Suppressing Flutter Vibrations by Parametric Inertia Excitation

2009 ◽  
Vol 76 (3) ◽  
Author(s):  
Fadi Dohnal ◽  
Aleš Tondl
Keyword(s):  
Parametric Excitation ◽  
Theoretical Study ◽  
Open Loop ◽  
Elastic Instability ◽  
Excitation Mechanism ◽  
Combination Frequency ◽  
Concentrated Mass ◽  
Time Harmonic ◽  
Flow Induced Vibrations ◽  
First Time

A theoretical study of a slender engineering structure with lateral and angular deflections is investigated under the action of flow-induced vibrations. This aero-elastic instability excites and couples the system’s bending and torsion modes. Semiactive means due to open-loop parametric excitation are introduced to stabilize this self-excitation mechanism. The parametric excitation mechanism is modeled by time-harmonic variation in the concentrated mass and/or moment of inertia. The conditions for full suppression of the self-excited vibrations are determined analytically and compared with numerical results of an example system. For the first time, example systems are presented for which parametric antiresonance is established at the parametric combination frequency of the sum type.

Experimental Results on Parametric Excitation Damping of an Axially Loaded Cantilever Beam

2009 ◽  
Author(s):  
Horst Ecker ◽  
Thomas Pumho¨ssel
Keyword(s):  
Cantilever Beam ◽  
Parametric Excitation ◽  
Vibration Suppression ◽  
Excitation Frequency ◽  
Open Loop ◽  
Piezo Actuator ◽  
Combination Frequency ◽  
Bending Vibrations ◽  
Periodic Force ◽  
Parametrically Excited

In various fields of engineering, e.g. aerospace applications, robotics or the bladings of turbomachinery, slender beam-like structures are in use and subject to free bending vibrations. Since such vibrations often are not wanted because they may degrade the performance or function of the structure, it is important to have a suitable means of vibration suppression available. In this experimental study we investigate a slender cantilever beam loaded with a controlled force at its tip. The force is always oriented towards the clamping point of the beam and generated by a piezo-actuator. Force control is based on an open-loop control without feedback from the structure. To enhance vibration suppression we take advantage of the additional damping observed when a periodic force modulation at a certain frequency is applied. From several theoretical studies it is known that parametrically excited systems show increased stability, and therefore enhanced damping properties, when the parametric excitation frequency is chosen near a certain combination frequency. Due to the almost axially applied force the cantilever beam system becomes a parametrically excited system and the effect mentioned can be observed. Numerous measurement runs have been carried out and vibration suppression as a function of the excitation frequency, the excitation amplitude and the beam initial deflection has been investigated. The results are in very good agreement with theoretical predictions and for the first time the numerical and analytical results obtained earlier are confirmed by experimental work.

scholarly journals Theoretical study of the pyrolysis of β-1,4-xylan: a detailed investigation on unimolecular concerted reactions

2021 ◽  
Vol 23 (4) ◽  
pp. 2605-2621
Author(s):  
M. Goussougli ◽  
B. Sirjean ◽  
P.-A. Glaude ◽  
R. Fournet
Keyword(s):  
Thermal Decomposition ◽  
Theoretical Study ◽  
First Time

A theoretical study of the thermal decomposition of β-1,4-xylan, a model polymer of hemicelluloses, is proposed for the first time.

scholarly journals Asymptotic Behavior of a Viscoelastic Fluid in a Closed Loop Thermosyphon: Physical Derivation, Asymptotic Analysis, and Numerical Experiments

2013 ◽  
Vol 2013 ◽  
pp. 1-20 ◽  
Author(s):  
Justine Yasappan ◽  
Ángela Jiménez-Casas ◽  
Mario Castro
Keyword(s):  
Asymptotic Behavior ◽  
Viscoelastic Fluid ◽  
Closed Loop ◽  
Theoretical Study ◽  
Equations Of Motion ◽  
Asymptotic Properties ◽  
Inertial Manifold ◽  
Thermal Gradients ◽  
External Temperature ◽  
First Time

Fluids subject to thermal gradients produce complex behaviors that arise from the competition with gravitational effects. Although such sort of systems have been widely studied in the literature for simple (Newtonian) fluids, the behavior of viscoelastic fluids has not been explored thus far. We present a theoretical study of the dynamics of a Maxwell viscoelastic fluid in a closed-loop thermosyphon. This sort of fluid presents elastic-like behavior and memory effects. We study the asymptotic properties of the fluid inside the thermosyphon and the exact equations of motion in the inertial manifold that characterizes the asymptotic behavior. We derive, for the first time, the mathematical derivations of the motion of a viscoelastic fluid in the interior of a closed-loop thermosyphon under the effects of natural convection and a given external temperature gradient.

Theoretical study of the Cl(2P) + SiH4 reaction: Global potential energy surface and product pair-correlated distributions. Comparison with experiment.

2021 ◽  
Author(s):  
J. Espinosa-Garcia ◽  
Jose Carlos Corchado
Keyword(s):  
Potential Energy ◽  
Potential Energy Surface ◽  
Energy Surface ◽  
Theoretical Study ◽  
Title Reaction ◽  
Comparison With Experiment ◽  
Explicitly Correlated ◽  
High Level ◽  
First Time ◽  
Product Pair

For the theoretical study of the title reaction, an analytical full-dimensional potential energy surface named PES-2021 was developed for the first time, by fitting high-level explicitly-correlated ab initio data. This...

CHARACTERISTICS OF AGE-DEPENDENT CHANGES IN THE URINE'S PROTEOM COMPOSITION OF THE HEALTHY PERSONS (EXPERIMENTAL AND THEORETICAL STUDY)

2020 ◽  
pp. 735-740
Author(s):  
Л. Х. Пастушкова ◽  
Д. Н. Каширина ◽  
А. Г. Гончарова ◽  
Н. Б. Захарова ◽  
Е. С. Тийс ◽  
...  
Keyword(s):  
Signaling Pathway ◽  
Insulin Signaling ◽  
Defense Mechanisms ◽  
Theoretical Study ◽  
Clinical Manifestations ◽  
Age Dependent ◽  
First Time ◽  
Healthy Persons ◽  
Over Time

Впервые описаны белки, достоверно увеличивающиеся и уменьшающиеся в моче с возрастом в интервале 20-60 лет. Охарактеризованы комбинации белков, связанных с изменением иммунных процессов, нарушением реологии крови, в том числе риском коагулопатии, противоопухолевых защитных механизмов, инсулинового сигнального пути, с изменением характеристик клеточного деления и качества новообразованной ткани. Таким образом, возрастная динамика основных процессов запускает каскад реакций, проявляющихся в замыкании «патологических биохимических кругов», которые формируют предпосылки к развитию заболеваний и, с течением времени, клинические проявления. For the first time proteins are described, reliably increasing and decreasing in urine with age in the range of 20 to 60 years. The combinations of proteins associated with changes in immune processes, violation of blood reology, including the risk of coagulopathy, anticancer defense mechanisms, insulin signaling pathway, changes in cell characteristics are characterized division and quality of the newly formed fabric. Thus, the age dynamics of the main processes triggers a cascade of reactions manifested in the closure of «pathological biochemical circles» that form the prerequisites for the development of diseases and, over time, clinical manifestations.

Vibration suppression and energy transfer by parametric excitation in drive systems

2012 ◽  
Vol 226 (8) ◽  
pp. 2000-2014 ◽  
Author(s):  
Horst Ecker ◽  
Thomas Pumhössel
Keyword(s):  
Energy Transfer ◽  
Parametric Excitation ◽  
Vibration Suppression ◽  
Negative Impact ◽  
Energy Transfer Mechanism ◽  
Engineering Systems ◽  
Excitation Mechanism ◽  
Electrical Drive ◽  
Excitation Mechanisms ◽  
Drive Systems

Drive systems may experience torsional vibrations due to various kinds of excitation mechanisms. In many engineering systems, however, such vibrations may have a negative impact on the performance and must be avoided or reduced to an acceptable level by all means. Self-excited vibrations are especially unwanted, since they may grow rapidly and not only degrade the performance but even damage machinery. In this contribution it is suggested to employ parametric stiffness excitation to suppress self-excited vibrations. In the first part of the article we study the basic energy transfer mechanism that is initiated by parametric excitation, and some general conclusions are drawn. In the second part, a hypothetic drivetrain, consisting of an electrical motor, a drive shaft and working rolls is investigated. A self-excitation mechanism is assumed to destabilize the drive system. Parametric excitation is introduced via the speed control of the electrical drive, and the capability of stabilizing the system by this measure is investigated. It is shown that the damping available in the system can be used much more effectively if parametric stiffness excitation is employed.

An experimental and theoretical study of the kinetics of the reaction between 3-hydroxy-3-methyl-2-butanone and OH radicals

RSC Advances ◽  
2015 ◽  
Vol 5 (34) ◽  
pp. 26559-26568 ◽  
Author(s):  
Angappan Mano Priya ◽  
Gisèle El Dib ◽  
Lakshmipathi Senthilkumar ◽  
Chantal Sleiman ◽  
Alexandre Tomas ◽  
...  
Keyword(s):  
Rate Constants ◽  
Theoretical Study ◽  
Oh Radicals ◽  
First Time ◽  
Kinetics Of

Absolute experimental and theoretical rate constants are determined for the first time for the reaction of 3-hydroxy-3-methyl-2-butanone with OH as a function of temperature. The atmospheric implications are discussed.

A Unified Frequency Equation and the Motion Analysis of a Moving Flexible Beam Carrying a Concentrated Mass

1999 ◽  
Author(s):  
S. Park ◽  
J. W. Lee ◽  
Y. Youm ◽  
W. K. Chung
Keyword(s):  
Natural Frequencies ◽  
Equations Of Motion ◽  
Frequency Equation ◽  
Open Loop ◽  
Mode Shapes ◽  
Flexible Beam ◽  
Lumped Mass ◽  
Concentrated Mass ◽  
Forcing Function ◽  
The Mathematical Model

Abstract In this paper, the mathematical model of a Bernoulli-Euler cantilever beam fixed on a moving cart and carrying an intermediate lumped mass is derived. The equations of motion of the beam-mass-cart system is analyzed utilizing unconstrained modal analysis, and a unified frequency equation which can be generally applied to this kind of system is obtained. The change of natural frequencies and mode shapes with respect to the change of the mass ratios of the beam, the lumped mass and the cart and to the position of the lumped mass is investigated. The open-loop responses of the system by arbitrary forcing function are also obtained through numerical simulations.

Rayleigh wave motions in an orthotropic half-space under time-harmonic loadings: A theoretical study

2020 ◽  
Vol 87 ◽  
pp. 171-179
Author(s):  
Duy Kien Dao ◽  
VanTrung Ngo ◽  
Haidang Phan ◽  
Chi Vinh Pham ◽  
Jaesun Lee ◽  
...  
Keyword(s):  
Rayleigh Wave ◽  
Half Space ◽  
Theoretical Study ◽  
Time Harmonic

scholarly journals Simultaneous Detection of Dopamine and Serotonin—A Comparative Experimental and Theoretical Study of Neurotransmitter Interactions

Biosensors ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 3 ◽  
Author(s):  
Felicia Manciu ◽  
Marian Manciu ◽  
John Ciubuc ◽  
Emma Sundin ◽  
Katia Ochoa ◽  
...  
Keyword(s):  
Experimental Study ◽  
Theoretical Study ◽  
Simultaneous Detection ◽  
Pharmaceutical Research ◽  
Label Free ◽  
Neural Processes ◽  
Experimental Approaches ◽  
Biological Relationship ◽  
First Time ◽  
Accurate Quantification

With the goal of accurately detecting and quantifying the amounts of dopamine (DA) and serotonin (5-HT) in mixtures of these neurotransmitters without using any labelling, we present a detailed, comparative computational and Raman experimental study. Although discrimination between these two analytes is achievable in such mixtures for concentrations in the millimolar range, their accurate quantification remains unattainable. As shown for the first time in this work, the formation of a new composite resulting from their interactions with each other is the main reason for this lack of quantification. While this new hydrogen-bonded complex further complicates potential analyte discrimination and quantification at concentrations characteristic of physiological levels (i.e., nanomolar concentrations), it can also open new avenues for its use in drug delivery and pharmaceutical research. This remark is based not only on chemical interactions analyzed here from both theoretical and experimental approaches, but also on biological relationship, with consideration of both functional and neural proximity perspectives. Thus, this research constitutes an important contribution toward better understanding of neural processes, as well as toward possible future development of label-free biosensors.

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