Rouhollah Fatehi

Bio: Rouhollah Fatehi is an academic researcher from Persian Gulf University. The author has contributed to research in topics: Smoothed-particle hydrodynamics & Reynolds number. The author has an hindex of 15, co-authored 41 publications receiving 662 citations. Previous affiliations of Rouhollah Fatehi include Sharif University of Technology.

Error estimation in smoothed particle hydrodynamics and a new scheme for second derivatives

Abstract: Several schemes for discretization of first and second derivatives are available in Smoothed Particle Hydrodynamics (SPH). Here, four schemes for approximation of the first derivative and three schemes for the second derivative are examined using a theoretical analysis based on Taylor series expansion both for regular and irregular particle distributions. Estimation of terms in the truncation errors shows that only the renormalized (the first-order consistent) scheme has acceptable convergence properties to approximate the first derivative. None of the second derivative schemes has the first-order consistency. Therefore, they converge only when the particle spacing decreases much faster than the smoothing length of the kernel function. In addition, using a modified renormalization tensor, a new SPH scheme is presented for approximating second derivatives that has the property of first-order consistency. To assess the computational performance of the proposed scheme, it is compared with the best available schemes when applied to a 2D heat equation. The numerical results show at least one order of magnitude improvement in accuracy when the new scheme is used. In addition, the new scheme has higher-order convergence rate on regular particle arrangements even for the case of only four particles in the neighborhood of each particle.

A modified SPH method for simulating motion of rigid bodies in Newtonian fluid flows

Abstract: A weakly compressible smoothed particle hydrodynamics (WCSPH) method is used along with a new no-slip boundary condition to simulate movement of rigid bodies in incompressible Newtonian fluid flows. It is shown that the new boundary treatment method helps to efficiently calculate the hydrodynamic interaction forces acting on moving bodies. To compensate the effect of truncated compact support near solid boundaries, the method needs specific consistent renormalized schemes for the first and second-order spatial derivatives. In order to resolve the problem of spurious pressure oscillations in the WCSPH method, a modification to the continuity equation is used which improves the stability of the numerical method. The performance of the proposed method is assessed by solving a number of two-dimensional low-Reynolds fluid flow problems containing circular solid bodies. Wherever possible, the results are compared with the available numerical data.

A consistent and fast weakly compressible smoothed particle hydrodynamics with a new wall boundary condition

Abstract: SUMMARY A modified weakly compressible smoothed particle hydrodynamics (WCSPH) is presented, which utilizes consistent discretization schemes for spatial derivatives in the flow equations. Here, each SPH particle is considered as a computational point that represents a specific part of the fluid. To overcome non-physical oscillations that usually arise in standard WCSPH, we modified the mass conservation equation by using a numerical filter. This modification is based on the difference between two discretization schemes used for the term ∇⋅∇Pρ. Furthermore, a new implementation of wall boundary condition in SPH is introduced. This condition is imposed on the pressure of wall boundary particles to ensure that the acceleration of each boundary particle in normal direction to the wall is zero. Thus, no penetration through walls will occur. To examine the performance of the modified method, we solved a series of two-dimensional incompressible internal flow benchmark problems. By comparing the result with analytical solutions and the results of the standard WCSPH, we show that the use of consistent schemes in conjunction with the proposed numerical filter improves both accuracy and speed of the numerical method. Copyright © 2011 John Wiley & Sons, Ltd.

SPH simulation of interacting solid bodies suspended in a shear flow of an Oldroyd-B fluid

Abstract: An explicit weakly compressible SPH method is introduced to study movement of suspended solid bodies in Oldroyd-B fluid flows. The proposed formulation does not need further stabilizing treatments and can be efficiently employed to study particulate flows with Deborah to Reynolds number ratios up to around 10. A modified boundary treatment technique is also presented which helps to deal with the movement of solid particles in the flow. The technique is computationally efficient and gives an improved evaluation of fluid-solid interaction forces. A number of test cases are solved to show performance of the proposed method in simulating particulate viscoelastic flows containing circular and non-circular cylinders. The effect of Deborah number on the particle trajectory has been investigated.

Design of a Biomass Power Plant for Burning Date Palm

Abstract: Date palm trees (Phoenix dactylifera L.) produce approximately 40 kg ofburnable waste including dried leaves, spathes, sheaths, and petioles annu-ally. In this paper, the potential of date palm waste as a bioenergy source hasbeen investigated. As a sample project, a power plant has been preliminarydesigned to simultaneously generate electrical power using a steam Rankinecycle and distilled water by the thermal desalination of seawater using a mul-tiple e ect evaporator. The results indicated that a small plant in BushehrProvince in southern Iran which burns 140,000 tons of waste annually canproduce approximately 62 GWh of electricity in conjunction with 2.27 mil-lion tons of distilled water. This production is equivalent to 75 GWhe/year.Environmental assessments revealed that the use of this amount of biomassleads to a net green-house gas (GHG) reduction of 40,500 tCO 2 /year. 9 Key words: Biomass energy, Date palm, Cogeneration, Thermal 10 desalination, Rankine cycle Corresponding author Tel.: +987714222170, Fax: +987714540376, email:fatehi@pgu.ac.ir

Smoothed particle hydrodynamics (SPH) for free-surface flows: past, present and future

Abstract: This paper assesses some recent trends in the novel numerical meshless method smoothed particle hydrodynamics, with particular focus on its potential use in modelling free-surface flows. Due to its Lagrangian nature, smoothed particle hydrodynamics (SPH) appears to be effective in solving diverse fluid-dynamic problems with highly nonlinear deformation such as wave breaking and impact, multi-phase mixing processes, jet impact, sloshing, flooding and tsunami inundation, and fluid–structure interactions. The paper considers the key areas of rapid progress and development, including the numerical formulations, SPH operators, remedies to problems within the classical formulations, novel methodologies to improve the stability and robustness of the method, boundary conditions, multi-fluid approaches, particle adaptivity, and hardware acceleration. The key ongoing challenges in SPH that must be addressed by academic research and industrial users are identified and discussed. Finally, a roadmap is propose...

Inertio-elastic focusing of bioparticles in microchannels at high throughput

Abstract: Controlled manipulation of particles from very large volumes of fluid at high throughput is critical for many biomedical, environmental and industrial applications. One promising approach is to use microfluidic technologies that rely on fluid inertia or elasticity to drive lateral migration of particles to stable equilibrium positions in a microchannel. Here, we report on a hydrodynamic approach that enables deterministic focusing of beads, mammalian cells and anisotropic hydrogel particles in a microchannel at extremely high flow rates. We show that on addition of micromolar concentrations of hyaluronic acid, the resulting fluid viscoelasticity can be used to control the focal position of particles at Reynolds numbers up to Re≈10,000 with corresponding flow rates and particle velocities up to 50 ml min−1 and 130 m s−1. This study explores a previously unattained regime of inertio-elastic fluid flow and demonstrates bioparticle focusing at flow rates that are the highest yet achieved. Controlled manipulation of particles from very large volumes of fluid at high throughput is critical for many real-world applications. Here, the authors show bioparticle focusing in a microchannel for a previously unattained regime of inertio-elastic flow at Reynolds numbers up to 10,000.