3D stability analysis of unsupported rectangular excavation under pseudo-static seismic body force

2021 ◽  
pp. 1-18
Author(s):  
Patteera Petchkaew ◽  
Suraparb Keawsawasvong ◽  
Weeradetch Tanapalungkorn ◽  
Suched Likitlersuang
Keyword(s):  
Stability Analysis ◽  
Body Force

scholarly journals Prospects for observing the magnetorotational instability in the plasma Couette experiment

2015 ◽  
Vol 81 (4) ◽  
Author(s):  
K. Flanagan ◽  
M. Clark ◽  
C. Collins ◽  
C. M. Cooper ◽  
I. V. Khalzov ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Body Force ◽  
Protoplanetary Disks ◽  
Azimuthal Velocity ◽  
Relevant Parameter ◽  
Magnetorotational Instability ◽  
Plasma Parameters ◽  
Global Stability Analysis ◽  
Two Fluid ◽  
Ideal Plasma

Many astrophysical disks, such as protoplanetary disks, are in a regime where non-ideal, plasma-specific magnetohydrodynamic (MHD) effects can significantly influence the behaviour of the magnetorotational instability (MRI). The possibility of studying these effects in the plasma Couette experiment (PCX) is discussed. An incompressible, dissipative global stability analysis is developed to include plasma-specific two-fluid effects and neutral collisions, which are inherently absent in analyses of Taylor–Couette flows (TCFs) in liquid metal experiments. It is shown that with boundary driven flows, a ion-neutral collision drag body force significantly affects the azimuthal velocity profile, thus limiting the flows to regime where the MRI is not present. Electrically driven flow (EDF) is proposed as an alternative body force flow drive in which the MRI can destabilize at more easily achievable plasma parameters. Scenarios for reaching MRI relevant parameter space and necessary hardware upgrades are described.

scholarly journals Purely elastic linear instabilities in parallel shear flows with free-slip boundary conditions

2021 ◽  
Vol 928 ◽  
Author(s):  
Martin Lellep ◽  
Moritz Linkmann ◽  
Bruno Eckhardt ◽  
Alexander Morozov
Keyword(s):  
Boundary Condition ◽  
Stability Analysis ◽  
Constitutive Model ◽  
Spatial Structure ◽  
Boundary Conditions ◽  
Shear Flows ◽  
Body Force ◽  
Slip Boundary Conditions ◽  
Slip Boundary ◽  
Parallel Shear Flows

We perform a linear stability analysis of viscoelastic plane Couette and plane Poiseuille flows with free-slip boundary conditions. The fluid is described by the Oldroyd-B constitutive model, and the flows are driven by a suitable body force. We find that both types of flow become linearly unstable, and we characterise the spatial structure of the unstable modes. By performing a boundary condition homotopy from the free-slip to no-slip boundaries, we demonstrate that the unstable modes are directly related to the least stable modes of the no-slip problem, destabilised under the free-slip situation. We discuss how our observations can be used to study recently discovered purely elastic turbulence in parallel shear flows.

Dynamics of falling films on the outside of a vertical rotating cylinder: waves, rivulets and dripping transitions

2017 ◽  
Vol 832 ◽  
pp. 189-211 ◽  
Author(s):  
Manuel Rietz ◽  
Benoit Scheid ◽  
François Gallaire ◽  
Nicolas Kofman ◽  
Reinhold Kneer ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Body Force ◽  
Rotating Cylinder ◽  
Taylor Instability ◽  
Large Radius ◽  
Control Parameters ◽  
Integral Boundary ◽  
Rayleigh Taylor Instability

Falling liquid films on the underside of a plate or on the outside of a rotating cylinder are subject to a destabilizing body force. The evolution of the film topology is determined by interactions between the Kapitza and the Rayleigh–Taylor instability, leading to complex patterning of the film surface and eventually fluid detachment from the substrate. This study experimentally investigates the evolution of the surface topology for a film on the outside of a vertical rotating cylinder of large radius. Shear at the liquid/air interface is suppressed through an outer, co-rotating cylinder. The film evolution is captured through high speed visualization in dependence of the control parameters, namely Reynolds number and rotation frequency. An increasing influence of the Rayleigh–Taylor instability for an increasing destabilizing body force (increasing rotational speed of the cylinder) is most notably observed in the form of a decreasing inception length of rivulet structures dominating the film topology. Wavelength as well as inception length of rivulets match the predictions from linear stability analysis of the classical Rayleigh–Taylor problem. In this context, experimental and supporting numerical results suggest that the emergence of rivulets occurs for any non-zero value of the destabilizing body force after a given evolution length that decreases with increasing body force. Fluid detachment from the substrate is found to be intimately related to the existence of rivulet structures. In dependence of the control parameters, detaching droplets are either observed as a result of interactions of solitary pulses of varying phase speed on rivulets, directly after destabilization of two-dimensional waves into rivulets or immediately at the fluid inlet. By comparison to the convective/absolute instability transition predicted by linear stability analysis of an integral boundary layer formulation of the problem in question, it is shown that the prediction of a predominant dripping mechanism lies beyond the scope of linear analysis.

Sign in / Sign up

Export Citation Format

Share Document