Experimental investigations were performed on the generation of resonant sound by flow in a pipeline containing two closely spaced orifice plates. The frequencies of the generated tone were scrutinized as the velocity was increased from 3 to 25 m/s. To determine the convection velocity of the vortices formed between two plates, measurements were made of the phase angle of the fluctuating velocity using a hot-wire anemometer. The vortex shedding frequency is locked into the pipe modes, but indicates a slight increase with an increase in the flow velocity. The ratio of the distance between the two orifice plates to the spacing of vortices is expressed by m+ε, where m is an integer and ε is a decimal part. It was found that the value of ε decreases with increasing flow velocity within a range from 0 to 0.5, and a change of the number of vortices or a frequency jump occurs when ε reaches a critical value.

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In this study, unsteady cavitation and cavitation instabilities are numerically analyzed around flat-plate cascade with three blades cyclic condition in water/air working fluid. The numerical method employing an original model “locally homogeneous model of compressible gas-liquid two-phase medium” is applied to numerical simulation. The method can simply treat the entire flow field inside and outside the cavity by one system equations. As a result of numerical analysis, occurrence and oscillation characteristics of three types of cavitation instabilities are reproduced, which are “cavitation surge”, “super-synchronous rotating cavitation” and “rotating-stall cavitation”. Additionally, flow fields around flat-plate cascade with slits on blades are analyzed in the conditions where the cavitation instabilities arise in the cascade without slit. Consequently, the suppression effect of the slit on the cavitation instabilities is confirmed.

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In this paper, we simulate directly the Aeolian tone emitted from a two-dimensional circular cylinder by the finite volume lattice Boltzmann method (FVLBM) using the two-dimensional thermal compressible lattice BGK model with the internal degrees of freedom on unstructured grid. We also introduce a novel third-order upwind scheme for the FVLBM, using quadratic polynomials interpolating two distribution functions and a first differential coefficient of distribution function, and by means of this, we obtain accurate results of the simulation of the acoustic waves that agree well with those by the very accurate computation based on the Navier-Stokes equation using the scheme with higher order accuracy. We show the applicability of the FVLBM to the direct simulation of aerodynamic sound from more complex shaped bodies on unstructured grid.

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For further improvement of indoor environments concerning air and noise pollutions, ventilation is one of the key factors. In this study, we develop the measuring technique of unsteady pressure on a rotating blade surface, to reveal the basic features of a cross-flow impeller. Specifically speaking, we consider the simplest model as the fundamental study, namely, the flow around the cross-flow impeller rotating with flat-plate blades in open space without any casings. On this impeller's blade, we measure the fluctuating pressures, which are discussed in comparison with flow visualizations with the particle-image velocimeter (PIV), velocity measurements by a hot-wire velocimeter (HW) and numerical simulations. As a result, by the compensation of the centrifugal-force effect, we get accurate pressures on the rotating blade, which are conditionally-averaged over a number of periods. The obtained experimental results can be also dedicated to CFD as standard benchmarks.

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Household cogeneration systems have been increasingly utilized for energy saving; however, their energy-saving effect in Japan is not necessarily sufficient due to their operational restriction that electricity generated by them cannot be transmitted to commercial electric power systems due to the regulation. To relax the restriction, the authors propose power interchange operation of multiple household gas engine cogeneration units and investigate its feasibility from the energy-saving viewpoint by an optimization approach. In this power interchange operation, a micro-grid using the units is constructed in a housing complex; electricity generated by them is shared among households without transmitting to a commercial electric power system outside the housing complex so that the operating time of these units may increase. To evaluate the energy-saving effect of the power interchange operation, a numerical analysis of operational strategies by the mixed-integer linear programming is conducted for ten households and three types of household energy supply configurations: the power interchange operation of the gas engine cogeneration units, a stand-alone operation of each gas engine cogeneration unit, and conventional energy supply system without the gas engine cogeneration unit. A computational result clarifies the advantage of the power interchange operation from the energy-saving viewpoint over the other energy supply configurations.

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The flame characteristics of confined flames are investigated for propane and hydrogen jet nonpremixed flames in cylindrical furnaces. The flame characteristics can be strongly dominated by the combination of the burner and furnace geometries. In the present study, the effects of the inner diameter of the cylindrical furnace D₁, the turbulence at the flame boundary, and the global equivalence ratio φ are examined in terms of the emission of NOx. The emission index of NOx, EINOx, decreases roughly with these parameters. The decrease in EINOx is thought to be related to the dilution of mixtures by the burned gas and the flame stretch. The dilution is attributable to vortices formed at the bottom of the furnace, and the flame stretch is attributable to the air velocity difference ΔUa created by two air nozzles. The EINOx characteristics are evaluated by the furnace Reynolds number Re, c based on the inner diameter of the furnace reflecting the dilution and the strain rate S∼Da^-1 based on the air velocity difference, where Da indicates the Damköhler number. The EINOx is well characterized by the factor D₁U_FΔUa, which is proportional to Re, cDa^-1. This result indicates that the confined nonpremixed flame is characterized by the furnace volume, not the flame volume, which is related to the reaction rate of the jet nonpremixed flame with coflowing air based on the flamelet model. This may imply that the furnace combustion should be modified from the flamelet concept owing to the dilution.

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Slip deformation in compatible-type tricrystal models subjected to tensile load is investigated by using a continuum-mechanics-based crystal plasticity analysis technique. Accumulation of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) are studied in detail. Mutual constraint of crystal grains through the grain boundary plane does not occur in the compatible-type tricrystals, however, results of the analysis show non-uniform deformation and high density of GNDs accumulated in the form of band in the crystal grains. The mechanism of non-uniform deformation and formation of GN dislocation structure corresponds to deformation bands in the compatible-type tricrystals is discussed from the viewpoint of the imaginary disclination-type displacement field around the grain boundary triple junction accompanying the multi-body interaction and mutual restraint of shape change of the crystal grain due to the slip deformation in the active slip systems.

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A reduction of environmental burdens is required in recent years to mitigate global warming, ozone layer depletion and etc. in manufacturing fields. Hence, a prediction system of the environmental burdens for machining operation has been developed so far. Hence, an evaluation indicator for “eco-efficiency” of a process and an operation planning is also proposed with considering the environmental burden, a manufacturing time and a total number of workpiece setup times in this research. Global warming is selected as impact category and the feasibility of the developed system and the evaluation indicator for the eco-efficiency is demonstrated in this paper.

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The effects of diesel fuel split-injection on the fuel-air ratio and the gas velocity distribution inside the combustion chamber are numerically investigated using a modified KIVA-3V code that incorporates an Enhanced Taylor Analogy Breakup (ETAB) model into the calculation of spray droplet breakup. The second injection in the split-injection scheme can generate a sudden increase in the flammable mixture area inside the chamber. Among the schemes evaluated, the split-injection configuration in which 75% of the fuel mass is injected during the first injection and the remaining fuel mass is injected after a 1.0-ms dwell is preferred as the optimum configuration with respect to particulate emission reduction. The configuration tends to produce the widest flammable area inside the chamber during the mixing-controlled combustion phase. The dwell duration in split-injection schemes does not have a linear correlation with the area of the flammable mixture. The gas velocity distributions do not change significantly when the fuel injection mass ratio and dwell duration are varied.

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Polymer electrolyte fuel cells, which have been developed for mobile equipment, are mainly direct methanol fuel cells (DMFC). From the standpoint of safety to a human body, it is desirable to use ethanol as fuel. In order to improve the performance of direct ethanol fuel cells (DEFC), it is necessary to investigate the fuel flow pattern in the anode flow channel with many sharp turn corners in the fuel cell, and to improve the channel shape. So, in this study, the velocity distribution of the water flow in a micro-channel was numerically analyzed using the authors' GTT code and the calculated results were verified by the velocity measurement with a line LDV system. For reducing the pressure loss in consideration of the suppression of flow stagnation in the channel, it was attempted to optimize the sharp turn corner shape by three-dimensional numerical flow analysis with a genetic algorithm (GA) and a shape with less pressure loss was found.

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This paper proposes an application of Learning Control algorithm to active control of fan noise. Learning control has been developed for the motion control of robot hand, for which a template of the trajectory is given. The robot learns an appropriate motion sequence by repeating trials of control when the error from the template is fed back to the controller. This control algorithm is transferred to the active control of periodic sound. The advantage of the learning control is found at compactness of the control program and quickness of the error convergence. The control experiment was successfully conducted for the fan noise applying the learning control to the periodic sound components. The experimental result proved the effectiveness of the learning control better than that of LMS feed forward control. In order to enhance the utility of the learning control the effect of the gain matrix to the quality of control is investigated by utilizing the numerical simulation. The trend of efficient matrix is shown numerically.

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A new concept for easy reduction of the sound reflection coefficient at an open duct end is proposed in this paper. If the duct side wall next to the open end is made of an appropriate perforated plate or porous material which can prevent abrupt change of the wall acoustic impedance to the free field condition, it is expected that sound reflection at that open end will be markedly reduced. This phenomenon is analyzed theoretically and proved experimentally. Some parameter studies clarify the optimum wall impedance of the porous side wall. Moreover a model test result shows that this technique is effective for reducing low-frequency sound radiated from a stack, as predicted by the analysis. This technique is useful and applicable to reducing the acoustic resonant factor in ducts, such as plant stacks and engine mufflers. As the result, the resonant sound radiation from an open duct end can be reduced.

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In this paper, we propose a new method for a hammering test by using image and sound signal processing techniques. A method for discriminating a property of an object with the use of generated sound when striking it with a hammer is called a hammering test. However, this method depends on human experience and skills. In addition, if we perform this test over a wide area of objects, it is required to manually record hammering positions one by one. Therefore, this paper proposes a hammering test system consisting of two video cameras that can acquire image and sound signals of a hammering scene. The shape of the object is measured by the image signal processing from the result of 3-D measurement of each hammering position, and the thickness or material of the object is estimated by the sound signal processing in time and frequency domains. The validity of proposed method is shown through experiments.

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In order to prevent global warming, the emission of greenhouse gases must be reduced. One way of enabling this is the effective utilization of green energy, also called renewable energy which necessitates the construction of infrastructure suitable for distributing it. In this study, a new transportation system related to buses is proposed, where the focus is on bus stops distributed in a region. In this system, a bus stop stores the electric power generated from green energy sources installed around it and supplies this power to buses. When a bus arrives at a bus stop, it is intermittently charged with a small amount of electricity, sufficient for it to travel to the next bus stop. The effectiveness of the proposed system is confirmed through a model experiment using a golf cart. The results confirm that the proposed cycling operation is possible by intermittent charge during the short stoppage of the bus, while passengers embark and disembark. The effectiveness of supplying electric power to a bus departing from a bus stop is also confirmed. In addition, the area of photovoltaic modules required at every bus stop is simulated.

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When a high-speed train passes through a hood-shaped short structure (the length along the railway is typically several times as long as the diameter of its cross section), such as an overpass or a snow shelter, “structure-passing waves (SPW),” which are a type of low-frequency noise, radiate from both openings of the structure toward the outside area. The SPW could create an environmental problem of a low-frequency noise along the tracks as train speeds increase, for it steeply grows in proportion to the third or fourth power of the train speed. In this study, model experiments and acoustic analyses were conducted to investigate the generation mechanism of SPW. The run-time required for the present method of analyses is a few seconds, as opposed to the several hours typically required for an entirely numerical approach. The results of the acoustic analyses, based on a method for predicting a compression wave within a hood-shaped structure generated by a passing train, generally agree well with the experimental results of SPW with some exceptions. This implies that SPW can be modeled as a superposition of the pressure waves radiating from both openings of the structure. In addition, our model experiment and acoustic analysis show that the magnitude of SPW tends to depend on train nose/tail profile.

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Experimental and numerical analysis of methanol steam reforming for a fuel cell have been carried out. The reforming catalyst is supported by metal honeycomb to decrease the heat capacity. Conversion performances are improved by segmenting the honeycomb catalyst into several blocks due to the enhancement of mixing of gases and heat transfer at the front edges of segmenting catalyst. Numerical simulation model for methanol steam reforming is developed by changing chemical reactions in the model for exhaust catalyst of internal combustion engines and using a smaller mass transfer coefficient for methanol steam reforming. The calculated results for a plate type methanol steam reformer which generates hydrogen of 7 kW (LHV) are also in good agreement with the measurements. The pattern of heat supply to catalysts and the reformer configuration affect conversion performances. It is predicted that the optimized methanol steam reformer for a 50 kW size fuel cell vehicle has a sufficient compactness.

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To use the pyrolysis residue of paper as an electromagnetic wave shielding structure, an appropriate compounding method was searched for along with a suitable uniting material. As a result, satisfactory strength and electroconductivity were obtained using emulsion resin. Then, we produced an electromagnetic wave shielding structure and examined its characteristics. The source of the electric wave was a cellular phone, and the reception circuit consisted of a germanium diode and a high-luminance light-emitting diode. A voltage depending on the strength of the electric wave is induced at both ends of the light-emitting diode. The reception circuit was places in the structure and the voltage induced at both ends of the light-emitting diode was measured. It was shown that the use of the shield resulted in an attenuation of about 18dB when the thickness of the wall of the structure was 8mm.

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This paper describes a new hybrid vibration suppression technique for flexible structures like beams and plates using piezoelectric elements and analog circuits. There are two main methods to suppress vibration of flexible structures. One is active vibration control and the other is passive vibration suppression. The former is often effective but has a stability problem. While the latter avoids such instability, its controlling force is small. Hence, this paper is proposing a new hybrid vibration suppression method that is stable and effective. The optimum values of the circuit are determined by simple formulations derived by Two Fixed Points Method. The proposed method is verified by experiments that demonstrate that the hybrid method works better than conventional passive vibration suppression methods.

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It is reported that the particulate matter in exhaust gas is reduced when oxygenated agents are added to diesel fuel, but the inhibition mechanisms is not established. To explain this mechanism, we investigates the amounts of particulate formation and analyzes thermal cracking and condensation polymerization components with a fluid reaction tube apparatus and nitrogen atmosphere. As a result of experiment, it became clear that inhibition mechanism of fine grain was different by fuel properties.

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This study examines a three-dimensional (3D) distribution of a magnetic field to obtain an analytical model of magnetic reluctance of rectangular iron cores whose ends face a working air gap in a magnetic system. An analytical solution is obtained without the boundary condition that the magnetic intensity is uniform in the direction of a magnetomotive force at the edge of an iron core's cross-section. Furthermore, the theory of generalized function (or distribution) is applied to convergence of a trigonometric infinite series. Consequently, the solution is an approximation. The magnetic reluctance is obtained from the ratio of the magnetomotive force along the iron-core surface to the magnetic flux. The reluctance is expressed with a part corresponding to a 2D model and a part with ends effect. To assess the model, approximated equations to simplify the calculation are given with numerical examples to compare the model with a 2D model without ends effect.

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