Linköping Electronic Conference Proceedings
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Thomson’s Telegram Decrypting a Secret Message from Albania, 1914
Get PDFThe Netherlands carried out its first international peace mission to Albania, from November 1913 to September 1914. The goal of this mission was to provide this newly formed kingdom with a solid law enforcement agency. The Dutch officers that were sent to Albania would face a divided country, torn between the powers of the Ottoman Empire and the European powers of that day. The mission commander, Major Lodewijk Thomson, was killed in battle under circumstances that are still unclear today. An encrypted Albanian telegram that recently emerged from his file in the Dutch military archives might shed some light on this part of history that is still shrouded in mystery. This article describes the cryptanalysis of the telegram, consisting of a modified hillclimbing algorithm, followed by manual analysis. The recovered message is then put in historical perspective
Importing FMU-3.0: challenges in proper handling of clocks
Get PDFCompared to FMI-2.0, FMI-3.0 provides support for events and clocks. The behavior of the FMU in the presence of events and clocks introduces new challenges for importing FMUs in block diagram environments such as Altair Activate and Scicos. This paper discusses some of these challenges and proposes implementation strategies for supporting the import of FMI-3.0 in Activate
A Dymola-Python framework for data-driven model creation and co-simulation
Get PDFThe introduction of cyber-physical systems has been a recent development in energy systems. Cyber-physical systems contain digital components for applications such as monitoring or control. In many cases, modeling multiple aspects of such cyber-physical systems poses a challenge to conventional simulation tools. In addition, recent modeling approaches, such as data-driven modeling, are being applied. The combination of such data-driven models, which may consist of a different architecture than traditional models, with traditional models can be implemented through co-simulation methods. In co-simulation, components created from different simulation tools can be combined and coupled through standardized interfaces. This work presents a framework for data-driven model generation and co-simulation. The framework is implemented in Python and Dymola and is based on the Functional Mock-up Interface (FMI) standard. The framework implements the creation of data-driven models in Python, the generation of Functional Mock-up Units (FMUs) through the frameworks uniFMU and pythonFMU, as well the creation of a testbench model in Dymola and the co-simulation of this model. The framework is demonstrated on the application of a solar collector from a single family house heating system
Towards Continuous Simulation Credibility Assessment
Get PDFWith the growing demand for virtual-informed decision-making in the development process of many engineering domains, the evidence in simulation results and thus simulation credibility becomes a critical aspect, in particular for releasing safety-relevant systems. However, simulation credibility is often interpreted to be of subjective nature. This paper summarizes basic assumptions for enabling the expression of credibility for building evidence in a more objective way. Based on these considerations, a concept is proposed that allows for an approximation of the credibility of simulations according to a discrete scale. The work is concluded by providing an implementation concept for a continuous simulation credibility assessment using a layered standard on top of the System Structure & Parameterization specification
A Transformer for SAG: What Does it Grade?
Get PDFAutomatic short-answer grading aims to predict human grades for short free-text answers to test questions, in order to support or replace human grading. Despite active research, there is to date no wide-spread use of ASAG in real-world teaching. One reason is a lack of transparency of popular methods like Transformer-based deep neural networks, which means that students and teachers cannot know how much to trust automated grading. We probe one such model using the adversarial attack paradigm to better understand their reliance on syntactic and semantic information in the student answers, and their vulnerability to the (easily manipulated) answer length. We find that the model is, reassuringly, likely to reject answers with missing syntactic and semantic information, but that it picks up on the correlation between answer length and correctness in standard training. Thus, real-world applications have to safeguard against exploitation of answer length
Characterization of the Flow (Breakup) Regimes in a Twin-Fluid Atomizer based on Nozzle Vibrations and Multivariate Analysis
Get PDFIn the study, a new non-intrusive approach based on acoustic chemometrics, which includes vibration signal collection using glued-on accelerometers, was assessed for the classification of the different flow (breakup) regimes spanning a whole range of fluids (water and air) flow rates in this twin-fluid atomizer (one-analyte system). This study aims to determine the flow regimes based on the dimensionless number (B), whose unique values correspond to different flow (breakup) regimes. The principal component analysis (PCA) was employed to visually classify the breakup regimes through cluster formation using score plots. The model prediction performance was studied using PLS-R, RMSEP values show error ranges within acceptable limit when tested on independent data. The present acoustic study can serve as a good alternative to the imaging methods employed for flow classification
Energy Reduction in Lithium-Ion Battery Manufacturing using Heat Pumps and Heat Exchanger Networks
Get PDFGlobal electric mobility is rapidly expanding. Hence, the demand for lithium-ion batteries is also increasing fast. Therefore, understanding energy minimization options in this rapidly growing industry is crucial for reducing the environmental impact as well as developing low-cost and sustainable batteries. The biggest contribution to greenhouse gas emissions is the cell manufacturing process. The most energy-intensive steps of cell manufacturing are electrode drying and dry room conditioning. Therefore, we developed process models for these two systems that can be used for evaluating various energy optimization techniques, such as heat pumps and heat exchanger networks. Further, various process options can be tested and benchmarked in terms of their overall energy consumption using these models. The results show that the power requirement may be reduced through all the options assessed, and available energy efficiency measures may substantially lower the energy footprint of cell production with strong relevance for subsequent greenhouse gas footprints
Studying the Effect of Pyrolysis Gas Composition on the Gasification Syngas Composition using CPFD Simulation
Get PDFA CPFD model for biomass gasification in a bubbling fluidized bed was developed using the Barracuda Virtual Reactor 17.4.1 commercial CFD code. Three simulation cases were performed at varying the reactor temperature and pyrolysis gas compositions. The effect of the pyrolysis step was found to be significant, especially on the production of CO, H2, and CH4. This is mainly because that the pyrolysis step converts 85% of the biomass weight into volatiles. Comparing the simulation results with the experimental data showed a good agreement on predicting CH4 and H2, whereas CO2 was overestimated, and CO was underestimated. This might be due to inaccuracies in the pyrolysis gas composition or high rates in the water-gas-shift reaction used in the simulation. The effects of temperature on the synthesis gas composition were further investigated. Increasing the temperature from 800°C to 900°C, increased the concentration of CO and H2 by 2.4% and 1.6% respectively, while decreased the concentration of CO2 and CH4 by 1.3% and 0.5%, respectively. The trends of gas compositions showed a good agreement with other literature data, except the trend of CH4. This might be due to the neglect of tar composition in the volatiles
CPFD Simulations on a Chlorination Fluidized Bed Reactor for Aluminum Production: an Optimization Study
Get PDFEarly CPFD simulation studies on designing a fluidized bed reactor for alumina chlorination showed that the model suffers from high particle outflow and dense phase bed channeling. The present study is aimed to optimize the previous alumina chlorination fluidized bed reactor model through modified geometry, parameter modifications, and improved meshing. To optimize the performance of the reactor, complex geometry with an extended top section was combined with a regular cylindrical reactor. Besides, the gas inlet pattern was changed from an ideal uniform distribution to a non-uniform one. Besides, the reactor’s inlet diameter is reduced, and the value for the particle sphericity and voidage has been updated based on experimental observations. The results show that the new reactor with an extended cross-sectional area on top has a significantly lower particle outflow even with the higher inlet superficial gas velocity. The paper discusses the optimization steps and relevant changes in reactor performances in detail
CPFD Modeling to study the Hydrodynamics of an Industrial Fluidized Bed Reactor for Alumina Chlorination
Get PDFAluminum is one of the most used metals. Since aluminum has a unique combination of appealing properties and effects, it allows significant energy savings in many applications, such as vehicles and buildings. Although this energy-saving leads to lower CO2 emissions, the production process of aluminum still dramatically impacts the environment. The process used exclusively in the aluminum industry is the Hall-Héroult process with a considerable carbon footprint and high energy consumption. As the best alternative, Alcoa's approach (which is not industrialized yet) is based on the chlorination of processed aluminum oxide, reducing the traditional method's negative impacts. Further to Alcoa’s effort, this study aims to investigate the possibility of a new low-carbon aluminum production process. This aim can be achieved by designing an industrial fluidized bed reactor with an external (due to high corrosion inside the reactor) gas-solid separation unit. The aim is to handle 0.6 kg/s of solid reactants and produce aluminum chloride as the main product. The research focuses on determining the best bed height based on the available reaction rates, choosing the best reactor dimension to reduce particle outflow under isothermal conditions (700°C). Autodesk Inventor® and Barracuda® are used for 3D modeling of the reactor and CFD simulation for multiphase (solid-gas) reactions, respectively. Although results have shown that the bed aspect ratio (H/D; H- bed Height and D- bed Diameter) does not affect the reaction, it highly affects the reactor’s hydrodynamics and particle outflow. The final design shows the best hydrodynamics belongs to bed aspect ratio equal to 2