Firstly, apologies if I've not put this in the right category - it's been a while since I've been on these forums much (And over a year since my last ride :cry: ).
I was daydreaming (I do that a lot) about water-slides/flumes today, no doubt induced by having played RCT3 for the first time in ages and building a massive swimming pool. I thought a bit about the physics of a flume, and also remembered a design I'd had a while ago for my 'dream water-slide', and I guess instead of keeping it all inside my head, I'd write it down so I don't have to remember it all over again - maximum daydream efficiency!
The 'physics' is just guesswork, trying to work out how a flume behaves so that I can do some simple calcs to see if my dream slide would be feasible. I'm posting it for feedback and also in the case that it is right, it might just be slightly useful for anyone else...
Firstly, the force on a rider: Unless it is a very slow slide, with a large tube diameter, then the rider is not going to be sitting. If a rider's lying down, then the 'vertical' G-force is actually experienced as chest-to-back (I refer to it as 'linear' but as it's not actually along the length of the slide, this isn't strictly correct).
I figure also that the experienced lateral G-force is greatly reduced because the rider's body is free to swing to the sides of the flume where they will experience linear G-force. The exception to this are the transitions/S-bends where the centripetal 'force' suddenly changes sides, but unless there is excessive friction then it is as if the body were free-falling horizontally to the other side of the tube.
So, when calculating the force on a rider on a turn, my guess is that there is only linear force on the rider, and the acceleration around a curve is always just v^2/r, without gravity. Once the curve acceleration is worked out, I'd work out the angle of the rider against the tube and the total acceleration with gravity, by doing something with the cosine of the acceleration against the sine of gravity (it's ages since I last did any maths and I'm ashamed to say I can't quite work it out in my head).
Obviously this is only true for when the rider has stabilized around a turn - in transitions, I am guessing that the lateral force does not contribute to the total force (and the rider experiences it as momentum rather than G-force), although there might be some extra linear force as the rider accelerates around the circular flume tube.
Also there is friction to be considered - I'm not trying to get a super-accurate design for my slide (because it'll probably never be built) but I've thought of a few ways that resistances might occur:
- Obviously, primarily the friction between the rider and the base of the flume.
- The air resistance. I'm wondering whether or not there is a slight draft on flumes, because of the constant stream of water, and riders, traveling down the enclosed space?
- If the section joins are rough, they could potentially slow the rider down?
- When the rider enters a transition, they will fly up the side of the flume. In theory, this should not slow them at all, since what they lose in kinetic energy, they will gain in potential energy which will be quickly converted back when they fall back down. But I figure that several factors can slow the rider on a transition: If the flume is not well supported, the tube might deform slightly, taking energy from the rider, if the rider slides past 90 degrees on the side of the flume, then they may fall a short distance before being 'caught' by the side of the flume again, and also, since the rider is of slightly different density to water, they are likely to traverse laterally through the stream, causing water resistance.
--
Here's the idea I had for my dream water-slide - you don't need to read it (as if you need to read this post at all...) but if anyone's interested -
Name: Black Hole
The flume would be built at the top of the flume tower (the pools I have visited often use a single tower with a spiral staircase to the flumes) but instead of flowing 'away' from the tower as the other flumes do, this one would travel straight down through the center of the tower.
The 'station' room would be a domed room with black sides and floor. It wouldn't have windows, but instead it'd be illuminated by LED/striplights that spiral around the floor and into the slide. The edges of the room would be flat for the people queuing and there'd be a barrier between the queue line and the center of the room.
In the center, the floor would drop away in a curved funnel shape (like the end of a trumpet). There'd be a clear plastic platform across the funnel, and clear cylinder in the center around a trapdoor, with a door in the side of it. Guests would enter the cylinder and stand on the trapdoor. There'd be a bar above them, so when the trapdoor opened, they could choose either to fall then, or hang onto the bar and let themselves drop.
The water would flow out of holes at the edge of the funnel, so that it swirled downwards into the tube. There'd also be a small amount of dry ice that would also flow around the funnel and be pulled downwards through the tube.
The flume would begin with a true vertical drop (I've seen pictures of flumes that claim to be vertical but they're actually just 70 degrees or so with a small initial curve to give a free-fall effect). The vertical drop would last for a few meters before curving slowly (to catch the rider gently) into a long spiral. The spiral would start out being very tight and steep (it would travel through the stairwell and coil around it, and have translucent sides so that other guests could watch the riders whizzing past) - but then as the gradient decreases, the radius would increase until it becomes more of a flat helix.
It would then curve slightly in the other direction, and rise slightly, and then switch back to curving in the first direction and downwards - the rider would be flung firstly to the side; then to the top; then to the other side of the tube, performing a sort of barrel roll.
This is footage of a 'looping' water slide, but later in the video the loop is shown not to be vertical, but tilted to only about 30 degrees off horizontal, making it more of an overbanked turn. I'm guessing that a true vertical loop is impractical mostly because the large climb would mean possible 'rollbacks'? But with a barrel roll, the flume only needs a tiny flick upwards, or even just a downwards turn - as long as it's enough to give the rider negative G-force.
And, in a thin flume (faster flumes seem to be far thinner than slow flumes), even if the rider has somehow slowed so that they no longer have sufficient speed, they'll either slide back down the side, or in the worst (and very unlikely) scenario, they will fall from the top of the tube and continue sliding on their belly.
The tube would be opaque in this section, but the flume would be lit by lights along the sides, which would spiral in the opposite direction to the motion of the barrel roll, giving the illusion that the rider had gone around the tube twice.
--
Oh, lastly (I know this is a long post - it's a bad habit of mine...) I'll just share a couple of tips for riding flumes! I haven't been to a pool or even a theme park in possibly almost 2 years now
but I remember that I had two favourite riding styles:
1: The toboggan (for massive speed) -
lie on your back and cross one leg over the other. Push both hands palm upwards into your lower back, and lift your hips off the tube. Hopefully, you'll now only be touching the slide with your elbows and one heel. If you keep this up for the whole slide, you'll soon pick up massive speed and fly around the corners. Unfortunately, for big guys like me, it puts a lot of pressure on the heel and elbows, and if the flume has rough section joins you can end up with slight bruising...
2: Spinning style -
I discovered this when I was trying to go backwards on the flume. Because you're not supposed to ride headfirst, I thought I'd try switching position after the first turn, and reorientating myself just before the end of the slide. But actually, it was far more fun just to keep turning. To get the best spin, curl up so that your knees are near your chest, and use your hands to pull yourself around. It's a fun game to try catching the corners as you go around them - obviously the inner side will pull you in the same direction as the turn, and the outer side will spin in the opposite direction!
--
So, yeah, does anyone else have any thoughts on the flume physics? I'd be pretty pleased if I actually got it right about the 'no experienced lateral force' thing.
If anyone read the 'dream slide', what do you think? Being an enthusiast, I keep a few other ideas in my head for awesome slides that may never be built.
And, has anyone tried the sliding techniques that I described, or have tips of their own?
Patrik
I was daydreaming (I do that a lot) about water-slides/flumes today, no doubt induced by having played RCT3 for the first time in ages and building a massive swimming pool. I thought a bit about the physics of a flume, and also remembered a design I'd had a while ago for my 'dream water-slide', and I guess instead of keeping it all inside my head, I'd write it down so I don't have to remember it all over again - maximum daydream efficiency!
The 'physics' is just guesswork, trying to work out how a flume behaves so that I can do some simple calcs to see if my dream slide would be feasible. I'm posting it for feedback and also in the case that it is right, it might just be slightly useful for anyone else...
Firstly, the force on a rider: Unless it is a very slow slide, with a large tube diameter, then the rider is not going to be sitting. If a rider's lying down, then the 'vertical' G-force is actually experienced as chest-to-back (I refer to it as 'linear' but as it's not actually along the length of the slide, this isn't strictly correct).
I figure also that the experienced lateral G-force is greatly reduced because the rider's body is free to swing to the sides of the flume where they will experience linear G-force. The exception to this are the transitions/S-bends where the centripetal 'force' suddenly changes sides, but unless there is excessive friction then it is as if the body were free-falling horizontally to the other side of the tube.
So, when calculating the force on a rider on a turn, my guess is that there is only linear force on the rider, and the acceleration around a curve is always just v^2/r, without gravity. Once the curve acceleration is worked out, I'd work out the angle of the rider against the tube and the total acceleration with gravity, by doing something with the cosine of the acceleration against the sine of gravity (it's ages since I last did any maths and I'm ashamed to say I can't quite work it out in my head).
Obviously this is only true for when the rider has stabilized around a turn - in transitions, I am guessing that the lateral force does not contribute to the total force (and the rider experiences it as momentum rather than G-force), although there might be some extra linear force as the rider accelerates around the circular flume tube.
Also there is friction to be considered - I'm not trying to get a super-accurate design for my slide (because it'll probably never be built) but I've thought of a few ways that resistances might occur:
- Obviously, primarily the friction between the rider and the base of the flume.
- The air resistance. I'm wondering whether or not there is a slight draft on flumes, because of the constant stream of water, and riders, traveling down the enclosed space?
- If the section joins are rough, they could potentially slow the rider down?
- When the rider enters a transition, they will fly up the side of the flume. In theory, this should not slow them at all, since what they lose in kinetic energy, they will gain in potential energy which will be quickly converted back when they fall back down. But I figure that several factors can slow the rider on a transition: If the flume is not well supported, the tube might deform slightly, taking energy from the rider, if the rider slides past 90 degrees on the side of the flume, then they may fall a short distance before being 'caught' by the side of the flume again, and also, since the rider is of slightly different density to water, they are likely to traverse laterally through the stream, causing water resistance.
--
Here's the idea I had for my dream water-slide - you don't need to read it (as if you need to read this post at all...) but if anyone's interested -
Name: Black Hole
The flume would be built at the top of the flume tower (the pools I have visited often use a single tower with a spiral staircase to the flumes) but instead of flowing 'away' from the tower as the other flumes do, this one would travel straight down through the center of the tower.
The 'station' room would be a domed room with black sides and floor. It wouldn't have windows, but instead it'd be illuminated by LED/striplights that spiral around the floor and into the slide. The edges of the room would be flat for the people queuing and there'd be a barrier between the queue line and the center of the room.
In the center, the floor would drop away in a curved funnel shape (like the end of a trumpet). There'd be a clear plastic platform across the funnel, and clear cylinder in the center around a trapdoor, with a door in the side of it. Guests would enter the cylinder and stand on the trapdoor. There'd be a bar above them, so when the trapdoor opened, they could choose either to fall then, or hang onto the bar and let themselves drop.
The water would flow out of holes at the edge of the funnel, so that it swirled downwards into the tube. There'd also be a small amount of dry ice that would also flow around the funnel and be pulled downwards through the tube.
The flume would begin with a true vertical drop (I've seen pictures of flumes that claim to be vertical but they're actually just 70 degrees or so with a small initial curve to give a free-fall effect). The vertical drop would last for a few meters before curving slowly (to catch the rider gently) into a long spiral. The spiral would start out being very tight and steep (it would travel through the stairwell and coil around it, and have translucent sides so that other guests could watch the riders whizzing past) - but then as the gradient decreases, the radius would increase until it becomes more of a flat helix.
It would then curve slightly in the other direction, and rise slightly, and then switch back to curving in the first direction and downwards - the rider would be flung firstly to the side; then to the top; then to the other side of the tube, performing a sort of barrel roll.
This is footage of a 'looping' water slide, but later in the video the loop is shown not to be vertical, but tilted to only about 30 degrees off horizontal, making it more of an overbanked turn. I'm guessing that a true vertical loop is impractical mostly because the large climb would mean possible 'rollbacks'? But with a barrel roll, the flume only needs a tiny flick upwards, or even just a downwards turn - as long as it's enough to give the rider negative G-force.
And, in a thin flume (faster flumes seem to be far thinner than slow flumes), even if the rider has somehow slowed so that they no longer have sufficient speed, they'll either slide back down the side, or in the worst (and very unlikely) scenario, they will fall from the top of the tube and continue sliding on their belly.
The tube would be opaque in this section, but the flume would be lit by lights along the sides, which would spiral in the opposite direction to the motion of the barrel roll, giving the illusion that the rider had gone around the tube twice.
--
Oh, lastly (I know this is a long post - it's a bad habit of mine...) I'll just share a couple of tips for riding flumes! I haven't been to a pool or even a theme park in possibly almost 2 years now
but I remember that I had two favourite riding styles:1: The toboggan (for massive speed) -
lie on your back and cross one leg over the other. Push both hands palm upwards into your lower back, and lift your hips off the tube. Hopefully, you'll now only be touching the slide with your elbows and one heel. If you keep this up for the whole slide, you'll soon pick up massive speed and fly around the corners. Unfortunately, for big guys like me, it puts a lot of pressure on the heel and elbows, and if the flume has rough section joins you can end up with slight bruising...
2: Spinning style -
I discovered this when I was trying to go backwards on the flume. Because you're not supposed to ride headfirst, I thought I'd try switching position after the first turn, and reorientating myself just before the end of the slide. But actually, it was far more fun just to keep turning. To get the best spin, curl up so that your knees are near your chest, and use your hands to pull yourself around. It's a fun game to try catching the corners as you go around them - obviously the inner side will pull you in the same direction as the turn, and the outer side will spin in the opposite direction!
--
So, yeah, does anyone else have any thoughts on the flume physics? I'd be pretty pleased if I actually got it right about the 'no experienced lateral force' thing.
If anyone read the 'dream slide', what do you think? Being an enthusiast, I keep a few other ideas in my head for awesome slides that may never be built.
And, has anyone tried the sliding techniques that I described, or have tips of their own?
Patrik
