References of "Maas, Stefan 50002241"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailEnergy performance comparison of ventilation-based heating versus water-based heating systems in an efficient residential building
Shirani, Arsalan UL; Merzkirch, Alexander; Leyer, Stephan UL et al

in Fluid Dynamics & Material Processing (in press)

The application of air-based heating systems as a possible approach to reduce the construction costs in highly efficient residential buildings is becoming popular. Air-based heating systems have been well ... [more ▼]

The application of air-based heating systems as a possible approach to reduce the construction costs in highly efficient residential buildings is becoming popular. Air-based heating systems have been well-known for their usage in passive houses during the past three decades. Available studies on such systems tend mostly to focus only on comparing exhaust air heat pump technology with conventional systems in efficient buildings. Moreover, most of the existing studies ignore the usual presence of the electrical heaters as backup. Besides, a comprehensive study and comparison between different air-based heating system concepts is still missing. In this study, four different air-based heating system concepts separated by the type of heat source of heat pump for heating and domestic hot water are defined. These systems are compared to four conventional heating system, including floor heating and direct electrical system employing dynamic annual simulations. According to simulation results, the systems with floor heating have shown the best system efficiencies and the lowest energy demand in comparison to the other systems. The main reason for this was the lower supply temperatures of the floor heating systems. Between the air heating systems, the system equipped with an outdoor air heat pump showed a better energy performance than an exhaust air system. The main reason for this could be attributed to the power limitation of exhaust air heat pump systems. [less ▲]

Detailed reference viewed: 37 (0 UL)
Full Text
See detailUmstellung eines Campingplatzes auf solare Energieversorgung
Latz, Sebastian UL; Maas, Stefan UL

in Konferenzbeiträge Bauphysiktage Kaiserslautern 2022 (2022), 5

Der fortschreitende Klimawandel verlangt ein Umschwenken, weg von der fossilen Energieversorgung und hin zu den Erneuerbaren, wobei nachhaltige Tourismusangebote auch verstärkt einbezogen werden müssen ... [more ▼]

Der fortschreitende Klimawandel verlangt ein Umschwenken, weg von der fossilen Energieversorgung und hin zu den Erneuerbaren, wobei nachhaltige Tourismusangebote auch verstärkt einbezogen werden müssen. Der Campingplatz Treviris liegt auf dem Gelände des Rudervereins Treviris Trier und verzeichnet jährlich von Mitte April bis Mitte Oktober zwischen 40 und 50.000 Übernachtungen. Im Zuge des Neubaus des Bootshauses wird der vorhandene Gasanschluss zurückgebaut und die gesamte Wärme- und Stromversorgung der Liegenschaft muss auf regenerative Energien umgestellt werden. So soll der Bedarf des Campingplatzes, des Bootshauses (KfW 40 EE), der angegliederten Wohnbebauung mit zehn Wohneinheiten (KfW 40+) sowie mehrere Ladestationen emissionsneutral durch Sonnenenergie versorgt werden. Hauptbestandteile des Konzeptes sind eine 105 kWpeak PV Anlage mit 90 kWh Batteriespeicher sowie zwei Wärmepumpen, die um eine 80 m² hybride solarthermische Photovoltaikanlage (PVT) auf dem Campingplatz ergänzt werden soll. Insbesondere die Warmwasserversorgung des Campingplatzes ist hierbei eine Herausforderung, da die auftretenden Leistungsspitzen von 4m3 Warmwasser (WW) in 2 h nicht ausschließlich mittels Wärmepumpe bereitgestellt werden können. Es wird auf Wärmespeicher mit zentraler Frischwasserstation zurückgegriffen. Für die Dimensionierung der Hauptkomponenten: PVT Feld, Wärmepumpe und Pufferspeicher wird eine Zeitreihenanalyse mit variierendem Bedarf und schwankendem Solarangebot durchgeführt. [less ▲]

Detailed reference viewed: 24 (0 UL)
Full Text
Peer Reviewed
See detailComparison of high-performance and conventional internal insulation materials based on hygrothermal analysis using in situ measurements and simulation
Latz, Sebastian UL; Maas, Stefan UL; Scholzen, Frank UL et al

in Bauphysik (2022), 1

Following the European directive to reduce CO2 emissions of existing buildings by improving energy efficiency, internal insulation systems play a central role in the renovation of historically valuable ... [more ▼]

Following the European directive to reduce CO2 emissions of existing buildings by improving energy efficiency, internal insulation systems play a central role in the renovation of historically valuable buildings which cannot be insulated from the outside for reasons of monumental protection, or in cases where no additional exterior space is available. However, besides the thermal property of insulation systems, there are other relevant properties to be considered before choosing an internal insulation system, such as the hygrothermal behavior which plays a particularly important role in diffusion-open interior insulation systems. As the internal insulation layer reduces the temperature of the existing wall during the heating season, its drying potential after rain events is considerably reduced. In addition to the effects of moisture from the outside (mainly wind driven rain), the entry of humidity from the inside through diffusion plays an important role. In the presented study, high performance insulation materials with nanostructure based on silicon dioxide and polyurethane are compared to conventional material based on wood fiber from a hygrothermal point of view by analyzing in situ measurements and simulations. [less ▲]

Detailed reference viewed: 46 (2 UL)
Full Text
Peer Reviewed
See detailAnalysis of residual stress relaxation of aluminum alloys EN AW 6061/-82 T6 under cyclic loading
Repplinger, Christian UL; Sellen, Stephan UL; Kedziora, Slawomir UL et al

in Fatigue and Fracture of Engineering Materials and Structures (2021)

Stress relaxation describes the reduction of stress under static or cyclic loading at a constant strain level. Several processes induce intentionally residual stresses, for example, autofrettage of thick ... [more ▼]

Stress relaxation describes the reduction of stress under static or cyclic loading at a constant strain level. Several processes induce intentionally residual stresses, for example, autofrettage of thick-walled pressurized tubes to improve their fatigue life. This well-known process induces residual compressive stresses at the critical inner surface by using a single static but controlled over- loading internal pressure. Relaxation of residual stresses due to cyclic loading in service would endanger the effectiveness of autofrettage and could finally lead to unexpected fatigue failure. In this study, strain-controlled experiments up to 500,000 load cycles and amending nonlinear finite element simulations were done for the aluminum alloys EN AW 6061 T6 and EN AW 6082 T6 to study potential cyclic stress relaxation in four-point bending tests after con- trolled single static plasticization for residual stress generation. This analysis identifies almost stable residual stresses for both materials under different cyclic strain-controlled load levels. [less ▲]

Detailed reference viewed: 35 (3 UL)
Full Text
See detailDichtungsanalyse von Elastomer-O-Ringen unter Hochdruck bei Raum- und Tieftemperatur
Repplinger, Christian UL; Sellen, Stephan UL; Maas, Stefan UL

in Repplinger, Christian (Ed.) 47. VDI-Jahrestagung: Schadensanalyse 2021 - Wasserstoff in metallischen Bauteilen und Mediale und klimatische Beanspruchung von polymeren Produkten (2021, October)

Detailed reference viewed: 38 (3 UL)
Full Text
Peer Reviewed
See detailINVESTIGATING THE INFLUENCE OF PERSONALIZED MUSCULOSKELETAL MODELS ON THE CALCULATED STRESSES IN THE PELVIC RING
Soliman, Ahmed Abdelsalam Mohamed UL; Kedziora, Slawomir UL; Kelm, Jens et al

Poster (2021, September)

This study investigates the influence of personalizing musculoskeletal models (MS) on muscles, contact joints forces and on stresses in the pelvic ring bones during normal gait loading cycle. All ... [more ▼]

This study investigates the influence of personalizing musculoskeletal models (MS) on muscles, contact joints forces and on stresses in the pelvic ring bones during normal gait loading cycle. All calculated forces are utilized to predict stress states in pelvis bones using Finite Element (FE) software. Customized MS models provides more precise muscle and contact forces. Additionally, it enables more automatic coupling between MS and FE environments by data transfer. [less ▲]

Detailed reference viewed: 44 (4 UL)
See detailVerringerung des Temperatureinflusses bei der Überwachung von Brücken am Beispiel von Messdaten aus Luxemburg
Kebig, Tanja UL; Dakhili, Khatereh UL; Nguyen, Viet Ha UL et al

Conference given outside the academic context (2021)

A rising number of concrete bridges are showing increasing damage due to corrosion and fatigue. In addition to the regular standard visual inspection, the bridge’s condition can also be recorded using ... [more ▼]

A rising number of concrete bridges are showing increasing damage due to corrosion and fatigue. In addition to the regular standard visual inspection, the bridge’s condition can also be recorded using additional tests with repeated static loading and/or dynamic tests. To determine any damage to a structure and to check its structural stability, it is crucial to know the exact system properties of the bridge in its undamaged reference state. The system behavior is influenced by damage and bearing conditions and environmental influences, such as the structure’s temperature. The influence of temperature can even cause larger changes in the measured quantities (bending line or modal parameters) than real damage. Therefore, temperature effects should be compensated before any condition analysis. The present work aims to demonstrate the influence of different bearing types and temperature on a real bridge beam. For this purpose, various static and dynamic tests were performed in the undamaged reference state. [less ▲]

Detailed reference viewed: 107 (27 UL)
Full Text
Peer Reviewed
See detailInvestigating the influence of personalized musculoskeletal models on the calculated muscles and joints forces
Soliman, Ahmed Abdelsalam Mohamed UL; Kedziora, Slawomir UL; Kelm, Jens et al

Poster (2021, July)

It was the objective to analyze the influence of personalization of musculoskeletal models (MS) on muscle and contact joint forces for frequent daily movements. For normal gait cycle, we detect ... [more ▼]

It was the objective to analyze the influence of personalization of musculoskeletal models (MS) on muscle and contact joint forces for frequent daily movements. For normal gait cycle, we detect approximately 20% for some muscles attached to the pelvis, as well as for maximum hip-joint contact force. [less ▲]

Detailed reference viewed: 32 (2 UL)
Full Text
Peer Reviewed
See detailRepeatability and precision of different static deflection measurements on a real bridge-part under outdoor conditions in view of damage detection
Kebig, Tanja UL; Nguyen, Viet Ha UL; Bender, Michél et al

in Cunha, A.; Caetano, E. (Eds.) Proceedings of the 10th International Conference on Structural Health Monitoring of Intelligent Infrastructure, SHMII 10 (2021, July)

A large number of concrete bridges show increasing damage due to corrosion and fatigue. The traditional visual inspection and subsequent assessment of concrete bridges is carried out regularly by an ... [more ▼]

A large number of concrete bridges show increasing damage due to corrosion and fatigue. The traditional visual inspection and subsequent assessment of concrete bridges is carried out regularly by an experienced engineer. This type of inspection can be time-consuming, costly and leading to errors. Hence, there is a great interest in complementary, alternative and easy-to-implement methods for condition monitoring of bridges. The University of Luxembourg tested different approaches on a part of a real bridge. Various tests were performed in the healthy reference state, e.g. loading tests with a movable test load according to today’s standards. The measurements in the reference state were repeated several times under outdoor conditions to monitor and document the real temperature influence. Displacement transducers were set up in the vertical and horizontal directions. Simultaneously, a new approach was used for determining the deflection with a laser-based system, that measured the displacements in the bridge’s longitudinal direction by an oblique reflector panel under a well-defined angle. The data gained from the laser-based measurement system were compared to the data from classical displacement transducers. In general, the comparison of the two measuring systems shows quite similar results. [less ▲]

Detailed reference viewed: 86 (7 UL)
Full Text
Peer Reviewed
See detailExperimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems
Shirani, Arsalan UL; Merzkirch, Alexander UL; Roesler, Jennifer et al

in Journal of Building Engineering (2021)

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat ... [more ▼]

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat pumps as an energy efficient heating technology to cover the heating and venting demand of the building is becoming conventional. The exhaust air heat pumps are attracting considerable interest due to their normally reasonable price and small footprint. This heat pump type is often installed as part of an air based heating system together with electrical heaters. These electrical heaters are installed to cover the residual heating demand and/or to insure thermal comfort. The technology of exhaust air heat pumps has been investigated in several studies. Available studies on exhaust air heat pumps have tended mostly to focus on comparison between different technologies utilized in efficient buildings. Almost all of the existing studies have ignored the actual application of this technology in air based heating systems together with electrical heaters. In this sense, there is still a need for discussion on the influence of different buildings’ standards and control strategies on the heating system performance. The present paper aims to call into question the energy efficiency of exhaust air heat pumps under different boundary conditions. In this study, the results of a long time field monitoring are utilized in order to model the dynamic behavior of an exhaust air heat pump in MATLAB/Simulink. The impact of different boundary conditions on the heat pump’s efficiency is studied and additionally compared to previous studies. The developed model is used for annual simulations of air based hybrid heating systems in three different building standards. Finally, the influence of control strategy on the system performance is investigated. It is shown that under certain boundary conditions and control strategy, the studied system could provide an efficient heating system with acceptable user comfort. Nevertheless, applying conventional heating control methods or installing the system in buildings with high heating energy demand could lead to high electrical energy consumption and/or undesirable thermal comfort. [less ▲]

Detailed reference viewed: 24 (0 UL)
Full Text
Peer Reviewed
See detailField monitoring data on a residential exhaust air heat pump system (air-to-air heat pump)
Shirani, Arsalan UL; Merzkirch, Alexander; Roesler, Jennifer et al

in Data in Brief (2021)

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains ... [more ▼]

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains measurement results of a field monitoring on a residential exhaust air heat pump system (air-to-air heat pump) in Germany. This data could be used to investigate the dynamic behaviour and performance of the exhaust air heat pump systems. The data set contains air temperature and humidity of all four sides of the heat pump unit. Moreover, the electrical consumption of the unit and the dynamic pressure difference on the exhaust side (as indication of the air volume rate) could be also found in the data set. [less ▲]

Detailed reference viewed: 30 (0 UL)
Full Text
Peer Reviewed
See detailReduction of temperature effects for bridge health monitoring
Nguyen, Viet Hà; Kebig, Tanja UL; Golinval, Jean-Claude et al

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 ▲]

Detailed reference viewed: 97 (15 UL)
Full Text
Peer Reviewed
See detailNumerical Assessment of two Implants for Pubic Ramus Fracture of human Pelvis applying Normal Gait loading
Ricci, Pierre-Louis; Gerich, Torsten; Kelm, Jens et al

Poster (2020, October)

Fractures of the anterior pelvic ring reduce patients` mobility and independence and increase mortality. Pelvic instability impairs the load transfer to the lower extremity. Restoring stability has ... [more ▼]

Fractures of the anterior pelvic ring reduce patients` mobility and independence and increase mortality. Pelvic instability impairs the load transfer to the lower extremity. Restoring stability has therefore been a crucial point of research. Most of the reported studies refer to loading on one leg stand without consideration of physiological muscle and contact-joint forces of the common vital daily movements. Our present study considers physiological gait loading of all acting muscles and Hip Joint Contact (HJC) forces of the pelvis. Those muscles and HJC forces were calculated by inverse dynamics for normal gait motion data and applied in Finite Element Analyses (FEA). The biomechanical stability provided to the anterior pelvic ring by two reconstructive techniques was investigated numerically: the iliopubic Subcutaneous Plate (SP) and the Supra-Acetabular External Fixator (SAFE). Numerical biomechanical assessment of two reconstructive devices for pubic ramus fracture. All muscles and HJC forces of normal gait were calculated by means of inverse dynamics software for a healthy patient considering a musculoskeletal model previously validated experimentally. The Finite Element (FE) model was developed for a pelvis with and without superior and/or inferior rami fractures. Furthermore, two FE models for SP and SAFE mounted on the rami fractured pelvis were designed considering fixation bearing at the lumbosacral joint. The calculated forces were implemented on the FE models following the anatomical orientation and attachments/insertions of each muscle. During the two moments of the gait with higher stresses: Left Heel Strike (LHS) and Right Toe-Off (RTO), strains and displacements were recorded and investigated at the fracture location in addition to the implant fixation points. Considering only right superior ramus fracture during LHS and RTO, recorded strains and displacements for both implants showed similar results. However, during RTO, the SAFE showed a slight reduction of strains at the posterior location by 6% compared to SP. When including both superior and inferior right ramus fractures, both devices did not show considerable difference in recorded strains. However, there were significant differences in the displacements between fracture extremities. The SP technique reduced these motions for both LHS and RTO by 40% compared to the gold standard SAFE technique. In cases of superior ramus fracture only, displacements for both reconstructive devices were similar due to the remaining stability provided by the intact inferior ramus. Both devices reduced stresses of the sacrum wing in LHS and RTO with slightly better results for SAFE. In case of superior and inferior pubic ramus fractures, the SP technique reduced the frontal opening of the fractured right pubic bone. The SAFE did not provide any improvements compared to the SP technique. [less ▲]

Detailed reference viewed: 41 (3 UL)
Full Text
Peer Reviewed
See detailInfluence of Thermal Energy Storage and Heat Pump Parametrization for Demand-Side-Management in a Nearly-Zero-Energy-Building using Model Predictive Control
Bechtel, Steffen UL; Rafii-Tabrizi, Sasan UL; Scholzen, Frank UL et al

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 ▲]

Detailed reference viewed: 195 (25 UL)
Full Text
Peer Reviewed
See detailNeuere Methoden zur Identifikation und Lokalisierung von Schäden an vorgespannten Betonbrücken
Maas, Stefan UL; Nguyen, Viet Ha UL; Kebig, Tanja UL

in Bischoff, Manfred; von Scheven, Malte; Oesterle, Bernd (Eds.) Baustatik-Baupraxis 14 (2020, March 23)

Zuerst wird ein rein statistischer Schadensindikator basierend auf der Hauptkomponentenanalyse vorgestellt. Wichtig sind Referenzmessungen im ungeschädigten Zustand, um Veränderungen zu identifizieren ... [more ▼]

Zuerst wird ein rein statistischer Schadensindikator basierend auf der Hauptkomponentenanalyse vorgestellt. Wichtig sind Referenzmessungen im ungeschädigten Zustand, um Veränderungen zu identifizieren. Bevor die Messdaten mit den Rechenmodellen kombiniert werden, müssen Temperatureffekte kompensiert werden, um dann die Schäden zu erkennen und zu lokalisieren. Ein „Model-Updating“ Prozess eines speziellen Finite-Elemente- Modells passt die Steifigkeitsmatrix an die gemessenen Eigenfrequenzen oder an die progressive Absenkung unter Eigengewicht an. [less ▲]

Detailed reference viewed: 129 (25 UL)
Full Text
Peer Reviewed
See detailInfluence of pubic symphysis stiffness on pelvic load distribution during single leg stance
Ricci, Pierre-Louis; Maas, Stefan UL; Gerich, Torsten et al

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 ▲]

Detailed reference viewed: 113 (9 UL)
Full Text
Peer Reviewed
See detailNumerical determination and experimental verification of the optimum autofrettage pressure for a complex aluminium high-pressure valve to foster crack closure
Repplinger, Christian UL; Sellen, Stephan; Kedziora, Slawomir UL et al

in Fatigue and Fracture of Engineering Materials and Structures (2020)

Detailed reference viewed: 120 (20 UL)
Full Text
Peer Reviewed
See detailDesigning an early failure indicator channel for an in-tank hydrogen valve via a fatigue-based approach
Cao, Thanh Binh UL; Kedziora, Slawomir UL; Sellen, Stephan et al

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 ▲]

Detailed reference viewed: 167 (15 UL)
Full Text
Peer Reviewed
See detailMechanical strength of a new plate compared to six previously tested opening wedge high tibial osteotomy implants
Diffo Kaze, Arnaud; Maas, Stefan UL; Belsey, James et al

in Journal of Experimental Orthopaedics (2019)

Background This study aimed to assess the mechanical static and fatigue strength provided by the FlexitSystem plate in medial opening wedge high tibial osteotomies (MOWHTO), and to compare it to six ... [more ▼]

Background This study aimed to assess the mechanical static and fatigue strength provided by the FlexitSystem plate in medial opening wedge high tibial osteotomies (MOWHTO), and to compare it to six previously tested implants: the TomoFix small stature, the TomoFix standard, the ContourLock, the iBalance, the second generation PEEKPower and the size 2 Activmotion. Thus, this will provide surgeons with data that will help in the choice of the most appropriate implant for MOWHTO. Methods Six fourth-generation tibial bone composites underwent a MOWHTO and each was fixed using six FlexitSystem plates, according to standard techniques. The same testing procedure that has already been previously defined, used and published, was used to investigate the static and dynamic strength of the prepared bone-implant constructs. The test consisted of static loading and cyclical loading for fatigue testing. Results During static testing, the group constituted by the FlexitSystem showed a fracture load higher than the physiological loading of slow walking (3.7 kN > 2.4 kN). Although this fracture load was relatively small compared to the average values for the other Implants from our previous studies, except for the TomoFix small stature and the Contour Lock. During fatigue testing, FlexitSystem group showed the smallest stiffness and higher lifespan than the TomoFix and the PEEKPower groups. Conclusions The FlexitSystem plate showed sufficient strength for static loading, and average fatigue strength compared to the previously tested implants. Full body dynamic loading of the tibia after MOWHTO with the investigated implants should be avoided for at least three weeks. Implants with a wider T-shaped proximal end, positioned onto the anteromedial side of the tibia head, or inserted in the osteotomy opening in a closed-wedge construction, provided higher mechanical strength than implants with small a T-shaped proximal end, centred onto the medial side of the tibia head. [less ▲]

Detailed reference viewed: 104 (4 UL)
Full Text
Peer Reviewed
See detailEnergy efficiency and indoor aire quality os seminar rooms in older buildings with and without mechanical ventilation
Maas, Stefan UL; da Cruz Antunes, Joël UL; Steffgen, Georges UL

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 ▲]

Detailed reference viewed: 124 (19 UL)