Categories and Load Types

As mentioned above, the basic idea behind MOSES is that one defines attributes which the program then uses to compute loads. Now, an attribute may create load from different sources. To distinguish these classes of loads, MOSES employs the concept of the "load type", which is simply a name given to each of the sources of loads, and is either: #DEAD, #WIND, #BUOY, #AMASS, or #DRAG, for the intrinsic loads, or a user supplied name which begins with a # for the applied loads. These names are used to control which type of load is applied to each load attractor. Here, #DEAD is the load due to weight, #WIND to wind, #BUOY is hydrostatic pressure, #AMASS is hydrodynamic pressure, and #DRAG is viscous water force.

For structural elements, one can select which of these forces will be applied. This is accomplished with the two options:

     -USE, USE(1), USE(2), ..., USE(i)

     -NUSE, NOT_USE(1), NOT_USE(2),  ..., NOT_USE(i)

Here, the values of USE(i) and NOT_USE(i) are the selectors for the names of the load types defined above. For example,

     -USE  @ -NUSE #WIND

Instructs MOSES to consider all of the load types except wind when computing the force on an element. These two options can be used on either DEFAULT, BEAM, or PLATE commands. When a structural element is defined, MOSES first sets the load type flags to those defined with &DEFAULT. Then either of these options encountered on the definition itself serve to alter the settings defined by those from &DEFAULT.

The options defined above allow one to effectively define which elements are exposed to different environments. To give the user even more control, there is an additional concept, the Category. Each load attribute in MOSES has a category name associated with it and each category name has a set of multipliers for each load type. The category name is associated with a load attribute when it is defined in a manner similar to the load type flags. The &DEFAULT command accepts two options:

     -BAS_CAT, BASE_CAT_NAME

     -EXT_CAT, EXTRA_CAT_NAME

the -BAS_CAT option defines a Category name, BASE_CAT_NAME, to the load attributes defined with the structural elements themselves. -EXT_CAT defines a Category name, EXTRA_CAT_NAME, for any additional load attributes (those which belong to Load Groups or those defined with a #ELAT command). Now, when a element or load attribute is defined, the default Category (either BASE_CAT_NAME or EXTRA_CAT_NAME) will be associated with it. This default association can be changed with the option

     -CATEGORY, CAT_NAME

which associates CAT_NAME with the attribute. This option is available on BEAM, or PLATE commands and any command which begins with a #. Reports are available which produce sums of weight and buoyancy by Category. As an example, consider

     BEAM BODY_NAME -CATEGORY INSIDE -NOTE Interior Beams ~CLASS ..

This defines a beam, associates it with a Category, INSIDE, and defines a description of the Category "Interior Beams".

Load Groups have a multiplier for the total force of the group. Initially this multiplier is set to one.

Control of all of these multipliers is available with the command:

     &APPLY, -OPTIONS

where the available options are:

     -PERCENT

     -FRACTION

     -FORCE  :NAME(1), VAL(1), .... :NAME(n), VAL(n)

     -LOAD_GROUP  :NAME(1), VAL(1), .... :NAME(n), VAL(n)

     -TIME  NAME, T(1), V(1), .... T(n), V(n)

     -PERIODIC  NAME, T(1), V(1), .... T(n), V(n)

     -CATEGORY  :CAT(1), :NAME(1), VAL(1), .... :NAME(n), VAL(n)

     -MARGIN  :CAT(1), VAL_INC(1), .... :CAT(n), VAL_INC(n)

The first two options define the way the VAL(i) are interpreted. If a VAL is preceded by a -PERCENT option, it is interpreted as a percent. If it is preceded by a -FRACTION, it is a multiplier. If neither of these options precedes a value, it is interpreted as a percent. In essence, percents are divided by 100 to convert them into multipliers.

The -FORCE option defines multipliers for user defined load sets. Here, :NAME(i) are selectors for these sets and VAL(i) are the multipliers one wishes to associate with the set. By default, all user defined load sets have a multiplier of zero. Thus, they will not be applied unless one uses this option.

The -LOAD_GROUP option defines multipliers for load groups. By default, these multipliers are one. Thus, one normally does not need this option. One can, however, turn off the force due to a load group using this option. For example,

     &APPLY -PERCENT -LOAD_GROUP  A_NAME 50 -FRACTION B_NAME 0.50

will apply 50 percent of load group A_NAME, and one half of load group B_NAME.

The -TIME and -PERIODIC options define multipliers which vary with time. Here, NAME is the name of either a LOAD_GROUP or a user defined load set. For both options, one simply specifies a set of multiplier pairs. At each event during a time domain simulation, MOSES will interpolate a multiplier from the specified values. If the -TIME option is used, the last value in the list will be used for times larger than the last. If the -PERIODIC option is used, then the defined values will be repeated with a period of the last time in the list. If NAME is later specified with -LOAD_GROUP or -FORCE options, the time variation will be "turned off".

The last two options control the load type multipliers for Categories. The -CATEGORY option allows one to control the multipliers for all load types while the -MARGIN option sets only the #DEAD, or weight, multiplier. Here, VAL(i) are the same as for the load group and load set options, while VAL_INC(i) are increases; i.e. the multiplier is really 100 or 1 plus VAL_INC depending upon -PERCENT or -FRACTION option in effect. Here, :CAT(i) is a selector for the Categories for which multipliers will be set and :NAME(i) are selectors for the load types. For example:

     &APPLY -PERCENT -CATEGORY STR_MODEL @ 0 #DEAD 105

will set the multipliers for category STR_MODEL to all zero except for the weight which will be applied with a multiplier of 1.05.