To improve patient safety in ambulance transport service, this paper proposes a new method for finding an optimal route of an ambulance depending on the disease or injury of a patient. Three transport cases are considered in this paper: Heart disease (HD), hemorrhagic cerebrovascular accident (HCVA) and fracture/dislocation (Fx/dx). The route optimality is measured with three evaluation functions. The first function evaluates an elapsed time from the scene of an emergency to a hospital. The second evaluates a blood pressure variation induced by the acceleration/deceleration motion of an ambulance. The third evaluates a compression load acting on the back of a patient due to the centrifugal force. They are calculated by applying the traveling model of an ambulance to the three-dimensional road network. The optimal route is selected in two stages. First, the candidate routes are found by solving the multiobjective optimization problem of minimizing the three evaluation functions. If the completely optimal solution (route), which minimizes the three functions simultaneously, is found, the selection process is finished. Otherwise, obtain the Pareto solutions to go to the second stage, in which a preference solution is selected from the Pareto solutions depending on the disease or injury of a patient. In the numerical example, the route selection is shown for HD, HCVA and Fx/dx. For the reference sake, the real routes of the ambulance recorded in Hiroshima City and the shortest routes obtained by Google Maps Navigation are also presented and compared to each other.
This paper introduces a two-degree-of-freedom pipe selection mechanism using contraction and extension unit composed of single tube and a T branch experiment of an in-pipe mobile robot equipped with this mechanism. Household piping is used for gas transportation to each household. If the pipe is cracked or corroded due to long-term use, it becomes difficult to supply a stable gas. Therefore, inspection of household piping is necessary. The existing methods require a lot of time for the inspection or it is difficult to inspect the entire pipeline. Therefore, in this study we developed an inspection robot for home piping using a mobile robot. To date, the robots proposed have been able to bend in the direction along the pipeline, as the tip of the robot passively bends when passing through the curved pipe. However, at the branch pipe, there is no mechanism that actively bends the tip of the robot, and the pipe cannot be selected and moved in a specific direction. Therefore, this paper proposes the application of a small pipe selection mechanism combining a ball-point pen knock mechanism and a wire bending mechanism to an in-pipe mobile robot using the pressure difference of a single tube.
In general, small robots can operate in narrow spaces, and large robots can traverse over rough terrains. Although a few robots with adjustable wheel diameter have been developed, they require multiple actuators for rotating the wheels and changing the wheel diameter. This paper proposes a wheel robot that can adjust the wheel diameter according to the wheel rotation. The robot uses a centrifugal force-aided diameter adjustable mechanism; the wheel diameter is expanded/contracted by a circular pantograph via the centrifugal force. Thus, the wheel diameter can be changed depending on the drive of the wheel. We adopt the circular pantograph mechanism to maintain the round shape of the wheel during expansion and contraction. We conducted experiments with the developed robot and found that the wheel diameter appropriately changes with the wheel acceleration and deceleration. The results show that the proposed mechanism improves the performance when climbing a step and operating in a narrow space. Further, the robot also had mechanical flexibility, which helps reduce the impact when facing a step. These characteristics could be achieved because the wheel was passively and adaptively deformed according to the running environment.
It is important to elucidate the lower limb motion based on the activation of lower limb muscles during pedaling to improve pedaling performance of cyclists. In previous studies, although the activation of these lower limb muscles has been investigated by a surface electromyogram (EMG), the evaluation of muscle contraction during pedaling has not been conducted. Muscle contraction refers to the muscle activation state accompanying a change (stretching / shortening) of the muscle length, and the exerted muscle strength and the status of muscle fatigue have complicated relationships that are difficult to be clarified. The purpose of this study is to propose a novel method to evaluate the muscle contraction during pedaling. Muscle contraction characteristics were analyzed to elucidate the pedaling motion based on relationships between muscle length variation (stretching / shortening) and contraction velocity and the strength of muscles. In the experiments, cyclists were instructed to perform their pedaling technique at two pedaling rates (cadence: 80–90 and 110–120 rpm). EMG signals were recorded from rectus femoris (RF), biceps femoris (HAM) and gastrocnemius (GAS). Pedal force was measured by a power meter (Pioneer Inc.). Furthermore, the lower limb motion during pedaling was measured using a 3D motion capture system. In addition, the muscle length model of the lower limb was constructed based on the Hill–Stroevo model to identify the lower limb muscle length during pedaling. The experimental results show that the proposed system evaluates the muscle activation and contraction during pedaling as well as the pedaling skill based on the muscle contraction. The analysis results of the muscle contraction show the importance of the hamstrings activation state during the pedaling motion.
In this paper, we propose a method to predict the failure of factory equipment by machine learning architectures using vibration data. We design the model so that we can predict robustly the failure of the equipment in advance. We use a Gaussian Mixture Model (GMM), a machine learning architecture, to calculate abnormality value which is used for the decision whether the state of the equipment is normal or abnormal by thresholding. We also use Long Short-Term Memory Autoencoder (LSTM-AE), one of the structures of the deep learning algorithm, for feature extraction. LSTM-AE model learns both spatial and temporal patterns which are difficult to capture with conventional machine learning algorithms. We conducted the prediction experiment using vibration data obtained from actual mechanical equipment, to confirm our method can predict the failure more robust than conventional methods. From this experiment, we found that the abnormality value tended to exceed a threshold value before the actual failure, indicating that the failure can be predicted in advance by our method. Besides, when compared with conventional methods, we found that the transition of abnormality and the accuracy of failure prediction were almost the same in all cases, but we also showed that the proposed method has superiority on robustness compared to conventional methods about the transition of abnormality and the setting of the threshold.
This study investigates an effect of inelastic non-proportional preloading on failure life in a followed high cycle fatigue for two steels, SUS316 stainless and Mod.9Cr-1Mo steels. Preloading tests were conducted using a servo controlling hydronic multiaxial fatigue testing machine which can apply an axial loading and torsional loading. Two types of loading paths under strain controlled were employed: a push-pull loading and a circle loading. The circle loading is the non-proportional loading in which axial strain ε and shear strain γ have 90-degree difference. Using the specimens fatigued in the inelastic preloading test, high cycle fatigue tests were conducted by a rotating bending fatigue testing machine. Based on the obtained results, effects of inelastic proportional and non-proportional preloading on the failure life in high cycle fatigue is discussed. The high cycle fatigue life for SUS316 stainless steel such as the materials of which crystal structures are FCC was increased due to cyclic hardening depending on inelastic non-proportional preloading. On the other hand, the life for Mod.9Cr-1Mo steel which has BCC was reduced by the cyclic softening induced by the preloading.
For judging whether two stresses maintain objectivity between different frames, appropriate criterion needs to be used. The criterion, c*u= cu・Q: Σ*= QT・Σ・Q has been normally used, but it was found that it did not have the ability to judge the essence of objectivity. Getting over the deadlock for judging quality of objectivity, the comparison of stress values is indispensable between frames under an identical stress tensor. As a result of examining the difference of stress values, the essential criterion for objectivity σCpq=σBpq+DMσBpq, DσCpq=DσBpq was given. It is shown that Jaumann stress increments DJσpq is not recognized as an objectivity stress increment. Even in such an environment, there are some proposals that DJσpq should be replaced instead of Dσpq in constitutive equations. Then, the spin included in DJσpq gives stress a fluctuation depending on the induced spin, which was presented in this manuscript.
Ground acoustic tests using stationary acoustic environments have been conducted to verify spacecraft resistance design against the transient random acoustic load during launch. Traditionally, a stationary acoustic test spectrum has been derived from a kind of short-time Fourier transform performed on transient random acoustic load, being enveloped. The envelopment, however, inevitably results not only in an excessively conservative spectrum, but also in the innate disparity between stationary and transient-random acoustic environments in their vibro-acoustic responses, diverting them from exhibiting equivalency for design verification. Furthermore, an excessively conservative spectrum forces unnecessary cost increase upon product design. One solution proposed in this paper is a method based on a vibro-acoustic single degree of freedom model, to derive the stationary acoustic environment condition with equivalent maximum load and cumulative fatigue damage of vibro-acoustic structure as in transient random acoustic environment condition, using extreme response spectrum and fatigue damage spectrum. The application of this method to actual flight acoustic data during launch demonstrates that it outweighs the conventional method in environmental resistance of structures with reduced conservative margin.
In a pressure vessel, a heat exchanger and a junction piping where cold and hot water are mixed, temperature fluctuation yields multiaxial stress and random amplitude loading conditions. In most cases, the loading becomes non-proportional loading in which directions of principal stress and strain are changed in a cycle. Fatigue lives under the non-proportional loading are reduced depending on non-proportionality of loading path. In this paper, cyclic deformation under multiaxial loading simulated thermal fatigue is discussed based on the test results and a method of fatigue life evaluation under complex multiaxial random loading is presented. T-shaped loading, in which reversed torsion loading with static tension (tension T-shape loading) or compression (compression T-shape loading) followed push-pull in a cycle, is used as the simulated loading in the junction piping. Fatigue lives under T-shaped loading depend on the number of the reversed torsion loading. The fatigue life is increased due to increase in the number of the reversed torsion loading which leads to relaxation of loading non-proportionality. The fatigue lives under compression T-shape loading is shorter than that under tension T-shape loading. The reason is effect of mean stress, which the mean stress in push-pull under compression T-shape loading is shifted to tension due to static compression stress relaxation by reversed torsion loading. Modified IS-method, which takes into account of mean stress by using centroid of loading path, is proposed to represent the reduction in non-proportionality and the stress relaxation in T-shape loading.
In the previous reports, a methodology for estimating noise radiation including airborne noise from a mechanical system under the operational condition by component test of a certain active subsystem using the in-situ blocked force approach, which is normally used for estimating only structure borne noise, was proposed and verified by numerical simulations of noise radiation from a cantilever rectangular plate. This paper describes experimental verification of the proposed methodology by application to rattle noise from a column type electric power steering system (EPS) for a vehicle. Therefore an EPS corresponds to the active subsystem and the other parts such as vehicle body correspond to passive subsystems. At first, a method of measuring rattle noise from an EPS under the operational conditions, i.e., running tests with a vehicle, was established. Since it is possible to apply the in-situ blocked force approach also to vehicle running tests and to estimate rattle noise, the measured and estimated rattle noises under an identical operational condition were compared and validity of the proposed methodology was confirmed. Next, a component test bench which enables to reproduce vibration behavior of an EPS under the operational conditions was developed, and rattle noise under an operational condition was estimated by means of the proposed methodology using both vibration accelerations measured with this component test bench and vibro-acoustic transfer functions measured with the vehicle under a static condition. Finally, the proposed methodology was verified by comparing the estimated and measured rattle noises under the operational condition. The proposed methodology is expected to replace time-consuming operational tests of a whole mechanical system to simple component tests of the active subsystem.
A first-order-reset element (FORE) controller is modified to adjust the vibration attenuation characteristic of a magnetic suspension system. The proportional-derivative (PD) feedback control is the simplest control method of stabilizing magnetic suspension systems. In the PD-controlled system, restoring force is produced with the proportional element and damping effect is produced with the derivative element. Meanwhile, a feedback control using a FORE has been proposed to stabilize magnetic suspension systems. The FORE replaces a linear integrator built into a first-order low-pass filter by a non-linear integrator. The proposed controller can stabilize a magnetic suspension system with one element. The restoring force and damping effect are generated simultaneously. However, the two effects could not be adjusted separately. To adjust the vibration attenuation characteristic, the FORE controller is modified to adjust the transition value at reset. The characteristics of the modified controller are studied through numerical analysis. Then the effectiveness of the modification is demonstrated by several simulations and experiments.
In the context of recent servitization of manufacturing characterized by IoT, Big data, and AI, we require a data-driven front-loading design of product with service. This paper proposes a design method of service system that encourages co-creation using a structural framework called TriCyPSS (Triple Cycles for Product Service System) from the viewpoints of service chain and continuous provision among client business, my business, and partner business. This paper shows a case study according to the method’s procedure and details notations using a system modeling method called i* (eye-star). Using them, we clarify value in use brought by the service chain and continuous provision as well as data utilization and information circulation. Finally, this paper employs the method together with business planning methods and tools for practical use.
Surface winding processes are simulated up to 49-70 laps by means of a FEM commercial software. The simulation model is composed of a flexible web with linear-isotropic nature, rigid core and rigid drum (or rigid two drums and a rider roll). Stress distributions of wound rolls, tension (tangential stress) change during winding and layer slippage are investigated. The main results are as follows. In case of single-drum surface winding, the roll stresses become larger as a friction coefficient between web layers, nip load, drum diameter or a line tension increases, or Young’s modulus decreases. Poisson’s ratio has little effect. The roll stresses depend on not only WIT (increased tension of the outermost layer due to the nip load), but a decreasing rate of tension at a web point during winding, and they have a cross relation with a value obtained by integrating a web tension varying curve from the start point where the web enters the roll to the end of winding. In case of two-drum surface winding with differential drum speeds, the web tension varies complicatedly at three nip zones and is larger between the rider roll and the second drum. The tension of the outermost layer decreases with increase in the roll diameter. The slippage occurs as the outer web layer pulls the inner in the roll rotational direction and is larger at the outer web layers. When speeds of the two drums are equal, the first drum drives the roll and the tension is larger between the second and the first drum. The slippage is the same as the differential drum speed case in the range of 2/3 of the roll thickness, but in the rest range, the slippage occurs in the opposite direction.
Today, offline programing is available on industrial manipulators and used in many factories. However, the absolute accuracy of robots is insufficient due to manufacturing and assembly tolerances, thus it is necessary to perform kinematic calibration in advance. Most of existing calibration methods require a large amount of measurements just to calibrate a robot. In addition, when programing the robot offline, it is also important to perform motion planning for safe and efficient operations. Appropriate motion planning enables the robot to move along the optimal route taking obstacle avoidance and cycle time reduction into account. For this purpose, the accurate measurement of the environment around the robot is required, but existing methods require a lot of work and time. Therefore, in order to reduce the time and effort required for kinematic calibration and environmental mapping, we developed a SKCLAM (Simultaneous Kinematic Calibration, Localization And Mapping) method, in which kinematic calibration and environmental mapping are performed simultaneously for a manipulator with an RGB-D sensor attached to its hand. In this study, in order to improve the accuracy of the SKCLAM method, we introduced checkerboard patterns. We verified the SKCLAM method with checkerboard patterns in both a virtual environment and a real environment. The results showed that the effectiveness and some limitations of our current implementation.
Mechanical snubbers and inertia mass dampers are known as vibration control devices that have inertia mass elements and generate the inertial resistance force. By adding the devices with the inertia mass elements to piping systems, we aim to reduce various responses of the piping systems during earthquake events. In this study, we propose a design method to optimize design parameters of mechanical snubbers installed on a single cross section beam (continuum model) piping system to achieve good dynamic responses of the beam while maintaining the structural integrity of the beam and the supporting device. A performance index considering various specifications related to mitigation of responses of the piping system for earthquake disturbances and the economic cost for installation of devices with some inequality constraints is defined. Design parameters to optimize the performance index are the number and the model size (capacity) of the mechanical snubbers, the value of the inertia mass and the placement of each snubber. The performance index is optimized with a genetic algorithm. A simulation example shows that we could search the optimal design parameters that show the good performance on vibration suppression while satisfying the considered constraints.
If the octet truss core, which is a space filling structure of half regular octahedrons and regular tetrahedrons, has excellent sound insulation characteristics, the possibility of using the octet truss core is sufficiently widened. From this fact, we have studied to obtain sound insulation characteristics of the flat plate and the plate with single core using acoustic tube by the finite element method (FEM) with high accuracy. The calculation of sound insulation performance by FEM was limited to the qualitative study so far. For example, the correction is required due to the difference from the theoretical value, and the magnitudes of the correction values differ depending on the test pieces. In this study, we considered the incident wave and compared the sound insulation calculation result by the FEM calculation using the non-reflective boundary at the rear end of the sound receiving room with the theoretical calculation. As a result, both calculation values were almost the same. Therefore, it can be said that when the magnitudes of the incident wave and the reflective wave are almost equal, a quantitative study is possible. Taking advantage of this fact, in this paper the sound insulation characteristics of the plate with single core are compared with that of flat plate, and the effects of the sound insulation characteristics by the aspect ratio of the core are examined.
In heat exchangers like a boiler, as a tube bank is set in a duct the alternative vortices occur behind a tube bank and the vortex shedding frequency increases with the flow velocity when the boiler is operated. High level sound is suddenly generated when the vortex frequency comes close to the acoustic natural frequency of the duct. The high level sound keeps the frequency and the amplitude constant even if the flow velocity increases in the case of small acoustic damping due to the self-excited mechanism. This is generally called the self-sustained tone and the factory is forced to stop the operation due to the complaints of the neighborhood. The effective countermeasure is required in the design stage. In general, the baffle plate is inserted in the tube bank but it is difficult to treat it, especially to the duct with plural tube banks. Then the other effective countermeasures are keenly anticipated. The author has many studies concerned to the clarification of the generation mechanism and the countermeasures and their effects. In recently, it is clarified that the perforated plate suppresses the high level sound. The author has a question what is the relation between the suppression effect of the perforated plate and the dimension ratio. Then in this paper, the acoustic experiments will be conducted by using the three different sizes of the ducts and perforated plates. The acoustic damping obtained by these experiments and analyses is compared. As a result, it was clarified that the acoustic damping ratio becomes smaller with larger of dimensional ratio.
Demand for high precision machining of complicated shapes has recently increased with the miniaturization of mechanical and electronic products. Therefore, further development of fine wire electrical discharge machining (EDM) technology using a thin wire electrode has been also requested. However, there might be a limit in improving the machining performance of fine wire EDM using conventional wire only by optimizing discharge pulse conditions and gap control. Therefore, it is essential to develop a new type of thin wire electrode for further improvement of wire EDM performance. In this study, high-zinc-content brass (γ-phase brass) coated steel core wire as a new type wire electrode was trially made to improve the machining stability. In wire EDM, zinc content of wire surface would contribute to rapidly cool down the gap by the evaporation due to its low boiling point. However, the surface of γ-phase brass coated wire tends to become rough in the heat treatment process of the wire. Thus, another type of the γ-phase brass coated wire with smoothed surface was also made by an extra finish drawing. The wire EDM characteristics using these wires were compared with those using conventional brass coated steel wire. Furthermore, the distribution of spark locations during process was evaluated by high-speed observation to investigate the influence of γ-phase brass and the surface roughness of wire. As a result, the cutting speed using the γ-phase brass coated steel wire with smoothed surface is faster than that using conventional wire because of uniform distribution of spark location.
This paper evaluated measurement accuracy and precision of ultrasonic spinning rheometry (USR), which can evaluate rheological properties through equation of motion and velocity information captured by ultrasonic velocity profiler (UVP), in cases that assumptions of two-dimensional one-directional flow are not perfectly satisfied. Time variation of effective viscosity in separating oil-water mixture was examined by USR to demonstrate its applicability for both time-dependent rheological properties and multiphase media, which cannot be evaluated by conventional torque-type rheometers. Decrease in pseudoplasticity and effective viscosity of the media with time during separation of water droplets from the media accompanied by monotonic decrease in diameter and volume fraction of the droplets on the measurement line, was quantified. The time variations show the same trend with formula theoretically derived for evaluating emulsion viscosity, but the viscosity was estimated larger than the theory. An increase of effective volume fraction or non-equilibrium flow field may have increased the viscosity.
In the field of precision positioning such as semiconductor exposure apparatus, vibration from the floor greatly influences the positioning accuracy. In order to prevent deterioration of accuracy, an anti-vibration apparatus is installed to isolate vibration. Along with high integration of semiconductor, the allowable value for disturbance vibration becomes severe, and improvement in the performance of the anti-vibration apparatus is required. The anti-vibration apparatus attenuates vibrations higher than natural frequency. Therefore, lowering the natural frequency is directly linked to performance improvement. Here we show stably lowering natural frequency by decreasing spring stiffness using variable structure system. We already proposed a method to decrease spring stiffness of the air spring. However, when trying to completely decrease the spring stiffness, excess or deficiency of decrease amount due to the uncertainty of the machine parameter occurs and it becomes unstable. This is because the polarity of the spring stiffness becomes positive, negative, and zero due to excess or deficiency, and the vibration characteristics greatly change. Therefore, the variable structure system aggressively switches the polarity of the spring stiffness on the phase plane. By geometrically designing the switching function on the phase plane under the vibration characteristics which change by switching, the equilibrium point becomes global asymptotically stable. In addition, the variable structure system has aspects of sliding mode control and converges to the equilibrium point without being affected by the uncertainty. The stability of the proposed method is guaranteed by the Lyapunov function. In addition, it was installed in an experimental apparatus to demonstrate the stability and effect on lowering natural frequency.
This paper describes the active DC current control of a zero-sequence load using a diode rectifier for a three-phase four-wire motor drive system, intended for application to (for example) a three-phase motor with an axial magnetic bearing. This motor drive system requires a three-phase inverter for rotation and a single-phase H-bridge inverter for magnetic suspension. To reduce the number of system components, the authors propose a unique current control method, where the suspension winding is connected between the neutral point of the Y-connected three-phase motor winding and the middle point of two split capacitors of the inverter. Such a wiring connection is called a three-phase four-wire system, and the current flowing in this suspension winding is defined as a zero-sequence current herein. Hence, only one three-phase inverter is required for the control of the three-phase motor current and single-phase magnetic suspension. However, the split capacitor voltages are unbalanced when DC current is provided to the zero-sequence load of the suspension winding because the capacitor voltage is proportional to the integral of the zero-sequence current. To supply DC current to the suspension winding and balance the split capacitor voltages, a novel circuit topology is proposed, where the diode rectifier circuit with suspension winding is connected to a zero-sequence load. When an AC current is provided to the zero-sequence load, a rectified current with a DC component is provided to the suspension winding, whereas the AC current flows in the split capacitors, thereby balancing the capacitor voltages. To verify the proposed DC current control, circuit simulations and experiments were performed. The experimental setup comprised a three-phase permanent magnet synchronous motor and a one-degree-of-freedom magnetic levitation. The test results show that the proposed method can provide a DC current to the suspension winding and control the magnetic levitation with balanced split capacitor voltages.
The purpose of this study is to investigate the effect of testing conditions, i.e., the strain rate and the gauge length, on the tensile properties of a single human hair. Moreover, the changes in the surface morphology of the hair under the tensile deformation is reported. Human hair has been found to hold various information on our body such as disease, aging, etc. And therefore, the information of hair is expected to be used in various fields for application in the future, e.g., as a sample for medical inspection. Because the mechanical properties of human hair are greatly affected by its internal structure, theses must be suitable parameters for above mentioned application. To conduct a tensile test of a single human hair under the optical microscope observation, a compact testing apparatus was developed, and the tensile test of a hair was performed under various conditions of strain rate and the gauge length. Young’s modulus was independent with the strain rate, and its average value was 3.45 GPa. Although the fracture stress showed the strain rate dependency, it was independent with the strain rate under 2 × 10-4 s-1. The average value of fracture stress without depending on the strain rate was 192 MPa. The fracture stress increased with decreasing the gauge length. This was considered that the less defects are included in the cortex for shorter testing section. Moreover, from the in-situ observation of the surface of the hair under the tensile deformation, the lift up of the edge of the cuticle was observed, and this behavior was quantitatively monitored as the delamination area. The delamination area of the outer cuticle monotonically increased with increasing the strain up to the fracture point.
We have developed a technique which can control the particle interval (spacing), velocity and timing in microchannel flow by exerting dielectrophoretic (DEP) force on the particles periodically over time and space using the boxcar electrode. Controlling the interval of the particles to align with even space in the microchannel can improve the performance of the sensor, sorter, and encapsulation system for particles and cells in the microfluidic devices. One of the concerns about this technique is whether we can align the particles when several particles are located in the same periodic area. In the present study, we conducted numerical simulations and measurements for the motion of 12μm polystyrene particles flowing in the boxcar electrode region to evaluate how the particles separate when they are located in the same periodic area, and understand their motion characteristics during the separation process. The result showed that the two particles approach each other, change their position, and separate due to the DEP forces, flow velocity distribution, and collision between the particles. The particle located in the downstream side then moves to the upstream periodic region in a repetitive manner until it fits in a vacant region. We measured the frequency distribution of the number of particles in the periodic area at the inlet and outlet of the boxcar electrode and observed only 0 and 1 particle in each periodic area at the outlet. This represents that particles entering the boxcar electrode region with random interval separate and align with even interval by the time they reach the outlet.
Biohybrid robots composed of synthetic skeletons and living components have recently gained interests as a solution to engineering biological dynamic systems. Among the living components, muscle tissues are used as actuators for biohybrid robots, resulting in vitro reproduction of various movements. Especially, swimming robots containing living muscle tissues or cardiomyocytes have been proposed as representative examples of biohybrid robots. However, these robots have limitations on reproducibility and controllability due to individual differences between each explanted living muscle tissues and the self-contraction of cardiomyocytes, respectively. To solve the issue, a swimming robot with cultured skeletal muscle tissue is required since it allows to control the shape and contraction of the cultured tissue. In this paper, we propose the construction method of a swimming robot with cultured skeletal muscle tissue. Our method can prevent spontaneous shrinkage before transferring the tissue from an appropriate culture substrate for tissue formation to the swimming robot. Using the method, we succeeded in the preparation of a swimming robot with three different robot skeleton and skeletal muscle tissues cultured under the same condition, regardless of the spontaneous shrinkage during culture. As a result, we obtained the relationship between shapes of robot skeletons and propulsion of the robot and confirmed that the robot can move forward by shaking a tail fin. We believe that the method for integrating skeletal muscle tissues with the synthetic skeleton will be useful for the easy preparation of biohybrid robots and devices.
For poly-dispersed nanoparticles, which have more than two peaks on their particle size distribution (PSD), it is important to determine the mean particle diameter and their dispersion at each peak in a liquid. Dynamic Light Scattering (DLS), that is one of a typical nanoparticle sizing method, has difficulty to determine the several peaks in the PSD for the poly-dispersed particles. On the other hand, Image analysis methods (IA) can distinguish the peak for both the primary particle and secondary particle in the PSD of poly-dispersed particles accurately. However, IA is a time-consuming method and it is difficult to apply the measurement of the PSD due to the requirement of measuring the large number of particles, one by one. The particles in the liquid are transferred to a substrate in air when observing the particle to measure their size and the size distribution. In this procedure, some particles usually aggregate with surrounding particles. It causes the difference between the PSD for dispersed particles in liquid and that of the particles on the substrate. In this study, we suggest a novel particle sizing method using “Nanoparticle chip”, that is nanoparticles grid on the substrate to maintain the poly-dispersed condition in the liquid, to develop IA for measuring the poly-dispersed particles in liquid. The dispersed condition of the particle on Nanoparticle chip can be kept from the condition in liquid when the particles are transferred to the substrate in air. Therefore, measuring the PSD on Nanoparticle chip is equal to measure the PSD in the liquid. In this paper, in order to verify the feasibility of the nanoparticle sizing using Nanoparticle chip to measure the PSD for poly-dispersed particles in the liquid, we performed a fundamental experiment to fabricate the Nanoparticle chip and to determine the PSD for poly-dispersed particles. In this report, it is reported that the PSD for the poly-dispersed particles, which is the mixture of 152nm particle and 498nm particle, using Nanoparticle chip.
Generating novel design concepts is a cornerstone for producing innovative products. Although many methods have been proposed for supporting the task, their performance depends on human ability. The ultimate goal of this research is to build a method supporting designers to generate novel design concepts with the knowledge of human creativity. Toward the goal, this research assumes that the more distant two function concepts chosen, the more novel idea would be come up with by the combination of the two concepts. Based on the assumption, this paper introduces a notion of novelty potential of the combination of two function concepts, and builds a method to assess it by the function similarity. Some alternative methods are proposed to calculate it with the integration of a lexical database for natural language called WordNet and a distributional semantics method called word2vec. They are verified with an evaluation experiment which performs correlation analysis between the human’s evaluation of the novelty potential and the proposed method’s assessment of function similarity. This paper discusses which method matches a human sense most, and its possibility for design concept generation based on the results of the experiment.
The time-dependent elastoplastic deformation behavior, i.e. viscoplastic deformation behavior, is observed in solids and structures subjected to high temperature under monotonic and cyclic loadings. Then, the deformation analysis is required by incorporating the rigorous viscoplastic constitutive equations capable of describing cyclic loading behavior at high temperature. There are two types of viscoplastic models, i.e. the overstress model and the creep model. The former is pertinent as the mechanical deformation behavior is reduced to that of the ordinary elastoplastic constitutive equation in the quasi-static deformation process, but the latter is impertinent as it is irrelevant to the ordinary one. Unfortunately, however, the existing overstress model is incapable of describing the cyclic loading behavior because the interior of the yield surface is assumed to be a purely-elastic domain. On the other hand, the subloading-overstress model possesses the basic structure capable of describing the viscoplastic deformation behavior under cyclic loadings, but the applicability to the prediction of real material behavior has not been verified hitherto. The mechanical tests of the spheroidal graphite cast iron under monotonic and cyclic loadings at high temperature and various strain rates are performed. The simulations of the test results are performed by the subloading-overstress model and the existing overstress model. Consequently, it is verified that the subloading-overstress model is capable of simulating the test results accurately.
The generation of burrs is unavoidable in most cases of mechanical machining. Leaving the burrs on the workpieces may cause various problems, thus the deburring process is necessary. Deburring process requires exclusive tools, and the tools are difficult to apply the workpieces with complicated shape. Laser machining is noncontact process thus it does not cause the deformation of workpiece and tool wear. Especially, fiber laser beam can be transmitted by flexible optical fibers so that it is easy to handle. The purpose of this study is to clarify the processing condition for achieving desired chamfering width with fiber laser. A series of experiments were performed by providing fiber laser beam to ferrous block’s right angle edge. In the experiments, the assist gas direction, the laser power, the processing speed, and the beam diameter were defined as processing parameters. Experimental results confirmed that defocused fiber laser beam can apply to chamfering ferrous materials. It also became clear that processing time can be shorten by processing fiber laser chamfering with higher laser power and higher scan speed. In addition, the results confirmed that the chamfering width is controlled by altering processing parameters as the input energy per unit time and unit volume are kept constant. Furthermore, the burrs on right angle edge can be removed by fiber laser, and the shape of deburred edge becomes rounded.
Ion beam etching is effectively used for the fabrication of high-precision optics. The main application of ion beam etching is to figure large optical surfaces to correct shape errors remaining on polished surfaces. To figure small or medium-size optical surfaces, the generation of an ion beam with a smaller diameter and a higher ion current is required. In this study, we designed a magnetic lens with quadrupole magnets using neodymium magnets to obtain an ion beam with a small diameter. The magnetic lens is installed between the outlet of an ion gun and a chamber, which enables the trajectory of the ion beam in the chamber to be changed. The trajectories of the ion beam and the ion particle distribution on a workpiece surface when a doublet or a triplet magnetic lens was used were simulated. Simulations were also conducted for ion beams with large and small emittances entering a magnetic lens. In the simulations, the ion beam without a magnetic lens was approximately 30 mm in diameter on a workpiece surface. The simulations showed that the doublet magnetic lens can converge the ion beam on a workpiece surface to an area of approximately 6 mm × 10 mm when the emittance is small. However, this lens is less capable of converging the ion beam in one direction when the emittance is large: the ion beam was converged to an area of approximately 6 mm × 27 mm on a workpiece surface for the large emittance. On the other hand, the triplet magnetic lens can converge the ion beam for both large and small emittances: the ion beams with large and small emittances converged to areas of approximately 4 mm × 4 mm and 10 mm × 5 mm, respectively.
This paper proposes an identification method for transient characteristic parameters of the leveling valve, especially focusing on the leveling valve which has a dead zone of flow rate and the time delay on starting supply/exhaust operation. The transient characteristics of the leveling valve is crucial to discuss the quasi-static decrement in wheel load when a railway vehicle passes a transition curve. However, it is difficult to identify the transient characteristics through the conventional shaking test because of the time delay of operation. To identify the transient characteristics, this paper proposes a stationary test method which utilizes the “pneumatically controllable leveling rod” to acquire the step response of the leveling valve. This paper also proposes a parameter optimization method using the hybrid PSO/gradient method involving narrowing-down of the parameter definition area to solve the optimization problem for the transient characteristic parameters of the leveling valve, of which objective function contains highly nonlinear dynamics. The proposed identification method is verified through numerical experiments and real vehicle experiments.
Mechanotransduction, in which mechanical forces and deformations are converted into biochemical signals to change gene expression, is critical for directing the differentiation of mesenchymal stem cells. A number of studies have indicated that a transcriptional regulator, yes-associated protein (YAP), localization change in course of the differentiation is a key for efficient osteogenic differentiation, however the detailed mechanism remains unclear. Here, we hypothesized that YAP localization is regulated by the mechanical interaction between actin cytoskeleton and nucleus, and the changes in the mechanical interaction at the right differentiation points underlie precise osteogenic differentiation. We analyzed the relationship among the three-dimensional morphologies of the actin and the nucleus, and nuclear-cytoplasmic localization of YAP based on the fluorescence images acquired in course of osteogenic differentiation. From undifferentiated to early stage of the differentiation, thick actin bundles were developed on the top of the nucleus, and nuclear height was decreased. At this stage, YAP was highly localized in the nucleus, which was suppressed by inhibition of actin polymerization with a pharmaceutical inhibitor. From middle to later stages of the differentiation, thick actin bundles decreased in some cells, and nuclear height tended to be higher than the other stages irrespective of the density of the actin fibers on top of the nucleus. At these stages, YAP nuclear localization was suppressed, which was unaffected by the inhibition of actin polymerization. YAP nuclear localization in the early stage of the osteogenic differentiation will be triggered by compressive forces applied from the actin bundles on the top surface of the nucleus. Then, from the middle to the later stages, suppression of YAP nuclear localization was because of less compressed nucleus, which was due to decrease in the compressive forces on the nucleus from the actin bundles, and probably ensured by the protection of the nuclear deformation.
This study aims to design a nervous system model to drive the realistic muscle-driven legs for quadrupedal robot locomotion. In this paper, we evaluate the nervous system model. We apply a two-level central pattern generator (CPG) for each leg, which generates locomotion rhythms and reproduces cat-like leg trajectories by driving different sets of the muscles at any timing during one cycle of moving the leg. The CPG received a sensory feedback of leg loading. A cat model, which has two hind legs with three joints driven by six muscle models, is controlled by our nervous system model. The cat's hind leg model was led at an arbitrary speed by active wheel attached in front of its torso. Then, this model changed own stride length and cycle duration in proportion to its speed and kept walking without changing any parameters, when the locomotion speed is forcibly increased by an external force of active wheel. In particular, it indicates that this CPG adapts to changes in the physical state due to external factors without a involvement of a higher brain, because we did not change the descending signal intensity from the higher brain at this time. Since similar phenomena have been reported in animal experiments, our results demonstrate that our nervous system may be an appropriate model.
In this study, a novel nondestructive evaluation method is proposed to investigate the fiber orientation distribution of discontinuous Carbon Fiber Reinforced Plastic (CFRP). The main concept is based on measuring thermal diffusivity distribution since it is related to the orientation of the fibers. The elliptical shape of the measured distribution is then analyzed by fitting. The slope and the eccentricity of the fitted ellipse are extracted and quantified as evaluation parameters. The experimental setup consists of a laser, a microscope and lock-in thermography system. The surface of the specimen is periodically heated by the laser spot and the thermal response at the backside of the specimen, which represents the in-plane thermal diffusivity distribution, is observed with the lock-in thermography camera. 64 points of four discontinuous CFRP of unknown orientation, manufactured with the same molding method, are evaluated. Furthermore, the local mechanical properties around the measurement points are measured. The results show positive correlation between the local mechanical properties and the fiber orientation. The effectiveness of the proposed method in predicting the mechanical property distribution of CFRP is also demonstrated.
When thermosetting resin changes from liquid to solid in cure process, the elasticity and volume also vary with the degree of reaction based on the tempearture history. Therefore, the accurate predictive model for the degree of reaction is necessary to set the appropriate temperature condition. Since the reaction model with multiple reaction peaks must consider the relationship of each reaction peak, it cannot be expressed only by single-reaction models proposed in the many previous studies. In this study, the reaction behavior for thermosetting resins with two reaction peaks was modeled by the reaction rate and ratio of total heat for each reaction peak. In addition, the diffusion control model for reaction which represents the decrease of the reaction rate by vitrification was applied to the reaction rate term for the second reaction peak. Furthermore, the temperature dependence of the diffusion control model was incorporated. The calculation results using the diffusion control model were agreed with non-isothermal differential scanning calorimetry (DSC) measurement data than Kamal model commonly used with or without temperature dependence. On the other hand, for isothermal measurement data, the temperature dependence diffusion control model was able to predict degree of reaction accurately at a temperature lower than the glass transition temperature.
In order to investigate fatigue properties of 18%Ni maraging steel at elevated temperature, rotating bending fatigue tests were conducted for plain and drilled specimens at room temperature (RT) and 673K in air. The specimens involved single-aged ones under an under-aging condition at 753K and double-aged ones in which the second aging was performed at 673K to the single-aged ones. Fatigue strength of the single-aged plain specimens was higher at 673K than at RT, though the static strength was inversely decreased at the elevated temperature. On the other hand, the single-aged drilled specimens exhibited nearly the same fatigue strength at both temperatures. It was found that hardness measured at RT increased with time in the single-aged plain specimens fatigued at 673K, which also appeared in the static aging at 673K. This hardness increase was considered to be attributed to precipitation hardening which might occur due to the existence of excess Mo solute atoms. On the other hand, crack observations revealed that crack initiation in the plain specimens was retarded markedly at 673K in comparison with that at RT, whereas crack propagation rate did not differ significantly between these temperatures and between the plain and drilled specimens. The marked delay of crack initiation in the plain specimens at 673K arose from the oxidation of their surfaces. It was also observed that the double-aging led to a large increase in fatigue strength at RT, but resulted in a slight increase at 673K. Based on these results, it was shown that the main reason of the increase in fatigue strength at 673K in the plain specimens was the suppression of crack initiation due to oxidation, while the increase in hardness observed at this temperature played a minor role.
To realize carbon fiber reinforced plastic (CFRP) mirrors, the high-precision polishing of an epoxy resin surface, which is the reflection surface of such mirrors, is required. To polish the surface with high quality, it is necessary to know the polishing characteristics of epoxy resin. However, unlike acrylic resin, there are few studies in which the polishing characteristics of epoxy resin were investigated. In this study, we polished test pieces of epoxy and acrylic resins in the same single batch under various conditions, and compared their removal rates. For this purpose, a new polishing technique that enables the simultaneous polishing of different materials under the same conditions was developed. We also evaluated the surface roughnesses for both resins before and after polishing. As a result, we found that the removal rate of epoxy resin was approximately 90% lower than that of acrylic resin under the polishing conditions using alumina abrasive grains and a suede pad. The roughness of the resulting epoxy surface was 4.76 nm RMS, which satisfies one specification of optics used in a space telescope.
Computer Aided Engineering (CAE) is indispensable for vehicle design to reduce the development cost; however, its computation time is a heavy burden when tuning design parameters. In this respect, several studies have been carried out for replacing CAE with machine learning-based surrogate models. In this paper, we propose a novel neural sequence network-based surrogate model for CAE using Recurrent Neural Networks (RNNs), which are neural networks that treat sequences such as temporal sequences. Our target task is the NCAP Fishhook test to evaluate vehicle dynamics of the rollover propensity. We propose a machine learning model with a sequential model to calculate the response of the NCAP Fishhook test from vehicle parameters such as tire and suspension characteristics. Our model reduced the error in approximately 10% for the NCAP Fishhook test dataset, which is generated with CAE, compared to that of the baseline neural network model with multi-layer perceptrons (MLPs). Furthermore, to improve performance and stability, our model has the following task-specific characteristics: (1) the skip connection, (2) the hybrid loss, and (3) the scheduled sampling. We confirmed that the skip connection reduced errors in the additional ablation study. Our experiments showed that the sequential model is effective as a surrogate model for CAE, and we also find that there is still room for the improvement regarding the dataset and the model because the accuracy is not saturated with the current dataset.
Electrochemical discharge machining (ECDM) is a machining method for inorganic insulators. When a tool electrode is fed at a constant rate, the removal rate is often decreased due to enlarging the gap length between the tool electrode and workpiece. In this paper, the effects of the applied voltage, which is a changeable condition during ECDM, and the initial gap length between the tool electrode and workpiece on the current waveforms and machining performance were experimentally investigated. Soda lime glass was machined with a tungsten electrode in NaCl solution. Plenty amount of bubbles were generated below an applied voltage of 45 V, and the removal amount was large. Though discharge strongly occurred over 50 V, the removal amount was small. With an increase of the applied voltage, lower frequency components of the current measured during ECDM were decreased. The initial gap did not affect the current waveforms. The mixture of long and short pulses accelerated removal at a low applied voltage. The phenomena around the tool electrode such as the bubble generation and discharge were distinguished by the principal component analysis (PCA). After a series of current pulses was divided into 12 periods, their statistical parameters were calculated, and the frequency components were calculated by the first Fourier transform. In both the cases, the applied voltage was distinguished by the PCA. The principal components obtained from the statistical parameter performed as essential parameters.
A steel containment vessel of PWR (Pressurized Water Reactor) has a circular cylindrical body and a hemispherical head. Since the containment vessel is a thin-walled shell structure, shear and bending buckling might occur in the cylindrical part under the seismic load which exceeds the design load. In the conformity assessment of existing nuclear power plants to the new regulatory standards established by NRA (Nuclear Regulation Authority) of government of Japan in 2013, the assessment of structural strength becomes more severe than that before construction due to the increase of design basis earthquake ground motion. If the existing power plant does not have sufficient structural strength against the seismic load, a countermeasure with reinforcements is required. In this study, the stiffened steel containment vessel is proposed by using the partial stiffening rings which has discontinuous, to avoid the interference with penetrations such as equipment hatch, air lock and piping. A series of buckling tests and elasto-plastic buckling analysis of scaled containment vessel model were conducted to verify the effectiveness of this reinforced structure. Through the buckling tests, it is confirmed that the buckling strength of steel containment vessel was improved by the partial stiffening rings as well as continuous rings. Moreover, the buckling behavior and the buckling load estimated by the elasto-plastic buckling analysis considering the material stress–strain relationship and the initial imperfection shape in test vessel suitably agreed with corresponding test results.
In order to realize a high speed and high space use efficiency transportation system in a vertical plane, authors conceived a concept to compose the system by multiple vertical rails and multiple self-propelled loading platforms so that such platforms can independently move along each rail and transfer between them. This paper focuses on the design of drive mechanism for such a self-propelled loading platform utilizing the friction force between the rail and the driving wheels. In order to enable to generate a large grip force enough to support and move the platform with payload without using additional actuators while flat rails with small unevenness and gaps are used, the following three principles of operation are applied: the friction drive wheels with less vibration and noise, grip force generation using self-servo effect, and wheel load equalizing based on the rocker-bogie. Through the kineto-static analysis of the proposed mechanism, the relationship between the design parameters such as the angle of the self-servo link and the dimensions of the wheel load equalizer link, operating conditions such as the loading weight, the eccentricity of the center of gravity, and the inclination of the body, and the grip force and the wheel load is studied, and the design parameters and their tendency which enable to run vertically have been clarified. Furthermore, based on the knowledge obtained through the analysis, a prototype was designed, and the stable and high-speed vertical running and running over unevenness and gap has been successfully achieved. From the above, it was shown that the design of drive mechanism based on the principle proposed in this paper was effective as the mechanism that can run on flat vertical rail.
In current mechanical machining technology, it is not easy to form an internal space shape inside a metal workpiece through a small-diameter entrance hole only by removal process. On the other hand, EDM is one of thermal machining methods that removes the material by the high temperature of discharges, and the tool electrode does not contact to the workpiece. The machining force acting on the electrode is very small. Therefore, it is highly expected that internal space shape may be machined if an optimum electrode structure can be designed. This study proposes a new internal space machining method by EDM using a revolution ball electrode consisting of a vertical rotation rod, a tilting rod, and an electrode ball. Experimental results show that the tilting angle between the vertical rotation rod and the tilting one can be changed by the rotation speed, and the electrode ball position can be controlled. Then, machining of some axially-symmetric spacial shapes, such as cylindrical shape and spherical one into a zinc alloy workpiece was succeeded. In addition, machining of internal space shapes by simultaneous two-axis control of the tilting angle and Z coordinate of electrode was possible. Therefore, this method has high possibility to create axially symmetric spatial shapes inside the metal.
This study has proposed the optimization process regarding the hydraulic transmission installed with construction and agricultural vehicles, in order to contribute to the quietness of the vehicles in which noise from the hydraulic system is expected to become noticeable due to the diversification of power sources. The pressure ripple as the noise source which is derived from the relative motion of pistons, cylinders and valves is non-linear system, and the genetic algorithm which is one of the evolutionary computations is used to search for the optimum solution of design variables. In addition to just search for the optimum solution, the readability of the design space has been obtained by the inductive approach, using many datasets generated in the process of the evolutionary computation. The decision tree, which is one of the techniques in machine learning, is used for the inductive approach and can make the readability of the design space regarding the pressure ripple generated in the hydraulic transmission without the dimensional reduction of the design space and the neglected interaction.
In this paper, the laminar-turbulent transition process of a mixing layer downstream of a two-dimensional nozzle exit was analyzed based on various information and complexity measures. Shannon entropy, permutation entropy, and approximated Kolmogorov complexity were also obtained. To obtain the Shannon entropy, the temporal probability distribution of the hot-wire output voltage data was determined and analyzed. In addition to the fluctuating velocity, its time derivative and the square of this derivative were analyzed. The Shannon entropy of the time derivative and its square slightly decreased downstream, in accordance with the increase in the time scale of the turbulence. When the length of the extracted data was constant, the permutation entropy of the time derivative and its square increased around the peripheral region of the mixing layer, in accordance with the intermittent nature of the velocity signals. The region is at the 3-4 times farther from the jet centerline than the region where the fluctuating velocity becomes maximum. When the length of the extracted data was varied in accordance with the integral time scale of turbulence, the permutation entropy initially decreased in the potential core and subsequently increased after the disappearance of the potential core, as the transition progressed. The approximated Kolmogorov complexity of the time derivative and its square were smaller than that of the fluctuating velocity. Owing to the simplification of the data, they slowly increased after the disappearance of the potential core and then quickly decreased after the development of turbulence.
Vascular access required to perform a dialysis treatment need to construct an arteriovenous fistula, though it has a problem of stenosis. It is considered to be caused by the influence of wall shear stress on the blood vessel wall. Recently, the influence of flow disturbance is also focused on as one of the causes, and is usually evaluated by the indexes such as TAWSS, transWSS, OSI and RRT. However, the correspondence of these indexes to the characteristic of flow disturbance is not clear. In the present study, these indexes are investigated with two different turbulence intensities, one is composed of fluctuation from the time averaged velocity, and the other is from the phase (ensemble) averaged velocity. As a result, it was found that TAWSS could estimate the extent of pulsatile flow unsteadiness, but the flow disturbance could not. TransWSS could evaluate the intensity of flow disturbance, only under the condition of high correlation between fluctuating velocity perpendicular to the main-flow and that parallel to the main-flow. Therefore, we formulated a new index capable of evaluating the disturbance with any characteristics. The new index shows reasonable performance for the purpose, althought it requires further improvement such as a formulation without post-processing using historical data.
In this study, we conduct finite element implementation of a Gent-Gent hyperelastic model for swollen elastomers. To this end, an inhomogeneous field theory for swollen elastomers is extended using the Gent-Gent model, which includes the effects of limiting chain extensibility and the second strain-invariant. The extended theory is implemented into a commercial finite element package using a user-defined material subroutine. The accuracy of the implementation is verified by analyzing Young’s modulus and Poisson’s ratio of swollen elastomers undergoing large deformations. Further, the inflation of a spherical balloon made of swollen elastomers is computed as an example. The results are verified with an analytical prediction and demonstrate the inflation behavior of swollen elastomers.
In this study, we clarify the effect of cyclopentane (CP), which is a formation reaction promoter and shifts the phase equilibrium curve to high temperature and low pressure, on the energy storage density of the proposed CO2 hydrate power generation system. The phase change should be shifted to a higher temperature for expanding the operating conditions of the power generation systems. In addition, the formation of hydrates is facilitated by the repeated formation and dissociation of gas hydrates (the memory effect). Although the memory effect mechanism during hydrate formation has not yet been clarified, its occurrence has been reported in many studies, where the reformation of each gas hydrate began more quickly when compared with the initial case. Hydrate formation and dissociation were conducted at least once in a day in the proposed power generation system. Therefore, the power generation cycle can be repeatedly performed in a short time period if the memory effect is effectively applied. Hence, we conducted experiments in the presence or absence of CP and with respect to the time duration of the dissociation state in the formation and dissociation cycles. Furthermore, we calculated the hydrate amount and the time required for its formation under each condition. Subsequently, the energy storage density of the proposed power generation system can be estimated based on the calculation results. The conducted experiments and calculations reveal that a CO2 hydrate power generation system containing CP is more beneficial when compared with a pure CO2 hydrate power generation system in terms of the energy storage density and the time required for storing energy.
A laser 2-focus velocimeter (L2F) was used for the measurements of the velocity and size of droplets in diesel fuel sprays. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3 μm, and the distance between two foci was 24 μm. The fuel was stored once in a common rail and was injected intermittently to the atmosphere. The diameter of the nozzle orifice was 0.15 mm, and the number of holes was 6. The injection pressure was set at 60 MPa, and the amounts of fuel were set at 1.1 and 7.0 mg per injection. It was confirmed that the size of droplets near the nozzle under a smaller amount of injection was smaller than the one under a larger amount of injection. The droplet size decrease rate in the direction of spray injection was found to be larger at the spray upstream region compared to at the spray downstream region. There was a positive correlation between the droplet size decrease rate under a smaller amount of injection and the one under a larger amount of injection. The droplet breakup of diesel sprays was less dependent on the injection amount.
Pulsating heat pipes (PHP) are increasingly attracting attention for their potential to downsize electronic devices to be designed. Unlike conventional heat pipes, PHP maintains high heat transfer performance despite having a smaller diameter, and have a smaller dependence on heating orientation. In this study, hydrofluoroolefins (HFO) are selected as an environmentally-friendly and non-flammable working fluid for PHP. The flat-plate PHP is made of aluminum alloy, and its dimensions are a length of 222 mm, a width of 55 mm, and a thickness of 3 mm. It is prepared the channel, which is 1.2 mm × 1.2 mm square, 22 turns, and closed-end serpentine. The working fluids are R1233zd(E) and R1336mzz(Z) as HFO, and the other is R245fa as one of conventional hydrofluorocarbon (HFC). The filling ratio of each working fluid is approximately 50 %. The flat-plate PHP is set vertically, heated in the top heating orientation, and measured the equivalent thermal conductivity. When the cooling temperature is 40 °C, the equivalent thermal conductivity with R1233zd(E) and R1336mzz(Z) are between 2500 and 4000 W/(m･K), and higher than that of R245fa. When the cooling temperature is −5 °C and the heat transport rate is less than 100 W, the equivalent thermal conductivity with all working fluids are equivalent, and R1233zd(E) and R1336mzz(Z) have larger temperature dependence than R245fa. The maximum heat transport rate with R1233zd(E) is the highest, and around 190 W. When the cooling temperature is 40 °C, the maximum heat transport rate with R1336mzz(Z) is 150W, and higher than that with R245fa (104W). From the above results, we have concluded that PHP with R1233zd(E) and R1336mzz(Z) have higher heat transport performance than that with R245fa, and R1233zd(E) and R1336mzz(Z) may replace as the working fluid for PHP, instead of conventional R245fa.
The fluid film lubrication problem is usually solved using classical Reynolds equation-based modeling to predict fluid film behavior such as pressure distribution and oil film thickness, which requires pressure boundary conditions at the locations of film formation and separation. When applying the classical approach to practical applications like rolling element bearings, it is difficult to specify boundary conditions at appropriate locations in order to solve the Reynolds equation due to complex geometry, unknown amount of oil lubricant around contacts, and interaction between multiple lubricated contacts. A general approach to solve the Navier-Stokes equations for predicting the fluid film behavior is proposed here using the moving particle simulation (MPS) method, which is a meshless, Lagrangian, particle-based method suitable to model moving or deforming boundaries, multiphase fluids, free surfaces, and complex geometry. When applying the MPS method to the micron-scale fluid film lubrication problem, calculating the viscous term is the key to ensure accuracy and robustness because the viscous forces are dominant over the other forces and affect the numerical stability. This study uses three different algorithms of the MPS method: (1) the semi-implicit MPS method, (2) the implicit MPS method, and (3) the explicit MPS method. They are employed by using virtual surface particles to enhance the robustness of the calculation of the pressure Poisson equation, and a sub-time step method enables the use of large time steps for calculating the viscous term explicitly. The proposed methods are applied to a plane Poiseuille flow and a fluid film lubrication in line contact, and show good agreement with analytical solutions of the velocity profile and the pressure profile respectively by using an appropriate initial particle distance and time step. A parametric study covering a wide range of initial particle distance and time step size reveals the stability conditions based on Courant number. The result confirmed that the implicit MPS method provides the best accuracy and stability, whereas the explicit MPS method is the best in terms of computational cost.
This study aims to examine the benefit of visual fatigue evaluation based on prefrontal cortex (PFC) measurement by near infrared spectroscopy (NIRS), and to evaluate fatigue on various colored LED backlit text. In our method, eight adult participants read a LED backlit text 10 minutes in a dark room. Before and after task, subjective fatigue questionnaire “Jikaku-sho shirabe”, subjective visual fatigue questionnaire (SVF), and the critical flicker-fusion frequency (CFF) were measured. The time-course of oxy-Hb in the PFC was measured using a 22-channel NIRS. Heart rate variability (HRV) was measured to access an autonomic nervous system balance. Six types of white LEDs were used for backlighting: general white as a control (W), high color-rendering white (WH), bluish white (WB), reddish white (WR), greenish white (WG), and yellowish white (WY). In our results, correlation analysis suggested that the development of central fatigue is related to deactivated condition in the mPFC, and the development of subjective visual fatigue is related to deactivated condition in the LPFC. In comparison between LED treatments, in WH condition, high subjective central fatigue, CFF decay and LF/HF were revealed, and the PFC inactivated. In WG condition, low subjective central fatigue and CFF decay revealed. Our findings suggested that participants get tired on high color-rendering white LED backlit text, and were less tired in greenish white LED backlit text. Also, NIRS provides benefits in the evaluation of visual fatigue.