Técnicas de cepillado

• Overview

• Executive Control Section

• Case Control Section

• Bulk Data Section

• Restarts

3.1

Overview

Before you can perform an aeroelastic analysis, you must have an input file for the finite element structural model that satisfies the descriptions in the NX Nastran Quick Reference Guide

regarding the Executive Control statements, the Case Control commands, and the Bulk Data entries. The descriptions of the input files in this chapter contains only the information related to the features that must be included in the input file to obtain a static aeroelastic, flutter, or dynamic aeroelastic response analysis, or aeroelastic design sensitivity and optimization.

3.2

Executive Control Section

A user typically runs NX Nastran by invoking one of the standard solution sequences. These sequences are a collection of DMAP statements that drive the analysis and the aeroelastic sequences are described inAeroelastic Solution Sequences. The aeroelastic analysis and design solution sequences are:

SOL 144 STATIC AEROELASTIC RESPONSE

SOL 145 AERODYNAMIC FLUTTER

SOL 146 DYNAMIC AEROELASTIC RESPONSE

SOL 200 SENSITIVITY AND OPTIMIZATION

Solution 200, in addition to performing sensitivity and optimization, is also a multidisciplinary analysis procedure. This solution sequence contains the analysis capabilities of SOLs 101 (Statics), 103 (Normal Modes), 105 (Buckling), 108 (Direct Frequency Response), 111 (Modal Frequency Response), 112 (Modal Transient Response), 144 (Static Aeroelasticity), and 145 (Aerodynamic Flutter). This makes it possible to perform static aeroelastic and flutter analyses in a single run.

3.3

Case Control Section

The Case Control Section is described in Case Control Commands in the NX Nastran Quick

Reference Guide. Fifteen Case Control data selection commands are available for aeroelastic

analyses and design and various outputs. This section provides a brief description of each of the commands.

Static Aeroelastic Trim Variable Selection

TRIM Selects a TRIM Bulk Data entry in static aeroelastic response.

Divergence Solution Selection

DIVERG Selects the number of eigenvalues and Mach numbers for the

aeroelastic divergence analysis.

Structural Damping and Transfer Function Selection

SDAMPING Selects a table that defines damping as a function of frequency.

TFL Selects the transfer function set that represents a servomechanism.

Aeroelastic Flutter Solution Selection

FMETHOD Selects the method to be used in aerodynamic flutter analysis.

CMETHOD Selects a complex eigenvalue method for flutter analysis.

METHOD Selects a real eigenvalue method for vibration analysis.

Dynamic Aeroelastic Load Selection

DLOAD Selects the dynamic load to be applied in a transient or frequency

response problem.

FREQUENCY Selects the set of frequencies to be solved in frequency response

problems.

GUST Selects the gust load in aeroelastic response analysis.

RANDOM Selects the RANDPS and RANDTi entries to be used in random

analysis.

TSTEP Selects integration and output time steps for transient problems.

Output Control

AEROF Requests the aerodynamic loads on the aerodynamic control points.

APRESSURE Requests the aerodynamic pressures in static aeroelastic response.

SET Lists identification numbers for output requests, or lists frequencies

3.4

Bulk Data Section

The Bulk Data entries required in the analysis of finite element models are described in the Bulk Data Entries in the NX Nastran Quick Reference Guide. This section provides a brief comment on those entries that are unique to NX Nastran’s aeroelastic capability. Table 3-1presents a list of these entries and indicates which ones are required (R) and available (A) in each of the solution sequences. SOL 146 typically requires significant dynamic analysis input [see the

NX Nastran Basic Dynamic Analysis User’s Guide] and SOL 200 typically contains significant

design model input [see the NX Nastran Design Sensitivity and Optimization User’s Guide that is not included here.

Table 3-1. Bulk Data Entries for Aeroelasticity

Solution Bulk Data Entry

144 145 146 200 AEFACT A A A A AELINK A A AELIST A A AERO R R A AEROS R A AESTAT A A AESURF A A CAERO1 A A A A CAERO2 A(1)* A A A

CAERO3 A(2) A A(3) A

CAERO4 A(2) A A(3) A

CAERO5 A(2) A A(3) A

DIVERG A A FLFACT R A FLUTTER R A GUST A A MKAERO1 R(4) R(4) A MKAERO2 R(4) R(4) A PAERO1 A A A A PAERO2 A(1) A A A

PAERO3 A(2) A A(3) A

PAERO4 A(2) A A(3) A

PAERO5 A(2) A A(3) A

PARAM A A R(5) A SET1 A A A A SET2 A A A A SPLINE1 A A A A SPLINE2 A A A A SPLINE3 A A A A TABRNDG A TRIM A A

Note

* Parenthetical numbers refer to the notes at the end of the table.

Notes:

1. CAERO2 and PAERO2 entries provides slender body aerodynamics and are only available for subsonic analyses.

2. In SOL 144, CAEROi and PAEROi for i = 3, 4, or 5 are not available for TRIM analysis; they can be used for DIVERGENCE analysis.

3. In SOL 146, CAEROi and PAEROi for i = 3, 4, or 5 are not available for GUST analysis but can be used for dynamic aeroelastic analysis with nonaerodynamic loading (e.g., store ejection or landing loads).

4. At least one MKAERO1 or MKAERO2 entry must be present for flutter and dynamic aeroelastic analyses.

5. For dynamic aeroelastic analysis, the Q parameter is required.

The descriptions of the Bulk Data entries found in the NX Nastran Quick Reference Guide are intended to be comprehensive so that extended descriptions are not presented here. Instead, brief comments are given which highlight features of the entry, particularly those that have been troublesome to users.

AEFACT Specifies lists of real numbers for the aerodynamic model required by the CAEROi and PAEROi entries. When the data refer to spanwise, chordwise, or bodywise division cuts, the data are in fractions of the span, chord, and body length, respectively.

AELINK Links aerodynamic extra points.

AELIST Defines aerodynamic elements associated with a control surface in static aeroelasticity.

AERO Aerodynamic parameter for unsteady aerodynamics. Note that

aerodynamic densities must be in consistent units; i.e., PARAM WTMASS does not apply to RHOREF.

AEROS Aerodynamic parameters for steady aerodynamics. The reference area (REFS) is input for half the vehicle when a half-span model is used. The reference span (REFB) is always the full vehicle span.

AESTAT Rigid body aerodynamic extra points. A number of prespecified labels are provided to invoke standard rigid body motions such as angle of attack or roll. If other labels are used, the burden is on the user to provide the corresponding forces.

AESURF Aerodynamic control surface extra points.

CAERO1 Defines a wing panel for Doublet-Lattice and/or ZONA51. The leading edge locations are input in the CP coordinate system of the entry while the edge chords are in the aerodynamic coordinate system specified by the AERO or AEROS entry. This convention also applies to the other CAEROi entries.

CAERO2 Body data for Doublet-Lattice aerodynamics.

CAERO4 Panel data for Strip Theory aerodynamics.

CAERO5 Panel data for Piston Theory aerodynamics. Sweep corrections (NTHRY = 2) cannot be used when the leading edge is subsonic sec Λ ≥ M

DIVERG Specifies static aeroelastic divergence analysis.

FLFACT Specification of real number required in a flutter analysis or a flutter sensitivity analysis. The alternate form is useful for obtaining a good distribution of k-values for V-G flutter plots when using the KE-flutter method.

FLUTTER Specifies flutter analysis. IMETH = S permits interpolation of the computed aerodynamic data on both Mach number and reduced frequency when employing the K- or KE-methods of flutter analysis.

GUST Specification of vertical gust parameters. The value of V on this entry must be identical with the VELOCITY input on the AERO entry.

MKAERO1 Specification of Mach number and reduced frequencies for aerodynamic matrix calculations.

MKAERO2 Alternate specifications of Mach numbers and reduced frequencies for aerodynamic matrix calculations.

PAERO1 Defines bodies associated with CAERO1 entries. A PAERO1 entry is required even when there are no bodies. Note that panels and bodies can be in the same interference group (IGID on the CAERO1 and CAERO2 entries) but not be associated. Associated bodies must be in the same interference group as the referencing panel.

PAERO2 Defines body properties. SeeSlender and Interference Bodiesfor an extensive discussion of this entry.

PAERO3 Additional specifications for Mach Box aerodynamics.

PAERO4 Additional specification for Strip Theory aerodynamics.

PARAM This entry, which may also appear in the Case Control Section, is used to provide scalar values used in performing solutions. Parameters in theNX Nastran Quick Reference Guide has a comprehensive discussion of all the NX Nastran PARAMs.

SET1 Selects grids to be used in the splining of aerodynamics. This entry is also used to select flutter modes to be used in flutter sensitivity and optimization.

SET2 An alternative specification of the grids to be used in the splining of aerodynamics.

SPLINE1 Specification of the two-dimensional spline.

SPLINE2 Specification of the one-dimensional spline.

SPLINE3 Alternative specification of the splining between structural and aerodynamic grids. Although this is provided primarily for control surfaces, it has general applicability.

TABRNDG Provides the simplified specification of atmospheric gust power spectral densities. The TABRND1 entry is available for the specification of spectra not supported by this entry.

TRIM Specifies a trim flight condition.

3.5

Restarts

A powerful feature of NX Nastran is its ability to use previously computed results in a subsequent analysis. The “restart” capability is briefly described in Solution Sequences in the

NX Nastran User’s Guide. This subsection first lists common scenarios in an aeroelastic analysis

that would benefit from the restart capability and then provides input data, with examples, required to perform the restart.