CFD Online Discussion Forums

CFD Online Discussion Forums (
-   Main CFD Forum (
-   -   Traps (

John C. Chien September 22, 2001 02:33

(1). As the world is becoming more unstable, I would like to share with you forum readers, the old Chinese saying: " Men, for wealth, die; birds, for food, perish." (2). Wealth and food can easily become traps for men and birds, respectively. (3). This is because of the conservation law of nature. (4). A person taking too much food, will become over-weighted. And his heart will have to work over-time. (5). A person collecting wealth, will become target and can't sleep well at night. (6). If you try to give away wealth and food, the center of gravity will be lowered. Thus, the world will become more stable. (7). To make progress, you will need a stable environment in the first place. In this world, "UP" and "DOWN" also must satisfy the conservation law of nature.

Greg Perkins September 22, 2001 03:26

Re: Traps
Thanks for you anecdotes John, but I don't understand what's this has got to do with CFD.


John C. Chien September 22, 2001 05:25

Re: Traps
(1). The connection is quite obvious, because I said so. That is the reason number one. (2). "but I don't understand what's this has got to do with CFD." is itself not quite related to CFD. That's the reason number two. (3). If a seemingly non-CFD related comment can stimulate the brain activity so that the message returned contains the word CFD, then the original comment is definitely related to CFD. That is the reason number three. (4). The title of the original comment (or message) was "traps". Following my CFD-WAR-Principle posted three years ago, it seems to me that there are traps here and there in the general CFD war. And the source of CFD traps can be related to the human behavior toward the "wealth" and "food". This is the proper identification of CFD traps. And that is the reason number four. (5). The message not only identified the source of traps, but also stated clearly the consequence of the activities, which are implicit in the word "for"'s. "for" is the active pursue of "wealth" and "food". And the consequence is either "to die" or "to perish". In other words, active pursue of resources is against the CFD conservation law of nature, thus, the activities will be terminated. CFD deals with the solutions which must satisfy the conservation law of nature. So, the example is parallel to the solution divergence when the nature law is not observed. That's the reason number five. (6). The forum is the human activities related to the CFD, which deals with the conservation law of nature. If the human behavior is not trained to observe the law of nature, then the error will likely to be placed in the CFD activities which can violate the strict conservation laws. Only the mind which follows the law of nature will have the chances of getting the true solution of CFD. DUI(drive under influence) can only lead to accident, before the driver can reach his destination. So, the nature law must be inside the mind(the brain? or?) first. That is the reason number six. (7). The CFD solution is always there, if not, no one will be looking for it. The same is true for the "wealth" and the "food". If there is no food and wealth, then we are not going to have discussions here at CFD forum. But that's not the source of the problem. The source of the problem is the "active pursue of wealth and food", that is the pursue in the one-way fashion. In CFD or forum, to stay alive means to avoid taking the one-way approach. The approach taken must follow the conservation law of nature. That is the reason number seven. (8). The human behavior can be individual in nature. It can be easily expanded to group behavior. The company, the organization and the nation are nothing but legal entities which try to enforce the individual behavior of greed or ambition. The existence can only be expressed in terms of the time. The human existence and the solution must co-exist or overlapped, otherwise, the activities to search for the CFD solution will not be successful. That is the reason number eight. (9).Since the CFD solution can be either long term, or highly transient, the effort to look for CFD solution must at least a long term one. That is the individual, the company, the organization or the nation, must try to stay healthy on a long term basis. That's the reason number nine. (10). In short, the wealth and food must be acquired and used following the conservation law of nature. Otherwise, the living entities will sooner or later be acquired by some other entities, or the nature. The forum is the training ground of this nature law. That is the reason number ten. The answers can be viewed in two ways: (a). my opportunity to get my brain more exercises, or (b). answers for readers to do their brain exercise. The same is true for: the water can float a boat, it can also sink the boat. (11). Life is always finite. (because of the conservation law) The CFD solution divergence simply means that the one-way method taken has to be terminated. But, then, do you have the ability to take in a different approach? Easy to say, but perhaps very hard to do.

Adrin Gharakhani September 22, 2001 14:42

Re: Traps
You are confusing conservation laws with stability conditions and other issues (a bit?)

There is nothing in the conservation law of wealth that says it has to be distributed homogeneously. All conservation says is that the total amount of wealth has to be conserved. So, if one gets richer and richer the conservation law predicts/suggests that it is at the expense of someone else getting poorer and poorer. It says nothing about the process, nothing about distribution (there may be pockets of rich among an otherwise uniformly distributed poor), and certainly nothing about stability.

To perform an analogous systems study better (and I agree that humans, their behaviors and the societal interactions in general can ideally be described/modeled in terms of systems dynamics) you need to add concepts such as entropy generation, chaotic dynamical systems and much more than just a simple law of conservation. The latter is a zeroth-order approximation. Borrowing from your CFD analogy, it is not sufficient to just satisfy the conservation of mass ... And even if we satisfy various moment conditions, the law of nature definitely allows coexistence of laminar and fully turbulent flow regimes ...

Adrin Gharakhani

John C. Chien September 22, 2001 16:15

Re: Traps
(1). I did not say that "conservation law " and "stability conditions and other issues" are related. In your first question, you did not define the stability conditions, and you ask whether I am confused about these issues. You will have to be more specific about your stability conditions before I can comment on it. (2).I did not say there is a "conservation law of wealth". And I am not sure that the wealth has to be "distributed homogeneously". Could you tell me the nature of this law and its distribution law? I am curious about your question number two. (3)."if one gets richer and richer...", it seems to me that you are trying to tell me your idea of this law which you have just presented. I was not talking about "richer" or "poorer" or "distribution". I think, you are forming your law of conservation. But I think, it is all right to do so since it is your brain activities. (4)."and I agree that humans, their behaviors and the societal interactions in general can ideally be described/modeled in terms of systems dynamics", I think, this is your another idea. I was not talking about the system dynamic modeling of human behaviors and the social interactions. How do we perform "system dynamic modeling"? I think, this is your another question. (5). " you need to add concepts such as entropy generation, chaotic dynamical systems ", well, you are trying to tell me how to perform this system dynamic modeling, I think. These are your ideas. By the way, entropy generation is not a concept, I think, it is the second law of thermodynamics. And I was not talking about the thermodynamics at all. But I guess, this is consistent with your system dynamic modeling. So, it is all right. (6)." the law of nature definitely allows coexistence of laminar and fully turbulent flow regimes ... ", this seems to be your another "innovative" idea. Fully turbulent flow comes from the laminar flow/ transitional flow. So, "definitely allows coexistence of ..." seems to be your perception of law of nature. My message was not in any way related to the transitional nature of laminar/turbulent flows. (7).In my posted message, item -11, I said "The CFD solution divergence simply means that the one-way method taken has to be terminated. But, then, do you have the ability to take in a different approach? Easy to say, but perhaps very hard to do. ". That was the key element of my message. And your answers have all confirmed my message. (8). "the one-way method taken" will lead to "divergence". As a result, your answers are diverging outward, instead of focusing on my original message. (9). "the ability to take in a different approach" could be the way out of the divergence. But if one can not put aside one's way of thinking and understand someone else way of thinking, and then take in that way of thinking, then it is going to be difficult to solve the divergence problems in CFD. (10). Now, back to my original message: "men, for wealth, die; birds, for food, perish." "for wealth" is one-way method, so is "for food", which lead to "death". In CFD, it leads to divergence. (better change somethings quick, relaxation factors or ...) In human behavior, (same as group behavior, company behavior or ...) the one-way method leads to death. (11). Then, what's wrong with "if one gets richer and richer"? There is nothing wrong with it, except that, if is the consequence of the one-way method, then based on this old saying, it will lead to death.(regardless whether it is individual, group, organization, company, or nation. was MS also heading in that direction? and other current examples in the news.) I did not invent that old saying, I am just trying to share with readers my interpretation.

John C. Chien September 23, 2001 15:07

Re: Traps,simple connection with CFD
(1). What is the goal of studying CFD? get a better paid job. (2). What is the goal of selling a CFD code? make more money. (3). These are very simple-minded thinking. Shall we say, it's along the line of "for wealth". (4). Now, let's take a look at the real CFD calculations. For a not-too-big mesh of 50x50x50=125,000, if we assume that there are six equations to solve and each takes 50 algebraic operations, it will take 125,000x300=46,500,000 operations to cover the whole computational domain. (5). Let's say, we are using iterative method and it requires 1,000 iterations to reach convergence. Then it is going to take a total of 46,500,000,000 algebraic operations from the begining to the end. That's a huge number for a not-too-big mesh size problem. (6). The reason behind is very simple. The program is looking for the final converged solution all the time, by changing the computed solution. For this reason, a simple "one-way method" is not going to accomplish the goal. (7). So, between the final solution obtained from 46,500,000,000 algebraic operations, and the simple goal of "getting a better paid job" or "making more money", there has to be millions of assumptions or lies. The chance of getting a good solution is similar to the probability in playing the lottery. (8). By the way, the energy efficient refrigerator by Maytag is finally arrived, to replace the 22 year old , heavy and noisy one made by GE. The new one has better insulation, lower energy consumption, more internal drawers. (9). So, there is still a chance to use CFD. In stead of "getting a better paid job" or "making more money", one really should be talking about designing products to operate more efficiently, or using less energy. (mass production of IC chips or shoes can not solve the world energy problem. It can only create environmental problem.) (10). If one is still thinking about finding a code to solve a problem and make a lot of money, then he will have to create millions of lies in the first place. CFD is for the best and the worst. The best who knows the solution is unlikely, and the worst who pretends to know the solution. Those who standing in between, it is a good idea to look at the products improvement, instead of making money in CFD.

Greg Perkins September 23, 2001 22:58

Re: Traps,simple connection with CFD
I'm sure that people using CFD are doing so for various reasons. Some might be wanting to investigate a process/physics as part of postgrad degree, others want to design a better product, others might just be doing it for fun!

If you just want to make money then obviously there are better ways! But not all people want to only make money!


John C. Chien September 24, 2001 01:18

Re: Traps,simple connection with CFD
(1). Well, I have to agree with you that not all people want to only make money. (2). At least, traditionally, Chinese place the businessmen at the bottom of the society. But I think, in US businessmen are at the top of the society. (3). Recently, airlines decided to lay off over 40,000 workers. Boeing alone decided to lay off up to 30,000 workers. I think, it can easily wipe out total polulation of CFD related engineers world wide, many times. The only reason for taking that action is for wealth, at the expense of workers. How about the rumour of last year related to another company like GE. (4). The point I was trying to make was: in CFD, it takes personal dedication to work on the very difficult issues related to nuumerical analysis and math modeling. Under the current environment in US, it is simply impossible to pursue CFD work. At the same time, there are tons of commercial codes one has to overcome before he will be able to have the opportunity to do some CFD work. (5). The "for wealth" approach with companies in US has already eliminated most of the CFD opportunities. And I don't think the research work of the center of turbulence at Stanford University is in anyway related to the industrial problems at all. (6). For this reason, it is important for those who are interested in CFD to realize that this is an expensive hobby. And I don't think I will be able to support it anymore. (7). Well, everyone has his own definition of CFD. And they are free to do CFD for any reason or just fun of it. But currently, in US, the industries are operating under "for wealth" approach. The CFD under this condition is no longer a viable solution at all. (8). As a matter of fact, the word "CFD" has already disappeared from the government organizations to private industries. It has been moved to the science department already. (9). Well, perhaps, you are going to tell me "how many are doing CFD in their graduate study?" , "how many are doing CFD to improve product desing?" and "how many are doing CFD for fun of it?" from your side of the globe. (10). This year, I am not working . and I am supporting this forum for "my brain exercise" only.

Jon September 24, 2001 03:43

Re: Traps,simple connection with CFD

I think you need a holiday.

Greg Perkins September 24, 2001 04:13

Re: Traps,simple connection with CFD
Here are some of my thoughts:

1) the current downturns are part of economic cycles, caused by many factors. However, the general trend over the past 25 years is clearly an increase in the use of numerical models, both in industrial design and research - whether you call it CFD or whatever.

2) the general trend in 1) is likely to continue in the foreseeable future. why? because such modelling is useful and almost certainly cheaper than experiments, prototyping etc. This doesn't mean those last ones are eliminated though.

3) companies should evaluate the value of CFD, FEA etc routinely, and there may be a need to decrease its use or increase its use etc. The important point here is that there are able and qualified people capable of making these sorts of judgements. Thus having some capability/experience is important, even if its not used 100% of the time. There's a whole range of factors here, and each organisation needs to determine that for themselves.

4) "experts" in CFD like other areas in professional engineering need to provide sound advice on the capability, potential etc of the tool. One potential difficulty which you've alluded to, is that vendors are trying to sell you something. But this is the case for all products/services and I think its up to organisation/companies etc. to properly evaluate this themselves. Perhaps one reason for a large take-up followed by a decrease in use, may be that the software tools aren't good enough for some industrial processes etc and they've been dumped by some users.

5) CFD is a very detailed modelling tool. Its not always the best tool. In my view, engineers should seek to gain exposure to a variety of methods etc etc. Being a dedicated CFD expert is only going to be useful career wise for a handful of people. On the other hand, engineers with a strong set of modelling skills, some experimental work and a knowledge of a range of proceeses, products are going to find a career more easily. So - don't just do CFD is probably a wise move - even if its your core skill. Everybody but people in CFD with vested interests will tell you that!

6) getting work doesn't seem to be that hard - at least compared to working through your PhD, as I'm doing now!


kalyan September 24, 2001 11:40

Re: Traps,simple connection with CFD
Greg has pretty nailed down as to why people do CFD modeling.

CFD is widely acknowledged to be an art in addition to science. You are not going to get anywhere with philosophy here. There is not a single piece of useful information in this discussion.

John C. Chien September 24, 2001 13:03

Re: Traps,simple connection with CFD
(1). If I am not working (for income), then everyday is a holiday already. (2). I think, people are very Chinese, they don't like to hear the negative part of the real life. (3). Unfortunately, every second of our life is war. People who are not prepared, simply can not survive for a long time.

Adrin Gharakhani September 24, 2001 13:32

Re: Traps
I was extending your analysis. (not developing "my laws of conservation") Obviously you have misinterpreted what I was saying. Since you were providing an analogy between CFD and human behavior, I extended it further to argue with the validity of (some of) your points.

I usually would not get myself involved with discussions of this sort on a CFD forum, but this was an interesting topic. Anyway, I will not go into further detail!

Adrin Gharakhani

John C. Chien September 24, 2001 13:45

Re: Traps,simple connection with CFD
(1). Are you the only one studying CFD in graduate school? How many? (2). Without the screening by a license system, without the strong voice of a union, without the precise definition of CFD, are you going to perform CFD ? (3). The basic problem is: there is no direct connection between CFD and the improved results (say product design, or physical understanding). (4). For CFD to be a viable method or tools, the results from CFD must represent something valuable. It also must have a large enough market for it (the result) in order to survive. (5). Even in aerospace industries, where they have been using CFD, when the design of aircraft is completed, do you think that the company still need to do CFD? In the production phase, they need only technicians. (6). So, the numerical analysis and math modeling has to take a different shape in real life, in order to survive. Even at schools, not every school can do research on Mars. (which is a decision, mainly political) (7). CFD is not useless. And I agree with you that almost every design in this world can benefit from doing CFD. Unfortunately, the connection to CFD is not established yet. (8). If you study law, you know you will have a job as a lawyer, and if you study medicine, you know you are going to become a MD. But if you study CFD and have a PhD, then, what are you going to be? (9). My way of thinking is: (a). force a company to have a CFD research department, (b). hire some PhD's to do research related to product improvement. Both are not acceptable, because companies are looking for people to design innovative products so that they can create new market for the products. (10). Doing research at schools is mainly related to teaching and political decision. So, it is an exception. (I mean, as long as there are students anxious to learn, and fund available.)

John C. Chien September 24, 2001 14:19

Re: Traps,simple connection with CFD
(1). I don't think "CFD is an art". When you get "underflow" or "overflow", you are dead. There is no more art. (2). The ability to get the right solution is linked to the correct formulation of the problem and the proper implementation of the boundary conditions. So, CFD is taught in engineering school and science department. (3). We can't say that CFD is an art just because it is not "mature". (4). And "PhD in CFD" simply means "Doctor of Philosophy in CFD". You can't do CFD right without philosophy. So far, there is no way to "invent" CFD solution yet.

John C. Chien September 24, 2001 14:41

Re: Traps
(1)."Since you were providing an analogy between CFD and human behavior", there is no analog between the two. (2). "CFD is numerical analysis and math modeling in fluid mechanics". (3). Analysis and Modeling "are" human behavior. (4). CFD is not a computer code which can put together by itself and perform calculations on its own. Every aspect of CFD is human behavior. (5). If you were running a long CFD code on someone's super-computer,(say doing DNS) and the project got cancelled, then you still have to pay for the computer time. (6). "computer" can be a machine, and it is largely a machine right now. But "CFD" is "human behavior" even if you are using someone's CFD codes. (7). For this reason, we have the cfd forum. This is not the place for a CFD code to talk to another CFD code. "CFD codes" are nothing but the "left-over stuff" of analysis and modeling by human being. Are we becoming the slaves of computers?

kalyan September 24, 2001 16:46

Re: Traps,simple connection with CFD
Most people who visit this forum are pre-occupied with specific areas with CFD that they are working on or trying to learn. Broad philosophical statements are OK from time to time, but dare I ask again, what has anyone learnt from the posting with this thread.

Prashant September 24, 2001 17:35

This is all crap
I agree with Kalyan. Philosophical statements and personal opinions should be kept out of this forum. Let's not make it some ordinary chat room. Jonas, what happened to that "monitoring the messeges" idea?

John C. Chien September 24, 2001 18:08

Re: This is all crap
(1). Are we repeating the same World Trade Center tragedy? (2). The forum will fail, because readers are unable to find the messages of the type they like. (3). The fix to that is "post one hundred messages readers like before making any comment". That's the conservation law here. (4). It was intended to stimulate more readers to post messages. To say that you don't like is only a first step. If you can't say something more about CFD, we are going to have nothing to read.

Mr. Me September 24, 2001 18:43

Re: Nothing is ever completely all [beep]
I think you should just change your preferences. Make it so that you only see the beginning thread. If you don't like the beginning thread then you don't have to take part in the discussion nor see the subsequent threads on that topic.

Personally I like to see people discuss things instead of people asking questions about where to find answers for their CFD homework problems...

Please, lets keep our minds open here. If you don't like something don't read it. Its that simple.

All times are GMT -4. The time now is 20:16.