Convergence and frequency-domain analysis of a discrete first-order model reference adaptive controller

SUMMARY We study the convergence properties of a direct model reference adaptive control system by applying techniques from numerical analysis. In particular, a first-order discrete system coupled to a minimal control synthesis algorithm discretized by the one-step one-stage zero-order-hold sampling is studied. This results in a strongly non-linear dynamic system owing to the adaptive mechanism where stability at steady state, i.e. at the operating point, equates to successful control. This paper focuses on the convergence analysis of the overall dynamical system for understanding accuracy, stability and performance at steadystate. The local stability of the steady state solution is considered by linearizing the system in the neighbourhood of an operating point when the input is a step function. This analysis allows us to specify two gain space domains which define the region of local stability. Moreover, both the accuracy and the frequency-domain analyses give insight into the range of adaptive control weightings that results in optimal performance of the minimal control synthesis algorithm and also highlights a possible approach to a priori selection of the time step and adaptive weighting values. The effectiveness of the proposed analysis is further demonstrated by simulations and experiments on a first-order plant. Copyright # 2006 John Wiley & Sons, Ltd

Partitioned time integration methods for hardware in the loop based on linearly implicit L-Stable Rosenbrock methods

Hardware in the loop based on dynamic substructuring was conceived to be a hybrid numerical-experimental technique to simulate the non-linear behaviour of an emulated structure. Its challenge is to ensure that both numerical and physical substructures interact in real time by means of actuators –transfer systems-. With this objective in mind, the development and implementation of partitioned real-time compatible Rosenbrock algorithms are presented in this paper. In detail, we shortly introduce monolithic linearly implicit L-stable algorithms with two stages; and in view of the analysis of complex emulated structures, we present a novel interfield partitioned algorithm. Both the stability and accuracy properties of the proposed algorithm are examined through analytical and numerical studies carried out on Single-DoF model problems. Moreover, a novel test rig conceived to perform both linear and nonlinear substructure tests is introduced, and tests on a two-DoF split-mass system are illustrated. The drawbacks of this algorithm are underlined and improvements are introduced on a companion solution procedure

An improved equivalent force control algorithm for hybrid seismic testing of nonlinear systems

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Identification of the hysteretic behaviour of a partial-strength steel-concrete moment-resisting frame structure subject to pseudodynamic tests

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Quasi-periodicity and multi-scale resonators for the reduction of seismic vibrations in fluid-solid systems

This paper presents a mathematical model for an industry-inspired problem of vibration isolation applied to elastic fluid-filled containers. A fundamental problem of suppression of vibrations within a finite-width frequency interval for a multi-scale fluid-solid system has been solved. We have developed a systematic approach employing full fluid-solid interaction and dispersion analysis, which can be applied to finite and periodic multi-scale systems. The analytical findings are accompanied by numerical simulations, including frequency response analyses and transient regime computations

Finite element model updating of a semi‐rigid moment resisting structure

Partial-strength composite steel–concrete moment-resisting frame structures can be designed to develop a ductile response in components of beam-to-column joints and column bases, including flexural yielding of beam end plates, shear yielding of column web panel zones and yielding of anchors. To evaluate the performance of a statically indeterminate structure under different earthquake intensities, a series of pseudo-dynamic, quasi-static cyclic and vibration tests were carried out at the European Laboratory for Structural Assessment of the Joint Research Centre at Ispra, Italy. The identified modal parameters from forced vibration tests at three different damage levels were used in order to quantify local and global damage indices by updating a 3D FE model of the structure with the non-linear Powell's Dog-Leg optimization method. Then, the Latin Hypercube Sampling technique, a variant of the Monte Carlo method, was employed to study the sensitivity of the updated parameters of the 3D model to modal inputs, caused by measurement noise. Rotations of beam-to-column joints and column bases, storey displacements and forces were employed during the final cyclic test in order to update a 2D FE model of the test structure. To avoid numerical instabilities during the detection of the non-linear behaviour of the structure, a novel technique based on the transformation of the origin coordinates in each half cycle was implemented. The identified joint behaviours allowed low-cycle fatigue energy-based damage indices to be applied. Copyright © 2009 John Wiley & Sons, Ltd

Seismic vulnerability of above-ground storage tanks with unanchored support conditions for Na-tech risks based on Gaussian process regression

AbstractThis paper aims to investigate the seismic vulnerability of an existing unanchored steel storage tank ideally installed in a refinery in Sicily (Italy), along the lines of performance-based earthquake engineering. Tank performance is estimated by means of component-level fragility curves for specific limit states. The assessment is based on a framework that relies on a three-dimensional finite element (3D FE) model and a low-fidelity demand model based on Gaussian process regression, which allows for cheaper simulations. Moreover, to approximate the system response corresponding to the random variation of both peak ground acceleration and liquid filling level, a second-order design of experiments method is adopted. Hence, a parametric investigation is conducted on a specific existing unanchored steel storage tank. The relevant 3D FE model is validated with an experimental campaign carried out on a shaking table test. Special attention is paid to the base uplift due to significant inelastic deformations that occur at the baseplate close to the welded baseplate-to-wall connection, offering extensive information on both capacity and demand. As a result, the tank performance is estimated by means of component-level fragility curves for the aforementioned limit state which are derived through Monte Carlo simulations. The flexibility of the proposed framework allows fragility curves to be derived considering both deterministic and random filling levels. The comparison of the seismic vulnerability of the tank obtained with probabilistic and deterministic mechanical models demonstrates the conservatism of the latter. The same trend is also exhibited in terms of risk assessment

A computational framework for fast‐time hybrid simulation based on partitioned time integration and state‐space modeling

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Seismic Vulnerability Analysis of a Coupled Tank-Piping System by Means of Hybrid Simulation and Acoustic Emission

AbstractIn order to shed light on the seismic response of complex industrial plants, advanced finite element models should take into account both multicomponents and relevant coupling effects. These models are usually computationally expensive and rely on significant computational resources. Moreover, the relationships between seismic action, system response and relevant damage levels are often characterized by a high level of nonlinearity, which requires a solid background of experimental data. Vulnerability and reliability analyses both depend on the adoption of a significant number of seismic waveforms that are generally not available when seismic risk evaluation is strictly site-specific. In addition, detection of most vulnerable components, i.e., pipe bends and welding points, is an important step to prevent leakage events. In order to handle these issues, a methodology based on a stochastic seismic ground motion model, hybrid simulation and acoustic emission is presented in this paper. The seismic model is able to generate synthetic ground motions coherent with site-specific analysis. In greater detail, the system is composed of a steel slender tank, i.e., the numerical substructure, and a piping network connected through a bolted flange joint, i.e., the physical substructure. Moreover, to monitor the seismic performance of the pipeline and harness the use of sensor technology, acoustic emission sensors are placed through the pipeline. Thus, real-time acoustic emission signals of the system under study are acquired using acoustic emission sensors. Moreover, in addition to seismic events, also a severe monotonic loading is exerted on the physical substructure. As a result, deformation levels of each critical component were investigated; and the processing of acoustic emission signals provided a more in-depth view of the damage of the analysed components