graph tut

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eta/PostGL

GRAPH TUTORIAL

A post-processor compatible with

LS-DYNA/PC

Version 1.0 GL

Release Date: March 1, 1999

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FORWARD

The concepts, methods, and examples presented in this text are for illustrative andeducational purposes only, and are not intended to be exhaustive or to apply to any

particular engineering problem or design.

This material is a compilation of data and figures from many sources.

Engineering Technology Associates, Inc. assumes no liability or responsibility to any

person or company for direct or indirect damages resulting from the use of any

information contained herein.

Engineering Technology Associates, Inc.

1133 E. Maple Rd., Suite 200

Troy, MI 48083-2896

Phone: (248) 729 - 3010

FAX: (248) 729 - 3020

Support: (800) eta - 3362

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Engineering Technology Associates, Inc., eta, the eta logo, eta/PostGL, and the

eta/PostGL PC logo are the registered trademarks of Engineering Technology Associates,

Inc. All other trademarks or names are the property of the respective owners.

Copyright 1999 Engineering Technology Associates, Inc. All rights reserved.

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TABLE OF CONTENTS

Introduction .......................................... ............................................... .................................. 1

Introducing eta/PostGL Graph 1.0....... ..... ...... ..... ..... ...... ..... ..... ...... ...... ..... ..... ...... ..... ..... .... 1

Ease of Use and Compatibility.............................. ............................................... ............. 1

Accuracy................................. .............................................. .......................................... 1

Reliability........................................ .............................................. .................................. 2

About This Guide ............................................. ............................................... ................ 2

Terms and Acronyms Used............... .............................................. ........................................ 3

Background .......................................... .............................................. .................................. 4

Getting Started.............. .............................................. .............................................. ............. 6

Running Graph for the First Time .......................................... ............................................ 6

LS-DYNA Interface ........................................... .............................................. ...............13

LS-DYNA State Data Files................................................................................. .............16

LS-DYNA Time Data Files .......................................... .............................................. .....20

Curve Operations ............................................. .............................................. .................23

Output and Microsoft Compatibility.................................................................................26

Message Systems....................................... ............................................... ......................28

MDI Operations ....................................... ............................................... ........................29

Conclusion ........................................ ............................................... ....................................30

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eta/PostGL Graph Tutorial 1

Introduction

Welcome to PostGL/Graph 1.0, eta's new time-related data processor on Microsoft

Windows platforms, i.e. Windows NT, Windows95, and Windows98. It can process allthe time data from LS-DYNA analysis. It is designed for easy use via its friendly user

interface, it has the state of the art engineering desired data processing capabilities in time

domain, e.g. curve arithmetic, signal filter and transform between time domain and

frequency domain, e.g. FFT.

The object-oriented design makes the PostGL/Graph robust and the versatile data

manipulation allows the data verification easier and post-processing of finite element

analysis more accurate.

Because of the unique file I/O design, the performance is also excellent even on lower-

end PCs and the various outputs allow data transfer and sharing more convenient. Ratherthan focus on one kind of data format, PostGL/Graph uses an external translator to

support virtually all kinds of data formats.

Introducing PostGL/Graph 1.0

As an effective data processing tool for time domain data, PostGL/Graph

represents time domain data as a curve in X-Y coordination curve window. With

the rich curve manipulation functions from PostGL/Graph, data representation is

flexible and visually perceptive. The 2D data representation allows for easier

engineering analysis. The 3D data representations are handled in the PostGL 3D

program from eta and its powerful animation features will give an application

engineer a broader view of the result. Together this package offers an effective

post-processing solution for scientific and engineering data visualization and

analysis.

Ease of Use and Compatibility

The user interface design makes the use of the program easy for both novice and

experienced users. The design follows Microsoft standard windows interface

designing paradigm. Any user with some knowledge of Microsoft programs, e.g.

Microsoft Word, will have an idea as to operating this program. PostGL/Graph

supports all LS-DYNA analysis output.

Accuracy

All the input data files are fully tested by eta QA engineers and the accuracy is

also fully verified. The results from the data processing are also compared with

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other commercial data processing packages and the comparison results are

consistent.

Reliability

The program passed tests on various configured PCs and different program run-time environments, including low memory test, heavy-load test and etc. The error

message system will report current resource shortage under extreme

circumstances and will gracefully abort the current operation.

About This Guide

This guide will help you get started with this program and tell you how to perform

the data analysis. It will also give an introduction on signal processing to help the

novice user gain the required knowledge needed to use this program. Refer to the

Users Manual for more details.

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Terms and Acronyms Used

PostGL An OpenGL-based post processor developed in eta.

PostGL/Graph A companion software of PostGL for time data analysis

developed at eta.FFT Forward Fast Fourier Transform.

IFFT Inverse Fast Fourier Transform.

MDI The Microsoft Multi-Document Interface.

Butterworth Filter An infinite-duration impulse filter of lowpass.

FIR Filter A finite-duration impulse response filter.

Graph Window MDI child windows from the perspective of GUI

interface window.

Curve Window eta defined windows which uses Graph Window as

container and has curve data inside.

FEA Finite element analysis.

LS-DYNA A finite element analysis package developed in LSTC.

Microsoft Graphics Metafile Microsoft defined graphic file format at meta-level of

device independence for graphics informationinterchange.

Microsoft Enhanced Graphics

Metafile

Object linking and embedding (OLE) supported metafile

format from Microsoft. It has more functionality than a

standard metafile.

JPEG (Joint Photographic Expert

Group)

A still image compression standard from International

Standard Organization (ISO).

Bitmapped image An image format simply using bits to store pixel color

information. In contrast to block color information

representation.

PostScript A document program file format from Adobe Systems

Inc. for interchange among different platforms. Its syntax

uses PostFix.

Encapsulated PostScript A standard format for importing and exportingPostScript language files among different documentation

systems, e.g. Latex.

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Background

In this section, an introduction on digital filter is presented, including the filter design,

usage and result interpretation. After the introduction, a brief review on FFT is given. For

further information, please refer to the cited reference. For the advanced user, skip this

section and begin "Getting Started."

There are four different filters implemented in eta PostGL/Graph 1.0, they are:

Average Filter Butterworth Filter Finite Impulse Response (FIR) Filter SAE FilterOne implementation of Discrete Fourier Transform (DFT) and the Fast Fourier Transform

(FFT) is also given. They are the forward FFT and backward FFT to switch the signal

representation between time domain and frequency domain.

We can call any output time data from finite element analysis (FEA) software signals

through this guide. The signals from FEA are in the form of discrete-time sequence via

sampling during the analysis. Usually the signal magnitude varies very much in a short

period of time. The noise disturbance intertwines the signal information and makes the

real signal unclear in the original data. The digital filter will help to eliminate the

disturbance so that the signal characteristics appear more clearly.

Filtering is a process by which the frequency spectrum of a signal can be modified. It can

be manipulated so that the result output signal conforms to some specification, e.g. SAE

Standard. These four filters are commonly required for automobile FEA engineering.

Refer to [1, 2, 3] on the following page for more details.

Neither time-domain analysis nor frequency-domain analysis can exploit the full

characteristics of signals. The combined approach will give an accurate and effective

method on signal analysis. Refer to [4] on the following page for more details. The

forward FFT, which can switch the signal representation from time-domain to frequency-

domain, allows the frequency-domain analysis. After analysis, the frequency data can be

switched back to time-domain via applying backward FFT.

The DFT is a basic operation to transform an ordered sequence of data samples from asignal, usually in a time-domain into the frequency-domain, so that the spectral

information about the signal can be represented explicitly. The FFT is a fast algorithm for

computing the DFT. There are various implementations of FFT when the samples are not

a power of two. The algorithms adopted in this package can deal with both cases, either

the number of samples is a power of two or not. Refer to [5] on the following page for

more details.

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References:

1) A.W.M Van Den Enden et al. Discrete-time Signal Processing, an Introduction,Prentice Hall, 1989.

2) Andreas Antoniou, Digital Filter, Analysis, Design and Application, Second Edition,McGram-Hill, 1993.

3) James V. Candy, Signal Processing: the Model-Based Approach, McGraw-Hill, 1993.4) Edited by Boualem Boashash, Time-Frequency Signal Analysis, Longman Cheshire,

Wiley Halsted Press, 1992.

5) Samuel D. Stearns et al. Signal Processing Algorithms in Fortran and C.

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Getting Started

Running Graph for the First Time

There are several ways to start PostGL/Graph. You can run through command-

line, LS-DYNA system call or Windows Explorer. If you have generated

Graph.gr file, you also can set the file association and activate the program there.

More information regarding a graph file will be given later in this guide. The

graph file from PostGL/Graph is the project output file which contains curve data

and curve window information and other related information. The eta

PostGL/Graph Display windows are shown in Figure 1:

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(Figure 1) eta PostGL/Graph 1.0 Display Windows

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There are several sub-windows:

A graphic display window holds the curve windows. This will occupy most of theprogram.

A dialogue window displays the user feedback or system message like a warningor operation prompts. The initial message is the eta logo and copyrightinformation.

A data input window allows the user to key in inputs for some operations. Theactual data fields vary according to the specific operation requirements.

A menu bar which has only two menu item as "Exit Program" and "Open File". A toolbar is shown to give the user an operation shortcut of two tool buttons. The

actions associated with them are "Open File" and "Exit Program." They are the

same as the corresponding menu items in the menu. If user wants to know theoperation associated with a button, point the mouse on the button for a short

while, the tool-tip will appear to tell the operation. All the buttons in this program

have tool-tip.

The status bar has two fields. One field displays current operation status and theother shows the curve point coordinates along the mouse pointer move after curve

data is loaded.

A Tab window with two Tab items, one is anonymous and the other is the GraphTab. After the curve data are loaded, the current Tab is automatically switched to

the Graph Tab.

Note: The interface layout fits the 1024 x 768 display or higher. However, if

the users PC has a lower resolution or its display is set to lower

resolution, a scrollbar will appear to allow the user to select operations

via scrolling the Tab Window. The bottom message window and data

input window will automatically switch left or right based on the user

operation requirements.

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After user selects the "Open File" operation, a standard file open dialog box will popup as

shown in Figure 2:

(Figure 2) eta PostGL/Graph 1.0 File Open Dialog Box.

There are 7 file formats used for input, as displayed in Figure 2 when the user clicks

"Files of type" selection box:

LS-DYNA Graph All LS-DYNA ASCII format files.

LS-DYNA Time History Data LS-DYNA Time History output files.

LS-DYNA State Data LS-DYNA State output files.

eta DYNA d3plot converted Data eta POSTGL converted LS-DYNA State output

files, e.g. .av file from eta PostGL.

eta List Directed Curve eta List Directed Curve data files.

eta Column Directed Curve eta Column Directed Curve data files.

eta PostGL/Graph Graph eta PostGL/Graph generated graph files.

(Table 1) Types of File for Reading.

After any curve data is read into the program, the interface is switched to a full functional

window as shown in Figure 3:

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The following is additional information:

1. There is always a working curve window with the title bar highlighted in the graphicdisplay window. The GAZ REAR IMPACT ANALYSIS-BASELINE RERUN

curve window in above case is the current working window.

2. The two list boxes in the Graph Tab window are entitled as Loaded Graphs andCorresponding Curves." Loaded Graphs lists the names of the loaded graph window

with the current title highlighted in red and the others in black. Corresponding Curves

lists the curves loaded in the working window. In the above case, there are 12 curves

in the working window and the colors of the curve names in Corresponding Curves

correspond to the curve colors in the working window.

3. When the name is too long and if user leaves mouse pointer on the name for while, atool-tip will tell the whole name of the possibly truncated name in the list boxes. If

the mouse pointer is idle for a while in the blank areas, the tool-tip window will

display either Graph List Box or the working window name based on theunderneath list box.

4. In Curve Operations, there are currently 22 allowed curve operations in twocategories: curve data operation buttons and curve object operation buttons. These

four actions belong to the object operation category: Dup (Curve Duplication), Paste

(Curve Paste), Copy (Curve Paste) and Del (Curve Deletion). All the others are in the

curve data operation category.

5. The button activation depends on the user-specified operations, i.e. unary, binary,multi-curve operation. If only one curve is highlighted in Corresponding Curves, all

the unary curve operation buttons are activated, and if two curves are highlighted, allthe binary curve operation buttons are activated and etc. Only activated button

operations are allowed.

6. There are tool-tips for all the operation buttons, but only when the button is activatedcan the tool-tip appear when mouse pointer is on the button.

7. The right field of the status window will show the curve window coordinates from themouse movement in the curve window. The user can use this feature to query the

point coordinates on the curve.

8. There is a user profile file in the local machines windows system directory, whichsaves all user default setting information like background color and curve highlightcolor. This file is automatically created after the first run of the program. The user

usually need not be aware of this file. However, if there is file name conflicts or

license problem, the user may need to directly edit this file or change conflicted file

name to other names (see also #9). This file name is EtaPost.ini.

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9. Sometimes when the users computer is re-configured or some environment ischanged, the system prompts the user for license information. The user may need to

exit the program, edit the file to remove the authorization information from the file

and key-in the previous assigned license code after the program prompts for it in the

next run. If this does not work, the user may need to request a new license for the

newly configured machine from an eta sales representative.

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LS-DYNA Interface

eta PostGL/Graph offers a convenient interface to LS-DYNA, the industry trusted

FEA software system. It directly supports LS-DYNA outputs and allows its post-

processing. The ASCII time history files, e.g. glstat, ncforc and etc, can be loadedusing the LS-DYNA Graph file type. All standard LS-DYNA ASCII files can be

identified directly from the File/Open dialog box. For example, there is a file and

its name is not one of the pre-assigned LS-DYNA file names, but its format

conforms to the global statistics file format, the user can rename this file name to

glstat and load the renamed glstat. The other way is to read the file, as in the

above example, selecting the file into the program. Next, the program will ask the

user to identify the file format. After checking the file name, the user can either

scroll up and down the dialogue window to select the file type via clicking the

corresponding line or key-in the format index. The index for current version is

shown as follows:

PostGL Graph file 0

List-Directed Curve file 1

Column-Directed Curve file 2

PostGL converted .av file 3

LS-DYNA ASCII glstat file 4

LS-DYNA ASCII matsum file 5

LS-DYNA ASCII nodout file 6

LS-DYNA ASCII nodfor file 7

LS-DYNA ASCII rcforc file 8

LS-DYNA ASCII deforc file 9

LS-DYNA ASCII rwforc file 10LS-DYNA ASCII secforc file 11

LS-DYNA ASCII abstat file 12

LS-DYNA ASCII sleout file 13

LS-DYNA ASCII rbdout file 14

LS-DYNA ASCII jntforc file 15

LS-DYNA ASCII elout file 16

LS-DYNA ASCII swforc file 17

LS-DYNA ASCII sbtout file 18

LS-DYNA ASCII bndout file 19

LS-DYNA ASCII gceout file 20

LS-DYNA ASCII ncforc file 21LS-DYNA ASCII spcforc file 22

LS-DYNA ASCII defgeo file 23

LS-DYNA ASCII tprint file 24

LS-DYNA ASCII ssstat file 25

LS-DYNA state binary file 26

LS-DYNA time binary file 27

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However, there might be new file to add later on. All ASCII format file index will

be added after 25 and binary format file will be added in the end. During the

reading of some files, a program bar will be displayed in the first field of the status

bar and a time interval selection dialog box will pop-up to allow the user to select

an interval to read. An example is illustrated in Figure 4.

(Figure 4) eta PostGL/Graph 1.0 File I/O Time Interval Selection Dialog Box.

In this figure, the data spans from time 0.0 to 2.47E-002. The user selected the

time interval at 4.752E-3 to 1.976E-2. Only information in the selected interval is

read in. The curve maximum and minimum value along X-axis is 4.752E-3 and

1.976E-2, respectively.

For files which have more than one type of information, the users interaction is

required to select an intent type. An example of this case is illustrated in Figure

5. Please be aware of not only the sbtout format file has multiple type data, thereare several others that are similar. Refer the Users Manual for more details.

Note: Some of the variables in the LS-DYNA ASCII files may not be

retrieved like some summary information. The arithmetic curve

operations can compute these variable curves. The Von Mises

(Effective Stress) can be computed using the Von Mises curve

operation, it needs six stress components, i.e. xx stress, yy stress, zz

stress, xy stress, yz stress, zx stress for the computation.

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(Figure 5) eta PostGL/Graph 1.0 Data Type Selection Dialog Box.

In this figure, when the program reads the sbtout file, there are three types of data

available. The dialog box allows the user to retrieve the needed data. The

available data type depends on the data file. Some sbtout file may only contain

seat belt and slip ring and no retractor information. Then the dialog will only list

the first two. Do not expect it will always pop-up a dialog box with the same

number of items in it. In some case if there is only one item in the file sbtout, a

dialog box may not come out at all.

eta PostGL/Graph can directly read in the LS-DYNA state data and LS-DYNA

time data. Although the two types of data format are very similar, the data layout

and file organization is quite different as explained in following subsections.

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LS-DYNA State Data Files

There are usually three types of time data in LS-DYNA state files. They are

global variable data, nodal data and element data. In the global variable data, it

contains global variable information, material information and rigid wall

information. There is coordinate data, velocity data, acceleration data andtemperature data in the nodal data section while some of them may not be present

based on the corresponding flags set elsewhere. There are four kinds of element

types in the element section. The four element types are brick element, brick shell

element, beam element and shell element. Different types of elements have

different variables and for the same element, the number of variables and the

variable types can also change upon the input model, database and analysis type.

Some elements may not present. Tables 2 7 show the possible variable types for

each data type.

Global Data Variable Types

Global variables Kinetic Energy, Internal Energy, Total Energy, X Velocity,

Y Velocity, Z Velocity, External Work.

Material variables Internal Energy, Kinetic Energy, X Velocity, Y Velocity, Z Velocity.

Rigid Wall Force.

(Table 2) LS-DYNA Global Variable Data.

Nodal Data Variable Types

Temperature of Nodal Data (if corresponding flag is set) Temperature.

Coordinate of Nodal Data (if corresponding flag is set) X, Y, Z coordinates.

Velocity of Nodal Data (if corresponding flag is set) X, Y, Z direction velocity.

Acceleration of Nodal Data (if corresponding flag is set) X, Y, Z direction acceleration.

(Table 3) LS-DYNA Nodal Data Variable Types.

Brick Element Data Variable Types

Cauchy Stress Sigma-XX, Sigma-YY, Sigma-ZZ, Sigma-XY,

Sigma-YZ, Sigma-ZX.

Other Effective plastics or material dependent variable.

Extra Variables Run-time dependent variables.

Epsilon Strain Epsilon-XX, Epsilon-YY, Epsilon-ZZ, Epsilon-XY,

Epsilon-YZ, Epsilon-ZX.

(Table 4) LS-DYNA Brick Element Data Variable Types

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Brick Shell Element Data Variable Types

Midsurface Cauchy Stress Sigma-XX, Sigma-YY, Sigma-ZZ,

Sigma-XY, Sigma-YZ, Sigma-ZX.

Midsurface Additional Variables Run-time dependent variables.

Innersurface Cauchy Stress Sigma-XX, Sigma-YY, Sigma-ZZ,


Innersurface Additional Variables Run-time dependent variables.Outersurface Cauchy Stress Sigma-XX, Sigma-YY, Sigma-ZZ,


Outersurface Additional Variables Run-time dependent variables.

Innersurface Strain Epsilon-XX, Epsilon-YY, Epsilon-ZZ,

Epsilon-XY, Epsilon-YZ, Epsilon-ZX.

Outersurface Strain Epsilon-XX, Epsilon-YY, Epsilon-ZZ,

Epsilon-XY, Epsilon-YZ, Epsilon-ZX.

(Table 5) LS-DYNA Brick Shell Element Data Variable Types.

Beam Element Variable Types

Beam elementVariable Types

Axial force, Shear resultant-s,Shear resultant-t, Bending moment-s,

Bending moment-t

Torsional resultant.

(Table 6) LS- DYNA Beam Element Data Variable Types.

Shell Element Data Variable Types

Midsurface Cauchy Stress in global

system

Sigma-XX, Sigma-YY, Sigma-ZZ,

Sigma-XY, Sigma-YZ, Sigma-ZX,

Effective plastic strain or material dependent variables.

Midsurface Additional variables Run-time dependent variables

Innersurface Cauchy Stress in global

system




Innersurface Additional variables Run-time dependent variables

Outersurface Cauchy Stress in global

system




Outersurface Additional variables Run-time dependent variables.

Shell Element Additional variables Run-time dependent variables.

Local ShellCoordinate System Based

Variables

Bending moment-mxx, Bending moment-myy, Bending

moment-mxy, Shear resultant-qxx, Shear resultant-qyy,

Normal resultant-nxx, Normal resultant-nyy, Normal

resultant-nxy, Thickness, Element dependent variables -

1, Element dependent variables 2.

Innersurface Strain in global system eps-xx, eps-yy, eps-zz, eps-xy, eps-yz, eps-zx.

Outersurface Strain in global system eps-xx, eps-yy, eps-zz, eps-xy, eps-yz, eps-zx.

Internal Energy (if corresponding flag

set)

Internal Energy.

(Table 7) LS-DYNA Shell Element Data Variable Types.

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(Figure 6) LS-DYNA State data selection dialog box.

eta PostGL/Graph will prompt the user to select the intent data to retrieve fromthe state files. The dialog box is shown in Figure 6. Only the actual contained

data types will be displayed and the list box items may change depending upon the

project. For example in Figure 6, there is no brick shell element in the d3plot file,

therefore brick shell element is not displayed in the d3plot file.

Note: For adapted meshed LS-DYNA state output, the model geometry

changes along with the progress of the analysis, as is the model

database. However, eta PostGL/Graph element list is based on the

initial database. The elements introduced during the analysis can not

be listed in the element selection dialog. There is a solution for this

situation if the user wants to view the various information concerningthose elements. First rename a mid-step d3plotxx batch file to the

initial file name. Second, move all the preceding files somewhere

else and then read that file as the d3plot start file. The program will

list the intermittent elements for user selection. This method is

illustrated in Figures 7 and 8.

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(Figures 7 and 8) Demonstration of the adapted meshed d3plot files reading of intermittent elements.

The initial state database only has 595 shell elements and the file in step 3 titled

d3plotab has 1171 shell elements. The user can also read any of the intermittentfiles to view the element lists and can easily figure out the element added in some

step.

Note: This program does not process the geometry information and it will

also not represent the time data in 3D form. Those functions can be

found in the PostGL 3D program.

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LS-DYNA Time Data Files

There are two differences between the LS-DYNA state files and LS-DYNA time

files. First, besides of all the time data in state files, there is a new group of data

that can be retrieved from LS-DYNA time data: nodal element data for brick,

brick shell and shell. Second, not all elements and nodes in the database have thetime data information stored. Here only the differences are given, refer to the

above section for the others.

Tables 8 10 give the variables for each element nodal data.

Nodal Brick data Variable Types

Node 1 Coordinate

Node 2 Coordinate

Node 3 Coordinate

Node 4 Coordinate

Node 5 Coordinate

Node 6 Coordinate

Node 7 Coordinate

Node 8 Coordinate

x, y, z coordinates for node 1








Node 1 Velocity

Node 2 Velocity

Node 3 Velocity

Node 4 Velocity

Node 5 Velocity

Node 6 Velocity

Node 7 Velocity

Node 8 Velocity

Velocity for node 1

Velocity for node 2

Velocity for node 3

Velocity for node 4

Velocity for node 5

Velocity for node 6

Velocity for node 7

Velocity for node 8

(Table 8) LS-DYNA Nodal Brick Element Data Variable Types.

Nodal Brick Shell Data Variable Types

Node 1 Coordinate

Node 2 Coordinate

Node 3 Coordinate

Node 4 Coordinate

Node 5 Coordinate

Node 6 Coordinate

Node 7 Coordinate

Node 8 Coordinate









Node 1 Velocity

Node 2 Velocity

Node 3 Velocity

Node 4 VelocityNode 5 Velocity

Node 6 Velocity

Node 7 Velocity

Node 8 Velocity

Velocity for node 1

Velocity for node 2

Velocity for node 3

Velocity for node 4Velocity for node 5

Velocity for node 6

Velocity for node 7

Velocity for node 8

(Table 9) LS-DYNA Nodal Brick Shell Element Data Variable Types.

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Nodal Shell Data Variable Types

Node 1 Coordinate

Node 2 Coordinate

Node 3 Coordinate

Node 4 Coordinate





Node 1 Velocity

Node 2 VelocityNode 3 Velocity

Node 4 Velocity

Velocity for node 1

Velocity for node 2Velocity for node 3

Velocity for node 4

(Table 10) LS-DYNA Nodal Shell Element Data Variable Types.

(Figure 9) Nodal Element Variable Selection Dialog Box.

After the user opens an LS-DYNA time data file, the related information is

retrieved and a variable selection dialog box pops up. Only the elements whose

nodal data information is available are listed in the dialog box. Figure 9 give an

example of variable selection for nodal element data. In this figure, there is only

one brick element and only eight nodes are listed.

As mentioned before, only elements or nodes whose nodal data are exported in

the time data files are available for query. An example on how to select elements

or nodes is illustrated in Figure 10.

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(Figure 10) Node Selection Dialog Box.

In this figure, there are 37 node data put in the time data files. The user can select from

only this list with the combination of its variables for nodal data query.

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Curve Operations

There are 22 operations on curve objects. These operations belong to two

categories: curve data operations and curve object operations. The User's Manual

has more detail information on individual operations. In this guide, some user

interface features and operation usage are listed as follows:

Some curve data operations require the sample frequency and intervals are thesame, e.g. binary arithmetic operations. Some other unary operations require a

minimum number of samples, e.g. Differentiation, Integration and etc. If the

user uses these operations without respecting these requirements. An error

message box will be popped up.

Only activated curve buttons are capable of showing tool tips. Buttonactivation is based on the selection of curves in the curve list box above the

curve operation container. Sometimes, upon user selection, the activation

does not match the selection. This case rarely happens, but it happens, theredraw function can correct this. The redraw function is in the right-mouse

pop-up menu as shown in Figure 11 and can also be found in the View menu.

(Figure 11) Right-mouse pop-up menu.

FFT and IFFT are Forward FFT and Inverse FFT (or Backward FFT). Asmentioned before, FFT changes the data in time domain to frequency domain

and IFFT does the reverse. After a curve is filtered by FFT, the unit on

abscissa will turn into frequency (Hz), while in time domain the unit is time

unit. In eta PostGL/Graph, the curve operation result curve(s) is still put in

the original curve window. The interpretations of different domain data in this

case are difficult. The user can create an empty curve window and copy the

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FFT transformed curve data to this window and delete the transformed curve

in the original window. See Figure 12.

(Figure 12) FFT and its Interpretation.

In this figure, the sig-yy stress from element 62037 was loaded in a curve window.

After applying the FFT filter on this curve, the transformed created curve wascopied to a newly created curve window with the new name, sig-yy #El. 62037

Layer 1 (FFT)." The new curves frequency scales from 0.0 to 9.96E+2. It is

quite clear there is no signal from frequency 2.0E+2 to 8.0E+2.

FFT and IFFT are implemented individually. The IFFT does not simplyrecover the original time domain data for the result of IFFT like other

programs. Therefore, the user can also perform further curve operation like

filtering on data in frequency domain and use the IFFT to inversely transform

back to time domain as shown in Figure 13.

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(Figure 13) Filtered data in frequency domain and transformed back to time domain using IFFT.

The original time domain curve data is filtered using forward FFT, the result

curves and their addition are shown in the right curve window (Curve Addition

(1) is the added curve). In the addition curve in the right curve window, the IFFT

filtered and the result curve is shown as Addition (1) IFFT in red in the left

curve window.

Digital Filtering using eta PostGL/Graph. There are four digital filters asdiscussed earlier. All the filters have the default parameters for convenience.

There are two classes of digital filter, non-recursive and recursive.Butterworth filter is the lowpass recursive filter and the FIR and average filter

are non-recursive filters. The computation is less for FIR filters than that for

Butterworth, but Butterworth gives more power and less signal loss. The step

for digital filter in eta PostGL/Graph works this way. Upon user requirement,

a digital filter is designed, then the curve data in time domain is filtered using

the designed filter and the result curve is shown in the same curve window for

easy comparison. For Butterworth, for example, the user specified parameters

are given in Figure 14:

(Figure 14) Butterworth design parameters input window.

There are four fields, i.e. Passband, Stopband, ripple and attenuation with defaults

for each field.

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Output and Microsoft Compatibility

eta PostGL/Graph interface design uses Microsoft interface design conventions,

the tool-tip features, usage of function keys and so on. Besides these, there are

various image formats from program output which are fully Microsoft compatible.

For printing directly to printer, eta PostGL/Graph does not use bitmap forimage printing, because it may drop down the plot quality. It exploits the

printers own draw capability for high quality plots. Notice that there is a

printer setup menu item in File menu on the menu bar. This option allows user

to specify paper layout and turn on/off printer options, like halftoning on color

printer. The printer setup option also allows the printing job management.

The Print to File function is different from that in lots of other programs. Itsupports 5 different formats as shown in Figure 15. For some formats, specific

tools may be needed to view them.

(Figure 15) Print to File File Save dialog box.

For Microsoft Enhanced Metafile format, there is no view functions exportedinside the file. In order to view and modify this file, metafile editor software is

needed with proper file association set. Refer to Metafile editor software for

more details. A demonstration as to inserting a metafile to Microsoft Word

and modify some picture properties inside Microsoft Word is illustrated in

Figure 16.

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(Figure 16) Demonstration on Metafile modification inside MS-WORD.

Copy to Clipboard is the standard Windows method of transferring databetween a source and a destination. Copy to Clipboard is a system service

shared by the entire Windows session. Using this function from the File menu,

you can copy a graph image directly to other Microsoft programs as a

bitmapped image provided that the destination program supports a bitmapped

image paste.

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Message Systems

eta PostGL/Graph has its own message handling system. Some outstanding

features are listed as follows:

1. If user is inside one operation and tries to execute another operation, either theprogram will yield the previous operation or a message box tells the user thecurrent operation can not be executed due to some unsatisfied precondition.

2. Forced yield capability. This will allow the user to stop some operations insidethe operation process. Using the Stop toolbar button to do this. Not all

functions are able to use this. These operations which may cause

inconsistency of the database must be performed atomically.

3. In case of an improper operation or error, a message box will tell the detailedrunning environment conditions and report the operation abort information

along with other information. This can help trace and diagnose the problemand make support work easier.

4. The global Undo capability can offer further convenient use of this program.All the curve operations and graphic object operations can be undone globally.

Use Undo Last Modification toolbar button to execute this function.

Note: Because of some unchecked synchronization problems, it may

keep asking questions. The user can use the Reset menu item to

reset the message system to pristine status Figure 11 shows the

right mouse pull-down menu with this item and can also be found

in the View menu. However, this case rarely happens.

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MDI OPERATIONS

This general interface design follows MDI paradigm like Microsoft Word. It can

accommodate multi-Graph windows. The following is additional information for

using MDI programs listed as follows:

1. The Windows menu has two groups with one for the graphic display windowoperation and the other showing all current loaded curve windows. The menu

is shown in Figure 17. There are four operations for the menu, i.e. Cascade,

Tile Horizontally, Tile Vertically, Close All. While operation Close All acts

the same as Exit, the other three operations have meaning only when there is

more than one curve window in the graphic display.

(Figure 17) Window menu.

2. In Figure 17, the bottom groups all current loaded curve windows and they areenumerated. The current working window is marked with the check mark. Be

advised that there is always one current working window in any MDIapplication. The user can also select another working curve window via

mouse clicking on that intent curve window name in this menu.

3. The other operations for MDI are the minimization, maximization and deletionin the upper-right corner of each graphic display window. The deletion

operation has same effect as graph deletion operation from menu or toolbar.

4. After the maximization of one graphic display, all the other windows aremaximized automatically. Then the user has to use either the Graph Window

in the Tab Window or the Windows menu to switch among the windows.

Note: If maximizing an empty curve window, it will be hard to turn it

back to normal window, because all the operation is disabled for an

empty graphic display window. There is a solution for this, use the

Windows menu to change it back.

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Conclusion

This concludes the Graph portion of the eta/PostGL Graph tutorial. For more information

about this portion of the program, consult the eta/PostGL Users Manual. For

information regarding the Post portion of this program please consult the eta/PostGL Posttutorial and the Users Manual.

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