Contents of the Journal of Mechanical Engineering 50, 3 (1999)

C. HOSCHL: Stresses, deformations and damping in interference-fits       145

E. WISZT, E. WISZTOVA: Energy balance of two coupled oscillators
subject to transient excitation                                          156

T. JOHNSON, T. W. CHIU: Numerical methods in the prediction 
of pressure fluctuations on board trains passing through tunnels         168

J. BAJKOWSKI, M. HAC: Application of FEM in modelling rigid and
flexible systems with joint clearances                                   177

V. KOMPIS, J. ORAVEC, J. BURY: Reciprocity based FEM                     188

Engineering note

J. HOMISIN, M. JURCO, A. GMITERKO, M. DOVICA: Simulation results 
of  static optimization of a torsionally oscillating 
mechanical system (in Slovak)                                            202

Press- or shrink-fitted joints of shafts and hubs (or pivots and walls etc.) are frequently used in machine design. The strength and reliability of such assemblies are commonly judged using only elementary formulas well known from many textbooks or manuals. This seems to be unsatisfactory in many cases, the accuracy of these formulas being low and such phenomena as surface roughness, stress concentration, plastic deformations, fretting corrosion, and fatigue being left aside. This paper gives a review of most important papers concerning such problems. Paradoxical slip and loosening of press-fitted pivots or rings will also be mentioned.

The response of two stiffness coupled oscillators, one of which is subjected to an initial impulse, is examined by an energy balance analysis. By use of a Fourier transform, an expression is derived which shows the decomposition of the total energy flow in the frequency plane. A further expression for the total energy flow is derived. It is shown how the total energy flow depends on parameters of the system. The analytically derived general relations are complemented by numerical calculations for some particular cases of the coupling.

As a train enters or leaves a tunnel, pressure waves are generated which travel up and down the tunnel at sonic speed. Due to the superposition of the waves, passengers experience complex pressure fluctuations which can cause aural discomfort. Railway tunnel operators need to ensure a satisfactory level of passenger aural comfort. Sizing the tunnel appropriately or pressure sealing the train are two possible methods to accomplish this.
This paper describes a one-dimensional numerical model based on the method of characteristics for the prediction of tunnel pressures. Also explained will be a finite difference model which gives accurate predictions of the internal pressure fluctuations on-board sealed trains.

In the paper the kinematic and dynamic analysis of planar flexible mechanisms is studied by using finite element method. The motion of any point belonging to the mechanism can be treated as a superposition of "large" (due to mechanism motion) and "small" (due to vibration) motions. The rigid body motion for systems with clearances is obtained by using modified truss-type elements. At the node with clearance connection the additional finite element with very small stiffness is introduced. The vibration analysis is made by using beam type finite elements. The influence of impacts due to the presence of clearance on vibration of links is investigated. As examples a crank rocker mechanism and a two-link planar manipulator are considered with one clearance between the links in the revolute joint.

This paper presents FE formulation in which the boundary tractions and displacements of the element are related using the Betti's reciprocity, similarly as that used by BEM, however, Trefftz polynomials are used as test functions and thus corresponding integral equations are regular, which is advantageous for numerical implementation. The displacements are supposed to be continuous between elements and the only equations which are not satisfied in linear problems are inter-element equilibrium equations. Variational formulation for a weak satisfaction of boundary tractions enables to obtain the global equations in discretized form. On numerical examples we will show that the present formulation gives very high accuracy even when the fields with very high gradients are approximated by these elements.
As the integration for the stiffness matrix formulation is taken over the element boundaries only, the shape of the element can be more general (polygon, circular boundaries, etc.) than it is in classical FEM formulations. Although numerical examples are shown for 2D elasticity, the extension to 3D and other field problems is straightforward.

Mechanical systems with piston engines as driving or driven aggregates represent torsionally oscillating mechanical systems (TOMS). Uneven excitation of individual pistons of the piston device or malfunction of some of the pistons are the most frequent reasons of TOMS failure. This results in occurrence of very intensive resonances in the working regime of given systems. The resonances are caused by the lower harmonic components of the exciting moment. Occurring resonances are the cause of increase of the dynamic load of the whole device.
It is possible to solve the above-described situation by the preliminary adjustment of the dynamic properties of flexible shaft clutches in the dynamics of the given system.
In regard to the development of new flexible shaft clutches, so called pneumatic tuners of torsional oscillations, we are striving to solve the described situation by the static optimization of TOMS on the base of the method of extremal regulation.