Calculating drag force on a rotating body

AI Thread Summary
Calculating the rotational drag on a submarine during yaw movements involves understanding how the hull's cross-section affects drag coefficients, particularly when turning. The drag experienced is influenced by the total velocity across different hull sections, with maximum drag near the bow and stern and minimum around the center of mass. The rudder plays a crucial role in creating differential drag between the port and starboard sides, generating a yaw moment that must counteract the submarine's yaw moment of inertia. Additionally, turning introduces friction and form drag, which can lead to undesired pitch and roll movements, requiring extra energy from the engines to maintain speed. Overall, the interplay between rotational and linear drag is complex and essential for achieving realistic submarine dynamics.
Massimo
Messages
10
Reaction score
6
TL;DR Summary
I want to know how to calculate the drag force acting against the rotational motion of a specific body, and if/how it affects simultaneous linear drag.
For context, I'm developing a submarine simulator with a heavy focus on realism, especially on the physics side of things. I've already implemented a fairly accurate linear drag model for forward/backward and rise/dive movements, but I'm not sure where to start with calculating the rotational drag against my submarine when it's turning from side to side (yaw movement); also, I have some questions about if/how rotational and linear drag affect each other in simultaneous rotational and linear movements, e.g. a submarine turning to the right while moving forward. Does anyone have any ideas?
 
Engineering news on Phys.org
Massimo said:
... also, I have some questions about if/how rotational and linear drag affect each other in simultaneous rotational and linear movements, e.g. a submarine turning to the right while moving forward. Does anyone have any ideas?
When turning, the section of the hull across the flow, is greatly increased because of the length of the hull. The drag coefficient is that for a circular section, not an elongated hull.
The highest drag on a road transport vehicle, is when there is a strong crosswind. The vector sum of ground speed, and the crosswind, becomes expensive in lost energy.
 
  • Like
Likes DeBangis21 and Lnewqban
Massimo said:
... I'm not sure where to start with calculating the rotational drag against my submarine when it's turning from side to side (yaw movement); also, I have some questions about if/how rotational and linear drag affect each other in simultaneous rotational and linear movements, e.g. a submarine turning to the right while moving forward. Does anyone have any ideas?
These articles may help you:
https://www.mdpi.com/2077-1312/9/12/1451

https://www.mdpi.com/2077-1312/10/10/1417

https://www.mdpi.com/2077-1312/11/11/2091

As you analyze the total velocity, and subsequent drag, acting on several cross-sections of the hull, you will see that those have a maximum value around the bow and the stern, as well as a minimum value around the center of mass of the ship (through which the yaw vertical axis passes).

Although the forward component of that total velocity is the same for all the sections, the tangential component is different in magnitude and direction for each section.

The main function of the rudder is to make the values of drag very different for each, the port and the starboard sides.
That induces a yaw moment, which must overcome the huge yaw moment of inertia during the beginning of the turn.

Once the rate of turn is stablished, that yaw moment fights the additional rotational drag that the turn itself is inducing.
That drag comes in the form of friction and form drag (less hydrodynamic surfaces and cross-sections shape facing the flow), plus certain amount of profile drag due to port and the starboard fins going through different types of flows.

Besides the rudder, other control surfaces may need to consume extra kinetic energy or forward moment of the ship, only to compensate for coupled not desired pitch and roll movements induced by the changes in the distribution of the dynamic forces during the turn, as well as for reducing drifting or skid by leaning the hull (similar to what boats and airplanes do).

Consider that the extra energy that turning requires must come from the engine(s), and that unless additional thrust is available, the forward velocity will get reduced; more as the turn is sharper.
 
diagram04.jpg
 
Posted June 2024 - 15 years after starting this class. I have learned a whole lot. To get to the short course on making your stock car, late model, hobby stock E-mod handle, look at the index below. Read all posts on Roll Center, Jacking effect and Why does car drive straight to the wall when I gas it? Also read You really have two race cars. This will cover 90% of problems you have. Simply put, the car pushes going in and is loose coming out. You do not have enuff downforce on the right...
I'm trying to decide what size and type of galvanized steel I need for 2 cantilever extensions. The cantilever is 5 ft. The space between the two cantilever arms is a 17 ft Gap the center 7 ft of the 17 ft Gap we'll need to Bear approximately 17,000 lb spread evenly from the front of the cantilever to the back of the cantilever over 5 ft. I will put support beams across these cantilever arms to support the load evenly
Thread 'What's the most likely cause for this carbon seal crack?'
We have a molded carbon graphite seal that is used in an inline axial piston, variable displacement hydraulic pump. One of our customers reported that, when using the “A” parts in the past, they only needed to replace them due to normal wear. However, after switching to our parts, the replacement cycle seems to be much shorter due to “broken” or “cracked” failures. This issue was identified after hydraulic fluid leakage was observed. According to their records, the same problem has occurred...
Back
Top