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Dynamic Phase Boundary Estimation using Electrical Impedance
Tomography
By Umer Zeeshan Ijaz,
Control Engineering Lab, Department of Electronic Engineering, Cheju National University, Cheju 690-756, Korea
Thesis Defense(Supervised by Professor Kyung Youn Kim)
Dated: 13.11.2007
2
CONTENTS
• Introduction• Electrical Impedance Tomography• Boundary Representation
– Fourier Coefficients– Front Points
• Extended Kalman Filter• Kinematic Models• Interacting Multiple Model Scheme• Unscented Kalman Filter• Gauss-Newton Unscented Kalman Filter
3
INTRODUCTIONChemical engineers frequently encounter the flow of a mixture of two fluids in
Liquid-gas or liquid-vapor mixtures condensers and evaporatorsgas-liquid reactors combustion systemstransport of some solid materialsslurry of the solid particles in a liquid, and pumping the mixture through a pipeLiquid-liquid mixtures in emulsions as well as liquid-liquid extraction.
Types of Flows
4
Electrical Impedance Tomography (EIT) is a imaging modality in which the internal resistivity distribution is reconstructed based on the measured voltages on the surface object.
COMPUTERCOMPUTER
ReconstructionAlgorithm
ReconstructionAlgorithm
Interface withInstrument
Interface withInstrument
VI
Concept of electrical impedance tomography
WHAT IS EIT?
5
• The forward problem calculates the voltages on the electrodes by using the injected current and assumed resistivity distribution.• The inverse problem reconstructs the resistivity distribution by using the voltage measurements on the electrodes.
Forward vs. inverse problem for EIT
FORWARD SOLVER VS INVERSE SOLVER
Inverse Solver
Forward Solverk calculatedV
1 somethingk k
0 measuredV
An iterative inverse solver
6
Governing Equation derived from Maxwell Equation
Boundary Conditions: Complete Electrode Model
MATHEMATICAL MODEL: FORWARD SOLVER
1.( ) 0u
1
1
1
on , 1, 2,...,
, 1, 2,...,
0 on
l
l l l
le
uu z U e l L
nudS I l L
nu
n
1
L
ll
e
1
0L
ll
I
1
0L
ll
U
Between electrodes, no current crosses the boundary if the impedance outside the imaged volume is much greater than that inside
There is an existence of a thin, high-impedance layer beneath electrodes delivering current. This layer may be modelled as the limit of a thin layer of thickness d and impedance z/d as d goes to zero. (use ohm’s law)
Beneath electrodes, neither potential nor the current crossing the boundary is known. Net current crossing the boundary beneath an electrode is equal to the current being delivered to it by tomograph electronics
Constraints: For the solution to be unique
7
FEM DISCRETIZATION OF FORWARD PROBLEM
Ab = I
1
1( , ) , , 1, 2,...,
l
L
i j i jell
i j dr dS i j Nz
B
11 1
1 1( , ) , 1, 2,..., ,
j
i ije e
i j dS dS i Nz z
C
1
1
11
1 1
| |
( , ) , , 1, 2,..., 1| || | j
j
ei j
zi j i j L
eei j
z z
D
| |le Electrode area i Basis function
( 1) ( 1)
( 1)
( 1)
N L N L
N L P
N L P
A
b
I
1, 2,..., 1j L
N-Nodes, L-Electrodes, m-elementsP-Patterns
1 2
34
N
1
L
2
DNNCN
CNBA TT
β
αb
IN
0I ˆ~
T
PNα PL )1(β
100
010
001
111
,,, 121
LnnnN
N
iii
h yxyxuu1
,,
1
1
L
jjj
hU n
Potential inside:
Potential on electrodes:
8
CURRENT INJECTION PROTOCOL
Current frame
0
0
cos( ), 1, 2,..., / 2
sin( ), 1, 2,..., / 2 1lp
ll
I p p LI
I p L
2 /l l L
Trigonometric (L-1 Curent Patterns)
cos( )l cos(2 )l sin( )l sin(2 )lcos(3 )l cos(4 )l sin(3 )l
Opposite (L/2 Current Patterns)
Adjacent (L Current Patterns)
0I
0I
0I0I
9
1
( ) ( )( )
( ) ( )
l
l
x xNl n n
l y yl n n n
x s sC s
y s s
1,2,...,l S
0 1
2 1 sin(2 )n n s
2 cos(2 )n n s
1,2,...n
1,2,...n
1 1 1 1 21 1 1,..., , ,..., ,..., , ,...,x x y y y y y N
N N N N
Truncated Fourier Coefficients Approach(Close Boundary)
BOUNDARY INTERFACE REPRESENTATION 1/2
A 0
A 1
A 3 A 2
C 1
C 3C 2
10
1 11 1( , ) cos , sin
d dX Y R R
R R
( , ) ( , )X Y x d
( , ) cos , sind d
X Y R RR R
11 2( , ,..., )Td d d d
x 0 x 1 x kxK
d 0
d 1 d kd K
fron t po in tsd k pa ram ete rs to be estim a ted
BOUNDARY INTERFACE REPRESENTATION 2/2Front Points Approach (Open Boundary)
2,..., 1
σ=σ0
σ=σ1
A0
A1
C
11
Inverse Solver
Forward Solverk calculatedV
1 somethingk k
0 measuredV
( )kJ
Inverse Solver
Forward Solverk calculatedV
1 somethingk k
0measuredV
k k
( )kJ
BOUNDARY INTERFACE FORWARD SOLVER 1/2
Changes required
( )kJ ( )kJ d
Analytical Jacobians
Boundary to Resistivity Profile Mapping (Forward Solver)
( )k kV ( )k kV d
0 1
1,
k
K L
k i j i jk A e
i j d dSz
B
Nji ,,2,1,
12
x 0 x 1 x kxK
d 0
d 1 d kd K
fron t po in tsd k pa ram e te rs to be estim a ted
s1
s2
Al
Ar
σl
σr
Sl
Sr
Cl(s)
Ni
Nj
( )l l r r
ee l r
S S
S S S
l
r
r
u
BOUNDARY INTERFACE FORWARD SOLVER 2/2
(a) description of interface with front points /fourier coefficients b) mesh elements above the interface/inside the target are assigned one conductivity value ; (c) mesh elements below the interface/outside the target are assigned second conductivity value ; (d) mesh elements lying on the interface are assigned area average conductivity values assigned using equation ; and (e)
final conductivity values at the end of assignment.
(a) (b) (c) (d) (e)
e
e
13
1 1 1k k k kd F d w
( )k k k kU V d v
| 1
| 1 | 1( ) ( )
k k
kk k k k k k k k
k d
VU V d d d v HOT
d
| 1 | 1( )k k k k k k k k k k ky U V d J d J d v
State Space Model
Random-walk modelNonlinear measurement equation
Linearizing the measurement equation about the predicted mean in the previous step
kF
[ ]Tk k kE w w Q
[ ]Tk k kE v v R
[ ] 0kE w [ ] 0kE v
Regularization
*
kk
R
yy
L d
| 1( )k k kk
R
J dH
L
k k k ky H d
[ ]Tk k kE v v R
[ , ]k kBlockdiag R I
INVERSE SOLVER
14
| 1 1 1| 1k k k k kd F d
| 1 1 1| 1 1 1T
k k k k k k kP F P F Q
1| 1 | 1( )T T
k k k k k k k k kK P H H P H
| | 1 | 1( )k k k k k k k k kd d K y H d
| 1 | 1 | 1( ) ( )k k k k k k k k k ky U V d J d d
*
kk
R
yy
L d
| 1( )k k kk
R
J dH
L
| | 1( )k k k k k kP I K H P
kUMeasurement Update
Time Update
|k kP|k kd
1| 1k kd 1| 1k kP 0|0d 0|0P
Jacobian
Forward Solver
,kQ[ , ]k kBlockdiag R I
,kF ,RL,,kR
Predefined
EXTENDED KALMAN FILTER (Front Points)
0|0 0|0,d P
1|0 1|0,d P
1|1 1|1,d P
2|2 2|2,d P
3|3 3|3,d P
4|4 4|4,d P
2|1 2|1,d P
3|2 3|2,d P
4|3 4|3,d P
1U
2U
3U
4U
15
EXTENDED KALMAN FILTER (Front Points) Results
3% Noise
10-Front Points, Contrast Ratio of 1:100, Moving every 4 Current Patterns (First two modes of cosine and sine with additional cosine in image reconstruction)
|| ||
|| ||estimated true
dtrue
d dRMSE
d
|| ||
|| ||estimated true
Utrue
U URMSE
U
16
Bubble moving with constant velocity Bubble moving with constant acceleration
Bubble expanding with constant velocity Bubble expanding with constant acceleration
KINEMATIC MODEL (Fourier Coefficients)
17
2
, ,12
1
.
Lmeas l homo ll
Lll
U UN D
I
, ,1 1
,1
.
L Lhomo l l meas l ll l
Lhomo l ll
U I U IP D
U I
Distinguishability can be defined as a measurement ability to differentiate between homogeneous and inhomogeneous conductivities inside the domain. Power distinguishability is defined as the measured power change between the homogeneous and inhomogeneous cases, divided by the power applied in homogeneous case.
OPTIMAL CURRENT PATTERN (Front Points)
-15 -10 -5 0 5 10 15
-15
-10
-5
0
5
10
15
e1
e2
e3
e4e5e6
e7
e8
e9
e10
e11
e12 e13
e14
e15
e16
1. Trigonometric method with first 2 modes of cosine and sine (4 injections; 5 EKF states with repeated use of the first cosine)2. Opposite method with e1-e9 and e5-e13 pairs (2 injections; 5 states with repeated use of e1-e9, e5-e13, e1-e9)3. Cross method with e3-e7, e5-e13 pairs (2 injections; 5 states with repeated use of e3-e7, e5-e13, e3-e7)4. Opposite method with e3-e11, e7-e15 pairs (2 injections; 5 states with repeated use of e3-e11, e7-e15, e3-e11)5. Opposite method with e3-e11, e7-e15, e5-e13 pairs (3 injections; 5 states with repeated use of e3-e11, e7-e15).
1 2 3 4 5
1% Noise
18
a) Bubble moving with constant velocity b) Bubble expanding with constant velocity c) Bubble moving with constant acceleration d) Bubble expanding with constant acceleration
Solid Line: True BoundaryDotted Line: Estimated Boundary
Solid Line: Kinematic ModelDotted Line: Random-Walk Model
KINEMATIC MODEL RESULTS (Fourier Coefficients)6-Fourier Coefficients, Contrast Ratio of 1:106 , Moving every current Pattern
19
1 ,...kQ
T.U
M.U
EKF12 ,...kQ
T.U
M.U
EKF23 ,...kQ
T.U
M.U
EKF3
IMM SCHEME (Fourier Coefficients) 1/3
1 1 1 11 1 1 1|k k k k ke y H
2 2 2 21 1 1 1|k k k k ke y H
3 3 3 31 1 1 1|k k k k ke y H
1 1 1 11 1 1| 1 1( )Tk k k k k kS H P H
2 2 2 21 1 1| 1 1( )Tk k k k k kS H P H
3 3 3 31 1 1| 1 1( )Tk k k k k kS H P H
1 1 1 11 1 1 1
11
1 1exp[ ( ) ( ) ]
22 | |
Tk k k k
k
L e S eS
2 2 2 2
1 1 1 12
1
1 1exp[ ( ) ( ) ]
22 | |
Tk k k k
k
L e S eS
3 3 3 3
1 1 1 13
1
1 1exp[ ( ) ( ) ]
22 | |
Tk k k k
k
L e S eS
11 1 1
1 1 2 31 1 1 2 1 3
kk
k k k
L c
L c L c L c
22 1 2
1 1 2 31 1 1 2 1 3
kk
k k k
L c
L c L c L c
33 1 3
1 1 2 31 1 1 2 1 3
kk
k k k
L c
L c L c L c
*As error decreases, modelling probability increases
20
IMM SCHEME (Fourier Coefficients) 2/3
11k 2
1k 3
1k
1k 2
k 3k
1|1 1|2 1|3, ,k k k 2|1 2|2 2|3, ,k k k 3|1 3|2 3|3, ,k k k 31 32 33, ,
21 22 23, ,
EKF2 EKF3EKF1
11 12 13, ,
Transition Probability
| 1i j iij kk
jc
1
Mi
j ij ki
c
0 |||
1
Mj i ji
k kk k ki
0 0 0 |
| | || | |1
[ ( )( ) ]M
j j j i ji i i Tk k k k k kk k k k k k k
i
P P
11| 1
11| 1
k k
k kP
21| 1
21| 1
k k
k kP
31| 1
31| 1
k k
k kP
Predefined
Mixing of estimates and error covariances
21
IMM SCHEME (Fourier Coefficients) 3/3
Interacting/Mixing of the Estimates
Filter 1 Filter M
Linearization
State Estimation Combination
Model Probability
Update
1|k k 1
|k kP |Mk k |
Mk kP
01|k k 01
|k kP 0|M
k k 0|M
k kP
11ke
11kS
11| 1k k
11| 1k kP 1| 1
Mk k 1| 1
Mk kP
11 1
Mk k
11
1
k
Mk
1ky
1| 1k k
1| 1k kP
1Mke 1
MkS
1ku
One-cycle flow diagram of the inverse solver with the IMM scheme.
EKF1
EKF2
EKF3
1k
2k
3k
22
5 10 15 20 25 300
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Patterns
Mod
el P
roba
bilit
y k
EKF1
EKF2
EKF3
EKF1 EKF2 EKF3 IMM
IMM SCHEME RESULTS (Fourier Coefficients)6-Fourier Coefficients, Contrast Ratio of 1:106, Moving after 8 current patterns
23
++
+ + + ++
+++
++
+ + + ++
+++
++
+ + + ++
++
+
++
+ + + ++
++
+
++
+ + + ++
+++
++
+ + + ++
+++
++
+ + + ++
+++
++
+ + + ++
+++
++
+ + + ++
++
+
+ +
+ +
++
+ +
+ +
++
+ +
+ +
++
+ ++ +
++
+ ++ +
++
+ ++ +
+++ +
+ ++
++
+ ++
+
+
+ +
++
+
+
+
++ ++ +
+ +
++
++ +
+++
+ ++
++
+ ++
+++ +++
++ +
++ ++
++ ++ ++++ ++++++ +++
+++ +
++++ +
++ + ++
+++ +
+++ ++
++
+++ +
+++ ++++
+++
+++ ++
++ +
Actual (Sampling)
true mean
mean
covariance
Linearized (EKF) UT
UT mean
UT covariance
sigma points
transformed sigma points
EKF mean
EKF covariance
UNSCENTED TRANSFORM
An example of unscented transform for mean and covariance propagation: a) actual; (b) first-order linearization (EKF); and (c) unscented transform
(a) (b) (c)
( )f ( )f
( )if
24
UNSCENTED KALMAN FILTER (1/4)
0 0ˆ ˆ[ ] [ ]a a T TE x x x 0 0
0
0 0 0 0 0
0 0
ˆ ˆ[( )( ) ] 0 0
0 0
a a a a a TE
P
P Q
R
x x x x
1 1 1 1 1 1ˆ ˆ ˆ( ) ( )a a a a a ak k k k k kM M
P Pχ x x x
Generate 2n+1 sigma points where n is the size of augmented vector
1ˆ ak x
Each point is the augmented vector
| 1 1 1.x xk k k k
Iχ χ χ
Run the state equation
2( )
, | 10
ˆM
mk i i k k
i
W
x χ
2( )
, | 1 , | 10
ˆ ˆ[ ][ ]M
c x x Tk i i k k k i k k k
i
W
P χ x χ x
Calculate predicted mean and covariance
State Space Model: 1 1.k k k Ix x w( )k k k kV U x v
[ ]Tk kE Qw w
[ ]Tk kE Rv v
[ ] 0kE w[ ] 0kE v
25
| 1 | 1 1( )xk k k k k kV
ψ χ χ2
( ), | 1
0
ˆM
mk i i k k
i
W
U ψ
Run the measurement equation and find the mean
Time update complete
Create covariance matrices2
( ), | 1 , | 1
0
ˆ ˆ[ ][ ]k k
Mc T
i i k k k i k k kU Ui
W
P ψ U ψ U
2( )
, | 1 , | 10
ˆˆ[ ][ ]k k
Mc T
x U i i k k k i k k ki
W
P χ x ψ U
The sigma points should move towards the mean and at the same time, the sigma points on x domain should move towards the mean
ˆkU
ˆkx
UNSCENTED KALMAN FILTER (2/4)
26
Calculate the gain and update the estimates and error covariance matrices
UNSCENTED KALMAN FILTER (3/4)
1k k k k
k x U U UΚ P P
ˆˆ ˆ ( )k k k k kU Κx x U
k k
Tk k k kU U
P P Κ P Κ
Actual measurement
True value
( )0 /( )mW M
( ) 20 /( ) (1 )cW M ( ) ( ) 1/{2( )}m ci iW W M
1,..., 2i M
Define weights
2M N L 2 ( )M M
where
Composite scaling parameter
Spread of sigma points, usually1e-3
Usually zero
Usually 2 for Gaussian distribution
Measurement update complete
27
ˆ ax Pa
.M
{ }aiχ
+ -
State Equation
Nonlinear Measurement Equation [FEM Forward Solver]
ˆ -x
P-
-U
{ }iψ
( ){ }miW
Weighted Mean
( ){ }ciW
Weighted Covariance
UUP
xUP
Kalman Gain
ˆ ax aP
k=k+1
Uk
k
UNSCENTED KALMAN FILTER (4/4)
Block diagram of unscented Kalman filter for phase boundary estimation
28
solid line : true, dotted line : EKF, dashed line : UKF
Phantom
Plastic Target
UKF RESULTS (Fourier Coefficients)32 Electrodes, 6-Fourier Coefficients, Contrast Ratio of 1:106, Moving after 6 current patterns
|| ||
|| ||estimated true
true
RMSE
29<EKF: -x- UKF : -o- >
2% Noise
3% Noise
Rippled surface
UKF RESULTS (Front Points)10-Front Points, Contrast Ratio of 1:100, moving every current pattern
30
1 1.k k k Ix x w( )k k k kV U x v
M
( )mow M
( ) 2(1 )cow M
( ) ( ) 1 1,..., 2
2( )m ci iw w i M
M
2 ( )M M
0 1kx 11 ( ) 1,...,
ki k x ix i M P
11 ( ) 1,..., 2ki k x ix i M M P
*( ) . iik I
2*( )( )
0
ˆM
imk i k
i
x w
2
*( ) *( )( )
0
ˆ ˆ ˆ[ ][ ]k
Mi ic T
x i k kk ki
w x x
P Q
ˆ ˆˆ ˆ ˆk kk k k x k xx x x
P P
2( )( )
0
ˆ ( )M
imk i k k
i
U w V
2
( ) ( )( )
0
ˆ ˆ ˆ[ ( ) ][ ( ) ]k
Mi ic T
U i k k k kk ki
w V U V U
P
2( ) ( )( )
0
ˆ ˆˆ[ ][ ( ) ]k k
Mi ic T
x U i k kk ki
w x h U
P
1 1
1
ˆ ˆˆ ( ) ( ( )
ˆ ˆ ˆ ( )) 1, 2,...
k k k
k k k
j jk x U U kk k
jTx U U k k
x x U V x
x x j
P P R
P P
State Equation
1ˆ ˆ ˆ ˆ( )k k k k k k k
Tx x x U U x U
P P P P R Pˆ jk kx x
Gauss-Newton Measurement Update
GAUSS-NEWTON UNSCENTED KALMAN FILTER
Offline
Online
kU
State Space Model
[ ]Tk kE Qw w
[ ]Tk kE Rv v
[ ] 0kE w[ ] 0kE v
31
2% Noise1% Noise 3% Noise
GNUKF RESULTS (Front Points)
32
-Analytical Jacobian used
-successful till 16 Frontpoints
-Contrast ratio of 1:10000
-3% Relative Noise
-Current patterns reduced to 4 / target remains static with 16 electrodes configuration based on distinguishability analysis for EKF
-Extended Kalman Filter and Unscented Kalman filter (recent) formulation for online monitoring
-Gauss Newton Unscented Kalman filter formulation for improvement over unscented Kalman filter
-With Unscented Kalman Filter and Gauss Newton Unscented Kalman Filter, image reconstruction using 1 current pattern is also possible.
Front points (open boundary)Fourier coefficients (close boundary)-Analytical Jacobian used
-6 coefficients to represent an elliptic object, can go for more, however, higher coefficients are quite sensitive
-Contrast ratio of 1:1000000
-3% Relative Noise
-Current patterns reduced to 6 / target remains static in experiments with 32 electrodes configuration.
-Extended Kalman Filter and Unscented Kalman filter (recent) formulation for online monitoring
-Interacting Multiple Model Scheme for time-varying process noises
-Kinematic models (velocity, acceleration) done for movement of air bubbles, void fractions
RESEARCH MILESTONES
33
Any Questions?
34
APPENDIX: Derivation of Jacobian 1/10In some cases, the voltages are measured only at some selected electrodes, not every electrode. Also, the selected electrodes may be different at each current pattern. The measured voltages at the measurement electrodes can be obtained asU
PEThT NβMUMU
where, is the number of the measurement electrodes and is the measurement matrix. The element is set to ‘1’ if the -th electrode is measured at the -th current pattern and otherwise set to zero. Furthermore, can be extracted directly from by introducing the extended mapping matrix
E ELM),( pM p
hU bN~
)1(),(~ LNLN0N and bNU
~h
where NL0 . Therefore, we have
bMbNMUMU~~ˆ ThT
where the extended measurement matrix is defined as
)1(~~ LNETNMM
If the pseudo-resistance matrix defined as
ELNT )1(1 ~~MAR or TMRA
~~
is given we can calculate the Jacobian matrix. The pseudo-resistance matrix can be easily obtained during the solution of the system equation
IMbRA~~~ T
INMN
00
βR
αRA ˆ~
~
2
1TT
or where ENN :),:1(~~
1 RR and ( 1)2 ( 1: 1,:) L EN N L R R
35
APPENDIX: Derivation of Jacobian 2/10
1 1ˆ
TU A AMA A I R b
d d d
Jacobian:
Front Points Approach
11 2
2
ˆ 0
0 0 0
T
T T
B BRU
d dR Rd R
1
ˆTU B
Rd d
1 1 1 1
1 1 1 1 1 1 1
X Y Y XB B B B B
d X d Y d R X R Y
B B
d Y
Y XB B B
d R X R Y
2,..., 1
36
, 1
1( , ) . ,
r l
L
r i j i jA elr l u l
B i j d dSz
, 1, 2,...,i j N
0
( , ) ( , )limd
B X X Y Y B X YB
d d
0 | ( )
( )lim .
u mm i j
l ui jAd m supp
dd
APPENDIX: Derivation of Jacobian 3/10
Since we are considering the stratified flow of two immiscible liquids therefore, the matrix B will be
37
12
( ) ( ) ( , , )C x S x x X X
Assuming that the interface is represented by a set of linear piecewise interpolation functions:
1[ , ]x X X,
11 1
1
( ) ( )Y Y
S x x X YX X
unit pulse defined for 1[ , ]x X X
Any small perturbation of results in small perturbation in and in
d X X Y Y
21 2 1 2( ) ( ) ( , , ) ( )C x S x x X X O
21 1 1( ) ( ) ( , , ) ( ) ( , , ) ( )C x S x x X X S x x X X O
2,..., 1 21( ) ( ) ( , , ) ( )C x S x x X X O
1 1
1 1
( )Y Y x X
S x X YX X X X
1 11
1 1
( )Y Y X x
S x X YX X X X
where
1[ , ]x X X
1[ , ]x X X
APPENDIX: Derivation of Jacobian 4/10
38
0
1lim ( , )
u mAdf x y d
d
APPENDIX: Derivation of Jacobian 5/10Considering the interface for mesh crossing elements ( )m i jsupp
( , ) .i jf x y where
For a small perturbation in only and will changed ( )P x 1( )P x
0
1lim ( , )
u mAdf x y d
d 1
10
1lim ( , )
X C C
X Cdf x y dydx
d
The function can be expanded about the interface ( , )f x y ( )C x
2( , ) ( , ) ( ) ( )y C
ff x y f x C y C O
y
Finally, we have
0
1lim ( , )
u mAdf x y d
d
2
1
2 1 21 1
2 1 2 1
1( , )
X
X
Y Y X xY X f x C dx
R X X X X
1
1
1 1
1 1
( , ) ( , )X X
X X
x X X xf x C dx f x C dx
X X X X
1
1 1
1 1
1( , )
X
X
Y Y x XY X f x C dx
R X X X X
1
2,..., 1
39
(X k ,Y k )
(X k -1,Y k -1)
(X k +1,Y k +1)
(X k ,Y k+Y k )
P k (x)P k +1(x)
TY P E 1TY P E 2
TY P E 2
TY P E 3
TY P E 4
TY P E 4
TY P E 5
Five types of interface-crossing elements in case of an arbitrarily small perturbation of kY in kY
.
There are five types of interface-crossing elements when kY is perturbed by an arbitrarily small perturbation of kY . Assume that there are only two intersections of the interface and the mesh faces and the intersections
),( 11 yx and ),( 22 yx where 21 xx . Recalling that jiyxf ),(
the integration for each type will be evaluated as
are denoted as is constant in a certain mesh,
TYPE 1: 1
212
1
1
2
),(),(
2
1
kk
kx
X kk
k
XX
XxCxfdx
XX
XxCxf
k
1
121112
1
1
2
),(),(
2
1
kk
kkx
x kk
k
XX
xxXxXxCxfdx
XX
XxCxfTYPE 2:
kk
kkkk
kk
kkkk
x
X kk
kX
x kk
k
XX
XxXXxX
XX
xXXxXXCxf
dxXX
xXdx
XX
XxCxf
k
k
1
2121
1
1111
1
1
1
1
2
),(
),(2
1TYPE 3:
kk
kkx
x kk
k
XX
xxxXxXCxfdx
XX
xXCxf
1
121121
1
1
2
),(),(
2
1
TYPE 4:
kk
kX
x kk
k
XX
xXCxfdx
XX
xXCxf
k
1
211
1
1
2
),(),(
1
1
TYPE 5:
APPENDIX: Derivation of Jacobian 6/10
40
Fourier Coefficients Approach
IA
MIAMb
MU ~~~~~ˆ 1
1
kkkknnnn
yxkn ,,
bA
AIAA
AIA
kkknnn
1111 ~~
bA
MAbA
MAbA
AMU
kkkkn
TT
n
TTT
nn
~~)(
~ˆ111
The derivative of the stiffness matrix with respect to the coefficient is
00
0B
Ak
k nn
)(|
0
0
)(lim
jim mk
k m Aji
kxn
d
supp
B
APPENDIX: Derivation of Jacobian 7/10
41
In order to obtain the Jacobian, now, let us consider the evaluation of the expression
mkA
dyxf
),(1
lim0
We define a new coordinate system where is the positively oriented coordinate along the closes curve , and is the coordinate outward normal from the region
),( ps s kC pkA
)(
)(
)(
)(
)(
)(
sy
sx
s
sp
sy
sx
s
p
k
k
The perturbed boundary will bekC~
)(~
)(~)(~
)(
)(
)(
)(sC
sy
sx
s
s
sy
sxs k
k
k
k
k
s1s2
C k
C k~
s
pTherefore,
2
1 000 ),(
),(),(
1),(
1limlim
s
ss pA
dpdssp
yxyxfdyxf
mk
APPENDIX: Derivation of Jacobian 8/10
42
The Jacobian for the transformation of the coordinate will be
pxpy
ds
dp
ds
dyds
dp
ds
dx
s
y
p
ys
x
p
x
sp
yx
),(
),(
The function can be expanded about the boundary ),( yxf kC
)(),0(),(),( 2
0
pOpp
fsfspfyxf
p
We have
2
1
2
1
),0(
)(),0(1
),(1
02
00
0
lim
lim
s
ss
s
ss pp
A
dsxysf
dpdspxpypOpp
fsf
dyxf
mk
APPENDIX: Derivation of Jacobian 9/10
43
In this, is evaluated at the boundary . When differentiating with respect to , that is perturbing , we have and .On the other hand when differentiating with respect to , we have and . Finally, the derivative of the matrix with respect to the coefficients becomes
),0( sf kCkx
n )(sxn )(sx
n 0 ky
n 0 )(syn
)()(|,0
2
1)()()(
jikmkk
CBm
s
sxnkCyxjikx
n
dsssy
supp
B
)()(|,0
2
1)()()(
jikmkk
CBm
s
synkCyxjiky
n
dsssx
supp
B
where
0|)( kmmk CCBdenotes the set of elements crossing kC
If , and constant in each element, we have ji )(sxk )(syk
)()(| 12
120
2
1)(
)()()(
jikmmk CBm
s
sxnjikx
n
dssss
sysy
supp
B
)()(| 12
120
2
1)(
)()()(
jikmmk CBm
s
synjiky
n
dssss
sxsx
supp
B
APPENDIX: Derivation of Jacobian 10/10