Negative Wind Pressure Research Articles

Influence of Ridge Height of Pipe-Framed Greenhouses on Wind Pressure Coefficients

Taller pipe-framed greenhouses (pipe houses hereafter) are required to maintain a buffer zone for an improved thermal environment or to install devices for controlling the thermal environment, such as movable curtains. This study investigates the effect of ridge height on the distributions of the wind pressure coefficient (C p ) on pipe houses based on a wind tunnel experiment using 1:20 scale models. The width and length of a standard pipe house in full scale were 6 and 50 m, respectively, while the ridge height was varied from 3.16 to 5.16 m. The results indicate that the C p distribution on the windward roof was strongly affected by the ridge height when the wind direction was normal to the ridge line. The windward roof was generally subjected to negative wind pressure (suction). The suction had a maximum value behind the windward eave, which increased in magnitude with an increase in ridge height. This effect may be related to the flow separation at the windward eave and reattachment on the windward roof. As a result, the drag and lift coefficients (C D and C L ) obtained from the C p distribution were also affected by the ridge height. High suctions were induced locally at the ridge corner of the leeward roof with an oblique wind.

A model of probability density function of non-Gaussian wind pressure with multiple samples

The extreme value of non-Gaussian wind pressure coefficients is usually estimated by fitting the probability density function (PDF) of maximum or minimum values while a large number of observations except the peak values in the measured samples are discarded. The implicit or explicit translation between non-Gaussian and Gaussian histories can also be utilized to estimate the extreme value of non-Gaussian wind pressure coefficients while the randomness of aerodynamic effect is not taken into account. The Hermite moment models are summarized and applied to formulate the PDF of non-Gaussian peak factors which is expressed as the joint PDF (JPDF) of the shape parameters of the Hermite moment model and the PDF of the translated Gaussian peak factors. After the variations of mean, standard deviation and non-Gaussian peak factor are considered, an innovative and analytical PDF formula of extreme wind pressure coefficients for multiple samples, which is expressed as a function of the JPDF of mean, standard deviation and the PDF of non-Gaussian peak factor, is presented in this paper. The theoretical developments are applied to establish the PDF and cumulative density function (CDF) of the negative peak wind pressure coefficients with multiple samples. It is verified that the analytical probability distribution model is a reasonable model to estimate the peak pressure coefficients.

Prediction of negative peak wind pressures on roofs of low-rise building

In this paper, a probability distribution which is consistent with the observed phenomenon at the roof corner and, also on other portions of the roof, of a low-rise building is proposed. The model is consistent with the choice of probability density function suggested by the statistical thermodynamics of open systems and turbulence modelling in fluid mechanics. After presenting the justification based on physical phenomenon and based on statistical arguments, the fit of alpha-stable distribution for prediction of extreme negative wind pressure coefficients is explored. The predictions are compared with those actually observed during wind tunnel experiments (using wind tunnel experimental data obtained from the aerodynamic database of Tokyo Polytechnic University), and those predicted by using Gumbel minimum and Hermite polynomial model. The predictions are also compared with those estimated using a recently proposed non-parametric model in regions where stability criterion (in skewness-kurtosis space) is satisfied. From the comparisons, it is noted that the proposed model can be used to estimate the extreme peak negative wind pressure coefficients. The model has an advantage that it is consistent with the physical processes proposed in the literature for explaining large fluctuations at the roof corners.

Finite Element Analysis on Negative Wind Pressure Stress of External Wall Insulation Layer

With excellent flame retardation and thermal insulation properties, SY self-temperature regulation and phase change energy-saving wall insulation material (the material) is composed of concrete and volcano perlite. At present, applied research of this material is not very thorough,especially under the condition of temperature variation, seasonal wind change in North China. In this paper, finite element analysis of external wall insulation layer of the Experimental Teaching Building in Taiyuan University of Science and Technology under negative wind pressure effect is performed. The negative wind load calculated is applied to the surface of the thermal insulation layer as uniform load, and the results show that the material used in the building which shorter than 80 meters in the Taiyuan area has no shedding or destruction under the negative air pressure. This material is safe and available.

Shielding Effects of Surrounding Buildings on Wind Loads on Low-Rise Building Roofs

Low-rise buildings are often built in groups, and their wind loads differ from those on isolated buildings. In this study, the wind pressures on flat roofs of low-rise buildings surrounded by similar buildings were measured with a series of wind tunnel tests. The general properties of the shielding effects of surrounding buildings were discussed. The effects of area density, relative height, and arrangement patterns of the surrounding buildings on the shielding factors of the smallest minimum negative extreme wind pressure coefficients and of the largest peak uplift force coefficients on the whole roof of the shielded building for all wind directions were analyzed. For practical purposes, both shielding factors were expressed as equations of the building area density and the relative height of the surrounding buildings based on the wind tunnel test data, which can cover most of the test results.

Wind Loads on Single-span Plastic Greenhouses and Solar Greenhouses

Wind tunnel tests were conducted in an NH-2-type wind tunnel to investigate the wind pressure coefficients and their distribution on the surfaces of a single-span plastic greenhouse and a solar greenhouse. Wind pressures at numerous points on the surfaces of the greenhouse models were simultaneously measured for various wind directions. The critical wind speeds, at which damage occurred on the surfaces of single-span plastic greenhouses and solar greenhouses, were derived. To clearly describe the wind pressure distribution on various surface zones of the greenhouses, the end surface and top surface of the plastic greenhouse and the transparent surface of the solar greenhouse were divided into nine zones, which were denoted as Zone I to Zone IX. The results were as follows: 1) At wind direction angles of 0° and 45°, the end surface of the single-span plastic greenhouse was on the windward side, and the maximum positive wind pressure coefficient was near 1. At wind direction angles of 90° and 180°, the entire end surface of the single-span plastic greenhouse was on the leeward side, and the maximum negative wind pressure coefficient was near −1. The maximum positive wind pressure on the end surface of the single-span plastic greenhouse appeared in Zone IV at a wind direction angle of 15°, whereas the maximum negative pressure appeared in Zone VIII at a wind direction angle of 105°. 2) Most of the wind pressure coefficients on the top surface of the plastic greenhouse were negative. The maximum positive and negative wind pressure coefficient on the top surface of the plastic greenhouse occurred in Zones I and II, respectively, at a wind direction angle of 60°. 3) At a wind direction angle of 0°, the distribution of wind pressure coefficient contours was steady in the middle and lower zones of the transparent surface of the solar greenhouse, and the wind pressure coefficients were positive. At a wind direction angle of 90°, the wind pressure coefficients were negative on the transparent surface of the solar greenhouse. A maximum positive wind pressure coefficient was attained at a wind direction angle of 30° in Zone IX, whereas the maximum suction force occurred in Zone VII at a wind direction angle of 135°. 4) The minimum critical wind speeds required to impair the single-span plastic greenhouse and solar greenhouse were 14.5 and 18.9 m·s−1, respectively.

Study on effect of wind on natural smoke exhaust of enclosure fire with a two-layer zone model

Effect of wind on natural smoke exhaust in enclosure fire with a two-layer zone model was studied in this paper. A “net wind pressure coefficient” was proposed to evaluate the significance of wind effect. Case calculations on quasi-steady vented stage of natural smoke exhaust were performed. It is shown that with a negative net wind pressure coefficient, performance of exhaust will be degraded by the wind, even invalidated. The critical wind speed invalidating natural smoke exhaust is found inversely proportional to the absolute value of the net wind pressure coefficient. Experimental data in a model room is presented and compared with the predicted values using the two-layer zone model. Good agreements were found between the predicted and experimental results except in the cases with a non-positive net wind pressure coefficient. Discrepancies are ascribed to the disturbance of the vent flow and stratification in the room by the wind. While activating natural smoke exhaust system in case of fire under the windy condition, positions of the smoke vent and air inlet should be located with consideration according to the wind direction to form a big positive net wind pressure coefficient as possible and to increase the exhaust efficiency.

Wind Tunnel Tests for Wind Pressure Distribution on Gable Roof Buildings

Gable roof buildings are widely used in industrial buildings. Based on wind tunnel tests with rigid models, wind pressure distributions on gable roof buildings with different aspect ratios were measured simultaneously. Some characteristics of the measured wind pressure field on the surfaces of the models were analyzed, including mean wind pressure, fluctuating wind pressure, peak negative wind pressure, and characteristics of proper orthogonal decomposition results of the measured wind pressure field. The results show that extremely high local suctions often occur in the leading edges of longitudinal wall and windward roof, roof corner, and roof ridge which are the severe damaged locations under strong wind. The aspect ratio of building has a certain effect on the mean wind pressure coefficients, and the effect relates to wind attack angle. Compared with experimental results, the region division of roof corner and roof ridge from AIJ2004 is more reasonable than those from CECS102:2002 and MBMA2006.The contributions of the first several eigenvectors to the overall wind pressure distributions become much bigger. The investigation can offer some basic understanding for estimating wind load distribution on gable roof buildings and facilitate wind-resistant design of cladding components and their connections considering wind load path.

Characteristics of Wind Loads Acting on Complex Long-Span Roof Structure

The Shenzhen New Railway Station (SNRS) has roof dimensions of 450 m long and 408 m wide. This paper presents the results of wind loads acting on the large-span roof structure. In the wind tunnel test, wind-induced pressures including mean and fluctuating components were measured from the roof of a 1:200 scale SNRS model under suburban boundary layer wind flow configuration in a boundary layer wind tunnel of HD-2 at Hunan University. Based on the data obtained simultaneously from the wind tunnel tests, the distributions of the mean and fluctuating wind pressure coefficients and the characteristics of probability density functions of wind pressures of typical pressure taps were analyzed in detailed. The outcomes of the experimental study indicate that: (1) The maximum mean negative wind pressure coefficients on the roof occur at the windward leading edge region, where the maximum fluctuating wind pressure coefficients occur also in this region; (2) There are some differences of the maximum mean negative wind pressure coefficients and RMS wind pressure coefficients under conditions with different number of trains inside the station, but such effects on the overall pressure distributions on the whole roof are negligible; (3) There are clearly negative skewed distributions for some pressure taps at the windward leading roof edge and much longer negative tails are observed, which follow Non-Gaussian distributions. The results presented in this paper are expected to be of considerable interest and of use to researchers and professionals involved in designing complex long-span roof structures.

Load-Carrying Capacity of Glass Panel on Different Wind Pressure Conditions

The variable regulation of maximum principle stress and deflection of glass panel in hidden curtain wall were analyzed by using uniform negative and positive wind pressure tests. The curve of maximum principle stress and deflection were compared in the two different wind pressure conditions. The glass panel used in specimen is monolithic toughened glass. The dimension of the glass panel is 1000mm×1000mm and its thickness is 6mm. The dimension of silicone structural sealant is 12mm×8mm. Test result indicated that the maximum principle stress and deflection of every test point increase linearly with the increasing of the uniform load from 0.5kPa to 2.0kPa; the curve of maximum principle stress and flexural performance of glass panel have obvious differences when the specimen was tested in negative and positive wind pressure. When the glass panel was tested in positive wind pressure, its load-carrying capability was better than it was tested in negative wind pressure. The flexural performance of glass panel was also in the same way.

Multisatellite observations of the outer zone electron variation during the November 3–4, 1993, magnetic storm

The disappearance and reappearance of outer zone energetic electrons during the November 3–4, 1993, magnetic storm is examined utilizing data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the Global Positioning System (GPS) series, and the Los Alamos National Laboratory (LANL) sensors onboard geosynchronous satellites. The relativistic electron flux drops during the main phase of the magnetic storm in association with the large negative interplanetary Bz and rapid solar wind pressure increase late on November 3. Outer zone electrons with E > 3 MeV measured by SAMPEX disappear for over 12 hours at the beginning of November 4. This represents a 3 orders of magnitude decrease down to the cosmic ray background of the detector. GPS and LANL sensors show similar effects, confirming that the flux drop of the energetic electrons occurs near the magnetic equator and at all pitch angles. Enhanced electron precipitation was measured by SAMPEX at L ≥ 3.5. The outer zone electron fluxes then recover and exceed prestorm levels within one day of the storm onset and the inner boundary of the outer zone moves inward to smaller L (<3). These multiple‐satellite measurements provide a data set which is examined in detail and used to determine the mechanisms contributing to the loss and recovery of the outer zone electron flux. The loss of the inner part of the outer zone electrons is partly due to the adiabatic effects associated with the decrease of Dst, while the loss of most of the outer part (those electrons initially at L ≥ 4.0) are due to either precipitation into the atmosphere or drift to the magnetopause because of the strong compression of the magnetosphere by the solar wind. The recovery of the energetic electron flux is due to the adiabatic effects associated with the increase in Dst, and at lower energies (<0.5 MeV) due to rapid radial diffusion driven by the strong magnetic activity during the recovery phase of the storm. Heating of the electrons by waves may contribute to the energization of the more energetic part (>1.0 MeV) of the outer zone electrons.