• Wind and Structures
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• v.29 no.4
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• pp.247-270
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• 2019

Wind-resistant design of existing cooling tower structures overlooks the impacts of rainfall. However, rainstorm will influence aerodynamic force on the tower surface directly. Under this circumstance, the structural response of the super-large cooling tower (SLCT) will become more complicated, and then the stability and safety of SLCT will receive significant impact. In this paper, surrounding wind fields of the world highest (210 m) cooling tower in Northwest China underthree typical wind velocities were simulated based on the wind-rain two-way coupling algorithm. Next, wind-rain coupling synchronous iteration calculations were conducted under 9 different wind speed-rainfall intensity combinations by adding the discrete phase model (DPM). On this basis, the influencing laws of different wind speed-rainfall intensity combinations on wind-driving rain, adhesive force of rain drops and rain pressure coefficients were discussed. The acting mechanisms of speed line, turbulence energy strength as well as running speed and trajectory of rain drops on structural surface in the wind-rain coupling field were disclosed. Moreover, the fitting formula of wind-rain coupling equivalent pressure coefficient of the cooling tower was proposed. A systematic contrast analysis on its 3D distribution pattern was carried out. Finally, coupling model of SLCT under different working conditions was constructed by combining the finite element method. Structural response, buckling stability and local stability of SLCT under different wind velocities and wind speed-rainfall intensity combinations were compared and analyzed. Major research conclusions can provide references to determine loads of similar SLCT accurately under extremely complicated working conditions.

• Wind and Structures
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• v.12 no.4
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• pp.299-312
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• 2009

It has long been studied about the flow around bluff bodies, but the effect of aspect ratio on the sharp-edged bodies in thick turbulent boundary layers is still argued. The author investigates the flow characteristics around a series of rectangular bodies ($40^d{\times}80^w{\times}80^h$, $80^d{\times}80^w{\times}80^h$ and $160^d{\times}80^w{\times}80^h$ in mm) placed in a deep turbulent boundary layer. The study is aiming to identify the extant Reynolds number independence of the rectangular bodies and furthermore understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the shape of bodies is changed, responsible for producing extreme suction pressures around the bluff bodies. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h, of 24,000, 46,000 and 67,000, and large enough that the mean boundary layer flow is effectively Reynolds number independent. The experiment includes wind tunnel work with the velocity and surface pressure measurements. The results show that the generation of the deep turbulent boundary layer in the wind tunnel and the surface pressure around the bodies were all independent of Reynolds number and the longitudinal length, but highly dependent of the transverse width.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.271-280
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• 2004

Assessment of image registration for Pressure Sensitive Paint (PSP) was performed. A 16 bit camera and LED lamp were used with Uni-FIB paint (ISSI). Because of model displacement and deformation at 'wind-on' condition, a large error of the intensity ratio was induced between 'wind-on' and' wind-off images. To correct the error, many kinds of image registrations were tested. At first, control points were marked on the model surface to find the coefficients of polynomial transform functions between the 'wind-off' 'wind-on' images. The 2nd-order polynomial function was sufficient for representing the model displacement and deformation. An automatic detection scheme was introduced to find the exact coordinates of the control points. The present automatic detection algorithm showed more accurate and user-friendly than the manual detection algorithm. Since the coordinates of transformed pixel were not integer, five interpolation methods were applied to get the exact pixel intensity after transforming the 'wind-on' image. Among these methods, the cubic convolution interpolation scheme gave the best result.

• Journal of Korean Association for Spatial Structures
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• v.12 no.3
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• pp.47-54
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• 2012

The roof surface of spatial structures is often damaged or destroyed because of its light weight roof structure and materials. Many of large scale stadiums have roof structure framed with steel truss or stay cable and wrapped or covered with membrane material Teflon, and this membrane material is easily damaged and its loss is quite serious. Through such examples, it was found that the studies on wind proof design of roofs of large space structures were not sufficiently made. This study conducted wind pressure experiment and fluid analysis in order to examine the aerodynamic characteristic of the roof shape of hyperbolic paraboloid spatial structures. Although the biggest minimum peak wind pressure coefficient was shown in the edges of the roof in the wind origin direction, it decreases with the advancement to the longitudinal direction of the roof.

• Wind and Structures
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• v.28 no.6
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• pp.389-404
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• 2019

In coastal regions, it is common to witness significant damages on low-rise buildings caused by hurricanes and other extreme wind events. These damages start at high pressure zones or weak building components, and then cascade to other building parts. The state-of-the-art in experimental and numerical aerodynamic load evaluation is to assume buildings with intact envelopes where wind acts only on the external walls and correct for internal pressure through separate aerodynamic studies. This approach fails to explain the effect of openings on (i) the external pressure, (ii) internal partition walls; and (iii) the load sharing between internal and external walls. During extreme events, non-structural components (e.g., windows, doors or rooftiles) could fail allowing the wind flow to enter the building, which can subject the internal walls to lateral loads that potentially can exceed their load capacities. Internal walls are typically designed for lower capacities compared to external walls. In the present work, an anticipated damage development scenario is modelled for a four-story building with a stepped gable roof. LES is used to examine the change in the internal and external wind flows for different level of assumed damages (starting from an intact building up to a case with failure in most windows and doors are observed). This study demonstrates that damages in non-structural components can increase the wind risk on the structural elements due to changes in the loading patterns. It also highlights the load sharing mechanisms in low rise buildings.

• Wind and Structures
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• v.25 no.2
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• pp.101-129
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• 2017

Local transient extreme wind loads caused by group tower-related interference are among the major reasons that lead to wind-induced damage of super-large cooling towers. Four-tower arrangements are the most commonly seen patterns for super-large cooling towers. We considered five typical four-tower arrangements in engineering practice, namely, single row, rectangular, rhombic, L-shaped, and oblique L-shaped. Wind tunnel tests for rigid body were performed to determine the influence of different arrangements on static and dynamic wind loads and extreme interference effect. The most unfavorable working conditions (i.e., the largest overall wind loads) were determined based on the overall aerodynamic coefficient under different four-tower arrangements. Then we calculated the one-, two- and three-dimensional aerodynamic loads under different four-tower arrangements. Statistical analyses were performed on the wind pressure signals in the amplitude and time domains under the most unfavorable working conditions. On this basis, the non-Gaussian distribution characteristics of aerodynamic loads on the surface of the cooling towers under different four-tower arrangements were analyzed. We applied the Sadek-Simiu procedure to the calculation of two- and three-dimensional aerodynamic loads in the cooling towers under the four-tower arrangements, and the extreme wind load distribution patterns under the most unfavorable working conditions in each arrangement were compared. Finally, we proposed a uniform equation for fitting the extreme wind loads under the four-tower arrangements; the accuracy and reliability of the equation were verified. Our research findings will contribute to the optimization of the four-tower arrangements and the determination of extreme wind loads of super-large cooling towers.

• Computational Structural Engineering
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• v.25 no.1
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• pp.13-16
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• 2012

• Wind and Structures
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• v.5 no.1
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• pp.1-14
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• 2002

Artificial Neural Networks (ANN) have the capability to develop functional relationships between input-output patterns obtained from any source. Thus ANN can be conveniently used to develop a generalised relationship from limited and sometimes inconsistent data, and can therefore also be applied to tackle the data obtained from wind tunnel tests on building models with large number of variables. In this paper ANN model has been developed for predicting wind induced pressures in various zones of a Gable Building from limited test data. The procedure is also extended to a case wherein interference effects on a gable roof building by a similar building are studied. It is found that the Artificial Neural Network modelling is seen to predict successfully, the pressure coefficients for any roof slope that has not been covered by the experimental study. It is seen that ANN modelling can lead to a reduction of the wind tunnel testing effort for interference studies to almost half.

• Wind and Structures
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• v.5 no.2_3_4
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• pp.291-300
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• 2002

An efficient large eddy simulation algorithm is used to compute surface pressure distributions on an eleven story (target) building on the NIST campus. Local meteorology, neighboring buildings, topography and large vegetation (trees) all play an important part in determining the flows and therefore the pressures experienced by the target. The wind profile imposed at the upstream surface of the computational domain follows a power law with an exponent representing a suburban terrain. This profile accounts for the flow retardation due to friction from the surface of the earth, but does not include fluctuations that would naturally occur in this flow. The effect of neighboring buildings on the time dependent surface pressures experienced by the target is examined. Comparison of the pressure fluctuations on the single target building alone with those on the target building in situ show that, owing to vortices shed by the upstream buildings, fluctuations are larger when such buildings are present. Even when buildings are lateral to or behind the target, the pressure disturbances generate significantly different flows around this building. A simple grid-free mathematical model of a tree is presented in which the trunk and the branches are each represented by a collection of spherical particles strung together like beads on a string. The drag from the tree, determined as the sum of the drags of the component particles, produces an oscillatory, spreading wake of slower fluid, suggesting that the behavior of trees as wind breakers can be modeled usefully.

• Journal of Applied Reliability
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• v.17 no.3
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• pp.224-235
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• 2017

Purpose: Reliability is the most important factor to detect defects as wind turbines are deployed in large blades. The methods of detecting defects are various, such as non-destructive inspection and thermal imaging inspection. We propose the phased array ultrasonic testing method of non-destructive testing. Methods: We propose the active pressure mechanism for wind power blade. The phase array ultrasonic inspection method is used for fault detection inner blade surface. Controlled pressure of mechanism with respect to z-axis is important for guarantee the result of phase array ultrasonic inspection. The model based control and proposed mechanism are utilized for overall system stability and effectiveness of system. Result: The result of proposed pressure mechanism B is more stable than A. Convergence speed is also faster than A. Conclusion: We confirmed the performance of the proposed constant pressure mechanism through experiments. Non-destructive testing was applied to the specimen to confirm the reliability of detecting defects.