Section 3 Dynamic load components
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 10 Ship Units - Chapter 2 Loads and Load Combinations - Section 3 Dynamic load components

Section 3 Dynamic load components

Parent topic: Chapter 2 Loads and Load Combinations

3.1 Symbols

3.1.1 For the purposes of this Section, the following symbols apply:
L = Rule length, in metres, as defined in Pt 4, Ch 1, 5 Definitions
B = moulded breadth, in metres, as defined in Pt 4, Ch 1, 5 Definitions
D = moulded depth, in metres, as defined in Pt 4, Ch 1, 5 Definitions
= block coefficient, as defined in Pt 4, Ch 1, 5 Definitions
= wave coefficient to be taken as:
= 0,0412L + 4,0 for L < 90
= 10,75 – for 90 ≤ L ≤ 300
= 10,75 for 300 < L ≤ 350
= 10,75 – for 350 < L ≤ 500
GM = metacentric height, in metres, as defined in Pt 10, Ch 2, 3.2 General 3.2.3.(a)
= roll radius of gyration, in metres, as defined in Pt 10, Ch 2, 3.2 General 3.2.3.(a)
= 1,2 for units without bilge keel
= 1,0 for units with bilge keel
Tθ = roll period, in seconds, as defined in Pt 10, Ch 2, 3.5 Motions 3.5.2.(a)
θ = roll amplitude, in degrees, as defined in Pt 10, Ch 2, 3.5 Motions 3.5.2.(b)
Tϕ = pitch period, in seconds, as defined in Pt 10, Ch 2, 3.5 Motions 3.5.3.(a)
ϕ = pitch amplitude, in degrees, as defined in Pt 10, Ch 2, 3.5 Motions 3.5.3.(b)
=

,whichever is the greater, in metres

= pitch radius and is to be taken as the greater of

, in metres

=
= deep load draught, in metres
= draught in the loading condition being considered, in metres
= common acceleration parameter, as defined in Pt 10, Ch 2, 3.6 Accelerations 3.6.2.(a)
= envelope vertical acceleration, in m/s2, as defined in Pt 10, Ch 2, 3.6 Accelerations 3.6.3.(a), at tank centre of gravity
= envelope transverse acceleration, in m/s2, as defined in Pt 10, Ch 2, 3.6 Accelerations 3.6.4.(a), at tank centre of gravity
= envelope longitudinal acceleration, in m/s2, as defined in Pt 10, Ch 2, 3.6 Accelerations 3.6.5.(a), at tank centre of gravity
= vertical acceleration due to heave, is to be taken as:
= g m/s2
= vertical acceleration due to pitch, is to be taken as:
= m/s2
= vertical acceleration due to roll, is to be taken as:
= m/s2
= transverse acceleration due to sway and yaw, is to be taken as:
= 0,3g m/s2
= transverse acceleration due to roll, is to be taken as:
= m/s2
= longitudinal acceleration due to surge, is to be taken as:
= 0,2g a0 m/s2
= longitudinal acceleration due to pitch, is to be taken as:
= m/s2
ρ = density, tonnes/m3, as defined in Pt 10, Ch 2, 1.2 Definitions 1.2.3
g = acceleration due to gravity, 9,81 m/s2
x = longitudinal coordinate of load point under consideration, in metres
y = transverse coordinate of load point under consideration, in metres
z = vertical coordinate of load point under consideration, in metres
= longitudinal coordinate of reference point, for dynamic tank pressures is to be taken as the middle of the tank length at the top of the tank, in metres
= transverse coordinate of reference point, for dynamic tank pressures is to be taken as the middle of the tank breadth at the top of the tank, in metres
= vertical coordinate of reference point, for dynamic tank pressures is to be taken as the highest point in the tank, in metres
= probability factor, as defined in Pt 10, Ch 2, 3.4 Return periods and probability factor, fprob, as appropriate
= environmental factor due to pitch motion, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2
= environmental factor due to vertical acceleration, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.6 Accelerations 3.6.3
= environmental factor due to transverse acceleration, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.6 Accelerations 3.6.4
= environmental factor due to longitudinal acceleration, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.6 Accelerations 3.6.5
= environmental factor due to vertical wave bending moment, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.7 Dynamic hull girder loads 3.7.1
= environmental factor due to horizontal wave bending moment, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.7 Dynamic hull girder loads 3.7.1
= environmental factor due to vertical wave shear force, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.7 Dynamic hull girder loads 3.7.2
= environmental factor due to dynamic wave pressure, as defined in Pt 10, Ch 2, 3.3 Environmental factors 3.3.2 and Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.

3.2 General

3.2.1  Basic components.
  1. Formulae for unit loads, motions and accelerations are given in this sub-Section. Values calculated in accordance with the LR ShipRight Procedure for Ship Units may be used instead.
  2. Formulae for the envelope value of the basic dynamic load components are also given. The basic load components are:
    1. vertical wave bending moment and shear force;
    2. horizontal wave bending moment;
    3. dynamic wave pressure;
    4. dynamic tank pressures.
3.2.2  Envelope load values.
  1. The envelope loads for scantling requirements and strength assessment are based on the specific return period given in Table 2.3.3 Return periods for scantling requirements and strength assessment.
3.2.3  Metacentric height and roll radius of gyration for FPSO.
  1. The metacentric height, GM, and roll radius of gyration, , should be calculated for typical loading conditions as indicated in Table 2.3.1 GM and kr. For the initial design of units storing oil in bulk (e.g. FPSOs), the values in Table 2.3.1 GM and kr may be used. The values in Table 2.3.1 GM and kr for deep draught condition may be used for the initial design of units for the flooded load scenario, see Pt 10, Ch 2, 5.1 Flooded condition.

3.3 Environmental factors

3.3.1 The environmental factors are used to derive the dynamic load components for the intended site-specific condition and for the transit condition.

3.3.2 For design purposes, the environmental factors considering motion are specified in Table 2.3.2 Environmental factors. For sites not included in Table 2.3.2 Environmental factors, the factors are to be calculated in accordance with the LR ShipRight Procedure for Ship Units.

3.3.3 The environmental factors for the operational condition may be used for the inspection/maintenance case. The environmental factors for the deep draught for the operational condition may be used for the flooded case.

3.4 Return periods and probability factor, fprob

3.4.1 For each load condition, the environmental loads for scantling requirements and strength assessment are to be determined at the return periods specified in Table 2.3.3 Return periods for scantling requirements and strength assessment.

3.4.2 In no case are the environmental loads used for the assessment of the hull structure for on-site operation, restricted service area transit and delivery voyage to be less than 50 per cent of the 25-year return period dynamic loads defined for unrestricted worldwide transit service.

3.4.3 Environmental loads derived for the same wave environment, but at a different return period, may be adjusted to the required return period by use of the probability factor . Therefore, when the environmental loads are derived for the return periods specified in Table 2.3.3 Return periods for scantling requirements and strength assessment, is to be taken as equal to 1. Probability factors should be derived in accordance with the LR ShipRight Procedure for Ship Units.

3.4.4 The site-specific environmental factors, given in Table 2.3.2 Environmental factors, give 100-year return period loads for the locations specified using all-year wave data. Therefore, when using these factors for the on-site operation condition, is to be taken as equal to 1.

3.4.5 At the request of the Owner and when consistent with the operational philosophy of the unit, seasonal environmental data may be used to derive the environmental loads for the inspection/maintenance condition. Alternatively, the all-year loads derived for the on-site operation condition may be used for the inspection/maintenance assessment, in conjunction with the probability factor derived to account for the difference between all-year loads and seasonal loads.

3.4.6 In no case are the environmental loads used for the assessment of the hull structure for on-site operation, inspection/maintenance and flooding in a harsh environment to be less than the 25-year return period dynamic loads defined for unrestricted worldwide transit, calculated for a vessel of the same particulars with metacentric height, GM, and roll radius of gyration, , taken from Table 2.3.1 GM and kr.

Table 2.3.1 GM and

Condition GM
Deep draught condition, usually a full load condition above 0,9 0,12B 0,35B
Partial load draught condition, usually a part load-part ballast condition 0,6 0,24B 0,40B
Light draught condition, usually a ballast condition 0,5 0,33B 0,45B
NOTE
Values for intermediate draughts may be calculated by linear interpolation.

Table 2.3.2 Environmental factors

Unit size and operating condition Environment see Note 2 Draught , see Note 1
Pitch at, and aft of, midship at 0,85L at FE
Aframax or VLCC Transit Unrestricted worldwide N/A 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0 1,0
Aframax Weather vaningr West of Shetland Is. Deep 1,3 0,8 1,2 1,4 1,7 0,8 2,0 1,0 1,2 1,6
Light 1,3 0,8 1,5 1,2 1,3 1,0 2,0 1,0 1,0 1,6
North Sea Deep 1,2 0,5 1,2 1,4 1,6 0,8 1,75 0,75 1,0 1,6
Light 1,2 0,7 1,5 1,2 1,2 1,0 1,75 1,0 1,0 1,6
Brazil Campos Basin Deep 0,6 0,5 1,0 0,65 0,75 0,5 0,75 0,5 0,5 0,8
Light 0,6 0,5 1,65 0,6 0,5 1,0 0,8 0,8 0,75 0,75
Western Australia (non-cyclonic) Deep 0,5 0,5 0,65 0,6 0,65 0,55 0,7 0,5 0,5 0,75
Light 0,5 0,5 0,75 0,5 0,5 0,55 0,7 0,5 0,5 0,7
VLCC Weather vaning Brazil Campos Basin Deep 0,55 0,50 0,50 0,50 0,60 0,50 0,90 0,60 0,60 0,70
Light 0,60 0,50 0,50 0,65 0,50 0,50 0,65 0,55 0,55 0,60
Western Australia (non-cyclonic) Deep 0,50 0,50 0,50 0,50 0,50 0,50 0,70 0,60 0,60 0,60
Light 0,50 0,50 0,50 0,55 0,50 0,50 0,60 0,50 0,50 0,55
VLCC spread moored Nigeria Deep 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50
Light 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50 0,50
NOTES
1. Values at intermediate locations may be calculated by linear interpolation. The values for weather vaning units are applicable to units that vane about the bow.
2. The geographic locations of the sites at which long-term environmental data has been used to derive the site-specific environmental factors are shown as follows:

Table 2.3.3 Return periods for scantling requirements and strength assessment

Operational condition Transit Normal on-site operation Inspection/maintenance Accidental
Delivery voyage Restricted Service area Unrestricted World-wide
Return period

1 year with all year data or

10 years with Seasonal data

 25 years 25 years 100 years

100 years with all year data or

100 years with seasonal data

where consistent with the operation of the unit, see also Pt 10, Ch 2, 3.4 Return periods and probability factor, fprob 3.4.5 and Note 1

1 year post-accidental
Environment World-wide or Owner-defined Transit route Restricted service area World-wide Site-specific Site-specific Site-specific

Note

1. Alternative return periods will be specially considered based on the duration of the inspection/maintenance period and the site specific environment.

3.5 Motions

3.5.1  General.
  1. The envelope values for unit motions are to be taken at the specific return period specified in Table 2.3.3 Return periods for scantling requirements and strength assessment.
3.5.2  Roll Motion.
  1. The roll period, T θ, is to be taken as:

    In the event of the roll period being equal to 25 seconds or more, in addition to first-order wave forces, roll excitation by environmental forces including second-order wave forces and dynamic wind gusts are to be considered as applicable. The calculation method is to be acceptable to LR.

  2. The roll amplitude, θ, is to be taken as:

    θ = degrees

3.5.3  Pitch motion.
  1. The characteristic pitch period, , is to be taken as:

    = seconds

    where

    = 0,6 (1 + ) L

  2. The pitch amplitude, ϕ, is to be taken as:

    ϕ = 1350 [1 + ] degrees

    where

    = is the non-dimensional Froude number and is defined as:

    =

    where

    V = is the vessel speed, in knots
    = zero at fixed locations
    =

    maximum transit speed for transit condition, see also Pt 10, Ch 1, 1.3 Application of transit conditions

    = is the length on the waterline at the load case draught, in metres.

3.6 Accelerations

3.6.1  General.
  1. The envelope values for combined translational accelerations due to motion in six degrees of freedom are given. The transverse and longitudinal components of acceleration include the component of gravity due to roll and pitch.
3.6.2  Common acceleration parameter.
  1. The common acceleration parameter, , is to be taken as:

3.6.3  Vertical acceleration.
  1. The envelope vertical acceleration, , at any position, is to be taken as:

    m/s2

3.6.4  Transverse acceleration.
  1. The envelope transverse acceleration, a t, at any position, is to be taken as:

    m/s2

3.6.5  Longitudinal acceleration.
  1. The envelope longitudinal acceleration, , at any position, is to be taken as:

    m/s2

3.7 Dynamic hull girder loads

3.7.1  Vertical and horizontal wave bending moments.
  1. The envelope hogging vertical wave bending moment, , and sagging vertical wave bending moment, , and horizontal wave bending moment, , are to be taken as:
3.7.2  Vertical wave shear force.
  1. The envelope positive and negative vertical wave shear forces, and , are to be taken as:

    =

    =

    where

    = distribution factor for positive vertical wave shear force along the vessel length and is to be taken as:
    = 0,0 at AE
    = 1,59 for 0,2L to 0,3L from AE
    = 0,7 for 0,4L to 0,6L from AE
    = 1,0 for 0,7L to 0,85L from AE
    = 0,0 at FE
    = distribution factor for negative vertical wave shear force along the vessel length and is to be taken as:
    = 0,0 at AE
    = 0,92 for 0,2L to 0,3L from AE
    = 0,7 for 0,4L to 0,6L from AE
    = 1,73 for 0,7L to 0,85L from AE
    = 0,0 at FE

    intermediate values of and are to be obtained by linear interpolation, see Figure 2.3.2 Positive vertical wave shear force distribution and Figure 2.3.3 Negative vertical wave shear force distribution respectively.

Figure 2.3.1 Vertical and horizontal wave bending moment distribution for scantling requirements and strength assessment

Figure 2.3.2 Positive vertical wave shear force distribution

Figure 2.3.3 Negative vertical wave shear force distribution

3.8 Dynamic local loads

3.8.1  General.
  1. This Section provides the envelope values for dynamic wave pressure, dynamic tank pressure, green sea load and dynamic deck loads.
  2. The envelope dynamic wave pressures are given in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.(a).
  3. The envelope green sea load given in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.3 only applies to scantling requirements and strength assessment.
  4. The envelope dynamic tank pressure is a combination of the inertial components due to vertical, transverse and longitudinal acceleration. The envelope dynamic tank pressure components are given in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.4.
  5. The envelope dynamic deck loads are given in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.5 and Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.6.
3.8.2  Dynamic wave pressure.
  1. The envelope dynamic wave pressure, , is to be taken as the greater of the following:

    kNm2

    kN/m2

    where

    • = local breadth at the waterline, for considered draught, not to be taken less than 0,5B, in metres
    • = ( + 0,8)
    • = – +
    • = 0,25 for |y | < 0,25
    • = for |y | ≥ 0,25
    • = at, and aft of, AE.
    • = between 0,2L and 0,7L from AE.
    • = + at, and forward of, FE.

    intermediate values to be obtained by linear interpolation

    • = 1,0 at, and aft of, AE.
    • = 0,7 for 0,2L to 0,7L from AE.
    • = 1,0 at, and forward of, FE.

    intermediate values to be obtained by linear interpolation

    , and are given in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.(b) for scantling requirements and strength assessment application.

  2. For scantling requirements and strength assessment, the envelope maximum dynamic wave pressure, , see Figure 2.3.4 Transverse distribution of maximum dynamic wave pressure for scantling requirements and strength assessment, and minimum dynamic wave pressure, , see Figure 2.3.5 Transverse distribution of minimum dynamic wave pressure for scantling requirements and strength assessment, are to be taken as:

    = kN/m2 below still waterline

    = – 10 (z – ) kN/m2

    for < z ≤ +

    = 0 kN/m2 for z > +

    = — kN/m2 below still waterline

    = 0 kN/m2 above still waterline

    where

    • is not to be taken as less than – g ( – z)

    where

    = envelope dynamic wave pressure, in kN/m2, as defined in Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.(a) with:

    = heading correction factor, see Pt 10, Ch 2, 6.3 Application of dynamic loads 6.3.1.(b)

    = pressure at waterline, to be taken as at still waterline, in kN/m2.

3.8.3  Green sea load.
  1. The envelope green sea load on the weather deck, , is to be taken as the greater of the following:

    = ( – ) kN/m2

    = 0,8 ( – ) kN/m2

    = 34,3 kN/m2

    where

    = 0,8 +

    = 0,5 +

    = 1,0 at, and forward of, 0,2L from AE.

    = 0,8 at, and aft of, AE.

    intermediate values to be obtained by linear interpolation

    = pressure at still waterline for considered draught, in kN/m2, see Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.(a)

    = pressure at still waterline for considered draught, in kN/m2, see Pt 10, Ch 2, 3.8 Dynamic local loads 3.8.2.(a)

    = distance from the deck to the still waterline at the applicable draught for the loading condition being considered, in metres

    Bwdk = local breadth at the weather deck, in metres

    Where loads are available from a model test, they may be used for design purposes.

3.8.4  Dynamic tank pressure.
  1. The envelope dynamic tank pressure, , due to vertical tank acceleration is to be taken as:

    = kN/m2 for strength assessment and scantling requirements.

  2. The envelope dynamic tank pressure, , due to transverse acceleration is to be taken as:

    = kN/m2 for strength assessment and scantling requirements.

    where

    = factor to account for ullage in cargo tanks, and is to be taken as:
    = 0,67 for cargo tanks, including cargo tanks designed for filling with water ballast
    = 1,0 for ballast and other tanks.
  3. The envelope dynamic tank pressure, , due to longitudinal acceleration is to be taken as:

    = kN/m2 for scantling requirements and strength assessment

    where

    = factor to account for ullage in cargo tanks, and is to be taken as:
    = 0,62 for cargo tanks, including cargo tanks designed for filling with water ballast
    = 1,0 for ballast and other tanks.
  4. For scantling requirements and strength assessment, the simultaneous acting dynamic tank pressure, , is to be taken as the summation of the components for the considered dynamic load case, see Pt 10, Ch 2, 6.3 Application of dynamic loads 6.3.6.
3.8.5  Dynamic deck pressure from distributed loading.
  1. The envelope dynamic deck pressure, , on decks, inner bottom and hatch covers is to be taken as:

    = kN/m2

    where

    = uniformly distributed pressure on lower decks and decks within superstructure, in kN/m2, as defined in Pt 10, Ch 2, 2.3 Local static loads 2.3.1.

3.8.6  Dynamic loads from heavy units.
  1. The envelope dynamic deck loads, , , , acting vertically, transversely and longitudinally on supporting structures and securing systems for heavy units of cargo, equipment or structural components are to be taken as:

    =

    =

    =

    where

    = mass of unit, in tonnes.

    Figure 2.3.4 Transverse distribution of maximum dynamic wave pressure for scantling requirements and strength assessment

    Figure 2.3.5 Transverse distribution of minimum dynamic wave pressure for scantling requirements and strength assessment
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