Characteristics Of Natural Wind Research Articles

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.

Comparative study on the wind characteristics of tunnel–bridge and tunnel–flat ground infrastructures on high-speed railway

The difference in natural wind characteristics of the tunnel–bridge (TB) and tunnel–flat ground (TF) infrastructure may result in varied aerodynamic behaviours of the high-speed railway train (HSRT). Hence, continuous natural wind sampling is conducted on typical TB and TF sites by using three ultrasonic and one three-cup anemometers. The mean and fluctuating wind characteristics of the two sites are compared and discussed in detail based on field measurement data. The main results can be concluded as follows: Firstly, the prevailing wind direction on the TB site is perpendicular to the running direction of the HSRT due to the occlusion effect, whereas the mean direction on the TF site is easily deflected by the near-ground vegetations and other obstacles. Secondly, the turbulence intensities of the TF site are larger than those of the TB site, and the lognormal distribution is applicable for describing the probability distribution of measured turbulence intensity on the two sites. Thirdly, the von Kármán spectrum accurately depicts the wind energy distribution of the TB and TF sites in the frequency domain, whereas the empirical spectrum adopted by the specification show inferior accuracy. Lastly, the coherence distance of the TB site is considerably longer than that of the TF site. The coherence distance of u and v components of the TB site is seven times longer than a train body (approximately 25 m), and that of u component of the TF site is shorter than two times of a train body.

Wind speed forecasting using multi-scale feature adaptive extraction ensemble model with error regression correction

Wind speed forecasting is vital for the operational safety and power generation quality of wind power systems. However, owing to the strong non-stationary and nonlinear characteristics of natural wind, high performance wind speed forecasting is still a challenging task. In this study, a novel multi-scale feature adaptive extraction (MSFAE) ensemble model is developed to provide accurate and reliable wind speed forecasting. The proposed model constructs six GWO-CNN-BiLSTM (GCNBiL) networks with different lengths of convolution operators, and extracts and learns the deep autocorrelation feature hidden in high-resolution data at different time scales. Subsequently, the proposed model employs a multi-objective cuckoo-search-moth-flame hybrid optimization (MOCSMFHO) algorithm to ensemble the forecasting results of six GCNBiL benchmark models. Finally, the model uses a multi-objective error regression method for error correction. Three actual wind series collected from Xinjiang, China, were selected to verify the proposed model. These case studies indicate that the proposed model outperforms all sixteen alternative models as well as the three state-of-the-art models with a 40% average improvement ratio. Moreover, the developed GCNBiL models have excellent prediction accuracy, resist overfitting, and show an 18% improvement in forecasting performance. Furthermore, the proposed MOCSMFHO algorithm possess both excellent global search accuracy and convergence speed, and can effectively integrate the prediction advantages of autocorrelation features in different time scales to obtain a 4% improvement in accuracy. The proposed multi-objective error regression correction method can also provide more than 26% improvement in prediction performance and delivers better error correction performance than the existing methods in practical applications.

Modelling aspects and risk analysis for road vehicles under non-stationary wind excitation

Strong crosswinds have a great influence on the stability of road vehicles. At exposed locations (e.g. embankments, long bridges), the topographical features may magnify the wind effects and thus cause accidents. In order to evaluate the accident risk of road vehicles in a more realistic way, the model for the wind-vehicle system has to take the non-stationary characteristics of natural wind into account and specific vehicle models for different vehicle types have to be developed. This paper details the mathematical model and physical scenario of road vehicles running under strong crosswinds. Possible road vehicle accidents due to excessive sideslip, yaw rotation and overturning are taken into account. In order to quantify the accident risk under strong crosswind, failure probabilities for different types of road vehicles are computed and analysed.

Investigations of flow field around two-dimensional simplified models with wind tunnel experiments

The effect of topographic features on wind velocity and turbulence intensity was evaluated by conducting wind tunnel experiments with Particle Image Velocimetry (PIV) system. In this study, to simulate the natural wind characteristics, the active turbulence grids and boundary layer generation frame were installed in the wind tunnel. The mean wind velocity, the velocity vector diagram and the turbulence intensity around the two-dimensional single simplified models were investigated. As a result, the flow was separated at the simplified model tip in all cases of models, and the countercurrent flow field was generated at the downstream side. Moreover, the clockwise circulation flow also moved to the upstream side in the case of large radius R. RX was followed by the name given the radius value of X. For the mainstream turbulence intensity, the ranges of high turbulence intensity were z/H < 2.8 for R1 model, z/H < 2.6 for R3 model, z/H < 2.5 for R6 model, z/H < 2.4 for R11 model, z/H < 2.2 for R20 model, z/H < 2.0 for R23 model, z/H < 1.9 for R25 model in the vertical direction. The quantitative measurement results of this paper provided a database for the validation of the wind velocity distributions of atmospheric turbulent flow in the hill and mountain regions.

Effects of wind guide plates on wind velocity acceleration and dune leveling: a case study in Ulan Buh Desert, China

The areas used to be covered by shifting sand dunes have been reclaimed rapidly in recent years. However, it is a challenge to reclaim high sand dunes because it is rather costly to level the high dunes to gentle arable lands. In this study, a wind guide plate was used to change the characteristics of natural wind to level the sand dunes. The use of wind energy could significantly increase the efficiency of dune leveling and decrease the cost. Low wind velocity is a typical characteristic in Ulan Buh Desert of China where the average wind speed is much lower than the threshold velocity for sand movement. The experiment of this study was conducted to accelerate the wind velocity by a wind guide plate to level a sand dune. Results show that the threshold velocity for sand movement is 3.32 m/s at 10 cm above the sand surface in Ulan Buh Desert. A wind guide plate set at an angle less than 50° could significantly increase the wind velocity. The wind velocity could be accelerated up to the threshold velocity for sand movement behind a plate when the plate is at the angles of 20°, 25°, 35° and 40°. The most significant acceleration of wind velocity appears at 1.5 and 3.0 m behind the plate with an angle of 25°. An obvious wind velocity acceleration zone exists behind the wind guide plate when the angles are at 25°, 35°, 40° and 45°, with the most obvious zone under the angle of 45°. The results also show that the total amount of sand transferred over the experimental period increased by 6.1% under the effects of wind guide plates compared to the sand moved without wind guide plates. The results of the study will provide theoretical and practical supports for desert management in sand dune areas.

Analysis and Simulation of Wind Turbine Optimal Control Considering wind Turbulence Characteristics

A maximum power point tracking (MPPT) algorithm of wind turbines considering wind turbulence characteristics is presented in this paper. The turbulence characteristics of natural wind are analyzed, and the natural wind speed model is established. A MPPT algorithm based on extremum-seeking control (ESC) is proposed, which considers the turbulence characteristics containing in wind speed. The goal of the MPPT algorithm is to keep the wind turbines running at the maximum wind energy utilization coefficient point stably. The algorithm is modeled and analyzed, and the simulation results show that the MPPT algorithm is correct and effective.

A two-degree-of-freedom aeroelastic model for the vibration of dry cylindrical body along unsteady air flow and its application to aerodynamic response of dry inclined cables

A two-degree-of-freedom aeroelastic model is proposed to study wind-induced response of bridge stay cables in the context of a rigid circular cylinder model oscillating in an arbitrary orientation with respect to the oncoming unsteady flow. Compared to the existing analytical models and wind tunnel studies, the proposed model can take into account the unsteady characteristics of natural wind and predict the evolving history of cable response. The validity of the proposed model is verified by the results from an earlier wind tunnel study. The rationality of defining a cable aerodynamic stability criterion using solely the Ur–Sc relation is discussed. Two different unsteady wind models are used to investigate the impact of flow unsteadiness on the wind-induced response of stay cables. A case study is presented to evaluate the aerodynamic behavior of a real bridge stay cable in unsteady/turbulent natural wind. Results show that while the emergence of critical Reynolds number regime is crucial for the onset of dry inclined cable galloping, the spanwise correlation of aerodynamic forces acting on a cable and the sustained duration of critical flow condition are the determining factors for the continuous growth of unstable cable response and the eventual occurrence of this type of aerodynamic instability.

Correlations in thermal comfort and natural wind

Many field surveys have shown that naturally ventilated buildings are favorable to human thermal comfort and may allow higher cooling temperatures than air-conditioned buildings. Recreating natural wind characteristics with a mechanical cooling system may diminish the drawbacks of conventional cooling systems such as drafts and high energy demands.Natural wind characteristics (wind velocity, direction, turbulent intensity, temperature and relative humidity) were recorded in a mountain environment and correlated with the human thermal sensation of 48 subjects. Natural wind fluctuation characteristics were analyzed using the Fast Fourier Transform (FFT) analysis. The dynamic characteristics of natural wind were averaged through the power spectrum exponent (β−value), which represents the energy distribution of the turbulent flow of natural wind. The power spectrum exponent (β−value) of the natural wind will decrease when the mean velocity increases, while it will increase when the turbulent intensity increases. The power spectrum exponent (β−value) was correlated (Spearman's rank coefficient=0.56, p<0.001) with thermal comfort. The power spectrum exponent (β-value) for people feeling comfortable has a median value of 1.62 [1.41–1.80 for the first and third quartiles, respectively] and the β−value for people feeling uncomfortable has a median value of 1.10 [0.97–1.25].

Long-term field measurement and analysis of the natural wind characteristics at the site of Xi-hou-men Bridge

In order to investigate the wind characteristics of coastal areas of China, a long-term field measurement of natural wind was carried out. Based on the field measurement results, this paper presents the natural wind characteristics of typhoons and strong monsoons at the site of Xi-hou-men Bridge, including mean wind speed, mean wind direction, mean wind elevation angle, turbulent intensity, gust factor, turbulence integral length scales, power spectrum of wind speed and spatial correlation of gusty wind, the profiles of mean wind speed and turbulent intensity, etc. The correlation among wind characteristics is analyzed in detail, and the similarities and differences of wind characteristics between typhoons and monsoons are analyzed. These results can provide detailed wind characteristics of coastal areas of China.

Wind Field Synthesis for Animating Wind-induced Vibration

We present a simple method to generate three-dimensional frozen and non-frozen turbulent wind fields for use in the animation of wind-induced motion. Our approach uses 1/f^_ noise to match the characteristics of natural wind. By employing a noise-based approach, the complexity as well as computational cost is reduced. Additionally, by considering key characteristics of actual wind that are applied in the structural engineering field, our proposed method is able to produce plausible results in outdoor wind field simulations. In this paper, we describe the implementation results of our proposed method and compare them with other existing approaches used to construct turbulent wind fields. The implementation and visualization are carried out for both two- and three-dimensional scenarios and compared with the results of other well-known methods.

An alternative approach to experimental simulation of wind characteristics in urban environments

The classical Counihan vortex generators for wind-tunnel simulations of the atmospheric boundary layer (ABL) flow were redesigned to experimentally simulate natural wind characteristics in urban environments. Three redesigned (truncated) vortex generators, a castellated barrier wall and a fetch of roughness elements were employed to reproduce a lower portion of the neutrally stratified ABL developing above an urban type terrain. A hot-wire anemometry system was used to measure mean velocity and velocity fluctuations. Investigated parameters were mean velocity, turbulence intensity, integral length scale of turbulence, and power spectral density of velocity fluctuations. Experimental results indicate that the truncated vortex generators developed for this study can be successfully employed in urban ABL part-depth wind-tunnel simulations, as they compare well with commonly applied empirical models and wind specifications for urban type terrain given in the ESDU 74031 data sheets.

Use of a Stochastic Regression Model GARCH for Wind Fluctuation Study

In contrast to mechanical ventilation, natural ventilation’s performance is usually impacted by uncertain factors, including wind fluctuations, outside air temperature variations, and occupants’ behaviours. These factors require a stochastic evaluation process for natural ventilation at the design stage such as quantifying the effective ventilation rates and optimising control strategy. A stochastic regression method based on GARCH (generalized autoregressive conditional heteroskedasticity) model is used in this paper to capture natural wind’s dynamic fluctuating characteristics and verify the existence of heteroskedasticity of wind fluctuation. The stochastic regression result is thus applied to forecast wind speed under natural ventilation condition. By comparing the power spectrum and phase space reconstruction against a simple Gaussian model generated fluctuating wind speed, we find wind speed forecasted from the GARCH model with a small modification maintains more dynamic characteristics of natural wind.

1304 小型風車の挙動解析を目的とした風速変化パターンの検出(OS13-1 大気海洋の流体現象と環境流体,オーガナイズドセッション)

In this study, in order to investigate the characteristics of natural wind for the purpose of the application to improvement in small wind turbines, triangle-like wind speed patterns have been detected from the wind data measured by a propeller-type anemometer. As a result, we observed that a Λ-type pattern tends to have the peak at one-third from the beginning and a V-type pattern tends to have the peak at one-third from the end.

Analysis of Aeroelastic Bridge Deck Response to Natural Wind

The paper discusses a practical method for numerically analysing bridge response to wind effects. A numerical scheme is used which incorporates the natural wind characteristics and the aeroelastic properties of the bridge deck in order to perform a coupled time-history analysis of the dynamic response. The application of the scheme to the footbridge Kehl-Strasbourg, a very slender cable-stayed bridge, is shown and the design of a sophisticated rocker-type Tuned Mass Damper system is outlined.

Study on dynamic characteristics of natural and mechanical wind in built environment using spectral analysis

What are the differences and similarities between natural and mechanical wind in built environment? This is an interesting question that has not been well answered yet. In the paper, spectral analysis is applied to study the dynamic characteristics of natural and mechanical wind in different conditions. The results show that in the frequency region sensitive to human sensation, the power spectrum characteristics of natural wind and mechanical wind have obvious differences as well as interesting connections. The power spectrum exponent ( β value) of natural wind is between 1.1 and 2.0 in the human sensitive frequency region, while the value of mechanical wind is between 0 and 0.5 around the air supply outlet. With the diffusion of mechanical wind, β value will increase gradually and reach the value of the typical natural wind when the mean velocity is lower than 0.25 m/s. Finally, the influence of spectral characteristics on human sensation for airflow is discussed.

Simplifying the simulation of stochastic wind velocity fields for long cable-stayed bridges

The spectral representation method has been greatly developed as the performance of computer was enhanced. For the time-domain analysis of long cable-stayed bridge, it is required to simulate wind velocity histories at many points arranged on the overall bridge. However, the number of these points is usually so large that the spectral representation method obviously becomes computationally prohibitive. In this paper, a practical method is introduced to simplify stochastic wind velocity field for long cable-stayed bridges. According to the properties of both the structural type and the vibration mode of long cable-stayed bridge, and considering the correlation characteristics of natural wind, an overall three-dimensional (i.e. three components of natural wind) wind velocity field of a long cable-stayed bridge can be simplified into many one-dimensional (i.e. just one component) wind velocity fields, respectively, along pylons and deck. The wind fluctuation along each pylon can be simulated independently by omitting the wind velocity correlation between one pylon and another. Using the explicitly expressed Cholesky's decomposition of the cross-spectral density matrix, the wind velocity field along the deck can be simulated relatively fast. The FFT (Fast Fourier Transform) technique is adopted to further improve the computational efficiency. As an example, the stochastic wind field of a three-pylon cable-stayed bridge is simulated. The spectrum and correlation characteristics of the simulated samples are checked, which demonstrates that the simulation results agree with the corresponding targets.

Aerodynamic admittance and the `strip theory’ for horizontal buffeting forces on a bridge deck

In wind tunnel tests of bridges for buffeting arising from fluctuating wind velocity, one of the items requiring attention is how to simulate the natural wind characteristics of the construction region. In wind tunnel tests of long-span cable-stayed bridges under construction, when two types of turbulent boundary layer with different wind characteristics were used, there was a tendency for the match between the wind tunnel test values and buffeting analysis values to vary with the type of turbulent boundary layer. Horizontal buffeting was considered for which there are fewer previous examples than for vertical buffeting. As a result of pursuing the cause of the lack of matching, it was found that the aerodynamic admittance used in the analysis and the measured aerodynamic admittance were quite different. This difference arose from the fact that the correlation of the fluctuating velocity spanwise was smaller than the value assumed in the analysis. Also, according to past research, there are many examples in which strip theory according to which the fluctuating wind velocity correlation and the fluctuating aerodynamic correlation are equivalent is not valid. Here, it is also considered whether or not the strip theory is valid for horizontal buffeting.

Full-scale measurement of wind-induced internal pressures in a high-rise building

Abstract The characteristics of wind-induced internal pressures in a high-rise building have been investigated. Full-scale measurement were taken using absolute pressure meters, which allowed high-resolution measurements. This paper outlines full-scale measurements of wind velocity, wind direction and external and internal pressures on a 29-story building, commencing in January 1993. It also describes the characteristics of natural wind above the building's penthouse and mean wind-induced internal pressures measured in September 1995 when a typhoon hit the Kanto area. The internal pressure coefficients obtained from these measurements were about −0.26, and were constant over the building's height. The influence of internal walls and doors on measured mean internal pressure coefficients was found to be insignificant, and roughly the same values were obtained at different locations on the same floor. The mean internal pressure coefficients estimated from the mean wind pressure coefficient obtained from wind tunnel testing was — −0.26, which is the same as that obtained from the full-scale measurement. Therefore, it is inferred that the mean wind pressure coefficient obtained from the wind tunnel testing is sufficient for examining average internal pressure.

Fatigue strength design for vortex-induced oscillation and buffeting of a bridge

Vortex-induced oscillation of bridges appears at relatively low wind speed. Large bridges are sometimes subjected to a large number of oscillation cycles by vortex-induced oscillation and buffeting. Fatigue strength design for these oscillations becomes an important problem for the design of a large bridge. To execute fatigue strength design reasonably for vortex-induced oscillation and buffeting, we put the characteristics of natural wind (i.e. wind direction, wind speed, and angle of attack) and the characteristics of bridge aerodynamics together. A computer makes fatigue strength design easy under several conditions. In this study, we propose a numerical stochastic method to calculate the number of cycles of vortex-induced oscillation and buffeting, considering that aerodynamic responses appear in a wide range of wind direction.