- variableThe name of the variable that this residual object operates on
C++ Type:NonlinearVariableName
Unit:(no unit assumed)
Controllable:No
Description:The name of the variable that this residual object operates on
Explicit Mass Damping
Adds Rayleigh mass damping, eta * M * v, to an ExplicitMixedOrder solid mechanics model.
Description
The purpose of this NodalKernel is to introduce Rayleigh mass damping into an ExplicitMixedOrder solid-mechanics model. Rayleigh mass damping is used to damp low frequency, long wavelength vibratory modes of the model. This is particularly useful in models where quasi-static solutions are of interest, as the low frequency modes can persist for many time steps if not damped. Related aside: high frequency, short wavelength vibratory models (eg, on the scale of a single element) are damped using stiffness_damping_coefficient in DynamicSolidMechanicsPhysics.
ExplicitMassDamping computes the residual contribution , where is a parameter chosen by the user, is the nodal mass, and is the old value of the velocity. The nodal mass, , must have been calculated by a MassMatrix Kernel, and its value depends on the density supplied to that Kernel. Usually, an ExplicitMassDamping Kernel should be attached to each of the displacement variables in the system (eg, disp_x, disp_y, disp_z).
Choosing an appropriate value of eta sometimes requires experimentation. A method can be found here. Alternately, here are some rough guidelines, noting that ExplicitMassDamping will damp low-frequency oscillations of your model.
Firstly, calculate the frequency, (rad/s), of the oscillations you wish to damp most effectively (ExplicitMassDamping will also damp other frequencies, but less efficiently). For instance:
If longitudinal waves (sometimes called "compressional waves") of half-wavelength are annoying, then . Often is similar to the size of your model.
If your model is a bar of length that is clamped at one end, and you wish to damp the fundamental frequency oscillations, then these oscillations have $\omega \approx L^{-2}\sqrt{E I / (\rho A)}.
In these, is the Young's modulus, the density, the bar's cross-sectional moment of inertia, and the bar's cross-sectional area.
Secondly, calculate the frequency, of the high-frequency oscillations that you wish to damp. Usually, these are , where the maximum is over all the elements in the model, and is the element side length.
Thirdly, choose the damping ratio, , which is a measure of how quickly oscillations decay relative to critical damping. Usually is a reasonable choice.
Fourthly, set . Usually , so this reduces to (with units 1/s). In addition, set the stiffness_damping_coefficient to (with units s).
!listing modules/solid_mechanics/test/tests/beam/dynamic/nodal_mass.csv
Input Parameters
- blockThe list of blocks (ids or names) that this object will be applied
C++ Type:std::vector<SubdomainName>
Controllable:No
Description:The list of blocks (ids or names) that this object will be applied
- boundaryThe list of boundaries (ids or names) from the mesh where this object applies
C++ Type:std::vector<BoundaryName>
Controllable:No
Description:The list of boundaries (ids or names) from the mesh where this object applies
- eta0Damping strength. Mass damping helps to damp low-frequency, large-scale oscillations. A reasonable value to use initially is eta = 2 * d * omega, where d is the damping fraction (typically 0.1) and omega is the lowest relevant frequency mode of the model. For instance, if the model is can oscillate longitudinally, omega = (pi / model_length) * sqrt(youngs_modulus / density)
Default:0
C++ Type:double
Unit:(no unit assumed)
Range:eta >= 0.0
Controllable:No
Description:Damping strength. Mass damping helps to damp low-frequency, large-scale oscillations. A reasonable value to use initially is eta = 2 * d * omega, where d is the damping fraction (typically 0.1) and omega is the lowest relevant frequency mode of the model. For instance, if the model is can oscillate longitudinally, omega = (pi / model_length) * sqrt(youngs_modulus / density)
- matrix_onlyFalseWhether this object is only doing assembly to matrices (no vectors)
Default:False
C++ Type:bool
Controllable:No
Description:Whether this object is only doing assembly to matrices (no vectors)
Optional Parameters
- absolute_value_vector_tagsThe tags for the vectors this residual object should fill with the absolute value of the residual contribution
C++ Type:std::vector<TagName>
Controllable:No
Description:The tags for the vectors this residual object should fill with the absolute value of the residual contribution
- extra_matrix_tagsThe extra tags for the matrices this Kernel should fill
C++ Type:std::vector<TagName>
Controllable:No
Description:The extra tags for the matrices this Kernel should fill
- extra_vector_tagsThe extra tags for the vectors this Kernel should fill
C++ Type:std::vector<TagName>
Controllable:No
Description:The extra tags for the vectors this Kernel should fill
- matrix_tagssystemThe tag for the matrices this Kernel should fill
Default:system
C++ Type:MultiMooseEnum
Controllable:No
Description:The tag for the matrices this Kernel should fill
- vector_tagsnontimeThe tag for the vectors this Kernel should fill
Default:nontime
C++ Type:MultiMooseEnum
Controllable:No
Description:The tag for the vectors this Kernel should fill
Contribution To Tagged Field Data Parameters
- control_tagsAdds user-defined labels for accessing object parameters via control logic.
C++ Type:std::vector<std::string>
Controllable:No
Description:Adds user-defined labels for accessing object parameters via control logic.
- diag_save_inThe name of auxiliary variables to save this BC's diagonal jacobian contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)
C++ Type:std::vector<AuxVariableName>
Unit:(no unit assumed)
Controllable:No
Description:The name of auxiliary variables to save this BC's diagonal jacobian contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)
- enableTrueSet the enabled status of the MooseObject.
Default:True
C++ Type:bool
Controllable:Yes
Description:Set the enabled status of the MooseObject.
- implicitTrueDetermines whether this object is calculated using an implicit or explicit form
Default:True
C++ Type:bool
Controllable:No
Description:Determines whether this object is calculated using an implicit or explicit form
- save_inThe name of auxiliary variables to save this BC's residual contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)
C++ Type:std::vector<AuxVariableName>
Unit:(no unit assumed)
Controllable:No
Description:The name of auxiliary variables to save this BC's residual contributions to. Everything about that variable must match everything about this variable (the type, what blocks it's on, etc.)
- search_methodnearest_node_connected_sidesChoice of search algorithm. All options begin by finding the nearest node in the primary boundary to a query point in the secondary boundary. In the default nearest_node_connected_sides algorithm, primary boundary elements are searched iff that nearest node is one of their nodes. This is fast to determine via a pregenerated node-to-elem map and is robust on conforming meshes. In the optional all_proximate_sides algorithm, primary boundary elements are searched iff they touch that nearest node, even if they are not topologically connected to it. This is more CPU-intensive but is necessary for robustness on any boundary surfaces which has disconnections (such as Flex IGA meshes) or non-conformity (such as hanging nodes in adaptively h-refined meshes).
Default:nearest_node_connected_sides
C++ Type:MooseEnum
Controllable:No
Description:Choice of search algorithm. All options begin by finding the nearest node in the primary boundary to a query point in the secondary boundary. In the default nearest_node_connected_sides algorithm, primary boundary elements are searched iff that nearest node is one of their nodes. This is fast to determine via a pregenerated node-to-elem map and is robust on conforming meshes. In the optional all_proximate_sides algorithm, primary boundary elements are searched iff they touch that nearest node, even if they are not topologically connected to it. This is more CPU-intensive but is necessary for robustness on any boundary surfaces which has disconnections (such as Flex IGA meshes) or non-conformity (such as hanging nodes in adaptively h-refined meshes).
- seed0The seed for the master random number generator
Default:0
C++ Type:unsigned int
Controllable:No
Description:The seed for the master random number generator
- use_displaced_meshFalseWhether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.
Default:False
C++ Type:bool
Controllable:No
Description:Whether or not this object should use the displaced mesh for computation. Note that in the case this is true but no displacements are provided in the Mesh block the undisplaced mesh will still be used.