| Applies To | |||
| Product(s): | AutoPIPE, | ||
| Version(s): | all | ||
| Area: | Modeling | ||
| Original Author: | Bentley Technical Support Group |
Dec 2014, AutoPIPE V8i 09.06.01.10
Problem:
How do I model Flex / Braided hose:
Solution:
Most flexible hoses fall into one of two categories, see the following for categories and suggested modeling approach:
1.Short stubby flex hosing between end connection. Usually very stiff but does allow a little bit of flexing between connection points.
Modeling
The flexible piping between the end connection is short enough where the user should consider its stiffness properties. Therefore, contact the manufacture of the flexible joint assembly and request all the values required by the Flexible Joint dialog in AutoPIPE. This info should include, overall length, stiffness in all 6 directions, weight, and pressure area.
Due to the construction, the hose material or outside braiding may be strong enough to withstand axial expansion. If true, then insert a tie/link support connecting the 2 end points of the Flexible Joint. Be sure to configure the support with the proper stiffness and gap to represent the amount of moment before the axial expansion would be restrained.
Conclusion: model using one flexible joints with appropriate stiffness values, weight, and Pressure Area. In addition, insert a support between Flexible Joint end points to restrain axial extension. Again, be sure to enter the appropriate stiffness and gap settings.
2. Lengths of flexible hose with end connection
Modeling
Flex hoses are typically so flexible that it is like a break in the pipe with no transfer of forces or moments. Therefore, recommend using a 1 or more flexible Joints back-to-back with low stiffnesses, unless the manufacturer can provide some stiffness values.
Suggest the following:
a. Appropriate stiffness values
Axial: If hose is resistant to pressure thrust suggest high value or Rigid. Otherwise use manufacture literature value.
Shear and Bend: suggest very low values (ex. 0.1 - 1.0) or use manufacture literature value.
Torsional: Use engineering judgement or manufacture literature value. Typically the braided jacket, as imaged above, resists rotational movements once tensioned. Therefore, suggest a moderately high value or Rigid. Otherwise use an iterative approach starting with a small value and iteratively increasing to see how it affects the analysis.
b. Weight: actual weight of hose / assembly equally distributed across the number of flexible joints used.
c. Pressure Area:
i. Assuming that the hose material or braiding will be strong enough to withstand the pressure thrust generated and will not be transferred down the pipe to supporting structure, Pressure Area = 0.00. Or, enter a pressure area value and insert tie/link support(s) connecting the 2 end points of the Flexible Joint(s) as mentioned above.
ii. Assuming that Hose material / assembly would not withstand pressure extension, Pressure Area = (enter pressure area value of hose).
Notes:
1. Due to possible instability issues during analysis, may need to provide a small non-zero stiffness value, e.g. 0.1 to 1 lb/in.
2. The weight of contents is controlled by the PipeID Specific gravity value used when inserting the Flexible joint. While the weight of hose assembly is controlled by the weight value entered on the Flexible joint dialog.
3. If adding Buoyance load to a flexible joint, buoyance force would be calculated based on the total Outside diameter per the PipeID of the flexible joint.
4. Remember that AutoPIPE cannot handle large deformation and forces/moments are based on original un-deformed geometry.
5. One could use Beam elements to represent a flexible hose, In this modeling approach enter non-standard section properties instead of stiffness.
See Also
Flexible Joint - Modeling Approaches, Tips, Techniques