• Wind and Structures
• /
• v.20 no.3
• /
• pp.423-448
• /
• 2015

In this paper the unsteady fluid-structure interaction (FSI) problems with large structural displacement are solved by partitioned solution approaches in the arbitrary Lagrangian-Eulerian finite element framework. The incompressible Navier-Stokes equations are solved by the characteristic-based split (CBS) scheme. Both a rigid body and a geometrically nonlinear solid are considered as the structural models. The latter is solved by Newton-Raphson procedure. The equation governing the structural motion is advanced by Newmark-${\beta}$ method in time. The dynamic mesh is updated by using moving submesh approach that cooperates with the ortho-semi-torsional spring analogy method. A mass source term (MST) is introduced into the CBS scheme to satisfy geometric conservation law. Three partitioned coupling strategies are developed to take FSI into account, involving the explicit, implicit and semi-implicit schemes. The semi-implicit scheme is a mixture of the explicit and implicit coupling schemes due to the fluid projection splitting. In this scheme MST is renewed for interfacial elements. Fixed-point algorithm with Aitken's ${\Delta}^2$ method is carried out to couple different solvers within the implicit and semi-implicit schemes. Flow-induced vibrations of a bridge deck and a flexible cantilever behind an obstacle are analyzed to test the performance of the proposed methods. The overall numerical results agree well with the existing data, demonstrating the validity and applicability of the present approaches.

• Wind and Structures
• /
• v.26 no.6
• /
• pp.369-382
• /
• 2018

Tornadoes are vertical swirling air formed because of the existence of layers of air with contrasting features of temperature, wind flow, moisture, and density. Tornadoes induce completely different wind forces than a straight-line (SL) wind. A suitably designed building for an SL wind may fail when exposed to a tornado-wind of the same wind speed. It is necessary to design buildings that are more resistant to tornadoes. In tornado-damaged areas, dome buildings seem to have less damage. As a dome structure is naturally wind resistant, domes have been used in back yards, as single family homes, as in-law quarters, man caves, game rooms, storm shelters, etc. However, little attention has been paid to the tornadic wind interactions with dome buildings. In this work, the tornado forces on a dome are computed using Computational Fluid Dynamics (CFD) for tornadic and SL wind. Then, the interaction of a tornado with a dome and a prism building are compared and analyzed. This work describes the results of the tornado wind effect on dome and prism buildings. The conclusions drawn from this study are illustrated in visualizations. The tornado force coefficients on a dome building are larger than SL wind forces, about 120% more in x- and y-directions and 280% more in z-direction. The tornado maximum pressure coefficients are also higher than SL wind by 150%. The tornado force coefficients on the prism are larger than the forces on the dome, about 100% more in x- and y-directions, and about 180% more in z-direction. The tornado maximum pressure coefficients on prism also are greater those on dome by 150% more. Hence, a dome building has less tornadic load than a prism because of its aerodynamic shape.

• Wind and Structures
• /
• v.9 no.4
• /
• pp.331-344
• /
• 2006

The cable-stayed-suspension hybrid bridge is a cooperative system developed from the traditional cable-stayed and suspension bridges, and takes some advantages of the two bridge systems. It is also becoming a competitive design alternative for some long and super long-span bridges. But due to its great flexibility, the flutter stability plays an important role in the design and construction of this bridge system. Considering the geometric nonlinearity of bridge structures and the effects of nonlinear wind-structure interaction, method and its solution procedure of three-dimensional nonlinear flutter stability analysis are firstly presented. Parametric analyses on the flutter stability of a cable-stayed-suspension hybrid bridge with main span of 1400 meters are then conducted by nonlinear flutter stability analysis, some design parameters that significantly influence the flutter stability are pointed out, and the favorable structural system of the bridge is also discussed based on the wind stability.

• Wind and Structures
• /
• v.21 no.1
• /
• pp.105-117
• /
• 2015

This paper presents a numerical characterization of real railway overhead cables based on computational fluid dynamics (CFD). Complete analysis of the aerodynamic coefficients of this type of cross section yields a more accurate modelling of pressure loads acting on moving cables than provided by current approaches used in design. Thus, the characterization of certain selected commercial cables is carried out in this work for different wind speeds and angles of attack. The aerodynamic lift and drag coefficients are herein determined for two different types of grooved cables, which establish a relevant data set for the railway industry. Finally, the influence of this characterization on the fluid-structure interaction (FSI) is proved, the static behavior of a catenary system is studied by means of the finite element method (FEM) in order to analyze the effect of different wind angles of attack on the stiffness distribution.

• Coupled systems mechanics
• /
• v.1 no.2
• /
• pp.133-154
• /
• 2012

In this paper a bridge flutter prediction is performed by using advanced numerical simulation. Two novel approaches were developed simultaneously by utilizing the ANSYS v12.1 commercial software package. The first one is a fluid-structure interaction simulation involving the three-dimensional elastic motion of a bridge deck and the fluid flow around it. The second one is an updated forced oscillation technique based on the dynamic mode shapes of the bridge. An aeroelastic wind tunnel model was constructed in order to validate the numerical results. Good agreement between the numerical results and the measurements proves the applicability of the novel methods in bridge flutter assessment.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.11 no.2
• /
• pp.648-661
• /
• 2019

Thin fabric-based yacht sails have a cambered shape to generate lift force; however, their shape can be easily deformed by wind pressure and also affected by the deformation of the mast. These deformations can change the airflow characteristics over the sail. Therefore, Fluid-Structure Interaction (FSI) analysis is needed to evaluate the sail force precisely. In this study, airflow over the deformed sail and rig was studied using FSI. Elastic deformation of the sail and rig was obtained by an aerodynamic calculation under dynamic pressure loading on the sail surface. The effects of rig deformation on the aerodynamic performance of the sail were examined according to the rig type and mast flexibilities. As a result, the changes of lift force for a fractional type rig with a thin mast section were more significant than with a masthead rig.

• Wind and Structures
• /
• v.30 no.4
• /
• pp.367-378
• /
• 2020

Two-dimensional Delayed Detached Eddy Simulation (DDES) was carried out to investigate the uniform flow over a twin-box bridge deck (TBBD) with various gap ratios of L/C=5.1%, 12.8%, 25.6%, 38.5%, 73.3% and 108.2% (L: the gap-width between two girders, C: the chord length of a single girder) at Reynolds number, Re=4×104. The aerodynamic coefficients of the prototype deck with gap ratio of 73.3% obtained from the present simulation were compared with the previous experimental and numerical data for different attack angles to validate the present numerical method. Particular attention is devoted to the fluctuating pressure distribution and forces, shear layer reattachment position, wake velocity and flow pattern in order to understand the effects of gap ratio on dynamic flow interaction with the twin-box bridge deck. The flow structure is sensitive to the gap, thus a change in L/C thus leads to single-side shedding regime at L/C≤25.6%, and co-shedding regime at L/C≥35.8% distinguished by drastic changes in flow structure and vortex shedding. The gap-ratio-dependent Strouhal number gradually increases from 0.12 to 0.27, though the domain frequencies of vortices shedding from two girders are identical. The mean and fluctuating pressure distributions is significantly influenced by the flow pattern, and thus the fluctuating lift force on two girders increases or decreases with increasing of L/C in the single-side shedding and co-shedding regime, respectively. In addition, the flow mechanisms for the variation in aerodynamic performance with respect to gap ratios are discussed in detail.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.4
• /
• pp.223-230
• /
• 2014

In this paper, the wind-induced response characteristics of freeform shaped tall building is studied by using FSI analysis. The analytical models are twist shaped ones at representing type of atypical tall building, and this study focused on the relationship between twist angle and wind acceleration. Firstly, 1-way FSI analysis is performed, so maximum lateral displacement of the analytical model for 100 years return period wind speed is calculated, then the elastic modulus of a structure that satisfies the constraints condition is evaluated. And 2-way FSI analysis is carried out. so acceleration of the analytical model for the evaluated modulus of elasticity and arbitrary density is predicted through time history analysis. The basic model is a set of a square shape, height is 400m, slenderness ratio is 8, and twist model is rotated at square model from 0 to 90 degrees at intervals of 15 degrees and from 90 to 360 degrees at intervals of 90 degrees. According to the result of predicting wind acceleration by the shape of each model, the wind vibration effect of square shape model is confirmed to be sensitive more than a twist shape ones.

• Wind and Structures
• /
• v.36 no.2
• /
• pp.91-103
• /
• 2023

Tuned liquid dampers (TLDs) are increasingly being used as efficient dynamic vibration absorbers to mitigate wind-induced vibration in super high-rise buildings. However, the damping characteristics of screens and the control effectiveness of actual structures must be investigated to improve the reliability of TLDs in engineering applications. In this study, a numerical TLD model is developed using computational fluid dynamics (CFD) and a simulation method for achieving the coupled vibration of the structure and TLD is proposed. The numerical results are verified using shaking table tests, and the effects of the solidity ratio and screen position on the TLD damping ratios are investigated. The TLD control effectiveness is obtained by simulating the wind-induced vibration response of a full-scale structure-TLD system to determine the optimal screen solidity ratio. The effects of the structural frequency, damping ratio, and wind load amplitude on the TLD performance are further analyzed. The TLD damping ratio increases nonlinearly with the solidity ratio, and it increases with the screens towards the tank center and then decreases slightly owing to the hydrodynamic interaction between screens. Full-scale coupled simulations demonstrated that the optimal TLD control effectiveness was achieved when the solidity ratio was 0.46. In addition, structural frequency shifts can significantly weaken the TLD performance. The control effectiveness decreases with an increase in the structural damping ratio, and is insensitive to the wind load amplitude within a certain range, implying that the TLD has a stable damping performance over a range of wind speed variations.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.04a
• /
• pp.68-75
• /
• 2009

In this study, aeroelastic response analyses have been conducted for a 3D wind turbine blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responsed of wind turbine blade. Vibration analyses of rotating wind-turbine blade have been conducted using the general nonlinear finite element program, SAMCEF (Ver.6.3). Reynolds-averaged Navier-Stokes (RANS)equations with spalart-allmaras turbulence model are solved for unsteady flow problems of the rotating turbine blade model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D turbine blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous Mach contour on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating wind-turbine blade model.