Research On Interference Effect And Wind-induced Vibration Of Double Tower In Large Power Plants

Rencently, since the fast development of Chinese electric power industry and theimplementation of the big projects first policy, height of the cooling tower wasrapidly rising. It is planning to build a tower in height of213m, which will be theworld’s highest tower. As this kind of thin shell rotating structure has thecharacteristics of small weight, low natural frequency, the wind load effect willbecome increasingly prominent, and the existing specification will be difficult toapply when the bulding size increases. Based on the engineering background of acooling tower under construction, this paper studied for the following works throughwind tunnel test, the finite element calculation and the theoretical derivation.(1) The surface roughness and the effective Reynolds number simulation.Through flow around ribbed cylinder test, this paper explored several aspects whichhave relationship with the Reynolds number effect, such as roughness, end plate, flowcondition and cylinder size. The results show that the roughness coefficient k/s is themain parameters affecting the wind pressure distribution. When puted the end plate on,it significantly reduced3d effect of the top section, but also made each middle layerresistance coefficient measurement generally decrease for about0.1, the minimumpressure coefficient rise up about0.1. Compared with uniform flow, turbulent flowbrings out significantly different mean and pulse shape coefficient distribution.Hyperbolic cooling tower’s effective Reynolds number simulation proves that flowaround circular cylinder results can also apply to cooling tower structure.(2) Interference effect of twin tower and discussing on methods of calculatinginterference coefficient. This paper studied on wind pressure distribution oftwin-tower arrangement under different tower distance and made a comparison withprevious research results. Different methods for calculating interference coefficientwere investigated. By theoretically derivation it is found that choosing mean value orextream value to calculate the interference coefficient must match with the windvibration coefficient. By experimental text, it is found that interference coefficientcalculated by the force coefficient or other load coefficient is hard to accuratelymeasure the interference effect of maximum response of the cooling tower. Therefore,this paper recommended using response to calculate interference factor directly.(3) Study on calculation methods of wind-induced vibration response. With time domain analysis, it reveals that combined with POD to extend wind pressure dataand ANSYS software to do time history calculation is a feasible and efficient method.Some programs were made to do the frequency domain analysis. Results show thatusing PEM and CQC method analysis with only50order modal can be in goodagreement with those obtained by the time domain method, and the SRSS method isnot suitable for analysis of cooling tower structure which has concentrated frequency.Through comparison of the power spectrum of response, it is found that frequencydomain method can recognise high-order vibration mode resonance component betterthan time domain method.(4) Investigation for the method of calculating wind vibration coefficient. Thewind vibration coefficient was calculated by the wind load factor method proposed byDavenport and the influence of damping ratio on the wind vibration coefficient wasdiscusses. The results show that the damping ratio in this example decreased from5%to1%, the wind vibration coefficient can rise up to15%. In view of the wind angle ofmaximum wind vibration coefficient and the maximum interference coefficient is hardto be the same, the value of equivalent wind vibration coefficient considering theeffect of interference was recommended. This paper also puted forward a newvibration load coefficient. Some calculation was made under several conditions suchas single tower, group towers and envelope of group tower. Results show that in therange of linear elastic, the layered wind load coefficient can make the static responseequivalent with the target response.(5) Study on the interference effect of the surrounding environment. This papermade some comparison for wind pressure distribution, wind vibration response,background response component and design parameters under three differentconditions, which were the single tower condition, twin towers condition and twintowers with surroundings condition. It is found that surroundings play a huge role ofinterference effect. Hence, this paper made the surroundings’ interference influencequantified, which can provide data for post-research.