The highly integrated, digital computer program, STARS (STructural Analysis RoutineS), has been designed as an efficient tool for analyzing practical engineering problems and for supporting relevant research and development activities. Each individual module (Fig. 1.1) of the program is general-purpose in nature and capable of solving a wide array of problems.
Theoretical basis of analysis performed by the program is contained in reference 2, which may be perceived as the relevant Theoretical Manual. The analysis is initiated by typing "stars" under c:stars directory. Then any of the major analysis modules, as shown in Fig. 1.2, can be run individually by commands srun, arun, etc..
Alternatively, one may type stars_gui to activate the GUI and STARS analyses can be started by clicking on the same, as appropriate (Fig. 1.3), which is self explanatory. These can be used along with run stream details presented in Appendix D, in conjunction with Figures 6.1 and 9.1, and also Tables 6.1 and 9.1 respectively, for convenient analysis of problems.
The SOLIDS (STRUCTURES) module is capable of analyzing static, stability, vibration, and dynamic-response problems for all types of structures, including spinning structures subjected to mechanical and thermal loading. Both linear and nonlinear analyses are conveniently performed by the program. The element library consists of an extensive number of one-, two-, and three-dimensional elements with general material properties, including composite and sandwich elements. Structural as well as viscous damping can be included in the analysis. The OPTIMIZER submodule enables effective design of a system and currently operational for structural problems. It is presently being expanded for other disciplines. The heat-conduction analysis capability in the program is effected through the SOLIDS HEAT TRANSFER module. Both steady state and transient analyses can be performed, including nonlinear effects. The element library consists of line, shell, and solid elements, including sandwich and composites. Figure 1.4 depicts the major features of this SOLIDS module. A variety of options are available for automatic model and data generation.
Figure 1.5 shows a schematic of the associated linear aeroelastic and aeroservoelastic (ASE) analyses, that also includes a recently augmented Gust response & Ride Quality module. The STARS- AEROS (aerodynamics) module is used to compute the linear unsteady aerodynamic forces on the structure, once the frequencies and mode shapes of the structure are derived from finite-element analysis employing the STARS-SOLIDS module. An alternative option enables input of measured modal data in lieu of calculated data. An aeroelastic (flutter) solution is then achieved using the k or p-k methods of the AEROS module. The user has to input details of the aerodynamic paneling to achieve the aeroelastic analysis. Subsequent linear ASE analysis is achieved by employing the STARS-ASE module. The user provides essential data to perform a polynomial curve fitting of unsteady aerodynamic forces resulting in the state-space matrices. For an alternative open-loop flutter analysis, these data consist of information on polynomial tension coefficients, previously calculated generalized masses, damping and modal characteristics, and a set of velocity values. Additional data, in lieu of velocity values, relating to coordinate transformations from Earth- to body-centered coordinate systems and sensor locations are needed for the subsequent ASE analysis for frequency-response calculations and for determining damping and frequency values. These additional data are achieved by the STARS-ASE-CONTROL submodule in which the primary data input relates to analog or digital controller blocks connectivity, associated transfer function polynomial descriptions and gain input, specifications for system output and input, and connection details between the plant and the blocks. This ASE analysis procedure can also be effectively used as the third flutter (state-space) solution option.
The STARS-CFDASE module is used for nonlinear CFD-based aeroelastic and ASE analyses (Figure 1.6). The STEADY submodule, which employs unstructured grids for domain discretization, can be effectively employed for the solution of fluid flow problems. The STARS-CFDASE module enables ready computation of unsteady aerodynamic forces employing the finite element-based structural and computational fluid dynamics (CFD) computations. Subsequent aeroelastic analysis predicts flutter and divergence characteristics of the structure, whereas the ASE analysis computes the required stability derivatives. Options are available for unsteady aerodynamics computation, which includes CFD, Piston and their ARMA (Auto Regressive Moving Average) counterparts for increased solution efficiency. The associated PROPULSION module essentially employs CFD techniques for simulation of flow-mixing phenomenon. Data pertaining to advanced material properties are stored in the MATERIALS module.
The AERO-ELASTIC-ACOUSTICS module can be employed for computing acoustic sound levels generated by unsteady aerodynamic pressure that are obtained by simulating the interaction of a flexible structure with air. Both sound pressure level (SPL) and acoustic wave frequencies can be calculated in this module. Aero-thermo-elastic-acoustics analysis can also be performed. Both linear and non-linear aerodynamic data can be used for acoustic simulations.
The NUMERICAL ANALYSIS module contains a number of efficient solution procedures for large, sparse, matrix linear equations and eigenvalue problems. A Progressive Simultaneous Iteration (PSI) methods as well as ARNOLDI and Lanczos techniques are available for large scale eigensolution of nonspinning and spinning structures as well as the quadratic matrix eigenvalue problem associated with a finite-dynamic element formulation.
A set of translator programs enable various CAD programs data to be converted into STARS format. A separate preprocessor submodule, PREPROCS, has been developed for automated generation of nodal, element, and other associated input data for any continuum. The PREPROCS submodule is capable of generating complex structural forms through duplication, mirror imaging, and cross-sectioning of modular representative structures. Appendix A contains the Preprocessor manual. A fully automated, three-dimensional mesh generation capability is an important feature of this module. The STARS postprocessor submodules, POSTPLOTS and POSTPLOTF, are used for extensive color plotting of various structural-, heat-transfer- and CFD-related solution results. Appendix B is the Postprocessor manual.
Section 2 describes the STARS-SOLIDS module of the program and highlights some of its important features. Section 3 provides the data input procedure. Section 4 provides summaries of input data and analysis results for sample test cases relevant to this module. Section 5 describes the various features of the aeroelastic and ASE analyses capabilities, and Section 6 provides data input details of various related submodules. A representative, integrated aero-structural-control sample problem is worked out in detail in Section 7. Section 8 provides details of CFD analysis, as well as nonlinear aeroelasticity and ASE. Details of data input for CFD-based aeroelastic and aeroservoelastic analyses are given in chapter 9. A complete set of such analyses, pertaining to a representative wing problem is presented in chapter 10. Examples of coupled problems are given in chapters 10 and 11.
Appendix A presents details of STARS PREPROCESSOR manual, suitable for automated model data generation. Postprocessing capabilities for graphical display of solution results are described in Appendix B. Appendix C provides the STARS systems description. Details of STARS analysis runstream are depicted in Appendix D, which should be of much help to the users in executing STARS solutions. All example problems provided herein have the corresponding input data in TESTCASES directory with three major submodules, namely SOLIDS, ASE (Aeros & Ase) and CFDASE.
