stonewall energy

136523806

请问各位，今天在做一个整车刚性墙碰撞，在后处理中glast文件中发现stonewall energy在40ms处迅速增大到很多，直接导致总能量急剧增大。我看了动能 内能 滑移能和沙漏都很正常，期待解答啊

136523806

那个路过的高手给个解答啊

136523806

求救斑竹

gdyu_yu

There are 3 parameters on Card 5 of *control_contact that deal with rigidwalls.
RWKSF affects behavior of geometric rigidwalls in implicit, which evidently are penalty-based.
________________________________________________________________

Regarding Energy:
Stonewall energy (better known as rigidwall energy) is dissipative and, according to the LS-DYNA Theory Manual, is the change in kinetic energy of the slave nodes
as a result of interaction with the rigidwall (p. 557 of the 2006 Theory Manual pdf file, Section 26.14).
In contrast, the non-frictional component of sliding interface energy (better known as contact energy) is elastic/recoverable.  

Thus two methods of modeling impact with a rigid surface...

(1) *rigidwall_planar

(2)  meshing a fixed, rigid surface with *mat_rigid and using *contact_...

... are not equivalent.

The first is a fully plastic impact; the second is a fully elastic impact (neglecting friction).


The friction component of rigidwall force also contributes to rigidwall energy as
demonstrated by ftp://ftp.lstc.com/outgoing/jday/rwall_friction.k.

gdyu_yu

In addition to these notes, see also
http://www.dynasupport.com/tutorial/ls-dyna-users-guide/energy-data/

Total energy reported in GLSTAT (see *database_glstat) is the sum of ...

internal energy
kinetic energy
sliding interface energy (better known as contact energy)
hourglass energy
system damping energy
stonewall energy (better known as rigidwall energy)

"Spring and damper energy" reported in the glstat file is the sum of internal energy
of discrete elements, seatbelt elements, and energy associated with joint stiffnesses
(*constrained_joint_stiffness....).  "Internal Energy" includes "Spring and
damper energy"  as well as internal energy of all other element types.
Thus "Spring and damper energy" is a subset of "Internal energy".

Two energy terms are written to jntforc in 971 R3.   
The first term "energy" is new in R3 and  corresponds to the "joint internal energy" in glstat.
It is associated with the penalty-based forces in the "constrained" DOF.
It does NOT appear when a Lagrange Multiplier formulation is used.
As of 1/2008, LS-PrePost is seemingly unable to plot the first energy term "energy"
found in jntforc.  I don't believe binout includes the first energy term in the jntforc data.
The second energy term "joint energy" is associated with *constrained_joint_stiffness
and is included as "spring and damper energy" and "internal energy" in glstat.

Recall that "spring and damper energy", whether from joint stiffness or from discrete elements,
is always included in "internal energy".

Energy values are written on a part-by-part basis in MATSUM
(see *database_matsum).

Hourglass energy is computed and written only if HGEN is set to 2 in
*control_energy.  Likewise, rigidwall energy and damping energy
are computed and written only if RWEN and RYLEN, respectively, are set to 2.
Stiffness damping energy is lumped into internal energy.
Mass damping energy appears as a separate line item "system damping energy".

Energy dissipated due to shell bulk viscosity was not calculated prior to
revision 4748 of v. 970.  In subsequent revisions, set TYPE=-2 to iclude this energy
in the energy balance.

The energy balance is perfect if
total energy = initial total energy + external work, or in other words if
the energy ratio (referred to in glstat as "total energy / initial energy"
although it actually is total energy / (initial energy + external work))
is equal to 1.0.

Note that added mass may cause the energy ratio to rise.  
(See http://ftp.lstc.com/anonymous/ou ... t3.noerode.mscale.k)

The History > Global energies do not include the
contributions of eroded
elements whereas the GLSTAT energies do include those
contributions.
Note that these eroded contributions can be plotted as
"Eroded Kinetic Energy"
and "Eroded Internal Energy" via ASCII > glstat.
Eroded energy is the energy associated with deleted elements (internal energy)
and deleted nodes
(kinetic energy).  Typically, the "energy ratio w/o eroded energy"
would be equal to 1 if no elements
have been deleted or less than one if elements have been deleted.  
The deleted elements should have no
bearing on the "total energy / initial energy" ratio.  
Overall energy ratio growth would be attributable to
some other event, e.g., added mass.
Restated, when an element erodes, the internal energy and kinetic energy in glstat
do not reflect the energy loss.  Instead the energy losses are recorded as
"eroded internal energy" and "eroded kinetic energy" in glstat.  
If you subtract "eroded internal energy" from "internal energy", you have the
internal energy of elements which remain in the simulation.  Likewise for kinetic energy.   
The matsum file's internal energy and kinetic energy
include only contributions from the remaining (noneroded) elements.
*** UPDATE ***
To invoke additional energy output to matsum associated with eroded elements, lumped mass/lumped inertia,
and non-structural mass, see IERODE in *control_output
*** END UPDATE ***

glstat includes the KE from the moving rigidwall.   matsum does not.

An example is attached.  Note that if ENMASS in *control_contact
is set to 2, the nodes associated with
the deleted elements are not deleted and the "eroded kinetic energy" is zero.  
(See http://ftp.lstc.com/anonymous/outgoing/jday/m3ball2plate.15.k)

The total energy via History > Global is simply the sum of KE
and internal energies and thus doesn't include such contributions
as contact energy or hourglass energy.


Negative internal energy in shells:

To combat this spurious effect,
- turn off shell thinning (ISTUPD)
- invoke bulk viscosity for shells (set TYPE = -2 in *control_bulk_viscosity)
- use *damping_part_stiffness for parts exhibiting neg. IE in matsum
    Try a small value first, e.g., .01.
    If RYLEN=2 in *control_energy, then the energy due to stiffness damping is
    calculated and included in internal energy.  
    (See  negative_internal_energy_in_shells for a case study)





Positive contact energy:

When friction is included in a contact definition, positive contact is to
be expected.  Friction SHOULD result in positive contact energy.  
In the absence of contact damping and contact friction,
one would hope to see zero (or very small) net contact energy
(net = sum of slave side energy and master side energy).  "Small" is a
matter of judgement -- 10% of peak internal energy might be considered
acceptable for contact energy in the absence of contact friction.
(http://ftp.lstc.com/anonymous/ou ... ct_damping_energy.k
appears to
illustrate that contact damping (VDC = 0, 30, 90) produces positive sliding
(or contact) energy)
See the text file "contact.friction" for more on frictional contact energy.


Negative contact energy:

Refer to p. 3.14, 3.15 of "Crashworthiness Engineering Course Notes" by Paul Du Bois.
Contact jane@lstc.com to purchase these notes.

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 could be 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-Prepost).  Actually, internal energy density is displayed,
i.e., internal energy/volume.  Hot spots in internal energy density usually indicate
where negative contact energy is focused.
Internal energy of solids can be written  in the R3 and R4 versions of LS-DYNA.
See *DATABASE_EXTENT_BINARY. The flag, HYDRO, in the 4th field of the 3rd card
controls this output. Either 3 or 5 additional history variables useful to
shock physics are output as the last history variables. For HYDRO=1, the
internal energy per reference volume, the reference volume, and the value of
the bulk viscosity are added to the database, and for HYDRO=2, the volume
strain and current density are also added.

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:

- Eliminate initial penetrations (look for "Warning" in messag file).

- 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.

- Reduce the time step scale factor.

- Set contact controls back to default except set SOFT=1 and IGNORE=1 (Optional
Card C).

-  For contact of sharp-edged surfaces, set SOFT=2 (applicable for segment-to-segment
contact only).  Furthermore, in v. 970,
setting SBOPT (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 SBOPT 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.

http://ftp.lstc.com/anonymous/outgoing/jday/faq/energy_balance

gdyu_yu

http://www.dynasupport.com/tutor ... /rigid-wall-contact

http://www.dynasupport.com/tutor ... s-guide/energy-data

http://www.dynaexamples.com/examples-manual/rigidwall/forces

Development of simplified safety assessment procedure for paratransit buses

http://www.cmm.il.pw.edu.pl/cd/pdf/061_f.pdf

136523806

太谢谢你了斑竹，好好学习下我

xssnait

问题解决没有？ 我也遇到了这个问题，上面的貌似没提解决办法啊

凤凰鸟

我也遇到了这个问题，求解决