Wind-Induced Effects And Control Of Large-Span Flexible Photovoltaic Support Structures

Large-span flexible photovoltaic support structures have been increasingly used due to their good site adaptability and economy.With the increase of the height and span of the support structure,its wind sensitivity is also highlighted.Nevertheless,there is still a lack of intensive theoretical and experimental research on the wind-induced response and wind-resistant design of large-span flexible support structures.This is also main reason for the significant wind-vibration response of this structure form under the strong wind.Therefore,it will have significant theoretical and engineering significance to carry out research on the wind-induced effects of large-span flexible photovoltaic supports.In this paper,a typical large-span flexible photovoltaic support structure is taken as the research object,and its wind-induced effect and control measures are systematically explored through wind tunnel tests,theoretical analysis and finite element numerical calculation methods.The main contents are as follows:1)The aeroelastic test and wind pressure test of a typical large-span flexible photovoltaic support structure were conducted under three inclineation angles of 0°,5°and 10°,respectively.The influence of wind speed,cable pretension and tilt angle on vertical displacement response was analyzed as well as the non-Gaussian characteristic of wind-induced displacement and the corresponding peak factor of the large-span photovoltaic support structure was studied and derived.In addition,finite element simulation was adopted to study wind-induced three-dimensional vibration characteristics of the support structure with different tilt angles.The study results indicate that vibration of the photovoltaic support structure increased with tilt angle.The maximum response occurs at 0° and 180° wind azimuths and the corresponding gust factors are basically between 4 and 5.Increasing pretension of the cable may be obviously useful to control wind-induced vibration while in is not helpful for the support structure with a tilt of 10°.For the support structure with tilted PV modules,wind-induced vibration has an approximate linear relationship with the square of ambient velocity.Further,high wind velocity can easily excite high order vertical modal response of the structure.Three-dimensional structural responses under wind actions mainly include a large portion of vertical vibration and a small portion of translational vibration,while the torsional response can be ignored.2)On the basis of the aeroelastic model test,empirical wavelet transform(EWT)and variational mode decomposition(VMD)method were adopted to identify and obtain the aerodynamic damping under different wind speed and azimuth,component inclination and pre-tension based on the improved random decrement technique,.The research results show that the aerodynamic damping is more sensitive to the change of the wind azimuths and it decreases as the wind speed increases.Under some wind speeds and wind azimuths,the aerodynamic damping value is even larger than the structural damping,which must be considered in the wind vibration analysis.When the modules are laid obliquely,the aerodynamic damping of the photovoltaic structure will have a negative value when wind azimuth is 180°.Additionally,in order to reflect the time-frequency characteristics of non-stationary response signals of flexible photovoltaic support structures,a modal identification method based on Fast Bayesian and short-time Fourier transform(STFT)is proposed.This method uses short-time Fourier transform to replace classical Fourier transform to identify modal parameters,so that the characteristics of modal parameters in both time and frequency domain can be obtained.Using time-domain decomposition decoupling(TDD)technology,the multi-DOF multi-modal response signal is converted into a single-DOF single-modal response signal,which improves the computational efficiency.The expression of NLLF(Negative log-likelihood function)was presented under high signal-to-noise ratio.Numerical examples are used to verify the validity of the proposed Fast Bayesian STFT method.In addition,the aeroelastic wind tunnel test data of a large-span flexible photovoltaic support structure was identified with the proposed method to derive the damping and frequency.The results are compared with ones obtained from the classical continuous wavelet transform(CWT)and Hilbert-Huang transform(HHT),which shows that the proposed method has good accuracy.3)The distribution characteristics of average wind pressure and fluctuating wind pressure coefficient of photovoltaic module panels under different wind azimuths and inclination angles were investigated through the rigid model pressure test.The extreme wind pressure change law of the components and the power spectrum of the fluctuating wind pressure under part of the wind azimuth was also indicated.On this basis,combined with the wind pressure distribution characteristics of photovoltaic modules,the wind-induced displacement response of the structure was analyzed by using the time domain method and the frequency domain method,and the multi-target equivalent static wind load and wind vibration coefficient of the structure were calculated.The research results show that when the module inclination angle is 10 degrees,the average wind pressure coefficient gradient distribution along the incoming flow direction and the absolute value decreases rapidly at wind azimuth of 0° and 180°.When the components are laid horizontally,the gradient distribution of the average wind pressure coefficient is not obvious.Meanwhile,the wind-induced displacement response of the flexible photovoltaic support structure is dominated by the resonance response.The first-order modal contribution is larger in the process of wind vibration of the structure.4)Based on the analysis of wind pressure distribution and displacement response characteristics,the ANSYS finite element numerical simulation software was used to study and compare the vibration reduction efficiency of TMD with different parameters,and put forward the control measures for the wind-induced response of the structure.