It is important to estimate the strength of the vehicle structure in the initial design stage of the vehicle development. The buckling of the plate is known to occurs in thin-walled structures before yielding, however, the structures can withstand loads even after buckling. The load acting on the thin-walled beam constituting the vehicle frameworks may be not only a compressive force and a bending moment but also a torsional torque. The purpose of this paper is to derive the equation for the torsional post-buckling behavior of a thin-walled square cross-section beam. When a torsional torque acts on a square cross-section beam, in-plane shear stress acts on the four plates constituting the cross section, which may cause shear buckling. Assuming that the same buckling deformation occurs on the four plates, Timoshenko's approximate expression can be applied as an out-of-plane displacement after shear buckling. The post-buckling stress distributions are calculated as a function of the out-of-plane displacement amplitude. Also, the post-buckling torsional constant and relationships between the torsional torque and the stresses are derived on the basis of Karman's effective width theory. The validity of derived expressions is examined by comparing with the computation results by the finite element method (FEM). As a result, in the target dimensional range of the plate (width-to-length ratio 1/3 or less), the absolute difference values of the derived relationship between the torsional torque and the maximum Mises stress are within 10% for FEM results. However, it is found that instable phenomena such as secondary buckling may occur as the width-to-length ratio of the plate becomes smaller. From the above results, it is found that the relational expression derived in this paper is sufficiently useful for calculating the torsional strength of a thin-walled square cross-section beam.
The relaminarization process of a turbulent boundary layer under a sink flow was investigated experimentally. The boundary layer was accelerated because of the contraction of the flow area. The mean and fluctuating velocity components were measured using a hot-wire anemometer. With relaminarization, the fluctuating velocity, which was normalized by the free-stream velocity, decreased. The degree of decrease differed between the streamwise and wall-normal components, depending on the distance from the wall. The conditional probabilities that two hot-wire probes separated in the spanwise direction simultaneously observed turbulent and nonturbulent flows were obtained. A spanwise-wide turbulent region was spread near the wall, but its width decreased as the distance from the wall increased. When the layer was relaminarized, this decrease in the spanwise width started near the wall. The low-speed streak spacing of the coherent structure was obtained from the lateral correlation coefficient of the streamwise fluctuating velocity and average spanwise spectra, and both parameters were somewhat consistent. Both the spanwise spacing of the streaks and the vertical scale of the coherent structure increased because of relaminarization. The conditional lateral correlation coefficient of the streamwise fluctuating velocity based on turbulence or nonturbulence was calculated. The streak spacing was slightly wider under nonturbulent conditions. This trend is consistent with the spreading behavior of the streak spacing, owing to relaminarization. With relaminarization, coherent structures became less frequent.
Based on the changes of catalyst properties, a model was constructed to estimate the rate constants of Standard-SCR, NH3 oxidation, and NO oxidation reactions over hydrothermally aged Cu-CHA catalyst. Moreover, the rate constants obtained by the constructed model were applied to the model for estimating NOx conversion over fresh catalyst constructed in previous studies, and the NOx conversion over hydrothermally aged catalyst was estimated. As a result, the calculated NOx conversion over hydrothermally aged Cu-CHA catalyst was in good agreement with the experimental results.
Vibration power generators that generate power from environmental vibrations are attracting attention as independent power sources for IoT sensors and the like. We have evaluated the power of an electromagnetic induction type vibration power generator connected to a load resistance when the environmental vibration is a sine wave and white noise. However, we did not evaluate the effect on the generated power of the converter that converts the AC output of the vibration power generator into a DC output. There have been several studies on converters connected to vibration power generators. It has been reported that a buck-boost converter can adjust the input resistance when the environmental vibration is a sine wave. However, there have been no reports on whether the input resistance can be adjusted when the environmental vibration is white noise. In an electromagnetic induction type vibration power generator, the resistance to maximize power is very different between a sine wave and white noise. Therefore, whether or not the converter input resistance can be adjusted even in the case of white noise is an important issue. We made a prototype converter with buck-boost capabilities and adjustable input resistance. The prototype was connected to an electromagnetic induction type vibration power generator, and the DC power for white noise with different acceleration levels was evaluated. As a result, we confirmed that the prototype converter was effective when the environmental vibration was white noise.
This paper addresses a method of classifying modal clusters to realize resonance control. Especially in this paper, this method is applied to the simultaneous placement of resonance frequencies of the multiple modes belonging to a specified modal cluster through a structural modification to a limited subsystem. The method is useful for separating the resonance frequency of the modal cluster to be designed from the peak frequency of the excitation spectrum all at once. Therefore, the paper proposes a method to consider the multiple modes of a whole structure formed from the same mode of the subsystem belonging to the same modal cluster by using the modal contribution analysis method which is proposed by the authors. Then, under the above definition of a modal cluster, we introduce a method of moving the resonance frequencies of multiple modes belonging to the same modal cluster together without significantly changing the resonance frequencies of multiple modes belonging to other modal clusters. Finally, its usefulness is shown by a numerical example.
In this paper, we present a new approach to data-driven update of table-typed controller gain in tracing control system. This type of control system is used in various precision processing systems for industrial products. It is important for a tracing control system to be maintained so as to achieve the accuracy of positioning for reducing the gap between the workpiece and the machining tool during the operation. In addition, it is also important to update the elements of the table in the controller as faciley from the practical points of view. The update of the controller by directly using the data without mathemaical models is one of the rational ways to realize them. From these backgrounds, we have previously applied FRIT (Fictitious Reference Iterative Tuning), which is a data-driven controller tuning method with only one-shot experiment, to update the table-typed controller in the tracing control system. However, this method requires calculations using a fictitious inverse system of an implemented controller, which leads to computational errors. In this paper, we propose a method utlizing VIMT (Virtual Internal Model Tuning) to update the table-typed controller without using its inverse system. Moerover, we update not only each gain in the table but also each corresponding range to improve the tracking accuracy of tracing control system.
In general, semiactive dampers have high performance of vibration control compared to passive dampers, but in order to adjust an optimized damping force for the damper, several condition of vibration systems, such kind of force, acceleration and displacement etc., is always monitored using sensors, and the resisting force of the damper is switched by the information from the sensors. One of the authors has researched before about an electromagnetic damper which converts kinetic energy into electrical energy and generates damping force by dissipating the energy electrically through terminal circuit of the generator. Since a voltage which is generated by the generator is proportional to a rotational speed, a velocity of the damper can be determined by measuring the voltage. In this study, a unique sensor less semiactive damper that generates the electromagnetic damping force by using the generator instead of the speed sensor in order to obtain switchable damping and improve the vibration control effect without any sensors. By connecting the terminal circuit of the generator with a resistor, rectifiers, a solid state relay and a capacitor, the voltage from the generator rises when the acceleration or speed exceeds a border, causing the relay to close and the damping force to passively switch. It is possible to adjust the switching timing by the capacitor. In order to confirm the effects, the damper was fabricated, and its resisting force characteristics of the damper were verified by experiments. Next, seismic vibration tests were conducted using a shaking table to investigate the vibration control effect of the damper by comparing the experimental and calculated results.
To predict traumatic injuries using a computational model, accurate mechanical properties of biological materials are required. Especially, soft tissue is a viscoelastic and rate sensitive material that exhibits the decaying stress response when a constant displacement is applied. Thus, it is important to precisely formulate the phenomenon of a stress relaxation, which is readily applicable to computational models. In the current work, we newly developed an identification method of time constants and Young’s moduli for the stress relaxation response of biological soft tissues by assuming that soft tissues can be described by a generalized Maxwell model. Firstly, the decaying stress response was decomposed into a set of slow-to-fast stress components using a low-pass filter. Subsequently, we identified the time constants and Young’s moduli for slow and fast variations independently by solving the optimal problem, in which the correlation coefficient was maximized between each stress component and a corresponding normalized stress component. This method is computationally cost efficient and can semi-automatically determine the number of springs of Maxwell model. By applying the newly proposed method to the experimental data obtained for neural fiber bundles and skeletal muscle fiber bundles subjected to uniaxial stretching, we successfully demonstrated that the stress relaxation response can be well predicted for the mechanical change even in the short time range (0.1–1 s) in addition to the long time range (10–100 s).
In this study, we researched correlations between the joint moments and the variables obtained from the experimental data to estimate the driver's joint moments in order to simulate the driver's behavior during turning considering the driver's intention when riding on a stand-up type Personal Mobility Vehicle (PMV). First, we measured human behavior, handle reaction force, and floor reaction force using motion capture, 6-axis force sensor, reaction force meter attached to the foot. From the obtained external forces and human behavior, the driver’s joint moments were calculated using inverse kinematic analysis and inverse dynamic analysis. The loads on the joints during the turn was examined, and it was found that the loads were greater in the shoulder, hip and ankle joints. Therefore, correlations such as external forces, vehicle velocity, and joint angle to the joint moments of the shoulder, hip, and ankle joints were investigated. As a result, it was found that the correlation with external force was high. Accordingly, the joint moments of the shoulder, hip and ankle joints were estimated by linear multiple regression analysis using the external force. The joint moments of the shoulder and ankle joints were estimated with good accuracy, but those of the hip joint were inaccurate. From these results, it can be interpreted that the joint moments of the shoulder and ankle joints depend on the external force applied to the hands and feet.
We propose a method for numerical material testing that does not explicitly assume boundary conditions in homogenization analyses for microstructures with random or localized inhomogeneities. Specifically, instead of the periodic constraint condition on the fluctuation displacement in the RVE, a condition is imposed such that the domain integral of the gradient is zero, which preserves the definition of macroscopic strain in the homogenization theory while also suppressing rigid body rotation. Then, a scale-separated variational problem is defined with this condition introduced as a constraint. Next, the governing equations of the two-variable boundary value problem (BVP) are derived by applying Lagrange multiplier method to this variational problem. The macroscopic BVP is degenerated to a material point, and the microscopic BVP is transformed into a form specialized for numerical material testing and then discretized by the finite element method (FEM). The discretized equations are extended by adding the degrees of freedom corresponding to macroscopic stress and strain. Since the proposed method does not require any restrictions on the external shape of the microstructure and the extraction of external boundaries, it is relatively easy to implement into the FEM. Several numerical examples are presented to demonstrate the validity of the proposed by comparing the results with those of the conventional approach.
In the wire and arc additive manufacturing (WAAM) technology that melts and deposits metal wire materials by arc discharge, it is possible to use a wide variety of wire materials and change the composition locally. However, CuSn alloys with a high Sn content have poor ductility and are difficult to process into wires. In this study, we proposed an accumulating method in which Sn wire is fed from the outside to the molten pool when deposition process using CuSn alloy wire with a low Sn content. In this paper, the relationship between wire feed rate and actual Sn content rate was investigated. Then, tensile tests and acoustic tests were conducted. As a result, Sn content rate of the additively manufactured materials was changed by varying the Sn wire feed rate. Moreover, it was clarified that the Sn content rate influences on mechanical properties and acoustic characteristics.
Since mechanical performances of the connecting part in the frame structure generally deteriorate, the mechanical performances may also deteriorate in the connecting part between the modules. If the design target is based on the existing parts, the boundaries divided into modules are naturally limited to the boundaries of the existing parts. In order to extract appropriate module boundaries, we propose a method using elements of finite element analysis which are smaller units than existing parts. In this study, we propose a modular design method of frame structure that suppresses the decrease of mechanical performances by using DSM (Design Structure Matrix) analysis. In DSM construction, not only the connection information of parts but also the von mises stress or strain energy indicating the mechanical state is added to the DSM, so that the module boundaries are not generated in that area with high mechanical loads. As a result, we showed that the mechanical performances of the modular structure extracted by adding the mechanical indicators are improved compared to the modular structure extracted only by the connection information of the parts.
To achieve simple and accurate modeling of human-like behavior with the aim of realizing a model-based design (MBD) methodology incorporating vehicle occupants, this research applied a simplified two-mass system for the upper body of a vehicle occupant and control laws derived based on natural human characteristics. To express the behavior of a seated occupant in response to lateral inputs, the motion of the upper body with respect to the vehicle and the motion of the head with respect to the upper body are modeled using a two-mass system projected onto a plane that includes the horizontal and vertical vehicle axes. Torques to maintain the posture calculated by the control laws were applied to each joint. This research focused on somatic and vestibular sensations as natural human characteristics. Somatic sensations are a source of information concerning the relative spatial and positional relationships between the body and its supporting surfaces (in this research, a vehicle). Seated occupant behavior to hold the upper body upright in the vehicle was defined as somatic feedback, which calculates torque based on the upper body posture angle. On the other hand, vestibular sensations are a source of information concerning the acceleration applied to the head. The vestibular system contains two types of receptor organs: the semicircular canals and the otoliths. The semicircular canals are the receptor organs for rotational acceleration of the head and are sensitive to rapid head motions. The otoliths are the receptor organs for linear acceleration of the head and are sensitive to slow head motions. In this research, we focused on the otoliths and otolithic feedback was defined as the tilting motion of the head against lateral acceleration, which generates torque based on the head posture angle and the lateral acceleration of the head. Validation experiment was performed on a test bench using a vibration generator and vehicle tests confirmed that the proposed model is capable of generally reproducing occupant behavior in response to lateral acceleration inputs.
The present study analyzes rear-end collisions and near misses with motorcycles using the near-miss database. Characteristics of the rear-end incidents with motorcycles are examined by comparing cases with passenger cars. A total of 101 cases are extracted for analyzed data including from the stable following situations to the rear-end incidents, with the near-miss levels of “accident,” “high,” and “medium.” For passenger cars, the same number of randomly extracted cases are compared with the data of motorcycles as the same near-miss levels. When the preceding vehicle is a motorcycle, the headway distance is shorter and the potential risk is higher than those of a passenger car. When the preceding vehicle is a passenger car, the relative velocity is higher near the near-miss timing, and there is no significant difference in the overt risk as a result. In order to prevent the rear-end collisions and near misses with motorcycles, it is important for drivers following motorcycles to avoid shortening the headway distance by predicting from the motorcycles behavior, and for motorcycle riders to avoid sudden maneuvers and to indicate their intentions earlier such as turn signals.
Physics model-based quantitative safety analysis method should be established both for meeting the strict flight safety requirement and maximize the mission flexibility of the flagship liquid rockets. Isogrid tank destruction model of the crack propagation triggered by the pre-generated longitudinal slit hole has been developed, based on the dynamic explicit FEM analysis and the crack propagation test methods for the model validation. The crack propagation test method for the flat panel with and without rib structures was proposed and demonstrated to obtain the valid data for the investigation of the destruction mechanisms and the model validations. From the test and computed results, it was found that the reason why the crack propagation direction changes when the rib angle is different is that the smaller the rib angle, the stronger the asymmetry of the shear stress distribution based on the crack propagation direction. As a result, the principal stress direction near the crack tip is inclined with respect to the load direction, and the propagation direction of the crack traveling perpendicular to the principal stress direction changes. The calculated crack propagation path and propagation velocity are in good agreement with the experimental data, indicating that it is an effective test method for identifying the parameters of the material model.
In this paper, we proposed a new industry-university collaboration model that effectively links university technology seeds to product development. In retrospect, development of technology seeds has been conducted mainly in most case by universities, making it difficult for such seeds to be applied directly to the technical challenges faced by companies. One of the major issues behind the difficulties is due to lack of sharing and understanding of the technological challenges by the university professors that the companies face. A new industry-university collaboration model consists of mechanism analysis by visualization of existing technologies to systematize and model phenomena, and research of new technology seeds based on models and practical development of the technology seeds will be jointly carried out by university professors and company engineers. In order to carry out this industry-university collaboration activities, regular study meetings are held to obtain the knowledge of university professors from various research fields, and technology development management is being implemented to supervise these collaboration activities. Proposed new industry-university collaboration model has actually proved that it is possible to develop the technology seeds to the practical level in multiple product development.