A general and systematic discussion on the use of the operational method of Laplace transform for numerically solving complex time-dependent linear problems is presented. Application of Laplace transform with respect to time on the governing differential equations as well as the boundary and initial conditions of the problem reduces it to one independent of time, which is solved in the transform domain by any convenient numerical technique, such as the finite element method, the finite difference method or the boundary integral equation method. Finally, the time domain solution is obtained by a numerical inversion of the transformed solution. Eight existing methods of numerical inversion of the Laplace transform are systematically discussed with respect to their use, range of applicability, accuracy and computational efficiency on the basis of some framework vibration problems. Other applications of the Laplace transform method in conjunction with the finite element method or the boundary integral equation method in the areas of earthquake dynamic response of frameworks, thermally induced beam vibrations, forced vibrations of cylindrical shells, dynamic stress concentrations around holes in plates and viscoelastic stress analysis are also briefly described to demonstrate the generality and advantages of the method against other known methods.

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N a t i o n a l Aeronaut i cs Space Admi n i s t r a t i onABSTRACT An a n a l y t i c a l i n v e s t i g a t i o n of a e r o e l a s t i c response o f m e t a l l i c and comp o s i t e p r o p f a n models i n yawed flow has been performed. The a n a l y t i c a l model i s based on t h e normal modes o f a r o t a t i n g b l a d e and t h e three-dimensional unsteady l i f t i n g s u r f a c e aerodynamic t h e o r y i n c l u d i n g b l a d e m i s t u n i n g . The c a l c u l a t e d b l a d e s t r e s s e s or s t r a i n s are compared w i t h p u b l i s h e d wind t u n n e l d a t a for two m e t a l l i c and t h r e e composite propfan wind t u n n e l models. The comp a r i s o n shows a good agreement between t h e o r y and experiment. A d d i t i o n a l param e t r i c r e s u l t s i n d i c a t e t h a t b l a d e response i s v e r y s e n s i t i v e tc! t h e blade s t i f f n e s s and a l s o t o b l a d e frequency and mode shape m i s t u n i n g . From these f i n d i n g s , i t i s concluded t h a t b o t h frequency and mode shape m i s t u n i n g should be i n c l u d e d i n a e r o e l a s t i c response a n a l y s i s . Furthermore, b o t h c a l c u l a t e d and measured s t r a i n s show t h a t combined b l a d e frequency and mode shape mistuni n g has b e n e f i c i a l e f f e c t s on response due t o yawed flow.