An elevator rope for a high-rise building is forcibly excited by the displacements of the building induced by wind forces and/or by long-period ground motion. In high-rise building, the elevator rope may resonate with natural frequency of the building, and lateral vibration becomes large; hence, effective solution to reduce the rope displacement is demanded. In this paper, a method to suppress the rope displacement by using dynamic damper is proposed. Rope lateral vibration is controlled by fluctuating rope tension using up-and-down motion of this dynamic damper. Finite difference analyses of rope vibration with dynamic damper are performed to verify the validity of this method. Experiments involving forced vibration of a rope whose length is constant are also performed. The optimal natural frequency of this dynamic damper is about 2 times of the natural frequency of the rope lateral vibration. The rope sway can be reduced to about 1/2, when the cage is stopped.
Although, in designing blades, it is assumed that all blades on a disk are identical (tuned system), the vibration characteristics of the blade is slightly different due to the manufacturing tolerance, the deviation of the material property, and so on (mistuned system). As a result, in the forced response of an actual bladed disk caused by the flow distortion, the responses of all blades become different, and the response of a certain blade may become extremely large, due to the split of the duplicated natural frequencies, the distortion of the vibration modes, and so on. On the other hand, it is suggested by many researchers that the mistuning suppresses the blade flutter, because the complete travelling wave mode is not formed in a disk. In other words, the effect of the mistuning acts on the dangerous side for the forced vibration, while on the safety side for the blade flutter. In this study, the stability analysis of the mistuned bladed disk is carried out using the reduced model with high fidelity, in order to research the effect of mistuning on the blade flutter in detail. In the analysis, the actual bladed disk experienced the blade flutter is analyzed, and the calculated results are compared with the experienced phenomena, to verify the validity of the analysis method.
This paper provides an adaptive control method for a magnetic levitation using finite element approximation. Thanks to noncontact and frictionless, magnetic levitation can move smoothly and position precisely an object. In addition, it also makes possible to measure small force applied to the object. However, the fundamental nature of electromagnetic force causes obstructive problems to measuring force correctly. In order to achieve both positioning and measuring force, the finite element approximation works smartly to obtain the model of the magnetic levitation system by the model reference adaptive control technique and correct the deviation of the system from the reference model. As the result, the magnetic levitation system behaves as a reference linear motion system, so that both positioning and measuring force become possible. To show the efficiency of this method, the control system is implemented in the digital signal processors and improve the tracking control performance by obtaining the finite element model of electromagnetic force, parameters of inertia and the center of gravity.
A disaster, such a heavy rain or an earth quake, breaks many roads. People, which are suffered a damage, needs rescue however transport and rescue trucks cannot move on a disorderly ground because the truck's load shifted by inclination of the load-platform. This study designs a high maneuverability vehicle with a balance control of a load-carrying platform. The proposed vehicle can transport the rescues and the injury people on the disorderly ground. This study detected a delay time in regard of controlling the motion of the load-carrying platform. Generalized Minimum Variance Control, which is one of the predictive control, is applied to the control system.
A ship is turned by steering. Then the ship is turned with constant angular velocity against the steering angle. However, the turning angular velocity is varied by blowing strong wind. A steering control system is designed to keep the constant turning angular velocity in the strong wind. First, the variation of the turning angular velocity is verified in regard of the strength and the direction of wind. Second, the ship's maneuverability is identified, which is expressed as Auto-Regressive eXogeneous (ARX) model, by each steering angle. Then the angular velocity of turning is controlled by applying Generalized Minimum Variance Control (GMVC) as one of predictive controls. Finally, the servo type GMVC is arranged with adjusting the wind's effect.
The evaluation methodologies of flow induced vibration on the dynamic stability of elastic beam structure are investigated. In this paper, the instability analysis methods of a beam subjected to a confined annular axial flow are dealt with. Such structures are reactor core structures of nuclear power plants, high-speed trains passing thorough a tunnel, and submarine resources production pipeline, so on. The relation between the annular axial flow velocity and the unstable dynamics of structures has to be clarified. We have compared two analysis methods which can evaluate the dynamic instability of such structures. In first analysis method, the fluid is treated as viscous fluid, and is governed by the Navier-Stokes equation, and the beam structure is treated as the Euler-Bernoulli beam. This is called as the viscous flow solution hereafter. In second analysis method, the fluid is treated as ideal fluid. The viscosity effect is added to the equation of motion. This is called as the nonviscous flow solution hereafter. The complex eigenvalue analysis of the fluid structure coupled equation of motion is performed in order to clarify the dynamic instability. Performing the parametric studies, the comparison between both solutions is investigated. Moreover, the numerical solutions are compared with the experiments which have already reported by one of authors. When an annular gap becomes smaller than other dimensions, it is found that the difference in the critical velocity between the viscous flow solution and the nonviscous flow solution is generated.
In this paper, we propose a feedforward control method for suppressing residual vibrations, which consist of first and second vibration mode amplitudes, of a flexible manipulator with a point-to-point (PTP) motion. To construct the mathematical model of the manipulator system accurately, the parameters of the equations of motion are experimentally identified. In the control technique, we attempt to express the joint angle by the combination of cycloidal function and polynomial function, which is useful for analyzing natural frequencies and vibration modes of composite laminated plates and shells. The trajectory of the joint angle depends on the coefficients of the polynomial function. To cancel the residual vibrations, the coefficients are tuned by a particle swarm optimization (PSO) algorithm. By driving the joint angle of the manipulator along the optimal trajectory, not only the first vibration mode but also the second vibration mode can be suppressed after positioning, i.e., feedforward vibration control can be achieved for the high-speed positioning. Results obtained from simulations and experiments demonstrate the effectiveness and feasibility of the proposed vibration control technique.
During fabrication process of laminated fibrous composites, asymmetric laminates result in skewed surfaces after curing due to strong anisotropy of each layer, and composites with specific lay-ups and dimensions show bi-stable states in terms of surface shapes. The present study performs a multi-objective optimization for the composite shell with bi-stable shapes. Objective functions are amount of averaged deformation between two stable shapes of shell (snap-thorough deformation) and critical temperature of surroundings which is the maximum temperature to keep the bi-stable characteristics. These properties indicate a trade-off relation each other and are maximized simultaneously by using an effective multi-objective genetic algorithm method, SPEA+. Shell shapes after curing are predicted by the thermal deformation analysis based on the Rayleigh-Ritz method with directly assumed strain functions. Calculated results agree well with those from experiments with respect to shell shapes, and the present multi-objective optimization reveals wide-ranging Pareto optimum solutions. The numerical results show that spirally laminated fiber orientation angles are effective to increase amount of snap-thorough deformation.
In one of the problems of the rotary machine, unbalance vibration synchronized with rotational frequency is well known. This vibration is caused by the unbalance of the mass of the rotor, the electromagnetic force of the active magnetic bearing (AMB), and the location of the AMB. As the methods to suppress this vibration, Peak-of-Gain Control (PGC) and Automatic Balancing System (ABS) using the tracking filter synchronized with the rotational frequency have been reported. By using the PGC (ABS), the bearing stiffness at the rotational frequency is increased (decreased). In addition, the phase is advanced by applying the compensation with the phase-variable type tracking filter, the N-cross control, and the compensation with the differentiator. The damping effects are increased in these compensation methods, however a change of the bearing stiffness is caused. Moreover, the compensation methods advanced phase cannot adjust the bearing stiffness and damping effects independently and cannot confirm only the damping effects. Accordingly, we investigate the mutual relationship between the compensation methods increased damping effects and indicate that the compensation method to minimize a change of the bearing stiffness with increasing the damping effects is the method with the phase-variable type tracking filter. These methods advanced phase can be considered as gain stabilization methods, and we propose Phase-Variable Control (PVC) classified as a phase stabilization method. The characteristics of the proposed PVC are adjusting the bearing stiffness and damping effects independently, having both characteristics of the conventional PGC and ABS, and changing the bearing stiffness and damping effects seamlessly. Furthermore, the proposed PVC can adjust the bearing stiffness and damping effects appropriately as the rotational speed increases, and we show that the whirling of the rotor is suppressed from the experimental results concerning rotational tests.
This paper describes the effect of vibration characteristics on a bicycle-rider-two infants system when the weight of infants and the seat position are changed. To examine vibration experienced by a rider and two infants, we investigated a vibration model on a bicycle-rider-two infants system and a simulation system. Input signals of the wheels were developed a sine waveform for the transient response and sine waveforms of a frequency from 1 to 20 Hz for the frequency response. Further, numerical analysis was performed by using these input signals. RMS (root-mean-square) values and P (peak) values were calculated for the evaluation of vibrations on infants and rider by the calculation. From these results, the relationship among the infant weight, the seat position and vibration characteristics of infants and rider was clarified by using the simulation system. Therefore, it was shown that the simulation system could be used as a tool to design the bicycle with a rider and two infants.
When an elevator rope for a high-rise building is forcibly excited by the displacements of the building induced by wind forces and/or by long-period ground motion, rope displacement becomes large even if the ground acceleration and the buildings acceleration is small. In previous paper, when elevator cage is stationary, a new practical method for reducing the rope vibration by using vibration suppressors is proposed for relaxing the restricted elevator operation. The advantage of using the vibration suppressors for reducing the rope lateral vibration is demonstrated through numerical calculation. Further, when center of the rope or 1/N position of the rope is pulled, exact solution to the free vibration of the rope with vibration suppressors has been presented. However, when arbitrary position of the rope is pulled, exact solution to the free vibration of the rope with vibration suppressors has not yet been obtained. In this paper, an exact solution to the free vibration of the rope with one vibration suppressor which located at the center of the rope is presented, when arbitrary position of the rope is pulled. The rope is modeled with string. Finite difference analyses of the rope vibration with vibration suppressor are also performed. The calculated results of the finite difference analyses correlated fairly well to the calculated results of the exact solution.
The authors proposed a model predictive control method for energy regenerative active vibration control systems. The control input of this method is composed of a linear sum of harmonic functions to reduce computational costs and this approach gives a simple way to predict the time averaged regenerated power. However, the predicted averaged power tends to be smaller than the actual averaged power because the disturbance input is ignored in the prediction process. In this paper, a modified predictive controller that uses a harmonic disturbance model and a minimal order observer to estimate and consider the disturbance input in the prediction process is proposed. Numerical simulations of a single degree of freedom (SDOF) system with the proposed controller show that the modified controller can improve the prediction quality of the time averaged regenerated power in the following cases. These are the cases that the type of the disturbance is sinusoidal input whose frequency is the natural frequency of the SDOF system or random input whose amplitude is small enough to satisfy control input constraint.
In order to improve fuel consumption, conventional HV (Hybrid Vehicle) control has intended to reduce exhaust heat power from engine and transform fuel into driving power as much as possible. However it causes deterioration of fuel consumption when engine exhaust heat is necessary like the condition that engine is warming up or heat power for cabin is supplying in winter. In this paper, engine and MG (Motor & Generator) driving power control of HV in engine warm-up period avoiding fuel economy deterioration and reducing warm-up time by balancing coolant temperature and SOC (State Of Charge) of battery is proposed. The principle of control is predictive control with HV model including engine, MG, battery and coolant characteristics. Engine and MG power, control manipulation value, are decided as minimizing cost function including warm-up time and fuel amount. As a result of verification with simulation, the proposed control achieves notable effect especially at the condition that small SOC margin is remained for its upper limit. In such a condition, conventional control keeps engine working until warm-up is completed in order not to stop supplying heat power for coolant, however the proposed control stops it as needed based on the balance of SOC and coolant temperature, and reduce warm-up time and fuel consumption.
The pace of globalization of vehicles has increased in recent years, along with new requirements for steering stability and durability in rough road conditions that had not been anticipated in Japan. Accordingly, the range of physical quantities such as acceleration and force needs more in-depth examination. The shock absorber is a component that particularly determines ride comfort. A shock absorber is composed of a piston and a cylinder. In general, when the piston speed is low, the damping force is generated by fluid passing through a fixed orifice. When the speed is higher, a valve opens in addition to the fixed orifice. This suppresses the damping force of the fluid flow, thus maintaining stability and improving ride comfort. Therefore, the damping characteristics of the shock absorber have a large non linearity. In addition, when the excitation frequency increases, hysteresis appears between the piston speed and the damping force. The parameters such as the loss factor and dynamic stiffness in the frequency domain can be used for steady-state response analysis. However for transient response analysis of bumps and rough road conditions that affect the ride comfort, those characteristics must be expressed in the time domain. Therefore, in this study, measurement results are used to build a physical model composed of frequency-independent elements as simple as possible. This allows a time domain analysis to be done for a shock absorber with non-linearities of complex structure and frequency dependence. The Maxwell model is used to take into account the non-linearity of damping force and represents the hysteresis and frequency dependence that can be found in the actual measurement results. Our model can provide a non-linearity in the damping characteristics of the dashpot of the Maxwell model. In addition, the effectiveness of the proposed method is verified by experimental analysis of the shock absorber only and the whole vehicle.
The gigantic and long-period earthquake motions were observed in Tokyo, Osaka and other by the East Japan Earthquake of March 11, 2011. Therefore, the super high-rise buildings located in Tokyo were excited by large amplitude with about 1m and long time over 10minite. As the result, the life lines of the super high-rise buildings were took large damages. For corresponding to such an accident, it is important to measure the displacement vibration instantly and take a controlling technology. However, such devices are not yet exist to measure the displacement vibration waves with large magnitude and long period. This paper proposes a novel seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. The seismometer-type absolute displacement sensor is consisted of a sensor body with a moving mass and its supporting springs, feedback control circuits and a third order phase lag compensator. The natural frequency of the sensor body located at 6.4Hz originally is reduced to 0.23Hz using by acceleration feedback mainly and then moving stroke of the moving mass is compressed to 1mm to 1/630mm. Moreover the new natural frequency of 0.23Hz developed by feedback control is sifted to 0.055Hz by the third order phase lag compensator. Therefore the sensor has a measuring range from 0.08Hz to 10Hz, in addition to no drift problems by the use of feedback control way. In this way, the seismometer-type absolute displacement sensor with the amazing ability has been realized to measure the long period over 10 second of earthquake waves. In addition, the large magnitude to measure 630mm is expected, nevertheless a small size with moving stroke of 1mm. So far as we know, such a sensor for measuring absolute displacement is very novel in the world. In this paper the ability of the sensor will be shown by simulation and experiment.
This paper proposes a novel seismometer-type absolute displacement sensor aimed at detecting earthquake waves with a large magnitude and long period. However, since the measuring range of the conventional displacement sensor is higher than the natural frequency of itself, it is difficult to detect a low frequency vibration below 1Hz using conventional seismic-type displacement sensors. In order to provide an absolute displacement detection which is capable of lowering the natural frequency and enlarging the detectable amplitude without causing a structural defect, the relative signals of displacement, velocity, and acceleration between a detected object and the auxiliary mass of the sensor are fed back into the sensor. In addition, a phase lag compensation is inserted to adjust phase angles, which are below a frequency lower than 1Hz. Theoretically, this sensor is able to detect a lower frequency range from 0.2Hz to 10Hz and large amplitude with 100 times to the movable range of the sensor. It has been demonstrated by experiments that the developed sensor with a small size and lightweight has a detecting range from 0.2 Hz to 10Hz for absolute displacement and velocity. As an additional advantage, the measurement displacement amplitude has been expanded to about 40dB (100 times) for detecting earthquake waves with large magnitude and long period. As the typical application example of the developed absolute displacement sensor, a seismic wave based on Hachinohe wave is used with well observation results.
Various soundproof wall have been developed for noise reduction. This paper experimentally investigated the performance of broad band noise reduction by pseudo periodic soundproof forest by placing trees on the shape of Penrose tile. Transmission of an incident acoustic wave can be modulated by the sonic crystal, which mostly consists of periodic array of solid bars. Then acoustic wave of specific frequency band cannot be transmitted in the forest, and consequently band gap arises. As it is known that the diameter and lattice space of sonic crystal have the relation to both bandwidth and center frequency of band gap, firstly the influence of these parameters were experimentally verified using conventional sonic crystals. Then pseudo periodic soundproof forest by referring to the Penrose tile, which fills a plane by two kinds of simple shape tile, was introduced to obtain broad band gap. Finally it was shown that the pseudo periodic structure can widen the band gap of conventional sonic crystal, and accordingly has advantage for broadband noise reduction by sound proof forest.
In this work one evaluates the energy harvestable from an airless tire equipped with piezoelectric bimorphs on both lateral surfaces of the tire's elastic elements, which can be either lamellar hinged spokes or tread supporting omega springs. Electrical power is obtained due to the cyclical bending or buckling of the piezoelectric bimorphs together with the associated elastic elements in the region of contact with the road. Piezoelectric bimorphs are metallic springs with lateral surfaces coated by a piezoelectric ceramic material. Models for the bending deformation of the spokes and omega springs, as well as for the electrical power generated by the airless tire are suggested. Then, variation of the bending and buckling deformation of the spokes and omega springs on the contact surface with the road is investigated for various values of the dimensionless length of contact and geometrical parameters of the tire. In the end, variation of the generated electrical power versus the travel speed of the vehicle for various geometrical parameters of the tire is clarified. The following main conclusions were inferred: generated electrical power is proportional to the density of the piezoelectric ceramic material, to the mean potential energy of deformation of the bended elastic elements, and to the dimensionless length of contact; it is also proportional to the second power of the global electromechanical constant of the piezoelectric bimorph, and to the third power of the vehicle's traveling velocity.
Objective lens actuators are mechanical devices for positioning the objective lens in optical disc drives. The moving part in the objective lens actuator, which is comprised of the objective lens, a holder holding the objective lens, and coils attached to the holder, is supported movably relative to the fixed part by suspension wires and moved electromagnetically in the focusing and tracking directions. The resonance of the supporting system with suspension wires occurs as a main resonance in the frequency response characteristics of an objective lens actuator. It influences the driving sensitivity and settling time of the servo system. Therefore, it is necessary to design the frequency and damping of the main resonance appropriately. The frequency response characteristic of a supporting system with suspension wires is different from the general response of a spring-mass-dashpot system due to the viscoelasticity of the silicone gel added to the suspension wires for damping. In this paper, silicone gel is considered as a spring, the elastic modulus of which is expressed in a function of the frequency so that the vibration model of the supporting system of suspension wires is described easily. Simulated results with this model showed good agreement with experimental results, and it was confirmed that this model is effective for analyzing the frequency response characteristics of objective lens actuators.
There are several types of sound localization methods. However, the almost methods are used for sound localization of middle frequency noise around 1kHz. In high frequency, the measurement of sound field needs huge load. Therefore the measurement of high frequency noise by sound localization methods is unrealistic. We are currently developing the Converted Nearfield Acoustic Holography method, which is converted method of conventional Nearfield Acoustic Holography method. This method can localize the high frequency noise source with few quantity of datum. Therefore the load in measurement is quite light. In this paper, the noise of a gear set and a linear slider are measured as examples of application of the Converted Nearfield Acoustic Holography method to the actual industrial elements. As a result, since this method has some deterioration of resolution in the reconstructed image, this method can localize high frequency noise source with quite quick measurement.
In this paper, we discussed the geometrically nonlinear system identification technology using auto regressive time series analysis. We focused on the transient response from large amplitude to small amplitude. In addition, we assumed that the transient response contains structural non-stationary. We derived the regression formula of instantaneous frequencies and amplitudes using method of averaging. We formulated estimation method of instantaneous frequencies using Kalman filter and auto-regressive model. In numerical simulation, we conducted the identification of load-deformation relationship. In the result, our proposed method could identify the load-deformation relationship in a high degree of accuracy. On the other hand, we conducted the verification of accuracy using least-square method. In this case, accuracy of our proposed method was higher than accuracy of least-square method. We conducted the identification experiment using geometrically nonlinear system. In tensile test, we observed the hard spring characteristic in our experimental system. In addition, we got the free damping oscillation. In the result of an identification experiment, our estimation result was in good agreement with experimental data. On the other hand, we tried the identification test using least-square method. But, we could not reconstruct load-deformation relationship. Therefore, we confirmed availability of our proposed method in low length data.
Frahm damper is the dynamic absorber without damping. This damper suppresses vibration in some range of excitation frequency using anti-resonance point of frequency response function. In this study, two DOF Frahm damper attached to two DOF system is investigated. Two combinations of the stiffnesses of two DOF Frahm damper for desired natural frequencies are obtained. The frequency response functions of the dampers alone show that these dampers have same resonance frequency and different anti-resonance frequency. In the point of vibration suppression, these dampers have same ability near the 1st natural frequency, but different characteristic near the 2nd natural frequency is observed. The damper with better performance suppresses vibration as well as two traditional Frahm dampers. To investigate the difference in the performance of the dampers, mode vectors are illustrated. In the mode vectors of the dampers alone, mode localization is observed in only one of the damper, which is effective in vibration suppression near the 2nd natural frequency. In the mode vectors of whole system, the components corresponding to the main system have almost same values. But the components corresponding to the damper has same characteristics of mode vectors of damper alone. The mode localization is observed in the two traditional Frahm dampers.
This paper addresses the development of an advanced parallel two-wheel vehicle that has an underslung vehicle body. The developed parallel two-wheel vehicle has the functions such as the self-standing structure by stable pendulum structure, the seat positioning system for compensating the deviation of the vehicle's gravity center including the passenger, and the active mass system for suppressing swaying of the vehicle body. The vehicle will be used by diverse passengers in the future. However, the sway suppression control of the vehicle body was developed without consideration for differences of the passenger's physical constitution in the conventional study. In this paper, the mathematical model of the swaying of vehicle body with passenger and its model parameters identification are proposed. In the model parameters identification, it is clarified that the model parameters of each passenger are similar except for the passenger's mass. Furthermore, the control parameters designed by backstepping method are independent to interference from the model parameters. Therefore, in design of the sway suppression control to the diverse passengers, the only passenger's mass is given to the control system. Finally, effectiveness of the proposed control system is verified by experiments using the parallel two-wheel vehicle.
Falling is a common problem in the growing elderly population and fall-risk assessment systems are needed for community-based fall prevention program. To improve motor and cognitive function simultaneously, rhythmic stepping exercise (RSE) has been proposed and we have developed a measurement system using a laser range sensor (LRS). However, there is to be danger of falls during the RSE depending on the motor function of the participant. Therefore, it is necessary to determine whether the participant is able to perform the RSE or not based on the evaluation of motor function. A one-leg standing test can evaluate the motor function of the participant in a short period of time. The aim of this study is to propose a method of measurement of one-leg standing for the qualification test of the RSE using an LRS. In the RSE measurement system, the LRS installed at the shin height to obtain the trajectory of both legs during the RSE. However, it is difficult to measure a start (foot-off) and end (foot-contact) time of one-leg standing from the two-dimensional distance data obtained by the LRS directly. To solve the problem, we propose a method to detect the behavior of foot-off and foot-contact based on not only the position and speed but also the width of the raising leg which are obtainable in the two-dimensional data. From the experimental results with elderly people, it was confirmed that the proposed method could measure the foot-off and foot-contact time in one-leg standing.
This paper proposes a control system design for an exoskelton motion assist device for workers engaged in physically demanding jobs. The exoskelton is designed to provide supports to 1 degree of freedom rotational motion of shoulder and elbow joints and it uses McKibben pneumatic actuators as its power source. Key technical consideration in the control system design should be put on assuring good transient response of the device against the intention of the user wearing the device, while simultaneously providing sufficient force/torque to balance unknown loads. This paper presents two degrees of freedom control system which fully utilizes the improved version of the phenomenological dynamic model of McKibben actuators which has been proposed by the authors recently. Results of the load carry experiments indicate the effectiveness of the proposed control system.
This paper describes the investigations of the characteristic about the sound generation of a nose flute experimentally. The nose flute is attached to the upper part of a container. If air is passed to a nose flute, sound will occur. The volume of a container is changed and the generated sound is measured. The natural frequencies of an experimental device are calculated and we confirm that it is in agreement with frequency of sound generated in experiment. We show that nose flute is a unique musical instrument with the point that a nose flute has only an edge part and uses people's mouth for a resonance body part. The frequencies of resonance sound can be calculated from the capacity in a mouth, the thickness and the area of an opening of a nose flute. When people play a nose flute, it is thought that only the first mode of vibration is used.
The effect of strain rate on the compressive properties, such as strength and absorbed energy, of polylactic acid resin foam was experimentally studied by carrying out the compression tests at various strain rates from 0.001 to 760 s-1. The polylactic acid resin is a kind of plant-derived plastics with low environmental load. It was found that the flow stress of polylactic acid resin foam during compressive deformation and the absorbed energy up to the strain of 0.6 increased with the increase of strain rates. The compressive strength of the foam was also strongly dependent on the density of specimen, despite the same material. Strain and strain-rate depending constitutive equation of polylactic acid resin foam was derived from true stress- true strain curves observed from compression tests at the wide range of strain rates.
The effects of reinforcement with the potassium hexatitanate short fiber on the machinability of the alloy under various cutting conditions were investigated. JIS-AC8A alloy was used as the matrix metal, and two kinds of potassium hexatitanate short fibers were used as the reinforcements. The composites were fabricated by squeeze casting. The machinability of the composites was compared with that of the composites reinforced with various reinforcements such as potassium titanate whisker and aluminum borate whisker. The reinforcements were randomly arranged in the alloy matrix, and no agglomeration of the reinforcements or porosity was observed, indicating that the melt infiltration into the reinforcement preform was perfectly accomplished. The cutting force and feed force of the alloy was reduced by the reinforcement. These force values when the potassium hexatitanate short fiber-reinforced composite was machined was smaller than that when the composites with other reinforcements were machined. The roughness of the machined surface of the alloy drastically decreased by the reinforcement under every cutting condition, and the surface roughness of composites was close to the theoretical roughness. The difference in roughness values between the composites was small. From the surface roughness values, the observation of the chip formation in the cutting process and the observation of machined surface, we have concluded that the reinforcements in the composite suppress the formation of the built-up edge during the cutting process. The machined surfaces and chip forms indicated that the reinforcements in the composite facilitated the shear deformation of the chips because the fibers were easily sheared by the cutting. The tool life when the potassium hexatitanate short fiber-reinforced composite was machined was significantly longer than that of aluminum borate whisker-reinforced composite.
Gigacycle fatigue tests were conducted on two heats of actual materials of storage cylinders used in hydrogen stations for verification tests. The storage cylinders were made of SCM435 steel and the test specimens were extracted in both longitudinal and circumferential directions. Ultrasonic and servo-hydraulic fatigue tests were carried out on hydrogen-charged and uncharged specimens. The two heats of the materials showed difference in microstructures, resulting in different mechanical properties. The hydrogen-charging introduced about 1.2 ppm of diffusible hydrogen, which decreased reduction of a cross-sectional area in tensile tests. In the fatigue tests on the uncharged specimens, only surface fracture occurred, showing negligible difference of fatigue strength between the heats and between the directions. The hydrogen-charged specimens, on the other hand, revealed different fatigue properties between the heats. Internal fractures originating from inclusions occurred in one heat and the gigacycle fatigue strength was decreased. The other heat showed no internal fracture and the degradation of the fatigue strength was negligible. The origins of the internal fractures were different between the directions, while the sizes were close. Accordingly, the difference of the fatigue strength was small between the directions. In summary, fatigue properties were not so match affected by microstructure unlike mechanical properties, while careful attentions were necessary for inclusions. The inclusion-induced internal fractures were strongly affected by hydrogen and this research demonstrated that this type of internal fractures could occur in actual materials.
This study aims to evaluate adhesion quality of oxide scale on low carbon steel plate at high temperature. The scratch test, indentation test and pull-out test are generally adopted to evaluate the adhesion quality of thin films. However, these methods requires contact between a probe and a specimen, and are not allowed to perform at high temperature. Since a laser spallation technique is a non-contact measuring method which produces tensile stress acting on an interface by ultrasonic wave, the method enables us to evaluate the adhesion quality at high temperature. In this study, adhesion quality of the oxide scale on low carbon steel was attempted to evaluate at room temperature and up to 200 °C with the laser spallation technique. The exfoliation which was induced by the laser spallation technique can be identified by change in correlation coefficient for a series of the waveform obtained at each energy of incident YAG laser. Tensile stress acting on interface was estimated from stress distribution of the wave propagating through the interface calculated with a numerical simulation. As a result, it was confirmed that the adhesion quality of the oxide scale increased with testing temperature. It may be because the residual stress which acts on an oxide scale/substrate interface decreased with temperature.
In recent years, the potential for oscillation of swing-type windows due to wind gusts, with accompanying breakage of stopper components and glass, has come under consideration. Generally, quality assessment support for wind load design restricts attention to cases involving evaluation of the exterior windproof pressure performance of closed windows, as provided for in the Building Standard Law enforcement ordinance and the building load indicators of the Architectural Institute of Japan. However, when a half-open swing-type window is subjected to oscillation by a wind gust, the stopper components of the window will be placed in arbitrary positions not characteristic of the closed structure, and dangers due to dynamic loading are experientially known to occur when a window oscillates due to wind gusting and then stops rapidly. A strong wind test was performed to measure the impact force imparted by wind, and the characteristics of the wind energy and resulting impact force were clarified. An impact force evaluation method based on a simple mechanical model was proposed. Furthermore, it was confirmed that the deformation of a plastic stopper component due to an impact force could be modeled via an empirical linear formula, derived experimentally using the impact force imparted in a drop weight load test. The proposed evaluation method is considered to be useful for the safety design of swing-type windows.
Resin lining is widely used as an anti-corrosion method for steel pipes. Since cavitation sometimes occurs near valves in piping system, it is necessary to consider not only the corrosion resistance but also the erosion resistance. The mechanical properties of the polymeric material change in various production methods, such as catalyst, density and mixing of the elastomer. However, few researches have been conducted from this point. In this paper, we examined the relationship between the mechanical properties and the erosion rate of a chloroprene rubber and a number of polyethylene materials produced by different methods. Power plants are operating for a long period. We examined the effect of aging by testing the aged material intended for usage in piping of power plant. We carried out the cavitation erosion tests by using a flowing apparatus as specified in the ASTM G134-95. Cavitation erosion of polyethylene occurred at 150 m/s or more. The flow velocity at 150 m/s and test time for 24hours is the appropriate experiment condition for cavitating liquid jet test of polyethylene. The maximum depth of erosion (MaxDER) of polyethylene decreases with the increase in tensile product and hardness. Among all the tested lining materials, the high density polyethylene (m-LLDPE-H) shows the best resistance to cavitation erosion in terms of MaxDE. The effect of aging on the erosion rate of polyethylene was small.
There are currently one or two kinds of strain gages to measure the stress intensity factor. It might not be sometimes easy to analyze the stress intensity factor with those gages. In this paper, it is reported that our development of the new stain gage enables us to measure the stress intensity factor more easily and practically. The following features of this strain gage to evaluate the stress intensity factor are presented in this paper. (1) Strain component εr measured around the crack tip is used to calculate the stress intensity factor. (2) To be more specifically, we employed the first and second terms of the series at the strain component εr around the crack tip for an evaluation of the stress intensity factor. The calculation method with using our developed strain gage does not require the crack length. The newly developed strain gage was bonded to around the crack tip of the specimens, where cracks were of the opening mode or the mixed mode. We carried out tensile tests on the test pieces bonded with the gage. In conclusion, the results indicate that the developed strain gage enables us to measure stress intensity factor with an error margin within ±10% of the analytical values.
This study describes a novel method for fabricating the plastic mold with microstructure by nanofiber imprinting (NFI) into Si form. The nanofiber was produced by electro-spinning (ES) process which provides a simple and versatile method for generating ultrathin fibers using variety of materials. The effects of ES condition on the diameter of nanofiber were investigated for optimizing to generate ultrafine fiber. By melting ES-nanofiber coated on Si forms that have various micro-structures including line and space pattern, multi-pillars and holes, the plastic molds with those micro-structures were replicated for polymethylmethacrylate (PMMA) polymer. The effect of aspect ratio in microstructure on the shape transcription was investigated by changing Si form from 1μm to 50μm in width for 10μm in height. The usefulness of ES-NFI method proposed in this study was also investigated by comparing with a conventional dipping method. The experimental result shown that the microstructures with 1μm wide to 10μm high could be formed precisely on the surface of plastic mold after melting ES-nanofiber with approx 100nm in mean diameter. It was shown that ES-NFI method was superior for fabricating the plastic mold with finer microstructures. This conclusion does not only attribute a good transcription to finer fiber, but it is considered to be obtained by in-situ extraction of solvent during ES process.
The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.
Multi-pass friction powder sintering process was proposed for fabricating a large plate of porous aluminum by the sintering and dissolution process. In this process, sintering of a powder mixture of aluminum and NaCl was achieved only the rotating tool plunged into the die filled with the powder mixture was made to traverse as in the case of multi-pass friction stir processing. In this study, porous aluminum plates of 60 mm × 30 mm × 5 mm with porosity of 70% were successfully fabricated by multi-pass friction powder sintering process. From measurements of temperature and torque, it was found that the entire sample had almost same sintering condition during the multi-pass friction powder sintering process. From X-ray computed tomography (CT) and scanning electron microscopy (SEM) observations of the pore structures of the fabricated porous aluminum plates, it was found that the entire sample had almost same pore shape and porosity that was similar to the NaCl morphology and proportion. From compression tests of the fabricated porous aluminum plates, it was found that entire sample exhibited a similar stress-strain curve to that of the previous work regardless of the position. This is considered to be attributed to the good bonding between aluminum particles during friction powder sintering process. From these results, it was indicated that multi-pass friction powder sintering process had a potential to fabricate the porous aluminum plate that was similar to the size of the tool traversing area.
In order to prevent failure of piping, limitation on flaw depth according to the circumferential flaw angle is prescribed in the Fitness-For-Service Codes (FFS Codes) of the Japan Society of Mechanical Engineers (JSME). First, the applicability of the limit load assessment method was examined when the flaw angle was large. Then, the influence of the crack growth estimation and flaw sizing errors on the reliability of the flaw evaluation was examined. Since the limit load assessment method can predict plastic collapse strength of a flawed pipe appropriately irrespective of a flaw angle, it is applicable to flaw evaluation even if a flaw angle becomes large. However, precision of flaw evaluation much depends on the variation of the material strength (flow stress) and the flaw size measurement error. Probabilistic analyses considering these variations were performed and influence on failure probability of a pipe was evaluated quantitatively. As a result, the simplified method for evaluating the safety factors according to those variations and satisfying target reliability was proposed. The proposed methods give the flaw evaluation result which has equivalent reliability irrespective of a flaw angle.
Deformation behaviors of polycrystalline metals are quite complex, and we are not easy to directly investigate them; thus, analyses employing simple models such as bicrystals are required. In this study, we conducted crystal plasticity analysis of unidirectional tensile tests, using compatible-symmetric-type bicrystal models with the not-inclined grain boundary and incompatible-type bicrystal model with the inclined grain boundary; we investigated changes in patterns of geometrically necessary dislocation (GND) bans and the density of GNDs in the initial deformation. In the condition where the grain boundary contacted with the constrained faces, GND bans were formed and the distribution was changed with changing the inclination angle α of the grain boundary. In contrast, GNDs were not localized in high density in the condition where the grain boundary contacted with the free surfaces; the changes were caused by two-reasons: one was changes of compatibility of the bicrystal model with changing the inclination angle α, and the other was that deformation shapes of the bicrystal model under tensile loading were changed with changing the inclination angle α and the deformation was constrained by the constrained faces. The compatibility of and average density of GNDs in the bicrystal model could be estimated using differences of components of Schmid tensors between the crystal grains.
It has been demonstrated in the present paper that compressive residual stress introduced by cavitation peening can prevent hydrogen invasion into surface of austenitic stainless steel JIS SUS316L. The specimen was treated by cavitation peening employing a cavitating jet in air. After that, the residual stress measurement was performed using an X-ray diffraction analysis with 2D method. Then the surface was catholically charged with hydrogen. Hydrogen content was evaluated by a thermal desorption analysis using a gas chromatography. The obtained results show the compressive residual stress reduces hydrogen content by 85 % when the compressive residual stress is 378 MPa. The hydrogen content decreases along with increase in the compressive residual stress. Considering a profile of the compressive residual stress with respect to depth from the surface, suppressive effect on hydrogen invasion and area of compressive residual stress in depth direction has a strong correlation whose correlation coefficient is 0.997 and the probability of uncorrected is less than 0.1 %.
Spent nuclear fuel assemblies are stored in the cask with the necessary protective function during the spent fuel transportation or storage. The structural integrity of the fuel rods for the impact load caused by cask mishandling drop accident has to be evaluated to realize more economical and safe operation. However, the experiments for the spent fuel rods accompany many of difficulties and the available experimental data is limited. Hence, the numerical simulation is useful method to predict and evaluate the dynamic response of the fuel rods. This paper deals with the dynamic response of the spent fuel rods under side drop condition. One spacer span of the fuel rod of the undermost layer during side drop is analyzed by finite element method (LS-DYNA). The fuel rod was held between the upper and lower spacers. In the numerical model, the fixed rigid base and the drop weight were connected to the lower and upper spacers, respectively. The numerical analyses were carried out by varying the impact speed of the drop weight and the spacer plate size. Further, the cases of entire drop, in which both the drop weight and fuel rod have the same impact speed, and weight drop, in which only the weight collides with the spent fuel rod placed on the rigid wall were also analyzed. It is found that the fuel pellet and cladding tube reached their yield stresses near the impact point even for the lowest impact speed (2.4m/s) regardless of the spacer size and drop conditions. The plastic region of the pellets is limited within one pellet and the corner part of the neighboring pellet even for the highest impact speed (13.3m/s). The deflection of the fuel rod increased from impact point to the end of the fuel rod in the entire drop condition, but it was limited near the impact point in the weight drop condition. Therefore, the weight drop condition may underestimate the deformation or damage of the spent fuel rod compared to the entire drop condition.
A Kriging-based method for efficiently searching materials was used to select additive elements in lead-free solders that are effective for suppressing the grain-boundary diffusion, which is the cause of smaller breaking elongation than lead-contained solders. By using the idea of the L9-orthogonal-array design methodology, we selected nine combinations of additive elements, and investigated the dependence of diffusion coefficients on four parameters (the atomic radius of the 1st additive, the cohesive energy of the 1st additive, the atomic radius of the 2nd additive, and the cohesive energy of the 2nd additive). The diffusion coefficients were calculated by using molecular-dynamics simulations. The calculation results showed that the diffusion can be suppressed when the atomic radii of the 1st and 2nd additives are close to that of tin (Sn), and when the cohesive energies of the 1st and 2nd additives are smaller than that of tin. According to these conditions, we found that two additives selected from silver (Ag), indium (In), and bismuth (Bi) are effective for suppressing the diffusion and for increasing the breaking elongation. Because these results were confirmed by tensile deformation test, the Kriging-based method is considered to be practical for effectively searching materials.
In the internal flow of the cross flow fan, the formation of the eccentric vortex centered on the rotor inner periphery is well known. So far, the relationship between fan shape and performance, and the formation mechanism and behavior of the eccentric vortex have been reported. However, few studies have focused on the relevance of the fan performance and the eccentric vortex. In this paper, the structure, behavior and driving power of the eccentric vortex are investigated. Next, the effect of the eccentric vortex on the performance is considered. As a result, the following becomes apparent. The entrance flow of the cross flow fan is sucked towards the eccentric vortex indicating strong suction pressure, and therefore, the velocity at the rotor inlet becomes non-uniform in the circumferential direction. Because inlet velocity becomes fast in the tongue side which is near the eccentric vortex, the driving power of the eccentric vortex becomes large. By generating swirling flow by the change of an entrance shape and decreasing tongue side velocity by the outward centrifugal force of this turning flow, the eccentric vortex power decreases and high fan efficiency is accomplished. Finally, the high-performance design guideline of the cross flow fan by controlling the eccentric vortex is proposed.
When two parallel plates confining a viscous fluid in a narrow gap between their plates separate from each other at a constant velocity, the free surface of the fluid disturbs like a dendrite or fingers. This phenomenon is referred to as meniscus instability. In the present study, the meniscus instability of a viscous fluid between two elastic sheets bonded to rigid substrates was examined theoretically and experimentally. Linear stability analysis was performed to obtain the wavelength of disturbances on free surface of the fluid. The elastic sheet was modeled by a linear spring in order to take into account of the deformation of elastic sheets. The wavelength was measured by using a video camera in experiment. These results were well agreed with each other by considering a normal viscous stress at the interface and the effect of the thickness of fluid film remaining on the plates. The minimum wavelength predicting from the theory was about 3.2 times larger as the initial film thickness of the fluid, and the experimental ones were about 3.0 to 5.0 times. The experimental wavelength in the elastic sheets was smaller than that in the parallel plates like as theoretical ones. This result suggests that deformation of the elastic sheets destabilizes the free surface of the fluid.
The purpose of the study is to design a woody biomass energy system and application to coal co-firing, and to evaluate the system considering the three dimensions of energy, economic, and environmental impact. The study targets five types of woody biomass; forest wood residues, forest thinnings, sawmill wood residues, construction wastes and pruned branches of fruit trees. The system contains of collecting of biomass, transporting raw materials, producing wood fuels, transporting wood fuels, and coal co-firing. The study evaluates six cases that differ in wood fuel production location and the type of wood fuel. The results of case study show that the potential of the biomass resource is 37 PJ/year and the availability is 3.6 PJ/year in Tohoku area. The case that pellets produced at the resource generation points has the lowest amount of energy consumption 0.9 PJ/year, wood fuel supply cost 3.2 JPY/MJ and CO2 emissions 0.66×103 t-CO2/year. It is also obtained that the drying process and transportation process have dominant effect on energy consumption and cost.
The effects of design parameters on natural convection heat transfer from a horizontal heated surface with a heated cylindrical pipe were estimated experimentally. The parameters considered were the heat flux of the horizontal heater and the aspect ratio of the heated cylinder. The flow fields around the horizontal heated surface and the heated cylinder were visualized. The results showed that flow characteristics have three distinctive patterns: non flow reversal, flow reversal occurred only in the heated cylinder and reached to the horizontal heater. The necessary conditions to determine the flow fields were discussed. With decreasing the distance of between the heaters and the aspect ratio of the heated cylinder, the ascending flow velocity in the pipe becomes low and flow reversal occurs. In all flow fields, an increasing in the heat flux of the horizontal heater enhances the heat transfer. In the case of no flow reversal and flow reversal occurred only in the heated cylinder, the heat transfer shows the same tendency and increases with increasing the aspect ratio of the heated cylinder. On the other hand, when flow reversal reaches to the horizontal heater, the heat transfer has a little influence on the heated cylinder conditions. Nusselt number is expressed as a function of the modified Rayleigh number of heaters and the nondimensional height.
Ammonia is regarded as one of the alternative fuels and regarded as a “hydrogen carrier”. Ammonia is an easily-liquefiable fuel. Therefore, it is a suitable fuel for transportation and storage. Also, ammonia can be produced in large quantities by using the Haber-Bosch process with low price. It is known that the laminar burning velocity of ammonia/air mixture is about 10 cm/s at near stoichiometric condition. This laminar burning velocity is very low compared with that of other fossil fuels. Therefore, in order to use ammonia as the alternative fuel, it is necessary to improve the laminar burning velocity of ammonia mixture. In this study, the oxygen-enriched combustion was applied to an ammonia/N2/O2 premixed flame and the effects of the oxygen-enriched combustion on the flammable range, the laminar burning velocity and the flame temperature were evaluated. Also, laminar burning velocity was calculated by using CHEMKIN-Pro. The chemical reaction set about ammonia oxidation, which reported by Lindstedt, was applied as the detailed elementary reactions. Results showed that oxygen concentration was necessary at least 26% to maintain ammonia flame stable. The laminar burning velocity was increased with the increase of O2 concentration in both experimental results and numerical results. At 30% O2 concentration and stoichiometric condition, the laminar burning velocity was 27.4 cm/s. Also, Ammonia flame temperature was around 2167 K under 30% O2 concentration.
Droplet behavior on a nanoparticles-assembled bi-porous layer foamed onto a heating surface is evaluated in order to evaluate whether the layer works as a boiling heat transfer promoter. The nanoparticles layer foamed by a boiling adhesion method is of bi-porous structure, which consists of nano scale of pore and micro scale of pore. A life time of a single droplet on heated bi-porous layer is evaluated. It is confirmed that wetting limit temperature drastically increases compared with that of a bare surface and that the nanoparticles-assembled bi-porous layer has quite a high potential to enhance the boiling heat transfer rate and the critical heat flux.
Oil derived from Jatropha is a potential alternative to fossil fuels for Diesel engines in Mozambique because it can be cheaper and more easily available than fatty acid methyl ester, though the physical properties, e.g. high viscosity, might be a problem. As an attempt to use Jatropha oil (JO) in Diesel engines, the present study mixed JO into kerosene. Engine tests as well as un-evaporating spray visualization were carried out. The results demonstrated that a single cylinder engine can be successfully operated with JO blended kerosene despite the fact that the ignition delay is slightly longer than diesel fuel. There were no significant changes of exhaust gas emissions. It is also clear that mixing JO into kerosene can contribute to the reductions of insoluble fraction and soluble organic fraction contained in particulate matter than mixing into diesel fuel.
Although polymer electrolyte fuel cells (PEFCs) have become commercially available, many problems remain to further improve the performance of PEFC and to popularize PEFCs. Water management in PEFC is closely related to cell performance. At high current density, generated water accumulates in gas diffusion layer and in gas channels of cathode, and the excessive water obstructs oxygen transport. The cell performance greatly decreases by blocking the oxygen transport. In order to improve the cell performance, it is necessary to remove effectively the generated water. In this study, to improve the water management in gas channels, novel gas channel with micro-grooves, which are manufactured inside gas channel walls, is adopted. The generated water from gas diffusion layer is removed through the micro-grooves to opposite-side of gas channel by the forces of capillary and shearing generated by air flow. The performance of the PEFC with and without micro-grooves was examined in various experimental conditions. Therefore, the cell performance was examined by changing the cell temperature, relative humidity of gas and air velocity. As the result, it was shown that the PEFC with micro-grooves showed higher performance than the conventional PEFC without grooves. Especially, the value of maximum current density was increased by about 23% when air velocity is 8.0m/s.