This paper reviews the situations and features of earthquake damage to industrial facilities, manufacturing companies, energy supply facilities, and mechanical structures and installations in Japan, and traces trends of countermeasure technology developed focusing on earthquake resistance and vibration control. In Japan, with the 1964 Niigata earthquake as the turning point, earthquake damage to industrial facilities became a social problem. With power stations being constructed in the 1960s, it also became an important technological policy to establish seismic design method for nonbuilding structures such as equipment and piping systems related to nuclear power. The Kobe earthquake in 1995 damaged production companies including leading manufacturers so extensively that it brought a new focus to seismic considerations. We studied the damage to typical equipment and installations and, based on this experience, investigated the features of damage modes to industrial facilities and machinery and considered corresponding technical measures. We present some examples and discuss progressive trends in seismic and vibration control technology following the Kobe earthquake. In particular, we focus on the new seismic design code for high-pressure gas facilities and the development of seismic and vibration control dampers and their applications.

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This paper presents a survey of fault diagnosis using support vector machine (SVM). It attempts to summarize and review the recent research and development of SVM in machine fault diagnosis. Numerous methods have been developed based on intelligent system. However, the use of SVM for machine fault diagnosis is still rare. In addition, this paper introduces the feasibility of SVM based on regression (SVR) for machine prognosis system. The proposed method is addressed to predict the upcoming state of machine based on previous condition. The viability of developed system is evaluated by using trending data of low methane compressor acquired from condition monitoring routine. The results show that SVR has potential and promise for reliable and robust forecasting tool in machine prognosis system.

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Blade failures represent the highest percentage of failures in gas turbines. This paper presents some typical examples of blade related failures. A literature review of common types of blade faults and research on detection methods are presented. Some methods are however less feasible under practical operating conditions in the plant. Three case studies of gas turbines vibrations are presented. The first case reports on stator blades and labyrinth glands rubs resulting in recurring shaft seizure during the coast down after load removal. Comparison of vibration spectrum undertaken a day before failure with prior data showed increase in specific blade passing frequencies (BPF) with increased side bands at intervals of the synchronous rpm. These increases were from 13 to 28 times above standard deviations of baseline datum. The stator blades rub was suspected to originate from a distorted casing. Another case relates experiences of a cracked shaft which resulted in severe rubbing during a run up. The unit experienced steady increase in vibration levels on the compressor non-drive end bearing several months prior to the incident. A full rub occurred as the unit passed through the second critical, with further development of a thermal bent shaft aggravating the problem with instantaneous severe vibration excursion. An approximate 200° phase shift was also noted. A 100 mm longitudinal crack on the shaft was found together with signs of severe rubs on the compressor blades. The third case involved time varying vibrations where vibration amplitudes and phase angles increased over a time period which dropped off after each time period; and repeated in regular cycles. This was due to oil leaks carbonization at the glands resulting in a rub. The paper concludes with a brief discussion on issues relating to relatively poor detection of blade faults in the plant.

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In Japan, about seventeen nuclear power stations are operating. The energy generated by nuclear power stations is about 30 percent of gross generated electric power in Japan. A lot of spent fuels come out of the nuclear power stations. The spent fuels are stored in a canister which is put in a concrete cask until reprocessed in the reprocessing facility. The cask is generically free-standing on a horizontal floor. Recently, the huge earthquakes frequently arise, so it is necessary to prevent the cask from overturning and the canister from breaking when an earthquake occurs. In this study, the cask-canister system is considered as a dual structure. The structure is freely standing on the floor. We analyze sliding and rocking motions of the structure subjected to a horizontal earthquake excitation.

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This paper describes the numerical calculations on the vibrations of a structure excited by two unbalanced rotors. When two rotors rotate on a base plate, which is free to vibrate horizontally, some kinds of vibration modes, i.e., in-phase synchronization, out-of-phase synchronization, and non-synchronization are observed. According to our investigation of rotor unbalance, we observed two types of non-synchronization. One is quasi-periodic vibration, and the other is chaos.

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Stochastic jump phenomena in the random responses of a Duffing oscillator subjected to nonwhite random excitation are investigated. The stochastic jump phenomena correspond to the existence of multiple stationary responses, which differ in the phase angle between excitation and response as well as the amplitude of responses. The response suddenly switches to other stationary response in the long sample function. The purpose of this paper is to propose the criterion that is able to distinguish between two states of the response when the band width of the random excitation becomes broader. In this study, we propose the product of each wavelet transform of the excitation and the response to estimate the phase angle between them. Numerical examples show that the product corresponds to the frequency decomposed phase angle between the excitation and the response, and successfully identifies the states of the response.

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In this paper, we propose an efficient procedure for finding the possible ranges of uncertain natural frequencies of a finite element (FE) model with uncertain parameters. Uncertain model parameters are described by input fuzzy numbers and then output fuzzy numbers are calculated by fuzzy arithmetic. The variation range of natural frequency is obtained from the membership function of output fuzzy number. The fuzzy arithmetic used is based on the α-cut concept and interval analysis. To reduce the computational effort for the interval analysis, the global optimization technique using response surface methodology (RSM) is introduced. Furthermore, we propose an approach for finding the feasible ranges of uncertain model parameters when the ranges of natural frequencies are specified. This is an inverse problem. A simple frame model is used to demonstrate the effectiveness of the proposed procedure and approach. The examples show that the membership functions of uncertain natural frequencies are efficiently and accurately estimated by the proposed procedure. In addition, the ranges of uncertain model parameters are properly evaluated by the proposed approach.

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In the past few decades, composite materials composed of straight fibers and polymer matrix have gained their status as the most promising material for light-weight structures. Technical merit of the composites as tailored material also provided practical advantages in the optimum design process. Recently, it is reported that the fabrication machine has been developed to make curved fibers embedded in the matrix material. Based on such technical advancement, this paper proposes an analytical method to study vibration of composite rectangular plates reinforced along curved lines. The approach is based on the Ritz method where variable fiber direction can be accommodated. For this purpose, the fibers continuously changing their direction are formulated as the variable bending stiffness in the total potential energy. A frequency equation is derived by the Ritz minimizing process, and frequency parameters are calculated as the eigenvlaues in the eigenvalue problem. In numerical results, the accuracy of the method is presented by comparing present results with FEM results. The advantages of present plate are confirmed by comparing natural frequencies and mode shapes with those of conventional composite and isotropic plates, and the effectiveness of the new solution to the most recent problem is demonstrated.

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Composite materials such as sandwich panels have been employed in many structural applications. Therefore, it is very important to obtain the dynamical properties of the composite materials. Also, an inverse analysis method has already been proposed by one of the authors to identify the layer elastic parameters of laminated composite materials using the FEM eigenvalue analysis and the sensitivity analysis. The purpose of this study is to improve the proposed identification method to apply to a sandwich panel and to identify the equivalent elastic parameters of a core material. By applying the experimental modal analysis technique to the sandwich panel, natural frequencies and mode shapes of the panel are obtained. From the obtained natural frequencies and mode shapes, the equivalent elastic parameters of the core material are identified numerically. Furthermore, the validity of the identified equivalent elastic parameters was shown.

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This paper models a railway carbody as a non-circular cylindrical shell with simply-supported ends, where the shell does not have end plates or other equipment attached. Transfer matrix method (TMM) was applied to the analysis of three-dimensional elastic vibration problems on this carbody. A 1/12 size carbody model was made for experimental studies to verify the validity of the numerical simulation. This model has end plates and was placed on soft sponge at both ends to simulate the freely-supported condition. Modal analysis was applied to the experimental model, and natural frequencies and mode shapes of vibration were measured. Comparing the results by TMM and experiments, the natural frequencies and mode shapes of vibration for lower modes show good agreement in spite of the differences in boundary conditions. The effect of stiffening members installed on the experimental model was also investigated.

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This study proposes an analytical method to deal with free vibration of shallow shells with generally curved surfaces expressed in terms of cubic polynomial functions. Such shell structures with variable curvature are recently found in automobile and other design-oriented structural applications. In the analysis an interpolating function of the third order is introduced to represent the required surface shape and the corresponding curvature is derived as a function of the position. The obtained curvature is substituted into the total potential energy of the shell, and the analytical procedure is shown to derive a frequency equation by the Ritz method. Numerical examples demonstrate that the vibration of shallow shells with various curved surfaces can be analyzed by the present method, and the effects of varying the coefficients of the cubic function in geometric expression are clarified on the natural frequencies and mode shapes.

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Recently, considerable attention of material scientists and mechanical engineers has been devoted to measurement based on atomic force microscopy (AFM). Self-excitation is known to be an effective excitation method for AFM probe to measure the surface of a biological molecule in liquid. For practical use of a probe in liquid, we must realize a self-sensing and self-actuating AFM probe using PZT instead of using a conventional optical lever method. However, frequency characteristics of the PZT are very complex in applications for probe behavior measurement. For detecting sensor characteristics, the dynamics of the cantilever to which the PZT is attached are extracted from the PZT sensor output signal. To this end, we examine the frequency response of the PZT output signal in the case where the cantilever is excited with constant response amplitude using a PZT actuator. Then, we establish a method to process the signal so that the frequency characteristic of the PZT sensor has no high gain for the frequency range other than the first natural frequency. Finally, we conduct experiments to verify that the resultant signal is suitable to generate van der Pol-type self-excited oscillation.

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In press working, unidirectional transmission of mechanical energy is expected in order to maximize the life of the dies. To realize this transmission, the author has developed a shock control system based on the sliding mode control technique. The controller makes a collision-receiving object effectively deform plastically by adjusting the force of the actuator inserted between the colliding objects, while the deformation of the colliding object is held at the necessity minimum. However, the actuator has to generate a large force corresponding to the impulsive force. Therefore, development of such an actuator is a formidable challenge. The author has proposed a semi-active shock control system in which the impulsive force is adjusted by a brake mechanism, although the system exhibits inferior performance. Thus, the author has also designed an actuator using a friction device for semi-active shock control, and proposed an active seatbelt system as an application. The effectiveness has been confirmed by a numerical simulation and model experiment. In this study, the optimal deformation change of the colliding object is theoretically examined in the case that the collision-receiving object has perfect plasticity and the colliding object has perfect elasticity. As a result, the optimal input condition is obtained so that the ratio of the maximum deformation of the collision-receiving object to the maximum deformation of the colliding object becomes the maximum. Additionally, the energy balance is examined.

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Giant magnetostrictive element has an advantage in excitation force at high frequencies, but has a weakness in the ability to produce vibration power at low frequencies. The purpose of this paper is to develop a new vibration actuator with improved characteristics at low frequencies by using electromagnetic force to assist the magnetostrictive element. A prototype of the actuator is designed and fabricated. The characteristics of the actuator are measured. The results of measured acceleration or force show an efficient excitation at high frequencies due to magnetostrictive element. It is also shown that the electromagnetic force improves the characteristics at low frequencies where the acceleration amplitude is flat at frequencies below 1kHz. It is confirmed that the magnetostrictive force and electromagnetic force are cooperatively working in this actuator. In addition, the actuator has an advantage in easiness of attachment to or removal from the wall because it sticks to the wall with magnetic force derived from the magnet equipped to produce bias magnetic flux in the magnetostrictive element. This allows flexible location selection of actuators when the actuators are used for vibration control.

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Semi-active vibration systems expend a small amount of energy to change the system parameters such as damping and stiffness. The variable damping and stiffness semi-active systems with base excitations have demonstrated excellent performances in the resonant and high frequency regions. For a forced vibration, it plays an important role in describing a building system with wind loading or a vehicle suspension with an engine vibration force; and the system stiffness has a large influence on the frequency response in the low frequency region. However, forced vibration systems with variable stiffness control have not been received significant attention. To address this issue, the performance of a variable stiffness system with a force excitation is studied in theoretical calculations and experiments. The responses to sinusoidal and random inputs showed that the system with stiffness on-off control had advantages of both soft and stiff systems in the whole frequency.

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A new gyroscopic sensor using active magnetic bearing (AMB) is studied both theoretically and experimentally. The proposed sensor works as a two-axis gyroscopic sensor and also as a three-axis servo-type accelerometer, which utilizes the control function of AMB. Angular velocities and accelerations are estimated from the control signals for canceling gyroscopic torque and inertial forces acting on the shaft of the AMB. In measuring two-axis angular velocity simultaneously, the control signals canceling inertial torque must be considered in addition to the gyroscopic toque for precise measurement. This paper presents the principles of two-axis angular velocity and acceleration measurement by AMB. In order to investigate the feasibility of the proposed sensor, several basic studies are carried out with a conventional-size AMB.

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In this paper, a preliminary study on a shape-recoverable shock absorption structure consisting of hysteretic spring elements combined with a buckling mechanism which could achieve both high energy absorption efficiency and high energy dissipation efficiency is presented. In order to illustrate the basic idea, a conceptual model consisting of a two-link mechanism and a hysteretic spring is investigated. The two-link mechanism with axial and lateral springs is frequently used as an elementary model for the buckling behavior of thin-walled structures. Without the lateral spring, it has a pair of stable equilibriums and one unstable equilibrium between them, so that it shows a snap-through buckling instability when loaded in the lateral direction. The load-deformation curve changes depending on the quantity of the lateral spring constant undergoing saddle-node bifurcation. After the bifurcation, the stable and unstable equilibriums except for the origin vanish, and only one stable equilibrium remains at the origin. This implies that, when combined with a strong spring, the load-deformation curve of the two-link mechanism has only a stable equilibrium at the origin, whereas it has another stable equilibrium when combined with a weak spring. Therefore, if combined with an appropriate hysteretic spring, the mechanism subjected to an impact will yield positive resistive force in the loading path, followed by stopping at the stable equilibrium with residual deformation when unloaded. After the impact, the residual deformation will be eliminated by applying a small amount of energy to trigger the bifurcation again. A proof-of-concept experimental model consisting of a two-link mechanism and a superelastic shape memory alloy (SMA) spring is developed for the demonstrative purpose. A prototype of superelastic SMA-based “woven” shells is also developed to show a possible application of the proposed concept.

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In recent years, the needs to achieve the eigenvalue optimization considering the NVH performance increase in the initial design of suspension systems. This paper presents an application of MBD (Multi-Body Dynamics) model to dynamic property optimization. A vehicle suspension is modeled by MBD and the vibration properties are analyzed based on the linearization of the system equation. The model can solve the dynamic properties as modal parameters such as natural frequencies, modal dampings and mode shapes. The targets of this model are to calculate the eigenvalue sensitivity with respect to each design parameter (mass, stiffness, damping and geometry of the link) and to optimize the eigenvalue by combining the structural modifications of these high sensitivity elements. By the sensitivity analysis, we can make sure which elements contribute to the dynamic characteristics of the system. The feasibility of the dynamic property optimization is examined by applying the presented approach to the suspension system model. The structural modification is carried out based on the sensitivity analysis in order to attain the required natural frequency change. As a result it is shown that the natural frequency is optimized based on the presented sensitivity analysis.

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Mass measurement using a relay feedback system was studied experimentally. The measurement system has an on-off relay with hysteresis and switches force acting on the object in relation to its velocity. Such nonlinear control induces a limit cycle in the feedback system. The mass of the object is determined from the period of this limit cycle. The apparatus manufactured for experimental study uses two voice coil motors (VCM's), one of which is for driving the object and the other is for generating prescribed disturbances. The effects of system parameters and disturbances on measurement accuracy were examined experimentally.

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The authors utilize the harmonic wavelet transform and successfully detect minute signs of small fault in a periodic monitored signal. It is important for the effectual detection of the minute signs to reduce the obstructive noise and edge effect. The edge effect is a peculiar phenomenon to wavelet transform and hampers effective detection. The authors devised useful methods to reduce the obstructive noise and the edge effect. Even if no visible information pertaining to a fault appeared in the monitored waveform, a minute sign of a small fault was successfully captured by the proposed method. In this paper, we extend the proposed technique to an important practical application. A fault generated in a gear tooth is focused on. It is demonstrated that our technique is capable of detecting minute signs arising from a small fault in a gear tooth operated in a constant rotating speed.

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Many classes of nonlinear systems can be represented by Volterra kernels. The authors have recently developed a method for identification of Volterra kernels of nonlinear systems by using M-sequence and correlation technique. In this paper, the authors propose a new method for identification of nonlinear mechanical systems by use of Volterra kernels. The nonlinear mechanical systems are approximated to a nonlinear vibrating system which consists of a mass, a dumper, a linear spring and nonlinear and springs. Then, the parameters, which represent the nonlinear springs are calculated by use of the Volterra kernels. From the results of computer simulation and experiment, the parameters that represent the nonlinear characteristics of the nonlinear mechanical systems can be identified by the proposed method.

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In 2005, the ban on riding tandem on motorcycles along expressways in Japan was lifted. Since this is likely to increase tandem riders, there is a need to improve the motorcycle stability of tandem riding from the perspectives of safety and comfort. A motorcycle becomes unstable at low speed. Thus, this study investigates the stability and handling properties in tandem riding on motorcycles at low speed. First, we did experiments and obtained the time responses of motorcycle behaviors and rider control after a passenger changes posture. Next, we constructed a multi-body model for a human-motorcycle tandem riding system that contains a controller that imitates the rider's driving operation. From simulation results, we obtained the effect of passenger's posture changes and such individual differences as upper-body mass and length. Finally, we designed a control system that applies a sliding mode control theory to reduce the effects of passenger's posture changes. After comparing the rider control model and the sliding mode control, the latter shows better control. This system also has robustness to uncertainty of passenger properties.

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This paper presents an approach to design multiobjective static output feedback H₂/H_∞/GH₂ controller for vehicle suspensions by using linear matrix inequalities (LMIs) and genetic algorithms (GAs). A quarter-car model with active suspension system is studied in this paper and three main performance requirements for an advanced vehicle suspension are considered. Among these requirements, the ride comfort performance is optimized by minimizing the H₂ norm from the road disturbance to the sprung mass acceleration, the road holding performance is improved by constraining the H_∞ norm from the road disturbance to the tyre deflection to be less than a given value, and the suspension deflection is guaranteed to be less than its hard limit by constraining the generalized H₂ norm from the road disturbance to the suspension deflection. In addition, the controller gain can be constrained naturally in GAs, which can avoid the actuator saturation problem. A static output feedback controller, which only uses the available sprung velocity and suspension deflection signals as feedback signals, is obtained. This multiobjective controller is realized by using GAs to search for the possible control gain matrix and then to resolve the LMIs together with the minimization optimization problem. The approach is validated by numerical simulation which shows that the designed static output feedback controller can achieve good active suspension performances in spite of its simplicity.

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The aerodynamic forces acting on representative cars of high-speed trains travelling in a tunnel have been studied theoretically, as well as the translational and rotational motions of these cars. The aerodynamic forces are simplified into one-dimensional sinusoidal ones. Each of the cars, coupled to others and supported by springs and dampers, has two degrees of freedom for translational and rotational motions. The results show that (a) the calculated aerodynamically-induced lateral force and yawing moment agree well with observations from running experiments; (b) the steady-state mode shapes agree well with those obtained previously from running experiments; and (c) the wavelength of the travelling aerodynamic force controls the phase differences among the cars of the train.

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Suppression of the vertical bending vibration of carbodies has recently become essential in improving the ride comfort of railway vehicles. In this paper, we propose a method of controlling vibration in the primary suspension of rolling stock to reduce carbody vibration. Systems conceivable for this purpose include a semi-active suspension system with variable axle dampers that can control damping force continuously by command current to the damping force control valve. Based on LQG control theory, we carried out numerical simulations and performed excitation testing with a carbody equivalent to an actual Shinkansen vehicle fitted with variable axle dampers to selectively suppress the first mode bending vibration of the carbody. The results show that this LQG control method reduces the power spectral density (PSD) of acceleration on the floor more effectively than the sky-hook control method, which does not consider the vibration modes of the carbody.

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Flow visualization tests and fluid force measurements were conducted in a water tunnel to investigate flow around and fluid forces on a cross-shaped tube (CST) in a cross-flow. The following results were obtained. Flow around a CST is classified into two patterns. One is perfect-separation flow for small incidence angle and the other is reattached flow for large incidence angle. The critical incidence angle where the flow pattern changes from the former to the latter is about 7.5°∼15°. At the critical angle, the mean drag and lift coefficients reach their minimum while the Strouhal number attains to the maximum. The amplitude of the fluctuating lift decreases as the incidence angle increases. These features of flow around and fluid forces on a CST are quite similar to those of a square prism. These results imply that one-degree-of-freedom galloping and vortex-induced vibration possibly occur for small incidence angle while ILEV (impingement of leading edge vortices) vibration might be caused for large incidence angle when a CST is elastically supported in a cross-flow.

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Cavitation represents one of the most common faults in pumps and could potentially lead to a series of failure in mechanical seal, impeller, bearing, shaft, motor, etc. In this work, an experimental rig was setup to investigate cavitation detection using vibration envelope analysis method, and measured parameters included sound, pressure and flow rate for feasibility of cavitation detection. The experiment testing included 3 operating points of the centrifugal pump (B.E.P, 90% of B.E.P and 80% of B.E.P). Suction pressure of the centrifugal pump was decreased gradually until the inception point of cavitation. Vibration measurements were undertaken at various locations including casing, bearing, suction and discharge flange of the centrifugal pump. Comparisons of envelope spectrums under cavitating and non-cavitating conditions were presented. Envelope analysis was proven useful in detecting cavitation over the 3 testing conditions. During the normal operating condition, vibration peak synchronous to rotational speed was more pronounced. It was however during cavitation condition, the half order sub-harmonic vibration component was clearly evident in the envelope spectrums undertaken at all measurement locations except at the pump bearing. The possible explanation of the strong sub-harmonic (½ of BPF) during cavitation existence in the centrifugal pump was due to insufficient time for the bubbles to collapse completely before the end of the single cycle.

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This paper deals with an experimental study on suppression of a residual sloshing in a liquid transport container by a bulkhead, which divides the container vertically into two sections. Inserting the bulkhead to the container, the sloshing mode is separated into two modes; the one is the sloshing mode of liquid column in a U-tube (U-tube-mode), and the other is the sloshing mode in the separated container (Bulkhead-mode). In this paper, the suppression effect by the bulkhead on residual sloshing, which is excited by sudden stop of the liquid transport container, is examined experimentally with changing aperture ratio of the bulkhead, types of the bulkhead plate with or without holes, and the size of holes. Moreover, the fluid flow in the container is visualized and the suppression mechanism by the bulkhead is discussed based on the flow visualization. As a result, detailed suppression effect by the bulkhead on the residual sloshing is clarified, and it is clarified that higher suppression effect by the bulkhead is caused by the energy dissipation due to the vortex generated at the edge of the bulkhead and swirl flow in the liquid. The vortex generated and swirl flow in the liquid play an important role in higher energy dissipation of sloshing.

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This paper deals with surface and interface sloshing in a tank containing two fluids of different desities. Scientific interest in this ploblem includes the need to quantify allowance loads on oil water separators and chemical plants. In this study, we give a Hamiltonian formulation of a system of two incompressible irrotational fluids with a dynamic free surface and interface. This study aims to analyze the linearized time history response and the linear properties (vibration mode and effect of surface tension on the natural frequency). As a result, it was revealed that this system has two different vibration modes (surface and interfacial mode) with same wave number and the surface tension causes natural frequency increases. The validity of the theory is verified by experimental results. This procedure can be directly applied to the nonlinear problem of this system.

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To improve the reliability and the thermal efficiency of LP Low pressure end blades of steam turbine, new standard series of LP end blades have been developed. The new LP end blades are characterized by the ISB (Integral Shroud Blade) structure. In the ISB structure, blades are continuously coupled by blade untwist due to centrifugal force when the blades rotate at high speed. This paper, first, explains the effect of the contact condition of the shroud on the vibration characteristics of the ISB structure, using the analysis method developed by authors. Second, the calculated natural frequency and blade damping are compared with the measured ones. From these results, the effect of the shroud contact condition on the vibration characteristics of the ISB structure is clarified, and the validity of the analysis method is confirmed.

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Oil damper is widely used in engineering to dissipate the energy of vibration, increase the stability. Oil damper provide damping force due to the viscosity of the oil or effects of squeezing film. The viscous damping coefficient is one important factor of the viscous damper. The oil damper referred in this paper is one of the important parts of a machine, and the damping coefficient is of great importance to the design of the machine. The damper is an over damped single freedom system with a very small mass. The stiffness and mass of the damper can't be changed due to the structure restrict. This presented paper reports the measurement on the damping coefficient of the referred oil damper. Several measurement methods were compared, and the most appropriate one was chosen. A measurement apparatus composed of an un-contacted exciter, a response sensor, and data acquisition devices was designed and developed, and the damping coefficient was measured successfully.

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This paper proposes a new method for the utilization of variable damping in a vibration system. A single-degree-of-freedom base-excited model with a variable damper is considered. The coefficient of variable damping can be changed as that in the case of a sine wave, i.e. parametric excitation whose frequency can be arbitrarily selected. One of the external forces acting on the mass through the damper from the base is equivalent to the product of the damping coefficient and the input velocity. By multiplying the input sine wave by the frequency-controlled sine wave of variable damping, a new vibration that has a frequency different from the input frequency arises. Therefore, the oscillation of the damping coefficient at a suitable frequency can generate a new vibrational component that has the same frequency as the eigen-oscillation of the vibration system. As a result, the vibration amplitude increases because of resonance. In this paper, we confirm the growth of the vibration amplitude by the proposed parametric excitation of damping by simulation and experiment.

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This paper describes the estimation method of transient sound radiating from a structure excited by random impact forces and the noise reduction design of a coin storage box of a coin counting machine. To represent the random impulses, the probabilistic model of random impact forces is derived by defining the collision position and time of impulses as probability variables and using the probability density functions of the variables. The probability density functions of the collision position and time are assumed as Gaussian probability distribution. The vibration displacement of the structure at each time step is represented through time-averaged function with respect to the above probability variables. The transient sound pressure is obtained by using a Rayleigh integral equation and the sound power is evaluated by integrating the sound pressure distribution in frequency domain. To check the accuracy of estimation based on the probabilistic model, the sound pressure and power radiated from the structure are measured. It is confirmed that the estimated frequency responses agrees well with the measured values in low frequency domain and that the proposed probabilistic model is effective for estimating the random impact sound. Next, using the above probabilistic model, the structural modification to reduce the sound power from the box is carried out. In this structural modification, straight dimples to cross the antinodes of the dominant mode of sound power are added. As a result of sound power measurement, it is confirmed that the proposed method is applicable to noise reduction design.

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An axially short expansion chamber in a duct acts as a resonator type muffler whose effective frequency is determined by the duct and chamber geometry. To modulate this frequency, the temperature of the air in a very short chamber consisting of two rectangular branches located symmetrically on opposite sides of a rectangular duct was changed. The transmissibility of the sound was measured for a plane wave propagating in the duct through the chamber section. Each effective frequency (resonant frequency), at which the maximum transmission loss was obtained, was summarized and considered using a simple side branch type muffler approximation. The frequency modulates regularly according to the temperature in the chamber. In practice, though, the range of frequency modulation is small versus the change in temperature. However, this method provides a means for the fine adjustment of the effective frequency to a target frequency for noise reduction.

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Active noise control (ANC) in 3-dimensional sound field, e.g. an office room, is investigated in this paper. Since the size of the controlled area normally depends on the wave length of the target noise, it is difficult to control in the whole room using ANC technique. Instead, around-head-control is investigated in this paper. To realize the around-head-control, an evaluation point is required to correspond with the head movement while controlling. However, the evaluation point movement while controlling has not been considered in a conventional ANC. Against this problem, a new algorithm is proposed in this paper. The algorithm updates filters by using Time-Delay filter and Distance-Attenuation coefficient. Time-Delay filter and Distance-Attenuation coefficient are calculated from the position of the evaluation point. The computer simulations are carried out, and the validity of the new algorithm is shown.

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Based on the experiences of the Malaysian Armed Forces (MAF), failure of the main rotor gearbox (MRGB) was one of the major contributing factors to helicopter breakdowns. Even though vibration and oil analysis are the effective techniques for monitoring the health of helicopter components, these two techniques were rarely combined to form an effective assessment tool in MAF. Results of the oil analysis were often used only for oil changing schedule while assessments of MRGB condition were mainly based on overall vibration readings. A study group was formed and given a mandate to improve the maintenance strategy of S61-A4 helicopter fleet in the MAF. The improvement consisted of a structured approach to the reassessment/redefinition suitable maintenance actions that should be taken for the MRGB. Basic and enhanced tools for condition monitoring (CM) are investigated to address the predominant failures of the MRGB. Quantitative accelerated life testing (QALT) was considered in this work with an intent to obtain the required reliability information in a shorter time with tests under normal stress conditions. These tests when performed correctly can provide valuable information about MRGB performance under normal operating conditions which enable maintenance personnel to make decision more quickly, accurately and economically. The time-to-failure and probability of failure information of the MRGB were generated by applying QALT analysis principles. This study is anticipated to make a dramatic change in its approach to CM, bringing significant savings and various benefits to MAF.

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Mechanical stimulation to bones affects bone formation such as decrease of bone mass of astronauts under zero gravity, walking rehabilitation to bone fracture and fracture repair with ultrasound devices. Bone cells have been reported to sense and response to mechanical stimulation at cellular level morphologically and metabolically. In the view of mechanical vibrations, bone cells are deformed according to mechanical stimulation and their mechanical characteristics. In this study, sinusoidal inertia force was applied to cultured osteoblasts, which are a kind of bone cells, and effects of frequency and acceleration amplitude of mechanical vibration on the cells were investigated in respect of the cell proliferation, bone matrix generation and alkaline phosphatase (ALP) gene expression. The results to be obtained are as follows. The significant difference of cell density and bone mass generation between the non-vibrating and vibrating groups is found. ALP gene expression shows a peak to frequency at 50 Hz and the value of it is approximately 4.5 times as high as that of the non-vibrating group in the case of the acceleration amplitude of 0.5 G. ALP gene expression at 0.5 G is significantly larger than at 0, 0.125 or 0.25 G in the case of the frequency of 50 Hz.

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This paper discusses the course keeping control problem for a small autonomous boat using low cost sensors. Comparing with full scale ships, a small boat is more sensitive to the environmental disturbances because of its small size and low inertia. The sensors available in the boat are a low cost GPS and a rate gyro while the commonly used compass in ship control is absent. The combined effect from disturbance, poor accuracy and significant delay in GPS measurement makes it a challenging task to achieve good performance. In this paper, we propose a simple dynamic model for the boat's horizontal motion. The model is based on the Nomoto's model and can be seen as an extension to it. The model describes the dynamics between rudder deflection and the boat's velocity vector angle while Nomoto's model reveals that between rudder deflection and the boat's yaw angle. With the proposed model there is no need for a yaw sensor for control if the boat's moving direction can be measured. GPS is a convenient device for that job. Based on the derived model, we apply mixed H₂/H_∞ control method to design the controller. It can guarantee the robust stability, and as the same time it can optimize the performance in the sense of H₂ norm. The experimental data show that the proposed approach is proved to be effective and useful.

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This paper focuses on the design of a modular multi-legged walking robot MiniQuad-I, which can be reconfigured into variety configurations, including quadruped and hexapod configurations for different tasks by changing the layout of modules. Critical design considerations when taking the adaptability, maintainability and extensibility in count simultaneously are discussed and then detailed designs of each module are presented. The biomimetic control architecture of MiniQuad-I is proposed, which can improve the capability of agility and independence of the robot. Simulations and experiments on crawling, object picking and obstacle avoiding are performed to verify functions of the MiniQuad-I.

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This study is concerned with a vibration control strategy for a flexible-link system to achieve effective vibration suppression. It is required that the control system adapts to the dynamic characteristic variation of the system. A smart-link system composed of piezoelectric actuators and gain-scheduled controller is proposed to cope with change of the variable parameters which causes the dynamic characteristic variation of the system. An adaptive control is conducted by scheduling some LTI controllers to keep the stability and performance against the change of the variable parameters. The appropriate actuator location is determined by the target mode shapes. The scheduling gains for the LTI controllers designed at their operating points are optimized to obtain effective vibration suppression of the system.

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Impact vibration such as a floor vibration caused by jumping of children or vibration of a press machine is very important engineering problem. The momentum exchange impact damper has been proposed to solve these problems. The basic principle of this damper is based on the energy transfer on collision of three body systems. However energy or momentum transfer at the impact is not explained theoretically. This paper considers the energy transfer incurred during collisions in three body systems. The three body systems considered herein consists of an impact mass, a main body and an absorber mass. When the impact mass collides with the main body, part of its kinetic energy is transferred to the main body. When the main body simultaneously collides with the absorber mass, part of the kinetic energy of the main body is transferred to the absorber mass. Consequently, the main body receives a small amount of shock and it is possible to keep the main body nearly stationary. In this study, the influence of contact frequency and natural frequency of the system on the energy transfer during collision is analyzed. A theoretical model is developed to analyze the effect of various system parameters. It is shown that the maximum transfer of energy that can be obtained occurs when the contact frequencies are the same. The theoretical analysis is validated with experimental results.

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In this study, we present a curve of the starting rolling displacement, which considers the starting region in which the rolling friction force depends on the displacement. We then analyze the nonlinear vibration of a one degree-of-freedom system with rolling friction force depending on the displacement. From the analytical results, it was found that a stopping motion is recognized below the resonance point, and above the resonance point, the vibration wave shows a clear sinusoidal. The parameter m that shows the energy loss in a system using a curve of the starting rolling displacement greatly affects the vibration characteristics, and the different characteristics appear in the case of m≥2 and m<2.

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The objects of this study are to present new gas seals, which have several control fins at a groove part of straight labyrinth seal, and to evaluate the dynamic characteristics of the seals experimentally and theoretically. The new seals are expected to reduce the tangential velocity and to control the instability of the rotor system. The experimental test results are presented for eight multiple-pocket grooved gas seals with different number of control fins and stages to put control fins. In the theoretical study, seal chamber is divided into two control volumes. Then, the equations are formulated for each control volumes. The fluid forces acting on the rotor are obtained. For the circumferential velocity, the groove part is divided into three control volumes then the decrease in circumferential velocity by the effect of the control fins is evaluated at each control volume. Then, the circumferential velocity and dynamic fluid force were measured for 8 types of seals which were changed the number of fins and location of the fins in the experiment. In the theoretical analysis the flow equation which suppress the circumferential velocity was taken into account in the conventional labyrinth seal equation and solved numerically. From the above experimental and theoretical investigations, the followings are concluded that control fin installed in the grooves is effective to suppress the circumferential velocity. The effect of the fins is large at the first and second stage from the inlet of a seal. The effect of fins on the stabilization of rotor was large for 8 and 4 fins in the first stage.

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