scholarly journals Formulae of Sediment Transport in Unsteady Flows (Part 2)

2020 ◽  
Author(s):  
Shu-Qing Yang
Keyword(s):  
Sediment Transport ◽  
Vertical Velocity ◽  
Reasonable Agreement ◽  
Unsteady Flows ◽  
Vertical Direction ◽  
Vertical Motion ◽  
Phase Lag ◽  
Streamwise Direction ◽  
Rouse Number ◽  
Almost All

Sediment transport (ST) in unsteady flows is a complex phenomenon that the existing formulae are often invalid to predict. Almost all existing ST formulae assume that sediment transport can be fully determined by parameters in streamwise direction without parameters in vertical direction. Different from this assumption, this paper highlights the importance of vertical motion and the vertical velocity is suggested to represent the vertical motion. A connection between unsteadiness and vertical velocity is established. New formulae in unsteady flows have been developed from inception of sediment motion, sediment discharge to suspension’s Rouse number. It is found that upward vertical velocity plays an important role for sediment transport, its temporal and spatial alternations are responsible for the phase lag phenomenon and bedform formation. Reasonable agreement between the measured and the proposed conceptual model was achieved.

scholarly journals Formulae of Sediment Transport in Steady Flows (Part 1)

2021 ◽  
Author(s):  
Shu-Qing Yang ◽  
Ishraq AL-Fadhly
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Vertical Velocity ◽  
Critical Shear Stress ◽  
Vertical Motion ◽  
Steady Flows ◽  
Leading Role ◽  
Natural Streams ◽  
Accelerating Flows ◽  
Shields Curve

This paper makes an attempt to answer why the observed critical shear stress for incipient sediment motion sometimes deviates from the Shields curve largely, and the influence of vertical velocity is analyzed as one of the reasons. The data with d50 = 0.016 ∼ 29.1 mm from natural streams and laboratory channels were analyzed. These measured data do not always agree with the Shields diagram’s prediction. The reasons responsible for the deviation have been re-examined and it is found that, among many factors, the vertical motion of sediment particles plays a leading role for the invalidity of Shield’s prediction. The positive/negative deviations are associated with the up/downward vertical velocity in decelerating/accelerating flows, and the Shields diagram is valid only when flow is uniform. A new theory for critical shear stress has been developed, a unified critical Shields stress for sediment transport has been established, which is valid to predict the critical shear stress of sediment with/without vertical motion.

scholarly journals Vertical Structure of Spiral Shocks in a Corrugated Galactic Disc

1983 ◽  
Vol 100 ◽  
pp. 145-146
Author(s):  
A. H. Nelson ◽  
T. Matsuda ◽  
T. Johns
Keyword(s):  
Density Profile ◽  
Vertical Velocity ◽  
Gas Flow ◽  
Vertical Structure ◽  
Vertical Motion ◽  
Shock Structure ◽  
Galactic Disc ◽  
Gaussian Density ◽  
Abundant Evidence ◽  
Steady Shock

Numerical calculations of spiral shocks in the gas discs of galaxies (1,2,3) usually assume that the disc is flat, i.e. the gas motion is purely horizontal. However there is abundant evidence that the discs of galaxies are warped and corrugated (4,5,6) and it is therefore of interest to consider the effect of the consequent vertical motion on the structure of spiral shocks. If one uses the tightly wound spiral approximation to calculate the gas flow in a vertical cut around a circular orbit (i.e the ⊝ -z plane, see Nelson & Matsuda (7) for details), then for a gas disc with Gaussian density profile in the z-direction and initially zero vertical velocity a doubly periodic spiral potential modulation produces the steady shock structure shown in Fig. 1. The shock structure is independent of z, and only a very small vertical motion appears with anti-symmetry about the mid-plane.

Combination Resonance of a Magnet Over a High-TC Superconductor Excited Vertically

2001 ◽  
Author(s):  
Toshihiko Sugiura ◽  
Masayuki Kondo
Keyword(s):  
Magnetic Force ◽  
Vertical Direction ◽  
Vertical Motion ◽  
Mirror Image ◽  
Image Method ◽  
Combination Resonance ◽  
Nonlinear Functions ◽  
High Tc ◽  
High Tc Superconductor ◽  
Oscillation Modes

Abstract This research deals with nonlinear dynamics of a permanent magnet freely levitated above a high-Tc superconductor (HTSC) excited in the vertical direction. Magnetic force and torque can be evaluated analytically by the advanced mirror image method as nonlinear functions of both displacement and roll angle of the magnet. Equations of 3 d.o.f. motion show that the magnet has two oscillation modes due to linear coupling of the horizontal and roll motions. The both modes can be excited by nonlinear coupling with vertical motion when the superconductor is exited vertically in the neighborhood of the sum of the natural frequency of each mode. Frequency response of this combination resonance was numerically simulated. This resonance was also observed in experiments.

scholarly journals The boundary condition for the vertical velocity and its interdependence with surface gas exchange

2017 ◽  
Author(s):  
Andrew S. Kowalski
Keyword(s):  
Boundary Condition ◽  
Vertical Velocity ◽  
Molecular Diffusion ◽  
Classical Mechanics ◽  
Vertical Motion ◽  
Diffusive Transport ◽  
Eddy Diffusivities ◽  
Air Stream ◽  
Upward Transport ◽  
Definition Of

Abstract. The law of conservation of linear momentum is applied to surface gas exchanges, employing scale analysis to diagnose the vertical velocity (w) in the boundary layer. Net upward momentum in the surface layer is forced by evaporation (E) and defines non-zero vertical motion, with a magnitude defined by the ratio of E to the air density, as w = E⁄ρ. This is true even right down at the surface where the boundary condition is w0 = E⁄ρ0. This Stefan flow velocity implies upward transport of a non-diffusive nature that is a general feature of the troposphere but is of particular importance at the surface, where it assists molecular diffusion with upward gas migration (of H2O, e.g.) but opposes that of downward-diffusing species like CO2 during daytime. The definition of flux-gradient relationships (eddy diffusivities) requires rectification to exclude non-diffusive transport, which does not depend on scalar gradients. At the microscopic scale, the role of non-diffusive transport in the process of evaporation from inside a narrow tube – with vapour transport into an overlying, horizontal air stream – was described long ago in classical mechanics, and is routinely accounted for by chemical engineers, but has been neglected by scientists studying stomatal conductance. Correctly accounting for non-diffusive transport through stomata, which can appreciably reduce net CO2 transport and marginally boost that of water vapour, should improve characterizations of ecosystem and plant functioning.

scholarly journals Characteristic nature of vertical motions observed in Arctic mixed-phase stratocumulus

2013 ◽  
Vol 13 (11) ◽  
pp. 31079-31125 ◽  
Author(s):  
J. Sedlar ◽  
M. D. Shupe
Keyword(s):  
Vertical Velocity ◽  
Vertical Mixing ◽  
Vertical Motion ◽  
Temperature Inversion ◽  
Arctic Sea Ice ◽  
Cloud Layer ◽  
Mixed Phase ◽  
The Arctic ◽  
Cloud Base ◽  
Mixed Phase Clouds

Abstract. Over the Arctic Ocean, little is known, observationally, on cloud-generated buoyant overturning vertical motions within mixed-phase stratocumulus clouds. Characteristics of such motions are important for understanding the diabatic processes associated with the vertical motions, the lifetime of the cloud layer and its micro- and macrophysical characteristics. In this study, we exploit a suite of surface-based remote sensors over the high Arctic sea ice during a week-long period of persistent stratocumulus in August 2008 to derive the in-cloud vertical motion characteristics. In-cloud vertical velocity skewness and variance profiles are found to be strikingly different from observations within lower-latiatude stratocumulus, suggesting these Arctic mixed-phase clouds interact differently with the atmospheric thermodynamics (cloud tops extending above a stable temperature inversion base) and with a different coupling state between surface and cloud. We find evidence of cloud-generated vertical mixing below cloud base, regardless of surface-cloud coupling state, although a decoupled surface-cloud state occurred most frequently. Detailed case studies are examined focusing on 3 levels within the cloud layer, where wavelet and power spectral analyses are applied to characterize the dominant temporal and horizontal scales associated with cloud-generated vertical motions. In general, we find a positively-correlated vertical motion signal across the full cloud layer depth. The coherency is dependent upon other non-cloud controlled factors, such as larger, mesoscale weather passages and radiative shielding of low-level stratocumulus by multiple cloud layers above. Despite the coherency in vertical velocity across the cloud, the velocity variances were always weaker near cloud top, relative to cloud mid and base. Taken in combination with the skewness, variance and thermodynamic profile characteristics, we observe vertical motions near cloud-top that behave differently than those from lower within the cloud layer. Spectral analysis indicates peak cloud-generated w variance timescales slowed only modestly during decoupled cases relative to coupled; horizontal wavelengths only slightly increased when transitioning from coupling to decoupling. The similarities in scales suggests that perhaps the dominant forcing for all cases is generated from the cloud layer, and it is not the surface forcing that characterizes the time and space scales of in-cloud vertical velocity variance. This points toward the resilient nature of Arctic mixed-phase clouds to persist when characterized by thermodynamic regimes unique to the Arctic.

scholarly journals SHEETFLOW SEDIMENT TRANSPORT UNDER SKEWED - ASYMMETRIC WAVES AND CURRENTS

2012 ◽  
Vol 1 (33) ◽  
pp. 50 ◽  
Author(s):  
Le Phuong Dong ◽  
Shinji Sato
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Fine Sand ◽  
Sand Transport ◽  
Phase Lag ◽  
Half Cycle ◽  
Experimental Conditions ◽  
Wide Range ◽  
Waves And Currents ◽  
Asymmetric Flows

Prototype scale laboratory experiments have been conducted to investigate the sheetflow sediment transport of uniform sands under different skewed-asymmetric oscillatory flows. Experimental results reveal that in most of the case with fine sand, the “cancelling effect”, which balances the on-/off-shore net transport under pure asymmetric/skewed flows and results a moderate net transport, was developed for combined skewed-asymmetric flow. However, under some certain conditions (T > 5s) with coarse sands, the onshore sediment transport was enhanced by 50% under combined skewed-asymmetric flows. Sand transport mechanism under oscillatory sheetflow conditions is also studied by comparing the maximum bed shear stress and the phase lag parameter at each half cycle. A comparison of measurements including the new experimental data with a number of practical sand transport formulations shows that the Dong et al. (2013) formulation performs the best in predicting the measured net transport rates over a wide range of experimental conditions

Comparison of Hydraulic Fracture Models for Highly Elongated Fractures of Variable Height

1986 ◽  
Vol 108 (2) ◽  
pp. 107-115 ◽  
Author(s):  
I. D. Palmer ◽  
C. T. Luiskutty
Keyword(s):  
Fluid Flow ◽  
Hydraulic Fracture ◽  
Reasonable Agreement ◽  
High Stress ◽  
Vertical Direction ◽  
Critical Examination ◽  
Wellbore Pressure ◽  
Fracture Models ◽  
Fracture Height ◽  
Stress Contrast

There is a pressing need to compare and evaluate hydraulic fracture models which are now being used by industry to predict variable fracture height. The fractures of concern here are vertical fractures which have a pronounced elongation in the direction of the payzone, i.e., there is a dominant one-dimensional fluid flow along the payzone direction. A summary is given of the modeling entailed in the basic ORU fracture model, which calculates fracture height as a function of distance from the wellbore in the case of a continuous sand bounded by zones of higher (but equal) minimum in-situ stress. The elastic parameters are assumed the same in each layer, and injected flow rates and fluid parameters are taken to be constant. Leak-off is included with spurt loss, as well as non-Newtonian flow. An advantage of the model is its small computer run time. Predictions for wellbore height and pressure from the ORU model are compared separately with the AMOCO and MIT pseudo-3D models. In one instance of high stress contrast the ORU wellbore pressure agrees fairly well with the AMOCO model, but the AMOCO wellbore height is greater by 32 percent. Comparison between the ORU and MIT models in two cases (also high stress contrast) indicates height disagreement at the wellbore by factors of 1.5–2.5 with the MIT model giving a lower height. Thus it appears there can be substantial discrepancies between all three models. Next we compare the ORU model results with six cases of elongated fractures from the TERRA-TEK fully-3D model. Although two of these cases are precluded due to anomolous discrepancies, the other four cases show reasonable agreement. We make a critical examination of assumptions that differ in all the models (e.g., the effective modulus-stiffness multiplier approximation in the AMOCO model, the effect of finite fluid flow in the vertical direction in the MIT model, and the effect of 2D flow and limited perforated height in the TERRA-TEK model). Suggestions are made for reconciling some of the discrepancies between the various models. For example, the ORU/AMOCO height discrepancy appears to be resolved; for other discrepancies we have no explanation. Our main conclusion is that the AMOCO, TERRA-TEK and ORU models for fracture height and bottomhole pressure are in reasonable agreement for highly elongated fractures. Despite the difficulties in understanding the different models, the comparisons herein are an encouraging first step towards normalizing these hydraulic fracture models.

Effect of different connection modes of electromagnets on the performance of levitation control

2018 ◽  
Vol 232 (8) ◽  
pp. 2111-2125 ◽  
Author(s):  
Zhang Min ◽  
Gao Chang ◽  
MA Weihua
Keyword(s):  
Vertical Direction ◽  
Vertical Motion ◽  
Vertical Displacement ◽  
Control Mode ◽  
Adjustment Process ◽  
Dynamic Adjustment ◽  
Series Connection ◽  
Relative Safety ◽  
The Mean ◽  
Mean Current

In medium- and low-speed maglev vehicles, each levitation module contains four electromagnetic coils. In order to find a better coil control mode, the difference between the series connection in the control mode of the first and third coils (M1,3) and the series connection in the control mode of the first and second coils (M1,2) was analysed in this paper. By applying a malposition excitation of +2 mm in the vertical direction of the track for comparing the dynamic adjustment processes of the levitation module (including the vertical motion and rotation) in the two control modes, according to the current fluctuation in the coils in the above processes, the extreme position parameters and the mean current values during the adjustment were obtained. The adjustment process was analysed based on the instantaneous levitation force and the torque of the plate at the extreme positions in different control modes; the performance of the levitation module in the adjustment process and during the fluctuation of the coil current was analysed. The results indicate that for the dangerous ends at the two extreme positions in the selected working condition, the vertical displacement in M1,3 reduces by 11.11 and 48.98%, respectively, compared with that in M1,2. In the whole adjustment process, the mean current of the front and rear controllers in M1,3 reduces by 0.25 and 0.36 A, respectively. Therefore, it has been concluded that with regard to the relative safety and coil heating during vibration of the levitation module, M1,3 performs better than M1,2.

Fast AFM Scanning With Parameter Space Based Robust Repetitive Control Designed Using the COMES Toolbox

2010 ◽  
Author(s):  
Serkan Necipog˘lu ◽  
Burak Demirel ◽  
Levent Gu¨venc¸
Keyword(s):  
Surface Topography ◽  
Repetitive Control ◽  
Vertical Motion ◽  
Research Area ◽  
Dynamic Responses ◽  
Phase Lag ◽  
Atomic Force ◽  
Control Scheme ◽  
Periodic Input ◽  
Scan Speed

Atomic Force Microscope (AFM) is a very strong and beneficial instrument for acquiring images at nanometer scale. Hence, obtaining better image quality and scan speed is a research area of great interest. Improving the dynamic responses of the scanning probe and the vertical motion of the scanner mechanisms are the two major areas of concentration in this sense. Improving the vertical dynamics is achieved either by designing more complex scanner mechanisms with higher bandwidth or designing more sophisticated controllers rather than the PI, PID or PIID types of controllers that are mostly used in practice. In this paper, the authors focus on designing a repetitive control scheme for fast and accurate scanning. It is possible to implement repetitive control to achieve this goal when it is considered that the successive lines of the scan are quite similar due to the very small steps taken to advance on the sample. Repetitive control can reject higher frequency disturbances due to the surface topography in AFM much better than a conventional controller can, as it can drive the error caused by any periodic input signal to zero. Besides increasing the scan speed, it is also important that the phase lag can be compensated perfectly using repetitive control, with the knowledge of the surface topography from the previous period by introducing appropriate phase advance.

Turbulence Measurements from Compliant Moorings. Part I: Motion Characterization

2017 ◽  
Vol 34 (6) ◽  
pp. 1235-1247 ◽  
Author(s):  
Samuel Harding ◽  
Levi Kilcher ◽  
Jim Thomson
Keyword(s):  
Vertical Direction ◽  
Vertical Motion ◽  
Inertial Subrange ◽  
Motion Sensors ◽  
Similar Frequency ◽  
Dynamic Motion ◽  
Flow Speeds ◽  
Motion Characterization ◽  
Motion Characteristics ◽  
Vessel Motion

AbstractHigh-fidelity measurements of turbulence in the ocean have long been challenging to collect, in particular in the middle of the water column. In response, a measurement technique has been developed to deploy an acoustic Doppler velocimeter (ADV) to midwater locations on a compliant mooring. A variety of instrumentation platforms have been deployed as part of this work with a range of dynamic motion characteristics. The platforms discussed herein include the streamlined StableMoor buoy (SMB), the Tidal Turbulence Mooring (TTM) system based on a conventional 0.9-m spherical buoy, and a 100-lb sounding weight suspended from the stern of a research vessel. The ADV head motion is computed from inertial motion sensors integrated into an ADV, and the spectra of these signals are investigated to quantify the motion of each platform. The SMB with a single ADV head mounted on the nose provided the most stable platform for the measurement of tidal turbulence in the inertial subrange for flow speeds exceeding 1.0 m s−1. The modification of the SMB with a transverse wing configuration for multiple ADVs showed a similar frequency response to the nose configuration in the horizontal plane but with large contamination in the vertical direction as a result of platform roll. While the ADV motion on the TTM was significant in the horizontal directions, the vertical motion of this configuration was the most stable of all configurations tested. The sounding weight measurements showed the greatest motion at the ADV head but are likely to be influenced by both prop-wash and vessel motion.

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