Pump&turbine - big difference in speeds

[Bartek22]

Hi guys,

I am trying to design foundation for heavy vibrant machinery using PVAP/SVAP software (I am not sure if anybody outside FLUOR knows this software). Because in software I am using for calculations there is only one place to input one speed I am not sure which one should I check.
Here's some machine properties:
Turbine:
speed 3700rpm, rotating weight is 3.4kN
Pump:
speed 595rpm, rotating weight is 13.7kN

Dynamic forces will be calculated using following formula:
Fdyn=speed*rotating weight/6000. Then I am going to calculate resultant force and its location somewhere in the middle.

Do you have any experience in similar problem. I want to check 4 cases
1-soil 20% stronger and pump speed
2-soil 20% stronger and turbine speed
3,4 similar but with 20% weaker soil.

Any help will be much appreciated.

Thanks a lot in advance for your help.

 

[kslee1000]

What not provide seperate foundation for each?

 

[Bartek22]

It's not that easy. Settelment is a priority in this case and we need to provide the same for pump+turbine and for pipes around. That is why it must to be placed on one foundation (together with pipe supports). Besides area around is very crowded so probably I will need to use micropiles to unify settlement (client requirement instead of one rigid slab for everything around).

 

[kslee1000]

I think this is more of vibration dominate problem, you need to know operation frequency of each to avoid synchronization, and the mass required for the foundation.

 

[Bartek22]

I know operation frequencies (see my first post).Mass will be designed to be 5-7 times bigger than the equipment.

 

[kslee1000]

Then shouldn't that be the frequency range to avoid for the foundation?

 

[Bartek22]

I need to know natural frequency of foundation to compare this with operating frequency. To avoid resonant ratio should be outside 0,7-1,3FR where FR is machine speed divided by natural frequency. As you can see, having different machine speeds causes that I have 2 ratios and I dont know if I can check it like that.
Assuming that natural frequency of foundation is constant I have two ratios, one for 595rpm and other for 3700rpm. I am simply not sure if I can check it this way.

 

[kslee1000]

Dynamic analysis on soil-foundation interaction has never been a simple task. I think you need to consider:

1. Engage a geotech to explore the subgrade.
2. Perform dynamic analysis on the concrete mass includes soil effects.
3. Consider using dampers/isolators/shock obsorbers on the machine(s).

Hope the attached PDF would lead you in right direction.