Ask a PhD candidate in aerospace engineering anything

[None !jyyGvyuDkk No.6205993]

It's that time again. My research is in computational fluid dynamics and aerodynamics, nothing directly space related.

Questions about grad school, aerodynamics, high performance computing are all good.

[Anonymous No.6205997]

>>6205993
Can you do triple integrals?

[Anonymous No.6205999]

I was wondering if you were still here.

I've taken a single class on compressible flow.
How do I get into vortices and flutter?
What book(s) would you recommend?

[None !jyyGvyuDkk No.6206001]

>>6205997
Uh, yes. Volume and Surface integrals in 3D space are the crux of fluid mechanics and CFD.

[None !jyyGvyuDkk No.6206003]

>>6205999
Hmmm... depends what particular areas you're into. There's lots of texts on turbulence, where vorticity is at the heart of everything. Honestly every turbulence text I own or have read has been pretty lousy, so at best I can tell you which ones are bad. I usually recommend Kundo/Cohen for a first or second general fluid mechanics text.


Aeroelastic flutter isn't something I've studied in great deal, but I'd look through the AIAA library.

Honestly after pouring through books during my qualifying exam studying, I know a lot more about shitty books than good ones.

[Anonymous No.6206008]

Do you believe in aliums?

[Anonymous No.6206009]

What's your IQ?

[Anonymous No.6206011]

>>6206001
>Surface integrals
>triple

[Anonymous No.6206012]

How one would go about developing an autopilot for getting a rocket into orbit?

[Anonymous No.6206014]

>>6206012
First, you'd download the code for mechjeb...

[Anonymous No.6206015]

how much time do you spend a day working on your research? is getting a PhD as difficult as most people claim? what do you plan on doing once you graduate?

[None !jyyGvyuDkk No.6206017]

>>6206009
I dunno. I guess I was interested in that in my teen years and got tested at 165. Being surrounded by brilliant people at a top university has a way of making you feel like an idiot though.

[Anonymous No.6206020]

Why are the equations for fluid dynamics identical to the ones for electromagnetism?

[None !jyyGvyuDkk No.6206022]

>>6206011
In CFD we evaluate surface integrals by using spatial derivatives which come from volume integrals via Green's theorem.

[None !jyyGvyuDkk No.6206029]

>>6206012

Step one is to take some courses on control theory.

[Anonymous No.6206027]

>>6206012
that's less aerospace and more control theory.
I would suggest looking into PID controllers.
Learn some feedback and maybe eventually get into LQR controllers

[None !jyyGvyuDkk No.6206035]

>>6206027
Control theory is a pretty important part of AerE education. I've taken two ugrad and two grad courses on it.

[Anonymous No.6206032]

>>6206014
I wasn't really thinking about KSP, is whatever mechjeb does actually applicable for an Sun-Earth-Moon system, or any kind of system?

[Anonymous No.6206037]

>>6206020
they aren't.

The equations I believe you are thinking about are about potential and flux, which are used for heat and mass diffusion, as well as fluids and electricity.

[None !jyyGvyuDkk No.6206048]

>>6206015
>how much time do you spend a day working on your research?

It varies. I treat it like a regular job, so if I have no other coursework/teaching about 50-60 hours a week, with the caveat that I spend every waking second that I'm not working thinking about what I should be working on, or mulling over ideas.

> is getting a PhD as difficult as most people claim?

It depends on a lot of factors, most importantly the person. Different schools/departments/fields vary drastically. I've seen a lot of brilliant hard-working people fail out due to sheer difficulty. Without question my qualifying exam was the single hardest thing I've ever done; it's notoriously hard in my department (notorious with aerospace industry veterans).

>what do you plan on doing once you graduate?

Leaning towards private space industry, but keeping avenues open for potential postdoc/academia work. A lot of it depends on how things work out in my personal life.

[Anonymous No.6206049]

>>6206027
>>6206029
I was thinking of optimizing the ascent trajectory of rocket on a dynamic system I modeled, to get it on some proper orbit.

Sadly, it's something I haven't actually found any solid sources on.

[None !jyyGvyuDkk No.6206050]

>>6206020
>Why are the equations for fluid dynamics identical to the ones for electromagnetism?

They're not identical. Are you asking why their functional forms are extremely similar? Because that's something I find interesting, but it's a direct result of how the physics work out.

[Anonymous No.6206051]

>>6206037
Hydrodynamic fluid velocity, vf Magnetic vector potential, A
Hydrodynamic fluid acceleration (af), dvf/dt Induced electric field (Ei), dA/dt
(Induced) Mass of the fluid, mf Electric charge, q
(Induced) Fluid density, f
Charge density, q
Virtual mass, mvirtual Relativistic mass, mrelativist
Acoustic gamma factor, a Lorentz Gamma factor, 
Acoustic impedance, Za Electromagnetic impedance, Zw
Compressibility of the fluid,  Permittivity of the vacuum, 0
(Surrounding) Fluid density, f
Permeability of the vacuum, μ0
Acceleration Inertia Force, - f
(vf/t) Acceleration Inertia Force, -q(A/t)
Virtual mass increase, - f
(vf )vf Relativistic mass increase, -q(v)A
Hydrodynamic Inertia Force, - f
(dvf/dt) Electromagnetic Inertia Force, -q(dA/dt)

[Anonymous No.6206053]

>>6206032
It's good enough for SpaceX.

They just loaded mechjeb into a conventional expendable rocket, and now it's reusable.

[Anonymous No.6206055]

>>6206050

Yep

[None !jyyGvyuDkk No.6206059]

>>6206049
Optimizing a trajectory isn't really the job of an autopilot / control theory. Controls are more about how to stay on a trajectory when there's deviations from it.

[Anonymous No.6206058]

>>6206053
Sounds like I am going to have to take a look at it then.

[Anonymous No.6206065]

>>6206050
Do you think its because of some underlining symmetry... like space-time being a super-fluid or something?

[Anonymous No.6206066]

>>6205993
>Questions about grad school, aerodynamics

Are they teaching you anything about non-rocket-based propulsion?

[None !jyyGvyuDkk No.6206071]

>>6206055
I guess there's a few things I can point to. They both deal with wave propagation (electromagnetic in Maxwell's and pressure in Navier Stokes), Curl terms you get when orthogonal things affect each other (B and E fields in Maxwell, vorticity in NS), divergence terms you always get when there's a point source of something, or you're otherwise interested in conservation of a scalar field...

[None !jyyGvyuDkk No.6206076]

>>6206065
>Do you think its because of some underlining symmetry... like space-time being a super-fluid or something?

No, it's because both equations come directly out of continuum mechanics -- they're just Cauchy equations with different stress tensors. When you're interested in physical conservation laws in 3D space, the forms of things tend to look similar purely out of geometry. Same in solid mechanics. It's why statics and mechanics courses are so important in early undergrad.

[Anonymous No.6206079]

>>6206059
Oops.

I probably would have to do both anyways.

Do you know of any books on the subject of optimizing such trajectories or something?

[None !jyyGvyuDkk No.6206085]

>>6206079
Roger R. Bate, Donald D. Mueller and Jerry E. White, Fundamentals of Astrodynamics. Good starting point for *what* constitutes an optimal trajectory, actual optimization comes later and is really kind of easy for simple dynamical systems.

[Anonymous No.6206096]

>>6206085
Thanks, going to check that out.

Anything besides me having to guess values would be an improvement.

[Anonymous No.6206094]

How old are you? When did you first develop an interest in this subject?

[None !jyyGvyuDkk No.6206099]

>>6206094
29, been interested ever since I was sketching airplanes and building models as a 5 year old.

[Anonymous No.6206101]

>>6205993

*tips fedora*

[Anonymous No.6206104]

>>6206071
>>6206076

Ok...kool, ever since I learned about potential flow, Ive always though there was some sort of deeper meaning in the similaritys.

On a related note, isn't that why Maxwell named the displacement current what he did, because he though it was a displacement the the aether or something?

[Anonymous No.6206109]

>>6206096
Trajectory, smajectory, the important thing is that you know to fuel your launch vehicle with hydrogen peroxide and aluminum hydride suspended in trisilane gelled with fumed silica.

400+ s of Isp at 1.5 g/cc. Hydrazine a shit.

[Anonymous No.6206108]

>>6206099

How naturally did the math come to you? Were you always a lucid analytical thinker?

[Anonymous No.6206112]

>>6206108
>How naturally did the math come to you? Were you always a lucid analytical thinker?

The math gets more and more intense when you get into the research end, but it all makes more sense... it's more connected. I've always been analytical/rational but with a lot of creativity (loved to draw and such as a kid)

[Anonymous No.6206170]

Could you take this man?

[None !jyyGvyuDkk No.6206190]

>>6206170
No.

[Anonymous No.6206210]

Where did you do your undergrad?

[Anonymous No.6206225]

>>6205993

can I be like you?

[Anonymous No.6206407]

>>6205993
If you could redo your application process again, what would you change?

What are the most important pieces of advice you could give to someone applying to graduate school next year?

[None !jyyGvyuDkk No.6206413]

>>6206407
>If you could redo your application process again, what would you change?

Honestly, nothing. The application process is one of the few things I'm confident that I did very well at. I got accepted into schools I never would've imagined.

>What are the most important pieces of advice you could give to someone applying to graduate school next year?

1) Have a very good idea of what exactly you want to study in grad school, and be familiar with the state of research in that area. You need to know about it to be good, and you need to really like it to be successful.

2) Find profs at various universities who are doing work that you want to do, and contact them directly. Talk to them about their research and needs for grad students. If they like you, you will get in.

[None !jyyGvyuDkk No.6206414]

>>6206210
A decent, respected-but-average state school.

[Anonymous No.6206415]

Do you do RC planes?

[None !jyyGvyuDkk No.6206433]

>>6206415
I used to. Last couple of years that I've been TA'ing I jump on the chance to help undergrads with those projects and I advise them.

[Anonymous No.6206439]

>>6206414
Georgia Tech?

[Anonymous No.6206444]

>>6206439
>>6206415
>>6206414

also, I'm currently comp sci, but Aerospace Engineering reallly interests me. Is there anyway to know for sure if its the thing ofr me, other than taking several courses in it?

[Anonymous No.6206447]

>>6205993
why do you use that picture?
who is he?

[Anonymous No.6206455]

how do you feel about your prospects post-doc?

are you ready to look for contracts every year and never get tenure?

[None !jyyGvyuDkk No.6206461]

>>6206439
No, and no one would describe georgia tech as "decent but average"

[None !jyyGvyuDkk No.6206463]

>>6206455
My industry prospects are fantastic, and I have very little desire to play the academic route.

[None !jyyGvyuDkk No.6206469]

>>6206444
If you're currently a student, try and get an internship at an aerospace company.

Go to every lecture you possibly can on campus related to aerospace.

[Anonymous No.6206490]

I'm focusing on the generation of 'HIT' by using the method proposed by -Rogallo-... (divergence free of homogeneous isotroy T in real space ).

In fourier space the mass conservation: kx*ux + ky*uy + kz*uz = 0 reaches the machine accuracy to the power -14.

However, after inverse Fourier tranfer, DIV*U approx O(1), which is not divergence free at all.

Also, I found that after the inverse Fourier of the U(k), the velocity field U(X) has image part.
I comfirmed that using both part of U in real space U(real, image ), by FFT, in Fourier Space the equation indeed valid, kx*ux + ky*uy + kz*uz to the O(-12).

I am quite sure that the generated random velocity in wave number space obeys the symmerty rules for both (real part and the image part).

Do you have experience about this?

[Anonymous No.6206497]

>>6206461
what would they describe it as, shit?

I'm enrolled there is why I'm wondering.

It's definitely no Stanford ;_;

[Anonymous No.6206504]

so what kind of work would a CFD guy be doing in private industry?

modeling the wind and turbines all day?

[None !jyyGvyuDkk No.6206509]

>>6206497
GaTech is generally considered in the top echelon in aerospace. Stanford sucks ass; take away the name brand and they have community college level quality.

[None !jyyGvyuDkk No.6206511]

>>6206504
CFD has all but replaced wind tunnels in aerodynamic design.

[Anonymous No.6206515]

>>6206490

Here, I have a supplementary text to a quite similar subject that I've been preparing this semester:

http://thatsmathematics.com/mathgen/paper.php?nameType%5B1%5D=custom&customName%5B1%5D=A.+Nonymous&nameType%5B2%5D=custom&customName%5B2%5D=&nameType%5B3%5D=custom&customName%5B3%5D=&nameType%5B4%5D=custom&customName%5B4%5D=&seed=1356546869&format=pdf

[Anonymous No.6206524]

>>6205993
ITT: self-absorbed faggots who think they know shit about shit because they have a piece of paper that dictates what they think they know.

You are all pathetic. Every. Last. One. Of. You.

[Anonymous No.6206526]

Where did you go to grad school?

[Anonymous No.6206527]

>>6206515

cool thanks

[Anonymous No.6206530]

>>6206524

Then why are you here?

[Anonymous No.6206540]

I'm a freshman engineering student, really having some trouble choosing what engineering specification to major in. I really REALLY want to go into aerospace, but my school (UBC) does not have it.

So my plan is to take whatever engineering is the most relevant to aerospace engineering so that I will be able to hold my own when I take aerospace engineering in grad school.

Here are my options:

>Engineering Physics
>Chemical & Biological Engineering
>Electrical Engineering
>Computer Engineering
>Materials Engineering
>Mechanical Engineering (Biomedical, Mechatronics or Thermofluids)
>Integrated Engineering
>Environmental Engineering
>Civil Eng

By far mechanical and Engineering Physics are the hardest ones to get into here.

Which would be most applicable do you think? For what I'd like to do in Aerospace/Astronautical Engineering - I pretty much want to have lots hands on experience with spacecraft/space technology (Not necessarily planes, but technology you might find on satellites, the ISS etc)

[Anonymous No.6206547]

>>6206540
Also if you could rank a few by applicability; because I really am not sure I can even get into eng physics or mechanical

[Anonymous No.6206570]

>>6206547
You could be a computer engineer to work in aerospace firms.

[Anonymous No.6206576]

>>6206570
No, I'm a hands on guy. I want to go into aerospace engineering also because I want a good shot at getting the hands on experience needed to become an astronaut.

[Anonymous No.6206759]

>>6206515
lol

[Anonymous No.6207738]

Here's some computational fluid dynamics for OP:

https://www.youtube.com/watch?v=QMYfkOtYYlg

[Anonymous No.6207742]

>>6206048
Why the fuck would you do a PhD if you want to go private ?
At least in my country a masters is what private R&D wants and requires, a PhD is usually for academia.

[Anonymous No.6208013]

>>6205993
I've played with the tiny bit of CFD that comes with my solidworks license. (one input area one output area no moving parts no transonic or supersonic flow, will do flows of air or water but not both and it fucking ignores temperature!)

So are there any free or open source tools you like?

Also interested in ray tracing shit that can handle rf to uv and dielectric constants and specific absorption rates and all that shit.

Also what about a space simulator that accounts for many gravitational forces to compute low energy transfers.

Computer shit is cool (^_^), but I cant find it.

[Anonymous No.6208061]

>>6205993

I'm a Masters student participating in the AIAA Graduate Missile Design Competition. We are developing our modeling and simulation environment. Have you ever worked with Missile DATCOM by any chance? Do you know much about ducted rockets? We are strongly considering using one for propulsion since our range requirement essentially eliminates a traditional solid rocket motor...

[Anonymous No.6208068]

>>6206540

I'm a masters student in AE and my undergrad was mechanical. I know a girl in my program who did her undergrad in physics. Anything else would likely struggle a bit more transitioning to AE, but anything is possible if you're willing to put in the work to learn it.

[Anonymous No.6208071]

>>6208013

Not OP but you may look into Openfoam.

[Anonymous No.6208096]

>>6208071
>Openfoam
Thanks man, that looks cool.

[Anonymous No.6208095]

>>6205993
Would you be willing to do my MATLAB project for some money?

[Anonymous No.6208107]

>>6208013
>(^_^)

:^)

[Anonymous No.6208118]

What do you think of this?

http://io9.com/5963263/how-nasa-will-build-its-very-first-warp-drive

>The Alcubierre Drive

>The idea came to White while he was considering a rather remarkable equation formulated by physicist Miguel Alcubierre. In his 1994 paper titled, "The Warp Drive: Hyper-Fast Travel Within General Relativity," Alcubierre suggested a mechanism by which space-time could be "warped" both in front of and behind a spacecraft.

Is there any way you could explain this in simple enough terms so a 2nd year physics student can understand?

[Anonymous No.6208126]

>>6208095
im not him, but give details?

[Anonymous No.6208129]

>>6208126
Can i get your email so i can send it to you to take a look at?

[Anonymous No.6208133]

>>6208129

[Anonymous No.6208140]

>>6208133
Sent an email to you

[Anonymous No.6208151]

>>6208133
check your spam box if you didn't get it

[Anonymous No.6208150]

What is the ratio between two orbits at which the most efficient transfer is no longer the most fuel efficient?

[Anonymous No.6208329]

>>6208118
makea bubble in your mind. now put that bubble though an O so that its middle is held in place, now grab both ends of the bubble, and shift your fingers in one direction.

the "forward" motion is cause by the now "voided" missing part of air where the bubble once occupied and tried to re-equalise the low pressure by sucking this forward. except instead of air in space its some space voodoo we don't exactly understand, may involve magnets.

[Anonymous No.6208442]

>>6206540

ME and AE undergrad programs are pretty similar in terms of what you learn. At my uni you would take the same classes first two years and then slightly different ones the next two. Aero kids take another structures class, gas dynamics, flight dynamics and spacecraft design and the ME kids take machine design and tech electives related to a specific field. I'm about to get my ME degree in about 4 days and feel pretty confident with the undergrad level aero topics so I would recommended mechanical if you can get in.

[Anonymous No.6208510]

>>6208329

well what is this "hand" that's causing the forward motion in the first place? What's the bubble? What's in the bubble? What does the O represent? Lot's of questions need to be filled in your explanation.

[Anonymous No.6208516]

>>6208510
>well what is this "hand" that's causing the forward motion in the first place? What's the bubble? What's in the bubble? What does the O represent?
That's more or less why we don't have one in real life.

[Anonymous No.6208527]

>>6208516

No I'm talking about how it's theoretically possible

[Anonymous No.6208589]

Favorite part manufacturer? Can be ones that only make a single small part too

[Anonymous No.6208636]

Advice for a college freshman ME major?

Have you ever played kerbal space program? if so, did you enjoy it, or is it too much like your (future?) work to have fun with?

What's your favorite project you've worked on so far?

Job with CIA/FBI working on super secret stuff, or job with Lockheed Martin working on other more weapons oriented secret stuff? Why?

Best internship?

[Anonymous No.6208649]

>>6205993
Are you getting your PhD via a corporate sponsored grad program, or did you go direct from BS to MS to PhD?
Because if you went the full academic route, how does it feel to know that you'll never recover the lost earnings?
As you progress through your thesis, was it worth it to directly join a grad program without first getting a job?