D.5.1 – NOVEL MOORING COMPONENTS PERFORMANCE

D.5.1 – NOVEL MOORING COMPONENTS PERFORMANCE AND DURABILITY

University of Exeter (UNEXE)

Lead authors: Chenyu Zhao (UNEXE), Pete Halswell (UNEXE), Lars Johanning (UNEXE) & Philipp Thies

(UNEXE)

Contributors: Giovanni Rinaldi (UNEXE), Juanjo De La Cuesta (FF), Paul Mc Evoy (TFI), Conor Casey

(TFI)

FLOTANT - Innovative, low cost, low

weight and safe floating wind

technology optimized for deep water

wind sites, has received funding from

the European Union´s Horizon 2020

research and innovation programme

under grant agreement No.815289

Deliverable 5.1 Test of mooring components

FLOTANT has received funding from the European Union´s Horizon 2020

research and innovation programme under grant agreement No.815289

Doc.Nº: 210701-FLT-WP5_D-5-1_v2 Date: 28/07/2021

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The FLOTANT Project owns the copyright of this document (in accordance with the terms described

in the Consortium Agreement), which is supplied confidentially and must not be used for any

purpose other than that for which it is supplied. It must not be reproduced either wholly or partially,

copied or transmitted to any person without the authorization of PLOCAN. FLOTANT is a

Cooperation Research Project funded by the European Union´s Horizon 2020 research and

innovation programme. This document reflects only the authors’ views. The Community is not

liable for any use that may be made of the information contained therein.

[Deliverable 5.1 – Novel mooring components performance and durability]

Project Acronym: FLOTANT

Project Title: Innovative, low cost, low weight and safe floating wind technology optimized for deep

water wind sites (FLOTANT).

Project Coordinators: Ayoze Castro – The Oceanic Platform of the Canary Islands (PLOCAN)

Programme:H2020-LC-SC3-2018

Topic: Developing solutions to reduce the cost and increase performance of renewable

technologies

Instrument: Research & Innovation Action (RIA)

Deliverable Code: 210728-FLT-WP5_D_5.1-v_2

Due date: 310721





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DISSEMINATION LEVEL

PU: Public x

PP: Restricted to other programme participants (including the Commission

Services)

RE: Restricted to a group specified by the consortium (including the Commission

Services)

CO: Confidential, only for members of the consortium (including the Commission

Services)

DOCUMENT HISTORY

Edit./Rev. Date Name

Prepared 01/05/21 Chenyu Zhao /Giovanni Rinaldi (UNEXE)

Checked 10/05/21 Pete Halswell (UNEXE)

Checked 30/06/21 Philipp Thies (UNEXE)

Approved 14/07/21 Lars Johanning (UNEXE)

Approved 28/07/21 Rubén Durán (COBRA)/ Alejandro Romero-Filgueira and

Ayoze Castro (PLOCAN)

DOCUMENT CHANGES RECORD

Edit./Rev. Date Chapters Reason for change

UNEXE/0 01/05/21 All Original Version

UNEXE/1 14/07/21 1.2;1.2.2; 1.3.1;

3.2; 3.2.1; 3.2.1.1;

3.3

Internal review process

UNEXE/2 28/07/21 All Consolidated version





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DISTRIBUTION LIST

Copy no.

Company/

Organization

(country)

Name and surname

1 PLOCAN (ES) Ayoze Castro, Alejandro Romero-Filgueira

2 UNEXE (UK) Lars Johanning, Philipp Thies, Giovanni Rinaldi, Chenyu Zhao

3 UEDIN (UK) Henry Jeffrey, Anna García-Teruel, Anup Nambiar

4 AIMPLAS (ES) Ferrán Martí, Blai López, Maria Algarra

5 ITA-RTWH (DE) Thomas Koehler, Dominik Granich, Oscar Bareiro

6 MARIN (NL) Erik-Jan de Ridder

7 TFI (IE) Paul McEvoy

8 ESTEYCO (ES) Lara Cerdán, Javier Nieto, Carlos Cortés, Ángeles Ortega

9 INNOSEA (FR) Rémy Pascal, Hélène Robic, Florian Surmont, Jordi Serret

10 INEA (SI) Igor Steiner, Aleksander Preglej, Marijan Vidmar

11 TX (UK) Sean Kelly

12 HB (UK) Ian Walters

13 FULGOR (EL) George Georgallis, Konstantinos Grivas, Anastasia Moraiti

14 AW (HR) Mateo Prsic, Miroslav Komlenovic

15 FF (ES) Bartolomé Mas, Juanjo De La Cuesta

16 COBRA (ES) Sara Muñoz, Rubén Durán, Gregorio Torres

17 BV (FR) Claire-Julie , Jonathan Boutrot, Jonathan Huet, Jimena Reachi





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Acknowledgements Funding for the FLOTANT project (Grant Agreement No. 815289) was received from the EU

Commission as part of the H2020 research and Innovation Programme.

The help and support, in preparing the proposal and executing the project, of the partner

institutions is also acknowledged: Plataforma Oceánica de Canarias (ES), The University of

Exeter (UK),The University of Edinburgh (UK), AIMPLAS-Asociación de Investigación Materiales

Plásticos y Conexas (ES), Rheinisch-Westfaelische Technische Hochschule Aachen (DE),

Stichting Maritiem Research Instituut Nederland (NL), Technology From Ideas Limited (IE),

Esteyco SA (ES), Innosea (FR), Inea Informatizacija Energetika Avtomatizacija DOO (SI),

Transmission Excellence Ltd (UK), Hydro Bond Engineering Limited (UK), FULGOR S.A.,

Hellenic Cables Industry (EL), Adria Winch DOO (HR), Future Fibres (ES), Cobra Instalaciones y

Servicios S.A (ES), Bureau Veritas Marine & Offshore Registre International de Classification de

Navires et eePlateformes Offshore (FR).





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Executive summary This report presents the test methodology and results to study the performance and durability of the

novel mooring components (termed the mooring cable and the polymer spring) developed in the

FLOTANT project. Following the ISO 17920:2015 test procedures the quasi-static and dynamic stiffness

values are measured. The component durability is assessed using the Thousand Cycle Load Limit (TCLL)

test. Two representative modelled sea states (for sites in Gran Canaria and West of Barra) are also studied

to evaluate the in-situ performance.

The test of the mooring cable includes two parts. In the Part I, the three 20Tn mooring cable samples

delivered in WP2 (D2.3) were tested, and their performance and durability were measured. The stiffness

of mooring cable samples is approximately 5 ± 0.3 kN/mm. The change of the stiffness is not significant in

the bed-in assessment. The final break loads of all samples, 207 kN with 11.2 kN Std. Dev., were very

closed to the designed MBL (196.2 kN). These results show very good uniformity between the

performance and durability of the three mooring cable samples. Two samples failed suddenly, and the

carbon fibres broke near the cable terminal; one sample failed less suddenly as individual carbon fibres

failed. The good results obtained in the fatigue tests depicted that not the antifouling and antibite

additives nor the embedment of optic fibre sensors within the line affect the cables’ performance as their

break strength after the tests met with the design break strength.

In the part II, first a detailed analysis was performed on the results obtained from the Fibre Optic sensors

installed on the cables. This study relied on one of the samples’ two of the three sensor-lines containing

three strain sensors each which were the only lines that reached the testing stage. The sensors

survivability was very low due to damages during cables’ manufacturing mainly. These sensors’ output,

though, provided stable and accurate results between the sensors at each line (0.9% - 2.3% deviations),

between the sensors from the two lines (3% deviation) and with the load output from the testbench (2.3%

deviation). The temperature sensor provided a stable measurement without significant changes due to

the test conditions.

Secondly, the part II also presents the tests and results from the 100Tn mooring line demonstrator

delivered in WP2 (D2.4) which was tested in ultimate tensile conditions. This sample broke at 69.8 Tn (a

30.2% below the objective). Also, the stiffness of the cable was over a 40% below target depicting a

manufacturing defect. The deviation in stiffness tells that the construction of the cable was not the correct

one and the individual carbon fibre rods were not working together, which lead to the reduction in break

strength too. This issue was not observed with the 20Tn samples that were produced in the same batch

and using the same raw materials. Hence, the 100Tn sample will be repeated with a reviewed

manufacturing process to ensure the cable meets with the targets. This sample will include also improved

fibre optic sensors to cope with the low strength of these observed in all the samples.

During the mooring spring test, two samples were tested. The stiffness is approximately 1± 0.2 kN/mm

and no significant changes were observed during the bedding-in assessment. The length creep of the

polymer spring was detected and more obvious with a higher load. The first sample began to fail during

the TCLL 60% case and failed completely in the TCLL 70% case. Analysis of the polymer cracks showed

quality control issues in the moulding process; these issues caused crack propagation during the testing.

An additional spring sample (sample 2) was subjected to some TfI specific characterisation and bedding

in before running through an accelerated TCLL test regime. To speed up the testing process the 10-50%,

and 10-60% TCLL tests were rolled into the 10-70% tests by adding an additional 215 cycles. The second

sample was subjected to the 10%-70% TCLL case (1215 cycles) and 10-80% TCLL case (2000 cycles). A shell

snap through was observed on the second polymer spring where one shell inverted from one stable shape

to another, this issue has been identified and is being addressed.





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TABLE OF CONTENTS

Acknowledgements ............................................................................................ 5

Executive summary ............................................................................................ 6

1 INTRODUCTION......................................................................................... 12 1.1 TASK 5.1 SCOPE ............................................................................................... 12 1.2 TEST FACILITY .................................................................................................. 13

1.2.1 Dynamic Marine Component (DMaC) ........................................................................... 13

1.2.2 Future Fibres’ 100 Tn Tensile Testbed ......................................................................... 14

1.3 NOVEL MOORING COMPONENTS ..................................................................... 15

1.3.1 MOORING CABLE .......................................................................................................... 15

1.3.2 POLYMER SPRINGS ...................................................................................................... 17

2 TEST PROCEDURE ...................................................................................... 18 2.1 STANDARDS AND INDUSTRY PRACTICES ........................................................... 18

2.1.1 ISO/TS 17920:2015 ......................................................................................................... 19

2.1.2 THOUSAND CYCLES LOAD LEVEL (TCLL) ................................................................. 20

2.1.3 SEA STATES TIME-SERIES........................................................................................... 21

2.2 TEST PLANS ..................................................................................................... 21

3 RESULTS .................................................................................................... 23 3.1 MOORING CABLE (Part I) .................................................................................. 23

3.1.1 ISO/TS 17920: 2015 ........................................................................................................ 24

3.1.2 STATES TIME-SERIES ................................................................................................... 26

3.1.3 TCLL ................................................................................................................................ 27

3.2 MOORING CABLE (PART II) ............................................................................... 31

3.2.1 20T Mooring demonstrators’ dynamic testing – Sensor’s output ............................. 31

3.2.2 100T Mooring demonstrator strength testing.............................................................. 37

3.3 MOORING CABLE CONCLUSIONS ...................................................................... 40 3.4 POLYMER SPRINGS .......................................................................................... 40

3.4.1 ISO/TS 17920: 2015 ........................................................................................................ 41

3.4.2 STATES TIME-SERIES ................................................................................................... 46

3.4.3 TCLL (sample 1) ............................................................................................................. 47

3.4.4 TCLL (Sample 2) ............................................................................................................. 50

3.4.5 Discussion ...................................................................................................................... 52

REFERENCES ...................................................................................................... 54

ANNEX 1 ............................................................................................................ 56 DMaC Calibration .................................................................................................... 56 Future Fibres 100 Tn Testbed Calibration .................................................................. 59





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LIST OF FIGURES

Figure 1. DMaC test facility. View from the headstock. ............................................................ 13

Figure 2. DMaC test facility. View from the tailstock................................................................ 14

Figure 3. Schematic illustration of DMaC test facility. .............................................................. 14

Figure 4. Future Fibres’ 100T tensile testbed. ........................................................................ 15

Figure 5. From left to right: Bundle of carbon rods - End resin cone technology. ...................... 16

Figure 6. Mooring cable section view.Standard carbon fibre-epoxy rods .................................. 16

Figure 7. Pin eye fitting of the hybrid mooring cable. ............................................................... 16

Figure 8. The layout of connections between test samples and DMaC ....................................... 17

Figure 9. Polymer springs renderings. ...................................................................................... 18

Figure 10. The layout of connections between test samples and DMaC ..................................... 18

Figure 11. Example of input load time series showing bedding-in (B.3.1, left), quasi-static (B.3.5.2)

and dynamic (B.3.5.3) loading, and break testing (B.3.1, right). ................................................ 19

Figure 12. TCLL procedure illustration (5 illustrated cycle is proportional to 1000 test cycles) [12].

................................................................................................................................................. 20

Figure 13: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, mooring

cable (a) BA2 (b) BA5 ............................................................................................................. 24

Figure 14: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA1 to BA7,

mooring cable sample 3 ............................................................................................................ 24

Figure 15: Load vs total elongation of ISO/TS 17920:2015 B.3.5.2 quasi-static stiffness test for

mooring cable sample 3. ........................................................................................................... 25

Figure 16: Load vs total elongation of ISO/TS 17920:2015 B.3.5.3 (F4 - 30-40% MBL) for mooring

cable sample 3. ......................................................................................................................... 26

Figure 17: Time vs total elongation under sea state of Gran Canaria, mooring cable ................ 27

Figure 18: Time vs total elongation under sea state of West of Barra, mooring cable ................ 27

Figure 19: Load vs total elongation of TCLL 50%, 1000 cycles, mooring cable ......................... 28

Figure 20: Load vs total elongation of TCLL 60%, 1000cycles, mooring cable .......................... 28

Figure 21: Load vs total elongation of TCLL 70%, 1000cyles , mooring cable .......................... 29

Figure 22: Load vs total elongation of TCLL 80%, 2000cyles, mooring cable ........................... 29

Figure 23: Load vs total elongation of break test of ISO/TS 17920:2015 ................................... 30

Figure 24: The failure of all three samples; sample 1 (bottom), 2 (middle) and 3 (top). ............. 30

Figure 25: Mooring line demonstrators – Sensors’ architecture. ............................................... 31

Figure 26 20T_03. TCLL60% TEST. OPTIC SENSORS’ STRAIN AND TEMPERATURE

RESULTS. ............................................................................................................................... 32






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RESULTS. DETAIL (I). ............................................................................................................ 33


RESULTS. DETAIL (II). ........................................................................................................... 33

Figure 29 20T_03. TCLL60% TEST. OPTIC SENSOR LINE 2. STRAIN RESULTS. DETAIL.

................................................................................................................................................. 34


................................................................................................................................................. 34

Figure 31 20T_03. TCLL60% TEST. OPTIC SENSORS’ LOAD RESULTS. DETAIL (I). ...... 35

Figure 32 20T_03. TCLL60% TEST. OPTIC SENSORS’ AND LOADCELL LOAD RESULTS.

DETAIL (II). ............................................................................................................................. 35

Figure 33 20T_03. TCLL70% TEST. OPTIC SENSORS’ STRAIN RESULTS. DETAIL (I). ... 36

Figure 34 20T_03. TCLL80% TEST. OPTIC SENSOR LINE 2. STRAIN RESULTS. ............ 36

Figure 35 100T. UTS TEST. LOADCELL AND OPTIC SENSOR’S TEMPERATURE RESULTS

(I). ............................................................................................................................................ 37

Figure 36 100T. UTS TEST. LOADCELL RESULTS (II). ....................................................... 38

Figure 37 100T. UTS TEST. LOADCELL AND STRAIN RESULTS (I). ................................. 39

Figure 38 100T. CABLE RESULT AFTER TEST. END DETAIL. ........................................... 39

Figure 39: Sample 1 Polymer Spring in DMaC ......................................................................... 40

Figure 40: Sample 2 Polymer Spring prior to delivery to DMaC............................................... 41

Figure 41: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA1, polymer

spring, sample 1 ....................................................................................................................... 41


spring, sample 1 ....................................................................................................................... 42


spring sample 1 ........................................................................................................................ 42


spring sample 1 ........................................................................................................................ 43


spring sample 1 ........................................................................................................................ 43

Figure 46: Load vs total elongation of ISO/TS 17920:2015 B.3.5.2 quasi-static stiffness test,

polymer spring sample 1 .......................................................................................................... 44

Figure 47: Load vs total elongation of ISO/TS 17920:2015 B.3.5.3 F3 dynamic stiffness test,






Figure 50: Time vs total elongation under sea state of Gran Canaria, polymer spring sample 1 47

Figure 51: Time vs total elongation under the sea state of West of Barra, polymer spring sample 1





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................................................................................................................................................. 47

Figure 52: Load vs total elongation of TCLL 10 to 50% (1000 cycles) polymer spring sample 1 48

Figure 53: Load vs total elongation of TCLL 10 to 60% (1000 cycles) polymer spring sample 1 48

Figure 54: Final TCLL test. Load vs stroke elongation of TCLL 10 to 70% polymer spring sample

1 ............................................................................................................................................... 49

Figure 55: Example of a radial crack on a polymer shell (sample 1). ......................................... 49

Figure 56: Sample 2 prior to starting testing in DMaC ............................................................. 50

Figure 57: The polymer spring sample 2 on completion of the TCLL testing. ........................... 51

Figure 58: Load vs stroke elongation of TCLL 10 to 70% polymer spring sample 2, Stroke means

the stroke of the hydraulic ram ................................................................................................ 51

Figure 59: Load vs stroke elongation of TCLL 10 to 80% polymer spring, sample 2 ................. 52

Figure 60: Frequency of Stress Ranges in the operating Sea State ............................................ 53

Figure 61: Estimated S/N Curve ............................................................................................... 54

LIST OF TABLES

Table 1. Test plan for the mooring cable (Part I). ..................................................................... 21

Table 2.Test plan for the polymer spring assembly. .................................................................. 22

Table 3 Bed-in Assessment of ISO/TS 17920:2015 B.3.1 ............................................................ 25

Table 4: The stiffness of the quasi-static stiffness test and dynamic stiffness of mooring cable

sample 3 ................................................................................................................................... 26

Table 5: Bed-in Assessment of ISO/TS 17920:2015 B.3.1, polymer spring sample 1. ... 44

Table 6: The stiffness of the quasi-static stiffness test and dynamic stiffness of polymer

spring sample 1. .................................................................................................................... 46





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Abbreviation table

MSA Mooring Shock Absorber

DMaC Dynamic Marine Component Test facility

TRL Technology Readiness Level

MBL Minimum Breaking Load

ISO International Standardisation Organisation

TCLL Thousands Cycles Load Level

CTF Number of Cycles to Failure

TLL Test Load Level at which CTF occurred

FBG Fibre Bragg grating

FO Fibre Optic

GFRP Glass Fibre Reinforced Polymer

NBL Nominal Breaking Load

MWL Maximum Working Load

UTS Ultimate Tensile Strength





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1 INTRODUCTION

The development of innovative components for offshore renewable energy systems involves,

among other processes, the experimental validation of the proposed concepts (i.e. prototype

testing). International standards and industry practices, eventually adjusted through experts’

elicitation, are used to this end. The main objective of FLOTANT Task 5.1 (Physical tests for novel

mooring components) was to conduct laboratory performance and durability testing of the novel

mooring shock absorber (MSA). The MSA is constituted by two main components: a cable made

of standard carbon fibre-epoxy rods, and a metal assembly with polymer springs for passive load

management. In order to advance the MSA towards full-scale commercial development it is

essential to characterise the performance and durability of these novel component. As such, in

order to validate the physical properties of these two components, testing activities consisted in:

- Undertaking prototype testing of the novel MSA; and

- Assessing the durability of the novel MSA through endurance testing.

The goal of these activities was to i) quantify and demonstrate the critical performance

characteristics of the MSA components and ii) understand the durability of the MSA components

and enable confidence in their lifetime performance.

UNEXE has the capability to test large-scale mooring systems under controlled laboratory

conditions, emulating realistic motions and loads. The purpose-built test rig, the Dynamic Marine

Component Test facility (DMaC), aims to replicate the forces and motions that components are

subjected to in offshore applications. The bench test is based on advances made during

Technology Readiness Level (TRL) 3/4 (prototype testing), allowing to de-risk the integration of

MSA components at future TRLs. In particular, durability criteria of the full-scale specimens were

assessed with a view towards future certification for the tether endurance.

In this deliverable, the testing activities conducted within FLOTANT Task 5.1 are detailed,

together with outcomes of the experiments. In the next sections, the scope of the task and the

test facility used for prototype testing are described. Thus, details and specifications of the novel

mooring components constituting the MSA system are provided. Next, the test procedures

defined according to international standards and best practices in the industry are provided with

the arranged test plans. Finally, results of the tests are provided, and their implications in view of

future developments discussed.

1.1 TASK 5.1 SCOPE

In order to gain confidence in the development towards commercialization of the novel mooring

components through experimental testing, three subtasks are identified within Task 5.1.

▪ Subtask 5.1.1: The critical performance characteristics are quantified and demonstrated

for the MSA, identifying to what extent sudden peak loads can be reduced in comparison

to a conventional mooring rope. Available load data from numerical simulations of the

implemented mooring system, including sudden peak loads, are replicated on the DMaC

test rig. This yields a displacement signal for the given sea state which serves as input

signal for testing a large-scale prototype of the MSA. This procedure allows to quantify

the stiffness and damping (hysteresis) characteristics of the MSA which are measures of

the effectiveness to reduce peak loads.

▪ Subtask 5.1.2: In order to be confident in the reliable and durable operation of the MSA

in extreme sea states, it is essential to test the components’ ability to withstand cyclic

loads in constant or varying rate without premature deterioration. Thus, the following tests





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are proposed: i) Test to quantify the full load-extension curve before and after every main

test run ii) a combination of load cycles that relate to a wave group (e.g. five waves) and

a scenario with high pre-tensions (reflecting storm conditions with high drift forces) iii)

Realistic storm sea conditions as scaled 3h test. The durability tests are carried out as

accelerated tests with increased stress intensity and load frequency. These tests aim to

accelerate the fatigue on the component to deliver confidence that its lifetime will be

acceptable.

▪ Subtask 5.1.3: In order to assess/quantify the scalability of the new materials used for the

carbon fibre mooring cables, 100T NBL mooring samples are tested at the facilities of

Future Fibres. Cable of 100 tons strength and 5 meters. Sensors will be also embedded

into the cable structure for its continuous stress/strain monitoring (Task 2.5). This sample

will be tested for production repeatability of ultra-high strength cables (FF). Linked to T2.2

Polymer Carbon Fibre Mooring Cables development and fabrication process.

1.2 TEST FACILITY

1.2.1 Dynamic Marine Component (DMaC)

The Dynamic Marine Component (DMaC) test facility, shown in Figure 1 and Figure 2, is a

purpose-built test rig designed to replicate the forces and motions, as well as the dynamic and

fatigue loads, that offshore components typically experience in-service. The main components of

the facility are hydraulically powered headstock and tailstock for the application of user-defined

(harmonic or irregular) loads. The tailstock can apply tension and compression forces or

displacements. The headstock can apply bending moments (torque) and angular displacements

in three degrees of freedom (roll, pitch, and yaw). This unique feature is particularly useful for the

testing of subsea components which are subjected to bending or torsion at one end (like mooring

cables, umbilical and risers). Additionally, the DMaC has been designed so that the components

being tested can be fully submerged in fresh water. A drawing of DMaC components and their

working principle is shown in Figure 3.

Figure 1. DMaC test facility. View from the headstock.





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Figure 2. DMaC test facility. View from the tailstock.

Figure 3. Schematic illustration of DMaC test facility.

The rig is capable of replicating dynamic tensile forces up to 20 t, static tensile forces up to 40

tonnes, and displacements up to 1 m. The maximum bending angle at the headstock is ±30º for

pitch and roll with up to 10 kN·m of bending moment. The maximum torque or yaw is 10 kN·m

with an infinite rotational displacement. A complete description of DMaC, together with the full

specifications and examples of past project, can be found at http://emps.exeter.ac.uk/renewable-

energy/facilities/dmac.

1.2.2 Future Fibres’ 100 Tn Tensile Testbed

The 100 Tn test facility is a custom-built tensile machine with 12m length span. It’s capable of

inducing up to 100Tones in quasi-static conditions and run fatigue (dynamic loading) tests with

maximum loads up to 30 Tones. Also, it can be setup to induce torsional loads reaching a

maximum Torque of 3000Nm and limitless rotation angle. Apart from force and torque,

displacement, strain and acceleration can be monitored through up to 16 digital and 4 optical data

acquisition channels (Figure 4).

http://emps.exeter.ac.uk/renewable-energy/facilities/dmac

http://emps.exeter.ac.uk/renewable-energy/facilities/dmac





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Figure 4. Future Fibres’ 100T tensile testbed.

1.3 NOVEL MOORING COMPONENTS

This section provides details of the novel mooring components developed in FLOTANT. Samples

of these components are tested within Task 5.1 in order to validate their performance and

durability characteristics.

1.3.1 MOORING CABLE

The first technology developed for FLOTANT mooring system is a mooring cable made of the

standard carbon fibre-epoxy rods. The structure and constituents of this component are shown in

Figure 5 and Figure 6. The mooring cable has a nominal strength (Nominal Breaking Load (NBL))

of 20 tons, with an outer diameter of 20 mm and a weight of 280 g/m (to which 2 x 3 kg terminations

have to be added). The full specifications of the hybrid mooring cable, including details on the

fabrication process, are available in FLOTANT deliverable D2.3. The lengths of the three samples

are 3587 mm (S1), 3584 mm (S2), 3584 mm (S3) and the total length of the metal terminal is

423.8 mm. The sample was connected to the DMaC test facility by means of clevis joints attached

to the pin eye fittings at the cable’s ends. One of the pin eye fittings is shown in Figure 7. During

the test, the two ends of the sample are connected with the headstock and the tailstock of DMaC

by shackles, respectively (Figure 8). The change rate of the measured elongation of the sample

may be slightly influenced before the shackles are fully taut (usually with a small load).





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Figure 5. From left to right: Bundle of carbon rods - End resin cone technology.

Figure 6. Mooring cable section view.Standard carbon fibre-epoxy rods

Figure 7. Pin eye fitting of the hybrid mooring cable.





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Figure 8. The layout of connections between test samples and DMaC

1.3.2 POLYMER SPRINGS

The second technology developed for FLOTANT mooring system is a polymer spring used to

obtain reductions during the peak loads. The polymer material is Hytrel, a high performance

engineered thermoplastic polymer designed for longstanding fatigue cycles in marine

environments. The polymer springs are mounted on a metal assembly, which constitutes the

frame for this component. A rendering of this assembly is shown in Figure 9.

The polymer and metalwork have different load levels, with the metalwork having a minimum

breaking load (MBL) of around 600kN (~60tons). However, the polymer has a safe working load

(SWL), which is the maximum load it is designed to see in a 50-year return period, of around

200kN (~20tons). As such, this value will be used as the nominal MBL for the whole assembly

during both the performance and durability tests. The 1:1 scaled prototype tested at DMaC

measures 1.75 m in length, and weights around 200 kg.

The full specifications of the polymer springs are available in FLOTANT deliverable D2.5. During

the test, the two ends of the sample are connected with the headstock and the tailstock of DMaC

by shackles, respectively (see Figure 10). The change rate of the measured elongation of the

sample may be slightly influenced before the shackles are fully taut (usually with a small load). A

draw-wire transducer was used to accurately measure the compression on the spring (without the

shackle rotation) by connecting it to the yellow, metal flanges at either end of the polymer.





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Figure 9. Polymer springs renderings.

Figure 10. The layout of connections between test samples and DMaC

2 TEST PROCEDURE

2.1 STANDARDS AND INDUSTRY PRACTICES

International standards and recommended practices are used to design test procedures that

measure the proposed innovation against a set of pre-established requirements. These allows for

the obtainment of important information regarding the characteristics of the tested components

and accelerates the path towards commercialization. In order to achieve the objectives proposed

in section 1.1, a combination of standards and test methods was used. The recommended

practices were then adjusted to capture the characteristics of the mooring components according





19

to the test objectives.

All tests are performed on wet samples and with the DMaC facility filled with water in order to

reproduce testing conditions as close as possible to the final operating conditions of the

components.

2.1.1 ISO/TS 17920:2015

The first standard selected to provide guidance during the experimental procedures is the ISO/TS

17920:2015 Fibre ropes for offshore stationkeeping – Aramid [1], established by the International

Standardisation Organisation (ISO). This standard provides comprehensive guidance for rope

handling, requirements for material properties and construction, and detailed test plans for

mooring parts samples. The choice of standard is based on different reasons. Firstly, it is a

standard widely accepted and commonly used in the mooring industry to characterise bedding-

in, quasi-static, dynamic and failure performance, and its use has been validated through a series

of past experiences [2–5]. Secondly, it is specific for offshore station keeping components and

provides detailed information and requirements for successful testing. Thirdly, because although

a standard for the particular composition of FLOTANT innovations was not available, ISO/TS

17920:2015 deals with high strength materials and having similar structure to one of the

constituents of the mooring cable (i.e. the nylon matrix). In this regard, other suitable standards

for offshore station keeping components, such as ISO19336:2015 and ISO 18692:2007 [6,7],

adopt the same test methodology for testing rope samples manufactured using different materials,

reinforcing the choice of this standard.

The guidelines provided in this standard are used to define the test procedures aimed at

determining the performance characteristics of the test specimens. These are defined in terms of

their quasi-static and dynamic stiffness and damping features. More in detail, the test procedure

described in ISO 17920 and similar, includes four main phases:

- bedding-in (phase B.3.1 (left hand side) in below figure),

- quasi-static loading (10-30% MBL; phase B.3.5.2 in below figure),

- dynamic loading at three mean load levels (20-30%(F3), 30-40%(F4) and 40-50%(F5)

MBL) and three cycles intervals (100, 200 and 300 cycles); (this is phase B.3.5.3A in

below figure), and

- break test (linear ramp to failure).

These phases, showing load values for the first set of measurements, are illustrated in Figure 11.

Figure 11. Example of input load time series showing bedding-in (B.3.1, left), quasi-static (B.3.5.2) and

dynamic (B.3.5.3) loading, and break testing (B.3.1, right).





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2.1.2 THOUSAND CYCLES LOAD LEVEL (TCLL)

In order to characterize the durability features of the tested samples, the Thousand Cycles Load

Level (TCLL) testing methodology is selected. This is documented in the ‘Guidelines for the

Purchasing and Testing of SPM Hawsers’ produced by the Oil Companies International Marine

Forum (OCIMF) society [8]. Also this is an internationally recognized standard providing detailed

guidelines for specification, purchasing and testing of marine components. The reason for

choosing this testing methodology lies in the identification of documents using this procedure for

tension fatigue testing of marine components [8–10]. The TCLL method is described as the most

commonly used testing standard for the characterization of tension fatigue performance and

component durability.

The TCLL test procedure consists in the application of cyclic loads over an extended period of

time, permitting the reproduction of degradation phenomena that the component would encounter

during its operating life. In this way, it is possible to quantify the impact of repeated load cycles

on the component, and measure how these affect the material’s strength and fabrication

characteristics. As a result, the life expectancy of the component can be estimated and compared

against the initial design objectives. The TCLL values indicate the maximum percentage of the

breaking strength at which a component can be cycle loaded 1,000 times [10].

The test procedure described in [10] was used. This consists in applying different levels of cyclic

loading to each sample as a percentage of the component’s minimum breaking load, with the load

always maintained above 1% MBL. The samples are subjected to 1,000 cycles for each of the

first three loads (50%, 60%, 70% of the MBL) and then, if they do not fail, 2,000 cycles at 80% of

MBL, for a total of 5,000 cycles. This procedure is shown in Figure 12. A period of 8s is used

between consecutive cycles, as established in [11]. If necessary and compatibly with both the

component and test rig capabilities, the samples can be then linearly loaded to failure to measure

the residual strength of the component.

Figure 12. TCLL procedure illustration (5 illustrated cycle is proportional to 1000 test cycles) [12].

In [12] TCLL is used to determine the theoretical load at which the sample would fail at the 1,000th

cycle, expressed as a % of the manufacturer’s minimum breaking strength. Thus, defining:





21

CTF= Number of Cycles to Failure

TLL = Test Load Level at which CTF occurred

TCLL can be calculated as: TCLL = 100% - ((6.91 (100% - TLL))/Ln CTF)

2.1.3 SEA STATES TIME-SERIES

To gain further understanding of the dynamic behavior of mooring components, these are tested

under the operational load conditions that would be experienced in the final environment chosen

for FLOTANT projects, i.e. Gran Canaria and West of Barra. The load envelopes can be designed

and modelled in software such as OrcaFlex [13], in order to perform a simulation test able to

reproduce accurate environmental conditions, mooring system parameters and motion

characteristics of the device.

A 2-hour representative of the operational conditions the mooring system would experience in the

two locations is selected from the Orcaflex numerical model. Thus, both curvature and axial

loading time series are extracted for use in the DMaC test rig. This procedure ensures that the

applied load time series incorporates the full spectrum of combined axial and bending variable

loading acting in offshore field deployments.

2.2 TEST PLANS

A total of 30 days of testing are available (20 days for the mooring cable and 10 days for the

polymer springs). According to this availability, the test objectives and the guidelines of the

identified standards and recommended practices are established in the test plans, see Table 1

and

Table 2. All percentages refer to the minimum breaking load of the components (20t for both the

mooring cable and the polymer spring). The break test was not practical or informative for the

polymer spring assembly, so it was not performed.

Bedding-in Assessment (BA) (phase B.3.1 of ISO 17920) at the end of each testing activity to

evaluate eventual modifications in the cable properties induced by the test just carried out. BA1

represents the initial bedding in stage and the BA2 to BA7 represent the bedding-assessment

after other testing activities (see Table 1 and Table 2).

Table 1. Test plan for the mooring cable (Part I).

Day Task Time (hrs)

1 Setup: Install assembly (Sample 1) + Water fill + test-rig setup and calibration 7.5

2 Sample 1 - ISO (F3, 20-30%) BA1+ bedding-in (B3.1) BA2 7.5

3 Sample 1 - Sea states time-series + bedding-in (B3.1) BA3 7.5

4 Sample 1 - TCLL 50% 1000 cycles + bedding-in (B3.1) BA4 7.5

5 Sample 1 - TCLL 60% 1000 cycles + bedding-in (B3.1) BA5 + TCLL 70% 1000 cycles + bedding-in (B3.1) BA6 7.5

6 Sample 1 - TCLL 80% 2000 cycles + bedding-in (B3.1) BA7 + Break test 7.5

7 Setup: removal sample 1 + soak sample 2 + setup and calibration test-rig 7.5

8 Sample 2 - ISO (F4, 30-40%) + bedding-in (B3.1) 7.5

9 Sample 2 - Sea states time-series + bedding-in (B3.1) 7.5





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10 Sample 2 - TCLL 50% 1000 cycles + bedding-in (B3.1) 7.5

11 Sample 2 - TCLL 60% 1000 cycles + bedding-in (B3.1) + TCLL 70% 1000 cycles + bedding-in (B3.1) 7.5

12 Sample 2 - TCLL 80% 2000 cycles + bedding-in (B3.1) + Break test 7.5

13 Setup: removal sample 2 + soak sample 3 + setup and calibration test-rig 7.5

14 Sample 3 - ISO (F5, 40-50%) + bedding-in (B3.1) 7.5

15 Sample 3 - Sea states time-series + bedding-in (B3.1) 7.5

16 Sample 3 - TCLL 50% 1000 cycles + bedding-in (B3.1) 7.5

17 Sample 3 - TCLL 60% 1000 cycles + bedding-in (B3.1) + TCLL 70% 1000 cycles + bedding-in (B3.1) 7.5

18 Sample 3 - TCLL 80% 2000 cycles + bedding-in (B3.1) + Break test 7.5

19 Data collection, analysis and elaboration 7.5

20 Pack down + sample preparation for reshipment 7.5

Total (hours) 150

Table 2.Test plan for the polymer spring assembly.

Day Task Time (hrs)

1 Setup: Install assembly (metal work + polymers) + Water fill + test-rig setup and calibration 7.5

2 Assembly - ISO (F3, 20-30%) BA1+ bedding-in (B3.1) BA2 7.5

3 Assembly - ISO (F4, 30-40%) + bedding-in (B3.1) BA3 7.5

4 Assembly - ISO (F5, 40-50%) + bedding-in (B3.1) BA4 7.5

5 Assembly - Sea states time-series + bedding-in (B3.1) BA5 7.5

6 Assembly - TCLL 50% 1000 cycles + bedding-in (B3.1) 7.5




10 Data collection, analysis and elaboration + sample preparation for reshipment 7.5

Total (hours) 75

The test plans for the two mooring components have been established according to a series of

considerations hereinafter provided:

- A combination of methodologies is necessary to characterise different aspects of the

components, namely performance, reliability and durability.

- The combined methodology exploits the following sources and recommended practices:

load data from given sea states, ISO 17920 and Thousand Cycles Load Level (TCLL)

- Execution of F3, F4 and F5 test sequences of ISO 17920 on three different (but identical)

samples, as per instructions in ISO 17920

- Test with given sea-states (provided by numerical model developed by TFI) after the ISO

17920 characterisation, but before the durability test to make sure that fatigue does not

affect the sample’s integrity





23

- Durability test as specified in the TCLL test of OCIMF (Oil Companies Int. Marine Forum)

standard. Each sample is subject to a total of 5000 cycles at increasing percentages of

the sample’s MBL (50% to 80%)

- Break test at the end of each sample’s durability test to determine residual strength and

compare it against nominal MBL

- One day before and after each test series to allow for:

o setup and calibration of the test-rig;

o sample’s preparation and positioning;

o data collection and analysis; and

o redundancy / repeatability in case of unexpected events.

3 RESULTS

3.1 MOORING CABLE (Part I)

Three samples of the mooring cables were used during the test for repeatability and the MBS of

the mooring cable is 20 tons, as stated by the manufacturer. The performance of all mooring cable

samples is very similar, see Figure 13. The stiffness (i.e. gradient of load against elongation

graph) of the mooring cables is nearly identical and there is a small offset in elongation due to

settling in the cable terminal. This report will only present results from Sample 3 because the

performance of the three samples is nearly identical and the results from Samples 1 and 2 are

included in the digital appendix.

(a)





24

(b)

Figure 13: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, mooring cable (a) BA2 (b)

BA5

3.1.1 ISO/TS 17920: 2015

The load versus total elongation measurements from Sample 3 BA1 to BA7 bed-in assessment

based on the ISO/TS 17920:2015 are shown in Figure 14. A linear relationship between the load

and the elongation was observed and the slope of result curve was very similar in all BA cases.

The nonlinear relationship was also found at the beginning stage during BA1 and BA3, which is

believed to be caused by the lazy shackle.

Figure 14: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA1 to BA7, mooring cable

sample 3





25

Table 3 presents the stiffness of the morning cable (sample 3) during the bed-in assessment.

Slightly changes of the sample stiffness were observed, ranging from 0.4% to 1%, which

demonstrates the mooring cable performance has not noticeably changed (<1%) during the test

program.

Table 3 Bed-in Assessment of ISO/TS 17920:2015 B.3.1

Case no. BA1 BA2 BA3 BA4 BA5 BA6 BA7

Stiffness

(kN/mm)

5.05 5.00 4.95 5.00 5.02 5.08 5.00

Change

(compared

to BA1 %)

/ 1% 1% 1% 0.4% 0.4% 1%

The load versus total elongation measurements of quasi-static stiffness test (B.3.5.2) and

dynamic stiffness test (30-40%(F4) MBL) of mooring cable sample 3 are shown in Figure 15 to

Figure 16 according to ISO/TS 17920:2015. These results show that the mooring cable has linear

relationship between load and elongation, no creep and minimal hysteresis (damping) during the

bedding-in, quasi-static and dynamic tests.

Table 4 presents the stiffness of the morning cable sample 3 during quasi-static and dynamic test.

Compared to the results in the Table 3, the mooring cable has a larger stiffness in both cases. It

is demonstrated that the stiffness of the mooring cable may perform slightly different under various

types of load.

Figure 15: Load vs total elongation of ISO/TS 17920:2015 B.3.5.2 quasi-static stiffness test for mooring cable

sample 3.





26

Figure 16: Load vs total elongation of ISO/TS 17920:2015 B.3.5.3 (F4 - 30-40% MBL) for mooring cable

sample 3.

Table 4: The stiffness of the quasi-static stiffness test and dynamic stiffness of mooring cable sample 3

Case Quasi-static test Dynamic F4

Stiffness (kN/mm) 5.25 5.17

3.1.2 STATES TIME-SERIES

The time versus total elongation measurements of mooring cable sample 3 under two sea states

(Gran Canaria and West of Barra) used in the FLOTANT project are shown in Figure 17 and

Figure 18. It is found that the mooring cable has a relatively larger mean elongation under the

Gran Canaria sea stare (23.5mm vs 9.5mm) while changing range of the elongation is smaller

(3.5mm vs 12.5mm).





27

Figure 17: Time vs total elongation under sea state of Gran Canaria, mooring cable

Figure 18: Time vs total elongation under sea state of West of Barra, mooring cable

3.1.3 TCLL

The load versus total elongation measurements of TCLL 50% to 70% 1000 cycles and TCLL 80%

2000 cycles of mooring cable sample 3 are shown from Figure 19 to Figure 22. These results

show that the mooring cable has linear relationship between load and elongation, slightly creep

and no minimal hysteresis (damping) during all TCLL cases. The creep is more significantly during

the case with a larger load.





28

Figure 19: Load vs total elongation of TCLL 50%, 1000 cycles, mooring cable

Figure 20: Load vs total elongation of TCLL 60%, 1000cycles, mooring cable





29

Figure 21: Load vs total elongation of TCLL 70%, 1000cyles , mooring cable

Figure 22: Load vs total elongation of TCLL 80%, 2000cyles, mooring cable

The load versus total elongation measurements of mooring cable sample 1, 2 & 3 in break test is presented in the Figure 23. The failure load of each mooring cable sample is 198 kN, 205 kN and 220 kN (mean 207 kN MBL and 11.2 kN standard deviation), respectively. The results demonstrated that the final break loads of all samples are proximity to the desired MBL (196 kN). Additionally, a noticeable step of the elongation is observed when the load is around 180 kN (sample 1 & 3 175kN, sample 2 185 kN). The step indicates the mooring cable (potentially the resin in the terminals) yielded and has caused permanent damage; however, this cannot be confirmed without further testing be unloading the cable after yield but before total failure.





30

Figure 23: Load vs total elongation of break test of ISO/TS 17920:2015

The failure of samples 2 and 3 were catastrophic with a sudden break and a sudden release of

the elastic energy. The event was too quick to observe on the recorded video; however, it is

anticipated that the failure was the cable terminal disconnecting from the carbon fibres, shown on

left side of Figure 24. Furthermore, the carbon fibres also broke near the headstock of DMaC test

rig, shown on right side of Figure 24, but it is expected that this was caused by the sudden release

of elastic energy and the cable impacted part of the headstock. The failure of sample 1 was not

catastrophic and the sample maintained some residual strength after total failure, as such the

sample did not impact the headstock and the carbon fibres did not break. Observations of sample

1 after failure showed some carbon fibres had broken during the testing and were protruding out

of the sheathing.

Figure 24: The failure of all three samples; sample 1 (bottom), 2 (middle) and 3 (top).





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3.2 MOORING CABLE (PART II)

This section is divided in two parts. The first analyses the outputs from the optic fibre sensors

from the 20Tn samples tested in dynamic submerged conditions. The second presents the test

and results from the 100Tn mooring line sample.

3.2.1 20T Mooring demonstrators’ dynamic testing – Sensor’s output

All mooring line demonstrators delivered within WP2 (D2.3 and D2.4) featured optic fibre FBG

strain and temperature sensors for temperature compensated load monitoring. Recalling “D2.7

Integrated Sensing”, these sensors were embedded within the mooring line and run parallel to

the structural carbon fibre rods. At the cable ends’, the sensors exit the terminal to allow their

connection. Each cable featured four sensor lines: three of them containing three FBG strain

sensors each, and the fourth containing a temperature probe in an architecture like that shown in

Figure 25.

Figure 25: Mooring line demonstrators – Sensors’ architecture.

These sensor lines involved an optic fibre array embedded into a GFRP rod. Unfortunately, these

GFRP rod which serves as a support for the optic lines were not strong enough due to their

reduced thickness (under 0.9mm) which led to significant failures (rods fracture) during the

manufacturing of the samples (mainly during the end resin cones casting and demoulding

process) and in the handling of the cables. As a result, the four mooring line demonstrators ended

up with the following number of operative sensors:

• 20T_01: Zero operative strain sensor lines. Operative temperature sensor.

o Two strain sensor lines broken during cable manufacturing.

o One strain sensor line broken during test setup.

• 20T_02: Zero operative strain sensor lines. Operative temperature sensor.

o Two strain sensor lines broken during cable manufacturing.

o One strain sensor line broken during cable shipping.





32

• 20T_03: Two operative strain sensor lines. Operative temperature sensor.

o One strain sensor line broken during cable manufacturing.

• 100T_01: Zero operative strain sensors. Operative temperature sensor.

o Three strain sensors broken during cable manufacturing.

Therefore, this section focused on the outputs from the sample 20T_03 during its dynamic tests.

Strains were monitored during the entire test protocol performed on the sample (dynamic

characterisation, durability assessment through TCLL and Sea States and break test).

3.2.1.1 TCLL 60%

This test was taken as reference to perform a detailed analysis and comparison between sensors’

and loadcell’s output. At this point of the testing, the sample had already been exposed to around

half of the testing protocol as defined in the test plan.

To give an example of the outputs obtained, Figure 26 shows the whole spectrum of strain and

temperature values from the TCLL60% test. In Figure 27 the first 20 cycles of this test can be

observed whereas Figure 28 highlights one single cycle. Figure 29 and Figure 30 include a closer

look into the outputs from each of the two operative strain sensor lines at the test sample. From

this data, it was found how the line 2 provided a maximum scatter from the average measurement

of a 0.9% whereas for the line 3 it was of 2.3%. Taking the six strain measurements (three at each

of the two FO lines) the maximum deviation from the average measurement was 3.0%. These

results confirmed that the sensors provided a consistent and replicable measurement and the

deviation within each line’s sensors and between the sensors at the two lines was no greater than

a 3%, which is an acceptable value.

Figure 26 20T_03. TCLL60% TEST. OPTIC SENSORS’ STRAIN AND TEMPERATURE RESULTS.





33


DETAIL (I).


DETAIL (II).





34



Regarding temperature, the probe provided consistent data all along the test and only 0.6°C

change was registered between the start and the end of the test, with a maximum temperature

change of 1.12°C between the maximum and minimum temperatures obtained. This depicts the

little temperature change of the sample due to the submerged conditions of the test.

Strain results were then translated into load from cable’s theoretical stiffness (24.3 MN), as shown

in Figure 31. In addition, Figure 32 includes the forces measured from testbed’s loadcell. The

difference between these two measurements was 2.3% in average. Again, this result confirmed

that the sensors provided not only a consistent reading but also an accurate one, hence validating

its use as load monitoring system.





35

Figure 31 20T_03. TCLL60% TEST. OPTIC SENSORS’ LOAD RESULTS. DETAIL (I).

Figure 32 20T_03. TCLL60% TEST. OPTIC SENSORS’ AND LOADCELL LOAD RESULTS. DETAIL (II).

3.2.1.2 TCLL 70%

This other stage of the TCLL procedure has been included in the report in order to highlight that

during this test, as observed in Figure 33, the line 3 of the three strain sensor lines stopped

working. The line failed at around 450 cycles and after being exposed to both Sea States time

series plus the ISO F3 stage and the corresponding bedding in phases. All these presumably led

to the failure under fatigue of this FO line.





36

Figure 33 20T_03. TCLL70% TEST. OPTIC SENSORS’ STRAIN RESULTS. DETAIL (I).

3.2.1.3 TCLL 80%

This test results depicted the failure of remaining sensor line number 2 after the first 100 cycles

of this test as it can be observed in Figure 34. This plot represents the load spectrum of the

TCLL80% test obtained from the FO strain signals which should run between 0 and 16T. Again,

this failure was probably due to the accumulated fatigue induced on the sample.

Figure 34 20T_03. TCLL80% TEST. OPTIC SENSOR LINE 2. STRAIN RESULTS.





37

All the results above presented depict that the FO FBG sensors provided an accurate correlation

with the actual loads observed by the cables. Also, despite their design was not strong enough

as proven by the manufacturing and installation issues, those sensors monitored during the tests

were able to last for most of the dynamic test program and started failing after the Sea States

simulation tests and once already completed the TCLL70% test. It’s worth highlighting that this

test condition is well above cables’ design MWL, hence represent load scenarios out of the lines’

design parameters.

3.2.2 100T Mooring demonstrator strength testing

The goal of this cable sample and test was to assess the scalability of the new materials used for

the novel mooring lines. Recalling, these involved a resin system with antifouling and anti-bite

additives as well as integrated sensors in the cable architecture. In addition, since the

development tests showed that the new manufacturing method provided satisfactory results

(validated latterly by the dynamic tests run by UNEXE) it was decided to manufacture the 100T

sample following the alterative new manufacturing method to assess the scalability of this one as

well.

The sample manufacturing is described in detail in the Deliverable D2.4.

Therefore, this sample was tested in UTS to find its maximum breaking load. The outputs were

recorded from FO temperature sensor, and testbed’s loadcell and extensimeter. Figure 35 shows

the Load and temperature time series whereas Figure 36 plots the load versus the axial

displacement.

Figure 35 100T. UTS TEST. LOADCELL AND OPTIC SENSOR’S TEMPERATURE RESULTS (I).





38

Figure 36 100T. UTS TEST. LOADCELL RESULTS (II).

As observed in the plots, the sample did not reach the 100 Tones target and failed at 69.84T,

which represents a 30.1% difference. Looking at the detailed strain results and the load until

failure (Figure 37) it can be observed that the stiffness of the cable also did not meet with the

theoretical value of 120 MN and only reached 70MN involving an error of a 41%. The failure strain,

however, matches with the expected one, hence relating the low breaking load with the lack of

cable stiffness. Moreover, the fact that the stiffness deviation is greater than that of the breaking

load, depicts that if the theoretical stiffness properties can be reached and assuming the linearity

of the cable response, the maximum breaking load of the mooring line could be even greater than

100T for this cable design parameters.

Furthermore, cable’s failure mode was not the exact expected one involving an overall composite

failure but a multiple rods’ failure which could tell than the rods bundle was not performing as a

whole, hence the lack in stiffness and strength. Figure 38 shows a detail of one of the cable’s

ends after testing.

This deviation from the theoretical values was not observed in the smaller 20T which were

manufactured using the same raw materials, featured the same type of FO sensors, were

designed using the same principles and were manufactured following the same procedure. In

fact, the 20T samples according to the results provided outstanding stiffness and residual strength

after the fatigue testing (which matched with cables’ design NBL). Therefore, it seems that the

deviation in results at the 100T was induced by the scalability of the manufacturing process which

should be review or something else related with the manufacturing procedure leading to the

presented incorrect failure mechanism.





39

Figure 37 100T. UTS TEST. LOADCELL AND STRAIN RESULTS (I).

Figure 38 100T. CABLE RESULT AFTER TEST. END DETAIL.





40

3.3 MOORING CABLE CONCLUSIONS

The tests results from the mooring line samples depicted the following:

• The construction and selection of materials for the 20Tn samples was correct to meet the

fatigue requirements. The rods manufactured with the integrated antifouling and antibite

additives provided satisfactory results in terms of fatigue resistance which was the biggest

concern about the potential side-effects from the additives (no sample failed during the

cyclic loadings) and strength (the residual strength of the cables remained unaffected

after the fatigue tests).

• The integrated sensors that could be monitored provided solid measurement between

the different outputs and accurate results when compared to testbeds’ load information.

• However, the sensor lines architecture was not strong enough for an industrial

environment and should be reviewed (GFRP rods thickness increase) to make them

suitable for this application.

• The 100Tn test result showed a discrepancy in the cable performance compared to that

from the 20Tn samples. The difference in failure mode and lack of stiffness depicted a

manufacturing defect since the other two innovations (the additives and the sensors) were

already validated in the harsh dynamic tests performed on the 20Tn samples and did not

to generate issues related with the cables’ break strength.

• Due to that, the 100Tn sample and test will be repeated with a reviewed manufacturing

method and increased diameter sensor lines to first confirm that the early failure was

related with the manufacturing process (and not with the material’s scalability) and then

to validate a more robust design for the optical sensor lines. This sample and test would

be ready by end of December 2021 (subjected to new sensors’ size availability).

3.4 POLYMER SPRINGS

Two samples were tested in DMaC. Sample 1 was delivered as separate components and

assembled in DMaC(Figure 39). Sample 2 addressed quality control issues in the polymer and

was assembled in Ireland and delivered to DMaC (Figure 40).

Figure 39: Sample 1 Polymer Spring in DMaC





41

Figure 40: Sample 2 Polymer Spring prior to delivery to DMaC

3.4.1 ISO/TS 17920: 2015

The load versus gauge elongation measurements of polymer spring in BA1 to BA5 bed-in

assessments based on the ISO/TS 17920:2015 are shown in Figure 41 to Figure 45. The load

versus elongation graphs show that there is creep under constant tension and hysteresis is

present.

Figure 41: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA1, polymer spring,

sample 1





42

Figure 42: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA2, polymer spring,

sample 1

Figure 43: Load vs total elongation of ISO/TS 17920:2015 B.3.1 bed-in assessment, BA3, polymer spring

sample 1





43


sample 1


sample 1





44

Table 5 presented the stiffness of the polymer spring during the bed-in assessment. It is found

that the stiffness trend to be a constant after the elongation exceeds 40mm. Slight changes in the

sample stiffness are observed in the bed in assessment, less than 3%.





45

Table 5: Bed-in Assessment of ISO/TS 17920:2015 B.3.1, polymer spring sample 1.

Case no. BA1 BA2 BA3 BA4 BA5

Stiffness

(kN/mm)

1.03 1.02 1.03 1.02 0.997

Change

(compared to

v1 )

% 0.97% 0% 0.97% 3%

The load versus total elongation measurements of quasi-static stiffness test (B.3.5.2) and

dynamic stiffness test (B.3.5.3. 20 to 30%(F3), 30 to 40%(F4) and 40% to 50% (F5) MBL) of

polymer springs are shown in Figure 46 to Figure 49 according to ISO/TS 17920:2015. The creep

of the polymer springs (under a constant load) and a linear relationship between the load and

total elongation can be observed in these results. Compared to the results in





46

Table 5 and Table 6, the stiffness of the polymer is slightly different in the different stages of the

ISO test.

Figure 46: Load vs total elongation of ISO/TS 17920:2015 B.3.5.2 quasi-static stiffness test, polymer spring

sample 1

Figure 47: Load vs total elongation of ISO/TS 17920:2015 B.3.5.3 F3 dynamic stiffness test, polymer spring

sample 1





47


sample 1


sample 1

Table 6: The stiffness of the quasi-static stiffness test and dynamic stiffness of polymer spring sample 1.

Case Quasi-static test Dynamic F3 Dynamic F4 Dynamic F5





48

Stiffness (kN/mm) 1.05 1.2 1.2 1.1

The completion of the ISO testing completed the bedding in phase of the testing.

3.4.2 STATES TIME-SERIES

The time versus total elongation measurements of polymer spring under two sea states (Gran

Canaria and West of Barra) used in the FLOTANT project are shown in Figure 50 and Figure 51.

Figure 50: Time vs total elongation under sea state of Gran Canaria, polymer spring sample 1

Figure 51: Time vs total elongation under the sea state of West of Barra, polymer spring sample 1





49

Polymer creep is observed in both sea states but especially in the Gran Canaria sea state (Figure

50) that has a higher background load, and lower variable loads. As expected, the background

load has a greater influence on the length creep of the polymer spring.

3.4.3 TCLL (sample 1)

The load versus total elongation measurements of TCLL 10 to 50% 1000 cycles, TCLL 10 to 60

% 1000 cycles and TCLL 10 to 70% 2000 cycles of the polymer spring are shown from Figure 21

to Figure 24.

The polymer spring began to fail during the TCLL 10 to 60 % 1000 cycles as indicated by the

elongation continually increasing at the 60% MBL load, see Figure 53. Complete failure occurred

during TCLL 10 to 70% after 2 cycles. As in the sea states, length creep of the polymer spring is

observed and it is more significant with higher load.

Figure 52: Load vs total elongation of TCLL 10 to 50% (1000 cycles) polymer spring sample 1





50

Figure 53: Load vs total elongation of TCLL 10 to 60% (1000 cycles) polymer spring sample 1

Figure 54: Final TCLL test. Load vs stroke elongation of TCLL 10 to 70% polymer spring sample 1

Cracks began to form in the spring and gradually progressed during the test program until failure.

The damage was marked (with white pen) as soon as it was observed and recorded on the test

log. The primary damage was axial cracking through the polymer shells, see Figure 55, but also

radial crack was observed. A total of 9 cracks were observed and recorded.





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Figure 55: Example of a radial crack on a polymer shell (sample 1).

Investigation of the cracks showed quality control issues in the polymer moulding. A second

sample was fabricated, addressing these issues and brought back to DMaC for testing.

Figure 56: Sample 2 prior to starting testing in DMaC





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3.4.4 TCLL (Sample 2)

The second sample was subjected to TfI’s characterization and bedding in regime that included

7 cycles to 200kN which it should only see once in its deployed life.

Following that, it was put through an accelerated TCLL test. Sample 2 was tested with 10%-70%

TCLL case (1,215 cycles) and 10-80% TCLL case (2,000 cycles). The 10%-50% TCLL and 10%-

60% TCLL cases were replicated by 215 cycles at 10%-70% MBL, see [10]. The load versus

stroke elongation measurements of sample 2 during both cases are shown in Figure 58 and

Figure 59. The raw-wire transducer was removed for the 10%-80% TCLL case to avoid damage

to the transducer. Shackle rotation meant nonlinear stiffness was observed when the load is under

20 kN.

On completion of the TCLL test regime, the sample 2 polymer spring remained functional. No

axial cracks were seen in the polymer showing that the quality control issues had been resolved.

Figure 57: The polymer spring sample 2 on completion of the TCLL testing.





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Figure 58: Load vs stroke elongation of TCLL 10 to 70% polymer spring sample 2, Stroke means the stroke of

the hydraulic ram

Figure 59: Load vs stroke elongation of TCLL 10 to 80% polymer spring, sample 2

The TCLL testing highlighted shell snap through on the polymer spring. This happens when one

shell is able to invert from one stable state to another. This has been identified as a possibility

and results in a negative slope in the force response. This only affects the force response and not

the spring performance so testing continued. With this testing we have confirmed the existence

of snap throughs and these will be addressed similarly to the moulding quality control.





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3.4.5 Discussion

The polymer spring was put through the ISO 17920 and TCLL tests identifying defects in the

fabrication. A second polymer spring was fabricated to address these issues and successfully

completed the TCLL durability tests.

Snap through of one of the polymer shells yielded a negative slope in the force response and also

exacerbated wear and fatigue of the polymer; this will be addressed. Despite this, the polymer

was subjected to greater than 3000 cycles at loads greater than 140kN, much more than a

polymer spring will see in a deployment.

The number of stress cycles on the polymer can be estimated using TfI’s simulations of polymer

stress over compression. By comparing the results, the stress ranges that the polymer saw during

the TCLL tests can be calculated as 9.2Mpa and 10.8 MPa respectively. This can be compared

to the stress ranges in a standard operating sea state where the peak stress range is calculated

at 3 MPa with most much lower (Figure 60)

Figure 60: Frequency of Stress Ranges in the operating Sea State

It is clear that the fatigue damage incurred during the 70% and 80% TCLLs is much greater than

that seen in an operational sea state and it is possible to make an estimate as to the how much

fatigue damage the TCLL tests incurred.

The stress ranges have already been estimated using the TfI polymer simulations. An S/N curve

is not available for Hytrel 5556 but one can be estimated by taking the two available data points

from the Hytrel Design Guide (Figure 61) and plotting them using the following power law equation





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Figure 61: Estimated S/N Curve

Using this estimated S/N plot the TCLL tests can be equated to ~500 years of fatigue from an

operational sea state. While assumptions have been made around the stress in the polymer and

the S/N curve, this figure is far in excess of planned 25 years deployment so it is unlikely that the

spring will fail due to fatigue. Despite the exceptionally high fatigue damage of the TCLLs, the

polymer spring functioned throughout this testing.

REFERENCES [1] International Organization for Standardization. Fibre ropes for offshore station keeping —

Aramid ISO/TS 17920 2015.

[2] Weller SD, Halswell P, Johanning L, Kosaka T, Nakatsuka H, Yamamoto I. Tension-Tension Testing of a Novel Mooring Rope Construction 2017. https://doi.org/10.1115/OMAE2017-61915.

[3] Harrold MJ, Thies PR, Newsam D, Ferreira CB, Johanning L. Large-scale testing of a hydraulic non-linear mooring system for floating offshore wind turbines. Ocean Eng 2020;206:107386. https://doi.org/https://doi.org/10.1016/j.oceaneng.2020.107386.

[4] Gordelier T, Parish D, Thies PR, Weller S, Davies P, Le Gac PY, et al. Assessing the performance durability of elastomeric moorings: Assembly investigations enhanced by sub-component tests. Ocean Eng 2018;155:411–24. https://doi.org/https://doi.org/10.1016/j.oceaneng.2018.02.014.

[5] Luxmoore JF, Grey S, Newsam D, Johanning L. Analytical performance assessment of a novel active mooring system for load reduction in marine energy converters. Ocean Eng 2016;124:215–25. https://doi.org/https://doi.org/10.1016/j.oceaneng.2016.07.047.

[6] International Organization for Standardization. Fibre ropes for offshore station keeping — Polyarylate ISO/TS 19336 2015;2015.

[7] International Organization for Standardization. Fibre ropes for offshore stationkeeping —





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Polyester ISO 18692 2007;2007.

[8] Oil Companies International Marine Forum (OCIMF). Guidelines for the Purchasing and Testing of SPM Hawsers. 2000.

[9] Lankhorst Euronete. What is TCLL? n.d. http://www.leaustralia.com.au/what-is-tcll/ (accessed June 10, 2020).

[10] Samson. Technical bulletin: Tension fatigue testing. 2020.

[11] Gordelier T, Parish D, Thies RP, Johanning L. A Novel Mooring Tether for Highly-Dynamic Offshore Applications; Mitigating Peak and Fatigue Loads via Selectable Axial Stiffness. J Mar Sci Eng 2015;3. https://doi.org/10.3390/jmse3041287.

[12] Thousand Cycle Load Level Procedure n.d. https://www.unols.org/sites/default/files/201710rvt_ap20.pdf.

[13] OrcaFlex documentation n.d. https://www.orcina.com/resources/documentation/ (accessed January 7, 2020).





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ANNEX 1

DMaC Calibration





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Future Fibres 100 Tn Testbed Calibration





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Documents

D.5.1 – NOVEL MOORING COMPONENTS PERFORMANCE