Low-fidelity simulators

The withheld information technique is used to explore the manner in which operators select and use information in process abnormalities. A particular abnormal process event is represented in a control panel "mock-up" or a "low-fidelity" simulator, and information is withheld from the worker until it is requested. This technique has been developed by Marshall et al. (1981) and has been used to elicit the diagnostic plans used by experienced workers during various process transients in a crude distillation imit. There are three main applications of this technique ... 

Low-fidelity simulators are generaUy focused on single skiUs that allow learners practice in isolation, on their own time, without much required feedback. Medium-fidelity simulators are more realistic in their representation of the task, but lack sufficient cues for the learner to be fuUy immersed in the situation. High-fidelity simulators provide adequate cues and feedback to aUow for fuU immersion and response to treatment interventions. Feedback can be objective measures built in to the simulator itself, or offer cues for feedback from an instructor [43]. 

Wang and Liu [51] made a very careful study of the flow bifurcation behavior in a slightly curved microscale duct (d/R = 5 x 10 ) where they examined the effect of increasing Dean number on the flow structure for a square section channel. A high-accuracy finite volume method was used to determine the bifurcation structure of the system. Their results showed that this simple system exhibits very complex behavior with a two-cell state at low Dean numbers changing to a temporally periodic oscillation, another steady two-cell state, a temporally intermittent oscillation and finally a chaotic temporal oscillation as the Dean number is increased. This work highlights the complexity of this very simple system and the need for high-fidelity simulations. 

Instabilities are present in the physical problem studied but they are also present in the numerical methods used to simulate these mechanisms. Most high-fidelity numerical schemes required for Computational Fluid D5mamics exhibit low dissipation and therefore multiple non-physical instabilities (wiggles) arise which can require significant efforts to be kept under control [374 362 340]. 

Some special types of foams are (1) structural foams (2) syntactic foams and multifoams and (3) reinforced foams. Structural foams (Figure 2.58c and d), which possess full-density skins and cellular cores, are similar to structural sandwich constructions or to human bones, which have solid surfaces but cellular cores. Structural foams may be manufactured by high pressure processes or by low-pressure processes (Figure 2.61). The first one may provide denser, smoother skins with greater fidelity to fine detail in the mold than maybe true of low-pressure processes. Fine wood detail, for example, is used for simulated wood furniture and simulated wood beams. Surfaces made by low-pressure processes may, however, show swirl or other textures, not necessarily detracting from their usefulness. Almost any thermoplastic or thermosetting polymer can be formulated into a structural foam. 

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