gmh-6532-2532 rev 0 draft final - dnv gl rev 0 document details and issue ... 1.2.3 foundation...

AMERICAN BUREAU OF SHIPPING

PHASE 2 BENCHMARKING OF 19905-1

GORILLA V AND 116C RIG DESIGNS

GMH-6532-2532 REV 0

Document details and issue record

Project: ISO Benchmark GM Doc. No.: GMH-6532-2532-REV 0

Made by: Bing Deng / Alberto Morandi File Name: GMH-6532-2532_Rev0.doc

Rev Date Document Status Prepared Reviewed Approved

0 11/08/2010 Issued for comments BD ACM ACM

MARINE OFFSHORE AND ENGINEERING CONSULTANTS

Client: ABS / ISO Benchmark Panel Date: 11/08/2010 Page: 1

Title: Phase 2 Benchmark of ISO 19901-5 Rev.: 0 Made: BD/ACM

American Global Maritime Inc. GM Doc. No.: GMH-6532-2532-R0

REVISION SHEET

Rev. Reason Page(s)

0 Draft Final Report 48




TABLE OF CONTENTS

1 SUMMARY ....................................................................................................................... 4

1.1 Instructions ........................................................................................................................... 4

1.2 Conclusions .......................................................................................................................... 4

1.3 Disclaimer ............................................................................................................................ 4

2 INTRODUCTION ............................................................................................................ 6

2.1 Background and Objectives .................................................................................................. 6

3 ANALYSIS METHODOLOGY ...................................................................................... 8

3.1 General ................................................................................................................................. 8

3.2 Information Sources ............................................................................................................. 9

4 RIG DETAILS ................................................................................................................ 10

4.1 Principal Dimensions ......................................................................................................... 10

4.2 Weights ............................................................................................................................... 11

4.3 Wind Areas ......................................................................................................................... 11

4.4 Leg Hydrodynamic Coefficients ........................................................................................ 13

4.5 Structural Properties in Detailed FE Model ....................................................................... 14

5 SITE DATA – GEOTECHNICAL ............................................................................... 15

5.1 General ............................................................................................................................... 15

5.2 RG V Geotechnical Analysis – Sand ................................................................................. 15

5.3 RG V Geotechnical Analysis – Clay .................................................................................. 16

5.4 116C Geotechnical Analysis – Sand .................................................................................. 17

5.5 116C Geotechnical Analysis – Clay ................................................................................... 18

5.6 Alignment Point 1 – Geotechnical Results ......................................................................... 19

6 SITE DATA - METOCEAN .......................................................................................... 21

6.1 Metocean Data for RG V .................................................................................................... 21

6.2 Metocean Data for 116C .................................................................................................... 22

7 KEY ELEVATIONS – AIR GAP AND LEG LENGTH ............................................ 24

7.1 General ............................................................................................................................... 24

8 DYNAMIC AMPLIFICATION FACTORS ................................................................ 27

8.1 Analysis Methodology ....................................................................................................... 27

8.2 Alignment Points 2 and 3 – Natural Period and DAF ........................................................ 28

9 UNITY CHECKS ........................................................................................................... 30

9.1 Analysis Methodology ....................................................................................................... 30

9.2 Global Loading and Leg Reactions – RG V Sand Case ..................................................... 35

9.3 Global Loading and Leg Reactions – RG V Clay Case ..................................................... 36

9.4 Global Loading and Leg Reactions – 116C ISO Sand Case .............................................. 37




9.5 Global Loading and Leg Reactions – 116C ISO Clay Case ............................................... 38

9.6 Global Loading and Leg Reactions – 116C SNAME Sand Case ....................................... 39

9.7 Global Loading and Leg Reactions – 116C SNAME Clay Case ....................................... 40

9.8 Alignment Point 4 - Base Shear, Overturning Moment and Leg Reactions ...................... 41

9.9 Alignment Point 5 – Unity Checks ..................................................................................... 42

9.10 Foundation Checks ............................................................................................................. 45

10 CONCLUSIONS AND RECOMMENDATIONS ....................................................... 47

10.1 Conclusions ........................................................................................................................ 47

10.2 Recommendations .............................................................................................................. 47

11 REFERENCES ............................................................................................................... 48

APPENDIX 1 Soil Properties

APPENDIX 2 Geotechnical Analysis

APPENDIX 3 Comments on ISO 19905-1

APPENDIX 4 Sage Soil Yield Surface Modification




1 SUMMARY

1.1 Instructions

1.1.1 Global Maritime (GM) was one of the consultants selected to participate in Phase

2 of the ISO 19901-5 benchmark study, coordinated by the American Bureau of

Shipping (ABS) on behalf of the Benchmarking Panel.

1.1.2 The project manager for ABS is Mr. John Stiff who is also a member of the

Benchmarking Panel together with: Pao-Lin Tan (ABS), Jim Brekke (Transocean),

Ward Turner (ExxonMobil), Dave Lewis (LEG), Yi Li (Diamond) and Rupert

Hunt (Shell).

1.1.3 The present report describes the methodology adopted and the results obtained for

the GM scope of work including alignment of results with other consultants.

1.2 Conclusions

1.2.1 The study did not identify any ‘show stoppers’ or major disconnection between

SNAME and ISO in terms of assessment results. It is noted that the standard

includes significant technical developments and will require from its future users a

high level of technical proficiency in many different areas.

1.2.2 Dynamic Amplification Factor (DAF) calculation issues aside, it seems that ISO

might be more favourable than SNAME due to the wave kinematics factors which

are generally κ <0.86. The present study adopted a wave kinematics factor κ =

0.86 in all ISO assessments.

1.2.3 Foundation checks controlled the assessment results in all cases, with particular

reference to sliding checks for sand cases. All sand cases failed the sliding checks

by a significant margin.

1.2.4 Some technical issues deserve further attention: a) Intrinsic / Apparent Wave for

DAF calculations; b) Random DAF calculation methods (Winterstein vs. Drag-

Inertia); c) Clearer recommendations for Flat / Rough & Conical Shape spudcans

(use Φ or δ).

1.2.5 It seems that a good quality random time-domain analysis on a simplified

structural model to check the foundations provides a very good indication of a rig

suitability for a given site as overturning, elevating system and structural checks

seldom seem to control the results of the assessment.

1.3 Disclaimer

1.3.1 This report is issued to ABS in confidence as per master services agreement

between ABS and American Global Maritime Inc.

1.3.2 The input data for the LeTourneau Super Gorilla rig design used in this study is

representative but was modified in relation to the correct design values to preserve




confidentiality. Therefore the data presented in this study should not be used in

future site assessments.

1.3.3 Input data for the LeTourneau 116C rig design is generally considered to be

known to most designers and consultants.

1.3.4 It is expected that ABS will verify any confidentiality issues with any potentially

affected parties prior to distribution of this report to other parties.

1.3.5 The work has been funded jointly by the IADC Jack-up Committee, Shell and

ExxonMobil. Technical, contractual and management support was provided by

ABS. Rig design data was provided by LeTourneau in addition to reviewing data

used and assumptions made in the study. Further technical support was provided

by the Benchmarking Panel. The support provided by these organizations is

greatly appreciated.




2 INTRODUCTION

2.1 Background and Objectives

2.1.1 ISO 19905-1 ‘Petroleum and natural gas industries – site-specific assessment of

mobile offshore units – Part 1: Jack-ups’ was developed using SNAME T&R 5-

5A as a starting point but has undergone substantial development since then. ISO

19905-1 was released as a Draft International Standard (DIS) and release as a

Final Draft International Standard (FDIS) is scheduled for late 2010 / early 2011.

2.1.2 Part of its verification process is a benchmark study to verify that it is complete

and produces reasonable results. Phase 1 of the benchmark study was completed

and comprised of a completeness check. The present report gives results for Phase

2 where a complete run through the entire (DIS) 19905-1 is undertaken to: a) make

numerical comparisons to ensure that the results obtained are in reasonable

compliance with the results of SNAME T&R 5-5A, Rev. 3; b) identify the reasons

for any discrepancies; c) provide detailed comments to be addressed by the ISO

working panels prior to release of the DIS.

2.1.3 In short, the Phase 2 main objective is to ensure ISO 19905-1 is useable by the

public and will deliver acceptable results. In addition, through careful

documentation, the work performed in Phase 2 will be used to produce a Go-By

document to ISO 19905-1.

2.1.4 The scope of work covered in Phase 2 and the consultants mobilized to perform

the work are shown in Tables 1.1 and 1.2 below.

Table 1.1 – Phase 2 Scope of Work Company Rig 1

(Lead Consultant)

Standard Rig 2 Standard Go-by

Global

Maritime

LeTourneau 116 C ISO 19905-1 and

SNAME T&R 5-5A

LeTourneau

Super Gorilla

ISO 19905-1 No

GL Noble

Denton

Keppel B Class ISO 19905-1 and

SNAME T&R 5-5A

LeTourneau

SuperGorilla

ISO 19905-1 and

SNAME T&R 5-5A

LeTourneau

Super Gorilla

Bennet &

Associates

Keppel B Class ISO 19905-1 116C ISO 19905-1 No

Gusto MSC GustoMSC CJ 62 ISO 19905-1 and

SNAME T&R 5-5A

- - No

Table 1.2 – Global Maritime Work Scope Case # Jack-up design Soil Condition Standard

1 LeTourneau 116C Sand SNAME 5-5a Rev 3, 2008

2 LeTourneau 116C Clay SNAME 5-5a Rev 3, 2008

3 LeTourneau 116C Sand ISO 19905-1, 2009-06-30*

4 LeTourneau 116C Clay ISO 19905-1, 2009-06-30*

5 LeTourneau Super Gorilla Sand ISO 19905-1, 2009-06-30*

6 LeTourneau Super Gorilla Clay ISO 19905-1, 2009-06-30*

*Including changes introduced up to December 2009




2.1.5 The benchmark study covers the Ultimate Limit State (ULS) and does not address

other limit states such as Serviceability (SLS), Fatigue (FLS) and Accidental

(ALS). Extreme wave loads are included and seismic loads are excluded. The rig

is assessed to a L1 exposure level in all cases.

2.1.6 Soil properties for sand and clay were provided by the Benchmark Panel,

Appendix 1. Global Maritime has used RPSE as a sub-contractor for the

geotechnical assessment and results are given in Appendix 2.

2.1.7 Alignment points between consultants were established as follows:

• Inputs: Weights, Centre of Gravity, Water Depth (LAT, tide and surge), Air

Gap, Leg and Spudcan Structure, Environmental Conditions (Maximum Wave

Height and Associated Period, Significant Wave Height and Spectral Peak

Period, Current Profile and 1-Minute Wind Velocity), Leg Hydrodynamic

Coefficients and Wind Areas.

• Alignment Point 1 - Geotechnical Analysis Parameters such as Penetration,

Initial Soil Stiffness, Soil Capacities.

• Alignment Point 2 - Global Stiffness and Natural Periods.

• Alignment Point 3 - Dynamic Amplification Factors.

• Alignment Point 4 - Base Shear, Overturning Moment and Leg Reactions.

• Aligment Point 5 - Unity Checks: Foundation, Structure, Overturning Moment

and Leg-Hull Connection.

2.1.8 The main issues identified during the work and comments to ISO 19905-1 were

compiled and are presented in Appendix 3.

2.1.9 All analyses and comments refer to document ‘ISO-DIS_19905-1_(E)-updated-

2009-12-10.doc’ dated 2nd

December 2009. Some of the comments may have been

addressed in later versions of the DIS. An up to date collated version of all

comments and responses is kept by ISO TC 67/SC 7/WG 7.

2.1.10 All results are presented primarily in metric units, although in some case the

results are presented both in metric and English units to facilitate comparisons

with values that are more familiar to designers / assessors. For example the 116C

hull elevated weight of 14,000 kips is more readily recognized than its equivalent

in metric units.




3 ANALYSIS METHODOLOGY

3.1 General

3.1.1 A deterministic two-stage approach was adopted as summarized in Figure 3.1. The

more detailed flowchart for the assessment is given in Figure 5.2-1 of 19905-1.

Figure 3.1 – General Analysis Procedure

3.1.2 In Stage 1 a simplified model of the rig was developed to evaluate the dynamic

amplification factors (DAFs). The simplified model captures the global mass

(including added mass on the legs) and stiffness of the hull, legs and leg-hull

connection. The simplified model also captures the leg drag and inertia wave

loading properties on the legs.

3.1.3 Random wave, time-domain analyses were performed using SACS and the most

probable maximum extreme values of base shear and overturning moment were

determined using the Winterstein’s method. In some cases the drag-inertia

parameter method was used for comparison purposes.




3.1.4 Foundation modelling used vertical, horizontal and rotational springs with the

rotational stiffness linearized at 80% of the initial stiffness. The lateral support

against the legs due to soil in case of backflow / infill (P-Y curves) was neglected

at this stage. Global large deflection (P-Delta) effects were included.

3.1.5 In Stage 2, detailed models were built in SACS for the site water depth,

penetration and air gap to obtain the unity checks. Such models included leg

members, jack-house and leg-hull connection members and a hull grillage model.

3.1.6 Hydrodynamic loads were generated by stepping a high order regular wave

together with the relevant current profile through the detailed leg model.

Aerodynamic loads were generated from the wind areas. Dynamic response loads

were represented by an inertial loadset derived from the DAFs determined in Stage

1. The unity checks (UCs) were then obtained from static analyses that included

global and local large deflection effects.

3.1.7 Non-linear foundation behaviour was included through an iterative adjustment of

the rotational spring stiffness until the combination of vertical, horizontal and

moment loads on the spudcans was found to stay within the soil yield surface.

Where backfilling / infilling was predicted, P-Y curves were used to represent the

soil restraint against the legs.

3.1.8 The simplified model used in Stage 1 was calibrated against the detailed model

used in Stage 2 for mass / weight, leg stiffness and leg-hull connections stiffness.

3.2 Information Sources

3.2.1 Input data consists of the following:

• Gorilla V simulation values provided by LeTourneau [1, 2]. Such input data is

representative but was modified in relation to the correct design values to

preserve confidentiality. Therefore the data presented in this study should not

be used in future site assessments.

• In-house data such as weights, leg structural drawings, GA drawings, hull

structural drawings, jack-house structural drawings, etc.

• Representative metocean data agreed by the consultants involved in the study.

3.2.2 In addition, instructions and data were received from the Benchmark Panel:

• Soil design data, Appendix 1.

• Adopt wave kinematics factor of 0.86 in all ISO assessments. Report ISO

wave kinematics factor for chosen sites. Adopt wave height reduction factor of

0.86 in all SNAME assessments.

• Model Test data may be used for hull wind areas in SNAME and ISO

assessments. Use calculated leg Cd D and Cm D2 in all assessments.

• Utilize Sage deep penetration modification to soil yield surface for SNAME

assessments, Appendix 4.




4 RIG DETAILS

4.1 Principal Dimensions

4.1.1 The principal rig dimensions used in this study are given in Tables 4.1 and 4.2. As

shown in Table 4.2 a Gulf of Mexico (GOM) and a North Sea (NS) variant were

used for the 116C.

Table 4.1 – RG V Principal Dimensions

Dimension feet meters

Hull Length 306.00 93.27

Hull Width 300.00 91.44

Hull Depth 36.00 10.97

Jack House Depth (from main deck) 51.28 15.63

Longitudinal Leg Spacing 189.01 57.61

Transverse Leg Spacing 218.01 66.45

Overall Leg Length 573.65 174.85

Spudcan Height 30.38 9.26

Table 4.2 – 116C Principal Dimensions

Dimension feet meters

Hull Length 243.1 74.1

Hull Width 200.5 61.1

Hull Depth 26.0 7.9

Jack House Depth (from main deck) 26.0 7.9

Longitudinal Leg Spacing 129.0 39.3

Transverse Leg Spacing 142.0 43.3

Overall Leg Length – GOM / NS 477 / 343 145.4 / 104.5

Spudcan Height 24.0 7.3




4.2 Weights

4.2.1 The RG V hull and leg weights are given in Table 4.3 below. A preload capacity

of 35,000 kips (155.7 MN) inclusive of buoyancy effects was used in this study. It

is noted that the rig may be able to develop higher preload capacity [2].

Table 4.3 – RG V Hull & Leg Weights

Item Kips Tonnes

Hull Storm Elevated Weight 42,725 19,394

Single Leg Dry Weight (include spudcan weight) 5,381 2,441

4.2.2 The 116-C hull and leg weights are given in Table 4.4 below. A preload capacity

of 12,000 kips (53.4 MN) exclusive of buoyancy was used in this study.

Table 4.4 – 116C Hull & Leg Weights

Item Kips Tonnes

Hull Storm Elevated Weight 14,100 6,396

Single Leg Dry Weight (include spudcan weight) –

477 ft (145.4m) Leg Length 2,507 1,137

Single Leg Dry Weight (include spudcan weight) –

343 ft (104.5m) Leg Length 1,945 882

4.2.3 For the purposes of this study it was assumed that a storm variable load

distribution can be developed such that the hull elevated weight LCG / TCG are at

the centroid of the three legs with the VCG at the main deck level.

4.2.4 It was also assumed that such variable load would not be reduced and therefore no

minimum variable load case was assessed. It was considered that the rig operator

can establish procedure to keep the full variable load on board for sites where

overturning / sliding can be an issue.

4.3 Wind Areas

4.3.1 The hull wind areas and centre of effort values (CoE) are listed in Tables 4.5 and

4.6, inclusive of shape coefficient Cs and exclusive of height coefficient

(calculated automatically in SACS). The 116C areas are broken down into a value

to cover items from the baseline to the top of the jack-house (A1, B1, etc.) and

another value to cover items above the top of the jack-house (A2, B2, etc.).

4.3.2 The CoE values are relative to the hull baseline. Figure 4.1 shows the reference for

the environmental headings – 0o heading is bow-on, 90

o heading is port-on, etc.




Figure 4.1 – Environmental Headings

Table 4.5 – RG V Hull Wind Areas & CoE’s

Heading (°) Area ID Area*Cs (m2) CoE (m)

0 A1 2397 18.7

30 B1 2710 19.6

60 C1 3664 19.4

90 D1 3521 19.3

120 E1 3040 20.8

150 F1 2702 19.8

180 G1 2646 16.4

Heading




Table 4.6 – 116C Hull Wind Areas & CoE’s

Heading (°) Area ID Area*Cs (m2) CoE (m)

0 A1 1045 11

A2 160 45

30 B1 900 11

B2 359 32

60 C1 882 10

C2 338 31

90 D1 849 9

D2 292 31

120 E1 832 11

E2 333 32

150 F1 872 11

F2 374 31

180 G1 856 11

G2 302 31

4.4 Leg Hydrodynamic Coefficients

4.4.1 Leg hydrodynamic coefficients are shown in Tables 4.7 and 4.8 and were

calculated considering smooth surface members above MWL+2m and rough

surface members (with marine growth of 12.5mm) below MWL+2m.

4.4.2 The coefficients include contributions from leg’s attachments such as jetting lines,

and raw water tower (RWT) structure/pipes where appropriate.




Table 4.7 – RG V Leg Hydrodynamic Coefficients

Storm Headings – Degrees, see Figure 4.1 0, 60, 120, 180 30, 90, 150, 180

Leg Sections Cd D (m) Cm D2 (m

2) Cd D (m) Cm D

2 (m

2)

Upper part legs (smooth, no raw water tower) 4.71 6.52 4.86 6.52

Upper intermediate part legs - stbd leg

(rough, no water tower) 6.20 7.12 6.34 7.12

Upper intermediate part legs - port leg

(rough, 1 raw water tower) 6.69 7.54 6.82 7.54

Upper intermediate part legs - bow leg

(rough, 2 raw water towers) 7.17 7.96 7.30 7.96

Lower intermediate part legs

(rough, no raw water tower) 6.20 7.12 6.34 7.12

Lower part legs– up to 42m TOC (rough) 6.59 8.07 6.74 8.07

Table 4.8 – 116C Leg Hydrodynamic Coefficients

Cd D (m) Cm D2 (m

2)

Rough 10.27 7.71

Smooth 8.74 7.43

4.5 Structural Properties in Detailed FE Model

4.5.1 Section properties for the leg members, jack-frame and guide structures were

determined from engineering drawings.

4.5.2 For the 116C the chords were considered to be reinforced by 4’’ x 2’’ flat bars

along the rack and 12’’ x 1’’ along the side plates. The reinforcement was applied

to the entire leg length.

4.5.3 For the RG V the stiffness and clearances for the pinion and chocks were modelled

as per instructions by LeTourneau [1,2].

4.5.4 For the 116C the pinion vertical stiffness was adopted as 900 kips / inch.




5 SITE DATA – GEOTECHNICAL

5.1 General

5.1.1 The study considered two representative soil profiles (clay and sand), Appendix 1.

The results of the geotechnical analysis performed by RPS are given in Appendix

2 and summarized in the following subsections.

5.2 RG V Geotechnical Analysis – Sand

Table 5.1 – RG V Geotechnical Analysis – Sand




5.3 RG V Geotechnical Analysis – Clay

Table 5.2 – RG V Geotechnical Analysis – Clay




5.4 116C Geotechnical Analysis – Sand

Table 5.3 – 116C Geotechnical Analysis – Sand




5.5 116C Geotechnical Analysis – Clay

Table 5.4 – 116C Geotechnical Analysis - Clay




5.6 Alignment Point 1 – Geotechnical Results

5.6.1 Tables 5.5 to 5.8 show the results obtained after resolution of the main issues

found during the alignment process.

Table 5.5 – Comparison of Aligned Results – Penetrations (m)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C

GM / RPS 2.7 2.8 28.8 27.6

116C

BASS 2.7 2.7 28.8 27.6

RG V

GM / RPS 0.9 - 42.5 -

RG V

GL ND 0.9 - 42.1 -

Table 5.6 – Comparison of Aligned Results – Initial Rotational Stiffness (MN-m/rad)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C

GM / RPS 18,139 19,347 120,340 102,982

116C

BASS 18,125 19,327 120,324 103,154

RG V

GM / RPS 65,239 - 501,565 -

RG V

GL ND 63,710 - 442,091 -

Table 5.7 – Comparison of Aligned Results – Vertical Capacity (MN)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C

GM / RPS 51.4 51.4 64.4 64.2

116C

BASS 51.4 51.4 51.0 51.0

RG V

GM / RPS 155.7 - 196.9 -

RG V

GL ND 155.7 - 193.2 -




Table 5.8 – Comparison of Aligned Results – Moment Capacity (MN-m)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C

GM / RPS 37.5 38.8 92.9 98.4

116C

BASS 37.5 38.7 90.3 69.0

RG V

GM / RPS 164.7 - 397.3 -

RG V

GL ND 164.8 - 387.3 -

5.6.2 In summary the aligned results are in good agreement for the most part although a

few discrepancies are noted. The analyses proceeded based on the results obtained

by the lead consultant (GM for the 116C and GL ND for the RG V).

5.6.3 There was close agreement between the results obtained by GM/ RPS for ISO and

for SNAME T&R 5-5A.




6 SITE DATA - METOCEAN

6.1 Metocean Data for RG V

6.1.1 The RG V is capable of operating in harsh environments for a water depth of 400ft

/ 122m or greater.

6.1.2 The environmental conditions selected for the study were based on 50-year

independent extremes for such water depth in the North Sea, usually in the

Northern part of the North Sea. The typical latitude-dependent spreading factor for

this region according to ISO 19901-5 is 0.90 and the corresponding wave

kinematics factor also according to ISO 19901-5 is 0.82. This study used a wave

kinematics factor of 0.86 as instructed by the Benchmark Panel.

6.1.3 An air gap of at least 19m / 62.3 ft was considered as in the North Sea the hull

baseline is required to clear the 10,000-year water surface elevation.

6.1.4 It is noted that these metocean conditions chosen are not too far from those

representing 100-year joint probabilities for the Central Gulf of Mexico during

hurricane season. The air gap chosen would meet the requirements of API RP 95J

for operation of jack-ups in the Gulf of Mexico during hurricane season. The wave

kinematics factor from ISO 19905-1 is lower than 0.80 for hurricane conditions.

6.1.5 For the sand site the shallow penetration allows the rig leg length to accommodate

the 400ft / 122m water depth.

6.1.6 For the clay site the water depth was reduced to 85m due to the deep penetration.

6.1.7 Tables 6.1 and 6.2 give the metocean data used for the sand and clay cases.

Table 6.1 – RG V Sand Case – Metocean Conditions

Imperial Metric

LAT 400.0 ft 121.92 m

Tidal Rise + Storm Surge 8.0 ft 2.44 m

MWL 402.0 ft 122.53 m

SWL 408.0 ft 124.36 m

Airgap from LAT to Keel 68.6 ft 20.91 m

Maximum Wave Height (Hmax) 88.0 ft 26.82 m

Associated Wave Period (Tass) 16.6 s 16.6 s

Deterministic Wave Height (Hdet) 75.69 ft 23.07 m

Significant Wave Height (Hs) 47.31 ft 14.42 m

Peak Wave Period (Tp) 16.6 s 16.6 s

Wind Speed 100 knots 51.44 m/sec

Current Speed:

Surface

Seabed

2.9 knots

1.6 knots

1.49 m/sec

0.82 m/sec




Table 6.2 – RG V Clay Case – Metocean Conditions

Imperial Metric

LAT 278.87 ft 85.00 m


MWL 280.87 ft 85.61 m

SWL 286.87 ft 87.44 m







Wind Speed 100 knots 51.44 m/sec

Current Speed: Surface

Seabed

2.9 knots

1.6 knots

1.49 m/sec

0.82 m/sec

6.2 Metocean Data for 116C

6.2.1 The environmental conditions for the sand case (Table 6.3) are based on 50-year

independent extremes typical of the Southern part of the North Sea. The typical

latitude-dependent spreading factor for this region according to ISO 19901-5 is

0.91 and the wave kinematics factor also according to ISO 19901-5 is 0.81. This

study used a wave kinematics factor of 0.86 as instructed by the Benchmark Panel.

Table 6.3 – 116C Sand Case – Metocean Conditions

Environmental Data Imperial Metric

LAT 210.0 ft 64.01 m


MWL 217.7 ft 66.35 m

SWL 231.0 ft 70.41 m







Wind Speed (1-min mean) 68.0 knots 35.0 m/s

Current Speed : Surface

25% of Water Depth

50% of Water Depth

75% of Water Depth

1 m above Seabed

2.92 knots

2.92 knots

2.92 knots

2.72 knots

1.75 knots

1.5 m/s

1.5 m/s

1.5 m/s

1.4 m/s

0.9 m/s




6.2.2 The environmental conditions for the clay case (Table 6.4) are based on 50-year

independent extremes for sudden hurricanes in the Gulf of Mexico as given in the

assessment case of the Gulf of Mexico Annex to SNAME T&R 5-5A.

Table 6.4 – 116C Clay Case – Metocean Conditions

Environmental Curves Assessment-

Imperial

Assessment-

Metric

LAT 250.0 ft 76.2 m


MWL 250.6 ft 76.38 m

SWL 252.5 ft 76.96 m







Wind Speed (1-min mean) 61.0 knots 31.4 m/s

Current Speed :

Surface

Mid-depth of Profile

Bottom of Profile

Seabed

1.45 knots

1.36 knots

1.27 knots

0.00 knots

0.75 m/s

0.70 m/s

0.65 m/s

0.00 m/s




7 KEY ELEVATIONS – AIR GAP AND LEG LENGTH

7.1 General

7.1.1 Figure 7.1 below shows the key elevations to be considered in the analyses.

Figure 7.1 – Key Elevations

7.1.2 The key elevations for the cases considered are shown in Tables 7.1 to 7.4. It can

be seen that a minimum clearance of 5ft between the top of the upper guide and

the top of the legs is maintained in all cases.

7.1.3 The origin is at the tip of the spudcan (TOC), so Ztp = 0.

7.1.4 For the 116C it was observed that the difference in penetrations calculated from

ISO and SNAME was not sufficient to significantly alter the results so the same

elevations were used in both cases.

Tip of spudcan (Ztp)

Reaction point (Zrp)

MWL (Zws)

Hull bottom (Zhb)

Rough Surf Zone (Zrs)

Upper Guide (Zug)

Leg top (Zlt)

Hull main deck (Zmd)

Lower Guide (Zlg)

Mudline (Zml)




Table 7.1 – RG V Key Elevations – Sand Case (air gap 20.91m/ 68.6 ft)

Elevations feet meters

Tip of Spucan 0.00 0.00

Support point 1.48 0.45

Mudline elevation 2.95 0.90

Top of spudcan 30.38 9.26

LAT level 402.95 122.82

MWL level 404.95 123.43

Split Rough / Smooth Leg @ (MWL+2m) 411.52 125.43

Hull Baseline (Keel) 471.57 143.73

Hull Grillage 489.57 149.22

Hull VCG 507.57 154.72

Top of Jack-House 558.83 170.33

Top of Leg 573.65 174.85

Table 7.2 - RG V Key Elevations - Clay Case (air gap 19.00 m/ 62.34 ft)






LAT level 416.83 127.05

MWL level 418.83 127.67




Hull VCG 515.17 157.02


Top of Leg 573.65 174.85




Table 7.3 – 116-C Sand Case - Key Elevations (for air gap of 20.11m / 66 ft)






LAT level 219.19 66.81

MWL level 226.89 69.16




Hull Main Deck Level 311.19 94.85


Top of Leg 343.00 104.55

Table 7.4 – 116-C Clay Case - Key Elevations (for air gap of 18.9m / 62 ft)






LAT level 340.55 103.80

MWL level 341.15 103.99




Hull Main Deck Level 428.55 130.62


Top of Leg 477.00 145.39




8 DYNAMIC AMPLIFICATION FACTORS

8.1 Analysis Methodology

8.1.1 The DAF’s were calculated from random time-domain analyzes using the

Winterstein method, which is allowed in both SNAME T&R 5-5A and ISO

19901-5. For comparison, some cases were also run using the drag-inertia

parameter.

8.1.2 A fixed damping equal to 7% of critical was assumed and the effect of relative

velocity / acceleration between the fluid and structure were not included. Added

mass on the submerged part of the legs was accounted for and linear (Wheeler)

stretching was applied to the current profile from the seafloor to the wave crest.

8.1.3 A simplified FE model of the unit was used to perform the dynamic simulations.

The legs are represented with equivalent beam elements and the hull is represented

by a simplified grillage with stiffness derived from engineering drawings. At the

connection between the legs and hull springs are used to model the horizontal,

vertical and rotational leg / hull connection stiffness.

8.1.4 A random wave-train of 3 hours simulation time was generated and the statistics of

the water surface elevation checked against recommended tolerances, this process

being repeated until acceptable statistics are obtained. The validated random wave

and current profile is passed through the structure in 0.5 second intervals, and at

each time step the total base shear (BS) and overturning moment (OTM) is

calculated. The statistical properties (mean, standard deviation, skewness and

kurtosis) of the BS and OTM responses are calculated in order to derive the most

probable maximum (MPM) value of BS and OTM. The DAF is defined as the

ratio of the MPM values with or without dynamic effects.

8.1.5 Such DAFs shall be applied to the maximum values of BS and OTM and not to the

amplitude as would be the case for the single degree of freedom DAF.

8.1.6 ISO 19901-5 requires that the Doppler effect of the waves riding on the current

profile is accounted for. This is not required when evaluating DAFs for SNAME

T&R 5-5A assessments.

8.1.7 Given the current velocities considered in this study (using the highest value

assumed as a block current), Figure 8.1 gives an indication of the magnitude of the

Doppler effects. Given the range of peak periods considered in the study (11 to

16.6 sec) and that for the most part the natural periods were fairly low (4.5 – 5.5

sec), this effect is not expected to be very pronounced.




Figure 8.1 – Doppler Effect for Study Cases

8.2 Alignment Points 2 and 3 – Natural Period and DAF

8.2.1 For the RG V initial comparisons between GL ND and GM indicated some

discrepancy in natural periods. The GL ND JUSTAS natural periods for the sand

cases inclusive of P-delta effects were of 10.6 seconds (pinned) and 8.0 seconds

(80% of initial rotational stiffness) and the corresponding FE results were 10.75 /

8.04 sec respectively. The GM corresponding results were of 10.0 and 7.6 seconds

respectively (from an FE model).

8.2.2 The results were aligned in accordance with the lead consultant (GL ND in this

case) and the corresponding DAF values are given in Tables 8.1 and 8.2.

Table 8.1 – RGV Sand Case DAFs (Aligned)

Storm Heading (degree) Base Shear DAF Overturning DAFs

60 1.13 1.35

90 1.12 1.33

120 1.11 1.31

Table 8.2 – RGV Clay Case DAFs (Aligned)


60 1.30 1.46

90 1.28 1.43

120 1.26 1.40

0.5

0.55

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

0 2 4 6 8 10 12 14 16 18 20 22 24

Apparent / Intrinsic

Intrinsic Period

RG V

116C




8.2.3 The higher DAF values for the clay case were obtained despite of a significantly

shallower water depth and deeper penetrations than in the sand case. This

illustrates the inherent conservatism in ignoring P-Y curves when evaluating

DAFs for the deep penetration case.

8.2.4 For the 116C, the initial comparisons showed good agreement between GM and

BASS for the sand case. The GM natural periods inclusive of P-delta effects were

6.2 sec (pinned) and 4.8 sec (80% of the initial rotational stiffness). The BASS

natural period for 80% of the initial rotational stiffness was 4.81 sec.

8.2.5 For the 116C clay case the GM natural period for 80% of the initial rotational

stiffness (with P-delta) was 5.3 sec and the BASS result was 5.1 sec.

8.2.6 Tables 8.3 and 8.4 show a comparison of the DAFs obtained. The ISO values are

generally a little higher than those from SNAME due to the Doppler effects. There

were some important discrepancies noted for the sand case while good agreement

was found for the clay cases. Generally the drag-inertia parameter seemed to give

more consistent results.

Table 8.3 – Comparison of 116-C Sand Case DAFs

ISO BS SNAME BS ISO OTM SNAME OTM

GM - Drag Inertia 1.12 1.10 1.20 1.16

GM - Winterstein 1.24 1.22 1.40 1.33

BASS 1.05 - 1.12 -

SDOF DAF = 1.20; Natural Period Tn = 4.80 s; Tp = 13.1 s

Table 8.4 – Comparison of 116-C Clay Case DAFs

ISO BS SNAME BS ISO OTM SNAME OTM

GM - Drag Inertia 1.16 1.15 1.36 1.33

GM - Winterstein 1.14 1.12 1.35 1.34

BASS 1.16 - 1.27 -

SDOF DAF = 1.39; Natural Period Tn = 5.30 s; Tp = 11.0 s

8.2.7 The final 116-C sand and clay aligned DAFs are listed in Tables 8.5 and 8.6.

Table 8.5 – 116-C Sand Case DAFs


60, 90, 120 SNAME 1.22 / ISO 1.24 SNAME 1.33 / ISO 1.40

Table 8.6 – 116-C Clay Case DAFs


60, 90, 120 SNAME 1.12 / ISO 1.14 SNAME 1.34 / ISO 1.35




9 UNITY CHECKS

9.1 Analysis Methodology

9.1.1 The global large displacement analysis is performed using a detailed 3-leg model

to assess the strength of the leg members and leg jacking system as well as

foundation integrity. Leg structure members, hull structure, gear units, jacking

bracing frame, guides and pinions are individually modelled using beam elements.

9.1.2 The lower and upper guides are represented by beam elements. Where the guide

elements connect to the leg chord elements, releases are specified in all six degrees

of freedom except the directions in which the guides work, thus ensuring the

restraint offered by the guides is representative of the actual situation.

9.1.3 The pinions are represented by elements that run between the gear unit and leg

chord members and model the appropriate pinion stiffness and clearance.

9.1.4 Section properties for the leg members, gear units and jacking bracing frame

structures were determined from engineering drawings. Section properties of the

tubular leg braces are calculated directly by SACS from the input of outside

diameter and tube thickness.

9.1.5 Hull dead weight was modelled by applying joint loads on joints located at the

VCG level and the weight was distributed with achieving the target COG of the

total hull weight. Hull weight is distributed in two zones, 25% of the weight on the

hull centre, and the remaining 75% of the weight around the legs to allow for

appropriate hull sagging leg moments to be included in the analysis.

9.1.6 The wind loads on the hull, drill package and legs as well as the wave/current

loads on the legs are automatically generated by SACS based on the input

environmental data, wind areas, equivalent leg hydrodynamic coefficients and

selected wave theory. Wind loads were calculated on the leg segment in the air gap

zone above the wave crest and the leg above the jack house. Appropriate

windshield zone was used to eliminate the wind force calculations on shielded leg

bays (i.e. inside the hull and the jack house).

9.1.7 The vertical and horizontal stiffness of the footing springs are set equal to the

small strain values. The rotational stiffness is taken to be non-linear and assumed

to degrade as the load vector on the foundation increases, hence giving the large

strain rotational stiffness. In essence the procedure requires the following steps:

• Initially set the rotational footing stiffness equal to their small strain value.

• Apply all loads to the FE model, i.e. gravity, wind, wave/current and inertia,

and perform a large displacement analysis.

• Extract the footing loads, i.e. vertical, horizontal and moment, and calculate

the revised (reduced) rotational footing stiffness for each leg.




• Rerun the large displacement analysis using the same loadset but with the

revised rotational footing stiffness. Extract the revised footing loads and again

calculate the revised rotational footing stiffness for each leg.

• Repeat the above as necessary until the footing loads on all legs converge to a

solution (i.e. satisfy the soil yield surface equation).

9.1.8 In case that the soil yield surface equation cannot be satisfied due to high footing

loadings, then the rotational stiffness will be degraded to a pinned footing

condition.

9.1.9 Calculate the unity check for foundations and overturning stability.

9.1.10 Given the internal member, pinion and chock loads from the analysis results, the

strength utilisation checks are performed.

9.1.11 Figures 9.1 to 9.4 show the FE models used.

Figure 9.1 – RG V Sand Case FE Model




Figure 9.2 – RG V Clay Case FE Model




Figure 9.3 – 116C Sand Case FE Model




Figure 9.4 – 116C Clay Case FE Model




9.2 Global Loading and Leg Reactions – RG V Sand Case

9.2.1 The global load component for representative environmental headings and the

resulting leg reactions for the RG V sand case are given in Tables 9.1 to 9.3 below.

OTM values are relative to the support point.

Table 9.1 – Wind Load Components – RG V Sand Case

Storm

Heading (°)

Hull Wind Leg Member Wind Total Wind

BS (KN) OTM (KN-m) BS (KN) OTM (KN-m) BS (KN) OTM (KN-m)

60 8,927 1,452,624 318 49,810 9,245 1,502,435

90 8,572 1,393,663 326 51,236 8,899 1,444,899

120 7,456 1,223,233 314 49,324 7,770 1,272,557

Table 9.2 – Global Load Components – RG V Sand Case

Storm

Heading (°)

Wave / Current Wind Inertia P-Delta Total

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 20,692 1,936,655 9,245 1,502,435 2,690 675,341 662,083 32,627 4,776,513

90 20,956 1,954,293 8,899 1,444,899 2,515 644,357 649,499 32,369 4,693,048

120 20,488 1,905,860 7,770 1,272,557 2,254 591,908 605,427 30,512 4,375,751

Table 9.3 – Leg Reactions – RG V Sand Case

Storm heading (o) Leg ID

BS Vertical Moment

KN KN KN-m

60

Bow 11,815 43,042 62,287

Port 11,726 43,007 62,024

Stbd 9,071 164,266 0

90

Bow 11,453 83,306 133,094

Port 11,639 14,893 0

Stbd 9,277 152,158 0

120

Bow 9,788 120,381 57,885

Port 10,984 9,425 0

Stbd 9,752 120,540 57,425




9.3 Global Loading and Leg Reactions – RG V Clay Case


resulting leg reactions for the RG V clay case are given in Tables 9.4 to 9.6 below.

OTM values are relative to the support point.

Table 9.4 – Wind Load Components – RG V Clay Case

Storm

Heading (°)



60 8,838 1,422,086 165 25,334 9,003 1,447,419

90 8,486 1,364,298 170 26,171 8,656 1,390,469

120 7,384 1,198,044 163 25,033 7,547 1,223,077

Table 9.5 – Global Load Components – RG V Clay Case

Storm

Heading (°)


BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 21,561 2,185,289 9,003 1,447,419 6,468 1,002,038 501,981 37,032

, 5,136,727

90 21,756 2,195,000 8,656 1,390,469 6,092 943,156 484,793 36,504 5,013,417

120 21,279 2,143,047 7,547 1,223,077 5,532 858,208 424,191 34,358 4,648,523

Table 9.6 – Leg Reactions – RG V Clay Case (Effect of P-Y Curves included)


BS Vertical Moment

KN KN KN-m

60

Bow 7,104 50,091 658,970

Port 6,322 50,046 653,438

Stbd 5,981 149,832 633,107

90

Bow 6,996 83,321 708,338

Port 5,692 27,636 577,994

Stbd 6,258 138,978 667,761

120

Bow 5,702 111,822 713,358

Port 4,740 26,318 582,043

Stbd 6,325 111,792 714,939




9.4 Global Loading and Leg Reactions – 116C ISO Sand Case


resulting leg reactions for the 116C ISO sand case are given in Tables 9.7 to 9.9

below. OTM values are relative to the support point.

Table 9.7 – Wind Load Components – 116C ISO Sand Case

Storm

Heading (°)



60 1,247 127,977 210 18,212 1,457 146,189

90 1,206 121,273 210 18,202 1,415 139,475

120 1,247 127,977 210 18,212 1,457 146,189

Table 9.8 – Global Load Components - 116C ISO Sand Case

Storm

Heading (°)


BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 12,902 688,958 1,512 151,079 3,097 274,539 124,881 17,511 1,239,457

90 12,782 678,505 1,415 139,475 3,068 271,145 122,560 17,265 1,211,686

120 12,676 671,349 1,457 146,189 3,042 269,084 121,633 17,175 1,208,255

Table 9.9 – Leg Reactions – 116C ISO Sand Case


BS Vertical Moment

KN KN KN-m

60

Bow 6,324 11,599 0

Port 6,315 10,450 0

Stbd 4,865 60,027 0

90

Bow 6,334 27,308 0

Port 6,015 -614 0

Stbd 4,924 55,377 0

120

Bow 5,572 42,705 0

Port 6,065 -4,502 0

Stbd 5,529 43,867 0




9.5 Global Loading and Leg Reactions – 116C ISO Clay Case


resulting leg reactions for the 116C ISO clay case are given in Tables 9.10 to 9.12

below. OTM values are relative to the support point.

Table 9.10 – Wind Load Components – 116C ISO Clay Case

Storm

Heading (°)



60 1,082 148,442 395 47,934 1,477 196,376

90 1,003 136,200 397 48,229 1,400 184,429

120 1,036 142,707 394 47,873 1,430 190,580

Table 9.11 – Global Load Components - 116C ISO Clay Case

Storm

Heading (°)


BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 3,956 350,052 1,477 196,376 554 121,140 38,978 5,987 706,546

90 3,631 316,689 1,400 184,429 509 110,173 33,531 5,540 644,822

120 3,530 308,169 1,430 190,580 495 108,787 31,738 5,454 639,273

Table 9.12 – Leg Reactions – 116C ISO Clay Case (Effect of P-Y Curves included)


BS Vertical Moment

KN KN KN-m

60

Bow 72 25,417 186,022

Port 63 25,070 185,723

Stbd 133 38,654 187,368

90

Bow 182 29,712 180,917

Port 144 22,829 172,144

Stbd 169 36,592 175,511

120

Bow 125 33,422 179,276

Port 249 22,053 169,354

Stbd 126 33,637 179,276




9.6 Global Loading and Leg Reactions – 116C SNAME Sand Case


resulting leg reactions for the 116C SNAME sand case are given in Tables 9.13 to

9.15 below. OTM values are relative to the support point.

Table 9.13 – Wind Load Components – 116C SNAME Sand Case

Storm

Heading (°)



60 1,301 132,763 208 18,029 1,509 150,792

90 1,205 121,184 207 18,008 1,412 139,192

120 1,246 127,889 207 18,019 1,454 145,908

Table 9.14 – Global Load Components - 116C SNAME Sand Case

Storm

Heading (°)


BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 12,907 690,239 1,509 150,792 2,840 226,915 122,131 17,255 1,190,078

90 12,787 679,778 1,412 139,192 2,813 224,112 119,782 17,012 1,162,864

120 12,681 672,618 1,454 145,908 2,790 222,410 118,891 16,924 1,159,826

Table 9.15 – Leg Reactions – 116C SNAME Sand Case


BS Vertical Moment

KN KN KN-m

60

Bow 6,218 12,218 0

Port 6,209 11,114 0

Stbd 4,820 58,735 0

90

Bow 6,250 27,305 0

Port 5,893 511 0

Stbd 4,877 54,246 0

120

Bow 5,508 42,087 0

Port 5,939 -3,228 0

Stbd 5,469 43,203 0




9.7 Global Loading and Leg Reactions – 116C SNAME Clay Case


resulting leg reactions for the 116C SNAME clay case are given in Tables 9.16 to

9.18 below. OTM values are relative to the support point.

Table 9.16 – Wind Load Components – 116C SNAME Clay Case

Storm

Heading (°)



60 1,090 149,500 420 50,726 1,510 200,226

90 1,011 137,213 423 51,014 1,434 188,227

120 1,043 143,708 420 50,664 1,463 194,372

Table 9.17 – Global Load Components - 116C SNAME Clay Case

Storm

Heading (°)


BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

OTM

(KN-m)

BS

(KN)

OTM

(KN-m)

60 3,957 345,351 1,510 200,226 475 116,045 39,863 5,942 701,485

90 3,632 312,401 1,434 188,227 436 105,540 29,705 5,502 635,874

120 3,531 303,991 1,463 194,372 424 104,226 28,166 5,418 630,756

Table 9.18 – Leg Reactions – 116C SNAME Clay Case (Effect of P-Y Curves included)


BS Vertical Moment

KN KN KN-m

60

Bow 97 25,359 180,891

Port 88 25,010 180,622

Stbd 185 38,772 175,774

90

Bow 198 29,714 182,091

Port 149 23,269 170,656

Stbd 171 36,150 174,051

120

Bow 126 33,200 177,841

Port 252 22,519 169,630

Stbd 126 33,393 177,837




9.8 Alignment Point 4 - Base Shear, Overturning Moment and Leg Reactions

9.8.1 Tables 9.19 to 9.21 show a comparison of the aligned base shear, overturning

moment (at the reaction point) and leg reaction values obtained. Generally there is

good agreement between the different consultants and the ISO results agree fairly

closely with those of SNAME.

9.8.2 Some discrepancy between consultants is observed in leg reactions for the clay

case as GM has used P-Y curves.

Table 9.19 – Comparison of Maximum Base Shear (MN)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C – GM

(60o

Heading) 17.51 17.26 5.99 5.94

116C – BASS

(60o

Heading) 17.99 - 6.09 -

RG V – GM

(60o

Heading) 32.6 - 37.0 -

RG V – GL ND

(60o

Heading) 33.4 - 36.3 -

Table 9.20 – Comparison of Maximum Overturning Moment (MN-m)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C – GM

(60o

Heading) 1,239 1,190 707 701

116C – BASS

(60o

Heading) 1,234 - 731 -

RG V – GM

(60o

Heading) 4,777 - 5,137 -

RG V – GL ND

(60o

Heading) 4,890 - 5,283 -




Table 9.21 – Comparison of Maximum / Minimum Vertical Leg Reactions (MN)

Sand

ISO

Sand

SNAME

Clay

ISO

Clay

SNAME

116C – GM

(60o

/ 120o

Head)

60.0 / -4.50 58.7 / -3.23 38.7 / 22.1 38.8 / 22.5

116C – BASS

(60o

/ 120o

Head)

59.8 / -4.63 - 41.6 / 17.9 -

RG V – GM

(60o

/ 120o

Head)

164.3 / 9.4 - 149.8 / 26.3 -

RG V – GL ND

(60o

/ 120o

Head)

164.5 / 10.5 - 161.3 / 18.3 -

9.9 Alignment Point 5 – Unity Checks

9.9.1 Table 9.22 summarizes the relevant unit checks for all cases analyzed by GM. The

clay cases include P-Y curves and for the 116C the lower guide was considered

aligned with a horizontal brace. Leg inclination effects were included as additional

chord loads. The chord buckling loads considered the unsupported length defined

from the outside face of the supporting braces. The unity check for the chords was

based on the multiplier to the member loads that would bring such loads exactly to

the chord plastic interaction equation.

Table 9.22 – Summary of Unity Checks

Strength Leg-Hull

Connection

OTM Bearing

Capacity

Sliding

116C - Sand

ISO

0.92 (Chord)

1.05 (Brace) 0.91 (Pinion) 1.18

1.28

(but pass*) Fail (Uplift)

116C - Sand

SNAME

0.94 (Chord)

1.04 (Brace) 0.89 (Pinion) 1.14

1.26

(but pass*) Fail (Uplift)

116C - Clay

ISO 0.33 (Chord) 0.38 (Pinion) 0.47 0.94 < 0.6

116C - Clay

SNAME 0.35 (Chord) 0.38 (Pinion) 0.46 0.95 < 0.6

RG V- Sand

ISO 0.94 (Chord) 0.83 (Chock) 0.93

1.16

(but pass*) 2.13

RG V- Clay

ISO 0.81 (Chord) 0.67 (Chock) 0.84 1.07** < 0.6

* Additional settlement is negligible

** Additional settlement of 2.5 – 3m, considered excessive




9.9.2 Tables 9.23 and 9.24 give a more detailed comparison of the unity checks obtained

by the different consultants.

Table 9.23 – Unity Checks for RG V (ISO)

Strength

(Chord, λc~0.5)

StormLOK OTM Bearing

Capacity

(Level 1)

Sliding

GM

Sand

1.03 (A.12.6.8)

0.94 (A.12.6.9)

0.83 0.93 (Max VDL) 1.16

(but pass*)

2.13

(Level 1)

GL ND

Sand

1.22 (A.12.6.8)

0.99 (A.12.6.9)

0.86 0.93 (Max VDL)

0.98 (Min VDL)

1.16

(but pass*)

1.20

(Level 2)

GM

Clay

0.88 (A.12.6.8)

0.81 (A.12.6.8)

0.67 0.84 (Max VDL) 1.07** <0.6

GL ND

Clay

1.14 (A.12.6.8)

0.96 (A.12.6.8)

0.83 0.85 (Max VDL)

0.87 (Min VDL)

1.13*** 0.41

* Additional settlement is negligible

** Additional settlement of 2.5 – 3m, considered excessive

*** Additional settlement of 7m, considered excessive

9.9.3 The ISO chord checks in Table 9.23 compare the results from equations A.12.6.8

and A.12.6.9 and the more beneficial nature of equation A.12.6.9 can be clearly

recognized. Figure 9.5 shows the location of the critical chord unity checks which

corresponded to the 90o heading.

Figure 9.5 – RG V Critical Chord UCs

Heading




Table 9.24 – Unity Checks for 116C (ISO)

Strength

(Chord, λc~0.3)

Pinion OTM Bearing

Capacity

(Level 1)

Sliding

GM

Sand

0.95 (Chord, A.12.6-8)

0.92 (Chord, A.12.6-9)

1.05 (Brace)

0.91 1.18 1.28

(but pass)

Fail

(Uplift)

BASS

Sand

1.10 (Chord)

1.21 (Brace)

0.95 1.18 1.12*

1.28**

(but pass)

Fail

(Uplift)

GM

Clay

0.35 (Chord, A.12.6-8)

0.33 (Chord, A.12.6-9)

0.38 0.47 0.94 <0.6

BASS

Clay

0.48 (Chord)

0.48 (Brace)

0.48 0.49 0.78* <0.6

* Original BASS value (no buoyancy, no resistance factor)

** Corrected for buoyancy and resistance factor of 1.1

9.9.4 The ISO chord checks in Table 9.24 again compare the results from equations

A.12.6.8 and A.12.6.9 and the more beneficial nature of equation A.12.6.9 can be

clearly recognized. However, in this case the difference is not as pronounced due

to the stocky nature of the 116C chords. The comparison is illustrated in Figure

9.6 where it is clearly seen that equation A.12.6.9 gives a greater benefit to the

more slender chords.

Figure 9.6 – Relative Increase in Column Buckling Capacity with Eq. A.12.6.9

1.00

1.02

1.04

1.06

1.08

1.10

1.12

1.14

1.16

1.18

1.20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Ra

tio

(A

.12

.6-9

/ A

.12

.6.8

)

λλλλc

RGV

116C

CJ62




9.9.5 Figure 9.7 shows the location of the critical chord unity checks which

corresponded to the 60o heading.

Figure 9.7 – 116C Critical Chord UCs

9.10 Foundation Checks

9.10.1 The RG V ISO sand case bearing capacity check was:

UC = 1.1 * 164.3 MN / 155.7 MN = 1.16

9.10.2 The assessment progressed to Step 3 where it was determined that the additional

settlement would be minimal.

9.10.3 The RG V ISO sand case sliding check was as follows:

UC = 1.25 * 11.0 / 6.5 = 2.12

FH = 11.0 MN; FV = 9.4 MN, QH = 6.5 MN (δ = Ф =34o), γR,Hfc= 1.25

9.10.4 The RG V ISO clay case bearing capacity check was:

UC = 1.1 * (149.8 + 41.2) MN / 196.9 MN = 1.07


settlement would be of 2.5 – 3m and therefore excessive. Sliding was not an issue

for this deep penetration.

9.10.6 The 116C ISO sand case bearing capacity check was:

UC = 1.1 * 60.0 MN / 51.4 MN = 1.28

Heading





settlement would be minimal.

9.10.8 The 116C ISO sand case showed negative reactions (uplift) and therefore failure

of the sliding checks.

9.10.9 The 116C ISO clay case bearing capacity check was:

UC = 1.1 * (38.7 + 16.4) MN / 64.4 MN = 0.94

9.10.10 Sliding was not an issue for this deep penetration.




10 CONCLUSIONS AND RECOMMENDATIONS

10.1 Conclusions

10.1.1 The study did not identify any ‘show stoppers’ or major disconnection between

SNAME and ISO in terms of assessment results. It is noted that the standard

includes significant technical developments and will require a high level of

technical proficiency from its future users in many different areas.

10.1.2 Dynamic Amplification Factor (DAF) calculation issues aside, it seems that ISO

might be generally more favourable than SNAME due to the wave kinematics

factors which are generally κ <0.86. The present study adopted a wave kinematics

factor κ = 0.86 in all ISO assessments.

10.1.3 Foundation checks controlled the assessment results in all cases, with particular

reference to sliding checks for sand cases. All sand cases failed the sliding checks

by a significant margin.

10.2 Recommendations

10.2.1 Some technical issues deserve further attention: a) Intrinsic / Apparent Wave for

DAF calculations; b) Random DAF calculation methods (Winterstein vs. Drag-

Inertia); c) Clearer recommendations for Flat / Rough & Conical Shape spudcans

(use Φ or δ).

10.2.2 It seems that a good quality random time-domain analysis on a simplified

structural model to check the foundations provides a very good indication of a rig

suitability for a given site as overturning, elevating system and structural checks

seldom seem to control the results of the assessment.




11 REFERENCES

/1/ LeTourneau. ‘Phase 2 ISO Benchmarking of Super Gorilla - LeTourneau Class

219-C Artificial Benchmarking Parameters’ email dated 16th

March 2010.

/2/ LeTourneau. ‘LeTourneau Comments on example "Go-By" Calculations for ISO

DIS 19905-1 (E)’ email dated 3rd

November 2010.

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