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The unsteady aerodynamic characteristics and interference effects of floating offshore wind turbine (FOWT) are mainly affected by the pitch motion of the ocean platform. Based on computational fluid dynamics (CFD) and advanced overset grid technology, the aerodynamic performance and wake characteristics of a fully configured wind turbine with rotating blades, nacelle , and tower are studied in this paper. The effects of the amplitude and frequency of pitch motion on the wind turbine aerodynamic loads and flow field are investigated herein in detail. The power and thrust between numerical simulation and experiment are compared. The results show that the grid and simulation parameters used in this study can accurately capture the aerodynamic characteristics and the flow field around wind turbines. The influence of the pitch amplitude and frequency on the performance of wind turbines is discussed. The complex flow interaction between the tip vortex, tower shedding vortex, and the turbulent wake was observed. The present results indicate that the pitch motion amplitude and frequency have a great influence on the power, thrust, and wake characteristics. [ABSTRACT FROM AUTHOR]

Wind tunnel experiments are performed to investigate the wake characteristics of a model wind turbine using Particle Image Velocimetry (PIV) and Hot-wire velocimetry. Results show that the velocity deficit at the hub height is the largest, and the stratification of the velocity shear layer at the blade tip is obvious. The instantaneous turbulence kinetic energy (T K E) level is much larger than the mean T K E , especially downstream of the blade tip. In the x / d T = 4 position of the wake region, the mean T K E increased by two times due to the blade tip disturbance. The Reynolds stresses also increase and the instantaneous value is the highest along the blade's tip. A thin vortex band appears at the root and tip of the blade, the vortex core expands and diffuses with the development of the wake along the downstream direction. The two-dimensional distributions of velocity spectra f Φ u reveal that the velocity fluctuation at x / d T = 2 location is small and that at x / d T = 4 position is the largest. Based on Jensen's wake model, a new theoretical wake model is proposed to predict the velocity distribution in the wind turbine wake. The calculated results of the wake model are in good agreement with the experimental data. • Particle image velocimetry and Hotwire are used to study the wake characteristics. • Velocity meandering and turbulence characteristics in the wake are captured. • Blade's tip vortex and velocity fluctuation in the wake are explored. • A new theoretical wake model is proposed to predict the velocity distribution. [ABSTRACT FROM AUTHOR]

In order to explore the impact load and instantaneous fluid pressure of transient flow on pump station system under the nonregulative operating conditions, the transient characteristics of an axial flow pump during start-up process are investigated experimentally and numerically. To simulate transient flow of the pump, the rational speed is set by force coupling. In order to simulate the movement of the gate with two flap doors attached, the moving mesh technique is adopted. The results of numerical simulation agree well with the experimental data. During the start-up transient process, the transient characteristics parameters, such as pump rotational speed, head, and flow rate change significantly. Transient impact head rises to a peak of 1.87 times the rated head as the rotational speed reaches the rated speed. The whole impeller passage is full of recirculation, flow separation and vortices. The pressure distribution of the impeller blade changes obviously. In the process of pump start-up, the vortex core zones gradually increase, massively appear at the leading edges of the blade and in the passage of the impeller at t = 0.6 s, and then decrease. Our studies could help to avoid pump vibration and blade crack in engineering. • The rotational speed was estimated from force coupling. • Transient impact peaks at the rated speed during the pump startup. • Recirculation and flow separation appeared in the whole impeller passage. • The vortex core zones increase at the leading edges of the blade then decrease. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Highly efficient photodegradation of five gaseous VOCs was achieved by Au/ZnCr–LDHs. • Kinetic equation and activation energy were calculated for o –xylene photodegradation. • Photodegradation drive force is very different for ZnCr–LDHs before and after Au supporting. • Electron transfer from LDHs to Au NPs results in the enhancement of photocatalytic property. • Intermediates were detected and degradation pathway was proposed. Abstract In this paper, factors of initial concentration, catalyst dosage, irradiation intensity, relative humidity and reaction temperature onto visible light gaseous o –xylene photodegradation by ZnCr layered double hydroxides (ZnCr–LDHs) and Au supported ZnCr–LDHs (Au/ZnCr–LDHs) were investigated. ZnCr–LDHs shows low removal efficiency for o –xylene photodegradation, while Au/ZnCr–LDHs exhibits both excellent photodegradation rate and high TOF values for o –xylene as well as other VOCs including benzene, o –xylene, m –xylene and p –xylene. The kinetic equation and activation energy were calculated for o –xylene photodegradation, which are ln (C / C 0) = − 1.143 × 10 4 e − 21.85 × 10 3 R T × [ A ] 0 0.3487 × [ B ] o 0.1889 × [ C ] 0 0.3730 × t and 21.85 kJ/mol for ZnCr–LDH ln (C / C 0) = − 1.315 × 10 3 e − 12.84 × 10 3 R T × [ A ] 0 0.6201 × [ B ] o 0.4962 × [ C ] 0 0.5382 × t and 12.84 kJ/mol for Au/ZnCr–LDHs. The obvious difference both in kinetic equation and activation energy suggests the reaction mechanism of ZnCr–LDHs and Au/ZnCr–LDHs should be very different. The active species inhabitation experiments show that the major drive of photocatalytic reaction for ZnCr–LDHs is hydroxyl radical, while for Au/ZnCr–LDHs it is the hole and hydroxide radical. It is also proved that the support of Au NPs onto LDHs would result in the transfer of photoexcited electrons from LDHs to Au NPs which results in the enhancement of photocatalytic property as well as photocatalytic mechanism change based on UV–vis, XPS, the contribution of different wavelength ranges of visible light onto photocatalytic efficiency and electrochemical tests. [ABSTRACT FROM AUTHOR]

Electrical safety is a major threat to public safety worldwide, with fires and explosions causing damage to property and loss of life. Detection and monitoring of the occurrence of destructive current spikes can provide valuable insights into system health and inform preventative maintenance. Current sensors based on the Magnetoelectric (ME) effect have been regarded as optimal solutions because of the low power consumption and high sensitivity of ME devices compared to conventional current sensors (current transformers, Hall-effect current sensors, etc.). However, none of the conventional sensing techniques can provide ex-situ recording or a means for a human-readable signal output. Development of a current sensor that can sense, visualize, and record a current level remains a challenge. Here, we report an electric current visualization sensor that uses a coupled magnetoelectric/electrochromic effect to transform environmental current energy into electrical signals, and subsequently to a color change readily interpreted by a human observer. The current visualization sensor uses a PZT piezoelectric microfiber composite (MFC) / FeSiB alloy (Metglas) laminate combined with a Prussian blue-based electrochromic device (ECD). Such a current sensor demonstrates high efficiency self-powered current sensing and non-volatile signal recording. [Display omitted] • An electric current visualization sensor that uses a coupled magnetoelectric-electrochromic effect has been designed. • The sensor has the ability to display the health status of electrical power system in an easy way to observe, nonvolatile display. • The current sensor demonstrates high efficiency self-powered current sensing and non-volatile signal recording. • The system is expected to provide new routes for health monitoring in power distribution systems. [ABSTRACT FROM AUTHOR]

The transmission and deposition of pathogenic bioaerosols and the subsequent contamination of the air and surfaces is well recognized as a potential route of hospital cross-infection. A full-scale experiment using Bacillus subtilis and computational fluid dynamics were utilized to model the bioaerosol characteristics in a two-bed hospital ward with a constant air change rate (12 ACH). The results indicated that the bioaerosol removal efficiency of unilateral downward ventilation was 50% higher than that of bilateral downward ventilation. Additionally, health care workers (HCWs) and nearby patients had lower breathing zone concentrations in the ward with unilateral downward ventilation. Furthermore, a partition played a positive role in protecting patients by reducing the amount of bioaerosol exposure. However, no obvious protective effect was observed with respect to the HCWs. Only 10% of the bioaerosol was deposited on the surfaces in the ward with unilateral downward ventilation, while up to 35% of the bioaerosol was deposited on the surfaces in the ward with bilateral downward ventilation during the 900 s. The main deposition locations of the bioaerosols were near the wall on the same side of the room as the patient's head in all cases. This study could provide scientific evidence for controlling cross-infection in hospital wards, as well as several guidelines for the disinfection of hospital wards. • Bioaerosol removal efficiency was quantitatively examined in ward with two types of typical downward ventilation. • Temporal and spatial distributions of bioaerosols in ward were determined in four cases. • Time-varying breathing zone concentrations of HCWs and nearby patients was quantitatively analyzed. • Effectiveness of partition in controlling spread of bioaerosols in the ward was explored. [ABSTRACT FROM AUTHOR]

• We explored factors modulating the dynamics of wind-turbine arrays under in-phase and out-of-phase oscillations. • Roll oscillations produced an increase of the combined power output across amplitudes and frequencies. • Combined turbine pitching did not resulted in power increase. • Wake past the arrays is significantly affected by the turbines oscillations. We experimentally explored the impact of in-phase and complete out-of-phase pitch and roll oscillations on the mean power output and the structure of the power fluctuations of turbines within 3 × 2 uniform arrays. The flow past selected configurations was also characterized with hotwire anemometry. The parameter space included combinations of three amplitudes and two frequencies of the turbine oscillations, and two turbine layouts; measurements with fixed units are also included for comparison. Results show that the structure of the flow past the wind-turbine arrays was significantly affected by the frequency of the tower oscillations. The turbines under in-phase pitching induced a signature that extended in the intermediate wake, which was measured up to 7 rotor diameters downwind of the last row of turbines. The roll oscillations produced an increase of the combined power output independent of the amplitude and frequency of the oscillations, where the complete out-of-phase motions resulted in larger values with a maximum at the largest amplitude of oscillations (β = 20 °) of over than 10 %. Opposite behavior occurred with the turbines under pitching, which led to negligible changes or decrease of the combined power with a maximum reduction of ~ 10 %. The spacing of the turbines substantially affected the power from the roll motions; however, this was not the case for the pitching. Finally, an inspection of the cross-correlation of the instantaneous power output of the turbines in the first and second rows revealed the strong modulation of the induced motions on the structure of the power fluctuations. [ABSTRACT FROM AUTHOR]

• We isolated factors affecting turbine power and wake dynamics due to turbine motions. • Pitch and roll induced distinct effects on the structure of the wake and power output. • Mean power increased with moderate tower oscillation regardless of the type of motion. • Oscillation-driven power fluctuations may be due to changes in the blade aerodynamics. Wind-tunnel experiments were performed to inspect the impact of a variety of pitch and roll oscillations of a model wind turbine on the instantaneous power output and wake. Particle image velocimetry and hotwire anemometry were used to characterize the flow in the wake; instantaneous power output was also obtained in each of the configurations. For comparison, measurements were also performed in a fixed wind turbine. Results show that the wake at the turbine symmetry plane is significantly altered by the imposed motions, where rolling induced the lowest momentum deficit. The mean power output of the turbine increased with moderate tower oscillations, namely ≲ 10 ° , independent of the type of motion. We argue that this is due to, at least, two distinctive processes. Namely, a relative gain due to the cube of the relative incoming velocity impinging the rotor in the pitching, and a momentum replenish in the rolling motion The power fluctuations exhibited a peak on the spectral content of the spectrum Φ P coincident with the frequencies of the pitching and rolling. They also revealed the effects of the oscillation within the low-frequency content of Φ P , which was likely due to the oscillation-driven changes in the aerodynamics of the blades. In particular, the pitch reduced the energy of the power fluctuations within frequencies below that of the pitching frequency, with stronger effect at larger amplitude of oscillations, θ. However, the roll motions reduced the energy of the power fluctuations in a relatively narrow band, and notorious only with θ ≳ 10 °. [ABSTRACT FROM AUTHOR]

Under the rapid development of wind turbines, the rotor size has substantially increased in recent years. To meet the key design criteria, finding a trade-off between aerodynamic, structure and noise (ASN) impact becomes a challenging problem. The blade cross-section is the basic element of the blade, its outer contour is the airfoil profile that produces aerodynamic loads as well as noise, and the inner part is the supporting composite material that provides enough stiffness to balance the loads. Modifying local blade sections can adjust the rotors' overall performance. However, in the work of blade-combined ASN optimization, the iterative process using traditional numerical simulation methods becomes extremely heavy. In this study, a sustainable database is created based on a large number of calculations of aerodynamic, structural and noise attributes at various cross-sections. Then a platform named AFML (Airfoil machine learning) for simultaneously predicting the comprehensive performance of the cross-section is constructed by using the integrated Gradient Boosting Regression Tree algorithm. Results show that the prediction accuracy of AFML is acceptable even for unseen inflow conditions. By calling the pre-trained AFML, ASN data of the cross-section can be immediately obtained, and the blade shape and inner structure can be updated quickly. [ABSTRACT FROM AUTHOR]

• Mass loss of concrete exposed to sewage flushing started early within one month. • Concrete at the condition of a low flushing rate deteriorated greatly after 2–3 months. • Corrosion layer formed in the sewage was more porous and had little protective effect. • Sewage flushing could alleviate the microbial induced concrete deterioration. • The designed flow velocity of sewage should not be lower than 1.0 m/s. Fully filled sewers are always subjected to a continuous sewage flushing state, and the corrosion layer of concrete structure formed and its influence on the deterioration would be different from that of partially filled sewers. To distinguish the differences between the deterioration of concrete below and above sewage level in sewers, performance of concrete and the microstructure of the corrosion layer exposed to the mimicked sewage and sulfuric acid flushing at various flow velocities were investigated in the laboratory. The experimental results revealed that the mass loss of concrete exposed to the sewage flushing started early within one month, and it increased with the flow velocity and flushing duration. Although the mass loss of concrete was not obvious at a relatively low flushing rate in the early period, it was considerably increased with serious deterioration after 2–3 months. Moreover, subjected to the mimicked sewage condition, the corrosion layer formed on the surface of specimens was more porous and easily to be washed away, and no clear corrosion front can be found. Such corrosion layer has little protective effect on the concrete as compared with the exposure to the sulfuric acid flushing. It was also unraveled that the sewage flushing at a high flow velocity in sewers can remove the alkaline surface and lead to the formation of a dense biofilm, and both of these behaviors could alleviate the microbial induced concrete deterioration. Referring to the results in the study, the designed flow velocity of sewage is suggested not to be lower than 1.0 m/s in the long run. [ABSTRACT FROM AUTHOR]

As the most important source of commodity grain in China, Northeast China plays a crucial role in guaranteeing national food security. The application of biochar in agricultural ecosystems has shown immense potential in ensuring crop yields while mitigating N 2 O emissions. However, the long-term impacts and mechanisms of successive application of corn stover and its derived biochar on soil N 2 O emission in the corn monocropping region, such as Northeast China, remain unclear. A five-year field experiment was conducted in Northeast China to fill this research gap regarding the soil nitrogen (N) cycle. Three experimental treatments were established: a control with no corn stover or biochar application (CK), corn stover returned yearly at a rate of 7.5 t ha−1 (ST), and biochar added yearly at a rate of 2.6 t ha−1 (BC) corresponding to 35% of the stover addition rate in ST. Identical mineral fertilizers were applied in all three treatments. The total accumulated N 2 O emissions across five analyzed growing seasons within the CK, ST, and BC treatments were 260.2, 184.0, and 151.0 mg N 2 O m−2, respectively, with significant 29.3% and 42.0% decreases observed in ST and BC treatments, respectively, compared with the control. Based on the annual average from 2013 to 2017, ST and BC treatments significantly increased soil pH and total N (TN) content and significantly decreased the levels of NO 3 ––N, NH 4 +-N, and soil bulk density (BD). Additionally, BC treatment remarkably lowered the average NH 4 +-N content than that under ST treatment by 24.1%. Both ST and BC showed a significant inhibitory effect on nitrate reductase (NR), nitrite reductase (NiR), and hydroxylamine reductase (HyR) activities related to denitrification. Soil N 2 O emission was significantly positively correlated with BD, NO 3 –-N, NH 4 +-N, NR, NiR, and HyR activities. Path analysis suggested that N 2 O emissions were primarily driven by NR and HyR activities and NO 3 –-N content. Overall, the applications of corn stover and its derived biochar are a feasible means of mitigating soil N 2 O emissions in the context of continuous corn cropping systems in mid-latitude regions like Northeast China, with biochar being more beneficial than stover application. • Biochar return was more effective in reducing N 2 O emission relative to corn stover. • N 2 O emission was positively correlated with BD, NH 4 +-N, NO 3 －-N, NR, NiR, and HyR. • N 2 O production was mainly attributable to HyR and NR activities and NO 3 －-N levels. • Biochar decreased BD and mineral N, inhibiting the activities of NR, NiR, and HyR. [ABSTRACT FROM AUTHOR]