OptiStruct and AcuSolve are
fully-integrated to perform a Direct Coupled Fluid-Structure Interaction (DC-FSI) Analysis
based on a partitioned staggered approach.
OptiStruct and AcuSolve
both include time-domain simulation capabilities that break the coupled solution
into a number of time steps. Since the governing equations of both OptiStruct and AcuSolve are
nonlinear, sub-iterations are typically required within each time step.
As the name suggests, Fluid-Structure Interaction simulates the interrelationship between fluid
flow and the solid body the fluid is in contact with. The behavior of the structure
affects the fluid and vice-versa in a coupled dynamic interaction that is captured
by dividing the time domain into time steps. For each time step, the exchanged
solution attributes are solved for from the governing equations until equilibrium
convergence is attained. Each such iteration run through towards convergence within
a time step is known as an exchange (in OptiStruct) or a
stagger (in AcuSolve). The fluid flow can be external to
the solid object, similar to an aircraft wing moving through air, or it can be
internal, like the flow of coolant in a condenser tube.
Target Applications
The Fluid-Structure Interaction capability aims at simulations of dynamic problems subjected to
fluid flow interactions and their complex interrelationship. It is recommended to
use this direct coupling method when the solid structural response variables
affecting the fluid domain vary significantly and result in large changes in the
fluid response. In this process, the responses from both domains are exchanged in
real time.
Note: For linear structural response the P-FSI (Practical FSI) solution
offered by AcuSolve may be more effective in solving
the linearized structural response with the nonlinear flow solution. For further
information on the P-FSI method, refer to the AcuSolve Command Reference Manual.
Supported Solutions
A large number of physical state variables affect the interrelationship between the structure and
the fluid domains. For example, pressure of the fluid at the interface can affect
displacement (and thereby the stress state) of the solid structure, and vice-versa.
The displacements at the structural interface can cause changes to fluid flow
leading to significant differences in fluid behavior across the entire domain.
Similarly, thermal loads on the structure can lead to temperature changes at the
structural interface, leading to a changing temperature field for the fluid.
Currently, in OptiStruct and AcuSolve the following solutions for the interaction is
supported:
Structural Fluid-Structure Interaction (Nonlinear Direct Transient
Structural Response of the structure).
Thermal Fluid-Structure Interaction (Linear Transient Heat Transfer Response
of the structure).
Combined structural and thermal heat transfer solutions in conjunction with fluid-structure interaction is currently not supported. You can either run Structural FSI or Thermal FSI, however, you cannot run both in the same run. In the following sections, SFSI refers to Structural Fluid-Structure Interaction and TFSI refers to Thermal Fluid-Structure Interaction for brevity and to avoid redundancy.