Talk:Motion compensator

We do like to contribute to the development of the motion compensator page. The following drawing perfectly indicates the difference between Active Heave Compensation & Passive Heave Compensation. Rexroth allows Wikipedia to use this picture. We don't know the exact procedure, but can this picture be referenced to while it's of importance to visualize the difference between AHC & PHC? Thanks. — Preceding unsigned comment added by DCBNWebcare (talk • contribs) 14:05, 8 October 2014 (UTC)

As I explained elsewhere, a motion compensator does not compensate for motion. It only helps decreasing teh effect of the relative motion. In fact there is not much difference between "tensioner", motion compensator and Heave compensator. A heave compensator is mostly used in the offshore industry, a motion compensator is used more general. The navy uses supply ships which give wireropes to other vessels etc. There is also a motion compensator in this system, but this is called motion compensator and not heave compensator. I think that it depends on the area of industry you are working in. Jeff 15:32, 12 February 2007 (UTC)

Maybe one can say that a heavecompensator is a special motion compensator. Whereas a motion compensator works in all directions, a heave compensator works only in the vertical direction. Jeff 13:01, 16 February 2007 (UTC)

Clarifications

I was trying to do some copy-editing, but I could only get so far without possibly changing the intended meaning. For instance:

In order to keep the changes in the force smal (sic), related to the movement, one has to increase the gas volume and decrease the hystereses (sic)of the installation.

Is it desirable to keep the changes in force small? Or the movement? Does one increase the gas volume continuously, or after each "heave", or at the time of installation? Is decreasing the hysteresis a trade-off, or a benefit?

To overcome the hystereses (sic) as well as the limitted (sic) gasvolume (sic), active elements can be added to the installation.

What are "active elements"? Are they added at the time of installation? Do these overcome the hysteresis? Does that imply the "active elements" are there so that the objects return to their original separation?

I like every cooperation. In fact it is ideal if the force remains constant, which means that there are no shocks. The movement is something the sea, together with the design of the vessel gives you! Decreasing the hysteresis means less force increase, so it is better. If you have the hysteresis, you have a shock everytime you change direction of movement.

It is a problem that it is difficult to make a picture, because this can say more than 100 words. In case you have a complete passive compensator, this is just a spring. If you have a full active compensator you have f.i a winch that is controled in both directions. If you have a semi active system, you have a passive system and parallel to this an active system in such a way that the passive system takes say 80 % of the power and the active part some 20 % of the power. It is also possible that the active part is only used with extreme heave.Some passive suystems are designed in such a way that later an active element can be added (sometimes a mediumseperator is used with a pistonrod going through, later an active cylinder could be mounted to this rod. Jeff 17:25, 11 February 2007 (UTC)

The main spring function is given by the gasvolume (sic), the pressure difference and the hysteresis is compensated by this extra device.

What device is doing the compensating here? The heave compensator itself, or the (additional?) gas volume? What is meant by "given"?
The gas volume is the spring, the compensator is the "in between" between gas volume and "load". Given meabs certain, sorry.

Jeff 17:46, 11 February 2007 (UTC)
If you can give me your mailadress, i can send you a handsketch Jeff 17:46, 11 February 2007 (UTC)

Left you a message on your Talk page. --Otheus 07:45, 12 February 2007 (UTC)

Still don't understand

This paragraph needs work. Let's try to get it right here, then move it to the page. --Otheus 17:30, 13 March 2007 (UTC)

As often is the case with motion compensators implemented as gas springs, order to minimize changes in the force relative to the motion, one must decrease the hysteresis of the installation.

Is this a tradeoff??

It is clear I think that if you have a hydraulic cylinder and the cylinder is via a mediumseperator connencted to a gasvolume that if the cylinder is pushed in, the gasvolume is decreased and the pressure and the force goes up. If the volume is small, the force increase is more than if the volume is large. A large volume costs a lot of money. You can imagine kinematic construction in order to save gas volume. Look to the drillstringcompensator of Maritime Hydraulics/Bosch Rexroth. The main cylinders are situated under an angle, so that the vertical forceincrease is smaller than the force increase in the cylinder.:Several patents exist on kinematicconstructions that give the same result (??)

for a traditional gas spring with ... ??

an increase in gas volume. To overcome the hysteresis as well as the limited gas volume, one can add active elements.

What is meant by "active elements"??

There is no possibility to overcome the hysteresis by passive elements (without adding external power). If you have a spring parallel to a hydraulic cylinder, the force can be taken for 80 % by the spring and for 20 % by the cylinder. In order to control the movement we have to control the cylinder and herefor power is needed.

The main spring function is given by the gas volume, the pressure difference and the hysteresis is compensated by this extra device.

What is meant by "extra device"?

This extra device is a cylinder in parallel to the spring or a winch parallel to the spring.

As normally there is a lot of energy related to heave compensators, it is almost impossible to have a full "active heave compensator": this energy also must be dissipated!

Where does the energy come from? The forces resulting from movement/motion? How is this energy normally dissipated?

Suppose the extra device is a winch. The winch is controled by hydraulic power during hauling. During veering the power is generated into heat and this heat must be cooled again, so you need power from the network on board of the ship.