Porous Barrier Research Articles

Status, Trends, and Drivers of Harmful Algal Blooms Along the Freshwater-to-Marine Gradient in the San Francisco Bay–Delta System

Harmful algal blooms (HABs) are on the rise worldwide. Known drivers for the proliferation and intensification of HAB events include increasing nutrient pollution, climate change, regulation and modification of hydrological flow, and the combined effect of climate drivers and nutrient pollution. The San Francisco Bay–Delta system has largely been immune to severe or acute HAB events, but there is both a potential and realized threat which has been underestimated and under-reported, in part because of the lack of coordinated sampling and data reporting. There is also increasing evidence that HABs must be considered in the context of a freshwater-to-marine continuum, and that the physical and political boundaries separating components of the Bay–Delta system are porous barriers to HABs and their toxins. Much remains to be learned about the ecology and physiology of HAB organisms in this system, but five primary environmental drivers can be identified: temperature, salinity, irradiance, nutrients, and stratification/residence time. All these drivers are responding rapidly to climate change, but nutrients are the primary variable that is largely under human control. Plans for the development of a comprehensive monitoring, prediction, and mitigation strategy across the freshwater-to-marine continuum have been documented; effectively following through on these plans provides a roadmap toward identifying the drivers and threats—and reducing the potential consequences now and in the future. While HABs alone are not a sufficient motivator for potentially costly and extensive mitigation efforts, there is strong evidence that decreasing nutrient loads, maintaining hydrological connectivity while minimizing stagnant regions, and managing the biota to maintain biodiversity of the Bay–Delta system will result in multiple co-benefits, including reduction of the HAB threat potential.

A 'print-pause-print' protocol for 3D printing microfluidics using multimaterial stereolithography.

Methods to make microfluidic chips using 3D printers have attracted much attention because these simple procedures allow rapid fabrication of ready-to-use products from digital 3D designs with minimal human intervention. Printing high-resolution chips that are simultaneously transparent, biocompatible and contain regions of dissimilar materials is an ongoing challenge. Transparency allows for the optical inspection of specimens containing cells and labeled biomolecules inside the chip. Being able to use different materials for different layers in the product increases the number of potential applications. In this 'print-pause-print' protocol, we describe detailed strategies for fabricating transparent biomicrofluidic devices and multimaterial chips using stereolithographic 3D printing. To print transparent biomicrofluidic chips, we developed a transparent resin based on poly(ethylene glycol) diacrylate (PEG-DA) (average molecular weight: 250 g/mol, PEG-DA-250) and a smooth chip surface technique achieved using glass. Cells can be successfully cultured and visualized on PEG-DA-250 prints and inside PEG-DA-250 microchannels. The multimaterial potential of the technique is exemplified using a molecular diffusion device that comprises parts made of two different materials: the channel walls, which are water impermeable, and a porous barrier structure, which is permeable to small molecules that diffuse through it. The two materials were prepared from two different molecular-weight PEG-DA-based printing resins. Alignment of the two dissimilar material structures is performed automatically by the printer during the printing process, which only requires a simple pause step to exchange the resins. The procedure takes less than 1 h and can facilitate chip-based applications including biomolecule analysis, cell biology, organ-on-a-chip and tissue engineering.

Water wave interaction with a circular arc shaped porous barrier submerged in a water of finite depth

Water wave interaction with a circular arc shaped porous barrier submerged in a water of finite depth

Solitary wave interaction with upright thin porous barriers

The interaction of fluid flow with porous barriers has numerous practical applications, including as a partial barrier to water waves that damp some of the approaching energy at the same time as allowing environmental flow. However, surprisingly little effort has been expended on understanding the fundamentals of this interaction. Therefore, this study aims to model the interaction between waves and thin, upright porous barriers. This is undertaken by modelling the porous barrier empirically within a Smoothed Particle Hydrodynamics (SPH) framework that is then used to model wave flume experiments. Although detailed modelling of the interaction is possible at the laboratory scale, it is not feasible in practical settings where a barrier will contain many thousands of holes that cannot be individually modelled. The key information needed to model the barrier empirically is obtained from solitary wave-porous barrier interaction experiments. Our results indicate that, for each barrier, irrespective of the properties of the wave interacting with it, there is a coefficient value that is able to account adequately for the energy dissipation by the barrier. The reliability of the approach has been demonstrated by comparing SPH model predictions against companion sinusoidal wave-porous barrier experimental measurements. The SPH model was then used to determine the energy dissipation characteristics of porous barriers kept at different draught to water depth ratio, D/d, without reference to the wave flume experiments. Simulation results indicate that barriers are more effective in dissipating the incident wave energy if its draught is over 75% of the water depth.

Plasma spraying porous thermal barrier coatings with high deposition efficiency: A solvable dilemma?

In addition to the selection of suitable materials, another way to lower the thermal conductivity and improve thermal cyclic performance of ceramic thermal barrier coatings is to produce microstructures with high porosity reaching up to 20 vol%, sometimes even more. The way to achieve this is by selecting suitable process parameters for plasma spraying, e.g. a low plasma enthalpy or a large spraying distance. The choice of the powder feedstock also plays a role. This attempts to melt the powder particles only partially, so that voids are not completely filled between the deposited splats. Hereby, the desired porosity is formed in the layer. Naturally, however, this is typically associated with losses in deposition efficiency. This dilemma is difficult to solve.In this work, spraying experiments were performed in which several process parameters were varied. An argon‑hydrogen mixture was used as plasma gas for the cascaded three-cathode torch. Porosities were obtained by image analysis and, for some samples, also by mercury intrusion; deposition efficiencies were determined gravimetrically. The resulting porosities and deposition efficiencies were combined in an evaluation function to compare different process parameters with respect to their effects on these two target parameters. The results show that the dilemma of optimizing porosity and deposition efficiencies simultaneously could only be solved well to a limited extent. This makes a systematic approach all the more important in order to identify optimum parameter sets within the bounds of what is possible.

Gravity wave scattering by retrofitted circular breakwaters using dual boundary integral formulation

In the present study, the gravity wave scattering by circular edged breakwaters in the presence of retrofits is analysed within the framework of linearized water wave theory. Various types of retrofits (say, porous shield) such as quarter-circular retrofit, semi-rectangular retrofit, semi-circular retrofit, and rectangular retrofit are investigated to protect the newly developed or existing circular breakwaters from the incident wave stroke. A dual boundary integral formulation is used to solve the boundary value problem considering the quadratic pressure drop boundary condition for the waves past the thin porous barriers. A generalized computer code is developed to accommodate the domain changes and is validated with the known results available in the literature. Various results such as the scattering coefficients (wave reflection, transmission and wave energy loss) and force coefficients (vertical and horizontal force on the breakwater and retrofit) are computed as a function of non-dimensional wave number and discussed. The sharp-edged retrofits (rectangular and semi-rectangular) display a considerable reduction of wave transmission as compared with smooth-edged retrofits, and the semi-circular breakwater with rectangular retrofit is suggested for further development of the porous structures. The effect of porous shield alone, breakwater alone, both breakwater and shield on incident wave energy distribution is also reported. The minimal wave transmission and higher wave damping coefficients attended occurred by the proposed breakwaters are identified when the shield porosity varies within 0.1≤μ≤0.2.

Water wave interaction with dual unequal horizontal flexible porous barriers using integral equations

ABSTRACT Under the assumption of linear wave theory, this work investigates the interaction of surface gravity waves with two asymmetric horizontal flexible porous barriers. Three types of barriers are considered, namely, (i) step barriers, (ii) partially overlapped barriers and (iii) fully overlapped barriers. Green's integral theorem and the boundary condition on the barriers are utilised to produce four integral equations for functions related to potential difference and normal velocity of fluid across the barriers which are solved numerically by an expansion-collocation method. As a result, the role of asymmetric flexible porous barriers with an additional comparison between dual and single horizontal flexible porous barriers is studied by analysing numerical solutions of different hydrodynamic quantities. This study shows that the upper barrier plays a major role compared to the lower one in the propagation of surface waves. The current analysis is validated by reviving previous results and utilising energy balance relationship.

Formulation, design and strategies for efficient nanotechnology-based nasal delivery systems

Abstract Objectives Nanotechnology-based nasal delivery systems have gained interest as a way of overcoming low drug bioavailability, limited brain exposure, fast metabolism and elimination, high doses and unwanted side effects. The main benefits of intranasal (IN) administration include the non-invasive method, easy accessibility, porous epithelial barrier and highly vascularized tissue. However, it is imperative to identify interactions between the materials used and the nasal biological environment to ensure proper release. Key findings We have examined principal factors in nasal administration, such as physiological aspects of the nose, drug and biopharmaceutical properties, formulation properties and nasal devices for drug delivery. Summary This review highlights new insights into different nanotechnology-based approaches for IN use and focuses on recent developments in topical nasal DDS, outlining the advantages and limitations of each system. This article confines itself to research and novel concepts and the different strategies developed to increase bioavailability, safety and a route to brain delivery.

Wave trapping due to composite pile-rock structure coupled with vertical barrier

The wave transformation due to pile-rock porous structure in combination with vertical porous barrier is studied under oblique wave action. The pile-rock breakwaters consists of two rows of closely spaced piles and a rock core between them is effective in dissipating wave energy when compared with traditional rigid breakwaters due to its reduced deadweight of construction materials and additional stability. Three different cases of the vertical barrier configurations such as fully-extended barrier, bottom-standing barrier and surface-piercing barrier placed in front of the pile-rock porous structure are considered for the investigation. The numerical study is performed using the eigenfunction expansion and the associated orthogonal mode-coupling relations considering the continuity of pressure and velocity for the vertical barrier, seaward and leeward structural interfaces. The Darcy’s law is incorporated for the flow through porous media and the porosity factor of the structure is introduced using the complex porous effect parameter. The numerical results for the wave reflection, transmission and dissipation coefficient, wave force on front and rear side of porous structure along with the wave force on the barrier interface are evaluated for different hydraulic characteristics. The analysis is presented for varying structural porosity, angle of incidence, structural thickness, friction factor, length between vertical barrier and porous structure for the three different cconfigurations of vertical barrier. The numerical investigation performed in the present study will be useful for the design and analysis of the composite breakwater system to protect the offshore facility from high waves.

A renewable energy harvesting wind barrier based on coaxial contrarotation for self-powered applications on railways

As high-speed and light trains develop, they will become more sensitive to crosswinds. Since strong crosswinds tend to occur in remote areas where power supply is difficult, converting wind energy into electricity to power the devices along the railway will be an effective solution. In this paper, an energy harvesting wind barrier (EHWB) based on coaxial contrarotation is designed to reduce crosswinds and generate electricity for self-powered applications on railways. The proposed EHWB consists of four parts: 1) a porous wind barrier; 2) coaxial contrarotating (CCR) wind turbines; 3) a generator module; and 4) an energy storage module. First, the porous wind barrier installed on both sides of the railway provides a sheltering effect for trains. Second, two CCR wind turbines are installed in the through-hole of the wind barrier to harvest wind energy. Then, the generator module converts wind energy into electrical energy by coils and magnets mounted separately with the wind turbines. Finally, the generated electricity is stored in supercapacitors through slip rings. The experiments show that an average output power of 0.8 W can be obtained by one EHWB unit, indicating that the proposed system has good performance and enormous potential for power generation and self-power applications.

Development and Characterisation of thick non-conventional yttria stabilised zirconia thermal barrier coating systems on aluminium and superalloys by sol-gel synthesised single unit dip-coating

ABSTRACT In the present paper, the two routes of preparation of seven weight% yttria stabilised zirconia (7YSZ) composite sols are proposed under optimised conditions. Sol of route-I was made from zirconium (IV) propoxide, yttrium nitrate hexahydrate-acetylaceone-water-1-propanol solvent, and sol of route-II was made from zirconium (IV) propoxide, yttrium nitrate hexahydrate-acetylacetone-sulphuric-acid-water-1-propanol solvent-2weight% polyvinyl alcohol (2PVA). After preparation of both sol, thermal behaviour was characterised using thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for checking the weight loss with respect to high temperature. Route-II YSZ sol-gel survived with practically no mass loss, while route-I had extensive degradation as well as considerable mass loss. In the second stages, both the sols were deposited onto as-air plasma sprayed CoNiCrAlY bond-coated substrates, i.e. superalloys IN800 and aluminium alloys AA2024-T351. The microstructure of route-I and route-II YSZ sol coating was characterised using scanning electron microscopy. Route-II deposited sol was found to be more porous, homogenised and thick thermal barrier coatings as compared to route-I sol. The presence of sulphuric acid enhanced the better processing control of sol-gel coatings with uniform surface, as confirmed by atomic force microscopy (AFM).

Semi-empirical modelling of hydraulic conductivity of clayey soils exposed to deionized and saline environments

Clay liners are widely used as porous membrane barriers to control solute transport and to prevent the leakage of leachate both in horizontal and vertical flow scenarios, such as the isolated base and ramps of sanitary landfills. Despite the primary importance of saturated hydraulic conductivity in a reliable simulation of fluid flow through clay barriers, there is no model to predict hydraulic conductivity of clayey soils permeated with saline aqueous solutions because most of the current models were developed for pure water. Therefore, the main motivation behind this study is to derive semi-empirical models for simulating the hydraulic conductivity of clayey soils in the presence of arbitrary solute concentrations in addition to deionized water. In order to achieve this goal, a relatively comprehensive dataset of 842 measured hydraulic conductivities was retrieved from the experimental literature, where almost 44% of them are related to certain solute concentrations. Afterwards, two modelling approaches were introduced; the first one is a modified form of Mbonimpa et al.'s (2002) model, in which the constants are adjusted to take into consideration the variations in liquid limit due to a change in solute concentration. A modification term was added to the model for the sake of accuracy. In the second approach, a new form of solute concentration-dependent hydraulic conductivity function was proposed, where special attention was given to void ratio and adaptive liquid limit as effective parameters. The results revealed that hydraulic conductivity predictions could be erroneous if the influence of solute concentrations in permeating fluid is ignored. An error analysis was conducted to examine the models' applicability and deviations. A blind independent set of data, including 132 data points, was also used to verify models. On the other hand, both newly proposed models could predict the hydraulic conductivity for a variety of soils, salt species, and concentrations well. Therefore, the proposed modelling approaches are somehow unique by considering the salinity of the pore fluid in addition to deionized water. More importantly, both models are comprised of easy-to-measure parameters with clear physics-based implications.

Seabed influence on wave scattering by a porous flexible barrier in a two-layer oblique sea

Seabed influence on wave scattering by a porous flexible barrier in a two-layer oblique sea

Simulation strategies for wind shields and porous barriers for bridge deck optimization

Wind shields and porous barriers are often positioned on bridge decks as ancillary structures. While being irrelevant from the structural point of view, it is well-known that their presence can deeply affect the deck aerodynamic performance. In particular, not only do they generally lead to an increase of the drag force, but also they modify the overall flow arrangement, so affecting all aerodynamic coefficients. In this paper, the numerical simulation of porous elements positioned on bridge sections is addressed following two approaches: in the first one, the pores are explicitly modeled, while in the second one a more convenient pressure-jump approach is adopted. In particular, the second approach has strong advantages compared to the first one, especially when simulations are used for optimization. The results obtained using these approaches are compared with each other and experimental measurements, highlighting strengths and limitations of both methodologies.

Porous thermal barrier coatings for enhancing the efficiency of internal combustion engines

Internal combustion engines have a key role in the social and economic advancement of modern society but also a significant contribution to greenhouse gas emissions. For these engines, to preserve their role, a higher efficiency, that dramatically reduces the environmental impact, is necessary. To achieve increased engine efficiency, a technical solution is to lower the heat losses in the combustion chamber. Among them, the heat losses to the pistons are the preferential route, due to their extensive impact on fuel consumption. In this paper, porous thermal barrier coatings with large pores were applied to the pistons of diesel engines to improve engine efficiency. Atmospheric Plasma Spray (APS) process and porosity former TBC feedstock were employed to obtain high porosity coatings with large pores. Scanning Electron Microscopy (SEM) was utilized to investigate the microstructure of the coating in coupons and pistons. The optical properties of the coatings were explored with two methods: the spectral normal hemispherical reflectivity at room temperature (SNHRRT) and spectral normal emissivity at high temperature (SNEHT). The coatings’ behavior under thermal cyclic conditions was assessed by Flame Rig Test. Microstructure analysis was also performed before and after the test to identify the failure mechanisms. The engine efficiency was evaluated by measuring the Indicated Specific Fuel Consumption (ISFC) in a single-cylinder engine test. The results showed that porous coating with large pores combined with a higher emissivity can withstand the engine environment well and have the potential to provide enhancements in engine efficiency.

Modeling of the effects of porous and solid barriers along the road from traffic emissions in idealized urban street canyons.

In this paper, numerical modeling of concentration propagation using various types of barriers and trees with porosity properties in an idealized urban canyon to protect nearby houses was considered. To solve this problem, a modification of the Reynolds-averaged Navier-Stokes equations is used to take into account the porous medium. To validate the mathematical model and the numerical algorithm, a test problem was solved without taking into account various barriers with a source of pollution. After validation, the main problem was solved, describing the emission process of pollutants between houses using different types of grass barriers and trees with different porosity properties. The numerical simulation data were compared with the calculated values using various types of grass barriers and trees. Taking into account the optimal properties of porous trees in combination with barriers, it was found that height of the barrier itself has a minor role in the spread of pollutants.

Numerical study of air pollution exposure in idealized urban street canyons: Porous and solid barriers

In this paper, it was considered the numerical modeling of concentration propagation using solid barriers and porous barriers of different heights in an idealized urban canyon to protect nearby houses. To solve this problem, a modification of the Reynolds-averaged Navier-Stokes equations was used to take into account the properties of the porous medium. To validate the mathematical model, a test problem was solved without taking into account various barriers. After validation, the main problem was solved, describing the process of pollutants emission between houses when using different types of vegetation barriers (solid and porous). All the obtained numerical results were compared with each other using different types of vegetation barriers. And the optimal porosity properties and permeability coefficient for vegetation barriers have been determined. So, from the obtained results, it can be noted that when using a solid green fence with a height of 0.1H, it was found that the concentration indicator significantly decreased compared to the results without barriers. But when comparing the indicators of the spread of the concentration with porous barriers after a height of 0.1H, a tendency to decrease in the maximum concentration is noticeable, but the average value of the concentration almost does not change.

Optimization of a porous wind barrier to reduce soiling and avoid shading losses of photovoltaic panels

This paper investigates numerically the use of a porous rock barrier for the mitigation of the Pv panel. The dust deposition behavior and its influences on the deposition rate for different particle sizes and conditions are analyzed. The CFD method was chosen to predict the dust deposition rates on the PV panel. In doing so, the discrete particle model was applied, while for the turbulent airflow, the k-ω shear stress transport turbulence model with two function profiles defined as UDF at the inlet were employed. We focused on the particle behavior and disposition rate as a function of barrier porosity and distance from the panel. The results indicate that the porosity, as well as the distance between the PV and the barrier, have a significant effect on the particle fluxes. The amount of particles deposited in the panel can be reduced by a rate of 86% for large particles, however, for small particles the reduction in the dust disposition rate is small compared to large ones, reaching 33%. The use of a porous barrier not only helped in terms of particle arrangement but also in terms of vortexes, which disappeared and consequently reduced the particles in suspension upstream of the PV panel. In this regard, we found that 50% is the optimal value.

Investigation of Oblique Flexural Gravity Wave Scattering by Two Submerged Thin Vertical Porous Barriers with Different Porosities

AbstractA hydroelastic model is developed here for studying the interaction of oblique water waves by two fully submerged thin vertical porous barriers placed some distance apart in a homogeneous f...

Mitigation of Hydroelastic Responses in a Very Large Floating Structure by a Connected Vertical Porous Flexible Barrier

The hydroelastic response of an elastic thin plate combined with a vertical porous flexible plate floating on a single- or a two-layer fluid is analyzed in the two-dimensional Cartesian coordinate system. The vertical and the horizontal plates are placed in an inverted-L shape and rigidly connected together. The problem is studied with the aid of the method of matched eigenfunction expansions within the framework of linear potential flow theory. The fluid is assumed to be inviscid and incompressible, and the motion is assumed to be irrotational. Time–harmonic incident waves of the traveling mode with a given angular frequency are considered. Then, the least-squares approximation method and the inner product are used to obtain the expansion coefficients of the velocity potentials. Graphical results show the interaction between the water waves and the structure. The effects of several physical parameters, including the length and the complex porous-effect parameter of the vertical plate, on the wave reflection and transmission are discussed. The results show that a vertical plate can effectively eliminate the hydroelastic response of the very large floating structure. The longer a vertical plate is, the more waves are reflected by the vertical plate. With the increase in the porous-effect parameter, the deflection of vertical plate decreases. Besides the effects of the flexural rigidity, the lateral stress, the mooring line angle, the fluid density ratio, and the position of interface on the wave reflection and transmission are discussed. Numerical results show the significant mitigation effect due to the presence of the additional vertical plate.