Upload
others
View
2
Download
0
Embed Size (px)
Citation preview
Calhoun: The NPS Institutional Archive
Faculty and Researcher Publications Faculty and Researcher Publications
2011-10
A Modeling Approach for Developing
System Performance Requirements (presentation)
Green, John M.
http://hdl.handle.net/10945/34360
A Modeling Approach for Developing System Performance
Requirements
John M. Green
Naval Postgraduate School
Issues to be Addressed
• The concept of system performance and how to measure effectiveness has been the topic of numerous papers of over the years.
• Typically the focus is on one system characteristic such as reliability (R) or operational availability (A0) though the Air Force Weapons System Effectiveness Industry Advisory Committee (WSEIAC) recommended that both are required along with system capability (C).
• This is in recognition that performance measures are extremely useful to the system engineer in five key areas:
1. Establishing requirements; 2. Assessing successful mission completion; 3. Isolating problems to gross areas; 4. Ranking problems relative to their potential to impact the mission; and 5. Providing a rational basis for evaluating and selecting between proposed
problem solutions and their resulting configurations.
2
Goal
• This presentation will present a top-down modeling approach based on functional flow block diagrams that shows how the system engineer can develop an overall system performance measure that is inclusive of R, A0, and C.
• It starts with the system concept and allows the system engineer to allocate performance at each layer of analysis, from system to components, ultimately providing detailed performance requirements which will provide a basis for evaluating candidate solutions.
3
Prediction
• Effectiveness calculations are about prediction
• Objective of prediction is twofold:
1. System effectiveness predictions form a basis for judging the adequacy of system capabilities
2. Cost-effectiveness predictions form a rational basis for management decisions.
4
Outline
• Three key studies
• Overview of the approach
• An example
• Summary
• References
5
Three Key Studies
– WSEIAC (Weapons System Effectiveness Industry Advisory Committee) Study (1964)
– MORS C2 Measures of Effectiveness Study (1986)
– Paper by John Marshall (1991)
– Other support work listed in references
6
# 1: WSEIAC Study
• Developed for the Air Force in 1964 and follows AFSC-375 series
• Looked at two approaches: 1. Immediately commit resources to an intuitively
plausible (re)design and surmount the problems as they arise, or
2. Explore in the “minds eye” the consequences of the (proposed) system characteristics in relation to mission objectives before irrevocably committing resources to any specific approach
• It is a framework for evaluating effectiveness
7
System Effectiveness
• Concluded that system effectiveness can be defined as a measure of the extent to which a system may be expected to achieve a set of specific mission requirements.
• System effectiveness is a function of three primary components: availability (A), dependability (D), and capability (C).
• Definition allows one to determine the effectiveness of any system type in the hierarchy of systems
8
Definitions
• Availability (A) – a measure of the condition of the system at the start of a mission, when the mission is called for at some random point in time.
• Dependability (D) – a measure of the system condition during the performance of the mission given its condition (availability) at the start of the mission.
• Capability (C) – a measure of the results of the mission given the condition of the system during the mission (dependability)
9
Mathematical Formulation
11 12 1
1 2
21 22 2
(0)
(0)
d d cE a a
d d c
1 2A a aSystem state (up/down)
1
0
2
(0)
(0)
cC
c
Capability at t0
11 12
21 22
d dD
d d
d11 = probability of operational at end given operational at start d12 = probability of fail at end given operational at start d21 = probability of operational at end given fail at start d22 = probability of fail at end given fail at start
10
#2: MORS C2 Study
DEC ISION
MAKER
IMPLEMENT
RESULTS
ANALYSIS R ESULTS
VALUES OF MEASURES
MEASUR ES FOR FUNCTIONS
SYNTHESIS OF STATICS
AND DYNAMICS
FUNCTIONS
SYSTEM ELEMENTS
PROBLEM STATEMENT
MODULAR COMMAND AND CONTROL
EVALUATION STRUCT URE (MCES)
AGGR EGATION
OF MEASURES
DATA GENERATION
EX, EXP, SIM, SUB JECTIVE
SPECIFICATION OF MEASURES
(CR ITERIA) MOP, MOE, MOFE
INTEGRATION OF SYSTEM
ELEMENTS AND FUNCTIONS
C2 PR OCESS
DEFINITION
C2 SYSTEM
BOUNDING
PROBLEM
FOR MULATION
Dimensional
Parameters
System
Subsystem
Environment
Force
MOPs
MOFEs
MOEs
1 2 3, , ,......., nMOP f p p p p
11
#3: John Marshall Paper
• Marshall developed a mathematical relationship between D, A, C, and S based on the work of Ball and Habayeb
• Related concept to an operational characteristics curve – Initial Curve is based solely on
the physics involved – Subsequent shape of the
curve is defined by variance in system design, operational usage, and environmental conditions
Threat Activity
Probability
Pta
Threat
Detect/Control/
Engage
Pdce
=Pcd*
Pcl
Threat
Attack
Pca
Ship Susceptability
Ph=P
ta*P
dce*P
ca
Ship Vulnerability
Pk/h
Ship Killability
Pk=P
h*P
k/h
Ship Survivability
Ps=1-P
k
Range
Derived
Performance
Curve
R
P
P
Cumulative
Probability
t1
Available
Performance
Curve1.0
12
A FFBD Example
http://en.wikipedia.org/wiki/Functional_flow_block_diagram
13
14
Aggregating Processes
Process A Process B Process CStart Outcome
t A B CP P P P
Process A
Process B
Start Outcome
t A B A BP P P P P
Process A
Process B
Process CStart Outcome
( )t c A B A BP P P P P P
Overview of the Approach
1. Establish the intended purpose of the system 2. Establish those system characteristics which
contribute to the designed ability of the system to accomplishment of the system purpose.
3. Measure/compute the numerical value that describes the degree to which each of these characteristics affects the accomplishment of the system purpose
4. Combine all computed/measured values into a form suitable to obtain a system operational value.
15
A SIMPLIFIED EXAMPLE
16
From the Ship’s Perspective
Prime Directive: Actively Defend Ship
Functions: Detect Control Engage
Track TEWA
Search
Radar
Optical
Search
Track
Radar
Allocated to:
Search
Auto
Track
Auto
TEWA
Weapons
Manual
Assign
Manual
Track
OR
OR
OR
Launch
OR
Functions
Process
Defend Ship against Cruise Missile Threats
17
Sensor Operational Objectives
• Required functions to be performed:
– Detection, Tracking, Classification, ID, Ranging
• Target characteristics and separation
• Coverage volume or area and background
• Atmospheric and weather conditions
18
19
Pd
R
Pd
R
Pd
R
Rmax
Rmax
IR
Radar
IFF
MIN
MAX
MIN
+
+
Topen fire
T
1.0
Tmax
T
1.0
TFC
T
1.0
TmaxT
min
Fire ControlC2
Max wait for
IFF response
Baseline Network
IFF Raleigh
Radar Swerling
IR Exponential
C2 Uniform
FC Fixed Time Delay
IFF Wait Fixed Time Delay
20
System Reaction Time
Distribution Reaction Time Distribution
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 5 10 15 20 25
Range (NM)
Cu
mu
lativ
e P
robabil
ity
Shown without effects of D, A, or S
Sensor Operational Objectives into Effectiveness
Performance Parameters (C) • Detection range • Tracking range • Classification range • ID range • Pd • SNR minimum • Spatial resolution • Sensitivity • Total FOV (look angle) • False alarm time • Frame time • Physical characteristics
Reliability Parameters
• Dependability
• Availability
• Survivability
21
Parameters Drive IR Sensor Design
• Optics
• Detectors
• Signal processing
• Display and recording
22
In Summary
• Presented a top-down modeling approach based on functional flow block diagrams that shows how the system engineer can develop an overall system performance measure that is inclusive of R, A0, and C.
• It started with the system concept which allows the system engineer to allocate performance at each layer of analysis, from system to components, ultimately providing detailed performance requirements which will provide a basis for evaluating candidate solutions.
• Approach can be useful to the system engineer in five key areas: 1. Establishing requirements; 2. Assessing successful mission completion; 3. Isolating problems to gross areas; 4. Ranking problems relative to their potential to impact the mission; and 5. Providing a rational basis for evaluating and selecting between proposed
problem solutions and their resulting configurations
23
24
Functional and Non-functional Performance
25
References
• Ball, Robert. The Fundamentals of Aircraft Combat Survivability Analysis and Design, AIAA Press, 1985
• Bard, Jonathon. An Analytical Model of the Reaction Time of a Naval Platform. IEEE Vol. SMC-11, No. 10 Oct. 1981, pp. 723-726
• DARCOM-P 706-101 CH. 24 • Habayeb, A. R. Systems Effectiveness, Pergamon Press, 1987 • Hitchens, Derek. • Friddell, Harold G. and Herbert G. Jacks. System Operational
Effectiveness (Reliability, Performance, Maintainability), 5th National Symposium on Reliability and Quality Control, January 1959
• Marshall, John. Effectiveness, Suitability & Performance, 59th MORS, 12 June 1991
26