PIV measurements in water waves
Atle Jensen
University of Oslo
PIV, 2003 – p.1/37
Outline of talk
history
results from experiments of
Stokes waves (Jensen et al. (2001))
irregular waves (Clamond et al. (2002), Jensen et
al. (2003))
solitary wave in constant depth (Jensen et al.
(2002))
solitary wave on a steep beach (Jensen et al. (2002)
high-speed piv (Sveen and Jensen (2002))
visualization with hsv
PIV, 2003 – p.2/37
History
Hydrodynamics Laboratory
Rebuilt in 1994-96
new ”large” wave tank
two-phase flow exp.
PTV implemented in 1996
extended PIV, 1998
high-speed PIV, 2001
PIV, 2003 – p.3/37
System Overview
PIV, 2003 – p.4/37
Camera 1:
at
Camera 2:
at
Local acceleration
Local accelerations
PIV, 2003 – p.5/37
by three point formula
and
Smoothing of
Particle accelerations; tracing
)
Tracing of pseudo particle (iterate for
Interpolation:
interior: bi-linear in quadrilaterals
boundary: linear in triangles
Extension: tracing through multiple steps
PIV, 2003 – p.6/37
Particle accelerations; regression
"#
"!
Acceleration (local+convection)
Problem: compute accurate gradients
#
%
('
% &
!
and
+-)
Regression applied to
point
,
gradients
+*)
' &
,
%
$
Least square fit for
Smoothing
domain around each
PIV, 2003 – p.7/37
Accelerations
+1
.
0
/0
Smoothing and virtual tracing.
Condition
3
2
standard deviation
4
0
/0
Options for
+1
time between velocities
characteristic accelerations
small changes of over
5
6
7 6
8
0
/0
Often
spatial noise
PIV, 2003 – p.8/37
Stokes waves
PIV, 2003 – p.9/37
A
=
B
+L
-K
IJ =
9
9
9
=
=
C
<
/;
A
=
=
#
E
F
B
G
H
D
D
9
9
=
=
C
<
/;
A
=
#
=
F
B
E
D
:
G
D
:
7
=
=
9
:
:
C
#
A
=
:
!
=
=
@?>
2
<
/;
B
9
Stokes waves
(1)
(2)
(3)
(4)
(5)
PIV, 2003 – p.10/37
M
,
M
O
M
N
,
0.1
#
PH
0
−0.1
−0.2
0.4
0.6
0.8
1
1.2
VW K
R
0.2
TUQ S R
0
’+’ experiments, solid is theory. From Jensen et al. (2001).
PIV, 2003 – p.11/37
Acceleration
0.1
#
PH
0
−0.1
−0.2
0.8
1
1.2
R
0.6
XY
0.4
VW K
0.2
XR
TUS
0
PIV, 2003 – p.12/37
^
- )
,
* )
H
2 , reference arrow
]
H
\]
6[
7 Z
Particle/local accelerations
PIV, 2003 – p.13/37
\]
6[
7 Z
2
]
7 6
8
H
_
Convective accelerations
, frame: averaging
PIV, 2003 – p.14/37
(cm)
PIV
H
2 ] b
Stok.
a`
#
Averaged acceleration
PIV, 2003 – p.15/37
Accuracy - Stokes waves
h
7 6
8
=
g
^[
7 f
ed^[
7 c
:
=
,
and
. Std. dev.,
0.6 % for the velocities and 2% for the accelerations.
^
6
7 6
8
=
g
h
7 c
ed^[
7 c
:
=
,
and
. The value
of std. dev is 3% for the velocities and 7% for the
accelerations.
7 6
8
.
C
C ^
7 6
8
6
5
5
6
7 6
8
.
7 6
8
h
=
=
Estimates of
.
good results for convective acceleration
PIV, 2003 – p.16/37
Irregular Wavetrain
PIV, 2003 – p.17/37
Irregular wavetrain
[
6h
m
l
7 6
8
7 l
peak enhancement factor
c
f
i
s
k
mean wave period
j
significant wave height
7 6
8
generated from a JONSWAP spectrum
m
g
g
m
,
6[
7 6
8
5
.
f
five waves measured from each wavetrain
PIV, 2003 – p.18/37
M
8
6
n
4
2
[cm]0
−2
−4
275
280
285
290
295
8
6
n
4
2
[cm]0
−2
−4
283
283.2
283.4
283.6
[s]
283.8
284
284.2
282.8
PIV, 2003 – p.19/37
15
−56cm/s
0.3
10
#
#
=
0.2
5
0.1
[cm]
0
0
−0.1
−0.2
−5
5
10
−1.5
−1
−0.5
=
9
and blue;
H
o
pH
, green;
, black;
Red;
pH
!
H
[cm]
0
0
−5
H
−10
(experiments). Solids and dashed are computations.
PIV, 2003 – p.20/37
Solitary wave in constant depth
PIV, 2003 – p.21/37
dg
c
7 6
7 6
8
[
5
.
,
dg
H
m
g
c
m
,
g
786
h
h
Z
PH
[
2
7 f
,
+1
H
Soliton
PIV, 2003 – p.22/37
reference arrow
r
s t u
v
H
M
Soliton,
M
q
,
PIV, 2003 – p.23/37
1
2
3
4
M
q
,
M
Soliton,
5
6
PIV, 2003 – p.24/37
yxw
M
q
,
M
Run-up,
y(cm)
}z
{yw
z|
8
6
4
2
0.50
0.25
0.15
0.10
0.05
0.00
-3
0
3
6
, reference arrow - g
7 6
8
5
,
.
3
2
,
4
x(cm)
PIV, 2003 – p.25/37
Conclusion
7 6
8
.
high accuracy when
~
good overall results for small
.
variable degree of success
and
must be “tuned” for acceleration
measurements
PIV, 2003 – p.26/37
high-speed PIV
(Sveen and Jensen(2002))
PIV, 2003 – p.27/37
Overview;high-speed PIV
Purpose:
1. to develope an affordable, digital, high speed camera
system for PIV and
2. to perform initial tests on real experiments using
in-house made PIV software.
Challenges:
Digital storage in real time
Illumination
Processing huge amounts of data
PIV, 2003 – p.28/37
What is “fast”
looking for consistent high speed
range from “a few seconds” to hour(s)
Many high speed cams use onboard memory. Limit
on recording length
We would like to stream data to a hard-drive.
A “regular” BW video camera - 25 fps, 8 bit colordepth,
512*512 pixels, outputs 6.25 Mb/s
Dalsa CA-D6-0512 - BW, 262 fps, 8 bit colordepth,
542*530 pixels, outputs 71.8Mb/s
PIV, 2003 – p.29/37
Hardware
Camera: Dalsa CA-D6-0512
Framegrabber: Coreco Imaging, PC-DIG-L, 4 input
channels
Computer:
dual PIII, 64 bit PCI-bus, Windows NT 4.0
onboard Ultra160 SCSI controller
storage on RAID-0 (software controlled), currently
using 4*36Gb disks
PIV, 2003 – p.30/37
Benchmark
Write speed depends on which disk sector is being
written
Varies from about 130Mb/s to about 90Mb/s
PIV, 2003 – p.31/37
Recording digitial video
Digital Video Recording software: Video SAVANT (by
IO industries)
Handles the writing of images to disk
Image processing
Problem no.1 - Large quantities of data to process
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Measurements of a solitary wave
Tests performed using 234fps.
play movie
PIV, 2003 – p.33/37
Conclusion
HSCS developed using “off-the-shelf” technology
system capable of streaming 262fps to hard-disk (in
real-time)
benchmark tests performed
PIV software developed-automasking
- Large data sets
Measurements performed on solitary wave
Additional tests to be performed May 2002
PIV, 2003 – p.34/37
visualization with hsv
PIV, 2003 – p.35/37
Visualisation with hsv
6
€c6
6
6
6
Tests performed together with Kristian and Per-Otto
(13122002).
Redlake MPRO,
Hz,
PIV, 2003 – p.36/37
future
breaking waves on a steep beach
aerated regions
“higher”-speed PIV
PIV, 2003 – p.37/37