Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Managing Infrastructure and Systems > Managing Infrastructure and Systems > Flashcards

Managing Infrastructure and Systems Flashcards

1
Q

Why do we want components and systems to be reliable?

A
  • Safety reasons

- Financial reasons (maintenance and delays are costly)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the purpose of system reliability analysis?

A

To evaluate the performance of a system using known

information about the system components and structure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why perform reliability analyses?

A

To assess the adequacy of engineering systems
– at the design stage or to assess upgrades.

To satisfy regulatory requirements
– demonstrate that a system is fit for purpose.

To support decision making, e.g.:
– to find a balance between safety and cost,
– to determine optimal maintenance strategies.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What can happen without reliability analyses?

A

• Decisions can be subjective and based on biased information.
• Decisions can be inconsistent and based on qualitative
measures or prejudices.
• Available finances can be used inefficiently.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the definition for Reliability?

A

Reliability, Rsys(t) : the probability that the system failure mode does not occur from 0 to time t, given that the system worked at time 0.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the definition for Unreliability?

A

Unreliability, Fsys(t) : the probability that the system failure mode occurs at least once from 0 to time t given that it worked at time 0.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the definition for Availability?

A

Availability, Asys(t) : the probability that the system is operational at
time t, given that it was operational at time 0.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the definition for Unavailability?

A

Unavailability, Qsys(t) : the probability that the system failure mode
exists at time t

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the definition for Failure rate?

A

Failure rate : the rate at which the system failure mode occurs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the definition of a path set?

A

A path set is a list of components, such that if they all work then the system is also in the working state.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the definition of a minimal path set?

A

Is a path set, such that if any component is removed the system no longer functions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the definition of a cut set?

A

Is a list of components, such that if they all fail then the system is also in the failed state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the definition of a minimal cut set?

A

Is a cut set, such that if any item is removed the system will no longer fail

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe what goes inside the connectivity matrix.

A

cij = k, where k is the number of edges from node i to node j.
(0 for diagonal)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Describe what goes inside the connection matrix.

A

1 for diagonal terms (certain to connect)
0 i f no connection
A where A is the component linking node to node

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Which 3 methods could you use to calculate the unreliability of an RBD that cannot be represented as a combination of series and parallel networks?

A

Solution Methods:
– Key Element Method.
– Conversion from Deltas to Stars.
– Minimal Path Set / Cut Set Evaluation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is the expression for…

a) system success using key element method
b) system failure using key element method

…. given that E is the key element

A

a) RSYS = (RX) (RE) + (RY) (QE)

b) QSYS = (QX)(RE) + (QY)(QE)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Give three matrix methods you can use to find the minimal path sets and state which matrix each method relates to

A

General Algorithm - using the connectivity matrix
Node Removal - using the connection matrix
Matrix multiplication - using the connection matrix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Give two uses of RBD analysis

A
  • Helps to find points of failure and identifies what is making the system unreliable
  • Shows a visual representation of a system and therefore reliability can be assessed without numbers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How could you improve a system’s reliability? (Once completing RBD analysis)

A
  • Reduce the amount of series systems
  • Increase the redundancy
  • Upgrade the components to ones with more reliability
  • Improve the accuracy of the data on the reliability on for the components
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How can you improve RBD analysis?

A
  • RBDs are often simplified. To improve analysis, create a more accurate model
  • Minimise assumptions and make sure any you do make are reasonable
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Why might an RBD analysis not be accurate?

A
  • RBDs don’t take into account the effect of not have all 3 in a 2/3 component working (i.e. if 1 fails it might still work but with less power)
  • The analysis doesn’t take into account time variations in demand
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is FMEA?

A

FMEA is a powerful design tool that analyses each potential failure mode in the system to examine the
effects on the system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is FMECA?

A

When FMEA is extended to classify each potential failure effect according to its severity the method is known as FMECA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Which stage in a product’s life cycle is it best to carry out FMEA?

A

Design stage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What are the advantages of FMEA?

A
  • Good data gathering process on existing systems
  • Rigorous
  • Systematic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are the disadvantages of FMEA?

A
  • Time-consuming

* Expensive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What type of analysis is FMEA? And what does it identify?

A

Qualitative analysis that identifies:
– potential system failure modes,
– the causes of the failure modes
– the effects on the system operation associated with the failure modes’ occurrence.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What are the two types of FMEA?

A

1) Product FMEA
– Analyses the product and how failure modes affect its operation.
E.g. Determine causes and effects of fire protection system failure
2) Process FMEA
– Analyses the process by which the product is built, maintained and
used.
– Examines how failures in the process affect product operation.
E.g. Determine causes and effects of failures while maintaining a fire protection system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What are the two approaches for FMEA?

A
  1. Functional (top-down) :
    – System decomposed to sub-assemblies (sub-system, modules,
    components)
    - Depending on the information available and study objective
    – Consider effects of loss of inputs and sub-assembly failures
    – Used in the early design stages
  2. Hardware (bottom-up):
    – Detailed system breakdown
    – Consider each individual component and effects of its failure modes
    – Used in detailed design
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are the eight steps involved in FMEA procedure?

A
  1. Define system:
    – Components, boundaries and interfaces
    – All modes of operation
    – Environment profile
    – Mission / phases and times in each phase
    – Mission / phase objectives
  2. Construct functional block diagrams:
    – Functional connection between sub-systems / components
    – Hierarchy level at which the analysis is done
  3. Note assumptions:
    – System and sub-system boundaries
    – Failure modes/failure rates, etc.
  4. Define system failure modes
  5. List component (sub-system) failure modes:
    – Review failure information prior to commencing study (failure modes can be found by investigation of failure data)
  6. Complete FMEA worksheets:
    – Analyse the effect at LOCAL and SYSTEM level for each component (sub-system) failure mode
    – Assume worst potential consequences
  7. Review worksheets to determine the reliability critical
    components
  8. Make recommendations for design improvements and further work
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What do the symbols stand for under the ‘Failure Mode Criticality Number’ section of the formula sheet?

A

lamda o = failure mode rate
lamda p = failure rate
alpha = proportion of failures in specified failure mode
beta = probability that expected failure effect will result
Cm = Criticality Number
t = mission or phase time period

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What does a vote gate mean in a fault tree?

A

Output event occurs if at least k of the n input events occur.

34
Q

What does a Priority AND gate mean in a fault tree?

A

Output event occurs if all input events occur in sequential order from left to right.

35
Q

What does a NOT gate mean in a fault tree?

A

Output event occurs if input event does not occur.

36
Q

What does an intermediate event represent in a fault tree?

A

System or component event description

37
Q

What does a basic event represent in a fault tree?

A

Basic event for which failure and repair data is available.

Usually represents a component failure.

38
Q

What does a house event represent in a fault tree?

A

Represents definitely occurring or definitely not occurring events.

39
Q

What does a transfer event represent in a fault tree?

A

Indicates that this part of the fault tree is developed in a different part of the diagram or on a different page.

40
Q

What do dual fault trees allow you to find?

A

minimal path sets

41
Q

What are the tree possible maintenance policies?

A
  1. No repair
  2. Repair when failure is revealed
    (unscheduled maintenance)
  3. Repair when failure is unrevealed and must be discovered
    (scheduled maintenance)
42
Q

What is the symbol for:

a) Failure rate (hazard rate)
b) Repair rate
c) Mean time to failure (MTTF)
d) Mean time to repair (MTTR)
e) Inspection interval

A

a) lamda
b) weird v
c) mew
d) tau
e) theata

43
Q

What does steady state mean?

A

t tends to infinity

44
Q

What are the drawbacks when using fault trees to calculate top event probability?

A

Using the inclusion-exclusion expansion to calculate the exact top event probability for large fault trees is not practical. Even for fast modern digital computers a calculation involving many cut sets can take a great deal of processing time.

45
Q

How do the approximations to the top event probability compare to each other?

A

Qsys is less than or equal to Min Cut Set Upper Bound which is less than or equal to Rare Event/ Upper Bound

46
Q

What do importance measures tell us?

A

Indicate, in some sense, the contribution each element of the system makes to the system failure event.

47
Q

What is the definition of ‘Critical State’?

A

A critical system state for component i is a state for the remaining n-1 components such that failure of component i causes the system to go from a working to a failed state.

48
Q

Give an example of a deterministic importance measure.

A

Structural Importance Measure

49
Q

Give examples of probabilistic availability importance measures.

A

Birnbaum’s Measure/Criticality Function
Criticality Measure of Importance
Fussell-Vesely Measure of Importance
Fussell-Vesely Measure of Cut Set Importance

50
Q

Give examples of probabilistic reliability importance measures.

A

Barlow-Proschan Measure of Initiator Importance

Sequential Contributory Measure of Enabler Importance

51
Q

How do you calculate the structural importance measure?

A

(number of critical states for component i) / (total number of states for the n-1 remaining components)

52
Q

What is the definition of Birnbaum’s Measure/Criticality Function?

A

The Criticality Function for a component i, Gi

(q) is the probability that the system is in a critical state for component i.

53
Q

What is the definition of Criticality Measure of Importance?

A

The probability that the system is in a critical state for component i and i has failed. (Weighted by QSYS).

54
Q

What is the definition of Fussell-Vesely Measure of Importance?

A

Probability of the union of all minimal cut sets containing i given that the system has failed.

55
Q

What is the definition of Fussell-Vesely Measure of Cut Set Importance?

A

Probability of occurrence of cut set i given that the system has failed.

56
Q

What is the definition of frequency/unconditional failure intensity?

A

The frequency of an event is the probability that the event occurs per unit time at time t.

57
Q

What assumption do we make when calculating unconditional failure intensity?

A

Basic events cannot occur simultaneously, i.e. only one basic event can occur in any time interval dt.

58
Q

What is the formula for unconditional failure intensity in terms of lamda and Q(t)

A

lambda( 1 - Q(t))

59
Q

How do you calculate minimal cut set frequency?

A

Sum of all the combinations of 1 w and the rest qs (using all letters/components in cut set)

60
Q

What is top event frequency? (Also known as system unconditional failure intensity)

A

The probability that the top event occurs at t

per unit time

61
Q

Why is it more accurate to use initiators and enablers in some cases?

A

As with many safety protection systems, the order of events is actually of vital importance to the occurrence of the top event.
If a hazardous event occurs after the protection systems have failed then there will be a dangerous system failure.
If the hazardous event occurs before the protection systems fail then the dangerous system failure will be avoided.

62
Q

What is an initiating event?

A

Perturb system variables and place a demand on

control/protection systems to respond.

63
Q

What is an enabling event?

A

Are inactive control/protection systems which permit initiating events to cause the top event.

64
Q

What is the definition of Barlow-Proschan Measure of Initiator Importance

A

The probability that initiating event i causes the system failure over the interval (0, t). [Weighted by W(0,t)].

65
Q

What is the definition of Sequential Contributory Measure of Enabler Importance

A

The probability that enabling event i permits an initiating event to cause system failure in (0, t). [Weighted by W(0,t)].

66
Q

Why would you use FTAs in real life?

A
  • To better understand a system and how it can fail
  • To calculate system unreliability and its unconditional failure intensity
  • To look at the way safety systems operate (through using initiators and enablers)
  • To identify areas of improvement for the system (through using importance measures)
67
Q

What does simulation seek to do and how?

A

Simulation seeks to “duplicate” the behaviour of the system under investigation by studying interactions among its components.

68
Q

Give an example of ‘next event scheduling’

A

Customers arrive and either go into service immediately if the server is idle or join a waiting line (queue) if the server is busy.

69
Q

Why might you use simulation/the Monte Carlo method instead of the analytical methods?

A

Problem Areas for Analytical Methods:
• Large Fault Trees / Networks.
• Complex Component Failure Distributions.
• Investigating Maintenance Philosophy (Queues).
• Considering more than two component states.
• Dependencies - failures or repairs.

70
Q

Give some desirable properties of random numbers.

A
  • Uniform ~ U [0,1]
  • Independent.
  • Fast

Additional Desirable Properties (Pseudo-random numbers):
• Long cycle lengths.
• Repeatable.

71
Q

What are four of the methods that can be used to generate random numbers?

A
  1. Die.
  2. Tables.
  3. Calculators (electronic noise).
    Pseudo-Random Numbers:
  4. Computer Algorithm
72
Q

What does modulo m mean?

A

keep dividing by m until you get a number less than m

73
Q

What is discrete event simulation?

A

• Component failure and repair characteristics can be represented by probability distributions and in this case simulation steps through time dealing with events chronologically.
• Discrete event simulation is used to model a system in this way.
• The times at which events occur are obtained by random
sampling from the appropriate probability distributions.

74
Q

What are the steps to complete the convolution method?

A
  • Generate 12 random numbers
  • Calculate the sum of these 12
  • t = ((x-6)*standard deviation)+mew

(remember, mew in this case can be MMTF or MMTR, depends what you’re looking at)

75
Q

Which time to failure would you take as the system time to failure from multiple component times in series?

A

The minimum

76
Q

Which time to failure would you take as the system time to failure from multiple component times in parallel?

A

The maximum

77
Q

What are the advantages of simulation?

A
  • Model Complex Systems.
  • Systems can be stochastic (random).
  • Vary operating conditions.
  • Vary system designs.
  • Vary maintenance strategies.
  • Can change time scales.
78
Q

What are the disadvantages of simulation

A
  • Exact solutions are not obtained.
  • Cost.
  • Time.
  • Validation process difficult.
79
Q

What should the initial conditions be?

A

Desire conditions that are “typical” or “representative” of real system.

80
Q

If the initial conditions are not obvious, what could you do?

A

– Ignore.
– “Warm Up” simulation
– Sample from a range of conditions.

Managing Infrastructure and Systems (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions