Q1. How is Buoyancy added in AutoPIPE?
Answer: In AutoPIPE buoyancy weight is applied in GR case. It has both longitudinal and transverse components. When the pipe is vertical, difference in pressure cap forces is the same as buoyancy load and the transverse buoyancy is zero. When the pipe is horizontal, the cap forces from external hydrostatic load adds longitudinal stress and associated movements in addition to non zero transverse (vertical) buoyancy load.
See AutoPIPE help "Submerged Piping Systems" for details on this subject.
Q2. Is Pipe insulation and Cladding accounted for in buoyancy?
Answer: Form the online help:
Clad thickness: For wind loading, hydrotest, buoyancy and wave loading, the total diameter of pipe includes the cladding thickness.
Insulation thickness: The insulation thickness is also used to calculate the surface area of the pipe for wind loads and buoyancy effects.
Q3. How do I know if Buoyancy loads are being applied to the pipe?
Answer: At this time there is no single reported value in AutoPIPE for the total Buoyancy at each node point or for the entire model.
Workaround, must have 2 identical models, where the only differency is in one model, apply Load> Buoyancy as required, and then compare the results of all the vertical support loads under GR load case. The difference between the total vertical support values between both models is the buoyancy load applied to the piping.
Remember All points with a vertical coordinate value less than the "Water surface elevation" value specified on the Load> Buoyancy dialog will be considered submerged (buoyancy load is applied). Piping above this value will be considered above water and NO buoyancy will be applied.
In addition, confirm Segment tab on the input grid, "Apply Buoyancy" column for check boxes where Buoyancy load is to be consideration for above / below "Water surface elevation" value:
Q4. Can you please explain the difference if any in how hydrodynamic loads are applied to both pipe sections utilising soil springs and pipe sections utilising v-stop supports.
Answer: In short there is not much difference. The pipe is supported by either soil springs or V-stop supports. The buoyancy load is another load case applied to the pipe as with any other load case (i.e. Wind). As you know buoyance load is applied with the gravity (GR) load case (combined total of dead weight and bouyancy weight). Also becuase of the general nature of the different supports, pipe movement may be restricted more so by a given soil springs than a V-stop. Regardless, when GR is evaluated the pipe will move as the supports will allow.
Q5. How delete Buoyancy loads from being applied in a model?
Answer: There are 2 ways to accomplish this
1. On the Segment tab on the input grid, uncheck / disable "Apply Buoyancy" for segments as needed.
2. Open the :Buoyancy (Loads > Environmental > Buoyancy) command and set values as seen below,
Press OK when finished.
Confirm if buoyance load is being applied to the model by reviewing a complete output report (Segment Data listing and Analysis summary)
Q5. What value of Ca should be used?
Answer:
Open the Buoyancy load dialog, place your cursor in the field for Ca value and press the keyboard F1 key to see help on this feature.
As mentioned the Ca value is an mass coefficient / factor that is multiplied by the mass of displaced fluid and will affect the frequencies for submerged piping.
The default value = 1.00, consider a value <1.0 to take less mass of displace fluid into consideration, or set Ca value >1.0 to consider more mass of displaced fluid during model analysis.
One may consider running an iterative approach of varying this setting and reviewing results to see how this may affect the results.
Bentley AutoPIPE