design guideline for stationkeeping systems of floating ......bsee contract e12pc00027 (ta&r 705)...

BSEE Contract E12PC00027 (TA&R 705)

Design Guideline for Stationkeeping Systems of Floating Offshore Wind Turbines

Project Close-out Meeting

ABS Corporate Technology

Offshore Renewables

4 June 2013

Agenda

� Introduction

� Overview of the Project

� Main Research Activities and Deliverables

� Summary and Recommendations

� Comments

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Project Overview

Objectives

� Conduct a state-of-the-art review of the design concepts, methodologies and technologies that are relevant to stationkeeping systems and global performance analyses of floating offshore wind turbines (FOWTs)

� Explore technical challenges and critical design parameters of FOWT stationkeeping systems

� Propose a design guideline for FOWT stationkeeping systems and global performance analyses

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Date Milestones

12 Jun 2012 Kickoff Meeting

9 Jul 2012 Summary report for Task 1: State-of-the-art

review

7 Aug 2012 Summary report for Task 2: Critical design

parameters and knowledge gaps

10 Jan 2013 Summary report for Task 3: Case studies

8 Mar 2013 Draft design guideline for stationekeeping

systems of FOWTs (Task 4)

9 May 2013 Final Report (Task 5)

ABS Project Team - Key Personnel

Project Milestones

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� Dr. Xiaohong Chen – Principal Investigator

� Responsible for all technical development

� Principal Engineer, Offshore Renewables Group, ABS Corporate Technology

� Ph.D., Ocean Engineering, Texas A&M University

� Dr. Qing Yu – Project Coordinator

� Assisting technical development

� Project management and point of contact

� Managing Principal Engineer, Offshore Renewables Group, ABS Corporate Technology

� Ph.D., Mechanical Engineering, Rensselaer Polytechnic Institute

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Main Research Activities and Deliverables

State-of-the-Art Review

� Over 160 publications were reviewed

� The results of state-of-the-art review were categorized into the main technical subjects including:

� Existing design concepts of FOWTs and their stationkeeping systems

� Typical stationkeeping systems for floating offshore oil and gas platforms

� Relevant design codes and standards

� Design and analysis software

� Global performance analysis procedures and methods

� FOWT model testing

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Design Parameters

� Configuration and properties of the floating support structure

� Configuration and properties of the wind turbine RNA

� Environmental conditions

� Electrical network conditions that affect the RNA operations

� Configuration and properties of the stationkeeping system

� Design parameters of the stationkeeping system may also include construction, installation, operation, inspection, maintenance and repair methods and procedures, electrical power cable layout, offshore wind farm configuration, etc.

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What’s Important

� Governing design load cases for FOWT stationkeeping systems

� Aerodynamic loads and damping with consideration of aeroelastic coupling effects

� Coupling effects of floating support structure, wind turbine RNA and its control system, mooring (or tendon) systems, and electrical power cables

� Direction-dependent dynamic responses of the stationkeeping system and the floating support structure

� Influence of the stationkeeping system on the natural frequencies of a floating support structure

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What’s Important (Cont’)

� Actions of turbine’s safety and control systems

� Time scale difference between wind speeds (normally 10 minutes or 1 hour) and storm waves (normally 3 hours)

� Simulation time duration that is sufficient to capture statistics of responses

� Number of realizations (random seeds) that can achieve statistical convergence for FOWTs subjected to both turbulent wind and irregular wave loading

� Wind farm wake effects

� Mooring hardware, material, and connection to hull and anchorages

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Design Challenges

� Leaner designs

� Smaller water plane area to reduce wave loads

� Less or non-redundant stationkeeping system

� Small foot-print of the stationkeeping system in a space-constrained offshore wind farm

� Effect of hull and tower motions on the RNAs

� Interactions of the control system of the wind turbine and motions of the floating support structures

� Serial production and mass deployment in a wind farm

� Availability of reliable design tools

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Case Study - Objectives

� To gain further insights into the dynamic interactions among the turbine, controller, tower, floating hull structure and stationkeeping system

� To study critical design parameters and modeling strategies for stationkeeping system

� To evaluate the relative importance of environmental loading due to wind, wave and current under various turbine design conditions.

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Case Study - Models

� Using the models developed for TA&R 669 and an existing Semi-submersible FOWT concept available in the public domain

� Modified to meet the requirements of the US OCS site conditions considered in this project

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ABS Case Study Model – SEMI FOWT

ABS Case Study Model – TLP FOWT

ABS Case Study Model – SPAR FOWT

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Case Study Model - Spar FOWT

� Reference: Jonkman, 2010, NREL/TP-500-47535

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Case Study Model – Semi-submersible FOWT

� Reference: Robertson, et al., 2012, IEA Wind Task 30 Report

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Case Study Model - TLP FOWT

� Reference: Jonkman and Matha, 2010, NREL/CP-500-46726

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Case Study Model - RNA

� NREL 5-MW Baseline Offshore Wind Turbine (Reference: Jonkman, et al., 2009, NREL/TP-500-38060)

� Tower height and hub height are modified

� Controller is based on the OC3-Hywind concept

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Case Study - Metocean Conditions

� GoM Central Region – API Bulletin 2INT-MET

� OR and ME – NOAA NDBC Buoy Data and Water Level Station Records

OR

Case Study - Load Cases

Turbine Operating Conditions

• Power production

(Vin, Vr, Vout)

• Start-up

• Normal shut-down

• Emergency shut-down

• Parked with fault

• Parked without fault

ME

GoM

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Environmental Conditions

• Operational environmental conditions

• Design storm condition with a return period of 1 year and 50 years

• Storm conditions for the survival (robustness) check

• Wind-Wave directionality (collinear and misaligned with multiple headings)

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Case Study - Simulation Tool

NREL FAST + TAMU Charm3D

Global Performance Analysis Program for the Integrated (“Coupled”) Turbine-Controller-Floater-Mooring Systems

Artistic Images Created by NREL

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Case Study - Analysis Approaches

� Time-Domain (TD) and Frequency-Domain (FD) approaches

� Quasi-static and dynamic mooring analysis methods

� Coupled and uncoupled analysis methods

� Intact and damaged conditions of stationkeeping system

� Wind, wave and current combinations

� Wind, wave and current directionality

� Number of realizations (seeds)

� Length of simulation time for extreme storm cases

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Case Study – Main Results (1)

� Normal Power Production and Parked Conditions

� Power production may result in higher responses than parked turbine in extreme storm conditions.

� Turbine components loads (blade root bending and shaft bending moments) are in general governed by DLC 1.3 (power production) in combination with the extreme turbulent wind model.

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Hull Heel Motion Tower Base Overturning Moment


� Effects of Environment Directionality and Misalignment

� Collinear wind and wave conditions in general result in larger maximum mooring loads and larger platform offsets.

� Misalignment of wind and wave may result in larger maximum platform yaw motion and larger maximum tower base loads, and lower minimum mooring loads.

Hull Offset Minimum Top Line Tension

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� Effects of Return Periods for Parked Turbines

� Ratios of maximum top line tension (500-year / 50-year)

– 1.17 to1.18 (Spar-OR)

– 1.40 to1.42 (Semi-GOM), 1.33 to 1.34 (Semi-OR) and 1.14 to 1.15 (Semi-ME)

– 1.15 to 1.17 (TLP-GOM), and 1.16 (TLP-OR)

Maximum Top Line Tension Maximum Top Line Tension

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� Governing Load Cases

� Maximum mooring line loads are in general governed by parked turbines in extreme 50-year storm conditions (except for Spar-ME).

� Transient events (DLC 1.4, 1.5, 3.x, 4.x and 5.x) may result in higher extreme values than normal power production case (DLC 1.3).

� In general fault conditions (yaw error and blade fault) govern the turbine component loads. However, the fault (i.e. abnormal) conditions have insignificant effects on hull offset and mooring loads.

Maximum Top Line Tension – Semi Maximum Top Line Tension - TLP

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� Relative Importance of Wind, Wave and Current Loads

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� Simulation Time Duration for Extreme Value Prediction

� There are differences in extreme values based on different simulation time durations, but the extreme values are reasonably close.

� Simulation time duration is important for the hull offset and the mooring line tension due to low frequency motions induced by wave drift forces and low frequency wind loads.

� For the operational load cases (for example DLC 1.3), when wind conditions are more important for the design, a 10-minute simulation time duration appears more reasonable.

� For DLC 1.6, both wind and wave conditions are important, 1-hour simulation time duration is recommended.

� For the turbine in the parked conditions and subjected to 1-year, 50year and 500-year return storm conditions, a longer simulation length, for instance 3 hours, is recommended for the global performance analyses.

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� Mooring Fatigue Analysis

� Under the same external conditions, the parked turbine induces more fatigue in the mooring lines than the turbine in power production.

� In the power production conditions, the load case defined by the rated wind speed causes less fatigue damage in the mooring system than the load case with a higher wind speed.

� The accumulation of the mooring fatigue damage due to transient events appears to be insignificant.

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Load Case Wind BIN Possibility Fatigue Life (Years)

(%) Line #1 Line #2 Line #3 Line #4 Line #5 Line #6 Line #7 Line #8

DLC 1.2 Power Production

BIN3 100 1448 1449 3.22E+07 3.68E+07 1148 1148 2.99E+07 3.21E+07

BIN5 100 622 621 4.06E+06 4.70E+06 378 378 4.15E+06 4.33E+06

BIN7 100 198 198 3.33E+05 3.51E+05 139 138 3.23E+05 3.29E+05

BIN9 100 67 66 2.80E+04 2.89E+04 47 47 2.55E+04 2.58E+04

DLC 6.4 Parked (Idling)

BIN3 100 1029 1029 8.82E+07 1.10E+08 972 972 8.66E+07 1.11E+08

BIN5 100 390 390 1.12E+07 1.34E+07 362 362 1.12E+07 1.32E+07

BIN7 100 117 117 8.47E+05 9.34E+05 104 104 8.40E+05 9.71E+05

BIN9 100 42 42 7.01E+04 7.33E+04 37 37 6.48E+04 7.16E+04

BIN11 100 22 22 6.55E+03 6.82E+03 19 19 6.16E+03 6.56E+03


� Tower Flexibility

� Important for tower loads

� Important for natural periods of roll and pitch of TLP FOWT

� No significant effects on hull motions and mooring line loads for Spar or Semi-submersible FOWT with compliant mooring systems

� Effects of Mooring Line Damage

� Important for mooring line loads, hull motions and tower loads

� No significant effects on loads on the parked turbine

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� Semi-coupled Analysis

� Loads due to turbine rotation are not captured

� More appropriate for parked turbines than rotating turbines

� Quasi-static Analysis (no mooring dynamic effect)

� Not adequate for predicting Spar FOWT mooring loads

� Maybe acceptable for predicting Semi-submersible and TLP FOWTs mooring loads

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Design Guideline for FOWT Stationkeeping Systems (1)

� Developed on the basis of

� Research carried out in this project (TA&R 705)

� BSEE TA&R 669 project

� Experience from the wind energy industry

� Common practices of designing stationkeeping systems for offshore oil and gas platforms

� The guideline is intended to be used as a “draft” which is expected be a starting point for developing

� Regulatory requirements

� Industry guideline

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Design Guideline for FOWT Stationkeeping Systems (2)

� Overall design considerations

� Design environmental conditions

� Design load cases and load calculations

� Global performance analysis methods

� Strength and fatigue design criteria of mooring lines and tendons

� Stationkeeping system hardware and material selection criteria

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Exposure Level

� ISO 19904-1 (2006) Definition

� FOWTs are mostly likely to be un-manned and considered in a consequence category equivalent to C2 of ISO 19904-1

� The proposed design criteria are for FOWTs having an exposure level equivalent to the medium (L2) exposure level as defined in ISO 19904-1

L2

C2 medium-consequence

S3 (unmanned)

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Redundant

Non redundant

Survival Load Cases

Redundant orNon redundant

Design Environmental Conditions

IEC 61400-3 Design Environmental

Conditions

Modifications

Based on Common Practice

of Designing Floating Production

Installations

Design Environmental Conditions for

FOWT Stationkeeping

Systems

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Design Loading Conditions

Loading Condition

Redundancy of the Stationkeeping System

Design Condition of the Stationkeeping System

Design Load Cases

Intact

Damaged condition – one broken line

Transient condition – one broken line

- Intact

-Intact

Redundant

Non-Redundant

Survival

Load Cases

Redundant or

Non-redundant

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Redundant

Non redundant 2.0

Survival Load

Cases

Redundant or

Non redundant

Global Performance Analyses

� To determine the global effects of environmental loads and other loads on a floating offshore wind turbine and its components

� Comprehensive guidance is provided to address

� Requirement on the global performance analysis software

� Implementation of various analysis approaches

– Time domain approach vs. frequency domain approach

– Dynamic analysis and quasi-static analysis

– Coupled analysis, semi-coupled analysis, and un-coupled analysis

� Global motion analysis

� Air gap (deck clearance or freeboard) analysis

� Mooring strength and fatigue analysis

� Recommendations for numerical simulations

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Strength Design Criteria for Mooring Lines or Tendons

Loading

Condition

Redundancy of the

Stationkeeping

System

Design Condition of the

Stationkeeping System

Safety

Factor

Design Load

Cases

Intact 1.67

Damaged condition - one broken line 1.25 ??

Transient condition - one broken line 1.05

- Intact

-Intact 1.05

Redundant

Non-Redundant

Survival Load Cases

Redundant or Non-redundant

2.0

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Fatigue Design Criteria for Mooring Lines or Tendons

� Fatigue resistance – applicable classification society criteria or equivalent industry standards

� Fatigue Design Factor (FDF)

� Reference is made to API RP 2T for further guidance on tendons

Inspectable and Repairable

Yes No

3 5

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Anchors

� Criteria for holding capacity

� Drag anchors

� Vertically loaded drag anchors (VLAs)

� Conventional pile anchors (driven, jetted, drilled and grouted)

� Suction pile anchors

� Other anchor types

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Hardware and Material Selection Criteria

� Guidance on design and analysis is referred to API RP 2SK, API RP 2T, ISO 19901-7, class society criteria, or other applicable industry standards

� Design load cases for the strength and fatigue analysis should be in accordance with the proposed design guideline

� For the non-redundant stationkeeping system, a 20% increase should be applied to those safety factors defined for the redundant stationkeeping system

� For the robustness check using the survival load cases as specified, the safety factor should be at least 1.05



Summary & Recommendations

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Summary

� Conducted a state-of-the-art review of technologies relevant to the design of Floating Offshore Wind Turbine (FOWT) stationkeeping systems

� Performed extensive case studies to explore the global response characteristics of typical FOWT conceptual designs with a particular focus on the sensitivity of FOWT global responses to various design and analysis parameters

� Identified important design parameters and technical challenges for the design of FOWT stationkeeping systems

� Proposed a design guideline to provide recommended practices for FOWT stationkeeping systems

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Recommendations for Future Research

� Validation of global performance analysis tools

� FOWT model testing method

� Study on FOWT Design Load Cases (DLCs)

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Responses to the Comments

Comments

� Suction Embedded Plate Anchors (SEPLA) and Dynamically Penetrating Anchors (torpedo anchors)

� Geotechnical design information for anchors

� What is the requirement if the tension check indicates negative tension? Is this check required for both the "intact" and "one tendon removed" case?

� Table 5.2 Survival Load Cases. Please elaborate on the derivation of these load cases and the rationale behind them.

� BOEM feels it would be preferable for the air gap criterion to be met in lieu of designing the facility and components to withstand the local and global wave forces. What arguments are there for allowing this situation to occur?

� Rationale behind development of these DLCs

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www.eagle.org

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design guideline for stationkeeping systems of floating ......bsee contract e12pc00027 (ta&r 705)...

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