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2012-10-24 20:14:12

System Dynamics
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  1. Explain the following concepts:

    Manufactunng is the orgamsed activity devoted to the transformation of raw materials into marketable goods. In the terminology of economics, these marketable goods are known as economic goods; they cannot be obtained without expenditure. This is in contrast to free goods, which are available in unlimited quantities at no cost. Manufacturing industry is also called a secondary industry, because this is the sector of a nation’s economy that is concerned with the processing of raw matenals supplied by the primary industry (agriculture, forestry, fishing, mining, extraction of minerals, and so on) into the end products. It is one of the most basic and important functions of human activity in modem industrial societies.
  2. Explain the following concepts:The definition of a system implies that it must have four distinct features. Name briefly discuss & give an example of each
    • According to its definition a System should have the following features:
    • An assembly of components. These components are the structural, operating, and flow parts of the system which can be individually identified. System components can also
    • be identified as input, process, output, feedback control, and restriction. The input and output of a system may sometimes also be referred to as the cause and effect, respectively

    • Components connected in an organised manner This indicates that the relationships between system components are important. Each component is related directly or indirectly to every other component in the system and affected by them. Without relationships there will be no systems. The concept of relationship constitutes one of
    • the fundamental differences between the doctrines of holism and reductionism. The relationships between the individual parts and the effects they have on each other are considered important by holism - hence a whole cannot be analysed without considering these interactions.

    • A logical objective or purpose. This implies that the systems we are concerned with are rational. That is, a logical objective must be explicitly identified. The purposeful
    • action of a system which transforms system input into system output should, therefore, conform to the ‘principle of causality”, that is, for every output or effect exhibited by
    • a rational system, there exists a defimte set of inputs of causes that influenced and produced that output. This implies that identical inputs to a rational system should  always be likely to produce identical outputs. Manufacturing systems are rational systems. A fortune-telling system using a crystal ball, for example, is regarded by modern science as an irrational system, because its inputs have no rational influence
    • on its outputs.

    Components which work together towards the common objective. It is the totality of the components which, together with their attributes and relationships, constitutes a particular system and provides the output for each given set of inputs.
  3. Draw a simple diagram to discuss the internal significance of manufacturing in a society
  4. Name the three revolutions in the history of manufacturing development.
    1) The Neolithic Revolution: The Age of Craftmanship

    2) The Industrial revolution: The Age of Mechanisation

    3) The new Industrial revolution: The Age of Information and Automation
  5. Explain the concept:

    Manufacturing system
    A manufacturing system usually employs a series of value-adding manufacturing processes to convert the raw materials into more useful forms and eventually into finished products. For example, in the process of manufacturing a machine-tool, pieces of metal are machined into parts. Various parts and other items are assembled into sub-assemblies; iron ore is smelted and converted into castings; steel plates are cut into various sizes and shapes and then welded into fabrications; and finally, these are assembled into the machine-tools. The outputs from one manufacturrng system may be utilised as the inputs to another.
  6. Explain the concept: 
    Manufacturing is the organised activity devoted to the transformation of raw materials into marketable goods. In the terminology of economics, these marketable goods are known as economic goods; they cannot be obtained without expenditure. This is in contrast to free goods, which are available in unlimited quantities at no cost. Manufacturing industry is also called a secondary industry, because this is the sector of a nation’s economy that is concerned with the processing of raw materials supplied by the primary industry (agriculture, forestry, fishing, mining, extraction of minerals, and so on) into the end products. It is one of the most basic and important functions of human activity in modern industrial societies.
  7. Definition of a System
    a collection of comoponents, for example people and/or machines, which are interelated in an organised way and work together towards the accomplishment of  of a certain logical and purposeful end.
  8. The definition of a system emplies that a system must have the following features :
    • 1.  An assembly of components
    • 2  Components connected in an organised manner
    • 3. A logical objective or purpose
    • 4. Components which work together towards the common objective
  9. Schematic representation of a basic system:
  10. Essential components of feedback control
    • 1) a controlled system parameter or condition

    2) a momtormg function which measures the current state of the controlled condition

    3) a decision-making function which compares the current state of condition with the desired condition 

    4) an actuator that alters the system state so as to reach the desired state.
  11. it is important for industrialised countries to maintain and even increase manufacturing competitiveness However, there are many things that can go wrong and factors that constrain this development Discuss these problems
    • manufacturing process itself becoming more complex and sophisticated as a result of rapid technological changes, but the general environment is changing because of tough international competition. Under these circumstances, efficiency and flexibility are of vital importance to the survival of a manufacturing industry, which has to operate under much more complex and difficult conditions than ever before. What is the right way to approach
    • the problem? This is the crucial question everyone involved in manufacturing should be asking.
    • Although it has often been suggested that manufacturing industries can become more productive by employing new and more sophisticated equipment and techniques, surveys
    • (see, for example, Miller et aL, 1981, Morecroft, 1983) have shown that in many cases the most significant factor is still the effectiveness of the administration system. Poor plannmg and control, material shortages, inefficient capacity allocation, lack of understanding of the nature of the organisation, and thus lack of formal guidance rules to aid management decision-making, may all result in low productivity, even though the investment in new
    • equipment may have improved local effectiveness.
    • Industrial competition in the new technological environment has shown that international and company competitiveness cannot be gained just by investing in new and sophisticated
    • technologies. Part of the key to improving productivity must be the systematic use of appropnate approaches, techniques and technologies to modernise existing manufacturing
    • systems or design new ones, together with good production management in operating them. In most cases being interested in new technology is not enough, because unless a systems approach is adopted, the use of new technology will not always point a company in the right direction.
  12. To explain the concept of a system more fully, use a simple system diagram (as used in the course notes) and a brief description to describe Department of Industrial Engineering as viewed as a system.
  13. What are the advantages generally associated with object-orientations’?
    Realistic view In comparison to the traditional methods, an O-O approach allows the analyst/designer to identify and manipulate a system abstraction in a more direct way, due to the fact that the real-world consists of physical entities, or objects, rather than functions/processes” 

    Flexibility. The modularised system structure consists of systemunits, which can be combined to execute the required application, and yet each of these units can be implemented or modified independently without affecting any other modules in the system.

    • Reusability and extensibility. Such an approach facilitates rapid system design/development by reusing components already available. Once a system component has
    • been defined, it can be used as the basis for other similar components; hence reducing duplicated effort in system development and modification.
  14. In order to develop a new manufacturing system, knowledge must be gained of the existing system and the factors that are important in measuring its performance Briefly discuss these Critical Success Factors
    • 1.  Capacity
    • 2.  Quality
    • 3.  Technology
    • 4.  Integration
    • 5.  Human system
    • 6.  Flexibility
    • 7.  Productivity
    • 8.  Facilities
    • 9.  Planning & control
    • 10. Time
  15. To model a system using the Q-O approach, five general steps  are needed Name and briefly discuss these five steps
    To model a system, the following general steps are then needed:

    • 1) Specify system structure in terms of class and inheritance   hierarchies
    • 2) Identify the objects and their attributes
    • 3) Identify the operations provided by and required of each object
    • 4) Establish the visibility of each object in relation to other objects, and hence its interface
    • 5) Establish the communication between objects through message-passing
  16. Discuss the differences between conventional approaches of functional decomposition and the object oriented approach
    • To get a clear picture of the object-oriented (O-O) approach, it would be a good idea to first Look at the differences between conventional and O-O methodologies. The main difference is that the former models a system at the system or sub-system level, whereas with the O-O
    • approach the system is modelled at the leveL of individual entities within the problem domain. Consequently, with the conventional approach a system is functionally decomposed using functions and processes as the building blocks so that the entities are passive data stores, manipulated by activities or procedures. The associated analysis/design procedure can be thought of as following a top-down process: the analyst starts with a high level abstract descnption of the function of the overall system and progressively breaks this down and refines it to produce successively less abstract descnptions of the function of smaller and smaller parts of the system.
    • In contrast, decomposition of the problem domain with an O-O approach is based on the classification of objects and their relationships with each other, resulting in systems entities which are self-contained in terms of their operations and the corresponding data, and which communicate explicitly with each other. It is not possible to categonse this as fundamentally top-down or bottom-up. The approach can include elements of both approaches; when an analyst reuses an existing object or class, it could be said that a bottom-up approach is being followed; on the other hand when decomposing parts of a system into smaller elements which are then mapped onto objects and classes, the approach is
    • more of a top-down one.
  17. The Problem Solving Model in System Engineering uses a specific cycle which can be graphically represented Make a sketch of this Problem Solving Cycle
  18. Basic concepts
    formalise certain useful O-O concepts. This can then be used to specify the structure of a manufacturing operation through an O-O perspective.
    •  Encapsulation
    • This refers to information hiding within an object: a principle, used when developing an overall program (system) structure, that each component of a program should encapsulate or hide a single design decision. The interface to each module is defined in such a way as to reveal as little as possible about its inner working (Oxford English Dictionary). An object
    • hides details about its implementation (structure and  operation). Such hidden information is not accessible by the user of this object.

    • Objects
    • Objects are an abstraction of the entities in the real world which encapsulate information about themselves, such as attribute values which determine their state, and a defined set of operations on that state which characterises their behaviour (that is, how they act and react to each other in terms of changes of their state). An object has an identity that denotes its separate position from other objects within a system. Since all the data needed by an object to perform its duties is encapsulated within it, there is no need for any shared data store. Once defined in such a way, objects can be stored and reused for other tasks of system development
    • independently of each other.

    • Attributes and Operation/Services
    • Attributes are named properties and hold abstract states of each object, which can only be manipulated by the operation or services of that object. Operations/services characterise the behaviour of an object, and are the only means for accessing, manipulating and modifying its attributes.

    • Messages
    • Each object has a visible interface comprising a list of services that it is able to provide (the external view of the object is nothing more than this interface). An object will communicate with another through a request, known as a message, which identifies the operation to be performed by the second object, and in response the ‘receiver” object will select and perform the service requested.

    • Classes
    • It is important to distinguish between an object and its class. A class is an object that acts as
    • a template, specifying the properties and behaviour for a set of similar objects in terms of:
    • . a set of attributes
    • . a set of messages defimng the external interface
    • . a set of services invoked by messages
    • Each object is considered to be an element, or an instance, of a class. Hence, a class is a specification for its instances and thus an abstraction. Classes are related through sub-class and super-class relationships. A class may have several sub-classes, through which individual procedures and data manipulation tasks are organised into a tree-structure. Objects at any level of this tree structure inherit behaviour of higher level objects.

    • Class-&-Object
    • A class and the object in that class. Objects are instantiated on the basis of class. Since all instances of a given class have the same structure and behave similarly, instantiation makes it possible to easily reuse the same definition to generate objects. Every object is an instance of one class, but a class may have no instances.

    • Inheritance
    • This allows the sharing of behaviour and data between objects through the definition of a sub class by using the template of its superclass(es). When a sub-class inherits commonalties from the super-class, the relationship is known as inheritance. When a sub-class inherits commonalties from two or more super-classes, it is called multiple inheritance.

    • Generalisation-Specialisation
    • In addition to the inherited structure and behaviour, a sub-class may possess its own specific attributes, services and messages. This is known as specialisalion. Specialisation allows the reuse of existing classes by defining new sub-classes, which are more specific than the existing abstractions. On the other hand, when two or more classes have an overlapping set of attributes and operations, they can be grouped together to create a new super-class
    • representing the abstraction of those overlapping commonalties. This process is known as generalisation.
  19. Types of Intergration with regards to Manufacturing System Integration
    • (1) Information Integration,
    • (2) Data Integration,
    • (3) Equipment Integration,
    • (4) Management Integration,
    • (5) Systems Designer Integration,
    • (6) User Integration.

  20. List The seven principles of IMP
  21. Explain what is IDEFo
    • IDEFo as it is more popularly known, is an activity modelling method for modelling activities and flows in a system. The dynamics of a system can also be modelled effectively. The IDEFo model consists of three components:
    • (1) a set of hierarchically decomposed diagrams,
    • (2) an accompanying text for the diagrams,
    • (3) a glossary of terms used in the diagrams.
    • IDEFo can be generally described in terms of three basic concepts:
    • 1) Cell Modelling Graphics, 
    • 2) Hierarchical Decomposition, and
    • 3) Disciplined Teamwork.
  22. Discuss the seven principles of IMP
    • Principle 1: Manufacturing systems are goal seeking
    • Principle 2: Manufacturing systems are holistic
    •           Bounding the Context
    •           Limitation of Information
    •           Viewpoint
    • Principle 3: Manufacturing systems are hierarchical
    •         Levels of Detail
    •         Levels of Abstraction
    • Principle 4: Manufacturing systems have technical
    • and social sub-systems
    •         Technical Subsystem
    •         Social Subsystem
    • Principle 5: Manufacturing systems transform inputs
    • into outputs
    • Principle 6: Manufacturing systems are open
    •          Transactional Environment
    •          Contextual Environment
    • Principle 7: Manufacturing systems are learning organisations
  23. Discuss the ideas for change
    • 1 Ideas on Management
    •       Management Responsibilities:
    •       Policy for Change
    •       Open-Ended Design Process
    • 2 Ideas on Designers
    •       Project Leader
    •       Project Organisation
    •       Conflict Resolution
    • 3 Ideas on Users
    •       Self design
    •       Resistance to Change
    • 4 Ideas on Information
    •      Structured Methodologies
    •      Abstraction
    • 5 Ideas on Data
    •      Standards
    •      Data Management
    • 6 Ideas on Equipment
    •     Group TechnoIo
    •     Machine Redundancy
  24. The IMP model:
    Five general stages in the project development cycle
    • 1 Context development
    •     Produce Contextual Inputs  
    •     Produce Transactional Variants 
    •     Develop Manufacturing Systems 
    • 2 Systems development
    •     Develop Manufacturing Strategy 
    •     Integrate New Systems  
    •     Provide Specialist Services 
    • 3 Projects development
    •     Develop Project Program 
    •     Manage Manufacturing Strategy 
    • 4 Project integration
    •     Manage Project Development  
    •     Develop New Systems  
    • 5 Project stages
  25. Some advantages of simulation are:
    . Changes to a system can be investigated without disrupting the operations of the system.

    . New designs/acquisitions of resources can be investigated before the actual capital layout is made.

    . Long ("never ending") processes are studied in a relatively short time.

    . Critical parameters in a system can be identified and studied.

    . Evaluation of alternatives.
  26. Some disadvantages of simulation are:
    . A good simulation analyst needs good training and experience, regardless of what simulation software vendors tell you.

    . The Interpretation of simulation results requires a sound statistical background, regardless of what simulation software vendors tell you.

    . Simulation studies can be expensive and time consuming in many cases. (Software packages may become cheaper in some cases).
  27. When building a model using the ARENA simulation software, name the ARENA module you will use in your model to: Measure the time an entity spends in a system (throughput time).
    Record Module
  28. When building a model using the ARENA simulation software, name the ARENA module you will use in your model to:

    Change the value of variable.
    Assign module
  29. When building a model using the ARENA simulation software, name the ARENA module you will use in your model to:

     Model the arrival/entry of entities into the system.
    Create Module
  30. When building a model using the ARENA simulation software, name the ARENA module you will use
    in your model to:  

    Choose between alternative options based on a specified probability.
    Decide Module
  31. When building a model using the ARENA simulation software, name the ARENA module you will use
    in your model to:

     Model the exit of an entity from the system.

    Dispose module
    Dispose module
  32. Define simulation modelling:
    Simulation refers to a broad collection of methods and applications to mimic the behaviour of real systems, usually on a Computer with appropriate software   

    •  Simulation is part of modelling tools, which includes mathematical models, physical models, iconic models etc. It is usually applied when the behaviour of complex (stochastic) systems is investigated. These include manufacturing systems where the industrial engineer is usually
    • involved. Simulation allows for “what ¡f.... ‘ questions to be asked when systems arc studied, i.e. an existing or proposed system is modelled with a simulation software package and the behaviour of the system is studied when parameters are changed. Systems are thus analysed to find an acceptable solution for its configuration, operating parameters etc.
  33. What are entities?
    • Entities are the items—customers, documents, parts—that are being served, produced, or otherwise acted on by your process. In business processes, they often are documents 
    • or electronic records (checks, contracts, applications, purchase orders). In service systems, entities usually are people (the customers being served in a restaurant, 
    • hospital, airport, etc.). Manufacturing models typically have some kind of part running through the process, whether it’s raw material, a subcomponent, or finished product.

    Other models might have different types of entities, such as data packets in network analysis or letters and boxes in package-handling facilities.
  34. Describe attributes of a simulation model:
    An attribute is a characteristic of all entities, but with a specific value that can differ from one entity to another. Attributes can be referenced in other modules (e.g. the Decide module), can be reassigned a new value with the Assign module, and can be used in any expression. Attribute values are unique for each entity, as compared to Variables which are global to the simulation module.
  35. Variables
    Reflects a characteristic of the system, regardless of entities

    Name, value of which there’s only one copy for the whole model 

    Not tied to entities Entities can access, change variables

    Travel time between stations Number of parts in system

    Simulation clock

    Writing on the wall 

    Some built-in by Arena, you can define others
  36. Resources
    What entities compete for  - People Equipment Space 

    Entity seizes a resource, uses it, releases it 

    • Think of a resource being assigned to an entity, rather than an entity “belonging to” a resource “A”
    • resource can have several units of capacity

    Seats at a table in a restaurant Identical ticketing agents at an airline counter

    Number of units of resource can be changed during the simulation