การศึกษาการสั่นสะเทือนจากแรงไม่สมดุลของเครื่องจักรต่อโครงสร้างอาคาร / สมนึก จรูญจิตเสถียร = A study of vibration induced by machine unbalanced force on a building structure / Somnuk Jaroonjitsathian
The purpose of this thesis was to study the effects of vibration due to machine unbalanced force on a building structure. The thesis consists mainly of three parts. First, developing a computer program “TFRAME” to analyze the natural frequencies, mode shapes and maximum responses of general structures subjected to harmonic loads by using FORTRAN language. Second, calculating the vibration responses of a 3-storey reinforcement concrete building of height 12 m., width 4 m. and depth 4 m. by using TFRAME. Last , comparing the results between program "TFRAME" and experimental structure made from steel of height 1.80 m. and width 0.60 m. with a small fan having angular velocity about 1300 RPM. "TFRAME” has been developed for solving the force vibration problems on a plane frame structure, by using the finite element method which divides the overall structure into several 2-D Euler's beam elements and creates a system of simultaneous differential equation representing vibration properties of the structure. Then, combines the equations of the structure with the isolating properties by using the conventional method. Finally, solves the simultaneous differential equations by transforming the generalize coordinates to the principle coordinates using modal matrix. The assuming structure with 39 beam components and 117 degree of freedoms analyzed by “TFRAME” showed that the structure has an finite number of natural frequencies. The first three modes of natural frequencies are lateral vibrations and the next three modes are symmetrical vibrations. Adding more weight in the structure will lower all natural frequencies especially where mode shape is higher. Next, direct installing of unbalanced machines on the structure indicated that the shape of maximum responses were similar to the shape of the nearest frequency between machine and the structure. And installing machine on the position where mode shape is higher, will increase all maximum responses. Finally, installing machine on an isolation base will changing all natural frequencies especially when the isolation frequency is tuned with the structural frequency in the same direction. The maximum responses behaved as same as direct installing but had less magnitude and higher weight of isolation base will lower magnitude of vibration.
