshev approach enables capturing the structural and electromechanical dynamic behaviour of structures having arbitrary geometries (using a cross-section mapping) and boundary conditions. To demonstrate the performance and validate the accuracy of the presented spectral element method, four case studies are investigated. In each case study, the predicted natural frequencies, structural and voltage FRFs are compared to those obtained from a finite element approach.
Composite materials are widely used in various industries because of their distinct properties. H... more Composite materials are widely used in various industries because of their distinct properties. Hybridization is an efficient way of designing composite panels to decrease the cost and/or weight while maintaining stiffness properties. In this study, an accurate and efficient framework is developed to optimize laminated sandwich panels composed of high-stiffness face sheets and low-stiffness core. The stiffness properties of face sheets and core are represented using lamination parameters. The governing equations are derived following first-order shear deformation theory and solved using the spectral Chebyshev approach. In multi-objective optimization problems, genetic algorithm is used to determine Pareto-optimal solutions for fundamental frequency, frequency gap, buckling load, and cost metrics. In these analyses, optimal lamination parameters and thickness are found for face-sheets and core of sandwich panels, and the results are presented as 2D and 3D Pareto-optimal design points. When the individual performance metrics lead to different optimum points, a scattering behavior is observed in the 3D Pareto sets whose boundaries are defined by the 2-objective Pareto fronts. The results provide insights into the design requirements for improving the dynamic and load-carrying behavior of sandwich laminates while minimizing the cost that presents the usability of the presented approach in the multi-objective optimization.
The purpose of the current study was to develop an accurate model to investigate the nonlinear re... more The purpose of the current study was to develop an accurate model to investigate the nonlinear resonances in an axially functionally graded beam rotating with time-dependent speed. To this end, two important features including stiffening and Coriolis effects are modeled based on nonlinear strain relations. Equations governing the axial, chordwise, and flapwise deformations about the determined steady-state equilibrium position are obtained, and the rotating speed variation is considered as a periodic disturbance about this equilibrium condition. Multi-mode discretization of the equations is performed via the spectral Chebyshev approach and the method of multiple scales for gyroscopic systems is employed to study the nonlinear behavior. After determining the required polynomial number based on convergence analysis, results obtained are verified by comparing to those found in literature and numerical simulations. Moreover, the model is validated based on simulations carried out by commercial finite element software. Properties of the functionally graded material and the values of average rotating speed leading to 2:1 internal resonance in the system are found. Time and steady-state responses of the system under primary and parametric resonances caused by the time-dependent rotating speed are investigated when the system is tuned to 2:1 internal resonance. A comprehensive study on the time response, frequency response, and stability behavior shows that the rotating axially functionally graded beam exhibits a complicated nonlinear behavior under the effect of the rotating speed fluctuation frequency, damping coefficient, and properties of the functionally graded material.
Composite materials are widely used in various industries because of their distinct properties. H... more Composite materials are widely used in various industries because of their distinct properties. Hybridization is an efficient way of designing composite panels to decrease the cost and/or weight while maintaining stiffness properties. In this study, an accurate and efficient framework is developed to optimize laminated sandwich panels composed of high-stiffness face sheets and low-stiffness core. The stiffness properties of face sheets and core are represented using lamination parameters. The governing equations are derived following first-order shear deformation theory and solved using the spectral Chebyshev approach. In multi-objective optimization problems, genetic algorithm is used to determine Pareto-optimal solutions for fundamental frequency, frequency gap, buckling load, and cost metrics. In these analyses, optimal lamination parameters and thickness are found for face-sheets and core of sandwich panels, and the results are presented as 2D and 3D Pareto-optimal design points. When the individual performance metrics lead to different optimum points, a scattering behavior is observed in the 3D Pareto sets whose boundaries are defined by the 2-objective Pareto fronts. The results provide insights into the design requirements for improving the dynamic and load-carrying behavior of sandwich laminates while minimizing the cost that presents the usability of the presented approach in the multi-objective optimization.
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Papers by Bekir Bediz