Define function
med ben rhouma
James M. Kennedy
Dear Med,
The introduction of the ability to couple the engineering model for air blast, *LOAD_BLAST_ENHANCED (LBE), with the Multi-Material Arbitrary Lagrange Eulerian (MM-ALE) solver, Slavik [2009], offer several advantages over the use of either technique for air blast simulations. In this brief look at LBE and MM-ALE coupling, the LS-DYNA required keywords are explained and some of the key parameters are investigated using simple examples. Based on these simple examples some recommendations for LBE and MM-ALE are provided:
Schwer, L.E., "A Brief Introduction to Coupling Load Blast Enhanced with Multi-Material ALE: The Best of Both Worlds for Air Blast Simulation", 9th German LS-DYNA Forum, Bamberg, Germany, October, 2010.
http://www.dynamore.de/dokumente/papers-1/2010-deutsches-forum/papers/J-I-01.pdf
A short tutorial on blast loading which included empirical pressure loads applied directly to nodes of a Lagrangian structure - *LOAD_BLAST_ENHANCED (LBE), a Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) method; and *LOAD_BLAST_ ENHANCED coupled with the Multi-Material Arbitrary Lagrange Eulerian (MM-ALE):
Slavik, T.P., "Blast Loading in LS-DYNA", Livermore Software Technology Corporation, Livermore, California, May, 2012.
http://ftp.lstc.com/anonymous/outgoing/support/PRESENTATIONS/blast_slavik_ucsd.pdf
The pressure histories from the vertical array measurements provided an opportunity to assess the accuracy of the LS-DYNA air blast engineering model referred to as *LOAD_BLAST_ENHANCED, and results from simulations using the LS-DYNA Eulerian solver usually referred to as Multi-Material Lagrangian Eulerian (MM-ALE). In addition to comparisons of maximum pressure, and time-of-arrival (TOA), the time integrated pressure histories provided maximum impulses for comparison:
Schwer, L., "Assessment of Mach Stem Pressures: Comparison of Experiments with Engineering and Eulerian Models", 9th European LS-DYNA Users Conference, Manchester, United Kingdom, May, 2013.
The Unified Facilities Criteria 3-340-02 provides blast wave reflection ratios as a function of angle-of-incidence. In an effort to assess the UFC information, comparisons were made with two different sets of small scale experiments and LS-DYNA Eulerian simulation results. Of interest to LS-DYNA users, the comparisons presented also included the simple analytical expression for reflection ratios as a function of angle-of-incident proposed by Randers-Pehrson and Banister, and used in the LS-DYNA algorithm *LOAD_BLAST_ENHANCED:
Schwer, L.E., "Air Blast Reflection Ratios and Angle of Incidence", 11th European LS-DYNA Users Conference, Salzburg, Austria, May, 2017.
When simulating structures subjected to the effects of blast loading, one might resort to three different methods of simulation. These methods are the empirical blast method, also known as *LOAD_BLAST_ENHANCED (LBE), the Arbitrary Lagrangian Eulerian (ALE) method, and a coupling method that allows the application of empirical blast loads (LBE) on air domain simulated with the ALE formulation. Furthermore, for the ALE method, both a mapping technique, that allows the mapping of data from 2D ALE simulations to 2D and 3D ALE meshes, and a complete 3D ALE simulation could be performed. In order to verify and compare the efficiency and accuracy of these air blast methods, an air blast loading on a reinforced concrete slab was modelled. Additionally, mesh convergence studies of 2D and 3D ALE simulations were performed:
Rebelo, H.B., and Cismasiu, C., "A Comparison between Three Air Blast Simulation Techniques in LS-DYNA", 11th European LS-DYNA Users Conference, Salzburg, Austria, May, 2017.
Sincerely,
James M. Kennedy
KBS2 Inc.
September 24, 2022
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James M. Kennedy
Dear Med,
http://ftp.lstc.com/anonymous/outgoing/jday/manuals/DRAFT_Vol_I.pdf
*DEFINE_FUNCTION
Purpose: Define a function that can be referenced by a limited number of keyword
options. The function arguments are different for each keyword that references
*DEFINE_FUNCTION. Unless stated otherwise, all the listed argument(s) in their
correct order must be included in the argument list. Some usages of *DEFINE_
FUNCTION allow random ordering of arguments and argument dropouts. See the
Individual keywords for the correct format. Some examples are shown below.
FID - Function ID. Functions, tables (see *DEFINE_TABLE), and load curves may
not share common IDs. A unique number must be defined.
FUNCTION - Arithmetic expression involving a combination of independent variables
and other functions, that is,“f(a,b,c)=a*2+b*c+sqrt(a*c),” where a, b, and c are the
independent variables. The function name, “f(a,b,c),” must be VARIABLE DESCRIPTION
unique since other functions can then use and reference this function. For example,
“g(a,b,c,d)=f(a,b,c)**2+d.” In this example, two *DEFINE_FUNCTION definitions
are needed to define functions f and g.
*comment
units: mks
Apply a hydrostatic pressure ramped up over a finite time = trise.
pressure on segment = rho * grav * depth of water
where depth of water is refy - y-coordinate of segment
and refy is the y-coordinate of the water surface
*DEFINE_FUNCTION
$# fid
10
$# function
float hpres(float t, float x, float y, float z, float x0, float y0,
float z0)
{
float fac, trise, refy, rho, grav;
trise = 0.1; refy = 0.5; rho = 1000.; grav = 9.81;
fac = 1.0;
if(t<=trise) fac = t/trise;
return fac*rho*grav*(refy-y);
}
*LOAD_SEGMENT_SET
1,10
The input description of *LOAD_SEGMENT_SET
*LOAD_SEGMENT_SET
Purpose: Apply the distributed pressure load over each segment in a segment set. See
*LOAD_SEGMENT for a description of the pressure sign convention and remarks on
higher order segment definitions.
LCID - Load curve ID (see *DEFINE_CURVE) or function ID (see *DEFINE_
FUNCTION). For a load curve ID the load curve must provide pressure as a function
of time. For a function ID the function is expected to have seven arguments: current
time minus the birth time, the current 𝑥, 𝑦, and 𝑧 coordinates, and the initial 𝑥, 𝑦, and
𝑧 coordinates.
----------------------------------------
I found some other notes which used the following programming:
*DEFINE_FUNCTION
10
float hpres(float t, float x, float y, float z, float x0, float y0,
float z0)
{
float fac, trise, refy, rho, grav, p;
trise=0.10; refy=0.5; rho=1000.; grav=9.81;
fac=1.0;
if(t<=trise) fac=t/trise;
p=fac*rho*grav*(refy-y);
return (p);
}
Example 2 illustrates that a programming language resembling C can be used to define
a function. Before a variable or function is used, its type must be declared. For example,
variable 𝑡 is real, so it has “float” preceding it in the function declaration. The braces
indicate the beginning and end of the function being programmed. Semicolons must
appear after each statement but several statements may appear on a single line. Please
refer to a C programming guide for more detailed information.
----------------------------------------
Sincerely,
James M. Kennedy
KBS2 Inc.
September 24, 2022
From: ls-d...@googlegroups.com [mailto:ls-d...@googlegroups.com] On Behalf Of med ben rhouma
Sent: Saturday, September 24, 2022 1:12 AM
To: ls-d...@googlegroups.com
Subject: [LS-DYNA2] Define function
Dear all
--
med ben rhouma
l...@schwer.net
2-Did anyone have a clue on how *LOAD_BLAST_ENHANCED is introduced in LS-DYNA?
Briefly, knowing the segment nodes, LS-DYNA computes the centroid of the segment. Then given the location of the bomb, the range and angle of incidence to the segment are determined. Lastly, the range is used in formula of pressure (incident or reflected) versus range, to determine the applied loading.
--len
From: ls-d...@googlegroups.com <ls-d...@googlegroups.com> On Behalf Of med ben rhouma
Sent: Friday, September 23, 2022 11:12 PM
To: ls-d...@googlegroups.com
Subject: [LS-DYNA2] Define function
Dear all
--
James Kennedy
Dear Med Ben,
Perhaps of some interest:
An empirically-based model for buried mine blast loading via the keyword *INITIAL_IMPULSE_MINE has been incorporated into LS-DYNA. This is an engineering model based upon experimental results, much like the air blast engineering model provided by *LOAD_BLAST_ENHNACED. Buried charge experiments by SwRI, Anderson et al. [2011], were used as validation. Comparisons were made with both the *INITIAL_IMPULSE_MINE engineering model and the detailed coupled 3D MM-ALE simulations. It is believed that this engineering model of buried charge impulse will be very effective in reducing CPU time during the initial stages of structures subject to land mine and IED explosions:
Schwer, L., and Slavik, T., "Buried Charge Engineering Model: Verification and Validation", 9th European LS-DYNA Users Conference, Manchester, United Kingdom, May, 2013.
A short tutorial on blast loading which included empirical pressure loads applied directly to nodes of a Lagrangian structure - *LOAD_BLAST_ENHANCED (LBE), a Multi-Material Arbitrary Lagrangian Eulerian (MM-ALE) method; and *LOAD_BLAST_ ENHANCED coupled with the Multi-Material Arbitrary Lagrange Eulerian (MM-ALE):
Slavik, T.P., "Blast Loading in LS-DYNA", Livermore Software Technology Corporation, Livermore, California, May, 2012.
http://ftp.lstc.com/anonymous/outgoing/support/PRESENTATIONS/blast_slavik_ucsd.pdf
A coupling method recently implemented in LS-DYNA allows empirical explosive blast loads to be applied to air domains treated with the multi-material arbitrary Lagrangian-Eulerian (MM-ALE) formulation. The new method presented here obviates modeling the explosive and air leading up the structure. Instead, only the air immediately surrounding the Lagrangian structures need be modeled with ALE, while effects of the far-field blast were applied to the outer face of that ALE air domain with the empirical blast equations:
Slavik, T.P., "A Coupling of Empirical Explosive Blast Loads to ALE Air Domains in LS-DYNA", IOP Conference Series: Materials Science and Engineering, Vol. 10, No. 1, 2010, 9th World Congress on Computational Mechanics and 4th Asian Pacific Congress on Computational Mechanics, Sydney, Australia, July, 2010.
http://iopscience.iop.org/1757-899X/10/1/012146/pdf/1757-899X_10_1_012146.pdf
Slavik, T.P., "A Coupling of Empirical Explosive Blast Loads to ALE Air Domains in LS-DYNA", 7th European LS-DYNA User's Conference, Salzburg, Austria, May, 2009.
Sincerely,
James M. Kennedy
KBS2 Inc.
September 20, 2023
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