Boundary conditions and event scaling of granular stick-slip events

2009 ◽  
Author(s):  
Karen E. Daniels ◽  
Nicholas W. Hayman ◽  
Masami Nakagawa ◽  
Stefan Luding
Keyword(s):  
Boundary Conditions ◽  
Stick Slip

STUDYING THE CONTACT POINT AND INTERFACE MOVING IN A SINUSOIDAL TUBE WITH LATTICE BOLTZMANN METHOD

2001 ◽  
Vol 15 (09) ◽  
pp. 1287-1303 ◽  
Author(s):  
HAI-PING FANG ◽  
LE-WEN FAN ◽  
ZUO-WEI WANG ◽  
ZHI-FANG LIN ◽  
YUE-HONG QIAN
Keyword(s):  
Boundary Conditions ◽  
Contact Line ◽  
Lattice Boltzmann ◽  
Complex Geometry ◽  
Contact Point ◽  
Point Contact ◽  
Immiscible Fluids ◽  
Lattice Boltzmann Model ◽  
Stick Slip ◽  
Bounce Back

The multicomponent nonideal gas lattice Boltzmann model by Shan and Chen (S-C) is used to study the immiscible displacement in a sinusoidal tube. The movement of interface and the contact point (contact line in three-dimension) is studied. Due to the roughness of the boundary, the contact point shows "stick-slip" mechanics. The "stick-slip" effect decreases as the speed of the interface increases. For fluids that are non-wetting, the interface is almost perpendicular to the boundaries at most time, although its shapes at different position of the tube are rather different. When the tube becomes narrow, the interface turns a complex curves rather than remains simple menisci. The velocity is found to vary considerably between the neighbor nodes close to the contact point, consistent with the experimental observation that the velocity is multi-values on the contact line. Finally, the effect of three boundary conditions is discussed. The average speed is found different for different boundary conditions. The simple bounce-back rule makes the contact point move fastest. Both the simple bounce-back and the no-slip bounce-back rules are more sensitive to the roughness of the boundary in comparison with the half-way bounce-back rule. The simulation results suggest that the S-C model may be a promising tool in simulating the displacement behaviour of two immiscible fluids in complex geometry.

Drag on Sticky and Janus (Slip-Stick) Spheres Confined in a Channel

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Manish Dhiman ◽  
Suru Aditya Ashutosh ◽  
Raghvendra Gupta ◽  
K. Anki Reddy
Keyword(s):  
Boundary Conditions ◽  
Drag Coefficient ◽  
Cross Section ◽  
Reynolds Numbers ◽  
Solid Particles ◽  
Janus Particles ◽  
Stick Slip ◽  
Slip Surfaces ◽  
Potential Applications ◽  
Channel Center

Abstract Flow over a sphere is a frequently occurring phenomenon in a range of industries. The sphere is confined in a channel in most of these applications. Therefore, it is important to understand the effect of confinement on the hydrodynamics of the flow around a sphere placed in a channel. These spheres can be bubbles, solid particles or droplets resulting in different boundary conditions (stick or slip) on the surface of the sphere. In recent years, Janus spheres having slip and stick boundary conditions on parts of the sphere have gained importance because of their potential applications. In this article, drag coefficient for a spherical particle fixed at the centerline of a channel of square cross-section is obtained computationally for stick, slip, and stick-slip surfaces of the sphere for a range of particle Reynolds numbers (1–80) and particle to channel size ratios (0.05–0.80). Further, the position of stick particle in the channel is varied to understand the effect of particle location on the drag coefficient. Correlations are proposed to calculate the drag coefficient for no-slip and Janus particles when the particle is at the channel center.

Stick-Slip Motion of Machine Tool Slideway

1974 ◽  
Vol 96 (2) ◽  
pp. 557-566 ◽  
Author(s):  
S. Kato ◽  
K. Yamaguchi ◽  
T. Matsubayashi
Keyword(s):  
Boundary Conditions ◽  
Machine Tool ◽  
Static Friction ◽  
Experimental Results ◽  
Kinetic Friction ◽  
Stick Slip ◽  
Frictional Coefficients ◽  
Stick Slip Motion ◽  
Slip Motion

Stick-slip motion of a moving element on an actual machine tool slideway is investigated experimentally under various sliding conditions, and the fundamental characteristics of the stick-slip motion are clarified. Based on these experimental results, the characteristics of static friction in the period of stick and kinetic friction in the period of slip are studied concretely so as to clarify the stick-slip process. It is shown experimentally that static and kinetic frictional coefficients can be expressed with simple formulas. Using these expressions, the boundary conditions for occurrence of stick-slip motion are examined, and the relation between properties of the stick-slip motion and frictional characteristics is explained quantitatively.

Scaling Concept for Axial Turbine Stages With Loosely Assembled Friction Bolts: The Linear Dynamic Assessment

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
J. Szwedowicz ◽  
Th. Secall-Wimmel ◽  
P. Dünck-Kerst ◽  
A. Sonnenschein ◽  
D. Regnery ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Dynamic Assessment ◽  
Steam Turbines ◽  
Fe Method ◽  
Stick Slip ◽  
Contact Conditions ◽  
Axial Turbine ◽  
Linear Dynamic ◽  
Air Jet ◽  
Resonance Frequencies

In the early 1980s, Siemens developed a last stage fast rotating condensation blading (SK) blade with strongly twisted and tapered profiles for industrial condensing steam turbines, which operate with variable speed under high steam mass flow and excessive condensing pressures. To suppress alternating stresses of the lowest blade resonances, conical friction bolts are loosely mounted at the upper parts of adjacent airfoils. Also, these bolts couple the rotating blades, since steam excitation is lower than the friction threshold force on the bolt contacts. These coupling and damping capabilities were proven experimentally for the smallest SK blade at the test rig of the real turbine. By considering the similar mechanical and aerodynamic characteristics based on the tested smallest airfoil, the entire SK-blade family has been scaled up for reliable utilization in more than 500 industrial turbines operating for diverse ranges of power and speed. A recent trend to very large compression units, like gas to liquids, acid terephtalic, or methanol plants, imposes a need for further enlargement of the SK-blade family and its friction bolt, whose mechanical properties have been proven experimentally for the smallest airfoil. In this paper, the mechanical capabilities of the smallest and large SK blades coupled by the bolts are verified by using the finite element (FE) method. The static analyses with friction sliding on airfoil interfaces and the linear dynamic behavior of tuned disk assemblies are considered. The FE mesh quality and the proper boundary conditions at the radial fork root are accomplished by getting good agreements between the computed and measured resonance frequencies of the large freestanding blade at standstill. The validated mesh refinement and root boundary conditions are used further in all numerical FE analyses. For the large SK-disk assembly under spin-pit conditions, the obtained FE results are in very good agreement with the experimental Campbell diagrams, which are measured with the three gauges that also identify the stick-slip and stuck bolt’s contact conditions. Concerning the gauge outputs and the FE steady-state blade resonances computed for the analytically determined air jet excitation, the experimental spin-pit results demonstrate that the bolts are mainly in stuck contact conditions. Only in very narrow frequency ranges around resonance peaks, microslips on the bolts occur due to the resonance amplification of blade vibrations. This is proven indirectly by comparison of the overall damping values evaluated from the blade resonances at standstill and in the spin pit. The described linear dynamic concept assesses properly static stresses and free vibrations of the scaled disk assembly with friction bolts. For the steam excitation, which generates dynamic contact reactions bigger than the friction threshold forces, the realistic blade responses need to be obtained from the blade simulation with friction (Szwedowicz, J., Secall-Wimmel, T., and Duenck-Kerst, P., 2007, “Damping Performance of Axial Turbine Stages With Loosely Assembled Friction Bolts; the Non-Linear Dynamic Assessment; Part II,” Proceedings of ASME Turbo Expo 2007, Montreal, Canada, May 14–17, ASME Paper No. GT2007-27506).

Investigation of Stick-Slip Severity in a Coupled Axial-Torsional Drillstring Dynamics Using a Two DOF Finite Element Model

2020 ◽  
Author(s):  
Ekaterina Wiktorski ◽  
Dan Sui
Keyword(s):  
Finite Element ◽  
Boundary Conditions ◽  
Axial Velocity ◽  
Slip Surface ◽  
Rotational Velocity ◽  
Friction Model ◽  
Drilling Process ◽  
Two Dimensional ◽  
Stick Slip ◽  
Torsional Oscillations

Abstract Drilling industry focuses nowadays on process optimization and cost reduction. Unwanted events should be predicted and avoided to increase drilling efficiency, improve safety, and save costs. Development and application of mathematical models enable us to understand the dynamics of the drilling process, learn parameter interaction and regulate system behavior. It is also a way to reduce the risk of occurrence of such events or mitigate negative outcomes. Challenges in two-dimensional modeling of drillstring vibrations include: (1) correct and precise interpretation of coupled two-dimensional motion, (2) use of sub-models, as down-hole weight on bit (WOB) model, downhole torque on bit (TOB) model and friction model, and (3) proper definition of associated boundary conditions. In this paper, we propose a two-dimensional axial-torsional model that considers these criteria. We present a new way to calculate downhole WOB, which can be used as an alternative to a constant WOB value. Dynamic boundary conditions are introduced to represent the respective phases of stick-slip. The model is formulated using the finite element method and intended for vertical wells. The main goal for developing this model is evaluation of the effect of surface rotational and axial velocities on the downhole drill bit dynamics. A dimensionless parameter, stick-slip severity, is used to represent the intensity of torsional oscillations. The developed model is based on mathematical relations and defined boundary conditions, which describe the dynamics of drillstring during stick-slip events. The model allows to study the effect of up to twelve input parameters on stick-slip severity to determine a suitable range. Results presented in this paper show that axial velocity applied from the surface may cause initiation of stick-slip, which in turn provokes axial vibrations. Increase in surface axial velocity leads to higher amplitude of downhole torsional oscillations. To mitigate stick-slip, surface rotational velocity should be increased.

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