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Computation of aerodynamic damping in aeroelastic system based on analytical and numerical approach
Chládek, Štěpán ; Horáček, Jaromír ; Zolotarev, Igor
The paper describes computation of aerodynamic damping and natural frequencies of aeroelastic systems. The damping is a critical parameter for the stability analysis of aeroelastic systems. Structural damping of the system is important for very low fluid flow velocities, however by increasing the flow velocity, the aerodynamic damping dominates in the instability search. The damping can be evaluated in time or in frequency domain. The presented computation of aerodynamic damping consists of two analytical and one numerical approach. The analytical approaches are represented by the well-known pk method and the unsteady panel method. The pk method is based on Theodorsen unsteady aerodynamics and on the computation of complex eigenvalues of the system as functions of the flow velocity. The unsteady panel method enables the computation of the interaction between aeroelastic system and fluid flow. The aerodynamic damping is evaluated in time domain from the system response to given initial conditions. The numerical approach is based on the finite volume method (FVM) modelling the complete fluid-structure interaction (FSI) coupled problem. The aerodynamic damping is also computed from the system response to a given initial condition. The results of the mentioned methods are compared for the profile NACA 0012 with two degrees of freedom (2-DOF) for plunge and pitch motion around an elastic axis.
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Using the proper orthogonal decomposition analysis for detecting pathologic vocal fold vibration
Štorkán, J. ; Vampola, T. ; Horáček, Jaromír
A three-dimensional (3D) finite element (FE) fully parametric model of the human larynx based on computer tomography (CT) measurements was developed and specially adapted for numerical simulation of vocal folds vibrations with collisions. The complex model consists of the vocal folds, arytenoids, thyroid and cricoid cartilages. The vocal fold tissue is modeled as a four layered material where part of the cover was substituted by a liquid layer modelling the superficial layer of lamina propria. The proper orthogonal decomposition (POD) analysis of the excited modes of vibration was used for detecting changes in vibration properties of the vocal folds caused by pathologic changes of vocal fold structure (vocal nodule).
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Numerical simulation of the effect of stiffness of lamina propria on the self-sustained oscillation of the vocal folds
Hájek, P. ; Švancara, P. ; Horáček, Jaromír ; Švec, J. G.
A two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction during selfsustained oscillation of the human vocal folds (VF) is presented in this paper. The aim is to analyze the effect of stiffness of lamina propria on VF vibrations. Such stiffness change can be caused by some VF pathologies. The developed FE model consists of the FE models of the VF, trachea and a simplified human vocal tract. The vocal tract model shaped for simulation of phonation of Czech vowel [a:] was created by converting data from the magnetic resonance images (MRI). The developed FE model includes VF contact, large deformations of the VF tissue, fluid-structure interaction (FSI), moving boundary of the fluid mesh (Arbitrary Lagrangian-Eulerian (ALE) approach), airflow separation during the glottis closure and solution of unsteady viscous compressible airflow described by the Navier-Stokes equations. The numerical simulations showed that higher values of lamina propria Young's modulus (stiffer lamina propria) result in a decrease of the maximum glottis opening. Stiffer lamina propria also requires the use of higher subglottal pressure to initiate self-sustained vibration of the VF.
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ENGINEERING MECHANICS 2016 - Book of full texts
Zolotarev, Igor ; Radolf, Vojtěch
The 22nd International Conference EM2016 aims to provide a forum for researchers, industry practitioners, engineers and postgraduate scholars to promote exchange and disseminate knowledge and experiences of the most recent results and advances in a wide range of topics in Engineering Mechanics, including, but not limited to: Biomechanics, Dynamics, Fluid Mechanics, Fracture Mechanics, Kinematics, Mechanics of Solids, Mechatronics, Reliability of Structures and Thermomechanics.
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Five-blade bunch with dry friction inter-connection forced by running excitation
Půst, Ladislav ; Pešek, Luděk ; Radolfová, Alena
The vibration of five-blade-bunch linked in the shroud by means dry-friction-elements is investigated. Quasi-stationary response curves are used for analysis of dynamic properties of isolated blade-bunches excited by running harmonic forces. This running wave excitation models the real excitation in the steam or gas turbine with different numbers of rotor and stator blades. Relation between the ratio of these blade-numbers and phase delay between neighboring blades is ascertained and the dynamic responses of isolated five-blade bunch are shown and analyzed in this paper. Gained theoretical results can be used for evaluation of data obtained from dynamic measurements on bladed disk.
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