1,720,966 research outputs found
Inverse methods for health monitoring and shape sensing of aerospace structures
No full textShape 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
Real-time displacement monitoring of a composite stiffened panel subjected to mechanical and thermal loads
No full textReal-time reconstruction of the deformed structural shape using in situ strain measurements is an inverse problem, commonly called shape sensing. The knowledge of the deformed structural shape in real time has important implications for assessing strain, stress, and failure states, and thus constitutes a key component of structural health monitoring. In addition, shape sensing is required for control and actuation of smart structures. In this paper, shape sensing analyses are carried out for typical composite stiffened structures using the inverse Finite Element Method (iFEM). By using a limited set of discrete strain data, iFEM allows full-field reconstruction of displacements that can thus be monitored also far from sensor locations. First, the iFEM theoretical framework and the formulation of a triangular, inverse shell element are briefly discussed. Then, a general strain-sensor configuration amenable to stiffened shell structures is proposed. Several numerical results are presented for static, dynamic, and thermal loadings. The robustness of the method with respect to input errors is also investigated. It is shown that iFEM is a viable methodology for shape sensing of composite stiffened structures, having the desired computational efficiency, accuracy, and robustness with respect to 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 characteristic
Shape sensing methods: Review and experimental comparison on a wing-shaped plate
Full text linkShape sensing, i.e., the reconstruction of the displacement field of a structure from some discrete surface strain measurements, is a fundamental capability for the structural health management of critical components. In this paper, a review of the shape sensing methodologies available in the open literature and of the different applications is provided. Then, for the first time, an experimental comparative study is presented among the main approaches in order to highlight their relative merits in presence of uncertainties affecting real applications. These approaches are, namely, the inverse Finite Element Method, the Modal Method and Ko’s Displacement Theory. A brief description of these methods is followed by the presentation of the experimental test results. A cantilevered, wing-shaped aluminum plate is let deform under its own weight, leading to bending and twisting. Using the experimental strain measurements as input data, the deflection field of the plate is reconstructed using the three aforementioned approaches and compared with the actual measured deflection. The inverse Finite Element Method is proven to be slightly more accurate and particularly attractive because it is versatile with respect to the boundary conditions and it does not require any information about material properties and loading conditions
Shape and stress sensing of multilayered composite and sandwich structures using an inverse Finite Element Method
Full text linkThe 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
A novel approach for displacement and stress monitoring of sandwich structures based on the inverse Finite Element Method
No full textThe real-time reconstruction of the displacement and stress fields from discrete-location strain measurements is a fundamental feature for monitoring systems, which is generally 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. Using a C0-discretization, 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 and stresses that may be 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-sensin
Beam shape sensing using inverse Finite Element Method: theory and experimental validation
No full textAn inverse Finite Element Method (iFEM) is presented for beam and frame structures. The method is aimed at reconstructing the complete displacement field starting from in situ measurements of surface strains. A laboratory experiment is conducted on a simple cantilever beam subjected to various static oadings. Experimentally measured strains are used within a single-element iFEM model to assess the efficiency and predictive capability of the approach with espect to uncertainties and measurement errors that unavoidably affect real structure
Dynamic shape reconstruction of three-dimensional frame structures using the inverse finite element method
No full textA 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
Shape sensing of three-dimensional frame structures using the inverse finite element method
No full textAn 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 approac
The inverse Finite Element Method for shape sensing of aerospace structures
No full textThe 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 characteristic
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