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The paper is devoted to the development of a device for protecting facilities with turn-to-turn insulation, namely transformers and wind generators in order to increase the reliability of operation of electrical power systems, renewable energy installations and energy storage systems. The paper presents the results of experimental studies of the parameters of a prototype frequency-dependent device, as well as an assessment of the effectiveness of suppression of high-frequency surge voltages by the proposed device. The results of four groups of measurements are shown, which were compared with each other and with the results of previously showed computer simulations. The high efficiency of the proposed device when influencing the slope and amplitude of short high-frequency transients is shown. It is indicated that the parameters proposed earlier in the simulation allow the device to be used effectively. A brief analysis of alternative methods and means of protection is provided, and the prospects for using the device as protective equipment for wind power plants are also considered. [ABSTRACT FROM AUTHOR]

In this paper, we present a simple strategy to identify Non-Terrestrial artefacts [NTAs; Haqq-Misra and Kopparapu (2012)] in or near geosynchronous Earth orbits (GEOs). We show that even the small pieces of reflective debris in orbit around the Earth can be identified through searches for multiple transients in old photographic plate material exposed before the launch of first human satellite in 1957. In order to separate between possible false point-like sources on photographic plates from real reflections, we present calculations to quantify the associated probabilities of alignments. We show that in an image with nine "simultaneous transients" at least four or five point sources along a line within a 10 ∗ 10 arcmin2 image box are a strong indicator of NTAs, corresponding to significance levels of 2.5 to 3. 9 σ. This given methodology can then be applied to set an upper limit to the prevalence of NTAs with reflective surfaces in geosynchronous orbits. • Our paper is motivated by the curious finding in Villarroel et al. (2021). • Photographic plate surveys from pre-satellite times are ideal to use in searches for non-terrestrial artefacts. • The methodology proposed is cheap and powerful as all image data sets already exists, are public and only need to be analysed. [ABSTRACT FROM AUTHOR]

• Experimental data on buried insulated wire response to fast transients provided. • Formulations for ground-return parameters of underground cables validated. • Demonstrates agreement between experimental measurements and EMT simulations. • Fills literature gap with measurements for earth-return effects in cables. • Supports integration of new ground-return expressions into EMT simulators. This paper presents experimental results on the transient response of a buried insulated wire subjected to fast transient signals. It reports measurements of voltage and current at the sending end, as well as the voltage at the receiving end of the insulated wire. The obtained experimental results are utilized to assess the accuracy of recent formulations proposed for computing the ground-return impedance and admittance of underground cables, which are important for simulation of transients using models based on the transmission line theory. The good agreement between measurements and simulations bolsters confidence in incorporating these newly proposed expressions for computing the cable's ground-return parameters into EMT-type simulators. [ABSTRACT FROM AUTHOR]

At present, as the demand for electricity increases in all sectors, there is an urgent need to introduce alternative renewable energy sources into modern energy systems. Renewable energy sources, which consist of solar (photovoltaic, PV), wind and hydro power, are key alternative sources of "green energy" energies, but it can also be used to produce "green" hydrogen. Thanks to scientific and technological progress, the cost of photovoltaic solar radiation converters is constantly decreasing at a high rate, which makes it possible to build solar power plants of sufficiently large capacity. In the coming decades, solar energy will become an incentive for the economic development of countries that have the maximum "solar" resource. The Republic of Tajikistan is one of these countries with a high potential for solar energy. The article presents an analysis of the resources and potential of solar energy in the Republic of Tajikistan. The study of electromagnetic transients in networks with photovoltaic solar power plants is performed. The main equations, simulation model and calculations of transients are presented, taking into account changes in voltage on DC buses. An algorithm for controlling the system of automatic control of output parameters is proposed. The analysis of dynamic and static modes in parallel operation of a solar power plant with the grid is carried out. A block diagram and computer model is constructed in the MATLAB package together with Simulink and Power System Blockset. [ABSTRACT FROM AUTHOR]

Conservation Biology fosters the study of Earth's ecosystems and biodiversity aiming at protecting species and their habitats from menaces causing the erosion of biotic interactions and extinctions. Its ultimate goal is to preserve biodiversity and promote sustainable ecological management maintaining both ecosystem's resilience and services. Ecosystems display complex patterns in time and space due to the intrinsic nonlinear nature of their interactions and can suffer regime shifts driven by the agents of global change. During the last decades, Ecology has turned from the equilibrium metaphor to the paradigm of non-equilibrium dynamics. This involves putting into the scene multiple stable states, nonlinear regime shifts, stochasticity, and ecological transients. These aspects are also crucial for biological conservation since they play a fundamental role in species' persistence, ecosystems' resilience, and in detecting warning signals prior to either the collapse or the recovery of the ecosystem. In this contribution, we discuss ecological regime shifts caused by tipping points in real ecosystems. Then, we provide information on some known dynamical features from theoretical ecology and dynamical systems theory associated to tipping points, mainly given by transient phenomena and the characteristic statistical patterns tied to early warning signals. These features are illustrated with a single-species mathematical model including facilitation and immigration. We also introduce and provide evidence of late warning signals as a way to identify when a tipping point has been surpassed but the system still remains in a transient state and recovery may be still possible. Our main goal is to near non-equilibrium concepts in Ecology to the conservationist community and promote bridges between such concepts and the management and conservation of ecosystems. • Ecosystems can suffer abrupt regime shifts driven by tipping points. • Even reducing or eliminating stressors that trigger tipping points, ecosystems may not return to their previous states. • To avoid the impacts of tipping points conservation policies may need to monitor the indicators of ecosystems' resilience. • We discuss how tipping points properties impact on ecosystems' conservation, management, and restoration. • We introduce late warning signals (LWS) and provide preliminary evidence of their existence. [ABSTRACT FROM AUTHOR]

We pursued a quantitative comparison of the continuum and mesoscale simulations of metal particle reactions in a condensed explosive. The continuum or homogeneous approximation assumed a single combustible mixture; contrastingly, in the present heterogeneous treatment of a mixture, aluminum and 1,3,5,7-tetranitro-1,3,5,7-tetrazocane were considered independent reactive granules of micron size with binder being inert material with strength. Both simulations similarly estimated the steady detonation velocity and peak pressure, while the early flame acceleration transients, marked by a complex flow structure behind the flame front, were observed only in the mesoscale simulation. The precise multi-interface processing techniques, combined with granule-level reactive flow models developed in this study, are deemed applicable to general heterogeneous solid fuel combustion studies related to granules of various size, shape, and reactivity. [ABSTRACT FROM AUTHOR]

The increasing incidence of extreme events combined with long-term pressures due to climate change and anthropogenic activities are seriously threatening ecosystems worldwide. Promoting ecological resilience (i.e., the ability of ecosystems to absorb changes and maintain their processes and functioning) is a pivotal target for biological conservation. Many empirical approaches to assess resilience have relied on the underlying assumption that, in the absence of disturbances, ecosystems would be in a 'static' baseline state. In reality, ecological systems are highly dynamic and undergo phases of development and reorganization resulting from natural successional changes and their response to multiple interacting variables. As such, ecosystem states can be better described by 'dynamic regimes' rather than stationary states. In this context, there is an urgent need to expand the common 'equilibrium-based' approaches used in empirical ecology to evaluate resilience so that they can be applied to non-static ecosystems. Here, we present our perspective on the relevance of approaches based on dynamic regimes to assess ecological resilience empirically. More specifically, we briefly review the concept of resilience and discuss the main challenges for empirical applications. Then, we review an approach based on ecological dynamic regimes and temporal trajectories that can be used to assess the ecological resilience of non-static ecosystems from empirical data. Approaches focused on dynamic regimes help evaluate the management effort necessary to restore a disturbed ecosystem. Besides, they facilitate the identification of the factors that must receive special attention for enhancing ecosystem resilience. • Many empirical studies assume 'static' reference states to quantify resilience. • Equilibrium paradigms contradict resilience theory and challenge biological conservation. • Transient dynamics, the stochasticity and dimensionality of data, and unstable basins of attraction should be considered. • Ecological dynamic regimes from empirical data bring new opportunities to assess resilience. • Non-equilibrium perspectives provide accurate information for conservation strategies. [ABSTRACT FROM AUTHOR]

This work considers multi-material topology optimization of compliant mechanisms under transient thermal and quasi-static mechanical conditions wherein thermally actuated devices are optimized for different operating conditions. The materials are modeled using finite strain thermo-hyperelasticity and a two way coupling between the energy balance and equilibrium equations is investigated. The design updates are generated from the gradient-based method of moving asymptotes optimizer and the sensitivities are computed using the time dependent adjoint sensitivity analysis. Results show the impact of designing for short versus long actuation times. [ABSTRACT FROM AUTHOR]

At present, we have almost as many theories to explain Fast Radio Bursts as we have Fast Radio Bursts observed. This landscape will be changing rapidly with CHIME/FRB, recently commissioned in Canada, and HIRAX, under construction in South Africa. This is an opportune time to review existing theories and their observational consequences, allowing us to efficiently curtail viable astrophysical models as more data becomes available. In this article we provide a currently up to date catalogue of the numerous and varied theories proposed for Fast Radio Bursts so far. We also launched an online evolving repository for the use and benefit of the community to dynamically update our theoretical knowledge and discuss constraints and uses of Fast Radio Bursts. [ABSTRACT FROM AUTHOR]

• Solving the time-dependent two-group neutron diffusion equation. • Nodal flux expansion method for hexagonal-z geometry. • Analytical coarse mesh finite difference formulation of the HEXNEM3 method. • Fully implicit scheme in time is used. • Modal decomposition in the energy domain is applied. An analytical coarse-mesh finite-difference (ACMFD) formulation of the HEXNEM3 nodal flux expansion method for solving the two-group neutron diffusion equation in hexagonal-z geometry is developed. In the time-dependent case, where an implicit differencing scheme in time is required for stability, nodal flux expansion necessitates iterating on the group sources. In order to avoid convergence issues, modal decomposition through matrix diagonalisation in the energy domain is first performed, and then the HEXNEM3 nodal expansion model is applied to the modes instead of fluxes, with boundary and continuity conditions on the scalar flux and the net current. The ACMFD formulation of HEXNEM3 has the advantage to produce an explicit non-homogeneous linear algebraic system for either the node-averaged fluxes or modes in all groups and nodes of a three-dimensional problem, with a free choice of any appropriate solution method. [ABSTRACT FROM AUTHOR]

We present Robbie : a general work-flow for the detection and characterization of radio variability and transient events in the image domain. Robbie is designed to work in a batch processing paradigm with a modular design so that components can be swapped out or upgraded to adapt to different input data, whilst retaining a consistent and coherent methodological approach. Robbie is based on commonly used and open software, and is encapsulated in a Makefile to aid portability and reproducibility. In this paper we describe the methodology behind Robbie , and demonstrate its use on real and simulated data. Robbie is available on GitHub. [ABSTRACT FROM AUTHOR]

The paper describes capabilities of a topological model of three-phase, five-limb transformer to accurately represent its response when subjected to geomagnetically induced currents. The model is validated by close agreement of the predicted values and waveforms of the currents, voltages, and reactive power with those measured in tests performed on two 400 MVA transformers connected back-to-back and to the Fingrid power network. Results demonstrate the importance of incorporating the network representation and dispel some misconceptions about the influence of the hysteretic properties of the core and tank in modeling five-limb transformers. [ABSTRACT FROM AUTHOR]

Highlights • For the first time, tube dynamics are applied to a dissipative system. • We propose a new method to obtain the wedge of velocity for transit orbits in a dissipative system. • For each energy, there is an elliptical boundary in which transit orbits are possible. • Transition tubes are found for both conservative and dissipative systems using a bisection method. Graphical abstract Abstract The equilibrium configuration of an engineering structure, able to withstand a certain loading condition, is usually associated with a local minimum of the underlying potential energy. However, in the nonlinear context, there may be other equilibria present, and this brings with it the possibility of a transition to an alternative (remote) minimum. That is, given a sufficient disturbance, the structure might buckle, perhaps suddenly, to another shape. This paper considers the dynamic mechanisms under which such transitions (typically via saddle points) occur. A two-mode Hamiltonian is developed for a shallow arch/buckled beam. The resulting form of the potential energy—two stable wells connected by rank-1 saddle points—shows an analogy with resonance transitions in celestial mechanics or molecular reconfigurations in chemistry, whereas here the transition corresponds to switching between two stable structural configurations. Then, from Hamilton's equations, the equilibria are determined and linearization of the equations of motion about the saddle is obtained. After computing the eigenvalues and eigenvectors of the coefficient matrix associated with the linearization, a symplectic transformation is given which puts the Hamiltonian into normal form and simplifies the equations, allowing us to use the conceptual framework known as tube dynamics. The flow in the equilibrium region of phase space as well as the invariant manifold tubes in position space are discussed. Also, we account for the addition of damping in the tube dynamics framework, which leads to a richer set of behaviors in transition dynamics than previously explored. [ABSTRACT FROM AUTHOR]

Highlights • Realistic optimal dispatch ensures microgrids can survive generator contingencies. • Formulations include generators and controller dynamics, voltages, line flows. • Computationally efficient cutting plane-like algorithm captures controller topology. • This work demonstrates the tradeoff between capital and operating costs. • The approach can be extended to microgrids that include synchronous machines. Abstract The reliability and resilience of the electrical power grids are essential to industry, economy and society. Microgrids that are able to island from the bulk electrical grid are one technology that may vastly improve electrical power service to customer loads. To achieve these improvements, an islanded microgrid should be able to operate through the loss of one of its generators without shedding electrical load. The loss of one generator will typically result in significant additional loads, including transient overloads, being placed on the remaining generators. There is also the possibility of additional generator tripping during these processes (i.e. cascading failures), which would likely result in the collapse of the microgrid. The novelty of our work consists in incorporating dynamic models of generator controllers into a microgrid optimal dispatch formulation with the ultimate goal to avoid operational failures and ensure the "survivability" of all-inverter microgrids to generator loss and transient overloads. The integration of generator and controller dynamics into the optimal dispatch formulation significantly increases the computational complexity. As we develop algorithms to restore speed of the optimization, our method can be readily implemented into a new operational strategy capable of an unprecedented level of reliability against generator contingencies. In addition, we quantitatively illustrate the effect of the survivability constraints on the microgrid operating costs and how the related trade-off between capital and operating costs should be taken into account at the design stage. The methods developed here also apply to the dispatch of off-grid microgrids. [ABSTRACT FROM AUTHOR]

• Implementation of a novel CFD-based model for reactor transient simulation. • Simulation of an unprotected loss of flow (ULOF) transient in a small lead cooled reactor (SEALER) • Comparison with a lumped-parameter model. • Study on the effect of the pump flywheel size. The recent development of small modular reactors needs to be followed by safety analysis using the newest available tools. This work focuses on one type of reactor, SEALER, which is a small lead cooled reactor intended for remote communities in Canada. Simulations of a loss of flow transients are performed using a CFD-based model that was specifically developed for this project. The CFD geometry includes the entire primary circuit with some simplifications. The fuel channel, steam generator and pumps use a simple geometry with momentum source and heat source/sink. Free surface level is modelled with the multiphase volume of fluid (VOF) method. The CFD part of the model is coupled to a custom code for heat transfer in the fuel rods and point kinetics for neutronics. Transient results show that core temperatures do not increase significantly and stay well below coolant boiling and fuel melting points. The CFD-based model presented here is compared against a lumped-parameter model using the same transient. It is shown that the evolution of the mass flow and temperature is significantly different and more detailed with the CFD-based model. Finally, the influence of the moment of inertia of the pump flywheel on the transient is explored. [ABSTRACT FROM AUTHOR]

Lightning strikes to conductors of overhead lines may cause high transient induced voltages at neighbouring pipelines. Thus, the computation of these voltages is important for the safe and reliable pipeline operation. This work investigates the effects of line parameters and soil modelling on the transient voltages induced at an aboveground pipeline due to lightning strikes to a phase conductor of a nearby overhead transmission line. Three different earth formulations are evaluated: the Carson, Wise, and the method of moments with surface operator combined with the extended transmission line approaches. Computations are performed using both frequency- and time-domain models, as well as constant and frequency-dependent soil electrical properties. CIGRE lightning current waveforms are employed in simulations derived on the basis of the statistical distributions of their parameters for negative first return-strokes. Transient induced voltage waveforms differ among the evaluated lightning currents, with higher peak values for shorter and steeper current wavefronts. Conservative results are obtained for the constant soil properties and Carson's earth formulations, which neglect, respectively, the dispersion of soil electrical properties and displacement current. • Transient voltages induced at aboveground pipelines caused by overhead power line. • The effects of line parameters and soil modelling are examined. • Three different earth formulations are evaluated. • Computations are performed using both frequency- and time-domain models. • Lightning current waveforms are employed in the simulations. [ABSTRACT FROM AUTHOR]

Transient-based earth fault protection is widely used in all types of resonant grounded networks, and though the operating principles of the commonly available relays are usually derived from radial networks, manufacturers claim applicability in meshed networks as well. This paper utilizes a laboratory setup to study the directional indication of four transient earth fault relays in non-radial resonant grounded networks. Two of the relays considered are widely used analog single-purpose transient earth fault relays, whereas the other two relays represent two transient-based earth fault functions found in modern protective devices. The paper verifies the location of crossover points according to the presented theory, i.e. fault locations for which relays transition between seeing faults as forward and reverse faults, and demonstrates the viability of the proposed theoretical analysis of crossover points. However, presented analytical formulae only describe the two analog relays accurately, whereas the two modern relays have a more complex operating principle which requires further analysis to quantify properly. Finally, it is shown that relay misoperation which is not easily fixed by communication between relays can occur, and it is suggested that network operators conduct detailed relay coordination when applying transient earth fault relays instead of relying on standardized settings. • Transient earth fault protection directionality in non-radial networks. • Comparison of relays based on first-half-wave-principle and on zero-sequence energy. • Verification of theoretical analysis using physical relays in laboratory. • Transient earth fault protection devices in the network should be coordinated. [ABSTRACT FROM AUTHOR]

Thanks to the growing computer power, it is now feasible to apply Monte Carlo methods to the solution of non-stationary transport problems in reactor physics and in criticality-safety, which play an instrumental role in producing reference numerical solutions for the analysis of transients occurring during normal and accidental behaviour. In this respect, a major scientific challenge is represented by the very different time scales of neutrons and precursors, which demand distinct strategies and variance reduction techniques with respect to stationary simulations. In this work we will present the principal algorithms and simulation methods that have been explored and selected for the kinetic capabilities of T ripoli -4®, the production Monte Carlo code developed at CEA. The efficiency of the tested methods will be demonstrated on simple geometries as well as on step reactivity insertion and extraction due to control rod movements for the experimental reactor SPERT-III E-core. The solutions obtained by using T ripoli -4® will be compared to the point-kinetics approximation and to the asymptotic analysis based on alpha eigenvalues. [ABSTRACT FROM AUTHOR]

In this paper we suggest an algorithm for estimation of the parameters detailing Oscillating Gaussian functions. The different components of the signal are first detected in the spectrogram. After this we exploit the fact that a Gaussian function may be perfectly reassigned into one single point given a correct scaling factor, where this scaling factor is a function of the unknown shape parameter of the Gaussian function. The scaled reassignment of the spectrogram is performed using a set of candidate scaling factors and the local Renyi entropy is used to measure the concentration of each component using every candidate scaling factor. The estimates are refined by using non-linear least squares. The algorithm is evaluated on both simulated and real data. [ABSTRACT FROM AUTHOR]

This paper presents a measurement procedure to be implemented in smart Power Quality Analyzers (PQA), and conceived to monitor service nodes in the current electrical network. It is thought on the need for developing measurement instruments capable of detecting newly PQ events, which commonly appear in the modern Smart Grid (SG), adding at the same time complementary information, regarding the real-time network state, than the conventional meters do. Its novelty resides in the deployment of the events’ trajectories in three types of 2D maps based in Higher-Order Statistics (HOS). The events under study appear isolated or in hybrid versions: sags and transients. Examining the HOS dynamics (trajectories in the HOS planes), the procedure allows the online detection and help detect specific types of events. Additionally, this trajectory-based method reveals some other features like hybrid events, the depth or event degree, the duration and the phase changes. The results are based on real-life signals, which have been surveyed in a building’s node. A complementary deviation index gathers the information regarding the individual distances between each statistic and its associated ideal value. [ABSTRACT FROM AUTHOR]

Combustion instability in gas turbine engines is often mitigated using fuel staging. Fuel staging, sometimes referred to as fuel splitting, is a strategy by which fuel is unevenly distributed between different nozzles of a multiple-nozzle combustor. These fuel splits are conducted in a transient manner in real engines, and the effects of these transients on instability are not well characterized. This work fills this gap by systematically studying the effects of transient fuel staging on self-excited combustion instability by varying the amount of staging fuel (staging amplitude), timescale in which the fuel is added (transient duration), and whether staging fuel is added or subtracted (transient direction). In this work, three staging amplitudes, five transient durations, and both transient directions are considered. The transient timescales are broadly divided into “short” duration transients, which have fuel delivery timescales shorter than the characteristic instability decay or onset timescales, and “long” duration transients, which have fuel delivery timescales longer than the characteristic instability decay or onset timescales. For short duration transients, we find the instability decay timescale depends on staging amplitude but does not depend on transient duration. For long duration transients, we find the instability decay timescale does not strongly depend on staging amplitude. The instability onset timescale is found to be longer and more variable between runs than the instability decay timescale for a given fuel delivery timescale. The onset timescale is also longer in duration and more variable than the decay timescale at a given fuel delivery timescale, implying that the instability rise process is overall more variable and slower than the instability decay process. Analysis of combustor damping rates show a strong dependence of damping rate on staging amplitude but no strong dependence on transient duration or direction. Instantaneous phase difference images between p ′ and q ˙ ′ are used to differentiate regions in the combustor that have constructive versus destructive interference between heat release rate oscillations and pressure fluctuations. The phase images show that p ′ and q ˙ ′ become in-phase early in the transient for the onset transients. [ABSTRACT FROM AUTHOR]

The advancement of the design of the Advanced Lead-cooled Fast Reactor European Demonstrator (ALFRED) beyond the conceptual phase, passes through the analysis of the impact of uncertainties, notably to what concerns safety-related conditions. Compliancy of plant safety to Design Extension Conditions is, according to IAEA and in line with the meaning itself of these beyond-design conditions, usually investigated by best estimates only. Due however to the demonstration nature of ALFRED, it was decided to assess the actual safety performances of this system even in ultimate conditions. To this regard, the emphasis was put on unprotected events like the UTOP (unprotected transient of over-power) and ULOOP (unprotected loss of offsite power, resulting from the combination of a loss of flow and loss of heat sink under unprotected conditions), pinpointed as the most challenging situations sought for the plant. The purpose of the present work, which has been divided in three parts, was then to assess the ultimate ALFRED safety margins against failure of the key core components and systems (Part III). To target this objective, the evaluation of uncertainties coming, on one hand, from nuclear data was performed at first, to retrieve their impact on the reactivity coefficients, thereby on the transient behavior driven by the latter (Part I); then, uncertainties from material properties, fabrication procedures, operation and measurement, and computational tools were propagated to assess their influence on the thermal-hydraulics of the system (Part II). In this work the efforts of Parts I and II are merged together and the effect of uncertainties on safety margins and salient parameters assessed. The retrieved uncertainties are propagated to the expected number of pins experiencing fuel melting during an UTOP and to the clad time-to-failure during an ULOOP. The former has been found to be quite affected by uncertainties, but still under limits not directly posing hazards to the people and the environment, even when extremely conservative assumptions are put forward; the latter shows a milder response to uncertainties, but always guaranteeing more than an order of magnitude of safety margin relative to WENRA recommendations. [ABSTRACT FROM AUTHOR]

The Combustion Dynamics group in the Rocket Propulsion Department at the German Aerospace Center (DLR), Lampoldshausen, strives to advance the understanding of dynamic processes in cryogenic rocket engines. Leveraging the test facilities and experimental expertise at DLR Lampoldshausen, the group has taken a primarily experimental approach to investigating transient flows, ignition, and combustion instabilities for over one and a half decades. This article provides a summary of recent achievements, and an overview of current and planned research activities. [ABSTRACT FROM AUTHOR]

In order to better understand and quantify the effect of instabilities in systems utilizing flow boiling heat transfer, the present study explores dynamic results for pressure drop, mass velocity, thermodynamic equilibrium quality, and heated wall temperature to ascertain and analyze the dominant modes in which they oscillate. Flow boiling experiments are conducted for a range of mass velocities with both subcooled and saturated inlet conditions in vertical upflow, vertical downflow, and horizontal flow orientations. High frequency pressure measurements are used to investigate the influence of individual flow loop components (flow boiling module, pump, pre-heater, condenser, etc. ) on dynamic behavior of the fluid, with fast Fourier transforms of the same used to provide critical frequency domain information. Conclusions from this analysis are used to isolate instabilities present within the system due to physical interplay between thermodynamic and hydrodynamic effects. Parametric analysis is undertaken to better understand the conditions under which these instabilities form and their impact on system performance. Several prior stability maps are presented, with new stability maps provided to better address contextual trends discovered in the present study. [ABSTRACT FROM AUTHOR]

Pumped storage hydro (PSH) based generation of electricity is a proven grid level storage technique. A new configuration i.e., adjustable speed PSH (AS-PSH) power plant is modeled and discussed in this paper. Hydrodynamic models are created using partial differential equations and the governor topology adopted from an existing, operational AS-PSH unit. Physics-based simulation of both hydrodynamics and power system dynamics has been studied individually in the past. This paper demonstrates a co-simulation of an AS-PSH unit between penstock hydrodynamics and power system events in a real-time environment. Co-simulation provides an insight into the dynamic and transient operation of AS-PSH connected to a bulk power system network. The two modes of AS-PSH operation presented in this paper are turbine and pump modes. A general philosophy of operating in turbine mode is prevalent in the field when the prices of electricity are high and in the pumping mode when prices are low. However, recently there is renewed interest in operating PSH to also provide ancillary services. A real-time co-simulation at sub-second regime of AS-PSH connected to the IEEE 14 bus test system is performed using digital real-time simulator and the results are discussed. [ABSTRACT FROM AUTHOR]

Most of the previous research on flash gas bypass (FGB) focused on performance improvement in steady state and demonstrated that compared to direct expansion mode (DX), FGB mode have better performance. However, the control strategy of flash gas bypass system and dynamic behavior during start-ups and transients were not yet clearly defined and investigated. In this paper, a novel control strategy has been proposed for an automobile air conditioning system operating in flash gas bypass mode with R134a as the refrigerant. The proposed control strategy utilized an electronic expansion valve (EV) for the control of subcooling from condenser outlet and a bypass valve (BV) for superheat from compressor inlet. Both start-up and transient system behaviors were studied. The experimental results showed that the proposed cycle control strategy was found to be able to provide reliable control to the system. In addition, proper sizing of bypass valve and flash gas bypass tank have also been studied. [ABSTRACT FROM AUTHOR]

Transient wall shear stress measurements using hot-film anemometry have been performed in a large-scale laboratory setup at high Reynolds numbers. Starting from Reynolds numbers 1.7 × 10 6 and 0.7 × 10 6 , the flow was brought to a complete rest by closing a knife gate thus replicating a pressure-time (also know as Gibson) flow rate measurement in a hydropower plant. Ensemble-averaged mean wall shear stresses obtained from 22 repeated runs have been compared with estimates obtained using the pressure-time method. The objective of the work has been to assess the accuracy of the frictional formulation entering the pressure-time integral. It is shown that both the standard method, a quasi-steady approach as well as the recently introduced unsteady method all reproduce the measured wall shear stresses quantitatively during most of the transient. The last phase, following the complete closure of the gate, which is characterized by a slow decay towards zero shear stress at the wall is, however, not captured by the available methods. In general, the unsteady formulation produces the smallest flow rate estimation error, which in turn, implies the best modeling of the frictional losses. [ABSTRACT FROM AUTHOR]

We derive, evaluate and validate comprehensive analytic modeling of the energy flows in parabolic trough solar thermal power plants. The analytic formulae are straightforward to implement and evaluate, relating to the heat transfer within and from the solar concentrators (including transients, mainly overnight heat losses), and the impact of solar field operation on turbine power and efficiency. Prior numerical simulations used to design solar thermal power systems have either been proprietary or devoid of a fully-reported source code - hence inaccessible or problematic for widespread use. Also, the dependence of these simulations on extensive numerical procedures does not provide a transparent physical picture that grants a clear understanding of how component and system performance vary with the principal operating and input variables - a drawback overcome by the analytic approach presented here. Published experimental measurements of sufficient extent to permit meaningful comparisons between theory and experiment for such solar thermal power plants are exceptionally limited. This narrow data base is used for model validation on both a monthly and an hourly basis. The analytic model is then applied to evaluating a solar power plant now being planned for northeast Brazil, also highlighting the energy-delivery advantages of low-latitude locations. [ABSTRACT FROM AUTHOR]

The impact of injector life on the spatio-temporal evolution of fuel spray quality was optically investigated using high speed imaging techniques. Both new and used injectors, which had been used in intense operation for up to 90,000 miles, were considered in this investigation. Used injectors are prone to wear, deposit formation, and altered internal nozzle flow. High resolution SEM images clearly portray the presence of carbonaceous deposits both at the injector tip as well as within the holes of used injectors. Investigations revealed that used injectors tend to produce a chaotic hole-to-hole variation at the start of each injection, resulting in an asymmetric early fuel spray penetration pattern in the first 500 μs. Often those sprays that suffered a reduced spray tip penetration rate at the start of injection also showed off-axis transient expansions, and those sprays appeared to be bulky compared to other sprays. Following the early asymmetric spray penetration phase of injection the retarded sprays undergo rapid acceleration with time, and this transformed the early asymmetric spray pattern into a nearly uniform spray pattern from all the orifices in the quasi-steady state regime. The hole-to-hole penetration variations and the resultant asymmetric spray structure at the early start are therefore short lived transient phenomena. However if the radial expansion of the spray is large during the early phase, the radially expanded plume remains almost at the same radial location due to lack of local axial momentum, even after different time instants of spray tip propagation. This appears as a bulge to the spray and can eventually end up as a stationary local pocket of fuel vapor close to the nozzle for the entire duration of injection. This may alter the ignition, flame lift-off and entrainment characteristics of sprays injected from used or deposit rich injectors. [ABSTRACT FROM AUTHOR]

Between 28 August 2011 and 8 September 2011, five 33kV OIP bushing failures occurred at JBB Ali Grid Station belongs to Oman Electricity Transmission Company (OETC). Three failures resulted in a complete loss of supply and around 130,000 consumers were reported with a lack of electricity. OETC assigned a third party investigator to conduct a power failure investigation in order to obtain a possible root cause for these failures. The investigation approach or process that were followed included the following phases: ·Phase 1: Facts finding and preliminary analysis ·Phase 2: Destructive dismantling and laboratory investigation through. ·Phase 3: Root cause analysis. From the investigation and buildup of hypothesis, no single most likely cause of failure could be identified. Metal migration and semi-conductive copper sulphide migration in the oil that led to surface contamination of insulation in the stress zone is considered causal factor for bushings insulation degradation. Copper sulphide in bushing was detected caused due to corrosive Sulphur in oil. There has to be another factor influencing the weakened insulation breakdown. The source of this factor can be found in the suspected frequently occurring earth faults in the 33 kV line feeders, leading to a line voltage to ground of 33 kV and transient over voltages due to switching off the faulted feeder. All the OIP bushings were supplied in the same patch filled with the same oil and operated in identical service conditions so degradation of insulation as chemical process can be considered in similar state. Electrically all bushings were subjected to identical voltage and load related stresses as transformers are operated in parallel. Thus combinations of these two factors are considered as causal factor for frequent breakdown of multiple bushings. [ABSTRACT FROM AUTHOR]

• An improved technique for the calculation parameters of lines/cables is proposed. • Proximity effects, earth return, and skin effect are accurately modeled. • Increased modeling flexibility is given with the new tool, such as multilayer soil and combined underground/aerial lines. • Theoretical review and explanations on the reunited techniques is presented. • Demonstrations on transient applications are provided. This paper presents a new tool for the computation of per-unit-length parameters for transmission line and cable models used for simulating electromagnetic transients (EMT). The proposed methodology is based on the MoM-SO theory and state-of-the-art formulations for the computation of the series impedance and shunt admittance parameters. The new tool has major advantages compared to traditional approaches available in EMT-type software. These advantages include accurate skin and proximity effect modeling, above-ground cable modeling, modeling of stranded wires in cables, representation of multilayer soil, coupled overhead lines and underground cables, etc. This paper presents the new tool together with demonstrations of transient simulations for practical examples. [ABSTRACT FROM AUTHOR]

• Most accurate impedance calculation for 3C armoured cables through 3D FEM models. • Solenoid effects responsible for discrepancies against less accurate 2.5D models. • Sequence impedance calculations applicable to both power and higher frequencies. • Effect of design parameters, e.g., armour pitch, lay direction and steel material. • Impact of solenoid effects on propagation characteristics and transient responses. Cables used in offshore windfarms are usually three-core (3C) with metallic armour. The series impedance at power frequency is necessary to estimate cable steady-state and fault condition performances, e.g., by calculating sequence impedances. The impedance at higher frequencies is also needed for transient analysis. Three-dimensional (3D) effects, being inevitably present in 3C cables, such as twisting effects, may be treated in a two-and-a-half-dimensional (2.5D) fashion. Although fast, this approach cannot account for the full 3D effects since it ignores solenoid effects. Thus, the calculated impedance may be inaccurate, potentially compromising the cable performance. 3D models based on finite element method are developed in this paper to consider the full 3D effects. The impedance is derived at power and higher frequencies. The proposed 3D method is evaluated against 2.5D methods. Solenoid effects appear to have a remarkable influence on impedance. Design aspects, such as the magnetic permeability and the pitch angle of the armour, are also examined. Finally, the effect on modal propagation characteristics is highlighted and the transient response is simulated. [ABSTRACT FROM AUTHOR]

A pressurized water reactor (PWR) is a multivariable system that consists of several subsystems such as a core, steam generator, pipings, and plenums that show highly nonlinear behavior. These components are prone to critical parameters that cause potential accidents and propagate to the entire system. Therefore, the PWR needs continuous and fast pre-accident assessment through modeling and predicting by leveraging powerful intelligence technologies. In this regard, this study demonstrates the potential of the nonlinear autoregressive with exogenous inputs (NARX) neural network modeling approach. The established NARX model is evaluated using PWR transients under perturbations in control rod velocity and core inlet coolant temperature. The trained network was then applied for state estimation, future prediction, and fault detection. The simulation results verified that the NARX model predicts the target value with good accuracy as compared with the nonlinear input-output (NIO) neural network strategy. Further, it is used to forecast the step-ahead values of the targets in the defined confidence interval and fault detection. Overall, the present study gives the benefit of the NARX approach for estimation and fault detection applications in other nuclear engineering fields. • The PWR system model was developed and simulated under perturbations. • The NARX strategy is adopted to model the PWR transients. • The produced NARX model was used for target variables prediction, future response forecast, and fault detection. • The simulation results verified that the NARX model successfully replicates the PWR transients. [ABSTRACT FROM AUTHOR]

Understanding the relationship between chemical erosion rates ( W ) and physical erosion rates ( E ) is of wide interest due to their roles in driving landscape evolution, supplying nutrients to soils and streams, and modulating the global carbon cycle. Measured relationships between W and E vary around the globe, with some regions exhibiting positive correlations between W and E , some negative correlations, and others no correlation within uncertainty. Here we use a numerical model for mineral weathering in well-mixed ridgetop regolith to explore how complex W – E relationships can be generated by simple transient perturbations in E . We show that a Gaussian perturbation in E can produce positive or negative responses in W , and can result in a variety of hysteresis loops – clockwise, counterclockwise, or figure-eight – in plots of W against E . The nature of the transient response depends on the shape of the steady-state W – E relationship, which is set by regolith mineralogy, and the ratio of E to the maximum possible regolith production rate. The response time of W is controlled by the response time of soluble mineral concentrations at low E , where soluble mineral concentrations are low, and by the response time of regolith thickness at high E , where regolith thickness is low. These complex W – E relationships arise in the absence of variations in climate and lithology, which suggests that transients may account for some of the observed differences in W – E relationships among field sites, even among sites that share the same climate and lithology. [ABSTRACT FROM AUTHOR]

Future unmanned air vehicles (UAVs) are expected to operate under the supervision of higher level control architectures that give instructions to engage and direct the UAV to perform a certain task. These instructions allow the UAV to make decisions along any point of its trajectory and then modify its flight path by using a sequence of reconfigurable controllers at the decision points. Assume that the UAV is flying with a transient and with a steady state contributing to a flight control mode (FCM) such as an altitude hold, an ascent and a descent mode when only longitudinal aircraft dynamics is considered. At the time of a decision, if the UAV bifurcates from its original (or parent) FCM in an effort to acquire a new (or a child) FCM and comply with a higher level instruction, then the UAV is said to be trustable. Mathematically, at the time of bifurcation where controller reconfiguration takes place, trustable UAV with the child trajectory must originate from a region where the stability regions of the parent and child trajectories intersect. In this paper, a procedure to reconfigure such FCMs and their controllers that develop the trustable UAV are presented. A three degree of freedom UAV is considered to illustrate the trustable UAV. [ABSTRACT FROM AUTHOR]

Insight into two different uniform atomic-scale microstructures of Cu- and Ti-oxides sputtered on polyethylene (PET) presenting different redox properties and a distinct bacterial inactivation dynamics. Co-sputtered (CuOx-TiO 2 -PET) consists mainly of CuO. It leads to bacterial inactivation kinetics within 20 min under very low intensity actinic light (0.5 mW/cm 2 ). The sequential sputtered (CuOx/TiO 2 -PET) consist mainly of Cu 2 O and led to bacterial inactivation within 90 min. Evidence for redox catalysis is present leading to bacterial inactivation by X-ray photoelectron spectroscopy (XPS). The Cu and Ti uniform distribution on the catalyst surface was mapped along the coating thickness by wavelength dispersive spectrometry (WDS). The inactivation time of E. coli determined by fluorescence stereomicroscopy was in agreement with the time found by agar plating. The short-lived transient intermediates on the co-sputtered catalyst were followed by laser spectroscopy in the femto/picosecond region (fs-ps). By atomic force microscopy (AFM) the roughness of the co-sputtered (CuO) and sequentially sputtered samples (Cu 2 O) were found respectively as 1.63 nm and 22.92 nm. The magnitude of the roughness was correlated with the bacterial inactivation times for both types of catalysts. The differentiated mechanisms for the vectorial charge transfer on co-sputtered and sequential sputtered CuOx/TiO 2 catalysts and it is suggested as one of the factors leading to a distinct bacterial inactivation kinetics. [ABSTRACT FROM AUTHOR]

A new method of analyzing reactor transients using the modified exponential time differencing method with Improved Quasi Static (IQS) model is developed and presented here. According to this method, the neutron flux is factored into amplitude function and shape function. The amplitude function is solved using the modified exponential time differencing method and the shape function is solved using implicit scheme. Using this method, a large time step can be chosen for solving the amplitude function and the shape function can also be solved by proportionately increasing the time step. This method is applied to estimate the transients in the well known CANDU 3D-PHWR kinetics benchmark, 3D-TWIGL Heterogeneous and 3D Homogeneous Reactors. These reactors contain different kinds of heterogeneities and the reactivity perturbations are also different. The transients in CANDU 3D-PHWR, simulated by LOCA, are estimated by this method for various time steps and the results are compared with other standard methods. From the comparison of results, it is established that this method is capable of estimating the transients using large time steps with good accuracy. A novel scheme to choose the time step for solving the amplitude function under constant and varying reactivity perturbations is also presented and applied here in the estimation of CANDU 3D-PHWR and 3D Homogeneous Reactor transients. It is also shown that by using large time steps, the transient computation time is reduced without affecting the accuracy and the error remains bounded. [ABSTRACT FROM AUTHOR]

This paper contributes to the simulation of transients and stability properties of singular states in engineering and environmental gas–solid systems. Qualitative properties of paths around equilibrium, quasi-equilibrium and disequilibrium states in closed and open systems are investigated by Lyapunov functions or functionals, V , determined by an original method. The method requires first to assume a constant-sign time derivative of V with respect to perturbed dynamical equations, V ˙ , and next to determine V itself from a matrix formula. Such functions V , which may be of an indefinite sign, describe qualitative properties of system paths, and may be derived from the derivatives V ˙ attributed to the constant-sign rates of entropy production or related exergy sink. Examples confirming the effectiveness of the approach for testing stability and qualitative properties of paths in non-reacting and reacting gas–solid systems are presented. A nontrivial example of the research benefit is presented in the paper in the form of the original classification of drying–moistening paths, based on the nontrivial saddle form of V in countercurrent systems and the focus form of V in co-current systems. [ABSTRACT FROM AUTHOR]

A stable and passive six-terminal model is developed for a 45-MVA generator step-up transformer based on frequency sweep measurements in the range 5 Hz-10 MHz and curve fitting with rational functions. The modeling employs separate treatment of the zero sequence system in combination with a new variant of the fast residue perturbation method for passivity enforcement. For use in system level simulations, the model can be employed in PSCAD, EMTP-RV and ATP. With ATP, the representation with an equivalent electrical circuit requires some care to prevent the occurrence of near zero circuit elements. Comparison with measured time domain responses at reduced voltage shows that the model can accurately reproduce transient voltage transfer between the windings while taking into account the loading effect of the connected system. The model also reproduces the transient recovery voltage (TRV) when interrupting short-circuit currents. As an application example, the model is demonstrated for simulation of resonant voltage transfer from the high-voltage side to the low-voltage side. In this setting, it is shown that the transformer input impedance can at high frequencies greatly influence the shape of the impinging overvoltages, thereby giving a self-protective effect against incoming overvoltages. [ABSTRACT FROM AUTHOR]

Real-time (RT) simulator is a powerful tool for analyzing operational and control algorithms in electric power systems engineering. For understanding the dynamic and transient behavior of a power systems, significant RT computation capabilities are essential. A single unit of RT simulator has limited simulation capabilities. The most common way of augmenting simulation capability is using a bank of locally connected RT simulators. However, creating a large-sized bank of RT simulators involves significant financial investments and hence may not be feasible at all research facilities. Power and energy systems research facilities that use RT simulators are at diverse physical locations. In addition to RT simulators, research facilities around the world house an array of facilities with unique power, energy, and control systems for innovative research. To leverage these unique research facilities, geographically distributed RT simulation based on Wide Area Network (WAN) is required. Typical RT simulators perform simulations with time-steps in the order of milliseconds to microseconds, whereas data latency for communication on WAN may be as high as a few hundred milliseconds. Such communication latency between RT simulators may lead to inaccuracies and instabilities in geographically distributed RT simulations. In this paper, the effect of communication latency on geographically distributed RT simulation is discussed and analyzed. In order to reduce the effect of the communication latency, a Real-Time Predictor (RTP), based on linear curve fitting is developed and integrated into the distributed RT simulation environment. Two geographically distributed digital RT simulators are used to perform dynamic simulations of an electric power system with a fixed communication latency and the predictor. Empirical results demonstrate the effects of communication latency on the simulation and the performance of the RTP to improve the accuracy of simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a method for identifying the faulty section in unearthed distribution networks connected with Doubly-Fed Induction Generator (DFIG)-based distributed generation. The proposed method depends on a dedicated transient-based selectivity function that is incorporated in an autonomous fault management procedure. Faulty section discrimination is performed by extracting the relative polarities of the front slopes at the terminals of each section generated by the fault current. The integration procedure of the protection selectivity function with the autonomous control is designed for the unearthed MV networks. Both earth and phase faults are considered in order to realize a broad, versatile and practical classification for such networks. Simulation cases are prepared using the ATP-EMTP package for testing purposes. The results corroborate the efficacy of the proposed method for classifying the faulty segment in distribution networks even for high impedance arcing faults as well as with considerable amounts of distributed wind turbines. [ABSTRACT FROM AUTHOR]

• A proposed design of a hierarchical protection scheme is presented. • Protective devices are optimally coordinated based on fault current transients. • Hybrid superconducting fault current limiters are optimally allocated to keep coordination under synchronous and inverter-based wind DGs. • Ride-through capability of wind DGs is integrated into the fault current limiter sizing problem. • Changes of network topology and variation of detected fault current are considered. A combined protection system has multiple types of devices such as directional overcurrent relays, reclosers, and fuses to protect distinct areas in a DG-incorporated network. An approach for setting all protective devices to realize complete coordination of adjacent ones taking transient responses into account is presented. The participation of synchronous generator-based and/or inverter-based wind DGs can degrade protection coordination. So, a scheme for sustaining coordination by optimal hybrid superconducting fault current limiters is proposed. The scheme can cope with variation of network topology; and handles the change of fault current level perceived by the protection device under a given topology. Moreover, instead of the conventional steady-state models, more realistic dynamic models of relays, reclosers, DGs, and fault current limiter are used. As a serious operation problem, undesired tripping of wind DGs under fault condition can occur due to the sag of terminal voltage below certain limits defined by national and international standards. Therefore, the proposed scheme prevents this undesired tripping of wind DGs by integrating its ride-through capability constraints into the fault current limiter allocation problem. The proposed approach is applied to the IEEE 9-bus and 30-bus systems. Results confirm the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

Temporal variations in the chemistry of infiltrating water into the subsurface are known to cause remobilization of colloids from the grain surfaces, thereby increasing the travel distance of the colloidal contaminants. Hence, it is essential to thoroughly understand the transport, deposition, and release mechanisms of colloids in the subsurface, through laboratory experiments and modeling. There are only a few experiments in which the chemistry of inflow water is changed rapidly during colloid transport. Also, although some models have been presented for simulating the effect of transient chemistry on the fate of colloids, there is no consensus in this regard, as the proposed models suffer from shortcomings. In this study, we systematically investigated the effect of temporal variations in ionic strength on the remobilization of deposited colloids in saturated porous media through laboratory column experiments and numerical modeling. Four sets of column experiments were performed, in which we injected carboxylate-modified latex colloids at a given ionic strength for a specified period. After breakthrough of colloids, the ionic strength of inflowing water was decreased in a stepwise manner to 0 mM (DI water). The initial ionic strength values of the four experiments were 100, 50, 25, and 10 mM. We observed partial release of deposited colloids after several steps of ionic strength decrease with significant release observed only when the ionic strength was reduced to below 10 mM. We also found that the fraction of released colloids decreased with increasing value of initial ionic strength of inflow water. We have developed a mathematical model incorporating a novel formulation for ionic strength-dependent deposition and release. The model is found to capture the colloid breakthrough curves reasonably well for all experiments with the same set of parameter values, except the one at the initial ionic strength of 25 mM. • A spike followed by a long tail in effluent for every step-decrease in ionic strength. • Significant release of colloids observed for ionic strength reduction below 10 mM. • A novel mathematical formulation for ionic strength-dependent deposition and release. [ABSTRACT FROM AUTHOR]

This paper presents a new protection method for High Voltage Direct Current (HVDC) system based on transient power. Behavior of the HVDC system during fault is studied. Variation of transient power and the relation between various parameters of the line are analyzed during each fault. Based on that the protection principle is developed. Transient power is obtained by measuring the voltage and current at the two terminals of the line. Identification of internal and external faults as well as location of DC lone fault can be done correctly and quickly from transient power. The test system is modeled using MATLAB - SIMULINK based on first CIGRE HVDC benchmark system. [ABSTRACT FROM AUTHOR]

In this paper, a method for the application of the black-box transformer models to the lumped-parameter transformer winding models is presented. The methodology is based on applying terminal transformer voltages as input parameters that could be provided by using the powerful black box vector fitting. Then, internal voltage distribution is determined by applying a lumped-parameter model approximation. In particular, the paper is focused on the direct computation of the internal voltage distribution, by avoiding a complicated procedure of solving the lumped-parameter winding model. The method is based on the transformation matrix utilization of the voltage distribution factors. This transformation matrix reflects the voltage distribution at specific internal points along the winding with respect to the input terminal voltages. At this stage, the inputs for the lumped-parameters model are provided by measured voltages at transformer terminals and the transformation matrix is determined through geometrical data of the transformer. The implementation of the proposed method with the black-box modeling approach in existing simulation software tools like EMTP is under development. The method is verified by comparing measured with computed waveforms. [ABSTRACT FROM AUTHOR]

Building energy and occupant health concerns have increased the desire for variable, dynamic indoors and hence the interest in comfort of non-uniform and/or transient thermal conditions. An extended thermal comfort field study in the Hermitage Amsterdam museum afforded a unique opportunity to analyse evolving subjective perception of occupants, upon their moving indoors, over the time they spent in the museum. Visitors’ responses were grouped depending on how long they had been inside when they filled up the survey. The mean thermal sensation vote of each time group bore a strong correlation with their average time duration. For visitors who had been inside for 20 min or less, the thermal sensation vote had a significant relation with the outdoor temperature but not the indoor temperature. As visitors spent longer indoors, percentage of them feeling warm decreased and percentage of neutral or cool feeling increased. In tandem, the percentage of visitors preferring to be warmer also increased with time. Gender based differences in thermal sensation and preference also had a gradual and logical evolution with time. In an evidence of alliesthesial response, all the visitors inside for 20 min or less, accepted their thermal environment. The overall evidence suggests that visitor’s subjective perception of the thermal environment undergoes a distinct evolution during their first hour indoors. [ABSTRACT FROM AUTHOR]

Transient disturbances in process measurements compromise the accuracy of some methods for plant-wide oscillation analysis. This paper presents a method to remove such transients while maintaining the dynamic features of the original measurement. The method is based on a nearest neighbors imputation technique. It replaces the removed transient with an estimate which is based on the time series of the whole measurement. The method is demonstrated on experimental and industrial case studies. The results demonstrate the efficacy of the method and recommended parameters. Furthermore, inconsistency indices are proposed which facilitate the automation of the method. [ABSTRACT FROM AUTHOR]

This paper presents an extension to a point kinetics model of fissile solution undergoing a transient through the development and addition of correlations which describe neutronics and thermal parameters and physical models. These correlations allow relevant parameters to be modelled as a function of time as the composition of the solution changes over time due to the addition of material and the evaporation of water from the surface of the solution. This allows the simulation of two scenarios. In the first scenario a critical system eventually becomes subcritical through under-moderation as its water content evaporates. In the second scenario an under-moderated system becomes critical as water is added before becoming subcritical as it becomes over-moderated. The models and correlations used in this paper are relatively idealised and are limited to a particular geometry and fissile solution composition. However, the results produced appear physically plausible and demonstrate that simulation of these processes are important to the long term development of transients in fissile solutions and provide a qualitative indication of the types of behaviour that may result in such situations. [ABSTRACT FROM AUTHOR]

The challenges that microchannel flow boiling technology faces are the lack of understanding of underlying mechanisms of heat transfer during various flow boiling regimes and a dearth of analytical models that can predict heat transfer. This paper aims to understand flow boiling heat transfer mechanisms by analyzing results obtained by synchronously captured high-speed flow visualizations with local, transient temperature data. Using Inverse Heat Conduction Problem (IHCP) solution methodology, the transient wetted surface heat flux and temperature as well as heat transfer coefficient are calculated. These are then correlated with the visual data. Experiments are performed on a single microchannel embedded with fast response temperature sensors located (630 µ m) below the wetted surface. The height, width and length of the microchannel are 0.42 mm, 2.54 mm and 25.4 mm respectively. De-ionized, de-gassed water is used as the working fluid. Two heat fluxes are tested at each of the mass fluxes of 182 kg/(m 2 s) and 380 kg/(m 2 s). Because of vapor confinement, slug flow is observed for the tested conditions. The present study provides detailed insights into the effect of various events such as passage of vapor slug, 3-phase contact line, partial-dry-out and liquid slug on transient heat transfer coefficient. Transient heat transfer coefficient peaks when thin film evaporation mechanism is prevalent. The peak value is influenced by the distance of bubble incipience as well as downstream events obstructing the flow. Heat transfer coefficient during the passage of liquid slug and 3-phase contact line were relatively lower for the tested experimental conditions. [ABSTRACT FROM AUTHOR]

This paper presents multi-purpose droop controllers for electronically-interfaced distributed generators (EI-DGs). These controllers allow the micro-grids to operate in grid-connected mode, islanded mode and mode transition transients with a unique control configuration. The active and reactive-power sharing among EI-DGs are satisfied by the proposed droop controllers in islanded mode. On the other hand, in the grid-connected mode, the droop controllers adjust the output active and reactive-powers of EI-DGs at the pre-programmed constant levels. The provision of sufficient damping capability and maintenance of the transient stability in all operational modes of EI-DGs are warranted by the suggested stabilizer. This stabilizer, which is designed using the passivity-based control (PBC) approach, is incorporated in the droop controllers to dampen power-angle, frequency and voltage deviations during large transients using solely local information. The primary source dynamics of EI-DGs are also considered. It is analytically proven that the presence of the primary source dynamics leads to attenuation of the damping capability of EI-DGs in transients. To compensate the adverse effect of the primary source dynamics during transients a novel compensator is inserted in the frequency-droop loop. Finally, time-domain simulations are performed on a multi-resources MG to verify the analytical results compared to those obtained, based on a recently-developed strategy. [ABSTRACT FROM AUTHOR]