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[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

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发表于 2004-2-2 11:29:15 | 显示全部楼层 |阅读模式

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[这个贴子最后由webmaster在 2004/03/09 01:10pm 第 3 次编辑]

发表于 2004-2-2 11:33:34 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

numerical modeling  或  numerical simulation
 楼主| 发表于 2004-2-2 15:03:41 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

有没有一个专门的词呢?
发表于 2004-2-2 22:05:43 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

“数值模拟”是指什么?举个例子?
发表于 2004-2-2 22:39:31 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

谢谢您。那么您就是说,把流体力学试验结果做成数值的动画图像?祝您每天都心情不错。
发表于 2004-2-3 00:35:10 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

正确思想不是天上掉下来的,同理,也不是白白地从自己脑子里蹦出来的。所以,我除了“自己多想想”,还找了些书来读读,才又来提问,以务求保证您心情不错。现在我理解是,数值模拟就是利用数值计算的方法,求解描写物理过程的方程组。也就是以计算机为平台,实现对真实物理过程的再现。这种方法是与实验室实验平行的实验方法。不知道这个说法有没有错?我还有一个问题是,数值模拟结果凭什么说是可靠的?
发表于 2004-2-3 09:51:48 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

[这个贴子最后由webmaster在 2004/03/01 12:34pm 第 1 次编辑]

“坚持下去,则您很快就会赶上我flowermoon”,请问,您说的这个“很快”是指什么时间尺度?
还有,您推荐的精辟的论述中有这么一句:
Often, numerical modelers trust the measurements more than the instrument builders do and experimental scientists trust modeling results more than model developers do.
这句话如果不是我理解有误或者作者笔误,那么是不是说,modelers偏偏最不信model结果?那还如何让别人相信model?
发表于 2004-2-3 13:43:58 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

接着您的思路说。从字面上看,modeler与model是生产者与产品的关系,若联系您所谓之“距离感”,更应该是比喻成俗话说的“孩子都是自己的好”那种,就是骨肉连心的“零距离之美”。是不是也有道理?
认真说起来,我们平常做实验,老师一直对我们强调,检验实验结果真实性的最重要的一个标准是其可重复性。由于实验室的实验需要许多手工操作,其中包含大量的人为因素,所以“可重复性”是至关重要的。而我以外行的考虑,对于数值模拟,是写好一堆方程交给computer处理,而对于computer的语言,只有“0”和“1”两种状态,以我的理解,应该就是等价于“准确”。那么,modelers为什么反而不相信,或者说很谨慎地对待model出来的结果呢?
发表于 2004-2-4 22:46:16 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

我看好像没有别人对这个话题有兴趣,是不是我的问题太菜?多谢您的耐心指教。既然您认定我是女生,我就顺同您的心意换一个比较漂亮的头像。这个花不用说也看得出是sunflower,您可以联想一下自己的名字,好像moon更阴柔一些吔。
“描述连续介质的偏微分方程,而给computer处理的方程是所谓离散化了的差分方程”,意味着数值模拟实际上是一个物理量离散化的过程,小于网格尺度的物理过程就不能够被分辨出来,通常采取所谓的次网格参数化方法来处理这些过程。这应该是模式结果误差的一个来源。对不对?那么还有其他可能的模式误差来源吗?
发表于 2004-2-5 17:04:26 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

我也是这么想的,所谓“闻道有先后,术业有专攻”嘛。欣闻您是理科女生,能否请问您的术业专攻是什么?
前面说到“连续与离散”的关系,也就是以差分方程代替微分方程,以数值解代替解析解(真解)的关系,我今天走在路上想到一个比喻。微分与差分,是不是就好比坡路与台阶的关系?如果我们要到达一个高度,沿坡路走就相当于解微分方程,如果坡路走不通,就建成一级一级的台阶,就相当于数值模式的网格,我们一步跨出的最小长度单位是一级台阶(一个网格),在一级台阶以小的距离,就假设物质属性是均匀的。至于实验室的实验,有时候就感觉象一个黑匣子,把条件设好了,就可以等结果出来了,那就有点搭乘电梯的意思了。我这么外行的想法,会不会贻笑大方?
您说的第二个模式误差来源是指描述物理过程的方程本身不完善,这是局限于我们对物理现象的认知程度。这个方面我还要再多想想。那么还有其他方面吗?
发表于 2004-2-6 00:36:14 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

flowermoon 和 tinge 的学术讨论很好,顶一下!
发表于 2004-2-6 11:41:07 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

“tinge和flowermoon关于流体数值模拟的问答录”这个题目好。本来我还想flowermoon是主角,理应叫做“flowermoon和tinge关于...”,可转念一想,“问答录”当然是tinge问在前,flowermoon答在后。flowermoon提到的windsnow和周华站长今天都来了,flowermoon自己反倒不见了?
发表于 2004-2-8 18:27:56 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

两位的讨论很精彩,我就不插嘴了。加威望一般情况是要帖子发到100个加1分。如果两位的精彩对话能够进行下去(换个话题也可),引起大家注目,也可以破格加威望。再如果你们的话题如江河之水滔滔不绝,还可以考虑专门为你们开辟个人论坛。希望看到你们更多的精彩对话!
发表于 2004-2-9 10:06:26 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

星期五听到flowermoon宣布“休息这么一、两天什么的”,这个周末就心安理得地玩去了!回来又看见周华站长说咱们的规矩是“计件工分制”,还鼓励我们细水长流地谈下去,汇入“流体中文网”的滔滔江水啥的,就来继续吧。
上次说到除了数值计算方法的问题,模式误差的另一个来源是描述物理过程的方程本身不完善。我听说对于方程组的解析求解,为了能够求解方程,物理学家经常要对方程组进行一些简化,就是忽略掉其中相对不重要的小项,仅保持大项,或者去掉非线性项,叫做对方程进行“线性化”。这种工作对于数学家而言,完全是认为不可理喻的,因为损失了准确性。而就一个物理学家而言,他的学问就是确定保留哪些项和忽略哪一些。我的问题是,对于数值求解,是不是保留的物理过程多而全就是最好的?
发表于 2004-2-9 13:07:37 | 显示全部楼层

[精彩]tinge等人关于流体数值模拟的问答录 (无内容)

[这个贴子最后由windsnow在 2004/02/10 00:52am 第 2 次编辑]

Flowermoon and tinge, I think you are both right about the relationships between modelers and models. Generally speaking, there are two different types of numerical models: models mainly used for scientific research to study a SPECIFIC physical process - mechanistic models, such as a DNS (Direct Numerical Simulation) model of a homogeneous fluid to study transition and development of turbulence (say, Type-A models); models mainly used for industrial/commercial applications that have to include ALL physical (and chemical) processes, such as a model with or without combustion processes under any geometric settings (say, Type-B models). When I made that statement about relationship between modelers and models (flowermoon called it "distance produces beauty") I was more or less thinking of Type-B models, which are the ones most people in this forum are interested in. Often, a single model of Type-B will need a big group of people to develop and will also need continuous refinement. On the one hand, Type-B commercial models like to include as many physical processes/options as possible. On the other hand, to make models workable one cannot include all the known physical processes in their precise forms, let alone the unknown or little known physical processes. As a result (of many people working on one model and many simply parameterized physical processes), the actual reliability of such a model may not be as good/trusted as a Type-A model that tinge most likely was thinking about. Generally speaking, a Type-A mechanistic model needs only one person or two people to develop (similar to the case that a child needs only a couple of two people to produce). Under such a circumstance, the relationship between the modeler and the model is more or less a parent-child relationship, which tinge also called it "beauty comes from zero-distance". The parent (modeler) not only knows each and every part of her/his child (the model) but she/he is also able to know the exact physics behind it because the only unknown part is the one she/he is going to study.
Although both flowermoon and tinge are right on their understanding to the modeler-model relationship, I think tinge should get a slightly higher marker than flowermoon at the end of their discussions because the word "modeler" rather than "modelers" was repeatedly used in their discussions. In other words, although I used "modelers" in my statement about the relationship, which corresponds to Type-B models, their discussions can be considered being focused on the Type-A models, which should have a "beauty comes from zero-distance" relationship.
On the surface, it appears that flowermoon plays a major role in the current Q-A (Question-and-Answer) discussions between tinge and flowermoon. It also appears that flowermoon has given good answers to all the questions raised by tinge. However, I believe that it is tinge who has been leading all the discussions! It seems that flowermoon knows quite a lot about numerical modeling of fluid but I think it is impossible for flowermoon to produce a good answer without a good question from tinge. I think tinge is artfully testing flowermoon's academic aptitude by slowly raising the level of difficulty of the questions. Although flowermoon might be right at guessing that tinge is a female, flowermoon has probably underestimated tinge's academic aptitude. I strongly believe that when all the keys to the puzzles are revealed at the end (if there is a happy ending) of the game it is most likely that tinge is much more experienced than flowermoon in numerical modeling of fluid.
I wish you both good luck and wish the discussions to continue for a long, long time.
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