When computing a transient simulation in HAMMER, the following error message is generated:
"Fatal Error in routine GETRD at 1."
This issue can occur when there is an initial surge at an air valve. It is recommended to check the pressure at the initial conditions for the air valve. If the pressure is negative, then the initial pressure is likely to be at odds with the initial air volume input field, which is typically set to zero. If the initial pressure is negative, air must initially be inside the air valve.
Enhancements have been made starting with the CONNECT Edition release of HAMMER, which should resolve this issue in most models. It is recommended that you upgrade to the latest version of the program. You can find steps to download the latest version at the following link: Downloading OpenFlows | Hydraulics and Hydrology software.
Although the model in this condition may compute without error in CONNECT Edition, the air valve will experience an initial surge due to the HGL suddenly jumping up to the air valve physical elevation, and corresponding initial air inflow. To resolve the issue, either adjust the elevation or hydraulic grade such that the initial pressure is positive, or add an initial air volume.
If there is actually normally part-full flow at the air valve at this high point (air valve always open, part full flow downstream for some distance), you may need to set the "Treat as junction?" property field to "False" and place the air valve in-line with the main pipeline. This will treat the air valve as a PSV in the initial conditions, causing the upstream pump to add enough head to raise the HGL up to the air valve elevation, preventing the negative pressure problem that results in the error in question. However in this case for transient purposes, it may be best to end the system at the air valve location using a Discharge To Atmosphere node element, since the transient waves would not travel through the part of the network that is flowing partially full. See the section called "What if my air valve is open during the Initial Conditions?" in the following link: Modeling Reference - Air Valves.
Modeling Reference - Air Valves