Asymmetric Pressure Distribution Research Articles

Valveless micropump driven by acoustic streaming

This paper describes two valveless micropumps built on a 260 µm thick PZT with 20 µm thick parylene acoustic Fresnel lenses with air cavities. The micropumps produce in-plane body force through acoustic streaming effect of high-intensity acoustic beam that is generated by acoustic wave interference. The fabricated micropumps were shown to move microspheres, which have a diameter of 70–90 µm and a density of 0.99 g cm−3, on the water surface to form U-shape streams of microspheres with a drift velocity of 7.3 cm s−1 when the micropumps were located 4 mm below the water surface and driven by 160 Vpeak-to-peak pulsed sinusoidal waves. The driven microspheres formed U-shape streaming even without any fluidic channel according to the serial connection of the pie-shaped lenses and top electrodes. A micropump with a straight-lined fluidic channel was also fabricated and tested to show a 9.2 cm s−1 microspheres' drift velocity and a 9.5 mL min−1 volume pumping rate when combined with the acrylic acoustic wave reflector. Both the Fresnel lens and top electrode were patterned in a pie-shape with its apex angle of 90° to form asymmetric acoustic pressure distribution at the focal plane of the acoustic Fresnel lenses in order to push water in one direction.

Time Factor in Consolidation: Critical Review

The magnitude of consolidation settlement is often calculated using Terzaghi's expression for average degree of consolidation (U) with respect to time. Developed during a time of limited computing capabilities, Terzaghi's series solution to the one-dimensional consolidation equation was generalized using dimensionless time factor (T), where a single U-T curve is used to describe the consolidation behaviour of both singly and doubly drained strata. As a result, any comparisons between one- and two-way drainage are indirect and confined to discrete values of time. By introducing a modified time factor T* in terms of layer thickness (D) instead of the maximum drainage pat length (Hdr), it is now possible to observe the effect of drainage conditions over a continuous range of time for a variety of asymmetric initial excess pore pressure distributions. although two separate U-T plots are required (for singly and doubly drained cases), the time factor at specific times remains the same for both cases, enabling a direct visual comparison. The importance of a revised time factor is evident when observing the endpoint of consolidation, which occurs as U approaches 100%. This occurs at T*≅0.5 for two-way drainage and at T*≅2 for one-way drainage, an observation not possible using the traditional expression for time factor.

Investigation on the mechanism of aeroelastic hazard during ground test of rocket nozzle

Side loads and aeroelastic stability of rocket nozzle were studied by solving Navier-Stokes equation coupled with structural equation of motion. The computation was implemented at different total pressure inlet conditions, and flow phenomena of free shock separation (FSS) and restricted shock separation (RSS) were captured. At certain total pressure inlet conditions, it was found that both kinds of separations existed in nozzle flow filed, while RSS exhibited combined space asymmetry and time unsteady characteristics. The corresponding asymmetric circumferential pressure distribution, strong pressure fluctuation in separation region and large range of displacement of shock wave all led to severe side loads. Besides, for flexible nozzles, the low pressure gradient in separation region might reduce structure stability at nozzle exit, resulting in large local deformation. It was also found that aeroelasticity exhibited buffeting characteristic due to the asymmetric separation, resulting in reduction of aeroelastic stability, even structure destruction. Moreover, aeroelasticity might amplify side loads and aggravate its growth rate. However, with increment of inlet pressure, nozzle aeroelastic stability was also increased when a full flow was nearly reached.

Consolidation Behavior of Soils Subjected to Asymmetric Initial Excess Pore Pressure Distributions with One-Way Drainage

A consolidating clay layer can be singly or doubly drained. The degree of consolidation is a function of the initial excess pore pressure distribution and the drainage conditions. Traditional geotechnical engineering practice assumes a uniform initial excess pore pressure distribution, for which the singly drained and doubly drained solutions to Terzaghi's one-dimensional consolidation theory are available in most textbooks. In this paper, several symmetric and asymmetric initial excess pore pressure distributions are studied using a series solution method. Excess pore pressure isochrones and average degree of consolidation plots are generated for all cases, assuming an impervious boundary at the base of the clay stratum. These plots enable users to determine the average degree of consolidation and pore pressure at a specific depth for a variety of loading scenarios. Pore pressure redistribution is also clearly more prevalent in singly drained clays, where pore-water pressures at certain depths increase at certain times, a phenomenon not generally expected during consolidation.

Shock waves interaction with a single inclusion buried in soil

The paper presents a study aimed at understanding the blast pressure action on an inclusion embedded in soil due to a nearby underground explosion. The soil is modeled as an elastic plastic material with irreversible bulk and deviatoric strains for which the modified Godunov method has been applied. Two common geometrical inclusions are investigated (circular and rectangular) and the pressure distribution along their circumferences has been studied for various standoff distances from the initial explosive’s cavity center. When the standoff distance is relatively small, the envelope of the pressure distribution shows that the maximum dynamic pressure is developed at some distance away from the axis of symmetry, otherwise asymmetrical pressure distribution is observed.

Wall Pressure Unsteadiness and Side Loads in Overexpanded Rocket Nozzles

Surveys of both the static and dynamic wall pressure signatures on the interior surface of a sub-scale, cold-flow and thrust optimized parabolic nozzle are conducted during fixed nozzle pressure ratios corresponding to FSS and RSS states. The motive is to develop a better understanding for the sources of off-axis loads during the transient start-up of overexpanded rocket nozzles. During FSS state, pressure spectra reveal frequency content resembling SWTBLI. Presumably, when the internal flow is in RSS state, separation bubbles are trapped by shocks and expansion waves; interactions between the separated flow regions and the waves produce asymmetric pressure distributions. An analysis of the azimuthal modes reveals how the breathing mode encompasses most of the resolved energy and that the side load inducing mode is coherent with the response moment measured by strain gauges mounted upstream of the nozzle on a flexible tube. Finally, the unsteady pressure is locally more energetic during RSS, albeit direct measurements of the response moments indicate higher side load activity when in FSS state. It is postulated that these discrepancies are attributed to cancellation effects between annular separation bubbles.

A Critical Reappraisal of the Average Degree of Consolidation

Since its development in 1925, Terzaghi’s expression for the average degree of consolidation has been extensively used in teaching, research and consulting to determine the consolidation settlement that has taken place at a specific time in a geotechnical problem. Recent research by the authors has revealed that the term degree of consolidation is not very meaningful when the initial pore pressure distribution is highly skewed. In view of these findings, a review of all aspects of Terzaghi’s consolidation theory is required, particularly when considering asymmetric initial pore pressure distributions. An exact method for estimating the consolidation settlement of a clay stratum using the mass flux per unit area out of the drainage boundaries is proposed. Graphical representations of both exact and traditional methods reveal identical average degree of consolidation curves. In light of this, Terzaghi’s expression for the average degree of consolidation was re-examined. Upon application of the original governing one-dimensional consolidation equation, it was found that the traditional and exact methods for calculating the average degree of consolidation are identical. Thus, the widespread proclivity for geotechnical engineers to use Terzaghi’s average degree of consolidation equation to estimate the consolidation settlement of a clay stratum has been validated.

볼트이음된 대골형 파형강판의 구조거동에 대한 실험적 평가

Deep corrugated steel plate structure has more compressive force and flexibility in bending behavior than short span structure. Asymmetric earth pressure distribution has occurred during construction. Ultimate strength and moment in domestic area, having superior ability at bending strain has been examined in this study. Based on the result of the study preceded, performance of Deep corrugated steel plate specimen has been evaluated by comparing increase of strength according to the increase of reinforcement content in bolt connections and failure mode of specimen.

Consolidation Behavior of Soils Subjected to Asymmetric Initial Excess Pore Pressure Distributions

Although the consolidation settlements beneath foundations and embankments are rarely one dimensional, Terzaghi's one-dimensional consolidation theory is often applied to these situations to approximate consolidation behavior. This paper investigates the consolidation behavior of a soil stratum subjected to various initial excess pore pressure distributions which occur under one-dimensional loading. The results show that analysis in terms of average degree of consolidation provides an incomplete representation of the consolidation behavior. While the average degree of consolidation curves for all uniform and linearly varying initial distributions are identical, the degree of consolidation isochrones for each distribution are unique. Furthermore, the application of a bottom-skewed initial excess pore pressure distribution results in a redistribution of pore pressures toward the skewed region so that an increase in excess pore pressure occurs at some depth after consolidation has already commenced. As a result, conventional consolidation relationships are considered inappropriate for these cases, and an alternative method of consolidation analysis in terms of normalized pore pressures is proposed.

Multi-objective exploration of the launch condition for a fluctuating punted kick in rugby on the basis of PSP measurement

We succeeded in obtaining PSP (Pressure-Sensitive Paint) measurements for a rugby ball. It was found that the seam of the ball is the trigger for initiating low pressure. Therefore, a slower spinning ball fluctuates during flight because of the asymmetrical pressure distribution on the sides of the ball. Based on the results from PSP measurements, multi-objective optimization of the fluctuating punted kick was carried out, and then the trade-offs between the objective functions and the control variables could be visualized using Self-Organizing Maps. It was found that the higher the spin rate at launch the greater the number of fluctuations; however, the hang time becomes shorter.

Simulation of the trajectory of a punted rugby ball taking into account the asymmetrical pressure distribution caused by the seams

This paper describes the effect of the seams of a rugby ball on the side force and the flight trajectory of the punted kick. Measurement of the aerodynamic force on a non-spinning rugby ball reveals that the side force coefficient depends on the position of the seam as well as the angle of attack. It was found from pressure-sensitive paint measurements that the seam of the ball is the trigger for initiating low pressure when the seam is situated around 60° from the stagnation point. The flight trajectory of the fluctuating ball can be obtained by numerically integrating the six degree-of-freedom non-linear equations of motion. It was shown that a slower spinning ball fluctuates from side to side during flight because of the asymmetrical pressure distribution on the sides of the ball.

Electrical Actuation of Textile Polymer Materials

Polymers used in textiles were found to be effective as actuator materials with large deformation. Particularly, the polymers with low dielectric constants used to be considered inactive to electric field were turned out to be efficient actuator materials. They were classified into three types; (1) polymer gels swollen with solvents, (2) plasticized polymers, (3) bulk polymers. From the viewpoint of easy-to-operate, polymer gel deformation with swelling and deswelling was excluded here. Swollen dielectric gels could be electrically deformed by solvent drag that induced asymmetric pressure distribution in the gels. Bending and crawling motions were observed in these materials. In the case of plasticized polymers, especially in the case of poly(vinyl chloride) with plasticizers, amoeba- like reversible creep deformation was found, and the strain with over several hundreds of percent was detected. The material was stable and could have been operated for over two years. Bulk polymer film like poly(ethylene terephthalate) was found to oscillate under an application of dc electric field. Of course, the Maxwell force induced elastic contractile deformation can be expected in all cases. The variation of the electrically induced deformation in dielectric polymer materials were demonstrated to be vast and expected application fields are also spread widely, particularly as artificial muscles.

1401 直交格子法を用いた流体解析を活用したBlu-ray Disc対応光ディスクドライブの冷却構造の開発(2)(OS14 ものつくりにおける流体解析技術,オーガナイズドセッション)

Complex flow structures in optical disc drives compatible for Blu-ray disc, were investigated by numerical flow simulation based on the Cartesian grid method. From the simulation results, we found that additional hole on the tray outside of the disc induced the secondary upward flow which was caused by asymmetric pressure and velocity distribution. And the experimental results showed that the cooling effect of the laser diode increased and the disc vibration was not influenced by the additional hole on the tray.

Unsteady Flow in a Turbocharger Centrifugal Compressor: Three-Dimensional Computational Fluid Dynamics Simulation and Numerical and Experimental Analysis of Impeller Blade Vibration

Experimental investigations on a single stage centrifugal compressor showed that measured blade vibration amplitudes vary considerably along a constant speed line from choke to surge. The unsteady flow has been analyzed to obtain detailed insight into the excitation mechanism. Therefore, a turbocharger compressor stage impeller has been modeled and simulated by means of computational fluid dynamics (CFD). Two operating points at off-design conditions were analyzed. One was close to choke and the second one close to the surge line. Transient CFD was employed, since only then a meaningful prediction of the blade excitation, caused by the unsteady flow situation, can be expected. Actually, it was observed that close to surge a steady state solution could not be obtained; only transient CFD could deliver a converged solution. The CFD results show the effect of the interaction between the inducer casing bleed system and the main flow. Additionally, the effect of the nonaxisymmetric components, such as the suction elbow and the discharge volute, was analyzed. The volute geometry itself had not been modeled. It turned out to be sufficient to impose a circumferentially asymmetric pressure distribution at the exit of the vaned diffuser to simulate the volute. Volute and suction elbow impose a circumferentially asymmetric flow field, which induces blade excitation. To understand the excitation mechanism, which causes the measured vibration behavior of the impeller, the time dependent pressure distribution on the impeller blades was transformed into the frequency domain by Fourier decomposition. The complex modal pressure data were imposed on the structure that was modeled by finite element methods (FEM). Following state-of-the-art calculations to analyze the free vibration behavior of the impeller, forced response calculations were carried out. Comparisons with the experimental results demonstrate that this employed methodology is capable of predicting the impeller’s vibration behavior under real engine conditions. Integrating the procedure into the design of centrifugal compressors will enhance the quality of the design process.

Side-Load Phenomena in Highly Overexpanded Rocket Nozzles

The operation of rocket engines in the overexpanded mode, that is, with the ambient pressure considerably higher than the nozzle exit wall pressure, can result in dangerous lateral loads acting on the nozzle. These loads occur as the boundary layer separates from the nozzle wall and the pressure distribution deviates from its usual axisymmetric shape. Different aerodynamic or even coupled aerodynamic/structural mechanic reasons can cause an asymmetric pressure distribution. A number of subscale tests have been performed, and three potential origins of side loads were observed and investigated, namely, the pressure fluctuations in the separation and recirculation zone due to the unsteadiness of the separation location, the transition of separation pattern between free-shock separation and restricted-shock separation, and aeroelastic coupling, which indeed cannot cause but do amply existing side loads to significant levels. All three mechanisms are described in detail, and methods are presented to calculate their magnitude and pressure ratio at which they occur.

Transient Flow Characteristics in Two-Dimensional Dual Bell Nozzle Models

In the present paper, the experimental and numerical investigations are performed to clarify the mechanism of the side load in the 2 D dual bell nozzles using two types of nozzle models. In the experiments, the flow field was visualized by the schlieren method and asymmetric one-side-attached jet patterns were observed. The asymmetric flow field produced the asymmetric wall pressure distributions, resulting in the side load occurrence. The numerical simulations show that the jet oscillations result in the asymmetric jet patterns. The jet oscillations are induced by the alternate vortex shedding from the shear layer between the jet and the atmosphere, resulting in the asymmetric movements of the separation points on the 2 nd nozzle surfaces.

On uniform planar shear flow around a circular cylinder at subcritical Reynolds number

An experimental investigation was conducted of a circular cylinder immersed in a uniform planar shear flow, where the approach velocity varies across the diameter of the cylinder. The study was motivated by some apparent discrepancies between numerical and experimental studies of the flow, and the general lack of experimental data, particularly in the subcritical Reynolds number regime. Of interest was the effect of shear on the vortex-shedding frequency and the mean aerodynamic forces, including the direction and origin of the steady mean lift force experienced by the cylinder, which has been the subject of contradictory results in the literature and for which measurements have rarely been reported. The circular cylinder was tested at Reynolds numbers from Re=4.0×10 4 to 9.0×10 4, and the dimensionless shear parameter ranged from K=0.02 to 0.07, which corresponds to a flow with low to moderate shear. The results from both the present and previous studies show that low to moderate shear causes a small increase in the Strouhal number, an increase in the mean base pressure coefficient, a reduction in the mean drag force coefficient, and a small mean lift force directed towards the low-velocity side. These effects are consistent with a narrowing, or reduction in width, of the cylinder near wake, which is supported by an asymmetric mean static pressure distribution on the surface of the cylinder.

Shaft Resistance of Single Vertical and Batter Piles Driven in Sand

An experimental investigation of the shaft resistance of single vertical and batter piles pushed into sand was conducted. A prototype laboratory setup was designed for testing relatively large model piles, inclined at an angle that varied between zero and 30° with the vertical. Two model piles having diameters of 38 and 76 mm were tested at a ratio of the pile’s length to diameter up to 40, and subjected to axial compression loading. The pile models were instrumented to allow direct measurements of the shaft resistance. A theoretical model was developed to take into account the asymmetrical earth pressure distribution around the pile shaft, the level of mobilization of the angle of friction between the pile shaft and the sand, and the pile diameter. The results predicted by the theory developed agreed well with the experimental results of the present investigation as well as other experimental and field results available in the literature. Design charts are presented for use in practice. The results of th...

スピンするデルタ翼の空力特性について

The experiments of a delta wing’s spin phenomena were conducted at the low speed wind tunnel of Nagoya University with its exit test section inclined vertically. The spin rate of the delta wing in the free rotation mode was measured as well as surface pressure distributions on the spinning delta wing. At low angles of attack the spin rate increases with sideslip angle, whereas near the stall angle, it decreases. At low angles of attack, when the wing has a sideslip angle, the upper surface pressures of the windward wing-half become lower than those of the leeward wing-half, while near the stall angle the latter become lower than the former. These asymmetric pressure distributions cause the spinning motion of the delta wing. It is evident from these pressure distributions and flow visualizations that a leading edge separation vortex makes an important role in spin phenomena of the delta wing. It is also found that at the equilibrium spin rate, the spanwise distribution of the pressure difference between upper and lower surfaces, ΔCp , shows a nearly symmetric pattern regarding the wing centerline.

액체로켓용 터보펌프 성능예측에 대한 수치해석적 연구

The hydraulic performance analysis of an entire pump system composed of inducer, impeller, volute and seal for the application of turbopumps is numerically performed using three-dimensional Navier-Stokes equations. A quasi-steady mixing-plane method is used on the impeller/volute interface to simulate the unsteady interaction phenomena. From this work, the effects of each component on the pump performance are investigated at design and off-design conditions through the analysis of flow structures and loss mechanisms. The computational results are in a good agreement with experimental ones in terms of the headrise and efficiency even though very complex flow structures are present. It is found that the asymmetric pressure distribution along the volute wall constitutes the main reason of the difference between experimental and computational results, due to the limitation of the quasi-steady method. Since the volute was found to be over-designed by the pressure distribution of the volute wall, re-design of the volute has been performed, resulting in an improved performance characteristic.