Several standards or manuals are available for the test methods of damping capacity of damping materials such as composites or laminated damping steel sheets, however, there are little documents focusing on lightly damped materials like metallic alloys. This study intends to provide a simple method for loss factor identification for metallic materials using common vibration measurement setups. Using slender beam shaped specimens, vibration measurement and data processing procedures are investigated in order to obtain loss factors with high reliability. It has been shown that applying a 6 dB bandwidth method together with spline interpolation technique to measured mechanical impedance, rather than commonly used half-power bandwidth method, leads to good results.

This paper describes a new analytical method to derive free vibration of vibration systems that have hysteretic damping. We cannot obtain practical solutions as general solutions of homogeneous differential equations because general solutions diverge to infinity when vibration systems have hysteretic damping. Therefore, approximate solution that uses viscous damping instead of hysteretic damping has been used thus far when the damping is relatively small. In addition, the analytical method that uses Fourier inverse transform was proposed to obtain the free vibration that does not diverge. The validity of this conventional method has not been proved because there are no exact solutions. Apart from this problem, this method has disadvantages that step responses cannot be derived directly, and computational load is large. To solve these problems, we propose a new analytical method that uses the Fourier series expansion of the excitation terms. Using this method, the solution of free vibration is given as the superposition of the solutions of forced vibrations. Both impulse and step responses of discrete and continuous vibration systems were analyzed using the proposed method in this paper. The effectiveness of the proposed method was verified through numerical simulations.

It is known that damping characteristics are improved by complexing fine particles in a viscoelastic material, however the relevant mechanism is unknown. This study focusses on the strain distribution in the composite material and investigate factors that may affect the change of damping characteristics. The X-ray computer tomography image was obtained with before and after a tensile load applied to the test piece, and we did a research on each factor through image processing. It was confirmed that a local strain occurred from this distribution, and suggested that this may be a factor promoting more energy dissipation.

The sound quality of a classical guitar is greatly influenced by the Sounding Board. Strutting is attached to the back of the Sounding Board to maintain strength. At the same time, it is known that the strutting layout has a great influence on the sound quality of the guitar. Today, the layout of strutting tends to be fixed. Therefore, we made a guitar with a characteristic by reducing the number of strutting. However, the professional player's evaluation was "uninteresting sound quality“. Therefore, we applied a one-week light aging effect to the guitar by acoustic vibration. In this evaluation, the sound quality was evaluated by the combination of sound extension and timbre. In addition, the expression of the timbre can be calculated from many combinations of excitation positions and excitation methods. This guitar had better Sound extension than the conventional guitar even in the light aging state. In addition, this guitar can be evaluated as having a wide range of tones and excellent sound quality, and the same results as the hearing evaluation of professional players were obtained.

In recent years, demand for acoustic signals has increased as a barrier-free equipment for the visually impaired people. However, a guide sound is a noise to neighbors, and a penetration rate of acoustic signals is very low. The purpose of this study is to develop a directional speaker by using piezoelectric vibrator. In the experiment, the rectangular flat panel speaker was produced experimentally, which is centrally excited by piezoelectric vibrator. In order to clarify to the directional mechanism, the visualization measurements using the spatial transfer function was evaluated. As a result, the prototype speaker had narrow directivity and generated the plane wave at a specific frequency. Furthermore, the formation of plane wave was affected by the near field of flat panel, in where three strongly sound radiations were observed.

In recent years, the noise of the engine and the intake and exhaust systems has decreased due to the improvement of vehicle performance, and the contribution of tire/road noise has increased relatively. There are two types of sound sources for tire/load noise, one relating to air resonance system and the other relating to the vibration system of structure. It is considered that the noise caused by tire vibration due to road surface in a low frequency band is affected by tire vibration characteristic. The purpose of this study is to clarify the effect of tire vibration characteristic on tire/road noise. In this study, the sound pressure characteristics were examined with the two tire preload condition and the effect of tire preload on sound pressure characteristics were investigated.

The small fan motors are used by many electronics for cooling device. They are essential for present industry. However, quality inspection of the small fan motor is conducted an organoleptic test by inspectors who have special skills which are based upon their auditory organs and tactual senses. It is not easy that inspectors will have mastered those skills. In addition, there is a problem of those skills sometimes depend upon their mental and physical condition. Therefore, quality assurance is considered insufficient. When we observed inspectors to perform organoleptic test of the small fan in the actual production line, organoleptic inspector diagnosed rotation sound and vibration of the small fan to turn the wrist and to close the ear in the state of holding the small fan. Then we considered an operation to excite a vibration to the small fan to add unsteady displacement. Therefore, The study measured the vibration acceleration signal of the small fan by equipment imitating the handling operation performed by the inspectors and aimed at realizing quality diagnosis by Mahalanobis’ Distance (below “MD”) from average value of measured vibration (Time average value of the RMS level of the vibration acceleration signal ) and its deviation (the difference between the maximum value and minimum value of the vibration acceleration level ).

Diesel cars having a diesel engine as a power source are widely used as railway vehicles that travel in non-electrified sections. When a driving device such as an engine fails, the vehicle cannot run, so it is desirable to detect an abnormality early to prevent the failure. Therefore, we are conducting research and development of a state monitoring method by vibration, targeting drive equipment such as engines. This time, an abnormal simulation test was carried out using a bench test, in which SiC was mixed into the transmission oil to promote wear inside the transmission. It was confirmed that the abnormal condition of the transmission can be detected by applying the condition monitoring method to the measured vibration data by reproducing the abnormal wear occurring in the bearing of the transmission, and the condition monitoring method is effective.

To simulate squeal noise at curved sections in railway lines and develop measures for the noise, a prediction model is required. In this study, an analytical model for a railway wheel and a rail, which are modeled with a disk and a roller, is developed. The model is based on vibration characteristics of the disk and the roller, which were derived from modal analysis, and the contact forces between them. This model also includes the two coupling modes, i.e. between the disk and the roller, between the vibration directions. By using the model, the disk vibration related to squeal noise are simulated and the peaks at the natural frequencies of the disk can be seen. These results show good agreement with the experimental results. This suggests that the model has potential to simulate the squeal noise. The model also shows that the disk vibration is greater when the natural frequencies of the roller in the vertical vibration are equal to that of the disk in the axial vibration. This indicates that the two couplings have the influence on the squeal noise.

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.

This paper is concerned with improving the accuracy of estimation of non-stationary inputs by using Kalman filter. The estimation accuracy is improved by updating weighted coefficients of covariance matrix every time step. In this paper, an augment system is derived in which state quantities include input forces. The state quantities of the system consist of displacements, velocities, and inputs. The acceleration responses are used as measuring quantities. Then, the state quantities are estimated by the Kalman filter. Here, a procedure is proposed to update the covariance matrix components related to the input. The estimated displacements are used to decide the weighted coefficients. The feasibility of real-time estimation is considered by using Brute force selection and the golden section algorithm. In this paper, the excitation input is applied to the mechanical structure with 5 degrees of freedom, and the excitation input is estimated from the vibration response. In this study, the input estimation is experimentally performed under various conditions, and the effectiveness of the method by updating the weighted coefficients is verified.

While developing a new product, modifications often occur by various reasons, like durability, cost, productivity and so on. At that time, engineers engaging the noise and vibration have to be inform the effects of the modification on the noise and vibration to the another engineers involved the development, quickly and efficiently. The proposed method satisfies these necessary and sufficient conditions for this requirement given as (1) Modal parameters of the whole structure before modification, (2) The difference of the stiffness and mass matrix of the FEM before and after modification around the modified area. To obtain the modal parameters of the whole structure before modification, the test of modal analysis is better than FEM because of the manpower and accuracy of the complicated structure. This paper shows accuracy of the estimated modal parameters of the structure after the modification, by using FEM and experimental data.

At liftoff, launch vehicles are subject to harmful acoustic loads due to the intense acoustic waves generated by propulsion systems. Dominant acoustic modes inside payload fairings are payload fairings correlated with ring mode of structure. Experimental and numerical modal analyses were conducted for a simplified fairing model to obtain the ring modes appeared from 10 kHz to 20 kHz. Although axisymmetric ring modes were obtained by the numerical modal analysis using Finite Element Method (FEM), asymmetric ring modes were obtained in the experiment. The deformation of ring modes were considered to be caused by bolt connections in the simplified fairing model, so, Bayesian optimization was applied to Finite Element Method analysis to estimate inhomogeneity of the bolt connections. Preliminary numerical experiment was conducted to study the application of Bayesian optimization in Finite Element Method for estimating bolt connections, then, this method was applied to the simplified fairing model. Asymmetric bolt connection was obtained in Bayesian optimization in Finite Element Method, and the ring mode shape obtained by the Finite Element Method showed reasonable agreement with the experimental result. The comparison confirmed the usefulness of this method.

Measurement of natural vibration of acoustic space is effective for noise reduction in the cabin room of vehicle (e.g. auto-mobile, railroad car and so on). In general, multi-point excitation is useful to measure natural vibration of threedimensional acoustic space with high damping on boundary surface. However, multi-point excitation needs adjustment of amplitude and phase for each actuator. Thus, multi-point excitation is difficult to implement. In this study, the measurement technique of natural vibrations of acoustic space by multi-point excitation using decentralized control with local feedback control is used. Local feedback control generates force in the direction of motion, which had been presented by authors. In this paper, the natural vibration of acoustic space with a shielding plate was measured.

Inverters and gaps between rotor-stator generally introduce numerous harmonics in the electromagnetic force waves, which may cause a significant increase in the vibration and acoustic noise of motors. Therefore, these noise and vibrations have to be reduced at motor design stage. The widely used numerical analysis software can perform the multiphysics analysis under the integrated environment such as the electromagnetic-vibration-acoustic collaborative analysis. However, this method has an increase of computational cost resulting from a model size, which may cause difficulty of using at the design stage. In this paper, we proposed a simple calculation model in order to alleviate these computational cost for these collaborative analysis. Firstly, vibration analysis of motor was simplified as mobility transform matrix by using double beam cylindrical structures. Secondly, acoustic analysis was simplified by using acoustic radiation efficiency. In this investigation, we verified the acoustic radiation properties of a cylindrical structures from the viewpoint of the acoustic radiation efficiency by both of experiment and analysis. Finally, the proposed model was validated by comparing predicted acoustic noise level with an experimental one of an industrial motor.

This paper is concerned with active control of acoustic radiation power of a multi-walled structure. In the past literature, optimal control of acoustic radiation power for a double-walled structure in which both walls of the acoustic space are surrounded by flexible walls has been studied. It has been clarified that the reduction level of an actively controlled doublewalled structure is greater than that of an actively controlled one-walled structure in the sense of sound transmission control. Thus, the number of flexible walls have an impact on the control effect. However, research on modelling and control of a triple or more walled structure have not sufficiently done. Therefore, this paper presents how to model and control a triple walled structure. First, in order to facilitate further numerical analysis of multiple-walled structures, we model triple-walled structures using block inverse matrices, which is different from the conventional method. Next, the validity of the theory using the block inverse matrix is verified by comparing with the result of the numerical analysis for the triple-walled structure in the previous research. Finally, we verify the optimal control of acoustic radiation power by two control elements in a triple-walled structure from the numerical perspective, comparing its characteristics with the case of control by one control element.

Parametric array loudspeaker（PAL）is a speaker that emits an ultrasonic wave modulated based on audible signals. The modulated signal is self-demodulated by the nonlinearity of air and can transmit audible sound. PAL has sharp directivity by using ultrasonic wave, and various uses are considered. Since the ultrasonic wave used in PAL is a finite amplitude sound wave, the basic equation of pressure propagation is expressed by the nonlinear wave equation. Conventional numerical analysis of the nonlinear wave has been performed by solving partial differential equations using the difference method, but there is a problem with the calculation time. In this study, we treated the PAL modulated wave as a one-dimensional nonlinear wave phenomenon, and analyzed using a concentrated mass model consisting of mass, spring, and damping. Then, we conducted the measurement experiment of the PAL wave and verified the accuracy of the analytical model by comparing the numerical analysis result with the experimental result. As a result, the sound pressure of ultrasonic wave were in good agreement, but the sound pressure of audible sound were not in agreement. Then, we showed the possibility of explaining the experimental result by examining the speaker driving method.

The authors have previously proposed the measurement method of normal-incidence sound absorption coefficient using eight microphones which enables the measurement in the high frequency range beyond the cut-on frequencies of the higher order acoustic modes in an impedance measurement tube. The proposed method utilizes the symmetry of sound field in the tube to eliminate the influence of the higher order modes. The maximum measurement frequency of the proposed method is about three times higher than the conventional prevalent method. In the proposed method, in order to reduce the influence of the first radial mode ((0, 1) mode), microphones are inserted into the measurement tube so that the acoustic centers of the microphones can match the nodal line of the (0, 1) mode. However, because of this microphone configurations, the microphones may disturb the sound field in the tube and cause scattering. When the scattering occurs, the normal incidence sound wave is converted to the waves of higher order modes, which can affect the measured absorption coefficient. Hence, this study proposes the technique to suppress the effect of the scattering. This technique involves installing a cross-shaped spacers between two microphones facing each other. Since the phases at the outside and inside of the (0, 1) mode nodal line are opposite, it is considered that inserting the spacer can prevent the excitation of the (0, 1) mode. Numerical simulations using the finite element method are performed to discuss the validity of the proposed technique.

Coin processing machine is generally used in financial institutions and stores. This machine automatically counts large number of coins. Hence, the radiated noise at the operational condition sometimes disturbs human activities such as conversation and makes neighboring people uncomfortable. Therefore, it is necessary to identify the main factors increasing the noise and measure them intensively. In this study, we investigated the main process of a coin processing machine generating large noise and the frequency band considering auditory characteristics. Through the loudness analysis using artificial head microphone, the loudness was large when a coin dropped to the turntable, stacker, and withdraw tray. In addition, the sound pressure level (SPL) at 2 ~ 4 kHz was found to increase the loudness. Through further analyses, the SPL at the target frequency band was clarified to be increased by head transfer function and the vibration characteristic of the parts. Based on these results, we conducted countermeasure to the withdrawal tray as an instance, which generated loud noise. As the result, the loudness at the target frequency band could be decreased about 55 % by inserting a soft material to the tray.

A ball mill is a type of grinding equipment. Hard balls called media and material to be ground are placed into a mill cylinder, and the mill is rotated. The material is ground by collision force of material with hard balls or the mill wall. It is difficult to predict grinding status of materials inside mill during operation. During operations, vibration and sound are generated from mill wall. In addition, vibration and sound of mill wall change depending on the grinding condition of materials. If the relationship between the grinding status of materials and the vibration and sound of the mill wall can be clarified, we are able to estimate grinding status of materials during operation. Authors have shown the characteristics of the vibration response and sound pressure when single size material is put into a mill. In the grinding process, material has distribution of diameter. In this study, an experiment with two different materials in the diameter is performed to exam the influence of distribution of material size. Besides, the vibration and radiated sound of the mill wall are predicted by a simulation model developed in our previous study. The experiment result shows that the vibration displacement and sound pressure decrease as the diameter of material decreases. Therefore, even if the material has the distribution of diameter, the relationship between the material diameter, the displacement and sound pressure of the mill wall does not change. The analysis results show the same tendency as the experiment results. Moreover, the analysis predicts decrease of the kinetic energies of each media and material particle when the diameter of material decreases.

The noise generated by random impacts on the thin-walled structure which has a rectangular convex is estimated. The identification of impact force is important for the estimation of impact noise. Many researches on impact force dealt with only single and vertical impact and did not deal with the randomness for impactor’s material, shape, mass, impact velocity, position and angle. In this research, the method to estimate the time history of impact force from the impact conditions is proposed. The relationship between the impact conditions and the time history of impact force is investigated by the striking experiments using a rigid pendulum with a force sensor attached at the tip of pendulum. According to the result, it is found that the time history of impact force depends on only impactor’s mass and impact velocity while other conditions are not affected. Then, the time history is approximated with the extreme function and use the empirical formula for the relationship between the impactor’s mass, the impact velocity, and the coefficient in the extreme function. For an example of thin-walled structures, the noise generated by random impacts on the thin plate having a rectangular convex is estimated using the approximate vibration analysis and the estimated impact force. The estimated noise agrees almost well with the measured noise. Moreover, the sound quality is evaluated by sharpness and the relationship between sound quality of random impact noise and design specifications like convex position and shape.

In case that structures are simple homogenous uniform such as thin plates or beams, the structure-borne sound can reduce on the basis of the structural intensity. Generally, structures have complex surface and it is difficult to measure structural intensity of complex surface structures because of the stress, moments and in-plane displacement. This paper derives structural intensity of thin shallow shells. As a result of this structural intensity formula, the out-of-plane components such as shear, bending and twisting have no concern with curvature of a shallow shell. Therefore, this paper make comparison with finite element method and finite difference method about its shear and bending components to verify this result. This paper also investigates the ratio of in-plane to out-of-plane of shallow shell to apply plate theory of structural intensity to shallow shells, and verify the direction error of structural intensity between the original structural intensity distribution and the structural intensity that applied plate theory to introduce how we can utilize the plate theory to shallow shells. As a result of this verification, Plate theory of structural intensity can compute approximately structural intensity of shallow shells provided that the shallow shell’s curvature is small, in brief, the out-of-plane components are dominant.

In this paper, a concept of sensitivity analysis focusing on vibration energy is proposed. Although research on the vibrational energy flow has been conducted sporadically, the method to control it has not been established. In this study, a sensitivity analysis equation to predict the change in vibration energy due to mass addition and damping is derived, and its validity is examined using the spring-mass system, and appropriate structural changes are discussed. The proposed sensitivity analysis equation is found to be in agreement with the actual structural modification results for the 5-DOF system. Next, structural changes are studied to control the vibrational energy flow in the 10-DOF system. A new path is added to the series spring mass system to reduce the vibration energy flowing to the main path, and the structure is modified to allow the vibration energy to flow to the additional path. After that, using sensitivity analysis, the mass accretion point where the vibration energy in the main path can be reduced in a specific frequency band was investigated, and the vibration energy was reduced. This paper confirms the validity of the proposed sensitivity analysis formulae for mass addition and attenuation addition.

A method to confine the acoustic pressure distribution near a loudspeaker array was proposed in the author’s earlier work. A potential application of the technology is personal audio. In principle, amplitude and phase of the individual loudspeakers are dependent on frequency. However, such frequency-dependent loudspeaker array would not be easy to implement. In this study, the frequency-independent loudspeaker array, which is easier to implement, is investigated. Because eigenvectors of the generalized radiation modes are weakly dependent on frequency, it can be expected that the frequency dependence of the loudspeakers’ amplitude and phase is negligible. It is shown in computer simulations that the frequency-independent loudspeaker array, which is designed at a fixed frequency, i.e., 300 Hz, successfully generates a confined acoustic filed between 300 Hz and 2700 Hz.

Acoustic metamaterials possess the artificially adjusted physical properties related to the propagation of waves, such as the density of the medium and volume modulus. The acoustic characteristic is governed by the structural shape rather than the physical properties of the material. In this study, we numerically investigated the deflection of transmitting sound by the acoustic metamaterials. Firstly, the equivalent sound velocity values necessary to achieve the designated deflection angle were given directly to the medium in each path without considering the metamaterial structure. The finite element analysis showed that three kinds of deflection angle, θ = 30°, 45°, and 60°, was successfully achieved at any frequency. Secondly, we devised an obstacle structure that generated a sound velocity gradient inside an acoustic metamaterial. It is found by the acoustic wave propagation analysis that the sound could be deflected in the frequency range from 500 Hz to 1.5 kHz. These investigations clearly showed that the sound waves can be deflected by using the acoustic metamaterials for the transmitted sound in two-dimensional space.

In active noise control，if total acoustic power is minimized，absorption and blowout of acoustic energy around the control source are balanced，and a zero power phenomenon occurs in which the time average of control power becomes zero. In this study, we aim at generalization of this phenomenon, the sound source is regarded as a flat plate structure embedded in an infinite baffle, and the generation condition of the zero power phenomenon is considered. First, we will clarify the reciprocity when the zero power phenomenon occurs in the case of three point sources. Next, the reciprocity of the zero power condition is clarified based on the control law derived from the sound sources emitted from the three flat plate structures.

This paper describes the noise control using neural networks during moving the evaluation point in a one-dimensional sound field. In the noise control, the Filtered-x LMS algorithm is widely used. However, this algorithm becomes uncontrollable when the secondary path characteristics from the control sound source to the evaluation point change by moving the evaluation point. To follow changes of the secondary path characteristics, we applied neural networks with the learning ability to the noise control system. So far, we have constructed the noise control system using neural networks and have shown the effectiveness of the control by numerical simulation. However, it has been reported that the control stability depends on the initial value of the internal parameter. In this paper, we consider that the cause is the neural network structure and propose a method of improving the control stability by changing the neural network structure related to its parameter. The effectiveness is investigated by comparing the control stability and performance of the proposed method with that of the conventional method in numerical simulation. The results show that the proposed method improves the control stability by 20% or more and has higher control performance than the conventional method.

In general, active noise control is not effective to attenuate high frequency noise. In this paper, the active noise control using heterodyne is proposed in order to realize the active noise control of high frequency noise with lower cost. Heterodyne is a signal processing technique that creates new frequency components by multiplying signals of two frequencies. By using this technique, if the frequencies of the input signal and the heterodyne wave are 𝜔 and 𝜔_", the frequencies of the output signals become summation and difference of 𝜔 and 𝜔_". Then, through appropriate filtering process, either one signal can be obtained. In this paper, frequency shift of 2000 Hz by using heterodyne with the square wave is considered to attenuate 2200-2400 Hz noise with the controller whose sampling frequency is 2000 Hz. Numerical analysis is conducted with two algorithms, Filtered-X LMS algorithm and Virtual Error Method. The former needs to identify acoustic characteristic before control and the later identifies acoustic characteristic during control. Two types of noise are demonstrated to be attenuated. One is the white noise and the other is the chirp noise. The frequency of each noise was 2200-2400 Hz . The white noise was largely attenuated with each algorithm (about 20 dB) and the chirp noise was also attenuated with Filtered-X LMS algorithm (about 15 dB). On the other hand, some problems were found with Virtual Error Method. Several peaks were detected in the error signal during control.

We tried to suppress the sound generated by the blower in the piping and use the sound to generate electricity. In the experiment, the air is blown from the blower into the pipe and the sound pressures are measured by microphones. A Helmholtz resonator is attached to the pipe to suppress sound. In this research, the sound generated by the rotation of the fan blades is targeted. The Helmholtz resonator was used to suppress the target sound. In addition, the sound was used to perform vibration power generation, and the amount of power generation was investigated. The characteristics of the resonance sound of a nose flute attached to the Helmholtz resonator were investigated, and it was clarified that the nose flute was more effective to generate electricity.

Noise countermeasures are an important engineering problem, and acoustic analysis methods for noise prediction and reduction have been widely studied. In general acoustic analysis, the temperature of the air is often assumed to be constant. However, the temperature gradient of the space may have a large effect on the sound pressure. For example, 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 formulate an acoustic space with a temperature gradient using a concentrated mass model. This model is consisted of the masses, springs and dampers. In addition, the relationship between temperature gradient and sound pressure is analyzed. In this paper, as a first step, a model using a linear spring is constructed, and the validity of the proposed model is confirmed by numerical calculation for a cylindrical pipe.

As a mechanism for generating tire noise, it is input to the tire due to interference with the road surface. The input vibration propagates through the tire, causing the tire to vibrate. The estimation method of structural radiation sound emitted by the vibration of the tire and other sound than its are collectively called tire road surface noise. In this study, we discuss the investigation using a rotating iron wheel to grasp the vibration phenomenon due to the interference between the tire and the road surface and to estimate the structural radiation sound generated from the tire. Unlike a tire, this rotating iron wheel is a structure with high rigidity and little quantity of the natural frequency．Therefore, this paper discusses the input power to the rotating body is identified using the experimental SEA, and the processing of the experimental SEA model obtained with limited measurement data is examined. First, the rotating iron wheel will be explained. Next, the conventional experimental SEA method is used to evaluate the input power from the road surface to the iron wheel when the iron wheel is rolled. Then, the evaluation result of the identified input power is examined and considered. Then, we show the possibility that the evaluation accuracy of the input power can be improved by numerically processing the frequency characteristics of the experimental SEA model constructed with limited measurement data.

We are developing an estimation method of radiation sound from automotive tire in operation by using experimental statistical energy analysis. It is, however, difficult to experimentally verify estimation results of the radiation sound. It is because tire is complicated structure with super-elastic damping and multi-layered materials, and there is no alternative method to measure the radiated sound from the tire. Also, the effect of acceleration of rolling tire is not understood. Then, we are trying to develop a numerical verification method of our method by using a simile rod or beam of which both edges are continuous like a ring, with a moving force. This paper describes the developments of a numerical simulation methods for the rod with continuous boundary and for acceleration effect based on the time-variant beam-forming algorithm. The displacements and energies calculated by these simulation methods were examined for steady and accelerating conditions. As a result, it was found that the acceleration effect is appeared in the frequency domain as the spectrum is overspread through wider frequency range.

A topology optimization method to design micro structures of sound-absorbing poroelastic media utilizing the homogenization method based on an asymptotic expantion is proposed in this study. Design sensitivities of homoginized propoerties with respect to design variables defined on nodes of a microscopic finite element model are derived by using the homoginization method and the adjoint variable method. Then, design sensitivities of macroscopic objective function,which is dissipated power in this study, with respect to design variables defined on nodes of a microscopic finite element model are derived by using the adjoint variable method. The design variables are updated by using Method of Moving Asymptotes (MMA). Here, the design sensitivities both in microscopic and macroscopic scales are verified by a numerical examples.

The purpose of this research is to expand the sound insulation performance of the exhaust gas purifying device called DPF (Diesel Particulate Filter) and improve the added value. The sound insulation performance is evaluated by sound pressure measurement by experiment and calculation by homogenization method. The calculation was performed by locating a finite element model, which is called a unit cell model, that reproduces the microscopic structure of the DPF at periodic intervals. The microscopic physical property values of the unit cell model were adjusted and calculated under multiple conditions. As a result, it was possible to confirm the validity of the evaluation method because the qualitative tendencies were consistent, although there was a quantitative discrepancy.

Aluminum and aluminum sintered materials are used for the walls and ceilings of houses and airports to ensure quietness. It is known that the aluminum sintered material can change the sound absorption characteristics depending on the size of the back air layer, and the larger the back air layer, the lower the peak of the sound absorption coefficient. However,the influence of the thickness of the aluminum sintered material and the grain size of the aluminum powder on the sound absorption characteristics has not been sufficiently investigated. In this study, we made a microscopic structural model of aluminum sintered material, calculated the sound absorption coefficient and flow resistance using the homogenization method, and examined the influence of the thickness of aluminum sintered material and the particle size of aluminum powder on the sound absorption .

Sound absorbing materials used in automobiles are usually attached to a vibrating structure. Here, a method of measuring the ratio of the velocity on the structure side to the velocity on the sound field side is examined. Since the velocity of the surface of the sound absorbing material is affected by the acoustic characteristics of the sound field in contact with it, the sound pressure on the surface of the sound absorbing material and the reaction force of the constraining point on the structure side are measured under acoustically excited condition, we proposed a method to obtain the velocity ratio using the reciprocal relation between structure and acoustics. By comparison with the calculation result of the finite element method, it is shown that there is a possibility to evaluate the characteristics of the sound absorbing material and the sound insulating material in which the sound absorbing material is combined.

We report effects of acoustic transmission loss of double-walled structure including thin-film cells by filling gasses. Our past experiment and computation showed that this double wall structure with filled air has higher sound insulation performance than the hollow double wall. This was because of diffraction originated from high inplane acoustic resistance of thin-film cells. Sound transmission loss of the double wall structures with different filling gasses (CO2 and He) were calculated by numerical analysis using finite element method (FEM) and transfer matrix method (TMM). Influences of low sound speed for CO2, and high sound speed for He were clarified on sound insulation properties when these gasses were filled in the thin-film cells in consideration of diffraction and total reflection.

In order to analyze how the sound emitted from the speaker of the car changes due to the influence of the wall, in the case of a box of rectangular parallelepiped (internal dimension 600 mm × 600 mm × 630 mm) with or without sound absorbing material (glass wool with a thickness of 50 mm) Experiments and calculations using the FE model were performed. The calculation results were able to reproduce the experimental results. It was also confirmed that the sound pressure level changes by about 20 dB above 500 Hz with and without glass wool. Next, we created a simple FE model that simulates the interior of an automobile, and the effect of sound absorption on the ceiling and floor, and the sound pressure level and sound pressure distribution when a sound absorbing material (PET material with a thickness of 50 mm)was added. The change of was measured using a real vehicle (Lexus UX) and analyzed by the FE model. It was confirmed that there was a difference in the sound pressure distribution from 100 Hz with and without PET.

The performance enhancement of the acoustic insulation is demanded for the high frequency for interior noise of automobile. A carpet having urethane adhered to a rubber skin is generally laminated on a floor panel of an automobile. In order to elucidate noise and vibration for this structure, the vibration transmission rate was measured using a test apparatus in which a carpet was laminated on a panel simulating the floor of an automobile. In addition, we modeled this experimental apparatus with finite elements and analyzed the vibration during displacement excitation. Biot-Allard model was used for felt and urethane. We calculate using separately identified Biot parameters and compare with experimental results and introduce the change of vibration and obtained findings when material is changed. In the low frequency range, the values changed significantly when the skin density, Young's modulus and loss factor of urethane were changed. In the high frequency range, the values changed significantly when the skin density and Young's modulus, porosity and Young's modulus and density of urethane were changed. If the spring constant of the connection spring between the panel and urethane is reduced (floating image), the transmission loss increases. If the connection spring is large, the transmission loss will be small, and it will be the smallest value for bonding.

We proposed the active suspension for rolling oscillation based on piecewise sampled-data control with finite-time settling function, termed vibration manipulation function (VMF). In the piecewise sampled-data control, the difference between the angle of the suspension base and the road surface profile was compensated by extending and retracting the actuator between the unsprung mass and the suspension base in each manipulation. By obtaining road surface profile in advance, active suspension worked much efficiently. Under the feedforward control of the angle between the suspension bases along vibration manipulation function, we can cease rolling vibration of the vehicle body at the end of each operation. From the simulation results, the proposed active suspension can suppress rolling vibration after various road surface irregularities. In addition, a large damping effect was obtained with a small amount of the actuator drive. The skyhook damper that was compared took several cycles to reduce the residual vibration.

This paper describes vibration analysis using finite element method with Model Strain Energy Method for steel panel connected by nonlinear concentrated springs under impact load. The panel is composed of steel layer having an Acoustic Black Hole with residual thickness. A viscoelastic damping layer is covered on different places of the black hole. Finite element for the nonlinear springs with hysteresis are expressed and are connected to the panel modeled by linear solid finite elements in consideration of complex modulus of elasticity. We calculated modal loss factors and transient responses including internal resonances in the eigen modes including coupled motions between the non-linear springs and the panel. From the dominant eigen modes and the time histories, we clarified effects of the Acoustic Black Hole having residual thickness and non-linear springs on the nonlinear damped responses.

This paper reports SEA (Statistical Energy Analysis) damping response analysis using FEM for two panels connected in L-shape with an acoustic black hole having a viscoelastic damping layer. The side edges of the L structure are fixed boundaries. And the other edges including the acoustic black hole are free. Generally, modal damping is influenced by not only shape of panels but also their boundaries. To explain for couplings in damping between SEA substructures, internal loss factors are identified using FEM and MSE（Modal Strain Energy）method. To know wave propagation between the substructures, coupling loss factors are calculated. Effects of the boundaries of L-shaped panel having the acoustic black hole on these SEA parameters are clarified.

Numerical analysis is performed to obtain damping responses for double wall structures inserted sound absorbing material. The base plate of the double wall structure has an acoustic black hole with residual thickness. The boundary at the opposite side of the black hole is fixed. This double wall structure and the acoustic black hole were modeled and numerically analyzed by FEM. Using the MSKE method proposed by Yamaguchi et al., we computed the vibration reduction and changes in vibration transmission of an acoustic black hole with residual thickness. By giving the residual thickness, in the lower frequency band, larger damping effects of the acoustic black hole for the base plate were obtained. However, less damping effects were appeared in the cover plate where no acoustic black hole exist.

This paper describes vibration damping analysis using finite element method with Model Strain Energy Method for structures having T-shaped cross section with a new acoustic black hole. Usually, Krylov type acoustic black hole is formed at one edge of a beam or a plate where its thickness decreasing shapely by following higher order power function. We proposed a new type structure which acoustic black hole exists in the edge of the beam or the plate as height of the web in the T-shaped structure decreasing by replacing its thickness like Krylov’s black hole. On the region of the acoustic black hole, viscoelastic vibration damping material is laminated. The new black hole with damping layer is modeled by linear solid finite elements in consideration of complex modulus of elasticity. We calculated modal loss factors and eigenmodes including coupled deformations among substructures in the T-shaped structure. We researched effects of this new acoustic black hole on the modal damping for each eigenmode.

Vibration suppression is an important technology both industrially and environmentally in order to realize a comfort industrial product with a safe structure. In this paper, we carry out for numerical simulation of damped vibration structure having porous material sandwiched by double walls. The cover plate in double walls has a Krylov type acoustic black hole. All edge where the black hole exists, has free boundary. Damping material is on the surface of the black hole. Numerical analysis is performed to clarify changes of vibration reduction and vibration transmission from the base plate to the cover plate due to the acoustic black hole using FEM and MSKE method proposed by Yamaguchi et al.

This paper describes hybrid vibration analysis using Statistical Energy Analysis（SEA）and FEM for two panels connected in L-shape with an acoustic black hole having a damping layer. The angle of the joint between the two flat plates in the L-shaped panel structure is changed. We focused on effects of changing the angle of the joint in the L-shaped panel structure on wave transmission characteristics between the two panels and damping effects due to the acoustic black hole.

FE models used for measurement of transmission loss (size : 300 mm × 300 mm) and impedance tube were created by using an acoustic metamaterial in which films were laminated on top and bottom of polypropylene (PP) processed into a honeycomb structure. Numerical calculation of sound transmission loss, comparison with experimental results, and various parameter studies were conducted. In the calculation of the transmission loss of the FE model of the impedance tube (Φ 100mm), it was possible to obtain a value close to the experimental result by changing the value of the spring stiffness which is the boundary condition. The attenuation of the boundary spring has no effect on the transmission loss of the 300 mm × 300 mm FE model. The hardness of the spring affects the low frequency stiffness line and the first dip (about 100Hz). The first dip is the effect of the vibration mode in which the entire honeycomb deforms out of plane. There is no effect in the frequency range higher than the drop frequency. Attenuation of honeycomb material has a great influence. The larger the value, the larger the transmission loss in all frequency ranges. The film attenuation affects the first dip (about 100Hz) and the second dip (about 2300Hz). The drop of about 2300 Hz is due to the film resonance of the film. When the Young's modulus of the film is increased, both the frequency and the value of the initial drop increase. There was almost no change in the frequency range higher than the drop frequency.

In recent years, hybrid vehicles and electric vehicles have become popular. In such vehicles, there is a problem that low and medium frequency noise such as road noise, which has been masked by noise from the engine, is offensive to the ears. The performance improvement of the sound insulation material in the low and middle frequency range can be achieved by increasing the mass and volume of the sound insulation material. However, it must be avoided from the viewpoint of vehicle weight reduction. Acoustic metamaterials are attracting attention in order to suppress low and medium frequency noise without increasing the thickness or mass of the sound insulation material. An acoustic metamaterial is an artificial structure that has a periodic structure smaller than the sound wave length, and has a resonant system in the periodic structure. By applying the acoustic metamaterial to the double-walled structure of the floor of the automobile, improvement of the sound insulation performance in the low and middle frequency range can be expected. In this research, we investigate an experimental evaluation of double wall soundproof structure using acoustic metamaterials with resonator and membrane.

In EVs and HVs that have become widespread in recent years, there is a problem that low and medium frequency noise such as wind noise and road noise is noticeable while noise caused by the engine decreases. To this problem, double wall acoustic metamaterials are highly effective. However, due to the resonance of the middle air layer and the resonator, there are frequency ranges in which the sound insulation performance degradation, this study proposes a structure in which the bottom of the resonator is thinned. By the resonance of the membrane, sound waves of opposite phase to the noise are generated, the transmitted sound waves are canceled, and extension of the functional frequency is examined.

To improve the quietness of automobiles, the sound insulation performance of automobile windows is required. However,the design of an automobile window has many restrictions and it is difficult to improve the sound insulation performance. Yamamoto proposed an acoustic metamaterial in which a Helmholtz resonator is periodically encapsulated in a glass plate. Theoretical calculations and numerical analysis show that the proposed acoustic metamaterial plate (AMP) improves the sound transmission loss (STL) at 2.1 kHz resonance frequency of the resonator. In this study, the sound pressure level,acceleration level and STL inside the closed space of a flat plate and AMP are measured by means of vibration and sound insulation tests, and the effectiveness of the proposed AMP is verified. In the vibration test, an AMP was fixed to an experimental jig on an air mount, and the sound pressure level and acceleration level were evaluated by shaking the experimental jig. In the sound insulation test, STL was calculated by measuring the sound pressure inside the device with an intensity probe using a small sound insulation test rig.