Computational fluid dynamics simulation of WEC in focused waves 

Water Power Technologies Office Peer Review 

Marine and Hydrokinetics Program 

Wave Energy Converter Modeling 

FOSWEC wave tank testing and WEC-Sim simulation 

Yi-Hsiang Yu 

National Renewable Energy Laboratory 

yi-hsiang.yu@nrel.gov, 303.384.7143 

February 14–16, 2017 

Washington, D.C.

NREL/PR-5000-68382

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.
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Project Overview 

Wave Energy Converter (WEC) Modeling: 

Empower the advancement of WEC technologies by enabling the efficient, 

accurate prediction of power performance and extreme loading to inform structural 

design and risk reduction through the development and validation of a suite of 

open-source design and analysis tools (WEC-Sim), open-access validation 

datasets, and an extreme condition modeling (ECM) framework and toolbox.

The Challenge: WECs are typically made up of multiple bodies and are designed 

to maximize their relative motion at dominant sea states (as resonant devices), 

resulting in complex nonlinear hydrodynamics, particularly during extreme sea 

states. 

• Uncertainty in predicting WEC performance is increasing the uncertainty for

WEC design optimization and wave energy cost estimation.

• Uncertainty in designing WEC devices to survive extreme conditions is slowing

the pace of technology development and increasing the investment risk.

Partnership 

• National Renewable Energy Laboratory (NREL) (PI: Yi-Hsiang Yu)

• Sandia National Laboratories (SNL) (PI: Kelley Ruehl; CO-PI: Ryan Coe)
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Technology 

Maturity 

Deployment 

Barriers 

Crosscutting 

Approaches 

• Enable access to testing 

facilities that help 

accelerate the pace of 

technology development 

• Improve resource 

characterization to 

optimize technologies, 

reduce deployment 

risks, and identify 

promising markets 

• Exchange of data 

information and 

expertise 

• Identify potential 

improvements to 

regulatory processes 

and requirements 

• Support research 

focused on retiring or 

mitigating environmental 

risks and reducing costs 

• Build awareness of 

MHK technologies 

• Ensure MHK interests 

are considered in 

coastal and marine 

planning processes 

• Evaluate deployment 

infrastructure needs and 

possible approaches to 

bridge gaps 

• Support project 

demonstrations to 

reduce risk and build 

investor confidence 

• Assess and 

communicate potential 

MHK market 

opportunities, including 

off-grid and non-electric 

• Inform incentives and 

policy measures 

• Develop, maintain, and 

communicate our 

national strategy 

• Support development of 

standards 

• Expand MHK technical 

and research 

community 

Program Strategic Priorities 

• Test and demonstrate 

prototypes 

• Develop cost-effective 

approaches for 

installation, grid 

integration, operations 

and maintenance 

• Conduct R&D for 

innovative MHK 

systems and 

components 

• Develop tools to 

optimize device and 

array performance and 

reliability 

• Develop and apply 

quantitative metrics to 

advance MHK 

technologies 

Market 

Development 
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Technology 

Maturity 

• Test and demonstrate prototypes

• Develop cost-effective approaches

for installation, grid integration,

operations, and maintenance

• Conduct R&D for innovative MHK

systems and components

• Develop tools to optimize device

and array performance and

reliability

• Develop and apply quantitative

metrics to advance MHK

technologies

Project Strategic Alignment 

The Impact 

• Provide the WEC industry with a set of

customizable open-source WEC performance

and extreme loading analysis tools/datasets to:

- Reduce WEC design uncertainty, improve

power performance, and improve survivability

in extreme conditions

- Accelerate pace of WEC technology

development with reduced investment risk

• The final products are validated, open-source,

WEC simulation tools, open-access validation

datasets, and documentation. Products can be

used and customized to meet industry needs.
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Develop a set of open-source tools that are validated and customizable to meet users’ 

needs, used to analyze WEC power performance, and predict the extreme loading on the 

system under critical wave environments 

• WEC-Sim code development: Simulate WEC devices comprising rigid bodies (multi-body 

dynamics), power-take-off systems (PTO-Sim), and mooring systems (MoorDyn)

• WEC-Sim validation testing: Perform wave tank test and develop an open-access 

validation dataset 

• ECM workshop and technical meeting: Exchange experience with the WEC community, 

understand current challenges, and investigate potential pathways to solve the challenges 

• ECM framework and WEC Design Response Toolbox (WDRT) development: Include 

relevant toolsets and numerical strategies to more accurately and efficiently evaluate system 

design loads 

• Dissemination and community support: Lead public training courses and webinars, and 

manage online Q&A forums to assist the WEC community’s utilization of models and 

methodologies 

• Industry support projects: Work with industry developers to improve their devices’ power 

performance and survivability by implementing WEC-Sim, the ECM Framework ,and the 

WDRT 

Technical Approach 
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Accomplishments and Progress 

(WEC-Sim) 

WEC-Sim development and release (v1.0 in 2014; v2.1 in 2016) 

Used by the WEC community to simulate WEC dynamics and reduce WEC 

design uncertainty and improve power performance 

• Helped Wave Energy Prize contestants (5/9 of the finalists) to analyze and 

improve their designs during the competition

• Large-scale adoption by industry/academia/researchers domestically and 

internationally, notably: 

Award: 

Won the 2015 International Conference on Ocean, Offshore and Arctic 

Engineering (OMAE) Center for Ocean Energy Research Competition (COER), 

established the team as the world leading modeling expert in the field 

WEC-Sim numerical model of 

the experimental testing 

WEC-Sim win at OMAE COER 

coding competition 
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Accomplishments and Progress 

(WEC-Sim) 

Completed WEC-Sim validation wave tank testing 

• An open-access validation dataset was developed and is 

available via the Marine and Hydrokinetic Data Repository 

• The multi-body WEC testing experience was invaluable 

and will help reduce technical barriers for WEC 

developers during future wave tank testing 

Participating/leading the International Energy Agency Ocean Energy Systems Task 10 

• This task on WEC modeling verification and validation will internationally assess the accuracy and 

establish confidence in the use of numerical models for WECs. 

WEC-Sim training courses/webinars: 

• Four training courses were held at the 2015 International Network on Offshore Renewable Energy 

Symposium, Oregon State University, 2016 Marine Energy Technology Symposium, and the University 

of Maine targeted at engaging and growing WEC-Sim user-community 

• Providing hands-on demonstrations accelerated the learning curve and increased understanding of the 

needs directly from community to incorporate them in the code developmentt 

WEC-Sim experimental testing at 

Hinsdale Wave Research Lab 
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ECM Framework and WEC WDRT: 

• An efficient and risk-based numerical strategy for predicting system 

design load and a set of tools for environmental characterization, 

extreme response statistics, fatigue, and equivalent design wave 

analysis were developed

• The framework and toolbox helps to reduce WEC design uncertainty 

and thereby minimize the investment risk

Industry Support Tasks

• Worked with M3 Wave to identify the cause, and investigate possible 

solutions for, scouring underneath and surrounding the M3 Wave 

device and thereby improve the system’s performance and reliability

• Working presently with Oscilla Power and Ecomerit to analyze their 

WEC’s system design loads

Accomplishments and Progress 

(ECM) 

The ECM workshop (Albuquerque, New Mexico in 2014) 

The ECM workshop was held to review the current state of knowledge on numerical and physical ECM for 

WECs, including knowledge leveraged from other floating and offshore systems, and investigation in to how 

these methodologies could be improved. 

Search for extreme 

events using WDRT 

Computational fluid dynamics simulations of a WEC in focused waves 
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Project Plan and Schedule 

Project Initiation and Completion Dates 

• WEC-Sim development began in FY13 and will end at the end of FY17 

• The ECM project began in Q2 FY14 and will end at the end of FY17 

• Industry FOA support (presented as part of ECM) began in FY16 and will end in FY17

Delayed and Slipped Milestones 

• FY15 Q3 ECM: CFD simulations for the DNV-GL proposed NUWAVE computational fluid dynamics (CFD) 

benchmarking project were canceled due to project suspension by DNV-GL

• FY15 Q3 WEC-Sim: The first phase of the validation wave tank testing was delayed due to contracting 

issues, and was completed in Q1 FY16 

• FY16 Q4 WEC-Sim: The release of the validation wave tank testing data through the MHK-DR was 

delayed due to support for the Wave Energy Prize project, and completed in Q1 FY17 

Go/No-Go Decisions 

• FY15 Q3 WEC-Sim: The WEC-Sim team advised against moving WEC-Sim away from a MATLAB platform 

to a fully open-source platform. Instead, it was recommended that future efforts focus on reviewing and 

adapting numerical modeling methods for novel types of WEC device. 

• FY15 Q3 ECM: The ECM team recommended against an ECM testing campaign in FY16 

• FY16 Q3 ECM: Based on a meeting with DOE HQ, an ECM research plan for FY17 has been outlined 
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Project Budget 

Budget Notes 

• FY16: $100k was transferred from another project as carryover, but is included here as BA 

as it is new funding to the project. 

Project Spending 

• 82% of current project budget has been expended. 

• The budget was split ~50/50 between NREL and Sandia. 

• The budget includes $500k for industry-support projects (Funding Opportunity 

Announcements [FOAs]) 

• These costs include the expense of numerical model development, wave tank testing, highperformance CFD simulation models, and hosting workshops and training classes 

Budget History 

FY2014 FY2015 FY2016

DOE Cost-Share DOE Cost-Share DOE Cost-Share

$1,725k $0 $2,338k $0 $2,314k $0
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Research Integration and 

Collaboration 

Partners, Subcontractors, and Collaborators 

Joint Partnership: NREL and SNL

Subcontracts: Oregon State University, Andrews-Cooper, Penn State Applied Research Laboratory, and 

University of Texas at Austin 

Communications and Technology Transfer 

Open-Source Codes 

• WEC-Sim: Available at https://github.com/WEC-Sim/WEC-Sim. The WEC-Sim site has ~170 unique visits 

per week, and 20+ pull requests (representative of contributions from outside collaborators) since 2014.

• The WEC Design Response Toolbox: Available at https://github.com/WEC-Sim/WDRT 

WEC-Sim Usage from 11/28-12/8 
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Research Integration and 

Collaboration 

Communications and Technology Transfer (Continued) 

Publications, Presentations and Other Technical Meetings 

• Results and accomplishments from the Wave Energy Converter Modeling project have been documented 

in journals and presented at international conferences, including OMAE, International Society of Offshore 

and Polar Engineers, European Wave and Tidal Energy Conference, Marine Energy Technology 

Symposium, IEEE, OCEANS, and IEEE Power & Energy Society, with a total of 20+ publications and 

10+ news articles

• A webinar of the ECM methodology was given for the Marine Energy Council in Q4 FY16 

• A roundtable meeting with researchers from the Office of Naval Research community, NREL, and SNL 

has been scheduled for Q2 FY17 

Industry Feedback 

• From OPT industry support project that utilized WEC-Sim: “Through the collaboration, we were able 

to obtain valuable insight on the performance of some of our float configurations in order to further 

optimize their design and performance in terms of maximizing their wave energy capture”
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WEC-Sim (available at: https://wec-sim.github.io/WEC-Sim/publications.html) 

• Y. Yu, M. Lawson, K. Ruehl, and C. Michelen, “Development and Demonstration of the 

WEC-Sim Wave Energy Converter Simulation Tool,” 2nd Marine Energy Technology 

Symposium, Seattle, WA, 2014. 

• Y. Yu, Y. Li, K. Hallett, and C. Hotimsky, “Design and Analysis for a Floating Oscillating 

Surge Wave Energy Converter,” OMAE 2014, San Francisco, CA, 2014. 

• M. Lawson, Y. Yu, A. Nelessen, K. Ruehl, and C. Michelen, “Implementing Nonlinear 

Buoyancy and Excitation Forces in the WEC-Sim Wave Energy Converter Modeling Tool,” 

OMAE 2014, San Francisco, CA, 2014. 

• K. Ruehl, C. Michelen, S. Kanner, M. Lawson, and Y. Yu, “Preliminary Verification and 

Validation of WEC-Sim, an Open-Source Wave Energy Converter Design Tool,” OMAE 

2014, San Francisco, CA, 2014. 

• M. Lawson, Y.-H. Yu, K. Ruehl, and C. Michelen, “Improving and Validating the WEC-Sim 

Wave Energy Converter Code,” 3rd Marine Energy Technology Symposium, DC, 2015. 

• N. Tom, M. Lawson, and Y. Yu, “Demonstration of the Recent Additions in Modeling 

Capabilities for the WEC-Sim Wave Energy Converter Design Tool," OMAE 2015, St. 

John’s, Newfoundland, Canada, 2015. 

• R. So, A. Simmons, T. Brekken, K. Ruehl, and C. Michelen, “Development of PTO-SIM: A 

Power Performance Module for the Open-Source Wave Energy Converter Code WEC-SIM,” 

OMAE 2015, St. John’s, Newfoundland, Canada, 2015. 

• M. Lawson, B. Garzon, F. Wendt, Y. Yu, and C. Michelen, “COER Hydrodynamics Modeling 

Competition: Modeling the Dynamic Response of a Floating Body Using the WEC-SIM and 

FAST Simulation Tools,” OMAE 2015, St. John’s, Newfoundland, Canada, 2015. 

• N. Tom, M. Lawson, and Y. Yu, “Recent Additions in the Modeling Capabilities for the WECSim-v1.1 Wave Energy Converter Design Tool,” ISOPE, Kona, HI, 2015. 

• R. So, S. Casey, S. Kanner, A. Simmons, and Brekken, T. K. A., “PTO-Sim: Development of 

a Power Take Off Modeling Tool for Ocean Wave Energy Conversion,” IEEE PES, 2015. 

• A. Simmons, T. Brekken, P. Lomonaco, and C. Michelen, “Creating a Dynamometer for 

Experimental Validation of Power Take-Off Forces on a Wave Energy Converter,” IEEE 

SusTech, 2015. 

• A. Combourieu, M. Lawson, A. Babarit, K. Ruehl, A. Roy, R. Costello, P. L. Weywada, and 

H. Bailey, “WEC3: Wave Energy Converters modeling Code Comparison project,” EWTEC 

2015, Nantes, France, 2015. 

• B. Bosma, K. Ruehl, A. Simmons, B. Gunawan, P. Lomonaco, and C. Kelley, “WEC-Sim 

Phase 1 Validation Testing—Experimental Setup and Initial Results,” OMAE 2016, Busan, 

Korea, 2016. 

• K. Ruehl, C. Michelen, B. Bosma, and Y.-H. Yu, “WEC-Sim Phase 1 Validation Testing—

Numerical Modeling of Experiments,” OMAE 2016, Busan, Korea, 2016. 

• Sirnivas S., Yu Y.-H., Hall M., and Bosma B., “Coupled Mooring Analyses for the WEC-Sim 

Wave Energy Converter Design Tool,” OMAE 2016, Busan, Korea, 2016. 

ECM (available at: http://wec-sim.github.io/WDRT/publications.html) 

• R.G. Coe, C. Michelen, A. Eckert-Gallup, Y. Yu and J. van Rij, “WDRT: A Toolbox for 

Design-Response Analysis of Wave Energy Converters,” 4th Marine Energy Technology 

Symposium, Washington, DC, 2016. 

• E. Quon, A. Platt, Y.-H. Yu, and M. Lawson, “Application of the Most Likely Extreme 

Response Method for Wave Energy Converters,” OMAE 2016, Busan, Korea, 2016. 

• A. C. Eckert-Gallup, C. J. Sallaberry, A. R. Dallman, and V. S. Neary, “Application of 

Principal Component Analysis (PCA) and Improved Joint Probability Distributions to the 

Inverse First-Order Reliability Method (I-FORM) for Predicting Extreme Sea States,” Ocean 

Engineering 112, 307–19, 2016. 

• C. Michelen, and R. Coe, “Comparison of Methods for Estimating Short-Term Extreme 

Response of Wave Energy Converters, ” IEEE OCEANS 2015, Washington, D.C., 2015. 

• Y.-H. Yu, J. Van Rij, R. G. Coe, and M. Lawson, “Development and Application of a 

Methodology for Predicting Wave Energy Converters Design Load,” OMAE 2015, St. Johns, 

Canada, 2015. 

• A. C. Eckert-Gallup, C. J. Sallaberry, A. R. Dallman, and V. S. Neary, “Modified Inverse 

First Order Reliability Method (I-FORM) for Predicting Extreme Sea States,” Tech. Rep. 

SAND2014-17550, Sandia National Laboratories, Albuquerque, NM, 2014. 

• R. Coe, V. Neary, M. Lawson, Y.-H. Yu, and J. Weber, “Extreme Conditions Modeling 

Workshop Report," Tech. Rep. NREL/ TP-5000-62305 SNL/ SAND2014-16384R, 2014. 

• R. G. Coe, and V. S. Neary, “Review of Methods for Modeling Wave Energy Converter Survival 

in Extreme Sea States,” 2nd Marine Energy Technology Symposium, Seattle, WA, 2014.

Research Integration and Collaboration 

List of Project Publications 
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Next Steps and Future Research 

FY17/Current Research 

WEC-Sim: Cultivate a broader WEC-Sim user/developer base and transfer ownership of WEC-Sim, including 

future developments and code maintenance, to industry developers and academic researchers to provide a 

well-validated foundation for the future technology innovation needs

ECM

• Perform design load case studies to formulate a cohesive repeatable methodology for ECM analysis that 

can be adopted by the WEC community

• Complete industry support FOA projects with reliable and survival analyses of the awardee WECs to help 

them accelerate the technology development by minimizing the design-loading uncertainty and potential 

deployment risk and establishing confidence to move the design concept forward

Educational Organization Support

• Work with universities and student organizations to establish an organization, and funding method, for 

supporting ocean renewable energy–related education in the United States 

Proposed Future Research 

• Lightweight composites, flexible materials, and innovative power take-offs and mooring designs are 

potential for WEC developers to further reduce levelized cost of energy and increase reliability 

• To address the needs to look into these multi-physics challenges, modeling approaches are proposed: 

 Simplified multi-physics design optimization models

 Coupling of numerical and physical modeling

 High-fidelity CFD/finite element analysis models to capture complex nonlinear phenomena 

Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly 

owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security 

Administration under contract DE-AC04-94AL85000. 

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the 

National Renewable Energy Laboratory. Funding for the work was provided by the DOE Office of Energy 

Efficiency and Renewable Energy, Wind and Water Power Technologies Office