In recent years, semi-active control has been attracting attention as a control method for seismic isolation devices from the viewpoint of safety and energy consumption, but most of them use sensors on the seismic isolation devices to switch attenuation, so it is caused by an earthquake. It is difficult to deal with the beginning of shaking. Therefore, in this study, we proposed a semi-active control method that switches the damping of the variable damping damper using the acceleration response spectrum calculated from the seismic motion data at nearby stations. As a result, it was shown that not only can we expect the response to the beginning of the Earthquake shaking, which was difficult to respond to until now, but also the maximum response and the convergence time of the Earthquake shaking can be improved by predicting and controlling the response from the seismic motion before arrival.

To become carbon neutral, offshore wind energy is getting more attention as a renewable energy source. Although most of the existing offshore wind turbines are built on fixed foundations, they are currently restricted by the water depth. As shallow waters along the coast in Japan are limited, floating offshore wind turbines applicable to water depths of 100 meters or more are considered desirable. Various studies on floating wind turbines have been conducted worldwide, however, the wave-induced vibration and power supply shortage when there is no wind power still remain as important issues to be addressed. In this study, we propose a new concept of a floating wind turbine with the inerter-integrated wave energy converter (WEC) to generate electricity from the wave-induced vibration of the floating body and reduce the oscillation of the wind turbine simultaneously. First, we propose the concept of the floating offshore wind turbine with WEC and a simple model including a rotational inertia mass is derived to verify the effectiveness. Then, the parameters of the inertia mass and electric damping by the motor are investigated to evaluate the power generation efficiency and the structural control performance.

In recent years, offshore wind energy has been attracting much attention as a renewable energy source, and various studies have been conducted around the world to achieve the practical use of offshore wind power converters. Among the various offshore wind power generation devices proposed so far, a floating body type is more suitable for the Japanese waters where the water depths are 50 m or more and easier to install than the other strategies, even though wave-induced vibration is a significant issue. On the other hand, a wave energy converter (WEC) with an inerter mechanism consisting of a rotational mass was proposed by the authors to enhance the power generation performance. This study proposes a floating wind turbine with the inerter-integrated WEC to generate electricity from the wave-induced vibration of the floating body and reduce the oscillation of the wind turbine simultaneously. First, a more reliable analytical model for the proposed device is developed considering the effects of additional mass, radiation damping, and wave excitation force on the floating body. Then, the effectiveness of the proposed mechanism is shown through numerical simulation studies to irregular waves generated by the JONSWAP spectrum using the derived model. The parameter for the damping by the motor is investigated to optimize the power generation efficiency and the structural control performance as well.

Japan is an earthquake-prone country. The 2018 Hokkaido Eastern Iburi earthquake damaged a coal-fired thermal power plants in Hokkaido and caused an electric outage throughout Hokkaido. Therefore, it is important to improve the seismic resistance of thermal power plants. In addition, the boiler of coal-fired power plants has a large and complicated shape, and it is necessary to model it based on actual measurement to evaluate the seismic response. Therefore, the purpose of this research is to improve seismic resistance by attaching multiple vibration damping devices to the boiler structure of coal-fired power plants to impose reins on the response during an earthquake. Also, the purpose is accuracy improvement of model.

The transmission coefficient of vibration in a single-degree-of-freedom vibration system is known to decrease by increasing the viscous damping, but not sufficiently in the high frequency range. The viscous damping coefficient of an object is changed by a magnetic damping mechanism using an eddy current, which can change the damping by turning the current to the electromagnet on and off without problems such as a friction and aging. In other words, the viscous damping is increased near the resonance point and decreased in the high frequency range by switching the current to the electromagnet on and off. The FFT is generally used to measure the frequency of the object, but a relatively long period of data is required to perform the FFT. Because the crossing of the resonance curve is a single point in the case of binary switching of the current, it is determined to use a low-pass filter in real time. In this paper, by changing the damping due to eddy current, the damping effect in a wide frequency range is verified by simulations and experiments.

When designing and evaluating the strength of the piping system of a nuclear power plant, ductile rupture or plastic collapse is often assumed to be the limit state. However, previous studies have reported that the primary failure mode of piping systems is fatigue. Therefore, it is important to conduct a fragility assessment of the piping system under the assumption that the failure mode is fatigue. In this study, the evaluation method of the relationship between the input acceleration and the fatigue failure probability in seismic response analysis was proposed by using probabilistic ε-N curve (P-ε-N curve). The linear cumulative damage was calculated as the ratio of equivalent cycle of earthquake to fatigue life of best-fit ε-N curve corresponding to the strain amplitude of P-ε-N curve of certain probability. The fatigue failure probability of this linear cumulative damage corresponds to the probability of the P-ε-N curve. Then, the fatigue failure probability of simple piping system was evaluated by the proposed method. The fatigue failure of the piping system was occurred on the elbow part. the circumferential strain was obtained by transforming from open-closed angle of elbow pipe.

Since a vibration test is one of the most important programs in the manufacturing industry, many companies carry out the vibration test. The knowledge such as the transfer function, which was obtained from these tests, have been accumulated. In this study, the failure probability evaluation method of the similar structure is investigated based on the statistical analysis of these test data. In previous studies, the cabinets with a simple structure was investigated. As a result, the failure probability of the cabinet could be estimated with the failure probability curve. The confirmation of the adaptability in the failure probability evaluation method, which has been developed, is necessary. Accordingly, the failure probability evaluation method of the under-floor equipment on railroad vehicle is investigated in this report. 42 units of under-floor equipment on railroad vehicle were investigated. At first, the under-floor equipment was classified in the test condition and the mass. Secondly, the representative transfer function was decided. Furthermore, the uncertainty was also decided. The failure probability curve was investigated based on HCLPF with this uncertainty. The failure probability in under-floor equipment on railroad vehicles could be estimated with this method. Accordingly, this failure probability evaluation method can be applied to other components. Furthermore, the failure probability evaluation was compared with the vibration test result, which was confirmed the failure. As a result, the effectiveness of this failure probability evaluation method was confirmed.

Monitoring structural integrity has been demanded to achieve a sustainable society against disasters, including seismic and extreme wind events, and thus Structural Health Monitoring (SHM) system is one of the significant technologies. The natural frequency and the yield displacement of structures will be the significant damage indexes to assess the structural integrity. However, they would contain variances to the design values. The structural integrity assessments using the SHM should allow for the uncertainties in structural specifications, such as the yield displacement, to improve the assessment accuracy. Additionally, the seismic ground motion will have uncertainties regarding the acceleration levels, spectral characteristics, and others. These uncertainties can lead to assessment difficulty, reducing the accuracy of the assessment. To overcome this problem, the authors propose the method using the deep Convolutional Neural Network. This method using CNN has two features. The first is to suggest employing the response spectra as the training data of CNN. The second is to create a simple CNN architecture with a high classifier accuracy using Bayesian optimization. This paper demonstrates that the feature values detected by CNN allow the structural integrity against the seismic events to accurately classifier even if containing the uncertainties in the structural specifications and the seismic ground motions.

Typical failure modes of components and their causes are analyzed based on seismic experience database of components in Japanese NPPs. This report describes the detail of the damages and their causes to bring deteriorated or loss of functions in 15 component classes. In addition, secondary damages due to failures in components, especially overflows/leakage of water, oil leakage, fires, are also detected. The findings obtained by the present analysis can be used to clarify the failure mode in fragility analysis or improve post-earthquake inspections.

Fall accidents of escalators occurred in the 2011 off the Pacific coast of Tohoku Earthquake. The Escalator whose accident occurred was connected the second floor to the third floor in commercial facilities of the steel frame building. In general, escalators are set on beams of buildings. Furthermore, one side or both sides of the support are not fixed because of preventing damage to the escalator from the interlaminar deformation of the building. However, the interlaminar deformation of the building occurred more than expected by the great earthquake. In consequence, the fall accidents occurred because the escalators came off from the beams of the buildings. After the escalator accidents, the seismic standard was revised in Japan. The interlayer displacement angle of buildings was considered more than before. From this, the overlap allowance is longer so the possibility of the fall accidents decreases so much. However, an unfixed part of the escalator may collide with a building beam due to the earthquake. Furthermore, the escalator may transform by the collision and affect to the safety of themselves. Accordingly, in this study, the dynamic behavior of the escalator with the building beam during earthquakes is investigated, furthermore the safety against the revised earthquake resistance standards is confirmed. In this paper, the analysis methods for the safety evaluation is investigated a three-meter lift escalator, which has fallen due to an earthquake. The 3/10 scale model based on the three-meter lift escalator which the top is not fixed was created. Further, the vibration experiment with the 3/10 scale escalator model was carried out. The behavior of the 3/10 scale escalator model was confirmed during the earthquakes. Moreover, the seismic response analysis was carried out with the lumped mass models. The restoring force characteristics of the escalator were modeled by bilinear method. The validity of the analysis model was confirmed by comparing the analysis results with the experimental results. In addition, four patterns of actual escalators were evaluated.

In this study, based on the results of FEM dynamic analysis, the restoration mechanism for the tank rocking motion is discussed by comparing the overturning moment calculated by the Housner’s theory and the restoring moment which is composed of the distribution of the uplift force and the weight of the tank shell. The comparison implies that the restoring moment which is composed of the distribution of the uplifting force and the weight of the tank shell is unlikely to be a function as a restoration mechanism against the overturning moment during the tank rocking motion. Furthermore, the rocking angular acceleration obtained from the equation of motion considering the effective moment of inertia of the content liquid and the results of the FEM dynamic analysis are compared. From the comparison, this study concludes that the rotational equilibrium equation for the tank rocking motion should be formulated as an equation of motion that takes into account the effective moment of inertia of the content liquid.

The vibration of piping system subjected to earthquake is a severe problem. However, the actual piping system is seems to be too complicated to analyze theoretically. Therefore, the finite element method is used to obtain the natural frequencies and mode shapes. For two-span beam, the theoretical method for the natural frequencies are written in the textbook of the vibrations of continuous systems. In this method, the beam is divided at the intermediate support, and the function for the displacement including unknown coefficients is assigned for each divided beam. The boundary conditions for the divided beams yield the characteristic equation for whole beam. In this report, same approach is extended for the piping system with the elbow and concentrated mass.

In recently year, large earthquakes have been observed in Japan, and installation of seismic isolation system can be considered in many fields, such as nuclear power plant (NPPs) and modern architecture, in terms of greatly reduction of seismic force. To introduce seismic isolation system into NPPs, the significant improvement of the safety and reliability can be expected. For the purposes of this paper, a slip and hardening of isolation rubber bearing and nonlinear behavior of building structures are considered as the ultimate characteristics that would affect to seismic risk of isolation device and/or superstructure. Furthermore, the effect of the ultimate characteristics on seismic risk of NPP and equipment and piping system in a building is investigated. As a result, although ultimate characteristics of building structure does not affect to the seismic risk of isolation system, the characteristics significantly affect to the seismic risk of equipment and piping system in NPP buildings.

This paper describes the measurement of vibration characteristics of the eMDVA (embedded Mass Vibration Absorber) and investigation to build a finite element (FE) model to express the measurement results correctly. The eMDVA is proposed by one of the authors as a multi-modal and multi-axis vibration reduction device; it consists of spherical viscoelastic material with embedded ball-like mass. In this study, some eMDVAs with different sizes of spherical viscoelastic material containing ball-like mass with a 3-axes acceleration pickup were made, and vibration measurement tests were carried out. Then FE models of the eMDVAs were built. The modeling of the viscoelastic properties of the viscoelastic sphere were especially discussed.

This paper describes a dynamic vibration absorber (DVA) that can be easily adjusted to the frequency changes of host structure. Viscoelastic material (urethane rubber) is used as spring and damping elements in the DVA to support each side of a rectangular auxiliary mass made of iron, and the rubber can be compressed by bolts and iron plates. By changing the number of the rubber and the amount of compression, the supporting stiffness of the auxiliary mass can be changed and the natural frequency of the DVA can be adjusted. The DVA is applied to an actual host structure (a rotational machine testing equipment). The vibration characteristics of the DVA and the effectiveness of the frequency adjustment mechanism are investigated, and the results of the vibration control effect are reported.

In general, semiactive damper has high vibration control performance by controlling passive elements like damping coefficient. The damper requires a power supply and sensors, when there is a power fail under some trouble, it cannot be controlled and would be malfunction. The authors have developed an electromagnetic type sensor less semiactive damper. This type of damper has variable damping force by using a motor due to the braking torque, and the damping coefficient can be switched by controlling the resistance of terminal circuit of the motor. In previous paper, a solid-state relay and rectifier circuit was inserted to the terminal, and the damping coefficient can be automatically switched without any sensors instead of the motor generated. In this paper, to investigate the effect of a capacitor connected to the terminal circuit in parallel, resisting force characteristics of the semiactive damper was introduced, and switch timing of the damping coefficient was confirmed theoretically and experimentally.

This research investigates the performance of actively-controlled tuned inertial electromagnetic transducers (TIMETs) and discusses the feasibility of the self-powered control scheme for the TIMETs as well. The TIMET consists of an inerter, a tuning spring, and a motor and can absorb kinetic energy effectively by taking advantage of the resonance effect of the inerter and convert it to electrical energy by the motor. So far, various kinds of inerter-based devices have been proposed; however, most of these devices are limited to passive or semi-active control strategies. Therefore, to investigate the effectiveness of the actively-controlled TIMETs, linear quadratic Gaussian (LQG)-based acceleration feedback control strategies are applied to a three-story benchmark building model with the TIMETs. In addition, the feasibility of the self-powered control scheme utilizing the absorbed energy is discussed by calculating the absorbed and injected energies. Numerical simulation studies show that the actively-controlled TIMETs work better than the passive system and that the self-powered system is feasible, depending upon the control forces, the energy conversion rate of a motor.

In this paper, the effect of the blade shape on the efficiency of damping by stirring granular materials. Compared to oil damper, this damper has the advantages of a simple structure, no possibility of granule leakage and no need for periodic maintenance. Granular materials were placed in the space between the cylinder container and the blade. The blade rotated sinusoidally using four-bar linkage. The rotation angle of the blade and the torque caused by the collision force were measured with an angle sensor and a torque sensor, respectively. The granular spherical particles used in this study are made of glass. Five blade shapes were used. It is shown that the stirring torque becomes larger for the fin type blade than for the plate type blade.

To improve the reliability of the loss factor identification technique for metallic alloys proposed by the authors using a slender beam and s-dB bandwidth method, this study first investigates the effects by the fixing conditions of the specimen, such as tightening torque and installing shims. According to the test results, tightening torque variations and inserting shims affect little on the loss factor. Loss factors of two different laminated metallic alloys were then measured under several heat treatment conditions. Some shape changes (warp) were observed at some heat treatment temperature, so numerical calculations using finite element analysis were carried out to check the change of obtained loss factor by the s-dB bandwidth method due to the warp. The numerical results have suggested that the warp about 15 mm versus beam length 500 mm doesn't affect substantially on the loss factor.

The purpose of this study is to investigate numerically the static and dynamic characteristics of a copper based shape memory alloy (SMA). In the previous study, we have proposed a vibration isolator using a Ti-Ni based post-buckled shape memory alloy to improve the isolation performance utilizing the negative tangent stiffness of post-buckled SMA and to mitigate the design requirement for the isolator. However, some inconvenient characteristics had been proved when Ti-Ni based SMA was applied to an isolator. Therefore, in this study, in order to overcome these inconvenient characteristics, we investigate the dynamic properties of a copper based SMA. Firstly, the static restoring force of post-buckled Cu based SMA was investigated. From the numerical result, the negative tangent stiffness of post-buckled SMA was stably observed and it was confirmed that the negative tangent stiffness arises when the phase transformation from austenite phase to martensite phase begins. Subsequently, the dynamic response of SMA was investigated. From this numerical result, it was confirmed that dynamically loaded SMA has good structural attenuation characteristics. In addition, the frequency response results showed that Cu based SMA has a reduction in the primary natural frequency and resonance peak compared to linear material.

In this study, we develop a vibration isolation system using an air suspension with a variable length slit restriction, clarify its dynamic characteristics, and build a system that automatically adjusts the damping coefficients and equilibrium position of a supported object. The proposed air suspension can provide the optimum equivalent damping coefficient by automatic damping adjustment mechanism. The optimum equivalent damping coefficient, which provides the minimum resonance amplitude, increases as mass of supported object increases. The damping coefficient can be varied by varying slit length of restriction. In order to vary slit length, the damping adjustment mechanism consists of a fixed plate, which has a partially circular groove, and a rotating flat plate faced to grooved plate. The variable length partially circular slit is foamed by two plates. The damping coefficient is almost proportional to an adjustment angle of the rotating flat plate in the adjustment mechanism. The adjustment angle which provides the minimum resonance amplitude can be obtained by equation of the supported mass. The proposed system consists of the air suspension, two pressure gauges measuring atmospheric pressure and static pressure in the cylinder, the damping coefficient tuning mechanism, a servo motor rotating the flat plate to tune the adjustment angle and a micro-computer calculating the optimum adjustment angle using signals of the pressure gauges. Even if the mass increases up to the half as much again and decreases down to the half of it of the nominal value, the minimum resonance amplitude is archived using adjustment mechanism.

In the present paper, the evaluation of the time average output of the time-invariant linear system is explained in the context of the covariance matrix as the solution to the Lyapunov equation. This problem reduces to simultaneous linear equations with respect to the elements of the covariance matrix. These general relations are applied to two cases, in which the primary system is subjected to the Gaussian white noise excitation, and the dynamic vibration absorber is optimized to minimize the time average of the squared displacement or the squared velocity. The optimum tuning ratios and the damping ratios for the compliance and mobility functions are given as exact solutions. The effects of the primary system damping of the optimal solution proven to be almost negligible.

W In this study, we dealt with the problem of optimizing the installation and parameters of each dynamic damper when two dynamic dampers are distributed and installed in a three-layer structure against the base excitation. First, the optimum design of the single dynamic damper with a mass ratio of 0.1 was performed by the method using the fixed-point theory and the exhaustive search method of the parameters, and it was found that the accuracy of the latter method was sufficient. Next, when the masses of the two dynamic dampers are equal (both have a mass ratio of 0.05), the installation positions of the two dynamic dampers and the parameters of each dynamic damper were optimized. It was found that the optimum installation position is 2F + 3F. The vibration suppression performance was equivalent to that when the mass of the single dynamic damper was multiplied by 1.05. Furthermore, when two dynamic dampers were installed on 2F + 3F and the mass distribution of each dynamic damper was optimized, the optimum mass ratio was 0.02 for the dynamic damper on the 2nd floor and 0.08 for the dynamic damper on the 3rd floor. The vibration suppression performance was equivalent to that when the mass of the single dynamic damper was multiplied by 1.15. Finally, as a result of sensitivity analysis of the parameters of the two optimally designed dynamic dampers, it was found that the damping ratio is more robust than the frequency ratio. In other words, it was found that it is necessary to pay attention to the accuracy of the spring constant when actually making a dynamic damper.

Tuned Mass Dampers (TMDs) are efficient passive damping devices that are widely used. The typical components are a mass, a spring and a dashpot. However, some parts which need to be maintained exist in TMDs. Therefore, tuned rolling-cylinder dampers (TRCDs) are proposed, and it is expected to overcome such problem. TRCDs are composed of a cylindrical container and multiple rolling elements, and the rolling elements rotate on cylindrical surface. TRCDs suppress horizontal vibration by rotation of the rolling elements and friction between rolling elements. The damping performance of TRCDs is adjusted by the size and number of rolling elements, but the optimum adjustment method has not been established. This paper presents the optical solution of TRCDs using particle swarm optimization (PSO). PSO is one of the methods to mathematical optimization problem, and it is possible to efficiently search for the best tuple from multiple combinations. In this study, PSO was introduced to optimize the radii of the rolling elements and the cylindrical container.

Beam like structures, such as columns, pipes, bridges and high-rise buildings, are difficult to reduce vibrating. A commonly approach to control these vibrations is to use a dynamic absorber. Most of the dynamic absorbers have been used to reduce the transverse motion of beam by exerting a shear force on beam (hereafter called shear type dynamic absorber). In a previous paper, the authors researched two types of dynamic absorber: one that exerts a bending moment on the beam (hereafter called a moment type dynamic absorber), and one that exerts both a shear force and a bending moment on the beam (hereafter called a shear and moment type dynamic absorber). When three types of dynamic absorbers were installed on cantilever and simply supported beams, the optimal conditions of the dynamic absorbers were derived. The results showed that the peak values of frequency response focusing on an absolute displacement were reduced in case of the moment type or the shear and moment type dynamic absorbers comparing to the shear type dynamic absorber. In order to investigate the effect of vibration suppression about a deflection of the beam, which is focusing on a relative displacement, an elastic vibration of the beam focusing on the relative displacement were derived, and the frequency responses about the relative displacement of the beam were obtained theoretically. Then numerical calculations were carried out, and the results are compared with those of the previous paper focusing on absolute displacement.

When predicting the electric power consumtion of EVs, the method of calculating the vehicle speed based on the accelerator operation of the driver is called forward calculation. In this case, the driver model performs speed control by setting the speed pattern of the driving mode as a speed target. On the other hand, the method of calculating the torque necessary for acceleration / deceleration and the current necessary to output the torque by the motor by tracing back from the load to the energy source based on the speed pattern as a starting point is called reverse calculation. Although different models are required for causal modeling, a model corresponding to both methods was constructed by utilizing the features of acausal modeling. This can reduce not only the maintenance cost of the simulation model, but also the difference between these models for forward and reverce calculation. The reverse calculation methed doesn’t need control models, and calculates faster than forward calculation.

Gearbox modeling with mixed continuous and discrete events has been studied for long time. The gearbox power loss depends on the angular velocity and load. In this report, the LossyGear model of the Modelica standard library was constructed with a new configuration from the viewpoint of system engineering utilizing the synchronous feature of Modelica Standard Library 4.0. The proposed method can also be regarded as a case study for general cyber-physical modeling approach.

1D Modeling Study Group of The Japan Society of Mechanical Engineers; Dynamics, Measurement and Control Division is focusing most on the formulation of 1D models. Formulation of a 1D model by applying mechanical, fluid, thermal and electrical systems based on a five-level 1D modeling method to embody the concept of 1D-CAE, which is considered to be very useful for physics formulation.

World has been struck with a pandemic Covid-19 in 2020. As a result, distance learning opportunities have been created on an unprecedented scale. This paper presents an attempt towards distant learning and manufacturing processes of vibration apparatuses in the situation where COVID-19 infection has spread. To grasp the condition of students during an online lecture, some quiz questions on mechanical vibrations were given using Google Forms. It is shown that the use of some recorded videos of the vibration apparatuses in distant learning has a positive educational impact on students. Under the difficult circumstances, three vibration apparatuses were made by students using online meeting.

This paper discussies teaching materials for vibration technology courses. Dynamics of Machinery is one of the four major dynamics of engineering education in universities, and Vibration Engineering is almost always included in the curriculum. However, why many engineers who graduated from an engineering school and became vibration engineers must to learn vibration engineering again from the basics? In this paper, we introduce the vibration engineering training materials for automotive engineers that were tried out by the JSAE NVH committee in 2020, and consider the intuitive technology behind the materials. In the vibration design of automobiles, the method of considering vibration phenomena by replacing them with the 1-DOF vibration system is traditionally used and has been instructed orally from senior engineers to junior. This paper also discusses the difference between the vibration education at universities and the vibration education at engineering fields.

Fan motors used for cooling data servers are generally controlled by inverters to save energy and reduce noise.At this time, noise is generated due to the inverter.Even manufacturers have taken noise countermeasures, it is difficult to reduce the noise completely.In this research, we focus on the output current of the inverter to qualify the current characteristics that cause noise. Furthermore, the noise countermeasures which were taken by manufacturers were investigated ,and the connection between the current characteristics and sound quality of the fan motor. From these results, we aim to propose a sound quality improvement method by changing the inverter output.

In this study, we attempted to decrease door vibration of a refrigerator in which the compressor was installed at top area for good usability. Through the operational test, the door vibration was found to be large at 18 rps. For the factor analysis, vibration mode analysis and operational transfer path analysis were applied. The result showed that the refrigerator twist mode at 18 Hz and the compressor vibration behavior along left-right direction were observed to be the main factor increasing the door vibration at 18 rps. Then, we inserted a steel plate between the compressor and the body along left-right direction to constrain the compressor vibration along the direction. As the result, the door could be reduced decreased largely effectively by the attachment of the bar.

This paper is concerned with the estimation of transient inputs by using the Kalman filter. An augment system is derived in which state quantities include input forces. Then the theoretical equation of motion was given in previous studies. However, it may be difficult to derive the equation of motion of the existing structure. We need to obtain the state space equations only from the vibration responses. Here, the augmented Kalman filter can estimate the input force in the state quantities and the accelerations of the observed quantities. The covariance matrices were adjusted to improve estimation accuracy in the previous study. An evaluation function of adjustment used rms of the errors between the estimated accelerations and the measured ones. The state quantities of the system derived from the theoretical equation of motion are displacements and velocities, but it is difficult for the physical quantities to specify the state quantities derived by the subspace method. In this paper, the input forces are estimated by the acceleration responses of the five-degree-of-freedom system, and the state space equation is estimated by the subspace method. We consider future issues from the estimation results.

This paper describes the attenuation of sound in the pipe. The complex density, which represents the sum of the inertial force of the fluid and the viscous damping, is used to attenuate the sound in the tube. For this complex density, the complex density that represents the attenuation of sound is derived assuming the Poiseuille flow, which is generally a steady flow. However, focusing on the fact that the sway of air when sound propagates is not a steady flow but a non-steady flow, the purpose of this study is to find the complex density by a new method. In addition, the validity of the complex density will be examined by comparing the specific acoustic impedance obtained in the experiment with the value of the specific acoustic impedance obtained from the obtained complex density.

In recent years, software-based music composition is becoming common among composers. In this study, we imitate the sound radiation about striking force using vibration transmission and acoustic characteristics of the structure of snare drums. The aim of the study is to propose a methodology that enables one to virtually reproduce the radiated sound accurately. In this report, results of experimental modal analysis by impulse excitation of membrane of snare drums are presented. We conducted the analysis with radiation sound pressure from battered membrane. The sound pressure was measured with a microphone which is located near the battered membrane. Then we compared the obtained modal characteristics with those predicted by theoretical analyses. By using mode assurance criterion, we identified that experimentally-obtained low-order modes have a correlation with the theoretically predicted modes. In addition, spatial orders of experimentally-obtained high-order modes illustrate that they match well with those of theoretically obtained modes. In conclusion, we identified experimental acoustic modes that agree with theoretical vibration modes.

The purpose of this study is to model the acoustic field in which gas and liquid coexist in a separated state, as typified by the space under the motor of a compressor installed in an air conditioner, as a concentrated-model consisting of masses, connecting springs, and connecting damping, and to propose a sound field design that reduces noise through analysis using this model. In order to validate the modeling of a sound field where gas and liquid coexist, eigenvalue analysis is performed using the mass and stiffness matrices of the model, and the effectiveness of the model is confirmed by comparing the obtained eigen-frequencies and eigen-modes with the theoretical solution. From the results of the forced vibration analysis using the concentrated-model, it was confirmed that the sound pressure peak becomes very large when the resonance occurs in the liquid region in the acoustic field, and the acoustic field design using the gas space as a dynamic vibration absorber was proposed as a method to suppress the sound pressure peak. The effect of this method was verified through analysis.

We paid attention to the change in sound quality due to the material change of the nut and saddle, which are the elastic support parts of the classical guitar. The materials used are ivory and carbon. There was a comment from the user that there was a difference in sound quality. As a result of comparing the two, the carbon material had a smaller sound elongation and tended to suppress the time-series change of the envelope. It was also found that the singularity of sound elongation may be related to the behavior as an antiresonance point around the saddle bridge in a specific harmonics.

Classical guitar has an aging effect that can be expected to improve sound quality by playing. However, the mechanism of its effect has not been clarified. Therefore, we are conducting research to clarify the structure of classical guitars and the characteristics of their components, build numerical models based on them, and elucidate the mechanism of the aging effect by numerical analysis. Here, the vibration characteristics of the constituent wood of the guitar are experimentally identified in consideration of anisotropy. Furthermore, the effect of the moisture content of wood on the vibration characteristics will be investigated.

Parametric speaker can radiate an audible sound beam with sharp directivity by using the non-linear interaction of ultrasonic waves. This radiated sound has directivity even after being reflected on the wall. In recent years, a sound absorption coefficient measurement method using a parametric speaker has been proposed, and parametric speakers are increasingly being used in acoustic spaces with reflective. When analyzing this sound wave, it is necessary to use discrete analysis method that enable analysis in closed space. Many discrete analyses by using finite difference time domain method have been proposed as analysis methods for parametric speakers, but these methods have problem that the calculation load is heavy. In previous study, we constructed a steady-state response analysis method that can efficiently analyze the audible sound of parametric speakers. The previous method is combined a nonlinear concentrated mass model and a perturbation method. In this report, we expand the previous method and construct the equation of motion described in sound pressure coordinates to reduce the computational load. The effectiveness of proposed method is confirmed by numerical calculation.

Noise countermeasures are an important engineering problem, and acoustic analysis methods for noise prediction and reduction have been widely studied. In a thermoacoustic engine, the sound is generated when the air vibrates due to the temperature gradient inside the pipe. Applying this effect may reduce noise by using the temperature distribution. Therefore, the purpose of this study is to analysis an acoustic space with a temperature gradient using a concentrated mass model. In previous study, we built a linear model of an acoustic tube with temperature gradient and validate the proposed model by numerical calculation of heat storage device in a cylindrical pipe. In this report, we propose the analysis method of self-excited thermoacoustic vibrations using the previous model. Two types of methods using a transfer matrix and a dynamic stiffness matrix is examined as methods for analyzing self-excited vibrations. The proposed methods are validated by comparison with the numerical calculation results shown in another study.

To simulate squeal noise at curved sections in railway lines and control the noise, a prediction model is required. In this study an analytical model for vibrations of both a railway wheel and rail has been developed for prediction of squeal noise. The model is based on complex lumped parameter system from vibration characteristics of the wheel and rail, and the contact forces between them. This model also includes the two coupling factors, i.e., between a wheel and rail, and, between the vibration directions. Parameters of the two-disc test rig that consists of two discs corresponding to a wheel and rail are applied to the model for the verification. By using the model, the vibration of both discs related to squeal noise are well simulated and the peaks at the natural frequencies of the discs can be seen. These results show good agreement with the experimental results. Through the comparison of time histories between the analysis of the model and experimental result, the overall trends that wheel vibration repeats greater and smaller can be also well simulated. This suggests that the proposed model simulates the vibration related to squeal noise.

In order to investigate the characteristics of curve squeal, a scale model test was performed using an improved experimental apparatus that made it possible to measure the vibration characteristics on a rail disc. It is found that dominant vibration modes of all rail discs are equivalent to those of the wheel disc. Also, the vibration of both discs tends to be intense depending on the diameter of rail discs. In addition, the vibration of a wheel disc related to the squeal noise is attenuated due to damping sheets attached to a rail disc. These would suggest that suppressing the vibration of rail and changing its vibration characteristics are effective in reducing wheel vibration and noise associated with the squeal.

Loudspeaker arrays which can confine the acoustic field in the near-field are investigated for realizing personal audio systems. Since the supposed listening point is in the near-field, possible layouts of the loudspeakers are, for example, neck speakers and open-ear speakers. The performance of these two examples are examined by numerical simulation in this study. In the neck speaker, the acoustic confinement was poor especially at a high frequency, because the listening point was not very close to the loudspeaker array. In the open-ear speaker, the acoustic confinement was good, because the listening point was very close to the loudspeaker array.

While driving a car on a road, noise from the collision of gravels rolled up by the tires makes a driver uncomfortable. The underside of the car may be coated with a damping layer on the steel plate to reduce noise. To estimate the effect of the damping layer on noise, the time history of the impact force is experimentally measured with an impact apparatus with a rigid pendulum and a force sensor which hits a coated rectangular plate. The impact force is then formulated as an approximate function with parameters of impactor’s mass and velocity. By using the approximate function of impact force, the vibration and sound pressure radiating from coated plate are estimated based on the Rayleigh-Ritz method where the coated plate is assumed as a pure plate with mechanical properties synthesized with those of damping layer and steel base plate. The estimated sound pressure agrees very well with the measured one. The effects of material and thickness of coated plates on the impact noise are revealed with the estimation.

In the modern society, development of noise abatement technologies for machines and structures have become an important issue to realize a comfortable sound environment for humans. The growing interest for noise problems may be due to the increase in large-scale industrial machinery such as engines, fans, blowers, transformers, and compressors. For these noises, it is necessary to choose different measures according to the characteristics of the noise generation mechanism. Noise prevention measures can be divided into two categories: passive noise control (PNC) and active noise control (ANC). Sound absorbing materials are commonly used for PNC. Although the materials can be adopted for noise environment in a wide frequency range, the sound reduction is not efficient specifically for a low-frequency noise. Therefore, ANC, in which secondary sound source is used to mute the target noise, is expected to be an effective means. In this study, we constructed a feedback type ANC system and evaluated the noise reduction performance by numerical simulation and experiment for controlling one-dimensional noise in a duct. The proposed system worked effectively for reducing the noise in the duct with a simple device configuration, however, the performance leveled off due to the amplification of the untargeted noise component. The part will be our future task.

In order to reduce interior noises in railway vehicles, it is necessary to comprehend both of transfer paths and the contribution ratio of them. Especially, the contribution ratio of each interior panel is analyzed by estimating transfer functions between a noise source and evaluation points of noise. This study focuses on estimating the transfer functions. We estimate transfer functions by exciting interior panels with vibration speakers in order to predict the interior noises. Firstly, the acceleration of an excited point and the sound pressure of the evaluation points are measured on excitation tests. Secondly, the two types of transfer functions, this is, single-input multiple-output (SIMO) type and multiple-input multiple-output (MIMO) type are estimated from the measured acceleration and sound pressure. Finally, the interior noises are predicted by multiplying the acceleration by the transfer functions. These methods are applied to the test railway vehicle. Predicted results by two types of transfer functions are compared with the measured interior noises. As a result, the interior noises are predicted precisely, in particular by use of MIMO type transfer functions.

Currently, Active Structural Intensity is mainly used for energy propagation evaluation in Intensity analysis. Therefore, this paper examines structural changes focusing on Reactive Structural Intensity, that expresses stationary component of energy transmission. We have derived the structural change sensitivity of Reactive Structural Intensity as well as Active Structural Intensity. Numerical simulation was performed with a spring mass damper system with four degrees of freedom. From the results of the sensitivity analysis, we achieved a reduction in intensity by adding mass.

The new idea is proposed that the vibration is transmitted between the smallest unit of component modes, and the combination of the modes mentioned above describes the dynamic characteristics of the entire system. Based on this idea, the vibration mechanism can be represented in a transmission path diagram using these modes, and the path can be changed by shifting the eigenvalues. In this paper, an example of applying this technique to the vehicle FE model for reducing road noise is introduced. The optimization aimed at reducing vibration response clarified the following two measures are proved to be effective. One is the suspension member bending mode should be placed at a higher frequency than the acoustic cavity back and forth mode, and the other is the windshield membrane 1st mode should be separated from the acoustic cavity back and forth mode. It seems to be applicable to many other vehicles, and it is believed a general solution has been obtained based on the characteristics of the components.

Transfer path analysis (TPA) has been used as a method for obtaining contribution from multiple vibration sources on the response point. Component TPA is recently proposed TPA method. This method enables us to predict the response point vibration when the input force is changed by employing a virtual force (Blocked force). In this study, we verified the difference between Blocked force and the actual transferred force (Contact force) used in an experimental condition. In addition, we also considered a motor attachment condition where both forces can be applied as almost same.

The present study is concerned with the application of radiated sound simulation by the virtual sensing. The virtual sensing is a method to estimate unobservable or unmeasurable state variables by combining exsisting measurement data with model information. When FE model is applied to the virtual sensing, vibration response data estimated at all nodes. Therefore, it enables to simulate sound radiation from mechanical structure with vibration response data. In this paper, it is illustrated how to estimate vibration response data, and simulate sound radiation. Finally, it tests how the quality of estimation for sound radiation.