What aspect of a numerical model does validation primarily ensure?

Validation of a numerical model primarily ensures that the model accurately simulates the physical system it is intended to represent. This process involves comparing the model's outputs against experimental or analytical results to verify that it correctly captures the relevant physics, behaviors, and characteristics of the system in question.

An accurate simulation is critical because the primary purpose of developing a numerical model is to obtain reliable predictions and insights about the physical phenomena under study. If the model fails to replicate the essential features of the real-world system, any conclusions drawn or decisions made based on its results may be flawed or misleading.

While user-friendliness, cost-effectiveness, and computational speed are certainly important factors in model development and application, they do not directly ensure that the model represents the system accurately; therefore, they are secondary considerations to the validation process.