Volume 12, number 2 (2018)

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    Modelling of the friction-vibration interactions in reactor core barrel couplings
    (University of West Bohemia, 2018) Zeman, Vladimír; Hlaváč, Zdeněk
    The key-groove couplings between the lower part of core barrel and reactor pressure vessel in the nuclear VVER-type reactor show assembly side clearances. Vibration of reactor components, caused by coolant pressure pulsations generated by main circulation pumps, produces impulse and friction contact forces in the above mentioned couplings. These forces are used for calculation of power and work of friction forces in the slipping contact surfaces between the key and the groove of the particular couplings and for their fretting wear prediction in dependence on the clearance values. The paper presents an original approach to mathematical modelling and simulation analysis of reactor nonlinear vibrations respecting friction-vibration interactions at all the key-groove couplings with clearances. The method is applied to VVER 1000/320 type reactor operated in the nuclear power plant Temelín in the Czech Republic.
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    Development of a constitutive model of soft tissues for FE analyses using a bottom-up approach
    (University of West Bohemia, 2018) Vychytil, Jan; Holeček, Miroslav
    This paper presents the development of a two-scale anisotropic hyperelastic material model whose microstructure is motivated by the arrangement of soft tissues. In a bottom-up approach, we start at the microscale, identifying the components that are relevant for our model. These components are represented by simplified mechanical elements, such as linear springs and incompressible volumes. The next step is to use the concept of the representative volume element connecting the micro- and macroscales. Introducing principal material directions, the notion of invariants and pseudo-invariants is employed to derive a formula for the strain energy function. In fact, two hyperelastic models are proposed. In the simplified one, the microstructure is formed of a network of linear springs. In the second one, an incompressible volume is added to the representation of the microstructure. This results in the model’s having a nonlinear response, with the strain energy function arising as a solution to a minimization problem. The properties of the strain energy function and the influence of anisotropy are demonstrated on a simple tension test and a simple shear test. Applications of the proposed model to the description of prestressed materials, non-affine deformations, and real tissue modelling are presented.
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    Numerical instability in the element-free Galerkin method for bi-material modeling
    (University of West Bohemia, 2018) Pannachet, Tanyada; Triyotee, Surachai; Boonpichetvong, Maetee
    This paper presents numerical results from modeling of bi-material problems using the element-free Galerkin method. The conventional EFG shape functions do not pass through the nodal data, imposition of nodal constraints brings difficulties, thus some special techniques must be employed. In bi-material problems, connecting the two subdomains of different properties may still be possible via Lagrange multipliers, penalty function, Nitsche’s formulation, or direct imposition when using a regularized weighting function to transform the EFG shape functions. All these mentioned technique s are explored and compared in this paper . Some remarks about numerical instabilities are reported.
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    Influence of boundary conditions on stochastic movement of biological molecular motors
    (University of West Bohemia, 2018) Krejčová, Milada; Holeček, Miroslav
    The aim of this work is to show the use of statistical physics in biomechanics, especially for modelling a muscle on molecular level. To approximate stochastic (Markovian) evolution in the spatial variable of muscle configuration, we solve the Fokker-Planck equation with the use of the Wang-Peskin-Elston algorithm. The approach is used for numerical simulation in MATLAB of the system time development with different boundary conditions.
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    Identification of material properties of foam used in motorcyclist protective equipment based on obtained experimental data and optimization algorithm
    (University of West Bohemia, 2018) Kaňáková, Sandra; Kottner, Radek
    This article deals with the material parameters identification of foam used in motorcyclist protective equipment, such as a shoulder pad. Experiments, namely a compression, a tension and an impact test were performed to obtain source and target data. The low-density foam material model was selected to characterize the foam. The material model was used in the finite element simulation. The numerical simulation of the impact test was used for an optimization. The parameters of the model were identified using an evolutionary algorithm in the optiSLang 3.0 software. The obtained material model will be used for the simulation of the standard test of protectors consisting of the foam used in motorcyclist protective equipment.
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    Investigation of heat and mass transfer processes in the combustion chambe of industrial power plant boiler. Part 2. Distribution of concentrations of O2, CO, CO2, NO
    (University of West Bohemia, 2018) Askarova, Aliya; Maximov, Valeriy; Bolegenova, Saltanat; Bolegenova, Symbat; Yergaliyeva, Aigul Balatbekovna; Šafařík, Pavel
    In the present paper, a study of furnace processes in the combustion chamber of the real energy boiler BKZ-160 of Almaty TPP-3 (Kazakhstan) using three-dimensional modeling methods has been carried out. Calculations of the combustion chamber for flame combustion of pulverized coal have been performed. The main purpose of this paper was to study the effect of fractional fuel composition on the concentration characteristics of the combustion process. Numerical simulation was carried out with two models of coal particle size distribution: monodisperse fuel flame (coal particle size identical and equal to 60 μm) and a polydisperse fuel flame (coal particle diameter varies from 10 to 120 μm). The polydisperse distribution corresponds to the fractional distribution (percentage of total coal particles) calculated for this boiler: the first fraction - 10% with dp=10 μm; 20% with dp=30 μm; 40% with dp=60 μm; 20% with dp=100 μm; 10% with dp=120 μm.The numerical simulation results of the influence of the pulverized coal particle size composition on concentration characteristics of combustion process are presented. The distributions of oxidizer (oxygen) and combustion products (NO, CO, CO2) are shown. Areas with the greatest concentration of gas products of burning are determined, regularities of formation of products and their concentration at the exit of fire chamber are also determined. The effect of fractional fuel composition on the obtained characteristics is sufficiently large, the empirical data obtained directly at TPP-3 show better convergence with the result of the computational experiment that confirms simultaneously the adequacy of the used physical and mathematical statement of the problem, as well as the validity of using the model of polyfractional distribution.