ANSYS AnalysisCompression Tools

Rotor DynamicsAdditional tools useful for modelingrotating machinery, such as electricturbo generators, in modal, harmonicand transient dynamic analyses

The design mantra "lighter, faster, stronger" is pervasive across industries from consumer electronics to space exploration. But as machines with rotating components get lighter, faster and stronger as well as spin faster, theyare increasingly susceptible to self-induced system-destroying vibrations.

Customers in the rotating machinery andother industries use ANSYS software toanalyze:

Bending deflection of shaftsTorsional oscillationsMisalignments of rotor axisBalancing of rotating parts

ANSYS® Dynamics Solutions

The ANSYS Family of Products

The ANSYS Dynamics Solution SetANSYS software provides extensive dynamics solution capabilities, including:

Modal analysis: for calculating the natural frequencies and mode shapes of a structure

Harmonic analysis: for determining the response of a structure to harmonically time-varying loads, such as those typically seen in rotating machinery

Transient dynamic analysis: for determining the response of a structure to arbitrarily time-varying loads in linear and nonlinear simulation environments. The most general and comprehensive of all dynamics analysis types, transientdynamics can be subdivided into:

Rigid dynamicsFlexible dynamics

Spectrum analysis: an extension of modal analysis for calculating stresses andstrains due to a response spectrum or a power spectral density (PSD) input (random vibrations)

Static analysis: often used to determine displacements, stresses, etc. under linear and nonlinear static loading conditions. Static analyses also can be used in conjunction with dynamic analyses for improved efficiencies, such as a pre-stressed modal simulation (as is typically done in the turbine development process).

Analysis compression tools: Dynamics analyses, particularly those with extensive nonlinearities, can be computationally demanding. Therefore, additionalanalysis compression tools include:

Rotor dynamics: useful for modeling rotating machinery, such as electric turbo- generators, in modal, harmonic and transient dynamic analysesComponent modal synthesis: for breaking up a single large problem into several reduced-order problemsDistributed ANSYS: for solving large models using multiple processorsVariational Technology: exposed in the ANSYS® DesignXplorer VT™ product; used to rapidly explore parametric model variations far faster than can be done when searching for an optimal configuration using traditional approaches

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Modeling gyroscopic moment, rotorwhirl and instability in multi-platendisk drive with ANSYS rotor dynamics tool set

ANSYS Modal AnalysisA modal analysis typically is used to determine the vibration characteristics (natural frequencies and mode shapes) of a structure or machine component in the design stage.It also can serve as a starting point for another more-detailed dynamic analysis, such asharmonic response or full transient dynamic analysis.

Modal analysis is one of the most basic dynamic analysis types available in ANSYS software — yet it can be more computationally time consuming than a typical static analysis. A reduced solver, utilizing automatically or manually selected master degrees-of-freedom (DOFs), is used to drastically reduce the problem size and solution time.Multiple time-saving modal solution methods are available in ANSYS software for modeextraction from the reduced solution, such as:

Block Lanczos method: typically used for large symmetric eigenvalue problems; utilizes a sparse matrix solverPCG Lanczos method: for very large symmetric eigenvalue problems (500,000+DOFs); especially useful to obtain a solution for the lowest modes to learn how themodel will behaveSubspace method: for large symmetric eigenvalue problems, though in most cases the Block Lanczos method is preferred for shorter run times with equivalent accuracyReduced (Householder) method: faster than the subspace method because it usesreduced (condensed) system matrices to calculate the solution; normally less accurate because the reduced mass matrix is approximateUnsymmetric method: used for problems with unsymmetric matrices, such as fluidstructure interaction (FSI) problems Damped method: for problems in which damping cannot be ignored, such as journal bearing problemsQR damped method: faster than the damped method; uses the reduced modaldamped matrix to calculate complex damped frequencies

Analysis Compression ToolsHigh-Performance

Computing

The high-performance computing optionof ANSYS software decreases solutiontime for full transient structural, staticstructural and modal analyses. Shownare the solution times and speedup factors for solving a 112-million degree-of-freedom modal analysis problem.

Distributed ANSYS (DANSYS): solvinglarge models using multiple processorsMultiprocessing is one way to reduceanalysis time. Multiprocessing computerenvironments (consisting of multipro-cessor servers or networked work-stations or clusters) may be employedto generate analysis results much morequickly. DANSYS runs equally well onboth shared memory parallel (SMP)machines, such as high-end servers,and a distributed memory parallel(DMP) cluster. DANSYS supports awide variety of analysis types including:• Static linear or nonlinear analyses

structural• Single field thermal analyses

(DOF: TEMP)• Full transient analyses for single-field

structural and single-field thermal analysis

• Modal analyses using block Lanczos and PCG_Lanczos solutions

• Structural harmonic analyses• Low-frequency electromagnetic

analysis• Coupled-field analyses including

structural_thermal, piezoresistive, electroelastic, piezoelectric, thermal_

electric, structural_thermoelectric, thermal_piezoelectric

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Finite element representation ofbody-in-white model of prototypeSUV as simulated with blockLanczos method modal analysis tofind critical low-frequency naturalvibration modes, which can causepassenger discomfort if excited

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ANSYS Harmonic AnalysisUsed extensively by companies that produce rotating machinery, ANSYS harmonicanalysis is employed to predict the sustained dynamic behavior of structures to consistent cyclic loading. Examples of rotating machines that produce or are subjected to harmonic loading include:

Turbines• Gas turbines for aircraft and

power generation• Steam turbines• Wind turbines• Water turbines• TurbopumpsInternal combustion enginesElectric motors and generatorsGas and fluid pumpsDisc drives

A harmonic analysis can be used to verify whether or not a machine design will successfully overcome resonance, fatigue and other harmful effects of forced vibrations.

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Analysis Compression Tools

ANSYS® VT AcceleratorTM softwarespeeds up the solution of nonlinearstructural static or transient analyses by reducing the total number of iterations for analyses not involving contact or plasticity. Additionally, theharmonic sweep feature of ANSYS VTAccelerator provides a high-perform-ance solution for forced-frequency simulations in structural analysis over arange of user-defined frequencies. Thestructural material may have frequency-dependent elasticity or damping.

Component modal synthesis: breakingup a single large problem into severalreduced-order problems saves time andprocessing resources; it also offers thefollowing additional advantages: • More accurate than a Guyan

reduction for modal, harmonic and transient analyses

• The ability to include experimental results, as the substructure model need not be purely mathematical

ANSYS geometry tools allow import and editing of chiller model from CAD system in preparation for rotating component analysis.Images courtesy Trane, a business of American Standard.

Rotordynamics investigation of rotating components of chiller assembly can be accelerated by using advanced techniques such ascomponent mode synthesis (CMS).

Chiller assembly results from modal and harmonic analyses areused to predict stability vibrationcharacteristics of machine before an expensive prototype is produced.

Analysis Compression ToolsANSYS® DesignXplorerTM

ANSYS DesignXplorer software, whichis based on Design of Experiments(DOE), works from within the ANSYS®

WorkbenchTM environment to performDOE analyses of any ANSYSWorkbench simulation, including thosewith CAD parameters. DOE is not limited in the types of analyses. ANSYSDesignXplorer allows the user to study,quantify and graph various structuraland thermal analysis responses on parts and assemblies. It incorporatesboth traditional and nontraditional optimization through a goal-driven optimization method. When coupled with ANSYS VT Accelerator software,ANSYS DesignXplorer can effectivelywork with structural transient analyses.

ANSYS Transient Dynamic AnalysisTransient dynamic analysis (sometimes called time_history analysis) is a techniqueused to determine the dynamic response of a structure under the action of any generaltime-dependent loads. Transient dynamic analyses are used to determine the time-vary-ing displacements, strains, stresses and forces in a structure as it responds to any combination of static and time-varying loads while simultaneously considering the effectsof inertia or damping.

Transient dynamic analysis in ANSYS software can be broadly classified as one of two types:

Rigid dynamics: In an assembly, all parts are considered to be infinitely stiff, no mesh is required and a special solver is used to drastically reduce the amount ofcompu-tational resources required. The primary focus of a rigid dynamics simulationis mechanism operation, part velocities and accelerations, as well as joint forcesencountered during the range of mechanism motion. The new ANSYS rigid dynamicsproduct is used for this type of simulation.Flexible dynamics: Some or all parts of an assembly are meshed and considered flexible based on the materials from which they are made. A flexible dynamics simulation typically is done after a rigid dynamics simulation is used to verify themodel setup. Flexible dynamics simulation can provide information about machineperformance, such as: • Will a machine or mechanism work adequately with light, more-flexible members,

or will stiffer but heavier members be required?• Will the forces transmitted through joints exceed the strength of the materials

being used?• At what rotational or translation speed will the mechanism experience plastic

deformation and begin to fail?• Will the mechanism’s natural frequencies be excited and lead to instability?• Will the repeated loading/unloading lead to fatigue and, if so, where?

A flexible dynamics simulation can be performed using ANSYS® Structural™, ANSYS®

Mechanical™ or ANSYS® Multiphysics™ products.

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Images courtesyDale Earnhardt Inc.

ANSYS Random Vibration AnalysesANSYS random vibration analyses are used to deter-mine the response of structures to random or time-dependent loading conditions, such as earthquakes,wind loads, ocean wave loads, jet engine thrust,rocket motor vibrations, and more. The random vibration analysis can be much less computationallyintensive than a full transient dynamic analysis whilestill providing design-guiding results. Types of random vibration analyses include:

Response spectrum: single and multi-point baseexcitation in which the results of a modal analysisare used with a known spectrum to calculate themodel’s displacements and stressesDynamic design analysis method (DDAM): a technique used to evaluate the shock resistanceof shipboard equipment. It is similar to theresponse spectrum method except the loading isderived from empirical equations and shock design tables.Power spectral density: a statistical-based random vibration method in which the input load histories are specified based on a probability distribution of theloading taking that particular value. An example application is the calculation ofthe probable response of a sensitive automotive electronic component to theengine and drive train vibrations while the vehicle travels rapidly down a rough road.

Exhaust manifold/catalytic converterassembly model utilized in PSD randomvibration analysis

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ANSYS Static AnalysisA static analysis can be a very smart first step in a dynamics simulation. Before investing in a dynamics simulation, a static analysis can be used for:

Model verification, answering questions such as:• Is contact set up correctly between parts of an assembly?• Are the defined boundary conditions providing the expected support?• Is the mesh refined in the locations of potentially significant distortion or stress concentrations?• Is there an inadvertent mesh discontinuity?• Do you need to model nonlinearities, which are computationally expensive, or do the static results

suggest that the potential nonlinearities aren’t required?Efficiently pre-loading or pre-stressing a model• Apply a constant rotational velocity to a turbine, for instance, pre-stressing the entire structure

including the turbine blades prior to a bird strike analysis.• Apply temperature loading from a previous thermal simulation to pre-stress the model thermally

in a single iteration before running a multi-iteration dynamics analysis.

The ANSYS AdvantageANSYS software provides customers with a competitive advantage through:

ANSYS® Workbench™, which provides a unified product development environment offering integration across a wide range of design processes — ranging from geometry modeling and editing, meshing and pre-processing to advanced analysis (structural, thermal, electromagnetics, CFD, etc.) to robust design optimizationProviding industry’s broadest range of physics capability in one integrated analysis environmentAdvanced meshing solutions to efficiently address high-aspect ratio geometry commonly associated with complex product applicationsAdvanced material models and contact types for simulating plastics, rubber, sliding surfaces and large deformations

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Dynamics Functionality by Product

ANSYS ANSYS ANSYS ANSYS® ANSYS Multiphysics Mechanical Structural Professional™ Professional

NLS NLTStructural Dynamic Analysis Type

Modal X X X X XSpectrum X X X X XHarmonic X X X X XRandom vibration X X X

Structural Linear FunctionalitySubstructuring X X XComponent mode synthesis X X XCyclic symmetry X X X X XMode superposition X X X X X

Structural Nonlinear FunctionalityGeometric X X X X Note 1Material X X X X XElement X X X X XLarge strain X X X XLarge deflection X X X XStress stiffening X X X XSpin softening X X X X

Material ModelingLinear elasticity X X X X XInelastic X X X XRate-independent X X X XRate-dependent X X X XNon-metal plasticity X X X XShape memory alloys X X X XCast iron X X X XHyperelasticity (isotropic/anisotropic) X X X XViscoplasticity and viscoelasticity X X X XCreep and swelling X X X XMaterial damping X X X XUser materials X X X XTemperature-dependent properties X X X X X

Solver TypesIterative X X X X XSparse direct X X X X XFrontal (wavefront) X X X X XDistributed memory PCG Note 2 Note 2 Note 2 Note 2 Note 2Distributed memory JCG Note 2 Note 2 Note 2 Note 2 Note 2Distributed sparse (Dsparse) Note 2 Note 2 Note 2 Note 2 Note 2Algebraic multi-grid (AMG) Note 2 Note 2 Note 2 Note 2 Note 2

GeneralParametric simulation X X X X XCAD parameter access Note 3 Note 3 Note 3 Note 3 Note 3ANSYS Parametric Design Language X X X X XDesign optimization Note 4 Note 4 Note 4 Note 4 Note 4

Note 1: Not available for 2-D plane and 3-D solid elementsNote 2: Available in ANSYS Mechanical HPC add-on module Note 3: Available through either the ANSYS DesignModeler add-on or with ANSYS Workbench when

used with a geometry interface and a parametrically supported CAD systemNote 4: Available through the ANSYS DesignXplorer add-on moduleNote 5: Rigid dynamics is available in a separate module, ANSYS Rigid Dynamics

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Image Credits: Some images courtesy Aavid Thermalloy, ICT Prague and Silesian University of Technology—Institute of Thermal Technology.

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ANSYS, Inc. SolutionsANSYS designs, develops, markets and globally supports engineering simulationsolutions used to predict how product designs will behave in manufacturing and real-world environments. Its integrated, modular and extensible set of solutionsaddresses the needs of organizations in a wide range of industries. ANSYS solutions qualify risk, enabling organizations to know if their designs are acceptableor unacceptable — not just that they will function as designed. ANSYS helps organizations achieve:

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About ANSYS, Inc.ANSYS, Inc., founded in 1970, develops and globally markets engineering simula-tion software and technologies widely used by engineers and designers across abroad spectrum of industries. The Company focuses on the development of openand flexible solutions that enable users to analyze designs directly on the desktop,providing a common platform for fast, efficient and cost-conscious product develop-ment, from design concept to final-stage testing and validation. The Company andits global network of channel partners provide sales, support and training for cus-tomers. Headquartered in Canonsburg, Pennsylvania, U.S.A., with more than 40strategic sales locations throughout the world, ANSYS, Inc. and its subsidiariesemploy approximately 1,400 people and distribute ANSYS products through a net-work of channel partners in over 40 countries.

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