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A Short Introduction About LS DYNA and the Input File

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A Short Introduction About LS DYNA and the Input File A Short Introduction to LS DYNA and the Input file LS DYNA • The input file is called Key-file (.key or .k) • A key-file is built up of keywords, which defines the problem • Every keyword starts with * • The Keyword is divided into columns and rows • The format can be written in fixed or free format (Fig. 1) • The keyfile can be edited in LS PrePost or direct in the keyfile with a text editor (e.g. Notepad++) Fig. 1. Example of a Keyword (*NODE) in the fix format (left) and the free format (right). LS DYNA • Important information about the different keywords can be found in LS DYNA Keyword manual. (Example in Fig. 2) Fig. 2. A page from the LS DYNA keyword manual, where you find e.g. information about the purpose of the keyword and what to input to the keyword. Example of a Keyword-file • You can see 8 keywords. • Comments starts with a $ A Fictive Example One the following pages a simple example will illustrate how you build a keyword-file. Let the fictive example be a plate that is constrained in one end and has a force acting vertically in one corner at the other end. How large is the vertical displacement at the free end? Before the problem can be solved in LS DYNA you need to define 1. The Geometry 2. The Material Properties 3. Load and Boundary Conditions The key-file could either be created in LS PrePost or in a text editor, e.g. Notepad++. In this example we will create the key-file in a text editor. On Bilda there is an example of how to create a key-file with LS PrePost. Define Geometry • Defined by nodes and elements. • In this example we will create six nodes and two elements Define Geometry: Nodes • The keyword for nodes is *NODE • You define the node identifier (Node ID) and the coordinates for the node. • You can see in the LS DYNA Keyword manual what to input. *NODE $ NID x y z 1 0.00 0.00 0.00 2 0.01 0.00 0.00 3 0.02 0.00 0.00 4 0.02 0.01 0.00 5 0.01 0.01 0.00 6 0.00 0.01 0.00 Define Geometry: Elements • The keyword for elements is *ELEMENT_{element type}. In this case shell elements are created (*ELEMENT_SHELL). • The node identifier is used to define the elements. *NODE $ NID x y z 1 0.00 0.00 0.00 2 0.01 0.00 0.00 3 0.02 0.00 0.00 4 0.02 0.01 0.00 5 0.01 0.01 0.00 6 0.00 0.01 0.00 *ELEMENT_SHELL $ EID PID N1 N2 N3 N4 1 50 1 2 5 6 2 51 2 3 4 5 Define Properties • The elements that will belong to the same part will be assigned a part identifier in the element keyword. • In this example we have two parts with one element in each. There are two parts in this example since the two elements will have different material properties. *ELEMENT_SHELL $ EID PID N1 N2 N3 N4 1 50 1 2 5 6 2 51 2 3 4 5 *PART $ PID SECID MID 50 50 50 *PART $ PID SECID MID 51 50 51 Define Properties: Material • The material keyword is defined by *MAT_{material model}. In this example two different material model are used *MAT_VISCOELASTIC and *MAT_ELASTIC • In LS DYNA there is around 200 different material models • The material identifier is used in the *PART to defined the material for the part. *PART $ PID SECID MID 50 50 50 *PART $ PID SECID MID 51 50 51 *MATERIAL_VISCOELASTIC $ MID RO BULK G0 GI BETA 50 7.7E3 5E+6 1.43E6 0.5E+6 0.02 *MATERIAL_ELASTIC $ MID RO E PR 51 7.7E3 210E9 0.29 Define Load • With the keyword *LOAD_NODE we can apply the force at one of the corner at the free end. • We define the size of the force with a curve (*DEFINE_CURVE). The values of the x- and y-axis can be scaled within the keyword. The scale factors are SFA (A stands for abscissa (x-axis)) and SFO (O stands for Ordinate (y-axis)). *LOAD_NODE $ NID, DOF, LCID 1, 1, 1 *DEFINE_CURVE $ LCID, SIDR, SFA, SFO F [kN] 1, 0, 1, 1, $ A1, O1 0, 0 1 0.01, 0 0.10, 1000.0 t [ms] 1.00, 1000.0 0 10 100 Define Boundary Conditions • The boundary conditions of a problem can be defined in different ways. One way will be shown here whereas another way will be shown in the Laboratory Assignment. • The boundary conditions for the fixed edge (NID 3 and NID 4) are defined within the node keyword. TC stands for translational constraints and RC stands for rotational constraints. From the LS DYNA Keyword manual: N4 *NODE $ NID x y z TC RC 1 0.00 0.00 0.00 N3 2 0.01 0.00 0.00 3 0.02 0.00 0.00 7 7 4 0.02 0.01 0.00 7 7 5 0.01 0.01 0.00 6 0.00 0.01 0.00 Control and Database • Control keyword cards are used to control the simulation. E.g. to define the length of the simulation (*CONTROL_TERMINATION). The control cards govern the entire model/simulation. • The database keyword cards are to define the printed output from the simulations. E.g. *DATABASE_BINARY_D3PLOT, which defines the printed output for the animation. • It is mandatory for all files to start with *KEYWORD and end with *END. Start a Simulation in LS DYNA • When you have created a keyfile you can run the simulations to get an answer to the question posed in the beginning “How large is the vertical displacement at the free end?” Write the keyword name Press to run • If you want more information about LS DYNA you can read “Getting_Started in the LS DYNA keyword manual. .
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