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The paper focuses on a study of turbulence decay in flow with streamwise gradient. For the first time, an analytical solution of this problem was obtained based on the k‐ε model of turbulence in one‐dimensional (1D) approximation, as well as on the symmetry properties of the system of differential equations. Lie group technique enabled reducing the problem to a linear differential equation. The analytical solution enabled parametric studies, which are computationally cheap in comparison to CFD based simulations. The lattice Boltzmann method (LBM) in two‐dimensional approximation (2D) was used to validate the analytical results. Large eddy simulation (LES) Smagorinsky approach was used to close the LBM model. Computations revealed that the rate of turbulence decay is significantly different for the cases of positive and negative streamwise pressure gradient. The further comparisons showed that the analytical solution underpredicts the predictions by the numerical methodology, which can be attributed to the simplified problem statement used to derive the closed‐form analytical solution. Comparisons of calculations with experiments revealed that the theoretical models used in the study underpredict the measurements for flows with a positive pressure gradient. Hence it can be concluded that the LBM technique combined with the LES Smagorinsky model requires the further modification.
The paper focused on an analytical analysis of the main features of heat transfer in incompressible steady-state flow in a microconfusor with account for the second-order slip boundary conditions. The second-order boundary conditions serve as a closure of a system of the continuity, transport, and energy differential equations. As a result, novel solutions were obtained for the velocity and temperature profiles, as well as for the friction coefficient and the Nusselt number. These solutions demonstrated that an increase in the Knudsen number leads to a decrease in the Nusselt number. It was shown that the account for the second-order terms in the boundary conditions noticeably affects the fluid flow characteristics and does not influence on the heat transfer characteristics. It was also revealed that flow slippage effects on heat transfer weaken with an increase in the Prandtl number.
Abstract
The paper represents an analysis of convective instability in a vertical cylindrical porous microchannel performed using the Galerkin method. The dependence of the critical Rayleigh number on the Darcy, Knudsen, and Prandtl numbers, as well as on the ratio of the thermal conductivities of the fluid and the wall, was obtained. It was shown that a decrease in permeability of the porous medium (in other words, increase in its porosity) causes an increase in flow stability. This effect is substantially nonlinear. Under the condition Da > 0.1, the effect of the porosity on the critical Rayleigh number practically vanishes. Strengthening of the slippage effects leads to an increase in the instability of the entire system. The slippage effect on the critical Rayleigh number is nonlinear. The level of nonlinearity depends on the Prandtl number. With an increase in the Prandtl number, the effect of slippage on the onset of convection weakens. With an increase in the ratio of the thermal conductivities of the fluid and the wall, the influence of the Prandtl number decreases. At high values of the Prandtl numbers (Pr > 10), its influence practically vanishes.
The paper presents results of the modelling of heat transfer at film boiling of a liquid in a porous medium on a vertical heated wall bordering with the porous medium. Such processes are observed at cooling of high-temperature surfaces of heat pipes, microstructural radiators etc. Heating conditions at the wall were the constant wall temperature or heat flux. The outer boundary of the vapor film was in contact with moving or stationary liquid inside the porous medium. An analytical solution was obtained for the problem of fluid flow and heat transfer using the porous medium model in the Darcy–Brinkman and Darcy–Brinkman–Forchheimer approximation. It was shown that heat transfer at film boiling in a porous medium was less intensive than in the absence of a porous medium (free fluid flow) and further decreased with the decreasing permeability of the porous medium. Significant differences were observed in frames of both models: 20% for small Darcy numbers at Da < 2 for the Darcy–Brinkman model, and 80% for the Darcy–Brinkman–Forchheimer model. In the Darcy–Brinkman model, depending on the interaction conditions at the vapor–liquid interface (no mechanical interaction or stationary fluid), a sharp decrease in heat transfer was observed for the Darcy numbers lower than five. The analytical predictions of heat transfer coefficients qualitatively agreed with the data of Cheng and Verma (Int J Heat Mass Transf 24:1151–1160, 1981) though demonstrated lower values of heat transfer coefficients for the conditions of the constant wall temperature and constant wall heat flux.
This paper investigates the state, development and drivers of banking market integration in the member countries of the Southern African Development Community (SADC) by employing interest rate data. We first conduct a principal component analysis and find evidence for both increasing monetary integration and banking integration in loan and deposit markets. These integration processes are not developing uniformly and we can identify a convergence club. As banking market integration can be a genuine process or simply be driven by monetary integration, we also investigate the interest rate pass through from national and South African Central bank interest rates onto national retail rates. With respect to the convergence club we find both, genuine and monetary-integration driven processes though the latter dominate. We conclude that a selective expansion of the Common Monetary Area is possible but needs to be complement by efficient financial development policies.
This investigation attempts to understand the eco‐hydrology of, and accordingly suggest an option to manage floodwater for agriculture in, the understudied and data‐sparse ephemeral Baraka River Basin within the hyper‐arid region of Sudan. Reference is made to the major feature of the basin, that is, the Toker Delta spate irrigation scheme. A point‐to‐pixel comparison of gridded and ground‐based data sets is performed to enhance the estimates of rainfall. Analysis of remotely sensed land use/cover data is performed. The results show a significant reduction of the grassland and barren areas explained by a significant expansion of the cropland and open shrubland (invasive mesquite trees) areas in the delta. The cotton sown area is highly dependent on the flooded area and the discharge volume in the delta. However, the area of this major crop has declined since the early 1990s in favour of cultivation of more profitable food crops. Expansion of mesquite in the delta is problematic, taking hold under increased floodwater, and can only be manged by clearance to provide crop cultivation area. There is a great potential for floodwater harvesting during the rainfall season (June to September). A total seasonal runoff volume of around 4.6 and 10.8 billion cubic metres is estimated at 90 and 50% probabilities of exceedance (reliabilities), respectively. Rather than leaving the runoff generated from rainfall events to pass to the Red Sea or be consumed by mesquite trees, a location for runoff harvesting structure in a highly suitable area is proposed. Such a structure will support any policy shifts towards planning and managing the basin water resources for use in irrigating the agricultural scheme.
This market research paper has been prepared under the supervision of Prof. Dr. Wolfgang Veit of Cologne University of Applied Sciences and Prof. Dr. Carol Scovotti of University of Wisconsin-Whitewater in the course of the inter-university cross-border collaboration student research project “Export Opportunity Surveys (EOS)”. This study explores vanilla export opportunities to the German and US markets.
Motion capturing plays an important role in computer animation and combines many different fields of research in media engineering, such as camera calibration, marker detection via image processing and 3D reconstruction. Most professional motion capture systems are distributed proprietarily by a handful of companies and do not grant much insight into detailed workflows. The motivation for the project this thesis is based on was to autonomously develop a simpler, yet similar system, which would capture static poses of a puppet. This thesis points out the designing steps of this system and illustrates how many of the aforementioned aspects of motion capturing are answered using the example of the stop-motion capture system, thus building a basis for the comprehension of more complex systems.
One-step preparation of bilayered films from kraft lignin and cellulose acetate to mimic tree bark
(2020)
This contribution presents the development of a dry-cast method for the one-step preparation of bio-based films from wood polymers that mimic the bilayered structure of tree bark, the natural protective layer of the tree. In a simplified view, natural bark can be considered as the superposition of an external homogeneous and non-porous layer (outer bark) and a porous substructure layer (inner bark). This work is a first step for the future development of bio-based biomimetic wood coatings. The film had a bark-like appearance and its total density, bulk density and porosity were similar to values measured in natural bark. Furthermore, the structural characteristics of the studied film, namely specific surface area (BET) and pore size distribution, as well as the performance of the water adsorption ability were investigated and discussed.
This market research paper has been prepared under the supervision of Prof. Dr. Wolfgang Veit of Cologne University of Applied Sciences and Prof. Dr. Carol Scovotti of University of Wisconsin-Whitewater in the course of the inter-university cross-border collaboration student research project “Export Opportunity Surveys (EOS)”. This study explores organic oats export opportunities to the German and US markets.
Aim: European cities are facing heighten hydrological risks as a result of climate change at the same time as ecological degradation has reduced the environmental capacity to absorb and regulate such fluctuations. Climate forecasts predict more intense convective rainfall and winter flood events in the Wupper Basin in Germany, against a background trend of reduced mean rainfall during the summer months. On 14 July 2021 intense convective rainfall fell at points across Western Germany and led to flash floods in the Wupper Basin, many sites were inundated and the Wupper and Dhünn rivers rose to new record highs. Green-blue infrastructure offers strategies to reduce the impacts of hazards at the same time as providing a range of co-benefits. A study was undertaken to find which green-blue interventions will be most effective at reducing the impacts of hydrometeorological hazards for a study area in the west of the Wupper basin. Furthermore, as landscape features are highly influential in hydrology, the study sought to establish which sites within the landscape can provide maximum results from green-blue interventions, with a minimum of change to current land uses.
Region: Europe, peri-urban and rural, undulating, low mountainous landscapes
Methods: Literature findings on observed and projected climate data are summarised and long-term rainfall data from the study area is analysed to confirm rainfall trends. A state-of-the-art review is conducted and summarised to form a toolbox of potential interventions. The most recent hazardous hydrometeorological event is analysed to inform the locational priorities of potential interventions. Landscape features that have the most influence on basin hydrology are identified from the literature. These sites are paired with green-blue interventions that are shown to have the highest potential impact on interception, infiltration, runoff and flooding. A series of spatial analyses are carried out to produce maps detailing location and intervention with high potential to reduce the impact of hydrometeorological hazards in the study area. All of the evidence gathered from the literature analysis is combined in an implementation guide for green-blue interventions in the Wupper Basin.
Results: The hazards caused by the hydrometeorological extremes of flooding and drought are addressed or minimised through the green-blue interventions that increase interception and infiltration and reduce runoff and flooding. Priority locations are identified as the riparian zone with slope ≤15%, hilltop, lower slope and toe slope, all locations with a slope ≥30% and areas with a high topographic wetness index (TWI). A series of spatial analyses were carried out and suggestions made including potential locations for retention or detention areas and ponds, sites for revegetation and potential locations for implementation of shelterbelts/hedgerows, buffer strips, conservation tillage or strip tillage, reduced mowing intensity or frequency and biochar additions. An implementation guide is created that provides a summary of the highest potential green-blue interventions and landscape locations, and a description of the mechanisms involved in addressing the hydrometeorological hazards.
Keywords: Green-blue interventions, hydrometeorological hazard reduction, Wupper Basin hydrology
Policy measures are essential tools for the transition from fossil fuels to renewable energy sources in the electricity generation. Feed-in tariffs (FITs) are the most used policy for support of renewable technologies globally. Nevertheless, Ecuador phased-out FITs in 2016 and adopted auctions in 2015. Ecuador’s implementation of auctions reflects an approach with little relation to practices in other countries and without a technology-specific design. On the other hand, Germany demonstrates a long trajectory in policy-making with vast experience in FITs. Moreover, in 2017 Germany adopted auctions as the official policy to support renewable projects with a scope larger than 750 kW. However, FITs are still in use and complement auctions.
This thesis analyses and compares the country-specific contexts where these policies are implemented through the lens of a multi-level perspective framework. As a result, the most important success factors in Germany have been identified: long-term planning, institutional continuity, legislative stability and principally an actively participating society, which is environmentally aware. Obstacles for the transition in Ecuador are institutional discontinuity, legislative inconsistency, the lack of long-term planning and absence of society as actors of the transition. Due to Germany’s pioneering role plus the successful growth of renewable sources during the last twenty years, their policy implementations appear desirable to adopt in other contexts. Therefore, a prospective transferability of the auction policy from Germany to Ecuador is additionally analyzed.
The teaching of civil engineering consists of different didactic approaches, such as lectures, group work or research-based teaching, depending on the respective courses. Currently, the metaverse is gaining importance in teaching and offers the possibility of a new teaching approach for civil engineering and especially for the teaching of courses from the areas of “Digital Design and Construction”. Although the advantages of teaching in the metaverse, such as location and time independence or a higher learning outcome, are mentioned in the literature, there are also challenges that must be considered when teaching in the metaverse. Against this background, this paper examines the implications of using the metaverse as a teaching tool in teaching “Digital Design and Construction”. The impact of teaching BIM in the metaverse is evaluated by (1) a literature review and workshops to evaluate use cases and demands for extended reality (XR) and the metaverse, (2) integrating XR and the metaverse in the courses and valuation by quantitative evaluations and (3) analyzing student papers of the courses and outcomes of a World Café. Due to these steps, this paper presents a novel approach by reflecting the students’ perspective. Furthermore, this paper presents a validated approach for integrating BIM and the metaverse in teaching.
We consider a risk model in discrete time with dividends and capital injections. The goal is to maximise the value of a dividend strategy. We show that the optimal strategy is of barrier type. That is, all capital above a certain threshold is paid as dividend. A second problem adds tax to the dividends but an injection leads to an exemption from tax. We show that the value function fulfils a Bellman equation. As a special case, we consider the case of premia of size one. In this case we show that the optimal strategy is a two barrier strategy. That is, there is a barrier if a next dividend of size one can be paid without tax and a barrier if the next dividend of size one will be taxed. In both models, we illustrate the findings by de Finetti’s example.
Conventional individual head-related transfer function (HRTF) measurements are demanding in terms of measurement time and equipment. For more flexibility, free body movement (FBM) measurement systems provide an easy-to-use way to measure full-spherical HRTF datasets with less effort. However, having no fixed measurement installation implies that the HRTFs are not sampled on a predefined regular grid but rely on the individual movements of the subject. Furthermore, depending on the measurement effort, a rather small number of measurements can be expected, ranging, for example, from 50 to 150 sampling points. Spherical harmonics (SH) interpolation has been extensively studied recently as one method to obtain full-spherical datasets from such sparse measurements, but previous studies primarily focused on regular full-spherical sampling grids. For irregular grids, it remains unclear up to which spatial order meaningful SH coefficients can be calculated and how the resulting interpolation error compares to regular grids. This study investigates SH interpolation of selected irregular grids obtained from HRTF measurements with an FBM system. Intending to derive general constraints for SH interpolation of irregular grids, the study analyzes how the variation of the SH order affects the interpolation results. Moreover, the study demonstrates the importance of Tikhonov regularization for SH interpolation, which is popular for solving ill-posed numerical problems associated with such irregular grids. As a key result, the study shows that the optimal SH order that minimizes the interpolation error depends mainly on the grid and the regularization strength but is almost independent of the selected HRTF set. Based on these results, the study proposes to determine the optimal SH order by minimizing the interpolation error of a reference HRTF set sampled on the sparse and irregular FBM grid. Finally, the study verifies the proposed method for estimating the optimal SH order by comparing interpolation results of irregular and equivalent regular grids, showing that the differences are small when the SH interpolation is optimally parameterized.
This paper gives an overview of the development of Fair Trade in six European countries: Austria, France, Germany, the Netherlands, Switzerland and the United Kingdom. After the description of the food retail industry and its market structures in these countries, the main European Fair Trade organizations are analyzed regarding their role within the Fair Trade system. The following part deals with the development of Fair Trade sales in general and with respect to the products coffee, tea, bananas, fruit juice and sugar. An overview of the main activities of national Fair Trade organizations, e.g. public relation activities, completes the analysis. This study shows the enormous upswing of Fair Trade during the last decade and the reasons for this development. Nevertheless, it comes to the conclusion that Fair Trade is still far away from being an essential part of the food retail industry in Europe.
This market research paper has been prepared under the supervision of Prof. Dr. Wolfgang Veit of Cologne University of Applied Sciences and Prof. Dr. Carol Scovotti of University of Wisconsin-Whitewater in the course of the inter-university cross-border collaboration student research project “Export Opportunity Surveys (EOS)”. This study explores walnuts export opportunities to the German and US markets.
This market research paper has been prepared under the supervision of Prof. Dr. Wolfgang Veit of TH Köln and Prof. Dr. Carol Scovotti of University of Wisconsin-Whitewater in the course of the inter-university cross-border collaboration student research project “Export Opportunity Surveys (EOS)”. This study explores organic lipstick export opportunities to the German and US markets.
Ten female and five male participants (age range 28–50 years) were recruited at esoteric fairs or via esoteric chatrooms. In a guided face-to-face interview, they reported origins and contents of their beliefs in e.g. esoteric practices, supernatural beings, rebirthing, channeling. Transcripts of the tape-recorded reports were subjected to a qualitative analysis. Exhaustive categorization of the narratives’ content revealed that paranormal beliefs were functional with regard to two fundamental motives – striving for mastery and valuing me and mine (striving for a positive evaluation of the self). Moreover, paranormal beliefs paved the way for goal-setting and leading a meaningful life but, on the negative side, could also result in social exclusion. Results are discussed with reference to the adaptive value of paranormal beliefs.
Intelligent use of energy is one of the keys to success for an energy revolution. To meet this challenge, smart meters are suitable tools because INTELLIGENT use of energy means not only to use efficiency technology, but also to determine load shifting potentials and use them accordingly. Especially farms with high power consumption are becoming increasingly concerned about reducing energy costs due to rising energy prices and need a systematic analysis of their operational energy flow. To find solutions for farms, the NaRoTec e.V., the TH Köln, and the Machinery Ring Höxter-Warburg have joined forces with partners and launched the project "Intelligent Energy in Agriculture", which is funded by the state of NRW. The aim of the project is to be able to give individual advice recommendations for energy optimization of agricultural holdings. This will be achieved inter alia through an operational energy audit and current measurements in different operating ranges. To achieve this, smart meters were installed in selected energy-intensive dairy and pig farms. As part of the project, the installed smart meter information about the consumption of various plants and their components were analyzed, regularities and adaptability in loading history identified, and the energy efficiency of the equipment and systems used verified (especially pumps, ventilators, feeding systems). Then recommendations were formulated to shift electricity-intensive processes to times with low electricity costs and high intrinsic power production. The resulting findings will be used as the basis for intelligent energy management in the further course of the project. Overall, efficiency streamlining measures in the field of ventilation and lighting systems, flexible dry feeding systems by decoupling power purchase and consumption, as well as energy savings and related CO2 savings were determined.