Grid Arrangement Research Articles

Investigation on the effect of metal foam properties on the PCM melting performance subjected to various heat fluxes

The purpose of this paper is to analyze the effects of structural and mechanical characteristics of metal foam on the melting behavior of phase change materials under the influence of different heat fluxes. To this aim, a two dimensional numerical model considering the non-equilibrium thermal factor, non-Darcy effect and local natural convection was used. The governing equations of PCM and metal foam are discretized using a finite volume method with a collocated grid arrangement. To simulate the melting of PCM, the enthalpy-porosity method is applied which computes the liquid fraction at each iteration, based on the enthalpy balance. The effect of metal foam characteristics (porosity, pores size and base material) and wall heat flux on the PCM melting time were investigated. The result showed that for both wall heat fluxes (4000 W m-2 and 8000 W m-2), foam structure and its mechanical properties have significant influence on the PCM melting time which these effects should be considered.

Computational Fluid Dynamics Analysis of Flow Patterns, Pressure Drop, and Heat Transfer Coefficient in Staggered and Inline Shell-Tube Heat Exchangers

In this numerical study, the heat transfer performance of shell-and-tube heat exchangers (STHXs) has been compared for two different tube arrangements. STHX having 21 and 24 tubes arranged in the inline and staggered grid has been considered for heat transfer analysis. Shell-and-tube heat exchanger with staggered grid arrangement has been observed to provide lesser thermal stratification as compared to the inline arrangement. Further, the study of variation in the mass flow rate of shell-side fluid having constant tube-side flow rate has been conducted for staggered grid structure STHX. The mass flow rate for the shell side has been varied from 0.1 kg/s to 0.5 kg/s, respectively, keeping the tube-side mass flow rate as constant at 0.25 kg/s. The influence of bulk mass-influx transfer rate on heat transfer efficiency, effectiveness, and pressure drop of shell-tube heat exchangers has been analyzed. CFD results were compared with analytical solutions, and it shows a good agreement between them. It has been observed that pressure drop is minimum for the flow rate of 0.1 kg/s, and outlet temperatures at the shell side and tube side have been predicted to be 40.94°C and 63.63°C, respectively.

Experimental study on solar air heater with encapsulated phase change material on its absorber plate

AbstractEffective usage of solar air heaters (SAH) is limited to specific time due to nonavailability and low intensity of solar radiation. In addition, SAH suffers from lower thermal efficiencies. Encapsulated phase change material (PCM) on absorber plate of SAH is one of the passive techniques to improve thermal efficiency of SAH as well as to extend its application to nonsunshine hours. In this article, capsules of circular and square cross sections filled with PCM were used on absorber plate of a double pass counter flow SAH and SAH efficiency was experimentally determined. Capsules were placed in inline and staggered grid arrangements perpendicular to the flow direction of the air and paraffin wax was used as the PCM. Experiments were conducted each day in two cycles (charging PCM from 10:00 am to 2:00 pm and discharging PCM from 4:30 pm to 5:30 pm), with fixed mass flow rate of air in between 0.00879 and 0.01484 kg/s. It is found from the results that, efficiency of SAH with square staggered encapsules is at an average of 15.8% higher than the remaining arrangements. During PCM discharge, air temperature at the SAH exit was at an average of 5.17°C greater than ambient temperature for all arrangements.

Study of mixed convection flow of power‐law fluids in a skewed lid‐driven cavity

AbstractThis study conducts a numerical simulation of mixed (combined) convective non‐Newtonian fluid flow inside a two‐dimensional cavity (skewed) having a moving lid. The upper and bottom extremities of the cavity with different temperatures and two insulated side walls cause natural convection. Moreover, the forced convection is maintained by the motion of the lid with constant velocity. The governing equations are nondimensionalized with appropriate transformations and then transformed into curvilinear coordinates. A finite volume numerical procedure with a collocated grid arrangement is used to solve these equations. Comparisons with previously reported results are carried out, which shows an excellent agreement. Non‐Newtonian behaviors such as pseudo‐plastic (shear‐thinning) and dilatant (shear‐thickening) are considered using the power‐law model, and thus the power‐law index is chosen accordingly. A wide range of the governing dimensionless parameters which affect the mixed convection flow inside the skewed cavity, including Grashof number (), Richardson number (), Reynolds number ( = 100 and 400), and power‐law index (). The Prandtl number ( = 10) is fixed and the skew angles (, and ) are considered for acute, right‐angle, and obtuse angles. The obtained numerical outcomes of the study are shown graphically and also in tabular form for vertical and horizontal velocities, streamlines, isotherms, temperature distributions, and the rate of heat transfer and insight physics of the flow features, are discussed thereafter. It can be concluded that the rate of heat transfer in the present case is sensitive to the skew‐angle as well as power‐law index, and the maximum heat transfer occurs in the case of dilatant (shear‐thickening) fluid.

Comparison of collocated methods of MCIM and PWIM for different solution algorithms in CVFEM

The pressure-velocity coupling method of MCIM (Mass Corrected Interpolation Method) and different solution algorithms of this method were previously developed and tested for steady and unsteady incompressible flows. But the effect of under-relaxation factors in cell-face velocities and the main equations never have been investigated. On the other hand, this method and its different algorithms never have been compared with similar and more common methods in the formulation of primitive variables and non-staggered grid arrangements. In this paper, the accuracy, performance, and computational efficiency of the different solution algorithms of MCIM are compared with the well-known PWIM (Pressure Weighted Interpolation Method) of Rhie & Chow. In this study, a fully coupled, segregated approach without any pressure correction and SIMPLE-like segregated algorithms are proposed for two methods of MCIM and PWIM on the control volume-based finite element (CVFEM) framework. Also, for each method, the proper under-relaxation factors for the main equations and cell-face velocities are introduced. The accuracy and performance of the proposed algorithms are demonstrated by solving different steady and unsteady benchmark problems, and the results of both methods for different algorithms are compared. The results indicate that the both methods have spatial 2nd-order accuracy approximately and are not very different from each other. The results also show that the numerical dissipation of the MCIM is much less than PWIM. Comparing the computational cost of the different algorithms of both methods shows that the coupled algorithm of the MCIM for steady and unsteady problems with different time steps and various grid numbers is at least 10% better than other algorithms.

Numerical Study of Partial Differential Equations by an Adaptive Diffusion Wavelet Method

In the paper, an adaptive diffusion wavelet method (ADWM) is developed to solve partial differential equations (PDEs) with different boundary conditions. We construct diffusion wavelets using an approximation of second-order differential operators. We test the squeezing error behavior corresponding to different parameters involved in the constructed diffusion wavelet, using two test functions. The diffusion wavelet is used to construct adaptive grid arrangements and the fast computation of the diffusion operator’s dual power. The constructed adaptive grid arrangements and dual power of diffusion operators are more effective for finding the numerical solutions of PDEs. Test problems verify the accuracy and efficiency of the proposed method. For each test problem, the processing time taken by ADWM is compared with the existing methods like the fast diffusion wavelet method (FDWM) and finite difference method (FDM). The proposed method (ADWM) takes lesser processing time than FDWM and FDM. We verify the convergence of the given method.

Cost Optimization Of Micro-Grid Of Renewable Energy Resources Connected With And Without Utility Grid

Arranging and enhancement of small-scale lattices in determined zone examined in this paper miniaturized scale framework is associated with and without grid to meet the load profiles, particular micro grid arrangements with age from sustainable power sources are developed. Better examinations are then conveyed utilizing HOMER vitality programming to decide cost of economy, measuring, and locating and framework designs. Micro grid is likewise associated with the network because of shortage of supported sustainable power sources. This paper shows a short differentiate among the assorted cost types of gear, control the board and launches for every one of the setups. The improvement result shows the most reduced expense per unit and it allots the positioning for every framework.

MODELLING AND DYNAMIC ANALYSIS OF THREE-DIRECTION GRID PRESTRESSED RETICULATED MEGA-STRUCTURE


 
 
 In this paper, the generation way of three-direction grid prestressed reticulated mega- structure is studied, and the three-direction grid prestressed reticulated mega-structure composite joint specific formation ideas are proposed. The important control parameters of three-direction grid prestressed reticulated mega-structure are determined, and the geometric modelling method of hexagon across the middle joint and octagon across the side joint is proposed. Coordinate formula of hexagonal and octagonal joints are derived to ensure reasonable grid arrangement and uniform stress distribution of the structure. Combined with the geometric parameters of the mega grid, a new method for creating the geometric model of three-direction grid prestressed mega reticulated structure is realized. The quadrangular pyramid space grid structure with the same length, span, rise and grid size and the three-direction grid prestressed grid structure are calculated, and the advantages of three-direction grid prestressed grid structure in dynamic performance are compared and analyzed.
 
 

WITHDRAWN: Cost Optimization of Micro-grid of Renewable Energy Resources Connected with and without Utility Grid

Arranging and enhancement of small-scale lattices in determined zone examined in this paper miniaturized scale framework is associated with and without grid to meet the load profiles, particular micro grid arrangements with age from sustainable power sources are developed. Better examinations are then conveyed utilizing HOMER vitality programming to decide cost of economy, measuring, and locating and framework designs. Micro grid is likewise associated with the network because of shortage of supported sustainable power sources. This paper shows a short differentiate among the assorted cost types of gear, control the board and launches for every one of the setups. The improvement result shows the most reduced expense per unit and it allots the positioning for every framework.

Piecewise linear interface-capturing volume-of-fluid method in axisymmetric cylindrical coordinates

The paper describes a novel implementation of the piecewise linear interface-capturing volume-of-fluid method (PLIC-VOF) in axisymmetric cylindrical coordinates. The principal innovative feature involved in this work is that both the forward and inverse reconstruction problems are solved analytically, resulting in an appreciable speed-up in computing time in comparison with an iterative approach. All reconstruction formulae are introduced explicitly, and an example illustrating their derivation is included for clarity. The numerical implementation of the PLIC-VOF interface tracking method developed here is described in detail, as well as its coupling with the 3D incompressible Navier-Stokes solver PSI-BOIL, which features a finite-volume approach based on a fixed, rectangular grid. This coupling includes a method to calculate the surface tension force within an axisymmetric VOF framework by means of height functions. The method is first verified to ensure its correct implementation in the code, and to evaluate its performance, and several advection tests are employed to demonstrate successful solution of the basic transport problem. It is shown that convergence to equilibrium may be achieved for static problems, involving the control of parasitic currents, for a variety of grid arrangements, and for different material properties. Several axisymmetric dam-break and rising bubble problems, for which high-quality measured data are available, are also presented to serve as validation tests. In all cases, very good agreement of simulation results with experimental data has been recorded, and the dynamics of the problem well reproduced.

On the suitability of second-order accurate finite-volume solvers for the simulation of atmospheric boundary layer flow

Abstract. The present work analyzes the quality and reliability of an important class of general-purpose, second-order accurate finite-volume (FV) solvers for the large-eddy simulation of a neutrally stratified atmospheric boundary layer (ABL) flow. The analysis is carried out within the OpenFOAM® framework, which is based on a colocated grid arrangement. A series of open-channel flow simulations are carried out using a static Smagorinsky model for subgrid scale momentum fluxes in combination with an algebraic equilibrium wall-layer model. The sensitivity of the solution to variations in numerical parameters such as grid resolution (up to 1603 control volumes), numerical solvers, and interpolation schemes for the discretization of nonlinear terms is evaluated and results are contrasted against those from a well-established mixed pseudospectral–finite-difference code. Considered flow statistics include mean streamwise velocity, resolved Reynolds stresses, velocity skewness and kurtosis, velocity spectra, and two-point autocorrelations. A quadrant analysis along with the examination of the conditionally averaged flow field are performed to investigate the mechanisms responsible for momentum transfer in the flow. It is found that at the selected grid resolutions, the considered class of FV-based solvers yields a poorly correlated flow field and is not able to accurately capture the dominant mechanisms responsible for momentum transport in the ABL. Specifically, the predicted flow field lacks the well-known sweep and ejection pairs organized side by side along the cross-stream direction, which are representative of a streamwise roll mode. This is especially true when using linear interpolation schemes for the discretization of nonlinear terms. This shortcoming leads to a misprediction of flow statistics that are relevant for ABL flow applications and to an enhanced sensitivity of the solution to variations in grid resolution, thus calling for future research aimed at reducing the impact of modeling and discretization errors.

A semi-implicit hybrid finite volume/finite element scheme for all Mach number flows on staggered unstructured meshes

In this paper a new hybrid semi-implicit finite volume / finite element (FV/FE) scheme is presented for the numerical solution of the compressible Euler and Navier–Stokes equations at all Mach numbers on unstructured staggered meshes in two and three space dimensions. The chosen grid arrangement consists of a primal simplex mesh composed of triangles or tetrahedra, and an edge-based / face-based staggered dual mesh. The governing equations are discretized in conservation form. The nonlinear convective terms of the equations, as well as the viscous stress tensor and the heat flux, are discretized on the dual mesh at the aid of an explicit local ADER finite volume scheme, while the implicit pressure terms are discretized at the aid of a continuous P1 finite element method on the nodes of the primal mesh. In the zero Mach number limit, the new scheme automatically reduces to the hybrid FV/FE approach forwarded in [1] for the incompressible Navier–Stokes equations. As such, the method is asymptotically consistent with the incompressible limit of the governing equations and can therefore be applied to flows at all Mach numbers. Due to the chosen semi-implicit discretization, the CFL restriction on the time step is only based on the magnitude of the flow velocity and not on the sound speed, hence the method is computationally efficient at low Mach numbers. In the chosen discretization, the only unknown is the scalar pressure field at the new time step. Furthermore, the resulting pressure system is symmetric and positive definite and can therefore be very efficiently solved with a matrix-free conjugate gradient method.In order to assess the capabilities of the new scheme, we show computational results for a large set of benchmark problems that range from the quasi incompressible low Mach number regime to compressible flows with shock waves.

Numerical Investigation of Turbulent Offset Jet Flow Over a Moving Flat Plate Using Low-Reynolds Number Turbulence Model

Abstract The present study reports the numerical simulation of turbulent plane offset jet flow over a moving plate. The effect of plate velocity on various flow characteristics is discussed in detail including the special case of a stationary plate. For turbulence closure, the low-Reynolds number (LRN) turbulence model proposed by Yang and Shih (YS) is applied because it is computationally robust and reported to work quite effectively in several complex flow situations. The computations have been carried out with a Reynolds number of 15,000 for various offset ratios (OR = 3, 7, and 11) and different velocity ratios (Uplate) of the plate in the range 0–2. The finite volume method (FVM) with a staggered grid arrangement has been used to solve the transport equations. The application of the LRN model along with the integration to wall (ITW) approach enables us to capture one closed loop of the Moffatt vortex near the left corner of the wall for the stationary plate case. The spreading of the jet has been found to reduce by increasing the velocity of the plate. The jet half-width lies very close to the wall for the plate to jet velocity 1.5 and 2. For two extreme limits of plate velocity, i.e., Uplate = 0 and 2, the nearly self-similar profiles are observed at different axial locations in the wall jet region. Also, the flow is observed to exhibit nearly self-similar behavior when velocity profiles are plotted for various offset ratios at a given axial location in the wall jet region for Uplate = 0 and 2. It has been found that the flow characteristics are significantly influenced by the plate velocity.

Numerical study of single helical piles and helical pile groups under compressive loading in cohesive and cohesionless soils

In recent years, the use of helical piles as a deep foundation option for structures has increased dramatically because they offer definite advantages over other solutions. The present study undertook a comprehensive investigation of the axial compressive behavior of helical piles in both sandy and clayey types of soil using finite element (FE) modeling. Since the helices of helical piles are more likely to disturb the soil adjacent to the pile, first some approaches are proposed to consider the effect of soil disturbance during a helical pile installation in numerical models. The numerical models have been validated and calibrated through full-scale compressive loading results using the ABAQUS software. The validated numerical models were used to investigate the load transfer mechanism of a typical helical pile in different types of sandy and clayey soil, and the numerically obtained ultimate bearing capacities were compared with the theoretical ones. Based on the comparison, it was found that the theoretical procedure overpredicts the ultimate capacity of helical piles in medium and dense sand. Additionally, different geometrical aspects of a typical helical pile were investigated using FE modeling in order to employ perfect geometry for studying the compressive behavior of a helical pile group with a square grid arrangement. The results revealed that the shape of the block failure mechanism in clayey soil differs from that in sandy soil. The acquired shapes are used to suggest a theoretical method for calculating the ultimate bearing capacity of a helical pile group based on the block failure mechanism.

Non-Newtonian effect on heat transfer and entropy generation of natural convection nanofluid flow inside a vertical wavy porous cavity

A numerical study on heat transfer and entropy generation in natural convection of non-Newtonian nanofluid flow has been explored within a differentially heated two-dimensional wavy porous cavity. In the present study, copper (Cu)–water nanofluid is considered for the investigation where the specific behavior of Cu nanoparticles in water is considered to behave as non-Newtonian based on previously established experimental results. The power-law model and the Brinkman-extended Darcy model has been used to characterize the non-Newtonian porous medium. The governing equations of the flow are solved using the finite volume method with the collocated grid arrangement. Numerical results are presented through streamlines, isotherms, local Nusselt number and entropy generation rate to study the effects of a range of Darcy number (Da), volume fractions (ϕ) of nanofluids, Rayleigh numbers (Ra), and the power-law index (n). Results show that the rate of heat transfer from the wavy wall to the medium becomes enhanced by decreasing the power-law index but increasing the volume fraction of nanoparticles. Increase of porosity level and buoyancy forces of the medium augments flow strength and results in a thinner boundary layer within the cavity. At negligible porosity level of the enclosure, effect of volume fraction of nanoparticles over thermal conductivity of the nanofluids is imperceptible. Interestingly, when the Darcy–Rayleigh number Ra^*gg 10, the power-law effect becomes more significant than the volume fraction effect in the augmentation of the convective heat transfer process. The local entropy generation is highly dominated by heat transfer irreversibility within the porous enclosure for all conditions of the flow medium. The particular wavy shape of the cavity strongly influences the heat transfer flow pattern and local entropy generation. Interestingly, contour graphs of local entropy generation and local Bejan number show a rotationally symmetric pattern of order two about the center of the wavy cavity.

Thirty Years of the Finite Volume Method for Solid Mechanics

Since early publications in the late 1980s and early 1990s, the finite volume method has been shown suitable for solid mechanics analyses. At present, there are several flavours of the method, which can be classified in a variety of ways, such as grid arrangement (cell-centred vs. staggered vs. vertex-centred), solution algorithm (implicit vs. explicit), and stabilisation strategy (Rhie–Chow vs. Jameson–Schmidt–Turkel vs. Godunov upwinding). This article gives an overview, historical perspective, comparison and critical analysis of the different approaches where a close comparison with the de facto standard for computational solid mechanics, the finite element method, is given. The article finishes with a look towards future research directions and steps required for finite volume solid mechanics to achieve more widespread acceptance.

Impact of surface hydrophobicity and ion steric effects on the electroosmotic flow and ion selectivity of a conical nanopore

The electroosmotic flow (EOF) and ion transport within a hydrophobic conical nanopore connecting reservoirs are studied numerically. The ion transport equation is modified to consider the ion steric effect for a finite ion size. The continuum-based model compiled with the modified Poisson–Nernst–Planck and Navier–Stokes equations are adopted for analyzing the hydrodynamics and electric field. The governing equations in their full form are solved in a coupled manner through a control volume approach over a nonuniform staggered grid arrangement. Analytic solutions for the EOF in the hydrophobic nanopore with large membrane thickness is obtained by including the volume exclusion effects in the electrochemical potential of the ionic species. The analytic solutions are obtained by considering the steric interactions based on either the Bikerman model or the Carnahan-Starling (CS) model. However, the numerical solutions are presented based on the CS model for steric interactions. The present numerical results for the hydrophobic nanopore with large pore length are validated with these analytic solutions and existing correlations based on experimental data. The fluid slip at the pore surface modifies the nanopores electrokinetic characteristics by modifying the convective transport of fluid and ions. We have elucidated the impact of pore hydrophobicity and ion steric interactions on the EOF, ionic current, ion concentration polarization (ICP) and ion selectivity when the pore length is considered to be in the order of the pore radius. The effect of pore length on the electrokinetics in the hydrophobic nanopore is also analyzed. Our numerical solution for large pore length merged with the analytic expression for the EOF in the hydrophobic nanopore of length much higher than the radius. Hydrophobicity creates significant enhancement in EOF and the rate of EOF augmentation is higher for the thinner Debye length. The perm-selectivity performance of the nanopore is enhanced when the wall is considered to be hydrophobic. The steric interactions of ions create an enhancement in EOF, ion selectivity, and ICP. The pore hydrophobicity diminishes the impact of these steric interactions.

Dynamics of stabilizer fins on the waterjet-propelled ship

An evaluation of the stabilizer fin's influence on the flow fields of a waterjet-propelled ship was studied by the Reynolds-Averaged Navier-Stokes (RANS) method. Model- and full-scale simulations of the unsteady multiphase flow were carried out both in the bare hull and the self-propulsion conditions. The reliability of grid arrangement and numerical methods was confirmed by the uncertainty analysis of the flow fields. The results indicated that the existence of stabilizer fins altered the turbulent boundary layer distribution around the hull and such disturbance extended to the capture areas of the waterjet's ingested flow. The discrepancy of the outer waterjet (OW) and the inner waterjet (IW) axial velocity distributions resulted in the difference of velocity non-uniformity in the pump inflow plane, and it also caused a relatively larger decrease in the duct efficiency of the OW. With respect to the scale effect of the flow fields, a relatively thinner boundary layer thickness and a higher non-uniformity of the internal flow were observed due to a higher turbulence in the full-scale simulation. It was noted that the model-scale computations underestimated the momentum velocity coefficients at station 1a, while they overestimated the duct efficiency in all cases, with or without the stabilizer fins.

Zero Tillage Systems Conserve Arbuscular Mycorrhizal Fungi, Enhancing Soil Glomalin and Water Stable Aggregates with Implications for Soil Stability

Arbuscular Mycorrhizal (AM) fungi form mutualistic symbiotic relationships with approximately 80% of terrestrial plant species, while producing the glycoprotein glomalin as a structural support molecule along their mycelial network. Glomalin confers two benefits for soils: (1) acting as a carbon and nitrogen storage molecule; (2) the binding of soil microaggregates (<250 µm) to form larger, more stable structures. The present study aimed to test the hypothesis that a correlation between glomalin and soil aggregation exists and that this is influenced by the method of seedbed preparation. The soils from two crops of winter wheat in Hertfordshire, UK, practising either conventional (20 cm soil inversion) or zero tillage exclusively, were sampled in a 50 m grid arrangement over a 12 month period. Glomalin and water stable aggregates (WSA) were quantified for each soil sample and found to be significantly greater in zero tillage soils compared to those of conventional tillage. A stronger correlation between WSA and glomalin was observed in zero tillage (Pearson’s coeffect 0.85) throughout the cropping year compared to conventional tillage (Pearson’s coeffect 0.07). The present study was able to conclude that zero tillage systems are beneficial for AM fungi, the enhancement of soil glomalin and soil erosion mitigation.

A Low Complexity Indoor Visible Light Positioning Method

The continuous positioning of a mobile user equipment (MU) in a prompt way is a fundamental requirement in several indoor applications related to ubiquitous computation, assisted living environments, and security/surveillance systems. Motivated by this fact, the current contribution reports a low-complexity visible light positioning (VLP) method suitable for indoor environments in the Big Data era. The proposed architecture consists of multiple light-emitting diodes (LEDs) as light sources and an MU equipped with a photodiode (PD). To guarantee higher spectral efficiency, the LEDs emit sinusoidal waveforms at slightly different predetermined frequencies. The light intensity received at the PD from every LED is continuously estimated after applying a short-time Fourier transformation. To this end, a grid-based numerical technique is proposed to recover the unknown MU position. Additionally, a closed-form solution is presented for the particular case of three LEDs that overrides the need for training points in the grid arrangement. Further, a method for handling noisy signals is proposed, based on averaging the calculated positions from densely overlapping received signals. Finally, a Kalman filter is employed as a post-processing precision improving tool. The proposed VLP efficiency is quantified through respective Monte Carlo simulations that allow the setting of different LED frequencies, received signal processing parameters, MU speed, and noise levels. The results reveal that the suggested approach is robust with significant tolerance in high ambient light levels, computationally efficient, and exhibits low positional error. Finally, to evaluate the performance improvements the new method introduces, we make comparisons against widely-used fingerprint approaches.