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Multifunctional membrane space structures have been developed in the past to realize solar arrays, array antennas, and other applications. However, the deployment of a folded membrane often requires fluctuating forces with high peaks, caused by the stiffness of the crease lines. This study proposes the use of a plain-woven textile as the base membrane for the planar deployment structures primarily because of its high packaging efficiency. The deployment forces required for the folded plain-woven textile structures to be employed in future space applications are experimentally measured. The deployment forces are compared between the proposed textile structures and the conventional film-based membranes to characterize the deployment behavior of the textile structures. Two types of experiments are conducted in this study for the one-dimensional deployment of v-folded membranes and the two-dimensional deployment of quarter Flasher origami structures, respectively. The advantages presented by the deployable textiles are as follows: (i) they require smaller and smoother deployment forces, and (ii) they are insensitive to imperfect boundary conditions. These features are important for the reliable deployment of future space structures.

Static weight estimation of a vehicle in motion is challenging, especially when the vehicle is accelerating and decelerating. This paper presents a new estimation method for accelerating and decelerating vehicles. This method uses at least two miniature load measurement devices cascaded in traffic lane and consideration of transfer load between the front and rear wheels of a motorbike. Both individual axle load and the gross mass of the motorbike are estimated with accuracy under field conditions.

Accurately and reliably measuring the gross weight and static load of the axles of moving vehicles, especially trucks, is important for preventing road damage and improving traffic safety and monitoring efficiency. This type of vehicle weight measurement is called “weigh-in-motion” (WIM). The conventional purpose of WIM is solely the estimation of the vehicle gross weight. However, WIM is also valuable for estimating the static axle load and the height of the vehicle’s center of gravity, and possibly additional measurements. In this study, a method based on the averaging principle is proposed for signal processing in WIM systems. A preliminary experimental investigation, which involved two types of motorbikes and a light truck as test vehicles, and miniature plate-type measurement devices built by the authors, is presented. The gross weight and the static load of each axle of the vehicles, which traveled at various speeds up to approximately 40 km/h, are estimated with high accuracy.

This paper investigates an on-orbit calibration method for a nonflat reflectarray antenna. This paper proposes the antenna calibration method that uses a shape measurement device. The analysis in this paper shows that, with the proposed calibration method, the gain reduction due to shape deformations can be effectively ameliorated.

For high data rate and long-distance communication of satellite, a large aperture antenna on satellite is required. However, it is difficult to make high flatness surface in space and the current study on large antennas for satellites assumes the high flatness structures. In this study, to construct the reflectarray antenna on the deployable membrane structure, we propose the active reflectarray which actively adjusts the reflection phase of elements by varactor diodes and compensate the low flatness surface. We analyze the nonflat reflectarray and confirm our proposed method.

This paper reports the development of a vibration monitoring system for wind turbine blades. This system is used to estimate the deflection at the tip blade on a wind turbine tower. Technical accidents of wind turbine blades have become increasingly common. Thus, regular monitoring of the blades is very important to prevent breakdowns, especially in cases when the blades begin to vibrate excessively. The monitoring system developed in this study satisfies two main objectives for practicality. First, our system is easy to install on existing wind turbines. Second, blade deflection is measured in real time. Our system can be operated using a few strain gages attached at the blade root, and the deflection is calculated based on the monitored stress. Thus, direct measurement of deflection at the blade tip is unnecessary. An estimation algorithm for this purpose is adopted based on the experimental modal analysis. This paper focuses on the evaluation of the estimation algorithm to investigate the feasibility of our system. Basic experiments were conducted using a simple blade model of a 300 W scaled wind turbine under rotation. Signals from the strain gages were acquired by a sensor network and sent to a computer through a wireless connection. The results show that the estimation accuracy is acceptably high. Therefore, we conclude that our proposed system is practical.

The bending stiffness of the wind turbine blades has decreased due to the trend of wind turbine upsizing. Consequently, the risk of blades breakage by hitting the tower has increased. In order to prevent such incidents, this study proposes a deflection monitoring system that can be installed to already operating wind turbine's blades. The monitoring system is composed of an estimation algorithm to detect blade deflection and a wireless sensor network as a hardware equipment. As for the estimation method for blade deflection, a strain-based estimation algorithm and an objective function for optimal sensor arrangement are proposed. Strain-based estimation algorithm is using a linear correlation between strain and deflections, which can be expressed in a form of a transformation matrix. The objective function includes the terms of strain sensitivity and condition number of the transformation matrix between strain and deflection. In order to calculate the objective function, a simplified experimental model of the blade is constructed by interpolating the mode shape of a blade from modal testing. The interpolation method is effective considering a practical use to operating wind turbines' blades since it is not necessary to establish a finite element model of a blade. On the other hand, a sensor network with wireless connection with an open source hardware is developed. It is installed to a 300 W scale wind turbine and vibration of the blade on operation is investigated.

Accepted: 2013-07-23, 資料番号: SA1004508000

This paper presents a new type of damping material composed of flexible porous material such as polyurethane foam and liquid such as water. This new type of damping material costs less than viscoelastic materials such as Sorbothane, and is anticipated to have a better damping effect. At the same time, installation of the new type of damping material is as easy as that of usual viscoelastic materials. The damping effect of this material on the vibration of a cantilever iron plate is experimentally compared with the one of a viscoelastic material. The damping effect on a rail piece with a length of 1.2m and a weight of 72kg is also experimentally investigated. The experimental results show a good damping effect. The design variables of this new damping material such as the liquid viscosity and the hardness of the porous material are thought to influence the damping effect, consequently are investigated by carrying out vibration testing of a cantilever iron plate (material:SS400, size:300×440×5mm, weight:5.2kg).

Friction between two relatively sliding surfaces in mechanical structures possibly excites unstable vibration, which emits squeal noise. In this paper, the authors propose an idea to predict the possibility of squeal noise occurrence in actual structures having relative sliding surfaces with friction by means of experimental modal analysis and experimental spatial matrix identification. Using spatial matrices that derived from experimental modal data, unstable mode coupling that causes squeal noise can be predicted. By this method it is possible to calculate the possibility of squeal noise incident and its frequency within the practical realistic range of friction coefficient and contact stiffness. The method is presented with showing an experimental verification study using a simple L shape frame.

Dry contact sliding between two structures is frequently found to generate squeal noise in certain topography condition of contact surface. Furthermore, a different surface topography may generate squeal noise at different frequencies. In this paper, authors investigate the effect of topography of contact surfaces to the normal contact stiffness, the tangential contact stiffness, and the friction coefficient. The normal and tangential contact stiffness are determined by a classical model of asperity on contact surface. These parameters will be the dominant factors of the squeal noise generation by means of mode-coupling analysis. Numerical simulation-based investigation is carried out using two simple models, i.e. a two-degree of freedom model and a simple space frame model. The simulation results show that a structure has only one or few pairs of couple modes with complex eigenvalues at certain contact conditions. For a system with multi-degrees of freedom, some mode shapes make couples in different contact conditions. On the other hand, smoother contact surfaces have higher normal and tangential contact stiffness. Furthermore, higher tangential contact stiffness and higher coefficient of friction will increase the possibility of squeal generation. Hence, it is understandable why the squeal noise appears and vanishes in some surface topography and has different frequencies at different values of surface roughness.

This paper presents a study of experimental identification of vibration force generated in a single cylinder outboard engine under a steady-state operation by means of linear structural modeling and equivalent force transformation. The identification is to determine a set of equivalent force vectors that can express actual vibration force generated by firing and inertia force due to dynamic motion of moving components in the engine. The vibration force generated in engines under steady-state operation will be independent of the boundary conditions excluding load condition. Therefore, once such vibration force can be modeled with practical accuracy, the result can be used as a database for CAE simulations of trouble shooting and design improvement analysis for noise and vibration, etc.

A theoretical method is presented for calculating the absorption coefficient of a multi-leaf microperforated panel absorber. In this work, the possibility of using multi-leaf type of microperforated panels without solid backing panel is investigated. The number of panels varies from 2 to n (≥2). The sound absorption coefficient is calculated based on electro-acoustic analogy by taking the sound transmission coefficient due to the absence of solid backing panel into consideration. The optimum performance of leaf microperforated panel absorber is also investigated as the function with respect to the design parameters such as perforation ratio, diameter of holes and distance between panels. The numerical results show that the configuration of leaf of microperforated panels can increase absorption coefficient at low frequency region. This fact will give an advantage to the multi-leaf microperforated panel over conventional microperforated panel arrangements. That is, to solve the problem of quite narrow frequency band absorption effect, especially in mid-high frequency region corresponding to their resonant frequencies, that the conventional microperforated panel arrangements inherently possess. Experiment results are also presented that show a reasonable agreement with the theoretical results. Some feasible application ideas of the multi-leaf type of arrangement are also presented.

A new type of microperforated panel absorber (MPA) that has holes of multiple sizes instead of uniform size is experimentally investigated. The objective of this research is to obtain a wide band sound absorber that is thin, durable, clean, and healthy. The first step of this research is to investigate the performance of MPA having two different sizes and the same numbers of holes. The investigation is then extended to a combination of three and four different sizes of holes with various spatial arrangements and various densities or percentages of each size of holes on panels. The hole diameters vary between 0.4 mm and 1 mm and the cavity depths vary between 10 mm and 15 mm. The results show that a multi-size MPA enhances the absorption rate and widens the effective frequency band. This study also proves that a multi-size MPA when compared with a uniform size MPA has better sound absorption characteristics with respect to the absorber thickness and absorption bandwidth. These results make it possible to build thin, single layer sound absorbers that are effective in wide frequency bands and have the advantage of being tunable.

資料番号: SA1160205000

This study clarifies the effect of thermal deformation in the reconfigurable space reflector system, through a series of experiments in a thermostatic chamber using a prototype of reconfigurable space reflectors. This study then discusses possible countermeasures against precision degradation of such system due to the thermal deformation, exploiting a finiteelement model that is tuned to the experimental results. Though reconfigurable reflector systems inherently have the mismatch in the coefficients of thermal expansion among their structural members, the effect of the mismatch may be minimized by a proper combination of several materials. The prototype used in this study is designed as a preliminary model of a secondary mirror for future radio astronomy satellites.

Modal curve fitting methods on frequency domain are based on the least square method to estimate the modal parameters from frequency response functions (FRFs in brief) of test structures. In order to minimize the least square errors between experimental and estimated FRFs, several kinds of weighting functions were proposed and widely applied in practical use. However, using the same weighting function in modal curve fitting for a set FRFs of test structure often makes the results of the FRFs of some measurement points be fitted with good accuracy but other ones be not. In this paper, the authors propose the combination use of various kinds of weighting functions in least square process of modal curve fitting methods to deal with the measurement data of actual and complex mechanical systems. This method automatically selects and applies the most appropriate weighting function to the FRF of each measurement point by comparing the minimum total relative mean square error (RMSE). The case study shows that the proposed idea allows the modal curve fitting method puts better curve fitting results out so that more accurate mathematical model will be obtained.

Bolted joints sometimes suffer bolt loosening and may sometimes induce accidents. Therefore. bolt loosening detection technologies are essential for many machines and structures having bolted joints. Authors have proposed a new bolt loosening detection sensor using a natural frequency change of a thin plate and validity of the sensor is shown by experimental results. However, it is difficult to detect the bolt loosening on early stage because the sensor is not so sensitive in high axial tension condition. In this paper. the mechanism of natural frequency change of the sensor induced by axial tension change of bolt is investigated with numerical and experimental results and two sensitivity improvement methods, using conical spring washers and size change of the sensor are examined. The results show that size change of the sensor is not effective for improvement of the sensitivity on early stage of bolt loosening and that conical spring washers change the contact area on each sensor surface and can improve the sensitivity on early stage of bolt loosening.

We have proposed a novel autonomous bolt loosening detection technique using thin plate type sensors to keep integrity of machines and structures. The thin plate type sensor consists of a thin plate and piezoelectric elements and bolt loosening is detected by the natural frequency change of the plate. The validity of the sensor is shown by experimental results in previous works. However, the edge length of the sonsor is six times of the diameter of the target bolt and too large for practical use, so that it is desired to miniaturize the sensor. We have also proposed to use an oscillator circuit whose oscillating frequency is determined by the natural frequency of the sensor to evaluate the natural frequency change induced by bolt loosening. However, the oscillating frequency of the circuit does not coincide with the natural frequency and difference between two frequencies is sensitive to circuit parameters. In this paper, we propose slit cut thin plate type sensor as a miniaturized sensor and modify the oscillator circuit for natural frequency evaluation. The slit cut thin plate type sensor consists of a plate that has slits and a ring type piezoelectric element. The slits of the sensor eliminate degenerate modes that have harmful effects on natural frequency tracking and improve the tolerance for noise. The modified oscillator circuit is based on positive velocity feedback and the oscillating frequency of the circuit coincides with the natural frequency perfectly.

Bolted joints are commonly used for many machines and structures. They sometimes suffer from bolt loosening and may sometimes induce accidents. Therefore, bolt loosening detection techniques are essential for many machines and structures having bolted joints. Authors have proposed a new bolt loosening detection sensor using a specific natural frequency of a thin plate and named it thin plate sensor. The natural frequency of the sensor is identified by admittance of piezoelectric elements attached to the plate without human commitments. However, this method requires a complicated setup consisting of a function generator, a voltage-current measurement circuit, A/D converters and a computer with data processing software. In this paper we propose a method to evaluate the natural frequency using an oscillator circuit as an easier means. The oscillator circuit consists of an amplifer and a feedback circuit. The feedback circust consists of a capacitor, piezoelectric elements of the thin-plate sensor and CR low-pass filters. The oscillating frequency of the circuit is automatically synchronized with the natural frequency of the plate. Experiments are conducted to measure the relation between axial tension of the bolt and the oscillating frequency and the validity of the present method is confirmed.

Many researchers have made efforts to develop structural health monitoring methods to detect damages, cracks, corrosion and bolt loosening using modal characteristics of structures. However, modal characteristics are affected by not only damages but also boundary conditions and loading conditions etc. In fact, local damages induce very slight change of modal parameter. Therefore, it will be difficult to apply most of these conventional methods to actual structures. In this paper, we propose a new structural health monitoring method to detect bolt loosening using the characteristics of local vibration modes of a thin plate sensor sandwiched between a bolt, a nut and washers in main structures. This sensor consists of a thin plate and some piezoelectric elements. In local mode vibration of the thin plate sensor, the bolt’s axial tension determines its boundary condition. Bolt loosening changes the boundary condition and natural frequencies of the sensor. However, main structure’s characteristics don’t affect sensor’s modal characteristics. Since our method attempts using local vibration modes it is important to distinguish the local vibration modes of interest from the global ones related to structures. We propose a technique to distinguish local modes using finite element method. Finally, we confirm the validity of the thin plate sensor experimentally.

The present paper describes a fundamental study on structural bending design to reduce noise using a new evolutionary population-based heuristic algorithm called the particle swarm optimization algorithm (PSOA). The particle swarm optimization algorithm is a parallel evolutionary computation technique proposed by Kennedy and Eberhart in 1995. This algorithm is based on the social behavior models for bird flocking, fish schooling and other models investigated by zoologists. Optimal structural design problems to reduce noise are highly nonlinear, so that most conventional methods are difficult to apply. The present paper investigates the applicability of PSOA to such problems. Optimal bending design of a vibrating plate using PSOA is performed in order to minimize noise radiation. PSOA can be effectively applied to such nonlinear acoustic radiation optimization.