碰撞计算中滑动能出现负值

hsyfy_2001

我在做一个碰撞仿真分析，计算过程中没有出现什么问题，查看能量曲线时，尽管总的能量保持恒定，但出现负的滑动能。仔细检查了模型和计算控制参数，没有发现明显有误之处。本人实在是不知道该从哪些方面入手来解决该问题。请各位大侠不吝赐教，本人甚为感谢！

jdcao

搜索一下！！新手要学会搜索

两只小蜜蜂

估计有大的初始穿透。
因为，有穿透的话，系统会把节点拉回，需要做功，消耗能量，导致滑动能出现负值。

jdcao

加分鼓励新手的乐于助人

hsyfy_2001

问题是如何减小初始渗透对最终计算结果的影响？
手动调整模型，工作量太大，而且不好操作。
在论坛里看到以为仁兄的帖子，通过调整罚函数因子可以消除初始渗透的影响。但不知道如何去调整这些参数

ayke

这个问题Dyna help的Total energy里面讲过，摘要如下。

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Negative contact energy:
Abrupt increases in negative contact energy may be caused by
undetected initial penetrations. Care in defining the initial geometry so
that shell offsets are properly taken into account is usually the most
effective step to reducing negative contact energy. Refer to sections
23.8.3 and 23.8.4 in the LS-DYNA Theory Manual (May 1998) for more
information on contact energy.

Negative contact energy sometimes is generated when parts slide relative
to each other. This has nothing to do with friction. I'm speaking of
negative energy from normal contact forces and normal penetrations.
When a penetrated node slides from its original master segment to an
adjacent though unconnected master segment and a penetration is
immediately detected, negative contact energy is the result.
If internal energy mirrors negative contact energy, i.e., the slope of
internal energy curve in glstat is equal and opposite that of the negative
contact energy curve, it;s possible that the problem is very localized with
low impact on the overall validity of the solution. You may be able to
isolate the local problem area(s) by fringing internal energy of your shell
parts (Fcomp > Misc > internal energy in LS-POST). Hot spots in internal
energy usually indicate where negative contact energy is focused.
If you have more than one contact defined, the sleout file
(*DATABASE_SLEOUT) will report contact energies for each contact
and so the focus of the negative contact energy investigation can be
narrowed.

Some general suggestions for combating negative contact energy are
as follows:
1.Eliminate initial penetrations (look for Warning in messag file).
2.Check for and eliminate redundant contact conditions. You should NOT
have more than one contact definition treating contact between the
same two parts or surfaces.
3.Reduce the time step scale factor.
4.Set contact controls back to default except set SOFT=1 and IGNORE=1
(Optional Card C).
5.For contact of sharp-edged surfaces, set SOFT=2 (applicable for
segment-to-segment contact only). Furthermore, in v. 970, setting
***OPT (formerly EDGE) to 4 is recommended for SOFT=2 contact where
relative sliding between parts occurs. For improved edge-to-edge
SOFT=2 contact behavior, set DEPTH to 5. Please note that SOFT=2
contact carries some additional expense, particularly using nondefault values of ***OPT or
DEPTH, and so should be used only where other contact
options (SOFT=0 or SOFT=1) are inadequate.
The specifics of your model may dictate that some other approach be
used.

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可能论坛系统对字符过滤的原因，请将上面“***”字符替换为"S_B"，中间的下划线不要。

tyut_syz

这个问题好象在理论手册中讲到了,原因有几个:1.有较大初始穿透;2.在计算中有未检测到的穿透;总之是穿透的原因多一些.具体解决办法手册上有三种,你可以看看.