Linköping Electronic Conference Proceedings
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Development of a simulation tool for design and off-design performance assessment of offshore combined heat and power cycles
Get PDFAmbitious targets for reducing carbon dioxide (CO2) emissions are set by Norwegian authorities to address the concerns about global warming. Emission reductions in the offshore heat and power sector can play a role in reaching these targets. Parts of the efforts in industry and academia to reduce offshore emissions are concerned with introducing new design configurations or proposing novel operational strategies for the combined heat and power cycles. Therefore, there is a desire to have a fast and reliable design and assessment tool to be used in the early design stage. Here, a generalized design and performance simulation tool is developed presenting a design point and off-design simulation of the offshore heat and power cycles. It helps the designer provide a fast and accurate thermodynamic assessment of proposed design solutions. The tool has a graphical user interface to facilitate working with the tool with a minimum level of effort and background knowledge from the user. Five part-load control strategies are included in the tool. The tool is verified with available data in the open literature and the results are shown to be in good agreement with the reference data. A combined heat and power cycle is designed and simulated at part-loads as a case study. The cycle includes a gas turbine, a process heat extraction unit, and an organic Rankine bottoming cycle. The simulated performance of the design case in various control strategies is compared showing a 2.5% emission reduction relative to the baseline control strategy
A Ray Tracer for optimizing solar concentrating systems: The case of discretized Compound Parabolic Concentrator
Get PDFConcentrating solar systems use reflective surfaces to concentrate sunlight onto a small area, where it is absorbed and converted to heat. Many classes of concentrating collectors such as Compound Parabolic Concentrators (CPCs), parabolic dish and parabolic trough are available, each with different concentrating ratio and maximum absorber temperature, depending on the type of applications. A simplified 3D Compound Parabolic Concentrator (CPC) with 2 rings and 4 sectors has been designed. The designed CPC is cost effective as it requires only 8 mirrors to cover the reflector surface. It does not require sun tracking, but have capability to accept incoming solar radiation over a relatively wide range of angles. For further capturing of the solar radiations, tilting of the CPC during a day can be made a few times. This study aims to model the discretized 3D CPC using the ray tracing, to optimize the CPC for achieving optimal interceptions on a 0.2 m diameter cylindrical absorber, placed inside the CPC. The ray tracing methodology is presented together with the results of the interceptions on the cylindrical absorber using the discretized CPC. Results show the effect of tilting the discretized CPC is not very strong as the interception values are slightly reduced and the curves a little bit not symmetric around the normal sun angles
Experimental PDE solver in Julia – comparison of flux limiting schemes
Get PDFFinite Volume Methods (FVM) are high quality methods for solving conservative/hyperbolic partial differential equations (PDEs). A popular class of high-resolution methods utilize a nonlinear combination of low order methods and high order methods via flux limiting functions. Another class of high-resolution methods is the class of weighted essentially non-oscillatory (WENO) schemes. Here, the focus is on flux limiting schemes. An experimental finite volume (FV) semi-discrete solver for systems of hyperbolic PDEs has been implemented in Julia, utilizing Julia’s DifferentialEquations.jl package for handling the time marching. A first order upwind formulation is used for the low order method, and a central second order formulation is used for the high order method. The PDE can be provided either in flux form, or in quasi-linear form. In the former case, automatic differentiation (AD) package ForwardDiff.jl is used to compute the Jacobians of the flux vector. Package LinearAlgebra.jl is used to compute the eigenspace of the Jacobians. The implementation allows for up to 3 internal/external coordinates. More than a dozen flux limiting functions are given, with the possibility of the users to write their own flux limiters. The implementation allows for user provided spatial discretization points, and source terms in the PDE. In this paper, we will compare various flux limiting schemes for PDEs with analytic solutions, and will also compare flux limiting schemes for a simple granulation model (layering). Possible extensions of the experimental implementation include: (i) higher order methods, (ii) more extensive support for boundary conditions, (iii) improved support for source terms
Optimal operation of grid-connected hydropower plants through voltage control methods
Get PDFThe ongoing decarbonization, and the rapid increase in renewable penetration in the electric grid, will demand enhanced flexible operational schemes of the conventional hydropower plants. This paper explores a grid-connected hydropower plant’s best-efficiency operating conditions when meeting the renewable energy transition. Power loss models combined with various voltage control methods are investigated for achieving optimal operation. This simulation study is carried out on a static F13Single Machine Infinite Bus (SMIB) environment to perform voltage control comparisons. Simulations show that the plant and grid power loss models can be utilized in an optimal controller setting to increase the accumulated average efficiency (AAE). However, optimal controllers had slow prediction times, and therefore a Reinforcement Learning (RL) method, A2C, has been trained to learn an optimal control policy that maximizes system efficiency. The RL agent supersedes the optimal control techniques with up to 40 times faster prediction times
LSTM-based PSS Design for Modern Power Systems
Get PDFWith the ever-increasing incorporation of wind and solar power in the electric power system, enhanced performance of classical bulk hydropower plants for robust operation of the power system is required. This current energy transition may cause a rapid increase in undesirable low-frequency oscillations (LFOs) in modern power system operations. A power system stabilizer (PSS) located at hydropower plants is one solution to damp such oscillations. This paper presents a new method based on Long Short-Term Memory (LSTM) neural networks for sine-wave phase shifting to possibly enhance PSS damping. The proposed controller considers the PSS input and the rotor speed deviation as a damped sinusoidal signal, simplifying PSS control and real-time optimization of PSSs parameters. Results show that the proposed LSTM architecture is able to learn multiple damped sine waves with different frequencies and decay rates. Therefore, the proposed controller can operate on the entire range of LFOs, unlike simple feedforward neural network (FNN) controllers, which can only learn and function on a single LFO frequency
Unsteady flow analysis of hinged and sliding door openings
Get PDFExisting thermal condition and indoor air quality have a big impact on our work performance, comfort, and health in an indoor environment. Apart from many other parameters, door motions and human movements play crucial role in mass and thermal exchange affecting safety and/or energy management issues in various situations. An isolation room in a hospital setup, for instance, helps to protect patients and staff against the risk of infection by airborne pathogens. Another example is cold storage room facilities, where temperature and moisture control are the key parameters for an optimal operation and energy usage. In this study, we present a transient flow analysis of door motions in indoor environment. The flow physics is resolved by solving 3D compressible RANS (Reynolds-averaged Navier-Stokes) equations together with the energy and species transport equations and two-equation turbulence models utilizing an overset mesh strategy to address the rigid body motion of doors in a relevant fluid domain involving air and sulfur hexafluoride (SF6). Simulations are performed for three different types of doors, namely a hinged door, a two-way sliding door, and a sliding door considering door opening and closing phases. Transient flow-field data through the door opening area have been processed and a comparative analysis is performed considering the mass flux of the constituents, normal velocity, cumulative mass exchange through the different doors
Digital Monitoring of Antibiotic Resistance (ABR) in Low- and Middle-Income Countries: A Narrative Literature Review
Get PDFThe objective of this narrative review is to provide an overview of the knowledge and gaps in the existing research on digital Antibiotic resistance (ABR) monitoring in Low- and middle-income countries (LMICs). ABR presents a complex threat to global health. One of the key global priorities is to address this challenge through effective monitoring. An analysis of the literature revealed the missing role of IS (Information systems) research in digital ABR monitoring. A thematic analysis of the identified literature on digital interventions for ABR revealed several gaps. This research contributes by providing potential research directions and identifying the role of IS research in ABR
Social media, physical activity and autism: better or bitter together? A scoping review
Get PDFThis review provides an overview of the existing research on social media, autism, and physical activity. We searched for publications on PubMed, PsycInfo, Embase, Education source, ERIC, IEEE Xplore, and the proceedings from conferences on health informatics and autism. Eight studies were included in this review. Studies reported mixed results on the link between social media, physical activity, and autism. Technology usage is related to sedentary time. However, physical activity interventions delivered through social media provide several benefits. Further research with stronger designs is needed to increase the knowledge of the role of social media on physical activity and autism
Who are the “Hard-to-Reach” groups in chronic-health and health technology research? – A scoping review
Get PDFMany in health and technology research opt to focus on those who are already “engaged”, not those who are considered “hard-to-reach” or “unreached”. This exacerbates the digital divide and inequity in healthcare. We report findings of a scoping review of literature in PubMed/Medline from 2000-2022. 90 of 795 articles were identified based upon 1) the health researchers’ recruitment of unreached groups with a chronic condition for active participation in a study and 2) clear definitions of who they considered to be unreached. Findings support the need for interdisciplinary and community-level involvement to reach and include unreached groups in health studies
Where not to lose the puck
Get PDFIn a fast-paced free-flow game as Ice Hockey the decision making of the players is crucial for the success of the team. A game in the Swedish Hockey League (SHL) has on average 244 possession changes where both teams play at full strength. Previous studies have shown that the most effective way to create scoring chances is by exiting and entering zones with the puck under control. On the contrary, this paper studies the question of risk and reward of different plays. Based on an extensive data-driven investigation of three full SHL seasons, the conclusion is that the best way not to concede goals is also by doing the transition plays with control. Specifically, a failed dump-out is 57% more likely to end up in the opponents scoring a goal than a failed outlet pass