为什么FEKO中PO方法的精度太差，怎么改进？

趋势是错误的，你需要看看是不是没有考虑什么设置，比如多次反射。

老大，能不能给个简单的例子
我不太懂怎么设置PO噢，
多次反射是不是在EDITFEKO里面设置?设置后怎么应用到计算中呀?
计算要用PO方法，需要设置几个地方呀?麻烦知道的朋友给出详解，谢谢了

http://bbs.rfeda.cn/read-htm-tid-14238-fpage-2.html
從二面角RCS看FEKO MOM and PO 物理光學法計算整理
◎UserManual上有：“the Number of reflections must be at least 2 to calculate the scattering from a dihedral and at least 3 for a trihedral.”計算二面角反射次數至少爲2，三面角反射次數至少要設爲3，以前沒仔細看啊，呵呵。
◎ Use multiple reflections: When this item is checked, multiple reflections are considered for the ray tracing. The number of reflections that must be considered is set in the Number of reflections dialog. This parameter determines the number of reflections to be taken into account for triangles with labels in the specified range. (For example, theNumber of reflections must be at least 2 to calculate the scattering from a dihedral and at least 3 for a trihedral.) Increasing the number of reflections that must be considered significantly increases computation time, and this should only be done based on physical considerations.

谢谢webhogo，你给的网页里给了产生这样问题的原因，我知道需要设置一下多次反射
现在的问题是能不能请教一下如何设置PO多次反射
是运行CADFEKO后打开模型，然后在"run“里启动EDITFEKO，设置里面的PO，然后OK就可以了吗?这个时候直接关掉EDITFEKO还是怎么的?有知道的大侠帮我解释一下，发几个图就更感激涕零了，呵呵

您 PRE 在另存一個檔案直接改。
執行 PreFEKO 在 執行 RUNFEKO 即可計算。
我隨便拿一個課本的範例改給您看。

非常感谢webhugo，您说我的我已经明白是怎么回事了，可是还有一些细节的问题
请问你说的方法是一个面一个面的添加多次散射，如果我的模型非常大，该怎么操作才能让所有的面都多次反射呢?

还有能不能把你的QQ告诉我，或者你加我为好友271052707
希望能向您学习，主要我现在做PO，FEKO用不熟不行呀，谢谢了

當模型很大的時候，這時可能就是架構跟把金錢投到硬體上的問題了。還有就是您是否有耐心等待PO多重反射得到的數據。
這個時候我可能會投資硬體，因為我無法等待那麼長的時間，我會選擇 MOM+MLFMM。
所以我最近購進 DELL-T7400 (Inte Xeon 5482 <4Core -12MB Cache> *2 + 64GB RAM + SAS 300GB - 15000rpm *3)的硬體來解決這類需要運算久+記憶體需求量大的問題。
當然 MOM + PO 也是可已有投機的方法，這時您可以大概估算電磁波行進的方向有關的面都選多重反射，無關的面部不需多重反射，當然這個方法很麻煩，但是在資源容許的範圍內，也是可以加速跟把您要的數據快速求得，而不失其精準度。
這正是仿真的精神。
Reference,
http://bbs.rfeda.cn/read-htm-tid-15812.html
微波仿真論壇 » FEKO » FEKO交流版 » 請高手看此喇叭如何添加端口
Creating file corrugated_horn_FIX.fek, please be patient ...
File corrugated_horn_FIX.fek has been created:
  17995 metallic triangles in free space
total times in hours:          801.703 seconds (    0.223 hours) 約13.35分鐘。
                   SUMMARY OF REQUIRED TIMES IN SECONDS
                                            CPU-time      runtime
Reading and constructing the geometry         1.125        1.125
Checking the geometry                         1.219        1.219
Initialisation of the Greens function         0.000        0.000
Calcul. of coupling for PO/Fock               0.000        0.000
Calcul. of matrix elements                  192.797      192.797
Calcul. of right-hand side vector             0.016        0.016
Preconditioning system of linear eqns.       19.156       19.156
Solution of the system of linear eqns.      582.078      582.078
Determination of surface currents             0.000        0.000
Calcul. of impedances/powers/losses           0.000        0.000
Calcul. of averaged SAR values                0.000        0.000
Calcul. of power ideal receiving ant.         0.000        0.000
Calcul. of cable coupling                     0.000        0.000
Calcul. of electric near field                0.000        0.000
Calcul. of magnetic near field                0.000        0.000
Calcul. of far field                          5.203        5.203
                            other              0.109        0.109
                                         -----------  -----------
                         total times:        801.703      801.703
               (total times in hours:          0.223        0.223)
Specified CPU-times are referring to the master process only
Sum of the CPU-times of all processes:     6413.625 seconds (    1.782 hours)
On average per process:                     801.703 seconds (    0.223 hours)
Peak memory usage during the whole solution:  743.474 MByte
(refers to the master process only)
Sum of the peak memory of all processes:        5.768 GByte
On average per process:                       738.302 MByte

老大，你说我是不是可以这样理解呢?
“FEKO中的PO如果不设置多次反射的话，PO方法只能给出RCS的大致趋势，精确度方面不是太够；
如果模型不是太大，面不是太多的话增加多次反射后就能够提高PO方法的仿真精度
如果模型太大，面数太多的话,最好增加硬件投资。如果不增加投资的话，可以选择PO+MLFMA的方法仿真”
您看我说的对吗?麻烦了，谢谢

[attachment=11249]
多次反射的關鍵在於入射方向跟觀測點，跟您的架構是否會造成多重反射才需假設多重反射。
PO 我記得好像無法跟 MLFMM 混用。
我會想用 MOM + MLFMM 的方法是因為不用考慮太多，只要您的硬體記憶體夠，這個方法的計算速度會比 PO 多重反射計算速度快。
MOM + PO + 多重反射，是真的很發時間，但是記憶體絕對是最節省的。
之前有看到有人在反應為何 PO 是高頻近似法了，理論上 Mesh 應該是不需這麼的多，這點我真的無法回答，我想需要論壇裡純做數值的人能否看一下他的原理，幫我解惑，呵呵！
關於 Mesh 會決定記憶體的問題，也許妳可以做一個苦工，把小弧面都變成小平面片狀，用 MOM + UTD來做，但是 UTD 的限制很多，要小心使用。
我附上一張時間跟內存需求供您參考。
[attachment=11249]

很怪事了好幾次都傳布上我在試一次
時間跟內存需求

非常感谢webhugo细致入微的解答，您的解答对我目前所做的工作有很大的启发和帮助。
目前因为找工作，手上的工作暂且放一放，所以以后如果还有问题，希望能和您，以及论坛的兄弟姐妹们讨论，再次感谢

还是没看到如何把所有的面都加上多次反射啊,有谁知道?

方法1.. 重點面都設定.
方法2. 將所有面改成是一個物件 使用"13.6 CB card" 再做全部多重反射.
13.6 CB card
This card is used to change or reassign the labels assigned to points, segments, triangles,
cuboids, polygonal plates, tetrahedral elements, etc.
Renaming labels is especially useful when more labels are created by using symmetry (SY
card) or transformations (TG card) or an imported geometry from CADFEKO, and for
example, edges or wedges in the PO area are considered or any other properties shall be
set by label (e.g. Skin effect). Structures created after the CB card are not affected.
In order to make the renaming of a whole set of different labels simpler, the Old label
field in the CB card is also supporting wild cards ‘*’ (an arbitrary sequence of characters)
and ‘?’ (a single arbitrary character). So for instance to rename all these labels
Cube.Face1
Cube.Face2
Cube.Face3
Cube.Face4
Cube.Face5
Cube.Face6
to a new label CubeSurface one could use six CB cards, but with the wild cards this is
much simpler to use just one CB card and specify the old label as
Cube.Face?
or also as
Cube.*
(depending on what other labels are also in the model).
Note that such wild cards are only supported in the Old label field of the CB card. The
New label must be unique.
Another possibility to do a bulk renaming of labels is to read a label mapping table from
an external file, which follows the syntax of the ANSA package. In ANSA version 11, this
file consists of an arbitrary number of lines
old_label | new_label
(i.e. the old and new label entries separated by the | character). Alternatively, the ANSA
version 12 format is also supported, where there is no | character to separate the old and
new label, but just white space (i.e. a space or tab character). Comments line are allowed
in these files and these are indicated using ‘**’ as the first characters of the line.
Some external meshing programs can for instance export a NASTRAN file along with
such a mapping table, and then by using the two commands
IN 3 3 "geometry.nas"
CB "geometry.txt"
one can get the model into FEKO with the proper names of the parts (i.e. the file
geometry.txt would then do a proper mapping of the NASTRAN property to the part
name in the original CAD program).

为什么PO加上多次反射后，计算时间大大增加