The coordinate system used to define vessel motions and, in particular, which direction is positive. That is, whether surge is positive forward or aft, whether heave is positive up or down and whether pitch is positive bow up or bow down.

Different modelling and design criteria will affect the nature of the 'ideal' RAO curves (as plotted graphically) being sought for a particular ship: for example, an ocean cruise liner will have a considerable emphasis placed upon minimizing accelerations to ensure the comfort of the passengers, while the stability concerns for a naval warship will be concentrated upon making the ship an effective weapons platform. I need your help," he tells Tantillo. "You remember my cousin? He sent me an invitation to his son's wedding and I need you to interpret the letter. I want to send him them something." Tantillo speaks fluent Italian. Frank doesn't.As well as displacement RAOs, which directly specify the motion of a vessel in waves, OrcaFlex can apply wave load RAOs, which represent instead the load (force and moment) on a vessel due to waves. In this case, the amplitude represents the magnitude of the force (in the surge, sway or heave direction) or moment (in the roll, pitch or yaw direction); the meaning of the phase remains unchanged. Example: There's only one table for two in the restaurant. "And if you're willing to wait, I'll feed you at that deuce," Pellegrino says. The first thing I noticed when we walked in was how bright the place is. It may be the brightest fine-dining establishment I've ever been to. The second thing I noticed was all the Christmas decorations (a story I'd read said they stay up year-round). Every chair at every table was full and the bar was crowded. An older bespectacled man sat on a stool in the corner, surveying the room, and motioned to suggest we sit at the two stools open next to him. I say to my wife, 'I wish I had a Rao's to go to. I wish I had a Rao's to go hang out in, to go sit at the bar and meet wonderful people, and then sit down and have a wonderful meal," he says. I can see why. The Orcina convention is to use the amplitude of response (in length units for surge, sway, heave, in degrees for roll, pitch, yaw) per unit wave amplitude, and to use the phase lag from the time the wave crest passes the RAO origin until the maximum positive excursion is reached (in other words, the phase origin being at the RAO origin). Mathematically, this is given by

Finding the forces on the ship when it is forced to oscillate in still water conditions. The forces are divided into: A surge force RAO of 300 kN/m in a wave of height 6m (and hence wave amplitude 3m) means that a vessel experiences a surge force varying harmonically between -900kN and +900kN over each wave cycle; a pitch moment RAO of 1e6 kN.m/m in the same wave means that the vessel experiences a moment about the y axis varying from -3e6 kN.m to +3e6 kN.m. A waiter comes over and says he's setting a table for us. We invite Frank to join us, since it's unclear whether he's eaten tonight, but he politely declines. He says he'll come sit with us later on, but he won't eat.Where x {\displaystyle x} is a rigid body motion such as heave, ω {\displaystyle \omega } is the oscillation frequency, M {\displaystyle M} is the structural mass and inertia A ( ω ) {\displaystyle A(\omega )} is the added mass (frequency dependent), B ( ω ) {\displaystyle B(\omega )} is the linear damping (frequency dependent), C {\displaystyle C} is the restoring force coefficient (stiffness matrix) and F ( ω ) {\displaystyle F(\omega )} is the harmonic excitation force proportional to the incoming wave ζ = ζ a e i ω t {\displaystyle \zeta =\zeta _{a}e I am that old! I could be your father!" says Frank, who will celebrate his 70th birthday this year.