Theoretical Stability Analysis of Self-Excited Vibration in a Thin Film Wrapped Around an Air-Turn Bar

2010 ◽  
Author(s):  
Masahiro Watanabe ◽  
Kensuke Hara
Keyword(s):  
Stability Analysis ◽  
Theoretical Model ◽  
Flow Instability ◽  
Equations Of Motion ◽  
Air Flow ◽  
Low Frequency ◽  
The Self ◽  
Excited Vibration ◽  
Basic Equations ◽  
Low Frequency Mode

This paper deals with a theoretical stability analysis of a self-excited vibration generated in a film wrapped around an air-turn bar. In this paper, firstly, vibration characteristics of the self-excited vibration are examined experimentally, and it is shown that two different types of self-excited vibration, which are low-frequency and high-frequency modes, occur in the film. Secondly, stability of the low-frequency mode is examined theoretically. A theoretical model of the film wrapped around the air-turn bar is developed. Basic equations of the air flow in the gap between the film and air-turn bar, and pressurized air flow inside the air-turn bar are derived. The characteristics equation of the system is derived from the basic equations of motion of the film coupled with the air flow. Instability condition in which the self-excited vibration occurs is shown as a function of air flow rate and tension applied to the film. Moreover, instability mechanism of the self-excited vibration is discussed based on the theoretical model.

scholarly journals Utilization of 2:1 Internal Resonance in Microsystems

Micromachines ◽  
2018 ◽  
Vol 9 (9) ◽  
pp. 448 ◽  
Author(s):  
Navid Noori ◽  
Atabak Sarrafan ◽  
Farid Golnaraghi ◽  
Behraad Bahreyni
Keyword(s):  
Internal Resonance ◽  
Mode Coupling ◽  
Equations Of Motion ◽  
Low Frequency ◽  
Nonlinear Behavior ◽  
Excitation Amplitude ◽  
Beam Structure ◽  
Nonlinear Mode Coupling ◽  
T Beam ◽  
Low Frequency Mode

In this paper, the nonlinear mode coupling at 2:1 internal resonance has been studied both analytically and experimentally. A modified micro T-beam structure is proposed, and the equations of motion are developed using Lagrange’s energy method. A two-variable expansion perturbation method is used to describe the nonlinear behavior of the system. It is shown that in a microresonator with 2:1 internal resonance, the low-frequency mode is autoparametrically excited after the excitation amplitude reaches a certain threshold. The effect of damping on the performance of the system is also investigated.

scholarly journals Self-sustained hydrodynamic oscillations in lifted jet diffusion flames: origin and control

2015 ◽  
Vol 775 ◽  
pp. 201-222 ◽  
Author(s):  
Ubaid Ali Qadri ◽  
Gary J. Chandler ◽  
Matthew P. Juniper
Keyword(s):  
Stability Analysis ◽  
High Frequency ◽  
Passive Control ◽  
Diffusion Flames ◽  
Low Frequency ◽  
Frequency Mode ◽  
High Frequency Mode ◽  
Jet Diffusion Flames ◽  
Local Stability Analysis ◽  
Low Frequency Mode

We use direct numerical simulation (DNS) of the Navier–Stokes equations in the low-Mach-number limit to investigate the hydrodynamic instability of a lifted jet diffusion flame. We obtain steady solutions for flames using a finite rate reaction chemistry, and perform a linear global stability analysis around these steady flames. We calculate the direct and adjoint global modes and use these to identify the regions of the flow that are responsible for causing oscillations in lifted jet diffusion flames, and to identify how passive control strategies might be used to control these oscillations. We also apply a local stability analysis to identify the instability mechanisms that are active. We find that two axisymmetric modes are responsible for the oscillations. The first is a high-frequency mode with wavemaker in the jet shear layer in the premixing zone. The second is a low-frequency mode with wavemaker in the outer part of the shear layer in the flame. We find that both of these modes are most sensitive to feedback involving perturbations to the density and axial momentum. Using the local stability analysis, we find that the high-frequency mode is caused by a resonant mode in the premixing region, and that the low-frequency mode is caused by a region of local absolute instability in the flame, not by the interaction between resonant modes, as proposed in Nichols et al. (Phys. Fluids, vol. 21, 2009, article 015110). Our linear analysis shows that passive control of the low-frequency mode may be feasible because regions up to three diameters away from the fuel jet are moderately sensitive to steady control forces.

Toward Developing a Conceptual Framework to explain Positive Thinking Based on Islamic View

2016 ◽  
Vol 2 ◽  
Author(s):  
Mohammad Kodayarifard ◽  
Bagher GhobariBonab ◽  
Saeed Akbari ZardKhaneh ◽  
Enayatollah Zamanpour ◽  
Saeid Zandi ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Cultural Values ◽  
Attachment Theory ◽  
Relational Theory ◽  
The Self ◽  
Automatic Thoughts ◽  
Thinking Styles ◽  
Positive Thinking ◽  
Future Expectations ◽  
Islamic View

The aim of the present study was to critically review theories and approaches related to positive thinking and to develop a theoretical model based on Islamic view, which is compatible with cultural values in Iran. To fulfill the stated aim, philosophical and historical foundations of positive thinking in different schools of thought including Leibnitz, Sadra, Kant, Freud and James were critically reviewed. In addition, the theoretical constructs associated with positive thinking including hope, positive automatic thoughts and paradigms of Seligman, Scheier and Carver in this regard were critically studied. Finally, based on the attachment theory of Bowlby, positive thinking was established on and its applications were explained for individuals' thinking styles about past events, present interpretations of events and future expectations. Since the attachment theory is a relational theory, positive thinking in this paradigm was discussed in a way that included individuals' relationship with transcendental being, others, nature, and the self.

scholarly journals Uncertainty Avoidance as a Moderating Factor to the Self-Congruity Concept: The Development of a Conceptual Framework

SAGE Open ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 215824402110018
Author(s):  
Shaohua Yang ◽  
Salmi Mohd Isa ◽  
T. Ramayah
Keyword(s):  
Theoretical Model ◽  
Conceptual Framework ◽  
Significant Contribution ◽  
Integrated Model ◽  
Uncertainty Avoidance ◽  
The Self ◽  
Destination Marketing ◽  
Tourism Research ◽  
Revisit Intention ◽  
Conceptual Paper

The aim of this article was to propose a framework based on the theory of self-congruity and on Hofstede’s uncertainty avoidance. The framework was to combine destination personality, self-congruity, uncertainty avoidance, and tourists’ revisit intention. The present conceptual paper proposed an integrated model of self-congruity which incorporates the effect of uncertainty avoidance. More importantly, the uncertainty avoidance was introduced as a moderator between self-congruity and revisit intention. Based on the theoretical framework proposed in this article, the estimated results affirmed the applicability of the theory of self-congruity for tourism research. Moreover, by extending the theoretical model through the incorporation of a variable of uncertainty avoidance in the context of tourism, this article offers a significant contribution to the tourism literature. It is important to understand how the theory of self-congruity applies across a broad cultural spectrum. This article also offers several implications for destination marketing organizations from a practical perspective.

Analytical Solution for Rotational Rub-Impact Plate Under Thermal Shock

2016 ◽  
Vol 32 (3) ◽  
pp. 297-311
Author(s):  
T.-Y. Zhao ◽  
H.-Q. Yuan ◽  
B.-B. Li ◽  
Z.-J. Li ◽  
L.-M. Liu
Keyword(s):  
Thermal Shock ◽  
High Frequency ◽  
Equations Of Motion ◽  
Low Frequency ◽  
Cantilever Plate ◽  
Analysis Method ◽  
Multiple Frequency ◽  
Width Direction ◽  
Blade Tip ◽  
High Frequency Vibrations

AbstractThe analysis method is developed to obtain dynamic characteristics of the rotating cantilever plate with thermal shock and tip-rub. Based on the variational principle, equations of motion are derived considering the differences between rubbing forces in the width direction of the plate. The transverse deformation is decomposed into quasi-static deformation of the cantilever plate with thermal shock and dynamic deformation of the rubbing plate under thermal shock. Then deformations are obtained through the calculation of modal characteristics of rotating cantilever plate and temperature distribution function. Special attention is paid to the influence of tip-rub and thermal shock on the plate. The results show that tip-rub has the characteristics of multiple frequency vibrations, and high frequency vibrations are significant. On the contrary, thermal shock shows the low frequency vibrations. The thermal shock makes the rubbing plate gradually change into low frequency vibrations. Because rub-induced vibrations are more complicated than those caused by thermal shock, tip-rub is easier to result in the destruction of the blade. The increasing friction coefficient intensifies vibrations of the rubbing plate. Minimizing friction coefficients can be an effective way to reduce rub-induced damage through reducing the surface roughness between the blade tip and the inner surface of the casing.

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