addExposed {FaultTree}

Add a Time Dependant, Non-Repairable, Event

Description

Adds a basic component event to a fault tree in which probability of failure is defined by a probability distribution and exposure time.

Usage

addExposed(DF, at, mttf, dist="exponential", param=NULL, display_under=NULL,
		tag="", exposure=NULL, label="", name="",name2="", description="")

Arguments

DF

A fault tree dataframe such as returned from ftree.make or related add... functions.

at

The ID or tag name of the parent node for this addition.

mttf

The mean time to failure. It is the user's responsibility to maintain constant units of time.

dist

The probabilty distribution to be used for defining probability of failure from mttf, and a possible extra parameter. Options for "exponential" and "weibull" have been implemented.

param

A vector containing shape and time_shift for weibull exposed events in that order.

display_under

Optionally, the ID of a sibling event under an OR gate for vertical alignment of the component node in the graphic display.

tag

A very short identifying string (typically 5 characters or less) uniquely identifying a basic event for minimal cutset evaluation

exposure

This is to be a seldom-used override of system mission time applicable only to exponentially exposed events.

label

An identifying string for the logic gate. Use of label in ftree.make defines the convention for rest of tree construction.

name

A short identifying string (typically less than 24 characters)

name2

A second line, if needed for the identifying string label

description

An optional string providing more detail for this probability.

Details

The lambda for exponential definition is taken as 1/mttf, which is the value stored in CFR for the tree node. Weibull distributions have a mean, which differs from the classical scale parameter by a factor determined as gamma(1+1/shape). The weibull scale is determined from the value stored in CFR (as 1/mttf) for the tree node. Additional parameters to fully define the specific distribution of expected failure times are the shape and any time_shift.

Value

Returns the input fault tree dataframe appended with an entry row for the defined failure event.

References

Ericson, Clifton A. II (2011) Fault Tree Analysis Primer CreateSpace Inc.

Nicholls, David [Editor] (2005) System Reliability Toolkit Reliability information Analysis Center

O'Connor, Patrick D.T. (1991) Practical Reliability Engineering John Wiley & Sons

Vesely, W.E., Goldberg, F.F., Roberts, N.H., Haasl, D.F. (1981) Fault Tree Handbook U.S. Nuclear Regulatory Commission

Vesely, W.E., Stamatelato, M., Dugan, J., Fragola, J., Minarick, J., Railsback, J. (2002) Fault Tree Handbook with Aerospace Applications NASA

Doelp, L.C., Lee, G.K., Linney, R.E., Ormsby R.W. (1984) Quantitative fault tree analysis: Gate-by-gate method Plant/Operations Progress Volume 3, Issue 4 American Institute of Chemical Engineers

Examples

mission_time<-0.5
mytree <-ftree.make(type="or", name="6-month task", name2="incomplete")
mytree <- addExposed(mytree,  at=1, mttf=3, name="pump fails",
   name2="before completion")