Energy Interchange Research Articles

Effects of material damping on flag flutter

Complex interactions of plates with ambient fluid are common in daily lives, e.g. flags flapping in wind, aerofoils oscillating in flow. Recently, the feasibility to harvest energy using the flutter motion has been demonstrated. The objectives of this study are to systematically explore the effects of the material damping on flag flutter, and then to study the energy interchange between the fluid and the flag. In this study, a two-dimensional model was developed. Three dimensionless parameters govern the system, i.e. the mass ratio between the structure and the fluid, the dimensionless fluid velocity and the dimensionless material damping. Results show that the critical velocity increases with the increase of the material damping. The oscillation frequency of the flag decreases with the increase of the material damping, and the time-averaged energy dissipation rate initially increases and then decreases. The increase of the material damping causes the transition of the system from a higher frequency oscillating state to a lower frequency oscillating state, and from a chaotic state to a periodic state.

A small-world methodology of analysis of interchange energy-networks: The European behaviour in the economical crisis

European energy policy pursues the objective of a sustainable, competitive and reliable supply of energy. In 2007, the European Commission adopted a proper energy policy for Europe supported by several documents and included an action plan to meet the major energy challenges Europe has to face. A farsighted diversified yearly mix of energies was suggested to countries, aiming at increasing security of supply and efficiency, but a wide and systemic view of energy interchanges between states was missing. In this paper, a Small-World methodology of analysis of Interchange Energy-Networks (IENs) is presented, with the aim of providing a useful tool for planning sustainable energy policies.A proof case is presented to validate the methodology by considering the European IEN behaviour in the period of economical crisis. This network is approached as a Small World Net from a modelling point of view, by supposing that connections between States are characterised by a probability value depending on economic/political relations between countries.

Toward second-moment closure modelling of compressible shear flows

AbstractCompressibility profoundly affects many aspects of turbulence in high-speed flows, most notably stability characteristics, anisotropy, kinetic–potential energy interchange and spectral cascade rate. We develop a unified framework for modelling pressure-related compressibility effects by characterizing the role and action of pressure in different speed regimes. Rapid distortion theory is used to examine the physical connection between the various compressibility effects leading to model form suggestions for pressure–strain correlation, pressure–dilatation and dissipation evolution equations. The closure coefficients are established using fixed-point analysis by requiring consistency between model and DNS asymptotic behaviour in compressible homogeneous shear flow. The closure models are employed to compute high-speed mixing layers and boundary layers. The self-similar mixing-layer profile, increased Reynolds stress anisotropy and diminished mixing-layer growth rates with increasing Mach number are all well captured. High-speed boundary-layer results are also adequately replicated even without the use of advanced thermal-flux models or low-Reynolds-number corrections.

Translational and rotational dynamics of colloidal particles in suspension: Effect of shear

We report a generalization of a nonequilibrium thermodynamic theory for the mesoscopic dynamics of radially symmetric interacting particles to anisotropic pairwise interactions and attain the one- and two-particle Fokker-Planck kinetics equations at a low-density limit that provides the translational-rotational coupling of their motion due to hydrodynamic interactions, from which we derived the balance equations of linear, angular momentum, and energy dissipation due to particle interactions and energy interchange with heat bath. In this low-density approximation, an already-known virial expression for the long-time translational collective diffusion coefficient of an orientational isotropic suspension in terms of the fluid equilibrium microstructure is recovered. An external shear flow induces, in the diffusive regime, vorticity effects into the rotational diffusion property of the colloidal particles. They manifest in the appearance of the particle's rotational viscosity due to vortex flow. The Smoluchowski equation that governs the dynamical relaxation of colloid microstructure due to particle's Brownian motion under stationary flow is provided.

NEURO-FUZZY CONTROL IN LOAD FORECASTING OF POWER SECTOR

Load forecasting is of vital importance for any power system. It helps in taking many decisions regarding energy purchasing and generation, maintenance, etc. Further, load forecasting provides information which is able to be used for energy interchange with other utilities. Over the years, a number of methods have been proposed for load forecasting. This paper focuses on short term load forecasting by using a hybrid model of neural networks and fuzzy logic.

The interaction of convection modes in a box of a saturated porous medium

Convection in an infinite layer of a porous medium occurs if the dimensionless Rayleigh number exceeds a critical value. This is also true for a box of a porous medium; however, each discrete modal solution has its own associated critical Rayleigh number. Usually just one mode will be generated at the onset of convection, but there are many critical box dimensions for which up to four modes share the same critical Rayleigh number, and all may be generated at the onset of convection. In such circumstances there will be a slow interchange of energy between the preferred modes. A perturbation method is applied to a system where three modes are generated at onset to yield a system of ordinary differential equations which govern the evolution of the amplitudes of the viable modes. Three unique cases arise, each with a different phase space structure. Critical boxes with ‘moderate’ aspect ratios are systematically categorised into these cases. While two of the examples represent the usual case where just one mode survives in the final state, the third example is a special case where it is possible for the three modes to coexist. The initial conditions determine which mode(s) will survive.

Identifying the optimum wind capacity for a power system with interconnection lines

This paper presents a general framework for identifying the optimum wind capacity to be integrated in a power system with interconnection lines. Wind generation is treated as negative demand, together with the load demand, which must be covered by the conventional power generation and the energy interchange with neighboring systems. Under the presumption that the time-varying wind and load together with the trading price with neighboring systems could be statistically modeled by specified probability distributions, a chance constrained programming (CCP) model is formulated to address the wind capacity planning problem. The objective is to maximize the yearly net profit of the entire power system subject to the operational constraints and the reliability requirement. Wind power curtailment and load shedding are allowed to improve the system flexibility but incur penalty costs. The optimization problem is solved using a hybrid intelligence algorithm incorporating Monte Carlo simulations, a neural network and a genetic algorithm. The feasibility of the proposed approach is verified by a case study on a given power system.

Characterization of Flow-Magnetic Field Interactions in Magneto-Hydrodynamic Turbulence

We examine the complex nonlinear flow-magnetic field dynamics in magneto-hydrodynamic (MHD) turbulence. Using direct numerical simulations (DNS), we investigate the dynamical interactions subject to the influence of a uniform applied background magnetic field. The initial magnetic and kinetic Reynolds numbers (based on Taylor microscale) are 45 and there are no initial magnetic field fluctuations. The sum total of turbulent magnetic and kinetic energies decays monotonically. With time, the turbulent magnetic fluctuations grow by extracting energy from velocity fluctuations. Expectedly, the distribution of energy between kinetic and magnetic fluctuations exhibits large periodic oscillations from the equipartition state due to Alfvén waves. We perform a detailed analysis of the flow-magnetic field coupling and posit a simple model for the energy interchange. Such dynamical analysis can provide the insight required for turbulence control and closure modeling strategies.

Multiscale approach combining nonadiabatic dynamics with long-time radiative and non-radiative decay: Dissociative ionization of heavy rare-gas tetramers revisited

A multiscale approach is proposed to address short-time nonadiabatic dynamics and long-time decay. We show the role of both radiative and non-radiative processes in cluster decay mechanisms on examples of rare-gas cluster fragmentation after electron impact ionization. Nonadiabatic molecular dynamics is used as an efficient tool for theoretical study on femto- and picosecond scales and a multiscale approach based on kinetic rates of radiative as well as non-radiative transitions, both considered as parallel reaction channels, is used for the analysis of the long-time system relaxation spanning times over microseconds to infinity. While the radiative processes are typically slow, the system relaxation through non-radiative electronic transitions connected with electron-nuclear interchange of energy may, on the other hand, significantly vary in kinetic rates according to kinetic couplings between relevant adiabatic states. While the predictions of picosecond molecular dynamics themselves fail, the results of the multiscale model for the electron-impact post-ionization fragmentation of krypton and xenon tetramers are in agreement with experiment, namely, in leading to the conclusion that charged monomers prevail. More specifically, on microsecond and longer scales, mainly slow radiative processes are substantial for krypton cluster decay, while for xenon the radiative and slow non-radiative processes compete. In general, the role of slow decay processes through non-radiative transitions is comparable with the role of radiative decay mechanism. The novel multiscale model substantially improves theoretical predictions for the xenon tetramer decay and also further improves the good agreement between theory and experiment we reached previously for krypton.

Assessment of Optimal Power Generation Mix considering Extensive Variable Renewable Energy and Nationwide Power Interchange

This paper evaluates optimal power generation mix considering massive deployment of variable renewable energy and regional power interchange. Japan has initiated feed-in-tariff (FIT) and expected significant introduction of PV and wind power for energy self-sufficiency and climate change. Wind power resource in Japan, however, concentrates mainly on Hokkaido and Tohoku region which is remote from electricity-consuming area such as Tokyo, and facilitating the considerable deployment of wind power requires the establishment of inter-regional power transmission line. On these backgrounds, we develop optimal power generation mix model including regional electricity exchange as large-scale linear programming model with 10 million variables and 30 million constraints. Calculated results show that regional grid expansion encourages wind power installation in Hokkaido and Tohoku region for supplying it to Tokyo area where PV power and stationary battery are alternatively replaced. The grid expansion, as well, promotes the shift of PV installation to Kyushu and Shikoku region which have longer sunshine duration, and interchangeably mitigates PV deployment in other regions through the transport of PV power from those two regions.

Integrability and optical solitons in a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system in fiber optics

In this paper, with symbolic computation, a generalized variable-coefficient coupled Hirota–Maxwell–Bloch system is studied, which can describe the ultrashort optical pulse propagation in a variable-coefficient nonlinear, dispersive fiber doped with two-level resonant atoms. Integrable conditions of such system are determined via the Painlevé analysis and the associated Lax pair is explicitly constructed. Furthermore, the analytic one- and two-soliton-like solutions are derived by virtue of the Darboux transformation. Through the graphical analysis of the soliton-like solutions obtained, the propagation features of optical solitons and their interaction behaviors are discussed. Different from the previous results, the two-soliton interaction is found to admit the energy interchanging property.

Investigation on the Effect of Airspeed and Altitude to Phugoid Mode of a Small Unmanned Blended Wing-Body Aircraft with Canard as a Longitudinal Control Surface

Phugoid mode is a lowly damped, low-frequency oscillatory motion representing vertical translation usually related to kinetic and potential energy interchange. MIL-F-8785C standard has ruled out qualitative specification requirements on measurement of flying and handling qualities of piloted aircraft. For phugoid mode, these requirements lie in the value of its damping ratio. Small aircraft is sensitive to atmospheric conditions and poor phugoid mode performance is observed in many unmanned aircraft. This paper discusses the effect of airspeed and altitude to phugoid mode of small, unmanned blended wing-body (BWB) aircraft named Baseline-II E-2. Baseline-II is a low subsonic, remotely-piloted UAV used to study the behaviour of a BWB-type aircraft. The case presented here is an E-2 version in which a specifically-designed canard is incorporated as its longitudinal control surface. Five Category B flight cases (airspeeds) per altitude-case, and three altitude cases (low, medium and high) are studied. Model-N dynamic model is introduced here to become the basis of flight simulation. The model is compared to models derived by other authors and approximation equations. The mean of simulating phugoid behaviour is using state-space representation of the aircraft using Matlab SIMULINK. The computations show that Baseline-II E-2 undamped natural frequency of phugoid mode is inversely-proportional to airspeed and reduces as altitude increases. These have adverse effect on its damping ratio that increases near parabolically when the aircraft flies faster, and reduces when it climbs up. The cause of these trends is looked into in detail and issues concerning Baseline-II E-2’s unsatisfactory and unstable phugoid mode oscillation at low speed are addressed.

Energy production planning of a network of micro combined heat and power generators

A promising and shortly emerging energy supply chain network based on residential-scale microgeneration through micro combined heat and power systems is proposed, modeled and optimized in this work. Interchange of electrical energy can take place among the members of this domestic microgrid, which is connected to the main electrical grid for potential power interchange with it. A mathematical programming framework is developed for the operational planning of such energy supply chain networks. The minimization of total costs (including microgeneration system’s startup and operating costs as well as electricity production revenue, sales, and purchases), under full heat demand satisfaction, constitutes the objective function in this study. Additionally, an alternative microgrid structure that allows the heat interchange within subgroups of the overall microgrid is proposed, and the initial mathematical programming formulation is extended to deal with this new aspect. An illustrative example is presented in order to highlight the particular significance of selecting a proper optimization goal that thoroughly takes into account the major operational, technical and economic driven factors of the problem in question. Also, a number of real-world size case studies are used to illustrate the efficiency, applicability and the potential benefits of the microgeneration energy supply chain networks suggested in this study. Finally, some concluding remarks are drawn and potential future research directions are identified.

FLUID-GRAVITY CORRESPONDENCE UNDER THE PRESENCE OF VISCOSITY

This work addresses the analogy between the speed of sound of a viscous, barotropic, and irrotational fluid and the equation of motion for a non-massive field in a curved manifold. It will be shown that the presence of viscosity implies the introduction, into the equation of motion of the gravitational analogue, of a source term which entails the flow of energy from the non-massive field to the curvature of the spacetime manifold. The stress–energy tensor is also computed and it is found not to be constant, which is consistent with such energy interchange.

Non-linear free periodic vibrations of variable stiffness composite laminated plates

Steady-state free vibrations, with large amplitude displacements, of variable stiffness composite laminated plates (VSCL) are analysed. The intentions of this research are: (1) to find out how the natural frequencies and (mode) shapes evolve with the displacement amplitude in this new type of laminated composite material; (2) to describe modal interactions in VSCL due to energy interchanges under the coupling induced by non-linearity; (3) to compare the VSCL with traditional, constant stiffness, laminated plates. The VSCL of interest here have curvilinear fibres and the numerical analysis carried out is based on a recently developed p-version finite element with hierarchic basis functions. The element follows first-order shear deformation theory and considers Von Karman’s non-linear terms. The time domain equations of motion are first reduced using the linear modes of vibration and then transformed to the frequency domain via the harmonic balance method. These frequency domain equations are solved by an arc-length continuation method.

A full dimensional grid empowered simulation of the CO2 + CO2 processes

A recently introduced bond-bond formulation of the intermolecular interaction has been extended to six-atom systems to the end of assembling a new potential energy surface (PES) and has been incorporated into a grid empowered simulator able to handle the modeling of the CO(2) + CO(2) processes. The proposed PES is full dimensional and accounts for the dependence of the intermolecular interaction on some basic physical properties of the colliding partners, including modulations induced by the monomer deformation. The used analytical formulation of the interaction involves a limited number of parameters, each having a clear physical meaning. Guess values for these parameters can also be obtained from analytical correlation formulae. Such estimates can then be fine tuned by exploiting experimental and theoretical information. The resulting PES well describes stretched and bent asymptotic CO(2) monomers as well as the CO(2)-CO(2) interaction in the most and less stable configurations. On this potential massive quasiclassical elastic and inelastic detailed scattering trajectories have been integrated, by exploiting the innovative computational technologies of the grid. The efficiency of the approach used and the reliability of the estimates of the dynamical properties obtained in this way is such that we can now plan a systematic evaluation of the state specific rate coefficient matrix elements needed for space craft reentry modeling. Here, we present probabilities and cross sections useful to rationalize some typical mechanisms characterizing the vibrational transitions of the CO(2) + CO(2) system on the flexible monomer proposed PES. On such PES, the key dynamical outcomes are: (a) there is a strong energy interchange between symmetric stretching of the reactants and bending of the products (and viceversa) while asymmetric stretching is strongly adiabatic (b) reactant energy is more efficiently allocated (with respect to the rigid monomers PES) as product vibration when reactant stretching modes are excited while the contrary is true when the reactant bending mode is excited.

Future ecological studies of Brazilian headwater streams under global-changes

This paper results from discussions triggered during the "Stream Ecology Symposium" that took place at the XIII Congress of the Brazilian Society of Limnology in September of 2011 in Natal, Brazil. Based on our experiences, we have raised several questions regarding ecological studies of headwater streams facing threats under global-changes and proposed numerous subjects to be addressed in future studies in Brazil. These studies deal with the necessity of knowing species biology and the elaboration of models to assess changes (which implies the availability of time-series or large-scale data sets); the ecology of riparian zones and the interchange of materials and energy across the land-water boundaries; forest conversions and standardized sampling strategies and data treatment to assess global change.

Effect of surface plasmon cross-talk on optical properties of closely packed nano-hole arrays

The integration and miniaturization of nanostructure-based optical devices based on interaction with surface plasmons requires the fabrication of patterns of multiple nanostructures with tight spacing. The effect of surface plasmon energy interchange (cross-talk) across large grids of nanostructures and its effect on the optical characteristics of individual nanostructures have not been investigated. In this paper, we experimentally fabricated a large grid of individual nano-hole arrays of various hole diameter, hole spacing, and inter-array spacing. The spectral optical transmission of each nano-hole array was measured and the effect of inter-array spacing on the transmission spectra and resonance wavelength was determined.

Distributed parametric effect in long lines and its applications

The article considers a parametric effect which takes place when the velocity of signal propagation in a long line changes. We found the analytical solution describing the form of the transformed signal for a line with losses, when line parameters change symmetrically. We also considered lines without losses, with asymmetrical change of parameters. Our theoretical results comply with experimental data. In certain conditions, such a line can be used as an amplifier. The parametric effect in optics is described by Maxwell's equations, while in case of a long line, the analysis is based on telegrapher's equations. However, it turns out that in the end, both in optics and electronics, the parametric effect is described by wave equations that are mathematically similar. This is because fundamentally, when the parameters of the propagating medium change, the parametric effect is physically based on energy interchange between the controlling (pump) signal and the transformed one. So, the obtained results can be used for analysis of parametric effects in optics and electronics.

Net modelling of energy mix among European Countries: A proposal for ruling new scenarios

European energy policy pursues the objective of a sustainable, competitive and secure supply of energy. In 2007, the European Commission adopted an energy policy for Europe, which was supported by several documents on different aspects of energy and included an action plan to meet the major energy challenges Europe has to face. A farsighted diversified yearly mix of energies was suggested to countries, aiming at increasing security of supply and efficiency, but a wide and contemporary view of energy interchanges between states was not available. In a previous work of the same authors, energy import/export interchanges between European States were used to develop a geographic overview at one-glance. In this paper, the enhanced Interchange Energy Network (IEN) is investigated from a modelling point of view, as a Small-World Net, by supposing that connections can exist between States with a probability depending also on economic/political relations between countries.