Virtual environments created through computer graphics are communications media (Licklider et al., 1978). Like other media, they have both physical and abstract components. Paper, for example, is a medium for communication. The paper is itself one possible physical embodiment of the abstraction of a two-dimensional surface onto which marks may be made. The corresponding abstraction for head-coupled, virtual image, stereoscopic displays that synthesize a coordinated sensory experience is an environment. These so-called “virtual reality” media have only recently caught the international public imagination (Pollack, 1989; D’Arcy, 1990; Stewart, 1991; Brehde, 1991), but they have arisen from continuous development in several technical and non-technical areas during the past 25 years (Brooks Jr., 1988; Ellis, 1990; Ellis, et al., 1991, 1993; Kalawsky, 1993). A well designed computer interface affords the user an efficient and effortless flow of information to and from the device with which he interacts. When users are given sufficient control over the pattern of this interaction, they themselves can evolve efficient interaction strategies that match the coding of their communications to the characteristics of their communication channel (Zipf, 1949; Mandelbrot, 1982; Ellis and Hitchcock, 1986; Grudin and Norman, 1991). But successful interface design should strive to reduce this adaptation period by analysis of the user’s task and performance limitations. This analysis requires understanding of the operative design metaphor for the interface in question. The dominant interaction metaphor for the computer interface changed in the 1980’s. Modern graphical interfaces, like those first developed at Xerox PARC (Smith et al., 1982) and used for the Apple Macintosh, have transformed the “conversational” interaction from one in which users “talked” to their computers to one in which they “acted out” their commands in a “desk-top” display. This so called desk-top metaphor provides the users with an illusion of an environment in which they enact wishes by manipulating symbols on a computer screen. Virtual environment displays represent a three-dimensional generalization of the two-dimensional “desk-top” metaphor. These synthetic environments may be experienced either from egocentric or exocentric viewpoints. That is to say, the users may appear to actually be in the environment or see themselves represented as a “You are here” symbol (Levine, 1984) which they can control.
Experimental and Numerical Studies in a Centrifugal Pump With Two-Dimensional Curved Blades in Cavitating Condition