I'm looking for tool in Hammer which makes the graph on the Figure below. It shows flow during the time in and out from hydropneumatic tank HT. It is taken from the materials from paper of Bentley.
And if my version 8i has this tool, is there an option to see the current volume in the HT?
You can create these from the Transient Results Viewer. There is a Time History tab. You will need to include report points for elements in your model. This is done in the transient calculation options. You have options to include all elements as report points or a selection of them. This link includes general information on doing this.
To view results like the volume in a hydropneumatic tank, you can do this with the Extended Node Data tab in the Transient Results Viewer. This feature is available in HAMMER V8i SELECTseries 5 or later. If you have an earlier version, you would need to use the Transient Analysis Detailed Report. The link above includes these steps as well. You will need to include a Report Period in the hydropnematic tank properties to be able to see results in the Extended Node Data tab or the Transient Analysis Detailed Report.
Answer Verified By: Boyan Borisov
Thanks for explanation.
I found Time History tab and I have made the in/out flow graph from hydropneumatic tank (HT).
And I have used Transient Analyses Detailed Report for looking the volumes of water in HT during the time.
Analyzing the volumes I find something that I can't explain. Initial volume in the HT is 75 litres (Figure 1). But in the Report in the first second it is written 0,024 m3 (Figure 2). Could we talk about that? There is explanation, of course, but what is it.
Later on, I have an addition to this post:
When the initial volume is changed to 10 litres, the volume in the first second in the report again is 24 litres. (Fig. 3 and Fig. 4). The total volume is again 150 litres.
I noticed that Volume (Tank) (not initial volume), i.e. Total volume affects the results. On Figure 5 and 6 are given the envelopes of pressures with "big" and "small" total volumes. When the total volume is under boundary value (e.g. 80 litres) there is a vacuum in the pipeline. The volume in the first second from transient Analyses Detailed Report this time is different (than 24) - 13 litres. The in/out flow rate of HT (Time History) also depends on total volume and may be variable gas pressure in air volume ...
May be before starting transient simulation Hammer calculates the volume of water in HT as a function of system characteristics like the total volume of HT and gas pressure in air volume outside the bladder, pump and system curves, etc.? And that is why, with this set of properties for HT, initial volume does not affect the results?
Your tank is set to use a bladder (has bladder = true) in which case HAMMER assumes that the pressure inside the full bladder is equal to the "preset pressure" (98 Kpa in your case) before the tank is installed and subjecting the tank to pipeline. Meaning, it determines the gas law relationship based on that preset pressure at the tank full volume. The bladder is then compressed based on that relationship along with the initial conditions pressure. This determines the starting gas volume at the first transient timestep. This is also why changes to the full volume impact the results, because they change the gas law relationship (if you keep the preset pressure the same).
For more information on how this works (including illustrations), see the "bladder" sections in the following article: Modeling Reference - Hydropneumatic Tanks
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Thanks, I understood the situation. I have one small secondary question. Which volume is given in the second column on Figure 2 and 3, after calculation based on initial conditions? I thought that it is the volume of water in the bladder, but after your explanation about main question I doubt.
Boyan Borisov said:Which volume is given in the second column on Figure 2 and 3, after calculation based on initial conditions?
It is the volume of gas in the tank - when the tank is connected to the system and subjected to system pressure, the gas/air in the tank compresses to the size that you see in the first row of those reports. If your tank is the "air in bladder" type, then it is the volume of air inside the bladder during the transient simulation and if it is the "water in bladder" type, it is the volume of air outside the bladder (but in the tank). There are illustrations in the article previously mentioned to show the difference.