Design/Simulation Software Advances Aero
In three key areas of aerospace—finite element analysis, composite material manufacturing, and requirements management for in-flight electronic hardware—the associated design and simulation software continues to get easier, more capable, and faster.
FEA meets 2010
Within the broad umbrella of avionics and aerospace, finite element analysis (FEA) software covers a variety of domains. Structural. Computational fluid dynamics. Turbomachinery. Fluid-structure iterations (FSI). Acoustics. Thermal. And more. Consider three mainstays from MSC.Software (mscsoftware.com). (1) Patran is a set of FEA tools for creating analysis-ready finite element models. (2) Dytran is a general-purpose, three-dimensional explicit FEA program for simulating and analyzing extreme, short-duration events involving structural materials deformations—think bird strikes on jet engines—and FSI. (3) Marc is a general-purpose, implicit, nonlinear FEA program for simulating and analyzing static, dynamic, and coupled physics problems. All three got bumped up a rev.
(1) Patran 2010 features has 64-bit support for Windows and Linux (it already supports Unix). Analysts can work on models 20 times larger than they could on 32-bit systems, according to MSC.Software officials. And the analysis is fast. For example, a group transform operation to create a duplicate set of 3.06 million tetrahedral finite elements and nearly 600,000 nodes took 60 seconds. This operation is not possible in 32-bit Patran. The Windows version of Patran 2010 sports the familiar Microsoft Office ribbon user interface. Patran’s standard toolbar has been replaced with a customizable “quick access bar” to hold commonly used commands and user-defined functions. Shift, control, and right button mouse clicks let analysts perform basic model zoom, pan, and rotate. Right-button mouse clicks alone provide a wealth of context-sensitive menu commands, such as verify and optimize model entities.
Patran also has a variety of multidiscipline (MD) and multiphysics enhancements. It now supports the composites capabilities introduced in MD Nastran R3, including support for 3D solid elements and shell models, PCOMP and PCOMPLS property data, and various material-failure models. Patran can plot Campbell diagrams for rotordynamic analyses (identifying critical speeds and stability). The program also supports several multiphysics capabilities found in Marc, including electrostatic, Joule heating, electrostatic-structural coupling, magnetostatics, and electromagnetics. With its updated Parasolid-based translators, Patran supports Catia V5 R19 from Dassault Systèmes, NX 5 (on Windows, NX 6) from Siemens PLM Software, and Pro/E Wildfire 4.0 from Parametric Technology Corporation.
(2) Dytran 2010. This analysis program includes advanced distributed memory parallel (DMP) capabilities for single- and multi-material hydro Euler and coupled analysis (i.e., FSI). DMP also supports biased mesh, coupling surface and output markers, geometry boundaries, and viscosities. In general, DMP significantly speeds up CPU-intensive analyses. Dytran 2010 can also solve new classes of FSI problems. For example, analysts can specify two boundary conditions that form a cyclic boundary by linking the outflow at one boundary with the inflow of another. Dytran runs on 32- and 64-bit Windows and Linux, and several Unix systems from Hewlett-Packard, Sun Microsystems, and IBM.
(3) Marc 2010 is optimized for multi-core parallelization. For instance, the Marc multifrontal solver uses multithreading, and the Pardiso (parallel direct sparse solver) can be used on shared-memory architectures (32- and 64-bit Windows and Linux systems; it already runs on Unix). The Mumps (multifrontal massively parallel sparse direct solver) in Marc can be used in both shared or distributed memory Windows and Linux environments. All of this lets analysts run bigger—and more complex models faster.
Marc has two new material models: The exponential cap model for modeling granular materials, such as powder metals, ceramics, and soils; and the 5th-order Mooney model for rubber analysis. Lagrange analysis handles large shell and beam rotations more accurately and with improved convergence, which helps in analyzing problems involving large deformations and large rotations. Enhancements in Marc’s VCCT capabilities help in predicting both crack onset and crack propagation. Last, two new user subroutines help in simulating delamination in composite parts: one to define a stress criterion for breaking up a glued connection; the other to customize a delamination index.
Better composites manufacturing
All new aircraft programs include a high amount of composites—more than 50% of the structures by weight—according to Steve Peck, director of product and market strategy for aerostructures at Vistagy Inc. (vistagy.com). So it’s no surprise that “software is an essential part of the overall aerostructures development process,” says Peck. Unlike conventional aerospace materials such as aluminum, composite design and manufacturing is far more complex, uncertain, variable. The use of composites is an exercise in trade-offs: geometry, material, and the manufacturing process itself. The software has to balance these tradeoffs, plus handle a multitude of problems inherent in aerospace composite manufacturing: the specialized art of composite design and manufacturing, huge volumes of data, the capture and reuse of engineering design data for downstream processes, and providing design/data traceability and design compliance.
AeroSuite from Vistagy for composite design consists of three software products (plus consulting services). First, there’s FiberSIM, which addresses the entire composites engineering process: concept design, laminate definition and ply creation, simulation, performance optimization, flat pattern generation, documentation, and manufacturing. Among the features of the current release are a global stagger profile that will assign a user-specified drop-off profile to an entire part; an enhanced partial boundary editor that helps reduce layer boundary calculations and recalculations by highlighting specific regions of a part; and a new design checker that alerts users when flat patterns need to be generated, plies need to be spliced, or objects are out of date. Also, enhancements to zone-based design lets users define a trimming or extending angle for zone transition areas, which simplifies generating complex transitional shapes.
Earlier this year, Vistagy integrated Automatic Ply Verification (APV) into FiberSIM. APV is a feature of the Laserguide laser projection system from Assembly Guidance Systems (assemblyguide.com). This projection system directs the accurate layup of composite plies. For APV, FiberSIM automatically generates two files. One from the 3D CAD model controls the laser projection system during ply layup. The other is an APV file, which contains a complete set of manufacturing commands that operators use to inspect each ply during manufacturing. This way, operators can document that hand-laid composites parts have been fabricated correctly.
Another program in AeroSuite is SyncroFIT (a group of products formerly known as “Airframe Development Environments”). SyncroFIT lets 3D CAD designers define and manage joints and interfaces between parts within complex assemblies, such as airframe assemblies and large aerostructures. It also manages the interactions of composite details within assemblies, which helps ensure compliance with fastener design rules. SyncroFIT performs various fastener-related design checks, including edge distance and pitch, countersink depth, angularity, and length-to-diameter ratio. These design checks help catch common fastener-related errors before design release.
Last in the AeroSuite line-up is the Quality Planning Environment (QPE), which helps ensure airframes are manufactured based on the design and manufacturing data created by FiberSIM and SyncroFIT (and saved in the CAD model). This ultimately shortens the time to generate inspection plans, reduces errors in planning, and tailors plans for quality assurance.
Ensuring electronic hardware compliance
One of the latest standards in aviation involves electronics hardware, which by extension includes device-level software. RTCA/DO-254 “Design Assurance Guidance for Airborne Electronic Hardware” is a standard enforced by the Federal Aviation Administration, European Aviation Safety Agency, and other aviation certification agencies. DO-254 helps ensure the safety of in-flight hard-
ware by requiring designs be traceable from requirements to implementation to test. Engineers must validate design requirements, demonstrate traceability from the requirements to the design, and document both this traceability and the verification of the design. Such compliance is costly. Automat-ing or otherwise facilitating key aspects of DO-254 compliance helps mitigate those costs.
Within the scope of DO-254 is documenting the hardware description language (HDL)—the coding that describes the digital logic in electronic circuits—as well as documenting the mechanism to review the code against requirements. Toward this goal is a collaboration between Mentor Graphics Corp. (mentor.com/products/fpga/do-254) and The Mathworks (mathworks.com/do-254). From Mentor Graphics is ReqTracer, which manages and traces device requirements from electronic system-level design and development, to electronic hardware design, to software design and verification. ReqTracer tracks requirements from multiple sources throughout the design process, provides documentation at any stage, and manages requirement changes.
From The Mathworks is Simulink HDL Coder. Here’s how it works. ReqTracer collects and manages requirements. These requirements drive an executable Simulink model. Engineers use this model to create a conceptual design, including implementation details. Engineers then use Simulink and Stateflow verification and validation tools to functionally test and analyze this model at the conceptual level. (The model’s links are bidirectional; it can drive the requirements in ReqTracer, further ensuring traceability.) The Simulink HDL Coder then automatically generates target-independent bit-true, cycle-accurate, synthesizable HDL code (IEEE-compliant Verilog and VHDL code) for the datapath and control sections of the detailed design. Engineers can verify the automatically generated HDL code using popular functional verification products, and they can map the automatically generated HDL code into FPGAs or ASICs using popular synthesis tools.
