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. 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 is pulled, theoretical solution to the free vibration of the rope with vibration suppressors has been presented. However, when 1/N position of the rope is pulled, theoretical solution to the free vibration of the rope with vibration suppressors has not yet been obtained. In this paper, a theoretical solution to the free vibration of the rope with vibration suppressors is presented, when 1/N position of the rope is pulled. Finite difference analysis of the rope vibration with vibration suppressors are also performed. The effect of the number of vibration suppressors on the natural frequency and rope deflection are clarified. The calculated results of the finite difference analyses are in fairly good agreement with the calculated results of the theoretical solution.

View full abstract

This paper presents a multiple sensor system to predict behavior patterns that occur when patients leave their beds. We originally developed a vibration bolt sensor using a piezoelectric cable and a pillow sensor using an accelerometer. Existing sensors such as clip sensors and mat sensors require restraint of patients. Moreover, these sensors present privacy problems. The features of our sensors are that they require no power supply or patient restraint. We evaluated our system using a basic experiment to predict seven behavior patterns. We obtained a result of predicted behavior patterns related to bed-leaving using only two sensors installed on a bed. Especially, our system can correctly detect behavior patterns of lateral sitting, which is a position that occurs when a patient tries to leave from the bed, and terminal sitting, which is the position immediately before bed-leaving. They were discerned from other behavior patterns.

View full abstract

It’s generally known that tangential force of wheel/rail interface which depends on a change of coefficient of friction between wheel and rail has a big influence on a steady lateral force of railway vehicle. According to our past researches, regardless of an attack angle, tangential force coefficient becomes smaller in the case with fine unevenness than in the case without fine unevenness on the surface by means of a two-disk rolling contact machine. In particular, a tangential force coefficient is more affected by the situation of with /without fine unevenness under low relative humidity condition. The conditions under low relative humidity are almost the same as the conditions that a coefficient of friction of wheel/rail is high. In this paper, in order to reduce steady lateral force during a railway vehicle passing curve, we proposed a new wheel tread profile with providing one streak of fine unevenness, called ‘Micro-ribbed wheel tread profile’ on a wheel tread away from a flange. We verified a validity of this wheel tread profile by applying a numerical analysis and a running test in RTRI. As a result, we confirmed that the Micro-ribbed wheel tread profile is effective to reduce the steady lateral force of the outside wheel/rail interface when the railway vehicle is passing curve under high coefficient of friction between wheel and rail.

View full abstract

This paper describes a vibration reduction system that can minimize the vertical vibrations of the human body in a vehicle. This system can control the mechanical properties of the seat cushions and seat back cushions, such as the spring constants and damping coefficients. In previous study, it was estimated a vibration model considering vibrations transmitted from the bottom of the seat and the footrest, and vibration reduction effects of the human body was examined by using this model. However, vibrations of a driver are transmitted from a steering wheel too. Therefore, it is necessary to investigate vibration reduction effects by a model including the upper arm, lower arm and steering wheel. The purpose of this paper is to clarify the vibration reduction effects for the driver by controlling mechanical properties of the seat. In this study,we design a vibration model of an occupant–seat–steering wheel–pedals system and a numerical analysis system, and examine the feasibility of the vibration reduction system based on the vibration model of the occupant–seat–steering wheel–pedals system. Further, a numerical analysis with an optimized algorithm is carried out to calculate the magnitude of vibrations transmitted to the human body. The feasibilities of both the vibration model and numerical analysis system were confirmed by comparing the results between the numerical analysis and the measurement. The vibration reduction system successfully reduced vibrations from the seat to the human body by the analytical results using ISO7096-EM5 and ISO7096-EM6. In addition, the validity of the proposal vibration model of the occupant–seat–steering wheel–pedals system was indicated by comparing the analytical results between the proposal vibration model and the vibration model of occupant–seat system.

View full abstract

In this study, to separate contributions of road and wind noise to vehicle interior using only response point signals measured at the vehicle interior, we tried to use independent component analysis (ICA). To verify and consider applicability of ICA for the contribution separation method, road and wind noise sources were combined through a simulation and a simple experiment, and the contributions of these sound sources to the mixed response signals were calculated using a frequency domain ICA to these response signals. As a result, the contributions of road and wind noise sources were calculated accurately when the source signals were combined through the simulation with transfer time gaps and frequency characteristics, but the accuracy of the separation was low by the permutation problem, where the continuity of the contribution is not kept along frequency, when the signals were combined through the simple experiment. Then, we considered a permutation solution method using correlation between calculated contribution of the independent component and the size of them. By applying the method, the contribution of these noise sources could be calculated accurately in both conditions. Consequently, the road and wind noise contribution could be separated accurately using only combined signals through the proposed method using ICA with the permutation solution.

View full abstract

Sit-to-stand (STS) rehabilitation equipment traditionally simulates natural movements of unspecified healthy people. This type of movement may not place the lowest load on a patient's body. These factors let us develop a novel and widely applicable system for rehabilitation purposes that suggests a motion that places low body loads at the lower limb joints. This paper describes the core computation in the system that calculates a STS movement that places a minimum body load by using Continuous Genetic Algorithm (CGA). The minimization process starts from measurement of kinematic and kinetic data of a human subject by using gyroscopic sensors and reaction force plates, and then estimation and evaluation of the body load are followed. The body load which is minimized during STS movement was quantified by an index value. The index value strongly correlates with the chair height. Decreasing this index value by changing the movement during STS transfer could reduce the impact on the body, which is the same amount of load placed on the body while standing up from a higher chair height. The angular displacements of the averaged natural STS movement of the subject were considered as one of the several ways to stand up and the movements were assessed by means of the index value in CGA. A modified STS movement that can minimize the body load was computed after the optimization and it could be a personalized optimum movement allowing users to conduct rehabilitation with lesser unnecessary body load.

View full abstract

When agricultural machines are operated on pavements, the vibration and noise caused by the interaction between the tire lugs and the road surface are inevitable. In conventional studies, it is considered that the dynamic behavior of a rolling agricultural tire is influenced by the vibration characteristics of the tire. Resonance occurs when the lug excitation frequency of the tire becomes equal to the natural frequency of the tire. In other words, the rolling tire shows large vibrations in the direction of the natural mode corresponding to the natural frequency of the tire. However, in the conventional equipment, the diameter of the drum is smaller than that of the tire. Therefore, the real running condition on the road was not realized by the rolling test using the conventional equipment. In this study, a new equipment is produced and the dynamic and vibratory characteristics of operating agricultural machine are investigated. The obtained results are compared to the conventional ones and the influence of the running condition on dynamic characteristics of rolling tire is investigated. As a result, it is confirmed that the real running condition on the road can be realized in rolling test using the new equipment and the dynamic characteristics of the real running condition is obtained.

View full abstract

This paper deals with the active control of transmitted sound power from an acoustic enclosure in which noise sources are installed. With the aim of revealing an effective active control method of the enclosure, a simple model which is cuboid and composed of one elastic panel (upper surface) and five rigid walls is considered by theoretical simulations and experiments. The authors have previously proposed the active control method of transmitted sound power through a panel based on feedforward control which four point force actuators are located on the nodal lines at the frequency which the modal coupling cancellation phenomenon occurs. In this study, this method is applied to the target elastic panel of the enclosure. The simulation results show that the transmitted sound power and the control effect greatly depend on the location of the noise source in the enclosure. In the case that the noise source is located at the asymmetric point with respect to the center of the panel, the control effect may decrease because of the influence of the even-ordered structural modes, which can be excited by the odd-ordered acoustic modes. In order to improve the control effect, the method using both the feedforward control and the direct velocity feedback control is proposed. Finally, experiments were carried out to demonstrate the validity and feasibility of the proposed method.

View full abstract

As the herringbone-grooved journal gas bearing can rotate silently at high speed with low friction, and moreover it can be small-sized, it is used a lot in the fields such as information appliances. In this paper, the equation of motion of the herringbone-grooved journal gas bearing is derived using the gas force which can be obtained by applying the Navier-Stokes equation for the grooved and the ridged parts of a journal. The stability analysis can be performed when a journal rotates with a high speed by using the stability analysis method of Routh-Hurwitz, the root locus of complex eigenvalue analysis, and the time history analysis due to transient response vibration. Comparing with the already published analytical results, the physical meanings which have not been clarified in the conventional study are reported as for the stability of herringbone-grooved journal gas bearing. The stability chart is shown to be determined by considering the forward whirl and the backward whirl. In addition, it is reported that the present analysis results show a good agreement with the already reported experimental results. Furthermore, the parameters study as for the specification of gas bearing is performed, and it is shown that the stability chart changes due to the influence of specifications complicatedly.

View full abstract

A vane used in a low pressure end of steam turbine is usually fixed to a shroud and a casing by welding both ends. In such a vane structure, the damping in loading operation is comprised of the material damping and the aerodynamic damping, because the structural damping is very small. Recently, in order to increase the reliability of a steam turbine vane, a hollow vane with a friction damper has been used. In this paper, for the purpose of clarifying the damping characteristics of the hollow vane with a friction damper, first, the excitation test of the model vane is carried out. Second, the analysis method for predicting the damping characteristics of the hollow vane with a friction damper is proposed. The validity of the analysis method is verified by comparing the measured damping characteristics of the vane with the calculated ones. Finally, the analysis of the actual steam turbine hollow vane with a friction damper is also carried out. From these results, the damping characteristics of the hollow vane with a friction damper are clarified.

View full abstract

This paper proposes SSM (Sensor Steering Mechanism) for a lateral guided vehicle with an articulated body. Authors demonstrated the simple lateral guiding method SSM for the front wheel steer type, the reverse phase four-wheel steer type and the rear wheel steer type vehicle. SSM presents the stable lateral guiding performance for automated vehicle which follows a straight and curved path created by guideway. This paper proposes a simplified SSM to remove the following servo system for the camera rotation. The simplified SSM is applied to 1/25 scaled articulated dump truck which is developed by the previous paper. The stability of the simplified SSM is discussed. Experimental and simulation results show the stable moving and the performance of proposed method.

View full abstract

Recently, DS (Directionally Solidified) and SC (Single Crystal) alloys have been widely applied for gas turbine blades instead of CC (Conventionally Casting) alloys. The SC blade consists of one columnar grain, and the DS blade consists of several columnar grains of SC, where the growing direction of the columnar crystal is set to the direction of the centrifugal force. The frequency deviation of the DS blade caused by the deviation of the material property seems to become larger than that of the CC blade, because of the number of the independent elastic constants more than the CC blade, the deviation of the elastic constants due to the deviation of the crystal growing direction, and so on. Therefore, the mistuning characteristics of the bladed disk consisting of the DS blades seem to be different from that of the CC blade. In this study, the mistuning analysis of the bladed disk consisting of the DS blades are carried out, considering the deviations of the elastic constants and the crystal angle of the DS blade. The FMM is used to analyze the mistuned bladed disk. The maximum amplitude of the mistuned bladed disk of the DS blade is estimated by the Monte Carlo simulation combining with the response surface method, and the calculated results are compared with those of the CC blades.

View full abstract

Using multiple linear regression analysis, we defined equations to describe basic psycho-acoustic quantities, such as sharpness, tonality, roughness and fluctuation strength, to estimate how people react to various types of auditory signals. The HEV/EV auditory signal is a very important audio-guidance for pedestrians. It must be recognizable in a city crowd, as well as within a comfortable hearing range. In common practice, sensory evaluation tests are used to estimate the human auditory experience, but these tests are expensive due to the large size of the required test pool. Through investigating the correlation between sensory evaluation test results and basic psycho-acoustic quantities for 22 signals, we developed equations that predict the results of sensory evaluation tests inexpensively. Our method has been confirmed through the agreement between results obtained from our equations and that of sensory evaluations. We showed that the tendency of actual sensory evaluation could be predicted by the prediction relation of sensory evaluation using the metrics of sharpness, tonality, roughness, and fluctuation strength. With the increase in the number of samples, the dispersion in the prediction range spread. Therefore, it seems that the related item which is not taken into the present consideration needs to be added for improvement in the further predictive accuracy.

View full abstract

This paper proposes a coaxial trirotor helicopter constructed with coaxial mechanism driven by one motor. There two types of trirotor unmanned aerial vehicles (UAVs) are existed. One is the single trirotor which has three motors for rotors and one servo motor for tilt angle. The other is the coaxial trirotor which has two rotors on each axis and six motors requires in total. In order to reduce the number of motor this paper discuses a coaxial mechanism which is driven by one motor. This mechanism is possible to suppress the reaction torques of each rotor. But, the counter torque of motor rotor in the direction to the rotor axis is remaining. For the control of yaw rotational angle and suppressing the reaming torque, one of the three axes has a servo motor for tilt angle rotation, as well as single trirotor type. In order to estimate the 3D orientation of trirotor, the integration of gyro sensors is mixed with inclinometers or magnetic campus to suppress the drifting by noise and vibration which is coming from the mechanical system. This paper is developed a trirotor type UAV with three motors and a servo motor. Experimental results show the advantage of proposed mechanism and control system.

View full abstract

To reduce the collision shock and injury risk to a baby in an in-car crib during a car crash, it is necessary to keep the force acting on the bed constant and below a certain allowable value. Toward this end, a semi-active in-car crib with joint application of regular and inverted pendulum mechanisms is proposed. This system not only reduces the impulsive force but also transfers the force to the baby's back via a spin control system, i.e., the force acts perpendicularly on the bed. The spin control system has previously been developed. In this study, an acceleration control system is developed. At first, three type of in-car crib system is introduced and compared. Next, the in-car crib with joint application of regular and inverted pendulum mechanism is described. It is supported like a pendulum by arms, and the pendulum system is supported like an inverted pendulum by arms. And, the control system, which keeps the acceleration of the bed constant and below a set value, is proposed. The acceleration on the bed is controlled by adjusting moments of the revolution joint between the base and the arm and the revolution joint between the arms. Then, its effectiveness is confirmed via numerical simulations. The proposed system gradually increases the acceleration affecting the bed and keeps it at about the set value of -25 G, when the vehicle decelerates at -30 G.

View full abstract

Floating roofs are used on large cylindrical storage tanks to prevent evaporation of oil. The single-deck floating roof considered herein consists of a thin circular plate, referred to as a "deck", attached to a buoyant ring with a hollow rectangular cross section referred to as a "pontoon". The deck plate is deformed to be created waves and is subjected to cyclic bending due to the wind load. Since this leads to the initiation of fatigue cracks at the welded joints, it is important to understand the wave characteristics in the deck plate. The authors have previously reported a computational fluid dynamics (CFD) analysis of a cylindrical storage tank under a wind load. The present paper describes an axisymmetric finite element analysis of the sloshing response of a single-deck floating roof on a cylindrical storage tank using the previous CFD results as the load conditions. It is assumed that the liquid is incompressible and inviscid, the roof exhibits linear elastic behavior, and the sidewalls and bottom of the tank are rigid. The effect of the wind velocity on the frequency and amplitude of vibrations in the deck plate is investigated. As a result, the relation between the amplitude of vibration and the wind velocity is shown. The predominant period of bending stress vibration of the deck plate is shorter than that of the waves.

View full abstract

Mechanical joints such as bolted and spot welded joints are widely used to join plate structures. The existence of contact interface in the joint increases the vibration damping in the structure because the energy dissipation due to friction occurs at the interface. In this paper, we propose a procedure for calculating the energy dissipation at the interface using finite element analysis to estimate the damping for the fundamental and the higher modes. We use the static contact analysis instead of the dynamic contact analysis to reduce computational effort and use the mode shapes of linear FE model of the joined plate structure as the forced displacement in the static contact analysis. This enables us to obtain the energy dissipation depending on the mode shape for each mode. To improve the calculation accuracy of the energy dissipation, we apply a surface load on the overlap (interface) region and find the necessary value of surface load. To validate the proposed procedure, the modal damping ratios estimated from the dissipated energy are compared with the measured damping ratios. The results show that the proposed procedure enables to accurately estimate the energy dissipation of the joined plate structure. The necessary surface load increases with increasing mode number and varies almost proportionally with the square of the angular frequency.

View full abstract

This paper proposes a brush-cutting robot which can cut high weeds and grass automatically by hand-held brush-cutter sold in hardware store. The robot vehicle is constructed with a center articulated body, a manipulating mechanism of the brush-cutter, motor controller and sensors for self-localization. In order to get its own position continuously, two Laser Range Finders (LRF), a GPS campus and odometry encoder for each wheel are installed. Authors proposed Sensor Steering Mechanism (SSM) for the lateral guided vehicle with steering mechanism. This robot is applied SSM for the center articulated body to follow the way point line on the 2-D map. The map for self-localization is constructed with a 0.1m by 0.1m grid that is measured by the 3-D LRF. The experimental set up was developed and installed in the control program and then autonomous mowing was tested, leading to the results of running and mowing in the quadrangle of the No. 4 building of science and engineering at National Defense Academy. As a result, the proposed system achieved an error of 0.2m or less for the way point line following performance. The developed brush-cutting robot successfully completed the work without untreated area by providing an appropriate overlap by the result.

View full abstract

This paper describes an experimental study on the characteristics of blade-shaft coupled bending vibration of a rotor system with a bladed disk. In a rotor with relatively long blades such as low-pressure steam turbines, the coupled vibration of shaft torsional and blade bending vibration with nodal diameter of zero (umbrella mode) must be considered in terms of reliability. The bending-torsion coupled resonance of rotor systems occurs under specific conditions, when the rotational speed is equal to the sum and/or difference of the bending natural frequency and torsional natural frequency. In this study, a test apparatus with a flexible rotor equipped with a bladed disk which simulates actual turbine blade structure was developed to study the coupled vibration characteristics of shaft bending and blade (κ=0). The rotor was excited with an active magnetic bearing for lateral direction and a servomotor for torsional direction. Resonance of a bladed disk with nodal diameter (κ) of zero, which was coupled with the rotor’s torsional vibration, occurred under the above specific condition with lateral excitation force where frequency was equal to the rotor’s bending natural frequency. In addition, resonance of rotor bending vibration was found when the rotor was excited in torsional direction of its natural frequency.

View full abstract

This paper proposes a damage localization method for a beam structure, which can discriminate a specific part of the structure involving contact-type damages such as cracks, delamination and loose bolt failures. When the structure is subjected to a low-frequency excitation, the scatter characteristics of high-frequency waves in the vicinity of the damage location may fluctuate in synchronization with the low-frequency vibration due to the contact acoustic nonlinearity. Thus, a high-frequency sinusoidal probe wave going through the damaged part undergo amplitude and phase modulation, and as a consequence, sideband-frequency waves emerge accompanied with the the probe wave. In this paper, it is derived that the damaged structural part can be discriminated by measuring in-coming and out-going wave components separately by a sensor array and evaluating the amplitude ratio between those components at the sideband frequency. Experiments using a beam specimen with a simulated damage is conducted to examine the validity of the proposed method.

View full abstract

Initiation and growth behaviors of a transverse crack occurred in interlaminar toughened CFRP cross-ply laminates under cyclic loading were evaluated. Specimens whose stacking sequence is [0/90₄]_S and [0/90₆]_S were formed with T800S/3900-2B prepreg. The specimen edges were observed with an optical microscope and a laser microscope to investigate the behavior of transverse crack initiation and growth. To observe the edge surface of the specimen at arbitrary loading cycles, a replica technique was used. In addition, soft X-ray photography was used to observe internal damage. The number of cycles to transverse crack initiation was predicted quantitatively by applying the normalized modified Paris law, which shows the relationship between transverse crack density growth rate and normalized energy release rate range associated with transverse crack formation. Analytical results showed good agreement with experimental results. It was found that transverse crack initiation in interlaminar toughened CFRP laminates can be evaluated by applying the normalized modified Paris law. Moreover, in comparison to the laminates with and without toughened layers, the fatigue life to transverse crack initiation was prolonged due to the toughened layers. From damage observation, it was cleared that a transverse crack path to the thickness direction of the laminate was prevented by polyamide particles in the toughened layers. Therefore, it was found that the toughened layers dispersed polyamide particles to prevent delamination are effective for obstructing initiation of a transverse crack under cyclic loading.

View full abstract

Ceramics are excellent in heat, abrasion and corrosion resistances, but their strength reliability for structural materials is not enough due to their brittle nature. On the other hand, ceramic matrix composites (CMCs) reinforced with ceramic fibers attract attention as a damage tolerating material, because toughness of CMCs is improved through various mechanisms such as fiber bridging, fiber breakage, pullout, interfacial debonding and crack deflection. Thus, clarification of the mechanical behavior of CMCs including such damages deepens its engineering significance. In this study, a new finite element (FE) model for the damage analysis of this material is proposed, in which the effect of Coulomb friction at the interface after fiber breaking or matrix cracking followed by the fiber/matrix debonding is taken into account. Although a limitation condition is incorporated into the model, the advantage of this model is that stress and strain distributions can be obtained by merely one calculation without iteration. The accuracy of this FE model was validated by comparing with the results of both the general-purpose FE analysis software and theoretical matrix crack model. In addition, we proposed a new interfacial contact state to apply this model to the hysteresis behavior of CMC under cyclic loading, and discussed its causes about changes in the hysteresis loop. Results of the present FE model showed that the fiber and matrix stress distributions behaved non-linearly in the interfacial debonding area, while these displayed a constant in the bonding area. This model also showed a good compatibility with the theoretical model and the general-purpose FE analysis. Thus, it is expected that this model can be applied for damage states such as matrix crack deflection, indeed difficult through the conventional theoretical models or general-purpose FE analysis. The present model also simulated well the shift and shape of the hysteresis loop with cyclic loading.

View full abstract

The aim of this study is to investigate the rheological behavior for a semi-solid forming of Al−25 mass % Si alloy, i.e., hypereutectic Al-Si alloy, using a self-made parallel-plate drop-forge viscometer. Drop-forge experiments show individually the features that the viscosity decreased in the early increasing shear rate stage and subsequently the viscosity turned to increase as the shear rate decreased. Thus, the viscosity takes a minimum around the maximum shear rate. The summarized behavior between the viscosity, μ[Pa･s], and the shear rate, γ [s^-1], can be described by a power-law model of μ＝1.78×10⁷γ^-1.5. The decrease in viscosity accompanied with the increase in the shear rate depends on both rises in the temperature and the applied force, not the duration of forging. The convex shape curve is observed between the effective duration and the viscosity and the effective duration reaches a maximum at around μ＝30 kPa･s where γ=70 s^-1. The origin of the profile is due to the lost of ability to transform the kinetic energy to distortion energy, which is caused by a decrease of deformation resistance accompanied with a decrease of viscosity. Then the viscosity μ＝30 kPa･s, which corresponds to the transition point from plastic forming to casting, seems to be the optimum condition for semi-solid forming.

View full abstract

The subloading surface model has been formulated and applied to the prediction of cyclic loading behavior of metals. However, the existing formulation of this model is limited to metals exhibiting only the cyclic hardening. In the present paper, the material functions prescribing the elastic-plastic transition are extended so as to describe the inverse and reloading behavior and the strain accumulation in cyclic loading more accurately for metals exhibiting not only the cyclic hardening but also the cyclic softening behavior. The experiments on the uniaxial cyclic loading of the seamless steel pipe P110 which exhibits the cyclic softening are performed for the mechanical ratcheting and the constant strain amplitudes. The simulations to the test data are performed by using the same set of material constants. Then, the validity of the extended model for the description of cyclic loading behavior of the seamless steel pipe is verified by comparisons with the test data.

View full abstract

The subloading surface model possesses the automatic controlling function to pull back the stress to the yield surface. However, this function is not concerned with the subyield state, i.e. the elastic to the plastic transitional state and thus the accurate solution cannot be obtained in the transitional state. Besides, the function is ineffective for large loading increments even in the yield state. In this article, the return-mapping in cutting-plane projection for the subloading surface model is formulated aiming at obtaining accurate solutions in a high efficiency in the whole loading state, i.e. the elastic-plastic transitional and the yield states. Then, the validity of the elastoplastic deformation analysis by the subloading surface analysis with the return-mapping and the consistent tangent modulus tensor is verified comparing with the analysis by the forward-Euler method.

View full abstract

In recent years, thermoplastic CFRP attracts considerable attention especially in aviation and automobile industries due to weldability of thermoplastic CFRP. Ultrasonic testing (UT) is commonly adopted as a testing method for inspecting weld parts although time cost on UT is thought to be problematic. Since eddy current testing (ET) is used for rapid inspection on electrically conductive materials, this paper presents an eddy current based approach for detecting defects in thermoplastic CFRP welded zones. However, it is difficult for conventional ET to detect delamination which is parallel to eddy current although delamination is one of the common forms of weld defect. To detect delamination in thermoplastic CFRP welded zones, new eddy current based approach which utilizes temperature characteristic of electrical conductivity is proposed. The proposal consists of two steps. Firstly, temperature difference between intact zones and defective zones is caused by heating the one side of the weld part. Secondly, the temperature difference is detected by ET utilizing temperature dependency of electrical conductivity.

View full abstract

The major aim of this paper is to derive simple closed-form solutions which can be easily calculated using spreadsheet software, for thin anisotropic cylinders under torsion, axial compression and combined loads that include the effect of layup anisotropy. Previously derived partial differential equations of equilibrium that are solved by including layup anisotropy but neglecting transverse shear deformation and closed-form solutions are obtained. One of the three solutions satisfies a simply supported condition, another a fully fixed condition, and both of these can be applied to cylinders that are shorter and longer than the length of the bending boundary layer. The third solution is called the bending boundary layer solution, and it can only be applied when the cylinder is longer than the length of the bending boundary layer. In addition, guidelines for dividing mesh in finite element analyses of anisotropic cylinders are discussed in terms of the precision of the bending stress on the edge. A comparison of the closed-form solution and the precise solution including both layup anisotropy and transverse shear deformation shows that differences appear only on the bending-boundary layer, the differences increase with the radius to thickness ratio decreases, and the closed-form solution gives a safe-side estimate for design purposes.

View full abstract

When a porous solid is subjected to both gas infiltration and heat transfer, thermal stresses are generated in such a solid. In the previous reports, fundamental theory for a porous solid under such a complex situation was developed, and then a thermal stress problem for a porous solid with a flat boundary surface subjected to a concentrated loading was solved completely. In this study, thermal stress problem for a porous infinite solid subjected to a point loading is investigated. A method of solution based upon displacement potential and Fourier integral transform techniques is applied to solve the problem as well as the way used in the previous report. Complete closed form of gas pressure, solid temperature, displacement and thermal stress field in the infinite porous media are presented. It was found that the asymptotic behavior around a point load is strongly affected by gas permeability and pressure of gas phase.

View full abstract

In this study, fatigue strength properties of interlaminar toughened CFRP laminates in the out-of-plane direction, or through thickness, were investigated. Thick laminates whose stacking sequence was unidirectional were formed with 88 plies of T800S/3900-2B prepreg. The T800S/3900-2B prepreg is constituted of fiber layer and interlaminar toughened layer in which polyamide particles are dispersed. The material properties of the thick laminates were measured by compression test and 4-points shear test. Spool specimens machined from the thick laminates were loaded in the out-of-plane direction. Stress distributions of spool specimens were evaluated by FE analysis. Fiber layer and interlaminar toughened layer in the each ply were modeled separately in the analysis. In comparison to the out-of-plane direction, the properties of in-plane transverse direction were investigated with 90° thin laminates. To evaluate the fatigue strength properties quantitatively, an analytical equation was introduced for the results of fatigue test. The fracture surfaces of the specimens after static and fatigue tests were observed by SEM. From the observation of the fracture surfaces after fatigue test, it was found that the interfacial debonding between fiber and matrix was occurred due to cyclic loading in both of specimens. In addition, it was observed that crack generated from debonding grew in the fiber layer until ultimate fracture. Moreover, the experimental and analytical results showed that, in comparison to the in-plane transverse direction, the fatigue life in the out-of-plane direction is shorter.

View full abstract

In this study, we have developed a propulsion mechanism using a fin with variable effective length spring as variable stiffness mechanics. We measured its thrust and the lateral forces in water tank with three dimensional flow and that with quasi two dimensional environment. Additionally, three dimensional numerical analysis of the propulsion mechanism was performed. Flow field around the fin and variations of thrust and lateral forces obtained in this numerical analysis were compared with the above experimental results in the condition of rigid fin. As a result, there was a quantitative agreement between the experiments and numerical analyses. Because the computational costs of three-dimensional fluid-structure interaction analyses are very expensive, two dimensional fluid-structure interaction analyses were performed in the conditions of elastic fins. Qualitative agreement was observed between the fluid-structure interaction analyses and the above experimental results of quasi-two dimensional environment. In these conditions, an evaluated value of thrust efficiency increased with the decrease of the stiffness of the fin. The flow fields around the elastic fins were visualized to discuss the flow dynamics around the fin. From this result, it was shown that the direction of jet flow generated by vortex pair at the fin edge was closed to the rear direction of the propulsion mechanism by decreasing the stiffness of the fin.

View full abstract

An experimental study is performed for dividing turbulent channel flow in 90 degree T-junction with sharp, inclined and rounded corners. Experiment is conducted for flow rate ratios of 0.2, 0.4, 0.6 and 0.8 (ratio between the flow rates in the branch and main channels) keeping the Reynolds number of the main flow at 4.0×10⁴. The width of the main channel H₁ is maintained at 30mm, and the width of the branch channel H₂ is changed into 15mm, 30mm and 45mm. The loss coefficient and wall static pressure coefficient are measured to quantify the energy loss. The local heat transfer coefficient is measured at the branch channel. To investigate the relationship between fluid flow and heat transfer, the velocity profiles are measured by a PIV system. Rounding the corner reduces the pressure loss in the branching flow. As the ratio of the width of branch channel to the width of main channel becomes small, the reduction rate of pressure loss in the branch flow increases. Whereas the pressure loss in the main channel basically remains unaffected. Except the low flow rate ratio, the heat transfer coefficient in the branch channel decreases at the rounded corner as compared with the sharp corner. Decrease of the heat transfer coefficient is related to the reduction of the recirculation region which occurs at the upstream wall of the branch channel.

View full abstract

This paper deals with the wake flow behind a vertical axis wind turbine, focusing on the variation in the wake structure relative to the tip-speed ratio λ. The wind turbine model was placed in the test section, 2m wide, 2m height and 5.3m long, of the low-speed wind tunnel. Measurements were made of the U and V components of the instantaneous velocity in the wake of the model for various tip-speed ratio λ of the wind turbine using an X type hot-wire. The instantaneous data obtained were used to determine time mean and phase-locked mean velocities and turbulence intensities. The momentum loss and fluctuation energy in the wake were also estimated as characteristic quantities. The results obtained showed that in a low tip-speed ratio range of λ/λ_opt<0.67 (λ_opt was an optimum tip-speed ratio to extract maximum power from the wind), the periodic fluctuation energy (PE) accounted for 40% of the total fluctuation energy (TE) because periodic and low-frequency velocity fluctuations were generated by the large-scale vortices induced by the dynamic stall of the turbine blades. The fluctuations decayed quickly and PE also became zero where λ/λ_opt exceeded approximately 0.7. In high tip-speed ratio λ/λ_opt>1.07, TE was equal to turbulent energy because high-frequency velocity fluctuations were generated by the instabilities of the separated shear-layer from the blades. The results showed that a medium tip-speed ratio range of 0.67<λ/λ_opt<1.07 was optimum for not only minimum momentum loss and fluctuation energy but also maximum wind turbine power.

View full abstract

On the opening delay of a discharge reed valve for compressors caused by the oil film in the clearance between the reed and the valve seat, effects of design conditions on the opening delay are analyzed through the experiment and the numerical simulation. Investigated are three kinds of conditions, the time rate of the bore pressure (compression speed), the oil viscosity, and the thickness of the reed. The experiment shows that the over-compression by the delay increases with increasing each of three condition values. The simulation reproduces qualitatively the effect of the bore pressure rate on the delay. The smaller bore pressure rate makes, under a certain bore pressure, the larger film thickness or the larger cavitation bubble diameter that results in the oil film rupture and the valve opening under the smaller bore pressure. The simulation also reproduces qualitatively the effect of the reed thickness. The larger reed thickness with the larger bending rigidity leads to the smaller reed deformation, the smaller oil film thickness, and the longer delay. On the oil film viscosity, the simulation fails in reproducing the change in the delay. The fail is due to the change in the oil film thickness of the simulation being smaller than that of the experiment. The experiment and simulation results indicate that, on all three conditions, the change in the increase of the oil film thickness leads to the change in the valve opening time and thereby the over-compression.

View full abstract

For the purpose of preparing for the further diffusion of wind power technology, the power reduction risk of wind power plants, i.e. a risk of frequent and large reduction in the output caused by time-varying wind speeds, needs to be decreased. Among measures against the risk, the geographical distribution of wind power plants needs to be examined first because additional facilities, such as backup power plants or electricity storages, are not required. This study quantitatively analyzes the risk reduction effect of geographically distributing wind power plants among 12 locations within the Hokkaido. The mean-CVaR (Conditional Value at Risk) model is adopted to estimate the optimum geographical distribution. We found that the share of time period with no power output can be reduced to mostly 0% by optimizing the geographical distribution while the share is more than 10% if all the wind power plants are intensively installed to the location with the highest average output. Another finding is that the geographical distribution can contribute to the risk reduction even among the locations in the Hokkaido that is a relatively smaller region compared with the regions surveyed by earlier studies. We also found that the CVaR is the better index of the power reduction risk of wind power plants than the standard deviation as far as focusing on the power reduction risk.

View full abstract

In the second report, a method for measuring the spatial distribution of the electric current generated in a PEFC from the frequency shift of the Nuclear Magnetic Resonance (NMR) signal of water acquired by eight planar surface coils inserted into the PEFC was described. In this paper, a newly-developed technique to calculate the current density distribution from the measured frequency shifts using inversion analysis is presented. In this technique, the PEFC is divided into eight elements, and the current which flows through the eight elements is searched so that the frequency shift calculated by magnetic field analysis and the frequency shift obtained by experiment come into agreement. In order to shorten the computation time consumed in this technique, an efficient algorithm was developed in which the current is searched by an iterative calculation using the equation between that relates the current and the spatial gradient of the frequency shift. The spatial distribution of the current density could be obtained using eight iterations of the inversion analysis algorithm.

View full abstract

The VCO (Valve Covered Orifice) nozzle is known to reduce unburned hydrocarbon emission from direct-injection diesel engine. However, high-pressure fuel injection causes needle eccentricity which results in non-uniformity of sprays and deterioration of emission characteristics. Present study numerically investigates the needle eccentricity effects on the internal flow of the large-scaled VCO nozzle by using STAR-CCM+ (ver. 8.02.011), and obtained results are compared with those of a corresponding experiment. Swirling flow is formed in the nozzle hole due to the needle eccentricity. As increasing the swirl strength, air entrainment from the nozzle hole outlet is generated, and spray cone angle is decreased. However, in the range of large needle eccentricity, growth of the swirling flow decays, and the spray cone angle is saturated at certain value. These tendencies are also observed in the experiment. Thus, it is confirmed that the present numerical simulation reproduce the actual phenomena qualitatively. Furthermore, effects of edge curvature of the nozzle hole inlet is also numerically investigated as a key factor acting on the internal flow characteristics. As the edge curvature increases, the swirling flow in the nozzle hole considerably grows, and the air entrainment into the nozzle hole is greatly enlarged. Also, spray characteristics is extremely changed.

View full abstract

Themocapillarity is of fundamental importance in material processing. The floating-zone method is a material processing for producing and purifying single crystals of metals and oxides. It is widely known that, using this method, a transition to three-dimensional oscillatory thermocapillary convection takes place in the melt. The oscillatory convection causes detrimental striations in the crystal structure. In this study, flow transition points (critical Marangoni numbers) and flow structures were investigated in a thermocapillary convection in a model of floating-zone method (full-zone liquid bridge) of the high Prandtl number fluid (Pr =28.1) under the normal gravity condition. In the liquid bridge, the convection changes from two-dimensional steady flow to three-dimensional oscillatory one at a flow transition point. The convection was visualized by tracer particles in order to find the flow transition point and the shape of the modal structures in the oscillatory flow. The dominant modal structures near the flow transition point were estimated using the shape of the particle free zone on a horizontal plane of the liquid bridge and superposition of several waves with azimuthal wave numbers by the method of the least squares. In the present study, the critical Marangoni number of the full-zone liquid bridge was almost one-half of that of the half-zone liquid bridge in aspect ratio 0.45 to 1.3 (aspect ratio: half-height of liquid bridge over radius of rods). The dominant modal structures were combination of azimuthal wave numbers with 1, 2, and 3 in a range of the aspect ratio concerned. It was found that the azimuthal wave numbers of the dominant modal structures did not depend on the aspect ratio. The dominant modal structures were a standing or a travelling wave, and changed from one to another irregularly. Trade-off of a power and a phase locking between each modal structure were observed.

View full abstract

A novel liquid-piston steam engine which can achieve high efficiency at low temperature region of T < 300 °C as well as high reliability and low cost is developed. In this study unsteady- local inner wall temperature is measured to clarify the phase change phenomena in the heating section of the liquid piston steam engine to improve the accuracy of the design method. Thin Platinum film temperature sensor with 1 kHz response has been deposited by sputtering on the heating surface of the hollow plane type liquid piston steam engine. Nucleate boiling begins when the liquid piston enters the heating section, and it terminates when the vapor pressure approaches saturation pressure. The evaporation of the liquid film continues after the liquid piston leaves out from the heating section. Vaporization model using both the mechanism of liquid film evaporation and nucleate boiling is valid. On the other hand, fluctuations of pressure and heat flux are observed in the experiment when liquid piston enters the heating section. In order to predict these fluctuations, it is necessary to consider the effect of steam bubbles mixed inside the liquid piston.

View full abstract

In the previous studies, it was confirmed that there is a microlayer that forms between a growing bubble and the heat transfer surface in nucleate pooling boiling. The initial microlayer thickness was found to increase linearly with distance from the bubble inception site. Although a large amount of heat transport results from the evaporation of microlayer during the growth process of bubble, the quantitative degree of contribution of microlayer evaporation was not elucidated. In this study, numerical simulation was carried out on the two phase vapor-liquid flow induced by the growth of a single bubble in nucleate boiling by using the VOF (Volume of Fluid) method. The objective of this study is to clarify the heat transfer characteristics, especially the effect of evaporation of microlayer in nucleate pool boiling. A special model for simulating the microlayer evaporation was proposed, in which the microlayer was not considered in the calculation of flow field while its amount of evaporation was considered by applying the source term of the basic equations as an existence of virtual microlayer. Similar tendencies were shown between the calculation and experimental results on the variations of microlayer radius and bubble volume. The proportion of the amount of evaporation from microlayer to the volume of bubble is generally agreed with the previous results, which showed the ratio of microlayer evaporation to the total vapor volume change was approximately 40 percent.

View full abstract

The present study investigates the effect of multiple dynamic absorbers on both forced chatter and regenerative chatter. The stability lobe of regenerative chatter is widely employed to find the axial depth of cut and the spindle speed in which regenerative chatter doesn't occur. However, the cutting force variation by the intermittent cutting with an end milling tool causes the forced chatter. The excitation frequency is determined by the spindle rotation frequency and the number of teeth. When the integral multiple of the excitation frequency approaches to the natural frequency of the tool and spindle system, resonance can be caused by the forced chatter. It is known that the resonance occurs in the spindle speed resistant to regenerative chatter. Therefore, it is important to take a countermeasure against not just the regenerative chatter but also the resonance caused by the forced chatter. In the present study, the cutting conditions which can lead to the regenerative chatter and the resonance are investigated by the direct numerical integration method. It is shown that an improvement in the regenerative chatter-free axial depth of cut can be obtained using the absorbers. Furthermore it is made clear that the absorbers have a significant suppression effect on not only the regenerative chatter but also the forced chatter.

View full abstract

Neuro-musculo-skeletal model has been developed that is capable of generating reasonable gait. However, the details of the ground reaction force waveform differ from real gait motion quantitatively. A whole-body walking model including the detailed foot model has not been proposed and a unified objective function has not been proposed. Therefore, the purposes of this study are to improve a forward dynamic walking simulation by developing a precise foot model and making a hybrid criterion for the generation of human gait motion by using the application and utilization of genetic algorithm for the optimized calculation. The dynamics of the human body has been represented by 22 three-dimensional rigid links with 78 muscles and 62 neural oscillators. Unknown neuronal parameters have been adjusted by a numerical search method using the evaluative criterion for locomotion that is defined by the locomotive energy efficiency, the toe clearance and the magnitude of the ground reaction force. As a result of adjustment of the neuronal parameters, walking 10 steps has been generated. The simulated walking pattern has closely agreed with actual human walking not only of joint movement but also of the mutual conversion of the mechanical energy and the magnitude of the ground reaction force.

View full abstract

An envelope distribution approach is developed for generation of narrowband non-Gaussian processes. The processes are prescribed by the probability density and the power spectrum. The proposed approach is based on the method of stochastic differential equation, in which the drift and diffusion coefficients are adjusted to match the given probability distribution and power spectral density. In order to construct the stochastic differential equation, a joint probability distribution which satisfies some conditions is needed. The probability distribution can be obtained from the envelope distribution corresponding to the target non-Gaussian distribution. The proposed approach is applicable to generation of narrowband processes with a variety of non-Gaussian probability densities. Examples are presented to illustrate the usefulness of the approach.

View full abstract

In this paper, we discuss integrated vehicle velocity and slip ratio tracking control under both deceleration and acceleration without the need for controller switching, and also propose a design method for such an integrated slip ratio controller based on the slip ratio dynamics. When a vehicle switches from acceleration to deceleration and vice versa, the slip ratio varies discontinuously. Here, the slip ratio is approximated to a continuous function by using a sigmoid function. And a controller is then designed by using feedback linearization, a disturbance observer, and sliding mode control theory based on the approximated slip ratio. The stability of the designed control system is proven by Lyapunov stability theorem. Finally, the effectiveness of the proposed control method is verified through numerical simulation.

View full abstract

A rotating shaft supported by a repulsive magnetic bearing may contact with a backup bearing during the passage of the critical speed, as a damping coefficient of the repulsive magnetic bearing is small. Various contacting vibrations between the shaft and the backup bearing due to the rotation of the inner ring of the backup bearing were observed in the experiment. In this paper, a theoretical model of a rotating shaft system is developed considering the freedom of rotation of the inner ring of the backup bearing. The characteristics of these contacting vibrations are clarified. This rotor model considers both slipping and rolling conditions in the contact at the backup bearing, and evaluates the transition phenomenon between them. The followings are clarified. The slipping forward whirling motion occurs when the friction coefficient is small. The rolling whirling motion occurs when the friction coefficient is large. In this case, the forward rolling motion occurs if the damping of the inner ring rotation is small, on the other hand, the backward rolling motion occurs with high whirling speed if the damping of the inner ring rotation is large. Then, the characteristics of the escapement from these contacting vibrations are also clarified and explained. Both the forward and backward rolling motions keep occurring even if the rotational speed increases to the range much larger than the critical speed. Furthermore, only the backward rolling motion keep occurring even if the rotational speed decreases to the range much smaller than the critical speed. These results were observed and confirmed experimentally. As a result, it is clarified that the friction in the contact should be low in order to escape from contacting situation rapidly and naturally after passing the critical speed.

View full abstract

It is important to detect abnormalities at an early stage to efficiently maintain industrial machines. Acoustic sensors, i.e., microphones, have an advantage in that they do not need to be in direct contact with the point of diagnostic. For using acoustic sensors, however, we must choose the best acoustic feature extraction method. The power spectrum method is often used for predictive diagnosis. Though, the differences between normal and abnormal power spectrum is small. Therefore, we focused on pitch changes to distinguish failure signals by calculating the inter frame peak frequency fluctuation with relative standard deviation (RSD). We evaluated its fluctuation by simulating motor failure, and found that the differential fundamental peak-frequency’s RSD is more than 10%. We confirmed the value that was not be detected during normal operation mode. And then, we concluded that using fluctuation in peak-frequency is suitable for early abnormal detection.

View full abstract

Concept of the system design is very important in industrial world. In contrast, lecture programs or practices for the system design are not sufficiently much provided in universities. In the present paper, an educational program for the system design using a torsional vibration experimental system is proposed. The program requires to students integration of control theory, material mechanics, and mechanical dynamics which are lectured in individual situations. And the students learn the general outline of the system design in the program. The program is effective for education of the system design which is a blind side of the educational program in universities.

View full abstract

Point contact theory between two bodies with constant curvature was built by H. Hertz. His theory is now widely known as "Hertzian contact theory" and it is widely applied to the calculation of the stiffness of ball bearings and CVJs. Calculation of the theory, however, has some difficulties: numerical calculation of the complete elliptic integrals and convergence calculation for ellipticity parameter are required. Some fitting equations have been already suggested to resolve the difficulties. They are convenient for hand calculation, but they are too rough to calculate with the latest high-spec computers. So more accurate algorithm for Hertzian contact theory is required. In this paper, rapid-convergence iterative method is suggested for computing the theoretical solution of Hertzian contact theory. The method can be programmed simply and converge rapidly because the method is based on "self-convergence algorithm" which is also suggested in this paper. As 10-digit accurate values can be get by 3 iterations, the method is fast enough to apply to dynamic simulations, in which point contact has to be evaluated very frequently.

View full abstract

This study is concerned with aerodynamic effects in passive pitching dynamics of insect flapping wings, which would be based on the Fluid-Structure Interaction (FSI). Thus, we evaluated them using three-dimensional numerical analyses for the FSI based on the finite element method. In the numerical analyses, the FSI in insect flapping wing is broken down into its constituent components in order to find the aerodynamic effects in the passive pitching dynamics as follows: (a) The dipteran passive pitching dynamics is based on the interaction between the wing's elastic and aerodynamic forces, while it is enhanced by the wing's inertial effect. (b) The air damping leads the mode of wing's natural vibration from underdamping to overdamping so as to form the characteristic pitching motion, where the damped natural vibration of the wing appears so as to enhance the wing rotation.

View full abstract

Planning human resource procurement, as well as planning cost, quality and capacity of production, is one of the crucial issues for enterprises in order to achieve the target sales and profit. For the planning, two issues should be addressed. First is how to transfer the necessary skills and knowledge, which is in the educational perspective and many studies and methodologies have been achieved in respect to the issue. Second is how to change the production processes where the human resources are allocated considering the effect of the design on the production capacity, cost and quality of the target processes along the human resource procurement schedule, which is in the management perspective. This paper focuses on the second issue. For instance, procuring and training many resources can minimized the human resource procurement schedule. It, however, might increase the quality and cost risks of the target production processes. Contrarily, gradually procuring and training human resources might reduces the quality and cost risks. It, however, increases the procurement schedule and risks of the opportunity loss. The strategies for procuring the necessary human resources are varied by the requirements to the management based on the enterprise strategy and surrounding market demands. In this paper, we applied the simulation based process evaluation methodology for quantitatively choosing the human resource procurement strategy appropriate to the management requirements. Firstly, we predicted the process performances in respect to the available human resources with our developing simulation tool. Secondary, we estimated the changes of process performances along the various human procurement strategies. Finally, we demonstrated how to choose a human resource procurement strategy appropriate to the management requirements.

View full abstract