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Substructure modules include models of relatively small regions in a structural system that needs to be modeled in detail. For example, one may want to model a link beam with detailed finite element models (or even physical specimens) while the rest of the structural system can be modeled with frame elements. At this stage, all substructure modules are assumed to be static modules which are rate-independent. There has been a few methods which allow integration of a dynamic subsystems to other dynamic systems, but such algorithms are not yet mature for general application to nonlinear dynamic problems.
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NICA |
To use a structural analysis software as a substructure module, it is necessary to implement functionalities to communicate with an integration module, to impose target displacements, and to return restoring forces of controlled DOFs back to the integration module. Many structural analysis tools, however, do not have such functionalities. In most cases, either the source code of the software needs to be modified, or an interface program needs to be used to allow the software to communicate through the network.
A program called NICA (Network Interface for Console Applications) has been developed for this purpose. The main functionality of NICA is to allow for communication between an integration module and a structural analysis software such as Zeus-NL, Abaqus, VecTor programs, or others. The communication between NICA and an integration module is based on the UTNP. The communication between NICA and a structural analysis software is primarily through named pipes or file input/output, which is somewhat slow and sometimes unreliable. Even when NICA is used as an interface program, some structural analysis software needs to be revised to allow communication with NICA. Ideally, the software would be modified such that it can directly communicate with an integration module using UTNP. Structural analysis programs that can be used as a substructure module through NICA are listed below. |
Zeus-NL |
ZEUS-NL is the analysis and simulation platform of the Mid-America Earthquake (MAE) Center. It is a state-of-the-art 3D static and dynamic analysis tool specifically developed for earthquake engineering applications. Its efficiency, accuracy, verification and user-friendly graphical user interface has made it easy to undertake inelastic large displacement analysis of complex frames using the fiber approach, with a suite of material models and elements.
To allow communication with an integration module, the source code of Zeus-NL was revised such that it can read displacement input through a console and output analysis results in a specific format. The revised version of Zeus-NL is distributed with UI-SimCor. The original version of Zeus-NL, which cannot communicate using UTNP, is available for download through the MAE Center. |
OpenSees |
OpenSees can serve as an integration module as well as a substructure module. When OpenSees is used as an integration module, a generic substructure element with UTNP is used. When OpenSees is used as a substructure module, it is necessary to impose a displacement command to a numerical model at each time step, and return restoring forces. This functionality can be directly implemented in OpenSees, similarly to the implementation in OpenFresco.
In the UT-SIM framework, OpenSees is integrated through NICA. The procedure is similar to the integration of Zeus-NL. At each time step, NICA generates a new input file for OpenSees based on the command from an integration module, runs OpenSees, and returns the analysis results. |
Generic console application |
NICA is configured such that any console application can be easily integrated to it. This functionality is added because many researchers develop their own research programs. The console application, however, needs to be revised such that displacement input and analysis results can be done through a standard console out. An example implementation is included in the distribution file of NICA.
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VecTor Programs |
The VecTor2 and VecTor4 programs have been revised such that it can directly communicate with an integration module using UTNP. Other VecTor programs will also have a similar functionality in the near future.
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NICON |
NICON is an interface program for actuator controllers which is necessary for hybrid simulations. Detailed explanation on NICON is available on Hybrid Simulation page.
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ACTIA |
ACTIA (Application for Camera Triggering and Image Acquisition), is a Matlab-based image acquisition program. It is a very useful tool to trigger high-resolution webcams and supported DSLRs during hybrid simulations. UI-SimCor can send triggering commands to ACTIA through the network which can ensure synchronization of all images with the simulation time step.
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