Comparison for MSC CJ62 rig of ISO versus SNAME for Clay and …€¦ · Comparison for MSC CJ62...
Transcript of Comparison for MSC CJ62 rig of ISO versus SNAME for Clay and …€¦ · Comparison for MSC CJ62...
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Phase 2 ISO 19905-1 Benchmarking study
GustoMSC21 Oct 2010
Comparison for MSC CJ62 rig of ISO
versus SNAME for Clay and Sand site
Basic data
Jack-up:
MSC design CJ62 type drilling rig
Some numbers in the analyses:
17118 t elevated (survival) weight
Triangular shaped hull, spacing 62 m
3 truss legs, leg length 175.3 m, chord spacing 16 m, X-brace
Spudcan (traditional shape), 250 m^2
Pre-load capacity per leg 13680 t
Fixation systems 9500
BLM rack-pinion jacking system type C170 (54 pinions)
Chords tubular with racks
Basic data
Spudcan / penetration data:
Some numbers in the analyses:
Pre-load at seabed applied: 152.9 MN
Effective diameter B = 17.84 m
Maximum bottom area 250 m^2
Tip to maximum area = 1.60 m
Basic data
site conditions:Site description North Sea (dense) sand GoM (deep) clay
General
Water depth (LAT) 104.7 80
Airgap 25 20
SWL 2 2.5
Metocean
Hmax 28 22.0
Tass 15.8 16.0
Wind 45 50
Current 1.00 1.50
Soil Dense sand Soft clay
Basic data
Wave kinematics & wave period:Site description North Sea sand - fixity GoM (deep) clay - fixity
Dynamics
Intrinsic wave period / DAF 15.8 s / 1.25 16.0 s / 1.16
Apparent wave period / DAF 15.2 s / 1.28 15.0 s / 1.18
Applied in assessment 1.28 for ISO
1.25 for SNAME
1.16 for ISO & SNAME
Wave kinematics
Latitude or region 58.50 North Sea TRS (GoM)
Directional spreading factor 0.90 0.87
Kinematics reduction factor 0.80 0.77
Applied in assessment 0.86 on kinematics ISO
0.86 on wave height
SNAME
0.86 on kinematics
Basic data
soil conditions sand site:Site description North Sea (dense) sand
type - Medium dense (silica) sand
Internal friction angle [deg] 34
Effective subm weight ’ [kN/m3] 11
Steel-soil friction angle [deg] 29 = ( – 5)
Relative density Dr [%] 65
Poisson’s ratio [-] 0.2
Shear modulus G 23765* sqrt(Vswl/(101.3A)
D50/D90 particle size 0.095mm / 0.15mm
Basic data
Foundation data:Site description North Sea (dense) sand
Leg penetration estimate [m] 1.4
Spudcan contact diameter [m] / [%] 14.0 / 80%
Foundation fixity
Shear modulus G [MPa] 50 (soil data)
Applied G in fixity [Mpa] 46 MPa, based on recommendations
Rotational stiffness [MNm/rad] 53000
Capacity VHM - Standard sand, VL0 = 152.9 MN
Basic data
soil conditions clay site:Site description GoM (deep) clay - fixity
type - Very soft to stiff calcareous clay
Shear strength [kPa] See table
Shear modulus [MPa] See table
OCR [-] 1.0 – 1.4 (see table)
Poisson’s ratio [-] 0.5
Sensitivity ratio [-] 2.7
Basic data
Foundation data:
**) Tables in ISO to be added to include effects of poisson’s ratio > 0
Site description GoM (deep) clay - fixity
Leg penetration estimate [m] 45.6
Gross capacity [MN] 190 (pre-load = 153)
Backfill (after pre-loading) [MN] 8 (8 m)
Shear modulus for fixity
Shear modulus G [MPa] 43 (soil data) => G/su = 730
Applied G in fixity [Mpa] 34 MPa, limited to G/su ≤ 600 in line
with recommendations
Embedment factor [-] 2.2 **), ISO gives 2.4
Rotational stiffness [MNm/rad] 284000 MNm/rad, ISO = 310000
Yield surface (ISO, gross cap) V=190, H=20, M = 401, a = 0.99
Yield surface (SNAME, net cap) V = 153, H = 19.2, M = 428, a = 0.99
Summary of results – sand site
North Sea site sand - pinned sand – fixity
ISO SNAME % ISO SNAME %
Leg penetration [m] 1.40 1.35-1.43 0% - -
SDOF-DAF 1.54 1.47 15% 1.28 1.25 12%
External OTM [MNm] 3022 2796 8% 2640 2486 6%
Max/
Min V reaction [MN]
144.7/
-0.5
140.0/
5.2
3%
/NA
131.6/
12.4
127.5/
16.0
3%
/NA
Chord Pu [MN] 119 111.1 7% 102 94.2 8%
Utilisations:
Holding 1.01 0.90 12% 0.80 0.76 5%
Chord 0.98 1.09 -10% 0.83 0.92 -10%
Overturning stab 1.08 0.97 11% 0.85 0.79 8%
Pre-load (1.05) (1.02) 3% (0.96) (0.93) 3%
VH bearing 1.39 1.27 9% 1.16 1.05 10%
Sliding (50% variable load) Leg lift 3.7 NA 1.36(1b) 0.98(1b) 39%
Sliding (100% variable load) > 5 2.9 NA 1.10 0.88 25%
Summary of results – sand site
Effect of apparent wave period in DAF (with fixity = 1.28) is 6%
more inertia load, 1% more total external loading and 0.5%
more vertical soil reaction
Effect of H = 0.86*H (SNAME) iso on wave kinematics (ISO) is
7% on w/c load, 5% on total external loading and 2.5% on
vertical soil reaction
Increased UC’s in general due to increased external loading
(see above). Chord improved. VH bearing check worse.
Two variations to see effects:
ISO using the exact external loading as in the SNAME case
ISO using the = 0.80 (new formula)
Summary of results – sand site
North Sea site ISO load variations SNAME
ISO
= 0.86
SNAME
ext loads
= 0.80 SNAME
External OTM [MNm] 2640 2486 2432 2486
Utilisations:
Holding 0.80 0.75 0.72 0.76
Chord 0.83 0.78 0.76 0.92
Pre-load (0.96) (0.93) (0.92) (0.93)
VH bearing 1.16 1.08 1.06 1.05
Sliding (50% variable load) 1.36 1.07 (2a)
0.98 (1b)
1.04 (2a)
0.89 (1b)
0.98
Sliding (100% variable load) 1.10 1.05 (2a)
0.88 (1b)
1.00 (2a)
0.77 (1b)
0.88
Summary of results – clay site
SNAME external loading and ISO external loading is based
both on: k = 0.86 on wave kinematics (not Height) and DAF on
intrinsic period.
Effect of apparent wave period in DAF is 15% more inertia load,
1% more total external loading and 0.5% more vertical soil
reaction
Effect of H = 0.86*H (SNAME) iso on wave kinematics (ISO) is
3% on w/c load, 2% on total external loading and 1.5% on
vertical soil reaction
Summary of results – clay site
Gulf of Mexico site Deep clay SNAME rev 3 orig
ISO SNAME % SNAME
Leg penetration [m] 45 45 0% -
SDOF-DAF 1.158 1.162 -2% 1.162 -2%
External OTM [MNm] 2743 2749 -0.2% 2749 -0.2%
Max reaction [MN] 162.9 115.5 3%(net) 126.2 -7%(net)
Fixity [%] 31% 35% 12% 20% 50%
Chord Pu [MN] 78.1 75 7% 89.5 -15%
Utilisations:
Holding 0.62 0.61 1% 0.73 -12%
Chord 0.65 0.73 -10% 0.87 -25%
(Pre-load) (0.91)net (0.90) 1% (0.97) -6%
VH bearing 1.05 0.80 30% 0.93 +12%
Sliding 0.67 0.66 1% 0.70 -4%
Summary of observations
In general the assessment progresses very similar: Leg penetration agree quite well
External loading (except apparent/intrinsic discussion)
Fixity (if SNAME has deep clay method and embedment updated)
Response
Holding, overturning
The step 1a pre-load check agrees, but is hardly ever allowed (H/V ratio exceeded or when fixity included)
The step 1b sliding check agrees
The structural check of the chord provides some significant improvement in the results (upto 20% due to safety and buckling load)
Foundation checks were found to be governing (by far)
The foundation (bearing) check level 2 needs some careful as it deviates from SNAME and adversely affects the outcome upto some 30 % in a step 2a/2b assessment (step 2c or step 3 has not been assessed) in terms of: The way to apply the material coefficient (on yield surface versus on capacity vector)
Excluding side resistance (a slice of the VHM surface)
Gross capacity versus net capacity (deep clay)
The foundation sliding for windward legs in SNAME is a pure step 1b check only, in ISO it is also the (relevant) VH bearing check, but here excludes side resistance
Chord strength
In general the chord strength check is similar, except: the material coefficient for axial loading is 1.10 (compared to 1.15 (1/0.85) for SNAME)
thechord axial strength Pn is based on a formula for Fy > 450 Mpa which gives more capacity
Discussion points
External loading:Wind load is identical
Wave/current loading affected by:
Application of kinematics reduction factor (method and value)
Inertia loading affected by use of apparent wave period i.s.o. intrinsic
Application of kin red fact directly on wave kinematics is the right way. Allowance to reduce the wave height underestimates OTM slightly. Both methods are presently allowed in both ISO and SNAME
ISO defines formula to calculate appropriate kin red fact for each rig&site specific case. The underlying method is in principle what is allowed to do (time domain simulation of wave/current loading in an irregular sea) in SNAME and ISO. The result may both be below and in excess of 0.86
In the present assessment cases using the appropriate kin red factor (0.80 NS and 0.77 GoM) in combination with DAFapparent leads to a reduction of external load:2.5% for NS
2508/2685 =>7% for GoM
Discussion points
The foundation (bearing) check level 2
Governing the assessment results upto step 2b assessment
Is more conservative than SNAME due to: The way to apply the material coefficient (on yield surface versus on capacity vector)
Excluding side resistance (a slice of the VHM surface)
Gross capacity versus net capacity (deep clay)
In the present (basic) cases the VH bearing check found was more conservative by:3% for sand (North Sea with same external loading)
30% for clay (GoM)
The pre-load check (net capacity) is in agreement, but inappropriate because of fixity in the calculations
The foundation sliding for windward legs in SNAME is a pure step 1b check only, in ISO it is also the (relevant) VH bearing check, but here excludes side resistance. Including the VH step 2a is relevant but should side resistance be included?
Sand check - comparison
0
2
4
6
8
10
12
14
16
18
20
0 20 40 60 80 100 120 140 160 180
VH & sliding comparison ISO - SNAMESAND - shallow penetration
ISO - factored yield
ISO - unfactored
Factored storm reactions [MN]
240 deg - leg 2
210 deg - leg 2
210 deg - leg 3
180 deg - leg 1
Sliding line (step 1b)
SNAME - unfactored
SNAME - allowed loads
Clay check - comparison
0.0
5.0
10.0
15.0
20.0
25.0
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0
VH & sliding comparisonISO - SNAME
CLAY deep penetration
ISO - unfactored
ISO - Factored VH yield surface
Step 1b Sliding check for windward legs
SNAME - yield unfact
SNAME - allowed loads
SNAME - sliding step 1b
vector loads
vector yield
Panel 4 update HamburgThe foundation (bearing) check level 2 with the proposed
Panel 4 change as of 19th October 2010:
For sand, with fixity, the UC was 1.16. Using the new definition and
m = 1.075 i.s.o. 1.10 for partial contact, we arrive at UC = 1.11
It agrees properly with SNAME results UC = 1.05, the difference
being load.
It is shown by the UC calculated using the exact SNAME loading F
= 7.59, V = 127.5 => UC = 1.05 (SNAME = 1.05)
Panel 4 Hamburg updateThe foundation (bearing) check level 2 with the proposed
Panel 4 change as of 19th October 2010:
For clay, with fixity, the UC was 1.05. Using the new definition and
m = 1.10 i.s.o. 1.15 for full contact, we arrive at UC = 0.93. SNAME
= 0.80
0.0
5.0
10.0
15.0
20.0
25.0
0.0 50.0 100.0 150.0 200.0
VH slice of VHM surface for M=0
unfactored gross capacity yield surface
Factored VH yield surface, gross capacity by 1.15vector loads
vector yield
Step 1b Sliding check for windward legs
Oct update of factored yield surface, factor 1.10 on net capacity