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The vibration-induced fatigue failure of small-bore piping is one of the common causes of failure trouble at nuclear power plants (NPPs). Therefore, the purpose of this study is to develop the measurement methods of vibration-induced stress for the screening to prevent from fatigue failure mechanism of small-bore piping. First, a measurement method using a single-mass model was introduced, and then, a measurement method using a two-mass model developed as an improved calculation model was proposed. These two kinds of models were validated by vibration tests using mock-up with small-bore branch piping. The results showed that the single-mass model could be used as the coarse screening. Additionally, the two-mass model was found to be suitable to the fine screening due to more accurate measurement of vibration-induced stress. Next, for small-bore piping with typical pattern configurations consisting of several masses and supports, the model considering the supports and the center of gravity being out of pipe centerline was developed and put into practical use. Finally, for the more complex small-bore piping with general piping configurations consisting of many bends, branches, or joints, the method based on the finite element analysis and using the measured values was developed. In the developed method, the differences between the natural frequency and the response acceleration obtained by the measurement and those values calculated using the analysis model are optimized to be enough small, and then, the vibration-induced stress is estimated by superposing the vibration modes of the small-bore piping with the static deformation representing the main piping vibration. In this study, the usability of the developed method was confirmed by the comparison with the numerical results without the measurement error, which were assumed to be the true values. The peak stress induced by vibration frequently occurs at the filet weld part between the small-bore piping and the main piping. The developed methods can be used for various weld geometries although the measurement method using strain gauges cannot be used for such weld parts. The failure possibility by vibration-induced fatigue can be evaluated by comparing the nominal stress measured by the methods in this study with the fatigue threshold stress divided by the stress concentration factor appropriate for the weld geometry.

To improve design and troubleshooting techniques of piping systems for operating power plants, it is necessary to investigate, by experiment and simulation, the behavior of fluid inside the piping system in detail. This study was conducted using full-scale piping system under conditions that could seriously threaten the plant operation, by matching pressure pulsations, acoustic resonance, and piping natural frequency. Although piping vibration is reported to influence fluid pressure pulsations, there were no such examples of influence in this experiment. Knowing that the opening ratio of the pressure control valve affects the boundary condition for acoustic resonance, experiment and simulation at different opening ratios were conducted. It has been suggested that the cases in which a valve partially open at 25% or less should not be taken as a closed end. This finding conflicts with such a widespread design assumption.

Vibration behavior and unstable phenomena of multi-connected bodies supported by damper-spring elements moving in a narrow flow passage are reported. These vibration phenomena have been often observed in high-speed trains running in tunnels, cleaning robots going through pipings and so on. The fluid forces acting on the multi-connected rigid bodies are obtained analytically on the basis of the Navier-Stokes equations applied to a narrow flow passage. The equations of coupled motion of the multi-connected bodies and fluid are derived. Using coupled equation, a stability analysis is performed. The effect of the flow velocity and number of bodies on the coupled mode is investigated. The influence of the boundary conditions of fluid pressure at connecting points is also investigated.

In this study, a vibration experiment with a reduced scale model of a large-size cylindrical water storage tank is performed in order to investigate the nonlinear vibration responses of the cylindrical tank when the beam-type and the oval-type vibrations are coupled. The sinusoidal sweep test is conducted by varying the input acceleration from smaller to larger input. As a result, the resonance frequency shifts to the lower frequency region and the response magnification factor becomes smaller as the input acceleration level becomes larger. Furthermore, when larger input is applied, the oval-type vibration has a subharmonic resonance of order one-half, and its displacement-amplitude grows up significantly. It can be assumed that the large amplitude of oval-type vibration generates a geometrical nonlinearity for the beam-type vibration.

The seismic-proof design of a large-scale cylindrical water storage tank has been an important issue for enormous earthquake. For enhancing its reliability, it is necessary to study the vibration behavior of the tank in more detail. This paper describes the results of a vibration test with a 1/10 reduced scale model of a large-scale cylindrical water storage tank, and also refers to the dynamic fluid pressure distribution and its influence on the seismic-proof design. Considering the differences between the experimental values and numerical design ones, it becomes obvious that there is a discrepancy between the positive and the negative pressures of the dynamic fluid pressure and that the dynamic fluid pressure depends on the acceleration magnitude. And it is suggested that such phenomena are caused by oval-type vibrations. They, however, have little effect on the seismic-proof design of the tank in the range of acceleration used in this study.

When thin cylindrical shells having freely supported end such as heat-shielding shells of after-burners, labyrinth air seals and annular structures in large diameter pipings are subjected to axial annular flow, an unstable vibration and a fatigue failure are apt to be occurred. In this paper, the unstable vibration of thin cylindrical shells is investigated cconsidering the fluid structure interaction between shells and fluid flowing through a narrow passage. The coupled equation of motion between shells and fluid is derived using Flugge's shell theory and Navier-Stokes equation. Especially, focusing on the higher circumferential vibrations, the unstable phenomenon of thin cylindrical shells is clarified by using root locus based on the complex eigenvalue analysis by using the mode functions obtained by the exact solution. The influence of shell-dimensions and so forth on the threshold of the instability of the coupled vibration of shells and flowing fluid are investigated and discussed.

A tuned mass damper is usually used to reduce wind-induced vibration of towers and high rise buildings. However it is not so effective for the structures of which the natural frequency is varied for the case of building up bridge-towers. For these structures the semi-active controlling method seems to be effective in reducing the vibration. This paper proposes a new semi-active vibration controlling method and an adaptive tuned mass damper ATMD consists of a pendulum and an analogue controlling system. In this system the tuning condition of the ATMD is realized by retaining the phase lag of the damper mass to the main structure to be 90°. The effectiveness of the proposed ATMD is evaluated analytically and experimentally.

In this paper, the stability of a thin cylindrical sheel subjected to an axial leakage flow is discussed. Here, we focus on a lateral vibration of a cylindrical shell, that is the beam-like vibration of a shell. The coupled equations between a shell and a fluid are obtained by using the Donnell's shell theory and the Navier Stokes equation. The influence of the axial velocity on the unstable vibration phenomena is clarified concerning the beam-like vibration mode of a shell. The applicable range of Donnel shell theorry is confirmed for axial leakage flow-induced vibration of a thin cylindrical shell. The numerical results on the shell theory are compared with those on beam theory which have been already reported by the authors. And, the numerical parameter studies are done for several dimensions of shell and fluid.

This paper deals with new-type dynamic vibration absorber for structures such as piping systems, buildings and towers. This dynamic absorber consists of balls and ball cases. It makes use of ball rotation for reducing the vibration of structures. The characteristics are shown as follows : (1) It is simple composition composed of some balls and ball cases and so it is low-cost type; (2) The frequency tuning is unnecessary, and so a preliminary measurement for adjustment is not necessary; (3) It is possible to correspond to any frequency without tuning; (4) It is compact and easy to install on structures. We applied this self-tuning dynamic absorber to a pipe branch of piping system and a view tower as a large structure. The effects of vibration reduction were evaluated by simulation analysis and vibration test using a shaking table.

Hysteresis elements such as elasto-plastic dampers are important elements for mechanical structures, especially for earthquake-proof structures. When such nonlinear supports are utilized for piping systems, the nonlinearities of the hysteresis elements and the geometrical complexity of the piping systems lead to complicated seismic responses, and thus further studies are required in order to enhance the reliability of the earthquake-proof design. In the seismic response analysis, the method of time history response analysis is widely used. In this paper, a method of nonlinear seismic response analysis for a piping systems using a combination of the FEM and the Differential Algebraic Equations (DAE) is proposed. As it is well known, the DAE is suitable for numerical analysis of time history responses for mechanical structures and machinery elements. According to the advantage of the DAE, the numerical modeling and simulation of a complex piping systems supported by the hysteresis elements can be easily carried out by using the proposed method. In order to verify the usefulness of the method, the time history responses of piping systems supported by a elasto-plastic damper is examined for seismic excitation by using the proposed method. The damper is modeled as a bilinear model. The effects of the second stiffness and the stiffness associated with the plastic deformation of the damper on the seismic responses are investigated using an actually recorded earthquake motion.

Hysteresis elements such as elasto-plastic dampers are important for mechanical structures. They have nonlinearities and thus the vibration characteristics of mechanical structures with hysteresis elements are not clarified yet and need further studies. In this paper, the investigation of the dynamical stability of mechanical structures with a hysteresis element is performed by means of describing function method, which is on the basis of linear approximation of the hysteresis element. The nonlinear vibration system is composed of a linear spring-mass-damper structure system of any order and a hysteresis damper. The describing function of a hysteresis damper is derived and it is shown that the function remains upper half plane in the complex plane. According to the passivity of the linear structure system, this fact leads to the vibration system that is stable for any harmonic excitation. Next, the responses for seismic excitation are examined in simulation by using two typical models of the hysteresis element, a bilinear model and a Ramberg-Osgood model. The effects of the second stiffness of the dampers and the amplitude of the excitation motion are investigated using an actually recorded earthquake motion. The simulation results imply that the determination of the second stiffness requires the trade-off between an oscillation and a drift for designing earthquake-proof mechanical structures with the hysteresis damper.

In this paper, the stability of the thin cylindrical shell subjected to an axial leakage flow is reported. We focus on the circumferential (ovaling) vibration of a shell in this study. Equations for a shell and a fluid are described by the Donnell's shell theory, and the Navier-Stokes equation respectively, and the coupled equations are derived. As a result, the added mass, added damping and added stiffness are calculated. The influence of the axial velocity on the unstable phenomena is clarified. The numerical simulations are shown as parameter studies.

Vibrational mechanisms of flow-induced vibration of a coil spring due to fluid flow were investigated and the mitigation methods were suggested. At first, as one of those vibrational behaviors, flow-induced vibration of a coil spring with a circular rod in the middle of it due to an axial flow was investigated experimentally using fundamental test apparatus. The effects of stiffness of springs, gap between springs and inner rod and initial compression of springs on the vibrational behavior were clarified, and a stability diagram is presented for the spring vibration. Based on the experimental results, the vibrational mechanisms of the coil spring with an inner rod were investigated. Finally, a design instruction on the mitigation of flow-induced vibration of coil springs including the cases of cross-flow-induced vibration and the axial-flow-induced vibration of a spring without an inner rod was summarized and suggested.

To reduce wind-induced vibration of tall buildings and bridge towers, tuned mass dampers are often used. These dampers are called “passive type” while the methods which reduce the vibration by controlling the motion of a large mass with an actuator are called “active type”. For these types we have to change or control the structural vibration characteristics themselves, therefore they need very large exciting forces, and the system will become very large for large structures. In this view point, new concepts have just begun to be studied, where the driving forces themselves will be controlled. In this paper, we proposed a new system for reducing the flow-induced vibration of the structures by utilizing fluid excitation force itself. In this system, as we control the direction of the driving forces, this system does not need so large control forces and the system becomes smaller and simpler. We investigated the feasibility of this system when applied to a bridge, a building and evaluated the effectiveness of driving forces by the wind test using a reduced scale model.

In this paper, the stability of a thin cylindrical shell subjected to axial leakage flow is discussed. In this paper, the first part of a study of the axial leakage flow-induced vibration of a thin cylindrical shell, we focus on axisymmetric vibration, that is, the ringlike vibration of a shell. The coupled equations between a shell and a fluid are obtained by using the Donnell’s shell theory and the Navier-Stokes equation. The added mass, added damping and added stiffness matrices in the coupled equations are described by utilizing unsteady fluid forces on a shell. The influence of the axial flow velocity on the unstable phenomena is clarified concerning axisymmetric vibration mode of shell. The numerical calculations are performed taking the dimensions of shell and fluid as parameters.

In this paper, the stability of a thin cylindrical shell subjected to axial leakage flow is discussed. In this paper, the second part of a study of the axial leakage flow-induced vibration of a thin cylindrical shell, we focus on lateral vibration, that is, the beamlike vibration of a shell. The coupled equations between a shell and a fluid are obtained by using the Donnell’s shell theory and the Navier-Stokes equation as same as the former paper. The influence of the axial velocity on the unstable vibration phenomena is clarified concerning the beamlike vibration mode of a shell. The numerical results on shell theory are compared with the ones on beam theory which have been already reported by the authors; and the numerical parameter studies are done for various dimensions of a shell and a fluid.

A herringbone-grooved gas-lubricated journal bearing can rotate silently at high speed with low friction, and moreover it can be small-sized. In this paper, the equation of motion of a herringbone-grooved gas-lubricated journal bearing is derived using the gas force which can be obtained by applying the Navier-Stokes equation to the grooved and the ridged parts of a journal. The stability analysis is performed by using the analysis method by Routh-Hurwitz, the root locus of complex eigenvalue analysis, and the transient time history response analysis. The physical meanings of the stability charts which have not been explained sufficiently in the conventional studies are clarified by considering the forward whirling motion and the backward whirling motion, and the more reasonable stability charts are proposed. In addition, it is reported that the present analysis results show a good agreement with the already reported experimental results. Furthermore, the parametric studies as for the specification of gas-lubricated bearing are performed, and it is shown that the stability charts are affected by the change of specifications intricately.Copyright © 2014 by ASME

The evaluation methodologies for the flow-induced vibration instability of a long flexible rod due to axial leakage-flow are reported. In the previous papers, the axisymmetric rods are regarded as rigid bodies, not as continuous bodies. In this paper, we deal with the rod as a continuous flexible body. The equations for the fluid and the structure are coupled analytically and the added mass, added damping, and added stiffness are derived by considering unsteady pressure acting on the rod. The relation between the axial velocity and the unstable phenomena is clarified. Concerning the critical flow velocity, the root locus (Argand diagram) is shown. We compared our results with the experimental results which one of the authors reported before.

Recently, the leakage-flow inside the mechanical structures such as rods in the cylinders, valves, seals and orifices, so on for controlling the flow volume and the fluid pressure tends to become larger aiming to increse the plant efficiency, which lead to the occurrence of the fluid-elastic instability of these structures. In this study, the fluid-elastic instability analysis procedure is proposed in order to establish the design criteria on protecting the key components from the flow-induced instability. The unsteady fluid force is derived theoretically for the simple segment and the equation of motion for the axisymmetric rods is conducted by the finite element method. Using these formulation the coupled equation of motion between fluid and structures is derived. The stability evaluation is performed using the Argand diagram obtained by plotting the real part and the imaginary part of the eigen value λ. Comparing the numerical values with the experimental values, this evaluation method is very efficient as the design criteria for the flow-induced instability.

This paper concerns a beam-type flutter of vertical pipes containing a flowing fluid and having the lower end immersed in fluid. The effect of surrounding fluid on motions of the pipe is assumed as a mass added to the immersed part of the pipe. The equivalent added mass is estimated using Morison's formula. The effects of the immersed length of the pipe on the critical flutter velocity are investigated. It is predicted theoretically that the lower end immersed in fluid may exert a considerable destabilizing effect, except in the case where the lower end is only slightly immersed in fluid and the mass ratio is as high as 0.75. Experiments with silicone-rubber tubes conveying water were conducted to check the theoretical predictions. It was confirmed that for sufficiently high flow velocities the tube was subject to violent flutter, and that the critical flutter velocity decreased with increasing immersed length of the lower end.

In this paper, active vortex control in flow across a barrage is investigated experimentally and theoretically. The special feature of the presented control method is that the vortex is controlled by the vibration of the control element, which is the front edge of the barrage and the generation point of the vortex. In the experimental study, the front edge of the barrage is acted upon by an excitor perpendicular to the flow direction. Firstly, the transfer function between the vibration of the control element and the pressure in the wake is determined. Then the feedback control is carried out with consideration of the phase shift obtained by the transfer function. In the theoretical study, the vortex filament method is used and the flow across a barrage is analyzed as a two-dimensional flow. The feedback control theory is used and the behaviour of the vortex is simulated. It is shown experimentally and theoretically that the vortex is suppressed by the vibration of the control element in the case of the specified phase shift.

When calculating the resonant response of bladed turbine disks, it has been expedient to assume that all blades on a given disk are identical. This leads to the prediction that all blades experience the same amplitude of displacement and stress when excited by forces harmonically related to the rotor speed. However, it has been shown experimentally that significant variations in these amplitudes occur for different blades on the same disk. These variations arise due to the effects of mistuning, which refers to small differences in blade characteristics. In this paper, effects of mistuning for free-standing blades and integral shroud blades are studied by means of Monte Carlo simulation and sensitivity analysis. It is found that weakly coupled systems with low damping are very sensitive to mistuning. Also, the validity of the lumped model used in this paper is examined by comparing the calculated results with experimental data.

Many heat-exchange tubes in a shell-and-tube-type heat exchanger are oscillated by means of the flow . of fluid through the heat exchanger. This flow is often cross flow and gas-liquid two-phase flow. Here, a brief review of studies on two-phase cross-flow-induced vibration is presented, and a summary of our work in this area provides a design methodology. Three types of vibration have been studied for tubes in two-phase cross-flow conditions: First, resonance of a tube due to vortex shedding is important primarily in single-phase flow, but also has been observed in homogeneous flow and even in two-phase flow. However, this vibration disappears in the slug flow or froth flow regions, which are important in numerous heat exchangers. Therefore, the vortex shedding phenomenon is not considered in this paper. Secondly, turbulent buffeting vibration is considered as the dominant phenomenon in the slug flow and froth flow regions. A method for estimating this type of random vibration is explained in this paper. Thirdly, an unstable form of vibration, so-called fluid elastic vibration, is also considered. The common method for estimating the instability boundary is similar to that used for single-phase flow; however, new insights on the method for two-phase flow are given in this paper.

This paper describes the results of vibration tests using a 1/10 reduced scale model of large-scale cylindrical water storage tanks to clarify their dynamic behavior under seismic excitation. The thin sidewall of the tanks is not so rigid that the vibration modes (sloshing and bulging) induced by earthquake can affect the distribution of their liquid pressure and seismic load. It is, therefore, important for the seismic design of water storage tanks to consider such elastic deformation theoretically and experimentally. In this study, vibration tests by shaking table are conducted using a reduced scale tank model partially filled with water to investigate the dynamic fluid pressure behavior and seismic-proof safety of the tanks. A small sinusoidal excitation test, large amplitude sinusoidal excitation test and seismic excitation test are conducted. The measured values are compared with the calculated ones by some conventional seismic design methods. The results reveal that the distribution shape and magnitude of the dynamic fluid pressure are different between under positive and negative pressures and depend on the magnitude of input acceleration. Further examination concludes that the oval-type vibration, which is a high-order vibration mode, occurring on the sidewall of the tanks affects the distribution shape and magnitude of dynamic fluid pressure. However, it is demonstrated that the vibration does not act as a seismic load in the conventional evaluation of seismic-proof safety.

We have applied H2 control to an electrohydraulic shaking table. In the application of H2 control to this device, we propose a method in which the H2 controller is designed based on a model of a whole analog feedback control system to make as much use as possible of a loop shaping function of robust control. This method is very practical because no changes in the analog feedback system are needed. As a result of the application to a 1-axis electrohydraulic shaking table of National Research Institute for Earth Science and Disaster Prevention, the Characteristics of a position control have been improved by 30% from 10.6 Hz to 13.6 Hz.

The fluidelastic vibration of a tube array caused by cross flow has been studied with a correspondence to a physical image. It is shown that an unstable vibration caused by a negative damping fluid force can be computed on the assumption that the unsteady fluid force acting on a tube in a tube array is calculated by the combination between the movement of the tube and the separation point along the tube surface, which is based on a visualized test. The boundary of the instability shows a reasonable coincidence with the other published data.

Recently, in order to improve power plant thermal efficiency, the turbine blade, which is the most important element of the turbine, has been used in the severe condition. Especially the blade root, which is inserted into a disc groove, supports the excessive centrifugal force. In this paper, effective methods of calculating the peak stress of the blade root and disc groove are presented. Since the geometry of the blade root and disc groove is complicated, the three-dimensional finite-element method is applied, including the nonlinear effect due to slippage between the root and groove. By using the above nonlinear finite-element method, contact and slip analysis is performed to obtain the converged peak stress. The effective linear analysis procedure for replacing the nonlinear analysis is also examined by comparing the calculated results of both methods.

The on-line computer test method is a new type of research technique to study the earthquake response bohavior of various types of structural elements, assemblages, and systems. It combines the experiment and numerical analysis and utilizes the benefits of both experimental and analytical research. In this study, we applied substructuring concepts to the on-line computer test method and developed a new algorithm which increases the accuracy of the substructuring method. By using this algorithm, we can simulate a more realistic elasto plastic seismic response of structures. For the purpose of development and verification of this algorithm, we prepared a small-scale on-line computer test system and simulated the high-level seismic response of a liquid tank which had seismic isolation devices.

Control rod drop verification experiments of a pressurized water reactor under seismic conditions are performed to confirm the insertion function of control rods into a core. To evaluate these tests, computer simulations are performed. A fuel assembly, control rods, guide tube and other associated structures are immersed in a water tank, and shaken by four hydraulic shakers. The scram time of control rods under seismic conditions was measured, and confirmed to meet the scram function. Moreover, vibrational response characteristics of core structure and dropping behavior of control rods in consideration of collisions are calculated by using a finite difference method. The behavior of the dropping control rods and the scram time obtained by the computer simulation show a very good agreement with the verification experimental results.

The intended aim of the paper is to provide the scope of the effect of an attached damper upon the stability of a cantilevered viscoelastic tubular pipe conveying fluid. The effect of the damping coefficient of a damper is investigated in detail in connection with the position of the damper as well. It is found that a damper attached to a thin pipe may have a little stabilizing effect on the pipe. Any damper attached to the pipe at the discharge end may be most destabilizing. A lumped mass accompanied by a damper may be destabilizing. The theoretical predictions were checked by some experiments.

A new type of the theory that solves the impact vibration problems is proposed here. The impact treated here is that a tube vibrates with the gap support, such as in a hole and to a flat bar. The theory is based on the modal synthesis analysis by using the fixed mode at the gap support. The results are compared with these of the usual modal analysis using the free mode at the support and the efficiency is proved by comparing the Rogers' previous paper and our test results.