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Yaw misalignment in powertrain degradation modeling for wind farm control in curtailed conditions
No full textA framework characterizing the degradation of wind turbines for use in multiple-input damage-aware farm control is suggested. The focus is on the fatigue damage of the powertrain (drivetrain + generator) system, but the methodology may be extended to other components. A database of steady-state damage analyses for different operating conditions (average wind speeds, turbulence levels, power demands, and yaw misalignment angles) using aero-hydro-servo-elastic simulations is first generated. Then, a weighted damage index based on probabilistic long-term fatigue damage analysis of the powertrain system components is suggested and used to represent degradation at the farm level for control purposes. The focus is on curtailed conditions where the farm controller dispatches power commands to individual turbines in order to track a demanded power reference (rather than seeking to maximize power) at the farm level. As a secondary objective, the controller seeks to mitigate degradation through a smart combination of power commands and yaw offset angles, making use of the weighted degradation index. The potential of the proposed approach is demonstrated through a case study on the TotalControl Reference Wind Power Plant in a FLORIS-based simulation framework. The proposed farm controller is compared with the conventional one without damage mitigation feature and with damage mitigation but without yaw angle as the control input. It is found that combining yawing and downregulation effectively slows down degradation on the main bearing and powertrain as a whole.Yaw misalignment in powertrain degradation modeling for wind farm control in curtailed conditionspublishedVersio
Adapting to climate change: snow load assessment of snow galleries on the Iron Ore Line in Northern Sweden
Get PDFThe snow galleries along the Iron Ore railway line in Northern Sweden have faced problems in recent years due to increasingly large snow loads, and several galleries have been damaged. These incidents motivated an evaluation of the maximum load supported by the galleries before collapse, which is presented in this study. In 2021, a monitoring system was installed in one of the main frames of two snow galleries built in the 1950s to follow up with temperature and displacements, including a trigger that sends out a warning message when a critical load is reached. A literature review on snow loads was performed, followed by calculations on snow distribution on the galleries based on the Eurocodes and National Swedish Standards. Finite element 2D and 3D models were created using AxisVM to accurately assess the efforts in the structural elements. Analysis and discussion are complemented by observations from site visits. It was concluded that the critical loads supported by the galleries are lower than the requirements of today’s standards, but since secondary construction elements were damaged before the main frames reached their full capacity, no major collapse has yet taken place. The cobweb effect (load re-distribution between the neighboring elements in a 3D structure) influenced the behavior of the galleries in the 3D analysis and the capacity of the main frames proved to be significantly increased compared to the 2D assessment.publishedVersio
On the inaccuracies of point-particle approach for char conversion modeling
Get PDFChar conversion is a complex phenomenon that involves not only heterogeneous reactions but also external and internal heat and mass transfer. Reactor-scale simulations often use a point-particle approach (PP approach) as sub-models for char conversion because of its low computational cost. Despite a number of simplifications involved in the PP approach, there are very few studies that systematically investigate the inaccuracies of the PP approach. This study aims to compare and identify when and why the PP approach deviates from resolved-particle simulations (RP approach). Simulations have been carried out for CO2 gasification of a char particle under zone II conditions (i.e., pore diffusion control) using both PP and RP approaches. Results showed significant deviations between the two approaches for the effectiveness factor, gas compositions, particle temperature, and particle diameter. The most significant sources of inaccuracies in the PP approach are negligence of the non-uniform temperature inside the particle and the inability to accurately model external heat transfer. Under the conditions with low effectiveness factors, the errors of intra-particle processes were dominant while the errors of external processes became dominant when effectiveness factors were close to unity. Because it assumes uniform internal temperature, the models applying the PP approach always predict higher effectiveness factors than the RP approach, despite its accurate estimation of intra-particle mass diffusion effects. As a consequence, the PP approach failed to predict the particle size changes accurately. Meanwhile, no conventional term for external heat transfer could explain the inaccuracy, indicating the importance of other sources of errors such as 2D/3D asymmetry or penetration of external flows inside the particles. © 2024 The Author(s) Author keywords Char gasification; Particle-resolved simulation; Point-particle method; Stefan flowOn the inaccuracies of point-particle approach for char conversion modelingpublishedVersio
Customer journeys and process mining – challenges and opportunities
Get PDFRecently, there has been increased awareness about the importance of data derived from actual customer journeys, including the subjective customer experience, in the analysis and evaluation of service quality. In this paper, we explore how customer journey analysis and process mining can be combined to advance the analysis and improvement of services. First, we demonstrate the strengths and weaknesses of both methodologies using a specific case study as an illustrative example. Subsequently, we delve into the synergies and challenges inherent in their combination, deriving practical guidelines. We then suggest avenues for further research questions in this cross-disciplinary approach. The paper underscores the potential of aligning these methodologies to provide a more accurate and complete understanding of service delivery, ultimately contributing to the enhancement of customer experience.publishedVersio
Quantifying the short-term asymmetric effects of renewable energy on the electricity merit-order curve
Get PDFAmidst the growing significance of renewable energy, this paper examines the asymmetric effects of renewable energy on electricity prices and transmission flows in the Nordics using hourly electricity data. Employing a novel panel asymmetric fixed-effects method, we quantify the non-linear impact of renewable generation technologies on the electricity supply curve. Contrary to previous research, our analysis challenges the assumption of wind having symmetric effects in electricity markets. Specifically, we suggest that an increase in renewable energy cannot lead to price reductions of the same magnitude as the price increases caused by a decrease in wind. In addition, we investigate interconnections between regions and explore asymmetries in transmission flows due to wind generation. Our findings reveal the presence of asymmetric effects in the Nordic electricity market, highlighting their significance in achieving a secure electricity system. These results offer valuable insights for governments, policymakers, and market participants for optimizing the electricity generation mix, prioritizing flexible systems, and making informed investment decisions. © 2024 The Author(s)Quantifying the short-term asymmetric effects of renewable energy on the electricity merit-order curvepublishedVersio
Transitioning e-commerce: Perceived pathways for the Norwegian urban freight sector
Get PDFE-commerce is becoming an increasingly visible feature of modern society that places increasing strain on transport systems. Research has hitherto paid substantial attention to ways in which e-commerce might modify personal travel behaviour but has been less attentive to the ramifications of e-commerce for urban freight. Although contemporary conditions of urban freight are increasingly scrutinised by scholars in several disciplines, this study peeks into the future of urban freight from the scholarly perspective of sustainability transitions. Specifically, we investigate what expectations Norwegian freight providers hold for the transition pathways of their own sector. We find that the Norwegian urban freight sector expects technological shifts to be most prominent, pointing to the replacement of vans and lorries with low-emission models. Conversely, although deemed important enough, the urban freight sector orients less towards behavioural shifts that enhance efficiencies within and across freight providers. To ensure more transformative effects in the transition pathways of urban freight, we thus advise decision-makers in urban planning to establish inclusive approaches to policy making that enhance the legitimacy of technological and behavioural shifts in urban freight alike.publishedVersio
Navigational support framework for maritime autonomous surface ships under onshore operation centers
Get PDFTo navigate, Maritime Autonomous Surface Ships (MASSs) must be able to determine their states. i.e., the positions and velocities, etc., by utilizing onboard IoT, and ship intelligence systems. Autonomous ship navigation can heavily rely on machine learning algorithms that can predict how vessels will maneuver in the future, based on past behavior, where vessel state estimation can play a main role. Due to multiple factors such as system failures, bad weather situations, local geographical conditions, and lack of system robustness, sometimes intelligent ship navigation systems may degrade the performance, i.e., may fail to respond or fail to find the safest route. To ensure safe and optimum operations in a selected sea area, MASSs need the necessary supporting tools for safe navigation. In this study, a navigational support framework of navigation monitoring, guidance, and control for MASS is presented in the aspects of Onshore Operation Centers (OOCs), including their respective challenges and possible solutions.acceptedVersio
Automated measurement method for assessing thermal-dependent electronic characteristics of thin boron-doped diamond-graphene nanowall structures
Get PDFThis paper investigates the electrical properties of boron-doped diamond-graphene (B:DG) nanostructures, focusing on their semiconductor characteristics. These nanostructures are synthesized on fused silica glass and Si wafer substrates to compare their behaviour on different surfaces. A specialized measurement system, incorporating Python-automated code, was developed for an in-depth analysis of electronic properties under various contact configurations. This approach allowed for a detailed exploration of charge transport mechanisms within the nanostructures. The research highlights a decrease in resistivity with increased deposition time, as shown by Arrhenius plot analysis. This trend is linked to the formation and evolution of multi-wall graphene structures. SEM images showed nanowall structures formed more readily on amorphous fused silica substrates, enabling unrestricted growth. TOF-SIMS analysis revealed uneven boron atom distribution through the film depth. A significant finding is a reduction in conductive activation energy in samples grown in microwave plasma from 197 meV to 87 meV as deposition time increased from 5 to 25 min. Furthermore, the study identifies a shift in transport mechanisms from variable range hopping (VRH) below 170 K to thermally activated (TA) conduction above 200 K. These insights advance our understanding of the electronic behaviours in B:DG nanostructures and underscore their potential in electronic device engineering, opening new paths for future research and technological developments.publishedVersio
Predictive Heating Control and Perceived Thermal Comfort in a Norwegian Office Building
Get PDFAn office building in Trondheim, Norway, was used as a case study to test the influence of Predictive Control (PC) for the optimization of energy use on the employees’ thermal comfort. A predictive control was implemented in the Building Energy Management System (BEMS) by operating on the supply temperature of the radiator circuit. A questionnaire was given to the employees to evaluate to what extent the operation of the predictive control influenced their perceived thermal comfort. Several factors known to influence employees’ satisfaction (such as office type, perceived noise level, level of control, perceived luminous environment, perceived indoor air quality, adaptation strategies, well-being) were investigated in the questionnaire. The evaluation shows that the occupants rated the perceived thermal comfort as equally good compared to the business-as-usual operation. This is an important finding toward the user acceptance of such predictive control schemes.publishedVersio