Creation of Damage Scenarios

If damage stability is to be assessed then you are required to select the appropriate damage scenarios in the Deterministic Data Input dialog, having first defined the details that are appropriate to each in the associated Damage Scenarios dialog box. A damage scenario is simply a list of assumed damaged compartments and is independent of any deadweight loading or intact condition. By implication, it is therefore independent of compartment contents in the intact state. The combination of a damage scenario, applied to a loading or intact condition, produces a damaged condition.

There are three different modes of damage available:

1. Where the vessel is free to attain its natural damaged equilibrium, for which no defining parameters are necessary.

2. As for 1 above, but where you supplies the first attempt in the iteration process.

3. Where the vessel is grounded, and in which case you specifies the final equilibrium after grounding. The grounding force is taken as the difference between the intact displacement and the displacement as grounded. This force is assumed to act at the center of contact and is used to correct the GMT due to the apparent rise in KG after grounding.

For each scenario, the damage extent is defined by identifying those compartments damaged (where damage results in a breach of watertight integrity), the type of damage assumed to be sustained, and associated extra data specific to that damage type. There are five types of damage available. They all adopt the lost buoyancy (constant displacement) method and are as defined below.

If the damaged compartment contained deadweight material (in the prior intact state to which the damage scenario is to be applied), then the use of any of the damage types listed below, will ensure that the deadweight remains in the compartment after the flood water has entered. The International Association of Classification Societies (IACS) Unified Requirements relating to Damaged Compartments, require that account is taken of the permeability of the cargo, when a compartment is damaged. An extra column has been added to the Tankplan/Contents Type page, for this to be entered (in percent). The effect of this when the compartment is damaged, is that water will be absorbed into the cargo with the given permeability. If the waterline is above the level of cargo in the compartment, then water will flow in to the void space above the cargo, irrespective of the cargo density and other characteristics. Note that this is now the default behavior. In previous versions of Calc, water would flow into any damaged compartment, ignoring any cargo that it contained. The previous behavior can be reproduced by assigning a 100% permeability to the relevant content types.

If the damaged compartment was empty prior to sustaining damage, then naturally in the damaged condition, the compartment will only contain flood water.

4. Compartment Flooded To Outside Waterline.

   Using this damage type, assumes the compartment will become flooded to the outside waterline.

5. Compartment Open To The Sea But Pressurized With Trapped Air.

   The use of this damage type assumes that air is unable to escape from the damaged compartment, thereby producing an internal pressure, which acts to reduce the level of the flood water in the compartment. you are required to supply the coordinates of the damage and the internal gauge pressure after the flood water has reached equilibrium. The flood level is then determined using the assumption that the head of flood water (at the point of damage) plus the internal additional air pressure, equals the external hydrostatic pressure head (at the point of damage).

6. Compartment Partly Flooded

   This damage type allows you to specify the amount of flood water in the compartment, in terms of its weight and density, that means, not to the outside waterline.This could be, for example, via hatch damage and green seas,

7. Water on Deck.

   This is a damage type specifically included to deal with the "Water on Deck" criteria for Passenger Ro-Ro vessels as specified in MSC 65/4/Rev 1. It considers the accumulation of water on the vehicle deck, the amount of which is dependent upon the freeboard after damage and on the significant wave height. The freeboard is defined as the least residual freeboard within the damage length, after damage, but without any water on the deck. To determine this, you have to either supply the x coordinates at each end of the damage length or the actual x, y, z coordinates of the vehicle deck at these two positions. For the former, the program measures the height from the deck (found from the geometry model at the x coordinates for the specified compartment(s)) down to the waterline. For the latter, the program simply measures the distance from the specified point down to the waterline. In either case, the point which gives the smaller freeboard not only then defines the freeboard but also becomes the point at which the height of accumulated water is applied. The height of water is determined from the following simple formulae, taken from the above regulations:

   • If fr >= 2.0 meters, height of water on deck = 0.0 meters

   • If fr <= 0.3 meters, height of water on deck = X meters,

   intermediate values are obtained by linear interpolation.

   • If hs >= 4.0 meters, height of water on deck is calculated as above

   • If hs <= 1.5 meters, water on deck = 0.0 meters

   intermediate values are obtained by linear interpolation.

   where

   • fr  = residual freeboard, and

   • hs = significant wave height.

   To provide flexibility, the value of X is entered on the Setup \ Options \ Stability dialog, but currently has a default value of 0.5, as given in the regulations. The significant wave height is also specified on the same dialog.

   As the vehicle deck is also considered to be damaged to the outside waterline, water on deck and damage flood water must be modelled simultaneously. The "Water on Deck" option provides this combined approach in the one damage type. For angles of heel where flood water enters the vehicle deck, the accumulated water is assumed to "float" above the outside waterline.

8. Obstruction.

   This damage type allows you to specify an obstruction (that means, a block of impermeable material such as vehicles, crates ) within a compartment. The obstruction is analogous to using a damage permeability, in that it only provides a restriction to flooding and does not affect intact capacities. Whereas the damage permeability is a uniform restriction (equivalent to a reduction in the density of the flood water), the obstruction has dimensions and position, specified by you. The main limitation is that you must idealise the obstruction as a single cuboid. It must also be ensured that the dimensions and position of the cuboid locate the obstruction entirely within the associated compartment.

   If you wish to model the restriction to flooding caused by solid cargo within a compartment, then the weight and position of the cargo must also be specified, on the Fixed Weight dialog. For consistency, you must then ensure that the damage scenarios which include the obstruction are then only used in conjunction with loading conditions which include the fixed weight.

The following additional options can be applied to compartments that are flooded to the outside waterline, or partly flooded:

9. Fall Out (Drop Out)

   If the damaged compartment contained deadweight material(in the intact state to which the damage scenario is applied), then the use of this option will ensure that the local deadweight falls out when damage is sustained. The same damage scenario can also be applied to intact states where the relevant compartments are empty. In this case, obviously no fall out will occur.

10. Stage Flooding

    The purpose of the stage flooding option is to simulate the progressive flooding of one or more compartments. you specifies the number of intermediate stages, and the percentage flooding for each stage for the flooded compartment.

    The program will first carry out a damaged calculation with all compartments flooded to the outside waterline, in order to determine the 100% flooded state of the compartments.

    Then damaged calculations for each stage, with the specified amount in each stage flooded compartment, will be done.

    Note:
    If you specify 100% in all stage flooded compartments, for a particular stage, this is not the same as the fully flooded state. This is because, for a stage, the amount of flood water remains constant throughout the heeling range, whereas for the fully flooded state, water is free to enter and leave the damaged compartment, as the vessel heels. Thus the GZ curves will not be the same.

    Also there is no specified time associated with the stages, so it can not be regarded as a true time based simulation.

    Stage flooding is specified on the Damaged Scenarios dialog in the Type column.

    Up to 5 stages can be specified. When the number of stages has been specified, the appropriate number of Param(eter) cells, will become active. you should enter the percentage fill for each stage in these cells.

    Calc will produce a condition report for each specified stage plus the fully flooded state.

The grounding point relative to the ship's co-ordinate system is specified on the Damage Scenarios/Other Data page together with the height of water above the point. The grounding force is included in the longitudinal strength, as well as the stability, calculations. If the grounding force becomes negative (that means, the ship floats off the grounding point), then a normal, ungrounded condition is assumed.