The problem of determining the maximum rotational speed of a gas turbine after a load rejection event (Gas Turbine Overspeed Analysis) using a complex simulation model is a major task in the engineering of gas turbines for power plants. In this paper two algorithms for optimization of expensive black-box functions are applied to the problem instead of the time-consuming commonly used simulation approach. Conventional optimization methods that are using the functions gradients are not applicable to this simulation study as they use information about the gradients of the objective function that are not available for this model. Both algorithm use radial basis functions to approximate the objective function for optimization. The algorithms are compared and it is shown that both are able to provide sufficient solutions for the problem mentioned using a little number of simulations or, in other words, in shorter time.