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Showing 3 results for Erfanian
Volume 8, Issue 1 (Winter 2020)
Abstract
Aims: Medusahead (Taeniatherum caput-medusae (L.) Nevski) and barbed goatgrass (Aegilops triuncialis L.) are two annual species that drastically affect rangelands worldwide. In the present study, the current distribution range of these species was investigated using ecological niche modelling (ENM), and then their distribution was predicted in 2040 and 2070.
Materials & Methods: In this study, using 19 bioclimatic variables and the recorded presence locations, the current distribution of T. caput-medusae and A. triuncialis was predicted using MaxEnt. Moreover, changes in the distribution ranges of these species in the future (2040 and 2070) were estimated.
Findings: According to the results, the mean temperature of the coldest quarter and Isothermality had the greatest effect on the distribution of A. triuncialis in the present and future. For T. caput-medusae distribution in the present, 2040, and 2070 the mean temperature of the coldest quarter had the highest effect on determining the potential distribution range of this plant. Accordingly, climate change will not affect the distribution range of barbed goatgrass, however, it may facilitate the expansion of medusahead to the upper elevations.
Conclusion: In the present, comparing the two, barbed goatgrass had a higher probability to invade rangelands of Iran. Climate change might facilitate the invasion of medusahead to upper elevations. Grazing exclusion is advised to control the range expansion of these two species where they are present.
Mohammad Reza Erfanian, Mohammad Moghiman,
Volume 15, Issue 2 (4-2015)
Abstract
In this study, the water entry problem of a spherical - nose projectile is investigated numerically and experimentally. For the numerical simulations, a three dimensional model of the projectile with six – degree – of – freedom rigid body motion is considered. A Coupled Eulerian - Lagrangian (CEL) method is employed for modeling fluid - structure interactions. Through Eulerian - Lagrangian contact, Eulerian material can interact with Lagrangian elements. Also, an equation of state model describes the hydrodynamic behavior of the material. The numerical results are well compared with the available experimental results of a falling sphere in the literature and also the experiments of the current study. The experiments are performed for a spherical-nose projectile in a water tank equipped with a launching system and a high speed camera. The simulation results such as air cavity shape and the projectile trajectory are compared with the presented experiment data. The good agreement observed between the numerical results and those of the experiments, revealed the accuracy and capability of the proposed numerical algorithm. Also it has been shown that the pinch – off time is a weak function of impact velocity, however, increasing velocity leads to a linear increase in depth of pinch - off.
Mohammad-Reza Erfanian, ,
Volume 18, Issue 2 (4-2018)
Abstract
In this paper, the three dimensional ventilated cavitating flow in the steady condition around a projectile model is simulated using CFD method combined with a sst k-ω turbulence model and volume-of-fluid technique, With the aid of CFD software ANSYS CFX. The numerical model is validated using comparisons between numerical predictions and existing experimental data and fairly good agreement is revealed. The numerical results show that with increasing the ventilation gas rate at constant Froude number, the cavity length gradually increases to a critical value and then remains fixed upon further increase in gas ventilation rate. Also, it has been observed that rear portion of larger cavity moves upwards due to gravitational effect. With increasing the ventilation gas rate, the gas leakage mechanism at rear portion of ventilated supercavity changes from the re-entrant jet closure mode to twin vortex closure mode. The variation of ventilation gas rate versus cavity length is a function of Froude number and the critical ventilation gas rate increases linearly with Froude number.
