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Measurement of the Indoor Air Temperature Distribution using Acoustic Travel-Time Tomography
No full textOne of the main criteria determining the thermal comfort of occupants is the air temperature. To monitor this parameter, a thermostat is traditionally mounted in the indoor environment for instance in office rooms in the workplaces, or directly on the radiator or in another location in a room. One of the drawbacks of this conventional method is the measurement at a certain location instead of the temperature distribution in the entire room including the occupant zone. As a result, the climatic conditions measured at the thermostat point may differ from those at the user's location. This not only negatively impacts the thermal comfort assessment but also leads to a waste of energy due to unnecessary heating and cooling. Moreover, for measuring the distribution of the air temperature under laboratory conditions, multiple thermal sensors should be installed in the area under investigation. This requires high effort in both installation and expense.
To overcome the shortcomings of traditional sensors, Acoustic travel-time TOMography (ATOM) offers an alternative based on measuring the transmission sound velocity signals. The basis of the ATOM technique is the first-order dependency of the sound velocity on the medium's temperature. The average sound velocity, along the propagation paths, can be determined by travel-times estimation of a defined acoustic signal between transducers. After the travel-times collection, the room is divided into several volumetric grid cells, i.e. voxels, whose sizes are defined depending on the dimension of the room and the number of sound paths. Accordingly, the spatial air temperature in each voxel can be determined using a suitable tomographic algorithm. Recent studies indicate that despite the great potential of this technique to detect room climate, few experiments have been conducted.
This thesis aims to develop the ATOM technique for indoor climatic applications while coupling the analysis methods of tomography and room acoustics. The method developed in this thesis uses high-energy early reflections in addition to the direct paths between transducers for travel time estimation. In this way, reflections can provide multiple sound paths that allow the room coverage to be maintained even when a few or even only one transmitter and receiver are used.
In the development of the ATOM measurement system, several approaches have been employed, including the development of numerical methods and simulations and conducting experimental measurements, each of which has contributed to the improvement of the system's accuracy. In order to effectively separate the early reflections and ensure adequate coverage of the room with sound paths, a numerical method was developed based on the optimization of the coordinates of the sound transducers in the test room. The validation of the optimal positioning method shows that the reconstructed temperatures were significantly improved by placing the transducers at the optimal coordinates derived from the developed numerical method. The other numerical method developed is related to the selection of the travel times of the early reflections. Accordingly, the detection of the travel times has been improved by adjusting the lengths of the multiple analysis time-windows according to the individual travel times in the reflectogram of the room impulse response. This can reduce the probability of trapping faulty travel times in the analysis time-windows.
The simulation model used in this thesis is based on the image source model (ISM) method for simulating the theoretical travel times of early reflection sound paths. The simulation model was developed to simulate the theoretical travel times up to third-order reflections.
The empirical measurements were carried out in the climate lab of the Chair of Building Physics under different boundary conditions, i.e., combinations of different room air temperatures under both steady-state and transient conditions, and different measurement setups. With the measurements under controllable conditions in the climate lab, the validity of the developed numerical methods was confirmed.
In this thesis, the performance of the ATOM measurement system was evaluated using two measurement setups. The setup for the initial investigations consists of an omnidirectional receiver and a near omnidirectional sound source, keeping the number of transducers as few as possible. This has led to accurately identify the sources of error that could occur in each part of the measuring system. The second measurement setup consists of two directional sound sources and one omnidirectional receiver. This arrangement of transducers allowed a higher number of well-detected travel times for tomography reconstruction, a better travel time estimation due to the directivity of the sound source, and better space utilization. Furthermore, this new measurement setup was tested to determine an optimal selection of the excitation signal. The results showed that for the utilized setup, a linear chirp signal with a frequency range of 200 - 4000 Hz and a signal duration of t = 1 s represents an optimal selection with respect to the reliability of the measured travel times and higher signal-to-noise ratio (SNR).
To evaluate the performance of the measuring setups, the ATOM temperatures were always compared with the temperatures of high-resolution NTC thermistors with an accuracy of ±0.2 K. The entire measurement program, including acoustic measurements, simulation, signal processing, and visualization of measurement results are performed in MATLAB software.
In addition, to reduce the uncertainty of the positioning of the transducers, the acoustic centre of the loudspeaker was determined experimentally for three types of excitation signals, namely MLS (maximum length sequence) signals with different lengths and duration, linear and logarithmic chirp signals with different defined frequency ranges. For this purpose, the climate lab was converted into a fully anechoic chamber by attaching absorption panels to the entire surfaces of the room. The measurement results indicated that the measurement of the acoustic centre of the sound source significantly reduces the displacement error of the transducer position.
Moreover, to measure the air temperature in an occupied room, an algorithm was developed that can convert distorted signals into pure reference signals using an adaptive filter. The measurement results confirm the validity of the approach for a temperature interval of 4 K inside the climate lab.
Accordingly, the accuracy of the reconstructed temperatures indicated that ATOM is very suitable for measuring the air temperature distribution in rooms
TESTING OF CONNECTIONS TAKEN FROM OLD NAILED ROOF TRUSSES
Full text linkExperimental testing of nailed connections taken from old roof trusses is presented in this paper. To enable the further use and preservation of nailed roof trusses, it is important to understand how the nail corrosion and aging processes of steel and wood affect the load-bearing capacity and deformation behaviour of such structures. The hypothesis was investigated whether corroded nails allow an increase in load-bearing capacity. Several old and new joints were tested in a first test series, and the results were very promising regarding the initial assumption. However, more tests must be carried out to verify the results
Physics-informed deep learning for three-dimensional transient heat transfer analysis of functionally graded materials
No full textWe present a physics-informed deep learning model for the transient heat transfer analysis of three-dimensional functionally graded materials (FGMs) employing a Runge–Kutta discrete time scheme. Firstly, the governing equation, associated boundary conditions and the initial condition for transient heat transfer analysis of FGMs with exponential material variations are presented. Then, the deep collocation method with the Runge–Kutta integration scheme for transient analysis is introduced. The prior physics that helps to generalize the physics-informed deep learning model is introduced by constraining the temperature variable with discrete time schemes and initial/boundary conditions. Further the fitted activation functions suitable for dynamic analysis are presented. Finally, we validate our approach through several numerical examples on FGMs with irregular shapes and a variety of boundary conditions. From numerical experiments, the predicted results with PIDL demonstrate well agreement with analytical solutions and other numerical methods in predicting of both temperature and flux distributions and can be adaptive to transient analysis of FGMs with different shapes, which can be the promising surrogate model in transient dynamic analysis
Der Bibliothek eine Stimme geben: Die Integration von Lobby-Arbeit in den beruflichen Alltag
No full textDass Lobby-Arbeit auch für Bibliotheken und damit auch für Bibliothekar:innen unverzichtbar ist, hat sich als Erkenntnis mittlerweile durchgesetzt. Im Folgenden soll – ausgehend von einer kurzen Betrachtung des Stellenwerts der Lobbyarbeit in der bibliothekarischen Verbandsarbeit – aufgezeigt werden, welche Rolle Lobbyaktivitäten im bibliothekarischen Alltag spielen könnten bzw. sollten
Verbindungen mit Nägeln im Holzbau – Die Erforschung und Entwicklung von Konstruktionsregeln
No full textDer Nagel als tragendes Holzverbindungsmittel ist heute gut bekannt. Doch noch vor 100 Jahren war das anders: sein statisch konstruktiver Gebrauch war verboten. Das änderte sich mit Beginn dessen Erforschung Ende der 1920er Jahre. Seit 1933 ist der Nagel Bestandteil der deutschen Regelwerke und findet seitdem breite Verwendung. Über weite Teile des 20. Jahrhunderts diente er in Not- und Sparkonstruktionen wie Brett- und Bohlenbindern als hocheffizientes Verbindungsmittel der Wahl. Diese materialsparenden Tragwerke waren bei der periodisch im-mer wiederkehrenden Ressourcenknappheit sehr gefragt und sind ein wichtiger Bestandteil der Konstruktionsgeschichte des Holzbaus. In dem folgenden Beitrag wird die Erforschung des Na-geltragverhaltens und die einhergehende fortlaufende Normierung behandelt. Die Errungen-schaften einzelner Forschungsvorhaben werden vorgestellt. Anhand eines Zeitstrahls werden Zusammenhänge zwischen Forschung und Normung gezeigt. Tabellen und Grafiken verdeutli-chen die Änderungen innerhalb der Normen von der ersten DIN 1052 im Jahr 1933 über die erste eigenständige Holzbaunorm in der DDR, der TGL 112-0730, aus 1963 bis zur DIN 1052- 1988. Dabei wird immer Bezug zum derzeitigen Entwurf des Eurocode 5 genommen. Allgemein zeigt sich, dass ein Großteil der heutigen Kenntnisse immer noch auf die Grundlagenforschung der 1930er Jahre zurückgeht.The nail as a load-bearing timber fastener is well known today. But 100 years ago, it was different: its structural use was not allowed. This changed with the beginning of systematical research at the end of the 1920s. Since 1933, the nail has been part of the German regulations and has been widely used ever since. For much of the 20th century, it served as the highly efficient fastener of choice especially in roof structures such as board and plank trusses. These material-saving load-bearing structural elements were always in demand due to the periodically recurring scarcity of material resources and are an important part in con-struction history. The following article deals with the research of the load-bearing behaviour of nails and the standardisation that has constantly accompanied it. The achievements of individual research projects are presented. A timeline shows the connections between research and standardisation. Tables and graphics illustrate the changes within the standards from the first DIN 1052 in 1933 to the first independent timber construction standard in the DDR, TGL 112-0730, from 1963 to DIN 1052-1988. Reference is al-ways made to the Eurocode 5 valid today. In general, it can be seen that a large part of today's knowledge still goes back to the basic research of the 1930s
Nägel im Holzbau – Die Erforschung des Trag- und Verformungsverhaltens
No full textDie Tragfähigkeit von Nägeln und Nagelverbindungen im Holzbau war lange Zeit ausschließlich über Tabellen, die auf experimentellen Untersuchungen basierten, geregelt. In den letzten 100 Jahren untersuchten unterschiedliche Forscher das Last-Verformungsverhalten dieser Verbindungen und entwickelten Modelle, mit denen auf Grundlage von analytischen Gleichungen die Tragfähigkeit und das Verformungsverhalten von Nägeln berechnet werden kann. Die zunächst in Not- und Sparkonstruktion eingesetzten Nägel werden heutzutage vor allem bei Tafelelementen verwendet. Im Bestand finden sich aber auch zahlreiche, teils weit gespannte Fachwerkkonstruktionen. In dem folgenden Beitrag werden die Erforschung und Entwicklung der Tragfähigkeit sowie des Verformungsverhaltens von genagelten Verbindungen detailliert und strukturiert erläutert. Die zugehörigen Meilensteine werden genauer betrachtet. Über unterschiedliche Methoden für die Bestimmung der Tragfähigkeit sowie mechanische Phänomene, die erst nach und nach entdeckt wurden, können in der aktuellen Normung sehr individuelle Verbindungen nachgewiesen und deren Verhalten beschrieben werden. Tabellen und Grafiken verdeutlichen die einzelnen Meilensteine der geschichtlichen Entwicklung und vergleichen konkret die normativen Regelungen seit Beginn der Einführung des Nagels in den Ingenieurholzbau in Deutschland. Hierbei kann gezeigt werden, dass einige Definitionen seit 1933 bis heute noch ihre Gültigkeit behalten.For a long time, the load-carrying capacity of nails and nail connections in timber structures was regulated only by tables based on experimental investigations. In the last 100 years, different researchers investigated the load-deformation behaviour of these connections and developed models with which the load-carrying capacity and deformation behaviour of nails can be estimated very precisely on the basis of analytical equations. At first used in material saving construction in economical difficult times, nails are nowadays ever-present in modern engineered timber structures. In the following article, the research and development of nail load-carrying capacity and its deformation behaviour will be basically explained, and the milestones will be examined in detail. Using different methods to consider mechanical phenomena, which were only discovered over time, individual connections can be verified in the current standards and their behaviour can be described. Tables and graphics illustrate the milestones of the historical development and specifically compare the normative regulations since the introduction of the nail in engineered timber construction in Germany. Here it can be shown that some definitions since 1933 still retain their relevance today
Programm gemeinnützige Liegenschaften. Strategie zur Förderung der öffentlich-zivilgesellschaftlichen Zusammenarbeit
No full textStädten kam bei demokratischen Innovationsprozessen immer eine zentrale Rolle zu. Die öffentlichen Verwaltungen der großen Städte stellten Regeln für die Einführung und Ausweitung der bürgerschaftlichen Partizipation auf und reagierten damit auf Erfahrungen und Forderungen, die von der schöpferischen politischen Kraft der sozialen und urbanen Bewegungen getragen wurden. Die Geschichte Barcelonas ist dafür ein typisches Beispiel.
Dank dieser sozialen Errungenschaften können wir von einer Reihe von Gütern und Dienstleistungen profitieren, die lokale Wohlfahrtssysteme ausmachen. Die Stadtverwal-tungen übernehmen die Aufgabe, Ressourcen und Dienstleistungen bereitzustellen, die nicht nur mit Wohlfahrt und Gesundheit in Verbindung stehen, sondern auch mit der Sorge um Umfeld und Umwelt, mit der Förderung von Maßnahmen in Bereichen wie Bildung, Kultur, Kunst oder Sport sowie mit der Dynamisierung von Wirtschaft und Gesellschaft. Ob zuständig oder nicht, die Kommunen müssen auf die Forderungen der Bürger*innen reagieren, sind sie doch die Verwaltungen, die den alltäglichen Problemen und Bedürfnissen am nächsten stehen. Daher liegt es weniger im Belieben der Stadtverwaltungen, ob sie notwendige Innova¬tionen anstoßen, sondern diese sind vielmehr Teil ihres Aufgabenbereichs.
Um den Bedürfnissen der Bürger*innen seitens der öffentlichen Verwaltung gerecht zu werden, kam in den meisten Fällen eine von zwei Methoden zur Anwendung: die direkte Verwaltung durch die Behörden oder die indirekte Verwaltung mit dem privaten Sektor. Mit dem Anbruch einer neuen Zeit, in der alternative Methoden an Bedeutung gewonnen haben, wächst das Interesse an Modellen öffentlich-zivilgesellschaftlicher Zusammenarbeit. Hauptziel dieser Modelle ist es, Verwaltungen und Bürgerschaft eine Zusammenarbeit im gemeinsamen und allgemeinen Interesse zu ermöglichen, indem Projekte unterstützt werden, die Zugang, Nähe und Partizipation in sich vereinen. Vor diesem Hintergrund bietet die Verwaltung öffent¬licher Ressourcen Möglichkeiten zur Entwicklung neuer Formen kollektiver Intelligenz, mit ge¬meinsamer Verantwortung und Synergie zwischen Institution und Bürgerschaft, sodass die Städte zu wahrhaft kooperativen Plattformen für öffentliche Innovationen werden
„Bausünde“ oder Denkmal? Zur Diskussion über den Umgang mit verschmähten Bauwerken
No full textFür die einen also „Bausünde“, für die anderen ein erhaltenswertes Bauwerk – wie geht man damit um? Für wen gilt wann etwas als „Bausünde“ und wann als erhaltenswert, welche Ziele werden damit verfolgt und Konzepte aufgezeigt? Inwieweit spielen beispielsweise Aspekte wie Ästhetik, Funktionalität oder der allgemeine gesellschaftliche Kontext bzw. Wandel sowie das jeweils aktuelle und bauzeitliche planerische Leitbild bzw. Verständnis eine Rolle bei der Verwendung des Begriffs und den Umgang für konkrete Bauwerke? Und inwieweit steht der Erhaltungswert bzw. eine Denkmalwürdigkeit damit im Verhältnis und wie kann damit planerisch umgegangen werden?
Der Diskussion über den Umgang mit verschmähten Bauwerken will sich die vorliegende Abschlussarbeit nähern. Als Bauwerke werden hierbei sowohl Gebäude und Plätze als auch zur Erinnerung gesetzte Objekte wie Statuen verstanden
Electromechanics and Hydrodynamics of Single Vesicles and Vesicle Doublet Using Phase-Field Isogeometric Analysis
No full textBiomembranes are selectively permeable barriers that separate the internal components of the cell from its surroundings. They have remarkable mechanical behavior which is characterized by many phenomena, but most noticeably their fluid-like in-plane behavior and solid-like out-of-plane behavior. Vesicles have been studied in the context of discrete models, such as Molecular Dynamics, Monte Carlo methods, Dissipative Particle Dynamics, and Brownian Dynamics. Those methods, however, tend to have high computational costs, which limited their uses for studying atomistic details. In order to broaden the scope of this research, we resort to the continuum models, where the atomistic details of the vesicles are neglected, and the focus shifts to the overall morphological evolution. Under the umbrella of continuum models, vesicles morphology has been studied extensively. However, most of those studies were limited to the mechanical response of vesicles by considering only the bending energy and aiming for the solution by minimizing the total energy of the system. Most of the literature is divided between two geometrical representation methods; the sharp interface methods and the diffusive interface methods. Both of those methods track the boundaries and interfaces implicitly. In this research, we focus our attention on solving two non-trivial problems. In the first one, we study a constrained Willmore problem coupled with an electrical field, and in the second one, we investigate the hydrodynamics of a vesicle doublet suspended in an external viscous fluid flow.
For the first problem, we solve a constrained Willmore problem coupled with an electrical field using isogeometric analysis to study the morphological evolution of vesicles subjected to static electrical fields. The model comprises two phases, the lipid bilayer, and the electrolyte. This two-phase problem is modeled using the phase-field method, which is a subclass of the diffusive interface methods mentioned earlier. The bending, flexoelectric, and dielectric energies of the model are reformulated using the phase-field parameter. A modified Augmented-Lagrangian (ALM) approach was used to satisfy the constraints while maintaining numerical stability and a relatively large time step. This approach guarantees the satisfaction of the constraints at each time step over the entire temporal domain.
In the second problem, we study the hydrodynamics of vesicle doublet suspended in an external viscous fluid flow. Vesicles in this part of the research are also modeled using the phase-field model. The bending energy and energies associated with enforcing the global volume and area are considered. In addition, the local inextensibility condition is ensured by introducing an additional equation to the system. To prevent the vesicles from numerically overlapping, we deploy an interaction energy definition to maintain a short-range repulsion between the vesicles. The fluid flow is modeled using the incompressible Navier-Stokes equations and the vesicle evolution in time is modeled using two advection equations describing the process of advecting each vesicle by the fluid flow. To overcome the velocity-pressure saddle point system, we apply the Residual-Based Variational MultiScale (RBVMS) method to the Navier-Stokes equations and solve the coupled systems using isogeometric analysis. We study vesicle doublet hydrodynamics in shear flow, planar extensional flow, and parabolic flow under various configurations and boundary conditions.
The results reveal several interesting points about the electrodynamics and hydrodynamics responses of single vesicles and vesicle doublets. But first, it can be seen that isogeometric analysis as a numerical tool has the ability to model and solve 4th-order PDEs in a primal variational framework at extreme efficiency and accuracy due to the abilities embedded within the NURBS functions without the need to reduce the order of the PDE by creating an intermediate environment. Refinement whether by knot insertion, order increasing or both is far easier to obtain than traditional mesh-based methods. Given the wide variety of phenomena in natural sciences and engineering that are mathematically modeled by high-order PDEs, the isogeometric analysis is among the most robust methods to address such problems as the basis functions can easily attain high global continuity.
On the applicational side, we study the vesicle morphological evolution based on the electromechanical liquid-crystal model in 3D settings. This model describing the evolution of vesicles is composed of time-dependent, highly nonlinear, high-order PDEs, which are nontrivial to solve. Solving this problem requires robust numerical methods, such as isogeometric analysis. We concluded that the vesicle tends to deform under increasing magnitudes of electric fields from the original sphere shape to an oblate-like shape. This evolution is affected by many factors and requires fine-tuning of several parameters, mainly the regularization parameter which controls the thickness of the diffusive interface width. But it is most affected by the method used for enforcing the constraints. The penalty method in presence of an electrical field tends to lock on the initial phase-field and prevent any evolution while a modified version of the ALM has proven to be sufficiently stable and accurate to let the phase-field evolve while satisfying the constraints over time at each time step. We show additionally the effect of including the flexoelectric nature of the Biomembranes in the computation and how it affects the shape evolution as well as the effect of having different conductivity ratios. All the examples were solved based on a staggered scheme, which reduces the computational cost significantly.
For the second part of the research, we consider vesicle doublet suspended in a shear flow, in a planar extensional flow, and in a parabolic flow. When the vesicle doublet is suspended in a shear flow, it can either slip past each other or slide on top of each other based on the value of the vertical displacement, that is the vertical distance between the center of masses between the two vesicles, and the velocity profile applied. When the vesicle doublet is suspended in a planar extensional flow in a configuration that resembles a junction, the time in which both vesicles separate depends largely on the value of the vertical displacement after displacing as much fluid from between the two vesicles. However, when the vesicles are suspended in a tubular channel with a parabolic fluid flow, they develop a parachute-like shape upon converging towards each other before exiting the computational domain from the predetermined outlets. This shape however is affected largely by the height of the tubular channel in which the vesicle is suspended. The velocity essential boundary conditions are imposed weakly and strongly. The weak implementation of the boundary conditions was used when the velocity profile was defined on the entire boundary, while the strong implementation was used when the velocity profile was defined on a part of the boundary. The strong implementation of the essential boundary conditions was done by selectively applying it to the predetermined set of elements in a parallel-based code. This allowed us to simulate vesicle hydrodynamics in a computational domain with multiple inlets and outlets. We also investigate the hydrodynamics of oblate-like shape vesicles in a parabolic flow. This work has been done in 2D configuration because of the immense computational load resulting from a large number of degrees of freedom, but we are actively seeking to expand it to 3D settings and test a broader set of parameters and geometrical configurations
Aesthetics of Maker Culture: the Active Role of the Audience
No full textIn this work, practice-based research is conducted to rethink the understanding of aesthetics, especially in relation to current media art. Granted, we live in times when technologies merge with living organisms, but we also live in times that provide unlimited resources of knowledge and maker tools. I raise the question: In what way does the hybridization of living organisms and non-living technologies affect art audiences in the culture that may be defined as Maker culture? My hypothesis is that active participation of an audience in an artwork is inevitable for experiencing the artwork itself, while also suggesting that the impact of the umwelt changes the perception of an artwork. I emphasize artistic projects that unfold through mutual interaction among diverse peers, including humans, non-human organisms, and machines. In my thesis, I pursue collaborative scenarios that lead to the realization of artistic ideas: (1) the development of ideas by others influenced by me and (2) the materialization of my own ideas influenced by others. By developing the scenarios of collaborative work as an artistic experience, I conclude that the role of an artist in Maker culture is to mediate different types of knowledge and different positions, whereas the role of the audience is to actively engage in the artwork itself. At the same time, aesthetics as experience is triggered by the other, including living and non-living actors. It is intended that the developed methodologies could be further adapted in artistic practices, philosophy, anthropology, and environmental studies