l.5. system modelling

Pemodelan Sistem (TKI 128)Teknik IndustriUNIJOYO

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Pemodelan Sistem: Model Konseptual

Disampaikan Oleh

M. Imron Mustajib, S.T., M.T.


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Referensi1. Daellenbach, H. G., (1994), “Systems and Decision Making”, John

Wiley & Sons, Chichester-England.

2. Murthy, D.N.P., Page, M.W., and Rodin,E.Y., Mathematical Modelling, Pergamon Press, 1990

3. Simatupang, T.M., (1995), Pemodelan Sistem, Nindita: Klaten

4. Tunas, B. (2007), “Memahami dan Memecahkan Masalah dengan Pendekatan Sistem”, PT Nimas Multima.


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OUTLINE

• A Situation Summary• Approaches for Describing A Relevant

System• System Models• Influence Diagrams• Quantitative Modelling


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Systems Modeling• We will apply the systems concepts and thinking

discussed before to a real-life problematic situation

• Define a relevant system for it. • Several cases –problematic situations discussed• System modelling: The process of

conceptualizing a system of interest.• This involves two steps: Describing a problem

situation and a relevant system


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A Situation Summary

• The first step when approaching a problem situation is to familiarize yourself with: – the situation– Its processes and structures– The people involved– Their aims and desires– Relationship between them– The hierarchy or power structure– The resources available– The data sources and information


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A Problem Situation• To get a “ feel” for anything you

discovered and seems relevant for describing the problem situation.

• Rich Picture Diagram is a useful tool for describing a problem situation


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Rich Picture Diagram

• A cartoon-like summary of everything the observer knows about the situation studied

• Diagram or concept -is not a system description

• Only one approach of making a situation summary


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Rich Picture: A Piece of Sky is Missing

• Problematic Situation• The person looking at the situation• The structural elements• The process elements• The relationships between structure and

process


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The Socio-Technical Model [Leavitt (1964)].

Structure

Technology (tools)

People (actors)

Task


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Rich Picture Diagram• Guidelines: • Elements of structure (All components of the situation

are relatively stable -e.g., all physical aspects)• Elements of process (All aspects that undergo change

-e.g., activities, flow and processing of materials)• Relationship between structure and process and

between process (how does the structure affect condition of process; one process affects other processes)


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Rich Picture Diagram• For human activity systems:

A rich picture should be included hard facts and soft facts.

• The rich picture is never finished• Common mistake:

Each item pictured needs to be connected one or more other items (Note that rich picture is not a system description)

• The uses of rich picture:An ideal vehicle for communicating with other people about complex and problematic situation


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Approaches for describing a relevant system

• A system description consists in specifyingthe transformation process(es) of the systemthe boundary of the systemthe components and subsystems and the structurethe inputs and the outputs (desired & undesired outputs)

• Two Approaches for describing a relevant system:– Structural Approach– Process Approach


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Structural Approach

• A typical structure usually found for situation considered, e.g., a waiting line structure.

• The situation is well understood• Using a known basic structure allows fast

progress toward a complete system description


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Process Approach

• No assumption about the possible system structure

• The observed processes and relationships are used to discover a good structure

• A good starting point is to determine from whose standpoint to view the system and then define the prime transformation process.

• Rules help in identifying the components, inputs and outputs of the system.


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Rules• Any aspect that affects the systems, but in turn is not

significantly affected by it, is an input from the environment system. This covers all external controls.

• Any aspect that is directly or indirectly affected or controlled by the system, but turn does not affected any other aspect of the system, is a system output.


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• Any entity that is either part of the system’s structure or

its transformation process(es) is a component of the system, unless it is an output of the system. Similarly, if the system or any of its components affects an entity or exercises control over it, then that entity is a component, unless it is a system output.

• Any aspect that does not affect the system, or is not affected by it, or not part of its structure or transformation process is irrelevant, and can be ignored


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System Models

• The activity of building a model is referred to as systems modeling.

• A model may be iconic, symbolic, or analogous

• Symbolic Models:– Representation of the relationships between

various entities or concept by means of symbols.


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Mathematical Models

• Relationships between various entities are expressed in the form of mathematical expressions:– Function, – Equation, and – Inequalities

• Example: Case Study C [Murthy, et.al. (1990)] –Optimal Production


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Case 1: The Ozone Hole

• A system for how the ozone layer in the stratosphere is gradually destroyed through the continued release of CFSs into the atmosphere, allowing a greater fraction of the sun’s uv-rays to reach the earth’s surface.

• Input:• Process:• Component• Structure:• Output:


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Case 2: Lubricating Oil Division (LOD)

• A situation summary• Identifying the problem• A system relevant• Influence diagram


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The Narrow System:[LOD]

• A system for the replenishment and stock control of packaged finished goods which keeps the total operating costs for the LOD as low as possible while maintaining the current level of customer service


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Relevant System:[LOD]

• To use the typical inventory/production control structure for defining the system

• But the problem situation includes aspects not normally found in such a structure –e.g. rules to meet big and small customer orders

• Use the Process Approach


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Relevant System:[LOD]• Big customer order is met by scheduling a special

production run (is it outside the narrow system ?)• This aspect affects the inventory/production control

system of LOD• Cutoff point is considered as one of the two decision

variables.• What type of control –open loop control (the customer

order classification –input to the system)


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Identifying the system aspects

• See Table 5-1.• The easiest way is to start out by listing

– The control inputs– The performance outputs– Any other system outputs, – Then followed by structure, process, component of

the system• Two potential inputs –breakdown in the

operation of the refinery and production capacities, are ignored (why?)


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Influence Diagrams (ID)

• Insightful for bringing out the transformation process of the system – in term of the structural and causal relationships between

systems components.• Depicts the influence relationship

– Between the inputs into a system and its component (the system variables)

– Between the component of the system, and– Between the component and the outputs of the system,

including performance measures(these influence relationship can usually be measured in

quantitative terms)


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Approach To Draw An ID• Control and other inputs ⇒ State variables ⇒ System

outputs (in a logical sequence)• For example, the customer order pattern (an input) &

cutoff point (a decision) determine order patterns (met from stock or special production run)

• Each customer order pattern determines the annual volume by spec-prod-run (AVPR) or annual volume met from stock (AVS).


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Approach To Draw An ID

• AVPR →the annual number of setups• Together with the cost of production setup

→the annual setup cost for special production run, and so forth.


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Summarizingproblemsituation

Identifyingproblem foranalysis

Decribingrelevantsystem

Building amathematicalmodel

Findingpreferredsolution

Validation &performancetesting

Analyzingsensitivityof solution

PlanningImplementation

Establishingcontrol oversolution

Following upsolution use

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10Implementingsolution

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FORWARD LINKAGES

PROJECT PROPOSAL

PROJECT REPORT

DOCUMENTATION &USER'S MANUAL

SOLUTION AUDIT

FORMULATION

MODELING

IMPLEMENTATON

BACKWARD LINKAGES

Figure 5-1: OR/MS methodology

l.5. system modelling

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