In this paper, an oil hydrauhc Line in which two pipes of different sizes are connected in series and terminute in a charnger. i. e. a composite fine system is consderde and the freqency characteristics are inventigated analytically and experimentally. The theoretical analysis is based on unsteady laninar flow of a viscous compresibbe fluid and the pressure low due to a sudden change of cross-section in a composite line is neglected. Because the propugation constant consisting of bessel functions is very comphcated, approximation to it is used in numerical calculation.
It is generally difficult to obtain exactly the frequency equation of this line system .This puper derives an approcinmate expression to the frequency equation considering the viscosity, applying the solutions of the non-viscus charicteriscic equation of this line system. Bu use of the solutions of it, the practical and fairly good approcimations to the sesonance frequency and the pressure amplitude ratio at the resonance point are given.It is shown that the approximation as the theoretical frequncy transfer function expressed by using infinte products agrees well with the theortical resules over relatively wide frequency range. The effects of the position where the cross-sectional area of pipe changes subbenly, the inner radius ratio of pipe and the colume of terminala chamber on the frequency aharacteristics of this line system are also described.

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Recently, electro-hydraulic servosystems have come to be applied widely to systems like material testing and vibration testing equipments.
The bandwidth of these systems is required to be broader than 100Hz. Therefore the spool valve servomotor, which plays an important role in the above-mentioned systems, is also required to have much better performance than conventional one in high frequency region.
However we have often experienced self-excited oscillation of the spool valve when we increase the supply pressure as a method of improving the characteristics in high frequency region of the existing servomotor.
To the authors' knowledge there are few published papers concerning self-excited oscillation of the servomotor. Therefore the purpose of this paper is to clarify theoretically and experimentally the cause of the above-mentioned self-excited oscillation by applying the authors' paper on the dynamic characteristics of the servomotor in high frequency region.
From the results of the theoretical and experimental researches, it becomes clear that the stable region of the servomotor can be decided by various parameters of the servomotor and they can be classified into three groups according to contribution to stability. Moreover it is clarified that the self-excited oscillation which once occurs does not grow except for special cases.

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The transition of the velocity distribution, due to a stepwise change of the flowrate, in the inlet region of a long circular tube is investigated analytically and experimentally.
It is shown from the results that the approximate time interval required for the transition of the velocity profile from the initial steady state to the final steady state on a certain cross-section of the tube is determined by ratio, distance between the section and the inlet to mean velocity.

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