1. PAT328, Section 3, March 2001S4-1MAR120, Section 4, December 2001 SECTION 4 ANALYSIS SETUP

2. PAT328, Section 3, March 2001S4-2MAR120, Section 4, December 2001 TABLE OF CONTENTS SectionPage 4.0 Analysis Setup Overview……………………………………………………………………………………………………………..4-3 The Analysis Form………………………………………………………………………………………………….4-4 The Analysis Form Five Available Actions……………………………………………………………………….4-5 The Analysis Form Three Available Objects……………………………………………………………………..4-6 The Analysis Form Three Available Methods……………………………………………………………………4-7 The Analysis Form Setting Up Jobs………………………………………………………………………………4-8 Step Creation / Analysis Procedure Selection Structural Type………………………………………………..4-9 Step Creation / Analysis Procedure Selection Thermal Type………………………………………………….4-10 Step Creation / Analysis Procedure Selection Coupled Type………………………………………………….4-11 The Newton Raphson Algorithm…………………………………………………………………………………..4-12 Arc-length Algorithms………………………………………………………………………………………………4-15 Time Scales………………………………………………………………………………………………………….4-19 Time Scales/automatic Time Incrementation…………………………………………………………………….4-22 Time Scales/solution Parameters…………………………………………………………………………………4-23 Solution Parameters / Read Temperature File………………………………………………………………….4-24 Selecting Load Cases For A Step…………………………………………………………………………………4-25 Requesting Output For A Step…………………………………………………………………………………….4-26

3. PAT328, Section 3, March 2001S4-3MAR120, Section 4, December 2001 How to setup and run an analysis  The Analysis Form in Detail  Concept of Step  Concept of Time Scales Using Subordinate Forms  Step Create Form Solution Type and Solution Parameters Selecting Load Cases and Requesting Output Setting Up and Using Different Jobs Changing the Type of Analysis The Newton-Raphson Algorithm Arc Length Algorithms OVERVIEW

4. PAT328, Section 3, March 2001S4-4MAR120, Section 4, December 2001 Analyzing the Entire Model Vs. Analyzing the Current Group (create appropriate load cases for each model) Analysis of Structural Type Vs. Analysis of Thermal Type (implemented in MSC.Patran 2001 Marc Preference Pop-up Object Menu Preferences/Analysis Form lets change Code & Type Database may have defined different codes & types You select the job to be performed Subordinate forms control the job(s) The analysis is performed when you Apply You give a name to a job THE ANALYSIS FORM

5. PAT328, Section 3, March 2001S4-5MAR120, Section 4, December 2001 Analyze  Setting up and launching analysis or creating input decks for MSC.Marc. Read Results  Import model or/and results from MSC.Marc output (“Post”) file.  Attach tool allows accessing results without actually importing them into the MSC.Patran database. Read Input File  Allows importing an existing MSC.Marc input deck into an MSC.Patran database. Delete and Monitor  Allows deleting jobs or result file attachments. Monitor  Allows monitoring of the MSC.Marc job while it runs. THE ANALYSIS FORM FIVE AVAILABLE ACTIONS

6. PAT328, Section 3, March 2001S4-6MAR120, Section 4, December 2001 Entire Model  All FEM entities (even the orphan ones –those belonging to no group) and some geometric entities existing in the database will be used. Concurrent Group  Only entities belonging to the current group will be used. This allows local or partial modeling –with appropriate load cases. Analysis Deck  MSC.Patran will launch (if installation allows it) an MSC.Marc analysis using the existing input deck for the selected jobname. THE ANALYSIS FORM THREE AVAILABLE OBJECTS

7. PAT328, Section 3, March 2001S4-7MAR120, Section 4, December 2001 Check Run Method(Model run)  The input for MSC.Marc as created by MSC.Patran is scrutinized for consistency.  A report is written into file jobname.msg Full Run Method (Model & History Run  The check run is done and if there are no fatal errors, the steps are executed in sequence. Analysis Deck  The MSC.Marc deck is created but no MSC.Marc job is launched. THE ANALYSIS FORM THREE AVAILABLE METHODS

8. PAT328, Section 3, March 2001S4-8MAR120, Section 4, December 2001 A “Job” may actually consist of a sequence of different analysis procedures, each called a “Load Step” (For example, a buckling analysis may follow a nonlinear static analysis in a single “Job”), loading, and different output requests. Steps are created in the “Load Step Creation” subordinate form. A sequence of “Steps” controls the sequence of analysis and loading. This sequence is defined in the “Load Step Selection” subordinate form. A job may be “Restarted” Different Steps may have different Load Cases (including Boundary Conditions) A step may have only one Solution Type THE ANALYSIS FORM SETTING UP JOBS

9. PAT328, Section 3, March 2001S4-9MAR120, Section 4, December 2001 A step may include only one of the 14 available analysis procedures in the form The “Default Static Step” is a Linear Static procedure. You may modify it, but you cannot change its name, and you may not delete it from the database. You don’t have to use it, though. Enter a meaningful job step name and select the solution type that best suits your problem. You may create as many as you want and later use all or some of them in any order you want. If no change has been made to the default MSC.Patran setup, just clicking Apply will make a full run of the default (linear) static step This is the default Analysis Type in the MSC.Patran Marc Preference. Each step has its own collection of:  Load Cases  Solution Parameters  Output Requests STEP CREATION / ANALYSIS PROCEDURE SELECTION STRUCTURAL TYPE

10. PAT328, Section 3, March 2001S4-10MAR120, Section 4, December 2001 Notice that changing the Analysis Type to thermal allows you to create a “Temperature initial Condition” set in the Loads/BCs form that you may later use in a structural type of analysis. STEP CREATION / ANALYSIS PROCEDURE SELECTION THERMAL TYPE (ALREADY IMPLEMENTED IN MSC.PATRAN 2001 MARC PREFERENCE)

11. PAT328, Section 3, March 2001S4-11MAR120, Section 4, December 2001 Notice that changing the Analysis Type to thermal allows you to create a “Temperature initial Condition” set in the Loads/BCs form that you may later use in a structural type of analysis. STEP CREATION / ANALYSIS PROCEDURE SELECTION COUPLED TYPE (EXPECTED TO BE IMPLEMENTED IN MSC.PATRAN 2002 MARC PREFERENCE)

12. PAT328, Section 3, March 2001S4-12MAR120, Section 4, December 2001 The basic statement is that of equilibrium or balance between internal forces { I } and external forces { P }  Static Equilibrium  Dynamic Equilibrium  Objective Function Before equilibrium is attained, The method fully includes nonlinear terms in equations It has a quadratic rate of convergence It is an incremental-iterative solution and solves equations efficiently Experience shows that the Newton-Raphson method is less likely to converge to an unstable configuration than to a stable one THE NEWTON RAPHSON ALGORITHM InertialDissipativeStiffness

13. PAT328, Section 3, March 2001S4-13MAR120, Section 4, December 2001 Taylor Series about estimate yields: Define Tangent Matrix: Drop quadratic term & compute correction Stop iterations when { F } is small enough THE NEWTON RAPHSON ALGORITHM (CONT.) + One-dimensional example

14. PAT328, Section 3, March 2001S4-14MAR120, Section 4, December 2001 The structure may be unable to generate the total internal {I} forces to balance the load {P} forces: Mathematically, the Jacobian is nil(1D: Tangent is zero!) Physically it corresponds to a state of unstable equilibrium This corresponds to a local minimum of energy. The slightest perturbation will unleash the exceeding energy. The bearable load is less than the objective load THE NEWTON RAPHSON ALGORITHM (CONT.)

15. PAT328, Section 3, March 2001S4-15MAR120, Section 4, December 2001 These algorithms solve simultaneously for loads and displacements in a nonlinear static analysis  The concept was introduced by Edward Riks I the early 1970’s  Two parameters are utilized The “arc-length” which measures the change in the solution and The “load proportionality factor” which reports the magnitude of the load as the structure deforms  The absence of “time” makes it impossible to use rate effects such as damping  The arc-length method such as the Riks method computes the bearable load but in general works well only near unstable conditions.  MSC.Marc offers several arc-length methods, all of them supported by MSC.Patran. ARC-LENGTH ALGORITHMS

16. PAT328, Section 3, March 2001S4-16MAR120, Section 4, December 2001 As shown in the Figure, assume that the solution is known at point A for load level. For arriving at point B on the equilibrium curve, you either reduce the step size or adapt the load level in the iteration process. To achieve this end, the equilibrium equations are augmented with a constraint equation expressed typically as the norm of incremental arc lengths. Hence, this allows the load level and the displacement to change from iteration to iteration until equilibrium is found. ARC-LENGTH ALGORITHMS (CONT.) The “arc length”, D l, is a Euclidean norm in the space of scaled displacements and loads as illustrated. The “load proportionality factor”,, allows the load to be computed as P N = P 0 N + P N where P 0 N is the dead load and P N is a nominal load vector The method works well if the equilibrium path in the load displacement space is smooth and does not branch. Otherwise, convergence and incrementation problems my occur.

17. PAT328, Section 3, March 2001S4-17MAR120, Section 4, December 2001 ARC-LENGTH ALGORITHMS (CONT.) Generally, this means that the method should always be applied to imperfect geometries, which basically converts a pure bifurcation behavior into a snap-through problem. Classic snap-through problems are characterized by a smooth load- displacement curve and do not exhibit bifurcation (branching) As a result, arc-length procedures solve this kind of problem easily Example: Typical Load versus displacement plot exhibiting buckling. This structure reaches a new stable configuration that permits it to later increase the loading past the original critical load. Critical Load Pcr

18. PAT328, Section 3, March 2001S4-18MAR120, Section 4, December 2001 Arc-length methods are not only useful for unstable cases. It can also speed up convergence in ill-conditioned problems that do not exhibit instability The response will grow quickly near the critical load if the imperfection is too small The method allows the analysis of a buckling problem as a problem with a continuous response instead of bifurcation, beginning with enforcing an initial imperfection in the shape of the buckling mode ARC-LENGTH ALGORITHMS (CONT.) Run a Bifurcation Buckling procedure to determine the maximum load bearable by the system Repeat the general analysis with a “dead” load of about 90% of the bearable load. Continue the analysis switching to the Riks method and applying the originally intended “reference” load General advise on using an arc length method:

19. PAT328, Section 3, March 2001S4-19MAR120, Section 4, December 2001 Time incrementation is (preferable) automatically controlled. Time, whether physically meaningful or not (static procedures), provides a scale over which a “history” of events is described. For any automatic load incrementation, care must be taken to approriately define the loading history in each loadcase. The load case should be defined between appropriate break points in the load history curve. For the example of the figures,  Correct results would be obtained upon defining three distinct loadcases between times 0, t1, t2, and t3 during the model preparation. However, if only one load case is defined for the entire load history between 0 and t3, the the total applied load for the loadcase is zero. TIME SCALES

20. PAT328, Section 3, March 2001S4-20MAR120, Section 4, December 2001 STEP  ATTEMPT  INCREMENT  ITERATION Step  It marks the overall history dependence of computing events  A Step includes one and only one Attempt  If the solution does not converge the increments is restarted and the iteration count is reset.  Sometimes the algorithm makes several attempts at finding the solution. (Each time it tries a smaller time increment) Increment  In static analysis, represents a load increment  In time-dependent analysis, represents the actual passage of time as meaningful to the problem being simulated  The magnitude of the increment is controlled by the algorithm in use. Often this is the Newton-Raphson method under requirements of a certain “radius of convergence” that obeys a number of accuracy and efficiency requirements TIME SCALES (CONT.)

21. PAT328, Section 3, March 2001S4-21MAR120, Section 4, December 2001 TIME SCALES (CONT) Iteration  These are the actual Newton- Raphson’s (or other algorithm’s) successive approximations to the solution  Each iteration produces a correction of the solution until the equilibrium is achieved (convergence) or the algorithm senses equilibrium cannot be achieved for the current time increment. Status File  MSC.Marc writes job status information in the file jobname.sts which can be accessed in the Analysis form with the Monitor action.  Steps are reported as cases and iterations are reported as cycles. At the end of the job the file includes an exit number which in the example below indicates that the minimum time step increment allowed was reached.

22. PAT328, Section 3, March 2001S4-22MAR120, Section 4, December 2001 The automatic time incrementation does the job for you but you have to give it a start by providing an initial time increment, a total time for the step and sometimes, a few other quantities depending on the procedure and problem Heuristic algorithm controls the accuracy of time integration Called “Adaptive” in MSC.Patran’s Load Increment Parameters form. Analogous to automatic mesh refinement but you refine the time discretization or the load incrementation instead of space. TIME SCALES/AUTOMATIC TIME INCREMENTATION.

23. PAT328, Section 3, March 2001S4-23MAR120, Section 4, December 2001 You have some control of the time scales under the “Load Increment Parameters” subordinate form  The data required depends upon the type of analysis run by the step (The form looks and behaves somewhat differently for each procedure type)  Setting these parameters is essential to the step creation  Since you may have more than one step using the same procedure but each step has its own name, you may have different parameters for similar steps  Automatic time is optional, but highly recommended TIME SCALES/SOLUTION PARAMETERS If Several Job Steps are selected, the total time of each step will be accumulated in the selected sequence (from top to bottom in the “Selected Job Step” panel above.)

24. PAT328, Section 3, March 2001S4-24MAR120, Section 4, December 2001 The Temperature Results File Input form for a Nonlinear Dynamic Transient step or for a Nonlinear Static step..  It uses the thermal_job.t16 results file from a previous thermal analysis job  The results file format may be BINARY or ASCII  MSC.MARC will linearly interpolate temperature values according to the total simulation time. SOLUTION PARAMETERS / READ TEMPERATURE FILE

25. PAT328, Section 3, March 2001S4-25MAR120, Section 4, December 2001 Creating a step includes selecting load cases Select the load case corresponding to the load step. Remember: the load case includes loads and boundary conditions Keep in mind that you are specifying total load, not incremental load. That is, select all load cases that belong to the step, even those you already used in the previous general step. Only those cases that are highlighted will be included in the step SELECTING LOAD CASES FOR A STEP

26. PAT328, Section 3, March 2001S4-26MAR120, Section 4, December 2001 Use a binary file format if you use the same type or make of computer for the analysis as you do for post-processing the results Usually you will output results every so many increments to reduce the size of the output file Results are written in file job_id.t16, which must be read back for post-processing, including visualizing results You must suppress your output as much as possible! (Nonlinear jobs can fill up your disk quite easily!!) Creating a step includes requesting output REQUESTING OUTPUT FOR A STEP

27. PAT328, Section 3, March 2001S4-27MAR120, Section 4, December 2001 Forms that allow requesting nodal and elements results from MSC.Marc REQUESTING OUTPUT FOR A STEP (CONT.)

28. PAT328, Section 3, March 2001S4-28MAR120, Section 4, December 2001