AFT Blog
You’ve built your AFT Fathom or AFT Arrow model, defined all pipes and junctions, specified your fluid properties and defined your pressure boundary conditions. But for some reason, your predicted flows are still not matching measured data. AFT Fathom or AFT Arrow is properly solving the fundamental equations, but it is likely that something is off in the inputted data. In many cases, this is the pipe’s resistance. Many factors can alter a pipe’s resistance, but the two primary reasons resistance may be incorrect is (1) corrosion of the pipe over time, which increases a pipe’s absolute roughness and (2) the buildup of residue on the walls of the pipeline, known as scaling, which decreases a pipe’s inner diameter. This decrease in diameter is very important and will increase a pipe’s resistance dramatically. Now you have a dilemma. You can’t cut open your pipe to see how much scaling there is or how much your pipe has corroded. What is the condition of your pipe? Using AFT Fathom GSC or AFT Arrow GSC, you can find out!
Often times when building larger network models, you may not be sure what the direction of the flow will be and running the model is the only way to determine the flow direction. In the below AFT Arrow model it might be hard to determine what way the flow convention is in some of the loops. After running this model there are cautions stating that flow is negative through junctions that may have loss factors that are dependent upon direction. What is the easiest way to fix this? You could compare your results, remember or make a table of what pipes...
Well that depends on how optimistic you are, but either way you can model partially full pipes with AFT Impulse! This means partially full along the axial direction, as opposed to partially full along the radial direction. This function only works for pipes that have a slope, and when the pipe is partially full it drains from the end with the higher elevation. Pipes which contain vacuum breaker valves, exit valves, spray discharges, or assigned pressures at the outlet can drain or fill during the transient. This draining or filling is limited to the specified pipe. AFT Impulse will not model...
Many engineers are familiar with gas accumulators and their ability to aid in surge suppression modeled in AFT Impulse, but what about liquid accumulators? Liquid accumulators are different from gas accumulators in that they are assumed to be liquid full and do not have any gas that can compress and expand in order to dampen pressure spikes caused by water hammer. Liquid accumulators change the system response to pressure spikes, but they operate differently than gas accumulators. There are only three required input parameters for liquid accumulators; Elevation, Elasticity, and Initial Volume. Figure 1: Liquid Accumulator Properties Window Initial Volume is...