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Tunnnel Simulations?
Ciao everybody,
I wonder if there are CFD-codes (commercial or research) around, which are able to predict the flowfield in a street tunnel including trafic such as cars or trains and ventilation. Important would be to model also the differents between having independent tubes per direction or just one tube for both directions. What would be the best way to model moving cars in a tunnel? The subject has some importance after major accidents in european street tunnels. Thank you! Ciao Heinz |
Re: Tunnnel Simulations?
(1). I don't think there are codes available which are able to predict the flow field in a tunnel..... (2). But I have seen papers which deal with flow through tunnel including exhaust gas problem using various approaches many years ago. (3). Don't worry about cars in a tunnel, cars are being replaced by SUV, and then trucks. Eventually, everyone will be driving a tank. If a German made car can not save a princess, a tank should do the job. (4). As long as there are well-trained CFD engineers and researchers, the problem can be solved. (5). I have heard about the grid-less CFD methods, and I think, pretty soon, there will be code-less CFD approaches. In the code-less CFD approach, the users simply input the information and select the answer.
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Re: Tunnnel Simulations?
Things like this have been done in the past with subway stations including moving trains using starcd. So I don't know why it should not work for car tunnels. Maybe there is a different physics working :) I don't know why John is that pessimistic about this case?
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Re: Tunnnel Simulations?
I know some of our clients have been using sliding mesh capability in FLUENT (e.g., Rampant and UNS) to model trains in tunnels.
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Re: Tunnnel Simulations?
I have seen CFX simulations of trains passing in tunnels, and they recently published a short story (in their newsletter) on subway fire ventilation based on work using CFX by ICF Kaiser Engineers Inc.
Also, Flow-3D has a moving obstacle capability that should allow the simulation of two vehicles passing in a tunnel. Both CFX and Flow Science (Flow-3D) are sponsers of this site. Good Luck! |
Re: Tunnnel Simulations?
I know of a paper performed using STAR-CD. "CFD Analysis of a Decelerating Train Entering an Underground Station"-Fred Mendoca (Computational Dynamics, Ltd. and Simon Drake (London Underground Ltd.). The analysis was performed using among other things, the transient arbitrary sliding interface capability in STAR-CD. Please feel free to contact me if you would like a copy.
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Re: Tunnnel Simulations?
please keep your promise to be away if you can not provide useful help
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Re: Tunnnel Simulations?
(1). It is surprised that people trust what they read on the electronic screen. (2). When I was away, I was busy checking out this efficient commercial CFD code. In the end, I was surprised, I found another big error in the output of this great commercial CFD code. (3). In the last three years alone, the three popular commercial CFD codes I have used all have serious errors in it. It would be crazy to trust anything about the commercial CFD codes. So far, I have not identified any names yet, because I don't think I can provide any useful help here to anyone who thinks that there is this great commercial CFD code ready to solve his problem.(4). Can the commercial CFD codes developers and lovers keep their promise to provide error-free codes?
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Re: Tunnnel Simulations?
(1). The opening statement was " I wonder if there are CFD-codes(commercial or research) around, which are able to predict the flow field....." (2). Do you understand English? It is like saying " Are there word processors around which can write a report for me? " (3). In the way the question was stated, human being simply does not exist at all. (4). The question should be " Has anyone solved this type of tunnel related problems? If it is possible, is the used of a commercial CFD code necessary?" (5). People in the commercial CFD codes think that they must have the emotional reaction while the code is being evaluated. (6). Code is a code. It does not have any feeling at all. If a code is bad, it is bad. Just throw it away. The real truth is that, a code is not a code. A code is someone's expression of his ideas. And the code itself does not know how to solve the problem of even formulate the problem, but people do! (7). I am very surprised that these questions are asked by people, not by the commercial CFD codes.
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Re: Tunnnel Simulations?
Hi,
One of STAR-CD tutorials deals with the problem of two trains getting past each other (with moving mesh). Also, a commercial company (don't know which) has done the analysis of the ventilation and fire control system for the Jubilee Line Extension (London England), including moving trains, underground stations and ventilation system. Look up the paper that Greg suggested - I think this is just the thing for you. A few more (cynical) comments to Mr. John C. Chien: 1) Well done, mate, you're thi first person on the planet with a bug-free CFD code (of, I guess, about 200k lines). Maybe you should sell it and make a fortune! 2) Some commercial codes are actually involved with things you see around you every day, so take my advice and: a) stay out of airplanes; b) stay out of cars; c) underground is a big no-no; d) I'd think twice before switching that computer on (ventilation); e) stop breathing, air-conditioning is screwy; f) lawn-mowers have engines and therefore are unsafe; g) electicity? uh-oh; h) even the vegetables (not to mention beer) in your fridge are not safe!! The best thing is to take a dive in the pool and relax... but even your swimming goggles are designed for minimum drag! |
Re: Tunnnel Simulations?
It is not my field, but my colleagues are working with STAR-CD and their own subroutines which simulates rows of cars by sources of momentum, turb. energy and exhausts too. They validate it with a mesurements in street canyons. Some papers should be somewhere too. That's just what I know. Have a nice rest of this summer. Matej
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Re: Tunnnel Simulations?
An mpeg of this tutorial is on my home page
http://www.beilke-cfd.de/train.mpg It shows the velocity magnitude. Have some fun and a nice day. I hope that the people from Computational Dynamics won't kill me therefor :) |
Re: Tunnnel Simulations?
(1). Great ideas!!! (2). How come I am not getting all of these outputs from the commercial CFD codes I use? (3). Which CFD code are you using to generate these ideas? (4). For only two digits, there is a huge million dollar market created for this thing called "Y2K". I am sure that a 200k lines commercial CFD code will create more than just a million dollar new market. I think, it is more profitable to work in this "CFD Y2K" field. (In a way, I got paid well to use commercial CFD codes to find errors. )
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Re: Tunnnel Simulations?
1):It is more helpful 2):if you list what you found in the codes 3):instead of how great you are. 4):People who are using those codes 5):can be aware of the errors in their practice.
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Re: Tunnnel Simulations?
yes, he is very annoying again.
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Re: Tunnnel Simulations?
Thank you Dr. Hrvoje Jasak for speaking up and giving good help to serious people on this board, and the suggestion to Jonh C. Chien. We need more people like you to give ideas which make technical sense to others and to benefit all readers. Thank you again for your posting.
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Re: Tunnnel Simulations?
(1). Don't you think that is the only purpose of the forum? (2). The great secret is to keep the secret of the code from the users ( a black box). (3). The greatest secret is to keep the secret of the secret away from the code vendors. (4). Why would a company spend a lot of money looking for problems in CFD codes? So they can find out how to build a better product. (5). So, both sides are not going to reveal their secrets to anyone. Not the vendor, not the user companies. (6). By the way, the use of a specific commercial CFD code in a company is a political decision ( not based on the accuracy of the results). You simply don't go to the engineers of a company and ask him to buy a commercial CFD license. Even the decision to use a common product like a CAD program in a company has been a multi-national strategic policy implementation. (as a result, engineers were forced to re-learn new codes from time to time. A waste of time.) (7). I like your response. A computer program can not understand the word like " annoying". A computer program can only say, " floating point over-flow", " ERROR message: xyz", and at best, something like " NOT COMPUTING !". It is not just annoying, the CFD in a company is already a global war already for sometimes.(this year, the s-brand program is out, and the t-brand program is in. Sorry, you can only do the benchmark testing when it is in the company's computer system. Contrary to our suggestions here. You can't cry in business world though.)
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Re: Tunnnel Simulations?
read your own msg on Aug 20. Don't wast other's time by reading your garbage. It is expensive to post here like you said. If you want to attack anyone, go to their e-mail. I have my e-mail address here too. You are way too annoying.
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Re: Tunnnel Simulations?
(1). Frankly speaking, most large company users are aware of the problems in the commercial CFD codes. (2). But, everyone would rather cover it up and continue their CFD business as usual. (3). Unless, you are the one who is paying for the license fee out of your pocket. Most CFD engineers don't have that kind of money.(4). You don't want to know the dark side of the commercial CFD codes, do you ? (5).The answer to your question is : take a systematic approach, learn how to use a commercial CFD code. It is like some sort of "defensive-driving". In this way, the vendors and the engineering users will be happy. The vendors gets their profit, and the users get the toy to play with. (6). Who cares about the company paying the license fee? Noboby. Investors are only interested in the stoke price. They don't care whether there are bugs in the programs. And an experienced CFD engineer by definition, is the one who knows a lot about the bugs in the commercial CFD codes. So, he can get the job done faster without getting the error messages. (you can always find out these common errors in person, but not in public.)
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Re: Tunnnel Simulations?
You said nothing but showing yourself off.
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Mesa thinks you talk too much
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Re: Tunnnel Simulations?
(1). How do I get rid of this virus attached to my posting? (2). Stop reading the posting, and you will get your peaceful mind back. You are playing back your old message from your brain. I normally don't keep track of my e-mail, I delete the mail after I have opened it. (3). I must say that, once the message is in your mind, it will last for the rest of your life. Don't read everything people posted here. (4). Anyway, it is not my intention to occupy your brain memory space. I don't know how to erase it for you. Sorry. (5). The only message I have is : " In real world, without a systematic protection approach, blindly running a commercial CFD code is just like reading a posted message, both can be hazardous to your health." (if you go back to read my previous posting, many times, or one hundred times, you are guaranteed to become much smarter. In the first 30 passes, it will become mechanical. In the second 30 passes, it will become automatic. In the last 30 passes, it will start to become innovative. I will have to stop here for my lunch. good luck for the exercise.)
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Re: Tunnnel Simulations?
John C. Chien 's MSG on Aug 20
Re: cheers to Jonas (292) - John C. Chien, Fri, 20 Aug 1999, 1:20 p.m. ----------------------------------------------------------- (1). It is quite expensive to post it here. It is going to cost a lot world wide. (2). Send him a e-mail next time. (3). Personal issue by e-mail, technical issue by the forum here, not vice versa. ------------------------------------------------------------ Re: cheers to Jonas (253) - John C. Chien, Sun, 22 Aug 1999, 11:24 a.m. ----------------------------------------------------------- (1). I have tried to keep this forum going for over a year now. (2). I think it is time for me to step aside so that sponsor of the commercial CFD codes can dedicate their time to answer questions created by the use of their codes (official of non-official, legal or illigal copies). (3). Will meet you sometime in the future. take care. ----------------------------------------------------------- |
Re: Tunnnel Simulations?
(1). Please Do Not Read my Posting. Thank you.
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Re: Tunnnel Simulations?
(1). Please Do Not Read my Posting. Thank you. (2). There is nothing in it.
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Thank God you finally got Addy's point for most of your postings.
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(1). Who's Addy ?
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Re: Tunnnel Simulations?
I thought you know better than everybody. If you don't know, I thought Addy should be your father. But don't trust anybody or anything as Dr.Hrvoje Jasak suggested to you:
Posted By: Dr. Hrvoje Jasak <aeg98@dial.pipex.com> Tue, 31 Aug 1999, 2:17 a.m. A few more (cynical) comments to Mr. John C. Chien: 1) Well done, mate, you're thi first person on the planet with a bug-free CFD code (of, I guess, about 200k lines). Maybe you should sell it and make a fortune! 2) Some commercial codes are actually involved with things you see around you every day, so take my advice and: a) stay out of airplanes; b) stay out of cars; c) underground is a big no-no; d) I'd think twice before switching that computer on (ventilation); e) stop breathing, air-conditioning is screwy; f) lawn-mowers have engines and therefore are unsafe; g) electicity? uh-oh; h) even the vegetables (not to mention beer) in your fridge are not safe!! The best thing is to take a dive in the pool and relax... but even your swimming goggles are designed for minimum drag! |
Re: Tunnnel Simulations?
A gentleman from NEC (the japanese company) gave a presentation here (penn state) this summer about sliding/interfacing mesh LES code they use for design. one of the cases he presented was of a bullet train entering a tunnel. the results looked pretty good (experimental comparison) and they were able to use it to make practical design changes. Jog\hn has a big beef with commercial codes, i think because he's pissed he didn't jump on the train and get some money. but anyway for engineers who want to do something, instead of worrying about whether their pressure distributions are within 3% of experimental results (especially since most of the time you don't have resources to do experiments anyway), try a reputable commercial code. and John if you don't intend to answer someone's question don't post to that thread. if you have a beef start another thread. Jonas lets us post just about anything we want so if you have something to say, say it but not in a thread started to answer a question
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Re: Tunnnel Simulations?
(1). I can only guess that you must be from the vendor side answering questions. (2). If that is the case, it is a good sign for the forum. Don't worry about me, I simply don't exist at all.
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Re: Tunnnel Simulations?
(1). Yes, this is exactly what I said before :" It is going to cost a lot world wide." (2). And You have just done that. (3). Emotional approach simply can not solve any CFD problem. (4). The first step to do is to have a open-source CFD code. So, nobody has to keep asking these mechanical questions related to a code. It is not fair for the users to spend a lot of time debugging codes using try-and-error approach. You simply can't sell a black box to general public without any support.
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(1). I agree with you. (2). I think it is a good idea. (3). It is a small world, and I'd better spend more time doing my own book reading. Thank you for the idea.
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Re: Tunnnel Simulations?
If you were not starting 'emotional' blah blah blah everytime, nobody would.
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Re: Tunnnel Simulations?
Guys (and girls!),
Let's not get carried away here: what I really want to make clear is that commercial CFD codes are not perfect, BUT for a large majority of the users they are fit for the purpose, and at least can give ~some~ insight where we can't do experiments (burning real cars in a real tunnel is definitely not a good idea, no matter how much experimental data you get ;-). However, no software I know (with the exception of TeX) is perfect; it may not even be fit for the problem you're trying to solve - all we can do is to try and make it better. So, when you want absolutely the best results and you don't care what it costs (I know such situations!), you cannot replace the "DIY" CFD people: they are highly skilled, very professional and (judging by myself) usually have a huge ego BUT they are able to beat any (general purpose) CFD code for their particular problem. Because of the huge experience of these people, they are usually extremely useful to newsgroups like ours, because "they've been 'round the block a few times" and seen some really weird stuff. Also, in my experience, it is always more fun writing your own (preferably big!) CFD code and beat the commercial opposition into the ground. But the fact remains: a commercial code will have 2 or 3 orders of magnitude more users than "your own" code, no matter how good it is. I would like to apologise for getting side-tracked, but I think we all need to let John know that we appreciate his experience and would like to hear more about the stuff he's really good at (there's always a lot to learn!). In the future I myself will try to stick to the technical points. |
Re: Tunnnel Simulations?
Using STAR-CD code written by Imperial College of England or whatever, I really do'nt see any sign of reaching the STAR. Only thing I can see when I close my eyes is more Penalty! Penalty!! & Penalty!!! for screwing up in design again. Good luck to all STAR-CD fan.
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Re: Tunnnel Simulations?
LES, sliding meshes, trains, burning cars..... In an application such as ventilation of a road tunnel it would be a fruitless task to try to define an accurate geometry of the moving/burning cars. In reality the number and speed of the vehicles would vary tremendously. If you accept that you can not define an accurate geometry then you really should:
a) halt the quest for quantative accuracy and go for qualitative CFD design instead. b) dump LES and sliding meshes and chose a more appropriate 'balanced' selection of numerics. If the geometry itself is 'blurred' or approximated then there really is no point going for a fancy turbulence model for example. c) have a clear understanding of exactly WHY you are conducting the simulation then use your intuition to define the model. d) Hey, why not consider representing the (car) occupied space of the tunnel with a porous media, an increase in turbulence and maybe also a collection of point sources of contaminant. If you turn your nose up at such approximations then a place in academia awaits you, if you're nodding your head even slightly then welcome to the wonderful world of (commerical?) CFD application. Robin. |
Re: Tunnnel Simulations?
The question was not if it is usefull to use sliding mesh ... but if it is possible.
In a first stage one can use the sliding mesh approach to see what happens (for some obstacles/cars). Later one should try to find easier ways to achive the same result. If you start with a simplification you cannot be sure if it works at all. |
Re: Tunnnel Simulations?
i agree with you that qualitative results are better than nothing and that the models you describe are appropriate for that purpose but in some cases the need for detailed reesults for detailed design is necessary. you made a comment about LES and i think it was directed at my previous message. i was just trying to relay what the person who made the presentation said not trying to endorse his approach. for the things he was trying to do ( detailed modifications) he did need precise fluid results. he said that his department was having too much problems with the complex turbulence models needed for the RANS so they went to LES because they felt the results were more reliable. i cannot evaluate that statement because i don't know enough about LES to make that judgement. i do know though that RANS results are highly turbulence model dependent. as for the sliding meshes they implemented that capability because the codes are used for design of a wide range of products (from trains to vacuum cleaners were the examples we were shown). i disagree mostly with your point (1) even though in the past i have said that qualitative results are of great value. there are many cases particularly in detail design where precise dense data is required. it would be nice if this wasn't the case (less multi-megabyte log files) but it is. the need to continue improving the accuracy and reliablity of CFD codes is still there and will continue to be for some time yet.
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(1). I heard that people here are getting rid of the S-code. (2). I guess that there must be reasons. So, they brought in this T-code. The T-code is like an orphan now, because the instructor is trying to push the use of their C-code. But so far it is not operational yet. I can't use any word freely, because of my reputation and my influence.
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