Learning Forum

[StacyLab]

Hi!

      I need to select a good workstation for CFD modeling in ANSYS for my Lab to buy. 

I understand that there's 25-40% decrease in simulation performances if all memory slots are not filled with the same amount of memory. - The specs of a DELL workstation option are listed below. I have 2 quick questions related to RAM choice:

1. Are 64GB (8x8GB) or 96GB (4x16GB + 4x8GB additional sticks) valid options? 

Or is it worth to consider reducing the cores number (for instance, 8C instead of 10C) and invest in larger RAM (8x16GB=128GB, for instance)?

2. Do I really need 192GB of RAM to match the minimum memory requirement?

 

Budget is ~ $6-7k. The workstation is needed for time-dependent, rigid-wall simulations (2M element mesh). As reference, I used to run these simulations on *2 CPU of 8 cores each (DELL Intel Xeon CPU 2650 0 @ 2.0 GHz), 64 GB of RAM, and 2 HHDs of 2TB each*. - The simulation would run for 2-3cycles in 4-6days.

Thanks a lot in advance for your help!

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Full specs (DELL Precision 5820 Tower):

Intel Xeon W-2115 (3.3GHz, 4.5 GHz Turbo, 10 Cores, 13.75MB Cache)

64-96 GB RAM

INVIDIA video card P4000 (8GB, 4 Displayport 1.4)

Operating System: Windows 10 Pro

Precision 5820 Tower 950 Chassis

Hard Drive Controllers: Integrated Intel AHCI SATA chipset controller (8x 6.0Gb/s), SW RAID 0,1,5,10

Hard Drive: 2.5” 512GB SATA SSD

2^nd Hard Drive: 2.5” 1T SATA SSD

3^rd Hard Drive: 2.5” 1T SATA SSD

 

 

*edited for clarity - apologize for confusion*

[Rob]

I've moved to installation as it'll get more attention. On physics support we're more likely be responsible for breaking computers...... 

I'd aim for around 4-6GB per core for most CFD applications (should be sufficient for around 2 million cells) : if you need more RAM the load on each core will be high so more parallel makes sense for speed. If you expect to build really big models for use on a cluster a high RAM machine is very useful. It depends on how big a model you're expecting to build, what physics you want to run and how much you can/want to spend. 

 

[StacyLab]

Okay, thanks. The budget is ~ $6-7k. And the workstation is needed for time-dependent simulations (fluid hypotheses: newtonian, laminar flow regime), under rigid-wall conditions. The number of mesh elements might go up to 4-5 million, but I don't think we'll run models much more complex than this. 

 

From your answer, I understand that 64GB (8x8GB) on that DELL Precision 5820 Tower might be sufficient for our scope (with 8-10 cores), and if we want to get larger RAM we might prefer parallel processors. Is this correct?

The goal is to have simulation time down to 1-2days.. Would that be the case with 64GB?

Thank you in advance for your help!

 

[Rob]

For 4-5M cells 64GB will be plenty. 

Can't comment on the speed, but steady should run well with that configuration. You'll see a benefit with more cores too: typically you get good speed up down to 50-100k cells per core. 

[StacyLab]

Thanks.. Just wanted to highlight that I'd run transient CFD simulations.

My previous workstation actually had  2 CPU of 8 cores each, 64GB of RAM, and 2 HHDs of 2TB each, and on this workstation similar simulations would run for 4-6 days.

My goal is to buy a new workstation to run faster simulations (ideally simulation time below 2 days).

 

Any suggestions on whether I should prefer 2 CPU, increase the number of cores and/or RAM size for the new workstation to achieve that goal?

 Thanks for your help!

[StacyLab]

For anyone interested in a solution for this post, after a little more research, I opted for a DELL T7820 2-CPU (6 memory slots/CPU):

• DUAL INTEL XEON SILVER (2.1GHz, 3.0GHz Turbo, 8 Cores, 11MB Cache) 

• NVIDIA video card P4000 (8GB, 4DP)

• 2 2TB-SSDs

• RAM size: either 96GB or 192GB  (~ $7k vs. $10k)

 

Main concepts I took in account for final choice are:

1. Parallel cores improve performances, so I opted for 2 CPU (8 Cores each).

2. Having all memory slots filled with the same memory maximizes simulation performances (otherwise 25-40% decrease in performances has been observed) - The DELL T7820 is a great option because it has only 6 memory slots/CPU (instead of 8 or 12), so they are easy to fill with the amount of memory needed

3. RAM: 96GB should be more than sufficient for our scope, 192GB has been suggested by the ANSYS performance team. - I wonder if the simulation time would actually decrease by a factor of 2 with 192GB for this 8-Core DELL T7820 2-CPU.

4. A minimum of P4000 Graphic card (8GB GDDR-VRAM) has been recommended.

 

A big thank to both the ANSYS team and the DELL customers service, who have been of great help!

[SmithAsani]

Hi...The appropriate response relies upon your degree of refinement. Do you need a natural OS? Would you like to utilize openly accessible libraries? Significant level dialects? Or on the other hand would you say you are helpful with a binding weapon and cycle level machine programming?

[Maurok13]

Hi SmithAsani i have a little question related to your issue, currently i'm carry out CFD simulations jet impingement some of that simulations using VOF, i have comercial laptop HP with only 4 cores, Intel i5 8th gen, my problem (transient) has 900k or 1 M cells so the simulation last around 10 days ! to reach a steady state also my pc runs with 3 Ghz, i'm think about acquire a Dell Precision 5750 buget $4000 the specifications are this
Intel Core Processor i7-10750H
Windows 10 Pro English
NVIDIA Quadro RTX 3000 w/6GB GDDR6
32GB, 2X16GB,DDR4 2933Mhz Non-ECC Memory
M.2 512GB PCIe NVMe Class 40 Solid State Drive
I don't know how to select the number of cores and with what RAM is going to work better (faster, i need to decrease the time of simulations).
can you please gave me a tip to select the hardware and how can get a roughly estimation of the time with this machine?

[Jeslu]

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Hello, I had a similar doubt and hence posting here. I am doing transient CFD simulation using Fluent and have around 12,00,000 elements. I was thinking of getting a new laptop. I see dell precision series with intel i9 with 8 cores, with Nvidia RTX T1200 or RTX A2000 or RTX A3000 etc as good options. But these graphic cards are not listed in the Ansys tested cards. https://www.ansys.com/content/dam/it-solutions/platform-support/graphical-display-graphics-cards-tested-2021-r2.pdf, https://www.ansys.com/content/dam/it-solutions/platform-support/graphical-display-graphics-cards-tested-2021-r1.pdf Would that mean it is not advisable to buy them?

Thanks in advance!

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[Rob]

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With 12M cells I'd be looking for 24-36 cores and 30+GB RAM. Our laptops are 4-6 core with 64 GB RAM, not sure if they get much quicker? The issue with the high core count single cpu's is whether the interconnect can handle the data traffic you get from a fully parallelised run.

Re the cards, if we don't test them we can't confirm if they will work. It doesn't mean they won't, just that we haven't tested them, so we can't recommend their use. My last, current & future laptops all had/have unsupported graphics cards.....

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