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Turbulence modeling - 4000 USD budget

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Old   June 10, 2015, 02:17
Default Turbulence modeling - 4000 USD budget
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Dear all,

I am quite new in hardware and hardware architecture. I am going to model a CFD problem, rather not complex with Fluent. Actually it's external 2-D flow with common turbulence model (no any additional model). consider a mesh size of 100,000 with time step of 0.0001. I just tried to run it on an ordinary desktop with processor Intel Core 2- 6600- 2.4 GHz, 4GB Ram. 10 seconds of flow time takes almost 27 hour. I may need to run it for up to 100 seconds. My budget is around 4000 USD. I just search the internet and I find it would more convenient to buy a workstation. please let me know what do you suggest.

Thanks,
Nima
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Old   June 10, 2015, 12:31
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Before spending that much money on a new Workstation, you should be absolutely sure that simulating such a small case with an URANS approach, an extremely small time step and a large physical time is necessary and makes sense. The parameters you gave sound unusual at least . If you are not 100 percent sure, feel free to ask for advice in the Fluent subsection of the forum.
The next step would be to find out how many Fluent licenses you have available and if you only need the workstation for problems of similar cell counts.
Then we can start to think about a reasonable configuration.
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Old   June 10, 2015, 14:12
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Quote:
Originally Posted by flotus1 View Post
Before spending that much money on a new Workstation, you should be absolutely sure that simulating such a small case with an URANS approach, an extremely small time step and a large physical time is necessary and makes sense. The parameters you gave sound unusual at least . If you are not 100 percent sure, feel free to ask for advice in the Fluent subsection of the forum.
The next step would be to find out how many Fluent licenses you have available and if you only need the workstation for problems of similar cell counts.
Then we can start to think about a reasonable configuration.
Thanks for your reply. well first of all the problem is vortex shedding behind a cylinder (originally for 2-D problem but I may want to solve it 3D with 3 times greater mesh size, approximately) . I will ask my question in CFD forums, but just to say, I chose the time step and physical time based on your advise on posts #2 and #4 at Flow over circular cylinder. actually I am looking for frequency of around 60 Hz over RE~40000.
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Old   June 12, 2015, 14:49
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Hi nima,
By spending less than 1500UDS you are able to buy a strong PC handle your problem, 4000 is too much for your problem
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Old   June 13, 2015, 23:12
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Hi nima,
By spending less than 1500UDS you are able to buy a strong PC handle your problem, 4000 is too much for your problem

Thanks,
4000 is my limit. I am searching for a proper config. It would be between 1000 and 2000. Can only a core I7 Intel handle the Job. How much Ram do you suggest?
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Old   June 15, 2015, 13:37
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My experience:
Hardware-Configuration for Fluent HPC-Pack (8x)

In brief:
- Core i7 5820
- Good X99 motherboard (I am using ASUS X99 PRO)
- You can never have enough RAM (avoid swapping to disk at all costs), mine has 64 GB.
- GPU accelerator (that will also act as your video card). Titan Zs are selling for about ~USD$1400 on eBay now.
- Make sure you have HPC (Academic) licenses.
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Old   June 19, 2015, 01:56
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Hi dear Nima,
you mentioned that with 4 Gig ram you can handle your problem, so i thing for your new configuration 16Gig is enough,if you are going to use your pc for a bigger problem in the future you can buy 32Gig (4*8Gig)
so i suggest these:
CPU: intel core i7 5820K
MB: Asus X99A/USB 3.1
RAM: GSkill Ripjaws 4 3200Mhz
i think it is better to buy a cpu cooler because your pc may work for long hours, so i think a good cpu cooler from Noctua can handle it, or you can buy a water cooler.the rest of it like power, case HDD or SSD is up to you, but i've heard that with SSD your pc can fly!!! and with this CPU you need to buy a VGA, i think a GTX 750Ti might be enough and econimc.a better and of course more expensive option is GTX 970 or 980.

but in my opinion an economic configuration is this:
CPU: intel core i7 4790K
MB: Asus Z97 Pro
RAM: G.Skill Trident X+Fan 2666Mhz
i think with the rest of pieces(without monitor and a an expensice VGA because the cpu has a VGA) it will cost you less than 1500UDS.
hope you will find these info helpful.Don't hesitate to ask more question
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Last edited by HyperNova; June 19, 2015 at 09:58.
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Old   June 19, 2015, 11:30
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Thank you Dave and Bijan. I have completely interested in i7-3820 or i7-4820. With almost 1/4 price they challenge Xeon series. I am now thinking about motherboard. I am gonna write a new post. Comment are welcome
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Old   June 19, 2015, 14:39
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No need to consider the obsolete socket 2011 platform.
The best bang for the buck in CFD in 2015 is the I7-5820k for the socket 2011-3.
Suitable configurations and most of the questions you raised in the new thread were discussed here:
New computer, 1500euros budget, opinions?
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Old   June 19, 2015, 15:22
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Quote:
Originally Posted by flotus1 View Post
No need to consider the obsolete socket 2011 platform.
The best bang for the buck in CFD in 2015 is the I7-5820k for the socket 2011-3.
Suitable configurations and most of the questions you raised in the new thread were discussed here:
New computer, 1500euros budget, opinions?
Thanks Alex. It's a good idea. But about I7-5820k, what is the merit of 68 GB/s bandwidth when maximum memory size 64 GB/s?
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Old   June 19, 2015, 15:40
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Memory bandwidth (measured in Gigabytes per second -> GB/s) has nothing to do with memory size (measured in Gigabytes -> GB).

The memory bandwidth is the speed at which data can be transferred from RAM to the CPU and back. And since there is a lot of data that has to be transferred in a CFD simulation, higher bandwidth usually means shorter simulation times.
The memory size is just the maximum amount of data that can be stored in RAM. As soon as the case you are running fits into the Memory, you wont see any benefit from a larger memory size.
And since a CPU wit 6 cores running at 3.3 GHz will read more than once every second from the RAM, being able to transfer more than the whole amount of RAM available once per second totally makes sense.
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Old   June 19, 2015, 16:36
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Quote:
Originally Posted by flotus1 View Post
Memory bandwidth (measured in Gigabytes per second -> GB/s) has nothing to do with memory size (measured in Gigabytes -> GB).

The memory bandwidth is the speed at which data can be transferred from RAM to the CPU and back. And since there is a lot of data that has to be transferred in a CFD simulation, higher bandwidth usually means shorter simulation times.
The memory size is just the maximum amount of data that can be stored in RAM. As soon as the case you are running fits into the Memory, you wont see any benefit from a larger memory size.
And since a CPU wit 6 cores running at 3.3 GHz will read more than once every second from the RAM, being able to transfer more than the whole amount of RAM available once per second totally makes sense.
Yeah It was my fault, the Unit [GB] for Maximum memory size. Just to add to your description, as the maximum memory size is a Processor characteristics and not of the ram, I found a better description and is: A maximum size of memory that a processor can support. As an analogy for Bandwidth and Max Memory Size difference we can assume a USB memory of maximum size e.g. 2 GB connected and the data based on the port speed can be transferred by any speed (e.g. 4 GB/s in future)
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