Seiichi Washio

Study of unsteady orifice flow characteristics in hydraulic oil lines

A technique to measure fluctuating differential pressures with high fidelity has been developed first. When applied to detecting differential pressures generated by an accelerated or decelerated liquid column, the technique turned out to be effective in finding unsteady flow rates. An experimental study has been carried out on periodically changing hydraulic oil flows through an orifice. The results support the validity of the traditional standpoint that characteristics of an unsteady orifice flow can be approximately represented by those of a steady-state one. When inspected in detail, however, a net pressure loss across an orifice in a periodical flow is delayed against a change of the flow rate. The resulting relation between the pressure loss and the flow rate describes a loop with a counter-clockwise hysteresis and a nonlinear twist along the steady-state one. Pressure recovery in a pulsating orifice flow varies with the flow rate almost along the steady-state relation, which is confirmed when the change is not fast.

Study on cavitation inception in hydraulic oil flow through a long two-dimensional constriction

Abstract It is known that the traditional ‘nucleus’ theory for cavitation is incompatible with certain facts physically and experimentally recognizable in oil hydraulic flows. In order to re-examine this issue, cavitation of hydraulic oil flow through a long two-dimensional acrylic constriction was observed by various techniques: stroboscopic photography with a microscope, laser beam transmission, pressure and noise measurements, and luminescence and electrical charge detection. It was revealed that, at the incipient stage of cavitation, one stationary microscopic cavity always emerges suddenly on the inlet edge. Light emission was also observed in the cavitation together with electrostatic charge. All the findings taken together, which cannot be consistently explained by nucleus theory, lead to the following hypothesis: at the separation point a tensile force rips a liquid particle from the wall, leaving behind a vacuum space, which forms the incipient stationary cavity on the edge.

Preliminary evaluation of stroboscopy system using multiple light sources for observation of pathological vocal fold oscillatory pattern.

Objectives: Laryngostroboscopy is used to check the oscillatory patterns of the vocal folds. However, the use of one single flash timing cannot give a clear view of abnormal vocal fold oscillations that have multiple fundamental frequencies. Visualization of such complex vocal fold movements will be helpful in the diagnosis of diplophonia, a pathological condition in which the vocal folds produce multiple tones at the same time. Methods: We developed a new stroboscopy-based technique using multiple light-emitting diodes (LEDs) and image analysis. Specific flash timings for each LED, suitable for accurate visualization, were determined on a computer according to an algorithm based on frequency analysis. The image analysis extracted the necessary parts of the captured images to yield a clear slow-motion view of the oscillations. The series of visualization procedures took advantage of the narrow-spectrum light property of LEDs, thereby yielding a degradation-free picture. Results: Feasibility tests using a mechanical vocal fold model demonstrated that this computer-assisted system allows observation of the pathological oscillatory patterns as one single video. They would not be clearly visualized by conventional stroboscopy. Conclusions: Because of its relatively simple use and inexpensive construction, the proposed technique can become one potential option for clinical assessment of pathological vocal fold oscillations.

Study on the cavitation mechanism in hydraulic oil flow using a needle projection

Abstract Cavitation occurring at a sharp projection in a hydraulic oil flow was observed in as much detail as possible, using, variously, a microscope, a high-speed video camera, laser beams, an electric charge detector and a photomultiplier. At the tip of the needle employed as a projection, a tiny cavity as small as several tens of micrometres in length suddenly emerged and would not go away. As cavitation became more vigorous, flashes occurred intermittently around the needle and positive electrical charges were generated which synchronized with the flashing. The electrode inserted downstream from the needle detected negative charge from the oil, which was also synchronous with the flashing. Observing the needle tip with the microscope made it possible to determine exactly the moment of cavitation inception, which turned out to depend on the oil temperature as well as the downstream pressure. All these findings tend to reinforce the ‘rip-off’ hypothesis previously proposed by the present authors for the cavitation mechanism.

Singular properties of flow separation as a real cause of cavitation inception

At the very beginning stage of cavitation an infinitesimal cavity suddenly emerges and rapidly grows on the wall close to the point of flow separation. The present paper intends to make clear the mechanism of this peculiar phenomenon previously discovered by the present authors in oil flows, by experimentally examining the characteristics of a separating flow. First, pressure and temperature distributions along a cylindrical smooth wall in an oil flow were measured across the point of separation, which has proved that both tensile stress and heat are really generated near the separation point. Second, a laminar air flow passing over a sharp edge was inspected by particle image velocimetry (PIV). The inspection of the separating flow based on the PIV data has revealed that fluid particle near the separation point is not only drastically stretched but also intensely sheared along the separation streamline. With all the results integrated, it has been concluded that the singular structure of a separating flow is the real cause of both tensile stress and heat generation. When thus generated tension exceeds a threshold, it possibly breaks the adhesion between the liquid and the wall, leaving a microscopic rift on the interface that would grow to a visible cavity.

Computer-aided technique for automatic determination of the relationship between transglottal pressure change and voice fundamental frequency.

Objectives: The effect of artificially altered transglottal pressures on the voice fundamental frequency (F0) is known to be associated with vocal fold stiffness. Its measurement, though useful as a potential diagnostic tool for noncontact assessment of vocal fold stiffness, often requires manual and painstaking determination of an unstable F0 of voice. Here, we provide a computer-aided technique that enables one to carry out the determination easily and accurately. Methods: Human subjects vocalized in accordance with a series of reference sounds from a speaker controlled by a computer. Transglottal pressures were altered by means of a valve embedded in a mouthpiece. Time-varying vocal F0 was extracted, without manual procedures, from a specific range of the voice spectrum determined on the basis of the controlled reference sounds. Results: The validity of the proposed technique was assessed for 11 healthy subjects. Fluctuating voice F0 was tracked automatically during experiments, providing the relationship between transglottal pressure change and F0 on the computer. Conclusions: The proposed technique overcomes the difficulty in automatic determination of the voice F0, which tends to be transient both in normal voice and in some types of pathological voice.

Derivation of diffusion coefficient of N 2 gas in rubber based on measurement using laser heterodyne interferometry

In this paper it is reported that the diffusion coefficient of N2 gas in a rubber sheet is derived based on combination of measurement using U-tube and laser heterodyne interferometry and one dimension diffusion theory successfully. Experiments were carried out under different pressure and temperature conditions to investigate the dependency of diffusion of gas in rubber. A conclusion has been drawn that diffusion of N2 gas in rubber may not be as easy to occur as N2 in VG10 mineral oil.

Measurement of the Thermal Diffusivity of Metallic Foils and Films by the Photoacoustic Method1

The thermal diffusivities of four kinds of metallic foils from 20 to 200μμm in thickness were measured by a photoacoustic method on the basis of the Rosencwaig and Gersho theory. The measured data for continuous foils of uniform microscopic structure almost agreed with the literature values. Measurements were also carried out on two kinds of metallic thin films with of 10μμm thickness produced by sputtering. The difference in thermal diffusivity between the foils and the sputtered films depended on the uniformity of the microscopic structure.

Axial transition of oscillatory oil flow in front of reciprocating piston (Numerical calculation and LDV measurement)

In front of a reciprocating piston in a pipe containing fluid, the velocity profile is assumed to vary continuously in the axial direction from a uniform one to that of an ordinary oscillatory viscous pipe flow. The present paper deals with theoretical and experimental discussions of this subject. Numerical calculations have indicated that the transition of velocity profiles is completed within a pipe radius away from the piston. In order to experimentally verify this finding, an LDV with a counter-type signal processor is used to measure velocities in oscillatory oil flows close to a reciprocating piston. Although a counter is usually not used for measuring unsteady flows, it has proved applicable to periodic flows when the data within the same range of phase angle are separately collected and stochastically processed in the same way as in an ordinary steady measurement. The measurements thus carried out have given satisfactory results which agree with the theoretical predictions.

Generation and Observation of Tensile Waves in Oil Columns

Tensile stresses in liquids are not necessarily a familiar idea in fluid engineering, so much less accepted is the reality of tensile waves travelling through a liquid continuum. The present paper aims at giving evident proof for the premise. In a pipe with its end closed, branching from the main line where column separation is started, alternating tensile and compressive waves have been beautifully created and measured. It has turned out that the ordinary viscous wave equation can properly predict the time profiles of the masured pressures, which reveals that a tensile wave propagates in oil at the same speed as a compressive one. The observations by use of a transparent acrylic tube have also revealed the rupturing of an oil column under an excessive transient tensile stress; in the aftermath there has emerged a bubble which is usually mistaken for the cause of cavitation, but is actually brought about by diffusive separation of gas from the oil into the rupture.