This paper describes elastic-plastic fracture mechanics assessment methods of a pipe having multiple circumferential cracks. Ductile fracture strength of a multiple cracked pipe was evaluated using J-integral based on a reference stress method. Using this result and plastic collapse strength, Z-factor used in elastic-plastic fracture mechanics assessment methods was calculated. Z-factor for the multiple cracks was less than that for a single crack in all the analyzed cases. Although the position of bending axis where the minimum plastic collapse strength is given differs from that where the minimum ductile fracture strength is given, the minimum ductile fracture strength is not less than the value which divided the minimum of plastic collapse strength by Z-factor for a single crack. Based on these results, the elastic-plasticity fracture mechanics assessment methods for the Fitness-for-Service Codes were proposed.
Aiming at an enhanced fatigue strength of various metal materials, surface treatment named cutting and rubbing process was developed. The surface of processed specimen of a quenched and tempered SCM435 had an extremely large value of compressive residual stresses (-2100 to -2600 MPa). Although the compressive residual stresses significantly decreased during an early stage of stressing, it tended to saturate to -1800 MPa before the repetitions of N ≈ 4×104 independent of stress values, even after a longer fatigue regime in excess of N = 107. Fatigue limit stress of the processed specimens was enhanced to approximately 1.5 times of a smooth specimen finished with #1000 emery paper, and most of the fracture surface origin exhibited fisheye pattern. Fatigue tests on the processed specimens with reduced residual stresses due to the heat treatment showed that the enhanced fatigue strength by the processing was attributed to the effect of compressive residual stresses rather than that of the processing- induced hardened-layer. The actual fatigue limit was much higher than the evaluated value of 500 MPa calculated from the fatigue limit prediction equation by Murakami, suggesting a greater contribution of compressive residual stresses near the surface layer on non-propagating internal fatigue cracks. In order to investigate the effect of residual stress on non-propagation of internal fatigue cracks, the monitoring of internal cracks in the specimens fatigued by N = 5×107 cycles of the fatigue limit stress was conducted, showing no internal cracks in the specimen interior in a range of the present experiment. The internal cracks should be generated at the stresses above the expected fatigue limit of 500 MPa, suggesting the formation of non-propagating internal cracks under the actual fatigue strength of 710 MPa. It is unclear that a mechanism of higher fatigue limit (710 MPa) than an expected fatigue limit (500 MPa) calculated using parameters obtained from their crack origin. The extremely high compressive residual stresses over the surface may be a cause of non-propagation of internal cracks, whereas the present rough monitoring could not detect the internal cracks.
Safety assessments of nuclear plants against tsunamis have been reviewed after the Fukushima Daiichi nuclear disaster caused by a tsunami during the Great East Japan Earthquake in March 2011. These assessments are required for the restarting of operations at nuclear plants. Integrity evaluations of nuclear plant facilities at impact of floating debris caused by a tsunami are performed on the basis of the estimated strain on a facility caused by the impact force. In this paper, drop impact tests were carried out using real scale specimens of a delivery pipe and a power supply unit that nuclear plant facilities comprise. A 1500-kg power supply unit impacted on a delivery pipe (318-mm in diameter, 5-m in length) under two impact speed conditions of 5.2 and 9.5 m/s. No noticeable penetration damage to the pipe was detected under either condition. Simulated results considering strain rate dependence and constitutive equations with power hardening law showed good agreement with the experimental results. This simulation model is effective to analyze the safety margin of apparatuses at impact.
Nondestructive inspection of structures in a high temperature environment is requested for safety and economic. An ultrasonic flaw detection system using an electromagnetic acoustic transducer (EMAT) is said to be suitable for high temperature environments. However, the electromagnetic induction coil (EM-coil) in part of a conventional EMAT is required to approach the surface of the specimen in principle. Therefore, it will be easy for it to undergo thermal and mechanical damage. In this research, a new type Lamb wave EMAT wound EM-coil around a ferromagnetic core has been developed to overcome such weak points. As the first step, a trial EMAT with a steel core and permanent magnet to add a biased magnetic field was tested to evaluate the influence of the direction of the bias magnetic field and the optimum magnetic flux density. It was proven that there is an optimum strength of the magnetic field, and the horizontal biased magnetic field was effective. Next, a trial EMAT with a steel core for a static and dynamic magnetic field was fabricated. The received signal by the electromagnet type trial EMAT was much stronger than that of the trial EMAT with permanent magnets. However, the strength was much weaker than that using a conventional Lamb wave EMAT. Therefore, a trial EMAT installed with a magnetic pole made of a PC-perm alloy was fabricated. The best signal was obtained without a biased magnetic field, but the signal was weaker than that of the trial EMAT with the steel core. Finally, the best signal the same as that by the conventional Lamb wave EMAT, was obtained using the trial EMAT installed with a steel core for the biased magnetic field and the PC-perm alloy for the dynamic magnetic field which are magnetically shielded.
This paper presents two numerical simulation methods for fatigue crack propagations with the plasticity-induced crack closure under arbitrary cyclic loading conditions. One of the methods is Direct Numerical Simulation (DNS) using S-version Finite Element Method (SFEM), which allows us to simulate the fatigue crack propagation by the combination of the global mesh representing whole structure and local meshes including cracks. Crack opening level due to the plasticity-induced crack closure is evaluated by the elastic-plastic analyses with the local mesh, which is used in the SFEM analyses and is rearranged to simulate the small size of plastic zone around crack tip. The crack growth rate affected by the plasticity-induced crack closure is calculated by a modified Paris ’law in which the stress intensity factor range is converted into an effective stress intensity factor range by multiplying the crack opening level. The crack shape is updated by the crack growth rate, and then, the local mesh is reconstructed in accordance with the updated crack shape. By repeating the processes, the developed method enables us simulating directly the fatigue crack propagation with the plasticity-induced crack closure effect. Another method is a simplified fatigue crack propagation analysis method, where the effective stress intensity factor range is approximately determined by the relationship between the maximum stress intensity factor and the crack opening level. The relationship is constructed in advance using a series of two-dimensional DNSs. The comparison with experimental results confirms that the developed methods have a capability to predict the propagation of surface cracks under bending and tensile loading conditions.
In the previous studies, a bolt-nut connection with slight pitch difference was considered towards realizing anti-loosening performance and high fatigue strength through axisymmetric finite element method (FEM) as well as experiment. In this study, screwing process before the nut touching the clamped body is analyzed through three dimensional FEM. Then, it is found that the prevailing torque during this screwing process is in good agreement with the experimental result. The prevailing torque varies depending on the pitch difference from 5 to 25 Nm and anti-loosening behavior is confirmed. After the nut toughing a clamped body, the tightening process is also analyzed. For normal nut, the tightening force coincides with the empirical formula. The tightening torque and tightening force relations are discussed with varying the pitch difference.
Ferroelectric behavior in mechanically strained SrTiO3 nanoporous is investigated using phase-field models. We find, in the paraelectric nanoporous, periodically arrayed ferroelectric nano-region is formed due to strain concentration, namely, polarization vortices emerge around each pore. Each ferroelectric region expands and connects each other with increasing strain, and ferroelectric network is finally formed. Since these ferroelectric regions can be regarded as a periodically arrayed ferroelectric nanomaterial embedded in a paraelectric material, this result means that periodically arrayed ferroelectric nanostructure, which may lead to novel functionalities, can be tailored through mechanical load. In addition, we find that the variation of load changes the geometrical characteristics of the ferroelectric structure such as shape and direction. Our finding provides a new concept to engineer future ferroelectric nanodevices by giving a new role to mechanical load.
This study carried out a theoretical examination of the method of preparing very long unidirectional CNTs/resin composites by the application of an electric field. In the simulations, a rotating cylindrical multiple electrode was used to apply an electric field to the suspension (CNTs/uncured resin). The suspension was arranged closely under the rotating cylindrical multiple electrode, and moved slowly and perpendicularly to the axis of the rotation. The passing speed of the suspension was set to be (A) extremely slow compared with, or (B) synchronized to the circumferential speed of the rotating cylindrical multiple electrode. Condition (A) corresponds to a case in which the thinned suspension moves slowly under the rotating cylindrical multiple electrode at a high speed. In this condition, a DC voltage is applied to the electrodes. Condition (B) corresponds to the case that in which suspension is spread by the rotating cylindrical multiple electrode. In this condition, direct, four-phase square wave, six-phase square wave or eight-phase square wave voltages are applied to the electrodes in the simulation. The static electric fields in the suspension at many angles of the rotating cylindrical multiple electrode were calculated by FEM. Intensities of the obtained electric fields were assigned to the equations introduced by the author, and the CNTs alignment angle and the moment acting on the CNTs in the suspension were estimated. From the simulated results, it can be concluded that very long unidirectional CNTs/resin composites could be prepared by the application of an electric field.
The underexpanded sonic jet issued from an axisymmetric convergent nozzle are experimentally investigated in which the nozzle is operated at a pressure ratio of 4.0 to produce a Mach disk in the jet plume. Multidirectional rainbow schlieren pictures of the jet acquired by rotating the nozzle about its longitudinal axis in equal angular intervals are utilized to reconstruct the jet three-dimensional density fields with both of the Abel inversion and convolution back-projection algorithms. The fine structure of the free-jet with a Mach disk in the first shock-cell is distinctly displayed with a two-dimensional density contour plot including the jet centerline and isopycnic surface representation for the jet 3D density field. Furthermore, the jet centerline density profile obtained from the present rainbow schlieren is quantitatively compared with that from the background oriented schlieren performed by ONERA in the past.
Large-eddy simulation (LES) of the cavitating turbulent flow around a hydrofoil was conducted. Especially, we focused on the improvement of the reproducibility of the hydrofoil performance under the condition of cavitation when considering the unsteadiness of the flow field sufficiently by LES. The analysis object is the cavitating turbulent flow around a Clark-Y11.7% hydrofoil at the angle-of-attack of 2 degrees. The weak compressibility was taken into account in the governing equation. The cavitation is represented by the cavity source based on the homogeneous fluid model. For LES, the subgrid scale (SGS) eddy viscosity was determined by solving the transport equation of SGS kinetic energy. Typical patterns of cavitation that was observed experimentally for various cavitation number were successfully reproduced: e.g., attached sheet cavitation of steady as well as unsteady modes. The reproducibility of the cavitation characteristics of the hydrofoil was improved in comparison with that by previous Reynolds-averaged turbulence models. In addition, by reducing the cavitation number, the slight increase of lift coefficient was observed before the breakdown. These are due to the streamline curvature around the sheet cavity. We found this feature is related to the unsteady motion of large-scale spanwise vortices. LES revealed that the vortices are intermittently generated by the baroclinic torque originated from the onset of sheet cavitation.
The purpose of this study is to obtain better physical understandings of the theoretical thresholds of the insonation acoustic pressure amplitudes for medical diagnostic ultrasound applications. For this purpose, a physical model in terms of non-linear resonance of single bubble volumetric oscillations has been developed, to reproduce the threshold insonation acoustic pressure amplitudes that are numerical solutions of Gilmore's equation. It is confirmed, under the condition of the adiabatic state change of the in-bubble gas with a maximum temperature of 5000 K, the present model well-reproduces the influences of the insonation center frequency, the liquid viscosity and surface tension in a range of 0.5 to 16 MHz, 0.0 to 8.0 mPa･s, and 30 to 70 mN/s, respectively, on the threshold insonation acoustic pressure amplitudes. Based on this model, a dimensionless physical index of the insonation acoustic pressure amplitude with a threshold value and a set of fundamental dimensionless parameters constituting that index are defined.
Performance evaluations of a firefighting pump are important for inspection of fire equipment. A standard protocol established by the Ministry of Internal Affairs and Communications is generally employed to measure the firefighting pump performance using the static pressure of a standard straightening pipe to calculate a nozzle pressure without any direct measurements at the core of the jet of the firefighting nozzle. This standard protocol is a convenient method to evaluate nozzle pressure using the standard firefighting nozzle designed for the standard straightening pipe which has diameter 65 mm. In late years, there are some opportunities for a large-capacity firefighting pump performance evaluations using a large diameter straightening pipe (75 mm). However, it is not applicable to the straightening pipe (75 mm), because the protocol is based on the empirical table for 65 mm pipe. In this study, a new estimated expression was devised for the nozzle pressure to evaluate for performance of the large-capacity firefighting pump. Empirical standard protocol, experimental value and ideal value calculated by Bernoulli's theorem were compared and discussed. Results was shown that the estimated expression was expansion of the empirical standard protocol and the validity was shown. By comparison with experimental values, the estimated expression was proven to be applicable to flow straightening pipe diameter 75 mm.
The control of circular jets has been studied extensively in the fluid dynamics literature. Most studies introduce an entrance pipe upstream of the nozzle outlet to straighten the flow. In this study, we studied the free jet emitted from a circular nozzle that converges with the entrance pipe. We identified the cause of the naturally occurring vortex ring at the beginning of the jet, and we designed a mechanical intervention that suppresses the vortex. This experiment was performed at Reynolds number Re = 1400–5600. In the experiment, the visualized jet cross section and the flow velocity measured by the hot-wire anemometer were processed with a fast Fourier transform to determine the frequency at which the vortex ring arises. The frequency of the naturally occurring vortex ring depends on acoustic resonance inside the nozzle and is affected by the length of the entrance pipe. Also, the generation frequency of the vortex ring did not increase linearly with Re, but instead increased in discrete steps. A nozzle modification was also tested, with an acoustic material installed inside the nozzle to suppress pressure fluctuations caused by resonance inside the nozzle. This test was performed at Re = 2000, 5000, and 8000. The acoustic material suppressed the naturally occurring vortex ring, which reduced jet diffusion.
Vibration problems often occur in development of rocket engine turbopump, and an axial vibration is one of these problems. Rocket turbopumps often use balance piston mechanism (BP) which is a self-balancing system in order to balance the large axial thrust derived from high discharged pressure. Turbopump rotor with BP is movable in axial direction and supported by fluid stiffness generated by BP. Although BP has a stable characteristic statistically, it becomes dynamically unstable in some cases because of compressibility of the fluid in BP chamber. Stability of BP has been studied in analysis approaches, but experimental approach has not been conducted yet. In this paper experimental research is conducted to confirm the occurrence of self-excited oscillation and compare the experimental results with one dimensional theoretical analysis. From the experimental results, effect of BP parameters on stability is revealed and it is concluded that there is contradictory relationship between BP static and dynamic characteristics.
An effective combustion technique is required in order to utilize low ignitability fuels. As one of the solution techniques, pilot injection strategies in diesel engines are widely employed to improve the ignition and exhaust emission characteristics. The aim of this study is to investigate the effect of pilot fuel injection. Fuels used in this study have different cetane indices, which were varied by the relative volumetric percentages of LCO (Light Cycle Oil) and diesel fuel. In addition, the distance between the injector tip and the wall was varied in order to investigate the wall effect on the pilot spray behavior and the subsequent ignition and combustion processes. The results showed that the ignition delay time of the low ignitability fuel was effectively reduced by the pilot fuel at low injection pressure. Visualization results revealed that the spray momentum of the pilot fuel is lost at vicinity of the injector tip. In the case of pilot injection at high injection pressure, the wall effect plays an important role for promoting the interaction between pilot and main spray. This is because the fuel/air mixture of the pilot spray drifts in the vicinity of the wall due to the spray impingement and it can prevent the dispersion of pilot spray before the interference with the main spray.
Effects of gas temperature and oxygen concentration on the soot formation of the axial jet laminar diffusion flame have been studied experimentally for the ambient gas mixtures of carbon-dioxide and oxygen. These data were compared to those for the ambient gas mixture of nitrogen and oxygen of 21%. The experiments showed that the flame heights for the mixture of carbon-dioxide and oxygen of 21% and that of nitrogen and oxygen 21% were about same and decreased with the increase of gas temperature. When the oxygen concentration was 21% in the ambient gas mixtures, the total soot volume for the ambient gas of nitrogen and oxygen were higher than that of carbon-dioxide and oxygen and increased with the increase of the gas temperature. When the ambient gases were the carbon-dioxide and oxygen mixtures, the total soot volume increased with the gas temperature for the fixed values of the oxygen concentration in the ambient gases. But, for the fixed ambient gas temperatures, the total soot volume increased with the increase of the oxygen concentration in the ambient gas and reached to a maximum, and then decreased slightly with the increase of the oxygen concentration. The variations of total soot volume were discussed by using the adiabatic flame temperatures for the experimental conditions. The plots of logarithm of the total soot volume for the inverse value of the adiabatic flame temperature show that the oxygen concentration has the strong effect on the total soot volume compared to the effect of the adiabatic flame temperature.
In recent years, ethanol has attracted attention as an environmentally substitute fuel because of exhaustion of petroleum resources and environmental issues. In this study, we investigated emission by using the ethanol water solution from 45 to 60 vol.% concentrations under continuous combustion region by using the swirl burner. In addition, we investigated the flame behavior, influence of flame shape and flame length on the exhaust gas temperature and reduction of emission such as CO and NOX. Furthermore, the influence of the swirl flow by the supply air on the spray shape and the influence of the liquid film on the combustion characteristics were also examined. The exhaust gas temperature was measured in a combustion chamber and exhaust pipe by using K type thermocouples. The main conclusion are as follows: 1) The liquid film/liquid column ratio near the nozzle increases with decreasing the spray angle and the fuel flow rate at the low ethanol water solution (E45). 2) The continuous combustible regions are bigger with increasing the fuel flow rate at the low ethanol water solution (E45). 3) The exhaust gas temperature decreases monotonically with increasing the air ratio in spite of the spray angle and the fuel flow rate at low ethanol water solution (E45, E60). 4) The CO emission of high fuel flow rate remarkably decreases than that of low fuel flow rate at any spray angle for the ethanol water solution (E60) under the air ratio λ from 1 to 1.4. 5) It is possible to realize the less than 10 ppm NOX emission by using the ethanol water solution of E60 under the wide range of air ratios. 6) It is possible to reduce the simultaneous reduction of CO and NOX emissions for the ethanol water solution (E60) under the high air ratio.
Global path planning is often used for initial path planning, as it allows robots to search for the feasible paths. However, it is very difficult to perform global path planning in a dynamic environment because it is hard to predict the behavior of moving obstacles. In this paper, we propose a method to perform a global path plan by using a spatiotemporal graph for environments with moving obstacles that perform predictable behavior. We provide a waiting path in a spatiotemporal graph and setting the waiting cost on it. Then, we show that it is possible to adjust the robot's behavior by using A* algorithm from the balance of moving cost and waiting cost. We also show that the global path from the current position to the goal position can be easily updated by using a spatiotemporal graph, even when moving obstacles change from the scheduled behavior. In order to validate the effectiveness of the proposed method, we apply it for return-path planning of an autonomous tour guide robot in a virtual museum. Finally, we show the simulation results and discuss the applicability of the proposed method in a dynamic environment.
This paper presents the experimental results of the transient characteristics of the tangential force between small cylindrical specimens assumed as a wheel after re-profiling and a new rail respectively, generated in the case where the frictional force is applied to the wheel/rail contact surface repeatedly, and also the results of the numerical analysis of the influence of the wheel/rail contact surface properties on the running performance of the railway vehicles. In the experiments, the tangential force characteristics in case of sweep under the different longitudinal slip change rate conditions have been obtained by means of a twin-disk sliding-frictional rolling machine equipped with the environmental device in RTRI. The experimental results show that the tangential force coefficient is smaller in the range of a low longitudinal slip ratio compared with the Kalker’s theoretical characteristics that are obtained by applying the Levi-Chartet’s formula of saturation, which are the steady characteristics of the tangential force, in case of the contact surface close to that after re-profiling, and that the tangential force coefficient becomes large when the frictional force is applied to the wheel/rail contact surface repeatedly. This means that the coefficient of friction becomes large due to the repetition of the rolling and sliding friction. In addition, in order to investigate the relation between the contact surface properties and the running performance of the railway vehicle, a numerical analysis using a simple wheel-rail dynamic model was carried out by comparing Kalker’s theoretical value with the experimental values. As a result of the numerical analysis, it’s clarified that in case of the power running, the wheel after re-profiling is more slippery than that without re-profiling after long run in the range of a low longitudinal slip ratio.
Although bladed disks are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all the blades on a disk are slightly different due to the manufacturing tolerance, deviations in the material properties, and wear during operation. These small variations break the cyclic symmetry. Bladed disks with small variations are referred to as a mistuned system. In the forced response of a mistuned bladed disk, the responses of all the blades become different, and the response of a certain blade may become extremely large due to splitting of the duplicated eigenvalues and distortion of the vibration modes. On the other hand, mistuning suppresses blade flutter, because the complete traveling wave mode is not formed in a disk. Although such mistuning phenomena of bladed disks have been studied since 1980s, almost all studies focused on the amplification factor of the displacement response, and few studies researched the amplification factor of the vibratory stress response. In the previous paper, authors studied the amplification factor expressed by the vibratory stress for bladed disks with the continuous ring-blade structure, using the reduced order model SNM (Subset of Nominal Modes), and pointed out that the amplification factor of the displacement and the vibratory stress is different. This work is a follow-up study on the previous paper. The amplification factor of the vibratory stress for bladed disks with the free-standing blade structure is studied, using the reduced order model SNM. Comparing the mistuning phenomena of bladed disks of the continuous ring-blade structure and the free-standing blade structure, the reason why the amplification factor of the displacement and the vibratory stress is different is clarified.
We attempt to measure the rotational characteristics of a ball in flight by using a baseball-like ball with a built-in acceleration sensor unit which consists of one three-axis sensor for low G and three sensors for High G. Two approaches for obtaining the rotational speed and its axis of the ball from outputs of the sensors are formulated; one is based on rotational component in the acceleration outputs and the other is based on translational one. We employ in the present approaches the assumption that the time variation of rotation axis can be neglected because it is sufficiently slow. In flight experiments, we obtain nine time series data of acceleration for straight and curve ball trajectories, respectively. By using these experimental data, we estimate the rotational speed and rotation axis with the present two algorithms. As the results, it is shown that the rotation axis keeps almost constant during the flight in each algorithm’s result and this means the validity of our assumption on rotation axis. The difference in the rotation axis obtained by the two algorithms ranges from 3.5 to 10.6 degrees in the straight ball data while it does from 3.9 to 18.8 degrees in the data of curve ball. Also, the averaged rotational speed in the nine trials is 12.56 rps in the straight data, and the difference between the algorithms indicates 0.10 rps (after pitching) and 0.17 rps (before catching). In the curve ball data, the averaged value and the difference between the algorithms are 19.22 rps, 0.10 rps (after pitching) and 0.14 rps (before catching), respectively. The present result shows the decrease of the rotational speed along flight trajectories, and it is probably the effect of aerodynamic torque.
Currently, personal mobility vehicles (PMVs) are attracting attention as intermediate- or short-range transportation. Bicycles are familiar PMVs that are also environmentally friendly and convenient. A small-wheel bicycle saves space and is easy to carry. However, a small-wheel bicycle running at low speed has poor upright stability and maneuverability. The purpose of this study is to improve its running stability by adopting a steer-by-wire system, which independently operates the steering gear and the tire. Sensors obtain the handle angle and actuators, instead of force from a mechanical connection, change the steering wheel angle. In this study, we carried out two experiments. First, we carried out straight running experiments to confirm the steering accuracy, upright stability, and maneuverability on a straight course. Second, we carried out turning experiments to confirm the upright stability and maneuverability on a course requiring changes in driving direction. It was confirmed that the proposed mechanism enhanced the upright stability compared with that of a conventional small-wheel bicycle. However, the maneuverability evaluations by the drivers showed that a conventional small wheel bicycle was better than the proposed steer-by-wire bicycle. The delay of motor control and the moment of inertia of the gearing might be the causes of this performance issue.
This paper addresses a plant that includes different time delays dependent on the polarity of control inputs. An example of such a system is a pneumatic isolation table, which consists of two valves of different lengths. For this plant, a switching control method depending on the control input polarity has been employed. Each polarity is considered as a separate single input system. Alternatively, this plant can also be considered as a two-input system by using both control inputs simultaneously. Thus, the conventional method might have restricted the control performance. Moreover, the switching control method determines an input value by considering the next step input beforehand. To improve control performance, a method comprising several steps in advance is proposed. It is a model predictive control (MPC). However, this method is difficult to apply to the switched system as it results in a problem of hybrid control. In the present paper, we consider this plant as a two-input system, and thus, improvement of control performance is expected. Moreover, the proposed view of the plant is not considered as a switched system. It enables MPC to be applied to the plant by solving a linearly constrained quadratic optimization problem. Finally, the control performance achieved by the proposed method is verified through numerical simulations.
In order to reduce the power consumption of the household refrigerator further, it is necessary to control the rotation frequency of a reciprocating compressor as low as possible. However, several natural frequencies of the compressor exist in the low rotation frequency region. Therefore, the resonance occur in the compressor due to the unbalance force arising from the piston motion synchronous with rotation frequency, and then the vibration of the compressor may be transmitted to the refrigerator. In this study, the compressor was set on a steel plate for experiment, and the vibration characteristic of the compressor supported by means of conventional four points support method is examined. Based on the obtained results, the five points support method is newly proposed in order to suppress the vibration transmission. In the proposed method, the compressor is supported by low stiffness support elements at the four corners and a high stiffness support element at the center. Analytical and experimental results confirm that the natural frequencies of the compressor can be reduced by means of the five points support method as compared with the four points support method. From the results of driving experiment, it was also proven that the resonance of the compressor is hardly occurred in the low rotation frequency region, and the vibration transmission from the compressor to the plate can be reduced.
Because horizontal multi-stage pumps have journal bearings and a balancing piston with narrow gap, it is needed to prevent self-excited vibrations caused by fluid forces in these gaps. For the rotor system, because it is challenging to find the stability limit with a strict model (1 D-FEM), it is better to reduce degree of freedom by fixing nodes of journal bearings and the balancing piston when one is looking to improve the stability limit. This paper suggests a method for finding the stability limit by 2 DOF model, and provides factors affecting the stability limit for horizontal multi-stage pumps. First, the rotor shape and the stiffness and damping of journal bearings and the balancing piston are configured and the rotor system is reduced to 2 DOF by constrained mode synthesis method based on the configurated shape and coefficients. By comparing the solutions calculated with 2 DOF and 1D-FEM, it is confirmed that 2 DOF models are suitable for unstable vibration analysis. Then, the average whirl λeqΩ is calculated by applying Bently-Muszynska model to the coefficients of the journal bearings and the balancing piston and it is concluded that the natural frequency ωn becomes equal to the average whirl λeqΩ at the stability limit. Finally, the influence of the natural frequency ωn and the average whirl λeqΩ on the stability limit is analysed for different cases.
The passive mechanical element that can change the stiffness by using particle jamming has been used for soft robots. The mechanical element can keep the shape by decreasing the internal air pressure, however, is not able to transform the shape by itself. Therefore, it has been used in combination with other actuators to transform the shape actively for the use of robots, which increases the complexity of the system. In this study, we developed a novel mechanical element that contains sponges inside the conventional mechanical element. Evacuating the inside air of the element increases the rigidity, same as the conventional one. At the same time, it compresses the sponges and transforms the shape of the element so that it can wrap the element around an object automatically. This novel mechanical element can be used for fixing or grasping objects or a body. The element requires only a vacuum pressure source; therefore, the system is simpler than conventional robots. This paper firstly shows the structure of the mechanical element and the optimization method from the viewpoint of deformability. Secondly, this paper shows the ability of wrapping various objects and that the contact pressure was constant regardless of the shape of the object. Finally, this paper discusses future applications and problems of the element.
Unmanned construction which includes teleoperation of construction machinery has been introduced after disasters in terms of operators’ safety. One of the most crucial problems in unmanned construction is that work efficiency is less than half compared with usual boarding operation owing mainly to lack of visual information. Environmental views from cameras installed at disaster sites are necessary for precise manipulation even if operators can watch a wide and three-dimensional cab view. Thus, we have investigated optimum and suitable pan and tilt angle of environmental views for precise manipulation including grasping and releasing by using a 1/20 scale model. Experimental analysis using an actual construction machinery is indispensable to apply results acquired by using a scale model for unmanned construction. Therefore, in the present work, we investigate optimum and suitable range of environmental views for precise operation by using an actual construction machinery. We focus on digging and releasing because construction machineries are usually used for digging gravel or sand, and release it to designated area including bed sections of dump trucks. The task of experiments using ZAXIS 35U was determined based on the model task of unmanned construction, including digging modeled to hook a target object and releasing it in the designated area. The results indicate that the optimum pan angle for digging is 60°, and suitable range of pan angle for digging is from 45° to 90°. Furthermore, the results suggest that the optimum tilt angle is 60°, and tilt angle between 45° and 90° affects a little on work efficiency.
Fall is one of the main factors causing the extension of the patient’s hospital stay. In some cases, fall leads the elderly patients to bone fracture, bedridden, and care state. Also in other cases, fall leads to fear, withdraw, and bedridden. However, the medical staff can’t keep eye on all the patients at all the time. Moreover, patient's condition and their environment change from moment to moment. Therefore, the primary screening is need to find the high risk patients and to focus attention on them. Furthermore, real-time risk assessment is need to prevent the patients from falling. In this paper, we propose and develop an automatic real-time fall risk assessment using deep learning as a primary screening of the patients in the hospital. By using our method, we construct a part of the nursing system to reduce the fall incidents and accidents of the patients, and the caregiving load of the medical staff. At the reception, proposed method recognizes patient’s appearance and estimates risks by classifying the fall risk levels according to a hospital’s clinical safety standard, and it stores those safety related information in the electric medical records of patients. While the patients stay in the hospital, medical staffs see the potential risks in the condition of the patients and their environment online through the wearable devices such as smart glasses, mobile terminals, and assistive mobile robots. We prepared a datasets including 16,000 images which collected from public datasets such as MIT places, educational video, actual incident location, and annotated them by ourselves for the clinical safety. The result show a fundamental experiment comparing with manual method by medical staffs and our proposed method surpasses real-time performance and coverage. These automatic fall risk assessment method using deep learning is novel to in clinical safety field.
This paper presents a new type of energy balance equation for a seismic isolation system, which consists of a restoring force element, a damping element and a bearing element, to improve the accuracy of seismic response predictions. The proposed energy balance equation has advantages that it can be taken into account the yield displacement and the bilinear factor for the damping element and the friction force for the bearing element as compared the previous energy balance equation. These advantages will lead to the seismic responses corresponding to the maximum shear force coefficient and the maximum response displacement for the seismic isolation system obtained from the time-history response analysis. This paper demonstrates that the proposed energy balance equation can capture the seismic responses obtained from the time-history response analysis taken into account the various ground motions. Additionally, the optimal damping force that leads to the reducing between the shear force coefficient and the response displacement is presented on the basis of the proposed energy balance equation.
Vehicles with a metal belt-type continuously variable transmission(CVT) that can run under optimal engine fuel consumption conditions have been popular. However, the CVT unit itself can improve in terms of the efficiency. This is possible as the clamping force of the ordinary CVT is much greater than the minimum force required to prevent a large belt slip, which results in excessive friction loss in the belt. The clamping force should be reduced to approximately equal the maximum belt friction force to prevent a large belt slip and improve the efficiency of the CVT unit. However, the belt friction force varies depending on its operating condition and age. Thus, an generating state of the maximum friction force should be detected in each running condition. In this study, we investigate the following three detection methods for the generating state. 1) detection using the speed ratio as a conventional method, 2) a detection method wherein the gradient of the belt friction force on the slip velocity between the pulley and belt is nearly 0 near the belt μ, and 3) a detection method wherein a correlation value between the input and output rotational speeds of the CVT decreases below 1.0. We have described the methods used in this study in detail, and discussed their performance and computational efficiency.
In many countries, the rate of aging in their populations is rapidly increasing. We expect the number of patients with amyotrophic lateral sclerosis (ALS) in bedridden state to increase. The patients are restricted in many aspects of their daily lives, including limited vision to the outside world except only what they can see from the inside of their rooms. This paper proposes an unmanned aerial vehicle (UAV) system using an eye-tracking device for ALS patients in order to improve their quality of life (QOL). This system consists of a UAV, a control screen, an eye-tracking device, a computer, and a transmitter. The UAV has a camera and the camera images are displayed on a control screen. The patient’s gaze position is detected by the eye-tracking device. By using this system, the patient will be able to control the UAV by moving his/her eyes while he/she looks at the camera images on the control screen. Firstly, we explain the research background. Secondly, we describe the overview of the UAV system. Thirdly, we explain the design method of the control screen considering field of vision, eye movements, and eye strain in order to reduce operational errors. Finally, we present experimental results to verify the effectiveness of this system and the control screen.
Safety is one of the most important issues in rehabilitation assist suits. We have proposed and developed a rehabilitation assist suit equipped with a velocity-based mechanical safety device (VBMSD) to address this issue. The assist suit aids flection and extension of a patient’s knee joint. The VBMSD switches off the motor of the assist suit when the angular velocity of the patient’s knee joint exceeds a preset threshold level. The VBMSD works even under failure of the assist suit’s computer, because it consists of only passive mechanical components without controllers, actuators, and batteries. In this VBMSD, the time delay between the instance of the velocity exceeding the threshold and the instance of the motor switched off is an important parameter. If the time delay is excessive, the motor may move a patient’s leg at unexpected high velocities. Therefore, it is necessary to analyze the length of time delay and to experimentally validate the analysis. The analysis will also be useful for the design of future VBMSDs. In this paper, we theoretically derive the time delay using the transient response analysis of the VBMSD. Furthermore, we simulate how quickly the VBMSD responds to a rapidly increasing velocity by using the derived time delay. Finally, we present experimental results to verify the analysis and simulation.
The objective of this study is to compare four kinds of hand assignments of slip-perception and stroke-reproduction task to dominant/nondominant hand for right handed persons based on a device that can present slippages to users via their fingerpad skin. The device is called an “active-wheel-based finger-tactile interface (AWB-FTI)” in this paper. It is an interface that embodies an active wheel being rotatable in any directions, with any speeds, and with any time durations. The movements result in slippage stimuli on users’ fingerpad skin. Then, users are supposed to recognize the slippages as line-segments in a mental image. The reproduction of the recognized line-segments as the hand strokes with proprioceptive sensations is effective for storing the recognition in users’ memory. The performance of the device is measured by a pair of tasks composed of the slip-perception task and the stroke-reproduction task. Each of the pair of tasks should be assigned to either dominant hand or nondominant one. That is, four hand assignments are defined for the perception and the reproduction: the hand used for perception and that for the reproduction are “Dominant×ipsilateral,” “Dominant×contralateral,” “Nondominant×ipsilateral,” and “Nondominant×contralateral.” The reproduction errors of the four hand assignments were measured through a comparative psychophysical experiment with the slip-perception and stroke-reproduction task. As a result, we found the following characteristics: (1) as for the slippage-speeds and -angles, the nondominant hand was better than the dominant one from the viewpoints of both random and systematic errors in the perceptual hand, while either nondominant or dominant hand showed no significant difference in the reproductive hand, (2) as for the slippage time-durations, the “Dominant×contralateral” was worst in the four hand assignments from the viewpoint of random errors, and the “Nondominant×contralateral” was best from the viewpoint of systematic errors.
If bearings for gear units of railway vehicles are damaged by seizing, parts of the bearings come off and damage the gear and the gear box, which may lead to the leakage of the gear oil and the defective rotation of the wheel sets. Tapered roller bearings are mostly used in the gear units in Japan. The sliding speeds at the contact surface between the roller end and the inner ring flange of the pinion bearings are higher than that of the gear bearings. In the pinion bearings, therefore, seizure may occur by metal-to-metal contact from inadequate lubrication between the roller end and the inner ring flange. In order to prevent seizure of the bearings and to improve the reliability of the gear units, it is important to clarify the causes of the inadequate lubrication and the mechanism developing from inadequate lubrication into seizure of the bearings. In this work, the effects of bearing rotational speeds and loads, gear oil temperatures and flow rates, and endplay (internal clearance of bearings) values on the performance of the bearings have been investigated by using a rotation testing apparatus for pinion bearings. As a result, it has been clarified that the heating value from bearings increase as the oil temperature decreases and as the oil flow rate increases. In addition, it has been found that the endplay value is greatly reduced when the rotational speed of the bearing rapidly accelerates to high speed under conditions where the temperature of the gear oil is relatively low.
Observational methods such as NIOSH lifting equation (NLE) are used for risk assessment of low back pain. The observational methods can easily assess the risk of low back pain, whereas they hardly consider the individual differences such as age and height. The aim of this study was to investigate the effect of age and height on L5/S1 compression force during manual material handling. The L5/S1 compression force was estimated by digital human modeling (DHM) simulation. The simulation conditions were the gender (male and female), age (20’s, 40’s, and 60’s), and height (approximately 5, 50, and 95%tile of Japanese male and female). The reduction of muscle strength due to aging was imitated by changing the maximum muscle force of the DHM based on a physical fitness measurement. The elder models (i.e., 40’s and 60’s) showed higher muscle activity of trunk muscles compared with the 20’s model, whereas the muscle activity of lower limb muscles decreased with increase of age. The L5/S1 compression forces of elder models for the male and female models were approximately 22% and 15–30% higher compared with those of 20’s, respectively. The trunk flexion angle of estimated working posture increased with increase of model’s height, and the L5/S1 compression forces of 50%tile and 95%tile models showed approximately 6–17% higher than that of 5%tile model. In addition, the NLE may underestimate the risk of low back pain when the horizontal distance of handled material is far.
The purpose of this paper is to show a new gravity compensator which allows for the passive vertical weightless motion. The conventional zero gravity simulators could not simulate the vertical balance and weightless motion passively at the same time. For example, the simulator using the counter weight of the same mass can only simulate half the acceleration of the weightless motion because an external force acts on both the object and the counter weight. On the other hand, the simulator using the low stiffness spring is difficult to balance. Firstly in this paper for such a trade-off, a new concept which is named degree of zero gravity (DOZ for short) is introduced. By using DOZ we can estimate how similarly the system simulates the acceleration in zero gravity. Secondly, a new gravity compensator which uses a heavy counter weight and a pantograph mechanism is introduced and evaluated by means of DOZ. When an external force acts on the object of the gravity compensator, most of the energy acts on the relatively lightweight object by using the heavy counter weight. It follows the passive vertical weightless motion of the object. Finally, numerical results show the effectiveness for the passive vertical weightless motion. The main results obtained are 0.86 times the acceleration in zero gravity when an external force is applied and the disturbance acceleration of 2.3 × 10−4g or less when an external force is not applied.