A theoretical solution to the free vibration of a string, where both ends are moving and the string length is constant such as a belt, has been already obtained. In this paper, a theoretical solution of forced vibration of an axially moving string, whose length is constant, is presented. Finite difference analyses of string vibration are also performed to verify the validity of this solution and to obtain the vibration characteristics of moving string. The calculated results of the finite difference analyses are in fairly good agreement with those of the theoretical solution. The effect of the moving speed on the resonant frequency and the anti-resonant frequency is clarified in the case that both ends are excited sinusoidally: When both ends are excited in same phase, even an asymmetric mode showed the resonance by the effect of moving.

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This paper proposes a vibration testing and health monitoring system based on an impulse response excited by a laser ablation. High power YAG pulse laser is used for producing an ideal impulse force on structural surface. It is possible to measure high frequency vibration responses in this system. A health monitoring system is constructed by this vibration testing system and a damage detecting algorithm. A microscopic damage of structures can be extracted by detecting fluctuations of high frequency vibration response with the present health monitoring system. In this study, loosening of bolt tightening torques is defined as the damage of the system. The damage is detected and identified by statistical evaluations of measured frequency response data with Recognition-Taguchi method. The effectiveness of the present approach is verified by experiment to detect and identify the loosening of bolts installed on an aluminum block structure.

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In the present study, we investigated a noise reduction method by which to accurately obtain transfer functions in running transfer path analysis (TPA) using the principal component regression method. In the running TPA method, correct extraction of noise components from the principal components, which consist of transfer functions, is important. A statistical verification method for extracting the noise components in the principal components was applied. Rather than using the size of the principal component, as is the case in the conventional method, in the method of the present study, the significance probability of each principal component with respect to the output signal was set as a noise detection criterion. Subsequently, the noise reduction performance was verified through a simple simulation, and the performances of the statistical method and the conventional method were compared. The results of this comparison revealed that the influence of noise was reduced from the calculated transfer function more effectively by applying the statistical method than the conventional method.

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This paper presents a method for identifying the input power to a structure in machine operation using energy analysis models such as the Statistical Energy Analysis (SEA) and Energy Distribution (ED) models. The basis of this method is that the vibrational energies of the respective subsystems during operation can be measured with a velocimeter or accelerometer at the same measurement locations as in the constructed SEA and ED models. Generally, the identification of the input force in machine operation is accomplished by Transfer Path Analysis (TPA). With TPA, however, identifying the input forces is difficult when their locations are not clear. On the other hand, energy analysis models are excellent in cases of unclear input force locations. As for the ED model, the model accuracy is high in the low-frequency range, although model construction is more demanding than for SEA. In this study, the accuracy of input power identification using SEA and ED models is verified through numerical analysis using the finite element method and experimental tests on a simple structure consisting of three subsystems connected in series. As a result, if the location and the number of excitation and response points can be distributed appropriately within the subsystem, the identification of input power is effective and quantitative.

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Evaluation methodologies for the flow-induced vibration of an elastic beam subjected to an axial flow confined in a narrow passage are reported. In this paper, by using the analytical method already proposed by one of authors, a parameter study is performed on the dynamic stability of an elastic beam subjected to axial flow confined a narrow passage. The effects of support conditions of structures, structural damping, and fluid characteristics on the dynamic stability are clarified. Especially, paying attention on the vicinity of critical velocity, the effects of stabilization or destabilization on flutter and divergence are investigated by changing fluid viscosity and structural damping.

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Mobile inverted pendulums are needed to be stabilized at all times using a safe control method. Previous approaches were based on a linearized model or feedback linearization. In this study, interconnection and damping assignment passivity-based control (IDA-PBC) is applied. The IDA-PBC is a nonlinear control method which has been shown to be powerful to stabilize underactuated mechanical systems. Although partial differential equations (PDEs) must be solved to derive the IDA-PBC controller and it is a difficult task in general, we show that the controller for the mobile inverted pendulum can be constructed. A systematic graphical method to select controller parameters that guarantee asymptotic stability and a procedure to estimate the domain of attraction are also proposed. Using this method, the pendulum is stabilized by restricting it to a predefined angle range. Simulation results show that the IDA-PBC controller performs fast responses theoretically ensuring sufficient domain of attraction. The effectiveness of the IDA-PBC controller is also verified in experiments. Especially control performance under an impulsive disturbance on the mobile inverted pendulum is verified. The IDA-PBC achieves as fast transient performance as a linear-quadratic regulator (LQR). In addition, we show that when the pendulum inclines quickly and largely due to the disturbance, the IDA-PBC controller can stabilize it whereas the LQR cannot.

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Recently, the riding comfort of passenger cars has become important, as well as driving performance and control stability. To improve riding comfort performance, it is necessary to evaluate comfort quantitatively and take discomfort-decreasing measures. In this study, using acceleration magnitude, frequency (below 3 Hz), phase difference, and acceleration amplitude ratio as the input parameters, the characteristics of vibratory sensibility were surveyed with driving posture in a shaking experiment to identify the parameters that affect sensation. A vibration experiment was conducted using the standing wave of two axes, X (fore and aft)-Z (vertical) and Y (lateral)-Z (vertical). As a result, the riding sensation tends to depend on the frequency and the amplitude ratio.
Next, the human body response was measured using an input condition in which the difference of sensation appeared notably in the experimental results of grasping the sensibility characteristics. Measurement points were the pre-head, occipital, chest, pelvis, and ischium. Moreover, we analyzed human vibration responses by observing the relative movements of body parts from the side-view and rear-view. We verified the correlation between these responses and sensations. As a result, this study shows that riding comfort can be improved by decreasing lateral vibration at the chest and pelvis.

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Recently, bladed disks with continuous ring type structure have been used in many kinds of turbomachinery due to its high reliability. The vibration characteristics of the bladed disk with continuous ring type structure have been studied extensively, and the effect of the friction damping on the forced vibration is almost clarified. On the other hand, few studies have been done on the effect of the friction damping on the blade flutter. In this paper, the stability analysis of the bladed disk with continuous ring type structure is carried out using the equivalent spring-mass model, and the effect of the friction damping on the blade flutter is clarified. From the results of the analysis, it is concluded that the stable steady vibration or the flutter always occurs when the aerodynamic damping of the blade becomes negative. Whether the blade vibration is stable or unstable depends on the magnitude of the aerodynamic damping and the initial condition. In other words, when the friction damping cannot suppress the self-excited vibration due to the large aerodynamic damping and the large initial amplitude, the amplitude of the blade vibration becomes larger and the flutter occurs.

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The dynamic characteristics and behavior of soft ground are greatly affected by the constituent soil grain shape. For multipass calculations of the action of tires on soft ground, it is important to take into consideration the elastic-plastic properties of the soil. We previously developed an efficient interactive model of a tire and soft ground that comprises a distributed lumped mass-spring model for the tire, a discrete element model for the upper ground section, and a mass-spring model for the lower ground section. In the present study, we have improved the previous soft ground model by considering the soil grain shape and the elastic-plastic properties of soft ground, and have analyzed the effect on the behavior of the tire and soft ground using numerical simulations. The results showed that soft ground composed of non-round soil grains exhibits higher shear strength and stability than is the case for round grains. In addition, it was found that the reversal of sinkage following the passage of a tire and the compaction due to multiple tire passes could be expressed qualitatively by modeling the elastic-plastic properties of the lower soft ground section.

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Shapes and lay-up configurations of laminated composite shallow shells are optimized simultaneously to maximize the fundamental frequency by a simple genetic algorithm method. The surface shape is defined by a cubic polynomial and this makes it possible to express a variety of surfaces with inconstant curvature radii by varying the values of the coefficients for each polynomial term. The coefficients and the lay-up configurations of the laminated shells are directly employed as design variables, and constraints are imposed on the coefficients and curvature radii to maintain the shallowness of the shells. The frequencies are calculated by using the Ritz method due to its flexibility with surface shapes. The results of the present analysis agreed well with experimental and finite element analysis results in terms of frequencies and mode shapes. The obtained optimum solutions resulted in higher fundamental frequencies than for shells with commonly emplyed surface shapes and lay-up configurations.

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This paper presents a response evaluator as a semi-active control method for a base isolated building in long-period earthquake response analysis. The absolute acceleration of each story and the relative displacement of an isolated layer are the input signals and the switching parameter for the damping coefficient is the output signal of the response evaluator. The response evaluator is designed by a multilayered neural network, and a genetic algorithm is used to adjust the neural network parameters which determine the performance of the response evaluator. Four oil dampers are installed in the isolated layer and each damping coefficient of the dampers is set to a different value to correspond to the various characteristics of earthquake motions, then the total damping force of the isolated layer is multi-step values, regardless of whether using oil dampers with two-step damping coefficients. By the numerical simulation with the proposed semi-active control method, both the acceleration of each story and the displacement of the isolated layer, which are in a trade-off relationship with each other, are reduced compared with the acceleration in the case of all damping coefficients being small (Soft) and the displacement of the isolated layer in the case of all damping coefficients being large (Hard).

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Tripod constant velocity joints are used in the driveshafts of front wheel drive vehicles. Thrust force generated by this joint causes lateral vibration in these vehicles. This paper surveys some methods for reducing the thrust force based on the mechanisms inducing the thrust force, focusing on a method that creates dual contact between a roller and groove. This method has the advantage of requiring only a few design modifications, but its thrust force reduction mechanism has yet to be clarified. Therefore, a theory was constructed to describe the induction of thrust force by this method through the application of sliding velocities generated between the roller and dual contact groove. Subsequently, the effect of the thrust force reduction was investigated. This paper also describes the appropriateness of this theory. It was validated by comparing theoretical results with computational results based on a multibody dynamics approach and with experimental results of a prototype joint equipped with the dual contact grooves.

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