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.

Numerical investigation and optimal design of fiber Bragg grating based wind pressure sensor

A wind pressure sensor based on fiber Bragg grating （FBG） for engineering structure was investigated in this paper. We established a transaction model of wind pressure to strain and proposed a method of temperature compensation. By finite element analysis, the basic parameters of the sensor were optimized with the aim of maximum strain under the basic wind pressure proposed in relative design code in China taking geometrical non-linearity into consideration. The result shows that the wind pressure sensor we proposed is well performed and have good sensing properties, which means it is a technically feasible solution.

Predicting roof-surface wind pressure induced by conical vortex using a BP neural network combined with POD

This study aims to examine the feasibility of predicting surface wind pressure induced by conical vortex using a backpropagation neural network(BPNN)combined with proper orthogonal decomposition(POD),in which a 1:150 scaled model with a large-span retractable roof was tested in wind tunnel under both laminar and turbulent flow conditions.The distributions of mean and fluctuating wind pressure coefficients were first described,and the effects of inflow turbulence,wind direction,roof opening were examined separately.For the prediction of wind pressure,the POD-BPNN model was trained using measurement data from adjacent points.The prediction results are overall satisfactory.The root-mean-square-error(RMSE)between test and predicted data lies mostly within 10%.In particular,the prediction of mean wind pressure is found to be better than that of fluctuating wind pressure.The outcomes in this study highlight that the proposed POD-BPNN model can be well used as a useful tool to predict surface wind pressure.

A cloud-based platform to predict wind pressure coefficients on buildings

Natural ventilation(NV)is a key passive strategy to design energy-efficient buildings and improve indoor air quality.Therefore,accurate modeling of the NV effects is a basic requirement to include this technique during the building design process.However,there is an important lack of wind pressure coefficients(CP)data,essential input parameters for NV models.Besides this,there are no simple but still reliable tools to predict CP data on buildings with arbitrary shapes and surrounding conditions,which means a significant limitation to NV modeling in real applications.For this reason,the present contribution proposes a novel cloud-based platform to predict wind pressure coefficients on buildings.The platform comprises a set of tools for performing fully unattended computational fluid dynamics(CFD)simulations of the atmospheric boundary layer and getting reliable CP data for actual scenarios.CFD-expert decisions throughout the entire workflow are implemented to automatize the generation of the computational domain,the meshing procedure the solution stage,and the post-processing of the results.To evaluate the performance of the platform,an exhaustive validation against wind tunnel experimental data is carried out for a wide range of case studies.These include buildings with openings,balconies,irregular floor-plans,and surrounding urban environments.The C_(P) results are in close agreement with experimental data,reducing 60%-77% the prediction error on the openings regarding the EnergyPlus software.The platform introduced shows being a reliable and practical C_(P) data source for NV modeling in real building design scenarios.

Wind pressure acting on greenhouses: A review

Greenhouses are widely used in agricultural and horticultural production.With the characteristics of lightweight,small stiffness and high flexibility,greenhouses are sensitive to wind loads.In the calculation of wind loads,the wind pressure coefficient(Cp)is essential.The rationality of the value directly affects the safety and economy of greenhouses.Therefore,the Cp values estimation is one of the most important issues in the design of greenhouses.In order to make full use of the existing research results,in this study,three main methods for estimating Cp values were analyzed,namely,full-scale field experiment,wind tunnel experiment and numerical simulation.Five factors influencing the Cp values were then reviewed including greenhouse design parameters,greenhouse group,overhanging eaves,ventilation and wind direction.Based on the existing researches,suggestions for future development and research work were also put forward.Owing to the flexibility and deformability of greenhouses,the fluid-solid coupling method should be used to analyze the effects of vibrations on wind pressures.The interaction of building parameters(such as the number of spans,ridge height,roof shape and slope angle)and terrain around the greenhouse should be taken into consideration comprehensively.The destructive vortices occurred on the greenhouse should be further investigated.

Effect of change in large and fast solar wind dynamic pressure on geosynchronous magnetic field

We present a comparison of changes in large and sharp solar wind dynamic pressure, observed by several spacecraft, with fast disturbances in the magnetospheric magnetic field, measured by the geosynchronous satellites. More than 260 changes in solar wind pressure during the period 1996-2003 are selected for this study. Large statistics show that an increase （a decrease） in dynamic pressure always results in an increase （a decrease） in the magnitude of geosynchronous magnetic field. The amplitude of response to the geomagnetic field strongly depends on the location of observer relative to the noon meridian, the value of pressure before disturbance, and the change in amplitude of pressure.

Effect of chimney shadow on the performance of wind supercharged solar chimney power plants:A numerical case study for the Spanish prototype

Three-dimensional numerical simulations for a solar chimney power plant(SCPP)and wind supercharged solar chimney power plant(WSSCPP)based on the Spanish prototype using the solar ray-tracing algorithm were performed to study the shadow effect of the chimney.The area of the shadow region increases with an increase in the incident angle of the solar rays.A parametric study was performed by varying the incident angle from 0°to 30°.The temperature and velocity distributions at different incident angles were analyzed.In addition,we investigated the chimney shadow effect in several comprehensive SCPP systems.The findings show that the turbine shaft powers of the SCPP and WSSCPP were reduced by 22.4%and 13.7%,respectively,when the incident angle increased from 0°to 30°.In conclusion,it is important to consider the chimney shadow effect when estimating the performance in the design and cost analysis of SCPP systems.

Structural Analysis of Timber Gridshell Covered by OSB Panels Considering the Effect of Wind

Timber gridshells have been increasingly gaining attention for combining structural efficiency with an attractive architectural design.The use of timber in this structural system gives freedom to the architectural configuration and implies light and efficient construction.This study presents a methodology for the structural analysis of a gridshell covered by OSB(oriented strand board)panels,taken as a case study,and evaluates the model using finite element analysis.The gridshell’s final geometry was obtained from simulations of the effect of permanent load on the mesh.The structural evaluation was numerically estimated via ANSYS software’s CFX platform,considering the effect of wind on the fluid-structure interaction,as well as the results of a static analysis of the structure,including ultimate and serviceability limit state verifications.To assess the influence of the OSB panels on the gridshell’s behavior,two values of elastic modulus are considered.The analysis of a timber gridshell,which covers a span of 14 m by 28 m,demonstrated that this lightweight structure can be considered rigid,and the increase in stiffness of the OSB panels,used as the structure’s coating,can represent an expressive strength and stiffness gain for this type of gridshell.

Wind tunnel simulation of wind loading on a solid structure of revolution

The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.

Study of the wind-pressure distribution of flat-roof parabolic condensers based on wind-tunnel tests

The structure of parabolic condensers makes them susceptible to wind load because of their thin and large windward mirrors.In this paper,the wind pressure on a model of a condenser mirror(1:35)on multistorey flat roofs is analysed via pressure measurement in a wind tunnel.The mean wind-pressure distribution law of flat-roof condenser mirrors(including the change law with working conditions and the maximum distribution characteristics)and the distribution law of fluctuating and extreme wind pressure are obtained.Furthermore,by comparison with the ground-based condenser distribution law,similarities and differences between the two are obtained.Research results show that the wind-pressure distribution law of flat-roof parabolic condenser mirrors is the same as those on the ground,but the mean wind-pressure coefficient(absolute value)is generally~30%smaller.Furthermore,the maximum effect is generally located at the windward mirror edge and the mirror is more susceptible to wind pressure in wind directions of 30°and 135°-150°.The results of this study can provide a theoretical reference for wind-resistant structure design and multistorey flat-roof condenser-related research.

Causes of seasonal sea level anomalies in the coastal region of the East China Sea

Based on the analysis of sea level, air temperature, sea surface temperature（SST）, air pressure and wind data during 1980-2013, the causes of seasonal sea level anomalies in the coastal region of the East China Sea（ECS） are investigated. The research results show：（1） sea level along the coastal region of the ECS takes on strong seasonal variation. The annual range is 30-45 cm, larger in the north than in the south. From north to south, the phase of sea level changes from 140° to 231°, with a difference of nearly 3 months.（2） Monthly mean sea level（MSL）anomalies often occur from August to next February along the coast region of the ECS. The number of sea level anomalies is at most from January to February and from August to October, showing a growing trend in recent years.（3） Anomalous wind field is an important factor to affect the sea level variation in the coastal region of the ECS. Monthly MSL anomaly is closely related to wind field anomaly and air pressure field anomaly. Wind-driven current is essentially consistent with sea surface height. In August 2012, the sea surface heights at the coastal stations driven by wind field have contributed 50%-80% of MSL anomalies.（4） The annual variations for sea level,SST and air temperature along the coastal region of the ECS are mainly caused by solar radiation with a period of12 months. But the correlation coefficients of sea level anomalies with SST anomalies and air temperature anomalies are all less than 0.1.（5） Seasonal sea level variations contain the long-term trends and all kinds of periodic changes. Sea level oscillations vary in different seasons in the coastal region of the ECS. In winter and spring, the oscillation of 4-7 a related to El Ni？o is stronger and its amplitude exceeds 2 cm. In summer and autumn, the oscillations of 2-3 a and quasi 9 a are most significant, and their amplitudes also exceed 2 cm. The height of sea level is lifted up when the different oscillations superposed. On the other hand, the height of sea level is fallen down.

Streamwise Vorticity Equation

A streamwise vorticity equation is derived in generalized natural coordinates. This equation reveals that the total change and local change of the streamwise vorticity are mainly determined by the curvature of streamline, unsteady feature of streamline and magnitude of velocity. This equation enables the study of mesoscale or small-scale systems since the term associated with pressure gradient force in the original vorticity equation is replaced by terms associated with streamlines and wind speed. With this modification the wind field rather than the pressure field is used in the calculation considering that 1) the pressure field is to adapt wind field. 2) Smoother and more consecutive streamline pattern is easier to obtain either by data analysis or by the numerical simulation. From this sense, this present study suggests the application of this equation to studying the evolution of severe storm system as well as other simplified cases. Key words Wind field instead of pressure field - Generalized natural coordinate - Streamwise vorticity This work was supported by the project on the study of the formative mechanism and predictive theory of the significant climate and weather disaster in China under Grant G 1998040907 and by the key project on the Dynamic Study of Severe Mesoscale Covective Systems sponsored by the National Natural Science Foundation of China under Grant No. 49735180.

Characteristics and possible causes of the seasonal sea level anomaly along the South China Sea coast

Based on sea level, air temperature, sea surface temperature（SST）, air pressure and wind data during 1980–2014,this paper uses Morlet wavelet transform, Estuarine Coastal Ocean Model（ECOM） and so on to investigate the characteristics and possible causes of seasonal sea level anomalies along the South China Sea（SCS） coast. The research results show that：（1） Seasonal sea level anomalies often occur from January to February and from June to October. The frequency of sea level anomalies is the most in August, showing a growing trend in recent years. In addition, the occurring frequency of negative sea level anomaly accounts for 50% of the total abnormal number.（2） The seasonal sea level anomalies are closely related to ENSO events. The negative anomalies always occurred during the El Ni？o events, while the positive anomalies occurred during the La Ni？a（late El Ni？o） events. In addition, the seasonal sea level oscillation periods of 4–7 a associated with ENSO are the strongest in winter, with the amplitude over 2 cm.（3） Abnormal wind is an important factor to affect the seasonal sea level anomalies in the coastal region of the SCS. Wind-driven sea level height（SSH） is basically consistent with the seasonal sea level anomalies. Moreover, the influence of the tropical cyclone in the coastal region of the SCS is concentrated in summer and autumn, contributing to the seasonal sea level anomalies.（4） Seasonal variations of sea level, SST and air temperature are basically consistent along the coast of the SCS, but the seasonal sea level anomalies have no much correlation with the SST and air temperature.

ADJUSTMENT OF WIND AND PRESSURE FIELDS IN THE BOUNDARY LAYER

The vertical transport of mass at the top of the boundary layer is considered as a link between the boundary layer and free atmosphere.The adjustment of the wind and pressure fields in the boundary layer is studied under the consideration of the interaction between the boundary layer and free atmosphere.The vertical motion at the top of the boundary layer is evaluated.The results show that the distinguished differ- ences of the present results from classical Ekman layer do exist and they are discussed in the paper.

Post-noon ionospheric absorption observed by the imaging riometers at polar cusp/cap conjugate stations

An example of post-noon ionospheric absorption observed by the imaging riometers at Ny-Alesund / Danmarkshavn in the arctic region and Zhongshan Station in Antarctic is presented. The post-noon absorption observed simultaneously between the hemispherical stations was a spike-type with weak intensity (<1 dB) during the high solar wind dynamic pressure. The absorption spikes might be caused by precipitation of highrenergy electrons (30 - 300 keV) in the closed dayside magnetosphere. It should be noted that the precipitation region of the absorption spike associated with the steep pressure increase (~ 13 nPa) was localized and shifted equatorward.

Device for determining critical wind speed of stalk breaking to evaluate maize lodging resistance

The accurate evaluation of the lodging resistance of maize plants can provide a basis for the breeding of lodging-resistant cultivars and the regulation of cultivation measures.However,the traditional methods for evaluating maize lodging resistance in terms of plant morphology and stalk mechanical strength have certain limitations.The objective of this research was to develop a device for determining the critical wind speed of maize stalk breaking.The device was equipped with a centrifugal fan to supply airflow and was powered by a frequency conversion motor.The frequency converter adjusted the motor speed and thus adjusted the wind speed.The wind speed decreased first and then increased with increasing height above the outlet of the device,and maximum wind speed can reach 40 m/s.This device was convenient for transportation in the field,has a low cost,and can quickly,accurately,and objectively determine the lodging resistance.Field tests showed that the device ran stably for a long time.The coefficient of variation of three repeated measurements was between 1.5%and 4.8%for four maize cultivars.The new device can measure the critical wind speed of maize lodging and identify the lodging resistance for different maize cultivars,cultivation practices,and plant health conditions,and can thus overcome barriers to measuring the maize lodging resistance under natural wind conditions.