1. A method of manufacturing a mechanical part, comprising: (a) constructing a system model for a mechanical system having the mechanical part and at least one other mechanical part of the mechanical system, the system model comprised of multiple subsystem models including a given subsystem model that includes the mechanical part; (b) evaluating the system model using initial subsystem designs and extracting interactions between the given subsystem model and other subsystems models; (c) updating the interactions for the given subsystem model; (d) performing subsystem design optimization on the given subsystem model using the subsystem model and most recently updated interactions while varying magnitude of stochastic variability on the interactions in a range on the order of 5% to 20% during the subsystem design optimization, thereby obtaining an updated subsystem design; and (e) manufacturing the mechanical part based on the updated subsystem design.