Deriving formulas for an unsteady virtual velocity of bedload tracers

2018 ◽  
Vol 43 (7) ◽  
pp. 1529-1541 ◽  
Author(s):  
Mario Klösch ◽  
Helmut Habersack
Keyword(s):  
Virtual Velocity

scholarly journals Bedload transport in a steep alpine stream: Assessment of sediment mobility and virtual velocity using the bedload tracking

2018 ◽  
Vol 40 ◽  
pp. 02027
Author(s):  
Riccardo Rainato ◽  
Lorenzo Picco ◽  
Daniele Oss Cazzador ◽  
Luca Mao
Keyword(s):  
Field Studies ◽  
Bedload Transport ◽  
Monitoring Methods ◽  
Fluvial Systems ◽  
Passive Integrated Transponders ◽  
Average Recovery Rate ◽  
Sediment Mobility ◽  
Alpine Stream ◽  
Virtual Velocity ◽  
Term Field

The bedload transport is challenging to analyze in field, consequently, several assumptions about it were made basing on laboratory researches or on short-term field studies. During the last decades several monitoring methods were developed to assess the bedload transport in the fluvial systems. The aim of this work is to investigate the transport of the coarse sediment material in a steep alpine stream, using the bedload tracking. The Rio Cordon is a typical alpine channel, located in the northeast of Italy. It is characterized by a rough streambed with a prevalent boulder-cascade and step pool morphology. Since 2011, 250 clasts equipped with Passive Integrated Transponders (PIT) were installed in the main channel, to analyze their mobility along a reach 320 m long. From November 2012 to August 2015, the transport induced by a range of hydraulic forcing between 0.44 m3 s-1 and 2.10 m3 s-1 was assessed by 10 PIT-surveys. First, the mobility expressed by the tracers was analyzed, observing marked differences in terms of travel distance. Then, the average recovery rate achieved during the tracer inventories (Rr > 70%) permitted to define the threshold discharge for each grain size class analyzed and, then, to assess the virtual velocity experienced by the tracers.

Peirce, Virtuality, and Semiotic

1998 ◽  
pp. 47-52 ◽  
Author(s):  
Peter Skagestad
Keyword(s):  
Common Noun ◽  
Philosophical Framework ◽  
Charles Peirce ◽  
Human Intellect ◽  
Virtual Velocity

The adjective 'virtual,' practically unheard-of a few years ago, has become a primary buzzword of the 90's. Yet the word 'virtual' is nothing new, although its ubiquity is new, as is perhaps its current meaning or meanings. In 1902 the word was defined by Charles Peirce as follows: 'A virtual X (where X is a common noun) is something, not an X, which has the deficiency (virtus) of an X.' Peirce also references Scotus's concept of virtual knowledge, the concept of virtual velocity in physics, and Edmund Burke's doctrine of virtual representation, which is not representation but is supposedly as good as. The concept of virtuality is deeply embedded in Peirce's doctrine of signs and hence in his semiotic doctrine of mind. In this Peircean doctrine, which has been more recently echoed in the writings of Wittgenstein and Popper, we find the most promising philosophical framework available for the understanding and advancement of the project of augmenting human intellect through the development and use of virtual technologies.

scholarly journals A Walking-in-Place Method for Virtual Reality Using Position and Orientation Tracking

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 2832 ◽  
Author(s):  
Juyoung Lee ◽  
Sang Chul Ahn ◽  
Jae-In Hwang
Keyword(s):  
Virtual Reality ◽  
Inertial Measurement Unit ◽  
Recognition Rate ◽  
Head Tilt ◽  
The Body ◽  
Measurement Unit ◽  
Position And Orientation ◽  
Intentional Motion ◽  
Navigation Method ◽  
Virtual Velocity

People are interested in traveling in an infinite virtual environment, but no standard navigation method exists yet in Virtual Reality (VR). The Walking-In-Place (WIP) technique is a navigation method that simulates movement to enable immersive travel with less simulator sickness in VR. However, attaching the sensor to the body is troublesome. A previously introduced method that performed WIP using an Inertial Measurement Unit (IMU) helped address this problem. That method does not require placement of additional sensors on the body. That study proved, through evaluation, the acceptable performance of WIP. However, this method has limitations, including a high step-recognition rate when the user does various body motions within the tracking area. Previous works also did not evaluate WIP step recognition accuracy. In this paper, we propose a novel WIP method using position and orientation tracking, which are provided in the most PC-based VR HMDs. Our method also does not require additional sensors on the body and is more stable than the IMU-based method for non-WIP motions. We evaluated our method with nine subjects and found that the WIP step accuracy was 99.32% regardless of head tilt, and the error rate was 0% for squat motion, which is a motion prone to error. We distinguish jog-in-place as “intentional motion” and others as “unintentional motion”. This shows that our method correctly recognizes only jog-in-place. We also apply the saw-tooth function virtual velocity to our method in a mathematical way. Natural navigation is possible when the virtual velocity approach is applied to the WIP method. Our method is useful for various applications which requires jogging.

Topological vortex dynamics in axisymmetric viscous flows

1994 ◽  
Vol 260 ◽  
pp. 57-80 ◽  
Author(s):  
Mogens V. Melander ◽  
Fazle Hussain
Keyword(s):  
Phase Portrait ◽  
Critical Points ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Saddle Points ◽  
Time History ◽  
Vorticity Field ◽  
Vortex Lines ◽  
Short Period ◽  
Virtual Velocity

The topology of vortex lines and surfaces is examined in incompressible viscous axisymmetric flows with swirl. We argue that the evolving topology of the vorticity field must be examined in terms of axisymmetric vortex surfaces rather than lines, because only the surfaces enjoy structural stability. The meridional cross-sections of these surfaces are the orbits of a dynamical system with the azimuthal circulation being a Hamiltonian H and with time as a bifurcation parameter μ. The dependence of H on μ is governed by the Navier–Stokes equations; their numerical solutions provide H. The level curves of H establish a time history for the motion of vortex surfaces, so that the circulation they contain remains constant. Equivalently, there exists a virtual velocity field in which the motion of the vortex surfaces is frozen almost everywhere; the exceptions occur at critical points in the phase portrait where the virtual velocity is singular. The separatrices emerging from saddle points partition the phase portrait into islands; each island corresponds to a structurally stable vortex structure. By using the flux of the meridional vorticity field, we obtain a precise definition of reconnection: the transfer of flux between islands. Local analysis near critical points shows that the virtual velocity (because of its singular behaviour) performs ‘cut-and-connect’ of vortex surfaces with the correct rate of circulation transfer - thereby validating the long-standing viscous ‘cut-and-connect’ scenario which implicitly assumes that vortex surfaces (and vortex lines) can be followed over a short period of time in a viscous fluid. Bifurcations in the phase portrait represent (contrary to reconnection) changes in the topology of the vorticity field, where islands spontaneously appear or disappear. Often such topology changes are catastrophic, because islands emerge or perish with finite circulation. These and other phenomena are illustrated by direct numerical simulations of vortex rings at a Reynolds number of 800.

Comparing Study on Real Drawbead and Equivalent Drawbead Based on Finite Element Analysis

2012 ◽  
Vol 430-432 ◽  
pp. 1056-1059
Author(s):  
Xiao Gang Qiu ◽  
Hao Huang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Deformation Behavior ◽  
Fe Simulation ◽  
Element Analysis ◽  
Explicit Finite Element ◽  
The Real ◽  
Finite Element Software ◽  
Simulation Results ◽  
Virtual Velocity

The dynamic explicit finite element software DYNAFORM was used to simulate the real and equivalent drawbead model. Analyzed the influence of the blank hold force (BHF) and virtual velocity on blank’s deformation behavior after passing through drawbead, compared the results of the FE simulation. The simulation results were confirmed by experiments. The study shows that the equivalent drawbead model can’t simulate the blank’s behavior precisely when it passing the real drawbeads, the effect of BHF on real drawbead model is larger than equal drawbead model; the proper range of virtual velocity was obtained at the same time.

Virtual velocity: Connecting the concepts of Kinematics and Virtual Work

2013 ◽  
Vol 56 ◽  
pp. 2249-2252
Author(s):  
Santiago Pujol ◽  
Madeline D. Nelson ◽  
J. Paul Smith-Pardo
Keyword(s):  
Virtual Work ◽  
Virtual Velocity

Lagrangian Expressions of the Hydrodynamic Forces Acting on a Rigid Body in the Presence of a Free Surface

1985 ◽  
Vol 29 (01) ◽  
pp. 12-22
Author(s):  
G. A. Athanassoulis ◽  
T. A. Loukakis
Keyword(s):  
Free Surface ◽  
Rigid Body ◽  
Hydrodynamic Pressure ◽  
Hydrodynamic Forces ◽  
Ship Motions ◽  
Analytical Dynamics ◽  
Motion Equations ◽  
Hydromechanical System ◽  
Complete Set ◽  
Virtual Velocity

The formalism of classical analytical dynamics is used in conjunction with the principle of virtual velocity to derive Lagrangian expressions for the hydrodynamic forces acting on a rigid body moving through an in-viscid and incompressible liquid with a free surface. Simultaneously, a corresponding Lagrangian expression is derived for the hydrodynamic pressure acting on the free surface itself. The expressions for the hydrodynamic forces degenerate to the classical ones if the free surface is not present, and the expression for the pressure is reduced to that obtained by Milder if the rigid boundaries are all kept fixed. The derived Lagrangian expressions for the hydrodynamic reactions are used to obtain a complete set of motion equations for the examined hydromechanical system, and to discuss another Lagrangian approach to the ship-motions problem, presented by Wang.

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