Project Commands in 9.1
From SysCAD Documentation
Navigation: User Guide -> Menu Commands -> Project Commands
This section shows the Project Commands in SysCAD 9.1. Refer to Project Commands in 9.2 for SysCAD 9.2.
Contents |
Settings
ProBal Setup
Command Path Project, ProBal Setup
This command will only be available in a ProBal project.
NOTE: SysCAD must be in the Edit mode for this command to be accessed.
This will open the Solver Dialog box:
- Convergence
The user may define the maximum number of iterations that SysCAD will perform before automatically halting. The maximum number of iterations allowed is 20000.
Changing the Relative (Rel) and Absolute (Abs) Tolerance can vary the accuracy and speed of the solution. By increasing the numbers the solution will converge faster, but will be less accurate.
A tolerance calculation is performed every iteration, for all species and heat flows in all units/links. See Tolerance Testing for more information.
The SysCAD model is considered converged if the calculated tolerance is less than or equal to 1.0 for all species and heat flows in all units/links for the last n consecutive iterations, where n = Rqd Converged Iters, as set by the user.
Changing the relative tolerance from 0.01 to 0.1 would increase the error margin by an order of magnitude.
Typically the relative tolerance would be greater than or equal to the absolute tolerance used.
The Method of solution can also be changed. Options available to the user are Direct Substitution, Adaptive Direct Substitution, or Wegstein Acceleration. For more information on convergence/tolerances, please refer to Tear Blocks.
- Active Pages
You can Activate or Deactivate flowsheets (Graphics Windows) in the SysCAD Project by selecting the flowsheet and pressing the appropriate buttons. When a Graphics Window is deactivated, all models on that graphics page will become inactive, thus not included in the solution. Any connections with other graphics pages will be disconnected (done in the Feeder/CrossPageConnector model). The user should check all feed and product streams when solving a simulation with deactivated graphics to ensure correct information is used.
This is not available if the drawing is not loaded in the Graphics Window.
- Options
The "initialise" option will re-initialise SysCAD variables at the first iteration. The Status display and Status pinned options displays the Solution dialog box.
Dynamic Setup
Command Path Project, Dynamic Setup
This command will only be available in a Dynamic project.
NOTE: SysCAD must be in the Edit mode for this command to be accessed.
This command will allow the user to change the dynamic simulation options, such as solving method, step sizes and so on prior to running the SysCAD dynamic simulation. These are done through the Dynamic dialog box. When the settings have been changed, press the OK button to save the new settings and close the dialog box.
Time
A number of options are available for controlling how long a dynamic simulation must run or solve for. These are: 'forever' where the solver never stops; 'to steady state' where solver runs until it detects there are no more changes in the process variables; 'for' a specified time span; 'until' a specified end time; 'for x steps' runs for a specified number of steps. The current time is shown, user can choose to synchronise the time with clock - NOTE this will automatically put your simulation into Real time, thus project cannot run in accelerated time option.
If Synchronise with clock option is NOT selected, user can choose to run the project in real time, solver will determine to speed up or slow down the simulation to meet with the real time clock.
Another option the user can choose is to have the simulation run in accelerated time, this is done by specifying a Real time multiplier, thus a real time multiplier of 8 will mean SysCAD is running 8 times faster than real time.
For users that would like to run the simulation as fast as possible without having to relate to real time, make sure the Real Time box is NOT selected, and then set the iteration and step size option on the Method's tab.
Method
The method used for the dynamic simulation can be changed here. The methods available are Euler, Runge-Kutta2 and Runge-Kutta4.
SysCAD solves the dynamics of a flowsheet in incremental time steps. The step size can be fixed or variable, depending on the integration method used. Only the Runge-Kutta4 allows variable step sizes.
- Fixed iteration size
The iteration size is fixed. The higher value results in faster relative speed, but less accurate solution. The maximum meaningful fixed iteration size that can be used is dependent on the dynamics (relative flow rates, volumes of units etc) of the process.
- Variable iteration size
With a variable iteration size the user defines the maximum and minimum iteration sizes. SysCAD uses a iteration size between these limits and aims to use the largest possible. The iteration size used is dependent on the dynamics response of the process. If changes are occurring rapidly or a significant change occurs (valve opened, tanks overflows) when SysCAD is solving the model, the iteration size is reduced until conditions have stabilised.
Once conditions have stabilised or the discontinuity has been passed, the iteration size is increased again.
A variable iteration size solution gives the most accuracy.
- Tolerances
The Relative and Absolute Tolerances can be set. The smaller the tolerance the more accurate the result, however, this will also slow down SysCAD considerably. Refer to convergence in ProBal Setup.
- Step size
A step size determines how often the values are updated in SysCAD. A step can be made up with multiple iterations. In the example above, the iteration size is 0.2 sec, and the step size is 1 sec, that is, each step is made up with 5 iterations. Number displays in trend windows and so on will be refreshed (or stored in historian) at the end of the step.
Network and Tears
The next two tab pages contain the solution network and tear stream settings. These can be used to improve the SysCAD speed in obtaining a solution.
A tear is required to solve models that contain one or more recycle streams. SysCAD determines the optimum position for the tears. The algorithm used to determine the position of the tears is described in the following paper:
Ollero P. and Amselem C., "Decomposition Algorithm for Chemical Process Simulation", Chem. Eng. Res. Des., 61, 303, (Sept. 1983)
SysCAD determines the position of the tears as part of the startup sequence each time the model is solved.
- Floor
For a dynamic simulation, if a tank overflows, it needs to go to the floor or a holding tank of a very large size. If the Spill Area on the network tab page is keep as Floor.Content, a tank called "Floor" should be drawn in the flowsheet. The volume of this unit can then be increase to a very large number to hold all spills. If a "floor" is missing, SysCAD will warn with a message in the Message Window.
Active Pages
You can Activate or Deactivate flowsheets (Graphics Windows) in the SysCAD Project by selecting the flowsheet and pressing the appropriate buttons. You may also deactivate a Graphics window via the Explorer Window.
When a Graphics Window is deactivated, all models on that graphics page will become inactive, thus not included in the solution. Any connections with other graphics pages will be disconnected (done in the Feeder/CrossPageConnector model). The user should check all feed and product streams when running a simulation with deactivated graphics to ensure correct information is used.
This is not available if the drawing is not loaded in the Graphics Window.
Options
Start up Actions:
- Empty All: This empty all holding vessels but not including pipes, then builds and solves for the first iteration.
- Zero Flows: This sets all pipes to zero flow, then builds and solves for the first iteration.
- Initialise All: This initialises unit operations where applicable.
- Reset Statistics: This resets all statistical models.
- Once Only:
Flow Options:
The momentum option will increase the speed of the dynamic simulation, however, this should be used with caution, as sometimes it may not produce the most accurate result.
Historian:
- Restart Historian at Start: This option clears any old data in the historian at the start of the simulation.
- Set time at Start: The SysCAD simulation time will be reset at start.
Compare Data
Command Path Project, Compare Data
NOTE: SysCAD must be in the Edit mode for this command to be accessed.
This command allows the user to compare two projects for its differences in tags and values. It is most useful to highlight changes in projects such as adding or deleting of unit operations or different operating conditions.
When the command is activated, it opens the Compare Projects Dialog box:
Choose the projects to be compared by using the browse buttons, select the comparison options and reporting file location. Press OK when ready to start the comparison, SysCAD will display the progress on the screen. When this is finished, open the PrjDiffs.csv file to analyse the results.
Another similar command is Snapshot/Scenario - Compare Scenario
