Zahit Mecitoğlu | Istanbul Technical University (original) (raw)

Papers by Zahit Mecitoğlu

TÜBİTAK MAG Proje15.07.2017Analitik ve sayısal hesaplamaların yapılabilmesi için İTÜ Uçak ve Uzay... more TÜBİTAK MAG Proje15.07.2017Analitik ve sayısal hesaplamaların yapılabilmesi için İTÜ Uçak ve Uzay Bilimleri FakültesiKompozit yapı laboratuvarında bulunan MTS (Universal test makinası) cihazı kullanılarak,proje kapsamında temin edilen kompozit malzemelerin mekanik özellikleri belirlenecektir.Daha sonra, anlık basınç yükü deneyleri gerçekleştirilecek ve literatürde var olan basınçfonksiyonlarına kıyasla daha genel analitik bir yaklaşım ortaya konulacaktır. Plağın çarpmadayanımının incelenmesinde LS-DYNA ticari sonlu elemanlar yazılımı kullanılacaktır. Anlıkbasınç yükü altındaki plak davranışı ise ANSYS sonlu elemanlar yazılımı ve yazılacak olan birMATHEMATICA kodu ile incelenecektir. Yapılan hesaplamalar ve analizler sonucundakatmanlı sandviç kompozit plağın bir ön yapısal tasarımı gerçekleştirilecektir. Projedekiaraştırmacıların önceki çalışmaları ve literatürdeki diğer çalışmalar anlık basınç yükünün plaküzerindeki değişiminin ve zamanla olan değişiminin seçilen basınç fonksiyonu t...

58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013

In this paper, the main shaft which is one of the important structural parts for a 500 kW wind tu... more In this paper, the main shaft which is one of the important structural parts for a 500 kW wind turbine has been designed. The fatigue criteria has been based on sizing the main shaft. The main shafts critic desing loads have been calculated by empirical formulas which are on the literatures. Oscillation moments of the torque and the flexural moments which is created by wind share, and effect of tower, etc. have been envisaged for analytical and numerical studies. In this study, the main shaft has been designed for infinite life using with ASME Elliptic criteria. There are two critic areas which are supported and connected to the gear box. In addition Iternational Electrotechnical Commision (IEC) 64100-1 standards have been based on the critic design load cases. The main shaft and the fasteners are modeled using the finite element method. The finite element model of the shaft is designed using with SOLID185 elements. Its static analysis have been achieved with using ANSYS 14.5 software. Also a comparison of two different approximations have been mentioned in this paper. The values of analitic and numerical of deplacement and stress are compared each.

Journal of Aeronautics and Space Technologies, 2017

Structural deformation of composite wind turbine blades affect the aerodynamic performance of the... more Structural deformation of composite wind turbine blades affect the aerodynamic performance of the rotor. To design better blades in terms of efficiency, aerodynamic performance and load mitigation, it is crucial to understand how blades act under operational loads. An interdisciplinary research should be conducted including composite structures and aerodynamics to analyze this interaction. This article focuses on the structural part and explains an easy to apply method to define sectional properties of a closed composite section. The method is based on Classical Lamination Theory (CLT) and it is assumed that the blade is a thin walled structure. Stress concentration and warping effects are ignored. During preliminary design phase, this method is useful to calculate bending and torsional stiffness values based on different lamination parameters and materials, it can also be used to investigate bending-torsion coupling effects. This article also includes parametric studies on NACA pro...

Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2014

In this study, the vibration of ceramic cylindrical panel covered by FGM coatings composed of zir... more In this study, the vibration of ceramic cylindrical panel covered by FGM coatings composed of zirconium oxide (ZrO2) and titanium-aloy (Ti6Al4V) is investigated. First, a sandwich cylindrical panel covered by FGM coatings is designed. After the derivation of basic equations are found expression for the frequency of ceramic cylindrical panels covered by FGM coatings. Discusses the influence of coatings profiles, sandwich shell characteristics, the radius-tothickness ratio and the core-to-coating thickness ratio on the dimensionless frequencies for FG and homogeneous sandwich cylindrical shells

Latin American Journal of Solids and Structures, 2018

In this study crashworthiness optimization of nested and concentric circular tubes under impact l... more In this study crashworthiness optimization of nested and concentric circular tubes under impact loading is performed by coupling Finite Element model, Response Surface Models and Genetic Algorithm. Specific Energy Absorption SEA and Crash Force Efficiency CFE are used in crashworthiness optimization since these criteria are important indicators for evaluating crashworthiness performance. Length and thickness of three concentric tubes as well as radius of one tube are adopted as design variables which are effective parameters on SEA and CFE. To reduce the computational cost of the optimization procedure, simple and computationally cheap Response Surface Models are created to replace finite element analyses in further calculations. The Non-dominated Sorting Genetic Algorithm-II NSGAII is applied to obtain the Pareto optimal solutions. Optimization results are presented for different selected designs that indicate relative importance of multi-objective functions. Results show that the total weight of the vehicles can be reduced by using nested tubes comparing to single tubes with identical masses. These designs can be adopted for use in practice.

International Journal of Aeronautical Science & Aerospace Research, 2016

This study is concerned with the aeroelastic behavior of a laminated composite rectangular plate ... more This study is concerned with the aeroelastic behavior of a laminated composite rectangular plate with temperature dependent material properties. Plate equations for homogenous linear elastic material and small deformations are derived in the frame of the Kirchhoff theory. Uniform and linear temperature distributions are considered on the layered composite plate and it is assumed that the material properties of fiber and matrix vary with the temperature. The aerodynamic forces are obtained by the piston theory. Equations of motion are derived in the variational form by the use of the Hamilton principle. The Equations are solved using the finite element method. The laminated composite plates are discretized with the Semi loof thin shell elements with eight nodes and a total of thirty-eight degrees of freedom. The free vibration results are in a good agreement with the results of literature. The effects of aspect ratio, temperature distribution and lamination on the flutter boundary have been examined. The flutter occurs at a high dynamic pressure for the plate with high aspect ratio. The high temperatures on the plate results in a decrease of the flutter boundary. The number of laminate for a constant plate thickness affects the flutter boundary until a certain laminate number.

Mathematical and Computational Applications, 1996

In this paper, dynamic response of composite cylindrical shells subjected to shock loading is stu... more In this paper, dynamic response of composite cylindrical shells subjected to shock loading is studied analytically. The equations of motion are based on Sanders theory of thin shell. The effects of transverse shear deformation and rotatory inertia are taken into account. The circular cylindrical thin shell with simply supported ends is subjected to a shock load, represented by an axially symmetric moving load at a constant speed along the longitudinal direction. The governing equations are solved analytically using the Assumed-Modes Method. The influences of geometrical parameters and composite material properties of circular cylindrical shells on the dynamic response are studied.

III European Conference on Computational Mechanics

ABSTRACT In this numerical study, vibrations of a cantilevered composite plate subjected to blast... more ABSTRACT In this numerical study, vibrations of a cantilevered composite plate subjected to blast loading are suppressed by the use of piezoelectric actuators. Friedlander’s exponential decay function is used for expressing the blast load model. Some parameters of the function are obtained from the experimental studies. A semiloof shell element is developed in order to account for piezoelectric effects. The composite plate is discretized by using the semiloof elements and stiffness and mass matrices of the plate are obtained from the finite element model. In order to reduce the degrees of freedom of the finite element model, mode summation method is used with weighted modal vector including dominant modes in the dynamic behavior. Free vibrations, static behavior and transient vibrations under the blast load are solved by using the full and reduced matrices as well as by using ANSYS software. All results are in a good agreement. State-space equations are obtained from the reduced finite element model. It is proved that the system equations satisfy the controllability condition in order to control the system. Since the system is also desired to be controlled by using a state observer, the observability condition is satisfied for the system. Since the system is on the stability boundary due to neglecting structural damping, the feedback gain matrix of the system is obtained by using optimal linear quadratic regulator (LQR) in order to guarantee the stability of the system. Structural vibrations have been suppressed successfully by using a state observer control system which estimates system states using displacements measured from sensors.

The Journal of the Acoustical Society of America, 1989

Advanced-degree dissertations in acoustics Editor's note: Abstracts of Doctoral and Master's degr... more Advanced-degree dissertations in acoustics Editor's note: Abstracts of Doctoral and Master's degree theses in acoustics will be welcomed at all times. Please note, however, that they must be double-spaced, formatted as shown below (don't make us $etype them, please!) with PACS numbers, and not over 200 words in length. Please submit two copies. Free vibrations of stiflened circular cylindrical shells [43.40.Vy]

The Journal of the Acoustical Society of America, 1989

The objective of this paper is to investigate the forced response of a stiffened circular cylindr... more The objective of this paper is to investigate the forced response of a stiffened circular cylindrical panel within the frame of Love's first approximation theory of elastic shells. The effects of stiffeners are taken into account by the orthotropic material approach, including the eccentricity of stiffeners. The variational equation of motion for the forced vibrations of thin elastic shells with clamped edges is derived from Hamilton's principle. The stiffened elastic panel is discretized by the Semiloof elements. Then, with the help of the variational equation, the matrix equation is obtained to determine the frequencies and mode shapes of the stiffened circular cylindrical elastic panel. Two types of stiffened shell panels are considered for forced-response analysis: the stiffened models by the stiffeners with rectangular cross section and with profile shape cross section. The influence of the spacings and dimensions of stiffeners on the forced response of the stiffened ci...

Journal of Sound and Vibration, 1996

This paper is concerned with the free vibrations of a stiffened conical thin shell within the con... more This paper is concerned with the free vibrations of a stiffened conical thin shell within the context of Donnell-Mushtari theory. A truncated cone with simply supported ends is reinforced by relatively closely spaced elastic stringers and/or rings. The tapered stringers are used to obtain an efficient stiffening. Change in the stringer spacing in the meridional direction is taken into account in the formulation. The stiffening elements are ''smeared out'' along the conical shell to yield a single equivalent orthotropic shell. The resulting orthotropic shell has a kind of inhomogeneity due to the tapered stringers. The equations of motion for the free vibrations of the stiffened conical shell are derived by the use of Hamilton's principle. The differential equations of the stiffened truncated conical shell, together with the boundary conditions, are solved by the use of the collocation method. Solutions are presented to show the influence of geometrical parameters and material properties on the vibration characteristics. The numerical results are compared with certain earlier results.

Journal of Intelligent Material Systems and Structures, 1993

A finite element formulation is presented for modeling the behavior of laminated composites with ... more A finite element formulation is presented for modeling the behavior of laminated composites with integrated piezoelectric sensors and actuators. This model is valid for both con tinuous and segmented piezoelectric elements that can be either surface bonded or embedded in the laminated plate. The present model takes into account the mass and the stiffness of the piezoelectric patches. The formulation is based on the first-order shear deformation theory, which is applicable for both thin and moderately thick plates. An additional feature of the present model is that it does not introduce the voltage as an additional degree of freedom. The charge/current generated by the sensor and the response of the plate to an actuator voltage can be computed independently. These features are then coupled with a constant-gain negative-velocity/positive-position feedback control algorithm to actively control the transient response of the plate in a closed loop. Numerical results are presented which i...

Composite Structures, 2012

... Cenk Aksoylar a , Corresponding Author Contact Information , E-mail The Corresponding Author ... more ... Cenk Aksoylar a , Corresponding Author Contact Information , E-mail The Corresponding Author , E-mail The Corresponding Author , Akın Ömercikoğlu b , Zahit Mecitoğlu c , Mehmet H. Omurtag d. a, Visiting Scholar, Dept. ... E-mail: mecit@itu.edu.tr 4Professor, Dept. ...

Havacılıkta İleri Teknolojiler ve Uygulamaları …, 2004

AIAA Journal, 2006

Résumé/Abstract This research deals with the derivation and solution of nonlinear dynamic equatio... more Résumé/Abstract This research deals with the derivation and solution of nonlinear dynamic equations of a clamped laminated plate exposed to blast load including structural damping effects. Dynamic equations of the plate are derived by the use of the virtual work principle. ...

AIAA Journal, 1996

This study presents the dynamic equations of a stiffened composite laminated conical thin shell u... more This study presents the dynamic equations of a stiffened composite laminated conical thin shell under the influence of initial stresses. The governing equations of a truncated conical shell are based on the Donnell-Mushtari theory of thin shells including the transverse shear deformation and rotary inertia. The extension-bending coupling is considered in the derivation. The composite laminated conical shell is also reinforced at uniform intervals by elastic rings and/or stringers. The stiffening elements are relatively closely spaced, and therefore the stiffeners are smeared out along the conical shell. The inhomogeneity of material properties because of temperature, moisture, or manufacturing processes is taken into account in the constitutive equations. A generalized variational theorem is derived so as to describe the complete set of the fundamental equations of the conical shell. Next, the uniqueness is examined in solutions of the dynamic equations of the conical shell, and the boundary and initial conditions are shown to be sufficient for the uniqueness in solutions. The equations of the laminated composite conical shell are solved by the use of the finite difference method as an illustrative example. The accuracy of results is tested by certain earlier results, and a good agreement is found.

AIAA Journal, 1999

This paper presents a theoretical analysis and correlation with numerical results of the displace... more This paper presents a theoretical analysis and correlation with numerical results of the displacement time histories of laminated composite panels exposed to normal blast shock waves. Nonlinear dynamic equations of the cylindrically curved laminated panels are derived by the use of the Lagrange equations in the frame of Love's theory of thin shells. The governing equations of the laminated curved panel are solved by Runge-Kutta method. In addition, ANSYS finite element software is used to obtain displacement time history numerically. The effect ofloading conditions and geometrical properties is examined on the dynamic behavior.

Fourth International Conference On Advances in Civil and Structural Engineering - CSE 2015, 2015

In this paper, the fatigue analysis part of a project which aims to develop a computer aided meth... more In this paper, the fatigue analysis part of a project which aims to develop a computer aided methodology for developing/designing of the polyethylene fuel tanks is presented. The fatigue performance of the polyethylene material based on the stress-life (S-N) approach is obtained by coupon tests. Dynamic "g forces", which act on the fuel tanks as base excitations, are obtained from the specific bad road runway experiments by the Mercedes-Benz Turk (MBT) R&D Center. In the finite element simulation, dynamic stresses are obtained for different fullness ratios of the tank by using PERMAS V15. Fluid-structure interaction problem is also considered, fluid (fuel) is modeled with acoustic elements, and structure (tank) is modeled with shell elements. Fatigue life prediction of the fuel tank is conducted by using the FEMFAT (Finite Element Fatigue Analysis) program. After evaluating results, some geometry optimization is performed. Finally, all fatigue analysis results are compared with the hydro-pulse test results for validation.

TÜBİTAK MAG Proje15.07.2017Analitik ve sayısal hesaplamaların yapılabilmesi için İTÜ Uçak ve Uzay... more TÜBİTAK MAG Proje15.07.2017Analitik ve sayısal hesaplamaların yapılabilmesi için İTÜ Uçak ve Uzay Bilimleri FakültesiKompozit yapı laboratuvarında bulunan MTS (Universal test makinası) cihazı kullanılarak,proje kapsamında temin edilen kompozit malzemelerin mekanik özellikleri belirlenecektir.Daha sonra, anlık basınç yükü deneyleri gerçekleştirilecek ve literatürde var olan basınçfonksiyonlarına kıyasla daha genel analitik bir yaklaşım ortaya konulacaktır. Plağın çarpmadayanımının incelenmesinde LS-DYNA ticari sonlu elemanlar yazılımı kullanılacaktır. Anlıkbasınç yükü altındaki plak davranışı ise ANSYS sonlu elemanlar yazılımı ve yazılacak olan birMATHEMATICA kodu ile incelenecektir. Yapılan hesaplamalar ve analizler sonucundakatmanlı sandviç kompozit plağın bir ön yapısal tasarımı gerçekleştirilecektir. Projedekiaraştırmacıların önceki çalışmaları ve literatürdeki diğer çalışmalar anlık basınç yükünün plaküzerindeki değişiminin ve zamanla olan değişiminin seçilen basınç fonksiyonu t...

58th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference

Teorik ve Uygulamalı Mekanik Türk Milli Komitesi, 2013

In this paper, the main shaft which is one of the important structural parts for a 500 kW wind tu... more In this paper, the main shaft which is one of the important structural parts for a 500 kW wind turbine has been designed. The fatigue criteria has been based on sizing the main shaft. The main shafts critic desing loads have been calculated by empirical formulas which are on the literatures. Oscillation moments of the torque and the flexural moments which is created by wind share, and effect of tower, etc. have been envisaged for analytical and numerical studies. In this study, the main shaft has been designed for infinite life using with ASME Elliptic criteria. There are two critic areas which are supported and connected to the gear box. In addition Iternational Electrotechnical Commision (IEC) 64100-1 standards have been based on the critic design load cases. The main shaft and the fasteners are modeled using the finite element method. The finite element model of the shaft is designed using with SOLID185 elements. Its static analysis have been achieved with using ANSYS 14.5 software. Also a comparison of two different approximations have been mentioned in this paper. The values of analitic and numerical of deplacement and stress are compared each.

Journal of Aeronautics and Space Technologies, 2017

Structural deformation of composite wind turbine blades affect the aerodynamic performance of the... more Structural deformation of composite wind turbine blades affect the aerodynamic performance of the rotor. To design better blades in terms of efficiency, aerodynamic performance and load mitigation, it is crucial to understand how blades act under operational loads. An interdisciplinary research should be conducted including composite structures and aerodynamics to analyze this interaction. This article focuses on the structural part and explains an easy to apply method to define sectional properties of a closed composite section. The method is based on Classical Lamination Theory (CLT) and it is assumed that the blade is a thin walled structure. Stress concentration and warping effects are ignored. During preliminary design phase, this method is useful to calculate bending and torsional stiffness values based on different lamination parameters and materials, it can also be used to investigate bending-torsion coupling effects. This article also includes parametric studies on NACA pro...

Süleyman Demirel Üniversitesi Fen Bilimleri Enstitüsü Dergisi, 2014

In this study, the vibration of ceramic cylindrical panel covered by FGM coatings composed of zir... more In this study, the vibration of ceramic cylindrical panel covered by FGM coatings composed of zirconium oxide (ZrO2) and titanium-aloy (Ti6Al4V) is investigated. First, a sandwich cylindrical panel covered by FGM coatings is designed. After the derivation of basic equations are found expression for the frequency of ceramic cylindrical panels covered by FGM coatings. Discusses the influence of coatings profiles, sandwich shell characteristics, the radius-tothickness ratio and the core-to-coating thickness ratio on the dimensionless frequencies for FG and homogeneous sandwich cylindrical shells

Latin American Journal of Solids and Structures, 2018

In this study crashworthiness optimization of nested and concentric circular tubes under impact l... more In this study crashworthiness optimization of nested and concentric circular tubes under impact loading is performed by coupling Finite Element model, Response Surface Models and Genetic Algorithm. Specific Energy Absorption SEA and Crash Force Efficiency CFE are used in crashworthiness optimization since these criteria are important indicators for evaluating crashworthiness performance. Length and thickness of three concentric tubes as well as radius of one tube are adopted as design variables which are effective parameters on SEA and CFE. To reduce the computational cost of the optimization procedure, simple and computationally cheap Response Surface Models are created to replace finite element analyses in further calculations. The Non-dominated Sorting Genetic Algorithm-II NSGAII is applied to obtain the Pareto optimal solutions. Optimization results are presented for different selected designs that indicate relative importance of multi-objective functions. Results show that the total weight of the vehicles can be reduced by using nested tubes comparing to single tubes with identical masses. These designs can be adopted for use in practice.

International Journal of Aeronautical Science & Aerospace Research, 2016

This study is concerned with the aeroelastic behavior of a laminated composite rectangular plate ... more This study is concerned with the aeroelastic behavior of a laminated composite rectangular plate with temperature dependent material properties. Plate equations for homogenous linear elastic material and small deformations are derived in the frame of the Kirchhoff theory. Uniform and linear temperature distributions are considered on the layered composite plate and it is assumed that the material properties of fiber and matrix vary with the temperature. The aerodynamic forces are obtained by the piston theory. Equations of motion are derived in the variational form by the use of the Hamilton principle. The Equations are solved using the finite element method. The laminated composite plates are discretized with the Semi loof thin shell elements with eight nodes and a total of thirty-eight degrees of freedom. The free vibration results are in a good agreement with the results of literature. The effects of aspect ratio, temperature distribution and lamination on the flutter boundary have been examined. The flutter occurs at a high dynamic pressure for the plate with high aspect ratio. The high temperatures on the plate results in a decrease of the flutter boundary. The number of laminate for a constant plate thickness affects the flutter boundary until a certain laminate number.

Mathematical and Computational Applications, 1996

In this paper, dynamic response of composite cylindrical shells subjected to shock loading is stu... more In this paper, dynamic response of composite cylindrical shells subjected to shock loading is studied analytically. The equations of motion are based on Sanders theory of thin shell. The effects of transverse shear deformation and rotatory inertia are taken into account. The circular cylindrical thin shell with simply supported ends is subjected to a shock load, represented by an axially symmetric moving load at a constant speed along the longitudinal direction. The governing equations are solved analytically using the Assumed-Modes Method. The influences of geometrical parameters and composite material properties of circular cylindrical shells on the dynamic response are studied.

III European Conference on Computational Mechanics

ABSTRACT In this numerical study, vibrations of a cantilevered composite plate subjected to blast... more ABSTRACT In this numerical study, vibrations of a cantilevered composite plate subjected to blast loading are suppressed by the use of piezoelectric actuators. Friedlander’s exponential decay function is used for expressing the blast load model. Some parameters of the function are obtained from the experimental studies. A semiloof shell element is developed in order to account for piezoelectric effects. The composite plate is discretized by using the semiloof elements and stiffness and mass matrices of the plate are obtained from the finite element model. In order to reduce the degrees of freedom of the finite element model, mode summation method is used with weighted modal vector including dominant modes in the dynamic behavior. Free vibrations, static behavior and transient vibrations under the blast load are solved by using the full and reduced matrices as well as by using ANSYS software. All results are in a good agreement. State-space equations are obtained from the reduced finite element model. It is proved that the system equations satisfy the controllability condition in order to control the system. Since the system is also desired to be controlled by using a state observer, the observability condition is satisfied for the system. Since the system is on the stability boundary due to neglecting structural damping, the feedback gain matrix of the system is obtained by using optimal linear quadratic regulator (LQR) in order to guarantee the stability of the system. Structural vibrations have been suppressed successfully by using a state observer control system which estimates system states using displacements measured from sensors.

The Journal of the Acoustical Society of America, 1989

Advanced-degree dissertations in acoustics Editor's note: Abstracts of Doctoral and Master's degr... more Advanced-degree dissertations in acoustics Editor's note: Abstracts of Doctoral and Master's degree theses in acoustics will be welcomed at all times. Please note, however, that they must be double-spaced, formatted as shown below (don't make us $etype them, please!) with PACS numbers, and not over 200 words in length. Please submit two copies. Free vibrations of stiflened circular cylindrical shells [43.40.Vy]

The Journal of the Acoustical Society of America, 1989

The objective of this paper is to investigate the forced response of a stiffened circular cylindr... more The objective of this paper is to investigate the forced response of a stiffened circular cylindrical panel within the frame of Love's first approximation theory of elastic shells. The effects of stiffeners are taken into account by the orthotropic material approach, including the eccentricity of stiffeners. The variational equation of motion for the forced vibrations of thin elastic shells with clamped edges is derived from Hamilton's principle. The stiffened elastic panel is discretized by the Semiloof elements. Then, with the help of the variational equation, the matrix equation is obtained to determine the frequencies and mode shapes of the stiffened circular cylindrical elastic panel. Two types of stiffened shell panels are considered for forced-response analysis: the stiffened models by the stiffeners with rectangular cross section and with profile shape cross section. The influence of the spacings and dimensions of stiffeners on the forced response of the stiffened ci...

Journal of Sound and Vibration, 1996

This paper is concerned with the free vibrations of a stiffened conical thin shell within the con... more This paper is concerned with the free vibrations of a stiffened conical thin shell within the context of Donnell-Mushtari theory. A truncated cone with simply supported ends is reinforced by relatively closely spaced elastic stringers and/or rings. The tapered stringers are used to obtain an efficient stiffening. Change in the stringer spacing in the meridional direction is taken into account in the formulation. The stiffening elements are ''smeared out'' along the conical shell to yield a single equivalent orthotropic shell. The resulting orthotropic shell has a kind of inhomogeneity due to the tapered stringers. The equations of motion for the free vibrations of the stiffened conical shell are derived by the use of Hamilton's principle. The differential equations of the stiffened truncated conical shell, together with the boundary conditions, are solved by the use of the collocation method. Solutions are presented to show the influence of geometrical parameters and material properties on the vibration characteristics. The numerical results are compared with certain earlier results.

Journal of Intelligent Material Systems and Structures, 1993

A finite element formulation is presented for modeling the behavior of laminated composites with ... more A finite element formulation is presented for modeling the behavior of laminated composites with integrated piezoelectric sensors and actuators. This model is valid for both con tinuous and segmented piezoelectric elements that can be either surface bonded or embedded in the laminated plate. The present model takes into account the mass and the stiffness of the piezoelectric patches. The formulation is based on the first-order shear deformation theory, which is applicable for both thin and moderately thick plates. An additional feature of the present model is that it does not introduce the voltage as an additional degree of freedom. The charge/current generated by the sensor and the response of the plate to an actuator voltage can be computed independently. These features are then coupled with a constant-gain negative-velocity/positive-position feedback control algorithm to actively control the transient response of the plate in a closed loop. Numerical results are presented which i...

Composite Structures, 2012

... Cenk Aksoylar a , Corresponding Author Contact Information , E-mail The Corresponding Author ... more ... Cenk Aksoylar a , Corresponding Author Contact Information , E-mail The Corresponding Author , E-mail The Corresponding Author , Akın Ömercikoğlu b , Zahit Mecitoğlu c , Mehmet H. Omurtag d. a, Visiting Scholar, Dept. ... E-mail: mecit@itu.edu.tr 4Professor, Dept. ...

Havacılıkta İleri Teknolojiler ve Uygulamaları …, 2004

AIAA Journal, 2006

Résumé/Abstract This research deals with the derivation and solution of nonlinear dynamic equatio... more Résumé/Abstract This research deals with the derivation and solution of nonlinear dynamic equations of a clamped laminated plate exposed to blast load including structural damping effects. Dynamic equations of the plate are derived by the use of the virtual work principle. ...

AIAA Journal, 1996

This study presents the dynamic equations of a stiffened composite laminated conical thin shell u... more This study presents the dynamic equations of a stiffened composite laminated conical thin shell under the influence of initial stresses. The governing equations of a truncated conical shell are based on the Donnell-Mushtari theory of thin shells including the transverse shear deformation and rotary inertia. The extension-bending coupling is considered in the derivation. The composite laminated conical shell is also reinforced at uniform intervals by elastic rings and/or stringers. The stiffening elements are relatively closely spaced, and therefore the stiffeners are smeared out along the conical shell. The inhomogeneity of material properties because of temperature, moisture, or manufacturing processes is taken into account in the constitutive equations. A generalized variational theorem is derived so as to describe the complete set of the fundamental equations of the conical shell. Next, the uniqueness is examined in solutions of the dynamic equations of the conical shell, and the boundary and initial conditions are shown to be sufficient for the uniqueness in solutions. The equations of the laminated composite conical shell are solved by the use of the finite difference method as an illustrative example. The accuracy of results is tested by certain earlier results, and a good agreement is found.

AIAA Journal, 1999

This paper presents a theoretical analysis and correlation with numerical results of the displace... more This paper presents a theoretical analysis and correlation with numerical results of the displacement time histories of laminated composite panels exposed to normal blast shock waves. Nonlinear dynamic equations of the cylindrically curved laminated panels are derived by the use of the Lagrange equations in the frame of Love's theory of thin shells. The governing equations of the laminated curved panel are solved by Runge-Kutta method. In addition, ANSYS finite element software is used to obtain displacement time history numerically. The effect ofloading conditions and geometrical properties is examined on the dynamic behavior.

Fourth International Conference On Advances in Civil and Structural Engineering - CSE 2015, 2015

In this paper, the fatigue analysis part of a project which aims to develop a computer aided meth... more In this paper, the fatigue analysis part of a project which aims to develop a computer aided methodology for developing/designing of the polyethylene fuel tanks is presented. The fatigue performance of the polyethylene material based on the stress-life (S-N) approach is obtained by coupon tests. Dynamic "g forces", which act on the fuel tanks as base excitations, are obtained from the specific bad road runway experiments by the Mercedes-Benz Turk (MBT) R&D Center. In the finite element simulation, dynamic stresses are obtained for different fullness ratios of the tank by using PERMAS V15. Fluid-structure interaction problem is also considered, fluid (fuel) is modeled with acoustic elements, and structure (tank) is modeled with shell elements. Fatigue life prediction of the fuel tank is conducted by using the FEMFAT (Finite Element Fatigue Analysis) program. After evaluating results, some geometry optimization is performed. Finally, all fatigue analysis results are compared with the hydro-pulse test results for validation.