In the typical textbook of vibration, only the classical boundary conditions (i.e., fixed and free) are explained. However, as the intermediate condition, there is an elastically supported boundary condition. In this study, as an attempt to find the optimal arrangement of nodes in the vibration of a continuous system, the second to fifth-order modes of the bar that is elastically supported at both ends were investigated. In order to change the position of a node, it is shown that the low order mode requires a support stiffness equal to the spring coefficient of the bar when it is considered as a spring. In higher-order modes, a support stiffness greater than the spring coefficient of the bar is required. The maximum displacement of a node is about one-third of the total length of the bar in the low-order mode and one-tenth of the total length of the bar in the high-order mode.

In this study, we investigate a time-domain method to identify linear parameters such as mass, damping coefficient, and stiffness, and nonlinear force of a nonlinear vibration system using a neural network (NN). In this method, excitation forces, accelerations, velocities, and displacements measured from experiments are input to the NN, and the NN learns the equilibrium of forces between the external force, inertial force, damping force, and restoring force to identify the characteristics of the vibration system. The proposed NN consists of a global NN that computes equilibrium of forces by linear and nonlinear sub-networks, and a local NN that extracts linear parameters from the nonlinear sub-networks. This study targets vibration systems with smooth nonlinear characteristics governed by Duffing's equation or Van der Pol's equation. Furthermore, as an example of a vibration system in which the slope of the nonlinear force, the dependent variable, increases when the displacement, the dependent variable, takes a value close to zero, we also target vibration systems in which the nonlinear force is expressed as a sinusoidal function. Then, the data obtained by numerically solving the equation of motion is regarded as the data obtained experimentally, and the validity is confirmed by identifying the linear parameters and nonlinear forces.

The authors have focused on nonlinear oscillating systems subjected to irregular inputs and have been engaged in research on higher-order spectral analysis. In this report, as an application of signal processing methods, we identify state quantities such as displacement and velocity sequentially using a "particle filter" related to Bayes' theorem. In addition, physical parameters are also identified sequentially as unknown state quantities. Higher-order spectra are also sequentially estimated in order to grasp the ever-changing nonlinear characteristics. This paper proposes a method for sequential estimation of higher-order spectra and nonlinear parameters in nonlinear vibration systems, presents the effectiveness of the method, and summarizes the issues involved.

In this study, we propose a classification system that matches the most appropriate power generation device to an arbitrary environmental vibration. Firstly, 40 types of ambient vibration data, such as machine vibration, window vibration, etc., are prepared. On the other hand, three types of magnetostrictive vibration power generation devices with different resonant properties are prepared. Secondly, a Convolutional Neural Network (CNN) that is built in the numerical analysis software MATLAB was used to construct the matching system. CNN is particularly effective for pattern recognition and data classification, which is to be dealt with in this research. The 30 types of ambient vibration data are used as input data, whereas the device identifier that shows the maximum open-circuit voltage is used as the teaching data. CNN learns the relationship between the characteristics of ambient vibration and the devices that showed the maximum open-circuit voltage. As a result, the accuracy of the CNN was 70% for 10 types of unknown environmental vibrations.

We examine the non-Gaussianity of joint response probability distributions of a linear system subjected to non-Gaussian random excitation. In our previous study, we calculated the joint response probability distribution of the displacement and velocity of the system. It was revealed that the distribution concentrates on a straight line (x′ axis), and the marginal distribution on the x′axis has the same non-Gaussianity as the excitation. In addition, we derived the solution of the straight line analytically. In this paper, first, we calculate the marginal probability density function on the x′ axis in order to investigate how the non-Gaussianity on the x′ axis varies with time and excitation bandwidth parameter. In this regard, we also derive the analytical solution of the marginal distribution when the excitation bandwidth is zero, and then, use it for comparison with the marginal distribution in the non-zero bandwidth case. It is found that the marginal distribution exhibits non-Gaussianity similar to that of the excitation at almost any time, however, the degree of the non-Gaussianity decreases temporarily with a period of 2π. Next, we calculate the marginal probability density function on the straight line perpendicular to the x′ axis and show that it does not have non-Gaussianity. This fact indicates that the excitation non-Gaussianity appears only on the x′ axis.

This study deals with the asymmetry of stochastic response of a linear system under external and parametric random excitations. The random excitations are modeled by zero-mean Gaussian processes possessing a non-white power spectral density with bandwidth and dominant frequency parameters. The correlation between the two excitations is characterized by their correlation coefficient. In order to examine the effect of the excitation correlation coefficient on response asymmetry, bispectral density is utilized, which is a generalization of a traditional power spectral density. The response asymmetry is evaluated in terms of skewness. First, the analytical method developed in our previous study for obtaining an approximate analytical solution of response bispectral density is extended to the case where the two excitations have arbitrary cross-spectral density. The analytical method consists of a Fourier series representation of the excitation based on the spectral representation theorem and a perturbation technique. In this study, the response bispectral density is normalized by using the response variance. The normalized bispectral density is the distribution of skewness in the frequency domain, and by integrating it over the entire frequency range, the response skewness is obtained. The validity of the approximate analytical solution is confirmed by comparing it with the Monte Carlo simulation result. Then, using the approximate solutions of the bispectral density and skewness, the following findings are made regarding the relationship between the response skewness and the correlation coefficient: (i) the response skewness changes approximately linearly with the correlation coefficient; (ii) the slope of the change can be approximated by the response skewness in the case that the correlation coefficient is equal to 1, i.e., the two excitations are identical.

An approximate analytical approach using complex fractional moments (CFMs) is developed for determining the transient response probability density of nonlinear oscillators with fractional derivative elements under Gaussian white noise. The CFM is defined as the Mellin transform of a probability density function. The system response is represented in the form of a pseudo-harmonic oscillation with amplitude and phase slowly varying with time. Equivalent linearization is first implemented to obtain an equivalent natural frequency and an equivalent damping coefficient of the oscillator. In this regard, simple formulas for determining them are proposed, in which both the nonlinear elements and the elastic and viscous contributions of the fractional elements are taken into account. Next, applying stochastic averaging, the response amplitude is described by a one-dimensional stochastic differential equation, and the corresponding Fokker-Planck equation is derived. The Mellin transform then converts the Fokker-Planck equation into coupled linear ordinary differential equations governing the evolution of amplitude CFMs, which are solved with a constraint corresponding to the normalization condition for a probability density. Finally, the inverse Mellin transform of the CFMs yields the amplitude probability density. The joint probability density of displacement and velocity is also obtained from the amplitude probability density in conjunction with the Jacobian of the pseudo-harmonic variable transformation for the response. Two nonlinear oscillators with fractional derivatives are considered in numerical examples. For both cases, the analytical results obtained by the proposed method are in good agreement with the results of the pertinent Monte Carlo simulation.

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 experimental approach. Therefore, it is necessary the experimental identification. First, the expansion of the identification algorithm to an actual experimental situation was conducted based on the displacement white noise excitation system. Furthermore, the experimental system was fabricated using the geometrical nonlinear spring. Moreover, the identification experiment was performed.

This paper presents the numerical structure analysis of CFRTP laminated stay rod 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 numerical calculation the 3-point bending problem is picked up for the laminates, and the deformations, the bending stresses and the bending strains are obtained numerically. The stiffness of the laminates is thus discussed from the numerical results.

Carbon fiber reinforced plastics (CFRP) may be used as flat plate capacitors by inserting dielectrics between each layer. Composite materials that have both structural material and capacitor functions are called structural capacitors. The electrodeposition resin molding (EDRM) method is a method of electrochemically impregnating resin between carbon fibers, and ideally, the fibers are completely covered with resin. To investigate the possibility of using CFRP made by EDRM as a structural capacitor, impedance and capacitance were measured using an impedance analyzer. The cross section of the CFRP was observed using SEM to confirm the coating of the carbon fibers by the resin. As a result, it was found that it is possible to make a structural capacitor by inserting a CNF layer as a dielectric. The measured capacitance was consistent with values obtained in previous studies. However, the possibility of using the CFRP made by EDRM as a structural capacitor could not be confirmed due to the contact of the carbon fibers.

Recently, it has become possible to manufacture carbon fiber reinforced plastics (CFRP) using 3D printing technology. This has made it possible to easily fabricate composite materials with complex shapes. The 3D printer for CFRP mainly uses thermoplastic matrix materials and they have mechanical properties different from those of CFRP composed of conventional thermosetting resins. Since CFRP is fabricated by gradual layering from a 3D printer head, 3D printed CFRP has different characteristics from even conventional thermoplastic CFRP fabricated by hot pressing or other methods. Dynamic mechanical properties such as vibration as well as static ones of 3D printed CFRP have not been fully investigated. For these reasons, the identification of material properties is required to calculate the vibration characteristics of 3D printed CFRP with a high accuracy. The objective of this study is to accurately identify the material constants of 3D printed CFRP and to perform numerical analysis of the vibration characteristics with high reproducibility.

When reinforcing a structure with long carbon fibers continuously injected by a 3D printer, the fiber bundle may be twisted at the fiber bends. In this study, the effects of the fiber bending area on the vibration properties of CFRTP rectangular plates, in which the fiber bends account for a relatively large proportion, are investigated experimentally and FEM analytically. In the middle of the rectangular plate is the fiber bending area. As a result, it is found that the rate of increase of the natural frequencies with respect to the bending fiber area ratio decreases to about 60% in the bending mode and to about 65% in the torsional mode. The trend of natural frequency variation in the bending vibration mode is found to be different depending on the boundary conditions. There is no effect of boundary conditions on the torsional mode.

Particle dampers (PD) can be embedded in structures fabricated via Selective Laser Melting (SLM) because the raw powder (particle size : several tens of micrometers) remains in closed spaces during the SLM. However, few studies have investigated the damping characteristics of PD using fine particles. In this study, to experimentally investigate the effect of fine particle size on damping properties, the equivalent damping coefficients of spherical zirconia balls with nominal particle sizes of 50, 100, 200, and 400 μm were measured under various vibration intensities and frequencies (from 100 to 800 Hz). Consequently, in the frequency range higher than 200 Hz, the equivalent damping coefficient of coarse particle sizes were greater than those of fine particles under acceleration lower than the 15.7-22.4 m/s²(rms) range. In contrast, the equivalent damping coefficients of the fine particles were greater than those of coarse particles under acceleration higher than the 15.7-22.4 m/s²(rms) range. Furthermore, to investigate the reason behind there tendencies, the behavior of particles with a nominal particle size of 50 μm, which is close to the raw powder, was observed through a window using a high-speed microscope camera. It was evident that in the low-acceleration range, inertial force did not prevail over static friction due to poor flowability caused by adhesion forces and that the material was always stationary against the enclosed container.

I propose a method for obtaining the strict solution of a stationary solution by which only the impact time of the vibro-impact system was assumed to be parameter for which no sticking occurred. The previously derived form of general solution by authors can be represented as superposition of general solution for linear system and successive impact feedback responses caused by impact nonlinearity. However, it is not practical to derive stationary solution in recursive feedback form, because impact time indices are diverged when limiting process for initial impact time to infinite past. To avoid these difficulties, I reconsider product and summation structure included in global general solution by pseudo-feedback form, improved summation product forms are constructed. Taking a limit to transfer an initial impact state in renewal form of general solution to infinite past, stationary solution can be derived without divergence of impact index parameters.

In end milling, chatter vibration generated during processing becomes a problem in processing accuracy. Chatter vibration is classified into forced chatter and self-excited chatter depending on the cause of the vibration. Especially, stability of self-excited chatter is very important, because it becomes large amplitude vibration if it occurs. Generally, the chatter vibration phenomenon in end milling is modeled as a periodic system with time delay. In our previous study, a numerical method to calculate characteristic exponents of a periodic system with time delay equal to the fundamental period accurately using Fourier series is proposed. In this study, using the proposed method, we verify the effect of anisotropic support on stability. It is shown that anisotropic support has a significant effect on stability and that the degree of stability depends on the relationship between the angle of principal axis of stiffness and the feed direction of machining.

Chatter vibration generated in thin-walled cylindrical workpiece is self-excited vibration caused by the coupling of two natural vibration modes (sine mode and cosine mode). The stability of the coupled vibration system can be determined by whether the gain of the open-loop transfer function is greater than 1 at the phase crossover frequency of the open-loop transfer function. The open-loop transfer function of this coupled vibration system is represented by the product of three quantities，cutting depth - principal force characteristics (block 1), principal force - thrust force characteristics (block 2), thrust force - translational displacement characteristics (block 3). Of these three, only thrust force - translational displacement characteristics reflect differences in workpiece dimensions. In this paper, it is shown that the generation of chatter vibration can be predicted from the value of thrust force - translational displacement characteristic at natural frequency (resonance peak value).

When microparticles are spread evenly and thickly inside an acoustic tube and resonated by a speaker, the particles move and rise against gravity, forming a pleated pattern. This phenomenon is sometimes used in sound visualization experiments because the height of the pattern changes with the sound pressure and the spacing of the pattern changes with the frequency. However, although this phenomenon has been studied for many years since its discovery, the principle of pattern generation has not yet been clarified. In a previous study, a clue to the pattern generation was obtained by considering the acoustic radiation force and the force acting on a sphere, which were obtained by considering the general sound pressure equation proposed by L.V.King down to minute quantities. In this study, the phenomenon that the shape of the pattern changes when a barrier is placed inside a conduit is theoretically demonstrated using an analytical method for a three-dimensional sound field under partial excitation.

In recent years, the shift from gasoline vehicles to hybrid vehicles (HV) and electric vehicles (EV) has become remarkable due to the promotion of low carbonization in the automobile industry. HV are classified according to the drive system and the number of motors installed. In the series system of HV, gear rattle may occur between the engine and the generator due to the torque fluctuation of it. In this report, we modeled a system for gear rattle, and examined the effect of setting parameters and the mechanism of it. As a result, the followings were clarified. First, the frequency response curve and the vibration waveform could be obtained from numerical integral for the equation of motion of the analysis model. Second, we were able to suppress the generation of gear rattle by reducing the stiffness of the damper and the amplitude of the dynamic torque. Moreover, it was confirmed that increasing the damping coefficient of the damper has the effect of suppressing the generation of gear rattle.

Reaming is a finishing process for expanding the pilot hole and improving the accuracy of roundness. However, there is a problem that the tool vibrates during machining and the accuracy of the drilled hole deteriorates. When vibration occurs, the machined hole deforms into a polygonal shape. Such phenomenon is called polygonal phenomenon or pattern formation phenomenon, and it occurs in drilling and BTA deep hole drilling. The polygonal phenomenon of a hole is characterized by a helical twist in the processing direction. In this report, we verified the optimum unequal interval blade for an 8-flute reamer, which has not been implemented yet, from theory and experiment. Normally, the evaluation of the accuracy of borehole is verified by measuring the roundness. However, it is needed to confirm the occurrence of polygonal deformation during machining. Therefore, in this study, we also investigated the detection method of the polygonal deformation by measuring the phase variation of the cutting force.

In recent years, sophistication of mechanical systems complicates derivation of their governing equations. On the other hand, with the recent development of data-driven modeling methods, discovery of the governing equation of relatively simple dynamical system is becoming feasible from measurement data. However, when mechanical systems involve piecewise-linear nonlinearity such as junction points or cracks, it is difficult to identify their governing equations using these methods. Furthermore, piecewise-linear systems have an issue that it is difficult to identify the switching point in the phase space where the system changes its state. To overcome this issue, this study proposes a method to identify not only the governing equations but also the switching points for piecewise-linear systems. It is shown that the proposed method can be successfully applied to generate the governing equation of a single degree of freedom oscillator that involves repetitive contacts with a spring. This dynamic model is a piecewise-linear system and has two states: the system with a spring and without the spring. In addition, an experimental apparatus was built and the proposed method was applied to the measured data. By optimizing the threshold value and order of candidate functions, it was able to derive governing equations that reproduce the dynamics of the experimental equipment.

When contact wires wear out on an electric railway, they must be replaced. For the Shinkansen, even if the wear is localized, the entire one drum is replaced instead of partial replacement. Therefore, there is a need to establish a partial replacement method for Shinkansen trains from the viewpoint of labor-saving and cost reduction in maintenance work. Therefore, this study analytically examines the effect of the irregularity in OCL.

The purpose of this study is to verify a novel acceleration and deceleration design method to suppress the residual vibration after positioning motions. In this study, a method to suppress vibration by appropriately designing jerk changes during acceleration and deceleration is proposed. To design the jerk changing, the amplitude map which can represents the relationships between the acceleration parameters and estimated amplitude of the vibration. The proposed method realizes to suppress the vibration amplitude without changing of the total positioning time. In order to verify the effectiveness of the method, an experimental set-up consists of a motor and torsion beam is developed. As the results of the verification, it is confirmed that the influence of the design parameter of the positional command can adequately be predicted by the amplitude map, and the designed command can effectively suppress the residual vibration.

In this research, we attempted to control the swing-up and swing-down of the pendulum through experiments and simulations. The vibration manipulation function (VFM), which is a finite-time-settling function, was used as the acceleration of the trolley. Considering the nonlinearity of the pendulum, the operation time of VFM was changed according to the natural period of the pendulum. In addition, the amplitude of VMF was modified by multiplying with a parameter α, which is a function of the lifting angle. This time, the operation time was limited to the natural period (τ) or half of it. Precise swing up and down control of the pendulum was succeeded at an angle of nearly 170 degrees, including the transitional states. Since these features are similar to the phenomenon in parametric resonance, their relationship is interesting.

The burden of vibration on the passengers of construction machinery and agricultural machinery is great, and long-term exposure to vibration leads to serious problems such as vibration disorders and accidents. Therefore, measures to reduce vibration have been taken by introducing a suspension under the seat. Conventional seat dampers are controlled by fixing the hardness of the seat, so that a harder seat absorbs less shock, but the vibration is quickly controlled. On the other hand, setting the seat hardness softly causes firm displacement and shock absorption, but the vibration does not converge quickly. In other words, the conventional control method does not achieve both shock absorption and quick convergence at the same time. Therefore, in this research, by enclosing a magneto-rheological fluid in the seat suspension and installing a damper that can adaptively change the viscosity according to the input of vibration, it is possible to maintain the damping performance and increase the comfort of the passenger. We verified a semi-active damping method that improves comfort. In this study, two types of semi-active damping methods, ON/OFF control and Fuzzy control, were used for verification.

Voltage-controlled suspension-type magnetic levitation systems are unstable systems in which, under uncontrolled conditions, the levitated object is either attracted to the electromagnet or falls. In addition, the electromagnetic force and the electrical characteristics of the circuit have strong nonlinearities. In this study, a magnetic levitation system is stabilized and controlled by fractional-order LQR control, which is a combination of LQR control and fractional calculus, in an actual experiment. In addition, for the case where a levitated object is controlled to a target position that deviates from the equilibrium point, a fractional-order servo LQR control method is developed. It is experimentally confirmed that the fractional-order LQR control has higher control performance than the conventional integer-order LQR control.

In terms of enhanced functionality and economic cost, development of lighter machines and structures is desired. However, reduction in size and weight can potentially result in increased vibration as a trade-off. Therefore, metastructures have recently been attracting attention for their ability to achieve downsizing and lightening while enhancing damping in low-frequency range. Metastructure blocks vibration propagation within a certain frequency range. In this study, we aim to insulate the propagation of vibration waves in arbitrary frequency range by incorporating magnetorheological elastomers as stiffness elements that can alter their own viscoelasticity by applying external magnetic field. In this report, we theoretically show the existence of a band gap in a simplified metastructure and numerically investigate the structure’s vibration characteristics. As the fundamental study, we evaluate the characteristics of a passive metastructure.

In this paper, the relationship between the structure that serves as metamaterial and the structure in which the band gap occurs is investigated. The results can be summarised as follows: 1)When structure is added to the main system, the conditions for metamaterialisation are part of the conditions for band gap generation. 2)The band gaps that occur when the main system itself undergoes periodic changes cannot be described as metamaterials. 3)The application of the band gap generation mechanism showed the possibility of creating propagation structures that reduce vibrations in the desired frequency range by coupling systems that do not have natural frequencies in the desired frequency range with coupling elements until the required magnitude is reached.

There are many situations in which shock transmission must be suppressed in the use of machinery, such as the protection of internal structures from shocks to which the product is subjected and the transmission of shocks due to the operation of internal mechanisms. There have been cases where rubber has been used in structures to absorb vibration, such as mounts used in machines, but there are also cases where rigidity is required. In this study, a 3D printer is used to create a structure with periodically arranged three-dimensional objects with different stress transfer characteristics, such as different cross-sectional areas, and the frequency response characteristics of the created structure are investigated. The power spectrum, coherence function, and transfer function of each specimen are measured by impact test, and evaluated by the transfer function. As a result of the experiment, it was confirmed that a band gap was generated in the periodic structure. It was also found that the bandgap frequency band shifted to lower frequencies as the number of steps in the periodic structure was increased.

In this study, we aimed to form band gaps in a periodically aligned beam consisting of two different internal structures with a single metallic material. First, dispersion analysis was carried out to investigate the bandgap frequency changes and the bandwidth when the composite beam's cross-sectional properties and the unit cell's length were varied. Then a composite beam having the first bandgap of less than 1 kHz with considerable frequency bandwidth was designed. The numerical parameter studies by changing the combinations of the cross-sectional properties showed that the bandwidth of the first bandgap becomes wider according to the physical difference of the unit cell. In addition, investigations of composite beams by changing the length of the unit cell showed a trend that the bandgap frequency shifts toward lower, and the bandwidth becomes smaller as the cell length is increased. Frequency response analyses using a finite element software Ansys for the above-designed composite beam were also carried out with different numbers of the unit cell, and the numerical results confirmed the formation of a bandgap as predicted by the dispersion analysis regardless of the unit cell numbers. Moreover, composite beams, having cross-sectional properties and length of the unit cell corresponding to the numerical studies, with different cell numbers were fabricated using a metal 3D printer. Vibration measurement tests were conducted, and the numerically predicted bandgap formation was demonstrated.

This study proposes local resonant metamaterials with lossy resonatros fabricated by selective laser melting; selective laser melting can embed particle dampers to closed spaces within the structures during fabrication process. Toward this end, the frequency- and acceleration-dependent damping properties of the particle dampers are first identified via the vibration testing. Subsequently, wave propagation within the metamaterial is analyzed using the dispersion analysis, which suggest that the damping properties by particle dampers can attenuate wave propagation in wide frequency ranges by combining the effects of local resonance and the particle dampers. Finally, the frequency response functions of the metamaterials are experimentally measured; the results confirm that particles can suppress vibrations in wide frequency ranges.

Connected Control Method (CCM) is a method of structural vibration control utilizing interaction force between multiple structures connected by springs and/or dampers. Ordinary CCM is not effective to identical structures because no relative motion occurs among identical structures.

In this paper, a novel CCM using Viscoelastic Media as coupling mechanism is presented. Putting Viscoelastic Media between two structures make a difference in shaking to get damping force.

Theoretical analysis and experimental evaluation using the peak gain and the minimum frequency area method are carried out and the effectiveness of the presented method and the difference from dynamic vibration absorber is confirmed.

In Japan, there have been many large earthquakes such as the Great East Japan Earthquake and the Kumamoto Earthquake, and it is expected that a Nankai Trough earthquake or an inland massive earthquake will occur within a few decades. These large earthquakes are expected to cause the functional failure or destruction of various devices and structures. In recent years, energy shortages due to the shutdown of nuclear power plants and the promotion of renewable energy have led to an increase in the installation of photovoltaic systems which are subject to economic risks due to the possibility of damage to mounts, foundations, and modules caused by large earthquakes. In this study, the effect of response reduction when a vibration control device is installed in a ground-mounted photovoltaic system and the appropriate installation method of the vibration control device will be investigated. The analytical model is proposed and improved by the comparison of analytical and experimental results. This report summarizes the verification of the basic performance by vibration tests and the mechanical property of the vibration control device by elemental tests.

In this study, we propose an optimum tuning procedure for an air suspension with a variable length slit restriction. The developed isolation system includes tuning systems of an equivalent damping coefficient and an equilibrium position of a supported object. The variable length slit is formed by a grooved plate and a rotating flat plate faced to the grooved plate. The damping coefficient is almost proportional to an adjustment angle of the rotating flat plate. An optimum adjustment angle which provides the minimum resonance amplitude corresponding to a resonance frequency can be obtained by equation showing a relationship between the supported mass and the optimum adjustment angle. If the excited frequency is lower than the resonance frequency, the optimum adjustment angle is very large. On the other hand, if the excited frequency is higher than the resonance frequency, the optimum adjustment angle is very small. The micro-computer calculates the optimum adjustment angle corresponding to the excited frequency which is obtained from the vibration of a foundation and controls the servo motor to adjust the damping coefficient. The equivalent damping coefficient of the proposed air suspension does not depend on the amplitude even if the slit length is changed.

Laminated metals consisting of different metallic materials are expected to have advantages over single metal materials; high damping capability is one such additional value. This report describes a numerical approach for evaluating the damping capability of laminated metals. For this purpose, we employed the classical lamination theory, which is widely applied to FRPs or damping steels with viscoelastic layers, in this study. The modal characteristics (natural frequencies and natural mode shapes), specific damping capacity and modal loss factor, and frequency response functions (FRFs) against excitation input for laminated metal beams are calculated using the proposed method. Those results are compared with those using a finite element (FE) analysis and experiments, and the validity of the proposed method has been confirmed. Numerical studies are conducted to search for highly advantageous configurations of two metals (aluminum and copper) in terms of lightweight, high stiffness, and high damping performance.

As a countermeasure to mitigate the catastrophic damage by an excessive seismic load beyond the design level, a concept of passive safety structure has been proposed recently. To apply this concept to the piping system, one of ideas is to cause the failure at pipe supports prior to the failure of pipe body itself, because the failure at support is minor failure compared to that at pipe body. However, there are few experimental data on seismic response behavior of piping system in which multiple supports failed during the seismic motion. In order to obtain the basic data for the seismic response behavior of such piping system, a shaking table test on a small-bore piping system model were conducted. As a result, it was confirmed that the support structures were continuously damaged during seismic wave input. The fundamental frequency of piping system was decreased due to the support failure, and it resulted in the decrease of the response acceleration of piping system.

Simple support structures such as U-bolt are used for the low-class piping based on the constant pitch span method. Recently, the integrity of the piping is required during the earthquake, and the demand for safety in nuclear power plants has been increased. As a result, the high seismic resistance has also been required for the low-class piping. In the response analysis, the support structure is only constrained the radial displacement, and the longitudinal displacement is not constrained. Depending on the routing of the piping, a large longitudinal response displacement may occur, and the structural integrity of the pipis and the support structure may not be ensured. Therefore, measures have been taken to add or reinforce support structures. In practice, pipes are subjected to the axial friction force by the support structure. The realistic response can be estimated with nonlinear characteristics. In this study, the seismic evaluation method for piping was investigated by the response spectra with the friction force. The friction force was replaced with the damping ratio which is equivalent to the energy absorbed by the friction force. The acceleration response spectra with the equivalent damping ratio were compared with the spectra which was calculated by the time history response analysis using the frictional force. As a result, the acceleration response spectra with the equivalent damping were larger about 1.3 times than the spectra using the frictional force. In the future, we will compare the stress calculated by the acceleration response spectra with the stress calculated using time history analysis considering friction force by support structures.

Simple support structures such as U-bolts are used for the low-class piping based on the constant pitch span method. Recently, the integrity of the piping is required during the earthquake, and the demand for safety in nuclear power plants has been increased. As a result, the high seismic resistance has also been required for the low-class piping. In the response analysis, the support structure is only constrained the radial displacement, and the longitudinal displacement is not constrained. Depending on the routing of the piping, a large longitudinal response displacement may occur, and the structural integrity of the pipes and the support structures may not be ensured. Therefore, measures have been taken to add or reinforce support structures. In practice, pipes are subjected to the longitudinal friction force by the support structure. The realistic response can be estimated with nonlinear characteristics of piping. In this study, the seismic evaluation method was investigated by the response spectra with the friction force. The friction force was replaced with the equivalent damping ratio calculated by the linear response analysis. The acceleration response spectra with the equivalent damping ratio were compared with the spectra which was calculated by the time history response analysis using the frictional force. As a result, the acceleration response spectra with the equivalent damping were larger about 1.5 times than the spectra using the frictional force. In the future, we will compare the stress calculated by the acceleration response spectra with the stress calculated using time history analysis considering friction force by support structures.

Piping systems are integral components of building facilities, with their functionality encompassing various roles. Numerous damage cases to these essential systems were reported in the aftermath of the Tohoku and Kumamoto earthquakes. Notably, some instances of failure were attributed to inadequacies in pipe support structures. These incidents have led to more rigorous safety standards for seismic design in building facilities, promoting the development of dampers that utilize friction, among other techniques, to enhance seismic resistance. However, conventional approaches to enhancing damping force through friction are not without issues. Given the metallic nature of both clamps and pipes, their points of contact tend to devolve into point contacts. This condition raises the risk of rattling and twisting, potentially yielding unstable responses in piping systems during seismic events. This paper introduces a novel pipe support structure that provides stable damping force through friction between the pipe and the support system. Static load tests were conducted using an actuator to validate the proposed structure's effectiveness. The resultant hysteresis loop of the load-displacement relationship demonstrated a stable damping force that closely aligns with the model shape expressed by Coulomb friction. Further, the consistency of these hysteresis loops suggests the potential for effective modeling using conventional, general-purpose codes. This research not only sheds light on the issues with current practices but also offers a viable solution that could enhance the seismic resilience of piping systems.

The seismic integrity of sodium-cooled fast reactor (SFR) designs in nuclear power plants is of paramount importance. Based on the static loading test, this study investigates the force-displacement relationship and load transference in a three-dimensional seismic isolation system that is envisaged for use in reactor buildings. In SFR designs, the necessity for thin-walled structures to maintain high-temperature structure integrity can unintentionally compromise the seismic design. Consequently, addressing horizontal and vertical seismic forces become vital for ensuring seismic resilience. Currently, there are no specific codes or standards governing the integration of Three-dimensional seismic isolation systems into nuclear reactor buildings. However, current guidelines for the design of horizontal seismic isolation systems emphasize the necessity to clarify the force-displacement relationship and load transfer under conditions of superimposed horizontal and vertical loads. This study involves static loading tests performed on a half-scale specimen, which is subjected to horizontal and vertical loads exceeding the design basis ground motions for the SFR. The findings affirm that the system's horizontal supporting function maintains the segregation of horizontal and vertical load transference, even under seismic loads that exceed the design basis ground motions.

In recent years, various seismic isolation devices have been developed to prevent damage from earthquakes. In this study, we focused on vertical seismic isolation and proposed a vertical seismic isolation device with three link-crank mechanisms arranged in a star shape. In this seismic isolation device, a motor is used to change the spring anchorage conditions, adjusting the rigidity characteristics of the device and allowing the resonance point to be manipulated. We took advantage of this feature to achieve resonance avoidance to escape from the resonance state. As a result of making common adjustments to all link and crank mechanisms, we were able to avoid resonance by reducing acceleration by 30% from before resonance avoidance, but it took approximately 20 seconds of motor operation to suppress transient vibration generated by the change in equilibrium position during avoidance. By adjusting the linkage and crank mechanism to prevent transient vibration, we were able to shorten the motor operation to 0.3 seconds.

There are two types of optimal design for dynamic vibration absorbers: fixed-points theory and minimum variance criterion. The reduction effect of dynamic vibration absorbers designed based on these two design theories on seismic response of piping systems was investigated. Though transfer functions or frequency response curves are usually used to evaluate the performance of dynamic vibration absorbers, the floor response spectrum which is generally used in seismic resistance evaluation was adopted in this study, because it targets non-stational random vibrations such as seismic waves. Using a small-bore piping with a dynamic vibration absorber modeled in a two-degree-of-freedom system, the response reduction effect based on two design theories was evaluated by comparing the floor response spectra for the seismic waves. As a result of the comparison, there was no difference between the reduction effect sizes of the two design theories. Also, these effects of reduction equally worked in addition to the response decreasing by the damping ratio of piping. For seismic waves, it was found that the difference between the response reduction effect of dynamic vibration absorbers based on the two design theories was unlikely to appear.

In this paper, we study reproducibilities of response behavior of high-speed-moving vehicle when using the reduced-order-model. The vehicle model is made up of 10 cars and has 210 degrees of freedom in total. It is considered 9 cases of sinusoidal waves (3 patterns of frequency: 1.0, 2.0, 3.0Hz, and 3 patterns of direction: East-West, Up-Down, North-South) as input waves, and analyze cars’ displacements. Then we make reduced-order-models by sparse estimation for each case and investigate the reproducibility which is estimated by correlation coefficient between original-model and reduced-order-model. Moreover, in order to reveal which modes are important to express movements of the vehicle, 210 vibration modes are divided into 8 groups, based on natural frequency of the vehicle. As a result, from the perspective of correlation coefficient, around 20 modes were necessary to reproduce the response behavior and these modes were chosen from specific groups. Furthermore, it turned out that correlation coefficient was not enough to estimate the accuracy of the reduced-order-model because the correlation coefficient was high when ‘phases’ of response behaviors of original model and reduced-order-model were match though their ‘amplitudes’ were not match. So we use another indicator, normalized mean square error (NMSE) to estimate the accuracy of ‘amplitude.’ As a result, 30-50 modes were necessary, that was nearly double modes when using correlation coefficient. Moreover, it needed more modes to express horizontal direction (y), yawing direction (ψ), and it needed less modes to express displacements of truck and wheel set than body.

Following a major earthquake leading to shut down of a nuclear reactor, it is crucial to rapidly assess the damage state of equipment to ensure a quick restart. In this study, we have developed a rapid method utilizing transfer learning to assess the degree of damage of components. The training images were made using capacity spectrum and demand spectrum. Only 80 images were used for this study. We tested four models (GoogleNet, ResNet, VGG16, and AlexNet), and have achieved estimation accuracy exceeding 90% for all models. Furthermore, a comparison with deep learning-based numerical estimation of ductility factor revealed that the transfer learning method is better than the numerical estimation by the deep learning. Therefore, we conclude that the transfer learning is effective for estimating seismic damage with a small amount of data. Moving forward, we intend to investigate the impact of training data volume and image data to the transfer learning.

Structural health monitoring (SHM) is essential for achieving Sustainable Development Goals (SDGs) and establishing Business Continuity Plans (BCPs). SHM fundamentally involves a comparison of measured physical properties with damage indices. However, setting these indices can be a challenge due to inherent uncertainties in structures. Deep learning techniques have recently been incorporated in SHM. Previous methods primarily employed response data, although the use of external force data has also shown promise. Notwithstanding, a critical limitation of deep learning is its high dependency on large data sets. This requirement may pose a hurdle given the possible constraints in obtaining extensive structural observation data. In this paper, authors introduce a novel SHM method utilizing deep learning. Our proposed method leverages the structure's response acceleration and the acceleration of the input seismic ground motion. The wavelet transform outcomes of each acceleration are integrated. The ensuing combined data, containing three-dimensional information, necessitates an ensemble of Convolutional Neural Networks (CNNs). The classification outcomes from each CNN are subsequently connected using neuro-fuzzy to deliver the network's output. The efficiency of the suggested method was confirmed through an analysis of experimental data, achieving an evaluation accuracy exceeding 90% during validation. Furthermore, we found that each CNN's output could be utilized to predict the occurrence timing of anomalies, demonstrating the applicability of our method.

Recent advancements in digitalization have resulted in the daily collection of vast amounts of data. To capitalize effectively on this wealth of information, it is imperative to address multivariate issues, many of which are classified as NP-hard problems. One potential solution lies in metaheuristic optimization methods, which offer shorter search times and the ability to generate approximate solutions. These techniques have seen applications across various domains. Nevertheless, a significant challenge posed by numerous representative metaheuristic methods involves the necessity for parameter configurations, the values of which notably impact convergence accuracy. This study proposes a novel optimization methodology grounded in metaheuristic optimization techniques that eliminate the need for problem-dependent accuracy affecting parameter settings. We assessed the efficacy of our method using standard benchmark functions and engineering benchmark problems. Furthermore, we employed it to search for multiple variables, such as historical curves, while conducting a nonlinear seismic response analysis in a real-world application scenario. Our findings confirm that our approach is not only more cost-effective but also superior in accuracy compared to previously used metaheuristic optimization methods.

The various vibration tests have been carried out, depending on a specification and a shape of the structure. However, the data obtained from these vibration tests are underutilized in the failure evaluation for vibration. In this study, the failure probability assessment method is investigated for classified structure based on these test data. Furthermore, an evaluation indicator, which can be evaluated regardless of differences in input waves, is necessary to adapt this method to other structures and equipment. In previous studies, the sine wave vibration tests with the simple examination specimens were carried out to investigate the accumulated vibration energy in the equipment. In this report, vibration tests were conducted by random waves. We compared the relationships between the accumulated energy to failure and the accumulated energy per unit time in cases of random waves and sine waves. In addition, to develop a method that can evaluate the possibility of failure without the vibration test, a failure assessment method with the analysis and material data was presented. As a result, even when random waves are input, the accumulated energy increased with increasing input acceleration. It is similar to the previous results by sine wave. Furthermore, by using FEM analysis, time history response analysis and S-N curve, it is possible to predict failure without conducting experiments. In the future, we will conduct the other random wave vibration tests at other materials and establish a failure probability assessment method.

The applicability to Japan of the American Society of Civil Engineers seismic design standard (ASCE/SEI 7-22) is examined with respect to a simple seismic design method considering the plastic region of machinery and equipment. Response analyses were conducted for seismic waves recorded in Japan using a simple, end-supported, 5-Masses model with bilinear force-deflection characteristics, and the following results were obtained: (1) When the yield capacity is set using the maximum acceleration value of the input wave as the static load, an element ductility factor of 3 to 5 is expected. (2) The standard’s recommends value of 2/3 of the response reduction factor can be appropriate for flexible systems, but for systems with high natural frequencies, it is necessary to consider the other effects such as an overstrength factor in addition to the effect of energy absorption by plasticization.

It is essential to evaluate fatigue damage of piping systems, especially those in existing nuclear installations that have experienced large earthquakes. In this study, shaking table tests were conducted to understand the seismic performance of pipe components. Elbow, equal tee and reducing tee were selected as typical geometries of the components. The test results demonstrated that the location of crack penetration depends on the geometry of the components and direction of the cyclic loading. It was also confirmed that there was a large margin in the cumulative fatigue usage factor based on the current design practice, and that the piping components had a sufficient margins for fatigue damages.

While impact dampers have the advantage of a simple structure that allows them to be installed in confined spaces, they have the disadvantages of noise at the collision of an impactor, damage to the container walls, and reduced damping performance under low acceleration. In order to solve these problems, liquid-filled particle dampers have been proposed. By enclosing the fluid, the particles are affected by the fluid when vibrations occur, and their movement becomes more active. In addition, fluid is pushed out of the small gaps between the individual particles, resulting in a greater energy loss. Although previous studies have investigated experimentally and numerically, the effect of conditions such as the mixing ratio of fluid and granular material on damping performance was not examined. In this study, the effects were investigated experimentally.

Dampers are often used in vibration control and isolation systems for machines and structures. In this study, damping efficiency induced by stirring granular materials was investigated to develop stirring type dampers. Compared to oil dampers, which are currently the mainstream, this type of damper is superior in terms of application to high-temperature environments and ease of maintenance. However, there is still room for further consideration on structure to obtain higher stirring resistance. In this study, we attempted to increase the stirring torque by enclosing magnetic particles and generating a magnetic field in the container. As a result, it was confirmed that the stirring torque was increased by the magnetic field.