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    • Rahul Ponginan

      Please click here for a short but important announcement   03/26/17

      Dear Users Our Commercial and Academic users around the world can use these same forums here as before i.e. the Altair Support Forum , Commercial users from India with solver queries can go to the Solver Forum for India Commercial Users , Academic Users from India and AOC India Participants are requested to go to the Forum for India Academic Users and AOC India Participants , We will be tending to all queries in all the forums promptly as before, thank you for your understanding. 

Rahul Ponginan

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Everything posted by Rahul Ponginan

  1. how to apply displacements as BCs?

    Hello, I am simulating a three point bending test, and want to apply a displacement of 20 milimeters in the z direction to two nodes in the probe's central line as initial condition. The goal is to check the force needed to obtain such strain. I have tried using SPC and SPCD cards, but all I obtain is an undeformed shape after the simulation. When I use an arbitrary force instead of a displacement, the results come as expected, though. I uploaded the .hm file with BCs and forces and the .hm file with displacement. Thank you in advance Gustavo Blazek
  2. A GUIDE TO solidThinking COMPOSE, eBook

    A GUIDE TO solidThinking COMPOSE for Beginners and Experienced Users
  3. A GUIDE TO solidThinking COMPOSE, eBook
  4. The equation of motion for a static analysis is as below: [K] {X} = {F} ------------------------------------------ (1) [K] --> Global Stiffness Matrix {X} --> Unknown Displacement {F} ---> External Force Applied. For the body to be in static equilibrium, the net force acting at every node must be zero. Therefore, the basic statement of static equilibrium is that the internal forces, I, and the external forces, F, must balance each other: [K] {X} is nothing but internal force 'I' Equation (1) now becomes, ==> I = F or I - F = 0 -----------------------------------(2) In Dynamic Analysis, the imbalance between the external and internal forces results in an acceleration: F - I = M a. F --> External Forces I ---> Internal Force M*a --> Inertial Forces (mass times acceleration) In linear static analysis the stiffness matrix is constant and shall not change/update throughout the analysis. There are many check need to be performed once you have linear static results for well conditioned problems. The equation (1) is decomposed one time to find the unknown displacement. [K] {X} ={F} After decomposition, a singularity may lead to an incorrect solution. In static analysis to obtain {X} (displacements). Using these displacements, One can calculate a “residual” loading vector as follows: [K] {X} -{F} =δ F This residual vector should theoretically be null (equation 2) but may not be null due to numeric roundoff. In Nonlinear static analysis, The stiffness matrix changes in each and every iteration since the stiffness matrix is dependent on the external load. The external load in Nonlinear static analysis is applied in increments and time here has no physical meaning. Time is just a convenient way to apply full load in nonlinear static analysis. In Optistruct the incremental load is controlled by 'NINC' field in the NLPARM card for NLSTAT load steps, this is a fixed load increment method. If you add the PARAM,EXPERTNL,YES to the deck, the time increment method becomes automatic in which case, the increment (load) is increased or cut back based on the convergence rate. NLGEOM loadstep has automatic time step by default. In NLGEOM loadstep the RAMP load curve can be defined using TABLED1 card and then refer this in NLOAD1 card. In nonlinear static analysis, OptiStruct uses the Newton-Raphson method to obtain solutions for nonlinear problems to maintain the residuals close to zero (equation 2) In a nonlinear analysis the solution usually cannot be calculated by solving a single system of equations, as would be done in a linear problem. Instead, the solution is found by applying the specified loads gradually and incrementally working toward the final solution. Therefore, OptiStruct breaks the simulation into a number of load increments (NINC) and finds the approximate equilibrium configuration at the end of each load increment. It is important that you clearly understand the difference between an analysis step (NLSTAT / NLGEOM), a load increment (NINC of NLPARM card), and an iteration (MAXITER of NLPARM card) The load history for a simulation consists of one or more steps. Within a step you will have many no of increments (NINC), within increment there can be many no. of iteration (MAXITER). OptiStruct checks the equilibrium equation ( equation 2) for each and every iteration. If the solution from an iteration is not converged, OptiStruct performs another iteration to try to bring the internal and external forces into balance. An increment is part of a step. An iteration is an attempt at finding an equilibrium solution in an increment when solving with an implicit method. If the model is not in equilibrium at the end of the iteration, OptiStruct tries another iteration. With every iteration the solution OptiStruct obtains should be closer to equilibrium; sometimes OptiStruct may need many iterations to obtain an equilibrium solution. When an equilibrium solution has been obtained, the increment is complete.
  5. The equation of motion for a static analysis is as below: [K] {X} = {F} ------------------------------------------ (1) [K] --> Global Stiffness Matrix {X} --> Unknown Displacement {F} ---> External Force Applied. For the body to be in static equilibrium, the net force acting at every node must be zero. Therefore, the basic statement of static equilibrium is that the internal forces, I, and the external forces, F, must balance each other: [K] {X} is nothing but internal force 'I' Equation (1) now becomes, ==> I = F or I - F = 0 -----------------------------------(2) In Dynamic Analysis, the imbalance between the external and internal forces results in an acceleration: F - I = M a. F --> External Forces I ---> Internal Force M*a --> Inertial Forces (mass times acceleration) In linear static analysis the stiffness matrix is constant and shall not change/update throughout the analysis. There are many check need to be performed once you have linear static results for well conditioned problems. The equation (1) is decomposed one time to find the unknown displacement. [K] {X} ={F} After decomposition, a singularity may lead to an incorrect solution. In static analysis to obtain {X} (displacements). Using these displacements, One can calculate a “residual” loading vector as follows: [K] {X} -{F} =δ F This residual vector should theoretically be null (equation 2) but may not be null due to numeric roundoff. In Nonlinear static analysis, The stiffness matrix changes in each and every iteration since the stiffness matrix is dependent on the external load. The external load in Nonlinear static analysis is applied in increments and time here has no physical meaning. Time is just a convenient way to apply full load in nonlinear static analysis. In Optistruct the incremental load is controlled by 'NINC' field in the NLPARM card for NLSTAT load steps, this is a fixed load increment method. If you add the PARAM,EXPERTNL,YES to the deck, the time increment method becomes automatic in which case, the increment (load) is increased or cut back based on the convergence rate. NLGEOM loadstep has automatic time step by default. In NLGEOM loadstep the RAMP load curve can be defined using TABLED1 card and then refer this in NLOAD1 card. In nonlinear static analysis, OptiStruct uses the Newton-Raphson method to obtain solutions for nonlinear problems to maintain the residuals close to zero (equation 2) In a nonlinear analysis the solution usually cannot be calculated by solving a single system of equations, as would be done in a linear problem. Instead, the solution is found by applying the specified loads gradually and incrementally working toward the final solution. Therefore, OptiStruct breaks the simulation into a number of load increments (NINC) and finds the approximate equilibrium configuration at the end of each load increment. It is important that you clearly understand the difference between an analysis step (NLSTAT / NLGEOM), a load increment (NINC of NLPARM card), and an iteration (MAXITER of NLPARM card) The load history for a simulation consists of one or more steps. Within a step you will have many no of increments (NINC), within increment there can be many no. of iteration (MAXITER). OptiStruct checks the equilibrium equation ( equation 2) for each and every iteration. If the solution from an iteration is not converged, OptiStruct performs another iteration to try to bring the internal and external forces into balance. An increment is part of a step. An iteration is an attempt at finding an equilibrium solution in an increment when solving with an implicit method. If the model is not in equilibrium at the end of the iteration, OptiStruct tries another iteration. With every iteration the solution OptiStruct obtains should be closer to equilibrium; sometimes OptiStruct may need many iterations to obtain an equilibrium solution. When an equilibrium solution has been obtained, the increment is complete.
  6. Optistruct tips and tricks

    Click here for Optistruct tips and tricks
  7. Optistruct tips and tricks

    Click here for Optistruct tips and tricks
  8. set-up of a composite simulation

    Here is a small and quick tutorial about the set-up of a composite simulation from a user. More description is listed on the video. >https://vimeo.com/45792239
  9. set-up of a composite simulation

  10. Common mistakes and errors

    The modeling pitfalls listed below can be considered as “appetizers” with the intention of making you think (and worry) more about the model set-up. More in-depth details regarding the different modeling pitfalls are provided in the remaining chapters of Practical aspects of Finite element simulation ebook. Geometry Simplification In many cases, it is appropriate or even required to simplify the imported geometry in order to achieve a better mesh quality. For instance, the required minimum element size must not be smaller than x millimeters. In order to solve this (project) related requirement, small fillets may be replaced by sharp edges, as shown in the images below. Even though this simplification was/is requested, keep in mind that your FEM model now “deviates” from the initial geometry. Meshing What kind of elements are you using in your model? Why are you using this element type? Did you use this element type before? You may mesh a thin walled 3D structure with 3D elements such as hexahedral or tetrahedral elements, or you may mesh the same structure with respect to its midsurface using 2D elements (trias or quads). aside from the “decision” of whether to use 2D or 3D elements, there are other “uncertainties” (or even errors) related to the different numerical characteristics of quad versus trias and hexahedral versus tetrahedral elements (see the chapters on 2D and 3D meshing). Another modeling error may be related to element size. The ultimate objective or aim is that the modeling results are independent of mesh size. Typically you need to re-run the analysis based on a finer mesh to check for convergence of the simulation results.As a rule of thumb, areas of interest should be meshed finer (smaller element size). Of utmost importance is the element quality. Keep in mind that the elements not only “reflect” the CAD model, but eventually the analysis is based on the finite elements. Hence, any deviation from the ideal element shape (e.g. perfect quadrilateral shape in case of a quad element) introduces numerical errors. The magnitude of such errors is generally difficult to assess. In the model shown below, some elements are not coupled to each other (i.e. duplicated nodes exist), hence the mesh is locally incompatible. The area along the edge where the elements are not coupled is marked in red. Still, the FEM program does not prompt any warning or error messages as this may be an intended model behavior. If the mesh is not intentionally detached (and the model is not checked for free edges), then this model error may remain unknown until the results are fully checked and understood. As shown in the contour plot below, the displacements are not continuous across some parts of the mesh. Also, keep in mind the orientation of the element normals. In the image below, a simple plate subjected to bending is shown. The stress contour plot (at the base of the elements Z1) reveals a sudden change of its sign from bending (positive) to compression (negative). The following figure helps to understand this situation. In the green area, Z1 is located at the top of the plate (tension) while in the blue area Z1 is located at the lower side of the element (compression). Material Inconsistencies in your unit system represent another likely source of error, i.e. mixing millimeters with meters, kilograms with tons, etc. Be especially cautious if you need to convert properties from one system to another (e.g. pound-force lbf to Newton). There will be no warning message associated with any typos, except the “typo” will cause the entire model to “collapse” during analysis. Boundary Conditions And Loads Applying boundary conditions and loads, as discussed in the chapter on Boundary Conditions and Loads, are extremely prone to errors. To be mentioned exemplarily, a modeling error may be introduced into the model by applying the constraints (or forces) to what is named temporary working nodes (in HyperMesh displayed as yellow nodes). As the temporary nodes (yellow nodes in the image above are not the same as finite element nodes, it may happen that the structure is not constrained or loaded as intended. “Ideally”, this may lead to rigid body modes (error message)or to questionable results due to an improperly constrained or loaded model. Visualization When visualizing results, a false sense of achievement that the analyst might experience especially after having struggled with the model, could lower his/her attention regarding details while looking at the results. Quite often, especially while you are new to FEM, one becomes blinded by contour plots. Hence, always check the magnitude of displacements and stresses in the first step. Despite a reasonably looking displacements (or stress) contour plot, you may see displacement values in the order of 104
  11. Common mistakes and errors

    Learn more about this from the FEA eBook http://www.altairuniversity.com/free-ebooks-2/free-ebook-practical-aspects-of-finite-element-simulation-a-study-guide/
  12. Essential Steps To Start With Nonlinear FEA

    Learn more about this from the FEA eBook http://www.altairuniversity.com/free-ebooks-2/free-ebook-practical-aspects-of-finite-element-simulation-a-study-guide/
  13. Essential Steps To Start With Nonlinear FEA
  14. Essential Steps To Start With Nonlinear FEA

    Essential Steps To Start With Nonlinear FEA • Learn first how the software works on a simple model before you use a nonlinear feature which you haven’t used. Also guess how your structural component will behave, i.e. check for available studies, reports and benchmarks . • Try to understand the software’s supporting documentation, its output and warnings. • Know what you are looking for. Prepare a list of questions you think your analysis should be able to answer. Design the analysis, including the model, material model, and boundary conditions, in order to answer the questions you have in mind. • Keep the final model as simple as possible. A linear analysis done first can provide a lot of information such as where are the high stresses in the model, where the initial contact may occur, and what level of load will introduce plasticity in the model. The results of the linear analysis may even point out that there is no need for a nonlinear analysis. Examples of such a situation include the yield limit not being reached, there is no contact, and the displacements are small. • Verify and validate the results of the nonlinear FEA solution. Verification means that “the model is computed correctly” from the numerical point of view. Wrong discretization with respect to the mesh size and time stepping are common errors. Validation asks the questions if “the correct model” is computed e.g. the geometry, material, boundary conditions, interactions etc coincide with the one acting in reality. • Try to look into the assumptions made with respect to the structural component, its geometry behavior with respect to large strain (On/Off), look into different material models if the earlier model is unable to give you a result you expect (sometimes software only make some models compatible with commonly used elements and in this case you might look into a possibility of changing the element formulation). Essential Steps To Start With Nonlinear FEA • Learn first how the software works on a simple model before you use a nonlinear feature which you haven’t used. Also guess how your structural component will behave, i.e. check for available studies, reports and benchmarks . • Try to understand the software’s supporting documentation, its output and warnings. • Know what you are looking for. Prepare a list of questions you think your analysis should be able to answer. Design the analysis, including the model, material model, and boundary conditions, in order to answer the questions you have in mind. • Keep the final model as simple as possible. A linear analysis done first can provide a lot of information such as where are the high stresses in the model, where the initial contact may occur, and what level of load will introduce plasticity in the model. The results of the linear analysis may even point out that there is no need for a nonlinear analysis. Examples of such a situation include the yield limit not being reached, there is no contact, and the displacements are small. • Verify and validate the results of the nonlinear FEA solution. Verification means that “the model is computed correctly” from the numerical point of view. Wrong discretization with respect to the mesh size and time stepping are common errors. Validation asks the questions if “the correct model” is computed e.g. the geometry, material, boundary conditions, interactions etc coincide with the one acting in reality. • Try to look into the assumptions made with respect to the structural component, its geometry behavior with respect to large strain (On/Off), look into different material models if the earlier model is unable to give you a result you expect (sometimes software only make some models compatible with commonly used elements and in this case you might look into a possibility of changing the element formulation).
  15. AcuSolve Training Material

    AcuSolve Introduction Training webinar recording. The recording is useful for any new user to get an overview of AcuSolve workflow. http://www.altairuniversity.com/getting-started/learn-acusolve-training-webinars/
  16. Common Mistakes And Errors

    The modeling pitfalls listed below can be considered as “appetizers” with the intention of making you think (and worry) more about the model set-up. More in-depth details regarding the different modeling pitfalls are provided in the remaining chapters of Practical aspects of Finite element simulation ebook. Geometry Simplification In many cases, it is appropriate or even required to simplify the imported geometry in order to achieve a better mesh quality. For instance, the required minimum element size must not be smaller than x millimeters. In order to solve this (project) related requirement, small fillets may be replaced by sharp edges, as shown in the images below. Even though this simplification was/is requested, keep in mind that your FEM model now “deviates” from the initial geometry. Meshing What kind of elements are you using in your model? Why are you using this element type? Did you use this element type before? You may mesh a thin walled 3D structure with 3D elements such as hexahedral or tetrahedral elements, or you may mesh the same structure with respect to its midsurface using 2D elements (trias or quads). aside from the “decision” of whether to use 2D or 3D elements, there are other “uncertainties” (or even errors) related to the different numerical characteristics of quad versus trias and hexahedral versus tetrahedral elements (see the chapters on 2D and 3D meshing). Another modeling error may be related to element size. The ultimate objective or aim is that the modeling results are independent of mesh size. Typically you need to re-run the analysis based on a finer mesh to check for convergence of the simulation results.As a rule of thumb, areas of interest should be meshed finer (smaller element size). Of utmost importance is the element quality. Keep in mind that the elements not only “reflect” the CAD model, but eventually the analysis is based on the finite elements. Hence, any deviation from the ideal element shape (e.g. perfect quadrilateral shape in case of a quad element) introduces numerical errors. The magnitude of such errors is generally difficult to assess. In the model shown below, some elements are not coupled to each other (i.e. duplicated nodes exist), hence the mesh is locally incompatible. The area along the edge where the elements are not coupled is marked in red. Still, the FEM program does not prompt any warning or error messages as this may be an intended model behavior. If the mesh is not intentionally detached (and the model is not checked for free edges), then this model error may remain unknown until the results are fully checked and understood. As shown in the contour plot below, the displacements are not continuous across some parts of the mesh. Also, keep in mind the orientation of the element normals. In the image below, a simple plate subjected to bending is shown. The stress contour plot (at the base of the elements Z1) reveals a sudden change of its sign from bending (positive) to compression (negative). The following figure helps to understand this situation. In the green area, Z1 is located at the top of the plate (tension) while in the blue area Z1 is located at the lower side of the element (compression). Material Inconsistencies in your unit system represent another likely source of error, i.e. mixing millimeters with meters, kilograms with tons, etc. Be especially cautious if you need to convert properties from one system to another (e.g. pound-force lbf to Newton). There will be no warning message associated with any typos, except the “typo” will cause the entire model to “collapse” during analysis. Boundary Conditions And Loads Applying boundary conditions and loads, as discussed in the chapter on Boundary Conditions and Loads, are extremely prone to errors. To be mentioned exemplarily, a modeling error may be introduced into the model by applying the constraints (or forces) to what is named temporary working nodes (in HyperMesh displayed as yellow nodes). As the temporary nodes (yellow nodes in the image above are not the same as finite element nodes, it may happen that the structure is not constrained or loaded as intended. “Ideally”, this may lead to rigid body modes (error message)or to questionable results due to an improperly constrained or loaded model. Visualization When visualizing results, a false sense of achievement that the analyst might experience especially after having struggled with the model, could lower his/her attention regarding details while looking at the results. Quite often, especially while you are new to FEM, one becomes blinded by contour plots. Hence, always check the magnitude of displacements and stresses in the first step. Despite a reasonably looking displacements (or stress) contour plot, you may see displacement values in the order of 104
  17. Common Mistakes And Errors

    Learn more about this from the FEA eBook http://www.altairuniversity.com/free-ebooks-2/free-ebook-practical-aspects-of-finite-element-simulation-a-study-guide/
  18. "Learn RADIOSS HyperMesh Interface" Videos - By Prashanth AR
  19. "Learn RADIOSS HyperMesh Interface" Videos - By Prashanth AR

    "Learn RADIOSS HyperMesh Interface" Videos - By Prashanth AR
  20. New Feature in HW 2017 – Collision Detection Tool
  21. New Feature in HW 2017 – Collision Detection Tool

    New Feature in HW 2017 – Collision Detection Tool (Click Here) A new feature called ‘Collision Detection ‘is introduced from HyperMesh 2017, which will check components or groups for element penetrations and intersections and we can fix those manually or automatically. Please note that the Collision Detection tool is only available in the RADIOSS and LS-DYNA user profiles. Penetration is defined as the overlap of the material thickness of shell elements, while Intersection is defined as elements that actually pass completely through one another: Any penetrations or intersections in the model can lead to weird model behavior and may also result in run termination. So, it is important and always recommended to fix the penetrations or intersections in the model.
  22. Radioss 2017 Reference Manual Documents, User Guide and Tutorials

    Hello All, Users can download RADIOSS 2017 Reference Guide , RADIOSS 2017 User Guide and RADIOSS 2017 Tutorial files from here. The model files for Student Edition users – accompaniment to the tutorials in Help can be downloaded from: http://www.altairuniversity.com/model-files-for-student-edition-users-accompaniment-to-the-tutorials-in-help/ RADIOSS_2017_Reference_Guide.pdf RADIOSS_2017_Tutorials_and_Examples.pdf RADIOSS_2017_User_Guide.pdf
  23. Explore HyperCrash 2017 New Features

    Altair HyperCrash is a CAE pre-processor developed to support RADIOSS, Altair's non-linear finite element solver. HyperCrash provides a comprehensive environment to study occupant simulations and other requirements of the crash-safety domain. Fully supporting RADIOSS and LS-DYNA solvers, combining the power of an intuitive GUI with an automated set of proven crash and safety modeling procedures, HyperCrash enables users to realize unprecedented time savings while achieving high-quality, accurate results. Learn about the Latest Features on HyperCrash 2017 from http://www.altairuniversity.com/learning-library/hypercrash-new-features/ Also, watch Winter Directed Learning Webinar Series – Crash Analysis with RADIOSS at http://www.altairuniversity.com/learning-library/2017-winter-directed-learning-webinar-series-crash-analysis-with-radioss/ You can also download the HyperCrash 2017 user guide from here: HyperCrash_2017_user_guide.pdf
  24. MotionView Tutorials

    http://www.altairuniversity.com/learning-library/?type=learninglibraryitem&search=&filter_resource_type=&filter_discipline=MBD&filter_language=&filter_source= Click here for MotionView Tutorials in the academic training centre
  25. Can't find MotionView in Student Edition

    After you start HyperWorks Student Edition please click on the client selector marked as “1” in the image below. Then select MotionView from the list. You need to start the solver (MotionSolve) from within MotionView. Please see the attached image.
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