Sri Redjeki Pudjaprasetya
https://en.wikipedia.org/wiki/Computational_fluid_dynamics
Komputasi Dinamika Fluida
merupakan cabang dari Mekanika Fluida yang menggunakan analisa
numerik dan algoritma untuk menyelesaikan dan menganalisa
permasalahan yang melibatkan aliran fluida.
-> Numerical simulation free surface flows,
menggunakan persamaan Shallow Water Equations (SWE),
atau SWE ++
Model SWE untuk simulasi masalah-masalah hidrodinamika pada sungai,
danau, area pantai, dan lain-lain.
Selain masalah hidrodinamika itu sendiri, penting juga mengkaji berbagai hal
yang terkait, seperti
• wave propagation
• flooding, inundation, runup
• transport of salt or heat
• decay of pollutants
• sedimentation
INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
• Pendahuluan
• Prinsip konservasi pada pipa U
• Model numerik staggered bagi SWE 1D
• Model numerik staggered bagi SWE 2D
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𝐴
𝑑𝑧
𝑑𝑡
= 𝐴 𝑢
konservasi massa
𝜌 𝐴𝐿
𝑑𝑢
𝑑𝑡
= 𝐴𝜌𝑔 −𝑧 − 𝑧
Konservasi momentum
𝑑𝑧
𝑑𝑡
𝑑𝑢
𝑑𝑡
=
−
0
2𝑔
1
𝐿
0
𝑧
𝑢
⟺
𝑑
2
𝑧
𝑑𝑡
2
+
2𝑔
𝐿
𝑧 = 0
A
: luas penampang
kaki U-tube
INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
U-tube
𝐴
𝑑𝑧
𝑑𝑡
= 𝐴 𝑢
konservasi mass
𝜌 𝐴𝐿
𝑑𝑢
𝑑𝑡
= 𝐴𝜌𝑔 −𝑧 − 𝑧
konservasi momentum
𝑑𝑧
𝑑𝑡
𝑑𝑢
𝑑𝑡
=
−
0
2𝑔
1
𝐿
0
𝑧
𝑢
⟺
𝑑
2
𝑧
+
2𝑔
𝑧 = 0
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A
: luas penampang
kaki U-tube
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Shallow water equations
Karena
dengan
𝑞 = ℎ𝑢 momentum horizontal
Bentuk equivalen dari SWE
ℎ
𝑡
+ ℎ𝑢
𝑥
= 0
ℎ𝑢
𝑡
+ ℎ𝑢
2
+
1
2
𝑔ℎ
2
𝑥
= 𝑔ℎ𝑑
𝑥
Staggered grid
mass
momentum
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Mass conservative
Momentum conservative approximation
Waves on U-tube series
Kondisi awal 𝜂 𝑥, 0 = cos
𝜋𝑥
𝐿
, 𝐿 = 4, 𝑔 = 9.81 𝑚/𝑠
2
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INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
Standing wave, linear SWE
Kondisi awal 𝜂 𝑥, 0 = cos
𝜋𝑥
𝐿
,
𝐿 = 200 m, depth = 4m,
𝑔 = 9.81 𝑚/𝑠
2
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A standing wave
on your coffee cup
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Standing wave, nonlinear SWE
Kondisi awal
𝜂 𝑥, 0 = cos
𝜋𝑥
𝐿
, 𝐿 = 200 m
depth = 4m, 𝑔 = 9.81 𝑚/𝑠
2
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INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
Dambreak on a dry bed
Kondisi awal
ℎ 𝑥, 0 =
10,
0,
𝑥 > 0
𝑥 < 0
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Dam break analytical solution
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Wave Classification
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INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
Tsunami wave characteristic
Model SWE cocok karena
𝑑
0
𝐿
=
4
Amplitude increases (shoaling)
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Linier shoaling
Nonlinear shoaling
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Waves uprush on a beach
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(I. Didenkulova, App. Wv. Math., 2009)
2D Shallow water equation
mass
momentum
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Closed basin:
homogeneous
Neumann b.c.
Cell for mom-x
Cell for mom-y
Cell for mass
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Conservative scheme for 2D SWE
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MA5273 Komputasi Dinamika Fluida
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Wave focusing
Pada perambatan gelombang air, tidak ada massa air yang
berpindah, melainkan energi gelombang berpindah.
Energy conserv.
Energy per unit area:
1
2
8
E
gH
1
1
2
1
g
C
b
H
H
C
b
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1
2
|
|
g
g
EC b
EC b
Simulation of refraction and shoaling
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INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
Ongoing Research:
tsunami generation, propagation and run up
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,
0
0
1
2
αt
d x t
d
ζ
e
H x b
H x
H x b
𝑡
𝑐
= 2.6 𝑠𝑒𝑐, 𝛼 = 0.4269 𝑠𝑒𝑐
−1
, 𝑔 = 9.8 𝑚/ sec
2
Compt. domain
−𝐿, 𝐿 , 𝐿 = 180 𝑘𝑚
Δ𝑥 = 0.5 𝑘𝑚, Δ𝑡 = 1 𝑠𝑒𝑐
𝜁
0
𝑑
0
= 0.17,
𝑏
𝑑
0
= 1.33,
𝑡
𝑐
𝑔𝑑
0
The packet of wave trains, preceded
with a wave of
negative wave front
.
https://en.wikipedia.org/wiki/Simulation#Computer_simulation
• Simulasi Komputer: usaha untuk memodelkan/meniru
alam atau situasi tertentu, sehingga dapat dipelajari dan
dianalisa mekanisme dari sistem tersebut.
• Simulasi komputer merupakan bagian penting untuk
mengkaji permasalahan di berbagai bidang ilmu dan
aplikasi.
• Simulasi komputer membantu kita untuk mendapatkan
insight. Contoh nyata: network traffic simulation.
Source:ena-ayobelajarbersama.blogspot.co.id
Simulasi aliran fluida melalui belokan/jalan menyempit
𝐴, 𝑣
Konservasi ‘massa’
𝜕𝐴
𝜕𝑡
+
𝜕(𝐴𝑣)
𝜕𝑥
= 0
Aliran kendaraan melalui belokan/jalan menyempit
𝐴, 𝑣
Konservasi ‘massa’
𝜕𝐴
𝜕𝑡
+
𝜕(𝐴𝑣)
𝜕𝑥
= 0
Dalam hal kondisi jalan menyempit
dari A menjadi 0.5A, apabila kendaraan2
pada jalur sempit melaju dengan kecepatan
dua kali lipat maka tidak akan terjadi
penumpukan kendaraan.
INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
• Metoda numerik yang bersumber dari prinsip
konservasi (massa, momentum, energi) telah
dapat menghasilkan skema yang efficient and
robust.
• Peranan matematikawan sangat dibutuhkan pada
tahap pemodelan serta pemilihan metode
numerik yang sesuai.
Kesimpulan & Diskusi
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INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG
References
1.
J. Kampf, Ocean Modeling for Beginners, Using Open-Source Software, Springer, 2009
2.
D. Durran, Numerical Methods for Fluid Dynamics, with application to Geophysics, 2
nd
ed., Springer, 2010
3.
M. Zijlema, Numerical Flows and Transports, TU Delft.
4.
Daiheng Ni, Lecture Notes on Traffic Flow
5.
G.S. Stelling, S.P.A. Duinmeijer, "A Staggered Conservative Scheme for Every Froude
Number in Rapidly Varied Shallow Water Flows", Int. J. for Numer. Meth. Fluids, 43, ),
1329-1354, (2003).
6.
G.S. Stelling, M. Zijlema, "An accurate and efficient finite-difference algorithm for
non-hydrostatic free-surface flow with application to wave propagation", Int. J. for Numer.
Meth. Fluids, 43, 1-23, (2003).
7.
S.R. Pudjaprasetya, I. Magdalena, Momentum Conservative Scheme for Shallow Water
Flows, East Asian Journal on Applied Mathematics (EAJAM), Vol. 4, No. 2, pp. 152-165,
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sr_pudjap©math.itb.ac.id
http://personal.fmipa.itb.ac.id/sr_pudjap/
Thank you
for your attention
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FMIPA, INSTITUT TEKNOLOGI BANDUNG
INDUSTRIAL AND FINANCIAL MATHEMATICS RESEARCH GROUP FMIPA, INSTITUT TEKNOLOGI BANDUNG