Tsunami Design UH SP11

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Dept. of Civil and Environmental Engineering Instructors: Michelle H. Teng (UH)

University of Hawaii at Manoa H. Ronald Riggs (UH)

Alicia Lyman-Holt (OSU)

Dan Cox (OSU)

TA: Krishna Lamichhane

Spring 2011 Project Period: March 8 April 26, 2011

CEE320 FLUID MECHANICS

Design Project on Tsunami Impact on Coastal Structures

(Adapted from the lab manual by Prof. Dan Cox at the Oregon State University)

Objectives

The objectives of this lab are to introduce the basics of the tsunami hazard and the fluid mechanics

equation for estimating the fluid load on structures as well as the basic structural analysis for designing

safe buildings to resist the fluid loading. In addition, we will also learn about the state-of-the-art facilities

at the tsunami wave laboratory at the Oregon State University (OSU) funded by the National Science

Foundation (NSF). Each team will build a small shelter model and the models will be shipped to OSU to

be tested in a large wave flume. Specifically, the models will be placed on an artificial beach and then a

tsunami wave will be generated by a wave maker. After the tsunami wave hits the shelter models, we will

observe the wave impact on each model through tele-observation at UH. This lab encourages us to

develop team working skills and creative thinking.

Tsunami Hazard

Tsunamis can be generated by undersea earthquakes, landslides, volcano eruptions and impact by

asteroids. Undersea earthquakes are the most common causes for tsunamis. Tsunamis generated by

powerful earthquakes of magnitude 8-9 can travel across a large ocean such as the Pacific Ocean and

impact on shorelines thousands of miles away from the original earthquake locations. These tsunamis arecalled distant tsunamis. Tsunamis generated by landslides or earthquakes of smaller magnitude are

usually less powerful and can cause damage only to coastal regions close to the landslide or earthquake

source. These tsunamis are called local tsunamis. Tsunamis are extremely long waves. In the open deep

ocean, the wavelength of a tsunami can be as long as several hundred kilometers while the amplitude of

the tsunami is usually very small (less than a 1m). When a tsunami reaches a coastal region where the

water depth decreases, the wavelength will become shorter while the amplitude can become much larger

causing severe damage to coastal structures, natural environment and loss of human lives. The

propagation speed c of a tsunami depends mainly on the water depth h and can be approximated by

ghc = . In the Pacific Ocean with an average water depth of about 4000-5000 m, tsunamis can travel

as fast as 800 km/hr. If a large tsunami is generated in Japan, it will take the tsunami about 7 hours to

reach Hawaii. For a tsunami generated in Chile, the traveling time to Hawaii is about 15 hours.

Being in the middle of the Pacific Ocean, Hawaii is especially vulnerable to tsunami attacks. During the

last century, Hawaii experienced several large tsunami events including the 1946 Aleutian tsunami, 1952

Kamchatka tsunami, the 1957 Aleutian tsunami, the 1960 Chilean tsunami and the1964 Alaskan tsunami.

The 1946 and 1960 tsunamis caused significant property damage in Hawaii and claimed more than 200

human lives especially in Hilo Bay on the Big Island. Even though we have not had a significant tsunami

attack in Hawaii since the 1960s, earthquake- and landslide-generated tsunamis have been active in other

parts of the Pacific basin. During the decade of 1990s alone, there were 10 tsunamis occurred and more


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than 4000 people lost their lives in these tsunamis including during the 1998 Papua New Guinea tsunami.

The most disastrous tsunami attack in the recent history is the 2004 Indian Ocean tsunami which killed

more than 200,000 people.

(1) (2)

(3) (4)

Figure 1. Tsunami damage to coastal communities. (1) 1946 Aleutian tsunami in Hawaii; (2) 1946

Aleutian tsunami in Hawaii; (3) 1960 Chilean tsunami in Hawaii; (4) 2004 Indian Ocean tsunami.

Proper warning can help to reduce the loss of human lives significantly especially for distant tsunamis.

However, for local tsunamis, the arrival time is extremely short. For example, if a tsunami is generated

near the Big Island, it will reach Oahu within 30 minutes. In this situation, we may not have sufficient

time to evacuate all the people from the inundation zone to a higher ground far from the beach. We may

need to use vertical evacuation instead. Vertical evaluation means moving people to the higher floors of


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the buildings located right inside the inundation zone. This requires that the engineers design and

construct sufficiently strong buildings to serve as shelters inside the inundation zone during tsunami

attacks.

Theoretical Background

Figure 2 shows a schematic sketch of tsunami inundation and impact on a structure such as a vertical

column. In this figure, His the offshore tsunami height, dis the flow depth at the structure, Uis the speed

of the tsunami as it flows past the structure, and L is the height of a single column.

Figure 2. Schematic sketch of the tsunami inundation problem for this project showing offshore and

onshore tsunami conditions. For the onshore inundation, the tsunami can be considered as a wall of

water with flow depth d. For this problem assume that the flow depth is larger than the column height L.

Figure 3 shows a schematic sketch of the idealized tsunami water force on a single column of length L.

For simplicity, we assume that the fluid drag force acts uniformly over the column and can be replaced

by a single drag force acting on the center of the column, FD. The drag force creates an overturningmoment equal to the product of the drag force times half the column length (MD = FD*L/2). This

overturning moment is resisted by the moment at the base of the column, M0, which depends on the

material properties of the column and foundation. When the drag force creates a moment that exceeds the

maximum resistive capability of the column, MD>(M0)crit, the structure fails.

Figure 3. Definition sketch for water force on a column (left) and free body diagram (right).


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In general, when a fluid is flowing around a solid body, the body will experience a total net force Fr

which is the fluid load on the body. This force depends on the fluid velocity, the shape and size of the

body and the fluid properties such as density and viscosity. Traditionally, we decompose the total force

into two components: the drag force FD, defined as the component of the force parallel to the direction of

the fluid flow, and the lift force FL,, defined as the component of the force perpendicular to the flow

direction. The lift force is usually important only when the solid body has a non-symmetrical shape orwhen the fluid flows towards the body with an attack angle. For this project, as for many civil

engineering applications, we will ignore the lift force and focus on the more important drag force.

The drag force by the fluid flow on a body can be estimated by the following equation:

AUCF DD2

2

1= (1)

where the dimensionless CD is called the drag coefficient, is the fluid density, and A is the projected

area of the body perpendicular to the flow direction. For example, if the body is a vertical square column,

then A equals to the column height times the column width.

Figure 4. Sketch of a fluid flow passing a solid object

The following table gives the drag coefficient values for flow passing around a circular column, and two

rectangular columns with different orientations to the flow direction.

Table 1. Drag Coefficient Values for Different Types of Columns


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Experimental Facility

To study tsunami propagation and inundation on coastal land experimentally, we usually need a wave

tank or a wave basin with a wave maker. In our CEE department at UH, there is a wave tank in the

hydraulics lab where we can conduct small-scale experiments on tsunamis. The tank is about 40 ft long, 4

ft wide and 3 ft deep. A photo of the wave tank with an artificial beach is shown in Figure 5.

Figure 5. The wave tank in the UH CEE Hydraulics Lab.

At the Oregon State University, there is a much larger wave basin which is funded by the National

Science Foundation. This basin is 48 m long, 26 m wide and 1.5 m deep. The wave maker can generate a

tsunami wave of maximum amplitude of 1 m. A larger facility can simulate wave conditions closer to

reality compared with a smaller facility. Figure 6 shows a photo of the basin. There are several videocameras mounted around the basin and the video images can be viewed by researchers at remote sites

through the internet connection.

Figure 6. The tsunami basin at the Oregon State University.


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In addition, there is also a large concrete wave flume being operated in the same wave laboratory at OSU.

This flume is 104 m long, 3.7 m wide and 4.6 m deep. It is also equipped with a computer controlled

wavemaker and all the necessary instruments including wave gages and video cameras. For this particular

project, the experiments will be done in the large wave flume at OSU. Figure 7 shows a photo of the

large wave flume.

Figure 7. The large wave flume at the Oregon State University.

Tasks, Supplies and Schedule

Task 1: Engineering Calculation and Testing of a Single Column

For the first part of this laboratory, we will use equation (1) and figures 2 and 3 to determine what

tsunami condition would cause the failure of a single vertical column in the experiment. The column that

we will use for the testing is provided in the construction kit for the project. Table 2 and the notes below

give us the information that we will need to complete the required engineering calculations. Note that for

this project, we will model both the wave height and the structural dimensions at a 1:50 scale.


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Table 2. Information on the tsunami conditions for this project

Offshore Onshore Calculations Observations

Field Lab Lab Lab FD M0 Failure? Failure?

Tsunami

Condition

H (m) H (cm) d (cm) U (m/s) (N) (N m)

1 7.5 15 5 1.64

2 10 20 14 2.96

3 15 30 22 4.47

Drag coefficient: CD = 1.5-2.0

Projected area of the single column: A = 5.8 cm2

Maximum moment for the column: (M0)crit= 0.05 N m (obtained from previous lab tests on the wood

material and foundation connection at OSU)

Task 2: Engineering Design and Testing of a Platform Shelter

The second part of this project involves the design of a tsunami shelter. The purpose of this shelter is toprovide an elevated platform for people to use as an evacuation shelter. The shelter has to be strong

enough to survive a 15 m high tsunami (offshore) with a local flow depth and flow speeds given in table

2. We need to optimize our design to get the maximum number of people out of harms way with a fixed

number of building pieces. Our structure will be designed, built, and tested at 1:50 scale, meaning all of

the lengths are 50 times smaller that real life. The water speed is 7.07 times smaller than real life. The

building materials are provided in the construction kit. Reserve one column for testing in Task 1.

After we complete both our engineering calculations and our design, mount a single column apart from

our structure in a way that the flow, when the structure is being tested, will be unobstructed (put it to the

side of the shelter, not behind the shelter). This single column will be used to test how well our theory

and observations matched.

Supplies the Construction Kit

Figure 8 shows a photo of the building materials supplied by OSU. We can use only the materials

supplied to construct the platform shelter model. The connections between columns and wall plates

should be made by using the double-sided Scotch tape. The structure should be mounted to the base

plate also using the tape. Please do not use nails or screws for any of the connections. When mounting

the structure to the base plate, please make sure that we leave at least a one- inch margin along all edges.


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Figure 8. The construction kit.

Schedule

Table 3. Schedule for this Project

Date Tasks

March 8, 10 Introduction and discussion about the project; distribution of

construction kits; in Holmes Hall 287March 9 April 11 Each team calculate, design and build the platform shelter

April 12 Each team submit the shelter model

April 14 All shelter models will be shipped to OSU

April 26 Both sections will tele-observe the testing ay the OSU

together in Holmes Hall 287

May 3 Group report due; electronic file in Word

Report Contents

1. Search the internet and find information on historical tsunamis including the 2004 Indian OceanTsunami. From the information and especially any photos showing coastal impact by tsunamis,

summarize which types of buildings survived the tsunamis well and which types did not. Include

photo evidence in the report;

2. Complete Table 2 and report the results;3. Explain the ideas behind your design of the platform shelter. Is an elevated platform a viable

engineering solution to tsunami evacuation?

4. Show sketches of your design of other types of structures that you think may also work well asshelters in the inundation zone during a tsunami attack. Explain the reasoning behind the design.

Tsunami Design UH SP11

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