Interior Compartments Interior Compartments

As mentioned above, interior compartments have attributes that exterior compartments do not need. These are specified with the options on the &DESCRIBE COMPARTMENT command that defines the compartment. The first or these options:



     -DESCRIPTION, DESC

allows one to specify a description for this compartment. If quotes are used this description can include blanks and be up to 40 characters in length. This description is simply printed with some &STATUSes and at the top of Tank Capacity reports.

Sounding tubes are used to define the level of contents in a compartment, and are defined with the option:



     -S_TUBE, *PT, *PB

Here, *PT is a point which defines the top (at the deck) of the tube and *PB defines the other end. If you do not define a sounding tube, then MOSES estimates a location for you.

The option:



     -MINIMUM, MPERC, SPGC

is used to define the "residual water" in compartments. When this value is defined, one cannot ballast below this level, and there is no free surface correction due to the minimum amount of water. The specific gravity of this "residual water" is stated using SPGC.

The last option defines the "holes" which pierce the surface of the compartment:



     -HOLES, HOLE(1), .... HOLE(n)

Holes are defined with the command


     &DESCRIBE HOLE, HOL_NAME, HOL_TYPE -OPTIONS

Here HOL_NAME is the name of the hole and HOL_TYPE is its type which must be either F_VALVE, WT_VENT, M_VENT, VENT, or V_VALVE. The type is used to control when water may flow into the compartment, so the distinction between vent and flood valves is strictly for operational purposes; i.e. both allow water into the compartment the same way when open. Of the vents, the WT_VENT is peculiar. It never allows water to flow into the compartment and is used strictly for reporting. A M_VENT is a "magic" vent in that it never goes under the water. The difference between a VENT and a V_VALVE is that a vent cannot be closed and hence a compartment with a vent can not have an internal pressure. VENTs and WT_VENTs are used to define traditional down-flooding points. The difference between the two is that the "non weather tight" points can get water inside due to splash, etc. These points are used primarily when assessing stability, but one can obtain &STATUSes of them. Down-flooding points (vents) are ignored when a compartment is flooded.

Holes have: a location, an area, a normal, and a friction factor and these are defined with the options:



     -POINT, POINT_NAME


     -AREA, AREA


     -NORMAL, NX, NY, NZ


     -FRICTION, F_FACTOR

Here, AREA is the cross sectional area of the valve (inches**2 or mm**2), POINT_NAME is the named of a point defining the centroid of the hold, NX, NY, and NZ are the components of the normal of the hole, and FRICT is the friction coefficient for the hole and piping system. The normal to the hole is actually the normal to the area of the hole and points out of the compartment. If some of this data is omitted, defaults will be used.

The flow rate is calculated by MOSES using the following equation:

     Q = U * AREA * SQRT(2GH) / SQRT(F_FACTOR)

where Q is the flow rate in cubic feet per minute or cubic meters per minute, G is the gravitational constant, H is the differential head (feet or meters), and U is a constant which makes the units work out correctly. The average flow rate between two subsequent events of a static process is used to calculate the time to flood a compartment.

For many cases one does not need all of this complexity. In particular if one only wants to check the intact stability of a vessel all he needs is a list of down-flooding points. To save work in this case, MOSES allows these to be defined directly on the &DESCRIBE COMPARTMENT command with the options:



     -WT_DOWN, *WD(1), *WD(2), ......


     -NWT_DOWN, *ND(1), *ND(2), ......

Here, the *WDs and *NDs are the names of points. Often one does not wish to build a complete model, so these options can be used on an exterior compartment to define down-flooding into non modeled volumes.

The string function


     &COMPARTMENT(:CMP_SELE -OPTION)

is useful when writing macros. It returns a string containing the information defined by -OPTION for each compartment selected by :CMP_SELE. For all values of -OPTION, there are more than one token returned for each compartment and the first token is the compartment name. The available options are:

     -PART
     -PIECES
     -HOLES
     -F_TYPE
     -MIN_WT_DOWN
     -MIN_NWT_DOWN
     -PERCENT
     -MAX_PERCENT
     -AMOUNT
     -MAX_AMOUNT
     -SOUNDING
     -ULLAGE
     -CG
     -FULL_CG
     -CG_DERIVATIVE
     -FS_MOMENT
     -MAX_DHEAD
     -PRESSURE
     -FLOW_RATE

-PIECES returns the name of the compartment and the name of each piece used to define the compartment. In a similar fashion, -PART provides the name of the compartment, and the part name to which the compartment belongs. -F_TYPE returns the flooding type, and -HOLES returns the names of the holes piercing the compartment. The next two options return a single token in addition to the compartment name: with -MIN_WT_DOWN it is the minimum height of all weather tight

down-flooding points and with -MIN_NWT_DOWN, the minimum height of all non weather tight down-flooding points. For the next six options, two tokens are returned in addition to the compartment name: a measure of the amount of ballast in the compartment and the specific gravity of the contents. The measure returned (the second token) is defined by the option selected: with -PERCENT it is the percentage full, with -MAX PERCENT it is the maximum percentage full, with -AMOUNT it is the amount in the compartment, in bforce units, with -MAX_AMOUNT it is the maximum amount in the compartment, in bforce units, with -SOUNDING it is the sounding in feet or meters, and with -ULLAGE it is the ullage in feet or meters. With the next five options, one token is returned in addition to the compartment name. -CG and -FULL_CG return four tokens, the name of the compartment and the X, Y, and Z part coordinates of the current location and full location of the center of gravity. The option -CG_DERIVATIVE also returns three tokens: the name of the compartment, and the longitudinal and transverse derivatives of the CG with respect to angle changes (feet or meters/deg). The option -FS_MOMENT returns three tokens: the name of the compartment, and the longitudinal and transverse free surface moments in bforce-blength. the compartment. The last three options return a single token in addition to the compartment name: