Experiments on hydraulic jumps over uneven bed for turbulent flow modelling validation in river flow and hydraulic structures.

This study presents a comprehensive dataset comprising multiple data packages derived from laboratory experiments on steady and unsteady hydraulic jumps interacting with a large-scale Gaussian-shaped bed obstacle in an open-channel flume. The primary objective was to accurately measure the impact of hydraulic jump on the free surface and the bed pressure along the obstacle, ensuring the transferability of the results. A multi-process method was followed: designed experiments were recorded, images were postprocessed, and water level data were digitalized. For steady conditions, the bed pressure along the obstacle were measured by piezometers. The repository data are organized and provided in a single package, supplemented by a second package containing panoramas for each experimental time instant and graphical representations of the data, facilitating rapid evaluation of the outcomes. This study provides versatile data that can be utilized in various ways, particularly for fluvial model validation and studying turbulence-driven phenomena in open-channel flows. The detailed methodology presented herein can contribute to the advancement of enhanced laboratory techniques to study similar flow problems.

Submarine channels formation driven by turbidity currents interacting with an erodible bed.

In this article, we explore the submarine channel formation driven by the interaction of turbidity currents with an erodible bed. The theoretical analysis considers the three-dimensional continuity and momentum equations of the fluid phase, and the advection-diffusion and Exner equations of the solid phase. The governing equations are linearized by imposing periodic perturbations on the base flow. We study the response of both the base flow (profiles of velocity and suspended sediment concentration) and perturbations (growth rate and perturbation fields) to changes in key parameters related to the flow and sediment transport. The growth rate and the critical wavenumber are examined for a given quintet formed by the gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer, Rouse number and erosion coefficient. The critical wavenumber reduces with an increase in gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer and erosion coefficient, while it increases with the Rouse number. For the submarine channel formation, we identify the upper threshold values for the gravitational parameter, longitudinal bed slope, sediment concentration at the edge of the driving layer and erosion coefficient and the lower threshold value for the Rouse number.

Cranial fibrous dysplasia: An institutional experience and review of the literature.

BACKGROUND: Cranial or craniofacial fibrous dysplasia (CFD) is a rare entity which most often presents with either incidental finding or with pain/cosmetic disfigurement or visual/hearing problems. Multidisciplinary treatment with close follow-up or medical management/surgery is options. Management of these lesions can often give satisfying results. There is a dearth of neurosurgical literature on this subject matter. Our objective was to review the clinical symptomatology and outcome of CFD patients managed in our institution. METHODS: This is a retrospective observational study of CFD patients managed in our institution over a period of 5 years. Clinical and radiological data were collected from departmental database. Outcomes were evaluated immediately and on 1-4 years follow-up. RESULTS: A total of 21 patients were managed over a period of 5 years with age ranging from 12 to 55 years and symptoms of cosmetic issues or visual disturbance. Preoperative computed tomography scan with 3D reconstruction with bone window was done in all patients. In most of the patients (16/20), immediate reconstruction was done following excision. Five patients were managed conservatively. Follow-up was obtained over a period ranging from 1 to 4 years and all (except one) patients are doing well. Only one patient had permanent visual impairment in spite of early intervention. CONCLUSION: Craniofacial dysplasia has various modalities of management. Careful selection of patients for surgical or conservative management is feasible with good results both in short and long term.

Mega riverbed-patterns: linear and weakly nonlinear perspectives.

In this paper, we explore the mega riverbed-patterns, whose longitudinal and vertical length dimensions scale with a few channel widths and the flow depth, respectively. We perform the stability analyses from both linear and weakly nonlinear perspectives by considering a steady-uniform flow in an erodible straight channel comprising a uniform sediment size. The mathematical framework stands on the dynamic coupling between the depth-averaged flow model and the particle transport model including both bedload and suspended load via the Exner equation, which drives the pattern formation. From the linear perspective, we employ the standard linearization technique by superimposing the periodic perturbations on the undisturbed system to find the dispersion relationship. From the weakly nonlinear perspective, we apply the centre-manifold-projection technique, where the fast dynamics of stable modes is projected on the slow dynamics of weakly unstable modes to obtain the Stuart-Landau equation for the amplitude dynamics. We examine the marginal stability, growth rate and amplitude of patterns for a given quintet formed by the channel aspect ratio, wavenumber of patterns, shear Reynolds number, Shields number and relative roughness number. This study highlights the sensitivity of pattern formation to the key parameters and shows how the classical results can be reconstructed on the parameter space.

Terminal fall velocity: the legacy of Stokes from the perspective of fluvial hydraulics.

This review article, dedicated to the bicentenary celebration of Sir George Gabriel Stokes' birthday, presents the state-of-the-science of terminal fall velocity, highlighting his rich legacy from the perspective of fluvial hydraulics. It summarizes the fluid drag on a particle and the current status of the drag coefficient from both the theoretical and empirical formulations, highlighting the three major realms-Stokesian, transitional and Newtonian realms. The force system that drives the particle motion falling through a fluid is described. The response of terminal fall velocity to key factors, which include particle shape, hindered settling and turbulence (nonlinear drag, vortex trapping, fast tracking and effects of loitering), is delineated. The article puts into focus the impact of terminal fall velocity on fluvial hydraulics, discussing the salient role that the terminal fall velocity plays in governing the hydrodynamics of the sediment threshold, bedload transport and suspended load transport. Finally, an innovative perspective is presented on the subject's future research track, emphasizing open questions.

Bed particle saltation in turbulent wall-shear flow: a review.

Bed particle saltation in turbulent wall-shear flow remains an intriguing phenomenon in applied hydro-dynamics. In this review, we report the current state of the art of bed particle saltation in turbulent wall-shear flow, highlighting the physical characteristics of bed particle saltation and its mathematical modelling. A critical appraisal of the mechanics of bed particle saltation is presented thorough ample experimental evidence. The salient features of bed particle saltation, encompassing the saltation height, saltation length, particle velocity, saltation duration, particle collision with the bed, particle rotation, particle resting time and particle re-entrainment, are thoroughly discussed. Both the deterministic and computational fluid dynamics approaches in modelling bed particle saltation are summarized, and the subtle role of the hydrodynamic forces is elaborated. The estimation of bedload flux in a fluvial environment, emanating from the mathematical modelling of bed particle saltation, is delineated using different modelling approaches. Finally, the challenges in modelling bed particle saltation are highlighted, and a new look at bed particle saltation is furnished.

Performance of a modified magnetostrictive energy harvester in mechanical vibration.

The field of harvesting electrical energy from ambient vibration has grown with rapid interest. Perpetual source of electrical energy can be extracted from structural vibrations. The paper deals with a technology for scavenging electricity from vibration using iron-gallium alloy. This alloy offers high ductile property and the effect of inverse magnetostriction is also quite high. In this paper, a bending type magnetostrictive prototype energy harvester has been considered. Volume of the used material is 7 × 2 × 42 mm3. Forced & free vibration characteristics have been examined on this prototype. Maximum conversion efficiency of 49% has been achieved at input frequency of 30 Hz.

Cobb syndrome: A rare cause of paraplegia.

Cobb syndrome is an exceedingly rare clinical condition defined by the presence of a vascular skin nevus and an angioma in the spinal canal at the same metamere. We report the case of a 14-year-old boy who presented with sudden onset paraplegia. Physical examination showed port-wine stains over buttock and thigh. Magnetic resonance (MR) angiogram of the dorso-lumbar spine revealed a large arteriovenous malformation (AVM) at D11-D12 to L2-L3 levels. These concurrent findings led to the diagnosis of Cobb's syndrome. The patient received orally administered prednisolone therapy and underwent endovascular embolization of spinal angioma. Cobb's syndrome is a rare disease entity and literature search revealed only a few case reports and series mentioning this condition to date. The importance lies in the recognition that cutaneous vascular lesions may clue to an associated spinal cord angioma or AVM that may lead to weakness or paralysis.

Reynolds averaged theory of turbulent shear flows over undulating beds and formation of sand waves.

Based on the Reynolds averaged Navier-Stokes (RANS) equations and the time-averaged continuity equation, a theory of turbulent shear flow over an undulating sand bed is developed addressing the instability criterion of plane sand beds in free-surface flows leading to the formation of sand waves. In the analysis, the integration of RANS equations leads to generalized Saint Venant equations, in which the time-averaged streamwise velocity is characterized by a power law obtained from turbulence closure, treating the curvilinear streamlines by the Boussinesq approximation. As a consequence, the modified pressure distribution has a departure from the traditionally linear hydrostatic pressure distribution. The instability analysis of a plane sand bed yields the curves of the Froude number versus nondimensional wave number, determining an instability zone for which at lower Froude numbers (less than 0.8), the plane bed becomes unstable with the formation of dunes; whereas at higher Froude numbers, the plane bed becomes unstable with the formation of standing waves and antidunes. For higher Froude numbers, the experimental data for antidunes lie within the unstable zone; while for lower Froude numbers, the same is found for dunes with some experimental scatter.