Contents of the Journal of Mechanical Engineering 48, 6 (1997)

TONDL, A.: Vibration absorbers for different excitations                
(Review paper) (in Czech)                                               377
 

ORAVSKY, V., SLIZEK, O.: Dynamic efficiency of a symmetric 
hydrostatic transmission at harmonic load. Part II. Analysis            
(in Slovak)                                                             387 


PETRUSKA, J., MACURA, P.: Pass rolling and material formability 
- numerical and experimental analysis                                   403 


DUDA, P., ZIELINSKI, A. P.: Stability and convergence of solutions 
in Trefftz-type algorithms                                              415


KOSKA, P., KOCANDRLE, P.: Direct boundary integral equation method 
for shape optimization of elastic bodies                                429

This article presents a survey of analysis results of absorber ability and efficiency for vibration quenching. Three types of absorbers: tuned mass-spring absorber, tuned pendulum absorber, and autoparametric pendulum absorber and three different excitations: external excitation, self-excitation, and parametric excitation are considered. The basic properties and demands for the optimal tuning and damping are presented. Some problems, which have not yet been sufficiently solved, are mentioned, as well.

The article directly links up with the article in the previous issue of this journal in which dynamic efficiency (dEf) of a symmetric hydrostatic transmission (HsT) at harmonic load was determined.

Here, dEf is analyzed in the space of 8 nondimensional parameters and compared with the quasistatic efficiency (at constant load and speed).

The analysis is carried out analytically and numerically and its results are presented in synoptical diagrams. Analysis shows that dEf HsT:

1. is mostly influenced by 3 "damping" factors: leaky transmittance, hydraulic resistance, and viscous friction in bearings of HsT. While the two first factors always decrease dEf, the last factor paradoxically can dEf even increase,

2. is always less or at most equal to 1 (for ideal HsT),

3. is less than the mean value of power transfer, which in resonant regions of HsT, can even be greater than 1,

4. is mostly nearly equal to or a bit less than qsEf.

Numerical and experimental analysis of a diamond-shape pass rolling is presented and the obtained stress and strain fields are compared. Strain intensity is then selected as a state variable, controlling the occurrence of fracture during large plastic deformation. Possibility of fracture under given thermodynamical conditions is studied. The suggested algorithm of fracture prediction can be generally used for a wide class of bulk forming processes.

Trefftz algorithms for solving boundary-value problems can become in certain cases unstable or weakly convergent. The paper investigates such cases and proposes a solution to the problem by regularization of respective matrices. The numerical examples illustrate the proposed technique. Concave areas are also considered.

A practical boundary element formulation for obtaining design sensitivities based on a direct application of the material derivative concept to the boundary integral equations is presented. Shape optimum design problems for peak stress minimization and minimum mean compliance are considered. The second order boundary elements with a cubic spline representation of the moving boundary are used for the numerical implementation.