Flexible Porous Membrane Research Articles

Experimental study on the performance of an array of vertical flexible porous membrane type breakwater under regular waves

Experimental investigation on the wave reflection, transmission, and wave energy dissipation of a vertical flexible porous multi-membrane type breakwater is conducted under regular waves. Tests are carried out for a wide range of wave periods, wave heights, membrane porosities, membrane spacing settings, and a different number of membranes. The present results of reflection and transmission coefficients are compared with numerical and experimental datasets available in the literature. Further, the performance of the present vertical flexible porous membrane type breakwater is analyzed by comparing different arrangements of vertical membranes via different wave quantities. The results of the present study can be useful to optimize the design of a vertical flexible porous multi-membrane type breakwater for coastal protection schemes.

Performance of a submerged flexible membrane and a breakwater in the presence of a seawall

In the present study, the performance of a submerged flexible porous membrane placed at a finite distance away from a partially reflecting seawall is investigated. Further, the membrane is floating over a porous breakwater which is bottom-standing in nature. The associated physical problem is solved using a numerical tool based on the dual boundary element method. Various physical quantities of interests such as the reflection coefficient, run-up coefficient, horizontal wave force acting on the seawall, and the maximum deflection coefficient of the membrane are studied for a variety of membrane, breakwater, and seawall parameters. The results demonstrate that the resonating behavior of the aforementioned physical quantities diminishes with the introduction of structural porosity in the membrane wave barrier. Further, the membrane having moderate width is effective in reducing the wave run-up in the lee side of the membrane for a broader range of incident wave frequencies. Moreover, the reflection coefficient, run-up coefficient, and wall force coefficient decrease in a nonlinear manner as the wavelength of the incident waves becomes shorter. The combined flexible membrane and rubble mound breakwater system can effectively create a tranquility zone in the lee side of the membrane wave barrier.

Wave attenuation by a submerged circular porous membrane

Wave action over a submerged circular flexible porous membrane is investigated and the impact of porosity in dampening the far-field wave amplitude is examined in a scattering of incoming waves. The unknown potential for the free surface and the membrane-covered regions are obtained by coupling the respective boundary conditions and Darcy’s law for permeable structure. The associated boundary value problem is solved using the method of expansions of the eigenfunctions as Fourier-Bessel series. To understand the efficiency of the present study, wave force excitation on the circular membrane, far-field scattering wave amplitude, energy dissipation, and flow distribution are computed and examined. The study shows that on the leeward side of the membrane the wave amplitude reduces drastically. In addition, the submergence depth has a significant impact on wave energy dissipation. This model will be beneficial in developing the mechanism to minimize wave force on coastal structures for a variety of marine operations. In addition, this structure has minimal environmental effects on different coastline processes and can therefore be used in a variety of coastal/ocean applications.

A Semi-Analytical Model for Studying Hydroelastic Behaviour of a Cylindrical Net Cage under Wave Action

In the present study, a semi-analytical model based on the small-amplitude wave theory is developed to describe the wave fields around a single gravity-type cylindrical open fish net cage. The cage may be submerged to different depths below the free-water surface. The fish cage net is modelled as a flexible porous membrane, and the deflection of the net chamber is expressed by the transverse vibration equation of strings. The velocity potential is expanded in the form of the Fourier–Bessel series and the unknown coefficients in these series are determined from matching the boundary conditions and the least squares method. The number of terms for the series solution to be used is determined from convergence studies. The model results exhibit significant hydroelastic characteristics of the net cages, including the distribution properties of wave surface, pressure drop at the net interface, structural deflection, and wave loading along the cage height. In addition, the relationships between wave forces on the net cage with hydrodynamic and structural parameters are also revealed. The findings presented herein should be useful to engineers who are designing fish cage systems.

Submerged breakwater of a flexible porous membrane with a vertical flexible porous wall over variable bottom topography

An analytical model of oblique wave interaction with a breakwater consisting of a submerged horizontal flexible porous membrane near a vertical porous barrier over variable bottom topography is developed based on linear water wave theory. Using Green's second identity, a mild-slope equation for oblique waves propagating over a submerged porous membrane and a finite variable bottom topography is derived. The analytical solution of the referred problem is obtained by using the eigenfunction expansion method along with the mild-slope equation and Darcy's law is used for wave past horizontal and vertical porous structure. The present results are compared with existing published analytical results and experimental data and observed that they have a good level of agreement. The effect of different design parameters on the wave quantities and wave forces on the porous wall in variable bottom depth is analyzed. It is found that full-wave reflection is drastically reduced and the wave energy is dissipated by the submerged horizontal flexible porous membrane and porous barrier. The analysis of the reflection and dissipation coefficients as well as wave forces on the vertical wall in terms of wave energy dissipation and wave loads by the proposed submerged flexible porous breakwater will be helpful for better understanding in the design of various types of protecting infrastructures for marine operations.

Mitigation of wave force on a circular flexible plate by a surface-piercing flexible porous barrier

Wave force acting on a circular flexible plate in the presence of a vertical surface-piercing flexible porous membrane is examined under the hypothesis of linear water wave theory. A semi-analytic solution is developed employing the Fourier-Bessel series expansion method along with the methods of separation of variables and least-squares approximation. To keep the outer flexible membrane at a desired position, clamped-moored condition is used. Appropriate orthogonal mode-coupling relationship for the eigenfunctions of the plate covered region is exploited in the expansion formulas together with the continuity of velocity and pressure for achieving the system of equations and to determine the unknowns. The effects of various physical parameters are analyzed by computing wave load on the structures, plate deflection and flow distribution. It is found that due to the presence of vertical flexible porous membrane, a significant amount of wave force on the plate is reduced. Thus, a cylindrical flexible porous membrane can be implemented to protect the inner circular flexible plate.

3D-Printed electrochemical sensor-integrated transwell systems

This work presents a 3D-printed, modular, electrochemical sensor-integrated transwell system for monitoring cellular and molecular events in situ without sample extraction or microfluidics-assisted downstream omics. Simple additive manufacturing techniques such as 3D printing, shadow masking, and molding are used to fabricate this modular system, which is autoclavable, biocompatible, and designed to operate following standard operating protocols (SOPs) of cellular biology. Integral to the platform is a flexible porous membrane, which is used as a cell culture substrate similarly to a commercial transwell insert. Multimodal electrochemical sensors fabricated on the membrane allow direct access to cells and their products. A pair of gold electrodes on the top side of the membrane measures impedance over the course of cell attachment and growth, characterized by an exponential decrease (~160% at 10 Hz) due to an increase in the double layer capacitance from secreted extracellular matrix (ECM) proteins. Cyclic voltammetry (CV) sensor electrodes, fabricated on the bottom side of the membrane, enable sensing of molecular release at the site of cell culture without the need for downstream fluidics. Real-time detection of ferrocene dimethanol injection across the membrane showed a three order-of-magnitude higher signal at the membrane than in the bulk media after reaching equilibrium. This modular sensor-integrated transwell system allows unprecedented direct, real-time, and noninvasive access to physical and biochemical information, which cannot be obtained in a conventional transwell system.

Composite breakwater of a submerged horizontal flexible porous membrane with a lower rubble mound

An analytical solution of a new composite breakwater consisting of a moored submerged flexible porous membrane and a submerged ruble mound below the membrane is presented. The semi-analytical solution is obtained based on the velocity potential decompositions where the consideration of a dispersion relation with complex wave numbers is not required. The convergence of the series solution is demonstrated by computing the values of the reflection, the transmission, the dissipation coefficients and the vertical force. In addition, the present results are compared against published numerical results and experimental data. In order to analyze the efficiency of the newly developed composite breakwater, the present results are compared with those of a single horizontal submerged moored porous membrane and a single rubble mound breakwater. Furthermore, the effects of design parameters on the performance of the composite breakwater are also analyzed in detail.

Wave energy dissipation by a floating circular flexible porous membrane in single and two-layer fluids

In this study, the impact of gravity wave on a circular elastic floating permeable membrane is investigated using linear water wave theory in both homogeneous and two-layer fluids. The matched eigenfunction expansion technique is employed to obtain an analytic solution of the boundary value problem. Further, the plane wave integral representation of Bessel and Hankel functions are applied to study the influence of porous structure in damping the far-field wave energy. In order to examine the effect of various physical parameters, heave force exerted on the membrane, deflection of the membrane, reflected and transmitted wave amplitudes, flow distribution around the structure and far-field energy dissipation are computed and analyzed for three different edge conditions such as (i) free edge, (ii) moored edge and (iii) clamped edge. The study reveals that the surface wave amplitude on the lee side of the structure decreases significantly in the presence of floating porous elastic membrane. Moreover, the membrane having clamped edge dissipates more wave energy as compared to that for moored and free edge conditions.

Wave energy dissipation of a submerged horizontal flexible porous membrane under oblique wave interaction

An analytical model associated with oblique wave interaction with a submerged horizontal flexible porous membrane is presented under the assumption of linearized small amplitude and structural response in finite water depth. The expansion formula associated with Green's functions using fundamental source potentials based on reduced wave equation is derived. Further, a physical problem of oblique wave interaction with a moored finite horizontal submerged flexible porous membrane on wave energy dissipation is illustrated to analyse the different design parameter based on matched eigenfunction expansion method. The roots of the complex dispersion relation are obtained by applying a perturbation scheme and the accuracy of the numerical computation is demonstrated by analysing the convergence of reflection, transmission, and dissipation coefficients for different spring stiffness and porous-effect parameters. Further, the correctness of the present solution is checked by validating against analytical, numerical boundary element method, and experimental data available in the literature. The effects of spring stiffness, porous-effect parameter, submergence depth, structural length, angle of incidence, and flow pattern on reflection, transmission, dissipation coefficients, membrane deflection, vertical force, and contour plots are analysed. The present analysis on different design parameters will be helpful for better understanding for engineers to design as an effective breakwater/wave absorber.

Periodontal Tissue Engineering with a Multiphasic Construct and Cell Sheets

This study reports on scaffold-based periodontal tissue engineering in a large preclinical animal model. A biphasic scaffold consisting of bone and periodontal ligament compartments manufactured by melt and solution electrospinning, respectively, was used for the delivery of in vitro matured cell sheets from 3 sources: gingival cells (GCs), bone marrow–derived mesenchymal stromal cells (Bm-MSCs), and periodontal ligament cells (PDLCs). The construct featured a 3-dimensional fibrous bone compartment with macroscopic pore size, while the periodontal compartment consisted of a flexible porous membrane for cell sheet delivery. The regenerative performance of the constructs was radiographically and histologically assessed in surgically created periodontal defects in sheep following 5 and 10 wk of healing. Histologic observation demonstrated that the constructs maintained their shape and volume throughout the entirety of the in vivo study and were well integrated with the surrounding tissue. There was also excellent tissue integration between the bone and periodontal ligament compartments as well as the tooth root interface, enabling the attachment of periodontal ligament fibers into newly formed cementum and bone. Bone coverage along the root surface increased between weeks 5 and 10 in the Bm-MSC and PDLC groups. At week 10, the micro–computed tomography results showed that the PDLC group had greater bone fill as compared with the empty scaffold, while the GC group had less bone than the 3 other groups (control, Bm-MSC, and PDLC). Periodontal regeneration, as measured by histologically verified new bone and cementum formation with obliquely inserted periodontal ligament fibers, increased between 5 and 10 wk for the empty, Bm-MSC, and PDLC groups, while the GC group was inferior to the Bm-MSC and PDLC groups at 10 wk. This study demonstrates that periodontal regeneration can be achieved via the utilization of a multiphasic construct, with Bm-MSCs and PDLCs obtaining superior results as compared with GC-derived cell sheets.

Enzymatic Low Volume Passive Sweat Based Assays for Multi-Biomarker Detection.

Simultaneous detection of correlated multi-biomarkers on a single low-cost platform in ultra-low fluid volumes with robustness is in growing demand for the development of wearable diagnostics. A non-faradaic biosensor for the simultaneous detection of alcohol, glucose, and lactate utilizing low volumes (1–5 μL) of sweat is demonstrated. Biosensing is implemented using nanotextured ZnO films integrated on a flexible porous membrane to achieve enhanced sensor performance. The ZnO sensing region is functionalized with enzymes specific for the detection of alcohol, glucose, and lactate in the ranges encompassing their physiologically relevant levels. A non-faradaic chronoamperometry technique is used to measure the current changes associated with interactions of the target biomarkers with their specific enzyme. The specificity performance of the biosensing platform was established in the presence of cortisol as the non-specific molecule. Biosensing performance of the platform in a continuous mode performed over a 1.5-h duration showed a stable current response to cumulative lifestyle biomarker concentrations with capability to distinguish reliably between low, mid, and high concentration ranges of alcohol (0.1, 25, 100 mg/dL), glucose (0.1, 10, 50 mg/dL), and lactate (1, 50, 100 mM). The low detection limits and a broader dynamic range for the lifestyle biomarker detection are quantified in this research demonstrating its suitability for translation into a wearable device.

Oblique wave trapping by vertical permeable membrane barriers located near a wall

The effectiveness of a vertical partial flexible porous membrane wave barrier located near a rigid vertical impermeable seawall for trapping obliquely incident surface gravity waves are analyzed in water of uniform depth under the assumption of linear water wave theory and small amplitude membrane barrier response. From the general formulation of the submerged membrane barrier, results for bottom-standing and surface-piercing barriers are computed and analyzed in special cases. Using the eigenfunction expansion method, the boundary-value problems are converted into series relations and then the required unknowns are obtained using the least squares approximation method. Various physical quantities of interests like reflection coefficient, wave energy dissipation, wave forces acting on the membrane barrier and the seawall are computed and analyzed for different values of the wave and structural parameters. The study will be useful in the design of the membrane wave barrier for the creation of tranquility zone in the lee side of the barrier to protect the seawall.

Superflexible Wood.

Flexible porous membranes have attracted increasing scientific interest due to their wide applications in flexible electronics, energy storage devices, sensors, and bioscaffolds. Here, inspired by nature, we develop a facile and scalable top-down approach for fabricating a superflexible, biocompatible, biodegradable three-dimensional (3D) porous membrane directly from natural wood (coded as flexible wood membrane) via a one-step chemical treatment. The superflexibility is attributed to both physical and chemical changes of the natural wood, particularly formation of the wavy structure formed by simple delignification induced by partial removal of lignin/hemicellulose. The flexible wood membrane, which inherits its unique 3D porous structure with aligned cellulose nanofibers, biodegradability, and biocompatibility from natural wood, combined with the superflexibility imparted by a simple chemical treatment, holds great potential for a range of applications. As an example, we demonstrate the application of the flexible, breathable wood membrane as a 3D bioscaffold for cell growth.

Gravity wave interaction with a flexible circular cage system

The present study deals with the hydroelastic analysis of a floating flexible circular cage system in finite water depth under the assumption of small amplitude waves and structural response. The flexible cage system is modeled as a surface-piercing porous flexible cylinder having a flexible porous membrane type bed which is under the action of uniform tension. Using the Fourier-Bessel series solution and least squares approximation method, the mathematical problem is handled for solution by matching the velocity and pressure at the fluid-structure interfaces. Further, the flexible cage system is assumed to be kept fixed at the free surface and the submerged end. The efficiency of the cage system is studied by analyzing the hydrodynamic force, effect of structural porosity and deflections of the flexible walls and bed of the cage system. The findings of the present study are helpful in the design of various types of floating cage system for marine aquaculture which can withstand the wave loads of varied nature at calm water location in the coastal area.

Oblique wave scattering by horizontal floating flexible porous membrane

The present study deals with the oblique wave scattering by a floating flexible porous membrane under the assumptions of small amplitude water wave theory and membrane response in both the cases of finite and infinite water depths. Using the Green’s function technique, the boundary value problems are converted into pairs of Fredholm integral equations in terms of the velocity potentials and their normal derivatives along the membrane. Using Simpson’s quadrature formula, various integrals are evaluated and the system of integral equations are reduced to a system of linear algebraic equations which are solved to find various physical quantities of interests. Energy balance relations are derived and used to check the accuracy of the computational results. Several results of physical interests are computed and analyzed to study the effects of various wave and structural parameters. The present study will be of immense importance in creating tranquility zone for protecting coastal infrastructures through the use of floating flexible porous membrane. The concept and methodology can be used to deal with wave-structure interaction problems in related branches of mathematical physics and engineering.

Wave scattering by flexible porous vertical membrane barrier in a two-layer fluid

The scattering of water waves by a flexible porous membrane barrier in a two-layer fluid having a free surface is analysed in two dimensions. The membrane barrier is extended over the entire water depth in a two-layer fluid, each fluid being of finite depth. In the present analysis, linear wave theory and small amplitude membrane response are assumed. The porous membrane barrier is tensioned and pinned at both the free surface and the seabed. The associated mixed boundary value problem is reduced to a linear system of equations by utilizing a general orthogonality relation along with least-squares approximation method. Because of the flow discontinuity at the interface, the eigenfunctions involved have a discontinuity at the interface and the orthogonality relation used is a generalization of the classical one corresponding to a single-layer fluid. The reflection and transmission coefficients for the surface and internal modes, the free surface and interface elevations and the nondimensional membrane deflection are computed for various physical parameters like the nondimensional tension parameter, porous-effect parameter, fluid density ratio, ratio of water depths of the two fluids to analyse the efficiency of a porous membrane as a wave barrier in the two-layer fluid.