Ls-Dyna_负体积问题

到最大的推荐值

0.5

。

*

对包含泡沫的接触，用

*co ntact

选项卡

B

来关掉

。

*

使用

*contact_inte rior

卡

用

part set

来定义需要用

contact_interior

来处理的

parts

，在

set_part

卡

1

的第

5

项< /p>

DA4

来定义

contact_inte rior

类型。

缺省类型是

1

，

推荐用于单一的压缩。

在版本

970

里，类型

1

的体单元可 以设置

type=2

，这样可以处理压缩和减切混合的模式。< /p>

*

如果用

m at_126

，尝试

ELFORM=0

*

尝试用

EFG

方程

(*section_solid_EFG)

。

因为这个方程非常费时，

所以只用在变形严重

的地方，而且只用于六面体单元。

See also: instability

English Version:

Negative Volumes in Foams (or other soft materials)

In materials that undergo extremely large

deformations, such as soft foams, an element may become so distorted that the

volume of the element is calculated as negative. This may

occur without the material reaching a failure criterion. There is an inherent

limit to how much deformation a Lagrangian mesh can

accommodate without some sort of mesh smoothing or remeshing taking place. A

negative volume calculation in LS-DYNA will cause the

calculation to terminate

unless

ERODE

in

*control_timestep is set

to 1

and DTMIN

in *control_termination is set to any nonzero value

in which case the offending element is deleted and the calculation continues

(in most cases). Even with ERODE and DTMIN set as described,

a negative volume may cause an error termination (see erode/negvol.k).

Some

approaches

that

can

help

to

overcome

negative

volumes

include

the

following.

- Simply stiffen up the material stress-strain curve at large strains. This

approach can be quite effective.

- Sometimes tailoring the initial mesh to accomodate a particular deformation

field will prevent formation of negative volumes. Again, negative volumes are

generally

only

an

issue

for

very

severe

deformation

problems

and

typically

occur

only in soft materials like foam.

- Reduce

the

timestep

scale

factor. The

default

of

0.9

may

not

be

sufficient

to prevent numerical instabilities.

- Avoid fully-integrated solids (formulations 2 and 3) which tend to be less

stable in situations involving large deformation or distortion.

(The fully integrated element is less robust than a 1-point element when

deformation is large because a negative Jacobian can occur at one of the

integration

points

while

the

element

as

a

whole

maintains

a

positive

volume. The

calculation

with

fully

integrated

element

will

therefore

terminate

with

a

negative

Jacobian much sooner than will a 1-point element. (lpb))

- Use

the

default

element

formulation

(1

point

solid)

with

type

4

or

5

hourglass

control (will stiffen response). Preferred hourglass formulations for foams

are:type 6 with coef.

= 1.0 if low velocity impact types

2 or

3 if

high velcocity

impact

- Model the foam with tetrahedral elements using solid element formulation 10

(see ~pdf/).

- Increase

the

DAMP

parameter

(foam

model

57)

to

the

maximum

recommended

value

of 0.5.

- Use optional card B of *contact to turn shooting node logic off for contacts

involving foam.

- Use *contact_interior.

A part set defines the parts to be treated by contact_interior. Attribute

4

(DA4

=

5th

field

of

Card

1)

of

the

part

set

defines

the

TYPE

of

contact_interior

used. The

default

TYPE

is

1

which

is

recommended

for

uniform

compression. In

version 970, solid formulation 1 elements

can

be

assigned

TYPE=2

which

treats

combined

modes

of

shear

and

compression.

- If mat_126 is used, try ELFORM = 0.

- Try EFG formulation (*section_solid_EFG). Use only where deformations are

severe as this formulation is very expensive. Use only with hex elements.

****************** *****************************************

See also:

转：

/blog/?p=22

负体积定义？

Negitive volume

负体积是由于

element

本身产生大变形造成自我体积的内面跑到外面接着被判断为负 体积。

关于负体积的解决办法？

< /p>

负体积多是网格畸变造成的，和网格质量以及材料、载荷条件都有关系。有可能的原因和解 决的方法大概有几种：

（

1