Extreme Wave Impact on a Flexible Plate Aliza Opila Abraham

102 Pages·2016·16.81 MB·English

Extreme Wave Impact on a Flexible Plate
by
Aliza Opila Abraham
Submitted to the Department of Mechanical Engineering
in partial fulfillment of the requirements for the degree of
Master of Science in Mechanical Engineering
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 2016
○c Massachusetts Institute of Technology 2016. All rights reserved.
Author ................................................................
Department of Mechanical Engineering
May 18, 2016
Certified by............................................................
Alexandra H. Techet
Associate Professor of Mechanical and Ocean Engineering
Thesis Supervisor
Accepted by ...........................................................
Rohan Abeyaratne
Chairman, Department Committee on Graduate Theses
2
Extreme Wave Impact on a Flexible Plate
by
Aliza Opila Abraham
Submitted to the Department of Mechanical Engineering
on May 18, 2016, in partial fulfillment of the
requirements for the degree of
Master of Science in Mechanical Engineering
Abstract
This thesis describes the use of a combination of various visual techniques to charac-
terize the flow-structure interaction of a breaking wave impacting a flexible vertically
mounted plate. Several experiments were conducted on a simulated dam break in
which water was rapidly released from a reservoir to generate a wave, which im-
pinged on a cantilevered stainless steel plate downstream. Two high speed cameras
collected data on the water and the plate simultaneously. Manual tracking of the
wave front and Particle Image Velocimetry (PIV) were used to gather water height,
wave speed, crest speed, vorticity, and particle speed, which were used to determine
the pressure exerted by the water on the plate. An algorithm was written to track
the edge of the plate to find plate deflection over time. The dynamic beam bending
equation was used to find the forces experienced by the plate, which were compared
to the pressure results. A series of waves of different heights and breaking locations
were tested, controlled by the ratio of the height of water initially in the tank and
the height of water in the dam break reservoir, for two different plate locations. The
properties of the wave varied depending on these parameters, as did the deflection
of the plate. The plate deformed more and the recorded velocities in the wave were
higherwhenthedepthratiodecreasedandwhentheplatewasmovedfartherfromthe
reservoir. These results shed light on the effect of breaking wave impacts on offshore
structures and ship hulls, taking into account the elasticity of these structures. They
also provide a test case for future numerical fluid-structure interaction simulation
techniques.
Thesis Supervisor: Alexandra H. Techet
Title: Associate Professor of Mechanical and Ocean Engineering
3
4
Acknowledgments
First I would like to thank my advisor, Professor Alexandra Techet for her guidance
throughout my time at MIT. Her encouragement and receptiveness to my ideas gave
me the confidence to try new things and the fortitude to persevere through challenges.
I am indebted to the Office of Naval Research and the MIT Energy Initiative for
providing funding for my master’s degree work. This project would not have been
possible without their support.
I would also like to thank my labmates, Andrea Lehn, Abhishek Bajpayee, and
Leah Mendelson. Andrea, I enjoyed chatting with you at coffee hour every Friday,
and sincerely appreciate your dedication to sustainability. Abhishek, thank you for
taking the time to give me life advice when I wasn’t sure what my next step would be.
Leah, thank you for all of your help throughout my time in this lab, from guidance
while setting up my first PIV experiment to advice about writing my thesis.
Thanks to my friends, at MIT and outside, for celebrating triumphs and com-
miserating about frustrations with me. They have kept my life balanced and fun.
Thanks especially to Jim and Jessica for all of our adventures and for dealing with
that mouse in our apartment.
Much appreciation goes out to my family. I would not be where I am today
without my parents’ endless support. They instilled in me an innate curiosity and
joy of learning that allows me to think big while still staying grounded. My sister
Elana has always been my role model for her outstanding work ethic, integrity, and
ambition, and my brother Joel never ceases to amaze me with his excitement about
the world and his uncanny ability to enchant everyone he meets.
Finally, I want to thank Grace Minix. I cannot overstate my gratitude for her con-
stant, unwavering support and kindness. Her patience and understanding throughout
this process has not gone unnoticed or unappreciated.
5
6
Contents
1 Introduction 17
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.2 Breaking Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.2.1 Onset of Breaking . . . . . . . . . . . . . . . . . . . . . . . . . 18
1.2.2 Types of Breaking Waves . . . . . . . . . . . . . . . . . . . . . 20
1.2.3 Breaking Wave Properties . . . . . . . . . . . . . . . . . . . . 21
1.3 Waves Impacting Structures . . . . . . . . . . . . . . . . . . . . . . . 22
1.3.1 Rigid Structures . . . . . . . . . . . . . . . . . . . . . . . . . . 23
1.3.2 Elastic Structures . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.4 Dam Break . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
1.4.1 Wet Bed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.4.2 Obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1.5 Outline of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2 Experimental Methods 31
2.1 Dam Break Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
2.2 Initiating Wave Breaking . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3 Two-Dimensionality . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.3.1 Pressure Sensor Data . . . . . . . . . . . . . . . . . . . . . . . 35
2.3.2 Top View of Wave . . . . . . . . . . . . . . . . . . . . . . . . 37
2.4 Flow Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4.1 Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
2.4.2 Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
7
2.5 Flow Data Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2.6 Plate Deflection Data . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.6.1 Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2.6.2 Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3 Wave Data and Analysis 47
3.1 Wave Speed and Crest Speed . . . . . . . . . . . . . . . . . . . . . . 47
3.2 PIV Vorticity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
3.3 PIV Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.4 Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
3.4.1 Comparison to Literature . . . . . . . . . . . . . . . . . . . . 62
3.4.2 Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
4 Plate Deflection Results and Analysis 73
4.1 Dependence on Depth Ratio and Plate Location . . . . . . . . . . . . 73
4.2 Comparison to Literature . . . . . . . . . . . . . . . . . . . . . . . . 75
4.3 Velocity and Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.4 Pressure and Deflection . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.5 The Dynamic Beam Bending Equation . . . . . . . . . . . . . . . . . 80
5 Conclusions 83
5.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.3 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
A Additional PIV Figures 87
8
List of Figures
1-1 Katsushika Hokusai’s The Great Wave off Kanagawa [17]. . . . . . . 18
1-2 Three different breaker types: (a) spilling, (b) plunging, and (c) surg-
ing. Adapted from Svendsen (2006) [43]. The current study focuses on
plunging breakers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1-3 Sample time histories of pressure, force, and deflection of a wave im-
pacting an elastic plate. Reprinted from Kirkgöz (1990) [23]. . . . . . 25
1-4 Effect of initial water depth on dam break wave front shape. Reprinted
from Jánosi, et al. [20]. . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1-5 Wavefront velocity as a function of initial downstream water depth
fromvariousexperimental,analytical,andnumericalstudies. Reprinted
from Leal, et al. [27]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
1-6 Normalized median peak pressure at different normalized heights along
a vertical plate impacted by a dam break wave for two different reser-
voir water heights. Reprinted from Lobovsky`, et al. [29]. . . . . . . . 29
1-7 Flexible plate deflection during dam break impact (left) and run-up
(right). Reprinted from Wemmenhove, et al. [45]. . . . . . . . . . . . 29
2-1 Photograph of experimental dam break setup with vertically mounted
plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
2-2 Wave shapes for depth ratios (a) 0.27, (b) 0.23, and (c) 0.21. . . . . . 34
2-3 Pressure sensor placement. . . . . . . . . . . . . . . . . . . . . . . . . 35
2-4 Pressure sensors D, B, and E readings during run-up events of 6 dif-
ferent water heights (reprinted from LaBine [25]). . . . . . . . . . . . 36
9
2-5 Viewofbreakingwavecrestfromabovetodemonstratetwo-dimensionality
of the setup. The green line highlights the leading edge of the wave crest. 37
2-6 Schematic of dam break setup during PIV experiments. . . . . . . . . 39
2-7 PIV video frame before (left) and after (right) masking. Arrows point
to areas that have been masked out. . . . . . . . . . . . . . . . . . . . 41
2-8 The plate deflection processing procedure. The images shown are
(a) the raw image from the camera, (b) the binary image, (c) the
black/whiteboundarieshighlighted,(d)thelargestblack/whitebound-
ary selected as the outline of the wave, (e) the front border selected as
the plate edge, (f) the edge smoothed, and (g) superimposed on the
original image. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
2-9 An example of water splashing across the plate edge through the gap
between the plate and the tank wall, necessitating smoothing in the
plate edge line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2-10 A demonstration of extending the line tracing the plate edge above the
water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
3-1 Observed wave speed mean and standard deviation as a function of
depth ratio 𝛼 compared to Stoker’s [42] analytical solution, as reported
by Leal, et al. [27]. The wave speed is normalized by (𝑔ℎ )0.5. . . . . 48
𝑢
3-2 Ratio of wave crest speed to wave speed in front of the plate for the
two different plate locations. . . . . . . . . . . . . . . . . . . . . . . . 49
3-3 Sample PIV vorticity data before impact for a case with the plate
mounted 84cm from the reservoir exit and 𝛼 = 0.23. The regions of
vorticity observed by Belden [3] are highlighted and the location of the
plate is indicated by a red line. . . . . . . . . . . . . . . . . . . . . . 50
3-4 SamplePIVvorticitydataafterimpactforacasewiththeplatemounted
84cm from the reservoir exit and 𝛼 = 0.23. The regions of vorticity
observed by Crespo, et al. [11] are highlighted and the location of the
plate is indicated by a red line. . . . . . . . . . . . . . . . . . . . . . 50
10