Contents of the Journal of Mechanical Engineering 48, 3 (1997)

HOSCHL, C.,  OKROUHLIK, M.: Numerical methods in mechanics of solids.
Part I.  Main ideas and mathematical models                              145


 
MALY, S.,  KABAT, V.: Application of the thermal analogy method to
mixing proportions at combustion (in Slovak)                             162



CARNOGURSKA, M.: Design strength calculation of spiral casing 
of a two-stage axial-radial hydraulic turbine by the finite 
element method (in Slovak)                                               173



DANEK, O.: Condensation of mathematical models of dynamic systems        
(in Czech)                                                               183


CABIB, E., SCHAEFER, R.: Optimal pretraction design in network 
structures                                                               191



CACKO, J.: Investigation of an influence of parasitic vibration 
on structure design in probabilistic dimensioning                        203

The aim of this survey is to present a concise information about various numerical methods for the solution of problems in mechanics of solids. While the Part I deals with main ideas on which these methods are based, the Part II - which is to follow - will cover details on numerical procedures for solving linear as well as nonlinear tasks and crucial remarks pertinent to their implementations.

The presented article deals with mixing proportions in combustion chambers of steam boilers within the framework of the thermal analogy method. The method is applied to a two-stage fluidized bed boiler at the thermal power station in Handlova. This boiler has been reconstructed successfully according to recommendations following from the results of laboratory measurements. The measurements performed at the applied boiler confirmed that the concentrations of CO and NO_x in the flue gases were smaller than the emission limit. Nevertheless, the thermal efficiency was increased at the same time.

In this paper the design strength of the spiral casing of the two-stage axial-radial hydraulic turbine is presented by the finite element method in the COSMOS/M environment. At present, no design models of the spiral casing calculated by traditional methods are known, therefore the completion of design strength of such a complicated shape as the spiral casing with the turbine casing provides a new and valuable information. In this paper two shapes of the spiral casing with the same hydraulic properties but with different geometry of external shape were analysed. These analyses took into consideration the stress positions and size of deformation. The results of model loading of turbine have shown an advantage of the construction with changed rib shapes.

The condensation is considered here as a spectral and modal true reduction from the r-dimensional space P^r to Pⁿ or P^m, where n,m < r. The solution is expressed by the equation of excited vibrations by means of Green resolvent and the coefficient matrices of condensed models are evaluated from the conditions of orthogonality and norm.

The paper contains mathematical results concerning existence, uniqueness and shape of solutions of the optimal pretraction design problem of a square, unconnected network. A comprehensive computational example for the network prestressed only by boundary fibers is presented. A homogenized equilibrium equation was used in both theoretical and numerical considerations.

Hitherto known procedures in probabilistic design of machine parts mostly suppose a stationary loading with only small random fluctuation that is superimposed on the carrier signal. Under variable dynamic loading, however, an analytical solution is usually impossible. The problem can be very effectively solved using a computer simulation method that is applied to a suitable reliability model. It is to be expected that the random fluctuation of parasitic vibration can considerably influence a strength resistance of structure components. Therefore, the advanced knowledge of the noise effect allows to reduce economy demands in a very significant way. The theoretical outline and the results of typical investigation examples are presented in the paper.