Running a Thermal Analysis

Transcription

1 Chapter 4: Running a Thermal Analysis 4 Running a Thermal Analysis Introduction 106 Review of the Analysis Form 107 Translation Parameters 111 Solution Types 115 Direct Text Input 121 Subcases 123 Subcase Select 137

2 106 Introduction 4.1 Introduction To run a thermal analysis, you use the procedure described below. Select the solution type Define the solution related input data Define the subcase data Select load cases Submit the job Read the analysis results The solution type can be either steady-state or transient analysis. The purpose of this step is to change the default settings of job-related input data, such as Maximum Run Time, Default Initial Temperature, Radiation Parameters, and options for view factor calculations. Similar to the previous step, the defaults for nonlinear iteration controls, time increments, and output requests can be altered in the Subcase Create section of the Analysis menu form. This step selects load case(s) for an analysis job. When a job is ready for analysis, the MSC Nastran solver can be retrieved by clicking on the Apply button on the main Analysis form. You can modify the default settings of translation parameters, or you can insert additional data entries using the Direct Text Input form before submitting your analysis job. The analysis results must be read into the Patran database by invoking the Read Output2 Action on the Analysis form. The results can then be processed by selecting the Results toggle on the Patran application selections. To submit a single load case, steady-state analysis job to MSC Nastran, you need only click on the Apply button on the main Analysis form. Patran will automatically control the appropriate default settings and other related selections. In the Patran MSC Nastran Interface, a subcase can be thought of as a Patran load case with some additional parameters (e.g., Output Requests) associated with it. This association is further strengthened since the default subcases are created for each load case and have the same name as their associated load case. In this document, the terms load case and subcase are used interchangeably. When a specific form is referenced, Load case and Subcase are capitalized.

3 Chapter 4: Running a Thermal Analysis Review of the Analysis Form Review of the Analysis Form The Analysis form appears when you select Analysis from the main form. To run an analysis, or to create an NASTRAN input file, select Analyze as the Action on the Analysis form. Other forms brought up by the Analysis form are used to define translation parameters, solution types, solution parameters, output requests, and load cases. These forms are described on the following pages. For further information, see The Analysis Form (p. 8) in the Patran Reference Manual. Patran File Group Viewport Viewing Display Preferences Tools Help Geometry FEM LBCs Matls Properties Load Cases Fields Analysis Results XY $# Session file patran.ses.01 started recording at 25 $# Recorded by Patran 03:36:58 PM $# FLEXlm Initialization complete. Acquiring license(s)... hp, 2

4 108 Review of the Analysis Form Analysis Form This form appears when you select Analysis from the main menu. When preparing for an analysis run, select Analyze as the Action. Analysis Action: Analyze Object: Entire Model Method: Analysis Deck Code: MSC Nastran Type: Thermal Actions can be set to: Analyze Read Output2 (p. 125) Read Input File (p. 571) in the Patran Interface to MSC Nastran Preference Guide (support is limited for thermal analysis) Delete (Ch. 6) in the Patran Interface to MSC Nastran Preference Guide Monitor (Ch. 5) in the Patran Analysis Manager User s Guide Abort (Ch. 6) in the Patran Analysis Manager User s Guide Available Jobs my_job Indicates the selected Analysis Code and Analysis Type, as defined in the Preferences>Analysis (p. 451) in the Patran Reference Manual. Job Name my_job Job Description MSC Nastran job created on 01-Feb-93 at 14:32:43 Name of job. Patran will use this name as the base filename for all resulting MSC Nastran files and message files. List of already existing jobs. If you select one of these jobs, the name will appear in the Job Name listbox and all input data for this job will be retrieved from the database. You can submit an existing job again simply by selecting it and clicking on Apply. It is often convenient to select an existing job, modify the input data as desired, and click on Apply to submit the new job.

5 Chapter 4: Running a Thermal Analysis Review of the Analysis Form 109 Job Description MSC Nastran job created on 01-Feb-93 at 14:32:43 Patran uses this text to generate the TITLE statement in the MSC Nastran Executive Control Section. Translation Parameters... Solution Type... Direct Text Input... Subcase Create... Opens the Direct Text Input form; this form allows you to enter data directly for the File Management, Executive Control, Case Control, and Bulk Data sections of the NASTRAN input file. Subcase Select... Analysis Manager... Selects one or more subcases for the analysis job. Opens the Patran Analysis Manager form. Apply Opens a form that allows you to choose either steadystate analysis or transient analysis and to specify settings for controlling the overall analysis job.

6 110 Review of the Analysis Form The following table outlines the selections for the Analyze action. Entire Model Current Group Existing Deck Object Method Full Run Check Run Analysis Deck Model Only Full Run Check Run Analysis Deck Model Only Full Run The Object indicates which part of the model is to be analyzed. There are three choices for thermal analysis: Entire Model, Current Group, and Existing Deck. Entire Model Current Group Existing Deck Indicates that the whole model is to be analyzed. Indicates that only part of the model is to be analyzed. To do this, you create a group of that part, confirm that it is the current group, then select Current Group as the Object. For more information, see The Group Menu (p. 280) in the Patran Reference Manual. Means that you wish simply to submit an existing input file to MSC Nastran. To form the input filename, Patran appends the suffix.bdf to the jobname appearing in the Job Name listbox. This file must reside in the current directory. The Method indicates how far the translation is to be taken.the methods are as follow: Full Run Check Run Analysis Deck Model Only Is the selected type if an Analysis Deck translation is performed, and the resulting input file is submitted to MSC Nastran for complete analysis. Is the selected type if an Analysis Deck translation is performed, and the resulting input file is submitted to MSC Nastran for a check run only. Is the selected type if the Model Deck translation is performed, plus all load case, analysis type and analysis parameter data are translated. A complete input file, ready for MSC Nastran, will be generated. Is the selected type if a Bulk Data file is created that contains only the model data including node, element, coordinate frame, element property, material property, and loads and boundary conditions data. The translation stops at that point.

7 Chapter 4: Running a Thermal Analysis Translation Parameters Translation Parameters This subordinate form appears when you click on the Translation Parameters button on the Analysis form. Defines the type of data output. Print specifies output of data to the MSC Nastran print file (.f06). OP2 specifies output of data to an MSC Nastran OUTPUT2 file (.op2). XDB specifies output of data to an MSC.Access database (.xdb). Data Output Data Output: OUTPUT2 Requests: OUTPUT2 Format: Tolerances Division: Numerical: Writing: Bulk Data Format Card Format: Translation Parameters Minimum Signif. Digits: 4 OP2 and Print P3 Built In Binary 1.0e e e-20 either Specifies type of OUTPUT2 commands. P3 Built In signals the use of MSC Nastran internal OUTPUT2 commands geared toward Patran. These commands are also appropriate for PATRAN 2. Alter File specifies the use of an external alter file found on the Patran file path and following the msc_v#_sol#.alt naming convention. See Files (App. A) for more details. CADA-X Alter specifies the use of an LMS CADA-X specific alter file that is identical to the Alter File but with an additional.lms extension, e.g., msc_v69_sol53.alt.lms. P2 Built In specifies use of MSC Nastran internal OUTPUT2 commands geared toward PATRAN 2. Specifies format of the MSC Nastran OUTPUT2 (*.op2) files. Use Text format when the resulting OUTPUT2 file must be transported between heterogeneous compute Defines various tolerances used during translation. Division is used to prevent division-by-zero errors. Numerical is used to determine if two real values are equal. Writing is used to determine if a value is approximately zero when generating a Bulk Data entry field. Node Coordinates: reference frame MSC Nastran Version: 69 Write Properties on Element Entries Numbering Options... Bulk Data Include File... OK Defaults Cancel

8 112 Translation Parameters Data Output Data Output: OUTPUT2 Requests: OUTPUT2 Format: OP2 and Print P3 Built In Binary Tolerances Division: Numerical: Writing: Bulk Data Format Card Format: Minimum Signif. Digits: 1.0e e e-20 either 4 Defines what type of fields are to be used in the Bulk Data entry. Entry format can be se to small, large, or either. If either is selected the Minimum Significant Digits value is use to determine whether the values on a particular Bulk Data entry can be placed in small fields or whether large fields are required. The small-field format consists of Bulk Data entry fields 8 columns wide; the large field format is 16 columns wide. Node Coordinates: reference frame MSC Nastran Version: 69 Write Properties on Element Entries Brings up a subordinate form, Numbering Options, 113, which defines automatic numbering offsets and possible syntaxes fo encoded IDs. Numbering Options... Bulk Data Include File... OK Defaults Cancel Brings up a standard file select form which allows you to select a file to be included in the Bulk Data Section of the NASTRAN inpu file. Writes CELAS2, CDAMP2, and CONROD Bulk Data entries instead of CELAS1, CDAMP1, and CROD entries. Note: Do not turn ON this option if your model has time varying temperature boundary conditions or conductor/capacitor elements. Defines which version of MSC Nastran is to be used. The version indicated here serves two purposes: to create the full name of the ALTER file to be used and to determine which Solution Sequence to be used. Be sure to specify only whole numbers and letters; e.g., 68 or 69. Defines which coordinate frame is to be used when generating the grid coordinates. The options are reference frame, analysis frame, or global. This setting should not affect the analysis. It only changes the method used in the

9 Chapter 4: Running a Thermal Analysis Translation Parameters 113 Numbering Options Patran allows you to define numbering offsets for IDs associated with model entities. To invoke this feature, you click on the Numbering Options button on the Translation Parameters form. Numbering Options Automatic Numbering Offsets: Element Properties: Material Properties: Data Tables: s: Load Sets: Indicates offsets for all IDs to be automatically assigned during translation. For example, if you type 100 into the Element Properties Offset box, the numbering of element properties in the resulting NASTRAN input file will begin at 101. Load Cases: Control Sets: Rigid Elements: Scalar Points: Begin. Contin. Marker: IDs Encoded in Names: Number Only Beginning Number Trailing Number A Specifies the continuation mnemonic format used on multiple line Bulk Data entries. Activates recognition of IDs encoded into the name of any named entry, such as a material. Recognizes and uses an ID if, and only if, the name of the entity is an actual number, such as 105. This option is ON by default. Recognizes an ID if the number begins the name, such as 52_shell_property. This option is OFF by default. Encoded Syntax Syntax Marker:. OK Defaults Cancel Recognizes an ID if it directly follows the first occurrence of the specified syntax. For example, with this option activated and the specified syntax set to., the ID assigned to a material given the name Steel_ would be 32. Recognizes an ID if it tails the name, such as shell_property_52. This option is OFF by default.

10 114 Translation Parameters Note that both the Patran Neutral file reader and the Patran MSC Nastran input file reader preserve the IDS of named entities with a. syntax, so that an MSC Nastran PSHELL entry of ID 12 will be assigned the name PSHELL.12. This last option allows great continuity between input model data and output model data. This option is ON by default, and the default Syntax Marker is. Note: The Encoded IDs option currently only works for element properties and material properties.

11 Chapter 4: Running a Thermal Analysis Solution Types Solution Types Three solution types are supported in the Patran MSC Nastran thermal interface: steady state, transient, and linear structural. The two thermal (only) analysis types employ nonlinear solution algorithms so that nonlinear material properties or boundary conditions can be included in the model. The linear structural analysis type (STRUCTURAL HEAT ANALYSIS) performs first a linear steady-state thermal analysis (SOL 153), then it performs a linear structural analysis (SOL 101) using the results of the thermal analysis as loading on the structural model. Use the form shown below to select the solution type. By default, a steady-state thermal analysis is requested. Performs linear or nonlinear steady-state thermal analysis usin MSC Nastran Solution Sequence 153. Performs linear or nonlinear transient thermal analysis using MSC Nastran Solution Sequence 159. Performs linear structurall analysis using MSC Nastran Solutio Sequence 101, and the temperature results from a linear steady-state thermal analysis. Brings up a form that controls various settings that pertain to the overall analysis process. Displays the MSC Nastran Solution Sequence number.

12 116 Solution Types Solution Parameters The solution parameter form contains options and subordinate forms for defining parameters that affect the overall analysis. The Subcase Parameter forms, described below, are used for setting input data that control the analysis only within a single subcase. You should always review the settings on both forms before submitting an analysis. Requests that the model singularities be constrained automatically. Select the Solution Sequence. If a static analysis is being performed (SOL 153) the choices are SOL 153, 400, or 600. If a transient analysis is being performed (SOL 159) the choices are SOL 159, 400, or 600. Controls whether or not the input file is printed to the Nastran output file (f06). Maximum number of lines to be written to the Nastran output file (f06). Maximum number of CPU minutes the analysis job is allowed to run. The job will terminate when this limit is reached. Buttons to bring up subordinate forms for additional parameters needed for radiation analysis. Select this button to specify what is to be output from the analysis. Defines the default initial temperature for all node points which have not been given an initial temperature by the Initial Temperature object of Loads/BCs.

13 Chapter 4: Running a Thermal Analysis Solution Types 117 Radiation Parameters Figure 4-1 The value of absolute temperature scale may be entered directly or selected from the menu. The value of the Stefan-Boltzmann constant must be input in units that are consistent with the rest of the model definition. Values in several different combinations of units are available for selection in the menu, or you can enter the value directly. View Factor Parameters This subordinate form defines parameters and output options to calculate view factors. For all the radiation enclosures selected, the Patran MSC Nastran forward translator automatically enables the Gaussian integration view factor calculation method by applying the terminology defined here. A more detailed description of the calculation of view factors can be found in the MSC Nastran Thermal Analysis User s Guide.

14 118 Solution Types Figure 4-2 Defines the view factor sum that the enclosure will be set to if the view factor summation of the enclosure is greater than 1.0. No scaling is performed if this databox is left blank. View Factor Parameters View Factor Scale = Gaussian Int Order (3rd Body Shading): 4 Gaussian Int Order (Self Shading): 4 Discretization Level = 4 Error Tolerance = 0.1 Assumed Level of Calculation = 1.0e-10 Assumed Degree of Warpage = 0.01 Defines Gaussian integration order for calculating net effective view factors in the presence of third-body shading. Defines Gaussian integration order for calculating net effective view factors in the presence of self shadowing. Defines the discretization level used in the semi-analytic contour integration method. Defines the assumed level of calculation below which the numbers are considered to be zero. Defines the assumed degree of warpage above which the actual value of Fii will be calculated. (For a flat surface F ii = 0.0) Defines the error tolerance above which a corrected view factor is calculated using the semi-analytic contour integration method. NOTE: See the MSC Nastran Thermal Analysis User s Guide for a description of error estimators for view factor calculation.

15 Chapter 4: Running a Thermal Analysis Solution Types 119 Defines diagnostic output request options for the radiation exchange surfaces. The output will be written to the NASTRAN output (f06) file. Diagnostic Output Requests Grid Table and Element Connectivity Surface Diagnostics View Factor Calculation Diagnostics Output Device Option: Both OK Defaults Cancel Defines the output device options (Both, Print, Punch, None) for printing or punching view factors onto RADLST/RADMTX entries. The printed view factors are written to the NASTRAN output (f06) file, while the punched view factors are written to a punch file, job_name.pch. If the FEM mesh and the application regions of loads and boundary conditions are not changed in subsequent runs, the lengthy view factor calculations may be skipped by including the RADLST/RADMTX punch files, which can be retrieved from the Bulk Data Include File menu in the Translation Parameters form. Solution Parameters for Transient Analysis Figure 4-3

16 120 Solution Types Controls the printout of model singularities. Solution Parameters Transient Solution Parameters Print Out Singularities Data Deck Echo: None Maximum Printed Lines = Maximum Run Time = 600 Default Init Temperature = 0.0 Radiation Parameters... View Factor Parameters... Controls whether or not the input filefile is printed to the NASTRAN output (f06) file Maximum number of lines to be written to the NASTRAN output (f06) file. Maximum number of CPU minutes the analysis job is allowed to run. The job will terminate when this limit is reached. The radiation and view factor input data forms are identical to those shown above for steady-state analysis. OK Defaults Cancel Defines the default initial temperature for all grid points which have not been given an initial temperature by the Initial Temperature Object of Loads/BCs.

17 Chapter 4: Running a Thermal Analysis Direct Text Input Direct Text Input This form allows you to enter entries directly in the File Management, Executive Control, Case Control, and Bulk Data sections of the NASTRAN input file. The input file reader 1 also creates these entries for any unsupported entries in the input file. If the data is entered by the user, the Write to Input file toggle default setting is ON. If the data comes from the input file reader, the default for the Input file toggle is OFF. A good practice is to review and edit the MSC Nastran input entries. If they should be written to any input files subsequently created by the interface, the appropriate Write to Input file toggle should be set to ON. Text entered into the Case Control section is written to the input file before the first subcase. The Direct Text Input option on the Subcase Create form should be used to enter text directly within a subcase definition. 1 The current input file reader provides limited support for thermal analysis.

18 122 Direct Text Input Switches to determine which data section the MSC NASTRAN input would be sent. Direct Text Input Bulk Data Section u u u u File Management Section Executive Control Section Case Control Section Bulk Data Section FMS Write To Input Deck EXEC Write To Input Deck CASE Write To Input Deck BULK Write To Input Deck OK Clear Reset Cancel Saves the current setting and data for the four sections and closes the form. Clears the current form. Resets the form back to the data values it had at the last OK. Resets all four forms back to its previous value and closes the form.

19 Chapter 4: Running a Thermal Analysis Subcases Subcases This form appears when you select the Subcase Create button on the Analysis form. The subcase is the MSC Nastran mechanism for associating loads and boundary conditions, output requests, and various other input data to be used during part of a complete run.

20 124 Subcases The Patran MSC Nastran interface automatically associates default parameters and output requests with each Patran load case to create a subcase with the same name as the load case. You can access the Subcase Parameters and Output Requests forms to view or modify these defaults. Solution Sequence: 153 Subcase Create Available Subcases Default Convection_Case Radiation_Case 100_BTU_Heat_Load Displays all the available subcases associated with the current Solution Sequence. Subcase Name Default Subcase Description This is the default subcase Available Load Cases Default Convection_Case Radiation_Case 100_BTU_Heat_Load Displays the subcase name that is being created, modified, or deleted. You can type in the subcase name or pick it from the Available Subcases listbox. Displays the description of the current subcase The description can be 256 characters long. Displays all the available loadcases in the curr database. Only one loadcase can be selected subcase. Subcase Options Subcase Parameters... Output Requests... Direct Text Input... These buttons bring up subordinate forms for additional input associated with the subcase. Apply Delete Cancel

21 Chapter 4: Running a Thermal Analysis Subcases 125 Note about Structural Heat Analysis: There can be only two subcases. First subcase has only thermal Loads/BCs (Case Control LOAD and SPC entries) and thermal Output Requests (Case Control THERMAL entry). Second subcase has only structural Loads/BCs (Case Control LOAD and SPC entries) and structural Output Requests (Case Control STRESS entry). The temperatures from the thermal analysis (first subcase) are a part of the structural Loads/BCs (Case Control TEMPERATURE(LOAD) = ID (ID of the first subcase) entry). Both thermal (Bulk Data MAT4 entry) and structural (Bulk Data MAT1 entry) material properties must exist. The IDs of the MAT4 and MAT1 entries must be equal. PARAM, HEATSTAT, YES in written to the Bulk Data section to enable this type of analysis. To set up and perform a chained thermal-structural analysis in one run using SOL 101. The procedure is to: 1. With Patran Preferences set to MSC Nastran, Structural, create and set up your structural LBCs and load case 1. Change the Patran Preferences to MSC Nastran, Thermal, create and set up your thermal LBCs and load case 1. Set the Solution Type to STRUCTURAL HEAT ANALYSIS 1. Set up two Subcases, one referencing the structural load case and the other referencing the thermal load case. 1. Select the two Subcases in the order: Thermal, Structural 1. Submit the job The Nastran run is submitted as a SOL 101 with two Subcases. The first subcase is the heat transfer run to determine the temperature loading. The temperature results from the first subcase are used along with any other structural LBCs called out in the second subcase, which is a SOL 101 run. PARAM, HEATSTAT, YES is written to the input file. Subcase Parameters The controls and parameters set on the Subcase Parameters forms apply to a single MSC Nastran subcase within the overall analysis run. Steady-State Subcase This subordinate form appears when the Subcase Parameters button is selected on the Subcase Create form and the solution type is Steady State. This form provides for the definition of the input data that controls the solution of the nonlinear equations. Occasionally, when solving a set of nonlinear equations, it may not be possible to obtain a solution directly with the total heat load applied. Instead, the solution is obtained by applying the loading in

22 126 Subcases increments, solving the system equations for the current fraction of the total load, and using that solution as the starting point for the next increment of load. This process continues until the desired total heat load is applied. It should be mentioned that the number of load increments has no effect on the accuracy of the solution-- it is merely a computational technique to aid in obtaining the solution efficiently. In linear or mildly nonlinear problems, a single increment is usually applied. In highly nonlinear problems, dozens of increments may be required to obtain a converged solution. This incremental procedure is only applicable with respect to applied heat loads and specified temperature boundary conditions. There is no incremental provision for convection or radiation boundary

23 Chapter 4: Running a Thermal Analysis Subcases 127 conditions. As a result, it is more common with highly nonlinear boundary conditions to exceed the nonlinear iteration limit. This defaults to 25 currently, but can be increased. Number of increments over which the heat load is applied. These parameters control aspects of the nonlinear equation solving process. For more information, see table on page 129. The convergence criteria are used to determine when the solution is sufficiently accurate to be considered converged. See page 129 for more information. See the next page for the contact table form.

24 128 Subcases Thermal Contact Table This data can optionally be defined for each individual contact pair (which is selected by clicking on the cell of the above contact body matrix) and is written to the BCTABLE bulk data entry. See the MSC Nastran Quick Reference Guide for more information.

25 Chapter 4: Running a Thermal Analysis Subcases 129 The parameters controlling the steady-state solution process are discussed more fully in the table below. More extensive information can be found in the MSC Nastran Thermal Analysis User s Guide. Parameter Name Matrix Update Method Number of Iterations per Update Allowable Iterations per Increment Convergence Criteria Temperature Error Temperature Tolerance Load Error Load Tolerance Work Error Work Tolerance Description This option determines the strategy used to determine how often to update (reform) the nonlinear conductance and radiation matrices. The three options are Automatic, Semi-Automatic, and Controlled Iters. The optimum strategy would result in the lowest computational cost. When the Automatic option is selected, MSC Nastran tries to select the most efficient strategy based on convergence rates. If Controlled Iters is selected, the matrices are updated after a prescribed number of iterations (determined by the Number of Iterations per Update parameter). When the Matrix Update Method is set to Controlled Iters, this is the number of iterations before the matrices are reformed. This parameter specifies the maximum number of allowed iterations in a load increment. If this number is exceeded, the load increment is halved and the iteration process repeated. The convergence criteria provide for the comparison of userrequested maximum levels of error and the error in the solution as estimated numerically. In this sense, the convergence criteria determine when the solution is sufficiently accurate to be considered converged. Any or all of the three convergence criteria listed below can be selected. When more than one criteria is selected, each one must be satisfied for convergence to be achieved. Indicates whether a temperature convergence criterion should be used. If Temperature Error is selected, the Temperature Tolerance field becomes active. A norm of the temperature increment vector calculated in the iteration must be less than this tolerance for a converged solution. Indicates whether a load convergence criteria should be used. If Load Error is selected, the Load Tolerance field becomes active. A norm of the residual heat load vector must be less than this tolerance for a converged solution. Indicates whether a work convergence criteria should be used. If Work Error is selected, the Work Tolerance field becomes active. The incremental work associated with the iteration must be less than this tolerance for a converged solution.

26 130 Subcases Transient Subcase Parameters This subordinate form appears when you select the Subcase Parameters button on the Subcase Create form and the solution type is Transient. This form provides for the definition of the input data that controls the solution of the nonlinear time-dependent equations. The integration in time is carried out using Newmark s method with variable time steps. An initial time step and the number of time steps must be input. Since the time increment is adjusted during the analysis,

27 Chapter 4: Running a Thermal Analysis Subcases 131 the actual number of time steps may not be equal to the input value. However, the total time duration will be close to the product of the input values. Subcase Parameters Initial Time Step = 0.01 Number of Time Steps = 100 Transient Nonlinear Iterations Matrix Update Method: Adaptive Number of Bisections per Update = 2 Allowable Iterations per Time Step = 10 Convergence Criteria Temperature Error Initial time increment for the Newmark method. This number is used along with the initial time step to calculate the total time duration. Defines the maximum number of time step bisections to be used in each matrix update. The maximum number of allowed iterations in a time step. Temperature Tolerance = Load Error Load Tolerance = Work Error Work Tolerance = 1.0e e e-06 The convergence criteria are described above for the steady-state case. The temperature convergence criteria must be selected if the analysis involves any time varying temperature boundary conditions. Fixed Time Steps Exit on Failure to Converge Directs MSC Nastran to use the initial time step for all time steps. This disables the automatic time stepping mechanism. OK Cancel If this toggle is ON, the run will terminate if the converge criteria are not met for any time step. If OFF, the run continues to the next time step.

28 132 Subcases Structural Heat Subcase Parameters This subordinate form appears when you select the Subcase Parameters button on the Subcase Create form and the solution type is Structural Heat. This form provides for the definition of the input data that controls the solution of the linear structural equations. The parameters that can be set have to do with 1) Default Load Temperature, 2) Rotor Dynamics, 3) Contact Table, and 4) Solvers/Options.. Default Load Temperature is for specifying the temperature at nodes for which the temperature has not been specified using Loads/BCs. By clicking Enable Rotor Dynamics, and clicking Specify Rotor Speed, several things are to be specified. They are 1) Reference Rotor, 2) the units of the speed, and 3) Rotor Speed. Clicking the Contact Table button displays the Contact Table form. This form is used to specify what and how contact bodies are to be in contact. For example, rubber seal (flexible) contacts door (rigid). See Thermal Contact Table, 128 Clicking the Solvers / Options button displays the Solvers / Options form that is used to specify the Solver Type (for example, Nastran Default or an iterative method), a Preconditioner method (for example, Cholesky), Maximum Number of Iterations, and other parameters. Output Requests The output requests forms allow you to define what result quantities will be written to the MSC Nastran print file for viewing and the OUTPUT2 file for import into Patran. A reasonable set of default result quantities are predefined. The simplest way to change these is to use the Basic Output Requests form.

29 Chapter 4: Running a Thermal Analysis Subcases 133 More control over output quantities is provided for sophisticated users by changing the Form Type menu from Basic to Advanced. The Basic form is shown below. Output Requests SUBCASE NAME: SOLUTION SEQUENCE: 159 Form Type: Basic Select Result Type Temperatures Heat Fluxes Applied Linear Loads Heats of Constraint Enthalpies Rate of Change of Enthalpies The available output requests depend on the active Solution Sequence as indicated by this value. This option menu is used to switch between the advanced and basic versions of this form. Displays the appropriate result types that may be selected for the solution sequence indicated at the top of the form. The output requests are selected one at a time by clicking. Output Requests THERMAL(SORT2,PRINT)=All FEM FLUX(SORT2,PRINT)=All FEM Displays the selected output requests for the subcase shown at the top of the form. Delete Deletes the output request highlighted in the Output Requests listbox. OK Defaults Cancel NOTE: The OK button accepts the output requests and closes the form. The Defaults button deletes all output requests and replaces them with defaults. The Cancel button closes the form without saving the output requests.

30 134 Subcases When the Form Type is set to Advanced, the Output Requests form expands to the form below. The same result types are available in the Select Result Type listbox, but more options are available to control these. Use this listbox to select the result type to be created. SUBCASE NAME: SOLUTION SEQUENCE: 153 Form Type: Advanced This listbox is used to select the group of nodes or elements to which the output requests relate. Output Requests Select Group(s)/SET All FEM Select Result Type Temperatures Heat Fluxes Applied Linear Loads Heats of Constraint Options Sorting: Output Device Opt: By Node/Element Print Output Requests THERMAL(SORT1,PRINT)=All FEM FLUX(SORT1,PRINT)=All FEM Create Delete Intermediate Output Option: No OK Defaults Cancel Creates output requests for highlighted result types. It also modifies highlighted output requests. The button label changes to reflect the operation. These options are appropriate for the highlighted result type. They also indicate the options that were selected for a highlighted output request. See Table 4-1. Use this listbox to select output requests that are to be modified or deleted. NOTE: The ALL FEM set must be selected to request the heat flux output associated with loads and boundary conditions.

31 Chapter 4: Running a Thermal Analysis Subcases 135 Table 4-1 Output Request Form Options Options Label Multiple Select Allowed Descriptions Sorting By Node/Element No Output is presented as tabular listing of nodes/elements for each load step or time. Output Device Options IntermediateO utput Options Percent of Step Output By Time/Load Step No Output is presented as tabular listing of load step/time for each node or element type. Print No Requests that the output be written to the NASTRAN output (f06) file. Punch No Requests that the output be written to the punch file (job_name.pch). Both No Requests that the output be written to the NASTRAN output (f06) file and the punch file (job_name.pch). Yes No All Once per subcase Once per subcase Once per subcase -- Once per subcase Intermediate outputs are requested for every computed load increment. Applicable for steadystate analysis only. Intermediate outputs are requested for the last load of the subcase. Applicable for steady-state analysis only. Intermediate outputs are requested for every computed and user-specified load increment. Applicable for steady-state analysis only. An integer n that specifies the percentage of intermediate outputs to be presented for transient analysis. Default = 100. Direct Text Input This form is used to directly enter entries into the Case Control section for the defined subcase.

32 136 Subcases Directly entered entries may potentially conflict with those created by the interface. Writing these entries to the file can be controlled with this toggle. Direct Text Input Write To Input Deck OK Clear Reset Cancel Saves the current setting and data and closes the form. Clears the current form. Resets the form back to the data values it had at the last OK. Resets the form back to its previous value and closes the form.

33 Chapter 4: Running a Thermal Analysis Subcase Select Subcase Select This form appears when you select the Subcase Select button on the Analysis form. It allows you to select a sequence of subcases associated with an analysis job. The Default subcase is selected automatically. If multiple subcases are selected, the subcases selected must contain identical sets of convection, radiation boundary conditions, and fixed value temperature boundary conditions because these boundary conditions are not subcase selectable in MSC Nastran thermal analysis. Subcase Select Subcases For Solution Sequence: 153 Default Second-Load-Case Radiation-Case Displays all the available subcases for the current solution sequence. The current solution sequence is displayed at the top of the form. Subcases Selected: Default Displays all subcases that have been associated with the current jobname. OK Cancel Within the current Patran MSC Nastran design, only those boundary conditions referred to as loads are subcase selectable. All heat flux types and temperature boundary specifications are defined as thermal loads, whereas all occurrences of convection and radiation are defined as boundary conditions and are not subcase selectable. As a result, the use of multiple subcases in MSC Nastran thermal analysis has limited utility and in general is not recommended.

34 138 Subcase Select