• 국제초고층학회논문집
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• 제8권4호
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• pp.291-302
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• 2019

We performed calculations combining optimization technologies and Computational Fluid Dynamics (CFD) aimed at reducing wind forces and mitigating wind environments (local strong winds) around buildings. However, the Reynolds Averaged Navier-stokes Simulation (RANS), which seems somewhat inaccurate, needs to be used to create a realistic CFD optimization tool. Therefore, in this study we explored the possibilities of optimizing calculations using RANS. We were able to demonstrate that building configurations advantageous to wind forces could be predicted even with RANS. We also demonstrated that building layouts was more effective than building configurations in mitigating local strong winds around tall buildings. Additionally, we used the Convolutional Neural Network (CNN) as an airflow prediction method alternative to CFD in order to increase the speed of optimization calculations, and validated its prediction accuracy.

• Wind and Structures
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• 제11권6호
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• pp.441-453
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• 2008

In this study, a partially earth-anchored cable system is studied in order to reduce the dynamic wind response of cable-stayed bridges. The employment of earth-anchored cables changes the dynamic characteristics of cable-stayed bridges under wind loads. In order to estimate the changes in the member forces, the spectral analysis for wind buffeting loads are performed and the peak responses are evaluated using 3-D finite element models of the three-span cable-stayed bridges with the partially earth-anchored cable system and with the self-anchored cable system, respectively. Comparing the results for the two different models, it is found that the earth-anchored cables affect longitudinal and vertical modes of the bridge. The changes of the natural frequencies for the longitudinal modes remarkably decrease the peak bending moment in the pylon and the movements at the expansion joints. The small changes of the natural frequencies for the vertical modes slightly increase bending moments and deflections in the girder. The original effects of the partially earth-anchored cable system are also shown under wind loads; the decrement of girder axial forces and bearing uplifting forces, and the increment of cable forces in the earth-anchored cables.

• Ocean Systems Engineering
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• 제11권1호
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• pp.17-42
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• 2021

Articulated loading platforms (ALPs) belongs to a class of offshore structures known as compliant. ALP motions have time periods falling in the wind excitation frequency range due to their compliant behaviour. This paper deals with the dynamic behavior of a double hinged ALP subjected to low-frequency wind forces with random waves. Nonlinear effects due to variable submergence, fluctuating buoyancy, variable added mass, and hydrodynamic forces are considered in the analysis. The random sea state is characterized by the Pierson-Moskowitz (P-M) spectrum. The wave forces on the submerged elements of the platform's shaft are calculated using Morison's Equation with Airy's linear wave theory ignoring diffraction effects. The fluctuating wind load has been estimated using Ochi and Shin wind velocity spectrum for offshore structures. The nonlinear dynamic equation of motion is solved in the time domain by the Wilson-θ method. The wind-structure interactions, along with the effect of various other parameters on the platform response, are investigated. The effect of offset of aerodynamic center (A.C.) with the center of gravity (C.G.) of platform superstructure has also been investigated. The outcome of the analyses indicates that low-frequency wind forces affect the response of ALP to a large extent, which otherwise is not enhanced in the presence of only waves. The mean wind modifies the mean position of the platform surge response to the positive side, causing an offset. Various power spectral densities (PSDs) under high and moderate sea states show that apart from the significant peak occurring at the two natural frequencies, other prominent peaks also appear at very low frequencies showing the influence of wind on the response.

• Wind and Structures
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• 제1권3호
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• pp.225-241
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• 1998

The high-rise supporting towers of long-span suspension and cable-stayed bridges commonly comprise a pair of slender prisms of roughly square cross-section with a center-to-centre spacing of from perhaps 2 to 6 widths and connected by one or more cross-ties. The tower columns may have a constant spacing as common for suspension bridges or the spacing may reduce towards the top of the tower. The present paper is concerned with the aerodynamics of such towers and describes an experimental investigation of the overall aerodynamic forces acting on a pair of square cylinders in two-dimensional flow. Wind tunnel pressure measurements were carried out in smooth flow and with a longitudinal intensity of turbulence 0.10. Different angles of attack were considered between $0^{\circ}$ and $90^{\circ}$, and separations between the two columns from twice to 13 times the side width of the column. The mean values of the overall forces proved to be related to the bias introduced in the flow by the interaction between the two cylinders; the overall rms forces are related to the level of coherence between the shedding-induced forces on the two cylinders and to their phase. Plots showing the variation of the force coefficients and Strouhal number as a function of the separation, together with the force coefficients spectra and lift cross-correlation functions are presented in the paper.

• Wind and Structures
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• 제18권1호
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• pp.1-20
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• 2014

Modern design of long suspension bridges must satisfy at the same time spanning very long distances and limiting their response against several external loads, even if of high intensity. Structural Control, with the solutions it provides, can offer a reliable contribution to limit internal forces and deformations in structural elements when extreme events occur. This positive aspect is very interesting when the dimensions of the structure are large. Herein, an updated numerical model of an existing suspension bridge is developed in a commercial finite element work frame, starting from original data. This model is used to reevaluate an optimization procedure for a passive control strategy, already proven effective with a simplified model of the buffeting wind forces. Such optimization procedure, previously implemented with a quasi-steady model of the buffeting excitation, is here reevaluated adopting a more refined version of the wind-structure interaction forces in which wind actions are applied on the towers and the cables considering drag forces only. For the deck a more refined formulation, based on the use of indicial functions, is adopted to reflect coupling with the bridge orientation and motion. It is shown that there is no variation of the previously identified optimal passive configuration.

• Wind and Structures
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• 제16권3호
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• pp.279-300
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• 2013

This paper presents a new analysis framework for predicting the internal buffeting forces in bridge components under skew wind. A linear regressive model between the internal buffeting force and deformation under normal wind is derived based on mathematical statistical theory. Applying this regression model under normal wind and the time history of buffeting displacement under skew wind with different yaw angles in wind tunnel tests, internal buffeting forces in bridge components can be obtained directly, without using the complex theory of buffeting analysis under skew wind. A self-anchored suspension bridge with a main span of 260 m and a steel arch bridge with a main span of 450 m are selected as case studies to illustrate the application of this linear regressive framework. The results show that the regressive model between internal buffeting force and displacement may be of high significance and can also be applied in the skew wind case with proper regressands, and the most unfavorable internal buffeting forces often occur under yaw wind.

• Wind and Structures
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• 제10권5호
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• pp.481-494
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• 2007

Downbursts are transient phenomena that produce wind profiles that are distinctly different from synoptic boundary layers. Wind field data from Computational Fluid Dynamics (CFD) simulations of isolated downburst-like impinging jets, are used to investigate structural loads of tall buildings due to these high intensity winds. The base shear forces and base moments of tall buildings of heights between 120 and 250 m produced by downburst winds of various scales are compared with the forces from the equivalent boundary layer gust winds, with matched 10-metre wind velocity. The wind profiles are mainly functions of the size of the downburst and the radial distance from the centre of the storm. Wind forces due to various downburst profiles are investigated by placing the building at different locations relative to the storm center as well as varying the size of the downburst. Overall it is found that downbursts larger than approx. 2,000 m in diameter might produce governing design wind loads above those from corresponding boundary layer winds for tall buildings.

• Wind and Structures
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• 제15권6호
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• pp.495-508
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• 2012

The present paper is focused on the prediction of the acrosswind aeroelastic response of square tall buildings. In particular, a semi-analytical procedure is proposed based on the assumption that square tall buildings, for reduced velocities corresponding to operational conditions, do not experience vortex shedding resonance or galloping and fall in the range of positive aerodynamic damping. Under these conditions, aeroelastic wind tunnel tests can be unnecessary and the response can be correctly evaluated using wind tunnel tests on rigid models and analytical modeling of the aerodynamic damping. The proposed procedure consists of two phases. First, simultaneous measurements of the pressure time histories are carried out in the wind tunnel on rigid models, in order to obtain the aerodynamic forces. Then, aeroelastic forces are analytically evaluated and the structural response is computed through direct integration of the equations of motion considering the contribution of both the aerodynamic and aeroelastic forces. The procedure, which gives a conservative estimate of the aeroelastic response, has the advantage that aeroelastic tests are avoided, at least in the preliminary design phase.

• Wind and Structures
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• 제29권2호
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• pp.111-127
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• 2019

The tapered and set-back type of unconventional designs have been used earlier in many buildings. These shapes are aerodynamically efficient and offer a significant amount of damping against wind-induced forces and excitations. Various studies have been conducted on these shapes earlier. The present study adopts a hybrid approach of turbulence modelling i.e., Detached-eddy Simulation (DES) to investigate the effect of height modified tapered and set-back buildings on aerodynamic forces and their sensitivity towards pressure. The modifications in the flow field around the building models are also investigated and discussed. Three tapering ratios (T.R.=(Bottom width- Top width)/Height) i.e., 5%, 10%, 15% are considered for tapered and set-back buildings. The results show that, mean and RMS along-wind and across-wind forces are reduced significantly for the aerodynamically modified buildings. The extent of reduction in the forces increases as the taper ratio is increased, however, the set-back modifications are more worthwhile than tapered showing greater reduction in the forces. The pressure distribution on the surfaces of the buildings are analyzed and in the last section, the influence of the flow field on the forces is discussed.

• Wind and Structures
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• 제15권4호
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• pp.301-311
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• 2012

This paper presents results from the structural monitoring of a steel wind tower characterized and presented in Part I of the paper. Monitoring period corresponds to about fifteen months of measurements. Results presented refer to stress distribution on shell and in bolts at different heights, stress fatigue spectra, section forces along height evaluated from the stress measurements and comparison with design forces, dynamic response in terms of accelerations, stresses, deflections and rotations.