scholarly journals Internal Gerstner waves: applications to dead water

2013 ◽  
Vol 93 (7) ◽  
pp. 1451-1457 ◽  
Author(s):  
Raphael Stuhlmeier
Keyword(s):  
Gerstner Waves ◽  
Dead Water

KAJIAN TRANSPORTASI SUNGAI MENGGUNAKAN KAPAL SEMIKATAMARAN

2017 ◽  
Vol 11 (2) ◽  
pp. 145-154
Author(s):  
Luhut Tumpal Parulian Sinaga
Keyword(s):  
Dead Water

Suatu usaha rekayasa engineering pemakaian kapal dengan efek gelombang yang tidak merusak lingkungan dan mampu berlayar pada kedalaman perairan terbatas perlu dibuat dan dikembangkan. Bentuk rekayasa lambung yang digunakan adalah  mengurangi tegangan permukaan air dengan cara membuat body ganda (semacam Tunnel ) di bawah permukaan air. Untuk selanjutnya body ganda di bawah permukaan air ini dinamakan dengan Kapal Hull Semi Catamaran (HSC). Rekayasa lambung kapal HSC dilaksanakan dengan pembuatan beberapa buah model kapal dengan variasi bentuk dan ukuran Tunnel. Gelombang timbul akibat pergerakan Kapal HSC diobservasi di kolam uji yang bisa dikontrol kedalaman perairannya. Dari observasi percobaan model kapal  yang dilakukan , Body kapal bentuk HSC lebih unggul bila dibandingkan dengan penggunaan bentuk body kapal konvensional , beberapa keunggulan yang diberikan bentuk kapal HSC diantaranya adalah pola dan tinggi gelombang timbul akibat pergerakan kapal lebih baik, effisiensi propeller akan meningkat (aliran yang masuk  propeller disc lebih baik dan efisien serta sudut kemiringan poros bisa diperkecil), pengaruh wake bisa dikurangi karena air mati  (dead water) di daerah buritan kapal tereduksi. Diharapkan  penggunaan kapal Hull Semi Catamaran sangatlah efektif digunakan sebagai sarana transportasi sungai maupun laut ( Sea River Ship ). Pengembangan, rekayasa dan inovasi bentuk Hull Semi Catamaran   dilaksanakan di Laboratorium Hidrodinamika  (UPT-BPPH, BPP Teknologi).

A new mechanism for generating a bolus within a double layer following Scott Russell

2021 ◽  
Author(s):  
Johan Fourdrinoy ◽  
Julien Dambrine ◽  
Madalina Petcu ◽  
Morgan Pierre ◽  
Germain Rousseaux
Keyword(s):  
Surface Deformation ◽  
Wave Train ◽  
Surrounding Medium ◽  
Negative Polarity ◽  
National Academy Of Sciences ◽  
Dispersive Waves ◽  
Dual Nature ◽  
Free Surface Deformation ◽  
Academy Of Sciences ◽  
Dead Water

<p>While seeking to revisit an old experiment of John Scott Russell, we discovered a new mechanism for generating a non-shoaling bolus (an ovoid coherent mass of recirculating mixed fluids immerged in a surrounding medium/a of different density/ies) propagating along a pycnocline. In a study about dead-water (Fourdrinoy et al. 2020), a wave resistance phenomenon induced by internal waves formation at the interface between waters of different densities, we modified the setup used by Scott Russell. The Scottish engineer studied the formation and propagation of dispersive waves when an object is removed from a laterally confined open channel with a shallow layer of water. The “vacuum” created by the mass removal generates a linear dispersive free surface deformation with a front of negative polarity followed by a wave train. If we extend this configuration to a two-layers stratification, we can observe a linear dispersive wave with negative polarity à la Scott Russell, propagating along the interface. In addition, the removal of the object generates under certain conditions a bolus which induces a mixing zone and a gradient transition layer. We will present this new method of boluses creation, as well as an experimental characterization with space-time diagrams thanks to a subpixel detection procedure.</p><p>The dual nature of the dead-water phenomenology: Nansen versus Ekman wave-making drags.<br>Johan Fourdrinoy, Julien Dambrine, Madalina Petcu, Morgan Pierre and Germain Rousseaux.<br>Proceedings of the National Academy of Sciences, Volume 117, Issue 29, p. 16739-16742, July 2020.</p>

scholarly journals Fluid boundaries shaping using the method of kinetic balance

2006 ◽  
Vol 10 (4) ◽  
pp. 153-162
Author(s):  
Miroslav Benisek ◽  
Svetislav Cantrak ◽  
Milos Nedeljkovic ◽  
Djordje Cantrak ◽  
Dejan Ilic ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Fluid Mechanics ◽  
Cross Sections ◽  
Hydraulic Engineering ◽  
Optimum Shape ◽  
Curved Channels ◽  
Unsteady Fluid Flow ◽  
Unsteady Fluid ◽  
Flow Boundaries ◽  
Dead Water

Fluid flow in curved channels with various cross-sections, as a common problem in theoretical and applied fluid mechanics, is a very complex and quite undiscovered phenomenon. Defining the optimum shape of the fluid flow boundaries, which would ensure minimum undesirable phenomena, like "dead water" zones, unsteady fluid flow, etc., is one of the crucial hydraulic engineering?s task. Method of kinetic balance is described and used for this purpose, what is illustrated with few examples. .

scholarly journals The dual nature of the dead-water phenomenology: Nansen versus Ekman wave-making drags

2020 ◽  
Vol 117 (29) ◽  
pp. 16770-16775
Author(s):  
Johan Fourdrinoy ◽  
Julien Dambrine ◽  
Madalina Petcu ◽  
Morgan Pierre ◽  
Germain Rousseaux
Keyword(s):  
Internal Waves ◽  
Laboratory Experiments ◽  
Analytical Description ◽  
Unsteady Motion ◽  
Linear Regime ◽  
Dual Nature ◽  
Asymptotic Speed ◽  
Propulsion Force ◽  
Initial Acceleration ◽  
Dead Water

A ship encounters a higher drag in a stratified fluid compared to a homogeneous one. Grouped under the same “dead-water” vocabulary, two wave-making resistance phenomena have been historically reported. The first, the Nansen wave-making drag, generates a stationary internal wake which produces a kinematic drag with a noticeable hysteresis. The second, the Ekman wave-making drag, is characterized by velocity oscillations caused by a dynamical resistance whose origin is still unclear. The latter has been justified previously by a periodic emission of nonlinear internal waves. Here we show that these speed variations are due to the generation of an internal dispersive undulating depression produced during the initial acceleration of the ship within a linear regime. The dispersive undulating depression front and its subsequent whelps act as a bumpy treadmill on which the ship would move back and forth. We provide an analytical description of the coupled dynamics of the ship and the wave, which demonstrates the unsteady motion of the ship. Thanks to dynamic calculations substantiated by laboratory experiments, we prove that this oscillating regime is only temporary: the ship will escape the transient Ekman regime while maintaining its propulsion force, reaching the asymptotic Nansen limit. In addition, we show that the lateral confinement, often imposed by experimental setups or in harbors and locks, exacerbates oscillations and modifies the asymptotic speed.

Selective withdrawal from a stably stratified fluid

1968 ◽  
Vol 32 (2) ◽  
pp. 209-223 ◽  
Author(s):  
I. R. Wood
Keyword(s):  
Single Layer ◽  
Layered System ◽  
Volume Discharge ◽  
Layer System ◽  
Minimum Width ◽  
Theoretical Predictions ◽  
Small Rise ◽  
Self Similar ◽  
The One ◽  
Dead Water

In this paper a reservoir connected through a horizontal contraction to a channel is considered. Both the reservoir and the channel are considered to contain a stable multi-layered system of fluids. The conditions under which there is a flow in only one layer, and the depth in this flowing layer decreases continuously from its depth in the reservoir to its depth in the channel, give the maximum discharge that can be obtained with a flow only from this single layer. For this case the volume discharge calculations are carried out at a single section (the section of minimum width). Where there are velocities in only two layers and the depth in each of these layers decreases continuously from their depths in the reservoir to their depths in the channel, the theory involves computations at two sections in the flow. These are the section of minimum width and a section upstream of the position of minimum width (the virtual point of control). For this flow it is shown that the solution is the one in which the velocity and density distributions are self similar and that the depths of the layers at the point of maximum contraction are two-thirds of those far upstream. It is then shown that for any stable continuous or discrete density stratification in the reservoir a self similar solution will satisfy the conditions for the depths of the flowing layers to decrease smoothly from the reservoir to downstream of the contraction. Again the ratio of the depth at the contraction to that far upstream is two-thirds.When there is a very large density difference between the fluid in the lower dead water and that in the lowest flowing streamline then this streamline becomes horizontal and may be considered as a frictionless bed. The flow when the bed is not horizontal but where there is a small rise in the channel at the position of maximum contraction is considered for the case where two discrete layers flow under a volume of dead water. In this case the velocity and density profiles are not self similar.Experiments have been carried out with a contraction in a flume for the withdrawal of two discrete layers from a three layer system and the withdrawal from a fluid with a linear density gradient. In both cases the reservoir and channel bed and hence the lowest streamline was effectively horizontal. These experiments confirmed the theoretical predictions.

Laboratory observations of mean flows under surface gravity waves

2007 ◽  
Vol 573 ◽  
pp. 131-147 ◽  
Author(s):  
S. G. MONISMITH ◽  
E. A. COWEN ◽  
H. M. NEPF ◽  
J. MAGNAUDET ◽  
L. THAIS
Keyword(s):  
Gravity Waves ◽  
Stokes Drift ◽  
Bottom Boundary Layer ◽  
Mean Velocity ◽  
Surface Gravity Waves ◽  
End Conditions ◽  
Different Types ◽  
Stokes Waves ◽  
Rotational Waves ◽  
Gerstner Waves

In this paper we present mean velocity distributions measured in several different wave flumes. The flows shown involve different types of mechanical wavemakers, channels of differing sizes, and two different end conditions. In all cases, when surface waves, nominally deep-water Stokes waves, are generated, counterflowing Eulerian flows appear that act to cancel locally, i.e. not in an integral sense, the mass transport associated with the Stokes drift. No existing theory of wave–current interactions explains this behaviour, although it is symptomatic of Gerstner waves, rotational waves that are exact solutions to the Euler equations. In shallow water (kH ≈ 1), this cancellation of the Stokes drift does not hold, suggesting that interactions between wave motions and the bottom boundary layer may also come into play.

scholarly journals Resurrecting dead-water phenomenon

2011 ◽  
Vol 18 (2) ◽  
pp. 193-208 ◽  
Author(s):  
M. J. Mercier ◽  
R. Vasseur ◽  
T. Dauxois
Keyword(s):  
Internal Waves ◽  
Large Amplitude ◽  
Experimental Studies ◽  
Nonlinear Effects ◽  
Stratified Fluid ◽  
Nonlinear Internal Waves ◽  
Induced Drag ◽  
Wave Induced ◽  
Dead Water ◽  
Peculiar Phenomenon

Abstract. We revisit experimental studies performed by Ekman on dead-water (Ekman, 1904) using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects. Dedicated to Fridtjöf Nansen born 150 yr ago (10 October 1861).

scholarly journals On the flow of air behind an inclined flat plate of infinite span

1927 ◽  
Vol 116 (773) ◽  
pp. 170-197 ◽  
Keyword(s):  
Flat Plate ◽  
Unit Length ◽  
Large Angle ◽  
Vortex System ◽  
Water Region ◽  
Infinite Extent ◽  
Freely Moving ◽  
The Individual ◽  
Moving Fluid ◽  
Dead Water

The general form of the flow behind an infinitely long thin flat plate inclined at a large angle to a fluid stream of infinite extent has been known for many years past. The essential features of the motion are illustrated in the smoke photograph given in fig. 1, Plate 6. At the edges, thin bands of vorticity are generated, which separate the freely-moving fluid from the “dead-water” region at the back of the plate; and at some distance behind, these vortex bands on account of their lack of stability roll up and form what is now commonly known as a vortex street (see fig. 2). Various theories for calculating the resistance of the plate have also been advanced from time to time. One of the earliest is the theory of “discontinuous” motion due to Kirchhoff and Rayleigh, who obtained the expression π sin α/4 + π sin α ρV 0 2 b (see symbols) for the normal force per unit length of the plate. More recently Kármán has obtained a formula for the resistance of a plate normal to the general flow, in terms of the dimensions of the vortex system at some distance behind the plate. In spite, however, of these and other important investigations, much more remains to be discovered before it can be said that the phenomenon of the flow is completely understood. No attempt has hitherto been made, as far as the writers are aware, to determine experimentally, at incidences below 90°, the frequency and speed with which the vortices pass downstream; the dimensions of the vortex system; the average strength of the individual vortices; or the rate at which vorticity is leaving the edges of the plate. The present investigation has been undertaken to furnish information on these features of the flow.

Sign in / Sign up

Export Citation Format

Share Document