| Abstract: | 本論文探討以直接預測法對三組不同的高層建築斷面模型橫風向接近共振鎖定(Lock-in)時之氣彈行為進行識別實驗，求得在無因次化風速下各模型之反應、線性氣動力阻尼、非線性氣動力阻尼及氣動力勁度並比較之，理論部份延續王軍翰的論文內容。
為進行共振鎖定時參數識別研究，本文使用三組相同高度（100㎝）但不同斷面之模型進行識別實驗，分別為正方形斷面（BD1）、矩形斷面（BD1/2）及矩形斷面（BD1/3）。各種斷面以不同轉動慣量及阻尼比分類，模型BD1進行了九組轉動慣量（低、中、高）及阻尼比（低、中、高）組合的試驗，模型BD1/2及模型BD1/3由於在阻尼比0.9％以上時，並不會有大振幅的反應產生，故僅進行了六組轉動慣量（低、中、高）及阻尼比（低、高）組合的試驗。同時為了探討在相似Scruton Number的條件下，其共振鎖定反應與三種氣動力參數是否仍會相似，特別調整一組較大的轉動慣量及較小的阻尼比之試驗與一組較小的轉動慣量及較大的阻尼比之試驗進行比較。
本研究利用直接預測法理論，配合實驗成功地進行不同斷面的建物在共振鎖定現象之氣動力參數識別，得到參數資料並建立相關資料庫。實驗反應顯示，模型BD1於不同轉動慣量及三組低、中、高的阻尼比試驗之試驗中，其皆在無因次化風速9左右進入共振鎖定現象，低阻尼的試驗中大振幅反應在高無因次化風速時仍持續發生，此種現象，很可能已經進入馳振（Galloping）狀態，須待後續研究進一步釐清。中、高阻尼比的試驗則各在不同的無因次化風速下脫離鎖定現象。而模型BD1/2及模型BD1/3，則分別依其不同轉動慣量及阻尼比組合，分別在不同的無因次化風速下進入及脫離共振鎖定現象。在氣動力參數方面，模型BD1的三種氣動力參數 、 、 均隨著無因次化風速增加而減小，模型BD1/2及模型BD1/3除 隨著無因次化風速增加而減小， 、 隨著無因次化風速增加有其不同的趨勢。另外在相似Scruton Number條件下之試驗中，除了模型BD1的兩組實驗組合結果較為相似外，BD1/2及BD1/3之二種實驗組合之結果差異頗大，除了進入共振鎖定之無因次化風速不一致之外，氣動力參數亦不相同。
This thesis investigates the aero-elastic behavior of the building models in the across-wind direction near lock-in by identifying their aerodynamic parameters using the direct prediction method that follows the formulation in the thesis of Mr. Wang. The aerodynamic parameters include linear and nonlinear aerodynamic damping, and linear aerodynamic stiffness.
The identification tests were conducted in the wind tunnel by using three building models of the same height（100㎝）but different section shapes. They are square section(BD1), rectangular section (BD1/2) and rectangular section (BD1/3). The model BD1 was categorized in nine sets of different combinations of mass moments of inertia (low, medium and high) and damping ratios (low, medium and high). The model BD1/2 and BD1/3 were categorized in six sets of different combinations of mass moments of inertia (low, medium and high) and damping ratios (low and high), because in these two cases the steady state response did not occur at the damping ratio above 0.9％. In addition, in order to investigate the aero-elastic behavior of buildings under the similar Scruton Number condition, the tests with the combinations of a large mass moment of inertia accompanied with a small damping ratio test and a small mass moment of inertia accompanied with a high damping ratio were performed for comparison.
The aerodynamic parameters of the building models with different section shapes near the lock-in stage were successfully identified by using the direct prediction method, and the results can serve as the database for practical application. The resonance effect of the model BD1 starts to occur at the reduced velocity of about nine. For the case with low damping ratio, the resonance amplitude keep increasing as the reduced velocity increases, which might be caused by the galloping effect that is worth investigating in the future study. For the case with medium and high damping ratios, the resonance and lock-in effect cease at different reduced velocities. The models BD1/2 and BD1/3 in different combinations of mass moments of inertia and damping ratios have their own trend in terms of the starting point and ceasing point of reduced velocity during the lock-in range. The three aerodynamic parameters (Y1,εand Y2) of the model BD1 decrease as the reduced wind velocity increases. The aerodynamic parameterεfor the model BD1/2 and BD1/3 decrease as the reduced wind velocity increase, however, the Y1 and Y2 have their different trends as the reduced wind velocity increases. Moreover, under similar Scruton Number, the aero-elastic results of the model BD1 are similar, but the results of the models BD1/2 and BD1/3 are completely different. |
