Coherency matrix-based proper orthogonal decomposition with application to wind field simulation

Proper Orthogonal Decomposition （POD） provides a powerful modal transformation tool for stochastic dynamics. In this paper, coherency matrix-based proper orthogonal decomposition （CPOD） is presented as an innovative form of the POD based on cross power spectral density matrices. By introducing a discretizing scheme, the CPOD-based spectral representation method is obtained for use in stochastic simulation. Moreover, some criteria are proposed that allow the truncation order of CPOD to be conveniently determined. A numerical example to illustrate the application of the proposed method for the simulation of a wind velocity field is provided.

Numerical simulation on flow field,wind erosion and sand sedimentation patterns over railway subgrades

The railway subgrades in the sandy areas act as an obstacle interfering wind-blown sand,causing sand erosion and sedimentation,which can disrupt the safe and stable operation of the railway system.Most previous studies mainly focus on the flow field around railway subgrades,however,the real erosion and sedimentation patterns are rarely studied.This study aims to analyze the erosion and sand sedimentation patterns of wind-blown sand over the subgrades with different heights and steel rails using the ratio of the wall shear stress to the critical value of erosion shear stress.Results show that wind erosion near the top of the upwind slope of the embankment and the shoulder on the upwind side are more severe,and the severity increases with an increase in the height of the embankment.With the increase of wind velocity,sand sedimentation both on the windward and leeside of the subgrade decreases and wind erosion by reverse flow occur.This study indicates that railways in sandy areas should be constructed with a moderate subgrade height(4 m).

CORRECTION OF ASYMMETRIC STRENGTHENING OF QUIKSCAT WIND FIELD AND ASSIMILATION APPLICATION IN TYPHOON SIMULATION

As an approach to the technological problem that the wind data of QuikSCAT scatterometer cannot accurately describe the zone of typhoon-level strong wind speed, some objective factors such as the typhoon moving speed, direction and friction are introduced in this study to construct the asymmetric strengthening of the QuikSCAT wind field. Then by adopting a technology of four-dimensional data assimilation, an experiment that includes both the assimilation and forecasting phases is designed to simulate Typhoon Rananim numerically. The results show that with model constraints and adjustment, this technology can incorporate the QuikSCAT wind data to the entire column of the model atmosphere, improve greatly the simulating effects of the whole-column wind, pressure field and the track as well as the simulated typhoon intensity covered by the forecast phase, and work positively for the forecasting of landfall locations.

Non-Gaussian Lagrangian Stochastic Model for Wind Field Simulation in the Surface Layer

Wind field simulation in the surface layer is often used to manage natural resources in terms of air quality,gene flow(through pollen drift),and plant disease transmission(spore dispersion).Although Lagrangian stochastic(LS)models describe stochastic wind behaviors,such models assume that wind velocities follow Gaussian distributions.However,measured surface-layer wind velocities show a strong skewness and kurtosis.This paper presents an improved model,a non-Gaussian LS model,which incorporates controllable non-Gaussian random variables to simulate the targeted non-Gaussian velocity distribution with more accurate skewness and kurtosis.Wind velocity statistics generated by the non-Gaussian model are evaluated by using the field data from the Cooperative Atmospheric Surface Exchange Study,October 1999 experimental dataset and comparing the data with statistics from the original Gaussian model.Results show that the non-Gaussian model improves the wind trajectory simulation by stably producing precise skewness and kurtosis in simulated wind velocities without sacrificing other features of the traditional Gaussian LS model,such as the accuracy in the mean and variance of simulated velocities.This improvement also leads to better accuracy in friction velocity(i.e.,a coupling of three-dimensional velocities).The model can also accommodate various non-Gaussian wind fields and a wide range of skewness–kurtosis combinations.Moreover,improved skewness and kurtosis in the simulated velocity will result in a significantly different dispersion for wind/particle simulations.Thus,the non-Gaussian model is worth applying to wind field simulation in the surface layer.

Numerical Simulation of Wind Field Characteristics around Two Adjacent High-Rise Buildings

This paper based on Reynolds-averaged Navier-Stokes equations standard ?model [1];the surface pressure on the wind field around two adjacent high-rise buildings was numerically simulated with software Fluent. The results show that with the influence of adjacent high-rise building, numerical simulation is a good way to study the wind field around high-rise building and the distribution of wind pressure on building’ surface. The pressures on the windward surface are positive with the maximum at 2/3 H height and have lower values on the top and bottom. The pressures on the leeward surface and two sides were negative. Due to the serious flow separation at the corner of building’s windward, the wind field has a high turbulent kinetic energy.

Application of FLUENT on fine-scale simulation of wind field over complex terrain

The state-of-art Computational Fluid Dynamics （CFD） codes FLUENT is applied in a fine-scale simulation of the wind field over a complex terrain. Several numerical tests are performed to validate the capability of FLUENT on describing the wind field details over a complex terrain. The results of the numerical tests show that FLUENT can simulate the wind field over extremely complex terrain, which cannot be simulated by mesoscale models. The reason why FLUENT can cope with extremely complex terrain, which can not be coped with by mesoscale models, relies on some particular techniques adopted by FLUENT, such as computer-aided design （CAD） technique, unstructured grid technique and finite volume method. Compared with mesoscale models, FLUENT can describe terrain in much more accurate details and can provide wind simulation results with higher resolution and more accuracy.

Multivariate stationary non-Gaussian process simulation for wind pressure fields

Stochastic simulation is an important means of acquiring fluctuating wind pressures for wind induced response analyses in structural engineering. The wind pressure acting on a large-span space structure can be characterized as a stationary non-Gaussian field. This paper reviews several simulation algorithms related to the Spectral Representation Method （SRM） and the Static Transformation Method （STM）. Polynomial and Exponential transformation functions （PSTM and ESTM） are discussed. Deficiencies in current algorithms, with respect to accuracy, stability and efficiency, are analyzed, and the algorithms are improved for better practical application. In order to verify the improved algorithm, wind pressure fields on a large-span roof are simulated and compared with wind tunnel data. The simulation results fit well with the wind tunnel data, and the algorithm accuracy, stability and efficiency are shown to be better than those of current algorithms.

Analysis of typhoon wind hazard in Shenzhen City by Monte-Carlo Simulation

As one of the most serious natural disasters,many typhoons affect southeastern China every year.Taking Shenzhen,a coastal city in southeast China as an example,we employed a Monte-Carlo simulation to generate a large number of virtual typhoons for wind hazard analysis.By analyzing 67-year historical typhoons data from 1949 to 2015 using the Best Track Dataset for Tropical Cyclones over the Western North Pacific recorded by the Shanghai Typhoon Institute,China Meteorological Administration(CMASTI),typhoon characteristic parameters were extracted and optimal statistical distributions established for the parameters in relation to Shenzhen.We employed the Monte-Carlo method to sample each distribution to generate the characteristic parameters of virtual typhoons.In addition,the Yah Meng(YM)wind field model was introduced,and the sensitivity of the YM model to several parameters discussed.Using the YM wind field model,extreme wind speeds were extracted from the virtual typhoons.The extreme wind speeds for different return periods were predicted and compared with the current structural code to provide improved wind load information for wind-resistant structural design.

Optimal design of vegetation in residential district with numerical simulation and field experiment

Vegetation plays a key role in improving wind environment of residential districts,and is helpful for creating a comfortable and beautiful living environment.The optimal design of vegetation for wind environment improvement in winter was investigated by carrying out field experiments in Heqingyuan residential area in Beijing,and after that,numerical simulation with SPOTE(simulation platform for outdoor thermal environment) experiments for outdoor thermal environment of vegetation was adopted for comparison.The conclusions were summarized as follows:1) By comparing the experimental data with simulation results,it could be concluded that the wind field simulated was consistent with the actual wind field,and the flow distribution impacted by vegetation could be accurately reflected;2) The wind velocity with vegetation was lower than that without vegetation,and the wind velocity was reduced by 46%;3) By adjusting arrangement and types of vegetation in the regions with excessively large wind velocity,the pedestrian-level wind velocity could be obviously improved through the simulation and comparison.

Numerical simulation study of gob air leakage field and gas migration regularity in downlink ventilation

Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influence of natural wind pressure to analyze the stope face differential pressure, gob air leakage field distribution and gas migration regularity theoretically. Established a two-dimensional physical model with one source and one doab, and applied computational fluid dynamics analysis software Fluent to do numerical simulation, analyzed and contrasted to the areas of gob air leakage on size and gas emission from gob to working face on strength when using the downlink ventilation and uplink ventilation. When applied downward ventilation in stope face, the air leakage field of gob nearly working face, and the air leakage intensity were smaller than uplink, this can effectively reduce the gas emission from gob to working face; when used downlink ventilation, the air leakage airflow carry the lower amount of gas to doab than uplink ventilation, and more easily to mix the gas, reduced the possibility of gas accumulation in upper comer and the stratified flows, it can provide protection to mine with safe and effective production.

Investigation on Temperature Field Calibration and Analysis of Wind Tunnel

For wind tunnels,it is essential to conduct temperature and flow field calibration on their test section,which is an important indicator for evaluating the quality of wind tunnel flow fields.In the paper,a truss composed of temperature sensors was used to calibrate the temperature field of a completed wind tunnel section.By adjusting the distance between the temperature measurement truss and the nozzle,as well as the wind speed,the temperature field distribution data at different positions could be obtained.Analyze these data to identify important factors that affect the distribution of temperature field.Simultaneously,the temperature field of the wind tunnel was simulated accordingly.The purpose is to further analyze the fluid heat transfer between air and wind tunnel walls through numerical simulation.Through the above analysis methods,the quality of the temperature field in the wind tunnel has been further verified,providing reference for future wind tunnel tests of relevant models.

NUMERICAL SIMULATION OF INTERANNUAL AND INTERDECADAL VARIABILITY OF SURFACE WIND OVER THE TROPICAL PACIFIC

A global atmospheric general circulation model (L9R15 AGCMs) forced by COADS SST was integrated from 1945 to 1993. Interannual and interdecadal variability of the simulated surface wind over the tropical Pacific was analyzed and shown to agree vey well with observation. Simulation of surface wind over the central-western equatorial Pacific was more successful than that over the eastern Pacific. Zonal propagating feature of interannual variability of the tropical Pacific wind anomalies and its decadal difference were also simulated successfully. The close agreement between simulation and observation on the existence of obvious interdecadal variability of tropical Pacific surface wind attested to the high simulation capability of AGCM.

An Elliptical Wind Field Model of Typhoons

An elliptical wind field model of typhoons is put forward based on the characteristics of the typhoon wind fields occurring in the Yellow Sea and Bohai Sea. By contrasting it with the circular typhoon wind field model, it is found that the elliptical model can adequately represent the real wind field and trace the process of a typhoon storm surge. The numerically simulated results of storm surges by using the elliptical model are in good agreement with the observations and markedly better than those by using the circular model.

Effects of a dipole-like crustal field on solar wind interaction with Mars

A three-dimensional four species multi-fluid magnetohydrodynamic (MHD) model was constructed to simulate the solar wind global interaction with Mars. The model was augmented to consider production and loss of the significant ion species in the Martian ionosphere, i.e., H^+, O2^+, O^+, CO^+2, associated with chemical reactions among all species. An ideal dipole-like local crustal field model was used to simplify the empirically measured Martian crustal field. Results of this simulation suggest that the magnetic pile-up region (MPR) and the velocity profile in the meridian plane are asymmetric, which is due to the nature of the multi-fluid model to decouple individual ion velocity resulting in occurrence of plume flow in the northern Martian magnetotail. In the presence of dipole magnetic field model, boundary layers, such as bow shock (BS) and magnetic pile-up boundary (MPB), become protuberant. Moreover, the crustal field has an inhibiting effect on the flux of ions escaping from Mars, an effect that occurs primarily in the region between the terminator (SZA 90°) and the Sun Mars line of the magnetotail (SZA 180°), partially around the terminator region. In contrast, near the tailward central line the crustal field has no significant impact on the escaping flux.

Large eddy simulation of flow over a three-dimensional hill with different slope angles

Slope variation will significantly affect the characteristics of the wind field around a hill.This paper conducts a large-eddy simulation(LES)on an ideal 3D hill to study the impact of slope on wind field properties.Eight slopes ranging from 10°to 45°at 5°intervals are considered,which covers most conventional hill slopes.The inflow turbulence for the LES is generated by adopting a modified generation method that combines the equilibrium boundary conditions with the Fluent inherent vortex method to improve the simulation accuracy.The time-averaged flow field and the instantaneous vortex structure under the eight slopes are comparatively analyzed.The accuracy of the present method is verified by comparison with experimental data.The slope can affect both the mean and fluctuating wind flow fields around the 3D hill,especially on the hilltop and the leeward side,where a critical slope of 25°can be observed.The fluctuating wind speeds at the tops of steep hills(with slope angles beyond 25°)decrease with increasing slope,while the opposite phenomenon occurs on gentle hills.With increasing slope,the energy of the high-speed descending airflow is enhanced and pushes the separated flow closer to the hill surface,resulting in increased wind speed near the wall boundary on the leeward side and inhibiting the development of turbulence.The vortex shedding trajectory in the wake region becomes wider and longer,suppressing the growth of the mean wind near the wall boundary and enhancing the turbulence intensity.

Wind Field Flow Characteristics Analysis of T4-72 Type Centrifugal Fan

In order to explore the internal wind field flow characteristics of T4-72 type centrifugal fan, the three-dimensional model was established based on PRO/E software. Combined with computational fluid Dynamics Software Fluent 6.3, the standard model and SIMPLEC algorithm were used to simulate the wind field inside the fan. Analysis of the flow characteristics, velocity distributed and pressure distributed of the internal fluid model of the T4-72 centrifugal fan, combined with the theoretical formula to obtain the full pressure, power and efficiency performance parameters of the fan. The centrifugal fan performance curve is drawn. While compared with the experimental data, it is found that the internal flow disturbance is strong when the fan is running under low load condition and high load condition, which affects the performance of the fan and reduces the life of the fan. The numerical simulation results are consistent with the experimental results. The overall performance parameters of the fan are in good agreement, verifying the reliability of the simulation results;when the fan works between 1 - 1.4 times the rated flow rate, it can obtain a more stable flow field while maintaining higher efficiency, which provides a new idea for the optimization of the subsequent fan.

Numerical study on surrounding rock mass temperature field of Kangding tunnel no.2 considering wind flow

Based on the Kangding Tunnel No.2 project,this study analyzes the heat exchange between air and the rock mass surrounding the tunnel under wind flow by the finite difference method.The influence of factors on the temperature field of a tunnel in cold regions,including ventilation and initial conditions,is investigated.The results show that:1)The lower the air temperature,the greater the wind speed,the larger the rock mass temperature influence circle and the greater the frozen depth;2)When the wind speed is less than 3 m/s,its change has an obvious impact on the rock mass temperature;3)For every drop of 5C in air temperature,the frozen depth increases by about 5 m,indicating that the air temperature is an essential factor affecting the rock mass temperature regime;4)The higher the initial rock mass temperature is,the smaller the influence circle on the rock mass is.And to a certain extent,it determines the temperature distribution in the rock mass within a specific range from the wall surface.

Simulated Influence of Mountainous Wind Farms Operations on Local Climate

Renewable energy sources,especially wind power,were believed to be able to slow down global warming;however,evidence in recent years shows that wind farms may also induce climate change.With the rapid development of wind power industry,the number of wind farms installed in mountains has gradually increased.Therefore,it is necessary to study the impact of wind farms in mountainous areas on local climate.The Suizhou and Dawu wind farms in northern Hubei Province were chosen for the present study on the impact of wind farm operations on the local climate in mountainous areas.The mesoscale meteorological numerical model Weather Research and Forecasting Model(WRF)and the Fitch model,together with turbulence correction factor,were used to simulate wind farm operations and study their effects on local climate.The results showed the characteristics of wind speed attenuation in mountainous wind farms:the amplitude and range of wind speed attenuation were stronger in the nighttime than in the daytime,and stronger in summer than in winter.The surface temperature increased and became more significant in summer.However,a cooling variation was observed above the surface warming center.The height of this center was higher in the daytime than it was in the nighttime.The latent heat flux in the wind farms decreased at night,accompanied by an increase in sensible heat flux.However,these changes were not significant.Some differences were observed between the impact of wind farms on the climate in the plains and the mountains.Such differences are more likely to be related to complex terrain conditions,climate conditions,and the density of wind turbines.The present study may provide support for the development and construction of wind farms in mountainous areas.

Numerical simulation analysis of wind field above pavement surface in different landforms by computational fluid dynamics approach

The temperature and moisture of the pavement structure can be greatly influenced by the wind speed above pavement surface.The wind speed above pavement surface not only is dominated by the wind speed of atmosphere,but also it is highly related to the landform and buildings around road.However,currently there are no studies about the wind field above pavement surface in consideration of the effect of the landform and buildings.A simulation method,which is combined with geographic information system(GIS),wind data from meteorological observatory and computational fluid dynamics(CFD)software,is employed to study the effect of the landform and the wind speed of atmosphere on the wind field above pavement surface.Three cases are studied,including an urban road,a coastal road and a mountainous road.Furthermore,the wind field distribution above road surface in different wind directions was studied in our work.Results indicate that the wind field above pavement surface can be greatly affected by the landforms,buildings and wind direction.This simulation method can provide reliable results for the wind field above pavement surface.The maximum relative errors between simulated and measured wind speed can be less than 20%in the analysis of the three cases.It is recommended that the CFD simulation method is a good tool to accurately know the wind field above pavement surface.

Numerical Simulation of Wind and Temperature Fields over Beijing Area in Summer

The non-hydrostatic mesoscale model MM5V3 is used to simulate the wind andtemperature fields of the atmospheric boundary layer over Beijing area in summer with the meshresolution of 1 km. The simulation results show that the numerical model can successfully simulatethe urban heat island effect and the wind and temperature fields which are affected by thecomplicated topography and urban heat island. The results show that: (1) the west area (from Haidianto Fengtai Districts) is always the high temperature center of Beijing, where the surfacetemperature is about 6 K higher than the other suburbs; and (2) due to the unique topography thewind of Beijing area during the daytime is southern anabatic wind and at the night is northernkatabatic wind. The results comparing well with the data from surface observation stations validatethe accuracy of the simulation.