Jasim Imran

Bio: Jasim Imran is an academic researcher from University of South Carolina. The author has contributed to research in topics: Turbidity current & Open-channel flow. The author has an hindex of 20, co-authored 20 publications receiving 2064 citations. Previous affiliations of Jasim Imran include University of Minnesota & Royal Dutch Shell.

Numerical Modeling of Three-Dimensional Flow Field Around Circular Piers

Abstract: A three-dimensional numerical model \IFLUENT\N is used to simulate the separated turbulent flow around vertical circular piers in clear water. Computations are performed using different turbulence models and results are compared with several sets of experimental data available in the literature. Despite commonly perceived weakness of the \Ik-e\N model in resolving three-dimensional (3D) open channel and geophysical flows, several variants of this turbulence model are found to have performed satisfactorily in reproducing the measured velocity profiles. However, model results obtained using the k- models show some discrepancy with the measured bed shear stress. The Reynolds stress model performed quite well in simulating velocity distribution on flat bed and scour hole as well as shear stress distribution on flat bed around circular piers. The study demonstrates that a robust 3D hydrodynamic model can effectively supplement experimental studies in understanding the complex flow field and the scour initiation process around piers of various size, shape, and dimension.

A nonlinear model of flow in meandering submarine and subaerial channels

Abstract: A generalized model of flow in meandering subaqueous and subaerial channels is developed The conservation equations of mass and momentum are depth/layer integrated, normalized, and represented as deviations from a straight base state This allows the determination of integrable forms which can be solved at both linear and nonlinear levels The effects of various flow and geometric parameters on the flow dynamics are studied Although the model is not limited to any specific planform, this study focuses on sine-generated curves In analysing the flow patterns, the turbidity current of the subaqueous case is simplified to a conservative density flow with water entrainment from above neglected The subaqueous model thus formally corresponds to a subcritical or only mildly supercritical mud-rich turbidity current By extension, however the analysis can be applied to a depositional or erosional current carrying sand that is changing only slowly in the streamwise direction By bringing the subaqueous and subaerial cases into a common form, flow behaviour in the two environments can be compared under similar geometric and boundary conditions A major difference between the two cases is the degree of superelevation of channel flow around bends, which is modest in the subaerial case but substantial in the subaqueous case Another difference concerns Coriolis effects: some of the largest subaqueous meandering systems are so large that Coriolis effects can become important The model is applied to meander bends on the youngest channel in the mid-fan region of the Amazon Fan and a mildly sinuous bend of the North-West Atlantic Mid-Ocean Channel In the absence of specific data on the turbid flows that created the channel, the model can be used to make inferences about the flow, and in particular the range of values of flow velocity and sediment concentration that would allow the growth and downfan migration of meander bends

Seismic Geomorphology and Stratigraphy of Depositional Elements in Deep-Water Settings

Abstract: Analyses of 3-D seismic data in predominantly basin-floor settings offshore Indonesia, Nigeria, and the Gulf of Mexico, reveal the extensive presence of gravity-flow depositional elements. Five key elements were observed: (1) turbidity-flow leveed channels, (2) channel-overbank sediment waves and levees, (3) frontal splays or distributary-channel complexes, (4) crevasse-splay complexes, and (5) debris-flow channels, lobes, and sheets. Each depositional element displays a unique morphology and seismic expression. The reservoir architecture of each of these depositional elements is a function of the interaction between sedimentary process, sea-floor morphology, and sediment grain-size distribution. (1) Turbidity-flow leveed-channel widths range from greater than 3 km to less than 200 m. Sinuosity ranges from moderate to high, and channel meanders in most instances migrate down-system. The high-amplitude reflection character that commonly characterizes these features suggests the presence of sand within the channels. In some instances, high-sinuosity channels are associated with (2) channel-overbank sediment-wave development in proximal overbank levee settings, especially in association with outer channel bends. These sediment waves reach heights of 20 m and spacings of 2-3 km. The crests of these sediment waves are oriented normal to the inferred transport direction of turbidity flows, and the waves have migrated in an up-flow direction. Channel-margin levee thickness decreases systematically down-system. Where levee thickness can no longer be resolved seismically, high-sinuosity channels feed (3) frontal splays or low-sinuosity, distributary-channel complexes. Low-sinuosity distributary-channel complexes are expressed as lobate sheets up to 5-10 km wide and tens of kilometers long that extend to the distal edges of these systems. They likely comprise sheet-like sandstone units consisting of shallow channelized and associated sand-rich overbank deposits. Also observed are (4) crevasse-splay deposits, which form as a result of the breaching of levees, commonly at channel bends. Similar to frontal splays, but smaller in size, these deposits commonly are characterized by sheet-like turbidites. (5) Debris-flow deposits comprise low-sinuosity channel fills, narrow elongate lobes, and sheets and are characterized seismically by contorted, chaotic, low-amplitude reflection patterns. These deposits commonly overlie striated or grooved pavements that can be up to tens of kilometers long, 15 m deep, and 25 m wide. Where flows are unconfined, striation patterns suggest that divergent flow is common. Debris-flow deposits extend as far basinward as turbidites, and individual debris-flow units can reach 80 m in thickness and commonly are marked by steep edges. Transparent to chaotic seismic reflection character suggest that these deposits are mud-rich. Stratigraphically, deep-water basin-floor successions commonly are characterized by mass-transport deposits at the base, overlain by turbidite frontal-splay deposits and subsequently by leveed-channel deposits. Capping this succession is another mass-transport unit ultimately overlain and draped by condensed-section deposits. This succession can be related to a cycle of relative sea-level change and associated events at the corresponding shelf edge. Commonly, deposition of a deep-water sequence is initiated with the onset of relative sea-level fall and ends with subsequent rapid relative sea-level rise.

Submarine landslides: advances and challenges

Abstract: Due to the recent development of well-integrated surveying techniques of the sea floor, significant improvements were achieved in mapping and describing the morphology and architecture of submarine...

Pyroclastic density currents and the sedimentation of ignimbrites

Abstract: Pyoclastic density currents are awesome volcanic phenomena that can wreak destruction on a regional scale and can impact global climate. They deposit ignimbrites, which include vast impact lansdscape-modifying sheets with volumes exceeding 1000 km3.This book takes stock of our understanding of pyroclastic density currents and presents a new conceptual framework for investigating how ignimbrites are deposited. It integrates the results of field-based studies, laboratory experiments and numerical modelling, including work on clastic sedimentologym and industrial particle transport. Topics covered include the behaviour or particulate currents, mechanisms of clast support and segregation, interpreting ignimbrite lithofacies and architectures, and future research directions. The new approach focuses on processes and conditions within the lower flow-boundary zone of currents. Superb diagrams explain many new concepts, while the 95 photographs make an explanatiry atlas of deposit types. This is essential reading for workers investigating volcanic hazards, and for anyone wishing to interpret modern or ancient ignimbrites, as well as other catastrophically emplaced sediments. “Given the depth of scholarship that they have brought to the subject, the power of their arguments, and the degree of synthesis with other fields, this would seemto qualify as a seminal work… I think that this will be the paper on the topic that others will have to contend with for many years to come.” Marcus Bursik, State University of New York

Dynamic single-thread channels maintained by the interaction of flow and vegetation

Abstract: Most rivers on Earth today flow as a single channel, in some cases with occasional islands, and follow a more or less sinuous course. However, single-thread channels have proven difficult to reproduce and study experimentally: experimental self-formed channels tend to widen and subdivide, leading to a braided pattern. Cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single-thread channel. We show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single-thread. Our experimental strategy, a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth, leads to the evolution of a dynamic self-maintaining single-thread channel with well-defined banks and floodplain. By eliminating weak flow paths, the vegetation “corrals” the water into a single dominant channel until the reduction in total wetted width leads to a new self-organized state in which the flow removes vegetated area as fast as it is produced. The new channel is deeper and has a broader distribution of depths than the braided one, with channel size adjusted to carry almost all the flood flow. The resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field, specifically erosion at the outside of bends, bend growth, and bar development. Our methodology provides a basis for experimental development of self-sustaining high-amplitude meanders and has applications for river management and basic research purposes.