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A passive scalar is a property that is affected by the flow field without affecting it. In this paper, first, the governing equations on the turbulent flows are solved and the property of a passive scalar in two dimensions is numerically studied. Having the values of the velocity components, the governing equation on transport of a passive scalar is solved. To compute the turbulent velocity field, the Large Eddy Simulation (LES) method using Smagorinsky subgrid scale is invoked. The flow in a cavity has been the basis to validate the accuracy of the generated computer code. To ensure the compatibility between the flow and the transport of passive scalar fields a similar LES approach is used. As a three-dimensional numerical solution for a turbulent flow fields needs a massive computational time and efforts, therefore a two-dimensional simulation used for a proper saving. Instead, to validate the numerical results, the range of the Reynolds number of the flow is kept within the range of the two-dimensional measurements. Comparison of the numerical results and the experimental measurements in two-dimension reveals the high accuracy of the results and compatibility between the flow and passive scalar fields. Ability of developed scheme to accurately handle transport of a passive scalar is promising to extend LES method into the transport of more species and hence to simulate reacting flows.

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Background: This study aimed to investigate the prevalence and potential risk factors of Staphylococcus aureus nasal carriage in household pets (cats and dogs) and their owners in Chlef province in Algeria and to determine the isolates antibiotic resistance profiles.
Materials & Methods: S. aureus was isolated from nasal swabs, identified by culture on mannitol salt agar (MSA), and confirmed by polymerase chain reaction (PCR) amplification of the nuc gene. Methicillin-resistant S. aureus (MRSA) isolates were identified by their resistance to cefoxitin and PCR targeting the mecA gene. Panton-Valentine leukocidin (PVL) toxin genes were screened by PCR. Antimicrobial resistance was determined by disc diffusion method. The effect of risk factors on S. aureus nasal carriage was evaluated using a multivariable generalized linear model (GLM).
Findings: A total of 110 nasal swabs were collected: 29, 31, and 50 from dogs, cats, and their owners, respectively. The nasal carriage rate of S. aureus was 25% in household pets (22.6% in cats and 27.6% in dogs) and 22% in their owners.
MRSA isolates were recovered only from pets (6.6%); 25% of them were multidrug resistant (MDR). One MDR MRSA isolate was PVL-positive.
The age of dogs was the only risk factor significantly associated with S. aureus nasal carriage.
Conclusion: The results revealed that nasal carriage of S. aureus in household pets was relatively high, raising concern about their potential risk to human health and stressing the importance of active surveillance of S. aureus carriage in pets.

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- Natural convection heat transfer in a square cavity induced by heated plate is investigated using the lattice Boltzmann method. A suitable forcing term is represented in the Boltzmann equation. With the representation, the Navier-Stokes equation can be derived from the lattice Boltzmann equation through the Chapman-Enskog expansion. Top and bottom of the cavity are adiabatic; the two vertical walls of the cavity have constant temperatures lower than the plate’s temperature. The flow is assumed to be two-dimensional. Air is chosen as a working fluid (Pr=0.71). The study is performed for different values of Grashof number ranging from 103 to 105 for different aspect ratios and position of heated plate. The effect of the position and aspect ratio of heated plate on heat transfer are discussed. With increase of the Grashof number, heat transfer rate is increased in both vertical and horizontal position of the plate. The obtained results of the lattice Boltzmann method are validated with those presented in the literature.

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Water-Alumina natural convection heat transfer in an inclined L shape cavity ABSTRACT A numerical investigation of water-alumina natural convection laminar flow in an inclined L shape cavity is performed. Two wall of the cavity are hot with the temperature of Th, two walls are cold with the temperature of Tc , and two other walls are thermally adiabatic. The two dimensional continuity, momentums and energy equations are solved numerically with a finite volume approach using the well known SIMPLE algorithm. The influence of pertinent parameters such as Rayleigh number, Ra, solid volume fraction, , inclination angle, , and cavity aspect ratio, A, on the fluid flow, fluid temperature and cavity heat transfer characteristics is studied. The results indicate that nanofluid with higher nanoparticles has better performance. The results also show that the inclination angle has a significant effect on the heat transfer performance at high Rayleigh numbers. Keywords: Natural convection, nanofluid, L shape cavity, Rayleigh number.

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In this paper, analysis the performance of PI, PI-like fuzzy, and parallel fuzzy P+ fuzzy I controllers for He-Ne lasers frequency stabilization by combination of frequency locking and power balanced methods is presented. He-Ne lasers can be attributed to an unstable system due to the influence of environmental factors on its' frequency. Therefore, the stabilization of He-Ne laser is so important in sensitive applications such as laser interferometers and nanometrology systems. The simulation results of controllers by powerful software MATLAB/SIMULINK-GUI show that parallel fuzzy P+ fuzzy I controller has better stabilization performance and integrated absolute error (IAE) than others. Also, frequency fluctuations of He-Ne laser is about 2×10^-11 by parallel fuzzy P+ fuzzy I controller.    

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Aims: Fine dust is one of the environmental challenges in dry areas, which disturb human comfort. Wind is the main factor in the movement of fine dust, and the movement pattern of wind is affected by the architecture of cities. The presence of a hole in the form is one of the design which affects the wind load and the flow of fine dust. The purpose of this research is to compare the distribution of fine dust in a tall building with horizontal cavity, with variable number and volume of cavity.

Methods: Numerical study was done by CFD. K-omega-SSD turbulence model is used. In order to the software data (the size and type of particles), the field sampling method has been used.

Findings: The findings of the research show that as the number of holes increases in volume and their size decreases, the wind speed inside the holes decreases and on the other hand, the movement behavior of the wind and accordingly the dispersion behavior of the particles become more uniform. In these cavities, the concentration of suspended particles increases and their size becomes smaller.

Conclusion: The results show that the design of the form with more holes and smaller volume is more suitable to deal with the phenomenon of fine dust and to achieve comfort in indoor environments. In addition, the design of the openings at higher heights and the depth of the holes reduces the settling rate of fine dust particles in the interior spaces.
 

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An efficient reduced-order modeling (ROM) approach to predict unsteady behavior of partial cavity flows is proposed. The unsteady potential flow along with the cavity effects is analyzed using the boundary element method (BEM). Partial cavity flow is modeled based on the partially non-linear model without re-gridding with some modification. Proposed reduced-order model (PROM) is based on the fluid eigenmodes. The spatial iterative scheme that is usually used to determine the cavity extent is efficiently removed in order to construct the flow eigensystem. Eigenanalysis and reduced-order modeling of unsteady flows over a NACA 16-006 section are performed using the proposed reduced-order modeling approach. Numerical examples are presented to demonstrate the accuracy of the proposed method. Comparison between the obtained results of the proposed method and those of conventional ones indicates that the present algorithm works well with sufficient accuracy. Finally, it is shown that the proposed method is computationally more efficient than the conventional one for unsteady sheet cavitation analysis on hydrofoils.

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In this paper, natural convection heat transfer inside an enclosure which is partially filled with porous layer is reported using lattice Boltzmann method. Generalized equations in modeling flow in porous media have been employed which are coupled with the lattice Boltzmann formulation of the momentum and energy equations. The present study investigates the effect of position of porous layer on heat transfer rate for different dimensionless parameters, such as Rayleigh number, Darcy number and porosity of the porous layer. In addition, a modified Rayleigh number is presented as an effective parameter which affects the degree of penetration of the fluid into the porous layers. The obtained results showed that the heat transfer rate in the case of vertical layer is more than that of horizontal porous layers.

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Abstract- In this paper, two-dimensional natural convection heat transfer in semi ellipse cavities is investigated using lattice Boltzmann method. The Prandtl number is taken as 0.71 that corresponds to that of air. Heat transfer and flow pattern are predicted at various Rayleigh numbers ranging from 104 to 106 for different aspect ratios. By increasing of the aspect ratio, the heat transfer rate in the cavity is increased for low Rayleigh numbers, but it is decreased for high Rayleigh numbers. The obtained results of the lattice Boltzmann method are validated with those presented in the literature and show that the lattice Boltzmann method can simulate heat transfer and flow pattern in complex cavities. Analysis of heat transfer in a semi-ellipse cavity using second order boundary condition on curved surfaces is among the novelties of the present work.

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In this paper, numerical solution of non-Newtonian fluid flow through a channel with a cavity is studied. Carreau-Yasuda non-Newtonian model which represent dependence of stress on shear rate well is used and the effect of n index of model on attribute of flow is considered. Governing equations are discretized using finite difference method on staggered mesh and the form of allocating flow parameters on staggered mesh is based on marker and cell method. For dependence between continuity and momentum equations, artificial compressibility method is used. Numerical results express that with decrease of n index, the developing length is increased and the velocity in center of channel and pressure drop of flow are decreased.

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In this work, mixed convection of Cu-water nanofluid in a trapezoidal enclosure with heat source on lateral walls has been numerically investigated. Vertical walls of the enclosure are kept at constant temperatures of Th and Tc, while horizontal walls are insulated. The mixed convection flow has been generated by passing the fluid through the enclosure and natural convection has been, also, investigated by holding the left wall at a temperature higher than the right wall. In order to examine the effect of the ports position, two cases were considered. Comparison between the results indicates that the rate of heat transfer is higher when the inlet port is near the cold wall than the hot wall. The results have been presented for various volume fractions, Richardson and Reynolds numbers. It was observed that for the considered Reynolds numbers and Richardson number, at a given Reynolds number and solid volume fraction, the Nusselt number increases with increasing the Richardson number. Moreover, at a given Richardson number and solid volume fraction, increasing the Reynolds number results in an increase in the Nusselt number. For the higher Richardson and Reynolds numbers, the nanofluid has more effect on the increase of the heat transfer performance.

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In this paper, the result of a numerical study on the natural convection in an inclined T shap cavity filled with Water-Cu nanofluid with the presence of a constant magnetic field was investigated. A heat source embedded on the bottom wall of enclosure, the upper wall is cold and the other walls are adiabatic. Discretization of the governing equations are achieved through a finite volume method and solved with SIMPLE algorithm. The Hartmann number has been varied from 0 to 80 and the cavity has been twisted under the angles between 0 to 90 degrees. The findings of study show that the effect magnetic field on the average Nusselt number is higher in high Reyleigh number. In Ra=105, the increase in nanofluid, to the Hartman number 20, contributes to decrease of the average number and in the Hartman number 40 and more, causes the average Nusselt number to increase. In Ra=106 , the increase in nanofluid, to the Hartman number 20, contributes to increase of the average number and in the Hartman number 40 and more, causes the average Nusselt number to decrease. The results also indicate that, the maximum heat transfer, in Ra=105 and Ra=106 accurse at 67.5° angle. the minimum heat transfer, in Ra=105 and Ra=106 accurse at 0° and 22.5° angle respectively.

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The nose and nasal cavity and sinuses are a parts of the upper respiratory system and study the air passage into the upper component of human airway is important to improve or cure deficiency in human respiration cycle. The nose performs many important physiological functions, including heating, humidifying and filtering inspired air, as well as sampling air to smell. Previously, numerical modeling of turbulent flow in nasal cavity, sinus, pharynx and larynx has rarely been employed Since the 1990s, with the development of computed tomography technology and computational fluid dynamics, a number of numerical studies on gas and particle flows in realistic nasal cavities have been conducted and provided precise data for deeper insight of the nature of nasal airflows. Also, most of pioneering studies in this field have been developed to the investigation of only nasal cavity without sinuses especially maxillary sinus So, this research is tried to study details of turbulent airflow through all spaces in human head that air can flow through. For this purpose, study has based on computed tomography scans image of a 26-years old female head, neck and chest without problems in her respiratory system from Shahid Chamran hospital, Shiraz, Iran. It is found that, nasal resistance was contribute up to half of the total airway resistance within the first 2-3 cm of the airway and the majority of the flow in this region remained close to the septum wall and only a small proportion reached the olfactory region.

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Taguchi method since 1980 is used as an effective way to optimize the design process engineering tests. In this paper by using of taguchi method optimal conditions of the mixed convection and entropy generation in a square cavity filled with Cu-water nanofluid is analyzed. For this purpose a L16 (43) orthogonal taguchi array is used. Discretization of the governing equations were achieved through a finite volume method and solved with SIMPLE algorithm. The effect of Richardson number (0.1-100 ), the volume fraction of copper nanoparticles (0-10%) and the wavelength of the wavy surface (0- 1) as an effective parameters for analyzing in four levels are considered. This analysis was performed for fixed Grashof number 104. The results show that the mean Nusselt number decreases by increase of the Richardson number, the volume fraction of nanoparticles and the wavelength of the wavy surface. It is found that the Flat plate (for wavy surface with the wavelength 0) and the volume fraction 0% in the Richardson number 0.1 is optimal design for heat transfer while the geometry with Ф=5%, Ri=100 and λ=0.25 is optimal design for entropy generation. Finally for maximum heat transfer and minimum entropy generation the geometry with Ф=0%, Ri =1 and λ=0.25 can be considered as an optimal design.

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In the present work, the elastodynamic field of scattering of an anti-plane high frequency elastic shear wave due to an embedded nano cylindrical cavity in an infinite elastic medium is obtained by considering the effects of couple-stresses. In the theories accounting the effects of couple-stresses in their formulations, a new characteristic length of material is introduced into the formulations, and so, these are capable to capture size effect at micro and nano scales. Also, in contrary to classical continuum theory which has difficulties in describing dispersion of wave at high frequencies, observed dispersive wave in experiments can be explained in the framework of these theories. In this work, the analytical expressions of elastodynamic fields around the cavity are obtained by considering equation of motion, dispersion relation and appropriate boundary conditions in the framework of two theories considering couple-stresses. Also, the dynamic stress concentration factor around the cavity within these theories is obtained, and, as a limiting case, the results of two cases of dynamic stress concentration factor in classical theory as well as static stress concentration factor in couple stress theories are recovered. In the framework of these theories, by several examples, the effects of frequency of incident wave and the ratio of couple stress characteristic length to the size of the cross section of the cavity on the displacement field, stress field and dynamic stress concentration factor around the cavity are studied, and the results are compared with the corresponding classical solutions.

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Development and application of high-speed underwater vehicle is the cause for considering super-cavitating flows by many researchers. Frictional drag decreases and vehicle’s velocity increases due to cavity generation. The objective of the present research is to find the coefficients of an optimized equation to estimate cavity length around a submercible vehicle equipped with a wedged-shaped cavitator which has important practical applications. For this purposes, the super cavitation phenomena has been simulated numerically around three bodies with different geometry. At first stage, to validate the results of numerical simulation of present work a well-established experimental result of a cylindrical body with hemispheric cap is used for comparison. This comparison is used for parameters effecting numerical method, turbulence flow model and mass transfer model. As this comparison is confirmed, the simulation is continued at second stage for super cavitation phenomena initiation around a wedged-shaped cavitator with two 15 and 45 degrees angle. At third stage, the super cavitation flow is analyzed around a submersible body equipped with a wedged-shaped cavitator. The cavity length and related coefficients are obtained for three cases using different cavitation numbers. The developed equation is similar for all cases with different coefficients. The averaged Navier-Stokes equations are solved in transient case using finite volume method. Different mass transfer models with turbulent flow models are used at different conditions. The numerical results are validated with experimental results of other researchers. Comparison is encouraging.

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This study presents a numerical investigation for laminar mixed convection flow of radiating gases in an inclined lid-driven cavity. The fluid is treated as a gray, absorbing, emitting and scattering medium. The governing differential equations consisting the continuity, momentum and energy are solved numerically by the computational fluid dynamics (CFD) techniques to obtain the velocity and temperature fields. Discretized forms of these equations are obtained by the finite volume method and solved using the SIMPLE algorithm. Since the gas is considered as a radiating medium, besides convection and conduction, radiative heat transfer also takes place in the gas flow. For computation of the radiative term in the gas energy equation, the radiative transfer equation (RTE) is solved numerically by the discrete ordinate method (DOM). The effect of lid driven speed, on the thermohydrodynamic behavior of two-dimensional cavity is carried out. Results are shown as contours of isotherms, streamlines and distributions of convective and total Nusselt numbers along the bottom wall of cavity. It is revealed that increasing in Reynolds number causes almost uniform temperature distribution in cavity, especially for 30° and 60° inclination angles.

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Cavity length estimation is important as supercavity condition is generated. The cavity length is function of cavity number and is calculated by relations deduced from experimental results which are different from each other and are not driven from analytical approaches. Literature survey shows that correlations based on cavity length in relation with Reynolds and cavity numbers have not been attempted. The present work purpose is to estimate analytical based relations for cavity length with respect to mass transfer, continuity and momentum conservation equations. This effort which has been conducted by order of magnitude method resulted in three relations. The first analytical based relation calculates cavity length versus cavity number. The obtained relation shows that cavity length is proportional with the inverse square root of cavity number. The second analytical relation calculates cavity length in respect to Reynolds number. It shows cavity length has proportional relation to Reynolds square root. The third analytical relation considers cavity number in respect to Reynolds number. The third relation shows that cavity number has inverse relation to Reynolds number. Unknown coefficients values of the relations obtained through comparison with the already existed experimental results. These analytical relations which are appropriate alternative to experimental based relations estimate cavity length in respect to cavity and Reynolds number.

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In this paper simulation of steady super cavitation phenomenon اhas been considered by using partial non-linear model of Boundary Element Method(BEM).The grid mesh used is fixed and the strength of dipole and source are constant on each element. With the assumption of a partial non-linear model the cavity condition is applied on the body with the assumption that cavity height is low. Thus there is not any calculation on the cavity surface, but it is restricted to only the panels on the body surface. Cavitation number is known at first and the cavity length is determined in every iteration. When the lengths obtained in two successive iterations are very close to each other it assumed to be the answer. Based on this method two Kutta conditions including Morino condition and Iterative Pressure Kutta Condition(IPKC) are studied to satisfy the wake surface condition. The application is a wing with NACA16006 section. Iterative pressure Kutta condition compared to Morino condition needs higher computational costs, but on the other hand leads to more accurate results. It has been shown that the simulation of the flow with super cavitation over wing leads to a pressure difference at the trailing edge of each strip if we use Morino’s Kutta condition. While if Iterative Pressure Kutta Condition is usedthe results are satisfactory. Comparing the results show that this method leads to very accurate predictions for the behavior of flows with cavitation, while significantly lower computational cost is required if we use the simple cavity closure condition.

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Abstract melting of Cyclohexane-Cu nano-material in a porous square cavity is studied numerically in this paper. At first initial temperature of the cavity is Ti that is equal to melting temperature of nano-material,Tm ,. The horizontal walls are adiabatic. Suddenly the left wall's temperature has changed to Th>Tm . The effective parameters in this case are and which appear in the nondimensionalized equations. Nondimensionalized governing equations are obtained based on the Darcy model; a control volume approach is used for solving these equations. The effect of the variation of mentioned parameters are investigated on the heat transfer rate, fluid flow, isotherms and melting time of nano-PCM. The results show that changing of any parameters will be effective on increase or decrease of heat transfer rate and melting process time. For example variation of has high effect on melt fraction in cavity with time. The results show that melting of PCM is prolonged when nano-particles are added. the increases of the Ra increases the natural convection heat transfer and therefore increases the melting rate, and deforms the melting line.