Create subsets and subset constraints within a zone

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In FlexSim, subsets can be used to control objects within a specific area, or zone, within your process flow.

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You can use a subset to monitor, apply rules to, or control how objects flow within a zone.

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Additionally, you can use a subset to gather statistics and analyze specific items within the zone.

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In this example, a flow that includes a Zone is already set up, along with a Dashboard to display statistics.

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In the Zone Properties, Use Max Content was applied previously as an easy way to limit the number of tokens in the Zone.

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However, a more flexible alternative is to use subsets, which can help you to set criteria for how and when tokens enter or exit a Zone,

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as well as to gather valuable statistics.

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To add a subset, first, add a Label to the tokens in your process flow.

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Add an Assign Labels activity beneath the Source.

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Then, for Assign Labels, add a Label with a Name of “Weight”.

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For Value, select Statistical Distribution > Uniform.

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In this case, leave the defaults of 5 and 15 for the Minimum and Maximum.

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This means that a random weight label will be applied to each token with a weight of between 5 and 15 pounds.

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Reset, Run, and Step the model forward.

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When you Stop the simulation and select a token, in Properties, under Labels,

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you see the Weight, which is 11.58 for Token 1 and 5.48 for Token 2.

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Now, you can use the weight label to apply a subset.

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Select the Zone.

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In Properties, ensure that Use Max Content is deselected, then click More Properties.

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In the Zone Properties dialog, there are multiple tabs for applying different criteria to the Zone.

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On the Subsets tab, click Add.

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For the Subset Name, type “Heavy Parts”.

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Notice that Include all tokens is the default for the Token Selection Criteria.

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Expand the drop-down to see examples of criteria for this field, such as Type = 1.

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In this case, enter “Weight >= 10”.

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This means that any token with a weight label greater than or equal to 10 will be included in the Heavy Parts subset.

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Click Apply, and then OK.

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Run the model, then Stop it and select the Zone.

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In Properties, click View Status.

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In the Zone Status dialog, Subsets tab, a table displays information about the Heavy Parts Subset,

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including the Current, Average, and Maximum number of Heavy Parts tokens in the zone.

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Run the model, and you can continue gathering statistics for this subset.

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Next, for the Dashboard, add a Zone Statistics > Bar Chart.

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In Properties, for Zone, sample the Zone in the process flow.

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Then, select the Statistic that you want to display for the subset.

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Subset Content reports the current number of tokens in the zone,

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while Subset Input and Subset Output report on the number of subset tokens that enter or exit the zone, respectively.

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In this case, select Subset Staytime.

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Back in Properties, select the desired Options.

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First, deselect Minimum.

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Since the Zone begins without tokens, the minimum will always be zero.

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Leave Current, Maximum, and Average selected, and then set the Subset/Calculation to Heavy Parts.

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When you run the model, on the Dashboard, you see the staytime for tokens that are part of the Heavy Parts subset.

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In this case, the Maximum time is 21.74.

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You can create subsets based on any label that you apply to your tokens.

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For example, you might create a subset based on an item type or the cost of an item.

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With Zone selected, again, click More Properties.

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In the Zone Properties dialog, this time, select Subset Constraints to add a constraint to the Heavy Parts subset.

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In this case, set the Calculation to Number of tokens, with a Value of 2.

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This means that a maximum of two Heavy Parts tokens are allowed in the Zone at a given time.

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Run the model, and then Stop it once there are several tokens waiting to enter the Zone.

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When you select the tokens in the Enter Zone activity, you see that each has a Weight label that is equal to or greater than 10,

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and each is part of the Heavy Parts subset.

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Therefore, these tokens must wait to enter the Zone, based on the constraint applied.

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Next, add a Line Chart to the Dashboard.

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Then, from Properties, sample the Zone.

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For the Statistic, notice that there are several available subset request statistics.

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Subset Request Content shows the number of tokens currently requesting to enter the Zone,

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while Subset Request Input and Output display the total number of tokens that have requested entry, and have then entered the Zone.

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In this case, select Subset Request Staytime to view the length of time that tokens are waiting to enter the zone at a given time.

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When the simulation is run, you see that this chart is not populating as intended.

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Note that in Properties, even though Heavy Parts was the default for the Subset/Calculation,

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you must actively select this field for the chart to display the corresponding statistics.

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To resolve the issue, reselect Subset Request Staytime for the Statistics, and then select Heavy Parts for the Subset/Calculation.

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Run the model, and then Stop once enough data is available.

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The chart populates as expected and displays the staytime for tokens waiting to enter the Zone at a given time.

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Now that you know how to use subsets and subset constraints to monitor, control the flow of, and gather data about items within a zone,

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you can further extend the functionality with the use of subset calculations and calculation constraints.