One of the limitations of HEC-RAS is that it is a one-dimensional model. Simply put, RAS assumes all flow moves along a singular dimension. For a given cross section, all of the flow is assumed to move either downstream, or all of it moves upstream, along the singular dimension (which can be defined as a […]
So many of us know that if you experience instabilities at or near your inline structure, you should bump up the Inline Structure Flow Stability Factor from the default of 1 to the most stable value of 3. But what is really going on when you do this? Here’s an example of a RAS model […]
Adding to the previous topic on the Theta Implicit Weighting Factor (Theta), this post takes an objective look at how the unsteady-flow option affects model output. Theta is a weighting factor for the spatial derivative used in solving the finite difference forms of the St. Venant equations. Adjusting Theta can improve model stability or increase […]
Written by Chris Goodell, P.E., D. WRE | WEST ConsultantsCopyright © RASModel.com. 2010. All rights reserved.I was recently emailed this question regarding steady flow versus unsteady flow results: “My question is fairly basic. I have heard from a couple of other engineers that when flood levels are generated with usteady flows that it is typical […]