Bøger udgivet af Fraunhofer IRB Verlag

Moderne Sichtbetonflächen stellen höchste Anforderungen an die Qualität von Planung, Bauablauf und Ausführung. Die in diesem Tagungsband publizierten Beiträge der Fachtagung »Digitalmoderne in Sichtbeton«, die am 7.09.2007 gemeinsam vom Deutschen Beton- und Bautechnik Verein E.V. und dem Fraunhofer-Informationszentrum Raum und Bau IRB veranstaltet wurde, sollen dazu beitragen, dass Beton mit gestalteten Oberflächen zielgenauer geplant, qualitätsbewusster hergestellt und sicherer beurteilt werden kann. Namhafte Architekten, Sachverständige und Juristen präsentieren aktuelle Erkenntnisse aus Forschung und Praxis.

Low temperature district heating (LTDH) offers possibilities for efficient heat supply based on renewable energies. For the analysis of LTDH, the exergetic assessment is a suitable method. Hence, an exergy-based assessment method was developed in which energy as well as economic and sustainability aspects are combined. As part of a technology comparison, the method is applied to case studies to verify the applicability of the assessment approach. The approach highlights innovative supply solutions by identifying the advantages and disadvantages of different supply strategies.

A growing urbanization, an increasing complexity of critical infrastructure and the formation of new threats are new challenges for urban areas and require a sustainable development and a stronger coping capacity with potential adverse events. Sustainability requires a strenghtening of resilience.Within this work, an integrated mathematical approach for the quantification of resilience is defined. This method allows a comprehensive evaluation of urban areas and the identification of weak spots. Statistical data are combined with physical models to assess the occurrence of multiple threats and their potential consequences. This risk based assessment is combined with time dependent recovery models to result in a quantity for resilience. Results of this framework can be applied to evaluate the effectiveness of single resilience phases, like prepare, prevent, protect, response and recover.Besides the mathematical formulation, application examples in this work assess exemplarily terroristic threats in urban surroundings with empirical information of historical events and engineering models to assess possible structural damage effects. The comparison of different urban footprints builds the basis for a resilient urban planning process.

Switch observability is a new observability concept for switched systems with unknown switching signals that is useful in the context of fault detection and identification. This notion, as well as the related concepts of switching signal observability and switching time observability, are investigated and fully characterized both for switched ODEs and switched DAEs. Switch observability is particularly useful in the context of fault detection and identification.A corresponding observer is designed. Also, the new concepts are applied to some power network example in order to highlight their use.

The scope of this dissertation is the development of a state observer for Power-to-Gas (PtG) plants. A physical performance model of an innovative reactor concept for different operation conditions has been developed and implemented in Matlab-Simulink. Experiments in a lab-scale PtG plant are used to validate the model; a comparison between the experimental and modelled data is presented. The experiments cover a wide temperature range, different operating pressures and inlet volumetric flows. Furthermore, experimental runs are carried out to determine the experimental value of the kinetic parameters, namely the activation energy (Ea), the pre-exponential factor of the Arrhenius form (A) and an empirical coefficient (n). The state observer predicts the performance of the reactor for a specific operating point and allows to identify a decrease of the reactor performance, such an identification of a system state leads to maintenance or modifications in the operating control..

The growth of heavily n-type doped silicon by the Czochralski method is frequently accompanied by the formation of dislocations. These dislocations lead to a reduction of yield and have therefore to be prevented. In this dissertation the reason for the formation of the dislocations is analyzed in detail.

One of the most dangerous situations when flying a helicopter is landing over dry sand or powder snow. The rotors swirl particles creating a dense cloud. With optical methods navigating through this cloud is impossible but for millimetre waves it becomes almost transparent. As a consequence millimetre waves are an outstanding choice for the development of imaging systems that can be used as a landing aid. The aim of this work is the 3D imaging of static scenes with a large field of view, good resolution and high dynamics. In this thesis a demonstrator system is presented, which is based on the MIMO principle and works with FMCW radar modules in the millimetre wavelength range. The set-up of the demonstrator system is explained and the hardware components are described. An algorithm for image reconstruction is presented as well as a calibration routine. An optimized antenne aperture is determined that enables unambiguous imaging of the half-space in front of the aperture with good resolution and low side lobes. Various measurements illustrate three-dimensional imaging capabilities and show long-range operation. In addition, the data acquisition rate is determined.

The rapidly-growing data throughput rates in a wide range of wireless communication applications are pushing the established semiconductor device technologies to their limits. Considerably higher levels of solid-state output power will therefore be needed to meet the demand in the next generation satellite communications as well as the RADAR systems. Owing to their superior material properties such as high breakdown fields and peak electron velocities, GaN-based high electron mobility transistors (HEMTs) have recently prevailed in high-power systems operating in the microwave frequency bands. On the other hand at the millimetre-wave (MMW) and sub-MMW frequencies, highly-scaled GaN HEMTs are prone to experiencing deteriorated high frequency characteristics which severely limit the high-power performance. In an attempt to overcome this, 3-dimensional GaN HEMT devices featuring the Tri-gate topology are developed in this work, exhibiting enhanced performance in terms of both off- and on-state figures of merit. The demonstrated results promote the great potential of Tri-gate GaN HEMTs for both MMW power amplifier and high-speed logic applications.

The process of co-molding of locally continuous-fiber reinforced structures with Sheet Molding Compound (SMC) has the potential to realize structures economically combining high stiffness with freedom in design. The objective is to combine the flowability of the SMC, needed to form ribs and to integrate inlays, with accurate position and intact shape of the continuous-fiber reinforcement. State-of-the-art in co-molding is still a near net-shape mold coverage of the SMC to prevent any flow. The introduction of a two-step curing resin results in a stiff reinforcement during co-molding, which endures the forces applied by the flowing SMC and therefore is not deformed. Furthermore, the second reaction step allows for chemical bonding to the SMC. To prevent displacement of the reinforcement, a novel fixation method is introduced by using magnetic. To realize this innovative co-molding concept a multidisciplinary approach is needed, including material characterization and material modelling, process simulation and magnetic field simulation and like-wise experiments. Hereby, the performance as well as the reliability of these hybrid structures are significantly improved.

In this work, mathematical models for combined depth and cake filtration are developed. Their formulation is either based on a moving or free boundary description. For the free boundary model existence and uniqueness of the solution is shown. To study the influence of the model parameters, two different tools are introduced, namely model reduction and parameter identification. Model reduction is used to study the sensitivity of the parameters and to accelerate the solution procedure. Multiple ways to construct a projection basis are discussed and reviewed. For parameter identification, an optimization framework for the free boundary problem is derived. Therefore a gradient algorithm in combination with an adjoint formulation is used. The models are compared to several experimental data and different mathematical aspects of the problem are tested, too. The results show that it is possible to reproduce the experimental data. It is further shown that a nonlinear pressure drop, often arising in cake filtration, can be explained by the model without considering compression of the cake.

The scope of this work is to investigate and to develop advanced HIPIMS processes for deposition of oxides, utilizing industrial-scale equipment and technology. Two classes of oxide materials were studied: insulating (aluminum oxide) and conducting oxides (indium-tin oxide and aluminum-doped zinc oxide). The electrical properties of the oxides have a significant influence on the process design, as the issues and approaches for deposition of insulating materials are fairly different from conducting materials. Different types of reactive process control were also investigated, utilizing optical emission spectroscopy to control the oxygen flow and lambda probes to control the discharge power. A non-reactive process was also studied for indium-tin oxide.

Electrochemical processes to form the metallization of high efficient silicon solar cells are developed. Direct metal plating on silicon, aluminum and indium tin oxide is investigated. This book deals with Electrochemical processes.

The highly accurate performance evaluation of photovoltaic devices has never been more important given the progress in photovoltaics. In this thesis, a spectral responsivity measurement set-up based on ultrashort laser pulses is developed that provides substantial reductions of measurement uncertainties.

Investigates several methods for the design of a pitch control system, which actively reduces the fatigue loads on the tower of a wind turbine. This work demonstrates that it is possible to design collective pitch controllers that allow to reduce the fore-aft tower bending loads due to 3p harmonic excitation.