In this study, the rolling contact fatigue (RCF) life of nitrided Cr-Mo steel, which has three types of different nitride compound layers, was investigated under contaminated lubrication. Specimen-γ’ has nitride compound layer which crystal structure is adjusted to γ’-Fe4N. Specimen-ε and specimen-εpor have the ε-Fe2-3N type nitride compound layer, however specimen-εpor has a porous layer on its outermost surface. To investigate the crucial factors on RCF life, material characteristics of the surface such as Vickers hardness, residual stress, resistance to indentations were evaluated. Changes of surface topography around Vickers indentation were measured through the RCF test under clean lubrication. As a result, the specimens with ε-Fe2-3N type nitride compound layer showed higher RCF fatigue life than that of specimen with γ’-Fe4N. The RCF life of specimen-εpor was the longest among the specimens, which was about 3-5 times longer than the RCF life of specimen-γ’. The rate of reduction in unevenness around the indentations was dramatically improved by the wear of the friable porous layer on the surface of specimen-εpor. Thus, the specimen-εpor with the hard ε-Fe2-3N type nitride compound layer and the friable porous layer kept the RCF life long under contaminated lubrication, because the stress concentration around the indentations decreased due to smooth indentation edge on the εpor surface.
One of the lightweight heat-resistant alloys, Ti-48Al-2Cr-2Nb (TiAl4822), has already been adopted to turbine blades for jet engines, but is manufactured by casting which requires expensive post process. Aerospace industry is intensively studying the additive manufacturing (AM) process for the engine parts. In this research, tensile and creep properties of additively manufactured TiAl4822 by electron beam melting (EBM) were studied. The mechanical tests were performed at 750 ℃ which is similar to the actual condition in low pressure turbine module. The effect of hot isostatic pressing (HIP) treatment on these properties was investigated because such information is very limited, even though HIP treatment is required in many aerospace parts. Near net shape specimens were prepared for both tensile and creep tests. The effect of the HIP treatment on the microstructure in the specimens was observed by scanning electron microscope (SEM). Electron back scatter diffraction (EBSD) was used to analyze the effect of the HIP treatment on microstructure such as area fraction of each phase and grain size in the specimen. The results showed that the benefit of sintering during the HIP treatment decreased the voids with a size of up to 40 μm and the defects with a size of millimeter order due to lack of fusion in the specimens. The HIP treatment improved both tensile and creep properties at 750 ℃. It was found that the HIP treatment improved creep life by 15% and elongation by 60%, and delayed the starting point of tertiary creep. This is mainly because the HIP treatment eliminated the defects caused by lack of fusion and made the material more ductile than as-built specimen. On the other hand, the microscopic analysis by EBSD revealed that the HIP treatment increased the average diameter of the grain and widened the distribution of grain size, with the increase of the area fraction of Ti3Al(α2). The increase of grain diameter could decrease the strength according to the Hall-Petch Law. In this research, however, the elimination of the defects such as the voids and the defects due to lack of fusion improved the tensile and creep properties. The results suggested that the post heat treatment including cooling process after HIP treatment to control the microstructure is important.
Loss of oral communication after total laryngectomy reduces the quality of life of the patient. Understanding the basic sound generation mechanisms in the larynx is necessary for the development of voice reconstruction. In this study, a model simulates the self-excited vibrations of the vocal cords in the larynx was constructed. Experimental measurements were performed on the model to identify the main factors and mechanisms of the sound generated by the model. The flow field downstream of the model was measured using PIV. Then, the sound pressure was estimated by applying the Ffowcs Williams-Hawking equation to the measured flow field. The estimated sound pressure was in good agreement with the actual sound pressure measured by the microphone. The main source of the generated sound was found to be the direct sound from an aerodynamic source in the downstream flow field of the model. The vortex structures in the vicinity of the slit are mainly related to this sound generation. As the slit opens and closes, the pressure near the slit fluctuates over time, and generates sound waves. This is related to the vortex structure identified by the Q-criterion occurring in the same region.
The design of a flow distribution to multiple branch channels is one of the key factors to realize the flow uniformity in a fuel cell stack. Especially for a disk-shape solid oxide fuel cell (SOFC) stack, it is necessary to clarify the optimum structure of the multiple branch channel composed of a multitude of disks. In this study, velocity fields in the parallel-stacked disk channels connected to a circular supply tube are measured by using a particle image velocimetry (PIV). The PIV experiments are performed in the SOFC stack model consisting of five-layers of disk channels. Each channel has a curvature at the inlet corner of the bottom wall, and a cylinder is installed coaxially inside the circular supply tube to control an inflow condition. Mean velocity vector fields in the disk channel indicate that a small scale vortex appears near the inlet of a lower disk channel and develops into a separation bubble with an increase in the cylinder diameter. The length and height of the separation bubble are found to increase with channel inlet Reynolds number, even at very low Reynolds numbers. Distributions of the flow rate through each disk channel are also examined. The curvature of the channel inlet corner has little influence on the flow rate profile, but the cylinder diameter significantly affects the flow distribution in each channel. A standard deviation of the flow rate distribution suggests that the method of installing a cylinder with optimum diameter is effective for realizing a uniform flow distribution.
The paper clarifies the effects of buoyancy on the mechanism of heat transfer in the wake of heated cylinder for X/D=5-40. Measurements are made by a thermo-anemometer. Reynolds numbers ReD=U0D/ν in non-heated condition are varied from 3000 to 10000 for the temperature differences Δθ from 0 to 225 ℃ (corresponding Richardson numbers RiD=0-0.0568). The dimensionless conservation for heat is valid in the heat transport equations in this flow field. In the equations, heat transportation are almost carried out with turbulent diffusion terms and production terms of mean temperature gradient. As for the momentum transportation, velocity fluctuation at vortex shedding frequency fc contributes mainly to transport heat in the upstream sections. But in the downstream sections, fluctuations at frequencies around fc play important role with breakdown of the Karman vortex street. Heat-transport mechanism in the heated cylinder wake is affected by both the non-symmetry construction and the vortex breakdown.
To clarify the mechanisms underlying airflow-induced vibrations of high-speed trains running through tunnels, large-eddy simulation of a large-scale flow structure around a simplified 6-car train model was conducted. Since actual trains run on one of the double track lines, the position of the train model was made to deviate from the tunnel center and hence the gap between one of the sides of the train and the tunnel wall is narrower than that of the other side. A train running in the open air was also calculated for comparison. The results of this study shed light on the generation mechanism of the pressure fluctuations acting on the side of high-speed trains as follows. Firstly, in the open air, the air velocity in the space between the underbody and the ground gradually decreases from the head toward the tail of the train. Thus, the air velocity is slower than that on both sides of the train, which generates shear flows near the bottom edges of both sides of the train. The shear flows cause large Karman vortex-like vortices (staggered Karman vortex street), which in turn lead to a meandering airflow beneath the underbody of the train. Secondly, in the tunnel, the air velocity not only in the gap between the underbody and the ground but also in the narrower gap between the side of the train and the tunnel wall gradually decreases from the head toward the tail of the train. In the same mechanism as the open air, a meandering airflow is generated throughout the side and underbody of the train and causes pressure fluctuations along the side of the train. Finally, it is demonstrated that the wavelength of pressure fluctuations along the side of the actual train can be estimated from the present LES results.
This paper discusses the new identification method of a linear single-degree-of-freedom system using Gaussian random vibration response. The propose method is based on the method of Maximum Likelihood Estimation (MLE). The likelihood function of the proposed method is composed from the analytical solution of Fokker-Planck equation. The estimation formulas of unknown parameter are obtained by maximization of the original likelihood function. The obtained estimators represent the population variance estimation problem of multivariate Gaussian model. Furthermore, the numerical identifications are conducted using the random vibration response by calculation result of the 4th Runge-Kutta method. In the result, the estimation performance of the propose method is confirmed in terms of the dependency of sample number and dependency of the damping coefficient. Especially, the proposed method is implied the application to identification problem of the large damping system. Quantification of the large damping characteristic is the important problem, because it is the difficult problem in the conventional identification method. Moreover, the benchmark tests are conducted with Half-Power Method (HPM) based on the spectral analysis and Auto-Regressive Method (ARM) based on the time series analysis, respectively. The results of the benchmark test are shown in the accuracy of the propose method is higher than its of HPM and ARM, respectively. Finally, the expansion to the recursive estimation algorithm is conducted using MLE estimator of recurrence form. In addition, the operation of the recursive algorithm is confirmed.
One of the most important stages in automatic visual inspection for specular surface objects is to generate an image data including features of defects for the inspection. We define the image for inspection as an image data including an intensity change due to surface defects. The type of surface defects on the specular object is classified into local reflectivity losses and local unevennesses. In this paper, we report a study on illuminating, imaging and image processing methods to generate the image for inspection in order to detect the local unevennesses. We considered a situation where a light emitting source displays a sinusoidal intensity pattern and a camera captures the reflection pattern on the specular surface. Numerical computations based on our theoretical analysis shows that the local unevennesses appears as phase gaps of the sinusoidal intensity pattern in the image data captured by the camera. We propose a processing method to convert the phase gaps into the intensity changes in the image for inspection. In addition, we mentioned operational problems to be solved when we apply our methods to an automatic visual inspection system. Furthermore, we discussed a possible method for detecting the local unevennesses with a depth of 1x10-3 mm from the image for inspection.
In recent years, robots are increasingly used for rescue activities and inspections at disaster sites. However, many robots have limited adaptive environment, and there are still problems in actual use. We are studying vacuum suction, which is considered to be able to adsorb to various objects among suction components. There were many problems with conventional suction component. For example, suction part using a flexible material is weak to the load from the shear direction of the suction surface. In this paper, the suction force generated from the suction surface is divided into the suction force and the retention force by the suction area. By separating the suction force and the retention force, the retention force almost holds the suction surface, but the suction force holds a part of it. As a result, a large load can be held in the rigid part, and the durability is improved. By separating the suction mechanism and the retention mechanism with bellows, it is possible to correct the difference between the coordinates of the suction pad and the coordinates of the hand of the robot, and there is also an advantage when mounting the suction component on the robot. When the impact load falls on the robot, the bellows can recover the suction state in the time it takes to extend due to the bellows. Also, conventional suction components were limited of suction surface. Therefore, we develop composite sealing material to adsorb more variable surface. We show the improvement of adaptability to granite, concrete blocks, tile with grooves, and so on by applying this material. We report on useful findings from the results and discussion.
The energy efficiency of the conventional flow control of hydraulic systems using the pressure loss of throttle valves, which are widely used in construction machinery, is very low. If the switching inertance hydraulic system which is a kind of PWM control hydraulic system is used, a significant improvement in energy regeneration efficiency can be expected. However, it is known that as the switching frequency of the valve increases, the regeneration rate decreases as the vibration mode due to the elasticity of the oil in the pipe system resonates with the valve switching frequency or its high-order component. Therefore, the aim of this study is to reduce the vibration due to the elasticity of oil in the pipe system and to improve the regeneration rate by using the phenomenon that the response decreases with antiresonance. In order to obtain a high regeneration rate even if the duty ratio of the valve is changed, the shape of the pipeline is studied so that the fundamental frequency component of the valve switching frequency and the frequency components of all harmonics up to the third order could be anti-resonant frequencies at the same time. Some calculations are carried out using the response analysis method and definition of efficiency, and it is shown that a higher regeneration rate can be obtained in the case of the proposed pipe shape than in the case of a straight pipe.
Kumamoto Castle, consisting some towers and the stone walls called ISHIGAKI, was severely damaged by Kumamoto earthquake in 2016. As Kumamoto Castle has some important cultural properties of Japan, prompt and accurate restoration works for the damaged stone walls and the castle are needed. For the restoration works, it was difficult to estimate all collapsed stone locations since the shapes of the stones are similar. For this problem, the estimation method of possible stones based on iterative closest point algorithm using photographic imagery has been studied. This algorithm showed a good result, however, about 20% of collapsed stones were not decided. In recent years, the utilization of stone’s 3D data has been studied to recognize of the possible stones precisely. For an efficient renovation, it is needed to measure 3D data automatically in a short period of time. In this paper, the scanning system of the collapsed stones controlled by a compact control moment gyroscope (CMG) crane and an elevator to move 3D scanner is proposed. Parameter change of CMG crane which caused by the stone shape and size is suppressed by the model error compensator (MEC). The CMG crane rotates the stone around according to the up-and-down motion of the 3D scanner moved by an elevator. The effectiveness of the proposed system to archiving 3D data is evaluated by scanning dummy stones experiments.
In the logistic system, it is necessary to reduce the weight of the structure to realize energy-saving and highly efficient conveyance of a stacker crane that conveys packages in a warehouse. On the other hand, a lightweight stacker crane becomes a flexible structure, and its movement and vibration control are very important and has been discussed by many studies from long ago. Many designs of dynamic FF controllers have been discussed. In this paper, we propose model following two degree of freedom control using a simple reference model that can simultaneously control vibration and motion by utilizing the internal integral characteristics of the model. We discuss FF command and reference signal considering constraints of actuator. As an FB controller with 2 degrees of freedom control, vibration sensor-less active control using motor position-controlled FB torque is proposed and its effectiveness is verified by simulation and experiment.
Generally, in control gain tuning, settling time and overshoot are altered to be smaller through time-consuming and labor-intensive experiments. Such experiments can be automatically performed in the computer in a short time if the time response can be predicted. Kaneko et al. proposed a new approach for predicting the response of a closed-loop system using one-shot experimental data, but this approach takes into consideration the structure of the closed-loop transfer function. Thus, two methods have been proposed that do not require the structure of the transfer function. One method is based on the finite impulse response estimated from one-shot experimental data by Matsui et al., but the design guideline for an unstable system is not shown. The other method is Virtual Time-response based Iterative Gain Evaluation and Redesign (V-Tiger), which is based on the frequency components of one-shot experimental data by Kosaka et al. However, this proposed V-Tiger has the following issues: 1) Inability to predict disturbance response and input disturbance response. 2) The initial value used for optimization must be a controller that stabilizes the system. Hence, in this paper, we describe the countermeasures against these issues.
An interaction through a negative-stiffness spring is introduced into a dual-mass dynamic vibration absorber (DVA) to lower its resonance frequency. DVA is one of the practical vibration control devices. In principles, it consists of an absorption mass and a spring. It can eliminate vibration at a specified frequency that equals the resonance frequency of the DVA. To eliminate low-frequency vibration, it is necessary to increase the absorption mass or lower the spring constant. The former method increases the size of the device and the latter method may cause difficulty in supporting the absorption mass. Although there are reports on the optimal design and robust optimal design of DVAs, there are few reports that focus on lowering the anti-resonance frequency. In addition, there are few studies on the parallel dual-mass DVA that has interference between the vibration absorption masses. This work focuses on parallel dual-mass DVA and proposes to insert a negative spring between the absorption masses. It is analytically shown that one of the resonance frequencies of the DVA can be set lower than that of the conventional DVA. Such characteristics are confirmed by numerical analyses and experiments.
The car is a main means of transportation all over the world. However, many people drive a car when they travel a short distance alone, that is inefficient in cost and space. Then, personal mobility vehicle (PMV), which is one or two-seater and has high environmental performance, is recently gathering attention. We focus on the three-wheeled vehicle with leaning mechanism called Narrow Tilting Vehicle (NTV) or narrow tilting three-wheeled (NTTW). Leaning mechanism, which gives tires degree of freedom, has an effect of stable cornering in the case of short tread width vehicle. To compere the motion of each leaning mechanism, we model the two types of NTV. One has two front frame which are linked to vehicle body by the arm and rotating respectively around the joint. The other one has a front frame that has two tires connected by the link. We derived equation of motion by referring to Sharp’s 4 DOF two-wheeled vehicle model, and carried out the three kinds of numerical analysis, eigenvalue analysis, modal analysis and running simulation. Through eigenvalue and modal analysis, we find out that NTVs have the same modes as Sharp’s 4 DOF model does, and they have the characteristic mode which vibrates steering and leaning mechanism. By running simulation, NTVs required larger steering torque than two-wheeled vehicle when the vehicle turn at the same angle.
When designing NVH (Noise, Vibration and Harshness) performance for complex structures such as automobiles, trains, and aircraft, it is rare to target all components of the whole structure and the subsystem be designed are often fixed. In recent years, the kernel Compliance Analysis (kCA) method has been proposed as a method for designing NVH performance by dividing a whole structure into two subsystems. When modifying the structure of the subsystem to be designed by using the kCA, it is an important index which mode of the subsystem has a large contribution to the resonance of a whole structure. However, in the conventional sensitivity of structural modification, only those that determine the contribution of the subsystem for each mode of a whole structure are found. This paper, therefore, derives a new index for understanding the relative importance of the modes of subsystems to the resonance of a whole structure. As the index is derived based on the kCA, it has good compatibility with the design of NVH performance by the kCA. After derivation of the index, the effectiveness of the index will be verified through a numerical example of the resonance assignment of a whole structure combined with the kCA.
The self-actuated shutdown system (SASS) is a reactor shutdown system that is able to achieve passively de-tach the absorber rod based on the coolant temperature rise under the any type of abnormal conditions and then the absorber rods will be inserted by the gravity forces within a few seconds. This capability is possible to add the active shutdown system, if a Curie-point temperature magnet system would be adopted. The temperature sensing alloy is designed and fabricated for de-tach under Unprotected Loss of Flow, Unprotected Transient Overpower, and Unprotected Loss of Heat Sink accidents, whereas the control rods would be well hold under the normal operating conditions. Since its impact on the reactor core design is less, its installation is excellent both in the safety enhancement and also in cost effectiveness. The SASS has been developed as a safety enhancement measure against the failures of the reactor shutdown system in sodium-cooled fast reactors. This paper contains the results of experimental studies in order to select appropriate materials for SASS. As a result, the feasibility and the reliability of candidate material for SASS has been confirmed.
The Sense of Agency (SoA) is the subjective awareness of controlling external world through one’s action. This paper proposes a mathematical model to explain the degree of SoA using information gain, representing the difference between expected and actual sensory responses to an operational action. We hypothesize that the degree of SoA is proportional to the inverse of information gain as a function of three parameters: prediction error, uncertainty and external noise. The model predicted that the prediction error decreases SoA, but uncertainty attenuates the decreases by prediction error. SoA in certain expectation is higher when prediction error is small, whereas SoA in uncertain expectation is high when prediction error is large. To validate the model prediction, we conducted two experiments with participants using varied operational delays as different level of prediction errors. Participants were adapted to expectation of low/high uncertainty and rated SoA at each delay. When prediction error was from 50 ms to 250 ms, the participants who were adapted to expectation of low uncertainty tended to rate lower SoA than the participants who ware adapted to high uncertainty (experiment 1). This tendency was also observed in event related potential N100 (experiment 2). These experimental results supported our model predictions.
Since the current manufacturing paradigm cannot get out of the mass production and mass consumption in correspondence with diversification and expansion of customer needs, today's manufacturing industry causes many problems such as sustainability issues typified by SDGs. The conventional design theory seems not to be sufficient for these problems because it does not deal with temporal changes of design objects. For solving this issue, we study “timeaxis design,” which explicitly deals with temporal changes in design. This paper proposes a timeaxis design (TaD) support method using patterns between temporal changes and countermeasures. First, we extract patterns of temporal changes and countermeasures to them from collected TaD cases. Next, we propose a TaD support method using these patterns. Finally, this paper illustrates timeaxis design of bicycle as a case study using the design support method. The TaD support method enables designers to design a product with introducing countermeasures against plausible temporal changes into design objects. The case study indicates that designers can find out TaD design solutions systematically using the proposed method.
The water lubrication characteristic of partial water-repellent (slip) type flat thrust bearings was examined. In this bearing, water-repellent (slip) regions and hydrophilic (non-slip) regions were alternately arranged in the slip direction, and the pressure to support the load was generated by discontinuity of shear flow rate in both regions. The measured pressure in slip direction increases in the water-repellent region and then decreases in the hydrophilic region, and it increases in proportion to the load. The fundamental lubrication characteristics of this bearing were considered based on the infinite-width bearing approximation theory that can explain the experimental tendency. On bearing surfaces with large slip length, the shear flow rate increases and a high pressure is generated, resulting in a large load capacity. However, the influence of pressure flow that suppresses the slip of shear flow increases, and the degree of increase in load capacity with increase of the slip length becomes low, under the condition of large slip length and thin film. On the other hand, the film thickness increases and the velocity gradient on the slip surface decreases under the same load for large slip length bearing, so the frictional force tends to decrease. However, the difference in friction force due to the difference in slip length is not remarkable. Since the degree of increase in frictional force is lower than that in load capacity in case of decreasing film thickness, the friction coefficient decreases with decreasing film thickness. Especially, a sudden decrease of friction coefficient is shown in the thin film region. Since the effect of slip on frictional force is also small, the difference in friction coefficient due to the difference in slip length decreases as the film thickness becomes thinner. The slip effect in this bearing acts to improve the bearing characteristics.
In this study, we propose a topology optimization method for dynamic problems to control the deformation of the structure. To derive a structure that minimizes the deformation due to transient loads for an isotropic linear elastic model, the strain energy and the squared norm of dynamic compliance are set as objective functions. The topology optimization method applies a density method based on the RAMP method. In the case of the density method, since a optimal structure is obtained by an optimization algorithm based on the gradient method, it is necessary to formulate design sensitivity equations that can appropriately take into account the target optimization problem. A generalized sensitivity analysis method is proposed by introducing the adjoint method and applying Newmark’s β method, which considers the displacement as an unknown quantity , and considering the equations of motion. Furthermore, the accuracy of the sensitivity is verified by using the finite difference method as a benchmark, and it is shown that the proposed design sensitivity has high accuracy. Finally, as a numerical example, we derive optimal structures for several optimization problems and discuss the optimization problem settings to obtain a structure that can control vibrations. The validity of the proposed method is demonstrated by deriving the optimal structure to control the vibration.
The international standards for safety of machinery mainly focuses on design requirements for occupational safety. However, there are some standards which remark about the hygienic design are included in that one. Because food machinery has the characteristic related to "safety design" and "hygienic design" both characteristics must be considered at the design stage. And we should have to consider about the problem that a protective measure may raise the different kind of risks at the time. However, it is not established the procedures to evaluate inclusive two risks that takes these contrary effects into consideration in the standards that mention the risk assessment process. Therefore, in the food machinery manufacturing industry, it is an urgent problem to address the concept of the risk reduction process handling two risks, and to develop a model. In order to contribute to the development of risk assessment based on international safety standards for the food machinery industry, this paper propose as it is not consider about kind of adequate protective measure, a procedure for considering for the most suitable combination of components of a protective measure by an iterative process are requested, thereby, that can reduce two kind of different risks in a well-balanced.