Introduction to the OpenMDAO FrameworkΒΆ

MDAO stands for Multidisciplinary Analysis and Optimization. OpenMDAO is an open source framework for analyzing and solving MDAO problems. In OpenMDAO, a problem is represented by a system of objects called components.

A Component is an object with an execute function that updates the values of its output variables based on the values of its input variables. You can connect the inputs and outputs of one component to those of other components, allowing data to be passed between them.

The following figure gives a conceptual view of what a simple Component might look like. This Component has two inputs (a, b) and one output (c). The calculation that it performs is to add the two inputs to produce the output.

The component is represented by a box with 2 inputs entering from the left and an output leaving at the right; calculation is performed inside the component.

Conceptual View of a Simple Component

Components within OpenMDAO can be as simple or complex as necessary. The inputs and outputs to a Component are Python objects, so they are not limited to being simple types like floating point or integer.

A Workflow is an object that executes a group of components in a particular order.

A Driver is a special kind of Component that executes a Workflow repeatedly until some condition is met. Some examples of Drivers are optimizers, solvers, and design space explorers.

An Assembly is a special kind of Component that contains other components. One of those components must be a Driver named driver. When an Assembly executes, it executes driver, which then executes its Workflow. A Driver’s Workflow may contain other Drivers, and each of those Drivers has a Workflow of its own. The hierarchical structure defined by the contents of an Assembly’s drivers and the contents of their workflows is called an iteration hierarchy.

The following figure shows an example of an iteration hierarchy involving four different Drivers. Note that in this example the same component, component2, appears in two different workflows.

Figure shows workflows for each of 4 drivers; the workflows contain a total of 5 components

View of an Iteration Hierarchy

The next figure shows the data flow within an Assembly having one Driver and four Components. A solid line between two Components indicates that one of them is supplying inputs to the other. Each dashed line between a Driver and a Component indicates a parameter, objective, or constraint in the Driver that references an input or output variable in the Component. The arrow at the end of a dashed or solid line indicates the direction of the data flow between two connected objects.

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View of an Assembly Showing Data Flow

Because an Assembly is also a Component, a hierarchy of assemblies can be constructed. For example, we could replace component3 from the figure above with an assembly containing two other components, resulting in the following:

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View of an Assembly within an Assembly

So assemblies allow us to organize our model into a hierarchy of submodels, and within each submodel, drivers and workflows give us a flexible way to define an iteration scheme.

The functionality of OpenMDAO can be extended through the use of plugins. In the figure below, objects of the sort found outside of the Framework box can be integrated into the framework as plugins. This means that a user can create any of these and the framework will understand how to interact with them. This is possible because plugins have a specific interface that the framework expects. To learn how to create your own plugins, see the Plugin Developer Guide.

A large circle contains plugins that surround the framework (a box); inside the framework are tools and interfaces.

Top Level Context Diagram

This concludes a brief introduction to OpenMDAO. Please see the next section for details on system requirements and how to install the software.

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