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An Alternative to Determine IM Parameters Trends Affected by Magnetic Saturation Using Two-Stage Flux-Decay Test by FEM
No full textIn this work, a two-stage flux-decay test is conducted to determine not only the induction machine parameters for a single current level but also their dependence on the current level. The goal of this work is to find an alternative parameter determination to the conventional method, which has several drawbacks when applied to variable speed applications. First, the theory of the T-form model (TFM) and flux-decay test are reviewed. Second, a new alternative determination method for identifying these parameters is presented. Third, a 2D electromagnetic finite element method (FEM) model of a vehicle traction induction machine (IM) is implemented to show the viability of the proposed method in a real design. Lastly, a comparison of results using the conventional method and analyzed the proposed method is presented, showing a good agreement
TOWARDS ADAPTABILITY AND CIRCULARITY OF TIMBER BUILDINGS
No full textThe construction industry has been a major contributor to resource consumption and global greenhouse gas (GHG) emissions, owed to high demand for building construction and the rapid urbanization trend. Timber construction has gained traction globally due to environmental advantages, such as renewability and carbon sequestration. However, sustainably available wood resources are limited. Extension of service life of timber structures is key to prolong their carbon stock. This paper showcases research projects carried out in Australia and Sweden that aim to design adaptable timber buildings capable of accommodating functional and spatial changes over time, thereby extending the service life of buildings and their components, as well as optimising their life cycles through spatial variations and repair of local damages to structural elements. This approach, known as Design for Adaptation (DfA) is an important step of the roadmap towards circular design solutions for timber buildings, which provide many economic, social and environmental benefits to all stakeholders and key players related to the building process, including manufacturers, engineers, architects, end-users, municipalities, and others
Turbulent burning velocity and thermodiffusive instability of premixed flames
No full textReported in the paper are results of unsteady three-dimensional direct numerical simulations of laminar and turbulent, lean hydrogen-air, complex-chemistry flames propagating\ua0in forced turbulence in a box. To explore the eventual influence of thermodiffusive instability of laminar flames on turbulent burning velocity, (i) a critical length scale that bounds regimes of unstable and stable laminar combustion is numerically determined by gradually decreasing the width of computational domain until a stable laminar flame is obtained and (ii) simulations of turbulent flames are performed by varying the width from \Lambda<\Lambda_{n} (in this case, the instability is suppressed) to \Lambda>\Lambda_{n} (in this case, the instability may grow). Moreover, simulations are performed either using mixture-averaged transport properties (low Lewis number flames) or setting diffusivities of all species equal to heat diffusivity of the mixture (equidiffusive flames), with all other things being equal. Obtained results show a significant increase in turbulent burning velocity when the boundary is crossed in weak turbulence, but almost equal values of are computed at \Lambda<\Lambda_{n} and \Lambda>\Lambda_{n} in moderately turbulent flames characterized by Karlovitz number equal to 3.4 or larger. These results imply that thermo-diffusive instability of laminar premixed flames substantially affects burning velocity in weak turbulence only, in line with a simple criterion proposed by Chomiak and Lipatnikov (Phys. Rev. E 107, 015102, 2023)
Assessment of Experimental, Computational, and Combined EFD/CFD Methods for Ship Performance Prediction
Get PDFIn today’s highly competitive market, alongside increasingly stringent regulatory requirements, the precise prediction of ship performance has assumed paramount importance for both design verification and operational evaluations. This thesis addresses the need for a comprehensive assessment of Experimental Fluid Dynamics (EFD), Computational Fluid Dynamics (CFD), and their combination to enhance the accuracy of performance predictions. Moreover, it explores the potential of combined EFD/CFD methods in improving power predictions by either replacing or complementing certain aspects of the existing methodology, while also introducing novel methods. The investigation identifies the Prohaska method as a prominent source of uncertainty in the ITTC-78 method. As an alternative, the CFD-based form factor method is meticulously examined, employing various codes and numerical approaches. The findings robustly establish the applicability and accuracy of the CFD-based form factor method, even when subjected to diverse numerical approaches and computational grids. Furthermore, best practice guidelines are derived for double-body RANS computations, ensuring compatibility with experimental form factors. Another debated issue within the ITTC-78 method is the very concept of form factor. This study conclusively affirms the Reynolds number dependence in form factors when the ITTC-57 line is employed. However, the numerical friction lines derived in this research, effectively eliminates these scale effects. Additionally, this study addresses conditions with flow separation, which renders the conventional form factor approach inadequate. A two form factor method (2−k method) is proposed to address instances of separated flow, complemented by an empirical correction formula for vessels with deep transom submergence and wetted transom flow. Furthermore, this thesis delves into the exploration of direct full-scale CFD computations for ship performance prediction. Extensive validation studies, encompassing numerous test cases and sea trials, are conducted to compare the accuracy of full-scale CFD computations with EFD based, and combined EFD/CFD methods. This thesis quantifies, for the first time in the literature, the difference in accuracy between fully computational and extrapolation-based methods using a large number of test cases and sea trials. The results indicate that while the prediction accuracy of full-scale CFD computations for power and RPM is lower than the other methods, the discrepancy is not substantial. Conversely, the investigations underscore that the combined EFD/CFD methods stand as the most accurate prediction method. Consequently, this thesis recommends incorporating combined EFD/CFD methods into the recommended procedures, as it offers immediate improvements to the existing ship performance prediction methods
Evidence of Nodal Superconductivity in Monolayer 1H-TaS2 with Hidden Order Fluctuations
Get PDFUnconventional superconductors represent one of the fundamental directions in modern quantum materials research. In particular, nodal superconductors are known to appear naturally in strongly correlated systems, including cuprate superconductors and heavy-fermion systems. Van der Waals materials hosting superconducting states are well known, yet nodal monolayer van der Waals superconductors have remained elusive. Here, using low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) experiments, it is shown that pristine monolayer 1H-TaS2 realizes a nodal superconducting state. Non-magnetic disorder drives the nodal superconducting state to a conventional gapped s-wave state. Furthermore, many-body excitations emerge close to the gap edge, signalling a potential unconventional pairing mechanism. The results demonstrate the emergence of nodal superconductivity in a van der Waals monolayer, providing a building block for van der Waals heterostructures exploiting unconventional superconducting\ua0states
Movement behavior of char particles in a bubbling fluidized bed at high temperature – The influence of particle shape
No full textThe movement of fuel particles has a strong effect on the spatial distribution in fluidized bed boilers, not only due to the resulting fuel mixing patterns but also to the impact on fuel conversion rate (through varied bed-fuel mass and heat transfer fuel). Thus, understanding the movement of char particles becomes critical in order to control the temperature and combustion characteristics of fluidized bed boilers. Further, the preferred orientations exhibited by non-spherical fuel particles are known to influence their motion. In this study, we developed (including experimental validation) a CFD-DEM framework to investigate the movement behavior (both translational and rotational) of a single char particle under combustion conditions (i.e. high temperature) in a fluidized bed. The work studies how the char movement is influenced by the fluidization velocity and the char particle shape: spherical (as typically adopted in modeling studies) vs. non-spherical. For non-spherical char particles, the impact of applying different degrees of particle homogeneity (glue index) in the modeling was also studied. The metrics applied to evaluate the char particle movement behavior were spatial distribution and linear and rotational velocity of the particle. The results show that the movement of spherical char particles is generally more vigorous than that of non-spherical ones. An increase in fluidization velocity yields a higher probability of populating the splash zone instead of the bed surface, due to the enhanced bubble flow. Increased fluidization velocity yields also higher rotational velocity (especially for non-spherical particles, for which the orientation angle distribution becomes eventually evenly distributed)
The RoboPol sample of optical polarimetric standards
Get PDFContext. Optical polarimeters are typically calibrated using measurements of stars with known and stable polarization parameters. However, there is a lack of such stars available across the sky. Many of the currently available standards are not suitable for medium and large telescopes due to their high brightness. Moreover, as we find, some of the polarimetric standards used are in fact variable or have polarization parameters that differ from their cataloged values. Aims. Our goal is to establish a sample of stable standards suitable for calibrating linear optical polarimeters with an accuracy down to 10-3 in fractional polarization. Methods. For 4 yr, we have been running a monitoring campaign of a sample of standard candidates comprised of 107 stars distributed across the northern sky. We analyzed the variability of the linear polarization of these stars, taking into account the non-Gaussian nature of fractional polarization measurements. For a subsample of nine stars, we also performed multiband polarization measurements. Results. We created a new catalog of 65 stars (see Table 2) that are stable, have small uncertainties of measured polarimetric parameters, and can be used as calibrators of polarimeters at medium and large telescopes
Take back our city: reclaiming shopping malls in Hong Kong
Get PDFShopping malls have replaced traditional public spaces and become an integral part of urban life in many cities. This paper seeks to explore the role of shopping malls as protest sites in Hong Kong during the Anti-Extradition Law Amendment Bill protest movement in 2019. As the protests decentralised and filtered throughout the city, shopping malls became sites of protest and battlegrounds between riot police and protesters. In addition to singing and chanting, organising sit-ins, and exhibiting protest art inside shopping malls, protesters also confronted mall employees as well as disrupted businesses. Based on information gathered through media reports, planning and policy documents, as well as ethnographic observations, this paper aims to examine the role of shopping malls in the urban development of Hong Kong, their function as public spaces during the protest movement, and how the politicisation of shopping malls shaped and sustained the protest movement. This paper contends that the protesters’ appropriation of shopping malls not only represented an important first step of reclaiming the right to the city, but also exemplified how such struggle and resistance can be extended beyond traditional protest sites and into different everyday spaces
The Sole Engineering Genius: A Professional Identity Not Fit for the Purpose of Gender Equality Projects
Get PDFDespite decades of directed efforts gender equality is still a challenge in many university level STEM institutions. Key reasons for this are found in disciplinary and institutional cultures. A crucial cultural element is professional identity. In this article, an ethnographic study of a gender equality program in a technical university in Sweden underpins the identification of a professional identity that we name: the ‘sole engineering genius’. This cultural figure displays features that run counter to measures promoting gender equality. As a component of engineering faculty’s self-perception as well as views of others, this figure provides rationales for rejecting the changes required to end gender inequality. Against the backdrop of research literature, we argue that this professional identity is not a local or national phenomenon, but likely a key factor in academic engineering culture transnationally that may continue to undermine gender equality strategies in STEM institutions
Advanced automotive radar front-end based on gapwaveguide technology
Get PDFThe pursuit of higher levels of autonomous driving necessitates the utilization of advanced radar sensors that possess improved environmental perception capabilities. Consequently, next-generation automotive radars require sophisticated antenna systems with high efficiency, thereby making waveguide antennas a more viable choice. In this context, it has been observed that gapwaveguides exhibit superior performance in comparison to traditional waveguides, particularly in terms of assembly reliability, when employed in the development of multi-layer waveguide antennas. Within the scope of this thesis, the primary objective is to comprehensively explore the design of front-ends for cutting-edge automotive radar sensors by leveraging the potential of gapwaveguide technology. The initial aspect of this thesis involves an exploration of integration techniques capable of achieving high performance in waveguide-based RF front-ends. In particular, the thesis introduces novel vertical gapwaveguide-to-microstrip transitions that facilitate the integration of RF front-ends featuring multi-layer configurations. Furthermore, this thesis introduces radar transceivers equipped with built-in waveguide-to-microstrip transitions, known as launcher-in-package, along with an imaging radar antenna featuring customized interconnections explicitly designed utilizing gapwaveguide technology to interface with the transceivers.Secondly, in light of the utilization of radar sensors incorporating orthogonal dual polarizations on the transmitting and/or receiving ends, an opportunity arises to acquire polarimetric information from the surrounding environment, thereby representing a promising advancement in the realm of autonomous driving. This thesis presents novel antenna designs based on gapwaveguide technology for polarimetric radar sensors. An 88 planar array utilizing double grooved circular waveguide polarizers is introduced, specifically designed for fixed beam, high gain polarimetric sensing applications. In addition, this thesis presents a polarimetric radar sensor that utilizes a MIMO configuration featuring single-CP transmitting antennas and dual-CP receiving antennas. The antenna design incorporates series-fed septum polarizers, which offer low-profile characteristics.In summary, this thesis undertakes a comprehensive investigation into the designs of advanced automotive radar front-ends utilizing gapwaveguide technology. The study explores the advancements in terms of integration techniques and polarimetric capability, demonstrating the potential of gapwaveguide technology for the practical implementation of waveguide-based RF front-ends. The utilization of such front-ends can significantly enhance the capabilities of autonomous driving systems