Hydrodynamic Perspective Research Articles

Sediment dynamics of a tropical tide-dominated estuary: Turbidity maximum, mangroves and the role of the Amazon River sediment load

We investigate tidal propagation and suspended-sediment dynamics in the Caeté river estuary, Southeastern Amazonian Coastal Zone, addressing gaps in knowledge about sources and mechanisms of sediment entrapment in well mixed, tropical estuaries. Bathymetric and sedimentologic surveys were undertaken during high- and low-discharge periods, and longitudinal and cross-sectional hydrodynamic measurements were made for a range of tide and fluvial discharge conditions. Results show that, from geomorphologic and hydrodynamic perspectives, the lower Caeté River is a typical tide-dominated estuary. There is a sediment-transport convergence in the middle estuary, forming an Estuarine Turbidity Maximum (ETM), and there are substantial displacements of the ETM on lunar and seasonal time scales. Superimposed variations of suspended-sediment concentrations (SSC) related to rainfall and local fluvial discharge (landward end), and the seasonal dynamics of the shelf (seaward end), result in complex suspended-sediment dynamics in the estuary. The source of mud to the estuary is likely the Amazon River plume and its shelf deposits. During the dry season and transitional periods, the estuary imports mud from the shelf and tidal processes accrete it on the mangrove flats. Our results indicate that sediment entrapped within the ETM can accumulate in adjacent mangrove forests, and that fluvial sediment might be of secondary relevance to development of coastal zone morphology on mangrove coasts.

Experimental and numerical investigation of fractal-tree-like heat exchanger manufactured by 3D printing

The manufacturing difficulties of complex fractal-tree-like heat exchangers have limited their industrial applications, although many evidences have shown that they have significant advantages in heat transfer. Nevertheless, the emerging 3D printing technology has brought great opportunity for the development of complex structured device. In the present study, three-dimensional (3D) fractal-tree-like heat exchangers were designed and manufactured using 3D printing technology. Their performance was evaluated from both thermal and hydrodynamic perspectives, the flow characteristics were investigated in detail. The results show that a fractal-tree-like heat exchanger can improve hydrodynamic performance, reduce pressure drops and has great heat transfer ability. In general, the fractal-tree-like heat exchanger has a comprehensive advantage over the traditional spiral-tube exchangers as it has a higher value of coefficient of performance (COP). Furthermore, the 3D printing provides a visual, efficient, and precise approach in the present research.

Hydrodynamic behaviour of European black poplar (Populus nigra L.) under coppice management along Mediterranean river ecosystems

AbstractThis study examined the hydrodynamic behaviour of European black poplar (Populus nigra L.) under coppice management in riparian areas with a multidisciplinary approach. An innovative procedure on the basis of the combination of plant allometric relations and hydrodynamic models was applied to assess drag forces and plant hydrodynamic bending as function of the basal diameter and module of elasticity, with a probabilistic approach. Cuttings of European black poplar from 2 close riverine environments of Southern Italy have been planted and subjected to the same coppice management strategy. The 2 different 3‐year‐old shoot poplar ensembles exhibited statistically similar morphological traits but stems with different module of elasticity. Drag forces were simulated with a model on the basis of the vegetative Cauchy number. Plant deformation under the hydrodynamic load was modelled as a base‐mounted cantilever beam. The differences in the observed elasticity were verified to be also significant from a hydrodynamic perspective. Diagrams were drawn to describe plant bending, drag forces, and basal momentum as function of basal diameter, accounting for the uncertainty in the module of elasticity. These results can be exploited for identifying objective hydrodynamic criteria to be adopted for coppice management of riparian woody vegetation in human controlled river ecosystems.

Role of co-occurring competition and facilitation in plant spacing hydrodynamics in water-limited environments.

Plant performance (i.e., fecundity, growth, survival) depends on an individual's access to space and resources. At the community level, plant performance is reflected in observable vegetation patterning (i.e., spacing distance, density) often controlled by limiting resources. Resource availability is, in turn, strongly dependent on plant patterning mediated by competitive and facilitative plant-plant interactions. Co-occurring competition and facilitation has never been specifically investigated from a hydrodynamic perspective. To address this knowledge gap, and to overcome limitations of field studies, three intermediate-scale laboratory experiments were conducted using a climate-controlled wind tunnel-porous media test facility to simulate the soil-plant-atmosphere continuum. The spacing between two synthetic plants, a design consideration introduced by the authors in a recent publication, was varied between experiments; edaphic and mean atmospheric conditions were held constant. The strength of the above- and belowground plant-plant interactions changed with spacing distance, allowing the creation of a hydrodynamic conceptual model based on established ecological theories. Greatest soil water loss was observed for the experiment with the smallest spacing where competition dominated. Facilitation dominated at the intermediate spacing; little to no interactions were observed for the largest plant spacing. Results suggest that there exists an optimal spacing distance range that lowers plant environmental stress, thus improving plant performance through reduced atmospheric demand and conservation of available soil water. These findings may provide a foundation for improving our understanding of many climatological, ecohydrological, and hydrological problems pertaining to the hydrodynamics of water-limited environments where plant-plant interactions and community self-organization are important.

Applications of unmanned aerial vehicles in fluvial remote sensing: An overview of recent achievements

Previously, understanding of the fluvial process from the ecological, morphological, and hydrodynamic perspectives has largely relied on the limited scale of in-situ field observation or the sparse spatial and temporal scale of satellite-based remote sensing. However, with the recent advent of unmanned aerial vehicles (UAVs) and concurrent advances in sensor technology, measurement campaign has been revolutionized and the view of rivers has fundamentally changed from the local scale to the holistic scale; the perspective has shifted from a static to a dynamic one. UAVs can provide a fine spatial and temporal resolution of measurements with a relatively low cost, which, as compared to conventional satellite or pilot-controlled airborne systems, can be more suitable for the analysis of fluvial processes in narrow rivers and small lakes. In this paper, we comprehensively review and document various crucial achievements driven by UAVs-based remote sensing in fluvial environments, among a variety of other relevant applications. Specifically, the paper highlights the UAV-based fluvial remote sensing in terms of riparian vegetation, hazardous aquatic algae blooms, submerged morphology, water-surface slope, sediment, flow velocity, and disasters, including flood inundation mapping.

Quantum non-equilibrium effects in rigidly-rotating thermal states

Based on known analytic results, the thermal expectation value of the stress-energy tensor (SET) operator for the massless Dirac field is analysed from a hydrodynamic perspective. Key to this analysis is the Landau decomposition of the SET, with the aid of which we find terms which are not present in the ideal SET predicted by kinetic theory. Moreover, the quantum corrections become dominant in the vicinity of the speed of light surface (SOL). While rigidly-rotating thermal states cannot be constructed for the Klein–Gordon field, we perform a similar analysis at the level of quantum corrections previously reported in the literature and we show that the Landau frame is well-defined only when the system is enclosed inside a boundary located inside or on the SOL. We discuss the relevance of these results for accretion disks around rapidly-rotating pulsars.

A Sea Scorpion's Strike: New Evidence of Extreme Lateral Flexibility in the Opisthosoma of Eurypterids.

Among the largest and most abundant aquatic predators during much of the early evolution of vertebrates, eurypterids have long been an iconic and intensely studied group of Paleozoic arthropods. We report a new specimen of the eurypterid Slimonia acuminata, which includes a fully articulated series of tail (postabdominal and telsonal) segments preserved in a tight lateral curve. Such a high degree of apparent lateral tail flexibility has not been previously recognized in eurypterids. From the perspective of hydrodynamics, the dorsoventrally flattened body plan of eurypterids would have limited the effectiveness of lateral tail motion as a means of propulsion. However, the long and serrated terminal tail spine of S. acuminata (and other eurypterids) would have made lateral tail strikes-which would have met a minimum of hydraulic resistance-an effective means of predatory attack and self-defense. Thus, many eurypterids are reinterpreted as substantially better-armed predators than previously supposed.

Optimization and simulation of a bionic fish tail driving system based on linear hypocycloid with hydrodynamics

The tail driving system based on linear hypocycloid has the advantages of adjustable phase difference, no quick-return, and combining speed reducer with transformation mechanism. The plane complex movement of the driving system was realized via a motion triangle with a linear hypocycloid planetary gear train and a linkage. In this article, we approach the question of which kind of parameter design can make this driving system more efficient in swimming from a hydrodynamic perspective. First, dynamic and hydrodynamic models were established with momentum theorem, Lagrange theorem, and two-dimensional foil theory. And then, hydrodynamic optimization on kinematic parameters (i.e. caudal peduncle’s reciprocation velocity and caudal fin swing angle) and structural parameters (i.e. swing amplitude, V planetary carrier’s angle, and sun gear’s radius) for a better propulsive efficiency was developed in detail. Second, influences of structural parameters on vortex ring were further conducted by numerical simulation in FLUENT. Finally, the prototype and experimental platform of the designed driving system were established, and the theoretical derivation of lift and lateral forces was testified by experiment.

The influence of bathymetry changes on low water level of Lake Poyang

基于2010年鄱阳湖最新地形，构建精细的鄱阳湖二维水动力数学模型，相同网格下构建1998年地形，分别模拟不同地形条件下2006年枯水年水位、流量时空分布，分析地形变化对水位、流量的影响，阐释地形影响的时空差异. 结果表明：相比1998年，2010年地形由于北部入江通道的下切，相同的2006年水文条件下，水位普遍降低；水位越低，上下游水面坡降越大，受地形影响越明显；低水位最大降幅1~2 m，而高水位最大不超过0.4 m，分别对应湖口9 m以下、15 m以上水位；地形对水位的影响程度都昌 >星子 >棠荫 >康山；都昌至湖口段水头差降低了2 m，水面坡度变缓，棠荫至都昌段水面坡度变陡，康山至湖口水头差基本不变；全年出湖总流量增加了6%；地形变化影响最显著为河道区，影响范围可波及大部分湖区，局部地形的变化使得子湖水面积也存在一定差异. 本研究首次基于水动力模拟量化了鄱阳湖地形变化对水位的影响程度和范围，结果可为水资源管理、江湖关系演变分析、湿地生态环境保护等提供科学参考.;A fine 2D hydrodynamic model of Lake Poyang was used to simulate the hydrological effect of the bathymetry changes between 1998 and 2010. Spatio temporal patterns of water levels and discharge in 2006 of two DEM were simulated to assess the bathymetry effect, considering 2006 as a typical dry year. Results showed that the north water way was deeper in 2010 than that in 1998, resulting in lower water levels. In low water level period, the water surface gradient was larger, and the effect of DEM changes was more significant than that in high level period.The low water levels decreased by 1-2 m corresponding to water level lower than 9 m at Hukou. The reductions of high water levels were lower than 0.4 m when water level at Hukou higher than 15 m. The influenced magnitude was largest at Duchang, followed by Xingzi, Tangyin and Kangshan.The water head from Duchang to Hukou decreased by 2 m in low level period. The water surface gradient decreased from Duchang to Xingzi, and increased from Tangyin to Duchang. There was no distinct gradient change from Kangshan to Hukou. The total discharge into the Yangtze River increased by 6%. The channel areas were most affected, however the influence of bathymetry changes spread across the most of the lake area.Water areas of some sub-lakes varied due to the local morphological changes. This study quantified magnitude and domain of the effect of bathymetry changes on Lake Poyang level from a hydrodynamic perspective. The outcomes may provide scientific support for water resource and ecological environment management, evolution and analysis of river-lake relationship.

Shear stress in a pressure-driven membrane system and its impact on membrane fouling from a hydrodynamic condition perspective: a review

Pressure-driven membrane technology has gained increasing popularity in municipal/domestic and industrial wastewater treatment, desalination, and water reclamation. Careful manipulation of surface shear stress, which plays a vital role in membrane fouling control from a purely hydrodynamic perspective, can minimise concentration polarisation of solute on flat sheet membranes, or enhance the particle back transport from hollow fibre membranes. This review considers the techniques to generate turbulence and shear at the membrane surface, the magnitude of shear stress, and the experimental, as well as numerical methods for evaluation of shear stress. The findings are presented in terms of the amount of shear stress reported to control membrane fouling in these systems. Operational disadvantages of fouling control via application of shear stress occur while changing the properties of the solute or particles, such as cell breakup, bacterial population change, or shear stress classification. The literature teaches that future developments on shear stress for membrane systems must be addressed, in addition to energy consumption, shear stress distribution and the development of combined analytical methods to characterise and visualise shear in situ for different membrane configurations. © 2016 Society of Chemical Industry

Hydrodynamic consideration in ocean current turbine design

Ocean currents are one of important resources of ocean energy. Although it is not widely harnessed at present, ocean current power has a vital potential for future electricity generation. In fact, several turbine systems have been proposed in the world. In the present, we consider what factors should be considered in designing the system from the perspective of hydrodynamics. As an example, a floating Kuroshio turbine system which is under development in Taiwan is employed to serve as the case study. The system consists of five major parts; i.e. a foil float which can be employed to adjust the system submergence depth, a twin contra-rotating turbine system for taking off the current energy, two nacelles housing power generators, a cross beam to connect two nacelle-and-turbine systems, and two vertical support to connect the foil float and the rest of the system.

Significant difference in the dynamics between strong and fragile glass formers.

Glass-forming liquids are often classified into strong glass formers with nearly Arrhenius behavior and fragile ones with super-Arrhenius behavior. We reveal a significant difference in the dynamics between these two types of glass formers through molecular dynamics simulations: In strong glass formers, the relaxation dynamics of density fluctuations is nondiffusive, whereas in fragile glass formers it exhibits diffusive behavior. We demonstrate that this distinction is a direct consequence of the fundamental difference in the underlying elementary relaxation process between these two dynamical classes of glass formers. For fragile glass formers, a density-exchange process proceeds the density relaxation, which takes place locally at the particle level in normal states but is increasingly cooperative and nonlocal as the temperature is lowered in supercooled states. On the other hand, in strong glass formers, such an exchange process is not necessary for density relaxation due to the presence of other local relaxation channels. Our finding provides a novel insight into Angell's classification scheme from a hydrodynamic perspective.

Random patterns in fish schooling enhance alertness: A hydrodynamic perspective

One of the most highly debated questions in the field of animal swarming and social behaviour is the collective random patterns and chaotic behaviour formed by some animal species, in particular if there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour —fish schooling— from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which include calculations of the hydrodynamic forces between slender bodies, show that such a behaviour may enhance the transfer of hydrodynamic information, and thus the survivability of the school could improve. These findings support the general hypothesis that a disordered and nontrivial collective behaviour of individuals within a nonlinear dynamical system is essential for optimising transfer of information —an optimisation that might be crucial for survival.

Comparison of the Performance of a Sutureless Bioprosthesis With Two Pericardial Stented Valves on Small Annuli: An In Vitro Study

Aortic valve replacement has evolved recently with the development of the sutureless bioprosthesis. One such valve is the Perceval bioprosthesis, which is built by mounting leaflets of bovine pericardium to a thin stent; this approach has the potential to provide an excellent fluid dynamic performance. We undertook an invitro study to compare the hydrodynamic performance of the sutureless bioprosthesis with two standard pericardial stented bioprostheses (Crown and Magna). Tests were conducted using a mock loop, testing on two sizes of the three prostheses. The prosthesis sizes were chosen to house the valves in porcine aortic roots with a native annulus diameter of 19 mm (n= 6) or 21 mm (n= 6). The stroke volume ranged from 25 mL to 105 mL at a simulated heart rate of 70 beats per minute. Mean pressure drop and energy loss rose with increasing stroke volume in all of the valves tested (p<0.001), with the sutureless valve showing the lowest values for both variables (p < 0.001). Effective orifice area values were stable across the stroke volume intervals and were larger in the sutureless valves (p < 0.001). All of the valves tested provided good fluid dynamic performances. The sutureless bioprosthesis provided the best performance with the least hindrance to flow behavior. From the hydrodynamic perspective, the sutureless prosthesis may present an advance in the evolution of bioprostheses, ensuring low gradients and potential for low incidence of patient-prosthesis mismatch even in small annuli.

Hydrodynamic optimisation of small arrays of heaving point absorbers

This paper describes the optimisation of arrays of wave energy converters (WECs) of point absorber type. The WECs are spherical in shape and operate in heave only. Arrays of five to seven devices are considered. To simplify the optimisation, the arrays are constrained to lie in a specified geometry, namely a straight line or a circle, thereby reducing the number of array variables. The array layout is optimised from a hydrodynamic perspective with respect to the spacing or angles between the devices. Following the work of McGuinness and Thomas (Eleventh European Wave and Tidal Energy Conference. Nantes, France, 2015), the objective function of the optimisation is taken to be the mean of the interaction factor, rather than the interaction factor itself. This mean is defined over a non-dimensional length measure of the array. This is motivated by the desire to produce arrays that are stable to changes in the incident wavelength. A more general optimisation is performed here than in McGuinness and Thomas (Eleventh European Wave and Tidal Energy Conference. Nantes, France, 2015), with no prescribed symmetry in the arrays. The behaviour of the optimal arrays is analysed with respect to performance and device motions. Closely spaced groups of devices are found to exist in some of the optimal arrays; the implications of this and the possibility of replacing these groups with larger devices are discussed. For circular arrays, it is shown that the inclusion of a further device at the circle centre tends to alter the overall performance of the array. Most optimal circular arrays formed a semi-circular pattern dependent on the incident wave direction. For all array geometries considered, it is seen that the incident wave angle has a large impact on the optimal layout and the overall performance.

Simulation of Water Quality under Different Reservoir Regulation Scenarios in the Tidal River

Reservoir regulation is one of the effective ways to improve water quality. However, when water quality requirement is considered, reservoir operation is complicated due to tidal regimes in the tidal rivers. The study was carried out in the tidal river reach between Dongjiang Hydro-Project and Shilong in Dongjiang River. To evaluate the effect of reservoir regulation on water quality, a two-dimensional hydrodynamic model combined with water quality has been developed. Under the scenarios of differrent flood discharge from the Shima River and different release discharge of Dongjiang Hydro-Project, water quality is simulated using the two-dimensional model. NH3-N and COD concentrations are taken as the major indicators for water quality. Results indicate that (1) water quality is related to the tidal fluctuation, NH3-N and COD concentrations increase at flood tide and decrease at ebb tide; (2) There is no obvious over-limit of COD concentration, NH3-N concentration is found as the main pollution impacts water quality at water intake; (3) flood discharge from Shima River flows back to the upper reach of water intake during higher high tidal period, NH3-N concentration non-compliance occurs, flood tide is the main factor which impacts water quality; (4) reservoir regulation of Dongjiang Hydro-Project causes a significant improvement on water quality, release discharge of Dongjiang Hydro-Project is determined to insure the water supply safety, which keeps tidal-induced backwater always flowing to lower reach of the water intake. The study provides a hydrodynamic perspective on water quality improvement due to reservoir regulation in the tidal river.

Gas and stellar spiral structures in tidally perturbed disc galaxies

Tidal interactions between disc galaxies and low mass companions are an established method for generating galactic spiral features. In this work we present a study of the structure and dynamics of spiral arms driven in interactions between disc galaxies and perturbing companions in 3-D N-body/smoothed hydrodynamical numerical simulations. Our specific aims are to characterize any differences between structures formed in the gas and stars from a purely hydrodynamical and gravitational perspective, and to find a limiting case for spiral structure generation. Through analysis of a number of different interacting cases, we find that there is very little difference between arm morphology, pitch angles and pattern speeds between the two media. The main differences are a minor offset between gas and stellar arms, clear spurring features in gaseous arms, and different radial migration of material in the stronger interacting cases. We investigate the minimum mass of a companion required to drive spiral structure in a galactic disc, finding the limiting spiral generation cases with companion masses of the order $1\times10^9M_\odot$, equivalent to only 4% of the stellar disc mass, or 0.5% of the total galactic mass of a Milky Way analogue.

Notes on Anomaly Induced Transport

Chiral anomalies give rise to dissipationless transport phenomena such as the chiral magnetic and vortical effects. In these notes I review the theory from a quantum field theoretic, hydrodynamic and holographic perspective. A physical interpretation of the otherwise somewhat obscure concepts of consistent and covariant anomalies will be given. Vanishing of the CME in strict equilibrium will be connected to the boundary conditions in momentum space imposed by the regularization. The role of the gravitational anomaly will be explained. That it contributes to transport in an unexpectedly low order in the derivative expansion can be easiest understood via holography. Anomalous transport is supposed to play also a key role in understanding the electronics of advanced materials, the Dirac- and Weyl (semi)metals. Anomaly related phenomena such as negative magnetoresistivity, anomalous Hall effect, thermal anomalous Hall effect and Fermi arcs can be understood via anomalous transport. Finally I briefly review a holographic model of Weyl semimetal which allows to infer a new phenomenon related to the gravitational anomaly: the presence of odd viscosity.

A novel heat transfer switch using the yield stress

We explore the feasibility of a novel method for the regulation of heat transfer across a cavity, by using a controllable yield stress in order to suppress the convective heat transfer. Practically, this type of control can be actuated with electro-rheological or magneto-rheological fluids. We demonstrate that above a given critical yield stress value only static steady regimes are possible, i.e. a purely conductive unyielded fluid fills the cavity. We show that this limit is governed by a balance of yield stress and buoyancy stresses, here described by $B$. With proper formulation the critical state can be described as a function of the domain geometry, and is independent of other dimensionless flow parameters (Rayleigh number, $\mathit{Ra}$, and Prandtl number, $\mathit{Pr}$). On the theoretical side, we examine the conditional stability of the static regime. We derive conservative conditions on disturbance energy to ensure that perturbations from a static regime decay to zero. Assuming stability, we show that the kinetic energy of the perturbed field decays to zero in a finite time, and give estimates for the stopping time, $t_{0}$. This allows us to predict the response of the system in suppressing advective heat transfer. The unconditional stability is also considered for the first time, illustrating the role of yield stress. We focus on the hydrodynamic characteristics of Bingham fluids in transition between conductive and convective limits. We use computational simulations to resolve the Navier–Stokes and energy equations for different yield stresses, and for different imposed controls. We show that depending on the initial conditions, a yield stress less than the critical value can result in temporary arrest of the flow. The temperature then develops conductively until the fluid yields and the flow restarts. We provide estimates of the hydrodynamic timescales of the problem and examples of flow transitions. In total, the theoretical and computational results establish that this methodology is feasible as a control, at least from a hydrodynamic perspective.

Hydrodynamic consideration of the finite size effect on the self-diffusion coefficient in a periodic rectangular parallelepiped system.

In the present study, we use molecular dynamics (MD) simulations to provide an insight into the system size effect on the self-diffusion coefficient of liquids in the periodic rectangular parallelepiped system, from the hydrodynamic perspective. We have previously shown that in the rectangular box system, the diffusivity exhibits anomalous behaviors, i.e., the diffusion tensor appears to be anisotropic despite the bulk liquid simulation and the diffusion component in the direction along the short side of rectangular box with a high aspect ratio exceeding the diffusivity in the infinite system [Kikugawa et al., J.Chem. Phys. 142, 024503 (2015)]. So far, the size effect on the diffusivity has been intensively studied in the cubic system and has been interpreted quite well by the theoretical considerations employing the hydrodynamic interaction. Here, we have extended the hydrodynamic theory to be applied to periodic rectangular box systems and compared the theoretical predictions with MD simulation results. As a result, the diffusivity predicted by the hydrodynamic theory shows good agreement with the MD results. In addition, the system size effect was examined in a rod-shaped rectangular box in which the two shorter side lengths were equivalent and a film-type rectangular box in which the two longer side lengths were equivalent. It is of interest that we found that the aspect ratio, at which the diffusivity coincides with that in the infinite system, is a universal constant independent of the cross-sectional area for the rod system or the thickness for the film system. By extracting the universal structure in the hydrodynamic description, we also suggested a simplified approximate model to accurately predict the size effect on the diffusivity over a practical range of aspect ratios.