Sciortino, who recently celebrated his 50th birthday at Rao's in Los Angeles, gets a table about once a month, but the days vary. Tonight he has a Monday. Next month he has a Thursday. Like the rest of the table owners, he gets his assignments at the beginning of the year. He's been coming here—"coming home," as he calls it—for 25 years. The system used to define wave direction. In OrcaFlex 0° means waves approaching the vessel from astern and 90° means waves coming from the starboard side, but if a different convention applies to your data then you must allow for this when entering the data.

On a computer the above algorithm was first introduced by using strip theory and Boundary Element Method. Today both of the methods are still used if the need for fast calculations outweigh the need for precise results and the ship designer knows the limitations of strip theory. More advanced programs that are used today utilizes Boundary Element Method through different applications (such as WAMIT, SESAM WADAM, MOSES, NeMOH and ANSYS AQWA) some may also include the effects of viscosity. The insight into the forces that governs the seakeeping behavior of a ship gained from the above are of course still valid within considered limits of free surface linearity. 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 Whose table are you at?" he asked. I said we weren't at a table and had stopped in for a drink. (The tables, as I knew, are all "owned" by regulars who come themselves, invite friends, or donate the table to charity auctions where just the reservation regularly sells for thousands).

Rao's Menu

Finding the forces on the ship when it is restrained from motion and subjected to regular waves. The forces acting on the body are:

In the above, "Ship" must be interpreted widely to also include other forms of floating structures. The obvious problem in the above method is the neglection of viscous forces which contribute heavily in modes of motion like surge and roll.Although OrcaFlex allows the RAO input data to use a wide range of systems, all OrcaFlex results use a right-handed system in which the positive movements are as follows: Surge There are many different conventions for defining RAOs. There have been attempts at standardisation, but these have not been successful so there remain differences between the main computer programs and model basins: some establishments even use different conventions for reporting model and computed data. The only safe course is to obtain a complete description of the system used for the data in each case. M + A ( ω ) ] x ¨ + B ( ω ) x ˙ + C x = F ( ω ) {\displaystyle {\big [}M+A(\omega ){\big ]}{\ddot {x}}+B(\omega ){\dot {x}}+Cx=F(\omega )}

It's 10:20 p.m. We've been here since 7:45, but the hours have gone by in a flash and I have no desire to give up my bar stool and leave the center of all the action. 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. One deuce," Emma—who's in graduate school and until recently worked part-time as a restaurant hostess—corrects me. The RAO is a transfer function that is only defined when the ship motions can be assumed to be linear. The above forces can then be assembled into an equation of motion: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. RAOs are effectively transfer functions used to determine the effect that a sea state will have upon the motion of a ship through the water, and therefore, for example, whether or not (in the case of cargo vessels) the addition of cargo to the vessel will require measures to be taken to improve stability and prevent the cargo from shifting within the vessel. Generation of extensive RAOs at the design phase allows shipbuilders to determine the modifications to a design that may be required for safety reasons (i.e., to make the design robust and resistant to capsizing or sinking in highly adverse sea conditions) or to improve performance (e.g., improve top speed, fuel consumption, stability in rough seas). RAOs are computed in tandem with the generation of a hydrodynamic database, which is a model of the effects of water pressure upon the ship's hull under a wide variety of flow conditions. Together, the RAOs and hydrodynamic database provide (inasmuch as this is possible within modelling and engineering constraints) certain assurances about the behavior of a proposed ship design. They also allow the designer to dimension the ship or structure so it will hold up to the most extreme sea states it will likely be subjected to (based on sea state statistics). The Diffraction forces, which are pressures that occur due to the disturbances in the water because of a body being present.

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: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 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. How we doing guys? I'm Joe," our waiter says. He sits down at the table. "What we like to do is, we serve everything family-style. For appetizers we have seafood salad, roasted peppers, baked clams, fried calamari, mozzarella in carrozza (that's deep fried), fresh mozzarella and tomato. We could do a salad. I also have mussels in white wine sauce. Those are the appetizers." Just think about what happened while you were here," he tells me, putting his hand on my forearm for emphasis. "You met my tailor. You met Tony Tantillo. You met Tony Abbot." (I met a trio of Tonys, if you include Tony the bartender.) "You met all these people. You met the congressman. You're seeing Rao's." And because it's so bright, which Frank says is because "it adds to the energy of the room," I really am seeing everything. However, OrcaFlex can accept RAO data using a wide range of different conventions, so you can input your RAO data in its original form and simply tell OrcaFlex what conventions apply to those data.