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A computational investigation of New MEXICO test cases operating under axial flow conditions is reported. Three wind speed cases (10, 15, 24 m/s) corresponding to three different tip speed ratios (10, 6.67, 4.17) when the turbine operates at 425.1 rpm were considered. ANSYS CFX 2021R1 was employed to perform simulations using Single Reference Frame (SRF) and Multiple Reference Frame (MRF) approaches. The flow field is computed by solving unsteady Reynolds Averaged Navier-Stokes (uRANS) equations coupled with SST k - ω turbulence model and Gamma-Theta transition model. Validation involved comparing CFD-predicted integral quantities, static pressure distributions, and loads with corresponding experimental values demonstrating reasonably good agreement at all three wind speeds. Overall, SRF exhibited slightly better wake predictions (hypothetical), while MRF predictions were closer to measurements for integral quantities, static pressure and loads. This study demonstrates the utility of uRANS-based 3D CFD computations in wind turbine aerodynamics studies. [ABSTRACT FROM AUTHOR]

The author has presented results of numerical modeling of the influence of the angle of attack of a thin width-limited plate with a short chord on the velocity field of the internal region of a turbulent boundary layer (TBL) and skin friction. The computations were performed by the large eddy simulation (LES) method at the Reynolds number Reθ = 540 calculated from the velocity on the channel axis and the momentum thickness. Changes in the average and pulsation characteristics of the three-dimensional velocity field under the impact of the wake of the plate and of tip vortices as functions of the angle of attack of the plate in the range ±1° have been analyzed. It has been shown that a determining influence on the formation of the velocity field is exerted by the tip vortices whose vorticity is opposite with the positive and negative angles of attack. The mean value of the skin-friction coefficient decreases by 6% at the positive angle of attack and by 14% at the negative angle with respect to the value of this coefficient in an unperturbed TBL. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbines (FOWTs) exhibit complex motion with multiple degrees of freedom due to the interaction of wind and waves. The aerodynamic performance and wake characteristics of these turbines are highly intricate and challenging to accurately capture. In this study, dynamic fluid body interaction (DFBI) and overset grid technology are employed to investigate the dynamic motion of a 5 MW FOWT. We use the volume of fluid (VOF) method and improved delayed detached eddy simulation (IDDES) model to investigate the aerodynamic performance and wake evolution mechanism for various wave periods and heights. According to the findings, the magnitude of the pitch motion increases with the period and height of the waves, leading to a decrease in both the power output and thrust; the maximum power was reduced by nearly 6.8% compared to a wind turbine without motion. The value of power and thrust reduction varies for different wave periods and heights, and is influenced by the relative speed and pitch angle, which play a crucial role. Wind–wave coupling has a significant impact on the evolution of both wake and vortex structures for FOWT. The wake shape downstream is also dynamically influenced by the waves. In the presence of wind and wave coupling, the interaction between the wind turbine and the wake is heightened, leading to the merger of two unstable vortex rings into a single, larger vortex ring. The research unveils a comprehensive picture of the offshore wind energy dynamics and wake field, which holds immense significance for the design of floating wind turbines and the optimization of wind farm layout. [ABSTRACT FROM AUTHOR]

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus.

Featured Application: (1) This paper innovatively establishes a model of mechanical energy exchange, describes the characteristics of energy exchange between the cable and fluid dynamics, and divides the four regions of cable motion. (2) In the manipulation state, the dynamic energy exchange between the cable and the wake results in the transient vibration response of the cable. The hydrodynamic wake generated by the underwater vehicle's motion has a considerable impact on the movement of the towed system underwater. This paper utilizes the lumped mass method to model the towed cable in order to improve the accuracy of predicting its position and attitude in the wake, and to determine the suitable cable-towed position. Velocity is transferred from the flow field to the cable dynamic model in an innovative way to imitate the motion of the cable. Several iterations are conducted to enhance the dynamic reactivity of the cable system. Numerical simulations are used to model both the straight towed and turning movements. The numerical calculation provides the characteristics of vorticity in the flow field formed by the energy exchange between the vorticity and the cable, as well as the gradually dissipating vorticity and momentum exchange characteristics at the trailing edge of the enclosure. The results indicate that the best location for the cable towed is where its motion does not cause any adhesion. On the other hand, the disadvantageous scenario for cable-towed systems occurs when the cable's movement causes substantial adhesion. This paper innovatively establishes a model of mechanical energy exchange, describes the characteristics of energy exchange between the cable and fluid dynamics, and divides the four regions of cable motion. In the manipulation state, the dynamic energy exchange between the cable and the wake results in the transient vibration response of the cable. The fluid structure coupling method can accurately determine the separation region of the towed point of the vehicle based on its compatibility (non-adhesive) and incompatibility (adhesive). The boundary of the region is defined to distinguish a free tow point from a wall-attached tow point. A transition zone has the possibility to change the pattern from a free tow to a wall-attached tow. The wake can be divided into free tow region, transition zone, and adjacent wall tow region by this fluid structure interaction assessment method. [ABSTRACT FROM AUTHOR]

Wind energy in the atmospheric boundary layer serves as the primary source for energy absorption and structural load on wind turbines. However, the impact of turbulent coherent structures on the aerodynamic performance and wake characteristics of wind turbines has not been comprehensively evaluated. In this study, the proper orthogonal decomposition (POD) method is employed to assess the influence of turbulent coherent structures of varying scales on the aerodynamic performance and wake characteristics of wind turbines in the neutral atmospheric boundary layer. The results show that turbulent coherent structures are the main factor that determines the wind velocity fluctuation, aerodynamic performance and wake characteristics of wind turbine in the atmospheric boundary layer. When considering the 13th or lower order POD mode, the wind velocity fluctuation increases with the increase of energy content (more POD modes) of the turbulent coherent structures. When considering the first 19 POD modes, the dynamic loads and power of wind turbine fluctuate with high frequencies, the thrust fluctuates in an amplitude range between 2.4 % and 13.9 % around the mean value, and the power fluctuates from 4.5 % to 28.6 % of the mean value. When considering the first 40 POD modes, the average power generation of the wind turbine increases by 26 % compared to the case with no turbulent structures considered. The study of turbine wake shows that turbulent coherent structures can expand the wind turbine wake approximately to a width of 2.5 D and a height of 3 D (D is the diameter of the wind turbine), offset the wake approximately to 2 D , and move forward the position of the wake vortex beginning to dissipation approximately to 7 D behind the wind turbine. In addition, turbulent coherent structures can accelerate the wake velocity recovery by increasing the momentum exchange between the atmospheric boundary layer and wind turbine wake. • A POD-based inflow generation method is established for wind turbine simulation. • Study into the coherent structures with various energy contributions on wind turbine performance. • Obtained the most influence energy contribution of coherent structures in the ABL. • Unveil the influence of coherent structures on the expansion and deflection of wind turbine wakes. [ABSTRACT FROM AUTHOR]

Commercial scale tidal stream turbines (TST) are expected to be deployed in shallow water where the depth varies from 1.5 to 3 turbine diameters. In this study, numerical simulation is conducted at realistic hydrodynamic conditions of potential tidal sites using the stationary actuator disc method at ambient turbulence varying from 5% to 20%, a range of rotor realistic rotor thrust coefficient from 0.64 to 0.98 and a rotor-diameter-to-depth ratio of 20% to 60%. The result shows that the TST wake is affected by the rotor-diameter-to-depth ratio, ambient turbulence, and thrust coefficient. The new empirical model is in accordance with the numerical simulation of a full-scale turbine and is validated with the TST experiment at different rotor-diameter-to-depth ratios with reasonable results in the far wake. This low computational model can benefit the investigation of tidal turbine parks at different configurations where the far wake is pertinent. [ABSTRACT FROM AUTHOR]

The energy harnessing from flow-induced vibrations (FIV) by an oscillating foil placed tandemly behind a circular cylinder (which serves as a vortex generator) is investigated. The foil is submerged in the wake produced by the fixed cylinder and could oscillate in the direction perpendicular to the incoming flow with single-degree freedom. The spacing ratio ranges from 1.0 to 5.0. The oncoming fluid velocity is U = 1–10 m/s, corresponding to the reduced velocity Ur = 3.81–38.08 and the Reynolds number Re = 9.58 × 103–9.58 × 104. Four harnessing damping ratios (ζharness = 0.0054–0.0216) are used to simulate the energy conversion conditions. The main conclusions are: (1) The optimal oscillation pattern related to the highest harnessed energy emerges as the spacing ratio close to 1.0. (2) The airflow energy converted by the foil is positively correlated with the harnessing damping ratio because the amplitude responses are similar at various harnessing damping ratios. A high velocity yields the highest harnessed power. (3) The harnessing efficiency of the foil could reach 48.89%, which is much more than that of an isolated flapping foil. [ABSTRACT FROM AUTHOR]

Objectives: Premature newborns are exposed to a great deal of over-stimulation, which can affect their cerebral development. For better sleep, certain practices should be recommended. The aim of this study was to evaluate the effect of a professional training program on the improvement of practices promoting respect for the newborn's sleep-wake cycle. Materials and Methods: This was an interventional study with a longitudinal, single-group, and before-and-after design. The experimental design followed a three-stage time series: Eight months before, three months after, then eight months after intervention. It targeted a comprehensive sample of 66 professionals. It took place between October 2020 and March 2022 at the Neonatal Intensive Care Unit of the Hassan II University Hospital in Fez, Morocco. It was based on an observation grid and a self-administered questionnaire, validated and tested with a Cronbach's alpha reliability of 0.91. Results: The light environment showed significant differences between the 1st and 3rd step (3.3% vs. 45.0%; P = 0.02; confidence interval [CI] = 13.644-10.456) for knowledge and (13.3% vs. 78.3%; P = 0.01; CI = 14.412-10.888) for practices; the noise environment showed a positive improvement between the 2nd and 3rd intervention (31.7% vs. 41.7%; P < 0.001; CI = 5.954-2.913) for knowledge and (65.0% vs. 73.3%; P < 0.001; CI = 3.597-1.236) for practices, with an average of (8.98 ± 0.30-28.15 ± 0.48; CI = 3.806-1.094) between the 1st and 3rd step. Practices surrounding sleep and wakefulness reported significant improvement between the three periods (14.35 ± 0.22 vs. 18.10 ± 0.35 vs. 19.90 ± 0.35; P P < 0.001; CI = 4.647-2.853) for sleep and (13.25 ± 0.48 vs. 22.27 ± 0.59; P < 0.001; CI = 10.563-7.471) for wakefulness with statistically significant correlations between knowledge and practices (0.426**) for sleep and (0.606**) for wakefulness. Conclusion: The study demonstrated the positive impact of this sleep management and assessment program on the development of professional skills. Its implementation requires rigorous application of developmental support strategies for individualized care in neonatology. [ABSTRACT FROM AUTHOR]

The Pumps as Turbines (PAT) is a well-established technology suitable for standalone micro-hydropower plants and energy recovery systems. But being lower performance than the dedicated turbines, there are continuous efforts to improve it keeping cost benefits intact. One of the recent modifications of the back cavity filling plays a crucial role in the performance of PAT which is not investigated in detail. In the present paper, the PAT back cavity is filled with a solid ring of various sizes and shapes (back cavity filling) to explore its impact. The developed test facility is used to validate the experimental results with the numerical results for the base case. A numerical model after validation has been employed to investigate the impact of back cavity filling on the internal flow dynamics and the PAT performance. Additionally, the study explored the influence of axial clearance on flow physics, associated losses, and the PAT performance, an aspect rarely discussed by researchers in the PAT mode. After back cavity filling, secondary flow-based disk friction losses were reduced, leading to a 3.5 % increase in PAT efficiency. An analysis of the axial clearance showed that increasing it from 0.015 to 0.076 (mean axial gap/impeller radius) led to a 2.6 % reduction in PAT efficiency. This decline can be primarily attributed to elevated losses associated with disk friction, increased volumetric losses, and the formation of a mixing zone at the impeller inlet, which impeded the flow into the impeller's flow zone. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Modifying surface characteristics and geometric structure to regulate heat transfer and flow fields is a classical issue. The study of wake dynamics and heat transfer efficiency in tandem grooved cylinders hold fundamental importance. This research proposes a configuration of tandem cylinders with triangle-grooved surfaces and numerical simulates the vorticity, fluid forces, Strouhal numbers, and convective heat transfer in tandem grooved cylinders. The parameters investigated include orientation angles θ = 0°, 30°, 45°, 60°, 90° and Reynolds numbers Re = 75, 100, 125, 150, 175, 200. This study focuses on how the triangle-grooved angle (θ) and Re affect wake dynamics and thermal performance. Numerical results are validated against available data in the literature for tandem smooth and tandem grooved cylinders. The results indicate that, compared to tandem smooth cylinders, the positive vorticity intensity of tandem grooved cylinders is 35.7 % higher, while the negative vorticity intensity is 23.5 % lower. Further observations show that at θ = 45°, the pressure variation on the upstream cylinder is most significant, approximately twice that at θ = 0° and θ = 90°. Notably, the variation values of the downstream cylinder (β = 0°) at θ = 0° and θ = 45° are triple and double that of the upstream cylinder in TF mode, respectively. Additionally, at θ = 0°, the root mean square lift coefficient of the downstream cylinder reaches the maximum value (Re = 75–100), approximately 1.34. When Re = 125, CL(rms),1 decreases by 15.7 % to 1.13. Particularly, when Re = 100–150, the time-averaged drag coefficient of the downstream cylinder shows a peak value of approximately 1.02. Interestingly, at Re = 200, a tadpole-shaped thermal distribution forms in the wake region of the upstream cylinder. Furthermore, the time-averaged Nusselt number ratio (θ = 0°) exhibits a trend opposite to other cases over a broader range (125 ≤ Re ≤ 200) and peaks at Re = 200, approximately 1.24.

The Pumps as Turbines (PAT) is a well-established technology suitable for standalone micro-hydropower plants and energy recovery systems. But being lower performance than the dedicated turbines, there are continuous efforts to improve it keeping cost benefits intact. One of the recent modifications of the back cavity filling plays a crucial role in the performance of PAT which is not investigated in detail. In the present paper, the PAT back cavity is filled with a solid ring of various sizes and shapes (back cavity filling) to explore its impact. The developed test facility is used to validate the experimental results with the numerical results for the base case. A numerical model after validation has been employed to investigate the impact of back cavity filling on the internal flow dynamics and the PAT performance. Additionally, the study explored the influence of axial clearance on flow physics, associated losses, and the PAT performance, an aspect rarely discussed by researchers in the PAT mode. After back cavity filling, secondary flow-based disk friction losses were reduced, leading to a 3.5 % increase in PAT efficiency. An analysis of the axial clearance showed that increasing it from 0.015 to 0.076 (mean axial gap/impeller radius) led to a 2.6 % reduction in PAT efficiency. This decline can be primarily attributed to elevated losses associated with disk friction, increased volumetric losses, and the formation of a mixing zone at the impeller inlet, which impeded the flow into the impeller's flow zone.

The hippocampus (HPC) plays a pivotal role in fear learning and memory. Our two recent studies suggest that rapid eye movement (REM) sleep via the HPC downregulates fear memory consolidation and promotes fear extinction. However, it is not clear whether and how the dorsal and the ventral HPC regulates fear memory differently; and how the HPC in wake regulates fear memory. By chemogenetic stimulating in the HPC directly and its afferent entorhinal cortex that selectively activated the HPC in REM sleep for 3-6 h post-fear-acquisition, we found that HPC activation in REM sleep consolidated fear extinction memory. In particular, dorsal HPC (dHPC) stimulation in REM sleep virtually eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. By contrast, chemogenetic stimulating HPC afferent the supramammillary nucleus (SUM) induced 3-hr wake with HPC activation impaired fear extinction. Finally, desipramine (DMI) injection that selectively eliminated REM sleep for >6 h impaired fear extinction. Our results demonstrate that the HPC is critical for fear memory regulation; and wake HPC and REM sleep HPC have an opposite role in fear extinction of respective impairment and consolidation. • HPC activation in REM sleep consolidated fear extinction memory. • The dorsal HPC stimulation in REM sleep eliminated fear memory by enhancing fear extinction and reducing fear memory consolidation. • Wake HPC and REM HPC have an opposite role in fear extinction of respective impairment and consolidation. [ABSTRACT FROM AUTHOR]

The present experimental work is focused on designing and standardizing a direct method of measuring the drag force on a tapered cylinder in a water tunnel. The model considered in the present study is a tapered cylinder of 70:1 taper ratio (with a mean diameter( D m ) of 8 mm) placed in a water tunnel test section. The drag force is measured directly, which is acquired by using a force transducer setup (strain-gauge-based), augmented with a lever arm to amplify or attenuate the force. Multiple calibrations of the load cells were done to ensure the repeatability of experiments. The taper cylinder model is suspended inside the water tunnel and the drag force is obtained for various Reynolds numbers (based on mean diameter). It was found that the drag coefficient was ≈ 10-20 % less than a circular cylinder. [ABSTRACT FROM AUTHOR]

In this paper, we present an overview of numerical simulation methods for the flow around typical underwater vehicles at high Reynolds numbers, which highlights the dominant flow structures in different regions of interest. This overview covers the forebody, midbody, stern, wake region, and appendages and summarizes flow phenomena, including laminar-to-turbulent transition, turbulent boundary layers, flow under the influence of curvatures, wake interactions, and all associated complex vortex structures. Furthermore, the current issues and challenges of capturing these flow structures are addressed. This overview provides a deep insight into the use of numerical simulation methods, including the Reynolds-averaged Navier–Stokes (RANS) method, large eddy simulation (LES) method, and the hybrid RANS/LES method, and evaluates their applicability in capturing detailed flow features. [ABSTRACT FROM AUTHOR]

Wakes produced by underwater vehicles, particularly submarines, in density-stratified fluids play a pivotal role across military, academic, and engineering domains. In comparison to homogeneous fluid environments, wakes in stratified flows exhibit distinctive phenomena, including upstream blocking, pancake eddies, internal waves, and variations in hydrodynamic performance. These phenomena are crucial for optimizing the operation of underwater vehicles. This review critically assesses the hydrodynamic and thermodynamic aspects of these wakes through an integration of theoretical, experimental, and numerical approaches. The hydrodynamic wake evolution, comprising near-wake, non-equilibrium, and quasi-two-dimensional regimes, is scrutinized. The underlying physics, encompassing energy transformation, vertical motion suppression, and momentum dissipation, are analyzed in detail. Special emphasis is placed on numerical methods, encompassing diverse approaches and turbulence models and highlighting their differences in fidelity and computational cost. Numerical simulations not only provide insights into the intricate interplay among various factors but also emerge as a crucial focal point for future research directions. In the realm of thermodynamic wakes, we delve into the thermal wake induced by the discharge of high-temperature cooling water and the cold wake resulting from the stirring of seawater. The generation, evolution, and ascent to the free surface of these wakes are explored. Additionally, this review identifies and analyzes current research shortcomings in each aspect. By systematically addressing existing knowledge gaps, our study contributes novel insights that propel academic progress and bear significant implications for submarine engineering. This work not only enhances our understanding of the intricate dynamics involved but also provides a foundation for future research endeavors in this critical field. [ABSTRACT FROM AUTHOR]

The mechanisms leading to the alternation between active (UP) and silent (DOWN) states during sleep slow waves (SWs) remain poorly understood. Previous models have explained the transition to the DOWN state by a progressive failure of excitation because of the build‐up of adaptation currents or synaptic depression. However, these models are at odds with recent studies suggesting a role for presynaptic inhibition by Martinotti cells (MaCs) in generating SWs. Here, we update a classical large‐scale model of sleep SWs to include MaCs and propose a different mechanism for the generation of SWs. In the wake mode, the network exhibits irregular and selective activity with low firing rates (FRs). Following an increase in the strength of background inputs and a modulation of synaptic strength and potassium leak potential mimicking the reduced effect of acetylcholine during sleep, the network enters a sleep‐like regime in which local increases of network activity trigger bursts of MaC activity, resulting in strong disfacilitation of the local network via presynaptic GABAB1a‐type inhibition. This model replicates findings on slow wave activity (SWA) during sleep that challenge previous models, including low and skewed FRs that are comparable between the wake and sleep modes, higher synchrony of transitions to DOWN states than to UP states, the possibility of triggering SWs by optogenetic stimulation of MaCs, and the local dependence of SWA on synaptic strength. Overall, this work points to a role for presynaptic inhibition by MaCs in the generation of DOWN states during sleep. [ABSTRACT FROM AUTHOR]

The use of wind energy, the area of wind farms, and the length of wind turbine blades continuously increase with the increase in energy demand. This study aims to simulate large wind farms in the atmospheric boundary layer with different double-rotor (DR) wind turbine arrangements using large eddy simulation. The effect of four DR wind turbine arrangements on the efficiency of a large wind farm was investigated in this study. All simulations were performed using the OpenFOAM solver. The performance of different turbine arrangements was investigated based on the mean velocity, the extent of the wake region, mean kinetic energy, and turbine power. Results showed that the arrangement of DR turbines with transverse spacing produces higher power than other layouts. Moreover, DR layouts produce the same power as single-rotor layouts with a short blade length. This scenario is important from an economic point of view. [ABSTRACT FROM AUTHOR]

Sleep during the midday, commonly referred to as siesta, is a common trait of animals that mainly sleep during the night. Work using Drosophila led to the identification of the daywake (dyw) gene, found to have anti‐siesta activity. Herein, we show that the DYW protein undergoes signal peptide‐dependent secretion, is present in the circulatory system, and accumulates in multiple organs, but, surprisingly, it is not detected in the brain where wake–sleep centers are located. The abundance of DYW in adult flies is regulated by age, sex, temperature, and the splicing efficiency of a nearby thermosensitive intron. We suggest that DYW regulates daytime wake–sleep balance in an indirect, extracerebral manner, via a multi‐organ network that interfaces with the circulatory system. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Submerged Reefs (SRs) are a kind of artificial fish habitat that can protect coasts and maintain ecological biodiversity. In this study, the flow field of the SR is simulated by solving a Reynolds-averaged Navier–Stokes equation closed with the Realizable k-ε model based on the finite volume method. The turbulent characteristics of SRs under different inflow velocities and submergences in the vicinity of the SR are analyzed. The wake vorticities are the primary turbulent pattern within and around the SR. The back wake and vorticity are chosen as critical indicators to quantitatively assess the hydrodynamic characteristics induced by the SR. The results show: (1) as the main flow passes through the SR, the upwelling is produced in front of the SR and a large-scale wake region is formed behind the SR which contains a clockwise vortex; (2) the length of the wake region formed behind the SR is positively and linearly correlated with both the inflow velocity and submergence; (3) the dipole-type vorticity patterns are induced within the compartment of the SR, where the area and average value of high vorticity have a positive correlation with the flow velocity and a negative correlation with the submergence, respectively. [ABSTRACT FROM AUTHOR]

Summary The circuitry underlying the initiation, maintenance, and coordination of wakefulness, rapid eye movement sleep, and non‐rapid eye movement sleep is not thoroughly understood. Sleep is thought to arise due to decreased activity in the ascending reticular arousal system, which originates in the brainstem and awakens the thalamus and cortex during wakefulness. Despite the conventional association of sleep–wake states with hippocampal rhythms, the mutual influence of the hippocampal formation in regulating vigilance states has been largely neglected. Here, we focus on the subiculum, the main output region of the hippocampal formation. The subiculum, particulary the ventral part, sends extensive monosynaptic projections to crucial regions implicated in sleep–wake regulation, including the thalamus, lateral hypothalamus, tuberomammillary nucleus, basal forebrain, ventrolateral preoptic nucleus, ventrolateral tegmental area, and suprachiasmatic nucleus. Additionally, second‐order projections from the subiculum are received by the laterodorsal tegmental nucleus, locus coeruleus, and median raphe nucleus, suggesting the potential involvement of the subiculum in the regulation of the sleep–wake cycle. We also discuss alterations in the subiculum observed in individuals with sleep disorders and in sleep‐deprived mice, underscoring the significance of investigating neuronal communication between the subiculum and pathways promoting both sleep and wakefulness. [ABSTRACT FROM AUTHOR]

Static axial induction control and tilt control are two strategies that have the potential to increase power production in wind farms, mitigating wake effects and increasing the available power for downstream turbines. In this study, wind tunnel experiments are performed to evaluate the efficiency of these two techniques. First, the axial induction of upstream turbines in wind farms comprising two, three, and five turbines is modified through the tip-speed ratio. This strategy is found to be ineffective in increasing power extraction. Next, the power extraction and flow through a two-turbine wind farm are evaluated, considering different tilt angles for the upstream turbine, under two levels of incoming flow turbulence intensities and turbine spacing distances. It is shown that forward tilting increases the overall power extraction by deflecting the wake downwards and promoting the entrainment of high-speed fluid in the upper shear layer, regardless of the turbine spacing distance and turbulence intensity level. Also, the wake is seen to recover faster due to the increased shear between the wake and the outer flow. Tilting a turbine backward deflects the wake upwards and pulls low-speed flow from under the turbine into the wake space, increasing the available power for downstream turbines, but it is not enough to increase global power extraction. Moreover, since the wake deflection under backward tilting is not limited by ground blockage, it leads to larger secondary steering compared with forward tilting. Finally, it is demonstrated that the secondary steering of the downstream turbine's wake influences the flow encountered by a turbine positioned farther downstream. [ABSTRACT FROM AUTHOR]

The study of the visual images of fluid flows is ongoing and has intensified in recent years by advancements in light sources and receivers. Both classical schlieren instruments of the IAB series and original developments acquired new qualities. The selection of the source and visualizing diaphragm shapes allow to register the fields of various components of the reflectivity and density gradient in stratified flows (examples are given). Anodic oxidation of tin–electrolytic precipitation–is used to visualize matter transfer from a compact source. The structure of the flow pattern around a horizontally moving sphere is visualized in a wide range of parameters. [ABSTRACT FROM AUTHOR]

Death cuts the thread of a life, which is why the creations and manifestations were more sober, and more unified, with more obvious ritual survivals from the original cultural background. Funeral customs expressed the sorrow of separation, the concerns and fears of the living, and the emotions connected to the departed soul. Throughout history, there have been diverse attitudes towards death, not only among different nations and ethnic groups but also within their respective environments. In the past, various ancient cultures had unique beliefs and rites of passage, which have been adopted and incorporated into the cultural heritage of present-day ethnic groups. [ABSTRACT FROM AUTHOR]

Flow around a cylinder is an important research problem in fluid mechanics. However, studies on traveling wave wall (TWW) flow control for the wake generated by the flow around a 3D cylinder remain limited. This study performs large eddy simulation (LES) to investigate the wake characteristics of flow around a three-dimensional (3D) circular cylinder with the TWW. The influence of the main control parameters of TWW on the aerodynamic forces and wake of the 3D cylinder is analyzed. The wake characteristics of the 3D cylinder at Re = 4 × 104 are obtained, and the traveling wave propagating downstream is achieved on the rear surface of the 3D cylinder using dynamic mesh. The control effects of wave amplitude, number of waves, and wave velocity of the traveling wave on the aerodynamic forces of the cylinder are analyzed, and the optimal control parameter combination is determined. The results demonstrate that the TWW control method completely eliminates the spanwise 3D flow characteristics of the cylinder when the amplitude ratio, number of waves, and velocity ratio are 0.02, 4, and 1.5, respectively. Moreover, it effectively suppresses the flow separation on the cylinder surface, eliminates the wake vortex, and suppresses vortex-induced vibration (VIV). [ABSTRACT FROM AUTHOR]

This article probes the convergence of meteorological disaster and memory in L’Île et une nuit by Daniel Maximin and La Case du commandeur by Édouard Glissant, reading fragments of these novels through reflections lifted from spiritual autobiographies by M. Jacqui Alexander and Mimerose Beaubrun. While anglophone Black studies scholar Christina Sharpe employs weather systems and climate as figures to apprehend the pervasiveness of antiblackness in today’s world, hurricane disaster takes another form as a device used by francophone Caribbean authors to observe and disrupt the ontological negation of Black people. Tracing the multiple resonances between ‘the wake’ (Sharpe, 2016) as a prismatic theoretical tool and meanings of water, passages, and wakefulness generated by hurricanes in Glissant and Maximin, this article explores the relation between this meteorological disaster event and an expansive consciousness of the human disasters of deportation and rupture. It pays attention to homonymic language tethering the eye of the hurricane and other manifestations of suspended wind and saltwater to the ‘vision’ or modes of sensorial knowing this phenomenon confers, addressing the ways in which African diaspora authors and spiritual practitioners understand the disaster of the Middle Passage through the disaster of the hurricane as temporally amplified, immanent, and beyond human.

In order to explore the wake interference effect of the wind farm and quantitatively predict the overall output efficiency under different wind farm layouts, the mathematical model and prediction program of the wake interference effect was constructed. The newly established model originates from the Jensen model, which was the most commonly used to predict the wake effect of a single wind turbine, and was based on the shadowing effect and shadowing mode of the upstream wind turbine on the downstream one in the wind farm layout. The variation of wind farm overall output efficiency with wind farm scale, row/ column spacing and wind direction angle in homogeneous arrangement mode, and with dislocation spacing and wind direction angle in staggered arrangement mode were studied. The results show that the overall output efficiency increases with the increase of row/ column spacing under different wind farm scales, and decreases with the increase of wind farm scales under different row/ column spacing. There are obvious differences in the overall output efficiency of the wind farm under different dislocation spacing and wind direction angle. It is necessary to reasonably arrange the row/ column spacing of wind turbines according to the wind direction where the wind farm is located, to maximize the overall output efficiency. Research can provide guidance for the prediction of wake interference effect under any wind farm layout and rational design of wind farm layout. [ABSTRACT FROM AUTHOR]

The free surface and pycnocline wake characteristics of SUBOFF were studied by simulations and experiments in a two-layer ocean. The experimental results showed that the simulation method accurately calculated the wake characteristics of the scaling model, and the simulation method was expanded to full-scale prototypes. When typical Froude numbers of flow is from 0.05 to 2.7, the submerged body velocity can influence the wake characteristics of the free surface and pycnocline interface. The wake system of the free surface would transform into a Kelvin wake, and the angles of the V-shaped divergent waves of the pycnocline interface would be reduced with the increasing Froude number. [ABSTRACT FROM AUTHOR]

Wall-modeled large eddy simulation (WMLES) is used to investigate turbulent fluctuations around an axisymmetric body of revolution. This study focuses on evaluating the ability of WMLES to predict the fluctuating flow over the axisymmetric hull and analyzing the evolution of turbulent fluctuations around the body. The geometry is the DARPA SUBOFF bare model and the Reynolds number is 1.2×107, based on the free-stream velocity and the length of the body. Near-wall flow structures and complex turbulent fluctuation fields are successfully captured. Time-averaged flow quantities, such as time-averaged pressure and skin-friction coefficients, and time-averaged velocity profiles on the stern, achieved great agreements between WMLES results and experimental data. Self-similarity of time-averaged velocity defects within a self-similar coordinate up to twelve diameters from the tail. A comprehensive analysis of second-order statistics in the mid-body, stern, and wake regions is condutced. Numerical results agree well with experimental data and previous wall-resolved large eddy simulation (WRLES) results about root mean square (rms) of radial and axial fluctuating velocities at the stern. Turbulent fluctuations including turbulent kinetic energy (TKE) and second-order velocity statistics are identified as dual peak behavior and non-self-similar over the wake length, consistent with previous findings in the literature. This assessment enhances the understanding of WMLES capabilities in capturing complex fluctuating flow around axisymmetric geometries. [ABSTRACT FROM AUTHOR]

Copyright of Francosphères is the property of Open Library of Humanities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents the jet mixing characteristics of sonic under expanded co-flowing jet by means of varying the lip thickness between the primary and secondary nozzle. The lip thicknesses between the nozzles chosen were 0.3Dp and 1.5Dp and their jet mixing characteristics is studied numerically for the nozzle pressure ratio of 5. The jet mixing effectiveness in the axial and radial directions were analysed by the total pressure decay plots and contours of Mach number, density gradient and turbulent kinetic energy. The results exhibit that, for the reduced lip thickness of 0.3Dp, the core of the primary jet is increased due to the encasing given by the surrounding jet. For the dominant lip thickness of 1.5Dp, the primary jet core is reduced due to the strong interaction between the primary and co-flowing jet. The various jet mixing phenomenon like shear layer between surrounding jet and atmosphere, recirculation zone and Mach disk were also analysed from the contour plots. [ABSTRACT FROM AUTHOR]

With the increased availability of experimental measurements aiming at probing wind resources and wind turbine operations, machine learning (ML) models are poised to advance our understanding of the physics underpinning the interaction between the atmospheric boundary layer and wind turbine arrays, the generated wakes and their interactions, and wind energy harvesting. However, the majority of the existing ML models for predicting wind turbine wakes merely recreate Computational fluid dynamics (CFD) simulated data with analogous accuracy but reduced computational costs, thus providing surrogate models rather than enhanced data-enabled physics insights. Although ML-based surrogate models are useful to overcome current limitations associated with the high computational costs of CFD models, using ML to unveil processes from experimental data or enhance modeling capabilities is deemed a potential research direction to pursue. In this letter, we discuss recent achievements in the realm of ML modeling of wind turbine wakes and operations, along with new promising research strategies.

The wake flow field around the parallel twin cylinders is complex, and a variety of complex wake patterns appear at different spacings. In this paper, based on the finite volume method, a numerical simulation of the flow around two-dimensional parallel cylinders with different spacings at low Reynolds number Re=200 was carried out. The flow field was ana-lyzed by modal comparison. The analysis results show that the proper orthogonal decomposition(POD) method can obtain the main characteristics of the dynamic system in space, and fewer modes contain most of the energy of the flow field. When the distance g=1.5 m, the interference between the upper and lower cylinders is weak, and the wake presents a periodic synchronous and co-directional pattern. When the distance g=0.35 m, the interference between the upper and lower cylinders is strong, and the flow phenomenon is more complicated. The wake presents an alternate flip pattern, and the flow field no longer has obvious periodic regularity. At the same time, the POD method can obtain the main spatial distribution chara-cteristics of the wake flow, with fewer modes containing most of the energy of the flow field, and the wake modal structure with a spacing of g=1.5 m is more compact and orderly than the modal structure with a spacing of g=0.35 m, which is closely related to the wake flow patterns under different spacing g.

The hydrodynamic wake generated by the underwater vehicle’s motion has a considerable impact on the movement of the towed system underwater. This paper utilizes the lumped mass method to model the towed cable in order to improve the accuracy of predicting its position and attitude in the wake, and to determine the suitable cable-towed position. Velocity is transferred from the flow field to the cable dynamic model in an innovative way to imitate the motion of the cable. Several iterations are conducted to enhance the dynamic reactivity of the cable system. Numerical simulations are used to model both the straight towed and turning movements. The numerical calculation provides the characteristics of vorticity in the flow field formed by the energy exchange between the vorticity and the cable, as well as the gradually dissipating vorticity and momentum exchange characteristics at the trailing edge of the enclosure. The results indicate that the best location for the cable towed is where its motion does not cause any adhesion. On the other hand, the disadvantageous scenario for cable-towed systems occurs when the cable’s movement causes substantial adhesion. This paper innovatively establishes a model of mechanical energy exchange, describes the characteristics of energy exchange between the cable and fluid dynamics, and divides the four regions of cable motion. In the manipulation state, the dynamic energy exchange between the cable and the wake results in the transient vibration response of the cable. The fluid structure coupling method can accurately determine the separation region of the towed point of the vehicle based on its compatibility (non-adhesive) and incompatibility (adhesive). The boundary of the region is defined to distinguish a free tow point from a wall-attached tow point. A transition zone has the possibility to change the pattern from a free tow to a wall-attached tow. The wake can be divided into free tow region, transition zone, and adjacent wall tow region by this fluid structure interaction assessment method.

Commercial scale tidal stream turbines (TST) are expected to be deployed in shallow water where the depth varies from 1.5 to 3 turbine diameters. In this study, numerical simulation is conducted at realistic hydrodynamic conditions of potential tidal sites using the stationary actuator disc method at ambient turbulence varying from 5% to 20%, a range of rotor realistic rotor thrust coefficient from 0.64 to 0.98 and a rotor-diameter-to-depth ratio of 20% to 60%. The result shows that the TST wake is affected by the rotor-diameter-to-depth ratio, ambient turbulence, and thrust coefficient. The new empirical model is in accordance with the numerical simulation of a full-scale turbine and is validated with the TST experiment at different rotor-diameter-to-depth ratios with reasonable results in the far wake. This low computational model can benefit the investigation of tidal turbine parks at different configurations where the far wake is pertinent.

The energy harnessing from flow-induced vibrations (FIV) by an oscillating foil placed tandemly behind a circular cylinder (which serves as a vortex generator) is investigated. The foil is submerged in the wake produced by the fixed cylinder and could oscillate in the direction perpendicular to the incoming flow with single-degree freedom. The spacing ratio ranges from 1.0 to 5.0. The oncoming fluid velocity is U = 1–10 m/s, corresponding to the reduced velocity Ur = 3.81–38.08 and the Reynolds number Re = 9.58 × 103–9.58 × 104. Four harnessing damping ratios (ζharness = 0.0054–0.0216) are used to simulate the energy conversion conditions. The main conclusions are: (1) The optimal oscillation pattern related to the highest harnessed energy emerges as the spacing ratio close to 1.0. (2) The airflow energy converted by the foil is positively correlated with the harnessing damping ratio because the amplitude responses are similar at various harnessing damping ratios. A high velocity yields the highest harnessed power. (3) The harnessing efficiency of the foil could reach 48.89%, which is much more than that of an isolated flapping foil.

Sleep-wake and fasting-feeding are tightly coupled behavioral states that require coordination between several brain regions. The mammalian lateral hypothalamus (LH) is a functionally and anatomically complex brain region harboring heterogeneous cell populations that regulate sleep, feeding, and energy metabolism. Significant attempts were made to understand the cellular and circuit bases of LH actions. Rapid advancements in genetic and electrophysiological manipulation help to understand the role of discrete LH cell populations. The opposing action of LH orexin/hypocretin and melanin-concentrating hormone (MCH) neurons on metabolic sensing and sleep-wake regulation make them the candidate to explore in detail. This review surveys the molecular, genetic, and neuronal components of orexin and MCH signaling in the regulation of sleep and metabolism. [ABSTRACT FROM AUTHOR]

The environment for the shipboard landing and takeoff of helicopters is extremely complex and significantly affects their safe flight. To address the intricate characteristics of the flow field during these operations, a simulation method suitable for rotor/ship wake vortex interaction is developed. This method couples the Delayed Detached Eddy Simulation (DDES) method and the momentum source method. The simulation of flow field characteristics of the SFS2 ship model under different conditions reveals that, in a rotor/ship coupling scenario, the inflow velocity in the wake zone of the flight deck is distributed in a "W" shape due to the influence of the rotor blade tip vortex. Under wind shear conditions, the rotor's influence on the wake is reduced, resulting in smaller velocity fluctuations compared to uniform inflow conditions. Moreover, the detached eddy is suppressed to some extent. It can be concluded that shear flow mitigates the unsteady characteristics of the ship's wake zone to some extent, which is beneficial to helicopter operations during takeoff and landing. [ABSTRACT FROM AUTHOR]

Summary: The sleep disorder narcolepsy, a hypocretin deficiency disorder thought to be due to degeneration of hypothalamic hypocretin/orexin neurons, is currently treated symptomatically. We evaluated the efficacy of two small molecule hypocretin/orexin receptor‐2 (HCRTR2) agonists in narcoleptic male orexin/tTA; TetO‐DTA mice. TAK‐925 (1–10 mg/kg, s.c.) and ARN‐776 (1–10 mg/kg, i.p.) were injected 15 min before dark onset in a repeated measures design. EEG, EMG, subcutaneous temperature (Tsc) and activity were recorded by telemetry; recordings for the first 6 h of the dark period were scored for sleep/wake and cataplexy. At all doses tested, TAK‐925 and ARN‐776 caused continuous wakefulness and eliminated sleep for the first hour. Both TAK‐925 and ARN‐776 caused dose‐related delays in NREM sleep onset. All doses of TAK‐925 and all but the lowest dose of ARN‐776 eliminated cataplexy during the first hour after treatment; the anti‐cataplectic effect of TAK‐925 persisted into the second hour for the highest dose. TAK‐925 and ARN‐776 also reduced the cumulative amount of cataplexy during the 6 h post‐dosing period. The acute increase in wakefulness produced by both HCRTR2 agonists was characterised by increased spectral power in the gamma EEG band. Although neither compound provoked a NREM sleep rebound, both compounds affected NREM EEG during the second hour post‐dosing. TAK‐925 and ARN‐776 also increased gross motor activity, running wheel activity, and Tsc, suggesting that the wake‐promoting and sleep‐suppressing activities of these compounds could be a consequence of hyperactivity. Nonetheless, the anti‐cataplectic activity of TAK‐925 and ARN‐776 is encouraging for the development of HCRTR2 agonists. [ABSTRACT FROM AUTHOR]

To improve the aerodynamic performance of a high-speed train (HST) and reduce the safety risk of wake movement on platform commuters, trackside workers, and surrounding infrastructure, an active flow control method based on synthetic jets (SJs) is proposed to suppress the wake of the HST. The wake of the HST controlled by synthetic jets with different momentum coefficients is simulated by the improved delayed detached eddy simulation (IDDES) method embedded in ANSYS Fluent. Then, the slipstream velocity, aerodynamic force, velocity field in the wake region are analyzed. The results show that synthetic jets can effectively reduce the amplitude of the slipstream velocity in the wake region, the aerodynamic drag, and the fluctuation of the aerodynamic side force of the tail car. Furthermore, the synthetic jets delay the flow separation on the side of the tail car through periodic ejection and suction, and then attenuate the vortex motion in the wake region. [ABSTRACT FROM AUTHOR]

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It is well known that biofouling increases a ship's resistance and nominal wake. For submarines, any change to the circumferential variation of the nominal wake in the propeller plane will affect the variation of the flow over the propeller blade, and hence the fluctuating forces, and noise, generated by the propeller. The ANSYS FLUENT commercial Reynolds-Averaged Navier Stokes Computational Fluid Dynamics solver was used to investigate the influence of both the longitudinal and vertical distribution of biofouling on the resistance and wake, including the circumferential variation of the nominal wake, on a submarine, using the well-known Suboff standard submarine. For the present work, the k-ε turbulence model was selected, as this is commonly used in this field and is generally considered acceptable. To handle different boundary layer thicknesses in the flow fields, the whole y+ formulation was employed, enabling automatic switching between low and high Reynolds boundary wall models. The numerical solver used for the simulations is based on the finite volume method, which discretizes the RANS equations. In this approach, a segregated model was utilized in the solver, and the convection terms were discretized using the second-order upwind scheme to enhance solution accuracy. The criteria for the near wall are between 30 and 100, and the value of y+ for the present case is 84. It is shown that fouling over only the forward third of the submarine results in a greater increase in resistance than fouling over only the aft third. Fouling over only the lower half of the submarine results in greater resistance than fouling over only the forward third, but less than fouling over the whole of the hull. Fouling over only the forward third of the hull has less influence on the circumferential variation of the wake than fouling over the aft third only of the hull. The results show the importance of keeping the forward area of the hull clean when considering resistance only, whereas keeping the aft area of the hull clean is important when considering the uniformity of the nominal wake into the propeller. [ABSTRACT FROM AUTHOR]

Dandelion is a classic example of a wind-dispersed plant and enabling long-distance seed dispersal. In 2018, Cummins et al. reported their results of freely flying tests and fixed tests on both real dandelion seeds and a separated vortex ring was found above the pappus of the dandelion using flow visualization techniques. The separated vortex ring is the main aerodynamic feature of the dandelion seed which enables its flight. However, the effect of the gap structure of the pappus on the vortex generation has not been fully understood. In the present study, in order to investigate the effect of the pappus's porosity on flow structure in the wake of pappus, drop tests and flow visualization experiments were conducted using a vertical airflow pipe for the pappus with different porosity. The experimental samples are artificially changed porosity of pappus by partially removing filaments for the real (inhabit in nature) dandelion pappus. The pappus's porosity affects the strength of vortices generated in the wake of the pappus and the vortex growth during posture changes in free-fall motion. This vortex behavior is strongly related to the aerodynamic forces acting on the pappus. [ABSTRACT FROM AUTHOR]