A new design method is proposed here to maximize the fundamental frequency of laminated composite plates reinforced by curvilinear fibers. Spline functions represent arbitrarily shaped fibers and the Ritz method generates frequency equations. The optimum curvilinear shapes are searched for the maximum fundamental frequencies using a genetic algorithm, and increments of data points which define the spline shape are used as design variables under the limited range of undulation. Comparison of the present analysis method gives good agreement with the finite element method in terms of natural frequencies and vibration modes, and the optimized results show that the present plate with optimally shaped curvilinear fibers gives higher or equal fundamental frequencies than those of conventional plates with optimally oriented parallel fibers.

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Experimental results are presented on chaotic vibrations of a rectangular plate with in-plane elastic constraint. The plate has initial imperfection. Opposite edges of the plate are clamped and the other edges are simply supported. One side of clamped edges is connected to elastic springs and is movable to in-plane direction. The simply-supported edges are connected to the boundaries with adhesive flexible films. Loading in-plane compressive force to the plate, the plate shows pre-buckled configuration with the type of a softening-and-hardening spring. Under periodic lateral excitation, chaotic responses are obtained in specific frequency regions. Predominant chaotic responses are examined with the Fourier spectra, the Poincaré projections and the maximum Lyapunov exponents. Furthermore, applying the Karhunen-Loéve method, contributions of vibration modes on the chaotic responses are confirmed. It is found that the chaotic responses are generated from the internal resonant vibrations with the first mode of vibration and higher modes of vibration. The chaotic responses are dominated by the lowest mode of vibration. The higher modes of vibration contribute from 11 to 20 percent to the chaos. As the exciting amplitude increases, the amplitude of the chaotic responses increases and frequency regions of the chaotic responses shift. In the larger amplitude of the response, the frequency region shifts to the higher range owing to the resonant response with the type of a hardening spring. In contrast, the frequency region shifts to the lower range when the amplitude of the chaotic response is smaller comparatively. The resonant response with the smaller amplitude corresponds to the type of a softening spring.

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This paper deals with response analysis of collision vibration in continuous system excited by periodic displacement with arbitrary functions. A system of steady vibration in a cantilever beam having an attached mass at free-end is considered. The cantilever beam has structural damping in the beam, and it is being put in the viscous fluid with hydrodynamic drag. The attached mass collides elastically with the coil spring clamped on asymmetrical faces when the amplitude of mass exceeds the clearance between the coil spring and the attached mass. Then, the restoring force is assumed to be an asymmetric piecewise-linear system. For such a system, the beam undergoes a nonlinear vibration when the attached mass collides with the coil spring. In order to analyze harmonic, superharmonic and subharmonic resonances for the system, Fourier series method is applied to obtain an exact solution for resulting vibration. Next, the numerical calculation is performed to obtain the resonance curves. The numerical results show effects of the mass ratio, the amplitude ratio of excitation, the spring constant ratio, the structural damping ratio and the external damping ratio on the resonance curves. The numerical experiments are also carried out to verify the numerical results.

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Head positioning accuracy of the hard disk drive should be improved to meet today's increasing performance demands. Vibration suppression of the arm in the hard disk drive is very important to enhance the servo bandwidth of the head positioning system. In this study, smart structure technology is introduced into the hard disk drive to suppress the vibration of the head actuator. It has been expected that the smart structure technology will contribute to the development of small and light-weight mechatronics devices with the required performance. First, modeling of the system is conducted with finite element method and modal analysis. Next, the actuator location and the control system are simultaneously optimized using genetic algorithm. Vibration control effect with the proposed vibration control mechanisms has been evaluated by some simulations.

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This paper reports on a study regarding modal property identification for railway vehicles using a linear prediction model. The relationship between input (excitation force or axlebox acceleration) and output (carbody acceleration) of an actual railway vehicle obtained by stationary or running tests is expressed by means of an ARX (Auto-Regressive eXogenious) model, and the procedure for the extraction of modal properties is described in detail. Determination of an appropriate model order (i.e., the order of the prediction coefficients in the ARX model) is specifically discussed from the viewpoint of practical use. The implementation of average estimation errors for two different parts of the analyzed data is proposed, and their effectiveness in determining the model order is evaluated. Suitability for the MIMO (multiple-input multipleoutput) problem using the ARX model is also described. It is shown that detailed modal characteristics can be successfully identified using the proposed method from measured data for both stationary and running tests.

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In order to stabilize the inherent unstable system like the inverted pendulum on a cart, severe judgment of situation is required. Accordingly, it can be expected that human operators exhibit complex behavior intermittently. This paper investigated the identification of the individual difference of human operator's behavior from time series data by using fuzzy inference and acquired individual skill of human operator. It also investigated the chaotic behavior of human operator and the formation of a complex system in the learning process of human operators with objects difficult to control. The operators in the experiment are skilled to some extent in stabilizing the inverted pendulum by training, and the data of ten trials per person were successively taken for an analysis, where the waveforms of pendulum angle and cart displacement were recorded. The maximum Lyapunov exponents were estimated from experimental time series data against embedding dimensions. It was found that the rules identified for a fuzzy controller from time series data of each operator showed well the human-generated decision-making characteristics with the chaos and the large amount of disorder and the individual difference of chaotic and complex human operation can be identified with fuzzy inference.

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Active noise control (ANC) in a three-dimensional sound field ( e.g., in an office) is investigated in this paper. As the size of the controlled area generally depends on the wavelength of the target noise, it is difficult to control the noise throughout an entire room using ANC. Instead, a noise control method in the vicinity of a subject's head (referred to as around-head control) is investigated in this paper. To realize around-head control, an evaluation point that mimics head movement is required. However, movement of the evaluation point during control has not been considered in conventional ANC. The authors earlier proposed control using a filter map to solve this problem. In this method, the controlled space is subdivided into small grids, and a filter map is produced by storing and updating filters in each grid. A new method of updating the map is proposed in this paper, in which a reliability index is calculated and used. The effectiveness of the proposed method is shown by numerical simulations using acoustic properties measured in an anechoic chamber.

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This paper presents a control system for active magnetic bearings (AMBs) considering the motions of the stator. AMBs require active control for stable support of the rotor. Many control methods for AMBs have been proposed. Most of them are designed with no regard to the stator motions because the stator is usually fixed on the base. However, in some applications, the stator moves with the object in which the AMB is mounted. In this paper, the influences of the stator motions on the relative angle of the rotor to the stator are investigated both theoretically and experimentally. In addition, the signals estimated by a disturbance observer are used to compensate the influences. The influences become remarkable at a low frequency range. The upper side of the remarkable range extends to higher frequency range when the gyroscopic effect is large. The influences are cancelled by the compensation using the observer. The effect of the cancellation depends on the estimation speed of the observer.

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A coupled inverted pendula model of competition and cooperation is proposed to obtain a purely mechanical implementation of dynamics comparable with the Lotka-Volterra competition dynamics. It is shown numerically that the proposed model can produce the four equilibria that can be compared to ecological coexistence, dominance, and scramble. It is also shown that the proposed model exhibits fractal dependence on initial conditions. The result implies that selection of the equilibria will be uncertain under finite accuracy of knowledge on initial conditions.

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A tripod constant velocity joint is used in the driveshaft of front wheel drive vehicles. Thrust force generated by this joint causes lateral vibration in these vehicles. To analyze the thrust force, a detailed model is constructed based on a multibody dynamics approach. This model includes all principal parts of the joint defined as rigid bodies and all force elements of contact and friction acting among these parts. This model utilizes a new contact modeling method of needle roller bearings for more precise and faster computation. By comparing computational and experimental results, the appropriateness of this model is verified and the principal factors inducing the second and third rotating order components of the thrust force are clarified. This paper also describes the influence of skewed needle rollers on the thrust force and evaluates the contribution of friction forces at each contact region to the thrust force.

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A model-based performance monitoring method for a heat exchange process, which is one of the key components of distributed energy supply systems, is developed. This performance monitoring, which utilizes a static input-output model of the process, first estimates the output process variables and heat exchange performance in response to variations in measured input process variables. The estimated output process variables are then compared with the measured ones. In this study, the effectiveness of the performance monitoring method in a transient state with irregular variations in water and steam flow rates is verified through a numerical simulation. The result shows sufficiency of the estimation accuracy of the output process variables and heat exchange performance and the capability of detecting the deterioration in the heat exchange performance in a transient state.

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Differential pressure transmitter with an orifice is widely used as a major field flowmeter. A major drawback of this flowmeter used at operation sites is the blockage of an impulse line, which connects a differential pressure transmitter with an orifice tap. In our previous studies, experiments at a water line showed that the diagnostic method based on the pressure fluctuations in the impulse line can diagnose the blockage in the steady state. In this method, however, there was a possibility of making a wrong diagnosis in the transient state. This paper clarifies the applicable conditions of two diagnostic methods: the diagnostic method based on the pressure fluctuations and the diagnostic method based on the phase difference. In particular, the effectiveness of two diagnostic methods in both steady and transient states is investigated by comparing the experimental results at an air line with those obtained at the water line. Through experimental investigations, the following results are derived: (1) The line pressure change has a harmful effect on the blockage diagnosis with the pressure fluctuations. (2) The diagnostic method based on the phase difference can diagnose the blockage even in the transient state; however, this method cannot diagnose the blockage, where the pressure fluctuations are not transmitted at an air line. Therefore, the method based on phase differences remains to be improved in the future work.

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Dynamic property of polyurethane foam is investigated experimentally. Polyurethane foam is loaded periodically with various amplitudes and various frequencies, and load, deflection and velocity of the polyurethane foam are measured. Using non-parametric identification technique in time domain, dynamic property of polyurethane foam is modelized as a function of velocity and deflection of polyurethane foam. Then we proposed a new model of dynamic property of polyurethane foam. Experiments are conducted with various conditions of size and compressibility, and the validity of the proposed model is confirmed. Difference of dynamic property by size and compressibility is investigated.

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