by Robert van Liere
In a joint project between CWI and the Netherlands Energy Research Foundation (ECN), insights, methods, techniques and tools are developed enabling researchers to apply computational steering in their simulations. Applications at ECN include the development of a ceramic foam burner.
The standard cycle in simulation is to prepare input, execute a simulation, and visualize the results. Performing these activities simultaneously realises greater insights and higher productivity. This is the underlying idea of Computational Steering: researchers change parameters of their simulation on the fly and immediately receive feedback on the effect. However, the development of a dedicated user-interface for a simulation is a time-consuming process, which requires the expertise of specialists on user-interfacing and computer graphics. Hence the CWI-ECN Computational Steering project, which started in 1992, aims to develop an environment in which researchers themselves can develop and use interfaces to their simulations.
The current focus is on development of a Computational Steering Environment (CSE) that encourages exploratory investigation by the researcher of his simulation. Such an environment should support direct manipulation of graphics objects that are also updated by the simulation, enable researchers to use computational steering without help from visualisation experts, and support multiple processes running simultaneously.
The main process in the CSE is the Data Manager, which manages a database of variables. Attributes (type, dimensions, etc.) and their current value are stored for each variable. Other processes (called satellites) can connect to and communicate with the Data Manager (see Figure 1). Satellites can create, read and write variables, and can subscribe to events, such as notification of mutations of a particular variable. The Data Manager takes care of event notification, enabling satellites to use the same data and to communicate with other satellites. A variety of general purpose satellites for standard tasks has been developed. Fro example, data can be logged, sliced, transformed, and calculated.
However, the most important satellite is a general purpose satellite for input and visualization of data. Parametrized Graphics Objects (PGOs) are used as the main concept for the general purpose interaction satellite, and the graphics editor as a metaphor for the design of the interface. The graphics editor has two modes:edit and run. In edit-mode, the researcher can create and edit graphics objects much like in MacDraw-like drawing editors. In run-mode, a two-way communication is established between the researcher and the simulation. Data is retrieved from the Data Manager and mapped onto the properties of the graphics objects. Also, the researcher can enter text, drag and pick objects, which is translated into changes of the values of variables in the Data Manager. Hence there is automatic support for the ususally time-consuming and error-prone direct manipulation of graphics objects.
Ceramic foam burners are studied intensively at ECN, both experimentally and computationally. The aim is to realise energy savings and to reduce NOx emissions. A one-dimensional mathematical model has been developed that incorporates a one-step chemical reaction, heat transfer between gas and ceramic, radiation from the burner surface to the surroundings, and radiative heat transfer within the ceramic foam. The CSE has been used to steer those simulations. Oxygen and gas concentrations, ceramic and gas temperatures, as well as the radiation and resulting NOx concentration are displayed. The user can control the surplus of air in the mixture and the desired power. These parameters control the air and gas flow. In the setting shown here, the burner is in a radiant mode: the mixture burns at the downstream edge of the ceramic foam. As a result, the foam heats up, and radiates its energy to the surroundings. This particular interface was developed in half a day, demonstrating that our approach effectively enables researchers to apply computational steering.
Ceramic Foam Burner: experimentally
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