On 28-1-2016 21:32, Sven Littkowski wrote:
> 3DWings: same problem. takes too much concentration to learn this
> modeller. I tried it once. Still, not giving up.
>

I can understand that. I think it is the way our brains function (or how 
we use our grey cells) that makes us more or less prone to learn quickly 
one method or another.

-- 
Thomas

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Yes. There are certain learning types among us humans. Some learn easier
while playing, others need to be alone, others do it again in a
different way. For me, mostly it's lack of time and explanations from
someone beside me.

but strange, still, that all that number writing is still easier for me,
than to use an editor where I can see what I am doing. :-)

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Since I don't have 6 months to render all 6 frames, I decided to create 
a panorama with most special features turned off. Enjoy.

http://isometricland.net/gearhead/ghpanotour_spinner.php


Mike

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Nice idea - I like it. Just the colors are very intensive. But then
again, a gray or otherwise dull environment would have a negative impact
on the psychology of your space colonists. Bright light and many strong
colors are known to have psychological advantages.

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Here is the final render, including all the surface features, 
atmosphere, area light, etc.

I am not doing another one of these any time soon, since it took over a 
week to render.


Mike

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Attachments:
Download 'gh_scene_spinner_cutaway_e.png' (1416 KB)

Preview of image 'gh_scene_spinner_cutaway_e.png'

Hey, where is my long posting about air movement inside the cylinder?
What happened with it? I worked over half an hour on that detailed answer.

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Seems, I have to write again my answer to the question of air movement
inside such a cylinder. Don't like to have to work two times on it.... :-(

ABOUT AIR INSIDE A ROTATING CYLINDER

First, a few important points to be kept in mind when reading my answer:
1
Air is like all gases flexible.
2
Warm air has less weight than cold air.
3
Since even air has its weight, it also has its own inertia.

Now let me answer your question. The cylinder rotates, and its inner
sides contain objects, such as buildings, moving objects (like humans
and vehicles, maybe even animals), and also trees and other plants.
Those all will "push" the air and get thus the air into motion. Over
time, the air at around all these objects will gain almost the same
speed as the inner walls of the cylinder and the objects on it.

But since air is flexible, the air at the outer areas moves initially
faster than the air along the central middle axis of the cylinder, but
over time, that air there tends to gain speed, too, pushed by the air
from the outer areas.

However, since air has its own inertia, the air especially at the inside
will never reach a full 100% of the air movement close to the walls of
the cylinder. And that is a factor that will cause gentle winds to start
to come into existence where the air-pushing objects end (on their
roofs) and where the area with non-pushed air begins, as air will move
around the edges and corners of all objects and escape to the only
possible direction: towards the center of the cylinder.

And there is another factor that will cause the existence of gentle
winds: heat sources. Each mammal (including humans) and some other
animals (like birds) produce body heat that is usually a bit higher than
the surrounding air. Engines are also heat sources. Depending on the
light source at the one end of the cylinder, maybe even bright walls and
reflective windows or walls can become heat sources. That heated air
will move upwards towards the center axis of the cylinder due to its
lower weight, and pushes the cooler air from the center downwards
towards the cylinder walls. The opposite effect could be seen atop water
surfaces when large enough: through condensation, the air right above
those water areas will be cooler.

Another factor for wind is probably the light source self at the one end
of the cylinder. It will heat up the air, that air will rise up towards
the middle and cooler air will take that place. That cooler air will
warm up, too, and push upwards and therefore, warmer air will
concentrate along the middle axis of the cylinder, moving away from the
light source as it produces more and more warm air that follows and
pushes. More towards the other, non-illuminated end of that cylinder,
that warmer air will have cooled down and sinks downwards, and from
there back along the walls towards the light source.

This means, we have two wind directions based on heat: one from the
light source towards the other end of the cylinder, and one from the
walls (warm objects there) upwards towards the center axis. And we have
one wind direction due to the rotation of the walls with all their
objects on it, that is a little gentle wind that feels like against the
rotation of the cylinder, and exists mostly close to the larger buildings.

If that habitat cylinder would be kilometers wide, and also much longer,
the wind powers would be larger. But as it is, I believe, the wind
speeds will not exceed 3 km/hour, maybe even much less. To me, that
sounds like a pleasant location.

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On 5-2-2016 6:24, Sven Littkowski wrote:
> Hey, where is my long posting about air movement inside the cylinder?
> What happened with it? I worked over half an hour on that detailed answer.
>

So is my mention of reading 'Rendezvous with Rama' (where, by the way, 
the topic is also treated).

-- 
Thomas

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Am 05.02.2016 um 06:49 schrieb Sven Littkowski:

> Now let me answer your question. The cylinder rotates, and its inner
> sides contain objects, such as buildings, moving objects (like humans
> and vehicles, maybe even animals), and also trees and other plants.
> Those all will "push" the air and get thus the air into motion. Over
> time, the air at around all these objects will gain almost the same
> speed as the inner walls of the cylinder and the objects on it.
> 
> But since air is flexible, the air at the outer areas moves initially
> faster than the air along the central middle axis of the cylinder, but
> over time, that air there tends to gain speed, too, pushed by the air
> from the outer areas.
> 
> However, since air has its own inertia, the air especially at the inside
> will never reach a full 100% of the air movement close to the walls of
> the cylinder.

You may be pretty much mistaken there.

First, let's look at what would happen /without/ any external influence.
If we do not input any energy, the system will approach equilibrium,
which would be characterized by the following conditions:

- All portions of the system will have the same temperature. As a
consequence, there will be no temperature-induced air movement.

- There will be no friction between the air and the ground, as any such
friction would transfer energy between the two, and therefore constitute
an indication that equilibrium has not yet been met. Note that absence
of friction between air and ground can only be achieved by having the
air rotate at the same speed as any ground structures at the same heigth.

- There will be no turbulences within the air, as any such turbulences
would transfer energy around within the body of air, and therefore again
constitute an indication that equilibrium has not yet been met. Note
that the absence of turbulences can only be achieved if the air moves
like a solid body would.

=> Without external energy input, the angular velocity will become
uniform across the entire system.


Now let's see what happens if we add a sustained heat source:

- If we heat up the air near the central axis, nothing much will happen:
Warmer air tends to travel inward, so we don't get any convection. We
would get some slow heat transfer outward, and a change in the pressure
gradient, but no noticeable movement.

- If on the other hand we heat up the air near the ground, that warmer
air will indeed, through convection, exchange its place with the cooler
air near the axis. However, as both layers of air initially have the
same angular velocity but different distance to the center, they have
different angular momentum, which needs to be conserved. The only two
mechanisms by which this can be achieved is (a) by transfer of angular
momentum from the warm air moving inward to the cold air moving outward
by means of friction (which is inefficient), or (b) by a change of
angular velocity in the respective bodies of air.

As a consequence, the warm inward-moving air will increase its angular
velocity beyond that of the ground, while the cold outward-moving air
will decrease its angular velocity below that of the ground, initially
resulting in a net wind at ground level.

- If the heat input continues, the convection will also continue, and
turbulences in the air will not subside; however, the net wind at ground
level will lead to a transfer of rotational energy between ground and
air until both ground and ground-level air generally move at the same
speed. Note that this effectively speeds up the ground-level air (while
slowing down the ground).

- The mechanism by which higher-level air is sped up, however, does
/not/ subside; to the contrary: With the ground-level air speeding up,
the difference in speed gets even more pronounced.


=> From what I see, we should expect the air near the ground to be
motionless overall, with winds only blowing from cooler ground regions
to warmer ones, while closer to the center we should expect a /higher/
angular air velocity than near the ground.

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Hi again, and thanks for the interesting sup topic we have entered here! :-)

At this interesting point, I would like to get some more input. I am
even considering, to post this question inside some Facebook or
independent Internet forum.

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