Wave and Force
Measurements in
Circular Compact Basin
Joao Alcino de Andrade Martins,
University of São Paulo – Brasil
Shigeru Naito, Osaka University – Japan
Munehiko Minoura, Osaka University – Japan
Yoshiaki Shimakawa, Osaka University – Japan
Naval and Ocean Laboratory Test Tanks
Mirror effect
Still water
Short crested irregular waves
Head sea, Follow sea,
Long crested Simultaneous Generation
irregular waves and Absorption of waves
Stochastic steady waves,
Arbitrary profiled waves,
Arbitrary configured basin
Advanced Multiple Organized Experimental BAsin
AMOEBA
Oblique waves,
Short crested
irregular waves (adapted from Naito, 2006)
Advanced Multiple Organized Experimental BAsin
Development of compact wave basin (1999)
zWave Generation
=> Regular, Irregular Naito and Co-Workers - Osaka University,
=> Transient, Osaka, Japan.
=> Multidirectional
zAbsorbing wave maker
=> No reflected waves
z Voice coil motor system
=> No friction,
=> Quick response
=> Simple mechanism
Main Characteristics
Diameter 1.6 m
Depth 0.25m
No. of wave maker 50
Period 0.33-0.71 s
AMOEBA Absorbing Wavemaker Unit
V.C.M.
Displacement
probe
70 Top View
Floating body 250
100
[Unit : mm]
Front view Side view Back View
Regular Wave Field
Two Dimensional Unidirectional Wave
(adapted from Naito et al., 1998)
Omnidirectional Concentration Waves
“Ring Waves”
(adapted from Naito et al., 1998)
Wave amplitude [mm]
20
y[mm]
1000 Exp.
15 Cal.
10
0
5
x[mm]
-1000 0
-1000 0 1000
-600 -400 -200 0
x[mm]
Measuring points Wave amplitude on x-axis
Irregular Wave Fields
Long Crested Waves
(adapted from Naito et al., 1999)
Heave Force Experimental Results in Sphere
Two Dimensional
(adapted from Naito et al., 1999)
Unidirectional
Regular Wave
y
・・
・i+1 Wave makers
i
・
i -1
・・
A x
Semi-submerged
Wave sphere
basin (Measuring point)
Arrangement of experiment
Platform Model First Order Forces
Heave and Surge Results
(adapted from Naito et al., 2001)
Platform Model
3D View and
MainData
Present Tests Setup into AMŒBA
I. Waves Only II.a; II.b - Four
Columns Platform
0.16 m
0.15 m
0.22 m
0.24 m
0.49 m
0.15 m
0.15 m
Model
0.16 m
4 3 2 1 0.8 m 4 3 2 1 4 3 1 2
0.15 m
0.28 m
0.41 m
0.15 m
0.15 m
0.34 m
0.24 m
0 NO
Wave Probe Wave propagation SCALE
n “n” location direction, all cases AMŒBA = 1.60 m diameter
(Martins, 2006)
Regular Wave Measurements
(Martins, 2006)
Wavemakers Uncontrolled Condition: Water Surface View and Measured Time Series
Controlled Absorbing Wavemakers: Water Surface View and Measured Time Series
Regular Wave Measurements
(Martins, 2006)
Wave Probes Calibration Wave Height distribution along wavepath (no model)
Regular Wave Test Setup Wave Height distribution along wavepath (with model)
Wave Diffraction Force Test Setup
Platform Model with Four Columns and Pontoon
(Martins, 2006)
Schematic drawing Platform Model Force Test Setup
Measured Forces Comparison
(Martins, 2006)
Forces Calculated: dotted lines; Measured by Naito: symbols;
Measured by Martins: line with symbol and error bar
Main Conclusions
• It is possible to generated an arbitrary wave field, in the range of 1.6
Hz to 3.0 Hz, with confidence within 10% deviation in wave
elevation. Exception to 1.8 Hz frequency and outside half radius
region centered circle;
• The absorbing wavemaker reflected less than 10% of the narrow
band long crested irregular waves spectrum energy Thus, these wave
fields can be generated for a long time;
• The platform model diffraction forces measured in regular and
transient waves, were within ±2% deviation band; and
• The experimental results for the diffraction force measured into
AMŒBA is within ±2% deviation band among tests and repetitions
and within ±7% among present tests results and those performed 8
years ago.
Acknowledgements
The authors express their gratitude to NAOE-Osaka
University Staff, especially to Mr. Yasuhiro
Shimizu for equipment preparation and support
during this research project.
