Impact Dynamics in Four-Segment Tilting Pad Journal Bearings Subjected to Pad Fluttering

This paper presents a transient analysis of the motion of unloaded upper pads in a tilting pad journal bearing. It is known that such pads can exhibit self-excited vibration called pad fluttering, which can initiate fatigue damage due to elastic contacts between the fluttering pad and the journal. Unlike previous studies, this work attempts to evaluate forces in the contact. This evaluation is done using a robust nonlinear model, which considers hydrodynamic lubrication, out-of-balance forces and Hertzian contacts. Furthermore, qualitative changes of the bearing’s components motions are analysed in a wide range of journal speeds using bifurcation diagrams, phase portraits and estimates of the largest Lyapunov coefficients. The analysis reveals the intriguing nature of the system, which bifurcates between the periodic motion, period-doubling and chaos.

Line scan-based rapid magnetic resonance imaging of repetitive motion

Two-dimensional (2D) line scan-based dynamic magnetic resonance imaging (MRI) is examined as a means to capture the interior of objects under repetitive motion with high spatiotemporal resolutions. The method was demonstrated in a 9.4-T animal MRI scanner where line-by-line segmented k-space acquisition enabled recording movements of an agarose phantom and quail eggs in different conditions—raw and cooked. A custom MR-compatible actuator which utilized the Lorentz force on its wire loops in the scanner’s main magnetic field effectively induced the required periodic movements of the objects inside the magnet. The line-by-line k-space segmentation was achieved by acquiring a single k-space line for every frame in a motion period before acquisition of another line with a different phase-encode gradient in the succeeding motion period. The reconstructed time-course images accurately represented the objects’ displacements with temporal resolutions up to 5.5 ms. The proposed method can drastically increase the temporal resolution of MRI for imaging rapid periodic motion of objects while preserving adequate spatial resolution for internal details when their movements are driven by a reliable motion-inducing mechanism.

First apsidal motion and light curve analysis of 162 eccentric eclipsing binaries from LMC

We present an extensive study of 162 early-type binary systems located in the LMC galaxy that show apsidal motion and have never been studied before. For the ample systems, we performed light curve and apsidal motion modelling for the first time. These systems have a median orbital period of 2.2 days and typical periods of the apsidal motion were derived to be of the order of decades. We identified two record-breaking systems. The first, OGLE LMC-ECL-22613, shows the shortest known apsidal motion period among systems with main sequence components (6.6 years); it contains a third component with an orbital period of 23 years. The second, OGLE LMC-ECL-17226, is an eccentric system with the shortest known orbital period (0.9879 days) and with quite fast apsidal motion period (11 years). Among the studied systems, 36 new triple-star candidates were identified based on the additional period variations. This represents more than 20% of all studied systems, which is in agreement with the statistics of multiples in our Galaxy. However, the fraction should only be considered as a lower limit of these early-type stars in the LMC because of our method of detection, data coverage, and limited precision of individual times of eclipses.

Nonlinear Dynamic Analysis of Rotor Rub-Impact System

A dynamic model of a double-disk rub-impact rotor-bearing system with rubbing fault is established. The dynamic differential equation of the system is solved by combining the numerical integration method with MATLAB. And the influence of rotor speed, disc eccentricity, and stator stiffness on the response of the rotor-bearing system is analyzed. In the rotor system, the time history diagram, the axis locus diagram, the phase diagram, and the Poincaré section diagram in different rotational speeds are drawn. The characteristics of the periodic motion, quasiperiodic motion, and chaotic motion of the system in a given speed range are described in detail. The ways of the system entering and leaving chaos are revealed. The transformation and evolution process of the periodic motion, quasiperiodic motion, and chaotic motion are also analyzed. It shows that the rotor system enters chaos by the way of the period-doubling bifurcation. With the increase of the eccentricity, the quasi-periodicity evolution is chaotic. The quasiperiodic motion evolves into the periodic three motion phenomenon. And the increase of the stator stiffness will reduce the chaotic motion period.

Nonlinear Dynamic Characteristics of Marine Rotor-Bearing System under Heaving Motion

In this paper, the influence of the heaving motion on the nonlinear dynamic behavior of the rotor-bearing system is considered. First, a mathematic model of the marine rotor-bearing system is developed on the short bearing theory in the noninertial reference system, in which the heaving motion is taken into account. Then its dynamic characteristics are analyzed based on the numerical integration method, such as the bifurcation diagram, the largest Lyapunov exponents (LLE), the steady-state response, and the rotor orbit and its Poincaré map. The results indicate that heaving motion has a great effect on the dynamics of the rotor system, which exhibits a period 1 motion at low rotating speed, with the increase of the rotating speed, the phenomena of the quasiperiodic, period 2, and double Hopf bifurcations appear. Its dynamic performance presents a period 1 motion, period 2, quasiperiodic, and chaotic oscillation.

A Robotic Diathermy System for Automated Capsulotomy

Background: Cataracts are the leading cause of blindness and are treated surgically. Capsulotomy describes the opening of the lens capsule during this surgery and is most commonly performed by manual tearing, thermal cutting, or laser ablation. This work focuses on the development of a flexible instrument for high precision capsulotomy, whose motion is controlled by a hybrid mechanical-magnetic actuation system. Methods: A flexible instrument with a magnetic tip was directed along a circular path with a hybrid mechanical-magnetic actuation system. The system’s motion control and thermal cutting behavior were tested on ex vivo porcine lenses. Results: Position control of the magnetic tip on a circular path with radius of 2.9[Formula: see text]mm resulted in a relative positioning error of 3% at a motion period of 60[Formula: see text]s. The instrument’s accuracy improves with decreasing speed. A fully automated capsulotomy is achieved on an ex vivo porcine lens capsule by continuously coagulating the tissue under controlled conditions. Conclusions: Robot assisted capsulotomy can be performed with excellent precision in ex vivo conditions.

Driver Seat Differential Pneumatic System with Air Damping

The paper shows a possibility of the tuning mechanical system by means of two pneumatic springs in a differential configuration connected with a throttle valve. The springs are inserted into the lead mechanism and connected to its parts, and to its supporting platform. The vibrations, transferred from the kinematic excitation of the base, are intended to be minimized. The vibration isolation by means of pneumatic springs is available in many technical systems, e.g. in supports of heavy machinery as well as in systems characterized by the human interaction, such as driver seats, ambulance couchettes, etc. The pneumatic springs provide the option of adaption of the stiffness, and herewith the adaption of the natural frequency of the system according to the exciting frequency. In cases of application of the object vibration isolation, they can change the load characteristics in a relative large range. In the studied case of the differential spring configuration, the springs are connected with an air pipe to the throttle valve. The air being exchanged during the motion period comes through the valve, the cross-section of which determines the time delay of the pneumatic sub-system thus creating a hysteresis of load characteristic of the spring support. This brings an additional, controllable damping to such a system that is profitable in most vibration isolation cases.