Linear Structural Analysis - Lawrence Berkeley National als/FEA/Workbench_Sim · PPT...

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Transcript of Linear Structural Analysis - Lawrence Berkeley National als/FEA/Workbench_Sim · PPT...

  • Static Structural Analysis

    Chapter Four

    ANSYS Workbench Simulation

    Training Manual

    Linear Static Structural Analysis

    Chapter Overview

    In this chapter, performing linear static structural analyses in Simulation will be covered:Geometry and ElementsContact and Types of Supported AssembliesEnvironment, including Loads and SupportsSolving ModelsResults and Postprocessing

    The capabilities described in this section are generally applicable to ANSYS DesignSpace Entra licenses and above.Some options discussed in this chapter may require more advanced licenses, but these are noted accordingly.Free vibration, harmonic, and nonlinear structural analyses are not discussed here but in their respective chapters.

    ANSYS Workbench Simulation

    Training Manual

    Linear Static Structural Analysis

    Basics of Linear Static Analysis

    For a linear static structural analysis, the displacements {x} are solved for in the matrix equation below:

    Assumptions:[K] is constantLinear elastic material behavior is assumedSmall deflection theory is usedSome nonlinear boundary conditions may be included{F} is statically appliedNo time-varying forces are consideredNo inertial effects (mass, damping) are includedIt is important to remember these assumptions related to linear static analysis. Nonlinear static and dynamic analyses are covered in later chapters.

    ANSYS Workbench Simulation

    Training Manual

    Linear Static Structural Analysis

    A. Geometry

    In structural analyses, all types of bodies supported by Simulation may be used.

    For surface bodies, thickness must be supplied in the Details view of the Geometry branch.

    The cross-section and orientation of line bodies are defined within DesignModeler and are imported into Simulation automatically.For line bodies, only displacement results are available.

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    Import of shell thickness from CAD system

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    Linear Static Structural Analysis

    Point Mass

    A Point Mass is available under the Geometry branch to mimic weight not explicitly modeledA point mass is associated with surface(s) onlyThe location can be defined by either:(x, y, z) coordinates in any user-defined Coordinate SystemSelecting vertices/edges/surfaces to define locationIn a structural static analysis, the point mass is affected by Acceleration, Standard Earth Gravity, and Rotational Velocity. No other loads affect a point mass.The mass is connected to selected surfacesassuming no stiffness between them. No rotational inertial terms are present.

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    Point Mass

    A point mass will be displayed as a round, grey spherea point mass in a linear static analysis can be used to account for the additional mass of a structure not modeledNo results are obtained for the Point Mass itself

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    Linear Static Structural Analysis

    Material Properties

    Youngs Modulus and Poissons Ratio are required for linear static structural analysesMaterial input is handled in the Engineering Data applicationMaterials are assigned per part in the geometry branchMass density is required if any inertial loads are presentThermal expansion coefficient and thermal conductivity are required if any thermal loads are presentStress Limits are needed if a Stress Tool result is presentFatigue Properties are needed if Fatigue Tool result is presentRequires Fatigue Module add-on license

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    Linear Static Structural Analysis

    Material Properties

    Engineering Data view shown below:

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    B. Assemblies Solid Body Contact

    When importing assemblies of solid parts, contact regions are automatically created between the solid bodies.Contact allows non-matching meshes at boundaries between solid partsTolerance controls under Contact branch allows the user to specify distance of auto contact detection via slider bar

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    Assemblies Solid Body Contact

    In Simulation, the concept of contact and target surfaces are used for each contact regionOne side of a contact region is referred to as a contact surface, the other side is referred to as a target surfaceThe contact surfaces are restricted from penetrating through the target surfaces however the opposite is not trueWhen one side is the contact and the other side is the target, this is called asymmetric contact. If both sides are made to be contact & target this is called symmetric contactBy default, Simulation uses symmetric contact for solid assembliesFor ANSYS Professional licenses and above, the user may change to asymmetric contact, as desired

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    Assemblies Solid Body Contact

    Four contact types are available:

    Bonded and No Separation contact are basically linear and require only 1 iterationFrictionless and Rough contact are nonlinear and require multiple iterations (small deflection theory is still assumed)An interface treatment option is available:Add Offset: input zero or non-zero value for initial adjustmentAdjusted to Touch: ANSYS closes any gap to a just touching position (ANSYS Professional and above)

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    Contact TypeIterationsNormal Behavior (Separation)Tangential Behavior (Sliding)

    Bonded1ClosedClosed

    No Separation1ClosedOpen

    FrictionlessMultipleOpenOpen

    RoughMultipleOpenClosed

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    Assemblies Solid Body Contact

    For the advanced user, some of the contact options can be modifiedFormulation can be changed from Pure Penalty to Augmented Lagrange, MPC, or Normal Lagrange.MPC is applicable to bonded contact onlyAugmented Lagrange is used in classic ANSYS

    Note: the MPC formulation writes constraint equations relating the movement of parts at an interface. This can be an attractive alternative to penalty method for bonded contact.

    Additional information on advanced contact is presented in the Workbench nonlinear course as well as the ANSYS documentation

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    Assemblies Solid Body Contact

    Advanced options (continued):Pin Ball Region:Inside pinball = near-field contactOutside pinball = far-field contactAllows the solver to more efficiently process contact calculations

    Other advanced contact options will be discussed in Chapter 11.

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    Assemblies Surface Body Contact

    For ANSYS Professional licenses and above, mixed assemblies of shells and solids are supportedMore contact options are exposed to the userContact postprocessing is also available (discussed later)

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    ANSYS Professional license does not support 175 at 8.0, initial release. It supports 175 at 8.0 SP 1, however.

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    Assemblies Surface Body Contact

    Edge contact is a subset of general contactFor contact including shell faces or solid edges, only bonded or no separation behavior is allowedFor contact involving shell edges, only bonded behavior using MPC formulation is allowedIf a gap exists the pinball region can beused to detect contact beyond the gap.

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    Assemblies Contact Summary

    Summary of contact types and options available in Simulation:

    She