## Dynamic Laboratory

**Rotor Dynamics Scaling Method**

This research investigates the method to predict dynamic characteristics of the rotor system using a scale model. Three scale models of the rotor system are made to experimentally validate the prediction of natural frequency and FRF of the system using a scaling factor. The validated simulation then expanded to predict the intricate design of the rotor system. The research also investigates the changing of natural frequency when the rotor spin. This changing of natural frequencies caused by the gyroscopic effect is predicted using the Champell diagram.

**Publication**

Dewi, D.K., **Abidin, Z.**, **Budiwantoro, B**. Et al. Dimensional analysis of a rotor system through FRF using transfer function and finite element methods. *J Mech Sci Technol ***34**, 1863-1870 (2020). https://doi.org/10.1007/s12206-020-0407-x

**Development of Vehicle Brake Tester**

Ministry of Transportation (MOT) requires many vehicle brake testers on their facilities. The braking efficiency of a vehicle is one of the critical parameters used to ensure transportation safety. From vehicle testing on brake tester rig, braking efficiency is measured. There are two types of brake tester usually used today, i.e., roller type and plate type. In this research, the advantages and weaknesses of those two were identified. Based on that, a new brake tester had been developed. The output of this new brake tester is not only braking efficiency but also tire characteristics. The tire characteristic discussed here is the longitudinal slip characteristic. Thus, we know not only the brake performance but also the tire condition.

**Publication**

**Patent **entitled “Alat untuk Mengukur Efisiensi Pengereman Kendaraan dengan Plat yang Digerakkan secara Manual” ( Registration Number: P00201807883)

**Patent** entitled “Alat untuk Mengukur Efisiensi Pengereman Kendaraan dengan Plat yang Digerakkan oleh Motor Listrik” ( Registration Number: P00201902190)

**Control Systems**

The application of PID to perform position control in the presence of Stribeck friction is believed to provoke the system trapped in limit cycle oscillation. This research aims to investigate the formulation of PID that will stabilize the position control of the DC motor in the presence of Stribeck friction. In order to diminish the limit cycle oscillation, the PID gain is set to meet global asymptotic stability in the Lyapunov sense as Kalman conjecture is fully applied. The analysis shows that the stability of the system depends on the friction properties near Stribeck velocity. Furthermore, the proposed PID formulation is found to be easy to be applied as the maximum integrator gain applied to the system is directly proportional to the given proportional gain.

**Publication**

**Vibration Root Mean Square **

The conventional RMS value calculation process will produce an error shown by the following graph. To overcome calculation error, a combination of PSO and LM algorithm is developed to find the parameters of a sinusoidal function model. If the model parameters are accurate, then the RMS value of a measured signal can be calculated based on the model. The developed algorithm will be investigated by simulations and experiments. The experiment equipment is shown in the figure below. In this experiment, the reference RMS value is calculated based on the peak-to-peak amplitude of the slider motion. From the results, it is shown that the developed algorithm gives a similar RMS value to the reference value. Besides, the developed algorithm also shows a smaller standard deviation (σ) value compare to RMS calculation based on the formula.

**Bearing Modelling **

Ball Pass Frequency Outer (BPFO) is a vibration signature of a roller bearing’s outer race defect. However, the experiment result had shown that the spectrum of a brand-new statically-loaded roller bearing also has a peak that corresponds to BPFO. This research aims to generate a mathematical model to explain that phenomenon. The goal has been achieved by elaborating the contact force of the rollers located inside the load zone. It is found that the interaction of contact forces among the rollers generates the fake-BPFO signal. Moreover, amplitude and frequency modulation occur as the unbalance and static load happen all at once. Hopefully, this modest research generates prudence on analyzing the vibration of a statically-loaded bearing as this research proves that a fake-BPFO might appear on the spectrum.