Eddy Motion Research Articles

Analysis of the Dynamics of the Lower Drill String Assembly in a Deep Well Coring Operation

In order to carry out the geological characteristics, evolution law and other scientific research of the deep strata in the extra-deep well, it is necessary to carry out the coring operation in the extra-deep depth. However, with the increase of drilling depth, the force of drill string in the underground becomes more and more complicated, and there is contact collision between the core and the core after the core tool is bent, which makes the core broken. Clarifying the dynamic behavior of the BHA during the extra-deep well coring process is helpful to obtain a more complete core. Therefore, this paper adopts the simulation analysis method to simulate the coring process of the extra-deep well with a 163.5mm diamond bit and a 140mm corer under the real drilling hole trajectory. The stress, eddy motion and the contact between the inner barrel of the core tool and the core of the lower 1000m drill assembly are analyzed. The results show that the hole expansion rate of coring bit is 2.5% in the process of low bit weight and low rotational speed. When the core is 8m, the core barrel is under compression, bending and torsion, and under the restriction of the centralizer and the core hole, the middle and upper part of the core tool bend greatly, and the contact degree with the core is high, and the larger contact force is easy to cause the lower core to fracture.

Modulating local winds and turbulence around a single building obstacle with the obstruction of tall vegetation

Strategic vegetation placement can significantly alter airflow patterns and turbulence, fostering desired wind environments. By comparing scenarios where vegetation is placed upstream, downstream or absent (treeless) relative to a single building using large-eddy simulation, this study provides detailed insights into the sensitivity of flow dynamics to the positioning of the vegetation. Upstream vegetation more significantly disrupts the flow patterns around the building obstacle, altering vertical wind profiles and modifying wake circulations, compared to downstream vegetation. A small shear layer developed at the plant top for upstream vegetation markedly influences turbulent kinetic energy (TKE) on both the leeward and windward sides of the building, shifting the inflection point in vertical TKE profiles by up to 0.13H. By contrast, smaller tree-building separations lead to an effective merging of their aerodynamic profiles, whereas larger separations confine the streamwise breadth of turbulent fluxes, amplifying flux exchanges in the spanwise direction. Spectral analyses reveal that upstream vegetation consistently results in higher power spectral densities of the streamwise turbulence in the residential area than downstream vegetation. While small-scale spanwise velocity fluctuations are found to be comparably energetic at the building's windward side for upstream vegetation, the power becomes substantially concentrated on large-scale eddies in the building wake region, providing specific insights into modulating turbulent eddy motions within the residential zone.

Particle motion under turbulent eddies: Inspiration for fine minerals flotation

Turbulent flow ubiquitous in flotation machines and contain multi-scale eddies. Compared to static environments, turbulence can increase particle kinetic energy and promote particle-bubble collision in mineral flotation. However, there have been few quantitative studies on turbulent eddies that affect particle motion, which limits the precise flow control of flotation processes. In this study, the motion characteristics of particles in isotropic turbulence were measured by particle tracking velocimetry, and the relationship between turbulent eddy and particle motion was quantitatively analyzed by 7-scale wavelet transform and fast Fourier transform. The measurement results show that the particle moves upward following a rotating turbulent eddy, and turbulent eddies with sizes of 35–119 µm and 127–288 µm drives the motion of dp = 74 µm and dp = 200 µm particles respectively. The turbulent acceleration of particles within a turbulent eddy can be calculated as aλ=Cε2/3λ-1/3. This study provides an eddy control basis for mineral flotation performance improvement.

Vortex Identification Method Based on Topological Analysis and Velocity Gradient Invariance

Abstract Analysis on eddy motion is the essential method for understanding viscous flows. Compared with the current methods to identify the vortex, the study presents a method to investigate vortex structures based on topological analysis and nonlinear dynamics, and establishes a connection between the direction of the vortex and the real eigenvalue of the velocity gradient tensor. The study highlights the significance of the real and imaginary parts of complex eigenvalues in vortex development, wherein the real part indicates topological stability and the imaginary part represents swirling strength, contributing to get the characters of the viscous flows.

Scale‐Awareness in an Eddy Energy Constrained Mesoscale Eddy Parameterization

AbstractThere is an increasing interest in mesoscale eddy parameterizations that are scale‐aware, normally interpreted to mean that a parameterization does not require parameter recalibration as the model resolution changes. Here we examine whether Gent–McWilliams (GM) based version of GEOMETRIC, a mesoscale eddy parameterization that is constrained by a parameterized eddy energy budget, is scale‐aware in its energetics. It is generally known that GM‐based schemes severely damp out explicit eddies, so the parameterized component would be expected to dominate across resolutions, and we might expect a negative answer to the question of energetic scale‐awareness. A consideration of why GM‐based schemes damp out explicit eddies leads a suggestion for what we term a splitting procedure: a definition of a “large‐scale” field is sought, and the eddy‐induced velocity from the GM‐scheme is computed from and acts only on the large‐scale field, allowing explicit and parameterized components to co‐exist. Within the context of an idealized re‐entrant channel model of the Southern Ocean, evidence is provided that the GM‐based version of GEOMETRIC is scale‐aware in the energetics as long as we employ a splitting procedure. The splitting procedure also leads to an improved representation of mean states without detrimental effects on the explicit eddy motions.

Supply mechanisms of the geostrophic mode in rotating turbulence: interactions with self, waves and eddies

Direct numerical simulations are performed in rotating turbulence for different regimes at various Rossby and inertial Reynolds numbers ( $\textit {Re}_I$ ). A new algorithm, adapted from stratified turbulence (Lam et al., J. Fluid Mech., vol. 923, 2021, A31) to rotating turbulence, permits to separate the three-dimensional velocity field into three parts: inertial waves (IWs), eddies and a geostrophic mode (GM). It uses the space–time properties of waves and their advection by the GM to filter the IWs from the rest of the motion. We obtain balance equations for the separate energies of waves, eddies and the GM. Their mutual interactions are evaluated and analysed via Sankey diagrams that provide a global picture of energy exchanges. When the flow is forced at large scale, it mainly feeds the wave part and the multiple interactions lead to energy dissipation in eddy and GM motion. We also show that, in addition to the wave/wave interaction that feeds the GM, corresponding to different mechanisms described in the literature, other non-documented interactions feed it, as the eddy/wave interaction or the eddy/eddy interaction at moderate $\textit {Re}_I$ . We propose a scale-by-scale analysis of the transfer to the GM: we show that transfers from wave or eddy occur at large scale, that they either inject or remove energy, and that this occurs with or without direct cascade depending on the kind of interaction, wave/wave, eddy/wave or eddy/eddy. The self-interaction of the GM is an inverse cascade for its horizontal component, shaping it into a very large-scale flow.

Large-eddy simulation of free-surface turbulent flow in a non-prismatic channel

Abstract Hydraulic engineering applications require a good knowledge of turbulent behaviour in non-prismatic channels. This paper aims to predict turbulent behaviour using large-eddy simulation (LES). The model channel has a warped transition. We perform two-phase LES of free-surface flow and validate the results using experimental data and benchmark solution. We discuss rigorous strategies for model set-up, parameter selection and parametric value assignment, including parameters in spectrum synthesiser (SS) and vortex method (VM) for inlet turbulence. The predicted flow displays complex structures due to eddy motions translated from upstream and locally generated by asymmetrical separation in the transition. The history of the flow dynamics may affect the flow development. The predicted velocity, energy spectrum, root-mean-square error, hit-rate and factor-of-two compare well with measurements and benchmark solution. Mapping mean-velocity distribution from experimental data, combined with SS, gives satisfactory inlet condition; alternatively, a 1/7th power-law for the mean-velocity, combined with VM, is acceptable. This paper uses the Okubo–Weiss parameter to delineate instantaneous coherent structures. The LES methods are reliable, efficient and cost-effective. As compared to the simulation of prismatic channels, the flow dynamics in non-prismatic channels exhibit flow separation and turbulence interactions, which increase the flow-complexity, while offering results with crucial practical applications.

Implementation of the Optical Flow to Estimate the Propagation of Eddies in the South Atlantic Ocean

The ocean is filled with mesoscale eddies that account for most of the oceanic kinetic energy. The importance of eddies in transporting properties and energy across the ocean basins has led to numerous efforts to track their motion. Here, we implement a computer vision technique—the optical flow—to map the pathways of mesoscale eddies in the South Atlantic Ocean. The optical flow is applied to the pairs of consecutive sea surface height maps produced from a nearly 30-year-long satellite altimetry record. In contrast to other methods to estimate the eddy propagation velocity, the optical flow can reveal the temporal evolution of eddy motion, which is particularly useful in the regions of strong currents. We present the time-dependent estimates of the speed and direction of eddy propagation in the Eulerian frame of reference. In an excellent agreement with earlier studies, the obtained pattern of eddy propagation reveals the interaction of eddies with the background flow and the bottom topography. We show that in the Antarctic Circumpolar Current, the variability of the eddy propagation velocity is correlated with the variability of the surface geostrophic velocity, demonstrating the robustness of the optical flow to detect the time-variable part of eddy motion.

Effects of Abrupt Cross-Section Area Change on theMultiparameter Propagation Characteristics of Premixed Methane–Air Explosion in Pipes

This paper explores the effects of an abrupt cross-section area change of gas pipes on the propagation law of explosion. For this, an explosion pipe experimental system was established, and a numerical research was conducted. By experimental and numerical simulation, the evolution of the overpressure, temperature, vorticity, and kinetic energy of shock waves of gas explosion in abrupt pipelines was investigated. This allowed us to obtain expressions for the attenuation coefficient, increase coefficient, and reflection coefficient of gas explosion overpressure. The study indicates that an abrupt increase of the pipeline cross-section area leads to a decrease of shock wave overpressure and vice versa. For a given change of cross-section area, the attenuation coefficient gradually increases as the initial peak overpressure rises, whereas the increase coefficient and reflection coefficient both present a decreasing trend. An abrupt change in the pipe structure can inhibit the propagation of gas explosion flames. The explosive gas is affected by the turbulence effect after passing through the middle large-diameter pipe, and the vorticity curve exhibits a clear peak. In addition, the large eddy motion caused by strong confinement increases the kinetic energy of the gas in pipes. The above research outcomes contribute to further enriching the basic theory of gas explosion for the study of gas explosion propagation in mining laneway.

Revisiting “bursts” in wall-bounded turbulent flows

In this paper, we demonstrate that the problem of turbulent bursts can be tackled through a complex systems approach. Specifically, by considering both duration and intensity of the bursting events, one can incorporate the effect of bursts on the turbulence statistics at any specified scale of the flow, thereby allowing one to connect the origin of bursts to the presence of organized eddy motions in turbulent flows called coherent structures. Through our approach we discover a particular aspect of universality associated with turbulent bursts and contribute toward the development of next-generation turbulence models by creating a union between complex systems science and fluid mechanics.

Automatic bundle-specific white matter fiber tracking tool using diffusion tensor imaging data: A pilot trial in the application of language-related glioma resection.

Cerebral neoplasms like gliomas may cause intracranial pressure increasing, neural tract deviation, infiltration, or destruction in peritumoral areas, leading to neuro-functional deficits. Novel tracking technology, such as DTI, can objectively reveal and visualize three-dimensional white matter trajectories; in combination with intraoperative navigation, it can help achieve maximum resection whilst minimizing neurological deficit. Since the reconstruction of DTI raw data largely relies on the technical engineering and anatomical experience of the operator; it is time-consuming and prone to operator-induced bias. Here, we develop new user-friendly software to automatically segment and reconstruct functionally active areas to facilitate precise surgery. In this pilot trial, we used an in-house developed software (DiffusionGo) specially designed for neurosurgeons, which integrated a reliable diffusion-weighted image (DWI) preprocessing pipeline that embedded several functionalities from software packages of FSL, MRtrix3, and ANTs. The preprocessing pipeline is as follows: 1. DWI denoising, 2. Gibbs-ringing removing, 3. Susceptibility distortion correction (process if opposite polarity data were acquired), 4. Eddy current and motion correction, and 5. Bias correction. Then, this fully automatic multiple assigned criteria algorithms for fiber tracking were used to achieve easy modeling and assist precision surgery. We demonstrated the application with three language-related cases in three different centers, including a left frontal, a left temporal, and a left frontal-temporal glioma, to achieve a favorable surgical outcome with language function preservation or recovery. The DTI tracking result using DiffusionGo showed robust consistency with direct cortical stimulation (DCS) finding. We believe that this fully automatic processing pipeline provides the neurosurgeon with a solution that may reduce time costs and operating errors and improve care quality and surgical procedure quality across different neurosurgical centers.

Dust Settling From Turbulent Layers in the Free Troposphere: Implications for the Saharan Air Layer

AbstractDesert dust accounts for a substantial fraction of the total atmospheric aerosol loading. It produces important impacts on the Earth system due to its nutrient content and interactions with radiation and clouds. However, current climate models greatly underestimate its airborne lifetime and transport. For instance, super coarse Saharan dust particles (with diameters greater than 10 µm) have repeatedly been detected in the Americas, but models fail to reproduce their transatlantic transport. In this study, we investigated the extent to which vertical turbulent mixing in the Saharan Air Layer (SAL) is capable of delaying particle deposition. We developed a theory based on the solution to a one‐dimensional dust mass balance and validated our results using large‐eddy simulation (LES) of a turbulent shear layer. We found that eddy motion can increase the lifetime of suspended particles by up to a factor of 2 when compared with laminar flows. Moreover, we found that the increase in a lifetime can be reliably estimated solely as a function of the particle Peclet number (the ratio of the mixing timescale to the settling timescale). By considering both the effects of turbulent mixing and dust asphericity, we explained to a large extent the presence of super coarse Saharan dust in the Caribbean observed during the Saharan Aerosol Long‐Range Transport and Aerosol‐Cloud‐Interaction Experiment (SALTRACE) field campaign. The theory for the lifetime of coarse particles in turbulent flows developed in this study is also expected to be applicable in other similar geophysical problems, such as phytoplankton sinking in the ocean mixed layer.

Bearing Fault Diagnosis Method Based on RCMFDE-SPLR and Ocean Predator Algorithm Optimizing Support Vector Machine.

For the problem that rolling bearing fault characteristics are difficult to extract accurately and the fault diagnosis accuracy is not high, an unsupervised characteristic selection method of refined composite multiscale fluctuation-based dispersion entropy (RCMFDE) combined with self-paced learning and low-redundant regularization (SPLR) is proposed, for which the fault diagnosis is carried out by support vector machine (SVM) optimized by the marine predator algorithm (MPA). First, we extract the entropy characteristics of the bearings under different fault states by RCMFDE and the introduction of the fine composite multiscale coarse-grained method and fluctuation strategy improves the stability and estimation accuracy of the bearing characteristics; then, a novel dimensionality-reduction method, SPLR, is used to select better entropy characteristics, and the local flow structure of the fault characteristics is preserved and the redundancy is constrained by two regularization terms; finally, using the MPA-optimized SVM classifier by combining Levy motion and Eddy motion strategies, the preferred RCMFDE is fed into the MPA-SVM model for fault diagnosis, for which the obtained bearing fault diagnosis accuracy is 97.67%. The results show that the RCMFDE can effectively improve the stability and accuracy of the bearing characteristics, the SPLR-based low-dimensional characteristics can suppress the redundancy characteristics and improve the effectiveness of the characteristics, and the MPA-based adaptive SVM model solves the parameter randomness problem and, therefore, the proposed method has outstanding superiority.

Robust dual-module velocity-selective arterial spin labeling (dm-VSASL) with velocity-selective saturation and inversion.

Compared to conventional arterial spin labeling (ASL) methods, velocity-selective ASL (VSASL) is more sensitive to artifacts from eddy currents, diffusion attenuation, and motion. Background suppression is typically suboptimal in VSASL, especially of CSF. As a result, the temporal SNR and quantification accuracy of VSASL are compromised, hindering its application despite its advantage of being delay-insensitive. A novel dual-module VSASL (dm-VSASL) strategy is developed to improve the SNR efficiency and the temporal SNR with a more balanced gradient configuration in the label/control image acquisition. This strategy applies for both VS saturation (VSS) and VS inversion (VSI) labeling. The dm-VSASL schemes were compared with single-module labeling and a previously developed multi-module schemes for the SNR performance, background suppression efficacy, and sensitivity to artifacts in simulation and in vivo experiments, using pulsed ASL as the reference. Dm-VSASL enabled more robust labeling and efficient backgroud suppre across brain tissues, especially of CSF, resulting in significantly reduced artifacts and improved temporal SNR. Compared to single-module labeling, dm-VSASL significantly improved the temporal SNR in gray (by 90.8% and 94.9% for dm-VSS and dm-VSI, respectively; P< 0.001) and white (by 41.5% and 55.1% for dm-VSS and dm-VSI, respectively; P< 0.002) matter. Dm-VSI also improved the SNR of VSI by 5.4% (P= 0.018). Dm-VSASL can significantly improve the robustness of VS labeling, reduce artifacts, and allow efficient background suppression. When implemented with VSI, it provides the highest SNR efficiency among VSASL methods. Dm-VSASL is a powerful ASL method for robust, accurate, and delay-insensitive perfusion mapping.

A new mesoscale eddy tracking methodology based on fast normalized cross-correlation and its validation in the Northwest Pacific

Most mesoscale eddy tracking methodologies used prior to this study evaluated eddy features using a distance-based proximity relationship, rather than considering similarities between eddies. This study applies a fast normalized cross-correlation methodology in the field of image registration to propose a novel mesoscale eddy tracking methodology that can rapidly and comprehensively calculate the similarities between two eddies and judge their relationship through the correlation coefficient, thus facilitating a more accurate mesoscale eddy trajectory tracking. The sea level anomaly data field is employed to identify the positions of eddies over time. The tracking methodology is then used to track the mesoscale eddy trajectories. After comparing the local nearest neighbor methodology (LNN) with our proposed new methodology in the Northwest Pacific Ocean, we conclude that the proposed methodology can address issues of discontinuity in tracking; especially in cases involving eddies with long lifespans. The tracking trajectories utilized in the proposed methodology achieve superior continuity and integrity and a higher degree of characterization than LNN, with the tracking results showing greater consistency with real eddy motion. The new methodology proposed in this paper has great significance for more widespread use.

Anisotropic Lagrangian dispersion in zonostrophic turbulence in a closed basin

This article studies the anisotropic particle dispersion in a continuously forced, two-dimensional turbulent flow on a β-plane. The flow is immersed in a large-scale closed basin with free-slip walls. The anisotropy is analyzed in two sets of numerical experiments characterized by the magnitude of the imposed, time-dependent forcing (weak and strong). Both experiments exhibit typical features of zonostrophic turbulence: eddy motions that, on average, form alternating east–west circulation bands due to the β-effect. The dispersion anisotropy is investigated through three Lagrangian statistics calculated by zonal and meridional components: (i) relative dispersion between pairs of particles; (ii) dispersion ellipses; and (iii) finite-scale Lyapunov exponents (FSLE), also measured with particle pairs. In the experiment with weak forcing, the relative dispersion and dispersion ellipses show anisotropy with a zonal preference toward the west; however, the FSLE did not reveal significant anisotropy. In the experiment with strong forcing, the relative dispersion and dispersion ellipses show zonal anisotropy toward the west when the particles are far from the boundaries. As the particles reach the western wall and are redistributed to fill the domain, the anisotropy ceases. The FSLE show zonal anisotropy for a wide range of particle separations. The results are examined further by using no-slip boundary conditions and a rectangular domain geometry.

Spatial Structure of Vertical Motions and Associated Heat Flux Induced by Mesoscale Eddies in the Upper Kuroshio‐Oyashio Extension

AbstractVertical motions induced by mesoscale eddies in the upper ocean play a vital role in the heat transport over the global ocean. However, the spatial structure of vertical eddy velocity and associated heat flux remains unclear. This study addresses this issue in the Kuroshio‐Oyashio Extension based on an eddy‐rich Community Earth System Model simulation. Adopting a mesoscale eddy composite analysis, we show that the vertical eddy velocity is enhanced at edges of mesoscale eddies with a maximum magnitude of 0.8 m day−1 in the upper ocean for anticyclonic eddies (AEs) and 0.5 m day−1 for cyclonic eddies (CEs). The associated vertical heat flux is upward, reaching 52 and 32 W m−2 along AEs' and CEs' periphery, respectively. Diagnostic analysis suggests that the enhanced vertical eddy motions at eddy edges are primarily attributed to the ageostrophic secondary circulation (ASC) under the turbulent thermal wind balance that accounts for more than 70% of the vertical eddy velocity and 80% of vertical eddy heat flux in the upper ocean. This ASC is stronger in winter than summer due to the intense turbulent mixing induced by strong surface cooling and wind stirring in winter. Accordingly, the vertical eddy velocity and associated heat flux exhibit a distinct seasonal cycle.

Effect of initial pressure on the propagation characteristics of supersonic turbulent jets in fuel jet ignition

The effects of initial pressure (Pini) on the propagation characteristics of supersonic turbulent jets (STJ) were studied experimentally in a constant volume chamber. Based on the top vortex motion, three types of flame propagation modes are identified: Mode 1, the vortex in the middle of the jet propagates; Mode 2, the vortex in the middle of the jet moves to the top and the tail; Mode 3, jet tail flame extinguished. Each mode follows a 3-stage propagation method: (a) a jet flame with a with a sharp drop in the flame tip velocity (VFTV); (b) a self-accelerating mushroom-shaped flame followed by turbulent flame with low frequency oscillation; (c) a turbulent flame with a drop in VFTV. The momentum dissipation causes the velocity to drop in stage I and stage III, and stage II is controlled by the eddy motion of the mushroom-shaped flame tip and the pulsation of the flow field. The experimental results show that higher Pini can stimulate a stronger interaction mechanism between flow field oscillation in the main combustion chamber (MCC) and chemical heat release oscillation in the pre-chamber (PCC). Based on an evaluation of the model correlations, we found that the jet penetration length showed a linear relationship with the product of the relative pressure fourth root and the time square root.

Numerical simulation and dynamic mode decomposition analysis of the flow past wings with spanwise waviness

This paper presents an investigation on the compressible flow past spanwise wavy wings with an incoming flow of and . The scale adaptive simulation is employed here to solve the Favre-averaged equations. Three wings, with the ratio of wavelengths (λ) to chord length (c) respectively equaling to 1/2 (W4), 1/3 (W6), 1/4 (W8), are aerodynamically investigated. The aerodynamic force and separation were compared. The results obtained show that the lift-to-drag ratio of W-8 is 12.7% and 14.4% higher than W-4 and W-6 because of the larger low-pressure regions, while the lift and drag coefficient curves of W-8 oscillate more strongly. Leading edge separated bubbles and dilation-type recirculation regions are observed in the flow field structures. Spanwise momentum transportation and local airflow downwash effect are generated by the flow around the separation regions. Spanwise momentum transportation and downwash effect play important roles in the flow control mechanism of spanwise wavy wings. Three components of three-dimensional velocity vectors are modally decomposed by dynamic mode decomposition method to reveal the flow control mechanisms and vortex structures. The main modes characterizing the motions of arched vortices and shear layer vortices have been obtained. Strouhal number (St) is adopted to define the periodic oscillations of vortex shedding. The St of the modes are related to the scale of the vortex structures in the flow field. Small-scale eddy motions have been decomposed in high-frequency modes, and thus the modes of the flow field are more meticulous for higher St.

Proper Orthogonal Decomposition Of The Turbulent Flow In An Impeller Of A Centrifugal Pump

The flow field in the channels of a centrifugal pump impeller contains eddy motions of a wide range of time and length scales and identifying coherent structures and their dynamic behavior is not a trivial task. Thus, modal decomposition techniques have been used in order to improve the knowledge on turbulence and coherent structures. In this work, the proper orthogonal decomposition (POD) method is employed to identify the occurrence and development of the dominant unsteady flow structures in a centrifugal pump impeller. For this, experiments using a time-resolved PIV system for different operating conditions of pump impeller were carried out. The results show that in the range of the pump's best efficiency point (BEP) there is no significant flow separation. As the flow rate starts to decrease from the BEP flow rate, unstable flow phenomenon begin to appear and develop in the impeller. The POD analysis reveals that for low flow rates, the flow is dominated by large-scale structures with higher energy, while for the BEP and high flow rates, the flow is dominated by smaller-scale structures.