• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.9-20
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• 2018

Due to integrated stochastic wind and wave loads, the supporting platform of a Floating Offshore Wind Turbine (FOWT) has to bear six Degrees of Freedom (DOF) motion, which makes the random cyclic loads acting on the structural components, for instance the tower base, more complicated than those on bottom-fixed or land-based wind turbines. These cyclic loads may cause unexpected fatigue damages on a FOWT. This paper presents a study on short-term fatigue damage at the tower base of a 5 MW FOWT with a spar-type platform. Fully coupled time-domain simulations code FAST is used and realistic environment conditions are considered to obtain the loads and structural stresses at the tower base. Then the cumulative fatigue damage is calculated based on rainflow counting method and Miner's rule. Moreover, the effects of the simulation length, the wind-wave misalignment, the wind-only condition and the wave-only condition on the fatigue damage are investigated. It is found that the wind and wave induced loads affect the tower base's axial stress separately and in a decoupled way, and the wave-induced fatigue damage is greater than that induced by the wind loads. Under the environment conditions with rated wind speed, the tower base experiences the highest fatigue damage when the joint probability of the wind and wave is included in the calculation. Moreover, it is also found that 1 h simulation length is sufficient to give an appropriate fatigue damage estimated life for FOWT.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.402-409
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• 2008

Wind loads and environments in realistic situations surrounded by neighboring buildings may be considerably different from those in idealized or simplified situations such as codes and standards. Interference effects of change in wind passage of a building group on wind loads and wind environments are reviewed. Wind-induced interference effects depend mainly on the building geometry and arrangement of these structures, their orientation and upstream terrain conditions. The most important factor among them may be the arrangement of building structures which can change the wind direction directly. Interference effects regarding wind loads are discussed with examples of window damages by typhoon and of pressure measurements in the boundary layer wind tunnel. Wind environment problems are also discussed, specially underlined on pedestrian comfort and safety. Various evaluation techniques or standards of wind environment are introduced. The change of wind velocity between the panel-type apartment buildings is examined, depending on the distance each other.

• Wind and Structures
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• 제22권6호
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• pp.685-701
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• 2016

Downbursts are of great harm to transmission lines and many towers can even be destroyed. The downburst wind field model by Chen and Letchford was applied, and the wind loads of two typical transmission towers in inland areas and littoral areas were calculated separately. Spatial finite element models of the transmission towers were established by elastic beam and link elements. The wind loads as well as the dead loads of conductors and insulators were simplified and applied on the suspension points by concentrated form. Structural analysis on two typical transmission towers under normal wind and downburst was completed. The bearing characteristics and the failure modes of the transmission towers under downburst were determined. The failure state of tower members can be judged by the calculated stress ratios. It shows that stress states of the tower members were mainly controlled by 45 degree wind load. For the inland areas with low deign wind velocity, though the structural height is not in the highest wind velocity zone of downburst, the wind load under downburst is much higher than that under normal wind. The main members above the transverse separator of the legs will be firstly destroyed. For the littoral areas with high deign wind velocity, the wind load under downburst is lower than under normal wind. Transmission towers are not controlled by the wind loads from downbursts in design process.

• Wind and Structures
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• 제22권3호
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• pp.307-328
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• 2016

This paper describes an investigation of the net wind loads on solar panels and wind loads on the underlying roof surface for panels mounted parallel to pitched roofs of domestic buildings. Typical solar panel array configurations were studied in a wind tunnel and the aerodynamic shape factors on the panels were put in a form appropriate for the Australian/New Zealand Wind Actions Standard AS/NZS 1170.2:2011. The results can also be used to obtain more refined design data on individual panels within an array. They also suggest values for the aerodynamic shape factors on the roof surface under the panels, based on a gust wind speed at roof height, of ${\pm}0.5$ for wind blowing parallel to the ridge, and ${\pm}0.6$ for wind blowing perpendicular to the ridge. The net loads on solar arrays in the middle portion of the roof are larger than those on the same portion of the roof without any solar panels, thus resulting in increased loads on the underlying roof structure.

• Wind and Structures
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• 제1권2호
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• pp.183-199
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• 1998

This paper discusses some of the findings arising from long-term monitoring of the wind effects on a transmission tower located on an exposed site in South-West England. Site wind speeds have been measured, together with the foundation loads at the base of each of the four legs. The results show good correlation between the wind speeds and leg strains (loads) for a given wind direction, as expected, for wind speeds in excess of 10 m/s. Comparisons between the measured strains and those determined from the UK Code of Practice for lattice towers (BS8100), for the same wind speed and direction, show that the Code over-estimates most of the measured foundation loads by a moderate amount of about 14% at the higher wind speeds. This tends to confirm the validity of the Code for assessing design foundation loads. A finite element analysis model has been used to examine the dynamic behaviour of the tower and conductor system. This shows that, in the absence of the conductor, the tower alone has similar natural frequencies of approximately 2.2 Hz in the both the first (transversal) and second (longitudinal) modes, whilst for the complete system and conductor oscillations dominate, giving similar frequencies of approximately 0.1 Hz for both the first and second modes.

• Wind and Structures
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• 제26권4호
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• pp.191-204
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• 2018

This article presents a study of the largest-ever (height = 220 m) cooling tower using the large eddy simulation (LES) method. Information about fluid fields around the tower and 3D aerodynamic time history in full construction process were obtained, and the wind pressure distribution along the entire tower predicted by the developed model was compared with standard curves and measured curves to validate the effectiveness of the simulating method. Based on that, average wind pressure distribution and characteristics of fluid fields in the construction process of ultra-large cooling tower were investigated. The characteristics of fluid fields in full construction process and their working principles were investigated based on wind speeds and vorticities under different construction conditions. Then, time domain characteristics of ultra-large cooling towers in full construction process, including fluctuating wind loads, extreme wind loads, lift and drag coefficients, and relationship of measuring points, were studied and fitting formula of extreme wind load as a function of height was developed based on the nonlinear least square method. Additionally, the frequency domain characteristics of wind loads on the constructing tower, including wind pressure power spectrum at typical measuring points, lift and drag power spectrum, circumferential correlations between typical measuring points, and vertical correlations of lift coefficient and drag coefficient, were analyzed. The results revealed that the random characteristics of fluctuating wind loads, as well as corresponding extreme wind pressure and power spectra curves, varied significantly and in real time with the height of the constructing tower. This study provides references for design of wind loads during construction period of ultra-large cooling towers.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1412-1415
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• 2005

Special considerations on the design of liquid storage tanks should be taken into account for seismic and wind loads. But Korean industrial standard KS B 6225 does not specify detailed guidelines for a design. It is therefore necessary to improve design guidelines for a seismic and wind-proof design in KS B 6225. The purpose of this study is provide a basis for the development of improved seismic and wind-proof design procedures, especially about seismic and wind loads.

• Wind and Structures
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• 제5권5호
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• pp.393-406
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• 2002

Aerodynamic pressures and forces were measured on a model of a solar panel containing six slender, parallel modules. Of particular importance to system design is the aerodynamically induced torque. The peak system torque was generally observed to occur at approach wind angles near the diagonals of the panel ($45^{\circ}$, $135^{\circ}$, $225^{\circ}$ and $315^{\circ}$) although large loads also occurred at $270^{\circ}$, where wind is in the plane of the panel, perpendicular to the individual modules. In this case, there was strong vortex shedding from the in-line modules, due to the observation that the module spacing was near the critical value for wake buffeting. The largest loads, however, occurred at a wind angle where there was limited vortex shedding ($330^{\circ}$). In this case, the bulk of the fluctuating torque came from turbulent velocity fluctuations, which acted in a quasi-steady sense, in the oncoming flow. A simple, quasi-steady, model for determining the peak system torque coefficient was developed.

• Wind and Structures
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• 제31권6호
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• pp.483-493
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• 2020

Large cylindrical floating-roof tanks, constructed as oil containers, are usually distributed regularly in open area and easily exposed to severe wind loads. However, wind pressures around these grouped squat tanks appear to have not been clearly given in design codes or thoroughly studied in existing researches. This paper conducts a detailed investigation on wind loads on the external wall of a four-tank group in square arrangement. To achieve that, wind tunnel tests are carried out on both empty and full tank groups, considering various wind angles and spacing. Results show that 3 regions in elevation can be identified on the tank shell according to the circumferential wind pressure distribution. The upper 2 regions cover a relatively small portion of the shell where excessive negative pressures are spotted, setting an alarm to the design of the top angle and stiffening rings. By comparing results on grouped tanks to those on an isolated tank, grouping effects concerning wind angle, tank position in group and spacing are discussed. Deviations on pressure distributions that will compromise structural safety are outlined, including the increase of negative pressures, the shift of maximum pressure locations as well as the change of positive pressure range. And, several potentially unfavourable wind pressure distributions are selected for further analyses.

• 대한조선학회논문집
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• 제52권1호
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• pp.43-51
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• 2015

This paper presents effect of aerodynamic loads on mooring line responses of a floating offshore wind turbine. A Matlab code based on blade element momentum (BEM) theory is developed to consider aerodynamic loads acting on NREL 5MW wind turbine. The aerodynamic loads are coupled with time-domain hydrodynamic analyses using one-way interaction scheme of the wave and wind loads. A semi-submersible floating platform which is from Offshore Code Comparison Collaborative Continuation(OC4) DeepCWind platform is used with catenary mooring lines simply composed of studless chain links. Average values of mooring peak tensions obtained from aerodynamic load consideration are significantly increased compared to those from simple wind drag force consideration. Consideration of aerodynamic loads also yield larger tension ranges which can be important factor to reduce fatigue life of the mooring lines.