Pengantar Sistem Dinamik - PowerPoint PPT Presentation

Loading...

PPT – Pengantar Sistem Dinamik PowerPoint presentation | free to download - id: 6fe201-ZjNhN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Pengantar Sistem Dinamik

Description:

Dr. Asep Sofyan Teknik Lingkungan ITB Email: asepsofyan_at_yahoo.com Sistem dinamik: Pemodelan dan simulasi komputer untuk mempelajari dan mengelola sistem umpan balik ... – PowerPoint PPT presentation

Number of Views:9
Avg rating:3.0/5.0
Date added: 11 September 2018
Slides: 32
Provided by: Hyu84
Learn more at: http://bhupalaka.files.wordpress.com
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Pengantar Sistem Dinamik


1
PengantarSistem Dinamik
  • Dr. Asep Sofyan
  • Teknik Lingkungan ITB
  • Email asepsofyan_at_yahoo.com

2
Apakah Sistem Dinamik itu?
  • Sistem dinamik Pemodelan dan simulasi komputer
    untuk mempelajari dan mengelola sistem umpan
    balik yang rumit (complex feedback systems),
    seperti bisnis, sistem lingkungan, sistem sosial,
    dsb.
  • Sistem
  • Kumpulan elemen yang saling berinteraksi,
    berfungsi bersama untuk tujuan tertentu.
  • Umpan balik menjadi sangat penting
  • Masalah dinamik
  • Mengandung jumlah (kuantitas) yang selalu
    bervariasi
  • Variasi dapat dijelaskan dalam hubungan sebab
    akibat
  • Hubungan sebab akibat dapat terjadi dalam sistem
    tertutup yang mengandung lingkaran umpan balik
    (feedback loops)

3
Sejarah
  • Cybernetics (Wiener, 1948) studi yang
    mempelajari bagaimana sistem biologi, rekayasa,
    sosial, dan ekonomi dikendalikan dan diatur
  • Industrial Dynamics (Forrester, 1961)
    mengaplikasikan prinsip cybernetics ke dalam
    sistem industri
  • System Dynamics karya Forrester semakin meluas
    meliputi sistem sosial dan ekonomi
  • Dengan perkembangan komputer yang sangat cepat,
    Sistem Dinamik menyediakan kerangka kerja dalam
    menyelesaikan permasalahan sistem sosial dan
    ekonomi

4
Tahap Pemodelan Sistem Dinamik
  1. Identifikasi masalah
  2. Membangun hipotesis dinamik yang menjelaskan
    hubungan sebab akibat dari masalah termaksud
  3. Membuat struktur dasar grafik sebab akibat
  4. Melengkapi grafik sebab akibat dengan informasi
  5. Mengubah grafik sebab akibat yang telah
    dilengkapi menjadi grafik alir Sistem Dinamik
  6. Menyalin grafik alir Sistem Dinamik kedalam
    program DYNAMO, Stella, Vensim, Powersim, atau
    persamaan matematika

5
Aspek penting
  • Berfikir dalam terminologi hubungan sebab akibat
  • Fokus pada keterkaitan umpan balik (feedback
    linkages) diantara komponen-komponen sistem
  • Membuat batasan sistem untuk menentukan komponen
    yang masuk dan tidak di dalam sistem

6
Hubungan Sebab Akibat
  • Berfikir sebab akibat adalah kunci dalam
    mengorganisir ide-ide dalam studi Sistem Dinamik
  • Gunakan kata menyebabkan atau mempengaruhi
    untuk menjelaskan hubungan antar komponen di
    dalam sistem
  • Contoh yang logis (misalnya hukum fisika)
  • makan? berat bertambah
  • api ? asap
  • Contoh yang tidak logis (sosiologi, ekonomi)
  • Pakai sabuk pengaman ? mengurangi korban fatal
    dalam kecelakaan lalu lintas

7
Umpan balik (Feedback)
  • Berfikir sebab akibat saja tidak cukup
  • laut ? evaporasi ? awan ? hujan ? laut ?
  • Umpan balik untuk mengatur/ mengendalikan
    sistem, yaitu berupa suatu sebab yang terlibat
    dalam sistem namun dapat mempengaruhi dirinya
    sendiri
  • Umpan balik sangat penting dalam studi Sistem
    Dinamik

8
Causal Loop Diagram (CLD)
CLD menunjukkan struktur umpan balik dari sistem
  • Gaji VS Kinerja
  • Gaji ? Kinerja
  • Kinerja ? Gaji
  • Lelah VS Tidur
  • Lelah ? tidur
  • Tidur ? lelah ?

9
Penanda CLD
jika penyebab naik, akibat akan naik
(pertumbuhan, penguatan), jika penyebab turun,
akibat akan turun - jika penyebab naik,
akibat akan turun, jika penyebab turun, akibat
akan naik



-
10
CLD dengan Positive Feedback Loop
  • Gaji ? Kinerja, Kinerja ? Gaji

Semakin gaji naik Semakin baik kinerja

Semakin baik kinerja Gaji akan semakin naik
Semakin gaji naik Semakin baik kinerja

11
CLD dng Negative Feedback Loop
  • Lelah ? Tidur, Tidur ? Lelah

The more I sleep The less tired I am
The less tired I am The less I sleep
The more tired I am The more I sleep
The less I sleep The more tired I am

-
12
CLD with Combined Feedback Loops(Population
Growth)



-
13
CLD with Nested Feedback Loops(Self-Regulating
Biosphere)
  • Evaporation ? clouds ? rain ? amount of water ?
    evaporation ?


-





-


14
Exogenous Items
  • Items that affect other items in the system but
    are not themselves affected by anything in the
    system
  • Arrows are drawn from these items but there are
    no arrows drawn to these items


-

15
Delays
  • Systems often respond sluggishly (dgn malas)
  • From the example below, once the trees are
    planted, the harvest rate can be 0 until the
    trees grow enough to harvest

delay
16
Loop Dominance
  • There are systems which have more than one
    feedback loop within them
  • A particular loop in a system of more than one
    loop is most responsible for the overall behavior
    of that system
  • The dominating loop might shift over time
  • When a feedback loop is within another, one loop
    must dominate
  • Stable conditions will exist when negative loops
    dominate positive loops

17
Example
18
Flow Graph Symbols
Level
Rate
Flow arc
Auxiliary
Cause-and-effect arc
Source/Sink
Constant
19
Level
  • Stock, accumulation, or state variable
  • A quantity that accumulates over time
  • Change its value by accumulating or integrating
    rates
  • Change continuously over time even when the rates
    are changing discontinuously

20
Rate/Flow
  • Flow, activity, movement
  • Change the values of levels
  • The value of a rate is
  • Not dependent on previous values of that rate
  • But dependent on the levels in a system along
    with exogenous influences

21
Auxiliary
  • Arise when the formulation of a levels influence
    on a rate involves one or more intermediate
    calculations
  • Often useful in formulating complex rate
    equations
  • Used for ease of communication and clarity
  • Value changes immediately in response to changes
    in levels or exogenous influences

22
Source and Sink
  • Source represents systems of levels and rates
    outside the boundary of the model
  • Sink is where flows terminate outside the system

23
Example 1 (Population and birth)
Population
24
Example 2 (Children and adults)
children
Adults
25
  • average lifetime 8
  • Units Year
  • birth rate 0.125
  • Units fraction/Year
  • births Population birth rate
  • Units rabbit/Year
  • deaths Population / average lifetime
  • Units rabbit/Year
  • Population INTEG(births - deaths,1000)
  • Units rabbit

26
From Causal Loop DiagramTo Simulation Models 1
Flow Graph
Causal Graph
R
L
  • Equations
  • dL/dt k1R(t)
  • R(t) k2L(t)
  • ? dL/dt k1k2L(t)

Block Model
L
L
?
k1k2
27
From Causal Loop DiagramTo Simulation Models 2
Equations dL/dt R1 R2 R2 k2L R1 k1 ?
dL/dt k1 - k2L
Flow Graph
R1
R2
L
Block Model
L1
L1
?
k2
k1
-
28
From Causal Loop DiagramTo Simulation Models 3
  • Equations
  • dL1/dt R1 R2
  • dL2/dt R2 R3
  • R1 k1
  • R2 K2 L1
  • R3 K3 L2
  • ? dL1/dt k1 k2L1
  • ? dL2/dt k2L1 K3L2

Flow Graph
R2
R3
R1
L2
L1
Block Model
L1
L2
L2
L1
?
?
-
k2
k3
k1
-
29
Building construction
  • Problem statement
  • Fixed area of available land for construction
  • New buildings are constructed while old buildings
    are demolished
  • Primary state variable will be the total number
    of buildings over time
  • Causal Graph

-
-
-
-
30
Simulation models
  • Equations
  • dBl/dt Cr Dr
  • Cr f1(CF, Bl)
  • Dr f2(AL,Bl)
  • CF f3(FLO)
  • FLO f4(LA,AA,Bl)

Flow Graph
Construction (C)
Demolition (D)
Industrial Buildings (B)
Average lifetime for buildings (AL)
Construction fraction (CF)
Fraction of land occupied (FLO)
Land available for industrial buildings (LA)
Average area per building (AA)
31
References
  • Simulation Model Design and Execution, Fishwick,
    Prentice-Hall, 1995 (Textbook)
  • Introduction to Computer Simulation A system
    dynamics modeling approach, Nancy Roberts et al,
    Addison-wesley, 1983
  • Business Dynamics Systems thinking and modeling
    for a complex world, John D. Sterman,
    McGraw-Hill,2000
About PowerShow.com