Reduction of temperature effects for bridge health monitoring

in Eccomas Proceedia (2020, November 23)

Structural health monitoring of concrete bridges can be achieved by tracking static load-testing results or dynamic properties as for example eigenfrequencies. Deviations from a healthy reference state ... [more ▼]

Structural health monitoring of concrete bridges can be achieved by tracking static load-testing results or dynamic properties as for example eigenfrequencies. Deviations from a healthy reference state can be used as damage indicators and even more, help to localize zones of stiffness reduction, i.e. cracking. However, outdoor temperature effects also lead to changes of monitored physical characteristics in the same order of magnitude as damage. Hence, temperature effects need to be removed prior to any condition analysis. The present paper presents a new two-step approach by applying physical compensation first, before using a statistical method based of Principal Component Analysis (PCA) or more exactly on principal vectors and singular values. This technique is here applied to eigenfrequencies, first of a new bridge without damage, but with extreme temperature variation due to thick asphalt layer and special bearing constraints, thus showing strong sensitivity along seasonal temperatures in the intact state. The second object is the Z24 Bridge in Switzerland, which is well documented in literature and where artificial damage was applied prior to demolition. The proposed techniques allow removing noise and temperature effects in a coherent and efficient way. The corrected measurement data can then be used in subsequent steps for its definite purpose, i.e. detection and localization of damage for instance by updating a numerical finite element model which allows assessing a stiffness loss. [less ▲]

Influence of Thermal Energy Storage and Heat Pump Parametrization for Demand-Side-Management in a Nearly-Zero-Energy-Building using Model Predictive Control

in Energy and Buildings (2020), 226

The rollout of the supply dependent generators wind turbines and photovoltaics leads to a flexibility demand that can be adressed from the consumer side, via Demand-Side-Management, as well. In single ... [more ▼]

The rollout of the supply dependent generators wind turbines and photovoltaics leads to a flexibility demand that can be adressed from the consumer side, via Demand-Side-Management, as well. In single family houses, the heat pump, in combination with thermal energy storage, can shift their energy comsumption according to price signals in order to reduce consumer costs. This paper analyses the impact of different heat storage sizes and heat pump powers on cost savings and shifting potential, focussing on the Luxembourgish context, when variable electricity prices based on the electricity market are applied. A model predictive controller determines the cost-optimal operating cycles of the heat pump. The building’s heat demand is predicted with the help of a neural network. The results of the parametric study show significant differences in energy efficiency and cost savings. Furthermore limitations of taking advantage of variable electicity prices due to the price structure are disclosed. The cost savings however do not give a sufficient incentive for the consumer to invest in optimizing the heating system for Demand-Side-Management purposes. By consequence, the potential and the efficiency of Demand-Side-Management are limited and further incentives are necessary. [less ▲]

Influence of pubic symphysis stiffness on pelvic load distribution during single leg stance

in International Journal of Numerical Methods in Biomedical Engineering (2020)

This study focuses on the influence of the softening and stiffening of pubic symphysis on the load distribution within the bones of the pelvic ring under the physiological loadings of the single leg ... [more ▼]

This study focuses on the influence of the softening and stiffening of pubic symphysis on the load distribution within the bones of the pelvic ring under the physiological loadings of the single leg stance. Muscle forces and joint reaction forces were first determined by inverse dynamics and applied to a linear finite element model of the pelvis. With normal pubic symphysis stiffness, high Von Mises stresses are located on the anterior surface to the sacrum around the sacroiliac joint and on the superior ramus, both on the side of the weightbearing leg. Softening of the pubic symphysis redirects the load backward, decreases the stresses at the anterior pelvis, and increases them at the posterior pelvis. A stiffening of the pubic symphysis redirects the load forward, increases the load on the posterior pelvis, and decreases them at the anterior pelvis. This investigation highlights the significance of the pubic symphysis on the load distribution of the pelvis and in maintaining the integrity of the structures. Its role should not be neglected when analyzing the pelvis. [less ▲]

Designing an early failure indicator channel for an in-tank hydrogen valve via a fatigue-based approach

in Journal of Computational Design and Engineering (2020)

This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve’s damages. To ... [more ▼]

This study introduced a fatigue-based approach to design and implement an indicator channel into an in-tank hydrogen valve. It was aimed at providing a mean to point out multiple early valve’s damages. To achieve the goal, the study was proposed to handle via three main phases. They included (i) the risk point determinations, (ii) the new valve design and the crack nucleation life estimations, as well as (iii) the simplified crack growth analyses. The obtained results firstly highlighted the construction of the test channel (TC), whose branches were located close to the predicted damage’s sites. The damages could be identified either when a crack reaches the TC (then forms a leakage) or indirectly via the crack propagations’ correlation. The results also pointed out that the TC-implemented valve could perform as similarly as the non-TC one in the non-treated condition. More importantly, this new structure was proved to have a capacity of satisfying the required minimal life of 1.5E5 cycles, depending on the combined uses of the specific material and the pre-treatment, among those considered. In addition, the results emphasized the complexity of the TC that could not be formed by the traditional manufacturing process. Hence, direct metal laser sintering was proposed for the associated prototype and the final TC was issued based on the fundamental requirements of the technique. Finally, it was suggested that practical experiments should essentially be carried out to yield more evidence to support the demonstrated results. [less ▲]

Energy efficiency and indoor aire quality os seminar rooms in older buildings with and without mechanical ventilation

in Bauphysik (2019), 41(October 2019, Heft 5), 243-251

The present paper reports on an experimental study performed in a seminar room of the University of Luxembourg in a building of the 1970ies without a major renovation. This lecture room is typical for ... [more ▼]

The present paper reports on an experimental study performed in a seminar room of the University of Luxembourg in a building of the 1970ies without a major renovation. This lecture room is typical for this building period and has a capacity of 60 seats. It is equipped with a mechanical ventilation system that is normally in operation on workdays for 11 hours a day in semester periods (8:00-19:00h), while windows can be opened manually. A Blower-Door-Test revealed that the room is not airtight. During a year, the ventilation system was shut “on” and “off” in periods of some weeks and the consumed final-energy was measured, as well as the indoor climate assessed by physical and psychological measurements. For instance, the measured CO2 concentrations are marginally better with the ventilation system "on", which was not perceived in any way by the occupants during the investigations. It was not possible to properly identify the impact of ventilation on the consumed heat-energy, as the room could not be thermally separated from the rest of the building. But with the system “on” there was a clear increase in consumed primary energy due to the electric consumption of the fans. No relationship between the perceived percentage of dissatisfied and perceived climate could be observed. It is concluded that the typical normal operation modus is questionable for seminar rooms in older buildings with variable occupancy and that a simple shut down or semi-automatic user controlled modus by low-cost retrofit seems advantageous. [less ▲]

Inbetriebnahme und Monitoring einer Feldtestfläche zur außenliegenden Lufttemperierung

in Völker, Conrad; Kornadt, Oliver; Jentsch, Mark (Eds.) et al Schriftenreihe der Professur Bauphysik, Bauphysiktage 2019 in Weimar - Bauphysik in Forschung und Praxis (2019, September 25)

Der Beitrag ist inhaltlich dem Forschungsprojekt „Low Exergy Utilisation - Einsatz von außen-liegender Wandtemperierung bei der Gebäudesanierung - Feldtest, CO2- Wärmepumpe mit Eisspeicher“ (kurz LEXU II ... [more ▼]

Der Beitrag ist inhaltlich dem Forschungsprojekt „Low Exergy Utilisation - Einsatz von außen-liegender Wandtemperierung bei der Gebäudesanierung - Feldtest, CO2- Wärmepumpe mit Eisspeicher“ (kurz LEXU II, Förderkennzeichen 0327370Y) zugeordnet. Im Rahmen des Pro-jektes wurde ein Großdemonstrator mit außenliegender Wand- und Lufttemperierung (kurz aWT & aLT) zusammen mit einem niederexergetischen Versorgungssystem, bestehend aus Eisspeicher, Wärmepumpe und PVT-Hybridkollektoren realisiert. Zur Heizperiode 2018/19 wurde die „Feldtestanlage“ in Betrieb genommen, sodass derzeit Messdaten generiert wer-den. In dem Forschungsprojekt wird der Demonstrator über eine Heizperiode und eine Kühl-periode messtechnisch begleitet und ausgewertet. Dabei wird der Großdemonstrator und alle Komponenten umfassend messtechnisch ausgewertet (~300 Messwerte). Ziel des Beitrags ist eine Darstellung der Grundlagen der außenliegenden Lufttemperierung, als niederexergetische und schnell regelbare Ergänzung zur außenliegenden Wandtemperie-rung. Bei der außenliegenden Lufttemperierung wird zwischen thermisch aktivierter Be-standswand und neuem Wärmedämm-Verbundsystem ein Luftspalt geschaffen, durch den Außenluft geführt und temperiert werden kann. Diese temperierte Außenluft wird dem dahin-terliegenden Raum (im Feldtest ein Büroraum mit rund 20 m² Grundfläche und zwei Arbeits-plätzen) als Frischluft zur Verfügung gestellt. Aufbauend auf den Grundlagen wird die Inbe-triebnahme der bereits umgesetzten Feldtestfläche mit möglichen Regelstrategien geschildert. Abschließend sollen erste Messergebnisse der Feldtestfläche dargestellt und diskutiert wer-den. Interessant sind hier vor allem (im Vergleich zur außenliegenden Wandtemperierung) die möglichen Zeitkonstanten und die erreichbaren Wärmeströme nach Innen (z.B. mögliche Wärmeübertragung als Kombination aus Konvektion im Luftspalt und Wärmeleitung durch die Bestandswand). Themengebiet: Energieeffiziente Gebäude & Bauphysik und Sanierung & Behaglichkeit und Raumklima [less ▲]

Graft materials provide greater static strength to medial opening wedge high tibial osteotomy than when no graft is included

in Journal of Experimental Orthopaedics (2019), 6(13),

Background The purpose of this study was to compare the stability of medial opening-wedge high tibial osteotomy (MOWHTO) with and without different graft materials. Good clinical and radiological outcomes ... [more ▼]

Background The purpose of this study was to compare the stability of medial opening-wedge high tibial osteotomy (MOWHTO) with and without different graft materials. Good clinical and radiological outcomes have been demonstrated when either using or not using graft materials during MOWHTO. Variations in the biomechanical properties of different graft types, regarding the stability they provide a MOWHTO, have not been previously investigated. Methods A 10 mm biplanar MOWHTO was performed on 15 artificial sawbone tibiae, which were fixed using the Activmotion 2 plate. Five bones had OSferion60 wedges (synthetic group), five had allograft bone wedges (allograft group), and five had no wedges (control group) inserted into the osteotomy gap. Static compression was applied axially to each specimen until failure of the osteotomy. Ultimate load, horizontal and vertical displacements were measured and used to calculate construct stiffness and valgus malrotation of the tibial head. Results The synthetic group failed at 6.3 kN, followed by the allograft group (6 kN), and the control group (4.5 kN). The most valgus malrotation of the tibial head was observed in the allograft group (2.6°). The synthetic group showed the highest stiffness at the medial side of the tibial head (9.54 kN·mm− 1), but the lowest stiffness at the lateral side (1.59 kN·mm-1). The allograft group showed high stiffness on the medial side of the tibial head (7.54 kN·mm− 1) as well as the highest stiffness on the lateral side (2.18 kN·mm− 1). Conclusions The use of graft materials in MOWHTO results in superior material properties compared to the use of no graft. The static strength of MOWHTO is highest when synthetic grafts are inserted into the osteotomy gap. Allograft wedges provide higher mechanical strength to a MOWHTO than when no graft used. In comparison to the synthetic grafts, allograft wedges result in the stiffness of the osteotomy being more similar at the medial and lateral cortices. [less ▲]

Materials, valves and sealing gaskets for high pressure applications

Poster (2019)

Biomechanical testing of osteotomy plates

Scientific Conference (2018, November 30)

Finite element analysis of the pelvis including gait muscle forces: an investigation into the effect of rami fractures on load transmission

in Journal of Experimental Orthopaedics (2018), 5(33), 1-9