Improving multi-objective reservoir operation optimization with sensitivity-informed dimension reduction

There is another ORE record for this article: http://hdl.handle.net/10871/21284This study investigates the effectiveness of a sensitivity-informed method for multi-objective operation of reservoir systems, which uses global sensitivity analysis as a screening tool to reduce computational demands. Sobol's method is used to screen insensitive decision variables and guide the formulation of the optimization problems with a significantly reduced number of decision variables. This sensitivity-informed method dramatically reduces the computational demands required for attaining high-quality approximations of optimal trade-off relationships between conflicting design objectives. The search results obtained from the reduced complexity multi-objective reservoir operation problems are then used to pre-condition the full search of the original optimization problem. In two case studies, the Dahuofang reservoir and the inter-basin multi-reservoir system in Liaoning province, China, sensitivity analysis results show that reservoir performance is strongly controlled by a small proportion of decision variables. Sensitivity-informed dimension reduction and pre-conditioning are evaluated in their ability to improve the efficiency and effectiveness of multi-objective evolutionary optimization. Overall, this study illustrates the efficiency and effectiveness of the sensitivity-informed method and the use of global sensitivity analysis to inform dimension reduction of optimization problems when solving complex multi-objective reservoir operation problems.China Postdoctoral Science FoundationNatural Science Foundation of Chin

Optimal Gear-Shifting of a Wet-Type Two-Speed Dual-Brake Transmission for an Electric Vehicle

In improving the efficiency of powertrain systems and ride comfort for electric vehicles (EVs), the transmission model is required to enable more accessible and more straightforward control of such vehicles. In this study, a wet-type, two-speed, dual-brake transmission system, as well as a new electromechanical clutch actuator, is presented for EVs. A new coordinated optimal shifting control strategy is then introduced to avoid sharp jerks during shifting processes in the transmission system. Based on a state-space model of the electromechanical clutch actuator and dual-brake transmission, we develop a linear quadratic regulator strategy by considering ride comfort and sliding friction work to obtain optimal control trajectories of the traction and shifting motors under model-based control. Simulations and bench tests are carried out to verify the performance of the proposed control laws. Results of the proposed coordinated control strategy show that noticeable improvements in terms of vehicle jerk and friction energy loss are achieved compared with an optimal control scheme only for the shifting motor as the input

Frequency regulation strategy of direct drive permanent magnet synchronous wind power generation system based on RPC principle

The continuous integration of renewable energy into the grid has reduced its inertia and damping levels. When disturbances occur, the grid is prone to frequency excursion issues, which restrict the further utilization of renewable energy. Consequently, an increasing number of grid codes require active participation of renewable energy sources in the system’s frequency regulation (FR). Direct-drive permanent magnet synchronous wind power systems, characterized by their simple structure and high reliability, have gradually become the mainstream in wind power systems. By controlling the pitch angle to reserve surplus power, the wind turbines can actively engage in frequency regulation during disturbances. However, due to limited power reserve capacity, traditional FR methods struggle with parameters tuning, thus failing to achieve the desired effect. To this end, this paper proposes an FR strategy for direct-drive permanent magnet synchronous wind power systems based on the principle of rapid power compensation (RPC). It circumvents the challenges associated with parameter tuning, and achieves optimal FR performance for wind turbine inverter under power-limited conditions. Firstly, it is demonstrated that the proposed RPC control, when making full use of power reserves, can achieve FR effects equivalent to optimal PD control through rigorous mathematical analysis. Subsequently, the RPC control is divided into four operating modes to address FR requirements under different conditions. The transitions between these modes are explained, and the detailed implementation of the RPC control is provided. Finally, the effectiveness and superiority of the proposed control strategy are validated through simulation based on Matlab/Simulink

Experimental comparison of Yb/Al/Ce and Yb/Al/P co-doped fibers on the suppression of transverse mode instability

We presented an experimental comparison of the core-composition difference on the suppression of the photodarkening and transverse mode instability effects. Two core-composition fibers, entailing Yb/Al/Ce and Yb/Al/P co-doped fibers, were fabricated by MCVD process combined with solution doping technique. The parameters of two fibers were almost the same. The PD-induced loss at equilibrium was 3.94 dB/m at 702 nm in Yb/Al/Ce fiber, while it was 0.99 dB/m in Yb/Al/P fiber. To obtain a deeper understanding of the impact of PD on laser performance, a bidirectional pumping fiber amplifier was constructed. Compared with Yb/Al/Ce co-doped fiber, the TMI thresholds of Yb/Al/P co-doped fiber were enhanced in co-pumped and counter-pumped schemes. Meanwhile, the slope efficiency in bidirectional scheme was promoted by 4%. Moreover, the transmittance at 638 nm confirmed the superior PD resistance of Yb/Al/P co-doped fiber. These experimental results pave the way for the further development of high-power fiber lasers

Dynamics and control of active sites in hierarchically nanostructured cobalt phosphide/chalcogenide-based electrocatalysts for water splitting

The rational design of efficient electrocatalysts for industrial water splitting is essential to generate sustainable hydrogen fuel. However, a comprehensive understanding of the complex catalytic mechanisms under harsh reaction conditions remains a major challenge. We apply a self-templated strategy to introduce hierarchically nanostructured “all-surface” Fe-doped cobalt phosphide nanoboxes (Co@CoFe–P NBs) as alternative electrocatalysts for industrial-scale applications. Operando Raman spectroscopy and X-ray absorption spectroscopy (XAS) experiments were carried out to track the dynamics of their structural reconstruction and the real catalytically active intermediates during water splitting. Our operando analyses reveal that partial Fe substitution in cobalt phosphides promotes a structural reconstruction into P–Co–O–Fe–P configurations with low-valence metal centers (M0/M+) during the hydrogen evolution reaction (HER). Results from density functional theory (DFT) demonstrate that these in situ reconstructed configurations significantly enhance the HER performance by lowering the energy barrier for water dissociation and by facilitating the adsorption/desorption of HER intermediates (H*). The competitive activity in the oxygen evolution reaction (OER) arises from the transformation of the reconstructed P–Co–O–Fe–P configurations into oxygen-bridged, high-valence CoIV–O–FeIV moieties as true active intermediates. In sharp contrast, the formation of such CoIII/IV–O–FeIII/IV moieties in Co–FeOOH is hindered under the same conditions, which outlines the key advantages of phosphide-based electrocatalysts. Ex situ studies of the as-synthesized reference cobalt sulfides (Co–S), Fe doped cobalt selenides (Co@CoFe–Se), and Fe doped cobalt tellurides (Co@CoFe–Te) further corroborate the observed structural transformations. These insights are vital to systematically exploit the intrinsic catalytic mechanisms of non-oxide, low-cost, and robust overall water splitting electrocatalysts for future energy conversion and storage

Sobol′’s sensitivity analysis for a distributed hydrological model of Yichun River Basin, China

Copyright © 2013 Elsevier. NOTICE: this is the author’s version of a work that was accepted for publication in Journal of Hydrology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Hydrology Vol. 480 (2013), DOI: 10.1016/j.jhydrol.2012.12.005This paper aims to provide an enhanced understanding of the parameter sensitivities of the Soil and Water Assessment Tool (SWAT) using a variance-based global sensitivity analysis, i.e., Sobol′’s method. The Yichun River Basin, China, is used as a case study, and the sensitivity of the SWAT parameters is analyzed under typical dry, normal and wet years, respectively. To reduce the number of model parameters, some spatial model parameters are grouped in terms of data availability and multipliers are then applied to parameter groups, reflecting spatial variation in the distributed SWAT model. The SWAT model performance is represented using two statistical metrics – Root Mean Square Error (RMSE) and Nash–Sutcliffe Efficiency (NSE) and two hydrological metrics – RunOff Coefficient Error (ROCE) and Slope of the Flow Duration Curve Error (SFDCE). The analysis reveals the individual effects of each parameter and its interactions with other parameters. Parameter interactions contribute to a significant portion of the variation in all metrics considered under moderate and wet years. In particular, the variation in the two hydrological metrics is dominated by the interactions, illustrating the necessity of choosing a global sensitivity analysis method that is able to consider interactions in the SWAT model identification process. In the dry year, however, the individual effects control the variation in the other three metrics except SFDCE. Further, the two statistical metrics fail to identify the SWAT parameters that control the flashiness (i.e., variability of mid-flows) and overall water balance. Overall, the results obtained from the global sensitivity analysis provide an in-depth understanding of the underlying hydrological processes under different metrics and climatic conditions in the case study catchment.National Natural Science Foundation of Chin

In-situ nanospectroscopic imaging of plasmon-induced two-dimensional [4+4]-cycloaddition polymerization on Au(111)

From Springer Nature via Jisc Publications RouterHistory: received 2021-01-14, accepted 2021-06-16, registration 2021-07-13, pub-electronic 2021-07-27, online 2021-07-27, collection 2021-12Publication status: PublishedFunder: EC | EU Framework Programme for Research and Innovation H2020 | H2020 Priority Excellent Science | H2020 European Research Council (H2020 Excellent Science - European Research Council); doi: https://doi.org/10.13039/100010663; Grant(s): 741431-2DNanoSpecFunder: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (Swiss National Science Foundation); doi: https://doi.org/10.13039/501100001711; Grant(s): URPP-LightChECFunder: EC | Horizon 2020 Framework Programme (EU Framework Programme for Research and Innovation H2020); doi: https://doi.org/10.13039/100010661; Grant(s): 841653-2DvdWHsFunder: the Swiss National Supercomputing Centre (CSCS) under Project ID uzh1 and s965Abstract: Plasmon-induced chemical reactions (PICRs) have recently become promising approaches for highly efficient light-chemical energy conversion. However, an in-depth understanding of their mechanisms at the nanoscale still remains challenging. Here, we present an in-situ investigation by tip-enhanced Raman spectroscopy (TERS) imaging of the plasmon-induced [4+4]-cycloaddition polymerization within anthracene-based monomer monolayers physisorbed on Au(111), and complement the experimental results with density functional theory (DFT) calculations. This two-dimensional (2D) polymerization can be flexibly triggered and manipulated by the hot carriers, and be monitored simultaneously by TERS in real time and space. TERS imaging provides direct evidence for covalent bond formation with ca. 3.7 nm spatial resolution under ambient conditions. Combined with DFT calculations, the TERS results demonstrate that the lateral polymerization on Au(111) occurs by a hot electron tunneling mechanism, and crosslinks form via a self-stimulating growth mechanism. We show that TERS is promising to be plasmon-induced nanolithography for organic 2D materials

ESTIMATING UNIVARIATE DISTRIBUTIONS VIA RELATIVE ENTROPY MINIMIZATION: CASE STUDIES ON FINANCIAL AND ECONOMIC DATA

We use minimum relative entropy (MRE) methods to estimate univariate probability density functions for a varied set of financial and economic variables, including S&P500 index returns, individual stock returns, power price returns and a number of housing-related economic variables. Some variables have fat tail distributions, others have finite support. Some variables have point masses in their distributions and others have multimodal distributions. We indicate specifically how the MRE approach can be tailored to the stylized facts of the variables that we consider and benchmark the MRE approach against alternative approaches. We find, for a number of variables, that the MRE approach outperforms the benchmark methods.Kullback-Leibler relative entropy, maximum likelihood, probability distribution, fat-tailed, point mass, stock return distribution, stock index return distribution, financial data, economic data, California Housing Data