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Defining Initial Acoustic Static Pressure
In Abaqus/Explicit you can define initial acoustic static pressure values at the acoustic nodes.
These values should correspond to static equilibrium and cannot be changed during
the analysis. You can specify the initial acoustic static pressure at two reference
locations in the model, and Abaqus/Explicit interpolates these data linearly to the acoustic nodes in the specified node set.
The linear interpolation is based on the projected position of each node onto the
line defined by the two reference nodes. If the value at only one reference location
is given, the initial acoustic static pressure is assumed to be uniform. The initial
acoustic static pressure is used only in the evaluation of the cavitation condition
(see Acoustic Medium) when
the acoustic medium is capable of undergoing cavitation.
Defining Initial Volume Fraction of Material
You can prescribe the initial volume fraction of material in an element in analyses
with progressive element activation (see Progressive Element Activation). At the beginning of an analysis the element must
be either inactive or fully active; therefore, the value of the initial volume
fraction must be equal to zero or one.
Defining Initial Volume Fraction of Material by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define the initial volume fraction of
material by importing field data as initial values of volume fraction at a
particular step and increment or a user-specified time from the output database
(.sim) file of a previous analysis. For more
information, see Importing Data from an Output Database File.
Defining Initial Normalized Concentration
In Abaqus/Standard you can define initial normalized concentration values for use with diffusion
elements in mass diffusion analysis (see Mass Diffusion Analysis).
Defining Initially Bonded Contact Surfaces
In Abaqus/Standard you can define initially bonded or partially bonded contact surfaces. This type
of initial condition is intended for use with the crack propagation capability (see
Crack Propagation Analysis). The
surfaces specified have to be different; this type of initial condition cannot be
used with self-contact.
If the crack propagation capability is not activated, the bonded portion of the surfaces do
not separate. In this case defining initially bonded contact surfaces would have the
same effect as defining tied contact, which generates a permanent bond between two
surfaces during the entire analysis (Defining Tied Contact in Abaqus/Standard).
Defining Initial Damage Initiation
You can define initial values for the damage initiation measure for the ductile,
shear, and the Müschenborn and Sonne forming limit diagram based damage initiation
criteria (Damage Initiation for Ductile Metals). This
capability is particularly useful in situations where a metal forming operation is
carried out in one analysis, which is followed by a separate analysis that subjects
the formed metal part to further deformation. The damage initiation measures at the
end of the first analysis can be directly specified as initial conditions for the
second analysis.
An alternate but approximate way of modeling initial conditions on damage initiation
is by specifying the initial values of the equivalent plastic strain. Abaqus computes damage initiation measures based on the specified initial equivalent
plastic strain, assuming a linear strain path between the initial (undeformed) state
and the final (deformed) state. This approximation does not work well for
deformation paths that deviate significantly from linearity in the strain space.
Defining Initial Damage Initiation for Rebars
Initial values for damage initiation can also be defined for rebars within
elements for the ductile and shear damage initiation criteria (see Defining Rebar as an Element Property).
Defining Initial Damage Initiation That Varies through the Thickness of Shell Elements
Initial values of damage initiation can be defined at each section point through
the thickness of shell elements for the ductile and shear damage initiation
criteria.
Defining Initial Damage Initiation by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial ductile and shear damage
initiation criteria by importing field data as initial values of damage
initiation at a particular step and increment or a user-specified time in the
output database (.sim) file of a previous analysis. For
more information, see Importing Data from an Output Database File.
Defining the Initial Location of an Enriched Feature
You can specify the initial location of an enriched feature, such as a crack, in an
Abaqus/Standard analysis (see Modeling Discontinuities as an Enriched Feature Using the Extended Finite Element Method). Two
signed distance functions per node are generally required to describe the crack
location, including the location of crack tips, in a cracked geometry. The first
signed distance function describes the crack surface, while the second is used to
construct an orthogonal surface such that the intersection of the two surfaces
defines the crack front. The first signed distance function is assigned only to
nodes of elements intersected by the crack, while the second is assigned only to
nodes of elements containing the crack tips. No explicit representation of the crack
is needed because the crack is entirely described by the nodal data.
Defining Initial Values of Element Solution-Dependent Variables
You can define initial values of solution-dependent state variables (see About User Subroutines and Utilities). The
initial values can be defined directly.
Defining Initial Values of Element Solution-Dependent Variables from an Output Database File
For three-dimensional continuum elements, you can define initial values of element
solution-dependent variables by importing field data as initial values of
element solution-dependent variables at a particular step and increment or a
user-specified time in the output database (.sim) file of a
previous analysis. For more information, see Importing Data from an Output Database File.
Defining Initial Values of Predefined Field Variables
You can define initial values of predefined field variables. The values can be
changed during an analysis (see Predefined Fields).
You must specify the field variable number being defined,
n. Any number of field variables can be used; each
must be numbered consecutively (1, 2, 3, etc.). Repeat the initial conditions
definition, with a different field variable number, to define initial conditions for
multiple field variables. The default is n=1.
The definition of initial field variable values must be compatible with the section
definition and with adjacent elements, as explained in Predefined Fields.
Defining Uniform Initial Fields
You can apply uniform initial field variables to either the entire model or to node sets
that you specify. Omit the node number or node set to apply the specified field variable
to all nodes in the model automatically.
You can specify uniform field variables with all element types, including beams and
shells. The specified uniform field is applied to all section points in beams and shells.
However, the definition of initial field variables must be compatible with the section
definition of the element and with adjacent elements, as explained in Predefined Fields. Abaqus issues a warning message during input file preprocessing if an initial field variable
is applied to any node that is associated with at least one shell or beam section that
specifies field variables using gradients and at least one section that directly specifies
the values of the field variables.
Initializing Predefined Field Variables with Nodal Temperature Records from a User-Specified Results File
You can define initial values of predefined field variables using nodal
temperature records from a particular step and increment of a results file from
a previous Abaqus analysis or from a results file you create (see Predefined Fields). The previous analysis is most commonly an
Abaqus/Standard heat transfer analysis. The use of the .fil file
extension is optional.
The part (.prt) file from the previous analysis is required
to read the initial values of predefined field variables from the results file
(Assembly Definition).
Both the previous model and the current model must be consistently defined in
terms of an assembly of part instances.
Defining Initial Predefined Field Variables Using Scalar Nodal Output from a User-Specified Output Database File
You can define initial values of predefined field variables using scalar nodal
output variables from a particular step and increment in the output database
file of a previous Abaqus/Standard analysis. For a list of scalar nodal output variables that can be used to
initialize a predefined field, see Predefined Fields.
The part (.prt) file from the previous analysis is required
to read initial values from the output database file (see Assembly Definition).
Both the previous model and the current model must be defined consistently in
terms of an assembly of part instances; node numbering must be the same, and
part instance naming must be the same.
The file extension is optional; however, only the output database file can be
used for this option.
Defining Initial Predefined Field Variables by Interpolating Scalar Nodal Output Variables for Dissimilar Meshes from a User-Specified Output Database File
When the mesh for one analysis is different from the mesh for the subsequent
analysis, Abaqus can interpolate scalar nodal output variables (using the undeformed mesh of
the original analysis) to predefined field variables that you choose. For a list
of supported scalar nodal output variables that can be used to define predefined
field variables, see Predefined Fields. This technique can
also be used in cases where the meshes match but the node number or part
instance naming differs between the analyses. Abaqus looks for the .odb extension automatically. The part
(.prt) file from the previous analysis is required if
that analysis model is defined in terms of an assembly of part instances (see
Assembly Definition).
Defining Initial Predefined Field Variables by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial predefined field variables
by importing field data at a particular step and increment or a user-specified
time in the output database (.sim) file of a previous
analysis. For more information, see Importing Data from an Output Database File.
Defining Initial Predefined Pore Fluid Pressure
You can associate a known (precomputed) pore fluid pressure field with a specific
predefined field variable (as discussed in Predefined Fields) and read the field into a static or an explicit dynamic stress analysis. To
initialize the pore fluid pressure field, you must initialize the corresponding
predefined field variable.
Defining Initial Fluid Electric Potential
In Abaqus/Standard you can define initial fluid electric potential values for use with coupled
thermal-electrochemical elements in a coupled thermal-electrochemical analysis (see
Coupled Thermal-Electrochemical Analysis).
Defining Initial Fluid Pressure in Fluid-Filled Structures
You can prescribe initial pressure for fluid-filled structures (see About Surface-Based Fluid Cavities).
Do not use this type of initial condition to define initial conditions in porous
media in Abaqus/Standard; use initial pore fluid pressures instead (see below).
Defining Initial Values of State Variables for Plastic Hardening
You can prescribe initial equivalent plastic strain and, if relevant, the initial
backstress tensor for elements that use one of the metal plasticity (Inelastic Behavior) or
Drucker-Prager (Extended Drucker-Prager Models)
material models. These initial quantities are intended for materials in a work
hardened state; they can be defined directly or by user subroutine HARDINI. You can also
prescribe initial values for the volumetric compacting plastic strain, , for elements that use the crushable foam material model with
volumetric hardening (Crushable Foam Plasticity Models).
You can also specify multiple backstresses for the nonlinear kinematic hardening
model. Optionally, you can specify the kinematic shift tensor (backstress) using the
full tensor format, regardless of the element type to which the initial conditions
are applied.
Defining Initial Equivalent Plastic Strain by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial equivalent plastic strain by
importing field data as equivalent plastic strain at a particular step and
increment or a user-specified time in the output database
(.sim) file of a previous analysis. For more
information, see Importing Data from an Output Database File.
Defining Initial Equivalent Plastic Strain and Backstress Tensor by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial equivalent plastic strain
and backstress tensor by importing field data as equivalent plastic strain and
backstress tensor at a particular step and increment or a user-specified time in
the output database (.sim) file of a previous analysis. For
more information, see Importing Data from an Output Database File.
Defining Hardening Parameters in User Subroutine HARDINI
For complicated cases in Abaqus/Standard user subroutine HARDINI can be used to
define the initial work hardening. In this case Abaqus/Standard calls the subroutine at the start of the analysis for each material point in
the model. You can then define the initial conditions at each point as a
function of coordinates, element number, etc.
Defining Elements Initially Open for Tangential Fluid Flow
Defining Initial Ion Concentration
In Abaqus/Standard you can define initial ion concentration values for use with coupled
thermal-electrochemical elements in a coupled thermal-electrochemical analysis (see
Coupled Thermal-Electrochemical Analysis).
Defining Initial Mass Flow Rates in Forced Convection Heat Transfer Elements
In Abaqus/Standard you can define the initial mass flow rate through forced convection heat transfer
elements. You can specify a predefined mass flow rate field to vary the value of the
mass flow rate within the analysis step (see Uncoupled Heat Transfer Analysis).
Defining Initial Values of Plastic Strain
You can define an initial plastic strain field on elements that use one of the metal
plasticity (Inelastic Behavior),
critical state (clay) plasticity (Critical State (Clay) Plasticity Model),
Drucker-Prager (Extended Drucker-Prager Models), or
soft rock plasticity models. The specified plastic strain values are applied
uniformly over the element unless they are defined at each section point through the
thickness in shell elements.
If a local coordinate system is defined (see Orientations), the
plastic strain components must be given in the local system.
Defining Initial Plastic Strains by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial plastic strains by importing
field data as initial plastic strains at a particular step and increment or a
user-specified time in the output database (.sim) file of a
previous analysis. For more information, see Importing Data from an Output Database File.
Defining Initial Pore Fluid Pressures in a Porous Medium
In Abaqus/Standard you can define the initial pore pressure, , for nodes in a coupled pore fluid diffusion/stress analysis (see
Coupled Pore Fluid Diffusion and Stress Analysis). The
initial pore pressure can be defined either directly as an elevation-dependent
function or by user subroutine UPOREP.
Elevation-Dependent Initial Pore Pressures
When an elevation-dependent pore pressure is prescribed for a particular node
set, the pore pressure in the vertical direction (assumed to be the
z-direction in three-dimensional and axisymmetric
models and the y-direction in two-dimensional models) is
assumed to vary linearly with this vertical coordinate. You must give two pairs
of pore pressure and elevation values to define the pore pressure distribution
throughout the node set. Enter only the first pore pressure value (omit the
second pore pressure value and the elevation values) to define a constant pore
pressure distribution.
Defining Initial Pore Pressures in User Subroutine UPOREP
For complicated cases initial pore pressure values can be defined by user subroutine UPOREP. In this case
Abaqus/Standard makes a call to subroutine UPOREP at the start of
the analysis for all nodes in the model. You can define the initial pore
pressure at each node as a function of coordinates, node number, etc.
Defining Initial Pore Pressure Values Using Nodal Pore Pressure Output from a User-Specified Output Database File
You can define initial pore pressure values using nodal pore pressure output
variables from a particular step and increment in the output database
(.odb) file of a previous Abaqus/Standard analysis. The file extension is optional; however, only the output database
file can be used.
For the same mesh pore pressure mapping, both the previous model and the current
model must be defined consistently, including node numbering, which must be the
same in both models. If the models are defined in terms of an assembly of part
instances, the part instance naming must be the same.
Interpolating Initial Pore Pressure Values for Dissimilar Pore Pressure Mapping Values in a User-Specified Output Database File
For dissimilar mesh pore pressure mapping, interpolation is required. You can
also limit the interpolation region by specifying the source region in the form
of an element set from which pore pressure is to be interpolated and the target
region in the form of a node set onto which the pore pressure is mapped.
Defining Initial Pressure Stress in a Mass Diffusion Analysis
In Abaqus/Standard you can specify the initial pressure stress, , at the nodes in a mass diffusion analysis (see Mass Diffusion Analysis).
Defining Initial Pressure Stress from a User-Specified Results File
You can define initial values of pressure stress as those values existing at a
particular step and increment in the results file of a previous Abaqus/Standard stress/displacement analysis (see Predefined Fields). The
use of the .fil file extension is optional. The initial
values of pressure stress cannot be read from the results file when the previous
model or the current model is defined in terms of an assembly of part instances
(Assembly Definition).
Defining Initial Void Ratios in a Porous Medium
In Abaqus/Standard you can specify the initial values of the void ratio, e, at
the nodes of a porous medium (see Coupled Pore Fluid Diffusion and Stress Analysis). The
initial void ratio can be defined either directly as an elevation-dependent
function, by interpolation from a previous output database file, or by user
subroutine VOIDRI.
Elevation-Dependent Initial Void Ratio
When an elevation-dependent void ratio is prescribed for a particular node set,
the void ratio in the vertical direction (assumed to be the
z-direction in three-dimensional and axisymmetric
models and the y-direction in two-dimensional models) is
assumed to vary linearly with this vertical coordinate. When the void ratio is
specified for a region meshed with fully integrated first-order elements, the
nodal values of void ratio are interpolated to the centroid of the element and
are assumed to be constant through the element. You must provide two pairs of
void ratio and elevation values to define the void ratio throughout the node
set. Enter only the first void ratio value (omit the second void ratio value and
the elevation values) to define a constant void ratio distribution.
Defining Void Ratio from a User-Specified Output Database
You can define initial void ratios from the output database
(.odb) file of a previous Abaqus/Standard soil analysis in which the void ratio is requested as output.
Interpolating Initial Void Ratios from Values in a User-Specified Output Database
When you define initial void ratios from the output database
(.odb) file of a previous Abaqus/Standard soil analysis, you can also limit the interpolation region by specifying the
source region in the form of an element set from which void ratios are to be
interpolated and the target region in the form of a node set onto which the void
ratios are mapped.
Defining Void Ratios in User Subroutine VOIDRI
For complicated cases initial values of the void ratios can be defined by user subroutine
VOIDRI. In this case
Abaqus/Standard makes a call to subroutine VOIDRI at the start of
the analysis for each material integration point in the model. You can then
define the initial void ratio at each point as a function of coordinates,
element number, etc.
Defining a Reference Mesh for Membrane Elements
In Abaqus/Explicit you can specify a reference mesh (initial metric) for membrane elements. This is
typically useful in finite element airbag simulations to model the wrinkles that
arise from the airbag folding process. A flat mesh may be suitable for the
unstressed reference configuration, but the initial state may require a
corresponding folded mesh defining the folded state. Defining a reference
configuration that is different from the initial configuration may result in nonzero
stresses and strains in the initial configuration based on the material definition.
If a reference mesh is specified for an element, any initial stress or strain
conditions specified for the same element are ignored.
If rebar layers are defined in membrane elements, the angular orientation defined in
the reference configuration is updated to obtain the same orientation in the initial
configuration.
You can define the reference mesh using either the element numbers and the
coordinates of the nodes in each element or the node numbers and the coordinates of
the nodes. The coordinates of all of the nodes in the element have to be specified
for both methods to have a valid initial condition for that element. The two
alternatives are mutually exclusive.
Defining Initial Relative Density
You can specify the initial values of the relative density field for a porous metal
plasticity material model (see Porous Metal Plasticity) or
equations of state (see Equation of State).
Defining Initial Angular and Translational Velocity
You can prescribe initial velocities in terms of an angular velocity and a
translational velocity. This type of initial condition is typically used to define
the initial velocity of a component of a rotating machine, such as a jet engine. The
initial velocities are specified by giving the angular velocity, ; the axis of rotation, defined from a point a
at to a point b at ; and a translational velocity, . The initial velocity of node N at is then
Defining Initial Saturation for a Porous Medium
In Abaqus/Standard you can define the initial saturation, s, for elements in a
coupled pore fluid diffusion/stress analysis (see Coupled Pore Fluid Diffusion and Stress Analysis). If
the porous material's absorption/exsorption behavior under partially saturated flow
conditions is not defined, the initial saturation is set to 1.0 by default.
Defining Initial Solid Electric Potential
In Abaqus/Standard you can define initial solid electric potential values for use with coupled
thermal-electrochemical elements in a coupled thermal-electrochemical analysis (see
Coupled Thermal-Electrochemical Analysis).
Defining the Initial Values of Solution-Dependent State Variables
You can define initial values of solution-dependent state variables (see About User Subroutines and Utilities). The
initial values can be defined directly or, in Abaqus/Standard, by user subroutine SDVINI. Values given
directly are applied uniformly over the element.
Defining the Initial Values of Solution-Dependent State Variables by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial values of solution-dependent
state variables by importing field data as initial values of solution-dependent
state variables at a particular step and increment or a user-specified time from
the output database (.sim) file of a previous analysis. For
more information, see Importing Data from an Output Database File.
Defining the Initial Values of Solution-Dependent State Variables for Rebars
The initial values of solution-dependent variables can also be defined for rebars
within elements. Rebars are discussed in Defining Rebar as an Element Property.
Defining the Initial Values of Solution-Dependent State Variables in User Subroutine SDVINI
For complicated cases in Abaqus/Standard user subroutine SDVINI can be used to
define the initial values of solution-dependent state variables. In this case
Abaqus/Standardmakes a call to subroutine SDVINI at the start of
the analysis for each material integration point in the model. You can then
define all solution-dependent state variables at each point as functions of
coordinates, element number, etc.
Defining Initial Specific Energy for Equations of State
In Abaqus/Explicit you can specify the initial values of the specific energy for equations of state
(see Equation of State).
Defining Spud Can Embedment or Spud Can Preload
In Abaqus/Standard you can define an initial embedment of a spud can. Alternatively, you can define
an initial vertical preload of a spud can (see Elastic-Plastic Joints).
Defining Initial Stresses
You can define an initial stress field. Initial stresses can be defined directly or, in Abaqus/Standard, by user subroutine SIGINI. Stress values
given directly are applied uniformly over the element unless they are defined at
each section point through the thickness in shell elements.
If a local coordinate system was defined (see Orientations),
stresses must be given in the local system.
In soils (porous medium) problems the initial effective stress should be given; see
Coupled Pore Fluid Diffusion and Stress Analysis for a
discussion of defining initial conditions in porous media.
If the section properties of beam elements or shell elements are defined by a general
section, the initial stress values are applied as initial section forces and
moments. In the case of beams initial conditions can be specified only for the axial
force, the bending moments, and the twisting moment. In the case of shells initial
conditions can be specified only for the membrane forces, the bending moments, and
the twisting moment. In both shells and beams initial conditions cannot be
prescribed for the transverse shear forces.
Initial contact stresses are calculated internally (see Initial Contact Stresses in Abaqus/Standard) by default providing initial conditions for
contact. These initial contact stress computations use the initial stresses that you
specify in the underlying elements of the contact surfaces and are meant to provide
an approximate equilibrating contact traction at contact interfaces.
Initial stress fields cannot be defined for spring elements. See Springs for a
discussion of defining initial forces in spring elements.
Initial stress fields cannot be defined for elements using a fabric material. However, an
initial stress and strain state can be introduced in a fabric material made of
membrane elements by defining a reference mesh (see Defining a Reference Mesh for Membrane Elements above).
Defining Initial Stresses That Vary through the Thickness of Shell Elements
Initial values of stress can be defined at each section point through the
thickness of shell elements.
Defining Initial Stresses in User Subroutine SIGINI
For complicated cases (such as elbow elements) in Abaqus/Standard the initial stress field can be defined by user subroutine SIGINI. In this case
Abaqus/Standard makes a call to subroutine SIGINI at the start of
the analysis for each material calculation point in the model. You can then
define all active stress components at each point as functions of coordinates,
element number, etc.
Defining Initial Stresses Using Stress Output from a User-Specified Output Database File
You can define initial stresses using stress output variables from a particular
step and increment in the output database (.odb or
.sim) file of a previous Abaqus/Standard analysis. This option is available only for continuum elements when the
stress output in the previous analysis was requested at the integration points
or at the centroid of the element.
In this case both the previous model and the current model must be defined
consistently. The element numbering and element types must be the same in both
models. If the models are defined in terms of an assembly of part instances,
part instance naming must be the same.
The file extension is optional; however, only the output database
(.odb or .sim) file can be used.
If no extension is specified, the .odb file is used.
Defining Initial Stresses by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial stresses by importing field
data from a particular step and increment or a user-specified time in the output
database (.sim) file of a previous analysis. For more
information, see Importing Data from an Output Database File.
Establishing Equilibrium in Abaqus/Standard
When initial stresses are given in Abaqus/Standard (including prestressing in reinforced concrete or interpolation of an old
solution onto a new mesh), the initial stress state may not be an exact
equilibrium state for the finite element model. Therefore, an initial step
should be included to allow Abaqus/Standard to check for equilibrium and iterate, if necessary, to achieve equilibrium.
In a soils analysis (that is, for models containing elements that include pore fluid pressure
as a variable) the geostatic stress field procedure (Geostatic Stress State)
should be used for the equilibrating step. Any initial loading (such as
geostatic gravity loads) that contributes to the initial equilibrium should be
included in this step definition. The initial time increment and the total time
specified in this step should be the same. The initial stresses are applied in
full at time zero; and if equilibrium can be achieved, this step converges in
one increment. Therefore, there is no benefit to incrementing.
To achieve equilibrium for all other analyses, a first step using the static procedure (Static Stress Analysis)
should be used. It is recommended that you specify the initial time increment to
be equal to the total time specified in this step so that Abaqus/Standard attempts to find equilibrium in one increment.
By default, Abaqus/Standard adopts a ramping technique over the first step. This allows Abaqus/Standard to use automatic incrementation if equilibrium cannot be found in one
increment. This ramping is achieved in the following manner:
-
An additional set of artificial or unbalanced stresses is defined at each
material point. These stresses are equal in magnitude to the initial
stresses but are of opposite sign. Therefore, the sum of the material
point initial stresses and these artificial stresses creates zero
internal forces at the beginning of the step.
-
The internal unbalanced stresses are ramped off linearly in time during the first step.
Therefore, at the end of the step the artificial stresses have been
removed completely and the remaining stresses in the material are the
stress state in equilibrium.
You can force Abaqus/Standard to achieve equilibrium in one increment by using a step variation on the
initial condition to resolve the unbalanced stress instead of ramping the stress
down over the entire step. If Abaqus/Standard cannot achieve equilibrium in one increment, the analysis ends.
If the equilibrating step does not converge, it indicates that the initial stress
state is so far from equilibrium with the applied loads that significantly large
deformations would be generated. This is generally not the intention of an
initial stress state; therefore, it suggests that you should recheck the
specified initial stresses and loads.
Establishing Equilibrium in Abaqus/Explicit
Abaqus/Explicit computes the initial acceleration at nodes taking into account the initial
stresses, the loads, and the boundary conditions in the initial configuration.
For an initially static problem, the specified boundary conditions, the initial
stresses, and the initial loading should be consistent with a static
equilibrium. Otherwise, the solution is likely to be noisy. The noise may be
reduced by introducing a dummy step with a temporary viscous loading to attempt
to reestablish a static equilibrium. Alternatively, you can introduce an initial
short step in which all degrees of freedom are fixed with boundary conditions
(all initial loads should be included in this initial step); in a second step,
release all but the actual boundary conditions.
Defining Elevation-Dependent (Geostatic) Initial Stresses
You can define elevation-dependent initial stresses. When a geostatic stress state is
prescribed for a particular element set, the stress in the vertical direction
(assumed to be the z-direction in three-dimensional and
axisymmetric models and the y-direction in two-dimensional
models) is assumed to vary (piecewise) linearly with this vertical coordinate.
For the vertical stress component, you must give two pairs of stress and elevation
values to define the stress throughout the element set. For material points lying
between the two elevations given, Abaqus will use linear interpolation to determine the initial stress; for points lying
outside the two elevations given, Abaqus will use linear extrapolation. In addition, horizontal (lateral) stress
components are given by entering one or two “coefficients of lateral stress,” which
define the lateral direct stress components as the vertical stress at the point
multiplied by the value of the coefficient. In axisymmetric cases only one value of
the coefficient of lateral stress is used and, therefore, only one value need be
entered.
Geostatic initial stresses are for use with continuum elements only. In Abaqus/Standard elevation-dependent initial stresses should be specified for beams and shells in
user subroutine SIGINI, as explained
earlier. In Abaqus/Explicit elevation-dependent initial stresses cannot be specified for beams and shells.
The geostatic stress state specified initially should be in equilibrium with the
applied loads (such as gravity) and boundary conditions. An initial step should be
included to allow Abaqus to check for equilibrium after this interpolation has been done; see the
discussion above on establishing equilibrium when an initial stress field is
applied.
Defining Initial Temperatures
You can define initial temperatures at the nodes of either heat transfer or
stress/displacement elements. The temperatures of stress/displacement elements can
be changed during an analysis (see Predefined Fields).
The definition of initial temperature values must be compatible with the section
definition of the element and with adjacent elements, as explained in Predefined Fields.
Defining Uniform Initial Temperatures
You can apply uniform initial temperatures to either the entire model or to node sets
that you specify. Omit the node number or node set to apply the specified temperature to
all nodes in the model automatically.
You can specify uniform temperature with all element types, including beams and shells.
The specified uniform temperature is applied to all section points in beams and shells.
However, the definition of initial temperature values must be compatible with the section
definition of the element and with adjacent elements, as explained in Predefined Fields. Abaqus issues a warning message during input file preprocessing if an initial temperature is
applied to any node that is associated with at least one shell or beam section that
specifies temperatures using gradients and at least one section that directly specifies
the values of temperature.
Defining Initial Temperatures from a User-Specified Results or Output Database File
You can define initial temperatures as those values existing as nodal
temperatures at a particular step and increment in the results or output
database file of a previous Abaqus/Standard heat transfer analysis (see Predefined Fields).
The part (.prt) file from the previous analysis is required
to read initial temperatures from the results or output database file (see Assembly Definition).
Both the previous model and the current model must be consistently defined in
terms of an assembly of part instances; node numbering must be the same, and
part instance naming must be the same.
The file extension is optional; however, if both results and output database
files exist, the results file will be used.
Defining Initial Temperatures by Importing Field Data from an Output Database File
For three-dimensional continuum elements, you can define initial temperatures by importing
field data as nodal temperatures at a particular step and increment or a
user-specified time in the output database (.sim) file of a
previous analysis. For more information, see Importing Data from an Output Database File.
Interpolating Initial Temperatures for Dissimilar Meshes from a User-Specified Results or Output Database File
When the mesh for the heat transfer analysis is different from the mesh for the
subsequent stress/displacement analysis, Abaqus can interpolate the temperature values from the nodes in the undeformed heat
transfer model to the current nodal temperatures. This technique can also be
used in cases where the meshes match but the node number or part instance naming
differs between the analyses. Only temperatures from an output database file can
be used for the interpolation; Abaqus will look for the .odb extension automatically. The part
(.prt) file from the previous analysis is required if
that analysis model is defined in terms of an assembly of part instances (see
Assembly Definition).
Interpolating Initial Temperatures for Dissimilar Meshes with User-Specified Regions
When regions of elements in the heat transfer analysis are close or touching, the
dissimilar mesh interpolation capability can result in an ambiguous temperature
association. For example, consider a node in the current model that lies on or
close to a boundary between two adjacent parts in the heat transfer model, and
consider a case where temperatures in these parts are different. When
interpolating, Abaqus will identify a corresponding parent element at the boundary for this node
from the heat transfer analysis. This parent element identification is done
using a tolerance-based search method. Hence, in this example the parent element
might be found in either of the adjacent parts, resulting in an ambiguous
temperature definition at the node. You can eliminate this ambiguity by
specifying the source regions from which temperatures are to be interpolated.
The source region refers to the heat transfer analysis and is specified by an
element set. The target region refers to the current analysis and is specified
by a node set.
Interpolating Initial Temperatures for Meshes That Differ Only in Element Order from a User-Specified Results or Output Database File
If the only difference in the meshes is the element order (first-order elements in the heat
transfer model and second-order elements in the stress/displacement model), in
Abaqus/Standard you can indicate that midside node temperatures in second-order elements are
to be interpolated from corner node temperatures read from the results or output
database file of the previous heat transfer analysis using first-order elements.
You must ensure that the corner node temperatures are not defined using a
mixture of direct data input and reading from the results or output database
file, since midside node temperatures that give unrealistic temperature fields
may result. In practice, the capability for calculating midside node
temperatures is most useful when temperatures generated by a heat transfer
analysis are read from the results or output database file for the whole mesh
during the stress analysis. Once the midside node capability is activated, the
capability remains active for the rest of the analysis, including for any
predefined temperature fields defined to change temperatures during the
analysis. The general interpolation and midside node capabilities are mutually
exclusive.
Defining the Initial Configuration in a One-Step Inverse Analysis
In a one-step inverse analysis you must define the initial configuration by
specifying initial conditions for the unfolded coordinates of all nodes in the part.
One-step inverse analysis uses the Newton method, which requires an initial estimate
of the solution as a starting point in the iterative algorithm. This starting point
is defined by specifying unfold coordinate initial conditions.
Defining Initial Velocities for Specified Degrees of Freedom
You can define initial velocities for specified degrees of freedom. When initial velocities
are given for dynamic analysis, they should be consistent with all of the
constraints on the model, especially time-dependent boundary conditions. Abaqus ensures that they are consistent with boundary conditions and with multi-point
and equation constraints but does not check for consistency with internal
constraints such as incompressibility of the material. In case of conflict, boundary
conditions take precedence over initial conditions.
Initial velocities must be defined in global directions, regardless of the use of
local transformations (Transformed Coordinate Systems).
Defining Initial Volume Fractions for Eulerian Elements
You can define initial volume fractions to create material within Eulerian elements
in Abaqus/Explicit. By default, these elements are filled with void. See Initial Conditions for a
description of strategies for initializing Eulerian materials.
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