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Low Cost Laser Rangefinder Evaluation
Krejsa, Jiří ; Věchet, Stanislav
Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. This paper evaluates the properties of currently (2018) the cheapest sensor available, particularly RPLidar A1M8, in order to determine whether it is usable in mobile robot development. As the sensor is based on triangulation principle, the increase of errors with the measured distance was expected, the experiments proved these expectations. Furthermore, the increasing, but linear trend in absolute measurement error was observed. The influence of surface material and color was also evaluated. The measurements indicate that RPLidar A1M8 can serve as a useful alternative for more expensive types of laser rangefinders.
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Computational time reversal method based on finite element method: influence of temperature
Mračko, Michal ; Kolman, Radek ; Kober, Jan ; Převorovský, Zdeněk ; Plešek, Jiří
Time reversal method is used to focus elastic waves to the location of the original source and reconstruct its source time function. The procedure consists of two steps: Frontal task and Reversal task. In the Frontal task, the medium is excited by an arbitrary source, elastic waves propagate through a body of interest and the dynamic response at few points on boundary is recorded. In the second step (say the Reversal task) the response signal is reversed in time and transmitted back into the medium resulting in focusing in the original source location. It is of practical importance to investigate a case when the medium changes its properties between the frontal and reversal wave propagation steps. An example is a problem of transferring experimentally recorded data to a computational model, where discrepancies in geometry, elastic properties and boundary conditions are expected. Our motivation is to develop a methodology for computation of time reversal problems in commercial finite element software. The results prove that this method is extremely sensitive to the change of temperature and one have to pay special attention to tuning of elastic parameters relevant to the\nexperiment.
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Finite element modeling of the signal propagation in a thin tube and comparison with experimental data
Kruisová, Alena ; Kolman, Radek ; Trnka, Jan ; Mračko, Michal
In finite element modeling of wave propagation problems, both the spatial and temporal discretization lead to dispersion errors. It means that the phase velocity of propagated wave is related to its frequency. In framework of temporal-spatial dispersion analysis, the time step size for implicit time integration method based on the Newmark method is proposed for linear and quadratic serendipity plane finite elements. In this paper, we verify the theoretical dispersion analysis by elastic wave propagation in thin tube, where experimental results are known. Such time step size was used in finite element modeling of the stress wave propagating in this thin steel tube, the results of simulations were compared with experimental results.
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Development, assessment and verification of finite element procedures for contact problems
Gabriel, Dušan ; Kopačka, Ján ; Masák, Jan ; Plešek, Jiří
A frictionless three-dimensional contact algorithm based on the pre-discretization penalty formulation was proposed. The algorithm proved to be robust, accurate and symmetry preserving—no master/slave surfaces have been introduced. It was implemented in the finite element code PMD (Package for Machine Design) for the solution of complex engineering problems. The capability of the algorithm was demonstrated in creep analysis of T-piece of the steam distributor of the CHEMOPETROL heating plant T200. Material properties were described by the probabilistic exponential model with damage. The purpose of the analysis was to compare the original version and the proposed design modification applied to one of T-pieces of the distributor when the proposed contact algorithm was employed to simulate the interaction between the collar and the pipe.
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Dynamics of four-planetary gearing box
Půst, Ladislav ; Pešek, Luděk ; Škuderová, Alena
Planetary gearboxes are more complicated than parallel-axis gear transmission systems and\ntherefore they need deeper dynamic analysis, which is important for reduction of noise and vibration. The main advantage of planetary gearings is the splitting of force flow into several planet wings, but it can be devaluated by unequal load sharing on planet stages. For improving, the floating sun wheal and flexible pins of planets are applied. Dynamic model of such a gearing box is derived in the paper and it is shown that the frequency spectrum contains many multiple eigen-frequencies. Examples of several eigen-modes and transfer functions of this four-planetary gearing box are presented as well. The problem of dimensional nonhomogeneous vectors and matrix is also mentioned.
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The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors
Zapoměl, Jaroslav ; Ferfecki, P. ; Sudhakar, A. ; Kozánek, Jan
Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between the magnetic rings, which may destabilize the rotor oscillations. The performed research was focused on the development of computational procedures for analysis of energy losses in the supports of magnetically lifted vertical rotors mounted in rolling element bearings and on analysis of stability of their vibration in a wide range of operating speeds. The computational simulations proved efficiency of the magnetic suspension.
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Numerical investigation of acoustic characteristics of 3D human vocal tract model with nasal cavities
Vampola, T. ; Štorkán, J. ; Horáček, Jaromír ; Radolf, Vojtěch
Acoustic resonance characteristics of 3D human vocal tract model without and with nasal and\nparanasal cavities were computed. Nasal cavities (NC) form the side branches of the human vocal tract and exhibit antiresonance and resonance properties which influence the produced voice quality. Developed FE models of acoustic spaces of nasal and vocal tract for vowel /a:/ are used to study the influence of (NC) on phonation. Acoustics frequency-modal characteristics are studied by modal analysis and numerical simulation of acoustic signals in time domain is performed by transient analysis of the FE models.
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Experimental investigation of settling slurry flow in inclined pipe sections
Vlasák, Pavel ; Chára, Zdeněk ; Matoušek, Václav ; Kesely, Mikoláš ; Konfršt, Jiří
Narrow particle size distribution glass beads-water slurry flow in the pipe sections of different inclination were investigated on an experimental pipe loop of inner diameter D = 100 mm. The study refers to the effect of pipe inclination and slurry velicity on local concentration distribution, pressure drop-velocity relationship, and deposition limit. The study revealed that the glass beads-water mixtures in the inclined pipe sections were significantly stratified: the solid particles moved principally close to the pipe invert, and for flow velocities close to the deposition limit sliding bed or stationary deposit is created even in inclined pipe sections.
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