- Clicking Save / Continue button will convert the time history into its equivalent force response spectrum in terms of Dynamic Load Factor versus Frequency and the screen “Spectrum Table Values “as shown in Fig. 5 will appear.
- Be sure to specify a unique spectrum name, as this processor will overwrite any existing files of the same name.
- By clicking OK, the processor will load the appropriate data in the Spectrum Definitions tab in Dynamic Input and move the data to the dynamic input
Once the spectrum profile is generated click on force sets button and enter the slug force with proper direction in the fields as shown in Fig. 6:
- Click on the + button to add more rows and – button to delete rows.
- In force set field input a numeric id which will be used to construct dynamic load cases.
After that click on Spectrum load cases menu and create the required load cases for dynamic analysis. You have to specify at least two load cases as shown.
- Operating + Dynamic for nozzle and support load checking.
- Sustained + Dynamic for stress checking.
Refer Fig. 7 for load case preparation
Finally click on control parameters button and select the load case for which you want to perform the analysis. Normally operating load case is selected (Refer Fig. 8) for dynamic analysis. Keep all other parameters as it is. Now click on batch run to obtain the analysis results. Fig 9 shows a typical analysis results.
- This figure shows a typical output screen for dynamic slug flow analysis.
- The highlighted node 10 is for nozzle.
- All support and nozzle loads to be checked.
- Stresses to be kept below code allowable values.
- The highlighted direction sign will show other load case combinations.
Few Important Points:
- Vibration due to any two phase flow can be reduced / arrested by proper supporting of the piping system. Normally following supports are used:
- HOLD DOWN SUPPORTS WITH 0 GAP
- GUIDE SUPPORTS WITH 0 GAP
- AXIAL STOPS WITH 0 GAP
Whenever modifying any support perform static analysis and keep the system stresses within allowable limit.
- Sometimes Vibration Absorbing Material (like PTFE) is used to reduce the Transfer of vibration to connected systems.
- It is preferred to keep natural frequency of piping system above 4 Hz for Vibration prone lines.
- The formation of Slug Flow can be reduced:
- By reducing line sizes to a minimum permitted by available pressure differentials.
- By using a low point effluent drain or bypass.
- By arranging the pipe configurations to protect against slug flow. E.g. in a pocketed line where liquid can collect, slug flow might develop. Hence pocket is to be avoided.
Request you to provide your input on the mentioned subject.