A Longitudinal-Bending Hybrid Linear Ultrasonic Motor and Its Driving Characteristic

As a new type of driver, linear ultrasonic motor (LUSM) is widely used in the high-tech field because of its low speed, high thrust, low noise, and no electromagnetic interference. However, as an actuator used in microdevices, most of the existing LUSMs are large in size and not compact in structure. In order to overcome these limitations, a new structure of linear ultrasonic motor’s stator is developed in this paper. The stator is similar to a tuning fork structure, which is divided into three parts: two driving feet, two driving legs, and the driving body. By using the first-order longitudinal vibration mode of the whole stator and the unique partial second-order bending vibration mode of the driving legs to achieve vibration mode degeneracy, a mode hybrid linear ultrasonic motor that is easy to miniaturize is proposed. Its working principle is analyzed. The dynamic analysis of the stator is carried out by using finite element software. The structure dimension of the stator and the driving frequency under the working mode are determined. At the same time, the feasibility of driving feet synthesizing elliptical motion is verified theoretically and experimentally. In addition, the LUSM test setup is built. The effects of driving frequency and Vpp on stator stall force and average velocity are studied. The results show that the maximum stall force can reach 99 mN, and the average velocity of the motor is 88.67 mm/s with Vpp = 320 V and driving frequency 80.2 kHz. The proposed LUSM is appropriate for use in occasions with quick return characteristics, like the controlling valve or nozzle of the printer. The research results provide guidance for the stator design of the linear ultrasonic motor.

A baseline-free method for damage identification in pipes from local vibration mode pair frequencies

As structural systems approach their end of service life, integrity assessment and condition monitoring during late life becomes necessary in order to identify damage due to age-related issues such as corrosion and fatigue and hence prevent failure. In this paper, a novel method of level 3 damage identification (i.e. detection, localisation and quantification) from local vibration mode pair (LVMP) frequencies is introduced. Detection is achieved by observation of LVMP frequencies within any of the vibration modes investigated while the location of the damage is predicted based on the ranking order of the LVMP frequency ratios and the damage is quantified in terms of material volume loss from pre-established quantification relations. The proposed method which is baseline-free (in the sense that it does not require vibration-based assessment or modal data from the undamaged state of the pipe) and solely frequency-dependent was found to be more than 90% accurate in detecting, locating and quantifying damage through a numerical verification study. It was also successfully assessed using experimental modal data obtained from laboratory tests performed on an aluminium pipe with artificially inflicted corrosion-like damage underscoring a novel concept in vibration-based damage identification for pipes.

Coriolis Force Sliding Mode Control Method for the Rotary Motion of the Central Rigid Body-Flexible Cantilever Beam System in TBM

Beam slab structure is often encountered in a complex tunnel boring machine. Beam slab structure is subject to dynamic load, which is easy to cause fatigue damage and affect its service life. Therefore, it is necessary to control the vibration of this kind of beam slab structure. In this study, the central rigid body-flexible beam model is established for the rotating beam and plate rotating around the y-axis. Based on the Hamilton variational principle, the dynamic equation of the central rigid body-flexible beam system is established, and the dynamic model of the central rigid body-flexible beam system considering the influence of Coriolis force and centrifugal force is given. The vibration control of the central rigid body-flexible beam system is studied. The vibration mode of the rotating Euler Bernoulli beam is determined by using the elastic wave and vibration mode theory. The influence of the rotating motion on the beam vibration is analyzed, and the variable structure control law is designed to suppress the beam vibration. Numerical simulation results show that the control method can effectively suppress the first-order and second-order vibration of the beam and verify the effectiveness of the control strategy.

Unexpected soil amplification effect on seismic performance of highway bridges during the Aegean earthquake of October 2020, Mw 6.6

On October 30, 2020, an earthquake about 70 km away from the city center of Izmir with a 4.3 million population has shaken the city tremendously and has resulted in destruction of many building type of structures due to an unexpected high soil-amplified vibrations very similar to the Mexico City earthquake in 1985. The bridges at the soil-amplified sites has performed in elastic range with no damage at all. In the city of Izmir, the 42 year old twin bridges located on the main transportation route, were tremendously shaken by the earthquake had observed to have no seismic induced damage. Surprisingly twin bridges suffering from the alkali silica reaction (ASR) over the years did not even pound to each other despite the small size of longitudinal gap between them. As it has been known, the past performance of Turkish designed bridges are typically succesfull with almost no damage as observed in the Van 2011 and Sivrice 2020 earthquake mainly due to allowing movements at their joints and to flexible type of framing. The focus of the paper is given to understand the successful performance of bridges and to investigate the non-pounded twin bridges of the Izmir city. In this scope, a bridge inspection has been performed and the twin bridges have been analyzed for the recorded ground motion. The results have indicated that the structures have been subjected to 0.3 g at their vibration modes and the twin bridges have a synchronized motion due to having the identical vibration mode shape with a period of 1.5 seconds

Nanoobject mass measurement using the node displacement of the second mode of the nanomechanical resonator

This work suggests a new approach to weighting the nanoscale objects placed at the tip of cantilever vibrating inside the camera of scanning electron microscope. In contrast to traditional approach to mass determination, we suggest tracing the shift of the node of the second vibration mode as an alternative to frequency shift measurement. We demonstrate the applicability of our approach to carbon nanowhisker cantilevers grown on tungsten needles by focused electron beam induced deposition. We compare experimentally the performance of the suggested approach with the traditional frequency shift-based method.

An effect of extra compactified dimensions of space in the molecule $$\hbox {NO}_{{2}}$$

The theory of large extra compactified dimensions of space (ADD-model) predicts that gravity may become strong in a compactification space of the size of a molecule and may affect the vibrational motion of a molecule. In triatomic molecules like $$\hbox {NO}_{{2}}$$ NO 2 nuclear dynamics is strongly coupled to electronic dynamics at the intersection of electronic states (conical intersection). We discuss experimental results on $$\hbox {NO}_{{2}}$$ NO 2 which reveal that the collision-free molecule optically excited into a symmetric stretch vibration mode of an electronic state with conical intersection undergoes an irreversible non-radiative transition into an asymmetric stretch vibration mode in combination with a change of the electronic state. We suggest ascribing this irreversible non-radiative transition to a gravitational perturbation on the vibrational motion in $$\hbox {NO}_{{2}}$$ NO 2 . This gravitational perturbation deactivates the upper state of the optical transition. The width of the absorption line is given by the characteristic time of the gravitational perturbation and not by the radiative lifetime of the excited molecular state. Graphical abstract