Preparing an Abaqus analysis for co-simulation involves the following:
identifying an Abaqus analysis step for co-simulation analysis;
identifying the co-simulation interface regions in the Abaqus model; and
identifying the fields exchanged during the co-simulation.
This section provides an overview of preparing an Abaqus analysis for a co-simulation. The discussion in this section is general and might not apply
to every product pairing.Co-Simulation between Abaqus Solvers provides setup, execution, and
limitation details for co-simulation between Abaqus solvers. For co-simulation between Abaqus and third-party analysis programs, consult the appropriate User’s Guide.
Identifying an Abaqus Step for Co-Simulation Analysis
The co-simulation event need not begin at the start of the first step in an Abaqus analysis. However, it does need to start with the beginning of an analysis step and end
within that analysis step. Hence, you need to define the step durations in Abaqus such that the start of the co-simulation event falls at the beginning of an Abaqus analysis step and to define that particular step so that the co-simulation event ends by
the end of that step. Regular loads and boundary conditions for the Abaqus model are specified as usual.
Communication with the coupled analysis is initiated as the co-simulation event begins and
is terminated when the co-simulation event time is reached. Abaqus might terminate the co-simulation event when the end of the analysis step is reached
before the co-simulation event time or when the analysis cannot proceed any further; for
example, because of convergence problems. In such a case, a warning message is issued to all
clients, and the co-simulation is terminated.
Co-simulation is supported by the following Abaqus procedures:
Identifying the Analysis Program Communicating with Abaqus during the Co-Simulation
You can couple Abaqus with another Abaqus analysis or Abaqus with certain third-party analysis programs using the SIMULIA Co-Simulation Engine. For details on coupling with third-party analysis programs, see the respective User's
Guides.
Identifying the Co-Simulation Interface Region
Interaction between two Abaqus models or between an Abaqus model and a third-party analysis model takes place through a common interface region
referred to as the co-simulation interface region. The co-simulation interface region can be
a set of discrete points, a surface region, or a volume region. You must be consistent in
your interface region definition; if you define a surface co-simulation region in one
analysis, then you must define a surface co-simulation region in the other analysis.
Furthermore, these co-simulation regions need to be colocated and have the same region
boundaries.
Interacting through Discrete Points
Interaction can occur through a set of discrete points where only nodal position
information without element topology information (for example, tributary area) defines the
co-simulation interface region. In this case the spatial mapping is limited to
point-to-point mapping, and you must ensure that there are matching nodes between the
models.
In Abaqus you can use a node set or a node-based surface to define a co-simulation interface
region consisting of discrete points.
Interacting through a Surface
Interaction between distinct domains occurs through a common interface surface. For
example, when a fluid interacts with a solid without penetrating it, the fluid-solid
interface is defined through a surface. In this case both nodal position and element
topology information define the co-simulation interface, and appropriate spatial mapping
between dissimilar surface meshes is performed to conservatively map fields.
Interacting through a Volume
Interaction between overlapping domains occurs through a volume. In this case both nodal
position and element topology information define the co-simulation region, and appropriate
spatial mapping between dissimilar volume meshes is performed to conservatively map
fields.
The interface region is defined by an element set.
Identifying the Fields Exchanged across a Co-Simulation Interface
The coupling of the domain models can be through loads and/or boundary conditions
prescribed at the co-simulation interface. In addition, mass, rotary inertia, and heat
capacitance terms can also be exchanged. Based on the physics and the interaction type and
its enforcement, you must specify the fields that are imported and/or exported in an Abaqus analysis during the co-simulation.
The co-simulation interface can consist of a group of discrete points (nodes), a surface
region, or a volume region. Not all fields can be exchanged across all region types.
This section provides a general overview of all fields available in Abaqus. For detailed information on the fields exchanged between two Abaqus solvers, see Structural-to-Structural Co-Simulation. For detailed information on
fields exchanged by Abaqus and a third-party analysis program, see the respective User’s Guides.
Procedures Involving Mechanical Degrees of Freedom
Table 1 lists the fields that can be exchanged for procedures supporting mechanical degrees of
freedom (degrees of freedom 1–6), their associated field identifiers, the supported
co-simulation interface region types, and which Abaqus solvers support import and export of the field values.
Table 1. Exchanging fields for procedures supporting mechanical degrees of freedom.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
UT or U
Displacement
P, S, V
S, E
S, E
L
VT or V
Velocity (transient procedures)
P, S, V
S, E
S, E
AT or A
Acceleration (transient procedures)
P, S, V
S
S, E
UR
Rotations
P, S
S, E
S, E
radians
VR
Angular velocity (transient procedures)
P, S
S, E
S, E
radians
AR
Angular acceleration (transient procedures)
P, S
S
S, E
radians
COORD
Current coordinates
P, S, V
S, E
CF
Concentrated forces
P, S, V
S, E
S, E
F
CM
Concentrated moments
P, S
S, E
S, E
P
Pressure normal to element surface
S
S
TRVEC
Traction vector
S
S
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
The following procedures support co-simulation using mechanical degrees of freedom:
Displacements (field IDUT or U) for the
translational degrees of freedom can be exported by Abaqus/Standard and Abaqus/Explicit. Displacements can be imported by Abaqus/Standard and Abaqus/Explicit. When imported, displacements are ramped from the values of the previous exchange
time point to those of the next target time point. In an implicit dynamic analysis,
velocity and acceleration must be imported when importing displacement. The
displacements are in the global coordinate system.
Displacements are available for points, surface regions, and volume regions in Abaqus/Standard and Abaqus/Explicit.
Displacements can be viewed in the Visualization module of Abaqus/CAE.
Velocity and Acceleration
Velocity (field IDVT
or V) and acceleration (field
IDAT or
A) for the translational degrees of freedom can be
imported and exported by Abaqus/Standard for transient procedures and by Abaqus/Explicit. In an implicit dynamic analysis, when importing velocity or acceleration, all three
fields—displacement, velocity, and acceleration—must be imported. Velocity and
acceleration are in the global coordinate system.
Velocity and acceleration are available for points, surface regions, and volume regions
in Abaqus/Standard and Abaqus/Explicit.
Rotations
Rotations (field IDUR) can be imported and exported by Abaqus/Standard and Abaqus/Explicit. In an implicit dynamic analysis, rotational velocity and rotational acceleration
must be imported when importing rotations. Rotations are in the global coordinate
system.
Rotations are available for points and surface regions.
Rotations can be viewed in the Visualization module of Abaqus/CAE.
Rotational Velocity and Rotational Acceleration
Rotational velocity (field IDVR) and rotational acceleration (field
IDAR) can be imported
and exported by Abaqus/Standard for transient procedures and by Abaqus/Explicit. In an implicit dynamic analysis, when importing rotational velocity or rotational
acceleration, all three fields—rotation, rotational velocity, and rotational
acceleration—must be imported. Rotational velocity and rotational acceleration are in
the global coordinate system.
Rotational velocity and rotational acceleration are available for points and surface
regions.
Current Coordinates
Current nodal coordinates (field IDCOORD) can be exported by Abaqus/Standard and Abaqus/Explicit. The coordinates are the current coordinates of the deformed structure whether small-
or large-displacement analysis is performed. In general, it is preferred to export
displacements (field IDUT or U) rather than
current coordinates when results are mapped between dissimilar interface regions. In
cases where the partner client does not retain the original coordinates, it might be
necessary to send current coordinate values rather than displacements.
Current coordinates are available for points, surface regions, and volume regions in
Abaqus/Standard and Abaqus/Explicit.
Concentrated Forces
Concentrated forces (field IDCF), if imported, are ramped from the values of the
previous exchange time point. The concentrated forces are in the global coordinate
system.
When exporting concentrated forces, Abaqus/Standard transfers reaction forces at interface nodes that have prescribed displacements. The
reaction forces are exported in the global coordinate system.
Concentrated forces are available for points, surface regions, and volume regions in
Abaqus/Standard and Abaqus/Explicit.
Concentrated normal forces can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
CF and for Abaqus/Explicit simulation by requesting output variable
FEXT.
Concentrated Moments
Concentrated moments (field IDCM), if imported, are ramped from the values of the
previous exchange time point to those of the next target time point. The concentrated
moments are in the global coordinate system.
Concentrated moments are available for points and surface regions in Abaqus/Standard and Abaqus/Explicit.
Concentrated moments can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
CM and for an Abaqus/Explicit simulation by requesting output variable
MEXT.
Normal Pressure
Normal pressure (field IDP), supported for import by Abaqus/Standard, is the traction normal component to the surface. Pressure values are ramped from the
values of the previous exchange time point to those of the next target time point when
imported into Abaqus/Standard. In most cases it is preferred to import concentrated forces (field
IDCF) because these
contain both the normal and shear traction components. For shell and membrane-like
structures, it might be preferable to import pressures rather than concentrated
forces.
Normal pressure can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
P.
Traction Vector
Traction vector (field IDTRVEC), supported for import by Abaqus/Standard, is a general traction vector acting on a surface. Traction values are ramped from
the values of the previous exchange time point to those of the next target time point
when imported into Abaqus/Standard. For shell and membrane-like structures, it might be preferable to import traction
rather than concentrated forces.
Normal pressure can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
P.
Procedures Involving Thermal Degrees of Freedom
Table 2 lists the thermal fields available for co-simulation exchange, their associated field
identifiers, the supported co-simulation interface region types, and which Abaqus solvers support import and export of the field values.
Table 2. Exchanging fields for procedures supporting thermal degrees of freedom.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
NT
Nodal temperature
P, S, V
S, E
S, E
CFL
Concentrated heat flux at a node
P, S, V
S, E
HFL
Heat flux normal to element surface
S
S
FILM
Film properties
S
S
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
The following procedures support co-simulation using thermal degrees of freedom:
Nodal temperature (field IDNT) can be imported and exported by Abaqus/Standard and Abaqus/Explicit. Temperature values are ramped from the values of the previous exchange time point to
those of the next target time point.
Temperature values can be exchanged either on the top surface
(SPOS) or the bottom surface
(SNEG) of structural elements. Temperatures cannot be
exchanged on double-sided surfaces. When exchanging temperatures on both the top and
bottom faces, define two different regions; one to exchange temperature on the top face
and the other to exchange temperature on the bottom face.
Nodal temperature values can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
NT.
Heat Flux
Use concentrated heat flux (field IDCFL) for heat entering at a node in Abaqus/Standard and Abaqus/Explicit. Concentrated heat flux is available for points, surface regions, and volume regions.
Heat flux values can be exchanged either on the top surface
(SPOS) or the bottom surface
(SNEG) of structural elements. Heat flux cannot be
exchanged on double-sided surfaces. When exchanging heat flux on both the top and bottom
faces, define two different regions; one to exchange heat flux on the top face and the
other to exchange heat flux on the bottom face.
Concentrated heat flux values can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
CFL.
Use surface heat flux (field IDHFL) for a distributed heat flux entering the surface
in Abaqus/Standard. Distributed heat flux is available only for surface regions.
Surface heat flux can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
FLUXS.
Film Properties
Use surface film properties (field IDFILM) to model convection governed by
where q is the heat flux entering the surface,
h is a film coefficient, is the wall temperature, and is the fluid or ambient temperature.
Both the film coefficient and fluid temperature are passed into Abaqus/Standard and are kept constant over the subsequent exchange interval. When the fluid and wall
temperatures coincide, an arbitrary small value for the heat transfer coefficient is
passed into Abaqus. To obtain reasonable film properties for the first exchange interval, you should
ensure that the wall temperatures are initialized properly in Abaqus and that you provide a good estimate for the initial fluid temperature.
Film properties are available only for surface regions in Abaqus/Standard.
Procedures Involving Pore Fluid Pressure
Table 3 lists additional fields that can be exchanged for a coupled pore fluid diffusion/stress
analysis, their associated field identifiers, the supported co-simulation interface region
types, and which Abaqus solvers support import and export of the field values.
Table 3. Exchanging fields for a coupled pore fluid diffusion/stress analysis.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
POR
Pore fluid pressure at a node
P, S, V
S
S
CFF
Concentrated fluid flow at a node
P, S, V
S
RVF
Reaction fluid volume flux due to prescribed pressure
P, S, V
S
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
The following procedure involving pore fluid pressure supports co-simulation:
Nodal pore pressure (field IDPOR) can be imported and exported by Abaqus/Standard for points, surface regions, and volume regions.
Nodal pore pressure values can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
POR.
Concentrated Fluid Flow
Fluid flow (field IDCFF) defines the seepage flow at a node. Concentrated
fluid flow can be imported by Abaqus/Standard for points, surface regions, and volume regions.
Concentrated fluid flow values can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
CFF.
Reaction Fluid Volume Flow
Reaction fluid volume flux (field IDRVF) defines the rate at which fluid volume is entering
or leaving the model through the node to maintain the prescribed pore pressure. Reaction
fluid volume flux can be exported by Abaqus/Standard for points, surface regions, and volume regions.
Procedures Involving Electromagnetic Response
Table 4 lists additional fields that can be exchanged for an electromagnetic analysis, their
associated field identifiers, the supported co-simulation interface region types, and
which Abaqus solvers support import and export of the field values.
Table 4. Exchanging fields for a electromagnetic analysis.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
EMJH
Joule heating flux due to flow of current
V
S
EMBF
Magnetic body force intensity vector due to flow of induced current
V
S
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
The following procedure involving electromagnetics supports co-simulation:
The Joule heating flux (field IDEMJH) can be exported by Abaqus/Standard for volume regions. It can be imported in a downstream heat transfer analysis as
concentrated nodal heat flux (field IDCFL).
Values for the Joule heating flux can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
EMJH.
Magnetic Body Force Intensity Vector
The magnetic body force intensity vector (field IDEMBF) can be exported by Abaqus/Standard for volume regions. It can be imported in a downstream stress analysis as
concentrated force (field IDCF).
Magnetic body force intensity vector values can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation by requesting output variable
EMBF.
Temperature and Independent Field Variables
Field variables are time-dependent, predefined fields that exist over the spatial domain
of the model (see Predefined Fields). Field
variables in conjunction with the co-simulation technique extend the possibilities of
multiphysics by allowing material point dependencies on an external field defined by
another application.
Field variables must be numbered consecutively starting with one. Field variables can be
defined:
by entering the data directly,
by reading an Abaqus results file or output database file,
in an Abaqus/Standard user subroutine, and
through the co-simulation interface.
If field variables are defined by multiple methods, Abaqus processes them in the order defined above. Care needs be taken when field variables are
used with structural elements, such as membranes and shells. In this case only the top or
bottom face forming the interface region receives a value.
Table 5 lists the temperature and independent field variables available for co-simulation
exchange, their associated field identifiers, the supported co-simulation interface region
types, and which Abaqus solvers support import and export of the field values.
Table 5. Exchanging temperature and independent field variables.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
NT
Temperature as field variable specified at nodes but interpolated to
integration points
V
S
FV1
Field variable 1
V
S
FV2
Field variable 2
V
S
FV3
Field variable 3
V
S
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
The following Abaqus/Standard procedures support import of temperature and independent field variables:
Temperature (field IDNT) can be imported for procedures that allow material
properties to be defined as a function of an external temperature field. When imported,
temperature values are ramped from the values of the previous exchange time point to
those of the next target time point.
Independent field variables (field IDs
FV1, FV2, and
FV3) can be imported by Abaqus/Standard, allowing material properties to be defined as a function of the external fields.
When imported, independent field variable values are ramped from the values of the
previous exchange time point to those of the next target time point.
Temperature as a field variable can be viewed in the Visualization module of Abaqus/CAE for an Abaqus/Standard simulation. You might notice differences when you compare the source and target
fields. There are two possible causes for these differences:
Field variables and temperature as a field variable are mapped accurately and
imported at nodes. However, when saved to the output database, these quantities are
interpolated to element integration points. When contouring, some averaging can occur
depending on the contouring parameters selected.
For fully integrated first-order elements, a selective reduced-integration technique
is employed (see Solid isoparametric quadrilaterals and hexahedra). In this case, field variables and temperature as a field variable
are averaged at the element center and saved to the output database.
Miscellaneous Fields
Table 6 lists miscellaneous fields available for co-simulation exchange, their associated field
identifiers, the supported co-simulation interface region types, and which Abaqus solvers support import and export of the field values.
Table 6. Exchanging miscellaneous fields.
Field ID
Fields
Interface Type1
Abaqus Solver2
Units
Import
Export
MASS or LUMPEDMASS
Mass
P, S
S, E
S, E
M
RI
Rotary inertia
P, S
S
E
1 P (points), S
(surface region), V (volume region)
2 S (Abaqus/Standard), E (Abaqus/Explicit)
Lumped Mass
Lumped mass values (field IDMASS or LUMPEDMASS) at
nodes can be exported and imported by Abaqus/Standard and Abaqus/Explicit.
Lumped mass is available for points and surface regions.
Rotary Inertia
Nodal (lumped) rotary inertia (field
IDRI) can be imported
by Abaqus/Standard and exported by Abaqus/Explicit over points or surface regions for models using structural elements.
Defining the Coupling and Rendezvousing Scheme
Different types of analyses have different time integration requirements that influence or
dictate the frequency of interaction between the analyses in a co-simulation to obtain an
accurate and robust solution. For example, consider the difference in time integration
between an implicit and an explicit dynamic analysis. Furthermore, Abaqus/Standard can adjust the increment sizes automatically to obtain an economical and accurate
solution for transient problems (see Incrementation). For example, consider a
transient heat transfer analysis modeling a diffusive process. Here, the analysis might use
small time increments at the beginning of the analysis where there is a high gradient in the
solution and large time increments toward the end of the analysis when steady state is
reached.
The parameters that you use to control these co-simulation exchanges depend on the
co-simulation interface that you are using.
You define the co-simulation algorithm and related exchange parameters in a
co-simulation configuration file.
For structural-to-structural co-simulation using Abaqus/Standard and Abaqus/Explicit, you must also provide co-simulation controls parameters in the input file.
Using the SIMULIA Co-Simulation Engine Configuration File
The SIMULIA Co-Simulation Engine employs an independent software component, termed the “director,” which defines all
aspects of the interaction for co-simulation between analysis programs and provides the
necessary instructions to implement the coupling and rendezvousing schemes. You provide the
director with relevant parameters for your scheme choices through the co-simulation
configuration file. When you use Abaqus/CAE to execute the co-simulation, the configuration file is created for you
automatically.
The configuration file must be in Extensible Markup Language
(XML) format, which uses the file extension
xml. You can define a configuration file through a predefined template,
or you can create a fully elaborated form of the configuration file.
Using predefined configuration templates
For the co-simulation analysis cases described in Co-Simulation between Abaqus Solvers, predefined templates that
define common coupling and rendezvousing schemes are available. To use one of the
predefined templates, you must create a configuration file with the structure shown below.
<?xml version="1.0" encoding="utf-8"?>
Required XML declaration line
<CoupledMultiphysicsSimulation>
Required XML root element; identifies file as describing a multiphysics simulation
<template_name>
<template_parameter_1>parameter_1_name</template_parameter_1>
<template_parameter_2>parameter_2_name</template_parameter_2>
<template_parameter_3>parameter_3_name</template_parameter_3>
</template_name>
Closure of the template element
</CoupledMultiphysicsSimulation>
Closure of the XML root element
At run time, the SIMULIA Co-Simulation Engine director applies your parameter settings to the template, creating an elaborated
configuration file that is then used in the co-simulation analysis. An elaborated
configuration file is defined as a configuration file that provides all details of the
configuration explicitly without referring to a template.
In cases where predefined templates are not available (such as coupling with an in-house
or third-party code) or are insufficient (for example, you want to exchange more variables
at the co-simulation interface region or adjust mapping tolerances), you must create an
elaborated configuration file. For tips on working with elaborated configuration files,
see “Advanced Uses of the SIMULIA Co-Simulation Engine Configuration File” in the Dassault Systèmes Knowledge Base at https://support.3ds.com/knowledge-base/. For detailed information
about the elaborated configuration file, see the SIMULIA Co-Simulation Engine Application Programing Interface (API) documentation.
Coupling and Rendezvousing Schemes for Elaborated Configuration Files
You define the co-simulation coupling and rendezvousing schemes in an elaborated
configuration file.
Coupling Scheme
The coupling scheme defines the sequence of exchanges between analysis programs and
whether a coupled simulation can be run in a serial, parallel, or implicit iterative
manner. When deciding on the coupling scheme, you should consider solution stability
issues as well as the utilization impact on your computing resources.
Parallel Explicit Coupling Scheme (Jacobi)
In a parallel explicit coupling scheme, both simulations are executed concurrently,
exchanging fields to update the respective solutions at the next target time. The
parallel coupling scheme might make more efficient use of computing resources; however,
it is considered less stable than the sequential scheme and should be employed only for
weakly coupled physics simulations using small coupling steps.
In a sequential explicit coupling scheme, the simulations are executed in sequential
order. One analysis leads while the other analysis lags the co-simulation.
The sequential explicit coupling scheme should be employed only for weakly coupled
physics simulations using small coupling steps.
Iterative Coupling Scheme
In an iterative coupling scheme, the simulations are executed in sequential order. One
analysis leads while the other analysis lags the co-simulation. Multiple exchanges per
coupling step are performed until termination criteria are met.
The termination criteria depend on the analyses in the co-simulation; for co-simulation
between Abaqus and third-party analysis products, consult the appropriate User’s Guide.
Coupling Step Size
The coupling step is the period between two consecutive exchanges and consequently
defines the frequency of exchange between the analyses in a co-simulation. The coupling
step size is established at the beginning of each coupling step and is used to compute the
target time (the time when the next synchronized exchange occurs).
The methods available in Abaqus for computing the coupling step size are described in the sections below. To determine
the methods available for a co-simulation partner analysis, consult the appropriate
third-party program documentation.
Constant Coupling Step Size
A constant user-defined coupling step size is the most basic method of defining a
coupling step size. Both analyses advance while exchanging data at target points
according to
where is a value that defines the coupling step size to be used throughout
the coupled simulation, is the target time, and is the time at the start of the coupling step.
Minimum Coupling Step Size
This method selects the minimum of the coupling step sizes suggested by each analysis.
Abaqus always uses the next increment suggested by its automatic incrementation as its
suggested coupling step size.
Maximum Coupling Step Size
This method selects the maximum of the coupling step sizes suggested by each analysis.
Abaqus always uses the next increment suggested by its automatic incrementation as its
suggested coupling step size.
Importing the Coupling Step Size
Abaqus can import a coupling step size suggested by the co-simulation partner analysis.
Exporting the Coupling Step Size
Abaqus can export a suggested coupling step size to the co-simulation partner analysis.
Time Incrementation Scheme
Abaqus might take multiple increments per coupling step, or you can force Abaqus to use a single increment per coupling step.
Typically, Abaqus might perform several increments (referred to as “subcycling”) during the coupling
step. During subcycling, Abaqus/Standard ramps the loads and boundary conditions (with the exception of film properties) from
the values at the end of the previous coupling step to the values at the target time,
while in Abaqus/Explicit the loads are applied at the start of the coupling step and kept constant over the
coupling step.
Subcycling allows Abaqus to use its own time incrementation to reach the target coupling time; specifically, it
allows Abaqus to cut back the increment size if there are nonlinear events that require the increment
size to be reduced.
In certain cases you can force Abaqus to use a time increment size dictated by the coupling step size (that is, no
subcycling). This allows both solvers to use the same time incrementation and avoid
interpolation of quantities during the coupling step. When proceeding in this “lockstep”
manner, Abaqus is not able to reduce the time increment to resolve nonlinear events and, consequently,
ends the simulation in cases where the nonlinear events require that the increment size be
reduced.
Model Dimension and Coordinate Systems
Two-dimensional and three-dimensional Abaqus models are fully supported. Axisymmetric Abaqus models are supported only for Abaqus/Standard to Abaqus/Explicit co-simulation. For co-simulations that do not support two-dimensional and axisymmetric
models, you can represent these models as a three-dimensional slice of unit thickness (or
wedge element) with the appropriate boundary conditions applied.
Vector quantities are defined according to Abaqus conventions; the first component represents the quantity along the
x-axis, the second quantity represents the quantity along the
y-axis, and the third quantity represents the quantity along the -axis (for three-dimensional models). For axisymmetric models in Abaqus the axis of revolution is about the y-axis. These conventions apply
to both the exported and the imported vector quantities.
All exported vector quantities are expressed in the global coordinate system of the Abaqus model, ignoring any transformation definitions. Similarly, the third-party program must
provide vector quantities that are imported into Abaqus in the global coordinate system of the Abaqus model.
The third-party analysis program might use different conventions, please refer to the
appropriate third-party program documentation for further modeling details and/or
limitations.
Unit System
Abaqus does not require that the analysis be run with a particular unit system. In general, the
unit system used in creating the Abaqus model might not be the same as that used with the third-party program model. When the two
unit systems differ, the fields exchanged between the two programs must go through a
transformation of units. Refer to the appropriate third-party program documentation for
further modeling details.
Restarting a Co-Simulation
Restart output must be synchronized between co-simulation analyses for a co-simulation
restart to be successful. You should request that restart data are written at the
co-simulation target times when both solutions are considered at equilibrium. For more
information, see Synchronizing Restart Information Written in a Co-Simulation. The solution time for the particular step/increment number from which Abaqus restarts must correspond to the coupled analysis solution.
Limitations
The following limitations apply:
The steps in the Abaqus model must be defined such that the co-simulation fits entirely within a single Abaqus step. Further, there can be only one co-simulation in the Abaqus job. You can use the restart capability to perform multiple co-simulations for an
analysis (see Restarting an Analysis).
A co-simulation surface or volume defined over beam, pipe, and truss elements or
defined over the edges of three-dimensional elements cannot be used as an interface
region. You should use discrete points to transfer loads and boundary conditions.
A co-simulation surface or volume defined over modified triangular elements or modified
tetrahedral elements cannot be used as an interface region.
Quadratic coupled temperature-displacement elements cannot be used as an interface
region in a co-simulation using the coupled temperature-displacement procedure.
When performing a co-simulation, output at specified time points might not be satisfied
at the requested times, depending on the synchronization parameters.
Abaqus/Explicit cannot use thread-based execution with co-simulation.
Because co-simulation is a general capability, no error message is issued if Abaqus encounters the conditions listed above. There might be further limitations depending on
the third-party analysis program being used. For more information, refer to the appropriate
third-party program documentation.