Nominal Operating Research Articles

A Stochastic Optimization Algorithm to Enhance Controllers of Photovoltaic Systems

Increasing energy needs, pollution of nature, and eventual depletion of resources have prompted humanity to obtain new technologies and produce energy using clean sources and renewables. In this paper, we design an advanced method to improve the performance of a sliding mode controller combined with control theory for a photovoltaic system. Specifically, we decouple the controlled output of the system from any perturbation source and assess the effectiveness of the results in terms of solution quality, closed-loop control stability, and dynamical convergence of the state variables. This study focuses on the climatic conditions that may affect the behavior of a solar energy plant to supply a motor with the highest possible efficiency and nominal operating conditions. The designed method enables us to obtain an optimal performance by means of advanced control techniques and a slime mould stochastic optimization algorithm. The efficiency and performance of this method are examined based on a benchmark model of a photovoltaic system via numerical analysis and simulation.

Impact and performance efficiency analysis of grid-tied solar photovoltaic system based on installation site environmental factors

The performance of solar photovoltaic systems tends to decline if the operating conditions change from the nominal operating cell temperature due to environmental factors. The major factors include temperature and humidity variations, which cause thermal losses and open-circuit voltage drops in photovoltaic panels. This study investigates the correlations between solar photovoltaic performance and environmental factors by quantifying the real-time variables including temperature, humidity, dewpoint temperature, and heat index. Furthermore, the study investigates the difference between real-time measured and theoretically calculated temperature values with the help of weather station data to investigate the impact of temperature difference on the overall percentage power loss of the systems. The panels were installed at three distinct sites (rooftop, parking shed, and ground-mounted) connected to the same grid-tied system. Results reveal that the photovoltaic panel temperature has an inverse relation with the dew temperature and the humidity of the surrounding environment. The heat index value was found slightly less at the peak solar hours during the 24 h cycle of the measurement. The difference and relationship between temperature and humidity are measured and losses are highlighted based on the instantaneous occurrence of variables. Based on a difference between measured and calculated temperature values, results reveal that PV systems faced 27.95%, 5.41%, and 0.82% power losses for ground, roof, and parking installed PV systems, respectively.

Transcritical Behavior of Methane in the Cooling Jacket of a Liquid-Oxygen/Liquid-Methane Rocket-Engine Demonstrator

The successful design of a liquid rocket engine is strictly linked to the development of efficient cooling systems, able to dissipate huge thermal loads coming from the combustion in the thrust chamber. Generally, cooling architectures are based on regenerative strategies, adopting fuels as coolants; and on cooling jackets, including several narrow axial channels allocated around the thrust chambers. Moreover, since cryogenic fuels are used, as in the case of oxygen/methane-based liquid rocket engines, the refrigerant is injected in liquid phase at supercritical pressure conditions and heated by the thermal load coming from the combustion chamber, which tends to experience transcritical conditions until behaving as a supercritical vapor before exiting the cooling jacket. The comprehension of fluid behavior inside the cooling jackets of liquid-oxygen/methane rocket engines as a function of different operative conditions represents not only a current topic but a critical issue for the development of future propulsion systems. Hence, the current manuscript discusses the results concerning the cooling jacket equipping the liquid-oxygen/liquid-methane demonstrator, designed and manufactured within the scope of HYPROB-NEW Italian Project. In particular, numerical results considering the nominal operating conditions and the influence of variables, such as the inlet temperature and pressure values of refrigerant as well as mass-flow rate, are shown to discuss the fluid transcritical behavior inside the cooling channels and give indications on the numerical methodologies, supporting the design of liquid-oxygen/liquid-methane rocket-engine cooling systems. Validation has been accomplished by means of experimental results obtained through a specific test article, provided with a cooling channel, characterized by dimensions representative of HYPROB DEMO-0A regenerative combustion chamber.

Experimental investigation of transverse quadrupolar beam oscillation in the Hefei Light Source-II storage ring

Research on the transverse beam dynamics issues and collective bunch behaviors in association with the higher-mode oscillation fields are important in analyzing beam properties and improving machine performance of particle accelerators. In this study, a simple effective excitation and detection scheme was developed to analyze the transverse quadrupole-mode beam oscillation in electron storage rings. Transverse quadrupole-mode beam oscillation was induced by the stripline transverse quadrupole kicker, and then, measured using the stripline beam position monitor in the Hefei Light Source-II storage ring. A spectrum analyzer was employed for the real-time detection of the excitation sidebands of the horizontal quadrupole-mode oscillation in both single-bunch and nominal multi-bunch operations. Additionally, the horizontal dipolar and quadrupolar kick factors are obtained as 6.992 × 1014 and −4.458 × 1014 V/mC with accuracy of 7.49% and 2.03%, respectively, for the single-bunch operation. The dipolar and quadrupolar kick factors in the nominal multi-bunch operation are −2.567 × 1013 and −2.344 × 1013 V/mC with accuracy of 3.53% and 4.91%, respectively. The experimental measurements thus validate the practicability and reliability of this scheme. Moreover, it is demonstrated that this excitation and detection method for the transverse quadrupole oscillation is valid for studying the properties of transverse higher-mode wakefields and related beam behaviors in storage ring light sources.

Trajectory Control for Vibrating Screen with Magnetorheological Dampers.

The article presents a method of vibrating screen trajectory control based on MR (magnetorheological) dampers applied in a screen suspension. A mathematical description of the dynamic screen model was derived, and parameters of this model were estimated based on experimental data from a semi-industrial vibrating screen. The investigated screen included a single mechanical exciter with unbalanced masses, generating a circular vibration trajectory and operating with over-resonant frequency close to 19 Hz. It was experimentally tested in several phases of operation: start-up, nominal operation at a target vibration frequency and shutdown. The implemented screen model was further extended and included several MR dampers oriented horizontally and vertically in the form of Bouc–Wen models. The Bouc–Wen model was identified based on experiments carried out for an MR damper subjected to harmonic excitations generated by the MTS (material testing system). Dominant frequencies of excitation varied by up to 20 Hz during experiments. The main novelty of the reported solution is that according to the proposed control algorithm, the desired forces generated by MR dampers emulate an additional virtual mechanical exciter of the vibrating screen. In turn, it interacts with the available exciter, resulting in conversion of the trajectory from circular to linear, which was validated in the presented study. For the purpose of simulation accuracy, the desired control force was additionally limited within the simulator by MR damper dissipative domain, which maps the constraints of a semi-active damper. The presented approach allows one to obtain a close to linear trajectory with only one exciter and with semi-active control of suspension stiffness. The results were successfully repeated with different configurations of desired trajectory, indicating that the effectiveness of the desired linear trajectory generation depends on its orientation. The reported findings may lead to the design of new vibrating screen constructions, taking advantage of the semi-active control of a suspension in the attenuation of disturbance resulting from varying processed material parameters.

Incipient Residual-Based Anomaly Detection in Power Electronic Devices

Power electronics (PE) and high-frequency switching circuits are key to superior performance of electric vehicles. It is vital to monitor the condition of the PE components in real-time for safety and reliability. In this article, we propose two anomaly detection methods based on a combination of data preprocessing to suppress noise and outliers, multivariate regression models to predict signals of interest under nominal operation, and sequential analysis of residuals. In particular, the methods utilize median filtering to extract <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state medians in each switching cycle in nonlinear autoregressive exogenous neural network models or filtered <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -state data in partial least squares-based models to represent the nominal circuit behavior. Optimal and approximate dynamic programming-based feature selection methods are developed to select the most informative signals or their transformations. Predictions from the learned models are used to generate the residuals for anomaly detection by Page’s cumulative sum test. The proposed models and anomaly detection methods are validated on three accelerated aging experimental datasets, comprised of 60 power <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> devices with low-frequency and high-frequency switching under disparate operating conditions. Due to the simplicity and efficiency of the data-driven anomaly detection schemes, the proposed methods can potentially be embedded in real-time digital platforms.

Proton-exchange membrane fuel cell ionomer hydration model using finite volume method

In this paper a dynamic membrane electrode assembly water transport model, based on the Finite Volume Method, is presented. The purpose of this paper is to provide an accessible and reproductible model capable of real time simulation. To this aim, a detailed explanation is provided regarding the equations and methods used to compute the physical-based fuel cell model. Additionally, the model is purposely developed using basic code (on Matlab™), to not be limited to a single programming language. Two phase water transport through multi-gaseous porous media (electrodes), interfacial transport, as well as diffusion, convection, and electro-osmosis within the polymer are considered. The main novelty relies in the restructuring of all equations into a single implicit system, which can iteratively be resolved through LU decomposition. This computationally efficient method allows the model to be capable of real-time simulation, by displaying the membrane water content profile evolution on a 3D figure. For nominal PEMFC operating conditions, a dry membrane reaches 35% of its final water concentration value after 2 s, and fully converges after 20 s. The final water content profile displays an 18% gradient (9 and 11 molecules per sulfonic acid sites on the anode and cathode sides, respectively). To calibrate and validate this model, mass transfer (flowmeter) and electrical (ohmmeter) methods have been applied.

Developing an Automated Tool for Quantitative Analysis of the Deconvoluted Electrochemical Impedance Response of a Solid Oxide Fuel Cell

Despite being commercially available, solid oxide fuel cell (SOFC) technology requires further study to understand its physicochemical processes for diagnostics, prognostics, and quality assurance purposes. Electrochemical impedance spectroscopy (EIS), a widely used characterization technique for SOFCs, is often accompanied by the distribution of relaxation times (DRT) as a method for deconvoluting the contribution of each physicochemical process from the aggregated impedance response spectra. While EIS yields valuable information for the operation of SOFCs, the quantitative analysis of the DRT and its shifts remains cumbersome. To address this issue, and to create a replicable benchmark for the assessment of DRT results, a custom tool was developed in MATLAB to numerically analyze the DRT spectra, identify the DRT peaks, and assess their deviation in terms of peak frequency and DRT amplitude from nominal operating conditions. The preliminary validation of the tool was carried out by applying the tool to an extensive experimental campaign on 23 SOFC button-sized samples from three production batches in which EIS measurements were performed in parametric operating conditions. It was concluded that the results of the automated analysis via the developed tool were in accordance with the qualitative analysis of previous studies. It is capable of providing adequate additional quantitative results in terms of DRT shifts for further analysis and provides the basis for better interoperability of DRT analyses between laboratories.

Demonstration of 13,011-h of operation of a proto-flight compact heaterless lanthanum hexaboride hollow cathode

As part of the flight qualification of the Hall thruster component of the Ascendant Sub-kW Transcelestial Electric Propulsion System (ASTRAEUS), the thruster's proto-flight compact heaterless lanthanum hexaboride hollow cathode was subjected to a long-duration wear test. The cathode was mounted in an ASTRAEUS Hall thruster simulator for the test, which provided a flight-like mechanical, thermal, and magnetic environment for the cathode. The ASTRAEUS cathode was successfully operated for 13,011 h at a discharge current of 4 A using xenon propellant, with a total of 1653 ignitions performed throughout the test. The cathode's discharge voltage and keeper floating potential were 23.3 V ± 1 V and 3.9 V ± 1 V, respectively, during nominal operation of the device, indicating stable operation that did not change or degrade over the entire duration of the test. Cathode characterizations performed periodically throughout the test, where the cathode was operated at different conditions from the nominal 4 A discharge current, showed that the cathode performance was virtually invariant with operation time. The test was voluntarily terminated due to programmatic constraints. An intermittent keeper-to-cathode short was observed during the test, which was traced to an issue with the weld schedule of the cathode's internal heat shield that allowed slight contact to occasionally develop. The intermittent short was able to be cleared using the existing capabilities of the ASTRAEUS power processing unit, did not prevent ignition of the cathode, and showed no detrimental effects to cathode performance during steady state operation. This test marks the world's first 10,000+ h flight qualification test of a compact heaterless lanthanum hexaboride hollow cathode to be used with a low-power magnetically shielded Hall thruster.

Left Ventricular Assist Devices: A Primer for the Non-Mechanical Circulatory Support Provider.

Survival after implant of a left ventricular assist device (LVAD) continues to improve for patients with end-stage heart failure. Meanwhile, more patients are implanted with a destination therapy, rather than bridge-to-transplant, indication, meaning the population of patients living long-term on LVADs will continue to grow. Non-LVAD healthcare providers will encounter such patients in their scope of practice, and familiarity and comfort with the physiology and operation of these devices and common problems is essential. This review article describes the history, development, and operation of the modern LVAD. Common LVAD-related complications such as bleeding, infection, stroke, and right heart failure are reviewed and an approach to the patient with an LVAD is suggested. Nominal operating parameters and device response to various physiologic conditions, including hypo- and hypervolemia, hypertension, and device failure, are reviewed.

Assessment of the operation safety margin of the HL-LHC superconducting recombination Dipole D2 in case of helium filling failure

After the successful completion of the cryogenic performance tests of the He II heat exchanger prototype for the D2 recombination dipole of the future HL-LHC project at CERN, specific measurements were performed to determine the operation safety margin in case of abnormal operating conditions. This is particularly relevant in case of the failure of liquid helium supply in the He II cold source. For nominal operation, the liquid level is regulated at a constant value and it is not necessary to know its value very accurately. However, in case of a partial drying of the heat exchanger due to discontinuation of the helium liquid supply, it is essential to monitor the absolute value of the liquid level to anticipate any cooling malfunction. This paper describes the procedure for an accurate in-situ He II level measurement as well as for the heat loss and mass flow rate estimates in a He II phase separator. The operation safety margins of the He II heat exchanger prototype for the D2 magnet are then analyzed for the different operating conditions considered during the HL-LHC runs in case of non-nominal liquid level in the He II cold source.

Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode

Solid Oxide Cells (SOCs) are under intensive development due to their great potential to meet the 2030 targets for decarbonization. One of their advantages is that they can work in reversible mode. However, in respect to durability, there are still some technical challenges. Although the quick development of experimental and modeling approaches gives insight into degradation mechanisms, an obligatory step that cannot be avoided is the performance of long-term tests. Taking into account the target for a commercial lifetime is 80,000 h, experiments lasting years are not acceptable for market needs. This work aims to develop accelerated stress tests (ASTs) for SOCs by the artificial aging of the fuel electrode via redox cycling, which follows the degradation processes of calendar aging (Ni coarsening and migration). However, it can cause irreversible damage by the formation of cracks at the interface anode/electrolyte. The advantages of the developed procedure are that it offers a mild level of oxidation, which can be governed and regulated by the direct impedance monitoring of the Ni network resistance changes during oxidation/reduction on a bare anode sample. Once the redox cycling conditions are fixed and the anode/electrolyte sample is checked for cracks, the procedure is introduced for the AST in full-cell configuration. The developed methodology is evaluated by a comparative analysis of current voltage and impedance measurements of pristine, artificially aged, and calendar-aged button cells, combined with microstructural characterization of their anodes. It can be applied in both fuel cell and electrolyzer mode. The results obtained in this study from the electrochemical tests show that the artificially aged experimental cell corresponds to at least 3500 h of nominal operation. The number of hours is much bigger in respect to the microstructural aging of the anode. Taking into consideration that the duration of the performed 20 redox cycles is about 50 to 60 working hours, the acceleration factor in respect to experimental timing is estimated to be higher than 60, without any damaging of the sample. This result shows that the selected approach is very promising for a large decrease in testing times for SOCs.

On the nonlinear dynamics of biomass throated tubular gasification reactors

The problem of modeling the complex nonlinear dynamics of continuous biomass throated gasification tubular reactors is addressed. The problem is solved with first principles modeling and efficient discretization-based bifurcation analysis, yielding a systematic and tractable means to characterize: (i) steady-state (SS) multiplicity, (ii) robust stability, (iii) bifurcation behavior, and (iv) transient behavior. The approach is illustrated and tested with a commercial Imbert pilot scale reactor case example, studied before with experiments and simulation, and with multiplicity-bifurcation assessment as open problem. It was found that: (i) the nominal operation is tristable (with three stable steady-states -SSs- and two unstable ones), (ii) the reactor can bebi or tristable (with three or five SSs, respectively), depending on the within-range air feed flow-biomass moisture content value pair, (iii) there are not limit cycles (LCs), and (iv) the transient behavior agrees with the multiplicity structure found in this study and reported experimental data. The developments and results are put in perspective with previous related studies.

Graph Coloring via Locally-Active Memristor Oscillatory Networks

This manuscript provides a comprehensive tutorial on the operating principles of a bio-inspired Cellular Nonlinear Network, leveraging the local activity of NbOx memristors to apply a spike-based computing paradigm, which is expected to deliver such a separation between the steady-state phases of its capacitively-coupled oscillators, relative to a reference cell, as to unveal the classification of the nodes of the associated graphs into the least number of groups, according to the rules of a non-deterministic polynomial-hard combinatorial optimization problem, known as vertex coloring. Besides providing the theoretical foundations of the bio-inspired signal-processing paradigm, implemented by the proposed Memristor Oscillatory Network, and presenting pedagogical examples, illustrating how the phase dynamics of the memristive computing engine enables to solve the graph coloring problem, the paper further presents strategies to compensate for an imbalance in the number of couplings per oscillator, to counteract the intrinsic variability observed in the electrical behaviours of memristor samples from the same batch, and to prevent the impasse appearing when the array attains a steady-state corresponding to a local minimum of the optimization goal. The proposed Memristor Cellular Nonlinear Network, endowed with ad hoc circuitry for the implementation of these control strategies, is found to classify the vertices of a wide set of graphs in a number of color groups lower than the cardinality of the set of colors identified by traditional either software or hardware competitor systems. Given that, under nominal operating conditions, a biological system, such as the brain, is naturally capable to optimise energy consumption in problem-solving activities, the capability of locally-active memristor nanotechnologies to enable the circuit implementation of bio-inspired signal processing paradigms is expected to pave the way toward electronics with higher time and energy efficiency than state-of-the-art purely-CMOS hardware.

Multi-Objective RANS Aerodynamic Optimization of a Hypersonic Intake Ramp at Mach 5

The work describes a systematic optimization strategy for designing hypersonic inlet intakes. A Reynolds-averaged Navier-Stokes database is mined using genetic algorithms to develop ideal designs for a priori defined targets. An intake geometry from the literature is adopted as a baseline. Thus, a steady-state numerical assessment is validated and the computational grid is tuned under nominal operating conditions. Following validation tasks, the model is used for multi-objective optimization. The latter aims at minimizing the drag coefficient while boosting the static and total pressure ratios, respectively. The Pareto optimal solutions are analyzed, emphasizing the flow patterns that result in the improvements. Although the approach is applied to a specific setup, the method is entirely general, offering a valuable flowchart for designing super/hypersonic inlets. Notably, because high-quality computational fluid dynamics strategies drive the innovation process, the latter accounts for the complex dynamics of such devices from the early design stages, including shock-wave/boundary-layer interactions and recirculating flow portions in the geometrical shaping.

Modeling and optimization of photovoltaic serpentine type thermal solar collector with thermal energy storage system for hot water and electricity generation for single residential building.

Increasing surface temperature has a significant effect on the electrical performance of photovoltaic (PV) panels. A closed-loop forced circulation serpentine tube design of cooling water system was used in this study for effectively management of the surface temperature of PV panels. A real-time experiment was first carried out with a PV panel with a cooling system at heat transfer fluid (HTF) flow rates of 60kgh-1, 120kgh-1, and 180kgh-1. Based on the experimentation, a correlation for a nominal operating cell temperature (NOCT) and thermal efficiency for collector was developed for experimental validation of useful energy gained, cell temperature, and electric power generation. The developed correlations were validated with the use of electric power electrical power and useful energy gained in photovoltaic serpentine thermal solar collector (PV/STSC) and fitting into the experimental results with a deviation of 1% and 2.5% respectively. Further, with the help of developed correlations, a system was developed in the TRNSYS tool through which an optimization study was performed based on electric and hot water demand. The findings indicated an optimal system with an 8-m2 PV/STSC area, a HTF flow rate of 60kgh-1, and thermal energy storage (TES) system having a volume and height of 280l and 0.8m could meet 91% and 33% of the hot water demand for Ac loads and 78% or DC loads, respectively.

A cybersecurity platform for simulating transient responses of emulated programmable logic controllers in instrumentation and control systems for a pwr plant

ABSTRACT This research used the developed LOBO Nuclear CyberSecurity (LOBO NCS) platform at the University of New Mexico to investigate potential cyber vulnerabilities of digital Instrumentation and Control (I&C) systems for components in a representative Pressurized Water Reactor (PWR) plant during simulated operation transients. This platform links physics-based MATLAB Simulink models to emulated or physical Programmable Logic Controllers (PLCs) in I&C systems. An efficient data transfer interface and broker are developed to manage and coordinate communication between the emulated PLCs and the Simulink models. Presented transient results are for the steam generator and the feedwater PLCs following an increase in steam load demand. Related results are for the pressurizer and the pressure and water-level PLCs during simulated surge-in and surge-out transients. These results are for nominal transient operations and when the emulated PLCs are subject to simulated false data injection attacks (FDIAs). Obtained results of the pressurizer and the pressure PLC using the LOBO-NCS are in excellent agreement with those using the DOE SCEPTRE framework at Sandia National Laboratories.

Photovoltaic performance assess by correcting the I-V curves in outdoor tests

The photovoltaic performance is conventionally defined at Standard Test Conditions (STC), considering mainly an irradiance of 1000 W/m2 and device temperature of 25 °C. Nevertheless, outdoor conditions involve additional variables, including their transient behavior, affecting the performance. Therefore, measuring the performance at STC in outdoor tests is not always possible. In order to estimate the performance at STC or other power rating conditions such as the Nominal Operating Cell Temperature (NOCT), this work translated the outdoor performance at the target conditions by combining three different I-V curves and corresponding weather data for three photovoltaic technologies. Hence, a random process was proposed to generate the dataset to be translated, ensuring reliability in the estimation due to the significant number of considered weather conditions combinations, covering a wide range of the outdoor performance behavior as a function of irradiance and temperature. Besides, the dataset was filtered using an irradiance and extrapolation range, improving the estimation by calculating relative error of less than 8% at STC and NOCT concerning the datasheet values. Finally, the procedure was extended to estimate the temperature coefficients allowing a complete performance validation concerning the datasheet.

Optimal Window-Symbolic Time Series Analysis for Pattern Classification and Anomaly Detection

This article proposes the optimal window-symbolic time series analysis (OW-STSA) methodology to optimize parameters of feature extraction and pattern classification in industrial processes. The underlying theory is built upon minimization of an empirical risk function to discriminate between nominal and anomalous operations of the physical process under consideration. In particular, the proposed methodology produces: optimized windows of the time series used for pattern classification and anomaly detection, and optimized identification of feature extractors and classifier parameters. The algorithm is realized by segmenting a given time series into windows of equal size. Then, the stationary state probability vector is computed for each window in the sense of OW-STSA for anomaly prediction with locally optimal accuracy of detection performance. The proposed methodology has been experimentally validated in laboratory environment with different classifiers for two distinct industrial processes. The first experiment addresses detection of fatigue failure in polycrystalline alloy structures using time series of ultrasonic signals. The second experiment investigates detection of thermoacoustic instability in an emulated combustion system using time series of pressure-wave signals. In both experiments, the proposed OW-STSA methodology yielded excellent detection performance of anomalous behavior with multiple classification techniques.

TEST BENCH EQUIPMENT OF KELDYSH RESEARCH CENTRE FOR TESTING HIGH-PERFORMANCE POWER AND PROPULSION SYSTEMS

Expanding space exploration in near-Earth space and deep space calls for an increase in power supply of space vehicles to a level of hundreds of kilowatts and higher. Pre-requisite for successful implementation of works on development of power propulsion systems of such power level, including those with nuclear energy sources, is availability of a full-scale experimental test bench equipment. A unique experimental test bench has been built and is successfully operating at JSC «Keldysh Research Center», which allows performing both research and developmental tests of key components of high-performance power and propulsion systems under conditions close to nominal operating conditions. The article describes the main components of JSC «Keldysh Research Center» test bench equipment, presents some results of the work fulfilled on it, outlines prospects for its furtherance and use in development of space high-performance power and propulsion systems. Key words: testing, ground developmental testing, power conversion system, test bench equipment, electric propulsion, power and propulsion system.