García-Espinosa et al 2016a - Revision history

Julio at 11:10, 4 April 2017

2017-04-04T11:10:26Z

Julio at 09:49, 4 April 2017

2017-04-04T09:49:43Z

Julio at 10:23, 24 December 2016

2016-12-24T10:23:58Z

Julio at 10:22, 24 December 2016

2016-12-24T10:22:29Z

Julio at 10:21, 24 December 2016

2016-12-24T10:21:23Z

Julio at 10:10, 24 December 2016

2016-12-24T10:10:13Z

Julio at 15:22, 23 December 2016

2016-12-23T15:22:52Z

Julio at 15:11, 23 December 2016

2016-12-23T15:11:27Z

Move page script: Move page script moved page García-Espinosa et al 2016b to García-Espinosa et al 2016a

2016-12-23T11:45:58Z

Move page script moved page García-Espinosa et al 2016b to García-Espinosa et al 2016a

Move page script: Move page script moved page García-Espinosa 2016b to García-Espinosa et al 2016b

2016-12-23T11:44:51Z

Move page script moved page García-Espinosa 2016b to García-Espinosa et al 2016b

@@ Line 390: / Line 390: @@
 {| style="font-size:75%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
 |-
-| {{#evt:service=youtube|id=https://youtu.be/WVkqkAIpCek|alignment=center}}
+| {{#evt:service=youtube|id=https://youtu.be/d7vzDiugF18|alignment=center}}
 |- style="text-align: center;"
 | '''Video 1.''' Spray generated by the 14 ft WAM-V hull at 25 knots.

@@ Line 388: / Line 388: @@
-{| style="font-size:120%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
+{| style="font-size:75%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
 |-
 | {{#evt:service=youtube|id=https://youtu.be/WVkqkAIpCek|alignment=center}}

@@ Line 394: / Line 394: @@
 | '''Video 1.''' Spray generated by the 14 ft WAM-V hull at 25 knots.
 |}
 As discussed in the previous section, the blue isosurface drawn in the pictures corresponds to the piecewise planar surface where the projected identity of the particles on the nodes takes a value 0. It has to be emphasized that this projection process implies a relevant loss of resolution; the flow is actually solved with twenty particles per element (on average) but the blue surface is constructed only with the weighted values on the nodes of the linear elements. In the zones where the developed flow involves a complex mixture of air and water, the free surface cannot be identified. In that case, the calculated isosurface should be understood only as a reference; below that isosurface we will find water with a relatively small proportion of air bubbles, and above it, we will find an increasing presence of air. In particular, the isosurface shows big bulges below the hull that should not be understood as air pockets, but as volumes where the air-water mixing phenomenon is quite complex.

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 The results of three representative cases are here presented. These correspond to three different speeds of the WAM-V, viz. ''U''=15 knots, ''U''=20 knots and ''U''=25 knots, respectively.
 {| style="width: 100%;border-collapse: collapse;"
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 |  style="text-align: center;vertical-align: top;"|<span style="text-align: center; font-size: 75%;">'''Figure 8.''' Details of the spray generated by the 14 ft WAM-V hull at 25 knots; YZ plane; Time = 3.52s</span>
 |}
 Next, a video of the spray generated by the 14 ft WAM-V hull at 25 knots is presented.
 {| style="font-size:120%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
@@ Line 393: / Line 396: @@
 As discussed in the previous section, the blue isosurface drawn in the pictures corresponds to the piecewise planar surface where the projected identity of the particles on the nodes takes a value 0. It has to be emphasized that this projection process implies a relevant loss of resolution; the flow is actually solved with twenty particles per element (on average) but the blue surface is constructed only with the weighted values on the nodes of the linear elements. In the zones where the developed flow involves a complex mixture of air and water, the free surface cannot be identified. In that case, the calculated isosurface should be understood only as a reference; below that isosurface we will find water with a relatively small proportion of air bubbles, and above it, we will find an increasing presence of air. In particular, the isosurface shows big bulges below the hull that should not be understood as air pockets, but as volumes where the air-water mixing phenomenon is quite complex.
 {| style="width: 100%;border-collapse: collapse;"

@@ Line 299: / Line 299: @@
 where <math display="inline">a</math> is the amplitude of the wave, <math display="inline">k</math> is the angular wavenumber, <math display="inline">g</math> is the acceleration due to gravity and <math display="inline">\omega</math>  is the angular frequency. Further ''U'' is the velocity with which the WAM-V moves relative to water and <math display="inline">u\left( x,y,t\right) ,\, v(x,y,t)</math> represent the spatial velocity components of the water in an inertial reference frame that moves with the WAM-V. The narrow strip at the inlet where the wave velocity is imposed has a width of  0.2m. This periodic velocity condition causes a disturbance which is propagated in the rest of the domain and whose motion is governed by the Navier-Stokes equations. In this case, only the near field of the problem is analyzed, and therefore the standard formulation of the fluid dynamics solver (i.e. not the diffraction-radiation splitting formulation) has been used.
 {| style="width: 100%;border-collapse: collapse;"
@@ Line 379: / Line 383: @@
 |}
-The total physical time of simulation was chosen as 4s. The time evolution was computed using 800 time steps of  0.005s each.
+Next, a video of the spray generated by the 14 ft WAM-V hull at 25 knots is presented.
-The results of three representative cases are here presented. These correspond to three different speeds of the WAM-V, viz. ''U''=15 knots, ''U''=20 knots and ''U''=25 knots, respectively.
+{| style="font-size:120%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
 As discussed in the previous section, the blue isosurface drawn in the pictures corresponds to the piecewise planar surface where the projected identity of the particles on the nodes takes a value 0. It has to be emphasized that this projection process implies a relevant loss of resolution; the flow is actually solved with twenty particles per element (on average) but the blue surface is constructed only with the weighted values on the nodes of the linear elements. In the zones where the developed flow involves a complex mixture of air and water, the free surface cannot be identified. In that case, the calculated isosurface should be understood only as a reference; below that isosurface we will find water with a relatively small proportion of air bubbles, and above it, we will find an increasing presence of air. In particular, the isosurface shows big bulges below the hull that should not be understood as air pockets, but as volumes where the air-water mixing phenomenon is quite complex.
@@ Line 387: / Line 396: @@
 {| style="width: 100%;border-collapse: collapse;"
 |-
-| <span style="text-align: center; font-size: 75%;">
+|  style="vertical-align: top;"|
-[[File:García-Espinosa_et_al_2016a_3013_Imagen1.jpg]]
+[[Image:García-Espinosa_et_al_2016a_3013_Imagen1.jpg|center|600px]]
-|}
-<div class="center" style="width: auto; margin-left: auto; margin-right: auto;">
+|-
-<span style="text-align: center; font-size: 75%;">'''Figure 9.''' XY plane view of the spray generated by the 14 ft WAM-V hull at 25 knots and time = 3:57 s.</span></div>
+|  style="text-align: center;vertical-align: top;"|<span id='_Ref451883427'></span>
-Finally, a video of the spray generated by the 14 ft WAM-V hull at 25 knots is presented.
+<span style="text-align: center; font-size: 75%;">'''Figure 9.''' XY plane view of the spray generated by the 14 ft WAM-V hull at 25 knots and time = 3:57 s.</span>
-−
-{| style="font-size:120%; color: #222222; border: 1px solid darkgray; background: #f3f3f3; table-layout: fixed; width:100%;"
-|-
-| {{#evt:service=youtube|id=https://youtu.be/WVkqkAIpCek|alignment=center}}
-|- style="text-align: center;"
-| '''Video 1.''' Spray generated by the 14 ft WAM-V hull at 25 knots.
 |}

← Older revision		Revision as of 15:11, 23 December 2016
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	Zhang, D.Z., Zou, Q.,VanderHeyden,W.B., Ma, X.: Material point method applied to multiphase flows. Journal of Computational Physics, Vol. 227, No. 6, 2008, pp. 3159–3173. DOI 10.1016/ j.jcp.2007.11.021.		Zhang, D.Z., Zou, Q.,VanderHeyden,W.B., Ma, X.: Material point method applied to multiphase flows. Journal of Computational Physics, Vol. 227, No. 6, 2008, pp. 3159–3173. DOI 10.1016/ j.jcp.2007.11.021.
−
−	~~==DISCUSSION==~~
−
−	~~Antonio Souto-Iglesias, Model Basin Research Group (CEHINAV)~~
−
−	~~Technical University of Madrid (UPM)~~
−
−	~~The paper presents a technique to model spray generation while navigating in waves by extending the modeling capabilities of the PFEM technique.~~
−
−	~~The appearance of the simulation results for a WAM-V vessel is amazing considering the difficulty of the problem and the complexity of the physics involved.~~
−
−	~~A few questions arise:~~
−
−	1. The authors motivate their analysis by indicating that spray generation may be a significant contribution to total resistance for this type of vessel. Do they know of any study that backs their statement? It would seem to this discusser that with such a blunt hull, pressure form drag or even wave generation would be far dominant.
−
−	~~2. The algorithm for spray generation is not clear. How does a particle cross the free surface (a material surface) and add up to the gas ones? Can they elaborate a bit on this?~~
−
−	3. Finally, it should be feasible to estimate some mass flow rate of spray that is generated, thus leading to some quantitative difference between the different speeds in Figs 7-9. Even though they are different velocities, the amount of generated spray and its penetration in the gas phase seems similar in the three pictures.
−
−	~~Thank you very much and congratulations to the authors for such an interesting paper and for tackling such a challenging problem.~~
−
−	~~==AUTHOR’S REPLY==~~
−
−	~~Thank you for your positive words and comments, each of which is addressed below.~~
−
−	1. There is no question that in full load condition, standard drag components should be dominant. However, WAM-V concept is a very light craft -with a minimum draft- and therefore pressure components of the drag are smaller compared to a conventional vessel. Furthermore, the generation of spray is those conditions is very important, which suggests that this is a relevant source of energy dissipation in this case.
−
−	2. The blue isosurface drawn in the pictures corresponds to the piecewise planar surface where the projected identity of the particles on the nodes takes a value 0. It has to be emphasized that this projection process implies a relevant loss of resolution; the flow is actually solved with twenty particles per element (on average) but the isosurface is constructed only with the weighted values on the nodes of the linear elements. Therefore, in the zones where the developed flow is highly complex, this isosurface should only be understood as a reference for the free surface, since there is no real free surface; below the isosurface, we will find water with a relatively small proportion of air bubbles, and above it, we will find an increasing presence of air.
−
−	3. It should be noted that the particles in the proposed model are just tracers that carry with them only the intrinsic properties of the flow. In particular, they have no associated mass. Therefore, the model cannot evaluate the generated mass flow rate of spray, but just give qualitative indications on the development of the phenomenon.
−
−	Our current research plan to improve the physics of the model proposes to enrich the model by incorporating the transport equations for the droplet size distribution in the semi-Lagrangian framework. This approach will imply that the particles will transport properties characterizing the droplet size distribution. The solution of this enriched problem will allow computing quantities like the mass flow rate.
−
−	~~==DISCUSSION==~~
−
−	~~Sergio Idelsohn, ICREA Research Professor~~
−
−	~~International Center for Numerical Methods in Engineering~~
−
−	~~The article describes the application of the method called PFEM to the evaluation of spray generated by a single vessel.~~
−
−	~~PFEM is a Lagrangian method based on particles that move along certain paths approximated by streamlines. The particles have no mass associated, are just tracers.~~
−
−	The advantage of such methods is the ease way for which the fluid may separate according with the particle velocities and the inertia forces of the particles. This possibility resembles the phenomenon of spray.
−
−	~~In fact, the phenomenon of the spray comes from something much more complicated; it has to do with the water and air viscosities together with the surface tension between the two fluids.~~
−
−	~~However, the results shown are quite convincing and at first glance give the impression of being similar to reality.~~
−
−	It would be desirable, since this article is part of a research project, that certain experimental results give some agreements to the numerical results. For example, the maximum height of the drops or the density of the air-drops for different vessel speeds. Without some of these comparisons, the numerical results have no meaning.
−
−	~~==AUTHOR’S REPLY==~~
−
−	~~First of all, the authors would like to thank Prof. Idelsohn for his valuable comments.~~
−
−	Regarding the need to validate the presented model, the authors completely agree on it. Unfortunately, no quantitative experimental data regarding the spray generation of the WAM-V is available. At this point, we were only able to perform some qualitative comparisons based on videos and pictures of different tests carried out on the 33’ WAM-V.
−
−	On the other hand, as stated in the paper, the current model only allows a limited analysis of the spray phenomenon, since relevant aspects of the physics are not considered. Our future research lines propose to improve the model physics and then to focus in the quantitative analysis including the necessary validation against experimental data.

← Older revision	Revision as of 11:45, 23 December 2016
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← Older revision	Revision as of 11:44, 23 December 2016
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