SWMM5 xsect.c Summary

 The xsect.c file in SWMM 5 is responsible for handling the cross-sectional geometry and hydraulic calculations for various types of conduits and channels. It provides functions to compute hydraulic parameters (such as area, wetted perimeter, hydraulic radius, section factor) based on the shape and dimensions of the cross-section, as well as to handle a variety of cross-sectional shapes used in drainage and stormwater systems.

Key Components of xsect.c:

1. Cross Section Geometry Functions:

   • Functions like getAofY(), getWofY(), getRofY(), and getYofA() compute the area, top width, hydraulic radius, and flow depth at a given value of depth or area for various cross-sections.
   • getSofA(), getRofA(), getdSdA(), and other functions calculate the section factor, hydraulic radius, and derivatives of section factor with respect to area, which are critical for hydraulic flow modeling using Manning's equation.

2. Cross Section Shape Types:

   • The file supports various geometric shapes for conduits and channels, such as:
     • Circular, Filled Circular, Egg Shaped, Horsehoe, Gothic, Catenary, Semicircular, Arch, Rectangular, Trapezoidal, Triangular, Parabolic, Power Function, Custom, Street Xsect (for streets), etc.
   • Each shape type has specialized functions for computing hydraulic parameters such as getRofA() (hydraulic radius for a given area) and getAofY() (area for a given depth).

3. Manning’s Equation:

   • Several functions in the file use Manning’s equation to calculate flow characteristics for different cross-sections, considering parameters like the flow area and wetted perimeter.
   • For instance, getSofA() computes the section factor (which is used in Manning’s equation) at a given area, while getRofA() calculates the hydraulic radius.

4. Flow Calculation for Special Shapes:

   • The file also includes specific calculations for special shapes like Eggshaped, Horsehoe, Gothic, Arch, Basket Handle, and Mod. Basket Handle shapes. These shapes require customized methods to compute parameters due to their unique geometry.

5. Handling Irregular and Custom Shapes:

   • For irregular and custom cross-sections, the file provides a way to define and compute the geometry based on user-defined data, supporting flexible configurations for modeling real-world drainage and stormwater systems.

6. Functions for Computing Critical Flow Depths:

   • getYcrit() computes the critical flow depth for a cross-section given a flow rate. The critical flow depth is important for flood modeling and for determining flow regime transitions (subcritical, critical, supercritical flow).

7. Street Cross-Sections:

   • xsect_setStreetXsectParams() is used for setting parameters for street cross-sections. Streets often have a unique shape, and this function models the geometry of streets with channels, curbs, gutters, and backing.

Functions Related to Geometry:

• xsect_isOpen(): Determines if the cross-section is open (e.g., an open channel or conduit) or closed.
• xsect_getSofA(): Computes the section factor (a measure of the ability of a section to convey flow) for a given area.
• xsect_getRofA(): Computes the hydraulic radius (ratio of flow area to wetted perimeter) for a given area.
• xsect_getYofA(): Returns the flow depth (Y) for a given flow area (A).
• xsect_getAofY(): Returns the flow area (A) for a given flow depth (Y).
• xsect_getWofY(): Returns the top width (W) of a cross-section at a given flow depth (Y).
• xsect_getdSdA(): Computes the derivative of the section factor with respect to area, used for flow calculations.

Specialized Shape Functions:

• Circular Shapes:

  • circ_getAofY(), circ_getRofA(), circ_getSofA(): Handle calculations for circular cross-sections.

• Filled Circular:

  • filled_circ_getYofA(), filled_circ_getRofA(), filled_circ_getAofY(): Handle filled circular sections, where part of the circle is filled with water.

• Rectangular and Trapezoidal:

  • rect_closed_getSofA(), rect_open_getSofA(): Handle closed and open rectangular cross-sections.
  • rect_triang_getSofA(), rect_round_getSofA(): Handle triangular and rounded rectangular cross-sections.

• Custom Shapes:

  • xsect_setCustomXsectParams(): Assigns parameters to custom-shaped cross-sections, allowing for flexible modeling based on user input.

Purpose:

• The primary purpose of xsect.c is to provide the necessary functions for calculating key hydraulic parameters like area, width, hydraulic radius, and section factor, which are essential for flow modeling in SWMM.

• The file allows SWMM to handle a wide variety of conduit and channel shapes, including standard shapes (circular, rectangular) and custom, user-defined shapes, ensuring flexibility and accuracy in hydraulic simulations.

• Through specialized functions for calculating flow characteristics and handling different cross-section shapes, xsect.c plays a critical role in SWMM's ability to model stormwater systems effectively, considering complex geometries and varying flow conditions.