Identification of flexible structures for robust control

Documentation is provided of the authors' experience with modeling and identification of an experimental flexible structure for the purpose of control design, with the primary aim being to motivate some important research directions in this area. A multi-input/multi-output (MIMO) model of the structure is generated using the finite element method. This model is inadequate for control design, due to its large variation from the experimental data. Chebyshev polynomials are employed to fit the data with single-input/multi-output (SIMO) transfer function models. Combining these SIMO models leads to a MIMO model with more modes than the original finite element model. To find a physically motivated model, an ad hoc model reduction technique which uses a priori knowledge of the structure is developed. The ad hoc approach is compared with balanced realization model reduction to determine its benefits. Descriptions of the errors between the model and experimental data are formulated for robust control design. Plots of select transfer function models and experimental data are included

Structural health monitoring and bridge condition assessment

Thesis (Ph.D.) University of Alaska Fairbanks, 2016This research is mainly in the field of structural identification and model calibration, optimal sensor placement, and structural health monitoring application for large-scale structures. The ultimate goal of this study is to identify the structure behavior and evaluate the health condition by using structural health monitoring system. To achieve this goal, this research firstly established two fiber optic structural health monitoring systems for a two-span truss bridge and a five-span steel girder bridge. Secondly, this research examined the empirical mode decomposition (EMD) method’s application by using the portable accelerometer system for a long steel girder bridge, and identified the accelerometer number requirements for comprehensively record bridge modal frequencies and damping. Thirdly, it developed a multi-direction model updating method which can update the bridge model by using static and dynamic measurement. Finally, this research studied the optimal static strain sensor placement and established a new method for model parameter identification and damage detection.Chapter 1: Introduction -- Chapter 2: Structural Health Monitoring of the Klehini River Bridge -- Chapter 3: Ambient Loading and Modal Parameters for the Chulitna River Bridge -- Chapter 4: Multi-direction Bridge Model Updating using Static and Dynamic Measurement -- Chapter 5: Optimal Static Strain Sensor Placement for Bridge Model Parameter Identification by using Numerical Optimization Method -- Chapter 6: Conclusions and Future Work

Integrated chaos generators

This paper surveys the different design issues, from mathematical model to silicon, involved on the design of integrated circuits for the generation of chaotic behavior.Comisión Interministerial de Ciencia y Tecnología 1FD97-1611(TIC)European Commission ESPRIT 3110

Methodologies for virtual sensing applied to aeronautical and ship structures

In this thesis the problem of achieving a full, experimentally based, representation of the load and elastic deflection response of aeronautical and ship structures is concerned by the development of numerical procedures and their assessment via related experimental activities. The objective is to provide reliable estimations of elastic deflections and external forces throughout the structure using noisy pointwise measurements. This issue is critical for some important structural engineering applications such as Structural Health Monitoring and Condition-Based Maintenance. The most important tools generally used for this purpose (e.g., Kalman filter) have been first reviewed, pointing strengths and critical issues out. Then, an approach based on an optimal second-order natural observer has been proposed also integrating this with signal processing approaches like discrete wavelet transform and finite-element component analysis approaches like dynamics condensation. The developed and integrated numerical framework was finally applied to the state estimation of two specific structures, namely, an aircraft and surface vessel operating under unsteady environmental conditions featured by wind gust or sea waves, respectively. More in detail, a scaled physical model of a fast catamaran, tested in the towing-tank, and a numerical model of a flexible aircraft were studied as significant test cases for assessing the introduced methodologies. Both the structures involved are interesting in their respective research fields. The accurate and complete estimation of the structural dynamics behavior of the fast catamaran is particularly interesting since in real world it might be exposed to critical slamming phenomena on the wetdeck region. The experimental set-up and in particular the choice of the structural measurements were crucial to have a minimum but reliable database for the reconstruction of the structural deflection field. By applying the above methodologies, it was also possible to provide a deeper insight relative to violent fluid-structure interaction phenomena and to evaluate possible fatigue-life reduction for components where direct monitoring was not possible. The other case study consists of an aircraft research model that experiences a particular kind of instability involving both aeroelasticity and flight dynamics. In such aeronautical application, the structural measurements are virtually obtained by means of simulations based on a flight dynamics and aeroelasticity toolbox developed for the present purpose and featured by an accurate description of the coupling caused by aerodynamic and inertial forces. This case has been performed to investigate numerically the technique proposed in this thesis by integrating the methodology with multi-resolution analysis

Optimization of modal analysis and cross-orthogonality techniques to insure finite element model correlation to test data

This work summarizes the views of current authors on the multifaceted problems associated with updating a finite element model with vibration test data. It presents the practical optimization solutions for each step from pre-test analysis, through the actual vibration test, through post-test orthogonality checks and subsequent model correlation

Research in structures, structural dynamics and materials, 1989

Topics addressed include: composite plates; buckling predictions; missile launch tube modeling; structural/control systems design; optimization of nonlinear R/C frames; error analysis for semi-analytic displacement; crack acoustic emission; and structural dynamics

Application of the Craig-Bampton model order reduction method to a composite structure: MACco, COMAC, COMAC-S and eCOMAC

The Craig-Bampton model order reduction (CBMOR) method based on the Rayleigh-Ritz approach was applied in a previous work to simulate dynamic behavior of a composite structure (CFRP) using the modal assurance criteria (MAC) and cross orthogonality (XOR) to validate the correlation. Different coordinate modal assurance criteria are applied to complement and verify the eigenfrequencies and eigenvectors obtained of the full and reduced models using substructures (super-elements). An improvement is observed per paired mode-sensor with the MAC per coordinates criterion (MACco) in a CFRP once the stiffness parameters are updated in the full model applying a mix-numerical experimental technique (MNET) using a design of experiments (DOE). The coordinate modal assurance criteria (COMAC) and the scaleCOMAC (COMACS) results of the full models display the best results respect to the reduced model. Furthermore, slight improvement of the enhanced COMAC (eCOMAC) results are observed in the reduced model despite having lower MAC performance. This approach complements the results of the previous work using several COMAC techniques, and demostrates the feasibility to achieve low COMACs results in the reduced finite element model once the stiffness parameters of the full element model are updated. The example was prepared and solved with MSC/NASTRAN SOL103 and SDTools-MATLAB for comparative purposes

Dual methods and approximation concepts in structural synthesis

Approximation concepts and dual method algorithms are combined to create a method for minimum weight design of structural systems. Approximation concepts convert the basic mathematical programming statement of the structural synthesis problem into a sequence of explicit primal problems of separable form. These problems are solved by constructing explicit dual functions, which are maximized subject to nonnegativity constraints on the dual variables. It is shown that the joining together of approximation concepts and dual methods can be viewed as a generalized optimality criteria approach. The dual method is successfully extended to deal with pure discrete and mixed continuous-discrete design variable problems. The power of the method presented is illustrated with numerical results for example problems, including a metallic swept wing and a thin delta wing with fiber composite skins

Hybrid simulation techniques in the structural analysis and testing of architectural heritage

L'abstract è presente nell'allegato / the abstract is in the attachmen

ROBUST MODEL DEVELOPMENT FOR EVALUATION OF EXISTING STRUCTURES

In the context of scientific computing, validation aims to determine the worthiness of a model in supporting critical decision making. This determination must occur given the imperfections in the mathematical representation resulting from the unavoidable idealizations of physics phenomena. Uncertainty in parameter values furthers the validation problems due to the inevitable lack of information about material properties, boundary conditions, loads, etc. which must be taken into account in making predictions about structural response. The determination of worthiness then becomes assessing whether an unavoidably imperfect mathematical model, subjected to poorly known input parameters, can predict sufficiently well in its intended purpose. The maximum degree of uncertainty in the model\u27s input parameters which the model can tolerate and still produce predictions within a predefined error tolerance is termed as robustness of the model. A trade-off exists between a model’s robustness to unavoidable uncertainty and its agreement with experiments, i.e. fidelity. This dissertation introduces the concept of satisfying boundary to evaluate such a trade-off. This boundary encompasses the model predictions that meet prescribed error tolerances. Decisions regarding allocation of resources for additional experiments to reduce uncertainty, relaxation of error tolerances, or the required confidence in the model predictions can be arrived at with the knowledge of this trade-off. This new approach for quantifying robustness based on satisfying boundaries is demonstrated on an application to a nonlinear finite element model of a historic masonry monument Fort Sumter