Kelvin-Helmholtz instability by SPH

In this paper, we have modeled the Kelvin-Helmholtz Instability (KHI) problem of an incompressible two-phase immiscible fluid in a stratified inviscid shear flow with interfacial tension using Smoothed Particle Hydrodynamics (SPH) method. The time dependent evolution of the two-fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. It was observed that the SPH method requires a Richardson number lower than unity (i.e.,Ri ∼ = 0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle a two-phase fluid flow with various density ratios

Psychiatric disorders among people living with HIV/AIDS in IRAN: Prevalence, severity, service utilization and unmet mental health needs

Background: HIV and psychiatric disorders are closely correlated and are accompanied by some similar risk factors. Objective: The aim of this study was to assess psychiatric comorbidity and health service utilization for mental problems among people living with HIV/AIDS in Iran. Methods: A total of 250 cases were randomly selected from a large referral center for HIV treatment and care in Tehran, Iran. Psychiatric disorders in the past 12 months including mood, anxiety, and substance use disorders were assessed through face-to-face interview, using a validated Persian translation of the Composite International Diagnostic Interview (CIDI v2.1). Severity of psychiatric disorders, social support, socio-economic status, service utilization and HIV-related indicators were assessed. Results: Participants consisted of 147 men and 103 women. Psychiatric disorders were found in 50.2 (95 confidence interval: 43.8�56.6) of the participants. Major depressive disorder was the most prevalent diagnosis (32.1), followed by substance use disorders (17.1). In bivariate analysis, psychiatric disorders were significantly higher among male gender, single and unemployed individuals and those with lower social support. In multivariate regression analysis, only social support was independently associated with psychiatric disorders. Among those with a psychiatric diagnosis, 41.1 had used a health service for mental problems and 53 had received minimally adequate treatment. Conclusion: The findings of the study highlight the importance of mental health services in the treatment of people living with HIV/AIDS. © 2018 Elsevier Inc

A parameter-free total Lagrangian smooth particle hydrodynamics algorithm applied to problems with free surfaces

This paper presents a new Smooth Particle Hydrodynamics computational framework for the solution of inviscid free surface flow problems. The formulation is based on the Total Lagrangian description of a system of first-order conservation laws written in terms of the linear momentum and the Jacobian of the deformation. One of the aims of this paper is to explore the use of Total Lagrangian description in the case of large deformations but without topological changes. In this case, the evaluation of spatial integrals is carried out with respect to the initial undeformed configuration, yielding an extremely efficient formulation where the need for continuous particle neighbouring search is completely circumvented. To guarantee stability from the SPH discretisation point of view, consistently derived Riemann-based numerical dissipation is suitably introduced where global numerical entropy production is demonstrated via a novel technique in terms of the time rate of the Hamiltonian of the system. Since the kernel derivatives presented in this work are fixed in the reference configuration, the non-physical clumping mechanism is completely removed. To fulfil conservation of the global angular momentum, a posteriori (least-squares) projection procedure is introduced. Finally, a wide spectrum of dedicated prototype problems is thoroughly examined. Through these tests, the SPH methodology overcomes by construction a number of persistent numerical drawbacks (e.g. hour-glassing, pressure instability, global conservation and/or completeness issues) commonly found in SPH literature, without resorting to the use of any ad-hoc user-defined artificial stabilisation parameters. Crucially, the overall SPH algorithm yields equal second order of convergence for both velocities and pressure

Age-Related Activity Changes in Arginine Phosphokinase in the House Fly, Musca Domestica L

The activity of ATP:L-arginine phosphotransferase (E.C.2.7.3.3.). Was shown to exhibit agedependent changes in both male and female house fly. Enzyme activity demonstrated more marked changes in the male than in the female, increasing 44-fold from emergence to a peak at 2 days of age and thereafter declining, at first sharply then gradually to a value at 14 days of age, representing a third of the activity found at the peak. Activity in the female fly also showed a peak at 2 days of age, which thereafter declined, although more gradually than was observed in the male. Activity changes expressed on a per fly or wet weight basis were nearly identical. Agerelated activity changes on a milligram protein basis demonstrated similar increases; however, the percentage decrease from the 2-day peaks were less striking, although highly significant. No kinetic or physical changes in the enzyme were detected, nor could any soluble inhibitors or activators of the enzyme be identified. The changes in arginine phosphokinase activity fall into a sequential pattern of enzyme changes, reflecting an apparently ordered mechanism underlying a decline in flight ability in this specie

Kelvin-Helmholtz instability by SPH

In this paper, we have modeled the Kelvin-Helmholtz Instability (KHI) problem of an incompressible two-phase immiscible fluid in a stratified inviscid shear flow with interfacial tension using Smoothed Particle Hydrodynamics (SPH) method. The time dependent evolution of the two-fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. It was observed that the SPH method requires a Richardson number lower than unity (i.e.,Ri ∼ = 0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle a two-phase fluid flow with various density ratios

Kelvin-helmholtz instability by SPH

cited By 0; Conference of 2nd International Conference on Particle-Based Methods, PARTICLES 2011 ; Conference Date: 26 October 2011 Through 28 October 2011; Conference Code:89485International audienceIn this paper, we have modeled the Kelvin-Helmholtz Instability (KHI) problem of an incompressible two-phase immiscible fluid in a stratified inviscid shear flow with interfacial tension using Smoothed Particle Hydrodynamics (SPH) method. The time dependent evolution of the two-fluid interface over a wide range of Richardson number (Ri) and for three different density ratios is numerically investigated. The simulation results are compared with analytical solutions in the linear regime. It was observed that the SPH method requires a Richardson number lower than unity (i.e., Ri ≅ 0.8) for the onset of KHI, and that the artificial viscosity plays a significant role in obtaining physically correct simulation results that are in agreement with analytical solutions. The numerical algorithm presented in this work can easily handle a two-phase fluid flow with various density ratios

Laminar-turbulent transition in supersonic boundary layers with surface heat transfer: A numerical study

WOS:000407958600003International audienceThrough high-resolution direct numerical simulations, the present study aims to investigate several laminar-to-turbulent transition scenarios in the presence of wall heat transfer for supersonic boundary layers over strongly heated/cooled and adiabatic flat plates. The laminar boundary layer is tripped using a suction and blowing technique with a single-frequency, multiple-spanwise wavenumber excitation. The results are evaluated and compared with linear stability theory to isolate the effect of wall heat transfer, as well as forcing parameters, on the transition. It was found that increasing the disturbance amplitude as well as perturbation frequency moves the transition upstream. Also, the effect of wall heating was seen to stabilize the flow and to postpone the transition, contrary to the wall cooling

Fluid-Structure Interaction simulation by smoothed particle hydrodynamics

cited By 1; Conference of ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting, FEDSM 2010 - ASME 2010 7th International Symposium on Fluid-Structure Interactions, Flow-Sound Interactions, and Flow-Induced Vibration and Noise, FSI2 and FIV+N ; Conference Date: 1 August 2010 Through 5 August 2010; Conference Code:87047International audienceIn this article, a modified SPH algorithm is proposed to solve Fluid-Structure Interaction (FSI) problems including fluid flow in interaction with compatible structures under a large deformation. To validate the current algorithm against available data in literature, we consider two important benchmark cases; namely, an oscillating elastic beam and dam breaking problems. The proposed algorithm is based on the elimination of the intermediate data transfer steps between the fluid and the solid structures, whereby resulting in an easy and time-saving simulation method. With the test application studied, we were able to prove the ability of the modified SPH method for solving of fluid and solid domains monolithically without the need to define an interfacial boundary condition or any additional steps to simulate the deformation of an elastic dam. Numerical results suggest that upon choosing correct SPH parameters such as smoothing function, and lengths, as well as coefficients for artificial viscosity and artificial stress, one can obtain results in satisfactorily agreement with numerical findings of earlier works. Copyright © 2010 by ASME

Three-dimensional numerical investigation of film boiling by the lattice Boltzmann method

WOS:000397229200006International audienceA three-dimensional lattice Boltzmann model is presented to simulate the film-boiling phenomenon. Single-and multimode film boilings are investigated. The flow and temperature fields around the vapor phase are obtained for various Jakob numbers. Furthermore, the effects of Jakob number on the Nusselt number and vapor tip velocity are investigated. The results show that on increasing the Jakob number, the bubble tip velocity increases while the Nusselt number decreases. Furthermore, it is found that in multimode film boiling, the peak and trough values of the local Nusselt number happen at the bubble position and the gap valleys between adjacent bubbles, respectively