The computational algorithms of dierent multiobjective optimization techniques and their applicat... more The computational algorithms of dierent multiobjective optimization techniques and their applications to structural systems are presented. The weighting, -constraint, goal programming and modied game theory methods are described along with a comparative study of the results. The conflicting nature of the objective functions is studied through two multiobjective optimization problems. Specically, the design of a 25-bar space truss and that of a satellite with flexible appendages are considered in numerical studies. The results from the multiobjective optimization methods are evaluated in terms of a supercriterion. It is con-cluded that the results obtained using the goal programming and modied game theory/goal programming approaches are properly balanced yielding the best compromise in the presence of conflicting objectives.
Linearconstitutiveequationsofa thermopiezomagneticmedium involving mechanical, electrical, magnet... more Linearconstitutiveequationsofa thermopiezomagneticmedium involving mechanical, electrical, magnetic, and thermal e elds are presented with the aid of a thermodynamic potential. A thermopiezomagnetic medium can be formed by bonding together a piezoelectric and magnetostrictive composite. Two energy functionals are dee ned. It is shown via Hamilton’ s principle that these functionals yield the equations of motion for the mechanical e eld, Maxwell’ s equilibrium equations for the electrical and magnetic e elds, and the generalized heat equation for the thermal e eld. Finite element equations for the thermopiezomagnetic media are obtained by using the linear constitutive equations in Hamilton’ s principle together with the e nite element approximations. The e nite element equations are utilized on an example two-layer smartstructure, which consistsof a piezoceramic (barium titanate ) layer at the bottom and a magnetoceramic (cobalt ferrite ) layer at the top. An electrostatic e eld appl...
Flow field in annular duct resembling a typical transition piece of gas turbine engine is conside... more Flow field in annular duct resembling a typical transition piece of gas turbine engine is considered. Velocity and temperature distributions in the duct and casing are predicated numerically using the FLUENT CFD code. The control volume approach is introduced when discretizing the governing equations of flow. Thermal stress development in the outer casing of the duct is computed using ANSYS FEM code. It is found that radial acceleration of flow at duct entry region lowers temperature in the casing in this region. The gradual increase in pressure along the axial direction prevents flow separation and formation of secondary flow in the duct. Axial stress component is compressive and its magnitude is almost uniform along the axial direction. The magnitude of von-Mises stress is less than the elastic limit of the substrate material.
Three-point bending tests are carried out to measure the Young's modulus of laser gas assisti... more Three-point bending tests are carried out to measure the Young's modulus of laser gas assisting nitrided, laser gas assisting nitrided and coated, heat treated and coated, specimens. The testing conditions are incorporated to simulate the material response to the bending load using finite element modelling (FEM) and the ANSYS code is utilized in this regard. Laser gas assisted nitriding is carried out using a CO 2 laser system while TiN coating is realized using the PVD coating unit. It is found that crack-free laser gas assisting nitrided layer of about 80 μm is achieved while TiN coatings thickness is about 2 μm. Young's modulus of TiN coating is similar to that obtained for laser gas assisting nitrided layer.
Water droplet impacting on a slanted dusty hydrophobic surface is examined in relation to dust mi... more Water droplet impacting on a slanted dusty hydrophobic surface is examined in relation to dust mitigation from surfaces. Impacting droplet characteristics including droplet spreading/retraction rates, slipping length, and rebound heights are analyzed via high-speed recording and a tracker program. The environmental dust characteristics in terms of size, shape, elemental composition, and surface free energy are evaluated by adopting the analytical methods. The findings reveal that the dynamic characteristics of the impacting droplet on the slanted hydrophobic surface are significantly influenced by the dust particles. The maximum droplet spreading over the dusty surface becomes smaller than that of the nondusty surface. The presence of the dust particles on the slanted hydrophobic surface increases energy dissipation, and the water droplet slipping length over the surface becomes less than that corresponding to the nondusty surface. Impacting droplet fluid infuses over the dust parti...
The development of nucleation theory makes possible to predict droplet formation in expanding ste... more The development of nucleation theory makes possible to predict droplet formation in expanding steam. The present study is conducted to investigate the nucleation process occurring during the flow through convergent-divergent nozzles. A kinetic theory approach for determining the rate of droplet growth has been developed successfully. The governing flow equations are developed for the free and continuous flow regimes. A numerical scheme is introduced to solve the resulting equations. To validate the predictions, an experiment is carried out to measure the droplet size and thermodynamic properties of steam expanding through a convergent-divergent nozzle. It is found that the amount of supersaturation is limited with pressure increase and the limiting degrees of supercooling and the resulting droplet sizes depend on the Wilson pressure and the expansion rate. The theoretical predictions are in good agreement with the experimental measurements and the process of nucleation in high pressure steam can, possibly, be described satisfactorily by the model developed in the present study.
The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pr... more The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pressure vessel industry. Upon fabrication, it is required that the whole structure is subjected to pressure testing. The test can be expensive as it necessitates pressurizing the whole structure typically having a large volume. Hence, it is proposed to make a “local test,” which is considerably simpler as it involves capping the small nozzle and testing only a relatively small portion of the structure. This paper investigates the accuracy and reliability of such an alternative test, using the finite-element method. Two different finite-element types are used in the study, specifically a shell-based element and a solid-based element. The verification of the finite-element results for two different cases shows that the models used in the study are valid. It also proves that the two element types yield very similar stress results. In addition, the study includes a numerical investigation of ...
In this paper, a substructural approach is proposed and successfully implemented for H/sub /spl i... more In this paper, a substructural approach is proposed and successfully implemented for H/sub /spl infin// robust controller design for nonlinear and fuzzy structures. Sensors and actuators are assumed to be discrete, located at some nodal points of the structure, and a nonlinear matrix differential equation is assumed to be the system model. The finite element method (FEM) applied to complex systems, usually results large dimensional models, and as the model dimension becomes larger and larger, controller design algorithms require more and more computation time and start to have numerical problems. To overcome these problems, there are two main research directions: Decentralized and substructural type approaches. In this paper, we adopt a substructural type approach based on the static condensation principle, and study the H/sub /spl infin// optimal controller design for nonlinear and fuzzy structures. The key point in our approach is doing the static condensation in the abstract state space for linearized models of nonlinear systems and use fuzzy control techniques for nonlinearities. Working with linearized models allows to formulate the problem as a convex optimization one expressed as Linear Matrix Inequalities (LMIs). Because of reduced problem size and hence reduced dimensions of the matrices involved, computation time is reduced and numerical reliability is increased. The proposed method is illustrated on several benchmark problems.
... 6. Avellaneda, M. and Harshe, G.(1994) Magnetoelectric effect in piezoelectric/magnetostricti... more ... 6. Avellaneda, M. and Harshe, G.(1994) Magnetoelectric effect in piezoelectric/magnetostrictive multilayer (2-2) composites. ... 11. Piezoelectric Ceramics Data Book, Morgan Matroc Limited, Transducer Products Division, Thomhill, Southampton, Hampshire, England 12. ...
The development of nucleation theory makes possible to predict droplet formation in expanding ste... more The development of nucleation theory makes possible to predict droplet formation in expanding steam. The present study is conducted to investigate the nucleation process occurring during the flow through convergent-divergent nozzles. A kinetic theory approach for determining the rate of droplet growth has been developed successfully. The governing flow equations are developed for the free and continuous flow regimes. A numerical scheme is introduced to solve the resulting equations. To validate the predictions, an experiment is carried out to measure the droplet size and thermodynamic properties of steam expanding through a convergent-divergent nozzle. It is found that the amount of supersaturation is limited with pressure increase and the limiting degrees of supercooling and the resulting droplet sizes depend on the Wilson pressure and the expansion rate. The theoretical predictions are in good agreement with the experimental measurements and the process of nucleation in high pressure steam can, possibly, be described satisfactorily by the model developed in the present study.
A superconducting Y-Ba-Cu-O with high Tc was prepared by arc casting to examine its effect on the... more A superconducting Y-Ba-Cu-O with high Tc was prepared by arc casting to examine its effect on the crystalline phases in the annealed samples. X-ray diffraction (XRD) studies were carried out to investigate the orthorhombic superconducting phases. An a.c. susceptibility study was carried out and image analysis was conducted to obtain the density and grain size of the products. In addition,
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2008
Numerical and experimental studies are carried out to investigate the usability of a piezoceramic... more Numerical and experimental studies are carried out to investigate the usability of a piezoceramic (PZT) sensor placed in the root of a stationary cantilever beam for measuring structural vibrations. The ability of the sensor for picking up the vibration signals during both the transient and steady-state phases is investigated. The piezoelectric equations obtained using the Hamilton's principle together with the finite-element approximation are utilized to extract the voltage outputs of the PZT sensor. An experimental set-up, to validate the theoretical results, is designed and manufactured. The experimentally measured sensor voltages are compared with the numerical ones. The results showed the excellent performance of the sensors in reading vibration signals of the beam. The root embedded PZT approach is an important step towards the application of measuring rotating blade vibrations.
Smart Structures and Materials 1999: Mathematics and Control in Smart Structures, 1999
ABSTRACT This paper presents a neural network controller for a piezoelectric controlled structure... more ABSTRACT This paper presents a neural network controller for a piezoelectric controlled structure by emulating the control performance of a Linear Quadratic Gaussian (LQG) controller. The configuration of the Artificial Neural Network (ANN) is simple, yet it is efficient in terms of its high learning speed and good generalization ability. A case study is presented to demonstrate the performance of the ANN controller versus the LQG controller. The test results for different disturbances on the structure show excellent agreement between the ANN and LQG controllers.
The computational algorithms of dierent multiobjective optimization techniques and their applicat... more The computational algorithms of dierent multiobjective optimization techniques and their applications to structural systems are presented. The weighting, -constraint, goal programming and modied game theory methods are described along with a comparative study of the results. The conflicting nature of the objective functions is studied through two multiobjective optimization problems. Specically, the design of a 25-bar space truss and that of a satellite with flexible appendages are considered in numerical studies. The results from the multiobjective optimization methods are evaluated in terms of a supercriterion. It is con-cluded that the results obtained using the goal programming and modied game theory/goal programming approaches are properly balanced yielding the best compromise in the presence of conflicting objectives.
Linearconstitutiveequationsofa thermopiezomagneticmedium involving mechanical, electrical, magnet... more Linearconstitutiveequationsofa thermopiezomagneticmedium involving mechanical, electrical, magnetic, and thermal e elds are presented with the aid of a thermodynamic potential. A thermopiezomagnetic medium can be formed by bonding together a piezoelectric and magnetostrictive composite. Two energy functionals are dee ned. It is shown via Hamilton’ s principle that these functionals yield the equations of motion for the mechanical e eld, Maxwell’ s equilibrium equations for the electrical and magnetic e elds, and the generalized heat equation for the thermal e eld. Finite element equations for the thermopiezomagnetic media are obtained by using the linear constitutive equations in Hamilton’ s principle together with the e nite element approximations. The e nite element equations are utilized on an example two-layer smartstructure, which consistsof a piezoceramic (barium titanate ) layer at the bottom and a magnetoceramic (cobalt ferrite ) layer at the top. An electrostatic e eld appl...
Flow field in annular duct resembling a typical transition piece of gas turbine engine is conside... more Flow field in annular duct resembling a typical transition piece of gas turbine engine is considered. Velocity and temperature distributions in the duct and casing are predicated numerically using the FLUENT CFD code. The control volume approach is introduced when discretizing the governing equations of flow. Thermal stress development in the outer casing of the duct is computed using ANSYS FEM code. It is found that radial acceleration of flow at duct entry region lowers temperature in the casing in this region. The gradual increase in pressure along the axial direction prevents flow separation and formation of secondary flow in the duct. Axial stress component is compressive and its magnitude is almost uniform along the axial direction. The magnitude of von-Mises stress is less than the elastic limit of the substrate material.
Three-point bending tests are carried out to measure the Young's modulus of laser gas assisti... more Three-point bending tests are carried out to measure the Young's modulus of laser gas assisting nitrided, laser gas assisting nitrided and coated, heat treated and coated, specimens. The testing conditions are incorporated to simulate the material response to the bending load using finite element modelling (FEM) and the ANSYS code is utilized in this regard. Laser gas assisted nitriding is carried out using a CO 2 laser system while TiN coating is realized using the PVD coating unit. It is found that crack-free laser gas assisting nitrided layer of about 80 μm is achieved while TiN coatings thickness is about 2 μm. Young's modulus of TiN coating is similar to that obtained for laser gas assisting nitrided layer.
Water droplet impacting on a slanted dusty hydrophobic surface is examined in relation to dust mi... more Water droplet impacting on a slanted dusty hydrophobic surface is examined in relation to dust mitigation from surfaces. Impacting droplet characteristics including droplet spreading/retraction rates, slipping length, and rebound heights are analyzed via high-speed recording and a tracker program. The environmental dust characteristics in terms of size, shape, elemental composition, and surface free energy are evaluated by adopting the analytical methods. The findings reveal that the dynamic characteristics of the impacting droplet on the slanted hydrophobic surface are significantly influenced by the dust particles. The maximum droplet spreading over the dusty surface becomes smaller than that of the nondusty surface. The presence of the dust particles on the slanted hydrophobic surface increases energy dissipation, and the water droplet slipping length over the surface becomes less than that corresponding to the nondusty surface. Impacting droplet fluid infuses over the dust parti...
The development of nucleation theory makes possible to predict droplet formation in expanding ste... more The development of nucleation theory makes possible to predict droplet formation in expanding steam. The present study is conducted to investigate the nucleation process occurring during the flow through convergent-divergent nozzles. A kinetic theory approach for determining the rate of droplet growth has been developed successfully. The governing flow equations are developed for the free and continuous flow regimes. A numerical scheme is introduced to solve the resulting equations. To validate the predictions, an experiment is carried out to measure the droplet size and thermodynamic properties of steam expanding through a convergent-divergent nozzle. It is found that the amount of supersaturation is limited with pressure increase and the limiting degrees of supercooling and the resulting droplet sizes depend on the Wilson pressure and the expansion rate. The theoretical predictions are in good agreement with the experimental measurements and the process of nucleation in high pressure steam can, possibly, be described satisfactorily by the model developed in the present study.
The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pr... more The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pressure vessel industry. Upon fabrication, it is required that the whole structure is subjected to pressure testing. The test can be expensive as it necessitates pressurizing the whole structure typically having a large volume. Hence, it is proposed to make a “local test,” which is considerably simpler as it involves capping the small nozzle and testing only a relatively small portion of the structure. This paper investigates the accuracy and reliability of such an alternative test, using the finite-element method. Two different finite-element types are used in the study, specifically a shell-based element and a solid-based element. The verification of the finite-element results for two different cases shows that the models used in the study are valid. It also proves that the two element types yield very similar stress results. In addition, the study includes a numerical investigation of ...
In this paper, a substructural approach is proposed and successfully implemented for H/sub /spl i... more In this paper, a substructural approach is proposed and successfully implemented for H/sub /spl infin// robust controller design for nonlinear and fuzzy structures. Sensors and actuators are assumed to be discrete, located at some nodal points of the structure, and a nonlinear matrix differential equation is assumed to be the system model. The finite element method (FEM) applied to complex systems, usually results large dimensional models, and as the model dimension becomes larger and larger, controller design algorithms require more and more computation time and start to have numerical problems. To overcome these problems, there are two main research directions: Decentralized and substructural type approaches. In this paper, we adopt a substructural type approach based on the static condensation principle, and study the H/sub /spl infin// optimal controller design for nonlinear and fuzzy structures. The key point in our approach is doing the static condensation in the abstract state space for linearized models of nonlinear systems and use fuzzy control techniques for nonlinearities. Working with linearized models allows to formulate the problem as a convex optimization one expressed as Linear Matrix Inequalities (LMIs). Because of reduced problem size and hence reduced dimensions of the matrices involved, computation time is reduced and numerical reliability is increased. The proposed method is illustrated on several benchmark problems.
... 6. Avellaneda, M. and Harshe, G.(1994) Magnetoelectric effect in piezoelectric/magnetostricti... more ... 6. Avellaneda, M. and Harshe, G.(1994) Magnetoelectric effect in piezoelectric/magnetostrictive multilayer (2-2) composites. ... 11. Piezoelectric Ceramics Data Book, Morgan Matroc Limited, Transducer Products Division, Thomhill, Southampton, Hampshire, England 12. ...
The development of nucleation theory makes possible to predict droplet formation in expanding ste... more The development of nucleation theory makes possible to predict droplet formation in expanding steam. The present study is conducted to investigate the nucleation process occurring during the flow through convergent-divergent nozzles. A kinetic theory approach for determining the rate of droplet growth has been developed successfully. The governing flow equations are developed for the free and continuous flow regimes. A numerical scheme is introduced to solve the resulting equations. To validate the predictions, an experiment is carried out to measure the droplet size and thermodynamic properties of steam expanding through a convergent-divergent nozzle. It is found that the amount of supersaturation is limited with pressure increase and the limiting degrees of supercooling and the resulting droplet sizes depend on the Wilson pressure and the expansion rate. The theoretical predictions are in good agreement with the experimental measurements and the process of nucleation in high pressure steam can, possibly, be described satisfactorily by the model developed in the present study.
A superconducting Y-Ba-Cu-O with high Tc was prepared by arc casting to examine its effect on the... more A superconducting Y-Ba-Cu-O with high Tc was prepared by arc casting to examine its effect on the crystalline phases in the annealed samples. X-ray diffraction (XRD) studies were carried out to investigate the orthorhombic superconducting phases. An a.c. susceptibility study was carried out and image analysis was conducted to obtain the density and grain size of the products. In addition,
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2008
Numerical and experimental studies are carried out to investigate the usability of a piezoceramic... more Numerical and experimental studies are carried out to investigate the usability of a piezoceramic (PZT) sensor placed in the root of a stationary cantilever beam for measuring structural vibrations. The ability of the sensor for picking up the vibration signals during both the transient and steady-state phases is investigated. The piezoelectric equations obtained using the Hamilton's principle together with the finite-element approximation are utilized to extract the voltage outputs of the PZT sensor. An experimental set-up, to validate the theoretical results, is designed and manufactured. The experimentally measured sensor voltages are compared with the numerical ones. The results showed the excellent performance of the sensors in reading vibration signals of the beam. The root embedded PZT approach is an important step towards the application of measuring rotating blade vibrations.
Smart Structures and Materials 1999: Mathematics and Control in Smart Structures, 1999
ABSTRACT This paper presents a neural network controller for a piezoelectric controlled structure... more ABSTRACT This paper presents a neural network controller for a piezoelectric controlled structure by emulating the control performance of a Linear Quadratic Gaussian (LQG) controller. The configuration of the Artificial Neural Network (ANN) is simple, yet it is efficient in terms of its high learning speed and good generalization ability. A case study is presented to demonstrate the performance of the ANN controller versus the LQG controller. The test results for different disturbances on the structure show excellent agreement between the ANN and LQG controllers.
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Papers by Mehmet Sunar