In order to apply the high strength steel sheet with tensile strength is above 1200MPa, it is necessary to assess the delayed fracture susceptibility caused by hydrogen entering from the environment where steel components are exposed, and also necessary to adopt proper evaluation method of the delayed fracture. In this study, to clarify the influence of various experimental methods on delayed fracture susceptibility of high tensile steel sheets, slow strain rate technique (SSRT), constant load test (CLT) and conventional strain rate technique (CSRT) were demonstrated using commercial high strength steel sheet, and the fracture surfaces were observed. The results show that fracture stress decreased with the increase in the diffusible hydrogen content, and the fracture limit curves of SSRT and CLT were almost the same, whereas that of CSRT shifted to higher stress level. The area fraction of brittle fracture of SSRT, which is the sum of intergranular and quasi-cleavage fracture, increasing with the diffusible hydrogen content, is almost the same as that of CLT, however the area fraction of brittle fracture of CSRT is lower. It is supposed that SSRT and CLT owe to accumulated hydrogen concentration and CSRT owes to accumulated less than that of the others. Thus, both SSRT and CLT are suitable methods to assess the delayed fracture susceptibility; SSRT is superior to the point of testing time, and CLT is superior to the point of reproducing the environments. However, CSRT is suitable to classify materials susceptibility of the delayed fracture immediately on the condition of high diffusible hydrogen content.
The mechanical properties of bio-absorbable plastics, which is used as a bon fixation, change in the body because the plastics is hydrolyzed under the body environment. Theoretical prediction of the bio-degradation process will be useful for the medical application of these materials. Thus, a simple analytical model to predict hydrolytic characteristics of polymeric materials is necessary. In this study, several samples of poly(lactic acid) with different initial molecular weights, crystallinity and sample sizes were immersed in a phosphate buffered solution and the changes in the molecular weight and crystallinity were investigated. Theoretical analyses on the variation of these properties were performed and the results were compared with the experimental data. It is clarified that the theoretical results have successfully predicted the bio-degradation process of poly(lactic acid).
In this study, sprayable fast-responding pressure-sensitive paint (fast-PSP) with low temperature sensitivity has been investigated. Fast-PSP has a porous binder composed of a polymer and nanoparticles to enhance the oxygen diffusivity. However, it is known that higher mass content of nanoparticles in the porous binder causes an increase in temperature sensitivity of fast-PSP. To develop fast-PSP with a temperature sensitivity of less than 1.0 %/K and a response time of less than 100μs, we employed poly(trimethylsilyl)propyne (poly(TMSP)), which is a glassy polymer with a large free volume and has the highest-oxygen permeability among the existing polymers, as a polymer. Three different nanoparticles of mesoporous silica, boron nitride (BN), and titanium silicon oxide were mixed with poly(TMSP) at various particle mass contents to form porous binder. We investigated the effect of particle type and particle mass content, dye concentration, and binder thickness on the static and dynamic characteristics of PSP. The newly developed fast-PSP successfully achieved a low temperature sensitivity of 0.7 %/K even at a fast response time of less than 100 μs when poly(TMSP) and mesoporous silica were mixed at particle mass contents of 50 to 60 wt%, and the binder thickness was 2 - 5μm.
The cavitation cloud generated by submerged high-speed water jet has periodicity. The periodicity is provided by alternately repeating the bubbles generation and shedding process and cavitation nucleus filling process. Therefore, the construction of the filling process allows control of the shedding frequency of the cavitation clouds and may improve the aggressive intensity of the cavitating jet. In this paper, the water flow holes were provided at the nozzle throat outlet in order to form a stable and continuous filling flow. The aggressive intensity of this nozzle was compared by the mass loss of JIS A1050P. In addition, the cavitating jet was observed with a high speed video camera to confirm the characteristics of the jet. As a result, the mass loss per unit area increased as the diameter of the water flow holes increased. It is speculated that the enhanced flow around the cavitating jet due to the action of the water flow holes caused the increase in the damming pressure on the specimen. The increase in damming pressure increased the impact density and collapse impact force of the cavitation bubbles. Moreover, the large water flow holes resulted in stabilization of the shedding frequency of the cavitation clouds and growth scale. It may be a factor that the stable supply of cavitation nuclei to the cavitation main generation field was realized. However, since the water flow holes did not change the shedding frequency significantly, it is considered that the influence of the frequency on the aggressive intensity is small in this experiment.
On the flaming combustion of highly densified cypress cylindrical briquette of which diameter/length ratio is 1/2 in the high temperature air, it was reported that the flaming combustion duration is proportional to the product of the inverse square of the specific surface area and the briquette density. However, the influence of biomass raw material on the combustion behavior is not clarified yet. To utilize various biomass as raw material of briquette fuel, the knowledge on this should be obtained. The objective of the present study is to confirm the influence of biomass raw material on the flaming combustion behavior, especially, the flaming combustion duration. Cypress, bamboo, rice husk and paper are used as raw material of the briquette. From the results of the thermogravimetric analysis and the estimation of lignin content in the biomass samples, it was observed that the activation energy decreases with increasing the lignin content. From the results of combustion experiments, it was found that the flaming combustion durations for each biomass raw material are proportional to the product of the inverse square of the specific surface area and the briquette density. It is suggested that these proportional constants have the correlation with the mass percentage of the cellulose in the biomass.
Boiling heat transfer using immiscible liquid mixtures is an innovative cooling technique for high-heat-density electronic devices. Immiscible liquid mixtures which are composed of more-volatile liquid with higher density and less-volatile liquid with lower density such as combination of FC-72 and Water are discussed here. In the case of pool boiling using immiscible liquid mixtures, more-volatile liquid on the heating surface is started boiling firstly, and then the more-volatile liquid reaches the critical heat flux as the heat flux increases. Subsequently, the less-volatile liquid is replaced with the more-volatile liquid and moves onto the heating surface, and this liquid is started boiling. This phenomenon is called a Boiling Refrigerant Transition, and the characteristics of heat transfer and flow behavior during Boiling Refrigerant Transition are not clear. Therefore, here the experiments under the conditions of various heights of more-volatile liquid layer and various mixture composed ratio by using two combinations of immiscible mixtures are carried out. The experimental results show that characteristics of heat transfer including Boiling Refrigerant Transition are only depending on the height of more-volatile liquid layer. And the relation between the observation of boiling behavior on the heating surface and characteristics of heat transfer is discussed.
In order to improve thermal efficiency of automobile engine, it is necessary to reduce the cooling loss. A method for analyzing local cooling loss (heat flux) using coaxial type thin film temperature sensor has been developed. Recently, results of heat flux analysis using the sensor composed of thermocouple materials standardized based on ANSI and JIS have been reported, but structure and measurement accuracy of its sensor are not clear enough. In this study, the measurement accuracy of sensor A composed of K type materials and sensor B whose body is combustion chamber material (aluminum alloy) was compared using numerical analysis (two-dimensional coordinate heat conduction equation when the sensor is embedded in combustion chamber). As a result, it was important to use same material as combustion chamber for sensor body to measure wall surface instantaneous temperature with high accuracy. Additionally, results of one-dimensional (axial direction) heat flux analysis when the material of the combustion chamber and the material of the sensor body are different had error, it was considered to effect of heat flow (temperature difference) in radial direction due to different thermal conductivity. Therefore, it was confirmed that newly proposed two-dimensional heat flux analysis method using temperature distribution in axial and radial direction can analyze more accurately than one-dimension. These numerical analysis results showed same tendency as measured verifications results.
We dealt with three-dimensional cellular premixed flames generated by hydrodynamic and diffusive-thermal instabilities to elucidate the effects of unburned-gas temperature and heat loss. To obtain the dispersion relation, a sinusoidal disturbance with sufficiently small amplitude was superimposed on a planar flame. As the unburned-gas temperature became lower and the heat loss became larger, the growth rate decreased and the unstable range narrowed, owing to the decrease of the burning velocity of a planar flame. Using the preheat zone thickness and burning velocity of a planar flame, the dispersion relation was normalized. With a decrease of unburned-gas temperature, the normalized growth rate increased and the normalized unstable range widened, which was because the temperature ratio of burned and unburned gases became larger. With an increase of heat loss, instability phenomena became noticeable, which was because diffusive-thermal instability became stronger. To investigate the characteristics of cellular flames generated by hydrodynamic and diffusive-thermal instabilities, we superimposed a disturbance with the critical wave number corresponding to the maximum growth rate. The superimposed disturbance evolved, and a hexagonal cellular flame formed. The obtained cellular fronts were qualitatively consistent with the experimental results. The cellular fronts became deeper as the unburned-gas temperature became lower, even though the growth rate decreased, which was due to the strength of thermal-expansion effects. As the heat loss became larger, the burning velocity of a cellular flame normalized by that of a planar flame increased. This was because diffusive-thermal effects became stronger owing to the increase of apparent Zeldovich number caused by the decrease of flame temperature.
An experimental study is currently being carried out to reveal the effects of the laser power for sintering on the cavity formation of a sintered test piece, and on the pool saturation boiling of deionized water under atmospheric pressure. The test piece is made of maraging steel, and sintered at 40W and 320W laser power by use of a laser type metal 3D printer. The existence of the cavities which become boiling nucleate on the sintered surface is examined in detail by use of an electric microscope. Boiling phenomena on the sintered surface are photographed by use of a high-speed video camera, and analyzed on a monitor. As a result, cavities were confirmed on streaks of doubly sintered seams on the surface when using the 40W laser. Regarding boiling on the surface of 40W condition, the number of active cavities increases with rising wall superheat, and the surface filled with growing bubbles. In 320W condition, on the other hand, no bubble region was observed on the surface, even in the range of high wall superheat, higher than in the case of 40W, due to melting. The optimal laser power may exist in the sintering process for active boiling cavities. The results include boiling curves and performance for latent heat transport, or apparent heat transfer coefficient per cavity.
In order to gain a better understanding of the latent heat transfer mechanism in pulsating heat pipes (PHPs), this study experimentally investigated the thickness characteristics of a liquid film that forms during oscillations of the liquid column within PHPs. Accordingly, the liquid column was oscillated sinusoidally under different oscillating conditions to simulate the flow phenomena. A circular tube with an inner diameter of 2 mm was used as the test channel; ethanol and FC-40 were used as working liquids. The average thickness of the liquid film formed due to the liquid column oscillations on the channel wall was determined by comparing the oscillation amplitudes of the tip of the liquid column obtained with and without the liquid film. It was confirmed that the average thickness of the liquid film varied based on the average capillary number for each working liquid. The time-average velocity of the tip of the liquid column, which was derived based on the assumption that the tip of the liquid column oscillates sinusoidally, was used as the characteristic velocity to calculate the average capillary number. The experimental results were compared with various correlations proposed in previous studies. The results show that the acceleration of the oscillating liquid column affected the liquid film thickness for a high average capillary number. For this high average capillary number, the rate of increase in liquid film thickness with the average capillary number decreased, and the liquid film thicknesses during the liquid column oscillation approached those under the steady condition. Furthermore, the liquid film thicknesses for the vertical channel were compared with those for the horizontal channel, and it was made clear that the effect of gravity on liquid film thickness is significant. Thus, the thickness characteristics of a liquid film during the liquid column oscillation within PHPs were clarified.
Estimation of no-line-of-sight (NLOS) condition is a key technology for practical indoor localization. In this paper, a novel method to estimate the NLOS sound source using ratio of peak and root mean square values of cross correlation function is proposed. The proposed method is evalueted with experiment in a room and compared with previously proposed method using assumption of Rice distribution. The estimated result of NLOS of the previous method do not show a monotonic increasing with degree of the NLOS, because of the existance of non-deniable reflective waves. On the other hand, the proposed method is possible to estimate the value which show monotonic increase with degree of NLOS. The proposed method may contribute to robust estimation of NLOS condition for indoor localization and robustness of the localization itself.
Selected from various Eigen modes of blading, nodal diameter κ= 0 and κ= 1 are both related to shaft torsional and/or axial vibration and shaft bending vibrations respectively. In order to avoid the possibility of 2f (f=power system frequency) from torsional vibration resonance, ISO specifies the final calculation results considering the combination between κ= 0 blade and torsional shaft vibration. Previous study has reported a global method for blade-shaft torsional coupled vibration analysis governing both κ= 0 and κ= 1 in a systematic manner, and torsional coupled vibration analysis was completed. However, it is also known that coupling of blade-shaft axial vibration also influences the resonance of blade-shaft system, and it is highly requested to estimate resonance frequency accurately. Thus, a method for blade-shaft coupled vibration analysis in consideration of axial vibration coupling is proposed and its feasibility is investigated. A scale model of steam turbine is targeted as an example and calculated resonance frequencies are compared with experimental data and FEM data. As a result, the new method in consideration of axial vibration coupling is feasible tool to calculate resonance frequencies more precisely than previous method.
A conventional method for acoustic impedance eduction in a flow duct is proposed. This method is based on the straight forward method. Assuming that a single mode propagates in the duct and the flow is uniform, propagation constants for both forward and retreat waves are explicitly calculated from three transfer functions between four microphones aligned in a line parallel to the flow duct. Two values of acoustic impedance are separately obtained from either of the propagation constants. The test section of our flow duct has a square cross section whose three walls are rigid and the rest wall is the acoustic impedance wall of interest. To verify the present method, we performed numerical simulations and experiments. First, the boundary element method was employed to obtain the sound pressure field in the flow duct without grazing flow; the target acoustic impedance was prescribed. The acoustic impedance is successfully reproduced by the present method from the sound pressures at virtual four microphones even when the retreat wave is apparent. Then, the acoustic impedance of a perforated plate without grazing flow was experimentally educed. The value agrees with the value measured by the 2-microphone-method in an impedance tube. Third, the acoustic impedance of the perforated plate with grazing flow of Mach number around 0.12 was educed. The resistance increases and both of the reactance and the rate of change in the reactance with frequency decrease from those values without grazing flow. In consequence, when the grazing flow exists, the maximum value of the sound absorption coefficient and its frequency increase, and the frequency range where the sound absorption coefficient shows higher value expands.
This paper describes a structure model construction for structural statistical energy analysis (SEA) using FEM. Identigying SEA parameter regardless of the excitation method is demanded effectively. The proposed method was based on a combination of SEA and vibration response by base excitation like large mass method, forced displacement vibration analysis and random vibration analysis. In order to evaluate the SEA parameters, it is necessary to calculate the subsystem energies and input power. However, the input power at the excitation point when the entire structure is oscilatted is unknown. So, it was assumed that the input power is proportional to the vibration energy of the excited subsystem. These method are effective on an analytical cost performance for the base excitation compared with the conventional force excitation method that is called rain-on-the-roof-exctation. In this study, firstly, the proposal method was validated through two oscillators coupled by a spring. Then it was also validated through L plate consiting of two subsystems. As a result, large mass method is valid for predicting the coupling loss factors between subsystems and in terms of analytical cost. Finally, the method was applied to two flat plates connected in 60, and 30 degrees configuration and a partial car model consisting of six subsystems, as a result, the method is shown to work quantitatively well to the internal loss factors and qualitatively well to the coupling loss factors.
Since interior noise of an electric vehicle driven by motor has no engine noise, the contribution of the road induced noise at the low-middle vehicle speed range is higher and the noise is more noticeable for passengers compared to a conventional internal combustion engine vehicle. For this background, to reduce the road induced noise, this paper proposes a new method for suppressing the resonance response of the two vibration systems coupled by springs, which simulate a car body assuming the use of semi-active stiffness control. When the compliance matrix at coupling degrees of freedom is decomposed into eigenvalues and eigenvectors, it is known that resonance responses of a whole structure depend on the product of the eigenvector corresponding to zero eigenvalue and the compliance matrices of subsystems. Therefore, we proposed a method to suppress resonance response by setting the product to a zero vector. Firstly, an eigenvector is specified to achieve the zero vector. Then, to realize the specified eigenvector, the coupling stiffness between two subsystems, which is used in semi-active control, is changed. Finally, we apply this method to a beam structure and verify its effectiveness.
This study aims at realization of Mechanical Gravity Canceller with tension transmission function via two rotational axes, which achieves a good balance between suitability for M-DOF and high load capacity. Providing high power of conventional manipulators causes a problem of increase in their size and weight. To solve this problem, it has been expected to use Mechanical Gravity Canceller (MGC), a device which can compensate torques by the manipulator’s weight and load with tension spring. While MGC succeeded in compensating the weight of M-DOF manipulator completely, there remains a risk of fatigue fracture of wire ropes in its actual use. This is caused by their large curvature bending. CT-MGC (Compression Type-MGC), a type of MGC consisting of compression spring and block slider crank mechanism, was developed to ensure the rigidity and safety of MGC. However, CT-MGC occupies a large space and so is not appropriate for an installment in M-DOF manipulator. To solve these problems of conventional MGC series, HLCC-MGC (High Load Capacity and Compact MGC) is developed. HLCC-MGC can avoid bending of wire rope in large curvature by transmitting tension via two rotational axes. This feature consists of two elements: arrangement of pulleys considering both a range of movement and a configuration of DOF, and use of parallel link rotator, newly developed rotational mechanism. The testing machine with two HLCC-MGCs can compensate gravity force of tip load imitating an end effector whose weight is 5.06 kg, while the weight itself is 5.88 kg.
In this study, we devised an active device which is used to suppress the essential tremor in human limb. The tremor can be observed in most human arms under excessive stress or chills, even he/she is at physically well condition. Therefore, the tremor may cause anyone a bad effect on precise operation, e.g. welding and surgery. In this work, experiments are performed where the simulated microscopic surgery is imposed on subjects whose fingers are equipped with the active mass damper attenuating the tremor in their hands. The damper is actively driven according to the state feedback controller designed according to the linear two-degrees-of-freedom vibration system model. Subjects were asked to grip a needle having a relatively small diameter using tweezers, and were also asked to insert it in a needle with a larger diameter. Tremors were measured while the subjects kept the tip of the needle in place. The damper was shown to be effective for attenuating vibration in human fingers.
Operational transfer path analysis is important in considering the countermeasure structure of the operating actual product for noise and vibration problems. But in the conventional method based on the least square method has some problems such as that reliability of the obtained results cannot be discussed. Therefore, we studied a method of Bayesian estimation for the FRF level and produced a trial calculation program to estimate by the Markov Chain Monte Carlo method, then verified the accuracy with the 2-input 1-output model. As a result, it was confirmed that the FRF level can be estimated with the reliability given as the probability distribution, and the expected value can be estimated with an error of 1.1 dB with respect to the true value of the preset FRF level. Next, in order to confirm the superiority of the proposed method to the conventional least square method, 10 sample data for evaluation with controlled inter dependencies are prepared, then FRF level estimated by proposed method has compared with that calculated by conventional method. Then, it was confirmed that the relation between FRF level estimated by each calculation methods and the independency of the prepared sample data. As a result, it was confirmed that all value estimated by proposed method show more accurately than conventional method.
A design system for simultaneous structure design optimization of multiple car models is developed and applied to a simultaneous design optimization of MAZDA CX-5 (SUV), MAZDA6 wagon (large vehicle), and MAZDA3 hatchback (small vehicle) to demonstrate feasibility of the developed design tool. The objectives of this design optimization problem are minimization of total weight of three car models and maximization of number of common thickness parts. This problem is difficult to find good Pareto-optimal designs because (1) number of design variable is large (222), and (2) number of constraints is large (45). To find the Pareto-optimal designs of this problem efficiently, an evolutionary multiobjective optimization algorithm named Cheetah is adopted. To evaluate crash performances accurately, a finite-element software LS-DYNA is used for each crash mode. To overcome difficulty in computational time, the K computer is used, where the required computational time is about 600 hours using 73,728 cores of the K computer. As a result, many designs that outperform the initial design developed by Mazda Motor Corporation are found and useful trade-off information between the minimization of total weight and maximization of number of common thickness parts is obtained.
In this paper, a formulation and some computational results of cycle jump method for finite strain elastic-plastic problems subject to cyclic loads are presented. The cycle jump method is to shorten the total computational time. An analysis using the cycle jump method is carried out such that a combination of a few cycles of cycle-by-cycle analysis and the cycle jump by extrapolating physical quantities such as the plastic strains for many cycles based on the results of preceding cycle-by-cycle analysis. The cycle-by-cycle analysis and the cycle jump are repeated until the desired load cycle is achieved. When the method is applied to the finite strain elastic-plastic problem, it involves the finite rotation and the finite stretch. Then, both of them are decomposed into the elastic and the plastic components. This paper presents appropriate treatments on the rotation and the stretch under the multiplicative decomposition of the deformation into the plastic and the elastic parts. Then, some numerical examples are shown. It is concluded that the proposed cycle jump approach performs well under a certain conditions. Such conditions are also described in the paper.
This paper presents a label recognition system aiming at being introduced to the inspection process in the water valve factory. This inspection process checks whether all the labels are pasted to the right place on the products. The numbering management that has been adopted in the current factory lines can help us with finding the missing or double pasting of the labels, but it never notifies the wrong-place pasting. Furthermore, this requires much time to prepare the same number of the parts including the labels. To solve these problems, we here introduce an image-based recognition method utilizing the deep-learning. Adopting the object recognition algorithm, not only the existence but also the pasted place of five pre-learned labels are inspected using several numbers of the frames within 1 second. The learning from about 3,000 sample data resulted in more than 95% correction rate in three of five labels though it fell nearly 80% for the others.
A new technique using a non-destructive inspection to predict the residual surface fatigue life of power transmission gears has recently attracted interest. This technique is advantageously applied to the preventive maintenance of a vehicle transmission, and also useful for developing power transmission gears with high reliability. However, the study of such a prediction has not yet been reported. The authors have carried out an experimental research concerning the subject using the X-ray diffraction method. The full-width at half-maximum (FWHM) was measured on the tooth surfaces of a pair of carburized gears by an X-ray diffractometer during a gear surface fatigue endurance test to investigate the progress of the surface fatigue. The results showed that the FWHM on the tooth surface fell rapidly at the beginning of the running. After that, under the condition of constant driving torque, the FWHM fell gradually in a higher Hertzian pressure area during the endurance running. On the other hand, the FWHM in a lower Hertzian pressure area was approximately stable. When the driving torque was changed during endurance running, the distinctive behavior of the FWHM was observed. Tooth surface damage occurred in a higher Hertzian pressure area when the normalized FWHM, newly developed by the authors, on the tooth surface decreased to a certain value. The authors propose a prediction method of the residual surface fatigue life of power transmission gears using the characteristic curve that expresses the relation between the normalized FWHM and the gear surface fatigue life.
In recent years, the speeding up of a rotary table using a worm gear pair has been required. In order to perform the speeding up of a rotary table, the multi-thread worm wheel is adopted in some cases. When a hob tool for cutting a worm wheel is likewise formed in multiple starts, a polygonal error occurs on the machined tooth surface and it cannot be manufactured with high precision. In this paper, a high precision manufacturing method of multi-thread worm wheel is proposed using a 5-axis controlled machining center. Meanwhile, the worm was manufactured using a NC worm grinding machine by a conventional method. The worm and worm wheel manufactured in these methods were meshed each other and the tooth contact patterns and transmission errors of the worm gear pairs were investigated experimentally. Furthermore, the tooth contact patterns and transmission errors were compared to the worm gear pair with the worm wheel machined using a hobbing machine. As a result, the validity of this manufacturing method was confirmed.
This paper describes a newly invented loading cam that provides a contact force for a planetary roller. A high-speed electric motor with a small reducer and high-power transmission efficiency realizes a powertrain system with a high power density because electric motors can be miniaturized to increase the rotational speed. Planetary traction drive roller reducers are suitable for high-speed driving to avoid meshing vibration as in gears; however, it is difficult to provide a sufficient loading force on the rollers to transmit power. A previously proposed planetary reducer with conical rollers could generate a contact force; however, it lost spin power at the point of contact. The pinion of a planetary roller contacts both a sun roller and a ring so that the pinion must exert a force in opposite directions, inside and outside, at the same time. The new loading mechanism has a pair of cams acting in opposing directions to generate a moment force during contact. This paper presents analytic equations for force and displacement on a pinion that was constructed to agree well with simulations and experimental results. The paper also describes how the analytical equations were used to design the cam and rollers. The cam causes skewing on a pinion because of its asymmetrical profile, which reduces the transmission efficiency. This skewing can be reduced to adjust the rigidity balance of contact points and components. The proposed cam achieves a loading system that provides a contact force to planetary rollers, which is the most important requirement for achieving a planetary roller reducer.
The PEEK material has been applied to a sliding bearing system in a power plant system because of its high mechanical durability. In the solid friction of the PEEK materials, the frictional heat becomes the important factor because the temperature increasing due to the frictional heat causes the rapidly increasing of the frictional coefficient of the specimen. In order to maintain the low frictional coefficient of the PEEK materials, the effective cooling method for the PEEK materials needs to be developed. In this study, the passive cooling method, which attaches the heat sink to the PEEK materials, was suggested. For evaluating the suggested cooling method of the PEEK materials, the calculation model adopting OpenFOAM, which is the open source software, has been developed. Adopting some functions and library of OpenFOAM, the frictional heat, heat resistance, and heat transfer coefficient on the heat sink were modeled. The sliding bearing experiment was conducted and time variation of the temperature and friction coefficient in the ring specimen were measured. The temperature variation in the ring specimen was compared with the calculation result. From the numerical calculation results, the developed calculation model could simulate the temperature time variation of the ring obtained in the experiment, when variation of the frictional coefficient, heat resistance, and heat transfer coefficient were modeled appropriately. Finally, the calculation predict ability using OpenFOAM in the considered situation was evaluated.
This study discussed design criteria for suppressing stick-slip using dynamic vibration absorber. First, a simplified analytical model that can quantify the effect of the dynamic vibration absorber on the occurrence and nonoccurrence conditions of stick-slip was proposed. The model comprises of two vibration systems, i.e., the primary vibration and additional mass systems. In the primary vibration system, stick-slip occurs due to the difference of static and kinetic friction acting on a sliding surface between a primary mass and driven rigid plane. In the additional mass system, an additional mass is connected to the primary mass in the primary vibration system by a linear spring and a dashpot. From the numerical simulations using this analytical model, it was verified that the presence of the additional mass is effective in suppressing stick-slip occurring in the primary vibration system. Secondary, based on the previous studies, i.e., the theories of stick-slip and dynamic vibration absorber, the discriminant equation of the boundary conditions for the occurrence and nonoccurrence of stick-slip was analytically derived. Through some numerical simulations, the validity of the discriminant equation proposed was discussed. It was confirmed that the proposed discriminant equation can accurately formulate the design guideline of the dynamic vibration absorber for suppressing stick-slip. Finally, as a conclusion of this study, the basic design strategy of the dynamic vibration absorber for suppressing stick-slip occurring in mechanical systems were discussed.
In this report, we propose a method to analyze the frequency and phase difference of self-excited vibration during cutting by using image analysis for the photographed image of the machined surface by end milling. It is widely known that, when chatter vibration occurs during cutting, periodic patterns, called chatter marks appear on the machined surface. In previous studies, the periodicity of chattering was judged by visual observation, but this reading operation was difficult, and advanced skills were required to obtain stable results. In this study, the periodicity of the chatter mark is analyzed from the frequency spectrum of a two-dimensional discrete Fourier transform. Image analysis of chatter marks by Fourier transform facilitates the evaluation of the periodicity from the entire image data, so it enables very robust frequency analysis compared to conventional methods. The machined surface images necessary for chatter mark analysis were acquired using a commercially available digital camera and machine tool. To verify the effectiveness of the proposed method, chattering vibration generated during side cutting with the end mill was estimated and compared by the image analysis of the chatter mark and vibration analysis with a displacement sensor. The values of both analysis results are close, and it is found that the proposed method is an effective method for chatter vibration analysis.
It is known that pressure fluctuations are generated from intermediate vehicles of Shinkansen trains. Those pressure fluctuations involve the infra-sound phenomenon with a wavelength longer than several meters. Past studies showed that the infra-sound consists of the aerodynamic and structure-borne components, and the aerodynamic component is originated in the high-speed airflow around vehicles. The generating mechanism of the aerodynamic component, however, had been remained unclear. In this paper, a new methodology applicable to railway field tests is proposed to evaluate low-frequency aerodynamic sound less than 100Hz. A field test was conducted at a flat land without noise barriers, in which fifteen ultra-low frequency microphones constituting a linear microphone array were arranged in line along rails. In order to determine the frequency spectrum and distance decay rate, another five ultra-low frequency microphones were deployed at measurement points 8.7m to 50m apart from the nearest track center. The reason why the flat measurement site was selected was to suppress the bridge noise and focus on the aerodynamic noise during a train passage. On processing the microphone array signal to identify sound sources in field tests, much attention should be paid for the number of averaging; the number of averaging were limited so that sound source identification was difficult in practice. In this analysis, therefore, more than 100 trains were measured and ensemble-averaged to clarify the relationship between the number of averaging and precision of determining sound sources. Our field test campaign showed that low-frequency aerodynamic sound was locally distributed around all sections between two neighbouring bogies and pantograph sections.
In the noise prediction on railway viaducts by numerical acoustic analysis, it is premised that the noise barriers have sufficient sound insulation performance. Considering that the sound transmission loss of the noise barrier has frequency characteristics, which are different for each noise barrier, it is desirable to take the sound insulation performance into consideration to avoid the overestimation of noise reduction effect. In this study, the sound insulation performance of the noise barrier is regarded as a sound damping component by set the different medium domain from the air domain in the analysis. The sound damping characteristics are represented by the complex wave number, which is set as the sound attenuation per unit length related with the transmission loss and the thickness of the noise barrier. As a result, it was confirmed that the sound attenuation corresponding to the transmission loss of the noise barrier can be set appropriately for the plane wave propagating model with consideration of the sound reflection caused by impedance discontinuity. In addition, FEM analyses were conducted for the railway viaduct assuming that the additional noise barrier made of the polycarbonate plate was installed. Consequently, it is concluded that the differences due to the transmission loss can be sufficiently evaluated because the distribution of sound pressure level outside the viaduct shows the influence of the transmitted sound from the additional noise barrier.