scholarly journals CURRENT CHARACTERISTICS IN THE PRESENCE OF NEAR-ORTHOGONAL WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 41
Author(s):  
Kian Yew Lim ◽  
Ole Secher Madsen ◽  
Hin Fatt Cheong
Keyword(s):  
Profile Analysis ◽  
Numerical Study ◽  
Flow Profile ◽  
Wave Direction ◽  
Mean Flow ◽  
Wave Basin ◽  
Current Interaction ◽  
The Mean ◽  
Current Flows ◽  
Wave Induced

An experimental study involving near-orthogonal wave-current interaction in a wave basin is reported in this paper. Due to previous shortcomings associated with 2D bottom configurations, i.e. occurrence of ripple-induced turning of flows close to the bed, the present experiments were conducted with the bottom covered by closely packed ceramic marbles (mean diameter of 1.25cm). Three types of flows were generated over this bottom: current-alone, wave-alone and combined wave-current flow. For current-alone and wave-current cases, the log-profile analysis was used to resolve the equivalent Nikuradse sand grain roughness, kn, while the energy dissipation method was used to estimate kn for wave-alone case. The results show that kn obtained for current- and wave-alone tests is roughly 2.2 times the diameter of the marbles. For orthogonal wave-current flows, the kn value, when used in combination with the Grant-Madsen (GM) model to reproduce the experimental apparent roughness, is found to be smaller than the measured current-alone and wave-alone kn. Similar under-prediction of bottom roughness is also observed when the GM model is compared with a numerical study, thus supporting the conjecture that when the current is weak compared to the waves, simple theoretical models like GM are not sufficiently sensitive to the angle of wave-current interaction. Experiments with currents at angles of 60° and 120° to the wave direction yield apparent roughness smaller than the 90° case, which is counter-intuitive since one would expect the mean flow to experience a stronger wave-induced turbulence when it is more aligned with the wave direction. This result indicates a possible contamination from wave-induced mass transport to the mean flow profile for non-orthogonal combined flow cases, and therefore highlights the need for other alternatives to the log-profile analysis when attempting to resolve kn from current velocity profiles from combined wave-current flows.

scholarly journals Generation of Reverse Meniscus Flow by Applying An Electromagnetic Brake

2021 ◽  
Author(s):  
Alexander Vakhrushev ◽  
Abdellah Kharicha ◽  
Ebrahim Karimi-Sibaki ◽  
Menghuai Wu ◽  
Andreas Ludwig ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Lorentz Force ◽  
Applied Magnetic Field ◽  
Numerical Study ◽  
Flow Direction ◽  
Experimental Studies ◽  
Submerged Entry Nozzle ◽  
Mean Flow ◽  
Slab Caster ◽  
The Mean

AbstractA numerical study is presented that deals with the flow in the mold of a continuous slab caster under the influence of a DC magnetic field (electromagnetic brakes (EMBrs)). The arrangement and geometry investigated here is based on a series of previous experimental studies carried out at the mini-LIMMCAST facility at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The magnetic field models a ruler-type EMBr and is installed in the region of the ports of the submerged entry nozzle (SEN). The current article considers magnet field strengths up to 441 mT, corresponding to a Hartmann number of about 600, and takes the electrical conductivity of the solidified shell into account. The numerical model of the turbulent flow under the applied magnetic field is implemented using the open-source CFD package OpenFOAM®. Our numerical results reveal that a growing magnitude of the applied magnetic field may cause a reversal of the flow direction at the meniscus surface, which is related the formation of a “multiroll” flow pattern in the mold. This phenomenon can be explained as a classical magnetohydrodynamics (MHD) effect: (1) the closure of the induced electric current results not primarily in a braking Lorentz force inside the jet but in an acceleration in regions of previously weak velocities, which initiates the formation of an opposite vortex (OV) close to the mean jet; (2) this vortex develops in size at the expense of the main vortex until it reaches the meniscus surface, where it becomes clearly visible. We also show that an acceleration of the meniscus flow must be expected when the applied magnetic field is smaller than a critical value. This acceleration is due to the transfer of kinetic energy from smaller turbulent structures into the mean flow. A further increase in the EMBr intensity leads to the expected damping of the mean flow and, consequently, to a reduction in the size of the upper roll. These investigations show that the Lorentz force cannot be reduced to a simple damping effect; depending on the field strength, its action is found to be topologically complex.

scholarly journals A numerical study on the impact of nonlinear interactions on the amplitude of the migrating semidiurnal tide

2006 ◽  
Vol 24 (12) ◽  
pp. 3241-3256 ◽  
Author(s):  
C. M. Huang ◽  
S. D. Zhang ◽  
F. Yi
Keyword(s):  
Numerical Study ◽  
Steady Solution ◽  
Nonlinear Interactions ◽  
Semidiurnal Tide ◽  
Mean Flow ◽  
Structure Variation ◽  
Amplitude Difference ◽  
The Mean ◽  
The Impact ◽  
Mlt Region

Abstract. To quantitatively study the effects of nonlinear interactions on tide structure, a nonlinear numerical tidal model is developed, and the reliability and convergence of the adopted algorithm and coding are checked by numerical experiments. Under the same conditions as those employed by the GSWM-00 (Global Scale Wave Model 2000), our model provides the nonlinear quasi-steady solution of the migrating semidiurnal tide, which differs from the GSWM-00 result (the linear steady solution) in the MLT region, especially above 100 km. Additionally, their amplitude difference displays a remarkable month-to-month variation, and its significant magnitudes occur during the month with strong semidiurnal tide. A quantitative analysis suggests that the main cause for the amplitude difference is that the initial migrating 12-h tide will interact with the mean flow as well as the nonlinearity-excited 6-h tide, and subsequently yield a new 12-h tidal part. Furthermore, our simulations also show that the mean flow/tidal interaction will significantly alter the background wind and temperature fields. The large magnitudes of the tidal amplitude difference and the background alteration indicate that the nonlinear processes involved in tidal propagations should be comprehensively considered in the description of global atmospheric dynamics in the MLT region. The comparisons among our simulations, the GSWMs and some observations of tides suggest that the nonlinearity-induced tidal structure variation could be a possible mechanism to account for some discrepancies between the GSWMs and the observations.

On the stability of an inviscid shear layer which is periodic in space and time

1967 ◽  
Vol 27 (4) ◽  
pp. 657-689 ◽  
Author(s):  
R. E. Kelly
Keyword(s):  
Growth Rate ◽  
Shear Layer ◽  
Finite Amplitude ◽  
Periodic Component ◽  
Periodic Flow ◽  
Flow Profile ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
The Stability

In experiments concerning the instability of free shear layers, oscillations have been observed in the downstream flow which have a frequency exactly half that of the dominant oscillation closer to the origin of the layer. The present analysis indicates that the phenomenon is due to a secondary instability associated with the nearly periodic flow which arises from the finite-amplitude growth of the fundamental disturbance.At first, however, the stability of inviscid shear flows, consisting of a non-zero mean component, together with a component periodic in the direction of flow and with time, is investigated fairly generally. It is found that the periodic component can serve as a means by which waves with twice the wavelength of the periodic component can be reinforced. The dependence of the growth rate of the subharmonic wave upon the amplitude of the periodic component is found for the case when the mean flow profile is of the hyperbolic-tangent type. In order that the subharmonic growth rate may exceed that of the most unstable disturbance associated with the mean flow, the amplitude of the streamwise component of the periodic flow is required to be about 12 % of the mean velocity difference across the shear layer. This represents order-of-magnitude agreement with experiment.Other possibilities of interaction between disturbances and the periodic flow are discussed, and the concluding section contains a discussion of the interactions on the basis of the energy equation.

Wave-induced mean flows in rotating shallow water with uniform potential vorticity

2018 ◽  
Vol 839 ◽  
pp. 408-429 ◽  
Author(s):  
Jim Thomas ◽  
Oliver Bühler ◽  
K. Shafer Smith
Keyword(s):  
Shallow Water ◽  
Potential Vorticity ◽  
Rotation Rate ◽  
Standing Waves ◽  
Leading Order ◽  
Mean Flow ◽  
Wave Fields ◽  
The Mean ◽  
Rotating Shallow Water ◽  
Wave Induced

Theoretical and numerical computations of the wave-induced mean flow in rotating shallow water with uniform potential vorticity are presented, with an eye towards applications in small-scale oceanography where potential-vorticity anomalies are often weak compared to the waves. The asymptotic computations are based on small-amplitude expansions and time averaging over the fast wave scale to define the mean flow. Importantly, we do not assume that the mean flow is balanced, i.e. we compute the full mean-flow response at leading order. Particular attention is paid to the concept of modified diagnostic relations, which link the leading-order Lagrangian-mean velocity field to certain wave properties known from the linear solution. Both steady and unsteady wave fields are considered, with specific examples that include propagating wavepackets and monochromatic standing waves. Very good agreement between the theoretical predictions and direct numerical simulations of the nonlinear system is demonstrated. In particular, we extend previous studies by considering the impact of unsteady wave fields on the mean flow, and by considering the total kinetic energy of the mean flow as a function of the rotation rate. Notably, monochromatic standing waves provide an explicit counterexample to the often observed tendency of the mean flow to decrease monotonically with the background rotation rate.

Numerical Study on Seakeeping Performance of a Damaged Ship

2019 ◽  
Author(s):  
Lu-Ning Cui ◽  
Yi Zheng ◽  
Yinggang Li ◽  
Ling Zhu ◽  
Mingsheng Chen
Keyword(s):  
Numerical Study ◽  
Rolling Motion ◽  
Wave Direction ◽  
Regular Waves ◽  
Motion Responses ◽  
Seakeeping Performance ◽  
Property Losses ◽  
Hull Damage ◽  
Wave Induced ◽  
Damaged Ship

Abstract Ships sailing in the sea may encounter collision, grounding or projectile impacting accidents, which may cause hull damage and subsequent compartment flooding. Due to the effect of the flooding water induced moment and the restoring moment, the damaged ship may have inclination and rolling motion. When the inclination or the rolling motion is too large, it may affect the safety and survivability of ship in navigation and cause severe casualties and property losses. In order to increase the navigation safety and survivability of the damaged ship, a numerical model is established based on the potential flow theory to investigate the seakeeping performance of the damaged ship in two scenarios, i.e., the case before ship damaged, and the case when the damaged ship reaching a relatively stable floating state. The heave, pitch and roll motion responses and corresponding wave-induced loads acting on the ship are analyzed in regular waves. In addition, the effects of the navigation speed and the wave direction on the seakeeping performance are also investigated.

scholarly journals Incidence and reflection of internal waves and wave-induced currents at a jump in buoyancy frequency

2014 ◽  
Vol 1 (1) ◽  
pp. 269-315
Author(s):  
J. P. McHugh
Keyword(s):  
Wave Packet ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Transmitted Waves ◽  
The Mean ◽  
Induced Currents ◽  
Wave Induced ◽  
The Waves

Abstract. Weakly nonlinear internal gravity waves are treated in a two-layer fluid with a set of nonlinear Schrodinger equations. The layers have a sharp interface with a jump in buoyance frequency approximately modelling the tropopause. The waves are periodic in the horizontal but modulated in the vertical and Boussinesq flow is assumed. The equation governing the incident wave packet is directly coupled to the equation for the reflected packet, while the equation governing transmitted waves is only coupled at the interface. Solutions are obtained numerically. The results indicate that the waves create a mean flow that is strong near and underneath the interface, and discontinuous at the interface. Furthermore, the mean flow has an oscillatory component with a vertical wavelength that decreases as the wave packet interacts with the interface.

scholarly journals THEORETICAL AND NUMERICAL STUDY OF WAVE-CURRENT INTERACTION IN STRONGLY-SHEARED FLOWS

2012 ◽  
Vol 1 (33) ◽  
pp. 2 ◽  
Author(s):  
Zhifei Dong ◽  
James T. Kirby
Keyword(s):  
Ocean Circulation ◽  
Numerical Study ◽  
Vertical Shear ◽  
Linear Wave ◽  
Mean Flow ◽  
Interaction Of Waves ◽  
Current Interaction ◽  
Flooding Events ◽  
New Framework ◽  
Small Mountainous Rivers

The application of wave-current interaction theory in ocean circulation models has been extensively developed over the past decade, with formulations extended to three dimensions and based either on radiation stress formulations or on the Craik-Leibovich formulation. However, few of these studies consider the interaction of waves with relatively strongly sheared current, in which current shear can affect linear wave dynamics at leading order. The problem arises from the study of the evolution of highly concentrated sediment plumes developing at the mouth of small mountainous rivers. Although the annually averaged discharge of these small mountainous rivers is trivial compared to large rivers, during the extreme flooding events triggered by typhoon or tropic cyclones, these rivers, most of which located at tectonically active mountain belts, can carry highly concentrated sediment ( up to several g/l in the river plume) into the ocean. The magnitude of river discharge velocity at the river mouth may reach several m/s, comparable to the wave phase speed in coastal water. In addition, these flooding events usually coincide with very energetic wave conditions induced by the storms. Therefore, the interaction of waves with strongly sheared current becomes a very important dynamic process at this kind of river plumes. In our study, we establish a new framework to describe the interaction of small amplitude surface gravity waves and strongly sheared currents, where shear can exist in both vertical and horizontal directions. To begin with, we limit the derivation to the case of a narrow-banded slowly varying wave train propagating shoreward in the coastal ocean outside of the surf zone. Accordingly, our problem is assumed to be finite depth without wave breaking. Later we can extend the formulation to describe a spectrum of surface waves and include wave energy dissipation. In contrast to existing formulations, where waves at most feel a weighted depth-average current which follows from a weak-current, weak-shear approximation, the present formulation allows for an arbitrary degree of vertical shear, leading to a description of the vertical structure of waves in terms of solutions to the Rayleigh stability equation. The resulting formulation leads to a conservation law for wave action, and forcing terms for the description of mean flow using the Craik-Leibovich vortex force formulation. This new framework of wave-current interaction can be applied to numerical model based on ROMS/SWAN to study dynamics in coastal waters.

A Numerical Study of Vortex Breakdown in Turbulent Swirling Flows

1999 ◽  
Vol 122 (1) ◽  
pp. 179-183 ◽  
Author(s):  
Robert E. Spall ◽  
Blake M. Ashby
Keyword(s):  
Reynolds Stress ◽  
Stokes Equations ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Reynolds Stress Model ◽  
Navier Stokes ◽  
Stress Model ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
The Mean

Solutions to the incompressible Reynolds-averaged Navier–Stokes equations have been obtained for turbulent vortex breakdown within a slightly diverging tube. Inlet boundary conditions were derived from available experimental data for the mean flow and turbulence kinetic energy. The performance of both two-equation and full differential Reynolds stress models was evaluated. Axisymmetric results revealed that the initiation of vortex breakdown was reasonably well predicted by the differential Reynolds stress model. However, the standard K-ε model failed to predict the occurrence of breakdown. The differential Reynolds stress model also predicted satisfactorily the mean azimuthal and axial velocity profiles downstream of the breakdown, whereas results using the K-ε model were unsatisfactory. [S0098-2202(00)01601-1]

Rayleigh-Be´nard Convection in a Small Aspect Ratio Enclosure: Part II—Bifurcation to Chaos

1993 ◽  
Vol 115 (2) ◽  
pp. 367-376 ◽  
Author(s):  
D. Mukutmoni ◽  
K. T. Yang
Keyword(s):  
Numerical Study ◽  
Period Doubling ◽  
Small Aspect Ratio ◽  
Mean Flow ◽  
Average Temperature ◽  
Aspect Ratios ◽  
Transition To Chaos ◽  
The Mean ◽  
Route To Chaos ◽  
Boussinesq Fluid

The present numerical study documents bifurcation sequences for Rayleigh-Be´nard convection in a rectangular enclosure with insulated sidewalls. The aspect ratios are 3.5 and 2.1 and the Boussinesq fluid is water (average temperature of 70°C) with a Prandtl number of 2.5. The transition to chaos observed in the simulations and experiments is similar to the period-doubling (Feigenbaum) route to chaos. However, special symmetry conditions must be imposed numerically, otherwise the route to chaos is different (Ruelle-Takens-Newhouse). In particular, the Feigenbaum route to chaos can be realized only if the oscillating velocity and temperature field preserves the fourfold symmetry that is observed in the mean flow in the horizontal plane.

scholarly journals Incidence and reflection of internal waves and wave-induced currents at a jump in buoyancy frequency

2015 ◽  
Vol 22 (3) ◽  
pp. 259-274 ◽  
Author(s):  
J. P. McHugh
Keyword(s):  
Wave Packet ◽  
Internal Gravity Waves ◽  
Buoyancy Frequency ◽  
Mean Flow ◽  
Weakly Nonlinear ◽  
Transmitted Waves ◽  
The Mean ◽  
Induced Currents ◽  
Wave Induced ◽  
The Waves

Abstract. Weakly nonlinear internal gravity waves are treated in a two-layer fluid with a set of nonlinear Schrodinger equations. The layers have a sharp interface with a jump in buoyancy frequency approximately modeling the tropopause. The waves are periodic in the horizontal but modulated in the vertical and Boussinesq flow is assumed. The equation governing the incident wave packet is directly coupled to the equation for the reflected packet, while the equation governing transmitted waves is only coupled at the interface. Solutions are obtained numerically. The results indicate that the waves create a mean flow that is strong near and underneath the interface, and discontinuous at the interface. Furthermore, the mean flow has an oscillatory component that can contaminate the wave envelope and has a vertical wavelength that decreases as the wave packet interacts with the interface.

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