Problem 1 - Explain

(a) Force summation method is preferred approach to calculate dynamic loads.

The force summation method differentiates to find the answer as opposed to integrating, which allows less error to propagate through the method.

(b) Finite element in time method is best suited to calculate steady periodic response. Time integration is more suited for transient response problems.

The boundary conditions of FET rely on a periodic response and hence is not suited to a non-periodic transient response. Time integration does not rely on the periodicity of the response and so can adapt to reflect transient changes easier.

(c) Stiffening of blades may reduce the life of blades.

A stiffer blade increases the natural flapping frequency, resulting in more fatigue cycles per use. Hence, due to the increased number of cycles per use, the service life of the blades decreases.

(d) Spatial finite element method results in a banded matrix that can be exploited during computation, whereas the finite element in time results in a fully populated matrix.

A space matrix that describes a system is sparse and banded as the response of one portion of the space typically only affects the response of those areas close to it. However, in time, all effects are coupled and hence the matrix is fully populated.

(e) A disturbed flap mode observed in fixed frame shows a low frequency regressive wave. What do you expect its flap frequency?

I would expect it to have a relatively high flapping frequency so as to allow a lag in its longitudinal flapping mode.