Weighted Amplitude Wave Superposition Research Articles

The Interference Effects of Wind Load and Wind-Induced Dynamic Response of Quayside Container Cranes

Strong wind has caused damage to group-arranged quayside container cranes in terminals and ports in recent years. Interference may amplify the wind loads in some cases. However, the interference effect among cranes has rarely been studied. In this study, high-frequency force balance tests were conducted to obtain the wind load of isolated and group-arranged container cranes. The results of the computational fluid dynamics simulation were validated by wind tunnel tests and provided the mean wind loads of all 15 types of member cranes. According to the results from wind tunnel tests, the fluctuating wind loads of each member were generated using the weighted amplitude wave superposition method. Based on dynamic finite element methods, the wind-induced responses were obtained considering the interference effect. It was found that the interference effect is the combined effects of both the shielding effect and the amplification of turbulence. Although in some cases the fluctuating and peak wind loads can increase by up to 16% and 6%, respectively, those in the most unfavorable cases are reduced by the interference effect. The interference factor for extreme nodal deformation is 0.56 and 0.69. The interference effect in container cranes mainly appears as a shielding effect, reducing the wind loads and response of the structures in unfavorable cases.

Large Eddy simulation of the fluctuating wind environment at a bridge site in the mountainous area

To have a comprehensive understanding of the complex wind environment at a bridge site in the mountainous area, a numerical simulation study of the wind environment under the mean and the fluctuating wind flow conditions was carried out and the results were compared. First, according to the weighted amplitude wave superposition (WAWS) method, the fluctuating wind speed time history was compiled by UDF. And the wind speed time history was added to the inlet boundary of a numerical empty wind tunnel to verify the feasibility of the simulation method of the fluctuating wind. Then, with a bridge in the mountainous area in Yunnan as the engineering background, a numerical simulation study of the wind environment of the bridge site area under the mean wind flow and the fluctuating wind flow was carried out by using FLUENT. The study indicates that Large Eddy Simulation (LES) method more accurate than Reynold average method with a sufficient number of grids and a short enough time step. The average wind characteristics of the bridge site under the mean wind and the fluctuating wind are not much different. The fluctuating wind characteristics at the bridge site are mainly affected by the terrain and the pulsating component of the wind flow. There are different terrain pulsation effects at the bridge site under different incoming flow directions.

Outdoor transportation of influenza virus under natural wind field

The transportation of influenza virus in a group of buildings under the condition of natural wind field was studied. The curves of natural wind power spectrum and the velocity field with respect to time were simulated by the improved weighted amplitude wave superposition with fast Fourier transform. According to Davenport spectrum, the approximation function of wind velocity field with respect to time was used to simplify the calculation efforts. The average wind field and natural wind field were adopted to simulate the microbial contamination diffusion in a group of buildings. In the case of natural wind, the virus particles are dispersed faster from buildings, and the contamination concentration is low. However, the large downwind area may face the threat of virus contamination.

Suppression of Vibrations Induced by Fluctuating Wind for Long-Span Cable-Stayed Bridge Using MR Dampers

Cable-stayed bridges subjected to wind excitations will cause intense vibration due to their high flexibility in characteristic. Employment of magnetorheological (MR) dampers to realize the vibration smart-control of cablestayed bridges has become a considerable research topic in recent decades. In this paper, the plane truss finite element model (FEM) of a cable-stayed bridge with MR dampers is established. Fluctuating wind field is generated using the weighted amplitude wave superposition (WAWS) method and Kaimal spectrum, and then the time-history sample curve of wind speed is obtained. Fluctuating wind-induced vibration of the long-span cable-stayed bridge installed with MR dampers is analyzed by linear quadratic regulator (LQR) classical optimal control strategy and LQR tri-state control strategy. After the optimal control force is calculated by LQR classical optimal control strategy, control parameters and the input currents of MR dampers can be determined according to the windinduced vibration by LQR tri-state control. Results show that longitudinal and vertical wind-induced vibration responses of the box girder of the cable-stayed bridge are reduced obviously when MR dampers are arranged between the box girder and pylons.

Multiscale simulation of wind field on a long-span bridge site in mountainous area

A multiscale coupling strategy is proposed in the present study to numerically simulate the wind field at bridge sites in mountainous areas. This paper mainly focuses on resolving the difficulty of configuring reasonable inlet boundary conditions to achieve the required wind field. Firstly, the inlet boundary values of the mean wind velocity in the mountainous area were provided by the Weather Research and Forecasting (WRF) mesoscale model. Then, the local wind environmental flows over the mountainous area were computed by the large eddy simulation (LES) in such a way that the Block Polynomial Interpolation (BPI) method was employed to interpolate the data from WRF to the grids at the inlet boundary of the LES computation domain. This BPI method provided a better solution to the inlet boundary problems caused by the "artificial cliff". The inflow turbulence generating method was used for the input of the fluctuating wind speed at the inlet boundary, where the fluctuating wind field that satisfies the characteristics of the wind field in the mountainous area was simulated according to the data measured at the bridge site station by using the Weighted Amplitude Wave Superposition (WAWS) method. Finally, the proposed methodology was applied to the Lishui Bridge in China as a case study. The numerical predictions were found in good agreement with the monitored data, assuring the good capabilities of the proposed methodology and its potential uses in practical engineering. Meanwhile, the wind field from different wind directions was systematically studied and the characteristics for the detailed wind field distribution were analyzed. The presented methodology can be served as a reference to the refined simulation for the fluctuating wind field in mountainous areas.

Detached-eddy and large-eddy simulations of wind effects on a high-rise structure

Abstract In this study, detached-eddy simulations (DES) and large-eddy simulations (LES) of wind effect on a high-rise structure with elliptical shape are performed. The aim of this study is to examine the accuracy of the numerical simulations for wind flow around a complex high-rise structure and investigate the effects of surface roughness on the wind loading. In order to reproduce appropriate inflow turbulence, the improved recycling method combined with the weighted amplitude wave superposition (WAWS) method is used to generate the inflow turbulence in the streamwise direction. Also, to study the surface roughness effects on the wind loading, the rough wall boundary conditions are adopted in the DES models. Typical results including the mean and fluctuating pressure coefficients, force spectra, Reynolds stresses and wind-induced top-floor response are obtained and compared with the corresponding wind tunnel experimental data. Through the cross-comparisons, the numerical results by the DES and LES models are found to be comparable with the experimental results. Additionally, the surface roughness effects on the wind loading is well reproduced with the DES models, such as the slow pressure recovery in the separation regions and the increased mean drag force coefficients. It is demonstrated through the validations that the DES and LES models and the numerical treatments adopted in this study can provide reasonably good results.

Application of vector form intrinsic finite element on integrated simulation of wind turbine

SummaryLarge wind turbine system is a periodic time‐varying system with many rigid‐flexible coupling bodies. It is difficult to deal with the singular stiffness matrix produced by the rotation of blades via the traditional finite element method. However, the vector form intrinsic finite element (VFIFE) method can effectively solve the geometric deformation of elastic continuum, the nonlinear or discrete constitutive model, the coupling motion continuum, and rigid body. In this study, a solver program of space beam element is developed by VFIFE method, and three typical examples are chosen to verify its accuracy. And then the integrated simulation of wind turbine system is established, and its dynamic response is analyzed. The natural frequencies of the turbine system, which are obtained by modal parameter identification, can agree well with the results obtained by traditional finite element method. The weighted amplitude wave superposition method and the proper orthogonal decomposition method as well as B‐spline surface interpolation are employed to obtain the wind time series of wind turbine under the normal operation condition. The wind‐induced dynamic response of wind turbine system is calculated by VFIFE method. The numerical results can reflect the periodic influence of gravity on the internal forces of blades and the interaction between blades and the tower.

LES of wind environments in urban residential areas based on an inflow turbulence generating approach

Wind environment in urban residential areas is an important index to consider when evaluating the living environment. However, due to the complexity of the flow field in residential areas, it is difficult to specify the correct inflow boundary conditions in the large eddy simulation (LES). In this paper, the weighted amplitude wave superposition (WAWS) is adopted to simulate the fluctuating velocity data, which satisfies the desired target wind field. The fluctuating velocity data are given to the inlet boundary of the LES by developing an UDF script, which is implemented into the FLUENT. Then, two numerical models - the empty numerical wind tunnel model and the numerical wind tunnel model with spires and roughness elements are established based on the wind tunnel experiment to verify the present method. Finally, the turbulence generation approach presented in this paper is used to carry out a numerical simulation on the wind environment in an urban residential area in Lisbon. The computational results are compared with the wind tunnel experimental data, showing that the numerical results in the LES have a good agreement with the experimental results, and the simulated flow field with the inlet fluctuations can generate a reasonable turbulent wind field. It also shows that strong wind velocities and turbulent kinetic energy occur at the passageways, which may affect the comfort of people in the residential neighborhood, and the small wind velocities and vortexes appear at the leeward corners of buildings, which may affect the spreading of the pollutants.

Wind field simulation of large horizontal‐axis wind turbine system under different operating conditions

SummaryThis paper proposes a technique of generating turbulent wind velocities on large horizontal‐axis wind turbine systems under different operating conditions. The rotational sampling effect, vertical wind shear and coherence between wind velocities at blades and on the tower were taken into account. Coordinate system of wind time series at certain discrete sampling points on the vertical plane of the wind turbine is generated by the hybrid weighted amplitude wave superposition and proper orthogonal decomposition (POD) methods. The POD eigenmodes on the blades after updating locations were calculated subsequently using B‐spline surface interpolation method, and the rotationally sampled wind velocities are reconstructed by taking advantage of POD method again. Examples are subsequently presented to validate this proposed technique and demonstrate the generation of wind velocities under different operating conditions. The results show that the simulated spectrum of turbulent wind velocities at blades corresponds well to the measured data and that on the tower agrees well with the fixed point Kaimal spectrum. The reasonable sampling points spacing is suggested to be about 10 m for the wind field simulation of wind turbine system. The proposed method is of great advantage in accuracy and efficiency, which is greatly significant for the fine analysis of multi‐megawatt wind turbines. Copyright © 2015 John Wiley & Sons, Ltd.

Feedforward and Feedback Vibration Control and Algorithm Design for Cable-Bridge Structure Nonlinear Systems

Technique of feedforward and feedback optimal vibration control and simulation for long-span cable-bridge coupled systems is developed. Buffeting loading systems of long-span cable-bridge structure are constructed by weighted amplitude wave superposition method. Nonlinear model of cable-bridge coupled vibration control system is established and the corresponding system of state space form is described. In order to reduce buffeting loading influence of the wind-induced vibration for the structure and improve the robust performance of the vibration control, based on semiactive vibration control devices and optimal control approach, a feedforward and feedback optimal vibration controller is designed, and an algorithm is presented for the vibration controller. Numerical simulation results are presented to illustrate the effectiveness of the proposed technique.

A new approach for simulation of non-Gaussian processes

To realise the significant non-Gaussian features of the wind pressure acting on structures, such as high-rise buildings and roof structures, a new simulation approach is proposed for generating sample functions of multivariate stationary non-Gaussian processes. A standard cubic polynomial is proposed to represent the translation of a Gaussian process to a non-Gaussian wind pressure process. Then a set of non-linear equations is derived to determine the parameters of the polynomial. The relation for translation of correlation functions is obtained based on the properties of the Gaussian stochastic vector. Also, the weighted amplitude wave superposition method is employed to generate the underlying Gaussian processes. Further, the proposed new approach is demonstrated by simulation of the non-Gaussian wind pressure field acting on a large-span stadium roof. The numerical results show that the proposed approach is quite accurate and efficient. Hence the method is advantageous for wind pressure field simulation of structures with a large number of nodes.

Vibrations of an aramid anchor cable subjected to turbulent wind

The vibration response of an initially pre-stressed anchor cable made of parallel-lay aramid fibres excited by a measured and artificially simulated spatial turbulent wind field is presented in the paper. Results of the analyses of in situ measured wind records are described. For selected data set statistical characteristics and power spectral density functions of the measured wind velocity components are calculated. The wind stochastic velocity fluctuation is modelled as a one-variate bi-dimensional random field. Cross-power spectral density functions, at different point locations are introduced. The combination of the weighted amplitude wave superposition method (WAWS) with the Shinozuka–Deodatis method is used for the analyzed problem. A time-dependent behaviour of the synthetic cable is investigated which is subjected to turbulent wind with large expected oscillations that arise as a result of slackening due to the relaxation effects. A nonlinear transient dynamic analysis is used in conjunction with the finite element method to determine the dynamic response of the cable subjected to turbulent wind at its initially prestressed state and in the selected times after the relaxation effect. The constitutive equation of the relaxation of the aramid cable follows an experimentally obtained law of the logarithmic type. To monitor the dependences of the individual quantities of cable vibration in the phase space, attractors and Poincaré maps are created by sampling the cable’s displacement and velocity at periods of relevant frequencies. Interesting findings based on the response of the cable with rheological properties to turbulent wind are presented.

Seismic response analysis of a double-deck long-span cable-stayed bridge under multi-support excitations

In this article, the effect of earthquake ground motions, especially spatially varying motion, on the seismic response of a long-span double-deck cable-stayed bridge is investigated. Static and dynamic response analyses, with the focus on internal forces on web members, are carried out on the Shanghai Minpu Bridge which is the longest long-span double-deck cable-stayed highway bridge. Firstly, a program for the generation of multi-ground motions has been developed, based on the multivariate stochastic processes of the weighted amplitude wave superposition method in FORTRAN. Secondly, a refined finite element model composed of beam and shell elements and a simplified model using equivalent beam elements to model girders of the bridge are established in ABAQUS. Geometrical nonlinear static analysis is performed to get initial equilibrium configuration of the bridge for both the above models. Modal analysis is carried out on the initial equilibrium configuration and the natures of mode shapes for the refined model are discussed in detail. The dynamic response analyses under two groups of uniform seismic excitation indicate that the two models result in approximately identical results. Thirdly, the effect of nonlinear viscous dampers, located between the tower and the girder, on movement due to seismic excitation is investigated on the simplified model under uniform excitation. Results show that the dampers magnify the shear force and moment on lower tower columns in the longitudinal direction, but have relatively small effect on the upper tower columns. The shear force and moment of the tower base increase with the damping coefficient in a certain range. Finally, the characteristics of internal force for towers, subsidiary piers, and web members (vertical and oblique web members and side oblique chords) under multipoint excitation are examined. It is concluded that the abrupt changes on the shear envelope curves at the intersection of the tower column and the lower transverse beam are aroused due to the eight nonlinear fluid viscous dampers. The lateral moment of the subsidiary piers increases with the distance from the tower to subsidiary piers. The maximum axial forces of web members of side-span vary acutely, especially those of the vertical and oblique members close to the piers. For side oblique chords, the maximum axial force is uniformly distributed with the exception of members at the piers and the mid-span sections. Therefore, attention should be paid to the fluctuation forces of cables in seismic analysis of long-span cable-stayed bridges, since the uplift of girder ends may cause severe damage to bridges.

Research on the Wind-induced Vibration Coefficient of Transmission Tower-line System

The six different non-linear finite element model of the transmission tower-line system which have different spans and different height difference was established by the finite element analysis software, and wind velocity time series with resorting to weighted amplitude wave superposition (WAWS) was simulated. Based on the established models and the simulated wind velocity time series, the wind-induced response of transmission tower-line system in time history was calculated to achieve wind-induced vibration coefficient of transmission towers of various models. By comparative analyzing, span and height difference on the impact of wind-induced vibration coefficient of transmission towers was studied. The results show that the span and height difference have a certain impact on wind-induced vibration coefficient of transmission towers, and the effects on tower top are more obvious than tower bottom. With the increase of span, wind-induced vibration coefficient reduces gradually, but with the increase of height difference, wind-induced vibration coefficient increases gradually.

Computer Simulation of Stochastic Wind Velocity Fields for Structural Response Analysis: Comparisons and Applications

The digital simulation of wind velocity fields, modeled as multivariate stationary Gaussian processes, is a widely adopted tool to generate the external input for response analysis of wind-sensitive nonlinear structures. The problem does not entail any theoretical difficulty, existing already a large number of well-established techniques, such as the accurate weighted amplitude wave superposition (WAWS) method. However, reducing the computational effort required by the WAWS method is sometimes necessary, especially when dealing with complex structures and high-dimensional simulation domains. In these cases, approximate formulas must be adopted, which however require an appropriate tuning of some fundamental parameters in such a way to achieve an acceptable level of accuracy if compared to that obtained using the WAWS method. Among the different techniques available for this purpose, autoregressive (AR) filters and algorithms exploiting the proper orthogonal decomposition (POD) of the spectral matrix deserve a special attention. In this paper, a properly organized way for implementing stochastic wind simulation algorithms is outlined at first. Then, taking the WAWS method as a reference from the viewpoint of the accuracy of the simulated samples, a comparative study between POD-based and AR techniques is proposed, with a particular attention to computational effort and memory requirements.

Stochastic Inlet Conditions for Large-Eddy Simulation of a Fully Turbulent Jet

A numerical study using the large-eddy simulation technique is performed to compare the behaviors of two different stochastic inlet condition methodologies, which are each intended to simulate a turbulent inflow for a round jet. The simple technique of Gaussian random forcing is tested as a baseline, and a version of the weighted amplitude wave superposition spectral representation method is tested as an improved technique

DYNAMIC RESPONSE OF WIND-EXCITED BUILDING USING CFD

Computational wind engineering as a new branch of computational fluid dynamics (CFD) has been developed recently to evaluate the interaction between wind and buildings numerically. In the present study, a systematic examination of wind effects on tall buildings and flow condition around buildings has been carried out using commercially available CFD software FLUENT 5. Both renormalization group (RNG) k–ε method and large eddy simulation (LES) with the Smagorinsky model are adopted as turbulence models and the results are compared with the wind-tunnel measurements. The weighted amplitude wave superposition (WAWS) method is used to generate atmospheric wind turbulence. The RNG k–ε method can predict the vortex shedding phenomenon well when compared with experiments for uniform flow input, but fails to predict the shedding frequency accurately for fluctuating incoming flow. On the other hand, the LES model shows reasonably good agreement with experiment in predicting vortex-shedding phenomenon for both uniform and fluctuating flows at inlet. Random-vibration based theory is employed for estimating r.m.s. response of tall buildings and the results compared well with the experimental results for a square building.