Investigation on the Nonlinear Vibration Characteristics of Current-Carrying Crescent Iced Conductors under Aerodynamic Forces, Ampere’s Forces, and Forced Excitation Conditions

Aiming at the problem of nonlinear vibration of current-carrying iced conductors, the aerodynamic forces are introduced into the previous vibration equation of current-carrying conductors that only considered Ampere’s forces. At the same time, on this basis, a forced excitation load is further introduced to study the influence of dynamic wind on the nonlinear vibration characteristics of current-carrying iced conductors, and a new current-carrying iced conductors system under the combined action of Ampere’s forces, forced excitation, and aerodynamic forces has been established, and the improved theoretical modeling of current-carrying iced transmission lines made the model more in line with practical engineering. Firstly, the model of current-carrying iced conductors was established, and then the vibration equation of the model was derived. And the vibration equation was transformed into a finite dimensional ordinary differential equation by using the Galerkin method. The amplitude-frequency response functions of the nonlinear forced primary resonances and super-harmonic and subharmonic resonances of the system are derived by using the multiscale method. Through numerical calculation, the influence of current-carrying, spacing, wind velocity, tension, and excitation amplitude on the response amplitude when the primary resonance of the system appears is analyzed, and the difference between the two working conditions (considering the aerodynamic forces and without considering aerodynamic forces) is compared. The influence of the variation of current-carrying i on the response amplitude of super-harmonic and subharmonic resonances and the stability of the steady-state solution of forced primary resonance was analyzed. The results show that the response amplitude and the nonlinearilty of system under the action of aerodynamic forces are smaller and weaker than without the action of aerodynamic forces; the variation of line parameters has a certain influence on the response amplitude of conductor and the nonlinearity of system; the response amplitudes of the primary resonance, super-harmonic resonance, and subharmonic resonance increase with the increase in the excitation amplitudes, and the resonance peak is offset towards the negative value of the tuning parameter σ, showing the characteristics of soft spring, and the response amplitudes are accompanied by complex nonlinear dynamic behaviors such as the multivalue and jump phenomenon. The change of current-carrying i has an obvious effect on the nonlinearity of the system. The nonlinear and response amplitudes of the system are also enhanced with the increase in wind velocity. The stability of the system is judged when the primary resonance occurs, and it is found that the response amplitude shows synchronization and the out-of-step phenomenon with the change of tuning parameters. The research results obtained in this paper would help to further improve the theoretical modeling about current-carrying iced lines, and the research of line parameters can give a certain reference value to practical engineering, and it will have a positive effect on the safe operation of high-voltage transmission lines.

Influence of the bolt size on the source of damping in automotive joints

Experimental tests are carried out on automotive bolted joints to study the influence of the bolt size on the source of damping during dynamic loading. Aluminium beams and five different bolt sizes are chosen and used to assemble single-lap joints under strictly controlled experiments. Measurements are taken to estimate the energy loss during forced excitation and to identify the source of damping in jointed structures, and an analogous monolithic solid beam is also used during the experimental investigation to isolate the joint effects and compare the data gathered. The dynamic response of the jointed structure exposed to forced excitation is captured under free-free boundary conditions. The motion of the assembled structure is identified by carrying out a finite element analysis.

Method for Excitation Control of Synchronous Motor in Start and Resynchronization Modes

In the article proposed a method for excitation control of synchronous motor in the starting, self-starting and resynchronization modes, which makes it possible to increase the stability or facilitate the pulling into synchronism of heavily loaded synchronous motors due to the alternating connection of the excitation winding to an additional active resistance or to an exciter with a forced excitation voltage. For this, on the basis of the instantaneous values measurements of the phase currents and stator voltages, the reactive and active powers are determined, and using a criterion equal to the power polynomial from the power ratio, the asynchronous mode is revealed. The control of switching the excitation winding to an additional resistance or to the exciter is car-ried out using another criterion, defined as a derivative of the asynchronous mode criterion. The results of mathematical modeling are presented, which confirm that the proposed method for controlling the excitation of a synchronous motor allows one to identify the asynchronous mode of both excited and non-excited synchronous motors and provide easier resynchronization conditions by increasing the torque of the synchronous motor at low slip values, as well as to ensure successful start and retraction in synchronism loaded synchronous motor.

Experimental Investigation for The Flow Induced Vibration for Pipe Inside Water

Forced vibration has been experimentally investigated on a model consists of circular pipe with1.6m length. The pipe built in tank (1.2m length, 0.6m height and 0.6m width) horizontally at 0.4m height with two different diameters d=15mm and d=35mm. The pipe conveying laminar flow in the fully developed region, of Reynolds number equals 2000. The experimental results of span pipe conveying water at five stations of forced excitation vibration were studied. The harmonic forced vibration with two different excitation frequencies (10 Hz and 15 Hz) are imposed at all of the five locations. The distance between two stations is (0.2m). Two conditions of pipe environment have been applied, the first in air and the other was immersed in water. It is concluded that the effect of flow induced vibration due to the pipe conveying fluid increases the maximum deflection when the fluid speed increases. The water surrounds the pipes reduce the effect of excitation vibration about (33 – 46%). The effect difference between the excitation frequencies was about (4 – 7%).