ЧИСЛЕННОЕ ОПИСАНИЕ ВЕТРОВЫХ НАГРУЗОК НА ПРИМЕРЕ ЗДАНИЯ В ФОРМЕ КОНУСА РЕЛО

More than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed. Wind flow over the foredunes is studied by means of the relative wind speed: the ratio between wind speed at a certain location and the reference wind speed at the same height. Relative wind speeds appear to be independent of general wind speed but dependent on wind direction. For perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness. Accelerations dominate over decelerations on the seaward slope. The pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes, but the magnitudes differ. An increase in foredune height from 6 to 10m leads to an increase in speed‐up near the top of the seaward slope from 110 to 150 per cent during onshore wind, but further increase of foredune height from 10 to 23m appears to have little effect, due to increased roughness and deflection of flow.Topography also influences the direction of the flow. Between beach and top, the flow deflects in the direction of the normal during onshore winds. During offshore winds the flow is deflected to the parallel. Near the dunefoot, deflection is always in the direction of the parallel, and increases with steeper topography. The maximum deflection near the dunefoot was 90°, over a 23 m high dune, observed during offshore winds.Patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations. Owing to speed‐up on the seaward front of the foredune, sand transport capacity of the wind increases, which results in erosion if vegetation is absent. During strong onshore wind, sand is lifted near the dunefoot and moves over the foredune in suspension. During weaker winds, vertical wind velocities do not exceed fall velocities of the sand grains, and most of the sand is deposited near the dunefoot.

Influence of surrounding buildings on wind flow around a building predicted by CFD simulations

With the advancement in material science, construction technology and structural analysis, a new building code was essential to keep pace with technological advantages. Recently introduced BNBC 2020 bridges the gap largely. A very basic change in lateral loading provision has occurred in the new code, which accounts for several newly defined parameters. For wind analysis, the new code introduces 3-second gust velocity as basic wind speed, wind pressure application in four cases that accounts for eccentricity. It considers topographic and internal pressure effect. A new seismic zoning is introduced in BNBC 2020 with revised PGA values and spectral acceleration. The code also introduces seismic design category and revised response reduction factor. All these changes will affect the design practice. To understand and compare lateral loading in different zones, a FEA of 20 storied RC building with and without core shear wall was analyzed using ETABS V18. The comparison shows that Rajshahi (Zone I) has lowest wind and seismic loading, Chattogram (Zone III) has highest seismic and wind loading while, Dhaka (Zone II) has moderate seismic and wind loading. Wall frame building has slightly larger seismic base shear while shear wall resists major portion of base shear and reduces top story displacement and story drift greatly. The cost of construction in zone III is significantly larger than in zone I and II. In all zones shear wall building imparts economic structural solution compared to bare frame against lateral loading for 20 storied buildings and the margin of economy increases with increasing lateral loading.

Wind loads on a building are sensitive to a number of factors, including the wind speed approaching the site, building height and shape, and the local influence of nearby buildings on the wind flow patterns. Building codes attempt to allow for these factors by providing simple formulae for calculating design wind loads that will be at least conservative. The American Society of Civil Engineers (ASCE) 7 Standard [1] and most other building codes recognize that for irregularly shaped buildings or structures that may have unusual response characteristics it is advisable to undertake detailed wind load studies or use wind tunnel methods of analysis. Wind tunnel methods determine the wind loading on a structure with increased precision, which leads to more economical and risk consistent structural designs than do code calculation methods. This paper describes the wind tunnel method of determining cladding wind loads, and provides comparisons between the wind tunnel method and code calculation methods for a 22-story building.

Advancements in computer software and hardware technology provide a new direction for analyzing engineering problems. Recently the field of wind engineering has gained significant momentum in the computer modelling process. This paper reviews the state of the art in computational wind engineering, including the finite element method, finite difference method, and control volume technique. A portion of this paper summarizes the research in this area carried out by the authors. Computations have been made for a variety of building configurations, including normal wind flow conditions for a building with different aspect ratios, and modelling wind environmental conditions around groups of buildings. The computer modelling technique may eventually enhance the design of buildings and structures against wind loading and supplement the current design practice of using building codes and standards or performing experiments in wind tunnels. Key words: buildings, computer modelling, pressure, velocity, wind engineering, wind tunnels.

Three-center cylindrical latticed shell closed cargo shed is a typical wind-sensitive structure, and wind load is one of the control loads in structural design. Based on the background of three three-center cylindrical latticed shell closed cargo sheds in a comprehensive wharf project, wind tunnel tests and numerical analysis on various factors affecting wind load of closed sheds were carried out. The influence of the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions on the wind load of the closed cargo shed was studied, the calculation results of closed cargo sheds designed by the wind load in wind tunnel test results, load codes and related literature are compared. Through the research, it is found that the ventilation roof, the opening and closing of doors and windows, the interference between three sheds, and the wind speed reduction related to wind directions had great influence on the wind tunnel test results, there were potential safety hazards in the structural design of closed sheds by the wind load in load codes and related literatures, the wind tunnel test of this kind of long-span closed sheds should be conducted before the detailed design, and the various actual working conditions of the sheds should be taken into account and correctly reflected during the wind tunnel test.

Calibration of the quasi-static and peak-factor approaches to the assessment of wind loads against the method of Cook and Mayne

Wind load is often defined as a static uniform distributed load in the design code, especially on small structures such as billboard, pedestrian cross bridge, etc. However, as a fluid, wind can deform from a laminar flow to a turbulence flow or it can also be amplified if enough disturbance around the object exists. If these small structures are not designed for a dynamic load or the corrected amplified load, it will collapse. This study aims to investigate the effect of street canyon width towards wind flow by observing a simplified model of 4 symmetrical high-rise buildings with changing street canyon width. The numerical model uses CFD with RANS in OpenFOAM v1912 which is validated with experimental results using a low wind speed wind tunnel and Particle Image Velocimetry (PIV). An Experiment has been performed in BBTA3 using a model with 1:420 scale, there are 2 models with different street canyon width. The result showed there is an increment of the mean wind speed about 5.92-20.20%.

Wind energy is considered as one of the most promising renewable energy sources due to its abundance and the high energy conversion efficiency of a wind turbine. Because wind flow is complex and highly variable, accurately predicting wind turbine responses such as power and loads speed is challenging. These responses are generally computed by computational wind turbine analysis tools that uses a wind flow as an input. In this study, we propose a machine learning approach to predict wind turbine responses using wind flow data as a direct input. Specifically, we use Multi-Tasks Convolutional Long Short-Term Memory Network to simultaneously predict the energy output and structural load from the target wind turbine while modeling the spatio-temporal structure of the input wind flow. The simulation experiment shows that the proposed model predicts the both outputs within a 5% error.

Computational fluid dynamic analysis of wind flow around Mangrove roots to reduce the damage due to heavy wind

The article is devoted to issues related to the probabilistic justification of the safety of nuclear power plants (NPP) when a high-speed military aircraft falls. The random parameters are the recurrence of falls and the direction of the aircraft's trajectory. The conservative value of the recurrence of falls, given in the IAEA documents, was used, which ensures a high degree of NPP safety. The aircraft approach is assumed to be equally probable from either side. The trajectory slope is specified taking into account the IAEA documents and statistics of aviation accidents.
 
 The aircraft impact load is applied to one of the structures, therefore the impact probability must be determined independently for each of them. It is proportional to the equivalent area of the building structure, depending on its size, shape, position in space and in relation to other structures. Expressions are given for the equivalent areas of structures of various shapes, typical for NPP. It is shown that if the aircraft crash is unintentional (accident), then with the usual dimensions of structures, the probability of an impact in them is less than the value, starting from which, according to Russian standards, it must be taken into account in the design basis of the NPP, i.e. it can be ignored. Dependencies are given for calculating the probability of an aircraft strike in the case of a deliberately organized accident (terrorist attack), in which the aircraft will surely fall on the territory of “Nuclear Island” of the NPP.
 
 The procedure for setting the design loads on the building structures of a NPP in the case of a deliberate aircraft fall based on the allowed probability of their realization is described. It is shown that this method of setting the loads makes it possible to substantiate their significant reduction, which leads to a reduction in the cost of the NPP while guaranteeing its safety. A probabilistic assessment of structures safety of existing NPP in the event of an aircraft impact is discussed.

Probabilistic serviceability-performance assessment of tall mass-timber buildings subjected to stochastic wind loads: Part I - structural design and wind tunnel testing

A numerical study of wind loads on a semisubmersible platform is presented on this paper. The techniques of Computational Fluid Dynamics (CFD), such as Reynolds Averaged Navier-Stokes Equations (RANS) model and Large Eddy Simulation (LES), etc., were adopted in this study to predict wind loads on and wind flows around the platform. The main objective of this study is to explore an effective and reliable approach for evaluation of wind loads on offshore structures by CFD methods. The computed results were compared with experimental data which obtained at wind tunnel test. It was found through the comparison that the LES with a dynamic sub grid-scale (SGS) model can give satisfactory predictions for mean and dynamic wind loads on the tall structures. Therefore, it is necessary to correctly simulate both the incident wind velocity profile and turbulence intensity profile in CFD computations to accurately predict wind effects on huge structures. The recommend CFD techniques and associated numerical treatments provide an effective way for designers to assess wind effects on offshore platforms and the need for a detailed wind tunnel test.

The seismic response of building structures can be estimated by several analysis methods. Each approach incorporates different assumptions and varies in complexity of application. The traditional approach is to employ equivalent static analysis methods while current design practice is moving towards an increased emphasis on nonlinear analysis methods. This study examined the seismic performance of multistory buildings designed according to Egyptian code. Nonlinear time history analysis is used for evaluation of equivalent static and response spectra procedures that recommended by Egyptian codes for seismic design of building structures. In this study, a preliminary seismic response analysis of two buildings was performed using three analysis procedures to evaluate the building seismic performance and the difference in global response predicted by the three methods. Moreover, three analysis procedures are evaluated for their ability to predict deformation demands in terms of inter-story drifts and potential failure mechanisms. Three ground motions of earthquake records are used for seismic demands evaluation of these buildings. The results demonstrated that, for the three analysis methods used in this study, different predictions of seismic response occurred. Furthermore, the results of the analyses are used to evaluate the advantages, limitations, and ease of application of each approach for seismic analysis. Each method is shown to have merits and deficiencies that should be considered when selecting a seismic analysis method for a particular building structure.

Sharing of Temporary Structures: Formalization and Planning Application