ProcedureActionTimeBranches.txt

Purpose

The ProcedureActionTimeBranches.txt input file allows multiple accident sequence branches to be generated when a procedure action is executed. The ADS-IDAC procedure following model allows the analyst to specify the time taken to execute each step action using a three-parameter Weibull probability density distribution. This file controls when and how many action execution time branches are generated to capture crew-to-crew variability.

• When only one action time branch is generated, the required action execution time equals the mean value of the Weibull distribution.
• When more than one branch is generated, the probability distribution is partitioned into segments and the time for each sequence branch is determined by the mean value over the associated partition.

Weibull Partition Method (Figure 19, Equation 11)

The partition boundaries are determined by dividing the probability range of the Weibull cumulative distribution function (CDF) into a number of segments equal to the number of desired branches. Each branch receives an equal probability mass from the CDF. For example, five branches produce five equal-probability segments with partition boundaries at CDF increments of 0.2.

The execution time for each branch is the mean time over its associated partition. For the first and second partitions (Equation 11):

$$t_{\text{partition 1}}=\frac{{\int }_0^{t_{1\text{-}2}}{t}_{\text{delay}}p(t_{\text{delay}})dt}{{\int }_0^{t_{1\text{-}2}}p(t_{\text{delay}})dt}$$$$t_{\text{partition 2}}=\frac{{\int }_{t_{1\text{-}2}}^{t_{2\text{-}3}}{t}_{\text{delay}}p(t_{\text{delay}})dt}{{\int }_{t_{1\text{-}2}}^{t_{2\text{-}3}}p(t_{\text{delay}})dt}$$

Where $t_{1\text{-}2}$ and $t_{2\text{-}3}$ are the partition boundaries between partitions 1 and 2, and partitions 2 and 3, respectively. For five branches, $F(t_{1\text{-}2})=0.2$ and $F(t_{2\text{-}3})=0.4$, where $F(t)$ is the cumulative probability density function.

INFO

Branching rules are tied to a specific combination of procedure, step, and action. Executing the same action from a different procedure step will not trigger branching.

Input File Format

Each entry is one line — procedure_name step_name action_name number_of_branches (matching the shipped BV4 file; the parser is token-based, so line breaks and other whitespace are interchangeable):

Procedure_Action_Time_Branches    number_of_items
procedure_name_1    step_name_1    action_name_1    number_of_branches_1
.
.
procedure_name_n    step_name_n    action_name_n    number_of_branches_n

Parameter Descriptions

Parameter	Type	Description	Example Value
number_of_items	Integer, ≥ 0	Number of action time branching events in the file. Setting to 0 disables all branching without requiring deletion of entries.	2
procedure_name	String	Procedure associated with the branching rule. Must match a valid procedure_name in Procedures.txt.	MPBG_SG_A_Increase_FWRV
step_name	String	Procedure step associated with the branching rule. Must match a valid step_name in Procedures.txt.	Step_1
action_name	String	Control panel action subject to time branching. Should match a control_name in ControlPanel.txt. The name is not validated when the file is read; if the control is never executed by the specified step, no branches are generated and no error is reported. Time delay steps use the reserved word Time.	X_SG_A_FWRV
number_of_branches	Integer, ≥ 1	Number of event sequence branches to generate. With 1, no branching occurs — the action time is the mean of the Weibull distribution.	2

TIP

Setting number_of_items to 0 disables all branching events without needing to delete entries. To activate only one branching event, move it to the top of the list and set number_of_items to 1. Only the first number_of_items entries are read — the BV4 reference file ships with a count of 0, so the example rows listed below its header are inert.

Execution

Each alternative defined here is opened as a child sequence that restarts from the branch point with that alternative applied. See How a Branch Alternative Executes.

Sample Input

Procedure_Action_Time_Branches    2
MPBG_SG_A_Increase_FWRV    Step_1             X_SG_A_FWRV    2
E_3                        Briefing_Hold_1    Time           3

Sample Explanation

• When action X_SG_A_FWRV is executed by procedure MPBG_SG_A_Increase_FWRV, step Step_1, 2 time branches are generated to model variability in the specified action time. Execution of X_SG_A_FWRV by any other procedure step will not generate branching events.

• When the time delay action Time is executed by procedure E_3, step Briefing_Hold_1, 3 action time branches are generated. This branching rule produces three delay times — a short time, a nominal time, and a long time — based on the time probability distribution specified for the action.