Gravity loading
Arumugam ce19d044
l...@schwer.net
Perhaps try *LOAD_BODY either with dynamic relaxation or a slow increase in the gravity *DEFINE_CURVE that keeps the kinetic energy less than 10% of the internal energy.
Also see the parameter IALEDR on the keyword *CONTROL_ALE
--len
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James M. Kennedy
Dear Arumugam,
LS-DYNA wave-structure interaction simulation using ALE (standard) and SPH models
------------------
ALE (standard) - Intermediate example presentation
https://www.dynaexamples.com/ale/intermediate-example
Intermediate : Wave-Structure Interaction
A container is partially filled with water subjected to gravity. As the wave propagates, it hits a rigid column placed roughly in the middle of the container.
Roughly 330,000 elements are in the ALE model with a cell discretization of 0.010 meters (m).
The Murnaghan equation of state has become available as a new keyword: *EOS_MURNAGHAN. This equation of state can be used to enforce quasi-static incompressibility while allowing for a reasonable time step in explicit calculations. Any ALE model part is therefore represented by a *MAT_NULL card, describing the density and viscosity of the material, and an *EOS_MURNAGHAN card, describing the pressure-density relationship.
-------------------
SPH - Intermediate example presentation
https://www.dynaexamples.com/sph/intermediate-examples/wavestructure
Intermediate : Wave-Structure Interaction
A container is partially filled with water subjected to gravity. As the wave propagates, it hits a rigid column placed roughly in the middle of the container. The total contact forces are recorded for the entire simulation, and compared to experimental data [1].
[1} Gomez-Gesteira, M., Crespo, A.J.C., Rogers, B.D. Dalrymple, R.A., Dominguez, J.M. and Barreiro, A., “SPHysics - Development of a Free-Surface Fluid Solver - Part 2: Efficiency and Test Cases,” Computers & Geosciences, Vol. 48, pp. 300–307, November, 2012.
https://www.sciencedirect.com/science/article/pii/S0098300412000842
[2] Yreux, E., "Fluid Flow Modeling with SPH in LS-DYNA", 15th International LS-DYNA Users Conference, Dearborn, Michigan, June, 2018.
The Murnaghan equation of state has become available as a new keyword: *EOS_MURNAGHAN. This equation of state can be used to enforce quasi-static incompressibility while allowing for a reasonable time step in explicit calculations. Any SPH model part is therefore represented by a *MAT_NULL card, describing the density and viscosity of the material, and an *EOS_MURNAGHAN card, describing the pressure-density relationship.
-------------------
Sincerely,
James M. Kennedy
KBS2 Inc.
December 24, 2021
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com] On Behalf Of Arumugam ce19d044
Sent: Thursday, December 23, 2021 11:14 PM
To: ls-d...@googlegroups.com
Subject: [LS-DYNA2] Gravity loading
Hi
--
James M. Kennedy
Dear Arumugam,
Some additional notes that may be of interest.
Gravity Load — Welcome to the LS-DYNA support site
Gravity Load
Gravity load is applied via the *LOAD_BODY_Z command (assuming the z-axis is vertical). Preloading due to gravity can be accomplished via a
- dynamic relaxation analysis (explicit or implicit), or
- as a separate implicit analysis, or
- during the early going of an explicit analysis.
To invoke implicit dynamic relaxation with velocity re-initialization,
- set idrflag=5 on *CONTROL_DYNAMIC_RELAXATION, and
- set a nonzero value of DRTERM on *CONTROL_DYNAMIC_RELAXATION, and
- set iphase=1 on *INITIAL_VELOCITY_GENERATION.
This will allow you to apply gravity (or other load) by implicit dynamic relaxation, then specify an initial velocity for your explicit impact analysis. The *CONTROL_IMPLICIT commands can be used to provide control to the implicit dynamic relaxation phase of the run.
(see also: implicit.dynamic_relaxation)
Detail remarks:
There are different approaches to preloading the system with gravity. All involve using the *LOAD_BODY command:
- Use dynamic relaxation to run a precursor, quasi-static analysis wherein gravity is ramped up to preload the structure. This involves defining two curves of acceleration vs. time. For the curve designated in the LCID field of *LOAD_BODY, set (in define_curve) SIDR to 0 and prescribed a constant acceleration vs. time. For the curve designated in the LCIDDR field of *LOAD_BODY, set SIDR to 1 and linearly ramp the acceleration from zero to the constant (gravity) value over a short period of time (say 10 ms) and then hold it constant. A binary record of the dynamic relaxation phase is written when the command *DATABASE_BINARY_D3DRLF is included in the input deck (set DT/CYCL to 1.).
- Invoke mass damping (*DAMPING_GLOBAL) in the early portion of an explicit dynamic analysis to eliminate dynamic oscillations due to the gravity (*LOAD_BODY) load. After a steady state solution is attained, eliminate the damping and introduce the dynamic loads.
If you're unconcerned about the dynamic effects of applying gravity suddenly, you wouldn't need to use dynamic relaxation or damping or even need to ramp the load up over time. Just define the load_body curve as a horizontal line (ordinate value equal to the gravitational acceleration).
Sincerely,
James M. Kennedy
KBS2 Inc.
December 24, 2021
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/01dd01d7f8e4%242d9fac70%2488df0550%24%40kbs2.com.
Arumugam ce19d044
l...@schwer.net
Current User Manual Volume I says:
“IALEDR -- Include ALE computations in the dynamic relaxation analysis
(*CONTROL_DYNAMIC_RELAXATION).”
You are likely using an OLD version of LS-DYNA. --len
James M. Kennedy
Dear Len,
The latest LS-DYNA User’s Manual also has this statement (page 4-1). Probably was not changed when
IALEDR was added (not sure?).
"LS-DYNA Keyword User's Manual - Volume I", LS-DYNA Dev/Revision 14226, Livermore Software
Technology Corporation, Livermore, California, October, 2021..
ALE does not support implicit time integration, nor does it support dynamic relaxation. Furthermore,
except for ALE formulation 5, which does support contact, ALE does not, in general, support contact.
--------------------------------
LS-DYNA R11.0.0 (R11.129956) released
https://www.dynasupport.com/news/ls-dyna-r11-0-0-r11-129956-released-1
*CONTROL_ALE (IALEDR=1, 4th line, 2nd column) and *CONTROL_DYNAMIC_RELAXATION:
Exclude ALE computations if IDRFLG=1 unless IALEDR=1.
Sincerely,
James M. Kennedy
KBS2 Inc.
December 27, 2021.
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com] On Behalf Of l...@schwer.net
Sent: Monday, December 27, 2021 8:17 AM
To: 'Arumugam ce19d044' <ce19...@smail.iitm.ac.in>
Cc: ls-d...@googlegroups.com
Subject: RE: [LS-DYNA2] Gravity loading
Current User Manual Volume I says:
.
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/001801d7fb2c%247b80a440%247281ecc0%24%40schwer.net.
Arumugam ce19d044
James M. Kennedy
Dear Arumugam,
If you are using R10.1, you will be limited as given by this message:
"ALE is not implemented for Dynamic Relaxation phase"
Sincerely,
James M. Kennedy
KBS2 Inc.
December, 28, 2021
To view this discussion on the web visit https://groups.google.com/d/msgid/ls-dyna2/CAG%2BwLY_1gTAx3iShHzaT7trhE5AwWvXZxpDTawpbOz6DSenBTQ%40mail.gmail.com.