Senast publicerade

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  • Post
    Phase-field modelling of fatigue crack propagation
    (2023) Degwekar, Sharvil; Purantagi, Ankeet Mohan; Tzanetou, Afroditi; Zetterlund, Gustav; Åkesson, Louise; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Johansson, Håkan; Larsson, Fredrik; Bharali, Ritukesh; Nezhad., Mohammad Salahi
    Fracture prediction and modeling are crucial in studying the behavior of materials under stress. This research focuses on utilizing the phase field method for accurate fracture prediction, which offers distinct advantages over traditional methods by representing fractures implicitly as smooth fields. The phase field method was implemented and analyzed using Matlab and COMSOL as tools, aiming to investigate and gain insights into the ease and feasibility of phase-field modelling for fatigue fracture problems. This was conducted mainly by introducing a fatigue degradation function, with the purpose of simulating the degrading process of the material after repeated cyclic loading. Through comprehensive analysis, quantities of interest such as the history variable, accumulated strain energy, and damage variable were examined. The obtained trends and results were found to align with existing literature, although neither calibration nor validation was conducted due to time limitations. Suggestions for future work include implementing a force-controlled load, calibration of the fatigue degradation function for a larger amount of load cycles, and validation with experimental data. Nevertheless, the results obtained from the fatigue implementation can provide a solid foundation for continued research. In conclusion, the progress during the project highlighted the potential of the phase-field model to predict fatigue fracture by modelling the crack through a damage field. Hence, fatigue prediction using phase-field modelling has the potential to make significant progress and thus contribute to less computationally expensive simulations for more complex fatigue fracture problems.
  • Post
    Project in railway technology: Damage from electric discharge in axle bearings on trains
    (2023) Möslinger, Tobias; Ali, Aboobakkar Nakeeb; Thomson, Oskar; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Chalmers University of Technology / Department of Mechanics and Maritime Sciences; Ekberg, Anders; Ekberg, Anders
    A summary of known information on damage in bearings due to electrical currents, with a special focus on railway applications is provided. The process of inspection of a possibly damaged bearing is described. Results are compiled, also providing some suggestions on handling the damage. Finally, all results are connected with each other. Some proposals for solutions of the current problem are given and some points of interest for further research are highlighted.
  • Post
    Handling increased need of maintenance to meet future freight demands: Deterioration and effective maintenance strategies for track system and rail vehicles
    (2022) Mattsson, Klara; Lee, Jaseung; Ligmajer, Oskar; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Kabo, Elena; Ekberg, Anders
    This report addresses future increased demands of freight on the Swedish railways. To achieve an increase in total freight, different forms of operations can be utilized like increasing the axle load, speed, or frequency which are all scenarios that will be evaluated in the report. The impact caused by those measures will affect both deterioration and the need for efficient maintenance regarding rail vehicles and track systems. Different methods of maintenance, both currently used and newly developed methods are discussed in this report to be able to evaluate how it is possible to become more efficient. The deterioration that occurs during the operation of freight trains is described in the report since an understanding is needed to address the problems and possible solutions. What also plays a vital role in the maintenance plan is to detect faults efficiently. To get an idea about how all of these issues are handled in the industry, interviews have been held with professional staff at four large companies in Sweden. Together with literature studies, this forms the foundation of this report.
  • Post
    Increasing freight transport capacity
    (2022) Carlsson, Johan; Edberg, Marcus; Gullberg, Viktor; Nieswand, Niklas; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Kabo, Elena; Ekberg, Anders
    The main objective of this report is to investigate how freight train capacity can be increased to enable transportation related to carbon capture and storage (CCS) on the Swedish railway system in order to achieve the carbon dioxide climate target. The increased need for sustainable transport will create a large demand on the existing railway network. To meet these demands, several measures need to be taken. To investigate this further, literature study, interviews, a case study and analysis of the current network were conducted. As the railway network is a complex system, a range of measures is suggested to counter a high capacity utilization within both shorter and longer time frames. In the report several line segments limiting the system capacity were identified. Several measures were suggested with regards to both railway infrastructure and train set-up. It is concluded that additional investments have to be made to handle ccs transportation.
  • Post
    Flow uniformity characterization in catalytic converters under turbulent inlet conditions
    (2022) Tylén, Oskar; Larsson, Jacob; Murali, Aravind; Rangaswamy, Sunil; Peyvandi, Ehsan; Larsson, Axel; Chalmers tekniska högskola // Institutionen för mekanik och maritima vetenskaper; Johansson, Håkan; Ström, Henrik; Sjöblom, Jonas; Nagarajan, Pratheeba Chanda
    In the sectors utilizing the combustion of fossil fuels, catalytic converters are commonly employed to reduce dangerous gases generated by combustion engines. For greater efficiency, it is critical to understand the exhaust flow homogeneity inside the converter. This work attempts to evaluate the added value of using Detached Eddy Simulation (DES) simulation over Reynolds-Averaged Navier-Stokes (RANS) simulation for analysis of turbulent flow inside catalytic converters. The meshing and simulation of the domain was carried out using ANSYS FLUENT and ANSYS Workbench. Initially a RANS simulation with k-ω SST turbulence model was carried out for a specific case to understand the behavior of the time averaged flow field with modeled turbulence and its effect on uniformity index. The results from the RANS simulation were, together with definitions of turbulent length scales, used to develop a mesh for DES simulation. In this process it was found that in order to resolve a sufficient amount of turbulence upstream of the monolith inlet, the DES simulation required a considerably finer grid than the RANS simulation. The DES simulation with k-ω SST model was used to simulate multiple retention times, attempting to achieve a quasi steady flow with resolved velocity fluctuations. However due to constraints on computational power, simulating until statistical convergence was not possible. The time averaged quantities were extracted from the DES simulation in order to make a fair comparison with RANS results. The uniformity indices of RANS and DES were then compared throughout the monolith of the catalytic converter. A difference of ∼1-1.5% in uniformity index was found from this comparison. Further more it was found that the resolved turbulence in the DES generates fluctuations of ∼3-6% in the uniformity index based on instantaneous quantities. The work concludes that for the exact case simulated, the possibility of increased accuracy when predicting uniformity index with DES instead of RANS does not outweigh the increased computational cost. However for different flow conditions, with larger mean velocity magnitude and less uniform flow, the measured difference between RANS and DES could make a larger difference for prediction of catalytic conversion efficiency. Hence in these cases it is possible that DES simulations are worth their computational cost. Whether this is the case or not would have to be examined through further research before coming to any definitive conclusions.