Rotation-induced axial oscillation of a composite nanoconvertor at low temperature

We propose a model of a nanostructure which can transform an input rotation into an output oscillation. In the model, the rotor has two identical internally hydrogenated deformable parts. The mechanism is that the rotation-induced centrifugal force and van der Waals force drive the recoverable deformation of the hydrogenated deformable parts, which gives rise to the axial translation of the free end of the rotor. Once the two hydrogenated deformable parts deform periodically, the free end of the rotor oscillates periodically in the axial direction. Molecular dynamics simulations are conducted to reveal the dynamic response of the system at low temperature. Four main types of deformation and the first three orders of vibration responses of the hydrogenated deformable parts are analyzed. Synchronous breathing vibration of the two hydrogenated deformable parts produces ideal oscillation with large amplitude. Asynchronous axial vibration of the hydrogenated deformable parts reduces the oscillation amplitude or produces beat vibration. The way to control the amplitude of the axial oscillation/vibration is given.

Ideal Oscillation of a Hydrogenated Deformable Rotor in a Gigahertz Rotation–Translation Nanoconverter at Low Temperatures

It was discovered that large-amplitude axial oscillation can occur on a rotor with an internally hydrogenated deformable part (HDP) in a rotation–translation nanoconverter. The dynamic outputs of the system were investigated using molecular dynamics simulations. When an input rotational frequency (100 GHz > ω > 20 GHz) was applied at one end of the rotor, the HDP deformed under the centrifugal and van der Waals forces, which simultaneously led to the axial translation of the other end of the rotor. Except at too high an input rotational frequency (e.g., >100 GHz), which led to eccentric rotation and even collapse of the system, the present system could generate a periodic axial oscillation with an amplitude above 0.5 nm at a temperature below 50 K. In other ranges of temperature and amplitude, the oscillation dampened quickly due to the drastic thermal vibrations of the atoms. Furthermore, the effects of the hydrogenation scheme and the length of HDP on the equilibrium position, amplitude, and frequency of oscillation were investigated. The conclusions can be applied to the design of an ideal nano-oscillator based on the present rotation–translation converter model.

Unsteady Vortex Breakdown Phenomena in an Enclosed Cylindrical Container With a Rotating Endwall Disk

A high-quality precision-controlled turntable apparatus was fabricated to probe the dynamic behavior of a viscous fluid contained in a cylindrical container. Vortex breakdown(s) produced by a rotating endwall disk was visualized by using a fluorescent dye injection technique, and its flow field was measured by using a particle image velocimetry. This flow is characterized by two non-dimensional parameters, i.e., the height-to-radius ratio H/R and the rotating Reynolds number Re = Ω2/v. Limiting boundaries for single, double and triple vortex breakdowns in steady flow were re-plotted to compare with the previous visualization studies of Escudier. The locations of stagnation points of the vortex breakdown bubble(s) in steady flow were measured quantitatively. The overall experimental results in the steady flow were in excellent agreement with Escudier’s data. In unsteady flow, the amplitude and time period of periodic axial oscillation, and the polar angle and time period of precession, were measured. The domains for periodic axial oscillation and for precession in unsteady flow were delineated.

Research on High Precision and Deterministic Figuring for Shaft Parts Based on Abrasive Belt Polishing

A deterministic figuring method for cylindrical surface based on abrasive belt polishing is proposed in this study in order to improve the geometric accuracy of metal shaft parts. The principal motion of material removal is performed through the axial oscillation of the abrasive belt, and the different material removal at different positions can be obtained through servo control of the machine tool spindle by removing high error spots on the cylindrical surface and finally deterministically corrects the roundness error. An abrasive belt-based deterministic figuring device was built, and the figuring experiments were performed on the surface of steel workpieces 100 mm in diameter and 130 mm in effective length. The roundness errors of the entire workpiece after twice figuring iterations decreased nearly from the initial 3 μm to 1 μm, which preliminary verified the feasibility of this method. This deterministic figuring method is expected to break the machining accuracy limit and improve the rotation precision of the precision shaft parts such as the aerostatic spindle.

Practical Approach to Functional Testing and Analytical Modeling of Axial Oscillation-Supported Drillstrings

Drillstrings that include one or more axial oscillation tools (AOTs) are referred to as axial oscillation-supported drillstrings. Downhole vibrations induced by these tools in the drillstring are the most efficient method for friction reduction and improving axial force transfer in high-angle and extended-reach wells. Functional testing of axial oscillation tools prior to downhole operations and modeling the dynamic response of axial oscillation-supported drillstring systems are required to predict the performance and functionality of AOTs. This study presents a practical approach for functional testing of axial oscillation tools and a new analytical model for predicting the dynamic response of axial oscillation-supported drillstrings operating at surface conditions. The axial oscillation-supported drillstring is modeled as an elastic continuous system subjected to viscous damping, frictional contact, and displacement (support excitation). The functional test is a unique experimental test procedure designed to measure the pressure drop, pressure fluctuations, and axial displacement of an axial oscillation tool while varying the flow rate and the spring rate of the tool. The introduction of the spring rate as a variable in the new model and functional testing is unique to this study and not considered in the existing literature. Axial displacement and acceleration predicted from the new model closely agrees with the results obtained from the functional tests. The accuracy of the model is also validated with the results of two previously published functional tests. The comparisons demonstrate an average deviation of approximately 14.5% between predictions and measurements. The axial displacement and pressure drop of AOT increased with flow rate or oscillation frequency. The amplitude of axial displacement increased with frequency because of increased pressure drop.