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Particle stream upgrades Issue Tools
issueid=1214 11-11-2015 11:59 PM
Addon Developer
Particle stream upgrades

This feature request concerns the current implementation of particle streams. If I remember correctly, the current implementation has remained unchanged since its introduction in the Nov. 5 2003 release. I think that after 12 years and 6 releases, it needs some upgrades.

The upgrades I have in mind mainly concerns the gravity interaction with particle streams. Currently when particle streams is used for the visualization of propellant venting pre-launch such as LOX vents on a launch vehicle, the particles get pulled downwards under the force of gravity. They should be in line with the direction they're generated with no interaction with gravity at all.

Also the current implementation seems to have problems with being generated at high vessel velocities such as during (re-)entry. I have spent quite some time trying to get the re-entry particle stream (RPS) of the beta rev. 42 default Atlantis to be more solid and nothing works, even using specs from particle streams I know are solid at lesser vessel velocities.

A more long term outlook for this one could be make exhausts actually be like real ones: http://www.orbiter-forum.com/showthr...ust#post489467
Issue Details
Issue Type Feature
Project ORBITER: 2010-P1 and newer
Status Implemented
Priority 6
Suggested Version 100830 (2010-P1)
Implemented Version (none)
Votes for this feature 0
Votes against this feature 0
Assigned Users (none)
Tags Graphics, Vessel Related

11-13-2015 03:22 PM
Orbiter Founder
 
Quote:
The upgrades I have in mind mainly concerns the gravity interaction with particle streams. Currently when particle streams is used for the visualization of propellant venting pre-launch such as LOX vents on a launch vehicle, the particles get pulled downwards under the force of gravity. They should be in line with the direction they're generated with no interaction with gravity at all.
Well, you can't turn off gravity altogether, or you end up with an inconsistent physics model. Imagine a vessel in orbit generating a particle stream (say venting some oxygen). The vessel propagates under the influence of gravity. If gravity doesn't act on the particles, you end up with the particles accelerating away from the vessel, i.e. you get a spurious pseudo-force.

Doesn't adjusting the atmospheric slow-down parameter and the initial velocity parameter provide the desired effect? At least that would be the physically correct model.

If you suspect that the current physics model for the particle streams is incorrect, can you specify exactly what you think is wrong (but without unphysical solutions like switching off gravity?)
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11-13-2015 07:08 PM
Addon Developer
 
Quote:
Originally Posted by martins
 Doesn't adjusting the atmospheric slow-down parameter and the initial velocity parameter provide the desired effect?
Nope. As far as venting is concerned, you might be thinking of the shuttle GOX Vent Arm (GVA) where the ET LOX vent as ducted away from the vehicle and dumped straight down. This is a special case devised to prevent ice formation on the vents that can break off and damage the orbiter TPS.

All other launch vehicles are not concerned with this and vents directly to the atmosphere. This creates a long horizontal plume emanating from the vent(s). No matter what I put in for v0 and atmslowdown, the plume(s) drop like they weigh a few tonnes instead of being feather-light.
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11-13-2015 11:55 PM
Aspiring rocket scientist
 
I do not understand the problem.

Are you trying to get particles to rise?
Reply
11-14-2015 08:17 AM
Addon Developer
 
Quote:
Originally Posted by Hlynkacg
 I do not understand the problem.

Are you trying to get particles to rise?
No, I'm trying to get them to stay at the same height as the stream that is creating them.

Take a look at this screenshot. It shows SLS venting GOX from both the Core Stage and the Large Upper Stage. Note how the LUS vent plume is dropping and pooling below the actual vent position (indicated by a red arrow).

It is supposed to stay at the same level and not make an arc downwards.

For the sake of comparision, I have also included a photo of the NRO-L55 Atlas V undergoing a Wet Dress Rehearsal (WDR) showing a nice horizontal GOX vent plume coming from the Atlas V LOX tank vent. On some days the plume(s) can be really large and long.


Reply
12-06-2015 12:53 AM
Addon Developer
 
This screenshot shows the problem with the current particle streams have with re-entry:


There's just no way to get it into a solid stream. I have played with every parameter and nothing works. You just get these separate particles.
Reply
05-07-2016 03:10 PM
Addon Developer
 
Here's a video showing the GOX venting of the largest launch vehicle to use LOX as the oxidizer so far, the Saturn V: http://www.youtube.com/watch?v=HkTev...EjHCKJml8fMDKs

Note the very long, GOX streams from the three stages, S-IC, S-II and S-IVB. I estimate that the streams are about 15 m long, comparing them to the Launcher Umbilical Tower (LUT) behind the LV (tower measures 12 m wide). And do note the lack of any gravitational droop in the streams. They're pretty much horizontal.
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05-23-2016 10:46 PM
Orbinaut
 
Has there been anything implemented regarding the reentry particle stream since last post? SSU user and the lack of effects on reentry kill the realism somewhat. Hope something has/is implemented.
Reply
08-16-2016 12:16 AM
Addon Developer
 
Quote:
Originally Posted by martins
 Well, you can't turn off gravity altogether, or you end up with an inconsistent physics model. Imagine a vessel in orbit generating a particle stream (say venting some oxygen). The vessel propagates under the influence of gravity. If gravity doesn't act on the particles, you end up with the particles accelerating away from the vessel, i.e. you get a spurious pseudo-force.

Doesn't adjusting the atmospheric slow-down parameter and the initial velocity parameter provide the desired effect? At least that would be the physically correct model.

If you suspect that the current physics model for the particle streams is incorrect, can you specify exactly what you think is wrong (but without unphysical solutions like switching off gravity?)
How about this, it doesn't ignore physics:
It's not gravity that pushes down the vent stream (be it hydrogen or oxygen) but the prevalent winds at the altitude of the vent port. Remember, winds can have both a horizontal and vertical component. Gases are very light and gravity doesn't have really that much effect on them (for example, even water vapor (gaseous dihydrogen monoxide) travels away from the direction of gravity).
Reply
08-31-2016 05:00 PM
Orbiter Founder
 
In Orbiter 2016, the gravitational acceleration of particle streams is now reduced as a function of atmosphere density. Is this new behaviour ok now?
Reply
08-31-2016 05:15 PM
Addon Developer
 
Quote:
Originally Posted by martins
 In Orbiter 2016, the gravitational acceleration of particle streams is now reduced as a function of atmosphere density. Is this new behaviour ok now?
Unfortunately no. They're still being pulled down. I think it's better compared to dust particles as these are very light yet still have a weight. That is how the particle streams should behave.
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08-31-2016 10:36 PM
Orbiter Founder
 
In case you tested that with the D3D9 client: can you also test with the inline client? I just realised that I forgot to push those changes to the external client implementation.
Reply
09-01-2016 01:03 AM
Addon Developer
 
Quote:
Originally Posted by martins
 In case you tested that with the D3D9 client: can you also test with the inline client? I just realised that I forgot to push those changes to the external client implementation.
There it looks a bit better, no sudden drop.
Reply
09-01-2016 10:05 PM
Donator
 
Quote:
Originally Posted by martins
 In case you tested that with the D3D9 client: can you also test with the inline client? I just realised that I forgot to push those changes to the external client implementation.
I take that as "would you please incorporate the changes of r54 into D3D9Client?"

I would like to have attached it here, but I can't attach files here
So please take a look at http://www.orbiter-forum.com/showthr...postcount=4115
Reply
09-01-2016 10:17 PM
Addon Developer
 
No issues and things look good. I think the issue can be closed.
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