Penyusunan Program Komputasi Pengidentifikasi Parameter Dinamik Balok Ditumpu Jepit-Bebas

Abstract

Operational Modal Analysis (OMA) is a new procedure to identify a structural vibrating system. In this paper, the operational modal analysis based on Ibrahim Time Domain Method. This method requires some displacement data from free vibration response of structure model. Here, a beam with clamped-free condition is used as a test model. Based on Finite Element Method, this beam is divided into 3 elements that consist of 6 degree of freedoms for each element (3 translations and 3 rotations). In this case, a fixed lumped mass is added to each translation node. The beam is excited in its clamped support by sinusoidal displacement during 0.1 s. After 0.1 s, the excitation is stopped and then the displacement data is recorded. Therefore, this condition could be assumed that recorded data represents free vibration response. For this purpose, some computation program was developed to predict the response of free vibration system. First, we make a program SINUS.FOR to produce a sinus displacement function. This function as a support motion is used as an input for program BALKEN.FOR that consist of various program, like Guyan Condensation, Cholesky Decomposition, Jacobi Method, Matrix Iteration Method, Phase Plane Method, Finite Difference Method, Houbolt Method, etc. This entire program is compiled by FORTRAN programming language. Next, the output of BALKEN.FOR that called matrix [A] become an input of program EIGENWERT-ITD.MW which is written in MAPLE programming languages. In this research, it is assumed that only the displacement of x1(t), x2(t) and x3(t) is known. It is known that to identify a system with 6 degrees of freedom, The Ibrahim Time Domain Method requires displacement responses. To fulfill this condition, we need 9 pseudo measurement stations. It means that each station with known displacement response has to be manipulated in such way so that it can produce 3 pseudo displacement response groups. The Result shows that the common error is below 5 %. Except, the damping ratio of mode number 5 is more than 10 %. While the other result can be identified better, especially for the natural frequency is identified very well.