Open Channel Hydraulics
This online engineering PDH interactive presentation focuses on the basic nature of flow in open channels and common ways of classifying open channel flow (laminar or turbulent, steady state or unsteady state, uniform or non-uniform, and critical, subcritical or supercritical). It presents several worked examples to gain practice in the use of the Manning equation for a variety of uniform open channel flow calculations. The presentation also presents the parameter “specific energy” and various calculations related to critical, subcritical and supercritical flow, including hydraulic jump calculations. It discusses the thirteen possible types of gradually varied non-uniform flow surface profiles. It illustrates the procedure and equations for step-wise calculation of gradually varied non-uniform surface profiles through the use of examples.
Flow of water may take place either as open channel flow or pressure flow. Pressure flow takes place in a closed conduit such as a pipe, and pressure is the primary driving force for the flow. For open channel flow, on the other hand, the flowing liquid has a free surface that is at atmospheric pressure and the driving force is gravity. Open channel flow takes place in natural channels like rivers and streams. It also occurs in manmade channels such as those used to transport wastewater or irrigation water and in circular sewers flowing partially full.
Many examples of open channel flow can be approximated as uniform flow allowing the use of the Manning equation for calculations. However, non-uniform flow calculations are needed in some open channel flow situations, in which the flow is clearly non-uniform. The concepts of supercritical, subcritical and critical flow, along with calculations related to those three flow regimes are need for non-uniform open channel flow analysis and calculations.
This 1 PDH online interactive presentation is intended primarily for civil, hydraulic, highway, environmental, chemical, mechanical, and industrial engineers, who are interested in learning more about open channel hydraulics.
This continuing education interactive presentation is intended to provide you with the following specific knowledge and skills:
- Understanding the difference between laminar and turbulent flow, steady state and unsteady state, as well as uniform and non-uniform open channel flow
- Calculating the hydraulic radius for flow of specified depth in an open channel with specified cross-sectional shape and size
- Calculating the Reynolds number for a specified open channel flow and determine whether the flow is laminar or turbulent flow
- Determining a value for the Manning roughness coefficient for flow in manmade or natural channels using the example tables provided in this course
- Using the Manning equation to calculate volumetric flow rate, average velocity, Manning roughness coefficient, or channel bottom slope, if given adequate information about a reach of an open channel
- Using the Manning equation with an iterative procedure to calculate normal depth for a specified volumetric flow rate, channel bottom slope, channel shape and size, and Manning roughness coefficient for a reach of open channel flow
- Performing calculations for full or partial full flow under gravity in a circular pipe
- Determining the critical depth for a specified volumetric flow rate through a rectangular channel of specified bottom width
- Determining the critical slope for a specified volumetric flow rate through an open channel of specified shape, size, and Manning roughness coefficient, with known critical depth
- Determining whether a specified volumetric flow rate through an open channel of given shape and size with known depth of flow will be critical, subcritical or supercritical flow
- Calculating the depth of flow after a hydraulic jump if given the depth of flow before the hydraulic jump, the volumetric flow rate and the shape and dimensions of the open channel.
- Identifying which type of surface profile (e.g. M1, M2, M3, S1, S2, S3, etc.) is present in a specified gradually varied flow situation
- Performing stepwise calculation of the surface profile for a specified gradually varied, non-uniform open channel flow
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