Study On Wind-induced Vibrations Of Solar Tower And Its Control Measurements

Solar energy is a type of clean and efficient green energy,and has been widely used all over the world in recent years,especially for the concentrated solar power(CSP)technology.At present,there are mainly four kinds of solar collector systems in CSP stations: the tower collector,the parabolic trough collector(PTC),the linear Fresnel reflector(LFR)and the parabolic dish collector.In particular,the solar power tower has attached much attention because of its easy to commercialize.Among the20 CSP stations first approved by the China Development and Reform Commission in September 2016,there were 9 stations proposed to be utilized with the solar power tower system.The solar tower,which locates at the center of a solar power tower generation system,is usually characterized by low fundamental frequencies,small damping,high flexible.It is very prone to produce large amplitude vibrations under wind loads,thus to reduce the power generation efficiency even to threaten the structural safety.Therefore,studies on the wind-induced vibrations of solar tower and its control attract much attentions of the engineers and researchers,recently.In this paper,the wind-induced responses of solar tower were carefully studied by wind tunnel tests and field measurements based on a 243-meter-high solar tower of Noor III power station in Morocco.Eddy current tuned mass dampers(TMD)were designed and manufactured to mitigate the wind-induced vibrations of the solar tower.The main works included in this paper are summarized as follows:(1)A novel method of designing and manufacturing elastic test models for reinforced concrete solar towers and similar structures was proposed.And a 1:200elastic test model for the solar tower of Noor III power station was manufactured with aluminum alloy by the proposed method.The dynamic parameters of the model were identified,the results show that the first damping ratio of the model is as low as 0.3%,and the natural frequencies and mode shapes agree well with the prototype results.In addition,an elastic model for a steel solar tower was also manufactured to study the difference in wind-induced responses between the concrete solar tower and the steel solar tower.(2)A series of wind tunnel tests based on the elastic model were conducted to study the characteristics of wind-induced vibrations of solar towers.The structural damping ratio of 0.3%,0.7%,1.0%,1.5% and 2.0% were realized accurately through sticking different tapes between the gaps of the coats of the model.And then the effects of structural damping to the responses of the vortex-induced vibration was carefully studied.The results show that the wind-induced responses of the tower is rather sensitive to the damping,when the damping ratio is up to 1.0%,the wind-induced responses especially the cross-wind induced responses would decreased sharply.In order to simulate the Reynolds number,rough ribs were used to increase the model roughness.The optimal parameters for the ribs were determined based on a series of force and pressure measurement wind tunnel tests.Then the wind-induced responses of the tower with the selected roughness were measured by using elastic wind tunnel tests.The results show that the RMS wind-induced responses of the solar tower are markedly reduced by taking the Reynolds number into account.Moreover,wind-induced responses of steel solar tower were also studied and compared with that of the concrete solar tower,it is found that no obvious cross-wind resonance responses could be observed for steel solar tower.Finally,whether the ACI307-08 code and GB50009-2012 code are suitable for the wind-resistant design of concrete solar tower was discussed based on the test and calculated results.(3)The effectiveness of TMD and helical stakes on the mitigation of wind-induced responses of the concrete solar tower were studied respectively by using elastic wind tunnel tests.A tiny tuned mass damper with conveniently adjustable eddy current damping was specially designed and manufactured for the scaled-down solar tower.Numerical simulations based on the COMSOL software were conducted to determine the key parameters of the eddy current damper,including the gas distance,the thickness of conductive plate and back iron.The structural parameters of the tiny TMD were experimental identified and its optimized values can be conveniently realized.Then wind tunnel tests of the elastic model with the proposed tiny eddy current TMD was conducted.Moreover,helical stakes were also used for the tests of the elastic solar tower,the parameters of the helical strakes were determined based on the GB50051-2002 code and CICIND standards which are specially suitable for the chimney design.The results show that the proposed TMD is effective in suppressing the wind-induced responses of the solar tower,while the helical strakes have little effect on it.(4)Four 10-ton TMDs with total mass ratio of 1.0% were designed and manufactured to reduce the wind-induced vibrations of the Noor ? solar tower.The damping of the TMD systems were supplied by eddy current damping.The parameters were determined based on wind-tunnel testing results and Den Hartog's optimization theory.The frequency and damping of the TMD can be adjusted conveniently through changing the pendulum length and the gas distance,respectively.In order to facilitate the parameter adjustment after the installation of the TMD systems to the tower,a series of testing were conducted in the factory to determine the relationship between the pendulum length and frequency,as well as the gas distance and damping ratio.The vibration control robustness of the TMDs against the frequency and damping detuning was investigated through theoretical analysis and numerical simulations.The four above-mentioned TMDs were symmetrically installed at the same height(237m)on the Noor III solar tower.Dynamic properties of the prototype solar tower were tested,and the structural parameters of the tower including natural frequencies and damping ratios were identified.The results show that the first structural damping ratio and frequency of the prototype solar tower are about 0.72% and 0.317 Hz,respectively.Based on the identified results,the pendulum length and the gas distance were precisely adjusted.The effects of the operated TMD number to the solar tower's damping ratios were carefully studied.Furthermore,wind-induced vibrations of the solar tower with/without the operation of the TMDs under wind velocity of about14?17m/s(15m above the ground)were also investigated.Field measurement results show that the TMDs system is effective to suppress wind-induced vibrations of the solar tower,the peak and mean of the wind-induced acceleration responses could be reduced by 39.4% and 56.4% with the operation of the four TMDs,respectively.