Three-dimensional Hydrodynamic Model Research Articles

A real-time simulation model of water quality with the impact of internal pollution for water source reservoir.

The water source reservoirs are the important urban water source in northern China. Although external pollution has been greatly improved, the internal pollutants in reservoirs continue to accumulate with the complex deposition and release processes, resulting in potential risks to water supply safety. To address the aforementioned issue, this paper proposed a simulation model of water quality named ECOlab EU1-WSR to simulate the spatio-temporal changes of water quality under the influence of internal pollution for the water source reservoirs. Based on the analysis of the water quality characteristics and the distribution of benthic vegetation in the reservoir, a three-dimensional hydrodynamic model was established based on MIKE3, the corresponding parameters and the related state variables were set, the ECOlab EU1-WSR model was established by secondly developing the original ECOlab EU1 template, and the real-time dynamic outputs of pollutant content in sediment were added to link the water quality index with sediment nutrition index for better revealing the impact of the internal pollution on the water quality. The performance of the model was evaluated by the case application on the water quality simulation of Daye reservoir and the optimization of the connection project between Daye reservoir and Xueye reservoir in Shandong Province China. The results showed that the model can accurately and simultaneously simulate the pollution in water and sediment by the comparative verification of hydrodynamics, water temperature, and water quality. Moreover, the model can effectively reflect the influence of the accumulation, deposition, and release of internal pollution on water quality by analyzing the correlation between the content of various pollution in water body and those in sediment, such as the total nitrogen and total phosphorus in the water body at the bottom of the water intake, were negatively correlated with the total nitrogen and total phosphorus in the sediments with correlation coefficients of 0.538 and 0.917, respectively. In addition, the optimal water inlet position and water flow rate of the connection project can be optimized and determined by using the model to effectively control water quality. The established model will be a useful tool for the design and management of a reservoir, the interconnection projects, and other water bodies by adaptively recoded.

Numerical Study on the Formation Mechanism of Plume Bulge in the Pearl River Estuary under the Influence of River Discharge

Previous studies have investigated the characteristics and influencing factors of plume bulge in the Pearl River Estuary (PRE) using observations and numerical simulations. However, the understanding of how river discharge affects plume bulge is not consistent, and the response mechanism of plume bulge to changes in river discharge has not been revealed in detail. In this study, a three-dimensional hydrodynamic Finite-Volume Coastal Ocean Model (FVCOM) is constructed, and five experiments were set to characterize the horizontal and vertical distribution of the plume bulge outside the PRE under different river discharge conditions during spring tide. The physical mechanisms of plume bulge generation and its response mechanisms to river discharge were discussed through standardized analysis and momentum diagnostic analysis. The results indicate that the plume bulge is sensitive to changes in river discharge. When the river discharge is relatively low (e.g., less than 11,720 m3/s observed in the dry season), the bulge cannot be formed. Conversely, when the river discharge is relatively high (e.g., exceeding 23,440 m3/s observed in flood season), the bulge is more significant. The plume bulge is formed by the anticyclonic flow resulting from the action of the Coriolis force on the strongly mixed river plume. The bulge remains stable under the combined effects of barotropic force, baroclinic gradient force, and Coriolis force. The reduction of river discharge weakens the mixing of freshwater and seawater, resulting in the reduction of both the volume and momentum of the river plume, and the balance between advective diffusion and Coriolis forces are altered, resulting in the plume, which is originally flushed out from the Lantau Channel, not being able to maintain the anticyclonic structure and instead floating out along the coast of the western side of the PRE, with the disappearance of the plume bulge. Due to the significant influence of plume bulges on the physical and biogeochemical interactions between estuaries and terrestrial environments, studying the physical mechanisms behind the formation of plume bulges is crucial.

Effects of low salinity water inflow on eelgrass and cultured bivalves in subarctic lagoons: Analysis using hydrodynamic model

Brackish water areas are affected by river inflows and changes in tidal level, resulting in large fluctuations in salinity. Prolonged exposure to low salinity water can have adverse effects on the growth of marine plants and animals. Characteristics of lagoons such as catchment area, bottom topography, and seawater exchange rate with the open ocean vary widely and the horizontal and vertical gradients of salinity and spatio-temporal variability are also diverse. In this study, we evaluated the impact of low salinity water inflows due to heavy rainfall on seagrass and cultured bivalves in two lagoons (Akkeshi-ko Lagoon and Notoro-ko Lagoon), which are located in the subarctic region of Japan and have contrasting geomorphological characteristics. Continuous observations of the physical environment were conducted by installing measurement equipment near the seafloor, and we ran ten year replicate calculations using a three-dimensional high-resolution hydrodynamic model. Simulation results were used to assess the risk of low salinity associated with heavy rainfall to eelgrass and bivalves (oyster, scallop, and clam). The model analysis showed that the magnitude and frequency of exposure to low salinity water varied greatly between and within lagoons. Akkeshi-ko Lagoon, which has a relatively large catchment area and shallow basin, was sometimes exposed to extremely low salinities, which could lead to the mortality of oysters during heavy rains once every few years. In contrast, salinity decline in Notoro-ko Lagoon is negligible even in years with heavy rainfall due to the high volume of water within the lagoon and small catchment area. With projections that the intensity of heavy rainfall will increase due to climate change, this study was able to evaluate the impact of changes in river flow on coastal ecosystems and aquaculture, and we discussed adaptation measures that may be necessary in the future.

Long-term developments in seasonal hypoxia and response to climate change: A three-decade modeling study in the Ariake Sea, Japan

Hypoxia in the Ariake Sea, Japan, is steadily increasing in both duration and spatial coverage. Hypoxia, defined as dissolved oxygen (DO) below 3 mg/L, is strongly associated with the amplified frequency of extreme rainfall events driven by climate change, which poses a mounting threat to marine ecosystems on a global scale. In this study, we employed a general three-dimensional (3-D) hydrodynamic coastal model and a phytoplankton-based ecosystem model to identify the potential cause of seasonal hypoxic events over three decades. The results indicated a substantial decrease in bottom DO levels from 1992 to 2021, with the rate of increase in hypoxic area being 8 km2/yr (95 % CI: −0.38, 16.2) and the anoxic area increasing from almost non-existent to 100 km2. Notably, among various environmental drivers, increased river discharge was identified as a pivotal factor in the occurrence of hypoxia. Large-scale river discharge events can potentially increase water stratification, leading to the formation of hypoxia. River discharge volume and the duration of bottom hypoxia in the Ariake Sea were correlated. The duration of hypoxia was strongly associated with river discharge magnitude, with correlation coefficients ranging from 0.56 to 0.82 across six observational stations. Furthermore, analysis of varied simulated environmental factors over multiple years revealed diverse responses to climate change, indicating that the Ariake Sea is prone to experiencing a decline in its physical and water quality conditions.

Influence of glacial influx on the hydrodynamics of Admiralty Bay, Antarctica - study based on combined hydrographic measurements and numerical modeling

This study investigates the impact of glacial water discharges on the hydrodynamics of a glacial bay in Antarctica, comparing it to well-studied northern hemisphere fjords. The research was carried out in Admiralty Bay (AB) in the South Shetland Islands, a wide bay adjacent to twenty marine-terminating glaciers. From December 2018 until February 2023, AB water properties were measured on 136 days. This dataset showed that a maximally two-layered stratification occurs in AB and that glacial water is always the most buoyant water mass. Using the Delft3D Flow, a three-dimensional hydrodynamical model of AB was developed. During tests, the vertical position and initial velocity of glacial discharges have been shown to be insignificant for the overall bay circulation. Fourteen model scenarios have been calculated with an increasing glacial influx added. The AB general circulation pattern consists of two cyclonic cells. Even in scenarios with significant glacial input, water level shifts and circulation are predominantly controlled by the ocean. Glacial freshwater is carried out of AB along its eastern boundary in a surface layer. Freshwater thickness in this outflow current is maximally 0.27-0.35 m. Within the inner AB inlets, significant glacial influx produces buoyancy-driven vertical circulation. Using an approach combining hydrographic and modeling data, a four-year timeseries of glacial influx volumes into AB has been produced. On average, glacial influx in summer is 10 times greater than in spring and winter and 3 times higher than in autumn. The annual glacial influx into AB was estimated at 0.434-0.632 Gt. Overall, the study demonstrated the unique characteristics of the topography and forcings that influence the hydrodynamics of an Antarctic glacial bay.

Modelling Turbulent Flows near Coastal Structures Using Various Turbulence Models

Introduction. The reduction in beach width due to erosion is a significant issue that can either be mitigated or exacerbated by coastal protection structures. Modelling breaking waves near the coast and around coastal structures can be used to determine their impact on the dynamics of the coastal zone. The objective of this study is to model and analyze the dynamics of turbulent structures around a single breakwater, obtained using two turbulence modelling schemes: RANS and LES.Materials and Methods. Turbulence induced by breaking waves was investigated. The modelling was based on bathymetric measurements conducted along the Azov Sea coast and a three-dimensional wave hydrodynamics model supplemented with various turbulence calculation configurations.Results. Modelling results of wave processes generating turbulent flows in the presence of coastal protection structures using different turbulence models were obtained. Results obtained based on Reynolds-averaged Navier-Stokes (RANS) equations are compared with the results of Large Eddy Simulation (LES) approach with Smagorinsky dynamic subgrid-scale model (DSM).Discussion and Conclusions. The results showed that wave heights simulated by LES were higher than those simulated by RANS in the front and leeward regions of the coastal protection structure and were lower in its upper part. Thus, according to LES, a greater amount of wave energy was preserved after passing over the breakwater. Velocity vectors of the water medium showed the formation of a vortex when LES was used, whereas no evidence of such turbulent vortices was detected in the case of RANS, confirming the better performance of LES for turbulence modelling in the coastal zone. According to the presented results, LES is the preferred tool for generating turbulence under incoming wave conditions in engineering practices.

Modeling Environmental Impacts of Intensive Shrimp Aquaculture: A Three-Dimensional Hydrodynamic Ecosystem Approach

Already a multibillion-dollar global industry, shrimp aquaculture, is growing all the time. The intensive method, which is the most common method in shrimp aquaculture, remains commercially challenged due to the expenditures associated with environmental pollution abatement. Although the comprehensive understanding of this intricate aquaculture environment has been advanced using mathematical modeling, recent attempts to improve the model’s structure have not yielded enough results. This work upgraded the previous method to a three-dimensional hydrodynamic ecosystem model with the effects of shrimps being replaced by approximation equations for the environmental assessment of a shrimp aquaculture pond in Kyushu District, Japan. Our approach was successful, as demonstrated by the high consistency of the simulation results when compared to observation data and the previous results. Additionally, we first revealed the impacts of stratification and confirmed the notable daily variation in the water quality. Our case study offers significant practical information on the characteristics of intensive shrimp aquaculture, implications for long-term sustainable operations, and future research priorities on local-scale ecosystem modeling.

Dynamics of currents in the Qiongzhou strait during spring and summer based on a numerical simulation

A high-precision three-dimensional hydrodynamic model based on the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM) was constructed to investigate the characteristics of residual currents in the Qiongzhou Strait during spring and summer. Results reveal an overall westward transport in the strait during spring and summer. However, the results also support the potential occurrence of transient eastward Eulerian residual currents, which should be evident predominantly at the surface in the central and eastern sections of the strait and mainly characterised by subtidal oscillations. The direction and intensity of these residual currents indicate a pronounced influence of pressure gradient forces on both sides of the strait. The eastward flow observed in spring may represent a compensatory mechanism resulting from the relaxation period of long-term easterly winds, whereas the generation of eastward residual currents in summer is influenced by wind stress curl differences in both the western and eastern areas of the strait. The direct impact of the summer monsoon on the flow field in the strait is relatively weak. Additionally, the direction and intensity of the residual currents in the strait exhibit potential interannual variations that are directly associated with interannual wind variations. This study provides valuable insights in relation to the ongoing discourse on the dynamics of residual currents in the Qiongzhou Strait.

Validation of tidal turbine wake simulations using an open regional-scale 3D model against 1MW machine and site measurements

Full-scale tidal turbines deployed in tidal channels are subjected to complex flow due to the effects of local bathymetry and coastline shape which modify the flow directionality, shear, twist and speed of the underlying tidally forced flow. In response to these effects, the wake of an operational tidal turbine will vary spatially and temporally. In order to predict wake form, which is a key step for scaling up tidal energy as developments move from single devices to arrays, we have developed and demonstrated an open source turbine-embedded regional three-dimensional (3D) hydrodynamic model for power and wake prediction. Simulation outputs have been validated against in-situ measurements acquired via ADCPs positioned downstream of and adjacent to the rotor-plane of an operating tidal turbine. Model predictive performance is parameterised by the relative difference between modelled and measured power-weighted rotor averaged velocity using speed binning and temporal-averaging. In the absence of the turbine representation, the difference between model and measurement for ebb and flood was found to be 0.81% and 1.04% respectively at the flow speed of 2.5 m/s. With the turbine represented as an actuator disc in the model, the averaged error of the velocity profiles in the wake is 4.4% and 5.2% at ADCP locations that are 3.7D and 6.2D downstream of the rotor plane during ebb. The model has been designed for use on moderately-priced workstations and the promising results, in terms of capturing key 3D flow features and predictions of wake velocity deficits, is a starting point for further development and may provide baseline data for alternative (e.g., higher fidelity, slower performance, or lower fidelity including 2D models with much faster performance).

The Impact of Effective Matter Mixing Based on Three-dimensional Hydrodynamical Models on the Molecule Formation in the Ejecta of SN 1987A

To investigate the impact of matter mixing on the formation of molecules in the ejecta of SN 1987A, time-dependent rate equations for chemical reactions are solved for one-zone and one-dimensional (1D) ejecta models of SN 1987A. The latter models are based on the 1D profiles obtained by angle-averaging of the three-dimensional (3D) hydrodynamical models, which effectively reflect the 3D matter mixing; the impact is demonstrated, for the first time, based on 3D hydrodynamical models. The distributions of initial seed atoms and radioactive 56Ni influenced by the mixing could affect the formation of molecules. By comparing the calculations for spherical cases and for several specified directions in the bipolar-like explosions in the 3D hydrodynamical models, the impact is discussed. The decay of 56Ni, practically 56Co at later phases, could heat the gas and delay the molecule formation. Additionally, Compton electrons produced by the decay could ionize atoms and molecules and could destroy molecules. Several chemical reactions involved with ions such as H+ and He+ could also destroy molecules. The mixing of 56Ni plays a nonnegligible role in both the formation and destruction of molecules through the processes above. The destructive processes of carbon monoxide and silicon monoxide due to the decay of 56Ni generally reduce the amounts. However, if the molecule formation is sufficiently delayed under a certain condition, the decay of 56Ni could locally increase the amounts through a sequence of reactions.

3D non-LTE modeling of the stellar center-to-limb variation for transmission spectroscopy studies

Context. Transmission spectroscopy is one of the most powerful techniques used to characterize transiting exoplanets, since it allows for the abundance of the atomic and molecular species in the planetary atmosphere to be measured. However, stellar lines may bias the determination of such abundances if their center-to-limb variations (CLVs) are not properly accounted for. Aims. This paper aims to show that three-dimensional (3D) radiation hydrodynamic models and the assumption of non-local ther-modynamic equilibrium (non-LTE) line formation are required for an accurate modeling of the stellar CLV of the Na I D1 and K I resonance lines on transmission spectra. Methods. We modeled the CLV of the Na I D1 and K I resonance lines in the Sun with 3D non-LTE radiative transfer. The synthetic spectra were compared to solar observations with high spatial and spectral resolution, including new data collected with the CRISP instrument at the Swedish 1-m Solar Telescope between µ = 0.1 and µ = 1.0. Results. Our 3D non-LTE modeling of the Na I D1 resonance line at 5896 Å and the K I 7699 Å resonance line in the Sun is in good agreement with the observed CLV in the solar spectrum. Moreover, the simulated CLV curve for a Jupiter-Sun system inferred with a 3D non-LTE analysis shows significant differences from the one obtained from a 1D atmosphere. The latter does indeed tend to overestimate the amplitude of the transmission curve by a factor that is on the same order of magnitude as a planetary absorption depth (i.e., up to 0.2%). Conclusions. This work highlights the fact that to correctly characterize exoplanetary atmospheres, 3D non-LTE synthetic spectra ought to be used to estimate the stellar CLV effect in transmission spectra of solar-like planet hosts. Moreover, since different spectral lines show different CLV curves for the same geometry of the planet-star system, it is fundamental to model the CLV individually for each line of interest. The work will be extended to other lines and FGK-type stars, allowing for synthetic high-resolution spectra to mitigate the stellar contamination of low-resolution planetary spectra, for example, those drawn from JWST.

Processes of stratification and vertical turbulent mixing in a choked lagoon system

This work concentrates on the processes of stratification and turbulent mixing in a choked shallow lagoon, Xiaohai Lagoon, by using a three-dimensional hydrodynamic model. The model results were processed to derive buoyancy frequency, shear production, gradient Richardson number, and buoyancy flux during the tidal cycles. The parameters regarding stratification and turbulent mixing exhibited significant heterogeneity within the lagoon. Shear production primarily occurred in the downstream region with complex shoreline and bed morphology, whereas stratification was predominantly developed in the flat upstream region by tidal strain and baroclinic strain, especially during the ebb tide. The salinity mixing indicated by buoyancy flux was thus mainly confined during the ebbs in the downstream region and the middle-lower layer of the upstream region. In addition, the distribution of the gradient Richardson number indicated dominances of shear instability and buoyancy effects in the downstream and upstream regions, respectively. By simulating various combinations of river discharges and offshore tidal ranges, we examined the variations of stratification and turbulent mixing within the lagoon's parameter space. The results revealed the influence of the interaction between tidal and runoff forces through a modulation of the salinity interface's moving range. Further investigation of the buoyancy balance underlying the variation in stratification revealed the dominance of straining and mixing, while advection played a secondary role. Straining dominance appeared at locations with sufficient streamwise density gradients in the upstream region during the ebb. The contribution of advection was essential, as straining and mixing largely counteracted each other's effects through their persistent competition. A conceptual model for the stratification and mixing patterns in choked lagoons during the tidal cycle was then proposed. This conceptual model clarifies the process of the interaction between stratification and turbulent mixing in the distinctive hydrological and geomorphic environments of choked lagoons and could serve as a conference for investigating other lagoon systems in the world.

Identifying Challenges to 3D Hydrodynamic Modeling for a Small, Stratified Tropical Lake in the Philippines

Three-dimensional hydrodynamic modeling for small, stratified tropical lakes in the Philippines and in Southeast Asia in general is not deeply explored. This study pioneers investigating the hydrodynamics of a small crater lake in the Philippines with a focus on temperature simulation using a Fantom Refined 3D model that has been tested mostly for temperate and sub-tropical lakes. The lake’s monthly temperature during the dry season served as a reference for the model’s initial condition and validation. For the simulation to proceed, input data such as weather, inflow, and bathymetry were prepared. In the absence of hourly meteorological data from local weather stations, this paper adopted the satellite weather data from Solcast. Simple correlation analysis of daily weather data between local stations and Solcast showed valid and acceptable results. Inflow values were estimated using the rational method while the stream temperature was estimated from a regression equation using air temperatures as input. The validated satellite-derived data and runoff model can therefore be employed for 3D modeling. The simulations resulted in extremely higher temperatures compared with those observed when using previous default model settings. Direct modifications were then applied to weather parameters, compromising their integrity but resulting in reasonable profiles. By adding scaling factors to heat flux equations and multiplying their components by 0.75 (shortwave), 1.35 (longwave), 0.935 (air temperature), and 0.80 (wind), better results were achieved. This study identifies several challenges in performing 3D hydrodynamic modeling, such as paucity in input hydro-meteorologic and limnologic data and the need for heat flux model improvement. Overall, this study was successful in employing 3D hydrodynamic modeling in a tropical lake, which can pave directions and serve as an excellent reference for future modeling in the same region.

Inverse problem for retrieving greenhouse gas fluxes at the non-uniform underlying surface from measurements of their concentrations at several levels

The study focuses on the formulation, analysis, and solution of the remote sensing inverse problem to retrieve surface carbon dioxide (CO2) fluxes from measurements of CO2 concentrations at different levels within the atmospheric boundary layer. A three-dimensional hydrodynamic model of turbulent greenhouse gas (GHG) transport was used as a forward model to link the surface GHG fluxes to the drone observations of GHG concentrations. The 3D model provides a GHG concentration distribution by solving the diffusion-advection equation using information on wind speed, its direction, and turbulent exchange coefficients. The surface GHG fluxes are considered as a boundary condition. The spatial distributions of wind speed and turbulence coefficient “for a moment in time” are computed from the relaxation problem for the averaged Navier-Stokes and continuity equations, using a 1.5 order closure scheme (E-ω model). The inverse problem is to retrieve a surface GHG flux by minimizing the difference between the measured and modelled concentrations at several levels. The algorithm was applied to estimate CO2 fluxes over a non-uniform forest canopy at the Roshny-Chu experimental site in the foothills of the Greater Caucasus (Chechen Republic). To test the forward numerical problem, data on surface topography, vegetation height and density, spatial distribution of photosynthetically active solar radiation, as well as data on plant photosynthesis and soil CO2 fluxes were used.

Analysis of Wave-Induced Forces on a Floating Rectangular Box with Analytical and Numerical Approaches

A three-dimensional mathematical hydrodynamic model associated with surface wave radiation by a floating rectangular box-type structure due to heave, sway, and roll motions in finite water depth is investigated based on small amplitude water wave theory and linear structural response. The analytical expressions for the radiation potentials, wave forces, and hydrodynamic coefficients are presented based on matched eigenfunction expansion method (MEFEM). The correctness of the analytical results of wave forces is compared with the construction of a numerical model using the open-source boundary element method code NEMOH. In addition, the present result is compared with the existing published experimental results available in the literature. The effects of the different design parameters on the floating box-type rectangular structure are studied by analyzing the vertical wave force, horizontal wave force, torque, added mass, and damping coefficients due to the heave, sway, and roll motions, and the comparison analysis between the forces is also analyzed in detail. Further, the effect of reflection and transmission coefficients by varying the structural width and drafts are analyzed.

Three-dimensional hydrodynamic modelling of saltwater ingression and circulation in a Brackish Lake Shinji, Japan

Lake Shinji is a mesohaline lake that has intermittent saline water intrusion from its east coast connection of Ohashi River. This intrusion is often in the shape of a very thin layer that moves along the Lake bottom and stayed at the center due to bowl shape bathymetry of the Lake having maximum depth at the center. To elucidate the intrusion mechanism a 3-D hydrodynamic model (EcoPARI) was employed in a hindcast mode covering the year 2012 from the beginning of January to the end of September. Initially, the core emphasis was given to the vertical turbulence diffusion model and optimum model parameters were determined to accurately simulate the hydrodynamics. It was highlighted by the numerical simulations that alteration of one model constant, which is the multiplying coefficient of Richardson number, “α”, is influential instead of altering all the constants to tune the turbulence model. The possibility of using differential model constants for temperature and salinity was also tested and it helped in the improvement of simulations. Finally, the performance of the model was also assessed under extreme weather conditions and a historical upwelling event was simulated. The model was able to reproduce the intrusion in the summer months as well as the upwelling event in September due to strong westerly winds caused by a nearby passing typhoon.

A Wetting and Drying Approach for a Mode-Nonsplit Discontinuous Galerkin Hydrodynamic Model with Application to Laizhou Bay

A wetting and drying treatment for a three-dimensional discontinuous Galerkin hydrodynamic model without mode splitting (external and internal modes) was developed. In this approach, computing elements are classified into wet, dry, and semidry elements, which are treated differently. In a Runge–Kutta time step, the reconstruction of the semidry elements and the combined utilization of two- and three-dimensional limiters help the model maintain stability. Numerical results show that the wetting and drying method can achieve a well-balanced property under the condition of still-water equilibrium and can reasonably describe the variation process of wetting and drying regions during a long wave run-up on a uniform slope and a tidal cycle in a basin with a variable slope. Analysis of the role of the limiters in the model indicated that the robustness of the three-dimensional hydrodynamic model can be effectively maintained when the two- and three-dimensional limiters are jointly applied for wetting and drying process simulation. A three-dimensional discontinuous Galerkin hydrodynamic model was applied with the presented wetting and drying method to simulate the tidal current evolution of a spring tidal cycle in southwestern Laizhou Bay in the Bohai Sea, in November 2003, and the simulated results of the water surface elevation and vertical layered current velocities agreed well with the measured data.

Modelling of fluid mud flow based on a three-dimensional hydrodynamic model : incorporating a 3D rheological model

Modeling fluid mud in estuaries and coastal areas is a complicated task due to its non-Newtonian characteristics. A continuous modeling approach was adopted to investigate the laminar flow of fluid mud, with a three-dimensional (3D) form of the Herschel–Bulkley rheological model introduced into the finite volume coastal ocean model (FVCOM) to calculate the apparent viscosity of fluid mud. The model was validated against two flume experiments for the laminar flow of fluid mud. The results showed that the developed model was capable of accurately reflecting the continuous distribution of velocity and density from the near-bottom to the upper water column. Based on the validated model, the difference between the 3D rheological model and a 1DV rheological model on the simulation results was assessed. The study found the results of the 1DV model and the 3D model show obvious differences. This illustrates the significant effect of apparent viscosity in horizontal direction taken into account by the 3D rheological model.

Effect of hydropower dam flow regulation on salt-water intrusion: São Francisco River, Brazil

The São Francisco River is the fourth largest river in Latin America, and particularly important since it crosses the Brazilian semi-arid region. During the 1960s–90s, a series of dams for hydropower were built in cascade, changing drastically the flow regime. To evaluate the influence of changes in the flow on hydrodynamic processes and saline intrusion in the estuary, a three-dimensional hydrodynamic model was applied to the system. The model was calibrated and validated from hydrodynamic data collected in the estuary. The simulated scenarios of river discharges were Qmin, Q10, Q80 and Qmax (corresponding to 600, 5000, 1200, and 12,000 m3.s−1, respectively), determined from historical river discharge observations. There was an increase in the mixing and a decrease in the river contribution after the installation of dams. The average salinity in the estuarine domain ranged from 0.7 g.kg−1 for intermediate pre-dam discharge to 15.6 g.kg−1 in the lowest discharges after the dam installations. The results of the simulations were used to establish an exponential relationship between fluvial discharge and saline intrusion, which can be used by management agencies to optimize the water quality in catchments for human consumption.

Thermocapillary convection modes and phase change heat transfer characteristics of three-dimensional metal foam composited phase change materials with different aspect ratios under microgravity

This work aims to investigate the flow, heat transfer and phase change characteristics of porous media composite phase change materials with different aspect ratios in the thermocapillary mode under microgravity. A three-dimensional hydrodynamic model of thermocapillary-enhanced phase change heat transfer in the composite is developed. The model considers the shear stress boundary conditions on the porous free surface, employing the enthalpy-porosity method and the Darcy–Forchheimer model to describe the phase change process and fluid flow within the porous matrix, respectively, and the local thermal non-equilibrium model to describe the transient heat energy transfer between the paraffin and copper foam. The effects of different Marangoni numbers (Ma), aspect ratios (AR), Darcy numbers (Da) and porosities (ε) on the phase change heat transfer are compared. The results show that the increase of Ma from 6 × 104 to 2 × 105 accelerates the thermocapillary effect, and positively affect the thermal transport inside the cavity. The total melting time of the composite is reduced by 22.6 %, the heat storage efficiency is improved by 31.1 %, and secondary vortices appear in the convection zone. The large AR is favorable to the development of thermocapillary convection, but it also causes the reduced temperature gradient and heat transfer area of the heat source as well as the increased heat transfer distance. Compared to AR = 1, the total melting time increased by 34.4 % and 46.9 % for AR of 1.95 and 2.25 at a larger Ma, while the heat storage efficiency decreased by 26.5 % and 33.7 %, respectively. For a fixed ε, the decrease in Da hinders the development of convection, thus weakening the heat transfer and storage performance of the composite, and also causes heat conduction to dominate the phase change process in advance.