Recently, in the steering control system based on the steer by wire and the automatic operation, it is possible to flexibly change the relationship between steering input and vehicle response characteristics. In the previous research, robust stabilization by H.inf. Control and model following control Automatic steering by LQG control optimal observer such as vehicle steering system considering uncertainty of vehicle dynamics model, improvement of vehicle performance by robust control rule, and inverted pendulum control by robust model matching Applied research has been applied. Based on such background, we extend the original state variables (yaw rate, transverse slip angle, and steering angle) of an optimal observer and add the disturbance model which models the frequency spectrum of the disturbance as a state variable, and estimate the disturbance value simultaneously with the estimation of the original state quantity. In this paper, we propose a new method of control law, which is based on the estimation of the disturbance value and to obtain the desired response by state feedback. This paper reports the effect of robust steering control law by combination of model matching and optimal observer capable of realizing robustness to input disturbance while realizing steering desired response by proposed steering control system. In the case of the robust control law for an automobile, it is assumed that the disturbance estimation by the optimal observer is suitable to suppress the whole disturbance energy. In this paper, we show the robust control effect of the steering control law on the real vehicle motion in the case where an optimal observer and an H∞filter are observers.
Various high-performance structures are ready to fabricate with the advent of the technology for the additive manufacturing. This additive manufacturing technology has a potential to improve manufacturing costs and may help to achieve high-performance aerospace structures. One of application candidates would be a wind tunnel wing model. A wing tunnel model requires sophisticated designs and precise fabrications for accurate experiments, which frequently increase manufacturing cost. At the same time, there are design trends of high aspect ratio wings to enhance flight performance of aircraft. Those wings may undergo large deformation during flights. Therefore, a geometrically nonlinear aeroelastic analysis of such flexible wings plays important role in design. In this paper, manufacturing accuracy and aeroelastic characteristics of an additively manufactured wing model are evaluated numerically and experimentally. The feasibility of such wings to use in wind tunnel tests is also demonstrated. In addition, a geometrically nonlinear aeroelastic analysis model, which have been developed in the previous study, is validated by comparing with results of the wind tunnel test for the additively manufactured highly flexible wing model. The effect of geometrical nonlinearity in aeroelastic characteristics of a highly flexible wing has been observed in the comparison between linear and nonlinear aeroelastic solutions and the wind tunnel result.
A gear case used at a bogie of a rolling stock is an important part to pack a small gear and a large gear that pass the driving force from a main mortar to a wheel. An axle, to which the small gear and the large gear connect, is housed in a gear case through an axle bearing for rotation. The defect of the axle bearings can affect the running safety of rolling stock. In this context we investigate a sensor using a hanging rubber, which can detect of damage of axle bearing in gear case. The hanging rubber is used as a fixing device, which attaches the gear case firmly to the bogie frame. By using hanging rubber for sensor, it can be easily installed for bogie. In addition, the loss of the sensor installed on the bogie and the risk of impact with flying object can be reduce. The sensor using the hanging rubber is incorporated with a piezoelectric elements. The piezoelectric elements can convert mechanical energy to electric energy, and vice versa. The defection of axle bearing in gear case can be detect by the electric signal generated from piezoelectric elements. The rotation test by rotation testing machine of gear system with sensor using hanging rubber is carried out. As the result of rotation test with damaged and normal small gears, it is confirmed that the damage can be detected by amplitude of electric voltage from piezoelectric element when the rotation speed is higher than 50km/h. In case of the rotation speed is lower than 50km/h, the damage can be detected by the frequency analysis of time wave.
This paper presents a basic study for developing a new adhesion improvement method for railway vehicles, focusing on the tangential force characteristics between wheels and rails. In our previous studies, the following phenomena have been confirmed. First, the tangential force of the wheel/rail is increased by repeated rolling and sliding frictional force, and the tangential force is stabilized by the oxide film covering the contact surface. In addition, the tangential force under the condition where the humidity around the contact surface is low tends to be larger than that under high humidity condition. And finally, these phenomena indicate that the friction coefficient of wheel/rail can be increased by instantaneously reducing the humidity around the contact surface. Therefore, in this paper, we propose a method for improving the frictional force that reflects the above-mentioned results in our previous studies. In the proposed method, assuming that it is applied to re-adhesion control of railway vehicles, the frictional force of the wheel/rail contact is temporarily increased by lowering the humidity around the contact surface by injecting dry nitrogen gas less than 30% humidity. To verify the proposed method, using a pair of the small cylindrical specimen, tangential force was measured under the conditions with different humidity. In addition, in order to confirm the effect on the braking performance of actual railway vehicle, numerical analysis was carried out. As a result, the experimental result showed the frictional force is increased by up to approximately 40% under high humidity condition, and it was confirmed by the numerical analysis that the proposed method has an improvement effect on the reduction of braking distance during dry nitrogen gas injection even if the humidity condition around the contact surface is high.
In evaluating the brake feeling of passenger cars, it is known that vehicle postures such as pitching and heave influence other than the relationship between pedal depression force and stroke and deceleration. In this study, we focused on the transitional posture change during braking and conducted an experiment using an active suspension vehicle. As a result of sensory evaluation, it was found that even if the brake performance was not changed at all, it was confirmed that the brake feeling changed only by the difference in the transient posture, and it was not always good to suppress the vibration. In addition, we devised a method to realize the vehicle posture that was highly evaluated in the experiment by transient control of the longitudinal force distribution of the brake, and confirmed the effect in the actual vehicle.
Rail wear does not develop in a short term, but it is closely related to crack initiation. Furthermore, there is a possibility that the worn profile of rail influences the curving performance or the running stability. However, worn profiles of rail changes complexity in each section (e.g. straight section, transition curve section, circular curve section) because the condition of wheel/rail contact changes gradually, according to the running condition of vehicle and track geometry conditions. Predicting the worn profiles of rail should be considered based on the results of the vehicle dynamics analysis. Therefore, it is very beneficial to predict the worn profiles of rail based on the analysis by using multibody dynamics. The purpose of this study is to develop the prediction model for worn profile of rail under the various angle of attack by using multibody dynamics. Especially, we focused on the wear development due to longitudinal slip and lateral slip. In the beginning of this study, the wear experiment was conducted by using the wheel/rail rolling contact equipment under the mixed slip conditions. Secondary, the prediction model with Simpack was developed. Then, wear predicting analysis was conducted in the same contact conditions as the experiments. Finally, we evaluated the results of analysis to validate the developed model under the various mixed slip conditions. As a result of the experiment and the analysis, it was revealed that the wear development under the mixed slip conditions can be evaluated by the contribution ratio of longitudinal slip and lateral slip.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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 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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.