Gas bearing is a mechanical element using gas as a lubricant, it has high rotational accuracy and low friction. However, gas bearing has a fault of small load capacity. If this bearing overcome it, practical range of this bearing will more spread. In this study, deal with gas bearing it made notches ―to improve bearing performance― at the rotor in the bearing. With this bearing structure, when internal force acts on the bearing surface opposite another one with notches, it is expected this bearing can obtain greater load capacity from the asymmetry of the bearing surface. On the other hand, stability and dynamic performance of the rotor and the gas bearing system are still unclear. In this study, dynamic characteristics of this bearing was calculated from analysis using perturbation method, and evaluated rotor stability using these. As a result, notches caused the diagonal term component of the equation of motion of the rotor to decrease, and these made the rotor unstable on the analysis. Further, as another analysis approach, we used non-linear orbit method to judge validity. As a result, both results were different. As one of the causes, it is considered that each is a linear, nonlinear method. Also, from the result of non-linear orbit method, it turned out that rotor orbit showed different aspects depending on conditions of notch size and rotation speed.
The hydrostatic gas bearing can achieve high accuracy and high rotation speed. However, the load capacity of the hydrostatic gas bearing is generally much smaller than that of mechanical rolling contact bearings. Therefore, if the static imbalance of the rotor is large, the rotor easily vibrates although the rotating speed is low. This is serious problem because contact between the rotor and the bearing may cause fatal damage to them. In order to solve this problem, the hydrostatic gas bearing with asymmetrically arranged gas supply holes has been proposed and developed. By this bearing mechanism, the load capacity increased, and the unbalanced rotor was operated at higher rotation frequency than supported by conventional bearing. Also the rotation frequency could be increased by increasing the gas supply pressure. That was demonstrated by numerical calculations and experiments. From this result, we thought that this bearing can theoretically reduce rotor vibration during rotation frequency modulation by controlled gas supply pressure. That was verified by the rotation experiment. As the result, the proposed bearing is possible to safely rotate the unbalance rotor during rotation frequency modulation. Also, this bearing were able to reduce rotor vibration at higher and wider rotation frequency range by arranged more gas supply hole to loaded side of the unbalance rotor. From above process, the effectiveness of this bearing mechanism was demonstrated.
Hydrostatic gas journal bearings can contactlessly support rotors by gas pressure. They provide advantages such as high precision rotation, high speed rotation and low friction loss. However, the load capacity of gas bearings is very small in comparison with rolling contact bearings, so they have been mainly applied to small size rotating machinery. In order to support heavier rotors and unbalanced rotors, we have developed an asymmetric gas supply system for the bearings. The system is supplied different gas pressure to the bearing surface from multiple supply holes in accordance with rotational state of the rotor. A test rig was fabricated by authors and a rotating test was carried out to verify the advantageous. The advantageous. The gas pressure was supplied by using servo valves. The control program was made using Matlab/Simlink software. The test bearing has diameter of 60 mm and the length of 120 mm. The results of the numerical simulation using non-linear orbit method was compared with the test results. Each approaches showed that the asymmetric gas supply system can be reduced the rotor vibration compared with the conventional symmetric gas supply system.
Since research on high-speed and high-precise positioning control using a servo system using magnetic levitation technology has been carried out in the past, it is expected that position control of a rotational shaft with high precision is also expected in an active magnetic bearing(AMB), which is an application of magnetic levitation technology. In recent study, one of the application is the analysis of rotor dynamics in arbitrary orbits is considered. Therefore, it is necessary to design a control system that can track with high precision. In this paper, an arbitrary whirling orbit control system of AMB is proposed. In order to demonstrate the effectiveness of the proposed control system, tracking control experiments are carried out on the positions of the rotor axes of circular and elliptical orbits.
Liquid annular seals with axially partial helical grooves were proposed to improve the efficiency and stability margin of pumps. Numerical analysis was carried out to investigate the effects of the axial length of the helical groove, gla , which is measured from the seal inlet, upon the static characteristics (leakage flow rate) and dynamic characteristics (dynamic fluid forces, dynamic coefficients, and whirl frequency ratio). The leakage flow rate Q for the partially helically grooved seals was lower than that of the conventional through helically grooved seal. Under a lower range of rotor spinning velocities N, Q decreases with gla. On the other hand, under a higher range of N, the quantitative difference in Q due to gla becomes small as compared with that under a lower range because the reduction in Q due to the pumping effect becomes more pronounced for a larger gla. For a small concentric whirling motion of the rotor, the radial dynamic fluid force suppressing the rotor whirling amplitude for the partially helically grooved seals was larger than that for the through helically grooved seal, and increased with decreasing gla. The tangential dynamic fluid force suppressing the rotor whirling motion for the partially helically grooved seals was larger than that for the through helically grooved seal. The magnitude of variation in the tangential dynamic force with the whirling angular velocity for the partially helically grooved seals was larger than that for the through helically grooved seal, and increased with decreasing gla. As a result, the partially helically grooved seals yielded larger main stiffness coefficient Km and damping coefficient Cm than the through helically grooved seal, and these coefficients increased with decreasing gla. The partially helically grooved seals also provided lower values of the cross-coupled stiffness coefficient Kc and the whirl-frequency ratio WFR defined as Kc /(Cmω), where ω is the angular velocity of the rotor spinning, than the through helically grooved seal under a lower range of N. The maximum value of N under which Kc and WFR for the partially helically grooved seals become lower than those for the through helically grooved seal increased with gla.
It is important to accurately estimate the fluid forces acting on the seal in the rotating machine and to predict the dynamic behavior of the rotor. In this paper, the fluid forces in the annular plane seal is numerically calculated by using finite-difference methods based on Navier-Stokes equations averaged in the radial direction. Then, the fluid structure interaction analysis (FSI analysis) is carried out in consideration of interaction between fluid forces and shaft vibration. In this FSI analysis, it is not necessary to assume the whirling orbit of rotor. Therefore it is possible to analyze the cases with even static eccentricity or elliptic orbit, and the behavior of the system in a wider operating condition can be predicted.
In rotating machinery, the rotor often whirls around static eccentricity position. The dynamic characteristics of seal has strong nonlinearity, and it effects on the case with the influence of static eccentricity. However, there are not so many studies that have investigated the dynamic characteristics considering the influence of large static eccentricity. This paper describes a method for the analysis of dynamic characteristic of annular plain seal in case of circular whirl with relatively large amplitude and static eccentricity using bulk-flow model. By considering of higher order components and coupled components when performing perturbation expansion, nonlinear components are analyzed. As a result, order asynchronous component of the rotordynamic fluid force are observed and explained.
Recently there is a great demand for reduction in size and weight of industrial motors. Therefore sometimes the motor casing has lower stiffness than conventional model and this stiffness becomes equal to the bearing stiffness. In this case, we need to consider support structure stiffness when we calculate the shaft vibration of the motor. In this paper, modeling the casing as dynamic stiffness, a vibration response prediction method was applied to the finite element method of rotating dynamics model. We also analyzed the effect of coupling stiffness between bearings and evaluated calculation error.
In order to improve CVT (Continuous Variable Transmission) used for automobiles, the breakdown test is assigned. When it was tested under conditions of a high-speed rotation and high load of transmitted torque at the examination, the torsional vibration problem in the input-output shaft system is generated and the examination can’t be continued. This paper considered the cause of this 198Hz-vibration problem the countermeasure. As a result, we got the following knowledge: (1) According to experiment including a variety of operation of testing machine, we found out that the limitation beyond stable zone depend upon the rotational speed and transmitted torque. (2) The analytical approaches gave two results: one understood that the onset of this unstable self-excited vibration stable condition is caused by the negative damping property of CVT belt frictional force and the other that the most severe vibration which should stop our machine is generated by the parametric excitation. The mechanism of this parametric excitation was made clear that it happens at very narrow condition of a certain frequency relationship, i.e., the deference between two natural frequencies of input and output shaft equals to the output shat speed. (3) For the troubleshooting, our solution is to install dynamic mass damper which is featured by setting the natural frequency of the damper being agreed with the natural frequency of the input shaft. Finally, I achieved stabilization of the self-excitation vibration.
When operating actual pumps, we need to check the stability limit. This paper suggests the reduction method of rotor system to 2 DOF, and simplified method for prediction of the stability limit. First, we set up the rotor shape, and stiffness and damping at journal bearings and annular seal. Then we check unstable mode by complex eigenvalue analysis with strict model (1D-FEM) and 2 DOF model, and prove 2 DOF model is enough for stability analysis. Next, we define λΩ for presenting cross stiffness of oil film dynamic property offered by Bently-Muszynska into 2 DOF model. 2 DOF model consists of whirl (rigid rotor) mode and whip (shaft bending) mode. Using the reduced model, we analyze the stability problem focusing on stability limit states. As a result, we found that the stability limit is equal to intersection of λΩ line and curve of undamped natural frequency ω1.
Although, in designing blades, it is assumed that all blades on a disk are identical (tuned system), the vibration characteristics of the blade is slightly different due to the manufacturing tolerance, the deviation of the material property, and so on (mistuned system). As a result, in the forced response of an actual bladed disk caused by the flow distortion, the responses of all blades become different, and the response of a certain blade may become extremely large, due to the split of the duplicated natural frequencies, the distortion of the vibration modes, and so on. On the other hand, it is suggested by many researchers that the mistuning suppresses the blade flutter, because the complete travelling wave mode is not formed in a disk. In other words, the effect of the mistuning acts on the dangerous side for the forced vibration, while on the safety side for the blade flutter. In this study, the stability analysis and the frequency response analysis of mistuned bladed disks are carried out using the reduced model with high fidelity, in order to research the vibration characteristics of typical mistuned bladed disks. Based on the analysis results, an optimal design procedure of mistuned bladed disks considering both of the forced response and the self-excited vibration is proposed.
Selected from various eigenmodes of blading, nodal diameter k= 0 and k= 1 are both related to shaft torsional and/or axial vibration and shaft bending vibrations respectively. In order to avoid the possibility of 2f (f=power system frequency) from torsional vibration resonance, ISO regulates the final calculation results considering the combination between k= 0 blade and torsional shaft vibration. Previous study has reported a global method for blade-shaft torsional coupled vibration analysis governing both k= 0 and k= 1 in a systematic manner, and torsional coupled vibration analysis was completed. However, it is also known that coupling of blade-shaft axial vibration also influences the resonance of blade-shaft system, and it is highly requested to estimate resonance frequency accurately. Thus, A method for blade-shaft coupled vibration analysis in consideration of axial vibration coupling is proposed and its feasibility is investigated. A scale model of steam turbine is targeted as an example and calculated resonance frequencies are compared with experimental data and FEM data. As a result, the new method in consideration of axial vibration coupling is feasible tool to calculate resonance frequencies more precisely than previous method. In addition, it is demonstrated that previous method is still effective when axial vibration is constraint
A vane used in a low pressure end of steam turbine is usually fixed to an inner shroud and an outer ring by welding both ends. In such a vane structure, the damping in loading operation is comprised of the material damping and the aerodynamic damping, because the structural damping is very small. In addition, steam turbine vanes are sometimes manufactured in a half-ring structure, where all vanes in an upper half and a lower half are connected by the shroud. In such a half-ring structure, the vane exhibits closely spaced natural frequencies of Toop (Tangential out-of-phase) modes, in which each vane in a half-ring vibrates like a fixed-fixed beam in a different phase. In such a steam turbine vane, the forced vibration and the self-excited vibration of Toop modes may become a serious issue. Therefore, in the design of the steam turbine vane, it becomes indispensable to evaluate the resonant response and the stability of Toop modes under the high loading condition. In this study, first, the vibration characteristics of steam turbine vane with a half-ring structure are studied by use of the results of FE analysis. Second, the reduced order model (the equivalent spring-mass model) of a half-ring structure is assembled, based on the results of FE analysis. Finally, the frequency response and random response analysis of the mistuned system of a half-ring structure is carried out by the modal analysis method. From these results, the vibration response characteristics of steam turbine vanes with a half-ring structure are clarified.
This paper describes vibration characteristics of a cantilevered flexible sheet subjected to a periodic gust. In an experiment, active plates are set at the upstream part of a wind-tunnel and generate the periodic gust. Moreover, a theoretical model to calculate a gust response using the Doublet-point method based on the unsteady lifting surface theory is developed. The frequency response of the sheet is examined with changing the frequency of the gust and flow velocity. Finally, the results of simulated transfer functions of the gust induced by active plates to the sheet are presented in comparison to the experimental data derived by the wind-tunnel experiment.
This paper presents an experimental study on flutter of a sheet under the influence of nearby structures. In the experiment, a flat plate (baffle plate) and a circular cylinder are used as the nearby structures. The sheet is supported at the leading edge and subjected to axial fluid flow and set near the structures (baffle plate and circular cylinder). In the experiment, we measured flutter velocity and corresponding frequency with gradually increasing the flow velocity of air. Then, we examined the influence of four experimental parameters related to the position of nearby structures (offset, gap width, plate thickness and circular cylinder diameter) on flutter characteristics. Moreover, influence of flow turbulence caused by these structures on flutter characteristics is discussed by flow visualization utilized smoking-wire
This paper presents experiments and an analysis on the self-excited vibration of a plate supported by air pressure. The unsteady fluid force acting on the plate is calculated based on the basic equation of two dimensional gap flow between the plate and a chamber surface. The effect of air compressibility in the chamber is taken into consideration in the basic equation. The system's characteristic equation is derived from the plate motion coupled with the unsteady fluid force acting on the plate. The influence of slit width and chamber volume on the unstable condition of the self-excited vibration is clarified comparing the analytical result with experiments. Lastly, the local work done by the unsteady fluid force acting on the plate (bottom surface) is shown, and the influence of slit width on the unsteady fluid force is discussed.
This paper presents a three dimensional flutter analysis and experiments of slender webs under tension in cross flow. In the flutter analysis, Doublet-point method based on the unsteady lifting surface theory is used to calculate unsteady fluid force acting on the web surface. The equation of motion of the web under tension is derived by using the finite element method. Flutter velocity, frequency and mode are predicted through the root locus of the flutter determinant of the system with changing flow velocity. The theoretical results are compared to experimental results to confirm validity. Moreover, the local work done by the fluid force acting on the web surface is calculated. Lastly, unified empirical equation of flutter velocities for several parameters of webs is proposed.
This study reports about the numerical simulation of the sheet flutter considering geometrical nonlinearity and wake shedding from trailing-edge. Recently, some studies of the energy harvesters using the flutter phenomenon were proposed. Previous researches employed some numerical models which are given by two dimensional flow or slender body approximation to evaluate this energy harvester. These models have a limitation in application range of the aspect ratio. We employ the three dimensional flutter model which is modeled by the finite element method with Absolute Nodal Coordinate Formulation: ANCF and Unsteady Vortex Lattice Method: UVLM. The equation of motion for flexible sheet has the Kelvin–Voigt-type material damping. The wake is shed to satisfy the unsteady Kutta’s condition at trailing-edge. At first, our numerical model under the uniform flow was compared with the previous work to verify the reproducibility of the experimental results. Using the validated simulation model, we investigated the relationship between the material damping and behavior of flutter. We clarified that material damping affect the flutter behavior and the efficiency of energy harvest due to flutter.
The stability of a flexible cantilevered plate subjected to parallel flow is investigated. As the flexible flat plates, the papers in a high speed printing machine, the thin plastic and metal films, the fluttering flag and the oscillating doom roof are enumerated. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The coupled equation of motion of a flexible cantilevered plate is derived into consideration with the added mass, added damping and added stiffness respectively. The complex eigenvalue analysis is performed for the stability analysis. In order to consider the accuracy of dynamic stability analysis, stability analysis method using unsteady oscillating wing theory are performed. This method replaces the vibration of the flexible flat plate with the circulation. When that flat plate vibrates unsteadily, the circulation is discharged from the trailing edge. In addition, This method fulfills Kutta condition that the flow velocity must be finite at the trailing edge of the flat plate. By comparing this method with two kinds of methods based on noncirculatory aerodynamics theory and circulatory aerodynamics theory which were previously examined by Fujita and Matsumoto, the validity and superiority or inferiority of the solution is investigated. The solution of oscillating wing theory and circulatory aerodynamics theory are comparatively well matched regardless of the mass ratio. The solution of noncirculatory aerodynamics theory are different from those solutions.
The dynamic stability of rectangular flexible plate often becomes a problem. As the flexible plate, the papers in a high speed printing machine, the thin plastic and metal films, the fluttering flag and the oscillating doom roof are enumerated. By two dimensional analysis, there is a limit in application range of the aspect ratio. In this paper, the dynamic stability of rectangular flexible plate is estimated in three dimensional model. The fluid is assumed to be treated as an ideal fluid in a subsonic domain, and the fluid pressure is calculated using the velocity potential theory. The unsteady fluid pressure is determined by using the the integral equations for the pressure along the span and the pressure along the chord under the boundary conditions in the Fourier space. The lateral deflection of plate is assumed to be expressed as a product of the cantilevered beam mode in the streamwise direction and the free-free bending beam mode in the spanwise direction. Applying the Galerkin method for the equation of motion of an elastic plate, the three dimensional coupled equation of motion of a flexible cantilevered plate is derived. The complex eigenvalue analysis is performed for the stability analysis. Changing the mass ratio and the aspect ratio, the root loci and the vibration modes of the plate and the fluid are investigated. And, the relationship between the critical fluid velocity and the mass ratio taking the aspect ratio as a parameter is investigated.
This paper investigated the effect of arrangement of tube banks on vortex shedding synchronization due to acoustic resonance. We measured the time variation of a phase between surface pressures related to the lift force on a tube and acoustic pressure on a side wall related to the acoustic particle velocity when acoustic resonance occurred in in-line tube banks. The measured tube was installed at the second rows in the tube banks. As the peak level of spectrum of surface pressure fluctuations increased, the coherence between vortex shedding and wall acoustic pressure in the tube banks also increased. We estimated the phase relation between the time data which were related to the lift force on a tube and acoustic particle velocity near the tube. In addition, we discussed the verification of the synchronization feedback for a coupling condition between a sound field and wake oscillator. Comparing this result with the analytical results, we reached to the conclusion that the acceleration feedback was most reasonable type of feedback. We discussed also the effect of arrangement of tube banks on vortex shedding synchronization.
A blower is a machine that gives rotational energy to gases from the impeller and discharges them from the outlet. Among blowers, the centrifugal turbo-blower is good at producing high-pressure and running with high efficiency. However, the noise of the blower is so large that it is required to reduce the noise. The centrifugal turbo-blower targeted in this research is especially noisy in low flow and high flow. Until now, this research group revealed the turbulence noise source in high flow and reduced the noise of the blower. On the other hand, the turbulence noise source in low flow have not been revealed yet. So, we reveal the turbulence noise source in low flow in this paper. First of all, when we measure time-base waveform of the noise and analyze frequency characteristics of that in low flow, we know blade passing frequency noise and turbulence noise have a big influence on the noise in low flow. So, we think that the turbulence noise in low flow is caused by the influence of blade passing, and then we measure velocity turbulence at blade following edge. As a result, we understand that the turbulence at blade following edge is the largest in low flow. From the above, we reveal that the turbulence at blade following edge is the turbulence noise source in low flow.
This study deals with the aerodynamic noise generated from perforated metal plate. Perforated metal is produced by punching the sheet metal using a press die. It has two kind of direction by characteristic cross-sectional shape. This experiment is defined as one direction is “Expansion” and the other direction is “Shrinkage”, and evaluation of flow velocity is “Average flow velocity from per hole”. In the experiment, the aerodynamic noise generated from the perforated metal is measured. The number of holes, direction of the plate and “average flow velocity from per hole” are varied in experiment. According to experimental results, When the direction of the perforated metal is “Expansion” and “Average flow velocity from per hole” is over 35m/s, partial overall value is 20~30dB larger than “Shrinkage”. In the case of “Shrinkage”, cross-sectional shape and arrangement of holes affect on flow field and aerodynamic noise.
Flow-induced acoustic resonances in piping with closed side branches are one of the phenomena causing severe structural vibration and fatigue damage of piping and components in many engineering applications such as power plants. In the United States, the steam dryer of the boiling water reactor was damaged by high-cycle fatigue due to acousticinduced vibration under a power uprating condition. Practical piping systems of power plants often have a steam flow, and moreover, the steam state can be not only dry steam but also wet steam, including nearly saturated conditions. Although many researchers have investigated acoustic resonances at side branches, the acoustic resonances under a wet steam flow have not yet been clarified since previous studies were mainly conducted under an air flow, and there have been few previous experiments performed under a steam flow, particularly a wet steam flow. From our previous experiments under low-pressure dry and wet steam flows using side branches with single-, tandem-, and coaxial-type arrangements, higher acoustical damping was confirmed under wet steam than that under dry steam, which is considered to be caused by the existing liquid phase. Although the static pressure in practical steam piping is often higher than that in our previous experiments, the effects of the static pressure on acoustical damping under a wet steam flow have not been clarified. In this paper, we give experimental results under higher-pressure dry and wet steam flows than those in our previous studies and discuss the influence of the static pressure on the pressure fluctuation of acoustic resonances under a wet steam flow.
Hydrogen combustion is attracting attentions because of zero CO2 emission. Recently, a gas turbine which uses hydrogen-rich fuel is being developed. In this study, we examined the influence of hydrogen-containing ratio on combustion oscillation for fuel mixtures of hydrogen and town gas (13A) experimentally and analytically. In the experiment, pressure oscillations were measured by a sensor which is installed at the bottom of the combustor. It is found that two oscillation frequencies near 200 Hz and 400 Hz were simultaneously detected in the case of hydrogen-containing fuels, whereas single oscillation frequency around 350 Hz was observed in the case of only 13A fuel. To understand this difference of oscillating frequencies, we conducted acoustic analysis considering the 𝑛 − τ model as the heat release model; this model has time delay τ. However, the simplest model, one-dimensional different diameter model, could not reproduce three types of oscillating frequencies obtained by the experiment. Besides, we used acoustic impedance measured with the experimental setup as the acoustic boundary condition of the bottom of the chamber. Time delay, flame position and temperature used for the correction of the acoustic impedance and the mean temperature in the chamber were calculated by the CFD analysis. As a result, it is found that hydrogen makes the natural frequencies a little higher, because temperature becomes higher and delay time becomes shorter.
Self-excited vibration called the combustion vibration occurs in the combustion apparatus. The vibration and noise adversely affect combustion apparatuses. Therefore it is necessary to control the generation of vibration. But the mechanism of the onset of vibration has not been sufficiently elucidated and countermeasures have not been established. The purpose of our research is to analyze the mechanism of generating the combustion vibration using a cellular automaton method (abbrev. CA). Since a combustion apparatus is in three-dimensions it is difficult to analyze. In this study we analyzed the combustion vibration with a Rijke tube which can be treated in a one-dimensional model. At first, We established the rule of the CA method. In addition, we developed a calculation model using CA method. As a result, we was able to confirm a state of the self-excitation vibration．But it became a different result from the actual experiment．In addition,I suggested that I used perforated plate as a vibration reduction plan．Using the experimental result,the parameters of the perforated plate were determined．We will conduct experiments in the future and confirm the sound abcorbing effect．
One of the mining methods of offshore gas field, Floating production, storage and offloading system (FPSO) is attracting attention. However, the sloshing in an oil-gas separator installed in FPSO excited by waves is expected to cause a serious problem. In order to reduce the sloshing wave height, one of the possible candidate is inserting perforated plates in the tank. In this research, the method for a precise estimation of sloshing wave height in a horizontal cylindrical tank with perforated plates under pitching excitation is proposed. To accomplish this purpose, the pressure loss due to perforated plate should be estimated precisely. Therefore, the relationship between flow velocity and pressure loss and the relationship between flow angle and pressure loss are investigated by CFD calculation. Then, the calculated wave height using the pressure loss calculated by CFD and wave height measured in experiment is compared. Finally, the method of calculating wave height is applied to the real scale FPSO.
Sloshing phenomena in containers under earthquakes often cause serious accidents. In case of an oil tank with floating roof, the sloshing phenomenon and the structural vibration should be treated as the coupled problem. Lagrangian fluid finite element model has been used for the analysis of the coupled problem because the compatibility and the equilibrium condition are automatically satisfied at the boundary between the fluid and the structure. However, the degree of freedom of the Lagrangian model becomes large because the fluid particles in the Lagrangian model move vertically and horizontally. In addition, the Lagrangian model has physically-meaningless spurious modes caused by the redundancy of the degree of freedom. In this paper, to establish the efficient and accurate analytical model for the coupled problem, liquid in a rectangular container is modeled as the nonlinear concentrated mass model. The model consists of masses, non-linear connecting springs and connecting dumpers. Some masses move horizontally, the others move vertically. The horizontally movable masses are governed by the equations of motion. The vertical displacements of masses are determined from the displacements of the horizontally movable masses based on the incompressibility of the liquid. The characteristics of the connecting springs are derived from the static and dynamic pressures of the liquid. The degree of freedom of the proposed model is smaller than that of Lagrangian model and the spurious modes does not occur in the proposed model. To confirm the validity of the proposed model, the frequency response of the model is compared with experimental result.
This paper describes a cart-type seismic isolator using restoring force of a pendulum instead of spring. This proposed seismic isolator is one degree of freedom vibration system. The natural frequency of the proposed method can be tuned easily with changing length of a pendulum. This characteristic is the advantage compared to the conventional methods. In addition, this paper describes the vibration suppression using the proposed cart as a dynamic vibration absorber. The optimum natural frequency and damping ratio of the proposed dynamic vibration absorber were theoretically derived using two fixed points method. The effectiveness of the proposed methods and theoretical analysis was verified through simulations and experiments.
In order to enhance the conventional damper performance, we propose an impact damper by using a cantilever-type impactor. The impact damper consists of a rotational spring and an impactor operating on a main system. The main system is damped by energy dissipation of collision of the impactor and the main system. In this paper we verified the damping performance of the proposed system through experiment and analysis. The experimental results showed that the peak vibrational amplitude of the main system can be reduced down to 89.6 % by attaching the impact damper. In addition, the analytical results showed qualitative agreement with the experimental result. We expect that a larger damping effect would be achieved by optimizing the coefficient of restitution.
After the accident in Fukushima, it becomes more a mandatory action to enhance the safety level of the nuclear power plant. It is highly requested to suggest measures to severe accident when input motion level exceeds the design basis earthquake. Most of reactions to severe accident occurred at the plant is enhancement of structural internal force. However, there is a limit to heighten the strength of the structure in order to enhance the seismic safety. As metal material has elastic and plastic deformation ranges, it is known that the latter shows wider deformation range than the former. All mechanical components are generally designed to behavior in elastic range for function maintenance while some mechanical components are fine to reflect elasto-plastic elements. Of most well-known is piping support element. It increases safety of the piping as piping support element deforms plastically by absorbing the energy when responding to the earthquake. It is considered one of the best-possible measures to secure the safety level in the area beyond the design basic accident such as severe accident measures. This study reviewed the vibration control capacity of the piping system by using the elasto-plastic damper. This paper compares the analytical model of the coil spring damper with the mechanical characteristics obtained from the experiments. Test result agrees well with the basic mechanical characteristic of the elasto-plastic damper. This paper discusses on the challenge of thermal expansion from pipe support area and their responses during earthquake.
The purpose of the present study is to clarify the fluid flow of an oil damper through numerical analysis in order to estimate the exact damping coefficient of an oil damper. The finite difference method was used to solve the governing equation of the fluid flow generated by a moving piston. Time steps based on the fractional step method and the arbitrary Lagrangian-Eulerian (ALE) method were adopted for the moving boundary. In the moving boundary problem, a masking method with a single block grid system was used to stabilize the computation . In other words, algebraic grid generation using a stretching function was used for the moving piston in the cylinder of the oil damper. The time-dependent coordinate system in the physical domain, which coincides with the contour of the moving boundary, is transformed into a stationary rectangular coordinate system in the computational domain. In order to valiade the caluculated results, they were compared with experimental results and the approximate algebraic solution. As a result, it became possible to estimate exactly the degree of contribution of the conversation term the Navier-Stokes equation on the damping coeffcient of the oil damper.
This study proposes a dynamic characteristics of structural displacement control system with Linked Fluid Inertia Mass Damper (LFIMD). In this paper, structural displacement control system is called the link mechanism, and its mechanism is constructed by hydraulic link mechanism. The link mechanism has three distinguishing properties; the first one is adjusting the ratio of story deflection, the second is preserving 1st mode frequency, the third is removing the vibration components in the second and subsequent modes. We know the shear force is redistributed when adjusting deformation with the damper by previous research. In the first part, we derive the redistribution method for shear forces with the theoretical solution for harmonic oscillation. Link mechanism changes the eigenvectors by redistributing the shear force from a relatively strong layer to a relatively weak layer. This system due to give the apparent stiffness to linked layers, and this signs of the stiffness is positive for weak layer and negative for strong layer. In the case of a two-layer structure, as the ratio of the eigenvectors is closer to 2.0, redistribution of shear forces decrease. Finally, we confirmed the relationship between stiffness distribution and the link force by shaking table test. And the test showed that the link mechanism can make story deflection uniform regardless of stiffness distribute.
The noise from the forging machine has been a serious problem. In order to reduce impact vibration, the momentum exchange impact dampers have been proposed in the previous researches. The basic principle of this damper is based on the energy transfer of the collision of three rigid bodies. This impact damper consists of a spring and a mass that is contacted with the bed of the forging machine. This impact damper is effective when the mass is nearly equal to the mass of the bed of the forging machine. However, the mass of the damper is usually insufficient for practical use. In order to solve this problem, Miyazaki et al. proposed an impact damper using pre-compressed spring; however, the effectiveness of this method was not verified through experiments. In this study, this problem is solved by using an electromagnet and a capacitor. The electrical current flows through the coil when the impact damper passes through the coil. The electromagnetic force is generated by the electrical current, and the electromagnetic force suppresses the vibration of the host structure. The effectiveness of the proposed method was verified through simulations and experiments.
Japan is earthquake-prone country. Over 20,000 people were dead by South Hyogo Earthquake in 1995 and Tohoku Pacific coast Earthquake in 2011. Falling of furniture causes human damages of about 40 [%] by these earthquake. It is important to avoid overturn of furniture. However, conventional devices are not popular. The reason is difficulty with installation. Even if these devices are installed, an effect may not be shown. For these reason, a device which is easy to install and effective. In this study, authors are developing new device which improves these problems. The new device is one kind of a tension rod. This new equipment has a damper．Authors examined the effectiveness of the furniture fall prevention device by using damper. In addition, the furniture was modeled to expect behavior during earthquakes. Authors experimented and compared experimental results with analysis results. As a result, authors confirmed the validity of this model. Using this analytical model, seismic response analysis using observed seismic wave was carried out. Analysis conditions were set assuming actual furniture. As a result, furniture fall prevention device is effective even if actual earthquake. However, the device loads strongly on ceiling by occurring force. Therefore, we found the problem to make the device better.
Japan is one of the most earthquake-prone countries in the world. In the Great East Japan Earthquake, power plants were severely damaged by strong ground motion and tsunami. In addition, power generation at some power plants had been stopped for a long time. The loss of the power generation impacted public institutions and industry. Therefore, improvement of the earthquake resistance of power plants is important. In particular, thermal power plants are important power plants supplying the Japanese electric power. In the thermal power plants, stoppers made of steel are installed between boiler and its support structure. However, these devices do not have enough damping against aftershocks following a main shock, because devices are damaged by repeated plastic deformation. Therefore, we propose installation the vibration control dampers between the boiler and its support structure in order to improve their earthquake resistance. In this paper, Examination of the parameter of the damper for each installation is conducted in order to suppress the response. In addition, the effect of the damper is verified by confirming the response behavior and comparing the conventional equipment. In the trend of the response, the relative displacement between the boiler and its support structure is suppressed by increased the parameter of the damper. In addition, the response acceleration of the boiler is increased by increased the parameter of the damper. In comparison of the damper, rectangle hysteresis damper has good vibration control performance. The rectangle hysteresis damper suppresses the cumulative relative displacement between the boiler and its support structure. Therefore, in case of installed the rectangle hysteresis damper, fatigue damage of the piping system installed between the boiler and its support structure are possibility prevented.
This paper deals with the control system design for active isolation table that loads a dynamical object. When elastic loads are put on the isolation table, vibration modes of the table are changed. Therefore, the controllers for the active isolation table should be designed taking account of elastic loads.In this research, an experimental active isolation table with an elastic load is built. Its dynamical model is identified by using experimental modal analysis or FEM analysis. A controller in horizontal direction is designed by using the model according to sub-optimal control theory, absolute velocity feed-back control theory and feed-forward control theory. It has been confirmed from previous research that good control performance in the horizontal direction can be obtained. In this research, to further improve the performance, the optimal controller was designed for vertical vibration and the performance was verified.
Desktop vibration isolators are often used as a platform for precision measuring instruments. This article discusses the accuracy of performance prediction methods for vibration isolators elastically supported by four air springs. Each air spring possesses a reservoir tank to ensure the natural frequency of the support system remains low and to provide adequate damping force. For practical use, air springs and reservoir tanks should be installed in separate locations and connected by a small-diameter pipe because desktop isolators must be thin. Our previous studies have shown that there is a secondary resonance point in systems supported by air springs with long pipes and reservoir tanks and that it is not simple to theoretically calculate the amplitude and frequency at this point because this type of air spring support system has nonlinear characteristics. In this study, the change in the vibration isolation performance of a desktop vibration isolator with the length of the pipe connecting the main air tank and the reservoir tank of an air spring-supported system was examined experimentally and approximated using theoretical calculations.
Magnetorheological elastomer (MRE) is a smart material that can change its stiffness depending on the magnetic field. The main objective of this paper is to develop a multi-layered MRE isolator having self-sensing property. The electric resistance of a conductive elastomer can be changed by its deformation. Such an electrical characteristic might be used for measuring oscillatory movement of vibration systems. While the MRE works as a stiffness-variable spring element in the system, the material also works as a sensor. At first, we investigated the electric characteristic of the conductive elastomer by measuring electrical impedance while the elastomer is compressed uniaxially. We found that the impedance magnitude was reduced linearly as the compressive deformation was increased. Second, the vibration isolator was fabricated by laminating thin MREs with uniform thickness. The anti-vibration performance of the isolator was then evaluated. By applying the magnetic field to the laminated MREs through an electromagnetic coil, the resonance frequency of the system was changed as much as 36.75 Hz. Furthermore, we measured the electrical signal while the conductive elastomer was excited sinusoidally. We found that the elastomer could produce the signal that corresponded to the frequency and magnitude of its own deformation.
The importance of simple and compact passive vibration isolator is increasingly growing owing to the demand for precision mechanical systems and measuring equipment. In particular, to suppress the vibration transmissibility for the vertical direction, nonlinear dynamic properties, which exhibit high static stiffness to support the weight of an isolated object and low tangent stiffness to reduce the natural frequency, are required. To realize such characteristics, the authors have proposed a nonlinear passive vibration isolator using the post-buckled L-shaped beam. However there is a problem that the second mode, which is dominated by rotational motion of the isolated object, is excited, and the transmissibility for vertical direction deteriorates. In this report, to suppress the excitation of undesirable mode, we propose a new model. Concretely, we newly propose isolation model, which is obtained by changing the direction of vertical beam to suppress the rotational motion of an isolation object, and investigate numerically and experimentally.
The Sompi method has been used to a spectral analysis method applied in the geoscience field and the analysis of volcanic earthquakes. By applying the acquired complex vibration data to the autoregressive process, it can be decomposed into wave components and noise components. This analysis method can be decomposed even at the same frequency damping ratio, so it is useful for evaluating the vibration characteristics of the structures. In this research, the purpose is to clarify the vibration characteristics of the structure using the Sompi method, and the validity of this method was verified by numerical simulation and excitation experiments. In the numerical simulation, the data obtained by synthesizing the damping waveform and the noise is generated and decomposed into the wave component and the noise component by the Sompi method. Furthermore, it was confirmed that it is possible to discriminate components of the same frequency with different damping ratios. In excitation experiments, experiments were conducted using impulse excitation to simple cantilever, and the first to third order natural frequencies and damping ratios were obtained by the Sompi method. In addition, changes in natural frequency and damping ratio when a weight was attached to a beam could also be confirmed by analysis by Sompi method.
The solid NMR (nuclear magnetic resonance) device can obtain high resolution as the hollow sample tube is rotated at ultra-high speed. The rotational speed exceeds over 4 million rpm. Hydro-inertia gas bearing is used in this device to support the rotor. The gas bearing can be operate high rotating speed although this type of bearing oprates by externally pressurized gas. In order to clarify the bearing characteristics,CFD (computation fluid dynamics) analysis has been conducted by authors. Negative pressure was generated localy in the bearing surface. It is thought that such pressure distribution contributes to realize of high speed rotation. This pressure distribution is expected to be affect the stability of vibration of the rotor. In this study,the vibration damping of the shaft supported by this bearing was measured and compared with the conventional type.
In order to further increase the travelling speed of the bullet trains, a deeper understanding of the hunting motion is required. Among various vibration modes associated to the snake-like movement of the railway vehicle, the hunting motion of the wheel axle requires the simplest analysis. However, even in such easy to understand case, analytical expressions for the natural frequency of hunting were obtained only for a geometrical model, which is unable to predict the damping effect induced by the contact of the wheels with the rails. In this work, in order to clarify the damping mechanism, related to the hunting motion of the wheel axle of a railway vehicle, a generalized dynamic model is proposed. Based on such model, analytic expressions for the damping coefficient and damped natural frequency are derived, without imposing restrictions on the ratio between the lateral and vertical creep coefficients. Influence of the travelling speed, wheel conicity, dimensionless mass of the wheel axle, ratio of the creep coefficients, ratio of the track span to the yawing diameter, etc., on the damping coefficient and damped natural frequency, is clarified.
After a suspended ceiling was damaged by great earthquake, a lot of people have been casualties by falling ceiling board, lighting fixtures and air-conditioning equipment, etc. Because damping ratio of iron anchor bolt is small and vibration of the suspended ceiling is not reduced in a short period of time, such an accident has happened. Currently, countermeasures to improve the earthquake resistance of the suspended ceiling is to fix the parts in the bolt and to install a reinforcing material in four directions of the hanging bolt. Then, there is a need for development of a using the new material, which is a lightweight, flame retardant, high heat resistance and high damping suspended ceiling having a seismic resistance and a seismic base isolation. The purpose of this study is to develop a ceiling by using the basalt fiber material hanging having the seismic resistance and the seismic base isolation. Basalt fiber material made of volcanic rock is the environment recycling material and, has a light weight, flame retardant, high heat resistance and high attenuation. In this study, using the new material, the design, analysis, testing and verification of the ceiling having the seismic resistance and aseismic base isolation.
This paper investigated the response of building that has a nonlinear isolated device at the bottom floor. The isolated structure resonates with long period earthquake and response displacement increases. In order to reduce the vibration of the building, multiple Tuned Mass Damper are installed at the highest floor. In this study, the multiple tuned mass damper (MTMD) parameters are considered. The MTMD’s optimal parameters that minimize response displacement of the structure’ top layer is found. Genetic Algorithm (GA) method is used for optimizing MTMD’s parameters. The building is vibrated under some case of earthquakes. .The results show the good effectiveness of GA method.
Multi-mass dynamic vibration absorbers (DVAs) have recently been studied with the aim of further improving their performance and avoiding performance deterioration due to changes in their system parameters. One of the present authors has previously reported a solution that provides the optimal tuning and damping conditions of the double-mass DVA and has demonstrated that it achieves better performance than the conventional single-mass DVA. The evaluation index of the performance used in that study was the minimization of the compliance transfer function. This evaluation function has the objective of minimizing the absolute displacement response of the primary system. However, it is important to suppress the absolute velocity response of the primary system to reduce the noise generated by the machine or structure. Therefore, in the present study, the optimal solutions for DVAs were obtained by minimizing the mobility transfer function rather than the compliance transfer function. In this study, an exact algebraic solution to the H∞ optimization for the series-type double-mass DVA was successfully derived.
It has been clarified that multiple-mass dynamic vibration absorbers (DVAs) have higher performance than the singlemass DVA. One of the authors has succeeded in deriving the optimal design solutions for series- and parallel-type doublemass DVAs based on the three different optimization criteria. As a result of the research, it was confirmed that the double-mass DVAs are surely superior to the single-mass DVA in the vibration suppression performance. The evaluation index of optimization at that time was the compliance transfer function which is the absolute displacement response of the primary system. However, when a building structure is subjected to a large earthquake, the structure often destroyed by excessive relative displacement between the ground and the building. Therefore, the optimal design condition of the DVAs for minimizing the relative displacement between the primary system and the foundation is searched in this report. The minimization condition of the absolute displacement and that of the relative displacement are similar but never the same. As with the minimization of the compliance transfer function for absolute displacement, we also derived optimal solutions based on three different optimization criteria, i.e., H∞ optimization, H2 optimization and stability maximization.
The elastic vibration of railway vehicle car body causes deterioration of ride comfort because the natural frequency of the vibration is the same frequency that people feel sensitively. Therefore, it is necessary to reduce the elastic vibration. It has been shown that passenger has large reduction effect against elastic vibration of railway vehicle car body. That effect is considered due to viscoelastic motion and multi-directional motion of human body. This study focuses on the latter one and aiming to develop a new vibration reduction device to mimic the multi-directional motion of passenger. In this paper, an experimented multi-directional dynamic vibration absorber (called MDDVA in this report) is developed. The MDDVA consist of a resiliently supported metal ball and elastic ball to support metal ball bottled in a rigid cylindrical vessel. The metal ball can vibrate multi-directionally in the vessel and is expected to work as a MDDVA. In addition, it can change the natural frequency of MDDVA by pressing the elastic balls from the top according to the natural frequency to the target car body. Excitation test using a scale model of railway vehicle is conducted to evaluate the effectiveness of the MDDVA. As a result, MDDVA can reduce the elastic vibration by adjusting the natural frequency of MDDVA to that of the scale model by pressing the elastic balls, and multi-modal vibration reduction effect is successfully observed.
A dynamic vibration absorber is usually used in order to achieve more efficient vibration control in case which damping devices are not directly installed to a primary system as like high rise buildings, bridges and pole like structures. A secondary system which has a spring and dash pot as dynamic absorber is put together with the primary mass, and the parameters of stiffness and damping should be arranged in optimal by using the Fixed-point theory. On the other hand, the author proposed a unique type of damper that has a changeable inertia mass effect by MR fluid in previous study. The effect of inertia mass, which is proportional to relative acceleration acting as a series inertia mass to objective, can make a natural frequency of the primary system lower and also have anti-resonance point at cut-off frequency. If the series inertia mass could be artificially varied, then it would be easy to control it. In this paper for the purpose of application to dynamic absorber, it is focused on how to apply the changeable series inertia mass into dynamic absorber, and what advantage is. An optimal parameters were determined by using conventional method as F-p theory at first, and then introduce the way how to switch the series inertia mass. Finally the advantage of inertia effect was investigated numerically.