Core Trajectory Research Articles

Practicing Islam in China the ‘right way’ – Islamic orthodoxy in the Muslim Sanzijing genre

ABSTRACT Reconciling their simultaneous identity as legitimate members of Chinese society and the transnational Muslim Umma has been a longstanding concern for Chinese-speaking Muslims, particularly those associated with what is now known as the Hui community. Over time, this challenge prompted Chinese Muslim scholars to grapple with the demands of Islamic law within the framework of Confucian cultural and legal hegemony. Their efforts led to the development of a regionalist understanding of Islamic orthodoxy, imbued with conceptual elements borrowed from Chinese traditions but fully consistent with the core principles of Sunni Islam. These efforts are systematically expounded within the Muslim Sanzijing genre, which features Islamic versions of the so-called “Three-Character Classic,” aiming to periodically address and reconcile the emergence of potential frictions between Islam and the Chinese law. The core trajectory of their combined narrative, as it pertains to Islamic orthodoxy and its development in the aftermath of the 18th century, constitutes the focus of this study.

Four-Dimensional Aircraft Trajectory Prediction with a Generative Deep Learning and Clustering Approach

Medium- and long-term four-dimensional (4D) aircraft trajectory prediction (TP) is a critical technology in air traffic management (ATM). This paper addresses the issue of existing medium- and long-term TP methods that are difficult to accurately fit aircraft trajectory data distributions. We propose a 4D TP method based on K-medoids clustering and conditional tabular generative adversarial networks (CTGAN), called C-CTGAN. Comparative experiments with four long short-term memory (LSTM)-based models and the original CTGAN model show that the proposed model’s TP accuracy is significantly higher than others when predicting medium- and long-term trajectories. When using the trajectory datasets without holding and a prediction time span of 10 min, compared to the convolutional neural network (CNN)-LSTM model, the C-CTGAN model reduces the mean absolute errors (MAEs) of core trajectory parameters, such as latitude, longitude, geometric altitude, and ground speed, by 69.89, 15.00, 74.07, and 84.21%, respectively. Compared to the original CTGAN model, the MAE is reduced by 20.43, 39.09, 31.98, and 17.07%, respectively. When using the trajectory datasets with holding, compared to the CNN-LSTM model, the C-CTGAN model shows MAE reductions of 14.08, 23.68, 31.46, and 2.86%, respectively. Compared to the original CTGAN, the reduction is 34.88, 2.69, 23.16, and 73.91%, respectively.

Feature-based deformation for flow visualization

We present an approach that supports the analysis of flow dynamics in the neighborhood of curved line-type features, such as vortex core lines, attachment lines, and trajectories. We achieve this with continuous deformation to the flow field to straighten such features. This provides “deformed frames of reference”, within which qualitative flow dynamics are better observable with respect to the feature. Our approach operates at interactive rates on graphics hardware, and supports exploration of large and complex datasets by continuously navigating the additional degree of freedom of deformation. We demonstrate the properties and the utility of our approach using synthetic and simulated flow fields, with a focus on the application to vortex core lines.Graphical abstract

Observation of pinning and pinning evasion dynamics of a magnetic vortex core

An understanding of the dynamics of magnetic textures as they interact with defects in the host material is critical for proposed applications that depend on controlled translation of these magnetic textures. We report on the experimental observation of magnetic vortex core (VC) trajectories as they are affected by a potential energy landscape arising from defects in thin, permalloy disks. We first map the VC pinning landscape using equilibrium Kerr microscopy, and then use multiplexed time-resolved Kerr microscopy to track in-plane dynamics of a magnetic VC in response to a magnetic field pulse with ns time resolution, and several-nm spatial resolution. The initial position of the VC is set by applying a static magnetic field to shift the dynamics relative to the pinning landscape. We observe the expected spiral trajectory as the VC relaxes to equilibrium over several tens of nanoseconds. However, in the presence of strong pinning, we also observe pinning evasion as the VC trajectory is deflected due to the pinning potential, and enhanced damping as the vortex becomes pinned. We compare to a simple model based on the Thiele equation of motion to understand these results.

An anomaly detection method based on ship behavior trajectory

An anomalous trajectory detection method based on ship trajectory clustering and prediction is proposed. The method consists of two modules, namely, trajectory clustering based on improved DBSCAN and Trajectory prediction by ProbSparse Attention-based Transformer. we propose the concept of ship behavior similarity for the first time in this paper, by decomposing the velocity according to the ship's heading to get ‘velocity coordinates' to replace latitude and longitude coordinates, on the basis of which the ship behavior trajectories are clustered and the core trajectories are extracted. By comparing the behavioral similarity between the predicted trajectory and the core trajectory with the preset threshold, it is judged whether the abnormal trajectory or the ship has abnormal operation. AF-DP is used in this method for compression of trajectory data, and Fast-DTW is used to calculate the behavioral similarity between trajectories. Notably, this is the first application of ProbSparse Attention-based Transformer in the maritime domain. The proposed method is applicable to inland river traffic near Wusongkou, Shanghai. The final experimental results show that the method we proposed can effectively identify the abnormal behaviors in the trajectory, and can provide technical support for the analysis of ship track data and the risk management of maritime transport in this region.

Experimental investigation on tip vortex cavity deformation and flow dynamics using high-speed imaging and laser Doppler velocimetry measurements

Cavitation affects engineering applications relating to aquatic operations. Tip vortex cavitation (TVC) leads to several technical problems, such as efficiency loss and noise. Hence, there is a need for a comprehensive understanding of the formation mechanism, shape distortions, and underlying physical phenomena of TVC. The dispersion relation of inertial waves on inviscid cavitating vortices is a valuable tool for predicting various TVC shapes. This study explains the patterns of flow around the tip of an elliptical foil and the cavity shape deformations under different flow conditions through experimental analysis. Experiments are conducted using a National Advisory Committee for Aeronautics hydrofoil in the cavitation tunnel at Chungnam National University. The appearance, development, and shapes of vortex cavitation are closely examined using high-speed imaging technology. There is good agreement between the vortex cavity shapes captured by this high-speed imaging and those derived in previous studies. Using laser Doppler velocimetry (LDV) measurements and analysis through image processing of high-speed images, we compare the vortex core trajectories in cavitating and non-cavitating conditions. There is a good match between the two, demonstrating the feasibility of predicting the flow behaviors around vortex cavities using LDV data. As the noise from the TVC is considered a significant source of underwater radiated noise we also measured sound pressure level, which exhibits abrupt changes at specific cavitation numbers, supporting the occurrence of the singing vortex phenomenon and highlighting its sensitivity to small variations in flow conditions. Furthermore, we obtain precise measurements of the instantaneous TVC diameter under different cavitation numbers, allowing the physical functionality of distinct TVC shapes to be determined. Our results significantly extend the scientific understanding of the flow around TVC and the fundamental causes of TVC distortions.

Zapiola Gyre, Velocities and Mixing, New Argo Insights

AbstractThe Zapiola Gyre is a large, full‐depth, bottom‐intensified, anticyclonic recirculation in the Argentine Basin. It rotates around the Zapiola Drift, a sedimentary rise standing a few hundred meters above the abyssal plain, tall enough to create closed contours of planetary potential vorticity. Hence the gyre has been posited to be an eddy‐driven free mode that is damped primarily by the bottom Ekman layer. It describes approximately a zonally elongated ellipse with a zonal semi‐major axis of ∼440 km and a meridional semi‐minor axis of ∼125 km. Its volume transport is estimated here at ∼110 (±25) × 106 m3 s−1. It has peak depth‐averaged meridional velocities of ∼0.06 and ∼0.08 m s−1, and peak depth‐averaged zonal velocities of ∼0.11 and ∼0.12 m s−1. Peak surface velocities are ∼57% of peak bottom velocities, consistent with the dynamics of a bottom‐intensified Taylor column in a stratified flow. Deep and Core Argo float trajectories follow the gyre, with a couple of Core Argo floats with 1000‐dbar parking depths executing more than three anticyclonic rotations around it, and Core Argo floats that approach within ∼75 km of the gyre center executing on average ∼1.7 circumnavigations. Deep Argo temperature‐salinity profiles combined with historical shipboard CTD profile data afford maps newly illuminating the advective swirling of water‐mass signatures around the gyre at the density of the North Atlantic Deep Water salinity maximum. Their patterns are consistent with a Peclet number of ∼30 estimated here using previously published lateral eddy diffusivities in the region.

On wake dynamics of a propeller operating under nonuniform behind-hull condition

The wake dynamics of the benchmark propeller INSEAN E779A operating in the nonuniform wake of a typical ship hull are investigated with large-eddy simulations. The flow features and evolution of vortex structures in the propeller wake are analyzed to evaluate the influences of the nonuniform inflow and to identify the instability mechanisms. Unlike the uniform inflow condition, the azimuthal-variant inflow velocity field results in an asymmetric and faster destabilization of the wake. Local mutual interaction among the neighboring tip vortices in the upper region of the wake, which shows a unique bridging-reconnection mechanism of vortex filaments, initiates the decomposition and destabilization of tip vortices and induces instability in the hub vortex. The power spectrum density (PSD) of kinetic energy is employed to analyze the transition characteristics of the tip vortices quantitatively. The hub vortex core circularity and trajectory envelope are calculated to quantify the long- and short-wave instabilities.

Influence of vortex interactions on the exergy transfer and performance of OWC wells turbine

To provide deep dives about aerodynamic loss mechanisms in Wells turbines for wave energy conversion, a loss audit analysis was performed by numerical experiments in a monoplane Wells turbine with guide vanes. The interactions between the tip-leakage and leading-edge vortices during the stall process were captured by an improved vortex identification method, which revealed the relationship between vortex interactions and stall mechanisms by identifying coherent structures and tracking the vortex core trajectory. Finally, the influence of vortex interactions on exergy transfer was quantified. The results indicate that the lost kinetic energy and mixing losses dominate the loss generation in the Wells turbine stage under stall conditions. Under the beneficial effect of tip leakage flow, leading-edge separation first begins at the equilibrium region between the tip-leakage and leading-edge vortices. As the leading-edge vortices expand toward the blade tip, the intensified leading-edge vortex interacts with the casing suction-side corner vortex and accelerates the dissipation of the tip-leakage vortices. Consequently, the contributions of viscous irreversibilities outweigh those of shaft work, being the dominant factor in the decrease in flow exergy, leading to a decrease in exergy utilization by 38.46% from the pre-stall condition to the stall condition.

Scripps Argo Trajectory-Based Velocity Product: Global Estimates of Absolute Velocity Derived from Core, Biogeochemical, and Deep Argo Float Trajectories at Parking Depth

Abstract Global estimates of absolute velocities can be derived from Argo float trajectories during drift at parking depth. A new velocity dataset developed and maintained at Scripps Institution of Oceanography is presented based on all Core, Biogeochemical, and Deep Argo float trajectories collected between 2001 and 2020. Discrepancies between velocity estimates from the Scripps dataset and other existing products including YoMaHa and ANDRO are associated with quality control criteria, as well as selected parking depth and cycle time. In the Scripps product, over 1.3 million velocity estimates are used to reconstruct a time-mean velocity field for the 800–1200 dbar layer at 1° horizontal resolution. This dataset provides a benchmark to evaluate the veracity of the BRAN2020 reanalysis in representing the observed variability of absolute velocities and offers a compelling opportunity for improved characterization and representation in forecast and reanalysis systems. Significance Statement The aim of this study is to provide observation-based estimates of the large-scale, subsurface ocean circulation. We exploit the drift of autonomous profiling floats to carefully isolate the inferred circulation at the parking depth, and combine observations from over 11 000 floats, sampling between 2001 and 2020, to deliver a new dataset with unprecedented accuracy. The new estimates of subsurface currents are suitable for assessing global models, reanalyses, and forecasts, and for constraining ocean circulation in data-assimilating models.

Vessel destination prediction: A stacking approach

This paper proposes a stacking model for ship destination prediction that incorporates both a static model of historical information, based on a Bayesian neural network (BNN) and a dynamic model of current trajectory information. We propose a modified DBSCAN clustering method for trajectory clustering and core trajectory identification. By identifying core (representative) trajectories, we do not need to follow previous studies that compare a current trajectory with each historical trajectory, which significantly reduces the computation time and increases the accuracy of our similarity calculation. In order to obtain the optimal weights for the static and dynamic models, we develop a multi-response constrained linear regression model. This method has high interpretability, as the weights directly indicate the different roles of static and dynamic models at different stages after departure. Our results show that the stacking model is highly accurate after three days from departure, indicating the indispensable role of both information types.

Hybrid RANS/LES study of tip leakage vortex instability and turbulence characteristics of a transonic turbine cascade

To conduct detailed investigations about vortex instability and turbulence characteristics near a transonic turbine tip region, a highly accuracy hybrid Reynolds averaged Navier Stokes (RANS) / large eddy simulation (LES) method, namely detached eddy simulation (DES)-type method, is adopted at the exit isentropic Mach number of 0.95. Validation results show that this hybrid method can provide an accurate prediction against experiments. In contrast with the RANS method, this method can exhibit superiority in capturing detailed small-scale flow structures and more realistic turbulence distribution. Based on various identification methods, two predominant instability patterns of tip leakage vortex (TLV), namely, vortex wandering and breakdown have been recognized successfully in its downstream progression. Due to the supplement of tip leakage flow (TLF), the TLV maintains a concentrated vortex morphology with a monotonically increasing transverse wandering magnitude inside the blade passage. Subsequently, the TLV breakdown phenomenon, which is mainly due to the high adverse pressure gradient aggravated by shock waves, can be observed downstream the trailing edge. Meanwhile, a “spiral-type” vortex breakdown is distinguished firstly in a transonic turbine environment, which cannot be found in the previous RANS literature. To investigate the nature of the vortex instability, we perform an analysis based on the vorticity transport equation, it's found that the convection term due to the velocity gradient dominated the leakage vorticity damping. Combined the triple decomposition with the proper orthogonal decomposition (POD) method, the mechanisms of vortex wandering have been further revealed, which exhibits non-zero perturbations in transverse modes and a helical mode in the streamwise direction. Furthermore, detailed analysis of the turbulence characteristics has been also conducted, which contains distributions of Reynolds stress terms and the turbulent kinetic energy (k) along the TLV core trajectory. It can be recognized that the high adverse pressure gradient by shock waves can result in a sharp increase of Reynolds normal stresses (τii), which can stretch the TLV in different directions and exerts detrimental effects on the vortex breakdown. As a complementary, the turbulent anisotropy is also evaluated by the Lumley triangle method, which exhibits a variation from the one-component anisotropy to a two-component morphology as the TLV migrating downstream, while a isotropic turbulence field may be formed downstream the trailing edge due to the intense mixing. Predicted turbulence characteristics, vortical instabilities, and their flow mechanism can provide guide towards lower loss design and flow control of the turbine blade.

Investigation on conical separation vortex generated by swept shock wave/turbulent boundary layer interaction

To study the effects of Mach number, Reynolds number and deflection angle on the conical separation vortex generated by swept shock wave/turbulent boundary layer interaction , the experimental and numerical simulation methods are used. The Mach numbers are Ma=2.95 and Ma=4. The deflection angles are 12°, 15° and 18°. The incoming boundary layer thickness δ0.99 is 4.6 mm, 23 mm and 115 mm. The evolution characteristics of the vortex, including the vortex core position, the vortex area and the vortex intensity, and the effects of Mach number, Reynolds number and deflection angle on them are analyzed. The results show that the core trajectory of the vortex is distributed along the rear shock foot line of the λ shock structure. The Reynolds number is the main factor affecting the separation vortex core. The vortex area increases linearly along the direction of the inviscid shock, and the Reynolds number and the Mach number both are the factors affecting the growth rate of the separation vortex. The vortex intensity increases linearly along the direction of the inviscid shock. The vortex intensity is mainly affected by the Mach number and the deflection angle, but is not affected by the Reynolds number.

Observation of Defect-Assisted Magnetic Vortex Core Reversal at Ultralow Critical Velocity

The stability of structures with nontrivial topology is a subject of great interest, both from fundamental and technological perspectives. The topology of a magnetic vortex, for example, results in high stability of the vortex core polarity, which is attractive for applications. This high stability, however, greatly impedes the required deterministic polarity switching, which is typically only achieved with large magnetic fields or strong dynamic driving. Here, we show that the interaction between the vortex core and manufactured nanoscale defects in the magnetic material lowers the required driving strength for core polarity reversal by more than an order of magnitude. We excite vortex dynamics in thin permalloy disks, and map the two-dimensional (2D) vortex core trajectory using 3D time-resolved Kerr microscopy. In pristine samples, we observe normal gyrotropic motion of the vortex core. After laser-induced generation of defects, however, we observe repeated vortex core reversal at much-reduced driving strength. Micromagnetic simulations reveal how local reduction of exchange coupling and saturation magnetization can create vortex core reversal sites for deterministic vortex core switching.

Stress-induced modification of gyration dynamics in stacked double-vortex structures studied by micromagnetic simulations

In this paper, using micromagnetic simulations, we investigate the stress-induced frequency tunability of double-vortex nano-oscillators comprising magnetostrictive and non-magnetostrictive ferromagnetic layers separated vertically by a non-magnetic spacer. We show that the relative orientations of the vortex core polarities p 1 and p 2 have a strong impact on the eigen-frequencies of the dynamic modes. When the two vortices with antiparallel polarities have different eigen-frequencies and the magnetostatic coupling between them is sufficiently strong, the stress-induced magnetoelastic anisotropy can lead to the single-frequency resonant gyration mode of the two vortex cores. Additionally, for the case of parallel polarities, we demonstrate that for sufficiently strong magnetostatic coupling, the magnetoelastic anisotropy leads to the coupled vortex gyration in the chaotic regime and to the lateral separation of the vortex core trajectories. These findings offer a path for achieving a fine control over gyration frequencies and trajectories in vortex-based oscillators via adjustable elastic stress, which can be easily generated and tuned electrically, mechanically or optically.

Numerical Analysis of the Effect of Cavitation on the Tip Leakage Vortex in an Axial-Flow Pump

To understand the effect of cavitation on the tip leakage vortex (TLV), turbulent cavitating flows were numerically investigated using the shear-stress transport (SST) k–ω turbulence model and the Zwart–Gerber–Belamri cavitation model. In this work, two computations were performed—one without cavitation and the other with cavitation—by changing the inlet pressure of the pump. The results showed that cavitation had little effect on the pressure difference between the blade surfaces for a certain cavitation number. Instead, it changed the clearance flow and TLV vortex structure. Cavitation caused the TLV core trajectory to be farther from the suction surface and closer to the endwall upstream of the blade. Cavitation also changed the vortex strength distribution, making the vortex more dispersed. The vortex flow velocity and turbulent kinetic energy were lower, and the pressure pulsation was more intense in the cavitating case. The vorticity transport equation was used to further analyze the influence of cavitation on the evolution of vortices. Cavitation could change the vortex stretching term and delay the vortex bending term. In addition, the vortex dilation term was drastically changed at the vapor–liquid interface.

Heavy Winter Precipitation Events with Extratropical Cyclone Diagnosed by GPM Products and Trajectory Analysis

Heavy precipitation events were identified during the cold seasons of 2014–2019 using two-day accumulated precipitation data at 137 stations of the Japan Meteorological Agency. The mechanisms for producing heavy precipitation regarding the structure of an occluding extratropical cyclone were analyzed using the products of the Dual-frequency Precipitation Radar (DPR) onboard the Global Precipitation Measurement (GPM) core satellite and trajectory analysis on the European Centre for Medium-range Weather Forecasts atmospheric reanalysis data. Upper-ranked events with heavy precipitation were predominantly caused by extratropical cyclones and were in mature stages. In the top 50 ranked events, three south-coast cyclones were nominated, and the relationships between developing the mesoscale precipitation system and airstreams were intensively diagnosed. Hourly precipitation changes at stations that recorded heavy precipitation were primarily affected by a combination of the warm conveyor belt (WCB), cold conveyor belt (CCB), and dry intrusion (DI). Wide-ranging stratiform precipitation east of the cyclone center was composed of low-level WCB over the CCB and upper WCB, and convective clouds around the cyclone center were associated with the upper DI over the WCB that provided an extreme precipitation rate at the surface, including the formation of a band-shaped precipitation system. Convective cloud activities also contributed to moist air advection over the stationary stratiform precipitation areas recognized as the upper WCB. DPR products also identified deep stratiform precipitation in the cloud-head area behind the cyclone center with mid-level (near-surface) latent heat release (absorption) with increased potential vorticity along the CCB, making feedback intensification of the cyclone possible.

Orbit-like trajectory of the vortex core in ferrimagnetic dots close to the compensation point

In physics, conserved quantities are key to understand and describe physical phenomena. These conserved quantities are related to Noether’s theorem and Lagrangian description in both classical mechanics and field theory. In this article we have found the equation of the vortex core trajectory in ferrimagnets close to the compensation point in terms of two conserved physical quantities, namely the energy, E, and a vector perpendicular to the orbit plane, A→=−L→+G→|r→c|2∕2 where G→, L→ and r→c are the topological gyrovector, the angular momentum and the position of the vortex core, respectively. We found that in the absence of a dissipative term, for small deviations of the vortex core, the trajectory is bounded between two concentric circles. On the contrary, under the action of a dissipative term proportional to the damping coefficient, A→ is no longer conservative and the vortex core moves either towards the center or out of the cylinder, depending on the circularity of the magnetic vortex and the intensity of the magnetic field applied in the plane of the cylinder.

Dynamics of periodically-excited vortices in swirling flames

This work investigates the dynamics of periodically-excited vortices in swirling cold flow and hot flame using high-speed particle image velocimetry, for three different Strouhal numbers, 0.68, 1.02, and 1.70. The periodic upstream perturbation induces coherent vortices in the shear layers both inside and outside of the flame surface. We find that the outer vortex rings (OVRs) play a dominant role in tuning the flame dynamics and heat release, whereas the inner vortex rings (IVRs) are related to the formation of the center recirculation zone (CRZ) and suffer from much stronger dissipation. The evolutions of core vorticity, circulation, trajectory, and convective velocity are quantitatively analyzed for the OVRs to understand two key mechanisms: vortex formation and vortex detachment. The results show that the growing and shedding of the OVRs are governed by the inlet shear layer as well as the variations in inlet velocity and acceleration. Furthermore, both the circulation increment during vortex formation and the vortex convection after detachment are qualitatively captured by existing vortex models, demonstrating the prospect of vortex dynamics in understanding general flame-vortex interaction problems.

Interaction of spin waves propagating along narrow domain walls with a magnetic vortex in a thin-film-nanostrip cross-structure

We studied, by micromagnetic simulations, the characteristic propagation behaviors of specific spin-wave modes along narrow domain walls in a specially designed thin-film-nanostrip cross-structure waveguide as well as their novel interaction behaviors with a single magnetic vortex placed at the cross-point. Only certain specific modes of spin waves well propagate along the given domain walls and then interact with the magnetic vortex. Through this robust interaction, vortex-gyration motions are also stimulated, which exhibit circular- and/or elliptical-shape core trajectories at the same frequencies as those of the pumping spin waves. The elliptical core trajectories of the stimulated vortex gyrations can be interpreted by the superposition of different amplitudes and phases of the clockwise and counterclockwise circular eigenmodes. According to the action–reaction effect, the phase and the amplitude of the propagating spin waves that pass through the vortex structure are modified differently into different arms of the nanostrip cross-structure. Thereby, the propagating spin waves are allowed to be transmitted and scattered with contrasting phases and amplitudes in different branch arms. This work provides a fundamental understanding of the interaction of spin waves propagating along domain walls with a magnetic soliton and also suggests potential applications to magnonic information processing devices.