Tomomi Nakajima

Localized Aortic Root Dissection with a Superior Mesenteric Artery Aneurysm

In this study, the case of a 46-year-old female patient with localized aortic root dissection and a superior mesenteric artery (SMA) aneurysm is described. Computed tomographic angiography could not clearly delineate an intimal flap in the aortic root, but it detected SMA aneurysm, which implied the presence of a vulnerability of the aortic wall. Finally, transesophageal echocardiography (TEE) evidently showed the intimal flap localized in the aortic root. The present case suggests that TEE is of paramount importance for detecting localized aortic root dissection. In addition, a coexisting vascular lesion may be a clue to diagnose another vascular lesion.

Damping Characteristics of Non-Synchronous Turbine Blade Vibration

In order to analyze turbine blades vibration caused by flutter, it is necessary to understand both aerodynamic damping and structural damping of high vibration stress. Flutter Vibration mode occurring in rated speed is non-synchronous mode. For measuring non-synchronous mode damping ratio of turbine blades, AC-type electromagnet which can generate high frequency excitation force was developed. Damping ratio characteristics of non-synchronous mode of nodal diameter 12,4 was measured in rotational test. For comparison, synchronous mode of nodal diameter 4 was measured, too. It was concluded as follows. (1) It is possible to excite non-synchronous mode by high frequency excitation electromagnet and calculate damping ratio from measurement resonance curve. (2) Damping ratio of non-synchronous mode ND12,4 was increased by increasing the excitation force. Synchronous mode ND4 is also a similar trend. (3) Nodal diameter 4 damping ratio of non-synchronous mode (Resonant speed=100%) was lower than synchronous mode (Resonant speed=75%).Copyright

Prediction of Unsteady Force for Axial Turbine Buckets (Effects of Nozzle-Bucket Axial Gap Length and Blade Count Ratio)

The purpose of this study is to investigate the unsteady force acting on steam turbine buckets which is induced by a potential field and a wake. The authors have already proposed a new method that can separate the unsteady force into a potential field interaction and a wake interaction from the unsteady viscous flow computation. It is understood from the previous work that simple expressions may be written for the relationships between the nozzle-bucket axial gap length and the unsteady force, which means the amplitude and the phase of the unsteady force with the nozzle passing frequency component.This paper adopts the blade count ratio as the factor to study the unsteady force of the bucket sections with different bucket heights in the same stage. Four points are seen from the results; points (a)–(c) do not depend on the blade count ratio. (a) The amplitudes of the unsteady force of each interaction can be approximated by an exponential or a power function of axial gap length. (b) The amplitudes of each interaction tend to become large when bucket turning angle is large. (c) The phase of the unsteady force of each interaction with the nozzle passing frequency component has a linear relationship with axial gap length. (d) The amplitudes of each interaction become the maximum value when the blade count ratio is 1.5.Copyright