[Next Section] [Previous Section] [FEQUTL Update Contents]

Enhancements and Modifications to the Full Equations Utilities (FEQUTL) Model, March 1995 to August 1999.
Note: This document is separate from the U.S. Geological Survey report by Franz and Melching (1997). This description of enhancements and modifications to the Full Equations Utilities Model has not been approved by the Director of the U.S. Geological Survey.

Section 5.17a ORIFICE Command

ORIFICE COMMAND

Purpose: ORIFICE computes a 2-D table of Type 13 for flow through a vertical orifice using the basic principles of orifice and weir flow as outlined in Section 4.0, Approximation of Hydraulic Characteristics of Control Structures.

LINE 1

 Variable:                    TAB Format:                       7X, I5 Example:                    TABLE#= 527
 Explanation: Gives the table number of the type 13 table to be created.

LINE 2

 Variable:                     LABEL Format:                       6X, A50
Example:                     LABEL= Bleed down at Alligator Lakes Dam

 Explanation: Gives a descriptive label for the table of type 13.

LINE 3

 Variable: HEAD Format: A80 Example: Numbr Shape  Edge VertD HoriD Invrt OrifC WeirC
 Explanation: Provides descriptive heading for information to follow. The example heading given should be used without change to provide compatibility with any future changes.

LINE 4

 Variables: Numbr, Shape, Edge, VertD, HoriD, Invrt, OrifC, WeirC Format: I6, 2A6, 5F6.0 Example: 1  CIRC SHARP   2.0   2.0   5.0   0.60  0.58
 Explanation: All input fields are 6 columns wide and COLUMNS ARE IMPORTANT. No part of any input item should fall outside of its field. Note that the headings define the field width. For example, the first column of the field for the vertical diameter of the orifice, VertD, starts in the column following the heading word, Edge, and ends in the column under the D in VertD.
 Numbr is the number of identical barrels that are to be included in the computations.
 Shape is the shape of the orifice opening. CIRCLE, CIRC, and ROUND designate a circular orifice. RECT designates a rectangular opening. INVTRI or TRI designate a symmetrical triangular opening with the apex of the triangle forming the invert of the opening. OTHER or ODD designates shapes defined by a user supplied function table. The number of this table appears in the field, OriTb. The table gives the width of the opening relative to the vertical diameter and at distances from the invert expressed relative to the vertical diameter. An example appears below.
 Edge gives the nature of the edge on the orifice. Currently the only option is SHARP to indicate a sharp-edged orifice. All the computations are done using equations related to a sharp-edged orifice. However, none of the coefficients are built into the command so that the user can effectively represent any edge configuration by selecting the correct coefficient. For example, if the edge of the orifice is rounded, a coefficient of 0.9 for the orifice flow might be a better value than the sharp-edged value of about 0.6.
 VertD is the vertical diameter for the orifice, that is, the maximum vertical distance in the orifice opening.
 HoriD is the horizontal diameter for the orifice, that is, the maximum horizontal distance from one edge of the opening to the other. May be omitted if Shape is any one of CIRC, ROUND, or CIRCLE.
 Invrt is the elevation of the invert of the orifice, that is, the lowest point in the opening.
 OrifC is the effective discharge coefficient for orifice flow. Values close to 0.6 apply approximately to wide range of shapes when the edge of the orifice is away from any boundary by more than the half-diameter of the orifice and the edge is sharp and has no rounding or beveling of its upstream edge.
 WeirC is the coefficient for weir flow expressed in dimensionless terms. A value of 0.58 is a good estimate for both rectangular and triangle weirs. Values close to 0.60 are good estimates for a circular weir. See Chapter 4 of the FEQUTL documentation for references.

LINE 5

 Variable: HEAD Format: A80 Example: AppTb OriTb MxZup MnHup MxPFD MnPFD LIPrc
 Explanation: Provides descriptive heading for information to follow. The example heading given should be used without change to provide compatibility with any future changes.

LINE 6

 Variables: AppTb, OriTb, MxZup, MnHup, MxPFD, MnPFD, LIPrc Format: 10F6.0 Example: 20.0 0.100 0.980 .0050 0.020
 Explanation: AppTb is the identification number for the cross section function table that describes the approach channel for the orifice. This input item is optional and can be left blank as in the example above. It is only needed if the orifice opening is a large fraction of the approach channel flow area. The correction for velocity head is only an approximation and may not be adequate if the velocity head is large. The orifice relationships are intended to approach Froude numbers less than about 0.5 and usually much less than this value.
 OriTb is the identification number for the function table of type 2, 3, or 4 that gives the relative width of the opening as a function of the relative height in the opening. The width is taken relative to the vertical diameter given on line 4 and the height is taken relative to the vertical diameter as given on line 4.
 MxZup is the maximum elevation that will not be exceeded by the water level upstream of the orifice. Determines the maximum head used in creating the 2-D table of type 13 describing the flow through the orifice.
 MnHup is the minimum positive head to use at the orifice for computing flows. This value should not be too small nor too large. A value of 0.01 feet is too small and 1.0 foot is too large. A value in the range of .05 to 0.1 of the orifice vertical diameter is suitable. The minimum positive head must not be greater than 0.125 of the vertical diameter. If it is, the ORIFICE command replaces it with 0.125D, where D is the vertical diameter of the orifice.
 MxPFD is the maximum partial free drop that is less than 1.0. This value should be in the range of 0.9 to 0.99. This value is used to define the spacing of points for interpolation of submerged flows for a given upstream head.
 MnPFD is the minimum positive partial free drop. This value is used with MxPFD andLIPrc to define the spacing of points for interpolation of submerged flows. Values in the range of 0.005 to 0.01 are generally adequate.
 LIPrc is the linear interpolation precision that defines an approximate relative error when interpolating a power function with a piecewise linear continuous function, that is, a linear spline. See page A-65 in the FEQUTL input description for more details. Values are in terms of relative error. Values in the range of 0.001 to 0.10 are defined by special tables in the file, TYPE5.TAB, read by FTABIN above. Values in the range of .01 to .06 probably are adequate.

Notes: The above cards with the command, ORIFICE, are repeated for each orifice. If there are 100 orifices then there will be 100 occurrences of the ORIFICE command in the input, each followed by the six lines of input as described above. Each orifice must have a unique id number for its 2-D table.

Back to Franz and Melching (1997) p. 91, for CULVERT command section 5.5
To update for new section 4.7a, Flow in Orifices