View source for Example Using SCT for Standby Rotation

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''This example appears in the [[Repairable_Systems_Analysis_Through_Simulation|System Analysis Reference book]]''.
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This example illustrates the use of state change triggers ([http://www.reliawiki.org/index.php/BlockSim_8:_State_Change_Triggers#State_Change_Triggers SCT]) in BlockSim Version 8 by using a simple standby configuration. ''Note that this example could also be done using the standby container functionality in BlockSim.'' 

More specifically, the following settings are illustrated:
#State Upon Repair: Default OFF unless SCT overridden
#Activate a block if any item from these associated maintenance group(s) goes down<br>

==== Problem Statement ====

Assume three devices A, B and C in a standby redundancy (or only one unit is needed for system operation). The system begins with device A working. When device A fails, B is turned on and repair actions are initiated on A. When B fails, C is turned on and so forth.

==== BlockSim Solution  ====

The BlockSim model of this system is shown in the figure below. 

[[Image:Blocksim Example Rotation example.png|center|200px]] 



*The failure distributions of all three blocks follow a Weibull distribution with Beta = 1.5 and Eta = 1,000 hours. 
*The repair distributions of the three blocks follow a Weibull distribution with Beta = 1.5 and Eta = 100 hours. 
*After repair, the blocks are "as good as new."


There are three maintenance groups, 2_A, 2_B and 2_C, set as follows:


*Block A belongs to maintenance group 2_A. 
**It has a state change trigger. 
***The initial state is ON and the state upon repair is "Default OFF unless SCT overridden." 
***If any item from maintenance group 2_C goes down, then activate this block. 



*Block B belongs to maintenance group 2_B. 
**It has a state change trigger. 
***The initial state is OFF and the state upon repair is "Default OFF unless SCT overridden." 
***If any item from maintenance group 2_A goes down, then activate this block. 


*Block C belongs to maintenance group 2_C. 
**It has a state change trigger. 
***The initial state is OFF and the state upon repair is "Default OFF unless SCT overridden." 
***If any item from maintenance group 2_B goes down, then activate this block. 


*All blocks A, B and C are as good as new after repair.

==== System Events  ====



The system event log for a single run through the simulation algorithm is shown in the Block Up/Down plot below, and is as follows:

#At 73 hours, Block A fails and activates Block B. 
#At 183 hours, Block B fails and activates Block C. 
#At 215 hours, Block B is done with repair. At this time, Block C is operating, so according to the settings, Block B is standby.
#At 238 hours, Block A is done with repair. At this time, Block C is operating. Thus Block A is standby. 
#At 349 hours, Block C fails and activates Block A. 
#At 396 hours, Block A fails and activates Block B. 
#At 398 hours, Block C is done with repair. At this time, Block B is operating. Thus Block C is standby. 
#At 432 hours, Block A is done with repair. At this time, Block B is operating. Thus Block A is standby. 
#At 506 hours, Block B fails and activates Block C. 
#At 515 hours, Block B is done with repair and stays standby because Block C is operating. 
#At 536 hours, Block C fails and activates Block A. 
#At 560 hours, Block A fails and activates Block B. 
#At 575 hours, Block B fails and makes a request to activate Block C. However, Block C is under repair at the time. Thus when Block C is done with repair at 606 hours, the OFF setting is overridden and it is operating immediately.
#At 661 hours, Block C fails and makes a request to activate Block A. However, Block A is under repair at the time. Thus when Block A is done with repair at 699 hours, the OFF setting is overridden and it is operating immediately. 
#Block B and Block C are done with repair at 682 hours and at 746 hours respectively. However, at these two time points, Block A is operating. Thus they are both standby upon repair according to the settings.



[[Image:Block Up Down plot for rotation example.png|center|450px]]