of any facility can be made by placing a horizontal mark in the figure at a height for each component that approximately reflects that facility. If the marks generally lie near the bottom of the columns, the facility is referred to as having a low level of simulation; if the characteristics generally lie near the top of the columns, the facility is referred to as offering a high level of simulation.

Practitioners of simulation generally accept that various levels of simulation are appropriate for different design situations. No definitive guidance is available to assist prospective users in determining the level of simulation needed for a particular problem. There is a dearth of quantitative information relative to selecting the level of simulation appropriate to a particular waterway design study. Nevertheless, if the level of simulation is not sufficient to capture an essential feature of the waterway, ship dynamics, or other key aspect of the real system, then the results of the simulation may be suspect. In practice, a higher level of simulation than what appears necessary is often used simply because the consequences of overlooking some subtle feature may have an important impact on vessel transit results. For example, the presence of a full bridge team to provide navigational support to the pilot would add to the face (that is, apparent) validity but would not necessarily add to the level of simulation. The actual contribution would depend on the capability of the bridge team to assess the operational situation and communicate this effectively. Thus, as with waterway design generally, the tendency in simulation is toward conservatism.

After the vessel (or vessels), environmental conditions, and appropriate simulator hardware are selected and installed, the simulation process occurs in three steps. In the preliminary phase, mathematical models of each simulation component are collected, and the various constants are identified (see Chapter 5). In the simulation phase, the model is exercised in either real time, fast time, or both. In the interpretation phase, the simulation results are assessed in terms of the risks posed by the channel design and potential alternative designs. However, because the simulation program is biased toward the most accident-prone situations, results must be carefully interpreted (see Chapter 6).

SUMMARY

The prospective user of shiphandling simulators for waterway design is confronted by several factors that complicate the decision to use a simulator. Given the range of technical considerations, careful examination of the capabilities, research methodologies, and results of available simulations is needed to assess simulator suitability for each individual waterway design project. Of equal importance is the selection of pilots for real-time simulations because they are critical to both the validity and credibility of results.



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