Wind Structure Research Articles

Economic Viability of Implementing Structural Health Monitoring Systems on the Support Structures of Bottom-Fixed Offshore Wind

Offshore wind (OSW) energy is a renewable source with strong prospects of development that may decisively contribute towards energy independence. Offshore wind is, however, not yet ubiquitously cost competitive, and frequently requires support schemes to finance its extensive capital requirements. Therefore, cost reduction strategies are necessary for the future development of offshore wind technologies. Even if structural health monitoring (SHM) systems are currently applied for the inspection of critical mechanical structures, they have not been the focus of research from offshore wind stakeholders. The main goal of this study is to evaluate the viability of SHM systems on the support structures of bottom-fixed offshore wind (BFOSW), alongside the impact of implementing these systems on life-cycle. Economic models are used to estimate the impact of implementing these systems, explained using a case-study of the Kaskasi farm in the German North Sea. General results indicate that installing SHM systems on the support structures of offshore wind can shift the maintenance strategies from preventive to predictive, allowing the intervals between inspections to be increased without a reduction on equipment availability. The greatest benefit is related with the possibility of extending the operational life of the farm.

On the passive shimming of a 7 T whole-body MRI superconducting magnet: Implementation with minimized ferromagnetic materials usage and operable magnetic force control.

Magnetic field shimming of the magnet is a routine practice in a magnetic resonance imaging (MRI) system. For clinically-used 1.5 T or 3 T MRI superconducting magnets, it is generally straightforward to achieve desired magnetic field uniformity with the passive shim technique. In comparison, superconducting shims with higher shimming efficiency are usually introduced in combination with passive shimming to satisfy the higher magnetic field uniformity requirement for ultrahigh field magnets (≥7 Tesla). However, superconducting shim usually involves a complex winding structure and low-temperature environment, bringing considerable engineering challenges and extra costs in practice. In this study, we aimed to improve the passive shimming method that can incorporate the unique electromagnetic properties of ultrahigh-field MRI magnets and is thus more effective for field corrections at 7T and above. In this work, we propose a dedicated passive shimming strategy for a 7 T whole-body MRI superconducting magnet. In this method, the iron usage and magnetic force due to the iron-field interaction are strictly managed to ensure a shim tray insert is operable by manpower (without specially designed tools). To validate the proposed shimming strategy, a shimming experiment was implemented on a 7 T/800mm superconducting magnet. Alternating with the odd and even shim trays in our two-round operation, the magnetic field inhomogeneity was successfully corrected from 85.36 to 7.91ppm, achieving the magnetic field quality elevation of more than one order of magnitude. The experimental results indicated that the proposed electromagnetic technology is expected to be effective for developing ultrahigh-field MRI instruments.

Analysis of Electromagnetic Characteristics of 6.5 MVA/25 kV HTS Traction Transformer Using T–A Formulation

Low AC loss of the winding of high-capacity high temperature superconducting (HTS) traction transformer is a very important link to introduce large capacity traction transformer into commercialization. A new winding structure is proposed for the transformer. The HV windings are made of double pancake coils (DPCs), which are wound by 4.8 mm-wide tapes, and the LV windings, which are wound by 12 mm-wide tapes, are solenoid coils. The electromagnetic characteristics of the new winding structure of the traction transformer are analyzed by <i>H</i>-formulation homogenization method and <i>T</i>-<i>A</i> formulation homogenization method respectively. Significant HTS tape cost reduction could be achieved without compromising AC loss by using hybrid windings into the new winding structure. We report that the <i>H</i>-formulation homogenization model and <i>T</i>-<i>A</i> formulation homogenization model are used to calculate the AC loss of the new winding structure with flux diverters (FDs) at the end. The results meet the design requirements of less than 2 kW, which shows the feasibility of the new winding structure. Due to the good convergence of <i>H</i>-formulation and poor convergence of <i>T</i>-<i>A</i> formulation under the homogenization model of the transformer, no one has used <i>T</i>-<i>A</i> formulation to calculate the electromagnetic characteristics of the transformer before. Due to the simplicity of <i>T</i>-<i>A</i> formulation applied to large-scale superconducting system, a new form of mesh generation is proposed to improve the convergence and accuracy of <i>T</i>-<i>A</i> formulation homogenization model calculation of the transformer in this paper. This paper verifies the correctness of the calculation of HTS transformer by <i>T</i>-<i>A</i> formulation, and provides a reference for the application of <i>T</i>-<i>A</i> formulation in more superconducting fields

Observing the onset of the accretion wake in Vela X-1

High-mass X-ray binaries (HMXBs) offer a unique opportunity to investigate accretion onto compact objects and the wind structure in massive stars. A key source for such studies is the bright neutron star HMXB Vela X-1 whose convenient physical and orbital parameters facilitate analyses and in particular enable studies of the wind structure in HMXBs. Here, we analyse simultaneous XMM-Newton and NuSTAR observations at ϕorb ≈ 0.36–0.52 and perform time-resolved spectral analysis down to the pulse period of the neutron star based on our previous NuSTAR-only results. For the first time, we are able to trace the onset of the wakes in a broad 0.5–78 keV range with a high-time resolution of ~283 s and compare our results with theoretical predictions. We observe a clear rise in the absorption column density of the stellar wind NH,1 starting at orbital phase ~0.44, corresponding to the wake structure entering our line of sight towards the neutron star, together with local extrema throughout the observation, which are possibly associated with clumps or other structures in the wind. Periods of high absorption reveal the presence of multiple fluorescent emission lines of highly ionised species, mainly in the soft-X-ray band between 0.5 and 4 keV, indicating photoionisation of the wind.

Improved Coreless Axial Flux Permanent-Magnet Machine With Nonuniformly Distributed Winding

The windings of coreless axial flux permanent-magnet machine (CAFPM) are exposed to the rotor magnetic field, where each back electromotive force (EMF) harmonic is induced not only by several different spatial field harmonics but also by the winding distribution. In order to reduce the time harmonics of back EMF for CAFPM with non-overlapping winding, one new winding structure with non-uniform distributed coils is proposed in this paper, in which the coils are arranged in a non-uniform way with annular distribution in the stator. Firstly, the relationship between uniform and non-uniform distributed windings is analyzed based on the phasor diagram of each coil EMF, and the analytical expression of back EMF under non-uniform distributed windings is established. Secondly, key performance indexes under different working states, like no-load, are investigated by three dimensional (3-D) finite element analysis (FEA). Finally, comprehensive experiments are carried out to verify related theoretical analysis, which demonstrate that the non-uniform distributed windings can effectively reduce the time harmonics and increase the working efficiency.

Dynamical influence of MJO phases on the onset of Indian monsoon

There is a need to understand the onset of monsoon dynamics as the date of onset of monsoon (DOM) is an important parameter in framing all the policy for the imminent season like crop choice, sowing schedule, disaster management, power distribution etc It is observed that the interannual variability of the DOM in India is about 7–8 days, making it more challenge to predict this at long lead. The MJO phases are linked with the different convection centres and hence, influences the global circulation process and the rainfall. In this paper the dynamical influence of the different phases of MJO are being quantified on DOM and its progress in continental India by using the multi-source atmospheric and oceanic parameters like wind structure, outgoing longwave radiation (OLR), sea surface temperature (SST). The linkage of the active and inactive phases of MJO along with the favourable conditions for DOM is obtained by using the pentad analysis of associated parameters in different clusters for both the wet and dry phases of MJO along with the strength for the period 1980–2018. Also the dynamics are studied for the early, normal and late onset years separately to understand the relation better. It is inferred that the wet (dry) phase leads to early (late) monsoon onset over Kerala (MOK) in India. To address the progress of monsoon the DOM in Rajasthan (MOR) is considered and the rainfall anomalies during MOK-MOR period are linked to the MJO phases. It is inferred that the wet MJO phase with negative OLR anomaly triggers the fast progress of monsoon over India. This understanding will surely help operational researchers and the NWP modellers for improving the methodologies for the advanced and accurate prediction of DOM.

High-Voltage Isolated Power Supply Structure for Gate Drivers of Medium-Voltage SiC Devices

This letter proposes two novel gate driver isolation structures with potted PCB windings and cylindrical rod-based cores to drive medium voltage (MV) silicon carbide (SiC) devices. The first design uses two cylindrical rod cores, each for the primary and secondary winding, and uses a coupling coil to improve the magnetic coupling between the primary and the secondary side. The second design improves upon the first design and uses a single cylindrical core for both the primary and the secondary windings, eliminates the coupling coil, and brings upon the ability to drive a half-bridge structure. Both structures are designed to maintain the required insulation standards. The isolation structures achieve a peak partial discharge (PD) voltage greater than 15 kV peak, with an isolation capacitance within 5 pF. The structure of the PCB windings and the ferrite cores for the designs provides excellent repeatability and easy manufacturability. Experimental results validate the design and operation of the gate driver isolation structures.

The Properties of Small Magnetic Flux Ropes inside the Solar Wind Come from Coronal Holes, Active Regions, and Quiet Sun

The origination and generation mechanisms of small magnetic flux ropes (SMFRs), which are important structures in solar wind, are not clearly known. In the present study, 1993 SMFRs immersed in coronal holes, active regions, and quiet-Sun solar wind are analyzed and compared. We find that the properties of SMFRs immersed in three types of solar wind are significantly different. The SMFRs are further classified into hot-SMFRs, cold-SMFRs, and normal-SMFRs, according to whether the O7+/O6+ is 30% elevated or dropped inside SMFRs as compared with background solar wind. Our studies show that the parameters of normal-SMFRs are similar to background in all three types of solar wind. The properties of hot-SMFRs and cold-SMFRs seem to be lying in two extremes. Statistically, the hot-SMFRs (cold-SMFRs) are associated with longer (shorter) duration, lower (higher) speeds and proton temperatures, higher (lower) charge states, helium abundance, and first ionization potential bias as compared with normal-SMFRs and background solar wind. The anticorrelations between speed and O7+/O6+ inside hot-SMFRs (normal-SMFRs) are different from (similar to) those in background solar wind. Most hot-SMFRs and cold-SMFRs should come from the Sun. Hot-SMFRs may come from streamers associated with plasma blobs and/or small-scale activities on the Sun. Cold-SMFRs may be accompanied by small-scale eruptions with lower-temperature materials. Both hot-SMFRs and cold-SMFRs could also be formed by magnetic erosions of interplanetary coronal mass ejections that do not contain or do contain cold-filament materials. The characteristics of normal-SMFRs can be explained reasonably by the two originations, both from the Sun and generated in the heliosphere.

The Effect of the Ambient Solar Wind Medium on a CME-driven Shock and the Associated Gradual Solar Energetic Particle Event

We present simulation results of a gradual solar energetic particle (SEP) event detected on 2021 October 9 by multiple spacecraft, including BepiColombo (Bepi) and near-Earth spacecraft such as the Advanced Composition Explorer (ACE). A peculiarity of this event is that the presence of a high-speed stream (HSS) affected the low-energy ion component (≲5 MeV) of the gradual SEP event at both Bepi and ACE, despite the HSS having only a modest solar wind speed increase. Using the EUHFORIA (European Heliospheric FORecasting Information Asset) magnetohydrodynamic model, we replicate the solar wind during the event and the coronal mass ejection (CME) that generated it. We then combine these results with the energetic particle transport model PARADISE (PArticle Radiation Asset Directed at Interplanetary Space Exploration). We find that the structure of the CME-driven shock was affected by the nonuniform solar wind, especially near the HSS, resulting in a shock wave front with strong variations in its properties such as its compression ratio and obliquity. By scaling the emission of energetic particles from the shock to the solar wind compression at the shock, an excellent match between the PARADISE simulation and in situ measurements of ≲5 MeV ions is obtained. Our modeling shows that the intricate intensity variations observed at both ACE and Bepi were influenced by the nonuniform emission of energetic particles from the deformed shock wave and demonstrates the influence of even modest background solar wind structures on the development of SEP events.

Voltage-Controlled Variable Inductor for Fixed-Frequency Critical Conduction Mode Operation

This study proposes a novel voltage-controlled variable inductor (VI) for fixing the switching frequency of DC-DC converters in the critical conduction mode (CRM). It overcomes the limitations of conventional current-controlled VIs such as complex winding structures, difficulties in control, and high sensitivity to temperature. In the proposed voltage-controlled VI, the primary-side inductance of a coupled inductor is regulated by an auxiliary voltage source on the secondary side. The auxiliary voltage source is implemented by an auxiliary DC-DC converter, which delivers power to the load in parallel with the main converter. The operating principle of the converter system for employing the proposed VI is presented, and a control loop is designed to fix the switching frequency, considering the small-signal model of the auxiliary converter. The validity of the proposed VI is experimentally verified using a prototype CRM boost converter with an output voltage of 400 V and a maximum power of 400 W. The switching frequency is fixed at 100 kHz and the soft switching of the main converter is maintained regardless of the input voltage and output power.

The extraordinarily large vortex structure of Typhoon In-fa (2021), observed by spaceborne microwave radiometer and synthetic aperture radar

Tropical cyclone (TC) vortex structure can be estimated from wind radii (34, 50, and 64 kt). Accurate wind radii are essential for assessing the impact range of TCs. Combining observations from active and passive microwave remote sensing instruments can provide long-time series data for monitoring changes in TC wind structure. Here, the evolution of the wind radii for Typhoon In-fa (2021), from its genesis to its first landfall, is evaluated using data from spaceborne microwave radiometers and synthetic aperture radars (SARs). Our results show that the retrieved wind radii are relatively close to those from the Joint Typhoon Warning Center (JTWC), the coastal automatic weather stations in China, and the advanced scatterometer. The time series for the wind radii show significant increasing trends during the lifecycle of In-fa and a massive vortex structure before In-fa made landfall. The average wind radii observed before landfall are all likely in the 90th percentile of the 2001–2021 JTWC historical wind radii records, indicating that the vortex structure is extraordinarily large before In-fa made landfall and represents a historical extreme. The extremely large vortex structure may be attributable to the interaction between In-fa and an extremely strong monsoon gyre.

Observed Surface Wind Field Structure of Severe Tropical Cyclones and Associated Precipitation

Using the International Best Track Archive for Climate Stewardship (IBTrACS) dataset, this study assessed the surface wind fields from high spatial resolution Synthetic Aperture Radar (SAR) observations, the fifth generation ECMWF reanalysis for the global climate and weather (ERA5) data and the Tropical Cyclone Winds and Inflow Angle Asymmetry (TCIAA) wind model. The results showed that SAR data are sufficient to reveal the surface wind field near a TC center and can accurately describe TC intensity and size under severe TC conditions. Then, a new, improved statistical wind structure model was set up using ERA5 data alone based on the assessment. In addition, the warm sea surface (SST &gt; 26.5 °C) produced stronger TC wind fields and heavier precipitation. When the SST was higher (lower), the heavy rainfall was located on the left (right) side of the TC track and the strong positive correlation between wind speed and precipitation increased as the SST decreased.

A Machine Learning–Based Approach to Time-series Wave Identification in the Solar Wind

The Wind spacecraft has yielded several decades of high-resolution magnetic field data, a large fraction of which displays small-scale structures. In particular, the solar wind is full of wavelike fluctuations that appear in both the field magnitude and its components. The nature of these fluctuations can be tied to the properties of other structures in the solar wind, such as shocks, that have implications for the time evolution of the solar wind. As such, having a large collection of wave events would facilitate further study of the effects that these fluctuations have on solar wind evolution. Given the large volume of magnetic field data available, machine learning is the most practical approach to classifying the myriad small-scale structures observed. To this end, a subset of Wind data is labeled and used as a training set for a multibranch 1D convolutional neural network aimed at classifying circularly polarized wave modes. Using this algorithm, a preliminary statistical study of 1 yr of data is performed, yielding about 300,000 wave intervals out of about 5,000,000 solar wind intervals. The wave intervals come about more often in the fast solar wind and at higher temperatures, and the number of waves per day is highly periodic. This machine learning–based approach to wave detection has the potential to be a powerful, inexpensive way to catalog waves throughout decades of spacecraft data.

Seven Sisters: a mission to study fundamental plasma physical processes in the solar wind and a pathfinder to advance space weather prediction

This paper summarizes the Seven Sisters solar wind mission concept and the outstanding science questions motivating the mission science objectives. The Seven Sisters mission includes seven individual spacecraft designed to uncover fundamental physical processes in the solar wind and provides up to ≈ 2 days of advanced space weather warnings for 550 Earth days during the mission. The mission will collect critical measurements of the thermal and suprathermal plasma and magnetic fields, utilizing, for the first time, Venus–Sun Lagrange points. The multi-spacecraft configuration makes it possible to distinguish between spatial and temporal changes, define gradients, and quantify cross-scale transport in solar wind structures. Seven Sisters will determine the 3-D structure of the solar wind and its transient phenomena and their evolution in the inner heliosphere. Data from the Seven Sisters mission will allow the identification of physical processes and the quantification of the relative contribution of different mechanisms responsible for suprathermal particle energization in the solar wind.

Hydrodynamic behaviour of composite bucket foundation with random waves

In real sea conditions, the effect of nonlinear phenomena, such as wave run-up and wave pressure, on the foundations of offshore wind structures may threaten the safety of the platforms. This study investigated the hydrodynamic behaviour of a composite bucket foundation (CBF) under random waves. A hydrodynamic simulation model of the interaction between random waves and the CBF was developed using the renormalisation group (RNG) k-ε model, which was verified through experiments. The relationship between wave run-up and wave parameters was studied, and the distributions of wave pressure around the CBF was described. The flow field and velocity vector distribution characteristics around the CBF were analysed. The results show that two types of wave fields appear around the CBF. The maximum run-up value of the CBF is 100%–150% higher than the minimum value, and the run-up value at the back side is 50%–70% higher than the minimum value. A larger wave steepness parameter leads to a smaller wave run-up value at the location of the smallest wave run-up value. The results can provide a reference for the practical application of a CBF.

Comparison of Aluminum and Copper Winding Materials for Switched Reluctance Machines with Finite Element Analysis

Today, with the decrease in fossil fuel reserves, interest in electric vehicles has grown. Undoubtedly, electric machines are one of the most important parts of electric vehicles. Studies on electrical machines directly affect vehicle performance. Since the electrical machine used is mounted on the vehicle, reducing the total weight without changing the output power will positively affect the overall performance of the vehicle. The windings used to create the magnetic field in electrical machines are made of copper. Electrical machinery manufacturers try to use completely different materials instead of copper or partially reduce its use. At this point, aluminum emerges as an attractive material for various manufacturers. This study analyzed the winding structure of a switched reluctance machine (SRM) proposed for an electric vehicle by using copper and aluminum at an equivalent resistance value, the results of which were compared. As a result of a 2D finite element analysis, it was observed that the machine’s output performance is largely kept when aluminum is used instead of copper for the winding. It was also observed that the aluminum total winding weight decreased by 43,40% compared to that of copper.

Investigation of low-level supergeostrophic wind and Ekman spiral as observed by a radar wind profiler in Beijing

The supergeostrophic flow remains seldomly reported from an observational perspective. Here, 1 year record of radar wind profiler measurements and ERA-5 reanalysis collected at Beijing observatory station are used to characterize the vertical structures of supergeostrophic wind and Ekman spirals in the lower troposphere. It is found that supergeostrophic flow shows significant diurnal variation, with lowest frequency for the supergeostrophic wind forming during daytime under clear-sky conditions, largely due to strong turbulent mixing and friction in the daytime. By comparison, the planetary boundary layer at night is stably stratified, the supergeostrophic wind occurs more frequently due to friction-induced decoupling from the ground surface. Furthermore, the presence of cloud makes the supergeostrophic wind occur more often in the daytime. Also, the geostrophic wind deviation within 1 km of atmosphere is found to be more negatively associated with the difference between surface temperature and 2-m air temperature compared with that in the altitude range of 1–3 km, indicating that the supergeostrophic wind near ground surface is more subject to the influence of heat flux. Intriguingly, most of the vertical wind profiles in the PBL are found not to follow Ekman spiral under neutral atmospheric conditions. The supergeostrophic winds contribute significantly to the magnitude of Ekman spirals in the upper mixed layer. Overall, the profiles and evolution features of the supergeostrophic wind and Ekman spirals observed in the lower troposphere in Beijing are much complicated than expected. The findings lay a solid foundation for better elucidating the low-level atmospheric dynamics in Beijing.

The S-Web Origin of Composition Enhancement in the Slow-to-moderate Speed Solar Wind

Connecting the solar wind observed throughout the heliosphere to its origins in the solar corona is one of the central aims of heliophysics. The variability in the magnetic field, bulk plasma, and heavy ion composition properties of the slow wind are thought to result from magnetic reconnection processes in the solar corona. We identify regions of enhanced variability and composition in the solar wind from 2003 April 15 to May 13 (Carrington Rotation 2002), observed by the Wind and Advanced Composition Explorer spacecraft, and demonstrate their relationship to the separatrix–web (hereafter, S-Web) structures describing the corona’s large-scale magnetic topology. There are four pseudostreamer (PS) wind intervals and two helmet streamer (HS) heliospheric current sheet/plasma sheet crossings (and an interplanetary coronal mass ejection), which all exhibit enhanced alpha-to-proton ratios and/or elevated ionic charge states of carbon, oxygen, and iron. We apply the magnetic helicity–partial variance of increments (H m –PVI) procedure to identify coherent magnetic structures and quantify their properties during each interval. The mean duration of these structures are ∼1 hr in both the HS and PS wind. We find a modest enhancement above the power-law fit to the PVI waiting-time distribution in the HS-associated wind at the 1.5–2 hr timescales that is absent from the PS intervals. We discuss our results in the context of previous observations of the ∼90 minutes periodic density structures in the slow solar wind, further development of the dynamic S-Web model, and future Parker Solar Probe and Solar Orbiter joint observational campaigns.

An Electromagnetic Design of Slotless Variable Reluctance PM-Resolver

This paper proposes a novel design of the variable reluctance permanent magnet (VRPM) resolvers. It utilizes a slotless stator to reduce the resolver volume. The proposed design overcomes the complex structure of windings by replacing them with magnetic flux measurement units (MFMU). The new design eliminates the computationally-expensive demodulation process of output signals by relying on none-modulated signals. An analytical model based on the nonlinear magnetic equivalent circuit (MEC) method is used to extract the output signals of the proposed resolver design. The accuracy of applied analytical model is verified against the time-stepping finite-element method (TSFEM). An optimization is implemented to best improve the resolver performance by saturating the stator ribs targeting a minimum possible PM volume. The design aims high flux density of iron to make the resolver robust against external distortions, but at the same time, the flux density of core is kept within the linear region of the B-H curve to avoid saturation. TSFEM is used to further analyze the performance of the optimal slotless VRPM-Resolver in details. The simulation results are verified by experimental tests on a prototyped resolver design.

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor

Asymmetric Winding Structure for Concentrated Winding Permanent Magnet Motors to Achieve a Low Torque Ripple and High Slot Fill Factor