MATLAB: Initial Pressure in Segmented Pipe LP Block

Question

Hi,

Recently, I've been investigating replacing the segmented pipe block from SimHydraulics with the segmented pipe LP block to account for head differences between pipeline entry and exit. The system being modelled runs at pressures above 100 bar, however the elevation effect is important, hence the reason to utilize the LP block. I've started modelling with the LP block, however I am slightly confused with one difference to the normal segmented pipe block.

In the normal block you can select the initial pressure condition for all nodes within the segmented pipeline. Generally, this is a constant pressure across my pipeline for steady start-up. however, with the segmented pipe LP block, no control over initial pressure is available. Further to that, there is no information in the documentation to suggest what initial pressure is assumed at each node within the LP pipe. I'm presuming it something like atmospheric pressure + elevation at that point. Can anyone help me out here?

Regards, Jack

Answer 1

To observe the pressure at each node, I recommend using the Simscape Logging Explorer:

http://www.mathworks.com/matlabcentral/fileexchange/28184-simscape-simulation-results-explorer

If you expand the data logged for the segmented pipe LP, you will be able to see a "ch_X" for each chamber part of the pipe.

What I observe is that the initial pressure is 0 for all chamber at t=0.

If you need something different, you have a few options:

- Using the Start From Steady State. You cannot really control the initial pressure, but it can make it start from something else than 0

- Specify initial states in the model configuration.

- Build your own segmented pipe using the basic blocks as illustrated in the doc. Using the Simscape language, the connections section and the connect function, this is not too bad. That way you will be able to specify the initial pressure for each chamber in your segmented pipe. Here is a link to get you started:

http://www.mathworks.com/help/physmod/simscape/lang/creating-composite-components.html