Eldorado - Repository of the TU Dortmund
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Dynamic modeling and robust optimal operation of the hydrothermal synthesis of zeolites in a continuous oscillatory baffled reactor
(2024-03-01) Semrau, Robin; Ramirez Mendoza, Heidy; Lutz, Cécile; Engell, Sebastian
Continuous flow synthesis offers major advantages in the production of specialty products, e.g. zeolites, such as tight temperature control and lower variation in product quality. Here we consider the hydrothermal synthesis of NaX zeolites in a continuous oscillatory baffled reactor (COBR). A process model is derived from physico-chemical relationships to analyze and optimize the operation of a pilot scale continuous oscillatory baffled reactor for zeolite synthesis. The process model is validated using plant data. Furthermore, the uncertainty of the model predictions is quantified. Based on this analysis, robust optimization is used to compute robust optimal operation points of the COBR. These optimal operation points are validated by the application to a real pilot plant.
Direct numerical simulation of dispersion and mixing in gas–liquid Dean-Taylor flow with influence of a 90° bend
(2024-09-01) Mierka, Otto; Münster, Raphael; Surkamp, Julia; Turek, Stefan; Kockmann, Norbert
Gas-liquid capillary flow finds widespread applications in reaction engineering, owing to its ability to facilitate precise control and efficient mixing. Incorporating compact and regular design with Coiled Flow Inverter (CFI) enhances process efficiency due to improved mixing as well as heat and mass transfer leading to a narrow residence time distribution. The impact of Dean and Taylor flow phenomena on mixing and dispersion within these systems underscores their significance, but is still not yet fully understood. Direct numerical simulation based on finite element method enables full 3D resolution of the flow field and detailed examination of laminar flow profiles, providing valuable insights into flow dynamics. Notably, the deflection of flow velocity from the center axis contributes is followed by tracking of particle with defined starting positions, aiding in flow visualization and dispersion characterization. In this CFD study, the helical flow with the influence of the centrifugal force and pitch (Dean flow) as well as the capillary two-phase flow (Taylor bubble) is described and characterized by particle dispersion and related histograms. Future prospects in this field include advancements in imaging techniques to capture intricate flow patterns, as well as refined particle tracking methods to better understand complex flow behavior.
Effective surface forces and non-coherent interfaces within the reduced relaxed micromorphic modeling of finite-size mechanical metamaterials
(2024-02-02) Perez Ramirez, Leonardo A.; Erel-Demore, Félix; Rizzi, Gianluca; Voss, Jendrik; Madeo, Angela
This paper introduces for the first time the concepts of non-coherent interfaces and microstructure-driven interface forces in the framework of micromorphic elasticity. It is shown that such concepts are of paramount importance when studying the response of finite-size mechanical metamaterials at the homogenized macro-scale. The need of introducing interface forces is elucidated through numerical examples comparing reduced relaxed micromorphic simulations to their full-microstructured counterparts. These results provide a milestone for the understanding of metamaterials’ modeling at the homogenized scale and for the use of micromorphic-type models to achieve an accurate upscaling towards larger-scale metamaterials’ structures.
Does instructional time at school influence study time at university? Evidence from an instructional time reform
(2024-05-09) Schwerter, Jakob; Netz, Nicolai; Hübner, Nicolas
Early-life environments can have long-lasting effects on individuals’ later life courses. Interestingly, research on the effects of school reforms has hardly adopted this perspective. Therefore, we investigate a staggered school reform that reduced the number of school years and increased weekly instructional time for secondary school students in most German federal states. We analyze this quasi-experiment in a difference-in-differences framework using nationally representative large-scale survey data on 69,513 students who attended university between 1998 and 2016. Using both TWFE and weighted-group ATT estimators, we find negative effects of reform exposure on hours spent attending classes and on self-study. Moreover, reform exposure increased the time gap between school completion and higher education entry. Our results support the view that research should examine unintended long-term effects of school reforms on individual life courses.
Directional importance sampling for dynamic reliability of linear structures under non-Gaussian white noise excitation
(2024-12-10) Zhang, Xuan-Yi; Misraji, Mauricio A.; Valdebenito, Marcos A.; Faes, Matthias G. R.
Reliability analysis of dynamic structural systems and its implications for structural design have garnered increasing attention. Sample-based methods prove insensitive to the dimension of the probability integral. Nontheless, a substantial number of realizations is necessary for estimating small failure probabilities, resulting in time-consuming computations. Recently, the Directional Importance Sampling (DIS) was introduced for linear structural systems subjected to Gaussian loads, showcasing the ability to accurately estimate small failure probabilities with a reduced number of simulations. However, this Gaussian assumption on the load makes the method inapplicable for realistic loading scenarios as they might be of non-Gaussian nature. This contribution develops the DIS method for linear structural systems subjected to loading characterized as non-Gaussian white noise. To take the advantage of both linearity in physical space and simplicity of Gaussian space, directional importance sampling is conducted in Gaussian space and the failure probability is estimated with the aid of physical space. The information is dynamically exchanged between physical and Gaussian spaces with the aid of normal and inverse-normal transformation techniques. The whole procedure of the developed DIS method is straightforward, and it provides an explicit estimator of the failure probability. The application of the developed DIS method is presented through three examples, illustrating its accuracy and efficiency for dynamic reliability analysis.