IRIS Pol. Torinohttps://iris.polito.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Mon, 14 Jun 2021 20:23:52 GMT2021-06-14T20:23:52Z10141The inverse Finite Element Method for shape sensing of aerospace structureshttp://hdl.handle.net/11583/2514492Titolo: The inverse Finite Element Method for shape sensing of aerospace structures
Abstract: The paper presents recent theoretical developments and numerical results obtained at NASA Langley Research Center, by Dr. Alex Tessler and co-workers, and at Politecnico di Torino, by the AESDO Group, addressing the inverse problem of “shape-sensing”, i.e., reconstruction of structural displacements using surface-measured strains. The theoretical framework of the inverse Finite Element Method (iFEM) is briefly presented. Both the original formulation for built-up shell structures and the recent formulation for truss, beam, and frame structures are described. Several numerical and experimental results for plate- and beam-like structures subjected to static and dynamic loads are presented. It is shown that iFEM is a valid approach for shape sensing due to its computational efficiency, accuracy, and robustness with respect to experimental strain-measurement errors. The iFEM shape-sensing methodology is particularly attractive because it does not require any information regarding applied loading, elastic material constants, inertial properties, or damping characteristics.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11583/25144922013-01-01T00:00:00ZInverse finite element method for three-dimensional frame structureshttp://hdl.handle.net/11583/2317602Titolo: Inverse finite element method for three-dimensional frame structures
Abstract: Report DIASP
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11583/23176022010-01-01T00:00:00ZInverse methods for health monitoring and shape sensing of aerospace structureshttp://hdl.handle.net/11583/2538725Titolo: Inverse methods for health monitoring and shape sensing of aerospace structures
Abstract: Shape sensing, i.e., reconstruction of the displacement field of a structure from surface-measured strains, has relevant implications for Structural Health Monitoring (SHM), as well as for control and actuation of smart structures. The knowledge of the full-field displacements implies that other essential response quantities such as stresses can be assessed, thus enabling real-time damage predictions by means of appropriate failure criteria. The inverse Finite Element Method (iFEM) is a shape-sensing methodology shown to be fast, accurate, and robust. In the present thesis, the general framework of iFEM, i.e., least-square variational statement and displacement-based finite element approximation, has been adopted to develop efficient and robust shape-sensing techniques, with focus on thin-walled structures, beam and frame structures and multilayered, composite and sandwich structures.
The theoretical framework of the iFEM and its original formulation for plates and shell structures, developed on the basis of the First-order Shear Deformation Theory (FSDT), are firstly summarized. Then, the variational principle for three-dimensional frame structures, based on Timoshenko beam theory, is reviewed. This is followed by a discussion of two C0-continuous, beam inverse elements, a 0th-order element, having constant shear-section strain along the element length, and a newly formulated 1st-order element, having linear shear section strain. The formulation, originally proposed for circular cross-section beams, is extended to rectangular beams. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. A new formulation for the shape sensing of multilayered composite and sandwich structures possessing a high degree of anisotropy and heterogeneity is herein presented. The new formulation employs the iFEM as a general framework and the Refined Zigzag Theory (RZT) as the underlying plate theory. A three-node inverse plate finite element is formulated, enabling robust and efficient modeling of arbitraty plate structures. A methodology to infer applied loads from iFEM-predicted displacements is proposed. The evaluated loads can then be used within a direct finite element analysis to evaluate high-fidelity finite element stress solution. Several example problems involving thin-walled structures, three-dimensional frame structures and multilayered, composite and sandwich structures, undergoing static and dynamic response, as well as thermal deformation, are discussed. To simulate experimentally measured strains and to establish reference displacements, high-fidelity MSC/NASTRAN finite element analyses are performed. For the sandwich plate problems, exact elasticity solution or direct RZT solution are employed to the same purpose. To enable the analysis of partially instrumented structures considered in the present example problems, a method to select optimal weights to be used in the weighted least-square formulation for plates with sparse strain data is proposed. Numerically simulated measurement errors, based on Gaussian distribution, are also considered in order to verify the stability and robustness of the iFEM methodology. Furthermore, a comparative study involving iFEM and other shape sensing methodologies existing in the literature is discussed. An experimental test campaign is presented aiming to demonstrate that iFEM for beam and plate structures is reliable when experimentally measured strains are used as input data. The accuracy and robustness of iFEM with respect to unavoidable measurement errors, due to strain sensor locations, measurement systems, and geometry imperfections, are demonstrated for both static and dynamic loadings.
The proposed methodology based on the iFEM is computationally efficient and accurate in reconstructing both static and time-varying displacement fields. Since only strain-displacement relationships are used, all type of structural deformation can be modeled without the knowledge of material properties, applied loading, or damping characteristics. For this reasons, the present shape sensing techniques are suitable for real-time Structural Health Monitoring.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11583/25387252014-01-01T00:00:00ZAn inverse finite element method for beam shape sensing: theoretical framework and experimental validationhttp://hdl.handle.net/11583/2534688Titolo: An inverse finite element method for beam shape sensing: theoretical framework and experimental validation
Abstract: Shape sensing, i.e., reconstruction of the displacement ﬁeld of a structure from surface-measured strains, has relevant implications for the monitoring, control and actuation of smart structures. The inverse ﬁnite element method (iFEM) is a shape-sensing methodology shown to be fast, accurate and robust. This paper aims to demonstrate that the recently presented iFEM for beam and frame structures is reliable when experimentally measured strains are used as input data. The theoretical framework of the methodology is ﬁrst reviewed. Timoshenko beam theory is adopted, including stretching, bending, transverse shear and torsion deformation modes. The variational statement and its discretization with C0-continuous inverse elements are briefly recalled. The three-dimensional displacement ﬁeld of the beam structure is reconstructed under the condition that least-squares compatibility is guaranteed between the measured strains and those interpolated within the inverse elements. The experimental setup is then described. A thin-walled cantilevered beam is subjected to different static and dynamic loads. Measured surface strains are used as input data for shape sensing at ﬁrst with a single inverse element. For the same test cases, convergence is also investigated using an increasing number of inverse elements. The iFEM-recovered deﬂections and twist rotations are then compared with those measured experimentally. The accuracy, convergence and robustness of the iFEM with respect to unavoidable measurement errors, due to strain sensor locations, measurement systems and geometry imperfections, are demonstrated for both static and dynamic loadings.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/11583/25346882014-01-01T00:00:00ZShape sensing of 3D frame structures using an inverse Finite Element Methodhttp://hdl.handle.net/11583/2498382Titolo: Shape sensing of 3D frame structures using an inverse Finite Element Method
Abstract: A robust and efficient computational method for reconstructing the elastodynamic structural response of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as “shape sensing”, this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving section strains (also known as strain measures) of Timoshenko theory for stretching, torsion, bending, and transverse shear. The present iFEM methodology is based on strain-displacement relations only, without invoking force equilibrium. Consequently, both static and time-varying displacement fields can be reconstructed without the knowledge of material properties, applied loading, or damping characteristics. Two finite elements capable of modeling frame structures are derived using interdependent interpolations, in which interior degrees of freedom are condensed out at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. Several example problems involving cantilevered beams and three-dimensional frame structures undergoing static and dynamic response are discussed. To simulate experimentally measured strains and to establish reference displacements, high-fidelity MSC/NASTRAN finite element analyses are performed. Furthermore, numerically simulated measurement errors, based on Gaussian distribution, are also considered in order to verify the stability and robustness of the methodology. The iFEM solution accuracy is examined with respect to various levels of discretization and the number of strain gauges.
Sun, 01 Jan 2012 00:00:00 GMThttp://hdl.handle.net/11583/24983822012-01-01T00:00:00ZDynamic shape reconstruction of three-dimensional frame structures using the inverse finite element methodhttp://hdl.handle.net/11583/2430193Titolo: Dynamic shape reconstruction of three-dimensional frame structures using the inverse finite element method
Abstract: A robust and efficient computational method for reconstructing the three-dimensional displacement field of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as “shape sensing”, this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving strain measures of Timoshenko theory for stretching, torsion, bending, and transverse shear. Two inverse-frame finite elements are derived using the interdependent interpolations whose interior degrees-of-freedom are condensed out exactly at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. As an example problem, a thin-walled, circular cross-section cantilevered beam subjected to harmonic excitations in the presence of structural damping is modeled using iFEM; where, to simulate strain-gauge values and to provide reference displacements, a high-fidelity MSC/NASTRAN shell finite element model is used. Examples of low and high-frequency dynamic motion are analyzed and the solution accuracy examined with respect to the increased fidelity of the iFEM’s discretization and the number of strain gauges.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11583/24301932011-01-01T00:00:00ZDynamic shape reconstruction of three-dimensional frame structures using the inverse finite element methodhttp://hdl.handle.net/11583/2467379.1Titolo: Dynamic shape reconstruction of three-dimensional frame structures using the inverse finite element method
Abstract: A robust and efficient computational method for reconstructing the three-dimensional displacement field of truss, beam, and frame structures, using measured surface-strain data, is presented. Known as “shape sensing”, this inverse problem has important implications for real-time actuation and control of smart structures, and for monitoring of structural integrity. The present formulation, based on the inverse Finite Element Method (iFEM), uses a least-squares variational principle involving strain measures of Timoshenko theory for stretching, torsion, bending, and transverse shear. Two inverse-frame finite elements are derived using interdependent interpolations whose interior degrees-of-freedom are condensed out at the element level. In addition, relationships between the order of kinematic-element interpolations and the number of required strain gauges are established. As an example problem, a thin-walled, circular cross-section cantilevered beam subjected to harmonic excitations in the presence of structural damping is modeled using iFEM; where, to simulate strain-gauge values and to provide reference displacements, a high-fidelity MSC/NASTRAN shell finite element model is used. Examples of low and high-frequency dynamic motion are analyzed and the solution accuracy examined with respect to various levels of discretization and the number of strain gauges.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/11583/2467379.12011-01-01T00:00:00ZShape and stress sensing of multilayered composite and sandwich structures using an inverse Finite Element Methodhttp://hdl.handle.net/11583/2510289Titolo: Shape and stress sensing of multilayered composite and sandwich structures using an inverse Finite Element Method
Abstract: The marked increase in the use of composite and sandwich material systems in aerospace, civil, and marine structures leads to the need for integrated structural health management systems. A key capability to enable such systems is the real-time reconstruction of structural deformations, stresses, and failure criteria that are inferred from in-situ, discrete-location strain measurements. This technology is commonly referred to as shape- and stress-sensing. Presented herein is a computationally efficient shape- and stress-sensing methodology that is ideally suited for applications to laminated composite and sandwich structures. The new approach employs the inverse Finite Element Method (iFEM) as a general framework and the Refined Zigzag Theory (RZT) as the underlying plate theory. A three-node inverse plate finite element is formulated. The element formulation enables robust and efficient modeling of plate structures instrumented with strain sensors that have arbitrary positions. The methodology leads to a set of linear algebraic equations that are solved efficiently for the unknown nodal displacements. These displacements are then used at the finite element level to compute full-field strains, stresses, and failure criteria that are in turn used to assess structural integrity. Numerical results for multilayered, highly heterogeneous laminates demonstrate the unique capability of this new formulation for shape- and stress-sensing.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/11583/25102892013-01-01T00:00:00ZShape sensing of three-dimensional frame structures using the inverse finite element methodhttp://hdl.handle.net/11583/2360549Titolo: Shape sensing of three-dimensional frame structures using the inverse finite element method
Abstract: An inverse finite element method is presented for beam and frame structures. The method is aimed at the reconstruction of the complete displacement field starting from in situ measurements of surface strains. Several numerical examples are presented for statically loaded beam and frame structures which demonstrate the predictive capability and accuracy of the approach.
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11583/23605492010-01-01T00:00:00ZFatigue crack initiation and propagation of a TiNi shape memory alloyhttp://hdl.handle.net/11583/2513483Titolo: Fatigue crack initiation and propagation of a TiNi shape memory alloy
Fri, 01 Jan 2010 00:00:00 GMThttp://hdl.handle.net/11583/25134832010-01-01T00:00:00Z