Point Sink Research Articles

Wave energy capture by an omnidirectional point sink oscillating water column system

The Oscillating Water Column (OWC) is one of the most popular Wave Energy Convertor (WEC) technologies, but the energy conversion efficiency is still very low and is a bottleneck to limit its application and commercialization. A novel OWC system comprising of a cylindrical OWC WEC and a parabolic wave reflector was proposed and a revolutionary breakthrough in the hydrodynamic efficiency was obtained. To further validate this new concept, three independent model domain scenarios are developed using the open-source computational fluid dynamics software OpenFOAM. The first simulation model investigates the hydrodynamic efficiency of the OWC in open sea conditions and the second scenario investigates the performance of the OWC when it is located adjacent to a solid, vertical wall which is orientated perpendicularly to the incident wave direction. The third model consists of a vertical wall with a parabolic opening in plan view and the OWC is located at the parabolic focal point. This novel system combines the directionally independent wave energy capture of a cylindrical OWC WEC with the particular energy focussing attribute of a parabolic reflector. The hydrodynamic efficiency performances are compared among the three cases. The hydrodynamic efficiency in the case of the OWC located adjacent to the straight solid breakwater is approximately 200% more efficient than the open seas condition. However, the hydrodynamic efficiency in the case of the OWC located at the parabolic breakwater focal point greatly outperforms the other cases and a hydrodynamic efficiency increment in the order of 650% is realized compared to the open seas condition. These findings have considerable significance for the future application of ocean wave energy convertors and their use as a viable and sustainable technology to meet the world’s energy requirements.

Group Analysis of the Plane Steady Vortex Submodel of Ideal Gas with Varying Entropy

The submodel of ideal gas motion being invariant with respect to the time translation and the space translation by one direct has 4 integrals in the case of vortex flows with the varying entropy. The system of nonlinear differential equations of the third order with one arbitrary element was obtained for a stream function and a specific volume. This element contains from the state equation and arbitrary functions of the integrals. The equivalent transformations were found for arbitrary element. The problem of the group classification was solved when admitted algebra was expanded for 8 cases of arbitrary element. The optimal systems of dissimilar subalgebras were obtained for the Lie algebras from the group classification. The example of the invariant vortex motion from the point source or sink was done. The regular partial invariant submodel was considered for the 2-dimensional subalgebra. It describes the turn of a vortex flow in the strip and on the plane with asymptotes for the stream line.

Production Data Analysis and Practical Applications in the Sulige Tight Gas Reservoir, Ordos Basin, China

Successful exploitation of tight sandstone gas is one of the important means to ensure the “increasing reserves and production” of the oil and gas initiative and also one of the important ways to ensure national energy security. To further improve the accuracy of historical matching of field data such as gas production and bottom-hole pressure during the production process of this type of gas reservoir, in this study, a new expression of wellbore pressure for the uniform flow of vertical fractured wells in Laplace space based on the point sink function model of vertical fractures in tight sandstone gas reservoirs is constructed. This innovation is based on a typical production data analysis plot of the Blasingame type that uses the numerical inversion decoupling mathematical equation. After analyzing the pressure and pressure derivative characteristics of each flow stage in the typical curves, a new technique of type-curve matching was proposed. In order to verify the correctness of the model and the application value of the field, based on the previous production data of Sulige Gas Field in China, a new set of production data diagnostic chart of tight sandstone gas reservoir was formed. A case analysis showed that the application of the production data analysis method and data diagnosis plot in the field accurately evaluated the development effect of the tight sandstone gas reservoirs, clarified the scale of effective sand bodies, and provided technical support for optimizing and improving the well pattern and realizing the efficient development of gas fields.

Solution of diffusivity equations with local sources/sinks and surrogate modeling using weak form Theory-guided Neural Network

Neural-network-based surrogate models are widely used to improve computational efficiency. Incorporating theoretical guidance into data-driven neural networks has improved their generalizability and accuracy. However, neural networks with strong form (partial differential equations) theoretical guidance have limited performance when strong discontinuity exists in the solution spaces, such as pressure discontinuity at sources/sinks in subsurface flow problems. In this study, we take advantage of weak form formulation and domain decomposition to deal with such difficulties. We propose two strategies based on our previously developed weak form Theory-guided Neural Network (TgNN-wf) to solve diffusivity equations with point sinks of either Dirichlet or Neumann type. Surrogate models are trained for well placement optimization and uncertainty analysis. Good agreement with numerical results is observed at lower computational costs, whereas strong form TgNN fails to provide satisfactory results, indicating the superiority of weak form formulation when solving discontinuous problems.

Sustainable Investing: A New Paradigm (Scene 2)

Gil is pulling on a baseball cap, trying to cover up the fact that he has not showered today. He signs into the Zoom call with Sydney and Eli for their Friday afternoon virtual social hour and to continue last week's discussion about sustainable investing. As he joins, Sydney is talking to Eli. Sydney: . . . so, yeah, even with shot number two done, I will still wear a mask. Oh, here's Gil (pauses, with a smirk)—nice hat, Gil. Gil: (ignoring the wisecrack) Wait—you already got both shots? How do you feel? Sydney: Okay, I guess. I'm just glad to be on a path to, hopefully, putting this behind me. (Changing the subject) Did you guys learn anything about ESG? Eli: I did. So, I was supposed to learn about E, the environmental aspects of ESG. Here—I'll share my screen. Eli fiddles with his computer and after a couple of tries, succeeds in sharing a slide presentation. Eli: (flashing a few slides) As we know, ESG stands for Environmental, Social, and Governance. It's a new focus of investors who believe a good ESG track record indicates a better investment. Gil: (inquisitively) Sure, but what does the environment have to do with sustainable investing and how does that relate to our work at the utility? Eli: (flipping to the next slide) Great lead-in, Gil. The E element includes things like water and climate change. For many investments, water availability, drought, and climate change are risk factors. In our jobs we address these risks, like our watershed protection program or drought response plans. Those plans help make us less risky to investors. Sydney: So, are we good on E? Eli: (looking upward with a head tilt) I think we're okay. But we can probably do more—especially communication and measurement to show how our work maintains continuity of operations. Gil: That makes sense. If we are environmentally prepared and resilient, lenders will have greater confidence in us, and we will be less of an investment risk. Eli: (no longer sharing his screen) You got it—it helps, of course, that we are already doing many of the right things for our community. And that's where Sydney takes over—the social part, right? Sydney: That's right. Like E, there's a lot to understanding the social, or S part, of ESG. Think of it this way. We provide water to our customers and that allows everything in our society to happen—public health, fire protection, economic prosperity, education, recreation, and more. (Sydney pauses to let that point sink in, then she continues). And as we do that, we need to respond to the demographic and social realities of our community. Gil: (with Eli looking equally perplexed) What are you talking about—we just provide the water? Sydney: Actually, we do so much more. Our service area has an aging and ethnically diverse population—other communities don't. Also, some of our customers have lead service lines and now there's PFAS, too. We don't just provide water, we provide it to our community, which has its own unique social issues—including COVID-19. Eli: I see. So we need to do the work of providing water and clearly addressing the social elements of our community—just like we're addressing all the environmental elements. Sydney: Yup. So how does governance fit into this? Gil: (adjusting his cap) That is easy, and hard. The easy part is that governance is a process for decision-making, and our board and leadership team are good at that. It's hard because, for those of us in the public sector, there are governance requirements at the local, state, and federal levels. Eli: (bewildered) That's a lot of government. Gil: It is. The way I see it, we need to understand the state and federal issues and take responsible action locally. Also—and here's the connection—we need to understand how our utility governance helps address our social and environmental challenges. Sydney: (decisively) I knew it! E, S, and G are all tied together. So, what now? Eli: (exhaling) Well, I anticipated that question. I already spoke to our general manager and she'd like us to come and talk to the leadership team about ESG at their next meeting. Gil: Really? That's great! Sydney: It sure is, and Gil (Sydney grins), nix the cap for that meeting. Scene 2 fades to black as Gil, Eli, and Sydney sign off. To be continued in next month's Last Drop.

Pattern selection in reaction diffusion systems.

Turing's theory of pattern formation has been used to describe the formation of self-organized periodic patterns in many biological, chemical, and physical systems. However, the use of such models is hindered by our inability to predict, in general, which pattern is obtained from a given set of model parameters. While much is known near the onset of the spatial instability, the mechanisms underlying pattern selection and dynamics away from onset are much less understood. Here, we provide physical insight into the dynamics of these systems. We find that peaks in a Turing pattern behave as point sinks, the dynamics of which is determined by the diffusive fluxes into them. As a result, peaks move toward a periodic steady-state configuration that minimizes the mass of the diffusive species. We also show that the preferred number of peaks at the final steady state is such that this mass is minimized. Our work presents mass minimization as a potential general principle for understanding pattern formation in reaction diffusion systems far from onset.

Distribution of Electrons and Ions Near an Absorbing Spherical Body in a Nonequilibrium Plasma

The applicability of the collision kinetic model of point sinks, viz., the linearized theory of screening of the electric field produced by a charged dust particle, based on the Vlasov equations for electrons and ions in a nonequilibrium plasma, which are supplemented with collision terms in the Bhatnagar–Gross–Crook form and effective point sinks to dust particle, is analyzed. The criterion for the applicability of the collision kinetic model of point sinks is the smallness of the deviation of the electron and ion number densities near an absorbing spherical body from unperturbed values. The distributions of electron and ion number densities obtained using the collision kinetic model of point sinks and the orbit motion limited approach are compared. It is shown that the latter approach is applicable only in the low-pressure limit, and upon an increase in pressure, the Coulomb asymptotics of the potential, which is proportional to the frequency electron and ion collisions with neutral atoms (molecules), renders the orbit motion limited approach inapplicable for calculating the ion distribution. It is established that the domain of applicability of the collision kinetic model of point sinks is close to the applicability domain of the Debye–Huckel theory.

Nitrate Fate and Decadal Shift Impacted by Land Use Change and Enhanced Rural Tourism Activities in a Typical Karst Aquifer System as Revealed by Dual Nitrate Isotopes and Hydrochemistry

Nitrate pollution in oxygenated karst aquifers is common due to nitrification and anthropogenic inputs. However, the shift of nitrogen sources influenced by enhanced rural tourism activities and land use changes are not well understood. In this study, hydrochemistry and dual nitrate isotopes of water samples from a karst basin in Chongqing, southwestern China were employed to investigate the nitrate fate and its decadal change during a period of 2007–2008 and 2017–2019. The results showed that δ15N nitrate and δ18O nitrate values at the groundwater basin resurgence averaged 9 ± 3.4‰ and 2.5 ± 3.4‰, respectively, with a mean NO3 – concentration of 19.7 ± 5.4 mg/L in 2017–2019, clearly exceeding natural background levels. The dual isotope results suggested that nitrification occurred at the sampled sites. From 2007–2008 to 2017–2019, the mean δ15N nitrate values from the primary sink point and the resurgence of the underground river water samples increased by 11.4‰ and 4.8‰, respectively. A Bayesian isotopic mixing model based on the nitrate isotopes revealed that soil organic nitrogen (SON) and manure and sewage (M&S) proportions for the groundwater increased by 34% and 23%, respectively, while chemical fertilizer (CF) and atmospheric precipitation (AP) proportions decreased by 32% and 25%, respectively. These decadal changes resulted from reforestation practices and enhanced rural tourism activities in the basin, which were evidenced by the land use change. The elevated nitrogen load from the rapid development of rural tourism is likely to increase this contamination in the near future if the infrastructure cannot meet the demands. The results from this study could contribute to minimizing environmental health risks in drinking water when rural tourism activities are increasing.

General analytical solutions of groundwater flow toward multi-dimensional sources/sinks in a confined aquifer with leakage and distributed recharge

A variety of hydrogeologic conditions and parameters play roles in obtaining analytical solutions for groundwater flow in aquifers. Changes of these influencing conditions typically require finding a new solution. Therefore, it is very useful if a general approach and solution can be provided to conveniently construct the solutions corresponding to the condition changes. In this study, two general analytical solutions for multi-dimensional groundwater flow in homogeneous, confined aquifers are derived using Green’s function method for instantaneous and continuous sources/sinks. A library of analytical solutions can be readily obtained by combining the general solutions with directional solutions for a variety of hydrogeologic and geometric conditions. The aquifer can be one-, two-, or three-dimensional and vertically and horizontally finite, semi-infinite, or infinite. The geometry of sources/sinks can be point, line, areal, and volumetric. Leakage from adjacent aquifers and distributed precipitation recharge are also included. The general solutions are validated by reported analytical solutions. A series of typical solutions for one-, two-, and three-dimensional groundwater flow are presented. A computational example is provided to compare the drawdown distributions caused by point, vertical line, vertical areal, and volumetric sinks. A field investigation and design at a groundwater-contaminated site using the derived analytical solution suggests that drainage slots (vertical areal sinks) can be an effective alternative to pumping wells (vertical line sinks) in lowering the groundwater level for a shallow aquifer.

Seepage to ditches and topographic depressions in saturated and unsaturated soils

An isobar generated by a line or point sink draining a confined semi-infinite aquifer is an analytic curve, to which a steady 2-D plane or axisymmetric Darcian flow converges. This sink may represent an excavation, ditch, or wadi on Earth, or a channel on Mars. The strength of the sink controls the form of the ditch depression: for 2-D flow, the shape of the isobar varies from a zero-depth channel to a semicircle; for axisymmetric flow, depressions as flat as a disk or as deep as a hemisphere are reconstructed. In the model of axisymmetric flow, a fictitious J.R. Philip's point sink is mirrored by an infinite array of sinks and sources placed along a vertical line perpendicular to a horizontal water table. A topographic depression is kept at constant capillary pressure (water content, Kirchhoff potential). None of these singularities belongs to the real flow domain, evaporating unsaturated Gardnerian soil. Saturated flow towards a triangular, empty or partially-filled ditch is tackled by conformal mappings and the solution of Riemann's problem in a reference plane. The obtained seepage flow rate is used as a right-hand side in an ODE of a Cauchy problem, the solution of which gives the draw-up curves, i.e., the rise of the water level in an initially empty trench. HYDRUS-2D computations for flows in saturated and unsaturated soils match well the analytical solutions. The modeling results are applied to assessments of real hydrological fluxes on Earth and paleo-reconstructions of Martian hydrology-geomorphology.

Phase-field calculations of sink strength in Al, Ni, and Fe: A detailed study of elastic effects

The sink strength and bias of edge dislocations, low-angle symmetric tilt grain boundaries (STGBs), and spherical cavities are calculated for Al, Ni and Fe using a phase-field approach in this work. The interactions between point defects (PDs) and sinks are incorporated in the present model. These interactions include an elastic contribution to the total free energy of the system, and the phenomenon of elastodiffusion which is often ignored and consists in the modification of the PD migration energy due the strain field generated by the sink. Specific spatial schemes and new algorithms have been developed and applied to perform the calculations due to the PD diffusion which becomes anisotropic and spatial dependent when elastodiffusion is taken into account. The results obtained show that the solution of Rauh and Simon systematically underestimates the sink strength of edge dislocations, especially for dumbells in Ni and Fe. STGBs with low misorientation angle and high density are biased sinks when elasticity (with and without elastodiffusion) is taken into account. It is also shown that taking into account the PD anisotropy at saddle point when the elastodiffusion is considered leads to a significant bias (>10%) of the cavity, which thus highlights the importance of the PD anisotropy at saddle point on the sink strength and bias calculations.

Extraction of density-layered fluid from a porous medium

We consider axisymmetric flow towards a point sink from a stratified fluid in a vertically confined aquifer. We present two approaches to solve the equations of flow for the linear density gradient case. Firstly, a series method results in an eigenfunction expansion in Whittaker functions. The second method is a simple finite difference method. Comparison of the two methods verifies the finite difference method is accurate, so that more complicated nonlinear, density stratification can be considered. Such nonlinear profiles cannot be considered with the eigenfunction approach. Interesting results for the case where the density stratification changes from linear to almost two-layer are presented, showing that in the nonlinear case there are certain values of flow rate for which a steady solution does not occur.

Experimental and modeling investigations of dropwise condensation out of convective humid air flow

In this work, experimental and modeling investigations of convective dropwise condensation from moist air are carried out for the mechanistic understanding of the influence of non-condensable gas. For modeling, different droplet growth models in the presence of non-condensable gas are firstly developed by treating the droplet as an isolated form. During dropwise condensation, the presence of non-condensable gas brings some specific condensation characteristics, including the interaction effect between droplets and convection mass transfer. However, those characteristics cannot be reasonably captured by the droplet growth model. In this work, the distributed point sink method and the droplet Sherwood number are used to evaluate the inter-droplet interaction and convection mass transfer, respectively. Combining those progresses, the droplet growth rate is predicted and the prediction is evaluated by the measurements. Based on the accurate prediction for the droplet condensation rate, a semi-analytical modeling method is released to predict convective dropwise condensation of moist air. It considers the latent heat by condensation and the sensible heat by forced convection. Finally, this work presents the direct comparisons of the overall heat flux measured in experiments and the prediction. Furthermore, mechanistic understanding is discussed simultaneously and conclusively. Throughout this work, we highlight the reduction (the diffusion resistance of water vapor and the inter-droplet interaction) and enhancement (convection mass transfer) factors for dropwise condensation in the presence of non-condensable gas. In addition, in the case of this work, large droplets are more beneficial for heat transfer of dropwise condensation.

Semi-analytical solution to one-dimensional consolidation of viscoelastic saturated soils subject to an inner point sink

PurposeThe purpose of this paper is to present a semi-analytical solution to one-dimensional (1D) consolidation induced by a constant inner point sink in viscoelastic saturated soils.Design/methodology/approachBased on the Kelvin–Voigt constitutive law and 1D consolidation equation of saturated soils subject to an inner sink, the analytical solutions of the effective stress, the pore pressure and the surface settlement in Laplace domain were derived by using Laplace transform. Then, the semi-analytical solutions of the pore pressure and the surface settlement in physical domain were obtained by implementing Laplace numerical inversion via Crump method.FindingsAs for the case of linear elasticity, it is shown that the simplified form of the presented solution in this study is the same as the available analytical solution in the literature. This to some degree depicts that the proposed solution in this paper is reliable. Finally, parameter studies were conducted to investigate the effects of the relevant parameters on the consolidation settlement of saturated soils. The presented solution and method are of great benefit to provide deep insights into the 1D consolidation behavior of viscoelastic saturated soils.Originality/valueThe presented solution and method are of great benefit to provide deep insights into the 1D consolidation behavior of viscoelastic saturated soils. Consolidation behavior of viscoelastic saturated soils could be reasonably predicted by using the proposed solution with considering variations of both flux and depth because of inner point sink.

A Systematic Upscaling of Nonlinear Chemical Uptake Within a Biofilm

When modeling transport of a chemical species to a colony of bacteria in a biofilm, it is computationally expensive to treat each bacterium even as a point sink, let alone to capture the finite nat...

Dynamic Multi Constraint Routing Based Efficient Data Transmission in MANET for Improved Sink Point Streaming

The mobile adhoc network (Manet) has been identified as keen networking scenario in modern internet world. The most networking solutions have been enabled to access through mobile devices. The physical characteristics of mobile nodes keep changing the topology of network at each second. However, achieving higher streaming performance is most important in point of quality of service. There exist numerous techniques to route data packets between the source and sink/destination nodes, but suffer with poor performance. To overcome the deficiency, a dynamic multi constraint routing algorithm has been presented in this paper. The method considers different parameters like energy, lifetime, traffic, mobility speed, direction and hop count in route selection. According to the above mentioned parameters, the multi constraint algorithm estimates streaming support score (SSS) for any route to perform routing of packets. The algorithm improved routing performance of routing and increases the streaming rate in Manet.

A Survey on Efficient Transmission and Routing for Improved Sink Point Streaming in MANET

A Survey on Efficient Transmission and Routing for Improved Sink Point Streaming in MANET

Dynamic Multi Constraint Routing Based Efficient Data Transmission in Manet for Improved Sink Point Streaming

The mobile adhoc network (Manet) has been identified as keen networking scenario in modern internet world. The most networking solutions have been enabled to access through mobile devices. The physical characteristics of mobile nodes keep changing the topology of network at each second. However, achieving higher streaming performance is most important in point of quality of service. There exist numerous techniques to route data packets between the source and sink/destination nodes, but suffer with poor performance. To overcome the deficiency, a dynamic multi constraint routing algorithm has been presented in this paper. The method considers different parameters like energy, lifetime, traffic, mobility speed, direction and hop count in route selection. According to the above mentioned parameters, the multi constraint algorithm estimates streaming support score (SSS) for any route to perform routing of packets. The algorithm improved routing performance of routing and increases the streaming rate in Manet.

Analytical solution of capture time to a partially penetrating well in a semi-infinite aquifer

Calculating the capture time of contaminant to a well is important in the context of both groundwater protection and aquifer remediation. Although partially penetrating wells are much more commonly used than fully penetrating wells, there is no analytical solution for capture time calculations, probably due to the challenges of mathematically modeling such types of wells. In this study, an analytical solution of capture time was developed, based on the assumption that a partially penetrating well was installed in a homogeneous and semi-infinite aquifer. For an example case, the capture time result by the analytical solution fitted well with result by a high-resolution particle tracking method established according to the fourth-order Runge-Kutta algorithm. The impacts of different parameters are analyzed, and results indicate that the effects of both screen length L and anisotropic ratio a2 on capture time T are spatially dependent. Such comparisons also demonstrate that the influence of the lower boundary is stronger as penetration increases. In the end we compare the analytical solution for a line sink with that for a point sink, and demonstrate that larger differences occur near the wellbore, however, at a sufficiently large distance from the wellbore, the capture time distributions become the same for both source types.

A fractional diffusion equation with sink term

Approaching dynamical aspects in systems with localised sink term is fundamentally relevant from the physical-experimental point of view. However, theoretical advances have not progressed much in this direction; this is due to the great difficulty of addressing such types of problems from an analytic point of view. In this work, we investigate the systems sink points (like traps) considering a dynamics governed by the like reaction–diffusion equation in the presence of fractional derivatives. In order to do so, making use of the continuous-time random walks theory we constructed a model that contains multiples sink terms, on sequence we analysed the problem for two cases: first, considering only a single sink term and, second, considering multiples sink point associated with a fractal set. In both cases, we present the analytic solution in terms of Fox and Mittag–Leffler functions. Moreover, we perform a calculus of the mean square displacement and survival probability. The proposal and the techniques used in this work are useful to describe anomalous diffusive phenomena and the transport of particles in irregular media.