Instability of a charged plane interface between two liquids with respect to the tangential discontinuity of a time-dependent velocity field

2000 ◽  
Vol 45 (1) ◽  
pp. 22-24
Author(s):  
A. I. Grigor’ev
Keyword(s):  
Velocity Field ◽  
Time Dependent ◽  
Plane Interface ◽  
Tangential Discontinuity

scholarly journals Inclusion of a time-dependent, non-local convection theory in a stellar evolution code

2006 ◽  
Vol 2 (S239) ◽  
pp. 314-316 ◽  
Author(s):  
Achim Weiss ◽  
Martin Flaskamp
Keyword(s):  
Velocity Field ◽  
Local Time ◽  
Stellar Evolution ◽  
Time Dependent ◽  
Test Cases ◽  
The Sun ◽  
Specific Test ◽  
Non Local ◽  
Convective Boundaries

AbstractThe non-local, time-dependent convection theory of Kuhfuß (1986) in both its one- and three-equation form has been implemented in the Garching stellar evolution code. We present details of the implementation and the difficulties encountered. Specific test cases have been calculated, among them a 5 M⊙ star and the Sun. These cases point out deficits of the theory. In particular, the assumption of an isotropic velocity field leads to too extensive overshooting and has to be modified at convective boundaries. Some encouraging aspects are indicated as well.

scholarly journals Modelling the trajectory of the corpses of mountaineers who disappeared in 1926 on Aletschgletscher, Switzerland

2014 ◽  
Vol 60 (220) ◽  
pp. 255-261 ◽  
Author(s):  
Guillaume Jouvet ◽  
Martin Funk
Keyword(s):  
Velocity Field ◽  
Weather Conditions ◽  
Space Time ◽  
Severe Weather ◽  
Time Dependent ◽  
Glacier Area ◽  
Glacier Surface ◽  
Space And Time ◽  
End Point

AbstractIn this paper we reconstruct the space–time trajectory beneath the surface of Aletschgletscher, Switzerland, of the corpses of three mountaineers that disappeared in March 1926 and reappeared at the glacier surface in June 2012. Our method integrates the time-dependent velocity field of an existing full-Stokes glacier model, starting at the point where the corpses were found at the glacier surface. Our main result is that we were able to localize the immersion location where the brothers presumably died. As a second result, the upstream end point of the computed trajectory emerges very close to the glacier surface in 1926, giving a new and global validation of the glacier model in space and time. Testing the sensitivity of the immersion location obtained with respect to the model and other uncertainties indicates an area of 0.6% of the entire glacier area where the accident could have occurred. Our result suggests that death was not caused by an avalanche or a fall into a crevasse; instead, it is likely that the mountaineers became disoriented in prolonged severe weather conditions and froze to death.

Magnetorheological Flow in Pipes: An Exploration of the Time-Variation of Herschel-Bulkley Parameters

2007 ◽  
Author(s):  
Mario F. Letelier ◽  
Juan S. Stockle ◽  
Dennis A. Siginer
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Unsteady Flow ◽  
Yield Stress ◽  
Magnetic Fluid ◽  
Time Variation ◽  
Power Index ◽  
Time Structure ◽  
Time Dependent ◽  
Constitutive Parameters

In this paper it is analyzed the effects on the flow of the time-variation of Herschel-Bulkley model of fluid constitutive parameters. In this way, the influence of a varying magnetic field on the unsteady flow of a magnetic fluid is explored. Yield stress, viscosity and power index are assumed time-dependent. In particular, linear variations in time of these parameters are considered. The characteristics of the velocity field is analyzed for different values of the constants that determine the time structure of the constitutive parameters.

Application of the Tornado-Like Flow Theory to the Study of Blood Flow in the Heart and Main Vessels: Study of the Potential Swirling Jets Structure in an Arbitrary Viscous Medium

2019 ◽  
Author(s):  
E. Talygin ◽  
G. Kiknadze ◽  
A. Agafonov ◽  
A. Gorodkov
Keyword(s):  
Blood Flow ◽  
Velocity Field ◽  
Analytical Solution ◽  
Coordinate System ◽  
Biologically Active ◽  
Time Dependent ◽  
Characteristic Functions ◽  
Swirling Jet ◽  
Cylindrical Coordinate ◽  
Definition Of

Abstract In previous works it has been proved that the dynamic geometry of the streamlined surface of the flow channel of the heart chambers and main arteries corresponds with a good agreement to the shape of the swirling flow streamlines. The vectorial velocity field of such a flow in a cylindrical coordinate system was described by means of specific analytical solution basing on the potentiality of the longitudinal and radial velocity components. The viscosity of the medium was taken into account only in the expression for the azimuthal velocity component and the significant effect of viscosity was manifested only in a narrow axial region of a swirling jet. The flow described by the above relations is quasipotential, axisymmetric, and convergent. The structural organization of this flow implies the elimination of rupture and stagnation zones, and minimizes the viscous losses. The proximity of the real blood flow under the normal conditions to the specified class of swirling flows allows us to determine the basic properties of the blood flow possessing the high pressure-flow characteristics without stability loss. The blood flow has an external border, and the interaction with the channel wall and between moving fluid elements is weak. These properties of the jet explain the possibility of a balanced blood flow in biologically active boundaries. Violation of the jet properties can lead to the excitation of biologically active components and trigger the corresponding cascade protective and compensatory processes. The evolution of the flow is determined by the time-dependent characteristic functions, which are the frequency characteristics of the rotating jet, as well as functions depending on the dimension of the swirling jet. Previous experimental studies revealed close connection between changes in the characteristic functions and dynamics of the cardiac cycle. Therefore, it is natural to express these functions in analytical form. For these purposes it was necessary to establish the link between these functions and the spatial characteristics of the swirling jet. To solve this problem the analytical solution for the velocity field of a swirling jet was substituted into the Navier-Stokes system and continuity differential equations in a cylindrical coordinate system. As a result, a new system of differential equations was obtained where the characteristic functions could be derived. The solution of these equations allows the identification of time-dependent characteristic functions, and the establishment of a link between the characteristic functions and the spatial coordinates of the swirling jet. This link gives the opportunity to substantiate a theoretical possibility for the modeling of quasipotential viscous flows with a given structure. The definition of characteristic functions makes it possible to obtain the exact solution which allows formalization of the boundary conditions for physical modeling and experimental study of this flow type. Such transformations allow the definition of the conditions supporting renewable swirling blood flow in the transport arterial segment of the circulatory system and provide the basis for new principles of modeling, diagnosis and surgical treatment of circulatory disorders associated with the changes in geometry of the heart and great vessels.

Inverse source problem based on two dimensionless dispersion-current functions in 2D evolution transport equations

2016 ◽  
Vol 24 (6) ◽  
Author(s):  
Adel Hamdi ◽  
Imed Mahfoudhi
Keyword(s):  
Velocity Field ◽  
Point Source ◽  
Time Dependent ◽  
Inverse Source Problem ◽  
Two Dimensional ◽  
Reaction Equation ◽  
Advection Dispersion ◽  
Dispersion Tensor ◽  
Spatially Varying ◽  
Dependent Point

AbstractThe paper deals with the nonlinear inverse source problem of identifying an unknown time-dependent point source occurring in a two-dimensional evolution advection-dispersion-reaction equation with spatially varying velocity field and dispersion tensor. The

scholarly journals Exact solutions for the unsteady rotational flow of a generalized second grade fluid through a circular cylinder

2010 ◽  
Vol 15 (4) ◽  
pp. 437-444 ◽  
Author(s):  
M. Kamran ◽  
M. Imran ◽  
M. Athar
Keyword(s):  
Velocity Field ◽  
Circular Cylinder ◽  
Time Dependent ◽  
Second Grade ◽  
Rotational Flow ◽  
Second Grade Fluid ◽  
Special Cases ◽  
Grade Fluid ◽  
Generalized Second Grade Fluid ◽  
Similar Solutions

Here the velocity field and the associated tangential stress corresponding to the rotational flow of a generalized second grade fluid within an infinite circular cylinder are determined by means of the Laplace and finite Hankel transforms. At time t = 0 the fluid is at rest and the motion is produced by the rotation of the cylinder around its axis with a time dependent angular velocity Ωt. The solutions that have been obtained are presented under series form in terms of the generalized G-functions. The similar solutions for the ordinary second grade and Newtonian fluids, performing the same motion, are obtained as special cases of our general solution.

Investigation of POD Bases for Flow Control on Disk Wakes

2010 ◽  
Author(s):  
Zachary Berger ◽  
Rory Bigger ◽  
Makan Fardad ◽  
Hiroshi Higuchi ◽  
Mark N. Glauser ◽  
...  
Keyword(s):  
Velocity Field ◽  
Flow Control ◽  
Linear Time ◽  
Open Loop ◽  
Synthetic Jet ◽  
Time Dependent ◽  
Space Representation ◽  
Control Input ◽  
Time Resolved ◽  
Lti System

This work investigates the effects of flow control on the near wake region of a disk in a water flow, utilizing the POD reconstructed time dependent velocity fields. Velocity measurements were collected using time resolved particle image velocimetry (TRPIV) at a Reynolds number of 20,000 based on the disk diameter, both with and without control. An open-loop control was applied via periodic synthetic jet excitation from the disk edge. With the advantage of a time resolved velocity database, we have the ability to reconstruct the time dependent velocity field in the wake of the disk. This reconstruction is done for the baseline and controlled cases using various POD truncations to observe velocity reconstructions, based on the overall energy of the system. In doing so, we will consider the convergence rate of the spatial eigenvalues when conducting our POD reconstruction of the fluctuating velocity field, for both the baseline and controlled cases. Since a complex flow exists in the wake of the disk, the goal will be to form a state space representation of the flow in the form of a linear time invariant (LTI) system. This model is simply a linearization of the flow around the baseline. Furthermore, our knowledge of the input control signal will allow us to predict the flow at a later instant in time. We would like to extract the most energetic modes of the system and thereby form our observer-based controller to close the loop. In order to accomplish this, and with a rich open-loop dataset at our disposal, we will first form the POD reconstruction of the baseline. We then form a new basis, obtained by taking the actuated (controlled) data and subtracting from it the components of the flow that fall in the subspace spanned by the baseline flow. This will characterize the flow field by capturing the effect of the control input (actuation), from which the parameters of the LTI system can be identified. Preliminary POD reconstruction shows that 60% of the energy is recovered from 20 POD modes of the total 511 modes for the baseline case; similarly 60% of the energy is also recovered from 100 POD modes of the total 1,024 modes for the actuated case.

Transient Blade Load Determination in behind Ship Condition based on CFD

2015 ◽  
Author(s):  
Norbert Bulten
Keyword(s):  
Fatigue Strength ◽  
Velocity Field ◽  
Time Dependent ◽  
Propeller Blade ◽  
Inflow Velocity ◽  
Flow Simulations ◽  
Load Fluctuation ◽  
Propeller Performance ◽  
The Impact

With the aid of detailed numerical flow simulations it has become possible to determine the isolated propeller blade load during a revolution. The load fluctuation on a single propeller blade can be clearly related to the inflow velocity field. Once the time dependent load, and consequently the performance, of a single blade has been identified, knowledge can be obtained on possible overall improvement of the propeller performance. Also the impact on fatigue strength can be addressed in more detail. In this paper the propeller blade load fluctuations have been analyzed for a propeller in behind ship and in a tunnel, operating as bow thruster. The impact of the inflow to the propeller on the occurring loads will be shown. In case of tunnel thruster units, also possible actions to improve the inflow will be analyzed.

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