| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Environment: | N/A |
| Area: | Modeling |
| Original Author: | Bentley Technical Support Group |
| Date Logged & Current Version | Dec. 2016 10.01.00.09 |
Problem:
Can all dynamic analysis (ex. Response Spectrum, time history, Harmonic, etc..) be performed on underwater piping correctly while using AutoPIPE?
Solution:
Hydrodynamic load case is added to a model by using Insert> Xtra Data> Hydrodynamic Data... command. Lift coefficient (Cl) value is used to calculate the lift forces due to the motion of a fluid body relative to the structure. Enter the lift coefficient to be used at the current point. If the default (0.0) lift factor is accepted, lift forces will not be calculated at the current point.
The lift force is calculated at each point using the Morison equation (see online help for details) in conjunction with the defined Wave loading(s). Each wave loading is applied during a specified Load case (ex. U1).
There are 2 approaches for modeling seabed piping, support the pipe with Soil properties or V-stops with large gaps above the pipe. This topic will focus on the V-stop methodology.
When reviewing the output report, remember in order to consider Gaps/Friction/Soil in a model it must be analyzed as a non-linear analysis. As a non-linear analysis load sequencing applies (see Non_Linear_Load_Sequencing.pdf, located in the AutoPIPE folder). With that said, concentrate on the report's operating condition / combination (ex. GrT1P1U1, ). If more understanding about the combination is required then review the individual results from the load case results (ex, Gr, T1, P1, U1) where due to load sequencing the result of the individual load cases are added together to arrive at the combination's results.
For example, provided the following model of seabed piping:
Wave loading is applied to load case (U1).
Hydrodynamic loading is applied to the entire pipe segment.
Point Load FORCES (N )
name combination X Y Z Result
------ ----------------------- ------ ------ ------ ------
E07 V - Stop Tag No.: <None> [ID: E07 1]
Gravity{1} 0 -95 0 95
Thermal 1{1} 0 0 0 0
Pressure 1{1} 0 0 0 0
User 1{1} 0 84 0 84
GT1P1U1{1} 0 -11 0 11
Note:
1. The operating condition due to Gravity +Thermal+Pressure+U1 (Wave Load) = 11 N acting vertically down.
2. All v-stops have a gap above the pipe, but under U1, there is a vertical Up (+y) load acting on the support. This is correct. Remember Load sequencing.
3. Do not for get about Buoyancy, the results above includes Buoyancy. If you are concerned about knowing the results of pipe movement due to only hydrodynamic data, be sure to uncheck Buoyancy on the Segment tab of the input grid.
Re-run the analysis, and review the results:
R E S T R A I N T R E A C T I O N S
Point Load FORCES (N )
name combination X Y Z Result
------ ----------------------- ------ ------ ------ ------
E07 V - Stop Tag No.: <None> [ID: E07 1]
Gravity{1} 0 -165 0 165
Thermal 1{1} 0 0 0 0
Pressure 1{1} 0 0 0 0
User 1{1} 0 84 0 84
GT1P1U1{1} 0 -81 0 81
Here we can see the true affect of hydrodynamic data on the pipeline, operating condition GrT1P1U1 = 81 N acting down. Notice how the Gravity load without Buoyancy was updated to 165 N from 95 N, again acting downward.
See Also
Model Subsea (Underwater) Piping