Azimuth Range Research Articles

Reflection imaging of complex geology in a crystalline environment using virtual-source seismology: case study from the Kylylahti polymetallic mine, Finland

Abstract. For the first time, we apply a full-scale 3D seismic virtual-source survey (VSS) for the purpose of near-mine mineral exploration. The data were acquired directly above the Kylylahti underground mine in Finland. Recorded ambient noise (AN) data are characterized using power spectral density (PSD) and beamforming. Data have the most energy at frequencies 25–90 Hz, and arrivals with velocities higher than 4 km s−1 have a wide range of azimuths. Based on the PSD and beamforming results, we created 10 d subset of AN recordings that were dominated by multi-azimuth high-velocity arrivals. We use an illumination diagnosis technique and location procedure to show that the AN recordings associated with high apparent velocities are related to body-wave events. Next, we produce 994 virtual-source gathers by applying seismic interferometry processing by cross-correlating AN at all receivers, resulting in full 3D VSS. We apply standard 3D time-domain reflection seismic data processing and imaging using both a selectively stacked subset and full passive data, and we validate the results against a pre-existing detailed geological information and 3D active-source survey data processed in the same way as the passive data. The resulting post-stack migrated sections show agreement of reflections between the passive and active data and indicate that VSS provides images where the active-source data are not available due to terrain restrictions. We conclude that while the all-noise approach provides some higher-quality reflections related to the inner geological contacts within the target formation and the general dipping trend of the formation, the selected subset is most efficient in resolving the base of formation.

Binaural pre-processing for contralateral sound field attenuation and improved speech-in-noise recognition

Understanding speech presented in competition with other sounds can be challenging. Here, we reason that in free-field settings, this task can be facilitated by attenuating the sound field contralateral to each ear and propose to achieve this by linear subtraction of the weighted contralateral stimulus. We mathematically justify setting the weight equal to the ratio of ipsilateral to contralateral head-related transfer functions (HRTFs) averaged over an appropriate azimuth range. The algorithm is implemented in the frequency domain and evaluated technically and experimentally for normal-hearing listeners in simulated free-field conditions. Results show that (1) it can substantially improve the signal-to-noise ratio (up to 30 dB) and the short-term objective intelligibility in the ear ipsilateral to the target source, particularly for maskers with speech-like spectra; (2) it can improve speech reception thresholds (SRTs) for sentences in competition with speech-shaped noise by up to 8.5 dB in bilateral listening and 10.0 dB in unilateral listening; (3) for sentences in competition with speech maskers and in bilateral listening, it can improve SRTs by 2 to 5 dB, depending on the number and location of the masker sources; (4) it hardly affects virtual sound-source lateralization; and (5) the improvements, and the algorithm's directivity pattern depend on the azimuth range used to calculate the weights. Contralateral HRTF-weighted subtraction may prove valuable for users of binaural hearing devices.

Inverse geodetic problem for long distance based on improved Vincenty’s formula

Abstract Solutions of geodetic problem is an important technical problem in geodesy. Based on the comprehensive analysis of the characteristics of Bessel’s formula and Vincenty’s formula, an improved algorithm is proposed. Firstly, arctangent formula is replaced by arccosine formula to calculate spherical surface angular distance. Secondly, Bessel’s formula is used to replace Vincenty’s formula in the singular region. Finally, the test formulas of geodetic line and azimuth are given. According to the test formula, four points are selected for the test, which are located in the equator, low latitude, middle latitude and high latitude. The geodesic length range of the test is 1000–18000 km and the azimuth range is 0 ∘ 0{\hspace{0.1667em}^{\circ }} – 360 ∘ 360{\hspace{0.1667em}^{\circ }} . The experimental results show that the improved algorithm can solve the problem of singularity and quadrant judgment well. The solution precision of geodetic line is better than 1 mm, and the precision of azimuth is less than 0.0001 second.

Effects of upstream shear flow on performance and flow characteristics of the drag-type hydrokinetic rotor

Effects of the incident shear flow on operational performance of a drag-type hydrokinetic rotor were investigated numerically. A flow visualization experiment was conducted to validate the numerical method. Energy conversion ability of the rotor under different incident shear flow conditions were analysed. The effects of the tip speed ratio were also taken into consideration. The results show that under the incident shear flow conditions, the upstream flow inclines downward and the velocity magnitudes at the upper and lower side of the rotor are significantly different, which affects the operation of the rotor. As the shear coefficient increases, the azimuthal angle range corresponding to the negative torque coefficient reduces and the fluctuation of the torque coefficient with the azimuthal angle appears delay phenomenon. The tip speed ratio has a great effect on the flow patterns around the rotor. The shape and position of the flow structures downstream of the rotor vary obviously with the tip speed ratio. The results are anticipated to provide sound support on the design and optimization of the drag-type hydrokinetic rotor in actual condition.

Parametric Modeling of Sea Clutter Doppler Spectra

For radar modeling and simulation of sea clutter, there are a number of key characteristics used to describe the observed features. These include the mean backscatter power, amplitude statistics, spatial and long-time temporal correlation, and the Doppler spectrum. Regarding the latter, a common modeling approach is to use the mean Doppler characteristics (width and center point) to relate to the sea conditions. However, this does not capture the time- and range-varying fluctuations of the Doppler spectra, which are important for assessing the behavior of coherent detection schemes. The evolving Doppler spectrum model offers a way to model these variations and can be described with a moderate number of parameters. Relating these to the observed geometry, environment and radar characteristics are important to make the models accessible. Previous work has characterized X-band radar sea clutter over a range of sea conditions and azimuth and grazing angles. In this article, new models are presented that capture variations with both the radar resolved area and integration time. This enables the evolved Doppler spectra model to be used over a much wider range of applications.

ONSHORE SEISMIC IMAGING USING DIFFERENT DATA DOMAIN IN NORTHERN NIGER DELTA, NIGERIA

Wide azimuth land acquisition, 3D data is spatially well sampled with a wide range of azimuth and the offsets distributed around those azimuths. This work examined how advance seismic processing technique has come onshore, using offset vector tile methods, high-fidelity, high-resolution is available for use on onshore data. Data were split into one hundred and twenty four vector tiles as a function of source-to-detector distance and azimuth relationship individual pre-trace is assigned an offset vector tiles number that is stored in the trace headers the number is based on the relative shot and receiver location for the trace. Data is regularized to maintain the necessary number of traces and the range of offset in each bin and allow to be filled then migration of the target lines and stacking. After regularization for both the common offset binning and the offset vector tiles (OVTs), it was observed that there is improved signal to noise ratio in the offset vector tiles as compare to the common offset binning, and there is overall improvement in event continuity on the OVTs result. Because onshore (land) data exhibit poor signal-to-noise ratios arising from irregular geometries and noise contamination a fundamental change in processing methods is required. The offset vector tiles (OVTs) have proven to be an effective and efficient tool for 3D wide azimuth acquisitions, the OVTs domain pre-processing, will yield a better imaging when compared to the common offset binning (COB) domain pre-processing.

New Evidence of the Holokinetic Sequences around Suakin-1 and -2in the Sudanese Red Sea Area Using Integrated Geophysical Interpretation

Suakin-1 and Suakin-2 wells are in the Sudanese Red Sea segment where the hydrocarbon generation had been proved by previous studies, however, no reasonable reserve was evidenced due to the complexities of the surrounding salt structures. Six seismic lines were tied to Suakin-1 and -2 to delineate the controlling salt tectonics. The salt evacuation (Roho) and other salt bodies were recognized and matched with similar salt structures in analogous stratigraphic conditions as the Gulf of Mexico and Angola margin. While a previous inconsistent interpretation in the study area marked the high amplitude horizon of the Lower Zeit formation as the top of the Dungunab formation. Three seismic features indicated the presence of salt dome (autochthonous): velocity pull-up, dragging of the sedimentary layers forming mini basins around the third feature, which is the relative transparency of the seismic signal in two piercing like bodies. This interpretation similarly demarcated that the salt escaped east-wards, thus the mapped welded salt is believed to be formed after the salt evacuation. A 3D seismic with a far offset and wide range of azimuth is recommended for detailed imaging.

Learning From Reliable Unlabeled Samples for Semi-Supervised SAR ATR

Synthetic aperture radar automatic target recognition (SAR ATR) has been suffering from the insufficient labeled samples as the annotation of SAR data is time-consuming. Thus, adding unlabeled samples into training has attracted the attention of researchers. In this letter, a semi-supervised method based on consistency criterion, domain adaptation and Top-k loss is proposed to alleviate the need for labeled samples. According to consistency criterion that samples generated by the weak and strong augmentations from the same sample belong to the same category, we use the weak and strong augmented unlabeled samples to predict pseudo labels and train the model respectively. Then, to overcome the issue caused by the domain discrepancy between labeled and unlabeled samples especially when labeled samples concentrate on a narrow azimuth range, a domain adaptation component is designed to reduce their discrepancy. Besides, considering the incorrect pseudo labels will hamper the model training, the Top-k loss is adopted for unlabeled samples to mitigate the negative effects. The experimental results on Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset demonstrate the superiority of our method in semi-supervised SAR ATR. Specifically, we achieve about a 14.29% improvement in recognition accuracy compared to the state-of-the-art when the labeled samples concentrate on a narrow azimuth range.

Millimeter-Wave Dual-Polarized Multibeam Endfire Antenna Array With a Small Ground Clearance

A dual-polarized multibeam endfire antenna array is presented for 5G millimeter-wave applications. The antenna element employs double-layer stack-up substrate integrated waveguides (SIWs) and stepped slot to serve as a polarizer. Dual-linear polarization can be generated when the two SIWs are fed with in-phase and out-of-phase signals. A resonated metallic loop and two pairs of bilateral connecting lines are loaded in front of the antenna aperture to improve impedance matching and enhance gains. The ground clearance is only 1.5 mm, thus is attractive to be applied for mobile terminals. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1 \times 4$ </tex-math></inline-formula> multibeam array is constructed to evaluate the beamforming capability. Butler matrix and 180° hybrid couplers are used to provide the required feeding signals. The measured bandwidth is larger than 10% for both polarizations, capable of covering n257 and n261 bands. The measured peak gains of vertical and horizontal polarizations are 9.38 and 9.51 dBi, with an overlapped 3 dB azimuthal range covering ±48°.

A Versatile Methodology for Reactor Pressure Vessel Aging Assessments

The operation of many nuclear pressurized water reactors is being extended beyond their design lifetime threshold. From the perspective of possible further lifetime extension, satisfying safety requirements is a priority. Characterization of the structural integrity of the reactor pressure vessel (RPV) is an important issue as it is a guiding parameter that influences the reactor lifetime. Embrittlement of RPV material is primarily induced by the bombardment of fast neutrons (with energies greater than 1 MeV). Consequently, fast neutron fluence is one of the quantities used by safety authorities to characterize the structural integrity of RPV. However, future RPV aging assessments might lean on new variables with respect to current laws, such as neutron fluence considering the whole neutron spectrum or displacements per atom (dpa) since the latter is more representative of overall damage generated in the RPV. In order to meet these challenges, a versatile calculation scheme for RPV aging assessments is proposed in this paper. The developed methodology allows one to compute (fast and non-fast) neutron fluence as well as dpa rate, using the Norgett-Robinson-Torrens dpa model and the Athermal Recombination Corrected dpa model, for a wide azimuthal and axial range on the RPV and in the capsules of the aging monitoring program (which contain dosimeters and vessel material samples). This methodology is based on a coupling between deterministic (CASMO5 and SIMULATE5) and Monte Carlo (MCNP6) numerical approaches. First, the deterministic approach is used to evaluate the full-core fission neutron source term. Second, Monte Carlo modeling is used to perform the neutron attenuation from the core to sites of interest, such as the RPV. The computational efficiency, accuracy, and potential benefits of the methodology are presented. Moreover, the frequency at which neutron transport calculations should be performed in order to obtain sufficiently accurate time-integrated data over a reactor cycle is discussed. Finally, the validity of the fast neutron fluence as an indicator of RPV aging is compared against the use of dpa.

Joint Sparsity for TomoSAR Imaging in Urban Areas Using Building POI and TerraSAR-X Staring Spotlight Data.

Synthetic aperture radar (SAR) tomography (TomoSAR) can obtain 3D imaging models of observed urban areas and can also discriminate different scatters in an azimuth–range pixel unit. Recently, compressive sensing (CS) has been applied to TomoSAR imaging with the use of very-high-resolution (VHR) SAR images delivered by modern SAR systems, such as TerraSAR-X and TanDEM-X. Compared with the traditional Fourier transform and spectrum estimation methods, using sparse information for TomoSAR imaging can obtain super-resolution power and robustness and is only minorly impacted by the sidelobe effect. However, due to the tight control of SAR satellite orbit, the number of acquisitions is usually too low to form a synthetic aperture in the elevation direction, and the baseline distribution of acquisitions is also uneven. In addition, artificial outliers may easily be generated in later TomoSAR processing, leading to a poor mapping product. Focusing on these problems, by synthesizing the opinions of various experts and scholarly works, this paper briefly reviews the research status of sparse TomoSAR imaging. Then, a joint sparse imaging algorithm, based on the building points of interest (POIs) and maximum likelihood estimation, is proposed to reduce the number of acquisitions required and reject the scatterer outliers. Moreover, we adopted the proposed novel workflow in the TerraSAR-X datasets in staring spotlight (ST) work mode. The experiments on simulation data and TerraSAR-X data stacks not only indicated the effectiveness of the proposed approach, but also proved the great potential of producing a high-precision dense point cloud from staring spotlight (ST) data.

Shallow soil effects for contrasting PGAs at nearby strong-motion stations during the 2017, Mj 5.2, southern Akita Prefecture earthquake

On September 8, 2017, an earthquake of Mj 5.2 occurred with the epicenter in southern Akita Prefecture, Japan, at 22:23 local time. According to the Japan Meteorological Agency (JMA), the focal depth was 9 km. Many strong-motion stations of K-NET and KiK-net recorded ground motions from the earthquake. The maximum horizontal vector peak ground acceleration (PGA) of approximately 136 cm/s2 was recorded at one of the KiK-net stations at an epicentral distance of about 8 km. However, despite being 37 km and 53 km far from the epicenter, two stations recorded PGAs of approximately 126 and 113 cm/s2, respectively, similar to that near the epicenter. Even though these PGAs are not rare, we found that the PGAs at the two sites strongly deviated from the median values suggested by a ground motion prediction equation (GMPE), while the nearby sites generally followed the GMPE. Available velocity models showed that shallow shear wave velocities, especially in the top 5 m, were lower (i.e., the soils were softer) at the two sites compared to those at their nearest neighboring sites. We compared the ratios of the PGAs and peak ground velocities (PGVs) at the two sites with respect to their neighboring sites for many earthquakes covering a wide range of magnitudes and azimuths. We found that the PGAs and PGVs at the two sites were systematically larger than those at the adjacent sites. Linear theoretical site amplifications using the available soil models gave peak frequencies around 6-8 Hz at the larger PGA sites. Bandpass-filtered records showed significantly larger PGAs around these frequencies at the larger PGA sites. The above results showed that local site condition is one of the major contributing factors to induce large PGAs. Furthermore, softer sites experience more substantial nonlinear site amplification than the stiffer sites when input motions exceed some threshold PGAs. This latter effect means that the softer sites can produce a variety of ground motion spectra. Nevertheless, the degree of damage to built structures depends on several factors, including the design and quality of construction. We expect that this study contributes to developing improved microzonation maps for earthquake disaster mitigation.

The far-field plasma characteristics of LHT40 low-power Hall thruster for commercial aerospace applications

To achieve a better insight into the far-field plasma spatial distribution and evolution characteristics of the 300 W class low-power Hall thruster (LHT) for commercial aerospace applications, a dedicated and integrated plasma diagnostic system composed of seventeen Faraday cups (FC) and two triple Langmuir probes (TLP) is established to investigate the time-averaged in situ spatial distribution characteristics of far-field ions and electrons. The ion current density (ICD), plasma potential, plasma density, and electron temperature at 1000 mm downstream of 300 W class LHT for commercial aerospace applications in the azimuthal angle range of −90° to 90° were investigated under the conditions of different anode mass flow rates and discharge voltages. The results demonstrated that ICD, beam divergence angle, and mass utilization efficiency increased with increasing anode mass rate. The double-wings phenomenon was observed in the spatial distribution of ICD at large angles from the thruster axis, which is attributed to charge exchange collisions at increasing vacuum backpressure. The plasma electron temperature, electron density, and plasma potential parameters derived from the TLP decreased rapidly in the angle range from 0° to 30° and did not exhibit significant variations above 30°, which was also in good agreement with the results of the measured divergence angle of the FC. The discrepancy of average ion speed was calculated. The maximum error is better than 31.5% which checks the consistency between the TLP’s results and that of FC to some extent.

A PCB‐stacked air‐filled Luneburg reflector lens antenna for 5G millimeter wave applications

AbstractA wideband Luneburg reflector lens antenna with multi‐beam scanning performance is proposed for 5G millimeter wave (MM‐wave) applications. The proposed lens antenna consists of two groups of PCBs, four feed antennas, and a reflector. Holes are drilled with various radius in each layer of PCB (except the top and the bottom layers), so the air spacing between the two groups of PCBs changes discretely, which realizes the graded refractive index (GRIN) of the Luneburg lens. Owing to the utilization of the reflector, the size of the proposed lens is reduced by half compared to the conventional cylinder Luneburg lens, and the aperture efficiency is enhanced since the radiation aperture is reduced. The measured −10 dB impedance bandwidth covers 32–38 GHz with isolations better than 19 dB. The radiation beams demonstrate an azimuthal scanning range of 20–66 deg. It is a good candidate for 5G MM‐wave applications.

Milky Way spiral arms from open clusters in Gaia EDR3

Context. The physical processes driving the formation of Galactic spiral arms are still under debate. Studies using open clusters favour the description of the Milky Way spiral arms as long-lived structures following the classical density wave theory. Current studies comparing the Gaia DR2 field stars kinematic information of the solar neighbourhood to simulations, find a better agreement with short-lived arms with a transient behaviour. Aims. Our aim is to provide an observational, data-driven view of the Milky Way spiral structure and its dynamics using open clusters as the main tracers, and to contrast it with simulation-based approaches. We used the most complete catalogue of Milky Way open clusters, with astrometric Gaia EDR3 updated parameters, estimated astrophysical information, and radial velocities, to revisit the nature of the spiral pattern of the Galaxy. Methods. We used a Gaussian mixture model to detect overdensities of open clusters younger than 30 Myr that correspond to the Perseus, Local, Sagittarius, and Scutum spiral Arms, respectively. We used the birthplaces of the open cluster population younger than 80 Myr to trace the evolution of the different spiral arms and compute their pattern speed. We analysed the age-distribution of the open clusters across the spiral arms to explore the differences in the rotational velocity of stars and spiral arms. Results. We are able to increase the range in Galactic azimuth where present-day spiral arms are described, better estimating its parameters by adding 264 young open clusters to the 84 high-mass star-forming regions used so far, thus increasing the number of tracers by 314%. We used the evolution of the open clusters from their birth positions to find that spiral arms nearly co-rotate with field stars at any given radius, discarding a common spiral pattern speed for the spiral arms explored. Conclusions. The derivation of different spiral pattern speeds for the different spiral arms disfavours classical density waves as the main drivers for the formation of the Milky Way spiral structure, and it is in better agreement with simulation-based approaches that tend to favour transient spirals. The increase in the number of known open clusters, as well as in their derived properties, allows us to use them as effective spiral structure tracers and homogenise the view from open clusters and field stars on the nature of the Galactic spiral arms.

A Pareto Multi‐Objective Optimization Approach for Anisotropic Shale Models

AbstractWhen the elastic parameters of rocks such as shales vary with the propagation direction of a passing seismic wave that rock is called anisotropic. Modern seismic data are typically acquired over a wide azimuth range using long offsets. For such data, optimum imaging and subsequent quantitative amplitude interpretation requires taking subsurface anisotropy adequately into account during execution of the quantitative interpretation workflow. Here, we present a multi‐objective approach to find an optimal solution using both well logs and seismic data. We include minimization of a seismic match objective function as a constraint to narrow the uncertainty distribution around model parameters and to ensure that the model is consistent with seismic as well as well log data. Consequently, the resulting anisotropy model can be used for both well logs and seismic data analysis. First, the Hudson‐Cheng crack model is used to obtain rock matrices properties and aspect ratio of a set of ellipsoidal cracks. Then, we obtain a set of non‐dominated solutions, which minimizes the rock physics model multi‐parameter objective function and the Amplitude‐Versus‐Offset objective function. The approach is applied to field data with one vertical well log and pre‐stack migrated seismic data. In spite of the low signal‐to‐noise ratio of the seismic data, the overall results are consistent with the rock physics model and fit the seismic amplitude variations, particularly for the confidently interpretable mid‐to‐far angles of incidence. Furthermore, we extend the approach to predict seismic anisotropy away from well calibration, to map the occurrence of high‐quality organic‐rich shales.

ANALYSIS OF SENSITIVITY OF TARGET TRACKING SYSTEMS TO EXTERNAL INTERFERENCE IN MULTICHANNEL RADARS WITH FIXED PARAMETERS

The multichannel and fixed parameters radars for tracking targets with the phased array antennas are widely used in modern military surveillance systems. The modular integration of a phased antenna array with digital processors allows to realize the command and control functions of antenna patterns for tracking multiple targets in the time resolution modes. Tracking of the air targets in range, radial speed and angular coordinates of evaluations and azimuth is provided by means of the multichannel radars without adaptation modes to the characteristics of external influences. Thus, adjusting the algorithms of tracking systems to the maximum maneuverability of the air targets can lead to a significant reduction in the accuracy of surveillance in comparison with the potentially achievable accuracy for such radars of tracking the linear flight targets in the long duration of time. In the case of adjusting the algorithms of tracking systems to either low intensity of flying targets, or lack of the aircraft maneuvering, it is possible to significantly increase the error of the aircraft flying information, and as a result to have a disruption of tracking the air targets. The increase in the parameters of the tracking error in relation to the influence of external interference were obtained as a result of the study. As a result of research, it is possible to assess the feasibility of adapting to certain characteristics of external influences, and provide recommendations for selecting and fixing the parameters of algorithms of tracking systems to ensure their versatility to surveillance targets with both high maneuverability, and implementing the stealth technology.

Three-Dimensional Slope Imaging Method for Ground-Based Real-Aperture Radar.

Traditional two-dimensional radar images can only reflect the target azimuth and slant range and thus suffer problems of geometric deformation and overlapping. The unique three-dimensional (3D) imaging capability of ground-based real-aperture radar can more accurately and directly achieve correlation between the radar image and the slope monitoring scenarios, thus providing reliable information for the early warning and forecasting of landslides and collapse disasters. The latest method of selecting a slope target from a high-resolution range profile includes two indexes: maximum amplitude and coherence, which will affect the accuracy of displacement measurement when there is an interference target. We present a three-dimensional slope imaging method based on smoothness constraints. On the basis of the latest method, the objective fact of the practically smooth and continuous distribution of slope surfaces is considered. This method can be used for image interpretation on strongly scattered targets within the slope. The independently developed ground-based real-aperture slope radar system was deployed in the Heidaigou Open-Pit Coal Mine in Inner Mongolia to carry out 3D slope imaging experiments. The effectiveness of this method in slope monitoring and imaging was confirmed by comparing the surface roughness and the spatial positions of the targets with the high-density point cloud data in the projective plane obtained during the same time period. We used RMSE function and roughness as two measures. It shows that the method presented in this paper is more suitable for actual three-dimensional slope imaging.

Wind Tunnel Experiments and Numerical Study on Performance Characteristics of an H-type Vertical Axis Wind Turbine in the Spanwise Direction

The aerodynamic forces and vortex characteristics of an H-type Vertical Axis Wind Turbine (VAWT) become complicated because of dynamic stall, particularly in the three-dimensional impact on the blade spanwise direction. This study focused on the evaluation of the aerodynamic performance and vortex characteristics of an H-type VAWT in the spanwise direction by numerical simulations and wind tunnel experiments. Pressure acting on the blade surface was obtained from multiport pressure measurement devices by wind tunnel. Meanwhile, the vortex field around different blade sections was investigated through numerical simulations. The stall behavior was analysed by comparing the results of numerical simulations and experiments. As a result, the tangential force of single blade was mainly contributed at the chordwise position of x/c≤0.4c and the power of single blade was mainly contributed at the azimuthal angle range of 60°≤θ≤150° in the blade section position region of 0≤z/(H/2)≤0.7. At the section position of z/(H/2)=0.5, the initial flow separation was found at the suction side and progressed forward to the leading edge. With the increase of the tip speed ratios, the decreasing position of the averaged local power coefficient of each section was closer to the middle section of z/(H/2)=0, and the attenuation speed became faster. The power coefficient reductions at the blade section position of z/(H/2)=0.9 were 38.29%, 46.78% and 56.42% when the tip speed ratios were 1.38, 2.19 and 2.58, respectively. The results of this study provided a better understanding of the development of the performance characteristics and vortex characteristics of H-type VAWT.

Tropical Cyclone Resistance to Strong Environmental Shear

AbstractIt is widely known that strong vertical wind shear (exceeding 10 m s−1) often weakens tropical cyclones (TCs). However, in some circumstances, a TC is able to resist this strong shear and even restrengthen. To better understand this phenomenon, a series of idealized simulations are conducted, followed by a statistical investigation of 40 years of Northern Hemisphere TCs. In the idealized simulations, a TC is embedded within a time-varying point-downscaling framework, which is used to gradually increase the environmental vertical wind shear to 14 m s−1 and then hold it constant. This controlled framework also allows for the separation of the TC-induced flow from the prescribed environmental flow. The TC-induced outflow is found to withstand the strong upper-tropospheric environmental flow, and this is manifested in the TC-induced shear difference (TCSD) vector. The TCSD vector, together with the environmental shear vector, defines an azimuthal range within which most of the asymmetric convection is located. The statistical analysis confirms the findings from the idealized simulations, and the results are not strongly sensitive to the TC intensity or basin. Moreover, compared with total shear, the inclusion of TCSD information creates a slightly better correlation with TC intensity change. Overall, the TCSD vector serves as a diagnostic to explain the ability of a TC to resist strong environmental shear through its outflow, and it could potentially be used as a parameter to predict future intensity change.