Wind Environment Research Articles

Impact of natural urban terrain on the pedestrian wind environment in neighborhoods: A CFD study with both wind and buoyancy-driven scenarios

The impact of topography on airflow has been studied at different scales, however the influence of urban natural terrain on local wind conditions is unclear. In this study, the impact of natural urban terrain on mean wind speed at the pedestrian level is investigated. A numerical study is conducted using a Large Eddy Simulation (LES) model for a high-density residential neighbourhood in Singapore with the natural terrain and a flat surface. The following two wind variations are examined (1) low wind speed and high temperature conditions for which the atmospheric boundary layer exhibits unstable thermal stratification; (2) annually averaged wind conditions with neutral thermal stratification. The results show that the overall impact of natural urban terrain on pedestrian wind speed is pronounced when the wind environment exhibits unstable thermal stratification i.e. buoyancy driven flows, compared with wind driven flows. For both cases, the results indicate a localized effect based on building density and proximity to steep terrain with spatial averages as high as approximately 0.8 m/s. In areas characterized by low density, fewer surrounding buildings, or open spaces, it is advisable to model the topography when it is shallow or steeply sloping. For medium density built areas, natural urban terrain modelling is also recommended. However, it is observed that in a high-density region, pedestrian wind flow is more strongly affected by the surrounding buildings than the terrain. These results are potentially important to balance computational cost and accuracy in urban wind simulations in urban areas with various densities and microclimate scenarios.

Buffeting reliability of high-rise bridge tower in mountain area based on CNN-BiLSTM

In recent years, the wind-induced vibration of structures has received a great deal of scholarly attention due to the increasing scale of large structures. In this study, an algorithm that combines a stochastic pseudo excitation method (SPEM), a convolutional neural network (CNN) and a bidirectional long short-term memory network (BiLSTM), named as SPEM-CNN-BiLSTM (SCBL), is proposed. The SCBL is a surrogate model consisting of three different computational modules, in which the SPEM can provide training samples for CNN-BiLSTM (CBL) network architecture, a convolutional layer extracts features of stochastic parameters and a BiLSTM handles time histories of bridge response. The accuracy of the SCBL prediction results is ensured by the set error threshold. The model also accounts for structural uncertainty in the inputs and is adapted during the training step to be more suitable for reliability analysis. According to the output qualified prediction data, the dynamic reliability based on the 99 % threshold is calculated by obtaining its probability density function, and the wind-induced vibration responses of uncertain bridge towers are studied. Firstly, the wind environment of the bridge tower was analyzed, and the average wind speed of 20 m/s among the bridge area was obtained by field measurements, and Computational Fluid Dynamics (CFD). Secondly, the proposed artificial neural network algorithm is applied to bridge jitter reliability analysis and compared with the traditionally recognized methods: the Monte Carlo method (MCM) and the stochastic pseudo excitation method (SPEM). The results of SCBL calculations are closer to the results of MCM than those of other methods. Additionally, the computational efficiency of the method is improved by 40 times over MCM and 2 times over SPEM. Finally, the data generated by the SCBL method will be used for reliability analysis. Uncertainties in structure, wind speed, and yaw angle all contribute to the uncertainty and dispersion of the stochastic response prediction. Among them, the uncertainty in wind speed has the greatest impact on the reliability.

Review of OpenFOAM applications in the computational wind engineering: from wind environment to wind structural engineering

Review of OpenFOAM applications in the computational wind engineering: from wind environment to wind structural engineering

Winter indoor thermal environment and livability analysis of traditional residential houses in northeast Sichuan, China

With the rapid development of the national economy, increasing attention has been given to the living environment in rural areas, especially indoor thermal and wind environments. This study conducted on-site measurements and questionnaire surveys during winter in the indoor environment of five villages in northeastern Sichuan. Eighty-nine traditional residences were selected to investigate their fundamental characteristics, indoor thermal environment, humidity conditions, and comfort levels. Questionnaires and comparative experiments were also conducted with natives and locals. This combination of objective data and subjective feedback provides a comprehensive perspective for assessing the indoor thermal environment. The results showed that when expressed as neutral temperature and humidity, the temperature difference was 2.36 °C, with little humidity difference. Residents exhibited higher tolerance towards the local thermal and humidity environment than nonlocal volunteers, who showed greater sensitivity to it. In addition, residents had a Predicted Mean Vote (PMV) value of −0.69 and a heat acceptance value of −1.78, while non-local volunteers had a PMV value of −0.76 and a heat acceptance value of −1.32. A detailed evaluation and analysis of the relationship between the indoor thermal environment and human comfort of local residential houses was carried out, providing technical guidance for energy conservation and thermal insulation of local buildings.

Wind-driven suspended triboelectric-electromagnetic hybrid generator with vibration elimination for environmental monitoring in the high-voltage power transmission line

The sustainable development of the high-voltage power transmission system puts forward more significant requirements IoT sensor network. Currently, a large number of the IoT sensors are installed on the high-voltage transmission lines, and environmental wind energy harvesting around the outdoor power transmission lines enables a promising and feasible solution to supply distributed sensors. However, the traditional floor-mounted wind energy nanogenerator with high requirements for placement and fixation is no longer applicable to the suspension scenario of the high-voltage power transmission lines. In this work, a wind-driven suspended triboelectric-electromagnetic hybrid generator (WS-TEHG) is designed as a suspended wind cup with a three-layered integrated structure, which can be integrated with the damping structure that hanged and installed on the power transmission line, demonstrating the simultaneously achieving high efficiency wind energy harvesting and the operation stability of the device. After the structural and material optimization, WS-TEHG can achieve efficient energy collection under wide-range of the wind speed from 2.6 to 17.3 m s−1, whose TENG and EMG produced instantaneous peak power from 0.2 to 7.9 mW and 0.6–85.1 mW, respectively. Moreover, a standardized power management based on LTC 3588-based double-channel circuit was established to co-manage the outputs of the two generating modules in the hybrid generator and enhance the continuous stability of the standardized voltage output, demonstrating a shorter undervoltage charge accumulation, a faster start-up process, a lower power consumption compared with the traditional power management. Finally, a self-powered environmental monitoring system by a WS-TEHG equipped with a standardized power management circuit was developed to provide the weather and climate information around the power transmission lines, thereby demonstrating a potential and feasible for large-scale self-powered application in the field of the high-voltage power transmission lines.

Experimental investigation on aerodynamic characteristics of flexible wing MAV under horizontal gust

A flexible wing micro air vehicle and a rigid wing micro air vehicle, both with flying wing designs, were designed and developed, and the aerodynamic characteristics of the flexible micro air vehicle and the rigid micro air vehicle under steady wind and horizontal gust were studied in a wind tunnel. The difference in aerodynamic characteristics between flexible wing and rigid wing micro air vehicles was given. The research results showed that the aerodynamic characteristics of a flexible wing were better than those of a rigid wing under both steady wind and horizontal gust environments, and a flexible wing had the ability to delay stall and mitigate the impact of gust, which was beneficial to stable flight. The particle image velocimetry measurement results showed that due to the deformation of the flexible wing, the flow patterns on the rigid wing and flexible wing surfaces were different, resulting in changes in the aerodynamic characteristics of micro air vehicles.

Finite element analysis of radial temperature of transmission conductor in low-temperature environment

Abstract Most existing studies simplify conductors as isothermal cylinders, neglecting their actual structure and the inter-conductor contacts. This is especially problematic in regions like Northeast and Northwest China, where the conductors face harsh working environments due to significant seasonal temperature variations. Additionally, there is a lack of research under extreme low-temperature conditions. Considering these factors, a temperature field in low-temperature environments was established based on the heat conduction equation. A finite element model and a mathematical model for the transmission conductor were developed using the actual structure of the JL/G1A-240/30 type steel-core aluminum stranded conductor as a reference. Constraint conditions were set, and the model was simulated under various environmental conditions using the finite element ANSYS software. This simulation calculated the radial temperature distribution of the conductors in low-temperature environments, along with the combined effects of transmission line current load, air convection cooling, sunlight intensity, and wind speed on the radial temperature distribution. The results indicate that this method can effectively determine the radial temperature values of transmission conductors under different meteorological conditions, which are significantly influenced by environmental temperature and wind speed. This is beneficial for enhancing the operational safety and stability of transmission lines, achieving dynamic capacity expansion, and improving the transmission capacity of the lines.

Adaptivity of a leaf-inspired wind energy harvester with respect to wind speed and direction

Environmental wind is a random phenomenon in both speed and direction, though it can be forecasted to some extent. An example of that is a gust which is an abrupt, but short-time change in wind speed and direction. Being a free and clean source for small-scale energy scavenging, attraction of wind is rapidly growing in the world of energy harvesters. In this paper, a leaf-like flapping wind energy harvester is introduced as the base structure in which a short-span airfoil is attached to the free end of a double-deck cantilever beam. A flap mechanism inspired by scales on sharks’ skin and a tail mechanism inspired by birds’ horizontal tail are proposed for integration to the base harvester to make it adaptive with respect to wind speed and direction, respectively. The use of the flap mechanism increases the leaf flapping frequency by +2.1 to +11.5 Hz at wind speeds of 1.5 to 6.0 m s−1. Therefore, since the output power of a vibrational harvester is a function of vibration frequency, a figure of merit or an efficiency parameter related to the output power will increase, as well. On the other hand, if there is a misalignment between the harvester’s heading and wind direction due to change of the latter one, the harvesting performance deteriorates. Although the base harvester can realign in certain ranges of sideslip angle at each wind speed, when the tail mechanism is integrated into that, it broadens the range of realignable sideslip angles at all the investigated wind speeds by up to 80 ∘ .

Bioclimatic analysis and spatial distribution of fascioliasis causative agents by assessment of Lymnaeidae snails in northwestern provinces of Iran

BackgroundSnails of the Lymnaeidae family are the intermediate hosts of Fasciola species, the causative agents of fascioliasis. The purpose of this study was to determine the prevalence of Fasciola species in lymnaeid snails and to investigate the association of geoclimatic factors and Fasciola species distribution in northwestern provinces of Iran using geographical information system (GIS) data.MethodsA total of 2000 lymnaeid snails were collected from 33 permanent and seasonal habitats in northwestern Iran during the period from June to November 2021. After identification by standard morphological keys, they were subjected to shedding and crushing methods. Different stages of Fasciola obtained from these snails were subjected to the ITS1 polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method for species identification. The associations of weather temperature, rainfall, humidity, evaporation, air pressure, wind speed, elevation, and land cover with the distribution of Fasciola species were investigated. Geographical and statistical analysis was performed using ArcMap and SPSS software, respectively, to determine factors related to Fasciola species distribution.ResultsOf the 2000 snails collected, 19 were infected with Fasciola hepatica (0.09%), six with F. gigantica (0.03%), and 13 with other trematodes. Among geoclimatic and environmental factors, mean humidity, maximum humidity, and wind speed were significantly higher in areas where F. hepatica was more common than F. gigantica. The altitude of F. hepatica-prevalent areas was generally lower than F. gigantica areas. No significant relationship was observed between other investigated geoclimatic factors and the distribution of infected snails.ConclusionsThe present study showed the relationship of humidity and wind speed with the distribution of snails infected with F. hepatica or F. gigantica in the northwestern regions of Iran. In contrast to F. gigantica, F. hepatica was more prevalent in low-altitude areas. Further research is recommended to elucidate the relationship between geoclimatic factors and the presence of intermediate hosts of the two Fasciola species.Graphical

Multi-Scale Urban Natural Ventilation Climate Guidance: A Case Study in the Shijiazhuang Metropolitan Area

The rapid development of urbanization has caused obstructed urban natural ventilation and the contribution rate of urbanization is relatively high. Therefore, there is an urgent need for urban development planning that should respect natural ventilation and local climate to reduce negative impacts. By optimizing the urban construction layout to reduce obstruction and leave a passageway for wind to blow in, the natural ventilation environment could be improved. This paper presents a promising approach for natural ventilation planning at both the city and community scales. Based on the assessment of wind environment, heat island intensity, and ventilation potential, the results revealed that winds blowing from the western and northern mountainous area of Shijiazhuang play a natural ventilation inlet role which can provide clean air. The SSHI and SHI were mainly distributed within the Second Ring Road, which has a large proportion of the low ventilation potential level. Thus, six first-class ventilation corridors and thirteen secondary corridors were recommended, which were set to be adapted to the dominant wind direction. Subsequently, an urban climate analysis map (UCAnMap) was developed considering climate sensitivity, and planning recommendations were provided for different climate zones. The relationship between architectural spatial structure and ventilation efficiency was analyzed; the results revealed that increasing the height of the buildings will decrease the proportion of comfortable wind zones, and the overall ventilation efficiency will weaken, so the average building height of a typical block should be controlled within 45 m, which matches ventilation performance requirements. The ventilation efficiency of the block has a certain negative correlation with the building density, and as the building density decreased by more than 10%, the proportion of the comfortable wind zones could increase by 4–5%.

Cannibals in PARADISE: The Effect of Merging Interplanetary Shocks on Solar Energetic Particle Events

Gradual solar energetic particle (SEP) events are associated with shocks driven by coronal mass ejections (CMEs). The merging of two CMEs (so-called cannibalistic CMEs) and the interaction of their associated shocks has been linked to some of the most powerful solar storms ever recorded. Multiple studies have focused on the observational aspects of these SEP events, yet only a handful have focused on modeling similar CME–CME interactions in the heliosphere using advanced magnetohydrodynamic (MHD) models. This work presents, to our knowledge, the first modeling results of a fully time-dependent 3D simulation that captures both the interaction of two CMEs and its effect on the acceleration and transport of SEPs. This is achieved by using an MHD model for the solar wind and CME propagation together with an integrated SEP model. We perform different simulations and compare the behavior of the energetic protons in three different solar wind environments, where a combination of two SEP-accelerating CMEs are modeled. We find that particle acceleration is significantly affected by the presence of both CMEs in the simulation. Initially, less efficient acceleration results in lower-energy particles. However, as the CMEs converge and their shocks eventually merge, particle acceleration is significantly enhanced through multiple acceleration processes between CME-driven shocks, resulting in higher particle intensities and energy levels.

Hidden regulator-based rotational triboelectric nanogenerator with tracing optimal working condition

The research on the rotational triboelectric nanogenerators (R-TENGs) is actively conducted by numerous groups, but its friction-based operation mechanism makes it challenging to simultaneously ensure electrical performance (including output voltage and power) and mechanical performance (such as stability and durability). In this study, a physically intelligent Hidden regulator-assisted design-based R-TENG (HR-TENG) is developed based on the self-adaptive mechanical kinetic design. The relationships between engaged forces and the output performance of R-TENG are investigated, and the normal force acting on the contact interface is unveiled as a hidden core of the output performance of R-TENG. Here, HR-TENG traces the optimal working conditions in real-time according to input energy conditions by itself with spontaneously adjusted friction by controlling the normal force with mechanically self-adjustable components. HR-TENG can be operated in a wide range of conditions of input energy source, and exhibit self-adaptive electrical performance while maintaining mechanical performance depending on the input energy conditions without human intervention. The behaviors of the mechanically self-adjustable components depending on the operation of HR-TENG are analyzed theoretically and experimentally based on kinetic dynamics, and the effect of the normal force on the electrical and mechanical output performances is investigated. The average coefficient of inner friction of HR-TENG is 0.27, and the maximum output voltage and peak power are 254 V and 0.726 mW, respectively. As a proof-of-concept demonstration, the electrical output of HR-TENG under a wide range of input wind conditions (wind speed of 4–22 m/s) is investigated, and the real-time tracing ability of HR-TENG to the optimal working conditions in the continuously changing wind environment is analyzed. The kinetic design of HR-TENG with the hidden regulator (normal force), which affects multiple direct factors of electrical and mechanical performances, can be introduced to various R-TENGs as a key strategy, and thus, it can be expected to serve as a design guideline for futuristic physical intelligence-assisted smart energy harvesters.

Thinking of Green, Low Carbon, and Energy-Saving Designs Based on the Variable Ventilation of Natatoriums: Taking the Jiading Natatorium of Tongji University as an Example

With the increasing demand for sports activities, sports architecture is flourishing. Creating a comfortable and healthy fitness environment while reducing energy consumption has become a focus for architects. Taking the Jiading Natatorium at Tongji University in Shanghai as an example, this study researched green energy in the variable ventilation of sports venues. The Autodesk Ecotect Analysis 2011 was used to conduct computational fluid dynamics (CFD) simulation analyses on four scenarios of opening and closing the swimming pool’s roof, with ventilation velocity as the primary evaluation indicator to assess the ventilation environment of each scenario. The relationship between the opening ratio of the roof and the ventilation environment of sports buildings was explored. The results showed that when the opening ratio is 37.5%, it achieves good ventilation effectiveness and avoids excessive wind pressure. The study also summarized six common forms of opening and closing roof structures and compared the differences in wind environments of different roof forms. The results indicated that the shape and opening ratio of the roof has a decisive impact on the distribution of indoor wind speed in buildings. Six optimal opening ratios for different roof forms in summer and suitable site conditions were summarized, providing a reference for the design and selection of swimming pool roofs. Furthermore, the wind speed distribution of different roof types showed a trend of gradually becoming uniform with the increase in opening area. However, the position of the wind speed peak is related to the form and size of the roof opening. This research provides valuable references for the low carbon and energy-efficient design of future swimming pool sports buildings.

The application of a high-density street-level air temperature observation network (HiSAN): Spatial and temporal variations of thermal and wind condition in different climatic condition types

Different patterns of urban development will result in different characteristics of the urban heat island effect (UHI). In order to explore the impacts of urban environment characteristics, wind conditions, and climatic condition types on UHI over different periods, this study adopted Tainan City as the study site, and utilized the surface roughness length and wind prediction, to evaluate the correlation between wind conditions and UHI, as well as the thermal environment affected by different environmental. The UHI characteristics were evaluated by using 100 measurement stations (HiSAN) located in different urban environments. The results revealed the expansion of the daily temperature range was associated with an increase in the eastwest UHI centroid point movement; wind conditions affected north-south shifts of UHI centroid point. The built environments was positively correlate with daytime (0.24) and nighttime (0.68) temperatures. Daytime water bodies notably cool surroundings (correlation -0.52), and green spaces enhance nighttime cooling (correlation -0.64). Wind speed negatively correlates with UHI deviation values during the daytime (-0.17) and nighttime (-0.58). The study highlights the impact of wind speeds and temperature ranges on UHI movement, emphasizing effective ventilation's role in urban cooling and quantifying the importance of water and green space in mitigating UHI.

On the Durability Performance of Two Adhesives to Be Used in Bonded Secondary Structures for Offshore Wind Installations.

The development of offshore wind farms requires robust bonding solutions that can withstand harsh marine conditions for the easy integration of secondary structures. This paper investigates the durability performance of two adhesives: Sikadur 30 epoxy resin and Loctite UK 1351 B25 urethane-based adhesive for use in offshore wind environments. Tensile tests on adhesive samples and accelerated aging tests were carried out under a variety of temperatures and environmental conditions, including both dry and wet conditions. The long-term effects of aging on adhesive integrity are investigated by simulating the operational life of offshore installations. The evolution of mechanical properties, studied under accelerated aging conditions, provides an important indication of the longevity of structures under normal conditions. The results show significant differences in performance between the two adhesives, highlighting their suitability for specific operating parameters. It should also be noted that for both adhesives, their exposure to different environments (seawater, distilled water, humid climate) over a prolonged period showed that (i) Loctite adhesive has a slightly faster initial uptake than Sikadur adhesive, but the latter reaches an asymptotic plateau with a lower maximum absorption rate than Loctite adhesive; and (ii) a progressive deterioration in the tensile properties occurred following an exponential function. Therefore, aging behavior results showed a clear correlation with the Arrhenius law, providing a predictive tool for the aging process and the aging process of the two adhesives followed Arrhenius kinetics. Ultimately, the knowledge gained from this study is intended to inform best practice in the use of adhesives, thereby improving the reliability and sustainability of the offshore renewable energy infrastructure.

Analysis and Reflection on the Green, Low-Carbon, and Energy-Saving Design of the Super High-Rise Building

Shanghai Tower has become a new landmark of Shanghai. In the current trend advocating green building and energy efficiency, considerations of wind loads and thermal characteristics of the perimeter structure of Shanghai Tower are crucial. This paper conducts comparative simulation studies on the wind environment of Shanghai Tower using Ecotect software, and stress analyses and thermal simulations of the perimeter structure using ANSYS software. The study compared three buildings’ surface wind pressure distributions using models with equal-volume and circular cross-sections. We found that the unique exterior design of the Shanghai Tower results in a more regular and uniform distribution of wind pressure on its surface compared to both circular and square planar models, with a lower average wind pressure value. In addition, the stress analysis results indicate significant differences in deformation and stress distribution between the windward and leeward sides. Enhancing the bending moment detection of the peripheral structure and optimizing the layout of detection points are recommended. Thermal simulation results show excessive heat conduction flux in winter conditions, suggesting optimization using passive energy-saving methods such as light-sensitive thermal insulation materials during winter. This research is a reference for designing other super-tall buildings prioritizing low-carbon energy efficiency and structural safety.

Study on the Impact of Tree Species on the Wind Environment in Tree Arrays Based on Fluid–Structure Interaction: A Case Study of Hangzhou Urban Area

In order to improve the level of the urban living environment and improve the comfort level of the microclimate, this paper investigates and simulates numerically the influence on the wind environment of different tree species in various tree array layouts, aiming to enhance wind comfort in tree landscapes and reduce the risk of high wind speeds. Initially, the study analyzes the commonly used tree species in Hangzhou’s urban tree arrays (beech, soapberry, and camphor trees), summarizing three types of tree array layouts: retention, through, and enclosure. Subsequently, standard tree models are established to define their crown porosity, trunk elastic modulus, and other physical characteristics. Using fluid–structure interaction methods, the impact of different tree species on the wind environment within various tree array layouts is numerically simulated at a wind speed of 14 m/s. In conclusion, the retention layout is most effective in controlling wind speed. Camphor trees perform excellently in reducing wind speed within both retention and enclosure tree array layouts, with wind reduction efficiencies of 16.06% and 14.09%, respectively. Soapberry trees show optimal wind speed reduction in the through layout, achieving 12.31%.

Fast Prediction and Optimization of Building Wind Environment Using CFD and Deep Learning Method

CFD offers advantages over wind tunnel experiments in the prediction and optimization of building wind environment; however, the computational costs associated with optimizing architectural wind environment remain a challenge. In this study, an approach that combines deep learning techniques with CFD simulations is proposed for the prediction and optimization of the architectural wind environment efficiently. A dataset of wind field is constructed using CFD simulation, considering various wind directions, wind speeds, and building spacing. Subsequently, a U-net deep learning model is trained as a surrogate model to rapidly predict the architectural wind field under different conditions. The results indicate that the model can accurately predict the wind field in buildings. The prediction time of building wind field is only 1/900 of that of CFD simulations, making it a viable surrogate model for wind environment optimization. Furthermore, considering all the building layouts and inflow conditions examined in this study, the maximum and minimum uniform wind speed area ratios Auni are 0.84 and 0.13, respectively. Under a single inflow speed, the maximum improvement in the Auni is 0.4, with an improvement rate of 48%. The results demonstrate the effectiveness of the proposed method as an efficient approach for optimizing architectural wind environment.

MoS2@ZIF-8-based aerogel with multiscale biomimetic structure achieving all-day desalination and wastewater purification

In emerging freshwater generation strategy, solar driven evaporation technology has been brought into focus owing to its non-pollution and facile facilities. However, maintaining high freshwater yield remains a challenge under natural circumstances. Herein, MoS2@ZIF-8-based aerogel featuring a lotus root hourglass-shaped structure (denoted as LMZA) for efficient freshwater production via hybrid energy harvesting is ingeniously devised. After being integrated with metallic 1 T phase MoS2 and a vertically aligned porous structure, LMZA not only achieves an outstanding evaporation rate at different incident angles and intensities, but also utilizes wind or environmental energy for evaporation. More importantly, the proposed LMZA also achieved a fast evaporation rate of 8.47 kg m-2h−1 under 4.0 m s−1 without solar irradiation, which fully eliminated the impact of solar intermittency. Afterward, LMZA with a cross-scale hierarchical structure for desalination exhibits an evaporation rate of up to 2.08 kg m-2h−1 under one sun irradiation in 20 wt% brine, and possesses exceptional adaptability and stability. Besides, another advantage of LMZA is the effective purification of cadmium-containing wastewater through water evaporation and in situ adsorption. The removal efficiency is 74 % under one sun irradiation, and the condensed water with undetected Cd(II) heavy metal ions was obtained. More importantly, combined with ambient factors such as wind and ambient temperature in the natural environment, the home-made device achieves all-day freshwater generation with a daily yield of 27.08 kg m−2. The investigation of the device and LMZA pioneers a novel design concept for high yield freshwater generation in practical applications.

Vibration control and stroke evaluation of bi-directional bistable nonlinear energy sinks applied in monopile offshore wind turbines during emergency shutdown

Monopile offshore wind turbines (OWTs) in complex wind and wave environments can generate more excessive vibrations in the fore-aft (FA) and side-to-side (SS) directions when emergency shutdowns occur, and therefore damping techniques to alleviate such vibrations are essential. Due to the potential frequency detuning (reduced damping effectiveness) of traditional tuned mass dampers (TMDs) and stroke issues (such as large strokes of TMDs and limited maximum strokes of unidirectional nonlinear energy sinks (NESs)) in existing absorbers, this paper proposes a bi-directional bistable nonlinear energy sink (BBNES) to mitigate the vibration of the OWT in the FA and SS directions during the emergency shutdown. First, the proposed device and its operation mechanism are elaborated, and an optimization method for the device is introduced. Then, the dynamic analysis model of the BBNES is developed for vibration control of the OWT and incorporated into a fully coupled numerical simulation tool with high fidelity, FAST v8. Subsequently, the responses of the OWT without and with the proposed BBNES and the bi-directional tuned mass damper (BTMD) are exhaustively investigated under diverse conditions (including mass ratios, wind-wave loadings, emergency shutdown times, wind-wave misalignments, and 1st mode natural frequencies of the OWT) to reveal their performances and compare them. The research results show that under most conditions, the BBNES and BTMD have a similar damping performance in the FA direction, whereas the BBNES has a slightly lower damping performance in the SS direction than the BTMD. In addition, except for the wind velocity of 8 m/s at the hub and the wind-wave misalignment of 90°, the FA stroke of the BBNES with a small mass ratio (i.e., 0.01∼0.035) is significantly smaller than that of the BTMD with the same mass ratio by more than 1.1 m, and even up to about 4 m. The SS stroke of the BBNES is slightly greater than that of the BTMD, and in most cases, the difference between both is less than 0.52 m. Therefore, the BBNES is superior to the BTMD in this regard. When the 1st mode natural frequency of the OWT decreases, the BTMD can lose its tuning efficacy and makes the tower more susceptible to resonance caused by 1p and wave loadings, while the BBNES is not affected by the 1st mode natural frequency variation of the OWT, demonstrating its stronger robustness.