[Haga]

Hi, pretty long time since I posted something here! Lateral sloshing can be simulated easily in CFX, but only managed to do so by lateral external excitation. How can the lateral slosh condition due to pitching be simulated?

[ghorrocks]

With a moving mesh approach you can move the tank in any direction you like.

[Haga]

@ Glenn..

Yes, am trying to crack it that way. If you find something sometime pls add it up here.

[nathanlee]

Hi im new to CFD and i am trying to simulate tank sloshing for 10s but apparently my time does not run at all. It always get stuck at 0.0s even though the system is running. Can anyone help me with this? Help is greatly appreciated!

[ghorrocks]

Please post your output file.

[nathanlee]

Hi as seen in the attached pictures, the water does not flow at all. The tank is moving at weird angles thou. Thanks for the help.

[ghorrocks]

Your simulation is in Fluent. Try the fluent forum.

But two general comments - have you set the gravity vector? And have you run the simulation long enough that the fluid would move?

[Haga]

10s is fair enough for simulation

[ghorrocks]

Not necessarily, it depends on the length and viscosity scales (and a few other parameters, not sure what non-dimensional number that is). If the fluid is highly viscous it will take a while for the fluid to move enough that you will see it.

[Haga]

glenn is right..if viscosity, impulse time etc are high, 10s is insufficient

[nathanlee]

Happy boxing day everyone. With reference to the sloshing tutorial, instead of moving the tank in -9.81m/s in the x direction, may i know how do i input the speed if my speed is in the form Asinwt where 'A= ampitute', 't = seconds' and 'w = 2*pi*f'. For example, how to input 2.5sin(80*pi)t where the tank is undergoing a vibratory motion in the x direction. Thanks for the help!

[ghorrocks]

Replace the constant value with a CEL expression. Several CFX tutorials show how to use CEL expressions.

[Haga]

Originally Posted by nathanlee

Happy boxing day everyone. With reference to the sloshing tutorial, instead of moving the tank in -9.81m/s in the x direction, may i know how do i input the speed if my speed is in the form Asinwt where 'A= ampitute', 't = seconds' and 'w = 2*pi*f'. For example, how to input 2.5sin(80*pi)t where the tank is undergoing a vibratory motion in the x direction. Thanks for the help!

Use CEL help to write functions.. 1st assign a func name say Gx.. and try as follows:

Gx = 2.5 [mm] * sine((80 [rad/s] * pi()) * t [sec])

it depends on your omega, amp & timestep size.


@ Glenn,

Pl verify on the feasibility of this expression in CFX (actually I posted it without referring back)..so not sure if my memory is correct

[ghorrocks]

There are a few minor problems with the CEL, but they would stop it from working and end the simulation with an error:
1) The sine function is "sin", not "sine".
2) The pi variable is pi, not pi().
3) The variable t is already in units of time. There is no need to define units for t as they are already defined.

Note I have not checked these through CFX either, but hopefully they are correct.

[nathanlee]

Thanks for the help, appreciate it! I will give it a try

[Haga]

Glenn, the CEL expressions have to be given such that each parameter is followed strictly by its unit in "[ ]"..otherwise you are correct.

Nathan, actually for acceleration as a variable expression, the 1st term in the sample excitation you asked would be steady state acceleration & not displacement. so the unit need to be "[mm/sec^2]" or so..

[ghorrocks]

Glenn, the CEL expressions have to be given such that each parameter is followed strictly by its unit in "[ ]"..otherwise you are correct.

For a numerical value this is correct. For a variable this is not good practise and probably will fail with an error (Not sure, I have not tried it). For a variable the units are specified either from where it is derived or from numerical values with their units specified.

[Haga]

here is a sample working expression

Gx = 2.5*sin(20*t[s]/1[s])

if after a particular time, this excitation has to stop, use step function for the value of Gx by giving it as a new expression. Then call it into the acceleration definition of the problem.

[ghorrocks]

I see, I was not aware an equation like that would even work.

Then I simply say it is bad practise. If the variable t is already a variable of time then the [s] is unnecessary, if the variable is of units other than time then I have no idea what it will do, but it sounds undefined.

If you remove the [s] does it still return exactly the same result?

[Haga]

if [s] is removed from t, then 1 [s] can also be removed, but there is inconsistency.