Mechatronics equipment are required to control the response of machines at high speed and with high accuracy. However, many machines include pinion stands, gear couplings, etc., and there are some roles in the transmission part. When the response of these machines is increased, chaos phenomenon occurs due to the backlash, which is an obstacle to high speed and high accuracy. In this study, we show the result that suppresses the chaos to the gear transmission system by applying the reset control by simulation.

Nonlinear characteristics of two DOF Duffing oscillator with fifth order term are investigated. The system used in this study has mass and stiffness proportional dampings simultaneously, and two combinations of stiffnesses that have same natural frequencies. In our previous reports for the same system, nonlinear characteristics were qualitatively studied using frequency response curves of modal coordinates. However, the quantitative criterion of the nonlinear characteristics is desirable. For one DOF Duffing oscillator, single backbone curve symbolically describes many frequency response curves for the various amplitude of the response. In this study, the coefficients of the backbone curves are evaluated and compared with the parameters of the system. The calculated examples show that the coefficients were successfully identified for the modal amplitudes with softening characteristics. However, for the case that the modal amplitudes had the softening and hardening characteristics, the backbone curves went out of the frequency response curves. The parameters of backbone curves were independent from the ratio between mass and stiffness proportional dampings.

In the aviation industry, a turbine casing of a jet engine has been lightened and thinned to improve the mileage. Chatter vibration can occur during machining of a low rigidity workpiece. Chatter vibration causes decline in processing accuracy, wear of cutting tool and undesired noise. The previous study reported chatter vibration can be suppressed by arranging the multiple tuned mass dampers (TMDs) at unequal pitches in the circumferential direction on the inner wall of workpiece. This study examines the optimum arrangement of TMDs in the circumferential direction to improve chatter suppression effect. An index for chatter vibration occurrence was defined from the predicted chatter vibration mode shapes when multiple TMDs were attached to a thin-walled cylindrical workpiece. The TMDs arrangements with high and low chatter suppression effect were determined by proposed indicator, and the chatter suppression effect was compared by performing cutting test for each of the TMDs arrangements. Consequently, it was confirmed the difference in the suppression effect of multiple TMDs attached to the workpiece at unequal pitch in the circumferential direction.

In the latest trend in engine technology, high-power engines and low cylinder engines are widely used. These engines contribute to strong torsional vibration due to engine combustion within the powertrain systems. On the other hand, automatic transmission (AT) is required to use a lock-up clutch system which links engine and gear train directly from low engine rotation speed. Lock-up damper, torsional spring in torque converter, is not enough to absorb the torsional vibration. Therefore, the centrifugal pendulum vibration absorber (CPVA) is developed to suppress the torsional vibration. The natural frequency of CPVA is proportional to engine rotation speed. Then it is expected to suppress torsional vibration in wide range of the engine rotation speed. However, the natural frequency of the CPVA varies due to the nonlinear when the vibration amplitude of CPVA is large. There is a space limitation problem to install larger size of CPVA to suppress the strong torsional vibration. To overcome this problem, a new physical pendulum type of centrifugal pendulum vibration absorber is developed. In this study, the optimal design for the physical pendulum type of centrifugal pendulum vibration absorber is discussed.

In this study, we developed an active device used to suppress the essential tremor in human limb. An active-type mass damper was introduced to mitigate tremor in human hand, where the mass was actively driven using a voice coil motor. In addition, a single-frequency adaptive notch filter-based controller was introduced to drive the damper mass. Experiments were carried out where the simulated microscopic surgery was imposed on subjects, whose forefinger was equipped with the active mass damper. The acceleration served as an error signal by which the adaptive filter coefficients were updated and the error function was minimized. Subjects were asked to grip a needle having a relatively small diameter using tweezers; they were also asked to insert it in a needle with a larger diameter. Furthermore, another notch filter-based dominant frequency estimation system was developed for the controller. Although the challenges still need to be solved, the active damper to be used with the adaptive-type controller was shown to be effective for attenuating the vibration.

An approximate analytical method based on complex fractional moments (CFMs) is proposed to obtain the transient response probability density function of a dynamic system with nonlinearity in both stiffness and damping excited by Gaussian white noise. The CFM is a new kind of statistical moment developed in recent years and is related to the Mellin transform of a probability density function. In the proposed method, first, the system response is expressed in the form of quasi-harmonic oscillation with amplitude and phase variables, and then, the equivalent natural frequency of the system, which is given as a function of the amplitude, is determined by the equivalent linearization method. Next, using the equivalent natural frequency and the stochastic averaging procedure, the Fokker-Planck equation governing the probability density of the response amplitude is derived. The Mellin transform of the Fokker-Planck equation yields the governing equations of the amplitude CFMs, which are given by simultaneous linear ordinary differential equations. Finally, the inverse Mellin transform of the CFMs obtained from the differential equations leads to the transient response probability density function. In numerical examples, two types of nonlinear stochastic oscillators are considered. The analytical results of the transient response probability densities obtained by the proposed method are in good agreement with the corresponding Monte Carlo simulation results, including their tail region.

We consider a linear system under additive and parametric Gaussian non-white random excitations and investigate the response asymmetry using bispectrum. The stochastic processes appeared in the additive excitation and parametric excitation are identical, and their power spectrum has bandwidth and dominant frequency parameters. Monte Carlo simulation is carried out in order to obtain stationary probability density function and skewness of the system response. The skewness is the 3rd-order central moment normalized by the standard deviation cubed and is a measure of the asymmetry of the probability density function. It is found that the shape of the stationary probability density function and skewness of the response dramatically changes depending on the bandwidth and dominant frequency parameters of the excitation. Next, we discuss the change of the response skewness based on the bispectrum. A bispectrum is a generalization of a traditional power spectral density and is the distribution of its 3rd-order central moment in the frequency domain. In this study, we use the response bispectrum normalized by the response standard deviation cubed as the distribution of the response skewness in the frequency domain. The normalized bispectrum has some peaks, and it is shown that the positions, height and sign of the peaks change depending on the dominant frequency parameter. Then, the change of the response asymmetry is explained from the vewpoint of the change of the peaks. Finally, we approximately analyze the normalized response bispectrum by perturbation method. The approximate solution well describes the change of the response bispectrum depending on the the dominant frequency parameters of the excitation.

An author proposed an identification method of linear 1-dof system using Gaussian random vibration response in a previous study. However, there is a problem that conventional method can’t obtain the information about the parameter distribution. In this paper, we considered the expand method to the distribution estimation of our proposed method based on variational Baye’s inference. At first, the identification problem is defined for a linear 1-degree-of-freedom (1-DOF) system which is subjected to the white noise excitation. Then, the excitation source to the 1-DOF system is assumed the displacement excitation owing to future experimental work. Moreover, a likelihood function is introduced using by analytical solution of Fokker-Planck equation in 1-DOF system, the likelihood was named the Maxwell-Boltzmann likelihood owing to differentiate from other likelihood. The variational Baye’s inference is applied to Maxwell-Boltzmann likelihood in 1-DOF system, in this case, the conjugated distributions are obtained between a prior distribution and a posterior distribution. A fundamental operation verification is conducted using the numerical simulation based on the 4-th Runge-Kutta method. Furthermore, the benchmark tests of estimation accuracy were conducted between the variational Baye’s method and the maximum likelihood estimation method. As a result, the effectiveness of variational Baye’s method was confirmed in the spring constant estimation.

We examine the joint response probability distributions of a linear system subjected to non-Gaussian random excitation with a wide range of bandwidth. In the previous studies, the transient response characteristics of linear systems subjected to non-Gaussian random excitation were investigated from the view point of the displacement response distribution and velocity response distribution. It was revealed that the probability distribution of the response varies significantly depending upon the bandwidth of the excitation power spectrum. In this paper, firstly, we calculate the joint response distribution of the displacement and velocity by Monte Carlo simulation. The non-Gaussian excitation is prescribed by both a probability density function and a power spectrum with bandwidth parameter. In order to find the response characteristics that appear commonly for different non-Gaussian excitations, we consider two kinds of non-Gaussian distributions for the probability distribution of the excitation. Their shapes are much different from a Gaussian distribution and also distinct from each other. For such non-Gaussian random excitations, the joint response distribution is obtained, and the relationship between the response distribution and the bandwidth of the excitation power spectrum is examined in detail. In addition, we also focus on the property of the distribution to concentrate on a straight line, which is important in discussing the non-Gaussianity in the response. When the bandwidth of the excitation is zero, the excitation can be considered as a step input. In this case, we can derive the solution of the straight line analytically. We illustrate the way of deriving the line for the zero bandwidth. Furthermore, it is shown that the line derived for the zero bandwidth can be used as the line even for the non-zero bandwidth. We also demonstrate that the duration for which the joint distribution concentrates on the straight line becomes shorter as the bandwidth becomes wider.

In this paper, we introduce fractional-order calculus into linear quadratic regulator (LQR) control, which is a typical modern control, and discuss control of a magnetic levitation system using a state observer described by a fractional-order differential equation. In the previous paper, LQR control using a fractional-order state observer with output feedback was applied to a linear control object. It is necessary to verify if the control is also effective for the nonlinear model. For an unstable target, an integrator is required to be designed to trace the target value. In this report, we propose an output-feedback-type servo LQR control system with a fractional-order state observer for a voltage-controlled suspention-type magnetic levitation system with strong nonlinearity.

This study deals with the positioning control problem of a one-link flexible manipulator consisting of two actuators which are a servomotor and a piezoelectric film, and then proposes a new feed-forward control method to suppress simultaneously the driving energy and residual vibration. Simulation and experiments were performed to verify the effectiveness of the proposed method. From this verification, it was confirmed that simultaneous optimization of the trajectory of servomotor and the input voltage of the piezoelectric film saves more energy than the only optimization of the trajectory. Therefore, we were able to establish an energy-saving feedforward control method by driving two actuators.

As railway vehicles become faster and lighter, the vibration of carbody tends to increase and that makes the ride comfort worse. In lateral and vertical rigid-body vibration, a number of reduction technologies have been put into practical use, such as semi-active suspensions and variable vertical dampers installed between carbody and bogie. In elastic vibration, various methods have been studied, such as control by previously mentioned dampers, stack-type piezoelectric actuators. However, these methods focused on only the bending vibrations, it has been difficult to reduce multiple elastic vibration modes simultaneously. The authors propose a method to simultaneously reduce multiple elastic vibration modes, including torsional vibration, by controlling internal pressure of air springs. Since this method uses existing devices, it is superior in weight, cost, and maintenance compared to installing a new vibration compensator. First of all, we developed railway vehicle analytical model that can express elastic vibration including torsional vibration. Furthermore, we designed a control system by H-infinity methods and verified vibration-reduction effect on the stationary excitation test of simple railway vehicle model. As a result, it was confirmed that multiple elastic vibration modes, including torsional vibration, can be reduced simultaneously.

Reaming is a finishing process that enlarges the drilled pilot holes to improve the accuracy of roundness. In machining using a reamer with regular tooth spacing, a polygonal deformation phenomenon called spiral mark occurs in the machined hole, due to self-excited vibration caused by time delay, which causes a problem of deterioration in product accuracy. In the previous studies, the authors clarified the generation mechanism of spiral marks and verified the suppressing effect of the spiral marks with the 6-blade irregular tooth spacing theoretically and experimentally. In this paper, the authors discuss the optimal design of 4-blade irregular tooth spacing reamers theoretically. The authors conducted the experiments to confirm the suppressive effect of the optimum design experimentally.

Coal-fired power generation is expected to continue to be used in the future. In this process, coal must first be pulverized, and vertical roller mills are used. However, during the pulverization process, abnormal vibration called self-excited vibration rarely occurs. In previous study, a small element testing machine was used to investigate this problem. The relationship between the slip ratio and the coefficient of friction between the roller and the powder showed a characteristic change when abnormal vibration occurred, but it is not clear whether this is the cause of the self-excited vibration. To investigate whether the characteristic relationship between the slip ratio and friction coefficient observed during abnormal vibration is a cause of self-excited vibration, a simulation model was created by applying the relationship between the slip ratio and friction coefficient in the experiment to a mechanical model for a small element testing machine and comparing the results with those of the experiment. As a result, the model was able to represent the vibration frequency that was confirmed in the experiment when abnormal vibration occurred. However, the dependence of the roller horizontal acceleration on the running speed could not be confirmed. The relationship between the slip ratio and the coefficient of friction could not be reproduced, but the change in the coefficient of friction could be reproduced. The vibration modes that are observed when abnormal vibration occurs were confirmed, but it is not clear whether they can be regarded as self-excited vibration or not.

Sliding of the pantograph head and contact wire causes frictional force acting on traveling pantograph head in horizontal direction. If the coefficient of friction between the pantograph head and contact wire is large, unstable vibration of the traveling pantograph could be observed. To analyze this vibration, a 2-dof pantograph model considering frictional force acting on the pantograph head based on the multi-body dynamics (MBD) has been proposed. However, elastic deformation of each element of the pantograph is not studied in this model. Therefore, this study proposes a pantograph model that considers friction characteristics of the pantograph based on the flexible multi-body dynamics (FMBD) approach. In this paper, a single-arm pantograph for shinkansen train is modeled using the FMBD technique. In addition, a stability analysis method based on the complex eigenvalue analysis for the pantograph model is proposed. Furthermore, excitation test of actual pantograph for Shinkansen train is carried out to identify its dynamic characteristics. Then mode shapes and natural frequencies of the pantograph are identified. Moreover, the stability analysis based on the complex eigenvalue analysis is carried out using identified parameters.

So far, there have been reports of experimental analysis of vehicle dynamic models and running resistance for wheelchairs, but theoretical analysis focusing on the tires themselves has not been made. Also, comparing wheelchair tires with automobile tires , the structure and shape are different, and the conditions such as operating speed are also different.

Therefore, in this study, I considered the model of tire deformation and the tire contact characteristics for wheelchair tires, and applied the theory of existing automobile engineering to predict the rolling resistance of wheelchair tires going straight on flat ground. I measured rolling resistance by experimental device and compared with the theoretical value.

This paper considers the control method of a vibration table for a vibration test system. Recently, the vibration test with a high frequency range is required for aircraft parts. Difficulty in vibration test with high frequency range is the resonance frequency of the vibration table or the testing product. First, a lot of researches to maximize natural frequency of the structure are reviewed. Secondary, to maximize natural frequency of the cantilever beam, the reshaping of the lengthening joint is discussed. CATIA V5 is used for the design and the numerical analysis. Finally, some shape of the cross section of the cantilever beam is evaluated by the numerical analysis. The best shape to achieve the maximization of natural frequency and lightening mass is proposed.

When an array of two identical pendula connected by a linear, torsion spring is subjected to vertical excitation, the two pendula may oscillate with different amplitudes. This is referred to as a localization phenomenon. In this paper, modal analysis is performed to investigate the cause of the phenomenon. The equations of motion for the two pendula are derived in the physical coordinate. First, in the linearized equations of motion, the natural frequencies and the corresponding modal vectors are determined. Then, the equations of motion in the physical coordinates are transformed to those in the modal coordinates. Van der Pol’s method is employed to obtain the frequency response curves for the principal parametric resonance in the modal coordinates, and the response curves for the physical coordinates are determined using the coordinate transformation. These theoretical response curves are validated by being compared to the time histories and their FFT results. The numerical results show that as the excitation frequency decreases, a branch of the response curves for the first mode undergoes a pitchfork bifurcation, which induces the second mode owing to the nonlinear coupling with the first mode, and the two modes appear simultaneously at a specific excitation frequency range. This is the reason why localization phenomena are observed in the physical coordinates.

Many mobile devices currently use wheels. Most of them have the problem that their mobility performance on level ground is hindered by steps. In addition, prior research on overcoming steps has focused on whether or not steps can be overcome, and has not considered swaying and vibration. Therefore, if such a wheel mechanism is applied, it is difficult to overcome a step with less burden on the passenger. Therefore, this study proposes an axle-moving wheel model that can reduce the force, vibration, and shock required to overcome a step. We will verify the usefulness of this model by applying it to the front wheel of a wheelchair, which is required to reduce shock and vibration.

This paper is a fundamental study of band gap generation by periodic structures.The relationship between the period and boundary conditions of the structure and the band gap produced was investigated for longitudinal waves in bars.The results are summarised as follows: 1)It is shown that the mechanism of band gap generation in the circular case is the separation of cos and sin modes. 2)It is shown that when the period of the structure is short, the mechanism of band gap generation in the finite-length and cyclic cases is almost the same.

As social infrastructures age, there is a need to improve the efficiency of inspection methods and develop automated technologies. In this study, we will develop a ”Defect-directed estimation scheme based on hyperbolic approximation model” to estimate the direction of defects in structures. The basic theory of the proposed model is to estimate the direction based on the delay of the same signal received by the two microphones. The model was implemented and tested on a concrete specimen, and it was confirmed that the direction of arrival of the signal could be estimated.

The authors devised a test equipment which automatically adjust its natural frequency to the excitation frequency. The equipment consists of a sector-like shaped base, a plate spring and a rotating shaft. The horizontal motion of the plate spring enables the equipment to change its own natural frequency. Under the excitation, the test equipment automatically matches its natural frequency to excitation frequency without any controllers. By applying this automatic tuning to a vibration energy harvester, it is possible to realize a device that can maintain high efficiency in an environment where the excitation frequency changes. However, the mechanism of the motion, how the test equipment automatically tunes its natural frequency into excitation frequency, has not been explained. In this study, we created an analytical model with rattles at the root of the plate spring so as to obtain effective results that is difficult to obtain through experiments. As a result, we found that the plate spring’s motion starts when the root of the plate spring conflicts with rattles, and vertical inertial force affects this motion.

The sliding surface in the mechanical system is required to move smoothly and stop at the target position. The sliding surface can move and stop by applying adequate friction force. The friction force is controlled by developing technology creating small textures on the surface at a few to a few hundred micrometer intervals. If friction force is reduced by applying this technology to large area sliding surfaces of generators, machine tools and so on, the machining effect is drastically improved. On the other hand, ultrasonic vibration is used in many manufacturing fields. It is well known that surface roughness is improved and stress is reduced using ultrasonic vibration. In this study, knurling is focused on creating texture. Machining technology is developed to create wear-resistant texture on large area sliding surfaces with high precision and efficiency using ultrasonic vibration during knurling. In this paper, the effect of ultrasonic vibration on creating texture using knurling is examined by the fundamental experiment. In the experiment of making a groove on the surface with an indenter using a 2-dimensional table, pressing force and friction force are measured. These forces are reduced using ultrasonic vibration.

Golf is the sports that have been enjoyed by the many people in Japan. The golf competition population in Japan is the second largest in the world. The many golfers aim to get the high score and are looking for the golf club which matched oneself from many commercially available golf clubs. Also, many golfers hope to getting the longer distance and raising the ball speed by the golf club (Driver) and various Drivers are being developed by manufacturers. Therefore, the study of the golf club shaft comes to attract more attention. In the previous study, the golf swing simulation using the finite element approach has already been proposed by the authors. In this simulation, considering the motion and torsion of the grip of the golfer, the golf swing was simulated. And, the proposed simulation requires the grip movements obtained from the swing video. In this study, a supporting index tool was made to measure the quantity of torsion of the wrist accurately. And the accuracy of the deflection of the golf club shaft and clubface orientation obtained by the proposed swing simulation is discussed.

Contact bounces of an electromagnetic contactor generate contact arc discharge which causes consumption and welding of contacts and shortening of a product lifetime. To reveal behavior of contact chattering and critical parameters of chattering duration, we perform dynamic study on the contact bounce of an electromagnetic contactor by building the 1-D physical model. The parameters of the physical components in the model are referred from designed values of a product and estimated from measurements of products and FEM analyses. We find the contact chattering duration in the simulation is 0.45 ms, which is consistent with result of chattering duration measurement of a product, 0 – 0.6 ms. Finally, we calculate sensitivity of chattering duration to each parameter and reveal that the initial and final load of the pressure spring and the mass of the moving and fixed contacts have some degree of impact to the chattering duration of the electromagnetic contactor.

In forestry work, vehicles such as heavy industry machines or tractors are used when they carry tools. When the vehicle run on group of particles, vibration occurs on the vehicle that causes deterioration in safety and ride comfort. It is important to clarify the characteristic and occurrence condition of vibration. In this study, Non-smooth DEM is used to analyze the vibration of vehicle. To improve the computational performance, vibration analysis method for a vehicle running on particle ground in a cylindrical coordinate system are proposed. The results of the analysis show that as the wheel speed increases, the amplitude also increases. In the case of multiple particle layers, as the number of particle layers decreases, the vibration becomes lower in frequency. At all damping natural frequencies, the vibration frequency is lower than damping natural frequency. Therefore, it was found that the vibration frequency is lowered by the particle ground.

In this study, we proposed a method for identifying random forces, assuming the case where random forces such as wind act on the layered structure. The identification method is to identify the power and cross spectrum of random force from the power and cross spectrum of measured response and the frequency response function of the structure identified in advance. After constructing the identification method for a general layered structure, we specifically took up a three-layered structure and verified the proposed method. In numerical examples, experiments, and numerical examples reproducing experiments, the power spectrum of the random force acting on the structure in the direct analysis could be identified with sufficient accuracy by the proposed method, so it was shown that the proposed method was effective for identification of random excitation.

It is important to identify modal damping ratios of natural vibrations for reduction of structural vibrations. Experimental modal analysis has been proposed to identified modal damping ratio. Half-power method is one of identification methods of the modal damping ratio. This method is commonly used to identify damping ratio; however, it is known that identification accuracy of damping ratio is low when the damping ratio is high. In this paper, the novel identification method of the damping ratio for the vibration system with large damping by half-power method using small-damped control is proposed. First, the theory of half-power-method and the overview of half-power method using small-damped control are explained. Second, the theory of identification method by half-power method using small-damped control and the measurement method of small-damped frequency response function are. Finally, the experimental investigation using single-degree-of-freedom system is conducted. The improvement of identification accuracy of damping ratio using proposed method is realized.

Sediment disasters cause landslide deaths, house damage, and traffic network shutdowns. Many local authorities specified the sediment disaster warning area and created a hazard map. However, the hazard map is based on an offline approach, which is insufficient for providing evacuation guidance for residents. Therefore, adaptive upgrading of hazard maps is required. The previous hazard map is based on a survey of the slope dimension and does not consider the soil internal parameter (i.e., soil cohesion, eigen friction angle). Thus, the sensing technology of the soil internal state is important to detect disaster signs. This study proposes a method for sensing the internal state of soil based on the natural frequencies of longitudinal vibration modes of elastic piles coupled to the ground. The internal state of the soil is defined by the adhesion force and the natural friction angle. This paper presents an integrated analysis of the natural frequencies of longitudinal expansion and contraction obtained from field experiments and soil test results obtained from compression tests.

The modified Kalman filter, incorporating stochastic dynamic analysis in the prediction step, was introduced in a previous paper to systematically deal with nonlinear and parameter uncertainty excitation systems. In addition, the KF-SDA filter was extended to parameter estimation problems. However, the problem of simultaneous estimation of state and unknown parameters has not been developed in previous research. The problem of simultaneous estimation of state and unknown parameters is of great engineering significance as a method of state estimation and system identification under the limitation of the number and types of sensors. This paper deals with a method to apply KF-SDA to the problem of simultaneous estimation of state and unknown parameters. As a basic verification of the proposed method, numerical simulations are performed for a single-degree-of-freedom system which is subject to random noise excitation of parameters. Furthermore, the cases that the estimated value and the true value agree and the cases that they do not agree are considered using the time required for convergence.

In this research, the system identification based on the maximum likelihood estimation method using the analytical solution of the Fokker-Plank equation is discussed in case of a nonlinear one-degree-of-freedom system. In previous work, an author was already reported about the verification result of the fundamental operation. However, there is a problem which the previous study didn’t consider the estimation accuracy loss by non-stationary response. Therefore, it is necessary understanding of the relationship between estimation accuracy and non-stationary response. In this paper, the moment equation analysis was conducted in order to understanding of the estimation accuracy mechanism. The non-stationarity and steady-state values are obtained from the moment equations. As the result, relaxation time of transient behavior was revealed in a case. Furthermore, the squared error surface is calculated based on each theoretical values about the moment.

Tailored Fiber Placement (TFP) is an embroidery technique that enables it possible to design free fiber shapes on base material sheets. The TFP generally creates curved fibers on a flat surface. However, CFRP structures are often used as shell structures rather than as flat plates, and there is not enough research to design fiber shapes on curved surfaces. In this research, we applied our previous optimization method for curved fiber shapes to shell structures. Curved fiber shapes were created by the linear combination of radial basis functions (RBFs) to represent complex fiber shapes. The fiber shape on a curved surface was represented by projecting the fiber shape on a plane surface using a coordinate transformation technique. Using this method, we investigated optimum fiber shapes to improve the first natural frequency of shell structure composites. The results showed that the optimum fiber shape gave higher natural frequencies than the linear fiber orientation. Obtained optimum fiber shape resulted in higher natural frequencies than the linear fiber orientation.

The present study applies the Bayesian optimization (BO) technique using a regression model obtained by Gaussian process to the open-hole tension (OHT) problem of composite structures. The design variables are lamination parameters that directly define stiffnesses for the total thickness of the composite plate without fiber orientation angles in each layer. To investigate the tradeoff relations in the present multi-objective optimization problem, Pareto solutions were obtained by non-dominated sorting of the samples explored by the BO. As a result of the numerical analysis, enough samples close to the Pareto solutions could be found with a small number of analyses. On the other hand, samples equivalent to single-objective optimization could not be found. This confirms the need to adjust the acquisition function to improve searching ability.

It is known that a filtering phenomenon, called a band gap, occurs in structures in which materials or structures with different properties are repeated, and vibration propagation is suppressed in the band gap frequency. This study intends to realize the band gap phenomena using composite beams consisting of metallic materials. First, the wave finite element analysis (WFEM) is applied to derive a dispersion curve, which indicated the conditions for the formation of a band gap. Next, by comparing the results of frequency response analysis using Ansys, the formation of band gaps is confirmed by showing no resonant peaks exist in the frequency bands where band gaps are predicted. By evaluating several periodic composite beams, it was found that the condition for widening the frequency band in which the band gap is formed is a large difference between the EI/ρA values of the two phases. Furthermore, by replacing the hollow beams with solid beams with ρA and EI set to be equivalent, it was shown that it is possible to predict the formation of a band gap by dispersion analysis using WFEM for beams with a complex structure.

With the development of 3D printers, it has become possible to 3D print materials containing carbon fibers. In this study, FE model that can reproduce the vibration characteristics of a test plate made with the 3D printer Mark Two. This study aims to create FE model that can reproduce the vibration characteristics of a test plate made with the Mark Two 3D printer when it is subjected to central excitation. Currently, the model can reproduce the vibration modes but is not able to reproduce the natural frequencies. One possible reason for this is that the value of the material constants used in the material constants used in the analysis may differ from the actual ones. To ensure the accuracy of the material constants used, the output of the material constant by the simultaneous identification method using the differential evolution method with APDL were applied to improve the reproducibility of the natural frequencies.

Thick cylindrical shells are used in various applications, and there are many studies on strength and vibration analysis. In vibration analysis of isotropic and orthotropic thick cylindrical shells, it is commonly assumed that displacements are affected by rotational inertia and shear deformation and the shell thickness does not change during deformation. On the other hand, vibration analysis of orthotropic cylinders has been studied based on three-dimensional analysis theory without these assumptions. However, vibration analysis of thick cylindrical shells based on three-dimensional analysis theory has not been conducted. Previously, we studied an orthotropic parallelepiped as a single continuum and reported the relationships between dimensions and natural angular frequencies and vibration modes. In this report, a thick cylindrical shell with deformation in thickness direction and orthotropy is investigated. The natural angular frequencies and modal functions of the axisymmetric vibration are derived using three-dimensional analytical theory. In the calculation example, the relationship between dimensionless axial wavenumber and natural angular frequencies and modal functions of the model with varying thickness ratios are illustrated. The frequency veering of natural angular frequencies occurs, and the wavenumber where the frequency veering occurs depends on the thickness ratio. The number of radial nodes varies independently of the frequency veering, and the sign of the slope of radial node vs. dimensionless wavenumber changes around the wavenumber where veering occurs. The number of axial nodes and their positions vary only around the value of the wavenumber where veering occurs.

This paper presents the numerical stiffness evaluations of CFRTP composite laminates made by prepreg patch, which is the CFRTP prepreg sheet cut into small pieces from an usual prepreg sheet. For this purpose, the numerical model is constructed by using the ACP function of commercial finite element analysis software, ANSYS. In calculation the 3-point bending problem is picked up, and the deformations and the bending stresses are obtained numerically. The stiffness of the laminates is thus discussed from the numerical results.

This study discusses identification of material constants of Single-Layer CFRP thin plate using vibration analysis with general purpose FEM code and differential evolution method. This identification method is a method to select material parameters to match the vibration characteristics of the experiment and the vibration characteristics of the analysis. In the method, a general-purpose FEM code calculates vibration modes and natural frequencies of thin CFRP plate using material parameters which are selected by differential evolution method (DE). To reduce number of generations, ILSDE (DE based on Improved Learning Strategy) is used instead of DE. The number of generations is lowest when the number of random select individual is three. Comparison of the reference data and the two FEM models show no significant difference in the identification results. The results show that the identification method has sufficient capability to reproduce well the experimental natural frequencies.

Tuned mass dampers (TMDs), which consist of an added mass and a spring/oil damper, are often installed to damp equipment and structures because they are compact and lightweight. However, there are some problems such as performance degradation due to age-related deterioration of springs and oil dampers. A tuned rolling-cylinder damper (TRCD), which does not use a spring or oil damper, has been proposed, which consists of an arc-shaped main vibration body and multiple rolling elements. The TRCD is simple in structure and is easy to install and durable. However, the combination of parameters such as the radius of the arc vessel, the number of rolling elements, and the radius to obtain the optimum damping performance has not been fully investigated. In this paper, an optimization of the TRCD was performed using an optimization technique called the Particle Swarm Optimization (PSO), and the validity was verified experimentally. In addition, the Distinct Element Method (DEM) was used to analyze the contact forces between rolling elements and between rolling elements and arc containers．

In this study, influence that the damping force properties of the damper using particle assemblage and the resonance curves of the vibration system with the damper received from flow rate of the inflow air were investigated experimentally. The damper was filled by the zirconia balls of 1.6 mm from 1.4 mm in diameter. The filling rate was 0.550. The damper was installed in the horizontal direction. And the air was poured into the damper from bottom side holes, and the air was poured into outside from upper side holes of the damper. The damping force of the damper decreased as the flow rate of the air is increased. However, the differences of the damping forces were small. And then the resonance curves of the vibration system with the damper were changed by the inflow air. When the flow rate of the inflow air is high, the amplitude of the vibration system became small.

In this work, an experimental and theoretical investigation on the damping phenomenon, occurring at movement of a permanent magnet inside a conductive pipe, is presented. Concretely, a neodymium magnet falling inside of a copper tube is experimentally investigated, and the falling time was measured for various dimensions (diameter and height) of the cylindrical magnet and various dimensions (inner and outer diameters) of the cylindrical pipe. A method to compute the electromagnetic damping coefficient, which does not require the value of the flux density of the magnet, is proposed. Influence of the dimensions of the magnet and pipe, and especially influence of the clearance between the magnet and pipe on the falling time and damping coefficient, is illustrated. During the performed tests, unexpectedly was observed that for certain combinations of the magnet and pipe, the magnet stopped inside the tube, being unable to continue its falling and finally exit the pipe. Such phenomenon, similar to the well-known sticky drawer effect is discussed, and a geometrical condition, to predict its occurrence is proposed.

In this study, we propose a method for estimating mass, center of gravity and moment of inertia of loading on vibration isolator using state quantities of air suspensions and clarify the usefulness of the proposed method by experiments. The air suspension is one of fundamental components of the vibration isolator that utilizes a stiffness caused by compressibility of air and damping effect caused by viscosity of air. The vibration characteristics of the vibration isolation system using air suspensions, which has the translational and rotational degree of freedoms, vary according to the characteristics of the loading such as the weight, the position of the center of gravity and the moment of inertia. The weight and the position of the center of gravity can be estimated from static characteristics. But the moment of inertia can only be estimated from the dynamic behavior. Therefore, the natural frequencies of the vibration system are measured and the moment of inertia is estimated using the relational expression between the natural frequencies and the moment of inertia. The loading is supported by a rubber film lifted by the air pressure fed into the air suspensions. In addition, the internal pressure of the air suspensions is measured by the pressure sensor in the tank of the air suspensions. In this experiment, in order to estimate the moment of inertia of the loading supported by the two air suspensions, the loading is freely vibrated and the natural frequencies are measured. In this study, the estimation errors of the weight, the position of the center of gravity, and the moment of inertia are within 10 [%] using the state quantities of the air suspensions and the natural frequency of the rotation mode.

An inertia effect is proportional to acceleration and mass as a negative force, keeps own situation of a body during movement under inertia law. It is obvious that the inertia mass effect is available to decrease own natural frequency and arise anti-resonance which can be shut down vibration in a special case. In previous paper the authors updated a vibration control device which was having variable moment of inertia by Magneto-Rheological fluid inside a flywheel. Ferrite particles of the MR fluid are clustered when magnetic field is applied by 8 electromagnets to the flywheel. It was clear that the inertia mass effect was varied as higher current, and vibration control effect under the earthquake was confirmed numerically and experimentally. If inertia mass effect can be switched depending on anti-resonance, vibration may be able to be suppressed under the earthquake. Recently some researchers focus reinforcement learning to decrease vibration. Therefore, to switch mass inertia effect, reinforcement learning is adopted. In this paper firstly the vibration control device with thin iron plate attached inside the flywheel is updated from prototype in order to get more inertia effect. Secondly, Deep Deterministic Policy Gradient (DDPG) which is a part of reinforcement algorithm is adopted in order to decrease vibration by inertia mass effect, and vibration tests of one degree-of-freedom were carried out.

In general, a semiactive damper has high performance of vibration control compared to passive damper. The damper requires a power supply and sensors in order to adjust an optimized damping force for the damper, several condition of vibration systems, such kind of force, acceleration and displacement etc. The authors have developed an electromagnetic type sensor less semiactive damper. In previous paper, the 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 was developed. By connecting the terminal circuit of the generator with a resistor, rectifiers and a solid-state relay(SSR), the voltage from the generator rises when the speed exceeds a border of relay, causing the relay to close and the damping force to automatically switch. In this paper, a new electromagnetic type sensor less semiactive damper with brushless direct drive motor was developed. Three phase full-wave rectifier circuit and SSR are connected to the motor in terminal. Resisting force of the damper were measured and the experimental results were compared with the theoretical results, and effect using rectifier was confirmed.

Multi-mode damping of elastic vibration is required for efficient vibration reduction of lightweight structures. In this study, a multi-axial dynamic vibration absorber (DVA) is made, and the possibility of multi-mode damping is investigated. The multi-axial DVA consists of a mass sphere supported in multi-directions by eight springs, and the mass sphere vibrates in multi-directions: this yields multi-mode damping. From the theoretical analysis, it is shown that the natural frequency in each axis can be adjusted by changing the dimension ratio of the frame connecting the fixed points of these eight springs. In this paper, the numerical vibration analysis of the multi-axial DVA was firstly carried out using a finite element (FE) commercial software Ansys to check the theoretical analysis. The numerical results showed that introducing "slip" is necessary at the contact area between the supporting springs and the mass sphere. Based on the results of the FE analysis, a multi-axial DVA was developed and attached to a model of the underframe of a railway vehicle. Finally, a series of excitation tests for the underframe model was conducted, and the multi-modal damping was confirmed.

A multi-axial dynamic vibration absorber (DVA) with adjustable natural frequency mechanism has been developed. Air-filled rubber tubes are used as the spring and damping elements of the DVA, which support each face of the iron cubic auxiliary mass. For the rubber tube, when the internal air pressure is increased, the support stiffness is increased by expansion and pressing between the acrylic plate (which constitutes the outer frame of the DVA) and the auxiliary mass. In this way, the natural frequencies of the DVA can be adjusted by manipulating the air pressure. As a first step to realize a multi-axis DVA with frequency tuning ability, this study reports the vibration characteristics of the developed DVA when the air pressure of the supporting rubber tubes is changed uniformly.

By a trial simulation, it was found that the frequency range of vibration reduction due to antiresonance was wider than that of the flam damper by installing several Dynamic Absorbers with similar natural frequencies and adjusting their damping factors. To expand this range to the maximum, we propose a parameter adjustment method for a Multi Dynamic Absorber using the basic theory of Transfer Path Analysis. A diagram showing the relationship between the numbers of installed dynamic dampers, the target value for reducing the vibration amplitude ratio, and the range of vibration reduction frequencies can be derived.

Multiplexing dynamic vibration absorbers (DVAs) provide better vibration control force compared to that obtained with classical single-mass DVAs. In fact, previous studies have shown that the vibration suppression performance of double-mass DVAs is superior to that of the single-mass DVAs. In the optimal design of a parallel-type double-mass DVA, five dimensionless design parameters must be optimized. One of them is the mass ratio of two DVAs arranged in parallel. However, in many cases, especially in the parallel-type, the mass ratio of two DVAs cannot be set to the optimal value, because existing structures and machine parts are sometimes used as DVAs. In this report, I investigated how the optimal values of other design parameters change when the two DVA masses are set equal, and finally, how bad the vibration suppression performance of DVA becomes.

An analytical evaluation of the effect of the plastic deformation of the support structure of mechanical components on reducing the seismic demand of the equipment is attempted using a simple two-masses model. The element ductility factor of the support structure is varied stepwise, and changes in the resonance curves of the sinusoidal acceleration wave input and the elasto-plastic seismic response curves of the strong-motion recorded waveform input are examined. Although a relatively small target element ductility factor is set in this report, which aims at a simplified seismic design method in the plastic region, it was observed that the seismic demand decreases significantly from the elastic state by slight plasticization of the support structure element, and the response spectrum becomes flat even in the resonance with the input motion and in the rigid region.

In the seismic PRA, tremendous computational and human resources are required to evaluate the seismic fragility curves of facilities in a nuclear building, so the development of a simple evaluation method has been desired. In this study, we propose and apply a non-iterative equivalent linearization method for evaluating the real capacity (median value of fragility curve) and propose a method that can easily evaluation seismic fragility curves. Then, the method was tested using 6 equivalent linearization models for equipment installed on the ground surface and comparing the results with those obtained using nonlinear analysis. The validation was done by using 37 ground motion records observed by Japan Meteorological Agency. As a result, the equivalent linearization method proposed by Liu et al. (2015) and Watabe et al (1985) can obtain relatively stable results. In particular, the equivalent linearization method of Liu et al. was found to be independent of parameter changes.