Introduction to OpenSees

Context for Simulation in Earthquake Engineering

Research and practice is moving towards Performance-Based Seismic Engineering, which depends on high-fidelity models and simulation to assess performance.
Simulation models capture knowledge from tests to leverage investment in limited experimentation.
Community-based, open-source software for simulation promotes innovation in research and advanced applications for practice.
NEES infrastructure is supporting OpenSees to provide simulation capability and integration with NEESit services for NEES research.

A software framework for simulation applications in earthquake engineering using finite element methods. OpenSees is not a code.
A communication mechanism for exchanging and building upon research accomplishments.
As open-source software, it has the potential for a community code for earthquake engineering.

Computation: Algorithms; Solvers; Parallel/distributed computing
Information Technology: Software framework; Databases; Visualization; Internet/grid computation
Models: Simulation models; Performance models; Limit state models; Material; component; system models

Basic approach: Modular software design for implementing and integrating modeling, numerical methods, and IT for scalable, robust simulation; Focus on capabilities needed for performance-based engineering; Programmable interfaces
Most users: a “code” for nonlinear analysis; Fully scriptable.
Generally: a software framework for developing simulation applications

A framework is NOT an executable.
A framework IS a set of cooperating software components for building applications in a specific domain.
The OpenSees framework is written primarily in the objectoriented language C++; though other languages namely C and Fortran are also used.
The abstract classes in the OpenSees framework define the interface. The concrete subclasses that exist the implementations. Other classes can be provided to extend the capabilities of the framework
Most users, however, will use OpenSees.exe which is, indeed, an executable.

In object-oriented programming, the program is seen as a collection of objects. Each object is capable of receiving messages, processing data, and sending messages to other objects.
Each object is of a particular type or Class. The class defines the data and methods of an object.
3 basic relationships between classes

IS-A (Truss is an Element)

KNOWS-A (Truss knows a Node)

HAS-A (Truss has a Material)

ModelBuilder: Constructs the objects in the model and adds them to the domain.
Domain (Central component): Holds the state of the model at time t and (t + dt)
Analysis: Moves the model from state at time t to state at time (t + dt)
Recorder: Monitors user defined parameters in the model during the analysis

Material: Uniaxial; nD; Section
GeomTransformation: Linear,Pdelta or Corotational; Convert element force and deforamtion quantities from the global coordinate system to the element basic system (local coordinates)

Provide their own main() function in C++ and link to framework.
Use OpenSees interpreterS. These are extensions of the Tcl interpreter for finite element analysis which are built using the OpenSees framework.
- OpenSees.exe (Sequential-computing version)
- OpseseesSP.exe (Parallel-computing version)
- OpenSeesMP.exe (Parallel-computing version)

Tcl is a programming language.

command arg1 arg2 …

Help
- dev.scriptics.com/scripting/primer.html
- Practical Programming in Tcl and Tk, Brent B. Welch.