In downhole drilling systems, self-excited torsional vibrations caused by the bit-rock interactions can affect the drilling process and lead to the premature failure of components. Especially self-excited oscillations of higher-order modes lead to critical dynamic loads. The slim drill string design and the naturally limited drilled borehole diameter limit the installation space, power supply and lead to numerous potentially critical self-excited torsional modes. Consequently, small and robust passive damping concepts are required. The variety of possible downhole boundary conditions and potential damper designs necessitates analytical solutions for effective damper design and optimization. In this paper, two nonlinear passive damper concepts are investigated regarding design and effectiveness to reduce self-excited high-frequency torsional oscillations in drill string dynamics. Based on a finite element model of a drill string, a suitable minimal model based on the identified critical mode is generated and solved analytically using the Multiple Scales Lindstedt-Poincaré (MSLP) method. The advantages of MSLP compared to conventional MS methods are shown for this example. On the basis of the analytical solution, parameter influences are determined, and design equations are derived. The analytical results are transferred to self-excited drill string vibrations and discussed using time domain simulations of the drill string model.

This paper presents a hybrid model to describe drill string dynamics for deep hole drilling. Generally, a typical rotary drill string has a length of several kilometers, but the diameter is less than half a meter. Due to the large ratio of length to diameter, a drill string is a very flexible system. Consequently, an operating drill string is always affected by axial, torsional and lateral vibrations, which potentially induce serious failures. In order to avoid fatal defects, simulations to forecast vibrations are necessary. The simulation should be capable to exhibit the complex dynamical phenomena, e.g. sick‐slip, forward whirl and backward whirl, and interactions between drill string and borehole. Usually, these simulations are very time‐consuming. In this work, a hybrid model consisting of lumped masses connected with weightless beam elements representing the drill string is developed. The interaction between the drill string and the borehole is implemented by unilateral constraints to describe the nonlinear contact behavior. It was shown that accuracy and simulating time were improved by this model with respect to classical finite‐element models. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Up to now a coherence between pain and technical systems has almost not been researched. Whereas some aspects of the nociceptive pain which serves human beings as a warning system and is also described as useful, can be transferred necessarily to technical systems. The idea of pain detection is an additional product of the Mesoscopic Particle Method [2-4]. Thereby the transformation of kinetic energy into heat energy caused by impact- and friction processes in the boundary layer of contact areas is described correctly with respect to thermodynamics. Between the properties of pain and heat there obviously exist analogies. Pain increases when certain external effects get higher and decreases smoothly, when the effect is taken off [5]. Generally pain is a vector of different phenomena. By means of the developed sensor concept the application of energy is detected including implicit frequency selective information about the jerk. It will experimentally and numerically be shown how e. g. a “hard-soft-detection” of surfaces can be evaluated by the developed sensor concept.

In drill string dynamics the Finite Element Method is usually applied to models of very long drill strings in a wellbore with arbitrary curvature. Taking account of geometrical constraint between the drill string and the wellbore, a high density of nodes is necessary. This density is much higher than the one needed to describe the natural vibrations properly, so this firstly leads to an extension of the computing time. A penalty function is frequently utilized to describe the contact problem between the drill string and the wellbore where the contact normal force acts only on the nodal points of the drill string. It was recognized that only node-to-surface contact models cannot fulfill this geometrical constraint, because the segment between two nodal points deeply penetrates the wellbore wall in some cases. A process with Gaussian points along the segment in time domain will be introduced, so that the drill string will be described according to this geometrical constraint with good accuracy but with a smaller density of nodes and less computing time.

The high speed railway brakes transfer a large amount of kinetic energy into heat. The temperature during a brake operation could reach values higher than 90 °C. The dynamics of the brake system is rather complicated with respect to the multiphysical phenomena. In this paper, the thermo‐mechanical coupling are investigated combined with the loos of brake material due to wear. The coupled model is discretized by conventional finite element method. Different coupled algorithms have been tested. Various scenarios have been simulated and shown reasonable results. The temperature and deformation on pad and disc, especially the thermal deformation of disc the so–called coning effect can also be prescribed with this coupled multiphysics model. Furthermore, the tapered wear on brake pads is also discussed as a requirement of railway brake design in terms of durability. Thereby, the Ehlers's model is normally used to minimize tapered wear by selecting an adequate point of applied braking force. An extended Ehlers's model is also presented here, which concerns wear effect based on Archard's model. (© 2016 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)