Articles written in Pramana – Journal of Physics
Volume 90 Issue 3 March 2018 Article ID 0039 Research Article
Continuous energy supply is critical and important to support oscillating behaviour; otherwise, the oscillator will die. For nonlinear and chaotic circuits, enough energy supply is also important to keep electric devices working. In this paper, Hamilton energy is calculated for dimensionless dynamical system (e.g., the chaotic Lorenz system) using Helmholtz’s theorem.The Hamilton energy is considered as a new variable and then the dynamical system is controlled by using the scheme of energy feedback. It is found that chaos can be suppressed even when intermittentfeedback scheme is applied. This scheme is effective to control chaos and to stabilise other dynamical systems.
Volume 93 Issue 4 October 2019 Article ID 0054 Research Article
The flow of a second grade fluid by a rotating stretched disk is considered. Brownian motion and thermophoresis characterise the nanofluid. Entropy generation in the presence of heat generation/absorption, Joule heating and nonlinear thermal radiation is discussed. Homotopic convergent solutions are developed. The behaviour of velocities (radial, axial, tangential), temperature, entropy generation, Bejan number, Nusselt number, skin friction and concentration is evaluated. The radial, axial and tangential velocities increase for larger viscoelastic parameters while the opposite trend is noted for temperature. Concentration decreases when Schmidt number and Brownian diffusion increase. Entropy generation increases when the Bejan number increase while the opposite is true for the Brinkman number and the magnetic parameter.
Volume 93 Issue 6 December 2019 Article ID 0096 Research Article
Two-dimensional magneto-Sisko nanofluid flow bounded by nonlinearly stretching sheet is studied. Thermophoretic diffusion and Brownian motion effects are also scrutinised. Additionally, impacts of activation energy, chemical reaction and nonlinear convection are considered. The purpose of this study is to analyse entropy generation in the Sisko fluid model. Suitable transformations are used to reduce the governing equation of motion, concentration and temperature. Effects of some pertinent variables on skin friction coefficient, temperature, velocity, concentration and Nusselt number are graphically presented. Clearly, for larger Brownian and thermophoresis parameters, the temperature increases while concentration distribution decreases with Brownian parameter. Bejan number is maximum away from the sheet in the case of shear thickening fluids while it approaches zero for shear thinning fluids.
Volume 93 Issue 6 December 2019 Article ID 0097 Research Article
This article addresses the flow of a thixotropic liquid with nanomaterials due to a stretching sheet of variable thickness. The stimulus effects of the heat source/sink and first-order chemical reaction are retained. Convective conditions of heat and mass transfer are also considered at the boundary. Unlike the classical consideration, the linear thermal radiation aspect is examined. The influence of emergent flow, heat and mass parameters on velocity, concentration and temperature fields are shown graphically. It is also noted that the velocity of the fluid significantly favours the non-Newtonian parameters. For higher values of radiation and heat source/sink parameter, the temperature rises.Moreover, a novel investigation on heat and mass transfer rates subject to nanomaterials (i.e. Brownian motion and thermophoresis) in the liquid has been carried out. Nonlinear systemsare solved by the optimal homotopy analysis method (OHAM). Convergence analysis has been executed and the optimal values are computed. The main advantage of the proposed technique is that it can be directly utilised inhighly nonlinear systems without using discretisation, linearisation and round-off errors. The table shows the results of the error analysis.
Volume 93 Issue 6 December 2019 Article ID 0095 Research Article
This paper examines the steady flow due to a rotating disk with variable thickness. Equations are modelled by considering the homogeneous–heterogeneous reactions and variable thermal conductivity. Themodified Von Karman transformations are utilised to convert the governing partial differential equations into dimensionless nonlinear ordinary differential equations. Convergent series solutions are computed. The impactof relevant parameters on flow fields is computed and interpreted. It is predicted that an increase in disk thickness index decreases the axial velocity while increases the radial and tangential velocities. The Nusselt number enhances by increasing the thickness parameter of a disk.
Volume 94 All articles Published: 28 February 2020 Article ID 0048 Research Article
The main focus in this study is to study the flow of a viscous fluid through a curved stretched surface. Soret and Dufour effects along with Joule heating are incorporated. Appropriate transformations yield the nonlinear ordinary differential system. Convergent series solutions of velocity, temperature and concentration are constructed. Graphical illustrations thoroughly demonstrate the features of the involved pertinent parameters. Skin friction coefficient, Nusselt and Sherwood numbers are also obtained and discussed graphically. Current computations reveal that the radial velocity experience decline with the increase of Hartman number. Further, fluid temperature declines for higher Prandtl and Soret numbers.
Volume 94, 2020
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