When doing a powered run, you have the option of entering a fixed RPM (where the propeller starts at that value and remains there for the entire run), or you may enter a time ramp. In this case, the RPM varies linearly from 0 to the RPM value that you have entered, over the number of seconds that you enter.


If you want to vary the RPM in a more precise way, you can create a table of RPM vs. time. In this example, we’ll assume that we have the following information from some previous full-scale tests:















Note that the final value for time (30 in this example) should be higher than the length of time you expect to analyze. There is no reason not to set it to something much higher, e.g., 100. 

We will use the expression editor capability in Simerics to model this behavior. First, in the Orca3D CFD interface, just put any value in the RPM field (e.g., 1000), and then generate the Simerics simulation file as normal (at the bottom of the dialog, check the box that says “Prepare files but don’t start simulation,” and then click Create Files). Now open Simerics and open your .spro file. Go to the Model window and select the Marine module. Then in the Properties window you will see an icon to open the Expression Editor as shown highlighted below. Click on that icon.

Once you open the Expression Editor you will see an editing window. One of the lines (probably the second) will say something like prpm1 = 1000 (or whatever RPM you set in Orca3D). Change that line to read, 


prpm1 = table(rpm.txt,time)


This expression means set the RPM for propeller 1 to be the value in the lookup table called "rpm.txt" using a lookup value of time. 

The last step is to create the table. Use a text editor to create a file called "rpm.txt" that must be located in the same folder where all the other Simerics files are located (this is the path you specified in Orca3D with a subfolder name corresponding to the rpm you entered). The data in the RPM text file should be of the following form. You may have fewer or more lines of data, but it is important that the value for "table size" is the number of values in the table. Save this file, and then start the simulation. 


<?xmlversion="1.0" encoding="ISO-8859-1"?>  

<table size="6"outside="extrapolation">  

# Time(sec)    RPM

0 0

0.1   350

7 475

13 650

16 850

30 850