Objective
The Objective is the goal of the sizing process - the variable of concern and whether it should be minimized or maximized.
A valid Objective variable must be calculable as a total for any potential system configuration. For example, a system can be sized to minimize or maximize weight because any pipe has a weight measured in a common unit. However, different pipes may have different pressure ratings - it does not make sense to maximize or minimize pressure rating as they cannot be added together and retain the same meaning. Further, the value must be available for all possible configurations - if some pipe sizes are of unknown weight, the sizing cannot proceed effectively because it is unknown whether choosing that size is an improvement or not.
The Objective is defined on the Sizing Objective panel.
Conceptual Example
Consider a simple problem - moving fluid from one large tank to another. The pressures and fluid levels in the tanks are fixed. The fluid must be transferred in a pipe of specialized material, and it is difficult to manufacture this material in small diameters, making them more expensive. The Objective is to select the cheapest pipe possible for the task.
Figure 1: Cost for different diameters of specialized piping
Clearly, there is a minimum cost between diameters "4" and "5."
Figure 2: Locating the Diameter with minimum cost
However, what if we are limited by other requirements? For example, we may have a minimum flow rate. This is a Design Requirement, and makes the problem more complex.
