ABAQUS provides built-in methods to solve the following types of multidisciplinary simulations:
For multidisciplinary problems for which ABAQUS does not provide a built-in solution procedure or where the solution procedure is limited in functionality, ABAQUS provides a general co-simulation technique. The ABAQUS co-simulation technique provides two applications, available as separate add-on analysis capabilities, for coupling ABAQUS and third-party analysis software. In both applications the interaction between subdomains is through a common interface over which data are exchanged in a synchronized manner between the ABAQUS analysis products and the third-party analysis software.
One application for the ABAQUS co-simulation technique is performing multidisciplinary analyses in which two or more distinct and coupled physical fields are modeled by different analysis software; for example, fluid-structure interaction (FSI) simulations performed in conjunction with computational fluid dynamics analysis software. The computational fluid dynamics software must support the Mesh-based parallel Code Coupling Interface (MpCCI).
Another application is solving complex problems where the model is divided into multiple domains and different analysis software are used to obtain solutions in each subdomain; for example, crash safety simulation performed in conjunction with the occupant simulation program MADYMO. This application makes use of an internal ABAQUS code coupling interface between ABAQUS/Explicit and MADYMO and does not require MpCCI.
The ABAQUS co-simulation technique:
is intended for coupling between ABAQUS and computational fluid dynamics software supporting the MpCCI interface to perform FSI simulations;
is intended for coupling between ABAQUS/Explicit and the occupant simulation program MADYMO to perform crash safety simulations;
can be used for multidisciplinary physical simulations between ABAQUS and any third-party analysis software supporting the MpCCI interface; and
is intended for advanced users with in-depth knowledge of ABAQUS and the third-party analysis software.
One subdomain may affect the response of another subdomain through one or more of the following:
the constitutive behavior, such as the yield stress defined as a function of temperature or stress defined as a function of other solution fields, such as thermal strains or the piezoelectric effect;
surface tractions/fluxes, such as a fluid exerting pressure on a structure;
body forces/fluxes, such as heat generation due to flow of current in a coupled thermal-electrical simulation;
contact forces, such as the forces due to contact between a vehicle and an occupant/pedestrian modeled as a separate subdomain; and
geometric changes, such as fluid in contact with a deforming structure.
Fluid-structure interaction (FSI) covers a very broad scope of problems in which fluid flow and structural deformation interact and affect one another. The interaction can be mechanical, thermal, or both. FSI applications include hemodynamics in an artery, fluid flow in a pump, airflow over an aircraft wing, heat exchange in a radiator, heat transfer in turbine discs, fluid sloshing in a tank, and hydroplaning of a tire. The use of the co-simulation capability to perform an FSI simulation is illustrated in “Closure of an air-filled door seal,” Section 2.3.1 of the ABAQUS Example Problems Manual.
Figure 13.1.1–1 classifies FSI problems. The complexity of the simulation increases from left to right. At the uppermost level one can distinguish between rigid and flexible structural response problems. Rigid structural response problems are effectively handled by most computational fluid dynamics analysis software; thus, an ABAQUS co-simulation need be employed only for flexible structures.
In some cases the coupling strength (influence coefficient) in one direction may be so small as to be negligible (e.g., mechanical response influence on a fluid for a small-deformation analysis). These cases permit the use of a sequential “one-way” analysis, where loads are passed from one analysis software to another analysis software but not vice versa.
The ABAQUS co-simulation interface allows for both “one-way” and “two-way” transfer of data. The structural response may be linear or nonlinear for material and geometric effects. Both steady-state and transient simulations are supported.
Crash safety simulation generally includes interaction between a vehicle and its occupant or a vehicle and a pedestrian. ABAQUS/Explicit is used to model the vehicle and MADYMO is used to model the occupant or the pedestrian.
In some cases the influence of the human response on the structural response of the vehicle is so small as to be negligible. In these cases only a part of the vehicle surrounding the human is used in a coupled analysis. The vehicle analysis is performed without the human, and the motion from a portion of the vehicle immediately surrounding the human is extracted as a submodel of the full vehicle response. The co-simulation technique is used to perform a coupled analysis with the human model and the vehicle submodel.
In an ABAQUS co-simulation the analysis domains are coupled in a staggered approach or loose manner; that is, the equations for each subdomain are solved separately, and loads and boundary conditions are exchanged at the common interface. In mathematical terms the interaction is through the “right-hand side” only, as depicted in Figure 13.1.1–2.
For example, in an FSI simulation the flow equations are solved by the computational fluid dynamics analysis software, and the structural equilibrium equations and heat transfer equations are solved by ABAQUS. Only the loads and boundary conditions at the interface are exchanged during the simulation. Similarly, in a crash safety simulation with the vehicle modeled in ABAQUS/Explicit and the dummy modeled in MADYMO, the interaction of the subdomains is resolved by application of the forces resulting from the contact condition between the interface of the two subdomains.The staggered approach is applicable to many problems that exhibit weak to moderate physics coupling. This approach may not be effective for problems that exhibit strong physics coupling. In such cases it is best to solve the problem with dedicated analysis software in which the solutions of all subdomains are combined into a single system and solved simultaneously (see Figure 13.1.1–3). Such solution approaches have their own numerical challenges and are not suited for general-purpose analysis software such as ABAQUS.
Figure 13.1.1–4 illustrates the coupling strength with an analogy in the frequency domain. Consider a lumped parameter dynamic system with a coupling impedance directly related to a response frequency
. In a staggered solution approach each subdomain is solved by temporarily ignoring the coupling terms represented by the gray spring and dashpot in Figure 13.1.1–4. When the response frequency and coupling impedance are low, a staggered approach will likely provide adequate solution accuracy and performance. However, when the response frequency is high, such that the coupling impedance is relatively large compared to the structure or fluid, you may encounter solution stability issues with the staggered approach. Performing a multidisciplinary analysis using the ABAQUS co-simulation technique involves the following steps:
Preparing the ABAQUS analysis for co-simulation (see “Preparing an ABAQUS analysis for co-simulation,” Section 13.1.2).
Preparing the third-party analysis software for co-simulation:
For fluid-structure interaction simulations, see the ABAQUS User's Guide for Fluid-Structure Interaction Using ABAQUS and FLUENT.
For crash safety simulations, see the ABAQUS User's Guide for Crash Safety Simulation Using ABAQUS/Explicit and MADYMO.
Executing the coupled analysis:
For fluid-structure interaction simulations, see “Co-simulation using MpCCI,” Section 13.1.3.
For crash safety simulations, see “Co-simulation with MADYMO,” Section 13.1.4.
For the latest support information and useful tips on running FSI simulations and crash safety simulations, consult the ABAQUS Answers in the ABAQUS Online Support System (AOSS). The ABAQUS Online Support System is accessible through the My ABAQUS section of the ABAQUS Home Page.
ABAQUS User's Guide for Fluid-Structure Interaction Using ABAQUS and FLUENT; available from Answer ID 2420 in the ABAQUS Online Support System.
ABAQUS User's Guide for Crash Safety Simulation Using ABAQUS/Explicit and MADYMO; available from Answer ID 2721 in the ABAQUS Online Support System.
For general information about MpCCI, see http://www.scai.fraunhofer.de. For specific information about MpCCI and running coupled simulations, consult the MpCCI User's Guide.
For general information about MADYMO, see http://www.automotive.tno.nl. For specific information about MADYMO, consult the MADYMO Reference Manual.
