6 Sloshing Pressures in Tanks

6.1 General

6.1.1 Application

This article applies to all liquid cargo, ballast tanks and other tanks with volume exceeding 100 m³, but does not apply to the water ballast cargo hold of bulk carriers.

6.1.2 The sloshing pressures defined in this article do not include the effect of impact pressures due to high velocity impacts with tank boundaries or internal structures. For tanks with a maximum effective sloshing breadth, b_slh, see [6.4.2], greater than 0.56 B or a maximum effective sloshing length, ℓ_slh, see [6.3.2], greater than 0.13 L at any filling level from 0.05 h_max to 0.95 h_max, see [6.3.3], a separate impact assessment is to be carried out in accordance with the Society procedures.

6.1.3 Sloshing pressure on tank boundaries and internal divisions

6.2 Minimum sloshing pressure

6.2.1 The minimum sloshing pressure, P_slh-min, for tanks of cellular construction, i.e. double hull construction with internal structures restricting the fluid motion, is to be taken as 12 kN/m².

The minimum sloshing pressure, P_slh-min, for cargo and all other tanks is to be taken as 20 kN/m².

6.3 Sloshing pressure due to longitudinal liquid motion

6.3.1 Application

The sloshing pressure due to longitudinal liquid motion, P_slh-lng, is to be taken as a constant value over the full tank depth and is to be taken as the greater of the sloshing pressures calculated for filling levels from 0.05 h_max to 0.95 h_max, in 0.05 h_max increments.

6.3.2 Effective sloshing length

The effective sloshing length, ℓ_slh, in m, is to be taken as defined in Table 11.

where:

n_WT : Number of transverse wash bulkheads in the tank.

α_WT : Transverse wash bulkhead coefficient, to be taken as (see Figure 11):

• 

For tanks with changing shape along the length and/or with web frames of different shape the transverse web frame coefficient, α_wf, may be taken as the weighted average of all web frame locations in the tank given as:

• 

A_OWT : Total area of openings, in m², in the transverse section in way of the wash bulkhead below the considered filling height.

A_tk-t-h : Total transverse cross sectional area, in m², of the tank below the considered filling height.

A_O-wf-h : Total area of openings, in m², in the transverse section in way of the web frame below the considered filling height.

n_wf : Number of transverse web frames, excluding wash bulkheads, in the tank.

ℓ_tk-h : Length of cargo tank, in m, at considered filling height.

Figure 11 : Transverse wash bulkhead coefficient

Figure 12 : Transverse web frame coefficient

6.3.3 Sloshing pressure in way of transverse bulkheads

The sloshing pressure in way of transverse bulkheads including wash bulkheads due to longitudinal liquid motion, P_slh-lng, in kN/m², for a particular filling level, is to be taken as:

where:

ℓ_slh : Effective sloshing length, in m, as defined in [6.3.2].

f_slh : Coefficient taken as:

h_fill : Filling height, measured from tank bottom, in m, see Figure 11.

6.3.4 Sloshing pressure on internal web frames or transverse stringers adjacent to a transverse bulkhead

For tanks with internal web frames the sloshing pressure acting on a web frame or transverse stringer adjacent to transverse bulkheads or transverse wash bulkheads due to longitudinal liquid motion, P_slh-wf, in kN/m², provided it is located within 0.25 from the bulkhead, is to be taken as:

where:

ℓ_slh : Effective sloshing length, in m, as defined in [6.3.2].

P_slh-lng : Sloshing pressure due to longitudinal liquid motion acting on transverse bulkhead, as defined in [6.3.3].

s_wf : Distance from transverse bulkhead to web frame under consideration, in m. The distribution of pressure across web frames and transverse stringers is given in Figure 13.

Figure 13 : Sloshing pressure distribution on transverse stringers and web frames

6.4 Sloshing pressure due to transverse liquid motion

6.4.1 Application

The sloshing pressure due to transverse liquid motion, P_slh-t, is to be taken constant as a constant value over the full tank depth and is to be taken as the greater of the sloshing pressures calculated for filling levels from 0.05 h_max to 0.95 h_max, in 0.05 h_max increments.

6.4.2 Effective sloshing breadth

The effective sloshing breadth, b_slh, in m, is to be taken as in Table 12, but not less than 0.3B.

where:

n_WL : Number of longitudinal wash bulkheads in the tank.

A_OWL : Total area of openings, in m², in the longitudinal section in way of the wash bulkhead below the considered filling height.

A_tk-L-h : Total longitudinal cross sectional area, in m², of the tank below the considered filling height.

A_O-grd-h : Total area of openings, in m², in the longitudinal section in way of the web frame below the considered filling height.

f_grd : Factor to account for number of longitudinal girders and longitudinal wash bulkheads in the tank, to be taken as:

n_grd : Number of longitudinal girders, excluding longitudinal wash bulkheads, in the tank.

b_tk-h : Breadth of cargo tank, in m, at considered filling height.

6.4.3 Sloshing pressure in way of longitudinal bulkheads

The sloshing pressure in way of longitudinal bulkheads including wash bulkheads due to transverse liquid motion, P_slh-t, in kN/m², for a particular filling level, is to be taken as:

where:

b_slh : Effective sloshing breadth defined in [6.4.2].

6.4.4 Sloshing pressure on internal girders or longitudinal stringers adjacent to longitudinal bulkheads

For tanks with internal girders or stringers, the sloshing pressure acting on the girder/web frame adjacent to longitudinal bulkheads and longitudinal wash bulkhead, P_slh-grd, in kN/m², provided it is located within 0.25 b_slh from the bulkhead, is to be taken as:

where:

b_slh : Effective sloshing breadth defined in [6.4.2].

P_slh-t : Sloshing pressure due to transverse liquid motion acting on longitudinal bulkhead, as defined in [6.4.3].

s_grd : Distance from longitudinal bulkhead to girder under consideration, in m.

The distribution of pressure across stringers is given in Figure 14. The distribution of pressure across longitudinal girders is similar to the deck web frame shown in Figure 13.

Figure 14 : Sloshing pressure distribution on longitudinal stringers and girders