Flow Divider Mechanical Spacers - 6 Wheel Design

Following up from speculation via numerical simulation, and in anticipation of physical experiments, I intend to lay out a specific form of mechanical support for the flow dividers. The goal here isn't to hold them in place against gravity (there is no gravity), or even really to push back against external forces. The goal is just to keep things in place against fluid forces.

The canonical description I've given of the flow dividers assumes that they are flexible sheets, but they do hold pressure. That is important here, in predicting what happens if you push against it. Each layer doesn't have rigidity directly, but physically wants to hold its shape the same way a balloon does.

Logical Path to Wheels

Start from the beginning, we will assume (still speculative, awaiting experiment) that the sheets experience wobble in the xy-plane (both directions other than in the axis of rotation). Further, we assume that this wobble gets worse with the number of sheets until it becomes destructive.

Now the key challenge here is that you can't just add a structure that everything attaches to, otherwise you defeat the entire goal. One structure would experience a large (unacceptable) relative velocity to most layers. So you want to add tracks? Like roller coasters? Sure. But as we have sheets N=1, 2, 3,... you must have those tracks attaching 1-to-2, which are moving relative to each other, and 2-to-3, and so on. Transmission of force has to go over many moving interfaces, which looks bad. Thankfully though, in the neutral state we know that there is no fluid force expected, it's just that movements from neutral position tend to worsen, not dampen.

Some of the most obvious intuitions are to:

• Put balls in-between the layers
• Put cylinders in-between the layers

There are other paths I want to go down with these approaches, but they both share the same general flaw that they are obviously very material inefficient and might be relatively bad for worsening friction. It's hard to imagine how you hold balls in place.

Cylinders might have better options to hold them in place. Imagine a circular strut that holes the "handles" of the rolling pins. But again, the rolling pins (cylinders) have to fill almost the full volume in-between flow dividers.

So we come to the conclusion that what we want is something like a limited number of balls, but what we can hold in place. That geometry gets a little weird. Make it a wheel, and now it starts to make sense. On top of that, you don't need to fill the entire space. Maybe just the top and the bottom of the straight region of the friction buffers. And given that top & bottom specification (2 locations vertically), what's the minimum number of locations we need to "pin down"? 3 within a given plane to stabilize a circle. So 3x2=6.

For the rest of this I want to describe this 6 wheel pattern. This is still just a rough draft, but presenting something with some logical clarity is nice to have around, have documented as a starting reference. It might not be needed, no one really knows. Certainly not me!

Wheel Position Around Tube

We need a picture for what I said about the "straight region of the friction buffers". For the center part of the rotation, we want even geometry, and then beyond that we have a region I call the "taper" which presents all kinds of unique problems. Wheels will be placed in that specific joint between the straight region and the taper region.

In the diagram I have here, I cut the top taper off. No reason, it's just a lot to draw... but this illustrates where the wheels would be. It's notable that I've taken a 7 (actually 8, close enough) sheet design, and the wheels divide it up into 3 parts. This will be important.

Wheel Position in Global Geometry of Gravity Tube

Now let's look from a cross-section view, this time of a more simple design of 5 layers - 2 layers of wheel separators and 3 layers of flow dividers.

This distinction between layer "types" is very important. The layers with wheels are inherently porous. That's how wheels work, there are moving parts. This doesn't rule out getting some flow-dividing benefit from those layers (and I think you would), but these can't be quite as effective as the other layers because they can't hold pressure. Because they can't hold pressure, the tapering solution is unclear. As you go towards the center, there can't be any outward pressure pushing the material in the taper out (because the wheel openings are letting that pressure out).

It would also be coherent to have wheel layers that are strictly for mechanical support.

From the cross-section view, let's take both types of layers and unfurl them. These are meant to be something like construction templates.

I've added a reinforced section to the flow divider layers. But it is very important that these don't need to cover the entirely length along the straightaway section. It only needs to have some rigidity around where the wheels might touch them. This is somewhat of an alternative to having the entire circle lined with wheels. We just look to have 1 rigid circle bumping against 3 wheels, which has stability.

Wheel Structure

But what would the actual wheels be? Remember that the flow dividers are moving relative to each other. So in the following diagram picture that. The rotation of the wheel will be going along with the movement of the sheets and also roughly with the flow (the exact flow shape is a weird rabbit hole in Google Scholar).

We have every reason to believe that the wheels will give relative little penalty to the friction/drag of the overall structure. Because there's no relative velocity between the wheel and the flow dividers.

I, importantly, envision a "sheath" like structure along the strut. This is to maintain the orientation of the wheel, so it doesn't flip over to the side.

The wheels are a thing that I am, now, working on some preliminary 3D printing ideas. For bucket-scale experiments. These wheels could be real and relevant for both the bucket experiments and full-scale space habitats. This concept of the wheel spacer layers is also somewhat coherent as garage-scale craft, just made of some metal bars.