arXiv subjects

Holger Class

Publications and source records attributed to Holger Class.

8 recordsLinked to original sources

arXiv2026

A Flexible Raspberry Pi-Based Data Logger Platform for Modbus Sensors with Ansible Deployment

This article presents LibrePiLogger, an open-source data logging platform based on the Raspberry Pi for environmental monitoring using Modbus sensors over RS-485. The system combines the AtmosPyre Python library for sensor communication with Ansible-based deployment automation, allowing researchers to deploy sensor networks by editing a single YAML inventory file. Two hardware configurations are described: a minimal setup using a Raspberry Pi Zero with an RS-485 HAT, and a maximal setup using a Raspberry Pi 4 with a USB-to-RS-485 converter. Currently implemented sensors include the Vaisala GMP252 for CO$_2$ and the RadonTech AlphaTRACER for $^{222}$Rn, with new sensors requiring approximately 100 lines of Python following a provided driver template. Data is logged to timestamped CSV files with JSON metadata. The system has been deployed for continuous CO$_2$ and $^{222}$Rn monitoring in a karst environment since spring 2025 and remains in active operation, demonstrating reliable long-term performance. All hardware designs, software, and deployment scripts are released under the GNU General Public License v3.0. Total hardware costs range from 54 to 63EUR (excluding housing), depending on the configuration.

cs.CE↗

arXiv2025

Benchmarking CO$_2$ Storage Simulations: Results from the 11th Society of Petroleum Engineers Comparative Solution Project

The 11th Society of Petroleum Engineers Comparative Solution Project (shortened SPE11 herein) benchmarked simulation tools for geological carbon dioxide (CO$_2$) storage. A total of 45 groups from leading research institutions and industry across the globe signed up to participate, with 18 ultimately contributing valid results that were included in the comparative study reported here. This paper summarizes the SPE11. A comprehensive introduction and qualitative discussion of the submitted data are provided, together with an overview of online resources for accessing the full depth of data. A global metric for analyzing the relative distance between submissions is proposed and used to conduct a quantitative analysis of the submissions. This analysis attempts to statistically resolve the key aspects influencing the variability between submissions. The study shows that the major qualitative variation between the submitted results is related to thermal effects, dissolution-driven convective mixing, and resolution of facies discontinuities. Moreover, a strong dependence on grid resolution is observed across all three versions of the SPE11. However, our quantitative analysis suggests that the observed variations are predominantly influenced by factors not documented in the technical responses provided by the participants. We therefore identify that unreported variations due to human choices within the process of setting up, conducting, and reporting on the simulations underlying each SPE11 submission are at least as impactful as the computational choices reported.

physics.geo-ph↗

arXiv2025

A hydro-geomechanical porous-media model to study effects of engineered carbonate precipitation in faults

Hydro-geomechanical models are required to predict or understand the impact of subsurface engineering applications as, for example, in gas storage in geological formations. This study puts a focus on engineered carbonate precipitation through biomineralization in a fault zone of a cap-rock to reduce gas leakage from a reservoir. Besides hydraulic properties like porosity and permeability, precipitated carbonates also change the mechanical properties of the rock. We present a conceptual modeling approach implemented into the open-source simulator Dumux and, after verification examples, at hand of a CO2-storage scenario, we discuss impacts of biomineralization on the stress distribution in the rock and potentially altered risks of fault reactivations and induced seismic events. The generic study shows the tendency towards increased stiffness due to precipitated carbonate, which may cause shear failure events to occur earlier than in an untreated setup, while the magnitude of the seismicity is smaller.

cs.CE↗

arXiv2025

Intermittent flow paths in biofilms grown in a microfluidic channel

Biofilms exposed to flow experience shear stress, which leads to a competitive interaction between the growth and development of a biofilm and shearing. In this study, Pseudonomas fluorescene biofilm was grown in a microfluidic channel and exposed to forced flow of an aqueous solution of variable velocity. It can be observed that under certain conditions preferential flow paths form with a dynamic, but quasi-steady state interaction of growth, detachment, and re-attachment. We find that the regimes for preferential flow path development are determined by nutrient availability and the ratio of shear stress versus the biofilm's ability to resist shear forces. The intermittent regime of flow paths is mainly driven by the supply with nutrients, which we confirm by comparison with a numerical model based on coarse-grained molecular dynamics and Lattice Boltzmann hydrodynamics.

physics.flu-dyn↗

arXiv2025

Numerical Investigation of Preferential Flow Paths in Enzymatically Induced Calcite Precipitation supported by Bayesian Model Analysis

The usability of enzymatically induced calcium carbonate precipitation (EICP) as a method for altering porous-media properties, soil stabilization, or biocementation depends on our ability to predict the spatial distribution of the precipitated calcium carbonate in porous media. While current REV-scale models are able to reproduce the main features of laboratory experiments, they neglect effects like the formation of preferential flow paths and the appearance of multiple polymorphs of calcium carbonate with differing properties. We show that extending an existing EICP model by the conceptual assumption of a mobile precipitate, amorphous calcium carbonate (ACC), allows for the formation of preferential flow paths when the initial porosity is heterogeneous. We apply sensitivity analysis and Bayesian inference to gain an understanding of the influence of characteristic parameters of ACC that are uncertain or unknown and compare two variations of the model based on different formulations of the ACC detachment term to analyse the plausibility of our hypothesis. An arbitrary Polynomial Chaos (aPC) surrogate model is trained based on the full model and used to reduce the computational cost of this study.

physics.comp-ph↗

arXiv2025

Implementation Pitfalls for Carbonate Mineral Dissolution -- a Technical Note

In systems with slow reaction kinetics, such as mineral dissolution processes, chemical equilibrium cannot be assumed and an accurate understanding of reaction rates is essential; discrepancies in parameter reporting can greatly affect simulation results. This technical note identifies an issue with the reporting of rate parameters for carbonate mineral dissolution in a widely used database for reactive transport modeling based on Palandri and Kharaka 2004. This misrepresentation leads to a considerable overestimation of reaction timescales. Using the simulators Reaktoro and DuMuX, we simulated a simple calcite dissolution batch test and compared the results to experimental data. By adjusting the parameter to align with established literature, we demonstrate an improved fit between simulated and experimental data. Discrepancies in reaction timescales were reduced by an order of magnitude, emphasizing the importance of regular validation of simulations with experimental data.

cs.CE↗

arXiv2023

The FluidFlower International Benchmark Study: Process, Modeling Results, and Comparison to Experimental Data

Successful deployment of geological carbon storage (GCS) requires an extensive use of reservoir simulators for screening, ranking and optimization of storage sites. However, the time scales of GCS are such that no sufficient long-term data is available yet to validate the simulators against. As a consequence, there is currently no solid basis for assessing the quality with which the dynamics of large-scale GCS operations can be forecasted. To meet this knowledge gap, we have conducted a major GCS validation benchmark study. To achieve reasonable time scales, a laboratory-size geological storage formation was constructed (the "FluidFlower"), forming the basis for both the experimental and computational work. A validation experiment consisting of repeated GCS operations was conducted in the FluidFlower, providing what we define as the true physical dynamics for this system. Nine different research groups from around the world provided forecasts, both individually and collaboratively, based on a detailed physical and petrophysical characterization of the FluidFlower sands. The major contribution of this paper is a report and discussion of the results of the validation benchmark study, complemented by a description of the benchmarking process and the participating computational models. The forecasts from the participating groups are compared to each other and to the experimental data by means of various indicative qualitative and quantitative measures. By this, we provide a detailed assessment of the capabilities of reservoir simulators and their users to capture both the injection and post-injection dynamics of the GCS operations.

physics.geo-ph↗

arXiv2019

DuMu$^\text{x}$ 3 -- an open-source simulator for solving flow and transport problems in porous media with a focus on model coupling

We present version 3 of the open-source simulator for flow and transport processes in porous media DuMu$^\text{x}$. DuMu$^\text{x}$ is based on the modular C++ framework Dune (Distributed and Unified Numerics Environment) and is developed as a research code with a focus on modularity and reusability. We describe recent efforts in improving the transparency and efficiency of the development process and community-building, as well as efforts towards quality assurance and reproducible research. In addition to a major redesign of many simulation components in order to facilitate setting up complex simulations in DuMu$^\text{x}$, version 3 introduces a more consistent abstraction of finite volume schemes. Finally, the new framework for multi-domain simulations is described, and three numerical examples demonstrate its flexibility.

cs.CE↗