scholarly journals Comparative Study on Non-Gaussian Characteristics of Wind Pressure for Rigid and Flexible Structures

2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
Lei Jiang ◽  
Jin-hua Li ◽  
Chun-xiang Li
Keyword(s):  
Empirical Formula ◽  
Flexible Structures ◽  
Wind Pressure ◽  
Windward Side ◽  
Leeward Side ◽  
Flexible Structure ◽  
Probability Density Distribution ◽  
Statistical Parameters ◽  
Rigid Structure ◽  
Non Gaussian

This paper summarizes a comprehensive study for non-Gaussian properties of wind pressure. The field measurements are implemented on the structure surface of a rigid structure, while a large-span membrane structure is selected as the flexible structure wind pressure contrast group. The non-Gaussian characteristics of measured pressure data were analyzed and discussed through probability density distribution, characteristic statistical parameters, power spectral density function, and the correlations, respectively. In general, the non-Gaussian characteristics of wind pressure present depending on tap location, wind direction, and structure geometry. In this study, the fluctuating wind pressures on the windward side and leeward side of the structures show obvious different degrees of non-Gaussian properties; that is, the surface of rigid structure shows strong non-Gaussian property in leeward, while the roof of flexible structure shows obvious non-Gaussian property in windward. Finally, this paper utilizes the present autospectrum empirical formula to fit the wind pressure power spectrum density of the measured data and obtains the conclusion that the existing empirical formula is not ideal for fitting of the flexible structure.

The Numerical Simulation of the Impact on the Hangzhou Bay Bridge Offshore Platform and the Sightseeing Tower

2012 ◽  
Vol 532-533 ◽  
pp. 352-356
Author(s):  
Hua Bai ◽  
Fang Liang Wang ◽  
Yu Li
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Surface Pressure ◽  
Wind Tunnel Test ◽  
Offshore Platform ◽  
Wind Pressure ◽  
Windward Side ◽  
Hangzhou Bay ◽  
Leeward Side ◽  
The Impact

In this paper, the distribution of surface wind pressure and wind speed of Hangzhou bay bridge, offshore platform and sightseeing tower is numerically simulated based on Fluent. Two turbulence models, standard k ε model and Realizable k ε model, are used. The influence of the wind pressure distribution of the offshore platform and sightseeing tower by Hangzhou bay bridge is also analyzed. And the detailed comparison between numerical simulation and wind tunnel test is given. Results show that the impact of Hangzhou bay bridge on platform and sightseeing tower occurs mainly with the angle of the wind less than 450. When the angle of the wind is more than 450, the impact is little. The upper of the sightseeing tower does not almost suffer the effect of other buildings. The surface pressure of the platform changes from 5% to 15% between under bridge and under non-bridge condition. The surface pressure of sightseeing tower changes from 0.05% to 3%. The influence on the platform by the bridge is significant but not significant on the sightseeing tower. The simulation results of the tower and mast structure given by both standard k ε model and Realizable k ε model find that the windward side is ideal; the crosswind side is the best; the leeward side is less than ideal. By contrast, the Realizable k ε model is a closer correlation with wind tunnel test than standard k ε model.

Investigation on the drag effect of a rolling element confined in the cavity of a cylindrical roller bearing

2021 ◽  
pp. 135065012110260
Author(s):  
Wenjun Gao ◽  
Shuo Zhang ◽  
Xiaohang Li ◽  
Zhenxia Liu
Keyword(s):  
Open Space ◽  
Roller Bearing ◽  
Flow Characteristics ◽  
Experimental Tests ◽  
Windward Side ◽  
Leeward Side ◽  
Drag Effect ◽  
Rolling Element ◽  
Cylindrical Roller Bearing ◽  
Cylindrical Roller

In cylindrical roller bearings, the drag effect may be induced by the rolling element translating in a fluid environment of the bearing cavity. In this article, the computational fluid dynamics method and experimental tests are employed to analyse its flow characteristics and pressure distribution. The results indicate that the pressure difference between the windward side and the leeward side of the cylinder is raised in view of it blocking the flow field. Four whirl vortexes are formed in four outlets of two wedge-shaped areas between the front part of the cylindrical surface and adjacent walls for the cylinder of L/ D = 1.5 at Re = 4.5 × 103. Vortex shedding is found in the direction of cylinder axis at Re = 4.5 × 104. The relationship between drag coefficient and Reynolds number is illustrated, obviously higher than that of the two-dimensional cylinder in open space.

scholarly journals 2.5D Flexible Wind Sensor Using Differential Plate Capacitors

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 3101
Author(s):  
Yu Wan ◽  
Zhenxiang Yi
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Parallel Plate ◽  
Electrode Array ◽  
Copper Electrode ◽  
Windward Side ◽  
Leeward Side ◽  
Electrode Layer ◽  
Young’S Moduli ◽  
Speed Up

In this paper, a novel 2.5-dimensional (2.5D) flexible wind sensor is proposed based on four differential plate capacitors. This design consists of a windward pillar, two electrode layers, and a support layer, which are all made of polydimethylsiloxane (PDMS) with different Young’s moduli. A 2 mm × 2 mm copper electrode array is located on each electrode layer, forming four parallel plate capacitors as the sensitive elements. The wind in the xy-plane tilts the windward pillar, decreasing two capacitances on the windward side and increasing two capacitances on the leeward side. The wind in the z-axis depresses the windward pillar, resulting in an increase of all four capacitances. Experiments demonstrate that this sensor can measure the wind speed up to 23.9 m/s and the wind direction over the full 360° range of the xy-plane. The sensitivities of wind speed are close to 4 fF·m−1·s and 3 fF·m−1·s in the xy-plane and z-axis, respectively.

Air movement and heat loss from sheep. II. Thermal insulation of fleece in wind

1980 ◽  
Vol 209 (1175) ◽  
pp. 209-217 ◽  
Keyword(s):  
Thermal Diffusivity ◽  
Heat Loss ◽  
Thermal Insulation ◽  
General Relation ◽  
Windward Side ◽  
Leeward Side ◽  
Sensible Heat ◽  
Bulk Resistance ◽  
Air Movement ◽  
Dimensionless Constant

Penetration of an animal’s coat by wind reduces its thermal insulation and increases heat loss to the environment. From studies of the sensible heat loss from a life-sized model sheep covered with fleece, the average fleece resistance r¯ f (s cm -1 ) was related to windspeed u (m s -1 ) by 1/ r¯ f ( u ) = l/ r¯ f (0) + cu , where c is a dimensionless constant. As c is expected to be inversely proportional to coat depth Î , the more general relation k¯ ( u ) = k¯ (0) + c'u was evaluated, where k¯ = Î / r¯ f is the thermal diffusivity (cm 2 s -1 ) of the fleece and c' = cÎ is another constant (cm). The orientation of the model to the wind had little effect on the bulk resistance of the fleece, but the resistance on the windward side was substantially lower than on the leeward side.

Non-Gaussian Wind Pressure on Prismatic Buildings. II: Numerical Simulation

2001 ◽  
Vol 127 (9) ◽  
pp. 990-995 ◽  
Author(s):  
Massimiliano Gioffrè ◽  
Vittorio Gusella ◽  
Mircea Grigoriu
Keyword(s):  
Numerical Simulation ◽  
Wind Pressure ◽  
Non Gaussian

Nonlinear Torsional Vibration Absorber for Flexible Structures

2018 ◽  
Vol 86 (2) ◽  
Author(s):  
Xiao-Ye Mao ◽  
Hu Ding ◽  
Li-Qun Chen
Keyword(s):  
High Efficiency ◽  
Rotation Angle ◽  
Flexible Structures ◽  
Nonlinear Energy Sink ◽  
Flexible Structure ◽  
Vibration Absorber ◽  
Special Perturbation ◽  
Energy Sink ◽  
Simulation Parameters ◽  
Nonlinear Energy

A new kind of nonlinear energy sink (NES) is proposed to control the vibration of a flexible structure with simply supported boundaries in the present work. The new kind of absorber is assembled at the end of structures and absorbs energy through the rotation angle at the end of the structure. It is easy to design and attached to the support of flexible structures. The structure and the absorber are coupled just with a nonlinear restoring moment and the damper in the absorber acts on the structure indirectly. In this way, all the linear characters of the flexible structure will not be changed. The system is investigated by a special perturbation method and verified by simulation. Parameters of the absorber are fully discussed to optimize the efficiency of it. For the resonance, the maximum motion is restrained up to 90% by the optimized absorber. For the impulse, the vibration of the structure could attenuate rapidly. In addition to the high efficiency, energy transmits to the absorber uniaxially. For the high efficiency, convenience of installation and the immutability of linear characters, the new kind of rotating absorber provides a very good strategy for the vibration control.

scholarly journals Mechanics based statistical prediction of structure size and geometry effects on safety factors for composites and other quasibrittle materials

2008 ◽  
Vol 35 (1-3) ◽  
pp. 53-71 ◽  
Author(s):  
Zdeněk Bazant
Keyword(s):  
Mathematical Description ◽  
Structural Strength ◽  
Journal Article ◽  
Statistical Prediction ◽  
Probability Density Distribution ◽  
Safety Factors ◽  
Statistical Parameters ◽  
Size And Shape ◽  
Quasibrittle Materials ◽  
Nominal Strength

The objective of this paper1 is a rational determination of safety factors of quasibrittle structures, taking into account their size and shape. To this end, it is necessary to establish the probability density distribution function (pdf) of the structural strength. For perfectly ductile and perfectly brittle materials, the proper pdf's of the nominal strength of structure are known to be Gaussian and Weibullian, respectively, and are invariable with structure size and geometry. However, for quasibrittle materials, many of which came recently to the forefront of attention, the pdf has recently been shown to depend on structure size and geometry, varying gradually from Gaussian pdf with a remote Weibull tail at small sizes to a fully Weibull pdf at large sizes. This recent result is reviewed, and then mathematically extended in two ways: 1) to a mathematical description of structural lifetime as a function of applied (time-invariable) nominal stress, and 2) to a mathematical description of the statistical parameters of the pdf of structural strength as a function of structure size and shape. Experimental verification and calibration is relegated to a subsequent journal article.

scholarly journals Dust-related impacts of mining operations on rangeland vegetation and soil: a case study in Yazd province, Iran

2021 ◽  
Author(s):  
Shahab IbrahimPour ◽  
Alireza KhavaninZadeh ◽  
Ruhollah Taghizadeh mehrjardi ◽  
Hans De Boeck ◽  
Alvina Gul
Keyword(s):  
Seed Germination ◽  
Vegetation Cover ◽  
Microbial Respiration ◽  
Germination Rate ◽  
Windward Side ◽  
Leeward Side ◽  
Mining Operations ◽  
Soil Microbial ◽  
Soil Microbial Respiration ◽  
The Impact

Abstract Destructive mining operations are affecting large areas of natural ecosystems, especially in arid lands. The present study aims at investigating the impact of iron mine exploitation on vegetation and soil in Nodoushan (Yazd province, central Iran). Based on the dominant wind, topography, slope, vegetation and soil of the area, soil and vegetation parameters close to ​the mine were recorded and analyzed according to the distance from the mine. In order to obtain the vegetation cover, a transect and plot on the windward and leeward side of the mine, with 100 m intervals and three replicates at each sampling location was used, yielding 96 soil samples. The amount of dust on the vegetation, the seed weight and seed germination rate of Artemisia sp. as the dominant species within the area, and the soil microbial respiration were measured. The relationship between vegetation cover and distance from the mine was not linear, which was due to an interplay between pollution from the mine and local grazing, while other factors did increase or decrease linearly. The results showed that, as the distance from the mine increased, the weight of 1000 seeds of Artemisia sp. was significantly increased from 271 to 494 mg and seed germination rate and soil microbial respiration were significantly increased from 11.7 to 48.4 % and from 4.5 to 5.9 mg CO2 g− 1 soil day− 1 respectively, while the amount of dust significantly decreased from 43.5 to 6 mg (g plant)−1 between the distance of 100 to 600 m from the mine in the leeward direction. A similar trend was observed in the windward side, though negative effects were lower compared to the same distance along the leeward sample locations. The direct and indirect effects on plant growth and health from mining impacts generally decreased linearly with increasing distance from the mine, up to at least 600 m. Our study serves as a showcase for the potential of bio-indicators as a cost-effective method for assessing impacts of mining activities on the surrounding environment.

scholarly journals ESTIMATION OF PEAK FACTOR FOR NON-GAUSSIAN WIND PRESSURE

2002 ◽  
Vol 67 (557) ◽  
pp. 79-84 ◽  
Author(s):  
Kazuyoshi NISHIJIMA ◽  
Jun KANDA ◽  
Hang CHOI
Keyword(s):  
Wind Pressure ◽  
Peak Factor ◽  
Non Gaussian
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