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See detailFault Detection Algorithm based on Null-Space Analysis for On-Line Structural Health Monitoring
Yan, Ai-Min; Golinval, Jean-Claude ULg; Marin, Frédéric

Conference given outside the academic context (2005)

Early diagnosis of structural damages or machinery malfunctions allows to reduce the maintenance cost of systems and to increase their reliability and safety. This paper addresses the damage detection ... [more ▼]

Early diagnosis of structural damages or machinery malfunctions allows to reduce the maintenance cost of systems and to increase their reliability and safety. This paper addresses the damage detection problem by statistical analysis on output-only measurements of structures. The developed method is based on subspace analysis of the Hankel matrices constructed by vibration measurement data. The column active subspace of the Hankel matrix defined by the first principal components is orthonormal to the column null-subspace defined by the remaining principal components. The residue in the orthonormality relation obtained from different data sets may be used to detect structural damages. It is illustrated that this null-space-based method constitutes an enhancement of the classical damage detection method based on principal component analysis (PCA). Several damage indicators are proposed to characterize the resulting residue matrices. The method is first illustrated on a numerical example and then, it is applied to vibration fatigue testing of a street-lighting device. Because of its simplicity and efficiency, the proposed algorithm is expected to be suitable for continuous on-line health monitoring of structures in practical situations. [less ▲]

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See detailFault detection based on Kernel Principal Component Analysis
Nguyen, Viet Ha ULg; Golinval, Jean-Claude ULg

in Engineering Structures (2010), 32

In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior may render the procedure of damage or fault detection more difficult. Principal ... [more ▼]

In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior may render the procedure of damage or fault detection more difficult. Principal Component Analysis (PCA) is known as a popular method for diagnosis but as it is basically a linear method, it may pass over some useful nonlinear features of the system behavior. One possible extension of PCA is Kernel PCA (KPCA), owing to the use of nonlinear kernel functions that allow to introduce nonlinear dependences between variables. The objective of this paper is to address the problem of fault detection (in terms of nonlinear activation) in mechanical systems using a KPCA-based method. The detection is achieved by comparing the subspaces between the reference and a current state of the system through the concept of subspace angle. It is shown in this work that the exploitation of the measurements in the form of block Hankel matrices can improve effectively the detection results. The method is illustrated on an experimental example consisting of a beam with a geometric nonlinearity. [less ▲]

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See detailFault detection in mechanical systems based on subspace features
Nguyen, Viet Ha ULg; Rutten, Christophe ULg; Golinval, Jean-Claude ULg

in International Conference on Noise and Vibration Engineering (2010, September)

In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior complicates the procedure of damage or fault detection. Principal Component ... [more ▼]

In the field of structural health monitoring or machine condition monitoring, the activation of nonlinear dynamic behavior complicates the procedure of damage or fault detection. Principal Component Analysis (PCA) is known as an efficient method for damage diagnosis. However, two drawbacks of PCA are the assumption of the linearity of the system and the need of many sensors. This article presents industrial applications of two possible extensions of PCA: Null subspace analysis (NSA) and Kernel PCA (KPCA). The advantages of NSA rely on its rapidity of use and its reliability. The KPCA method, through the use of nonlinear kernel functions, allows to introduce nonlinear dependences between variables. The objective is to address the problem of fault detection in mechanical systems using subspace-based methods. The detection is achieved by comparing the subspace features between the reference and a current state through statistics. Industrial data are used as illustration of the methods. [less ▲]

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See detailFault Diagnosis in Industrial Systems Based on Blind Source Separation Techniques Using One Single Vibration Sensor
Nguyen, Viet Ha; Rutten, Christophe; Golinval, Jean-Claude ULg

in Shock & Vibration (2012), 19(5), 795-801

In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In ... [more ▼]

In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In machine condition monitoring, the number of available vibration sensors is often small and it is not unusual that only one single sensor is used to monitor a machine. The aim of this paper is to propose an extension of fault detection techniques that may be used when a reduced set of sensors or even one single sensor is available. Fault detection techniques considered here are based on output-only methods coming from the Blind Source Separation (BSS) family, namely Principal Component Analysis (PCA) and Second Order Blind Identification (SOBI). The advantages of PCA or SOBI rely on their rapidity of use and their reliability. Based on these methods, subspace identification may be performed by using the concept of block Hankel matrices which make possible the use of only one single measurement signal. Thus, the problem of fault detection in mechanical systems can be solved by using subspaces built from active principal components or modal vectors. It consists in comparing subspace features between the reference (undamaged) state and a current state. The angular coherence between subspaces is a good indicator of a dynamic change in the system due to the occurrence of faults or damages. The robustness of the methods is illustrated on industrial examples. [less ▲]

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See detailFault Diagnosis in Industrial Systems Based on Blind Source Separation Techniques Using One Single Vibration Sensor
Nguyen, Viet Ha ULg; Rutten, Christophe ULg; Golinval, Jean-Claude ULg

in Maia NNM, Neves MM (Ed.) International Conference on Structural Engineering Dynamics (ICEDyn 2011) - Proceedings (2011)

In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In ... [more ▼]

In the field of structural health monitoring or machine condition monitoring, most vibration based methods reported in the literature require to measure responses at several locations on the structure. In machine condition monitoring, the number of available vibration sensors is often small and it is not unusual that only one single sensor is used to monitor a machine. The aim of this paper is to propose an extension of fault detection techniques that may be used when a reduced set of sensors or even one single sensor is available. Fault detection techniques considered here are based on output-only methods coming from the Blind Source Separation (BSS) family, namely Principal Component Analysis (PCA) and Second Order Blind Identification (SOBI). The advantages of PCA or SOBI rely on their rapidity of use and their reliability. Based on these methods, subspace identification may be performed by using the concept of block Hankel matrices which make possible the use of only one single measurement signal. Thus, the problem of fault detection in mechanical systems can be solved by using subspaces built from active principal components or modal vectors. It consists in comparing subspace features between the reference (undamaged) state and a current state. The angular coherence between subspaces is a good indicator of a dynamic change in the system due to the occurrence of faults or damages. The robustness of the methods is illustrated on industrial examples. [less ▲]

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See detailFault re-activation, stress interaction and rupture propagation of the 1981 Corinth earthquake sequence
Hubert, Aurelia ULg; King, G. C. P.; Armijo, R. et al

in Earth and Planetary Science Letters (1996), 142

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See detailFauna vs flora contribution to the leaf epiphytes biomass in a Posidonia oceanica seagrass bed (Revellata Bay, Corsica).
Lepoint, Gilles ULg; Havelange, Stéphane; Gobert, Sylvie ULg et al

in Hydrobiologia (1999), 394

The epiphyte biomass of Posidonia oceanica (L.) Delile leaves is mainly related to the substrate leaf availability. It decreases with increasing depth and increases from winter to summer, following the ... [more ▼]

The epiphyte biomass of Posidonia oceanica (L.) Delile leaves is mainly related to the substrate leaf availability. It decreases with increasing depth and increases from winter to summer, following the leaf biomass changes. In Revellata Bay (Gulf of Calvi, Corsica), at shallow depth (10m in this study) where photophilous algae grow, the fixed epifauna biomass accounts for about one third of leaf epiphytes biomass. At deeper depths in the Revellata Bay (20 and 30m), where shade-tolerant algae are dominant among epiflora, epifauna may account for more than half the leaf epiphytes biomass. [less ▲]

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See detailFaunal/floral and isotopic responses to Milankovitch precession cycles and environmental changes in the upper Gulpen Formation (Upper Maastrichtian) at the CBR-Lixhe and ENCI-Maastricht bv quarries
Felder, P. J.; Keppens, E.; De Clercq, Bernadette ULg et al

in Netherlands Journal of Geosciences-Geologie en Mijnbouw (2003), 82(3), 275-281

Two sections, just below the Nivelle Horizon in the upper Gulpen Formation (Upper Maastrichtian), and seven kilometres apart (CBR-Lixhe and ENCI-Maastricht bv quarries) have been analysed (samples every 5 ... [more ▼]

Two sections, just below the Nivelle Horizon in the upper Gulpen Formation (Upper Maastrichtian), and seven kilometres apart (CBR-Lixhe and ENCI-Maastricht bv quarries) have been analysed (samples every 5 cm) for dinocyst, pollen grains and bioclast contents as well as for carbon and oxygen isotopic composition, to obtain better insight into the influence of weathering on these sediments. The CBR section lies above groundwater level, while that at the ENCI quarry is some metres below. At the former quarry we recognised the influences of weathering (karst) nearby. At ENCI, palynological, bioclast and stable isotope results of the carbonate phase (mainly consisting of coccoliths) co-vary remarkably, displaying two cycles which may be interpreted tentatively as climatic fluctuations. The partial derivative(18)O curve varies roughly between -1.6parts per thousand and -1.1parts per thousand (on PDB scale), corresponding to a temperature change of about 2degreesC. Less negative values (i.e. cooler seawater) coincide with larger amounts of pollen of Normapolles and Triporates type assumed to represent temperate forest elements of a vegetation also containing tropical elements such as palms. Assuming the 5 cm sample intervals at ENCI to correspond to 1 ka, climatic maxima (and minima) may be 20-25 ka apart, obviously recalling Milankovitch precession cycles. These are independent of a sharp sedimentological change noted in the upper part of the lowest cycle (samples 42 to 24). Upwards of sample 42, bioclast contents increase and dinocysts, Spiniferites in particular, decrease significantly, corresponding to a marked shallowing. This turning point is also recorded in the partial derivative(13)C curve at ENCI. Bioclast percentages appear to follow composite trends that are influenced by both climatic and sedimentological conditions. [less ▲]

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See detailLa faune de la Meuse belge
Damas, Hubert ULg

in 63ème session de l'association française pour l'avancement des sciences, Liège, 1939 (1941)

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See detailFaune entomologique du Grand-Duché de Luxembourg : III : Cantharoidea (col.)
Magis, Noël ULg

in Archives de l'Institut grand-ducal de Luxembourg. Section des sciences naturelles, physiques et mathématiques (1956), XXIII

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See detailFaune entomologique glaciaire du plateau de la Baraque Michel
Fredericq, Léon ULg

in La Terre Wallone : catalogue régionaliste (1924)

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See detailFaune et flore de la Formation de Sika (Dévonien inférieur) dans la presqu'île de Dô Son (Viêt-Nam).
Janvier, Philippe; Blieck, Alain; Gerrienne, Philippe ULg et al

in Bulletin du Museum National d’Histoire Naturelle (1987), 92(3), 291-301

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See detailLa faune et la flore glaciaires du plateau de la Baraque-Michel (point culminant de l'Ardenne)
Fredericq, Léon ULg

in Bulletin de l'Académie Royale des Sciences, des Lettres et des Beaux-Arts de Belgique. Sciences (1904)

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See detailFaune médiévale et post-médiévale du château de Franchimont (Theux)
Gautier, Achilles; Vanguestaine, Marie; Hoffsummer, Patrick ULg

in Vie archéologique (2005), 64

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See detailFaunistique des macrophyini de la Belgique et du Grand-Duché de Luxembourg (Hyménoptères : Tenthredinidae) : 1. Genre Pachyprotasis Hartig, 1837
Magis, Noël ULg

in Bulletin de la Société Royale des Sciences de Liège (1984), 53(5), 327-339

Le genre Pachyprothasis HARTIG est représenté en Belgique et au Grand-Duché de Luxembourg par quatre des cinq espèces vivant en Europe. L'analyse de l'information disponible démontre que P. simulans (KLUG ... [more ▼]

Le genre Pachyprothasis HARTIG est représenté en Belgique et au Grand-Duché de Luxembourg par quatre des cinq espèces vivant en Europe. L'analyse de l'information disponible démontre que P. simulans (KLUG) et P. variegata (FALLEN) ont toujours été des espèces rares dans la dition. P. antennata (KLUG) y était plus prospère jusqu'en 1949 et doit être considérée aujourd'hui comme étant en régression. P. rapae (LINNE) est de très loin l'espèce la plus abondante, la plus fréquente et la plus répandue dans les deux pays. L'analyse des dates de récolte montre que cette dernière est bivoltine; cette caractéristique biologique la distingue des trois autres. Le recensement des plantes-hôtes montre que les larves des quatre espèces doivent toute êtres classées parmi les polyphages du premier degré. [less ▲]

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See detailFaunistique des macrophyini de la Belgique et du Grand-Duché de Luxembourg (Hyménoptères : Tenthredinidae) : 2. Généralités sur le genre Macrophya DAHLBOM; inventaire des espèces apparentées à M. albicincta (SCHRANK)
Magis, Noël ULg

in Bulletin de la Société Royale des Sciences de Liège (1984), 53(6), 437-449

The species belonging to the epinota-group of Macrophya DAHLBOM, living in Belgium and Grand Duchy of Luxembourg have been inventoried. A key for their identification is given. Some aspects of the ... [more ▼]

The species belonging to the epinota-group of Macrophya DAHLBOM, living in Belgium and Grand Duchy of Luxembourg have been inventoried. A key for their identification is given. Some aspects of the variability (coloration of scutellum, dimensions of wing's veins) between M. albicincta (SCHRANK) and M. alboannulata COSTA are analysed and compared with results obtained in France. This variability is perhaps of clinal type. From faunistical point of view, the geographical repartition, the phenology and the relative frequency of all species are related. [less ▲]

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See detailFaunistique des macrophyini de la Belgique et du Grand-Duché de Luxembourg (Hyménoptères : Tenthredinidae) : 3. Les Macrophya des groupes blanda-duodecimpunctata et chrysura
Magis, Noël ULg

in Bulletin de la Société Royale des Sciences de Liège (1985), 54(1), 45-54

The chorology of the Macrophya DALHBOM, belonging to the blanda-duodecimpunctata (4 spec.) and to the chrysura group (2 spec.) respectively, is described in Belgium and Great-Duchy of Luxembourg. The ... [more ▼]

The chorology of the Macrophya DALHBOM, belonging to the blanda-duodecimpunctata (4 spec.) and to the chrysura group (2 spec.) respectively, is described in Belgium and Great-Duchy of Luxembourg. The phenology of these species is recorded. Comparison of data obtained in Belgium before and after 1950 indicates a regression of M. blanda (FABRICIUS) and M. diversipes (SCHRANK). M. erythrocnema COSIA and M. recognata ZOMBORI have been discovered only 20 years ago, they appear to be recent immigrants in the country. M. recognata so far known from 5 localities, seems most able to take root as M. erythrocnema. [less ▲]

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