Defining a Launchway Assembly Defining a Launchway Assembly

A launchway is a complicated set of connections which are collectively referenced within MOSES by the name &LWAY. The launchway is composed of at least two launch legs each one of which is defined via the command:


     ASSEMBLY LLEG, *J(1),*J(2), .. *J(n), BODY_NAME(1), XB, YB, ZB, :B1(1), .. \
     :B1(n) BODY_NAME(2) :B2(1), .....  :B2(n),  -OPTIONS

and the available options are:


     -FRIC, DYNFRC

     -TPIN, TPRIDEP, XP, YP, ZP, MAX_ANGLE, TSECDEP, DIST

     -BEAM, LENP, EIP, LENS, EIS

Here, *J(1), ... *J(n) are the node names of the nodes along the launch cradle of the jacket, in order, where *J(1) is the first node which will enter the water and *J(n) is the last node which will enter the water. The launch cradle is considered the part of the jacket that rests on the barge skidway. An illustration of the node arrangement is shown in Figure 23. BODY_NAME(1) is the body name assigned to the barge where the tiltpins are attached, and XB, YB, and ZB are the coordinates, in the BODY_NAME(1) body system, of the beginning of the skidway on body BODY_NAME(1). Here, the skidway should be considered to be at the height of the jacket launch leg centerline above the barge origin. Also, :B1(i) are selectors for the nodes in BODY_NAME(1) which will be used for connecting the jacket to the barge. BODY_NAME(2) is the name of an optional second body over which the skidway may pass, and :B2(i) are again node selectors.

The dynamic coefficient of friction for the launchway is specified with the -FRIC option as DYNFRC. The tiltbeam geometry for the launchway is specified via the -TPIN option. Here, XP, YP, and ZP are the body coordinates of the primary tiltpin (feet or meters), TPRIDEP is the height of the primary tiltbeam (feet or meters), MAX_ANGLE, the maximum angle the tiltbeam is allowed to rotate until the secondary tiltbeam becomes active (deg.), TSECDEP, is the height of the secondary tiltbeam (feet or meters), and DIST is the distance along the skidway from the primary tiltbeam to the secondary one (feet or meters). Here again, the depth of the beams should be considered to be the vertical distance from the tiltpin to the centerline of the jacket leg. If there is no secondary tiltbeam, one should omit the values for MAX_ANGLE, TSECDEP, and DIST. An illustration of the tiltbeam is shown in Figure 24.

The stiffness of a tiltbeam is input using the -BEAM option. Here, LENP is the length of the primary tiltbeam (feet or meters), and EIP is the stiffness (bforce-ft**2 or bforce-meters**2). LENS and EIS are the length and stiffness values for the secondary tiltbeam, respectively. If there is no secondary tiltbeam, these values should be omitted.

The order of input of the ASSEMBLY LLEG commands is important as it is used to establish the launch coordinate system of the jacket. The axes of this coordinate system are set as follows: The X axis is parallel to a line connecting *J(1) and *J(n), and is directed towards *J(1). The jacket is launched in the positive X direction. The origin of this system is midway between the trailing joints given on the first and last ASSEMBLY LLEG commands, and the Y axis is along the line connecting the *J(n) on the last ASSEMBLY LLEG input with *J(n) on the first one input. The Z axis is determined from the right hand rule.

At the conclusion of the MEDIT Menu, the orientation of the body systems will, in general, change. MOSES will change the body system of the jacket as described above. It will also change the orientation of the barges so that their body X axis will be aligned with that of the jacket. In contrast to the jacket, there is no translation of the barges' body system.