Gravity Modulation Research Articles

Effect of Variable Viscosity and Gravity Modulation on Linear and Non-Linear Rayleigh-Benard Convection in Viscoelastic Ferromagnetic Liquids

The combined effect of various parameters of gravity modulation on the onset of ferroconvection is studied for both linear and non-linear stability. The effect of various parameters of ferroconvection is studied for linear stability analysis. The resulting seven-mode generalized Lorenz model obtained in non-linear stability analysis is solved using Runge -Kutta-Felberg 45 method to analyze the heat transfer. Consequently the individual effect of gravity modulation on heat transport has been investigated. Further, the effect of physical parameters on heat transport has been analyzed and depicted graphically. The low-frequency gravity modulation is observed to get an effective influence on the stability of the system. Therefore ferro convection can be advanced or delayed by controlling different governing parameters. It shows that the influence of gravity modulation stabilizes system.

Gravity Compensation Modular Robot: Proposal and Prototyping

If a robot system can take various shapes, then it can play various roles, such as humanoid, dog robot, and robot arm. A modular robot is a robot system in which robots are configured using multiple modules, and it is possible to configure robots of other shapes by varying the combinations of the modules. In conventional modular robots, the shape is restricted by gravity, and configurable shapes are limited. In this study, we propose a gravity compensation modular robot to solve this problem. This paper describes the design and prototyping of the gravity compensation modular robot, and provides examples of robot shapes configured using the gravity compensation modules and motion experiments of the robots. In the experiments, there were motions that the robots could perform and could not perform. We considered the lack in the gravity compensation level and module rigidity as the main factor of the failures. This paper also discusses the solutions to these problems.

G-Jitter Free Convection Flow of Nanofluid in The Three-Dimensional Stagnation Point Region

The three dimensional free convection boundary layer flow near a stagnation point region is embedded in viscous nanofluid with the effect of g-jitter is studied in this paper. Copper (Cu) and aluminium oxide (Al2O3) types of water base nanofluid are cho- sen with the constant Prandtl number, Pr=6.2. Based on Tiwari-Das nanofluid model, the boundary layer equation used is converted into a non-dimensional form by adopting non- dimensional variables and is solved numerically by engaging an implicit finite-difference scheme known as Keller-box method. Behaviors of fluid flow such as skin friction and Nusset number are studied by the controlled parameters including oscillation frequency, amplitude of gravity modulation and nanoparticles volume fraction. The reduced skin friction and Nusset number are presented graphically and discussed for different values of principal curvatures ratio at the nodal point. The numerical results shows that, in- crement occurs in the values of Nusset number with the presence of solid nanoparticles together with the values of the skin friction. It is worth mentioning that for the plane stagnation point there is an absence of reduced skin friction along the y-direction where as for axisymmetric stagnation point, the reduced skin friction for both directions are the same. As nanoparticles volume fraction increased, the skin friction increased as well as the Nusset number. The results, indicated that skin frictions of copper are found higher than aluminium oxide.

Comparison of the effects of three types of time-periodic body force on linear and non-linear stability of convection in nanoliquids

Abstract The effect of three different types of time-periodic vertical oscillations of the Rayleigh–Benard system involving Newtonian nanoliquids is studied in the paper. Twenty nanoliquids are considered for investigation and it is found that enhanced heat transport is seen in all of them compared to what is observed in the corresponding carrier liquids without the nanoparticles. The increase in the amplitude of the vertical vibration is shown to augment convection in the nanoliquids whereas increase in frequency is to inhibit convection. On comparing the extent of heat transport in the presence of modulation with that in its absence, it was found that heat transport diminished in the former case. It was also found that the trigonometric sine type of gravity modulation transports heat intermediate to that of triangular and square types. The triangular type inhibits heat transport while square type enhances heat transport leading one to conclude that heat transport in a Rayleigh–Benard system can be enhanced by using a combination of dilute concentration of nanoparticles and gravity modulation using a square wave.

Effects MHD and Heat Generation on Mixed Convection Flow of Jeffrey Fluid in Microgravity Environment over an Inclined Stretching Sheet

In this paper, Jeffrey fluid is studied in a microgravity environment. Unsteady two-dimensional incompressible and laminar g-Jitter mixed convective boundary layer flow over an inclined stretching sheet is examined. Heat generation and Magnetohydrodynamic MHD effects are also considered. The governing boundary layer equations together with boundary conditions are converted into a non-similar arrangement using appropriate similarity conversions. The transformed system of equations is resolved mathematically by employing an implicit finite difference pattern through quasi-linearization method. Numerical results of temperature, velocity, local heat transfer, and local skin friction coefficient are computed and plotted graphically. It is found that local skin friction and local heat transfer coefficients increased for increasing Deborah number when the magnitude of the gravity modulation is unity. Assessment with previously published results showed an excellent agreement.

Chaotic Convection of Viscoelastic Fluid in Porous Medium Under G-Jitter

The present article aims at investigating the effect of gravity modulation on chaotic convection of a viscoelastic fluid in porous media. For this, the problem is reduced into Lorenz system (non-autonomous) by employing the truncated Galerkin expansion method. The system shows transitions from periodic to chaotic behavior on increasing the scaled Rayleigh number R. The amplitude of modulation advances the chaotic nature in the system while the frequency of modulation has a tendency to delay the chaotic behavior which is in good agreement with the results due to [1]. The behavior of the scaled relaxation and retardation parameter on the system is also studied. The phase portrait and time domain diagrams of the Lorenz system for suitable parameter values have been used to analyze the system.

Three-pronged convection in a cubic cavity under modulating gravity

Three-dimensional thermal convection in a cubic cavity heated from one wall and chilled from its opposite wall in the terrestrial-gravity and zero-gravity fields with and without a sinusoidal modulation is investigated numerically. The gravity and its modulation are parallel to the temperature gradient. An incompressible fluid with Prandtl number Pr = 7.1 (water) is considered and hence the Boussinesq approximation is used. The gravity-modulation parameters are a vibrational Rayleigh number Raη and a non-dimentional gravity-modulation frequency ω. Here the authors report a novel ‘trident’ flow structure in laminar and steady thermal convection, which consists of a point-symmetric pair of three-pronged flows, namely, three ascending streams and three descending streams in the cube. This flow structure is stable and persistent in the sense that it is observed in all three situations: a stationary cube under the terrestrial gravity, an oscillating cube under the terrestrial gravity, and an oscillating cube under zero gravity. A POD analysis confirmed this observation. Tested parameters are Rayleigh number Ra = 8.0 × 104 in the terrestrial-gravity field without the gravity modulation or Ra = 1.0 × 104; and the gravity modulation in the terrestrial-gravity field Raη = 1.0 × 105 and ω = 5.0 in the terrestrial-gravity field and Raη = 1.1 × 105 and ω = 5.0 in the zero-gravity field.

Vibrational effect on internal heated porous medium in the presence of chaos

The present article investigates a chaotic convection under modulation in the presence of internal heat generation. The viscoelastic fluid saturating porous medium, heated from below is considered; a modified Darcy’s momentum equation and heat generation term used in energy equation. An autonomous system of fourth order differential equations have been deduced by using truncated Galerkin expansions. The asymptotic behavior can be stationary, periodic, or chaotic, depending upon the values of system parameters. It is found that a better combination of values of modulation parameters and scaled Rayleigh, internal Rayleigh numbers provides a way for chaos. Both a temperature and gravity modulation of the medium is to enhance or diminish the behavior of chaotic nature of the system. Due to high internal heat generation there is a chance to devolve a new kind of stable or unstable points in the system. Finally, heat transfer results are presented in terms of Nusselt number.

Correction to: Effect of trigonometric sine, square and triangular wavetype time-periodic gravity-aligned oscillations on Rayleigh–Bénard convection in Newtonian liquids and Newtonian Nanoliquids

The influence of trigonometric sine, square and triangular wave-types of time-periodic gravity-aligned oscillations on Rayleigh–Benard convection in Newtonian liquids and in Newtonian nanoliquids is studied in the paper using the generalized Buongiorno two-phase model. The five-mode Lorenz model is derived under the assumptions of Boussinesq approximation, small-scale convective motion and some slip mechanisms. Using the method of multiscales, the Lorenz model is transformed to a Ginzburg–Landau equation the solution of which helps in quantifying the heat transport through the Nusselt number. Enhancement of heat transport in Newtonian liquids due to the presence of nanoparticles/nanotubes is clearly explained. The study reveals that all the three wave types of gravity modulation delay the onset of convection and thereby to a diminishment of heat transport. It is also found that in the case of trigonometric sine type of gravity modulation heat transport is intermediate to that of the cases of triangular and square types. The paper is the first such work that attempts to theoretically explain the effect of three different wave-types of gravity modulation on onset of convection and heat transport in the presence/absence of nanoparticles/nanotubes. Comparing the heat transport by the single-phase and by the generalized two-phase models, the conclusion is that the single-phase model under-predicts heat transport in nanoliquids irrespective of the type of gravity modulation being effected on the system. The results of the present study reiterate the findings of related experimental and numerical studies.

The fate of self-aligned rolls in gravity modulated magnetoconvection

We explore the modifications brought about by gravity modulation in self-aligned two-dimensional (2D) stationary rolls and higher-order convective instabilities with horizontal magnetic field. The Chandrasekhar number plays no role in determining critical values of the forcing parameters for convection to begin. The onset is in the form of 2D rolls with periodically varying intensity. The external magnetic field is solely responsible for aligning the rolls while the induced magnetic field comes into play after three-dimensional convection sets in. Gravity modulation destabilizes the system and results in chaotic flow much earlier above onset.

Study of Weakly nonlinear Mass transport in Newtonian Fluid with Applied Magnetic Field under Concentration/Gravity modulation

AbstractIn the present paper, a weakly nonlinear stability analysis is used to analyze the effect of time-periodic concentration/gravity modulation on mass transport. We have considered an infinite horizontal fluid layer with constant appliedmagnetic flux salted from above, subjected to an imposed time-periodic boundary concentration (ITBC) or gravity modulation (ITGM). In the case of ITBC, the concentration gradient between the plates of the fluid layer consists of a steady part and a time-dependent oscillatory part. The concentration of both walls is modulated. In the case of ITGM, the gravity fleld consists of two parts: a constant part and an externally imposed time periodic part, which can be realized by oscillating the fluid layer. We have expanded the infinitesimal disturbances in terms of power series of an amplitude of modulation, which is assumed to be small. Ginzburg-Landau equation is derived for dinding the rate of mass transfer. Effect of various parameters on the mass transport is also discussed. It is found that the mass transport can be controlled by suitably adjusting the frequency and amplitude of modulation.

Gravity modulation effect on ferromagnetic convection in a Darcy-Brinkman layer of porous medium

The influence of a timedependent body force on the threshold of convective instability in a magnetic fluid filled horizontal porous layer is investigated. The gravity modulation effect is treated by employing a perturbation method. The correction Rayleigh number is computedas a function of the modulation frequency, porous and magnetic parameters. It is expounded that, for small and reasonable values of the modulation frequency, gravity modulation and magnetic mechanism have opposing influence on the stability. The study further explicates that, when the gravity modulation frequency increases beyond all bounds, manifestation of the disappearance of the magnetic and porous medium effects on the stability is highly likely.

Feedback Control of Chaos in Porous Medium under G-jitter Effects

In the present paper, we studied feedback control of chaotic convection in porous medium under gravity modulation. A non-autonomous system having three differential equations is obtained by employing the truncated Galerkin expansion method in to the modulated momentum and energy equations, called as Lorenz system in the literature. The parameter R demonstrates either periodic or chaotic behavior of the system as increasing R. It is also found that the influence of amplitude of modulation is to advance the chaotic nature in the system whereas the feedback control and frequency of modulation parameters have tendency to delay the chaotic behavior.

The Gravity Module Assembly used in airborne full tensor gradiometry surveys

ABSTRACTIn airborne gravity gradiometry, the Gravity Module Assembly is an optional gravimeter unit that is mounted on the same stabilized platform as the Full Tensor Gradiometer. Direct measurements of the gravity field are needed from this device to constrain the long wavelengths when gradient data are integrated mathematically to form high‐resolution gravity fields. The Gravity Module Assembly is, however, capable of providing independent gravity data with a specification approaching that expected from a dedicated airborne gravity system. Presented here is an error analysis of data from this instrument collected alongside the Full Tensor Gradiometer during an airborne survey. By having both gradiometry and gravity datasets, comparisons of the information content in these two types of measurement are made.

Effect of Gravity Modulation on Single Component Convection in a Couple Stress Fluid with Maxwell-Cattaneo Law

The outset of convection in a thin layer of couple stress fluid is analyzed using the linear stability analysis when the fluid is heated from below. In order to assimilate the inertial effects Maxwell-Cattaneo law is used in lieu of the classical Fourier's heat conduction law. The normal mode analysis is used to arrive at the eigenvalues of the perturbed state and a regular perturbation method to find the analytical solutions. The effect of Cattaneo number, couple stress parameter and Prandtl number is discussed and it is concluded that gravity modulation can delay or advance the onset of convection.

Study of a periodically forced magnetohydrodynamic system using Floquet analysis and nonlinear Galerkin modelling

We present a detailed study of Rayleigh–Benard magnetoconvection with periodic gravity modulation and uniform vertical magnetic field. Linear stability analysis is carried out using Floquet theory to construct the stability boundaries in order to estimate the magnitude of forcing amplitude $$\epsilon $$ required for having convection in the system for a fixed Rayleigh number Ra, wave number k and modulating frequency $$\Omega $$ . The effects of varying Prandtl number Pr and Chandrasekhar number Q on the threshold of convection are also investigated. A higher Pr value reduces the value of the threshold, whereas a higher Q value increases it. Bicritical states are also observed at which the minimum forcing amplitude needed for convection to begin occurs at two different k values in harmonic and sub-harmonic regions, respectively. We also construct a nonlinear Galerkin model and compare the results with those obtained from linear stability analysis. Two-dimensional (2D) oscillatory convection is observed at the onset, while quasiperiodic and chaotic behaviours are found at higher Ra values. 2D as well as nonlinear convective flow patterns are observed for primary and higher-order instabilities, respectively. Bifurcation diagrams with respect to different parameters such as $$\epsilon $$ , Ra and Q are provided for thorough understanding of the forced nonlinear system.

Feedback Control of Chaos in Porous Medium under G-jitter Effects

In the present paper, we studied feedback control of chaotic convection in porous medium under gravity modulation. A non-autonomous system having three differential equations is obtained by employing the truncated Galerkin expansion method in to the modulated momentum and energy equations, called as Lorenz system in the literature. The parameter R demonstrates either periodic or chaotic behavior of the system as increasing R. It is also found that the influence of amplitude of modulation is to advance the chaotic nature in the system whereas the feedback control and frequency of modulation parameters have tendency to delay the chaotic behavior.

Chaotic Darcy-Brinkman convection in a fluid saturated porous layer subjected to gravity modulation

Abstract On the basis of Darcy-Brinkman model, the chaotic convection in a couple stress fluid saturated porous media under gravity modulation is investigated using the nonlinear stability analyses. The transition from steady convection to chaos is analysed with the effect of Darcy-Brinkman couple stress parameter and the gravity modulation. The results show that the chaotic behavior is connected with the critical value of Rayleigh number which is dependent upon the oscillation frequency and the Darcy-Brinkman couple stress parameter. If the oscillation frequency Ω is not zero, the Rayleigh number value R of the chaotic behavior increases with the increase of the Darcy-Brinkman couple stress parameter. The Darcy-Brinkman couple stress parameter and the gravity modulation decrease the rate of heat transfer.

Microgravity modulation effects on free convection problems LBM simulation

In this paper, microgravity modulation effects on free convection in a cavity are investigated using the lattice Boltzmann method. In order to create microgravity modulation, a sinusoidal time-dependent function is considered. Parameters of the flow are chosen such that the maximum Rayleigh number approaches 106. The natural frequency of the system is obtained at first. Afterwards, effects of different frequencies on the flow and heat transfer fields are investigated in detail. Results are presented in four different frequency ratios categorized as (1) ω*=1200, 1100, 120, and 110; (2) ω*=18, 15, 13, and 12; (3) ω* = 0.75, 0.85, and 0.95; and (4) the last one is considered for natural frequency as a special case of ω* = 1. Furthermore, the fast Fourier transformation is used to describe the cavity flow behavior. The results indicated that at low frequency, the system has enough time to adapt itself with the gravity modulation while historical effects do not disappear. Increasing the frequency changes the behavior of the system and different flow patterns appear. Finally, at the natural frequency (ω* = 1), all system modes are stimulated and a strange flow pattern is formed.

Convection in an Anisotropic Porous Medium with Temperature Dependent Viscosity and Throughflow under G-jittera

In the present article, we study the combined effect of variable viscosity and throughflow in an anisotropic porous media under gravity modulation by reducing the model equations into Ginzgburg-Landau equation. A weakly non-linear stability analysis has been performed by adopting power series expansion in terms of the amplitude (assumed to be small) of gravity modulation. The Nusselt number is obtained in terms of the amplitude for the stationary mode of convection. Heat transfer mechanism is done by Nusselt number by taking different parameters, and depicted it graphically. Further, it is found that on increasing the value of thermo-rheological parameter, heat transport is more in the system. An increment in the amplitude (frequency) of gravity modulation enhances (diminishes) the heat transport. The behavior of Vadasz number, anisotropic parameters, and Peclet number are also studied.