1. A method for simulating a surface of a structure in a virtual space, the method comprising: creating a failure mode condition for excluding invalid samples, wherein the failure mode condition is a rate of change value for a part feature exceeding a rate of change constraint; determining relative positions in the virtual space of a plurality of points on the surface of the structure using the rate of change constraint, wherein the rate of change constraint is a maximum deviation of the surface for the plurality of points over a specified distance along the surface for the part feature, wherein each point in the plurality of points is displaced by the rate of change constant; and generating in a processor a virtual model of the surface of the structure in the virtual space using the points, wherein each point is displaced independent of a neighboring point; using the virtual model and the rate of change constraint, comparing a rate of change value for the part feature to the rate of change constraint; and responsive to the rate of change value for the part feature exceeding the rate of change constraint, identifying the sample as an invalid sample.