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

Stresses, deformations and damping in interference-fits

C. HOSCHL

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.

E. WISZT, E. WISZTOVA

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.

T. JOHNSON, T. W. CHIU

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.

J. BAJKOWSKI, M. HAC

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.

V. KOMPIS, J. ORAVEC, J. BURY

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.

Simulation results of static optimization of a torsionally oscillating mechanical system

J. HOMISIN, M. JURCO, A. GMITERKO, M. DOVICA

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.