SearcharxivSearch

arXiv subjects

Sougata Mandal

Publications and source records attributed to Sougata Mandal.

4 recordsLinked to original sources

Flow dynamics in a wavy channel filled with anisotropic porous material under the effect of wall slip

In this study, a theoretical and graphical analysis is conducted to examine the effects of wall-velocity slip, anisotropic ratio, and porosity parameter on a two-dimensional, viscous, laminar, and incompressible flow through a wavy channel filled with anisotropic porous media. The flow is assumed to be steady and symmetric, with a constant volumetric flow rate imposed along the channel walls. The governing equations are described using the Darcy-Brinman model coupled with the continuity equation, while the tangential velocity at the wavy boundaries is represented through Navier slip conditions. An analytical solution is obtained using a perturbation approach under physically consistent boundary conditions. The effects of key parameters, including anisotropic ratio, Darcy number, and slip parameter, on flow characteristics such as axial velocity, pressure gradient, shear stress, and streamline patterns are examined in detail and presented graphically. The results indicate that wall velocity slip significantly reduces flow reversal, enhances near-wall velocity, and decreases the center-line velocity. For a fixed non-zero slip, a decrease in the Darcy number leads to a pronounced modification in the velocity profile, while increased slip further strengthens near-wall flow and weakens the core flow. Additionally, the streamline analysis reveals that velocity slip plays an important role in controlling flow separation near the crest of the wavy wall. In the case of isotropic porous media with a large amplitude wavy channel, flow separation can also be effectively regulated. Overall, the study demonstrates that velocity slip provides a powerful mechanism for controlling flow behavior by altering the shear distribution within the perturbed flow, with potential applications in technological, geophysical, and biophysical transport systems.

physics.flu-dyn

Conservation laws, a new class of group invariant solutions, and its applications for the Whitham Broer Kaup model

The Whitham Broer Kaup (WBK) equations provide a fundamental framework for modeling shallow water wave dynamics, effectively capturing both nonlinear and dispersive effects. In this study, we construct a new class of analytical and numerical solutions for the WBK system using Lie symmetry analysis. By determining an optimal system of one-dimensional subalgebras, we obtain symmetry reductions that lead to new kinds of exact wave solutions expressed in hyperbolic, trigonometric, and rational forms. The influence of key physical parameters on wave structure is systematically explored, revealing their role in shaping the velocity and surface profiles of the waves. An important aspect of this work is the application of the WBK model to tsunami wave propagation, demonstrating its capability to simulate the generation, evolution, and spatial spreading of long surface waves in coastal regions. This highlights the practical relevance of the WBK equations in geophysical and oceanographic contexts. Additionally, employing the direct multiplier method, we derive a complete set of local conservation laws for the governing WBK model, ensuring the preservation of key physical properties. These findings enhance the understanding of shallow water wave behavior, unify existing research, and provide a framework for further exploration.

physics.flu-dyn

Electric field induced negative capacitance in semiconducting polymer

Electric field dependent capacitance and dielectric loss in poly(3-hexylthiophene) are measured by precision capacitance bridge. Carrier mobility and density are estimated from fits to current-voltage and capacitance data. The capacitance varies largely at lower frequency, and it decreases at higher electric fields. The negative capacitance at low frequency and high field is due to the negative phase angle between the dipole field and the ac signal. The intrinsic carrier density is calculated from fits to the Mott-Schottky equation, and this is consistent with I-V data analysis. At higher frequency, the carriers do not follow the ac signal and their density drops; and the flatband potential increases mainly due to the build-in potentials within ordered and amorphous regions in the sample.

physics.app-ph

Impedance measurements in undoped and doped regioregular poly(3-hexylthiophene)

The semiconducting properties of regioregular poly(3-hexylthiophene) are characterized by impedance measurements, from 40 Hz to 100 MHz. X-ray diffraction shows the presence of both ordered and disordered regions. The analysis of impedance data by Nyquist plots show two semi-circular arcs, and its size is reduced by d.c. bias. Also, the carrier variation by light and chemical doping alters the shape and size of arcs. The fits to the data and equivalent circuits show considerable changes in the resistive, capacitive and constant-phase element parameters as the carrier density increases. The increase in carrier density reduces the relaxation time in ordered regions, and it does not alter much in disordered regions.

cond-mat.mtrl-sci