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A bluff body like a marine structure can be vibrated variously by a separation flow around it. In this study, we focused on in-line oscillation of a circular cylinder under free vibration tests in two degrees of freedom. We studied typical characteristics of in-line oscillation of circular cylinders both in a smooth flow and in a turbulent flow in water tunnel tests. The circular cylinders with finite span lengths were supported elastically in two degrees of freedom. As a result, the response amplitude in the 2nd excitation region is dampened more sensitively with increasing reduced mass-damping parameter Cn than in the 1st excitation region compared with the results of circular cylinder that can oscillate only in one degree of freedom. Also the amplitude in 2nd excitation region is dampened in a turbulent flow, and the lissajous figure of a circular cylinder changed from a figure of 8 to a complex ellipse.

Active magnetic bearing (AMB) equipped rotating machinery requires control for low unbalance vibration at low driving power. In order to estimate both the unbalance resonance vibration and the bearing reaction force, an unbalance response analysis program considering the bearing reaction force is developed. Using this program, the optimum control technique is evaluated for flexible rotors supported by AMBs, regarding the following four means: PID, Ncross, Ncut+Ncross and Feed Forward (FF) Excitation. FF Excitation is recommended with respect to low resonance amplitude and low control current in order to pass the first bending critical speed.

In this paper, nonlinear imbalance response and forced damped natural frequency are calculated for horizontal Jeffcott rotors supported by oil film damper bearings having no centering springs. The former calculation reveals that there exists four types of synchronous imbalance responses. In one of the four types, the vibration amplitide can become infinitely large, and this dangerous type of vibration can appear easily with increasing imbalance. The latter calculation reveals that the stability margin, which is determined from the calculated complex eigenvalues, greatly depends on the type of synchronous response that happens to appear.

A calculation method utilizing the computational fluid dynamics technique for the linear rotordynamic characteristics of labyrinth seals is presented. First, the static flow, in which the rotor is concentric with the seal, is calculated taking into account the viscosity change with turbulence and the compressibility. Next, the perturbation flow is computed based on this static flow. The perturbation equations may be treated as a two-dimensional problem by separating the angle variable. In this calculation, coefficients of spring, damping, and acceleration are separately calculated. The difference equations of control volumes adjacent to the rotor are first obtained in a three-dimensional form, then transformed into the two-dimensional one by applying the fast fourier transform technique to the coefficients of these equations. The present calculation method is verified by calculating for a straight-through labyrinth seal whose empirically determined flow state has been published. It is shown that rotor instability can be initiated through the cross-coupling term of spring, if the inlet swirl is intense enough, that its diagonal term differs greatly from the conventionally accepted value and that the mere determination of cavity pressure is insufficient to infer the pressure distribution that exists across a fin.

This paper proposes a new method for rotor dynamics calculations, called the transfer coefficient method, which is more convenient than the conventional transfer matrix method. By treating only the displacement as the independent variable, where both the displacement and the force are considered as independent variables in the transfer matrix method, this method promises a substantial saving of computational time without loss of the accuracy of calculation. There are two types of transfer coefficient methods. In the first, the coefficients are treated as independent of the vibration frequencies, while in the other, the coefficients are considered dependent on the frequencies. Formulation of a fundamental rotor system and applications for either type are discussed in detail with a bearing box, a branched system, and a multi spool system as examples.