What to buy ?
 

Hello CFD community ? My question is what you recommend to buy for 2.500$. Would you buy one UNIX workstation or several PCs? What is the optimum for this money ? Thanks

Re: What to buy ?
 

For $2,500 UNIX workstations are out of the question - they are much more expensive. If you prefer UNIX I would recommend you to buy a 1.7GHz P4 (the P4 runs Fluent very well!) with 512MB memory and install RedHat Linux on it. You should be able to get a decent 19" screen and a good graphics card (GeForce3) in the $2500 budget. Dell sells a nice budget-machine (Dimension 8100).

If you want to run large cases a nice alternative could be an Athlon 1.33 GHz machine with more memory (1 gig or so) - CPU and memory is cheaper for this config so you can buy more memory. The performance running Fluent on the P4-config will be about about 40% better than the AMD-config though, unless of course you need more memory than you can afford with the P4-config.

Re: What to buy ?
 

Thanks for your answer ? But what about two processor machine if I did not buy monitor ? I have also heard that P4 uses old technology and is not as good as it is promoted.Does AMD support two-processor platforms ?

Re: What to buy ?
 

AMD just released a SMP board and technology, but it is literally brand new and relatively expensive - approximately 500 bucks for one of the few boards available. I haven't heard any problems using the P4, so I would go that route.

~patrick

Re: What to buy ?
 

Until recently neither the P4 nor the Athlon was available in dual-CPU configurations. However, this is changing - dual CPU P4 machines were recently launched. Dell, for example, sells a nice new machine called Precision 530 which you can get Linux pre-loaded on. However, you will not get one of these for $2500, even if you skip the montior. A bare-bone dual P4 1.7 GHz with 512 MB RDRAM (minimum) will cost about $3500 I think. AMD is also just about to launch a dual-CPU Athlon version (code-named Palomino). I still haven't seen any machines based on it though - should be out in a few months I think.

Re: What to buy ?
 

Jonas,

Sorry to stick my neck out on a non-CFD topic, but do you have something to backup your claim of 40% better performance on the P4 1.7GHz wrt an Athlon 1.33 GHz. Is that true?

The general word around is that for the same clock speed the Athlon is 30% faster than a PIII on x86 code. And it is generally accepted that the P4 runs x86 code which is non-P4 optimised slower than the fastest PIII or fastest Athlon. See www.tomshardware.com for example, especially the mpeg-4 encoding articles. There is no reason to believe that CFD software would not behave similarily. Even if memory bandwidth was an issue, it would not make a 40% difference, maybe 10% at most.

So, unless Fluent compiles specifically for the P4, which I would think is unlikely because the compilers were just released recently, then something is amiss.

Dan.

Re: What to buy ?
 

Yes, I have hard benchmark-numbers comparing Fluent 5.5.14 on a 1.5 GHz P4 with RDRAM, an 1.33 GHz AMD Athlon with SDRAM and an 1.33 GHz AMD Athlon with DDR SDRAM. Several different cases were run. Here is a typical example:

<TABLE CELLPADDING=10> <TR><TD>Processor</TD><TD>Memory</TD><TD>Speed</TD></TR <TR><TD>1.5 GHz P4</TD><TD>PC800 RDRAM</TD><TD>1.33</TD></TR> <TR><TD>1.33 GHz AMD Athlon</TD><TD>PC2100 DDR-SDRAM</TD><TD>1.05</TD></TR> <TD>1.33 GHz AMD Athlon</TD><TD>PC133 SDRAM</TD><TD>1.00</TD></TR> </TABLE>

As you can see the 1.5 GHz P4 is here 30% faster than then Athlon. I agree with you that this is surpricing and before I saw these results I were also sceptical of the P4. Note also that the Fluent version used is the standard shipping 5.5.14, which is not in any way optimized for the P4. The benchmarks were run on RedHat Linux.

As a side note - the 1.7GHz P4 is probably now the fastest single-CPU Fluent machine available now, beating the most expensive workstations from HP, Compaq and SGI!

Re: What to buy ?
 

Check the SPEC comparisons. These are good benchmarks for Fluent and other computation intensive programs.

Floating point scores: P4 1.7 GHz is 598, Athlon 1.3 GHz is 414. Result: 44% faster for the P4.

Integer scores: P4 is 593, Athlon is 496. Result: 19% faster for the P4.

The Athlons are faster for many other programs (like those shown at tomshardware.com and other GAMING ONLY sites), but for pure computations P4 should be from 19% to 44% faster.

Re: What to buy ?
 

The spec numbers are not really relevant here since the P4 numbers were produced by Intel using P4-optimizing in-house compilers that make use of the new SSE2 extensions. No commrecial CFD codes use this as far as I know.

Re: What to buy ?
 

For the moment, I agree that there are probably no optimized SSE2 CFD codes. However, I can see no reason why these codes won't be available soon. But, for now we will not see the benefit of these new commands. From all the reviews that I have seen the SSE2 optimizations speed up the processor by roughly 10%-15%. Lets ASSUME this is also correct for Fluent calculations. Dividing my previous post numbers by 1.15:

Floating point: P4 is 598/1.15=520, Athlon is 414, Result: 25% faster for the P4. (This is very similiar to the 26% speed difference you reported earlier.)

Integer result: P4 is 593/1.15=516, Athlon is 496, Result is 4% faster for the P4.

Conclusion, until Fluent is optimized using SSE2, I'd expect 4% to 25% faster for the top P4 compared to current top Athlon for CFD codes. True, the memory cost of the RDRAM is excessive, so there is a better Performance/Price ratio for current Athlon computers. However, I was trying to point out to Dan Williams that the P4 can give nearly the 30%-40% increase that you originally claimed. No benchmark is perfect (applicable to all programs), but the SPEC numbers are a great start, until Fluent updates their own benchmarks (they don't have any Intel processor faster than 733 MHz or a single Athlon listed).

Re: What to buy ?
 

First, www.tomshardware.com is one of the best sources of PC hardware reviews that I know of - certainly not to be dismissed with a simple "gamers only site" comment!

SSE2 optimizations can produce dramatic speed improvements for floating-point intensive applications like CFD, much more than the 10-15% you mention. For example, when Intel-engineers worked on improving the Flask MPEG encoding benchmark with SSE2 instructions they managed to increased the performance by a factor of 3.5! (see here).

There is one good reason why we won't see SSE2 optimized commercial CFD codes for some time - there is, as far as I know, no released compiler on the market yet which can produce this kind of code. Intel has released a beta-version of their compiler, but this was just recently and the beta-period extends over the summer (ends in September I think). CFD vendors are now starting to test it, but it will certianly take some time before they release a version compiled with this compiler - I guess that they will wait until the compiler is out of beta. When I asked Fluent about this a year ago they had no plans to produce a P4 optimized version, but I think that they are starting to change their mind now that they see how well the P4 runs the non-optimized Fluent version.

Re: What to buy ?
 

Your example of FlasK MPEG encoding could be quite misleading to some readers. The recompiled program did improve by a factor of 3.66 when using SSE2 optimizations. However, the P3 and Athlon which do not have SSE2 capability also improved by nearly a factor of 2 each. Note: tomshardware.com has an update to that link which claims that the Athlon would have improved by even more than a factor of 2 if the code was optimized for the Athlon. Thus I agree that SSE2 optimizations can improve performance. However the claim of a factor of 3.5 is quite misleading, since there was much more optimizing done than just adding SSE2 capability.

If Fluent would run 3.5 times faster just from a simple recompilation, then they certainly should have enormous pressure from its users to recompile. I wish it was true - simulations that usually take 1 week would then require only 2 days without a single hardware upgrade...

I appologize, I should have said "Gamers focused". Tomshardware has some very good advice in its reviews. However, I'd avoid taking the comments in the forums section to heart since the vast majority of them are gamers. For example, post a question asking if upgrading to a 3Dlabs® Wildcat II 5110® would help your performance. (I've tried; 95+% of the responses said that the card is worthless and its performance can be topped by even cheap, old videocards. That may be true for some games but the Wildcat is easily the fastest available for CAD...)

Re: What to buy ?
 

Sure, the 3.5 time improvement is quite extreme, and probably not represantative of what a CFD code would get. However, it clearly illustrates the performance difference you can get by optimizing code. Since the spec-numbers for the P4 were produced by Intel I assume that they used every possible tweak to make them as good as possible, like they did with the Flask MPEG test.

Re: What to buy ?
 

This is all quite interesting, but it still doesn't change the fact that the for the same clock speed the Athlon architecture is 30% faster than a PIII and only slightly slower (5-10% at most) than a P4. So, all AMD has to do is improve the architecutre and ramp the clock speed and they will have the lead again. The fact that intel is 30-40% faster than an Athlon by simply using 30% more clock speed does not impress me. (Note that I'm not a big Intel fan though).

Other than intels compilers, I don't know of a compiler that makes SSE2 optimised P4 code either, so until the compilers are officially released there's not a lot one can do. In the mean time Portland Group and the DVF compiler both produce optimised code for the SSE (on PIII) instructions, and implement cache prefetching (both PIII and Athlon). These optimisations add roughly 30% more performance to compiling without them.

Dan.

Re: What to buy ?
 

(1). I think the current PC speed is fast enough to do most simple 3-D cfd problems. (2). I bought my first Radio Shack computer for around US$2500.(it had one MHZ CPU in it) (3). Now the Clock speed is 1000 times faster. Between 8-bit CPU and 32-bit CPU, there is a speed up ratio of 4 to access the same length word. So, the total speed ration would be around 4000 times.(4). With 2500 dollars, I would buy two computers, a laptop (around 1500 dollars) and a desktop model (around 1000 dollars). (5). The speed of CPU is going to hit the limit soon. This is because the current speed is far too fast for the office word processing application, and the investment in research to increase the speed is also very high. (one of the Intel founder has just retired recently). (6). My feeling is: two GHZ is adequate for average CFD applications. For me, one GHZ should bring my 3-D code into less than one hour range. (my simple 3-D code using Pentium/100 took about one hour) (7). So, if you are still using the very slow and big commercial codes, you should start looking at the possibility of writing your own codes. (8). I am not writing cfd codes right now, because of the limited market. (9). With the current poor PC market, the speed of CPU will probably stay in the one to two GHZ range for some time in the future. From my point of view, it is adequate for most cfd applications, if you are writing your own codes for average applications. (this rules out reacting flows and multi-phase flows)

Re: What to buy ?
 

Dan:

Continuing your logic...

The mac G4 733 MHz is roughly the same speed as an Athlon 1.3 GHz, thus the G4 is 77% faster clock-for-clock (if only macs could ramp up the speed...)

The Intel Itanium 800 MHz is roughly double the speed of Intels P4 1.7 GHz, thus it is 400% faster clock-for-clock (if only Intel could ramp up its Itanium speed more than Intel ramps up its P4 speed...)

I could go on for a while. There is a major reason why Athlons aren't past 1.4 GHz - they produce enormous amounts of heat, so much that AMD can barely cool them down enough. Increasing the speed will produce more heat and thus burn up the processors. It is not simple for AMD to just ramp up the clock speed. If only there was a way of modeling the cooling of the processor to get around this limitation (hint CFD).

Of course AMD will shrink their die size (to produce less heat) as soon as they have the technology, but so will Intel - bringing us back to square one.

My point is that many companies can get similar results with vastly different clock speeds. So, comparing processors clock-for-clock is quite meaningless. The only resonable comparison is to get the top processor you can afford of each brand and compare those speeds (keeping in mind that the prices may vary by 1000%, even within the same company).

I assume Jonas's Fluent benchmarks are accurate; the P4 is 30% faster than the Athlon. However the P4 costs roughly 50% more than the Athlon. For the $2500 budget, a P4 may be out of Kim's price range. Dual Athlons are available now and may be just inside Kim's range (I think the motherboard price is exceedingly high). Dual P4s are out of the question, Kim needs at least $3500 if not $5000. Dual P3s are also just out of Kim's reach at $3000 for a good model. I've never seen a good SUN, SGI, etc... for $2500.

Re: What to buy ?
 

(1). More than a year ago, there was a PC with a dedicated liquid cooling system to cool the CPU for over-clocked applications. I don't know whether it was a prototype or a commercial system. So, CPU cooling is definitely an issue. (2). Such dedicated cooling system has long been used in the super-computers such as CRAY computer. The successful development of CRAY computer depended on the cooling system. (3). Such dedicated cooling system for PC is not going to be very practical, because of the power shortage in California. You have to realize that, with all the computing power available to NASA, the first hypersonic X-43A(?) testing was a failure in first few seconds as reported in news a couple of days ago. They must have been developing the so-called CFD codes for the last 15 years for such applications. (4). What you need is affordable computers and an outstanding person who understand the problem to be solved. CFD codes and faster computers are necessary, but the key to the success is "human brain".(which is always very hard to find)

Re: What to buy ?
 

A) Home computer users who want the most out of their machine do create liquid cooling systems for their PC, although they are rare. I bet tomshardware.com will give instructions on how to build/purchase one.

B) Few computers are practical without any power, in California or elsewhere.

C) I heard in the news that the X43-A was distroyed before it started the test, not after as it appeared you were saying. So far the rocket is the most likely reason it failed, not the aerodynamics of the test plane. Thus it appears that CFD may not have had any role in the X43-A failure.

D) I agree completely: we need computers that are affordable and fast. And we certainly all could use more experience and training!

E) Since both Intel and AMD expect 2 GHz machines by the end of this year, why do you feel they will stall out at 2 GHz? I think the momentum will push it to 4-5 GHz before we get any stalling (IE research these companies have been doing for the last few years will result in faster computers before any cut back on new research funding will have an impact). But that is just my humble opinion.

Re: What to buy ?
 

Either you completely missed my point, or you are being somewhat sarcastic ;-). If you could run a G4 at 1.3GHz or the P4 at 800 Mhz then you can get an idea of the advantage of the CPU design.

So, comparing different vendors processors at the same clock speed is not meaningless. I would concede that the comparison is somewhat academic, as it only gives you an idea of the performance of the overal chip design relative to another vendor, and your not going to purchas a P4 1.7GHz and run it at 1.3GHz right!

It is a well known fact that AMD will reduce their power consumption, by further reducing their die size. and making architectural changes. Something like this is not all that difficult for a decent CPU manufacturer. I can't remember the code name of the Athlon 4, but it's due out pretty soon. Simply check their roadmap at Toms hardware.

I agree that Jonas benchmarks a genuine, yet somewhat suprising. I'll be interested to run some things on a P4 once I have access to one.

Dan

Re: What to buy ?
 

(1). Faster computer will cost more. and I think, you will agree with me on that. (2). The reason why it is getting cheaper, is " most computers have been made in Taiwan" and that kept the cost low. (3). The transition is being made now to sustain that low cost idea: to make the PC in the third world countries, including China. (4). But with the difference in political systems (between US and the third world coumputer makers), someting is going to happen. (5). First possibility is: US will develop faster CPU, and the cost of computer will stay low by moving to the countries with cheaper labor cost. (not likely to happen,because US does not like the third world countries to have high tech CPU. (6). The other possibility is: slow down the development in CPU speed, and lower the cost of computer. (not likely to happen, becuase the companies in Taiwan are not going to make enough money to survive through selling hardware alone.) (7). In either way, the CPU companies will try to co-exist instead of pushing the clock speed to a higher level. Average business companies are not going to benefit from this CPU upgrade, because they need faster computer to do word processing. (8). And even if they can use it to speed up the network, the users will have to pay the price, thus higher cost for the customer. (9). It is like B-2 bomber case, they can continue to improve the aircraft, until the government can afford only one aircraft. The only reason why CPU maker can continue to push the clock speed higher in the past, is because makers in Taiwan are helping the world market to keep the cost low. Without that, CPU is not going to find a motherboard. (10). So, it is the end of the boom era for the CPU and the PC market. Unless, the cost is going to be absorbed by the user of PC, which will include the new CPU research cost, and the cost of living increase in Taiwan. It is just common sense.

Re: What to buy ?
 

Good NEWS!!! Our budget has increased to $12.500. What is your suggestion now ? Double P4/1.7 GHz with 2 GB of PC800 RDRAM ? Or should we start thinking of UNIX machine ? When is the Itanium machine going to be released ? Many thanks for your responses.

Re: What to buy ?
 

$12,000 can get you a dual P4 with 4GB of memory, which is most likely the fastest machine available for Fluent.

Re: What to buy ?
 

That is a drastic change in the picture. Now we need more information to give you any reasonable answer.

For example: how large/complex will your cases be - thus will you need 1 GB, 4 GB, ... , 64 GB of memory?

How much time do you have to do the simulations - 1 day/simulation, 1 week/simulation, 1 month/simulation?

When do you want to start the simulations - as soon as possible, or can you wait until the second generation Itanium?

Do you need Unix or Windows operating systems?

How many processors are allowed in your license?

Will the computer be used for another purpose?

Are multiple simulations needed at the same time - would you rather have one large computer or several smaller computers?

My thoughts: the Itanium should be available, but I'd avoid it. Itanium seems to just be a trial run for Intel, and the next generation is supposed to be much better (Does anyone here know if Fluent will support it?). I can't forsee the need for more than 2GB of memory, at least within that budget. RDRAM should take a major price drop by the end of the year (rumors of 50% drop possible). Thus if you go the P4 route, get less memory now and give yourself upgrading room.

Re: What to buy ?
 

This may seem overly simplistic, but here is how I look at it:

Different processors operate at a wide range of frequencies - 800 MHz, 1.4 GHz, 1.7 GHz, etc... I'll create two theoretical computers: Computer A performs 200 million calculations per second (20 MHz) while computer B performs 10 million calculations per second (10 MHz).

Different processors perform a wide range of functions per clock tick. For example, computer A performs 1 calculation per tick and computer B performs 10 calculations per tick.

The resulting computer speed is frequency multiplied by the number of calculations per tick:

A: (20 million ticks/sec)*(1 calc/tick)=20 million calculations per second.

B: (10 million ticks/sec)*(10 calc/tick)=100 million calculations per second.

From this theoretical example, computer B is 5 times as fast as computer A. That is all that is important. Comparing just the frequency or comparing just the number of calculations per tick is meaningless to the end user. Only the product of the two should ever be compared.

It may add far too much to the price of computer B to increase the frequency. Thus the manufacturer may not have plans to further increase the frequency of computer B. The frequency number taken separately is meaningless (except for the marketing division's headaches) as computer B makes up for this frequency difference with more efficient calculations/tick.

The P4 is currently quite inefficient compared to other processors when comparing just the number of calculations performed per clock tick (that is your argument and I agree completely). However, the P4 makes up for this inefficiency by running at a higher frequency. The net result is that the P4 performance is remarkably similar to the Athlon.

Re: What to buy ?
 

I have a case with 400,000 cells that require more than 14 GB of memory. The reason is that Fluent's coupled solver is a memory hug. In the problem, there are 14 species with finite rate kinetics. Fortunately, we have a Compaq ES40 server to tackle the job. My recommendation is that you should get as much memory as you can afford. With 12,000, dual P4 should be a good buy.

Re: What to buy ?
 

This subject seems to have drawn a lot of interest (and speculation). We have done comparisons of several processors while running Fluent 4.5.

We originally had a 300 MHz Pentium II. To speed things up, we bought a 1 GHz AMD Athalon with 512 Megs of RAM. On small test cases (of a few thousand cells) the Athalon was indeed just over 3 times faster than the 300 MHz PII. With cases of 100,000 cells or more, the speed up dropped dramatically, at times, less than 1.5 times faster.

Lots of e-mails to Fluent and AMD did not yield any answers. The large cases could fit into RAM quite comfortably so swapping out of memory wasn't a problem. Maybe it was the memory speed. AMD's web-site showed the Athalon speed was compiler dependant.

Since CFD modeling is a major part of our business, we got tired of looking at the L1 cache and compilers and test cases. We bought a 1.5 GHz Pentium 4 with 512 Meg of RDRAM. This gave a speed up (even for larger cases) of just over 4 compared to the old 300 MHz PII. Not great but better than the Athalon. We just bought a new 1.7 GHz P4 with 1 Gig of RAM so we can run two cases at a time.

The Athalon is now hooked up to a scanner for occasional use.

If you want to spend time doing CFD rather running benchmarks sometimes it pays to go with the flow. You can't always use factors from generic benchmarks to determine how CFD progams will respond.

Re: What to buy ?
 

There are many cases where 14 GB of memory might be needed. However, I have not yet seen any machine with 14 GB of memory for $12000. I thought those Compaq ES40 servers started at $29,000 (for the bare bones system).

I thought Athlon computers had a max of 2 GB memory, and P4 have a max of 4 GB memory. (I could be wrong though). If any computer exists at around $12000 with 14GB of memory, please let me know.

Re: What to buy ?
 

Fluent will support Itanium. They've had an Itanium-port in-house for some time I think. SGI has worked together with Fluent on porting and optimizing Fluent to the Itanium.

About performance - Six months ago I talked to one person, at a company which I can't disclose, who had done extensive work on porting CFD codes to Itanium platforms. He was not at all impressed by the performance of the Itanium and he thought we'd have to wait for the McKinnley (the successor to Itanium) to get good performance. This was six months ago though and things might have changed since then... Intel are constantly improving their compilers (the Itanium is very dependent on new compiler technologies).

Re: What to buy ?
 

In fact, $12,000 can get almost 6GB of memory if you consider a cluster with AMD or P3 1GHz chips. Fluent runs pretty good on linux cluster. It is very stable and has much less trouble in compiling UDF in Fluent 5 in comparison to Compaq ES40. Not for long, you can probably acquire systems with 14GB of memory for $12,000.

Re: What to buy ?
 

Kim, check out www.microway.com, their dual p3 beowolf cluster is the best buy for you money. For $12,050 you can buy 8-processor dual P3 1GHz linux cluster with a total of 7GB of memory and still have $1,500 left. The recommended system has 256MB of RAM in each box. A total of 4 boxes cost $8,625. You can buy extra RAM from www.crucial.com. The 512MB DIMM has a price of $200. Each box can accomodate 4 DIMM. If you maximize the RAM, then you will get a 4-unit, 8-processor system with 8GB of RAM for only $11,825.

Re: What to buy ?
 

This is getting pretty funny. What you just said compeletly supports what I said. So, I think we agree completely!

Dan.

Re: What to buy ?
 

Always the pragmitist! Your right. Who cares really, just get the fastest computer you can afford. At any one time there probably isn't more than a factor of 2-5 difference between any CPU which is currently on the market anyhow, so it's probably not worth the time to worry about it to much

Dan.

Re: What to buy ?
 

to Scott question: We are running cases that need from 1 to 2 GB of RAM, in future maybe more. As we optimize flow passages in turbomachinary we need a fast response to make an immediate correction, we can dispose of up to 10 licenses for Linux.This machine is only used for computing. Do you have any experience using beowulf cluster and Fluent? I was a bit surprised with what Jonas said about Itanium. Anyone else with this kind of information ? Right now I am thinking of double P4 with lots of RDRAM. Do you recommend this configuration? I am dissapointed with UNIX machines. They are almost as fast as PCs, maybe more stable, but their upgrade is very very expensive. We are getting to have a museum of old workstations at our department.

Re: What to buy ?
 

We've run Fluent on Linux clusters for more than two years. Experience has been extremly good - has given us almost ten times more computing power per dollar compared to buying expensive parallell UNIX machines from HP or SGI. Stability has also been fantastic - better than all our HP UNIX machines. We recently expanded our cluster with 100 new PIII 1GHz CPUs - if you are interested I can post some benchmarks of it, which you can compare to the ones posted at fluent's web-site.

If you only want computing power (not pre and post-processing) and run relatively large cases (more than say 200,000 cells) a linux-cluster is definitly a good choice, probably the best.

There are some issues with combustion and discrete-phase on Linux clusters though, so if you run that make sure that you have it tested on a cluster before you invest.

Re: What to buy ?
 

I'm purchasing another dual P4 with moderate 1GB RDRAM on July 1st, so this is a good option for me. I will upgrade memory at the end of the year (I hope that Rambus comes through with their projected RDRAM price cuts). If you go this route, you should be able to get two machines with $12000. However, you seem to only need one fast simulation at a time.

I wish I had the opportunity to use a cluster, but it isn't possible for me yet (maybe in a year or two). I currently have the free university Fluent license for up to 5 non-unix CPUs. Thus I can't make a cluster, but two dual machines running separately is great with a third machine using the fifth license for post-processing. I have seen results that seem to show the clusters having the best price/performance ratio. I'd definately look into this possibility since you have a 10 CPU license and since you need only 1 simulation to run as fast as possible. You should be able to get 6 good P3 machines with 512 MB memory each and one P3 with 1 GB memory in your price range. (The main machine needs more memory). If you go with Athlons, you could probably get an 8th machine. Ask around for better advice, since I have no experience.

Rumor has it that the Itanium has the potential for great floating point processing but is very lackluster with everything else. McKinnley is supposed to dwarf Itanium's capabilities. Think of it this way, Itanium was supposed to be out a few years ago and thus it must be at least partially based on old technology (it would have been the king of computers 2 years ago). Although, the McKinnley performance may just be marketing hype...

Until McKinnley comes around, I can see no advantage of specialized unix machines for CFD (unless you have much more than $12000 to spend).

Re: What to buy ?
 

(1). In the current issue of PC World, July issue, page-164, "top 10 power pcs", the comment says:"does clock speed matter? AMD's newest Athlon processor, running at 1333 MHZ trails its Intel Pentium-4 rivals on paper. But on the desktop, 1333-MHZ Athlon systems handily defeat their P4 rivals, including a new 1.7-GHZ HP model that was too pricy for our chart. Top speed doesn't always make a top contender, though."(2). So, that's for business world. (3). For cfd world, "Who knows What's in the Black Box". So, it is likely that we are talking about the inefficiency of the black box, rather than well-designed bussiness software or hardware.

UDS DIffusivity...
 

Hi;

i'm a having a difficulty with UDS modeling. I'm trying to define the UDS Diffusivity with a UDF, and it gives me the following error.

Error: UDS_Diffusivity: unrecognized diffusivity method for UDS-0: 198172680. Error Object: ()

I've changed the UDS Diffusivity to a constant value and defined it from materials panel, but i'm still getting the same error. Since manual does not cover anything in detail about UDS modeling, can you please help me?

I'd appreciate your help...

Thanks...

Anisotropic UDS DIffusivity...
 

Does anybody know how to give anisotropic UDS diffusivity?

Thanks in advance. Anu

Re: Anisotropic UDS DIffusivity...
 

You cant do this with Fluent.

You need to write your own udf to implement anisotropy in Fluent. This can be done by applying the divergence theorem and calculating face fluxes via some interpolation of the cell centered values. Its not fun!....

Greg

Re: Anisotropic UDS DIffusivity...
 

Thank you very much for your reply. What do I do after calculating the face fluxes? Can you elaborate your suggestion a little bit. Can't I do this by calculating d_x*(d2U/dx2) and d_y*(d2U/dy2) and making adjustment in the source term for the UDS. Here d_x and d_y are diffusivities in x and y direction and d2U/dx2 and d2U/dy2 are the second derivative of the UDS wrt x and y directions. So the uds eqn. will be as follows,

Unstead term + Convective term + Diffusive term = Source term,

where source term will be, S = Diffusive term - {d_x*(d2U/dx2) + d_y*(d2U/dy2)}

The diffusive term will be calculated as,

d*{d2U/dx2 + d2U/dy2}.

Here d is the diffusivity entered in the materials panel.

Would it be a correct way for the above problem?

Thanking you, Anugrah