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Economic model predictive control (EMPC) has received increasing attention in the wind energy community due to its ability to trade‐off economic objectives with ease. However, for wind turbine applications, inherent nonlinearities, such as from aerodynamics, pose difficulties in attaining a convex optimal control problem (OCP), by which real‐time deployment is not only possible but also a globally optimal solution is guaranteed. A variable transformation can be utilized to obtain a convex OCP, where nominal variables, such as rotational speed, pitch angle, and torque, are exchanged with an alternative set in terms of power and energy. The ensuing convex EMPC (CEMPC) possesses linear dynamics, convex constraints, and concave economic objectives and has been successfully employed to address power control and tower fatigue alleviation. This work focuses on extending the blade loads mitigation aspect of the CEMPC framework by exploiting its individual pitch control (IPC) capabilities, resulting in a novel CEMPC‐IPC technique. This extension is made possible by reformulating static blade and rotor moments in terms of individual blade aerodynamic powers and rotational kinetic energy of the drivetrain. The effectiveness of the proposed method is showcased in a mid‐fidelity wind turbine simulation environment in various wind cases, in which comparisons with a basic CEMPC without load mitigation capability and a baseline IPC are made. [ABSTRACT FROM AUTHOR]

In this study, the whole chloroplast genome of Ulmus bergmanniana was sequenced, assembled, annotated and characterized for the first time. The results showed that the total length of U. bergmanniana chloroplast genome was 160,060 bp and the GC content was 35.52%, which had the typical circular double-stranded tetrad structure of angiosperm chloroplast genome. It includes a large single-copy region (LSC), a small single-copy region (SSC), and a pair of inverted repeat regions (IRa/IRb), with lengths of 88,161 bp, 19,029 bp, and 26,435 bp, respectively. A total of 131 genes were annotated, including 86 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Based on the chloroplast genome sequences of 14 plants in U. bergmanniana and NCBI database, the phylogenetic tree was constructed, and the phylogenetic position of U. bergmanniana in Ulmaceae was determined. The results will provide a theoretical basis for molecular identification and resource development and utilization of U. bergmanniana.

The Janus functional thermal device (JFTD) can produce different thermal modulation effects on the heat flow incident from different directions. To solve the problems of material anisotropy and non-interaction with the external environment in the thermal target region of the previous JFTD, an open JFTD is proposed by using a moving thermal conductive medium in four rectangular modules on the background thermal conductive plate. The thermal target region within the proposed open JFTD is an isotropic thermal conductive medium (e.g., the same as the background medium), which can be connected to the external region. The simulated results show that the proposed open JFTD performs as a thermal concentrator for the heat flows with incident angles between 0° and the critical angle and a thermal cloak for the heat flows with incident angles between the critical angle and 90°, which can be applied to the separate processing of multiple heat flows from different directions in various integrated systems. [ABSTRACT FROM AUTHOR]

High-entropy oxide (HEO) nanoparticles have been regarded as a promising catalytic material system for oxygen evolution reaction in recent years. However, their traditional physical and chemical synthesis remains challenges due to the limitation of fabricating controllable small size HEO nanoparticles. Herein, a general and novel method of low-energy-recoil ion implantation and subsequent annealing is successfully developed to synthesize high-entropy oxide nanoparticles catalysts. By controlling the fluence of irradiation Ar+ ions, the size and the load of HEO nanoparticles can be accurately controlled. The obtained (FeCoNiCrAl)O HEO nanoparticles exhibit an overpotential of 295 mV at 10 mA cm−2, a small Tafel slope of 39 mV dec−1 and good stability in 1 M KOH, which is much better than the properties of binary and medium entropy oxide counterparts prepared by the same method, showing the good application prospect of low-energy-recoil ion implantation in the preparation of complicated multi-element-metal oxide nanoparticles. [ABSTRACT FROM AUTHOR]

Ulmus szechuanica is a species of Sect.Ulmus and Ser.Nitentes in Ulmaceae, and it is an endangered wild plant in China. The complete chloroplast genome (cp) of U. szechuanica was reported in this study. The result showed that the cp genome was 159,703 bp in length including a large single-copy (LSC) 88,039 bp and a small single-copy (SSC) 19,072 bp, which were separated by two inverted repeats (IRs) of 26,296 bp with the typical quadripartite structure, respectively. The genome encoded 131 genes, including 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The GC content was 35.53%. Chloroplast sequences were used for constructing phylogenetic tree to determine the evolutionary status of U. szechuanica. The maximum-likelihood phylogenetic analysis showed that U. szechuanica displayed a closer kinship to five other Ulmus species. This study provides important information for identification and conservation of species, germplasm resources utilization, and genetic engineering of Ulmus. The cp will provide a reference for future studies on species evolution of Ulmus.

This study was conducted to sequence, assemble, annotate, and characterize the complete chloroplast (cp) genome sequence of Ulmus lanceaefolia. The result showed that the cp genome was 158,652 bp in length with 35.63% GC content, including a large single-copy (LSC) region of 87,119 bp, a small single-copy (SSC) region of 18,697 bp and an inverted repeat sequence (IRa/IRb) region of 26,418 bp, which was a typical tetrad structure. We had identified a total of 132 genes, including 87 protein-coding genes, eight rRNA genes, and 37 tRNA genes. The phylogenetic trees were constructed based on the cp genome sequences of U. lanceaefolia and 12 plants in the NCBI database, and the phylogenetic positions of U. lanceaefolia in the Ulmaceae were identified.

Ulmus elongata is a species of Sect. Chaetoptelea (Liemb.) S chneid in Ulmaceae, and it is an endangered wild plant listed in the second class of the Protected Plants in China. The complete chloroplast genome (cp) of U. elongata was reported in this study. The result showed that the cp genome was 159,230 bp in length including a large single-copy (LSC) 87,718 bp and a small single-copy (SSC) 18,690 bp, which were separated by two inverted repeats (IRs) of 26,411 bp with the typical quadripartite structure, respectively. The genome encoded 132 genes, including 87 protein-coding genes, 37 tRNA genes, and eight rRNA genes. The GC content was 35.57%. Chloroplast sequences were used for constructing phylogenetic tree to determine the evolutionary status of U. elongata. The maximum-likelihood phylogenetic analysis showed that U. elongata was clustered with five other Ulmus species, and the relationship between Ulmus and Zelkova was closest. The success of cp genome assembly of U. elongata has laid a foundation for the study of chloroplast molecular biology and can effectively promote the study of genetic breeding and molecular evolution of U. elongata.

Developing highly efficient, low cost, and stable electrocatalysts that work at a large current density is crucial for upgrading the current industrial electrochemical water splitting to produce H2. Molybdenum selenide (MoSe2) is a promising 2D transition metal dichalcogenide (TMD), however, its reported output is inadequate due to its inert basal plane. Herein, the catalytic activity of MoSe2 nanosheet arrays is activated by a novel and controllable method of He+ ion irradiation to introduce multiple vacancies simultaneously into their inert basal planes. The vacancies activated MoSe2 have improved electrocatalytic performance and stability with a minimum overpotential of 90 mV at 10 mA cm−2, a Tafel slope of 49 mV dec−1 and high stability of 650 h at the industry‐level large current density of 1000 mA cm−2 compared to several hours for the pristine sample. The DFT results reveal that single Se and single Mo vacancies on the MoSe2 basal plane can efficiently increase the electrical conductivity and reduce energy barriers for water dissociation and subsequent proton adsorption, thus improving the electrocatalytic capability. This finding proves the application of ion beam in defect engineering for effective hydrogen evolution in TMDs‐based catalysts. [ABSTRACT FROM AUTHOR]

A novel 3D‐printed biodegradable cage composed of polycaprolactone (PCL) and beta‐tricalcium phosphate (β‐TCP) in a mass ratio of 50:50, with stable resorption patterns and mechanical strength has been developed for lumbar interbody fusion. This is a prospective cohort study to evaluate the short‐ and mid‐term safety and efficacy of this biodegradable cage in posterior lumbar interbody fusion (PLIF) surgery. This was a prospective single‐arm pilot clinical trial in 22 patients with a follow‐up time of 1, 3, 6, and 12 months, postoperatively. Clinical outcomes were assessed using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) and Visual analogue scale (VAS) for leg pain and low back pain. Radiological examination included X‐ray, CT scan, and three‐dimensional reconstruction to evaluate surgical indications, intervertebral space height (ISH), intervertebral bone fusion and cage degradation. A total of 22 patients was included, with an average age of 53.5 years. Among 22 patients, one patient lost to follow‐up and one patient withdrew from the clinical trial because of cage retropulsion. The remaining 20 patients showed significant improvement in clinical and imaging outcomes compared to the preoperative period. The overall mean VAS for back decreased from 5.85 ± 0.99 preoperatively to 1.15 ± 0.86 at the 12‐month follow‐up (p <.001); the VAS for leg decreased from 5.75 ± 1.11 to 1.05 ± 0.76 (p <.001); the JOA score improved from 13.8 ± 2.64 to 26.45 ± 2.46 (p <.001). The mean intervertebral space height (ISH) increased from 11.01 ± 1.75 mm preoperatively to 12.67 ± 1.89 mm at the 12‐month follow‐up and the bone fusion reached 95.2% (20/21 disc segments). Partial resorption (inferior to 50% compared with the initial cage size) were found in all cages (21/21). The clinical and radiological assessments showed that the application of 3D‐printed biodegradable PCL/β‐TCP cages in PLIF yielded satisfactory results at the 12‐month follow‐up. In the future, long‐term clinical observations and controlled clinical trials are required to further validate the safety and efficacy of this novel cage. [ABSTRACT FROM AUTHOR]

During aerobic exposure of silage, the fatty acid and amino acid composition may alter the quality and palatability, resulting in economic losses in livestock production. The objective of this study was to evaluate the effects of Lactiplantibacillus plantarum (LP), Lenti Lentilactobacillus buchneri (LB), and a mixture of LP and LB (PB) on the fatty acids, amino acids, and antioxidant capacity of Leymus chinensis silage during aerobic exposure. The lactic acid bacteria were added at 1 × 106 CFU/g. The silage treatments were opened after 60 days of fermentation, and sampled on days 0, 4, and 8 of aerobic exposure. The LB group had higher total fatty acid and polyunsaturated fatty acid content, and less decrease in amino acid content and antioxidant capacity, while the LP group had a higher monounsaturated fatty acid content but a larger decrease in all indicators after exposure. Correlation analysis showed that Lactobacillus, Cryptococcus, Penicillium, and Thermoascus were more correlated with fatty acid changes, and that Lactobacillus, Actinomyces, Clostridium, and Penicillium were more correlated with amino acid changes. In conclusion, Lentilactobacillus buchneri could effectively improve the antioxidant capacity and fatty acid and amino acid contents of Leymus chinensis silage during aerobic exposure, while Lactiplantibacillus plantarum could effectively improve the content of each index of Leymus chinensis silage at opening, but deterioration was faster during aerobic exposure. [ABSTRACT FROM AUTHOR]

Silage of native grasses can alleviate seasonal forage supply imbalance in pastures and provide additional sources to meet forage demand. The study aimed to investigate the effects of Lactobacillus plantarum (LP), Lactobacillus buchneri (LB), and Lactobacillus plantarum in combination with Lactobacillus buchneri (PB) on the nutritional quality, fermentation quality, and microbial community of native grass silage at 2, 7, 15, and 60 days after ensiling and at 4 and 8 days after aerobic exposure. The results showed that dry matter content, crude protein content, the number of lactic acid bacteria, and lactic acid and acetic acid content increased and pH and ammonia nitrogen content decreased after lactic acid bacteria (LAB) inoculation compared with the control group (CK). LP had the lowest pH and highest lactic acid content but did not have greater aerobic stability. LB maintained a lower pH level and acetic acid remained at a higher level after aerobic exposure; aerobic bacteria, coliform bacteria, yeast, and molds all decreased in number, which effectively improved aerobic stability. The effect of the compound addition of LAB was in between the two other treatments, having higher crude protein content, lactic acid and acetic acid content, lower pH, and ammonia nitrogen content. At the phylum level, the dominant phylum changed from Proteobacteria to Firmicutes after ensiling, and at the genus level, Lactiplantibacillus and Lentilactobacillus were the dominant genera in both LAB added groups, while Limosilactobacillus was the dominant genus in the CK treatment. In conclusion, the addition of LAB can improve native grass silage quality by changing bacterial community structure. LP is beneficial to improve the fermentation quality in the ensiling stage, LB is beneficial to inhibit silage deterioration in the aerobic exposure stage, and compound LAB addition is more beneficial to be applied in native grass silage. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effects of cellulase (CE) and lactic acid bacteria (LAB) on Caragana korshinskii silage by analyzing the fermentation parameters, chemical composition, and bacterial community. The Caragana korshinskii was harvested at the fruiting period and treated with cellulase and LAB alone as a control treatment with no additive (CK). The ensiling performance and bacterial community were determined after 3, 7, 15, 30, and 60 days of fermentation process. Compared with the CK group, the pH, dry matter loss, and ammonia nitrogen content were significantly (p < 0.05) decreased in the LAB and CE treatments. Compared with the CK and LAB group, the contents of acid detergent fiber, neutral detergent fiber, and acid detergent lignin in the CE group decreased significantly (p < 0.05), and the water-soluble carbohydrates, acetic acid, and lactic acid concentrations increased significantly (p < 0.05). At the genus level of microorganisms, the addition of cellulase and LAB significantly reduced the microbial diversity. Compared with the CK group (78.05%), the relative abundance of Lactiplantibacillus in the CE group (90.19%) and LAB group (88.40%) significantly (p < 0.05) increased. The relative abundance of Pediococcus in the CE group (3.66%) and LAB group (2.14%) was significantly (p < 0.05) lower than that in the CK group (14.73%). Predicted functional profiling of 16S rRNA genes revealed that the addition of cellulase and LAB increased the pyruvate metabolic pathway during Caragana korshinskii silage, thereby increasing the accumulation of lactic acid concentration. The addition of cellulase expressed a better advantage in the biosynthetic capacity of lysine. In summary, the addition of cellulase and LAB could adjust the bacterial community to improve the silage quality of Caragana korshinskii, and the addition of cellulase exhibited better results than the LAB additives. [ABSTRACT FROM AUTHOR]

Because of the wide selectivity of ferromagnetic and ferroelectric (FE) components, electric-field (E-field) control of magnetism via strain mediation can be easily realized through composite multiferroic heterostructures. Here, an MgO-based magnetic tunnel junction (MTJ) is chosen rationally as the ferromagnetic constitution and a high-activity (001)-Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-0.3PT) single crystal is selected as the FE component to create a multiferroic MTJ/FE hybrid structure. The shape of tunneling magnetoresistance (TMR) versus in situ E-fields imprints the butterfly loop of the piezo-strain of the FE without magnetic-field bias. The E-field-controlled change in the TMR ratio is up to â€"0.27% without magnetic-field bias. Moreover, when a typical magnetic field (∼ ±10 Oe) is applied along the minor axis of the MTJ, the butterfly loop is changed significantly by the E-fields relative to that without magnetic-field bias. This suggests that the E-field-controlled junction resistance is spin-dependent and correlated with magnetization switching in the free layer of the MTJ. In addition, based on such a multiferroic heterostructure, a strain-gauge factor up to approximately 40 is achieved, which decreases further with a sign change from positive to negative with increasing magnetic fields. This multiferroic hybrid structure is a promising avenue to control TMR through E-fields in low-power-consumption spintronic and straintronic devices at room temperature. [ABSTRACT FROM AUTHOR]

In the next decade, further digitalisation of the entire wind energy project lifecycle is expected to be a major driver for reducing project costs and risks. In this paper, a literature review on the challenges related to implementation of digitalisation in the wind energy industry is first carried out, showing that there is a strong need for new solutions that enable co-innovation within and between organisations. Therefore, a new collaboration method based on a digital ecosystem is developed and demonstrated. The method is centred around specific "challenges", which are defined by "challenge providers" within a topical "space" and made available to participants via a digital platform. The data required in order to solve a particular "challenge" are provided by the "challenge providers" under the confidentiality conditions they specify. The method is demonstrated via a case study, the EDP Wind Turbine Fault Detection Challenge. Six submitted solutions using diverse approaches are evaluated. Two of the solutions perform significantly better than EDP's existing solution in terms of Total Prediction Costs (saving up to €120,000). The digital ecosystem is found to be a promising solution for enabling co-innovation in wind energy in general, providing a number of tangible benefits for both challenge and solution providers. [ABSTRACT FROM AUTHOR]

Over the past decades, Floating Offshore Wind Turbine (FOWT) has gained increasing attention in wind engineering due to the rapidly growing energy demands. However, difficulties in turbine maintenance will increase due to the harsh operational conditions. Fault diagnosis techniques play a crucial role to enhance the reliability of FOWTs and reduce the cost of offshore wind energy. In this paper, a novel data‐driven fault diagnosis method using regularized dynamic canonical correlation analysis (RDCCA) and Fisher discriminant analysis (FDA) is proposed for FOWTs. Specifically, to overcome the collinearity problem that exists in measured process data, dynamic canonical correlation analysis with a regularization scheme, is developed to exploit the relationship between input and output signals. Then, the residual signals are generated from the established RDCCA model for fault detection. To further classify the fault type, an FDA model is trained from the residual signals of different training faulty data sets. Simulations on a FOWT baseline model based on the widely used National Renewable Energy Laboratory FAST simulator are carried out to demonstrate the feasibility and efficacy of the proposed fault detection and classification method. Results have shown many salient features of the proposed method with potential applications in FOWTs. [ABSTRACT FROM AUTHOR]

Individual pitch control (IPC) is an effective and widely used strategy to mitigate blade loads in wind turbines. However, conventional IPC fails to cope with blade and actuator faults, and this situation may lead to an emergency shutdown and increased maintenance costs. In this paper, a fault‐tolerant individual pitch control (FTIPC) scheme is developed to accommodate these faults in floating offshore wind turbines (FOWTs), based on a Subspace Predictive Repetitive Control (SPRC) approach. To fulfill this goal, an online subspace identification paradigm is implemented to derive a linear approximation of the FOWT system dynamics. Then, a repetitive control law is formulated to attain load mitigation under operating conditions, both in healthy and faulty conditions. Since the excitation noise used for the online subspace identification may interfere with the nominal power generation of the wind turbine, a novel excitation technique is developed to restrict excitation at specific frequencies. Results show that significant load reductions are achieved by FTIPC, while effectively accommodating blade and actuator faults and while restricting the energy of the persistently exciting control action. [ABSTRACT FROM AUTHOR]

Summary: This paper focuses on the steady‐state power distribution region of the modular multilevel converter (MMC) and the matching among its multiple constraints. First, an equivalent model of the steady‐state MMC is established, and its basic power distribution region is solved based on analysis. Second, the influence of the AC current constraint, the AC outlet voltage constraint, the modulation index constraint, the DC current constraint, and the DC voltage constraint on the power distribution region are studied through the phasor analysis method. The power distribution region under the multiple constraints is obtained, and the parameters matching principle among these constraints are studied. Finally, in PSCAD/EMTDC, the simulation results validate the correctness of the obtained power distribution region and the effectiveness of the parameters matching principle among the multiple constraints. [ABSTRACT FROM AUTHOR]

Incipient fault detection plays a crucial role in preventing the occurrence of serious faults or failures in industrial processes. In most industrial processes, linear, and nonlinear relationships coexist. To improve fault detection performance, both linear and nonlinear features should be considered simultaneously. In this article, a novel hybrid linear-nonlinear statistical modeling approach for data-driven incipient fault detection is proposed by closely integrating recently developed canonical variate dissimilarity analysis and mixed kernel principal component analysis (MKPCA) using a serial model structure. Specifically, canonical variate analysis (CVA) is first applied to estimate the canonical variables (CVs) from the collected process data. Linear features are extracted from the estimated CVs. Then, the canonical variate dissimilarity (CVD) which quantifies model residuals in the CVA state-subspace is calculated using the estimated CVs. To explore the nonlinear features, the nonlinear principal components are extracted as nonlinear features through performing MKPCA on CVD. Fault detection indices are formed based on Hotelling's T2 as well as Q statistics from the extracted linear and nonlinear features. Moreover, kernel density estimation is utilized to determine the control limits. The effectiveness of the proposed method is demonstrated by the comparisons with other relevant methods via simulations based on a closed-loop continuous stirred-tank reactor process. [ABSTRACT FROM AUTHOR]

In this article, a novel data-driven fault diagnosis method by combining deep canonical variate analysis and Fisher discriminant analysis (DCVA-FDA) is proposed for complex industrial processes. Inspired by the recently developed deep canonical correlation analysis, a new nonlinear canonical variate analysis (CVA) called DCVA is first developed by incorporating deep neural networks into CVA. Based on DCVA, a residual generator is designed for the fault diagnosis process. FDA is applied in the feature space spanned by residual vectors. Then, a Bayesian inference classifier is performed in the reduced dimensional space of FDA to label the class of process data. A continuous stirred-tank reactor and an industrial benchmark of the Tennessee Eastman process are carried out to test the performance of DCVA-FDA fault diagnosis. The experimental results demonstrate that the proposed DCVA-FDA fault diagnosis is able to significantly improve the fault diagnosis performance when compared to other methods also examined in this article. [ABSTRACT FROM AUTHOR]

In this study, we assembled and annotated the chloroplast (cp) genome of the Euonymus species Euonymus fortunei , Euonymus phellomanus , and Euonymus maackii , and performed a series of analyses to investigate gene structure, GC content, sequence alignment, and nucleic acid diversity, with the objectives of identifying positive selection genes and understanding evolutionary relationships. The results indicated that the Euonymus cp genome was 156,860–157,611bp in length and exhibited a typical circular tetrad structure. Similar to the majority of angiosperm chloroplast genomes, the results yielded a large single-copy region (LSC) (85,826–86,299bp) and a small single-copy region (SSC) (18,319–18,536bp), separated by a pair of sequences (IRA and IRB; 26,341–26,700bp) with the same encoding but in opposite directions. The chloroplast genome was annotated to 130–131 genes, including 85–86 protein coding genes, 37 tRNA genes, and eight rRNA genes, with GC contents of 37.26–37.31%. The GC content was variable among regions and was highest in the inverted repeat (IR) region. The IR boundary of Euonymus happened expanding resulting that the rps19 entered into IR region and doubled completely. Such fluctuations at the border positions might be helpful in determining evolutionary relationships among Euonymus. The simple-sequence repeats (SSRs) of Euonymus species were composed primarily of single nucleotides (A)n and (T)n, and were mostly 10–12bp in length, with an obvious A/T bias. We identified several loci with suitable polymorphism with the potential use as molecular markers for inferring the phylogeny within the genus Euonymus. Signatures of positive selection were seen in rpoB protein encoding genes. Based on data from the whole chloroplast genome, common single copy genes, and the LSC, SSC, and IR regions, we constructed an evolutionary tree of Euonymus and related species, the results of which were consistent with traditional taxonomic classifications. It showed that E. fortunei sister to the Euonymus japonicus , whereby E. maackii appeared as sister to Euonymus hamiltonianus. Our study provides important genetic information to support further investigations into the phylogenetic development and adaptive evolution of Euonymus species. [ABSTRACT FROM AUTHOR]

A hyper-lens with planar object/image surfaces and uniform magnification factor is designed based on directional projecting property of optic-null medium (ONM). The proposed planar hyper-lens only requires one homogeneous anisotropic medium, i.e. ONM. We use metallic plates inside ϵ-near-zero medium to realize the proposed hyper-lens. 0.191λ0 resolution is observed (0.238λ0 can be clearly resolved) in experimental measurement, which consists very well with 3D numerical simulations and verifies the performance of the proposed planar hyper-lens. The planar hyper-lens with uniform pre-designed magnification factor may have some applications in super-resolution imaging technology. [ABSTRACT FROM AUTHOR]

A curved metasurface radome is designed to extend the scanning angle of a phased‐array antenna. Unlike the previous method, using negative index materials or transformation media (inhomogeneous and anisotropic), herein, only ordinary natural materials, i.e., a single‐layer well‐arranged ceramic block, are used, to realize the functions of the angle extending effect. The designed radome has a smaller size, lighter weight, a large angle extending effect, and is easy for fabrication. Therefore, the proposed method is more likely to be used in practical applications. The performance of the radome is verified by both numerical simulations and experimental demonstrations. [ABSTRACT FROM AUTHOR]

The voltage source converter based high voltage direct current transmission system with the true bipolar wiring mode features higher flexibility and reliability, yet it cannot be without a proper and effective coordinated control strategy, which is the key to the safe and reliable operation of the system as well as the effective and full utilization of renewable energy on a large scale. A step further from the conventional droop control strategy, the coordinated control strategy based on operating point optimization is proposed in this paper. This paper first illustrates and examines the coordinated control method at the system level in view of special wiring and control modes; it then looks into the method of operating point optimization seeking to achieve both safe and cost-effective operation; and the paper finally demonstrates the effectiveness of the coordinated control strategy verified by MATLAB and PSCAD simulations from the perspective of system operating point deviation, security, and cost-effectiveness. [ABSTRACT FROM AUTHOR]

VSC-HVDC grid is one of the important development directions of the smart grid in the future. The arc characteristics of transient fault on the transmission line are the theoretical basis for determining reclosing time and reclosing strategy of DC circuit breaker. In this study, the process of the transient single-pole ground fault on the true bipolar VSC-HVDC transmission line is analysed and the arc model of the fault is determined according to the fault characteristics. Then a two-terminal voltage source converter-high voltage direct current (VSC-HVDC) system including this arc model is built in power systems computer aided design (PSCAD). The primary and secondary arc characteristics of the transient single-pole ground fault on the transmission lines are simulated and compared with the arc in AC system. It is shown that the arc extinction time of the flexible DC transmission system is lesser than that of the AC system at the same voltage level. [ABSTRACT FROM AUTHOR]

The paper introduces a set of modeling methods to predict the failure probability of offshore wind turbines in the China coastal waters. In detail, a series of full-set three-dimensional meteorology simulations are conducted using the Weather Research and Forecast model to provide the extreme wind fields, while the extreme wave fields are predicted according to the conditional probability model. After the extreme wind and wave fields are prepared, the ultimate loads on the three critical parts of an OC4-DeepCwind semisubmersible wind turbine are simulated using the fatigue, aerodynamics, structures, and turbulence code, which in turn leads to the prediction of the failure probability. It has been found that the OC4-DeepCwind semisubmersible constructed in the Taiwan Strait has higher chance to fail under typhoon conditions than in other parts of the China coastal waters, showing a maximum failure probability of 0.6. In addition, the failure probabilities in the South and East China Sea are in the range of 0.3–0.45. The probability densities of the ultimate loads show, in some cases, a bimodal shape, which indicates that the loads as well as the failure probability are not in a simple linear relationship with the extreme wind speeds and wave heights/periods. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials have become a novel and effective way to control sound waves and design acoustic devices. In this study, we design a 3D acoustic metamaterial lens (AML) to achieve point-to-point acoustic communication in air: any acoustic source (a speaker) in air enclosed by such an AML can produce an acoustic image where the acoustic wave is focused (the field intensity is at a maximum, and the listener can receive the information), while the acoustic field at other spatial positions is low enough that listeners can hear almost nothing. Unlike a conventional elliptical reflective mirror, the acoustic source can be moved around inside our proposed AML. Numerical simulations are given to verify the performance of the proposed AML. [ABSTRACT FROM AUTHOR]

The typhoon-resistant design should be given priority when constructing offshore wind farms in China coastal waters, where typhoons pose serious threats on the safety of offshore structures. A classical power-law model with the specific exponent of ${\text{0.11}}$ has been recommended by the code (IEC 61400-3 2009) to estimate the profile of extreme wind speed versus ${\text{50}}$ years return period. Its use in the typhoon-resistant design of offshore wind turbines in China coastal waters has, however, not been validated. In the present study, a series of full-set three-dimensional meteorology simulations are conducted to provide the artificial typhoon wind fields for the evaluation of code recommendations. The simulations reveal that the classical power-law with the exponent of ${\text{0.11}}$ is inadequate to estimate the extreme wind speed profile over China coastal waters. Based on the simulated typhoon wind fields, an empirical correction ratio and a scale factor are developed to adjust the classical power-law model to estimate the vertical variation of extreme wind speeds with any desired return periods over China coastal waters. More specifically, the correct ratio revises the power-law model to provide more accurate estimates of 50 years return period extreme wind speed profiles while the scale factor projects extreme wind speeds with other desired return periods. [ABSTRACT FROM AUTHOR]