Mehrdad Ahmadinejad

Particles experience oscillatory straining flows in a variety of situations, including flow in a wavy-walled conduit (such as a clothes dryer vent), colloidal particle transport through porous media, peristaltic transport, and particulate flows subject to acoustic excitation. Under the action of an oscillating straining flow, particulates exhibit a tendency to cluster at the center of straining due to the effects of particle inertia—a phenomenon referred to as oscillatory clustering. However, in the presence of a porous medium or other external bodies, particle oscillatory motion may be temporarily hindered. The capture-and-release events of random hindering act as a stochastic random walk, leading to diffusion of the particles in a process referred to as oscillatory diffusion. The current paper explores the dynamics of particulate flows subject to both oscillatory clustering and diffusion in both one and three dimensions using a stochastically perturbed discrete element method for particle simulation. The rates of clustering and diffusion are determined analytically, and situations exhibiting a combination of oscillatory clustering and diffusion are examined.

Heavy reliance on fossil fuels for power generation leads to significant energy waste, high operating costs, and substantial CO ₂ emissions, highlighting the urgent need for climate‐responsive solutions, such as hydrogen‐based energy systems. This article introduces and optimizes a novel hydrogen‐based multi‐generation system that combines Compressed Air Energy Storage (CAES), a Proton Exchange Membrane Electrolyzer (PEME), and an Organic Rankine Cycle (ORC) to enhance thermodynamic performance and reduce environmental impacts. Using Response Surface Methodology (RSM) in Minitab, six system scenarios incorporating different organic fluids and oils in the ORC are evaluated under varying climatic conditions (Paris, London, San Francisco, and Dubai), representing temperate, maritime, and hot desert climates. The optimal scenario achieves an Exergy Round Trip Efficiency (ERTE) of 64.28%, a cost rate reduction of 62.5 $/h, and a CO ₂ emission decrease of 56.26 kg kWh ⁻¹ . The findings suggest that strategic deployment of the proposed system in temperate climates substantially boosts system performance and reduces environmental cost. This research offers practical and theoretical advancements in sustainable hydrogen‐based power solutions, directly contributing to Sustainable Development Goals (SDG) 7 and 13 through improved energy efficiency, reduced emissions, and climate‐responsive design. Future work should explore adaptive control strategies, low‐cost materials, and assessments in extreme climates.

A study was conducted to understand the effect of superparamagnetic nanoparticles on a viscoelastic hydrogel subject to an oscillating magnetic field directed tangent to the hydrogel surface. A capture–release kinetic model was formulated for the dynamic transition of nanoparticles between a freely oscillating state in the Newtonian solvent and a hydrogel-bound captured state. The viscoelastic hydrogel is modeled as an Oldroyd-B fluid. A parametric analysis was conducted to understand regimes of system behavior in terms of key dimensionless parameters. Increasing the viscous-to-thermal work ratio enhances detachment, while higher adhesion energy promotes particle retention by the hydrogel. The magnetic field amplitude controls both uptake rate and oscillatory strength, and the relative matrix-solvent velocity shapes the harmonic content of the response. A bifurcation was observed at a critical value of the ratio of retardation to relaxation times. For values of this ratio less than the critical value, the system exhibits multi-periodic elastic-regime responses, whereas for values of the ratio above the critical ratio, the system collapses into mono-periodic viscous-regime behavior. The capture rate coefficient includes an absolute value, so its product with sinusoidal magnetic forcing yields only odd harmonics in the response. Elastic waves propagate from the no-slip base, and height-averaged particle counts oscillate at twice the driving frequency. These findings elucidate how nonlinear capture–release kinetics and viscoelastic memory produce multi-periodic and odd-harmonic-dominated dynamics, informing the design of switchable smart materials for on-demand drug delivery and biofilm control.

A study was conducted of the effect of superparamagnetic nanoparticles on a hydrogel in the presence of an oscillating magnetic field directed tangent to the hydrogel surface. The oscillating magnetic field causes the particles to oscillate laterally in the hydrogel, with some of the particles adhering to the hydrogel matrix and other particles moving freely through the hydrogel pore spaces. The analysis was performed for a three-phase matrix-water-particles model, in which the solvent (water) and hydrogel matrix are interacting continua and the particles are a discrete phase. The study examined the effect of fluid elasticity on wave propagation due to the no-slip boundary condition acting under the transversely oscillating magnetic field. A memory effect within the fluid results in a deviation of the minimum and maximum shear rates observed in one half of the oscillation period from those observed in the other half of the oscillation period. The behavior of the hydrogel with different values of the governing dimensionless parameters was assessed. The matrix Reynolds number, the Deborah number, and the ratio of matrix relaxation to retardation times were all observed to have significant influence on the hydrogel viscoelastic response and on the wave propagation within the hydrogel. The phase difference between the water and matrix oscillations is strongly influenced by the phase interaction force coefficient, the Deborah number, and the ratio of free to captured particles. The system is found to approach an asymptotic state at a high Deborah number, which is independent of the value of the Deborah number.