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A process block can be used to represent where fluids are combined or separated to create other fluid types (e.g., a reactor, mixer or distillation tower). Therefore, process blocks can have multiple inputs of various types, and multiple outputs of various types.
To configure a process block, in addition to the common block properties, you will need to describe how the block behaves. The first step is to assign a universal reliability definition (URD) in the Universal Reliability Definition area. The URD uses a model to describe the block's reliability characteristics and may also include a corrective task and/or scheduled tasks.
To assign a URD to a block, you can either select an existing URD or create a new one. Click the URD field and then click the arrow to display the URD wizard. In the wizard, you can click Select Existing URD to display a list of the available URDs. You can also click Create New URD to open the Universal Reliability Definition window; in this window, specify the failure model and any associated tasks, then click OK to create the new URD and apply it to the block.
Once a URD has been assigned to the block, you can view and/or edit its properties from the URD wizard by clicking the View/Edit icon.
You can remove the URD from the block by clicking the Remove icon in the URD wizard.
You can also add, change or edit the components of the URD (i.e., the model, corrective task and/or scheduled tasks) directly from the URD area. Be aware that any changes you make here will apply everywhere that the URD is used.
If no URD is assigned to the block, you can create a new model for the block by clicking the Model field and then clicking the arrow. This opens the Model wizard, which allows you to define a model for the block; this has the effect of automatically creating a new URD that uses the new model and assigning it to the block.
In addition, you will need to specify the following:
Operation
Set block as failed
if selected, indicates that the block is "off" or absent
from the system. An X will be displayed on the block to indicate
that it is failed. The block will be considered to be failed throughout
the entire simulation and no maintenance actions will be performed
(i.e., any failure and maintenance properties will be ignored).
This option can be used for "what-if" analyses to investigate
the impact of a block on system metrics such as throughput, cost,
etc. You can also set this option by selecting the block in the
diagram and choosing Process
Flow > Settings > Set Block as Failed.
When this option is selected, no other properties will be available
for the block; note, however, that any properties you have already
specified are simply hidden because they are not relevant. The
settings will reappear if you clear the Set
block as failed option.
Duty cycle allows you to model situations where the actual usage of a block during system operation is not identical to the usage for which you have data (either from testing or from the field). This can include situations where the item:
Does not operate continuously (e.g., a DVD drive that was tested in continuous operation, but in actual use within a computer accumulates only 18 minutes of usage for every hour the computer operates).
Is subjected to loads that are greater than or less than the rated loads (e.g., a motor that is rated to operate at 1,000 rpm but is being used at 800 rpm).
Is affected by changes in environmental stress (e.g., a laptop computer that is typically used indoors at room temperature, but is being used outdoors in tropical conditions).
In these cases, continuous operation at the rated load is considered to be a duty cycle of 1. Any other level of usage is expressed as a percentage of the rated load value or operating time. For example, consider the DVD drive mentioned above; its duty cycle value would be 18 min / 60 min = 0.3. A duty cycle value higher than 1 indicates a load in excess of the rated value.
Consequential Costs allows you to choose or create models to represent costs that are always associated with the block. Cost per failure uses a cost model, and Downtime rate and Uptime rate use cost per unit time models. If no models are assigned, it is assumed that there are no additional costs.
Maintenance Group allows you to specify the maintenance group that the block belongs to.
State Change Triggers
Enable state change triggers
(SCT) allows you to specify the starting state of the block
(i.e., off or on) and its state upon repair, then specify events
that will activate and/or deactivate the block during simulation.
You can choose to activate or deactivate the block when items
in specified maintenance groups go down or are restored. The current
block does not need to be part of the specified maintenance group
to use this functionality. This allows you to model a cold standby
configuration (i.e., one where the component cannot fail when
in standby) without using a standby container, which may be useful
if you are using a parallel or complex configuration, as blocks
can be connected only in series in standby containers.
To add a state change trigger, click the Add
icon in the Add a State Change
Trigger field. The State Change Trigger window will appear,
allowing you to define the trigger. Each trigger that you add
will then be displayed in the Block Properties window. To edit
an existing state change trigger, click the Edit
icon for the state change trigger to open the State Change Trigger
window.
Throughput can be used to define a mass balance equation (e.g., 4.032 kg H2 + 31.998 kg O2 = 36.030 kg H2O) that will constrain the ratios of fluids entering and exiting the process block, or to combine or break streams in a prescribed manner (e.g., 100kg H2O input goes to 60kg H2O on output A and 40kg H2O output B). The ratios defined here constrain both input and output; limiting input of one type will reduce the amount of any other inputs accepted and, consequently, the amount of output. Similarly, if there is decreased capacity in one location downstream, the amounts of all outputs and, consequently, the amount of inputs accepted by the process block, will be reduced accordingly.
Units allows you to specify the units used for measuring input/output (mass) and time. For example, you might measure throughput in terms of kilograms per hour.
Inputs and Outputs define the mass coefficients used in the ratios that determine how much of each input is accepted and how much of each output is sent. The sum of the input coefficients must be equal to the sum of the output coefficients.
Maximum output defines, for each connected path, a maximum amount of output that can be sent to the path.
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