Straight Vertical Walls Research Articles

Generation of nonlinear gravity waves based on the harmonic polynomial cell method incorporated with a mass source

A nonlinear numerical wave tank is established using the Harmonic Polynomial Cell (HPC) method, which is incorporated with a mass source. The numerical wave tank consists of the mass source wave generation region and the working region, with sponge layers at both ends for wave absorption. In the mass source region, a generalized HPC method is applied to solve the inhomogeneous elliptic boundary value problems. The Poisson equation's special solution is represented by a bi-quadratic function. In the remaining domains, the HPC method is employed with harmonic polynomials to solve the problems governed by the Laplace equation in each grid cell. The free surface is tackled by the immersed boundary method (IB-HPC), and the kinematic and dynamic conditions of the free surface are described using a semi-Lagrangian approach. A variety of waves propagation are simulated, including Second-order Stokes wave, fifth-order Stokes wave, solitary wave, fifth-order Fenton stream function wave, random wave and the interaction with a straight vertical wall. The numerical solutions are compared with theoretical solutions. The numerical simulation results demonstrate that the present method can generate arbitrary two-dimensional wave fields by specifying an appropriate source function. Additionally, the reflected waves can propagate through the wave generation region, ensuring that the process of wave generation is not affected by the reflections.

Numerical Study of Heat Transfer by Mixed Convection in a Cavity Filled With Nanofluid: Influence of Reynolds and Grashof Numbers

In this work, a numerical study of stationary laminar mixed convection in a ventilated square cavity has been presented. The cavity is filled with different nanofluids and contains two gates (ports) to enter and exit the flow. The straight vertical wall is maintained at a warm temperature, while the other walls are considered adiabatic. The equations governing flow and heat transfer have been solved by the finite volume method using a second-order centered Upwind scheme. Numerical simulations are carried out in the case of pure water fluid, and mixtures of this basic fluid and nanoparticles (Ag and Cu), for Ri varying from (0.04 to 4) and a volume fraction of the nanoparticles between (0% and 10%). The study presented in this work is devoted to a dynamic study in which the Grashof number is fixed at 104, and the Reynolds number is varied. The numerical results obtained show that the heat transfer increases with the increase in the volume fraction also that the enhancement of the product of entropy generation and heat transfer increases considerably with the increase in the Reynolds number. The most effective nanoparticles for increasing the heat exchange rate are Ag. The latter is characterized by a large local Nusselt number, that is to say, a very good heat transfer compared to that of metallic Cu nanoparticles.

Numerical Simulation of Natural Convection in A Cavity Filled with A Nanofluid Who’s Wall Containing the Heat Source Is Inclined

In this work, we study by numerical simulation the natural convection in a trapezoidal cavity filled with a nanofluid whose wall containing the heat source is successively inclined at an angle varying from 0 to 60 ° at the most (in order to maintain a valid model straight vertical wall) with respect to the horizontal. The upper and lower walls on either side of the heat source are adiabatic while the other walls are subjected to a constant cold temperature. The hydrodynamic and thermal phenomena are described by the equations of Navier-Stockes and energy. The models Brinkman and Wasp are used to describe the thermo-physical properties of the nanofluid (water- ).The finite element method; based on the Galerkin principle; is used to solve the system of partial differential equations. We consider the effect of the solid volume fraction for different values ??of the Rayleigh number on the results obtained, in the form of isotherms and local, modified Nusselt numbers.

Lattice Boltzmann method for shallow water flow with wave radiation stress

The protection of the marine environment is of growing concern, and the development of hydrodynamic models is required to study ocean processes. In this work, a two-dimensional hydrodynamic lattice Boltzmann model was developed to study wave–current coupling problems that combine wave radiation, bed shear stress and wind shear stress. The model is based on nonlinear shallow water equations and two different forms are developed to model wave radiation stress. The first form uses an additional external force term, including a weight factor in the lattice Boltzmann equation at the streaming step. The second form modifies a local equilibrium distribution function at the collision step. Von Neumann stability method is used to study the two schemes. This model was verified by three classic cases: waves diffracted by a straight vertical wall, waves diffracted by two breakwaters, and waves in a circular channel. The numerical results demonstrate the validity of the proposed model, indicating that it can accurately describe the characteristics of water flow with interactions between waves and currents.

Experimental evaluation of the melting behaviours of paraffin within a hemicylindrical storage cell

Abstract Phase change materials (PCM) have been widely used as latent energy storage media due to their useful high energy density with small storage volume at nearly constant temperatures throughout solidification and melting. In this paper, experimental evaluation of the melting of a paraffin wax (RT58) PCM inside a hemicylindrical storage cell is outlined. The cell is heated on its straight vertical wall by means of flowing hot water, while the curved side of the cell is thermally insulated. The temperatures of the PCM at various locations are measured using thermocouples, while a digital camera is used to visualise the melting process. A set of experiments is performed to examine the influence of variation of hot water temperature on various melting characteristics including the temperature field of the PCM, the progress of the melting front, the melt fraction, the stored energy, and the Nusselt number. The experimental findings reveal that increasing hot water temperature leads to a reduction of melting time and increases in the stored energy and the Nusselt number. The melting process is expedited by 15.4 and 16.5% when the temperature of hot water increases from 80 °C to 85 °C, and from 85 °C to 90 °C, respectively.

A fully Eulerian multiphase model of windblown sand coupled with morphodynamic evolution: Erosion, transport, deposition, and avalanching

Modeling unsteady windblown sand dynamics requires not only treatment of the sand present in the air as a suspended constituent of a mixture but also consideration of erosion and sedimentation phenomena and consequently of the morphodynamic evolution of the sand-bed surface, including avalanching, especially in the presence of natural or human-built obstacles, artifacts, and infrastructures. With this aim in mind, we present a comprehensive multiphase model capable of accurately simulating all the physical phenomena mentioned above, producing satisfactory results, with reasonable computational effort. As test cases, two- and three-dimensional simulations of dune evolution are reported, as is windblown sand transport over a straight vertical wall. Examples of sand transport around other obstacles are given to show the flexibility of the model and its usefulness for such engineering applications.

A sign of mobility and cultural exchange? The ceramics with scribble line ornamentation from Lysa Hora cemetery

the fourth type after D.Y. Telegin typology has been found in the Lysa Gora cemetery. This type is represented by biconical vessels with the flat bottom and straight «collar» rim. Inside of this type, we are able to identify subtypes by their size, type and ornament disposition on the body of a vessel. The vessels with the flat bottom, straight vertical walls and cut to the middle rim are most common. In the second period biconical vessels with the big flat “collar” rim became more popular. The plot of the composition and ornaments that decorated the body of the vessel in the first and second period also was changed. The ornament in the first period is the imprints of the comb punches forming the horizontal rows, the fir-tree, the zigzag, the ribbons, limited by the scratched lines, the comb marks. The ornament in the first period is the imprints of the comb punches forming the horizontal rows, the fir-tree, the zigzag, the ribbons, limited by the scratched lines, the comb marks. In the second period – the ornament of the triangular stroked decoration and the shaded horizontal lines, which form plots: geometric compositions, fir trees, nets, extends. A linear ornament consists of cut, screwed or flattened lines. Often, it is a straight line, in some cases there are curvilinear compositions, sometimes wavy ornament. In different periods of culture, there are certain differences in the motifs of patterns, the ways of their placement, the degree of coverage of the ornament of the surface of vessels. In the first period of culture, the pattern on vessels did not adhere to a clear horizontal zonation. Pots of the second period are ornamented from the rim to bottom. Sometimes the pattern enters the inside of the neck and rim of the vessel, as well as the bottom. The style of geometric rectilinear ornament prevails, which most often includes horizontal rows and stripes. Rows consist of impressions of the comb, the triangular short stroked decoration. Impressions of the comb, the triangular short stroked decoration in individual rows have a slope to the right or to the left, resulting in a pattern having a kind of fir tree. Less often, the ornamental field consisted of several horizontal stripes, separated by the triangular stroked decoration of the necks or flattened lines. The entire strip is covered with lines from the stroked decoration or impressions of the comb. Sometimes the entire strip filled with “broken” rows, which in general creates a motive of short vertical columns. However, curvilinear pattern of ornament did not common for this period. The feature of ceramics is its ornamented bottom. Patterns consist of concentric circles, elongated-oval circles, radial lines. At the end of the second – at the beginning of the third period of the Dnieper-Donetsk culture region a tendency is to create a pattern with a predominance of vertical or oblique columns and stripes, more often there is a pattern of ornament in the form of individual figures (triangles, lozenges, which sparsely cover the surface of the vessel). The development and change of the disposition of ornament on ceramics is one of the keys to understand socio-cultural connections on the territory of the Dnieper-Donetsk cultural region.

The optimal design of a flap gate array in front of a straight vertical wall: Resonance of the natural modes and enhancement of the exciting torque

We consider a wave energy converter made of an array of Q neighbouring floating flap gates with finite thickness in front of a straight vertical wall in constant depth. Solutions of the radiation and scattering problems are achieved by application of Green's theorem and Green's function yielding a system of hypersingular integral equations for the velocity potential expanded in terms of Legendre polynomials. We investigate how the distance between the array and the vertical wall affects the performance of the array under the action of monochromatic and random waves. We show that large values of the exciting torque on the gates can be obtained by tuning the wall distance with the resonance of the natural modes of the array; this in turn yields large power extraction for a wide range of frequencies.

Numerical Study on Effect of Volume Fraction of Nanoparticles on Rayleigh-Bernard Convection in Different Enclosures

Numerical investigations of Rayleigh-Bernard convection in enclosures of different modified bottom and top surfaces filled with Au-Water Nanofluid with different volume fractions are presented. This paper describes a numerical predication of heat transfer and fluid flow characteristics inside enclosures bounded by modified bottom and top surfaces and two periodic straight vertical walls. Simulations are carried out for a Rayleigh number of 6×104 and two aspect ratios (0.25 & 0.5) with working fluid as Au-Water Nanofluid and The same analyses are performed with the Nanofluid having Au nanoparticles of same size and different volume fraction of φ = 5%, 10%, 15% and 20 % in order to see the effect of Nanofluid volume fraction on heat transfer. The Boussinesq approximation is used in order to take density change effect in the governing equations. The study investigates the effect of the nanoparticles volume fraction, and the aspect ratio on the heat transfer. The results are presented in terms of isotherms, streamlines local and average surface Nusselt numbers. Results show that the flow and isotherms are affected by the geometry shape and by the presence of nanoparticles with different volume fractions. It is also shown that for a fixed value of aspect ratio, the convective heat transfer is decreased for the increase in volume fraction of Nanofluid.

NUMERICAL STIMULATION OF RAYLEIGH BERNARD CONVECTION IN WAVY ENCLOSURES

Enclosures are frequently encountered in practice, and heat transfer through them is of practical interest. Heat transfer in enclosed space is complicated by the fact that fluid in the enclosure, in general, does not remain constant. The fluid adjacent to the hotter surface rises and the fluid adjacent to the cooler one falls, setting a rotionary motion within the enclosure that enhances the heat transfer through the enclosure. This paper describes a numerical predication of heat transfer and fluid flow characteristics inside an enclosure bounded by horizontal wavy walls and two periodic straight vertical walls. Governing equation were discretized using an implicit finite difference method, based on finite volume approach. Simulation was carried out for a range of Rayleigh number (104-106) and Aspect ratio (0.35-0.75) for the fluid having Prandtl number 0.71. Results are presented by streamlines, isotherms and local Nusselt numbers. It is observed that flow and thermal field inside the enclosure are affected by the shape of enclosure and heat transfer rate increases as Rayleigh number increase.

Size-Tunable Porous Anodic Alumina Nano-Structure for Biosensing

A porous anodic alumina (PAA) film has been investigated to realise highly-ordered nano-porous structures. A two-step anodization process is used to anodize aluminium into size-controllable aluminium oxide. In this paper, we investigate how anodization parameters affect nano-porous structures, such as voltage and time of pretreatment, anodization voltage and time, pore widening time. The results showed pretreatment is important to obtain a smooth surface for anodizing. The pore size is controllable between 30 and 80 nm, with a linear fit curve. The interpore size is constant at around 95 nm, and the pore densities are between 1010 and 1011 cm–2. The formation of straight vertical walls is crucial if the PAA film is to be subsequently used as the template for the growth of metal nanowire arrays.

On the impact of wind curls on coastal currents

Studies of upwelling and coastally-trapped wave theory, as developed over the past thirty years, have largely neglected effects of cross-shelf variation in wind stress and the resulting wind stress curl. However, recent satellite-based observations (QuikSCAT) of global wind stress patterns show significant and persistent wind stress curls extending well offshore in some coastal regions including the Benguela System. Motivated by this example, we use a relatively simple analytical model to investigate explicitly the impact of cross-shelf variation in wind stress on the structure of the coastal currents. The model is based on the linear Boussinesq equations of a stratified, flat bottomed coastal ocean on a f-plane (southern hemisphere), bounded by a straight vertical wall. The model includes a wind mixed layer and a linear friction rate. The model equations are solved using the method of Green's functions. There are two mechanisms imposing divergencies of the Ekman transport, (1) coastal inhibition and (2) wind stress curl. In the first case the coastal flows are affected significantly by Kelvin waves, due to the waveguide properties of boundaries. In the second case, the wind stress curl generates vertical motion and hence horizontal pressure gradients, where the associated geostrophic flows are limited by friction only. As a result, complex flow patterns with counter-currents can emerge. In order to highlight the role of wind stress curls, the responses of the coastal ocean to different cross-shore variations of the alongshore wind stress are compared with the baseline case of no wind curl.

Reactive ion etching of InP with Br2-containing gases to produce smooth, vertical walls: Fabrication of etched-faceted lasers

We describe the reactive ion etching of InP using a mixture of Br2 and either N2 or Ar. We report the first fabrication of straight vertical walls in InP at a very fast etching rate of 2 μm/min. By using a mixture of Br2 and Ar and raising the substrate temperature, smooth walls are obtained. To demonstrate that the etched walls can be used as laser mirrors, we fabricated etched-faceted lasers with threshold currents of 19.0 mA for a laser with one etched and one cleaved facet and 26.6 mA for a laser with two etched facets.