This paper studies the free vibration characteristics of CFRP laminated composite plates made by prepreg patches. For this purpose CFRP rectangular plates are made by using prepreg patches and conventional prepreg, and then the free vibration characteristics of the plates are evaluated experimentally by impulsive excitation test.
Boom sprayers which spread agricultural chemicals to the wide area are used for the vast farmland. In addition to the fact that the scale of agriculture in Hokkaido is larger than other regions, hilly areas are often used. This causes vibrational excitations of the long booms of sprayer system, and boom vibrations invoke nonuniform distributions of agricultural chemicals. The authors have proposed an effective vibration isolation system with balancing weights in the past tsudy but these weights results in vast increase of the proposed system. In this study, the topology optimization technique is applied to the first boom and carbon fiber reinforced plastics (CFRP) are employed for the second boom. The weight of the boom is successfully reduced from optimization and material alternation with keeping the vibration characteristics similar with the existing structure.
An autoclave molding with prepregs is the most general method of CFRP manufacturing. It is well known that this method is time and energy consuming and prevents the cost reduction of CFRPs. Therefore, aiming to improve CFRP productivity, some manufacturing methods without the autoclave have been proposed such as a vacuumed resin transfer molding（VaRTM）method. The authors have been also proposed a new CFRP manufacturing method that is an electro deposition resin molding（EDRM）method. The EDRM is an application of the electro deposition technology which has been used as a coating technology for automobiles, and it is suitable for mass productions. In our previous studies, static mechanical properties including stiffnesses and strength of CFRPs molded by the EDRM have been investigated, but their dynamic properties have not been done yet. Therefore, in this study, in order to evaluate the vibration characteristics of CFRPs produced by the EDRM, an experimental modal analysis and finite element analysis（FEA） were performed on CFRP specimens with straight and curved reinforcing fibers. The specimens were also manufactured by the VaRTM method and their vibration damping characteristics were compared. It was confirmed from numerical and experimental results that natural frequencies and eigenmode shapes agree well with high accuracy, and the FEA is useful for the specimen manufactured by the EDRM. It is also found that CFRPs produced by the EDRM has greater modal damping ratios than CFRPs by the VaRTM.
In this study, damping properties of normal and damped CFRP laminated beams with 0 deg. and 90 deg. orientation angles were experimentally evaluated by using central oscillation method under 1 atm and vacuum conditions. It is observed that all the damped CFRP laminates had higher loss factors as compared to those without damping interlayer at their center interfaces. Comparisons of the results under 1 atm and vacuum conditions showed that structural damping by atmosphere had quite large affects on the measured loss factors, indicating that the precise measurements of loss factors should be conducted under the vacuum condition.
In production and life practice, composite laminated plate is playing a absolutely irreplaceable role, therefore, it is very important for the performance is good or bad, and the performance of composite laminated plate, of course is determined by its material and structure, in our rules on the dosage of specific material and size, the internal structure of the different is the laminated plates of mechanics performance of the most important cause for this difference. Laminated composite structure design need to select suitable constituent materials and arrangement of its internal structure, and by using the path of the change of composite layer, we can preparation of variable stiffness composite laminated plate, making it more buckling load, to meet our needs. In this article, we will explain laying fiber curve, the preparation process of composite laminated plate method. Using this method, in the laminated plate layer fiber after using the appropriate path, its internal stress and strain will also corresponding change, to make the composite board get better mechanical properties. We will use commercial software ABAQUS to modeling the process of the calculation, in laying path and in a straight line for the buckling of laminated plate after comparing, we can find that the curve path layer of variable stiffness of composite laminated plate buckling load, significantly higher than the stiffness of plate.
In the development the machine structure such as cars, we predict NVH(Noise, Vibration and Harshness) performance using CAE(Computer Aided Engineering）. This has resulted in that we can identify problems, realize early solutions for them and greatly shorten development period. However, in the market, the needs for reducing the frame weight has been increasing more and more due to CO2 emission regulation and energy saving, and vibration noise likely to occur on mechanical structure. Therefore, we need an analysis method to efficiently suggest countermeasure for ensuring NVH performance. We focus on Mutual Mean Compliance (MMC) as one of the methods to support understanding for vibration phenomena. MMC is a method that can specify the part to be modified by multiplying the transfer power and the transfer function in the whole system. MMC can propose effective structural change guidelines for the frequency of interest, but this method has a problem that there is a possibility of increasing the response of the adjacent peak due to the structural change with the focused frequency.
In this research, we developed a sensitivity calculation algorithm with a bandwidth in a frequency band containing two peaks. Then, we propose a structure change guideline that can reduce responses in the focused frequency band. When the threshold value was set high, it was confirmed that the response prediction was performed with high accuracy by using the proposed algorithm. However, when the threshold value was set low and the number of elements for changing the structure was increased, the accuracy deteriorated. That reason is to increase the amount of structural change. Since the sensitivity can be assumed to be linear when the amount of design change is small, it was concluded in this study that the analysis result and the response prediction match precisely within the linear range of sensitivity. We also concluded that the proposed algorithm can reduce the response in the bandwidth.
This study discusses validation of an identification method of material properties of a single layer CFRP thin plate. This identification method is a method to select material parameters to match the vibration characteristics of the experiment and the vibration characteristics of the analysis. In the method, the Ritz method calculates vibration modes and natural frequencies of thin CFRP plate using material parameters which are selected by differential evolution method (DE). Some simulation data are used to probe the validity of the identification method. This method was able to identify the orientation angle of CFRP plate and elastic coefficients. Identification of Poisson's ratio had a large error. In the case of experimental data, the method could not identify difference orientation angle of the plate correctly. This seems to be because the torsional mode of vibration has some errors in the experiment.
Damping materials are used everywhere to reduce the vibration level. On the vehicle, weight reduction and high damping effect is required to reduce environmental impact. Many studies have been conducted to find a topological optimal distribution with high damping effect with a small amount of damping material. However, many methods require finite element analysis many times due to eigenmode sensitivity. In addition, if there is a problem with the optimal shape, it is necessary to use a filter or change the penalty parameter and perform optimization again. This paper proposes a method to linearize the optimization problem, assuming that the distribution of damping material does not affect the eigenmode in order to reduce the number of finite element analysis. Several numerical examples are provided to show effectiveness of proposed method. As a result of verification, the optimal distribution and loss factor of proposed method and conventional method are almost the same for a large-scale finite element analysis model. Moreover, this paper shows that the assumption approximately holds by using the modal assurance criterion. As long as the assumption holds, by using the proposed method, a dramatic improvement in time efficiency when performing optimization with difference conditions many times can be expected.
Lightweight structure is required due to ecological considerations. However, the lightweight requirements conflict with noise and vibration (NV) performance. To satisfy both of lightweight solution and NV performance, vibration reduction based on periodic structures is of interest because the periodic structures have wave filtering characteristics which inhibit elastic wave propagation at the frequency ranges referred as band gaps.
This paper presents a vibration reduction method using the band gaps of periodic shell structures. The frequency of band gaps can be calculated by using reduced FEA model which is applied the Bloch’s theory. We can design shapes of unit cells using the calculated band gaps which relate to frequency range with vibration reduction. Frequency response of a finite periodic shell is carried out to demonstrate vibration reduction based on the band gaps. The results of analysis suggested that the band gaps of periodic shell restrain formation of natural vibration.
In recent years, audio products are increasing in demand with the development of music culture. Generally equivalent circuits have been used in the design and development of earphones and headphones. However, in the development and evaluation using the equivalent circuit, the expression of the vibration characteristics of the diaphragm is generally limited to one-degree-of-freedom system, and the influence of the so-called divided vibration of the diaphragm due to the higher order vibration modes, which may appear in the high frequency band, cannot be expressed. In this research, numerical results on natural vibration modes and frequency responses of a headphone diaphragm are presented. Results of actual diaphragm model are compared and discussed with those of simplified models.
The body of a railway vehicle can be regarded as a combination of thin plate structures. As a simple vibration analysis method that can handle elastic vibration of such a structure, vibration analysis method of thin anisotropic plate and arbitrary boundary conditions is proposed. In this report, the formulation based on the energy principle is performed, and vibration measurement is conducted with a structure simulating the underframe of a railway vehicle at 1/10 scale. Numerical calculation is carried out using a orthotropic plate as an analysis model. From the results of measured and numerical calculation, the validity of the proposed method was examined by comparing the mode shape and the natural frequency. It can be found that the proposed orthotropic plate model gives the natural frequencies closer to the measured result than the isotropic plate model.
This paper proposes a novel robotic arm for astronautical development by using honeycomb structure. Space robotic arm should possess lightweight, highrigidity, and compact. Honeycomb structure that is used mainly for large panels is one of such lightweight and highrigidity material. In this study, Honeycomb structure is introduced to realize compact and lightweight arm. To avoid the influence of adherence, the experimental specimens are integrally shaped by using 3D printer. Theoretical and experimental evaluation of the integrally shaped honeycomb arm is carried out. Comparison with SRMS (Canada arm), the partial superiority of the presented honeycomb arm is confirmed. Besides, the integral shaping using 3D printer is confirmed to be effective to avoid the influence of adherence.
The current seismic design codes of aboveground oil storage tanks (ASTs) are conducted based on the beam-type vibration with circumferential wave number m=1. The oval-type vibration with m≧2 in which shell plate vibrates in a petal shape due to local mass and stiffness, initial imperfection or nonlinear vibration occurs in ASTs. The initial stress due to hydrostatic pressure was reported to increase the natural frequency in high m range by several studies. The circumferential tensile stress on shell plates caused by hydrostatic pressure increases the stiffness and as a result the natural frequency is also increased. Wind girders are installed to the shell plates in ASTs for the prevention of buckling by wind pressure. The wind girder which is a ring stiffener increases the stiffness of the shell plate. In this paper, the natural frequency of the oval-type vibration in a large sized AST is analyzed and the effect of the wind girder on natural frequency is studied. The method is the free vibration analysis by axisymmetric finite element method considering coupled vibration of internal liquid and tank.
In this study, the elastic vibration characteristics of the square tubular structure simulated with about 1/10 size of the railway car body are investigated in detail. The influence of end restraints and mass distribution on the floor, which are likely to affect the structural change, was examined, and the plan of structural modification to reduce the elastic vibration of this structure was discussed. The results of experimental modal analysis suggest that the structure under study has a strong tendency to vibrate independently of the frame and the upper structure, and it is also confirmed that the deformation of the upper structure is large.
The self-excited vibrations of a pipe conveying fluid have been studied as a typical example of the unstable vibrations in continuous mechanical systems. When the flow velocity exceeds a certain value, a certain mode on the pipe vibration becomes unstable and the post flutter phenomena become a problem. When a lumped mass is attached at the lower end, Copeland and Moon clarified from the visual inspection in experiments that a clamped cantilevered pipe exhibits some kinds of non-planar complex motions. From their pioneering experimental study, it has been well known that a large end mass enriches the dynamics of pipe conveying fluid. In this study, we conduct the series of experiments of self-excited vibrations in cantilevered pipes that are hung vertically and have end masses. The experiments are conducted to capture the complex non-planar motions using the end mass and the flow velocity as the control parameters. We conduct the measurements of pipe displacements in three dimensional spaces by the image processing system. The image processing system enables us to conduct the non-contact measurements at 200 frames per second. From the quantitative measurements of pipe vibrations, we confirmed some kinds of pipe motions i.e. planar pipe vibration, non-planar rotational vibration, rotating planar vibration.
This paper investigates the unstable vibrations in an offshore floating wind turbine blade subjected to vertical wave excitation. The blade is modeled as a rigid bar connected to a horizontal, rotational shaft with a rotational spring, and inclines to only edgewise direction. The vertical motion of the rotational shaft is synchronized to a floater motion subjected to vertical wave excitation. The equation of motion of the blade includes parametric excitation terms which have the excitation frequency of the wave, Ω, and the rotational speed of the blade, ω. In the theoretical analysis for the linearized model, the regions where unstable vibrations occur, referred to as unstable regions, are theoretically determined and compared with the results of numerical simulations. The influence of the wave excitation and the rotational speed of the blade on the unstable regions are examined. The swept sine tests for the nonlinear model are conducted to calculate the frequency response curves with respect to the rotational speed of the blade and the excitation frequency of the wave. They confirm that the unstable vibrations occur within the regions where p=(Ω+nω)/2 (n=±1, ±2, ±3…, p is the natural frequency), is satisfied. They also demonstrate that resonances occur near Ω and ω where p=Ω+nω (n=0, ±1, ±2, ±3, ...) is satisfied.
This paper describes a method to reduce the propagation of bending waves by the occurrence of interference. In order to produce interference in the beam, it is necessary to reflect waves at two points on the beam. In this research, we proposed two methods to make reflection points: one method is to thicken a part of the beam, and the other method is to install a mass at each of two points on the beam. The governing equations were theoretically formulated using the modal analysis. The effectiveness of the proposed method was verified through simulations and experiments.
In this research, I confirmed the accuracy of vibration mode measurement of copper plate for application measurement of time-averaged pulse strobe digital holography interferometry. Laser displacement meter and time-averaged pulse strobe digital holographic interferometry were used to confirm the accuracy of the amplitude quantity. Time-averaged pulse strobe digital holography interferometry can record the maximum displacement of vibration and can visualize the displacement state by using a light chopper with a duty ratio of 50%. The test piece is fixed in a cantilevered manner, and the vibration mode is excited by direct vibration by the vibrator. The displacement of this method was compared with the displacement of the laser displacement meter to confirm the vibration measurement accuracy of this method. The vibration modes of the copper plate were measured from the first to fifth modes. As a result of comparing each measurement data, a difference of about 0.5 μm occurred at the maximum.
The railway current collection system consists of a line and a pantograph. We take up the problem of the contact loss between a rigid conductor line and a pantograph. In order to avoid the damage on the line surface by the electric ark, it is important to prevent the contact loss. From the series of experiments with an actual pantograph system, an essential model that regards the contact loss as impact oscillations between a rigid conductor line and a pantograph was proposed. This model consists of a spring supported mass and an external exciting source that is pushed against the mass. In this paper, in order to suppress the impact oscillations, we add an oscillatory system coupled to the spring-mass system. Then, we consider the impact oscillations between the excitation source and the main mass in the two -degrees-of-freedom system. We numerically investigate the problems and obtain the bifurcating motions. When the exciting frequency is near the second mode natural frequency in the two-degrees-of-freedom system, the impact oscillations between the main mass and the external excitation source is suppressed. We conducted a series of experiments in order to verify the theoretical results. The experimental results also reveal the suppression of the impact oscillations. The experimental results qualitatively well agreed with the theoretical predictions.
The purpose of this research is to investigate the bounce vibration behavior of a mirror inside a SLR camera using multiple regression analysis. Rebound vibration is measured using the two plates model, which is bonded by double-sided tape. This bonded mirror model consists of body part and mirror part. Although rebound amount changes due to the change of the body shape and the bonding position, it is not clear which mirror model is effective for suppressing the rebound amount. As a result of the multiple regression analysis, it was found that the amount of bounce was suppressed as the position of the center of gravity of the body part and the bonding position were brought closer to the stopper collision part.
This study deals with the suppression of the rebound vibration of the mirror inside the single-lens reflex camera. By changing the positional relationship of the two stoppers, it is possible to suppress the rebound of the mirror. In addition, there is an optimal stopper position that suppresses mirror rebound. It is suggested that changing the position of the stopper slows the speed at which the mirror rebound that the rebound is suppressed.
The occurrence of the low frequency vibration in vibroimpact systems such as vibrating sieve reduces the reliability of the system and precludes normal operation when its amplitude is excessive. For suppressing the low frequency vibration, this paper analytically investigates the effect of a dynamic absorber on vibration characteristics. The system investigated comprises two masses which can move only in the vertical direction under gravity. The lower mass is supported by a spring and subjected to a periodic exciting force, whereas the upper mass bounces freely on the lower mass. The effect of the parameters of a dynamic absorber mounted on the lower mass is examined, showing that there is an optimal set of values for the natural frequency and the damping ratio to prevent the low frequency vibration.
Disk grinder is a type of electric tool that rotates a disk-shaped grinding wheel with a motor to grind and cut the surface of a workpiece such as metal or wood. At this time, the worker is at risk of developing hand-arm vibration problems by receiving vibration on the hand-arm part. In this study, we aim to reduce the vibration from the viewpoint of engineering in order to reduce the risk of developing hand-arm vibration problems in the disk grinder. First, an experiment was conducted to investigate the cause of vibration of the disk grinder. As a result, it was found that the cause of vibration of the disk grinder is forced vibration by unbalance, vibration by motor characteristics, and self-exited vibration by friction generated between the disk and the work material at the time of contact. In particular, it was found that self-excited vibration due to friction had a large effect on hand-arm vibration. In this study, dynamic absorber was used to control the self-excited vibration due to the friction generated in the disk grinder. The vibration control effect was confirmed when a properly tuned dynamic absorber was attached to the disk grinder. Therefore, it was found that a dynamic absorber is effective for the reduction of vibration of the disk grinder.
In recent years, vibration durability of automobile parts become more and more important to meet weight reduction of automobile parts and complication of shape. In the vibration test, it is desirable to flexibly assemble the jig according to the shape of the part, however, this may reduce the natural frequencies. In this study, analytical and experimental result are presented on natural frequencies and their modes of box-shaped jigs made of resin for vibration test. The jig is an integral structure cut out from a resin material block. Two types of fix conditions were considered for this study. One is fixed only with bolts at the bottom, while the other is fixed with fastening parts proposed in this study to increase the natural frequencies. Analytical and experimental results on natural vibration modes of the jigs fixed under the two conditions are compared. Furthermore, the results are compared with experimental results of a jig model with the same shape composed of resin plates with bonding, witch show high rigidity of the proposed model.
This paper deals with the quenching problem of electromagnetic vibration of the motor stator in the wide frequency region around the natural frequency. Two vibration quenching methods were considered, namely, the method using two dynamic absorbers, and that using together three elements of imperfect mass, spring supports and Houde dampers. The iron stator of motor is modeled by circular ring, and vibration quenching devices are installed on the outside of iron stator to quench the forced vibration caused by the rotating distributed electromagnetic force. The solutions of forced vibration are obtained by the theoretical analysis, and those are compared with the solutions obtained by the finite element method and numerical integration. Following was made clear: (1) The vibration quenching effect is high when pair of dynamic absorbers is set to the places close to the distance between the loop and node of the quenching target mode. (2) When three elements of imperfect mass, spring supports and Houde damper are used, the vibration quenching effect is high, and in particular, its effect becomes higher when the distance between the two Houde dampers is close to that between the loop and node of the quenching target mode like the method using the pair of dynamic absorbers. (3) When quenching vibration using three elements, to obtain almost the same quenching effect as the pair of dynamic absorbers, the mass of the Houde dampers are needed about 10 times the mass of the dynamic absorbers. (4) The results obtained by the theoretical analysis using ring theory and those obtained by the finite element method and numerical integration agreed well each other in each vibration quenching method.
In recent year, the gear devices have been used in high speed rotation areas due to electrification of cars. It is assumed that the eigenvalues of the gear shafts affect the vibration of the gear system due to the high speed rotation of the gears. There have been many theoretical studies on the dynamic characteristics of gear pairs. However, there have been few research reports calculated bearing load fluctuation considering the shafts and bearings. Therefore, in this research, the vibration characteristics in the gear system including the shafts and bearings are clarified theoretically. The meshing of the gear pairs is expressed by a spring-mass system of a single degree of freedom system, tooth profile error, nonlinear tooth stiffness and tooth separation are taken into consideration. In addition, the gear shafts and bearings are modeled by an Euler-Bernoulli beam supported by the springs. First, the excitation force generated by the meshing of the gears is calculated. Next, the vibration of the gear shafts is calculated using the excitation force by obtained by meshing calculation of gear pair. Finally, the circumferential vibration of the gear pair, the dynamic deflection of the gear shaft, and the bearing load fluctuation are obtained.
By using piecewise sampled-data control with rotational vibration manipulation function, we try to control rotational inverted pendulum at inverted equilibrium point. In the case of control by operating time (Δt = 0.1τ) derived from previous research, we found the angular velocity of the arm increases and the centrifugal force components interfered with control. Moreover, the inverted angle has error from the inverted equilibrium point. For improvement, when setting some defiation to the target angle, the inverted angle approaches to π, and the angular velocity of the arm was decreased during the inverted control. We found that we can control the rotational inverted pendulum by setting the deviation angle appropriately in this method.
Vibration manipulation function as finite time settling function was used to design trajectories of the trolley of 2-dimensional overhead-travelling crane around an obstacle under piecewise feedforward control or piecewise sampled-data control. In this study, square-like or regular-octagon-like round path was planned to suppress vibration of the suspended load and to avoid collision to the obstacle. Two stage operations were performed to change the velocity of the trolley with operational angle α. In case the velocity change of the trolley, i.e. α, was small, piecewise feedforward control was succeeded along the designed routes. However, when the velocity change of the trolley was larger, we couldn’t suppress the vibration of the load, because of the nonlinearity of the pendulum. Regular-octagon-like path was better to control the crane, since velocity changing was small. When the crane was moved under the piecewise sampled-data control, the trajectory of load became more robust. However, the paths of the trolley itself were deformed. By limiting the acceleration small, open-loop control can be well performed in the 2-dimensional overhead-travelling crane.
The efficient transportation by overhead cranes needs fast and accurate positioning, but residual vibration which prevents positioning accuracy generally tends to be induced by fast transportation. In previous paper, we proposed a control method which is based on the characteristic the residual vibration is completely suppressed in a linear undamped system when excited by an external force which does not contain the natural frequency component of the system. To apply this characteristic to nonlinear damped systems, we defined the apparent external force which includes the influence of system nonlinearity and damping. It was confirmed that the residual vibration is suppressed by eliminating natural frequency component from the apparent external force when the rope length is constant. However, if the height of the cargo is different before and after the transportation, it is needed to consider the rope length variation. Therefore, this paper modifies the apparent external force to include the influence of the rope length variation as well as nonlinearity and damping. Numerical simulations demonstrate that this method can suppress the residual vibration when the rope length varies in time. Furthermore, optimization is applied to not only the trolley trajectory but also the rope length variation, and consequently decrease the maximum swing angle of the cargo during transportation.
This paper presents a proposal for a robust feedforward control technique for a rotary crane to suppress residual vibrations in point-to-point (PTP) motion. In the proposed method, the trajectory profile of the PTP motion is generated through a cycloidal function whose input is the output of Gaussian functions. The obtained trajectory is dependent upon the coefficients of the Gaussian functions. To achieve the suppression of the residual vibrations even if the load position of the rotary crane varies, the coefficients are tuned by metaheuristic algorithms. By driving the boom of the rotary crane along the obtained optimal trajectory, the antisway motion can be realized after the PTP motion. The simulation and experimental results are compared with those of the previous study, revealing the effectiveness of the proposed method.
Passive dynamic walking is a gait on a shallow slope without active control. The walking cycle is generated by the dynamics and action of gravity only. A natural motion like a human walking and high efficiency are its merits. Passive dynamic walking is considered as a kind of self-excited vibration in which continuous motion governed by a nonlinear equation of motion and impact motion at switching of legs are repeated alternately. Many kinds of nonlinear phenomena are observed in this walk. In this paper, we propose an analytical model of a straight-lagged biped passive walker considering the motion of upper body. Also, the steady state solution is investigated numerically. Furthermore, comparing with double inverted pendulum, the effect of the springs and dampers at the ankle and the hip on the stability of walking is studied.
Expanding degrees of freedom in vibration systems is an effective way to improve the power generation efficiency of energy-harvesting devices from the vibrating source, since the system becomes responsive for a wide frequency range due to the appearance of multiple resonant peaks. A magnetostrictive-type vibration energy harvester that uses an iron-gallium alloy (Galfenol) has received much attention in recent years. Deformation of the cantilever yields a flux change due to tensile or compression stress, and the flux variation leads to the generation of voltage on the wound coils. This energy harvesting technology has advantages over conventional types with respect to the compactness and efficiency, and it is extremely robust and has low electrical impedance. In this study, the differential evolution (DE), known as a kind of global optimization techniques, was introduced for the parameter design of the harvester that comprised a folded beam structure with a concentrated mass at the beam end. Using DE, we numerically explored the best combination of the folded beam dimension that minimized the bandwidth between the first and second natural frequency of the harvester. The proposed design has led the device more responsive to the narrowband disturbances.
In recent mechanical systems, vibration problems have become obvious as the size and working speed of the equipment becomes smaller and faster. Much attention has been paid to develop vibration control devices, e.g., the vibration isolators and absorbers. The size of the absorbers is expected to be smaller in view of space saving and weight reduction. However, constitutive physical characteristics limit realization of the compact design without sacrificing the required damping performance. Specifically, it is difficult to attenuate low-frequency vibration by a miniaturized vibration control device. In the present study, we propose a novel active-type mass damper for vibration control of structures. By using a relatively small, a high frequency driven actuator to drive the mass with an amplitude-modulated control signal, the low frequency damping force can be demodulated. Mathematical formulation of the driving principle, both numerical and experimental verification of the low-frequency acceleration component to be used for the inertial control force are shown.
Sliding surface in mechanical system is required to move smoothly and stop. Sliding surface can move and stop by giving adequate friction force. Friction force is controlled by developing technology creating small texture on the surface with a few micrometer to a few hundred micrometer interval. If friction force is reduced by applying the technology to large area of sliding surface of airplane, generator and machine tool so on, machining effect is rapidly improved. It is necessary to develop machining technology to create texture with high precision and efficiency. On the other hand, ultrasonic vibration is used in many manufacturing fields. It is well known that surface roughness is improved and reduce stress using ultrasonic vibration. In this study, machining technology creating wear resistant texture on large area sliding surface with high precision and efficiency using ultrasonic vibration during knurling is developed. In this paper, effect of ultrasonic vibration is examined by the fundamental experiment. A horn to amplify ultrasonic vibration is designed and made. Frequency of ultrasonic vibration is measured and it is found that desired frequency is available. In the experiment making a groove on the surface with indenter using 2 dimensional table, pressing force and friction force are measured. Pressing force and friction force are reduced using ultrasonic vibration.
When self-synchronization occurs in a system where multiple nonlinear self-excited oscillators with different natural frequencies are coupled, all oscillators vibrate at one specific frequency due to their interaction. While many researchers have examined characteristics of this phenomenon, the mechanism has not been completely clarified. In order to obtain new comprehensions into the occurrence mechanism, this paper considers a system consisting of two DC motors, and analyzes the energy condition necessary for synchronization, for the two cases of co-rotation and counter-rotation. It is seen that the derived condition is able to predict the range of synchronized frequency and the applied voltage where synchronization occurs.
This research concerns high efficiency propulsion method of multi-articulated robot by decentralized control using local feedback control. Recently, various robots which are useful when disasters happened have been studied. At the time of disaster, these robots need to promote with high efficiency. To answer this demand, the propulsion method using resonance was proposed. On the other hand, natural frequencies of propulsion robot are varying in synchronization with the change of external environment. In this paper, the control method of propulsion robot which drives at the resonance point automatically is proposed. Especially, investigation of the proposed method for large degree of freedom robot is done. Firstly, vibration propulsion mechanism is introduced. This device promotes using the difference of friction coefficient between moving forward and moving backward. It is easy to measure natural frequencies of the device without the difference of friction coefficient. Secondly, the design method controller of decentralized control is shown. The proposed decentralized control uses the local feedback control. The driving method using local feedback control can oscillate natural vibration of vibration propulsion mechanism by self-excited vibration. The decentralized control realizes the synchronization of the actuators through natural vibration mode by the force entrainment of the self-excited oscillator. The propulsion experiment by centralized control and decentralized control is examined to evaluate propulsion efficiency. As the result, the propulsion method by decentralized control is high efficiency as compared with the method by centralized control.
This paper theoretically investigates localization phenomena using the modal analysis in a nonlinear array with N pendula connected by weak, linear springs when the array is subjected to horizontal harmonic excitation. In the theoretical analysis, the equations of motion for the system are derived in the two different ways, i.e., by using the physical coordinates and the modal coordinates. The equations of motion expressed in a form of the modal coordinates, i.e., a set of the modal equations of motion, form an autoparametric system because only the first mode is directly excited by the external force and the other modes are not directly excited by the external force but are nonlinearly coupled with the first mode. Van der Pol’s method is employed to obtain the solutions of the harmonic oscillations. In the numerical calculations, the frequency response curves of the amplitudes and phase angles in the cases of N=2 and 3 are presented. It is found that localization phenomena can be observed in the physical coordinate system when multiple modes simultaneously appear. The charts of the displacement vectors of the harmonic oscillations are also presented and explain that the localization phenomena are observed as the results of superposing the multiple modes excited by the autoparametric effect.
In the construction site, an electric hammer, a type of hand held vibrating tool, is used to crush concrete, asphalt and so on. The frequent user of this tool is at high risk for developing the hand-arm vibration syndrome because of excessive exposure to hand-arm vibrations. In order to prevent the disease, it is required to keep the vibration of the tool’s gripes as low as possible. The purpose of the present study is the development of a very low-vibrational electric hammer using self-synchronization phenomena in order to address the problem of the hand-arm vibration syndrome. In previous research, we developed a prototype with synchronous vibration generating mechanism for electric hammer, and performed performance evaluation by sand compaction test. As a result, we succeeded in generating a motion state for the purpose of simultaneously achieving excitation of the striking part and vibration suppression of the holding part. However, there were problems such as lack of impact forces and that the target exercise state did not occur depending on the condition. Therefore, in this study, we tried to change system parameters and DC motor for the purpose of improvement of crushing capacity and stable operation.
The aim of this study is to investigate the possibility of vibration suppression of multiple modes for a system with a piecewise linear type dynamic absorber without dampers and to consider the vibration suppression mechanism. The effects of parameters of the piecewise linear type dynamic absorber on vibration suppression are investigated using numerical analysis. The results show that the piecewise linear type dynamic absorber with particular parameters suppresses multiple modes vibration. The time series data of the frequency being suppressed shows intermittent chaotic vibration. In addition, when the apparent stiffness and the apparent damping coefficient were calculated from the relative displacement and the internal force between the main system and the piecewise linear type dynamic absorber, focusing on the exciting frequency component, it was found that the apparent characteristics were close to the optimal design values for each mode.
Torsional vibration is noticeable in engines with a reduced number of cylinders for the purpose of reducing automobile exhaust gas. To suppress the torsional vibration, centrifugal pendulum vibration absorbers (CPVA) have been used in the engine. Many non-linear analyses of CPVA used point mass model, and there are few analyses of CPVA used rigid body model. In this research, numerical simulation of tuned rigid body CPVA has performed. The influence of the moment of inertia on the damping effect of the torsional vibration was verified. Moreover it indicated sufficient damping effect may not be obtained depending on the value of the moment of inertia.
The authors proposed a damping device called switched mass damper．In the switched mass damper，a light mass ma is attached to the mass m of the primary system through a spring and a dashpot，and another mass mb is connected to or disconnected from the light mass ma using a friction clutch depending on the displacement of the light mass ma. In the previous reports，the authors showed that the switched mass damper has good damping performance for the mass switching pattern in which mb is disconnected when the displacement of ma becomes smaller than a given threshold and mb is connected when the displacement of ma becomes larger than the threshold. With further investigation, it has been found that reversing the mass switching pattern has possibility to increase the damping performance. In this report, first, damping performance for the reversed mass switching pattern is studied in detail through numerical simulation by examining the effect of each parameter of the switched mass damper on damping performance. Then, the result is confirmed by experiment.
This study aims at developing a design method of a fractional-order PD controller and clarifying merits of the fractional-order PD controller. A fractional-order PD controller contains the non-integer differential order as a design parameter in addition to the proportional gain and the derivative gain. Therefore, the fractional-order PD controller can satisfy one more design specification than a normal integer-order PD controller can. In this report, besides the requirements on the gain crossover frequency and the phase margin, the condition on robustness is added. Based on those relationships, the proportional gain, the derivative gain and the non-integer differential order of the fractional-order PD controller are obtained with a graph-aided design method. Finally, the proposed design procedure of the fractional-order PD controller is applied to a vibration suppression problem of a flexible cantilever beam. Comparing with a usual PD controller, some control effects of the fractional-order PD controller are investigated by numerical simulation. Especially, the characteristics of the proportional gain, the derivative gain and the non-integer differential order of the fractionalorder PD controller are obtained as the gain crossover frequency is varied. It is confirmed that the fractional-order PD controller can be designed in the gain crossover frequency range where the normal PD controller can not satisfy the design specifications.
In this paper, an approximate solution of the optimal parameters by H∞ optimization of the viscoelastic dynamic vibration absorber (DVA) attached to a damped primary system is proposed. The viscoelastic DVA is described by the fractional differential Voigt model. The approximate solution is derived combining a method in which the viscoelastic DVA is regarded as a equivalent viscous DVA and the fixed point theory for a damped system. The effectiveness of the present method is demonstrated by comparing the approximate solution with the numerical results. Finally, the damping performance of the viscoelastic DVA is evaluated using approximate solution. And it is shown that the damping performance is slightly improved compared to the conventional viscous DVA if the optimum parameters are given.
This paper deals with the vibration quenching problem of the single-degree-of-freedom system with a limited power supply using a Hula-Hoop and displacement magnification mechanism. This system is forced by the centrifugal force of rotating unbalance. If the unbalance is small, the amplitude of vibration becomes small and Hula-Hoop does not rotate. Therefore, two types of displacement magnification mechanisms are adopted, namely the mechanism using cantilever and that using beams with fixed ends that move. The quenching effects and the compactness of the mechanisms are studied. Following was made clear by the numerical integration of the equation of motion and the experiment: (1) Main system is quenched well by enlarging the displacement at the rotational center of Hula-Hoop using each type of displacement magnification mechanism. (2) The magnification of displacement is larger in using cantilever than in using beams with fixed ends that move. (3) The frequency range suitable for vibration quenching is wider in using beams with fixed ends that move than in using cantilever. (4) The optimal vibration quenching condition is obtained for Hula-Hoop and displacement magnification mechanism. (5) The characteristics of the solutions obtained by the numerical integration method coincide qualitatively with those of the results obtained by the experiment.
Recently, we have proposed an active vibration control system by using synchronization properties of non-linear oscillators. In this system, a single oscillator has the role as amplifier that emphasizes the vibration response of target structures. However, to generate various vibration patterns for the structures’ multiple vibration mode, using networks consisting of a number of oscillators is effective. Therefore, in this paper discusses a network structure generating multiple vibration patterns.
A rational dimension reduction method based on a new type of complex modal analysis is developed in order to accurately analyze nonlinear vibrations generated in large-scale structures with local strong nonlinearity, global weak nonlinearity and non-proportional damping at low computation cost. In the proposed method, first, the state variables of weakly nonlinear nodes are transformed into modal coordinates using complex constrained modes obtained by fixing strongly nonlinear nodes. Next, a reduced model is derived by selecting a small number of modal coordinates that have a significant effect on the computational accuracy of the solution, and coupling them with the state variables of strongly nonlinear nodes expressed in physical coordinates. In that process, the remaining modal coordinates that have little effect on the computational accuracy are appropriately approximated and integrated into the equations of motion for strongly nonlinear nodes as correction terms. Furthermore, in order to improve computational efficiency, the global weakly nonlinear forces are directly computed from modal coordinates. It was confirmed that periodic solutions and their stability can be computed from the reduced model constructed by these procedures with a very high computational accuracy and at a high computational speed.
In this paper, PFT-HYS (Hysteresis system using the restoring force model of power function type) method is applied to the nonlinear vibration analysis of the seismic isolation laminated rubber and seismic response was analyzed using a model of high-rise structure with the isolation rubber. Also, the modified bilinear method which is used widely is applied and compared with the analysis results of PFT-HYS method. In this result, it was found that PFT-HYS method can express the response of the structure. Moreover, based on the response analysis results of the PFT-HYS method, the hysteresis restoration force characteristics of the isolation rubber to minimize the response of the isolation structure were optimized. As a result, it was found that the optimal hysteresis force characteristics are different in the optimization result which minimizes the response displacement of the seismic isolation layer and the optimization result which minimizes the response acceleration of the top floor.
This research deals with analytical results on nonlinear forced vibrations of a thin shell-panel including clamped edges．At the boundaries of two opposite edges, the shell-panel is simply supported, and at the other two edges the panel is simply supports or clamped．Coordinate function of deflection is assumed with the product of power series and trigonometric function．Neglecting the effect of in-plane inertia force, the Donnell type equations are applied as the governing equations of the shell-panel．Stress function is introduced to satisfy compatibility equation and in-plane boundary condition ,Applying the Galerkin procedure, equation of motion is reduced to a set of nonlinear ordinary differential equations．Nonlinear periodic responses of thin shell-panel with various curvatures including clamped edges are analyzed using the above calculation method under periodic excitation force with the harmonic balance method．
Vibration suppressors are used to resolve the problem of collisions and entanglement to the hoistway equipment caused by the rope sway due to the resonance of the building and the elevator rope. Vibration suppressors have the effect of changing the natural frequency of the elevator rope and prevent resonance. In this paper, theoretical solution to the free vibration of the rope is obtained, in the case where two vibration suppressors are located at βL and (1-β)L, where L is rope length, β is an arbitrary value. Two types of initial rope displacement are considered: trapezoid-like displacement and triangle wave-like displacement. Obtained natural frequencies are 1/(1-β) times and 2/(1+β/3) times of the original natural frequency respectively. Further, finite difference analysis of the rope vibration with vibration suppressors is also performed to obtain the frequency response curves. Resonance frequencies obtained by the finite difference analyses are in good agreement with the natural frequencies for the free vibration. Vibration modes obtained by the finite difference analyses are similar to that for the free vibration.
In this study, we aim at obtaining the grinding conditions that suppresses chatter vibration without lowering machining efficiency. Although we focused on only on the degrees of freedom in the horizontal direction and the vertical direction up to now, this time we have derived a new analytical model and implemented it, with a viewpoint on the degree of freedom of rotation direction. By conducting eigenvalue analysis on the analysis model, it is verified whether generation of self-excited chatter vibration can be suppressed or not. The studies have shown that the new model can display the dynamic instability. The cause of dynamic instability is the asymmetry of the stiffness matrix, which physically is due to connectivity between horizontal motion mode and rotational motion mode.