Floating point error invalid number,fluent典型错误

turbulent viscosity limited to viscosity ratio of1.000 000e+005in2cells

Error：Floating point error: invalid number 1 这个应该是湍流模型的选取与第一层网格高度之间不满足近壁处理关系而产

生的问题，如果你没有使用壁面函数的话，第一层网格高度尽可能地小点儿，比如取为弦长的百万分之一左右；另外，边界条件中关于湍流量的设置不合理也会导致这个警告。

2 （不推荐）solve-controls-limits Maximum Turb. Viscosity Ratio 加多两个0，估计是一些单元的最大Turb. Viscosity Ratio超出了限定值

（）恕我直言，你的这个方法只是治标不治本，他这个问题多数是由于网格尺度太大引起的。也可能是边界条件上的湍流相关参数不合理导致的。[br][br][以下内容由larky 在2007年06月23日00:00am 时添加] [br]

调大限制值可能导致发散

3 这是一个办法，能够解决一部分问题，有一些问题无论你怎么调整都没有用，如果出现这种情况可以通过调整初始流场，找到合适的初始值大部分能够解决，其实如果只是一开始初现这个问题，可以不作调整，除非影响到收敛性

4 在别的论坛上看到的：

为了尽快收敛对异值进行的限制，对最后收敛结果无影响

1）如果边界条件设置合理，一般来说会在收敛后自动消除。

2）为了加快收敛对异常的数值进行的限制（以引用2楼），是加快收敛的一种措施。

3）但是如果你的问题中流场变化很大，有可能在最后还会有。

4）如果网格不好会经常出现这种现象。

5）如果不想看见它总是报告而影响计算速度（写屏会降低计算速度），可以在下面把它关闭：

solve->control->flow limit....具体记不住了，自己看看就知道了。

5 我也遇到这种情况,不过是在叠代求解的前一百多步,后面就没有了.因此我想

是否是因为前面计算的误差大引起?而随着计算误差的减少,就消失了.如果是这样,就可以放心啦.

6 一般是边界上或是网格质量差的地方出现了奇点.由于是数值耗散,随着迭代次数越多,影响整个流场的范围越大,最终可能导致这个流场发散.

如果是网格质量差的地方出现,就只能重划网格了

如果是在边界上,一般是湍流相关参数设置不合理造成的,改成固定湍流比可能能解决

7 Why don't you try as follows (If you still have the same warning, please go to the next step. Usually, the initial flow condition used for the RSM run is obtained from the RNG k-e model result);

First step:

Solve - Controls - Solution -Default => iteration

Second Step:

Dicrase "Under-relaxation factors" => iteration

Third Step:

Adaptation of cells : I usaually use y+ and velocity gradient conditions => iteration

Fourth Step:

Regenerate mesh, goto step 1

If your solution stats to converge, you can increase under-relaxation factors.

If you have converged solutions, you can increase the order of the discretizatio n parameters (for ex. 1st -> 2nd -> QUICK etc.)

8. Once I posted a big message on this issue, I am pasting that message again, you can read this:

{

well this is one common problem lot of people have asked about it before. i will try to summarize the approach i take to solve this problem.

first of all

the very basic cause of this warning is the wrong set up of boundary conditio ns.So if you are sure that nothing is wrong with the set up of the problem, you can follow the following things.

The origin of the problem lies in the fact that if the solver calculates the valu e of k and e or omega (in two equation models) wrongly, it’s very likely it will calculate turbulent viscosity wrongly and thus we get the warning. In the ideal condition, as the solution converges the warning should go away and we all live happily ever after. But generally this does not have so happy ending. The reason is mainly we have a case which is very large and convergence is already difficult and which is exacerbated by the wrong calculations of turbul ent quantities. So what are the remedies for it.

The usual remedy is to switch to coupled solver,and work with it, and this u sually solves the problem. But my personal thinking is that if the case is inco mpressible the coupled solver may not work well there. But yes this is one so lution. The second solution which is far more stable is, and if you fail to get the solution from coupled solver too, switch to FAS,increase the number of p re post iterations, make the coarsening levels to 4, (4 is more than enough). A nd this converges almost every problem, but there are case where you might f ail to get convergence.

Anyway if you are stuck with segregated solver (like me), what are the option s.

First of all if we consider that the divergence is because of turbulence quantiti es, we may want to force the convergence on these quantities before we move to next iteration.

The way I do is this, I change the multigrid options for k, e to V cycle, mak e the pres sweeps to 1 post sweeps to 2, and chose Bicgstab as smoother. An d let it run.

Sometimes I just want to first get the best approaximation of k,e for the flow field I have, for this I usually switch off the solver for momentum equations and just solve for k,e or k, omega till I get warning free turbulent field, then I switch on all the equations and go on to iterate further.

This approach works well, but it has one problem. if the mesh size is very lar ge say around 3 million cells then even to first get the turbulent quantities to converge might take day or two. So what to do in this case.

Whenever I have to do calculations for the cases around 2-3 million cells, I m ake two meshes one very very coarse,with same boundary conditions as finer mesh (which is of course around 3 million cells).Now first I get converged solution on coarse mesh, which I can get in hour or two. Then go to file->int erpolate, and write the data for corresponding zones, and then when you read t he fine mesh read this initial guess from same file->interpolate->read.

And here switch off the momentum calculations do some calculations only for turbulent quantites, (if u get viscocity warning, it will soon go away, though I never got warning here since the solution is already converged), so after say 3-4 calculations switch on solver for all the quantities and go on to iterate, yo u will get converged solution.

(well on coarse grid you can use FAS to force convergence, its quite handy th ere).

Hope this will be useful.

}

Error: Floating point error: invalid number

wgf332(站内联系TA)

看看关于interface的介绍吧，interface是成对出现的。你改用双精度试试看

夏之篮(站内联系TA)

这个问题在FLUENT FAQ里面有涉及。

应该边界条件设置或UDF程序的问题

其实湍流粘性比受限制这个问题很常见，出现这个原因主要有两个：

1：源项或者方程边界设置有错误

Error: Floating point error: invalid number

Error Object: ()

这个问题就是比较通俗的随之而来的错误，其实就是我们常说的溢出，分为上溢出和下溢出，这个不是调整solve-limit-viscosity ratio可以解决的，具体形成原因在FAQ中有比较详细的说明。

当边界条件设置不合理，如动量方程源项很大（出现异常的局部速度等等），不合理的边界处理等，或者某些情况下的亚松弛因子过大也会导致出现溢出。

之所以谈到溢出这个问题，最后是为了说明在修改solve-limit-viscosity ，不可

盲目，默认值一般是最佳值。

一些情况下，手动修改湍流方程进行计算的时候，也会导致这一问题。

2：湍流边界条件的不合理

这个就是最常见的原因，也是FAQ中的解释。

边界及初值选择合适的湍流强度和湍流尺度，或者合适和K或者E，对收敛起着非常重要的作用。

给定的参数不合理，就会有湍流粘性比受限制的警告，具体怎么设置，可以参见FLUENT的湍流模拟的HELP，有详细的步骤。

asunbird(站内联系TA)

FAQ是Frequently Asked Questions （常见问题解答）吗？嗯，回头找来看看，谢谢剖析，很深刻哈！

junfugan(站内联系TA)

Originally posted by 夏之篮at 2009-8-2 17

这个问题在FLUENT FAQ里面有涉及。

应该边界条件设置或UDF程序的问题

其实湍流粘性比受限制这个问题很常见，出现这个原因主要有两个：

1：源项或者方程边界设置有错误

Error: Floating point error: inva ...

回答太官方了吧；

前几天自己刚写了udf，也出现这个问题，你看一下方程里有没有分母为0 的情况出现，这个地方就注意一下，强制不为0；还有问题的话可以把中间数据输出来看

zhangvio(站内联系TA)

我以前也出现过几次这样的error，把网格好好改改就好了。我的模型比较简单，现在可以全都用六面体来划分了。不知道你的模型能适用不。下面是我以前搜到的一些东西，希望能对你有帮助。

What does "floating point error" mean? How can I avoid it?

The floating point error has been reported many times and discussed a lot. He re are some of the answers found in the Fluent Forum:

From numerical computation view point , the basic operations performed by co mputer are represented inside computer in what is called floating point number s. The errors that are either because of invalid numeric computation initiated b y user or limitation of machine that is used are floating point errors.

1)Invalid Operations:- Simplest example is if one uses Newton Raphson root fi nding method to solve f(x)=0 and for some Nth iteration if we get x = x(N) such that derivative of function f(x), f';(x(N))=0 then formula for calculating ne xt iterate x(N+1) = x(N) - f(x(N))/f';(x(N)) requires division by f';(x(N)) which is zero. Here you get divide by zero type of floating point error.

2) Over or Underflow:- Another type is having data with either too large or to o small magnitude called ';overflow'; or ';underflow'; respectively.Such data can not be physically represented on computer for direct processing by arithmetic p rocessing part of Processor.

3) Rounding off errors :- While rounding off a decimal number , some signifi cant digits are lost which cannot be recovered . e.g. if we round off 0.1 to int eger (not greater than it called ';floor'; of the given no.) then it is zero. If this value if further used for computation then it may lead to several errors. SOLVER AND ITERATION -----I think if you set shorter time step, it may b e good. Or changing little Under-Relaxiation-Factors, it may be good. In my e xperience, I set 1/3 Under-Relaxiation-Factors as default.? -----?also lower the v alues of under relaxation factor and use the coupled implicit solver? -----?Try t o change under-relaxation factors and if it is unsteady problem maybe time ste p is to large.? -----?you can improve the ratio in the solve--control--limits, may be that can help.? -----?you will need to decrease the Courant number? -----?If you still get the error, initialize the domain with nothing to ';Compute from...'; Then click ';init';. Again select the surface from which you want to compute the initial values & iterate. This should work.? -----?Another reason could be a to high courant number - that means, that the steps between two iterations ar e too large and the change in the results is too large as well (high residuals)? GRID PROBLEMS -----?this error comes when I start scaling grid. in gambit, all my dimension is in mm, when in fluent i convert it in meter using buttone SCALE. after it, when i iterate, about hundred iteration, this error appeared. b ut when i not scale my drawing to m...and let it be as in gambit..then the iter ation is success. -----?hi I think you should check your mesh grid mesh is ver y high. your problem solve by selection a low mesh.? -----?Your mesh is so h eavy that your computers resources are not enough. try to use coarser mesh.? BOUNDARY CONDITIONS -----?In my case I had set a wall boundary condit ion instead of an axis boundary condition and then FLuent refuses to calculate telling me ';floating point error';.? -----?Your Boudary Conditions do not repre sent real physis.? -----?wrong boundary condition definition might cause the flo ating point error. For example setting an internal boundary as interior? -----?On ce I had the problem, simulating a 2D chamber with a symmetry BC. I set th e symmetry somewhere as ?axe symmetric? and the floating point error occur? -----?check the turbulence parameter you set. reduce the turbulence intensity to less that one for first, say 50 iterations.

MULTI PROCESSOR ISSUES -----"I';ve had similar problems recently with flo ating point errors on a multi processor simulation. The solution for my proble m seems to be to run on a single processor, where it runs fine....??

WRONG INITIATION ----- Initiating the case with wrong conditions may lead to floating point error when the iterations start.

我试了还是没有解决

其实湍流粘性比受限制这个问题很常见，我分析出现这个原因主要有两个：1：源项或者方程边界设置有错误

Error: Floating point error: invalid number

Error Object: ()

这个问题就是比较通俗的随之而来的错误，其实就是我们常说的溢出，分为上溢出和下溢出，这个不是调整solve-limit-viscosity ratio可以解决的，具体形成原因在FAQ中有比较详细的说明。

当边界条件设置不合理，如动量方程源项很大（出现异常的局部速度等等），不合理的边界处理等，或者某些情况下的亚松弛因子过大也会导致出现溢出。

之所以谈到溢出这个问题，最后是为了说明在修改solve-limit-viscosity ，不可盲目，默认值一般是最佳值。

一些情况下，手动修改湍流方程进行计算的时候，也会导致这一问题。

2：湍流边界条件的不合理

这个就是最常见的原因，也是FAQ中的解释。

边界及初值选择合适的湍流强度和湍流尺度，或者合适和K或者E，对收敛起着非常重要的作用。

给定的参数不合理，就会有湍流粘性比受限制的警告，具体怎么设置，可以参见FLUENT的湍流模拟的HELP，有详细的步骤。

原因: 数据矩阵求解过程中出现的问题。

方法:1、检查网格质量。

2、检查边界条件和初始条件。

3、对问题进行深入分析，对比模拟情况与真实情况之间的差距。

turbulent viscosity limited2008-11-08

作者：曾经深深爱过一个人

https://www.360docs.net/doc/929872151.html,/blog/cns!747fec30db0aa7c5!116.entryhttp://www.b https://www.360docs.net/doc/929872151.html,/discuz/viewthread.php?tid=63TurbulentViscosityRatioLimitedto1e+5in××××××cellsTurbulentViscosityRatioLimitedto1e+5in××××××cells直到计算收敛结束。

1.上限是默认值1e+5没有改过；

2.同样的计算模型和设置，当用标准k－epsilon 模型和RNGk-epsilon模型时，迭代可以收敛；而用RSM模型时，很快就发散；

3.网格的问题基本可以排除；

4.我怀疑是湍流的初始条件设置有问题：计算模拟的是风洞试验，采取直接给出k,epsilon的方式。

参考的资料有试验中测得的湍流强度数据，平均风速知道，k可以直接计算，约为5.8；在确定epsilon时，参考Fluenthelp中有一个用于风洞试验中估计epsilon 的近似公式，计算约为0.02左右。Help中特别说明，用此epsilon时，应反过来在另一确定epsilon的计算式（由(mut/mu)估计）中校验TurbulentViscosityRatio 不会太大；校验的结果TurbulentViscosityRatio为e+7~8量级，超过了Fluent默认上限。本人是新手，对TurbulentViscosityRatio上限的含义不很清楚，加之对本计算模型湍流参数取值没有很大把握，故没有更改限制，因此计算中一直显示上面的提示。

请教各路高手和版主：1.根据湍流尺度（turbulencelengthscale）可以计算epsilon；看到有的文献说，风洞试验中计算得到的湍流积分尺度（intergralscaleofturbulence）就是湍流尺度，我表示怀疑；这两者是不是一样的？

2.对于风洞试验模拟大气边界层底部结构风流场，湍流参数怎样给定较为合适，epsilon大致在什么量级？

3.TurbulentViscosityRatio在什么范围？意思是湍流粘性率超过了fluent所设定的极限。FLUENT对压力、温度和湍流量应用了限制值。这些限制的目的就是为了保证在计算中，绝对压力或者温度不是零、负值或者过大，并保证湍流量不会过大。

FLUENT还对温度的减小速度作了限制，以避免温度变为零或者负值。注意：一般说来你不需要改变默认的解的限制。如果压力，温度或者湍流量被重复地重置到限制值，控制台窗口就会出现适当的警告消息，此时你需要检查尺寸，边界条件和属性以确保问题的设定正确，并找出问题中变量为零或如此之大的原因。你可以用标记功能（用于适应中标记单元）来辨别哪个单元的值等于所设定的限制。（用等值适应面板，具体参阅等值适应一节。）在很稀少的情况下，你可能需要改变解的限制，但是如果要这样做的话，你必须清楚求解器会有这种非常情况的原因。比方说，你可能知道流域内温度超过5000K。如果你要将温度的极限设置超过5000K，要确定任何温度相关属性对于这么高的温度都被适当的定义。

还有一个就是说在压力出口处发生了回流出现回流后影响不影响计算精度主要是看实际有没有回流。如果实际有回流，则计算出来的回流是确实存在的。则此时的回流参数应靠试验来确定。所谓的回流参数是指计算中一旦出现回流，则从出口流回来的物理量（如组分）是多少！当实验中没有回流，而计算中出现回流时，要分成两种情况来讨论。在讨论这个以前，有必要将产生假回流的原因仔细说一下。产生假回流主要是由于不好的初始条件或是上次迭代的结果所计算

的系数被代入使矩阵迭代而产生的结果。这样说，则可把问题分为两类。一类是计算中出现回流，而计算最后没有回流的，这样的话，可以将迭代中没有回流以后的任意步看作初始条件，这样设不设回流参数都是无所谓的。

第二种问题是计算最后还有回流。这就可能是你边界条件或是物性什么的原因了，即使设置回流参数，结果也是不足取的。

====================================计算中不断出

现：.turbulentviscositylimitedtoviscosityratioof1.000000e+005in262718cellsH!是何故?为了尽快收敛对异常的数值进行的限制，对最后收敛结果无影响如果太大会影响结果吧1）如果边界条件设置合理，一般来说会在收敛后自动消除。&T1;2）为了加快收敛对异常的数值进行的限制（以引用2楼），是加快收敛的一种措施。3）但是如果你的问题中流场变化很大，有可能在最有还会有。

iP5L\4）如果网格不好会经常出现这种现象。/tIio5）如果不想看见它总是报告而影响计算速度（写屏会降低计算速度），可以在下面把它关闭：

9O>_Rqsolve->control->flowlimit....具体记不住了，自己看看就知道了。~qexr,迭代过程中出现了反流而且还有湍流粘度超过了限制最后不收敛了怎么解决呢我也遇到过这个问题.]b}主要是网格质量太差!rH4