Equation Tab

• Non-negative – Select this check box to ensure that flows won't make the stock take on negative values.

• Type – Use this option to select how the initial value is calculated for the conveyor: Continuous or Discrete.

  If you select Continuous, the initial value for the conveyor is spread evenly over the length of the conveyor, and flows out of it in a steady stream. Unless the inflow is from a queue, this is selected by default.

  If you select Discrete, the initial value is separated into "packages", so it flows out of the conveyor in separate chunks. The initial value is spread over the conveyor, but the packages are stacked in the last DT of each conveyor slat. If the conveyor's inflow is from a queue, Discrete is automatically selected and can't be changed.

• Accept – Use this option to select how much you want the conveyor to accept from its upstream queue: Single batch or Multiple batches.

  Accept applies only to inflows from queues. Any inflows from a cloud stock, oven, or conveyor will be treated as if Multiples batches is selected. If there are no inflows from queues, the Single batch option will be disabled.

  If any of the conveyor's inflows come from a queue, you can select either option. If you select Single batch, the conveyor will take the next batch in one of the queues each DT, subject to the inflow limit and capacity constraint. Multiple batches will make the conveyor take as much as it can from all the queues, leaving the queues empty if there are no capacity constraints on the conveyor.

  Note: The quantity the conveyor can accept is always subject to the values in the conveyor's Capacity and Inflow limit parameters.

• Split batches - This option is only available if at least one of the conveyor's inflows is from a queue.

  

  Select this check box to allow the conveyor take only a portion of the "next" item in the queue, if the conveyor has reached its Inflow Limit or Capacity. If this check box is not selected, the flow from the queue will be set to zero (0) if the flow exceeds the values in the Capacity or Inflow limit parameters. This can lead to queue blockage.

• Accept – Use this option to select how much of the value you want the oven to accept from its inflows: Single batch or Multiple batches.

  Accept applies only to inflows from queues. Any inflows from a cloud stock, oven, or conveyor will be treated as if Multiples batches is selected. If the inflow is not from a queue, the Single batch option will be disabled.

  If the oven's inflow comes from a queue, you can select either option. If you select Single batch, the oven will take the next batch in the queue each DT, subject to the inflow limit and capacity constraint. Multiple batches will make the oven take as much as it can from the queue, potentially leaving the queue empty.

  Note: The quantity the oven can accept is determined by its capacity, as specified in the Capacity parameter.

  Tip: To represent a processor that takes only the "next" item from the upstream queue, select the Single batch option, select the DT builtin for the fill time, and specify a large capacity.

• Split batches – This option is only available if the oven's inflows are all queues.

  

  Select this check box to let the oven take a portion of the "next" batch in the queue, in order to fill itself to capacity. If this check box is not selected, the flow from the queue will be set to zero (0) whenever the flow exceeds the values in the oven's Capacity parameter. This can lead to queue blockage.

When you first view the Equation tab for a flow, the type of flow you chose when you first placed it will be selected. To change the type, select the appropriate option here.

Type (not available for flows into or out of conveyors or queues which are always uniflows).

• Uniflow – Select this option to have the flow move in only one direction. With uniflows, the flow volume only takes on non-negative values. Biflows can take on any value.

  

• Biflow – Select this option to have the flow move in two directions. With biflows, the flow volume can be any value (negative or positive). If you select this option, a second, dashed, arrowhead will appear on the flow to point in the direction of the negative flow. It's not possible to have a biflow connected to a conveyor, queue, or oven.

  

• Time Stamp – Select this option to time stamp the flow. This option is only available when the flow is connected to a conveyor, oven or queue or when selected Cycle-time as the integration method and the flow is into a non-negative stock. If you select this, flows will be marked with a clock when the cycle time integration method is selected.

  

• Unit conversion – Select this check box to convert the units of measure for the flow as material moves through the flow pipe. This is useful when you're modeling processes like assembly (which transforms raw materials into finished goods) or chemical processes (which involve molecular transformations).

  When you select the Unit conversion check box for a flow, a shaded half-circle will appear in the flow regulator on the diagram, to indicate that unit conversion is taking place.

  

  The Unit conversion check box is only available for uniflow flows that connect two stocks (where the flow is conserved). The default is no unit conversion.

• Inflow multiplier – This box appears when the Unit conversion check box is selected.

  The inflow multiplier is the value the upstream stock's value should be multiplied by. The resulting value becomes the downstream stock's value.

  The value can be either a number or a model variable from the Required Inputs list. The default value is 1.0.

  To specify a value in this box, you can type a number, use the calculator buttons to enter a number, or click a variable name in the Required Inputs list.

  When the model runs, the software reports the values for the flow before unit conversion has taken place.

• Attribute Value – Select this check box to attach an attribute value to the flow. The value will be tracked through subsequent discrete stocks and their flows. The attribute will also be tracked through non-negative stocks with no biflows if the cycle-time integration method is selected. See Attribute and Cycle Time Tracking.

  The Attribute Value check box is only available on uniflows that connect to a conveyor, queue or oven (or that connect into a non-negative stock with no biflows if cycle-time is selected as the integration technique).

  An equation box appears when the Attribute Value check box is selected. Enter the equation for the attribute. The value of the equation at the time the flow occurs will be used to track material associated with the flow from that time.

  To specify a value in this box, you can type a number, use the calculator buttons to enter a number, or click a variable name in the Required Inputs list.

  Note You can use the attribute value to prioritize queue inflows (see Queue Computation). In this case the smaller the number the higher the priority (1st, 2nd and so on though you need not use whole numbers). Attribute values can also be used to control downstream queue outflows as noted below.

• Restrict by Attribute – Select this check box to restrict queue outflows to only batches of material having the selected value.

  The Restrict by Attribute check box is only available on outflows from Queues.

  An editing box appears when the Restrict by Attribute check box is selected. Enter a comma separated (semi colon separated if you are using , as a decimal in equations) set of integer values. Only batches that have attributes matching one of these values will be processed by the outflows.

  Note If attribute values are not integers they will be rounded when making a comparison to the list of values specified.

  Note If Restrict by Attribute is selected for a queue outflow, no other outflows will process batches with matching attributes unless you include the same value in another queue outflow. See Queue Computation for more discussion.

Conveyor Flows



• Conveyor fill determines how material will enter the conveyor. By default everything enters at the beginning, but you can also spread the input out - see Spreading Conveyor Inputs.

  Leakage – This option is available if the flow is the second or subsequent outflow for a conveyor.

  Select the type of leakage this flow represents: Linear or Exponential.

  If you select the Linear option, the total amount that will leak for any given inflow will be the contribution of that inflow to the stock value (inflow*DT) multiplied by the leakage fraction. The leakage will be spread evenly in time over the leak zone. In steady state, the total leakage will be inflow*leak_fraction, and each slat in the leak zone will leak the total amount divided by the number of slats in the leak zone. In this case, the units of measure for the leakage fraction must be Dimensionless.

  If you select the Exponential option, the amount that leaks from each slat within the leakage zone is equal to the slat contents times the leakage fraction, generating an exponential decay in the amount leaked across the leakage zone. In this case, the units of measure for the leakage fraction must be per time unit (e.g. Per Month, if the model is in Months).

  For Linear leakage, the total amount leaked doesn't change with the length of the leakage zone, whereas for Exponential leakage, it does.

  Note: To specify the leak fraction, use the Leak fraction box in the flow's Parameters section.

• Select the Leak integers check box to round leakage flow to the nearest integer value. If DT is one that means the flow will be an integer. If DT is less than 1, it means the flow multiplied by DT will be an integer, so that the affected stocks only change by integer values.

• The Leak zone is defined by the blue sliders. By default, the entire conveyor will be selected as the leak-prone section.

  Use the sliders to specify the size of the leak zone. The leak zone is expressed as a percentage of the conveyor's transit time, which is applied to the inflow as it enters the conveyor.

  To specify the leak zone, move the Start and End sliders to select the appropriate percentage. A leak zone percentage of 100 implies that the entire conveyor is leak-prone.

  By default, the leak zone is 100%, and leakage occurs across the entire conveyor. To have the leakage occur at the end of the conveyor, move the start slider as far to the end as you can (99).

  Tip: You can have multiple leakage flows from a conveyor; each leakage flow can have different leakage fractions, to create different leakage zones. For example, you can create a leakage flow of 10% for the first half of the conveyor and another leakage flow of 20% for the second half of the conveyor. Do this by adding additional flows and defining their leakage zones differently.

• Overflow – This check box is available if the flow is the second or subsequent outflow for a queue.

  Select this check box to make the flow an overflow. When a higher priority flow is blocked because of capacity constraints, the flow will be routed through the overflow. For more information see Queue Computation.

• Purge old entries – This box is available if the flow is an outflow from a queue and is not connected to a conveyor or oven. See Queue Computation for details.

  Enter the equation for the attribute. The value of the equation at the time the flow occurs will be used to track material associated with the flow from that time.

  To specify a value in this box, you can type a number, use the calculator buttons to enter a number, or click a variable name in the Required Inputs list.

• Transit time – Use this parameter to specify the time it takes for material to pass through the conveyor.

  To specify a constant transit time, type a single number in this box. When you specify a constant transit time, all material that enters the conveyor will use the number you specify for the transit time.

  To specify a variable transit time, define an equation in this box. For an equation, you can use other model variables, builtins, algebraic operators, or a graphical function.

• FIFO –Check this to have the conveyor always maintain the order of its contents when the transit time changes.

  If this is not checked the transit time when material enters the conveyor will determine when the material will leave the conveyor. SeeTraditional Conveyor Computation.

  If this is checked the transit time will determine how quickly material will leave the conveyor based on the amounts of material added to the conveyor at previous times. See FIFO Conveyor Computation.

  Note If the transit time does not change, checking the FIFO option does not have any effect on the results.

• Sample – Use this parameter to sample the conveyor's transit time whenever the equation you specify equals anything other than zero (0).

  To use this parameter, select the Sample check box and then type an equation in the box that appears.

  Whenever the sample equation isn't equal to zero (0), the current value of the transit time equation will be used for the transit time of material flowing onto the conveyor. If the sample equation is equal to zero (0), the transit time doesn't change. Material will exit the conveyor when the sampled transit time has expired.

  If you don't select the Sample check box, units will be assigned to the transit time so that it's calculated as the units enter the conveyor.

• Inflow limit – Use this parameter to limit the inflow into the conveyor. Inflows per unit time won't be allowed to exceed the value you specify here. To allow an unlimited inflow limit for the conveyor, set the value to infinity by typing INF (or by pressing option-5 on a Mac).

  This parameter isn't available if the conveyor's inflow is a conveyor or an oven, because, in that case, the flow rate is controlled by the upstream conveyor or oven.

  Notes: If the Discrete option is selected for the conveyor, the entire inflow limit will flow during one DT.
  
  If the conveyor has multiple inflows and there's an inflow limit set for the conveyor, the inflows are prioritized so that the multiple flows enter the conveyor in order of their priority. For more information about how flows are prioritized, see Flow prioritization.

• Capacity – Use this parameter to limit the capacity of the conveyor. Inflows per unit of time won't be allowed to fill the conveyor to a greater capacity than the value you specify here. To allow an unlimited capacity for the conveyor, set the value to infinity by typing INF (or by pressing option-5 on a Mac).

  Note: If the conveyor has multiple inflows and there's a Capacity limit set for the conveyor, the inflows are prioritized; multiple flows enter the conveyor in order of their priority. For more information about how flows are prioritized, see Flow prioritization.

  This parameter isn't available if the conveyor's inflow is a conveyor or an oven, because, in that case, the flow rate is controlled by the upstream conveyor or oven.

• Arrest – Use this parameter to have the converter stop whenever the equation you specify equals anything other than zero (0).

  To use this parameter, select the Arrest check box and then type an equation in the box that appears.

  Whenever the arrest equation is not equal to zero (0), the conveyor will stop. Inflows and outflows to the conveyor will be set to zero (0). The conveyor will start where it left off when the arrest equation is equal to zero (0).

  Note: The Arrest option is disabled when an inflow to the conveyor comes from a conveyor or an oven.

• Cook time – Use this parameter to specify how long the oven "cooks" a batch before opening its door and releasing the contents. Material exits from the oven when the cook time expires.

  You can specify a constant cook time or a variable cook time.

  To specify a constant cook time, type a single number. When the oven closes its door, it'll use this number as the cook time for the batch.

  To specify a variable cook time, use model variables, builtins, algebraic operators, or a graphical function. The cook time that's calculated as the oven closes its door will be used for the batch.

  Note: If you're using a statistical builtin to generate a variable cook time, be sure to generate random numbers within the oven's equation. Don't generate random numbers in an external converter and use that converter to define the oven time. If you generate random numbers externally, the sequence of cook times won't conform to the distribution you've specified for the converter.

• Fill time – Use this parameter to specify how long the oven door should stay open during a given cook cycle. To allow an unlimited fill time for the oven, set the value to infinity by typing INF (or by pressing option-5 on a Mac). To set the fill time to the DT, specify the DT builtin in this box.

• Capacity – Use this parameter to specify how much material the oven can hold at once. When the capacity is reached or the fill time expires (whichever comes first), the oven will close its doors and begin "cooking" its contents.

  To specify the oven's capacity, enter a value or an equation. For an equation, you can use required inputs, builtins, algebraic operators, or a graphical function.

  Tips: To represent a capacity-constrained situation, select the One at a time option, specify a long fill time, and specify a small capacity.
  
  To represent a processor that takes only the "next" item from the upstream queue, select the One at a time option, select the DT builtin for the fill time, and specify a large capacity.

• Arrest – Use this parameter to have the oven stop whenever the equation you specify equals anything other than zero (0).

  To use this parameter, select the Arrest check box and then type an equation in the box that appears.

  Whenever the arrest equation is not equal to zero (0), the oven will stop. Inflows and outflows to the oven will be set to zero (0). The oven will start where it left off when the arrest equation is equal to zero (0).

• Queue parameters are displayed only for queues.

  

  Use dispatch priorities and round robin selection – Check this to have outflows from the queue rotate priority based on the last oven that was filled from the queue. If the ovens have the same characteristics (capacity, fill time and cook time) this will dispatch to each in turn. If this is not checked the first oven will always be given priority, and later ovens may not be used at all.

  Oven priorities are determined by the order the flows were connected to the conveyor, or sequentially by array element if the oven has more dimensions than the queue.

• Flow parameters are displayed only for conveyor leakages and queue outflows.

  Conveyor Leakages

  

  Leak fraction – This parameter is available if the flow is a leakage flow from a conveyor. The leak fraction is used to determine the leakage flow volume. Whatever enters the conveyor, multiplied by the leakage fraction, exits through the leakage flow.

  Define a leakage fraction by using a constant, other model variables, builtins, algebraic operators, or a graphical function. The leakage fraction must be in the 0-1 range. Numbers outside this range will be forced to the nearest endpoint.

  For Linear leakage flows, the total amount to leak is equal to the inflow times the DT times the leakage fraction, and this amount is distributed evenly across the leakage zone of the conveyer (each slat leaks the total amount divided by the number of slats). The total amount leaked doesn't change with the length of the leakage zone.

  For Exponential leakage flows, the amount that leaks from each slat within the leakage zone is equal to the slat contents times the leakage fraction, generating an exponential decay in the amount leaked across the leakage zone. The total amount leaked changes with the length of the leakage zone.

  To specify the type of leak (Linear or Exponential) and the leak zone for the flow, use the options in the flow's Options section.

  Ignore losses from earlier leak zones, if checked, causes the leak fraction to refer to the amount originally entering the conveyor rather that the amount left in the conveyor at the beginning of the leak zone (after other leakages have already occurred). This option is only available if there are multiple leakages and at least one of them has a leak zone that starts later than the beginning (0). See Traditional Conveyor Computation for more discussion.

  Queue Outflows

  

  Dispatch priority determines how to look for places to put the outflows from a queue. This has an effect only if there is more than one outflow and the checkbox is checked. In this case the smaller priority number outflows will be processed first. See Queue Computation for more discussion.

  Use dispatch priorities and round robin selection, if checked, will use the specified priority and use a round robin dispatch approach for outflows of the same priority.

  Note Checking Use dispatch priorities and round robin selection will change it for all outflows and for the upstream queue.

Type a constant or specify a variable or algebraic expression that evaluates to a single value.

The initial value can be either a number, a sequence of numbers separated by , (; if using , for decimal separators), or an expression involving variables. Use one of the following methods to define the initial value:

• Type a single number in the Equation box. This value will be evenly spread over the length of the conveyor.

• Type an expression involving other model variables.

  Note: When the Discrete option is selected, the conveyor will be initialized so that the material flows out in discrete "packets". The initial value will not be portioned out over the entire conveyor, but stacked in the last DT of each conveyor slat.

• Type a series of numbers, separated by commas; each number corresponds to a unit of time in the conveyor's Transit time. Any slats not initialized will default to the last value provided. The first number you type will be the first to exit from the conveyor.

  Note: When the Discrete option is selected, the conveyor will be initialized so that the material flows out in discrete "packets" with all material stacked at the last DT of each slot. Otherwise, each initial value you provide will be spread over one time unit within the conveyor.

• Type a single 0 (zero) to represent a queue that's initially empty.
• Type a series of positive numbers, separated by commas, each representing one queue slot. The first number you type will be the first to exit from the queue.

Type a single non-negative number that isn't greater than the oven's capacity.

Type a constant or define an algebraic expression that evaluates to a single value. All required inputs have to be used in the equation for the flow.

Type a constant or define an algebraic expression that evaluates to a single value. All required inputs have to be used in the equation for the converter.