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- 2015 (93) (remove)
The sizing of simple resonators like guitar strings or laser mirrors is directly connected to the wavelength and represents no complex optimisation problem. This is not the case with liquid-filled acoustic resonators of non-trivial geometries, where several masses and stiffnesses of the structure and the fluid have to fit together. This creates a scenario of many competing and interacting resonances varying in relative strength and frequency when design parameters change. Hence, the resonator design involves a parameter-tuning problem with many local optima. As its solution evolutionary algorithms (EA) coupled to a forced-harmonic FE simulation are presented. A new hybrid EA is proposed and compared to two state-of-theart EAs based on selected test problems. The motivating background is the search for better resonators suitable for sonofusion experiments where extreme states of matter are sought in collapsing cavitation bubbles.
Superplasticizers are utilized both to improve the fluidity during the placement and to reduce the water content of concretes. Both effects have also an impact on the properties of the hardened concrete. As a side effect the presence of superplasticizers affects the strength development of concretes that is strongly retarded. This may lead to an ecomomical drawback of the concrete manufacturing. The present work is aimed at gaining insights on the causes of the retarding effect of superplasticizers on the hydration of Portland cement. In order to simplify the complex interactions occurring during the hydration of Portland cement the majority of the work focuses on the interaction of superplasticizer and tricalcium silicate (Ca3SiO5 or C3S, the main compound of Portland cement clinker). The tests are performed in three main parts accompanied by methods as for example isothermal conduction calorimetry, electrical conductivity, Electron Microscopy, ICP-OES, TOC, as well as Analytical Ultracentrifugation.
In the first main part and based on the interaction of cations and anionic charges of polymers, the interactions between calcium ions and superplasticizers are investigated. As a main effect calcium ions are complexed by the functional groups of the polymers (carboxy, sulfonic). Calcium ions may be both dissolved in the aqueous phase and a constitute of particle interfaces. Besides these effects it is furthermore shown that superplasticizers induce the formation of nanoscaled particles which are dispersed in the aqueous phase (cluster formation). Analogous to recent findings in the field of biomineralization, it is reasonable to assume that these nanoparticles influence the crystal growth by their assembly process.
Based on the assumption that superplasticizers hinder either or both dissolution and precipitation and by that retard the cement hydration, the impact on separate reactions is investigated. On experiments that address the solubility of C-S-H phases and portlandite, it is shown that complexation of calcium ions in the aqueous phase by functional groups of polymers increases the solubility of portlandite. Contrary, in case of C-S-H solubility the complexation of calcium ions in solution leads to decrease of the calcium ion concentration in the aqueous phase. These effects are explained by differences in adsorption of polymers on C-S-H phases and portlandite. It is proposed that adsorption is stronger on C-S-H phases compared to portlandite due to the increased specific surface area of C-S-H phases. Following that, it is claimed that before polymers are able to adsorb on C-S-H phases the functional groups must be screened by calcium ions in the aqueous phase. It is further shown that data regarding the impact of superplasticizers on the unconstrained dissolution rate of C3S does not provide a clear relation to the overall retarding effect occurring during the hydration of C3S. Both increased and decreased dissolution rate with respect to the reference sample are detected. If the complexation capability of the superplasticizers is considered then also a reduced dissolution rate of C3S is determined. Despite the fact that the global hydration process is accelerated, the addition of calcite leads to a slower dissolution rate. Thus, a hindered unconstrained dissolution of C3S as possibly cause for the retarding effect still remains open for discussion. In the last section of this part, the pure crystallization of hydrate phases (C-S-H phases, portlandite) is fathomed. Results clearly show that superplasticizers prolong the induction time and modify the rate of crystal growth during pure crystallization in particular due to the complexation of ions in solution. But this effect is insufficient to account for the overall retarding effect. Further important factors are the blocking of crystal growth faces by adsorbed polymers and the dispersion of nanoscaled particles which hinders their agglomeration in order to build up crystals.
In the last main part of the work, the previously gathered results are utilized in order to investigate hydration kinetics. During hydration, dissolution and precipitation occur in parallel. Thereby, special attention is laid on the ion composition of the aqueous phase of C3S pastes and suspensions in order to determine the rate limiting step. All in all it is concluded that the retarding effect of superplasticizers on the hydration of tricalcium silicate is based on the retardation of crystallization of hydrate phases (C-S-H phases and portlandite). Thereby, the two effects complexation of calcium ions on surfaces and stabilization of nanoscaled particles are of major importance. These mechanisms may partly be compensated by template performance and increase in solubility by complexation of ions in solution. The decreased dissolution rate of C3S by the presence of superplasticizers during the in parallel occuring hydration process can only be assessed indirectly by means of the development of the ion concentrations in the aqueous phase (reaction path). Whether this observation is the cause or the consequence within the dissolution-precipitation process and therefore accounts for the retarding effect remains a topic for further investigations.
Besides these results it is shown that superplasticizers can be associated chemically with inhibitors because they reduce the frequency factor to end the induction period. Because the activation energy is widely unaffected it is shown that the basic reaction mechanism sustain. Furthermore, a method was developed which permits for the first time the determination of ion concentrations in the aqueous phase of C3S pastes in-situ. It is shown that during the C3S hydration the ion concentration in the aqueous phase is developed correspondingly to the heat release rate (calorimetry). The method permits the differentiation of the acceleration period in three stages. It is emphasized that crystallization of the product phases of C3S hydration, namely C-S-H phases and portlandite, are responsible for the end of the induction period.
IFC-BASED MONITORING INFORMATION MODELING FOR DATA MANAGEMENT IN STRUCTURAL HEALTH MONITORING
(2015)
This conceptual paper discusses opportunities and challenges towards the digital representation of structural health monitoring systems using the Industry Foundation Classes (IFC) standard. State-of-the-art sensor nodes, collecting structural and environmental data from civil infrastructure systems, are capable of processing and analyzing the data sets directly on-board the nodes. Structural health monitoring (SHM) based on sensor nodes that possess so called “on-chip intelligence” is, in this study, referred to as “intelligent SHM”, and the infrastructure system being equipped with an intelligent SHM system is referred to as “intelligent infrastructure”. Although intelligent SHM will continue to grow, it is not possible, on a well-defined formalism, to digitally represent information about sensors, about the overall SHM system, and about the monitoring strategies being implemented (“monitoring-related information”). Based on a review of available SHM regulations and guidelines as well as existing sensor models and sensor modeling languages, this conceptual paper investigates how to digitally represent monitoring-related information in a semantic model. With the Industry Foundation Classes, there exists an open standard for the digital representation of building information; however, it is not possible to represent monitoring-related information using the IFC object model. This paper proposes a conceptual approach for extending the current IFC object model in order to include monitoring-related information. Taking civil infrastructure systems as an illustrative example, it becomes possible to adequately represent, process, and exchange monitoring-related information throughout the whole life cycle of civil infrastructure systems, which is referred to as monitoring information modeling (MIM). However, since this paper is conceptual, additional research efforts are required to further investigate, implement, and validate the proposed concepts and methods.
Der vorliegende Text beschreibt die intensive Erforschung von Wabenplatten aus Papierwerkstoffen, die durch Faltprozesse neue räumliche Zustände einnehmen können und somit ihr ursprüngliches Anwendungsspektrum erweitern. Die gezeigten Lösungsansätze bewegen sich dabei im Spannungsfeld von Architektur und Ingenieurbau, denn die gefalteten Bauteile sind nicht nur äußerst tragfähig sondern besitzen auch eine ästhetische Form. Die entwickelten Verfahren und Konstruktionen werden auf einem hohen architektonischen Niveau präsentiert und mit einfachen ingenieurtechnischen Methoden verifiziert. Zur Lösungsfindung werden geometrische Verfahren ebenso angewendet wie konstruktive Faustformeln und Recherchen aus Architektur und Forschung.
Der Fokus der Arbeit liegt auf der Untersuchung von Faltungen in Wabenplatten. Während der Auseinandersetzung mit der Thematik erschienen jedoch viele weitere Aspekte als sehr interessant und bearbeitungswürdig. Als theoretische Grundlage dieser Arbeit werden deshalb die geschichtliche Entwicklung und die gesellschaftliche Bedeutung von Papier und Papierwerkstoffen analysiert und deren Produktionsprozesse beleuchtet. Diese Vorgehensweise ermöglicht eine Einordnung des Potentials und der Bedeutung des Werkstoffs Papier. Der Kontext der Arbeit wird dadurch gestärkt und führt zu interessanten zukünftigen Forschungsansätzen.
Intensive Untersuchungen widmen sich der geometrischen Bestimmung von Faltungen in Wabenplatten aus Papierwerkstoffen sowie deren Manifestation als konstruktive Bauteile. Auch die statischen Eigenschaften der Elemente und ihr Konstruktionspotential werden erforscht und aufbereitet. Wichtige Impulse aus Forschung und Technik fließen in die Recherche der Arbeit ein und erlauben die Verortung der Ergebnisse im architektonischen Kontext. Versuchsreihen und Materialstudien an Prototypen belegen die Ergebnisse virtueller und rechnerischer Studien. Konzepte zur parametrischen Berechnung und Visualisierung der Forschungsergebnisse werden präsentiert und zeigen zukunftsfähige Planungshilfen für die Industrie auf. Etliche Testreihen zu unterschiedlichsten Abdichtungskonzepten führen zur Realisierung eines sehenswerten Experimentalbaus. Er erlaubt die dauerhafte Untersuchung der entwickelten Bauteile unter realistischen Bedingungen und bestätigt deren Leistungsfähigkeit. Dadurch wird nicht nur ein dauerhaftes Monitoring und eine Evaluierung der Leistungsdaten möglich sondern es wird auch der sichtbare Beweis erbracht, dass mit Papierwerkstoffen effiziente und hochwertige Architekturen zu realisieren sind, welche das enorme gestalterische Potential von gefalteten Wabenplatten ausnutzen.
Generell hat sich im Forschungsprojekt insbesondere durch die Gespräche mit den Hochschulvertretern bestätigt, dass für qualitativ hochwertige Lehre und Forschung qualitativ hochwertige Flächen in ausreichendem Umfang notwendig sind.
Ein Ziel der Forschungsarbeit ist die Entwicklung von Modellen zur Allokation und Steuerung von Flächenressourcen in Hochschulen. Ausgehend von Darstellungen und Erfahrungen für die Flächensteuerung aus Unternehmen, anderen Bereichen der öffentlichen Verwaltung und Forschungseinrichtungen wurden mögliche Steuerungsverfahren für Hochschulen untersucht. Es wurde ein Steuerungsmodell für Hochschulen entwickelt, das auf die hochschulinternen und die extern wirksamen Rahmenbedingungen reagiert.
Die hochschulinterne Flächenallokation wird zum einen maßgeblich von externen Rahmen-bedingungen und zum zweiten von internen Prozessen, Abläufen und Strukturen beeinflusst. Die Kenntnis dieser Bedingungen wird als Voraussetzung für die Benennung von Erfolgsfak-toren für die Implementation neuer Steuerungsmodelle angenommen. Analysiert wurden daher die liegenschaftspolitischen und die organisatorischen Rahmenbedingungen sowie die steuerungsrelevanten Eigenschaften der Flächen selber.
Die Bau-Ausstellung zu Beginn des 20. Jahrhunderts oder „Die Schwierigkeit zu wohnen“, so lautet der Titel der Arbeit und legt damit ihren Fokus offen. Sie betrachtet ein um 1900 aufkommendes Ausstellungsphänomen in seinen ersten Dekaden; in einer Zeit, in der das Wohnen problematisiert wurde.
Der Praxis des Wohnens ist Anfang des 20. Jahrhunderts seine Selbstverständlichkeit abgesprochen worden. Die Bau-Ausstellung wird als ein Symptom dieses Verlusts interpretiert und zugleich als Versuch, ihm entgegenzuwirken. Statt sie innerdisziplinär als eine architekturgeschichtliche Episode der Moderne rein positivistisch zu beschreiben, legt die vorliegende Arbeit im Typus der Bau-Ausstellung eine weit reichende Problematik frei, die kulturphilosophische ebenso wie medientheoretische Dimensionen hat: Inwieweit lässt sich das Wohnen überhaupt ausstellen? Wie kann man eine alltägliche Praxis, die kaum eine Definition erlaubt, zeigen? Den Umgang mit dieser Aporie untersucht die Arbeit.
As human thought was developing, likewise, the technology used for illumination was growing. But a haul through history, reviewing its pages and analyzing it, inherently brings up old and new question, like: Is it possible to alter negatively the image of historic buildings and monuments through inadequate lighting to the degree of distorting the perception that people have of the work? and if so, what are the causes that generate it? Do the light designers take into consideration criteria to protect not only historic buildings and monuments, but also the environment? What are the consequences that may generate the inadequate lighting of urban heritage to the environment? What are the factors to consider for a proper illumination of urban heritage? The answers to these questions will help lay the foundation for proper illumination of the urban heritage, avoiding at the maximum the light pollution and the effects that it generates, seeking a balance and harmonious reconciliation between the technology, urban heritage and environment, taking as a framework and the case study the urban heritage of a city from the colonial era in southern Mexico, with pre-Hispanic roots and where today you can still see through its streets and buildings an atmosphere of mysticism reflection of their folklore and traditions, this city is known as Chiapa de Corzo, Chiapas.
The Laguerre polynomials appear naturally in many branches of pure and applied mathematics and mathematical physics. Debnath introduced the Laguerre transform and derived some of its properties. He also discussed the applications in study of heat conduction and to the oscillations of a very long and heavy chain with variable tension. An explicit boundedness for some class of Laguerre integral transforms will be present.
In photogrammetry and computer vision the trifocal tensor is used to describe the geometric relation between projections of points in three views. In this paper we analyze the stability and accuracy of the metric trifocal tensor for calibrated cameras. Since a minimal parameterization of the metric trifocal tensor is challenging, the additional constraints of the interior orientation are applied to the well-known projective 6-point and 7-point algorithms for three images. The experimental results show that the linear 7-point algorithm fails for some noise-free degenerated cases, whereas the minimal 6-point algorithm seems to be competitive even with realistic noise.