In this report, adhesive strength criteria are investigated experimentally and analytically. The cylindrical butt joint specimen and the round bar butt joint specimen with various thickness (30～1000μm) of adhesive layer are subjected to various combined tensile and torsion loadings in the experiments. Apparent critical fracture loci are obtained in the stress plane composed by the average tensile stress σ and the maximum shear stress τmax for various adhesive thicknesses, which are approximated to ellipses and the lengths of axis of these ellipses in both σ and τmax directions decrease linearly with increasing adhesive thickness in log-scale. Effects of adhesive thickness on the critical stress is larger in σ directions than in τmax direction. Principal stress, principal strain and von Mises stress distributions at around the adhesive interface edge of these specimens under the critical load are obtained by the elasto-plastic finite element analysis using MARC. As a result, the mean value of von Mises stress distribution at the singularity area which is 0.4 % long of adhesive layer thickness from the interface edge, is found to be the most dominant factor in determining the adhesive strength. Also, it is found that the critical Mises stress as the strength of adhesive joints decreases linearly with increasing adhesive thickness in log-scale. The critical stress value can be obtained directly as the critical von Mises stress at the interface edge from a torsion test of a round bar butt joint specimen and a corresponding numerical stress analysis.
Recently, high strength steel is used increasingly for plates which constitute the frame structures of vehicles. Since these plates become thinner, the buckling on the plates has been recognized as an important issue for automotive industries. For this issue, various methods have been proposed and are currently in practical use. In this paper, the buckling stress relation equations of the plate are discussed which is the basis of buckling analysis of a structure, and on the basis of the buckling stress relation equation of a single plate, the relation equation of compression and shear is shown under axis compression force and twisting torque on the box beam composed by thin plates. And, the approximate expression for the compression buckling stress is proposed by the knowledge of the buckling eigenvalue equation by the energy method and the approximate expression of the twisting. The accuracy of the approximate expression and relation equation is investigated as compared with the results from the buckling eigenvalue analysis by FEM. As the results, well-known relation equations of the plates can be obtained by approximating the buckling eigenequations by the energy method assuming the deformed shape function with low-order terms. Also the compression buckling stress of the box beam determined by a single plate theory does not have enough accuracy, and it is necessary to consider the coupling with adjacent plates. The difference between the proposed expression and results by FEM is less than about 6% for the aspect ratio of the cross section between 0.3 and 1.0. And then, the shown buckling stress relation equation of compression and torsion has up to 12% difference from the results by FEM.
Stress singularity usually occurs at a vertex of interface in a three-dimensional joint. Crack frequently initiates at a vertex and a joint fails under an external force and a thermal load. In the present paper, stress distribution near a small crack occurring at a vertex in a three-dimensional joint is investigated under a tensile load, and stress intensity factor at the crack tip are determined along the crack tip front. The joint is composed of Si and resin. In the analysis, three kinds of crack shape, triangular, quarter circular and concave shapes, are supposed as an initial crack shape. Stresses are normalized using the singular stress around the vertex since the crack exists in the stress singular field. The stress intensity factor in the quarter circular crack increases and that in the others decreases as approaching side surfaces. The quantity of energy release due to a crack initiation is calculated using relative displacements of the crack and the stress distribution of singular stress field. The quantity for the concave shape crack is the largest in the three kinds of crack shape.
The sealing performance of bolted flange connections with ring joint gaskets is examined. The nominal size of flange used is 3B (3 inch) and the ring gasket types are chosen as octagonal and oval. The material of the gaskets is chosen as aluminum and Cr-Mo steel. The sealing performance measurements were carried out when bolts of the connection were tightened in accordance with JIS B2251 and ASME PCC-1. Furthermore, the contact stress and plastic strain distributions at the contact surfaces between the gasket and the flange groove are calculated using FEM. It is found newly that the sealing performance of the connections with both octagonal and oval gaskets is drastically improved when the plastic deformation occurs at the contact surfaces annularly, and that the sealing performance of the connection tightened with scattered bolt preloads is found to be worse than that tightened with uniform bolt preloads. The contact gasket stress changes are demonstrated. It is found that a reduction in the contact gasket stress is small when internal pressure is applied. The effects of gasket material and the difference in the two tightening methods is small on the sealing performance, while the effect of the minimum bolt preload in the connection is substantial. The sealing performance of the connection with oval gasket is better under smaller bolt preload than that with octagonal gasket because of the smaller contact area in the oval gasket.
A deriving method of bending roll position in forming of glasses frame is proposed. The proposed method requires not the computational simulations but only some simple bending tests. To obtain a relationship between bending roll position and bent curvature which depends on material and cross-sectional shape of bent wire, simplified bending experiments in steady bending condition for getting constant curvature are carried out. The experimentally obtained relationship is used in the formulation of deriving the bending roll position for forming glasses frame having curvature distribution. To validate the proposed method, three different shapes are formed by the proposed and conventional methods. The difference between the designed and formed shapes is evaluated by a sum of absolute of shape deviation, and the value by the proposed method is smaller up to about 50 % than that by the conventional method.
The influence on performance during the revolution of a straight-bladed vertical axis wind turbine (VAWT) is discussed, focusing on the effect of the blade number. A data campaign has been performed for two, three, four and five-bladed rotors in wind tunnel. Firstly, rotor performances have been compared with the results of an experiment based on the use of the NACA 0021 airfoil, such as rotor torque and power. And then, for each rotor configuration, flow field characteristics are investigated at optimum values of tip speed ratio by means of Laser Doppler Velocimeter (LDV), allowing a quantification of the influence of blade number on flow geometric features and dynamic quantities. Finally, the velocity distribution around wind turbine, velocity deficits in wake region and turbulence intensity in flow field are compared for the analyzed architectures, achieving a quantification of the effect of blade number on overall rotor performance. In this research, according to the wind tunnel experiments, wind velocity field and performance (power coefficient and torque coefficient) are obtained through LDV system and torque meter, respectively. For example, a wide low wind velocity field appeared from the wind turbine internal region to downstream area. In addition, velocity vector had an asymmetry with respect to the x-axis at the downstream side of the rotor, and the reverse flow was generated at some region of downstream side for the blade numbers of 4 and 5. This result provided a theoretical guiding significance to the development of VAWT simplified load model.
In swash plate type piston pumps and motors, the slippers are used under heavy load. So the slippers are designed as a hydrostatic bearing to ensure reliability. However slippers behavior during operation is very complex, we must take into consideration rapid changes in the hydraulic, centrifugal force and oil-film lubrication of sliding parts. In this study, a test for slippers was conducted under quasi-static state and analysis to simulate it was performed. By considering the elastic deformation of a slipper due to hydraulic pressure in the analysis, analysis results of center displacements of the slipper are in good agreement with the experimental results. In the analysis, multi body dynamics model was coupled with hydrodynamic analysis of oil-film, which makes it relatively easy to take into account effect of other mechanical components and dynamic changes. This technique can also be applied to the analysis that takes into account the other components of the pump motor.
Compact centrifugal blowers with vaned diffusers are often used in home electric vacuum cleaners. To achieve high efficiency and low noise, it is important to improve the performance of impellers and diffusers. In this study, the authors used a large solidity diffuser whose flow duct is low in height. The authors studied the influence of internal flow on the diffuser performance by using PIV and pressure measurement and visualizing the flow field in detail. From the authors' measurement results, low velocity was observed in the middle span section and the pressure side in the middle of the overlapped region. Pressure recovery increased gradually at the downstream of the low velocity region. From the authors' simulation results, the authors found that in the low velocity area, limiting streamlines from hub and shroud sides concentrate toward the mid-span, which lead to low velocity in the middle of the overlapped region. Compared with diffusers with small radial curvatures, diffusers with large radial curvatures are more likely to suppress secondary flow generated from the hub and shroud sides of the pressure side of the overlapped regions. Also, by suppressing separation at the hub-side and suction-side surface of the overlapped region, it is possible to improve the flow stagnation at the mid-span of the overlapped region. The authors can therefore achieve high blower efficiency by gaining larger pressure recovery at the rear part of the overlapped region.
Labyrinth seals have the potential to cause rotordynamic instability induced by the fluid force of seal flows. We conducted a computational fluid dynamics (CFD) study to investigate the rotordynamic characteristics of the shaft labyrinth seal of a steam turbine. The effects of different seal gap (0.42～0.85 mm) and seal length (47.6～357 mm) were systematically investigated. The predicted stiffness coefficients increased with increasing seal length as expected, but short seals (<100 mm) indicated a stronger dependence on seal length. Through the investigation of flow fields, it was found that this could be attributed to two causes: first the decay of circumferential velocity component along seal flow direction, and second lower fluid force in the cavities adjacent to seal entrance and outlet regions which greatly affects the fluid force of short seals. Stiffness coefficients of short seals indicated strong dependence on seal gap and increased inversely with decreasing gap while stiffness coefficients of long seals depend less on the gap. The seal fluid force increases for small gap seals, but the circumferential velocity decays faster, and this could offset the increase in the fluid force. This effect appears more pronounced in the long seal.
Characteristics of compact schemes combined with compact filters for compressible flows are numerically investigated on the Sod's problem in this study. Tridiagonal 6th, 8th and pentadiagonal 10th order compact schemes developed by Lele and 4th order compact scheme developed by Kim are used for the spatial derivatives and compact filters proposed by Lele, Gaitonde, Zhanxin, Kim are examined under CFL=1.0 condition. L1 and L2 norm are calculated from errors on velocity field from the end of expansion wave to shock. Results show that the compact filter developed by Gaitonde (free parameter is near 0.5) with Lele's 6th order compact scheme makes large error near the end of expansion wave and it cannot remove numerical oscillations perfectly near boundary. It is also revealed by the tests with Gaitonde's 8th order compact filter that the higher order compact scheme developed by Lele makes smaller L1 and L2 norms and the 4th order compact scheme developed by Kim makes the smallest L1 and L2 norm. In addition, it is found by the tests with Kim's 6th order compact filter that the higher order compact scheme developed by Lele makes smaller L1 and L2 norms and the 4th order compact scheme developed by Kim makes the smallest L1 and L2 norm. In all combinations of compact schemes and compact filters assessed in the present paper, although no combination of them can suppress spurious oscillations near the end of expansion wave and a shock perfectly, Kim's 4th order compact scheme combined with Kim's 6th order compact filter is the most appropriate to capture shock.
We measure concentrations of reactive species and streamwise velocity simultaneously near the turbulent/non-turbulent (T/NT) interface in a planar liquid jet with a second-order chemical reaction A + B → R. The reactants A and B are premixed into the jet and ambient flows, respectively. We use an I-type hot-film probe and an optical fiber probe based on the light absorption spectrometry to measure the streamwise velocity and the concentrations of the reactive species. We investigate the two interfaces perpendicular to the streamwise direction: leading edge, across which the turbulent region turns into the non-turbulent region toward streamwise direction, and trailing edge, across which the non-turbulent region turns into the turbulent region toward streamwise direction. We calculate the conditional statistics conditioned on the time elapsed from the time when the interface is detected. The results show that the conditional statistics of the concentrations vary drastically near the T/NT interface, and the variations in the conditional statistics near the leading edge are larger than those near the trailing edge. The width of the interface with the large variation in the conditional mean concentration near the T/NT interface is almost independent of the chemical species and the Damköhler number. Because the reactant A only exists in the turbulent region, the chemical reaction takes place in the turbulent region. The chemical reaction rate near the leading edge is larger than that near the trailing edge. This difference between the leading and trailing edges relates to the velocity near the T/NT interface.
The main objective of this study is to evaluate energy saving potentials of polymer electrolyte fuel cell cogeneration systems integrated with solar cell and battery installed into residential houses. There exist many alternative operational policies in the above systems, and the mathematical planning approach is taken to derive the rational system's operational solution based on the mixed-integer linear planning method. In the numerical analysis of this study, energy saving characteristics of 12 alternative systems are compared respectively, and as one of main obtained results, it become clear that the energy saving effects to install battery into the systems depend largely on the operational policy of the system together with the evaluation criterion of adverse electricity from the solar cell to the electric grid. In other words, in the case of giving high priority to the self-consumption of electricity from the solar cell within the house, the energy saving potential to install battery increases largely, but few effects are noticed in other cases.
Emulsion fuel is regarded as one of the possible fuels for reducing the emissions of pollutants from combustion systems. This study investigated the effect of droplet size on combustion and emission characteristics for both pure diesel and emulsion fuel in preheated ambient air. A burner equipped with a twin fluid atomizer was used to vary Sauter mean droplet diameter (SMD) of spray. Water percentage of 5 and 10 vol% in W/O emulsion fuel was used. Experimental results show that both emulsion fuel had lower EICO2 than diesel fuel. This result shows combustion efficiency of emulsion fuel was lower than that of diesel fuel. As the preheated ambient air temperature TAmbi was increased to 473 K, combustion efficiency of emulsion fuels was improved. In emulsion fuel combustion, NO emission was lower than pure diesel fuel combustion. The vaporization of water in emulsion fuels reduced local flame temperature and thus reduced the NO formation. Smaller fuel droplet SMD had higher NO emission for pure diesel fuel. However, NO emission had no dependence on fuel droplet SMD for emulsion fuel. Emulsion fuels also had lower flame luminance as compared with diesel fuel alone. This is caused by lower soot emission of emulsion fuels.
The principle of corresponding state on the fluctuation structure, which is the spatial distribution of various clusters of molecules caused by density fluctuations, in supercritical states around the critical points has been investigated. In this paper, we performed Molecular Dynamics (MD) simulation to extract the fluctuation structure around the critical points of 2-Center-Lennard-Jones (2CLJ) fluids, whose characteristics change by their molecular elongations. First, we indentified some critical points of 2CLJ fluids with comparatively shorter elongations applying Lotfi's function, which correctly describes the liquid-vapor coexistence line of Lennard-Jones (LJ) fluid, and successfully defined each critical point. Next, two methods were applied in the estimation of the fluctuation structure: one is the evaluation of the dispersion of the number of molecules at a certain domain, and the other is the calculation of static structure factor. As a result, in 2CLJ fluids which have shorter molecular elongations comparatively, the principle of corresponding state is satisfied because of the small differences in the fluctuation structures extracted in the present two methods. On the other hand, some results imply that the fluctuation may decrease in 2CLJ fluids which have the longer molecular elongations although more accurate evaluation of the critical points in those fluids is necessary for the further investigation.
This study is carried out for the purpose of collecting data that is based on the evaluation of the equivalent fatigue load for a small wind turbine. The equivalent fatigue load is indicated as the method of designing load calculation in IEC 61400-2 ed.2 DLC1.1. In this study, it is performed fatigue load test for the commercial model of the small wind turbine, and it is evaluated the applicability of S-N diagram as material specification and the material factor “m” for S-N diagram model. It is cleared that S-N diagram as material specification is able to apply to the evaluation for blade fatigue load. Moreover, it is indicated experimentally the material factor “m” of 10 to a single material of G-FRP that is composed as general small wind turbine's blades. Furthermore, it is suggested the estimated method of the equivalent fatigue load by using the fatigue load function of Simplified Load Model (SLM) and it is made a trial calculation by this method.
Performance of an anode-supported solid oxide fuel cell was investigated under several conditions of current cycles. The current cycles between 0 A/cm2 and the maximum current density were repeated. The cell was composed of 8 mol % Y2O3-ZrO2 (YSZ) electrolyte, Ni-YSZ fuel electrode and La0.8Sr0.2MnO3 air electrode, and did not have other active functional layers which contact with the electrolyte. By repeating a current cycle at the operating temperature of 1273 K, the terminal voltage gradually decreased. It was found that the deterioration of performance was due to the increase of the resistance in the higher frequency region, not the ohm resistance by electrochemical impedance spectroscopy. This deterioration of performance was not influenced by hydrogen gas flow rate over the range of 30 to 100 ml/min. As the time of non-current constituted between the cycles was extended, the deterioration of performance decreased, and the deterioration did not occur at all under the condition of the time of non-current exceeding 5 hours. As the operating temperature decreased to 1123 K, also, the increase of the resistance in the higher frequency region by the current cycles was reduced.
The objective of this study is to develop the wearable haptic device having widely operating range and highly efficient dynamic characteristics of the end-effector located on the tip of the haptic device. The conventional haptic device displays pseudo translational force to the operator's hand. However, there is a problem that the dynamic characteristics of the end-effector of these devices are restricted to the response of motion of the actuator. To improve the dynamic characteristics of the end-effector, the variable structure control which is able to choose either connection or disconnection between the actuator and the end-effector is developed. The proposed system controls (opens or closes) the hinge mechanism, so that the actuator and the end-effector can be connected or disconnected depending on the opened or closed status of the hinge mechanism. Accordingly, we develop the control system including the coordinate transformation of the displaying force using the angle sensor by taking into account large range of motion in the end-effector. To confirm the effectiveness of the proposed control method, experiments of force display for human operators were carried out. The experimental results show that the proposed system is able to improve the dynamic characteristics of the end-effector and to amplify the operating range of the hand motion in the force non-displayed condition.
This paper describes the attitude control method for overturning prevention for a lunar planetary lander which uses a semi-active damper on the landing leg. In order to achieve safe landing on uneven terrain especially a sloped ground, a novel landing gear system is required. The landing leg with variable damping is one of the solutions for touchdown without overturning. Conventional landing gear for lunar and planetary lander has a fixed shock attenuation parameter and it is not used proactively for attitude control of the lander in the touchdown sequence. By controlling the damping coefficient of the each landing leg, it becomes possible to suppress the disturbance on the attitude of the lander, and it prevents overturning. First, the strategies for the overturn prevention for the lander by changing damping coefficient of landing legs are shown and the control rules based on the lander and landing leg state values are proposed. In the second place, the mathematical model of lander based on the differential algebraic equation in vertical two-dimensional plane is presented. Besides footpad-ground contact model is also described. Finally, touchdown simulations on a sloped terrain with the proposed landing gear control method are shown. Numerical simulations show that the proposed landing gear system works well during the touchdown on a sloped terrain.
Magnetic bearing motors have the advantages of no friction loss, no lubrication, and so on. However, these motors are not used widely because of their high cost and large size. To overcome these limitations, a self-bearing motor having a simple structure with distributed windings has been proposed. The rotor consists of a permanent magnet and an iron yoke that rotates within the body. The stator consists of two six-phase distributed windings and is installed between the permanent magnet and the back yoke of the rotor. A Lorentz force, generated by the interaction between the stator current and the magnetic field of the permanent magnet, controls the rotational speed and radial position of the rotor. The motor had used hall sensors to detect the rotational angle. In this paper, a sensorless controller without hall sensors is introduced. Finally, the performance of the controller is verified with rotational tests.
The bending stiffness at the stepped cross-section of a rotor decreases in accordance with the elasticity in the face of the cross-section. This study proposes a method to deal with this decrease in bending stiffness in one dimensional (1D) beam modeling. The 1D beam modeling is widely used in practice to predict the rotor vibration characteristics represented by the eigenvalues because reasonable accuracy can be obtained in shorter computational time compared to three dimensional (3D) modeling—this is applicable to precisely predict the vibration including the cross-sectional face elasticity. Furthermore, the 1D beam modeling is especially useful to save computational time for identifying optimum rotor shapes or dimensions in which iterative complex eigenvalue calculations are required. In the 1D beam modeling, however, the decrease in bending stiffness is not included unless a special treatment is introduced into it. In this paper, the authors propose an accurate and easy-to-use 1D beam modeling method which takes into account the cross-sectional face elasticity of a rotor shaft with stepped cross-sections. This newly proposed method considerably reduces the calculation error regarding the rotor's bending stiffness—an inherent functional limitation of the 1D beam modeling.
Multi-portal Human Interface (M-HI) as an innovative human interface for power assist systems has been researched and developed. The M-HI allows users to apply the operational force anywhere on the power assist system. When users control the PAS on its arbitrary point, The operational point motion is different from the end-effecter motion, even if the end-effecter move as ideal motion for users. The phenomenon affects user's maneuverability decrease. In this paper, impedance paremeters on the operational point are forcused. The relationsihp between the operational point motion and maneuverability are analyzed in terms of the impedance parameters. To evaluate the maneuverability of PAS applied M-HI, The impedance parameters of each operational point is calculated. Furthermore, modification of impedance parameters on the operational point is proposed. However, the method raise end-effecter motion error, the modification amount optimization is required. In this paper, the optimization method and results of fundamental maneuverability evaluations are shown.
A fluid damper that applies electric and magnetic fields to a conductive fluid and ferrite particles is developed in order to act as both of a passive and a semiactive type vibration control device. The damper consists of a long by-pass pipe, electromagnets, electrodes, a piston, a cylinder, a conductive fluid, and ferrite particles. The eight electromagnets are installed around the by-pass pipe. The eight electrodes are fixed, and the ferrite particles are put inside the by-pass pipe, respectively. The conductive fluid is entirely filled in the cylinder, the tube and the by-pass pipe. Magnetic flux density in the by-pass pipe can be switched by not only applied voltage of the coil but also multi pole conditions of the electromagnets. An electromagnetic induction force of the conductive fluid and particles is caused by Fleming's left hand rule when both of magnetic and electric fields are applied in transverse. Furthermore, the ferrite particles virtually act as an artificial orifice due to clustering, therefore the resisting force can be changed. Test damper is manufactured. Theories of damping, magnetic induction and liquid inertia effects are introduced, respectively. Magnetic flux densities in four cases of multi pole conditions are measured, and analyzed by FEM. Resisting force characteristics of the test damper using the conductive fluid with the ferrite particles are measured under sinusoidal harmonic excitation. The experimental results are compared with the theoretical results. Finally, the effects of electromagnetic induction and a feasible study are confirmed experimentally and theoretically.
In the present study, we developed a new feed correction mechanism which corrected not only a positioning error (i.e., feed deviation) but also an angular error (i.e., yaw of a table). A correction mechanism including two piezoelectric actuators was constructed and installed between double nuts. The correction mechanism corrects positioning error if both piezoelectric actuators are expanded to the same length, and corrects angular error if one piezoelectric actuator is expanded and the other is contracted. First, the positioning and angular errors correction functions were investigated separately. A load was applied to one side of the table in order to simulate a counter force during machining. In the positioning error correction, a low-frequency component of positioning error was corrected effectively under the condition that the load for the table was set to at least 50 N. In the angular error correction, the correction capability was comparable to that of the positioning error correction up to the maximum load torque to the table, 1.4 Nm. The load torque was limited to 1.4 Nm because both piezoelectric actuators reached their saturation voltage. Finally, simultaneous correction of positioning error and angular error was examined, and the simultaneous correction capability was confirmed to be equivalent to the separate correction capabilities.
Vibration measurements of a road-wheel were demonstrated using a fiber Bragg grating sensor (FBG sensor) and a flat-belt test machinery. Davis and Kersey's method to measure Bragg wavelength of an FBG sensor was applied in the tests. An assembled wheel of a tire and a road-wheel for an automobile was set on the machinery. When the flat-belt ran at the velocities of 10～200 km/h, the belt rotated the wheel at the velocities of the belt. The vertical load between the wheel and the belt was loaded by weights of 400 kg. An FBG sensor was attached to the back surface of the road wheel to measure radial vibrations of the wheel. The Bragg wavelength changes without the 0-Hz elements possessed almost the same waveforms against the non-dimensional time by the 1-cycle period under different velocity conditions of the flat-belt running. The waveforms show two peaks in the longer wavelength side and one peak in the shorter wavelength side in one-periods. The waveforms seem to be general in radial vibrations of wheels. The spectra of Bragg wavelength changes show the two major peak frequencies. One is the rotational first-order frequency and the other is the rotational second-order frequency. The powers of the two frequencies are almost same. The spectra also show that the FBG sensor detected wide frequency-range vibrations from 1 Hz to 1.3 kHz. These results reveal that FBG sensors are effective to measure vibrations of wheels. Moreover, the testing and evaluating techniques in the test using an FBG sensor facilitate to measure vibrations of rotating wheels.
In this paper, we propose to calculate a likelihood based on a quasi-euclidean norm for a fast and robust particle-filter-based self-localization of mobile robots. The quasi-euclidean norm can be calculated faster than the conventional L2 norm. Furthermore, such norm is much robust to noises than the L1 or L2 norm. In this work, we perform self-localization experiments based on the L1 norm, L2 norm and quasi euclidean norm likelihood to compare the robustness and processing time. Through these experiments, we confirm the effectiveness of our method.
To prepare exhaustion of oil supplies, alternative lubricant which is good for environment will be required. Water is expected to be a suitable lubricant. However in water lubrication, high wear and seizure come to be problems because of water's low viscosity. Surface texturing is one of the methods reported to overcome these problems. So in this paper, effects of surface brush structure and wettability are investigated expecting improvement of water lubrication property. At first, we conducted thrust cylinder friction test using six kinds of polytetrafluoroethylene(PTFE) specimen; flat, hydrophilized flat, all-brush, hydrophilized all-brush, pattern-brush and hydrophilized pattern-brush. To prepare these specimens, the brush structure was made by irradiating nitrogen ion beam and hydrophilic treatment was conducted by exposing PTFE specimens to plasma generated in the atmosphere of argon and water in vacuum chamber. As results of tests, we found hydrophilized pattern-brush specimen showed good seizure resistance. Then, we prepared hydrophilic pattern specimen which was made by eliminating brush on hydrophilic pattern-brush specimen and conducted friction test to know effectiveness of brush structure inside pattern. As a result, hydrophilic pattern-brush specimen showed better seizure resistance than hydrophilic pattern specimen. So, we concluded that hydrophilic brush structure inside pattern can improve seizure resistance in water lubrication.
When human body is punched by the boxing glove, both of the body surface and the boxing glove deform in a complex shape. The purpose of this study is to develop a flexible sensor that can be used in such interface. Firstly, several mechanical phenomena, which are the cause of error signal of the sensor, are discussed. These are the influences of out-of-plane bending deformation, shear force caused by rubbing force, shear force caused by the Poisson's effect of contact material, and the transverse compressive force caused by the overhanging deformation of flexible material. Then as a sensor that can eliminate the error factors of these, a distribution type impact sensor in which sixteen sensor elements are arranged in a 4x4 matrix is developed. Punching experiments using a boxing glove are carried out by installing the sensor on the load cell, on the concrete wall and on the sandbag. From the experiment, it is found that the impact force can be measured with good accuracy by using the sensor. Despite the sensor has inadequate distribution number of sensor elements, the sensor structure includes mechanical requirements for the flexible impact sensor.
Dielectric relaxation method has been proposed for the possibility of real-time detection of thrombosis by exploiting the electrical properties of the blood. In-vitro experiments were conducted with bovine blood to measure relative permittivity and dielectric loss in the case of various hematocrit values under static blood condition. As a result, the relaxation frequency of the electrode and red blood cells were observed at 20 kHz and 2 MHz respectively. The characteristics frequency showing the permittivity of the red blood cells membrane was in the range of 60 kHz to 1 MHz. The time variations of resistivity and relative permittivity were observed at this frequency range of characteristics frequency of red blood cell membrane. Resistivity and relative permittivity measured at this frequency range increased in the case of the increase in the hematocrit values. Additionally, a peak was observed in the temporal change in relative permittivity only in the case of that frequency range. Moreover, from the results of visual check of thrombosis, this peak indicated the start of the micro-thrombus formation. This phenomenon was specific to the thrombosis, and was observed only in the presence of red blood cells. The experiments showed the possibility of the real time detection of thrombosis for implantable ventricular assistance devices, heart-lung machines and artificial kidney.
Concerning most of track-and-field athletics such as the marathon, it is important to clarify the flow around track runners and to evaluate their air resistances (or wind resistances, drags). In wind-tunnel experiments which are the most effective approaches to such a problem as well as field observasions and numerical analyses the moving-belt system is indispensable for precise aerodynamic measurements, if the so-called “ground effect” is negligible. In the present study, we develop a moving-belt system, and show its basic performance such as the distributions of time-mean velocity and turbulent intensity above the moving-belt system using a hot-wire anemometer. Then, the authors investigate the air resistance of a runner in solo running and of a runner in duet running in various duet-running formations. Especially for duet-running formations, the authors reveal the optimum one.
In the study reported here, the operational characteristics of a human-gearshift lever system were experimentally analyzed in consideration of the mechanical properties of the human arm and related effects on muscle activity. The results highlighted three points in particular: (1) It is possible to determine positioning that facilitates operation as well as the operational direction of the gearshift lever based on force manipulability in consideration of human joint-torque characteristics; (2) subjects feel that handling is easier when arm muscle activities in push and pull operations are almost equal during translational lever movement; and (3) the gearshift lever operation speed and the force-stroke characteristics have a very significant effect on whether operation is favorable or poor. Comprehensive consideration of these results is expected to be useful in the design of a human-vehicle gearshift lever system.