Band Gap Characteristics of Nonrotating Passive Periodic Drill String

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Yaser Alsaffar ◽  
Sadok Sassi ◽  
Amr Baz
Keyword(s):  
Dynamical Behavior ◽  
Element Model ◽  
Drill String ◽  
Design Tool ◽  
Complex Nature ◽  
Frequency Bands ◽  
New Class ◽  
Modes Of Vibration ◽  
Specific Frequency ◽  
Scalable Design

A new class of drill strings is investigated whereby strategically designed and placed periodic inserts are utilized to filter out the vibration transmission along the drill strings. Such mechanical filtering capabilities allow the vibrations to propagate along the periodic drill string only within specific frequency bands called the “pass bands” and completely block it within other frequency bands called the “stop bands.” The design and the location of the inserts are selected to confine the dominant modes of vibration of the drill string within the stop bands generated by the periodic arrangement of the inserts in order to completely block the propagation of the vibrations. A finite element model (FEM) that simulates the operation of this new class of drill strings is developed to describe the complex nature of the vibration encountered during drilling operations. Experimental prototype of the passive periodic drill string was built and tested to demonstrate the feasibility and effectiveness of the concept of periodic drill string in mitigating undesirable vibrations. The experimental results are used to validate the developed theoretical model and to develop a scalable design tool that can be used to predict the dynamical behavior of this new class of drill strings.

scholarly journals Vibration of Periodic Drill-Strings with Local Sources of Resonance

Vibration ◽  
2021 ◽  
Vol 4 (3) ◽  
pp. 586-601
Author(s):  
Wael Akl ◽  
Hajid Alsupie ◽  
Sadok Sassi ◽  
Amr M. Baz
Keyword(s):  
Low Frequency ◽  
Element Model ◽  
Drill String ◽  
Design Parameters ◽  
Bending Vibrations ◽  
New Class ◽  
Simultaneous Control ◽  
Mechanical Filter ◽  
Modes Of Vibration ◽  
Proper Design

A new class of drill-strings is proposed for attenuating undesirable vibrations to ensure effective operation. The drill-string is provided with passive periodic inserts, which are integrated with sources of local resonance (LR). The inserts make the drill-string act as a low frequency pass mechanical filter for the transmission of vibration along the drill-string. Proper design of the periodic inserts with sources of LR tend to shift these stop bands towards zones of lower frequencies to enable confining the dominant modes of vibration of the drill-string within these bands. In this manner, propagation of the vibration along the drill-string can be completely blocked. A finite element model (FEM) is developed using ANSYS to investigate the bandgap characteristics of the proposed drill-string with sources of LR. The developed FEM accounts for bending, torsional, and axial vibrations of the drill-string in order to demonstrate the effectiveness of the periodic inserts with LR in simultaneous control of these combined modes as compared to conventional solid periodic inserts, which are only limited to controlling bending vibrations. The effect of the design parameters of the periodic inserts with LR on the bandgap characteristics of the drill-string is investigated to establish guidelines of this class of drill-strings.

Passive Periodic Engine Mount

2008 ◽  
Author(s):  
Ling Zheng ◽  
Woojin Jung ◽  
Zheng Gu ◽  
A. Baz
Keyword(s):  
Spectral Width ◽  
Shear Mode ◽  
Effective Width ◽  
Frequency Bands ◽  
Automotive Engine ◽  
New Class ◽  
Mechanical Filter ◽  
Transfer Matrix Approach ◽  
Specific Frequency ◽  
Engine Mount

The transmission of automotive engine vibrations to the chassis is isolated using a new class of mounts which rely in their operation on optimally designed and periodically distributed viscoelastic inserts. The proposed mount acts as mechanical filter for impeding the propagation of vibration within specific frequency bands called the ‘Stop Bands’. The spectral width of these bands is enhanced by making the viscoelastic inserts operate in a shear mode rather than compression mode. The theory governing the operation of this class of periodic mounts is presented using the theory of finite elements combined with the transfer matrix approach. The predictions of the performance of the mount are validated against the predictions of the commercial finite element code ANSYS and against experimental results obtained from prototypes of plain and periodic mounts. The obtained results demonstrate the feasibility of the shear mode periodic mount as an effectiveness means for blocking the transmission of vibration over a broad frequency band. Extending the effective width of the operating frequency bands of this class of mount through active control means is the ultimate goal of this study.

Active Vibration Control of Periodic Rotating Shafts

Aerospace ◽  
2004 ◽  
Author(s):  
M. Toso ◽  
A. Baz ◽  
D. Pines
Keyword(s):  
Transfer Matrix ◽  
Control Strategies ◽  
Spectral Characteristics ◽  
Active Vibration Control ◽  
Element Model ◽  
Rotating Shaft ◽  
Transverse Waves ◽  
Frequency Bands ◽  
Specific Frequency ◽  
Rotating Shafts

The propagation of transverse waves in periodic rotating shafts is controlled actively by using piezoelectric inserts which are placed periodically along these shafts. The control strategies aim at tuning the unique filtering characteristis of the periodic shafts in such manner that prevent the propagation of the waves within specific frequency bands called “stop bands.” The spectral characteristics of these “stop bands” are controlled in response to the shaft vibration. A finite element model is developed for this class of actively controlled periodic shafts which is then used to generate the “transfer matrix” for the unit cell of these shafts. The eigenvalues of the resulting transfer matrix are utilized to predict the characteristics of the stop and the pass bands of the rotating shaft as function of the shaft geometry, rotation speed, and control gains of the active inserts. The obtained characteristics are validated experimentally using shafts driven via gearbox assembly which subject the shafts to broadband excitations. The obtained results are also compared with the characteristics of passive shafts with stepped periodic geometries. Such a comparison aims at demonstrating the effectiveness of the active periodic shafts in redistributing the energy spectrum by confining the propagation to specific frequency bands. Particular emphasis is placed on studying the effect of the active control strategies on the vibration damping characteristics of the shafts. The proposed class of active periodic shafts can be useful in numerous critical applications such as the drive shafts of helicopters where transmitted vibrations can have detrimental effect on the performance of the tail rotor. Other applications are only limited by our imagination.

Periodic Struts for Gearbox Support System

2005 ◽  
Vol 11 (6) ◽  
pp. 709-721 ◽  
Author(s):  
S. Asiri ◽  
A. Baz ◽  
D. Pines
Keyword(s):  
Wave Propagation ◽  
Critical Frequency ◽  
Periodic Structures ◽  
Design Parameters ◽  
Force Transmission ◽  
Frequency Bands ◽  
New Class ◽  
Spatial Domains ◽  
Specific Frequency ◽  
Vibration And Sound Radiation

Passive periodic structures exhibit unique dynamic characteristics that make them act as mechanical filters for wave propagation. As a result, waves can propagate along the periodic structures only within specific frequency bands called “pass bands” and wave propagation is completely blocked within other frequency bands called “stop bands”. In this paper, the emphasis is placed on developing a new class of these periodic structures called passive periodic struts, which can be used to support gearbox systems on the airframes of helicopters. When designed properly, the passive periodic strut can stop the propagation of vibration from the gearbox to the airframe within critical frequency bands, consequently minimizing the effects of transmission of undesirable vibration and sound radiation to the helicopter cabin. The theory governing the operation of this class of passive periodic struts is introduced and their filtering characteristics are demonstrated experimentally as a function of their design parameters. The presented concept of the passive periodic strut can be easily used in many applications to control the wave propagation and the force transmission in both the spectral and spatial domains in an attempt to stop/confine the propagation of undesirable disturbances.

Numerical Study for Global Detection of Cracks Embedded in Beams

1999 ◽  
Author(s):  
S. A. Lipsey ◽  
Y. W. Kwon
Keyword(s):  
Finite Element ◽  
Dynamic Analysis ◽  
Natural Frequency ◽  
Mode Shape ◽  
Numerical Study ◽  
Element Model ◽  
Mode Shapes ◽  
Linear Effect ◽  
Modes Of Vibration ◽  
Damage Simulation

Abstract Damage reduces the flexural stiffness of a structure, thereby altering its dynamic response, specifically the natural frequency, damping values, and the mode shapes associated with each natural frequency. Considerable effort has been put into obtaining a correlation between the changes in these parameters and the location and amount of the damage in beam structures. Most numerical research employed elements with reduced beam dimensions or material properties such as modulus of elasticity to simulate damage in the beam. This approach to damage simulation neglects the non-linear effect that a crack has on the different modes of vibration and their corresponding natural frequencies. In this paper, finite element modeling techniques are utilized to directly represent an embedded crack. The results of the dynamic analysis are then compared to the results of the dynamic analysis of the reduced modulus finite element model. Different modal parameters including both mode shape displacement and mode shape curvature are investigated to determine the most sensitive indicator of damage and its location.

A Modular Mechanism for Downhole Weight-on-Bit and Torque Reaction in Small Diameter Boreholes

2021 ◽  
pp. 1-15
Author(s):  
Anirban Mazumdar ◽  
Stephen Buerger ◽  
Adam Foris ◽  
Jiann-cherng Su
Keyword(s):  
Axial Force ◽  
Small Diameter ◽  
Field Testing ◽  
Drill String ◽  
Force Transmission ◽  
Drilling Performance ◽  
Weight On Bit ◽  
In Series ◽  
Mechanical Devices ◽  
Scalable Design

Abstract Drilling systems that use downhole rotation must react torque either through the drill-string or near the motor to achieve effective drilling performance. Problems with drill-string loading such as buckling, friction, and twist become more severe as hole diameter decreases. Therefore, for small holes, reacting torque downhole without interfering with the application of weight-on-bit, is preferred. In this paper we present a novel mechanism that enables effective and controllable downhole weight on bit transmission and torque reaction. This scalable design achieves its unique performance through four key features: 1) mechanical advantage based on geometry, 2) direction dependent behavior using rolling and sliding contact, 3) modular scalability by combining modules in series, and 4) torque reaction and weight on bit that are proportional to applied axial force. As a result, simple mechanical devices can be used to react large torques while allowing controlled force to be transmitted to the drill bit. We outline our design, provide theoretical predictions of performance, and validate the results using full-scale testing. The experimental results include laboratory studies as well as limited field testing using a percussive hammer. These results demonstrate effective torque reaction, axial force transmission, favorable scaling with multiple modules, and predictable performance that is proportional to applied force.

Effect of Geometric Shape of Periodic Cavities in Attenuating Baseframe Vibration

2020 ◽  
Author(s):  
S. N. Das ◽  
Kachita Kohli ◽  
Ayush Kumar ◽  
G. R. Sabareesh
Keyword(s):  
Stop Band ◽  
Rotating Machinery ◽  
Vibration Level ◽  
Structural Vibrations ◽  
Frequency Bands ◽  
Natural Modes ◽  
Vibration Attenuation ◽  
Specific Frequency ◽  
Different Shapes ◽  
Air Cavities

Abstract Vibration attenuation is an important factor while designing rotating machinery since frequency lying in the range corresponding to natural modes of structures can result in resonance and ultimately failure. Damping dissipates energy in the system, which reduces the vibration level. The mitigation of vibrations can be achieved by designing the base frame with periodic air holes. The periodicity in air holes result in vibration attenuation by providing a stop band. A finite element-based approach is developed to predict the modal and frequency response. The analysis is carried out with different shapes of periodic cavities in order to study the effectiveness of periodic stop bands in attenuating vibrations. The amount of mass removed due to the periodic cavities is kept constant. It is seen that better attenuation is obtained in case of periodic cavities compared to a uniform base frame. Among the different geometries tested, rectangular cavities showed better results than circular and square cavities. As a result, it is seen that waves propagate along periodic cells only within specific frequency bands called the “Pass bands”, while these waves are completely blocked within other frequency bands called the “Stopbands”. The air cavities filter structural vibrations in certain frequency bands resulting in effective attenuation.

scholarly journals Modeling the Biomechanical Influence of Epilaryngeal Stricture on the Vocal Folds: A Low-Dimensional Model of Vocal–Ventricular Fold Coupling

2014 ◽  
Vol 57 (2) ◽  
Author(s):  
Scott R. Moisik ◽  
John H. Esling
Keyword(s):  
Dynamical Behavior ◽  
Model Performance ◽  
Vocal Folds ◽  
Element Model ◽  
Dynamical Response ◽  
Lumped Element ◽  
Glottal Stop ◽  
Lumped Element Model ◽  
Low Dimensional ◽  
Ventricular Folds

Purpose Physiological and phonetic studies suggest that, at moderate levels of epilaryngeal stricture, the ventricular folds impinge upon the vocal folds and influence their dynamical behavior, which is thought to be responsible for constricted laryngeal sounds. In this work, the authors examine this hypothesis through biomechanical modeling. Method The dynamical response of a low-dimensional, lumped-element model of the vocal folds under the influence of vocal–ventricular fold coupling was evaluated. The model was assessed for F0 and cover-mass phase difference. Case studies of simulations of different constricted phonation types and of glottal stop illustrate various additional aspects of model performance. Results Simulated vocal–ventricular fold coupling lowers F0 and perturbs the mucosal wave. It also appears to reinforce irregular patterns of oscillation, and it can enhance laryngeal closure in glottal stop production. Conclusion The effects of simulated vocal–ventricular fold coupling are consistent with sounds, such as creaky voice, harsh voice, and glottal stop, that have been observed to involve epilaryngeal stricture and apparent contact between the vocal folds and ventricular folds. This supports the view that vocal–ventricular fold coupling is important in the vibratory dynamics of such sounds and, furthermore, suggests that these sounds may intrinsically require epilaryngeal stricture.

Allee’s Effect Bifurcation in Generalized Logistic Maps

2019 ◽  
Vol 29 (03) ◽  
pp. 1950039
Author(s):  
J. Leonel Rocha ◽  
Abdel-Kaddous Taha
Keyword(s):  
Allee Effect ◽  
Dynamical Behavior ◽  
Complete Classification ◽  
Unimodal Maps ◽  
New Class ◽  
New Type ◽  
Local And Global Bifurcations ◽  
One Dimensional Maps ◽  
Necessary And Sufficient

This paper concerns the study of the Allee effect on the dynamical behavior of a new class of generalized logistic maps. The fundamentals of the dynamics of this 4-parameter family of one-dimensional maps are presented. A complete classification of the nature and stability of its fixed points is provided. The main results relate to the Allee effect bifurcation: a new type of bifurcation introduced for this class of unimodal maps. A necessary and sufficient condition so that the Allee fixed point is a snap-back repeller is established. In addition, in the parameters space is defined an Allee’s effect region, which determines the existence of an essential extinction for the generalized logistic maps. Local and global bifurcations of generalized logistic maps are investigated.

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