Vladimír Kutiš

3D-beam element with continuous variation of the cross-sectional area

Abstract This paper presents the exact stiffness matrix of 3D-beam element with a class of continuously varying cross-sectional properties, which is derived using direct stiffness method and transfer functions of the beam. A nodal load vector for continuously distributed beam loading is also described using transfer functions. All the transfer functions, which occur in the stiffness matrix and nodal load vector, are evaluated numerically. Results of numerical experiments show that this new element satisfies all the relevant equations.

Computational modelling and advanced simulations

Introduction 1. Nonlinear Dynamic Analysis of Partially Supported Beam-Columns on Nonlinear Elastic Foundation Including Shear Deformation Effect, by E.J. Sapountzakis, A.E. Kampitsis 2. Mechanics of viscoelastic plates made of FGMs, by H. Altenbach, V.A. Eremeyev 3. Indirect Trefftz method for solving Cauchy problem of linear piezoelectricity, by G. Dziatkiewicz, P. Fedelinski 4. New Phenomenological Model for Solid Foams, by V. Goga 5. The Effect of an Interphase on Micro-Crack Behaviour in Polymer Composites, by P. Hutar, L. Nahlik, Z. Majer, Z. Knesl 6. Temperature Fields in Short Fibre Composites, by V. Kompis, Z. Murcinkova, M. Ockay 7. Simulation of Distributed Detection of Ammonia Gas, by O. Sykora, J. Aubrecht, R. Klepacek, L. Kalvoda 8. Exact Solution of Bending Free Vibration Problem of the FGM Beams with Effect of Axial Force, by J. Murin, M. Aminbaghai, V. Kutis 9. Wavelet Analysis of the Shear Stress in Soil Layer Caused by Dynamic Excitation A. Borowiec 10. Strength of Composites with Short Fibres, by E. Kormanikova, D. Riecky, M. zmindak 11. A direct boundary element formulation for the first plane problem in the dual system of micropolar elasticity, by Gy. Szeidl, J. Dudra 12. Implementation of meshless method for a problem of a plate large deflection, by A. Uscilowska 13. Modelling and Spatial Discretization in Depletion Calculations of the Fast Reactor Cell with HELIOS 1.10, by R. Zajac, P. Darilek, V. Necas 14. Linear Algebra Issues in a Family of Advanced Hybrid Finite Elements, by N.A. Dumont, C.A. Aguilar Maron 15. On Drilling Degrees of Freedom, by S. Kugler, P.A. Fotiu, Justin Murin 16. Hybrid System for Optimal Design of Mechanical Properties of Composites, by J. Wisniewski, K. Dems 17. Analysis of Representative Volume Elements with Random Microcracks, by P. Fedelinski 18. Application of general boundary element method for numerical solution of bioheat transfer equation, by E. Majchrzak.

Modal Analysis of Gallium Nitride Membrane for Pressure Sensing Device

A circular high electron mobility transistor (C-HEMT) prepared on the AlGaN/GaN membrane surface has been investigated and its potential for pressure sensing has been already demonstrated. The key issue in the design process of such heterostructure based MEMS sensors is the stress engineering. This way we can scale the sensor performance, measured pressure range and sensitivity. Especially, the knowledge of the exact value of the residual stress in membranes (caused by deposition process) helps us to optimize the sensing devices. In this work, the residual stress determination method in gallium nitride circular shaped membrane is reported. It is shown that resonant frequency method using Laser Doppler Vibrometry (LDV) for membrane vibration measurement seems to be an appropriate technique to determine the residual stress in micro-scale membranes. Circularly shaped AlGaN/GaN micro-membranes are excited by acoustic short time pulse. The decay oscillating motion of the membrane is recorded by oscilloscope. By FFT spectral analysis of the signals the resonance frequencies are obtained. For the sample studied, the natural frequency mode resonance peak is used to define the residual stress level. To verify the observed stress in investigated membranes, prestressed modal analysis in finite element method (FEM) code ANSYS is performed. The stress extracted from the measured frequency is taken as an initial stress state of the modelled membrane. Experimentally obtained shock spectra are compared with that computed by FEM simulation.

Effect of Non-Uniform Torsion on Elastostatics of a Frame of Hollow Rectangular Cross-Section

Abstract In this paper, results of numerical simulations and measurements are presented concerning the non-uniform torsion and bending of an angled members of hollow cross-section. In numerical simulation, our linear-elastic 3D Timoshenko warping beam finite element is used, which allows consideration of non-uniform torsion. The finite element is suitable for analysis of spatial structures consisting of beams with constant open and closed cross-sections. The effect of the secondary torsional moment and of the shear forces on the deformation is included in the local finite beam element stiffness matrix. The warping part of the first derivative of the twist angle due to bimoment is considered as an additional degree of freedom at the nodes of the finite elements. Standard beam, shell and solid finite elements are also used in the comparative stress and deformation simulations. Results of the numerical experiments are discussed, compared, and evaluated. Measurements are performed for confirmation of the calculated results.

Thermo-Hydraulic Behaviour of Coolant in Nuclear Reactor VVER-440 Under Refuelling Conditions

Abstract The paper presents the numerical simulation of thermo-hydraulic behaviour of coolant in the VVER- 440 nuclear reactor under standard outage conditions. Heating-up and flow of coolant between the reactor pressure vessel and spent fuel storage pool are discussed.

Influence of Bypass on Thermo-Hydraulics of VVER 440 Fuel Assembly

Abstract The paper deals with CFD modelling and simulation of coolant flow within the nuclear reactor VVER 440 fuel assembly. The influence of coolant flow in bypass on the temperature distribution at the outlet of the fuel assembly and pressure drop was investigated. Only steady-state analyses were performed. Boundary conditions are based on operating conditions. ANSYS CFX is chosen as the main CFD software tool, where all analyses are performed.

Modeling of Coolant Flow Within the Spent Fuel Storage Pool of a VVER 440 Reactor

Abstract The article deals with modelling of coolant flow within the spent fuel storage pool of a VVER 440 reactor. The spent fuel storage pool is modelled in a state of standard reactor operation. The coolant heating from the remaining thermal power of stored spent fuel assemblies was also modelled.

CFD Analysis of Downcomer of Nuclear Reactor VVER 440

Abstract The paper is focused on CFD analyses of the coolant flow in the nuclear reactor VVER 440. The goal of the analyses is to investigate the influence of the orifice diameter on the mass flow through individual fuel assemblies in the reactor core. The diameter of orifice can be changed during the operation of a nuclear power plant. Considered boundary conditions in the investigated region of the coolant are based on nominal coolant flow conditions in the nuclear reactor VVER 440.

ELASTOSTATIC AND MODAL AND BUCKLING ANALYSIS OF SPATIAL FGM BEAM STRUCTURES

In this contribution, a homogenized beam finite element of double symmetric crosssection made of a Functionally Graded Material (FGM) is presented, which can be used for static, modal and buckling analysis of single beams and beam structures with three directional variation of material properties. The material properties in a real beam can vary continuously in longitudinal direction while the variation with respect the transversal and lateral directions is assumed to be symmetric in a continuous or discontinuous manner. The shear force deformation effect and the effect of inertia and rotary inertia are taken into account. Additionally, the longitudinally varying Winkler elastic foundation and the effect of axial force are included by the finite element equations as well. Homogenization of spatially varying material properties to effective quantities with a longitudinal variation is done by the extended mixture rules and multilayer method (MLM). For the homogenized beam the 1212 finite element effective matrix, consisting of the linearized stiffness and consistent mass inertia terms, is established. Numerical experiments are made concerning static, modal and buckling analyses of single FGM beam and beam structures to show the accuracy and effectiveness of the proposed FGM beam finite element.

NUMERICAL SOLUTION OF DIFFERENTIAL EQUATIONS WITH NON-CONSTANT COEFFICIENTS

Abstract. Nowadays, new materials like Functionally Graded Material (FGM) are necessary for sophisticated structures like MEMS systems, advanced electronic devices, etc. Computer modelling of such complex systems, like structures with spatial variation of material properties (e.g. FGM) are, using commercial FEM code with classic elements, needs remarkable effort during preparation phase and sufficient computer equipment for solution phase because of necessity the numbers of elements and material models. Therefore new methods for modeling and simulation of FGM beams with spatial variation of material properties are developed. In the proposed contribution, semi-analytical method (based on calculation of transfer functions and transfer constants) for solution of differential equation with non-constant polynomial coefficients, is presented. This method is used in derivation process (for setting up the transfer matrix) of our new beam finite elements for modeling and simulation of Functionally Graded Material (FGM) beam structures (e.g. new 3D FGM beam finite element for modal and structural analysis, new FGM beam finite elements for coupled electro-thermo-mechanical analysis). Numerical experiments are made to show the accuracy and effectiveness of this method.