Science Collected Works - Research Publications
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ItemWave Attenuation by Multiple Outer Porous Barriers in the Presence of an Inner Rigid Cylinder(ASCE-AMER SOC CIVIL ENGINEERS, 2020-01-01)The wave forces acting on a rigid cylinder are investigated in the presence of multiple outer porous cylindrical barriers by assuming the linear water wave theory. A Bessel series solution is obtained for the boundary value problem by using the methods of eigenfunction expansion and least-squares approximation. Two configurations of outer porous barriers are considered, namely bottom-standing and surface-piercing. As a special case, the effect of fully extended barriers is studied. The wave loads exerted on the cylinders, free surface elevations, and flow distribution around the structures are computed and analyzed for different physical parameters. The present theory is ratified with the result available in the literature for a single fully extended outer porous barrier. The study reveals that the hydrodynamic forces exerted on the inner impermeable cylinder are reduced significantly as the number of outer porous barriers is increased. Thus, multiple outer fully extended or partial porous barriers can be set up to protect the inner rigid cylinder.
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ItemWave energy dissipation by a floating circular flexible porous membrane in single and two-layer fluids(Elsevier, 2020-06-15)In this study, the impact of gravity wave on a circular elastic floating permeable membrane is investigated using linear water wave theory in both homogeneous and two-layer fluids. The matched eigenfunction expansion technique is employed to obtain an analytic solution of the boundary value problem. Further, the plane wave integral representation of Bessel and Hankel functions are applied to study the influence of porous structure in damping the far-field wave energy. In order to examine the effect of various physical parameters, heave force exerted on the membrane, deflection of the membrane, reflected and transmitted wave amplitudes, flow distribution around the structure and far-field energy dissipation are computed and analyzed for three different edge conditions such as (i) free edge, (ii) moored edge and (iii) clamped edge. The study reveals that the surface wave amplitude on the lee side of the structure decreases significantly in the presence of floating porous elastic membrane. Moreover, the membrane having clamped edge dissipates more wave energy as compared to that for moored and free edge conditions.
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ItemEffect of imposed shear on the dynamics of a contaminated two-layer film flow down a slippery incline(AIP Publishing, 2020-10-01)The linear instability of a surfactant-laden two-layer falling film over an inclined slippery wall is analyzed under the influence of external shear, which is imposed on the top surface of the flow. The free surface of the flow and the interface among the fluids are contaminated by insoluble surfactants. Dynamics of the fluid layers are governed by the Navier–Stokes equations, and the surfactant transport equations regulate the motion of the insoluble surfactants at the interface and free surface. Instability mechanisms are compared by imposing the external shear along and opposite to the flow direction. A coupled Orr–Sommerfeld system of equations is derived using the perturbation technique and normal mode analysis. The eigenmodes corresponding to the Orr–Sommerfeld eigenvalue problem are obtained by employing the spectral collocation method. The numerical results imply that the stronger external shear destabilizes the interface mode instability. However, a stabilizing impact of the external shear on the surface mode is noticed if the shear is imposed in the flow direction, which is in contrast to the role of imposed external shear on the surface mode for a surfactant-laden single layer falling film. Furthermore, in the presence of strong imposed shear, the overall stabilization of the surface mode by wall velocity slip for the stratified two-fluid flow is also contrary to that of the single fluid case. The interface mode behaves differently in the two zones at the moderate Reynolds numbers, and higher external shear magnifies the interfacial instability in both zones. An opposite trend is observed in the case of surface instability. Moreover, the impression of shear mode on the primary instability is analyzed in the high Reynolds number regime with sufficiently low inclination angle. Under such configuration, dominance of the shear mode over the surface mode is observed due to the weaker impact of the gravitational force on the surface instability. The shear mode can also be stabilized by applying the external shear in the counter direction of the streamwise flow. Conclusively, the extra imposed shear on the stratified two-layer falling film plays an active role in the control of the attitude of the instabilities.