Influence Of Torsional Vibrations Research Articles

Experimental Study on Ultrasonic-Assisted End Milling Forces in 2195 Aluminum-Lithium Alloy.

To achieve high-quality machining of the 2195 aluminum-lithium alloy, this paper presents an experimental study on the effect of milling processing parameters on milling forces and surface topography, during which conventional milling and longitudinal-torsional ultrasonic vibration milling of the 2195 Al-Li alloy were performed. The characterization of the tool tip trajectory illustrates some of the advantages of ultrasonic machining, which include variable depth of cut and tool chip pulling. The differences in milling forces between conventional milling and longitudinal-torsional ultrasonic vibration machining were compared using orthogonal tests, and the effect of ultrasonic vibration on milling forces was investigated in detail. The maximum reduction of milling force Fy in the feed direction under the influence of torsional vibration is 62% and 54% for larger feed per tooth and cutting depth, respectively. The high-frequency impact generated by the longitudinal vibration not only reduces the chip accumulation on the surface, but also smooths out the tool-tooth scratches and creates a regular surface profile. In addition, the characteristics of the milling force signals of the two machining methods were analyzed, and the analysis of the spectrum of the collected milling forces revealed that the ultrasonic vibration caused the high-frequency components of the milling forces Fy and Fz. The orthogonal result analysis and single-factor result analysis verified the superiority of ultrasonic machining, provided parameter selection for subsequent aluminum-lithium alloy machining, and bridged the gap of longitudinal torsional ultrasonic vibration machining of 2195 aluminum-lithium alloy in the study of milling force.

Analysis of the influence of gear tooth friction on dynamic force in a spur gear

The main objective of this paper is to investigate the influence of tooth friction on the dynamic force of the gearbox. This is one of the most insignificantly investigated aspects of the gearbox work, despite both experimental and theoretical research conducted. For this reason, it is not entirely possible to establish the friction force determining the friction coefficient due to the complexity of the process. Currently, various approaches are taken in calculating dynamic models, among others excluding friction, Coulomb models, models in which the value of the friction coefficient depends on the sliding velocity, and the application of complex elastohydrodynamic models. Due to such different approaches, it was decided to examine the influence of tooth friction on the dynamic force for the stationary work conditions of the gearbox. Moreover, a new gear tooth friction model was developed, based on the Coulomb model of friction and rolling friction. The results were obtained for four friction models and, in the fifth case, without including it. Furthermore, the influence of torsional vibration on the friction lever arm was analysed.

Effectiveness of the segment method in absolute and joint coordinates when modelling risers

This paper presents two formulations of the segment method: one with absolute coordinates and the second with joint coordinates. The nonlinear equations of motion of slender links are derived from the Lagrange equations by means of the methods used in multibody systems. Values of forces and moments acting in the connections between the segments are defined using a new and unique procedure which enables the mutual interaction of bending and torsion to be considered. The models take into account the influence of the velocity of the internal fluid flow on the riser’s dynamics. The dynamic analysis of a riser with fluid flow requires calculation of the curvature by approximation of the Euler angles with polynomials of the second order. The influence of the sea environment, such as added mass of water, drag and buoyancy forces as well as sea current, is considered. In addition, the influence of torsion is discussed. Validation is carried out for both models by comparing the authors’ own results with those obtained from experimental measurements presented in the literature and from COMSOL, Riflex and Abaqus software. The validation is concerned with vibrations of cables and the riser with internal fluid flow as well as with frequencies of free and forced vibrations of a riser fully or partially submerged in water. The numerical effectiveness of both formulations is examined for dynamic analysis of the riser, whose top end is moving in a horizontal plane. Conclusions concerned with the effectiveness of both formulations of the segment method and the influence of torsional vibrations on numerical results are formulated.

A Portable Digital Torsional Vibration Analysis System and its Signal Processing

Shaft torsional vibration is critical to rotating machinery as internal combustion engines because it may cause disasters if we ignore its significance. This paper introduced a portable digital system we developed to derive torsional vibration signal by a Hall Effect transducer. By analyzing the signal in frequency domain, we furthered the study on the influence of torsional vibration in each order under various rotation rates to determine the torsional resonant frequency. Moreover, a comparison between several signal processing methods in frequency domain was investigated and an optimum method for the spectrum correction obtained subsequently. Experiments conducted by this portable digital system showed its good performance in shaft torsional vibration measurements, analysis and trouble diagnosis.

Influence of Torsional Vibrations on the Photoluminescence Characteristics of Dye Solutions

The influence of torsional vibrations of fluorophore molecule on polarization spectra and absorption/emission vibronic band profiles of isotropic dye solutions has been considered. Basing on the concept of luminescence center (LC) and assuming that (1) electronic transitions in the LC may be assisted by torsion-vibrational excitations, and (2) reorientations of the LC can be described in terms of Stokes–Einstein rotational diffusion, the formula for time-dependent emission anisotropy, \(r(\tilde \nu _{\text{a}} ,\tilde \nu _{\text{f}} {\text{ }}t)\) as a function of excitation, \(\tilde \nu _{\text{a}}\), and observation, \(\tilde \nu _{\text{f}}\) frequencies has been obtained. It comprises depolarization by combined reorientations of the fluorophore molecule, i.e., its torsional vibrations with respect to the LC, and rotational diffusion of the LC. This approach is a generalization of the appropriate results obtained earlier by Ehrenberg and Rigler and, independently, by Chuang and Isenthal. The considered model has specific property that the torsional vibrations appear both as depolarizing factor for \(r(\tilde \nu _{\text{a}} ,\tilde \nu _{\text{f}} {\text{ }}t)\) and as shaping factor for absorption/emission bands, resulting in the variation of the emission anisotropy across appropriate band profiles. This is demonstrated graphically using numerical results obtained for a simplified, one-dimensional torsional oscillator. It is also shown that observed absorption and emission spectra of coumarin solutions can be reproduced using this model with appropriate potentials for restoring forces.

Investigation of oscillatory problems of hydraulic generating units equipped with Francis turbines

In the paper a method is presented for the study of oscillatory problems of hydraulic generating units equipped with Francis turbines. The accurate equations of the turbine are implemented for the simulation, taking into account water hammer effect. Partial derivatives of turbine flow rate and torque with respect to head and gate opening are deduced from real measurements for the whole leading range. Speed governor dynamics are fully simulated, and the influence of torsional vibrations is studied. The vibration response of the unit to draft tube surges is investigated and the risk of excessive oscillations is evaluated. The approach was developed for diagnosis of excessive vibrations of Kastraki hydro power station in Greece.

Influence of Torsional Vibrations on Lateral Oscillations of Induction Motor Rotors

Influence of Torsional Vibrations on Lateral Oscillations of Induction Motor Rotors

The influence of torsional vibrations on the molecular configuration determined by gas electron diffraction

As a consequence of intramolecular vibrations distorted apparent structures may result from an electron diffraction analysis of molecules possessing symmetrical equilibrium configuration. The amount of torsional distortion gives information concerning the barrier height to internal rotation. An approach is suggested to estimate barrier heights on the basis of average torsional angles as determined from electron diffraction, and expressions of the rotation-dependent distances as obtained from a Taylor expansion by neglecting higher order terms.

Influence of torsional vibrations and deferred rotations of molecules on the nuclear quadrupole resonance frequency in molecular crystals

Influence of torsional vibrations and deferred rotations of molecules on the nuclear quadrupole resonance frequency in molecular crystals