Introduction
Calculating a model is a critical step in the FluidFlow workflow. Once you've built your network and defined all the required inputs, the calculation process analyzes your system and provides results for flow rates, pressures, temperatures, and other parameters throughout your network. This guide explains how to initiate calculations and customize calculation options to suit your specific modeling needs.
Basic Calculation Process
Step 1: Pre-Calculation Verification
Ensure all required inputs are defined (pipe sizes, materials, fluid properties, etc.)
Verify boundary conditions (pressures, flows, temperatures)
Check for any disconnected components or incomplete sections
Step 2: Initiating the Calculation
Click the Calculate button in the toolbar
Alternatively, press Ctrl + F8 on your keyboard
The calculation process will begin, with progress indicated in the status bar
Step 3: Reviewing Calculation Status
Once complete, a notification will appear in the status bar
Successful calculation: "Calculation complete" message appears
Failed calculation: "Calculation Error" message appears
Check for red highlights in the model, which indicate errors or warnings
Customizing Calculation Options
FluidFlow allows you to customize various aspects of the calculation process through the Calculation Options dialog. To access these options:
Go to Options | Calculation in the main menu
Alternatively, press F2 on your keyboard
Overview of Calculation Options Tabs
Current Network
This tab simply displays details about the currently active model, providing information such as:
File Name
Number of nodes and pipes
Status
Convergence count
Number of warning messages
Convergence Criteria
This tab provides controls for fine-tuning solver parameters, particularly useful for large, complex networks that struggle to converge.
Note: Adjust these settings only when necessary. After troubleshooting, use the Reset to Defaults button to restore recommended settings and maintain maximum accuracy.
Global Settings
Defaults - Control constants and assumptions used throughout the calculation
Assume Zero Flow: During iteration, pipe sections with flow equal to or below the specified value are treated as having zero flow. This assists model convergence, especially in complex systems, by removing these sections from the iteration process.
Inclusions - Configure additional factors to consider in calculations
Automatically include correction factors for centrifugal pumps handling fluids with different viscosities than water
Consider losses due to expansions and reductions near control valves
Enable advanced iteration for more accurate friction factor calculations across all flow regimes
Convergence Aids - These settings are particularly helpful in systems with open pipes or resistances
Prevent backflow originating from open pipes or resistances during iteration
Heat Transfer - Select the pipe heat loss outside coefficient model to be used for component heat loss calculations
Gas
Configure settings specific to gas systems:
Set reference conditions for gas volumes (normal or standard)
Include or disregard the Joule Thomson effect in heat transfer models
Configure options for gas lines experiencing condensation due to heat loss, with or without steam vapor trap arrangements
Two-Phase
Select the correlation to be applied in two-phase flow calculations:
Whalley criteria (automatically selects from three correlations — Friedel, Chisholm, or Lockhart Martinelli)
Drift Flux Model (2007)
Beggs & Brill (Extended Regions)
Friedel
Muller-Steinhagen-Heck
Chisholm-Baroczy
Lockhart-Martinelli
Homogenous Equilibrium Model
Slurry
Customize settings for specialized flow types:
Select pressure loss correlations and set constants for slurry and non-Newtonian flow calculations
Choose correlations for heterogeneous settling slurries
Configure deposition velocity correlations
Set model assumptions, such as considering inclined piping when elevation differences are present (automatically adjusts pressure losses and deposition velocity calculations)
Option to assume all solid particles are spherical in settling and deposition velocity estimations
Pulp & Paper Stock
Customize calculations for pulp and paper applications:
Select pressure loss correlations (TAPPI or Moller K)
For TAPPI: Choose the TAPPI pulp type to be applied
For Moller K: Define the pulp property constants used in the correlation
Applying Calculation Options
When you've finished configuring your calculation options:
Apply to All Open Networks: Check this option to apply your settings to all open modeling files
Default: Check this box to store your preferences for future FluidFlow sessions
Reset to Defaults: Click this button to return all options to their original configuration
Best Practices
Keep calculation settings at their defaults unless there's a clear need for change
Document any modifications made to calculation options for project traceability
After troubleshooting or specialized analysis, reset options to defaults
Use convergence aids and other assumed values cautiously—overuse may mask real flow behaviors
Verify calculation results against expected values or hand calculations for critical sections
FAQs
Q: How do I know if my calculation was successful?
A: The status bar will display "Calculation complete", flow arrows should appear to indicate flow direction, and there are no error messages present.
Q: Should I change convergence criteria for every project?
A: No. Only adjust these settings for large or complex networks that fail to converge with default settings.
Q: What happens if I select the wrong correlation?
A: The solver may produce less accurate results. Always choose correlations that best match your fluid type and flow regime.
Q: Can I save my custom setup for all future projects?
A: Yes, by checking the Default box before closing the options window.
Q: What should I do if my model fails to converge?
A: First, check for modeling errors or unrealistic inputs. If none are found, try adjusting the convergence criteria or using convergence aids in the Calculation Options.
Conclusion
The calculation process is where FluidFlow transforms your model inputs into meaningful engineering results. While the default calculation settings are suitable for most applications, the ability to customize calculation options gives you the flexibility to handle specialized cases and complex systems.
By understanding how to initiate calculations and adjust calculation options when necessary, you can ensure your FluidFlow models deliver accurate, reliable predictions for your fluid system designs.
Mastering the calculation process and options in FluidFlow empowers you to solve even the most challenging fluid system problems with confidence, ensuring optimal designs and preventing costly errors in real-world applications.