Recent Submissions
Coherent mesh representation for parallel I/O of unstructured polyhedral meshes
(2024) Weiß, R. Gregor; Lesnik, Sergey; Galeazzo, Flavio C. C.; Ruopp, Andreas; Rusche, Henrik
This paper presents a new mesh data layout for parallel I/O of linear unstructured polyhedral meshes. The new mesh representation infers coherence across entities of different topological dimensions, i.e., grid cells, faces, and points. The coherence due to cell-to-face and face-to-point connectivities of the mesh is formulated as a tree data structure distributed across processors. The mesh distribution across processors creates consecutive and contiguous slices that render an optimized data access pattern for parallel I/O. A file format using the coherent mesh representation, developed and tested with OpenFOAM, enables the usability of the software at unprecedented scales. Further implications of the coherent and sliceable mesh representation arise due to simplifications in partitioning and diminished pre- and post-processing overheads.
Convective drying of porous media : comparison of phase-field simulations with microfluidic experiments
(2024) Maier, Lukas; Brosch, Sebastian; Gaehr, Magnus; Linkhorst, John; Wessling, Matthias; Nieken, Ulrich
Convective drying of porous media is central to many engineering applications, ranging from spray drying over water management in fuel cells to food drying. To improve these processes, a deep understanding of drying phenomena in porous media is crucial. Therefore, detailed simulation of multiphase flows with phase change is of great importance to investigate the complex processes involved in drying porous media. While many studies aim to access the phenomena solely by simulations, here we succeed to compare comprehensively simulations with an experimental methodology based on microfluidic multiphase flow studies in engineered porous media. In this contribution, we propose a Navier-Stokes Cahn-Hilliard model coupled with balance equations for heat and moisture to simulate the two-phase flow with phase change. The phase distribution of the two fluids air and water is modeled by the Phase-Field equation. Comparisons with experiments are rare in the literature and usually involve very simple cases. We compare our simulation with convective drying experiments of porous media. Experimentally, the interface propagation of the water-air interface was visualized in detail during drying in a structured microfluidic cell made from PDMS. The drying pattern and the drying time in the experiment are very well reproduced by our simulation. This validation will enable the application for the presented Navier-Stokes Cahn-Hilliard model in more complex cases focused more on applications, e.g., in the field of fibrous materials.
Modeling and analysis of droplet evaporation at the interface of a coupled free-flow-porous medium system
(2024) Veyskarami, Maziar; Bringedal, Carina; Helmig, Rainer
Evaporation of droplets formed at the interface of a coupled free-flow–porous medium system enormously affects the exchange of mass, momentum, and energy between the two domains. In this work, we develop a model to describe multiple droplets’ evaporation at the interface, in which new sets of coupling conditions including the evaporating droplets are developed to describe the interactions between the free flow and the porous medium. Employing pore-network modeling to describe the porous medium, we take the exchanges occurring on the droplet-pore and droplet-free-flow interfaces into account. In this model, we describe the droplet evaporation as a diffusion-driven process, where vapor from the droplet surface diffuses into the surrounding free flow due to the concentration gradient. To validate the model, we compare the simulation results for the evaporation of a single droplet in a channel with experimental data, demonstrating that our model accurately describes the evaporation process. Then, we examine the impact of free-flow and porous medium properties on droplet evaporation. The results show that, among other factors, velocity and relative humidity in the free-flow domain, as well as pore temperature in the porous medium, play key roles in the droplet evaporation process.
Upscaling and effective behavior for two-phase porous-medium flow using a diffuse interface model
(2024) Kelm, Mathis; Bringedal, Carina; Flemisch, Bernd
We investigate two-phase flow in porous media and derive a two-scale model, which incorporates pore-scale phase distribution and surface tension into the effective behavior at the larger Darcy scale. The free-boundary problem at the pore scale is modeled using a diffuse interface approach in the form of a coupled Allen-Cahn Navier-Stokes system with an additional momentum flux due to surface tension forces. Using periodic homogenization and formal asymptotic expansions, a two-scale model with cell problems for phase evolution and velocity contributions is derived. We investigate the computed effective parameters and their relation to the saturation for different fluid distributions, in comparison to commonly used relative permeability saturation curves. The two-scale model yields non-monotone relations for relative permeability and saturation. The strong dependence on local fluid distribution and effects captured by the cell problems highlights the importance of incorporating pore-scale information into the macro-scale equations.
Why Aristotle isn’t a virtue ethicist : living well and virtuously in Aristotelian and contemporary aretaic ethics
(2024) Kaya, Deniz A.
Drawing on Anscombe, in this essay I argue that we should not take Aristotle to be a moral philosopher, nor a virtue ethicist. This is because contemporary virtue ethics has little to do with Aristotelian ethics. While contemporary virtue ethics (or aretaic moral theory, as one may call it) operates on the level of moral and thus categorical norms, Aristotelian ethics-an aretaic life ethics-is primarily concerned with pragmatic norms. The main question for Aristotle is what a good general conduct of life is. The major concern of aretaic moral theory, on the other hand, is to provide a criterion of morally right action and hence to define the concepts of the morally right, the impermissible and moral duty in aretaic terms. This shows that contemporary authors assume a primacy of virtue, while Aristotle assumes a primacy of eudaimonia. I illustrate this distinction by addressing the question of how the virtues benefit their possessor.
Investigation of different throat concepts for precipitation processes in saturated pore-network models
(2024) Schollenberger, Theresa; Wolff, Lars von; Bringedal, Carina; Pop, Iuliu Sorin; Rohde, Christian; Helmig, Rainer
The development of reliable mathematical models and numerical discretization methods is important for the understanding of salt precipitation in porous media, which is relevant for environmental problems like soil salinization. Models on the pore scale are necessary to represent local heterogeneities in precipitation and to include the influence of solution-air-solid interfaces. A pore-network model for saturated flow, which includes the precipitation reaction of salt, is presented. It is implemented in the open-source simulator DuMu X. In this paper, we restrict ourselves to one-phase flow as a first step. Since the throat transmissibilities determine the flow behaviour in the pore network, different concepts for the decreasing throat transmissibility due to precipitation are investigated. We consider four concepts for the amount of precipitation in the throats. Three concepts use information from the adjacent pore bodies, and one employs a pore-throat model obtained by averaging the resolved pore-scale model in a thin-tube. They lead to different permeability developments, which are caused by the different distribution of the precipitate between the pore bodies and throats. We additionally apply two different concepts for the calculation of the transmissibility. One obtains the precipitate distribution from analytical assumptions, the other from a geometric minimization principle using a phase-field evolution equation. The two concepts do not show substantial differences for the permeability development as long as simple pore-throat geometries are used. Finally, advantages and disadvantages of the concepts are discussed in the context of the considered physical problem and a reasonable effort for the implementation and computational costs.
Soil organic carbon as an indicator of land use impacts in life cycle assessment
(2024) De Laurentiis, Valeria; Maier, Stephanie; Horn, Rafael; Uusitalo, Ville; Hiederer, Roland; Chéron-Bessou, Cécile; Morais, Tiago; Grant, Tim; Milà i Canals, Llorenç; Sala, Serenella
Purpose. Anthropogenic activities are a major driver of soil and land degradation. Due to the spatial heterogeneity of soil properties and the global nature of most value chains, the modelling of the impacts of land use on soil quality for application in life cycle assessment (LCA) requires a regionalised assessment with global coverage. This paper proposes an approach to quantify the impacts of land use on soil quality, using changes in soil organic carbon (SOC) stocks as a proxy, following the latest recommendation of the Life Cycle Initiative.
Methods. An operational set of SOC-based characterisation factors for land occupation and land transformation were derived using spatial datasets (1 km resolution) and aggregated at the national and global levels. The developed characterisation factors were tested by means of a case study analysis, investigating the impact on soil quality caused by land use activities necessary to provide three alternative energy supply systems for passenger car transport (biomethane, ethanol, and solar electricity). Results obtained by applying characterisation factors at local, regional, and national levels were compared, to investigate the role of the level of regionalisation on the resulting impacts.
Results and discussion. Global maps of characterisation factors are presented for the 56 land use types commonly used in LCA databases, together with national and global values. Urban and industrial land uses present the highest impacts on SOC stocks, followed by severely degraded pastures and intensively managed arable lands. Instead, values obtained for extensive pastures, flooded crops, and urban green areas often report an increase in SOC stocks. Results show that the ranking of impacts of the three energy systems considered in the case study analysis is not affected by the level of regionalisation of the analysis. In the case of biomethane energy supply, impacts assessed using national characterisation factors are more than double those obtained with local characterisation factors, with less significant differences in the other two cases.
Conclusions. The integration of soil quality aspects in life cycle impact assessment methods is a crucial challenge due to the key role of soil conservation in ensuring food security and environmental protection. This approach allows the quantification of land use impacts on SOC stocks, taken as a proxy of soil quality. Further research needs to improve the assessment of land use impacts in LCA are identified, such as the ability to reflect the effects of agricultural and forestry management practices.
Systematising the LCA approaches’ soup : a framework based on text mining
(2024) Di Bari, Roberta; Alaux, Nicolas; Saade, Marcella; Hong, Sun Hea; Horn, Rafael; Passer, Alexander
Purpose. It is challenging for practitioners to navigate through the multitude of life cycle assessment (LCA) approaches due to the rich literature and a lack of systematisation. The LCA flexibility allowed by standards results in a multitude of applications and, as referred to in previous works, as an “alphabet soup”. This paper proposes a scheme for a clearer classification of currently used LCA approaches, with consideration of the 4-stage framework coming from standards.
Methods. This systematisation was first established through literature research serving as a preliminary tentative framework. A text mining task was carried out in a second stage, involving 2044 published articles among 7558 of the last 10 years. For text mining, a dictionary collected keywords and synonyms of the LCA approaches. Such keywords were then extracted from the text together with their context (multiword). The final multiword analysis allowed the association of each keyword (i.e. each LCA approach) with a specific LCA stage (Goal and Scope, Life Cycle Inventory, Life Cycle Impact Assessment, Interpretation). The preliminary framework was adapted, further enriched and validated based on the text mining results.
Results. As a result of the text mining activities, the preliminary tentative framework was partially confirmed and enriched with new insights, especially in the field of “explorative” LCA approaches, which also include “prospective” and “scenario-based” LCA. For most of the currently used LCA approaches, a link to a unique LCA stage was not recorded. However, clear trends were detected. The text mining task also highlighted a high number of works in which different approaches are compared or counterposed, especially in the field of attributional and consequential LCA. Some issues were found with the connotations of “traditional” approaches, which could be defined more specifically as “non-explorative”.
Conclusions. Unlike other works focused on notions from selected literature, text mining activities can provide bottom-up feedback on a larger scale more automatically. In addition, this work brought out novel LCA approaches, for which future developments will confirm a final definition and systematisation. As an additional advantage, the presented methodology is easily replicable. Hence, the presented framework can be updated along with developments in LCA approaches.
Cradle-to-gate life cycle assessment of cylindrical sulfide-based solid-state batteries
(2024) Rietdorf, Chantal; De la Rúa, Cristina; Kiemel, Steffen; Miehe, Robert
PurposeSolid-state batteries (SSBs) are a current research hotspot, as they are safer and have a higher energy density than state-of-the-art lithium-ion batteries (LIBs). To date, their production only occurs on a laboratory scale, which provides a good opportunity to analyze the associated environmental impacts prior to industrialization. This paper investigates the environmental impacts of the production of cylindrical SSB, to identify environmental hotspots and optimization potentials.MethodsHere, an attributional cradle-to-gate life cycle assessment (LCA) is performed, focusing on SSBs that use a NMC811/lithium germanium phosphorous sulfide (LiGPS) composite cathode, a sulfide-based solid separator electrolyte, and a lithium metal anode. The life cycle impact assessment (LCIA) is performed in Umberto 11 using the Environmental Footprint 3.1 method with primary and literature data and the Evoinvent 3.9 database for background data.Results and discussionThe results show climate change impacts of 205.43 kg CO2 eq./kwh (for the base case), with hotspots primarily attributable to the electrolyte and cathode production, and more specifically to the LiPS and LiGPS synthesis as well as to the cathode active material. Additionally, the scenario analysis shows that an upscaling of the LiPS and LiGPS synthesis reduces environmental impacts across all assessed impact categories. In addition, it was shown that the use of an in situ anode further improves the overall environmental performance, while the use of alternative cathode active materials, such as NMC622 and LFP did not lead to any improvements, at least with reference to the storage capacity.ConclusionThe article highlights the environmental hotspots of sulfide-based SSB production, namely electrolyte and catholyte synthesis. The results show that upscaling the synthesis reduces the environmental impact and that cells with higher energy density show a favorable environmental performance. However, SSBs are still in the development stage and no final recommendation can be made at this time.
Frontend and backend electronics achieving flexibility and scalability for tomographic tactile sensing
(2024) Sánchez-Delgado, Alberto; Garg, Keshav; Scherjon, Cor; Lee, Hyosang
Tactile sensing is essential for robots to adequately interact with the physical world, but creating tactile sensors for the robot’s soft and flexible body surface has been a challenge. The resistance tomography-based tactile sensors have been introduced as a promising approach to creating soft tactile skins because the sensor fabrication can be greatly simplified with the aid of a computation model. This article introduces an electronic design strategy dividing frontend and backend electronics for the resistance tomography-based tactile sensors. In this scheme, the frontend is made of the piezoresistive structure and electrodes that can be changed depending on the required geometry. The backend is the electronic circuit for resistance tomography, which can be used for various frontend geometries. To evaluate the use of a unified backend for different frontend geometries, two frontend specimens with a square shape and a circular shape are tested. The minimum detectable contact force and the minimum discernible contact distance are calculated as 0.83×10-4 N/mm 2, 2.51 mm for the square-shaped frontend and 1.19×10-4 N/mm 2, 3.42 mm for the circular-shaped frontend. The results indicated that the proposed electronic design strategy can be used to create tactile skins with different scales and geometries while keeping the same backend design.