Help with SACS Transportation Inertia Load analysis

Dear Colleagues,

Hi I am new with SACS, and am working on inertia loading generation with SACS tow module. I have some confusion with the notation system that SACS tow adopt.

Let's say we have conventional seakeeping coordinate system (X-surge, Y-sway, Z-Heave, with their corresponding rotation). For roll motion (+), the body inertia translation force will be in the opposite direction of the motion translation components. Hence, the inertia force should be in sway (+) and heave (+). However, the result from SACS tow suggests for such motion, the translation forces in sway (-) and heave (+) (see figure below). Anybody can help me to understand this? I could be wrong or lack of understanding in this case. Thank you for taking your time to read this problem, any help will be much appreciated.

  • I am trying to apply inertial moments about different axes to effect shift in center of gravity of the structure which is planned to be lifted in the fabrication yard. How can one introduce rotational moments in the offshore module? Is the capability only in "Tow Module"?

  • I didn't have you towinp file, but lst file shows you defined 5 load cases with roll+-, pitch +- and heave+. I suppose the first 4 have only roll/pitch angle and heav+ have only Z acceleration?

    The roll/pitch data specified in "Motion" command is the roll/pitch angle with heave acceleration.  Roll and pitch angle can be positive or negative, a positive roll angle means jacket and barge placed at location below, and hence it cause an acceleration in +Y direction with inertia load in -Y. You have question about heave force from load case "ROL+'" or load case "HAV+"?

    For a transportation analysis, both max and min roll/pitch angle (positive and negative value)should be considered together with a heave acceleration.