Assistance in planning and decision making:
The Hyde RRS System has been installed on many vessels worldwide. From this and other experience, a computer simulation program has been devised as an aide in determining suitable candidates for the application of RRS. The results of this program have proved to be conservatively accurate when the parameters of the candidate vessel fall within the limits for which the simulator is designed.
Hyde Marine Systems is pleased to provide a simulation of our standard "roll up test", which is a predictor of RRS performance in beam seas, to all qualified customers.
Many of our potential customers have had questions about the application of the Hyde RRS System. One particular concern, the long term "wear and tear" effect on the ship's steering gear, is well founded in the sense that its proper operation is crucial to the steering of the ship. Another matter often discussed is the effect of frequent rudder movement on the course. It is hoped that the information given above has addressed these and other issues related to the use of a Hyde RRS System.
Roll decay simulation:
Roll decay simulation tests require ship data as requested on the attached form. The simulation procedure proceeds as follows:
The simulator is comprised of three mathematical models which are used in a computer to represent: (1) the ocean, (2) the vessel, and (3) the RRS rudder control system. In simulation, we use the rudder to "roll up" the ship to a maximum roll angle by moving the rudder back and forth with a period equal to the natural roll period of the vessel. After about 100 seconds of this periodic rudder movement, the ship is seen (see graphs of one simulation run) to be rolling to a constant peak amplitude. The angle to which the vessel can be rolled is a measure of the maximum roll energy that can be imparted by the rudder to the ship for a particular ship speed, rudder size, etc. The purpose of the RRS system is to use this capability to impart roll energy in a manner opposite to the roll energy imparted by waves and thus "cancel" or "damp" wave roll energy.
In other words, the larger the roll up amplitude achieved by the rudder after (say) 100 seconds of moving the rudder back and forth at the ship's natural roll frequency, the larger the wave roll amplitude that can be damped by the rudder will be. Several factors have influence on this maximum roll up amplitude: (1) the size (area) of the rudder, (2) the rudder's distance from the axis of roll, (3) the rudder's lift characteristics (i.e. a high lift rudder will generate more roll torque than a conventional rudder), (4) the speed of the ship, and (5) the rudder rate or maximum rate at which the rudder can be moved. After determining the maximum roll up angle for the ship, we can compare the ship's natural roll damping characteristic with its roll damping characteristic when the Hyde RRS System is active.
Each simulation run produces graphs that plot: (1) roll angle, and (2) rudder angle as a function of time. The graph of roll angle plots: (1) natural roll damping, and (2) RRS roll damping. The first of the time marks, which are positioned from left to right on the roll angle plots, mark the points when the rudder was commanded to return to the amidships position for plot 1 and when the RRS system was turned on plot 2. The second and third time marks indicate the location of peaks in plots 1 and 2 used to compute percentage roll reduction by the following formula:
Roll Reduction = 100 * ((amplitude 1) - (amplitude 2)) / (amplitude 1)
This "roll up" method of estimation simulates the effect of the Hyde RRS System for a ship rolling in a beam sea with waves at a frequency equal to the ship's natural roll period.
The estimate produced by this test is usually equaled or exceeded by an actual sea trial of the vessel after installation of the RRS. This is also a good predictor of the actual reduction achieved in waves for a beam sea. For other angles of actual wave incidence, say stern quartering seas, both rolling and RRS performance may be somewhat reduced.
To fill get an estimate of how RRS would preform on a vessel, please click here.