Path: TopS2-ThesesAerospace Engineering-FTMD2011

IDENTIFICATION OF FLUTTER DERIVATIVES OF BRIDGE DECKS FROM WIND TUNNEL TEST DATA

Master Theses from JBPTITBPP / 2017-10-09 10:19:32
Oleh : HADYAN HAFIZH (NIM : 23609002); Pembimbing: Dr. Ir. Leonardo Gunawan; Dr. Ir. Hari Muhammad, S2 - Aerospace Engineering
Dibuat : 2011, dengan 8 file

Keyword : Modeling of bridge deck, Flutter derivatives, Parameter identification, Wind tunnel test, Aeroelasticity. Pemodelan dek jembatan, Flutter derivatives, Identifikasi Parameter, Uji Terowongan Angin, Aeroelastisitas.

Aeroelastic phenomena should be considered during the design phase of long span bridge. One of the aeroelastic problems is flutter, the dynamic instability that may cause structural failure at a wind speed called the flutter



speed. The prediction of flutter speed needs a thorough modeling of bridge stiffness, inertias, and especially its unsteady aerodynamic forces. The potential flow theory is not applicable to calculate unsteady aerodynamics of oscillating bridges due to their non-streamlined and complex geometry, and the non avoidable flow separation. A semi empirical model proposed by Scanlan is used.



In this model, relation between unsteady aerodynamic forces and motion of the bridge is modelled using parameters called flutter derivatives. The flutter derivatives have to be identified from free vibration response of an elastic bridge at several wind-speeds.



This thesis presents wind tunnel tests and flutter derivatives identification of aeroelastic bridge models. Three bridge sections were designed, built, and tested in a wind-tunnel. Data obtained from the tests were displacement of the bridge model at some wind speeds which was mixed with noises. A zero-phase band pass filter (BPF) which was designed in MATLAB successfully removed the noises from measured data. Then an identification method called Modified Ibrahim Time Domain method was employed to identify the modal parameters of the system at each wind speed. Simulations of the bridge responses by using



the identified modal parameters could represent the measured data excactly. The flutter derivatives of each bridge section at a wind speed were then calculated



from the difference of effective stiffness and damping matices to those at zero wind speed. The identified flutter derivatives were verified by using theoretical flutter derivatives of a flat plate calculated based on Theodorsen model.



The identified flutter derivatives coefficients H1*, H3*, A1*, and A3* have similar trend to those of flat plates, while H4* and A4* had different trend than those of flat plates. For trapezium section, flutter derivatives coefficient H2* have also different trend than those of flat plates.



The identified flutter derivatives of diamond section were also compared to results of other researcher, which had good agreements with those of flat plates due to the closeness of its slenderness ratio to that of flat plate. The comparison showed that the identified flutter derivatives have similar trends with those other researcher except for H4* and A4*.



It could be concluded that the measurement procedure used in this research was able to produce flutter derivatives which are in good agreements with those produced by other researcher.

Deskripsi Alternatif :

Dalam fase desain jembatan bentang panjang berbagai fenomena aeroelastik merupakan aspek yang perlu diperhatikan. Salah satu fenomena tersebut adalah flutter, yaitu ketidakstabilan dinamik yang dapat mengakibatkan kegagalan struktur yang terjadi pada suatu kecepatan angin



tertentu dan disebut sebagai kecepatan flutter. Prediksi kecepatan flutter memerlukan pemodelan kekakuan, inersia dan terutama gaya-gaya aerodinamika jembatan. Teori aliran potensial tidak dapat digunakan untuk menghitung gaya-gaya aerodinamika tak stasioner pada jembatan karena bentuknya yang kompleks, aliran udara di sekitarnya tidak stream-lined, dan terjadi pelepasan aliran. Untuk menghitung gaya-gaya aerodinamika pada jembatan digunakan model semi empiris yang diajukan oleh Scanlan. Dalam model ini, hubungan antara gaya-gaya aerodinamika dan gerakan jembatan



dimodelkan menggunakan parameter flutter derivatives. Parameter ini didapat dari pengujian terowongan angin pada berbagai kecepatan angin.



Thesis ini melaporkan pengujian terowongan angin dan identifikasi flutter derivatives pada tiga buah penampang jembatan. Tiga jenis model dek jembatan yaitu rectangular, diamond, dan trapezium telah didesain, dibangun, dan diuji dalam terowongan angin. Hasil dari pengujian pada terowongan angin adalah sinyal perpindahan yang bercampur dengan noise. Untuk dapat menghilangkan noise tersebut maka proses filter dilakukan. Sebuah zero-phase band pass filter (BPF) telah didesain di MATLAB® dan diimplementasikan pada



data hasil uji terowongan angin yang terbukti dapat menghilangkan noise pada rentang frekwensi yang didesain. Untuk mendapatkan harga flutter derivatives dari data perpindahan yang telah difilter, digunakan sebuah metode sistem identifikasi yaitu metode Modified Ibrahim Time Domain (MITD). Hasil identifikasi berupa parameter modal terbukti dapat mensimulasikan respon dek jembatan yang sesuai dengan respon dek jembatan hasil pengukuran. Flutter



derivatives pada berbagai kecepatan kemudian dihitung dari perbedaan matriks kekakuan efektif dan redaman efektif pada tiap kecepatan angin terhadap matriks kekakuan dan redaman efektif tanpa angin.



Validasi terhadap hasil identifikasi dilakukan menggunakan flutter derivatives pelat tipis yang dihitung mengikuti fungsi Theodorsen. Koefisien flutter derivatives H1*, H3*, A1*, and A3* hasil identifikasi memiliki trend yang while H4* and A4* sama dengan flutter derivatives pelat tipis, sedangkan koefisien flutter derivatives H2* memiliki trend yang berbeda dengan flutter derivatives pelat tipis. Perbedaan trend flutter derivatives hasil identifikasi terhadap pelat tipis juga ditunjukkan oleh koefisien flutter derivatives H4* and A4*. untuk kasus trapezium section.



Dari hasil-hasil ini dapat disimpulkan bahwa prosedur pengukuran yang dilakukan telah memberi hasil yang sesuai dengan hail peneliti lain.

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  • Pembimbing:



    Dr. Ir. Leonardo Gunawan;



    Dr. Ir. Hari Muhammad, Editor: Alice Diniarti

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