NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Experimental Wave Tank Test 

for Reference Model 3 FloatingPoint Absorber Wave Energy 

Converter Project

Y.-H. Yu, M. Lawson, and Y. Li

National Renewable Energy Laboratory

M. Previsic and J. Epler

Re Vision Consulting

J. Lou

Oregon State University

Technical Report

NREL/TP-5000-62951

January 2015
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Experimental Wave Tank Test 

for Reference Model 3 

Floating-Point Absorber Wave 

Energy Converter Project 

Y.-H. Yu, M. Lawson, and Y. Li

National Renewable Energy Laboratory

M. Previsic and J. Epler

Re Vision Consulting

J. Lou

Oregon State University

Prepared under Task No. WA14.1A01 

Technical Report

NREL/TP-5000-62951

January 2015
NOTICE

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Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

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or favoring by the United States government or any agency thereof. The views and opinions of authors

expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

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Cover Photos: (left to right) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 

16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721.

NREL prints on paper that contains recycled content. 
iii

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Acknowledgments

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-

GO28308 with the National Renewable Energy Laboratory and Contract No. DE-AC04-94-

AL85000 with Re Vision Consulting, LLC, through a subcontract with Sandia National 

Laboratories. Funding for this work was provided by the DOE Office of Energy Efficiency and 

Renewable Energy, Wind and Water Power Technologies Office.
iv

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List of Acronyms

FPA floating-point absorber

PTO power take-off

RAO response amplitude operator

RM reference model

WEC wave energy converter
v

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Executive Summary

The U.S. Department of Energy established a reference model (RM) project to benchmark a set 

of marine and hydrokinetic technologies including current (tidal, open-ocean, and river) turbines 

and wave energy converters. The objectives of the project were to 1) evaluate the status of these

technologies and their readiness for commercial applications, and 2) assess the potential cost of 

energy and identify cost-reduction pathways and areas where additional research could be best 

applied to accelerate technology development to market readiness.

This report is an addendum to SAND2013-9040: Methodology for Design and Economic 

Analysis of Marine Energy Conversion (MEC) Technologies and describes the experimental 

wave tank tests conducted during the RM3 floating-point absorber (FPA) wave energy converter 

study. In the RM3 project, three sets of experimental wave tank tests were conducted to study 

FPA wave energy converter systems during both operational and extreme sea states. The 

specifications are listed in Table ES-1. The first set of wave tank tests focused on a locked FPA, 

which did not include a power take-off system, and analyzed the hydrodynamics of an FPA 

during extreme wave (survival) conditions. The second and third sets of tests evaluated the FPA 

power output during operational wave environments. The objective of this report is to provide 

experimental data sets for validating numerical simulation studies of wave tank tests. The wave 

tank test settings, model dimensions and properties, and post-processed data sets—including the 

measured wave environment, hydrodynamic response, and the estimated power output—are 

documented.

Table ES-1. Specifications of the Wave Tank Tests

Test 

Number Type Model Scale Date Wave Tank Note

1 Locked-point 

absorber 1/100 10/2010

University of 

California at

Berkeley

Tested a locked FPA system (no 

power take-off); focused on 

extreme waves

2 Heave-only power 

performance 1/33 8/2011

University of 

California at

San Diego

Tested the power performance of 

a two-body heave-only FPA 

system

3

Mooring-connected 

power 

performance

1/33 11/2011

University of 

California at

San Diego

Tested the power performance of 

a two-body FPA system with a 

larger diameter float and mooring 

connections
vi

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table of Contents

1 Introduction........................................................................................................................................... 1

2 Test #1: Locked FPA Wave Tank Test................................................................................................ 2

2.1 Tank Test Setup............................................................................................................................. 2

2.2 Wave Tank Test Results................................................................................................................ 5

3 Test #2: Heave-Only FPA Power Performance Test.......................................................................... 8

3.1 Tank Test Setup............................................................................................................................. 8

3.2 Wave Tank Test Results................................................................................................................ 9

4 Test #3: Moored FPA Power Performance Test............................................................................... 12

4.1 Tank Test Setup........................................................................................................................... 12

4.2 Wave Tank Test Results.............................................................................................................. 14

5 Summary.............................................................................................................................................. 17

References................................................................................................................................................. 18
vii

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List of Figures

Figure 1. Schematic of the wave tank at the University of California at Berkeley....................................... 2

Figure 2. Locked FPA wave tank test and instrumentation setup. Photo by Ye Li, NREL 20118................. 2

Figure 3. Mooring line configuration (clockwise from top): side view, top view, and snapshot. Photo by 

Ye Li, NREL 20117................................................................................................................... 3

Figure 4. Schematic of the locked FPA model ............................................................................................. 4

Figure 5. Decay test time histories for the heave (top) and pitch (bottom) responses at full scale (scaled by 

the initial displacement and rotational angle) .......................................................................... 6

Figure 6. Heave (top), surge (middle), and pitch (bottom) RAOs for the locked FPA (scaled by the wave 

height) ...................................................................................................................................... 7

Figure 7. Schematic of the wave tank at the Scripps Institution of Oceanography at the University of 

California at San Diego............................................................................................................ 8

Figure 8. Heave-only FPA wave tank test. Photos by Yi-Hsiang Yu, NREL ................................................ 8

Figure 9. Schematic of the heave-only FPA testing model (model scale).................................................... 9

Figure 10. Relative heave RAO for the heave-only FPA at full scale ........................................................ 11

Figure 11. Power output for the heave-only FPA at full scale.................................................................... 11

Figure 12. Moored FPA power performance test setup. Photos (clockwise from left) by Mike Lawson, 

Mike Lawson, and Yi-Hsiang Yu............................................................................................ 12

Figure 13. Schematic of the two-body FPA (in inches).............................................................................. 13

Figure 14. PTO design: (a) configuration schematic, (b) hydraulic piston, and (c) orifice design inside the 

piston. Illustrations from Previsic, Shoele, and Epler 2014 .................................................. 14

Figure 15. Relative heave RAO of the model at full scale.......................................................................... 16

Figure 16. Power output of the model at full scale ..................................................................................... 16

List of Tables

Table ES-1. Specifications of the Wave Tank Tests..................................................................................... v

Table 1. Specifications of the Wave Tank Tests........................................................................................... 1

Table 2. Mooring Line Configuration (Model Scale)................................................................................... 3

Table 3. Properties of the FPA Model (Model Scale)................................................................................... 4

Table 4. Matrix for the Locked FPA Tank Test (Full Scale)........................................................................ 5

Table 5. Mass Properties for the Heave-Only Testing Model (Model Scale)............................................... 9

Table 6. Matrix for the Heave-Only FPA Power Performance Tank Test (Full Scale).............................. 10

Table 7. Mooring Line Configuration (Model Scale)................................................................................. 12

Table 8. Mass Properties for the Moored Testing Model (Model Scale).................................................... 13

Table 9. Matrix for the Moored FPA Power Performance Tank Test (Full Scale)..................................... 15
1

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

1 Introduction

The U.S. Department of Energy established a reference model (RM) project to benchmark a set 

of marine and hydrokinetic technologies including current (tidal, open-ocean, and river) turbines 

and wave energy converters (WECs). The project’s objectives were to 1) evaluate the status of 

these technologies and their readiness for commercial applications, and 2) assess the potential 

cost of energy and identify cost-reduction pathways and areas where additional research could be 

best applied to accelerate technology development to market readiness.

In the RM3 floating-point absorber (FPA) project, a series of experimental wave tank tests was 

performed to understand the hydrodynamic and power performance of FPA wave energy 

converter systems. Researchers from the National Renewable Energy Laboratory and Re Vision 

Consulting performed three sets of experimental wave tank tests (the specifications are shown in 

Table 1). The first set tested a locked FPA (no relative motion of the two main bodies), which 

did not include a power take-off (PTO) system, and analyzed the hydrodynamics of an FPA 

during extreme wave (survival) conditions. The second and third sets of the wave tank tests

evaluated the FPA power output during operational wave environments. 

Table 1. Specifications of the Wave Tank Tests

Test 

Number Type Model Scale Date Wave Tank Note

1 Locked-point 

absorber 1/100 10/2010

University of 

California at

Berkeley

Tested a locked FPA system (no 

PTO); focused on extreme waves

2 Heave-only power 

performance 1/33 8/2011

University of 

California at

San Diego

Tested the power performance of 

a two-body heave-only FPA 

system

3

Mooring-connected 

power 

performance

1/33 11/2011

University of 

California at

San Diego

Tested the power performance of 

a two-body FPA system with a 

larger diameter float and mooring 

connections

The model designs and levelized cost of energy estimations for the RM3 project were described 

in Methodology for Design and Economic Analysis of Marine Energy Conversion (MEC) 

Technologies (Neary et al. 2014). The objective of this report is to provide experimental data sets 

that can be useful for validating numerical simulation studies. Preliminary use of this data was

presented in Previsic, Shoele, and Epler 2014; Ruehl et al. 2014; Yu et al. 2014a and 2014b; and 

Yu and Li 2013. The following sections of this report present the wave tank and test article setup 

and measured results for each set of the experimental tests. For consistency, all results are 

presented in full scale, except for the model dimensions and properties and test settings.
2

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2 Test #1: Locked FPA Wave Tank Test

The locked FPA wave tank test was conducted at the University of California at Berkeley in 

December 2010. The test focused on extreme wave condition analysis. Because the FPA system 

generally has a survival mode that locks the float to the central column during an extreme wave 

environment, we designed the testing model as a single rigid body without a PTO representation.

This section presents the tank test setup and the measured testing model response.

2.1 Tank Test Setup

The dimensions of the wave tank at the University of California at Berkeley are plotted in Figure 

1, and the experimental setup is shown in Figure 2.

Figure 1. Schematic of the wave tank at the University of California at Berkeley

Figure 2. Locked FPA wave tank test and instrumentation setup. Photo by Ye Li, NREL 20118
3 

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The wave tank was designed to test ships and large offshore structures but was not intended to 

test moored floating systems, therefore four metal piles were installed on the tank’s sidewalls 

(two piles on each side) to attach the mooring lines. As shown in Figure 3, the FPA device was 

connected to eight mooring lines, and each mooring line was connected to a metal pile on the 

sidewall. These eight lines were located in two layers, and each layer had four lines in the 

configuration of a cross. The properties of the mooring settings are given in Table 2. 

 

Figure 3. Mooring line configuration (clockwise from top): side view, top view, and snapshot. 

Photo by Ye Li, NREL 20117 

Table 2. Mooring Line Configuration (Model Scale) 

Mooring Settings 1/100-Scale Model 

Top layer connection 0.05 meters (m) below mean free surface 

Bottom layer connection 0.10 m above the damping plate 

Spring stiffness ≈ 0.7 Newton (N)/m (each line) 

 
4

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To test the system during extreme wave conditions (large wave height scenarios), the test was 

conducted using a 1/100-scale model because of the tank’s limited wave-making capability. 

Figure 4 shows the geometry and dimensions of the testing model, and its mass properties are 

listed in Table 3. Note that the mass of the models listed in the table includes the mass of the 

device and the target plate for the motion tracking system. 

Figure 4. Schematic of the locked FPA model

Table 3. Properties of the FPA Model (Model Scale)

Model Properties 1/100-Scale Model

Center of gravity 0.23 m below mean free surface

Moment of inertia for pitch 7.22 grams (g)*m2

Mass 313 g

Researchers placed an analog wave gauge 5.2 meters (m) upstream of the FPA to measure the 

incoming wave height. Next, we attached a plate with passive markers (that could be targeted by 

the motion-tracking system) to the buoy, whereas the surge, heave, and pitch motions were 

captured by the two-dimensional motion-tracking system, which was installed next to the wave 

tank.
5

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2.2 Wave Tank Test Results

Table 4 provides the test cases for the locked FPA wave tank trials, including heave and pitch

decay tests (no mooring and no incoming wave) and regular wave tests, where the model was 

connected to the mooring system. The testing model root-mean-square (RMS) response values in 

heave, surge, and pitch at the center of gravity and the measured wave heights and wave periods 

are also listed in Table 4. Although the tank test focused on extreme wave conditions (design 

wave heights of 9 m and 15 m at full scale), wave tank tests with a wave height of about 3 m

(full scale) were also conducted for reference purposes. 

Table 4. Matrix for the Locked FPA Tank Test (Full Scale)

Decay Test

Heave decay Initial displacement was 2 m

Pitch decay Initial pitch angle was 5.7 degrees

Regular Waves

Test 

Number

Measured 

Wave Height

Meters (m)

Measured 

Wave Period

Seconds (s)

Measured 

RMS Surge

(m)

Measured 

RMS Heave

(m)

Measured 

RMS Pitch

Radian (rad)

1 3.07 17.52 2.81 3.44 0.14

2 3.21 15.02 2.72 3.43 0.14

3 3.24 12.42 2.51 4.23 0.10

4 3.11 10.18 1.13 4.10 0.04

5 3.02 9.38 1.05 3.72 0.06

6 3.04 8.70 1.43 2.87 0.07

7 3.01 7.50 1.51 2.26 0.08

8 9.37 17.58 8.50 11.09 0.26

9 9.74 14.88 7.18 10.56 0.22

10 9.73 12.46 4.74 8.53 0.08

11 9.61 11.22 3.07 5.68 0.11

12 8.75 10.18 2.86 4.48 0.14

13 9.16 9.53 3.30 3.67 0.16

14 8.92 8.86 3.68 3.15 0.16

15 15.67 17.58 13.82 14.96 0.27

16 15.52 14.76 12.02 11.49 0.18

17 15.47 12.53 7.32 8.96 0.11

18 15.17 11.12 5.72 6.34 0.10

19 14.63 10.25 5.06 4.98 0.11

20 13.97 9.47 4.24 3.94 0.12

21 13.32 8.84 3.70 2.79 0.12

In the heave decay test, the FPA device was lifted with an initial displacement of Hin=0.02 m 

(model scale). In the pitch decay test, the device was initially rotated with an angle of αin=5.7 

degrees, whereas the initial displacement in surge was minimized. The time histories of the 

heave and pitch response (α) in the decay test are plotted in Figure 5.
6

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Figure 5. Decay test time histories for the heave (top) and pitch (bottom) responses at full scale

(scaled by the initial displacement and rotational angle)

For the tests in regular waves, the response amplitude operators (RAOs) were calculated from 

five oscillations. To analyze the trend in the hydrodynamic response of the locked model, 

particularly during the extreme waves, we plotted the RAOs for the designed 9-m and 15-m 

wave scenarios and the third-order polynomial regressions against the wave frequency, as shown 

in Figure 6.
7

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Figure 6. Heave (top), surge (middle), and pitch (bottom) RAOs for the locked FPA (scaled by the 

wave height)
8 

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3 Test #2: Heave-Only FPA Power Performance Test 

This set of experimental wave tank tests was conducted at the Scripps Institution of 

Oceanography at the University of California at San Diego during August 2011. This section 

presents the test setup and results from the first power performance wave tank test. 

3.1 Tank Test Setup 

Figure 7 shows the settings and dimensions of the wave tank. Instead of connecting the testing 

model to the mooring lines, a carriage-connected heave guide was used so that the testing model 

was constrained to move in heave only. 

Figure 7. Schematic of the wave tank at the Scripps Institution of Oceanography at the University 

of California at San Diego 

Figure 8 shows the experimental setup for the wave tank tests. A miniature hydraulic cylinder in 

a closed hydraulic circuit with a needle valve provided damping to the relative motion to 

represent the PTO system, and the PTO force was measured using a load cell. The potentiometer 

was used throughout the tests to record the relative motion between the float and reaction plate. 

The linear potentiometer measurements were also validated by a camera tracking system, which 

consisted of five cameras that were arranged in a semicircle around the model. 

Figure 8. Heave-only FPA wave tank test. Photos by Yi-Hsiang Yu, NREL

A 1/33-scale testing model was used in the study. The dimensions and model properties are 

shown in Figure 9 and Table 5. 
9

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Figure 9. Schematic of the heave-only FPA testing model (model scale)

Table 5. Mass Properties for the Heave-Only Testing Model (Model Scale)

Component Mass (kg)

Float

A. Float 3.220

D. Top roller 0.115

E. Bottom roller 0.117

Spar/plate

B. Central column 0.745

C. Damping plate 1.108

F Cylinder and clamps 0.205

H. Load cell 0.012

I. Needle valve 0.015

J. Linear pot (short) 0.077

K. Linear pot (long) 0.114

Not on the testing model G. Heave guides 0.116

3.2 Wave Tank Test Results

Table 6 lists the test cases and measured results for the heave-only FPA power performance trials 

in regular waves with a wave height of 2.5 m (full scale), a range of wave periods, and PTO

damping coefficients. 
10

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Table 6. Matrix for the Heave-Only FPA Power Performance Tank Test (Full Scale)

Test 

Number

Measured 

Wave Height

(m)

Measured 

Wave Period

(s)

Measured RMS 

Relative Motion

(m)

Avg. Power 

Output

Kilowatts 

(kW)

Estimated PTO 

Damping Coefficients

kilonewton-seconds

per meter (kNs/m)

1 2.54 7.91 1.37 154.42 1,041.05

2 2.58 10.08 0.93 62.91 1,511.14

3 2.45 12.03 0.74 27.59 1,460.76

4 2.55 10.05 1.13 75.98 1,209.57

5 2.56 10.07 1.13 78.78 1,257.87

6 2.58 7.94 1.52 193.87 1,067.16

7 2.50 5.92 0.69 68.57 1,034.33

8 2.53 5.98 0.62 67.30 1,254.14

9 2.66 8.00 1.47 184.99 1,116.68

10 2.57 10.02 1.04 75.53 1,430.68

11 2.50 11.93 0.69 27.04 1,642.75

12 2.71 14.05 0.53 14.51 2,028.18

13 2.53 11.82 0.71 30.75 1,729.45

14 2.54 11.85 0.67 30.55 1,911.97

15 2.55 10.06 1.02 77.36 1,525.51

16 2.61 7.87 1.28 195.19 1,501.80

17 2.55 5.97 0.54 56.93 1,425.26

18 2.54 5.97 0.45 48.82 1,707.77

19 2.64 8.02 1.19 196.14 1,814.67

20 2.61 10.01 0.90 76.79 1,919.40

21 2.53 11.89 0.60 27.66 2,209.27

22 2.53 11.94 0.48 21.96 2,791.55

23 2.54 10.00 0.79 69.67 2,288.26

24 2.64 7.95 0.94 175.19 2,549.57

25 2.61 6.01 0.36 39.32 2,181.83

26 2.64 8.01 1.43 148.71 939.85

The power output was calculated as the product of the PTO force and the relative velocity 

between the float and the reaction plate, as in

P = FPPP × urrr

where P is the power, FPTO is the measured PTO force, and urel is the relative velocity between 

the float and spar/plate. The averaged power was calculated as the integration of the 

instantaneous power over time divided by the relevant signal duration, after the transient 

response had damped out and only the steady-state response remained. The PTO damping was 

adjusted by turning the needle valve of the hydraulic circuit. Note that the PTO forces from the 

tank test showed a higher force on the compression stroke than the extension stroke and needle 
11

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valve PTO design did not provide a linear constant damping coefficient for each case. For 

simplicity, we estimate the averaged PTO damping coefficient by assuming that the relative 

motion is close to a harmonic function, which gives

CPPP = 2P

(ωArrr)2

where Arel is the measured amplitude of the relative motion between the float and the spar/plate 

and ω is the incident wave frequency.

For PTO damping coefficients between 1,500 kilonewton-seconds per meter (kNs/m) and 2,000 

kNs/m, we plotted the relative heave motion between the float and spar/plate and the calculated 

power output (scaled by H2) against wave frequency in Figure 10 and Figure 11, respectively. 

Third-order polynomial regressions were used to represent the trend of the relative motion and 

power output with respect to the wave frequency.

Figure 10. Relative heave RAO for the heave-only FPA at full scale

Figure 11. Power output for the heave-only FPA at full scale
12

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4 Test #3: Moored FPA Power Performance Test

Like the heave-only FPA power performance test, the moored FPA power performance test was 

conducted at the Scripps Institution of Oceanography at the University of California, San Diego. 

This experimental wave tank test took place during November 2011. This section presents the

test setup and results from the second power performance wave tank test.

4.1 Tank Test Setup

Figure 12 shows the experimental setup for this wave tank test. The testing model was connected 

to a set of four mooring lines (Table 7) and each mooring line was connected to one of four 

metal piles located on the sidewall. This mooring setup was similar to that used in the locked 

FPA wave tank test; however, only four mooring lines (single layer) were used for this study

rather than the eight mooring lines (two layers) used in the locked FPA wave tank test conducted 

at the University of California at Berkeley.

Figure 12. Moored FPA power performance test setup. Photos (clockwise from left) by Mike 

Lawson, Mike Lawson, and Yi-Hsiang Yu

Table 7. Mooring Line Configuration (Model Scale)

Mooring Settings 1/33-Scale Model

Connect to Spar/plate

Connection location ≈ 0.5 m below mean free surface

Spring stiffness ≈ 0.06 kN/m (each line)
13

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The dimensions and mass properties of the (1/33-scale) FPA testing model are presented in 

Figure 13 and Table 8. The mass properties included the mass of the device structure and ballast. 

We assumed that both the float and center spar with plate were located at their equilibrium 

positions.

Figure 13. Schematic of the two-body FPA (in inches)

Table 8. Mass Properties for the Moored Testing Model (Model Scale)

Component Mass (kg) Center of 

Gravity (m)

Diagonal Moment of Inertia 

at the Center of Gravity (kgm2

)

Float 20.23 [0,0,–0.022] [0.53,0.54,0.95]

Spar/plate

Reaction plate and column 12.38

[0,0,–0.65] [3.5,3.5,0.73]

Spar ballast 9.70

PTO 3.24

Linear pot 0.08

Figure 14 shows a schematic of the PTO design used in the tank test. A hydraulic piston with 

multiple orifices was used to represent the PTO in the tank test. The orifices could be opened and 

closed to control the PTO damping to the system. The PTO was placed inside the column with 

the top end of the cylinder approximately 25 cm below the column top. We used a 0.4-

kilonewton (kN) load cell responding only to axial tension and compression to measure the PTO 

damping. Note that the PTO damping from the orifice design was still nonlinear. Nevertheless, 

the orifice design provided better control of the damping coefficient, so the damping would not 

be influenced by the flow around the model caused by the model motion and incoming waves.
14

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Figure 14. PTO design: (a) configuration schematic, (b) hydraulic piston, and (c) orifice design 

inside the piston. Illustrations from Previsic, Shoele, and Epler 2014

4.2 Wave Tank Test Results

Table 9 shows the test case and measured results from the moored FPA power performance wave 

tank test during regular waves with a target wave height of 3 m (full scale) and a range of wave 

periods. The tank test was performed for a range of PTO damping coefficients to maximize the 

design power output. The power output was calculated by multiplying the PTO force with the 

relative velocity between the float and reaction plate following the equation presented in the 

heave-only FPA power performance test section. 

To analyze the power output and the relative heave motion between the float and spar/plate, the 

selected results were grouped into two sets of PTO damping coefficients and plotted against the 

wave frequency, as shown in Figure 15 and Figure 16. The lower value set ranged from 2,000

kNs/m to 2,500 kNs/m, and the higher set ranged from 6,100 kNs/m to 8,100 kNs/m. Third-order 

polynomial regressions were also used to represent the trend of the relative motion and power 

output.
15

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Table 9. Matrix for the Moored FPA Power Performance Tank Test (Full Scale)

Test 

Number

Measured 

Wave Height

(m)

Measured 

Wave Period

(s)

Measured RMS 

Relative Motion

(m)

Avg. Power 

Output

(kW)

Estimated PTO 

Damping Coefficients

(kNs/m)

1 2.89 8.01 1.29 445.61 3,454.43

2 2.91 7.99 0.66 278.29 8,173.09

3 2.85 12.06 2.10 190.65 1,272.97

4 3.04 13.95 2.10 118.00 1,051.02

5 2.89 12.03 2.21 90.31 541.00

6 2.86 12.04 2.18 128.40 793.36

7 3.02 8.01 1.34 502.35 3,662.68

8 3.04 11.97 1.94 446.37 3,456.58

9 3.06 17.93 1.71 103.46 2,302.43

10 3.13 18.05 1.00 104.18 6,920.91

11 2.88 10.02 1.37 561.70 6,100.71

12 3.10 12.02 1.63 554.08 6,119.01

13 2.92 12.04 1.40 538.16 8,080.95

14 3.04 14.00 1.43 357.54 6,954.87

15 2.99 17.91 1.19 109.53 4,992.32

16 3.07 8.02 1.65 538.58 2,577.32

17 2.89 10.05 1.99 467.75 2,425.97

18 2.88 8.97 1.97 632.07 2,645.85

19 2.90 10.98 2.09 410.75 2,306.68

20 2.93 12.00 2.08 319.47 2,143.78

21 2.88 16.05 2.08 138.80 1,667.15

22 3.01 10.99 1.36 592.16 7,845.68

23 2.96 12.08 1.47 563.34 7,738.28

24 3.06 13.97 1.48 368.81 6,703.53

25 3.00 17.88 1.25 113.82 4,751.38

26 3.03 7.99 1.69 543.60 2,471.90

27 3.07 10.04 2.07 498.45 2,378.72

28 3.06 10.96 2.12 410.95 2,228.63

29 2.90 11.97 2.11 314.56 2,056.72

30 3.01 14.05 2.07 184.12 1,723.74

31 2.85 16.03 2.10 134.85 1,590.63

32 2.96 8.01 2.12 494.30 1,436.86

33 2.99 17.91 2.13 50.06 718.62
16

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Figure 15. Relative heave RAO of the model at full scale

Figure 16. Power output of the model at full scale
17

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

5 Summary

This report is a supporting document for the RM project report (Neary et al. 2014), and it

describes the experimental wave tank tests conducted during the RM3 floating-point absorber 

wave energy converter study. As part of that project, three sets of experimental wave tank tests 

were conducted to study FPA wave energy converter systems during both operational and 

extreme sea states. This report documents the wave tank test setup, model dimensions and 

properties, and the analyzed data sets. The analyzed data sets include a list of test cases,

hydrodynamic response, and the estimated power output.
18

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

References 

Neary, V.S.; Previsic, M.; Jepsen, R.A.; Lawson, M.J.; Yu, Y.-H.; Copping, A.E.; Fontaine, 

A.A.; Hallett, K.C.; Murray, D.K. (2014). Methodology for Design and Economic Analysis of 

Marine Energy Conversion (MEC) Technologies. Albuquerque, New Mexico: Sandia National 

Laboratories.

Previsic, M.; Shoele, K.; Epler, J. (2014). “Validation of Theoretical Performance Results Using 

Wave Tank Testing of Heaving Point Absorber Wave Energy Conversion Device Working 

Against a Subsea Reaction Plate.” Second Marine Energy Technology Symposium Proceedings;

August 15–18, 2014, Seattle, Washington.

Ruehl, K.; Michelen, C.; Kanner, S.; Lawson, M.; Yu, Y.-H. (2014). “Preliminary Verification 

and Validation of WEC-Sim, an Open-Source Wave Energy Converter Design Tool.” 33rd 

International Conference on Ocean, Offshore and Arctic Engineering Proceedings; June 8–13, 

2014, San Francisco, California. New York: American Society of Mechanical Engineers.

Yu, Y.-H.; Lawson, M.; Ruehl, K.; Michelen, C. (2014a). “Development and Demonstration of 

the WEC-Sim Wave Energy Converter Simulation Tool.” Second Marine Energy Technology 

Symposium Proceedings; August 15–18, 2014. Seattle, Washington.

Yu, Y.-H.; Li, Y. (2013). “Reynolds-Averaged Navier-Stokes Simulation of the Heave 

Performance of a Two-Body Floating-Point Absorber Wave Energy System.” Computers & 

Fluids (73); pp. 104–114.

Yu, Y.-H.; Li, Y.; Hallett, K.; Hotimsky, C. (2014b). “Design and Analysis for a Floating 

Oscillating Surge Wave Energy Converter.” 33rd International Conference on Ocean, Offshore 

and Arctic Engineering Proceedings; June 8–13, 2014, San Francisco, California. New York: 

American Society of Mechanical Engineers.