UNO Engineering Forum
September 19, 2014
Water Wave Impact on Ship Structures
Christine M. Ikeda, Ph.D.
School of Naval Architecture and Marine Engineering
Carolyn Judge
Sponsored by:
Outline
• A Hydrodynamics Point of View on the Slamming Impacts
experienced by High-Speed Craft: Dynamic Pressures
• Classical Wedge Drop Study Revisited
• Tow-Tank Experiments on Planing Craft in Regular Waves
Acknowledgements:
Results
shown
fromon
theHigh-Speed
United States
Naval
• Structural
Response of
Slamming
Loads
Craft:
FullAcademy
by ONR,
and the project principal investigator
Field
Strainwere
and funded
Deflection
Measurements
was
Carolyn Wedge
Judge. Drop Study Revisited
• Classical
• Tow-Tank
on Semi-Planing
Craft inStaff
Regular
Special
thanksExperiments
to the Hydromechanics
Laboratory
at theand
United
Irregular
States
Navalwaves.
Academy:
Dan Rhodes, Mark Pavkov, Bill Beaver, and John Zselecsky
Hydrodynamic
loading
Ship
Structure
Structural
Response
Christine Ikeda
2
Slamming Impacts on High-Speed Marine Vessels
•
Research Questions:
• Is there a better way to design marine vehicles if we understand the physics of
slamming events?
• What happens if the bottom of the hull deflects?
• How does the use of composites or aluminum in ship-building affect the physics and
strength of the hull?
• Laboratory-scaled experimental studies seeking to provide insight into the
physics of the slamming events
• Slamming motions and forces are a function of wave
topography, impact angle, forward speed, and body
orientation during impact
• Classic wedge drop experiment with new contributions:
Spray Root and high-density pressure measurements
• Tow-tank experiments on model-scaled planing
hull in different wave conditions
Image courtesy of Combatant Craft Division
(CCD) Little Creek
3
Experimental Details
• Acrylic wedge, constructed
Tekscan
Map
with 1.3-cm thick plates
• Deadrise angle, β = 20°
• Dimensions in cm
• Length in and out of
screen: 60 cm
Drop heights
ranging from 8 to
64~cm
PCB
Measurements:
• Vertical Acceleration: Accelerometer
• Vertical position: String Potentiometer
• High-Speed Video:
Phantom Miro M320S
• Pressure on bottom surface
• Point Measurements: PCB Piezotronics
• Mapping System: Tekscan
Highspeed
camera
Pressure Measurements
•
Bottom layout of pressure measurement locations
•
6 point pressure transducers
•
Pressure mapping system (consists of an array of measurement points)
Single “sensel”
or measurement point
Field of View for Highspeed Camera
Point-pressure
sensors
Pressure mapping
system
High-Speed Video
New Contribution
Video recorded at a speed of
4,000 frames per second and
played back at 3 frames per
second
(1333 times slower than real life)
What was measured?
P1 P2 P P4
3
P5
P6
Keel Impact
Chine impact
measured from
videos
C. Ikeda, and C. Judge. Impact Pressures and Spray
Root Propagation of a Free-Falling wedge.
Submitted to Experiments in Fluids, May 2014.
Similarity Solution
7.9 cm
31.8 cm
63.5 cm
Similarity Solution
Pressure Contours
Christine Ikeda
10
Pressure Contours
Christine Ikeda
11
Pressure Contours
Christine Ikeda
12
Pressure Contours
Christine Ikeda
13
Pressure Contours
Christine Ikeda
14
Pressure Contours
Christine Ikeda
15
Spray Root and Pressure Correlations
Increasing Drop Height
The lines show the computed spray root position versus time.
The symbols show the position of the peak pressure versus time
Christine Ikeda
16
High-Speed Craft
Experiments performed at the United States Naval Academy
Experimental Facilities
•
Dual flap, servo hydraulic control wavemaker
•
Regular, irregular and transient waves; frequency
range 0.3 to 1.4 Hz
Wave Characteristics
• Tow-speed: 6.4 m/s
• Bretschneider Spectrum to develop irregular wave model of a
Sea State 3 Condition
• 9.4 cm significant wave height
• 1.7 s modal period
• Regular Wave field based on the most probable waves from
Bretschneider Spectrum
• Wave Height: 6.1 cm
• Wave Period: 1.1 s
Planing Hull Characteristics
• Fixed degrees of
Freedom:
• Sway, roll, yaw,
surge (fixed to
carriage)
• Free in
• Heave, Pitch
Full-Scale
Model-Scale I
Model-Scale II
Overall Length (m [ft])
13.0 [42.8]
1.2 [4]
2.4 [8]
Maximum Beam (m [ft])
4.0 [13.1]
0.37 [1.2]
0.73 [2.4]
15.9 [35000]
0.013 [27.9]
0.12 [223]
LCG (m [ft])
4.6 [15.1]
0.42 [1.4]
0.85 [2.82]
KG (m [ft])
1.5 [4.8]
0.14 [0.45]
0.27[0.9]
Displacement (metric tons [lb])
Measurements
•
Accelerations
• A1 triaxial accelerometer (Heave, Sway and Surge)
• A2 & A3 Heave (vertical accelerations only)
•
Heave and Pitch measured at the LCG
•
Incoming water surface (encounter wave) at 52 cm in front of the bow
•
Wave Height elevation at 30.5 m from the wavemaker (fixed in tow tank)
Pressure Measurements
•
Point – Pressure
Transducers:
• PCB Piezotronics Model
113B28
• Range: 344.7 kPa
• Temperature effects
mitigated with dielectric
grease
• No hydrostatic pressure
reading
•
Pressure Mapping System
• Tekscan High-Speed
Pressure Mapping
System
• Range: 690 kPa
• Reads hydrostatic
pressure
Sensor Name
#1
#2
#3
PCB
Tekscan Model Number
5051
9550
5570
N/A
Measurement Area (cm2)
31
108
175
N/A
Sensel Area (mm2)
0.64
50.4
22.9
24
Number of Sensels
1936
42
264
N/A
Sample Rate (kHz)
0.73
20.4
4.4
20
Tow-Speed: 6.4 m/s (12.4 knots), Regular Waves
Movie Taken at 400 fps and played back at 10 fps
Run 44
Identification of Single Impact
• Use of acceleration-time histories to identify a single slam event
• Free-fall or zero vertical acceleration followed by short duration
high, upward acceleration from slam
• Heave, Pitch and Wave history
• behavior consistent with the slam event characteristics
• Run 44
Single Impact Event (Run 44)
Tow-Speed: 6.4 m/s (12.4 knots), Regular Waves
Movie Taken at 400 fps and played back at 2 fps
Pressure Time History Run 44
• Point sensor measurement
area: 24 mm2
• Sample Rate: 20kHz
• Sensel measurement area:
0.64 mm2
Must assume that the planing motion is
• about
Sample
Rate: 730 Hz
symmetric
the keel
Spatial Pressure Correlation Run 44
P23
P23
P22
P22
P21
P21
P21
P21
P22
P22
P23
P23
Spatial Pressure Correlation Run 44
P23
P23
P22
P22
P21
P21
P21
P21
P22
P22
P23
P23
Tow Speed: 9 m/s (17.5 knots), Regular waves
2.4-m long model
Movie taken at 1400 fps and played back at 150 fps
Christine Ikeda
29
Conclusions and Future Work
Wedge Drop Experiment
•
Novel method of quantifying the spray root propagation
•
Pressure measurements correlate well with measured spray root propagation
•
Calculated maximum velocity at impact and verification of similarity solution
•
Understanding of the basic physics of these impact events can allow for the development of
design tools and can aid in computer model validation
High-Speed Planing Craft
•
146 total runs with about 15-20 impacts per run  still a work in progress
•
Analysis of pressure measurements show a discrepancy in pressure magnitudes between
the two methods, but qualitatively look reasonable
•
Isolating of individual slamming events using vertical acceleration data show there are
different types of behavior based on how the ship hits the water surface, curvature of water
surface
Structural Response
Experiments to be performed at the University of New Orleans
Deflection of Ship Hull Bottoms
•
Why is this a concern?
• Wide-spread use of composite materials in ship-building that are more likely to deflect
• High-Speed craft slamming into large waves can severely injury passengers; consider
an autonomous craft and focus shifts to not damaging the equipment on-board
Ghavami, K. and Khedmati, M.R., Finite Element Analysis - Applications in
Mechanical Engineering, 2012
•
Image courtesy of Combatant Craft Division
(CCD) Little Creek
Research Questions:
• How does the pressure-field in the fluid deform the structure?
• How does the structure deformation affect the pressure field?
32
Deflection of Ship Hull Bottoms
• How can a ship be designed to take into account composite materials
or deflections in the hull bottom?
• Conduct experimental study to determine the strength of the a
composite deformable hull
• Wedge drop study
• Semi-planing study
• Use of Digital Image Correlation (DIC) as an non-intrusive way to measure the
full field strain on the structure
• Use of Stereo DIC will allow for out-of-plane deflection
• Continue to explore fluid dynamics of this problem in addition to the structural
motions and deformation (What does the spray root behavior look like on highspeed craft?)
33
Classical Wedge Drop Study Revisited
• Prismatic Wedges with thin-bottom plates: Aluminum Alloys and
Composites
• Traditional measurements such as pressure, acceleration, heave
• Full-field strain measurements taken with Stereo- Digital Image
Correlation to compute out-of-plane deflections
Camera 1
Highspeed
cameras
Spatial
Correlation
Camera 2
t
t
1
1
t
t
2
2
Christine Ikeda
34
Semi-Planing Craft in Waves
•
Scale-model hulls with thin-bottoms: Aluminum Alloys and Composites
•
Traditional measurements such as pressure, acceleration, heave, pitch, roll
•
Full-field strain measurements taken with Stereo- Digital Image Correlation to
compute out-of-plane deflections
Christine Ikeda
35
Final Remarks
•
Fluid-Structure Interaction problems are present in many every-day applications.
•
The physics of this interaction is interesting and can provide many new
innovations/designs.
Image courtesy of Combatant Craft Division
(CCD) Little Creek
Off-Shore
Off-ShoreWind
WindTurbine
TurbineFarm,
Farm,Press-Release
Press-ReleasePhoto
Photofrom
fromSiemens
Siemens
36
References
Ikeda, C., Fluid–Structure Interactions: Implosions of Shell Structures and Wave Impact on a Flat Plate. PhD thesis,
University of Maryland, College Park, August 2012.
37