Large Amplitude Harmonic Vibration under Pulse Doppler Measurement

A flow velocity or tissue motion can be measured by pulse Doppler method. However, when the method is applied to a sinusoid motion or harmonic vibration, the estimation result is deviated. In this paper, the generalized theory of pulse Doppler measurement to the sinusoid motion is explained and the relation between the estimation deviation and the real value is given. Furthermore, a special case of binary velocity estimation is expanded and simulated with different parameters. This simulation result suggested that different selection of parameters may fundamentally affect the output of pulse Doppler estimation.

Research on the Application of VPython 3D Dynamic Visualization in the Teaching of College Physics

As there are numerous physics formulas in addition to them being theoretical, college students generally consider the concepts of physics as abstract, in which they are not able to apply what they have learned. For 3D dynamic animation and visualization in the teaching of college physics, VPyton has many advantages, and it provides useful exploration for students to overcome obstacles in college physics learning. Taking the teaching of simple harmonic vibration, optics, molecular thermal motion, and electric field as examples, this article discusses the application of VPython in the human-computer interactive teaching mode of college physics, which provides a beneficial exploration and new way to improve students’ engineering skills and numeracy, as well as to respond to the national “new engineering education” reform in China.

A Vibration Sensor-Based Method for Generating the Precise Rotor Orbit Shape with General Notch Filter Method for New Rotor Seal Design Testing and Diagnostics

Verification of the behaviour of new designs of rotor seals is a crucial phase necessary for their use in rotary machines. Therefore, experimental equipment for the verification of properties that have an effect on rotor dynamics is being developed in the test laboratories of the manufacturers of these components all over the world. In order to be able to compare the analytically derived and experimentally identified values of the seal parameters, specific requirements for the rotor vibration pattern during experiments are usually set. The rotor vibration signal must contain the specified dominant components, while the others, usually caused by unbalance, must be attenuated. Technological advances have made it possible to use magnetic bearings in test equipment to support the rotor and as a rotor vibration exciter. Active magnetic bearings allow control of the vibrations of the rotor and generate the desired shape of the rotor orbit. This article presents a solution developed for a real test rig equipped with active magnetic bearings and rotor vibration sensors, which is to be used for testing a new design of rotor seals. Generating the exact shape of the orbit is challenging. The exact shape of the rotor orbit is necessary to compare the experimentally and numerically identified properties of the seal. The generalized notch filter method is used to compensate for the undesired harmonic vibrations. In addition, a novel modified generalized notch filter is introduced, which is used for harmonic vibration generation. The excitation of harmonic vibration of the rotor in an AMB system is generally done by injecting the harmonic current into the control loop of each AMB axis. The motion of the rotor in the AMB axis is coupled, therefore adjustment of the amplitudes and phases of the injected signals may be tedious. The novel general notch filter algorithm achieves the desired harmonic vibration of the rotor automatically. At first, the general notch filter algorithm is simulated and the functionality is confirmed. Finally, an experimental test device with an active magnetic bearing is used for verification of the algorithm. The measured data are presented to demonstrate that this approach can be used for precise rotor orbit shape generation by active magnetic bearings.

Fabrication of Digital Harmonic Vibration Practicum Using Phototransistor Sensor with Arduino-Uno Microcontroller

The problem in the harmonic vibration practicum is in calculating time accurately. Commonly, the time counter used was a stopwatch, but it was unable to provide valid data. As a result, the student has difficulty seeing the relationship between concepts with practical results in the laboratory. To overcome these problems, in this study, we developed a harmonic vibration practicum tool that is equipped with a digital timer using an Arduino Uno microcontroller as a light sensor. An Arduino can be programmed via a PC according to the wishes of the developer. This study was development research using a 4-D model (Define-design-develop-dissemination). The define and design stages respectively to find problems in the harmonic vibration practicum tool. The tool is finally designed and then calibrated, validated, and practical. The calibration results show that the percentage difference for repetition measurement and comparison that values with theory was 0.008% and 3.98%, respectively. In addition, the validation results show an average percentage of 87% or very valid. For practicality, the result through a limited test of Physics students of IAIN Batusangkar in the second semester shows a very practical response with a percentage of 85.96%. Due to time constraints, the dissemination stages have not been carried out in this study.

Harmonic vibration moment suppression using hybrid repetitive control for active magnetic bearing system

The active magnetic bearing system exhibits mass imbalance and sensor runout which cause the system to generate harmonic vibration force and moment. Repetitive control is an effective method to eliminate such harmonic vibration. Traditional repetitive control will eliminate all of the harmonic frequency components. However, in a practical system, the odd harmonic components usually dominate. Meanwhile, the existing method only suppresses the vibration force in the magnetic bearing system, and there is little research on the suppression of moment. Aiming at these problems, the harmonic vibration moment of the active magnetic bearing system is taken as the control object. This study investigates a hybrid control method that combines a second-order odd harmonic repetitive control with finite-dimensional repetitive control. And the virtual variable sampling is applied to construct any virtual sampling period in the proposed method, which effectively solves the problem of non-integer delay of digital repetitive control. The stability of the active magnetic bearing system is analyzed. The experimental results show that this method has faster response speed and better robustness when the frequency fluctuates.