This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first ...This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.展开更多
This paper presents an analytical solution for free vibration analysis of thick rectangular isotropic plates coupled with a bounded fluid for various boundary conditions. In order to consider displacement theories of ...This paper presents an analytical solution for free vibration analysis of thick rectangular isotropic plates coupled with a bounded fluid for various boundary conditions. In order to consider displacement theories of an arbitrary order, the Carrera Unified Formulation(CUF) is used. The eigenvalue problem is obtained by using the energy functional, considering plate and fluid kinetic energies as well as the potential energy of the plate. The Ritz method is used to evaluate the displacement variables, and the functions used in the Ritz series can be adjusted to consider any of the classical boundary conditions. The convergence of the solution is analyzed, and a validation of results considering open literature and 3D finite element software is performed. Parametric studies are carried out to obtain natural frequencies as a function of the side-to-thickness ratio, plate aspect ratio, fluid domain size, plate boundary conditions, and fluid-solid density ratio. Pressure and velocity in the fluid domain are evaluated in order to establish the consistency of the solution.Accurate results for thick plates are obtained with a much lower computational cost compared to that of 3D finite element solutions.展开更多
This paper extends to composite plates including piezoelectric plies the variable kinematics plate modeling approach called Sublaminate Generalized Unified Formulation(SGUF).Two-dimensional plate equations are obtaine...This paper extends to composite plates including piezoelectric plies the variable kinematics plate modeling approach called Sublaminate Generalized Unified Formulation(SGUF).Two-dimensional plate equations are obtained upon defining a priori the through-thickness distribution of the displacement field and electric potential.According to SGUF,independent approximations can be adopted for the four components of these generalized displacements:an Equivalent Single Layer(ESL)or Layer-Wise(LW)description over an arbitrary group of plies constituting the composite plate(the sublaminate)and the polynomial order employed in each sublaminate.The solution of the two-dimensional equations is sought in weak form by means of a Ritz method.In this work,boundary functions are used in conjunction with the domain approximation expressed by an orthogonal basis spanned by Legendre polynomials.The proposed computational tool is capable to represent electroded surfaces with equipotentiality conditions.Free-vibration problems as well as static problems involving actuator and sensor configurations are addressed.Two case studies are presented,which demonstrate the high accuracy of the proposed Ritz-SGUF approach.A model assessment is proposed for showcasing to which extent the SGUF approach allows a reduction of the number of unknowns with a controlled impact on the accuracy of the result.展开更多
This paper presents an analytical solution for static analysis of thick rectangular beams with different boundary conditions. Carrera＇s Unified Formulation（CUF） is used in order to consider shear deformation theori...This paper presents an analytical solution for static analysis of thick rectangular beams with different boundary conditions. Carrera＇s Unified Formulation（CUF） is used in order to consider shear deformation theories of arbitrary order. The novelty of the present work is that a boundary discontinuous Fourier approach is used to consider clamped boundary conditions in the analytical solution, unlike Navier-type solutions which are restricted to simply supported beams.Governing equations are obtained by employing the principle of virtual work. The numerical accuracy of results is ascertained by studying the convergence of the solution and comparing the results to those of a 3D finite element solution. Beams subjected to bending due to a uniform pressure load and subjected to torsion due to opposite linear forces are considered. Overall, accurate results close to those of 3D finite element solutions are obtained, which can be used to validate finite element results or other approximate methods.展开更多
The buckling of thin-walled structures is presented using the 1D finite element based refined beam theory formulation that permits us to obtain N-order expansions for the three displacement fields over the section dom...The buckling of thin-walled structures is presented using the 1D finite element based refined beam theory formulation that permits us to obtain N-order expansions for the three displacement fields over the section domain.These higher-order models are obtained in the framework of the Carrera unified formulation(CUF).CUF is a hierarchical formulation in which the refined models are obtained with no need for ad hoc formulations.Beam theories are obtained on the basis of Taylor-type and Lagrange polynomial expansions.Assessments of these theories have been carried out by their applications to studies related to the buckling of various beam structures,like the beams with square cross section,I-section,thin rectangular cross section,and annular beams.The results obtained match very well with those from commercial finite element softwares with a significantly less computational cost.Further,various types of modes like the bending modes,axial modes,torsional modes,and circumferential shell-type modes are observed.展开更多
Panel flutter phenomena can be strongly affected by thermal loads,and so a refined aeroelastic model is presented.Higher-order shell theories are used as structural models.The aerodynamic forces are described using th...Panel flutter phenomena can be strongly affected by thermal loads,and so a refined aeroelastic model is presented.Higher-order shell theories are used as structural models.The aerodynamic forces are described using the Piston theory.The temperature is considered uniform over the thickness of the panel.The aero-thermo-elastic model is derived in the framework of the Carrera unified formulation(CUF),therefore the matrices are expressed in a compact form using the″fundamental nuclei″.Composite and sandwich structures are considered and different boundary conditions are taken into account.The effects of the thermal load on the aeroelastic behavior are investigated.展开更多
In the present work,a new class of finite elements(FEs)for the analysis of composite and sandwich plates embedding piezoelectric skins and patches is proposed.By making use of node-by-node variable plate theory assump...In the present work,a new class of finite elements(FEs)for the analysis of composite and sandwich plates embedding piezoelectric skins and patches is proposed.By making use of node-by-node variable plate theory assumptions,the new finite element allows for the simultaneous analysis of different subregions of the problem domain with different kinematics and accuracy,in a global/local sense.As a consequence,the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states,and their electro-mechanical coupling present a complex distribution.The primary advantage is that no ad-hoc techniques and mathematical artifices are required to mix the fields coming from two different and kinematically incompatible adjacent elements,because the plate structural theory varies within the finite element itself.In other words,the structural theory of the plate element is a property of the FE node in this present approach,and the continuity between two adjacent elements is ensured by adopting the same kinematics at the interface nodes.The finite element arrays of the generic plate element are formulated in terms of fundamental nuclei,which are invariants of the theory approximation order and the modeling technique(Equivalent-Single-Layer,Layer-Wise).In this work,the attention is focused on the use of Legendre polynomial expansions to describe the through-the-thickness unknowns to develop advanced plate theories.Several numerical investigations,such as composite and sandwich multilayered plates embedding piezoelectric skins and patches with various load,boundary conditions,and piezoelectric material polarizations,are carried out to validate and demonstrate the accuracy and efficiency of the present plate element,including comparison with various closed-form and FE solutions from the literature.展开更多
The present article considers the free-vibration analysis of plate structures with piezoelectric patches by means of a plate finite element with variable through-the-thickness layer-wise kinematic.The refined models u...The present article considers the free-vibration analysis of plate structures with piezoelectric patches by means of a plate finite element with variable through-the-thickness layer-wise kinematic.The refined models used are derived from Carrera’s Unified Formulation(CUF)and they permit the vibration modes along the thickness to be accurately described.The finite-element method is employed and the plate element implemented has nine nodes,and the mixed interpolation of tensorial component(MITC)method is used to contrast the membrane and shear locking phenomenon.The related governing equations are derived from the principle of virtual displacement,extended to the analysis of electromechanical problems.An isotropic plate with piezoelectric patches is analyzed,with clamped-free boundary conditions and subjected to open-and short-circuit configurations.The results,obtained with different theories,are compared with the higher-order type solutions given in the literature.The conclusion is reached that the plate element based on the CUF is more suitable and efficient compared to the classical models in the study of multilayered structures embedding piezo-patches.展开更多
The present paper presents an innovative approach for the numerical modeling of piezo-electric transducers for the health-monitoring of layered structures.The numerical approach has been developed in the frameworks of...The present paper presents an innovative approach for the numerical modeling of piezo-electric transducers for the health-monitoring of layered structures.The numerical approach has been developed in the frameworks of the Carrera Unified Formulation.This computa-tional tool allows refined numerical models to be derived in a unified and efficient fashion.The use of higher-order models and the cap-ability to connect different kinematic models using the node-depen-dent kinematic approach has led to an efficient modeling technique for global-local analysis.This approach can refine the model only in those regions where it is required,e.g.,the areas where piezo-electric transducers are placed.The model has been used to study embedded and surface-mounted sensors.The accuracy of the pre-sent model has been verified by comparing the current results with numerical and experimental data from the literature.Different mod-eling solutions have been developed,mixing one-,two-and threedimensional finite elements.The results show that the use of the present modeling technique allows the computational cost to be reduced with respect to the classical approaches preserving the ccuracy of the results in the critical areas.展开更多
In this work,a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed.The main idea of models coupling is developed by presenting the conce...In this work,a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed.The main idea of models coupling is developed by presenting the concept of nodal dependent kinematics where the same finite element can present at each node a different approximation of the main unknowns by setting a nodewise through-the-thickness approximation base.In a global/local approach scenario,the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states,and their electro-mechanical coupling present a complex distribution.Several numerical investigations are carried out to validate the accuracy and efficiency of the present shell element.An accurate representation of mechanical stresses and electric displacements in localized zones is possible with reduction of the computational costs if an accurate distribution of the higherorder kinematic capabilities is performed.On the contrary,the accuracy of the solution in terms of mechanical displacements and electric potential values depends on the global approximation over the whole structure.The efficacy of the present node-dependent variable kinematic models,thus,depends on the characteristics of the problem under consideration as well as on the required analysis type.展开更多
文摘This paper provides a unified formulation of optimal guidance-to-collision law for a target with an arbitrary acceleration or deceleration.The collision course for general target acceleration or deceleration is first determined from the engagement geometry in conjunction with the nonlinear engagement kinematics in the proposed approach.The heading error defined in the collision course is then adopted as a variable to be nullified for accomplishing the intercept condition.The proposed guidance law is derived based on the heading error dynamics and the optimal error dynamics to ensure optimality and finite-time convergence.As illustrative examples,the proposed guidance command for a constant target acceleration and a target deceleration in the form of a quadratic function of speed are provided.Additionally,the time-to-go prediction method is suggested for implementing the proposed method.The characteristics of the proposed guidance command are analytically investigated to provide insight into the proposed method.The key benefits of the proposed method lie in not producing unnecessary guidance commands near a target compared to other methods and ensuring optimality in guidance command even in the nonlinear engagement kinematics.Finally,numerical simulations are performed to validate the proposed method and to show our findings.
基金"Diseno y optimización de dispositivos de drenaje para pacientes con glaucoma mediante el uso de modelos computacionales de ojos"founded by Cienciactiva,CON-CYTEC,under the contract number N°008-2016-FONDECYTthe financial support from the Peruvian Government
文摘This paper presents an analytical solution for free vibration analysis of thick rectangular isotropic plates coupled with a bounded fluid for various boundary conditions. In order to consider displacement theories of an arbitrary order, the Carrera Unified Formulation(CUF) is used. The eigenvalue problem is obtained by using the energy functional, considering plate and fluid kinetic energies as well as the potential energy of the plate. The Ritz method is used to evaluate the displacement variables, and the functions used in the Ritz series can be adjusted to consider any of the classical boundary conditions. The convergence of the solution is analyzed, and a validation of results considering open literature and 3D finite element software is performed. Parametric studies are carried out to obtain natural frequencies as a function of the side-to-thickness ratio, plate aspect ratio, fluid domain size, plate boundary conditions, and fluid-solid density ratio. Pressure and velocity in the fluid domain are evaluated in order to establish the consistency of the solution.Accurate results for thick plates are obtained with a much lower computational cost compared to that of 3D finite element solutions.
文摘This paper extends to composite plates including piezoelectric plies the variable kinematics plate modeling approach called Sublaminate Generalized Unified Formulation(SGUF).Two-dimensional plate equations are obtained upon defining a priori the through-thickness distribution of the displacement field and electric potential.According to SGUF,independent approximations can be adopted for the four components of these generalized displacements:an Equivalent Single Layer(ESL)or Layer-Wise(LW)description over an arbitrary group of plies constituting the composite plate(the sublaminate)and the polynomial order employed in each sublaminate.The solution of the two-dimensional equations is sought in weak form by means of a Ritz method.In this work,boundary functions are used in conjunction with the domain approximation expressed by an orthogonal basis spanned by Legendre polynomials.The proposed computational tool is capable to represent electroded surfaces with equipotentiality conditions.Free-vibration problems as well as static problems involving actuator and sensor configurations are addressed.Two case studies are presented,which demonstrate the high accuracy of the proposed Ritz-SGUF approach.A model assessment is proposed for showcasing to which extent the SGUF approach allows a reduction of the number of unknowns with a controlled impact on the accuracy of the result.
文摘This paper presents an analytical solution for static analysis of thick rectangular beams with different boundary conditions. Carrera＇s Unified Formulation（CUF） is used in order to consider shear deformation theories of arbitrary order. The novelty of the present work is that a boundary discontinuous Fourier approach is used to consider clamped boundary conditions in the analytical solution, unlike Navier-type solutions which are restricted to simply supported beams.Governing equations are obtained by employing the principle of virtual work. The numerical accuracy of results is ascertained by studying the convergence of the solution and comparing the results to those of a 3D finite element solution. Beams subjected to bending due to a uniform pressure load and subjected to torsion due to opposite linear forces are considered. Overall, accurate results close to those of 3D finite element solutions are obtained, which can be used to validate finite element results or other approximate methods.
文摘The buckling of thin-walled structures is presented using the 1D finite element based refined beam theory formulation that permits us to obtain N-order expansions for the three displacement fields over the section domain.These higher-order models are obtained in the framework of the Carrera unified formulation(CUF).CUF is a hierarchical formulation in which the refined models are obtained with no need for ad hoc formulations.Beam theories are obtained on the basis of Taylor-type and Lagrange polynomial expansions.Assessments of these theories have been carried out by their applications to studies related to the buckling of various beam structures,like the beams with square cross section,I-section,thin rectangular cross section,and annular beams.The results obtained match very well with those from commercial finite element softwares with a significantly less computational cost.Further,various types of modes like the bending modes,axial modes,torsional modes,and circumferential shell-type modes are observed.
文摘Panel flutter phenomena can be strongly affected by thermal loads,and so a refined aeroelastic model is presented.Higher-order shell theories are used as structural models.The aerodynamic forces are described using the Piston theory.The temperature is considered uniform over the thickness of the panel.The aero-thermo-elastic model is derived in the framework of the Carrera unified formulation(CUF),therefore the matrices are expressed in a compact form using the″fundamental nuclei″.Composite and sandwich structures are considered and different boundary conditions are taken into account.The effects of the thermal load on the aeroelastic behavior are investigated.
基金This work was supported by the Russian Science Foundation[15-19-30002]。
文摘In the present work,a new class of finite elements(FEs)for the analysis of composite and sandwich plates embedding piezoelectric skins and patches is proposed.By making use of node-by-node variable plate theory assumptions,the new finite element allows for the simultaneous analysis of different subregions of the problem domain with different kinematics and accuracy,in a global/local sense.As a consequence,the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states,and their electro-mechanical coupling present a complex distribution.The primary advantage is that no ad-hoc techniques and mathematical artifices are required to mix the fields coming from two different and kinematically incompatible adjacent elements,because the plate structural theory varies within the finite element itself.In other words,the structural theory of the plate element is a property of the FE node in this present approach,and the continuity between two adjacent elements is ensured by adopting the same kinematics at the interface nodes.The finite element arrays of the generic plate element are formulated in terms of fundamental nuclei,which are invariants of the theory approximation order and the modeling technique(Equivalent-Single-Layer,Layer-Wise).In this work,the attention is focused on the use of Legendre polynomial expansions to describe the through-the-thickness unknowns to develop advanced plate theories.Several numerical investigations,such as composite and sandwich multilayered plates embedding piezoelectric skins and patches with various load,boundary conditions,and piezoelectric material polarizations,are carried out to validate and demonstrate the accuracy and efficiency of the present plate element,including comparison with various closed-form and FE solutions from the literature.
文摘The present article considers the free-vibration analysis of plate structures with piezoelectric patches by means of a plate finite element with variable through-the-thickness layer-wise kinematic.The refined models used are derived from Carrera’s Unified Formulation(CUF)and they permit the vibration modes along the thickness to be accurately described.The finite-element method is employed and the plate element implemented has nine nodes,and the mixed interpolation of tensorial component(MITC)method is used to contrast the membrane and shear locking phenomenon.The related governing equations are derived from the principle of virtual displacement,extended to the analysis of electromechanical problems.An isotropic plate with piezoelectric patches is analyzed,with clamped-free boundary conditions and subjected to open-and short-circuit configurations.The results,obtained with different theories,are compared with the higher-order type solutions given in the literature.The conclusion is reached that the plate element based on the CUF is more suitable and efficient compared to the classical models in the study of multilayered structures embedding piezo-patches.
文摘The present paper presents an innovative approach for the numerical modeling of piezo-electric transducers for the health-monitoring of layered structures.The numerical approach has been developed in the frameworks of the Carrera Unified Formulation.This computa-tional tool allows refined numerical models to be derived in a unified and efficient fashion.The use of higher-order models and the cap-ability to connect different kinematic models using the node-depen-dent kinematic approach has led to an efficient modeling technique for global-local analysis.This approach can refine the model only in those regions where it is required,e.g.,the areas where piezo-electric transducers are placed.The model has been used to study embedded and surface-mounted sensors.The accuracy of the pre-sent model has been verified by comparing the current results with numerical and experimental data from the literature.Different mod-eling solutions have been developed,mixing one-,two-and threedimensional finite elements.The results show that the use of the present modeling technique allows the computational cost to be reduced with respect to the classical approaches preserving the ccuracy of the results in the critical areas.
基金This work was supported by the Russian Science Foundation[15-19-30002]。
文摘In this work,a new class of finite elements for the analysis of composite and sandwich shells embedding piezoelectric skins and patches is proposed.The main idea of models coupling is developed by presenting the concept of nodal dependent kinematics where the same finite element can present at each node a different approximation of the main unknowns by setting a nodewise through-the-thickness approximation base.In a global/local approach scenario,the computational costs can be reduced drastically by assuming refined theories only in those zones/nodes of the structural domain where the resulting strain and stress states,and their electro-mechanical coupling present a complex distribution.Several numerical investigations are carried out to validate the accuracy and efficiency of the present shell element.An accurate representation of mechanical stresses and electric displacements in localized zones is possible with reduction of the computational costs if an accurate distribution of the higherorder kinematic capabilities is performed.On the contrary,the accuracy of the solution in terms of mechanical displacements and electric potential values depends on the global approximation over the whole structure.The efficacy of the present node-dependent variable kinematic models,thus,depends on the characteristics of the problem under consideration as well as on the required analysis type.
