FEMAP Basics Tutorial

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FEMAP/Nastran Basics of finite element modelling using beam elements Version10 (Femap/NxNastran) Tapani Halme LUT-Metal

Transcript of FEMAP Basics Tutorial

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FEMAP/Nastran Basics of finite element modelling using beam elements Version10 (Femap/NxNastran) Tapani Halme LUT-Metal

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Some basic functions and defaults: The exteremely important number of Undo –commands ( or familiar Cntrl-Z ) should be set higher than default 15, e.g. maximum of 90 levels. Can be found in File/Preferences –command chain and in Database –sheet:

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FEMAP/Nastran’s basic view:

Pre-processing (i.e.modelling), analysis and post-processing follows finite element basic procedure using pull-down menus:

1. Geometry (points, lines, surfaces etc.) 2. Model (material model, element properties, loading, boundary conditions,

analysis type and solver start) 3. Modify (changes after errors and otherwise) 4. List (numerical listings) 5. Delete 6. View (general pre- and postprocessing graphics options)

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EXAMPLE Model the frame structure shown in picture and solve the statics to obtain displacements and beam bending internal forcest: Material is steel and the web of the profile is in picture plane. Use a = 1000 mm and F = 1000 N. Using Geometry –pull down menu create first the required points (Geometry/Point/Locate). Set origo in the roller point and input the following values (you need to set point at the point load and at the start of the distributed load in the vertical beam) : 1: x = 0 y = 0 z = 0 2: x = 4000 y = 0 z = 0 3: x = 6000 y = 0 z = 0 4: x = 8000 y = 0 z = 0 5: x = 9000 y = 0 z = 0 6: x = 6000 y = 2000 z = 0 7: x = 6000 y = 6000 z = 0 The last pop-up window should be:

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The command continues as default in FEMAP so you have to cancel the command chain when the program thus press Cancel. Select Autoscale from View –pull-down menu (or use Cntrl-A for shortcut) to see all the points in the view:

Create lines between points from Geometry –pull-down menu choosing Curve-Line-Points and giving the end points of a line. The cursor ‘traps’ to the nearest point by default when moving the cursor by mouse (or fill the fields numerically):

The results shold be graphically:

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At this stage only the geometry, i.e. points and lines are created and in the next phase the finite element pre-processing is required to create meshing on the geometry, i.e. create nodes and elements. Before that the material and element property must be defined (Material, Property). Material is created using Model –pull-down menu and choosing Material –function:

Input the material properties, basically elastic modulus and shear modulus (notice Poisson’s ratio from which the program calculates shear modulus, i.e. G = E/[2*(1+ny)] ).

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In this case material density is not required as self weight is not needed in the analysis. The element type and properties are defined in Model –pull-down menus Property -command:

The plate element type is a default in FEMAP so we change the type pressing Elem/Property and setting Beam as element type and choosing the material:

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Then press Shape and choose from menu I-Beam or Wide Flange (W) and input cross-section values:

Pressing OK results (you can give your own name in Title –window):

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Mesh the geometry, i.e. the lines, using Mesh –pull-down menus Mesh Control/Size along curve –command chain:

Set10 elements for the ‘long’ lines:

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and 3 elements for the three shorter lines and only two elements for the sortest line which should result:

Now create nodes and elements using Mesh –pull-down menus Geometry – Curve –command. Choose all horizontal lines, i.e. 1-4 (or curves in FEMAP) and set the property:

The orientation of the element, i.e. y –direction of the profile (local coordinate system in element) is defined by setting a vector in global system:

The default is thus vector which is in the global X –direction. However, we have to change the vector so that the orientation is in the global Y –direction, otherwise the creation of the elements fails.

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Orientation must be (it is irrelevant the value in Y –box, any value which is positive is enough):

The elements in the vertical part of the frame can be formed the same way, only in this case the default value 1,0,0 for the vector tip is valid as then the profile y –vector is parallel to the global Y –vector. Use the Preview –command to graphically check the orientation of the beam. Select from View –pull-down menu Options, and set the element shape on:

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The view can be rotated using View –pull-down menus Rotate –command which gives different possibilities. Other option is to press F8 –button which gives the following options for views:

Select Isometric and press Cntrl-A (autoscale) to fit the model into main window. Tip: you can dynamically rotate the view by pressing mouse’s left button and moving the cursor.

Now check that no coincident or overlapping nodes are in the model. Use Tools –pull-down menus Check - Coincident Nodes –command chain. Choose all nodes:

The external loading is created in Model –pull-down menus Load –command, in which the first function is Set, with which the loading case is defined. Several loading cases can be created for the model but in this example all the loads are set in one load set:

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Create point load choosing from Model/Load –command chain Nodal and pick with cursor the corresponding node. The load is set then in positive Y -direction:

Then create point moment as previously with point load. Notice that Femap uses right-hand rule, i.e. the moment is in the negative Z –direction:

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Select View –pull-down menus Options and set the beam in line format to remove the cross-section to a better graphical representation in loading. The distributed load is set by selecting Load / Elemental. Select by cursor the elements and set the loading:

The loading can be set either in local coordinate system (element own coordinate system) or in global coordinate system. In this case choose global direction:

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Set the distributed load for the vertical component similarly. Notice that the loading is either 2 kN/m or 2 N/mm and the direction is global positive X -direction:

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Next define the boundary conditions using Model –pull-down menus Constraint –command. First set the constraint set:

Then choose Model/Constraint –chain the Nodal –function and pick node 1. All other degrees of freedom are free except the global X –direction. Thus, choose (degree of freedom = DOF) TX:

The highest node in vertical beam is pinned, thus DOF’s TX, TY and TZ are constrained:

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Graphically the constraints are shown as numbers. i.e. 1 = X, 2 = Y etc:

Notice that the boundary conditions do not support the movement in Z –direction and also the rotation about the global X –direction is free. The solution is to constraint these DOF’s in all nodes (notice that the additional constraints are superimposed to the previously constrained DOF’s):

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The analysis type and the solution options are defined in the Model –pull-down menus Analysis –command, from which a new analysis is chosen (New) and then the following fields are filled: title is arbitrary, analysis program (NX Nastran) and analysis type (Static):

choose OK (Next command leads to a selection of parameters but in this case defaults values are sufficient) and then press Analyze -button:

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The solution procedure id shown in the left window:

The Messages shows the general information about solution process. View –pull-down menus Select –function is the most important post-processing option:

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Select from Deformed Style options Deform to show the exaggerated deformations of the structure. Deformed and Contour Data selection gives the following window:

Select Deformation 1..Total Translation and press OK:

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Some graphics options:. Quick Options icon gives window:

Quick Options View Select

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Select All Entities Off and set from Mesh –options Element On results:

Take View/Select –chain and set Beam Diagram option On and press Deformed and Contour Data to choose from Contour:

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The result is beam bending distribution:

Similarly shear distribution:

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and axial force distribution:

The maximum axial stresses are obtained selecting Beam EndA Max Combined stress: