Load Curve Editor

The Multiplier Table Editor is a utility that can be used to easily create load curves for loads in time-dependent analyses. This utility can be accessed by pressing the Curve button or View / Edit Load Curve button in the load dialog. (The name of the button may vary from load to load or analysis type to analysis type.) The number in the Load Curve field will be the number of the load curve that will be created in the Multiplier Table Editor. If you enter a number of an existing load curve, that curve will appear in the editor. If you enter a number of a nonexistent load curve, an empty load curve will be passed to the editor. After a load curve is created in the Multiplier Table Editor, you can also view it in the Analysis Parameters dialog.

Attention: Although the title of the editor and input column is Multiplier, implying that it multiplies the assigned load, some load types use this value as an added value to the assigned load. Refer to the documentation for each load type to understand how the Multiplier is used.

Create Load Curve Data

There are numerous ways to create the input for the load curve.

  1. Using the Spreadsheet. The spreadsheet can be used to enter data points that will be connected with straight lines to define a load curve. Use the Add Row command or the Delete Row(s) command to adjust the number of rows in the spreadsheet. Select a cell in the spreadsheet and enter the new number. The coordinate defined by the data pair on the row will be added in the graphical display to the right.
  2. Dragging the Points. Once the load curve data is entered, the left mouse button can be used to drag the data point in the graphical display up or down, there by changing the multiplier value.
  3. Importing Existing Data. If the load curve exists as a comma-separated text file, with the time value in the first column and the multiplier value in the second column (separated by a comma), use the Import CSV menu to browse for the file. The imported data will overwrite the current load curve data. This data could be created in a spreadsheet and saved in the CSV format, or may be measured data created by a test instrument.
    Tip: The values in the comma-separated file are imported using the active Display Units. Change the Display Units if necessary before importing the data. For example, a value of 3.14 is imported as 3.14 second if the Display Units have time in seconds, and 3.14 minutes if the Display Units are minutes.
  4. Entering a Formula. If the load curve is a mathematical formula, choose the Equation Editor menu. A dialog will appear allowing you to specify an equation to define the load curve. Enter the time at which you want this equation to begin in the Start X field. Enter the time at which you want this equation to end in the End X field. Specify how often you want a data point defined in the Interval field. The load curve will be interpolated with straight lines connecting these data points. Define the equation you want to use in the Equation field. Use X as the variable. You can use one of the predefined functions below by clicking on it and dragging it into the Equation field or by typing it. For example, the equation 5*SIN(3.25*(2*p)*X) would generate a sine curve with an amplitude of 5, and a frequency of 3.25 Hz. For a Start X of 0, End X of 0.33, and Interval of 0.01, the generated curve would be just over once cycle (1/3.25 Hz = 0.308 seconds) with 30 data points in the cycle. If the Overwrite Nodes check box is activated, the Equation Editor will erase all the data points when you change the equation and use only the data points created by the new equation. To create a piecewise function with different equations during different time periods, you will want to deactivate this option.

( )

Parentheses to group expressions.

^

Raise a value to a power

* / + -

Multiplication, division, addition, and subtraction

ABS

This function will take the absolute value of the argument.

ARCCOS

This function will take the inverse cosine of the argument. The result is in radians.

ARCOSH

This function will take the inverse of the hyperbolic cosine of the argument. The result is in radians.

ARCSIN

This function will take the inverse sine of the argument. The result is in radians.

ARCTAN

This function will take the inverse tangent of the argument. The result is in radians.

ARSINH

This function will take the inverse of the hyperbolic sine of the argument. The result is in radians.

ARTANH

This function will take the inverse hyperbolic tangent of the argument. The result is in radians.

COS

This function will take the cosine of the argument, in radians.

COSH

This function will calculate the hyperbolic cosine of the argument. The equation used is: .

DEG

This function will multiply the argument by a factor of. This will, in effect, convert the argument from radians to degrees.

EXP

This function will raise the constant e to the argument.

INT

This function will truncate the value after the decimal point for all values in the argument. Therefore, if the argument in this function is 1.2345, the output of this function would be 1.0.

LN

This function will take to natural logarithm of the argument.

LOG

This function will calculate the logarithm (base 10) of the argument.

P

The value of pi (3.1415926).

RAD

This function will multiply the argument by a factor of .This will, in effect, convert the argument from degrees to radians.

SIN

This function will take the sine of the argument, in radians.

SINH

This function will calculate the hyperbolic sine of the argument. The equation used is: .

SQR

This function will take the square root of the argument.

TAN

This function will take the tangent of the argument. The quotient of the sine value and the cosine value.

TANH

This function will take the hyperbolic tangent of the argument. The quotient of the hyperbolic sine value and the hyperbolic cosine value.

Since the load curve data needs to be in ascending order, use the Sort button to sort the rows as necessary.

Other Options

  • Export CSV: Use this menu to save the load curve to a comma-separated text file (CSV).
  • Export Image: Use this menu to save the image currently shown in the graph area to an image file. You can save it with the following graphic file extensions: .bmp, .jpg, .tif, .png, .pcx, and .tga.
  • Print Table: Use this menu to print the load curve table (spreadsheet).
  • Print Plot: Use this menu to print the display area.

Parent topic: Loads and Constraints