View Single Post
Old 04-23-2021, 12:59 PM   #3
AMZ
Watch
 
Join Date: Jul 2018
Location: FRANCE at Montpellier
Posts: 16
Downloads: 39
Uploads: 0
Default

Thank you for your reply


"Quote the Autor


the game currently, the u-boats (and other ships for that matter) feel very much like they are on “rails”. IRL though boats and ships do a whole lot of slipping and sliding. I implemented a simplified physics model to demonstrate how boats actually behave. It’s tuned to exaggerate the adverse effects of using the rudder, and the sliding of the boat to make it easier to see. It’s available here: https://scratch.mit.edu/projects/395033149
You have achieved a good visualization of the slip effect due to the rudder. Of course for educational reasons you have exaggerated it."


You can follow the same process for the tern dive plane.
Note, as long as you apply an angle to the rudder, the heading will change.
It is the same for the rotation of pitch, as long as the diving plane angle exists, the submarine trim angle changes.




"Quote the Autor


About the model:
The model is based on Newtonian physics. Both the rudder and the hull of the boat itself are considered lifting surfaces. That is the water acts upon them with a force perpendicular to the surface, proportional to speed squared, however in my simulation I had to settle for just proportional to speed, to prevent the simulation form freaking out when speed got moderately high. The amount of force is also dependent on the angle of attack relative to the incoming waterstream. In my simulation I chose to use the sine of the angle of attack as the function, which is not quite right either, but it was easy to do. A lookup table would probably be better. In addition to those forces there is also the thrust from the propeller and water friction, also proportional to the speed."


The Newtonian model used for the rudder action on the surface can be applied to the vertical plane of the dive. We can afford to simplify this way, because what matters is the behavior of the submarine observed in reality.
The application of the Newtonian model is very complex, often it is necessary to apply it with parameters applicable on a case by case basis (or step by step) and for certain transitions independent of each other.

I recall that the sine of the angle of attack compared to the flow of the fluid at the instant "t" which is no longer horizontal but varies with the angle of the submarine trim
I ask your attention to the fact that the Stern dive plane has a greater action than the front one, because it deflects the flow of the propellers thus increasing the torque.



"Quote the Autor


Once all the forces have been summed up, the velocity vector is decomposed. The forces are added to the velocity vector to get the new course and speed. Lastly the torques are summed up, and added to the angular velocity of the boat, and the boat, and the angular velocity is added to the heading of the boat. For both these steps it is important to consider the time since the last step of course, otherwise the simulation will run differently depending on how fast the physics can be calculated. I did not consider this in my simulation, so slow computers may have slightly different results.

Other factors that I have overlooked in my model is the effect of propwash over the rudders, which makes them much more effective when the propellers are driving the boat forwards. The twin-prop design also offers some stabializing torque when the props are driven close to the speed at which the boat is moving. Also I have neglected to account for the effect that the turning of the boat has on the angle of attack on the rudders. And lastly there may exist different flow-regimes, depending on speed and angle of attack, which would also influence the forces involved, which I have not modeled, but could be approximated with lookup-tables if necessary."


Yes sir,
agree with you, but I am not talking about the change of course with the action of the rudder.

Currently at Wolfpack, the changes depth with the trim of the boat do not correspond to the reality of underwater navigation.
By keeping the planes to dive at the maximum angle, under water the submarine's attitude angle remains limited to 8 ° for a speed of 4 knots, ditto for a speed of 7 knots limits the angle d 'attitude at 13 °

The angles of the diving plane must induce a possible trim angle of 45 °.
Like the rudder, dive planes should constantly vary the trim angle, as long as they are at an angle other than zero.



"Quote the Autor


Given that I was able to throw together this demo in about a day in a coding language I never used before suggests to me that this should be not too hard to add to the game. Though there might of course be limitations with how things are implemented in game that makes things more challenging. "


So it would be good to apply it also on the dive planes.



"Quote the author


How would this affect the gameplay?
The coxswain would obviously have more of a challenge. In order to make a clean turn so that the job of the sailors becomes easy, he / she must anticipate the response of the boats to a greater extent than the current system. There is more delay before the boat begins to turn, and the turn must also be “stopped” properly. Just straightening the rudder will not move the boat forward, that is just not how boats operate.

It should be simple enough to add turbulence and wake-up effects to this pattern, making the helm a full-time job, as IRL would be. "

Yes, but to a lesser extent concerning the action of diving planes. The sliding effect in diving navigation on the vertical plane is very very weak, the submarine navigates in the water without variation in the volume and its geometry of the hull. I remind you that the sliding effect that you are studying (see at the beginning), only applies to rudder and surface navigation, depending on the parameters of the differential metacentre of the hull.
In submerged cruise, it's different.


Believe my experience on this subject, please take my comments into consideration.




To resume

The dive-man, once the trim angle of submarine has been obtained (Example: 30 °), brings the aft diving plane back to zero, then maintains the trim with small movements of the diving plane,.
To return to the horizontal, it must adopt the opposite behavior by giving an opposite diving planes angle.


Thebow diving plane is mainly used for the depth adjustment. The stern diving plane is mainly used to quickly change depth by changing the trim of the submarine (pitch axis), so that the propulsion participates in this action.
This is useful to act against accidental flooding.


Beyond 45 ° of the submarine's trim, one can fear a loss of hydrostatic stability and integrity of the installations, an electrolyte spill, a loss of battery, a loss of propulsion and ... a shutdown.



If it can help you

With pleasure
__________________
On peut braver les lois humaines mais non résister aux lois de la nature.
Vingt mille lieues sous les mers (1869) - Jules Verne

Last edited by AMZ; 04-26-2021 at 11:44 AM.
AMZ is offline   Reply With Quote