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2:40 am
January 20, 2010
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rpulkrabek
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I think the project committer status will work fine. I will do the merge later tonight when I get home. I understand how to do it and will explain the steps after I do it. And you're right, it is quite straight forward.
It might also be beneficial to put the Rocket's work with SketchUp in the repository. Rocket, what do you think? Dropbox can be used as a sort of intermediate solution to share files, while the repository is a more official way to share files/code.
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7:19 am
January 20, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 402 | |
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I'd also like committer status, if you don't mind.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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7:38 am
January 20, 2010
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Luke Maurits
| | Adelaide, Australia | |
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Certainly! I just need an email address associated with a Google account. Post one here or PM me and I'll set you up.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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7:31 am
January 21, 2010
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Rocket-To-The-Moon
| | Altus, Oklahoma, USA | |
| Member | posts 685 | |
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rpulkrabek said:
It might also be beneficial to put the Rocket's work with SketchUp in the repository. Rocket, what do you think? Dropbox can be used as a sort of intermediate solution to share files, while the repository is a more official way to share files/code.
I am more than happy to upload all of the SketchUp drawings to the repository. I can't do it now because I am working 12-14 hour days 6-7 days per week, but once I get back on a normal schedule I will definitely make everything available.
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Main Workgroups: Propulsion & Spacecraft Engineering
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7:38 am
January 21, 2010
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rpulkrabek
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7:46 am
January 21, 2010
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rpulkrabek
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Rocket-To-The-Moon said:
I am more than happy to upload all of the SketchUp drawings to the repository. I can't do it now because I am working 12-14 hour days 6-7 days per week, but once I get back on a normal schedule I will definitely make everything available.
Yes, no problem. More importantly, good luck with that work schedule :S
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7:53 am
January 21, 2010
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Rocket-To-The-Moon
| | Altus, Oklahoma, USA | |
| Member | posts 685 | |
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The renders look pretty nice. This is real engineering work going on here and I like it!
What are the dimensions of this rocket?
One quick critique: What are your thoughts on lengthening the body of the rocket? I am concerned that there may not be enough propellant to achieve the mission with such a stubby rocket. Both CSXT and the NZ rockets were much more slender.
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Main Workgroups: Propulsion & Spacecraft Engineering
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7:55 am
January 21, 2010
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rpulkrabek
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How does editing the wiki work? Can I/we put one of these pictures in for the OHKLA site? If I feel I could add information, do I change or ask for permission from the community before a change occurs?
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8:08 am
January 21, 2010
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rpulkrabek
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Rocket-To-The-Moon said:
The renders look pretty nice. This is real engineering work going on here and I like it!
What are the dimensions of this rocket?
One quick critique: What are your thoughts on lengthening the body of the rocket? I am concerned that there may not be enough propellant to achieve the mission with such a stubby rocket. Both CSXT and the NZ rockets were much more slender.
Currently, it is nearly 7m in height and 510mm in outside diameter. I have a complete open mind about changing dimensions. I think the final dimensions should be determined based on calculations, which, I am unsure of what to take into account. I remember HEAT 1X from CS had a height of 6.2m and a diameter of 640mm. I was only modelling after these dimensions, with out knowing why. The good thing about a community is that they can tell me what's best :) I am also really pessimistic about the current nozzle geometry. I need to investigate more through CFD what is best. So, long story short, yes, let's change the dimensions.
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12:20 pm
January 21, 2010
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rpulkrabek
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The changes are now pushed through to the repository. I explained how to get the files to view the 3D model before, but here are the instructions again. You can now make a clone of these files to your PC and view them. Here are some quick steps that would be needed to view the Pro/E files:
- Download mercurial: http://mercurial.selenic.com/.
- In Windows, click the blue download button.
- Ubuntu: $ apt-get install mercurial
- Fedora: $ yum install mercurial
- OpenSUSE: $ zypper install mercurial
- Gentoo: $ emerge mercurial
- Mac OS X: ???
2. Go to the command line or terminal (Windows: click start, then run and enter "cmd". In Linux: you should probably know).
- navigate to the directory you want to put the files, or stay at the current location and move the files later on: $ cd /go/to/where/you/want
- enter this command (with out the $): $ hg clone https://cstart.googlecode.com/hg/ cstart
- You will now have the entire clone in a directory called cstart. You can then navigate to cstart/projects/ohkla/ProE to see the Pro/E files.
3. Download either eDrawings from SolidWorks (make sure to check the Pro/E check box before downloading) or ProductView from PTC (after filling in a form).
4. To view the entire assembly, open ohkla.asm.1 in either eDrawings or ProductView (if opened in ProductView, click on "Default View" in the left column). In eDrawings, click and hold middle mouse button to rotate. In ProductView, click and hold right mouse button to rotate.
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4:05 am
January 22, 2010
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Luke Maurits
| | Adelaide, Australia | |
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rpulkrabek said:How does editing the wiki work? Can I/we put one of these pictures in for the OHKLA site? If I feel I could add information, do I change or ask for permission from the community before a change occurs?
I think that it would certainly be appropriate for you to make changes to the OHKLA Wiki pages, including putting up some of these pictures. There is so little good information about OHKLA up there right now that it's not worth waiting too long on getting consensus. Something is always better than nothing, and since you've been doing such good work on this largely single handedly you should absolutely feel free to do some significant Wiki work too.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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3:33 am
January 24, 2010
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rpulkrabek
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Luke Maurits said:
I think that it would certainly be appropriate for you to make changes to the OHKLA Wiki pages, including putting up some of these pictures. There is so little good information about OHKLA up there right now that it's not worth waiting too long on getting consensus. Something is always better than nothing, and since you've been doing such good work on this largely single handedly you should absolutely feel free to do some significant Wiki work too.
I'll get to this soon (hopefully within a day or two). I wanted to do another cfd of the nozzle with a more relevant design of OHKLA, but unfortunately, I don't have the RAM required (I currently have 4Gb) to do a simulation of the assembly, so I am creating a simplified model, with the same geometry, but it is then considered as one part. All of the results will still be relevant.
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1:04 am
January 25, 2010
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rpulkrabek
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A quick update on the OHKLA design. I ran a CFD with the fuel grain geometry. I then discovered that this has a large effect on the nozzle geometry, as you can see from the picture.
 
So, as they say, "Back to the drawing board". I'll modify the nozzle geometry. I'll make it smaller, which will hopefully help with drag.
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1:14 am
January 25, 2010
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brmj
| | Rochester, New York, United States | |
| Member | posts 402 | |
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I know next to nothing about CFD, so what I'm about to say may be bogus, but I think I might see a problem here. The amount of gases coming out of the grooves ought to be higher, I suspect, because the reaction scales with surface area, not available volume. It is only unreacted oxidizer that ought to just flow through the thing from one end to the other. Not sure how this would effect the results, or if this is even an issue.
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Main work groups: Propulsion (booster), Spacecraft Engineering, Computer Systems, Navigation and Guidance (software)
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1:37 am
January 25, 2010
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rpulkrabek
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I also suspect that there would be more gas flowing through the grooves. I can adjust the amount of stream lines, but the end result is that the majority of the fluid flows right through the center of the nozzle. This may also be due to the stopper I have put into place. I think that if I made the inlet of the nozzle a bit smaller and then adjusted the throat and outlet accordingly, there would be a better result.
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7:38 am
January 26, 2010
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rpulkrabek
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| Member | posts 348 | |
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Getting better…
It's possible for me to give about 4 inputs, such as the radii of the nozzle, and do 1000 tests and ask for the results of the thrust. I am, however, currently stuck with how to transfer the parameters from CAD to CFD. I have to look into some documentation for this.
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2:45 am
February 2, 2010
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rpulkrabek
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Post edited 2:50 am – February 2, 2010 by rpulkrabek
An update on what I have been doing:
I made a simplified model to only include the nozzle and the fuel grain to determine the best nozzle geometry. From there, I made 7 parameters which to try and optimize to determine the highest amount of thrust for a 3MPa combustion.
The equation I used for thrust is:
Thrust=m_dot*V_exit+(P_exit-P_atm)*A_exit
where:
m_dot=mass flow rate
V_exit=Velocity at the exit
P_exit=Pressure at the exit
P_atm=atmospheric pressure
A_exit=area of the nozzle exit
This first picture shows the 7 parameters of the cross section of the nozzle that is rotated to form the second picture.
 
From these parameters, I can perform multiple simulations and then see the effects of what modifying one of these parameters will do. Each time I run this, 80 simulations are done, so, it takes my PC about a full day to do the calculations. From a given starting point, the following graphs are produced:
If I optimize each parameter according to the graphs (which are then updated to a different curve, sometimes going up instead of down), I get the following geometry:
Running this geometry through the simulation gives the following result with a thrust of 251,585N:
This is quite an undesirable result. I assume it was producing this high thrust due to the large outlet area of the nozzle. If I keep this geometry and sort of cut off the excess, meaning, I cut right where the fluid turns from red to yellow, I will get the following result with a calculated thrust of 155,212N:
I understand that many design constraints will change, and that I will have to rerun these simulations. At least for now, I am learning what geometry changes affect the thrust.
With that said, guidance from those who understand more or have more experience to point me in the right direction is welcome.
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3:24 am
February 2, 2010
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Luke Maurits
| | Adelaide, Australia | |
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| posts 1483 | |
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rpulkrabek, you are an absolute hero of CSTART. It's really impressive to see the amount of entirely solo work you are putting into OHKLA.
I can't really comment on what you've done here because I don't have the experience to know what is right or wrong, good or bad, but this has reminded me that I've been really lazy with regards to that hybrid rocket book I borrowed and answering your questions. I will try to get on this in the next couple of days to help you out.
I'll also do a bit of a search to try to find amateur rocketry groups with experience in high-thrust hybrid engines, particularly those who seem inclined toward open source, so that we can start compiling a list of people to solicit for guidance on OHKLA.
Once again, kudos to you for doing so much hard work, I hope you are learning lots and having a blast.
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Main CLLARE workgroups: Mission Planning, Navigation and Guidance. I do maths, physics, C, Python and Java.
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6:13 am
February 2, 2010
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rpulkrabek
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| Member | posts 348 | |
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Luke Maurits said:
rpulkrabek, you are an absolute hero of CSTART. It's really impressive to see the amount of entirely solo work you are putting into OHKLA.
I can't really comment on what you've done here because I don't have the experience to know what is right or wrong, good or bad, but this has reminded me that I've been really lazy with regards to that hybrid rocket book I borrowed and answering your questions. I will try to get on this in the next couple of days to help you out.
I'll also do a bit of a search to try to find amateur rocketry groups with experience in high-thrust hybrid engines, particularly those who seem inclined toward open source, so that we can start compiling a list of people to solicit for guidance on OHKLA.
Once again, kudos to you for doing so much hard work, I hope you are learning lots and having a blast.
Well, I really can't take that much credit. I just understand a few basics of the design and am fortunate enough to have access to some powerful software. I then just learn the software and have it do the heavy lifting.
Don't feel lazy. It appears to me that you are the most active one here. Don't feel like you need to read into that book for me. My suggestion is to put your emphasis on the CLLARE work you have been doing. Otherwise, if you are curious about what the book has to say, and you feel you would enjoy reading it, then let me know.
And yes, I am learning a lot and yes, it is a blast :)
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6:43 am
February 8, 2010
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rpulkrabek
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| Member | posts 348 | |
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At this point, I think I have settled with a nozzle geometry. If I try to optimize thrust, I get a CFD result where the fluid doesn't flow uniformly. I then thought it would be best to optimize the average fluid velocity at the outlet of the nozzle. The result is with a rocket that has a calculated thrust of about 143 kN for a combustion of 3 MPa, which is only an initial guess of combustion pressure. Here are the resulting images:
I put the background white for the second picture in case we would want to manipulate it with Gimp for any promotional use.
I am sure many things will change, but I now feel this is a good place to start with OHKLA.
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