Negative Sliding Energy in SLEOUT
Akhil Sreekumar
James Kennedy
Dear Akhil,
What version/revision of LS-DYNA are you using?
-----------------------------------
First and foremost, use the latest version/revision of LS-DYNA available.
______________________
*CONTACT_
DEPTH - Search depth in automatic contact to check for nodal penetration through the
closest contact segments. A value of 1 (one segment) is sufficiently accurate for most crash
applications and is much less expensive. By default, this value is 2 (two segments) for im-
proved accuracy, except for *CONTACT_AUTOMATIC_GENERAL which has a default
of 3.
LT.0: |DEPTH| is the load curve ID defining searching depth as
a function of time. (not available when SOFT = 2)
See About SOFT = 2 for segment-based contact options controlled by DEPTH.
About SOFT = 2:
What is Segment-Based Contact
Traditionally, to determine contact, the nodes of one surface are checked to see if they
penetrate the segments of another surface. The direction of the applied penalty force
depends on the direction of the reference segment’s normal vector at the contact point.
(See more in LS-DYNA User’s Manual).
For SOFT = 2, the SBOPT parameter on optional Card A controls several options. Setting
DEPTH = 1 for pinball edge-to-edge checking is not recommended and is included only for
backward compatibility. For edge-to-edge checking setting DEPTH = 5 is recommended
instead (see below). The warped segment option more accurately checks for penetration of
warped surfaces. The sliding option uses neighbor segment information to improve sliding
behavior. It is primarily useful for preventing segments from incorrectly catching nodes on
a sliding surface.
For SOFT = 2, the DEPTH parameter controls several additional options for segment based
contact.
1. DEPTH = 2 (default; but not recommended). Surface penetrations measured
at nodes are checked.
3. DEPTH = 5. Both surface penetrations and edge-to-edge penetrations are checked.
______________________
Sincerely,
James M. Kennedy
KBS2 Inc.
March 6, 2023
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James Kennedy
Dear Akhil,
First and foremost, use the latest version/revision of LS-DYNA available.
Fix seg fault when using shell type 15, axisymmetric volume weighted, with
*MAT_ADD_EROSION and also materials with equation-of-states.
6. 2D Axisymmetric Solid Elements. The 2D axisymmetric solid elements come
in two types: area weighted (type 14) and volume weighted (type 15).
a) High explosive applications work best with the area weighted approach
and structural applications work best with the volume weighted approach.
The volume weighted approach can lead to problems along the axis of symmetry
under very large deformations. Often the symmetry condition is not
obeyed, and the elements will kink along the axis.
b) The volume weighted approach must be used if 2D shell elements are used
in the mesh. Type 14 and 15 elements cannot be mixed in the same calculation.
Sincerely,
James M. Kennedy
KBS2 Inc.
March 6, 2023
From:
ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com]
On Behalf Of Akhil Sreekumar
Sent: Monday, March 06, 2023 12:48 PM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] Negative Sliding Energy in SLEOUT
Hallo Everyone,
I have an interesting topic today for all.
Below i have attached pictures of two bodies impacting each other, and also the contact settings used in this simulation.
No frictional value is given in contacts,
Contact is a unique type, it is established as a self-contact, ie the both parts are in one Slave set., no master part.
I have read that the contact sliding energy should be small compared to the internal energy of a simulation. !
Any ideas if the value shown here wrong or right ?
Wishing all a good day
Akhil
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James Kennedy
Dear Akhil,
Hourglass notes from https://www.dynasupport.com/howtos/element/hourglass
Hourglass types
Stiffness-based HG control (types 4,5) is generally more effective than viscous HG control for structural
parts. Usually, when stiffness-based HG control is invoked, I like to reduce the HG coefficient, usually
in the range of .03 to .05, soas to minimize nonphysical stiffening of the response and at the same time
effectively inhibiting hourglass modes. For high velocity impacts, viscosity-based HG control (types 1,2,3)
is recommended even for solid/structural parts.
Type 8 HG control applies only to shell formulation 16. This HG type activates warping stiffness in type
16 shells so that warping of the element does not degrade the solution. Type 16 shells will solve the so-called
twisted Beam problem correctly if HG type 8 is invoked.
Type 6 HG control invokes an assumed-strain co-rotational formulation for type 1 solid elements and under-
integrated 2D solids (shell types 13 and 15). With the HG type set to 6 and the hourglass coefficient set to
1.0, an elastic part need only be modeled with a single type 1 solid through its thickness to achieve the exact
bending stiffness. Type 6 HG control should always be used for type 1 solids in implicit simulations (in fact,
this is done automatically in v. 970).
The hourglass coefficient for type 6 HG control will typically range from 0.1 (default) to 1.0. For elastic material,
use 1.0. For other materials, the choice of HG coefficient is not obvious. Even looking at results, it may be difficult
to quantify the 'goodness' of the hourglass coefficient used. Too low a value may result in visible hourglass modes
of deformation (unlikely). Too high a value may result in overly stiff behavior. It may be necessary to run the
model twice to see if the results exhibit any sensitivity to the hourglass coefficient. Checking the hourglass energy
is a good idea.
The default hourglass coefficient of 0.1 is superseded by any nonzero value given for QH in *CONTROL_HOUR-
GLASS. I see nothing in the manual to contradict this interpretation. The manual does say that the default hour-
glass type in *HOURGLASS is 1 regardless of what's given in *CONTROL_HOURGLASS. Unless I missed
something, no such note appears with regard to hourglass coefficient. The lesson here is that users should specify
a nonzero hourglass coefficient wherever *HOURGLASS is used. Otherwise, the user may, as you did, inadvert-
ently change the intended coefficient by use of *CONTROL_HOURGLASS.
Sincerely,
James M. Kennedy
KBS2 Inc.
March 6, 2023
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com]
On Behalf Of Akhil Sreekumar
Sent: Monday, March 06, 2023 12:48 PM
To: LS-DYNA2 <ls-d...@googlegroups.com>
Subject: [LS-DYNA2] Negative Sliding Energy in SLEOUT
Hallo Everyone,
--
Akhil Sreekumar
James Kennedy
Dear Akhil,
____________________
What version/revision of LS-DYNA are you using?
-----------------------------------
First and foremost, use the latest version/revision of LS-DYNA available.
______________________
ls-dyna_smp_d_R712_winx64_ifort131.exe (used in presentation below) was built in January, 2015 (over 8 years back)
Balaban, B., and Kurtoglu, I., "An Investigation of AA7075-T651 Plate Perforation Using Different Projectile Nose
Shapes", 10th European LS-DYNA Users Conference, Wurzburg, Germany, May, 2015.
ls-dyna_mpp_d_R713_winx64_ifort131.exe (used in presentation below) was built in June, 2016 (almost 7 years back)
Basaran, G., and Gurses, E., "Numerical Study of High Velocity Impact Response of Vehicle Armor Combination
Using LS-DYNA", 11th European LS-DYNA Users Conference, Salzburg, Austria, May, 2017.
______________________
Sincerely,
James M. Kennedy
KBS2 Inc.
March 6, 2023
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/CH2PR13MB35278030ECAA2341FAF4B63691B69%40CH2PR13MB3527.namprd13.prod.outlook.com.