Wave loading analysis in Femap

[BlasMolero]

Hello Experts!,
For the study of the structural behavior of the walls of a typical swimming pool meshed with 2-D Shell CQUAD4 elements I need to simulate in Simcenter FEMAP with NASTRAN the loading effect of a barrel of 120 kg dropping over the free surface of the water:
[ul]
[li]The pool is full of water.[/li]
[li]A barrel with a diameter of 450 mm and a capacity of 120 liters and weight of 120 kg is placed at 640 mm over the surface of the water.[/li]
[li]The barrel is dropped over the pool.[/li]
[li]We need to calculate the pressure distribution in the walls of the pool to perform structural analysis to obtain stresses & displacements results.[/li]
[/ul]

The key here is to know how to estimate in a reasonable way in FEMAP (not very conservative neither under-estimate or incorrect) the peak pressure load distribution that receive the walls of the pool due to the impact of the barrel using an equivalent static loading, the real situation is obviously very complex.
It is not immediately clear to me how it could be simplified to a loading scenario which would make for a meaningful analysis.
If anybody have some ideas as to how to proceed is welcome, please inform, thanks!.
Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[FEA way]

That's a very interesting case for a simulation. A free surface CFD study with rigid body dynamics or FSI could predict this but I understand that you don't have the tools for that and want to perform a purely mechanical analysis. For that, you will need to calculate two things:
1) parameters of waves forming after barrel impact - propagation of such spherical waves is described by Huygen's principle
2) load acting on the pool's walls when waves hit it - this is described in the article "Loading Conditions Due to Violent Wave Impacts on Coastal Structures with Cantilever Surfaces" by D. Kisacik - various approaches are presented, including linear wave theory - ocean waves are assumed but maybe it would also make sense for spherical ones caused by impact

The problem is that literature about the design of ships and offshore structures assumes that waves are induced by wind and not by impact. Such impact could be caused by meteorite fall but then the velocities are too large to use those considerations here.

 

[rb1957]

two phase CFD ?

the barrel looks to have neutral buoyancy.

if the height 640mm or 640m ?

I can't help but think ... 120kg you say ... humm, that's a large-ish human ... doing a "cannonball" ??

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[ThomasH]

Hi Blas,
When I read the discription of the load case there is sometning that I find odd.

It says a barrel with the mass 120 kg basically dropped from the height 640 m (meters ?). That seems unreasonable high to me. 640 millimeters may be a bit low but 640 meters means a huge energy to consider. But I also thought about rb1957's human doing a cannonball . And that may be entirely irrelevant .

But I would start with the energy that need to be handled (E = (m * v^2)/2) and see if the pool walls have the strength and flexibility to meet the requirements. I would start simple just to get a first indication.

How is the pool built?

Thomas

 

[BlasMolero]

Hello all!,
Yes, I see a typo in the image, the height of the 120 kg barrel is 0.64 m, ie, 640 mm.
The material of the pool is plastic.

Well, thanks to all, I see not immediate answer exist, I run the CFD code "FloEFD for SOLID EDGE" but it is NOT possible to simulate and obtain the pressure distribution results caused by a barrel dropping over the water surfaces as this would involve surface tension effects and also meshes of the barrel colliding with the water surface. The Free Surface model in its current implementation in FloEFD is not able to take this into account, only STAR-CCM+ can do it but not access to it.

Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[rb1957]

"h"eight ...

how deep is the water in the pool ?

I suspect that this simple question is astonishingly difficult to answer.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[BlasMolero]

Hello!,
The deep of water in the swimming pool is around 1.2 meters, ie, 1200 mm.
Best regards,
Blas.

~~~~~~~~~~~~~~~~~~~~~~
Blas Molero Hidalgo
Ingeniero Industrial
Director

IBERISA
48004 BILBAO (SPAIN)
WEB:

http://www.iberisa.com

Blog de FEMAP & NX Nastran:

http://iberisa.wordpress.com/

 

[ThomasH]

Hello

The kinetic energy in the barrel will transform to kinetic energy for the barrel and an influenced water volume. Since the pool is plastic it is probably very flexible even if there (probably) also is a more rigid frame involved. But I think that the total mass of water influenced by the barrel will be significantly larger than the mass of the barrel.

I agree with rb1957 that a correct answer is probably difficult to find. But does it have to be exactly "corrct"? What is the ultimate purpose for the analysis?

It should be possible to determine the flexibility of the walls with some accuracy. From that you can get a ballpark number of how much the water can be displaced and then you have inertia forces to balance the energy from the barrels impact.

I am just "thinking ot load" so the speak. I haven't done any of the actual math but I suspect that the load case is not really a problem and that a simplified approch might suffice.

I suspect thet this arrangement for a pool is not unique.

Thomas