Natural Wind Speed Research Articles

Analysis of structural dynamic response of vertical sound barriers under natural wind and vehicle induced pulsating wind effects

Abstract Aiming at the influence of natural wind and vehicle-induced pulsating wind on vertical sound barriers, a finite element plug-in panel sound barrier is established based on the finite element method for dynamic response analysis. This paper establishes a sound barrier finite element analysis model based on finite element analysis software. It takes the 8-span vertical sound barrier as the basic working condition to analyze the dynamic response analysis of the sound barrier structure under the action of natural wind of different grades, i.e., the influence of pressure and displacement; the dynamic response of the sound barrier structure with a natural wind speed of 7 grades or more. In addition, it analyzes the dynamic properties of the sound barrier structure caused by train-induced pulsating wind pressure at speeds of more than 200 km/h, i.e., the influence of pressure and displacement, and investigates the dynamic characteristics of different vehicles with different wind speeds, pressure, and displacement. Furthermore, the response of the vertical sound barrier at different vehicle speeds is also explored, and the results are compared to examine its dynamic response. The research findings show that the sound barrier structure does not resonate during the self-resonance analysis, but the vibration of adjacent sound barrier panels affects each other. As natural wind speeds increase, the displacement of the steel column endpoints of the vertical sound barrier gradually increases; along the length of the sound barrier, the change of the peak pressure at the top of the steel columns and the top of the unit plate shows a symmetrical trend, and the displacements of the steel columns and the top of the unit plate show a trend of gradual increase in the travelling direction, and they both increase at the end of the column. The displacement of the top of the steel column and the top of the unit plate both show a trend of gradual increase along the direction of the vehicle, and both reach the maximum value at the end of the steel column and the unit plate. With the increase in vehicle speed, the overall peak displacement value also increases synchronously.

Study on the Effect of Natural Wind on the Smoke Spread Law of Extra-Long Tunnel Fires with Inclined Shafts for Air Supply and Exhaust

High-temperature smoke generated by tunnel fires is the most important factor causing casualties. To explore the influence of natural wind on fire smoke movement in an extra-long highway tunnel based on the Taihang Mountain Tunnel, the distribution law of natural wind in the tunnel was obtained by on-site monitoring of the meteorological conditions at the tunnel site. A three-dimensional fire dynamics tunnel model considering an inclined shaft smoke exhaust was established, and the influence of natural wind on tunnel temperature distribution, smoke spread and smoke exhaust efficiency was studied. The results show that the natural wind speed of the Taihang Mountain Tunnel is mainly concentrated at 0~3 m/s. The main wind direction of the natural wind on the left tunnel is opposite to the driving direction, and the distribution probability of the main wind direction in each section is 81.27% and 72.15%, respectively. The main wind direction of the right tunnel is the same as the driving direction, and the distribution probability of the main wind direction in each section is 56.78%, 69.73%, 67.32% and 64.65%, respectively. The negative natural wind can inhibit the smoke spread downstream of the smoke exhaust port, but it is not conducive to the smoke exhaust. The positive natural wind promotes the smoke spread to the downstream of the smoke exhaust port, and the larger the natural wind speed, the longer the spread length. Natural wind reduces the smoke exhaust efficiency. For positive or negative natural wind with a guaranteed rate of 70%, the smoke exhaust efficiency is reduced by 27.76% and 15.59%, respectively, compared with the condition without natural wind. The research results can provide a useful reference for the design of fire smoke exhausts and smoke control schemes in extra-long highway tunnels.

Multitemporal Field-Based Maize Plant Height Information Extraction and Verification Using Solid-State LiDAR

Plant height is regarded as a key indicator that is crucial for assessing the crop growth status and predicting yield. In this study, an advanced method based on solid-state LiDAR technology is proposed, which is specifically designed to accurately capture the phenotypic characteristics of plant height during the maize growth cycle. By segmenting the scanned point cloud of maize, detailed point cloud data of a single maize plant were successfully extracted, from which stem information was accurately measured to obtain accurate plant height information. In this study, we will concentrate on the analysis of individual maize plants. Leveraging the advantages of solid-state LiDAR technology in precisely capturing phenotypic information, the data processing approach for individual maize plants, as compared to an entire maize community, will better restore the maize’s original growth patterns. This will enable the acquisition of more accurate maize plant height information and more clearly demonstrate the potential of solid-state LiDAR in capturing detailed phenotypic information. To enhance the universality of the research findings, this study meticulously selected key growth stages of maize for data validation and comparison, encompassing the tasseling, silking, and maturity phases. At these crucial stages, 20 maize plants at the tasseling stage, 40 at the flowering stage, and 40 at the maturity stage were randomly selected, totaling 100 samples for analysis. Each sample not only included actual measurement values but also included plant height information extracted using point cloud technology. The observation period was set from 20 June to 20 September 2021. This period encompasses the three key growth stages of maize described above, and each growth stage included one round of data collection, with three rounds of data collection each, each spaced about a week apart, for a total of nine data collections. To ensure the accuracy and reliability of the data, all collections were performed at noon when the natural wind speed was controlled within the range of 0 to 1.5 m/s and the weather was clear. The findings demonstrate that the root mean square error (RMSE) of the maize plant height data, procured through LiDAR technology, stands at 1.27 cm, the mean absolute percentage error (MAPE) hovers around 0.77%, and the peak R2 value attained is 0.99. These metrics collectively attest to the method’s ongoing high efficiency and precision in capturing the plant height information. In the comparative study of different stem growth stages, especially at the maturity stage, the MAPE of the plant height was reduced to 0.57%, which is a significant improvement compared to the performance at the nodulation and sprouting stage. These results effectively demonstrate that the maize phenotypic information extraction method based on solid-state LiDAR technology is not only highly accurate and effective but is also effective on individual plants, which provides a reliable reference for applying the technique to a wider range of plant populations and extending it to the whole farmland.

Research on a New Soundscape Evaluation Method Suitable for Scenic Areas

Existing studies have focused mainly on the environmental quality of scenic spots, such as sufficient oxygen content in the air and a high concentration of negative oxygen ions. The perceptions of soundscape in scenic areas are generally good, but there are few reports on the quantitative evaluation of soundscape quality in scenic areas. In this study, we analysed existing methods for evaluating the soundscape of a landscape, evaluated the soundscape comfort of scenic spots, analysed and refined the natural environmental factors affecting the soundscape, and proposed for the first time to use physical environmental indicators such as the air temperature difference, relative humidity, natural illuminance ratio and wind speed as environmental evaluation variables. A quantitative method was used to calculate the soundscape comfort index (SSI) of the landscape. The physical environmental indicators related to famous scenic spots in China, namely, Qingcheng mountain field testing and a subjective soundscape of tourist satisfaction survey, were used to calculate the corresponding soundscape comfort index values, and a quantitative analysis of soundscape comfort and differences in temperature, relative humidity, the illumination ratio, and the correlation between the equivalent sound level A was performed. The measured values of the temperature difference and light ratio were significantly correlated with the soundscape comfort index. The distribution of sound landscape comfort was given by a GIS map, and soundscape comfort was evaluated scientifically. The correlations between soundscape comfort and landscape patch number (PN), landscape patch density (PD), diversity index (Shannon), and landscape shape index (LSI) were quantitatively analysed, which confirmed that the perception of soundscape comfort was affected by landscape space to different degrees. This study has scientific significance and application value for the soundscape evaluation of scenic areas and has significance for soundscape evaluation and design strategies for urban landscapes.

Experiments and CFD simulation of downwash airflow and fog distribution discharged from a single-rotor UAV fitted with a pulse-jet thermal fogging machine

A single-rotor UAV fitted with a pulse-jet thermal fogging machine was developed. Computational fluid dynamics (CFD) was employed to simulate the downwash airflow and fog distribution of a single-rotor UAV fitted with a pulse-jet thermal fogger. The developed CFD models were validated in three steps by comparing the calculated results with the measurement experiments. Predicted air velocities of the single-rotor UAV downwash airflow agreed well with measured velocities. The model was also able to predict the fog droplet deposition density of the pulse-jet thermal fogger alone, and fitted to the single-rotor UAV, with the relative errors within 20% and 30%, respectively. The validated CFD model was then employed to investigate the effects of the headwind, crosswind and UAV operating height on the downwash airflow and the fog distribution. Results indicated that when the pulse-jet thermal fogging machine was mounted on the UAV, crosswinds needed to be avoided. At the UAV flight speed of 2 m s−1 and natural wind speed of 1 m s−1, a modest headwind appearance could help improve thermal fogging efficiency at different operating heights. The results have important research value and practical significance for improving the pesticide efficiency of UAV sprayers.

Construction and Evaluation of The Wind Tunnel Technique for Estimating Ammonia Volatilization from Land

Agriculture is mainly responsible for ammonia (NH3) volatilization. Among all agricultural activities, livestock and especially animal manures are the most important sources of NH3 emissions. Manure application which not only exacerbate greenhouse gas emissions, but also leads to eutrophication of water bodies. Many studies have shown that surface application of manure can lead to large ammonia losses and run off, on the other hand that tillage can substantially reduce these losses. It is necessary to determine ammonia flux from manure-amended soils to improve management manure handling practices for minimizing agriculture’s impact on the environment. From this point of view, one of the direct measured method was used to determine this volatilization. The objections of this work were: i) The design, construction, physical calibration, and operation of the little wind tunnels. ii) Recover ammonia loss from bovine slurry by little wind tunnel method. iii) Determine the effect of slurry application depth on ammonia emission. The little wind tunnel system consisted of plastic canopy covering the treatment area (2 m long by 0.5 m wide). By was using a fan, it was imitated the natural wind speed in the test area (1-1.5 m/s). Nitrogen losses were measured with this method in surface application, 50 mm and 100 mm subsurface. In the surface application, the highest ammonia emission was observed. It was approximately 68% higher in compared to another methods. There is significantly (P=0.05) different in the ammonia emission, between the surface apply method and injection manure in soil methods. But There isn’t any significantly different between ammonia emission amount in injection subsurface methods (100 mm and 50 mm deep).

Wind Speed Prediction Based on Error Compensation

Wind speed prediction is very important in the field of wind power generation technology. It is helpful for increasing the quantity and quality of generated wind power from wind farms. By using univariate wind speed time series, this paper proposes a hybrid wind speed prediction model based on Autoregressive Moving Average-Support Vector Regression (ARMA-SVR) and error compensation. First, to explore the balance between the computation cost and the sufficiency of the input features, the characteristics of ARMA are employed to determine the number of historical wind speeds for the prediction model. According to the selected number of input features, the original data are divided into multiple groups that can be used to train the SVR-based wind speed prediction model. Furthermore, in order to compensate for the time lag introduced by the frequent and sharp fluctuations in natural wind speed, a novel Extreme Learning Machine (ELM)-based error correction technique is developed to decrease the deviations between the predicted wind speed and its real values. By this means, more accurate wind speed prediction results can be obtained. Finally, verification studies are conducted by using real data collected from actual wind farms. Comparison results demonstrate that the proposed method can achieve better prediction results than traditional approaches.

Research on time-varying meshing stiffness of wind turbine gearbox considering tooth surface wear

The time-varying meshing stiffness (TVMS) is an important element of the gear system. In this paper, the TVMS of each gear set of a wind turbine gearbox is calculated based on the principle of potential energy method, where wear is the most likely failure in the operation of a wind turbine gearbox. Therefore, the Archard wear model is brought into it, and theoretically the analytical formula of stiffness considering tooth wear is derived, and the time-varying wear depth is deduced as the natural wind speed keeps changing and the input torque of the wind turbine gearbox keeps changing. The interrelationship between gear tooth wear and meshing pressure angle and number of meshes is studied in depth, and the TVMS of each gear set under wear is calculated using the modified tooth profile model. The results show that the tooth profile wear depth is related to the gear meshing angle, and the tooth profile wear depth becomes larger as the number of meshes increases, thus reducing the TVMS of the wind turbine, and the TVMS shows irregular fluctuations under time-varying wear.

Comparative Study of Grid Frequency Stability Using Flywheel-Based Variable-Speed Drive and Energy Capacitor System

Recently, there has been a rise in the integration of renewable energy sources into power grids. As a result of this, there is a need to carry out new studies in order to understand the dynamics of power grids during disturbances that is mainly caused by the stochastic nature of wind energy. The operation of modern power grids that are tied to wind farms follows a stipulated grid requirement or grid codes, considering the allowable threshold frequency variation during grid dynamics. This paper presents a comparative study of two frequency control schemes considering grid frequency stability using two frequency control topologies. A novel dynamic flywheel scheme with a doubly fed induction generator (DFIG) variable-speed wind turbine with the coordinated control of excess kinetic energy and mechanical torque during operation was the first scheme, and a control strategy of an energy capacitor system (ECS) with a squirrel cage induction generator fixed-speed wind turbine (FSWT) was the second scheme. The salient part of this study was that the DFIG maximum point power tracking for effective smoothing of the output of the wind generator in the first scheme was designed based on the control strategy of its reference power to achieve smoothing of the wind power at the terminals of the wind generator. The model system employed in this work was a wind farm that is tied to a conventional power grid made of steam and hydro synchronous turbines. For an effective and fair comparison of results, the same natural wind speed was used in PSCAD/EMTDC for both schemes. When no control, Scheme 1, and Scheme 2 were implemented, the frequency dips were 47.20, 49.99, and 49.99 Hz with overshoots of 50.500, 50.005, and 50.001 Hz and recovery times of over 600.00, 0.01, 0.01 s, respectively, for the frequency variable.

Prediction Method of Tunnel Natural Wind Based on Open-Source Meteorological Parameters

The rational use of natural wind in extra-long tunnels for feedforward operation ventilation control can dramatically reduce tunnel operation costs. However, traditional tunnel natural wind calculation theory lacks a prediction function. This paper proposes a three-stage tunnel natural wind prediction method relying on the Yanglin Tunnel in Yunnan, China based on the massive meteorological parameters provided by the open-source national meteorological stations around the tunnel, which make up for the partial deficiency of the meteorological parameters of the tunnel portal. The multi-layer perceptron model (MLP) was used to predict the real-time meteorological parameters of the tunnel portal using the data from four national meteorological stations. The nonlinear autoregressive network model (NARX) was used to predict the meteorological parameters of the tunnel portal in the next period based on the predicted and measured real-time data. The natural wind speed in the tunnel was obtained by a theoretical calculation method using the predicted meteorological parameters. The final tunnel natural wind prediction results are in good agreement with the field measured data, which indicates that the research results of this paper can play a guiding role in the feedforward regulation of tunnel operation fans.

A Wind-Driven Rotating Micro-Hybrid Nanogenerator for Powering Environmental Monitoring Devices.

In recent years, environmental problems caused by natural disasters due to global warming have seriously affected human production and life. Fortunately, with the rapid rise of the Internet of Things (IoT) technology and the decreasing power consumption of microelectronic devices, it is possible to set up a multi-node environmental monitoring system. However, regular replacement of conventional chemical batteries for the huge number of microelectronic devices still faces great challenges, especially in remote areas. In this study, we developed a rotating hybrid nanogenerator for wind energy harvesting. Using the output characteristics of triboelectric nanogenerator (TENG) with low frequency and high voltage and electromagnetic generator (EMG) with high frequency and high current, we are able to effectively broaden the output voltage range while shortening the capacitor voltage rising time, thus obtaining energy harvesting at wide frequency wind speed. The TENG adopts the flexible contact method of arch-shaped film to solve the problem of insufficient flexible contact and the short service life of the rotating triboelectric generator. After 80,000 cycles of TENG operation, the maximum output voltage drops by 7.9%, which can maintain a good and stable output. Through experimental tests, the maximum output power of this triboelectric nanogenerator is 0.55 mW at 400 rpm (wind speed of about 8.3 m/s) and TENG part at an external load of 5 MΩ. The maximum output power of the EMG part is 15.5 mW at an external load of 360 Ω. The hybrid nanogenerator can continuously supply power to the anemometer after running for 9 s and 35 s under the simulated wind speed of 8.3 m/s and natural wind speed of 5.6 m/s, respectively. It provides a reference value for solving the power supply problem of low-power environmental monitoring equipment.

Computation of Total Electric Field Considering Natural Wind Under High-Altitude UHVDC Transmission Lines

With the rapid development of ultra high-voltage DC (UHVDC) transmission technology, the total electric field problem in high-altitude dc transmission lines is more important. Therefore, this article proposes a calculation model of the ion flow field at high altitude based on the natural wind model and the gas motion theory. First, the initial charge density is assumed, and then, Poisson’s equation is solved by the finite-element method (FEM). The measured wind speed and altitude are introduced into the natural wind model and the ion mobility model, and the natural wind speed and the ion mobility of each node are obtained. Subsequently, the current continuity equation is calculated by this information and the upstream FEM. When the calculation results do not meet the steady-state convergence conditions, the charge density on the conductor surface is iteratively corrected. The calculation model is verified by the measurement results of the ±800-kV UHVDC transmission line at the National Engineering Laboratory for Ultrahigh Voltage Technology (Kunming) of the China Southern Power Grid. The research shows that with the increase of altitude, the ion mobility gradually becomes larger, and the total electric field at ground level also increases. Due to the influence of wind, the peak value of the total electric field at ground level is obviously shifted, and the maximum peak values are on the downwind side. This model in this article can accurately calculate the total electric field of UHVDC transmission lines at high altitude considering the natural wind and provide a reference for the design of transmission lines.

Field test and numerical reconstitution of natural winds at the tunnel entrance section of high-speed railway

PurposeThe purpose of this paper is to understand the natural wind field characteristics of the tunnel entrance section and analyzing the aerodynamic performance of high-speed railway trains (HSRTs) under natural winds.Design/methodology/approachThree typical tunnel entrance section sites, namely, tunnel–bridge in a dry canyon (TBDC), tunnel–bridge in a river canyon (TBRC) and tunnel–flat ground (TF), are selected to conduct a continuous wind field measurement. Based on the measured wind characteristics, the natural winds of the TBDC and TF sites are reconstituted and imported into the two corresponding full-scale computational fluid dynamics models. The aerodynamic loads of the HSRT running on TBDC and TF with reconstituted winds are simply analyzed.FindingsThe von Kármán spectrum can be used to describe the wind field at the tunnel entrance section. In the reconstituted natural wind condition, a time-varying feature of wind speed distribution and leeward side vortex around the HSRT caused by the wind speed fluctuation is found. The fluctuating amplitude of aerodynamic loads at the TBDC infrastructure is up to 97.9% larger than that at the TF infrastructure.Originality/valueThe natural wind characteristics at tunnel entrance sections on the high-speed railway are first measured and analyzed. A numerical reconstitution scheme considering the temporal and spatial variation of natural wind speed is proposed and verified based on field measurement results. The aerodynamic performance of an HSRT under reconstituted natural winds is first investigated.

Influence of Road Types on Transiting Test for Aerodynamic Coefficient Measurements Using Passive Wind Generated by a Moving Vehicle

A transiting test using vehicle-driving passive wind is a novel experimental technique to perform aerodynamic tests, proposed by the authors. However, this low-cost, short-cycle, and symmetrical test method can be influenced by many factors. In this paper, a comparative study on the influence of road types on a transiting test of aerodynamic coefficient measurements is presented. The tests were carried out on three different roads (expressway, viaduct highway, and tunnel highway); for each road type, structure models with and without end plates were investigated. For all the road types, measured turbulence intensity (around 4%) was similar to that of the wind tunnel test under the following conditions: 3 °C temperature, 42% humidity, 0.28 m/s natural wind speed, vehicle driving in a straight line with stable speed, and no traffic flow. All the tests were conducted under the above conditions. To deal with the interference components in the original data signals obtained from a viaduct highway and tunnel highway, a low-pass filter with a 1 Hz cutoff frequency was used. With wind attack angles changing, the tendency of the aerodynamic coefficients of the test model in the transiting test showed satisfactory consistency with that of the wind tunnel test; and the results exhibited fine repeatability. Regarding the drag coefficients, the test model with end plates was in good agreement with those from the wind tunnel test. Compared with the wind tunnel test, the results of expressway showed the best consistency, considering turbulence intensity, pavement surface roughness, and other factors. Thus, the transiting test in future research should be conducted on the expressway, with end plates installed on both ends of the structure model.

Field measurement of wind shielding effect of bridge tower for wind-vehicle-bridge system

Although the wind barrier was set near the bridge tower, more than 10 traffic accidents under crosswinds happen in the bridge tower area within 1 month of the opening operation of a cross-sea bridge. To investigate the wind shielding effect of the bridge tower, a field measurement scheme of wind-vehicle-bridge system, which is a step-by-step test method, was presented and performed on a long span cable-stayed bridge. Firstly, the horizontal profile of wind speed of bridge deck near bridge tower was obtained through the anemometers. Then, the dynamic response of the bridge was measured under the action of normal operating vehicle when the natural wind speed is low. Finally, the response of the moving car was measured when passing through bridge tower, and the wind speed was recorded simultaneously. The results show that the wind-vehicle-bridge system can be tested by step-by-step test method to understand the wind shielding effect of bridge tower. The displacement response of the bridge is still very small when two large trucks meet, and the coupling effect between the vehicle and the bridge is insignificant when a single car passes through the bridge tower. Due to a large porosity of the anti-collision guardrail, the wind speed at the height of 1 m from the bridge deck has changed dramatically when the car leaves the bridge tower on the windward and entering or leaving the bridge tower on the leeward. Among them, the leeward side change is more obvious, and the response of the leeward side vehicle is also greater. The suitable decrease of the anti-collision guardrail porosity in the bridge tower region will improve the running safety of vehicles.

Wind Speed Variation Mapped Using SAR before and after Commissioning of Offshore Wind Farms

When installing offshore wind farms (OWFs) adjacent to the coast, one needs to consider the combined effects of the wind wakes caused by the OWFs and natural horizontal coastal wind speed gradients (HCWSGs). This study exploits the full Sentinel 1A/B and Envisat archive of synthetic aperture radar (SAR) imagery covering the northern European seas. More than 8700 SAR scenes fit well with our selection criteria and are processed as wind maps for the height 10 m above the sea surface. For eight selected wind farm sites, we systematically compare the wind flow variation before and after wind farm commissioning. Before the commissioning, we observe wind speed gradients up to ±4% for onshore and offshore winds. After the commissioning, we detect a 2–10% reduction in the mean wind speed downstream of the turbines after taking into account the background wind speed gradients. These velocity deficits are proportional to the OWF capacity. Our findings indicate that wind speed maps retrieved from SAR can be used to quantify the complex interactions between natural HCWSGs and turbine-induced effects on the mean wind climate. Ultimately, this can be used in connection with farm planning in coastal waters.

Development of a thoron chamber for calibration of thoron monitors under natural wind speed conditions

To examine the response of diffusion-type detectors for thoron under wind speeds similar to natural air ventilation, a special design thoron chamber was developed with a dynamic circulating air-flow field forced by fans. Wind speeds of 0–0.52 m s−1 were adjusted by control of the fan rotation rate according to a linear model, with higher wind speeds contributing to more homogenous air flow status. Thoron concentrations, ranging between 3.2 × 103 and 3.7 × 104 Bq m−3, were easily available through different injection conditions and 220Rn gas sources with high and stable emanation coefficient. The stability and homogeneity of thoron concentrations was controlled within 5.0% and the concentrations in the direction of wind speed had minimal differences compared with the other direction. Higher wind speeds also improved the stability and homogeneity of thoron concentrations. The design and construction of the thoron chamber functioned well in controlling thoron concentration. The response of an AlphaGUARD monitor to thoron was examined in the thoron chamber under different wind speeds. The study revealed a monitor response to thoron (rates of thoron infiltration into the detection chamber of the monitor) respectively was from 0.044 to 0.065 under winds speeds from 0.05 to 0.51 m s−1. Reproducible and controlled expourse conditions can be provided for testing thoron monitors.

Smoothing of Wind Power Output Fluctuations by Particle Filter

Wind power generation is a renewable energy source that has been gradually introduced in a variety of applications. However, this power is generated by the wind, and thus it is variable power source that fluctuates according to wind speed variations. This may cause frequency fluctuations in power systems, which can adversely affect the power grid operations. In this study, a method using a particle filter to predict the expected value of fluctuating wind power is proposed. The effect of the proposed method on suppressing grid system frequency fluctuations is evaluated by simulation analysis for a grid system with permanent magnet synchronous generator (PMSG) based wind turbines under natural wind speed fluctuations.

Optimization strategy of wind energy harvesting via triboelectric-electromagnetic flexible cooperation

As a favorable renewable energy source, wind energy has the advantages of large reserves and wide distribution. To harvest wind energy effectively, an optimization strategy of wind energy harvesting is proposed in this paper, which flexibly combines the complementary advantages of the triboelectric nanogenerator (TENG) and electromagnetic generator (EMG) in different energy harvesting environments. Specifically, in weak wind environments, the TENG operates independently to harvest energy. While, once the wind speed increases to the critical wind speed, the EMG starts and operates coordinately with the TENG, which will effectively increase the energy harvesting capacity of the wind energy harvester. Based on this optimization strategy, the flexible cooperation triboelectric-electromagnetic harvester (FC-TEH) is designed. The FC-TEH could flexibly adjust energy harvesting capability according to variants of wind speed and adapt to the instability of natural wind. Experiments demonstrate that at the critical wind speed of 6 m/s, the FC-TEH reaches the critical speed (108 rpm). At natural wind speeds of about 8 m/s, the FC-TEH can successfully power a Bluetooth thermometer with a rated power of 20 mW. The optimization strategy will provide important guidance and reference for wind energy harvesting.

Numerical study on effect of natural wind and piston wind on anti-freezing length of tunnels with high geo-temperature in cold region

Taking Zilashan Tunnel as an example, a three-dimensional unsteady heat transfer model of surrounding rock, tunnel lining and wind flow was established. The reliability of the temperature calculation model was verified by a 1:30 model test and field test. The influences of natural wind speed, natural wind temperature, train speed and traffic volume on the anti-freezing length of tunnels in cold regions were studied. In particular, this paper focuses on the influence of piston wind direction on the anti-freezing length of the tunnel during 50 years of operation. The results show that the maximum anti-freezing length is positively correlated with the velocity of the natural wind, and the maximum anti-freezing length increases by 787 m on average when the velocity of the natural wind increases by 1 m/s. The maximum anti-freezing length is 2352 m when only the influence of natural wind is considered. When the average temperature of the natural wind is greater than 5 °C, the anti-freezing length of Zilashan Tunnel is 0 m. The maximum anti-freezing length increases with the increase of train speed. The anti-freezing length is the longest when the natural wind is in the same direction as the piston wind, and the minimum anti-freezing length is more than 1200 m under different train speeds. When the traffic volume is 20 trains/day, the anti-freezing length increases with the increase of train speed regardless of the direction of piston wind. Under most working conditions, the surrounding rock near the tunnel entrance will freeze; when the traffic volume is greater than 20 trains/day, the surrounding rock near the tunnel exit will freeze with the natural wind speed and train speed at 1.5 m/s and 200 km/h respectively.