# ANSYS CFX - Buoyancy

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 August 16, 2017, 12:41 ANSYS CFX - Buoyancy #1 New Member   glik Join Date: Jun 2017 Posts: 5 Rep Power: 7 I would like to use two differents buoyancy values (in x axle), depending on the height (y axle). I tried something like that : if(y<9[m],g1,g2)*if(y>0[m],1,0), but of course it doesn't work. Does someone have an idea plz ?

 August 16, 2017, 19:44 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,321 Rep Power: 138 This sounds like an XY problem to me..... (http://xyproblem.info/) Can you explain what you are trying to do? Also what do you mean by "change buoyancy"? I have no idea what the variables g1 and g2 mean.

August 17, 2017, 04:34
#3
New Member

glik
Join Date: Jun 2017
Posts: 5
Rep Power: 7
Hello ghorrocks, thanks for helping.

In fact I would like to simulate a tank which is submitted by an earthquake, but in a static problem, and using Housner (impulsive and convective modes-accelerations).

So I have 1 acceleration from the bottom of the tank to the three quarters to the height (for example), and a second acceleration from the three quarters to the top of the tank.
But my problem is, these accelerations are not in the verticale axle.

Is it clearer ?
Attached Images
 Figure-1-Spring-mounted-masses-after-Housner-1957.png (29.5 KB, 24 views)

 August 17, 2017, 04:42 #4 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,321 Rep Power: 138 Isn't the image you show the forces applied on the tank by the fluid, not the acceleration on the fluid? So this is not a varying acceleration, but a varying force - and a force applied to the tank. How can you model a transient earthquake using a static model? You can do modal analysis in FEA, but CFX does not support this.

 August 17, 2017, 12:38 #5 New Member   glik Join Date: Jun 2017 Posts: 5 Rep Power: 7 No it shows the acceleration of the earthquake. Accelerations g(impulsive) and g(convective) are my input datas. But maybe I can do something with the force, by calculating it from the acceleration. And I just want to submit the fluid to these accelerations, and show the maximal pressure under the wall. So it's not necessary for me to model a transient earthquake.

 August 17, 2017, 19:38 #6 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,321 Rep Power: 138 Why not do the obvious thing and use moving mesh in a transient simulation to move the tank following the earthquake displacement versus time? Then the fluid will do its motion and generate the appropriate pressures on the tank walls. This is the standard way of doing this sort of simulation.

 Tags buoyancy, cfd