Toshihiko Komatsuzaki

Design of a Real-Time Adaptively Tuned Dynamic Vibration Absorber with a Variable Stiffness Property Using Magnetorheological Elastomer

An elastomer composite with controllable stiffness, known as a magnetorheological elastomer (MRE), is used in a dynamic vibration absorber whose natural frequency is tuned adaptively to the disturbance frequency through the application of an external magnetic field. The field-dependent property test of the fabricated MRE sample shows that the stiffness changes by more than six times compared to the baseline property value at a 40% iron powder volume concentration. The MRE is then used to fabricate a frequency-tunable dynamic absorber for mitigating transient vibrations of a one-degree-of-freedom system. Investigations show that the proposed absorber outperforms a conventional passive-type absorber throughout the tunable frequency range.

Study on Acoustic Field with Fractal Boundary Using Cellular Automata

In the present study, characteristics of the acoustic field in an enclosure bounded by fractal walls are investigated using Cellular Automata (CA). CA is a discrete system which consists of finite state variables arranged on uniform grid. The dynamics of CA is expressed by temporary updating the states of cells according to the local interaction rules, defined among a cell and its neighbors. In this paper, the effect of fractal shaped boundary structure to the reverberation and sound absorption characteristics of an enclosure is investigated for two dimensional acoustic wave propagation model described by CA. Local rules are provided for the construction of fractal patterns as well as representation of wave propagation phenomena. It is known by the numerical simulations that the damping enhancement and also frequency-selective absorbing behavior is seen for specific fractal patterns and stage numbers.

Fuzzy Semiactive Vibration Control of Structures Using Magnetorheological Elastomer

In this research, a novel variable stiffness vibration isolator that uses magnetorheological elastomers (MREs) accompanied with a fuzzy semiactive vibration control was developed. Firstly, the viscoelastic characteristics of MREs in shear mode were clarified systematically in order to achieve a mathematical basis for the controller development. Secondly, the fuzzy semiactive vibration control with a strategy based on the Lyapunov theory and dynamic characteristic of MREs was proposed for minimizing the movement of the isolator. In the conventional semiactive algorithm, the command applied current of MRE-based isolator is set at either minimum or maximum value which causes high acceleration and jerk peaks periodically, thus leading to the degeneration of the overall system quality. However, the fuzzy semiactive algorithm presented here is able to produce the sufficient applied current and thus viscoelastic force is desirably produced. The effectiveness of the developed isolator was evaluated numerically by MATLAB simulation and experimentally in comparison with the performances of a passive system and a system with on-off type semiactive controller. The results showed that the developed controller was successful in overcoming the disadvantages of conventional on-off semiactive control.

Modeling of sound absorption by porous materials using cellular automata

In the present study, acoustic wave propagation in acoustic tube in-corporating sound absorbing material is simulated using Cellular Automata (CA) CA is a discrete system which consists of finite state variables, arranged on a uniform grid (cell) CA dynamics is described by a local interaction rule, which is used for computation of new state of each cell from the present state at every time step In this study an acoustic tube model is introduced in which absorbing material is characterized by direct modeling of porosity and flow resistance Direct numerical simulation CA model is performed and evaluated by absorption coefficient using standing wave ratio measure The results showed good correspondence with analytical solutions.

Analytical method for steady state vibration of system with localized non-linearities using convolution integral and Galerkin method

Abstract The analytical method using transfer function or impulse response is very effective for analyzing non-linear systems with localized non-linearities. This is because the number of non-linear equations can be reduced to that of the equations with respect to points connected with the non-linear element. In the present paper, analytical method for the steady state vibration of non-linear system including subharmonic vibration is proposed by utilizing convolution integral and the impulse response. The Galerkin method is introduced to solve the non-linear equations formulated by the convolution integral, and then the steady state vibration is obtained. An advantage of the present method is that stability or instability of the steady state vibration can be discriminated by the transient analysis from convolution integral. The three-degree-of-freedom mass–spring system is shown as a numerical example and the proposed method is verified by comparing with the result by Runge–Kutta–Gill method.

Fuzzy Semi-Active Control of Multi-Degree-of-Freedom Structure Using Magnetorheological Elastomers

Magnetorheological elastomer (MRE), used in semi-active control, has recently emerged as a smart material that could potentially improve traditional systems in controlling structural vibrations. This study considers two main issues concerning the application of an MRE. The first issue is the modelling and identification of the viscoelastic property, and the second is the formulation of an effective control strategy based on the fuzzy logic system. Firstly, a nonlinear dynamic MRE model was developed to simulate the dynamic behavior of MRE. In this model, the viscoelastic force of the material as an output was calculated from displacement, frequency, and magnetic flux density as inputs. The MRE model consisted of three components including the viscoelasticity of host elastomer, magnetic field-induced property, and interfacial slippage that were modeled by analogy with a standard linear solid model (Zener model), a stiffness variable spring, and a smooth Coulomb friction, respectively. The model parameters were identified by manipulating two sets of data that were measured by changing applied electric current and harmonic excitation frequency. A good agreement was obtained between numerical and experimental results. The proposed model offers a beneficial solution to numerically investigate vibration control strategies. Secondly, a fuzzy semi-active controller was designed for seismic protection of building with an MRE-based isolator. The control strategy was designed to determine the command applied current. The proposed strategy is fully adequate to the nonlinearity of the isolator and works independently with the building structure. The efficiency of the proposed fuzzy semi-active controller was investigated numerically by MATLAB simulations, whose performance was compared with that of passive systems and a system with traditional semi-active controller. Numerical results show that the developed fuzzy semi-active controller not only mitigates the responses of both the base floor and the superstructure, but also has an ability to control structural vibrations adaptively to the different intensity ground motions.Copyright

Folded Spring and Mechanically Switching SSHI for High Performance Miniature Piezoelectric Vibration Energy Harvester

To downsize the clamp area and increase the output power of the harvester, we developed a miniature piezoelectric vibration energy harvester with combining a Z-shaped folded spring and a mechanically-switching SSHI (synchronized switch harvesting on inductor). The overall harvester size is 4×2×3 cm3. The FEM analysis revealed that the output power increases and the value of the 1st and 2nd resonance frequencies move closer as the angle of the Z-shaped spring decreases, therefore, the smaller angle would be more promising. The experimental results showed that the maximum output power of our harvester for the 1st (20.2 Hz) and 2nd (53.0 Hz) resonance frequencies at the applied acceleration of 4.9 m/s2 are 088 and 0.98 mW, respectively. The reason for a marked enhancement of the output power for the 2nd resonance frequency is attributed to the vertical movement of the 2nd vibrational mode which applies larger mechanical stress to the piezo ceramic and achieves better electrical contact between the tip of the Z-shaped spring and the spring plunger.

A broadband frequency-tunable dynamic absorber for the vibration control of structures

A passive-type dynamic vibration absorber (DVA) is basically a mass-spring system that suppresses the vibration of a structure at a particular frequency. Since the natural frequency of the DVA is usually tuned to a frequency of particular excitation, the DVA is especially effective when the excitation frequency is close to the natural frequency of the structure. Fixing the physical properties of the DVA limits the application to a narrowband, harmonically excited vibration problem. A frequency-tunable DVA that can modulate its stiffness provides adaptability to the vibration control device against non-stationary disturbances. In this paper, we suggest a broadband frequency-tunable DVA whose natural frequency can be extended by 300% to the nominal value using the magnetorheological elastomers (MREs). The frequency adjustability of the proposed absorber is first shown. The real-time vibration control performance of the frequency-tunable absorber for an acoustically excited plate having multiple resonant peaks is then evaluated. Investigations show that the vibration of the structure can be effectively reduced with an improved performance by the DVA in comparison to the conventional passive- type absorber.

MRE-Based Adaptive-Tuned Dynamic Absorber With Self-Sensing Function for Vibration Control of Structures

Magneto-rheological elastomer (MRE) is known as class of smart materials whose elastic property can be varied by the applied external magnetic field. For the use of semi-active vibration control, any kind of external sensor such as accelerometer or displacement sensor is usually used to monitor the real-time response of structures while leaving cost, proper installation and maintenance problems for real applications. In addition to the field-dependent stiffness change property of MRE, the electrical resistance of the composite is also changed by the induced strain within the elastomer providing a new self-sensing feature as a multifunctional material. In the present study, a novel dynamic vibration absorber having self-sensing function and adaptability using Magneto-rheological elastomer is developed. The natural frequency of the absorber is instantaneously tuned to a dominant frequency extracted from the strain signal. The damping performance of the absorber is investigated by applying the absorber to a fundamental base-excited 1-dof vibration system. Investigations show that the vibration of the target structure exposed to a non-stationary disturbance can be satisfactorily reduced by the proposed frequency-tunable dynamic absorber without the use of an external sensor, at the exceeding performance in comparison to conventional passive-type dynamic absorber.© 2014 ASME

Adaptive Tuned Dynamic Vibration Absorber With Variable Stiffness Property Using Magneto-Rheological Elastomers

A passive type dynamic vibration absorber offers advantages in reliability and simple constitution, however, the use of the absorber with fixed property is usually limited to harmonically excited case, where the damper is only effective for pre-determined narrow frequency range. Design of the damper following well-known optimal tuning theory could extend the effective frequency range, yet the damping performance remains at a certain amount. In this paper, the stiffness controllable elastomer composite known as Magnetorheological elastomer (MRE) is applied to the dynamic absorber whose natural frequency is tunable by the external magnetic field. MREs are first fabricated and their field-dependent properties are investigated. The MRE is then applied to a dynamic absorber along with stiffness switching scheme so that the vibration of 1-DOF structure is damped more effectively. Investigations show that the vibration of the structure can be fully reduced by the proposed dynamic absorber with variable stiffness functionality.Copyright