Polymer Electrolyte Fuel Cell (PEFC) is desired to be operated over 90℃ during the period from 2020 to 2025 in Japan. The aim of this study is to clarify the impact of microporous layer (MPL) on the temperature profile of interface between polymer electrolyte membrane (PEM) and catalyst layer at the cathode (i.e., the reaction surface) in a single PEFC with an initial temperature of cell (Tini) from 80℃ to 100℃. An 1D multi-plate heat transfer model based on temperature data of separator measured using thermograph in power generation was developed to evaluate temperature of the reaction surface (Treact). This study investigated the effect of MPL, Tini, flow rate and relative humidity of supply gas on Treact distribution. As a result, it is found that the impact of flow rate of supply gas on Treact distribution is little irrespective of MPL, Tini and relative humidity of supply gas. When MPL is not coated, Treact – Tini is higher by 2℃ - 3℃ and relatively flat compared to MPL coating condition and Treact – Tini with MPL is increased by 1℃ from the inlet to outlet of cell irrespective of Tini and relative humidity of supply gas. In addition, it is revealed that Treact – Tini with MPL is the highest when the relative humidity of supply gas is 40 %RH at the anode and 40 %RH at the cathode, which is the lowest relative humidity condition in this study.
In case pressurized water or vapor leaks from a failed heat transfer tube in a steam generator of a sodium-cooled fast reactor, a high-velocity, high-temperature, and corrosive jet with sodium-water chemical reaction may cause tube failure propagation. In this study, a numerical analysis method to predict the occurrence of tube failure propagation by overheating rupture was developed to expand an application range of an existing computer code. This method consists of the elemental analysis models for a sodium-side temperature distribution formed by a reacting jet, water-side thermal hydraulics, heat transfer of a tube, and tube failure by internal pressure. To evaluate event progress at a shortest computation time, the elemental analysis models of this code were constructed from the experimental data, semi-theoretical correlations, or one-dimensional equations. Applicability of the method was investigated through the computation of an experiment on water vapor discharging in liquid sodium. In this experiment, one tube for water vapor discharging and the 91 target tubes were placed in a liquid sodium pool. Temperature of the target tubes increased by the effect of the reacting jet in this computation. Some of the target tubes near the initial water leak resulted in overheating rupture as with the experimental result. This computation demonstrated that the proposed method could predict the occurrence of overheating rupture and provide conservative results.
In this paper, two-phase flow and ion transportation in an alkaline water electrolysis are discussed with three-dimensional coupling numerical simulation to reveal the influence of a bubble in the alkaline water electrolysis on the cell efficiency to achieve high-efficiency energy conversion of electrical energy to hydrogen energy. Two-phase flow numerical simulation model is not a void ratio model that is mainly used in previous studies, but is a direct simulation model with Lattices Kinetic Scheme that enables microscale flow simulation. Moreover, the concentration distribution is calculated with Maxwell equation and Nernst-Planks equation, and is fully coupled to the three-dimensional two-phase flow. The numerical simulations are conducted for w/o bubble condition and w/ bubble condition with varying applied current density to evaluate the influence of a bubble at various operating conditions. The results show that the bubble in the electrolyte induces mixing flow between a bubble and an electrode, and the concentration of potassium hydroxide (KOH) around the anode is increased. This increase of concentration increases the conductivity of the electrolyte and suppresses the overpotential in the electrolyte. Moreover, the anodic activation overpotential is also suppressed by the increased concentration on the anode. These overvoltage suppressions become much more prominent at high current density operating condition of the cell. The mixing with the bubble changes the concentration around the bubble. However, concentration distant from the bubble also changes and suppresses the overpotential with the change in electrical field.
Understanding of the onset of boiling plays an important role in the design of boiling equipment. Therefore, many studies have been reported so far, but most of these concerned with the upward flow condition. Moreover, the onset of boiling condition in downward flow is complex due to stagnant and/or reverse bubble caused by buoyancy force on thermal-non-equilibrium flow field, thus the correlation for upward flow cannot be applied directly to downward flow. The purpose of this study is to clarify the characteristics of onset of boiling under downward flow. In the experiment, the onset of boiling condition was measured by using several size of test sections under upward and downward flow conditions. Experimental results expressed the typical two kinds of tendencies, i.e. thermal dominant and the thermal-fluid dominant conditions, with the difference of heating length of test section. In the case of thermal-fluid dominant condition, the difference between upward and downward flows was also clearly observed. On the basis of experimental results, the modified Bowring’s and modified Levy’s correlations are proposed for each region, and these modified correlations show good agreements with the experimental results in each condition.
It is necessary to simulate a eutectic melting reaction and relocation behavior of boron carbide (B4C) as a control rod material and stainless steel (SS) during a core disruptive accident in an advanced sodium-cooled fast reactor designed in Japan because the B4C-SS eutectic relocation behavior has a large uncertainty in the reactivity history based on a simple calculation. A physical model simulating the eutectic melting reaction and relocation was developed and implemented into a severe accident simulation code. The developed model must be validated by using test data. To validate the physical model, therefore, the visualization tests of SS-B4C eutectic melting reaction was carried out by contacting SS melts of several kg with a B4C pellet heated up to about 1500 °C. The tests have shown the eutectic reaction visualization as well as freezing and relocation of the B4C-SS eutectic in upper part of the solidified test piece due to the density separation. Post-test material analyses by using X-ray diffraction and transmission electron microscope techniques have indicated that FeB appeared at the B4C-SS contact interface and (Fe,Cr)2B at the top surface of the test piece. Glow discharge optical emission spectrometry has been applied to quantitative analysis of boron concentration distributions. The boron concentration was high at the upper surface and near the original position of the B4C pellet.
The effect of taking a miniature sample scoop on the creep life of ASME Grade 91 (9Cr steel) piping was experimentally assessed. Internal pressure tests were conducted at 650oC on tubular specimens of virgin and long-term used 9Cr steels having scoop on the outer surface, which simulate taking a sample scoop. When the ratio of scoop depth to wall thickness of the specimen was 8%, the creep life decreased to 85% of that of scoop-free specimen. On the other hand, no creep life reduction was observed in the materials with the depth ratio of 5%. Finite element analyses were conducted on the tubular specimens under the test conditions and actual-size piping under actual service conditions, where the ratio of the scoop depth was about 5% in both cases. The stress and strain concentration states near the scoop of the actual-size piping were almost the same as those of the tubular specimens, indicating that the test results were valid for the actual piping. Thus, it was concluded that taking a miniature sample to a scoop of up to 5% of the thickness of the steel has a negligible effect on the creep life of the piping.
In order to reduce CO2 emission from coal-fired boiler, it is expected that ammonia is used as a fuel which has no carbon content. In that case, it is concerned that NOx concentration in flue gas increases because ammonia has more nitrogen content than coal. In this study, with 10 MWth test furnace, ammonia and pulverized coal co-firing test was conducted with ammonia velocity as a parameter at 20 % co-firing rate. The result shows that NOx concentration in flue gas of co-firing is as same as that of single coal combustion. In addition, co-firing test for evaluating effect of two-stage combustion ratio, heat input and fuel ratio on NOx was conducted. The results show that condition for reducing NOx concentration in ammonia co-firing is clarified.
A film-laminated microfluidic device was fabricated to analyze an electrode slurry used to form a porous electrode of polymer electrolyte fuel cells, and sorting of particles in the slurry was demonstrated. The electrode slurry contains carbon black and polymer electrolyte. Agglomerated particles in the slurry can affect the porous structure, which contains micro-cracks, surface roughness, and inhomogeneous pore size distribution, and resultant cell performance. The agglomerated particles settle down faster than small particles based on Stokes’ law. Therefore, in the present study, the microfluidic device, which has a flow channel with top and bottom branches of inlet and outlet in the direction of gravitational force, was used to sort agglomerates. A silica slurry was supplied, and the sorting of single-micrometer scale particle was demonstrated. The sorted particles in the flow channel were observed by optical microscopy. Sorting efficiency decreased with increasing flow rate. This result was consistent with a numerical simulation. Electrode slurries with/without ultrasonication were supplied to the microfluidic device and were evaluated in the same way. A large number of the agglomerated particles were successfully sorted to the bottom branch of the outlet. The slurry with ultrasonication showed a smaller number of agglomerated particles than the slurry without ultrasonication because the agglomerated particles were broken down into smaller particles by generation and demise of cavitation in the ultrasonication process. The extracted agglomerates were directly observed by scanning electron microscopy. Agglomerated particle size was in several single micrometers.
Reducing CO2 emissions by the effective use of renewable energy is one of the most important issues around the world. Therefore, many researchers have analyzed not only the development of individual high-performance equipment, but also the area-wide energy utilization systems. One of the area-wide energy utilization systems is a district heating and cooling system. However, conventional systems that utilize the steam and chilled water produced by the boiler and the chiller have some issues. Hence, the CO2 network system has been proposed by researchers in EPFL, Switzerland. The system uses the latent heat of CO2 refrigerant to transport and exchange unused heat to specific areas by employing decentralized heat pumps on demand-side. The proposed system is expected to significantly reduce energy consumption compared with the conventional system. In this paper, we analyzed the energy-saving effect by introducing the system to Japan based on CO2 emissions reduction in 2030. As a result, it was confirmed that the annual energy consumption and CO2 emissions resulting from equipment operation could be reduced by about 80% and 60% compared with the conventional system. By using the surplus electric power from renewable energy as the power supply source of the proposed system, it contributes to the construction of the optimal system for energy interchange.
Sodium fire is one of key issues in sodium-cooled fast reactor (SFR) plants. JAEA has developed sodium fire analysis codes, a zone model code SPHINCS and a field model code AQUA-SF, to evaluate the consequence of sodium fire events. This paper describes a PIRT (Phenomena Identification and Ranking Table) process for sodium fire events. Ranking table for important phenomena and an assessment matrix are completed. Because a sodium fire event in an SFR plant involves complex phenomena, the ranking table has been established through both element- and sequence-based phenomena analyses in addition to the engineering judgement. The assessment matrix confirms sufficiency of experimental data for validation of models corresponding to the identified important phenomena in the sodium fire analysis codes. As a part of comprehensive validation based on the assessment matrix, an experimental analysis for a large-scale sodium spray fire experiment Run-E1 is conducted by using the SPHINCS and AQUA-SF codes. The analytical results of the both codes show good agreements with the experimental data of gas pressure transient. Difference from the experimental result of the maximum pressure are about 5% smaller in the SPHINCS code and about 10% larger in the AQUA-SF code. General validity for the codes would be confirmed through the comprehensive validation based on the assessment matrix.
The hybrid ocean thermal energy conversion (OTEC) cycle is a combined system of a desalination and an OTEC, which generates power using the temperature difference between the surface and depth in the ocean. The system will produce the electric power and the distilled water from seawater, simultaneously. This cycle uses low pressure steam as warm heat source generated by a flash evaporation in vacuumed condition instead of flowing the surface seawater. This method has advantages: to prevent the performance degradation of the evaporator caused by the fouling due to marine organisms, to improve the heat transfer, and to allow to use the stainless steels instead of the titanium for an evaporator of OTEC for cost reduction. In this study, the parameter analysis was conducted to examine the effect of the working fluid flow rate and the evaporator heat transfer performance on the net power generation, water production ratio, and exergy efficiency based on concept of the finite-time thermodynamics. As the results, the evaporator heat transfer performance increases the power output, the exergy efficiency, and the maximum performance in each condition are increased, respectively. Notably, the maximum net power output is proportional to square of difference between a root of warm seawater temperature and a root of cold seawater temperature, whereas the water production ratio is proportional to temperature difference between a warm and a cold heat source temperatures.
Various bonding materials have been developed for power semiconductor products. However, the fatigue characteristics of many of these materials are difficult to evaluate uniformly using a conventional test, and this difficulty represents an obstacle to ensure proper material selection. In this report, we developed a new experimental method that can evaluate the fatigue properties of thin bonding layers. The conclusions of this report are shown below. (a) In developed method, the specimen with bonding layer is subjected to a two-way, four-point bending load. This method enables an evaluation even for a bonding material that can form only a thin layer. Furthermore, our method enables carrying out a fatigue test without any additional deformation even when substantial creep or ratchet deformation occurs in the bonding material. The high-speed examination is also possible to obtain high-cycle fatigue strengths. (b) We conducted a fatigue test on a Sn3.5Ag0.75Cu solder bonding layer. The results were that the fracture mode was good agreement with an actual joining structure. Moreover, the fatigue life obtained by our method in this test range followed the Coffin-Manson rule with high accuracy. (c) We found the relationship between the strain of bonding layer and the fatigue life using finite element analysis. The result was that the fatigue life curve of bonding layers was good agreement with that of bulk materials.
For stringent cost reduction with sufficient safety of a high pressure hydrogen tank made by carbon fiber reinforced plastic (CFRP) installed in a fuel cell vehicle, a method to precisely predict the burst pressure of the tank has been intensely required. CFRP layers in the tank consist of complicated meso-structures with carbon fiber bundles and matrix resin, in which crimps of the bundles are stacked by a filament winding process. We propose a method to predict the burst pressure by zooming analysis of conventional axisymmetric continuum model of the whole tank with the meso-scale model. The proposed method is validated through the burst test of tank with accurate prediction of the burst pressure by means of the carbon fiber rupture in the meso-scale model.
Thermal barrier coating (TBC) is deposited onto the surface of gas turbine blade in order to prevent from a high-temperature combustion gas flow. Crack and delamination of ceramic top coating (TC), which come from a high heat flux loading, are serious problem in TBC. In this study, the rapid thermal cycling device based on a laser irradiation was developed. It was then investigated how those damages progress in TC subjected to rapid thermal cyclic loading based on the cross-sectional observation and the monitoring of acoustic emission (AE). As a result, a sintered layer was formed beneath the surface of the TC. It was also found that both vertical and horizontal cracks were initiated and propagated in TC. The monitoring of AE revealed that these cracks are initiated in cooling periods and vertical cracks are also formed in TC at early stage of thermal cycles. In addition, AE counts were strongly related to maximum temperature condition. Finally, mechanical factors of those damages were discussed based upon theoretical evaluation using the TBC model including the sintering phenomenon. It was identified that the damage was initiated with temperature gradient in the TC for early stage of thermal cycles and was progressed with a tensile stress accumulated due to sintered layer formation for later stage.
Measurements in the wake of a heated cylinder are made by a thermo-anemometer. The purpose is to make clear the effects of buoyancy of heated cylinder on the mechanism of momentum transportation in the wake. In this work, the diameter of the cylinder is D=0.030 m, Reynolds numbers ReD=U0D/ν are 3000～10000, Δθ=0～225 K and Richardson number RiD=gβΔθD/U02=0～0.0568. The causes of antisymmetric configuration in the horizontal heated cylinder wake are the downward motion of the vortex streets in upstream sections, and in downstream sections, the upward stretching of upper side vortices due to buoyancy. The antisymmetric wake configuration, caused by heating, affects on the mechanism of momentum transportation. In the upstream sections, velocity fluctuation at the vortex shedding frequency fc plays an important role in the momentum transportation, but in the downstream sections, the breakdown of the shedding vortices are accelerated by heating, and the main contribution to the momentum transportation supersedes by velocity fluctuations at frequencies lower than fc.
Imbibition of single droplet onto porous surface can be observed in engineering devices such as the oil mist filter, inkjet printings, etc. This two-phase flow is governed by physical properties of liquid and porous media. When the droplet size is comparable to the pore scale, the droplet behavior additionally depends on the structural characteristics of the porous media, which has not been clarified yet. It requires to consider not only the physical properties of two-phase flow but also the solid structure. We employed the phase-field lattice Boltzmann method (PFLBM) to compute the two-phase flow on the complicated structures. Since the conventional PFLBM has less precision in the solid representation, wettability and the phase volume consideration on curved boundaries, we improved this method by employing hybrid interpolated bounce-back scheme in the three dimensional system with considering wall normal direction geometrically. It shows the reasonable droplet behavior on a flat plate inclined from the grid line. A static droplet on a sphere is represented by the reasonable position and shape of the contact line. The phase-volume error derived from the conventional interpolated bounce-back is successfully suppressed. Next, the characteristic of the droplet entrapment and/or infiltration by isotropic open cell (Kelvin cell) porous media is numerically studied. It is found that the threshold wettability exists between entrapment and infiltration regardless of the surface topology of the porous media. As the droplet size becomes smaller, the effect of the porous surface becomes remarkable in the threshold contact angle and infiltration ratio at higher contact angle. In case of the droplet entrapment above the porous surface, the lyophobicity of the porous surface becomes remarkable, which merges to the given contact angle at the super-lyophobicity due to the less wetted ligaments.
The vibrational and rotational temperatures in a spark-discharge plasma were measured using optical emission spectroscopy in the cylinder of an engine operating at 1000 rpm. Based on the observed spectrum, the nitrogen molecule emissions from 370 to 385 nm were measured in an air atmosphere without fuel injection. The plasma temperatures were estimated by fitting a theoretically calculated spectrum. When the spark discharge timing was retarded, an unknown band head (different from that corresponding to nitrogen molecule emissions) appeared. This made temperature estimation difficult. Two experiments were performed in an attempt to examine the origin of the unknown band head. One involved using a pure nitrogen atmosphere, instead of air, in the cylinder. However, due to the appearance of a strong nitrogen ion band head, part of the nitrogen molecule spectrum could not be identified. The second experiment addressed the emissions from the spark plug electrodes. The band head was presumed to be a result of emissions from Fe, Ir, Rh, and Cr. The experiment was performed using a spark-plug with electrodes with reduced amounts of these elements. The band head for temperature measurement was hidden by unknown band heads. As a result, estimation of the temperatures in the plasma was not possible later than the discharge timing of 60 ° BTDC. At a discharge timing of 60 ° BTDC (ambient pressure = 0.25 MPa, ambient temperature = 390 K, flow rate = 20 m/s), the vibrational temperature in the spark-discharge plasma was 9200 K while the rotational temperature was 2300 K.
The present numerical investigation deals with the natural convection in a vertical cylindrical enclosure with a water-based Al2O3 nanofluids. The enclosure with an aspect ratio of 1 (= diameter / height) is filled with Al2O3-water nanofluids or pure water. These fluids are isothermally heated from below and cooled from above, while the sidewall is thermally insulated. Both fluids are assumed to be Newtonian and incompressible, with laminar flows. In addition, Al2O3-water nanofluids are assumed to be a single-phase (homogeneous) fluid, due to the extremely tiny particles and very low volume fraction of the suspended nanoparticles, even though nanofluids are a mixture in which nanoparticles are dispersed in a base fluid. Thermophysical properties of Al2O3-water nanofluids are estimated by the experimental correlation equations reported by Khanafer and Vafai. The main objective of this numerical investigation is to clarify the influences of the reference temperature, the nanoparticle diameter, the volume fraction of Al2O3 nanoparticles, and the Rayleigh number on the convective heat transfer of the one-sided natural convection of Al2O3-water nanofluids induced in the enclosure. Transient three-dimensional numerical results are presented over a wide range of reference temperatures (θ0 = 293.15, 303.15, 313.15 K), nanoparticle diameters (dp = 25, 50, 100 nm) , volume fractions of Al2O3 nanoparticles ( φp = 0 - 0.04), and Rayleigh numbers (Ra = 104, 105). Furthermore, the convective heat transfer characteristics of the unique one-sided natural convections of Al2O3-water nanofluids and water are presented by the average Nusselt number, isotherms, and particle paths. Comparison between the one-sided natural convection of Al2O3-water nanofluids and that of water shows that the deterioration of the natural convective heat transfer of Al2O3-water nanofluids is observed with the decrease of the nanoparticle diameter and with the increase of the volume fraction of Al2O3 nanoparticles under three different reference temperatures and two different Rayleigh numbers. However, the degree of deterioration depends on the reference temperature and the Rayleigh number.
An effective method for handling turbulent fluctuations in temperature and in partial pressure of infrared-active gas is proposed in order to make a fairly accurate simulation within feasible calculation load in relation to radiative heat transfer in the large-scale hydrocarbon flame formed in industrial furnaces. As for the case of large-scale turbulent hydrogen flame in industrial furnace, an effective method for handling turbulent fluctuations has been proposed and verified in our previous papers. And yet, it’s applicability to large-scale turbulent hydrocarbon flames has not been confirmed. In this paper, the abovementioned method is examined as to the applicability to hydrocarbon flames, and then, an improved method is proposed. In regard to the method proposed in our previous papers to reduce the enormous calculation load contingent on detailed non-gray analysis like line-by-line analysis, it’s validity is easily confirmed not only for hydrogen flames but also for hydrocarbon flames. On the other hand, the method proposed in our previous paper for reducing the calculation load required for tracing turbulent fluctuation in temperature in great detail cannot give satisfactory results in relation to the large-scale hydrocarbon flame. So, in this paper, major attention is concentrated on the improvement of our method for reducing the calculation load associated with detailed trace of turbulent fluctuation. The assumption that temperature fluctuations of arbitrary two positions are independent from each other and the treatment of energy radiation associated with turbulent fluctuation are maintained also for hydrocarbon flames. In contrast, the treatment of fluctuating absorption is changed from the case of hydrogen flames. While the temporal mean amount of absorption is evaluated using the absorption coefficient at temporal mean temperature in the case of hydrogen flames, such value is evaluated using the temporal mean value of instantaneous absorptance. Validity of the improved method is examined on a model optical path imaging the typical course of radiative energy in large-scale industrial furnaces fueled by propane. It is indicated by examination that the error caused by improved method is satisfactorily smaller than that caused by entire disregard of turbulent fluctuation of temperature and gas composition. Moreover, this improvement related to the treatment of turbulent fluctuation is satisfactorily valid even if coupled with our efficient method for treating complicated spectrum of absorption coefficient.
Unstable behavior of hydrogen-air lean premixed flames was studied by numerical calculations of two-dimensional unsteady reactive flow to clarify the effects of unburned-gas temperature, heat loss and scale. We adopted the numerical model containing the detailed hydrogen-oxygen combustion with 17 elementary reactions of 8 reactive species and a nitrogen diluent, compressibility, viscosity, heat conduction, molecular diffusion, and heat loss of Newtonian type. A disturbance with sufficiently small amplitude was superimposed on a planar flame to obtain the relation between the growth rate and wave number, i.e. dispersion relation, and the linearly most unstable wave number, i.e. critical wave number. As the unburned-gas temperature became lower and the heat loss increased, the growth rate decreased and the unstable range narrowed. These were due mainly to the decrease of flame temperature and burning velocity. To study the characteristics of cellular flames, the disturbance with the critical wave number was superimposed. The disturbance developed owing to intrinsic instability, and then the cellular shape of flame fronts appeared. The burning velocity of a cellular flame normalized by that of a planar flame became larger as the unburned-gas temperature became lower and the heat loss increased. The burning velocity of a cellular flame became monotonically larger with an increase in scale. This was because that the long-wavelength components of disturbances affected the unstable behavior of cellular flames.
The number of speed changes of stepped automatic transmissions (ATs) for vehicles is increased in order to optimize the operating points of internal combustion engines. As a result, the mechanical structure of ATs has become increasingly complex. This advanced complexity leads to torsional vibration in ATs. Computational simulations are carried out utilizing the one-dimensional model of the powertrain of the vehicle. The simulation results show that the torsional vibration level does not decrease proportionally with the acceleration of engine speed; the reason for this remains unknown. From the detailed investigation of the simulation results, it was observed that the idle parts and clearances in the AT caused the nonlinear torsional vibration in the powertrain. The idle parts periodically collide with the main geartrain in the AT synchronizing with the engine torque, and work as the active damping. As a result, the torsional vibration in the powertrain is suppressed. On the other hand, when the idle parts do not collide with the main geartrain in the AT, the torsional vibration level in the powertrain becomes equal to that of the model which originally did not contain idle parts. From the relationship between the period of the engine torque and the clearances in the AT, the angular velocities of the idle parts are derived for the periodic collision between the idle parts and main geartrain in the AT. The experimental results of the motor bench show that the nonlinear torsional vibration occurs in the experimental AT.
In this paper, we propose the active noise control method for the same phase sources distributed on the circle. These sources, which have zero lobe mode, is radiate from the duct fan without attenuation in the duct. Therefore, noise control is need for these sources, which have zero lobe mode. At first, we propose the first ANC method with two control speakers set outside of the duct. This method assume the virtual sound source, which imitate the same phase sources distributed on the circle, is set on the center of the duct edge. We verify this assumption is proper for the same phase sources distributed on the circle with the numerical simulation. Second, we propose the second ANC method with more than three control speakers, which imitate the characteristic of the same phase sources distributed on the circle correctly to improve the attenuation effect. Moreover, we propose the index of the attenuation level. The numerical simulation confirms the validity of the proposed index for the second ANC method. In addition, we verified the attenuation effect of the second ANC method is higher than the first ANC method. The points of these methods to attenuate zero lobe mode are the number of the control speakers are less than conventional method and control speakers are set outside of the duct with considering the sound power attenuation.
It is necessary to separate the multiple resonance frequencies of a vehicle body from outstanding peaks of excitation spectrum to reduce the road induced noise of cars. A vehicle body is always excited by the transmitted forces from a chassis system, and worse the transmitted forces change in real time with road surfaces. Therefore, we suggest that semi-active control of the vibration characteristics of a car body is useful for reducing road induced noise of cars. In this paper, we derived a design method of joint stiffness for simultaneous placement of multiple resonance frequencies. Specifically, we have focused our efforts to make an eigenvalue of a kernel compliance matrix to zero at the assigned natural frequencies by changing the joint stiffness connecting a main system and a subsystem. Consequently, it is enabled to control the multiple resonance frequencies of a whole structure with low computational cost.
The dynamic stability of rectangular flexible plate often becomes a problem. As the flexible plate, the papers in a high-speed printing machine, the thin plastic, the thin metal, the fluttering flag and the oscillating doom roof are enumerated. In this paper, the dynamic stability of cantilevered rectangular plate is estimated in three-dimensional model. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. This fluid pressure is determined by using the integral equations for the pressure along the span and the pressure along the chord under the boundary conditions in the Fourier space. The lateral deflection of plate is assumed to be expressed as a product of the cantilevered beam mode in the streamwise direction and the free-free bending beam mode in the spanwise direction. Applying the Galerkin method for the equation of motion of an elastic plate, the three-dimensional coupled equation of motion of a cantilevered rectangular plate is derived. The complex eigenvalue analysis is performed for the stability analysis. Changing the mass ratio and the aspect ratio, the root loci, the vibration modes of the plate and the fluid pressure are investigated. And, the relationship between the critical fluid velocity and the mass ratio taking the aspect ratio as a parameter is investigated.
This paper deals with the vibration quenching problem of the single-degree-of-freedom system with a limited power supply using a Hula-Hoop and displacement magnification mechanism. This system is forced by the centrifugal force of rotating unbalance. If the unbalance is small, the amplitude of vibration of the main system becomes small and Hula-Hoop does not rotate. Therefore, the vibration of main system is not quenched. To solve this problem, the two types of displacement magnification mechanisms are adopted, namely, the one is the mechanism using beams with fixed ends that move and the other is that using cantilever. The quenching effects and the quenching frequency regions are studied. Following was made clear by the numerical integration of the equation of motion and the experiment: (1) The main system is quenched well by enlarging the displacement at the rotational center of Hula-Hoop using each type of displacement magnification mechanism. (2) The optimal vibration quenching condition of the Hula-Hoop and the displacement magnification mechanism for the first mode is obtained. (3) The frequency regions suitable for vibration quenching are the regions those are higher than the natural frequencies. (4) The vibration mode and the phase relation between unbalance and Hula-Hoop are made clear in each vibration mode. (5) The characteristics of the solutions obtained by the numerical integration method coincide qualitatively with those of the results obtained by the experiment.
In this paper, sound absorption properties of poroelastic lattice structure are investigated through numerical simulation and measurement. The lattice structures discussed in this paper are composed of slender beams only (BCC) and beams and shells (BCC-S), and can be fabricated by using the selective laser metal melting machine. In our numerical investigation, the homogenization method is used to calculate a macroscopic elastic tensor for a solid phase, an equivalent density and a bulk modulus for a fluid phase. Also, the sound absorption coefficient for normal incidence can be calculated by using these macroscopic parameters. The obtained numerical result of the sound absorption coefficient agrees qualitatively with the experimental result. In particular, it is found that the dense BCC-S structure attains sufficient sound absorption capacity in comparison with other conventional sound absorption materials.
In this paper, we consider transporting a liquid container on a cart containing an active vibration reducer, which has a parallel linkage mechanism with six degrees of freedom. Sloshing in the liquid container is generated by the movement of the cart running on an uneven road. To damp the sloshing, the liquid container is tilted and moved horizontally by using the active vibration reducer. The damping control system consists of both disturbance suppression control (DS) and a frequency-dependent optimal servo (FS). The acceleration added to the container while the cart is running on uneven roads is reduced by using DS. The residual sloshing is suppressed by using FS. In this study, only (1, 1) mode sloshing is modeled as a pendulum-type sloshing model in the control system. When a suddenly changing acceleration is added to the liquid container, higher-mode sloshing that is not modeled in the control system is easily generated and causes spillover. DS is also useful to avoid this phenomenon. The weighting matrix of the quadratic performance index for FS is efficiently determined using a genetic algorithm (GA). The amplitude of sloshing is considered for GA fitness. Further, the usefulness of the proposed control system is verified through an experiment. Using both DS and FS, the damping performance improves by approximately 79% compared to without control, and 18% compared to using FS alone.
In this paper, we propose a new method to identify the error factors between an actual structure and the finite element (FE) model. The FE model updating using sensitivity and optimization algorithm conventionally is used to ensure high accuracy. Parametric design variables such as thickness and elastic modulus are adopted as updating variables in many cases. However, their application is limited because the actual error factors are often non-parametric variables. The existing concept of utilizing the driving point frequency response function (FRF) has often been applied in engineering. With this technique, the driving point FRFs of the actual structure and FE model are compared to determine the error factors. However, it is difficult to accurately recognize such factors. This is because FRF is calculated from time history, which includes the reflection wave of the entire system. To overcome this limitation, a new method is proposed that involves the use of driving point transient response. When a particular component is excited, its vibration propagates as a wave that moves toward the entire system. The driving point transient response is measured immediately after excitation and is restricted to the excited component only. The comparison of the driving point transient response of the actual structure and the FE model response enables us to determine if the excited component is the cause of the error. To determine the contribution of the excited component to the transient response, a time domain mutual mean compliance is used. As an application, the proposed method using the driving point transient response and the mutual mean compliance is applied to a simple beam structure.
In this study, Ti-6Al-4V alloy was machined at high cutting speed of 200 m/min, and the tool wear progress and the cutting mechanics were experimentally investigated in order to clarify an effective cooling method. The cooling method used in this study was five kinds of cooling method, namely dry, wet, oil-mist, water-mist and oil-water-mixed. The mist was supplied by MQL device. The quantity of water and oil can be regulated in this device. The tool wear was measured in each experimental condition. And the relation between the tool wear and the chip length was investigated. The results obtained as follows: In the cutting with the TiAlN coated cemented carbide tools at the cutting speed 200 m/min, the wear progress in the oil mist cutting and oil-water-mixed cutting were slower than that in dry and wet cutting. Adhesion of the chips on the tool was prevented by the lubricating oil-mist and the air compressed blew the chips. And the proper amount of the water in the oil-water-mixed mist was important condition. Tool wear was progressed easily because the thermal shock in case of the wet condition and the large quantity of the oil-water-mixed mist conditions. The connection of the chips got longer as the tool wear was increasing.
The kick-start is one of the commonly used block start techniques in competitive swimming. Since swimmers push off first with the rear leg and then with the front leg during the kick-start, leg extension timings relative to the rear leg push-off would affect horizontal take-off velocity. The purpose of this study was to investigate the effects of leg extension timings during kick-start on swimming start performance. Based on the empirically obtained human body kinematic data during kick-start, the whole body was modeled as nine rigid-body segments to simulate kick-start performance for five Japanese collegiate male swimmers. Front leg extension timing was adjusted by shifting the time-series data of the front foot segment, front lower segment and front thigh segment angles were shifted 0.01 to 0.04 sec (T-0.01 to T-0.04) earlier from the original data (T0). The kick-start motion was simulated using both forward and inverse kinematics under some simplifying assumptions with geometric constraints. As a result, the horizontal take-off velocity increased for three swimmers, whereas it decreased for the other two swimmers when front leg extension timing became earlier. The vertical take-off velocity and take-off angle increased as front leg extension timing became earlier. These results indicate that front leg extension timings would either positively or negatively affect horizontal take-off velocity depending on vertical take-off velocity. Therefore, for the swimmer take-off downward, earlier front leg extension timing would allow them to generate a greater horizontal take-off velocity on kick-start.
Studies to develop understandings of rolling noise, which has great influence on wayside noise in the frequency range 250 Hz to 4k Hz, have been carried out widely by measurements and theoretical models. In some studies, when a train runs on a gentle curved track, wheel/rail noise is greater by more than 5 dB. And, it is found that this is closely related to noise at higher frequencies above 10 kHz (referred to as high-frequency noise), which is different from squeal noise, e.g. mechanism due to contact between inside rail and wheel tread. Such high-frequency noise is observed on both low-speed (160 km/h at most) and high-speed railway lines. Previous studies in Japan found that, on a low-speed railway line, the dominant sources of high-frequency noise are the wheels on the outside rail. But, on a high-speed railway line, the characteristics of the high-frequency noise generated in the curved section remained unclear. In this paper, the contribution of the high-frequency noise to wayside noise on a high-speed railway line is investigated in field tests and static experiments, the latter involving shaker excitation. It is found that, during the passage of a train, the wheels on the outside rail are the dominant noise source. And, the wheel noise is found to depend on the train speed. Furthermore, source localization related to the wheel noise above 10 kHz is carried out through field tests with a directional microphone. These results show that the wheel noise above 10 kHz is mainly generated by the outside leading wheel of each bogie.
The characteristic scenario of the Hiyari-Hatto event (i.e., a near-miss incident) wherein a driver is making a right turn is extracted from the Near-Miss Incident Database created by the Smart Mobility Research Center of the Tokyo University of Agriculture and Technology. It is confirmed that in this scenario, there exists a human error: the driver did not notice the pedestrian although the pedestrian is within the driver's field of view. Closer observation of the driver's eye movements reveals that the driver's line of sight is fixed once the driver starts making a turn. Using a novel and unprecedented measurement method, the time at which the driver recognizes the pedestrian can be pinpointed. This method is tested through the driving simulation experiment at an intersection with traffic lights, and the results confirm that there is a high possibility that the driver can miss the pedestrian after the driver starts making a turn.
In order to avoid an obstacle automatically for an automated vehicle, this paper investigated a method to generate a target trajectory using a clothoid curve and to control the vehicle. Although a mathematical constraints or a potential methods are often used to generate the target trajectory for an obstacle avoidance, it requires trial and error and experience, and it is also necessary to consider the vehicle’s drivability. The clothoid curve is often used for a road curve design, therefore, the curve is considered to be suitable for the characteristics of a vehicle driving. Although a clothoid curve passing through a target point is necessary for obstacle avoidance, such clothoid curve is often obtained by trial and error. Therefore, the numerical analyses were executed to obtain the characteristics of the clothoid curve, then, the method was investigated to generate the clothoid curve to pass through the target point. Furthermore, a method to generate a target avoidance trajectory was also investigated expanding the generated clothoid curve based on the traveling characteristics of a vehicle. For driving on the target trajectory satisfactory, both the position and turning angle of the vehicle are controlled by means of a steering manuplation. The controller was constructed using a 1-input 2-output system, therefore, it is very difficult to satisfy both value at the same time. Furthermore, it is also necessary to consider a nonholonomic characteristics of the vehicle. From these point, this paper investigated the optimal control using nonlinear least square probrem sequential quadratic programming(NLSSQP) by means of the time behaviour of input and output in the evaluation value. Well expected results are obtained and shown in the simulation and the experiment.
Rail corrugation that causes the vibration and the noise is a phenomenon in which roughness patterns of approximately regular wavelengths are formed on the rail running surface by trains running. In the previous paper, we have already explained the growth mechanism and the wavelength determination mechanism of the rail corrugation from the dynamic point of view and verified their validity by comparing them with the field data. In this paper, we verify three influence factors of the elastically supported beam model left as subjects in the previous paper. As a result of analyses, it is confirmed that when the track structure is usually used type, the effect of the rail axial force on the growth mechanism of the rail corrugation and the error compared with the analysis results by the model of the moving coordinate system are negligible, and the analysis by the elastically supported beam model is valid including at near the anti-resonance frequency of the elastic support track system.