In this paper, a flexible morphing wing with piezoelectric materials for morphing actuation is studied. The objectives of this paper are 1) to develop an integrated geometrically nonlinear electro-aeroelastic framework, which allows evaluating performances of flexible morphing wings with piezoelectric actuators, 2) to validate the developed analysis framework, and 3) to demonstrate the capability of the framework and explore the performance. This paper provides a description of the electro-aeroelastic equations of morphing wings taking into account piezoelectric effects, which can be used to actuate morphing wings. The electro-mechanical model is validated by comparing with experimental results. The validation with a single macro fiber composite showed a very good agreement between the experimental result and the simulation. The result of an actuation test with an integrated corrugated structure and macro fiber composite also reasonably agreed with the solution from the present code. Aeroelastic behaviors of a corrugated wing with the piezoelectric actuator are then explored. The camber morphing wing with the corrugated structure actuated by the piezoelectric actuator could provide a larger lift in the vicinity of the trailing edge. Such a camber morphing has a good potential to control aeroelastic response by wing morphing with piezoelectric actuation.
The double cylindrical tube achieving an arbitrary twist distribution was applied to a spar of a twist morphing structure and the applicability was demonstrated through a twisting experiment and a wind tunnel test. In the previous study, we developed the double cylindrical tube which achieves an arbitrary twist distribution and its basic theory has been derived. In this study, we developed and fabricated a wing twist morphing structure of which spar was the double cylindrical tube. Then a theoretical formulation for the twist angle of the wing twist morphing structure considering its skin was derived. Some experiments were carried out and it was confirmed that the specimen could be twisted to the target twist distribution under wind loads (wind speed was about 12 m/s). Furthermore, the specimen could be twisted regardless of the twisting direction, and the maximum error of the twisting angle was 18.1% at the wing tip. We also evaluated aerodynamic data, and calculated aerodynamic coefficients for each angle of attack. These experimental results demonstrate the applicability of the double cylindrical tube to wing twist morphing structure and reveal that the developed morphing structure can contribute to the enhancement of flight performance by twisting itself.
Rail corrugation is such phenomenon that roughness patterns of approximately regular wavelengths are formed on the rail running surface by trains running, and cause the vibration and the noise. In the previous papers of ours, we have already explained the growth mechanism and the wavelength determination mechanism of the rail corrugation from the dynamic point of view and verified their validity by comparing them with the field data. In this paper, we report the results of simulation analyses of the characteristics of each step of formation, growth and saturation of the rail corrugation using a discrete elastic support model close to the actual track. As a result of the simulation, the following are confirmed : (1) at the formation step, by providing a minute and irregular wheel load fluctuation, rail surface roughnesses are formed with such wavelengths that their amplification factor of roughness amplitude is maximal and greater than 1.0. (2) at the growth step, as the contact length of the wheel / rail becomes longer, growth of roughness of the short wavelength is suppressed. (3) at the saturation step, when the roughness amplitude increases and the wheel loses the contact with the rail, the growth is suppressed and the roughness amplitude saturates. Based on these results, we present the progress process of the rail corrugation and the ways to approach the countermeasures.
This paper presents a method for generating a 3D point-cloud map using multilayer laser scanner mounted on two-wheeled vehicle. The vehicle identifies its own 3D pose (position and attitude) in a laser-scan period using the normal-distributions transform (NDT) scan-matching method. The vehicle’s pose is updated in a period shorter than the laser-scan period using its attitude and angular velocity measured by an inertial measurement unit (IMU). The pose estimation is based on extended Kalman filter under the assumption that the vehicle moves at nearly constant translational and angular velocities. The vehicle’s pose is further estimated in a period shorter than measurement period of the IMU using a linear interpolation method. The estimated poses of the vehicle are applied to distortion correction of laser-scan data, and a point-cloud map is generated based on the corrected laser-scan data. Experimental results of mapping a road environment using 32-layer laser scanner mounted on a bicycle show the performance of the proposed method in comparison with conventional methods of distortion correction of laser-scan data.
This paper presents a tracking (estimating position, velocity and size) of moving objects, such as cars, two-wheeled vehicles, and pedestrians, using a multilayer laser scanner mounted on a two-wheeled vehicle. The vehicle obtains its own pose (position and attitude) by on-board global navigation satellite system/inertial navigation system (GNSS/INS) unit and corrects the distortion of the laser-scan data by interpolating the pose information. The corrected laser-scan data is mapped onto 3D voxel map represented in the world coordinate flame. Subsequently, the vehicle extracts the interested laser-scan data from the current laser-scan data using normal distributions transform (NDT) scan matching based map-subtraction method. The extracted scan data are mapped onto an elevation map, and moving objects are detected based on an occupancy grid method. Finally, detected moving objects are tracked based on the Bayesian Filter. Experimental results show the performance of the proposed method.
The frictional force acts to the travelling pantograph head in horizontal direction due to sliding of the pantograph head and contact wire. Therefore, vertical motion of the pantograph head is generated by link mechanism of the pantograph. If the coefficient of friction between the pantograph head and contact wire is large, instability of the travelling pantograph could be observed. Although pantographs are modelled as lumped mass system and multi-body system, the unstable behavior of the travelling pantograph was not studied. This study proposes a 2-dimensional pantograph model that considers friction characteristics of the pantograph head based on the multi-body dynamics (MBD) approach. In this paper, a single-arm pantograph for shinkansen train is modelled using the MBD technique. Furthermore, a stability analysis method based on the complex eigenvalue analysis for the pantograph model is proposed. The equation of motion of the pantograph model is derived based on both the differential algebraic equation (DAE) and the linear dynamics equation (LDE). Results of the LDE-based stability analysis of the developed MBD pantograph models are shown. Then the obtained stability is validated based on the DAE-based time history response simulation of the pantograph models.
Energy-efficient driving is one of the major effective methods to reduce energy consumption of railway system. It has substantial advantage that need much less investment cost than other countermeasures. However, that has not been investigated in detail at short headway situation in rush hours where two trains interact with each other through signaling systems to prevent train collision. In this situation, some trains make unexpected accelerations and decelerations much often to track the preceding train and increase energy loss. Here we show theoretically what driving technique is much better from energy consumption point of view. In the simulation, we examine a technique to drive a train in an energy-efficient way when the preceding train is delayed departing station by simulations. The dynamic programming (DP) is employed to optimize the energy-efficient train speed profile and modified to implement the behavior of fixed-block signaling systems. The sensitivity analysis to change the delay of first train is made to clarify the relation between energy consumption and train delay propagation to the second train. The results show that it can suppress energy consumption less than or equal to regular running time situation.
Morphing wings, which control the flight by changing their own shapes, have attracted much attention by their potential for improving aerodynamic performance. Corrugated structures, which have flexibility in the corrugation direction and high rigidity in the transverse direction to the corrugation, were proposed as good candidates for morphing wings. This research suggests a new fluid-structure interaction (FSI) analysis model which shows better accuracy at low computational cost for the design of flexible morphing wings. A RANS based computational fluid dynamics (CFD) solver, UTCart, and a panel method, XFOIL, are both implemented in the FSI analysis combined with nonlinear flexible beam model in the present scheme. Aerodynamic pressure distributions obtained using UTCart are different from those obtained by the traditional XFOIL analysis, especially when angle of attack is high. This leads to the differences in the driving forces to deform the wing. In contrast, the differences in the deformed shapes of the airfoils are relatively small between the two. With the knowledge obtained above, a new FSI analysis model is proposed; in the FSI analysis model, firstly the deformation of the airfoil in the airflow is analyzed using XFOIL, and after the deformation shape is obtained, UTCart evaluates the aerodynamic performances and the pressure distribution of the converged airfoil, and finally the driving force is recalculated using the pressure distribution newly obtained by UTCart.
Dynamic contact behavior occurs between wheels and rails while the train is running, it is an unsteady phenomenon and becomes more complicated when passing through a curved section. To examine the mechanism of this phenomenon, the authors have developed a dynamic rolling contact tool, called “Wheel/Rail rolling contact simulator,” using a large-scale parallel finite element method (FEM). This tool uses the Lagrange multiplier method to calculate the contact force in the normal direction between the wheel and the rail, and it is possible to obtain a precise contact force distribution within the contact surface. In this paper, we introduce a developed algorithm to make the finite element (FE) model of the curved section automatically. Then, we reproduce the rolling behavior in the curved section with one bogie model for validation of the developed numerical simulation method and discuss the behavior in the contact patch of each wheel. As a result, the calculated summation of the wheel load and lateral force of all wheels indicate a quantitatively good agreement in comparison to the initial condition. Moreover, the dynamic behavior of the bogie during the rolling from the straight section to the transition curve section has been qualitatively good. In the future, improvement of the boundary conditions such as the bottom of the rail, and the use of fine mesh on the wheel/rail contact surface model will be carried out to do the quantitative comparison with the actual phenomenon.
Fretting wear is surface damage caused by repeated slight relative slips between two contact surfaces. In railway applications, fretting wear may occur between the inner ring and the backing ring of an axle journal tapered roller bearing. The authors found that a nonuniform pressure distribution between the inner ring and the backing ring deteriorates the fretting wear; a backing ring grooved on its oil seal sliding surface has been proposed to attain a uniform distribution in the radial direction. It was also shown that the fretting wear can be suppressed by coating the backing ring side face with segment‐structured diamond‐like carbon (DLC) film, which is capable to follow the deformation of the backing ring. In this work, a rotation test of a full‐scale railway axle bearing using a backing ring combined with these two approaches has been conducted to investigate the suppression effect of the fretting wear. Results indicate that the effect of the segment‐structured DLC film decreases in comparison with the case where only the film was applied. It is conceivable that the relative sliding motion in the radial direction occurred since the segment‐structured DLC film was not indented into the inner ring large side face due to the reduction in the contact pressure by the grooved backing ring. It is concluded that the combined effect of the groove and the film is not so apparent.
Path planning is essential for the autonomous driving or advanced driver assistance systems. Efficiency and ride comfort of vehicles is achieved by path planning using smooth reference paths where there is no discontinuity. If we want to ensure the continuity at the connecting points of sequentially generated paths, it is necessary that the curvature at the endpoints of each paths can be specified. In this research, the method to generate such a smooth path is proposed. The proposed paths are composed of three clothoid curves, which have same length and are connected with no discontinuity of curvatures and tangent angles. It is shown that the proposed method can generate a path in at most a few iterations and that the path can be easily tracked by using curvature information. A discussion of preferable combinations of path generating method and path tracking method is also given.
A wheel/rail profile wear is a factor that affects the behavior of railway vehicles such as riding comfort, running stability, running safety and maintenance schedule. To predict wheel/rail profile wear theoretically with dynamic model of the vehicle-track systems, wear coefficient is necessary and these parameters are generally gained from laboratory test such as twin disk test. It is difficult to gain wear coefficient accurately from field data, because the wheel/rail contact conditions which decisive for wear have big variations. On the other hand, there are railway systems in which vehicles of the same type run on the dedicated track with the same operation pattern. In this case, there is possibility to generalize wear coefficient. In this study, we focus on this point, a large amount of wheel profiles from Tokaido Shinkansen, one of high-speed trains in Japan, was investigated. In this paper, wheel wear characteristics of coupled motion is pointed out and these wear characteristics are attempted to demonstrate from a view point of vehicle dynamics.
In the unlikely event of a train collision, the on-board safety features play a critical role in protecting the passengers. The UK’s Railway Safety and Standards Board has established a Railway Group Standard GM/RT2100 (RGS) to develop a crashworthy structural design of interior fittings, and this standard is considered to be one of the most advanced specifications of its type. This standard provides a sled test method to evaluate the injury that is caused to passengers who are seated in a transverse seating arrangement. However, there is no standard to evaluate the injury that is caused to passengers occupying longitudinal seats. Commuter trains in some big cities in Japan mostly depict longitudinal seating arrangements, which is similar to that observed in some metro trains in European countries. A previous study observed that handrails exhibit an ability to reduce the secondary impact velocity of the passenger’s head to interior fittings, and this was ascertained in case studies through numerical simulations. The purpose of this study is to estimate the severity of injuries the occupants of longitudinal seats suffer and to investigate the effect of reducing the severity of injury to passengers using handrails in a sled test. It was found that the passengers seated on a longitudinal seat with a high risk of injuries are those seated third-furthest away from the bench-end partition and that the severity of head and thorax injury decreased significantly because of a handrail.
JR east is developing a new ground coil to handle future speed increments in Shinkansen trains, as it is necessary to expand response distance of ground coils to cope with higher speeds. In addition, when lowering the mounting position of ground coils (as a measure against damage from falling ice), a need arises to adjust (expand) response distance. Therefore, in this research, we investigated measures to expand response distance of ground coils from the view point of feasibility, while maintaining compatibility with the current method. This research proved that an external power supply is effective for expanding response distance, so we have built a prototype ground coil with a built-in battery as a means of external power supply. The voltage detection control circuit supplies battery power only when electromagnetic waves are detected. The circuit configuration also uses a voltage induced by electromagnetic waves. This allows the battery to be used for more than 10 years. The high-speed rotation test confirmed that the prototype ground coil is capable of coping with 400 km/h even 300 mm from the ground coil and the on-board antenna. A falling-weight test confirmed that a new sturdier mounting base was capable of withstanding a load equivalent of 400 km/h. Since it was conformed that the prototype’s sufficient performance, we now plan to conduct a field test for practical use.
Creep damage preferentially extends at a stress concentration portion in components such as steam turbines and boilers. Therefore, in order to maintain reliable operation of these components, it is necessary to clarify the relationship between the creep damage extension process and the stress states in the stress concentration portion. In this study, creep tests using four kinds of round notch bar specimens with different notch radius (notch tip radius 0.1mm(R0.1), 0.5mm(R0.5), 2.0mm(R2.0) and 4.0mm(R4.0)) on a Mod. 9Cr-1Mo steel have been conducted to clarify influence of stress conditions on creep damage extension process and rupture time. Creep rupture time increases with increasing elastic stress concentration factor under the same nominal stress. Distribution pattern of measured void number density from notch root surface to specimen center was different depending on the notch radius. The void number density around the notch root surface is higher than that around the specimen center in R0.1 and R0.5, while the void number density increases toward the specimen center in R2.0 and R4.0. Finite element creep analyses of the round notch bar specimens indicate that triaxial tensile stress yields on the notch root section with different distribution of the triaxiality factor depending on the notch radius. The distribution of the triaxiality factor of each round notch bar specimen corresponded to the distribution of the void number density. Rupture time of the round notch bar specimens can not be predicted by applying the representative stress such as the maximum stress and Mises equivalent stress. A new rupture time prediction procedure using an area average creep damage evaluation method, in which total creep damage accumulated on the notch root section of the specimen was divided by area of the section, was proposed. Rupture times of the notch specimens were accurately predicted by the proposed procedure without showing any dependency of the elastic stress concentration factor.
An artificial intelligence evaluation system using neural network was developed for upgrading the creep damage assessment methodology through image analysis of EBSD(Electron BackScateer Diffraction pattern) maps. KAM(Kernel Average Misorientation) maps were obtained for creep damaged austenitic stainless steel SUS 304HTB and the stratified data were manipulated as the representatives of damage degrees. The system consists of an input layer, intermediate layers and an output layer. As the activation function, ReLU(Rectified Linear Unit) function is used for the intermediate layers and Softmax function is used for the output layer. The evaluation results of the proposed system were compared with the results of the conventional quantitative damage evaluation method. As a result, the estimated damage accuracy of the artificial intelligence evaluation system developed in this research was proved to be improved by about 3.3% compared with the estimated damage accuracy using the conventional evaluation method. Furthermore, the accuracy was improved by about 6.7% after the optimization of the neural network compared with the conventional evaluation method. Moreover, it was proved this system had sufficient robustness through the check tests for the case of extremely missing EBSD image. Thus machine learning utilizing neural network was expected to be a potential method for versatile data analysis applicable to various sort of metallographic study.
Chemical reaction near turbulent/non-turbulent (T/NT) interface in liquid phase turbulent flow was investigated experimentally. The concentrations of reactive species near the T/NT interface in a planar liquid jet with a second-order chemical reaction A+B → R was measured with different stoichiometric mixture ratios. The reactants A and B were premixed into the jet and ambient flows, respectively. The optical fiber probe based on the light absorption spectrometry was used to measure the instantaneous concentrations of the reactive species. The T/NT interfaces were separated into two types (i.e. leading edge and trailing edge) and investigated separately. Mean concentration conditioned on the distance from the T/NT interface was calculated. It was found that the thickness where large concentration change of the reactive species occurs are order of Taylor’s microscale and does not depend on stoichiometric mixture ratio. In addition concentration profile of product R near the T/NT interface does not depend on stoichiometric mixture ratio, while equilibrium limit clearly depend on stoichiometric mixture ratio. This means that near the T/NT scalar mixing does not reach molecular level and chemical reaction is not active.
It was shown in the past bench-mark simulation of cavitation that a lift of hydrofoil is underestimated in the break-down region in the condition of transient cavitation at high angle of attack in which cavitation has highly unsteady behavior. The authors assume that one of the reasons of the underestimation is lack of consideration of liberation of dissolved non-condensable gas and assuming the threshold of cavitation appearance at saturated vapor pressure in all the conventional numerical method of cavitation. In the present experiment of cavitation tunnel, it was shown that the liberation amount of dissolved oxygen is larger in unsteady cavitating flow than in quasi-steady cavitating flow although the cavity volumes are almost same. The experimental result gives a reason on the assumption and indicates that the dynamic stimulation with unsteady cavitating flow causes the liberation of non-condensable gas. In the numerical simulation of cavitation, the dynamic stimulation was modeled by turbulent energy, Reynolds stress, production term and baroclinic torque, respectively. The liberation models were applied for homogeneous numerical method of vaporous cavitation, then the threshold value of appearance of cavitation changes according to the local flow field. In the numerical result, it was shown that the underestimation of lift was partially improved by considering liberation of non-condensable gas by the dynamic stimulation of baroclinic torque in the unsteady cavitating flow.
The flow structures of a submerged vortex that appears in a model pump sump have been fully clarified by performing large eddy simulation (LES) of a model vortex in a simplified computational model. The computational model had a sufficiently fine grid that could resolve the vortex core. The model sump is composed of a 2,500 mm-long water channel of rectangular cross section with a width of 300 mm and a water height of 150 mm and a vertical suction pipe with a 100 mm diameter installed at its downstream end. Our previous large eddy simulations (LES), which used approximately 2 billion grids and were applied to the whole pump sump, has fully clarified the origin and formation mechanism of a submerged vortex and an air-entrained vortex. In these computations, however, the static pressure in the vortex core decreased by only 5 kPa at a channel velocity of 0.37 m/s. The decrease in the static pressure was far smaller than the one for which one can expect initiation of cavitation in the vortex core. In the corresponding experiment, however, appearance of a submerged vortex was confirmed by the occurrence of cavitation in the vortex core. Therefore, the decrease in the static pressure is most likely to be underpredicted in our previous LES. Insufficient grid resolution was assumed to be one of the reasons for this underprediction. In the present study, LES with a sufficiently fine grid was applied to a simplified computational model that represents the stretch of a submerged vortex under a constant acceleration of the vertical velocity. Vertical and tangential velocities obtained by averaging those profiles of a submerged vortex computed in the previous LES were prescribed at the bottom wall of the computational domain as the inflow boundary conditions. In the present LES, the static pressure has decreased by more than 100 kPa. In addition, parametric studies with different initial swirl numbers varied from 0.08 to 10.9 have fully clarified the behavior of a submerged vortex. It is found that a strong submerged vortex appears only at a relatively small range of the swirl-number from 0.8 to 2.
A McKibben-type pneumatic actuator (MPA) has been widely used for various robots, and dynamic motion with MPA has been realized with a simple control method. However, motion analysis of robot using MPA has not been done enough yet due to complicated output characteristics of MPA. The purpose of our research is to establish a motion analysis method of a robot using MPA to realize more dynamic and stable movement. For that purpose, in this paper, we propose a new model of MPA suitable for motion analysis which is not too complicated. The proposed model is derived from linearly approximating the model proposed in our previous study about the length of MPA, and its coefficient can be theoretically obtained. First, verification experiments of the proposed model were performed on MPA of three lengths, and it was confirmed that the correlation coefficient between the proposed model and experimental results was sufficiently large. Next, we verified the effectiveness of the proposed model when the model was applied to an actual robot.MPA was mounted on a two-dimensional leg robot, realizing bending and stretching exercise was performed. It is confirmed that high tracking performance could be realized by pressure inputs design based on the proposed model. The results of these verification experiments indicate that the proposed model is sufficiently effective.
In this study, we develop a new track having a belt made of a fiber and experimentally evaluate its traveling performance. The developed track has a belt made of a high strength and high modulus super fiber. In this track, the tension of the belt is adjustable and the misalignment of the belt along the track travel can be prevented. To evaluate the traveling performance of this fiber track, we conducted two types of experiments in a sandbox covered with loose silica. Traveling tests were first conducted using a single-track traveling test system. In the tests, tracks, which had belts made of various materials and different structures, traveled while pulling various traction loads, and the relationship between drawbar pull and slip ratio of each track were measured. From the experiments, it was shown that the track made of a para-aramid mesh had a high traveling performance. Subsequently, a mobile robot named VAMOS, which is equipped with four tracks made of the para-aramid mesh, was developed. Traction tests were conducted using VAMOS in the sandbox. In the tests, VAMOS traveled on a loose ground while pulling various traction loads. From the traveling tests using the VAMOS, it was quantitatively confirmed that the developed track had high traveling performance on a mobile robot.
Statistical energy analysis (SEA) is a method for understanding energy transfer paths related to vibration noise generation. In SEA, a target object is separated virtually into subsystems among which the transfer of vibration energy can be quantified. Conventionally, SEA is applied to structures that comprise thin plates, such as the bodies of large ships. The structure is then designed so that the transfer of vibration energy is varied to avoid energy being concentrated on any one subsystem. Although SEA is an effective method for preventing vibration noise problems, it becomes critically inaccurate when applied to structures with low modal density. This paper is aimed at clarifying an appropriate measuring process for constructing SEA models with two subsystems that provides high accuracy for structures with arbitrary modal densities. Evaluations of three simplified structures with different modal densities are conducted to determine how to improve the conventional measurement method.
In this study, we propose a frequency estimation method based on an adaptive line enhancer (ALE) algorithm to be used for changing property of the frequency-tunable dynamic vibration absorber (DVA). The method is known to have an excellent noise tolerance feature compared to the conventional method, and is possible to estimate the signal frequency with high accuracy by repeatedly optimizing the filter coefficients. An elastomer composite with controllable stiffness, known as a magnetorheological elastomer (MRE), is used in a dynamic vibration absorber whose natural frequency is tuned adaptively to the disturbance frequency through the application of an external magnetic field. Firstly, we explain the structure of a variable stiffness DVA and the mechanism of the proposed frequency tuning algorithm. Secondly, the test result of the DVA properties, namely, the natural frequency and damping ratio is shown. By taking full advantage of the frequency adjustability of the proposed DVA, we then evaluated the real-time vibration control performance for an acoustically excited plate having multiple resonant peaks. The sweep excitation tests show that the vibration of the structure can be effectively reduced with an improved performance by using the adaptive-tuned DVA to be used with the proposed frequency estimation algorithm.
Active vibration suppression should have high performance and has been studied and applied over the years. However, its practical applications are limited to large objects due to its implementation cost or design man-hour. In previous study, we proposed a distributed general-purpose active vibration suppression system which can be applied to various relatively small-size equipment with add-on style. Additionally we have developed a network distributed controller which have I/O number scalability. In this paper, the development of the active vibration suppression system for electron microscope is described as an application example. The electron microscope is an inspection device which observes sample with an electron beam irradiated from the top of its column. This column has two inclining modes which, when affected by vibration, cause image blur. Therefore, to avoid their vibration, a biaxial vibration suppression system which damps two inclining modes was developed. In this process, first, an inertial actuator using multilayer piezoelectric devices was developed as the damping actuator, and its characteristics were investigated. Then, the biaxial active vibration suppression system was constructed with the actuators for a dummy column, which had two inclining modes and was able to reproduce the vibration characteristics of the electron microscope. Finally, a controller with two inputs and two outputs was designed for the biaxial active vibration system. Evaluation of the vibration damping performance showed that both modes were damped in more than 15 dB.
This report describes the study on the lubrication characteristics of porous journal bearings, which were made with oil impregnated sintered materials having some hydrodynamic shapes, to apply them for a DC Spindle Motor’s bearing system. Herring Bone (I & II), Three Lobed Type or Sleeve as radial hydrodynamic shapes were proposed, and four kinds of specimens were produced for porous journal bearings with pivot supported shaft conditions. They were examined experimentally to optimize the hydrodynamic shape of porous journal bearings by measuring the lubrication characteristics at the shaft starting state under sine-wave vibrated conditions. This report particularly refers to the experimental examination into the shaft rotating behaviors, which were identified the rotational modes with Frequency Spectrum Analysis of Time History Waveform (T.H.W.) of the shaft such as the above-mentioned lubrication characteristics under the same conditions. Furthermore, it was investigated to discuss the influences of vibrated frequency changes to the lubrication characteristics by measuring the T.H.W. of the shaft under the above conditions.
Eddy current method which is uninfluenced by oil film rupture or viscosity change was employed as a simple in-situ estimation method of bearing load acting on deep groove ball bearing operating under low rotational speed. The estimation of the bearing load was performed through the observation of output voltage change of eddy current flaw detector. The output voltage is influenced with the inductance change of the coil in probe that is decided by the mean gap between ball and outer ring which has weak leakage magnetic flux. Since the mean gap is determined with the elastic deformation of contact point due to the bearing load, then measurement of the bearing load becomes possible with the observation of output voltage. The excitation frequency which shows the maximum sensitivity for the change of mean gap is determined by the balance of the increasing effect of eddy current intensity according to the increase of excitation frequency and of the skin effect decreasing the penetration depth of eddy current in high frequency region. Since the leakage magnetic flux region on the rear surface of outer ring in high excitation frequency case becomes narrow due to the skin effect, the evaluation of mean gap using high frequency is carried out within the thin gap region in the vicinity of contact point of ball and outer ring, compared to low excitation frequency case having thicker mean gap due to the wide leakage magnetic flux region. Then, the output voltage change for the bearing load becomes large and measurement sensitivity is improved. As mentioned above, the basic characteristics of eddy current method for the measurement of bearing load were examined, and the potential of this technique as the simple bearing load measurement method was cleared experimentally.
Mechanical systems have many joints within. It is well known that the parameters such as contact stiffness, static friction coefficient, kinetic friction coefficient and attenuation coefficient affect static, kinetic, thermal and motion characteristic of them strongly. In these parameters, the static friction coefficient reigns the character of maximum fixing resistance. However, conventional devices cannot be applied to measure the precise static friction coefficient on the coupling surfaces due to their tiny contact surface, unstable loading method and moment force acts on the contact surface. In this paper, we report a novel device we developed for measuring the static friction coefficient between fixed coupling surfaces which solves problems of the conventional devices. The new device enabled stable surface contact and uniform surface pressure by deploying the bearing unit with aligning function at the loading system. In addition, the frictional force applied on the same plane of the contact face of the specimen eliminated moment force. Furthermore, test result shows no component force except the load and frictional force. Moreover, the peak of the frictional force was successfully captured by choosing the proper sampling rate on data logger. Finally, the verification test confirmed that the developed measurement device is able to evaluate the influence of the surface roughness on the static friction coefficient.
The frame stiffness in a racing bicycle might influence not only toughness as the frame structure but also performance of an athlete. The purpose of this study is to clarify biodynamic relations between the frame stiffness in a racing bicycle and the physical loads of an athlete by using a forward dynamics simulation model. The human body structure was represented by the 13-rigid-links and 23-degrees-of-freedom model. Based on the theory of multibody dynamics, the frame structure was expressed by combination of 12 rigid pipes, and the frame stiffness was modeled by rotational springs at the connecting joint between the rigid pipes. Spring coefficients were changed according to the thickness of the frame pipes. The pedaling load from the crank was computed by the angular velocity and angular acceleration of the crank. Moreover, the driving force in the bicycle was additionally defined to consider the influence of the frame weight on the human joint load. The human body model was driven by the joint toques to minimize the cost function consisting of the joint loads in the human body and the driving force in the bicycle, and also to keep desired angular velocity of the crank. Validity of the simulation was evaluated by comparing the joint angles and torques with the measured ones. As for the result, the larger stiffness of the frame resulted in smaller the joint loads in the human body, and optimal stiffness would be determined by the balance between the joint loads in the human body and the driving force in the bicycle.
Vibration suppressors are used to change the natural frequency of an elevator rope and prevent resonance. The displacement of the parts of the elevator rope at both the ends is small compared to that of the center part of the rope; therefore, it is not necessary to position the vibration suppressors in the parts on either ends. In this paper, three types of theoretical solution to the free vibration of the rope is obtained, in the case where vibration suppressors are located between x=pL/N and (p+q)L/N, where L is rope length, p, q and N(=2p+q) are integer. Obtained natural frequencies are 2N/(N+1) times, 2N/(N+p) times and 2N/(N+p/2) times of the original natural frequency. Further, finite difference analysis of the rope vibration with vibration suppressors is also performed to obtain the frequency response curves. Resonance frequencies obtained by the finite difference analyses are in good agreement with the natural frequencies for the free vibration. Vibration modes obtained by the finite difference analyses are similar to that for the free vibration.