[EpicFruit]

Hi everyone, I'm in the process of choosing components to upgrade my PC in the next month or two, and I would like to get some feedback and/or recommendations on hardware.

I exclusively use STAR-CCM+ for personal projects and research, running half-car sims that are usually between 8-12 million cells. I'm currently using an i5-4670K(4 cores, no hyperthreading) with 2x8GB of RAM at 1600MHz. Yeah it's not a lot of computing power for CFD, but it gets the job done, eventually. I know that going to a workstation platform with quad-channel memory would be best, but my PC's travel requirements and my limited budget confines me to the mini-ITX form factor with mainstream processors. I guess what I'm really looking for is a less-worse setup.

My CPU choices going forward are between the Ryzen 7 2700X and the i7-8700K, I've not been able to find any information on the performance of STAR-CCM+ using either of those chips, but I would imagine that the 8 core 16 thread Ryzen would be a bit better off than the 6 core 12 thread i7, due to being able to run more processes in parallel. I don't know if single-core performance will make a bigger difference than core count, so please share if you have any past experience with these chips in CFD.

My RAM choices are between another 2x8GB setup, or a 2x16GB one, both at 3200MHz. Obviously the big question here is whether it's worth the extra cost to get 32GB of RAM if it's all dual-channel at 3200MHz. I understand that extra RAM usually allows for bigger simulations with more cells, but if the only difference here is capacity, would I really benefit that much from it? In one of my typical simulations with 9-9.5 million cells, RAM usage is shown to be around 12GB in task manager, so there's some headroom, though not a massive amount. I can see myself doing full-car sims in the future if I go with the extra RAM, but other than that I can't think of any other reasons at the moment.

I'm not willing/able to switch away from a mini-ITX system, so I believe these are my best possible choices right now given the form factor limitations. I know that there is an X299 ITX motherboard out there, but I have found that it wouldn't really be suited to everything else I do, mainly in terms of features, noise/cooling, and cost.

Anyway, please let me know what you think!

[trampoCFD]

Hi Will,
Do you have an unlimited core license and access to fast Wifi or LAN internet access during your travels?
If yes to both, I'd buy a second-hand server with as many cores as possible, to sit in your main office and get a small laptop with medium grade graphics card and an SSD to set up and post-process your simulations while travelling. I'd RDP into the server from the laptop, and use Resilio Sync (https://www.resilio.com/individuals/) to sync your CFD files on your 2 computers. I use Resilio connect on my cloud computing service and it's fantastic technology.

RAM: for the same model, RAM usage increases with the number of cores you use. I personally would not be comfortable with so little RAM, but I run many different simulations sizes.

Btw, a 12 million cells aerodynamic model scales well on 500-1000 cores in STAR-CCM+. You'd get an x100-x200 speedup compared to your current set up. If your university has a cluster, that might be worth looking into getting STAR-CCM+ running on it :-)

[EpicFruit]

That's an interesting idea, to run simulations remotely on a server. I can definitely see that being viable if like you said, I had unlimited licenses and a strong internet connection, but unfortunately the internet connection will never be strong enough in my case since I will likely be in a different continent from the server. But it is an interesting idea for perhaps another one of my usage applications.

I forgot that RAM usage increases with the number of cores being used, I've read that before and it is a very strong reason for me to go with 2x16GB of RAM indeed. It unfortunately will be the most expensive part of my upgrade. Once I get my CPU upgraded I will probably be running twice as many cores, so you've brought up a very good point.

I wouldn't hesitate to use a cluster if I could get my hands on one, but at the moment I'm not in university, and would still like to have something of my own for CFD when I return to university later this year. I'm sure the place where I'm going(Cranfield University) will have clusters available, but high demands will likely limit my access to it.

[trampoCFD]

The beauty of resilio Sync is that it works with any internet speed, and recovers from connection failure automatically. So you log off you computer but keep it on, and the file sync happens at whatever internet speed you've got.
For RDP, you do need a good internet connection, but it doesn't have to be incredibly fast, in fact, 2mbps up and down might be sufficient as long as the latency is not too bad.
If you're in China though, I don't think resilio have implemented a fix to the GFW yet...

[flotus1]

If you are set on an ITX system that has to be as small as possible, there are a few things to consider:

• Ryzen 7 2700x will be easier to cool than an I7-8700k or I5-8600k in a small form factor thanks to the soldered IHS. Even the AMD stock cooler might do the job if you manage to fit it into your case (height: 93mm) and don't need it to be silent.
• Intel CPUs come with integrated Graphics, so you don't necessarily need an additional graphics card for basic pre- and post-processing

Tough choice on the performance side, I would expect them to perform somewhat similar in CFD using all cores, maybe with a slight edge for Intel. For single-threaded workloads, Intels Mainstream CPUs are still faster. Disclaimer: This is an extrapolation of my knowledge, I have never seen benchmarks for CCM+ with these chips.
Since you are limited to 2 DIMM slots, I would strongly recommend to start with 32GB of RAM. With the goal of DDR4-3200 on Ryzen, make sure to use memory with Samsung B-die chips. And if RAM makes the setup too pricey, you can offset some of the cost by stepping down to an I5-8600k. You might end up deactivating SMT/Hyperthreading anyway.