STRUCTURAL MODEL UPDATING USING VIBRATION MEASUREMENTS

Abstract. A multi-objective optimization framework is presented for updating finite element models of structures based on vibration measurements. The method results in multiple Paret

Formal development and evaluation of narrow passageway system operations

This study applies a new intelligent transportation methodology for transforming informal operations concepts for narrow passageway systems into system-level designs, which will formal enough to support automated validation of anticipated component- and system-level behaviours. Models and specifications of behaviour are formally designed as labelled transition systems. Each object is the management system is assumed to have behaviour that can be defined by a finite state machine; thus, the waterway management system architecture is modelled as a network of communicating finite state machines. Architecture-level behaviours are validated using the Labelled Transition System Analyzer (LTSA). We exercise the methodology by working step by step through the synthesis and validation of a high-level behaviour model for a vessel passing through a waterway network (i.e., canal)

Structural model updating using vibration measurements

A multi-objective optimization framework is presented for updating finite element models of structures based on vibration measurements. The method results in multiple Pareto optimal structural models that are consistent with the measured data and the residuals used to measure the discrepancies between the measured and the finite element model predicted characteristics. The relation between the multi-objective identification method, Bayesian in-ference method, and conventional single-objective weighted residuals methods for model up-dating is discussed. Computational algorithms for the efficient and reliable solution of the resulting optimization problems are presented. The algorithms are classified to gradient-based, evolutionary strategies and hybrid techniques. In particular, efficient algorithms are introduced for reducing the computational cost involved in estimating the gradients of the ob-jective functions representing the modal residuals. Specifically, a formulation requiring the solution of the adjoint problem is presented, avoiding the explicit estimation of the gradients of the modal characteristics. The adjoint method is also extended to carry out efficiently the estimation of the Hessian of the objective function. The computational cost for estimating the gradients and Hessian is shown to be independent of the number of structural model parame-ters. The methodology is particularly efficient to system with several number of model param-eters and large number of DOFs where repeated gradient and Hessian evaluations are computationally time consuming. Component mode synthesis methods dividing the structure to linear substructural components with fixed properties and linear substructural components with uncertain properties are incorporated into the methodology to further reduce the compu-tational effort required in optimization problems. The linear substructures with fixed proper-ties are represented by their lower contributing modes which remain unchanged during the model updating process. The method is particular effective for finite element models with large number of DOF and for parameter estimation in localized areas of a structure. Theoret-ical and computational developments are illustrated by updating finite element models of a laboratory building using impact hammer measurements and multi-span reinforced concrete bridges using ambient vibration measurements

Αγορά ομολόγων και ειδήσεις: η περίπτωση των ελληνικών κρατικών ομολόγων

Σκοπός της παρούσας εργασίας είναι να παρουσιάσει τον τρόπο με τον οποίο οι ειδήσεις, οικονομικής φύσεως και μή, επιδρούν στην αγορά κρατικών ομολόγων. Θα δειχθεί ότι τόσο οι εκπλήξεις σε προγραμματισμένες ανακοινώσεις οικονομικών δεικτών, όσο και άλλα απρόοπτα γεγονότα ασκούν σημαντικές πιέσεις στη συγκεκριμένη αγορά. Μέσα από την οικονομική θεωρία, αλλά και εμπειρική ανάλυση θα εξηγηθεί η επίδραση των ειδήσεων στην αγορά ομολόγων. Η υπάρχουσα βιβλιογραφία έχει μελετήσει το ζήτημα από διάφορες οπτικές, με κύριες για τη δική μας προσέγγιση αυτές των Piazzesi (2001), Balduzzi, Elton & Green (1999), Campbell & Ammer (1993), Beetsma et al (2012) και Jiang, Konstandinidi & Skiadopoulos (2012). Αυτή η επίδραση γίνεται αντιληπτή μέσα από το άνοιγμα (spread) των αποδόσεων ανάμεσα σε έναν κρατικό τίτλο και τον, αντίστοιχης διάρκειας, «άνευ κινδύνου» τίτλο. Πέραν της θεωρητικής ανάλυσης των προσδιοριστικών παραγόντων τιμολόγησης ομολόγων, επικεντρωνόμαστε στην αντίδραση της ελληνικής απόδοσης και του spread στην ειδησεογραφία τόσο εγχώρια, όσο και διεθνή, κατά τη διάρκεια της κρίσης χρέους στην οποία βρίσκεται η Ελλάδα από τα τέλη του 2009. Παρατηρείται η συσχέτιση του spread με κάποια μακροοικονομικά μεγέθη, και παράλληλα διαπιστώνεται ότι το spread ακολουθεί πορεία όμοια με την ελληνική απόδοση, παρά το γεγονός ότι μεγάλο μέρος των ειδήσεων δεν προέρχεται και δεν αφορά την Ελλάδα.This thesis’ purpose is to present the way that news, economic or not, affect the sovereign bond market. It is shown that not only surprises in scheduled announcements of economic indices, but also other unexpected events can put pressure on this specific market. Using the economic theory and empirical analyses, the news’ effect on the sovereign bonds will be examined. Perspectives that played a crucial role to our approach are those of Piazzesi (2001), Balduzzi, Elton & Green (1999), Campbell & Ammer (1993), Beetsma et al (2012) and Jiang, Konstandinidi & Skiadopoulos (2012). Through them, it is explained that news has a strong effect on the government bonds. This effect can be conceived with the use of the spread between the yield to maturity of a sovereign bond and another “risk-free” bond with the same maturity. Beyond the bond pricing factors’ analysis, our focus will be on the reaction of the Greek spread to news reports, both domestic and international, during the current debt-crisis that Greece experiences since the end of 2009. The spread-macroeconomic factors correlation is observed and at the same time we can see that the spread’s path is almost identical with that of the greek yield’s, despite the fact that many news reports are international, and not domestic

Road Upgrading in Terms of Geometric and Functional Characteristics

The road network plays a vital role in the economy of any country and maintaining the infrastructure at a level that serves the current traffic needs is a critical element. Road maintenance directly affects road users. If it is not adequate or if it is not done in time, the damage that will occur, in a national and provincial network, may be unmanageable and will affect the increased operating costs of vehicles, delays in travel, increase in the accident index and generally reduce the reliability of transport services. When corrective interventions can no longer be postponed or cancelled, extensive restoration and reconstruction work takes place, which costs much more than the simple / preventive maintenance that can be planned and carried out in a timely manner. The protection of the existing road network is necessary and its maintenance in good condition is a dominant issue for a Management Body and often precedes as a priority even a new investment in the field of road infrastructure. This paper focuses on road network management from the point of view of upgrading and maintenance. An optimization methodology is proposed depending on the condition of the road, so that the choice of operation is optimal for the current situation. In this way, unnecessary expenses, which are brought about by the usual maintenance works, are avoided, while the street cannot serve modern traffic needs efficiently

Hierarchal object-oriented models for management of narrow passageways

Narrow passageways are a significant source of traffic congestion and delay in transportation networks. With traffic volumes expected to increase significantly in the foreseeable future, the effective management of these passageways is needed to mitigate the undesirable impact of these bottlenecks on transportation system safety, performance and cost. In an effort to address the significant challenges associated with the analysis, design, and implementation of appropriate management operations for narrow passageways, an object-based model for the management of narrow passageways in the transportation network is developed. The object model is developed in two steps. The first step identifies high-level management functionality, objects, and associated data/information sources that are common to all narrow passageway applications. In the second step, functionality of the object model is customized to the specific needs of the narrow passageway application domain (e.g., waterways and work zones).peer-reviewe

Finite element model updating of an experimental vehicle model using measured modal characteristics

Methods for modal identification and structural model updating are employed to develop high fidelity finite element models of an experimental vehicle model using acceleration measurements. The identification of modal characteristics of the vehicle is based on ac-celeration time histories obtained from impulse hammer tests. An available modal identification software is used to obtain the modal characteristics from the analysis of the various sets of vibration measurements. A high modal density modal model is obtained. The modal characteristics are then used to update an increasingly complex set of finite element models of the vehicle. A multi-objective structural identification method is used for estimating the parameters of the finite element structural models based on minimizing the modal residu-als. The method results in multiple Pareto optimal structural models that are consistent with the measured modal data and the modal residuals used to measure the discrepancies between the measured modal values and the modal values predicted by the model. Single objective structural identification methods are also evaluated as special cases of the proposed multi-objective identification method. The multi-objective framework and the corresponding compu-tational tools provide the whole spectrum of optimal models and can thus be viewed as a gen-eralization of the available conventional methods. The results indicate that there is wide variety of Pareto optimal structural models that trade off the fit in various measured quanti-ties. These Pareto optimal models are due to uncertainties arising from model and measure-ment errors. The size of the observed variations depends on the information contained in the measured data, as well as the size of model and measurement errors. The effectiveness of the updated models and the predictive capabilities of the Pareto vehicle models are assessed

Fatigue lifetime estimation in structures using ambient vibration measurements

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. Available frequency domain stochastic fatigue methods based on Miner’s damage rule, S-N fatigue cycle curves and Dirlik’s probability distribution of the stress range are used to predict the expected fatigue accumulation of the structure in terms of the power spectral density of the stress processes. In predicting the damage and fatigue lifetime, it is assumed that the unmeasured excitations can be modeled by stationary stochastic processes. The power spectral densities of stresses at unmeasured locations are estimated from the response time history measurements available at the limited measured locations using Kalman filter and a model of the structure. The proposed formulation is demonstrated using a MDOF spring-mass chain model arising from structures that consist of members with uniaxial stress states

Identification of dynamic models of Metsovo (Greece) Bridge using ambient vibration measurements

Available methods for structural model updating are employed to develop high fidelity models of the Metsovo bridge using ambient vibration measurements. The Metsovo bridge, the highest bridge of the Egnatia Odos Motorway, is a two-branch balanced cantilever ravine bridge. It has a total length of 357m, a very long central span of 235m, and a height of 110m for the taller pier. Ambient vibration measurements are available during different construction phases of the bridge for both bridge branches, as well as after the completed construction phases of the bridge. Operational modal analysis software is used to obtain the modal characteristics of the bridge for the various sets of vibration measurements. The modal characteristics are then used to update an increasingly complex set of finite element models of the bridge. These models are based on beam and solid elements. A multi-objective structural identification method is used for estimating the parameters of the finite element structural models based on minimising the modal residuals. The method results in multiple Pareto optimal structural models that are consistent with the measured modal data and the modal residuals used to measure the discrepancies between the measured modal values and the modal values predicted by the model. Single objective structural identification methods are also evaluated as special cases of the proposed multi-objective identification method. The effectiveness of the updated models and their predictive capabilities are assessed. In particular, the variability of the Pareto optimal models and their associated response prediction variability are explored. It is demonstrated that the Pareto optimal structural models may vary, depending on the fidelity of the model class employed and the size of measurement errors. The developed high fidelity finite element models are used for checking design assumptions and for carrying out more accurate predictions of structural response

Combined Ground Deformation Study Of Broader Area Of Patras Gulf (W. Greece) Using PSI-WAP, DGPS And Seismicity Analyses

Long-term ground deformation monitoring using the Persistent Scatterer Interferometry Wide Area Product (PSI-WAP) technique for the period 1992-2003, combined with Differential GPS measurements and seismicity analysis has provided useful information about the tectonic motions of the tectonically complex area of Patras Gulf (Western Greece), and lead to new insights on the geotectonic regime of this region. Descending ERS radar images were used to compile the PSI-WAP product that has been calibrated using the absolute velocity field of available GPS stations in the area. It has been found that the deformation of the southern part of Patras Gulf near the coastline has been characterized by considerable subsidence (>-5mm/yr), where unconsolidated sediments usually prevail, compared to the northern part of the gulf. Significant subsidence has also been identified in areas along the down-throw side of possible faults, as well as areas where extensive ground water pumping has occurred for irrigation. These results correlate well with local GPS and seismicity data