Konstanz University of Applied Sciences

Konstanz, Germany
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Burkhart D.,University of Kaiserslautern | Hamann B.,University of California at Davis | Umlauf G.,Konstanz University of Applied Sciences
Computer Graphics Forum | Year: 2010

We present a volumetric iso-geometric finite element analysis based on Catmull-Clark solids. This concept allows one to use the same representation for the modeling, the physical simulation, and the visualization, which optimizes the design process and narrows the gap between CAD and CAE. In our method the boundary of the solid model is a Catmull-Clark surface with optional corners and creases to support the modeling phase. The crucial point in the simulation phase is the need to perform efficient integration for the elements. We propose a method similar to the standard subdivision surface evaluation technique, such that numerical quadrature can be used. Experiments show that our approach converges faster than methods based on tri-linear and tri-quadratic elements. However, the topological structure of Catmull-Clark elements is as simple as the structure of linear elements. Furthermore, the Catmull-Clark elements we use are C2-continuous on the boundary and in the interior except for irregular vertices and edges. Journal compilation © 2010 The Eurographics Association and Blackwell Publishing Ltd.

Schwamberger V.,Max Planck Institute for Biological Cybernetics | Franz M.O.,Konstanz University of Applied Sciences
MM and Sec'10 - Proceedings of the 2010 ACM SIGMM Multimedia and Security Workshop | Year: 2010

Most current algorithms for blind steganalysis of images are based on a two-stages approach: First, features are extracted in order to reduce dimensionality and to highlight potential manipulations; second, a classifier trained on pairs of clean and stego images finds a decision rule for these features to detect stego images. Thereby, vector components might vary significantly in their values, hence normalization of the feature vectors is crucial. Furthermore, most classifiers contain free parameters, and an automatic model selection step has to be carried out for adapting these parameters. However, the commonly used cross-validation destroys some information needed by the classifier because of the arbitrary splitting of image pairs (stego and clean version) in the training set. In this paper, we propose simple modifications of normalization and for standard cross-validation. In our experiments, we show that these methods lead to a significant improvement of the standard blind steganalyzer of Lyu and Farid. © 2010 ACM.

Eck O.,Konstanz University of Applied Sciences | Schaefer D.,Georgia Institute of Technology
Advanced Engineering Informatics | Year: 2011

A mechatronic system is a synergistic integration of mechanical, electrical, electronic and software technologies into electromechanical systems. Unfortunately, mechanical, electrical, and software data are often handled in separate Product Data Management (PDM) systems with no automated sharing of data between them or links between their data. Presently, this is a significant drawback with regard to supporting the collaborative and integrated design of mechatronic systems. One underlying research question to be addressed is: "How can such domain-specific PDM systems be integrated and what are the standards needed for this?" Our starting point for addressing this question is to look into how engineering data is stored today. We believe that the more intelligent and sophisticated the mechanisms for file management are, the more Computer-aided Engineering systems will benefit from them in terms of making integrated cross-disciplinary product development more efficient. However, while Computer-Aided Design and Engineering (CAD/CAE) systems and related tools such as, for example, Product Data Management (PDM), Engineering Data Management (EDM), etc. have significantly matured over the past ten years, most of their associated database systems are still based on traditional file systems and hierarchical directory structures. In light of this context, we will initially discuss a number of disadvantages of current file management systems. In the body of the paper our main contribution is presented. That is, a formal mathematical model of a new semantic file system, SIL (Semantics Instead of Location), that allows engineers to access data based on semantic information rather than storage location is proposed. A major difference between our approach and previous related work is that we do not aim at yet another point solution and, instead, propose an approach that may be employed by next generation engineering data processing systems on a larger scale. In addition, a corresponding programming interface along with a graphical user interface used as a file browser is presented and the benefits of utilizing the proposed semantic file system for product data management in the field of integrated design of mechatronic systems are discussed. © 2010 Elsevier Ltd. All rights reserved.

Johst M.,Konstanz University of Applied Sciences | Rothstein B.,Konstanz University of Applied Sciences
Renewable and Sustainable Energy Reviews | Year: 2014

In Germany, in the coming decades, nuclear and some coal power plants shall be substituted mainly by photovoltaic (PV) and wind turbines. In this study the impact of PV+wind electricity feed-in on the operation of thermoelectric power plants and the corresponding water consumption was analyzed for July 2011-June 2013. Using hourly time-series of electricity demand, feed-in by renewables, and net export of power abroad, cycling of all thermoelectric power plants along the River Neckar was simulated and the corresponding cooling water amount was calculated. The study show that the electricity generation by PV+wind results in a 7% reduction of cooling water consumption, that equals 43 l per total MWh. The substitution of coal power plants by PV+wind is highest in spring and autumn due to a coincidence of medium-high electricity demand and high electricity feed-in by PV+wind. Water consumption reduction varies seasonally between 4% and 11%. Over one day a maximum of 28,690 m.© 2014 Elsevier Ltd. All rights reserved.

Thimm T.,Konstanz University of Applied Sciences
Sustainable Development | Year: 2016

Sustainable tourism in Kerala is on the rise. Therefore, this South Indian state is assessed according to the sustainable tourism criteria of the Strasdas et al. (2007) framework. Kerala as a state does not qualify as a sustainable tourism destination, although individual success stories at the NGO and government level exist. This conceptual paper delivers a detailed analysis of the three dimensions of sustainability, i.e. ecology, economy and socio-cultural aspects, of the 'Kerala tourism model' and discusses the question of whether this model can be transferred to other developing countries. © 2016 John Wiley & Sons, Ltd and ERP Environment.

On February 22, 2011 the city of Christchurch in New Zealand was struck by an unexpectedly strong earthquake, causing 181 casualties and yet unknown socio-economic losses. More than 50 % of the buildings in the CBD were severely damaged, 25 to 30 % beyond repair. From March 25 to April 2 the author had the opportunity to join a reconnaissance team of the American Precast Concrete Institute (PCI) in order to inspect the damage that buildings and bridges suffered. Because the standard of earthquake resistant design is very high in New Zealand, and because the corresponding New Zealand design codes have been the basis for seismic design codes world wide since the early 1980's, it was particularly interesting to study the performance of modern buildings designed using capacity design principles. The paper describes the situation during the stay in Christchurch with respect to safety issues, the civil defence operations and the procedure followed by local authorities to evaluate the safety of damaged buildings. Also, the peculiarities of the February 22, 2011 earthquake and some of the significant examples of damage suffered by multi-storey buildings despite of modern design principles are discussed. Looking at two modern buildings that escaped the February 22 earthquake with almost no damage, a brief outlook is finally given on new earthquake resistant design concepts that will significantly reduce the expected economic losses. © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Karl Bernhard is one of the significant German civil engineers of the beginning of the 20th century. His two bridges along the Heerstrasse in Berlin, the Stössensee Bridge and the Frey Bridge which are crossing the Havel River, have been since 1909 of paramount importance for the East-West traffic connection of the city. The Frey Bridge was demolished in March 2015 in order to make room for a new substitution bridge. How was it possible at all that from a historical and traffic-technical point of view such an important construction has been neglected so long that it became ripe for demolition? And although it was under preservation since 1971? This article is a homage to Bernhard's Havel Bridge and follows up its rich history. © 2016 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

Gekeler M.W.,Konstanz University of Applied Sciences
Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering | Year: 2013

The Soft Switching Three Level Inverter (S3L) was first presented in 2011. It represents a novel topology for pulse width modulation (PWM) inverters that are used in electrical drives, in grid supply inverters for photovoltaic and wind power plants and for power supplies. It has a rather simple structure and is thus economically priced. It is completely operated in soft switching mode and consequently only displays very low switching losses. As a result, the efficiency rate is very high and particularly high switching frequency values can be achieved. In the present paper, the functionality is described, prototypes with output power from 20 kVA to 90 kVA are presented and results are specified. © 2013 Chinese Society for Electrical Engineering.

Garloff J.,Konstanz University of Applied Sciences
Computing | Year: 2012

The paper considers systems of linear interval equations, i.e., linear systems where the coefficients of the matrix and the right hand side vary between given bounds. We focus on symmetric matrices and consider direct methods for the enclosure of the solution set of such a system. One of these methods is the interval Cholesky method, which is obtained from the ordinary Cholesky decomposition by replacing the real numbers by the related intervals and the real operations by the respective interval operations. We present a method by which the diagonal entries of the interval Cholesky factor can be tightened for positive definite interval matrices, such that a breakdown of the algorithm can be prevented. In the case of positive definite symmetric Toeplitz matrices, a further tightening of the diagonal entries and also of other entries of the Cholesky factor is possible. Finally, we numerically compare the interval Cholesky method with interval variants of two methods which exploit the Toeplitz structure with respect to the computing time and the quality of the enclosure of the solution set. © 2011 Springer-Verlag.

Birkholzer T.,Konstanz University of Applied Sciences
2012 International Conference on Software and System Process, ICSSP 2012 - Proceedings | Year: 2012

Simulation is an important method and tool in many fields of engineering. Compared to these, simulation plays only a minor role in the field of software processes and software engineering. Examining this discrepancy, four theses are formulated as suggestions for future directions of software process simulation: 1. Simulation requires efforts, but "not simulating" might cause considerable costs as well, e.g. by wrong assumptions or expectations. These costs must be addressed and understood as well. 2. A model is always a simplification with many uncertainties. However, this is not a counter-argument by itself but must be evaluated in the perspective of purpose and available alternatives. 3. Future process simulation models must and will be much more complex than today. The necessary complexity can only be handled by relying on a rich set of mature components. This requires a joined effort and appreciation of the respective groundwork. 4. There are areas of software process modelling, which have already achieved some maturity, e.g. the interrelationships of volume of work, productivity, resources, and defect injection and removal. However, there are other aspects, which need further research to develop adequate modeling concepts, e.g. influence of architectural quality on later process stages, influence of process area capabilities within a dynamic simulation, or combined effects of human factors like time pressure, motivation, or knowledge acquisition. © 2012 IEEE.

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