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Control of chaos and intermittent periodic motions in Rayleigh-Bard convection using a feedback controller
Control of regular convective motion, chaos and periodic motion in the Rayleigh-Bard system is studied by considering a feedback control mechanism that considers the dependence of the heating (cooling) of the two boundary plates on one another. This set up ensures that the different flow regimes (convective, chaotic and periodic) in the system have no mechanical interference and the control remains an external mechanism. The rheostatic influence of feedback control on these flows is demonstrated by investigating in detail the critical Rayleigh number in the case of regular convective motion and the Hopf-Rayleigh number in the case of chaotic motion. For mild coupling between lower and upper boundary temperatures, periodic motions are intermittently observed in an otherwise chaotic regime at times when the system arrives at a situation (fuelling zone) wherein it needs to conserve energy in order to sustain chaos at subsequent times. For strong coupling between the boundary temperatures, an interesting situation arises wherein chaos makes a delayed and brief appearance and gives way to a prolonged spell of periodic motion. Features of the classical Rayleigh-Bard system are retained but each regime makes a delayed appearance. The Author(s), under exclusive licence to Springer Nature B.V. 2024. -
Control of chaos in Darcy-Bard axisymmetric convection in a cylindrical enclosure using a uniform vertical cross-flow
The linear and weakly nonlinear stability analyses of Darcy-Bard convection of a Newtonian fluid experiencing a uniform vertical cross-flow is investigated in the paper for various aspect ratios. Making use of the Maclaurin series representation, an expression for axial eigenfunctions is obtained with the radial eigenfunction being a Bessel function of first kind. These eigenfunctions are influenced by the Peclet number, Pe, the non-dimensional number that signifies the rate of vertical cross-flow. The modified-Vadasz-Lorenz model obtained in this paper has newly defined non-dimensional parameters that capture the influence of vertical cross-flow. From the linear stability analysis, it is found that the effect of introducing vertical cross-flow is to stabilize the system. Using a weakly nonlinear stability analysis, the closed-form expression of the Hopf-Rayleigh number as a function of Pe is obtained. Furthermore, the behavior of the modified-Vadasz-Lorenz model is analyzed using the largest Lyapunov exponent and the bifurcation diagram. This gives information about the intensity of chaos and occurrence of the periodic motion. We observe that the influence of vertical cross-flow is to increase the value of the Hopf-Rayleigh number and thereby to delay the onset of chaos. Furthermore, the appearance of the first periodic point is preponed due to the vertical cross-flow. As the rate of vertical cross-flow increases, the intensity of chaos decreases, thereby indicating that the effect of introducing vertical cross-flow is to suppress chaos. 2024 Author(s). -
Control of NOx from a DI diesel engine with hot EGR and ethanol fumigation: An experimental investigation
Oxides of nitrogen (NOx) are one of the major hazardous pollutants from diesel engine emission. Various control technologies exist for its control but each technique has advantages and disadvantages. At present, there is no single optimal technique that can control NOx without other side effects. Technologies available for NOx reductions either cause fuel penalty or increase other polluting emissions. Exhaust Gas Recirculation is an effective technique in controlling oxides of nitrogen in diesel engines but do not become attractive at higher loads and higher percentage of recirculated gas as combustion tends to deteriorate at higher loads leading to reduced engine thermal efficiency and increased hydrocarbon and smoke emission. Ethanol is an established alternate fuel used in diesel engine either as a blend or fumigated using a separate injector. Experiments were conducted on a single cylinder diesel engine to examine the effect of EGR temperature on NOx and other emission constituents. Hot EGR gave better results up to 30% EGR rate but EGR cooling was found better in terms of NOx reductions and efficiency. It was found that NOx reductions up to 88% was possible but at the cost of about 18% loss in thermal efficiency. This inconvenience of fuel penalty caused by Exhaust Gas Recirculation can be overcome by applying ethanol fumigation. The findings of experimental results for this combined technique are presented in this paper. With this combined technique, apart from reducing the oxides of nitrogen, engine power and efficiency approaches to that of only diesel combustion condition with improvements in smoke, hydrocarbon and carbon monoxide emissions. 2013 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg. -
Controlled reaction time of TiO2 and cocktail co-sensitization for improved DSSC performance
Solar energy stands out as a promising alternative to traditional energy sources, with dye-sensitized solar cells (DSSC) proving to be a highly effective means of harnessing this renewable energy. However, recent studies highlight the efficacy of employing a photoanode with mixed phases of Titanium Dioxide (TiO2) nanoparticles in DSSCs. The conventional approach to preparing mixed-phase TiO2 involves a time-consuming process with high-temperature annealing. In the present work, a novel microwave-assisted solvothermal synthesis of mixed-phase TiO2, which significantly reduces the preparation time has been reported. Moreover, we have enhanced device performance by co-sensitizing carbon dots (CDs) with various natural dyes and synthetic dye. The device prepared using CDs co-sensitized with Brassica oleraceavar.capitataf.rubra exhibited comparable efficiency (3.66%) with that obtained for N719-sensitized DSSC (3.85%). Further improvement in efficiency (4.81%) was obtained on sensitizing CDs with N719 dye. The comprehensive analysis of device performance using these innovative methods represents a noteworthy advancement in the realm of solar energy harvesting, with unexplored possibilities that could shape the future of sustainable energy solutions. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024. -
Controlling Node Failure Localization in Data Networks Using Probing Mechanisms
In this paper, we prospect the potency of node failure localization in network communication from dual states (normal/fizzle) of the source to destination paths. To localize the failure nodes individually in the scheduled nodes, dissimilar path states must connect with various events of failure nodes. But, this situation is inapplicable or not easier to investigate or apply on enormous networks due to the obligation of any viable failure nodes. This objective is to deploy the set of adequate conditions for recognizing a set of failures in a set of arbitrary nodes which can be verified in a stipulated time. To avoid the above situation, probing mechanisms are assimilated additionally as a combination for network topology and locations of scrutinizes. Three probing mechanisms are considering which vary depending on measurement paths. Both the procedures can be transformed into single-node possessions by which they can be calculated effectively based on the given conditions. The exceeding measures are proposed for measuring the potency of failure localization which can be utilized for assessing the effect of different factors, which comprises topology, total monitors, and probing mechanisms. 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. -
Controlling RayleighBard Magnetoconvection in Newtonian Nanoliquids by Rotational, Gravitational and Temperature Modulations: A Comparative Study
The effect of three different types of time periodic modulations on the RayleighBard magnetic system involving Newtonian nanoliquids is studied. Multiple-scale analysis (homogenization method) is used to arrive at the GinzburgLandau equation. The curiosity in the work is to know the individual effects of (1) rotation, (2) gravity and (3) temperature modulations on RayleighBard magnetoconvection in weakly electrically conducting Newtonian nanoliquids. A significant effort in this research is devoted toward linear and nonlinear stability analyses as well as the homogenization method which leads to the GinzburgLandau evolution equation. Although several studies have concluded similar results for nanoliquids compared with those of pure base fluids, many fundamental issues like the choice of phenomenological models for the thermo-physical properties and the best type of nanoparticles are not well understood. This research focuses on several important issues involving mathematical and computational problems arising in heat transfer analysis in the presence of nanoliquids. Effects of various nanoliquid parameters, frequency and amplitude of modulation on heat transport are analyzed. This investigation focuses on five nanoliquids, with water as a carrier liquid and five nanoparticles, viz. copper, copper oxide, silver, alumina and titania. Enhanced heat transport was observed for rotation, gravity and temperature modulations. In the case of rotation modulation, it is found that increase in the amplitude of modulation results in a decrease in the critical Rayleigh number and thereby to an increase in the mean Nusselt number. The increase in the amplitude of the gravity modulation is shown to enhance the heat transport, whereas increase in frequency is to inhibit the heat transport. Two types of temperature modulations are considered, viz. in-phase (synchronous) and out-of-phase (asynchronous) temperature modulations with the assumption that the boundary temperatures vary sinusoidally with time. The amplitudes of modulation are considered to be very small. In the case of in-phase modulation, there is no significant difference between the heat transports in the presence and in the absence of temperature modulation. On this reason, out-of-phase temperature modulation is used to either enhance or diminish heat transport by suitably adjusting the frequency and phase difference of the modulated temperature. The effect of magnetic field, in all three cases of modulations, is to inhibit the onset of convection and thereby diminish the heat transport. 2022, King Fahd University of Petroleum & Minerals. -
Controlling the Accuracy and Efficiency of Collision Detection in 2d Games using Hitboxes
Collision detection is a process in game development that involves checking if two or more objects have intersected or collided with each other. It is a fundamental aspect of game mechanics that cannot be overlooked. Games invloves assets/sprites, which tend to be drawn digitally with the help of a computer program. This paper discusses controlling and detecting collisions in games that make use of PNG images as game assets. The conventional way to detect collision in a game is to check if the object is within the bounding box of another object or asset. However, such a method lacks realism and doesn't work well with much complex shapes as the game might register a hit when another object collides with the transparent part of the object being checked for collision. In order to overcome these limitations, the proposed algorithm divides the entire image into smaller rectangles and stores its coordinates in an array. The array is then pruned by removing coordinates with no translucent or opaque elements. Collision is detected by checking if any of the points of the collision object is inside the image array. 2023 IEEE. -
Convection in a horizontal layer of water with three diffusing components
Triple diffusive convection in water is modelled with properties like density, specific heat, thermal conductivity, thermal diffusivity and thermal expansion, modified in the presence of salts. The GinzburgLandau equation is derived to study heat and mass transports of different combinations of salts in water. A table is prepared documenting the actual values of thermophysical properties of water with different salts and the critical Rayleigh number is calculated. This information is used in the estimation of Nusselt and Sherwood numbers and their relative magnitudes are commented upon. A detailed study on different single, double and triple diffusive systems is done and comparison is made of the results. The local nonlinear stability analysis made via a GinzburgLandau model mimics many properties of the original governing equations, namely, Hamiltonian character and a bounded solution. 2020, Springer Nature Switzerland AG. -
Convective heat and mass transports and chaos in two-component systems: comparison of results of physically realistic boundary conditions with those of artificial ones
Linear and weakly nonlinear stability analyses of double-diffusive convection in two-component liquids with either potassium chloride (KCl) or sodium chloride (NaCl) aqueous solution, and heat being present is investigated in the paper for free, and rigid, isothermal, iso-solutal boundaries. Using the thermophysical values of the aqueous solutions, we have shown that the stationary convection is the preferred mode at onset and that sub-critical motion is possible. We found that the critical thermal Rayleigh number for water+NaCl+heat is higher compared to that of water+KCl+heat. The study shows that for water+KCl+heat, the transition from convective motion to chaotic motion occurs at rH= 27.2 for free boundaries and at 48.5 for rigid boundaries. Here, rH denotes the Hopf thermal Rayleigh number. Further, the existence of windows of mildly chaotic points and fully periodic intervals are reported using Lyapunov exponents and bifurcation diagrams. Chaotic motions in both the aqueous solutions are nearly identical. The percentage increase in heat transport in the double-diffusive system involving NaCl is nearly 1% more than that of KCl in the case of free boundaries, whereas in the case of realistic boundaries it is nearly 1.6%. The comparison of the Nusselt and the Sherwood numbers between water+KCl and water+NaCl leads us to the conclusion that the aqueous solution with lower Lewis number transports maximum heat in the case of free boundaries and opposite is seen in the case of rigid boundaries due to the boundary effect. The many qualitative similarities between the results of artificial and realistic boundaries are highlighted. 2021, Akadiai Kiad Budapest, Hungary. -
Convective Heat Transfer in Maxwell- Cattaneo Dielectric Fluids
International journal of Computational Engineering Research Vol.3, Issue 3,pp. 347-355 ISSN No. 2250-3005 -
Convective instability analysis of couple-stress dielectric fluid saturated anisotropic porous medium with radiation effect
Purpose: The effects of anisotropy and radiation cannot be considered negligible while investigating the stability of the fluid in convection. Hence, the purpose of this paper is to analyze how these effects could affect the system while considering a couple-stress dielectric fluid. Therefore, the study establishes the effect of thermal radiation in a couple-stress dielectric fluid with an anisotropic porous medium using Goody's approach (Goody, 1956). Design/methodology/approach: To analyze the effect of radiation on the onset of convection, the MilneEddington approximation is employed to convert radiative heat flux to thermal heat flux. The equations are further developed to approximate for transparent and opaque medium. Stability of the quiescent state within the framework of linear theory is performed. The principle of exchange of stabilities is shown to be valid by means of single-term Galerkin method. Large values of conductionradiation and absorptivity parameters are avoided as fluid is considered as liquid rather than gas. Findings: The radiative heat transfer effect on a couple-stress dielectric fluid saturated anisotropic porous medium is examined in terms of MilneEddington approximation. The effect of couple-stress, dielectric, anisotropy and radiation parameters are analyzed graphically for both transparent and opaque medium. It is observed that the conductionradiation parameter stabilizes the system; in addition, the critical DarcyRayleigh number also shows a stabilizing effect in the absence of couple-stress, dielectric and anisotropy parameters, for both transparent and opaque medium. Furthermore, the absorptivity parameter stabilizes the system in the transparent medium, whereas it exhibits a dual effect in the case of an opaque medium. It was also found that an increase in thermal and mechanical anisotropy parameters shows an increase in the cell size, whereas the increase in DarcyRoberts number and conductionradiation parameter decreases the cell size. The validity of principle of exchange of stability is performed and concluded that marginal stability is the preferred mode than oscillatory. Originality/value: The effects of anisotropy and radiation on RayleighBard convection by considering a couple-stress dielectric fluid has been analyzed for the first time. 2020, Emerald Publishing Limited. -
Convective instability in a horizontal porous layer saturated with a chemically reacting Maxwell fluid
The problem of onset of convective instability in a horizontal inert porous layer saturated with a Maxwell viscoelastic fluid subject to zero-order chemical reaction is investigated by linear stability analysis. Modified Darcy-Maxwell model is used to describe the fluid motion. The horizontal porous layer is cooled from the upper boundary while an isothermal boundary condition is imposed at the lower boundary. Closed form solution pertaining to the basic quiescent state is obtained. The resulting eigenvalue problem is solved approximately using the Galerkin method. The Rayleigh number, characterizing the stability of the system, is calculated as a function of viscoelastic parameter, Darcy-Prandtl number, normalized porosity, and the Frank-Kamenetskii number. The possibility of oscillatory instability is discussed. 2013 AIP Publishing LLC. -
Convective instability in a horizontal porous layer saturated with a chemically reacting viscoelastic fluid
The thesis is concerned with Rayleigh-Benard convection in a horizontal porous layer saturated with a viscoelastic fluid subject to a zero order exothermic chemical reaction. Modified Darcy law is employed to describe the fluid motion. The effect of viscoelasticity, chemical reaction, and rotation on the onset of convection is considered. The findings of the problems investigated in the thesis may prove useful in heat transfer application situations with viscoelastic fluids as working medium. -
CONVECTIVE INSTABILITY IN POROUS MEDIA: IMPACT OF CHEMICAL REACTION ON MAXWELL-CATTANEO COUPLE-STRESS FERROMAGNETIC FLUIDS; [??????????? ??????????? ? ???????? ???????????: ????? ???????? ??????? ?? ?????????? ??? ?????????-???????? ? ????????????? ???????]
The current study analyzes the initiation of convection in a Maxwell-Cattaneo couple-stress ferrofluid within a porous layer, considering the effects of a chemical reaction. Small perturbations are applied to the fluid under the assumption of a zero-order energy release chemical reaction. The system is cooled from the upper layer while maintaining a steady temperature at the lower boundary. We employed linear stability analysis and determined Rayleigh number using the Galerkin Method (GM). This study emphasizes the influence of magnetic, chemical, Maxwell-Cattaneo, and couple-stress parameters on the initiation of ferro-convection. The findings indicate that both magnetic and chemical reaction parameters hasten the initiation of ferro-convection, while the porous medium and couple-stress parameters have a stabilizing effect. Notably, it is demonstrated that the destabilizing effects of chemical reactions and magnetic stresses can be effectively regulated in the presence of couple-stresses. The solutions provide insights into the potential application of ferromagnetic fluids for controlling efficient heat transfer mechanisms. 2024 Oles Honchar Dnipro National University. -
Convective Instability of Ferromagnetic Fluids in A Porous Medium
The thesis is concerned with the study of Rayleigh-Bard ferroconvection in a horizontal porous layer. Darcy-Brinkman law is employed to describe the fluid motion. The effect of second sound,thermal radiation, internal heat generation, variable viscosity and surface tension on the onset of Darcy-Brinkman ferroconvection is considered. newlineThe findings of the problems investigated in the thesis have implications for heat transfer applications wherein magnetic fluids serve as working media. The summary of the problems addressed in the thesis is given newlinebelow. Ferroconvection in a horizontal layer of porous medium with second sound The problem of Rayleigh-Bard convection in a ferromagnetic fluid saturated porous medium with the Maxwell-Cattaneo law is studied by newlinethe method of small perturbation. Modified Darcy-Brinkman model is used to describe the fluid motion. The horizontal porous layer is cooled from the upper boundary, while an isothermal boundary condition is imposed at the lower boundary. The fluid and solid matrix are assumed to be in local thermal equilibrium. The non-classical Maxwell-Cattaneo heat flux law involves a wave type heat transport and does not suffer from the newlinephysically unacceptable drawback of infinite heat propagation speed. The resulting eigenvalue problem is solved exactly for simplified boundary conditions and closed form solutions for both stationary and oscillatory instability are obtained. Some of the known cases have been deduced as newlinelimiting cases of the present study. The influence of porous, magnetic, and non-magnetic parameters on the onset of ferroconvection has been analyzed. It is found that magnetic stresses and second sound hasten the onset of Darcy-Brinkman ferroconvection. As the magnetic equation of newlinestate becomes more and more nonlinear, ferroconvection in a porous layer in the presence of second sound is advanced. However, it is delayed when the porous parameters are increased. -
Convergence of Health Expenditure and Health Outcomes in Central Europe and the Baltic Region
This research work examines the convergence of health expenditure in Central Europe and the Baltic region. The study reveals the absolute convergence in per capita health expenditures, indicating similar health outcomes for all eleven countries of the region. However, there is a divergence in health expenditure and outcomes across the eleven countries. Notably, public health expenditure diverges in Denmark, Estonia, Finland, and Norway, while, private health expenditure converges in Poland, Russia, and Sweden. Despite an overall convergence in life expectancy at birth across the countries, mortality rates due to non-communicable diseases only converge in Estonia. 2024 Taylor & Francis Group, LLC. -
Convergence of retail banking interest rates to households in euro area: time-varying measurement and determinants
This study measures time-varying progress of retail banking (to households) interest rates convergence and examines its determinants for twelve countries of the euro area, between 2003 and 2014. First, we measure convergence of interest rates using five different time-varying indicators, namely asymmetric dynamic conditional correlation (ADCC), beta convergence, sigma convergence, variance ratio, and dynamic cointegration. We then estimate panel regressions for each type of interest rate to identify the determinants of convergence over pre-crisis and crisis periods. The estimated ADCC is employed as the dependent variable and explanatory variables measure potential macroeconomic, external linkages, industry-specific, institutional and sociological determinants. The results reveal that convergence is weak and heterogeneous across sub-periods (pre-crisis and crisis), economic groups (core and periphery), product type (savings and credit) and products maturities (short, medium and long). Among the fundamental determinants, inflation, output correlation, and sociological factors strongly impact convergence, however, the explanatory power of determinants weakens during the crisis period. 2019, Springer-Verlag GmbH Germany, part of Springer Nature. -
Convergence of retail banking interest rates to households in euro area: Time-varying measurement and determinants /
International Economics and Economic Policy, Vol.17, Issue 1, pp.25-65 -
Convergent replicated data structures that tolerate eventual consistency in NoSQL databases
The Eventual consistency is a new type of database approach that has emerged in the field of NoSQL, which provides tremendous benefits over the traditional databases as it allows one to scale an application to new levels. The consistency models used by NoSQL database is explained in this paper. It elaborates how the eventually consistent data structure ensures consistency on storage system with multiple independent components which replicate data with loose coordination. The paper also discusses the eventually consistent model that ensures that all updates are applied in a consistent manner to all replicas. 2013 IEEE.