ORCID Profile
0000-0001-7419-044X
Current Organisations
Nanyang Technological University
,
University of Melbourne
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Publisher: American Geophysical Union (AGU)
Date: 02-2020
DOI: 10.1029/2019WR026181
Abstract: This paper aims to explore the combined main flow and turbulence influence on sediment pickup rates by investigating four purposely devised cases, namely, (1) unobstructed flow over a plane bed (2) unobstructed flow over a rigid‐dune bed (3) flow obstructed by a horizontal pipe and (4) flow obstructed by a vertical pipe. The four cases were used to represent typical scenarios of mean flow combined with turbulence of varying intensities. By analyzing the dependence of sediment pickup rate on different combinations of the mean and turbulent flow parameters, a modified densimetric Froude number, incorporating both the bulk‐averaged velocity and maximum root‐mean‐square value of the fluctuating velocity, is found to be reasonably correlated with the measured pickup rates for all the four cases. Consequently, by relating the pickup rate with the dimensionless particle diameter and the modified densimetric Froude number, a generalized equation that predicts the pickup rates under both unobstructed as well as obstructed flow conditions is obtained.
Publisher: Wiley
Date: 20-04-2022
Publisher: American Society of Civil Engineers (ASCE)
Date: 06-2014
Publisher: American Geophysical Union (AGU)
Date: 10-2022
DOI: 10.1029/2022JB024593
Abstract: We present analog experiments on dike propagation, followed by a numerical model of horizontal and vertical growth, which is partially analytical and partially based on empirical observations. Experimental results show that the growth rates are similar until buoyancy becomes significant and, afterward, vertical growth dominates. The numerical model is defined for different conditions in a homogeneous medium: (a) constant flux, fracture‐limited propagation (b) constant flux, viscous‐limited propagation and (c) variable flux dependent on the driving pressure and dike dimensions. These conditions distinguish between cases when the influx depends on the deeper source of magma (e.g., a conduit, independent of the dike geometry) and when it depends on the dike, so the influx can change as it grows. In all cases, the ratio of vertical to horizontal propagation is proportional to the ratio of buoyancy pressure to source pressure, in which buoyancy drives vertical propagation. We test the numerical model on dikes observed at Piton de la Fournaise, in which the dimensions were estimated using geodetic and seismic data. The results show that the final dimensions can be reproduced using magma‐crust density differences of 50–300 kg/m 3 , viscosities of 30–300 Pa·s, influxes of 50–750 m 3 /s and shear moduli of ∼10 GPa. The modeled magma and host rock parameters agree with previous studies of the volcano, while the flux is higher than what is typically observed during eruption. This implies a variable injection condition, in which the flux peaks during propagation and diminishes by the onset of eruption.
Publisher: American Society of Civil Engineers (ASCE)
Date: 2020
Publisher: American Geophysical Union (AGU)
Date: 11-2019
DOI: 10.1029/2019JB017665
Publisher: American Geophysical Union (AGU)
Date: 03-2023
DOI: 10.1029/2022JB025463
Abstract: We conducted analogue experiments to examine flux‐driven and buoyancy‐driven magma ascent, which included a series of isothermal experiments and thermal, solidification‐prone experiments. We measured the internal flow using 2D particle image velocimetry, which indicates that buoyancy has a strong control on the flow pattern of isothermal dikes. Dikes that are not buoyant (likely driven by source pressure) take on a circulating pattern, while buoyant dikes assume an ascending flow pattern. Solidification modifies the flow field so that flow is confined to the dike's upper head region. The lower tail becomes mostly solidified, with a narrow conduit connecting the source to the head. We interpret that this conduit acts as a high velocity point source to the head, promoting a circulating flow pattern, even as the dike becomes buoyant. We then perform particle tracking velocimetry on several particles to illustrate the complexity of their paths. In a circulating flow pattern, particles rise to the top of the dike, descend near the lateral edge, and then are drawn back into the upward flow. In an ascending pattern, particles ascend slightly faster than the propagation velocity, and therefore are pushed to the side as they approach the upper tip. In erupting dikes, particles simply flow to the vent. In the context of crystal growth in magmatic dikes, these results suggest that crystal growth patterns (e.g., normal or oscillatory zoning) can reflect the magma flow pattern, and potentially the driving forces.
Publisher: Elsevier BV
Date: 09-2010
Publisher: Elsevier BV
Date: 2023
DOI: 10.1016/J.ENVRES.2022.114493
Abstract: This paper revisits the 2011 Great Flood in central Thailand to answer one of the hotly debated questions at the time "Could the operation decisions of the flood control structures substantially mitigate the flood impacts in the downstream areas?". Using a numerical modeling approach, we develop a hypothesis such that the two upstream dam reservoirs: Bhumibol and Sirikit had more accurately forecasted the typhoon-triggered abnormal rainfall volumes and released more water earlier to save the storage capacity via 17 different scenarios or alternative operation schemes. We subsequently quantify the potential improvements, or reduced flood impacts in the downstream catchments, solely by changing the operation schemes of these two dam reservoirs, with all other conditions remaining unchanged. We observed that changing the operation schemes could have reduced only the flood depth while offering very limited improvements in terms of inundated areas for the lower Chao Phraya River Basin. Among 17 scenarios simulated, the inundated areas could have been reduced at most by 3.68%. This result justifies the limited role of these mega structures in the upstream during the disaster on one hand, while pointing to the necessity of handling local rainfall differently on the other. The paper expands the discussion into how the government of Thailand has drawn the lessons from the 2011 flood to better prepare themselves against the lurking flood risk in 2021, also triggered by tropical cyclones. The highlighted initiatives, both technical and institutional, could have provided important references for the large river catchment managers in Southeast Asia and with implications of our method beyond the present application region.
Publisher: American Geophysical Union (AGU)
Date: 09-2019
DOI: 10.1029/2019JB018191
Abstract: We investigate the conditions under which magma prefers to migrate through the crust via a dike or a conduit geometry. We performed a series of analogue experiments, repeatedly injecting warm, liquid gelatin, into a cold, solid gelatin medium and allowing the structure to evolve with time. We varied the liquid flux and the time interval between discrete injections of gelatin. The time interval controls the geometry of the migration, in that long intervals allow the intrusions to solidify, favoring the propagation of new dikes. Short time intervals allow the magma to channelize into a conduit. These times are characterized by the Fourier number ( Fo ), a ratio of time and thermal diffusion to dike thickness, so that long times scales have Fo 10 2 and short time scales have Fo 10 0 . Between these time scales, a transitional behavior exists, in which new dikes nest inside of previous dikes. The flux controls the distance a dike can propagate before solidifying, in that high fluxes favor continual propagation, whereas low fluxes favor dike arrest due to solidification. For vertically propagating dikes, this indicates whether or not a dike can erupt. A transitional behavior exist, in which dikes may erupt at the surface in an unstable, on‐and‐off fashion. We supplemented the experimental findings with a 2‐D numerical model of thermal conduction to characterize the temperature gradient in the crust as a function of intrusion recurrence frequency. For very infrequent intrusions ( Fo 10 4 to 10 5 ) all thermal energy is lost, while more frequent intrusions allow heat to build up nearby.
Publisher: Springer Science and Business Media LLC
Date: 16-05-2015
Publisher: Elsevier BV
Date: 03-2017
No related grants have been discovered for Adel Emadzadeh.