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 are 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 arbitrary position of the rope is pulled, exact solution to the free vibration of the rope with vibration suppressor, which located at the center of the rope and the gap between rope and vibration suppressor is 0, has been presented. However, in the case where the position of vibration suppressor is center of the rope and the gap between rope and vibration suppressor is not 0, no exact solution to the free vibration has yet been obtained. In this paper, an exact solution to the free vibration of this case is presented. In the analysis, the rope is modeled with string. Finite difference analyses of the rope vibration with vibration suppressor are also performed to verify the validity of this exact solution. The calculated results of the finite difference analyses are in fairly good agreement with those of the exact solution.
A vane used in a low pressure end of steam turbine is usually fixed to an inner shroud and an outer ring 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. In such a steam turbine vane, the total damping may become negative, and the flutter may occur under the high loading condition. Therefore, in the design of the steam turbine vane, it becomes indispensable to evaluate the stability under the high loading condition. In this study, first, the vibration characteristics of steam turbine vane with grouped vane structure are examined in detail by use of the results of FE analysis. Second, the reduced order model (the equivalent spring-mass model) of the whole vane structure is assembled, based on the results of FE analysis. The stability analysis of the whole vane structure is carried out using the reduced order model, and the effect of the design parameter of the vane on the flutter is clarified. Finally, the mistuning analysis of the whole vane structure is carried out, using the Monte Carlo simulation, and the effect of the frequency deviation on the stability is clarified.
Although bladed disks of turbomachinery are nominally designed to be cyclically symmetric (tuned system), the vibration characteristics of all blades on a disk are slightly different due to the manufacturing tolerance, the deviation of the material property, the wear during operation, and so on. These small variations break the cyclic symmetry, and split the eigenvalue pares. The actual bladed disks with the small variations are referred to a mistuned system. In the forced response of a mistuned bladed disk, 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 eigenvalues, the distortion of the vibration modes, and so on. On the other hand, many researchers suggest that the mistuning suppresses the blade flutter, because the complete travelling wave mode is not formed in a disk. In other words, the main conclusions of researches on mistuning are that while mistuning has an undesirable effect on the forced response, it has a beneficial (stabilizing) effect on the blade flutter (the self-excited vibration). Although such mistuning phenomena of bladed disks have been studied extensively since 1980s, almost all studies focused on the mistuning effect of the displacement response, and few studies researched the mistuning effect of the vibratory stress response. In this study, the frequency response analysis of the mistuned simple bladed disk is carried out. Comparing the mistuning effect of the displacement response with that of the vibratory stress response, the mistuning effect evaluated by the vibratory stress is studied in detail.
This paper proposes an automatic tuning method for a motor speed control system. Parameters of a PI controller and a low-pass filter (LPF) for motor speed signal are automatically derived satisfying required specifications of a time constant of step response and a tolerable steady-state error of ramp response. In addition, cut-off frequency of the LPF is set as low as possible, which solves the problem of a tradeoff between response speed and noise reduction. The method helps people to tune a speed controller without trial and error and reduces man-hour for developments. In the derivation of the proposed method, the coefficient diagram method (CDM) is utilized. In this paper, the stability index, the equivalent time constant, and the representation of characteristic polynomial defined in the CDM are theoretically linked to the specifications of the step and ramp responses. This enables the proposed method to directly incorporate the required performance for tuning the PI controller and the LPF. Simulations results show that the proposed method derive a desirable controller which satisfies the specifications as theoretically expected. Effectiveness is also verified in experiments in the presence of sensor noise of a resolver and the controller achieves desired performance without trial and error tuning of the parameters.
Dynamic fluid forces acting on an impeller of a diffuser type mixed flow pump have been studied. The behavior of the thrust generated by the vortex occurrence in a pump intake sump was investigated. The force of distinct discontinuities such as hysteresis phenomenon from a pump hydraulic performance was measured. In pump partial load operation the radial thrust increases discontinuously because of the reverse flow at impeller inlet. The radial and axial thrust discontinuities occur at different threshold flow rates when increasing or decreasing the pump discharge flow thereby composing a hysteresis loop. Synchronous and non-synchronous components of radial thrust increase during the onset of reverse flow zones. A prediction method for dynamic radial thrust was derived based on Black's theory. Qualitative comparison with the measured experimental results for dynamic radial thrust showed reasonable agreement around pump best efficiency flow rate. The pump intake sump test apparatus, in which both an air-entrained surface vortex and a submerged vortex will occur, was employed and the radial thrust was measured. The level of radial thrust is dependent on the pump intake sump water level. The radial thrust begins to increase due to the occurrence of a full air core vortex to intake. When submerged as well as full air core continuous vortices occur, the radial thrust and the fluctuation of total pump head become abruptly large. The fluctuation of radial thrust becomes the highest when the impeller blade cutting the air-drawing large vortex imposes shock-like forces which generate not only an unbalance force but also nZ vane passing component.
An active magnetic bearing (AMB) is utilized widely in vacuum apparatuses such as a turbo molecular pump (TMP). The rotor supported by the AMB in the TMP is vibrated by the unbalance of the mass of the rotor, the electromagnetic force of the AMB and the location of the AMB. As the methods to suppress this vibration, phase-variable type Peak-of-Gain Control (JIS B 0913-1, Unbalance Force Counteracting Control: UFCC), phase-variable type Automatic Balancing System (JIS B 0913-1, Unbalance Force Rejection Control: UFRC) and Phase-Variable Control (PVC) have been reported. The UFCC (UFRC) suppresses the vibration by increasing (decreasing) the bearing stiffness and giving the damping effects at the rotational frequency. However, the relationship between the UFCC and the UFRC is not expressed. Accordingly, we investigate the UFCC (UFRC) is corresponded to the UFRC (UFCC) by using the phase changes. On the other hand, the repetitive control which is one of the periodic disturbance suppression methods also has been proposed. The control suppresses the unbalance vibration based on the internal model principle. For the unbalance vibration compensation, we clarify the UFCC is considered as repetitive control by using the pole assignment. Moreover, we show the unbalance vibration is further suppressed by using the UFCC which is corresponded to the rotational frequency and the second harmonic.
Outer tub of a front-loading washer-dryer supported by the vibration isolation structure is vibrated by imbalance of clothes inside the drum. In dehydration, it is required to reduce the vibration of the outer tub by the multiple countermeasures because drum rotational speed revs up and passes through the multiple resonances. In this study, a multi-objective optimum design approach was proposed to reduce vibration considering cloth mass, and also to reduce mass of the anti-vibration-weight bolted on the outer tub. This approach consists of three steps; the first part is to narrow the search range by an analysis of influence, the second is to obtain a response surface, and the third is to search for Pareto set by the response surface in detail. As a result, Pareto set, which consist of the location and mass of anti-vibration-weight to reduce vibration of two modes considering cloth, was obtained. This result would provide the validity of the proposed approach.
As vehicle engines become lighter, smaller, and more powerful, stress prediction of the main bearings has become an important aspect of strength design measures for the cylinder block. To predict the stress of the engine main bearings under actual working conditions, a flexible multibody dynamics (FMBD) solver was developed with a built-in elastohydrodynamic lubrication solver for the main bearings. The dynamic behavior of the engine system under actual working conditions was then calculated and the results were used to calculate the stress. To reduce the stress calculation cost, rather than inputting the actual working load into a finite element model (FEM) of the whole engine as a boundary condition, the stress was calculated by inputting the dynamic behavior into a small FEM consisting only of the main bearing as a displacement boundary condition. Verification of the test results confirmed that this model is capable of highly precisely predicting the actual working strain of main bearing portions susceptible to fatigue-related fractures. It was confirmed that the developed model could predict the actual working strain if the highest natural frequency of the eigenmode utilized by the FMBD analysis was set to 50kHz or higher.
Noise reduction of industrial products has been required for dealing with noise problem and satisfying comfortable living space. To reduce noise of the products, we need to identify surface that radiates the noise, and take measure against the noise. As a method to identify sound source, inverse-numerical acoustic analysis (INA) has been proposed. INA is a method that identifies surface vibration of the sound source by using acoustic transfer functions and actual sound pressures which are measured at field points located near the sound source. In the INA, the measured sound pressures are used as the input data. For measuring sound pressures, we need to decide the arrangement of the field points, namely the number of microphones and its positions. The increase of field points leads to longer test and analysis time. Therefore, guidelines for the field point arrangement are needed to carry out the INA efficiently. In this study, we focused on the standard deviations of distance between sound source elements and field points, and proposed new evaluation function for optimal selection of the field points based on the standard deviations. The effectiveness of the new evaluation function had been verified by using plate model. As a result, we confirmed that the selection of optimal field point arrangement was achieved by using two guidelines, which are condition number and the new evaluation function we proposed.
From the view point of the environmental protection and convenience for transportation, a bicycle is one of the effective forms of the personal mobility vehicles. It is known that a small wheel bicycle running at low speed has less upright stability. In this study, Steer-by-Wire system is used to steer and stabilize a small wheel bicycle. In a bicycle with Steer-by-wire system, the mechanical connection between handlebar and steer-assembly is replaced by electronic connection with actuators, sensors and a controller. The system can enhance the upright stability of a bicycle by a control system. This study aims to enhance the upright stability of a small wheel bicycle at low speed. Firstly, we conducted the eigenvalue analysis to evaluate the upright stability of a bicycle and examined the difference of the stability between a bicycle with normal wheel and a small wheel one. Secondly, we designed the mechanism of Steer-by-Wire system and examined the effectiveness of Steer-by-Wire system in a small wheel bicycle. Finally, we investigated the behavior of a small wheel bicycle with Steer-by-Wire system when the system is subjected to disturbance torque. As a result, we found that Steer-by-Wire system could enhance the upright stability of a small wheel bicycle at a low speed.
This study develops a rotary-type active vibration control device (Active Wheel Damper, AWD) using a fly-wheel to control vibrations in flexible structures. The AWD achieves lightweight and higher inertia by the fly-wheel, and can be mounted on the flexible structure easily. In addition, the AWD can realize sky-hook controller easily because it can measure the absolute angular velocity of the flexible structure by the gyro sensor. So, the AWD uses Sky-hook With Disturbance Cancellation (SWDC) control, which is combined controller of a sky-hook control and a disturbance cancellation control with very high vibration suppression potential. However, control performance depends on the resolutions of sensors (Analog-Digital converters) and controller outputs (Digital-Analog converters), and higher cost is necessary for using the higher resolution sensors and controllers. In general, control performance deteriorates due to using low cost instruments with low resolutions. This paper investigates a method for cost-performance improvement of the AWD by using the dynamic quantizer (DQ) for practical use. So this study applies the dynamic quantizer into the SWDC controller of the AWD to prevent performance deterioration due to using the sensor and controllers with low resolutions. In addition, the parameters of the dynamic quantizer is optimized by Genetic Algorithm (GA) to achieve higher control performance under the condition using low resolution instruments. Usefulness and the performance of the proposed method are shown by numerical simulations.
This study reports about the numerical simulation of the sheet flutter in passage flow with large deformation and vortex shedding from trailing-edge. The equation of motion for flexible sheet has the Kelvin-Voigt-type material damping. Discrete vortices are shed to satisfy the regularity condition of flow at trailing-edge. At first, our numerical model under the uniform flow was compared with the preceding study to verify this model. Using the validated simulation model, we investigated the relationship among the material damping, width of passage and behavior of flutter. We clarified that material damping and passage width affect the flutter behavior and the efficiency of energy harvest due to flutter.
When agricultural machines are operated on pavements, the vibration and noise caused by interaction between the tire lugs and the road surface are inevitable. Therefore, it is important to investigate the lug excitation force occurring on a rolling agricultural tire in order to clarify the vibration generation mechanism. In our previous study, it was confirmed that the dynamic behavior of a rolling tire is influenced by the vibration characteristics of the tire. Further, only the rigid modes among the natural modes could affect the rolling tire behavior. Therefore, we modelled the tire as a circular rigid ring supported on an elastic foundation with a contact model. This rigid ring model can represent those modes of vibration of the tire in which the tire ring moves as a rigid body and the equations of motion for translational motion are derived. In order to identify the lug excitation force, the shaft displacement and the shaft force during rolling motion are measured by rolling test. The tire ring displacement, supposed to be the vibration due to lug excitation frequency, is identified from the measured data using least squares method. The shaft forces predicted by the calculation using the identified parameters show good agreement with measured shaft forces. So, the validity of this identification method are confirmed. Finally, the lug excitation forces are identified.
The stability of a flexible cantilevered plate subjected to a parallel flow is investigated. As the flexible flat plates, the papers in a high speed printing machine, the thin plastic and metal films, the fluttering flag and the oscillating doom roof are enumerated. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The coupled equation of motion of a flexible cantilevered plate is derived into consideration with the added mass, added damping and added stiffness respectively. The complex eigenvalue analysis is performed for the stability analysis. In order to consider the accuracy of dynamic stability analysis, three stability analysis method are proposed. Firstly, the analysis method based on boundary conditions in the half space surrounded by leading edge and trailing edge is performed. Hereafter, let's call it the coupled solution. Secondly, the analysis method based on the non-circulatory aerodynamic theory is performed. Let's call it the non-circulatory solution.Thirdly, the analysis method which fulfills Kutta condition is performed. Let's call it the circulatory solution.The following is made to be clear through three solutions. When the mass ratio of a fluid system for a structure system is small, the flutter of the lower mode such as a second mode become predominant. And, when the mass ratio is large, the higher mode flutter appears. Although the critical velocities of the coupled solution and the non-circulatory solution are higher than that of the circulatory solution in the second mode flutter with lower mass ratio, the critical velocities of the circulatory solution becomes higher than those of the coupled solution and the non-circulatory solution when the mass ratio increases.
A magnetic damper composed of a permanent magnet and a conducing plate has the advantage that the magnetic damper can generate a damping force with no physically contact. The conducting plate needs to be thickened in order to obtain a stronger magnetic damping force, since the magnitude of the magnetic flux produced by a permanent magnet is limited. However, it is known that the magnitude of the magnetic damping force is limited, even if the conducting plate of the magnetic damper has a large thickness. It has been considered that skin effect by eddy currents is the cause of this limited magnetic damping force. In addition, it is known that eddy currents have a very slight effect on the natural frequency of a structure with a magnetic damper. In this paper, the coil method considering inductances is proposed as one of the modeling methods for magnetic dampers consisting of a ring magnet and a conducting disk moving relatively in an axial direction. Applying this method, a modal analysis of the free and the forced vibration of a 1-DOF system with a magnetic damper are performed, and the magnetic damping and the magnetic stiffness considering the skin effect, are introduced. Furthermore, the experiments are performed in order to confirm the practicality of the method. The analytical results are found to be in agreement with the experimental results.
This paper describes 5-axis centralized feedback control system for a single-rotor helicopter. Optimal control theory is directly applied to 25-state Multiple-Input Multiple-Output (MIMO) analytical linear model of a small-scale unmanned helicopter without decoupling the motion dynamics. The linear Kalman filter is also designed for an estimation of the blade flapping and lagging angles and the down-wash which are utilized in the state feedback control law. In the comparison with the distributed control system using the Single-Input Single-Output (SISO) controller which is common approach for flight control, this full-axis centralized control system includes the effects of cross-coupling dynamics and enables a design for full control-axis at once in a short amount of time. Flight test with this method demonstrated a steady hover control performance through attitude, position, and main rotor speed. Simple tuning way of weighting matrix used in the quadratic cost function is also presented to deal with a difficult problem caused by a large number of design parameters or the undesirable coupled vibration. Stability analysis of the closed loop system using MIMO plant model reveals that MIMO controller provides greater and better balance stability margins for every control-axis than SISO controller does. In addition, a frequency characteristic analysis is conducted using MIMO plant models based on different flight conditions, which showed a good robustness of the MIMO controller toward modeling errors and also the effect of extra flight conditions on the robustness of each control-axis.
Applications of small unmanned helicopters are rapidly growing in the civilian and commercial field such as pesticide spraying, aerial filming, and inspection. However, accidents often happen from deficient of operator skill, which leads to a large demand for reliable and skilled pilot. This paper describes the development of operator training support system that improves manual operation skill of the helicopter in safety under an actual environment. When attitude angle, velocity, or position exceed threshold values as a result of poor maneuvering or wind effect, manual inputs are automatically switched to control inputs and the helicopter is recovered to stabilized hover. The recovery controller is designed using quaternion-based formulation for nonlinear helicopter kinematics. The angular rate commands are calculated from quaternion error defined as the minimum-angle rotation required to decrease translational speed. To execute a high speed tracking control of angular rate, two-degrees-of-freedom servo system is applied to the inner loop dynamics. Nonlinear simulation and experiment result with this controller show smooth recovery maneuver from large attitude angle to hover state as if controlled by skilled pilot. A series of flight test with the operator training support system demonstrated the validity of the proposed architecture for accident avoidance during operator training. This system will contribute to safe and efficient operator training of unmanned helicopters.
In recent years, AEBS (Autonomous Emergency Braking System) has been put to practical use by various automotive companies. This system detects the front obstacle by using a camera or a laser and then brakes an automotive automatically. However, the load on the occupants is not considered in the current AEBS. On the other hand, increase of aged drivers has become an issue to be considered in the effort of enhancing safety performance of vehicle collision avoidance system. In order to solve this issue, we proposed a control system design model that can take into account the driver behavior during braking. Although, the new problem that the collision avoidance performance deteriorates so as to close an obstacle by the deceleration control using stationary LQR (Linear Quadratic Regulator) has been confirmed. Therefore, this study verifies an effectiveness of the vehicle deceleration control system using the time-varying feedback control. Moreover, we compared the performance of four methods for the load on driver and braking distance. The simulation results show that the proposed method can reduce the load on the driver and improve the collision avoidance performance.
Sloshing phenomena in containers during earthquakes often cause serious accidents. For oil tanks with a floating roof, sloshing and structural vibration should be treated as a coupled problem. A Lagrangian fluid finite element method has been used to analyze the coupled problem because the compatibility and the equilibrium conditions are automatically satisfied at the boundary between the fluid and the structure. However, the number of degrees of freedom of the Lagrangian method becomes large because the fluid particles move vertically and horizontally. In addition, the Lagrangian model has physically meaningless spurious modes caused by redundancy in the degrees of freedom. In this paper, liquid in a rectangular container is modeled with a linear concentrated mass model to establish an efficient, accurate analytical model for the coupled problem. The model consists of masses and connecting springs. The masses move horizontally and the vertical liquid motion is considered as vertically movable points. The masses are governed by the equations of motion. The vertical displacements of the moving points are determined from the displacements of the masses based on the incompressibility of the liquid. The characteristics of the connecting springs are derived from the static and dynamic pressures of the liquid. In the proposed model, there are fewer degrees of freedom than in the Lagrangian model and the spurious modes do not occur. The proposed model is validated by comparing the calculated natural frequencies and natural modes with the theoretical values.
This report shows effect of sound insulation by adhesion of porous materials and film laminated panel. It deals a technique for estimating damped vibration of automotive body panels with sound-proof structures. It calculates damping properties for sound-proof structures involving elastic body, viscoelastic body and Biot type porous materials by three-dimensional finite element method. In this analysis, particle displacement vectors for internal air in the porous materials are adopted as unknowns for the discretized equations for finite element method. And displacement vectors for frame in the porous materials are also selected as the unknowns. A numerical code is developed. For numerical examples, Biot type porous materials are sandwiched between panel and film, and laminated film. Frequency response functions were calculated for panels laminated with porous material (felt) and viscoelastic body (film) and porous material (felt) using this technique, the calculation results almost agreed with the experimental results. And effect of the vibration performance by with/without adhesion is clarified. At with adhesion, the internal air and the frame in the porous material are same vibration. But at without adhesion, the internal air and the frame in the porous material are greatly different vibration. It is thought that change of sound insulation takes place by this.
This report deals with sound absorption coefficient prediction technique of ultrafine fiber. As the sound absorption material used for the interior noise reduction of the automobile, the fiber with a diameter of several μm is considered. When a fiber diameter becomes small, usually a sound absorption coefficient increases. But predictive precision was bad by the conventional performance prediction technique. I developed the technique to predict a sound absorption coefficient from the fiber diameter and the fiber density and the material thickness and the material density. The experiment expression of relations was drawn from the experimental results about the flow resistivity and the thermal characteristic length. And I introduce the technique used Limp frame model to predict a sound absorption coefficient for the ultrafine fiber. There diameters are 1-4μm. This paper shows comparison of the experimental results and the calculation results, and this technique is useful.
The Fukushima Daiichi (1F) accident in unit 1 to 4 was likely to be caused by the tsunami induced loss of emergency power and seawater heat sink that is consistently elucidated based on the performance of the plants until the tsunami hit after the seismic SCRAM by Great East Japan Earthquake. However it is fact that the actual damages of components have difficulty to be completely inspected under high radioactivity, and to make clear distinction between tsunami induced damage and seismic induced damage. This paper will support above conclusion based on the result of seismic response analysis for safety related components of each plant, the result of the plant walk down in the similar unit in the same station, and also the result of analysis for the observed seismic records from the perspective of generalization of the damage possibility of nuclear components designed by Japanese seismic standards. The result of seismic response analysis using observed seismic motion shows all safety related components fulfill the seismic criteria and seem to maintain structural integrity. Also we could find few seismic induced damage in the walk down for unit 5 of 1F that shows similar result would be expected in unit 1 to 4. It is concluded that the design method using seismic static load contributes additional robustness of nuclear components, even the lower seismic class components, and that the damage by the earthquake should be quite limited based on the analysis of observed seismic motions.
The present work proposes the shear type body force dipole (BFD) in addition to the normal type to simulate residual stress fields more properly. Expressions for the displacements and stresses induced by the BFD are derived and formulated in the boundary integral equations which govern the elastic field. In the first step of the numerical approach, the sensitivity matrix is constructed to correlate the BFD distributions with the boundary stresses, and is transformed into the generalized inverse matrix by the singular value decomposition technique. Then the generalized inverse matrix is operated on the boundary stresses so that the unknown BFD distributions are evaluated. Based on the study for the effect of the shear type BFD on stress and displacement, discussions are focused to the accuracy of the inverse analysis and the influencing factors such as the number of stress data. The use of the boundary displacement besides the stress data is not important to improve the accuracy in the present problem. It is also suggested that the accuracy of the evaluated BFD distribution can be improved by the following iteration of forward stress analysis so as to minimize the stress error norm at the boundary.
The purpose of this study is to clarify the effect of the fiber crimps in braided carbon fiber reinforced plastics pipe (Braid pipe). Braid pipes with different crimp angles were fabricated by using carbon fiber with different fineness for the braiding yarn and different 0° fiber contents. Larger fineness of carbon fiber and/or more content of 0° fiber made the crimp angle larger. The braiding angle was ±45° and 0° fiber (MEY) was inserted between braiding yarns. 0° fiber content was changed as, 0%, 15% and 29%. The effects of crimp on the bending property and the torsion property were investigated comparing with SW pipes with non-crimp structure made by Sheet Winding method. As regarding bending property, Braid pipe performed 75% to 95% of the bending modulus of the SW pipe. With the increase in the crimp angle, the bending modulus was linearly decreased. The longitudinal yarn in Braid pipe with gap between braiding yarns had crimp and bending strength was decreased. The Poisson's ratio of Braid pipe was smaller by 67% than that of SW pipe. The crimp in longitudinal yarn and Poisson's ratio had greater effect on the bending strength than the crimp of braiding yarn. As regarding torsion property, both of the torsion modulus and strength were decreased with the increase in the crimp angle at braiding yarn. The crimp had 2.5 times greater effect on torsion strength than torsion modulus. It was clarified that the effect of crimp at braiding yarn on the mechanical properties depended on the angle between fiber orientation and the principal stress directions.
In this research, impact reduction effect of acrylic foam film was clarified by using dynamic three-point bending testing machine. The specimens were an aluminum alloy (JIS A6063) beams with an acrylic foam films on surfaces of the beams. The acrylic foam film had thickness of 700 μm and density of 0.5 mg/mm3 on a polyethylene terephthalate substrate film with a thickness of 38 μm. The aluminum alloy beam had thickness of 3, 6 and 10 mm. The input and output bars in the three-point bending testing machine were made of aluminum alloy (JIS A7075-T6). The bars were 2 m in length and 12 mm in diameter. The striker made of polycarbonate was 200 mm in length and 12 mm in diameter. Impact load was applied to the input bar by colliding the striker. Impact load and reaction load were calculated from strain histories of the input and output bars due to one-dimensional elasto-dynamic theory. Histories of the impact loads for the specimens with the acrylic foam film were lower than the one for the specimens without the acrylic foam film. The maximum impact loads for the specimens 10 mm in thickness with the acrylic foam film was 20% smaller than the one for the specimens without the film. The acrylic foam films were found to be effective to the impact load reduction for higher stiffness of a structure.
Low cycle fatigue tests at elevated temperature were conducted on a Ni-based directionally solidified superalloy with small holes subjected to transverse loading. To investigate the effect of the arrangement and the orientation of crystal grains on the crack initiation, the electron back-scatter diffraction (EBSD) method was applied on the surface of the tested specimens. In addition, finite element analysis that considered the plastic behavior of crystal grains was performed to evaluate the relationship between the crack initiation and the local stress that developed along the hole edges. The results are summarized below. It was shown that the number of cycles to crack initiation tended to be small along the hole edges located on the grain boundaries by classifying the hole edges according to the position of the hole edge and the grain boundary. In addition, it was small along the hole edges located in the grain whose secondary axis was more inclined than the grain located in the opposite surface. The results of FEM analysis revealed that high stress developed along those hole edges. The location where high stress developed correlated with the number of crack initiation cycles not only among the hole edges in one specimen but also among the specimens subjected to different nominal strain range.
The warp deformation behavior for various viscoelastic four-layer laminated structure consisting of epoxy resin, printed board and steel which modeled electronic devices caused by a series of thermal load from heating to cooling was examined by experiment and viscoelastic stress analysis based on linear viscoelastic theory. As a result, it was clarified that the warp deformation behavior of laminated structure containing resin was influenced by thickness and viscoelastic properties of epoxy resin and printed board such as modulus of longitudinal elasticity and thermal expansion coefficient depending on temperature and time, and that the warp deformation behavior of viscoelastic four-layer laminated structure was determined by the balance between flexural rigidity of laminated structure and bending moment caused with the thermal expansion or shrinkage of constituent materials. The warp deformation behavior of laminated structure containing resin could be predicted in general by analysis in consideration of the characteristic of viscoelasticity.
We investigated nonlinear ultrasonic characterization, nonlinear three-wave interaction, of the pure copper during fatigue with EMAR (Electromagnetic Acoustic Resonance), which was the combination with ultrasonic resonance and non-contacting transducer, EMAT (Electromagnetic Acoustic Transducer). In nonlinear three-wave interaction method, two intersecting ultrasonic waves produced a scattered wave when the resonance condition was satisfied. The amplitude in resonant scattering wave was measured. Nonlinear three-wave interaction method exhibited high sensitivity to micro-structural change of the damaged material. It rapidly increased from 50% of fatigue life to the fracture. TEM (Transmission Electron Microscope) and EBSD (Electron Backscatter Diffraction) observations supported this phenomenon caused by dislocation movement. The sensitivity in three-wave interaction method was higher than that in linear methods. The noncontact resonance-EMAT measurement can monitor the evolution of nonlinearity throughout the fatigue life and has a potential to assess the damage advance and to predict the fatigue life of metals.
In this paper, the compressive response of an egg-box panel was investigated using a nonlinear FE analysis. The egg-box panel was based on spherical shells and frusta, and its compressive response was predicted by considering the theoretical compressive responses of the spherical shell and frusta individually. Given that the material’s strain-hardening characteristics enhance the compressive response of the egg-box panel, the compressive response would be underestimated by using the initial yield stress as a material parameter. Instead, the flow stress based on the initial yield stress, the strain-hardening exponent in the nonlinear stress-strain curve and the ultimate tensile strength were effective for estimating the compressive response of egg-box panel. Also, the compressive load continued to increase as the displacement increased. By adopting appropriate dimensions for the flat-shaped basement in the egg-box panel, a uniform load-displacement curve could be obtained.
In this paper, a database of the identically-distributed inherent strain within mechanical melting zone is developed and then applied for simplified distortion analysis in multi-layer and multi-pass welding of heavy section plate. First, numerical and experimental investigations of weld angular distortion were performed for multi-layer and multi-pass welding of heavy section plate to verify the simplified weld distortion analysis based on the theory of inherent strain. Next, the effect of residual stress due to precedent welding pass on inherent strain produced in current welding pass was investigated based on the fundamental bead-on-plate model to improve a database of the identically-distributed inherent strain within mechanical melting zone, which was already developed for single pass welding, for multi-layer and multi-pass welding. The usefulness of the developed database of inherent strain was validated for simplified distortion analysis in multi-layer and multi-pass welding of heavy section plate. Then, the simplified weld distortion analysis based on developed database of inherent strain was applied to quantify the effect of weld pass sequence on angular distortion in multi-layer and multi-pass welding of heavy section plate. Based on the results, the developed system can be expected to be a useful weld design support tool for accurately predicting weld distortion and managing construction quality in welded large structures.
Peening is the process which is able to be generated compressive residual stress and is known to be effective for preventing SCC initiation and improvement of fatigue strength. Laser peening is used for the nuclear power plant components in order to prevent SCC initiation. Although it is reported that the compressive residual stress decreases due to applied stresses under general operating condition, the change of residual stress might be large under excessive loading such as an earthquake. The objectives of this study are to evaluate the relaxation behavior of the compressive residual stress due to laser peening and to confirm the surface residual stress after loading. Therefore laser peened round bar test specimens of SUS316L which is used for the reactor internals of nuclear power plant were loaded at room temperature and elevated temperature and then surface residual stresses were measured by X-ray diffraction method. In the results of this test, it was confirmed that the compressive residual stress remained after applying uniform stress larger than 0.2 % proof stress, and the effect of cyclic loading on the residual stress was small. The effect of applying compressive stress on the residual stress relaxation was confirmed to be less than that of applying tensile stress. Plastic deformation through a whole cross section causes the change in the residual stress distribution. As a result, the surface compressive residual stress is released. It was shown that the effect of specimen size on residual stress relaxation and the residual stress relaxation behavior in the stress concentration region can be explained by assumed stress relaxation mechanism.
Thermodynamic effect of cavitation is a favorable effect for pumps, in which cavity volume is suppressed and suction performance of the pump is improved. When evaporation occurs in low pressure region inside the pump, local temperature is decreased by the latent heat, the local saturated pressure decreases, then the cavity is suppressed. The thermodynamic effect is known to appear when the main stream temperature closes to critical temperature of the fluid. In order to clarify the basic characteristics of the thermodynamic effect of cavitation, high temperature and high pressure water tunnel is constructed, in which the free stream temperature can be increased to 140°C. In this study, by using high accuracy measuring technique of temperature inside a cavity, temperature distribution inside a supercavitation on a hydrofoil in a hot water at 80°C and the variation of temperature depression inside a supercavitation from room temperature water at 20°C to hot water at 80 °C are measured. And the temperature depression is predicted in more high temperature region by using theoretical prediction. Additionally, through comparison of cavity length between room temperature water and hot water, the thermodynamic effect in hot water is discussed.
The behavior of mono-dispersed spherical bubbles rising along an inclined flat plate has been observed experimentally and the effects of the inclination angle and the air flow rate have been investigated. This study considers the clustering behavior of bubbles for the range of bubble Reynolds number Re from 100 to 200 (Re being based on the bubble diameter and bubble rising velocity along the flat plate). When the number density of bubbles becomes higher and the rising velocity along an inclined flat plate becomes slower, the bubbles tend to be horizontally arranged in line and such arrangements pile up to the bubble cluster. The spatial distribution of bubbles has been evaluated by the pair distribution function, which shows the frequent existence of side-by-side bubble pairs and the preferential accumulation within the range of about 8d (d is the average bubble diameter) corresponding to the size of the typical bubble cluster. Also, the statistics of the velocity difference of bubble pairs has been analyzed in order to evaluate the bubble-bubble interaction quantitatively. For the bubble pair moving in line, the trailing bubble becomes faster by the effect of the leading bubble, which leads to the tandem configuration of two bubbles. However, since the tandem configuration is unstable, the resultant rotational velocities around the other bubble centers cause the side-by-side configuration of the bubble pair. This process forms horizontally aligned bubbles.
A cavitation inception theory of a vapor bubble in flowing liquid is presented by taking account of a set of fluid dynamics boundary conditions for nonequilibrium evaporation at the bubble wall. The boundary conditions for the vapor temperature, pressure and density at the wall are a set of solutions of the polyatomic type of ES-BGK Boltzmann equation. The evaporation rate and the vapor-liquid temperature discontinuity at the bubble wall are treated in a physically correct way at a molecular level. The theory also considers the translational motion of the bubble in a flowing liquid with arbitrary relative velocity between the bubble and the surrounding liquid. The translational motion largely reduces the liquid pressure at the bubble wall, and the inception process of cavitation is thereby influenced greatly. Furthermore, the numerical calculation of expansion process of the vapor bubble is performed for the case where the bubble is instantaneously exposed to the low liquid pressure, and its results are compared with those of the equilibrium evaporation. A critical liquid pressure considered as a criterion of expansion and contraction of the bubble is numerically estimated for the various relative velocities between the bubble and the liquid and the various initial bubble radii, and it is compared with the pressure of the classical theory. Numerical calculation reveals that the critical pressure for the relative velocity of zero in the case of nonequilibrium evaporation or condensation is lower than the classical one in any initial bubble radius.
The self-circulating thermosyphon (SCTS) operates without external pumping power. It is a closed loop of pipe and consists of heater, condenser, heat exchanger and recuperator. In this paper the basic performance of SCTS was examined experimentally under various back ground pressures and power inputs to the heater. Experimental results showed that the stable operation of SCTS was limited by the minimum input power overcoming the total losses of the system and the maximum power within the ability of the condenser. At fixed back ground pressure, mass flow rate and quality of water vapor in heater were confirmed to increase with the power input. As back ground pressure increased, mass flow rate was prone to decline. Those suggest that the main driving force of SCTS is buoyancy force of the vapor. Thermal transport efficiency ranged from 0.4 to 0.9 as far as the present conditions are concerned.
Natural convective heat transfer from downward-facing, heated rectangular plates to air has been investigated experimentally. Main concerns were directed to the influence of aspect ratios on the heat transfer from the plates. For the sake of this, a total of 32 rectangular plates having different width W = 35-500 mm and aspect ratios AR = 1, 2, 3, 5, 8, were fabricated and tested. The experiments began with the visualizations of the flow fields adjacent to the plates, then, the measurements of average Nusselt numbers followed. The flow visualizations using smoke depicted that the flows remain laminar throughout the present plates. The average Nusselt numbers NuW measured with the plates of different aspect ratios were plotted with the Rayleigh numbers RaW, where NuW and RaW are based on the short side-length of the plates. The plots showed a monotonous decrease with the aspect ratios. The above Nusselt and Rayleigh numbers were next converted to those based on the equivalent diameter de of the plates. Then, the Nusselt numbers Nude showed almost identical variations with the Rayleigh numbers Rade regardless of the aspect ratios. Based on these results, empirical correlations for the average Nusselt numbers from the plates of arbitrary aspect ratios were proposed.
The aqueous lithium-air battery has been receiving considerable research attention owing to its high theoretical energy density. This property is important from the perspective of enabling electric vehicles to rival the performance of gasoline-powered vehicles. However, high-power discharge has not yet been achieved. Because ion transport phenomena in the battery determine its current density, molecular interpretation of the electrolyte is required to improve battery performance. In this study, molecular dynamics simulation of LiCl electrolyte in a high-electric field was performed to elucidate the behavior of ions and molecules in the electrical double layer near the electrode. The results showed that the H2O molecules were clearly oriented by the electric field, and Cl- and Li+ formed ion-pairs or ion-clusters in the electrolyte. Those structures more easily formed under higher electric field conditions. It is considered that hydrated ion structures were difficult to form with the oriented H2O molecules. In contrast, the highly mobile ions produced by the electric field were more likely to bond with each other. The effect of the electric field on diffusion phenomena was also investigated. Fast migration of independent ions (Cl- and Li+) was caused by electrophoresis. Ion-pairs and ion-clusters were not forced to migrate because the net electric charge of the structures was zero. Our results show that a small number of independent ions play a key role in the passage of electric current through the electrolyte.
In places such as nuclear power plant disaster area, which it is difficult for human workers to enter, robots are required to scout those places instead of human workers. In this paper, we present a mobile manipulator HELIOS X for a nuclear plant decommissioning task. Firstly, we address demands and specifications for the robot, considering the mission of reconnaissance. Then we outline the system of the robot, mainly focusing on the following mechanism:“Crank Wheel”, “ Main Arm ”,“ Sphere Link Wrist ”,“ Camera Arm ”,“ Control System ”and“ System architecture ”. Especially, we installed 3 degree of freedom“ Camera Arm ”on the“ Main Arm ”, in order to improve functionality of remote control system. This enables the operator to monitor both the gripper and its overall view of the robot.“ Camera Arm ” helps the operator to recognize the distance from an object to the gripper, because the operator can interactively move the viewpoint of the camera, and monitor from another camera angle without changing the gripper’s position. We confirmed the basic functionality of mobile base,“ Main Arm ”and“ Camera Arm ”through hardware experiments. We also demonstrated that HELIOS X could pass through the pull-to-open door with a substantial closing force when the operator watched camera view only.
Recently, cooling fans have been used for not only general industrial machines but also precision machines, such as medical care products and optical equipment, and these generate more requirements about vibration limitations. The main vibration of cooling fans caused by rotating unbalance and resonance has been reduced, so electromagnetic induced vibration, which was not considered before, now has to be reduced. The purpose of this study is to control the electromagnetic induced vibration of 2 poles three-phase induction motors that rotate fast, such as for cooling fans. In this paper, it is shown that, the number of coils that is one of the magnet wire specification controls electromagnetic force and electromagnetic induced vibration by an experimental study of 2 poles three-phase induction motor that has an output of 70W, as follows; the difference of magnet wire specification can be quantified by the space distribution of magnetomotive force (SDMF), SDMF can be inferred from measuring data of magnetic flux by sensor wire method to be confirmed identical to the theory, the effective value of the difference between SDMF and a sine wave has correlation with electromagnetic induced vibration and increasing number of coils from 1 coil / pole / phase to 3 coils reduces the effective value of the difference between SDMF and a sine wave, and also reduces electromagnetic induced vibration about 20 dB.
Since the accident at Fukushima Daiichi Nuclear Power Station in 2011, the robots for exploring the power station buildings have been working and developing. Each floor of the building has a high ceiling, and it is important to check the pipes near the ceiling. However, the existing robots used for exploring high places in the building have lift mechanisms attached to them and cannot climb stairs because of their heavy weight and little traveling performance. In this paper, we propose a system for exploring a high place of the upper floor by using Unmanned Aerial Vehicles (UAVs), especially multicopters and UGVs as substitutes for the lift-type robots. In the power station building, robots go through passageways to explore, so the size of the robots is defined by the width of the passageway. On the other hand, the multicopter is more efficient and can carry heavier payload when it uses large propellers. Therefore, we have developed a multicopter whose arm can fold when on the UGV to decrease the width of the robot and automatically extend when it flies. Furthermore, we have developed a tether-winding helipad to land the multicopter automatically with high accuracy. Finally, we have tested and confirmed the availability of the proposed system with the UGV.
This paper proposes a design method of a PD controller with consideration of acceleration responses of an auxiliary mass for active mass dampers (AMDs) operated by a combination system of a neural oscillator and position controller. In the former proposed controller, a desired value of the auxiliary mass was calculated by the output of the oscillator synchronized with the structure's vibration response, and the auxiliary mass was operated to the desired value by the position controller, then the resulting motion of the auxiliary mass mitigated the vibration of the structure. This system can easily solve the stroke limitation problem of the AMD by saturating the desired value of the auxiliary mass within the limit, however the ratio of the control force to the mitigation of the structural acceleration, called as cost-performance, is worse than the system designed by the ordinary linear control method. Therefore, the purpose of this paper is the improvement in the cost-performance of the system by reconsidering the design method of position controller's gains. For this purpose, the gains of the position controller are designed with consideration of the acceleration response of the auxiliary mass, that is tried to approach asymptotically to the ideal sine wave. Numerical simulations with several types of earthquakes indicate that the modified controller has better cost-performance when compared with the former controller.
In numerical simulation, dynamic model is necessary to predict the product performance such as strength of structure, noise, and vibration. The prediction accuracy depends on the accuracy of parameter identification. For installed or completed products, an experiment must be done to identify structural properties such as Young's modulus or density. This experiment allows us to accurately predict the product performance regardless of product dispersion and aging deterioration. Hence there are many studies about identification methods of the structural parameters of beams. In these studies, the structural parameters were derived from natural frequencies of a beam with/without an additional mass. However, no study can obtain the parameters under unknown boundary conditions. In this study, we proposed a new simple method to identify line density of beams. This method assumes that mode shapes of a beam do not change regardless of additional masses. This study proposes an experimental method for arrangements of additional masses, which can keep mode shapes unchanged. In the numerical analysis, a finite element method is used to obtain the natural frequencies of a beam with/without additional masses. The natural frequencies and the weight of the additional masses are used to identify line density of the beams. We also verify the method through experiment.
This paper proposes a design method that uses electric power steering (EPS) to reduce the effort required for handling in a vehicle. To accomplish this, the design must reduce the physical effort required of the driver, improve the controllability of vehicle dynamics, and adjust steering feedback to adopt the driver's characteristics. The influence of the stability factor and rear cornering compliance on handling and the effects of modifying these conditions were investigated. In addition, in order to compensate for the influence of these factors, EPS compensation features are addressed. Thus, desired steering characteristics are discussed as a function of steering frequency and yaw rate magnitude based on yaw rate and a Lissajous figure of steering torque. The influence of the stability factor and rear cornering compliance on a stable handling feeling are proven by simulation and linear analysis, and the conditions that cause a loss of this feeling of stability, even when vehicle dynamics are stable, are explored. EPS compensation functions are proposed against the influence of the stability factor and rear cornering compliance on the sense of handling. Furthermore, other EPS functions are proposed to compensate for the response from yaw rate to steering torque and to help the driver better understand the vehicle's behavior. Finally, the effects of EPS compensation functions on reducing the effort required for handling are demonstrated by a test where a single lane change was performed.
Standing up motion would be effective for maintaining or improving the function of motor and circulatory system. By standing up in daily life, wheelchair users with lower limbs motor dysfunctions could prevent the development of physiological dysfunctions, such as deep vein thrombosis and disuse syndrome. The purpose of this study is to develop a standing up motion support system for such wheelchair users without any mounting sensors and devices, and to confirm the effectiveness of the developed system through a standing experiment with a wheelchair user who has lower limbs motor dysfunctions. We developed a wheelchair type motion support system and seat reaction force (SRF) sensor. Since the SRF decreases in standing up preliminary motion, the SRF sensor measures the decrease of user's SRF in order to detect the standing up preliminary motion. The system supports standing up motion while SRF decreases less than that during sitting posture. A basic experiment is carried out to confirm the measurement accuracy of the developed SRF sensor. The results of the basic experiment showed that the errors between the true weight and the SRF calculated by the sensor ware within ±10 N. A standing experiment with a spinal cord injury participant who can't stand up by oneself was performed to confirm that the system could detect the user's standing preliminary motion and can support active motion. The results showed that the system started to support user's standing up motion after the system could detect the decrease of the SRF. In addition, the user could stand up actively by using the system. In conclusion, the developed system was effective in helping the wheelchair users to stand up actively in daily life.