Bottom Flow Research Articles

A Theory of Standing Meanders of the Antarctic Circumpolar Current and Their Response to Wind

Abstract Standing meanders of the Antarctic Circumpolar Current (ACC) and associated eddy hotspots play an important role for the meridional heat flux and downward momentum transfer in the Southern Ocean. Previous modeling studies show that the vorticity balance characterizing standing meanders in the upper ocean is dominated by advection of relative vorticity and stretching. Through the adjustment of this vorticity balance, standing meanders have been suggested to provide a pathway for the transfer of the momentum input by the wind from the surface to the bottom, leading to stronger bottom flows and energy dissipation. However, the dynamics governing the meander formation and its adjustment to wind remain unclear. Here we develop a quasigeostrophic theory and combine it with a regional model of the Macquarie Ridge region and an idealized channel model to explore the dynamics and vertical structure of standing meanders of the ACC. The results show that the entire vertical structure of the meander, including its dynamics in the upper ocean, is controlled by the bottom flow interacting with topography. Based on our results, we suggest a novel mechanism for the response of the ACC to wind in which “flexing” of the meander, or change in its curvature, is a response to changes in the bottom (barotropic) flow. Stronger bottom flow in response to stronger wind interacts with topography and generates a larger-amplitude Rossby wave propagating into the upper ocean. The ACC mean shear aloft amplifies the Rossby wave and leads to a larger-amplitude meander in the upper ocean dominated by advection of relative vorticity and stretching.

Charm and Bottom Quark Energy Loss and Flow Measurements in Au\(+\)Au Collisions by the PHENIX Experiment

Charm and Bottom Quark Energy Loss and Flow Measurements in Au\(+\)Au Collisions by the PHENIX Experiment

Investigation of a two-dimensional photovoltaic thermal system using hybrid nanofluids and a rotating cylinder.

This article focuses on a numerical investigation aimed at enhancing the electrical performance of a two-dimensional photovoltaic thermal system (PV/T) through the application of cooling using hybrid nanofluids. The hybrid nanofluids consist of titanium oxide and silver nanoparticles suspended in water, while the PV/T system is based on polycrystalline silicon, copper, and a flow channel with a rotating cylinder. PV/T devices generate electricity from sunlight, but their performance degrades over time due to the heat generated by solar radiation. Therefore, nanofluids can be circulated through the bottom flow channel to cool the device. This study utilizes 2D incompressible Navier-Stokes equations to control fluid flow and energy equations to manage energy distribution. The COMSOL 6.0 finite element software is employed for comprehensive modeling and simulation. To enhance the performance of the PV/T system, a parametric study is conducted by varying the Reynolds number (ranging from 100 to 1000), cylinder rotational speed (varying from 0.01 to 0.2 m s-1), and silver volume fraction (ranging from 0.01 to 0.2). The results show that increasing the Reynolds number and the volume fraction of silver leads to a reduction in the maximum temperature of the cell. The maximum temperature of the cell also decreases with the rotational speed of the cylinder but only for high Reynolds numbers. By applying the present model, the cell's efficiency is improved by 5.93%.

Multi-layer flow field mapping in a small-scale shallow water reservoir by coastal acoustic tomography

Long-term, high-precision and spatiotemporal observation of current structure in small-scale waters is important for underwater research and water resources management. In this paper, a reciprocal sound transmission experiment was conducted using three Coastal Acoustic tomography (CAT) systems within 300 m spacing in Huangcai reservoir, Hunan, China from 14 to 16, Sep 2020. The multi-arrival reciprocal paths between each pair of stations were identified with the help of ray simulation. 3-D CAT data which penetrated the full depth of water were obtained. The flow field along vertical slice were mapped and showed consistency with Acoustic Doppler Current Profiler (ADCP) and Temperature Depth (TD) data. A standard deviation of 0.73 m/s at the bottom layer were observed, indicating strong bottom flows in the reservoir. Furthermore, to visualize the strong bottom flow, the horizontal flow fields in the bottom layer were mapped by 3-D inversion technique. The feasibility of the technique was validated by three measures: 1) comparison between range average current and horizontal flow field; 2) Uncertainty analysis; 3) Check net volume transport. This work proves the CAT combined with 3-D inversion technique has the potentials to provide real-time 3-D current data for water researches.

Lab‐Scale Investigation of Slickwater Impact on Methane Desorption on Longmaxi Gas Shale

AbstractAfter multistage hydraulic fracking, a huge amount of slickwater stuck in shale gas formation significantly affects the shale‐gas‐well production performance. A set of comparative experiments to illustrate slickwater and its chemicals' impact on the methane desorption on shale powders were performed. The influence of slickwater and its chemicals on desorption isotherm, desorption efficiency, and adsorbed phase methane content as well as cumulative gas production was analyzed. The findings reflect the synthetic slickwater impact on methane desorption on shale powders, indicating that it can be helpful to optimize slickwater formulation and design shale‐gas‐well bottom flow pressure to obtain higher gas production. Also, the observations and analysis give a supplement for improving shale gas recovery through studying the function of chemical additives in slickwater on methane desorption.

Typhoon Effects on the Vertical Chlorophyll Distribution on the Northern Shelf of the South China Sea

AbstractTyphoon Merbok passed through the northern South China Sea and landed near the Pearl River Estuary in June 2017. Field observations showed that the chlorophyll‐a (Chla) concentration in the bottom/subsurface chlorophyll maximum (BCM/SCM) layer decreased in both nearshore and offshore regions after Merbok. In addition, the BCM/SCM layer became shallower in the nearshore region and deeper in the offshore region after Merbok. A coupled physical‐biogeochemical model was applied to investigate the driving mechanism for this Chla change. During the typhoon, the spatial movement of plume water was responsible for the surface Chla change in the nearshore region, and vertical mixing increased Chla in the upper layer and decreased it in the SCM layer in the offshore region. Shortly after the typhoon, surface Chla increased and bottom Chla decreased in the nearshore region, which was associated with strengthened bottom flow and vertical mixing. When the typhoon‐induced mixing decreased, upwelling tended to shoal the BCM layer in the nearshore region, and phytoplankton production increased Chla in the BCM layer. In the offshore region, vertical mixing was the dominant mechanism for Chla redistribution during the typhoon, which decreased Chla in the SCM layer and resulted in a deeper SCM layer. A few days after the typhoon, phytoplankton production also contributed to the Chla change particularly in the subsurface layer, which was stronger in the nearshore region than that in the offshore region. These findings may contribute to the understanding of phytoplankton dynamics in response to typhoons in coastal areas.

On convective instabilities in a rotating fluid with stably stratified layer and thermally heterogeneous boundary

The onset of convection in a rotating plane layer due to a vertical temperature gradient is studied in this paper. The background stratification is modulated by lateral temperature variations and stable stratification aimed at understating the Earth's outer core convection subject to thermal core–mantle interaction. At the top boundary, sinusoidal and Gaussian temperature variations are imposed apart from the reference case of isothermal condition used in the classical Rayleigh–Benard convection. The additional modulating conditions break the top–bottom flow symmetry leading to flow localization and asymmetry that exhibit modified temporal dynamics unlike that of the classical Rayleigh–Benard cells. The threshold for convection is lowered with flows occurring in surplus heat flux regions caused by the imposed conditions. Despite flow suppression in the stable layer, rapid rotation favors the penetration of convection rolls with smaller wavelengths. The lateral variations in temperature imposed at the top boundary enhance such axial penetration with a laterally varying penetrative extent resulting in a modified clustered flow structure unlike the reference case. With both modulating conditions imposed, the onset of overstable modes is favored for low Prandtl numbers, a regime which is relevant to the Earth's core conditions. With rapid rotation, a novel mode of traveling wave instability occurs at the onset of convection, the propagation direction of which is controlled by the lateral temperature gradients at the top boundary. The onset of oscillatory modes is suppressed by the imposition of the modulating conditions indicated by the significant lowering of the transition Prandtl number.

On the Resin Transfer Molding (RTM) Infiltration of Fiber-Reinforced Composites Made by Tailored Fiber Placement.

Tailored fiber placement (TFP) is a preform manufacturing process in which rovings made of fibrous material are stitched onto a base material, increasing the freedom for the placement of fibers. Due to the particular kinematics of the process, the infiltration of TFP preforms with resin transfer molding (RTM) is sensitive to multiple processes and material parameters, such as injection pressure, resin viscosity, and fiber architecture. An experimental study is conducted to investigate the influence of TFP manufacturing parameters on the infiltration process. A transparent RTM tool that enables visual tracking of the resin flow front was developed and constructed. Microsection evaluations were produced to observe the thickness of each part of the composite and evaluate the fiber volume content of that part. Qualitative results have shown that the infiltration process in TFP structures is strongly influenced by a top and bottom flow layer. The stitching points and the yarn also create channels for the resin to flow. Furthermore, the stitching creates some eye-like regions, which are resin-rich zones and are normally not taken into account during the infusion of TFP parts.

Optimization and Control for Separation of Ethyl Benzene from C8 Aromatic Hydrocarbons with Extractive Distillation

Extractive distillation has great significance for the separation of ethylbenzene from C8 aromatic hydrocarbons. Herein, a distillation process for the separation of ethylbenzene was designed using methyl phenylacetate as an extractant. A genetic algorithm (GA) was used to evaluate the economic and environmental factors of the process, and Aspen Dynamic was used to assess the dynamic performance. The sequential optimization method was used to obtain the initial process parameters. Then, the total annual cost and CO2 emissions were minimized by NSGA-III to increase the economic and environmental benefits. To enhance the search performance of GA, the mutation probability and crossover probability were studied and adjusted. The optimal total annual cost and CO2 emissions were 11.7% and 23.7% lower than those of the initial process. Based on a steady process, two control strategies, which were the flow rate of the recycling solvent controlled by entrainer makeup flow rate (CS1) and the bottom flow rate of the extractant recovery column (CS2), were designed. The results showed that the temperature deviation of CS2 was smaller than that of CS1, and the temperature of the process was more stable under the control of CS2.

Bedforms of Bonifacio Strait (Western Mediterranean): hydrodynamics, coastal outline, supply and sediment distribution

Abstract This paper shows the results of high-resolution survey on the continental shelf of Bonifacio Strait (north Sardinia). Multisensor and multiscale data obtained by means of sub-bottom profiler CHIRP and multibeam and side-scan sonar made it possible to identify the morphological features of bedforms. The analysis of both side-scan sonar sonograms mosaic and high-resolution seismic data allowed us to perform a detailed mapping of various substrates highlighting the presence of complex bedform associations. These bedform associations are typical of continental shelf environments affected by high-speed bottom currents. Multisource data analysis integrated by sedimentological study allowed us to identify the directions of sediment movements on the seabed and the progradation of bedforms. Locally, it was found that the bedforms of mobile bottoms are still active and they persist for more than a decade. The path of the currents’ circulation revealed that in the Bonifacio Strait, the bottom currents flow westwards, opposed to the prevailing sea surface flows.

Influences of Tidal Effect on Upper Ocean Responses to Typhoon Passages Surrounding Shore Region off Northeast Taiwan

In this study, the Regional Ocean Modelling System (ROMS) with a spatial resolution of 2 km is used to understand the cooling responses in the sea northeast of Taiwan associated with multiple typhoons. Sea level measurements derived from in situ tidal gauges and continuous temperature measured by a moored buoy deployed at Longdong were used to validate the model’s performance. Six far-field typhoons with similar tracks, namely, Utor (2001), Dujuan (2003), Sanvu (2005), Nanmadol (2011), Usagi (2013), and Meranti (2016), were systematically investigated to demonstrate the influences of tidal effect on upper ocean responses to typhoon passages surrounding shore regions. After integrating tidal forcing, model-simulated cold wakes behind typhoon passages were essentially enhanced. Compared with observations, the cold wakes were reproduced more realistically. Tides could promote a cooling response through the following potential mechanisms: (1) tidal mixing destratifies the water column, (2) a stronger northward current leads to a sharper bottom thermocline, (3) tidal residual currents (southward) drive the offshore-ward (downslope) bottom Ekman flow and lead to the overturning of cold bottom water and warm subsurface water, (4) the increase in bottom stress due to the interaction of tidal currents and bottom topography results in the destratification of the bottom water column, and (5) the wind–tide coupled effect. Nevertheless, the exact mechanism dominating the process of a typhoon–tide-induced stronger upper ocean response depends on different typhoon activities, tidal regimes, stratification, and bathymetry and needs further investigations. In this study, we suggest that including tidal effects is essential for the modeling of upper ocean responses to typhoon passages near the shore regions.

Transverse Nonuniformity of Air–Water Flow and Lateral Wall Effects in Quasi-Two-Dimensional Hydraulic Jump

Flow field characterization in high-aerated flows often involves flow imaging techniques through transparent sidewalls, and the results may be subject to sidewall effects and thus differ from the central flow behaviors. This paper contributes an experimental investigation of the sidewall effects on the air-water flow distributions in quasi-two-dimensional hydraulic jumps in a rectangular flume. The tested hydraulic jumps are characterized by preaerated approach flows and large inflow Froude numbers from 10.6 to 15.1. The air-water flow properties are measured intrusively along the centerline, sidewall, and transverse cross sections to provide a three-dimensional view of the aerated flow structure. Substantial redistribution of the bubbly flow is observed due to the presence of lateral aeration boundary layers in the high-speed jet-shear region, compared to the less affected free-surface roller. The magnitude difference between the central and lateral air-water flow properties is more distinct in terms of bubble count rate and less evident for void fraction and interfacial velocity, while the affected area is broader for void fraction distributions. The results suggest a concentration of high-speed jet flow in the central bottom flow column, where the jet layer is thicker, the recirculation roller is smaller, and the proportion of small-size bubbles is higher. The width of the central flow region free of the sidewall effects is approximately 60% to 80% of the flume width in the present facility, narrower on the bottom, and broader at the free surface. The findings demonstrate that the transverse variation of air-water flow and the difference between the central and lateral flow fields should not be ignored for the high-speed flow regions of hydraulic jump. A correct assessment of the sidewall effects is essential for interpreting imaging-based measurement of highly-aerated flow.

Land use change and baseflow recession modelling in Wuryantoro Watershed, Wonogiri Regency, Central Java Province, Indonesia

Hydrological phenomena on the scale of a watershed are complex and may never be understood holistically. One of the innovations in baseflow hydrological modelling is the analysis of the baseflow recession curve, generally expressed as the natural storage of river flows and containing valuable information about the properties and characteristics of natural aquifer storage. This study aims to model land use change and baseflow recession in the Wuryantoro watershed, Wonogiri Regency, Central Java Province. The research method uses an exponential model in which changes in the characteristics of a baseflow recession are a function of land use changes over a certain period. The calibration of the seven graphical models of land use change against the characteristics of the baseflow recession shows that the seven curves of the land use change graphic model have model coefficients and curve slopes that vary from gentle to steep. The slope of the gentle and steep curve describes the bottom flow deposits' condition over time. The state of water storage in the seven better graphical models is that the change of forest remains forest followed by the change of agriculture into the forest, forest into the settlement, change of agricultural land into the settlement, change of forest to agricultural land, settlement remains settlement and change of agricultural land remains agrarian land.

Hydraulically Controlled Bottom Flow in the Orkney Passage

Supercritical hydraulically controlled overflow of Antarctic Bottom Water from the Weddell Sea has been observed in the Orkney Passage during field measurements in February 2022. The Orkney Passage is the main pathway for the densest layer of Antarctic Bottom Water flow from the Weddell Sea to the Scotia Sea. The bottom current overflows the sill across the passage and flows down from the crest of the sill at 3600 m deeper than 4000 m. The descending flow accelerates because of the difference in the height of the sill and its foot. An estimate of the Froude number of this flow was greater than unity. Near the foot of the slope the kinetic energy of the flow becomes insufficient to continue moving in this regime. The flow slows down, and strong mixing and warming of the bottom water occurs due to the exchange with the surrounding waters. This hydrodynamic phenomenon is called supercritical hydraulically controlled flow. However, the flow of bottom water continues further and eventually fills the abyssal depths of the Atlantic.

Two-layer analytical model for estimation of layer thickness and flow using Diffuse Correlation Spectroscopy.

Diffuse correlation spectroscopy (DCS) has been widely explored for its ability to measure cerebral blood flow (CBF), however, mostly under the assumption that the human head is homogenous. In addition to CBF, knowledge of extracerebral layers, such as skull thickness, can be informative and crucial for patient with brain complications such as traumatic brain injuries. To bridge the gap, this study explored the feasibility of simultaneously extracting skull thickness and flow in the cortex layer using DCS. We validated a two-layer analytical model that assumed the skull as top layer with a finite thickness and the brain cortex as bottom layer with semi-infinite geometry. The model fitted for thickness of the top layer and flow of the bottom layer, while assumed other parameters as constant. The accuracy of the two-layer model was tested against the conventional single-layer model using measurements from custom made two-layer phantoms mimicking skull and brain. We found that the fitted top layer thickness at each source detector (SD) distance is correlated with the expected thickness. For the fitted bottom layer flow, the two-layer model fits relatively consistent flow across all top layer thicknesses. In comparison, the conventional one-layer model increasingly underestimates the bottom layer flow as top layer thickness increases. The overall accuracy of estimating first layer thickness and flow depends on the SD distance in relationship to first layer thickness. Lastly, we quantified the influence of uncertainties in the optical properties of each layer. We found that uncertainties in the optical properties only mildly influence the fitted thickness and flow. In this work we demonstrate the feasibility of simultaneously extracting of layer thickness and flow using a two-layer DCS model. Findings from this work may introduce a robust and cost-effective approach towards simultaneous bedside assessment of skull thickness and cerebral blood flow.

Design and flow field analysis of impregnated diamond bit for seafloor drill in soft-hard interlaced strata

According to the seafloor drill working conditions and the complex formation characteristics of the seafloor, this paper aims to improve the adaptability of the diamond bit to the formation and the coring quality. The cutter tooth design scheme of the impregnated diamond bit is proposed, and Fluent analyzes the flow field of drilling fluid at the bottom hole. The results show that the cone cutting tooth bit with the primary and assistant nozzles can directly avoid 85.33% drilling fluid flushing core and reduce the disturbance of drilling fluid to the core samples. The water passage structure of the bit is reasonable, and the upward return velocity of the drilling fluid can be stabilized between 0.7 and 1.8 m/s, which meets the requirements of the upward return of cuttings in seabed strata, and has a good hole wall protection performance. Based on the bottom-jet diamond bit, the assistant nozzles are added. The drilling fluid of the assistant nozzles can better cover the bit crown, conductive to cooling the bit crown. The drilling fluid of the main nozzles can timely up-return along the outer annulus hole wall, conducive to the up-return of the cuttings with drilling fluid. This study can extend existing designs of a seafloor coring bits and bottom hole flow field analysis methods.

Numerical simulation of electromagnetic heating of heavy oil reservoir based on multi-physical fields coupling model

ABSTRACT Electromagnetic (EM) heating is an advanced technology that can improve the oil recovery rate. Previous studies usually focus on the coupling of EM and thermal reservoir models, with little attention to multi-phase flow in EM heating. In order to accurately analyze the heat and mass transfer in the reservoir under EM heating, this work developed an advanced model coupling the EM-temperature-seepage fields, in which the variation of the physical properties of heavy oil reservoirs has been considered. In addition, the influence of the EM heating factors is also analyzed. The results show a significant saturation partitioning in the heat and mass transfer in heavy oil reservoirs under EM heating, and heavy oil flows more rapidly in areas of high oil saturation. Increasing the EM frequency and power can extend the heating range of the reservoir, but it can cause a dramatic rise in the temperature of the antenna. When the temperature of the production well induces heavy oil flow, increasing the production pressure can significantly improve output. The average flow rate of heavy oil at the producing well increased by 17.61% when the bottom flow pressure decreased from 19 MPa to 17 MPa. The study of the distance between the production well and the antenna finds that the average temperature of the production well is only 463.06 K when the antenna spacing is 15 m. Compared with other situations, 10 m is the most suitable for efficient and continuous exploitation of heavy oil.

Exploring the three-dimensional flow-sediment dynamics and trapping mechanisms in a curved estuary: The role of salinity and circulation

Combined with the observed data in the wet season in June 2015, structures of longitudinal and lateral residual current and characteristics of the estuarine turbidity maximum (ETM) in the Yongjiang estuary (YE) are studied using a three-dimensional baroclinic flow and sediment numerical model. The mechanisms of residual current and sediment trapping are investigated according to the momentum balance analysis and sediment transport decomposition. The results show that at spring tide, the outflowing longitudinal residual current is dominated by longitudinal advection and barotropic pressure gradient. At neap tide, a remarkable baroclinic effect emerges at the bottom of the river mouth area, driving the landward residual current and forming the estuarine circulation. Lateral residual current at upstream bends with lower salinity is dominated by longitudinal advection and barotropic pressure gradient. The flow directs toward the concave bank at the surface and toward the convex bank near the bottom at these sections. At downstream bends with higher salinity, the lateral residual current is greatly affected by the baroclinic gradient, which will shift the lateral flow circulation structure. In transition straight reaches located at Qingshuipu and Zhenhai, the lateral residual current presents a double-cell circulation with surface convergence and bottom divergence. During spring tide, the ETM is located near Qingshuipu, driven by landward tidal pumping transport due to the strong tidal energy. During neap tide, a strong exchange flow generates landward circulation transport around the river mouth, and the ETM moves downstream to Zhenhai. At bends, sediment along the cross section is laterally trapped on the convex bank, driven by bottom lateral flow induced circulation transport. While in transition straight reaches, high turbidity is still concentrated in the deep groove, caused by bottom divergent flow and circulation transport.

Insights into the Mixing Efficiency of Submesoscale Centrifugal–Symmetric Instabilities

Abstract Submesoscale processes provide a pathway for energy to transfer from the balanced circulation to turbulent dissipation. One class of submesoscale phenomena that has been shown to be particularly effective at removing energy from the balanced flow is centrifugal–symmetric instabilities (CSIs), which grow via geostrophic shear production. CSIs have been observed to generate significant mixing in both the surface boundary layer and bottom boundary layer flows along bathymetry, where they have been implicated in the mixing and water mass transformation of Antarctic Bottom Water. However, the mixing efficiency (i.e., the fraction of the energy extracted from the flow used to irreversibly mix the fluid) of these instabilities remains uncertain, making estimates of mixing and energy dissipation due to CSI difficult. In this work we use large-eddy simulations to investigate the mixing efficiency of CSIs in the submesoscale range. We find that centrifugally dominated CSIs (i.e., CSI mostly driven by horizontal shear production) tend to have a higher mixing efficiency than symmetrically dominated ones (i.e., driven by vertical shear production). The mixing efficiency associated with CSIs can therefore alternately be significantly higher or significantly lower than the canonical value used by most studies. These results can be understood in light of recent work on stratified turbulence, whereby CSIs control the background state of the flow in which smaller-scale secondary overturning instabilities develop, thus actively modifying the characteristics of mixing by Kelvin–Helmholtz instabilities. Our results also suggest that it may be possible to predict the mixing efficiency with more readily measurable parameters (viz., the Richardson and Rossby numbers), which would allow for parameterization of this effect.

Northeast Greenland: ice‐free shelf edge at 79.4°N around the Last Glacial Maximum 25.5–17.5 ka

The size of the last glacial ice sheet on the Northeast (NE) Greenland shelf and its interaction with ocean circulation have been the subject of debate. Here we provide insights into the extent of the ice sheet around the Last Glacial Maximum (LGM) and investigate timing and strength of changes in the flow of Atlantic Water. The study is based on a multiproxy investigation of a marine sediment core, gravity core DA17‐NG‐ST01‐019G, from 323‐m water depth at the NE Greenland shelf edge at 79.4°N. We present benthic and planktic foraminiferal distribution data, AMS‐14C dates, sedimentological (ice‐rafted debris (IRD) and grain sizes), and geochemical (XRF) data in combination with geophysical (sub‐bottom profiler) data. The oldest sediments at the study site are dated to 25.5–17.5 ka, encompassing the time frame from the beginning of the LGM to the early deglaciation. This part is overlain by sediments from the late deglaciation and Holocene. The deposits dating from the LGM are very rich in both planktic and benthic foraminifera and macrofossils of excellent preservation. The faunas show that the site generally was affected by a strong flow of relatively warm subsurface Atlantic Water during the LGM and Early Holocene. Conditions turned more polar with cold bottom water flow in the Middle–Late Holocene (c. 7.5 ka to Recent) with presence of mainly agglutinated benthic foraminiferal species. Our data from the LGM also indicate that the deposits were mixed by iceberg scouring, confirmed by the geophysical data showing extensive ploughing of the sediments on the outer shelf area. The results further indicate that the Greenland Ice Sheet did not reach to the edge of the NE Greenland shelf at 79.4°N during the LGM 24–18 ka.