Add a new nearness case

To add a new Nearness Case, press the button on the Nearness Manager Toolbar.

To configure the Case:

1. Uniquely identify the Nearness Case via a Case name.

2. Specify the cuts and properties of these cuts that are used in the Case.

3. Specify the Scale and Weight for each of the Nearness criteria.

4. Test the Nearness Case.

These steps are described below.

5. Choose a Case name by entering the name for the Case in the Name textbox.

   Once you have elected to add a new Nearness Case, you should enter a name for the Case. The Case Name is used to refer to the Case in the Nearness Case List.

6. Add criteria to the Nearness Case.

   A Nearness Case is made of a collection of criteria which define the cuts and properties that will be used to determine the similarity between an assay (the Comparison Assay) and the Reference Assay. The criteria in the Nearness Case are managed using the icons below the Criteria section:

   • - Add a new criterion to the Nearness Case

   • - Edit the selected criterion

   • - Remove the selected criterion from the Nearness Case

   Right-clicking the column headers in the Criteria section dialog allows the parameters to be grouped. By grouping together cuts or properties it is easier to see related settings together.

   Each Nearness criterion is defined by the following information:

   • Cut - the cut of whole crude that will be used for comparison

   • Property - the property value that will be used for comparison

   • Scale - a number that defines the range the property value of the comparison assay may differ from the reference assay value and still be considered similar; click the to automatically calculate a value based on the spread of cut/property values for Database assays

   • Method - whether the property value of the comparison assay and reference assay are compared directly (Linear), or using a logarithmic scale (Logarithmic)

   • Weighting - the importance of the this particular criterion to the overall Nearness calculation.

   Each criterion evaluates to a number between zero and one, where a value of one indicates that the cut/property value of the reference assay is equal to the cut/property value of the comparison assay. Values close to one indicate for this criterion the comparison assay is similar to the reference assay.

   To calculate the overall Nearness, the Nearness for each individual Criterion is combined using a weighted average.

   Scale

   The Scale of the Nearness criterion is used to define how much the property value of the assay being compared to the reference assay may differ from property value of the reference assay. That is, it defines the range of property value that may be considered 'near'.

   After setting the Cut and Property click the Calculate Scale button to automatically determine an appropriate value for the Scale. This is based on the spread of the cut/property value for the assays present in the Database.

   The Nearness Calculation shows how the Scale is used in the calculation of each Nearness criterion. The Nearness value for each criterion is inversely proportional to the Scale for that criterion. Increasing the value for the Scale increases the range over which the comparison assay property value could differ from the reference assay property value and still be considered near. For a single criterion, if the property value of the comparison assay is already close to the property value of the reference assay then a change in Scale will not have a significant effect on the criterion Nearness, as the assays are already 'near'. However for a comparison assay with a significantly different property value, increasing the Scale would result in a significant increase in Nearness.

   Increasing the Scale increases the number of assays that return a high Nearness value for the particular criterion.

   The following table shows the result of changing the value of Scale when comparing the freeze point of the kerosene fraction using Escravos as the reference assay, and comparing Brent Blend and Arab Light.

   Reference/Comparison Assay	Δ Freeze Point (Kerosene)	Nearness Value
   	Scale	10	20
   Escravos / Brent Blend	0.864	0.9646	0.9908
   Escravos / Arab Light	7.151	0.4044	0.6625

   Method

   Two options are available for the calculation method:

   • Linear - the property value of the reference assay is compared directly to the property value of the comparison assay

   • Logarithmic - the logarithm (base 10) of the property value of the reference assay is compared to the logarithm of the property value of the comparison assay.

   The logarithm method should be used when the property profile increases exponentially. For example, when comparing viscosities where the cut property values for an assay may vary substantially it may be more appropriate to compare the logarithm value rather than the original value.

   Weighting

   The Weighting of the criterion indicates its importance to the overall Nearness calculation. Each criterion evaluates a Nearness value, and these values are combined to give a single overall Nearness value. Each separate Nearness value is combined using its weighting, so Criteria with high weightings have more influence on the final Nearness value.

   For example, when comparing crudes similarities between their yield profiles would often be considered important, and so yield criteria would often have high weightings associated. Similarities between metal content may also be considered, but would probably not be as important, so these therefore would have a lower value for their weighting.

   After creating a new Nearness Case, close the Nearness Manager and immediately add the new Nearness type to the current Database View with a standard reference assay. Re-open the Nearness Manager and add the different criteria to the Nearness Case as normal. After adding each criterion click the Apply button to see the effect the criterion has on the Nearness column in the Database view for many assays at once.

7. Test the Nearness Case. After setting up all the separate Nearness criteria click the Test button to review the results of the Nearness calculation.

   Set a reference assay and the assay to compare it with in the Test Crude 1 and Test Crude 2 fields by clicking the button and using the Select Crudes dialog.

   Values for Scale and Weight can be changed in the Test Nearness dialog and the effect on results reviewed.

   Right-clicking the column headers in the Test Nearness dialog allows the parameters to be grouped. By grouping together cuts or properties it is easier to see related settings together.

   The Test Nearness dialog shows the following columns:

   • Cut - the cut of crude being compared

   • Property - the property being compared

   • Scale - the range of property value

   • Weight - the importance of the criterion to the overall Nearness calculation

   • Value 1 - the cut/property value for Test Crude 1

   • Value 2 - the cut/property value for Test Crude 2

   • Result - the non-weighted value returned for the particular cut/property combination using the entered Scale and Method.

   The overall Nearness value displayed in the dialog is calculated by determining the weighted average of the individual criterion results.