Toshihiko Asami

Desktop vibration isolators are often used as a platform for precision measuring instruments. This article discusses the accuracy of performance prediction methods for vibration isolators elastically supported by four air springs. Each air spring possesses a reservoir tank to ensure the natural frequency of the support system remains low and to provide adequate damping force. For practical use, air springs and reservoir tanks should be installed in separate locations and connected by a small-diameter pipe because desktop isolators must be thin. Our previous studies have shown that there is a secondary resonance point in systems supported by air springs with long pipes and reservoir tanks and that it is not simple to theoretically calculate the amplitude and frequency at this point because this type of air spring support system has nonlinear characteristics. In this study, the change in the vibration isolation performance of a desktop vibration isolator with the length of the pipe connecting the main air tank and the reservoir tank of an air spring-supported system was examined experimentally and approximated using theoretical calculations.

The purpose of the present study is to clarify the fluid flow of an oil damper through numerical analysis in order to estimate the exact damping coefficient of an oil damper. The finite difference method was used to solve the governing equation of the fluid flow generated by a moving piston. Time steps based on the fractional step method and the arbitrary Lagrangian-Eulerian (ALE) method were adopted for the moving boundary. In the moving boundary problem, a masking method with a single block grid system was used to stabilize the computation . In other words, algebraic grid generation using a stretching function was used for the moving piston in the cylinder of the oil damper. The time-dependent coordinate system in the physical domain, which coincides with the contour of the moving boundary, is transformed into a stationary rectangular coordinate system in the computational domain. In order to valiade the caluculated results, they were compared with experimental results and the approximate algebraic solution. As a result, it became possible to estimate exactly the degree of contribution of the conversation term the Navier-Stokes equation on the damping coeffcient of the oil damper.

<p>The vibration isolator discussed in this study consists of two rectangular plates with four air springs inserted between them. Each air spring has a main tank and reservoir tank connected by a small diameter pipe. Because this structure has week rigidity in the horizontal direction, guide shafts are provided to constrain the movement of the table only in the vertical direction. The guide shafts are supported by gas bearings to minimize sliding friction. Both the equivalent spring constant and the equivalent damping coefficient of the vibration isolator are generated by two of the cause. One is caused by the air flow, which can be calculated theoretically. The other is generated by the compression, expansion and sliding friction of the rubber membrane, which is impossible to calculate. The latter was measured experimentally. Thus, the frequency response of the vibration isolator system was calculated from a simplified expression. The calculation results are in good agreement with the eperimental values, and the correctness of our calculation method has been demonstrated.</p>

<p>Hydroinertia gas journal bearings have been used for ultra high-speed rotational machines such as those used in solid state nuclear magnetic resonance (NMR) devices. This type of bearing has inherent orifice restrictors and a large radial clearance compared with conventional externally pressurized gas journal bearings. The large radial clearance makes these bearings suitable for use with a rapidly rotation sample tube (shaft) since instabilities are suppressed by the reduction in hydrodynamic effects. These bearings achieve stable operation for ultra high-speed rotation of spiner shaft at several million rpm. However, solid state NMR devices require a further high speed rotation because of improvement of analysis precision. Therefore, a hydroinertia gas bearing with supply holes inclined in the direction of rotation has been presented. In this bearing, viscous frictional loss is thought to be reduced since this mechanism provides gas flow in the rotational direction. This study reseach practical utillty and the characteristics of this bearings by using a a computational fluid dynamics analysis. This report presents the change of dynamic characteristics of bearings for rotation.</p>

This paper describes visualization and measurements of pressure distribution by using Pressure-Sensitive Paint (PSP) for externally pressurized thrust gas bearing. The test bearing diameter is 30 mm. Numerical calculation of pressure distribution was carried out using divergence formulation method. Obtained results by experiments were compared with calculated results, it was quantitatively evaluated.

Externally pressurized gas journal bearings with an asymmetric gas supply mechanism have a large load capacity compared with conventional symmetric gas supply bearings. We propose that the bearing is applicable for use in an X-ray CT gantry. The adaptation of this gas bearing to the device can conceivably increase the rotational speed and decrease the operating noise. This is effective for reduction of radiation exposure and stress on a patient. To verify the effectiveness of the bearing, rotational tests using a 60 mm diameter test bearing was conducted. The rotor vibration amplitude decreased under controlled supply pressure conditions compared with conventional supply pressure conditions.

In this paper, we propose a method for analyzing the vibration properties of contact wires of trains by the Transfer Matrix Method (TMM), regarding them as a periodic structure. When the train speed rises, self-excitation vibration of the wires becomes large. The self-excitation vibration causes pantagraph bounce, and the performance of the power transmission becomes low. For such problems, many researchers have proposed the analysis of the wires. However, these methods are not suitable for the vibration of wires because it has become complicated by the wave propagation phenomenon. Proposed TMM in this study, contact wires is assumed to be a periodic structure like a truss bridge or a hull construction. The structure has damping characteristic by geometric or material discontinuity. We think that this method is an easy technique for vibration analysis since vibration properties of the wire can be simplified greatly by studying the unit cell which is the smallest unit of repetition of the structure. Using this method, the vibration characteristics of the contact wire become clear by investigating the propagation constant of the wire; the frequency band where constant becomes real number is the vibration attenuation domain (Stop-band), and the frequency band where the propagation constant becomes imaginary number is the vibration amplifying domain (Pass-band). We examined the desirable placement of the stop band and the pass band for the vibration suppression of the wire, with changing the hanging wire ropes.

This study proposes a health monitoring for a structure using the accurately controlled elastic waves. As a basic test in this paper, the vibration mode of the frame structure was compared with both impulse response and the accurately controlled elastic waves. As a result, each results were qualitatively agreement and it was proved that presumption of the vibration mode of the structure using this method is effective. In addition, the phase delay program was made for detecteing the phase delay caused by the defect of a structure. The usefulness of this program was verified using the artificial signal.

Today, the air springs are widely used as the vibration isolators for the cars, railway vehicle, and anti-vibration tables, etc. Many air springs have two air tanks called the main tank and reservoir tank. The air tanks are usually connected by an orifice or a small pipe, of those we study a small pipe type air spring. In the past studies, the pipe is treated as a straight pipe. However, due to the space constraints, it is difficult to design the pipe as a straight pipe. Furthermore, there may be an orifice in the connector portion which connects the tank and pipe. Therefore, in the present study we investigated by experiments and numerical analysis the following two effects : (1) bending of small pipe and (2) orifice in the connector. As a result, we have confirmed that a significant effect appears in the dynamic characteristics of the air springs when the pipe is bent or the orifice is provided in the connector. In addition, we made it clear that the cause is due to the change of the flow rate of air through the pipe.