Steady-state Behavior Research Articles

Exploration of the effect of fractional elements in nonlinear transmission lines

Purpose The purpose of this paper is to explore how fractional derivatives affect the transient and steady-state behaviour of nonlinear transmission lines. This problem is of significance for high-frequency design of systems such as high-speed sampling systems and radar systems. Design/methodology/approach This paper shall consider the transient and steady-state responses of nonlinear transmission lines when fractional derivatives are considered. A lumped-parameter model is considered and the product-integration implicit trapezoidal rule shall be used for simulations. Findings The important observation is that small deviations of the order of the derivative from an integer order can have a significant effect on the transient and steady-state behaviour. This includes a change in the speed of the wave on the transmission line and on its damping. Originality/value The work is novel as it uses a lumped-parameter model with nonlinear capacitors and explores the effect on the dynamical behaviour when fractional derivatives are present. This is in contrast to the typical approach of using a partial differential equation derived under certain assumptions such as the nature of the nonlinear capacitor.

Development and Validation of a Capacitor–Current Circuit Model for Evaporation-Induced Electricity

Evaporation-induced electricity is a promising approach for sustainable energy generation which is particularly suited for off-grid and Internet-of-Things (IoT) applications. Despite significant progress, the mechanism of electricity generation remains debated due to complex factors. In this study, we introduce a simplified capacitor–current circuit model to describe the behavior of evaporation-induced electricity. The primary objective of this work is to provide a framework for understanding the transient and steady-state behavior of this phenomenon. We validated this model using experimental data from wood-based nanogenerators with citric acid modified microchannels. The fitting results revealed a steady-state current of approximately 9.832 μA and an initial peak current of 16.168 μA with a time constant of 621.395 s. These findings were explained by a hybrid model incorporating a capacitor and current source components, and subsequent discharge through internal resistance. This simplified model paves the way for better understanding and optimization of evaporation-induced electricity, highlighting potential improvements in device design for enhanced performance. While improving device performance is beyond the scope of this study, the insights gained from this model offer a foundation for future optimization and the enhanced performance of evaporation-induced electricity generation devices.

Asymmetry Between Queues with Correlated Service and Correlated Arrivals

It is known that a correlation in either the service or interarrival times causes a deterioration in the performance of a queuing system. This study aimed to determine which of the two correlations—in the service times or in the interarrival times—has a stronger influence on the expected queue length, assuming an identical autocorrelation function in both cases. To achieve this goal, a formula for the expected queue length in a system with correlated arrivals was derived first. This new formula, along with a known formula for the expected queue length in a system with correlated service, was used to compare the influence of the two correlations. Various scenarios were studied, such as cases where the common correlation was positive or negative, where the variance of the service or interarrival time was low or high, and where the system load was low or high. Furthermore, both the time-dependent and the steady-state behaviors of the systems were compared. The following two key observations were made. If the impact of other factors on the queue length is minor, then a positive correlation has a worse effect on the queue length when present in service times than in arrival times. On the contrary, a negative correlation has a worse effect on the queue length when present in arrival times than in service times.

Control of max-plus linear systems using feedback cycle shaping

For “Timed Event Graphs”, linear equations can be written in the max-plus algebra that describe the firing dynamics. In some cases, independent events/inputs can be used to influence the system dynamics in order to achieve a desired specification. In this setting, significant attention has been devoted to the mathematical development of controllers that achieve these desired specifications. In this article, a methodology is provided for solving a max-plus linear control problem as an extension of the result in Gonçalves et al. (2017). A condition is provided that induces into the system a periodic behavior in steady state and also shapes the response to comply with the specifications. Furthermore, the controller’s causality is addressed.

Simulation of Doubly Fed Induction generator (DFIG) for Steady state analysis when connected to a wind farm for power system stability

In this paper, a 2MW variable speed, pitch-regulated Doubly-fed Induction Generator (DFIG) with a speed range of 800-2000 rpm was studied for steady-state analysis. The DFIG was modelled in the Matlab/Simulink environment. The rotor-side converter utilized closed-loop stator flux-oriented vector control for managing the DFIG model. This method allows for rapid control and experimenting of grid-connected, variable speed DFIG wind turbines to examine their steady-state and energetic characteristics beneath ordinary and disturbed wind conditions when connected to a wind farm. The steady-state behavior of the wind turbine generator was derived at two different magnetizing levels: one with the reactive power of the stator equal to zero (Qs = 0), and the other with the direct current of the rotor equal to zero (Idr = 0). Simulation results show that the machine has higher efficiency when magnetized through the stator as compared with magnetization of the machine through the rotor. To come out with the DFIG transitory stability simulation results traditional controllers' for active and reactive power were compared with an adaptive adaptive tracking, self-tuned feedforward proportional integral regulating model for peak performance. Additionally, stability and instability were studied by solving the Swing equation using the Runge-Kutta method of order four. In a steady-state condition for the generator, the acceleration torque (Ta) reaches zero, which signifies that the mechanical torque (Tm) matches the electrical torque (Te). In the stability investigation, Tm is assumed to be constant. The findings provide valuable insights into the control strategies required for enhancing the reliability and efficiency of wind turbines in variable wind conditions.

An Experimental and Theoretical Study of Gear Vibro-impacts Caused by Torque Reversals

Abstract Rapid shift towards electrified powertrains has provided gear train dynamics researchers with new challenges, one of them being transient vibro-impact behavior caused by torque reversals during the drive and regenerative braking modes of operation. Contrary to ample studies on the steady-state dynamic behavior to aid with gear whine and rattle related noise and vibration problems, the transient behavior associated with such torque reversals has not been investigated extensively. Accordingly, this paper studies the dynamic response of a single-mesh gear system subjected to external torque reversals. A reduced-order dynamic model is proposed, accompanied by a computationally efficient piecewise-linear solution method. An experimental set-up of the same system is developed. Measurements within a wide spectrum of operating conditions and system parameters are compared to the model predictions for its validation. At the end, the model is employed for key parameter sensitivity studies on the influence of drivetrain stiffness, backlash and torque magnitudes on the resultant vibro-impact behavior depicted by an impact severity index.

Global stability and asymptotic profiles of a partially degenerate reaction diffusion Cholera model with asymptomatic individuals

Abstract Considering the prevalence of asymptomatic individuals during the spread of disease, this article develops a model of degenerate reaction diffusion Cholera with asymptomatic individuals. First, the well-posedness of model is studied, including the global existence of solutions and the existence of attractor. Second, the basic reproduction number ℛ 0 {{\mathcal{ {\mathcal R} }}}_{0} is defined to determine whether the disease is vanishing or persistent. In particular, we also analyze the asymptotic behavior of the endemic steady state when the diffusion rate of susceptible or asymptomatic individuals tends to 0 or infinity. Finally, by fitting the theoretical results with some numerical simulations, we find that the spatial distribution of disease and local epidemic risk are less affected by the mobility of susceptible populations, whereas the mobility of asymptomatic or symptomatic populations significantly affects the spatial and temporal distribution of infected populations. In addition, we found that the proportion of asymptomatic individuals to infected individuals is also a key factor in disease epidemics, and how to quickly diagnose asymptomatic individuals for disease control and prevention should be of a particular concern.

Stochastic analysis of frequency-domain adaptive filters

This study investigates the convergence behaviors of a family of frequency-domain adaptive filters (FDAFs) under both exact- and under-modeling situations. The stochastic analysis is conducted by transforming the frequency-domain equations into their time-domain counterparts. We discuss the transient and steady-state convergence behaviors of four FDAF versions, i.e., the constrained FDAFs with and without step-normalization, the unconstrained FDAFs with and without step-normalization, and we also present the upper bounds of step size for mean stability and mean-square stability. Starting from the expression for the steady-state mean weight vector, this study investigates whether the FDAFs can converge to unknown system impulse responses and optimum Wiener solutions. Moreover, we provide the closed-form minimum mean-square error (MMSE) that each FDAF can achieve. The difference between the current work and our previous one is threefold. First, the presented time-domain analysis is much easier to handle and has a more explicit physical meaning than that in the frequency domain. Second, we here consider an arbitrary overlap factor between consecutive blocks, while our previous analysis only focuses on 50% overlap. Third, the presented MMSE expressions and excess mean-square error (EMSE) approximations have not been given before. Simulations reveal high consistency between the experimental and theoretical results.

Machine Learning Optimization of Non-Kasha Behavior and of Transient Dynamics in Model Retinal Isomerization.

Designing a model of retinal isomerization in rhodopsin, the first step in vision, that accounts for both experimental transient and stationary state observables is challenging. Here, multiobjective Bayesian optimization is employed to refine the parameters of a minimal two-state-two-mode (TM) model describing the photoisomerization of retinal in rhodopsin. The optimized retinal model predicts excitation wavelength-dependent fluorescence spectra that closely align with experimentally observed non-Kasha behavior in the nonequilibrium steady state. Further, adjustments to the potential energy surface within the TM model reduce the discrepancies across the time domain. Overall, agreement with experimental data is excellent.

El Botellón: Modeling the Movement of Crowds in a City

A simulation of crowd movement in a city is studied under various assumptions about interactions between people. We find, in general, that there are two modes of steady-state behavior. The crowd may be distributed across the city, or it may end up gathered in one place. A mathematical model describes the long-term behavior and shows that this change in behavior is sensitive to a critical parameter setting in our model. Some alternative interpretations of the results are formulated.

Stability and dynamic response of centrifugal pendulum vibration absorber based on nonlinear hybrid damping

Centrifugal pendulum vibration absorber (CPVA) have emerged as an extremely effective method to mitigate torsional vibrations in rotating machinery. Previous studies have predominantly focused on viscous damping between pendulums and rotor, largely ignoring other damping mechanisms. However, recent experimental endeavors have revealed a hybrid damping concept that combines rolling and viscous damping, providing a more realistic portrayal of CPVA dynamics in vehicular applications. This study builds on prior investigations by incorporating nonlinear hybrid damping of the pendulums and investigating the steady-state and transient behavior of the CPVA within gravitational and centrifugal force fields. We propose a methodology for deriving pendulum equations of motion based on perturbation and multiple scales. Subsequently, we investigated the CPVA’s critical stability and bifurcation as well as a variety of nonlinear phenomena, using numerical simulations to validate our results. Furthermore, our study revealed a novel phenomenon known as the ‘phase jump’ for the pendulum. It is worth noting that the CPVA’s dynamic performance can be improved and the local nonlinear response can be reduced by adjusting the share and magnitude of the rolling and viscous damping coefficients. This study provides insights for optimizing the CPVA’s performance and advancing its efficacy.

An empirical carbon degradation reaction model for the high-speed computation in an integrated fuel cell system simulator and its validation by the accelerated stress test data of the commercial fuel cells

An empirical model to estimate the carbon corrosion rate was developed for a year-long and system-scale durability simulation in an acceptable accuracy and computational time for wide range of the cathode electrode potential, temperature, and humidity. The relative error of the overall carbon corrosion extent during a test pattern at 80 C and 100% RH was 5.5 %. The coefficient of determination (R2) of the increase in the concentration overpotential after 30000 voltage cycles was 6.1 %. The computational time with a standard laptop was 705 times faster than the actual experimental time. Experimental: The MEA and GDL of 2nd-generation MIRAI were used for the carbon corrosion rate measurement. The steady-state and transient carbon corrosion rates at 0.2–0.95 V, 20–100 % relative humidity, and 40–80 °C were measured by the experimental apparatus shown in Fig. 1. The cell voltage was controlled following the profile shown in Fig. 2 by potentiostat. H2 and N2 were supplied to the anode and cathode of the single cell with the active area of 25 cm2. The humidity of the supplied gas was controlled by the bubble humidifier. The carbon corrosion reaction rate was calculated from the measured IR absorbance measured at the cathode outlet with an FT-IR. A condenser was installed between the cathode outlet and the FT-IR and the temperature inside was controlled at 5 °C to prevent the water droplets from affecting the IR absorbance. Modeling methods: The following assumptions of the entire carbon corrosion reactions in the literatures [1][2] were adopted: The surface fractions of C=O/C–OH/C–H and PtO/PtOH/Pt are determined by the physical models consisting of electrochemical reaction rate and the mass balance; the carbon corrosion rate is calculated by the reaction rate equation from the surface fractions of C–OH and PtOH. In this study, only changes in the C–OH and PtOH surface fractions were considered by the simple empirical models described by Eqs. [1]–[7], Table 1, and Fig. 3. Solving the model equations does not require an iterative calculation for the convergence of the solution and high-speed computation in the integrated system simulator the current authors had presented [3] was expected. The parameters in Table 1 and Fig. 3 were calibrated by the experimental results of the steady state and transient behaviors of CO2 concentration. The model was implemented on MATLAB/Simulink environment as the open loop simulator. Results and discussion: The experimental results of the CO2 measurement are shown by the red lines in Figs 4(a)–4(c). The dynamic behaviors of the carbon corrosion rates were as follows: the measured CO2 mole fraction increased rapidly following the stepwise change in the voltage; its peaks were higher when the voltage was stepped up than when stepped down; its peaks were higher when the step width of the voltage was greater; its peaks were higher in cases of the higher humidity and higher temperature. The simulated CO2 mole fractions in a wide range of humidity and temperature are shown by the blue lines in Fig. 4(a)–4(c). The developed simulator reproduced the overall carbon corrosion extent within the relative error of 5.5 % as shown in of Fig. 4(a). The voltage cycle test using the MEA of 2nd-generation MIRAI at 0.95–0.6V, 80 °C, and 100 % relative humidity [4] was reproduced by the developed simulator. Fig. 5 shows the calculated carbon fractional retention after 500, 1000, 3000, 10000, and 30000 voltage cycles. As shown in Fig. 6, the increase in the concentration overpotentials caused by the carbon corrosion was expressed by the empirical function of the correction factors of the mass transfer resistance and agglomerate coefficient in the current authors’ FC stack model [5]. These correction factors were determined to reproduce the experimental polarization curves collected with the MEA of 2nd-generation MIRAI [5]. Fig. 6 shows the experimental and simulated increase in the concentration overpotential. The coefficient of determination (R2) of the increase in the concentration overpotential after 30000 cycles was 6.1 %. The computational speed was 705 times faster than the actual experimental time with a standard laptop (Toshiba dynabook G83/HS; Intel Core i7-1165G7 @ 2.80 GHz / 2.80 GHz CPU; 16 GB RAM).

Lithium Redox Behavior at Liquid Lithium-Lead Alloy Electrodes in Molten LiCl–KCl

IntroductionFusion energy is vital in a carbon-free society and stable energy supply. The advanced liquid blanket concepts allow high-efficiency (~50%) power generation by applying gas-turbine cycles. In particular, liquid Li17Pb83 (lithium-lead eutectic alloy) coolant enables higher-temperature (850~1000 ℃) heat applications, such as effective hydrogen and synthetic fuel production, and process heat for industrial uses. For realizing the Li17Pb83 blanket systems, molten salt electrochemistry technologies can be applied to lithium isotope enrichment, high-purity Li17Pb83 production, and online lithium replenishment for the lithium burn-up through neutron nuclear reaction: 6Li(n,t)4He, under the operation of a fusion reactor. These application developments need to obtain the chemical activity of lithium (a Li) and to clarify lithium redox behavior at liquid LixPb100-x electrodes; 0 < x ≤ 17 at.%. Previous studies investigated the a Li in liquid LixPb100-x [1,2], and lithium redox potential (E Li) was estimated according to the following Nernst equation: E Li =E Li 0+(RT/F)ln(a Li+ /a Li in alloy). Thus, this study aims to clarify the lithium oxidation/reduction behavior at the LixPb100-x electrodes.ExperimentalThe experimental apparatus was installed in a glove box under a purified argon gas atmosphere. The working electrodes were a coil-like Ni wire (φ: 0.5 mm, A: 1.0 cm2), liquid Pb (A: 0.28 cm2), and liquid LixPb100-x (x: 4.6 or 14.8, A: 0.28 cm2). The liquid Pb and LixPb100-x were stored in J-shaped glass tubes (made of borosilicate glass, φ: 8 mm, t: 1 mm). The molar ratio of the LixPb100-x was quantified by ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). The quasi-reference electrode was a coil-like Mo wire (φ: 0.5 mm), and the redox potential was calibrated with Li+/Li standard potential. The counter electrode was a glassy carbon plate (t: 1 mm). The electrolytic bath was LiCl-KCl eutectic, and the bath temperature was controlled within ±2 ℃. Cyclic voltammetry and amperometry were performed at 500 ℃ to investigate the unsteady-state and steady-state polarization behaviors, respectively. In polarization measurements, the open circuit potential and chrono-amperometry were applied to adjust the lithium concentration of the LixPb100-x electrodes.Results and DiscussionFigure 1 shows cyclic voltammograms obtained at Ni, Pb, Li4.6Pb95.4, and Li14.8Pb85.2 electrodes at 500 ℃. Li+-ion was reduced and formed into lithium metal at 0.0 V on the surface of the Ni electrode. Nickel is significantly difficult to alloy with lithium[3], thus deposited lithium can be regarded as a pure substance: a Li = 1.0. Li+-ion was reduced and immediately dissolved in the liquid Pb, Li4.6Pb95.4, and Li14.8Pb85.2 electrodes. The relationship of E Li was summarized as follows: Ni < Li14.8Pb85.2 < Li4.6Pb95.4 < Pb. According to the Nernst equation, these results suggest that the relationship of a Li is estimated as follows: 0.0 < Pb < Li4.6Pb95.4 < Li14.8Pb85.2 < Ni = 1.0. The increasing tendency of a Li is in good agreement with the previous studies[1,2].Figure 2 shows steady-state polarization curves obtained at Li4.6Pb95.4 and Li14.8Pb85.2 electrodes at 500 ℃. In the case that the absolute value of overpotential (η) was large enough, current density (i) was an exponential of η in both electrodes. The polarization curves were fitted well with the following Tafel equations: η » 0, i ≃ i a = i0exp(αa Fη/RT), η « 0, i ≃ i c = i0exp(αc Fη/RT). These results suggest that a charge transfer is the rate-limiting step of lithium redox behavior at the LixPb100-x electrodes. The lithium redox behaviors at different temperatures will be presented at the meeting.

Analytical Considerations for Hydraulic Resistance Models of Electrochemical Cells

The distributed resistance analogy (DRA) was originally developed to build three-dimensional (3-D) computational fluid dynamics (CFD) models of heat exchangers [1], and subsequentially substantially modified/extended for the physicochemical hydrodynamics occurring in electrochemical devices such as fuel cell and electrolyzer stacks [2]. DRA based macrohomogeneous models eliminate the requirement to construct very large computational meshes by replacing viscous/diffusion terms in the governing Navier-Stokes equations with simple rate terms for pressure drop, heat, and mass transfer. This results in the required computational effort being reduced by two (2) orders of magnitude. Typically, macrohomogeneous hydraulic resistance models are validated by comparison with experimental results, and/or with those obtained with detailed numerical simulations (DNS) for any given design.This paper examines the theoretical foundation of the methodology by simultaneously considering both macroscopic and microscopic force and mass balances within an idealized polymer electrolyte membrane fuel/electrolyzer cell in the form of a plane duct with an electric current being applied along one or more boundaries. Both constant and variable current density are considered.For constant current density, the analytical solutions of Berman [3] and Jorne [4], for plane ducts, are derived in integral form from the well-known differential forms, and then compared to CFD results based both on the DRA and DNS formulations, which the authors employ within the OpenFOAM code suite.For variable current density, it is presumed that the oxygen/current density, j(x), and associated wall velocity, follow a power law distribution as a function of λ [5, 6], where λ is the (oxygen or water) stoichiometric number. Using Berman’s approach, Kulikovsky [7] solved the problem under conditions of variable current density. Comparisons are made for the present numerical calculations based on both DRA and DNS CFD methods with those of Kulikovsky [7]. Both fuel cell and electrolyzer modes of operation are considered.The results of the microscopic and macroscopic balances are presented and discussed in detail, in terms of pressure drop and shear stresses. The presence of mass injection/suction leads to both boundary (shear) and inertial (added mass) effects in the momentum/pressure equation, which have not be considered before. However, it is shown that these effects are second-order, and can often be neglected locally, at least for the current densities encountered today in polymer electrolyte membrane fuel and electrolysis cells. It is thus shown, by comparison to analytical and semi-analytical results, that the DRA approximation is based on sound reasoning, and leads to reliable solutions for flow-field simulations in the channels of electrochemical cells and stacks.References Patankar, S.V. and D.B. Spalding, A Calculation Procedure for the Transient and Steady-state Behavior of Shell-and-tube Heat Exchangers, in Heat Exchangers: Design and Theory Sourcebook, N. Afgan and E.U. Schlünder, Editors. 1974, Scripta Book Company: Washington. D.C. p. 155-176. Beale, S.B. and S.V. Zhubrin, A distributed resistance analogy for solid oxide fuel cells. Numerical Heat Transfer, Part B, 2005. 47(6): p. 573-591. Berman, A.S., Laminar Flow in Channels with Porous Walls. Journal of Applied Physics, 1953. 24(9): p. 1232-1235. Jorne, J., Mass-Transfer in Laminar-Flow Channel with Porous Wall. Journal of the Electrochemical Society, 1982. 129(8): p. 1727-1733. Kulikovsky, A.A., The effect of stoichiometric ratio λ on the performance of a polymer electrolyte fuel cell. Electrochimica Acta, 2004. 49(4): p. 617-625. Kulikovsky, A.A., A. Kucernak, and A.A. Kornyshev, Feeding PEM fuel cells. Electrochimica Acta, 2005. 50(6): p. 1323-1333. Kulikovsky, A., Laminar Flow in a PEM Fuel Cell Cathode Channel. Journal of The Electrochemical Society, 2023. 170(2): p. 024510.

Transient and Steady-State Evaluation of Distributed Generation in Medium-Voltage Distribution Networks

As power generation systems with increasingly higher capacities are interconnected with distribution networks, a pressing need arises for a thorough analysis of their integration and the subsequent impacts on medium-voltage lines. This study conducts a comprehensive evaluation, encompassing both steady-state and transient behaviours, leading to a holistic assessment of a real-world biogas generation system integrated into a medium-voltage network. Although the methodology does not introduce revolutionary concepts, its detailed application on a real feeder under various operating conditions adds practical value to the existing body of knowledge. The methodology explores various aspects, including voltage profiles, load capacity, power losses, short-circuit currents, and protection coordination in steady-state conditions. Additionally, a transient analysis is performed to examine the system’s response under fault conditions. This systematic approach provides a deep understanding of the system’s behaviour across diverse operational scenarios, enriching the field with practical insights. The key contributions of this study include identifying the effects of distributed generation systems (DGSs) on short-circuit currents, protection coordination, and defining voltage levels that briefly exceed the CBEMA quality curve. The benefits of incorporating a generation system into a distribution network are discussed from various technical perspectives. In a peak demand scenario, with a 1.72 MW generation capacity, the phase current experiences a notable reduction of 35.78%. Concurrently, the minimum peak demand voltage increases from 12.62 to 12.83 kV compared to a nominal voltage of 12.7 kV. Furthermore, the contribution of the generation system to the short-circuit current remains minimal, staying below 4% even under the most adverse conditions. However, our findings reveal that voltage levels exceed the upper limit of the CBEMA quality curve briefly during a single-phase fault with generation, which could potentially damage electronic equipment connected to the grid. Nonetheless, the likelihood of encountering a single-phase grounding fault with zero resistance remains low.

Steady State Behavior of the Free Recall Dynamics of Working Memory

Steady State Behavior of the Free Recall Dynamics of Working Memory

Dynamic unbalance identification in steady-state rotating machinery: A hybrid methodology integrating physical and data-driven techniques

Rotating machinery plays a strategic role in key industrial sectors, making its analysis a subject of great interest for both academia and industry. Effective maintenance planning for this equipment is essential for asset management and for meeting current industrial requirements. To address this demand, this work presents a novel unbalance identification approach based on a digital representation of a rotating machine's dynamic behavior in relation to the development of specific faults. A hybrid methodology is proposed, integrating Finite Element Modeling, a Kalman Filter for parameter estimation, and Referenced Moving Window Principal Component Analysis. This Principal Component Analysis extension enhances vibration pattern recognition, enabling accurate fault quantification directly from slight changes in the system's steady-state behavior. The methodology uniquely eliminates the need for phase angle measurements, facilitating continuous monitoring of unbalance progression in steady-state conditions. Two case studies demonstrate the methodology's potential: one utilizing synthetic data from a Floating Production Storage and Offloading centrifugal compressor unit, and the other based on real data from a hydroelectric turbine-generator. These studies illustrate the integration of computational modeling, data-driven analysis, and monitored vibration data, achieving robust and accurate unbalance identification. This approach provides valuable insights into current capabilities and opens promising pathways for future applications, particularly in the digital twin domain for rotating machinery.

Experimental and numerical analysis of a waste-gated turbine for automotive turbocharged engine

Abstract This work presents the results of an experimental campaign focused on the steady state behaviour of a waste-gated turbocharger turbine for spark ignition engine. In a first step, the turbine behaviour under different openings of the waste-gate valve is analysed through an experimental campaign performed at the test rig for components of propulsion systems of the University of Genoa. Based on this experimental activity, a specific numerical model is developed to study the interaction between the rotor channel and the waste-gate valve. A 1D schematization of the experimental test rig is implemented within the commercial GT-Power code, including the turbine, the waste-gate valve, and the upstream and downstream circuits. In the turbine schematization, the “wheel-map”, estimated by means of the 1D software, is utilized. A preliminary tuning is carried out based on the turbine characteristic map measured with the waste-gate valve in the fully closed position. Then, the influence of various positions of the by-pass valve on the definition of turbine characteristic curves is investigated under steady flow condition. A refined model of the waste-gate system reveals to be necessary to correctly reproduce the swallowing capacity of the by-pass port. The waste-gate model is tuned against the experimental findings for a completely closed turbine wheel and various settings of the waste-gate valve. Finally, once the 1D models of the turbine and of the waste-gate system are independently tuned, their behaviour under parallel flow is analysed. The proposed numerical and experimental results demonstrate the mutual interaction of the two components. In addition, it is highlighted that the turbine and the waste-gate circuit cannot be considered as two systems working in parallel under the same pressure ratio, as usually assumed in 1D codes.

Hierarchical optimal operation for bipolar DC distribution networks with remote residential communities

To facilitate the seamless integration of renewable energy, bipolar DC distribution networks (Bi-DCDNs) have been widely adopted in various applications, including the Shenzhen Future Building, the Boeing 787 aircraft, and DC LED lighting systems in Singapore. Bi-DCDNs incorporate diverse flexible devices to improve both economic efficiency and security. However, a comprehensive coordination framework considering the regulatory heterogeneity among these flexible devices remains absent. Hence, this paper proposes a hierarchical coordination framework for flexible devices in Bi-DCDNs. More specifically, the upper-level model considers the operational differences of the DC transformer (DCT) in various modes to determine the optimal switching scheme for reducing losses; In the lower-level model, the control parameters of the DCT, energy storage systems (ESSs), and DC electrical springs (DCESs) are coordinated to enhance voltage quality. Furthermore, to accurately capture the steady-state behavior of flexible devices, the hierarchical framework incorporates the Newton-Raphson power flow method. This method formulates a steady-state model for multiple flexible devices and demonstrates the impact of different control modes of DCT on power flow. Subsequently, a genetic algorithm is used to solve the proposed model, ensuring that suboptimal decisions made at the upper level are rectified at the lower level, and vice versa. The numerical results indicate that the proposed framework achieves the optimal operation for both reduced losses and enhanced voltage quality in Bi-DCDNs. Furthermore, it exhibits advantageous applications for Bi-DCDNs with additional DCTs for remote residential communities.

Solving for the Thermal Vibration Behaviors of Functionally Graded Stepped Conical Curved Plates with Point Connection Conditions

This paper proposed a degree-of-freedom reduction model for the rapid and unified solution of the modal and steady-state response behavior of functionally graded stepped conical curved plates with point connections under thermal environments. Within the framework of the first-order shear deformation theory, the two-dimensional spectral Chebyshev method and the fixed interface modal synthesis method were combined to derive the degree-of-freedom reduction model for functionally graded conical curved plates under thermal environments. Each reduction model was assembled considering external load excitations. Virtual springs were used to equivalently handle the coupling interface forces and point connection interface forces, further establishing a thermal vibration response analysis model for functionally graded stepped conical curved plates with point connections. In numerical examples, this degree-of-freedom reduction model was compared with experimental results and overall finite element results, validating the accuracy of the model and the advantages of rapid solution. Additionally, this degree-of-freedom reduction model was applied to quickly analyze the effects of material parameters and point connection parameters on the thermal steady-state response of the structure, providing a theoretical basis for the environmental adaptability design, verification, and evaluation of such structures.