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Riverine transport of nutrients and carbon from inland waters to the coastal and finally the open ocean alters marine primary production (PP) and carbon (C) uptake regionally and globally. So far, this process has not been fully represented and evaluated in the state-of-the-art Earth system models. Here we assess changes in marine PP and C uptake projected under the Representative Concentration Pathway 4.5 climate scenario using the Norwegian Earth system model, with four riverine transport configurations for nutrients (nitrogen, phosphorus, silicon, and iron), carbon, and total alkalinity: deactivated, fixed at a recent-past level, coupled to simulated freshwater runoff, and following four plausible future scenarios. The inclusion of riverine nutrients and carbon at the 1970 level improves the simulated contemporary spatial distribution of annual mean PP and air–sea CO2 fluxes relative to observations, especially on the continental margins (5.4 % reduction in root mean square error (RMSE) for PP) and in the North Atlantic region (7.4 % reduction in RMSE for C uptake). While the riverine nutrients and C input is kept constant, its impact on projected PP and C uptake is expressed differently in the future period from the historical period. Riverine nutrient inputs lessen nutrient limitation under future warmer conditions as stratification increases and thus lessen the projected decline in PP by up to 0.66 ± 0.02 Pg C yr−1 (29.5 %) globally, when comparing the 1950–1999 with the 2050–2099 period. The riverine impact on projected C uptake depends on the balance between the net effect of riverine-nutrient-induced C uptake and riverine-C-induced CO2 outgassing. In the two idealized riverine configurations the riverine inputs result in a weak net C sink of 0.03–0.04 ± 0.01 Pg C yr−1, while in the more plausible riverine configurations the riverine inputs cause a net C source of 0.11 ± 0.03 Pg C yr−1. It implies that the effect of increased riverine C may be larger than the effect of nutrient inputs in the future on the projections of ocean C uptake, while in the historical period increased nutrient inputs are considered the largest driver. The results are subject to model limitations related to resolution and process representations that potentially cause underestimation of impacts. High-resolution global or regional models with an adequate representation of physical and biogeochemical shelf processes should be used to assess the impact of future riverine scenarios more accurately.

The Gulf of Riga is a relatively shallow bay connected to the deeper central Baltic Sea (Baltic Proper) via straits with sills. The decrease in the near-bottom oxygen levels from spring to autumn is a common feature in the gulf, but in 2018, extensive hypoxia was observed. We analyzed temperature, salinity, oxygen, and nutrient data collected in 2018, along with historical data available from environmental databases. Meteorological and hydrological data from the study year were compared with their long-term means and variability. We suggest that pronounced oxygen depletion occurred in 2018 due to a distinct development of vertical stratification. Seasonal stratification developed early and was stronger in spring–summer 2018 than on average due to high heat flux and weak winds. Dominating northeasterly winds in early spring and summer supported the inflow of saltier waters from the Baltic Proper that created an additional deep pycnocline restricting vertical transport between the near-bottom layer (NBL) and the water column above. The estimated oxygen consumption rate in the NBL in spring–summer 2018 was about 1.7 mmolO2m-2h-1, which exceeded the oxygen input to the NBL due to advection and vertical mixing. Such a consumption rate leads to near-bottom hypoxia in all years when vertical mixing in autumn reaches the seabed later than on average according to the long-term (1979–2018) meteorological conditions. The observed increase in phosphate concentrations in the NBL in summer 2018 suggests a significant sediment phosphorus release in hypoxic conditions counteracting the mitigation measures to combat eutrophication. Since climate change projections predict that meteorological conditions comparable to those in 2018 will occur more frequently, extensive hypoxia would be more common in the Gulf of Riga and other coastal basins with similar morphology and human-induced elevated input of nutrients.

Oxygen isotope (δ18O) sclerochronology of benthic marine molluscs provides a means of reconstructing the seasonal range in seafloor temperature, subject to use of an appropriate equation relating shell δ18O to temperature and water δ18O, a reasonably accurate estimation of water δ18O, and due consideration of growth-rate effects. Taking these factors into account, δ18O data from late Pliocene bivalves of the southern North Sea basin (Belgium and the Netherlands) indicate a seasonal seafloor range a little smaller than now in the area. Microgrowth-increment data from Aequipecten opercularis, together with the species composition of the bivalve assemblage and aspects of preservation, suggest a setting below the summer thermocline for all but the latest material investigated. This implies a higher summer temperature at the surface than on the seafloor and consequently a greater seasonal range. A reasonable (3 ∘C) estimate of the difference between maximum seafloor and surface temperature under circumstances of summer stratification points to seasonal surface ranges in excess of the present value (12.4 ∘C nearby). Using a model-derived estimate of water δ18O (0.0 ‰), summer surface temperature was initially in the cool temperate range ( ∘C) and then (during the Mid-Piacenzian Warm Period; MPWP) increased into the warm temperate range (>20 ∘C) before reverting to cool temperate values (in conjunction with shallowing and a loss of summer stratification). This pattern is in agreement with biotic-assemblage evidence. Winter temperature was firmly in the cool temperate range ( ∘C) throughout, contrary to previous interpretations. Averaging of summer and winter surface temperatures for the MPWP provides a figure for annual sea surface temperature that is 2–3 ∘C higher than the present value (10.9 ∘C nearby) and in close agreement with a figure obtained by averaging alkenone and TEX86 temperatures for the MPWP from the Netherlands. These proxies, however, respectively, underestimate summer temperature and overestimate winter temperature, giving an incomplete picture of seasonality. A higher annual temperature than now is consistent with the notion of global warmth in the MPWP, but a low winter temperature in the southern North Sea basin suggests regional reduction in oceanic heat supply, contrasting with other interpretations of North Atlantic oceanography during the interval. Carbonate clumped isotope (Δ47) and biomineral unit thermometry offer means of checking the δ18O-based temperatures.

Deep convection in the Gulf of Lion is believed to be primarily driven by the mistral winds. However, our findings show that the seasonal atmospheric change provides roughly two-thirds of the buoyancy loss required for deep convection to occur for the year 2012 to 2013, with the mistral supplying the final third. Two NEMOMED12 ocean simulations of the Mediterranean Sea were run from 1 August 2012 to 31 July 2013, forced with two sets of atmospheric-forcing data from a RegIPSL coupled run within the Med-CORDEX framework. One set of atmospheric-forcing data was left unmodified, while the other was filtered to remove the signal of the mistral. The control simulation featured deep convection, while the seasonal simulation did not. A simple model was derived by relating the anomaly scale forcing (the difference between the control and seasonal runs) and the seasonal scale forcing to the ocean response through the stratification index. This simple model revealed that the mistral's effect on buoyancy loss depends more on its strength rather than its frequency or duration. The simple model also revealed that the seasonal cycle of the stratification index is equal to the net surface heat flux over the course of the year, with the stratification maximum and minimum occurring roughly at the fall and spring equinoxes.

The employment of 1D model of the thermal stratification in the tank of an air to water heat pump (AWHP) may accurately predict the evolution of the temperatures at the different layers. The study predicted the water temperatures at different levels in a 150 L tank coupled with 1.2 kW heat pump unit. A data acquisition system was designed and built to monitor the input and output parameters used in the model to evaluate the evolution of the water layers’ temperatures. The results depicted that the 1D linear model accurately predicted the evolution of the water temperatures at each layer due to thermal stratification with a determination coefficient ( R 2) and root mean square error (RMSE) of 0.9932 and 0.9253. The modelled validation showed a very good R 2 and RMSE of 0.9940 and 0.8595. The average thermal energy gained and the average COP due to the first hour heating rating (the withdrawal of 150 L of the hot water) was 5.67% lowered under the stratification condition when compared to the scenario without stratification. The p -values show no significant differences among the water temperatures at the different layers due to first hour heating rating. The study will encourage researchers and energy service companies to highlight the impact of thermal stratification regarding to the dynamics of an AWHP.

Coastal marine boundary layer jets (CMBLJs) play an important role in coastal and inland rainfall in South China. Using 21-yr ERA5 and CMORPH rainfall data, two main CMBLJs are found on the either side of Hainan Island (named as BLJ-WEST vs BLJ-EAST), which are always strengthened jointly. Both the two CMBLJs often occur in the pre-summer rainy season and exhibit evident diurnal cycle with a maximum at night. With the emergence of the CMBLJs, rainfall is significantly enhanced in South China, particularly downstream of each CMBLJ. The response of rainfall to the CMBLJs is mainly attributed to the convergence at the terminus of the CMBLJ, terrain-induced lifting and relevant atmospheric stratification. Coastal rainfall at the downstream of the BLJ-WEST is much weaker than that of the BLJ-EAST because of higher CIN over Beibu Gulf, which is caused by lower temperature lapse rate and adiabatic heating in lee of the Annamite Range. The inland rainfall increases along with the CMBLJs’ intensity, whereas coastal rainfall reaches a maximum in the presence of moderate CMBLJs rather than stronger CMBLJs. Stronger CMBLJs induce stronger dynamic lifting but higher CIN near the coastal area. Additionally, CAPE near the coast does not become highest with strongest CMBLJs, because the CAPE generation contributed by coastal dynamic lifting can be offset by the negative contribution caused by the horizontal advection of the cold and dry air from Indochina Peninsula. Therefore, anomalous dynamic lifting, moisture flux convergence, and CAPE/CIN associated with the CMBLJs’ intensity jointly result in anomalous rainfall.

The motion trajectory of hydrogen leakage is an essential safe issue for the application of hydrogen energy. A dimensionless fast-running motion trajectory prediction model is proposed to predict the dispersion characteristics of the buoyant jet of hydrogen leakage for the accident. The impact of different leakage angles, leakage velocity and thermal stratification of ambient air on hydrogen leakage behavior was analyzed. The new developed model was verified by experimental results in literatures. Leakage hydrogen can flow upwards freely in a uniform environment. However, it shows an oscillating trajectory at a certain height in a thermally stratified environment, which is so called “locking phenomenon”. The trajectory of hydrogen leakage is upward and hydrogen gathers at the top of the space to form stratification in a uniform environment, while the hydrogen leakage shows an oscillating trajectory at a certain height in a thermal stratification environment. With the increase of Froude number Fr, it shows that the stable height and maximum height of the leakage airflow have a trend of rising first and then falling in a thermally stratified environment. The findings are expected to give guidance in real-world situations, for example, a larger Fr value and a larger temperature gradient can lead to a decrease in the stable height in the thermally stratified environment. It is found that the fitting of the stable height with different temperature gradients satisfies the power function relationship. This work is expected to be helpful for reducing hydrogen leakage accumulation and explosion risk.

The Arabian Gulf is a very significant ocean body, which hosts more than 55% of the oil reserves of the world and produces about 30% of the total production, and thus, it is likely to face high risk and adverse problems by the intensified environmental stressors and severe climatic changes. Therefore, understanding the hydrography of the Gulf is very essential to identify various marine environmental issues and subsequently, developing marine protection and management plans. In this study, hydrography data collected at 11 stations along 3 linear transects in the early summer of 2016 were analyzed. The physicochemical parameters exhibited apparent variations along each transect, both laterally and vertically, connected to stratification, formation of different water masses and excessive heating. The temperature and salinity decreased laterally from nearshore to offshore, while layered density structures were identified in the offshore regions. The pH, dissolved oxygen (DO) and chlorophyll fluorescence (Fo) exhibited distinct horizontal and vertical variations. The observed pH is within the normal ranges, indicating that seawater acidification may not be a threat. The highest DO (6.13–8.37 mg/l) was observed in a layer of 24-36 m water depth in the deeper regions of the central transect.

Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that the conventional triple flame structure is prevalent during the initial stage of flame kernel growth. Both premixed and nonpremixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis further reveals the effects of flame stretch and fuel pyrolysis on flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for the PFS-assisted lean operation in the LES context. It is found that the G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the nonpremixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

Located in the northern South China Sea, the Pearl River Estuary (PRE) is one of the most important estuaries in China and is surrounded by several megacities. Hypoxia mainly occurs in the bottom waters of the PRE during summer and is more prominent near the Humen outlet and the subestuary outside Modaomen and Jitimen. A well-validated three-dimensional (3-D) coupled physical-biogeochemical model was used to explore the changes in dissolved oxygen (DO) dynamics and hypoxic conditions in the PRE over an intra-annual cycle and elucidate the processes controlling the generation, development, and dissipation of hypoxia. In summer, oxygen consumption due to the high-intensity sediment oxygen demand (SOD) intensified by large inputs of riverine particulate organic carbon (POC) exceeded the DO supplemented by vertical diffusion (largely inhibited by strong fresh water–induced stratification), thus leading to a significant decrease in DO in the bottom waters; in other seasons, these DO source and sink terms were nearly balanced so that the bottom DO concentrations were maintained at higher levels. Moreover, the lag analysis shows that there is an approximately 2-month lag between riverine POC and SOD. By comparison, the low-oxygen area near Humen has a controlling mechanism distinct from that of the subestuary outside Modaomen and Jitimen. Specifically, the timely and sufficient oxygen supplement brought by vertical diffusion can replenish the bottom DO consumed by SOD in this region, and the formation and development of low-oxygen conditions (DO ≤ 4 mg L−1) is mainly affected by riverine low-oxygen inflows. In summary, our study clarified that the terrestrial organic pollutant input and low-oxygen water from the upper reaches have an important impact on the DO in different areas of the PRE, especially the low-oxygen area near Humen, which is controlled by the water quality of the upper reaches. This conclusion is of great significance for regional environmental management.

Hot water storage (HWS) tanks are one of the commonly employed sensible energy storage systems that store heat energy using water as the storage medium. Hot water tanks store thermal energy from multiple energy sources and practise several utilization methods, however, identifying the best approach to effectively utilize the stored thermal energy inside the tank from the energy efficiency point of view is critical. Present work focuses on the transient numerical investigation of a domestic, multi-sourced HWS tank. Thermal behaviour of HWS tank is analysed in three dynamic operational modes, namely charging, continuous delivery, and discharging operation. The axis-symmetric, two-dimensional model of the double coiled, vertical HWS tank of cylindrical shape is simulated using ANSYS Fluent. The numerical model is validated against the experiment data in charging mode. Influence of operating modes on the degree of thermal stratification is determined. Axial temperature evolution, dimensionless Stratification, and Richardson numbers are calculated and compared for each operational case. Results show that thermal stratification depends on the location of heating source inside the tank under the given operational mode. The degree of stratification in both the charging and continuous delivery modes is improved when the heat exchanger coil installed at the upper portion of the tank is functioning. The Stratification numbers are 0.28 and 0.32 after 30 min in the charging mode, and continuous delivery mode, respectively. The study compares thermal performance of HWS tank in different conditions and reveals the evolution of the thermal stratification with time, which are essential in designing stratified HWS tanks.

Seasonal shifts in phytoplankton accumulation and loss largely follow changes in mixed layer depth, but the impact of mixed layer depth on cell physiology remains unexplored. Here, we investigate the physiological state of phytoplankton populations associated with distinct bloom phases and mixing regimes in the North Atlantic. Stratification and deep mixing alter community physiology and viral production, effectively shaping accumulation rates. Communities in relatively deep, early-spring mixed layers are characterized by low levels of stress and high accumulation rates, while those in the recently shallowed mixed layers in late-spring have high levels of oxidative stress. Prolonged stratification into early autumn manifests in negative accumulation rates, along with pronounced signatures of compromised membranes, death-related protease activity, virus production, nutrient drawdown, and lipid markers indicative of nutrient stress. Positive accumulation renews during mixed layer deepening with transition into winter, concomitant with enhanced nutrient supply and lessened viral pressure., Phytoplankton are important primary producers. Here the authors investigate phytoplankton physiological changes associated with bloom phases and mixing regimes in the North Atlantic, finding that stratification and deep mixing shape accumulation rates by altering physiology and viral production.

The systematic discrepancies in both tsunami arrival time and leading negative phase (LNP) were identified for the recent transoceanic tsunami on 16 September 2015 in Illapel, Chile by examining the wave characteristics from the tsunami records at 21 Deep-ocean Assessment and Reporting of Tsunami (DART) sites and 29 coastal tide gauge stations. The results revealed systematic travel time delay of as much as 22 min (approximately 1.7% of the total travel time) relative to the simulated long waves from the 2015 Chilean tsunami. The delay discrepancy was found to increase with travel time. It was difficult to identify the LNP from the near-shore observation system due to the strong background noise, but the initial negative phase feature became more obvious as the tsunami propagated away from the source area in the deep ocean. We determined that the LNP for the Chilean tsunami had an average duration of 33 min, which was close to the dominant period of the tsunami source. Most of the amplitude ratios to the first elevation phase were approximately 40%, with the largest equivalent to the first positive phase amplitude. We performed numerical analyses by applying the corrected long wave model, which accounted for the effects of seawater density stratification due to compressibility, self-attraction and loading (SAL) of the Earth, and wave dispersion compared with observed tsunami waveforms. We attempted to accurately calculate the arrival time and LNP, and to understand how much of a role the physical mechanism played in the discrepancies for the moderate transoceanic tsunami event. The mainly focus of the study is to quantitatively evaluate the contribution of each secondary physical effect to the systematic discrepancies using the corrected shallow water model. Taking all of these effects into consideration, our results demonstrated good agreement between the observed and simulated waveforms. We can conclude that the corrected shallow water model can reduce the tsunami propagation speed and reproduce the LNP, which is observed for tsunamis that have propagated over long distances frequently. The travel time delay between the observed and corrected simulated waveforms is reduced to

The strait studied in this paper, “Sundalagið Norður”, is the northern part of a narrow body of seawater separating the two largest islands in the Faroe Islands (Faroes). It has shallow sills in both ends and considerably deeper waters in between. South of the southern end of the strait there is an amphidromic region for the semidiurnal tides so that the tidal range is much lower south of the strait than north of it. The resulting tidal forcing generates periodically varying inflow of seawater across the northern sill, but only a part of that manages to cross the narrow and shallow southern sill. Combined with a large input of freshwater, this gives the strait a fjord-like character. To investigate how this fjord-like character affects the circulation within the strait and its exchanges with outside waters, a pilot project was initiated to simulate the dynamics of the strait with a high-resolution ocean model for a month. The model simulations show clearly the dominance of tidal forcing over freshwater (estuarine) and wind on timescales up to a day. On longer timescales, the simulations indicate systematic variations in the net flows (averaged over a diurnal tidal period) through both the upper and deeper layers. These long-period variations of net flow in the model simulations are forced by sea level differences between both ends of the strait generated by the dominant fortnightly and monthly tidal constituents (Mf, MSf, Mm, MSm). Harmonic analysis of sea level records from two tide gauges located off each end of the strait demonstrates that this behaviour is not a model artefact and it has pronounced effects on the strait. Not only does it induce long-period (mainly fortnightly) variations in the net flow through the strait, but it also generates variations in the estuarine characteristics. According to the model simulations, periods with net southward flow, typically lasting a week, have a strait-like character with net southward flow almost everywhere. Periods with net northward flow, in contrast, have a more fjord-like character with stronger salinity stratification and a southward counter-flow in the deep layer. This also induces a large difference in renewal rate of the deep water between the two periods, which is important to consider for human utilization of the strait, especially the local aquaculture plant. The combination of topographic, freshwater, and tidal characteristics creating these long-period variations is rather unusual, and it is not known whether similar systems exist elsewhere, but the long-period variations tend to be masked by the stronger semidiurnal and diurnal variations and may easily be overlooked.

Gasoline compression ignition combustion has demonstrated the potential of getting high fuel efficiency. In this work, two engine models are established in the commercial software Converge 2.3 based on the experimental results of an optical engine and a modified metal engine. The effect mechanism of mixture stratification and the influence of compound control strategy on gasoline compression ignition (GCI) combustion and soot emissions under high load condition are investigated. Results show that synergistic effect of physics and chemistry is the dominant control mechanism of GCI combustion. Stronger mixture stratification can effectively reduce the maximum pressure rise rate (MPRR) and improve the indicated thermal efficiency (ITE) and emissions; applying high EGR will significantly reduce OH radical in the cylinder and subsequently weaken the soot oxidation process, resulting in high soot emission; under the premise of reasonable NOx emission and MPRR, the soot emission can be effectively reduced with a proper advanced main injection timing. The effect of temperature on the soot oxidation process is the primary mechanism for the ultimate soot emission at different main injection timings; properly increasing the interval between the pre‐ and main injection can reduce NOx and soot emissions under the premise of ensuring that the MPRR is within the upper limit. However, the effect is not significant because of the small proportion of preinjection fuel.

This work presents ship-based measurements of fog off St John’s, Newfoundland, on 13 September 2018 during the Coastal Fog field campaign. The measurements included cloud-particle spectra, cloud-base height and aerosol backscatter, radiation, turbulence, visibility, and sea-surface temperature. Radiosonde soundings were made at intervals of less than 2 h. Fog occurred in two episodes during the passage of an eastward-moving synoptic low-pressure system. The boundary-layer structure during the first fog episode consisted of three layers, separated by two saturated temperature inversions, and capped by a subsidence inversion. The lowest layer was fog, and the upper layers were cloud. The second fog episode consisted of one well-mixed fog layer capped by a subsidence inversion. Low wind speeds and stable stratification maintained low surface-layer turbulence during fog. Droplet size distributions had typical bimodal distributions. The visibility correlated with the droplet number concentration and liquid water content. The air temperature was higher than the sea-surface temperature for the first 30 min of the first fog episode but was lower than the sea for the remainder of all fog. The sensible heat flux was upward, from sea to air, for the first 62% of the first fog episode and then reversed to downward, from air to sea, for the remainder of the first fog episode and the second fog episode. The counter-gradient heat fluxes observed (i.e., opposite to what is expected from the instantaneous air–sea temperature difference) appear to be related to turbulence, entrainment, and stratification in the fog layer that overwhelmed the influence of the air–sea temperature difference. While the synoptic-scale dynamics preconditioned the area for fog formation, the final step of fog appearance in this case was nuanced by stratification–turbulence interactions, local advective processes, and microphysical environment.

In the present article, it is examined the steady bio-convective hybridized micropolar nanofluid flow with the stratification conditions above a vertical exponentially stretching surface. The SWCNT+MWCNT are used in a base fluid of water to formulate the Hybrid nanoparticles in the current article. To examine the mass and heat transfer rate, the activation energy and Cattaneo-Christov heat flux are factored into the equation. The relevant transformations are manipulated to transfer the flow model into the coupled non-linear ODEs. To answer the coupled equations, the Bvp4c Matlab approach is being used. The conclusion of various parameters is examined graphically. The physical numbers observed via graphs, such as friction factor, local Sherwood number and local microorganism number. It is worth noticing that the axial and angular velocity reduces close the boundary and enhances away from the boundary with the escalation of solid volume fraction of SWCNT and MWCNT. Further, as increases the Peclet number, microorganism stratification parameters, and bio-convection Schmidt number, the microorganism sketch declines.

Our study explores the variability of chlorophyll a and phycocyanin as well as the taxonomic and functional structure of phytoplankton in epilimnetic and metalimnetic strata regarding the main environmental features of the water column. The maximum phytoplankton pigment concentrations are located differently depending on the type of thermal stratification and light availability. In general, there were three situations observed during the summer stratification: the euphotic zone did not extend to the thermocline and the highest chlorophyll concentration developed above the thermocline level, at the bottom of the euphotic zone (type I); the euphotic zone reached beyond the thermocline, and the maximum chlorophyll concentration occurred above the thermocline (type II); or the euphotic zone was much greater than the thermocline depth and the peak phytoplankton density was located below the thermocline (type III). In metalimnetic samples, the most dominant cyanobacteria belonged to the Reynolds Functional Groups (RFG) H1, S1, and Lo; their occurrence differed depending on the types of light and thermal regimes. It was assumed that vertical heterogeneity affects the ecological status assessment based on phytoplankton. Calculating the two applied indices (TI index and Q index) based on metalimnetic and epilimnetic data (as opposed to only epilimnetic data) yielded worse ecological status in > 70% of cases.

In this paper, the variation of bubble size and number in the separation process of vibrated fluidized bed as well as the influence of bubble movement on the axial distribution of fine coal in different positions of the bed were studied. The result revealed that the size and number of bubbles is correlated with the fine coal separation effect in the separation process. When the bed is in a uniform and stable fluidized state, the size of bubbles in the separation process was in the range of 1–2.5 cm and the number of bubbles was reduced by nearly 50%, which is helpful to promote the stratification and segregation of fine coal. Thereby, after separation, the ash content of refined coal products of anthracite and 1/3 coking coal was reduced to 12.1% and 23.7% respectively, and the content of refined coal was up to 42.5% and 68.5% respectively, which show that the vibrated fluidized bed has a good separation performance, and can separate efficiently the coal of size −6 + 1 mm.

In this work, we experimentally investigate secondary waves in rotating detonation combustor (RDC) operation. Secondary waves are finite-strength periodic perturbations of the field, which manifest as reacting fronts and/or pressure rise rotating around the annulus superimposed to one or more detonation waves. Secondary waves interact with the detonation wave, affecting the operation of the RDC, as well as the potential of realizing pressure gain. Through analysis of high-speed end-view chemiluminescence imaging in the detonation channel, the characteristics (speed, multiplicity, and strength) of different systems of waves are identified. The analysis indicates that in addition to the main detonation wave, two secondary wave systems are present: (1) a pair of co-rotating waves moving counter to the detonation wave at a speed near the acoustic speed of the products of combustion and (2) a wave moving counter to the detonation wave at a speed near that of the detonation wave. These two types of secondary waves are consistently observed in three canonical injection schemes. We further investigated the impact of the wave pair on the structure of the main detonation wave in one inlet configuration. By constructing conditional phase-averaged distributions of the pressure and OH* emission over the interaction between the detonation and secondary waves, we reconstruct the structure of the detonation wave during the interaction. The results show that there is a nonlinear interaction between the detonation and secondary waves, which results in an augmentation of the pressure rise (increase by as much as 60%) across the detonation wave as well as partial suppression of the heat release as the two waves interact (variation up to an order of magnitude). This nonlinear interaction is supported by differences in the temporal response of the air and fuel streams subject to the propagation of secondary waves, generating fill region stratification leading to the partial suppression of heat release when the secondary wave collides with the main detonation wave.

Large amplitude internal waves in the ocean propagate in a dynamic, highly variable environment with changes in background current, local depth, and stratification. The Dubreil-Jacotin-Long, or DJL, theory of exact internal solitary waves can account for a background shear, doing so at a cost of algebraic complexity and a lack of a mathematical proof of algorithm convergence. Waves in the presence of shear that is strong enough to preclude theoretical calculations have been reported in observations. We report on high resolution simulations of stratified adjustment in the presence of strong shear currents. We find instances of large amplitude solitary-like waves with recirculating cores in parameter regimes for which DJL theory fails, and of wave types that are completely different in shape from classical internal solitary waves. Both are spontaneously generated from general initial conditions. Some of the waves observed are associated with critical layers, but others exhibit a propagation speed that is very near the background current maximum. As such they are not freely propagating solitary waves, and a DJL theory would not apply. We thus provide a partial reconciliation between observations and theory.

In this study, we diagnose the time variability and vertical structure of the high- and low-frequency motions on the Mississippi-Alabama Shelf as observed with a bottom-mounted ADCP (Acoustic Doppler Current Profiler) and CTD (Conductivity-Temperature-Depth). The mooring was deployed about 20 km offshore of Mobile Bay for a period from May 17 to August 23, 2018. At this latitude, the diurnal land and sea breeze has the same frequency as the local inertial frequency. Similar to the wind, the observed high-frequency baroclinic velocities (> 30 cm/s) have a broadband diurnal peak and more energy in the clockwise motions. About 60% of the variance in these motions is due to mode 1, which resembles a two-layer structure with surface and bottom velocities that are 180∘ out of phase. These are all characteristics of wind-driven motions that interact with the coastal wall. The month of June features the best conditions for energetic near-inertial motions: upwelling, consistent sea breeze, and a more continuous instead of a two-layer stratification. This causes near-inertial energy to be also projected on a baroclinic mode 2, featuring a subsurface maximum. This maximum may be attributed to the downward propagation of near-inertial internal wave energy. The observed alongshore low-frequency flows and the up- and downwelling are mostly driven by low-frequency winds. About 83% of the variance in the alongshore low-frequency flows is due to mode 1, which eigenfunction resembles a vertically sheared flow. We find that the amplitude of the near-inertial motions is modulated by the up- and downwelling. During downwelling, the near-inertial baroclinic kinetic energy is greatly reduced because of a reduction in stratification and weaker diurnal winds.

Turbidity from glacial meltwater limits light penetration with potential ecological consequences. Using profiles of temperature, conductivity, and turbidity, we examine the physical processes driving changes in the epilimnetic turbidity of Carpenter Reservoir, a long and narrow, glacier-fed reservoir in southwest British Columbia, Canada. Following the onset of permanent summer stratification, the relatively dense inflows plunged into the hypolimnion, and despite the high glacial load entering the reservoir, the epilimnion cleared due to particle settling. Using a one-dimensional (longitudinal) diffusion equation for a decaying substance to describe the variation in epilimnetic turbidity, we obtain two nondimensional parameters: the epilimnetic inflow parameter, $$\mathcal {I}$$ I , a measure of the turbidity flux into the epilimnion; and the dispersion parameter, $${\mathcal {D}}$$ D , a measure of longitudinal dispersion. In the case of Carpenter Reservoir: $$\mathcal {I}\ll 1$$ I ≪ 1 , indicating that turbidity declines over the summer; and $${\mathcal {D}}\ll 1$$ D ≪ 1 , indicating a strong gradient in turbidity along the epilimnion. Using our theoretical formulation of epilimnetic turbidity variations in conjunction with monthly field surveys, we compute the particle settling velocity ($${\sim}{0.25}\,{\hbox {m}\,\hbox {d}^{-1}}$$ ∼ 0.25 m d - 1 ), the longitudinal dispersion coefficient (50–70 $${\hbox {m}^{2}\,\hbox {s}^{-1}}$$ m 2 s - 1 ), and the flux of turbid water into the epilimnion ($${\sim }1{\%}$$ ∼ 1 % of the total inflow). Our approach is applicable to other reservoirs and can be used to investigate changes in turbidity in response to changes in $$\mathcal {I}$$ I and $${\mathcal {D}}$$ D .

The work presented in this paper aimed at investigating soil stratification and flow movement direction effects on the equivalent normal coefficient of permeability,(keq)n, of a layered soil system...

The 2016 safety Final Rule requires states to have access to annual average daily traffic (AADT) for all public paved roads, including non-Federal aid-system (NFAS) roads. The latter account approximately for 75% of the total roadway mileage in the country making it difficult for agencies to collect traffic data on these roads. Many agencies use stratified sampling procedures to develop default AADT estimates for uncounted segments; however, there is limited guidance and information about how to stratify the network effectively. The goal of this paper is to enhance transportation agencies’ ability to improve existing stratification schemes, design new schemes, and ultimately develop more accurate AADT estimates for NFAS roads. The paper presents the results from five pilot studies that validated and compared the performance of current, updated, and new (traditional and decision-tree-based) schemes using readily available data. According to the results, the median absolute percent error of existing AADT estimates, developed by state agencies, ranged between 71% and 120%. Updating these schemes using recent counts resulted in an AADT accuracy improvement of 25%. The best-performing schemes were developed using DTs that improved the AADT accuracy of existing schemes by 41%. Overall, having more strata and very homogenous strata is better than having fewer strata and more samples within each stratum. The analysis revealed that a key to selecting an effective scheme is to determine a critical point, beyond which creating more strata improves the AADT accuracy marginally but increases the required sample size exponentially.

Deoxygenation has frequently appeared in coastal ecosystems over the past century due to the joint influence of increasing anthropogenically induced nutrient inputs and global warming. The semi-enclosed Bohai Sea is a typical system that is prone to deoxygenation, with regular hypoxia events consistently recorded in recent decades. Based on in-situ observation data collected in large-scale voyage surveys in the Bohai Sea during 2008–2017, the seasonal variability in dissolved oxygen (DO) and its controlling mechanisms were studied. The results indicated that in spring and autumn, the DO distributions exhibited similar spatial patterns in the surface and bottom layers, while in summer, its spatial distribution was characterized by large-scale oxygen-poor zones distributed off the Qinhuangdao Coast and the central southern Bohai Sea in the bottom layer. The controlling mechanisms of the DO distribution varied from season to season. Spring and autumn DO distributions were dominated by the seawater temperature. Under the combined effects of stratification and decomposition, the summer bottom DO exhibited dual-core distribution. On the one hand, stratification could greatly impede vertical mixing, resulting in reduced bottom DO replenishment. On the other hand, the increased bottom organic matter intensified the decomposition processes, inducing massive DO consumption and elevated dissolved inorganic nitrogen concentrations. In addition, the stronger stratification might be the reason for the more severe deoxygenation in the southern oxygen-poor zones in summer. Our study provides guidance for an in-depth understanding of the DO seasonality in the Bohai Sea and the mechanisms that modulate it and for the improvement of hypoxia forecasts in ocean models.

The heterogeneities of the gravity field (HGF) deform the fields of air pressure, density, and temperature and affect the temperature regime of the boundary layer of the atmosphere, as well as the heat exchange between the air and the underlying surface. This work considers a stationary analytical model intended for estimation of the amplitudes of these effects, which resulted in analytical equations for profiles of temperature disturbances and amplitudes of deviations of the vertical heat fluxes on the surfaces. In addition to the amplitudes of the HGF, the latter most strongly depend on the ambient background stratification. In highly anomalous regions, the amplitudes of deviations of heat fluxes can reach and exceed 1 W/m2, which gives grounds to take into account the HGF in climate calculations and numerical models of the atmosphere.

The empirical relationships between the friction speed (dynamic speed) and the crosswind speed are considered for different conditions (time of the day, season, stratification type, observation site, and measurement altitude). Initial experimental data used to derive these relationships were acquired by ultrasonic weather stations operating in the surface air layer at different observation sites.

We investigate by theoretical means the motion of a gravity current (GC) released from a lock into an ambient fluid in a horizontal channel of non-rectangular cross-section area (CSA) like triangle, trapezoid or semicircle. The lock contains an internal stratification, in particular a layer of density ρ L overlain by a layer of density ρ U , where ρ o ρ U ρ L and ρ o is the density of the ambient fluid. Assuming a Boussinesq and large Reynolds flow, we develop a new self-contained model for the prediction of the motion of the GC, in particular the position and speed of the nose x N ( t ) and u N ( t ) , where t is the time from release. Upon an appropriate scaling the system of equations and boundary conditions is reduced to a form amenable to analysis and solution by the methods employed for the non-stratified flow. The solution reveals an initial slumping with constant u N , and eventually the transition at x V to the viscous regime. A self similar phase of the form x N ∼ t β can develop only for CSA of power-law shape, in which case the constant β depends on the shape but not on the stratification. The stability is also considered, and we show that the flow is stable with few exception. Unfortunately, experimental data for comparisons are not available, and we hope that the sharp present results will motivate the performance of needed experimental tests.

The conditions for the onset of instability of stratified heavy geomasses are analytically investigated in the work. The geomaterial forming a geomass is supposed to be elastic and to possess both bulk and shear stiffnesses. The unperturbed equilibrium state of the geomass is isostatic, i.e., characterized by hydrostatic stress field. The depth stratification of density and elastic properties of geomaterial is considered as continuous. The characteristics of stratifications of elastic and density parameters, that surely lead to the onset of instability, are obtained. The obtained sufficient conditions for instability are compared with obtained earlier by the authors the sufficient conditions for stability. Possible geophysical applications of the results are considered.

This paper presents the measured active and passive fluxes of carbon (C), nitrogen (N), and phosphorus (P) and their response to seasonal and event-driven oceanographic changes in the northern South China Sea (NSCS). The total vertical flux of carbon (TFC) is defined as the sum of active and passive fluxes of biogenic carbon in the surface layer, which may be considered as the central part of marine carbon cycle. These active and passive fluxes of N and P were also considered to understand stoichiometric flux patterns and the roles of nutrients involved in the TFC. The magnitudes of total C, N, and P fluxes were, respectively, estimated to be 71.9–347 (mean ± SD, 163 ± 70) mgCm-2d-1, 13.0–30.5 (21.2.± 4.9) mgNm-2d-1, and 1.02–2.97 (1.94 ± 0.44) mgPm-2d-1, which were higher than most previously reported vertical fluxes in open oceans, likely because a quarter of the fluxes was contributed from active fluxes that were unaccounted for in vertical fluxes previously. Moreover, the passive fluxes dominated the total vertical fluxes and were estimated to be 65.3–255 (125 ± 64.9) mgCm-2d-1 (77 ± 52 % of total C flux), 11.9–23.2 (17.6 ± 4.2) mgNm-2d-1 (83 ± 28 % of total N flux), and 0.89–1.98 (1.44 ± 0.33) mgPm-2d-1 (74 ± 24 % of total P flux). Vertical fluxes of dissolved organic C, N, and P were small (< 5 %) relative to passive fluxes. The contrasting patterns of active and passive fluxes found between summer and winter could mainly be attributed to surface warming and stratification in summer and cooling and wind-induced turbulence for pumping nutrients into the euphotic zone in winter. In addition to seasonal variations, the impact of anticyclonic eddies and internal-wave events on enhancing active and passive fluxes was apparent in the NSCS. Both active and passive fluxes were likely driven by nutrient availability within the euphotic zone, which was ultimately controlled by the changes in internal and external forcings. The nutrient availability also determined the inventory of chlorophyll a and new production, thereby allowing the estimates of active and passive fluxes for unmeasured events. To a first approximation, the South China Sea (SCS) may effectively transfer 0.208 ± 0.089 Gt C yr−1 into the ocean's interior, accounting for approximately 1.89 ± 0.81 % of the global C flux. The internal forcing and climatic conditions are likely critical factors in determining the seasonal and event-driven variability of total vertical fluxes in the NSCS.

An empirical model of the saltating aleurite and sand particle size distribution has been developed based on the measurements of the differential number concentrations in the size range from 30 to 330 μm using a size distribution approximation of the sum of two lognormal distributions. Approximations of the vertical profiles of distribution parameters have been derived for the layer from 0 to 15 cm. Vertical profiles of the modal size of the coarse particles in the saltation layer from 3 to 15 cm and in the surface air layer from 0.125 to 16 m are compared with measurements in the Aral region.

The present work focuses on the study of mixed convection of a purely viscous shear-thinning fluid in a horizontal annular eccentric duct. The inner and outer cylinders are heated with constant and uniform heat flux densities. The objective of this work is to study the effect of the variation of eccentricity, rheological behavior of the fluid as well as the thermodependency of the rheological parameters on the reorganization of the flow and thermal stratification caused by the buoyancy forces. At the entrance of the heating zone, the dynamic regime is assumed to be established and the temperature profile uniform. The conservation equations are solved numerically using a finite difference method with implicit schemes. A secondary azimuthal flow, induced by natural convection, develops downstream of the inlet section. This flow creates a stratification of the thermal field on a given section of the duct, which intensifies downstream from the entrance. On the other hand, the decrease in consistency with increasing temperature near the heated walls produces a centrifugal radial flow towards the walls. The presence of an eccentricity induces in turn a significant effect on the main dynamic field and the stratification of the thermal field. Two cases of upward and downward eccentricity are treated. These show that an upward shift increases the stratification of the thermal field, while the stratification begins to weaken from a certain amount of eccentricity in the case of downward shift. This represents an important result in terms of possible industrial applications. We may indeed conclude that an appropriate choice of downward eccentricity can reduce the thermal stratification, observed experimentally in the case of a concentric heated annular duct [1], when this stratification is undesirable. The choice of this eccentricity depends on rheological and thermal properties of the fluid.

Measurements of atmospheric turbulence at a site in Ferryland (Newfoundland) during the C-FOG (Coastal-Fog) field campaign in September–October 2018 are used to study meteorological parameters, turbulence statistics, internal boundary layers, and scaling laws for turbulent mixing in the coastal zone. We observe stable/unstable shallow internal boundary layers with a region of unstable/stable stratification above with onshore flow from a relatively warm/cold sea onto the cold/heated land during the night/day. This study compares surface fluxes and other turbulence statistics as well as different scaling laws with and without fog. While both complexity of the coastal landforms and foggy conditions nominally violate assumptions underlying Monin–Obukhov similarity theory (MOST), our observations show that the non-dimensional standard deviations of the velocity components and the dissipation rate of turbulence kinetic energy obey MOST reasonably well for all measurement levels, stability conditions, and wind directions for both fog and no fog cases. However, the data scatter for the normalized dissipation rate is somewhat greater compared with the normalized standard deviations of the wind components. The bias and relatively larger scatter of normalized standard deviations for scalars in near-neutral conditions is likely associated with the underlying inhomogeneous coastal surface. According to the C-FOG data, during a fog event the moisture flux data become irregular and the latent heat flux is often negative (downward). Our observations also demonstrate poor agreement between normalized standard deviations of specific humidity with MOST for foggy conditions; its statistical dependence on the MOST stability parameter is weak at best in fog.

The Kitikmeot Sea is a semi-enclosed, east–west waterway in the southern Canadian Arctic Archipelago (CAA). In the present work, the ice conditions, stratification, and circulation of the Kitikmeot...

We conducted hydrographic observations throughout the year to investigate seasonal variations of the hypoxic water mass distribution in the Upper Gulf of Thailand (UGoT). Hypoxic water masses were observed from June to November, with half of the UGoT occupied by hypoxic water in September. A hypoxic water mass appeared in the northeastern part of the UGoT in June and August, and moved westward over time. Low-salinity surface water moved from east to west as the rotational direction of surface circulation shifted with the reversal of monsoon winds. Westward movement of low-salinity water causes strong stratification in the northwestern part of the UGoT, leading to severe hypoxia. Numerical experiments showed high dissolved oxygen consumption rates around and offshore of river mouths, where hypoxic water is generated. This finding suggests that hypoxic water masses are transported to the south by physical processes. We examined how flooding affects hypoxic water mass formation. The volume of hypoxia in a flood year was approximately 2.5 times greater than in a normal year. In addition, hypoxia occurred in the dry season and extensive hypoxia was observed in the year after flooding. These results suggest that the hypoxic water mass persists for a long time after flooding.

The under-consideration article discloses the features of nonlinear mixed convective boundary layer flow of radiative Casson fluid along non-uniform heat source or sink. The generalized Fourier’s and Fick’s laws and thermophoretic effect are taken to analyze the transportation of heat and mass. The stratification and suction/injection effect are also implemented on the boundary of the sheet. The flow modeled equations are converted into system of coupled nonlinear ODEs by adopting similarity variables. These coupled equations are numerically computed with built-in Bvp4c technique. The developing parameters are described graphically via velocity profile, temperature, and concentration distribution. It is worth revealing that the higher values of the Casson fluid parameter and magnetic field parameter retarded the fluid velocity. It is also noticed that strong temperature is achieved for the higher estimation of non-uniform heat source/sink parameter. Further, enhancement is occurred in the shear stresses, by the enlargement of mixed convection and buoyancy ratio parameter.

Salinity-driven density stratification of the upper Arctic Ocean isolates sea-ice cover and cold, nutrient-poor surface waters from underlying warmer, nutrient-rich waters. Recently, stratification has strengthened in the western Arctic but has weakened in the eastern Arctic; it is unknown if these trends will continue. Here we present foraminifera-bound nitrogen isotopes from Arctic Ocean sediments since 35,000 years ago to reconstruct past changes in nutrient sources and the degree of nutrient consumption in surface waters, the latter reflecting stratification. During the last ice age and early deglaciation, the Arctic was dominated by Atlantic-sourced nitrate and incomplete nitrate consumption, indicating weaker stratification. Starting at 11,000 years ago in the western Arctic, there is a clear isotopic signal of Pacific-sourced nitrate and complete nitrate consumption associated with the flooding of the Bering Strait. These changes reveal that the strong stratification of the western Arctic relies on low-salinity inflow through the Bering Strait. In the central Arctic, nitrate consumption was complete during the early Holocene, then declined after 5,000 years ago as summer insolation decreased. This sequence suggests that precipitation and riverine freshwater fluxes control the stratification of the central Arctic Ocean. Based on these findings, ongoing warming will cause strong stratification to expand into the central Arctic, slowing the nutrient supply to surface waters and thus limiting future phytoplankton productivity., Nature Geoscience, 14 (9), ISSN:1752-0908, ISSN:1752-0894

As a serious consequence of ocean warming and increased stratification, a rapid decrease in dissolved oxygen (DO) content of the world's oceans has attracted more and more attention recently. In open oceans, the decline of DO is characterized by the expansion of oxygen minimum zones (OMZs) in the ocean interior. Vast OMZs exist within the mesopelagic zones of the Tropical Western Pacific (TWP), but have gained very little attention. In this study, we focus on characteristics of OMZs in three typical seamounts areas (named Y3, M2, and Kocebu, respectively) of the TWP. Based on distributions of DO, the OMZs of the three seamounts areas are very different in scope, thickness, and the minimum oxygen content. The significantly different characteristics of OMZs at the seamounts are mainly because they are located in regions affected by different ventilation and consumption characteristic. To quantitatively describe the intensity of OMZs, a parameter, IOMZ, is firstly proposed. According to this quantitative parameter, the intensity order of OMZs for the three seamounts areas is Kocebu>M2>Y3. Potential biogeochemical effects of OMZs in the three seamounts areas are discussed using IOMZ. With higher IOMZ, the degradation of particulate organic carbon (POC) tends to be lower. Yet because of the limited data, their relationship still need more research to prove. However, if this relationship holds in global oceans, the presence of seamounts would-under climate warming with expanding OMZs-promote vertical transport of POC resulting in an enhanced biological pump. Our study provides a new way to quantitatively study the impact of OMZs on the efficiency of biological pump.

Recent studies have demonstrated the ability of seismic oceanography to reveal finescale vertical structures of water column in the oceans based on multichannel seismic (MCS) reflection data. Such information can clarify the dynamic processes of mixing, exchange, and translation of water mass and energy. In this study, we present four MCS lines and satellite data to show high-resolution seismic images of shallow waters over the Shatsky Rise in the Northwest Pacific Ocean, where the Kuroshio Extension passes and bifurcates. One of our MCS transects crossed the center of an anticyclonic warm eddy on August 28, 2010, confirmed by satellite data such as sea level anomaly (SLA), geostrophic current anomaly (GCA), and sea surface temperature anomaly (SSTa). The seismic image showed that the eddy vertical structure featured a bowl-like shape and onion-like internal layering. The slightly tilted ( 2°–3°) at the boundaries between water masses with differing properties. In addition, the discrepancies in SLA, GCA, and SSTa between water masses resulted in different seismic reflectivities. The water masses with high SLA, anticyclonic GCA and positive SSTa featured high-amplitude, continuous, clear-layered, and non-linear reflections, whereas those with low SLA, cyclonic GCA, and negative SSTa were associated with weak, fragmented, less stratification, and more linear reflectors.

This study investigates the interannual modes of the tropical Pacific using salinity from observations, ocean reanalysis output and CMIP6 products. Here we propose two indices of sea surface salinity (SSS), a monopole mode and a dipole mode, to identify the El Niño—South Oscillation (ENSO) and its diversity, respectively. The monopole mode is primarily controlled by atmospheric forcing, namely, the enhanced precipitation that induces negative SSS anomalies across nearly the entire tropical Pacific. The dipole mode is mainly forced by oceanic dynamics, with zonal current transporting fresh water from the western fresh pool into the western-central and salty water from the subtropics into the eastern tropical Pacific. Under a global warming condition, an increase in the monopole and dipole mode variance indicates an increase in both the central and eastern Pacific El Niño variability. The increase in central Pacific El Niño variability is largely due to enhanced vertical stratification during global warming in the upper layer, with intensified zonal advection. An eastern Pacific El Niño-like warming pattern contributes to the increase in eastern Pacific El Niño, with enhanced precipitation over the central-eastern tropical Pacific.

Solar hot water storage tanks with mantle heat exchangers are widely used in balcony wall-mounted solar heating system in China. The thermal behaviour of a novelty mantle solar water tank with vertical inlet and outlet water tubes has been investigated both experimentally and numerically. Dimensionless parameter can well characterize the stratification of water and thermocline dynamics in the water tank. In the discharging mode, as the dimensionless time increases, the thermocline thickness gradually increases, and the mixing in the water tank intensifies. The dimensionless exergy gradually decreases with the increase of the dimensionless time.

This study is aimed at proposing an analytical approach of modeling groundwater flows in an unconfined aquifer with multiple vertical soil layers. First, a mathematical problem was built describing groundwater flow in an unconfined aquifer of N-layered vertical soils with an inclined base. Then, an analytical solution to the problem was proposed after a solution of separable form was sought and the eigenfunction expansion technique was used. This solution can address any vertically multilayered soil stratification with temporally varied rainfall recharge. Finally, the presented solution was verified by employing previous analytical solutions and numerical results modeled using Modflow software. Through this study, the presented analytical mathematical model, instead of a numerical mathematical model, of groundwater in a multilayered aquifer is an effective tool for estimating the groundwater level.

Typical injection schemes of rotating detonation combustors inject fuel locally into the combustion channel, creating stratified fuel-rich and fuel-lean mixing regions. In this study, premixed hydrogen and air rotating detonations are explored in a rotating detonation combustor through premixing part of the fuel into the oxidizer flow. The objective is to investigate the effect of premixing on the operation of the combustor. Three premixing schemes are examined where the detonation wave speeds are analyzed. The results show that in premixing, the fuel-lean regions became more favorable for continuous detonation propagation when premixed with the bypass fuel, resulting in higher detonation wave speeds. This phenomenon is shown to be independent of the global fuel-air equivalence ratio and the amount of fuel premixed into the oxidizer. As such, combustor performance and the operational regime could be improved with lean hydrogen premixing amounts in the main flow oxidizer.

Three sites with different surface roughness were selected to explore the turbulent/synoptic separation and self-similar wall-attached coherent structures in the atmospheric surface layer. At each site, the facility permits synchronous multi-point measurements of three-dimensional wind velocity and temperature at different heights, as well as synchronous measurements via the global positioning system among the three sites. A filter based on the linear coherent spectrum between two sites (separated by 500 m) is adopted to separate turbulent and synoptic signals. After the separation, the two-point correlations of the filtered turbulent streamwise velocity component reveal that increasing surface roughness leads to less coherence in both the wall-normal and streamwise directions. The present results with unstable stratification and different surface roughness also demonstrate good agreement with the self-similar range of the wall-attached turbulence reported in Baars et al. (J Fluid Mech 823:R2, 2017). The aspect ratio of coherent structures (defined as the ratio of streamwise wavelength to the wall-normal offset) for the streamwise and spanwise velocity components and temperature increases with increasing surface roughness.

Drag reduction (DR) by additives in single- and two-phase fluid transport has enormous engineering and economic benefits. An ample amount of work has been done with regards to understanding the mechanism of DR for developed flows in straight conduits. There is however a limited understanding of the effects of drag-reducing agents (DRAs) on under-developed flows in bends and more so for liquid–liquid two-phase flows in and around the bend. This study therefore investigates the influence of U-bend on polymer drag reduction and flow patterns for oil–water two-phase flows. The ranges for oil and water superficial velocities tested were $$0.04\le {U}_{so}\le 0.950 {m}/{s}$$ and $$0.13\le {U}_{sw}\le 1.10 {m}/{s}$$ , respectively. The test section consists of $$19-{mm}$$ ID clear polyvinyl chloride straight tubes and return bend ( $$R=100 {mm}$$ ). Measurements were carried out for developed flow upstream of the bend, at the U-bend and at two under-developed flow sub-sections downstream of the bend. The addition of polymer imposed partial or complete flow stratification in all test sections. In all test sections, drag reduction increased with flow rate of water and reduced with oil fraction in the region of strong turbulence. For high mixture velocities, DR upstream of the bend was highest while the least was recorded at the bend. The highest DR upstream of the bend, in the U-bend and at the two downstream under-developed flow sub-sections were 40%, 34%, 28%, and 29%, respectively.