Search Results (33)

Many electromechanical specialists have attempted to move away from the classical method of designing windings of electrical machines using the star of slot electromotive forces, but their approaches are not always simple or universal. This article proposes a straightforward algorithmic method of winding synthesis based on number theory, which makes it possible to compute the distribution table of symmetrical multiphase, multimodular windings. Analytical expressions are provided for determining the assignment of coils to the corresponding phases, phase zones, and winding modules by sampling coils from a closed-ring structure. The method allows one to determine the direction of coil connections within a phase and covers both overlapping and non-overlapping windings. Three characteristic cases of the relationship between the number of coils and the number of pole pairs in multiphase alternating-current electrical machines are analyzed from the perspective of number theory. Conditions for implementing symmetrical windings are presented. The distribution factors of modular windings for higher field harmonics are evaluated. To validate the approach, examples of application and experimental results are provided. Full article

This study analyzed the spatial patterns of species composition and biodiversity according to elevation on Mt. Gyebangsan, a representative protected ecosystem and the national park in Korea. Based on existing vegetation survey data, differences in species composition heterogeneity according to elevation were verified using non-metric multidimensional scaling and multi-response permutation procedure analyses. Significant differences were identified using the Sørensen distance measure. Zeta (ζ)-diversity was analyzed based on the number of shared species among habitats to quantitatively interpret the structural characteristics of biodiversity along the altitudinal gradient. The analysis revealed that the understory species composition became increasingly distinct and alpha-diversity increased with elevation. High-elevation areas (A3, A4) experienced frequent physical disturbances, including wind damage and limited moisture, resulting in active canopy openings. Consequently, rhizomatous species, including Sasa borealis rapidly covered the ground, influencing the understory vegetation structure. ζ-Diversity analysis showed that the ζ-ratio in high-elevation regions sharply declined with increasing ζ-order, indicating limited species overlap among habitats and the dominance of deterministic processes. Thus, altitudinal gradients represent a key factor in shaping biodiversity, indicating that climatic variables directly affect understory distribution and species turnover. This study quantitatively assessed biodiversity and ecological heterogeneity within the national park, providing a scientific foundation for biodiversity conservation and management. Full article

Wind data are often cyclostationary due to cyclic variations, non-constant variance resulting from fluctuating weather conditions, and structural breaks due to transient behaviour (due to wind gusts and turbulence), resulting in unreliable wind power supply. In wavelet hybrid forecasting, wind prediction accuracy depends heavily on the decomposition level ($L$) and the wavelet filter technique selected. Hence, we examined the efficacy of wind predictions as a function of $L$and wavelet filters. In the proposed hybrid approach, differential evolution (DE) optimises the decomposition level of various wavelet filters (i.e., least asymmetric (LA), Daubechies (DB), and Morris minimum-bandwidth (MB)) using the maximal overlap discrete wavelet transform (MODWT), allowing for the decomposition of wind data into more statistically sound sub-signals. These sub-signals are used as inputs into the gated recurrent unit (GRU) to accurately capture wind speed. The final predicted values are obtained by reconciling the sub-signal predictions using multiresolution analysis (MRA) to form wavelet-MODWT-GRUs. Using wind data from three Wind Atlas South Africa (WASA) locations, Alexander Bay, Humansdorp, and Jozini, the root mean square error, mean absolute error, coefficient of determination, probability integral transform, pinball loss, and Dawid-Sebastiani showed that the MB-MODWT-GRU at $L=3$ was best across the three locations. Full article

Pollination is essential for producing temperate-zone tree fruits like apples (Malus × domestica). While traditionally considered insect-dependent, this view may result from orchard designs tailored to European honeybees. Previous research showed that low-seed apples could develop in insect exclusion nets, suggesting wind as an alternative pollinator. This study investigated the paternal origin of seeds and fruit set under nets compared to open canopies. Netted canopies of ‘Gala’, Fuji’, and ‘Honeycrisp’ set commercial fruit numbers without manual thinning. To determine the parental source of seeds, genotyping was performed using 16 SNP markers tailored for distinguishing apple cultivars, with primer design and genotyping conducted via the KASP™ system. Results showed significant genetic overlap between seeds from netted and non-netted fruits and nearby pollinizers, ruling out self-pollination. Netted canopies retained fruits with similar or fewer seeds compared to abscised fruits in open canopies, indicating fruit set depends on the population’s seed content rather than individual fruit seed count. These findings supporting the hypothesis that apple trees are adapted to utilize both wind and insect pollination. While wind pollination offers a sustainable approach, it requires adjustments in orchard design to ensure sufficient pollen transfer for reliable fertilization and yield. Full article

Similar to armature back electromotive force (armature back-EMF), the back-EMF also exists in the field winding of hybrid excited machines. However, the existence of field back electromotive force (field back-EMF) is harmful to the safe and stable operation of machine systems, e.g., higher losses, lower efficiency, higher torque ripple, and reduced control performance. This paper systematically investigates the influence of armature/field winding configurations together with stator/rotor pole combinations on the field back-EMF ripple in hybrid excited machines with switched-flux stators. The two-dimensional (2D) time-stepping finite element modeling and prototyping experiments are used for the research. The investigated field and armature coil pitches equal to 1, i.e., non-overlapped windings. The influential factors that are investigated in this paper mainly include the number of layers of field/armature windings, the number of field/armature coils, and the stator/rotor pole combinations. The results show that the field back-EMF’s harmonic order and peak-to-peak value are closely associated with field/armature winding configurations and stator/rotor pole combinations under various conditions. Finally, for validation of the results predicted by the finite element method, a prototype machine is built and tested. Overall, non-overlapped double-layer armature and field windings are recommended for the hybrid excited switched flux machines with various stator/rotor pole combinations to realize relatively lower field back-EMF under different conditions. Full article

As the largest non-gravitational force, solar radiation pressure (SRP) causes significant errors in precise orbit determination (POD) of the BeiDou global navigation satellite system (BDS-3) medium Earth orbit (MEO) satellite. This is mainly due to the imperfect modeling of the satellite’s cuboid body. Since the BDS-3’s inter-satellite link (ISL) can enhance the orbit estimation of BDS-3 satellites, the aim of this study is to establish an a priori SRP model for the satellite body using 281-day ISL observations to reduce the systematic errors in the final orbits. The adjustable box wind (ABW) model is employed to refine the optical parameters for the satellite buses. The self-shadow effect caused by the search and rescue (SAR) antenna is considered. Satellite laser ranging (SLR), day-boundary discontinuity (DBD), and overlapping Allan deviation (OADEV) are utilized as indicators to assess the performance of the a priori model. With the a priori model developed by both ISL and ground observation, the slopes of SLR residual for the China Academy of Space Technology (CAST) and Shanghai Engineering Center for Microsatellites (SECM) satellites decrease from −0.097 cm/deg and 0.067 cm/deg to −0.004 cm/deg and −0.009 cm/deg, respectively. The standard deviation decreased by 21.8% and 26.6%, respectively. There are slight enhancements in the average values of DBD and OADEV, and a reduced β-dependent variation is observed in the OADEV of the corresponding clock offset. We also found that considering the SAR antenna only slightly improves the orbit accuracy. These results demonstrate that an a priori model established for the BDS-3 MEO satellite body can reduce the systematic errors in orbits, and the parameters estimated using both ISL and ground observation are superior to those estimated using only ground observation. Full article

Offshore wind-to-hydrogen production is an effective means of solving the problems of large-scale grid-connected consumption and high power transmission costs of offshore wind power. Site selection is a core component in planning offshore wind-to-hydrogen facilities, involving careful consideration of multiple factors, and is a classic multi-criteria decision-making problem. Therefore, this study proposes a multi-criteria decision-making method based on the two-dimensional linguistic cloud model to optimize site selection for offshore wind-to-hydrogen bases. Firstly, the alternative schemes are evaluated using two-dimensional linguistic information, and a new model for transforming two-dimensional linguistic information into a normal cloud is constructed. Then, the cloud area overlap degree is defined to calculate the interaction factor between decision-makers, and a multi-objective programming model based on maximum deviation-minimum correlation is established. Following this, the Pareto solution of criteria weights is solved using the non-dominated sorting genetic algorithm II, and the alternatives are sorted and selected through the cloud-weighted average operator. Finally, an index system was constructed in terms of resource conditions, planning conditions, external conditions, and other dimensions, and a case study was conducted using the location of offshore wind-to-hydrogen production bases in Shanghai. The method proposed in this study demonstrates strong robustness and can provide a basis for these multi-criteria decision-making problems with solid qualitative characteristics. Full article

Utilizing non-overlap windings has emerged as a favourable choice for minimizing electrical machine manufacturing costs, among other benefits. Nevertheless, it is widely acknowledged that these windings exhibit a notable level of harmonic contents in the resultant magnetomotive force, which can detrimentally impact machine performance, particularly in terms of torque ripple. In the context of wind energy conversion, maintaining low torque ripple is an essential and demanding prerequisite. Medium-speed wind generators present a good trade-off between high energy yield and low gearbox ratios. So far, medium-speed non-overlap winding wound-rotor synchronous generator (WRSG) technologies have been limited to 10/12 and the less common 16/18 pole/slot combinations. In this study, the analysis of a high-pole number combination (24/27 pole/slots) non-overlap WRSG is carried out to theoretically and comparatively predict the electromagnetic and radial force mechanical stress performance analysis with the 16/18 machine with a phase-shifted non-overlap winding (PSW), at 5 MW power level. The study, which is founded on the finite element analysis (FEA) technique, shows that the 24/27 machine exhibits comparable average torque and torque ripple, lower core losses and significantly reduced radial forces compared to the 16/18 PSW-WRSG. However, the 16/18 PSW-WRSG has a 50% reduction in the radial forces compared to the conventional 16/18 non-overlap winding. Experimental vibration analysis of a 3 kW 16/18 WRSG test machine confirms the radial force and vibration reduction in the phase-shifted winding. Full article

Considering the practical conditions, it has been observed that the support structures of wind turbines inevitably experience bending and axial compression, both during the installation phase and throughout their operational lifespan. The monopile is the most commonly utilized support structure for offshore applications and a reliable method for creating a detachable section within these structures is using a Pile-in-Pile (PIP) slip joint. Consequently, the behavior of PIP slip joints, under combined axial compression and bending, has been meticulously investigated. To facilitate a thorough analysis, overlapping lengths proportional to the pile diameters have been used, encompassing three distinct variations. This approach allows for a comprehensive understanding of structural integrity and performance under varying stress conditions, which are comprehensively understood and accounted for in design considerations. The current study builds upon assessing the pure bending characteristics of slip joints in cylindrical hollow section (CHS) structures. Additionally, two ring stoppers have been strategically employed inside the piles to withstand the axial load. Furthermore, the complexity of the pressure acting in the overlapping length, attributed to the frictional coefficient in that region, has been carefully addressed. The current research also encompasses a comprehensive overview of the P-M envelopes for the existing arrangements, with a particular focus on non-linear buckling, which is known to significantly influence the performance of tubular structures. Finally, a design equation was introduced to concisely describe the behavior of the components and compare it with other design equations provided by an established code. Full article

In order to ease the structure and manufacturing process of the variable reluctance (VR) resolver, the three-phase symmetrical single-layer winding commonly used in the stator winding of permanent magnet synchronous motors (PMSM) is applied to the VR resolver in this paper. The proposed resolver has the same winding direction and number of turns on all teeth. And the non-overlapping distribution of the three-phase windings of the resolver is ensured. For this novel resolver, the resolver-to-digital conversion (RDC) method references the ultra-high-frequency (UHF) signal injection method used when a PMSM is powered off and restarted. Instead of the need for the orthogonal envelope RDC required by conventional resolvers, the absolute position of the rotor can be obtained. In this paper, the prototype of the proposed resolver and the peripheral circuits are fabricated and compared with the position detected by the optical encoder, and the validity of the proposed resolver and the accuracy of the RDC are verified by the results of the comparison experiments. Full article

The impact of supercooled water droplets is the cause of aircraft icing, and the acquisition of impingement characteristics is the key to icing prediction and the design of ice protection systems. The introduction of water droplet collection efficiency is required to obtain the characteristics for the Lagrangian method. In this work, a traditional flow tube method, a local flow tube method, and a statistical method are established to calculate the local collection efficiency, based on Lagrangian droplet trajectories. Through the numerical simulations of the air–droplet flow field around an NACA 0012 airfoil, the accuracies of the three methods in regard to collection efficiency are verified. Then, these three methods are applied to obtain the results for water droplet trajectories and the collection efficiency of an S-shaped duct, a 2D engine cone section and an icing wind tunnel. The results show that the distributions of water droplet collection efficiency obtained by the three methods are consistent and the three methods are all feasible when the water droplets do not overlap or cross before hitting the aircraft surfaces. When the water droplets are shadowed by upstream surfaces or blown by air injection, the droplet trajectories might overlap or even cross, and the local collection efficiencies obtained by the traditional flow tube method, local flow tube method, and statistical method might differ. The statistical method is relatively accurate. However, not all the droplet impingement characteristics obtained by the three methods are different due to these effects, and the non-crossing of the droplet trajectories is not a necessary condition for the use of the flow tube method. The effects of trajectory crossings are analyzed and discussed in detail in different situations for the three methods. This work is helpful for understanding and accurately calculating the droplet impingement characteristics and is of great significance for simulations of the aircraft icing process and anti/de-icing range. Full article

Frames made of polymer composites are increasingly used in the aerospace, automotive, and agricultural industries. A frequently used technology in the production line of composite frames is winding rovings onto a non-load-bearing frame to form the structure using an industrial robot and a winding head, which is solidified through a subsequent heat-treatment pressure process. In this technology, the most difficult procedure is the winding of the curved parts of a composite frame. The primary concern is to ensure the proper winding angles, minimize the gaps and overlaps, and ensure the homogeneity of the wound layers. In practice, the curved frame parts very often geometrically form sections of a torus. In this work, the difficulty of achieving a uniform winding of toroidal parts is described and quantified. It is shown that attaining the required winding quality depends significantly on the geometrical parameters of the torus in question. A mathematical model with a detailed procedure describing how to determine the number of rovings of a given width on toroidal parts is presented. The results of this work are illustrated with practical examples of today’s industrial problems. Full article

To address the issues of low detection accuracy, slow detection speed, high missed detection rate, and high false detection rate in the detection of surface defects on pre-impregnated composite materials during the automated tape laying and winding process, an improved YOLOv5 (You Only Look Once version 5) algorithm model was proposed to achieve the high-precision, real-time detection of surface defects. By leveraging this improvement, the necessity for frequent manual interventions, inspection interventions, and subsequent rework during the automated lay-up process of composite materials can be significantly reduced. Firstly, to improve the detection accuracy, an attention mechanism called “CA (coordinate attention)” was introduced to enhance the feature extraction ability, and a Separate CA structure was used to improve the detection speed. Secondly, we used an improved loss function “SIoU (SCYLLA-Intersection over Union) loss” to replace the original “CIoU (Complete-Intersection over Union) loss”, which introduced an angle loss as a penalty term to consider the directional factor and improve the stability of the target box regression. Finally, Soft-SIoU-NMS was used to replace the original NMS (non-maximum suppression) of YOLOv5 to improve the detection of overlapping defects. The results showed that the improved model had a good detection performance for surface defects on pre-impregnated composite materials during the automated tape laying and winding process. The FPS (frames per second) increased from 66.7 to 72.1, and the mAP (mean average precision) of the test set increased from 92.6% to 97.2%. These improvements ensured that the detection accuracy, as measured by the mAP, surpassed 95%, while maintaining a detection speed of over 70 FPS, thereby meeting the requirements for real-time online detection. Full article

A 1.29 GHz wind profiler was developed under a private–military–government cooperative wind profiler radar development project in the Republic of Korea. During the test operation period, radio frequency interference (RFI) contamination occurred in the spectrum. In addition to the general shape, with a continuous appearance depending on the altitude, the spectrum showed complex shapes, such as discontinuous and overlapping frequencies. The RFI characteristics in the wind profiler spectra were analyzed, and a new algorithm was developed to remove multiple RFI (MRFI). Meteorological and non-meteorological signals were separated by filtering with a spectrum width threshold of 0.1 m/s. A continuity check was performed to determine MRFI in the non-meteorological signal. The number of gates in which the same radial velocity is continuous was determined based on whether the beam was vertical or oblique; a rough continuity test was performed, considering exceptional circumstances for the meteorological signal. For overlapping MRFI, the process was repeated. Spectral contamination by MRFI was removed through filtering and iterated scans; the continuity of wind vectors calculated from the improved spectral radial velocity was verified. Good-quality wind vectors can be produced even in a bad-radio-frequency environment if proper quality control is performed. Full article

Lake Tana, the largest inland water body in Ethiopia, has witnessed significant changes due to ongoing urbanization and socioeconomic activities in recent times. In this study, the two-decade recordings of moderate resolution imaging spectroradiometer (MODIS) were used to derive Forel–Ule index (FUI). The FUI, which ranges from 1 (dark-blue pristine water) to 21 (yellowish-brown polluted water), is important to fully understand the quality and trophic state of the lake in the last two decades. The analysis of FUI over a period of 22 years (2000–2021) indicates that Lake Tana is in a eutrophic state as confirmed by FUI values ranging from 11 to 17. This is in agreement with the trophic state index (TSI) estimated from MERIS diversity-II chlorophyll a (Chl$\_a$) measurements for the overlapping 2003-2011 period. The categorical skill scores show that FUI-based lake water trophic state classification relative to MERIS-based TSI has a high performance. FUI has a positive correlation with TSI, (Chl$\_a$), turbidity, and total suspended matter (TSM) and negative relations with Chl$\_a$ and TSM (at the lake shoreline) and colored dissolved organic matter. The annual, interannual and seasonal spatial distribution of FUI over the lake show a marked variation. The hydro-meteorological, land-use–land-cover (LULC) related processes are found to modulate the spatiotemporal variability of water quality within the range of lower and upper extremes of the eutrophic state as revealed from the FUI composite analysis. The FUI composites were obtained for the terciles and extreme percentiles of variables representing hydro-meteorological and LULC processes. High FUI composite (poor water quality) is associated with above-normal and extremely high (85 percentile) lake bottom layer temperature, wind speed, precipitation, surface runoff, and hydrometeorological drought as captured by high negative standardized precipitation-evapotranspiration index (SPEI). In contrast, a high FUI composite is observed during below-normal and extremely low (15 percentile) lake skin temperature and evaporation. Conversely good water quality (i.e., low FUI) was observed during times of below-normal and above-normal values of the above two sets of drivers respectively. Moreover, FUI varies in response to seasonal NDVI/EVI variabilities. The relationship between water quality and its drivers is consistent with the expected physical processes under different ranges of the drivers. High wind speed, for instance, displaces algae blooms to the shoreline whereas intense precipitation and increased runoff lead to high sediment loads. Increasing lake skin temperature increases evaporation, thereby decreasing water volume and increasing insoluble nutrients, while the increasing lake bottom layer temperature increases microbial activity, thereby enhancing the phosphorus load. Moreover, during drought events, the low inflow and high temperature allow algal bloom, Chl$\_a$, and suspended particles to increase, whereas high vegetation leads to an increase in the non-point sources of total phosphorus and nitrogen. Full article