An Introduction to LUSAS ModellerChapter 1 Introduction An Introduction to LUSAS Modeller LUSAS is an associative feature-based Modeller. The model geometry is entered in terms of features which are sub-divided (discretised) into finite elements in order to perform the analysis. Increasing the discretisation of the features will usually result in an increase in accuracy of the solution, but with a corresponding increase in solution time and disk space required. The features in LUSAS form a hierarchy, that is Volumes are comprised of Surfaces, which in turn are made up of Lines or Combined Lines, which are defined by Points. Creating a model A model is a graphical representation consisting of geometric features (points, lines, surfaces, volumes) and assigned attributes (materials, loading, supports, mesh). The geometry is defined using a whole range of tools under the Geometry menu, or the buttons on the Smart define toolbar (and advanced define toolbar). Attributes are defined from the Attributes menu. Once defined attributes are listed in the Treeview . Treeview As your model progresses, it will grow in complexity. The Treeview is used to organise various aspects of your model into a graphical tree frame. It has five panels showing Window Layers , Groups , Attributes , Loadcases and Utilities . The Treeview uses drag and drop functionality. For example, an attribute in the Treeview can be assigned to selected geometry by dragging the attribute onto the model. 1 Chapter 1 Introduction The Shortcut Menu Although all commands can be accessed from the main menu at the top of the LUSAS interface. then choose Properties from the shortcut menu. in fact most objects have properties. Menus Buttons Popup Help Contents Help Treeview Graphics Window Graphics Window Text output Status bar LUSAS Modeller Interface 2 . or a single geometric feature. To view an object’s properties. Properties Many important parts of a LUSAS model are contained within Property dialogs. Properties may relate to the whole model or the current window. pressing the right-hand mouse button with an object selected usually displays a shortcut menu with relevant commands attached. select it with the right mouse button. or certain parts of the LUSAS screen. q Finally. These can be powerful tools in the search of information. Adjoining elements with common nodes will interact. every dialog includes a Help button to answer such questions as What does this mean? Or How do I use this dialog? What is Finite Element Analysis? Until the advent of computers. however. Engineering Problem Finite Element Model Zoom in on individual elements The real engineering problem responds in an infinite number of ways to external forces. q From the Help menu choose Help Topics to browse the full Help files They include the LUSAS User Guide. the only way to find the answer to the engineering question "What would happen if I did this to my new design?" was to build a prototype and carry out the necessary tests. then click on any toolbar button or menu entry (even when greyed out). we must divide the complex shape up into lots of smaller simpler shapes. is not a simple process. These are the finite elements that give the method its name. Today computers allow designs to be assessed much more quickly and easily. The manner in which the Finite Element Model will react is given by the 3 . . q Also from the Help Topics is a comprehensive keyword Index and full text search facility. Since we cannot calculate the response of a complex shape to any external loading. Click on the Help button. The Help consists of the following: q The Help button on the Main toolbar which is used to get contextsensitive help on the LUSAS interface.What is Finite Element Analysis? Getting Help LUSAS contains a comprehensive Help system. reference help files such as the Element Library and Fully Worked Examples to take you through step-by-step FE analyses. The shape of each finite element is defined by the coordinates of its nodes. Evaluating a complex engineering design by exact mathematical models. dat) suitable for processing by LUSAS.and post-processing graphical user interface. LUSAS Finite Element System A complete finite element analysis involves three stages. For a mechanical analysis.). The dataset is then assigned to chosen features. Surfaces and Volumes) and Attributes (Materials. Since we can express the response of a single Finite Element to a known stimulus we can build up a model for the whole structure by assembling all of the simple expressions into a set of simultaneous equations with the degrees of freedom at each node as the unknowns. q LUSAS Solver performs the Finite Element Analysis. Combined Lines. 4 . Lines. For example. Features can be defined by entering coordinates.Chapter 1 Introduction degrees of freedom. For example. a threedimensional solid element has three degrees of freedom at each node representing the three global directions in which it may move. q Assign the Attribute or Attributes. Creating a Model A model is a graphical representation consisting of Geometry (Points. Supports. For a thermal analysis. Loading. q Pre-Processing q Finite Element Solver q Results-Processing The LUSAS Finite Element System consists of two parts to perform a full analysis: q LUSAS Modeller is a fully interactive pre. Each part of the model is created in two steps: q Define the Feature or Attribute. the gradients and fluxes can be calculated from the potentials. once the displacements are known the strains and stresses can be calculated. See Using LUSAS for a quick introduction to the LUSAS interface. etc. selecting Points on the screen or by using utilities such as transformations. then assigning properties. to assign a Point Load (Attribute) to a Point (Feature) representing the corner of a platform. then outputting the information as a formatted data file (. Mesh. An attribute is first defined by creating an attribute dataset. which are expressed at the nodes. Pre-Processing Pre-processing involves creating a geometric representation of the structure. These are then solved using a matrix solution technique. and post-processor for the LUSAS solver.What should I be reading? To complete a model it may be necessary to define additional utilities called control datasets. solves the stiffness matrix. These are used to control the progress of advanced analyses. LUSAS Modeller is the pre. 5 . LUSAS create a data file from the model. Many different ways of viewing results are supported: q q q q q q q q q Contour plots (averaged/smoothed) Contour plots (unaveraged/unsmoothed) Undeformed/Deformed Mesh Plots Wood-Armer Reinforcement Calculations Animated Display of Modes/Load Increments Section Line/Slice Plots Yield Flag Plots Graph Plotting Vector Plots What should I be reading? This section outlines the content of the Manuals comprising the LUSAS Help. Finite Element Solver Once a model has been created click on the solve button to begin the solution stage. The results file will contain some or all of the following data: q q q q q q Stresses Strains Displacements Velocities Accelerations Residuals q q q q q q Reactions Yield flags Potentials Fluxes Gradients Named variables q Combination datasets q Envelope definitions q Fatigue datasets q Strain energy Results-Processing Results-processing involves using a selection of tools for viewing and analysing the results file produced by the Solver. and produces a results file (.mys). LUSAS Modeller User Manual Gives a general overview of the LUSAS program. This manual contains full details of the data syntax supported by LUSAS. Element Reference Manual Contains full element specifications. q Constitutive Material Model formulations. including nodal extrapolation and calculation of Wood-Armer reinforcement moments. q Geometric Nonlinearity. Solver Reference Manual The data files required by the LUSAS solver can be edited directly with a text editor. Theory Manual Contains more detailed theoretical information for the more experienced user. 6 . eigenvalue extraction. The topics covered include: q Analysis procedures including: linear. Worked Examples Contains a step by step guide using fully-featured examples to help you get to grips with the pre. slidelines and thermal surfaces. It covers topics specific to LUSAS and where appropriate lists references to other publications. nonlinear. and a whole range of other useful information is contained in this manual.and post-processing and analysis considerations for a range of different analysis types. q Element formulation theory. General term definitions are supplied in the form of a glossary. Fourier analysis and superelement analysis. constraint equations. dynamics. Glossary General term definitions are supplied in the form of a glossary. all forms of field analysis. Modeller Reference Manual Contains a full reference to the command language used in the LUSAS Modeller. This is the place to go to find out which functionality your elements support and what output you will obtain from your element selection. modal analysis.Chapter 1 Introduction What sort of analysis can I attempt? What elements should I use? What material properties are relevant? This. q More complex post-processing calculations. q Loads and Boundary Conditions with particular reference to general load types. This includes programs such as Excel. As the model is built up areas of the model may be grouped together. The V13 brief was simply to provide the functionality of V12 in a windows format. This enables the user to concentrate on engineering analysis not the software. Upwards Compatibility To enable existing users to upgrade to the new system with the minimum of disruption upwards compatibility between model file formats is maintained. Each window provides a view onto the data so when modifications are made the view is updated in all windows automatically. These groups may be manipulated to speed up data preparation and enable parts of the model to be temporarily hidden. "Tool Tips" provide instant help on any button or command.What's new in Version 13? What's new in Version 13? New Windows User Interface The user interface is built around a consistent theme in which standard windows concepts have been adopted to ensure new users find it familiar and easy to use. The graphical display is controlled using layers. A number of industry standard scripting languages have been implemented which enable data to be imported and exported to any ActiveX compliant program. The interface uses the windows tree views to display a description of data to be visualised. To enable extensive customisation the database objects and groups will be accessible within the scripting language. The existing command line is maintained as far as is possible so old command scripts can be run 7 . Online Help As with all good windows products the on-line help is extensive. Dialog help provides a step by step guide describing how to carry out commonly used operations and a full hypertext help system enable the user to quickly browse the manuals. Access and Word and scripting languages such as Visual Basic Script and Java. full pan and zoom and dynamic rotation. The user interface enables multiple windows to be created to simultaneously display different parts of the model at different orientations. This provides extensive customisation opportunities with tools which are already familiar to engineers. Scripting Scripting is an important component of any system which is to be customised to provide a solution for a particular engineering discipline. Each layers properties provide fine control on the displayed information. The new scripting language will enable customisation of the menus toolbars and it will also have facilities to prompt the user for input via user defined dialogs. All windows enable powerful cursor selection. Slicing Slices may be cut through the model on arbitrary planes. vector and discrete value data. The contour range and vector/diagram scales can be controlled locally in each window or set globally to apply to all windows. Contouring uses either shaded or hidden line contours to display nodal or element based results. Attribute Definition & Assignment Attributes are assigned to the geometry model using "Drag and Drop". These properties allow customisation of the display which is automatic updated. contour. Multiple animations may be displayed simultaneously. Attribute visualisation is enabled via the view properties. Animation sequences may be saved for future use. The results or loadcase on slices can also be changed without the need to redefine the slice. All buttons use icons which may invoke intelligent forms where additional data may be entered. The many display options are controlled via the layers properties. Results Viewing Results are viewed using layers for diagram. Commands can also be typed into the command line dialog. Animation Single loadcase and multiple loadcase animations are now generated by an animation wizard. The animation windows allows interaction with the animation using a set of play buttons similar to a tape player. Loadcases are selected on a window basis so it is possible to have two views each of which are displaying results for different loadcases. 8 .Chapter 1 Introduction with the minimum number of changes. Multiple slices can now be accommodated and made visible or invisible in any particular view. As the attributes are defined they appear in the tree view where they are identified by their title. Assigning the attributes is carried out by simply selecting the required attribute and dropping it onto the current geometry selection. Since all attributes are named by the user a simple database of properties can easily be maintained. Where possible sensible defaults based on the current selection are used. Toolbars with drop down buttons are used extensively to minimise the number of menu picks so the geometry can be built up quickly. Geometry Generation The philosophy adopted in the new user interface is "Select then do". Printing The graphical windows may be printed using the standard windows printer functionality and can operate in either a working mode for building the model or a page layout mode for building results presentations. These graphs can be added to and modified. Fatigue The fatigue response of the model maybe determined in terms of loglife or damage in response to a fatigue load spectrum and an S-N curve. Expose is still available for viewing and converting picture files.wmf) or picture file. Graphing Graphing is carried out using a graphing wizard which guides the user through the steps of several types of results graphs. These features together with the new analysis features for LUSAS 13 are summarised below. Either an IMD loadcase maybe defined to give the response of the whole model to a specified excitation at a particular frequency or time step or alternatively the graphing wizard maybe used to compute the response of a selected node over a range of frequencies or time steps. composite properties can now be assigned to 9 . The grid can be cut and paste into a spreadsheet for further user defined results calculations. Improved Functionality In addition to enhancements to existing facilities a number of new features have been added to the software since the release of LUSAS 12. Interactive Modal Dynamics Results for linear dynamics may be computed from an eigenvalue analysis. Composite Thick Shell and Beam Elements To enable inter-lamina shear to be output from composite shell elements so the composite failure criteria can be used. Picture may also be saved as standard Windows meta files (. The results maybe displayed in textual form in a grid which may also be printed using standard windows printer functionality. The data in the graph is also presented in the form of a grid which can be cut and pasted into a spreadsheet for more extensive graphing presentation capabilities.What's new in Version 13? Combinations and Envelopes Combinations and envelopes of loadcases maybe defined and used in just the same way as standard loadcases. These elements enable composite delaminations to be modelled using an incremental nonlinear analysis. A set of failure criteria have been used to represent fibre and matrix failure. No initial crack is inserted so the interface elements can be placed in the model at potential delamination sites where they will lie dormant until failure occurs. These elements have no geometric properties and are assumed to have no thickness. creep and damage models currently available in LUSAS. To enable the low order beams to be used with composite materials these elements have been modified to accommodate multiple cross section input where each section can have a different materials assignment. Hoffman. This enables the viscoelastic material behaviour to be represented by a viscoelastic shear modulus Gv and a decay constant b. Tsai-Wu (with Cowin extension). The model can be used with the LUSAS solid composite elements. Composite Delamination Both 2D and 3D composite delamination interface elements have been added to LUSAS. Interface elements are embedded into the finite element model and assigned delamination properties using a nonlinear material model. 10 . Viscoelasticity A viscoelastic facility has been implemented which can be coupled with the linear elastic and non-linear plasticity. Composite Matrix Failure Modelling The Hashin composite damage model has been implemented within LUSAS to model matrix/fibre failure in composite materials.Chapter 1 Introduction the low order thick shell elements. If the strength exceeds the strength threshold value in the opening or tearing directions the material properties of the interface element are reduced linearly as defined by the material parameters and complete failure is assumed to have occurred when the fracture energy is exceeded. Composite Failure Criteria Composite failure criteria provide a means of predicting composite failure from the linear stresses distribution. These failure criteria result in a degradation of the Young’s modulus. The element INT6 is for use in 2D analysis and the element INT16 is for use in 3D analysis. Unlike the composite failure criteria this matrix failure modelling models progressive failure using a nonlinear analysis. Eccentricity input has also been added to these element so they can be used with the low order thick beam elements to model ribbed panels. shear modulus and Poisson’s ratio where the damage has occurred. and Hashin (fibre and matrix) composite failure criteria have been added. The model implemented restricts the viscoelastic effects to the deviatoric component of the material response. Within LUSAS the commonly used Tsai-Hill. are permitted at any one time. no crushing is allowed). Neo Hookean and Henky rubber models already available in version 12 have been extended to work with a new large strain formulation. standard section properties and interfacing to Autoloader. This is set to 21 for 3D. The multi crack model assumes that. Each direction defines a possible cracking plane and for each of these planes there is a separate yield surface and set of yield state variables. This model may be used to represent the nonlinear material effects associated with the cracking of concrete. at any one material point. axisymmetric and 3D solid analysis. closest to the principal strain directions. wedges or tetrahedral elements at this stage.What's new in Version 13? Viscoelasticity imposed in this way acts like a spring-damper in parallel with the elastic-plastic. there are a pre defined number of permissible crack directions. 11 . It should be noted that all large strain elements are low order quadrilateral and hexahedral and do not include triangles. 8 for plane stress and 9 for plane strain and axisymmetric. Initial customisations provided by FEA include grillage generation. Pore Water Pressure Modelling High order plain strain elements have been added to LUSAS to model soil consolidation problems. This means rubber is now available for all categories of continuum analysis. Mooney Rivlin. plane strain. Coupling of the viscoelastic and the existing nonlinear material behaviour enables hysteresis effects to be modelled. These elements have both displacement and pressure degrees of freedom which are fully coupled. The transient process of soil consolidation is achieved by carrying out a transient analysis in which a variable time stepping scheme has been adopted. Only 3 active (open or opening) cracks (2 for plane stress). Axisymmetric Rubber Model The Ogden. In the compression-compression region the material is assumed to behave elastically (i. damage and creep response. Concrete Cracking Model A new multiple non orthogonal cracking concrete model has been implemented for plane stress. Customisation The scripting language developed for version 13 provides the user with an extensive opportunity for customisation of the product. prestress load generator in accordance with BS5400.e. These new facilities can be used in conjunction with the existing birth and death facilities to enable problems involving long term excavation and construction in clays to be carried out. More customisations will follow in future versions of the system.