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University of South-Eastern Norway Page 1August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Overview of course
FM 1015 Modeling of Dynamic SystemsBernt Lie
Professor
Faculty of Technology, Natural Sciences and Maritime Sciences
University of South-Eastern Norway Page 2August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Content
• Learning material• Model forms: ODE vs. DAE• Notation and units• Balance laws• Constitutive models• Models in Modelica• Reduction of DAE to ODE• Analysis• Exam tips• Modelica Example• Summary
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
University of South-Eastern Norway Page 3August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Learning material …includes
• Lecture notes (free PDF file, syllabus is ca. 350 pp. out of 650+ pp.)
• A number of video tutorials
• 3 sets of quizzes (to get started)
• A compulsory group task/”project”, with oral presentation (counts 40% in grade)
• Written exam (based on group task), counts 60% in grade)
• Notes on the Modelica language (optional). Use Modelica, Python, Julia, and/or MATLAB to solve group “project”
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
University of South-Eastern Norway Page 4August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Model forms: ODE vs. DAE
ODE:
• State – system history
• Input – influences system
• Parameter – constants
• Output – system response
DAE (simplified):
• As for ODE +
– Algebraic variable
• State in ODE and DAE may be different
• Functions in ODE and DAE are different
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
dxdt
fx,u;
y gx,u;
dxdt
fx, z,u;
0 gx, z,u;
y hx, z,u;
University of South-Eastern Norway Page 5August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Notation and units
• Notation
– Single letter – avoid assumed multiplication
– Decoration or indices to distinguish
• Units
– Terms that are equal or terms that are added/subtracted same unit!!
– Argument of transcendental ++ functions should be dimensionless
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
Re R e ?
Re ?
NRe !
dm
dt m i m e
m e K h
h
sin xx
, ln xx
University of South-Eastern Norway Page 6August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Balance laws
Material balance• Total mass balance:
• Mass species balance:
• Molar species balance:
With 𝑛_𝑠 species, we can only have 𝑛_𝑠independent material balances!!• Level + concentration for liquid• (Partial) pressure for gas
Momentum balance
Energy balance
Thermal energy balance
Use:
• Velocity, flow rate (MB)
• Temperature (EB)
Accumulated variables 𝑥 in DAE
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
dm
dt m i m e
dm j
dt m j,i m j,e m j,g
dnj
dt n j,i n j,e n j,g
dMdt
M i M e F
dE
dt Ė i Ėe W Q
dU
dt H i H e W v W f Q
University of South-Eastern Norway Page 7August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Constitutive models I
Types of constitutive models:
• EOS – Equation of State, e.g. ideal gas law
• Introduction of intensive quantities
• Enthalpy:
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
pjV n jRT
p j
pj
mV
m
V
ĉ j mj
V
mj
V
c j n j
V
n j
V
j mj
m
x j n j
n
m V
m j ĉ jV jm
n j c jV x jn
H U pV
H mĤ nH
H m Ĥ nH
dĤ ĉpdT V 1 pTdp
dH c pdT V 1 pTdp
ĉp ĤT p
; c p HT p
p 1
VVT p
1
VVT p
H j1
ns
Hj; H j1
ns
H j
University of South-Eastern Norway Page 8August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Constitutive models II
• Bernoulli’s law
• Reaction
• Diffusion
• Kinetic and potential energy
• Friction
• Heat flow
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
m Cv fup
p C v fu h
h
v j v 1ĉ jĴ j v 1
c jJ j
Ĵ j D jĉ j
x, J j D j
c j
x
K 12
mv2, K 12
J2
P mgy, P ksy0 y
F f KAf, K 12|v |v, NRe
vD
f
16NRe
, NRe 2.1 103
1
f 4 log
10NRe f 0.4, NRe 2.3 103, 4 104
Sr
0, r Rnr , Qnrns
r j,g n j,g
V
n j,g
V, rg Tr
Q c k T
x, Q w2b
hTw Tb
1U
j1
nb
1hj
j1
ns j
k j
Q r T4
University of South-Eastern Norway Page 9August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Reduction of DAE to ODE
• Reduction of DAE by elimination of algebraic qtys.
• Example:
• Classification:
• Resulting ODE
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
dxdt
fx, z,u;
0 gx, z,u;
dxdt
fx,u;
dmdt
m i m e
m V
V Ah
m e K hh
x m
u m i
,A,K,h
z m e,V,h
dhdt
m iK h
h
A, dm
dt m i K m
Ah
x h, x m
K,h,,A, K,h,,A
u m i
University of South-Eastern Norway Page 10August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Models in Modelica
Modelica: language for model description
– Equation based, i.e., order of equations immaterial
– Supports general DAEs
including special case:
Modeling vs. Modelica
– Accumulation quantities from balance laws are differential variables:
– States need initial values, e.g.:
– Inputs and parameters are easy to find
– Remaining variables are algebraic:
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
F dx
dt,x, z,u; 0
dxdt
fx, z,u;
0 gx, z,u;
x m,mj,nj,M,U
xt 0
z m i,m e,m j,i,n j,i, ,n j,g,
M i, ,H i, ,c j ,V ,v,Ĥ,
University of South-Eastern Norway Page 11August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Analysis
• Solution of linear ODE
• Linear model asymptotically stable if:
• Time constant
• Linearization:
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
dxdt
Ax Bu
xt expAt x0 0
t
expABud
expAt I At 12At2 1
n!Atn
j : jA 0 dxdt
fx,u; dx
dt Ax Bu
A f
x , B
f
u
University of South-Eastern Norway Page 12August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Exam tips
• Before exam:
– Re-work project
– [Exam will be based on/extend project]
– Look over course summary
– Try to solve past exams
– Work with Examples in lecture notes
– Only read those parts of lecture notes needed to understand problems
• During exam:
– Come in good time
– Bring blue or black pen. Do not use pencil or red/green colored pens.
– Answer briefly and straight to the point – there is no time for wordy prose
– Answer clearly – you don’t score by using «fancy»/ unclear explanations
– You don’t pay for the paper – don’t write densely
– Don’t write in the margin
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
University of South-Eastern Norway Page 13August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Modelica Example: Outline
• Liquid tank: Model Modelica code
• Focus:
– DAE model
– input-output
– two objects from one class
– time varying input
• Conclusions
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
University of South-Eastern Norway Page 14August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Modelica Example: Liquid tank model Modelica code
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic SystemsVideo
University of South-Eastern Norway Page 15August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Modelica Example: Conclusions
• Encoding DAE model to Modelica code
• Model with both input and output
• Instantiating two models for comparing systems
• Time varying input with if-else structure
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems
University of South-Eastern Norway Page 16August 10, 2018 |
FM1015: Modeling of Dynamic Systems
© Bernt Lie
Summary
• Modeling of dynamic system:– System: well defined subset of world
– Dynamic: inertial effects
– Model: mathematical model
– Relates inputs to outputs
– Based on mechanistic understanding/classical physics
– Basic analysis
– Need to know: balance laws, Need to understand: constitutive eqs.
• Particular characteristics:– Little emphasis on model manipulation
– Keep model as DAE
– Complete examples: model development + description using Modelica + simulation using OpenModelica
Bernt Lie: Overview of course FM 1015 Modeling of Dynamic Systems