Contents of Journal of Mechanical Engineering 63, 3 (2012) 



                                                                       
TONDL, A. PUST, L.: On the phenomenon "Parametric anti-resonance"            125

KOMPIŠ, V., MURČINKOVÁ, Z., FERENCEY, V.: Computational simulation 
of composite materials reinforced by fibres with large aspect ratio          139

JIN XU-XING: Optimum synthesis method of mechanical press driven by 
non-circular gears                                                           155

ELBASHBESHY, E. M. A., EMAM, T. G., SAYED, E. A.: Effect of pressure 
work on free convection flow from a vertical circular cone with variable 
surface heat flux                                                            169



Abstracts



On the phenomenon "Parametric anti-resonance"

A. TONDL, L. PUST

The aim of this contribution is to present a survey of the main research results dealing with the phenomenon "parametric anti-resonance" and to stimulate the interests of designers for its application in engineering practice especially in machinery and for devices where vibrations are undesirable for the safe run. It is interesting that this phenomenon can be used for vibrations suppressing for all kind of excitations, i.e. not only externally, but also for self-excitation and undesirable parametric resonance.


Computational simulation of composite materials reinforced by fibres with large aspect ratio

V. KOMPIŠ, Z. MURČINKOVÁ, V. FERENCEY

1D continuous source functions - fundamental solutions and their derivatives located along fibre axes are used to simulate the interactions of matrix and reinforcing elements in composite materials, when the primary field is a scalar function (e.g. temperature in heat conduction) or a vector function (e.g. displacement in elasticity). The inter-domain continuity is specified in discrete points on fibres boundaries. Intensities of the source functions are defined by 1D NURBS and computed in LS sense in all fibres. The inter-domain continuity equations have to be completed by balance equations (energy, equilibrium, etc.) in order to obtain temperature, displacement, etc. in the centre of each fibre. Gradients of displacements (strains) and temperature are supposed to be constant in cross-sections of the fibres and are computed iteratively by considering them to be linear along fibres in the first step and both the values, in the centre of the fibre and its change along the fibre axis, are computed in the next steps. Material of both matrix and fibres is assumed to be homogeneous and isotropic. Three numerical examples giving two fibres overlapping in some length in infinite matrix show the numerical behaviour of the problem for heat conduction.


Optimum synthesis method of mechanical press driven by non-circular gears

JIN XU-XING

A new type of mechanical press which has a crank-slider mechanism and a pair of non-circular gears is presented in this paper. The crank is attached to the driven gear, so that the motion law of the slider is determined by the non-\linebreak -circular gears, and the displacement curve of the slider can be easily changed to meet different processing requirements, which is necessary for the multi-variety and small batch manufacturing.
The purpose of this study is to achieve excellent motion characteristics of the press; firstly, a quintic polynomial curve is suggested for defining the desired motion of the slider. Then, an optimal method is proposed to obtain the pitch curves of the non-circular gears, the object function and constraints for optimization are discussed and suggested to obtain feasible design. Finally, an example is introduced to illuminate the press performance; the results demonstrate that the optimum synthesis method is effective.



Effect of pressure work on free convection flow from a vertical circular cone with variable surface heat flux

E. M. A. ELBASHBESHY, T. G. EMAM, E. A. SAYED

The effect of pressure work on free convection flow from a vertical circular cone with variable surface heat flux is considered. Similarity solutions for boundary layer equations are found to exist when the surface heat flux is proportional to xn (where x is distance measured from the leading edge). The governing system of partial differential equations is reduced to a system of ordinary differential equations. Mathematica has been used to solve such system after obtaining the missed initial conditions. Comparison of numerical results is made with previously published results under the special cases, the results are found to be in a good agreement. The solutions are presented in terms of local skin-friction, local Nusselt number, velocity and temperature profiles for values of Prandtl number, pressure work parameter and heat flux gradient parameter.