Marine Engineering Specialists -- Bentley Systems has acquired Ultramarine's MOSES Software [ Press Release ]
Jackup Definition

Jackup Definition:

Jackups are different from most vessels in that they contain things which may move about. In particular, there are legs which can be raised or lowered, cranes which boom in or out and which rotate, and perhaps a cantilever which slides out over a platform. Although it may not be obvious, MOSES provides the capability to model these things and change their positions as an analysis proceeds. To make it easier to combine these pieces into a jackup, a set of macros is provided. (Click Here to see the documentation). With the Jackup Generation Macros, one can define legs, cranes, and a cantilever (with a mast) and move them about during a MOSES analysis.

Here, we have two samples of jackups - a "standard" three leg jackup and a mat jackup. The data files for each is similar in that once the jackup exterior and "spud cans" are defined, the remainder simply defines items which will attract wind and down flooding points. The command files for both do basically nothing but plot pictures of the system and compute hydrostatics. The real difference between the two is the definition of the hull and the "cans", and these will be discussed below.

The important thing about these samples is that once the model is completed, each of the movable pieces can be moved with a single command during the analysis.

Three Leg Jackup:

The following files are discussed below

This sample is a "standard" three leg jackup. The hull of this jackup is complicated, and the model is generated in the &SURFACE Menu using the file jh_gen.cif. Basically, the hull consists of

  • A basic hull,
  • Leg Wells cut from the basic hull,
  • Thruster tunnels added to the basic hull, and
  • A crane pedestal added to the basic hull

We begin by defining the "blocks" which will be used to make the finial hull: BASIC_HULL, PORT_LEG, STRB_LEG, AFT_LEG, CRANE, P_THRUST, S_THRUST, RACK1, RACK2, and RACK3. All of these are defined "simply" with planes and offsets except the thruster blocks. Each of these is formed by combining three blocks.

Once we have the basic blocks, the rest is simple: find the

  • Difference BASIC_HULL with each leg well,
  • Difference with each rack cutout,
  • Union with the crane pedestal
  • Union with each thruster
Notice that each operation creates a new block that is used as the basic block in the next operation. Now, we "rename" the last block. This throws away much of the junk created (very small panels, duplicate points, etc) and changes the name in a rational order. Finally, the results are emitted so that they can be used as MOSES input for assembling a total jackup model. The file mod00001.txt contains the results. In this example, the results file is "inserted into the jackup.dat file. Notice that we did not form any compartments for the hull, so this model will be useful only for intact stability.

For this example, the legs all have the same type of Spud Cans and these are defined with "PGEN" blocks in the macro CAN_MAC at the top of the data file (Click Here To look at it)

Mat Jackup:

The following files are discussed below

The Mat Jackup sample is different from the three leg example in that, with a mat, all legs must move together. Thus, only one leg can have a "can" which is the mat. The mat itself is complicated. It is composed of several compartments some of which are always flooded and some of which are always buoyant. For damage stability, we will want to flood the buoyant ones. Thus, the mat generation file (Click Here to view it) will emit compartments as well as an exterior. The definition of the exterior is similar to that for the three leg jackup (Click Here to view it), so we will not give a blow by blow description of it. The mat, on the other hand has another interesting feature - for the mat to move with the legs, it must be in the same part as the leg to which it is attached. This is accomplished by using the command 

   emit @  -part leg_cb
where the name of the part is the same as the leg to which it is attached.