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Papers by H. Nevzat Ozguven
Volume 6: Structures and Dynamics, Parts A and B, 2010
ABSTRACT Forced response analysis of bladed disk assemblies plays a crucial role in rotor blade d... more ABSTRACT Forced response analysis of bladed disk assemblies plays a crucial role in rotor blade design, and therefore has been investigated by researchers extensively. However, due to lack of computation power, several studies in the literature utilize either linear mistuned models which are short of capturing nonlinear effects, or non-linear tuned models which do not catch the effects of mistuning. Studying the combined effect of the two, namely non-linearity and mistuning, is relatively recent and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom related with the non-linear elements. In this paper, a new approach is proposed to predict forced response of frictionally damped mistuned bladed disk assemblies in modal domain. A friction element, which enables normal load variation and separation of the contact interface, is utilized to determine the non-linear contact forces in three-dimensional space, and harmonic balance method is used to obtain a relationship between the non-linear contact forces and the relative motion. As mistuning phenomenon destroys the cyclic symmetry, modeling the whole assembly rather than a sector of it is necessary, which increases the number of non-linear elements required considerably. In the proposed approach, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is proportional to the number of modes retained, rather than the number of degrees of freedom related with the nonlinear elements. Therefore, the proposed approach can be applied to realistic bladed disk models without increasing the number of non-linear equations. Moreover, to accomplish this it is not required to use a reduced order model in the method suggested. Two case studies are presented to illustrate the implementation of the method: a lumped parameter bladed disk model and an academic bladed disk model with shrouds.
Journal of Vibration and Acoustics, 1984
The critical speed of a shaft-disk system can be approximately determined from a single degree-of... more The critical speed of a shaft-disk system can be approximately determined from a single degree-of-freedom model. The errors in the critical speed predictions obtained from such a model are investigated. The percentage errors are plotted against disk to shaft mass ratio for different bearings and various disk locations.
Journal of Mechanical Design, 2013
Design optimization of structural systems is often iterative, time consuming and is limited by th... more Design optimization of structural systems is often iterative, time consuming and is limited by the knowledge of the designer. For that reason, a rapid design optimization scheme is desirable to avoid such problems. This paper presents and integrates two design methodologies for efficient conceptual design of structural systems involving computationally intensive analysis. The first design methodology used in this paper is structural modification technique (SMT). The SMT utilizes the frequency response functions (FRFs) of the original model for the reanalysis of the structure that is subjected to structural modification. The receptances of the original structure are coupled with the dynamic stiffness of the components that are added to or removed from the original structure to perform the structural modification. Then, the coupled matrices are used to calculate the mobility matrices of the modified structure in an efficient way. The second design methodology used in this paper is neu...
Vibration, 2020
In stepped-sine testing of strongly nonlinear structures with the classical force-control strateg... more In stepped-sine testing of strongly nonlinear structures with the classical force-control strategy, corrective force perturbations of a standard controller used to capture the reference signal in the proximity of turning points of frequency response curves may often lead to a premature jump before reaching the actual resonance peak. Accordingly, a classical force-control approach is not suitable to identify backbone curves of strongly nonlinear structures. This paper shows that currently available commercial modal test equipment can accurately identify backbone curves of strongly nonlinear structures by using Response-Controlled stepped-sine Testing (RCT) and the Harmonic Force Surface (HFS) concept, both recently proposed by the authors. These methods can be applied to systems where there are many nonlinearities at several different (and even unknown) locations. However, these techniques are not applicable to systems where internal resonances occur. In RCT, the displacement amplitu...
International Journal of Machine Tools and Manufacture, 2010
Journal of Vibration and Acoustics
A nonlinear dynamic model of a multi-mesh involute spur pinion-driven face-gear split-torque driv... more A nonlinear dynamic model of a multi-mesh involute spur pinion-driven face-gear split-torque drive system is developed. The lumped mass model consists of five pinions and two face-gears with seven rotational degrees-of-freedom. Model includes two inputs, two outputs, and three idler gears meshing with two identical face gears at the bottom and top of the assembly. Face-gear tooth form and corresponding spur gear teeth are established by differential geometry and the theory of gearing. Face-gear drive system mesh stiffnesses are established by utilizing Finite Strip Method for the first time in the literature. The mesh stiffness and damping are time-variant. The model includes clearance type nonlinearity. The Harmonic Balance Method (HBM) is utilized to solve the nonlinear differential equations of motion. The results are compared with the time simulation results. The stability is checked with Floquet Theory and bifurcation diagrams from Poincare Sections. The model is fully capable ...
International Journal of Automation Technology
An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle ... more An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF), which are needed in chatter stability analyses. For this purpose, a structural modification method that is an efficient tool for updating FRFs is used. The mass removed by machining is considered to be a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter-free material removal rates considering part dynamics.
Conference Proceedings of the Society for Experimental Mechanics Series, 2013
ABSTRACT Piezoelectric materials have proven themselves to be used as actuators for active vibrat... more ABSTRACT Piezoelectric materials have proven themselves to be used as actuators for active vibration control. In this study, the active vibration control of a cylindrical shell by means of piezoelectric actuators is investigated. As the most important stage of controlling the vibrations, this paper focuses on the optimal placement of piezo patch actuators. It is aimed in this study to determine the optimum locations of piezo patches on a cylindrical shell by using finite element model of the system. In optimization, the spillover effects, which are caused by accidentally excited higher modes of the structure are also taken into account.
J Sound Vib, 1981
A method for the dynamic analysis of continuously and non-proportionally damped plates is discuss... more A method for the dynamic analysis of continuously and non-proportionally damped plates is discussed. The method is quite general and suitable for various damping treatments, such as in multilayer plates with damping layers. The transverse vibrations of partially coated plates under harmonic excitation are analyzed by the proposed method. The results of the undamped modal analysis made by classical finite element methods are used in the suggested lumped parameter analysis. The receptance matrices of coated plates have been computed at undamped natural frequencies. The computational results have been verified by comparison with experimental values for partially and fully coated rectangular plates.
Proceedings of Spie the International Society For Optical Engineering, Aug 19, 2010
Dynamic modeling of optical systems in order to study vibration effect on performance. [Proceedin... more Dynamic modeling of optical systems in order to study vibration effect on performance. [Proceedings of SPIE 7786, 77860U (2010)]. Ahmet Levent Avşar, H. Nevzat Özgüven. Abstract. In order to determine the vibration effects ...
Precision Engineering, 2015
Conference Proceedings of the Society for Experimental Mechanics Series, 2013
Volume 6: Structures and Dynamics, Parts A and B, 2010
ABSTRACT Forced response analysis of bladed disk assemblies plays a crucial role in rotor blade d... more ABSTRACT Forced response analysis of bladed disk assemblies plays a crucial role in rotor blade design, and therefore has been investigated by researchers extensively. However, due to lack of computation power, several studies in the literature utilize either linear mistuned models which are short of capturing nonlinear effects, or non-linear tuned models which do not catch the effects of mistuning. Studying the combined effect of the two, namely non-linearity and mistuning, is relatively recent and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom related with the non-linear elements. In this paper, a new approach is proposed to predict forced response of frictionally damped mistuned bladed disk assemblies in modal domain. A friction element, which enables normal load variation and separation of the contact interface, is utilized to determine the non-linear contact forces in three-dimensional space, and harmonic balance method is used to obtain a relationship between the non-linear contact forces and the relative motion. As mistuning phenomenon destroys the cyclic symmetry, modeling the whole assembly rather than a sector of it is necessary, which increases the number of non-linear elements required considerably. In the proposed approach, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is proportional to the number of modes retained, rather than the number of degrees of freedom related with the nonlinear elements. Therefore, the proposed approach can be applied to realistic bladed disk models without increasing the number of non-linear equations. Moreover, to accomplish this it is not required to use a reduced order model in the method suggested. Two case studies are presented to illustrate the implementation of the method: a lumped parameter bladed disk model and an academic bladed disk model with shrouds.
Journal of Vibration and Acoustics, 1984
The critical speed of a shaft-disk system can be approximately determined from a single degree-of... more The critical speed of a shaft-disk system can be approximately determined from a single degree-of-freedom model. The errors in the critical speed predictions obtained from such a model are investigated. The percentage errors are plotted against disk to shaft mass ratio for different bearings and various disk locations.
Journal of Mechanical Design, 2013
Design optimization of structural systems is often iterative, time consuming and is limited by th... more Design optimization of structural systems is often iterative, time consuming and is limited by the knowledge of the designer. For that reason, a rapid design optimization scheme is desirable to avoid such problems. This paper presents and integrates two design methodologies for efficient conceptual design of structural systems involving computationally intensive analysis. The first design methodology used in this paper is structural modification technique (SMT). The SMT utilizes the frequency response functions (FRFs) of the original model for the reanalysis of the structure that is subjected to structural modification. The receptances of the original structure are coupled with the dynamic stiffness of the components that are added to or removed from the original structure to perform the structural modification. Then, the coupled matrices are used to calculate the mobility matrices of the modified structure in an efficient way. The second design methodology used in this paper is neu...
Vibration, 2020
In stepped-sine testing of strongly nonlinear structures with the classical force-control strateg... more In stepped-sine testing of strongly nonlinear structures with the classical force-control strategy, corrective force perturbations of a standard controller used to capture the reference signal in the proximity of turning points of frequency response curves may often lead to a premature jump before reaching the actual resonance peak. Accordingly, a classical force-control approach is not suitable to identify backbone curves of strongly nonlinear structures. This paper shows that currently available commercial modal test equipment can accurately identify backbone curves of strongly nonlinear structures by using Response-Controlled stepped-sine Testing (RCT) and the Harmonic Force Surface (HFS) concept, both recently proposed by the authors. These methods can be applied to systems where there are many nonlinearities at several different (and even unknown) locations. However, these techniques are not applicable to systems where internal resonances occur. In RCT, the displacement amplitu...
International Journal of Machine Tools and Manufacture, 2010
Journal of Vibration and Acoustics
A nonlinear dynamic model of a multi-mesh involute spur pinion-driven face-gear split-torque driv... more A nonlinear dynamic model of a multi-mesh involute spur pinion-driven face-gear split-torque drive system is developed. The lumped mass model consists of five pinions and two face-gears with seven rotational degrees-of-freedom. Model includes two inputs, two outputs, and three idler gears meshing with two identical face gears at the bottom and top of the assembly. Face-gear tooth form and corresponding spur gear teeth are established by differential geometry and the theory of gearing. Face-gear drive system mesh stiffnesses are established by utilizing Finite Strip Method for the first time in the literature. The mesh stiffness and damping are time-variant. The model includes clearance type nonlinearity. The Harmonic Balance Method (HBM) is utilized to solve the nonlinear differential equations of motion. The results are compared with the time simulation results. The stability is checked with Floquet Theory and bifurcation diagrams from Poincare Sections. The model is fully capable ...
International Journal of Automation Technology
An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle ... more An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF), which are needed in chatter stability analyses. For this purpose, a structural modification method that is an efficient tool for updating FRFs is used. The mass removed by machining is considered to be a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter-free material removal rates considering part dynamics.
Conference Proceedings of the Society for Experimental Mechanics Series, 2013
ABSTRACT Piezoelectric materials have proven themselves to be used as actuators for active vibrat... more ABSTRACT Piezoelectric materials have proven themselves to be used as actuators for active vibration control. In this study, the active vibration control of a cylindrical shell by means of piezoelectric actuators is investigated. As the most important stage of controlling the vibrations, this paper focuses on the optimal placement of piezo patch actuators. It is aimed in this study to determine the optimum locations of piezo patches on a cylindrical shell by using finite element model of the system. In optimization, the spillover effects, which are caused by accidentally excited higher modes of the structure are also taken into account.
J Sound Vib, 1981
A method for the dynamic analysis of continuously and non-proportionally damped plates is discuss... more A method for the dynamic analysis of continuously and non-proportionally damped plates is discussed. The method is quite general and suitable for various damping treatments, such as in multilayer plates with damping layers. The transverse vibrations of partially coated plates under harmonic excitation are analyzed by the proposed method. The results of the undamped modal analysis made by classical finite element methods are used in the suggested lumped parameter analysis. The receptance matrices of coated plates have been computed at undamped natural frequencies. The computational results have been verified by comparison with experimental values for partially and fully coated rectangular plates.
Proceedings of Spie the International Society For Optical Engineering, Aug 19, 2010
Dynamic modeling of optical systems in order to study vibration effect on performance. [Proceedin... more Dynamic modeling of optical systems in order to study vibration effect on performance. [Proceedings of SPIE 7786, 77860U (2010)]. Ahmet Levent Avşar, H. Nevzat Özgüven. Abstract. In order to determine the vibration effects ...
Precision Engineering, 2015
Conference Proceedings of the Society for Experimental Mechanics Series, 2013