Parametric excitation of corkscrew instability of a ?-pinch by a high-frequency longitudinal current

1972 ◽  
Vol 11 (2) ◽  
pp. 216-221
Author(s):  
M. G. Nikulin
Keyword(s):  
Parametric Excitation ◽  
High Frequency ◽  
Longitudinal Current

Synchronization of Self-Oscillations by Parametric Excitation

1998 ◽  
Vol 08 (07) ◽  
pp. 1605-1612 ◽  
Author(s):  
V. Astakhov ◽  
A. Shabunin ◽  
V. Anishchenko
Keyword(s):  
Parametric Excitation ◽  
High Frequency ◽  
Chaos Control ◽  
The Self ◽  
Control Technique ◽  
Periodic Modulation ◽  
Threshold Values

This paper is devoted to the problem of synchronization of symmetrically coupled self-oscillators exhibiting chaos by means of chaos control technique. We use a nonfeedback method of control, in particular, high frequency periodic modulation of the coefficient of coupling. The model of Chua's circuits coupled via capacity is considered in this work. We study the possibility of synchronization in dependence on amplitude and frequency of modulation for various values of the parameters of the self-oscillators. The dependence of the threshold values of the amplitude of the synchronizing influence on coefficient is presented.

scholarly journals Parametric excitation of high‐frequency electromagnetic waves by the lower‐frequency dipole pumping

1993 ◽  
Vol 5 (1) ◽  
pp. 92-103 ◽  
Author(s):  
K. V. Gamayunov ◽  
G. V. Khazanov ◽  
E. N. Krivorutsky ◽  
A. A. Veryaev
Keyword(s):  
Parametric Excitation ◽  
High Frequency ◽  
Electromagnetic Waves

Energy transfer through parametric excitation to reduce self-excited drill string vibrations

2021 ◽  
pp. 107754632110310
Author(s):  
Vincent Kulke ◽  
Georg-Peter Ostermeyer
Keyword(s):  
Energy Transfer ◽  
Parametric Excitation ◽  
High Frequency ◽  
Drill String ◽  
Alternative Methods ◽  
Installation Space ◽  
Energy Output ◽  
Torsional Oscillations ◽  
Bottom Hole ◽  
Bottom Hole Assembly

Drilling a wellbore can result in several types of vibration that lead to inefficient drilling and premature failure of drill string components. These vibrations are subdivided based on their operating direction into lateral, torsional, and axial vibrations. Especially in hard and dense formations, high-frequency torsional oscillations are found in the bottom-hole assembly (BHA). These critical vibrations are induced by a self-excitation mechanism caused by the bit–rock interaction. Self-excitation mechanisms are regenerative effects, mode coupling, or a velocity-dependent torque characteristic at the drill bit. To increase drilling performance and reduce tool failure due to high-frequency torsional oscillations, the critical vibration amplitudes localized at the bottom-hole assembly need to be minimized. Increasing the damping of self-excited systems to affect the energy output during vibration is a common approach to mitigate self-excited vibrations. In drilling systems, the achievable damping is naturally limited by the small installation space due to the drilled borehole diameter. Therefore, alternative methods to influence vibrations are necessary. Applying parametric excitation in self-excited systems can result in a parametric anti-resonance and therefore in an energy transfer within different modes of the structure. This allows, among other benefits, improved utilization of the structural damping. In this article, the influence of additional stiffness–based parametric excitation on self-excited torsional vibration in downhole drilling systems is investigated. For this purpose, a finite element model of a drill string is reduced using the component mode synthesis and analyzed with the goal to mitigate torsional vibrations. The multiple degree of freedom drill string model is investigated regarding the additional energy transfer due to the parametric excitation. Robustness of various parameters, especially with regard to the positioning within the bottom-hole assembly, is analyzed and discussed. Additionally, the problem of multiple unstable self-excited modes due to the nonlinear velocity-dependent torque characteristic in drilling systems is addressed.

Wave Manipulation of Two-Dimensional Periodic Lattice by Parametric Excitation

2019 ◽  
Vol 87 (1) ◽  
Author(s):  
Xiao-Dong Yang ◽  
Qing-Dian Cui ◽  
Wei Zhang
Keyword(s):  
Parametric Excitation ◽  
Elastic Waves ◽  
High Frequency ◽  
Low Frequency ◽  
Waveguide Structure ◽  
Phononic Crystals ◽  
Periodic Lattice ◽  
Two Dimensional ◽  
Time Dynamic ◽  
Mechanical Waves

Abstract Phononic crystals composed of delicately designed periodic units are used to control spatial and spectral properties of acoustic or elastic waves. The ability to manipulate transmitting waves in a real-time dynamic manner provides a new concept in programable phononic crystals and metamaterials. In this study, the mechanical waves and bandgaps in a two-dimensional spring-mass array loaded by high-frequency parametric excitation have been investigated by both analytical and numerical methods. It is found that the high-frequency parametric excitation provides an equivalent additional stiffness which leads to low-frequency bandgaps. By tuning the parametric excitation, the versatility of such a dynamic modulating technique has been presented. The waveguide structure has also been designed and studied by non-uniformly distributed parametric excitations.

Sign in / Sign up

Export Citation Format

Share Document