Propagation Of Disturbances Research Articles

Invasive species modulate the structure and stability of a multilayer mutualistic network.

Species interactions are critical for maintaining community structure and dynamics, but the effects of invasive species on multitrophic networks remain poorly understood. We leveraged an ongoing invasion scenario in Patagonia, Argentina, to explore how non-native ungulates affect multitrophic networks. Ungulates disrupt a hummingbird-mistletoe-marsupial keystone interaction, which alters community composition. We sampled pollination and seed dispersal interactions in intact and invaded sites. We constructed pollination and seed dispersal networks for each site, which we connected via shared plants. We calculated pollination-seed dispersal connectivity, identified clusters of highly connected species, and quantified species' roles in connecting species clusters. To link structural variation to stability, we quantified network tolerance to single random species removal (disturbance propagation) and sequential species removal (robustness) using a stochastic coextinction model. Ungulates reduced the connectivity between pollination and seed dispersal and produced fewer clusters with a skewed size distribution. Moreover, species shifted their structural role, fragmenting the network by reducing the 'bridges' among species clusters. These structural changes altered the dynamics of cascading effects, increasing disturbance propagation and reducing network robustness. Our results highlight invasive species' role in altering community structure and subsequent stability in multitrophic communities.

Transonic buffet alleviation via virtual control surfaces

In this work, computational fluid dynamics simulations are carried out to assess the ability of control surfaces to alleviate or suppress transonic buffet. Among the available control surfaces, upper trailing edge flaps were considered since they modify the aerofoil pressure distribution and fix the shock at an upstream position. Spoilers were also studied as they produce a similar effect by interfering with the pressure disturbance propagation in the boundary layer and prevent buffet. For both devices, the sensitivities to geometric parameters are studied. The effectiveness of these buffet control methods is first assessed for 2D computations around different wing sections. As spoilers were considered more effective, results on a 3D configuration are provided to discuss the influence of finite-span devices on aerodynamic performance. In addition, a simple model accounting for changes in the flight Mach number together with the spoiler is presented to simulate a simple flight scenario and provide an effective strategy for buffet suppression. In the framework of numerical investigations, the adoption of virtual control surfaces allows for avoiding difficulties associated with the modelling of slotted and deployable devices.

The modeling of interaction between fuel element cladding and steam

This work simulates a close to emergency case in the reactor core - the material of fuel element cladding is subjected to steam flow. The presented model takes into account several processes occurring together - the admittance of oxygen and hydrogen, the propagation of heat, diffusion and mechanical disturbances, chemical reaction. The transfer mechanism of oxygen and hydrogen under the action of the stress gradient is taken into account. The model is suitable to describe the processes at very small times, corresponding to short thermal impulses and initial stages of surface interrelation with steam flow. The all short-time accompanying processes (10-9 −10-12 s) affect the changes in the material exposed to steam contact, but they are not easily accessible for direct observation. The problem was solved numerically. The temperature in our numerical experiment is not too high, but it is already sufficient for introduction of hydrogen and oxygen into the Zr-1%Nb surface, as well as for oxidation of zirconium. Examples of calculations are presented. It shows how different-scale processes interact with each other and to what distortions in the distributions of all interacting quantities this leads. Examples of calculations for different durations of vapor interaction with cladding surface are presented. It is shown that the concentration of oxygen and hydrogen in Zr alloy increases when the vapor action is too long-term.

Distributed heat release effects on entropy generation by premixed, laminar flames

This article studies the generation of entropy disturbances by laminar premixed flames. The total entropy generation equals the integrated ratio of the local heat release rate and the local temperature, namely, [Formula: see text]. Due to this path dependency, evaluating this integral requires an understanding of how the heat release is distributed in the temperature space. Several studies evaluate the local entropy generation as [Formula: see text], where [Formula: see text] refers to the burned gas temperature, implicitly assuming all the heat release occurs at [Formula: see text]. Such an approximation is motivated by the high activation energy nature of combustion chemistry. This work evaluates this assumption by comparing it to results from one-dimensional premixed flame calculations for hydrogen, methane, and propane-air flames over a range of pressures, equivalence ratios, and preheat temperatures, quantified via the ratio [Formula: see text]. We show that this assumption is quite reasonable for methane and propane-air flames (with errors ranging from 5% to 25%) but deviates significantly from the exact results for hydrogen flames (where errors can be as high as 50%). In general, the peak heat release moves to lower temperatures as preheat temperature is increased. Noting that the temperature sensitivity of heat release is directly related to the activation energy, we use Law's approach to extract global activation energies and show that the deviations of [Formula: see text] from unity can be approximately correlated with [Formula: see text]. Finally, we show that significant improvements in entropy generation calculations can be obtained by estimating [Formula: see text] using [Formula: see text], where [Formula: see text] is the temperature at which the reaction rate peaks. This estimation leads to predictions of ∼5% within the exact value for the hydrocarbon cases but can still be in significant error for hydrogen at certain conditions.

Proactive Defense Strategy Against Uncertainty Induced Voltage Disturbance Propagation in Deregulated Market Oriented Greener Grids

Renewable resource proliferation results in clusters with reactive power interdependence within emerging deregulated power grids. The clusters generally form as balancing areas (BA) and the reactive power interdependence is endured through voltage-controlled areas. In such grids, renewable generation uncertainty could manifest as propagating voltage disturbances towards the relatively weaker clusters. Operational and topological constraints of locally optimized conventional reactive support systems limit their capability in alleviating the propagation. This work demonstrates voltage disturbance propagation between BAs and proposes a framework to defend and mitigate them. The framework comprises a proactive resource procurement followed by a proactive first line of defense and a two-stage mitigation strategy. The strategy intelligently utilizes distributed resources through wide area supplementary control. The strategy avails the cyber-physical features of the grid to formulate the multi-criterion decision logic and associated defense as well as mitigation plan. This complex process is realized by an analytical hierarchical process (AHP). Extensive case studies conducted on modified IEEE 68 bus system illustrates the vitality of this decision logic and validates the effectiveness of defense plan and real-time mitigation strategy. The proposed approach also leads to better utilization of available reactive resources and facilitates improved participation in the deregulated market.

Ionospheric Response to the 6 February 2023 Turkey–Syria Earthquake

Two strong earthquakes occurred in Turkey on 6 February 2023, at 01:17:34 (nighttime, Mw = 7.8) and at 10:24:50 UT (daytime, Mw = 7.5). The seismo-ionospheric impact is an important part of the near-Earth environment state. This paper provides the first results on the ionospheric effects associated with the aforementioned earthquakes. We used data from global navigation satellite system (GNSS) receivers and ionosondes. We found that both earthquakes generated circle disturbance in the ionosphere, detected by GNSS data. The amplitude of the ionospheric response caused by daytime M7.5 earthquake exceeded by five times that caused by nighttime M7.8 earthquake: 0.5 TECU/min and 0.1 TECU/min, respectively, according to the ROTI data. The velocities of the earthquake-related ionospheric waves were ~2000 m/s, as measured by ROTI, for the M7.5 earthquake. TEC variations with 2–10 min periods showed velocities from 1500 to 900 m/s as disturbances evolved. Ionospheric disturbances occurred around epicenters and propagated to the south by means of 2–10 min TEC variations. ROTI data showed a more symmetric distribution with irregularities observed both to the South and to the North from 10:24:50 UT epicenter. The ionospheric effects were recorded over 750 km from the epicenters. Ionosonde located 420/490 km from the epicenters did not catch ionospheric effects. The results show significant asymmetry in the propagation of coseismic ionospheric disturbances. We observed coseismic ionospheric disturbances associated with Rayleigh mode and acoustic modes, but we did not observe disturbances associated with acoustic gravity mode.

Study of workshop network stability based on pinning control in disturbance environment

In the production process, the manufacturing behavior and all the essential factors are affected by several disturbance factors, showing a complex dynamic fluctuation law. It makes the stability control process a difficult problem in environmental constraints. In this paper, the workshop production process is considered, and an improved coupled map lattice workshop production network state model is proposed. On this basis, the controller with the function of resource load protection is designed, and the network state model of the workshop based on the pinning control is developed. Three kinds of stability control strategies, SAC (Self-adaption Control) , SC (Self-acting Control) and PC (Pinning Control) , are designed based on disturbance triggering behavior and node state transition rules. In addition, two control effect evaluation indexes, RTS (Recovery Time Steps) and NFT (Node Failure Times) are designed. Considering the actual production data of diesel fuel injection system parts production workshop as example, the model is simulated and verified. The results show that under different disturbance intensities, compared with the SAC strategy, the RTS-Average value of the PC strategy is reduced by 29.83% on average, and the NFT-Average values are reduced by 46.9% on average. This proves that the pinning control strategy has certain advantages in controlling time length and propagation scale of disturbance propagation.

A Multipath Model for Disturbance Propagation in Electrical Power Networks

This paper deals with the nature of propagation of disturbance spectrum through the power lines of an electric power system. A multi-path propagation model is proposed based on the reflection and refraction theory of wave propagation. The developed model captures the spatio-temporal aspect of disturbance propagation and is validated for a wide band of frequency. The proof of concept for the developed model is shown on a 2-bus system with a disturbance at a point between the buses. Results are validated in time domain with electromagnetic transient simulation programming.

One-dimensional nonlinear model of generalized thermo-electroelasticity

We investigate a one-dimensional restriction of a nonlinear model of thermo-electroelasticity in extended thermodynamics and in the quasi-electrostatic regime (see Ghaleb et al. in Int J Eng Sci 119:29–39, 2017. https://doi.org/10.1016/j.ijengsci.2017.06.010). An additional dependence of the thermal conductivity and the thermal relaxation time on temperature and heat flux is introduced. The aim of the present work is to assess the effect of some quadratic nonlinear couplings between the mechanical, thermal and electric fields. Such couplings are known to have a crucial effect on the stability of the solutions. It is confirmed that there are two speeds of wave propagation of disturbances, the coupled thermoelastic wave and the heat wave. Formulae are provided for both speeds, showing their explicit dependence on temperature, heat flux and electric field. The purely thermal case is briefly considered. The present results may be useful for the description of a broad range of interactions in large polarizable slabs of electro-thermoelastic materials and for the design of such materials.

Bacterial Foraging Algorithm for a Neural Network Learning Improvement in an Automatic Generation Controller

The frequency diversion in hybrid power systems is a major challenge due to the unpredictable power generation of renewable energies. An automatic generation controller (AGC) system is utilised in a hybrid power system to correct the frequency when the power generation of renewable energies and consumers’ load demand are changing rapidly. While a neural network (NN) model based on a back-propagation (BP) training algorithm is commonly used to design AGCs, it requires a complicated training methodology and a longer processing time. In this paper, a bacterial foraging algorithm (BF) was employed to enhance the learning of the NN model for AGCs based on adequately identifying the initial weights of the model. Hence, the training error of the NN model was addressed quickly when it was compared with the traditional NN model, resulting in an accurate signal prediction. To assess the proposed AGC, a power system with a photovoltaic (PV) generation test model was designed using MATLAB/Simulink. The outcomes of this research demonstrate that the AGC of the BF-NN-based model was effective in correcting the frequency of the hybrid power system and minimising its overshoot under various conditions. The BP-NN was compared to a PID, showing that the former achieved the lowest standard transit time of 5.20 s under the mismatching power conditions of load disturbance and PV power generation fluctuation.

Exponential horn revisited: wave equation, normal modes and experimental measurements

In this work, a theoretical analysis is first presented to find the wave equation corresponding to the propagation of disturbances in the air contained inside a tube of variable cross section. In particular, the case of a tube with a circular cross section whose area varies exponentially as a function of the axial coordinate is studied. The hypotheses of the model used are discussed and the solutions of the wave equation obtained are presented. Secondly, and with the aim of validating the model used, measurements are made on a tube such as the one described, built using a 3D printer.

Design, testing and control of a smart haptic interface driven by 3D-printed soft pneumatic actuators for virtual reality-based hand rehabilitation

This work presents the main steps of design and testing of a novel haptic interface and adaptive admittance control scheme for optimal regulation of the human–machine interaction in hand rehabilitation mediated by a smart system in virtual–reality environment. The prototype development is the result of an integrated HW/SW design and, moreover, the advantages from additive manufacturing techniques and mechanical properties of soft materials are exploited for the realization steps. Indeed, to make the interface smart, a network of piezo-resistive force sensors is embedded into the user’s command interface and the acquired signals are used for the adaptive regulation of human–machine interaction. Another distinctive feature of the haptic interface, which enables to identify this latter as a smart system, is the interaction control based on the estimation of the user’s intention within a novel scheme of adaptive admittance control. The enhanced training process in rehabilitation assisted by the haptic interface and virtual environment has been experimentally validated during a series of goal-directed tasks. The improvement of the motor performance of the user under the assistance of the adaptive admittance control has been experimentally evaluated. Further results show that the rehabilitation system supports the quantitative assessment of the robustness of the motor learning performance of the hand under the generation of haptic disturbances.

Interaction of shock train with cavity shear layer in a scramjet isolator

The interaction between the self-excited shock train flow and the cavity shear layer in a scramjet isolator is investigated numerically using detached-eddy simulations. The effect of changing the position of the shock train by controlling the back pressure ratio and the effect of changing the cavity front wall angle are analyzed using unsteady statistics and modal analysis. The propagation mechanism of the pressure disturbance was investigated by spatiotemporal cross-correlation coefficient analysis. In the present numerical study, a constant isolator section with a cavity front wall (θ = 90° and 60°) was considered, followed by a diffuser section simulated at Mach number 2.2 with three different back pressure ratios (pb/p∞ = 0.7, 5.0, and 6.0). The change in back pressure provides three different conditions (i.e., no shock train, shock train ends before the leading edge of the cavity, and shock train present above the cavity). To understand the unsteady dynamics of the interaction of the shear layer with the shock train, the spatiotemporal trajectory of the wall pressure and the centerline pressure distribution, the spatiotemporal cross-correlation coefficient, and the modal analysis by dynamic mode decomposition are obtained. The results show that the low-frequency shock train oscillation dominates the self-sustained cavity oscillation. The spatiotemporal cross-correlation between the wall surface and the center of the cavity bottom wall indicates the propagation of local disturbances originating from the separated boundary layer caused by the shock and the recirculation zone in the corners of the cavity. Dynamic mode decomposition analysis shows the shear layer at the leading edge of the cavity and the downstream propagation of large eddies from the cavity. It also shows the pairing of coherent structures between the shock train and the recirculation zone of the cavity.

Propagation of Solar disturbances in the heliosphere to a distance of 100 au

Explosive solar activities cause heliospheric disturbances. A simple scheme of simulating the propagation of shock waves in the heliosphere is devised to study such disturbances caused by solar flares. This scheme, the HAF scheme, is capable of simulating the propagation of many shock waves generated during extended periods up to a distance of 100 au (200 days) during periods when many solar disturbances can occur. The capability of the scheme is demonstrated in reproducing: (1) Multi-events with multi-satellite data within 2 au: (2) The heliospheric conditions at Ulysses/ Cassini within 10 au. (3) A successful reproduction of a Pioneer 11 event at 30 au. (4) The heliospheric condition up to 100 au in 2004, in addition to (5) reproducing recurrent geomagnetic srorms. Thus, the method presented here is simple enough in predicting a rough overall pattern of heliospheric disturbances on a day-to-day basis without MHD simulations. In this paper, we assembled systematically (in terms of distance from the sun) the above multiple results during the development of the HAF scheme in different periods by many researchers. It is hoped that much better schemes will be developed by extending and improving the HAF scheme.

Assessment of Voltage Fluctuations for Battery Storage Systems Providing Frequency Response Services

This paper investigates voltage fluctuations caused by the operation of battery energy storage (BES) units which provide frequency response (FR) and fast frequency response (FFR) services using a test network based on a typical part of the United Kingdom (UK) mainland system. This paper provides an overview of current FR/FFR services currently used in the UK, and a summary of their typical modes of operation. Using DIgSILENT Powerfactory, the paper introduces a simple frequency disturbance generator to mimic typical frequency disturbances that would occur in the UK network, and then subsequently uses a representative test distribution network to show how voltage disturbances associated with BES units can develop across the electrical network. The paper provides a contribution to knowledge by creating a systematic approach for assessing voltage disturbance and flicker concerns for BES units on island networks, using a simple control algorithm and novel frequency disturbance generator.

A sliding mode frequency control scheme for wind turbines participating in frequency regulation support in power systems

With high penetration of wind power, the apparent inertia of power systems is decreased, which seriously affects the safety and stability of the system frequency. Therefore, a novel sliding mode frequency control (SMFC) scheme is proposed for the wind turbines participating in frequency regulation support (FRS) in power systems, which can significantly improve the dynamic characteristics of the system frequency. At first, a power system frequency response model considering wind turbines participation in FRS is derived. In this model, the load disturbance, wind power disturbance and synchronous generator frequency regulation dynamics are combined as a lumped disturbance. Then, the design of the proposed SMFC scheme, which combines the super-twisting sliding-mode disturbance observer (STSMDO) with the super-twisting sliding-mode frequency controller (STSMFC), is introduced. The proposed STSMFC has ability to tune the system dynamics easily by choosing suitable sliding surface matrix via eigenvalue assignment method or optimal sliding manifold design. In such a frequency control scheme, the stability of the system frequency is guaranteed by the STSMFC, whereas the STSMDO is employed to estimate the lumped disturbance. Finally, numerical simulations verify the effectiveness and superiority of the proposed SMFC scheme.

Modulation and Annihilation of Aeroelastic Limit-Cycle Oscillations Using a Variable-Frequency Disturbance Generator

Nonlinear aeroelastic limit-cycle oscillations (LCOs) have become an area of interest due to both detrimental effects on flying vehicles and use in renewable energy harvesting. Initial studies on the interaction between aeroelastic systems and incoming flow disturbances have shown that disturbances can have significant effects on LCO amplitude, with some cases resulting in spontaneous annihilation of the LCO. This paper explores this interaction through wind-tunnel experiments using a variable-frequency disturbance generator to produce flow disturbances at frequencies near the inherent LCO frequency of an aeroelastic system with pitching and heaving degrees of freedom. The results show that incoming disturbances produced at frequencies approaching the LCO frequency from below produce a cyclic growth-decay in LCO amplitude that resembles interference between multiple sine waves with slightly varying frequencies. An aeroelastic inverse technique is applied to the results to study the transfer of energy between the pitching and heaving degrees of freedom as well as the aerodynamic power moving into and out of the system. Finally, the growth-decay cycles are shown to both excite LCOs in an initially stationary wing and annihilate preexisting LCOs in the same wing by appropriately timing the initiation and termination of disturbance generator motion.

The influence of vacancy generation on the impurity distribution in the target under the conditions of surface treatment by a particle beam

AbstractThe paper presents a nonlinear coupled isothermal model of the process of surface treatment by a particle beam. The model takes into account the interaction between the diffusion of impurity and propagation of mechanical disturbances, as well as the transfer of the introduced impurity with the vacancy mechanism and under the action of stresses. The nonlinear problem is solved numerically using an implicit symmetric difference scheme of the second order approximation in time and spatial coordinates. The finite time of mass flux relaxation and the dependence of diffusion coefficient on the composition and on the concentration of vacancies lead to peculiarities in the propagation of both the concentration wave and the wave of mechanical disturbances. Vacancy generation contributes to the acceleration of impurity propagation and increased strain/stresses.

PDE based Analysis for Propagation of Disturbance by Users Mobility in Mobile Network System

Analyzing the nature of mobile user mobility in a given network system is one of the basic metric for the traffic performance analysis in land-mobile cellular communications. This paper focuses on the partial differential equation (PDE) based analysis on the mobile user mobility; and proposes a new concept of user flow density wave in the mobile network system. The theoretical formulation for measuring the characteristics of network traffic performance deals with the propagation of disturbance produced by the velocity and density characteristics of the mobile users in a given network system; while most of the recent works uses the idea mobile users’ velocity characteristics and the network traffic layout. The proposed flow density wave concept is also used to characterize the mobile jamming.

Siberian Radioheliograph: sunspot oscillations in 3–6 GHz band

ABSTRACT We present the first observations of spatially resolved oscillation sources obtained with the Siberian Radioheliograph at 3–6 GHz. We have found significant flux oscillations with periods of about 3, 5, and 13 min emitted from AR12833. The 3-min periodicity dominates at higher frequencies. It was found that the apparent level of oscillations depends on the active region location on the disc, and scales down towards the limbs. The oscillations were studied in detail during 1 h interval on 2021 June 19. We found that sources of 3-min oscillations were located above the umbra and their emission is extraordinary polarized. The 5- and 13-min periods were manifested in emission at lower frequencies, down to 2.8 GHz. Sources with 5-min periodicity were located near the umbra/penumbra boundary and in the pore region. Positions of sources with 13-min oscillations were different at 3.1 and 4.7 GHz. We found consistency between spatial location of the oscillation sources in radio and ultraviolet at 171 and 304 Å. There is significant correlation of signals in two ranges. Time delays between microwave oscillations increase as the frequency decreases, which can be explained by upward propagation of periodic disturbances. The localization of oscillation sources is probably related to magnetic structures with different wave cut-off frequencies at different heights.