AFT Blog
There are many (six!) ways to define a pump transient event in AFT Impulse. This gives you great flexibility in creating a model that behaves the way you want it to. One thing true for all pumps is that they must be started at least once. Pump startups often cause significant transient effects on the system so you may wish to model this with AFT Impulse. Even narrowing your pump transient down to a startup, there are still four models left to choose from: Without InertiaStartup With Inertia and No Back Flow or Reverse SpeedStartup With Inertia - Four Quadrant, Known...
To define any transient event in AFT Impulse or AFT Fathom XTS the application must know when it begins. To do so, the user should know how time and event logic is approached in AFT’s transient solvers. In this article, we will discuss the three different time bases used in the applications, the selection of a single or repeating event, and the many possible triggering events that can start the user defined transient. The user defines these items in the Initiation of Transient section of the junction’s Transient tab. The requirements for each junction can vary, but the general approach applies...
In AFT Fathom and AFT Impulse, it is possible to model a submerged pump where a short and possibly frictionless suction pipe for the pump’s inlet does not need to be modeled. When modeling a submerged pump, there are two options available for specifying the system inlet boundary condition at the pump suction. As shown in Figure 1 below, the Submerged Pump’s Suction Pressure can either be specified as “Head (HGL)” or “Pressure”. Modeling a submerged pump is not the only time where the “Head (HGL)” or “Pressure” choices will arise. If an Exit Valve (i.e., a valve that discharges...
AFT Fathom can easily generate a pump and system curve for your piping system. Creating a pump and system curve for a simple system with a single flow path and no control features is an easy and typically well-understood process. However, as piping systems are quite complicated with lots of branch points, control features, and dynamic interactions, creating a useful system curve can quickly become a common source of confusion. This three-part blog series is going to help clarify concepts regarding pump and system curves to better understand them. This Part 1 blog will discuss the basics of what pump...
Have you ever finished running an AFT Impulse model and then received the following Warning message shown in Figure 1 and then wondered what it means? During a waterhammer analysis, the flowrates are constantly changing all throughout the system, therefore, the velocities and Reynold's numbers are also constantly changing. The friction factors will also be constantly changing during the transient. By default, AFT Impulse will use the friction factors that are obtained during the steady-state analysis and then use the same friction factors during the transient and they will be assumed to remain constant. Since it is possible for the flowrates...
Previously, we talked about the Graph Guide, creating Stacked graphs and Dual-Y graphs, and visualizing the results using Animated graphs. This final installment will focus on the various ways to format graphs so they are exactly how you want them to look. In general, there are several ways to set the formatting for the various parts and regions of a graph. I will start with the model we made in the previous blog – the AFT Impulse model, ‘Pump Startup With Event Transient.imp’, which is installed in the Examples folder. Many of the formatting options are gathered together on the Formatting...
Previously, we talked about the Graph Guide and how to create Stacked Graphs and Dual-Y graphs. With AFT Impulse and with AFT Fathom’s XTS module, a great way to see how parameters change over time is through animated graphs. For the purpose of continuity, I am going to again start with the AFT Impulse model, ‘Pump Startup With Event Transient.imp’, which is installed in the Examples folder, and use the ‘One Pump Start With One Running’ scenario. In the previous blogs, we used a Stacked Graph and a Dual-Y Axis Graph to examine the pressures and flows at two valves (J6...