Related Work

Rocstar Multiphysics Application

Illinois Rocstar Multiphysics Application Coupling Toolkit (IMPACT)

Under a separate Phase II DOE SBIR, we are developing IMPACT, the Illinois Rocstar Multiphysics Application Coupling Toolkit. IMPACT is a multiphysics software integration environment that facilitates the integration of multiple parallel software components for the purpose of generating multiphysics simulation capabilities. The code is an open-source, multiphysics infrastructure based on the Rocstar simulation suite. This work leverages experience gained over 15 years of development, ownership, and operation of a massively parallel multiphysics simulation application Rocstar initially developed under the DOE ASCI program at the University of Illinois Center for Simulation of Advanced Rockets.

Illustration of IMPACT structure and components. (1) High level depiction of the IMPACT infrastructure layers. (2) Application integration creates an application module. (3) Orchestration and orchestrator constructs that drive the system. Legend: component interfaces (CI), component-side client (CSC), and model interfaces (MI). Note color consistency.

A high level depiction of the IMPACT infrastructure layers is shown above (1 - red box) with the layers in order of decreasing generality. The back (red) layer represents a software integration toolkit that provides the basic constructs allowing applications to publish native data structures and functions. In this context, by publish we mean that the application can describe and provide access to native data structures and functions by outside software. Modules or user applications (green) are those that provide the "primary" domain-specific capabilities that must be integrated into the composite software system.

Application integration using the multiphysics infrastructure will be a recurring theme throughout the project. Each software application accessed through IMPACT need not be integrated with the general procedure shown in the inset of the diagram above (2 - green box). It is important to note that these steps are only necessary for those applications that are used in concert for coupled simulations. Because IMPACT features the ability to perform multiscale, multifidelity simulations using integrated tools, we can encapsulate new applications in this manner, such that they can later be coupled for multiphysics capabilities at some later point in time.

After creating an application module, development of the simulation orchestrator is the next step in the implementation of an integrated simulation application, an overview of which is provided above (3 - blue box). Once the multiple application modules have been created, an orchestrator must be created to implement the coupling scheme and drive the simulation by managing the control flow and the intermodule interactions. The IMPACT infrastructure provides an orchestration toolkit called the Simulation Integration Manager (SIM). The SIM provides constructs designed to be used in the implementation of orchestrators. It is instructive to think of the orchestrator as having three main functionalities: driver and driver logistics, coupling algorithm, and component agents.

Illinois Rocstar has experience in these areas as a current Phase II effort on the IMPACT project focuses on integration of several free simulation packages and creation of simple orchestrators. We will tailor these constructs to the specific physics application and for appropriate information transfer from the overlying interface through the network to the compute platform or other remove system.

• Driver and driver logistics: The orchestrator is responsible for loading the application modules, managing their MPI communicators (if necessary), and managing the control flow among the components of the integrated simulation. The SIM offers basic constructs for handling these functions for synchronized operation of serial and MPI parallel components.
• Coupling algorithm: The SIM offers three constructs for building coupling algorithms. The coupling objects encapsulate a scheduler that executes actions in a particular order and/or progression to actuate the coupling algorithm. The actions are a general abstraction and encapsulation for almost any procedural set of instructions. Typical actions include invoking modules and interpolating between meshes. The key consideration in the implementation of this part of the system is that the interface to each domain-specific model (i.e., the so-called model interface (MI)) is defined by what the coupling algorithm requires. This consideration puts some restrictions on the possible choices for the domain-specific simulation applications that this coupling algorithm may utilize in the integrated simulation.
• Component agents: Once the driver and coupling algorithm are in place, and model interface defined, the domain-specific application modules are plugged into the simulation by using SIM’s agent construct. An agent is responsible for interfacing with an application module's component interface (CI) and presenting the required model interface to the coupling object.

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