This paper presents a study to reduce flexural vibrations of rail vehicle carbody, which have large impact on ride quality, by utilizing deformation of an elastic body as a dynamic vibration absorber (DVA). Donut-shape (called "torus" in this study) is proposed as the elastic body considering practical application to rail vehicles. A numerical model to design an elastic torus using finite element (FE) analysis was developed, and it has been demonstrated that the shape and the size of a torus can be determined so as to have desired natural frequency by the FE model. A torus dedicated to a DVA for rail vehicles made of rubber filled with water was designed and manufactured actually. In order to validate the DVA effect of the water-filled elastic torus, a series of stationary vibration tests using a commuter-type test vehicle with stainless steel carbody was conducted. Since the tested vehicle showed two peaks on the frequency response function (FRF) measured on the floor and both of them should be reduced simultaneously to improve ride quality of the vehicle, the authors applied the elastic torus as "double-decker" style (stack a torus up on another torus). Both of the peaks were successfully reduced by applying the double-decker elastic torus. It has been confirmed that the multi-modal vibration reduction effect was achieved because a set of double-decker torus act like a two-degrees-of-freedom (2-DOF) system. Influence on the vibration reduction effect by the difference of the number of applied tori and their distribution on the floor were investigated.
This study aims to create a system that can be used to evaluate vehicle characteristics while simultaneously controlling human body behavior through numerical simulations. The proposed system consists of a vehicle model, a human body dynamics model, and a musculoskeletal model. In the present paper, a human body dynamics model using multibody dynamics is proposed. However, attempting to implement a whole-body model would necessitate dealing with multiple degrees of freedom and give rise to problematic phenomena. Furthermore, the influences of human motion are uncertain and difficult to parameterize. Accordingly, in the present research, the human model is limited to the head and trunk of a human body riding inside a vehicle. This human body dynamics model is composed of an internal model and an external model. The internal model incorporates a motion control model. The internal model, which is composed of an inverse model and a forward model, generates commands to control body motion, while the external model simulates the actual body motion. Then, in order to identify the parameters of the motion control model, the motion of maintaining posture is measured using a simple experimental device that can simulate horizontal acceleration applied to a subject. In order to demonstrate the effectiveness of the proposed human body dynamics model, a simple human dummy model (which simulates the experimental model used for experiments such as automobile collisions) that consists of only a spring and a damper was created. Comparing this dummy model with the human body dynamics model reveals that the human body dynamics model can simulate details of human motion that the simple dummy model cannot.
In recent years, the speed of express train has been raised by the improvement of technology about the vehicle, truck and electric. However, the speedup of railway vehicle caused high frequency vibration, and thus riding comfort is deteriorated by the resonance of the back seat. In this study, a passenger model with multi-body dynamics (MBD) was established a seat design guideline to reduce the vibration including high frequency. First, in order to construct the passenger model, the authors investigated the vibration characteristics of the passenger and the seat by a vibration test. The vibration test was performed under inputting linear sweep wave from 0.2 Hz to 40 Hz in the front-back or the vertical directions, and accelerations of the passenger's head, shoulders, chest, belly, thighs and the seat were measured. Next, a passenger model with 13 masses and 23 degrees of freedom was constructed by using MBD. Afterward, simulation studies were carried out under linear sweep wave, and the authors compared the simulation result with the experimental one. The simulation result shows the good agreement with the experimental one, and therefore the validity of the passenger model is verified.
This study proposes a newly developed structure for a frequency-dependent orifice for an air spring of a passenger train vehicle. This frequency-dependent orifice reduced both the rolling motion and the vertical vibration at high frequency. This paper also presents the numerical simulation results. Optimal settings of the springs and dampers of the bogie are essential for reducing the uncomfortable carbody motion while the train is running. The air springs provide insulation and damping through air compressibility in the bellows and pressure loss of the airflow passing through an orifice installed between the air spring and the auxiliary reservoir. The frequency characteristics of a standard air spring show a peak at a frequency of ~1 Hz of the rolling motion of the carbody. A smaller orifice seems to be one of the solutions to change this characteristic. However, this method worsens the damping property at high frequency. To solve this problem, a frequency-dependent orifice with active vibration control technology has been proposed. This orifice improves the vertical vibration at low frequencies and the rolling motion of the carbody; however, it does not improve the properties at high frequencies. The results of our previous research left issues such as the need to improve the high-frequency response in a future study. The results of this study show that our newly developed frequency-dependent orifice effectively reduces the vertical vibration at high frequency with no external power supply. We are planning further simulations including realistic disturbance and a running test using a prototype of the frequency-dependent orifice.
It is known that the center pin of a car body strikes strongly against the lateral displacement stopper of the bogie when the vehicle vibrates widely in the case of earthquake motion with a predominant frequency of over 1.4 Hz. During such movement, and due to considerably large wheel/rail lateral force and bogie rolling, etc., there is a risk of the wheel jumping to a height above the wheel flange, which in turn may result in derailment. It is thought that larger gap between the lateral displacement stopper and the center pin will improve running safety by buffering the strong impact against the lateral displacement stopper and because of a better vibration-damping effect of the lateral damper. Running safety effectively improves using a specially designed anti-seismic lateral damper which can provide large damping forces during a major earthquake. Accordingly, in this research, for the purpose of improving running safety in the case of an earthquake, a crushable lateral displacement stopper was developed with the same nominal gap from the center pin as currently used devices, in the normal condition, but which can expand in the case of a strong impact due to a large earthquake, in order to ensure vehicle running stability and quality. The crushable stopper is designed to be used together with a specially designed anti-seismic lateral damper. RTRI developed a mechanical crushable stopper with a mechanical fuse for the movable mechanism in order to expand gap in abnormal conditions, in such major earthquake. The seat of the lateral displacement stopper rubber gets displaced in the same direction as the expanding gap, if a predetermined load (a set moving load) acts on the stopper. Moreover, repeated loading test was carried out to confirm the influence of the repeated loading during usual operation.
This study proposes a track condition monitoring technique using car-body acceleration that can be easily measured by an in-service vehicle for the sake of an increase in safety of railway transportation. This paper demonstrates the possibility of estimating track irregularities of conventional railway tracks using car-body acceleration only. The methodology proposed uses inverse dynamics to estimate track irregularity from car-body acceleration, applying a Kalman filter to solve this problem. This technique estimates the track irregularity in the longitudinal plane (track geometry and 10m-chord versine). The Kalman filter is able to apply to inverse analysis by expressing track geometry as a random walk model, and incorporating the model in an equation of state. The estimation technique can support a change of the vehicle velocity by selecting an appropriate impulse response in the measurement equation for the vehicle velocity. Estimation results in simulation and full scale tests revealed that the proposed estimation technique is effective for track condition monitoring with acceptable accuracy for conventional railways.
We report on a system of “Virtual running test environment for railway vehicles” based on the Hardware-In-the-Loop Simulation (HILS) approach that can replace most of the parts of an actual running test with a bench test and a computer simulation. If it is possible to reproduce the motion of a railway vehicle running on a track in detail by the use of the “Virtual running test environment for railway vehicles” system, an acceleration of the development process and the improvement of the quality of the railway vehicles can be expected. In this report, we introduce the entire configuration system. We introduce a number of actual uses of the system to achieve test objectives such as “Reproduction of the actual running test of a train set on the bench test,” “Performance evaluation of component equipped with the actual running vehicle,” and “Performance evaluation of unrealized virtual component.” Finally, we demonstrate some results. As an example, we conduct an excitation test of an actual car on the rolling stock testing plant in RTRI. We reproduce the actual running conditions of a three-car train and obtain good agreement between the HILS test and the target results.
In this paper, the authors propose “regenerative brake notch” method which follows the maximum regenerative brake force according to the vehicle speed. This specially designed brake force reference selected by the train driver aims at saving the kinetic energy which originally would be dissipated by the mechanical brake in the high speed range. By means of the regenerative brake notch, it is able to save much kinetic energy, but the brake section is slightly prolonged. Another drawback of this method is how to inform the starting braking point to the driver, because this brake system does not generate constant regenerative brake force all over the speed range. To cope with this problem, the authors propose the utilization of imaginary train that run along with the real train in combination with the preinstalled train information control system (TICS) to obtain the correct starting braking point and inform to the driver. The running profiles of these trains are compared to obtain the correct starting braking point. By means of this method, only the point to start braking is required and the driver can regulate the brake force in the lower speed range to stop the train at the station. In this paper, the energy saving effect by the regenerative brake notch is compared with the conventional constant deceleration brake notch in terms of running distance, error of the starting braking point and rail adhesion coefficient. Through the calculation study, the energy saving effect and usefulness of the proposed regenerative brake notch is revealed.
Innovative electro-magnetic energy conversion device has been developed. This device has co-axial configuration with liquid metal filled inside under applied magnetic field. The azimuthal liquid metal flow is decelerated by Lorentz force acting as a body force. The rotational torque continuously increases with excessive kinetic energy converted into electric energy by increasing magnetic field. The static and dynamic characteristics of the device have experimentally investigated with AC servo-motor as a driving source. The experimental results show that the rotational torque can be controlled with electric power extraction by applied magnetic field and external load resistance. The liquid metal inside the device is driven in the azimuthal direction directly by the electrically insulated propeller on the shaft and the electric power is extracted with proportionally to the square of shaft rotational speed. The required rotational torque increases with applied magnetic flux density due to dominant eddy current induced by non-uniform magnetic field in azimuthal direction. The constant rotational speed can be maintained with power generation by controlling applied magnetic flux density even for increasing input torque. It was clarified that the time constant for the control of the rotational speed becomes smallest when the changing time of applied magnetic flux density and that of input torque are equal.
In the design of the Advanced Sodium-cooled Fast Reactor in Japan, the mean velocity of the coolant is approximately 9 m/s in the primary hot leg (H/L) piping, which has a diameter of 1.27 m. The Reynolds number in the H/L piping reaches 4.2 × 107. Furthermore, a short elbow, which has Rc/D = 1.0 (Rc: curvature radius, D: pipe diameter), is used in the H/L piping to achieve a compact plant layout and reduces plant construction costs. In the H/L piping, flow-induced vibration (FIV) is a concern due to the excitation force caused by pressure fluctuation in the short elbow. In a previous study, the relation between flow separation and pressure fluctuations in the short elbow was investigated under the specific inlet condition of a flat velocity profile of time-averaged axial velocity and relatively low velocity fluctuation intensity. However, the inlet velocity condition of the H/L in a reactor may be a highly turbulent non-uniform profile owing to the complex geometry in the reactor vessel (R/V). In this report, the influence of inlet velocity condition on the unsteady velocity characteristics in the short elbow was studied. Although the flow around the inlet of the H/L in the R/V could not be simulated completely, the inlet velocity conditions were controlled by installing a perforated plate, which appropriately plugged the flow holes. Then, controlled flow patterns were established at a position 2D upstream of the elbow inlet. Observed flow structures by particle image velocimetry indicated that the inlet velocity profiles affected a circumferential secondary flow, which then affected an area of flow separation at the elbow. It was also found that the velocity fluctuation at low frequency components observed upstream of the elbow could remain in downstream of the elbow though its intensity was attenuated.
Noticing the color variation of torrefied woody biomass with pyrolysis process, a non-invasive method to estimate energy properties such as elemental contents, higher heating value and energy yield is investigated. When the torrefied biofuel is produced and utilized, the quality control concerning energy properties is indispensable. The energy properties of torrefied woody biomass are correlated with its mass yield, and the relationship between mass yields and colorimetric values defined by CIELAB is experimentally examined. The results obtained for torrefied Japanese cedar are as follows. (1) The energy properties of torrefied Japanese cedar are expressed by simple relations of mass yield. The optimum torrefaction condition to produce torrefied biofuel can be evaluated by the mass yield. (2) To estimate the mass yield of torrefied Japanese cedar, the experimental correlations with colorimetric values are proposed. In the case of the sap-wood and heart-wood samples for brightness, L* above 45, the mass yield is correlated with L*, and in the case of the sap-wood, heart-wood and bark samples for L* below 45, the mass yield is correlated with color coordinate, a*. From the comparison between predicted mass yields and experimental data, it is found that the proposed experimental correlations can estimate the mass yield within an accuracy of ±10%. Therefore, the energy properties of torrefied Japanese cedar is easy to be checked by using the present non-invasive estimation method with colorimetric values.
We investigate a topology optimisation based on the level set method for a design problem of carpet cloaking devices. In topology optimisation of carpet cloaking devices, we need to calculate the electromagnetic response in a semi-infinite domain. We use the boundary element method (BEM) for the electromagnetic analysis since the BEM is more suitable to topology optimisation in wave field than the finite element method; the infinite domain can be evaluated exactly and mesh generation is required only on a boundary with the BEM. Along with the detailed formulation of the BEM-based topology optimisation, we present some numerical examples of design for carpet cloaks. We have confirmed that the designed carpet cloaking devices effectively work for the cases where permittivity, wavelength and angle of incidence are fixed. In addition, we have confirmed that cloaking devices for perturbed permittivity and wavelength can be obtained by redefining the objective function with the KS function.
The demand for robots in various application fields has been increasing in recent years. Robots are becoming active in a greater variety of environments, so there is a growing need for higher robot mobility that ensures safe and smooth movement. That need has drawn attention to the omnidirectional vehicle (ODV). ODV's can move forward and backward and turn to the left and right, but they can also move directly sideways and diagonally, and rotate in a fixed position. This high mobility enables an ODV to change direction in a small space, to parallel park easily, and perform other adaptive movements that are suitable to the vehicle environment. Omni-directional mobility has previously required special mechanisms that have been associated with problems of durability and stability. To address those problems, we have developed a nonholonomic ODV that uses two-wheel modules equipped with ordinary tires. However, the stability and smooth motion of the vehicle is usually affected by the load from the road surface, so a control system that distributes that load appropriately over all the motors is needed. Another problem is that there may be a loss of total driving force and vehicle speed under conditions in which the tires spin freely without traction. To maintain total driving force, a torque compensation system for each of the wheels is important. Here, we propose a method for load distribution control and a method for skid compensation control and present test results that show the effectiveness of the proposed methods.
In order to overcome adaptation deficiency of PHEV power assembly controlling strategy in complicated driving cycle, adaptive matching controlling strategy of driving-cycle fuzzy recognition was presented. The driving cycles of automobiles were classified in 3 types: rural cycle (RC), urban cycle (UC) and expressway cycle (EC). Based on information of automobile speed and acceleration, environment cycle is recognized via fuzzy inference, on those basis, adaptation of power matching model was realized. Moreover, simulation of power matching adaptive controlling strategy designed in this paper was conducted in ADVISOR. The designed controlling strategy and the electric-assisted controlling strategy were compared and analyzed. The results indicated that compared with electric-assisted controlling strategy, power-matching adaptive strategy of PHEV based on driving-cycle fuzzy recognition could further reduce energy consumption and exhaust emission, which proved that the newly designed controlling strategy could adapt driving cycles and enhance intellectualization of full vehicle.
The Niigata-ken Chuetsu-Oki Earthquake (hereinafter referred to as “the NCO Earthquake”) occurred in 2007 with a hypocenter very close to Kashiwazaki-Kariwa Nuclear Power Station of Tokyo Electric Power Company Holdings, Inc. (hereinafter referred to as “TEPCO”). TEPCO's subsequent plant investigation, earthquake response analysis using observation records and large-scale shaking table tests have provided us valuable experiences, including the fact that safety related components were undamaged and non-safety-related components sustained only limited damage. This paper describes the time history analysis of components whose damage states are based on excessive stress or deformations due to elastoplastic behavior. The input ground motions for the time history response analysis were records from the NCO Earthquake. The components were modeled with simplified bi-linear models representing their load-deflection characteristics; one of the analysis results was the maximum ductility factor of each component when subjected to the NCO Earthquake motions. Based on the assumption that increasing ductility factor values is correlated with damage to components, this paper discusses the threshold of the ductility factor that affected to the damages to components. This paper concludes that the ductility factor could be considered as a damage indicating parameter (DIP) to components whose damage states are a function of plastic deformation. If this ductility factor is reflected in the seismic design, it is considered to contribute to the improvement of the diversity and the reliability of the seismic design system of nuclear power plants.
The present paper deals with the vibration control of a suspended simple pendulum system, namely, a model of a crane rope and a load mass, by the lateral motion of the support. Wave control of the acceleration of the support was derived based on the connecting condition of a real pendulum (rope and mass) to multiple wave-controlled homogeneous simple pendulums that exist virtually above the support. Velocity and position feedback control of the support was added in order to position the support at other than the original position. During winding up or down of the load mass, the system becomes a non-homogeneous simple pendulum system and the wave propagation exhibits a kind of mode localization that reduces the vibration control performance. The feedback control canceled the mode localization and provided better control performance than the pure wave control. The effective feedback coefficients of systems during winding up and down of the load mass were investigated. Based on simulation and experimental results, the proposed control was demonstrated to be useful and practical for real crane systems.
Recently, in order to decrease the number of traffic accident, various automotive safety technologies have been studied. As one of those technologies, the authors have proposed the autonomous frontal obstacle avoidance system, which recognizes a frontal obstacle such as a pedestrian, predicts the location of collision based on the obstacle's motion and avoids collision by autonomous evasive steering. The proposed system calculates avoidance trajectory once at the start of avoidance. Therefore, it cannot handle the situation that the obstacle's motion changes. Especially in the case that the obstacle accelerates after its appearance, the system will cause a collision with the obstacle. Since pedestrians' motion in the real world is not always constant, change of motion of the obstacle must be considered. Therefore, in this paper, the authors improve the system so that it can handle those situations by adding an updating function of avoidance trajectory. This paper first describe the derivation of avoidance trajectory from the vehicle state in evasive motion. Next, the autonomous frontal obstacle system is redesigned by building peripheral functions such as collision forecasting functions and appropriate trajectory selection function and integrating them. The redesigned system is examined by numerical simulations and compared with the previously proposed systems to verify the validity and effectiveness. The results indicate that the system proposed in this paper is valid and more effective than the previously proposed system.