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Due to increasing numbers of wind energy converters, the accurate assessment of the lifespan of their structural parts and the entire converter system is becoming more and more paramount. Lifespan-oriented design, inspections and remedial maintenance are challenging because of their complex dynamic behavior. Wind energy converters are subjected to stochastic turbulent wind loading causing corresponding stochastic structural response and vibrations associated with an extreme number of stress cycles (up to 109 according to the rotation of the blades). Currently, wind energy converters are constructed for a service life of about 20 years. However, this estimation is more or less made by rule of thumb and not backed by profound scientific analyses or accurate simulations. By contrast, modern structural health monitoring systems allow an improved identification of deteriorations and, thereupon, to drastically advance the lifespan assessment of wind energy converters. In particular, monitoring systems based on artificial intelligence techniques represent a promising approach towards cost-efficient and reliable real-time monitoring. Therefore, an innovative real-time structural health monitoring concept based on software agents is introduced in this contribution. For a short time, this concept is also turned into a real-world monitoring system developed in a DFG joint research project in the authors’ institute at the Ruhr-University Bochum. In this paper, primarily the agent-based development, implementation and application of the monitoring system is addressed, focusing on the real-time monitoring tasks in the deserved detail.
This paper presents a robust model updating strategy for system identification of wind turbines. To control the updating parameters and to avoid ill-conditioning, the global sensitivity analysis using the elementary effects method is conducted. The formulation of the objective function is based on M¨uller-Slany’s strategy for multi-criteria functions. As a simulationbased optimization, a simulation adapter is developed to interface the simulation software ANSYS and the locally developed optimization software MOPACK. Model updating is firstly tested on the beam model of the rotor blade. The defect between the numerical model and the reference has been markedly reduced by the process of model updating. The effect of model updating becomes more pronounced in the comparison of the measured and the numerical properties of the wind turbine model. The deviations of the frequencies of the updated model are rather small. The complete comparison including the free vibration modes by the modal assurance criteria shows the excellent coincidence of the modal parameters of the updated model with the ones from the measurements. By successful implementation of the model validation via model updating, the applicability and effectiveness of the solution concept has been demonstrated.
LIFETIME-ORIENTED OPTIMIZATION OF BRIDGE TIE RODS EXPOSED TO VORTEX-INDUCED ACROSS-WIND VIBRATIONS
(2006)
In recent years, damages in welded connections plates of vertical tie rods of several arched steel bridges have been reported. These damages are due to fatigue caused by wind-induced vibrations. In the present study, such phenomena are examined, and the corresponding lifetime of a reference bridge in Münster-Hiltrup, Germany, is estimated, based on the actual shape of the connection plate. Also, the results obtained are compared to the expected lifetime of a connection plate, whose geometry has been optimized separately. The structural optimization, focussing on the shape of the cut at the hanger ends, has been carried out using evolution strategies. The oscillation amplitudes have been computed by means of the Newmark-Wilson time-step method, using an appropriate load model, which has been validated by on-site experiments on the selected reference bridge. Corresponding stress-amplitudes are evaluated by multiplying the oscillation amplitudes with a stress concentration factor. This factor has been computed on the basis of a finite element model of the system "hanger-welding-connection plate", applying solid elements, according to the notch stress approach. The damage estimation takes into account the stochastics of the exciting wind process, as well as the stochastics of the material parameters (fatigue strength) given in terms of Woehler-curves. The shape optimization results in a substantial increase of the estimated hanger lifetime. The comparison of the lifetimes of the bulk plate and of the welding revealed that, in the optimized structure, the welding, being the most sensitive part in the original structure, shows much more resistance against potential damages than the bulk material.
In order to model and simulate collapses of large scale complex structures, a user-friendly and high performance software system is essential. Because a large number of simulation experiments have to be performed, therefore, next to an appropriate simulation model and high performance computing, efficient interactive control and visualization capabilities of model parameters and simulation results are crucial. To this respect, this contribution is concerned with advancements of the software system CADCE (Computer Aided Demolition using Controlled Explosives) that is extended under particular consideration of computational steering concepts. Thereby, focus is placed on problems and solutions for the collapse simulation of real world large scale complex structures. The simulation model applied is based on a multilevel approach embedding finite element models on a local as well as a near field length scale, and multibody models on a global scale. Within the global level simulation, relevant effects of the local and the near field scale, such as fracture and failure processes of the reinforced concrete parts, are approximated by means of tailor-made multibody subsystems. These subsystems employ force elements representing nonlinear material characteristics in terms of force/displacement relationships that, in advance, are determined by finite element analysis. In particular, enhancements concerning the efficiency of the multibody model and improvements of the user interaction are presented that are crucial for the capability of the computational steering. Some scenarios of collapse simulations of real world large scale structures demonstrate the implementation of the above mentioned approaches within the computational steering.
Die Bauwerksüberwachung gewinnt aus sicherheitstechnischen sowie aus wirtschaftlichen Gründen zunehmend an Bedeutung. Nicht nur die Bauwerkssicherheit kann durch leistungsfähige Monitoring-Systeme angemessen beurteilt, auch die Nutzungsdauer bestehender Bauwerke kann durch die gewonnenen Informationen deutlich verlängert werden. Das vorliegende Papier beschreibt die Entwicklung eines webbasierten Talsperren-Monitoring-Systems, das die automatisierte Erfassung von Daten vor Ort sowie die computergestützte Aufbereitung und Analyse der gesammelten Messdaten ermöglicht. Das Monitoring-System ist durch seinen modularen Aufbau nicht auf die Talsperren-Überwachung beschränkt, sondern kann ohne großen Aufwand an andere Überwachungsaufgaben angepasst werden. Das System besteht aus drei wesentlichen Modulen: (i) einer erweiterbaren Klassenbibliothek, die die Steuerung der im Bauwerk installierten Messelektronik ermöglicht, (ii) einem webbasierten Datenerfassungsmodul, das neben der automatischen Datenerfassung eine Fernsteuerung der Messelektronik erlaubt und Funktionen zur Verwaltung der Überwachungsaufgaben bereitstellt, sowie (iii) einem webbasierten Visualisierungs- und Auswertungsmodul zur Aufbereitung und Analyse der gesammelten Daten. Alle an der Überwachung beteiligten Mitarbeiter können mit einem üblichen Web-Browser über das Internet auf das entwickelte System zugreifen; ein Zugriff mittels Mobiltelefon ist alternativ möglich. Das implementierte Talsperren-Monitoring-System begleitet die beteiligten Fachleute von der Erfassung der Daten vor Ort bis hin zur Aufbereitung und Analyse der Messdaten an zentraler Stelle: Die Mitarbeiter werden durch einen einfachen Zugriff auf die installierte Messelektronik, automatisierte Messungen und umfangreiche Analysefunktionalitäten bei ihren spezifischen Aufgaben unterstützt. Der bisherige manuelle Arbeitsaufwand für Datenerfassung, -transfer und Analyse wird somit deutlich reduziert.
Although there are some good reasons to design engineering software as a stand-alone application for a single computer, there are also numerous possibilities for creating distributed engineering applications, in particular using the Internet. This paper presents some typical scenarios how engineering applications can benefit from including network capabilities. Also, some examples of Internet-based engineering applications are discussed to show how the concepts presented can be implemented.
In this contribution the software design and implementation of an analysis server for the computation of failure probabilities in structural engineering is presented. The structures considered are described in terms of an equivalent Finite Element model, the stochastic properties, like e.g. the scatter of the material behavior or the incoming load, are represented using suitable random variables. Within the software framework, a Client-Server-Architecture has been implemented, employing the middleware CORBA for the communication between the distributed modules. The analysis server offers the possibility to compute failure probabilities for stochastically defined structures. Therefore, several different approximation (FORM, SORM) and simulation methods (Monte Carlo Simulation and Importance Sampling) have been implemented. This paper closes in showing several examples computed on the analysis server.
The optimization of continuous structures requires careful attention to discretization errors. Compared to ordinary low order formulation (h-elements) in conjunction with an adaptive mesh refinement in each optimization step, the use of high order finite elements (so called p-elements) has several advantages. However, compared to the h-method a higher order finite element analysis program poses higher demands from a software engineering point of view. In this article the basics of an object oriented higher order finite element system especially tailored to the use in structural optimization is presented. Besides the design of the system, aspects related to the employed implementation language Java are discussed.
The influence of vortex-induces vibrations on vertical tie rods has been proved as a determinant load factor in the lifetime-oriented dimensioning of arched steel bridges. Particularly, the welded connection plates between the suspenders and the arches often exhibit cracks induced primarily rods. In this context, the synchronization of the vortex-shedding to the rod motion in a critical wind velocity range, the so-called lock-in effect, is of essential interest.
Der lebensdauerorientierte Entwurf von Stabbogenbrücken, mit Zuschnitt auf die Auslegung von Hängern, die durch Ermüdung infolge wirbelinduzierter Querschwingungen gefährdet sind, wird als stochastisches semi-infinites Optimierungsproblem formuliert. Zur Lösung dieses Problems sind mehrere Modellierungsebenen erforderlich, so dass ein Mehrebenenproblem entsteht. Es wird der derzeitige Entwicklungs- und Implementierungsstand bei der Umsetzung des Mehrebenenproblems in ein Entwurfsleitsystem (Software) aufgezeigt. Außerdem werden die Konzepte der noch ausstehenden Forschungsarbeit, die bereits erfolgreich beim lebensdauerorientierten Entwurf von Industriehallen mit Rahmensystem als Haupttragwerk eingesetzt wurden, diskutiert und ihre Einbildung in die bisher umgesetzte Forschungsarbeit erläutert.