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A modified mathematical model of an asynchronous electric drive of the rotor – a drill string – a bit – a rock is considered and implemented, which develops and generalizes the results of previously performed studies. The model includes the following subsystems: a model of an asynchronous drive with vector control; a model of formation of the resistance moment at the bottom of the bit, taking into account the peculiarities of the interaction between the bit and the rock; a model of a multi-mass mechanical part that takes into account the deformation of the drill string; subsystem for the drilling rig energy-technological parameters formation. The integrated model makes it possible to calculate and evaluate the selected drilling modes, taking into account their electro-mechanical, energy and technological efficiency and the dynamics of drilling processes. The performed computer simulation of drilling modes confirmed the possibility of a stick-slip effect accompanied by high-frequency vibrations during bit stops, which may change the direction of rotation of the bit, its accelerated wear and unscrewing of the drilling tool. Long bit stops lead to a significant decrease in the average bit rotation speed, which can explain the decrease in the ROP and increase in energy consumption when drilling in the zone of unstable bit rotation. The model can be used as a base for further improvement of rotary drilling control systems.

This study investigated the influence of the wax layer on the micro-friction behavior of the energetic crystal surface by constructing the lubricating interface between wax and β-HMX crystals. The nano-scratch testing of β-HMX crystals with and without wax coating was conducted under the ramp-loading (0–3.5 ​mN) mode and the constant-loading (0.4 ​mN) mode. The testing results are as follows. Compared with the dry friction of β-HMX crystals without wax coating, wax can significantly improve the contact friction between the energetic crystals and the rigid micro-convex body. The influence of wax on the interface friction highly depends on the external load conditions. Under the ramp-loading mode, the wax layer can greatly reduce the average coefficient of friction (COF) from ∼0.7 (dry friction) to ∼0.2 (lubricating interface) and inhibit COF fluctuation. The inherent mechanism of wax reducing the interface friction works in the following way. Wax can effectively suppress the plowing effect of the rigid micro-convex body on the β-HMX crystal surface and further inhibit the occurrence of brittle fracture and crack defects. The wax layer can also suppress the friction anisotropy of the β-HMX crystal surface, significantly reducing the probability of high COF (>0.4). The distribution probabilities of COF in the range of 0–0.1 and 0–0.3 were 33% and 89%, respectively. The stick-slip effect of the friction behavior was observed under the constant-loading mode, with the COF varying periodically with the sliding distance. These study results can help understand the desensitization mechanisms of wax on the energetic crystal surface at a micro-scale quantitative level and provide a necessary basis for building the friction hot-spot model under dry friction and wax lubrication.

Friction is an important source of dissipation in dynamical systems. Properly considering it in the numerical model is fundamental to obtain stable and representative responses in structures and mechanisms. This is especially significant for the well-known Coulomb model due to discontinuity in force when stick-slip transition occurs. In this work an improved friction force model is proposed to smooth the force transition at null velocity, with an additional parameter obtained from the own system state. The improved model is employed in sliding connections of plane frames finite elements. A total Lagrangian Finite Element Method (FEM) formulation based on a positional description of the motion is employed. Using a variational principle, frictional dissipation is added to the total mechanical energy to develop the equations of motion. The resulting nonlinear equations are solved by the Newton-Raphson method accounting for the friction force update in the iterative process. Examples are presented to show the formulation effectiveness and possibilities in simulating dynamical systems that present the stick-slip effect. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the wax layer on the micro-friction behavior of the energetic crystal surface by constructing the lubricating interface between wax and β-HMX crystals. The nano-scratch testing of β-HMX crystals with and without wax coating was conducted under the ramp-loading (0-3.5 mN) mode and the constant-loading (0.4 mN) mode. The testing results are as follows. Compared with the dry friction of β-HMX crystals without wax coating, wax can significantly improve the contact friction between the energetic crystals and the rigid micro-convex body. The influence of wax on the interface friction highly depends on the external load conditions. Under the ramp-loading mode, the wax layer can greatly reduce the average coefficient of friction (COF) from ~0.7 (dry friction) to ~0.2 (lubricating interface) and inhibit COF fluctuation. The inherent mechanism of wax reducing the interface friction works in the following way. Wax can effectively suppress the plowing effect of the rigid micro-convex body on the β-HMX crystal surface and further inhibit the occurrence of brittle fracture and crack defects. The wax layer can also suppress the friction anisotropy of the β-HMX crystal surface, significantly reducing the probability of high COF (>0.4). The distribution probabilities of COF in the range of 0-0.1 and 0-0.3 were 33% and 89%, respectively. The stick-slip effect of the friction behavior was observed under the constant-loading mode, with the COF varying periodically with the sliding distance. These study results can help understand the desensitization mechanisms of wax on the energetic crystal surface at a micro-scale quantitative level and provide a necessary basis for building the friction hot-spot model under dry friction and wax lubrication. [ABSTRACT FROM AUTHOR]

In this work, the lubricating models of Cu–Zn alloy with and without the Zinc oxide (ZnO) layer were established. Molecular dynamics (MD) simulation is employed to investigate the lubrication behavior of n-hexadecane on the ZnO layer at the nanoscale. The diffusion of lubricants molecules, and the interaction and stick–slip effect between the friction pairs and the lubricants are systematically explored. The results show that the ZnO layer limits the diffusion of n-hexadecane molecules and the formed lubricating films in the model of the substrate with the ZnO layer are obvious and stable. During the sliding process, ZnO molecules have strong interaction with lubricants molecules and adsorb lubricants molecules on the surface to form adsorption film. The stick–slip effect in the lubricating films generates periodic shear stress and reduces the wear of the friction pair. The ZnO layer causes lubricants molecules to be arranged regularly on the surface into a stable structure. [ABSTRACT FROM AUTHOR]

With the availability of educational digital data acquisition systems, it has also become possible in physics education to generate ‘big’ data sets by (a) measuring multiple variables simultaneously, (b) increasing the sample rate, (c) extending the measurement duration, or (d) choosing a combination among these three options. In the context of this paper, we will use a simple acceleration experiment to show that a higher sample rate, resulting in a larger data set, quantitatively reveals the stick-slip effect. For this purpose, two variables are measured simultaneously, first with a low and then with a high sample rate. The purpose of this paper is to illustrate that dealing with ‘big’ data sets can add value to experimentation in physics labs by dealing with data sets that more accurately describe observations. [ABSTRACT FROM AUTHOR]

Pneumatic cylinders are widely used in highly dynamic processes, such as handling and conveying tasks. They must work both reliably and accurately. The positioning accuracy suffers from the stick-slip effect due to strong adhesive forces during the seal contact and the associated high breakaway forces. To achieve smooth motion of the piston rod and increased position accuracy despite highly variable position dynamics, sliding friction and breakaway force must be reduced. This contribution presents a specially designed linear tribometer that has two types of control. Velocity control allows the investigation of sliding friction mechanisms. Friction force control allows investigation of the breakaway force. Due to its bearing type, the nearly disturbance-free detection of stick-slip transients and the dynamic contact behavior of the sliding friction force was possible. The reduction of the friction force was achieved by a superposition of the piston rod's movement by longitudinal ultrasonic vibrations. This led to significant reductions in friction forces at the rubber/metal interface. In addition, the effects of ultrasonic frequency and vibration amplitude on the friction reduction were investigated. With regard to the breakaway force, significant success was achieved by the excitation. The force control made it possible to identify the characteristic movement of the sealing ring during a breakaway process. [ABSTRACT FROM AUTHOR]

The stick-slip is one of negative phenomena caused by friction in servo systems. It is a consequence of complicated nonlinear friction characteristics, especially the so-called Stribeck effect. Much research has been done on control algorithms suppressing the stick-slip, but no simple solution has been found. In this work, a new approach is proposed based on genetic programming. The genetic programming is a machine learning technique constructing symbolic representation of programs or expressions by evolutionary process. In this way, the servo control algorithm optimally suppressing the stick-slip is discovered. The GP training is conducted on a simulated servo system, as the experiments would last too long in real-time. The feedback for the control algorithm is based on the sensors of position, velocity and acceleration. Variants with full and reduced sensor sets are considered. Ideal and quantized position measurements are also analyzed. The results reveal that the genetic programming can successfully discover a control algorithm effectively suppressing the stick-slip. However, it is not an easy task and relatively large size of population and a big number of generations are required. Real measurement results in worse control quality. Acceleration feedback has no apparent impact on the algorithms performance, while velocity feedback is important.

This paper proposes a multi-stage FPS-TMD system with variable friction coefficient in order to improve the performance of FPS-TMD and expand its application due to the inherent nonlinearity of FPS-TMD. The equation of motion of multi-stage FPS-TMD system is established by Lagrange principle. The numerical solution to the multi-stage FPS-TMD system is obtained considering stick-slip effect of FPS. A multi-objective optimization design method for the multi-stage FPS-TMD system is presented basesd on nondominated sorting genetic algorithm Ⅱ. A landscape tower is used as numerical example and a two-stage FPS-TMD system is designed and analyzed with the traditional TMD and FPS-TMD systems. The research results show that the two-stage FPS-TMD system with variable friction coefficient provide more energy dissipation capacity during moderate earthquake and reduce structure displacement response by 16.34% as compared with the constant friction FPS-TMD system during minor earthquake. Moreover, the FPS-TMD system with variable friction is slightly better than the conventional TMD designed by Den hartog formula. [ABSTRACT FROM AUTHOR]

The nanoscale friction behavior of quartz-quartz and quartz-kaolinite interfaces is investigated through Steered Molecular Dynamics (SMD) simulations. The effects of normal load, sliding velocity, temperature, and hydration on the friction behavior are discussed, and the friction mechanism of quartz and quartz/kaolinite interface is revealed. The friction coefficients of all systems at different cases are obtained and compared with other experimental results for validation. The simulation results show that the stick-slip effect in all interfaces was found during the friction process, where the higher the sliding velocity and hydration, or the lower the normal load, the weaker the stick-slip effect. The friction load increased with the rising normal load, and the relationship between shear stress and normal load was approximately linear. The friction coefficient and cohesion of the quartz-quartz interface could rise with the increasing sliding velocity or the decreasing temperature. Moreover, the friction coefficient of quartz-kaolinite was significantly smaller than that of quartz-quartz, indicating that the presence of clay could weaken the frictional strength of quartz. The effect of the interlayer water film on friction behavior was rather complex, showing the lubricating or bonding role, which has been discussed and analyzed in the present study. [Display omitted] • The stick-slip effect was found in the quartz-quartz interface during the friction process. • The higher the sliding velocity and hydration, or the lower the normal load, the weaker the stick-slip effect. • The presence of clay could weaken the frictional strength of quartz. • Friction coefficient and cohesion of quartz rose with the rising sliding velocity or decreasing temperature. • The relationship between shear stress and normal load was linear in nanoscale friction. [ABSTRACT FROM AUTHOR]

Pneumatic cylinders are widely used in highly dynamic processes, such as handling and conveying tasks. They must work both reliably and accurately. The positioning accuracy suffers from the stick-slip effect due to strong adhesive forces during the seal contact and the associated high breakaway forces. To achieve smooth motion of the piston rod and increased position accuracy despite highly variable position dynamics, sliding friction and breakaway force must be reduced. This contribution presents a specially designed linear tribometer that has two types of control. Velocity control allows the investigation of sliding friction mechanisms. Friction force control allows investigation of the breakaway force. Due to its bearing type, the nearly disturbance-free detection of stick-slip transients and the dynamic contact behavior of the sliding friction force was possible. The reduction of the friction force was achieved by a superposition of the piston rod’s movement by longitudinal ultrasonic vibrations. This led to significant reductions in friction forces at the rubber/metal interface. In addition, the effects of ultrasonic frequency and vibration amplitude on the friction reduction were investigated. With regard to the breakaway force, significant success was achieved by the excitation. The force control made it possible to identify the characteristic movement of the sealing ring during a breakaway process.

The work was a mathematical model that describes the effect of the sliding attachment (stick-slip), taking into account hereditarity. explicit finite-difference scheme for the corresponding. Cauchy problem was constructed. Built on the basis of its waveform and phase trajectories

This paper deals with the mechanical properties of the double bass and double bass bow. The sound of the instrument, as well as the vibrations of the bow, were recorded while playing. The sound was recorded with a microphone, while a sensor, placed on the bow’s stick, registered its vibrations. By observing these signals, from double bass and bow, the correlation between them was determined in order to explain the bow-string mechanism.

The main object of this study is to investigate the influence that different modelling assumptions of the curved surface sliding (CSS) bearings may have on the lateral-torsional response of irregular base-isolated structures located in near-fault area, characterized by fling-step and directivity effects with large amplitudes and long period horizontal velocity pulses. The second aim is to evaluate the effects of different design assumptions of the CSS system. To this end, a six-storey base-isolated reinforced concrete (r.c.) framed building, with an L-shaped plan and setbacks in elevation, is designed assuming low- and medium-type friction properties, both with two in-plan distributions of the dynamic-fast friction coefficient, corresponding to: (i) the same value for all isolators; (ii) a different value for each isolator. Four additional cases are compared reducing the friction coefficient in accordance with a temperature increase up to 250 °C during ground motions. A computer code for the nonlinear dynamic analysis is developed, in order to compare five models of the CSS bearings that consider constant and variable axial loads combined with constant and variable friction coefficients as function of sliding velocity, axial pressure and stick-slip effect. A lumped plasticity model is used to describe the inelastic behaviour of the superstructure, including a 26-flat surface modelling of the axial load-biaxial bending moment elastic domain at the end sections of r.c. frame members. Near-fault ground motions with significant horizontal components are selected and scaled in line with the design hypotheses adopted for the test structure. [ABSTRACT FROM AUTHOR]

Axial-torsional coupled percussive drilling is a novel technology to enhance the rate of penetration (ROP), which takes advantage of both axial and torsional percussive drilling technologies. Our paper focuses on experimental investigations on coupled percussive drilling. A novel experiment setup, using a rock breaking tester, was developed to carry out dynamic drilling tests on granite specimens under different impact modes, weight on bit (WOB), rotation rates, and lithologies. Based on the optimization analysis of window functions, by combining the fast Fourier transform (FFT) and short-time Fourier transform (STFT) processing methods, the spectrum and 3D time-frequency-amplitude evolution characteristics of coupling impact response signals were demonstrated. According to experimental results, a high-frequency and high-amplitude rotational rate and lower torque are produced in coupling impact. The agglomeration of the cutting force is alleviated and the occurrence of "stick-slip effect" is slowed down. Compared with axial impact, the penetration depth and ROP are increased by 173.38% and 182.74% in coupling impact, respectively. As the WOB increases, a stable-high frequency and high amplitude rock breaking torque is generated, which increases the cutting force and ROP. There is an optimal ratio between the rotation rate controlled by the axial rotator and the torsional impact frequency, which takes advantage of axial and torsional percussion for a bit and obtains the optimal speed-raising effect. The variation of rock mechanical properties has a significant influence on the amplitude of time domain signals in coupling impact. Our results in this paper are of great value for future studies of axial-torsional coupled percussive drilling. • A novel experiment setup, using a rock breaking tester, was developed to carry out dynamic drilling tests on granite specimens under different impact modes in our paper. • Compared with axial impact, a high-frequency and high-amplitude rotational rate and lower torque are produced in coupling impact. • A stable-frequency and high-amplitude rock breaking torque is generated with the WOB increases. • An optimal ratio between the rotation rate and the torsional impact frequency obtains the optimal speed-raising effect. • The variation of rock mechanical properties has an effect on the amplitude of time domain signals in coupling impact, but has no effect on frequency. [ABSTRACT FROM AUTHOR]

A vibration-driven system is modelled to achieve the expected planar locomotion in the present paper. The system is composed of a main rigid body and two internal and movable masses. Coulomb dry friction and nonholonomic constraint of the body are considered to model stick-slip effect and to ensure the motion without sideslip. It is seen that driving periodically the two masses in two orthogonal directions leads to the expected planar locomotion. Correspondingly, the translational and rotary velocities of the system are analytically obtained. As a result, the system can move not only along oblique line in any given slope but also along folding lines derived from the oblique lines in the different slopes. [ABSTRACT FROM AUTHOR]

New analytical solutions are derived for the frictional sliding of rigid blocks to idealized ground acceleration pulses. These excitations are indicative of near-fault earthquake motions affected by forward fault-rupture directivity, which may inflict large permanent displacements in the absence of substantial frictional resistance at the sliding interface. The scope of this study is threefold: (1) to derive analytical solutions for a wide set of idealized pulses; (2) to investigate the effects of symmetric and asymmetric sliding under both unilateral and bilateral excitation conditions; and (3) to explore alternative normalization schemes of peak sliding with reference to peak pulse acceleration, velocity, duration, and shape. A generalized exponential function, capable of simulating an infinite number of pulse waveforms based on a single parameter, is employed to this end. Results are presented in the form of dimensionless closed-form expressions and graphs that provide insight into the physics of the nonlinear problem. [ABSTRACT FROM AUTHOR]

The stick-slip is one of negative phenomena caused by friction in servo systems. It is a consequence of complicated nonlinear friction characteristics, especially the so-called Stribeck effect. Much research has been done on control algorithms suppressing the stick-slip, but no simple solution has been found. In this work, a new approach is proposed based on genetic programming. The genetic programming is a machine learning technique constructing symbolic representation of programs or expressions by evolutionary process. In this way, the servo control algorithm optimally suppressing the stick-slip is discovered. The GP training is conducted on a simulated servo system, as the experiments would last too long in real-time. The feedback for the control algorithm is based on the sensors of position, velocity and acceleration. Variants with full and reduced sensor sets are considered. Ideal and quantized position measurements are also analyzed. The results reveal that the genetic programming can successfully discover a control algorithm effectively suppressing the stick-slip. However, it is not an easy task and relatively large size of population and a big number of generations are required. Real measurement results in worse control quality. Acceleration feedback has no apparent impact on the algorithms performance, while velocity feedback is important. [ABSTRACT FROM AUTHOR]

The present paper deals with an effective and alternative adjustment method for precise alignments of components of precision engineering and optics—the so-called method of stepped transfer of momentum bases on measured stroke impulses, which act onto a pre-stressed object and effect stepwise movements. The strokes are generated and applied to the components in several directions by special electromechanical hammers by means of a PC software and a measurement device. The automatic operation is finished if the target position of the object is attained. Achieved adjustment accuracies for the fixed components may be in the sub-micron range. The paper discusses theory and experiment of motion behavior of pushed components under the influence of applied momentum, pre-stressing and frictional forces. Additionally, it describes the wide application range of this adjustment method on the basis of developed prototypes. [Copyright &y& Elsevier]

• Hysteresis effect of the friction force in unsteady motion is analyzed. • The Effects of acceleration sign-changes in hydrodynamic regime are examined. • Solution of the unsteady Navier-Stokes equation in the hydrodynamic regime is provided. • An improved friction model subjected to acceleration sign-changes is presented. A friction model for evaluating friction force of a Radial Shaft Sealing Ring (RSSR) in contact with the rotating shaft subjected to unsteady motion is presented. The model takes both the magnitude and the acceleration sign-changes from positive to negative into account and removes the shortcoming of the existing friction models in the sliding domain. It is shown that acceleration has a pronounced influence on the hydrodynamic regime. The results signify that hysteresis behavior exists in the boundary, mixed lubrication and hydrodynamic regimes as well as the pre-sliding domain, making the conventional Stribeck friction model unsuitable for characterization of friction behavior. To account for the hysteresis effect in the hydrodynamic regime, the model incorporates the solution of the unsteady Navier-Stokes equation that accommodates the magnitude as well as the sign change in the acceleration (and, hence, the viscous friction). In addition to the hysteresis, the results show a frictional lag when the motion starts from stick to slip. Test results are presented at low speed, and unknown parameters of the friction model are determined using an experimental test rig. [ABSTRACT FROM AUTHOR]