Uncertainty Tool

The Uncertainty Tool allows analysis of the effects of uncertainty in the input data on the Total Operating & Support Cost and the top level CAPE cost structure items. Uncertainty may be modeled for any input that consists of a single value, annual cost profile table row or Throughput item that is enabled in the current data record. A range of probability distributions is available for representing uncertainty about each input. The model is then executed a specified number of times and a probability density function (S-Curve) is displayed.

The inputs in all sectors are displayed in a tree structure. The tree can be expanded or collapsed by clicking on the + and – signs. The tree can be fully expanded or collapsed, or a single node fully expanded through a popup menu that is accessed by right-clicking on the tree structure. Some items in the tree will not be available if they disabled in the main data record.

When an item is first selected it will be given a Triangular distribution by default. The distribution and/or parameter values can be changed by double-clicking on the distribution text or clicking the Ellipse button in the last column of the Selected Inputs table. A dialog will be displayed that allows the sampling distribution to be set. The form also shows the input name, the value in the current data record, and the allowable boundary limits for values of the input.

Uncertainty Tool - Uncertainty inputs

Uncertainty Input form

To change the distribution type, click on the Change button and then select the distribution from the pull-down list. If the selection is changed, then default values are provided for the parameters, which can be edited as required. A warning will be given if parameter values are set that are invalid for the distribution. From OSCAM Air v4.2 correlation can be defined with another input in the Uncertainty Input list (see Uncertainty Correlation).

Click on the Help button to get more information on each probability distribution that is available in the tool.

Uncertainty Tool - Set Sampling Distribution

Uncertainty Set Distribution dialog

A graphical view of the distribution is available by clicking on the Graph tab. This shows the probability distribution for the current parameters’ values. Click on the Parameters tab to return to the parameters view.

Uncertainty Tool - Probability Distribution Graph

A probability distribution graph for the selected parameters can be viewed

Click OK to accept any changes to the probability distribution or Cancel to ignore all changes that have been made.

Any data in the Uncertainty input form will be saved with the data record. If any changes are made to the Uncertainty input form the record name will change to red to indicate that the changes are unsaved.

The Random Number Stream is used to determine the sequence of random numbers that are used for setting input values during the uncertainty run. If two uncertainty runs are performed on a data record that have the same random streams and the same number of replications then the results of the two runs will be identical. A random number stream can be specified by un-checking the Auto box and entering a value between 0 and 999999999. If the Auto box is checked then a random number stream will automatically be generated when the run button is selected. In either case, the random number stream that was used will be displayed on the Uncertainty Results form.

Uncertainty Tool - Uncertainty Run Control

The section of the Uncertainty Input form that is used to define the number of runs and the random number stream

For OSCAM Air v4.2 onwards it is possible to preview/review input sample data and to pause uncertainty analysis runs to review the uncertainty analysis results to date.

The output form will automatically be displayed when the tool has finished executing. The output form has two graph views: S-Curve and Bar Chart, and there is a tabular view breaking down uncertainty results into 5th percentiles. Click on the view using the tabs at the top of the output form.

By default the costs shown will be Total O&S Costs + Non-O&S Costs. This selection can be changed using the drop-down box in the top-right corner of the output form. A range of options exist, including reporting only O&S costs or any of the 1st level CAPE output structure items.

Uncertainty Tool - results view drop-down selection box

The Uncertainty results form has a drop-down box to select which cost categories are viewed in the results

The S-Curve shows a cumulative probability plot for the selected cost item. Under the graph is an information bar that shows the values on the graph scale for the current position of the cursor. To read the values for a specific point on the line, move the cursor to that point on the line and look at the values in the bar. Note that the values in the information bar relate to the position of the cursor - if it is not positioned on the line it will report the values where the cursor is positioned, not the values of the nearest point on the line. There is also the option of displaying the 5th percentiles on the line, using the Show Percentile Markers check box. The value for a 5th percentile can be seen by hovering the mouse cursor on the appropriate line marker.

Uncertainty Tool - s-curve results graph

Uncertainty results s-curve showing 5th percentile markers

The Bar Chart divides the results up into a number of bars (the number of bars depends on the number of runs) and shows the relative and absolute frequencies for each bar. Like the S-Curve, the Bar Chart also has an information bar that shows the position of the cursor. The cursor should be positioned at the top of the bar to read the relative and absolute frequencies. The positioning of the cursor on the left, middle or right side of a bar will show its lower bound, mid-point or upper bound respectively.

To copy the chart to the clipboard the pop up menu can be accessed using the right mouse button. Select Copy Graph to Clipboard.

To copy the Uncertainty data to the clipboard right-click the mouse button over the graph and select the Copy Data to Clipboard. From OSCAM Air v4.2 onwards there are several options available for layout of the data which can be set via a Configure Uncertainty Results Full Data Export dialog.

The Percentile Table shows the select cost item broken down into 5th percentiles. The right-click menu on this table has options to print the table, copy the table to the clipboard (as data values that can be copied into a spreadsheet), or copy the summary statistics to the clipboard.

Uncertainty Tool - Percentile Table

Uncertainty Results Table displaying values for every 5th percentile