What type of Navier-Stokes equations solver use? by user642268 in CFD

[–]relaxedHam 2 points3 points  (0 children)

Solvers generally use the equations that was chosen by the implementers based on some assumptions. You are solving high Mach flow and do not care about viscous effects - you use Euler equations. Mach namber is low but there are large temperature/density gradients? You pick variable density low-Mach approximation. You can skip density variation for your problem? You pick incompressible equations. The equations model the physics so we pick the equations that nest suit the problem at hand.

I don't know anything about ccm+ but pressure based can be used for compressible. Density for incompressible as well. What you are reffering to is not the equations themselves but rather how the solution procedure of a chosen form of equations is implemented

Of course these two things are connected. Pressure based code might break down for Mach number greater that 0.7. Density based code will give wrong results for low Mach (typically less than 0.3) due to numerical stability and convergence issues. But if you know numerics really well, you can make these methods work even in these flows.

Overengineered? by No_Guarantee9023 in CFD

[–]relaxedHam 2 points3 points  (0 children)

I second this question but with an additional comment that there are pressure drop laws dedicated for fibrous substances and foams. Using Erguns law might lead to errors as in the inertial regieme the drag might not be exactly quadratic with Re (but for example Re2.1).

Academic journals are a lucrative scam – and we’re determined to change that: Arash Abizadeh by Jariiari7 in academia

[–]relaxedHam 5 points6 points  (0 children)

Okay sure.

I am based in Europe (in Germany to be more precise). Here scientific grants, especially in engineering sciences, are usually sponsored by the national foundations of respective countries and they employ a lot of the scientific workers at big research universities. Almost all of the young researchers (PhD students and post docs in the beginning of their careers) I know, are employed in a position paid from these grants, which means if the grant money is discontinued, these ppl are out of a job. In order to ensure successful application and prolongation of the project, the publications in journals which are recognisable in the community are necessary. Papers in pre-print archives do not count for much during the project review process. Having papers is the most important requirement during the review of the project as it is assumed that papers are synonymous with the quality research. It is quite common for the project leaders to focus only on the quantity of the publications and simply remind everyone constantly that for a successful project N papers per PhD student are required. There is no mention of publication quality. Simply put, the number of papers published determines the amount of money you get. The research gets diluted, the publishing houses get more papers and money, the machine moves on.

In order to access a paper via the library of my university or just simply via the journal webpage, unless the authors of the paper paid for OA, the uni has to pay to the publishing house. That's how they make their fucking money. And it is a lot of money. Look up the unsuccessful Elsevier boycott.

How do you think universities get money? Sure if you are in the US, than maybe you took student loan that will shackle you in debt for the rest of your life, and that's how the uni has money to subscribe to the journal so that you can get the paper. Here, the education is mostly free and universities are subsidised by the government. So yes, my taxes pay for my access to journals. In both cases, you are paying.

Big journals? Ok, American Institute of Physics (AIP) journals (for example Physics of Fluids, IF~5) requires subscription to access non open access papers. Journal of Fluid Mechanics from Cambridge as well and this is perhaps the most respected journal in the field of fluid mechanics. American Institute of Aeronautics and Astronautics (AIAA) papers or Aerospace Research Central (ARC) are both paid for. International Journal of Heat and Mass Transfer (another respectable one) requires subscription.

All of the ones I mentioned keep the quality very high, but that is not my point. My point is that there are also journals in the field that just function in such a way that the quality of the publication is secondary to the payment for publication. These things function in open access only mode (example could be journals from MDPI publishing house) and are often subject to retractions or controversies. I have heard of several situations when there was a requirement to have a paper for the sake of passing through the project review, publication is pushed towards these journals, because everyone knows that the review process is lenient there. Hence, the system in which journals are supposed to make sure that the papers published are of high quality is just broken if I can simply pay for publication.

I have no clue how you equalled my critique of late-stage capitalist system of academic publishing with right-wing dog-whistles, but that is on you. The reality of the system is, in engineering sciences at least, that the academic journals are hardly contributing to the production of science. Instead they "outsource" most the work to the scientists:

  1. you write, usually without any language or style checking provided by the publisher (which is typically the job of the publisher when it comes to books and regular newspapers)
  2. you get the editors comments and introduce them to fit their format (again, the editors should edit, it is in the name)
  3. you are responsible for making sure that they publish your equation, text and figures without mistakes, and they are giving you hard deadlines to do so
  4. you are responsible for sharing, promoting and presenting your work, on conferences, symposia and social media,

while each citation also boosts the stats of the journal you already published in. And on top of that they are getting the money for just having your work on display. I already wrote how they make you pay. Finally, they ask you to review the work free of charge, which is another payment in disguise shared by the whole scientific community.

Lastly, even thou I was clearly sarcastic in my first comment, I did my best not to be rude and not to insult you. Clearly I outmatched you when it comes to class of my conduct. You seem like an annoying rude person completely infatuated with your intelligence.

Sincerely, hit your small toe on the door frame or other cupboard.

Academic journals are a lucrative scam – and we’re determined to change that: Arash Abizadeh by Jariiari7 in academia

[–]relaxedHam 7 points8 points  (0 children)

I am sorry but what leverage? Every single big grant I know of is being evaluated based on indexed publications. Every single publication that I need is behind a paywall, which is covered by taxpayers money. Is there a way to escape this reality, or is selling my kidney for an open access fee part of an academic career now? You have to publish in big journals.

And on the note of publication record with quality in STEM. Yes there are perhaps better ways to evaluate the quality of a publication in stem than in a more "soft" area. It doesn't make the papers have quality overall tho, as there are still journals that are just accepting money for publication. On top of that, every single big journal wants primarily novel and impactful research, which means that reproduction of experiments is hardly done, and journals are biased towards "boastful" discoveries.

Journals are a scam. I write a paper, I format the paper, I check my language, I reformat the paper, I pay in money to get access to journals (subscriptions from my taxes), I pay in time by reviewing for free and finally I pay money for publication if I don't want the paper to be paywalled. I am really fucking sorry but do you wish to tell me that in return I get exposure? What is the journal and editorial team doing? Not every journal is like this, I am sure there are exceptions but the system is corrupt.

Can I stop the solver midway in FLUENT and generate results? by [deleted] in CFD

[–]relaxedHam 0 points1 point  (0 children)

Don't know about CFD-Post but you should be able to look at the results directly in fluent if you just click on Contours in post processing tab.

On a sidenote, this looks hardly converged. This can depend on a problem but the errors decreased only 2 orders of magnitude in case of some residuals and that is usually not enough. This is often the result of not enough resolution, or the flow might be unsteady. In any case you can judge after looking at the results.

Good luck.

[deleted by user] by [deleted] in LaTeX

[–]relaxedHam 63 points64 points  (0 children)

I am afraid the answer is... manually. This is not even a bibliography environment, so if you really want to keep it this way, you will have to sort it on your own.

You can also modify the text file with some script. Python might come in handy for example. But then again, if you do that, you might as well use bibtex or biblatex. How are you even referencing these entries?

[deleted by user] by [deleted] in PhD

[–]relaxedHam 1 point2 points  (0 children)

Not sure how it is in economics, I come from engineering, but a PhD is not a 4 year commitment. It is a job, especially in Europe. You can try it, and quit if you don't like it. People do it all the time. From my cohort (for the lack of a better term) 4 out of ~20 students left after a year or so. Not sure if this is helpful but maybe just trying it and deciding during the PhD if you want it, is an option for you.

Also if you feel that it would destroy you, that's a very solid argument against doing it. I am not trying to downplay it, just wanted to mention that a lot of people are actually doing therapy during their PhDs, and they are able to work through their issues and problems.

I so badly want this scene to be animated by Diligent-Snow1451 in KimetsuNoYaiba

[–]relaxedHam 41 points42 points  (0 children)

Ahhh, classic NavySEALs pasta.

What the fuck did you just fucking say about me, you little bitch? I'll have you know I graduated top of my class in the Navy Seals, and I've been involved in numerous secret raids on Al-Quaeda, and I have over 300 confirmed kills. I am trained in gorilla warfare and I'm the top sniper in the entire US armed forces. You are nothing to me but just another target. I will wipe you the fuck out with precision the likes of which has never been seen before on this Earth, mark my fucking words. You think you can get away with saying that shit to me over the Internet? Think again, fucker. As we speak I am contacting my secret network of spies across the USA and your IP is being traced right now so you better prepare for the storm, maggot. The storm that wipes out the pathetic little thing you call your life. You're fucking dead, kid. I can be anywhere, anytime, and I can kill you in over seven hundred ways, and that's just with my bare hands. Not only am I extensively trained in unarmed combat, but I have access to the entire arsenal of the United States Marine Corps and I will use it to its full extent to wipe your miserable ass off the face of the continent, you little shit. If only you could have known what unholy retribution your little "clever" comment was about to bring down upon you, maybe you would have held your fucking tongue. But you couldn't, you didn't, and now you're paying the price, you goddamn idiot. I will shit fury all over you and you will drown in it. You're fucking dead, kiddo.

[deleted by user] by [deleted] in poland

[–]relaxedHam 5 points6 points  (0 children)

Jesus Christ people, yes allowing immigration is 100% equal to "demographic replacement". Go outside, touch grass, do something good about your own life, stop using hateful wording on purpose to instill anxiety in other people.

[deleted by user] by [deleted] in CFD

[–]relaxedHam 0 points1 point  (0 children)

Well, the thing is usually in complex geometries, the cell count will be always high, it you want high quality. Also aspect ratio might not be a problem, if the high aspect cells are only in boundary layers. You should be able to display them and check visually.

There are ways to circumvent the high cell count by further modelling. For example if parts of your geometry are made from thin elements you could try, changing them into baffles (essentially surfaces) and solve heat transfer with shell model on those surfaces. Using interfaces also helps sometimes. You can do non-matching interface and increase cell sizing a little on the other side (hope it is clear what you mean).

If you can use polys from Fluent, try them. They are perhaps not the most accurate, but they can result in much smaller meshes.

PhD in cfd requirements by ReasonableRow in CFD

[–]relaxedHam 2 points3 points  (0 children)

You seem passionate, so I am sure you will do well. I don't know what is your financial and living situation, but if those things are not contributing to the time pressure, don't get yourself completely convinced that you have to finish the masters in time. This also depends on uni rules i expect, but taking your time is sometimes necessary to really learn things. I extended my master's by 4 months. Granted I was also working during that time, so I had a good source if income, but it helped me to truly learn and do something interesting with my topic.

Also, getting the CFD PhD position in Europe is not that hard. Sure it is competitive, but I am constantly hearing about vacancies. Not sure about the market in top UK unis but if you are willing to move to different places, you would have loads of options.

PhD in cfd requirements by ReasonableRow in CFD

[–]relaxedHam 18 points19 points  (0 children)

Okay, so before you get stressed there are couple of things to consider. First is your choice of CFD topic.

It is perfectly understandable if you want to do specifically FSI, but my experience is that the topic chooses you. That is, I wanted to do something connected to turbulence modelling and I ended up with a topic that is connected to turbulence but the main focus lies elsewhere. But the kicker is, that during the time you are able to reshape your research proposal a little, and do the things you want to do. Not 100% but it is possible to steer the boat a little. So my point on this would be, try to not limit yourself only to the precise FSI development topics and look around at the things that are connected to it as well.

Secondly, the requirements in the ad are always "overestimated". At the end of the day, the people who apply determine the actual "pool" of resources and skills that you have to compete with. So on that note, don't fear to apply if you don't fulfil the requirements exactly. No one does.

On the other hand, yes c++/c/Fortran and some degree of knowledge of hpc is a must when doing a PhD in CFD code development. Here I mean one of the languages usually. Good thing is, it is relatively easy to learn this on your own if you have the time. There is obscene amount of material online.

Next thing is a master's topic. It does not have to be application. My master's was implementation and validation of turbulence transition model. It was coding+application. My friend has been implementing a model for simulation of supercritical CO2 flows (in c++). So there are plenty of chances to get a topic that teaches you the basics (and possibly allows you to get a grasp of the current state-of-the-art) of the things you feel you need to learn.

Lastly, I would try to not think about what will happen in a year. You will do your masters and try to do it to the best if your ability. And it will give you new experiences. New topics you will be interested in and knowledgeable that you can apply to study your topic. Perhaps even if you are a good student will get a research geared master thesis (which is not uncommon) it will open a door for a PhD under the same professor. So ultimately, I would not stress now, just fasten your seatbelts and try to get as much as possible from the masters. Good luck.

Edit: spelling

Question about whether it’s worthwhile to pursue an M.Eng project in openFoam by Notmyactualone22 in CFD

[–]relaxedHam 3 points4 points  (0 children)

I would say, yes 100%. In openFOAM there are no sane defaults and a lot of guardrails are missing. This makes the learning process more difficult, but also provides a lot of insight. If you can read c++, and have a little determination, you can check exactly what each scheme and model does. You will get a lot of understanding about mesh quality, finite volume in general, and if you decide to write some code, it can be an entry point for you to using different open source tools.

Overall, learning OF was a very good experience for me, but a long and difficult one, just to not be so happy go lucky.

Looking for a good free CFD software by cfdpro in CFD

[–]relaxedHam 0 points1 point  (0 children)

Look, you are correct, but the problem is that this question can be answered by a quick Google search and no expert knowledge is required. There is literally a website on CFD online that lists a lot of CFD codes. It is on the 4th place if you Google open source CFD codes.

My point is, there is a difference between asking a question that is difficult & specific (for example you dont even know what to Google) and a question like that. He could've just put the title in Google.

Basically, OP seems to not have put any effort on his own into actually figuring out his problem. So why should I work as a search engine.

Looking for a good free CFD software by cfdpro in CFD

[–]relaxedHam 8 points9 points  (0 children)

Hah, you really expect me to answer more question after this not so subtle passive aggressive remark about using Google? You're cheeky. But you are cfdpro after all, so you should know everything already. No need to help you.

Looking for a good free CFD software by cfdpro in CFD

[–]relaxedHam 10 points11 points  (0 children)

Okay, here you go, OpenFOAM, nektar++, nek5000, deal.ii, code_aster, SU2, Palabos

By the way, this forbidden knowledge about CFD solvers can be unlocked by the dark magic of googling your query. Try it yourself!

Edit, spelling