Universitätsbibliothek
Weimar Open Access

Scalarization methods are a category of multiobjective optimization (MOO) methods. These methods allow the usage of conventional single objective optimization algorithms, as scalarization methods reformulate the MOO problem into a single objective optimization problem. The scalarization methods analysed within this thesis are the Weighted Sum (WS), the Epsilon-Constraint (EC), and the MinMax (MM) method. After explaining the approach of each method, the WS, EC and MM are applied, a-posteriori, to three different examples: to the Kursawe function; to the ten bar truss, a common benchmark problem in structural optimization; and to the metamodel of an aero engine exit module. The aim is to evaluate and compare the performance of each scalarization method that is examined within this thesis. The evaluation is conducted using performance metrics, such as the hypervolume and the generational distance, as well as using visual comparison. The application to the three examples gives insight into the advantages and disadvantages of each method, and provides further understanding of an adequate application of the methods concerning high dimensional optimization problems.

Renewable energy use is on the rise and these alternative resources of energy can help combat with the climate change. Around 80% of the world's electricity comes from coal and petroleum however, the renewables are the fastest growing source of energy in the world. Solar, wind, hydro, geothermal and biogas are the most common forms of renewable energy. Among them, wind energy is emerging as a reliable and large-scaled source of power production. The recent research and confidence in the performance has led to the construction of more and bigger wind turbines around the world. As wind turbines are getting bigger, a concern regarding their safety is also in discussion. Wind turbines are expensive machinery to construct and the enormous capital investment is one of the main reasons, why many countries are unable to adopt to the wind energy. Generally, a reliable wind turbine will result in better performance and assist in minimizing the cost of operation. If a wind turbine fails, it's a loss of investment and can be harmful for the surrounding habitat. This thesis aims towards estimating the reliability of an offshore wind turbine. A model of Jacket type offshore wind turbine is prepared by using finite element software package ABAQUS and is compared with the structural failure criteria of the wind turbine tower. UQLab, which is a general uncertainty quantification framework developed at ETH Zürich, is used for the reliability analysis. Several probabilistic methods are included in the framework of UQLab, which include Monte Carlo, First Order Reliability Analysis and Adaptive Kriging Monte Carlo simulation. This reliability study is performed only for the structural failure of the wind turbine but it can be extended to many other forms of failures e.g. reliability for power production, or reliability for different component failures etc. It's a useful tool that can be utilized to estimate the reliability of future wind turbines, that could result in more safer and better performance of wind turbines.

Structural optimization has gained considerable attention in the design of structural engineering structures, especially in the preliminary phase. This study introduces an unconventional approach for structural optimization by utilizing the Energy method with Integral Material Behavior (EIM), based on the Lagrange’s principle of minimum potential energy. An automated two-level optimization search process is proposed, which integrates the EIM, as an alternative method for nonlinear structural analysis, and the bilevel optimization. The proposed procedure secures the equilibrium through minimizing the potential energy on one level, and on a higher level, a design objective function. For this, the most robust strategy of bilevel optimization, the nested method is used. The function of the potential energy is investigated along with its instabilities for physical nonlinear analysis through principle examples, by which the advantages and limitations using this method are reviewed. Furthermore, optimization algorithms are discussed. A numerical fully functional code is developed for nonlinear cross section, element and 2D frame analysis, utilizing different finite elements and is verified against existing EIM programs. As a proof of concept, the method is applied on selected examples using this code on cross section and element level. For the former one a comparison is made with standard procedure, by employing the equilibrium equations within the constrains. The validation of the element level was proven by a theoretical solution of an arch bridge and finally, a truss bridge is optimized. Most of the principle examples are chosen to be adequate for the everyday engineering practice, to demonstrate the effectiveness of the proposed method. This study implies that with further development, this method could become just as competitive as the conventional structural optimization techniques using the Finite Element Method.

The aim of my research is to observe the variance of energy efficiency of a typical multi-story office building under the exposure of different climatic conditions. Energy efficiency requirements in building codes or energy standards are among the most important single measures for buildings’ energy efficiency. Therefore, this study can be set up for a better understanding of how energy efficiency of a building changes under the effect of adverse to moderate climatic conditions which possess a mentionable effect on the operation of a building. This thesis is structured in three balanced and conceptual steps. Following the aim of the project, the virtual building model is to be analyzed under the effect of seven distinct climatic conditions namely work environment of New Delhi, Mumbai, Berlin, Lisbon, Copenhagen, Dubai and Montreal. Firstly, the task is to do a complete literature research based on the scope of similar researches and studying the problems in detail along with the theoritical background all the concepts which are implemented to get the numerical results. This chapter also comprises a detailed study of the climatic conditions of the above-mentioned cities. Different climatic traits like temperature variations, count of heating and cooling degree days, relative humidity, temperature range and comfort zonal charts for the specified cities are studied in detail. This study helps to understand the effect of these adverse to moderate climates on the operation of the building. On the second step, the virtual building model is prepared on a software platform named Revit Structures. This virtual building model is not necessarily a complete building, but it has the relevant functionalities of a real building. We perform the energy analysis and the heating and cooling analysis on this virtual building model to study the operational outcome of the building under different climatic conditions in detail. By the end of these above two tasks, two scenarios are observed. On one hand, we have a literature research and on the other hand we have the numerical results. Therefore, finally we present a comparative scenario based on the energy efficient performances of the building under such variant climatic conditions. This is followed by the prediction of thermal comfort level inside the building and it based on Fanger’s PMV Model. Understanding the literature and the numerical values in detail helps us to predict the index thermal comfort level inside the building. The conclusion of this master thesis focuses mainly on the scopes of improvement of energy efficiency requirements in energy codes if any, differentiated according to specific locations. The initial aim of my hypothesis which is to study the impacts of climatic variations on the energy efficient performances of a building is fulfilled but as such topics have very deep and broad roots, the scope of further improvements is always predominant.

With Building Information Modeling (BIM) prominently used in Architecture Engineering Construction (AEC) industry, the main focus of this innovative technology lies on those professionals such as architects, engineers, managers, etc., wherein a vulnerable interested party, construction workers especially low-skilled workers, has been inadvertently ignored. Noticed that the shortage of skilled workers becomes an escalating challenge and traditional training methods have flaws when confronting this challenge in construction sector, the emerging of new instructional methods, which are including instructional video and BIM-based learning environment, can otherwise bring some new ideas to help solve such shortage problem. The intent of this research is to design a training program for low-skilled construction workers to improve their construction skills, which includes its training content “instructional videos” and its delivery medium “mobile application”. The methodology of this research adopts “design-oriented approach” and its research method belongs to quantitative research method. In the thesis, the design and development process of its concept and system for this training program are presented. After statistic analysis of questionnaire results which comes from a survey on construction workers, the favorable and unfavorable aspects about this instructional video are revealed, which confirms the functionality of instructional video on low-skilled workers. In the end, limitations and suggested future works for this research have been clarified.