scholarly journals LARGE-SCALE EXPERIMENTS ON WAVE-INDUCED SHALLOW TURBULENT COHERENT STRUCTURES

2018 ◽  
pp. 54
Author(s):  
Nikos Kalligeris ◽  
Patrick J. Lynett
Keyword(s):  
Coherent Structures ◽  
High Speed ◽  
Large Scale ◽  
Incoming Wave ◽  
Tsunami Waves ◽  
2011 Tohoku Tsunami ◽  
Turbulent Coherent Structures ◽  
Near Shore ◽  
Tohoku Tsunami ◽  
Wave Induced

There are numerous reports of large-scale "whirlpools" being generated in the near-shore during tsunami events (Borrero et al., 2015). These features, termed tsunamiincluded turbulent coherent structures (TCS), form due to flow separation at sharp coastline features. During the 2011 Tohoku tsunami, the generation of a large-scale TCS was captured at port Oarai in a helicopter footage (Lynett et al., 2012). The TCS was spinning for tens of minutes, entraining boats in the high-speed rotational flow, until it was washed away by the next incoming wave. TCS generation can potentially control the hazard for small amplitude tsunami waves in ports and harbors (Borrero et al., 2015; Kalligeris et al., 2016).

scholarly journals Modulation of the turbulence regeneration cycle by inertial particles in planar Couette flow

2018 ◽  
Vol 861 ◽  
pp. 901-929 ◽  
Author(s):  
G. Wang ◽  
D. H. Richter
Keyword(s):  
Reynolds Number ◽  
Couette Flow ◽  
Coherent Structures ◽  
Large Scale ◽  
Relative Length ◽  
Dominant Factor ◽  
Inertial Particles ◽  
Streamwise Vorticity ◽  
Turbulent Coherent Structures ◽  
Regeneration Cycle

Two-way coupled direct numerical simulations are used to investigate the effects of inertial particles on self-sustained, turbulent coherent structures (i.e. the so-called regeneration cycle) in plane Couette flow at low Reynolds number just above the onset of transition. Tests show two limiting behaviours with increasing particle inertia, similar to the results from previous linear stability analyses: low-inertia particles trigger the laminar-to-turbulent instability whereas high-inertia particles tend to stabilize turbulence due to the extra dissipation induced by particle–fluid coupling. Furthermore, it is found that the streamwise coupling between phases is the dominant factor in damping of the turbulence and is highly related to the spatial distribution of the particles. The presence of particles in different turbulent coherent structures (large-scale vortices or large-scale streaks) determines the turbulent kinetic energy of particulate phase, which is related to the particle response time scaled by the turnover time of large-scale vortices. By quantitatively investigating the periodic character of the whole regeneration cycle and the phase difference between linked sub-steps, we show that the presence of inertial particles does not alter the periodic nature of the cycle or the relative length of each of the sub-steps. Instead, high-inertia particles greatly weaken the large-scale vortices as well as the streamwise vorticity stretching and lift-up effects, thereby suppressing the fluctuating amplitude of the large-scale streaks. The primary influence of low-inertia particles, however, is to strengthen the large-scale vortices, which fosters the cycle and ultimately reduces the critical Reynolds number.

Filamentary Currents in Turbulent Magnetic Reconnection

2020 ◽  
Author(s):  
Meng Zhou ◽  
Xiaohua Deng ◽  
Zhihong Zhong ◽  
Ye Pang
Keyword(s):  
Plasma Physics ◽  
Magnetic Reconnection ◽  
Current Sheet ◽  
Coherent Structures ◽  
High Speed ◽  
Large Scale ◽  
Magnetic Energy ◽  
Normal Direction ◽  
Neutral Sheet ◽  
Current Filaments

<p>Magnetic reconnection and turbulence are the two most important energy conversion phenomena in plasma physics. Magnetic reconnection and turbulence are often intertwined. For example, reconnection occurs in thin current layers formed during cascades of turbulence, while reconnection in large-scale current sheet also evolves into turbulence. How energy is dissipated and how particles are accelerated in turbulent magnetic reconnection are outstanding questions in magnetic reconnection and turbulence. Here we report MMS observations of filamentary currents in turbulent outflows in the Earth's magnetotail. We found sub-ion-scale filamentary currents in high-speed outflows that evolved into turbulent states. The normal direction of these current filaments is mainly along the X<sub>GSM</sub> direction, which is distinct from the neutral sheet. Some filamentary currents were reconnecting, thereby further dissipating the magnetic energy far from the X line. We notice that turbulent reconnection is more efficient in energizing electrons than laminar reconnection. Coherent structures composed of these filaments may be important in accelerating particles during turbulent reconnection.  </p>

scholarly journals Large Scale Coastal Behavior of the 2011 Tohoku Tsunami

2012 ◽  
Vol 68 (2) ◽  
pp. I_136-I_140
Author(s):  
Ryoichi ITO ◽  
Shinji SATO ◽  
Haijiang LIU ◽  
Yoshimitsu TAJIMA
Keyword(s):  
Large Scale ◽  
2011 Tohoku Tsunami ◽  
Tohoku Tsunami

scholarly journals Experimental Evidence of the Influence of Recurves on Wave Loads at Vertical Seawalls

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 889 ◽  
Author(s):  
Dimitris Stagonas ◽  
Rajendran Ravindar ◽  
Venkatachalam Sriram ◽  
Stefan Schimmels
Keyword(s):  
Large Scale ◽  
Vertical Wall ◽  
Breaking Waves ◽  
Wave Loads ◽  
Incoming Wave ◽  
Wave Heights ◽  
The Mean ◽  
Peak Pressures ◽  
Wave Induced ◽  
Incident Waves

The role of recurves on top of seawalls in reducing overtopping has been previously shown but their influence in the distribution and magnitude of wave-induced pressures and forces on the seawall remains largely unexplored. This paper deals with the effects of different recurve geometries on the loads acting on the vertical wall. Three geometries with different arc lengths, or extremity angles (αe), were investigated in large-scale physical model tests with regular waves, resulting in a range of pulsating (non-breaking waves) to impulsive (breaking waves) conditions at the structure. As the waves hit the seawall, the up-rushing flow is deflected seawards by the recurve and eventually, re-enters the underlying water column and interacts with the next incoming wave. The re-entering water mass is, intuitively, expected to alter the incident waves but it was found that the recurve shape does not affect wave heights significantly. For purely pulsating conditions, the influence of αe on peak pressures and forces was also negligible. In marked contrast, the mean of the maximum impulsive pressure and force peaks increased, even by a factor of more than two, with the extremity angle. While there is no clear relation between the shape of the recurve and the mean peak pressures and forces, interestingly the mean of the 10% highest forces increases gradually with αe and this effect becomes more pronounced with increasing impact intensity.

On the coherent structure of the axisymmetric mixing layer: a flow-visualization study

1981 ◽  
Vol 104 ◽  
pp. 263-294 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
A. R. Clark
Keyword(s):  
Coherent Structures ◽  
Coherent Structure ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Space Time ◽  
Convection Velocity ◽  
Low Speed ◽  
Large Scale Structures ◽  
Scale Structures

In an effort to resolve some controversies regarding the turbulent mixing-layer structure, the near field of a large (18 cm diameter) air jet has been investigated for the jet exit speed of 30 m s−1. The smoke-laden axisymmetric mixing layer has been illuminated by a thin sheet of laser light in an azimuthal plane passing through the jet axis. High-speed visualization films of the mixing layer in the region of its self-preservation (of which a few picture sequences depicting space-time evolutions of the structure of the layer are presented) reveal that most of the time the mixing layer is in a state of disorganization, consisting of relatively smaller scale, random and diffuse turbulent motions; only occasionally are organized distinct large-scale coherent structures formed. The survival distances of the large-scale structures are found to be comparable to their average sizes. The survival time of these structures is about one ‘turnover’ time, each being roughly about five times the local characteristic time scale of the mixing layer. It is seen that tearing is as dominant a mode of large-scale interaction as pairing is; large-scale structures are continually sheared and typically fragmented due to a segment on the high-speed side being torn and swept away from the slower-moving outer portion. Evolution of the large structures occur not primarily through complete pairing as widely believed but quite frequently through ‘fractional pairing’ between segments which have been torn from different upstream large-scale coherent structures or through ‘partial pairing’ when one structure captures only a part of another. The movies show that along with entrainment of non-vortical ambient fluid, radially outward ejection of vortical fluid into the ambient is an important aspect of jet mixing. From aligned displays of ciné film frame sequences, space-time trajectories of identifiable vortical fluid elements have been traced. The convection velocity variation across the shear layer and even the overall structure convection velocity measured from these trajectories agree with those determined from the wave-number-celerity spectra, obtained from double-Fourier transformation of longitudinal velocity space-time correlation measurements with hot-wires.The visualization films do not bear out the two-street vortex ring model recently propounded by Lau. Based on our observations, we propose that tearing, ‘slippage’ and fractional and partial pairings are responsible for the observed radial variation of structure passage frequency, and the causes of the different coherent structures educed by Bruun on the high- and low-speed sides of the mixing layer and for Yule's failure in educing a coherent structure on the low-speed side of the layer.

scholarly journals Possible Factors Promoting Car Evacuation in the 2011 Tohoku Tsunami Revealed by Analysing a Large-Scale Questionnaire Survey in Kesennuma City

Geosciences ◽  
2017 ◽  
Vol 7 (4) ◽  
pp. 112 ◽  
Author(s):  
Fumiyasu Makinoshima ◽  
Yoshi Abe ◽  
Fumihiko Imamura ◽  
Gaku Machida ◽  
Yukimi Takeshita
Keyword(s):  
Questionnaire Survey ◽  
Large Scale ◽  
2011 Tohoku Tsunami ◽  
Tohoku Tsunami

scholarly journals THE 2010 CHILEAN AND THE 2011 TOHOKU TSUNAMI WAVES IMPACT TO RIVERS IN THE TOHOKU REGION, JAPAN

2012 ◽  
Vol 1 (33) ◽  
pp. 7 ◽  
Author(s):  
Hitoshi Tanaka ◽  
Nguyen Xuan Tinh
Keyword(s):  
Travel Time ◽  
Environmental Problem ◽  
Tsunami Wave ◽  
Wave Theory ◽  
Large River ◽  
Tsunami Waves ◽  
2011 Tohoku Tsunami ◽  
Tsunami Travel Time ◽  
Tohoku Tsunami ◽  
Chilean Tsunami

As a result when tsunami invades into river, it may not only a threat of damages to the banks but also cause the environmental problem such as inundation. Therefore, study of tsunami impacts to rivers becomes more important. The main objectives of this study are to investigate the tsunami wave propagation at different river morphologies based on real time measurements during the 2010 Chilean Tsunami and 2011 Tohoku Tsunami events. The aim is to learn empirically from the last extreme events tsunamis in order to suggest a better solution in terms of river and coastal management in the future. The analyzed results have been shown that the tsunami wave can be affected up to several tens kilometer upstream of a large river and the measured tsunami travel time inside the river is almost similar to the tsunami travel time calculated by using the long wave theory.

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