Penetrating flows of an aqueous solution of sodium salicylate (NaSal) through an aqueous solution of cetyltrimethylammonium bromide (CTAB) in a circular tube were investigated experimentally. The NaSal solution flowed through the CTAB solution while displacing it. Network structures of wormlike micelles are formed on the interface between the solutions, and gelation occurs there. Although each test fluid has a similar Newtonian viscosity, CTAB/NaSal mixtures had strong viscoelasticity, and their viscosity greatly increased because of the gelation. Consequently, several flow patterns that do not appear in the case of Newtonian/Newtonian penetrating flows were observed. The flow patterns of the core of the penetrating flow were classified into five patterns and were mapped onto a plane of the molar concentration ratio S of NaSal to CTAB and the penetration velocity U. The core exhibited a saw-tooth pattern at small U, which changed to a corkscrew pattern or an elastic recoil pattern as U increased. Elastic recoil patterns appeared at S = 3.0 and 5.0, where the relaxation time of a CTAB/NaSal solution is relatively long. Furthermore, a novel flow pattern in which the core flow exhibits repeated elastic recoiling was observed. In this pattern, the contracting part of the core flow exhibited alternate stretching and recoiling. Moreover, a unique phenomenon of a penetrating flow with gelation was observed. In this phenomenon, a stable tip was newly formed by the gelation after the breakup of a core. The displacement rate decreases with increasing penetration velocity and tends to be small when unstable flow patterns appear.
The flow characteristics of wood pulp suspensions in circular pipes have been investigated experimentally. In studying the flow mechanism, we mainly consider the yield shear stress, which represents the fiber-network strength in the flocculation of pulp fibers. The experimental results for five regimes, into which the flow was classified on the basis of the behavior of pulp fibers and the flow characteristics, as reported in the author's recent work (2010), were correlated with the fiber concentration Cs in equation of the form τ=aCsb where τ is the shear stress on the pipe wall and a and b are constant. The yield shear stresses were determined by the measurement of the pressure loss. They are not dependent so much on the pipe diameter and become large with increase of the pulp-fiber concentration. The flocculation of pulp fibers starts to become loose near the pipe wall when a shear stress exceeding about four times the yield shear stress acts on the suspension. The values of the disruptive and dispersive shear stresses are formulated as simple expressions depending on only the fiber concentration. Furthermore, the corresponding critical and turbulent Reynolds numbers are presented. The pressure loss of the pulp suspension in the turbulent flow becomes smaller than that for water, and the ratio of both can be expressed by a simple empirical equation.
Wormlike micelle surfactant solutions showed turbulent drag reduction effects in pipe flows. It was well-known that SIS (Shear Induced Structure), reported in previous studies, made them. However, inner diameters (characteristic length) of pipes used in the previous studies were in the order of millimeter. Thus, shear rates were limited to the order of 104s-1 at a maximum. In the present study, flow properties of water and wormlike micelle surfactant solutions were investigated at higher shear rates using capillaries whose inner diameters ranged from 133 μm to 2.87 mm. Because the observed Reynolds number estimated for the micron-sized capillaries ranged from 102 to 104, drag reduction effects were observed as a pseudo-laminarization, which is a phenomenon that transition from laminar flows to turbulent flows with the increase in the Reynolds number delays. Viscosity measurements using a capillary method indicated that the surfactant solution used in the present study had non-Newtonian viscosity. Therefore, the Reynolds number of the surfactant solution flow was estimated by the generalized Reynolds number. By using a jet thrust method, elastic properties of wormlike micelle surfactant solutions were measured in the corresponding to the viscosity measurement. For water, the resultant pressure drops (the frictional coefficient of pipes) agreed with both the prediction of laminar flows and the Blasius expression. Laminar flows were maintained up to 4.2×103 of the Reynolds number in surfactant solutions, independently of the used diameters. In other words, these results suggested that the pseudo-laminarization was occurred in the capillary flows. Moreover, the relationship between the shear rate at which the surfactant viscosity asymptotically approached to the water one and the transition to turbulent flows was discussed to clarify their correlation.
Flow-induced orientational changes of an aqueous polymer solution in planer channels have been studied utilizing optical rheometric technics. Two kinds of 1:4 abrupt expansion channels with the same width and different heights of 1 mm and 0.2 mm were tested in the experiments. 0.5 wt% xanthan gum solution was examined as the test fluid with non-Newtonian and viscoelastic properties due to the network structures of the polymer. The optical rheometric device measuring birefringence and orientation angle of the polymer was adapted to a microscope. We have obtained remarkable differences in the development of birefringence between these cases. In the case with channel height of 1 mm, the birefringence measured on the centerline of the channel was rapidly decreased just after the expansion, then showed temporal increase. It is considered that this characteristic change in the birefringence corresponded to the rapid disordering and subsequent alignment of the polymer perpendicular to the flow direction because of the negative elongational flow generated after the expansion. After these regions, the polymer gradually aligned parallel to the flow direction. In contrast, the temporal increase in birefringence and alignment to the transverse direction in molecular orientation was not observed in the case with channel height of 0.2 mm. Flow-induced orientational changes of polymers in planar channels with expansions were considerably affected with the combination of local shear rate and elongational rate changes.
This paper is concerned with the development of magnetic fluid micro devices. Liquid responses of a magnetic fluid adsorbed on a ring-shaped permanent magnet subject to alternating magnetic fields were investigated. The magnetic fluid adsorbed on the permanent magnet forms a hole, and the diameter of magnetic hole may be changed by external magnetic fields. Frequency characteristics of micro diaphragm mechanism based on the magnetic fluid-permanent magnet element system were examined experimentally. Liquid surface responses of the magnetic fluid were examined over the wide frequency range. It was revealed that the frequency of the liquid surface motion corresponds to the frequency of external alternating magnetic field. The magnetic field distributions around the element system were also measured, and relations between the magnetic field distribution and magnetic fluid surface motion were discussed. Furthermore, the improved model of the magnet-magnetic fluid element was produced, and its driving characteristics were obtained experimentally.
Slot coating flows of concentrated dispersion systems of disk-like particles were numerically analyzed using a computational method that couples finite element computations of macro flows of the dispersion systems and micro simulations of the orientation behavior of the particles. The inter-particle interaction was included into the simulation using a Maier-Saupe type mean field potential function. The Brownian configuration field method was adapted to the computation of the particle motion for the reduction of computational costs. Furthermore effects of solvent evaporation from the free surface of a coated liquid film were considered in the present simulation. The potential strength was changed according to the particle concentration to consider the effect of solvent evaporation on the inter-particle interaction. The particles tended to orient just downstream of a slot die because of the elongation flow in this region, and the orientation relaxed as the particles flowed downstream. However, in a downstream region the orientation was fixed since the inter-particle interaction was intensified because of the increase in the particle concentration due to the solvent evaporation. The present simulation captured change in the orientation distribution of the particles due to the solvent evaporation and such information is useful for the process design of coating considering the relation between the particle behavior during the process and the function of products.
Flow dynamics of magneto-rheological (MR) fluid in a branch pipe as a simple model of a cracked pipe and a blood vessel with wounds is clarified by considering the effects of magnetic field intensity, inner diameter of a branch channel and wall elasticity of a pipe. It is shown that a MR fluid cluster shuts down a branch leakage flow without reducing main flow by measuring a mass flow rate of MR fluid in a branch channel under magnetic field. Main channels made of acrylic, silicone and polyvinyl alcohol-hydrogel (PVA-H) were used in order to evaluate the effect of channel elasticity on flow dynamics of MR fluid. The seal effect was quantitatively clarified by evaluating the endurance pressure of the cluster in a branch channel. Furthermore, the break down behavior of clusters formed in a branch channel was experimentally analyzed by visualizing the flow dynamics of MR fluid cluster in order to clarify the difference in endurance pressure depending on the pipe materials.
In order to measure the flow characteristics of polymer melt with high melt index, e.g. polyester and polyethylene terephtalate (PET) used for fiber processing, we discuss the utility of the cup-type jig for measurement of the steady-state shear flow characteristics in the rotational-type rheometer, especially parallel plate rheometer, by using the viscoelastic flow simulation. The multiple mode Phan-Thien Tanner (PTT) model was employed as the constitutive equation. We considered the deviation between the rheological data from the parallel plate rheometer with cup-type jig and the data from the normal parallel plate rheometer with the same disk diameter. As a result, the deviation of shear viscosity increased with the distance between the disk and the cup-type jig. The average value of the deviation of shear viscosity increased linearly with this distance. Then, the absolute value of the deviation of the first normal stress difference also seems to increase with this distance. On the other hand, the deviations of shear viscosity and the first normal stress difference are almost independent of the cup-type radius in the region over about 1.2 times of jig diameter divided by the disk radius. These results imply that large radius of cup-type jig and narrow distance between the disk and the cup-type jig would be suitable for measurement of polymer melt flow characteristics using the parallel plate rheometer with the cup-type jig. In addition, these obtained results would imply that to use the cup-type jig is valid for measurement of rheological data.
The flow interaction between bubbles is known to have an influence on acceleration of the bubbles rising velocity and the bubbles shape under static pressure field. We previously reported that pressure oscillation is effective for enhancing rising velocity of a small bubble in viscous shear-thinning fluid. In the present study, flow interaction between two small bubbles placed in the vertical direction under pressure-oscillating field, which is applied from the bottom side, is investigated experimentally. The three fluid types of different rheological properties, sodium polyacrylate, carboxy-methyl cellulose sodium salt and xanthan gum, are selected and tested. With a help of strobe scope lighting, we successfully monitor trace of the moving bubbles clearly through a high density video camera. Two non-dimensional parameters of each of the bubbles, normal rising velocity of bubble ε and non-dimensional acceleration Gb, are compared for the test fluids. It was found that the rising velocity of the lower bubble is higher than that of the upper bubble; that is strongly enhanced in the case of closer bubbles; and finally the bubbles move together and form a cluster, whereas natural rising velocity of the bubbles without pressure oscillation are the same. In addition, a ratio of distance between the bubbles center L and bubble diameter D and non-dimensional rising velocity ε are compared. After experiment we found that rising velocity of the lower bubble depends on the distance between bubbles and non-dimensional acceleration.
Rheometers have been used extensively for evaluating dynamic viscoelasticity of viscoelastic fluids by measuring the stress response to the sinusoidal strain applied to the fluids. It was reported that dynamic viscoelasticity was also derived based on the propagation velocity and the damping ratio of the shear waves propagating in the fluids. In this study, a polarization imaging camera and a particle image velocimetly (PIV) are utilized to visualize shear waves generated by an oscillating plate in a viscoelastic wormlike micellar fluid in order to derive dynamic viscoelasticity. Entangled wormlike micellar fluid of 3.0×10-3 mol/l cetyltrimethylammonium bromide (CTAB) water solution with additive of sodium salicylate (NaSal) as counter ions at a molar ratio of S =4 was used in this study for a test fluid. Propagation velocities were obtained from a sequence of visualized images of propagating waves, which show good agreement to the velocities calculated from the products of wave frequencies and wavelengths. Damping wave profiles were derived from the retardation distributions which were calculated from the captured birefringence images. The dynamic viscoelasticity data derived from the propagation velocities and the damping ratios were in close agreement to the measured data using a rheometer, which shows validity of this method at relatively high frequencies. When the ratio of the amplitude to the wavelength exceeds a critical value, onsets of equilibrium points rising are observed in the damping retardation profiles depending on the amplitude, which attributes to the orientation of micelles on the plate.
It is difficult to remove well dispersed fine particles from dilute slurry, because filtration and evaporation process requires a lot of time and energy. Electrophoresis is known as a method of moving fine particles. Therefore, the electrophoresis technique is used to collect fine particles from such slurry as a paste of concentrated fine particles on electrodes. The viscous paste on the electrode is slowly falling down during electrophoresis process, finally drops from the electrode. This may affect recovery rate of the fine particles. In this paper, we studied transport phenomena of 5wt% alumina slurry under electric field for producing the concentrated particles from the alumina slurry. The concentration rate of the particles is evaluated from weight of the concentrated particles. Time-dependent behavior of the concentration rate shows a good agreement with the theoretical approach. Since the alumina slurry is a power-law fluid, we applied shear between electrodes. The concentration rate of the particles is successfully enhanced due to decreasing in the apparent viscosity. In addition, we measured rheological properties of the concentrated particles.
The motion of a bubble rising in sodium acrylate polymer (SAP) solutions is experimentally explored. In this study, 0.3 and 0.6 wt% SAP solutions with shear-thinning and elastic properties are prepared. The bubble rise motion depending on the value of the suspending viscosity is examined covering from small to large-sized bubbles. Consequently, it is confirmed that bubbles rising in the SAP solutions have cusped shapes due to the elastic effect except for large deformed bubbles in the 0.6 wt% SAP solution. In addition, the bubble rise motion in the viscoelastic liquid is considered and discussed based on effective physical parameters and the terminal bubble rise velocity. In the experiment using the 0.6 wt% SAP solution, it is observed that a jump discontinuity of the terminal bubble rise velocity has occurred. It is verified that the velocity jump in this study doesn't arise from the change in the bubble shape caused by the elastic effect. It is shown that effective Reynolds and Morton numbers allow us to systematically organize the bubble rise motion in the viscoelastic liquid with taking the shear-thinning effect into account. One can reasonably analyze viscoelastic bubble morphology by applying effective Reynolds and Morton numbers and Deborah number to a viscoelastic non-Newtonian system.
Regular geometrical patterns are formed on a sliding flow on a tilted plate when a viscoelastic fluid jet falls down from a nozzle exit to the plate by gravity. A part of the jet near the collision point to the tilted plate is oscillated to the flow direction and/or the horizontal direction by stacking on the plate at a suitable condition and it makes the regular patterns. Several regular, quasi-regular and random patterns are formed on the plate by adjusting the title angle of the plate and the height of the nozzle exit from the collision point at the plate. The pattern maps that are a chart to show the distribution of each pattern according to the nozzle height and the title angle of the plate were drawn and it makes clear that the regular patterns appear the range of the tilt angle from 30 to 60 degrees. The sliding flow velocity on the plate is an important factor for the pattern formation and is also affected by the flow rate, the nozzle diameter and the viscoelastic properties of the fluid. The sliding flow velocity and the period of the pattern are measured for the in-line stacking type and the horizontal stacking type as a representative regular pattern. The border of the in-line stacking type and horizontal stacking type coincides with the critical height for the deformation transmission property on the viscoelastic fluid jet driven by gravity, as reported by Tomita and Takahashi (Transactions of the Japan Society of Mechanical Engineers, Series B, Vol.56, No.529, 1990). The oscillation period of these regular patterns normalized by relaxation time was evaluated by the dimensional analysis method and an empirical formula to describe the oscillation period of the patterns was presented.
In the present study we report the flow characteristics of a steady flow of viscoelastic fluid in a curved pipe of 90 degree bend. The liquid mode consideration is a model-fluid, which is newly made to investigate the viscoelastic fluid. The flow behavior in the curved pipe was examined by experimentally and analytically at low Reynolds numbers. The visualization of flow in the curved pipe was achieved using a hydrogen bubble method, in which micro-size hydrogen bubbles are generated by a thin platinum wire with passing DC current. The finite element method was used to obtain the analytical solution for the viscoelastic character in the curved pipe. The rheorogical characterization was made by measuring the model-fluid with a precision rheometer. Then the model-fluid was characterized by White-Metzner model and Herschel-Bulkley model as the constitutive equation, for the numerical analysis. The obtained results from the visualization by the hydrogen bubble method were well predicted by the analytical verification, showing distorted plug-flow behavior at the curved pipe, while the Newtonian flow behavior (predicted by the analytical simulation) is almost kept Poiseuille flow behavior. It is found that the pseudoplastic and elasticity in the fluid strongly affect the flow velocity distribution in the curved pipe.
Non-linear viscoelastic behavior of a wormlike micellar solution of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in the large amplitude oscillatory shear (LAOS) is examined. A transient response of the shear stress after applying a large amplitude sinusoidal strain is measured by the stress control rheometer. The start-up wave form of the shear stress is divided by four patterns, such as (a) no-stress overshoot, (b) linear shear hardening, (c) extreme shear hardening related with SIS and (d) stress fluctuation, by increasing the strain amplitude. After three cycles, the stress wave becomes a periodic steady pattern. The obvious non-linear behavior, the pattern (c) and (d), is observed at the strain amplitude γ0 = 3 or higher. The periodic stress signal in the periodic steady state is evaluated by both the geometrical interpretation and the LAOS analysis of the new frameworks. As a result of separating the viscous and the elastic ingredient stress from the measuring stress, the rheology property changes suddenly around γ0 = 20. These characteristics correspond closely to specific flow behavior of a start-up shear flow in the same shear strain. The micelles structure is changed over a certain shear rate and strain, as known by SIS, shear-induced structure, and generate the opaque in the solution. In this case, the solution begins to be opaque at shear strain γ = 3 and becomes most opaque around γ = 20. Moreover, the onset condition coincides with the appearance of the higher odd harmonics in the periodic stress signal analyzed by FFT method.
The effect of shear flow on an optical anisotropic film of chromonic liquid crystal by use of applicator was investigated. Some chromonic dyes form a rod like aggregation in an aqueous solution and change to a chromonic liquid crystal in a certain concentration and temperature of the solution. When the chromonic liquid crystal is applied to a glass substrate by an applicator, the aggregates in the chromonic liquid crystal are oriented in one direction in the thin film, and it exhibits an optical anisotropy such as birefringence and dicrhoism. The orientation process of the aggregates during application, however, is still unknown in detail. The application process, especially shear region, was considered to be important to make the optical anisotropy film having a uniform and high dichroism. The shear flow would have the multi-domain collapsed and transformed to mono-domain. In the present experiment, small texture disappeared when the chromonic liquid crystal under the shear flow was observed by microscope, however the optically measured dichroism and birefringence by the laser did not vary even though the shear rate changed widely. The birefringence is ten times larger at the exit of applicator, which is elongation region, than the one just under the applicator. The shear flow shows limited effectiveness against the molecular orientation. It would be the elongation flow that is more effective to produce a good optical anisotropic film.
In this study, we have investigated the fluidity responses after a shear flow reversal of carbon nanotube (CNT) suspensions with Newtonian carrier liquids in stress-sweep tests. The suspensions have showed transient decrease in viscosity, i.e., increase in fluidity, after the flow reversal in shearing direction. Moreover, i.e. transient shear thickening phenomena, in viscosity were observed at a certain shear rate. In order to quantitatively clarify the viscosity recovery, a typical strain γp corresponding to the peak of viscosity recovery was estimated. Independence of γp from stress sweep-rates applied was shown for respective suspensions. Moreover, dependence of viscosity of the carrier liquid and volume fraction of CNT was also examined. I n the result, it is clarified that lower γp was obtained with light carrier liquids and high volume fraction. It is considered that these results will be correlated to the change in flowing structure of CNTs depending on the shear rate applied.
We have developed liquid crystalline microactuators which can drive in two or four ways. These actuators consist simply of two glass plates on which patterned electrodes and alignment layers have been treated. For a 2-way actuator, the glass plate is divided into two areas which have positive and negative tilt angles of molecular orientation, respectively; the rotational directions of molecules are opposite to each other, so that when an electric field is applied to one area the actuator moves forward, whereas it moves backward when an electric field is applied to the other area. For a 4-way actuator, hybrid molecular orientation mode is employed and four separated electrodes are patterned only on the upper glass plate; four electrodes correspond to forward, backward, rightward, and leftward movements, respectively. Comparison of the driving speeds of these two actuators with that of a 1-way actuator shows that the driving speed of a 2-way actuator is a half of that of a 1-way actuator, since only a half area of a glass plate contributes to driving forward or backward for a 2-way actuator. The driving speed of a 4-way actuator is much less than 1/4 of that of a 1-way actuator because of the hybrid molecular orientation mode.
For a thermotropic liquid crystal, its phase state depends on temperature, and nematic and isotropic phases, which behave like a fluid macroscopically, can coexist by adjusting its temperature. We have developed a liquid-like micromanipulator operated by a phase interfacial force induced between nematic and isotropic phases of a liquid crystal. In this experiment, we have used 4-cyano-4'-pentyl biphenyl as a thermotropic liquid crystal, mixed microparticles with the diameter of 9 - 30 μm in the liquid crystal, and controlled the temperature distribution of the liquid crystal sandwiched between two glass plates by two sets of Peltier devices. The moving speed of a phase interface decreased linearly with increasing the temperature of the higher-temperature Peltier devices. We have tried to manipulate the particles in the liquid crystal by moving a phase interface. The particles are successfully driven only for the case that the area of nematic phase expands, and the maximum phase interfacial force is evaluated through the motion equation of a particle to get 1.4 nN. It is also found that the interfacial force is independent of the size of particles, which is explainable qualitatively on the basis of the deformation of molecular orientation field in the nematic phase due to the presence of particles.
Inertio-elastic instability characteristics of visco-elastic fluids sweeping a micro-cavity mounted in a micro-duct have been investigated in order to develop a effective micro mixer. The cavity depth, the cavity length and the width of the wider flow path were fixed at 200, 1,000 and 400 μm, respectively while the solvent Reynolds number was changed from 0.100 to 100. As a visco-elastic fluid, a cationic surfactant/counter-ion system was applied. The molar ratio of counter-ion to surfactant was changed from 1.5 to 10 in order to control rheological characteristics of the fluid. Flow visualization experiments were performed with a high-speed camera mounted on a microscope. From the results, it was that a tonguing motion of the separation fluid bubble tip formed in the downstream region in the cavity occurs at a certain Weissenberg number larger than 200 due to the inertio-elastic instability. The fluctuating bulge structure was also observed on the upstream side wall of the cavity in a higher range of the Weissenberg number. These characteristics were considered to be effective for a mixing process. It was also found that the separation bubble size is determined with Weissenberg number for all fluids treated in this study, but the previous correlation suggested for a macro-scale system does not agree with the present results. This indicated that some different relaxation structure exists in a micro-scale system.
In order to investigate the relationship between hydrogen-induced hardening of austenitic stainless steel and the hydrogen content, the spherical micro-indentation tests and thermal desorption analysis have been conducted on hydrogen charged austenitic stainless steel JIS SUS316L. Due to the relatively low hydrogen embrittlement susceptibility, this material has been widely used in a hydrogen environment. Hydrogen has been charged by using a cathodic method. In order to change the hydrogen content, charging current density and charging time were changed from 0.01 to 1.0 mA/mm2, from 0 to 48 h, respectively. The obtained results show the hardness increases along with charging current density and charging time. The maximum change in the hardness is 28 %. Hydrogen content also depends on the charging current density and charging time. These relationships result in the strong linear correlation between hydrogen-induced hardening rate and the hydrogen content. Their correlation factor is 0.98 and the probability that these are uncorrelated is less than 0.001 %. The depth of hydrogen absorption was investigated by using secondary ion mass spectroscopy (SIMS). Hydrogen-induced hardening might be due to dislocation-pinning effect of hydrogen during indentation process. This phenomenon is dependent on not so much hydrogen absorption depth as hydrogen content. By using this phenomenon, there is a possibility to apply micro-indentation tests for evaluation of local hydrogen content.
Hydrogen storage alloy has a potential material to become one of the most promising candidates as an effective storage system and it has higher safety and storage density than other storage systems. The Mg-based hydrogen storage alloy has the advantage of high hydrogen storage density (7.6 wt% in MgH2), light weight and low cost, while it needs to improve its slow reaction kinetics and high desorption temperature for practical applications. In this research, we prepared the Mg/Fe multi-layer films with the pulsed laser deposition (PLD) method and studied their hydrogen absorption and desorption properties for the effects of the order of layer and the Ti layer on the surface. The differential scanning calorimetry (DSC) and X-Ray diffraction (XRD) were carried out to characterize the hydrogen desorption temperature and the hydride. As a result, it found that Polyimide/Fe/Mg/Ti multi-layer showed to make the magnesium hydride after hydrogenation and to leave it at 245°C and that is 173°C lower than that of pure magnesium hydride and Polyimide/Mg/Fe/Ti, Polyimide/Fe/Mg and SUS304/Fe/Mg/Ti showed no hydrogen desorption after the hydrogenation.
Application of sophisticated cooling systems and thermal barrier coatings to advanced gas turbine components impels the structural materials be in service under a significantly graded temperature condition. Whereas the graded temperature enhances thermal or internal stress which leads to thermo-mechanical fatigue failure in conjunction with external load, the thermal stress can also be relaxed time-dependently by creep. Since the temperature gradation may get more pronounced in future, a material design concept will be required under such circumstances. In this work a simple two-dimensional model is constructed to semi-quantitatively estimate the creep deformation and internal or thermal stress state for a high temperature component which uniformly deformed under a graded temperature condition. Based on the model the numerical calculations were carried out for some representative cases, by employing elastic-creep constitutive equation: one is a case without no external load, and the other is a case when an external tensile load is applied. The calculation indicated that in the former case the thermal stress deforms the component in compression when the stress relaxation is more significant at the higher temperature side than at the lower temperature side. Not only the range of graded temperature, but also the distribution shape is found to remarkably affect the behavior. It is also indicated, as a reflection of the above behavior that the component can deform in compression at early stage even when the external stress in tension is applied to the component, followed by tensile deformation. Of particular importance for structural design is that the stress promotion always takes place at the lower temperature side in the component. These behaviors are summarized as a function of relative magnitude between the thermal stress and external stress
This paper presents results of studies carried out to evaluate the probability of silicon particle refinement in hypereutectic Al-25 mass% Si alloy through a uniaxial compression test using cylindrical specimen at over the eutectic melting point Tm = 850 K (577 °C). The test conditions were a combination of temperatures of 580 and 590 °C, compression rates of 5, 25, and 125 mm/min, and compression stroke of 5, 10, and 12 mm. The effects on silicon particle refinement assessed by measuring equivalent strain, mean strain rate, power rate, and shear rate. Specimens show the barreled shape due to low compression rate and also the load versus displacement curves showed the work softening nature. The results indicated that the finer silicon grains were obtained in cases of lower test temperature, higher compression rate, and larger compression stroke. Greater applied strain, strain rate, power rate, and shear rate were affected on the refinement of silicon grain. The only satisfying result showing strong correlation was obtained from the relationship between shear rate and silicon grain size on a double logarithmic plot ; the effect of the shear rate, γ[s-1], and tested temperature, T [K], on silicon grain size, G[mm], was expressed using power-law model G = 0.08(T-Tm)0.4γ-0.24/(T-Tm). The relation showed that high shear rate operation at just above the melting point must be the optimum condition.
Magnesium alloy is the lightest material in all practical metals, and has the excellent mechanical properties. From such reasons, the alloy is noticed as the attractive material in various fields. However, the alloy has the weak points that are inferior for heat and corrosion resistance. Therefore, it will be possible to guarantee the safety security of structure parts, if the information on the fracture strain and life, etc. are evaluated by the signals detected from the alloy under those use environment. The three type specimens of the virgin, the heat history (i.e. repeatedly gave the heating to the virgin specimen) and the corrosion specimen (i.e. immersed the virgin specimen into solution) are prepared in this study. Then, the tensile test was carried out for each specimen, and the AE signals emitted in the testing were detected. Frequency and fractal dimension analysis were carried out in order to extract the features of those signals. From such analysis results, the feature extraction of the signal by the elasticity twin deformation was done, because that deformation participates in the degradation of mechanical properties. As the result, the following things became clear under the experimental condition in this study: The frequency component of the signals caused by that deformation is near 550 kHz. The fractal dimensions Fd of those signal show the value over 1.85. Then, it was examined whether the fracture strain is evaluated by the Ib value (Improved b-value) led from the frequency distribution of the Fd. As the result, the effectiveness of this method proposed under the experimental conditions in this study was confirmed. Therefore, the possibility for the prediction of that strain by the AE signal detected in elastic region was shown.
In this research, probabilistic fatigue load estimation by the aeroelastic modeling was carried out for a small wind turbine with 1m diameter. The results were compared with the simplified load model which is a deterministic method, and quantitative evaluation of the difference between two methods was presented. An aeroelastic simulation code for 5 bladed wind turbines is used for aeroelastic modeling. This code is based on NREL's FAST and modified for 5 bladed turbines by authors. On the fatigue analysis, wind condition is set to be IEC 61400-2 Ed.2 DLC1.1 which is assumed to be equivalent condition of simplified load model. From the time series results from aeroelastic analysis, the load amplitude and cycles are counted. Then the cycles are weighted by wind speed probability distribution correspond to IEC 61400-2 Class I to IV. The result from aeroelastic modelling was similar to one from simplified load model in Class I but different in other Classes. The reason is that the fatigue load in high wind speed, which is not encompassed with simplified load model, is dominant for fatigue load with target turbine's model regardless of IEC Class. Therefore it is important to consider probability of wind speed over all operating condition in fatigue load estimation.
This paper presents a normalized deconvolution approach for a digital holographic particle measurement in order to decrease the elongation of the reconstructed particles along the depth direction. The performance of this approach is evaluated using numerical simulations, and its practicality is experimentally demonstrated. In the numerical simulations, the performance is evaluated mainly based on the cross-correlation between the true distribution and the deconvolution results. Tests were carried out for two types of recording systems and three kinds of reconstructed information. The results indicate that the most accurate particle images were obtained using the phase-shifting observation method and reconstructed quantities that contain phase information, such as the complex amplitude. Furthermore, the RMS error in the particle depth position is found to be improved especially for higher number density within the particle distribution. Experimental measurements with standard particles confirm that particle elongation along the depth direction can be successfully suppressed using the normalized deconvolution method. The experimental results thus confirm that this method is useful for real particle measurements.
The loss coefficient and the flow fields downstream of the typical models of gate valves are investigated experimentally from the surface pressure and velocity distributions measured in the air-pipe flow at Reynolds number 4×104 and the various visualization methods. The attention as the gate valve model is paid to the gate plate, which is an essential part of the various practical gate valves. The gate plate has three different fundamental shape types named convex-type, flat-type and concave-type, based on the shape of the plate head projecting from the inner pipe wall. The aim of this study is to clarify the effects of shape, height ratio and thickness ratio of the gate valve plate on the loss coefficient and flow field in the turbulent pipe flow. The height ratio is the relative height defined as the gate-plate height, which is the height from the inner-wall surface to the head along the center line of the valve plate, to the pipe diameter. It varies from 0.1 to 0.8. The thickness ratio defined as the gate-plate thickness to the pipe diameter is kept at 0.1 for the flat-type and concave-type gate plates, and varies in 0.1, 0.3 and 0.5 for the convex-type gate plate. As a result, the loss coefficient is strongly dependent on the shape type and the height ratio, and is slightly dependent on the thickness ratio. The shape type and the height ratio are able to be replaced by the open-area ratio to estimate the loss coefficient as one parameter independent on them. The necklace vortex is produced in front of the gate valve plate, and they flows downstream above the head of the gate plate. A three-dimensional recirculating flow region is produced behind the gate plate, and there is a strong secondary flow and a recirculating region longer than the center reattachment length along the symmetrical plane of the valve plate in the case of the gate valve plate with a small open-area ratio.
In this paper, direct numerical simulations of the sound from vortex dipole rebound from an adiabatic non-slip wall are performed to investigate the impacts of the boundary schemes combined with the 6th order compact scheme on the capability of capturing the acoustic waves generated by vortical flows near a wall. The free parameter of the compact filter α=0.45 and α=0.49 are chosen to clarify effects of boundary schemes in high wave number region. Results show that some boundary schemes make the computations unstable and high order boundary schemes are not always appropriate. It is found that in the case of α=0.45, no remarkable difference is found in the results computed by each boundary scheme. On the other hand, in the case of α=0.49, the vorticity of vortex dipole almost does not depend on the each scheme. However, the vorticity of secondary vortex on the wall computed depends on the each boundary scheme and spatial resolution. This causes large difference in the distributions of vorticity and sound waves. It is therefore clearly understood that the characteristics of the first derivative of the boundary schemes combined with the 6th order compact scheme in the high wave number band affect the capability to precisely capture the aerodynamic sound. When the compact filter's free parameter is chosen to be α=0.49, the boundary schemes have a strong influence on the computation of aerodynamic sound. Special attention to a combination of boundary and compact schemes is required to perform accurate computations of aerodynamic sound generated by flows near a wall.
This paper reports on the behavior of shock triple points on the detonation wave propagating in the rectangular tube, which is obtained from the experimental observation and numerical analysis. Used gas mixtures are the equimolar gas mixture of acetylene and oxygen in the experiment, and the stoichiometric hydrogen and oxygen in the numerical analysis. However, if there are the specific number of shock triple points in the tube, the numerical analysis using finite difference method which is composed of semi-implicit MacCormack TVD scheme can reproduce the propagation behavior obtained by experiment. Therefore, the propagation mode of detonation is identified by geometry of emission points and emission trajectories of the experimental observation. And then, the detailed propagation mechanism of its detonation which is difficult to observe in the experiment has been revealed.
In thermal design of mechanical and electronic equipment with increasing complexity, it is important to estimate thermal contact resistance correctly. In the present study, photo-acoustic method (PAM) is applied, with the aid of theoretical considerations, to the measurements of thermal contact resistance between solids. PAM is one of the non-contact and non-destructive methods for detecting thermal properties of various materials. This method is used to extract thermal contact resistance from the data of maximum phase delay of thermal response to periodically modulated irradiation light. For comparisons, steady-state method with constant heat flux is also performed. The results of both methods show the similar tendency and the same order values.
Heat transfer measurement has been done for a low speed water channel with an insertion of rotation circular cylinder in order to find an effective way to achieve high heat transfer enhancement by dynamic flow control method. In the present study, a ratio of the gap between the cylinder and heat transfer wall to the cylinder diameter was kept to be 0.6. The diameter based Reynolds number was set for 200 and 400. It was found that the cylinder rotation achieves remarkable heat transfer enhancement. Counter clockwise rotation, the direction of which accelerates the gap flow, intensifies the unsteady vortex in the shear layer above the low speed area downstream the circular cylinder and this enhances the wall heat transfer over the extensive downstream region. Heat transfer enhancement becomes large as the rotation speed becomes higher within the present experimental condition. Clockwise rotation suppresses the vortex formation, although high speed rotation induces the fast flow approaching near the wall and achieves large heat transfer enhancement there.
For the safety design of a Sodium-cooled Fast Reactor, it is strongly required that the molten material which is released from a core region has to be solidified and cooled down in a reactor vessel by breaking up in the sodium coolant during a Core Disruptive Accident in terms of Post Accident Heat Removal. In this paper, in order to investigate the effects of the surface solidification on the jet breakup, the experimental results using a low melting point alloy and water are reported. The jet breakup behavior is observed with a high speed video camera, the front position of the jet and the jet breakup length are estimated with the visual observation results. In the high injection velocity conditions, it is found that the jet breakup is dominated by fragmentation induced by the surface instability due to the relative velocity even in the surface solidification condition. In addition, it is also found that the tendency of the jet breakup length is close to Epstein's correlation.
Explanation is given about a rational method to evaluate tornado-borne missile speed, flight distance and flight height to be used for safety design of a nuclear power plant. In the method, the authors employed Fujita's DBT-77 model as a tornado wind model to take the near-ground tornado wind profile into account. A liftoff model of an object on the ground was developed by conservatively modeling the lift force due to ground effect. The wind field model and the liftoff model have been compiled together with a conventional flight model into a computer code, named TONBOS. In this study, especially, the code is verified for one- and two-dimensional free-fall problems as well as a case of 1957 Dallas tornado wind field model, whose solutions are theoretically or numerically known. Finally, the code is validated by typical car behaviors characterized by tornado wind speeds of the enhanced Fujita scale, as well as by an actual event where a truck was blown away by a tornado which struck a part of the town of Saroma, Hokkaido in November, 2006.
Water condensation on a hydrophobic surface with nanoscale hydrophilic regions was investigated to reveal the condensation mechanism of submicron-scale droplets. This feature was found on the graphite step-terrace structured surface; step surfaces are more wettable relative to terrace surfaces, and it was precisely characterized using an atomic force microscope. Condensation experiments were conducted using an environmental scanning electron microscope and droplets were observed to line up on preferentially along the graphite steps. Observed droplets ranged from 150 to 300 nm in diameter and the droplet interval depends on the width of hydrophobic region. The heterogeneous nucleation theory was extended to consider attracted water molecules on hydrophilic step surface, which enable us to explain the current observed result under unsaturated condition. As a result, proposed theory shows qualitatively that narrower hydrophobic region induces short droplet interval. Our suggestion for design the hybrid hydrophilic-hydrophobic surface would enable the development of surface that will perform high heat transfer at dropwise condensation.
This paper discusses the efficiency and completeness of a sweeping task to ensure the reliability of sweeping robots. The map information is necessary in order to ensure the completeness of sweeping, but it is not practical to give the preliminary map information to the robot. When the robot generates the map online, the reliability of the map is low in the beginning of the sweeping task. Therefore, the robot cannot use globally motion control. In the latter half of sweeping, unswept area are scattered like detached lands. The map has high reliability at this time, and the motion control using the whole map information is effective. The reliability of the map is gradually increased during the sweeping task, the robot should switch the motion control from locally to globally in accordance with it. In this paper, we propose the new motion control method for a sweeping robot in unknown environments. The robot selects mainly local motion control method at an early stage in this algorithm. As time goes on, the probability of the global motion control method selecting is increased. Even though the robot does not know the area of environment, the robot behaves as the above. Simulation and experimental results show the proposed method is more effective than the behavior-based method.
This paper describes a development of bird's-eye view system for teleoperation. Emergent disaster recoveries are important when natural disaters occur. Unmanned construction is used to recover from natural disasters such as landslide and pyroclastic flow. This construction method has no risk of secondary disaster because workers teleoperate construction machines at remote site. However, traditional unmanned construction is an inefficient way because captured images from a camera mounted on a construction machine usually has blind spots. We propose an easy calibration method to create bird's-eye view images which can reduce blind spots from multiple cameras. Our method helps workers understand environment easily and operate construction machines safely. We evaluate working efficiency by integrating our bird's-eye view system into actual unmanned constuction systems under actual field conditions.
Equivalent non-Gaussian excitation method is developed to obtain the statistical moments up to 4th order of the response of non-Gaussian randomly excited systems. The non-Gaussian excitation is prescribed by the probability density function and the power spectrum. The excitation is governed by the Itôstochastic differential equation. Generally, moment equations for the response, which are derived from the stochastic differential equation for the excitation and the equation of motion of the system, are not closed form due to the complex nonlinearity of the diffusion coefficient in the governing equation for the excitation even though the system is linear. In equivalent non-Gaussian excitation method, the diffusion coefficient is replaced with the equivalent diffusion coefficient approximately to obtain a closed set of the moment equations. The square of the equivalent diffusion coefficient is expressed by a second-order polynomial. The coefficients of the polynomial are determined according to the criterion of minimization of the mean square error between the original diffusion coefficient and the equivalent diffusion coefficient. In order to assess the validity of the present method, a linear system subjected to a non-Gaussian random excitation with the generalized Gaussian distribution and the power spectral density with the bandwidth parameter is analyzed. From the comparison with the Monte Carlo simulations, It is shown that for obtaining the variance and the kurtosis of the response, the proposed method is applicable to the case of the non-Gaussian excitation with a wide range of the kurtosis and the bandwidth. In order to discuss the accuracy of the method, the statistical moments of the equivalent non-Gaussian excitation are also investigated.
Many active seismic isolation systems and active seismic vibration control systems have now being produced to reduce earthquake damage as much as possible by suffering from recent frequent huge earthquakes. Existing active vibration isolation device systems are controlled by computers. They are driven by the commands given to actuator. Those commands are calculated as control inputs using movements of earthquake, building and actuator monitored with electric sensors. These systems have such advantage that the control characteristics can be changed easily by modifying the program algorithm. However, these electronic systems have some points of weakness. Computer itself and software should be updated to the latest model every several years. Small troubles like electrical disconnection, or electronic component parts aging deterioration or malfunction could cause total functional failure. In case the worst case takes place, it might go out of control. To solve this problem replacement of computer control instruction with highly reliable machinery mechanism using no electronic component is proposed in this study. The method of replacement of electronic control with machinery mechanism is as follows. Through link mechanism relative movement displacement between earthquake and building seismic vibration is transmitted to spool as command signal and direction of hydraulic pressure is changed to activate for seismic control
In the transport system of a thin steel plate production line, there is a problem that the quality of the plate surface deteriorates over time because the plate is usually in contact with rollers. Accordingly, studies of electromagnetic levitation technology have been carried out. However, when a flexible thin steel plate is targeted for levitation, levitation control becomes difficult because the thin plate undergoes increased flexure. To solve this problem, we proposed a levitation of a flexible thin steel plate that was bent to an extent which did not induce plastic deformation. Bent magnetic levitation apparatus was developed and bending levitation performance of thin steel plate was examined. Thin steel plates with a thickness of 0.18mm, 0.24mm, 0.27mm and 0.30mm were levitated to evaluate the relationship between tilt angle of electromagnets and levitation probability. Furthermore, to elucidate the optimal tilt angle of electromagnets, shapes of steel plates were analyzed using finite difference method and effective tilt angle was estimated. As a result, levitation probability increased by bending a steel plate to the extent that did not exceed natural deflection angle. Also, the optimal tilt angle of electromagnets can be estimated by shape analysis result and matched the experimental result. In developing the bent magnetic levitation apparatus, the optimal tilt angle of electromagnets was verified.
Palpation is an important diagnostic technique in medicine. However, it is subjective, and successful diagnosis depends on the skill and experience of the doctor. Therefore, a quantitative method for measuring the hardness of the living body and detecting abnormal tissue is desirable. In this paper, we propose a concentrated mass model of the body to analyze its motion in an indentation test. The model consists of masses, connecting springs, connecting dampers, base support springs, and base support dampers. The mass is the mass of the elastic body, the connecting spring is derived from the normal stress, and the base support spring is derived from the shear stress. Furthermore, we develop a method to measure the Young's modulus and the position of abnormal tissue with the model when a column contactor is pressed into the body. To confirm the validity of the method, we measured the Young's modulus of silicone. The measurement results by the proposed method agreed with the value obtained with a parallel disk rotary rheometer. Moreover, our method gave accurate values for the Young's modulus of the second layer of two-layered silicone and the distance from the surface to the second layer. These results confirmed that our method is capable of measuring the Young's modulus of the soft materials and the boundary depth in two-layered objects.
The machine for forcibly stopping a car, enforcement device, is used for prevention of the traffic accident and for the safety securement of a human. However, sufficient investigation and research for the performance improvement of the enforcement device have not been reported. Therefore, it is necessary to understand the characteristics and behavior of the machine for improvement of the collision safety and the reliability of the machine, and optimization of the structure. In this study, collision and stop behavior and braking distance of the enforcement device were investigated for characteristic evaluation. The basic theory for the braking distance was derived using the impulse momentum equation and the law of the conservation of energy. By this basic theory, effective arm angle range of enforcement device was clarified. And also, the collision test was carried out by simple model of the enforcement device and the vehicle. The behavior of the enforcement device was examined by the simple model with 3 kinds of different arm angles. The braking distance by the experiment was well agreement with theoretical result. It is possible to optimize and improve the enforcement device by these evaluations of collision behavior.
In this report, we focus on a maneuvering problem of an amphibian vehicle for rescue, and a novel manueuvering support system for the vehicle on the surface of water is proposed by applying a nonlinear state feedback control law for trajectory control. To simplify the problem, we consider only viscous friction among the external forces and ignore other external forces which are applied to the vehicle on the surface of water. We consider that the vehicle should not drift sideways for an excellent driving performance. Thereby, we propose to employ three ducted fans as additional propulsion devices. Each of the two ducted fans, which are attached symmetrically to the left and right side of the vehicle, has a swiveling function in order to generate a lateral force. The other ducted fan, which is attached to the center rear of the vehicle, generates a longitudinal propulsive force. To design a nonlinear state feedback control law, we define ‘Maneuvering Trajectory’ as a trajectory which is generated by the maneuver of the vehicle's pilot and we construct a Lyapunov-like function for the trajectory control system. Then the feasibility of the proposed system is verified by evaluating the tracking error against a reference trajectory through several numerical simulations.
To reduce the absolute acceleration and displacement of buildings during earthquakes, this paper proposes an optimal control system design method considering structural limitation of a semi-active damper. The semi-active damper incorporates a high and low switchable damping coefficient. The limitation is that the semi-active damper is able to generate control force only in the reverse direction of the velocity. In this paper, the structural passive limitation is considered by geometric relationship between the control force and damper velocity, and the area of desired control force is represented to an equation of an ellipse. By calculating the optimal control force within the limitation, an optimal control system that reduces degradation in control performance is realized. Moreover, it is possible to design the control system based on the structural characteristic and geometric configuration without parameter tuning using design seismic wave. The proposed design method is applied to the base isolated single-degree-of-freedom model with semi-active oil dampers. The control performance of the proposed method is verified through simulation using several kinds of seismic waves.
The method using Gaussian mixture model and moment equations is developed to obtain the probability density of the stationary response of a nonlinear system subjected to non-Gaussian random excitation. The excitation is characterized by the probability density function and the power spectrum. In this paper, the stationary response distribution of the system is approximated by the Gaussian mixture model, which is expressed by the weighted sum of several Gaussian distributions with the different parameters. The parameters in the model are determined according to the moment equations for the response and the excitation. The proposed method is applied to a Duffing oscillator subjected to non-Gaussian excitation with the gamma distribution and the power spectral density characterized by the bandwidth parameter. The analytical results of the stationary response distributions are compared with simulation results. The results show this method is valid for the highly skewed excitation with a wide range of the bandwidth parameter. The influences of the shape of the distribution and the bandwidth of the excitation on the response distributions are also investigated.
Popularity of clean energy vehicles (CEVs) are expected in order to reduce CO2 emissions to mitigate the global warming. However, the popularity provides not only environmental but also economic impacts. An EV requires a battery, but does not require the engine parts any more, which will bring a structural change of the auto parts industry. It is necessary to understand the characteristics of parts used in each CEV type and analyze the economic effects before considering the portfolio for introducing CEVs. In this study, CEV types which have a battery or a fuel cell based powertrain system are considered as well as gasoline, diesel or natural gas engines. This paper proposes an economic ripple effect model using the Input-Output Table. Simulation results show economic impacts in Japan in 2020 and 2030 for the target sales of CEVs assumed by the Ministry of the Environment in 2010. For example, simulation results indicates that production amount in Japan in 2030 is expected to decrease about 1.5 trillion yen compared to 2010.
Design for pitting (surface crack initiated rolling fatigue wear) at rolling-sliding contact surface under mixed lubrication condition is based on the combination of maximum contact pressure (Hertzian stress) and lubrication condition (ratio of surface roughness value and oil film thickness value). However there is indirect relationship in the combination of contact pressure and lubrication condition to the pitting phenomena. The origins of rolling fatigue pit are the micro cracks at contact surface due to tangential force. In this paper, the pitting test results are re-examined from a standpoint of influence of the tangential force on pitting. The new parameter f·(pH/HB)2 based on the friction coefficient estimation formula by Matsumoto for pitting design is introduced. And it is cleared that the new parameter has same value in pitting limit to every different contact pressure and lubrication condition. In conclusion, it is necessary to reconsider the pitting design method for power transmission gears excepted tangential force from consideration.
As a rationalization way of power generating plant construction using three-dimensional measurement, the calculation approach of optimum cutting surfaces of extra length parts which are given at both ends of pipe spools has been developed. In piping work between two pieces of equipment, pipe spools are sequentially welded from one side to the other side. At this time, a little amount of installation error which derives from welding distortion and manufacturing error of each spool is piled up on the piping route. Thus, the last pipe spools which are connected between the terminal equipment and a next-to-last pipe spools, have extra length parts at both ends to adjust the installation error, and are cut at appropriate position at the construction sites. But it is difficult to estimate accurate cutting amount at the construction site because the extra length parts often have to be cut diagonally with respect to original end faces to fit the last pipe spools with high accuracy to existing pipes which have three-dimensional misalignments. So, in this study, the connecting position of the last pipe spools into existing pipes which makes the diagonal cutting angles of both pipe ends even and minimum has defined as the optimum solution, and calculation approach to get the optimum solution has been developed. As results of verification test with using mock up pipes and trial use at construction site, the validity of the calculation approach has confirmed.
In the process plant, random vibration with shell mode excited by the turbulence generated at tee connection might cause problems such as piping damage. Author proposed a new evaluation index in the previous work to evaluate the random vibration with shell mode at tee connection downstream and the adequacy of the index was confirmed by the experiment with 1.5 inch × 4 inch piping system with 45 deg combining tee connection so as to confirm the adequacy of the index proposed in the previous work. This paper presents the experimental study results to investigate the effects of branch size and combining angle. In the experiment the branch area ratio to the main pipe area were varied from 0.0146 to 1.00, and two combining angles, 90 and 45 degrees were examined. As a result, it was confirmed the proposed index could evaluate vibration stress adequately for wide range of the branch pipe area ratio. And the vibration stress for the piping system with 90 deg connection is around 1.4 times of that with 45 deg tee connection.