• Title, Summary, Keyword: wind-induced deformation

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Beam finite element model of a vibrate wind blade in large elastic deformation

  • Hamdi, Hedi;Farah, Khaled
    • Wind and Structures
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    • v.26 no.1
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    • pp.25-34
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    • 2018
  • This paper presents a beam finite element model of a vibrate wind blade in large elastic deformation subjected to the aerodynamic, centrifugal, gyroscopic and gravity loads. The gyroscopic loads applied to the blade are induced by her simultaneous vibration and rotation. The proposed beam finite element model is based on a simplex interpolation method and it is mainly intended to the numerical analysis of wind blades vibration in large elastic deformation. For this purpose, the theory of the sheared beams and the finite element method are combined to develop the algebraic equations system governing the three-dimensional motion of blade vibration. The applicability of the theoretical approach is elucidated through an original case study. Also, the static deformation of the used wind blade is assessed by appropriate software using a solid finite element model in order to show the effectiveness of the obtained results. To simulate the nonlinear dynamic response of wind blade, the predictor-corrector Newmark scheme is applied and the stability of numerical process is approved during a large time of blade functioning. Finally, the influence of the modified geometrical stiffness on the amplitudes and frequencies of the wind blade vibration induced by the sinusoidal excitation of gravity is analyzed.

Probability of exceeding the serviceability limit of antenna masts

  • Kammel, Christian
    • Wind and Structures
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    • v.4 no.4
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    • pp.353-366
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    • 2001
  • With respect to serviceability, antenna masts should be designed so that wind-induced motion will not cause unacceptable lack of transmission for broadcasting users and wireless communication. For such antenna masts with directional radio transmission the serviceability limit state is predominantly governed by the tolerable change of the broadcasting angle of the mounted antenna assembly and therefore by the tip distortion of the mast. In this paper it will be shown that refinements of the present state of design of antenna masts are possible by using the statistics of extremes applied to extreme wind situations and by consideration of the statistical and reliability requirements given by the operator such as frequency and return period of passing the serviceability limit.

Assessment of Image Registration for Pressure-Sensitive Paint (Pressure Sensitive Paint를 이용한 압력장 측정기술의 이미지 등록에 관한 연구)

  • Chang, Young-Ki;Park, Sang-Hyun;Sung, Hyung-Jin
    • 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.

Vortex-induced oscillations of bridges: theoretical linkages between sectional model tests and full bridge responses

  • Zhang, Zhitian;Ge, Yaojun;Chen, Zhengqing
    • Wind and Structures
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    • v.19 no.3
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    • pp.233-247
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    • 2014
  • Vortex-induced oscillation is a type of aeroelastic phenomenon, to which extended structures such as long-span bridges are most susceptible. The vortex-induced vibration (VIV) behaviors of a concerned bridge were investigated conventionally in virtue of wind tunnel tests on string-mounted sectional models. This necessitates the building of a linkage between the response of the sectional model and that of the prototype structure. Although many released literatures have related to this issue and provided suggestions, there is a lack of consistency among them. In this study, some theoretical models describing the vortex-induced structural motion, including the linear empirical model, the nonlinear empirical model and the modified (or generalized) nonlinear empirical model, are firstly reviewed. Then, the concept of equivalent mass density is introduced based on the principle that an equal input of energy should result in identical structural amplitudes. Based on these, the theoretical linkages between the amplitude of a section model and that corresponding to the prototype bridge are discussed with different analytical models. Theoretical derivation indicates that such connections are dependent mainly on two factors, one is the presupposed shape of deformation, and the other is the theoretical VIV model employed. The theoretical analysis in this study shows that, in comparison to the nonlinear empirical models, the linear one can result in obvious larger estimations of the full bridges' responses, especially in cases of cable-stayed bridges.

Structural analysis and optimization of large cooling tower subjected to wind loads based on the iteration of pressure

  • Li, Gang;Cao, Wen-Bin
    • Structural Engineering and Mechanics
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    • v.46 no.5
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    • pp.735-753
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    • 2013
  • The wind load is always the dominant load of cooling tower due to its large size, complex geometry and thin-wall structure. At present, when computing the wind-induced response of the large-scale cooling tower, the wind pressure distribution is obtained based on code regulations, wind tunnel test or computational fluid dynamic (CFD) analysis, and then is imposed on the tower structure. However, such method fails to consider the change of the wind load with the deformation of cooling tower, which may result in error of the wind load. In this paper, the analysis of the large cooling tower based on the iterative method for wind pressure is studied, in which the advantages of CFD and finite element method (FEM) are combined in order to improve the accuracy. The comparative study of the results obtained from the code regulations and iterative method is conducted. The results show that with the increase of the mean wind speed, the difference between the methods becomes bigger. On the other hand, based on the design of experiment (DOE), an approximate model is built for the optimal design of the large-scale cooling tower by a two-level optimization strategy, which makes use of code-based design method and the proposed iterative method. The results of the numerical example demonstrate the feasibility and efficiency of the proposed method.

An Evaluation of the Structural Stability of a Clip Type Prefabricated Greenhouse under Strong Wind and Heavy Snow Conditions (조립식 클립형 비닐하우스의 강풍 및 폭설시 구조 안정성 평가)

  • Ro, Kyoung-Chul
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.6
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    • pp.3423-3428
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    • 2014
  • Numerical studies were performed to evaluate the structural safety of a greenhouse under both snow and wind loads. In the case of a wind load, fluid-structure interaction (FSI) method was used to consider the local pressure distributions on the greenhouse-induced by aerodynamic characteristics. The results showed that the maximum stress and deformation occur near the junction of pipe supports and rafters of the roof, where connecting clips are installed. Moreover, the wind load is a more severe condition than a snow load. Overall, these results will be used to design a prefabricated connecting clip with easy installation and low maintenance.

The inertial coefficient for fluctuating flow through a dominant opening in a building

  • Xu, Haiwei;Yu, Shice;Lou, Wenjuan
    • Wind and Structures
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    • v.18 no.1
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    • pp.57-67
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    • 2014
  • For a building with a dominant windward wall opening, the wind-induced internal pressure response can be described by a second-order non-linear differential equation. However, there are two ill-defined parameters in the governing equation: the inertial coefficient $C_I$ and the loss coefficient $C_L$. Lack of knowledge of these two parameters restricts the practical use of the governing equation. This study was primarily focused on finding an accurate reference value for $C_I$, and the paper presents a systematic investigation of the factors influencing the inertial coefficient for a wind-tunnel model building including: opening configuration and location, wind speed and direction, approaching flow turbulence, the model material, and the installation method. A numerical model was used to simulate the volume deformation under internal pressure, and to predict the bulk modulus of an experimental model. In considering the structural flexibility, an alternative approach was proposed to ensure accurate internal volume distortions, so that similarity of internal pressure responses between model-scale and full-scale building was maintained. The research showed 0.8 to be a reasonable standard value for the inertial coefficient.

Lock-in and drag amplification effects in slender line-like structures through CFD

  • Belver, Ali Vasallo;Iban, Antolin Lorenzana;Rossi, Riccardo
    • Wind and Structures
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    • v.15 no.3
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    • pp.189-208
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    • 2012
  • Lock-in and drag amplification phenomena are studied for a flexible cantilever using a simplified fluid-structure interaction approach. Instead of solving the 3D domain, a simplified setup is devised, in which 2D flow problems are solved on a number of planes parallel to the wind direction and transversal to the structure. On such planes, the incompressible Navier-Stokes equations are solved to estimate the fluid action at different positions of the line-like structure. The fluid flow on each plane is coupled with the structural deformation at the corresponding position, affecting the dynamic behaviour of the system. An Arbitrary Lagrangian-Eulerian (ALE) approach is used to take in account the deformation of the domain, and a fractional-step scheme is used to solve the fluid field. The stabilization of incompressibility and convection is achieved through orthogonal quasi-static subscales, an approach that is believed to provide a first step towards turbulence modelling. In order to model the structural problem, a special one-dimensional element for thin walled cross-section beam is implemented. The standard second-order Bossak method is used for the time integration of the structural problem.

Experimental investigation on a freestanding bridge tower under wind and wave loads

  • Bai, Xiaodong;Guo, Anxin;Liu, Hao;Chen, Wenli;Liu, Gao;Liu, Tianchen;Chen, Shangyou;Li, Hui
    • Structural Engineering and Mechanics
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    • v.57 no.5
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    • pp.951-968
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    • 2016
  • Long-span cross-strait bridges extending into deep-sea waters are exposed to complex marine environments. During the construction stage, the flexible freestanding bridge towers are more vulnerable to environmental loads imposed by wind and wave loads. This paper presents an experimental investigation on the dynamic responses of a 389-m-high freestanding bridge tower model in a test facility with a wind tunnel and a wave flume. An elastic bridge model with a geometric scale of 1:150 was designed based on Froude similarity and was tested under wind-only, wave-only and wind-wave combined conditions. The dynamic responses obtained from the tests indicate that large deformation under resonant sea states could be a structural challenge. The dominant role of the wind loads and the wave loads change according to the sea states. The joint wind and wave loads have complex effects on the dynamic responses of the structure, depending on the approaching direction angle and the fluid-induced vibration mechanisms of the waves and wind.

Aerodynamic and Structural Design of 6kW Class Vertical-Axis Wind Turbine (6kW급 수직축 풍력발전기 형상 및 구조설계)

  • Kim, Dong-Hyun;Choi, Hyun-Chul;Lee, Jong-Wook;Ryu, Gyeong-Joong;Kim, Sung-Bok;Kim, Kwang-Won;Nam, Hyo-Woo;Lee, Myoung-Goo
    • The KSFM Journal of Fluid Machinery
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    • v.14 no.2
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    • pp.52-58
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    • 2011
  • In this study, the design and verification of 6 kW class lift-type vertical-axis wind turbine (VAWT) has been conducted using advanced CAE technique based on computational fluid dynamics (CFD), finite element method (FEM), and computational structural dynamics (CSD). Designed aerodynamic performance of the VAWT model is tested using unsteady CFD method. Designed structural safety is also tested through the evaluation of maximum induced stress level and resonance characteristics using FEM and CSD methods. It is importantly shown that the effect of master eccentricity due to rotational inertia needs to be carefully considered to additionally investigate dynamic stress and deformation level of the designed VAWT system.