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EXPERT SYSTEM SHELL ARCHITECTURE BASED ON DECISION NETWORK
Věchet, Stanislav ; Krejsa, Jiří ; Chen, K.S.
Presented paper deals with preliminary design of an empty expert system suitable for system monitoring in various engineering applications. Discussed expert system is rule-based with the possibility of importance factor definition within each rule. The deduced result can be composited from more than one possible hypothesis based on different confidence level. The core of the system is based on Bayesian decision network and simple autonomous mobile robot use-case is used for results presentation.
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THE EVALUATION OF HOKUYO URG-04LX-UGO1 LASER RANGE FINDER DATA
Krejsa, Jiří ; Věchet, Stanislav
Laser range finders are essential sensors in mobile robot navigation tasks, such as robot localization, or simultaneous localization and mapping. As the probabilistic approach is commonly used to fuse the robot motion model with sensor data, the knowledge of the sensor parameters, such as linearity, variance, etc. is essential for fusing algorithms to perform correctly. This paper presents the results of extensive tests on performance of Hokuyo URG-04LX-UG01 range finder, that becomes nowadays popular among robot designers due to its reasonable cost, compact dimensions and low weight. The influence of obstacle color, error distribution and offset drift are examined.
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Modelling of Flow in Linear Blade Cascade with Thick Trailing Edge at a Lower Reynolds Number
Straka, P. ; Příhoda, Jaromír
In the paper there are compared results of numerical simulation of compressible turbulent flow through a low-pressure turbine blade cascade with relatively thick trailing edges for various physical models. Steady, unsteady, fully turbulent, transitional, two-dimensional and three-dimensional models are compared. Results show that: a) steady simulation gives an incorrect prediction of the boundary layer development, b) two-dimensional unsteady simulation leads to inaccurate prediction of the far wake development and c) only three-dimensional unsteady transitional simulation gives sufficiently accurate prediction. Results of numerical simulations are compared with the experimental data.
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An explicit time scheme with local time stepping for one-dimensional wave propagation in a bimaterial bar
Kolman, Radek ; Cho, S.S. ; Gonzalez, J.G. ; Park, K.C. ; Berezovski, A.
In this paper, we test a two-time step explicit scheme with local time stepping. The standard explicit time scheme in finite element analysis is not able to keep accuracy of stress distribution through meshes with different local Courant numbers for each finite element. The used two-time step scheme with the diagonal mass matrix is based on the modification of the central difference method with pullback interpolation. We present a numerical example of one-dimensional wave propagation in a bimaterial elastic bar. Based on numerical tests, the employed time scheme with pullback interpolation and local stepping technique is able to eliminate spurious oscillations in stress distribution in numerical modelling of shock wave propagation in heterogeneous materials.
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Computationally Efficient Model of the Human Vocal Fold
Štorkán, J. ; Vampola, T. ; Horáček, Jaromír
One mass model of the vocal folds with three degrees of freedom in 2D space was created and used to simulate the movement of the vocal folds. Vocal folds are modeled as a solid mass stored flexibly in 2D. The model is excited by aerodynamic forces. The flow is solved by analytical model incompressible and non-viscous fluid with constant flow. In case of close of the glottis are aerodynamic forces replaced by Hertz model of the contact forces. Movement equations are solved by numerical method. The model allows to solve the movement of the vocal folds in the time domain, pressure field acting on the vocal folds or contact pressures.
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Effect of turbulence in FE model of human vocal folds self-oscillation
Hájek, P. ; Švancara, Pavel ; Horáček, Jaromír ; Švec, J.G.
The purpose of the study is to determine whether a turbulence model in fluid flow calculation affects the vocal folds (VF) vibration and the acoustics of human vocal tract (VT). The objective is examined using a two-dimensional (2D) finite element (FE) model of the fluid-structure-acoustic interaction for self-sustained oscillations of the VF. The FE model consists of the models of the VF, the trachea and a simplified model of the human VT. The developed FE model includes large deformations of the VF tissue and VF contact interrupting the airflow during glottis closure. The airflow is modelled by the unsteady viscous compressible Navier-Stokes equations, without and with the Shear Stress Transport (SST) turbulence model. Fluid-structure interaction (FSI) and morphing of the fluid mesh are realized using Arbitrary Lagrangian-Eulerian (ALE) approach. The method is applied on the FE model of the VT shaped for the Czech vowel [a:]. Also effect of varying stiffness of the superficial lamina propria (SLP) is analyzed. The numerical simulations showed that considering of the turbulence affects mainly higher frequencies apparent in a frequency spectrum of the VT acoustics.
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Explicit dynamic finite element analysis of a firing pin assembly
Mochar, Dominik ; Gabriel, Dušan ; Masák, Jan ; Kopačka, Ján ; Kolman, Radek ; Plešek, Jiří ; Hynek, P. ; Vtípil, J.
In this paper, explicit dynamic finite element analysis of a firing pin assembly was performed. Two different geometries of the firing pin were considered using the finite element software PMD and Abaqus. For both variants there was evaluated a stress distribution at the critical point of a tested component, that is going to be later used for a fatigue analysis of the firing pin.
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Reduction of the energy losses by application of controllable squeeze film dampers
Zapoměl, Jaroslav ; Ferfecki, Petr ; Kozánek, Jan
The unbalance induces lateral oscillations of rotors and forces transmitted to the rotor casing. The squeeze film dampers with integrated rolling element bearings represent a technological solution, which enables to reduce their magnitude, and consequently the resistance against the rotor rotation. To achieve optimum performance of the damping devices, their damping effect must be adapable to the current rotor speed. This paper reports a proposal of a controllable squeeze film damper, the damping effect of which is controlled mechanically by shifting its outer ring in the axial direction. The developed mathematical model of the damper is based on assumptions of the classical theory of lubrication and is completed with implementation of a gas cavitation. The results of the computational simulations show that an appropriate control of the damping force enables to reduce the energy losses in a wide range of operating speeds.
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