Ece Engr 501 Chapter 02
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Transcript of Ece Engr 501 Chapter 02
This material is copyrighted and is the property of Colorado State University
Structure of Complex Systems
Chapter 2
This material is copyrighted and is the property of Colorado State University
2.1 System Building Blocks and
Interfaces
• System engineers need broad knowledge of several
interacting disciplines.
• How deep does understanding need to be?
• Sufficient to recognize
– Program risks
– Technological performance limits
– Interfacing requirements
– Trade-off analyses among design alternatives
This material is copyrighted and is the property of Colorado State University
2.2 Hierarchy of Complex Systems
• Definition of a “system” is inherently applicable to different levels of aggregation of complex interacting elements.
• Every system is a subsystem of a higher-level system, and every subsystem may itself be regarded as a system.
• “System of systems.”
This material is copyrighted and is the property of Colorado State University
Model of a Complex System
• The scope of a “system” is ambiguous.
• Modeling is one of the basic tools of systems
engineering.
• Purpose – to define a relatively simple and readily
understood system architecture.
This material is copyrighted and is the property of Colorado State University
• Complex systems have a hierarchical structure.
• Subsystems are major interacting elements
• Subsystems are composed of more simple functional entities, down to primitive elements, called parts.
• Common used terminology: system and subsystem for uppermost levels; parts for the lowest.
• Intermediate levels are called components and subcomponents.
This material is copyrighted and is the property of Colorado State University
Definition of System Levels
– Possess the properties of an
engineered system, as defined
in Chapter 2
– Perform a significant useful
service with only the aid of
human operators and
standard infrastructures (e.g.
power grid, highways, fueling
stations, communication lines,
etc.)
Systems:
While these distinctions are
somewhat arbitrary, we still
need to agree on common
definitions to facilitate
discussion.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
• Subsystem – a major portion of the system that
performs a closely related subset of the overall
system functions
• Component – middle level of system elements;
often correspond to configuration items (CIs) in
government system acquisition notation.
• Subcomponents – perform elementary functions
• Parts – perform on significant function except in
combinations with other parts.
This material is copyrighted and is the property of Colorado State University
Domains of the Systems Engineer and
Design Specialist
• Components are products fitting within the domain of industrial
design specialists.
• Specification of components, especially to define performance and
ensure compatible interfaces, is the task of systems engineering.
• When a subcomponent or part happens to be critical to the
systems operation (e.g., the ill-fated seal in the space shuttle
Challenger’s booster rocket), the systems engineer should be
prepared to learn enough about its behavior to identify its
potential impact on the system as a whole.
This material is copyrighted and is the property of Colorado State University
Components level – point at which two knowledge
domains “overlap.” This is where the systems
engineer and design specialist must communicate
effectively.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
2.3 System Building Blocks
• Component - an intermediate level of elements that recur in a variety of systems, which typically constitute product lines of commercial organizations.
•
• Result: advanced and versatile products that can finda large market (and hence achieve a low cost) in a variety of system applications.
• COTS (commercial off-the-shelf) components attempt to capitalize on economies of scale found in the commercial component market.
This material is copyrighted and is the property of Colorado State University
• Functions on the component level – first to
provide a significant functional capability, as
well as being found in a variety of different
systems.
• Components – basic system building blocks
This material is copyrighted and is the property of Colorado State University
Functional Building Blocks: Functional
Elements
• Information – the content of all knowledge
and communication
• Material – the substance of all physical
objects
• Energy – which energizes the operation and
movement of all active system components
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• Subdivide into two classes
– Elements dealing with propagating information (e.g., radio signals) are called signal elements
– Elements dealing with stationary information (e.g., computer programs) are called data elements
• Results in four classes of system functional elements:
– Signal elements: sense and communicate information
– Data elements: interpret, organize, and manipulate information
– Material elements: provide structure and transformation of materials
– Energy elements, provide energy and motive power
This material is copyrighted and is the property of Colorado State University
• A set of generic functional elements are also defined.
• Criteria to ensure elements are neither trivially simple
nor inordinately complex:
– Significance – Each functional element must
perform a distinct and significant function, typically
involving several elementary functions
– Singularity – Each functional element should fall
largely within the technical scope of a single
engineering discipline
– Commonality – The function performed by each
element can be found in a wide variety of system
types
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The system inputs are transformed and processed through the interconnected functions to provide the desired system outputs.
The functional design of
any system may be
defined by conceptually
combining and
interconnecting the
identified functional
elements.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
Physical Building Blocks: Components
• Component elements or simply
components - the physical embodiments of
the functional elements, consisting of
hardware and software.
– Have the same distinguishing characteristics
– Are at the same level in the system hierarchy.
This material is copyrighted and is the property of Colorado State University
Issues with implementing
functional elements into
components:
reliability, form and fit,
compatibility with the
operational environment,
maintainability,
producibility, testability,
safety, cost, integrity of the
functional design.
The system-level significance of these factors must be
understood.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
Applications of System Building Blocks
• Identifying the classes of functions that need to be performed by the system may help group the appropriate functional elements into subsystems, and thus facilitate functional partitioning and definition.
• Identifying the individual functional building blocks may help define the nature of the interfaces within and between subsystems.
• The interrelation between the functional elements and the corresponding one or more physical implementations can help visualize the physical architecture of the system.
• The commonly occurring examples of the system building blocks may suggest the kinds of technology appropriate to their implementation, including possible alternatives.
This material is copyrighted and is the property of Colorado State University
2.4 The System Environment
• Everything outside of the system that interacts
with the system. This interaction is the main
substance of system requirements.
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System Boundaries
• Necessary to precisely define what is inside the system and what is outside.
• In a functional sense, the operators are integral parts of the system. However, operators constitute elements of the system environment, and impose interface requirements that the system must be engineered to accommodate. In our definition, the operators are considered external to the system.
• For example, the electrical power grid is a standard source of electricity, an essential element in its operational environment, and interfacing requirements.
This material is copyrighted and is the property of Colorado State University
Types of Environmental Interactions
• Distinguish between primary and secondary
interactions.
• Primary – represent functional inputs, outputs, and
controls
• Secondary – relate to elements that interact with
the system in an indirect nonfunctional manner, such
as physical supports, ambient temperature, etc.
This material is copyrighted and is the property of Colorado State University
Primary • Inputs and Outputs
• System Operators
– Human-machine interface is one of the most critical, but also most complex to define and test
• Operational maintenance
– Designed to provide access for monitoring, testing, and repair.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
Secondary • Support Systems
– Standard available resources with which it must interface harmoniously
– Examples: electric power grids, automobile filling stations
• System Housing
– Operating site, which imposes compatibility constraints on the system
• Shipping and Handling Environment
– Transport from the manufacturing site to the operating site
– Examples: extreme temperatures, humidity, shock and vibration. Sometimes more stressful than those of the operating environment.
This material is copyrighted and is the property of Colorado State University
2.5 Interfaces and Interactions
• Interfaces, external and internal
• Proper interface control is crucial. This involves:
– Identification and description of interfaces as part of system concept definition, and
– Coordination and control of interfaces to maintain system integrity during the engineering development, production, and subsequent system enhancements.
This material is copyrighted and is the property of Colorado State University
Interactions
• Interactions between two individual elements of the system are effected through the interface connecting the two.
• Requires access to a number of vital system functions for testing purposes.
• Built-in tests (BIT)
• The definition of such interfaces is also the concern of the systems engineer.
This material is copyrighted and is the property of Colorado State University
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
Interface Elements
• Three different types
– Connectors, which facilitate the transmission of
electricity, fluid, force, and so on between
components
– Isolators, which inhibit such interactions
– Converters, which alter the form of the
interaction medium.
This material is copyrighted and is the property of Colorado State University
Points to note:
• The function of connecting nonadjacent system components by
cables, pipes, levers, and so on, is often not part of a particular
system component.
• The relative simplicity of interface elements belies their critical
role in ensuring system performance and reliability. Experience has
shown that a large fraction of system failures occurs at interfaces.
•The function of making or breaking a connection between two components is an important design feature.
Source: Kossiakoff, A., & Sweet, W. (2003). Systems engineering : principles
and practice. Hoboken, N.J. : Wiley-Interscience.
This material is copyrighted and is the property of Colorado State University
Homework Problems (page 48) 2.1) Referring to Figure 2-1, list a similar hierarchy consisting of a typical
subsystem, component, subcomponent, and part for (a) a terminal air traffic control system, (b) a personal computer system, (c) an automobile, and (d) an electric power plant. For each system you need only name one example at each level.
2.4) The last column of Table 2-1 lists examples of the applications of the 23 functional elements. List one other example application than the one listed for three elements in each of the four classes of elements.
2.6) For a passenger automobile, partition the principal parts into four subsystems and their components. (Do not include auxiliary functions such as environmental, entertainment.) For the subsystems, group together components concerned with each primary function. For defining the components, use the principles of significance, (performs an important function), singularity (largely falls within a simple discipline), and commonality (found in a variety of system types). Indicate where you may have doubts. Draw a block diagram relating the subsystems and components to the system and to each other.