References of "Maas, Stefan 50002241"
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See detailVOLUME FLOW UNBALANCES AND SHORTCUTS IN DECENTRALIZED AND CENTRALIZED VENTILATION UNITS – FIELD TESTS IN RESIDENTIAL BUILDINGS
Merzkirch, Alexander UL; Maas, Stefan UL; Scholzen, Frank UL et al

Scientific Conference (2014)

Centralized and decentralized mechanical ventilation have become state-of-the-art in modern energy-efficient residential buildings. Calculations for the energy demand of buildings are done with nominal ... [more ▼]

Centralized and decentralized mechanical ventilation have become state-of-the-art in modern energy-efficient residential buildings. Calculations for the energy demand of buildings are done with nominal values of the ventilation units, assuming a proper function of the devices. The used ventilation concepts may be divided into two main categories- centralized and decentralized units and both come with advantages and disadvantages in terms of energy efficiency. In Luxembourg, a comprehensive field test has been performed in order to evaluate and compare their performance in practice. It could be shown that ventilation systems often do not meet the expectations. High unbalances in volume flows, high sensitivity to pressure differences and recirculation were measured in several cases. Only a proper installation and balancing of the systems can ensure an energy efficient function. [less ▲]

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See detailMeasured and perceived indoor comfort versus energy efficiency and users‟ control in Luxembourg‟s new school buildings
Brensing, Jessica UL; Schweizer-Ries, Petra; Thewes, Andreas UL et al

Scientific Conference (2013, September)

Room climate can be evident for job productivity and individual ́s health. Its realisation is often of high relevance for the building ́s energy consumption e.g. air conditioning vs. natural ventilation ... [more ▼]

Room climate can be evident for job productivity and individual ́s health. Its realisation is often of high relevance for the building ́s energy consumption e.g. air conditioning vs. natural ventilation. New school buildings in Luxembourg differ significantly regarding to energy consumption, heating, air-conditioning technology and technical control as well as interaction means given to the user. Several studies have shown that personal control plays an important role for the satisfaction with the room climate. Central research question was, how the technological control has to be designed that energy is used efficiently and users are still satisfied with the room climate. In this study technical features to control the room climate e.g. features for ventilation, opening windows and heating systems were summarized to an overall control factor to be compared with perceived control by the users. Physical room climate and its users ́ satisfaction level were measuredas well as the buildings ́ individual energy consumption levels were taken into account. 342 Teachers were asked by a standardised questionnaire during winter 2010/2011 in 31 new school buildings in Luxembourg, in 17 schools technical devices for air temperature, quality and humidity were installed. The results show a strong correlation between perceived control and room climate satisfaction as well as a significant correlation between the technical control factor and perceived control. Further results will be examined. [less ▲]

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See detailDETECTION AND LOCALISATION OF DAMAGE ON INDUSTRIALLY PRODUCED CONCRETE SLABS THROUGH TIME- AND FREQUENCY-DOMAIN APPROACHES
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

in Carrera, E.; Miglioretti, F; Petrolo, M. (Eds.) 6th ECCOMAS Thematic Conference on Smart Structures and Materials (SMART2013), Torino 24-26 June 2013 (2013, June)

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency ... [more ▼]

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency-domain methods are used for the diagnostics. It consists in practical output-only techniques as Stochastic Subspace Identification (SSI) for modal identification or Enhanced Principal Component Analysis (EPCA) for detecting the presence of damage. The use of the Hankel matrix instead of the observation matrix improves effectively the robustness of these methods. Damage localization is based on Frequency Response Functions (FRFs) and sensitivity analysis of PCA results. The efficiency of the above-mentioned methods has been demonstrated in earlier studies mainly on numerical examples and small-scale laboratory experiments. It was also tested successfully on industrial examples to perform machine condition monitoring using a reduced set of sensors. In this work, the investigation is performed on precast prestressed and non-prestressed concrete slabs. Successive damages were artificially introduced in the slabs by loading heavy weights and by cutting steel wires, which induced cracks in the structure. The examples show the consequences of the considered techniques for damage identification. The results that are very different between prestressed and non-prestressed slabs may be used as input for the condition control of this kind of structures. [less ▲]

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See detailUSE OF TIME- AND FREQUENCY-DOMAIN APPROACHES FOR DAMAGE DETECTION IN CIVIL ENGINEERING STRUCTURES
Nguyen, Viet Ha UL; Mahowald, Jean UL; Golinval, Jean-Claude et al

in Maia, NNM; Matos Neves, M.; Chedas Sampaio, R.P. (Eds.) International Conference on Structural Engineering Dynamics (ICEDyn 2013) - Sesimbra 17-19 June 2013 (2013, June)

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the ... [more ▼]

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques. [less ▲]

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See detailStatic and dynamic differences in fixation stability between a spacer plate and a small stature plate fixator used for high tibial osteotomies – A biomechanical bone composite study
Maas, Stefan UL; Diffo Kaze, Arnaud UL; Dueck, Klaus et al

in ISRN Orthopedics (2013), 2013

Background: The objective of the present study was to comparemechanical strength and stability of the newly designed spacer plate with the gold standard plate for the treatment of medial knee joint ... [more ▼]

Background: The objective of the present study was to comparemechanical strength and stability of the newly designed spacer plate with the gold standard plate for the treatment of medial knee joint osteoarthritis. Materials and Methods: Ten fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomy (HTO) according to standard techniques, using five TomoFix plates and five Contour Lock plates. Static compression load to failure and load-controlled cyclical fatigue failure tests were performed. Forces and horizontal displacements were measured; plastic deformations and dynamic stiffness were determined. Results and Discussion: In all samples, rotation of the tibial head and fracture of the opposite cortex were observed. Behaviors of the specimens under static loading were comparable between groups. Cyclic testing revealed lateral significant higher stiffness untilfailure for the Contour Lock compared to the TomoFix plate. No visible implant failure was observed in any group. Conclusion: Considering the static analysis, both plates offered sufficient stability under physiologic loads of up to 3000N. The Contour Lock plate-fixated specimens showed a higher stability during the cyclic testing, supposedly due to the wider distance between the fixation screws. [less ▲]

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See detailEnergy performance assessment of an existing double-skin façade: measurements and simulation
Carton, Julien UL; Scholzen, Frank UL; Thomas, Sébastien et al

in Energy Forum - Solar Building Skins, 06 - 07 December 2012, Italy (2012, December)

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity ... [more ▼]

An existing office building with an active double skin façade in Luxembourg has been analyzed. In the first step in-situ measurements have been performed. For this purpose outside, inside and cavity conditions have been measured for representative summer and winter conditions. In a second step, a thermal simulation using TRNSYS was performed. The simulation model has been compared to the time limited series of measurements and thus has been validated for some of the annual meteorological conditions. Then the model has been extrapolated to a whole year in order to assess the energy performance of the given façade. Further a parametric study of alternative façades has been carried out based on the validated simulation model to assess their own performances. For the given case study building, the double skin concept energetically performs well compared to other concepts with non outside (non weather exposed) solar protection, but worse than an external solar protection. The thermal comfort level in the rooms has also been determined by simulation - the calculated room averaged comfort level is quite optimal, but further investigations regarding the local comfort close to the glazed façades still have to be achieved. [less ▲]

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See detailSchallanalyse eines Autokühlers mit Ventilator; Vergleichende Ortung mit Schallpegelmesser, Beamforming, Holographie und Intensitätssonde
Maas, Stefan UL; Hanus, Vincent UL; Adam, Ken UL

in VDI Berichte 2170 (2012, November 14)

Es wurde die Schallentstehung an einem Autokühler (56 x 40 x 15 cm) mit Ventilator (Ф42 cm) in einer Labormessung am weich aufgehängtem Kühler untersucht, wobei verschiedene Verfahren zur ... [more ▼]

Es wurde die Schallentstehung an einem Autokühler (56 x 40 x 15 cm) mit Ventilator (Ф42 cm) in einer Labormessung am weich aufgehängtem Kühler untersucht, wobei verschiedene Verfahren zur Schallquellenortung getestet wurden. Es wird über die Messungen, deren Ergebnisse und deren Probleme berichtet, die sich aus der Luftströmung und aus dem 3-dimensionalen Messobjekt (15 cm Dicke) ergeben. Die Messung wurde durch DELPHI Powertrain Systems Luxemburg initiiert und von dort begleitet. Die Interpretation bezüglich der Schallentstehung ist nicht ganz eindeutig. [less ▲]

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See detailModern damage detection by using static assessment methods for efficient rehabilitation
Scherbaum, Frank; Mahowald, Jean; Waldmann, Danièle UL et al

in Proceedings (2012, September)

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See detailWIE VIEL ENERGIE VERBRAUCHEN NEUE UNTERRICHTS- UND BÜROGEBÄUDE IN LUXEMBURG?
Maas, Stefan UL; Scholzen, Frank UL; Thewes, Andreas UL et al

in Cahier Scientifique - Revue Technique Luxembourgeoise (2012)

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den ... [more ▼]

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den Industriesektor zurückzuführen waren und nur 20 % auf die Gebäude, hat sich dies bis zum Jahr 2009 deutlich verändert. Demzufolge entfallen nur noch 30 % auf den Industriesektor, 25 % auf Verkehr (nach Abzug der Treibstoffexporte) und 45 % auf den Verbrauch des Tertiären Sektors3, welcher sowohl die privaten und die öffentlichen Haushalte, als auch Dienstleistungsgebäude beinhaltet. Die Direktive 2010/31/EG2 fordert von den Mitgliedstaaten die nationalen Normen weiterhin zu verschärfen und Pläne zu erstellen, um die Anzahl an Niedrigstenergiegebäuden weiter zu erhöhen. Um die Energieströme in Gebäuden besser zu verstehen, Sparmaßnahmen zu erarbeiten und mögliche Bewertungen über das Energieeinsparpotential für Gebäude durchführen zu können, sind jedoch aussagekräftige Verbrauchsdatenanalysen notwendig, die leider oftmals noch nicht in verlässlicher Qualität vorliegen. In der Direktive wird zudem empfohlen für die Berechnung eine Unterteilung aller Gebäude in angemessene Kategorien vorzunehmen, welche von Einfamilienhäusern (EFH), über Bürogebäude und Unterrichtsgebäude bis hin zu Krankenhäuser, Hotels und Sportanlagen reicht. In einer ersten Studie der Universität Luxemburg4 wurden bereits neuere EFH in Luxemburg hinsichtlich ihres realen Energieverbrauches untersucht und ausgewertet. [less ▲]

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See detailDamage assessment of concrete structures through dynamic testing methods. Part 1 - Laboartory Test
Maas, Stefan UL; Zürbes, Arno; Waldmann, Danièle UL et al

in Journal of Engineering Structures (2012), 34

The present paper is split into two parts: Part 1 is about laboratory tests whereas the second part deals with experiments on real bridges. This article aims at summarizing several experimental dynamic ... [more ▼]

The present paper is split into two parts: Part 1 is about laboratory tests whereas the second part deals with experiments on real bridges. This article aims at summarizing several experimental dynamic testing methods with different damage indicators to evaluate the state of prestressed as well as of passively reinforced concrete structures. First the differences between prestressed and passively reinforced concrete are repeated for static behavior, before the transition to dynamics is made. As it will be proved in the following that the amount of nonlinearities increases with damage, harmonic excitation is favorable to realize good testing conditions. It is applied to visualize variations in linear as well as in non-linear structural characteristics, which are subsequently used as damage indicators, e.g. the drop of the eigenfrequencies, the changes in damping and modeshapes, the occurrence of higher harmonics and a varying dependency of the eigenfrequency on excitation force amplitude. These different indicators will be used on passively reinforced beam elements and industrially produced prestressed slabs in the first part and on two real post-tensioned bridges in the second part. All these structures were in good order and condition before artificial damage was applied in multiple steps and the sensitivity of each damage indicator was analyzed. [less ▲]

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See detailDamage Detection on the Champangshiehl Bridge using Blind Source Separation
Nguyen, Viet Ha UL; Rutten, Christophe; Golinval, Jean-Claude et al

in Proceedings of the Third International Symposium on Life-Cycle Civil Engineering, IALCCE’12 (2012)

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See detailShear stresses in honeycomb sandwich plates: Analytical solution, finite element method and experimental verification
Wahl, Laurent UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Journal of Sandwich Structures & Materials (2012), 4

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of ... [more ▼]

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of aluminium. Compared to normal plates, sandwich panels have a very high stiffness and simultaneously a low weight. The core of these structures is mainly subjected to shear stresses. The shear stresses depend strongly on the angle of the load application. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. When doing finite element simulations of honeycomb cores, often the core is homogenized in order to reduce the calculation time. In this article, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. The equations are validated by finite element simulations and partially by tests. Three-point bending tests and additionally some Food Cart Roller Tests were conducted in order to test the panels in different angles. [less ▲]

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See detailShear Stresses in Honeycomb Sandwich Plates: Analytical Solution, Finite Elemente Method and Experimental Verification
Wahl, Laurent UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Journal of Sandwich Structures & Materials (2012), 14(4), 449-468

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of ... [more ▼]

Honeycomb composite structures are used in airplanes, railway cars and vehicles. The sandwich panels consist of two stiff face sheets of aluminium, which are bonded to a very lightweight honeycomb core of aluminium. Compared to normal plates, sandwich panels have a very high stiffness and simultaneously a low weight. The core of these structures is mainly subjected to shear stresses. The shear stresses depend strongly on the angle of the load application. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. When doing finite element simulations of honeycomb cores, often the core is homogenized in order to reduce the calculation time. In this article, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. The equations are validated by finite element simulations and partially by tests. Three-point bending tests and additionally some Food Cart Roller Tests were conducted in order to test the panels in different angles. [less ▲]

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See detailDamage assessment of concrete structures through dynamic testing methods. Part 2: Bridge tests
Maas, Stefan UL; Zürbes, Arno; Waldmann, Danièle UL et al

in Engineerig Structures (2012), 34

The present paper is split into two parts: in the first part the different dynamic damage indicators are defined and applied to beam and slab structures under laboratory conditions, whereas the present ... [more ▼]

The present paper is split into two parts: in the first part the different dynamic damage indicators are defined and applied to beam and slab structures under laboratory conditions, whereas the present second part deals with experiments carried out on two real post-tensioned bridges. The damage indicators defined in part one are based on swept sine excitation and esveal the drop of the eigenfrequencies, the changes in damping, the varying dependency range of the first eigenfrequency on excitation force amplitude and the occurrence of higher harmonics, which changed the Total Harmonic Distorsion (THD) and a special transfer-function called TF or FRFsmall. In the first part it was proved that the amount of nonlinearities varies with damage and that harmonic excitation is favorable for good test conditions. In the laboratory this can easily be done using an electric or hydraulic shaker, but on real bridges this kind of excitation becomes more complicated due to the higher forces and the necessity to provide counter bearing for any shaker system. That is why two machines were designed and used to excite big structures harmonically, e.g. real bridges in this part. The different indicators are applied to assess the state of two post-tensioned bridges, which had been in good order and condition before artificial damage in multiple steps was caused. It turns out that the decrease in the eigenfrequencies is the most important damage indicator, provided temperature and mass dependant effects can be eliminated. All other indicators may be used as supplements to give correct tendencies, but no strict limits. [less ▲]

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See detailStatic and dynamic testing on prestressed concrete slab elements with artificial bond deficiencies
Mahowald, Jean UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Proceedings of the 4th Bond in Concrete Conference, Vol. 1: General Aspects of Bond (2012)

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See detailDamage Identification and Localisation Using Changes in Modal Parameters for Civil Engineering Structures
Mahowald, Jean UL; Maas, Stefan UL; Waldmann, Danièle UL et al

in Proceedings of the International Conference on Noise and Vibration Engineering (2012)

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See detailDynamic damage identification using linear and nonlinear testing methods on a two-span prestressed concrete bridge
Mahowald, Jean UL; Maas, Stefan UL; Scherbaum, Frank UL et al

in Proceedings of the Third International Symposium on Life-Cycle Civil Engineering, IALCCE’12 (2012)

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See detailIntegrative analysis of the energy flow in a steel plant and a comprehensive approach to increase the energy efficiency
Tarrés Font, Joana UL; Maas, Stefan UL; Scholzen, Frank UL et al

in Proceedings METEC InSteelCON 2011, Düsseldorf Germany, CCD Congress Center, Düsseldorf, 27.06-01.07. (2011, July)

Steel industry is a highly intensive energy consumer. The energy used by the studied electric steelmaking plant could supply 25,000 households with thermal energy and 100,000 households with electrical ... [more ▼]

Steel industry is a highly intensive energy consumer. The energy used by the studied electric steelmaking plant could supply 25,000 households with thermal energy and 100,000 households with electrical energy. Increasing the energy efficiency of a steel plant will not only have impact in the reduction of greenhouse emissions but also in an increase of the competitiveness of the plant. A Luxembourgish steel plant is studied in detail and several options for energy savings are identified. Promising energy efficiency gains can be achieved by the optimization of the electric arc furnace and the reheating furnaces and by the improvement of the logistics between the continuous casting and the reheating furnace. The possibilities of energy recovery for heating purposes and for the generation of electricity with ORC- (Organic Rankine Cycle) or KALINAtechnologies are studied. In addition there is the opportunity to deliver hot water to a near district-heating system using otherwise lost energy and creating regional synergies. Nevertheless there is a need to develop a comprehensive and integrative approach to find a good overall solution instead of treating each step separately. The University of Luxembourg in collaboration with a Luxembourgish steel plant is developing a methodology to assess the technical, economical and environmental aspects of each solution. The objective is to assist in the decision-making in the company’s energy efficiency strategy and to perform a comparative analysis of the different solutions in order to propose an optimized plant, based on its feasibility due to local restrictions and different energy price scenarios. This ideal plant will be composed of individual elements, which proved their effectiveness in different real plants, so that the approach stays applied [less ▲]

Detailed reference viewed: 142 (2 UL)