Hiroshi Higo

A New One Dimensional Modeling Method for Complex Oil Passage Coupled With CFD Results

Oil pipes are indispensable to a hydraulic circuit. The linear model of pipe based on the Hagen-Poiseuille law is commonly used and very convenient in the analyses. However, real oil passages, such as in manifolds and oil passages in an automatic transmission in a car, have complex configurations. As they are quite three-dimensional and have various kinds of pressure drops on the inside, it is sometimes unsuitable to represent the real oil passages using the linear model. As the result of applying it to the real oil passage, the equivalent pipe length would sometimes be very long unrealistically. Moreover, the inertia effect of oil column in the passage is sometimes non-negligible.This study represents a way to model real oil passages into a dynamically-equivalent pipe model using its CAD data and CFD results. The pressure drop is represented by the non-linear model of pipe and the coefficients are calculated from ΔP-Q curve of the passage which is obtained by CFD steady flow analysis. The inertia effect of oil column is calculated by CFD unsteady flow analysis and its coefficient is obtained from the solution of the differential equation which is expressed by a correlation coefficient. As a result, a new model of pipe is successfully obtained with the same effects of resistance and inertia as the real oil passage. The simulation using the new model of pipe agrees well with the experimental results. This modeling way is applicable to all oil passages with any 3-D configuration.Copyright

3 Dimensional Vortex Structure around Free Falling Rectangular Pillar

3 dimensional vortex structure around free falling rectangular pillar was studied in comparison with circular cylinder. Both objects are close to square shape in front view but flow fields measured by PIV method were different. Vortex pair starting from the upper corner was stretched to upper direction in case of rectangular pillar, while it was observed at upper surface in case of circular cylinder. On the upper surface of rectangular pillar, water flows out in front view, while in side view water flows in.

Bondgraph analysis on pressure fluctuation in hydraulic pipes

The bond graph method is a unified approach to represent a system combined with mechanical, hydraulic and electrical sub-systems. Recently, this method has been used to design hydraulic systems as well as to analyze their dynamic characteristics. Pipes are indispensable for hydraulic systems as an element transporting hydraulic power between components. Pipes often play an important role on pressure fluctuations. Considering a total hydraulic system, it is important and convenient to use a unified approach to analyze the dynamic characteristics in the other components as well as pipes. A basic bond graph model of a pipe has already been established as a lumped parameter system. With the reliability of the lump model of a pipe, a bond graph method would be more useful and more convenient for designing hydraulic circuits. The reliability of a bond graph lump model of a pipe on pressure fluctuations was investigated by using a straight and connected pipe through comparing the results by bond graphs with the results by a characteristic method and experiments. This study proved that a bond graph lump model showed the same precision as other results with a suitable number of pipe element lump models.

Measurements of velocity distribution along depth using low coherence interferometry

A new optical measurement method of a flow velocity distribution along the depth using low coherence interference techniques is proposed and demonstrated. In the proposed method, fluctuations of the interference signal formed with the reference and backscattering lights are detected by the optical heterodyne scheme. It is shown experimentally that the width of the spectrum of the interference signal is proportional to the flow velocity. The dynamic range is determined by the time constants of the fast Fourier transform (FFT) processor and lock-in amplifier used in the experiment.