Feature Articles - Altair University
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Engine Dynamic Analysis Using Flexible Bodies Harold Thomas, Director of Solver Technology, Altair insider.altairhyperworks.com It’s time to shorten engine dynamic analyses, thanks to a tighter integration between Altair OptiStruct ® and AVL EXCITE. Finite element models are extensively used in research and development of automotive engines. Modal condensation techniques are used to reduce large Degrees of Freedom (DOF) models to Flexible Bodies, in order to be used in dynamic analysis. There are two types of Flexible Bodies used in Multi-Body Dynamic (MBD) analysis: fixed (such as an engine block) and moving (such as a crankshaft or connecting rod). The Flexible Bodies are created using the Component Mode Synthesis (CMS) with the Craig-Bampton reduction method. The number of DOF can be reduced from the number of Finite Element DOF to just a few hundred Craig-Bampton modes. In addition to the reduced mass, stiffness, and damping matrices, the inertial invariants need to be calculated for the moving Flexible Bodies. Also, some of the model information can be stored along with interior point modal vectors so that the MBD software can show movement of the Flexible Body in its post-processor. The movement is calculated by multiplying the calculated modal participation coefficients by the modal vector for each point for each time or frequency step. After the MBD analysis is performed by Software such as AVL EXCITE and SIMPACK, the calculated modal participation coefficients for the Flexible Body can used to calculate the elemental stresses and strains in either the time or frequency domain. This is done by multiplying the modal participation coefficients by the modal stresses or strains for each time or frequency step. Insider Visit the HyperWorks Insider for more Feature Articles at insider.altairhyperworks.com About Altair Altair’s vision is to radically change the way organizations design products and make decisions. We take a collaborative approach to solving diverse and challenging problems through the strategic application of technology and engineering expertise. Developing and applying simulation technology to synthesize and optimize product development processes for improved business performance is our specialty. From computer-aided engineering to high performance computing, from industrial design to cloud analytics, for the past 30 years Altair has been leading the charge to advance the frontiers of knowledge, delivering innovation to more than 5,000 corporate clients representing the automotive, aerospace, government and defense industries and a growing client presence in the electronics, architecture engineering and construction, and energy markets. Performance Simulation Technology HyperWorks is an enterprise simulation solution for rapid design exploration and decision-making. As one of the most comprehensive, open-architecture CAE solutions in the industry, HyperWorks includes best-in-class modeling, analysis, visualization and data management solutions for linear, nonlinear, structural optimization, fluid-structure interaction, and multi-body dynamics applications. www.altairhyperworks.com About HyperWorks ® Listed below are HyperWorks ® applications. Copyright© 2014 Altair Engineering Inc. All Rights Reserved for: HyperMesh ® , HyperCrash ® , OptiStruct ® , RADIOSS ® , HyperView ® , HyperView Player ® , HyperStudy ® , HyperGraph ® , MotionView ® , MotionSolve ® , HyperForm ® , HyperXtrude ® , Process Manager ™ , Templex ™ , Data Manager ™ , MediaView ™ , BatchMesher ™ , TextView ™ , HyperMath ® , Manufacturing Solutions ™ , HyperWeld ® , HyperMold ® , solidThinking ® , solidThinking Evolve ™ , solidThinking Inspire ® , Durability Director ™ , Suspension Director ™ , AcuSolve ® , AcuConsole ® , HyperWorks On-Demand ™ , HyperWorks Enterprise ™ , PBS Works ™ , PBS Professional ® , GridWorks ™ , PBS GridWorks ® , PBS ™ , Portable Batch System ® , PBS Analytics ™ , PBS Desktop ™ , e-BioChem ™ , e-Compute ™ and e-Render ™ . All other marks are the property of their respective owners. Altair Engineering, Inc., World Headquarters: 1820 E. Big Beaver Rd., Troy, MI 48083-2031 USA Phone: +1.248.614.2400 • Fax: +1.248.614.2411 • www.altair.com • [email protected]
Transcript of Feature Articles - Altair University
Engine Dynamic Analysis Using Flexible BodiesHarold Thomas, Director of Solver Technology, Altair
insider.altairhyperworks.com
It’s time to shorten engine dynamic analyses, thanks to a tighter integration between Altair OptiStruct® and AVL EXCITE. Finite element models are extensively used in research and development of automotive engines. Modal condensation techniques are used to reduce large Degrees of Freedom (DOF) models to Flexible Bodies, in order to be used in dynamic analysis.
There are two types of Flexible Bodies used in Multi-Body Dynamic (MBD) analysis: fixed (such as an engine block) and moving (such as a crankshaft or connecting rod). The Flexible Bodies are created using the Component Mode Synthesis (CMS) with the Craig-Bampton reduction method. The number of DOF can be reduced from the number of Finite Element DOF to just a few hundred Craig-Bampton modes. In addition to the reduced mass, stiffness, and damping matrices, the inertial invariants need to be calculated for the moving Flexible Bodies. Also, some of the model information can be stored along with interior point modal vectors so that the MBD software can show movement of the Flexible Body in its post-processor. The movement is calculated by multiplying the calculated modal participation coefficients by the modal vector for each point for each time or frequency step.
After the MBD analysis is performed by Software such as AVL EXCITE and SIMPACK, the calculated modal participation coefficients for the Flexible Body can used to calculate the elemental stresses and strains in either the time or frequency domain. This is done by multiplying the modal participation coefficients by the modal stresses or strains for each time or frequency step.
Insider
Visit the HyperWorks Insider for more
Feature Articlesat insider.altairhyperworks.com
About Altair
Altair’s vision is to radically change the way organizations design
products and make decisions. We take a collaborative approach to
solving diverse and challenging problems through the strategic
application of technology and engineering expertise. Developing and
applying simulation technology to synthesize and optimize product
development processes for improved business performance is our specialty.
From computer-aided engineering to high performance computing,
from industrial design to cloud analytics, for the past 30 years Altair
has been leading the charge to advance the frontiers of knowledge,
delivering innovation to more than 5,000 corporate clients representing
the automotive, aerospace, government and defense industries and
a growing client presence in the electronics, architecture engineering
and construction, and energy markets.
Performance Simulation Technology
HyperWorks is an enterprise simulation solution for rapid design
exploration and decision-making. As one of the most comprehensive,
open-architecture CAE solutions in the industry, HyperWorks includes
best-in-class modeling, analysis, visualization and data management
solutions for linear, nonlinear, structural optimization, fluid-structure
interaction, and multi-body dynamics applications.
www.altairhyperworks.com
About HyperWorks®
Listed below are HyperWorks® applications. Copyright© 2014 Altair Engineering Inc. All Rights Reserved for: HyperMesh®, HyperCrash®, OptiStruct®, RADIOSS®, HyperView®, HyperView Player®, HyperStudy®, HyperGraph®, MotionView®, MotionSolve®, HyperForm®, HyperXtrude®, Process Manager™, Templex™, Data Manager™, MediaView™, BatchMesher™, TextView™, HyperMath®, Manufacturing Solutions™, HyperWeld®,
HyperMold®, solidThinking®, solidThinking Evolve™, solidThinking Inspire®, Durability Director™, Suspension Director™, AcuSolve®, AcuConsole®, HyperWorks On-Demand™, HyperWorks Enterprise™, PBS Works™, PBS Professional®, GridWorks™, PBS GridWorks®, PBS™, Portable Batch System®, PBS Analytics™, PBS Desktop™, e-BioChem™, e-Compute™ and e-Render™. All other marks are the property of their respective owners.
Altair Engineering, Inc., World Headquarters: 1820 E. Big Beaver Rd., Troy, MI 48083-2031 USAPhone: +1.248.614.2400 • Fax: +1.248.614.2411 • www.altair.com • [email protected]
insider.altairhyperworks.com
Engine Dynamic Analysis Using Flexible Bodies
The modal stresses and strains are calculated during the Flexible Body reduction step and stored for later use in the stress or strain recovery step. The stresses and strains can then be passed to Fatigue Software using the .op2 or .h3d files.
With most Finite Element Software, the reduced matrices, model information, interior point modal vectors, and the full mass matrix are written to a number of different files. Special DMAP, macro’s, or scripts are needed to tell the Finite Element software to create these files After the files are generated, a translator is used to calculate the inertial invariants for moving parts and then generate the input data file for the MBD software. This calculation and translation can take hours for some models. The intermediate files can be many Gigabytes of data. With Altair OptiStruct, this step is not required. OptiStruct automatically calculates the inertial invariants and directly writes the MBD input data file directly. These are the .fbi file for SIMPACK and the .exb file for AVL EXCITE.
In addition, no DMAP, macro, or scripts are required. The only input data needed is PARAM, SIMPACK for SIMPACK or PARAM, EXCEXB for AVL EXCITE.
The modal condensation time for OptiStruct can be reduced from many hours, or even days, with Lanczos to just 1 to 2 hours using the AMSES solver that is built into OptiStruct. The AMSES solver uses a multi-level sub-structuring technique to dramatically reduce this calculation time. AMSES is provided at no additional cost in OptiStruct and runs on both Linux and Windows.
The solver is so fast that these reductions can be done on a local workstation, or even laptop, rather than on an expensive server. Many Flexible bodies can be made up of more than one component, for example a crankshaft and flywheel. OptiStruct offers tied contact to connect these two components even if the meshes do not match at the interface.
For the second step of stress or strain recovery, most Finite Element software needs to recreate the modal stresses and strains, which can take hours. With OptiStruct, the modal stresses and strains are stored in the .h3d file during the Flexible Body creation run. Using these stored modal stresses and the modal participation coefficients from the MBD analysis, the element stresses and strains can be calculated in just a few seconds or minutes, as it is just a matrix-matrix multiply.
The integration of OptiStruct can reduce the time required for the entire engine dynamic analyses process from days to just a few hours by utilizing AMSES with fast Flexible Bodies generation, reduced matrices and inertial invariants with MBD input data file, and fast fatigue analysis calculation of element stresses or strains.
Insider
Crankshaft meshing for AVL EXCITE. Depiction of an engine block. Comparison between full and partial model surface results.
