Free Water Surface Research Articles

Investigating the Effects of Blockage Ratio on the Performance of a Surface-piercing Propeller in Free Surface Water Tunnel Tests

This paper investigates the effect of the immersion ratio parameter on the hydrodynamic performance of three surface-piercing propellers with diameters of 0.125, 0.132 and 0.140m at different advancing speeds. Experimental tests have been carried out in the free surface water tunnel of the Babol Noshirvani University of Technology. The results showed that the maximum thrust coefficient of three propellers occurs in the velocity range of 3-3.5 m/s. This interval represents the transition area of the three propellers. Also, the effect of the blockage ratio on the hydrodynamic coefficients of three propellers relative to the advance coefficient has been studied. By increasing the immersion depth raises the propeller's wet surface and increases the thrust and torque hydrodynamic coefficients. However, growing the propeller's diameter to 0.140m causes the effect of the blockage ratio parameter by increasing the immersion and the propeller's torque experiences a decreasing trend. Therefore, maximum propeller efficiency value with diameter 0.140m in immersion ratio 0.60 and 0.70, incresing 38% and 44%, respectively; relative to other proepllers. Also, the curve of the efficiency gradient of three propellers in the optimum immersion ratio of 0.40 compared to the advancing coefficient shows that the maximum efficiency gradient occurs in the range of 0.7 to 0.9.

Experimental Study to Investigate Effect of Pitch Ratio and Number of Blades on Hydrodynamic Performance of Surface Piercing Propellers

Surface piercing propellers are special supercavitation propellers operating at free surface. These propellers are designed to have the best performance at the highest speed. The geometric parameters of the number of blades and the pitch ratio will significantly impact the critical advance coefficient range, ventilation and consequently the hydrodynamic performance of the propeller. Therefore, in this paper, the effect of two crucial parameters of pitch ratio and number of blades were experimentally studied in free surface water tunnel. After calibration and evaluation of uncertainty, two 5-bladed propellers with same section profile and pitch ratio of 1.5 and 1.4 used to investigate effect of pitch ratio. The results of two 5-blade and 6-blade propellers with same section profile and pitch ratio of 1.4 were compared. The immersion ratio was 40%, and the shaft inclination angle was zero. Results showed that increasing the pitch ratio increased the thrust and torque coefficients by 30%; while increasing the critical advance coefficient. Consequently that has led to the development of a full ventilation range and improved hydrodynamic performance of the propeller. In addition, by increasing the number of blades, at values greater than the critical advance coefficient, the thrust and torque coefficients were increased by 10%. However, the critical advanced coefficient changes were negligible. Comparing the results in the three-dimensional contours showed that with the change in the number of blades, by increasing the pitch ratio, the critical advance coefficient increased; which led to a further increase in efficiency.

Hamiltonian model for water waves in a triangular domain

We present a Hamiltonian model for free surface water waves in a 2-D symmetric triangular domain with sides that have a 45∘ slope. The construction uses a new amplitude expansion for the free surface, and a Lagrangian formulation of the water problem that is based on a formal mechanical/geometrical analogy of the fluid motion to geodesic motion in a potential force field. We define an approximate Lagrangian by choosing a physically plausible generalized coordinate and obtain the Hamiltonian by the Legendre transform. Hamilton’s equations are presented in spectral form using a known explicit construction of the linear normal modes for the domain considered. A key step is the approximation of a Dirichlet–Neumann operator appearing in the kinetic energy.

Breaking the Saturated Vapor Layer with a Thin Porous Membrane.

The main idea of membrane distillation is to use a porous hydrophobic membrane as a barrier that isolates vapor from aqueous solutions. It is similar to the evaporation process from a free water surface but introduces solid-liquid interfaces and solid-vapor interfaces to a liquid-vapor interface. The transmembrane mass flux of a membrane-distillation process is affected by the membrane's intrinsic properties and the temperature gradient across the membrane. It is interesting and important to know whether the evaporation process of membrane distillation is faster or slower than that of a free-surface evaporation under the same conditions and know the capacity of the transmembrane mass flux of a membrane-distillation process. In this work, a set of proof-of-principle experiments with various water surface/membrane interfacial conditions is performed. The effect and mechanism of membrane-induced evaporation are investigated. Moreover, a practical engineering model is proposed based on mathematical fitting and audacious simplification, which reflects the capacity of transmembrane flux.

Numerical study of hydraulic characteristics of impulse waves generated by subaerial landslides

Impulse waves generated by subaerial landslides of a block model along a frictionless surface are investigated numerically based on a combination of immersed boundary method and lattice Boltzmann method. A wave propagation model is proposed through machine learning. The observed impulse waves are classified into Stokes-like waves, solitary-like waves, cnoidal-like waves, and bore-like waves. The influence of the slope angle and the slide front angle on the generation and propagation of impulse waves is investigated from the perspectives of the quantitative analyses on primary wave amplitude and energy transformation. The energy release, dissipation, and propagation of the impulsive waves are investigated based on energy conservation principles. The wave propagation model based on the random forest model is established upon a priori classification of wave types. By comparison with the available numerical results, the accuracy of the proposed wave propagation model in predicting free water surface elevations is demonstrated.

Numerical modeling of the dam-break flood over natural rivers on movable beds

Abstract In the present work, a modified numerical model was developed to simulate the water flow during a dam break with the mud layer transfer of different heights, consisting of three phases (water, air, and a phase for deposition). To carry out a numerical simulation of this process, a mathematical model based on the VOF (volume of fluid) method was modified, taking into account the movement of the water-free surface, which is carried out by the movement of water flow based on the Newtonian fluid model, and the movement of mud impurities is based on the non-Newtonian fluid model. Validation of the constructed model for the influence of three-dimensional features of the flow on morphological changes is carried out by a modified mathematical model and compared with the results of calculation for two-dimensional (2D) and three-dimensional (3D) models. The proposed method for modeling is applied on a real complex terrain, which was based on the Kargalinka – a river in Almaty and the Almaty region of Kazakhstan, the right tributary of the Kaskelen River. Simulation analysis is carried out for cases with different deposit heights. All results of the numerical simulation can be visually viewed using graphs and illustrations.

Role of constructed wetlands in mitigating the challenges of industrial growth and climate change impacts in the context of developing countries

One of the most persistent issues affecting individuals in developing countries is the lack of access to safe drinking water and sanitary facilities. The adoption of centralized water, energy, and cost-intensive technology has proven ineffective in addressing the complex water-related challenges that have arisen as a consequence of growing urbanization in developing nations. Constructed wetlands have emerged as an effective wastewater treatment solution with natural applications. The fundamental goal of this study is to offer a complete overview of the wide variety of practices, uses, and investigations of constructed wetlands systems for eliminating different pollutants from wastewater in developing countries leading to placing them in the context of climate change, environmental resource planning, and sustainable wastewater treatment systems. CWs offer significant levels of treatment performances with hybrid systems achieving contaminant removal efficiencies up to 93.82% for total suspended solids, 85.65% for chemical oxygen demand, and 80.11% for ammonia nitrogen which is adequate with respect to other viable alternatives. In terms of Biological Oxygen Demand (BOD5), the highest elimination (84.06%) was achieved in hybrid systems when compared to Free water surface CWs (65.34%), Horizontal sub-surface CWs (75.1%), and Floating treatment wetland (55.29%). The maximum power density generation through the microbial fuel cell-based constructed wetlands ranges between 50 and 86 mW/m2in Bangladesh (integrated tidal flow) and 852 mW/m3in China (vertical flow), and the production of bioenergy has been evidenced up to 1,836.5 GJ/hector/year. Annually, wastewater treatment plant systems (WTPs) generate around a hundred times more Methane (CH4), Nitrous oxide (N2O), and carbon dioxide (CO2) than CWs. In metropolitan cities, WTPs may lead to a considerable increase in upstream land use, which could be minimized by promoting CWs in these areas. The potential utility of different CWs in protecting and preserving estuarine quality within the present regulatory framework is finally addressed in the study, emphasizing that it can balance the impacts of industrial expansions in developing countries for subsequent mitigation and adaptation to climate change.

Moisture Retention and Multi-mechanistic Transport Behavior in Nanoporous Coal.

Coal-water interactions induced by water retention in coals control the performance of coalbed methane reservoirs and coal utilizations. Experimental measurements on Illinois coal samples using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, low-temperature N2 adsorption, low-pressure CO2 adsorption, and dynamic water vapor sorption were carried out. A mechanism-based isothermal model of water vapor sorption was proposed to estimate the water adsorption capacity at varied relative humidity, which implicitly considered both monolayer and multilayer adsorptions and capillary condensation. The analytical models for quantifying the stage-based diffusion coefficients as well as the apparent diffusion coefficients at different relative humidities were proposed and well validated. The contributions of different diffusion regimes to the total mass flow were discussed. At the first stage, both free water vapor diffusion and surface diffusion of adsorbed water molecules contribute to the total mass flow whereas the apparent diffusion at this stage is dominated by latter flow regime; during the second stage, the contribution of free water vapor flow to the apparent flow can be neglected and the mass transfer at this stage is still dominated by the surface diffusion flow; upon reaching the critical relative humidity, the flow in capillary condensation will dominate the total mass flow.

The Effects of Irrigation, Topping, and Interrow Spacing on the Yield and Quality of Hemp (Cannabis sativa L.) Fibers in Temperate Climatic Conditions

The study was aimed at determining the most suitable irrigation schedule program for hemp grown for fibers by using evaporation from the free water surface (Eo), measured by a Class A pan and related crop plant coefficient (Kc). The experiment, carried out in Vojvodina, a northern part of the Republic of Serbia, included three irrigation regimes: I1, I2, and I3 corresponding, respectively, to daily evaporation from an open water surface (Eo), two interrow spacings: RS1 (12.5 cm) and RS2 (25 cm), and topped (T) and not topped (NT) variants. The Kc values used for the calculation of daily evapotranspiration (ETd) were 0.42 for April and May and 1.00 (I1), 0.80 (I2), and 0.60 (I3) from June to the harvest. In addition, the nonirrigated (Io) control variant was also included in the trial. The dioecious fiber hemp variety Marina was used for the trials. Irrigation was carried out by a drip irrigation system and was scheduled based on the water budget method. It started when readily available water (RAW) in the soil layer of 0.4 m was completely depleted by the plants. In the first year of the study, irrigation did not influence the yield of hemp fiber, but in the second one, the best result was achieved for the irrigation variant I1. Interrow spacing did not have a statistically significant effect on both the hemp fiber yield and the quality. The topping of plants significantly decreased the yield of hemp, and it is not recommended when the hemp is cultivated for fibers. The quality of the hemp fibers was not influenced by irrigation, inter-row spacing, and topping. The rate of hemp evapotranspiration was in an interval of 312 mm (ETa) to 520 mm (ETm). The highest values of IWUE and ETWUE in both years and the bark yield in the first year were detected for the I3 irrigation variant, which suggested that the crop plant coefficient (Kc) of 0.6 could be recommended for the correction of Eo values in the calculation of the daily evapotranspiration of hemp (ETd) from June to August. The yield response factor (Ky) with values of 0.22 and 0.60 for the total growing season reveals that, in rainy years, hemp for fiber production could be grown without irrigation in the temperate climate of the Vojvodina region. However, such years are rare. Without doubt, irrigation of fiber hemp is recommended in the mentioned region in order to obtain high yields of good quality product.

A new symmetric interior penalty discontinuous Galerkin formulation for the Serre–Green–Naghdi equations

AbstractIn this work, we investigate the construction of a new discontinuous Galerkin discrete formulation to approximate the solution of Serre–Green–Naghdi (SGN) equations in the one‐dimensional horizontal framework. Such equations describe the time evolution of shallow water free surface flows in the fully nonlinear and weakly dispersive asymptotic approximation regime. A new non‐conforming discrete formulation belonging to the family of symmetric interior penalty discontinuous Galerkin methods is introduced to accurately approximate the solutions of the second order elliptic operator occurring in the SGN equations. We show that the corresponding discrete bilinear form enjoys some consistency and coercivity properties, thus ensuring that the corresponding discrete problem is well‐posed. The resulting global discrete formulation is then validated through an extended set of benchmarks, including convergence studies and comparisons with data taken from experiments.

Performance and sustainability of a multi-stage free water surface constructed wetland under seasonal change and shock loading

Multi-stage constructed wetlands (CWs) are widely used for water quality improvement, especially in the treatment of wastewater. Many studies focus on their treatment efficiency under steady loading, but fewer studies consider their sustainability under variable conditions. This study examines the multi-stage CWs in the Hong Kong Wetland Park for their long-term performance and sustainability in terms of water quality under seasonal changes, storm events, and shock loadings of pollutants. The results show that the multistage design performs well and is stable under these changing conditions. In such multistage CWs, the type of units and some changing conditions (e.g., inflow concentrations, seasonal changes of vegetation, and water levels) also affect the performance of the whole system. Compared to individual CW, a multi-stage CW system could recover more quickly on dissolved oxygen (DO), and ammonia nitrogen (NH4), but slowly on biochemical oxygen demand (BOD) and total phosphorus (TP). A pre-processing and buffering area is necessary to handle the shock loadings of BOD and TP in such a multistage CW system. Although water levels recover quickly in both, it is difficult to return to original water levels in multi-stage CWs compared to single ones. Besides, for sustainable operation, attention should be paid to the DO of the inlet, and aeration measures might be taken.

Microplastic dynamics in a free water surface constructed wetland

This study investigates microplastic (MPs) dynamics of a recently established surface flow 2100 population equivalent polishing constructed wetland (CW) receiving 1.4 ML per day of secondary treated wastewater. MPs type, size ranges and concentrations were measured along the CW at a 2-months sampling campaign. The CW received an average of 5·106 MPs per day (6 MPs per liter), mostly 100–1000 μm-sized synthetic fibers followed by fragments in the same size range. 95 % of MPs were retained, resulting in 0.30 ± 0.09 MPs per liter in CW effluent. Most MPs (97 %) were trapped within the first 20 % of the CW which consisted of a settling pond and shallow vegetated treatment cells and provided an areal removal rate > 4000 MP m−2 d−1. Data and microscopic analysis indicate MPs erosion and fragmentation in the CW. Turbidity and suspended solids were no indicator for MP removal due to water fowl activity, algal growth, and preferential flow conditions. This is the first study on MP dynamics in an independently operating full scale free water surface CW incorporated into a municipal wastewater treatment scheme. Surface flow CWs can retain MPs effectively but accumulation in CW sediments and substrate needs to be considered when further utilized or recycled.

Artificial aeration of an overloaded constructed wetland improves hypoxia but does not ameliorate high nitrogen loads

High organic loadings to constructed wetlands can result in water quality issues such as low dissolved oxygen and high ammonium concentrations, with artificial aeration a potential mitigation option. This study compared baseline (no aeration – NA), continuous aeration (CA), and intermittent aeration (IA) conditions to improve water quality in a tertiary treatment free water surface constructed wetland (FWS CW) with night time hypoxia/anoxia, and high nutrient concentrations. The response variables included dissolved oxygen (DO), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total phosphorus (TP), phosphate (PO43–-P), and dissolved organic carbon (DOC). In situ aeration and monitoring was performed from April to June 2021 in a large, field-scale FWS CW, the Laratinga wetlands Mount Barker, South Australia.The results demonstrated that DO increased by an average 2.11 mg L−1 from NA to CA during the night and 1.26 mg L−1 and 1.84 mg L−1 from NA to IA during the night and day respectively when averaging over the basins. The C/N ratio was very low and there was no significant influence of DO on DOC concentrations. There was no significant difference in TN concentrations with the application of aeration aside from a decrease in the channel at night from NA to IA, and an increase in NH4+-N resulted under IA compared with NA in Basin 1 and 2 during the day. This implies that the N loadings exceeded the wetland's ability to complete nutrient conversions at a rate that aligns with input rate. The concentrations of NO3−-N increased at night under CA and IA treatments suggesting that some nitrification was promoted, or there was inhibition of dissimilatory nitrate reduction to ammonium. The concentrations of TP and PO43–-P significantly increased with the aeration compared with no aeration, however there was no difference between the aeration treatments. This suggested that increased sediment resuspension during aeration increased P in the water. There was no change in DOC with the application of aeration. Overall, the DO increased with aeration application and may be able to better support the wetland ecology; however, the Laratinga wetland is overloaded and the capacity of the wetland to effectively transform and remove nutrients is inhibited, even with the application of artificial aeration.

Numerical Modeling of Interactions between Solitary Waves and Floating Breakwaters

In the current numerical work, a 2D wave tank has been planned to explain the shared impacts among three different solitary waves and three different floating breakwaters by applying Reynolds-Averaged Navier-Stokes models and the volume of fluid method. Three dissimilar floating breakwaters (i.e., square breakwater, circular breakwater, and modified breakwater) were chosen. A total of eighteen cases were investigated, including three different floating breakwaters, a solitary wave (SW) with three different wave heights, and two different densities of floating breakwaters. We achieved the production of a solitary wave by moving a wave paddle (WP) and the motion of floating breakwater in two various directions by applying two different codes as user-defined functions. The dynamic mesh technique has been employed for re-forming mesh during the motion of the wave paddle and the floating breakwater. The numerical calculations have been confirmed by some numerical, analytical, and experimental case studies. First, the generation of a SW using the WP movement and the free motion of a heaving round cylinder on the free surface of motionless water were modeled and validated. Additionally, the effects of various parameters, including floating breakwater shape, floating breakwater density, and solitary wave height, on the hydrodynamic performances of the floating breakwater, the floating breakwater’s motions, and the free-surface elevation were considered under various conditions.

Mathematical Modelling and Experimental Study of an Enhanced Double-Slope Glass Solar Still

Solar desalination is considered an important technology for solving the water shortage problem. In this research, a mathematical modeling and experimental study of an enhanced double-slope glass solar still were developed and evaluated based on a comparison with the conventional one. The two solar still were designed and fabricated at the Faculty of Engineering, University of Tabuk, and compared in the same operating climate conditions. The solar radiation model was developed, tested, and used with the solar still mathematical modeling to predict water productivity and daily efficiency. Copper T shape pieces were used in the solar still basin to increase the free water surface area inside the still at a water depth of 3 cm. The results indicated that the average measured and calculated values of accumulated productivity for conventional solar still were 3.01 and 3.32 L/m2.day respectively with a deviation of 9.3%. The corresponding average values for the enhanced solar still were 7.03 and 8.16 L/m2.day respectively. In addition, it can be noticed that the maximum measured daily thermal efficiency was about 56.4% and 25.31% for enhanced and conventional solar still respectively. Also, the cost evaluation was performed, and the results concluded that the enhanced double-slope glass solar still with cost per liter was about 0.0024 $/L/m2. The modeling and experimental results were compared based on the statistical evaluation methods and it is clear that the proposed mathematical model gives a good prediction of solar radiation and performance for the enhanced doubleslope glass solar still.

Experimental study and numerical simulation of flow over the inclined airfoil-shaped weir in rectangular channel

In order to find an integrated flow measurement and control facility with stable outflow form, a series of experiments and numerical simulations were performed for the inclined airfoil-shaped weir. Based on the experimental and simulated data, the stage-discharge relationship was deduced by using dimensional analysis and incomplete self-similarity theory. And two flow measurement formulas with inclination angle of 0°–45° were obtained through different fitting schemes. The variation law of discharge ratio with inclination angle and the accuracy comparison of flow measurement formulas were analyzed. Moreover, the Froude number, critical submergence degree, head loss and velocity distribution of the flow field over the weir were studied. The results show that streamlined airfoil improves the stability of flow behind the weir. The average relative error of the free water surface line data between experiments and simulations is 5.05%, which indicates the reliability of the numerical simulation. The discharge ratio proposed in the fitting scheme I takes the 25° inclination angle as the limit, which increases slightly at first and then decreases gradually, and the flow measurement relative errors of the two fitting formulas are all within ±7%. The average Froude number of the upstream reference section at each inclination angle is less than 0.25, the critical submergence range is between 0.87 and 0.96, and the relative head loss ranges from 3.54% to 12.16%, so as to ensure the accuracy of flow measurement.

Influence of cross-section shape on energy harvesting from transverse flow-induced vibrations of bluff bodies

Hydroelastic experiments have been carried out in a free surface water channel to study the influence of the cross-section shape on the mechanical energy transfer from a uniform flow to a self-excited crossflow oscillating prism. Seventeen cross-section shapes were tested with the same mechanical properties (say, mass ratio and mechanical damping) and aspect ratio. Then, the study was focused on the role of the cross-section shape and reduced velocity on the prism dynamics and energy transfer from the fluid flow. It has been found that the geometric centroid of the semi-cross-section and the afterbody length of the cross-section represent a simple and effective metric to characterise the energy transfer. Two related dimensionless geometric parameters are introduced. The dependence of the energy transfer with these two parameters is studied and used to design successfully ‘in advance’ cross-section shapes with high energy transfer efficiencies. It has been observed from particle image velocimetry measurements that large energy transfer shapes are those in which, under strong oscillations, the flow follows the cross-section contour of one side and is fully detached on the other side.

Experimental and numerical investigation of squat submarines hydrodynamic performances

This paper empirically examines the hydrodynamic performances of squat submarines under the resistance and wave tests beside numerical investigation of pressure drag reduction techniques. Despite vast information about the operation of the streamlined fluid vessels, there is not much information about the geometries and hydrodynamic behaviors of squat vessels with L/D ratios below four. This study experimentally investigates the impacts of various relative depths and flow inclinations, intending to find drag, heave, and sway forces at the velocities of 0.5, 1.0, 1.5, 2.0, and 2.5-m/s. A one-tenth scaled model of a squat submarine is examined under the resistance and wave train scenarios as the captive model in the towing tank experiments via 110 unique testing scenarios. Then, different pressure drag reduction techniques on the full-scale submarine are evaluated numerically at one-phase fluid by developing stern geometric optimization, nose rod devices, water corridors, and surface patterns at the bow and stern. Results present drag forces increase up to 150% at the 0.5D level for the resistance and wave tests due to the influences of the free surface water. The drag coefficients at the fully submerged depth of 6D differ by up to 13.3% between the numerical and experimental evaluations.

Structure and Reactivity of CoFe2O4(001) Surfaces in Contact with a Thin Water Film

CoFe2O4 is a promising catalytic material for many chemical reactions. We used ab initio molecular dynamic simulations to study the structure and reactivity of the A- and B-terminations of the low-index CoFe2O4(001) surfaces to water adsorption at room temperature. Upon adsorption, water partly dissociates on both termination with a higher dissociation degree on the A-termination (30% versus 19%). The 2-fold coordinated Fe3+(tet) in the tetrahedral voids and the 5-fold coordinated Fe3+(oct) in the octahedral voids are the main active sites for water dissociation on the A- and B-termination, respectively. Molecular water, hydroxydes, and surface OH resulting from proton transfer to surface oxygens are present on the surfaces. Both water-free surface terminations undergo reconstruction. The outermost Fe3+(tet) on the A-termination and B-termination move towards the nearby unoccupied octahedral voids. In the presence of a thin film of 32 water molecules, the reconstructions are partially and completely lifted on the A- and B-termination, respectively.

Global Bifurcation of Capillary-Gravity Water Waves With Overhanging Profiles and Arbitrary Vorticity

Abstract We study two-dimensional periodic capillary-gravity water waves propagating at the free surface of water in a flow with arbitrary, prescribed vorticity over a flat bed. Using conformal mappings and a new reformulation of Bernoulli’s equation, the problem is equivalently cast into the form “identity plus compact”, which is amenable to Rabinowitz’s global bifurcation theorem, while no restrictions on the geometry of the surface profile and no assumptions regarding the absence of stagnation points in the flow have to be made. Within the scope of this new formulation, local curves and global families of solutions, bifurcating from laminar flows with a flat surface, are constructed.