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1
Content available remote Semi-Active Vibration Control with Shunted Piezoceramics
Oleśkiewicz R., Neubauer M., Krzyżyński T., Popp K.
Machine Dynamics Problems
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2005
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Vol. 29, No. 4
109-125
EN
Piezoelectric materials because of their unique ability of converting mechanical energy into electrical energy and vice versa can be found in numerous mechanical vibration damping applications. Connecting a suitable shunt branch to the piezoelectric actuator results in an electromechanical vibration damping or absorbing system, depending on the complex impedance describing the external network. A limited performance of the pure passive techniques involving resistive and inductive elements depending only on the electromechanical coupling coefficient can be significantly increased by the use of the negative capacitance element. Such an approach requires external power supply because of the necessary impedance converter built up of the operational amplifiers. The paper presents the recent research on the negative capacitance application in semi passive vibration control systems with piezoceramics, where the different configurations of external RLC-networks are analyzed. The electromechanical system consists of one degree of freedom spring mass damper oscillator with a piezoelectric actuator placed between the mass and the base. The analysis is performed in a general, normalized form, highlighting the influence of the negative capacitance and the general electromechanical coupling coefficient of the piezoceramics. The optimal parameters of the shunt branch resulting in maximal damping and absorbing performance of the system are given in an analytical form. The analytical results have been experimentally verified using a test rig.
2
Content available remote Friction-Induced Vibrations : Excitation Mechanisms and Counter Measures
Popp K., Lindner M., Rudolph M.
Machine Dynamics Problems
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2004
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Vol. 28, No. 2
37-40
EN
Friction is an all-day-phenomenon and everybody is familiar with it. From an engineering point of view two different phenomena can be distinguished. First, the resistance against the start of a relative motion of bodies which is caused by the contact between these bodies. Secondly, the resistance against an existing relative motion of two contacting bodies. In the first case, the phenomenon is called static friction. It is of great use in technical applications as it enables for example fixing of parts by screws or driving of land vehicles by wheels. In the second case, the effort to sustain a sliding motion is called kinetic friction. Usually, this effect is unwanted in engineering because it is responsible for the transformation of kinetic energy into heat and, thus, additional energy consumption, as well as for the wear of parts by relative motion.
3
Content available remote Experimental and Analytical Investigation of Rubber Adhesion
Kröger M., Popp K., Kendziorra N.
Machine Dynamics Problems
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2004
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Vol. 28, No. 1
79-89
EN
The total friction between tyre and road is based on hysteresis induced friction and adhesion induced friction. A pendulum test rig is designed for experimental investigations of the adhesion effect of rubber and the geometrical and material influences. Based on the Hertzian contact theory the hysteresis and adhesion is described by energy considerations.
4
Content available remote Stick-Slip Vibrations of Pneumatic Seals
Lindner M., Kröger M., Popp K.
Machine Dynamics Problems
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2001
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Vol. 25, No. 3/4
121-130
EN
In the present paper the dynamic friction process of a pneumatic seal is investigated. A test facility for measuring forces, displacements and velocities on a lubricated seal lip has been used. The measurements indicate that the friction force depends on several parameters. Stick-slip effects are found in the low velocity range. After the identification of the system parameters these vibrations have been modelled. It turned out that dynamic friction force can be described well by a first order differential equation.
5
Content available remote Dynamics and Control of an Elastic Guideway under a Moving Load
Popp K., Reckmann H.
Machine Dynamics Problems
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2001
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Vol. 25, No. 3/4
131-133
EN
[Extended abstract]. In recent years lightweight structures became increasingly important in engineering. A fast motion or a high-speed manoeuvre on such a flexible system often leads to uncontrolled vibrations with high amplitudes and deflections due to the low weight and the lack of structural damping...
6
Content available remote Energy Absorption by Plastic Deformation Using Inversion of Tubes
Kröger M., Popp K.
Machine Dynamics Problems
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2000
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Vol. 24, No. 1
101-103
7
Content available remote Stability Behaviour of a Railway Bogie
Kaiser I., Popp K.
Machine Dynamics Problems
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1998
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Vol. 20
123-138
EN
Some modern high-speed trains show the phenomenon of grumbling noise. Together with this phenomenon, polygonalisation of the wheels occurs, i.e. the wheels of these trains lose their roundness after short running time. A possible cause for this behaviour are periodic fluctuations of the wheel loads. These fluctuations can result from unbalance forces in the wheelset or from periodic track stiffnesses due to passing the sleepers. The wheel load fluctuations lead to fluctuations of the creep coefficients, which can cause parametric excited vibrations. This leads to a loss of stability at lower speeds than the critical speed, which is calculated with constant wheel loads. For models of wheelset, which are known from literature, it is assumed, that the wheel loads for both wheels are equal. Here, with respect to wheel load fluctuations, we allow different wheel loads at the left and right wheel contact. Thus, the mechanical system loses its symmetric structure. This results in a coupling of the antisymmetric and symmetric motions of the wheelset and the bogie. Therefore, new equations of motion have been developed, which describe a bogie with different wheel loads at the left and right wheels. The stability of this system is investigated to find parametric instabilities.
8
Content available remote On Steady State Dynamics of Railway Tracks Modelled as Continuous Periodic Structures
Kruse H., Popp K., Krzyżyński T.
Machine Dynamics Problems
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1998
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Vol. 20
149-166
EN
This paper deals with an advanced linear model for the vertical track motion. Left and right rail and sleepers are modelled as Timoshenko beams. The pads and the ballast/ subsoil can have an arbitrary frequency dependent complex stiffness. Hence, an additional damping due to wave radiation in the subsoil can be considered. The steady state solution for the system under uniformly moving harmonic forces is derived by Fourier and Laplace transform techniques. Numerical calculations are performed with system parameters of a track commonly used in Germany. The influence of the non-continuous rail support and the system behaviour at critical pairs of load velocity and load frequency are investigated. Furthermore, the consequences of shear deformation of the rails and the effect of the sleeper elasticity on the system dynamics are examined.
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