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CRES PULL OUT TESTS

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Scope

This benchmark checks the static restoring force and tensions of a mooring system mounted on  a semi-submersible floating support structure for an offshore wind turbine. No other external forces are applied on the structure while the waterline is calm throughout the experiment.

Data Accessibility

The benchmark is offered to participants of IRPWIND WP6

Objectives

The objective of this benchmark is the correct simulation of the response of both the structure and the mooring system under the influence of externally imposed forces and moments.

Input data

The participants of the benchmark will be granted access to MT2016 F-049 MARINTEK report and to the geometry specifications of the semisubmersible floater for running with their numerical models. The following data can be derived from the provided files:

  • Geometry and material properties of both support structure and  mooring system
  • Scaling factors for simulation of the experiment on a scale 1:30
  • The vectors of restoring forces and moments  exerted on the floater as well as their attachment points on the structure
  • The mooring system layout, i.e. the anchor locations on the basin floor and the fairlead positions on the floater

Validation data

The partners must provide the following data:

  • Time-series of the floater barycentre
  • Time series of  the norms of all three mooring line tensions
  • Visualization material (Pictures or videos) showing the motion of the floater during the simulation

Model runs

Modeling input information

There are four pull out tests to be simulated, as tabulated in the following table:

Test no.

Test identification

Description

1010

PULLOUT INLINE 0D NO WIRES

Pullout in surge toward +X

1020

PULLOUT INBETWEEN 180D NO WIRES

Pullout in surge toward -X

1030

PULLOUT YAW NO WIRES

Pull column 1 and 2 +/-X to give positive yaw

1040

PULLOUT 90D NO WIRES

Pullout in sway toward +Y

These tests correspond to four different loadings, imposed with winches attached to the edges of the basin and on the model just above the water lines. Upon the imposition of the loads the platform moves off the initial balance position under the influence of the pretensions as predicted by the second Newton's law. The motion gradually decays as the floater approaches the new terminal position where it balances under static loading. Each of the tests consists of a number of subtests of increasing loading as tabulated in detail in tables (17-20) of the MARINTEK report. The input data are tabulated, in a nutshell, as follows:

Test no. 1010 Pull out test in +x

Subtest no.

Offset (m)

Restoring Force (kN)

Maximum line tension (kN)

1

0.00

0

1595

2

1.03

110

1671

3

4

5

6

7

8

24.19

5020

6148

Test no. 1020 Pull out test in -x

Subtest no.

Offset (m)

Restoring Force (kN)

Maximum line tension (kN)

1

0.00

0

1595

2

2.52

240

1680

3

4

5

6

7

14.95

1305

2223

Test no. 1010 Pull out test in +y

Subtest no.

Offset (m)

Restoring Force (kN)

Maximum line tension (kN)

1

0.00

0

1595

2

0.97

94

1654

3

4

5

6

7

Test no. 1010 Pull out test in +x

Subtest no.

Offset (deg)

Restoring Moment (kNm)

Maximum line tension (kN)

1

0.00

0

1595

2

0.37

2221

1596

3

4

5

7.12

23672

1625

Special attention must be paid on the units, since all results provided in the MARINTEC report are in prototype scale.

Output data

The requested output data are ascii files in the following form:
INSTITUTION NAME_PULL_OUT_TEST_#ΤEST_#SUBΤEST.dat
For example CRES would provide the following file: CRES_PULL_OUT_TESTS_1010_1.dat
The format of the output data file is as follows:

Time (sec)  Barx (m)  Bary (m) Barz (m)  Tension #1 (N)  Tension #2 (N) Tension #3 (N)  Max Tension (N) Offset (m)
0.                   5.0                 0              0                  50                   50                       50                          50              0.
0.0001           4.99               0              0                  51                   51                       48                          51              0.01

The symbols Barx,Bary,Barz stand for the coordinates of the barycenter of the structure in the cartesian global coordinate system of MARINTEK and Tension for the mooring line force on each pontoon (MARINTEK numbering of 3 pontoons).

Remarks

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Terms and Conditions

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