Curves are objects that contain data pairs representing a relationship between two variables in a hydraulic model.
A curve is used by InfoWater Pro to calculate the value of one variable based on the value of another variable. For example, given a flow for a specific pump at a specific time, InfoWater Pro determines the head for the pump from its pump curve (i.e., head vs. flow).
Each curve is given a unique identifier within InfoWater Pro. It is highly recommended that you provide a detailed description to assist in curve selection when defining a curve. Curves are assigned to nodes and pipes through the Attribute tab in the Model Explorer.
The Curve dialog box allows you to create, edit, clone, and delete curves. It shows all existing curves on the top and the highlighted curve's data in both tabular and graphical format on the bottom.
Curve Dialog Toolbar
Refer to the Object Dialog Toolbar for the Operation tab within the Model Explorer.
ID & Description
This box shows the ID and description of curves. Click Edit on the Curve Dialog Toolbar to revise the description.
Curve Type
Select the curve type from the pull-down list. The following list shows all available curve types:
General - Describes multi-purpose curves.
Volume vs Depth - Describes how tank volume changes with depth.
The curve for variable-area tanks is defined as the volume of the tank versus its corresponding depth. It is important to note that the volume must be defined in cubic feet (ft3) or cubic meters (m3) and not in any other unit (such as gallons or MG). This curve now relates to having the volume of the tank on the (Y-axis) with the corresponding depth on the (X-axis). A sample table and curve are provided below:
Head vs Flow - Describes pump operation.
A Pump Curve represents the relationship between the head and flow rate that a pump can deliver at its nominal speed setting. Head is the head gain imparted to the water by the pump and is plotted on the vertical (Y) axis of the curve. Flow rate is plotted on the horizontal (X) axis. A valid pump curve must have decreasing head with increasing flow.
When four or more data points are provided for the pump, the resulting head-flow curve is called a Multi-Point Pump Curve. It will be expressed as a piecewise linear curve of up to the last data point entered. This provides an accurate representation of the pump operation over the flow range specified. For pumps with multiple-point curves, the curve consists of a collection of points defining the head (Y-axis) as a function of flow rate (X-axis). A sample table and curve are provided below:
Pump Efficiency vs. Flow - Describes energy management and cost analyses.
Required for an Energy Management analysis, pump efficiency may be specified as a constant or as varying over a specified flow range. For pump efficiency curves, the curve consists of a collection of points defining the relationship between efficiency as a percentage (Y-axis) and flow rate in flow units (X-axis). A sample table and curve are provided below:
NPSH vs. Flow - Determines the cavitation index of a pump.
The required NPSH is evaluated from the multiple point curve (NPSH required vs flow) supplied. This curve is based on performance tests and is normally available from the pump manufacturer. NPSH is defined as the total head at the suction side of the pump minus the vapor pressure head of the liquid being transported. A sample table and curve are provided below:
Headloss vs Flow - Describes general purpose valves or float valves.
Used for General Purpose Valves and Float Valves, the curve consists of a collection of points defining the headloss across the valve (Y-axis) and flow rate in flow units (X-axis). A sample table and curve are provided below:
Minorloss vs. % Open - Models motorized throttled valves.
For Motorized Throttled Valves (MTVs), a Minor Loss Coefficient Curve consists of a collection of points defining the minor loss coefficient K (Y-axis) as a function of the percentage (degree) opening setting (X-axis). It provides the capability to model valves with unique headloss characteristics such as cone and butterfly valves. A sample table and curve are provided below:
% Demand vs Pressure - Models pressure dependent demands.
In certain situations, you may wish to create a hydraulic model that more accurately reflects "real-world" conditions. As pressure drops, so too does demand. Knowing this, you can assign a demand vs. pressure curve for selected junctions in the system. The Pressure-Demand Curve is used to describe how the demand flow rate (Y-axis) varies as a function of the pressure (X-axis) available at the node. The demand flow rate (Y-axis) is expressed as a percentage of the base demand with 100 equating to 100% of the base demand. The Demand vs. Pressure curve provides the capability to model situations where pressure-dependent demands are significant in a water distribution system:
Each curve is identified by a unique identifier within InfoWater Pro. It is advised that when defining curves, a detailed description is also provided to assist in curve selection.
Carbon Footprint vs Diameter - Describes the measurement of carbon footprint and diameter.
Pressure vs Flow - Describes pressure and water flow.
Pressure vs Pressure - Describes pressure versus pressure.
Curve Editor
The Curve Editor is located on the bottom left and used to create or modify the data points for the highlighted curve. After the number of rows for the curve has been entered, use this box to type in the values for the curve. When a value is entered, it will automatically be reflected in the adjacent graph. The Windows Copy (Ctrl-C) and Paste (Ctrl-V) functions may be used to populate values to the curve editing box. It is possible to copy and paste rows and columns from a spreadsheet to the curve editing box. Click Set Rows first to set the proper number of rows.
Insert Row Button - Selects the row in which to insert a new record, and then inserts a new row.
Append Row Button - Creates a row at the end of the table.
Delete Row Button - By selecting one or more rows, click this icon to delete those records.
Set Rows Button - Enables you to specify the number of rows to create in the curve. If 12 rows are desired, type 12 in the dialog box.
Block Edit Button - Enables you to perform a block edit on the selected records to some value specified by the user.
Format Button - Enables you to justify the text in the curve table, apply a comma separator, and to specify the number of decimal places for the curve.
Save Button - Saves the current curve data to a text file.
Load Button - Opens and reads curve data from a data text file.
Curve Graph Display
The Curve Graph Display is located on the bottom right and used to demonstrates the highlighted curve's data points graphically.
Curve Graph Toolbar - Refer to the General Graph Toolbar.
Transpose Display Axes - Select this box to transpose the x-axis and y-axis.
You are also able to edit data points on the graph. First to highlight the desired column (x or y column) in the curve editing box, click Edit in the Curve Graph Toolbar to enable editing, select a specific data point, and click another location in the graph to get a new value, which is displayed in the curve editing box too.
Managing Curves
Edit a Curve
From the curve dialog box, you can change any X,Y value as necessary to reflect the relationship between the two values (e.g. more flow at the same head). You can also edit the graph directly by selecting either the X or Y field to the left and then clicking the graph. With the X or Y field highlighted, you can adjust the graph accordingly.
Delete a Curve
To delete a curve, click the appropriate curve (this curve should be listed under Curve in your InfoWater Pro Browser > Operation tab), right-click and choose Delete.
Assign a Curve to an Entity
For example, to assign a curve to a pump, using the Select tool on your Model Explorer - Attribute Tab, highlight the pump and under the Modeling section of the Model Explorer - Attribute Tab click the Curve cell. Using the down arrow button select the desired curve.