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Chapter 4: Running a Thermal AnalysisPatran Interface to MSC Nastran Thermal

4Running 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

Patran Interface to MSC Nastran ThermalIntroduction

106

4.1 IntroductionTo run a thermal analysis, you use the procedure described below.

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.

Select the solution type The solution type can be either steady-state or transient analysis.

Define the solution related input data 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.

Define the subcase data 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.

Select load cases This step selects load case(s) for an analysis job.

Submit the 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.

Read the analysis results 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.

107Chapter 4: Running a Thermal AnalysisReview of the Analysis Form

4.2 Review of the Analysis FormThe 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.

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Patran Interface to MSC Nastran ThermalReview of the Analysis Form

108

Analysis FormThis form appears when you select Analysis from the main menu. When preparing for an analysis run, select Analyze as the Action.

Analysis

AnalyzeAction:

Code:

Entire ModelObject:

Analysis DeckMethod:

Job Name

Name of job. Patran will use this name as the base filename for all resulting MSC Nastran files and message files.

Indicates the selected Analysis Code and Analysis Type, as defined in the Preferences>Analysis (p. 451) in the Patran Reference Manual.

Available Jobs

MSC Nastran

Type: Thermal

my_job

Job Description

MSC Nastran job created on01-Feb-93 at 14:32:43

Actions can be set to:AnalyzeRead 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 GuideAbort (Ch. 6) in the Patran Analysis Manager User’s Guide

my_job

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.

109Chapter 4: Running a Thermal AnalysisReview of the Analysis Form

Translation Parameters...

Solution Type...

Apply

Job Description

MSC Nastran job created on01-Feb-93 at 14:32:43

Patran uses this text to generate the TITLE statement in the MSC Nastran Executive Control Section.

Subcase Select...

Subcase Create...

Opens the Patran Analysis Manager form.

Direct Text Input...

Analysis Manager...

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.

Opens a form that allows you to choose either steady-state analysis or transient analysis and to specify settings for controlling the overall analysis job.

Selects one or more subcases for the analysis job.

Patran Interface to MSC Nastran ThermalReview of the Analysis Form

110

The following table outlines the selections for the Analyze action.

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.

The Method indicates how far the translation is to be taken.The methods are as follow:

Object Method

Entire Model Full RunCheck Run

Analysis DeckModel Only

Current Group Full RunCheck Run

Analysis DeckModel Only

Existing Deck Full Run

Entire Model Indicates that the whole model is to be analyzed.

Current Group 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.

Existing Deck 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.

Full Run Is the selected type if an Analysis Deck translation is performed, and the resulting input file is submitted to MSC Nastran for complete analysis.

Check Run 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.

Analysis Deck 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.

Model Only 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.

111Chapter 4: Running a Thermal AnalysisTranslation Parameters

4.3 Translation ParametersThis subordinate form appears when you click on the Translation Parameters button on the Analysis form.

Translation Parameters

Data Output

Data Output: OP2 and Print

OUTPUT2 Requests: P3 Built In

OUTPUT2 Format: Binary

Tolerances

Division: 1.0e-08

Numerical: 1.0e-04

Writing: 1.0e-20

Bulk Data Format

Card Format: either

Minimum Signif. Digits: 4

Node Coordinates: reference frame

MSC Nastran Version: 69

Numbering Options...

Bulk Data Include File...

OK Defaults Cancel

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.

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).

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

Write Properties on Element Entries

Patran Interface to MSC Nastran ThermalTranslation Parameters

112

Defines what type of fields are to be used inthe Bulk Data entry. Entry format can be seto small, large, or either. If either is selectedthe Minimum Significant Digits value is useto 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.

Brings up a subordinate form, Numbering Options, 113, which defines automatic numbering offsets and possible syntaxes foencoded IDs.

OP2 and PrintData Output:

P3 Built InOUTPUT2 Requests:

Binary OUTPUT2 Format:

Data Output

1.0e-08Division:

1.0e-04Numerical:

1.0e-20Writing:

Tolerances

either Card Format:

4Minimum Signif. Digits:

Bulk Data Format

reference frame Node Coordinates:

69MSC Nastran Version:

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 inpufile.

Write Properties on Element Entries

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

id ti It l d t i hi h di t f i f d i th CP fi ld f th GRID B lk D t t

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.

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.

113Chapter 4: Running a Thermal AnalysisTranslation Parameters

Numbering OptionsPatran 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

0Element Properties:

0Material Properties:

0Data Tables:

0Load Sets:

0Load Cases:

0Control Sets:

0Rigid Elements:

0Scalar Points:

Automatic Numbering Offsets:

+ ABegin. Contin. Marker:

Number Only

Beginning Number

Trailing Number

Encoded Syntax

.Syntax Marker:

IDs Encoded in Names:

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_1027.32” would be 32.

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.

Recognizes an ID if it tails the name, such as “shell_property_52.” This option is OFF by default.

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.

s:

Patran Interface to MSC Nastran ThermalTranslation Parameters

114

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.

115Chapter 4: Running a Thermal AnalysisSolution Types

4.4 Solution TypesThree 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.

Brings up a form that controls various settings that pertain to the overall analysis process.

Displays the MSC Nastran Solution Sequence number.

Performs linear or nonlinear steady-state thermal analysis usinMSC Nastran Solution Sequence 153.

Performs linear or nonlinear transient thermal analysis using MSC Nastran Solution Sequence 159.

Performs linear structurall analysis using MSC Nastran SolutioSequence 101, and the temperature results from a linear steady-state thermal analysis.

Patran Interface to MSC Nastran ThermalSolution Types

116

Solution ParametersThe 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.

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.

Requests that the model singularities be constrained automatically.

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.

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.

Select this button to specify what is to be output from the analysis.


Radiation Parameters

Figure 4-1

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.

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.

The value of “absolute temperature scale” may be entered directly or selected from the menu.


118

Figure 4-2

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 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.

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 error tolerance above which a corrected view factor is calculated using 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 Fii = 0.0)

NOTE: See the MSC Nastran Thermal Analysis User’s Guide for a description of error estimators for view factor calculation.


Solution Parameters for Transient Analysis

Figure 4-3

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.

Defines diagnostic output request options for the radiation exchange surfaces. The output will be written to the NASTRAN output (f06) file.


120

Solution Parameters

Transient Solution Parameters

Print Out Singularities

Data Deck Echo: None

Maximum Printed Lines = 999999999

Maximum Run Time = 600

Default Init Temperature = 0.0

Radiation Parameters...

View Factor Parameters...

OK Defaults Cancel

The radiation and view factor input data forms are identical to those shown above for steady-state analysis.

Controls whether or not the input filefile isprinted to the NASTRAN output (f06) file

Maximum number of lines to be written tothe NASTRAN output (f06) file.

Maximum number of CPU minutes the analysis job is allowed to run. The job willterminate when this limit is reached.

Controls the printout of model singularities.

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.

121Chapter 4: Running a Thermal AnalysisDirect Text Input

4.5 Direct Text InputThis 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 reader1 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.

1The current input file reader provides limited support for thermal analysis.

Patran Interface to MSC Nastran ThermalDirect Text Input

122

Direct Text Input

Bulk Data Section

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

Switches to determine which data section the MSC ⁄NASTRAN input would be sent.

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.

uu

uu

uu

u

123Chapter 4: Running a Thermal AnalysisSubcases

4.6 SubcasesThis 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.

Patran Interface to MSC Nastran ThermalSubcases

124

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.

Subcase Create

Solution Sequence: 153

Available Subcases

Convection_Case

Radiation_Case100_BTU_Heat_Load

Subcase Name

Subcase Description

Available Load Cases

Default

Subcase Options

Apply Delete Cancel

Subcase Parameters...

Output Requests...

Direct Text Input...

Default

Default

This is the default subcase

Displays all the available subcases associated with the current Solution Sequence.

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 subcaseThe description can be 256 characters long.

Displays all the available loadcases in the currdatabase. Only one loadcase can be selected subcase.

Convection_Case

Radiation_Case

These buttons bring up subordinate forms for additional input associated with the subcase.

100_BTU_Heat_Load


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 ParametersThe 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


126

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


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.


128

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.


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 Description

Matrix Update Method 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).

Number of Iterations per Update

When the Matrix Update Method is set to Controlled Iters, this is the number of iterations before the matrices are reformed.

Allowable Iterations per Increment

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.

Convergence Criteria The convergence criteria provide for the comparison of user-requested 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.

Temperature Error

Temperature Tolerance

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.

Load Error

Load Tolerance

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.

Work Error

Work Tolerance

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.


130

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,


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

Temperature Tolerance = 1.0e-02

Load Error

Load Tolerance = 1.0e-03

Work Error

Work Tolerance = 1.0e-06

Fixed Time Steps

Exit on Failure to Converge

OK Cancel

Initial time increment for the Newmark method.

This number is used along with the initial time step to calculate the total time duration.

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.

Directs MSC Nastran to use the initial time step for all time steps. This disables the automatic time stepping mechanism.

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.

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.


132

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..

Output RequestsThe 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.

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.


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

TemperaturesHeat FluxesApplied Linear LoadsHeats of ConstraintEnthalpiesRate of Change of Enthalpies

Output Requests

THERMAL(SORT2,PRINT)=All FEMFLUX(SORT2,PRINT)=All FEM

Delete

OK Defaults Cancel

The available output requests depend on the active Solution Sequence as indicated by this value.

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.

Displays the selected output requests for the subcase shown at the top of the form.

This option menu is used to switch between the advanced and basic versions of this form.

Deletes the output request highlighted in the Output Requests listbox.

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.


134

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.

Output RequestsSUBCASE NAME: SOLUTION SEQUENCE: 153

Form Type: Advanced

Select Result Type

TemperaturesHeat FluxesApplied Linear LoadsHeats of Constraint

Output Requests

THERMAL(SORT1,PRINT)=All FEMFLUX(SORT1,PRINT)=All FEM

Create

Delete

OK Defaults Cancel

Select Group(s)/SET

All FEM

Options

Sorting: By Node/Element

Output Device Opt: Print

Intermediate Output Option: No

This listbox is used to select the group of nodes or elements to which the output requests relate.

Use this listbox to select the result type to be created.

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.

Creates output requests for highlighted result types. It also modifies highlighted output requests. The button label changes to reflect the operation.

NOTE: The ALL FEM set must be selected to request the heat flux output associated with loads and boundary conditions.


Table 4-1 Output Request Form Options

Direct Text InputThis form is used to directly enter entries into the Case Control section for the defined subcase.

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.

By Time/Load Step

No Output is presented as tabular listing of load step/time for each node or element type.

Output Device Options

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).

IntermediateOutput Options

Yes Once per subcase

Intermediate outputs are requested for every computed load increment. Applicable for steady-state analysis only.

No Once per subcase

Intermediate outputs are requested for the last load of the subcase. Applicable for steady-state analysis only.

All Once per subcase

Intermediate outputs are requested for every computed and user-specified load increment. Applicable for steady-state analysis only.

Percent of Step Output

-- Once per subcase

An integer ‘n’ that specifies the percentage of intermediate outputs to be presented for transient analysis. Default = 100.


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Direct Text Input

Write To Input Deck

OK Clear Reset Cancel

Directly entered entries may potentially conflict with those created by the interface. Writing these entries to the file can be controlled with this toggle.

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.

137Chapter 4: Running a Thermal AnalysisSubcase Select

4.7 Subcase SelectThis 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.

Displays all the available subcases for the current solution sequence. The current solution sequence is displayed at the top of the form.

Displays all subcases that have been associated with the current jobname.

Subcase Select

Subcases For Solution Sequence: 153

Default

Subcases Selected:

Default

OK Cancel

Second-Load-Case Radiation-Case

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.

Patran Interface to MSC Nastran ThermalSubcase Select

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