Fault Detection of Dynamical Systems with Nonstationary Inputs

A distributed alternating optimization approach to canonical correlation analysis based fault detection for dynamic systems.

A signal processing technique for analysing both the transient natural excitations and the vibration structures response, capable of determining the time variations in the amplitude and in the frequency content of these structures, is presented. This technique makes use of an impulse invariant transformation for obtaining an equivalent model of the vibration structure, represented by a parallel-form realization of second-order subsystems, corresponding to different modes of vibration, having as input a stationary independent and identically distributed sequence. The method was applied for detection of changes in dynamic characteristics of a vibrating structure, a multi-story concrete building subject to an earthquake ground motion.

The change detection and diagnosis methods have gained considerable attention in scientif c research and appears to be the central issue in various application areas. These applications need some robust change detection schemes to work well and separate the changes in the experimental conditions from the real changes in the system, especially for systems with arbitrary and non-stationary known or unknown inputs. The objective of the paper is to develop a such kind of change detection and diagnosis scheme, able to discriminate the model parameter and noise variance changes. Finally, we include some Monte-Carlo simulations for change detection in a second order FIR model and experimental results obtained in analysis of seismic signals, using the proposed approach.

The model-based approach to fault detection in dynamic systems has been receiving more and more attention over the last two decades, in the contexts of both research and real plant application.KeywordsFuzzy LogicFault DetectionFault DiagnosisResidual EvaluationResidual GenerationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper uses the Popov-Tsypkin multiplier (which has intimate connections to the mixed structured singular value theory) to design robust H/sub /spl infin// estimators for uncertain linear discrete-time systems and considers the application of robust H/sub /spl infin// estimators to robust fault detection. The key to estimator-based, robust fault detection is to generate residuals which are robust against plant uncertainties and external disturbance inputs, which in turn requires the design of robust estimators. The robust H/sub /spl infin// estimation problem is formulated as a Riccati equation feasibility problem in which a cost function is minimized subject to a Riccati equation constraint. The robust H/sub /spl infin// estimator framework is then applied to the robust fault detection of dynamic systems.

This paper presents a new approach to the design of robust fault detection systems via a genetic algorithm. To achieve robustness, a number of performance indices are introduced, which are expressed in the frequency domain to account for the frequency distributions of incipient faults, noise and modelling uncertainty. All objectives are then reformulated into a set of inequality constraints on performance indices. A genetic algorithm is thus used to search an optimal solution to satisfy these inequality constraints. The approach developed is applied to a flight control system example and results show that incipient sensor faults can be detected reliably in the presence of modelling uncertainty.

To reveal the dynamic behavior of a railway embankment slope subjected to seismic excitation, a shaking table model test was performed on a 1:8 scale embankment slope. Different types of seismic wave of differing amplitudes were applied to study the dynamic behavior of the embankment slope, and white noise excitations were interspersed among the seismic waves to observe the changes of dynamic characteristics of the embankment slope. Residual deformation behaviors of the embankment slope were also investigated. The results of the tests show that the natural frequency of the embankment slope exhibits a decreasing trend and that the damping ratio exhibits an increasing trend. The embankment slope exhibits a significant amplification effect on the input acceleration, and the acceleration response differs greatly when subjected to different seismic excitations of differing spectrum characteristics. The filler of the embankment slope affects the changes of the spectrum characteristics of the seismic wave. The filler performs a filtering effect on high-frequency seismic waves and amplifies the energy of low-frequency seismic waves, especially when the frequency is close to the natural frequency of the embankment slope. A bidirectional excitation creates a greater acceleration response than a unidirectional excitation does. The seismic residual deformation of the embankment slope occurs under the seismic subsidence mode.

PV simulators are now mandatorily used to evaluate the performance of balance of system viz. battery chargers, inverters and unidirectional DC-DC simulators to avoid the time-consuming and costly field testing process. Moreover, to precisely tune the MPPT controller, we often require sustained environmental condition and status-quo for parameters; thus, PV simulators have become indispensible equipment for PV system prototyping. Further, as MPPT algorithms are more-or-less standardized, the PV simulator may be more effectively integrated with Incremental Conductance based MPPT algorithm to realize the integrated PV simulator (IPVS). Since the characteristics of each PV panel varies from manufacturer to manufacturer and parameters are selectable, the PWM frequency of buck converter used for hardware realization of IPVS and selection of an appropriate sampling rate for PV simulator for realizing the quantized digital emulation of PV panel closed to its actual operation becomes critical. This paper presents the development of a low cost microcontroller based real time IPVS which controls the interfaced buck type MPPT DC-DC power converter for emulation of PV panel close to its actual operation with flexibility or dynamic changes in characteristics. The developed algorithm is able to configure both the PV module of any make or type to its characteristics and related dynamics to be simulated and the environmental conditions under which it operates. The presented experimental results demonstrate the effectiveness of the proposed method in replicating of I-V characteristics of considered PV panel with high accuracy.

Damage assessment in reinforced concrete beams using eigenfrequencies and mode shape derivatives

Amaç: Bu çalışmada, deprem, patlama, çarpma gibi aşırı yüklere maruz kalan yapıların dinamik karakteristiklerinin değişimi ile hasar seviyeleri arasındaki ilişki araştırılmıştır. Böylece bu çalışmada hasar oluşan yapıların hemen kullanılabilmesi için hızlı bir yöntem önerilmiştir. Yöntem: Yapılan çalışma, deneysel ölçümler ve sayısal çözümler olmak üzere iki bölümden oluşmaktadır. Çalışma için, tek serbestlik dereceli, dört kolonlu, çelik bir model yapı imal edilerek ivmeölçer yardımı ile titreşimleri kayıt edilmiştir. Yapı için hasarsız, orta hasar ve ağır hasar olmak üzere üç senaryo tanımlanmıştır. Hasar senaryolarının her biri kolonların bağ koşulları değiştirilerek sağlanmıştır. Bulgular: Alınan ivme kayıtları Seismosignal yazılımı ile işlenerek her bir hasar senaryosu için yapı serbest titreşim periyotları belirlenmiştir. Çalışmanın sayısal kısmında ise hasarsız ve hasarlı yapıların sonlu eleman yöntemi kullanılarak serbest titreşim periyotları hesaplanmıştır. Sonuç: Deneysel ve sayısal yöntemlerden elde edilen sonuçların uyumlu olduğu gösterilmiştir. Yapılan çalışma sonucunda; yapıların serbest titreşim periyotlarının, yapıda oluşan hasar durumlarının belirlenmesinde kullanılabileceği ifade edilmiştir.

Story shear and torsional moment-based pushover procedure for asymmetric-plan buildings using an adaptive capacity spectrum method

The present work reports results from an extensive set of measurements which has been performed in order to formulate standard method to remove temperature changes from impedance measurements. The other issue addressed here is the investigation of influence of boundary condition and temperature changes on electromechanical impedance measurement for structural member. Due to electromechanical coupling, changes in dynamic characteristics can be seen in electrical impedance of piezoelectric transducer. Two different systems have been used during this measurement process. System based on FBG sensors has been used for temperature changes measurement while PZT transducers mounted on the structure with impedance analyser were used for electrical parameters measurement. During research electrical impedance and resistance of piezoelectric transducer were measured in order to analyze changes in amplitude of peaks and the frequency shift of peaks due to temperature variations and different configurations of the beam.

Using laser vibrometry, a modal analysis of sheet samples of a carbon fiber composite with different stacking and single impact damage of energy from 5 up to 25 J was performed. The dependences of the damping coefficient on the impact energy are obtained for various stackings of the composite layers for the first three eigenmodes. The features of changing the damping coefficient are established for the selected stacks of layers. The values of the energy of impact damage are determined at which the greatest changes in the damping coefficient occur. Peculiarities of changing the speed of propagation of acoustic waves in damaged composites are revealed depending on the impact energy and the type of layers stacking.

The slender type tool usually can be used in milling the thin-walled components in a narrow and deep processing space, and the tool and the workpiece are usually deemed a system because the stiffness of both is closed. The milling stability is influenced by both the coupling deflection and dynamic characteristics of the tool-workpiece system. In order to investigate the time variation of the coupling deflection and dynamic characteristics of the tool-workpiece system, a new computational model was established in this paper. The workpiece was divided into several milling units, and the whole milling process was divided into a series of corresponding sub-milling processes. The coupling deflection of the tool-workpiece system in the sub-milling process was induced by milling force, and the milling force in the next sub-milling process was reversely induced by the coupling deflection of the tool-workpiece system, and by this analogy. Therefore, the thicknesses of units were different under the interaction between the milling forces and the coupling deflections. The changes of dynamic characteristics of the tool-workpiece system were induced by the changes of thicknesses of units. Based on the influences of the coupling deflection and the dynamic characteristics of the tool-workpiece system, a new stability lobe diagram which can show different stability zones and chatter zones in different process positions was obtained. Experimental testing has been conducted to validate the newly established model.

Changes of dynamic characteristics in the neonatal external ear canal wall from birth to 6 months