dnv lifting
TRANSCRIPT
DNV Marine Operations’ Rules for Subsea Lift Operations
Simplified Methods for Prediction of Hydrodynamic Forces
Tormod Bøe
DNV Marine Operations
29th November 2011
DNV Marine Operations' Rules for Subsea Lift Operations Slide 2 29. November 2011
Content
Brief overview of relevant DNV publications
DNV Rules for Marine Operations, 1996,
Pt.2 Ch.5 Lifting – Capacity Checks
Simplified Methods for prediction of Hydrodynamic Forces
o in Splash Zone, DNV-RP-H103 Ch.4
o in Deepwater, DNV-RP-H103 Ch.5
DNV Marine Operations' Rules for Subsea Lift Operations Slide 3 29. November 2011
Relevant DNV Publications
Lifting- and subsea operations :
Specially planned non-routine operations Routine operations
DNV Standard for Certification No.2.22 Lifting Appliances
October 2011
DNV Rules for Planning and Execution of
Marine Operations – 1996 and
DNV-OS-H101 Marine Operations, General - 2011
’Specially planned, non-routine operations of
limited durations, at sea. Marine operations are
normally related to temporary phases as e.g.
load transfer, transportation and installation.’
DNV-OS-E402 Offshore
Standard for Diving Systems
October 2010
DNV Standard for Certification
No. 2.7-3 Portable Offshore Units
May 2011
DNV Marine Operations' Rules for Subsea Lift Operations Slide 4 29. November 2011
DNV-RP-C205 Environmental Conditions and Environmental Loads October 2010
DNV-RP-H101 Risk Management in Marine and Subsea Operations, January 2003
DNV-RP-H102 Marine Operations during Removal of Offshore Installations, April 2004
DNV-RP-H103 Modelling and Analysis of Marine Operations, April 2011
Relevant DNV Publications - Other
DNV Marine Operations' Rules for Subsea Lift Operations Slide 5 29. November 2011
Relevant DNV Publications - WebSite
Most DNV publications can be downloaded for free at:
http://www.dnv.com
The 1996 DNV Rules for Marine Operations is not in the DNV intranet site.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 6 29. November 2011
Content
Brief overview of relevant DNV publications
DNV Rules for Marine Operations, 1996,
Pt.2 Ch.5 Lifting – Capacity Checks
Simplified Methods for prediction of Hydrodynamic Forces
o in Splash Zone, DNV-RP-H103 Ch.4
o in Deepwater, DNV-RP-H103 Ch.5
DNV Marine Operations' Rules for Subsea Lift Operations Slide 7 29. November 2011
Capacity Checks - DNV 1996 Rules
Dynamic loads, lift in air
Crane capacity
Rigging capacity, (slings, shackles, etc.)
Structural steel capacity (lifted object, lifting points, spreader bars, etc.)
Part 2 Chapter 5
Dynamic loads for subsea lifts are estimated according to DNV-RP-H103
DNV Marine Operations' Rules for Subsea Lift Operations Slide 8 29. November 2011
Capacity Checks – DAF for Lift in Air
Dynamic loads are accounted for by
using a Dynamic Amplification Factor
(DAF).
DAF in air may be caused by e.g.
variation in hoisting speeds or motions
of crane vessel and lifted object.
The given table is applicable for
offshore lift in air in minor sea states,
typically Hs < 2-2.5m.
DAF must be estimated separately for
lifts in air at higher seastates and for
subsea lifts !
Table 2.1 Pt.2 Ch.5 Sec.2.2.4.4
DNV Marine Operations' Rules for Subsea Lift Operations Slide 9 29. November 2011
The dynamic hook load, DHL, is given by:
DHL = DAF*(W+Wrig) + F(SPL)
ref. Pt.2 Ch.5 Sec.2.4.2.1
Capacity Checks - Crane Capacity
W is the weight of the structure, including a weight inaccuracy factor
The DHL should be checked against available crane capacity
The crane capacity decrease when the lifting radius increase.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 10 29. November 2011
The maximum dynamic sling load, Fsling, can be calculated by:
Fsling = DHL∙SKL∙kCoG∙DW / sin φ
ref. Pt.2 Ch.5 Sec.2.4.2.3-6
where:
Capacity Checks - Sling Loads
SKL = Skew load factor → extra loading
caused by equipment and fabrication tolerances.
kCoG = CoG factor → inaccuracies in estimated
position of centre of gravity.
DW = vertical weight distribution → e.g.
DWA = (8/15)∙(7/13) in sling A.
φ = sling angle from the horizontal plane.
Example :
DNV Marine Operations' Rules for Subsea Lift Operations Slide 11 29. November 2011
”Safe working load”, SWL, and ” MBL, of the shackle are checked by :
a) Fsling < SWL∙ DAF
and b) Fsling < MBL / 3.3
Both criteria shall be fulfilled (Pt.2 Ch.5 Sec.3.2.1.2)
The sling capacity ”Minimum breaking load”, MBL, is checked by:
The safety factor is minimum sf ≥ 3.0. (Pt.2 Ch.5 Sec.3.1.2)
Capacity Checks - Slings and Shackles
sf
slingsling
γ
MBLF
DNV Marine Operations' Rules for Subsea Lift Operations Slide 12 29. November 2011
Lifting points:
The load factor f = 1.3, is increased by a
consequence factor, C = 1.3, so that total
design faktor, design , becomes:
design = c∙ f = 1.3 ∙ 1.3 = 1.7
The design load acting on the lift point becomes:
Fdesign = design∙ Fsling = 1.7∙ Fsling
Capacity Checks – Structural Steel
Other lifting equipment:
A consequence factor of C = 1.3 should be applied on lifting yokes, spreader bars, plateshackles, etc.
Structural strength of Lifted Object:
The following consequence factors
should be applied :
A lateral load of minimum 3% of the design load shall be included. This load acts in the shackle bow !
(ref. Pt.2.Ch.5 Sec.2.4.3.4) Table 4.1 Pt.2 Ch.5 Sec.4.1.2
DNV Marine Operations' Rules for Subsea Lift Operations Slide 13 29. November 2011
Capacity Checks – Summary
Capacity
of lifting
equipment
Weight of lifted object
and lifting equipment
Skew load, CoG and sling angle
Safety factors
Lift in air: VMO Rules Pt.2 Ch.5
Subsea lift: DNV-RP-H103
Compute Apply
Fsling
Crane
capacity DHL
DAF
Check
DNV Marine Operations' Rules for Subsea Lift Operations Slide 14 29. November 2011
Content
Brief overview of relevant DNV publications
DNV Rules for Marine Operations, 1996,
Pt.2 Ch.5 Lifting – Capacity Checks
Simplified Methods for prediction of Hydrodynamic Forces
o in Splash Zone, DNV-RP-H103 Ch.4
o in Deepwater, DNV-RP-H103 Ch.5
DNV Marine Operations' Rules for Subsea Lift Operations Slide 15 29. November 2011
Simplified Method, Splash Zone - DNV-RP-H103
The Recommended Practice; ”DNV-RP-H103 Modelling and Analysis of Marine Operations” was issued april 2009. Latest revision is april 2011.
A Simplified Method for calculating hydrodynamic forces on objects lifted through wave zone is included in chapter 4.
This Simplified Method supersedes the calculation guidelines in DNV Rules for Marine Operations, 1996, Pt.2 Ch.6.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 16 29. November 2011
Simplified Method, Splash Zone - Assumptions
The Simplified Method is based upon the following main assumptions:
the horizontal extent of the lifted object is
small compared to the wave length
the vertical motion of the object is equal the
vertical crane tip motion
vertical motion of object and water dominates
→ other motions can be disregarded
The intention of the Simplified Method is to give simple conservative estimates of the forces acting on the object.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 17 29. November 2011
New Simplified Method - Assumptions
Time-domain analysis:
• Coupled multi-body
systems with individual
forces and motions.
• Wind, wave and current
forces.
• Geometry modelled.
• Motions for all degrees
of freedom computed.
• Non-linearities included.
• Coupling effects.
• Continous lowering
simulations.
• Varying added mass.
• Statistical analysis of
responses.
• Visualization of lift.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 18 29. November 2011
Simplified Method, Splash Zone - Crane Tip Motions
The Simplified Method is unapplicable if the crane tip oscillation period or the wave period is close to the resonance period, Tn , of the hoisting system
K
AMTn
332
Heave, pitch and roll RAOs for the vessel should be combined with crane tip position to find the vertical motion of the crane tip
If operation reference period is within 30 minutes, the most probable largest responses may be taken as 1.80 times the significant responses
Unless the vessel heading is fixed, vessel response should be analysed for wave directions at least ±15° off the applied vessel heading
DNV Marine Operations' Rules for Subsea Lift Operations Slide 19 29. November 2011
Simplified Method, Splash Zone - Wave Periods
139.8 zTg
Hs
A lower limit of Hmax=1.8·Hs=λ/7 with
wavelength λ=g·Tz2/2π is here used.
g
H
zTS
6.10A lower limit of Hmax=1.8·Hs=λ/10 with wavelength
λ=g·Tz2/2π is here used.
There are two alternative approaches:
Alt-1) Wave periods are included:
Analyses should cover the following zero-crossing wave period range:
Alt-2) Wave periods are disregarded:
Operation procedures should in this case reflect that the calculations are only valid for waves longer than:
DNV Marine Operations' Rules for Subsea Lift Operations Slide 20 29. November 2011
Alt-1) Wave periods are included:
The wave amplitude, wave particle velocity and acceleration can be taken as:
Simplified Method, Splash Zone - Wave Kinematics
Sa H 9.0
gT
zaw
z
d
eT
v2
24
2
gT
zaw
z
d
eT
a2
24
22
sHd35.0
v esHg30.0w
sHd35.0
a eg10.0w
Alt-2) Wave periods are disregarded:
The wave particle velocity and acceleration can be taken as:
d : distance from water plane to CoG of submerged part of object
DNV Marine Operations' Rules for Subsea Lift Operations Slide 21 29. November 2011
Slamming impact force
Slamming forces are short-term impulse
forces that acts when the structure hits the
water surface.
AS is the relevant slamming area on the
exposed structure part. Cs is slamming coeff.
The slamming velocity, vs, is :
Simplified Method, Splash Zone - Hydrodynamic Forces
22
wctcs vvvv
gVF
Varying buoyancy force
Varying buoyancy, Fρ , is the change in
buoyancy due to the water surface
elevation.
δV is the change in volume of displaced
water from still water surface to wave crest
or wave trough.
vc = lowering speed
vct = vertical crane tip velocity vw = vertical water particle velocity at water surface
22~ctawAV
gVF
ζa = wave amplitude
ηct = crane tip motion amplitude
Ãw = mean water line area in the
wave surface zone
DNV Marine Operations' Rules for Subsea Lift Operations Slide 22 29. November 2011
Mass force
“Mass force” is here a combination of inertia force, Froude-Kriloff force and diffraction force.
Crane tip acceleration and water particle acceleration are assumed statistically independent.
Drag force
Drag forces are flow resistance on submerged part of the structure. The drag forces are related to relative velocity between object and water particles.
The drag coefficient, CD, in oscillatory flow for complex subsea structures may typically be CD ≥ 2.5.
Relative velocity are found by :
Simplified Method, Splash Zone - Hydrodynamic Forces
22
wctcr vvvv
vc = lowering/hoisting speed vct = vertical crane tip velocity vw = vertical water particle velocity at water depth , d Ap = horizontal projected area
M = mass of object in air A33 = heave added mass of object act = vertical crane tip acceleration V = volume of displaced water relative to the still water level aw = vertical water particle acceleration at water depth, d
2
33
2
33 wctM aAVaAMF
DNV Marine Operations' Rules for Subsea Lift Operations Slide 23 29. November 2011
Simplified Method, Splash Zone - Basics
Forces:
• Weight [N]
• Buoyancy [N] Weight = M*gmoon
Weight = M*g
Buoyancy = ρ*V*g
Properties:
• Mass, M [kg]
• Volume, V [m3]
• Added mass, A33 [kg]
DNV Marine Operations' Rules for Subsea Lift Operations Slide 24 29. November 2011
Simplified Method, Splash Zone - Added Mass
Hydrodynamic added mass for flat plates
ba4
76.0A 233
Example:
Flat plate where length, b, above breadth, a, is b/a = 2.0 :
DNV Marine Operations' Rules for Subsea Lift Operations Slide 25 29. November 2011
Simplified Method, Splash Zone - Added Mass
Added Mass Increase due to Body Height
The following simplified approximation of the added mass in heave for a three-dimensional body with vertical sides may be applied :
o332
2
33 A)1(2
11A
p
p
Ah
A
where
A33o = added mass for a flat plate with a shape equal to the horizontal projected area of the object
h = height of the object
Ap = horizontal projected area of the object
and
Added Mass Increase due to Body Height
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
0 0.5 1 1.5 2 2.5
ln [ 1+ (h/sqrt(A)) ]
A33
/A33
o
1+SQRT((1-lambda 2̂)/(2*(1+lambda 2̂)))
DNV Marine Operations' Rules for Subsea Lift Operations Slide 26 29. November 2011
Added Mass from Partly Enclosed Volume
Simplified Method, Splash Zone - Added Mass
A volume of water partly enlosed within large plated surfaces will also contribute to the added mass, e.g.:
The volume of water inside suction anchors or foundation buckets.
The volume of water between large plated mudmat surfaces and roof structures.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 27 29. November 2011
Added Mass Reduction due to Perforation
Simplified Method, Splash Zone - Added Mass
No reduction applied in added mass when perforation is small. A significant drop in the
added mass for larger perforation rates. Reduction factor applicable for p<50.
.
Effect of perforation on added mass
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50Perforation
Ad
ded
Mass R
ed
ucti
on
Facto
r
e^-P/28
BucketKC0.1-H4D-NiMo
BucketKC0.6-H4D-NiMo
BucketKC1.2-H4D-NiMo
BucketKC0.5-H0.5D-NiMo
BucketKC1.5-H0.5D-NiMo
BucketKC2.5-H0.5D-NiMo
BucketKC3.5-H0.5D-NiMo
PLET-KC1-4
Roof-A0.5-2.5+
Hatch20-KCp0.5-1.8
Hatch18-KCp0.3-0.8
BucketKC0.1
BucketKC0.6
BucketKC1.2
RoofKCp0.1-0.27
RoofKCp0.1-0.37
DNV-Curve
Mudmat CFD
0.1A
A
S33
33
34/)5p(cos3.07.0A
A
S33
33
28
p10
S33
33 eA
A
if p< 5
if 5 < p < 34
if 34 < p < 50
Recommended reduction:
A33S = added mass for a non-
perforated structure.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 28 29. November 2011
Simplified Method, Splash Zone - Hydrodynamic Forces
The hydrodynamic force is a time dependent function of slamming impact force, varying buoyancy, hydrodynamic mass forces and drag forces. In the Simplified Method the forces may be combined as follows:
22 )()( FFFFFMD slamhyd
The structure may be divided into main items and surfaces contributing to the hydrodynamic force
Water particle velocity and acceleration are related to the vertical centre of gravity for each main item. Mass and drag forces contributions are then summarized :
i
iMM FF i
iDD FF
FMi and FDi are the individual force contributions from each main item
DNV Marine Operations' Rules for Subsea Lift Operations Slide 29 29. November 2011
Simplified Method, Splash Zone - Load Cases Example
Load Case 1
Still water level beneath top of ventilated buckets
Slamming impact force, Fslam, acts on top of buckets. Inertia force to be included.
Varying buoyancy force, Fρ , drag force, FD and hydrodynamic part of mass force, FM are negligible.
The static and hydrodynamic force should be calculated for different stages. Relevant
load cases for deployment of a protection structure could be:
Load Case 2
Still water level above top of buckets
Slamming impact force, Fslam, is zero
Varying buoyancy, Fρ , drag force, FD and mass force, FM, are calculated. Velocity and acceleration are related to CoG of submerged part of structure.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 30 29. November 2011
Simplified Method, Splash Zone - Load Cases Example
Load Case 3
Still water level beneath roof cover.
Slamming impact force, Fslam, acts on the roof cover.
Varying buoyancy, Fρ , drag force, FD and mass force, FM are calculated on the rest of the structure. Drag- and mass forces acts mainly on the buckets and is related to a depth, d, down to CoG of submerged part of the structure.
Load Case 4
Still water level above roof cover.
Slamming impact force, Fslam, and varying
buoyancy, Fρ, is zero.
Drag force, FD and mass force, FM are calculated
individually. The total mass and drag force is the
sum of the individual load components, e.g. :
FD= FDroof + FDlegs+ FDbuckets applying correct CoGs
DNV Marine Operations' Rules for Subsea Lift Operations Slide 31 29. November 2011
Simplified Method, Splash Zone - Load Cases Example
DNV Marine Operations' Rules for Subsea Lift Operations Slide 32 29. November 2011
Simplified Method, Splash Zone - Static Weight
In addition, the weight inaccuracy factor should be applied
DNV Marine Operations' Rules for Subsea Lift Operations Slide 33 29. November 2011
Simplified Method, Splash Zone - DAF
Capacity Checks
The capacities of crane, lifting equipment and lifted object are checked as for lift in air. The following relation should be applied:
where
Mg : weight of object [N]
Ftotal : is the characteristic total force on the (partly or fully) submerged object. Taken as the largest of;
Ftotal = Fstatic-max + Fhyd or
Ftotal = Fstatic-max + Fsnap
Fstatic-max is the maximum static weight of the submerged object including flooding and weight inaccuracy factor
Fhyd is the hydrodynamic force
Fsnap is the snap load (normally to be avoided)
Mg
FDAF total
DNV Marine Operations' Rules for Subsea Lift Operations Slide 34 29. November 2011
Simplified Method, Splash Zone - Slack Slings
The Slack Sling Criterion.
Snap forces shall as far as possible be avoided. Weather crietria should be adjusted to ensure this.
The following criterion should be fulfilled in order to ensure that snap loads are avoided:
minstatichyd F9.0F
Fstatic-min = weight before flooding, including a weight reduction implied by the weight inaccuracy factor.
Simplified Method, Splash Zone - Results
Tables can be computed giving an overview of operable seastates
Maximum allowable Fhyd is derived from max allowable DAF and the slack sling criterion
Red results are above installation limit
”Outside” means non-existent seastates
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 35
Hydrodynamic force on object, FhydTz\Hs 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
2.0 12.24 Outside Outside Outside Outside Outside Outside Outside
2.5 8.33 Outside Outside Outside Outside Outside Outside Outside
3.0 6.14 20.45 Outside Outside Outside Outside Outside Outside
3.5 4.79 15.54 32.45 Outside Outside Outside Outside Outside
4.0 3.89 12.34 25.53 Outside Outside Outside Outside Outside
4.5 3.29 10.19 20.89 35.40 53.71 Outside Outside Outside
5.0 2.87 8.73 17.76 29.97 45.35 63.92 Outside Outside
5.5 2.57 7.70 15.57 26.17 39.52 55.61 74.44 Outside
6.0 2.35 6.92 13.90 23.30 35.10 49.32 65.96 85.00
6.5 2.16 6.27 12.53 20.94 31.49 44.18 59.02 76.01
7.0 2.00 5.72 11.36 18.92 28.40 39.79 53.10 68.33
7.5 1.85 5.24 10.34 17.17 25.72 35.98 47.97 61.68
8.0 1.73 4.82 9.46 15.65 23.39 32.68 43.52 55.91
8.5 1.62 4.45 8.68 14.32 21.36 29.81 39.66 50.91
9.0 1.52 4.13 8.01 13.17 19.60 27.31 36.30 46.56
9.5 1.43 3.84 7.42 12.16 18.06 25.13 33.37 42.76
10.0 1.36 3.59 6.90 11.27 16.71 23.22 30.79 39.44
10.5 1.29 3.37 6.43 10.48 15.51 21.53 28.52 36.50
11.0 1.23 3.17 6.02 9.78 14.45 20.03 26.51 33.90
11.5 1.17 2.99 5.66 9.16 13.50 18.69 24.71 31.58
12.0 1.12 2.83 5.33 8.60 12.65 17.49 23.10 29.50
12.5 1.07 2.69 5.03 8.09 11.89 16.41 21.65 27.62
13.0 1.03 2.55 4.75 7.63 11.19 15.42 20.34 25.93
DNV Marine Operations' Rules for Subsea Lift Operations Slide 36 29. November 2011
Simplified Method, Splash Zone - Summary
DAF within
capacity
requirements
Object motion equal crane tip
Wave kinematics dependent on
assumed Hs,Tz seastate
Different deployment levels
Structure divided in main items
Compute Apply
No slack
slings Fhyd
Check
DAF
Fd, Fm,
Fslam and Fρ
DNV Marine Operations' Rules for Subsea Lift Operations Slide 37 29. November 2011
Simplified Method, Splash Zone - Summary
The simplified method
assumes that:
• Vertical motion of
structure is equal
to the crane tip
motion.
• The horizontal
extension of the
structure is small.
• Only vertical
motion is present.
More accurate
calculations can be
performed applying:
• Regular design
wave approach
(Ch. 3.4.2)
• Time domain
analyses
• CFD analyses
DNV Marine Operations' Rules for Subsea Lift Operations Slide 38 29. November 2011
Content
Brief overview of relevant DNV publications
DNV Rules for Marine Operations, 1996,
Pt.2 Ch.5 Lifting – Capacity Checks
Simplified Methods for prediction of Hydrodynamic Forces
o in Splash Zone, DNV-RP-H103 Ch.4
o in Deepwater, DNV-RP-H103 Ch.5
Deepwater Operations - Challenges
Challenges :
Static weight at crane tip increases linearly with cable length.
The resonance period of the lifting system increases with cable length. Dynamic forces may increase due to resonant amplification induced by the vertical crane tip motion.
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 39
Dynamic Forces – Vertical resonance
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 40
Simplified Method, Deepwater - Assumptions
The following main assumptions are applied:
the subsea structure is lowered into deepwater and is unaffected by wave forces
the vertical motion of crane tip and subsea structure dominates → other motions can be disregarded
Offset due to current forces is disregarded
Heave compensation systems are not taken into account
DNV-RP-H103 Chapter 5 includes a simplified method for estimating dynamic response of lowered object.
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 41
Case Study – Main Data
The subsea structure mass is 97 tonnes
Water depth is 3000 m
The crane cable is a conventional steel wire
No heave compensation system
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 42
Case Study – Crane Tip Motion
Lift at side of crane vessel
Wave heading 15° off bow
RAO in heave, pitch and roll are combined in order to find the vertical motion at the crane tip
Vessel’s natural period in roll at T=9s dominates
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 43
Case Study – Dynamic Load at Lifted Object
Comparison with a non-linear time-domain FE analysis
Dynamic amplification 20% higher at natural period T0=9s
Dynamic amp. at T=1.5s due to longitudinal pressure waves
No wave energy at T=1.5s, hence deviation is acceptable
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 44
Cable length L=2750m
Case Study – Dynamic Load at Lifted Object
Transfer functions for dynamic load in cable and crane tip motion are combined with a wave spectrum S(ω)
Jonswap wave spectrum with Hs=2.0m and Tp=9s is applied
Most probable largest response for dynamic force in cable is found by:
A duration time t =30 minutes gives Fd=530kN in this case
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 45
Case Study – Dynamic Load at Lifted Object
Calculations are repeated for a range of seastates
Hs=2.0m gives acceptable dynamic loads for all wave periods
Natural period of the lifting system is T0=9s
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 46
Case Study – Dynamic Load at Lifted Object
Calculations are repeated for a range of cable lengths
Max Fd for all Tz values
Fd<0.9*Fstatic in order to avoid risk of snap loads due to slack slings; Fd < 68t
Capacity requirement of crane and cable governs for cable lengths above L>2250m due to weight of cable
Non-operable seastates
29. November 2011 DNV Marine Operations' Rules for Subsea Lift Operations Slide 47
DNV Marine Operations' Rules for Subsea Lift Operations Slide 48 29. November 2011
Simplified Method, Deepwater - Summary
DNV-RP-H103 chapter 5 contains a simplified method for
establishing dynamic loads and limiting weather criteria during
deepwater lifting operations
Most probable largest dynamic load in the lifting line is computed
taking into account dynamic amplification due to resonance
effects
The simplified method is well suited for common spreadsheet
programs or other computer software for engineering
calculations.
DNV Marine Operations' Rules for Subsea Lift Operations Slide 49 29. November 2011
.. Questions ??
DNV Marine Operations' Rules for Subsea Lift Operations Slide 50 29. November 2011